turner(iv) preface the national instructional media institute (nimi) was established in 1986 at...

(i)

NATIONAL INSTRUCTIONALMEDIA INSTITUTE, CHENNAI

Post Box No. 3142, CTI Campus, Guindy, Chennai - 600 032

DIRECTORATE GENERAL OF TRAININGMINISTRY OF SKILL DEVELOPMENT & ENTREPRENEURSHIP

GOVERNMENT OF INDIA

TRADE THEORY

SECTOR: Production & Manufacturing

TURNER

4th Semester

NSQF LEVEL - 5

Copyright @ NIMI Not to be Republished

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Sector : TurnerDuration : 2 - YearsTrade : Turner 4th Semester - Trade Theory - NSQF level 5

Copyright© 2018 National Instructional Media Institute, Chennai

First Edition : December 2018 Copies : 1,000

Rs.230/-

All rights reserved.

No part of this publication can be reproduced or transmitted in any form or by any means, electronic or mechanical,including photocopy, recording or any information storage and retrieval system, without permission in writing from theNational Instructional Media Institute, Chennai.

Published by:

NATIONAL INSTRUCTIONAL MEDIA INSTITUTEP. B. No.3142, CTI Campus, Guindy Industrial Estate,

Guindy, Chennai - 600 032.Phone : 044 - 2250 0248, 2250 0657, 2250 2421

Fax : 91 - 44 - 2250 0791email : [email protected], [email protected]

Website: www.nimi.gov.in


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FOREWORD

The Government of India has set an ambitious target of imparting skills to 30 crores people, one out ofevery four Indians, by 2020 to help them secure jobs as part of the National Skills Development Policy.Industrial Training Institutes (ITIs) play a vital role in this process especially in terms of providing skilledmanpower. Keeping this in mind, and for providing the current industry relevant skill training to Trainees,ITI syllabus has been recently updated with the help of Mentor Councils comprising various stakeholder'sviz. Industries, Entrepreneurs, Academicians and representatives from ITIs.

The National Instructional Media Institute (NIMI), Chennai has now come up with instructional material tosuit the revised curriculum for Turner 4th Semester Trade Theory NSQF Level - 5 in Production &Manufacturing Sector under Semester Pattern. The NSQF Level - 5 Trade Theory will help the traineesto get an international equivalency standard where their skill proficiency and competency will be dulyrecognized across the globe and this will also increase the scope of recognition of prior learning. NSQFLevel - 5 trainees will also get the opportunities to promote life long learning and skill development. I haveno doubt that with NSQF Level - 5 the trainers and trainees of ITIs, and all stakeholders will derivemaximum benefits from these IMPs and that NIMI's effort will go a long way in improving the quality ofVocational training in the country.

The Executive Director & Staff of NIMI and members of Media Development Committee deserveappreciation for their contribution in bringing out this publication.

Jai Hind

RAJESH AGGARWALDirector General/ Addl.Secretary

Ministry of Skill Development & Entrepreneurship,Government of India.

New Delhi - 110 001


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PREFACE

The National Instructional Media Institute (NIMI) was established in 1986 at Chennai by then DirectorateGeneral of Employment and Training (D.G.E & T), Ministry of Labour and Employment, (now under DirectorateGeneral of Training, Ministry of Skill Development and Entrepreneurship) Government of India, with technicalassistance from the Govt. of the Federal Republic of Germany. The prime objective of this institute is todevelop and provide instructional materials for various trades as per the prescribed syllabi under the Craftsmanand Apprenticeship Training Schemes.

The instructional materials are created keeping in mind, the main objective of Vocational Training underNCVT/NAC in India, which is to help an individual to master skills to do a job. The instructional materialsare generated in the form of Instructional Media Packages (IMPs). An IMP consists of Theory book,Practical book, Test and Assignment book, Instructor Guide, Audio Visual Aid (Wall charts andTransparencies) and other support materials.

The trade practical book consists of series of exercises to be completed by the trainees in the workshop.These exercises are designed to ensure that all the skills in the prescribed syllabus are covered. Thetrade theory book provides related theoretical knowledge required to enable the trainee to do a job. Thetest and assignments will enable the instructor to give assignments for the evaluation of the performanceof a trainee. The wall charts and transparencies are unique, as they not only help the instructor to effectivelypresent a topic but also help him to assess the trainee's understanding. The instructor guide enables theinstructor to plan his schedule of instruction, plan the raw material requirements, day to day lessons anddemonstrations.

IMPs also deals with the complex skills required to be developed for effective team work. Necessary carehas also been taken to include important skill areas of allied trades as prescribed in the syllabus.

The availability of a complete Instructional Media Package in an institute helps both the trainer andmanagement to impart effective training.

The IMPs are the outcome of collective efforts of the staff members of NIMI and the members of theMedia Development Committees specially drawn from Public and Private sector industries, various traininginstitutes under the Directorate General of Training (DGT), Government and Private ITIs.

NIMI would like to take this opportunity to convey sincere thanks to the Directors of Employment & Trainingof various State Governments, Training Departments of Industries both in the Public and Private sectors,Officers of DGT and DGT field institutes, proof readers, individual media developers and coordinators, butfor whose active support NIMI would not have been able to bring out this materials.

R. P. DHINGRAChennai - 600 032 EXECUTIVE DIRECTOR


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ACKNOWLEDGEMENT

National Instructional Media Institute (NIMI) sincerely acknowledges with thanks for the co-operation and

contribution extended by the following Media Developers and their sponsoring organisations to bring out this

Instructional Material (Trade Theory) for the trade of Turner under the Production & Manufacturing sector for

ITI.

MEDIA DEVELOPMENT COMMITTEE MEMBERS

Shri. Natarajan _ Training OfficerGovt. I.T.I SalemTamil Nadu

Shri. Dayala moorthy _ Assistant Training officerGovt. I.T.I VelloreTamil Nadu

Shri. M. Sampath _ Training Officer (Retd)MDC MemberChennai - 600032

Shri. R. Purushottaman _ Assistant Director (Retd)MSME, ChennaiTamil Nadu

Shri. T. Janakiram _ Assistant Director RtdGovt. RIC Chennai (N)Tamil Nadu

Shri. R. Sekaran _ JTO RtdGovt. I.T.I AmbatturTamil Nadu

NIMI CO-ORDIANTORS

Shri. K. Srinivasa Rao _ Joint Director,NIMI, Chennai - 32

Shri. N. Ashfaq Ahmed _ Assitant Manager,Co-ordinator, NIMI, Chennai - 32

NIMI records its appreciation for the Data Entry, CAD, DTP operators for their excellent and devoted services inthe process of development of this Instructional Material.

NIMI also acknowledges with thanks the invaluable efforts rendered by all other NIMI staff who have contributed towardsthe development of this Instructional Material.

NIMI is also grateful to everyone who has directly or indirectly helped in developing this Instructional Material.


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INTRODUCTION

TRADE THEORY

The manual of trade theory consists of theoritical information for the Fourth Semester couse of the TurnerTrade. The contents are sequenced according to the practical exercise contained in the manual on Tradepractical. Attempt has been made to relate the theoritical aspects with the skill covered in each exercise tothe extent possible. This co-relation is maintained to help the trainees to develop the perceptional capabilitiesfor performing the skills.

The manual is divided into six modules. The distribution of time for the practicals in the six modules are givenbelow.

Module 1 Introduction to CNC 25 Hrs

Module 2 CNC Turning 75 Hrs

Module 3 Tool setting and data input 75 Hrs

Module 4 Programme and Simulation 75 Hrs

Module 5 CNC Turning operations 75 Hrs

Module 6 Advance Turning 200Hrs

Total 525 Hrs

The Trade Theory has to be taught and learnt along with the corresponding exercise contained in the manualon trade practical. The indication about the corresponding practical exercise are given in every sheet of thismanual.

It will be preferable to teach/learn the trade theory connected to each exercise atleast one class beforeperforming the related skills in the shop floor. The trade theory is to be treated as an integral part of eachexercise.

The material is not the purpose of self learning and should be considered as supplementary to class roominstruction.

TRADE PRACTICAL

The trade practical manual is intended to be used in workshop . It consists of a series of practical exercies tobe completed by the trainees during the Fouth Semester course of the Turner trade supplemented andsupported by instructions/ informations to assist in performing the exercises. These exercises are designedto ensure that all the skills in the prescribed syllabus are covered.

The skill training in the computer lab is planned through a series of practical exercises centered around somepractical project. However, there are few instance where the individual exercise does not form a part of project.

While developing the practical manual a sincere effort was made to prepare each exercise which will be easyto understand and carry out even by below average trainee. However the development team accept that thereis scope for further improvement. NIMI, looks forward to the suggestions from the experienced training facultyfor improving the manual.


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CONTENTS

Lesson No. Title of the Lesson Page No.

Module 1: Introduction to CNC4.1.111 CNC Technology basics 1

4.1.112 Machine model, control system and specification 6

4.1.113 Axis convention of CNC machine 18

4.1.114 Importance of feedback system and Concept of co-ordinate geometry 23

4.1.115 Coordinate Geometry & Machine Axis 25

Module 2: CNC Turning

4.2.116 -117 Preparation of part programming 30

4.2.118 Operational modes 44

4.2.119 Types of offsets 48

4.2.120 Tool path study of machining operation (Straight turning) 52

4.2.121 -122 Cutting parameters, cutting speed and feed, depth of cut,CSM,tool wear, tool life 60

Module 3: Tool setting and Data Input

4.3.123-124 Cutting tool materials for Turning 68

4.3.125 Tool Geometry, Insert Type, Nomenclature of Inserts 74

4.3.126 Describe tooling system for turning 77

4.3.127 Setting work and tool offset 79

4.3.128 Describe tooling system for CNC Turning centres 80

4.3.129 Cutting tool material for CNC turning 81

4.3.130 ISO Nomenclature for Turning tool holder, boring tool holder, indexable insert 82

4.3.131 Tool holders and inserts for radial grooving, face grooving,

threading and drilling 85

Module 4: Programme and Simulation

4.4.132 Preparation of Part programming as per drawing 87

4.4.133 Checking using CNC Simulator 93

4.4.134 Process and tool selection (CNC) 94

4.4.135 Part programme for Grooving 95

4.4.136 Part progarmme for drilling 96

4.4.137 Part progarmme for boring 97

4.4.138 Part progarmme for threading 99


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Module 5: CNC Turning Operations

4.5.139 Programming on CNC Tapping 101

4.5.140 CNC Programme for Grooving (OD/ID) 103

4.5.141 CNC Programming for threading 105

4.5.142 Trouble shooting in CNC machines 107

4.5.143 Factors affecting quality & productivity 114

4.5.144 Parting off Operation in a CNC 119

4.5.145 Bar Feeding System through Bar Feeder 117

4.5.146 Input and Output of data 118

4.5.147 DNC system 123

4.5.148 Use of CAM Programme 124

Module 6 : Advance Turning

4.6.149 Setting of tool for taper threads, calculation of taper setting and thread depth 126

4.6.150 Interchangeability meaning, procedure for adoption, quality controlprocedure for quality production 135

4.6.151-152 Importance of Technical term used in Industry 158

4.6.153 Terms used in part drawings and Geometrical tolerances, and symbols 175

4.6.154-156 Automatic lathe - types - parts, toolholders, theory of calculation 184

Lesson No. Title of the Lesson Page No.


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LEARNING / ASSESSABLE OUTCOME

On completion of this book you shall be able to

• Set (Both job and tool) CNC turning centre and produce componentsas per drawing by preparing part programme.

• Manufacture and assemble components to produce utility itemsby performing different operations and observing principle ofinterchangability and check functionality item (screw jack, vicespindle, box nut, marking block, drill chuck, collet chuck etc, bydifferent operation).

• Threading (Square thread) BSW, ACME, Metric, thread on taper,different boring operations.

• Make a process plan to produce components by performingspecial operations on lathe and check for accuracy.

• Perform special operation in CNC lathe worm shaft cutting, boring,threading etc.,.


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SYLLABUS

Fourth Semester Duration: Six Month

WeekNo.

79

80-82

Ref. LearningOutcome

• Set (both job andtool) CNC turncentre and producecomponents as perdrawing bypreparing partprogramme.

-do-

Professional Skills (Trade Practical) with Indicative hours

111. Personal and CNC machineSafety: Safe handling of tools, equipment and CNCmachine. (2 hrs.)

112. Identify CNC machine, CNC console. (5 hrs.)

113. Demonstration of CNC lathe machine and its parts - bed, spindle motor and drive, chuck, tailstock, turret, axes motor and ball screws, guide ways, LM guides, console, control switches,coolant system, hydraulic system, chip conveyor, steady rest. (7 hrs.)

114. Working of parts explained using Multimedia based simulator for CNC parts shown on machine. (6 hrs.)

115. Identify machine over travel limits and emergency stop. (1 hrs.)

116. Conduct a preliminary check of the readiness of the CNC turning centre viz., cleanliness of machine, referencing – zero return, functioning of lubrication, coolant level, correct working of sub-system. (2 hrs.)

117. Identification of safety switches and interlocking of DIH modes. (1 hrs.)

118. Machine starting & operating in Reference Point, JOG and Incremental Modes. (12 hrs.)

119. Check CNC part programming with simple exercises and using various programming codes and words. (12 hrs.)

120. Check the programme simulation on machine OR practice in simulation software in respective control system. (12 hrs.)

Professional Knowledge(Trade Theory)

CNC technology basics:Difference between CNC andconventional lathes.Advantages and disadvantages ofCNC machines over conventionalmachines.Machine model, control systemand specification.Axes convention of CNC machine- Machine axes identification forCNC turncentre.Importance of feedback devicesfor CNC control.Concept of Co-ordinate geometry,concept of machine axis.

Programming – sequence, formats,different codes and words.Co-ordinate system points andsimulations.Work-piece zero points and ISO/DIN G and M codes for CNC.Different types of programmingtechniques of CNC machine.Describe the stock removal cycle inCNC turning for OD / ID operation.L/H and R/H tool relation on speed.Describe CNC interpolation, openand close loop control systems. Co-ordinate systems and Points.Program execution in differentmodes like manual, single blockand auto.Absolute and incrementalprogramming.Canned cycles.Cutting parameters- cutting speed,feed rate , depth of cut, constantsurface speed, limiting spindlespeed, tool wear,tool life, relative effect of eachcutting parameter on tool life.


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83-85

86-88

-do-

-do-

121. Absolute and incremental programming assignments and simulations. (12 hrs.)

122. Linear interpolation, and Circular interpolation assignments and simulations on soft ware. (24hrs.)

123. Perform Work and tool setting:- Job zero/work coordinate system and tool setup and live tool setup. (12 hrs.)

124. Carryout jaw adjustment according to Diameter and tooling setup on Turret. (12hrs.)

125. CNC turning centre operation in various modes: JOG, EDIT, MDI, SINGLE BLOCK, AUTO. (12 hrs.)

126. Program entry. (2 hrs.)127. Set the tool offsets, entry of

tool nose radius and orientation. (12 hrs.)

128. Conduct work off set measurement, Tool off set measurement and entry in CNC Control. (8 hrs.)

129. Make Tool nose radius and tool orientation entry in CNC control.(6 hrs.)

130. Jaw removal and mounting on CNC Lathe. (4 hrs.)

131. Manual Data Input (MDI) and MPG mode operations and checking of zero offsets and

tool offsets. (9 hrs.)

132. Program checking in dry run, single block modes. (6 hrs.)

133. Checking finish size by over sizing through tool offsets. (9 hrs.)

134. Part program preparation, Simulation & Automatic Mode Execution for the exercise on Simple turning & Facing (step

turning) (10 hrs.)135. Part program preparation,

Simulation & Automatic Mode Execution for the exercise on Turning with Radius / chamfer with TNRC. (10 hrs.)

Selection of cutting parameters froma tool manufacturer’s catalog forvarious operations.Process planning & sequencing,tool layout & selection and cuttingparameters selection.Tool path study of machiningoperations.Prepare various programs as perdrawing.

Tool Nose Radius Compensation(G41/42) and its importance

(TNRC).Cutting tool materials, cutting toolgeometry – insert types, holder

types, insert cutting edge geometry.

- Describe Tooling system for turning

- Setting work and tool offsets.- Describe the tooling systems

for CNC TURNING Centers.- Cutting tool materials for CNC Turning and its applications- ISO nomenclature for turning tool

holders, boring tool holders, indexable inserts.

- Tool holders and inserts for radial grooving, face grooving, threading, drilling.

Prepare various part programs as perdrawing & check using CNC simulator.Processes and Tool selection related togrooving, drilling, boring & threading


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89-91 -do-

136. Part program preparation, Simulation & Automatic Mode Execution of CNC Machine for the exercise on Blue print programming contours with TNRC. (10 hrs.)

137. Machining parts on CNC lathe with parallel, taper, step, radius turning, grooving & threading. (15 hrs.)

138. Carryout Drilling /Boring cycles in CNC Turning. (15 hrs.) (First 60 % of the practice is on CNC machine simulator, followed by 40 % on machine.)

139. Geometry Wear Correction. Geometry and wear offset correction. (10 hrs.)

140. Produce components on CNC Machine involving different turning operations viz.,

• h Stock removal cycle OD• h Drilling / boring cycles• h Stock removal cycle ID• h Carryout threading in different

pitches. (18 hrs.)141. Produce components by involving

turning operation and partprogramme exercises of C N Cturning viz.,

• h Grooving and thread cutting OD

• h Grooving and thread cutting ID

• h Threading cycle OD• h Sub programs with repetition• h Using Sub Programs &

Cycles in the Main Program. (18 hrs.)

142. Part off: Part Prog. (4 hrs.)143. Produce job involving profile

turning, threading on taper, boring, etc. operations. (22 hrs.)

144. Demo on M/C on bar feeding system. (simulation/ video)

(1 hrs.)145. DNC system setup.

(Optional)146. Run the machine on DNC mode.(Optional)147.CAM programme

execution.(Optional)148. Data Input-Output on

CNCmachine. (2 hrs.)

- Describe Tapping on CNC turning.

- Programming for Grooving/Threading on OD/ ID in CNC Turning.

- Trouble shooting in CNC lathe machine

- Identify Factors affecting turned part quality/ productivity.

- Parting off operation explanation.

- Bar feeding system through bar feeder.

- Input and Output of Data.- DNC system. Interlacing

with PC.- Use of CAM Programme.

(Optional)


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92 - 93

94-95

96

97

Manufacture andassemble componentsto produce utility itemsby performing differentoperations & observingprinciple ofinterchangeability andcheck functionality.[Utility item: - screwjack/ vice spindle/Box nut, Markingblock, drill chuck,collet chuck etc.;different operations:- threading (Square,BSW, ACME,Metric), Thread ontaper, differentboring (Plain,stepped)]

-do-

Make a processplan to producecomponents byperforming specialoperations on latheand check foraccuracy. [Accuracy- ±0.02mm or proofmachining &±0.05mm bore;Special operation -Worm shaft cutting(shaft) boring,threading etc.]

-do-

149. Theard on taper surface(Vee form) (50 hrs.)

150.Manufacturing& Assembly of Screw jack/vice/Box nut byperforming different latheoperation.(To use earlierproduce screw jack).(50 hrs.)

151. Prepare different types of documentation as per industrial need by different methods of recording information. (4 hrs.)

152. Turn Bevel gear blank. (21 hrs.)

153. Read a part drawing, makeaprocess plan

Setting of tool for taperthreadscalculation of tapersetting and thread depth.Heat treatment – meaning &procedure hardening,tempering, carbonizing etc.Different types of metal usedinengineering application.

Interchangeability meaning,procedure for adoption, qualitycontrol procedure for qualityproduction.

Importance of Technical Englishtermsused in industry –(in simpledefinitiononly)Technical forms, processcharts,activity logs in required formats ofindustry, estimation, cycle time,productivity reports, job cards.

Terms used in part drawings andinterpretation of drawings –tolerances,geometrical symbols - cylindricity,parallelism. etc.


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98

99

100 -101

102-103

104

-do- 154. Practice of special operationson lathes - worm gear cutting.(Shaft) (25 hrs.)

155. Boring on lathe using soft jaws to make bush with collar(standard) on non ferrous metaland check with dial bore gaugeto accuracy of +/- 0.05 mm.(15 hrs.)

156. Make Arbor support bush. (Proof Machining) (10 hrs.)

In-plant training/ Project work (Any Project to be done onCNC machine)1. Taper Sunk2. Socket With Split Collet3. Screw Jack4. Spindle With Hub5. Morse Taper Eccentric6. Crank Shaft With Taper Sleeve

-do-

Automatic lathe-its main parts,types diff. Tools used-circulartool etc

Related theory andcalculation.

Revision

Examination


1

Production & Manufacturing Related Theory for Exercise 4.1.111Turner - Introduction to CNC

CNC Technology basicsObjectives: At the end of this lesson you shall be able to• describe the fundamentals of NC controls• state the present status of CNC technology• state the different between conventional lathe and CNC lathe• state the specification of CNC lathe• state the advantages and disadvantages of CNC.

When the computer was invented, the inventor himselfmust not have dreamt of the use of computers in variousfields of life which is drastically changing the entirescenario of the Universe. It is now an integral part of ourday to day life. There is lot of research going on with thehelp of computers in the field of factory automation. Thedeclining cost of computers coupled with the invention ofMulti task high speed micro processors, really made anindustrial revolution and there seems to be no end forthis. A distinct trend can be observed in industries whichinclude an increase in the use of Computer controlledMachine tools, the application of new manufacturingsystems, such as laser beam machines and appearanceof new generation of industrial robots in the productionline, the manufacturing management through MRP I, MRPII & MRP III etc.(Material Resource Planning)

Evolution of automationAutomatically controlled factory is nothing more than thelatest development in the industrial revolution that beganin Europe two centuries ago and progressed through thefollowing stages:

- Mechanisation started in 1870 at the beginning ofindustrial revolution with simple production machines.

- In 18th Century fixed automatic mechanism andtransfer lines came into existence for faster outputand shorter production time.

- Simple automatic control machines and copyingmachines were invented in the later part of the 18thcentury. After 1950 the industrial automation wasstarted. In this second phase of the industrialautomation/revolution, workers, instead of physicallyperforming all the task are placed in the control of themachines.

Progressive change after 1950 is as follows- The introduction of numerical control (NC) in 1952

opened a new era in automation.

- The extension of NC was Computerised NumericalControl (CNC) machine tools in which computer (MicroProcessor) is included as an integral part of the controlsystem.

- Commercial Industrial robot was manufactured in1961 along with CNC systems. The use of theserobots, are well utilised only after 1970's.

- The next logical extension is a fully automated factorywhich employs a flexible manufacturing system (FMS)and Computer Aided Design/Computer AidedManufacturing (CAD/CAM) techniques.

- The latest of the above is Computer IntegratedManufacturing (CIM) which includes battery of CNCmachines, with flexible modules for manufacturing toolhead changers, automatic material handling systemlike AGV's (Automated Guided Vehicle) etc withminimum number of operating personnels.

Fundamentals of NC controlsNC equipment has been defined by Electronics IndustriesAssociation (EIA) as "A system in which actions arecontrolled by the direct insertion of numerical data at somepoint. The system must automatically interpret at someportion of the data".

In a typical NC system the part program is prepared on apunched tape. The part programme is arranged in blocksof information needed for processing a segment of workpiece, the segment of length, speed, etc.

Advantage of NC machine are- Complex shapes can be machined easily

- Accuracy and repeatability is achieved.

- High production rate

- Reduced component rejection

- Less operator skill and involvement

There are many disadvantages of NC system:

- If tape is spoiled the entire programme ofmanufacturing will be affected

- Editing of the program in tape is not very easy.

- Manual loading of tape is a laborious job.

- Instruction are read, block by block and carried outwhich is slow when compared to CNC machine tools:

- If the punch reader is not reading the program properlythen the entire production is lost.

Computer numerical controlA dedicated micro processor or mini computer on themachine control makes the computer numerical control.CNC machines are very popular coupled with lots of otheradvantages:


2

-

Advantages

- Accuracy and repeatability is very high

- Reduced scrap and rework

- Reduced inspection time

- Ease of inter changeability of machined parts

- Reduced space

- Reduced material handling

- Less paper work

- Less lead time

- Less inventory

- Easy editing of programme

- Complicated shapes and contours are easilymanufactured with quality assurance and betterproduction management.

- Better utilisation of machines.

- Reduced tooling

- Reduced operator skill

- Jig not used but with minimum fixtures

- Reduced floor space

- Higher level of integration such as DNC, FMS, CAD/CAM, CIM etc.,

Disadvantages of CNC machines

- High cost of machine

- High cost of training needs

- High Maintenance cost

Major advantages of CNC machines are

- Higher production

- High quality production

These are achieved through:

Higher production

A. Keeping idle time as minimum as possible

B. Keeping machining time to a minimum

A Keeping idle time as minimum

1 Loading/unloading : Through quick work holdingand work handling systemlike pallets, robots etc.

2 Tool Change time : Kept as minimum by ATC,quick change tool turret etc.(max.time is less than 8sec.)

3 Movement of slide : Rapid movement is easilyachieved through best servofeedback motors

4 Changing of cutting : Step less Speed, feed etc areconditions changed easily through

programming instruction.

5 In process control : Self diagnosing and gaugingthrough measuring probesthe parts and tools areavailable as an in-processcontrol.

B Keeping machining time to minimum

Higher metal removal rate through

- Proper cutting tools

- Rigid machine spindle

- Higher spindle power

- Higher feed power

- Rigid structure

- Multi spindle

- Multi turrets etc.

Higher quality is achieved

- Servo mechanism - For correction of feedthrough motors

- Curvic coupling - For quick indexing

- Linear motion guides - For heavy load movementof slides.

- Linear ball screw - For accurate friction freebacklash free movement

- Encoders and tacho - For accurate positioninggenerator and velocity error correction

etc.

Applications of CNC

In automobile, aircraft and general engineering industry,CNC machines are common sight now a days. CNC isused to control almost all types of machines and some ofthe commonly used machines are listed below:

- CNC lathes

- CNC Milling/drilling machine

- CNC turning centres.

- CNC Turn mill centre

- CNC Machine centre, Multi machining centre

- CNC Tool and cutter grinding.

- CNC Grinding machine, surface, cylindrical etc.

- CNC boring and jig boring machines etc.

- CNC EDM, Wire cut EDM etc.

- CNC Gear hobbing, gear shaping, gear grinding etc.

- CNC Electron beam welding

- CNC Laser/plasma/arc welding machine etc

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.1.111Copyright @ NIMI Not to be Republished

3

- CNC Co-ordinate measuring machines

- CNC Nibbling press, press brakes, turret

Present status CNC technology

Now a days, CNC controllers with system like Sinumeric,Fanuc, Friera, Allen Brandly, Mazak etc come with graphic

display of tool, paths, along with other software's haveconsiderably reduce the manual part programming ofthree dimensional jobs.

User defined parametric programming, Standard Cycleslike stock removal, drilling milling pattern etc are now aday's standard component of the Systems.

Some latest controls are having "DOS" front end withCAD/CAM facility in which one can design a componentand get the computer assisted part programmes (CAPP)and proving the component on the machine control itselfwithout wasting much time and money. Modern machinetools have multi spindle with a spindle speed of 75000

rpm; Cutting feed rate of 5000 mm/min, and rapid traverseof 20000 mm/min. Use of multi various sensing elementswith adaptive controls, remote diagnostics system makesthe machine more versatile and free from accidents.


4

The silent and salient use of computers in factoryautomation and in factory management will boost thequality and quantity in production, which in turn willdefinitely change the lifestyle of the people in future.

Advantages of CNC machines over conventionallathes

- Less manual work.

- Semi skilled operator can operate the machine.

- Greater accuracy.

- More flexibility.

- Alteration in dimension is easier through programme.

- Simulation is possible with that we can verify thedimensions of the component.

- Production rate is more.

- Profitability is high.

- Repeatability is very high compared to conventionallathe.

- One operator can operate more than one machine.

- Lesser production cost.

- Reduced part inventory.

- Reduced floor space requirements.

- Improved manufacturing control.

- Complicated parts shape can be easily machined.

- More number of tools are made available

Disadvantages of CNC machines

- Higher investment cost.

- Higher maintenance cost.

- Training of CNC operator involves more cost.

- Semi skilled or unskilled operator cannot doprogramming in CNC.

- Cost of spare parts and tool cost are high.

- Suitable for mass production only.

Difference between conventional and CNC lathes

Conventional lathe CNC

1 Involves more manual Less manual workwork

2 Skilled labour needed Basic Skill is enough

3 Less accuracy More accuracy

4 Less flexible More flexible

5 No part programming Part programmingrequired

6 Any alteration is Re-programming fordifficult dimensional changes

made easier manually7 For every component Once the programme is

machining is done done, the computerwith great care. takes care

8 Simulation or trial Simulation or trial runrun not possible possible and correction

may be done if required.

9 Less production rate More production rate

10 Repeatability is not Rate of repeatabilitypossible is high

11 Individual operator One operator canrequired for each operate more thanmachine one machine


5

SPECIFICATIONS OF C.N.C LATHE

1 No. of controlled axis 2

2 Interpolation Linear/circular/parabolic

3 Maximum swing over bed 320 mm

4 Maximum machining length 245 mm

5 Collet ID = 56 mm OD = 48 mm

6 Spindle taper hole ∅52 mm

7 Maximum bar dia ∅38 mm

8 Spindle head type A2 - 5

9 Spindle speed range 60 to 5000 R.P.M

10 Main motor 3.70 KW

11 Chuck size ∅200 mm

12 Chuck type Hydraulic, solid

13 Rapid transfer speed on x axis 18 metre/min

14 Rapid transfer speed on z axis 18 metre/min

15 X axis travel 200 mm

16 Z axis travel 320 mm

17 Guideway type Linear guideway

18 Turret type Gang type

19 Turret tool Boring bar size 20/20 mm ∅20 mm

20 Weight 1700 Kg

21 Dimensions 1600x1250x1650 mm


6


Machine model, control system and specificationObjectives : At the end of this lesson you shall be able to• explain the control panel• list the control keys and learn technical specification of CNC machine• list the address keys.


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EMCO CONTROL PANEL

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.1.112

IntroductionThe CNC control system of a machine tool includes mainlycontrol unit and the motion control system. The motioncontrol system includes servo motor, drives, axispostioning devices. The control systems are classified

as contouring system, point to point system, closed loop/open loop system and based on number of axis of themachine.The details of the control unit and the controlsystems are shown in the following pages.

1 Power consumption main motor (relative display)

2 Chuck open/closed

3 Sleeve forwards

4 Sleeve backwards

5

6 Central lubrication manual with display

7 Tool turret, manual operation

8 Coolant On/Off with display

9 Single item for bar feed with display

10

11 Drives On

12 Drives off

13 Control On

14 Feed rate override switch 0-120%

15 Emergency-off button


8

Alarm (red)The display is bright whenever an alarm oc-curs. The alarm number is displayed on thescreen. The alarms are explained in thealarm list.

Position not yet reached (green)The display is bright until the set positionhas been reached.

Feed stop (red)The display is bright if the feed is stoppedwhile the program is running.

Program running (green)The display is bright until the program hasbeen completed. Even if the machine is notmoving.

Key assignment display (yellow)If the "key assignment display is bright, thelower-case function (the bottom function) ofa dual-function key is displayed in the inputline when the dual function key is depressed.If the "key assignment." Display is not bright,the upper function is entered. Switchover isexecuted automatically by the controller af-ter a word has been entered in the partscases, switchover can be executed bymeans of key in the address keypad.

Keys and display field Display field


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Address keys/numeric keys

SINUMERIC 810 T

SINUMERIC 810 M

Address keys, numeric keys and symbol keys

parameter ionInterpolat Address

5 Number


4 Number

data Position Address

9 Number


8 Number


7 Number

condition path Address

x)

number block Address

x)

block Skip

x)

program of Start

x)

Alternate changeover to top andbottom functions. The display is theneither bright or dark.



x)


x)


6 Number


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Entering a wordThe word in the input line is transferredto the parts program memory, or intolist displays or input forms.

Modifying a wordThe word identified with the correctionpointer is replaced by the word in theinput line. The addresses of both wordsmust be identical.

Delete inputThe input line is deleted character-by-character. If the key remains depressedthe characters entered are deleted insequence until the input line is empty.

Delete word/blockThe word identified by the correctionpointer is deleted in the parts programmemory if the respective address is inthe input line. A complete block isdeleted if the respective block numberis in the input line.

x)

In the input line characters appear which are not nor-mally permitted for normal programming.

The characters a,b,c,d,e,f are required to enter or modifycommands in CLB00 machine code.(@----).

Input and correction

correction tool Address

2 Number

Feed Address

1 Number

A AngleAddress

Mulitiplication

U Radius Address

x)unassigned

B Radius Address

x)


6 Number

block of End

Additional

function AuxiliaryAddress

character Space

number Tool Address

point Decimal

speed Spindle Address

0 Number

function l AdditionaAddress

line input Sign

function l AdditionaAddress

nSubtractio

passes of No. Address

x)

Subroutine Address

3 Number


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Channel selection switchThe CRT display is switched to the channelselected. Selection is by repeated depress-ing of the channel selection switch.

Acknowledging alarmsAlarm form alarm No. 3000 onwards, e.g."General programming error" alarm can beacknowledged with this key. "Rest alarm isnot acknowledged!

Actual value display selection withdouble-height charactersIf the key is depressed again, the previousdisplay reappears.

Search keySearching for a particular address or wordin the parts program memory. The expres-sion appearing in the input line when thesearch key is depressed is looked for. Afterthe search key has been depressed, the cor-rection pointer marks the next expressionfound.

Integrated machine control panel

Diagnostics and start upSelection of machine data and switching tostart-up state after entering pass word.

Paging backwards/forwardsThe CRT display is paged up or down onepage at a time.

Correction pointer backwards/forwardsThe correction pointer is moved backwardsor forwards block-by-block.

If the key remains depressed, the correctpointer goes to the beginning or end of theprogram.

Correction pointer left/rightThe correction pointer is moved to the leftor right word-by-word. The correction pointerjumps from the beginning of the block to theend of the previous block or from the end ofthe block to the beginning of the followingblock. If the key remains depressed, thecorrection pointer goes to the beginning orend of the program.

Integrated machine control panel

SINUMERIC 810 T

SINUMERIC 810 M

Control keys


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Feed slower/fasterThe programmed feed is modified in the fol-lowing increments from 0% to 120 % 0%1% 2% 4% 6% 8% 10% 20% 30% 40% 50%60% 70% 75% 80% 85% 90% 95% 100%105% 110% 115% 120%.

If the key is depressed constantly the endposition is approached. The percentagevalue set is displayed in the basic display.

In rapid traverse mode the 100% value isnot exceed.

Spindle speed slower/fasterThe programmed spindle speed can bemodified in increments of 5 % in the rangeof 50 % to 120 % . If the key is depressedconstantly, the final position is approachedin increment of 5 %. The percentage valueset is shown in the basic display.

Operating mode selection keyThe following modes can be selected via asoft key:

PRESETMDI AUTOMATICJOG INC 1 TO INC 10,000(manual encoder)REPOSAUTOMATICREFPOINTProgram STOP

The running program is interrupted Theprogram can be resumed with "ProgramSTART".

Program STARTA parts program is started. The functionsstored are transferred to the PLC in au-tomatic mode.

Spindle STOP/START

Feed STOP/START

Rapid traverse override keyIf this key is depressed simultaneouslywith the direction keys the axes are tra-versed in rapid traverse mode.

Universal interface port

ResetThe running program is aborted Alarmsare deleted (up to alarm No. 2999). Thecontroller is brought to the basic state!

Single blockThe parts program is processed block-by-block. Start is by means of "ProgramSTART".

Direction keysWhen the direction keys are actuated,the axes are traversed in jog mode.


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CALL PROGRAM FORM MEMORY FOR EXECUTION

Switch control to reset

Main program or subroutine

Enter program number

Store

Program control, if desired (see next page)

Single block, if desired

Cycle start


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PROCEDURE FOR BLOCK SEARCHING:1 Select the AUTOMATIC pressing MODE button.

2 Close the feed rate completely.

3 Press (Etc key) and bring the BLOCK SEARCH menu.

4 Enter the necessary block number/sub program blocknumber.

5 Press START.

6 Confirm whether the required block reached on theMonitor at N

7 Press MODE button for bringing the REPOS mode,and select REPOS.

8 Bring the offset values to Zero by Pressing the neces-sary (+) or (-) direction keys X,Y,Z and feed rate con-trol switch at > 0%

9 Press > (etc key) to bring Over Store.

10 Enter necessary Tool number, Spindle speed, "T","D","S","M" code.

11 Press CYCLE START key.

12 Bring Automatic mode by pressing MODE key.

13 Press ACTUAL BLOCK (Look at the Cursor and theblock search complete).

14 Continue to Run the program by pressing Cycle Startkey and watch Distance to go Actual position and theActual values. ('G' codes, M,F,S,T,D, etc.)

BLOCK SEARCHING AND RUNNING PROGRAMME

AUTOMATIC


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Machine models

CNC machines are generally grouped under 2 axis and3 axis or multi axis system. Horizontal 2 axis (x and z)are termed as CNC lathe and the vertical CNC machinesare called as machining centre.

The machine models are also based on the spindle drivesnamely.

- Separately excited DC shut motor

- 3 Phase AC induction motor

The CNC machine models are also based feed drivesare

- AC servometer

- DC servometer

- Brushless DC servometer

- Stepper motor or liner motor

Technical Specification of CNC machines

1 Traverse x’ - 600 mm (Saddle movement)

y’ - 450 mm (Head movement)

z’ - 420 mm (Column movement)

2 Pallet Pallet size - 500x500mm

Max load - 500 Kgf

indexing position - 360 degree

3 Spindle 11.Kw continuous 14.2 (intermitent)

Type of motor ACand drive

Bearing dia 100 mm

Spindle taper ISO 40

4 Spindle speedsSpindle range 40 - 4000 Rpm or

60 - 6000 Rpm (optional)

Constant range 40- 4000 Rpm or60 - 1500 Rpm (Optional)

Constant power 1000-4000 Rpm orrange 1500-6000 Rpm (Optional)

5 Feeds

Rapid traverse 20 M/min

x,y,z Axis cutting 1 to 10000 mm/minfeed rate

6 Feed Motor

Torque X and 18.5 Nm

Y axes z - Axis 29 Nm


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7 Thrust CapacityX - Axis 600 KgfY - Axis 600 KgfZ - Axis 1000Kgf

8 Ball ScrewPitch 12 mmDia 50 mm

9 Auto Tool changerNo of tools 24 NosMax. Tool Dia 10 mmMax. Tool Weight 15 KgfMax.Tool length 350 mmTool changing time 6 to 12 seconds based on tools

10 Twin pallet changerNo of pockets 2 NosPallet changing Time 25 Sec

11 HydraulicMotor power 3.7 KwTank Capacity 90 litres Indian Oil servo 32 or equivalent

12 Machining capacityMilling capacity (steel55 - 65 Kg/mm square) 100 cc/min

Drilling capacity (Steel55-65 Kg/mm square) 30 mm diameter

Tapping Capacity (Steel55 -65 Kg/mm square) M 24 x 1.5 mm

13 Machining capacityMachining capacity 10000Kg

14 Floor space requirement 5900mm (w) x5550mm (L)

Basic machine x 3100 (H)

15 Air requirement 16 Ipm at 5 kg/ Sq.cm

16 Electrical supply 50 KVA

Control SystemIn CNC machines there are mainly two types of controlsystem,namely

1 Open loop control system (Fig 1)

2 Closed loop control system (Fig 2)

Open lop control system (Fig 1)In an open loop control system (Fig 1) in which there is noarrangement for detecting or comparing the actual positionof the cutting tool on the job with the command studies.

Therefore, this system is not providing any check to seethat the commanded position has actually beenachieved.There is no feed back of information to the

control also. These system are not good where extremelyaccurate positioning is required.

Closed loop control system (Fig 2)Closed loop control (Fig 2) is a term which is used veryoften when we talk about CNC machines. This termsignifies, that the control system has provisions to ensure


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tha the tool reaches the desired position, at the correctfeed rate, even if some errors creep in due to unforeseenreasons.

For instance in the previous example 60,000 pulses sentin 2minutes by the control should cause a tool travel of60 mm at 30 mm/min, but even if the control sends thesepulses it cannot be ensured that the tool has reallytravelled exactly 60 mm.

A closed loop control has a device called encoder and thiscan continuously ascertain the distance actually travelledby the tool and then monitor the same, in the form offeedback signals to the control. The control studies thisfeedbacck information and takes corrective action in caseany error is detected in the tool position/feed rate.

Another control system is based on 5 axis & above

• Motion type CNC control system

• Loop control system

• Number of axis type CNC control


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Axis convention of CNC machineObjectives: At the end of this lesson you shall be able to• identify CNC machine by number of axes• identify CNC machines by orientation of axes• understand NC coordinate and learn X and Y axis movement.

Types of CNC milling machinesMilling machines can divided into three categories

1 by the no of axes

(two, three or more)

2 by the orientation of axes

(vertical or horizontal)

3 by the presence or absence of a tool changer.

The spindle motion is up and down in vertical milling/machining centre.

The spindle motion is in and out in horizontal milling/machining centre.

These machines are capable to perform the followingoperations:

Drilling, Reaming, boring, tapping, profiling, thread cuttingand many other operations.

ATC: Automatic Tool changer.

APC: Automatic pallet changer

CNC: Computer Numerical Control

With the above advanced features built in millingmachines become the new breed of machine tools calledmachining centres.

Machine axesThe machining centres are provided with minimum threeaxes of ‘X’,’Y’&’Z’ axis and fourth axis machines becomemore flexible i.e the fourth axis ‘A’ for vertical model and‘B’ of horizontal model. The machine with five or moreaxes is of higher level of capacity.

In aircraft industry 5 axes profile milling machine is usedfor complex shapes and to reach cavities and variousangles.

Meaning of half / full axis in NC language (what is half /full axis machine)

A full axis vertical machine has X,Y,Z as primary axesand indexing table designated as ‘A’ axis which canposition but cannot rotate simultnesously is called 3 1/2axes machine. If the machine is equipped with full rotatingtable, simultaneously then it is called four axis machinetool.

In the milling systems, three most common machine toolsare

CNC vertical machining centre - VMC

CNC horizontal machining centre - HMC

CNC horizontal boring mill

Vertical Machining Centres (Fig 1)

VMC is for flat type of work where the machining is doneon only one face of the part in single set up.

An optional fourth axis can be provided by mounting rotarytable to the main table either vertically or horizontallydepending on the desired results and the model type.

In the combination with a tailstock (usually supplied) thefourth axis in the vertical configuration can be used formachining long parts,which need support at both ends.

For programming two types of systems are followed. Inone type programming always takes place form the viewpoint of the spindle, not the operators eye, view as iflooking straight down at 90o towards the machine, fordevelopment of the tool motion.

In the second type, various markers located some wherein the machine itself, show the positive and negativemotion of the machine axes. For programming,thesemarkers should be ignored. The programming directionsare exactly opposite to the markers on the machine tool.

Horizontal machining centers (Fig 2)

Horizontal CNC machining centres are also categorizedas multi - tool and versatile machines, and are used for


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cubical parts, where the majority of machining has to bedone on more than one face in a single setup.

There are many applications in this area. Commonexamples are large parts, such as pump housings, gearcases, manifolds, engine blocks and so on. Horizontalmachining centres always include a special indexing tableand are typically equipped with a pallet changer and otherfeatures.

Axis - nomenclatureThe basic designation of the axis (i.e.), in Fig 3 which isX, Y, Z, is decided by the right hand thumb rule and themain spindle axis. The thumb indicates X - axis, fore fingerindicates Y - axis and the middle finger indicates Z - axis.

Auxillary axes on NC machineApart from each side movement axes on the machine,some other auxillary axes can exist. E.g. Rotary table.This rotary table axis is designed as A axis if it is parallelto X direction. Similarly B and C axes for Y and Zrespectively.

Right hand ruleThe rotary movements about X, Y and Z are designatedas A, B and C respectively. The right hand rule is used to

define the positive direction of the coordinate axes asper the Fig 4.

Z - axis (Fig 5)

The axis of the main (i.e. principle) machine spindle,whether it be the axis of the tool spindle or the axis aboutwhich the work piece rotates, is denoted as the Z axis.On machine tools, which do not possess principle spindle(e.g. planning machines) the Z - axis is perpendicular tothe work holding surface.

X - axisThe X - axis is always horizontal, parallel to the workholding surface and perpendicular to the z - axis.

Y - axisThe Y - axis is perpendicular to both Z and X axis.

Milling tool coordinate system (Fig 6)

Classification of machines.CNC machines can be classified by various ways,

a) According to number of axisCNC machine can be classified as

• 2 axis machineProduction & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.1.113Copyright @ NIMI Not to be Republished

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Straight cut controlThe system provides feed motion in two axes (but notsimultaneously) and hence their capability is limited toperforming milling either along X axis or along Y axis.(Fig 8)

• 3 axis machine

• 4 axis machine

It should be noted that each axis has it own drive motor.

b) According to CNC systemThere are three types of CNC systems based on theircapability in providing feed in different axes.

• 1 Point -to- point control

• 2 Straight cut control

• 3 Contouring control

Point-to-point controlMachines with point-to-point control provide only one feedaxis while the other two axes can perform only rapidmotion. Machines with point-to-points control are suitedonly for drilling operations. (Fig 7 )

Contouring controlThis can provide feed control in 3 axes. They are alsocapable of providing simultaneous feed in 2 or 3 axis.

Milling machine with contouring control can mill contoursmade up of straight lines and arc/circular elements..Depending on the number of axes that can besimultaneously fed, contouring controls are furtherclassified as 2D control, 2 1/2D control and 3D control.

i) 2D controlMachines with 2D control can be simultaneous feed onlyin two of the 3 axes. They can mill only contours withconstant depth that too in just one plane ( X-Y) (Fig 9& 10)

ii) 2 1/2D controlMachines with 2 1/2D control can have simultaneousfeed of any of the two axis X-Y, X-Z,Y,Z and, hence theycan mill contours (of constant depth) in any one of the 3planes. (Figs 11 & 12)


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Machine axis identificationNC coordinates system (Fig 1)

All the NC machine toolmaker’s use of Cartesiancoordinate system for the sake of simplicity. The guidingcoordinate system followed for designating the axes isthe well known as right hand coordinate system.

Designation of axesFirst axes to be identified is the z axis .This is then followedby x and y axes respectively.


Part programming for turning centersDiameter programmingThe dimensioning of a turned component is generallyspecified by its diameters. However, in turning operation,the tool should approach the work piece in radial directionfor matching. Hence, for the sake of simplicity, most ofthe turning centers are provided with diameterprogramming facility.

This means that all the movements of the tool alongX-axis should be doubled to represent the diametral ratherthan radial movement. The selection of radius or diameterprogramming depends upon the system variable setduring the integration of controller with the machine tool.

Axis system(Fig 2)

In turning centers, the spindle axis is designated as Z.The radial axis perpendicular to the z-axis and awaytoward the principle tool post is termed as x-axis .Themachine datum or home position may be the intersectionof spindle axis and clamping plane. At the start, thecontroller display will show the axis position with respectto home The work piece datum is fixed by the programmeron the work piece for the convenience of partprogramming. The difference between the tool tip positionand the turret datum is termed as offset.

Z-axisThe z-axis motion is along the spindle axis or parallel tothe spindle axis. In the case of machine without a spindlesuch as shapers and planers, the z-axis is perpendicularto the work holding surface.

For machines such as milling, drilling and lathe, the cuttingtools move in the negative z direction to move a tool intothe work piece. The positive z motion increases theclearance between the tool holder and work piece surface.

When there are several spindles and slide ways, thespindle perpendicular to the work holding surface may


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be chosen as the principle spindle. The primary Z motionis then related to the primary spindle. The tool motions ofother spindles or slides, designated as U, V, W and P, Q,R respectively.(Fig 3)

X-axisThe principle motion direction of cutting tool on the workpiece is designated as x-axis .It is perpendicular to thez-axis and should be horizontal and parallel to the workholding surface whenever possible.


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Imporatance of feedback system and Concept of co-ordinate geometryObjectives: At the end of this lesson you shall be able to• understand feedback system• understand the cartesian coordinate system• understand the four quadrants• explain the difference between polar and rectangular coordinates.

Importance of feedFeed Back System:• The feedback system is also referred to as the

measuring system.

• It uses position and speed transducers to continouslyand monitor the position at which the cutting tool islocated at any particular instant.

• The MCU uses the difference between referencesignals and feedback signals to generate the controlsignals for correcting position and speed errors.(Fig 1)

A Cartesian coordinate system is coordinate systemthat specifies each point uniquely in a plane by a pair ofnumerical coordinates, which are the signed distanceto the point from two fixed perpendicular directed lines,measured in the same unit of length. Each reference lineis called a coordinate axis of the system, and the pointwhere they meet is its orgin, at ordered pair (0,0). Thecoordinates can also be defined as the positions of theperpendicular projections of the point on to the two axes,expressed as signed distances from the origin.

One can use the same principle to specify the position ofany point in three-dimensional space by three cartesiancoordinates, its signed distances to three mutallyperpendicular planes (or, equivalently, by its perpendicularprojection onto three mutually perpendicular lines). Ingeneral, n-cartesian coordinates (an element of real n-space) specify the point in an n-dimensioanl Euclideanspace for any dimension n. These coordinates are equal,up to sign, to distances from the point to n mutuallyperpendicular hyper planes.

Coordinate system and ordered pairsA coordinate system is a two-dimensional number line,for example, two perpendicular number lines or axes.

This is a typical coordinate system:

The horizontal axis is called the x-axis and the verticalaxis is called the y-axis.

The centre of the coordinate system (where the linesintersect) is called the origin. The axes intersect whereboth x and y are zero and is taken as origin Thecoordinates of the origin are (0,0).

An ordered pair contains the coordinates of one point inthe coordinate system. A point is named by its orderedpair in the form of (x,y). The first number corresponds tothe X-coordinate and the second to the Y-coordinate.

To graph a point, you draw a dot at the coordinates thatcorresponds to the ordered pair. It’s always a good ideato start at the orgin. The x-coordinate tells you how manysteps you have a take to the right (positive) or left(negative) on the x-axis. And the y-coordinate tells youhow many steps to move up (positive) or down (negative)on the y-axis.

The ordered pair (3,4) if found in the coordinate systemwhen you move 3 steps to the right on the x-axis and 4upwards on the y-axis.(Fig 3)

The ordered pair (-7, 1) is found in the coordinate systemwhen you mave 7 steps to the left on the x-axis and 1step upwards on the y-axis.(Fig 3)


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In mathematics, the polar coordinate system is a two-dimensional coordinate system in which each point on aplane is determined by a distance from a reference pointand an angle from a reference direction.

The reference point (analogous to the orgin of a Cartesiancoordinate system) is called the pole, and the ray fromthe pole in the reference direction is the polar axis. Thedistance from the pole is called the radial coordinate orradius, and the angle is called the angular coordinate,polar angle.

Uniqueness of polar coordinate & conversion tocartesian coordinate.Adding any number full turns (360°) to the angularcoordinate does not change the corresponding direction.Similarly any polar coordinate is identical to the coordinatewith the negative radial component and in the oppositedirection. The polar co-ordinates ‘r ’ and ø can beconverted into the cartesian coordinate (x,y) by using thetrignometric functions sine & cosine.

x = r cos ø

y = r sin ø

r = x2+y2 r = length of line, ø= its angle with axis

To find out the coordinates of a point in the coordinatesysem you do the opposite. Begin at the point and followa vertical line either up or down to the x-axis. There isyour x-coordinate. And then do the same but following ahorizontal line to find the y-coordinate.

Absolute coordinatesAbsolute coordinates are based on the orgin (0,0), whichis the intersection of the X and Y axes. Use absolutecoordinates when you know the precise X and Y valuesof the point.

With dynamic input, you specify absolute coordinates withthe # prefix is not used. For example, entering #3,4specifies a point 3 units along the X axis and 4 units alongthe Y axis from the orgin.

The following example draws a line beginning at an Xvalue of -2, Y value of 1, and an endpoint at 3,4. Enterthe following in the tooltip.

Command: lineFrom point: #-2,1To point: #3,4The line is located as follows:(Fig 4)

To point: #0,3To point: #-5,-3Polar coordinate systemPoints in the polar coordinate system with pole O andpolar axis L. The point with radial coordinate 3 and angularcoordinate 60 degrees or (3, 60°). and the point (4, 210°)represents polar coordinates.

Relative coordinates or incremental coordinateRelative coordinates are based on the last point entered.Use relative coordinates when you know the location of apoint in relation to the previous point.

To specify relative coordinates, precede the coordinatevalues with an @ sign. For example, entering @3,4specifies a point 3 units along the X axis and 4 units alongthe Y axis from the last point specified.

The following example draws the sides of a triangle. Thefirst side is a line starting at the absolute coordinates -2,1and ending at a point 5 units in the X direction and 0 unitsin the Y direction. The second side is a line starting at theendpoint of the first line and ending at a point 0 units inthe X direction and 3 units in the Y direction. The final linesegment uses relative coordinates to return to the startingpoint.

Command: lineFrom point: #-2,1To point: #5,0


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Coordinate Geometry & Machine AxisObjectives: At the end of this lesson you shall be able to• understand the machine coordinate system• state real number line• understand cartesion coordinates system• understand the cartesian coordinates of three-dimensional space.

Machine coordinate systemMost of the CNC machinery have a default coordinateassumed during power up of machine coordinate system.The origin of the system is called machine origin are homezero location. Home zero is usually located at the toolchange position.

In the manufacturing industry, with regard to numericallycontrolled machine tools, the phrase machine coordinatesystem refers to the physical limits of the motion of themachine in each of its axes, and to the numerical coordinatewhich is assigned (by the machine tool builder) to each ofthese limits. CNC Machinery refers to machines anddevices that are controlled by the using programmedcommands which are encoded on to a storage medium,and NC refers to the automation of machine tools that areoperated by abstract commands programmed andencoded onto a storage medium.

The cartesian coordinate systemCartesian coordinates allow one to specify the location ofa point in the plane, or in three dimensional space. thecartesian coordinates or rectangular coordinates systemof a point are a pair of numbers (in two dimensions) or atriplet of numbers (in three - dimensions) that specifiedsigned distances from the coordinate axis. First we mustunderstand a coordinate system to define our directionsand relative positions (axis) and a reference position(origin). A coordinate system can be rectangular or polar,

Just as points on the line can be placed in one to onecorrespondence with the real number line, so points inplane can be placed in one to one correspondence withpairs of real number line by using two coordinate lines. Todo this, we construct two perpendicular coordinate linethat intersect at their origins, for convenience. Assign aset of equally space graduations to the x and y axesstarting at the origin and going in both directions, left andright (x axis) and up and down (y axis) point along eachaxis may be established.We make one of the numberlines vertical with its positive direction upward andnegative direction downward. The other number lineshorizontal with its positive direction upward to the right andnegative direction to the left. The two number lines arecalled coordinate axes; the horizontal line is the x axis, thevertical line is the y axis, and the coordinate axes togetherform the cartesian coordinate system or a rectangularcoordinate system. The point of intersection of thecoordinate axes is denoted by O and is the origin of thecoordinate system. See Fig 1.

It is basically, Two Real Number lines Put Together, onegoing left - right, and the other going up- down. Thehorizontal line is called x-axis and the vertical line is calledy-axis.

The originThe point (0,0) is given the special name “The Origin” ,and is given the letter “O”.

Rral number lineThe basis of this system is the real number line marked atequal intervals. The axis is labeled (X,Y or Z). One pointon the line is designated as the Origin. Numbers on oneside of the line are marked as positive and those to theother side marked negative. See Fig 2.

Cartesian coordiantes of the planeA plane in which a rectangular coordinate system hasbeen introduced is a coordinate plane or an x-y-plane. Wewill now show how to establish a one to onecorrespondence between points in a coordinate planeand pairs of real number. If A is a point coordinate plane,then we draw two lines through A, one perpendicular tothe x-axis and one perpendicular to the y-axis. If the firstline intersects the x-axis at the point with coordinate x andthe second line intersects the y-axis at the point withcoordinate y, then we associate the pair (x,y) with the A(See Fig 2). The number a is the x-coordinate or abcissaof P and the number b is the y-coordinate or ordinate of p;we say that A is the point with coordinate (x,y) and denote


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the point by A (x,y). The point (0,0) is given the specialname “The Origin” , and is sometimes given the letter “O”.

Abscissa and OrdinateThe words “Abscissa” and “Ordinate” ... they are just thex and y values:

• Abscissa: the horizontal (“x”) value in a pair ofcoordinates: how far along the point is.

• Ordinate: the vertical (“y”) value in a pair of coordinates:how far up or down the point is.

Negative Values of X and YThe Real Number Line, you can also have negativevalues.

Neagative: start at zero and head in the opposite direction;See Fig 4

So, for a negative number:

• go left for x

• go down for y

For example (-3,-5) means :

go left along the x axis 3 then go up 5 in the y-axis.(Quadrant II x is negative , y is positive)

And (-3,-5) means :

go left along the axis 3 then go down 5 in the y-axis.(Quadrant III x is negative ,y is negative)

Using Cartesian Coordinates, mark a point on a graph byhow far along and how far up it is; See Fig 5. The point(12,5) is 12 units along the x-axis, and 5 units up on the y-axis.

X and Y AxisThe horizontal line is called x-axis and vertical line iscalled y-axis; both line runs through zero origin,(0,0) putthem together on a graph ... See Fig 6.

It is basically, a set of two real Number lines.

Axis: The reference line from which distances aremeasured.

Example:

Point (6,4) is

Go along the x direction 6 units then go up 4 units up in they direction then “plot the dot”.

And you can remember which axis is which by:

• the horizontal distance first,

• then the vertical distance.

Ordered pairThe number are separated by a comma, and parenthesesare put around the whole thing like this: (7,4)

Example: (7,4) means 7 units to the right (x-axis), and 4units up(y-axis)


27

Cartesian coordinates of three dimensional spaceIn three-dimensional space (xyz space), oriented at rightangles to the xy-plane. The z axis, passes through theorigin of the xy-plane. Coordinates are determinedaccording to the east-west for x-axis north-south for y-axis, and up -down for the z-axis displacements from theorigin. The Cartesian coordinarte system is based onthree mutually perpendicular coordinate axes: the x-axis,the y-axis, and the z-axis, See Fig 6 below. The three axesintersect at the point called the origin. You can imaginethe origin being the point where the walls in the corner ofa room meet the floor. The x-axis is the horizontal linealong which the wall to your left and the floor intersect.The y-axis is the vertical line along which the wall to yourright and the floor intersect. the z-axis is the vertical linealongwhich the walls intersect. the parts of the lines thatyou see while standing in the room are the positive portionof each of the axes. The negative part of these axes wouldbe the continuations of the lines outside of the room.

Three-dimensional cartesian coordinate axes. Arepresentation of the three- dimensional cartesiancoordinate system. The positive x-axis , y-axis, andpositive z-axis are the sides labeled by x,y,z. The origin isthe intersection of all the axes. The branch of each axison the opposite side of the origin (the unlabeled side) osthe negative part.

When dealing with 3-dimensional motion, is to set up asuitable coordinate system. The most stright-forwardtype of coordinate system is called a Cartesian system. ACartesian coordinate system consists of three mutuallyperpendicular axes, the X, Y, and Z-axes. By convention,the orientation of these axes is such that when the indexfinger, the middle finger, and the thumb of the right -handare configured so as to be mutually perpendicular, theindex finger, the middle finger, and the thumb can bealigned along the X,Y,Z-axes respectively. Such acoordinate system is termed right-handed. See Fig 7. Thepoint of intersection of the three coordinate axes istermed the origin of the coordinate system.

The Cartesian coordinates of a point in three dimensionsare a triplet of numbers (x,y,z). The three numbers, orcoordinates, specify the signed distance from the originalong the x,y, and z- coordinate axis respectively. Theycan be visualized by forming the box with edges parallel

to the coordinate axis and opposite corners at the originand the given point.

The points may now be defined in a three dimensionalvolume or space. This permits to define points in threedimensions from the origin. The Cartesian coordinates(x,y,z) of a point in three-dimensions specify the signeddistance from the origin along the x,y, and z-axes,respectively. Z-axis points become the third entry whendefining coordinate locations.

Given the above corner-of-room analogy, we could formthe Cartesian coordinates of the point at the top of yourhead,as follows. Imagine that you are five meters tall thez-axis, and that you walk two meters from the origin alongthe x-axis, then turn left and walk parallel to the y-axis fourmeters into the room. the Cartesian coordinates of thepoint at the top of your head would be (2,4,5).

For example, a notation of (2,4,5) corresponds to thevalue of X2, Y4, and Z5. See Fig 9.

3 DIMENSIONS

Cartesian coordinates can be used for locating points in 3dimensions as in this example:

Figure 10. The point (2,4,5) is shown in three-dimensionalCartesian coordinates.


28

QUADRANTS

The coordinate axes divide the plane into four parts,called quadrants (See Fig 11). The quadrants are numbercounter clockwise,starting from the upper right,labeledI,II,III,IV with axes designations as shown in illustrationsbelow.

When we include negative values, the x and y divide thespace up into 4 pieces:

(They are numbered in a counter clockwise direction)

In Quadrant I : both x and y are positiveIn Quadrant II : x is negative (y is still positive)In Quadrant III : both x and y are negativeIn Quadrant IV : x is positive again, while y is negative.

Quadrant X(Horizontal) Y(Vertical) Example

l Positive Positive (3,2)

ll Negative Positive (-5,2)

lll Negative Negative (-2,-1)

lV Positive Negative (2,-5)


29

Example: the point “A” (3,2) is 3 units along the x-axis,and 2 units up the y-axis.

Both x and y are positive, so that point is i “Quadrant I”

Example: The point “C” (-2,-1) is 2 units along the axis inthe negative direction, and 1 unit down the y-axis in thenegative direction.

Both x and y are negative, so that point is in “Quadrant III

DIMENSIONS: 1,2,3 AND MORE...

1 The Real Number Line can only go:

• Left-right

• So any position needs just one number.

2 Cartesian coordinates can go:

• Left-right, and

• Up-down

• So any position needs two numbers

3 3 Dimensions

• Left-right,

• Up-down, and

• Forward-backward

• So any point can be located with (x,y,z) coordinates.


30

Production & Manufacturing Related Theory for Exercise 4.2.116 & 4.2.117Turner - CNC Turning

Preparation of part programmingObjectives : At the end of this exercise you shall be able to• explain part programming preparation• identify the G code and M codes.IntroductionPart programming comprises of collection of data,arrangement of information in a standard format andcalculation of tool path, the data relates to dimensions offeature, direction of cutting , tool required, sequencing,and familiarity with NC system codes.

Preparation of part programming1 Block numbers / sequence number (N words)Each block of the program has a sequence number whichis used to identify the sequence of a block of data in itwhich in ascending numerical order. When the partprogram is read from the tape, each sequence numberis displayed on the panel of NC machine tool, as long asthat block commands are performed. This enables theoperators to know which sequence of block is beingperformed practically by the tool. It consists of a character'N' followed by a three digit number raising from '0' to'999'.

2 Preparatory Function (G-words)The preparatory function is used to initiate the controlcommands, typically involve a cutter motion i.e. Itprepares the MCU to be ready to perform a specificoperation and interpret, the data which follows the way ofthis function. It is represented by the character 'G' followedby a two digit number i.e.'00 to 99'.These codes areexplained and listed separately.

3 Dimension words (X, Y & Z words)These dimension word are also known as 'co-ordinates'.Which give the position of the tool motion .These wordscan be of two types:

a) Linear dimension words

- X, Y, Z for primary or main motion.

- U, V, W for secondary motion parallel toX, Y, Z axes respectively.

- p, q, r for another third type motion parallel to X,Y,Zaxes respectively.

b) Angular Dimension Words

- a, b, c, for angular motion around X, Y, Z axesrespectively.

- I, J, K in case of thread cutting is for position of arccentre; thread lead parallel to X, Y, Z axes.

These words are represented by an alphabet representingthe axes followed by five or six digits depending upon theinput resolution given. The following points may be notedwhile calculating the number:

- Decimal point should be not be allowed e.g. x = 7.875will be represented as X07875 in a five system i.e.the last three digits are used for the decimal part ofthe number. Some machines allow omission of leadingzeros, hence the same can be represented as X7875.

- It is recommended that dimensions should beexpressed in mm.

- All angular dimensions should be expressed as adecimal fraction of a revolution.

- In absolute system, all dimensions should be positive.

- In incremental system the '+','-'sign represent thedirection of motion.

4 Feed Rate Word(F - word)It is used to program the proper feed rate, to be given inmm/min or mm/rev as determined by the prior 'G' codeselection G94 and G95 respectively. This word isapplicable to straight line or contouring machines,because in PTP systems a constant feed rate is used inmoving from point to point.

It is represented by "F" followed by three digit numbere.g.F100 represents a feed rate of 100 mm/min.

5 Spindle speed / cutting speed word (S - word)It specifies the cutting speed of the process or the rpm ofspindle. It is also represented by 'S' followed by the threedigit number .If the speed is given in meter per min. thenthe speed is converted in rpm rounded to two digitaccuracy, e.g. S-800 represents the 800 rpm of spindle.

6 Tool selection word (T - word)It consists of "T" followed by max five digits in the codednumber. Different numbers are used for each cutting tool.When the "t" numbers read from the tape ,the appropriatetool is automatically selected by ATC(Automatic toolchanger).Hence this word is used only for machines withATC or programmable tool turret .e.g. T01,T02,T03………….. represents the tool selection word. Also,sometimes T-word used for representing a tool offsetnumber corresponding to X Y and Z directions. With thehelp of two additional digits, given after a decimal point.(In HMT T-70,9 pairs of tools offset can be stored).

7 Miscellaneous words (M-words)It consists of character M followed by two digit numberrepresenting an auxiliary function such as turning ON/OFF spindle ,coolant ON/OFF or rewinding the tape.These functions do not relate two dimensional movementof the machine. This is more explained in next topic.


31

8 End of Block (EOB)It identifies the end of instruction block.

G and M codes (G-codes)This is the preparatory function word, consists of theaddress character G followed by a two digit code number,known as G-code. This comes after the sequence numberword and a Tab Code. There are two types of G codesmodal and non-modal. Modal codes remain active untilcancelled by a contradictory and code of same class .e.g.G70 is a modal code which defines that the dimensionalunits are metric. It will remain active until cancelled byG-71,which tells that the dimensional units are in inchesnow. Non-modal G codes are active only in the block inwhich they are programmed.G04 is non-modal code.

List of G codesG codes are instructions describing machine toolmovement. A G code quite often requires otherinformation such as feed rate or axes coordinates TheFANUC standard has a large selection of G codes, all ofwhich may not be available on all the machines. Thereare three G code system: A, B and C. System A is themost commonly used. Following is the list of somecommon G codes of system A:

Code Group Description*G00 01 Rapid traverse

G01 01 Linear interpolation

G02 01 CW circular interpolation

G03 01 CCW circular interpolation

G04 00 Dwell time

G10 00 Offset setting by program

G20 06 Inch data input

G21 06 mm data input

G27 00 Reference point (Home)return check

G28 00 Reference point (Home) return

G30 00 Return to secondreference point(Home)

G32 01 Thread cutting

G34 01 Variable lead thread cutting

G40 07 Tool nose radius compensation cancel

G41 07 Tool nose radiuscompensation left

G42 07 Tool nose radiuscompensation right

G50 00 Work coordinate change /maximum spindle speedsetting

G54-G59 14 Work piece coordinatesystem (G54 is default)

G70 00 Finishing cycle

G71 00 Multiple turning cycle(Stock removal in turning)

G72 00 Multiple facing cycle(Stock removal in facing)

G73 00 Pattern repeating cycle

G74 00 Peck drilling cycle

G75 00 Grooving cycle

G76 00 Multiple threading cycle

G90 01 Single turning cycle

G92 01 Single threading cycle

G94 01 Single facing cycle

G96 02 Constant surface speed

*G97 02 Constant RPM

G98 05 Feed per minute

*G99 05 Feed per revolution

When the power is turned ‘ON’ or ‘Reset button’ ispressed, the ‘G’ codes with * mark become active.

List of M codesThe list given below is a typical representative list .All ofthese may not be available on all the machines. On theother hand, some machine may use some extra codealso. Note that most of the m codes, except a few suchas M00, M01, M02, M03, M04, M05, M06, M08, M09,M19, M30, M98 and M99,are machine specific. Refer tothe specific machine manual for the list of available Mcodes and their functions. M codes are defined andimplemented by the machine tool builder. The controlmanufactured defines only G codes which are same onall the machines with the same control.

M00 Program stop

M01 Optional stop

M02 End of program execution

M03 Spindle forward(CW , as viewed towardsthe tail-stock)

M04 Spindle reverse (C CW , as viewed

towards the tail-stock)

M05 Spindle stop

M06 Auto tool change V (not needed on recentcontrols)

M08 Coolant ON

M09 Coolant OFF

M10 Chuck open (for machines with automaticchuck)

M11 Chuck close

M13 Spindle forward and coolant ON /sub-spindleon

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.116 & 4.2.117Copyright @ NIMI Not to be Republished

32

ExampleO1203;N1;G28 U 0.0 W 0.0;G50 S 1200 T 0300;________________ ;________________; Partprogram

________________ ;M01;

N2;G28 U 0.0 W 0.0;G50 S 1200 T 0200;________________ ;________________ ; Part program

________________ ;

M01;M30;Decimal point inputDecimal point is used to input the units like Distance,Time, and Angle .

X 25.0 is use for input the distance value . X25.0 equal to25mm or 25 inch.

G04 X1.0 is used to input the dwell time value.X1.0 isequal to one second.

A45 is used for input the angle value.A90 is equal to 45°

The following are the same meaning, in the case ofdecimal point.

X20.

X20.0 All are same meaning ofX20.00 movement of X 20 mm

X20.000

If the Decimal point is eliminated. The system read inmicrons.

X 50 = 0.05mm

X 500 = 0.5mm

X 5000 = 5.0mm

Decimal point can be input for the following addresses.

X, Z, U, W, A, B, C, I, J, K, P, R, Q, F.

Note:1 micron=0.001mm

1 mm=1000 microns

M14 Spindle reverse and coolant ON/sub OFF

M19 Spindle orientation

M25 Quill extend

M26 Quill retract

M29 DNC mode

M30 Program reset and rewind

M38 Door open (for machines with automaticdoor)

M39 Door close

M40 Parts catcher extend

M41 Parts catcher retract

M43 Swarf conveyor forward

M44 Swarf conveyor reverse

M45 Swarf conveyor stop

M48 Lock feed and speed at 100%

M49 Cancel M48 (default)

M52 Threading pull out angle=90° (default)

M53 Cancel M52

M56 Internal chucking

M57 External chucking

M62 Auxiliary output-1 on

M63 Auxiliary output-2 on

M64 Auxiliary output-1 off

M65 Auxiliary output-2 off

M66 Wait for input -1

M67 Wait for input-2

M68 Turret indexing (tool changes) onLy athome position

M69 Turret indexing anywhere

M70 Mirror in X on

M76 Wait for input -1 to go low

M77 Wait for input -2 to go low

M80 Mirror in X off

M98 Subprogram call

M99 Return to the calling program

Part programA set of commands given to the NC for machine motionis called a program. A program is composed of numberof Blocks. Part program is use to specify the machiningprocess for the cutting tools.


33

1 inch=25.4mm

1 sec=1000 millisec

Structure or format of a part programThe complete part program for a given componentconsists of a beginning code of %.A part program consistsof large number of blocks each representing an operationto be carried out in the machining of the part. The wordsin each block are usually given in the following order.

- Sequence number(N-word)

- Preparatory word(G-word)

- Coordinates (X-,Y-,Z- words for linear axes; A-, B-, C-words for rotational axes)

- Feed rate (F-word)

- Spindle speed(S-word)

% (Program start)O3642 (Program number)

Blocks N010 -------------------------------------------N100 M02; (Program end)

- Tool selection(T-word)

- Miscellaneous command (M-word)

- End -of-block(EOB symbol)

The structure of part program used in Fanuc controller isgiven below.

Program numberEach of the program that is stored in the controllermemory requires an identification. It is used while runningand editing of the programs directly from the controlconsole. This identification is specified in terms of aprogram number with ‘O’ word address. The number canbe a maximum of four digits.

Sequence number (N-word)Each block in a part program always starts with a blocknumber, which is used as identification of the block. It isprogrammed with a ‘N’ word address.

Coordinate functionThe coordinate values are specified using the wordaddress such as X, Y, Z, U, V, W, I, J, K, etc. All theseword address are normally signed along with decimalpoint depending upon the resolution available in themachine tool.

CommentsParentheses are used to add comments in the programto clarify the individual function that are used to addcomments in the program .When the controllerencounters the opening parenthesis. It ignores all theinformation till it reaches the closing parenthesis.

N Sequence number to identifya block.

G Preparatory word thatprepares the controller forinstruction given in the block.

X, Y, Z Coordinate data for threelinear axes.

U, V, W Coordinate data forincremental moves in turningin the X,Y and Z directionsrespectively.

A, B, C Coordinate data for threerotational axes X, Y and Z.

R Radius of arc, used incircular interpolation.

I, J, K. Coordinate values of arccentre, corresponding to X, Yand Z-axes respectively.

F Feed rate per minute orrevolution in either inches ormillimeters.

S Spindle rotation speed.

T Tool selection, used formachine tools with automatictool changer or turrets.

D Tool diameter word used foroffsetting the tool.

P It is used to store cutter radiusdata in offset register.It defines first contour blocknumber in canned cycles.

Q It defines last contour blocknumber in canned cycles.

M Miscellaneous function.

Address Function

ExampleN010 G00 Z50 M05(Spindle stops and rapidly moves up)

Table common word addresses used in word addressformat

M01 - Optional stop

This function is same as ‘M00’, But it will stop only whenOptional stop button in the Machine panel is ‘ON’. Thencycle is started to continue by pressing Cycle Start Button.


34

2. G00 Z-----------;

3. G00 X------ Z----;

G00 - code used for the following operations

1 Machining start

Making the tool approach the work piece.

2 During machining

Moving the tool to next command position whenit is not in conduct with the work piece.

3 Machine end

Separating the tool from the work piece.

G01 - Linear interpolation (straight cutting)

The cutter moves at specified feed rate. The feed rate isspecified by address 'F' in the program.

Format

1 G01 X------- F-----;

Application

a Facing

b Grooving etc.

2 G01 Z-----F-------;

Application

a. Straight turning

b. Drilling etc

3 G01 X-----Z------F------;

Application

a. Taper turningb. Chamfering

Where ‘F’ is the cutting feedrate specified in mm/Rev.

Function FThe feed rate is used to move the tool from one point toanother point with constant feedrate. Feed is normally isgiven mm/rev. or mm/min. The rapid traverse rate andfeed rate both are controlled by feed override switches inthe machine panel.

ExampleF Four digits number following

the address F

M02 - Programme end

The code is inserted at the end of the program. Themachine stops permanently. Spindle rotation, Feed ofaxis and coolant discharge all stops. The system is resetby pressing Reset button in the machine panel and newcycle is started by pressing Cycle start.

M03 - Spindle ON clockwise

By programming ‘M03’ the spindle is enabled to run inthe clockwise direction.

M04 - Spindle ON counter clockwise

By programming M04 the spindle is enabled to run in thecounter clockwise direction.

M05 - Spindle stop

By programming ‘M05’ the spindle rotation is stopped.

M08 - Coolant ON

By programming ‘M08’ coolant motor switches ‘ON’.

M09 - Coolant OFF

By programming ‘M09’ coolant motor switches ‘OFF’.

M30 - Program end & rewind

When CNC reads the code ‘M30’ the main program Endand Rewind . That is the CNC control returns the cursorto the starting line of the program.

G - Codes (preparatory functions)

G codes take active part in part program execution andare programmed by letter G followed by two digits.

G codes once programmed, remains active until another.G code of the same group is programmed, after whichthe previous one gets cancelled, are said to be modal.

G codes which remains active only in the block in whichit is programmed, is said to be Blockwise active (or) oneshot G code.

G00 - Rapid traverse

The Tool moves at a rapid (fast) traverse rate with linearinterpolation. The rapid traverse rate depends upon themachine type (for example maximum speed in a twowheeler is 80-120 Km/hr depends on type of make).

This can be used in air movement like positioning,relieving, non contact with work piece.

Format

1. G00 X ---------;


35

G01 X 50.0 Z -50.0 F0.1; X -axis & Z - axis move withfeed 0.1mm/Rev.

Circular interpolation (Fig.1)

G02-Circular interpolation clockwise direction

G03-Circular interpolation Anti clockwise direction

Example

G04 U 1.0 (Dwell of 1.0 second)

NoteDecimal point is not available in ‘P’

Ex. Dwell of 2.5 seconds.

G04 U 2.5

G04 X 2.5

G04 P 2500

G28 - Zero Return (Home Position, First Referencevalue)

It is an inherent position on a machine axis. AutomaticReference Point Return is a function to return each axisto this inherent position automatically.

1 G28 U0

2 G28 W0

3 G28 U0 W0

G30 - Second reference return

It is same as G28.But is to settled before First ReferenceValue (G28). It is called Temporary Reference Value.

1 G30 U0

2 G30 W0

3 G30 U0 W0

G50 - Co-ordinate value setting & maximumspindle speed setting1 G50 X---Z---;

Ex. G50 X 300.0 Z 150.0;

2 G50 X---Z---S---;

Ex. G50 X300.0 Z 150.0 S 3000

G96-Constant Surface Speed Control(Cutting Speed Specification)

The G96 is used with an "S"-Function.

The G96 is used when the cutting speed is specified.

When G96 command is used the spindle speed ischanged automatically, as the cutting diameter ischanged. That is for smaller work piece of its cuttingdiameter, the spindle speed becomes higher.

Calculation for cutting speed

mtr/min

1000

DNV ==

π

Format

;03

02−−−−−−−−

⎭⎬⎫

FRZXG

G

OR

;03

02−−−−−−−−

⎭⎬⎫

FRZXG

G

Where

X Z - End point of Arc

I K - Distance between start point of arc tocenter point of arc in X & Z axis

R - Radius of the arc

F - Feed

Command I and K specify the distance from the startpoint of arc to the center point of arc must be specifiedincrementally even under Absolute mode and sign (+) or(-) for Values I & K is determined by the direction.

Example

G02 X 40.0 Z-5.0 R 5.0 F 0.1

G03 X 40.0 Z-5.0 R5.0 F 0.1

Where, R=Radius

G04-Dwell

If a block with G04 is real during automatic operation, thefeed is stopped for the time followed U, X, P, and thenthe next block will be executed.

Format

G04 (U, X, P) time


36

Where

V = cutting speedD = Diameter of the work piece in ‘millimeter’N = spindle speed in rpm

G97-Constant Surface Speed Control Cancel (SpindleSpeed Specification)

The G97 is used when the spindle rotating speed isspecified.

Ex. G97 S300 M03.

With this spindle rotates at 300 rpm.

For the following should use G97 always

a. Threading

b. Tapping

c. Drilling etc

Tool function (Fig.2)

the number on offset screen (WEAR)

2 Tool Geometry offset

The distance from top of the tool fixed on turret at machinezero point to the work piece zero point is input as toolgeometry offset with this the CNC recognizes the positionof work piece zero point. Input the offset amount to thesame number as the number on offset screen(Geometry).

Address: T

A four digits number address T Specifies the tool numberand tool offset number.

Format

Example : T01 01

Tool Number

The left most two digits specify the number of tool.

Offset Number

The right most two digits specify the number of tool off-set.

Types of Offsets

There are two types offsets:

1 Wear offset

2 Geometrical offset

1 Wear offset

The tool is moved adding the wear amount to part pro-gram. Input the offset amount to the same number as

Tool geometry offset (Fig.3)

This offset amount is not need to be cancelled after ev-ery tool use because the next input of tool geometry off-set cancels former offset automatically.

Tool wear offset

The tool wear offset is used to modify the finished workpiece dimension in order to keep them within theirtolerances. The programmed path is shifted by the offsetamount parallel to X and Z axes. The offset amount isinput to "TOOL OFFSET /WEAR".

When the control reads T0101 and executes, the tool isshifted by amount which is input in the tool wear offsetnumber (X-0.600, Z0.300).After the machining the tool is returned near the startingpoint and if T0100 (Tool wear offset cancel) is executed,it returns to the starting point before offset. The samemovement is executed for other tools, only to assign toolwear offset numbers which are required on theprogramming and the amount to be offset should bedecided by the operator.

Procedure for setting work coordinate system (Fig.4)

Step 1 Make sure that the component is securelyclamped.

Step 2 Now bring one of the tool near the face of thejob.

Step 3 I. Select MDI mode.II. Press PROGRAM button.

Step 4 Enter S500

Step 5 Select handle/jog mode and select theappropriate feed.

Step 6 Rotate the spindle in CW or CCW dependingon the type of the tool.


37

Step 7 Light facing out be taken up to the center.

Step 8 After the finish cut, move the tool back in x only.do not disturb Z-axis.

Step 9 Now switch off the spindle.

Step 10 Press MENU offset. The wear geometricaland work shift are displayed on CRT.

Step 11 Now, press GEOM soft key and position thecursor using cursor movement buttons to berequired offset number corresponding to thetool used.

Step 12 Press measure(m) key and press Z. EnterZero(MZ0).

Step 13 Now rotate the spindle in appropriate directionand machine on OD

Step 14 Do not move X.

Step 15 Take Z away from the job.

Step 16 Stop the spindle.

Step 17 Press MENU OFFSET PB.

Step 18 Press 'GEOM' soft key.

Step 19 Position the cursor to the required tool offsetnumber.

Step 20 Press M….X….

Step 21 Input "The OD dimension measured. The X-The X-offset for the said tool is set.

Step 22 Repeat the procedure for all tools.

Step 23 After taking offset, select MDI and issue S0.

Programming method

In CNC for programming in Lathe, Absolute Commandand Incremental Command are available.

Absolute method (Fig.5)

In absolute dimensions programming, all the points ofthe tool is coming from the datum point (or) zero point. InCNC Lathe machines "X" and "Z" is the absolute input.The "X" means diameter of work piece and the "Z" meansdistance from the finished end surface of work piece.

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.116 & 4.2.117

All the travel commands for tool are mean their co-ordinate value from the work piece zero point (X0, Z0).

Position X Z

1 30.0 0.0

2 30.0 - 10.0

3 40.0 - 10.0

4 40.0 - 25.0

5 50.0 - 25.0

6 50.0 - 45.0

In the above figure, points 1 to 6 can be specified asfollows in absolute dimension programming.

Incremental method (Fig.6)

In this system, tool move from the previous point. In theincremental programming the address "U" (diametrical)for "X" axis and the address "W" for "Z" axis are used todistinguish incremental program from the absoluteprogram.

The incremental command should have the direction (+/-) and distance from currently specified point to nextcommand point.

ExampleIn the Fig.6 the points, 1 to 6 can be specified as followsin incremental dimension programming.


38

Position U W1 30.0 0.0

2 0.0 -10.0

3 10.0 0.0

4 0.0 -15.0

5 10.0 0.0

6 0.0 -20.0

The tool path for finish cutting of a profile can be easilyderived by offsetting the nose radius. However, at thebeginning and end of inclined path, it is necessary to makecalculation based on simple trigonometry for the offsetpoint from the original contour. By using the cuttercompensation, the need for all complex calculations willbe eliminated. The programming for the finishing cuttingwill be the direct path of the actual contour to be machined.(Fig.7)

However, even after compensating the nose radius, thepoint of contact between the tool nose and the work piecewill still be along the nose radius periphery which will bechanging depending upon the orientation of the tool withrespect to the cut surface. For example, the tool will leavea small amount of metal along the inclined surface, whenthe tool nose radius compensation is not active. For thispurpose, the turning centre controllers will provide thenecessary correction.

If the correction is active, then the controller automaticallycompensates and removes the unwanted material.However, in order for the correction to be active, thecontroller will have to know the correct orientation of thenose radius with respect to the machining surface. Forthis purpose, nose radius direction is included in thetool-offset registers.

Tool nose radius compensation (Fig.8)

The following data's must be specified to carry outautomatic tool nose radius compensation, to obtainrequired profile exactly.


– Give in the program (finish turning and boring). G41(Tool Left) or G42 (Tool Right), The position of toolviewing along the traveling direction and G40 (ToolNose Radius Compensation Cancel). (Fig.9)

– Input nose radius of tool to R in geometry offset.

– Input the imaginal nose position to T in geometry offset.(Figs 10&11)


39

Part programmingObjectives : At the end of this lesson you shall be able to• define the part programming• list the APT programming sequence.

Part programming

Definition wise "The part program is a sequence ofinstructions which describe the work which has to be doneon a part, in the form required by a computer under thecontrol of an NC computer program".

Actually, part programming for NC production consistsof the collection of all data required to produce the part,the calculation of the tool path etc. in a standard format,which is in the form acceptable to its MCU or in otherwords, it is the task of preparing a program sheet. Alldata is fed into the NC system using a standardizedperforated or punched tape. Hence, the methods of partprogramming can be of two types depending upon thetwo techniques employed to produce a punched tape:

- Manual part programming

- Computer aided part programming

Manual part programming

In manual part programming, the data required formachining, is written in a standard format known asprogram manuscripts. Each horizontal line in a manuscriptrepresents a "block" of information.

Computer aided part programming

If the component requires a great deal of machining suchas in case of milling machines or contouring application,calculation of cutter paths requires more calculations andsometimes if a machining centre is used then selectingdifferent tool for drilling, tapping, boring and milling makesall this part programming more tedious and timeconsuming. More mistakes are also likely to occur. Thus,we use a general purpose computer as an add, to reducelabour involved in part programming. Also one of thehigh level language such as APT (AutomaticallyProgrammed Tools), ADAPT, SPLIT, 2CL, AUTO STOPis used for writing a computer programme, which hasEnglish like statements. A translator known as 'compiler'program is used to translate it in a form acceptable toMCU.

The work load of a part programmer is greately reduced,because he has to do only following things:

a. Define the work part geometry by defining it in theform line segments, circles, arcs etc.

b. If there is any repetition work such as drilling a numberof equal size and equal speed holes, then only definingthe dimensions of single hole.

c. Specifying the operation sequence and the relativeposition of repetitive job as in case of (b) with otherlocations.

A computer aided programming method would do the

translation of APT program; automatically generate theabsolute locations of paths for repetitive jobs, with thehelp of a program.

Procedure for developing manual part programme

The part programming requires an NC programmer toconsider some fundamental elements before the actualprogramming steps of a part takes place. The elementsto be considered are as follows:

- Type of dimensioning system

- Axis designation

- NC words

- Standard G and M codes

- Tape programming format

- Machine tool zero point setting

Automatically programmed tools (APT)

Introduction

Computer Aided Part Programming (CAPP) offer solutionto these type of complex programmes. It makes use ofrepeated patterns of events which occur often on most ofthe engineering components.

With the advent of programming languages the job ofpart programmer has reduced to:

i. Define the geometry of work piece.

ii. Specify the sequence of operations and tool path.

The job of computer in CAPP consists of the followingsteps

a. Input translation

b. Arithmetic calculation

c. Cutter offset computation

d Post processor

Programming languages

Different types of languages available for NC programingare:

APT

APT is an acronym for Automatically Programmed Tools.It is the oldest and largest Computer Aided ProgrammingLanguage is developed by MIT. It is used for 5 axis controlof the 'tool' in three dimensional space. The tool can be adrafting pencil, a point spray nozzle or even a cutting flametorch.

This language is nowadays used for positioning systemsas well as will perform the mathematical calculations


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required for complex continuous path surfaceapplications.

ADAPT

It is an 'Adaptation of APT. It is a smaller version of APT

used on small computer. It is very mach suitable for 2½

axis control.

AUTOMAP

Another subset of APT used for Numerical controlprogramming.

EXAPT

Extended subset of APT using same instruction withadditional boring and turning data also. Sometimes havingfacility to automatically calculate feeds and speeds.

PROMPT

Interactive language mainly designed for lathes,machining centres and flame cutters etc.

The APT language

The APT language is the NC language. It is also used asthe computer program which performs the calculationsto generate cutter positions based on APT statements.

These statements are given as under:

i Geometry Statements / Definition statements (Definethe geometric elements of the work piece).

ii Motion statements/movement statements (Define thepath taken by the cutting tool).

iii Post processor statements (Define the feeds andspeeds and to actuate other features of the machine).

iv Auxiliary Statements/Miscellaneous statements(Define the part, tool tolerance etc). It is a 3-D systemthat can be used to control up to five axes. This canbe used to control a variety of different machiningoperations.

APT programming sequence

There are approximately 400 words in APT vocabulary.The operations of developing a programme in APT arefollowed in a sequence as follows:

a Labelling the part. The part on the drawing is dividedinto some basic geometric elements like lines, planesand circles. Different elements are given differentlabels and names. These elements are also neededto be specified by their Cartesian co-ordinates.

b Prepare the program manuscript. The programme inAPT is then transferred on manuscript paper; the fourtype of instructions are written in a program:

- General information used to identify the part suchas PART NO, diameter of the cutter tool withCUTTER/ .0975. These type of information isrequired by post processor for calculation andidentifying purpose, coming under miscellaneousinformation. NO POST, CLRPRNT, INTOL andOUTTOL are other statements coming under thiscategory.

- Geometrical statements that define the geometryof the tool movements with reference to work part.The starting of these statements is from definingpoints by POINT statement. These all are almostself-explanatory.

- Movement statements directing the sequence ofmovement of tool for following a particular path.

- Auxilliary statement for setting speed, feed and toolchange etc.

c The program either typed with keyboard on computeror punched on cards or tape.

d In some cases, the computer produces the computedtool positions.

e The final computer output after post processing isgiven on magnetic tape or punched card.

f This magnetic tape or punched cards are fed intoReader Unit, of machine to start machining.

The syntax rules for APT are very near to FORTRANlanguage. It uses alphabets from A, B….YZ and numerals0, 1, 2, 3….8, 9. Special symbols used are: '/' usedsometimes for separating a single statements into twoparts ',' (comma) for separating different entities.

'()' used for nested definition , Arithmetic operators are'+' (add), '-' (subtract), '*' (multiply). '/' (division), '**' forexponentiation. The symbols used for defining geometricelements are:

- POINT

- LINE

- CIRCLE

- PLANE

- CENTER

- RADIUS

Parametric subroutines

Consider a component as shown in Fig 1, which has arepetition feature namely square recess.


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Writing a programme for such a component would involvemaking a cycle of some moves which can be referred toas a "routine" for producing just one recess.

"A subroutine is a portion of a programme, complete initself, which is stored in computer after programmingonce. It is called with required data when required againin a program". It is usually placed at the end of mainprogramme. Consider another example in Fig 2.

A group of 5 holes occur in same geometric pattern. Asimple solution may be giving a D0-loop, but making'subroutine' will simply further the programming by placingthe single pattern in 'Subroutine', even if the holes atlocation 1 are of different size than at 2.

The major difference between canned cycles andsubroutines is that canned cycles are more of fixed typeand they cater for easy programming of machine featuresthat are often required, hence are more suitable forgeneral situations. But if sometimes a part requires apattern, that is required a no. of times on a particularcomponent, then a subroutine is the best solution. Theparametric subroutine is useful for turning, roughing outs,thread cutting, keyway milling, drilling etc. Where asequence of motions is evolved. A few of them are givenin Fig 3 below:

Fig 3 (a) Turning subroutine

Fig 4 (b) Milling subroutine

Fig 5 (c) Nesting of two subroutines.

The table given below shows the difference betweencanned cycle, loops and subroutines:

Nesting

The best way of writing an efficient part programme is toplace one or more loops in a subroutine i.e. repeatingsome pattern at a fixed relative position within a subrou-tine program. This is known as "Nesting" of subroutines.This is explained with the help of Fig 3 and Fig 4.

Normally the machine movements (operations) are writtenin a subroutine without dimensions and while calling thesubroutine, the X, Y, Z etc. Parameters are passed simply.The general format for writing a subroutine is:

1 Subroutine

2 Program information

3 End of subroutine

Defining a subroutine

a The subroutine is not defined by a subroutine numberbut is simply added with a sequence number follow-ing the main program.

b All blocks in a subroutine are numbered from 'N001'onwards as if independent program.

S.no Canned cycle Loops Subroutine 1 Consist of some These are, These are,

very common repeating some moves (general) moves some moves (operations)on of different m/cs on a a component coded. component for a variable

for a fixed number ofno. of times times.

2 They don’t allow They allow to They allow to optimisation of change only make their program in their the no. of own cycles times movements with different fixed for operation.operations are parametric

to be repeated. dimensions atdifferentlocations i.e.user definedcarried cycles.


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N005 : Call subroutine for two times for at70mm (i.e. at location 50 mm apart)and 120 mm (i.e. atlocation 50 mm + 50 mm apart)

N006 : Cancel cycle

N007 : Retract tool

N008 : End

(Subroutine)N001 : Incremental mode

N002 : Drill here itself because drill locatedat centre of pattern.

Z - depth = (Plate thickness + chipclearance)

= 5 mm + 0.3 dia of drill (6mm)

= 5 + 0.3 x 6 = 5 + 2 = 7 mm (appx)

R = -2 mm (given)

N003 : Drill by moving on path (1) i.e.X X - 10Y← Y + 10

N004 : Drill hole following path (2), i.e.X←sameY←Y - 20

Again some G - codes or M-codes are to be assignedfor:

i Jump to a subroutine location (Call a sub) by a codee.g. G25, M98, G37.

ii Start of subroutine.

iii End of subroutine e.g. G26, M99, G39.

L code is used to describe how many times asubroutine is to be repeated.For our reference purpose, we will use M98,M99 for respective coding of Begin, calling andEnd of subroutine.Ex: Make use of subroutines for making partprogramme of part shown in Fig 6.

The thickness of plate is 5 mm. R-plane may be assumedat 2 mm above plate surface. Z-0 at plate surface.

N001 G00 G71 G80 G90 Metric mode cancel

G80 G90 any previous cycle.Set absolute mode

N002 S3500 F105 M06 Set speed feed,replace

T1 M03 tool and start spindle

N003 G00 X02000 Set position to ‘A’Y02000 M08

N004 P009 M98 Call the subroutine ofdrilling 5 holes, atprogram location ‘P009’

N006 G90 G80 Z00000 Absolute mode, cancelM09 cycle coolant off

N007 G00 X00000 Rapid to (0,0) spindleY00000 M05 stop

N008 M30 End of programme

: 009 Start of subrouting

N001 G91 Set incremental mode

N002 G81 Z00700 R-00200 Drill hole at that verylocation i.e.centre

N003 X-01000 Y+01000 Drill hole at location (1)

Explanation: (main programme)

N001 & N002 : Setting feed, speed & Tool.

N003 : Locate tool above position 'A'.

N004 : Call the subroutine for "drilling finalholes and locating drill at a distanceof 50 mm".

Main programme

N004 Y - 02000 At location (2)

N005 X + 02000 At location (3)

N006 Y + 02000 At location (4)

N007 G80 Cancel cycle

N008 G00 X+05000 Move to next relativeY-01000 position B

N009 M99 Return back to mainprog.


←


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T h e r


N005 : Drill hole following path (3)X← X + 20Y = same

N006 : Drill hole following path (4), i.e.X = sameY←Y + 20

N007 : Cancel cycle don't drill more

N008 : Locate drill at 50 mm apart on x-axisand 10 mm below Ylast position, i.e.

X ←X + 50

Y← Y - 10

N009 : Return

MACROS

Macros are another type of subroutines which are givenan identify and stored within memory or macrofile usedfor machining a complete component. A macro may havefixed dimensions or it may have parametric variables.This is also sometimes referred to as only 'Parametricsubroutines'. These are very useful when programminga family of parts that have same shape but vary in size asshown in Fig 8

There are four components a,b,c,&d

1. ‘a’ has two diameter ø1 and ø2

2. ‘b’has ø2 portion increased in length

3. ‘c’ has ø1 portion increased in diameter

4. ‘d’ has ø2 portion eliminated

Mirror image

It reverses simply the sign + ve or - ve of an axis directionas in Fig 9

Calling the centre line of this part as X0, Y0 the pattern ismachined. Then mirror imaging along X-axis by callingsubroutine and then mirroring both components alongY-axis to get final shapes.


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Production & Manufacturing Related Theory for Exercise 4.2.118Turner - CNC Turning

Operational modesObjectives : At the end of this lesson you shall be able to• state the various operational modes• state the work piece zero point.• state the tool zero point• explain the machine reference point• list the various types of offset• prepare the part program for facing, plain turning, step turning, chamfering turning, radius turning and

drilling.

Operational modesSingle block modeThis mode will function when the mode switch is set inAUTO mode only. If we switch on the single block switchand push the cycle start button, then the single block inthe programme only will be executed. For the executionof the next block then again cycle start button should bepressed. If the single block switch is in off position, thenthe program will be executed continuously.

Auto modeFor this mode, the mode switch is set in AUTO mode. Inthis mode the program will be executed continuously oneblock after another block.

In this mode if we press the cycle start button, the currentprogram in the CRT panel will be executed.

Manual mode: MDI modeMDI mode means manual data input. With this mode,we can input the program command manually andexecute the program.

Jog modeJog mode is used for moving the turret in X and Z direction.After selecting jog mode if we press 'X+' axis button, theturret will move in 'X+' direction. In the same manner wecan move in the ‘Z’ direction also.

Incremental jog modeThis mode is used to move the turret in micron level. Bypressing the axis button, in this mode, we can move thebutton in 0.001, 0.01, 0.1, 1 mm range.

Edit modeThis mode is used to edit the program. In this mode editkey should be in 'ON' position, to input a program.

Zero points and reference pointsZero pointIn CNC machines, tool movements are controlled bycoordinate systems. The origin of the co-ordinate systemis considered as zero point. In some of the CNCmachines, the zero point may be located at a fixed placeand cannot be changed. This is known as fixed zero point.Some other machines, a zero point may be established

by moving the slides so that the cutting tool is placed inthe desired position in relation to the work pieces. This isknown as floating zero point.

Machine zero point or machine datum (M)It is a fixed point on a machine specified by themanufacturer. This point is the zero point for thecoordinate system of the machine controller. In turningcentre, the machine zero point is generally at the centreof the spindle nose face as shown in Fig 1. In machiningcentres, it is either fixed at centre of the table or a pointalong the edge of the traverse range.

Work piece zero point (W)This point determines the work piece coordinate systemin relation to the machine zero point as shown in Fig 2.This point is chosen by the part programmer and input tothe machine controller. The position of this point may bechosen in such a way that the dimensions of the workpiece drawing can be easily converted into coordinatevalues. For turned components, it is placed along thespindle axis in line with the right or left end face of thework piece. It is also known as program zero point.


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Tool zero point (T)When machining a work piece, the tool must be controlledin precise relationship with the work piece along the Whenmachining a work piece, the tool must be controlled inprecise relationship with the work piece along themachining path. This requires a point in the tool turret betaken as reference point, which is known as tool zeropoint.

At the tools in the tool turret have different shapes andsizes, the Offset distance between the tool zero point andwork piece zero point is measured and entered in to thecomputer. This known as tool offset setting.

Machine reference point (R)Machine reference point is also known as home positionas shown in Fig 3. It is used for calibrating the measuringsystem of the sides and tool movements. It is determinedby the manufactures.

The value of the machine reference coordinates (XMR,ZMR) is fixed and cannot be changed by the user. Thepositioning of the reference point is accuratelypredetermined in every transverse axis by the trip dogsand limit switches.

Programming details (Fig 4)

------------- This line indicates the tool moves at rapidfeed (G00)

------------- This line indicates the tool moves atlinear interpolation (G01)

Operation devicesEdit alphanumeric keysUsed to edit the part program, tool offsets, work offsetsetc..

Feed rate override switchEnables manual overriding of the programmed feed rateduring part machining. Can be varied between 0% and120% of the programmed feed rate, in steps of 10%.

Rapid rate override switchEnables manual overriding of the rapid traverse rateduring rapid motions. Can be varied between 0% and100% of the programmed feed rate, in steps if 25%.

Spindle speed override switchEnables manual overriding of the spindle speed duringpart machining.

Feed holdStops the motion of all axes temporarily during machining.

Cycle startMachine restStops all functions being executed, like spindle rotation,axes motion, etc.

Emergency stopUsed when the machine is to be halted suddenly, like incase of tool breakage. Pressing it shuts down all systemsof the machine except the console-axes drives, spindledrive, coolant pump, hydraulic power pack etc.

Single block ON/OFFWhen OFF, execution of the part program is automaticand continuous. When ON, part program is executedblock-wise. In block-wise execution the cycle start buttonmust be pressed to execute each block.

Coolant ON/OFF Controls the coolant.

Data input/outputUsed to transfer data between the machine and anexternal device like a PC. Data that can be transferred ispart program, PLC data, tool offset and work offset.

Chip conveyor forward backward Moves the chipconveyor.

Dry runSets the Dry run mode ON or OFF. The Dry run mode isused to check the part program by executing it withoutactually cutting a part. During this mode commandedfeedrate in the part program is not effective, and the axesmoves at a fixed Dry run feed rate. Dry run feed rate istypically 1000 mm/min to 5000mm/min.

Machine lock and auxiliary function lockSets the Machine lock mode ON or OFF. The machinelock mode is used to check the part program by executingit without any axes motions and miscellaneous functions


46

RPM =r/minπD

1000 . vn =

Cutting speed m/min1000

.D.nv

π=

Metal removal rate V = V.S.A cm3/min

Power required k Wη 6 0 0 0

v . s . A. k sP =

like tool change, spindle rotation, etc. The screen displayappears as during normal execution.

Operational modes− Auto mode

− Edit mode

− MDI mode (Manual data input)

− Jog mode

− MPG mode (manual pulse generation) data

− Input/output mode

− Zero return mode

I) Selection of tools, speed feed & depth of cutD = work piece diameter mm

V = cutting speed m/min

S = Feed mm/r

N = RPM r/min

A = Depth of cut mm

N = Efficiency for example 0.75

Ks = Specific cutting force N/mm2

V = Metal removal rate cm3/min

P = power required kW

R = nose radius mm

K = Constant for example 1.4

Rt = Profile depth μm

Ra= Surface finish μm

Ks=1800 N/mm² and a machine efficiency factor=0.75are used.

k w2 5

v .s .A.P =

III) Approximate value for surface finish

8r

1000 2sktR depth Profile =

The constant k is dependant on two factors, the workpiece material and how well the cutting edge profile isreproduced on the work piece. In normal machine steelk=1.4, Surface finish Ra = Rt/3.5.

Surface Ra = s2.50/R

IV) Effect of nose radius and feed rate on the surfacefinish requirements

The table below gives the recommended maximumvalues of feed rate for finishing normal steels, whenturning materials which give rise to edge build-up, thecutting speed must be sufficiently, high to avoid suchtendencies, if possible When turning highly abrasivematerials, the feed rates should be reduced by about 20%.To convert Ra to CLA multiply by 40.

II) Approximate value for power requiredThe above formula for power is exact but the specificcutting force ks is included. The ks-value is hard to setbecause it is dependent on many factors. Such as workpiece materials, chip breaker, cutting rake, feed settingangle chip thickness.

A simplified formula for approximate power required isshown below, Based on the most common type ofapplication-medium rough to rough turning of normalsteel, with a light-cutting edge-a specific cutting force.

Nose radius, mm

0.2 0.4 0.8 1.2 1.6 2.4

Ra value Feed rate, mm/rev

0.6 0.05 0.07 0.10 0.12 0.14 0.17

1.6 0.08 0.12 0.16 0.20 0.23 0.29

3.2 0.12 0.26 0.23 0.29 0.33 0.40

6.3 0.23 0.33 0.40 0.47 0.57

8.0 0.40 0.49 0.57 0.69

A large nose radius will usually result in a better surfacefinish, provided that the cutting edge is sufficiently sharpand that the larger nose radius does not give rise tovibrations. It is recommended that the depth of cut forfinishing should be more than the nose radius of thechosen insert. Fillet, etc on the component often restrictthe choice of nose radius on finishing.

V) Cutting speed-wear lifeProviding the machining conditions are good i.e. stabilityof the work piece and tool, it is possible to increase thewear life of the insert.

To achieve longer wear life, the cutting speed must bereduced. Multiply the recommended cutting speeds bythe following factors

The cutting speeds given in this guide are for 30 min.wearlife. If higher surface speeds are required that wear lifewill decrease.


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VI) Edge condition factors (Fig.5)- Fixed conditions

- Material specification

- Amount of material to be removed

- Component dimension

- Component shape

- Hardness

- Surface condition

- Operation

- Finish requirement

- Type of machine

- Condition of machine

- Power available

- Chucking or clamping method

Approx. wear lifein minutes Factor

* 15 1.25 x V* 30 1.00 x V 45 0.89 x V

Once the fixed conditions have been considered, thetooling and data parameters can be variable conditions

- Select carbide grade

- Select radius

- Select insert shape

- Select insert size

- Select insert rake

- Select tool size

- Select tool-holder shank size

- Select tool-holder style

Now the cutting speed, depth of cut and the feed overrevolution can be selected.


48


Types of offsetsObjective: At the end of this lesson you shall be able to• list the types of offsets used in CNC machine• trace the tool path from the given program.

Types of offsets

There are three types of offsets used in CNC machineoperation.

They are:

i Work offset (or) zero offset

ii Geometrical offset

iii Wear offset

Work offset (or) zero offset.Every manufacturer fix a reference point on the spindleof the machine according to the design of manufacturing.

The tool will take the command and move with referenceto this machine reference point.

To make the tool to move with reference to the job, workoffset or zero offset has to be taken.

Procedure for taking work offset

Clamp the job in the chuck of the machine.

Set the tool in the required order set in the machine turret.

Set the jog mode or the tool and touch the face of the job.

With the use of a paper check the proper contact of toolwith the face.

Now select the work co-ordinate system from G54 to G59.

Enter the z value in the selected work co-ordinate system

Now touch the diameter with the same tool.

Check the contact of the tool with the job using a paper.

Now enter the diameter of the job in the tool contact pointin the x value in the selected work co-ordinate system.

This particular work co-ordinate system should bementioned in the part program.

Geometrical offset

The tools used in CNC machine are of different geometry.The length of the tools vary accordingly.

Even if the work offset is taken for a tool it will not suit theother tools

So for every tool offset is taken and entered in tool offsetvalue in work co-ordinate system

Because of this every tool will take the work zero point asorigin

The procedure for geometrical offset is given below

Clamp the job in the chuck of the machine

Set the tool in the required order in the machine turret

Select the jog mode or MPG mode

Select the first tool and touch the face of the job

Check with a piece of paper whether the contact of toolwith the job is proper

Now take the geometrical offset page and enter underthe tool number the command MZ 0 (zero)

This command will clear any previous values and willmeasure the current tools tool offset in Z axis

Now touch the tool to a know diameter on the component

Again in the tool-geometry page enter the command MX(The value of the diameter) for example if the diameter is50mm then MX50

Follow the same procedure for the remaining tools

enter the MZ and MX commands for various tools in theunder respective tool number.

Wear offset

Because of long running the tool tip may wear out andthe dimension of the job may increase or decrease fromthe original programmed dimension

To recitify this defect wear offset is used

Procedure for entering wear offset

If the programmed size is X40.49 and the machine sizeis 40.44 in this 0.04 mm is reduced due to tool wear.

To rectify this take the tool offset number of the worn outtool.

In that tools wear offset number enter the value U0.04.

In the inner diameter defects instead of positive valueput U-0.04 in the wear offset number.

Tool offset number and wear offset number are same.


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Program Explanation

N001 G91 G71 G94 Increnental mode; metric units, feed rate is given in mm/min

N002 G00 X0 Z0 M03 S1000 F100 Set the tool at (0, 0) position. Assign spindlespeed and rate.

N003 M08 G01 X-2.5 Depth of cut of 2.5 mm is given.

N004 G01 Z-30 Tool is moving towards left by-30 mm (plain turning)

N005 G01 X5 Z-30 Taper turning for the length of 30 mm

N006 G00 Z60 Tool retracts to its initial position

N007 G00 X +5 Again, infeed of 5 mm is given


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Program Explanation

N008 G01 X-2.5 Depth of cut 2.5mm is again given

N009 G01Z-30 Simple turning operation for the length of -30mm

N010 G01 X 5Z-30 Taper turning operation for the length of -30mm isperformed

N011G00 X 0Z0 Tool moves to (0,0) position

N012 M09 M05 M02 Coolant off, spindle stop, end of the program

Step turning

Program Explanation

N001 G91 G71 G94 Absolute mode; metric units, feed rate is given in mm/min

N002 G00 X0 Z0 M03 S1000 F100 Set the tool at (0, 0) position

N002 G00 Z+2 Move the tool towards right by 2mm

N003 G00 X-5 Infeed of 5mm is given to reach position A


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Program Explanation

N004 G01 X-0.5 F100 Depth of cut of 0.5mm is given with a feed rate of

100mm/min.

N005 G33 Z-52 K3 M03 S100 Threading operation for a length of 52mm (50+2) witha pitch length of 3mm

N006 G00 X1 F300 Tool goes back by 1mm

N007 G00 Z+52 Tool rapidly moves to position A

N008 G00 X - 1.5 F100 Instead of 1.5mm is given with a feed rate of 100 mm/min.

N009 G33 Z-52 K3 M03 S100 Threading operation is again performed for a length of 52 mm (50+2)

N010 G00 X2 Tool goes back by 2mm

N011 M02 End of program


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Tool path study of machining operation (Straight turning)Objective : At the end of this lesson you shall be able to• trace the tool path of the given drawing with linear interpolation• learn to programme for straight turning, step turning and taper turning• learn incremental method programming.

%O0020 (Fig 2)

G28 U0 W0 ;G50 S3000 T0200 ;

G96 S200 M03 ;G00 X60.0 Z0.0 T0202 M08 ;

G01 X0.0 F0.1 ;G00 X30.0 Z2.0 ;

G01 Z-20.0 F0.2 ;X50.0 ;

Z-35.0 ;X60.0 ;

Z50.0 ;G00 X55.0 Z2.0 M09 ;

G28 U0 W0 M05 ;M01 ;M30 ;

Mixed method programming

%

O0021 (Fig 3)

N1 ;

G28 U0 W0 ;

G50 S3000 T0100 ;

G96 S200 M03 ;

G00 X50.0 Z0.0 T0101 M08 ;

G01 X0.0 F0.12 ;

%O0019 (Fig 1)

N1 ;G28 U0 W0 ;

G50 S3000 T0100 ;G96 S200 M03 ;G00 X55.0 Z0.0 T0101 M08 ;

G01 X0.0 F0.1 ;G00 X50.0 Z2.0 ;

G01 Z70.0 F0.2 Z-70 ;G00 X55.0 Z2.0 M09 ;

G28 U0 W0 M05 ;M01 ;

M30 ;

Step turning

Straight turning


53

G00 X50.0 W2.0 ;G01 Z-40 F0.12 ;X60 ;W-30 ;X80 ;W-40 ;X100 ;W-40 ;G00 U5.0 Z5.0 M09 ;G28 U0 W0 M05 ;M01 ;M30 ;

Incremental method programming

%O0022 (Fig 4)N1 ;G28 U0 W0 ;G50 S3000 T0100 ;G96 S200 M03 ;G00 X30.0 Z0.0 T0101 M08 ;G01 X0.0 F0.1 ;G00 U46.0 W2.0 ;G01 W-2.0 F0.1 ;G01 U4.0 W-2.0 F0.1 ;G01 W-28 F0.1 ;U10.0 ;W-25.0 ;U10.0 W-10.0 ;W-20.0 ;G00 U5.0 W90.0 M09 ;G28 U0 W0 M05 ;M01 ;M30 ;

Taper turning

%O0023 (Fig 5)N1 ;G28 U0 W0 ;G50 S3000 T0500 ;G96 S200 M03 ;G00 X55.0 Z0.0 T0505 M08 ;G01 X0.0 F0.1 ;G00 X25.0 Z2.0 ;X30.0 Z-1.5 F0.1 ;Z-30.0 ;X50.0 Z-40.0 ;Z-55.0 ;G00 X60.0 Z2.0 M09 ;G28 U0 W0 M05 ;M01 ;M30 ;

Radius operation


54

%O0024 (Fig 6)N1 ;G28 U0 W0 ;G50 S2000 T0600 ;G96 S250 M03 ;G00 X65.0 Z0.0 T0606 M08 ;G01 X0.0 F0.12 ;G00 X20.0 Z2.0 ;G01 Z0.0 F0.2 ;G03 X25.0 Z-2.5 R2.5 F0.1 ;G01 Z-20.0 F0.12 ;X40.0 Z-30.0 ;Z-35.0 ;G02 X50.0 Z-40.0 R5.0 F0.12 ;G01 X50.0 F0.12 ;Z-55.0 ;G00 X65.0 Z2.0 M09 ;G28 U0 W0 M05 ;M01 ;M30 ;

Taper turning

%O0025 (Fig 7)N1 ;G28 U0 W0 ;G50 S3000 T0600 ;G96 S200 M03 ;G00 X30.0 Z0.0 T0606 M08 ;G01 X0.0 F0.1 ;G00 X21.47 Z2.0 ;G01 X28.0 Z-7.0 F0.12 ;Z-32.0 ;X38.0 Z-45.738 ;Z-65.738 ;G00 X40.0 Z2.0 M09 ;

G28 U0 W0 M05 ;M01 ;M30 ;

CalculationTo calculate diameterMethod 1

Tan θ = Tan = ADJ

OPP

Tan 25° =7

OPP

Opp = 0.4663 X 7

Opp = 3.264 mm

X = 2 X Opp.

X = 2 X 3.264

X = 6.528 mm

d = D - X

d = 28 - 6.528

d = 21.47mm

Method II

Tan θ =2 L

dD −

Tan 25 =L X 2

d28 −

0.4663 =1 4

d2 8−

d = 28 - 6.528d = 21.47 mm

To calculate length

Tan θ =2 L

dD −

Tan 20 =2L

2838 −

L =0.36392

10

×

D = D-X

L =

0.7279

10

L = 13.738 mm


55

Canned cyclesObjective : At the end of this exercise you shall be able to• state the cycle used in CNC program• learn to program for all canned cycles• learn to program for threading OD/ID.

Canned cyclesCanned cycle is used in stock removal operation inturning. In this cycle, the tool is positioned at the startingpoint. The finishing contour of the pocket is to beprogrammed like the normal programming using G code.

G70 - Finishing cycle (Fig 9)

Format:G70 P_Q_F_;P : Starting Block Number

Q : Ending Block Number

F : Finishing Feed

G71 - Turning cycle(Fig 10)

Format

G71 U_R_;G71 P_Q_U_W_F_;

U : Depth of cut per pass in X Axis (Radial value)

R : Relief Amount

P : Starting Block Number


U : Finishing Allowance in X Axis

W : Finishing Allowance in z Axis

F : Feed

Example for G71 turning cycle

Blank size: f 55 X 50

%

O0026 (Fig 11)

N1 ;G28 U0 W0 ;

G50 S1200 T0300 ;G96 S250 M03 ;

G00 X65.0 Z0.0 T0303 M08 ;G01 X0.0 F0.1 ;

G00 X61.0 Z2.0 ;G71 U1.0 R1.0 ;

G71 P10 Q20 U1.0 W0.5 F0.3 ;N10 G00 X30.0 ;

G01 Z-20.0 F0.1 ;X46.0 Z-28.0 ;

Z-38.0 ;G1 X71 ;

G03 X75.0 Z-40 R2 ;G01 Z-63 ;

N20 Z-63.0 ;G00 X65.0 Z2.0 M09 ;

G28 U0 W0 M05 ;M01 ;

N2 ; (OD FINISHINING)


56

G28 U0 W0 ;

G50 S2600 T0700 ;

G96 S150 M03 ;

G00 X26.0 Z0.0 T0705 M08 ;

G01 X0.0 F0.1 ;

G00 X65.0 Z3.0 ;

G70 P10 Q20 F0.12 ;

G00 X65.0 Z2.0 M09 ;

G28 U0 W0 ;

M30 ;

G72 - Facing cycle

FormatG72 W_R_;G72 P_Q_U_W_F_;W : Depth of cut per pass in Z Axis

R : Relief Amount

P : Starting Block Number


U : Finishing Allowance In X Axis

W : Finishing Allowance In Z Axis

F : Feed

Example for G72 Facing cycle%

O0027 (Fig 12)

N1 ;

G28 U0 W0 ;

G50 S1300 T0200 ;

G96 S150 M03 ;

G00 X55.0 Z2.0 T0202 M08 ;

G72 W1.0 R2 ;

G72 P20 Q30 U1.0 W0.5 F0.3 ;

N20 G00 Z-65.0;

G01 X40 ;

Z-53.0 ;

X25.0 Z-45.0 ;

Z-25.0

X20.0 Z-15.0 ;

Z0.0 ;

N30 ;

G00 X55.0 Z2.0 M09 ;

G28 U0 W0 M05 ;

M01 ;

N2 ; (OD Finishing)

G28 U0 W0 ;

G50 S2600 T0700 ;

G96 S150 M03 ;

G00 X55.0 Z2.0 T0707 M08 ;

G70 P20 Q30 F0.12 ;

G00 X65.0 Z2.0 M09 ;

G28 U0 W0 M05 ;

M30 ;

G73 - Pattern repeating cycle(Fig 13)

Format:G73 U_W_R_;G73 P_Q_U_W_F_;

U : Total amount of stock in X axis (radial value)

W : Total amount of stocks in Z axis

R : Number of passes

P : Starting block number

Q : Ending block number

U : Finishing allowance In X axis

W : Finishing allowance in Z axis

F : FeedProduction & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.120Copyright @ NIMI Not to be Republished

57

%

O0028 (Fig 14,15)

N1 ;

G28 U0 W0 ;

G50 S1200 T0300 ;

G96 S250 M03 ;

G00 X55.0 Z2.0 T0303 M08 ;

G73 U5.0 W3.0 R6 ;

G73 P40 Q50 U0.5 W0.1 F0.3 ;

N40 G00 X20.0 ;

G01 Z0.0 ;

X24.0 Z-2.0 ;

Z-16.0 ;

G02 X32.0 Z-2.0 R4.0 ;

G01 Z-36.0 ;

G03 X44.0 Z-42.0 R6.0 ;

N50 G01 Z-54.0 ;

G00 X55.0 Z2.0 M09 ;

G28 U0 W0 M05 ;

M01;

N2 ;

G28 U0 W0 ;

G50 S2600 T0700 ;

G96 S150 M03 ;

G00 X28.0 Z0.0 T0707 M08 ;

G01 X0.0 F0.1 ;

G00 X55.0 Z2.0 ;

G70 P40 Q50 F0.12 ;

G00 X65.0 Z2.0 M09 ;

G28 U0 W0 ;

M30 ;

G74 - Peck drilling cycle

FormatG74 R_;G74 Z___Q___F___;

R : Retract value

Z : Depth of the hole

Q : Depth of cut per pass in Microns

F : Feed rate

%

O0029 (Fig 16)

N1 ; (C.D)

G28 U0 W0 ;

T0200 ;

G97 S1500 M04 ;

G00 X0.0 Z5.0 T0202 M08 ;

G01 Z-3.0 F0.12 ;

G00 Z5.0 M09 ;

G28 U0 W0 M05 ;

M01 ;

N2 ;

U0 W0 ;

T0700 ;

G97 SI500 M04 ;Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.120Copyright @ NIMI Not to be Republished

58

G00 X0.0 Z5.0 T0707 M08 ;

G74 R4.0 ;

G74 Z-50.0 Q8000 F0.05 ;

G00 Z5.0 M09 ;

G28 U0 W0 M05 ;

M30 ;

G75 - Grooving cycle(Fig 17)

Format :G75 R___;G75 X____Z___P____Q___R___F___;

R : Relieving the tool (mm)X : Groove diameter (mm)Z : Groove length (mm)P : Depth of cut in X axis in microns

(Radial value)Q : Shift value in Z axis (microns)F : Feed

%O0030 (Fig 18)

G28 U0 W0 ;T0500 ;

G97 S1200 M03 ;G00 X52.0 Z5.0 T0505 M08 ;

G00 Z-26.0 ;G75 R2.0 ;

G75 X30.0 Z-37.0 P500 Q3000 F0.05 ;G00 X46.0 ;

Z5.0 M09 ;G28 U0 W0 M05 ;

M30 ;

G76 - Multiple thread cutting cycle(Fig 19)Format:

G76 P___Q____R___;G76 X___Z___P___Q____F____;

Explanation for the cycle:

P : NCAN : Number of finishing passesC : Chamfer amountA : Included angle

Q : Minimum depth of cut in microns (radial value)R : Finishing depth of cut in microns (radial value)X : External threading (minor dia) internal

threading(major dia)Z : Thread lengthP : Height of thread (microns)Q : First depth of cut in microns (radial value)F : Feed (pitch of the thread)

ExampleOD Threading


59

%

O0031 (Fig 20)

G28 U0 W0 ;

T0400 ;

G97 S600 M04 ;

G00 X32.0 Z5.0 T0404 M08 ;

G76 P030060 Q150 R20 ;

G76 X27.404 Z-42.0 P1298 Q300 F2.0 ;

G00 X32.0 ;

Z5.0 M09 ;

G28 U0 W0 M05 ;

M30 ;

Threading calculation

Minor dia, d = D - (2h)

(h = 0.649 p, for metric thread)

h = 0.649 2.0=1.298 mm.

d = 30 - (2 1.298)

= 27.404 mm.

ID Threading (Fig 21)

Threading calculationMinor dia, d = D - (2h)

(h = 0.649 P, for metric thread)

h = 0.649 2.0 = 1.298 mm

d = 40 - (2 X 1.298)

=37.404 mm.

%

O0032 (Fig 22)

G28 U0 W0 ;

T0500 ;

G97 S600 M04 ;

G00 X38.0 Z5.0 T0505 M08 ;

G76 P030060 Q150 R20 ;

G76 X40 Z-110.0 P1298 Q300 F2.0 ;

G00 X38.0 ;

Z5.0 M09 ;

G28 U0 W0 M05 ;

M30 ;


60

Production & Manufacturing Related Theory for Exercise 4.2.121 &122Turner - CNC Turning

Cutting parameters, cutting speed and feed, depth of cut,CSM, tool wear, toollifeObjectives: At the end of this lesson you shall be able to• differentiate between cutting speed and feed• state select the recommended cutting speed for different materials from the chart• state the factors governing the cutting speed• state the factors governing feed & learn about interpolation.

Cutting speed is the speed at which the cutting edgepasses over the material, and it is expressed in metresper minute. When a work of a diameter ‘d’ is turned inone revolution the length of the portion of work in contactwith the tool is πxdxn. This is converted into metres andexpressed in a formula form as

/min.metre

1000D .N.

V�

�

Where V = cutting speed in m/min

π = 3.14

D = diameter of the work in mm

N = RPM

When more material is to be removed in lesser time, ahigher cutting speed is needed. This makes the spindleto run faster but the life of the tool will be reduced due tomore heat being developed. The recommended cuttingspeeds are given in a chart. As far as possible therecommended cutting speeds are to be chosen from thechart and the spindle speed calcualted before performingthe operation. (Fig 2) correct cutting speed will providehigher tool life under normal working condition.

Cutting speed 120m/min length of metal passing calculated r.p.m. of spindlecutting tool in 1 revolution

____ 78.56mm 1528

____ 157.12mm 756

___ 235.68mm 509.3

Cutting speed (Fig 1)


61

ExampleFind out the rpm of a spindle of a 50mm bar to cut at

25m/minute ; V =

1000

DN×π; N =

D

V1000

×π

50 x 3.14

251000×=

3.14

500 = 159 r.p.m

Factors governing the cutting speedFinish required

depth of cut

tool geometry

properties and rigidity of the cutting tool and its mounting

properties of the workpiece material

rigidity of the workpiece

type of cutting fluid used

rigidity of the machine tool

Feed (Fig 3)

The feed of the tool is the distance it moves along thework for each revolution of the work, and it is expressedin mm/rev.

Factors governing feedTool geometry

surface finish required on the work

rigidity of the tool

coolant used

Rate of metal removalThe volume of metal removal is the volume of chip that isremoved from the work in one minute, and is found bymultiplying the cutting speed, feed rate and the depth ofcut.

For super HSS tools the feeds would remainthe same, but cutting speeds could beincreased by 15% to 20%.

Cutting speeds and feeds for H.S.S. tools

TABLE 1

Material being Feed Cutting speed turned mm/rev m/min

Aluminium 0.2-1.00 70-100

Brass (alpha)-ductile 0.2-1.00 50-80

Brass (free cutting) 0.2-1.5 70-100

Bronze(phosphor) 0.2-1.00 35-70

Cast iron(grey) 0.15-0.7 25-40

Copper 0.2-1.00 35-70

Steel(mild) 0.2-1.00 35-80

Steel

(medium-carbon) 0.15-0.7 30-35

Steel (alloy high

tensile) 0.08-0.3 5-10

Thermosettingplastics 0.2-1.00 35-50

Depth of cutThe depth of cut is the difference between machined andun machined surface.

If D1 = initial diameter

D2 = Final diameter

A lower speed range is suitable for heavy, roughcuts.A higher speed range is suitable for light,finishing cuts.The feed is selected to suit the finish requiredand the rate of metal removalWhen carbide tools are used, 3 to 4 timeshigher cutting speed than that of the H.S.S.tools may be chosen.The recommended cutting speed and feed ratefor H.S.S. tools are listed on Table 1.

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.121 & 122Copyright @ NIMI Not to be Republished

62

Depth of cut = 2

D2D1−

The relationship between limiting spindle speed andthe constant cutting speedwhen working with Constant cutting speed Mode, thespindle speed increases as the tool moves towards theaxis. The spindle speed is calculated using the equation.

diameter of the

N = RPM of the spindle

As per the above equation,at a specific cutting speed(say V=250m/mm) when the dia is 30mm the spindlespeed shall be 2652 rpm. when the diameter is reducedto 20mm the spindle speed would be 3978 and if thediameter reduces to 1mm the spindle speed would goup to 79577 rpm, and at certain diameter spindle speedmay go beyond the machine’s capacity. similarly whento tool go near the axis point, the spindle speed RPMwould be theoritically infinity since the diameter at axisis (D=0)

��.0

1000V

D

1000VN

�� .

However, the CNC machine has certain maximumspindle speed permissible, which should be specified in

our programme, and this is known as limiting spindlespeed. Once programmed, when the spindle reaches thislimiting value of speed, the controlled clamps it and therest of the operations are carried out at a constant speed,limiting spindle speed. This will ensure that any possibledamage due to variationof spindle speed, is prevented.

As an example, when we desire to carry out, at constantcutting speed of 250m/min at 3000 RPM, the programmeas per Fanuc shall be

G96 S250

G92 S3000

What is the benefit of fixing Limiting spindle speed in theprogramme?

If a component is rigidly fixed in the chuck and thecomponent is cylindrical, spindle maximum. speed is setas limiting spindle speed. If the part is not circular orcylindrical, and is held in a fixture, not balanced, thecentrifugal forces may cause the part to fly off, or it mayspoil the fixture itself, if the Limiting speed is notprogrammed.

At the axis of the part, in fact, the RPM would theoreticallybe infinity (D is zero). The machine however has a certainmaximum spindle RPM, so in the CNC program we needto specify what this maximum speed.

InterpolationObjectives: At the end of this lesson you shall be able to• define the interpolation• state the purpose of interpolation• list the type of interpolation.

InterpolationAs the co - ordinates of points on the profile of the jobvary continuously, it is necessary to define the path ofsmall segment.

This tedious work is done by the computer by means of“ interpolator”.

DefinitionThe methods by which control system calculate theintermediate points and the speed of the motor is knownas interpolation.

The parameters supplied may be

i) Radius

ii) Start and end point of a curve

iii) Radius and centre of a circle

iv) Gradient angle for a line

Types of interpolationsInterpolations are classified as

i) Linear interpolation

ii) Circular interpolation

iii) Helical interpolation

iv) Parabolic interpolation

v) Logarithmic interpolation

vi) Exponential interpolation of these the linear andcirculate interpolators are commonly employed.

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.121 & 122

dD where1000

πDNV(met/min) ��


63

Linear interpolationIn this interpolation, the interpolated points lie on thestraight line joining a pair of given points. (Fig 1a)

This is done in two or three dimensions.

The fast of linear interpolator is to supply velocitycommands to several axes simultaneously in pps (pulsesper second) (Fig 1b)

By changing the frequency of the pulses, the feed can becontrolled.

The linear interpolator consists of Digital DifferentialAnalyser (DDA) integrators one for each axis of motionhence each integrator functions separately one for X- axisand the other for Y - axis. (Fig 2a)

Circular interpolationIn circular interpolation, the interpolated points lie on aspecific circle between a pair of fixed points.

In most cases, the circular interpolation is limited to onequadrant in the machine tool system. (Fig 2b)

The input data should consists of the distances betweenthe initial point and the centre of the circle.

Two Digital Differential Analysers (DDA) are required forcircular interpolation.

Advantages of circular interpolation areBetter surface finish

Greater accuracy

Less total machining time

Lower working costs.

Circular interpolationThe circular interpolation,• Code G02 (clockwise)

• Code G03 (anti - clockwise)

A circular interpolation permits the traversing of the toolwith a defined speed along a circular path from the presentStart-points to the programmed destionation point.

Apart from the destination points co-ordinates, the controlunit here also needs statements about the sense ofrotation and the centre of the circle. The centre is enteredwith I,J and K with incremental dimensions with the centrepoints as origin.

The following assignment applies:

• I for the x - axis

• J for the Y - axis

• K for the Z - axis


64

Programming example with G2: Explanation:(Fig 3).........

N40 G0 X30 Y40 Z2 With rapid traverse to

N50 G1 Z-5 F100 the start point Groov

N60 G2 X50 Y40 I10 J-7 ing with Z Circular

N70 G1 Z2 F1000 interpolation clockwise

The following example decribes an anti-clockwise circularinterpolation as shown in the sketch above.

The end-point in the sketch is now the startingpoint for the circular interpolation.

Programming example with G3: Explanation:(Fig 4)

.........

N40 G0 X50 Y40 Z2 With rapid traverse to

N50 G1 Z-5 F100 the start point

N60 G3 X30 Y40 I-10 J-7 Circular interpolation

N70 G1 Z2 F1000 anti-clockwise

Circular Interpolation with mixed programmingParticularly the incremental statement of the centre ofthe circle usually represents some difficulties to theoperator in practice, since it must often be evaluated usingtriangle calculations.

This is a prime example of where the mixed co-ordinateprogramming of the interpolation parameters in absolutedimensions comes in useful.

Programming example Explanation:

.........

N40 G0 X30 Y40 Z2 Circle centre absolute,

N50 G1 Z-5

N60 G2 X50 Y40 I=AC(40) J=AC(33)

N70 G1 F2 F1000


65

Principle of position controlObjectives: At the end of this lesson you shall be able to• explain the principle of position control in a CNC machine• explain the terms pulse and pulse frequency• state the difference between closed loop and open loop control• state feedback/measuring systems used in CNC machines.

It has already been stated that the slides of CNCmachine are driven by servo motors.

The feed rate and position to be reached by the slide(tool) are indicated to the control by means of aprogramme line such as the one given below.

G91 G71 G01 x 60 F30

The meaning of the above instruction is that the toolshould travel a distance of 60 min along the x axis at afeed rate of 30 mm/min from its existing positon. In otherwords the tool should travel a distance of 60 mm in 2minutes.

Principle of position control

The above instruction requires that the feed motor shouldrotate at a predetermined r.p.m for a period of 2 minutes:and to achieve this, the feed motor should receive therequired quantity of electrical energy. This calls forregulation of the input current to the motor and basicallywhat the computer in the CNC machine does for positioncontrol is nothing but regulating the current input to thefeed motor.

The control computer after receiving a travel instructionperform certain calculations and arrive at the number ofpulsed to be sent out in the given time in order to achievethe required travel. ( It may be noted that the basic outputfrom any computer is an intermittent supply of low strengthelectric current called pulse or signal) Usually one pulsesent out by the control causes a tool travel of 0.001, andHence, in the above example to achieve a travel of 60mmin 2 minutes, the control after reading the above programline would send 60,000 pulses(60#0.001) in 2 minutes.

Pulse frequencyThis term refers to number of pulses sent per second inthe above case the pulse frequency is 500/S (60,000/120). The pulse frequency , it may be noted, isproportionate to the feed rate.

The pulse output by the computer being of low strengthand intermitted in nature, is not directly send to the drivemotor, Instead the intermitted current is converted to anequivalent continuous form, and is also strengthenedsuitably.

The feed motor thus receives a regulated supply ofcontinuous current for a specified time interval, and hence,ensures a tool travel as instructed by the programme

Open loop control system (Fig 1)

In an open loop control system (Fig 1) in which there isno arrangement for detecting or comparing the actualposition of the cutting tool on the job with the commandedvalue.

Therefore, this system is not providing any check to seethat the commanded position has actually been achieved.There is no feed back of information to the control also.These system are not good where extremely accuratepositioning is required.

Closed loop control (Fig 2 )

Closed loop control (Fig 2) is a term which is used veryoften when we talk about CNC machines. This termsignifies, that the control system has provisions to ensurethat the tool reaches the desired position, at the correctfeed rate, even if some errors creep in due to unforeseenreasons.

For instance in the previous example 60,000 pulses sentin 2 minutes by the control should cause a tool travel of60mm at 30 mm/min, but even if the control sends thesemay pulses it cannot be ensured that the tool has reallytravelled exactly 60 mm.

A closed loop control has a device called encoder andthis can continuously ascertain the distance acutally trav-elled by the tool and then monitor the same, in the formof feedback signals to the control. The control studiesthis feedback information and takes corrective action incase any error is detected in the tool position/feed rate.


66

Tool lifeObjectives: At the end of this lesson you shall be able to• state the relationship between cutting speed and tool life• explain tool life index equation• determine the maximum cutting speed for a given tool life.

Relationship between cutting speed and tool lifeDuration of correct cutting to the anticipated surface finishbetween grinding is termed as tool life. In metal cutting,increase in cutting speed increases power requirement.Therefore, the mechanical energy is converted into heatenergy at the cutting edge. Much of the heat is absorbedby the cutting tool with corresponding increase intemperature, resulting in softening of the cutting tool,which is the reason for inefficient cutting action. Theeffect of this reduction in tool life is largely present in highcarbon steels. Hence, they have to be operated at lowercutting speeds.

Cutting materials such as high speed steel, metalliccarbides and oxides can operate at much highertemperatures without reduction in hardness.

Fig 1 shows graphically the relationship between cuttingspeed and tool life curve in logarithmic form. A smallincrease in cutting speed from A to B causes largereduction in tool life from C to D, while small reduction incutting speed causes a large increase in tool life.

Thus when the machine gearbox does not give therequired cutting speed, it is better to use the next lowerspeed rather than the higher speed.

Tool life index

The relationship between tool life and cutting speed canbe represented by the following equation for most practicalpurposes.

Vt n = C

where V = cutting speed in m/min.

0.2

0.140.125

0.15

0.2

0.15

t = tool life in minutes

n and C are constants for a given set of conditions.

The value of n lies between 0.1 to 0.2 and typical valuesare given in the following table.

The following example is shown to determine the maxi-mum cutting speed for a given tool life.

Table Tool life index

Material and conditions Tool material n

3 1/2% nickel steel Cemented carbide

3 1/2% nickel steel (roughing) Highspeed steel

3 1/2% nickel steel (finishing) Highspeed steel

High carbon, high chromium die steel Cemented carbide

High carbon steel Highspeed steel

Medium carbon steel High-peed steel

Mild steel Highspeed steel

Cast iron Cemented carbide


67

From the calculations, tool life is doubled by reduction ofcutting speed by 8.3 percent, or reduction of tool life canbe calculated for an increase of 8.3 percent in cuttingspeed. Hence, it is always important to select a lowercutting speed, rather than a higher cutting speed, if themachine controls do not give optimum value.

Tool life calculations are useful in achieving optimumoperating conditions of cutting tools. Modern cutting toolmaterials are singularly resistant to softening under theheat of normal cutting and usually fail in two ways asshown in Fig 2.

a) Wear of clearance face

b) Crater of rake face

The above conditions can be corrected only by regrindingimmediately for effective metal cutting.

Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.2.121 & 122

Example

The life of a lathe tool is 8 hours when operating at acutting speed of 40 m/min. Given that Vtn = C, find thehighest cutting speed that will give a tool life of 16 hours.The value of n is 0.125.

(i) Determine the value of Log C from initial conditions.

C = Vt1n where

V = 40 m/min.

t1 = 480 min.

n = 0.125

Log C = Log V + n Log t1

= log40 + (0.125 Log480)

=1.6021 + (0.125 x 2.681)

=1.6021 + 0.3351

=1.9372

(ii) Determine Vmax for revised conditions

Vmax =

Where t2 = 960 min. (16x60)

Log Vmax = Log C – n Log t2

= 1.9372 – (0.125 x log960)

= 1.9372 – (0.125 x 2.9823)

= 1.9372 – 0.3728

= 1.5644 antilog 0.5644

Vmax is 36.68 m/min.

n2t

C


68

Production & Manufacturing Related Theory for Exercise 4.3.123-124Turner - Tool setting and Data Input

Cutting tool materials for TurningObjectives: At the end of this lesson you shall be able to• explain the properties of cutting tool• state the types of tool material.

Cutting tool materials and their propertiesTool materials are the subject of intense development. Theyare the product of an evolvement that has taken placealmost entirely during the twentieth century, and especiallysince the thirties. Machining which took one hundredminutes in 1900, today takes less than one minute. It isnot an exaggeration to say that the evolvement of toolmaterials has been one of the major contributing factorsthat has helped to make the modern, efficient industrialworld.

Today, there is a tool material to optimize every metalcutting operation-one that will cut a certain work piece,under certain conditions in the best way. Not only havecompletely new materials appeared but high speed steel,which was the major break through at the beginning of thecentury, has been developed to machine several timesfaster. It is however, the introduction and continuousimprovement of hard materials that have really improvedmetal cutting during the recent decades.

Cutting tool propertiesThe most important properties required by a cutting toolmaterial are,

ToughnessAbility to withstand the various cutting forces duringmachining.

HardnessAbility to retain hardness under severe working conditions.

High resistance to wear The material must withstand excessive wear even thoughthe relative hardness of the tool materials changes.

Frictional coefficientThe frictional coefficient must remain low for minimumwear and reasonable surface finish.

Cost and easiness in fabricationThe cost and easiness of fabrication should have withinreasonable limits.

Evolution of cutting tools- 1910-1920: High speed steel

- 1920's: Cemented carbide

- 1950's: Cermets (Tic -based)

- 1960's: Alumina-based ceramic

- 1970: CVD coated carbide

- 1980: First engineered carbide substrate(cobalt-enrichment)

- 1982: First SiAION ceramic

- 1985: First PVD coated carbide

- Mid 80's: Modern cermets (TiCN-based)

- Late 80's: SiC whisker reinforced Al2o3 ceramic

- Early 90's: Advanced Sialons

- Mid 90's: thin film diamond coated carbide

- Late 90's: PVD coated PCBN

- 2000: Advanced pre-coat & post-coat treatments

Cutting tool materialsMetal cutting environment (Fig.1)

- Heat (thermal deformation)

- Pressure (deformation, fracture)

- Wear (pure abrasion, chemical wear, notching)

- Interrupted cuts (thermal & mechanical cycling)

Types of tool materialsThe selection of proper tool materials depends on the typeof service to which the tool is subjected. The commonlyused cutting materials are:

Carbon steels- It is basically high carbon steel with percentage of

carbon in the range of 0.8 to 1.5

- It may only be used in manufacture of tools operatingat low cutting speed (12m/min).

- They are comparatively cheap, easy to forge and simpleto harden.

- Disadvantage of carbon tool steel is their comparativelylow heat and wear resistance.


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High speed steel- It is the general purpose metal for low and medium

cutting speeds owing to its superior hot hardness andresistance to wear.

- HSS can operate at cutting speeds 2 to 3 times higherthan for carbon steels and retain its hardness up to900°C.

- Tungsten in HSS provides hot hardness and formstability. Molybdenum maintains keenness of thecutting edge. Cobalt makes the cutting tool morewear resistant.

Stellites- Stellites is the trade name of a non-ferrous cast alloy

composed of cobalt, chromium and tungsten.

- The range of elements in these alloys is 40% to 48%cobalt, 30% to 35%, chromium and tungsten.

- Stellites can be operated on steel at cutting speeds 2times higher than for HSS.

- They are used for non metal cutting application suchas rubbers, plastics etc.,

Carbides- They are composed principally of carbon mixed with

other elements.

- The basic ingredient of most carbides is tungstencarbide, which is extremely hard. Pure tungstenpowder, is mixed under high heat(1500°C) with purecarbon in the ratio of 94% and 6% weight.

- The two types of carbides are the tungsten and titaniumand both are more wear resistant.

Coated carbides- The coated carbide has substrate and coating layer

- Substrate-for toughness having hard material and softmaterial (cobalt + carbide)

- Coating -Layer of carbide (very hard)

- Perform well on all work material

- Better impact strength to resist fracture

- Allow good coating adhesion

Ceramics- The latest development in the metal cutting tool uses

aluminium oxide, generally referred to as ceramics.

- Compacting aluminium oxide powder in a mould atabout 280 kg/sq.cm or more makes ceramic tools. Thepart is then sintered at 2200 °C. This method is knownas cold pressing.

- Ceramic tool material are made in the form of tips thatare to be clamped on metal shanks

- The tools have low conductivity and extremely highcompressive strength, but they are quite brittle andhave a low bending strength.

- They can with stand temperature up to 1200°C andcan be used at cutting speeds 4 times that of carbideand up to 40 times that of HSS.

- To give them increased strength often ceramic withmetal bond know as cermets is used.

- Heat conductivity of ceramics being very low the toolsare generally used without coolant.

CermetsCermets -Ceramics and Metal

Characteristics of cermets- High Hardness

- High Hot Hardness

- Resist oxidation

- Low Friction

Advantage of cermets- High efficiency

- Long life

- Large batch

- Avoid Build Up Edge

- Surface Finish Control

- Cermets Have the properties of higher cutting speedand wear resistance which enables hard part turning.

Diamond- The diamond is the hardest known material and can

be run at cutting speed about 50 times greater thanthat of HSS tool and 5 to 6 times of tool life thancarbide.

- Diamond is incompressible, readily conducts heat andhas low coefficient of friction.

- Diamond are suitable for cutting very hard materialsuch as glass, non-ferrous materials, plastics etc.,

- For poly crystalline diamond (PCD) the tool life is 30times of carbide.

The following picture shows the comparison of thevarious materials in terms of their properties. (Fig 2)


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The second letter specifies the relief angles (Fig.4).

Tool insertsCarbides and other harder tool materials are very costly.Moreover, they cannot be machined. So, only tool tips aremade for such materials using powder metallurgytechnique. In this method, the tool material is taken in apowder form. It is mixed with a suitable binder (in powderform) and compressed in the shape of an insert.

Inserts are available in various shapes such as triangle,square, rectangle, pentagon, hexagon, octagon, diamondshaped and circle. They cannot be resharpened, but theyhave a number of cutting edges. (Fig 3)

Inserts are produced in various sizes and thicknesses.Smallest possible size is chosen to produce the desireddepth of cut. Thickness of an insert affects its strength.Hence, for a large depth of cut and feed, a thicker insert ischosen.

ISO standard is commonly followed for specifying inserts.An example is CNMG120408. The first letter, C in thiscase , indicates the shape of the insert. The commontypes are:

Symbol ShapeS Square

T triangular

H hexagonal

O octagonal

P pentagonal

L rectangular

R round

A, B, K parallelogram (nose angles85°, 82° and 55° respectively)

C, D, E, F, M, V Diamond shaped or rhombic(nose angles 80°, 55°, 75°, 50°,86°, 35 ° respectively)

W Trigon (nose angle 80°)

Symbol Relief Angle N 0°

A 3°

B 5°

C 7°

P 11°

D 15°

E 20°

F 25°

G 30°

The third letter specifies tolerances on various dimensions(Fig.4) (e.g., thickness) of the insert. The different toleranceclasses are A, F, C, H, E, G (absolute values) and J, K,L,M,N,U (tolerance values depend on the diameter of theinscribed circle of the insert)

Significance of the fourth letterThe fourth letter describes the overall geometrical featuresof the insert (refer table). For example, an insert may ormay not have a hole at the centre. The hole may becylindrical or cylindrical with single or doublecountersink.The insert may or may not have a chip-breaker.The chip-breaker may be single-sided or double-sided.-


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Symbol Hole Shape of Hole Chip-Breaker

N without

R without no hole single-sided

F double -sided

A cylindrical without

M single-sided

G double -sided

W cylindrical withoutwith 40o-60o

T countersiink single sided

Q with cylindrical withoutwith 40°-60°double double-sidedcountersink

B cylindrical withoutwith 70°-90°

H countersink single-sided

C cylindrical without

J with 70°-90° double-sideddoublecountersink

X special shape

.

Cutting edge condition (Fig.5a)

F for sharp,

T for chamfered,

E for honed and

S for chamfered and honed.

This information , however, is non-obligatory.

Cutting direction (Fig.5b)

L for machining with left - rotated (CCW) spindle (M04),

R for machining with right - rotated (CW) spindle (M03)and N for both left-and right - rotated.

The appropriate character designations are appended tothe right, after the radius specification.

Tool holders for latheThere is an ISO designation system for tool holders also,to suit various types of inserts. The first five charactersdescribe insert clamping method, compatible insert shape,insert holding style of the tool holder (side cutting edgeangle/end cutting edge angle and straight shank/offsetshank), clearance angle and cutting direction, respectively.Next four digits specify shank height and shank width inmm (two digits for each). Tool length is specified next, bya character code. The next and the last two digits specify


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TABLE 1ISO designation for lathe tool holders (Contd.)

1st character 2nd character 3rd character 4th character 5th character

M=top clamp A-85° A = 0° side N = 0° R = right -handand lock pin via parallelogram cutting striaghtthe bore shank

P = lock pin via the B = 82° B = 15° side cutting A = 3° L = left-handbore only parallelogram cutting straight shank

C=top clamp only C=80° diamond C = 0° end cutting B = 5° N - neutralstraight shank

S=centre D=55° diamond D = 45° side cutting, C = 7°screw lock only 45°end cutting,

straight shank X = other methods E = 75° E = 30° side P = 11°

diamond cutting, straight shankH = hexagon F = 0° end D = 15°

cutting, offset shankK = 55° G = 0° side E = 20°

parallelogram cutting, offset shankL = rectangle H = -17.5° side F = 25°

cutting, offset shank M = 86° diamond J = -3° side G = 30°

cutting,offset shankO = octagon K=15° end cutting,

offset shankP = pentagon L=5°sidecutting,5°

cutting, offset shankR = round M=40°side cutting

50° end cutting,straight shank

S = square N=27°sidecutting,straight shank

T = triangle P=-27.5°side cutting,offset shank

V = 35° R=15°side diamondcutting, offset shank

W = 80° S = 45° sidetrigon cutting, offset shank

T=30°side cutting,offset shank

U=3°endcutting,offsetshank

V=17.5°side cutting,straight shank

W = 30° end cutting,offset, shank

Y= 5° end cuttingofffsest, shank

Insert holding Insert shape Tool holder Insert relief Handmethod style (clearance)


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cutting edge length in mm. Manufacturers, specificcodes may be appended in the end. (Figs 6 & 7)

Insert clamping method (S) Retained via centralscrew

Compatible insert shape (C) 80° diamond

Style of the tool holder body (L) -5° side cuttingedge angle, 5° endcutting edge angleand offset shank

Clearance angle (C) 7°

Cutting direction (R) Right-hand

Shank height (25) 25 mm

Shank width (25) 25 mm

Tool length (M) 150 mm

Cutting edge length (12) 12 mm

Manufacture specific information None

Boring bars for lathe (Figs 8&9)There is a similar ISO designation system for the internaltool hodlders also (which are called boring bars). SeeFig.8 and Fig.9 for details. Refer to Table 1 also for shapesnot shown in these figures. In fact, tool length, clampingmethod, compatible insert shape, body style, clearance

angle and cutting edge length have the samerepresentation for tool holders as well as boring bars.For a boring bar, the cutting. If cutting is possible withclockwise rotation (MO3) of the spindle. The example,considered in the figure is S32u SSKCR12 type boringbar. Manufacturer-specific information may be appendedin the end, after a gap. Separating dash (1) is also usedin place of gaps. Referring to Table 1 and Figs 8&9, thedescription of S32U SKKCR12 is as follows:

Shank type (S) Steel shank

Shank diameter (32) f 32 mm

Tool length (U) 350 mm

Insert clamping method Retained via central screw

Compatible insert shape (S) Square

Style of the boring bar -15o end cutting edgebody (R) angle. offset shank.

Clearance angle (C) 7o

Cutting direction (R) Right-rotated (CW spindle)


Manufacturer - specific

information None


74

Production & Manufacturing Related theory for Exercise 4.3.125Turner - Tool setting and Data Input

Tool Geometry, Insert Type, Nomenclature of InsertsObjectives: At the end of this lesson you shall be able to• discuss the features of tool geometry• identify various tool angles• state what is a negative rake angle and its features• learn various types of inserts• understand nomendature of insert and ISO designation.

Tool GeometryThe tool geometry of cutting tool is a complicated subject.It is very difficult to determine the scope of the tool face.The straight edged tool moving with a constant velocity unthe direction perpendicular to the work is known as toolgeometry. The cutting tool geometry deals mainly withfactors like approach angle,cutting angle, training angle,clearance angles,rake angle . The following sketchesindicates various angles (tool geometry) relating to fFcinftool,rough turning tool,finish turning tool,parting tool,boringtool. The advantages of negative rake is also explained.

The carbide turning tools generally used for various turningoperations are listed below.

- Straight round nose

- Right hand and left hand roughing tool

- Facing tool

- Right and left hand knife edge tool

- Heavy duty roughing tool

- Cranked round nose tool

- Recessing tool

- Parting tool

- Screw cutting tool.

The various cutting angles provided in these tools are asfollows. (Fig 1)

1 Approach angle

2 Cutting angle

3 Trailing angle

4a Front clearance-primary

4b Front clearance-secondary

5a Side clearance-primary

5b Side clearance-secondary

6 Top rake-negative

7 Side rake

These angles for various tools are shown in the figures.(IS 2163-1973 and 2163-1976)

Generally the manufacturers of carbide tools maintainthese angles while manufacturing these tools. Hence it isonly needed to maintain these angles while re-sharpen-ing.

The illustrations are as indicated below.

1 Facing tool (Fig 2)

2 Rough turning tool (Fig 3)


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3 Finish turning tool (Fig 4)

4 Parting off tool (Fig 5)

5 Boring tool (Fig 6)

Negative rake is used in cemented carbide tip tool for roughturning.

The true rake angle is the resultant of front rake and siderake angles. The top rake may be positive, zero or negativeas shown in Figure 7.

Most of the cutting tools have positive rake angles. Turningtools for brass have zero rake as the metal chips are shortand do not exert excessive cutting pressure on the toolface while cutting. Zero rake increases the strength of thetool and prevents the cutting edge from digging into thework.

Negative rake angle

It is used to achieve the following advantages.

- The cutting edge becomes stronger.

- It can withstand excessive compressive loads.

- The tool can be operated at higher cutting speeds.

- It decreases tool wear and increases the tool life.

- Heavier depth of cut can be given.

The limiting conditions for the applications of negative raketurning tools are:

– the machine must have a wider range of high spindlespeeds

– the machine and the tool-holding devices must be quiterigid and must be free from vibrations since thecemented carbide tip may chip off under vibrations

– provision must be there for quickly dissipating the higherdegree of heat generated during machining

– the power of the motor of the machine must be atleast10 to 15% higher than that provided on machines onwhich positive rake tools are used under similar workingconditions.

Tool inserts

Carbides and other harder tool materials are very costly.Moreover, they cannot be machined. So, only tool tips aremade for such materials using powder metallurgytechnique. In this method, the tool material is taken in apowder form. It is mixed with a suitable binder (in powderform) and compressed in the shape of an insert.

Inserts are available in various shapes such as triangle,square, rectangle, pentagon, hexagon, octagon, diamondshaped and circle. They cannot be resharpened, but theyhave a number of cutting edges. (Fig 8)

Inserts are produced in various sizes and thicknesses.Smallest possible size is chosen to produce the desireddepth of cut. Thickness of an insert affects its strength.Hence, for a large depth of cut and feed, a thicker insert ischosen.


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ISO standard is commonly followed for specifying inserts.An example is CNMG120408. The first letter, C in thiscase , indicates the shape of the insert. The commontypes are:

Symbol ShapeS Square

T triangular

H hexagonal

O octagonal

P pentagonal

L rectangular

R round

A, B, K parallelogram (nose angles85°, 82° and 55° respectively)

C, D, E, F, M, V Diamond shaped or rhombic(nose angles 80°, 55°, 75°,50°, 86°, 35 ° respectively)

W Trigon (nose angle 80°)

Symbol Relief AngleN 0°

A 3°

B 5°

C 7°

P 11°

D 15°

E 20°

F 25°

G 30°

The third letter specifies tolerances on various dimensions(Fig.4) (e.g., thickness) of the insert. The different toleranceclasses are A, F, C, H, E, G (absolute values) and J, K, L,M, N, U (tolerance values depend on the diameter of theinscribed circle of the insert).

The second letter specifies the relief angles (Fig 9).


77

Production & Manufacturing Related Theory for Exercise 4.3.126Turner - Tool setting and Data Input

Describe tooling system for turningObjectives: At the end of this lesson you shall be able to• learn about the tooling system used in lathe understand the characteristics of tool material• learn about the fixing of tool - tips.

Tooling System

For ordinary lathe turning (SSSC) lathe the operator suchas sliding, surfacing, screw cutting and taper turningoperation, We use the standard element of the lathe itselfnamely compound rest.

The compound rest can hold only one tool at a fine, and wasreplaced square tool post in which for tools can be held oneach face.

Important Tooling System includes self chuck, fonjawchuck, collect chuck, faceplate chuck to hold the job.

In older days high speed steel, hardened was used as a tol,which was ground to required tool shape. But modern daysthe tool holder are made out of medium carbon steel shankwith the tool brazed or filled in the form of topped tool. theparts of a throw-away tip tool is shown in Fig 1

The tool-holder for holding throw-way tips are speciallydesigned. They are made to accommodate different shapesof inserts. Othe rfeatures like different angles and chipbreakers are incorporated in the tool-holders. They aremade up of alloy steel.

Parts of a throw-away tip tool-holder (Fig 1)

The parts of a throw-away tool-holder are as shown inFig 1 above. Different types of tool-holders are used forholding different shapes of throw-away tips.(Fig 2)

Tool-holders for internal machining (Fig 3 & 4)

The cartidges (one of the parts of an internal tool-holderof carbide is called the cartridge) are used for internalboring work. It as used along with the standard bar. The

cartridges are available in different sizes to hold differentsizes to hold different inserts of multi-cutting edges.


78

With light duty cartrudges minimum size of bore will be 32mm (1.26”), and with medium duty cartridges the sizes willbe 45 mm (1.77”).

The following are the points to be noted when using carbidethrow-away inserts for machining.

• Select proper tool post.

• Select the correct size and shape of tool-holder to fixthe tool bit.

• Ensure the tool is set at the centre of the axis.

• Do not overhang the tool-holder.

• Use appropriate spped and feed while using the throw-away tips.

• Use copious supply of coolant while machining withthrow-away tips.

Fig 5 indicates threading tool held on a square tool post,used for threading a component.


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Setting work and tool offsetObjective: At the end of this lesson you shall be able to• list the types of offsets used in CNC machine• trace the tool path from the given program.

Types of offsets

There are three types of offsets used in CNC machineoperation.

They are:

i Work offset (or) zero offset

ii Geometrical offset

iii Wear offset

work offset (or) zero offset.

Every manufacturer fix a reference point on the spindle ofthe machine according to the design of manufacturing.

The tool will take the command and move with referenceto this machine reference point.


Procedure for taking work offset


Set the tool in the required order set in the machine turret.


With the use of a paper check the proper contact of toolwith the face.

Now select the work co-ordinate system from G54 to G59.

Enter the z value in the selected work co-ordinate system



Now enter the diameter of the job in the tool contact pointin the x value in the selected work co-ordinate system.

This particular work co-ordinate system should bementioned in the part program.

Geometrical offset

The tools used in CNC machine are of different geometry.The length of the tools vary accordingly.

Even if the work offset is taken for a tool it will not suit theother tools

So for every tool offset is taken and entered in tool offsetvalue in work co-ordinate system.

Because of this every tool will take the work zero point asorigin

The procedure for geometrical offset is given below

Clamp the job in the chuck of the machine

Set the tool in the required order in the machine turret

Select the jog mode or MPG mode

Select the first tool and touch the face of the job

Check with a piece of paper whether the contact of toolwith the job is proper

Now take the geometrical offset page and enter under thetool number the command MZ 0 (zero)

This command will clear any previous values and willmeasure the current tools tool offset in Z axis

Now touch the tool to a know diameter on the component

Again in the tool-gemetry page enter the command MX(The value of the diamter) for example if the diameter is50mm then MX50


enter the MZ and MX commands for various tools in theunder respective tool number.

Wear offset

Because of long running the tool tip may wear out and thedimension of the job may increase or decrease from theoriginal programmed dimension

To recitify this defect wear offset is used

Procedure for entering wear offset

If the programmed size is X40.49 and the machine size is40.44 in this 0.04 mm is reduced due to tool wear.


In that tools wear offset number enter the value U0.04.

In the inner diameter defects instead of positive value putU-0.04 in the wear offset number.

Tool offset number and wear offset number are same.=


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Describe tooling system for CNC Turning centresObjective: At the end of this lesson you shall be able to• learn what are the elements of a tooling system in CNC• understand the locking fixture and roleution knob• learn the factors of selecting a tool holder.

The Tooling System for a CNC machine includes, universalquide change chuck, adopters for drilling, reaming andtapping adjustable adopter floating holders,

non-reversible quick change tapping chuck, hydraulicchuck.

The fixture to hold the tool is to be designed based on theturret head. A tool holder locking fixture is shown below atFig 1

Tools can be convenients and quickly clamped to toolhanders, for which collet type chucks are used. The Fig 2indicates CNC tool holder with ER collets.

The collets have a shoot range and comes in differentsizes. A set of collets is shown in the Fig 2

Tool holders for machining cetre provide a standard spindlenose taper (Fig 3) and size for insertion of tool holders. Thetool holder knob in the tool holder allows the locking. Thelocking drawbar to pull the tool firmly into the spindle andto released auomatically. The retention knob is eitherflange type, threaded type or tapered size.

Selection of tool holder

The three factors that determine the selection of toolholders for a job include flange type, spindle taper nunmberand cutting tool to be used. In selection of an adapter, thefollowing must be considered

• Gauge distance

• Diameter of cutting tool shawk

• Adapter outside daimeter


81

tool life is estimated using formula V(T)n = C Where

V = cutting speed , m/min.

T = Tool life in minutes

C = Cutting speed for tool life of 1 minute

n = Taylor exponent

Tool material Typical ‘n’ value

HS steel 0.08 - 0.2

Cast alloy 0.1 - 0.15

carbide 0.2 - 0.5

ceramic 0.5 - 0.7


Cutting tool material for CNC turningObjective: At the end of this lesson you shall be able to• identify the cutting tool material for CNC• learn the characteristics of cutting tool making.

Cutting tool for CNC

Though carbon steels, containing 0.9% C, 1% manganese,duly hardened for 62 HRC used in older days, High speedsteel is invariably used for ordinary lathe turning. HSS alsoused for tools like drill, reverse taps, dies etc;but had amaximum cutting speed of 60m/min However for CNCcoated carbide or sintered carbide were used which hadhigh thermal conductivity.

Presently Coated Carbide tools, using titanium nitride,titanium carbide and Aluminium oxide with a thicknessupto 15 micron is used for increased tool life. Cubic boronnitride (CBN) a hardest material is used for machining alloyand tool steel. These tool bits are coated with thick layerof poly crystaline boron nitride sintered onto a carbidesubstrate under pressure and this can have as high as 310metres/min of cutting speed.

Diamond tools are for more specific application, replacing(PCD), polycrystalline diamond. This tool can be used forvery high speed machining. Aluminium Alloys andnon-metallic material. This tool can go up to a high cuttingspeed of 2000m/min.

The tool life of a CNC tool is more important factor and the


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Sl.No Parameter Brain How is this decided

1 Insert clamping method Selection based on cutting forces top clampingis the most steady,screw clamping is the best.

2 Insert type Decided by the contour that you want to turn

3 Holder style

4 Insert clearance cycle Positive/negative based on applicaton

5 Hand of holder Decided based whether you want to cut towardsthe chuck or away from chuck and turret position

6 Shank height Decided by machine

7 Shank width

8 Holder length Decision based on part Geometry

9 Insert cutting edge length Decision based on depth of cut you want to use


ISO Nomenclature for Turning tool holder, boring tool holder, indexableinsertObjective: At the end of this lesson you shall be able to• understand ISO nomenclature for turning tool holder• learn about boring tool holder• learn about indexable inserts.

Turning holders names follows an ISO nomenclaturestandard If you are working on a CNC shop floor in the lathe,knowing ISO nomenclature is a must. The name lookscomplicated but actually it is very easy to interpret

6 Shank length

7 shank width

8 Holder length

9 Insert cutting edge length.

When selecting a holder there are in fact only 4 parametersthat you really need to understand to select the right holderfor your application. There are numbers marked as Nos.2,3,4 and 9 respectively. The others are automaticallydecided.

In the table below you have to use only your brain inselecting the parameter, Where there is a brain symbol inthe rows.

1 Insert clamping method

2 Insert shape

3 Holder style

4 Insert clearance angle

5 Hand of holder

P C L N L 25 25 M - 12

1 2 3 4 5 6 7 8 9


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Tool holders for lathe

There is an ISO designation system for tool holders also,to suit various types of inserts. The first five charactersdescribe insert clamping method, compatible insert shape,insert holding style of the tool holder (side cutting edgeangle/end cutting edge angle and straight shank/offsetshank), clearance angle and cutting direction, respectively.Next four digits specify shank height and shank width inmm (two digits for each). Tool length is specified next, bya character code. The next and the last two digits specifycutting edge length in mm. Manufacturers, specific codesmay be appended in the end. (Figs 6 & 7)

angle and cutting edge length have the samerepresentation for tool holders as well as boring bars.For a boring bar, the cutting. If cutting is possible withclockwise rotation (MO3) of the spindle. The example,considered in the figure is S32u SSKCR12 type boringbar. Manufacturer-specific information may be appendedin the end, after a gap. Separating dash (1) is also used inplace of gaps. Referring to Table 1 and Figs 8&9, thedescription of S32U SKKCR12 is as follows:

Shank type (S) Steel shank

Shank diameter (32) f 32 mm

Tool length (U) 350 mm

Insert clamping method Retained via central screw

Compatible insert shape (S) Square

Style of the boring bar -15o end cutting edgebody (R) angle. offset shank.

Clearance angle (C) 7o

Cutting direction (R) Right-rotated (CW spindle)


Manufacturer-specificinformation None

Indexable Insert

Inserts are very for machining various application. Thiscan be used either in lathe or in a milling machine. Theselective indexable insert commonly used are shownbelow:

1 Boring insertThis is mainly used for internal machining including boringoperation.


Insert clamping method (S) Retained via centralscrew

Compatible insert shape (C) 80° diamond

Style of the tool holder body (L) -5° side cuttingedge angle, 5° endcutting edge angleand offset shank

Clearance angle (C) 7°

Cutting direction (R) Right-hand





Manufacturer specific information None

Boring bars for lathe (Figs 1&2)

There is a similar ISO designation system for the internaltool hodlders also (which are called boring bars). See Fig.1and Fig.2 for details. Refer to Table 1 also for shapes notshown in these figures. In fact, tool length, clampingmethod, compatible insert shape, body style, clearance


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2 Cut-off insertThese type of inserts are used to parting or cutting purpose,generally referred as cut-off inserts.

3 Grooving insertThis insert is mainly used when grooving is needed in acomponent.

4 Threading insertThis type is mainly used for fine threading both in latheand in a milling machine.


85

Production & Manufacturing Related theory for Exercise 4.3.131Turner - Tool setting and Data Input

Tool holders and inserts for radial grooving, face grooving, threading anddrillingObjectives: At the end of this lesson you shall be able to• understand the ISO designation of tool holders for CNC machine• learn about various shapes of tool inserts• learn about the type of clamping for tool holder• understand the clearance angle and included angle of inserts.Tool holders

For CNC machine tool, we need special tool holders, andthe conventional holders used in ordinary lathe and othermachine tool may not fit. The tool holders for CNCmachines are specified under ISO designation holders. Itcan be clamp type, screw type, locking pin via the boreetc;

The shape of the tool holder can be either straight shanktype or off-set shank type. Another classification of thetool holder is Right hand (R), left hand (L) and neutral type(N) The tool holders are so designed to suit the variousshapes of available inserts.

The nomenclature and ISO designation of lathe tool holderis shown in Table1.

ISO designation for lathe tool holders (Contd.)1st character 2nd character 3rd character 4th character 5th character

Insert holding Insert shape Tool holder Insert relief Handmethod style (clearance)

M=top clamp A-85° A = 0° side N = 0° R = right -handand lock pin via parallelogram cutting striaght

the bore shank

P = lock pin via the B = 82° B = 15° side cutting A = 3° L = left-handbore only parallelogram cutting straight

shank

C=top clamp only C=80° diamond C = 0° end cutting B = 5° N - neutralstraight shank

S=centre D=55° diamond D = 45° side cutting, C = 7°screw lock only 45° end cutting,

straight shank

X = other methods E = 75° E = 30° side P = 11°diamond cutting, straight

shank

H = hexagon F = 0° end D = 15°cutting, offset shank

K = 55° G = 0° side E = 20°parallelogram cutting, offset shank

L = rectangle H = -17.5° side F = 25°cutting, offset shank

M = 86° diamond J = -3° side G = 30°cutting,offset shank

O = octagon K = 15° endcutting, offset shank

P = pentagon L = 5° side cutting, 5°endcutting, offset shank


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The included angle of the tool inserts generally varies 55°to 85°. The inserts can be rectangular pentagonal,hexagonal, triangular, circular, diamond shape etc.

There is a special tool holder used in CNC machines forboring bars, Which is generally steel shank type, with alength of 350 mm, retained through central screw, withoffset shank. The clearance angle for boring bar tool isaround 7°.The details of boring bar is shown in





Manufacturer specific information None


87

Production & Manufacturing Related Theory for Exercise 4.4.132Turner - Programming and Simulation

Preparation of Part programmingObjectives: At the end of this lesson you shall be able to• define the part programming• state the purpose of preparatory (G codes) & Miscellanious function (M codes)• develop the part programming.

Part programmingDefinition wise “the part program is a sequence of instructionswhich describe the work which has to be done on a part, inthe form required by a computer under the control of an NCcomputer program”.

Actually, part programming for NC production consists ofthe collection of all data required to produce the part, thecalculation of the tool path etc. in a standard format. Themethods of part programming can be of two types dependingupon the two techniques employed to produce a punchedtape

- Manual part programming

- Computer aided part programming.

Manual part programmingIn manual part programming, the data required for machining,is written in a standard format known as programmanuscripts. Each horizontal line in a manuscript representsa ‘block’ of information.

Computer aided part programmingIf the component requires a great deal of machining suchas in case of milling machines or contouring applications,calculation of cutter paths requires more calculations andsometimes if a machining centre is used then selectingdifferent tool for drilling, tapping, boring and milling makesall this part programming more tedious and time consuming.More mistakes are also likely to occur Thus, we usegeneral purpose computer as an add, to reduce labourinvolved in part programming. Also one of the high level

language such as APT (Automatically Programmed Tools),ADAPT, SPLIT, 2CL, romance, auto stop is used for writinga computer programme.

Procedure for developing manual part program

The part programming requires an NC programmer toconsider some fundamental elements before the actualprogramming steps of a part takes place. The elements tobe considered are as follows.

Types of dimensioning system- Axis designation

- NCwords

- Standard G and M Codes

- Tape programming format

- Machine tool zero point setting

Type of dimensioningAfter deciding what NC machines is best suitable andavailable for the application, we determine what type ofdimensioning system “he machine uses i.e., whether anabsolute or incremental dimensional system. (Explainedin previous chapter).

Axis designationAnother consideration is designation the axis of the machinetool. In most cases the programmer already known thisfundamental element when he select the NC machine toolfor his job. The most important factor in axis designation isthe location and position of the spindle.

The part programmer also determines how many axes areavailable on machine tool i.e. X, Y, Z, a, bar c and so on.Also whether machine tool has a continuous path and pointto point control system.

NC wordsIn order to understand the language of NC informationprocessing the following definitions should be understood

A ‘bit’ is the basic unit of information represented by eitherthe absence or the presence of a hole punched on the tape.Bit is an abbreviation of “Binary digit”, which can be ‘0’ or’1'.

A code or character is the series of combination of ‘1’ s and‘0’ s. It represents a number of an alphabet or any symbol.

An NC word is a unit of information, such as a dimension(e.g. X01 000 orY1 0025) or feed rate (e.g. F1000 and so on.

A block is a collection of complete group of NC wordsrepresenting a single NC instruction (e.g. N1G01 X100Z100 F100). An end of block (EOB) symbol is used toseparate the blocks.

Block number/sequence number (N - words)Each block of the program has a sequence number whichis used to identify the sequence of a block of data in it whichis in ascending numerical order. This enables the operatorto know which sequence of block is being preformedpractically by the tool. It consists of a character ‘N’ followedby a three digit number raising from ‘0’ to ‘999’.

Preparatory functions (G - words)The preparatory function is used to initiate the controlcommands, typically involving a cutter motion i.e. it preparesthe MCU to be ready to perform a specific operation andinterpret, the data which follows the way of this function. Itis represented by the character ‘G’ followed by a two digit


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number i.e. ’00 to 99'. These codes are explained and listedseparately.

Dimension words (X,Y and Z words)These dimension words are also known as ‘co - ordinates’.Which give the position of the tool motion. These words canbe of two types.

Linear dimension words- X,Y,Z for primary or main motion.

- U, V, W for secondary motion parallel to X, Y, Z axesrespectively.

- p, q, r for another third type motion parallel to X, Y, Zaxes respectively.

Angular dimension words- a, b, c for angular motion around X,Y, Z axes respectively.

- I,J,K in case of thread cutting is for position of arccentre, thread lead parallel to X, Y, Z axes.

These words are represented by an alphabet representingthe axes followed by five or six digits depending upon theinput resolution given.

Feed rate word (F - word)It is used to program the proper feed rate, to be given in mm/min or mm/rev as determined by the prior ‘G’ code selectionG94 and G95 respectively.

It is represented by ‘F’ followed by three digit number e.g.F100 represents a feed rate of 100 mm/ min.

Spindle speed/cutting speed word (S) - word)It specifies the cutting speed of the process or the rpm ofspindle. It is also represented by ‘S’ followed by the threedigit number. If the speed is given in meter per min. Thenthe speed is converted in rpm rounded to two digit accuracy,e.g. S - 800 represents the 800 rpm of spindle.

Tool selection word (T - word)It consists of ‘T’ followed by max five digits in the codednumber Different numbers are used for each cutting tools.When the T number is read from the tape, the appropriatetool is automatically selected by ATC (Automatic ToolChanger). Hence this word is used only for machines withATC or programmable tool turret. e.g. T01, T02, T03……..represents the tool selection word.

Miscellaneous words (M - words)It consists of character M followed by two digit numberrepresenting an auxiliary function such as turning ON/OFFspindle, coolant ON/OFF.

End of Block (EOB)It identifies the end of instruction block.

G and M codes (G, codes)This is the preparatory function word, consists of theaddress character G followed by a two digit code number,known as G - code. This comes after the sequence numberword and a tab code. There are two types of G - codes

model and non - model. Model codes remain active untilcancelled by a contradictory and code of same class. e.g.G70 is a model code which defines that the dimensionalunits are metric. It will remain active until cancelled by G- 71, which tells that the dimensional units are in inchesnow. Non - model G codes are active only in the block inwhich they are programmed. G04 is non- model code.

CNC program procedure (Figs 1 & 2)

The following are the steps involved in the development ofa part program and its proving.

Process planning: The programmer carryout a carefulstudy of part drawing to prepare the process plan. Itincludes the following

- Machine tools used

- Fixtures required

- Sequence of operations

- Cutting tools required

- Process parameters

Axes - selection: The reference axes should be chosen sothat the coordinates for various features can be determinedeasily.


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Tool selection: Various tools are feasible for a givenoperation, but some of them would be more economicalthan others So it is essential to chose the right tool for thejob.

Cutting process parameters planning: For a given tooland the operation, the appropriate process parameterssuch as speed, feed and depth of cut are to be selected.These may be taken from the handbooks supplied by thecutting tool manufacturer or based on the shop experience.

Job and tool setup planning: The initial position of joband tool are defined carefully.

Tool path planning: A careful planning of the tool pathensures that the required manufacturing specifications areachieved at the lowest cost.

Part program writing: This involves the actual writing ofthe part programs undertaking the format and syntaxrestrictions into account

Part program providing: Once the part program iscreated, ‘it should be verified before it can be loaded on themachine controller for the manufacture of the component.A trial run can be carried out with or without the tool or workpiece to enable visualization of movements taking place,and any collision possible between the tool, the work pieceand the clamping device.

Definition of character, word and blockBit: A binary digit is called a bit. In includes 0 or 1. Inpunched tape, the values 0 or 1 are represented by theabsence or presence of a hole in a certain row and columnposition.

Character: A character is formed from a row of bits. Acharacter is a combination of bits representing a numericaldigit (0 to 9), an alphabetical letter (A - Z and a - z ), or asymbol.

Word: Award is formed from a sequence of characters. Aword specifies a detail about the operation, such as X -position, Y - position, feed rate, or spindle speed.

Block: A block is formed from a collection of words. A blockis one complete NC instruction. It specifies a destinationfor the move, the speed and feed of the cutting operation,and other commands that determine what the machine willdo.

Block formatThe order in which words appear in a block of instruction iscalled the format. The following are the block formats usedin NC programming.

Fixed sequential format: This formal was used on manyof the first commercially available NC machines. Eachinstruction block contain five words in only numerical dataand in a very fixed order.

Example

00100703003

00200706003

Fixed sequential format with tab ignored: This is thesame as the fixed sequential format except that TAB codesare used to separate the words for easier reading.

Example

001 00 70 30 03

002 00 70 60 03

Tab sequential format: This is same as fixed sequentialformat with tag ignored except that words with the samevalue as in the preceding block can be omitted in thesequence.

Example

001 00 70 30 03

002 00 60

Word address format: This format uses a letter prefix toidentify the type of word. Repeated words can be omitted.The words run together, which makes the code difficult toread.

Example

N001G00X70Y30M03

N002Y60

Word address format with tab separation and variableword order: This is the same format as word addressformat except that words are separated by TAB, and thewords in the block can be listed in any order. It is the blockformat used on all modern CNC controllers.

Example

N001 G00 X70 Y30 M03

N002 Y60

Structure or format of a part programThe complete part program for a given component consistsof a beginning code of %. A part program consists of largenumber of blocks each representing an operation to becarried out in the machining of the part. The words in eachblock are usually given in the following order.

- Sequence number (N - word)

- Preparatory word (G - word)

- Coordinates (X -, Y-,Z- words for linear axes; A-, B-,C-words for rotational axes)

- Feed rate (F -word)

- Spindle speed (S - word)

- Tool selection (T·· word)

- Miscellaneous command (M - word)

- End - of - block (EOB symbol)

The structure of part program used in fanuc controller isgiven below. .

%; (program start)

03642 (program number)

N010Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.4.132Copyright @ NIMI Not to be Republished

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Blocks ................

N100 M02; (program end)

M30 (program rewind)

Program numberEach of the program that is stored in the controller memoryrequires an identification. It is used while running andediting of the programs directly from the control console.This identification is specified in terms of a program numberwith 0 word address. The number can be a maximum off ourdigits.

Sequence number (N - word)Each block in a part program always starts with a blocknumber, which is used as identification of the block. It isprogrammed with a N word address.

Coordinate functionThe coordinate values are specified using the word addresssuch as X,Y, Z, U, V, W, I, J, K, etc. All these wordaddresses are normally signed along with decimal pointdepending upon the resolution available in the machinetool.

CommentsParentheses are used to add comments in the program toclarify the individual functions that are used in the program.When the controller encounters the opening parenthesis,it ignores all the information till it reaches the closingparenthesis.

ExampleN010 GOO Z50 M05 (Spindle stops and rapidly moves up)Table - common word addresses used in word addressformat.

Address Function

N Sequence number to identify a block.

G Preparatory word that prepares thecontroller for instruction given in the block.

X,Y,Z Coordinate date for three linear axes.

U,V,W Coordinate data for incremental movesin turning in the X, Y and Z directionsrespectively

A,B,C Coordinate data for three rotational axesX, Y and Z respectively.

R Radius of are, used in circularinterpolation.

I,J,K Coordinate values of arc centre,corresponding to X,Y and Z-axesrespectively.

F Feed rate per minute or revolution ineither inches or millimeters.

S Spindle rotation speed.

T Tool selection, used for machine toolswith automatic tool changer or turrets.

D Tool diameter word used for offsettingthe tool.

P It is used to store cutter radius data inoffset register. It defines first contourblock number in canned cycles.

Q It defines last contour block number incanned cycles.

M Miscellaneous function.

Types of offsetsObjective: At the end of this lesson you shall be able to• list the types of offsets used in CNC machine.

Types of offsetsThere are three type of offsets used in CNC machineoperation. They are:

(i) Work offset (or) zero offset

(ii) Geometrical offset

(iii) Wear offset

Work offset (or) zero offsetEvery manufacturer fix a reference point on the spindle ofthe machine according to the design of manufacturing.

The tool will take the command and move with reference tothis machine reference point.


Procedure for taking work offsetClamp the job in the chuck of the machine

Set the tool In the required order set in the machine turret


With the use of 2 paper check the proper contact of tool withthe face.

Now select the work co - ordinate system from G54 to G59.

Enter the Z value in the selected work co - ordinate system.



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Now enter the diameter of the job in the tool contact pointin the X value in the selected work co - ordinate system

This particular work co - ordinate system should bementioned in the part program.

Geometrical offsetThe tools used in a CNC machine are of differentgeometry. The length of the tools vary accordingly.

Even if the work offset is taken for a tool it will not suit theother tools.

So for every tool offset is taken and entered in tool offsetvalue in work co - ordinate system.

Because of this every tool will take the work zero point asorigin.

The procedure for geometrical offset is given below.


Set the tools in the required order in the machine turret.

Select the jog mode or MPG mode.

Select the first tool and touch the face of the job.

Check with a piece of paper whether the contact of toolwith the job is proper.

Now take the geometrical offset page and enter under thetool number the command Z 0 (zero).

This command will clear any previous values and will mea-sure the current tools tool offset in Z axis.

Now touch the tool to a know diameter on the component.

Again in the tool - geometry page enter the command X(The value of the diameter) for example if the diameter is50 mm then X50.


Enter the Z and X commands for various tools in the underrespective tool number.

Wear offsetBecause of long running the tool tip may wear out and thedimension of the job may increase or decrease from theoriginal programmed dimension.

To rectify this defect wear offset is used.

Procedure for entering wear offsetIf the programmed size is X40.48 and the machine size is40.44 in this 0.04 mm is reduced due to tool wear.


In that tools wear offset number enter the value U0.04

In the inner diameter defects instead of positive value putU - 0.04 in the wear offset number.

The tool offset number and wear offset number are same.

Reference points of CNC machinesObjective: At the end of this lesson you shall be able to• explain the features of reference point applied in CNC machine tools.

Zero and reference points on CNC machine toolsReference zero points are the base or starting points thatare chosen as the reference for calculating the coordi-nates of the other points. Also, reference zero points arecalled the zero points. CNC controls use the followingzero points to facilitate the programming of tool paths.

M Machining reference zero point

W Work part zero point

R Relative point

Machine zero point

M

The machine zero point is the origin of the machine coor-dinate system. It is set by the machine tool manufacturerand cannot be changed.

The machine zero is labelled with an M and representedby the symbol shown above.

Normally the machine zero is not directly used as thereference point for writing part programs. It may be usedin one of the following three applications.

- Initial set - up of the machine.

- As the reference point for other reference points suchas reference return points, work zeros, and programzeros.

- As the tool change position.

Work part zero point

W

A work part zero point is the origin of the work piece'scoordinate system. It is used to determine the work's co-ordinate system in relation to the machine zero point. Thework zero points are often referred to as set - up pointsbecause they are the location for setting up the workpieceon the machine table. some CNC controls allow the useof multiple work zero points in one machine set up oroperation. The work zero point is labelled by W and repre-sented by the symbol above.

The work zero point can be chosen by the programmer atany convenient location within the working envelope of themachine. It is recommended that you place the workpiecezero point in a way that it can be easily located and mea-sured on the workpiece.


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Reference return point

RIn Fig 1 reference return points are the locations to whichthe machine table or the spindle is returned. They areidentified by the letter R and are represented by the abovesymbol.

The location of the first reference return point is preciselypredetermined in each moving axis in relation to the ma-chine zero point. Because of this, it can be used for cali-brating and regulating the measuring system of the slidetable and spindle.

Specifically, the reference point is used in four situations

- When the control is powered up, all axes always mustbe positioned at the reference return point to calibratethe measuring system.

- The machine must be re-positioned to the referencereturn point for re-establishing the proper coordinatevalue in situations such as losing the current positiondata due to electrical failure or improper operation.

- All axes must be retracted to the reference pointbefore the tool change can take place.

- At the end of the program, all axes must be retractedto the reference return point to reset the control sys-tem for re - running the part program or running a newprogram.


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CNC Simulation ProcessObjectives: At the end of this lesson you shall be able to• understand the function of a CNC simulation• learn the benefits of simulator.

Simulation process in a CNC machine system is a programverification activity. Most of the CNC machines come withsuitable simulation software installed.

This software simulates the tool movement on a graphicscreen. The software first checks the program syntax.

When the program is found correct, the simulation starts.

In simulation, the dimensions of the given component isshown on the screen and the chosen tool start moving withrespect to the program command.

The resulting shape that will be obtained on completion ofsimulation represents the final size & shape of component.

Simulation (verification of program) can be done block byblock.

With this software, it is easily possible to analyse the toolpath, during the turning process.

The flow chart for simulation process is shown below:-

Purpose of Simulator

The purpose of CNC Simulator Pro is to provide the CNCcommunity with a versatile Full 3D simulator with CAD/CAM capability. In the simulator you may find different typeof machines like milling machines, router, lathes, cutter,3D printer etc,.

It automatically adapt your part programmes to differentCNC machines. The simulator solution provides the breakdown of the details of tools used during the job, thepositioning of fixtures & part for multi-setup operation;through providing a shop floor documentation.

The traditional APT-based simulation system, only simulatethe planned tool-path where as modern advance controlEnulator, delivers a more meaning simulation, recreatinghow the machine will react the G-code generated by yourpost-processor. It provides powerful validation methodallowing users to determine the association betweenG-code & specific operations inside the NC program.

Ex: G04 X2.0 [Dwell at 2 second]

X30.25 Y5.00

G03 X35.25 Y10.00

G01 X35.25 Y50.10 - ToolpathG03 X5.00 Y50.10

G03 X35.25 Y10.00

Most common used of simulator:-• Technical Training for programmers & operators in

Training center.

• Editing/simulation in design dept.

• Machining time estimate.

• In preparing equation processing.


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Process and tool selection (CNC)Objectives: At the end of this lesson you shall be able to• understand selection of tool for CNC• understand the factors contributing for tool selection• learn about MachiningCloud APP.

The main factors that should be considered while writing aCNC programme, is what type of tooling should be selectedfor a specific job. Making the right selection depends onhow well one understand the vital factors that may haveimpact on the job.

The selection of tool is based on:

• The machine being used for the manufacture.

• The material used for the job.

• The quantity of machining parts.

• The requirement of the customer.

• The specification of the tool to be used.

All the above five factors are related and interlinked. All theinformation are avaliable in Router of Tool Directory.

The tool used for CNC mainly depends on the type ofmaterial used, type of workdone, quality of finish neededthe no.of components to be run etc,.

CNC machine may have different tool configuration. Oneshould know which tool configuration is suitable for hardmaterial or a typical raw material. The Direction of cut, isanother factor which affects the tool life, and quality of thecut based on customer specification, the cutting speed,spindle speed & feed are important in the manufacturingprocess.

The tool selection has to be done following the steps shownbelow:

step 1: What type of machining is needed?

Collect the machine drawing of the finished partand collet important information such assize,shape, stock material,speed & feed for variousoperation, namely turning, facing, boring etc.

step 2: What is the work piece material?

Ascertain the workpiece material & the parameterslike chip forming, material hardness, alloyelements.These information have significantinfluence on the spindle speed & feed rates.

step 3: What are the Capabilties of your machine?

This includes machine HP, stability, horizontal orvertical type, spindles type & size, no.of axes,

workpiece clamping. Similarly tool holding detailssuch as Holding strength, axis/radial runout, tooloverhang etc needs to be considered.

step 4: What Machining Operation needed?

The operation can be face turning, OD turning, IDturning (Boring), grooving/profiling, threading ofthe components. Geometry & tolerancespermissible such as dimensional accuracy,surface finish, part distortion, surface integerityetc.

step 5: In what order should operations to be performed?

This includes minimising tool changes, traveldistance between operations, achiving shortestcycle time, maintaining consistency etc,.

spet 6: What type of tool are needed?

Parameters such as part material/tool mateial,depth of cut to be given, smallest concave radiusetc are to be taken into consideration to decidethe tool material, inserts, shape, tolerance etc,.

C & W inserts are used for rough machining

D & V inserts are used for finish machining.

Square or round shape inserts used for grooving.

3 point inserts are used for threading.

step 7: Are the required tools available?

MachiningCloud APP is an independent providerof CNC cutting tool product data. This providesmost up-to-date information, directly obtainedfrom the manufacturer. Information can be obtainedby download Machining Cloud APP.

step 8: What feeds & speeds should I use?

Material run better at specific SFM. Therecommended SFM for cutting aluminium is 150to 400. SFM is the combination of cut diameter &RPM. SFM is constant for a material. RPM modeG97 is useful for centre cutting operations (drilling)CSS mode (G96) is useful for good surface finish,better tool life. (SFM- Surface Feet / Minute,CSS- Common Surface Speed)


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Part programe for GroovingObjectives: At the end of this lesson you shall be able to• learn about G75 grooving cycle• understand that grooving linking with parting• follow the part programme of a grooving cycle.

IntroductionGrooving is an important & complicated operation inturning. G75 is the grooving cycle in ‘X’ in a CNC machine.

Grooving is an operation in which the tool is plunged intosurface of the work piece until the proper depth is reached.The grooving has to be done step by step and groovingcycles have been developed which allows for wide groovesto be cut with multiple passes by a specific shift value witha Q-word, and P word for depth of cut.

In grooving, the grooving tool is positioned to the start point,then call the canned cycle. The tool will take an initial cutto the finished diameter. Then it will retract to the startingX-position & move over in the Z axis by the amount specifiedwith the P-word. The tool will make several passes until itreaches the programmed Z cooridnate. If the X coordinateis programmed to zero grooving will become parting.

The syntax of G75 code is as follows:

G75 R___;G75 X___Z___P___Q___F___;

Where,

R = Reliving the tool

X = Groove diameter (mm)

Z = Groove length (mm)

P = Depth of cut in ‘x’ axis in microns (radial value)

Q = Shift value in Z axis microns

F = Feed

Grooving canned cycle [G75]

Grooving cycle (G75)%

O0013

N1;

G28 U0 W0;

G97 S600 M03;

T0303; [4mm groove width]

G00 X31.0 Z5.0 M08;

G01 Z-29.0 F0.1;

G75 R1.0;

G75 X20.0 Z-37.0 P500 Q4000 F0.08;

G00 X35.0;

Z5.0 M09;

G28 U0 W0;

M05;

M30;


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Part Programming for DrillingObjectives: At the end of this lesson you shall be able to• understand the part programme for drilling in CNC machine.

The part program is a sequance of instructions, whichdecribe the work, which has to be done on a component inthe form as required by a computer under the control of aNC computer program. All data is fed into numerical controlsystem using standard format.

In manual part programming: The programmer firstperpares the manuscripts which is typed on flexo writer,and carried out in the machine.

Important details for a part programming:-

• Machining sequence, tool start up point, cutting depth,tool paths.

• Cutting conditions, spindle speed, feed rate, coolantetc.

• Selection of cutting tool.

In drilling operation in CNC, a special program of G74 isused, Known “Peck” cycle and a part programme for drillingusing the above G74 cycle is given below:

G74 - Peck drilling cycle

FormatG74 R__;G74 Z___Q___F___;

R : Retract value

Z : Depth of the hole

Q : Depth of cut per pass in Microns

F : Feed rate

%

O0029

N1; (C.D)

G28 U0 W0;

T0200;

G97 S1500 M04;

G00 X0.0 Z5.0 T0202 M08;

G01 Z-6.0 F0.12;

G00 Z5.0 M09;

G28 U0 W0 M05;

M01;

N2;

G28 U0 W0;

T0700;

G97 S1500 M04;

G00 X0.0 Z5.0 T0707 M08;

G74 R4.0;

G74 Z-50.0 Q8000 F0.05;

G00 Z5.0 M09;

G28 U0 W0 M05;

M30;


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Production & Manufacturing Related Theory for Exercise 4.4.137Turner - Programming and simulation

Part Programme for BoringObjectives : At the end of this lesson you shall be able to• understand the programme for boring in CNC machine.

Boring operation in CNC is preceeded by a drilling operation.Hence the component should be initially programmed fordrilling either manual or G74 canned cycle. The importantfactors to be considered for part programming for boringoperation includes:

1 Boring sequence, tool start point, cutting depth, toolpath.

2 Cutting parameters, spindle speed, feed rate, coolant,cutting condition ect.

3 The boring is carried out in steps with 4 operation withinitial heavy cuts followed by lesser feed.

4 Selection of correct cutting tool, and cutting speedsuitable for the component should be done.

The part programming for the sbove component is indicated,with normal boring operation.(Boring)

N51; S1200 M03LF

N52 T6 D6 M06LF

N53 G0 X17 Z2 M08LF

N54 G0 X19LF

N55 G01 Z-62 F100LF

N56 G0 X17 Z2LF

N57 G0 X19.7LF

N58 G01 Z-62 F100LF

N59 G0 X17 Z2LF

N60 G0 X20.7LF

N61 G01 Z-30 F100LF

N62 G0 X17 Z2LF

N63 G0 X22.7LF

N64 G01 Z-30 F100LF

N65 G0 X17 Z2LF

N66 G0 X22.7LF

N67 G01 Z-30 F100LF

N68 G0 X17 Z2LF

N69 G0 X23.7LF

N70 G01 Z-30 F100LF

N71 G0 X17 Z2LF

N72 G0 X24LF

N73 G01 Z-30 F100LF

N74 G01 X20 F100LF

N75 G01 Z-62 F100LF

N76 G00 X17 Z2 M09LF

N77 G0 G90 G53 Z180 Z0LF

N78 D0LFCopyright @ NIMI Not to be Republished

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N79 M05LF

N80 M30LF

2nd Operation:%8

N1 G0 G90 G53 X180 Z0LF

N2 S1500 M03LF

N3 T1 D1 M06LF

N4 G0 X52 Z5 M08LF

N5 G0 Z0LF

N6 G01 X0 F100LF

N7 G00 X49 Z2LF

N8 G01 Z-25 F100LF

N9 G00 X48 Z2LF

N10 G01 Z-25 F100LF

N11 G00 X55 Z10 M09LF

N12 G0 G90 G53 X180 Z0LF

N13 D0LF

N14 M05LF

N15 M30LF


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Part Programme for ThreadingObjectives : At the end of this lesson you shall be able to• understand the programme for external and internal threading in CNC machine.

The threading operation in a CNC machine is precceded bya turning operation. The threading programme will thereforehave rough turning G73 and finish turning G72 operation.The external threading is represented in N29 and internalthreading in N48 blocks of the part programe for thecomponent shown below.

(Threading)

N26 S900 M04LF

N27 T5 D5 M06LF

N28 G0 X33 Z5 M08LF

N29 R20=1.5 R21=28 R22=0 R23=3R24=-0.97 R25=0.02 R26=3 R27=2R28=5 R29=30 R31=26.05 R32=-22

LF

N30 L97 P1LF

N31 G0 X50 Z10 M08LF

N32 G0 G90 G53 X180 Z0LF

N33 D0LF

N34 M05LF

N35 M01LF

N36 M30LF

(ID Threading)

N45 S1000 M04LF

N46 T8 D8 M06LF

N47 G0 X28 Z5 M08LF

N48 R20=1.5 R21=280.53 R22=0 R23=2R24=-0.973 R25=0.03 R26=3 R27=2R28=5 R29=30 R31=30 R32=-52

LF

N49 L97 P1LF

N50 G0 X25LF

N51 G0 Z10 M09LF

N52 G0 G90 X53 X180 Z0LF

N53 D0LF

N54 M05LF

N55 M30LF

G76 - Multiple therad cutting cycleFormat:

G76 P____Q____R____;G76 X____Z____P____Q____F____;


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Explanation for the cycle:P : NCA

N : Number of finishing passesC : Chamber amountA : Included angle

Q : Minimum depth of cut in microns (radial value)R : Finishing depth of cut in microns (radial value)X : External therading (minor dia) internal threading

(minor dia)Z : Thread lengthP : Height of thread (microns)Q : Firast depth of cut in microns (radial value)F : Feed (pitch of the thread)

ExampleOD Threading

G76 X27.404 Z-42.0 P1238 Q300 R20;G00 X32.0;Z5.0 M09;G28 U0 W0 M05;M30;Threading calculationMinor dia, d = D - (2h)(h = 0.649 p, for metric thread)h = 0.649 2.0 = 1.298 mm.d = 30 - (2 1.298) = 27.404 mm.ID Threading%

O0032G28 U0 W0;T0500;G97 S600 M04;G00 X38.0 Z5.0 T0505 M08;G76 P030060 Q150 R20;G76 X40 Z-110.0 P1298 Q300 F2.0;G00 X38.0;Z5.0 M09;G28 U0 W0 M05;M30;Threading calculation

%O0031G28 U0 W0;T0400;G97 S600 M04;G00 X32.0 Z5.0 T0404 M08;G76 P0300 Q150 R20;

Minor dia, d = D - (2h)(h = 0.649 p, for metric thread)h = 0.649 2.0 = 1.298 mm.d = 40 - (2 1.298) = 37.404 mm.Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.4.138Copyright @ NIMI Not to be Republished

101

Production & Manufacturing Related Theory for Exercise 4.5.139Turner - CNC Turning Operation

Programming on CNC TappingObjectives : At the end of this lesson you shall be able to• learn what is G84 code in CNC• understand tapping cycle• learn the differefce between rigid tapping & long form tapping.

G84 code in CNC progrmming refers to tapping cycle inCNC. This is carried out with tapping heads, and Tension/Compression tap holders.

G84 code is commonly used program for tapping, used onthreaded holes. There are two ways of tapping program.

• One using tapping cycle with rigid tapping capabilities.

• Long Form (no canned cycle needed) programmingwhen a tapping head is used that do not have rigid tapping.

To use rigid tapping, the CNC machine should support thesynchronnisation of feed motion with the spindle speed.

G84 code is tapping RH threads with M3 spindle rotation.

G74 code is tapping LH threads with M4

Rigid motion mode is used in Fanuc control using M29code.

Advantages• A tapping head may have a gear ratio that allows it to

retract faster. You will want to change feed rate whenretracting.

• A Dwell at the bottom of the hole may be helpful as thespindle reverse to even out the amount of springadjustment being used.

• It is possible to drag the feed rate a bit.

Tapping comes under canned cycle with intermittent feed,with Dwell spinlde CW with feed retraction in Z direction asshown in table below.

Example: Tap 1/4-20 thread 0.500” deep at 0,

Here is the Gcode

M03;

M8 (Speed & feed rate)

S400 F20 (Tapping)

Z1.0;

G00 X0.0 Y0.0;

G01 M29;

G84 Z-0.5 R02;

M03 spindle in right direction

M8 collant ON

S400 Spindle speed 400rpm & feed rate 20

Next we move to save Z&XY.

Switch G01 & M29 to turn rigid tapping lastly G84 is runwith Z indicating coordinate & R retracting coordinate.

If we had more holes to be tapped we can list their XYcoordinate, viz

G84 Z-0.5 R0.2;

X0.0 Y1.0 etc etc;


102

TABLE 1

Canned cycle used in OMC

G-code Application Z-direction operation at the Retraction inbottom of the hole Z direction

G73 High speed peck drilling Intermittent feed Dwell-spindle rotates FeedCW spindle orientationTool tip moved oppositeto cutting & retracted

G76 Fine boring Feed ------- -------

G80 Canceling of G81-G89 ------- ------- -------Cycles

G81 Centre/spot drilling Feed ------- -------

G82 Counter bore/counter sink Feed Dwell Rapid traverse

G83 Peck/deep hole drilling Intermittent feed ------- Rapid traverse

G84 Tapping cycle Feed Dwell spindle CW Feed

G85 Boringcycle Feed ------- Feed

G86 Boring cycle Feed Spindle stop Rapid traverse

G87 Back boring cycle Feed Spindle CW Rapid traverse

G88 Boring cycle Feed Dwell-spindle stop Manual retract

G89 Boring Feed Dwell Feed


103

Grooving is a very difficult operation amoungst turningoperation. In CNC G75-code is meant for grooving cycle inx axis. The explanation of parameters of Fanuc G75grooving cycle is as shown below.

Explanation of parameters of Fanuc G75 groovingcycleN10 G75 R

N20 G75 X Z P Q R

G75 First CNC Programming Block

R = Return amount

G75 Second CNC Programming Block

X = Groove Depth

Z = Last groove position in z-axis

P = Peck increment in x-axis

Q = Stepping in z-axis

R = Relif amount at end of the cut.

G75 Canned Cycle Grooving CNC ProgrammingExample


CNC Programme for Grooving OD/IDObjectives : At the end of this lesson you shall be able to• learn parameters of grooving cycle• understand reading a grooving program.

Job sequence• Switch on the CPU and monitor.

• Selct the software.

• Study the drawing.

• Enter the programme in edit mode.

• Using cycles.

• Select required tool and clamping devices.

• Connect the interface cable from external device to CNClathe machine.

• Execute the programme.

A detailed part programme of a component involvingturning, drilling,groove using G75 canned cycle is shownbelow

Part ProgramO0009

N1: (Turning)

G28 U0 W0;

G50 S2000 T0101;

G96 S200 M03;

G00 X30.0 Z5.0 M08;

Z0.0;

G01 X-1.0 F0.1;

G00 X28.0 Z2.0;

G71 U1.0 R1.0; ;

G71 P10 Q20 U0.0 W0.0 F0.1;

N10 G50 S500 T0100

N20 G97 S400 M03

N30 G00 X90.0 Z1.0 T0101

N40 X82.0 Z-60.0

N50 G75 R1.0

N60 G75 X60.0 Z-20.0 P3000 Q20000 F0.1

N70 G00 X90.0

N80 X200.0 Z200.0 T0100

N90 M30


104

M01;

N4; (OD Grooving 3 mm width)G28 U0 W0;

G97 S600 M03;

T0303;

G00 X22.0 Z5.0 M08;

G01 Z-23.0 F0.1;

G75 R2.0;G75 X16.0 Z-25.0 P500 Q2000 F0.06;G00 X25.0;

Z5.0 M09;

G28 U0 W0;

M05;

M01;

N5; (Threading)

G28 U0 W0;

G97 S600 M04;

T0505;

G00 X22.0 Z5.0 M08;

G01 Z3.0 F0.1;

G76 P030060 Q150 R20;

G76 X16.177 Z-22.0 P1622 Q300 F2.5;

G00 X25.0 Z5.0 M09;

G28 U0 W0;

M05;

M01;

M30;

%

N10 G01 Z0.0 F0.1;

X16.0;

X20.0 Z-2.0;

Z-25.0;

X24.0 Z-40.0

N20 G01 Z-50.0 F0.1;

G00 X30.0 Z5.0 M09;

G28 U0 W0;

M05;

M01;

N2; (Centre drill)

G28 U0 W0;

G97 S2000 M04;

T0202;

G00 X0.0 Z5.0 M08;

G01 Z-6.0 F0.08;

G00 Z5.0 M09;

G28 U0 W0;

M05;

M01;

N3; (ø6 Drill)

G28 U0 W0;

G97 S1800 M04;

T0404;

G00 X0.0 Z5.0 M08;

G74 R2.0;

G74 Z-53.0 Q10000 F0.06;

G00 Z5.0 M09;

G28 U0 W0;

M05;


105


CNC programming on ThreadingObjectives : At the end of this lesson you shall be able to• learn about G-WIZARD software• programme for thread canning cycle• understand the difference between single line and double line command.

The important thing in thread authing operation is to fix upthe thread start and thread end positions. The end positionis easier in Z axis, as we know the length of threadedcomponent. For thread cutting in CNC lathe, G-Wizardthread calculator software, provides complete databasefor all threads.

The start position is interesting as we start threadingsomewhere from outside the threads. You need to leavesome allowance in Z to give CNC machineto synchronizethe feed rate with spindle rotational position, Cuttingthread puts more stress on the cutter. Thread height, taperamount, thread pitch or lead, therad infeed angle (TNangle) are important in making the programme.

G76 is threading cycle followed in CNC Program.

Tips & thoughts on passes in threading cycle is detailedbelow.

G76 Threading Cycle Tips and Thoughts on PassesPassesThe number of passes that must be cut to make yourthread is very important. Take too few passes, and surfacefinish is apt to be poor and you might even break yourthreading tool by forcing it to work too hard. Take toomany passes and you're going to waste a lot of time.

You can't change most of the information relating to thethread's specifications, so your primary tools for controllingthe number of passes include:

– Start Position: Turn things down as I describe aboveto minimize the work the threading tool must do.

– First Pass Depth: Pick the largest pass you can. G-Wizard Calculator will give you a good recommendationhere.

– Minimum Pass Depth: Try to avoid using this parametertoo much and set it to your Finish Allowance.

– Finish Allowance: A smaller finish allowance can meanlarger roughing passes remove most of the material.Just remember, too small an allowance will force yourcutter to rub.

– Spring Passes: You shouldn't need more than 2 passesand 1 may suffice. Experiment with your particularsituation to see if you can get by with 1 or perhapseven no spring passes.

Your next challenge will be in determining how manypasses the cycle will actually make. This is not easy asG76 will dynamically change the depth of each pass afterthe first to equalize the amount of material removed. You

have to do quite a lot of calculation to figure out exactlyhow many passes will be made.

But there if you have a GCode Simulator, it may be ableto help out. Take a look at this screen shot of G-WizardEditor:

Fanuc Double Line G76 Threading CycleG76 P(m) (r) (a) Q(dmin) R(d)G76 X(U) Z(W) R(i) P(k) Q(d) F(L)P Word: The P-word has 6 digits consisting of three 2-digit clusters for m, r, and a.

m: Repetitive finishing count (1 to 99)-spring passes.

r: Chamfering amount (1 to 99)

a: Angle of Tool Nose. Select 80, 60, 55, 30, 29 or 0degrees.

Q Word: dmin is the Minimum Cutting Depth. If the depthof either a roughing or finish pass is less than this, it isclamped to be at least this much.

R Word: d is the finish allowance.

X/Z/U/W words (2nd line): Specify the coordinates of theend point. X, Z use the current mode (absolute or relative)while U, W can be used to specify a relative position.

R Word (2nd line): i is the taper amount when cuttingtapered threads.

P Word (2nd line): k is the thread height expressed as aradius (not diameter) value.

Q Word (2nd line): d is the depth of the first cut.

F Word (2nd line): L is the lead of the thread.

Example: Fanuc 2 line G76 cutting a tapered pipe thread:

Fanuc Single Line G76 Threading CycleG76 X.. Z.. I.. K.. D.. F.. A.. P..X = Diameter of last threading pass

Z = Position of the thread end

I = Taper over total length

K = Single depth of the thread - positive

D = Depth of first threading pass - positive

A = Included angle of the insert - positive

P = Infeed method (one of 4)

Haas G76 Threading CycleG76 D.. K.. X.. Z.. U.. W.. I.. P.. F.. A..Copyright @ NIMI Not to be Republished

106

D = Initial cut depth

K = Thread height

Z* = Z-axis absolute ending location. Determines threadlength.

U* = X-axis incremental distance to end. May be usedinstead of X.

W* = Z-axis incremental distance to end. May be usedinstead of Z.

I* = Thread taper amount (radius measure).

P* = Subsequent pass positioning method (1-4)

F* = Feedrate

A* = Tool nose angle (0 -120 degrees. 0 assumed if notspecified)

LinuxCNC / PathPilot G76 Threading CycleG76 P.. Z.. I.. J.. R.. K.. Q.. H.. E.. L..P = Thread pitch in distance per revolution

Z = Final position of threads

I = Thread Peak offset. Negative for external, positive forinternal.

J = Initial cut depth

K = Full thread depth

R = Depth digression (optional). R = 1 is constant depth,R =2 is constant areas.

Q = Compound slide angle (optional)

H = Spring passes (optional)

E = Distance along drive line for taper

L = Which end of the thread gets tapered. L0 = no taper.L1 = entry taper. L2 = exit taper. L3 = entry and exittaper.

Mach 3 G76 Threading CycleG76 X.. Z.. Q.. P.. H.. I.. R.. K.. L.. C.. B.. T.. J..X = X end

Z = Z end

P = Pitch

H = Depth of first pass

I = Infeed angle

R = X Start (optional)

K = Z Start (optional)

L = chamfer (optional)

C = X Clearance

B = Depth Last Pass (optional)

T = Taper (optional)

J = Minimum depth per pass (optional)


107

Production & Manufacturing RelatedTheory for Exercise 4.5.142Turner - CNC Turning Operation

Trouble shooting in CNC machinesObjectives : At the end of this lesson you shall be able to• learn trouble shooting of CNC machines• understand electrical/electronic problems & remedy• understand hydraulic problem & remedy.

Introduction: A CNC Machine operates onelectrical,electronics mechanical, pneumatic and hydraulicsystem invovled in its automation. If one of the aboveelements doesnot function or function partially the wholemachine will come to stand still position. In CNC machinetrouble shooting arises due to electrical,servo andmechanical problems.

The trouble shooting can be split in to:

1 PLC trouble shooting

2 Low voltage problem

3 Power up problem

4 Zero return problem

5 Door inter lock circuit problems

6 Relay board repair and problems

7 Hydraulic system trouble shooting

General causes of failure in electrical and electronicdevices

• Poor earthing

• Loose connection

• Dust particles or coolant entry

• Improper ventillation

• Blocked air circulation

• Poor supply voltage condition

• Sag for duration less than 2.5 seconds

• Surge for duration less than 2.5 seconds

• Spike (very high voltage lasting for few micro seconds)

• Blockout/Brown out greater than 2.5 seconds

• EMI (electromagnetic interference) affect switchingdrill, leads to data corruption.

Tips1 Earthing between servo amplifier and CNC machine is

a wrong practice. CNC mchine and electrical cabinetshould be earthed directly individually.

2 Loose connections leads to failure of CRT monitors,input/output cards, measuring circuit, interfaces.

3 Dust particles results in short circuit,corrosion of tracts,PCBs and fuse getting blown. To avoid this dustprotective guards should be fitted.

4 Improper ventillation results in malfunctioning ofelectronic circuits.

5 Poor supply voltage with poor voltage regulation affectsthe sensitive electronic device. Suggested not to operatewelding machines near CNC machine.

6 Electrostatic charges transfer from human body maydamage electronic components,leads to lose of dataand hence, store PCBs in anti-static covers.

Poor switching devices like contactors,chokes.Transformers are to be grouped & separated from CNCsystem. The AC cables should not run parallel for longdistance.

Safety Interlocks in CNC machines:

Power chucks should be damped befroe execution inMDA, Auto mode or single mode.

During cycle, in case of pressure failure, both spindle andaxis should stop.

If slide lubrication system fail, cycle may continue till M30/M02 of programme. The fault has to be rectified for cyclerestart.

Jogging of axis is not permitted when the cycle is inprogress. Spindle & collant stops automatically with M30/M02 command.

If an unspecified battery is used (For memory, pulse coder)it may explode. Replace the battery only with the specifiedone (A02B-0177-K106). Dispose used batteries inaccordance with applicable laws.

Trouble shooting of Alarm 960 due to abnormal 24V inputpower (Fish bone diagram) is shown.


108

Trouble shooting on specific elements

Elements Sympton Remedy

1 Motor Surface Cutting fluid on motor Clean the motor

2 Fan motor Not rotating Tighten the loose connection,remove dirt etc

3 Motor shaft bearing Unusual sound Replace Bearing

4 Abnormal vibration Noise Check all Bearing, belts,etc

5 Cooling air path Clogged with dust Clean air path

6 Interlock safety circuit control cabinet Check all interlock keys fullyengaged at rest.

Check interlock module incontrol cabinet, checkcontacters

7 Chuck/Actuator Hyd, pump not running Check ladder diagram

Power ON and test, setthe pressure higher

Check input signal of foot switch

8 Soft over travel machine Brake does not stop axis Reset after completing zeroalarm occurs on zero returning return

9 CNC is crashed (some slips CNC control gets goofed up Power down & then backup orduring machine switch) reset

Backup battery Needs replacement Keep encoder position whenpower is shut off

Lubrication pump problem Noise in axis Double the oil

Axis motor overload alarms Check for leaks

Check the distribution mainfoldClean the filter if clogged, ensurecorrect oil is fed.

Shaft jammed, Defective motor, PLC malfunction, Fuse onspindle drive etc are other causes.

Effects :Spindle not rotating

The cause and effect diagram shown, can be furtherdeveloped by adding some more causes.

By carrying out the corrective action the problem can besorted out.


109

Remedies For Chart 1a Any or all of the following: Replace dirty filters. When

strainers in solvent compatible with system fluid. Cleanclogged inlet line. Clean reservoir breather vent. Changesystem fluid. Change to proper pump drive motor speed.Overhaul or replace super-charge pump. Fluid may betoo cold.

b Any or all of the following: Tighten leaky inletconnection. Fill reservoir to proper level (with rateexception all return lines should be below fluid level inreservoir). Bleed air from system. Replace pump shaftseal (and shaft if worn at seal journal).

c Align Unit and check condition of seals, bearings andcoupling.

d Install pressure gauge and adjust to correct pressure.

e Overhaul or replace.

Remedies For Chart 2a Any or all following: Replace dirty filters.clean clogged

inlet line. Clean reservoir breather vent. Change systemfluid. Change to proper pump drive motor speed.Overhaul or replace supercharge pump.

b Any or all the following: Tighten leaky inlet connections.Fill reservoir to proper level (with rare exception all returnlines should be below fluid level in reservoir). Bleed airfrom system. Replace pump shaft seal (and shaft ifworn at seal journal).

c A link unit and check condition of seals and bearings.Locate and correct mechanical binding.Check for work load in excess of circuit design.

d Install pressure gauge and adjust to correct pressure(keep atleast 125 psi difference between valve settings)


f Change filters and also system fluid if improper viscosity.Fill reservoir to proper level.

g Clean cooler and/or cooler strainer. Replace coolercontrol valve. Repair or replace cooler.

Remedies For Chart 3a Any or all of the following : Replace dirty filters, clogged

inlet line. Clean reservoir breather vent. Fill reservoir toproper level. Overhaul or replace supercharger pump.

b Tighten leaky connection. Bleed air from system.

c Check for damaged pump or pump drive. Replace andalign coupling.

d Adjust


f Check-position of manually operated controls. Checkelectrical circuit on solenoid operated controls. Repairor replace pressure pump.

g Reverse for rotation.

h Replace with correct unit.

Remedies For Chart - 4a Replace dirty filters and system fluid.

b Tighten leak connecitons (fill reservoir to proper leveland bleed air from system).

c Check gas valve for leakage. Charge to correctpressure. Overhaul of defectives.

d Adjust.


Remedies For Chart - 5a Fluid may be too-cold or should be changed to clean

fluid of correct viscosity.

b Locate bind and repair.

c Adjust, repair or replace.

d Clean and adjust or replace. Check conditons of systemfluid and filters.


f Repair command console or interconnecting wires.

g Lubricate.

h Adjust, repair or replace counterbalance valve.


110 Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.5.142Copyright @ NIMI Not to be Republished

111Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.5.142Copyright @ NIMI Not to be Republished

112 Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.5.142Copyright @ NIMI Not to be Republished

113Production & Manufacturing : Turner (NSQF Level-5) - RT for Ex - 4.5.142Copyright @ NIMI Not to be Republished

114


Factors affecting Quality & ProductivityObjectives : At the end of this lesson you shall be able to• understand the definition of quality• learn characteristic & elements of quality• learn the increased productivity through implements TPM.

Introduction

Quality & Productivity are vital requirements of modernadvanced manufacturing techonologies. Better quality isachieved through adopting (TQM) and higher productivitycan be achieved through implementing Total ProductiveMaintenance (TPM).

To achieve exact quality, we should know the real meaningof quality which is defined by many Quality Experts suchas,

Quality:

• Is fitness for use

• Should be aimed at needs of customer

• As the conformance to requirements

• Meeting the customer satisfaction

• Meeting all the characteristic of a product as perspecification

• As per ISO defined as ratio of P/E, with P performance& E Expectation

Importance of Quality:• Quality can be result in,

• Bringing out customer delight

• Increasing market share, easy marketability

• Increasing customer base with more repeatedcustomers

• Increased profitability

• Becoming an industrial hero,entering globalisation

• Increased morale of the employees of ISO unit

Dimensions of Qulaity:• The various paramters of quality of a product can be

listed out as:

• Performance of the product

• Features of the product

• Conformance with the requirement of product standard

• Reliability of the product not failing within stipulated lifecycle

• Durability of product life

• Providing service after sales & fully resolving problems& complaints

• Customer handling and care is a highly sensitivity area

• Meeting customer’s delight through improving aesthetics

• Estabilishing reputation through past performance andother intangible efforts.

Quality characteristic:It can be broadly grouped under Design, Conformance,Assurance & Control,

Quality of DesignQuality of design is the excellence of the design in relationto the ease of manufacture and meeting the customerrequirements.

Quality of conformanceQuality of conformance is the fidelity with which a productor a service conforms to the specified requirements.

Quality AssuranceQuality Assurance comprises of all those planned andsystematic actions necessary to provide adequateconfidence that a material, structure, component or systemwill perform satisfactorily in service. Quality assuranceincludes quality control.

Quality ControlQuality control comprises of all those quality assuranceactions related to the physical characteristics of a material,structure, component or system which provide the meansto measure and maintain the material, structure,component or system to pre-determined requirements. Themain aim of quality control is defect prevention.

Predictive MaintenanceIn predictive technique, on the prediction of any fault,maintenance is being done. It is comparatively a newermaintenance technique.

In this technique, equipment condition is measuredperiodically or on a continuous basis.

This enables maintenance staff to take a timely actionsuch as equipment adjustments, repairs and overhaul.

Predictive maintenance extends the service life of anequipment without any fear of failure.


115

TPM Implementation (Fig 1) work culture resulting in better product quality andproductivity.

ObjectivesGet operators in touch with their equipment to make themmore familiar with it, develop curiosity and sense ofbelonging of ownership and concern.Establish and maintain basic equipments conditions bythorough cleaning, lubricating and Tightening.Increase the availability of plant and Machinery, capacityutilization and to improve overall equipment efficiency.TPM TargetP Productivity improvement…………. 1.5 to 2 times

• Reduction in Number of SporadicFailure …………………………… 1/10 to 1/250

• Equipment Operating…………… 1.5 to 2 timesQ Reduction in Product Defects…….. 1/10

Reduction in Customer Claims…… 1/4C Reduction in Maintenance Cost…. 30%D Reduction in Product Inventories.. 0S Reduction in Accident, Elimination

of Pollution ………………………… 0M Increase in Number of Employee

Suggestions …………………… 5 to 10 times

The Goals OF TPMMaximize equipment effectiveness (Improve Overallefficiency)

Equipment effectiveness increases the productivity byminimizing input and aiming maximum output. Though"Output" means not only the quantity of production, butalso the better quality, lower cost, timely delivery, improvedindustrial safety & hygiene, higher moral and favourableworking environment. Equipment effectiveness is increasedby the reduction of the following six big losses:

• Downtime losses• Break down• Setup & adjustment

• Speed losses• Idling & Minor stoppages• Reduced speed

• Defect losses• Defects in the process and reworks• Reduced yield between machine startup and stable

production

For a productive manufacturing system, a goodmaintenance is the fundamental requirement. TPM is allabout keeping the plant and equipment at its highestproductive level through co-operation of all areas of theorganization. This approach does not disregard thetechniques such as predictive and preventive maintenance.Predictive maintenance and preventive maintenance arethe basis for a successful TPM environment.

Benefits of TPMThe properly implemented TPM has made excellentprogress in a number of areas. These include:

• Increased equipment productivity• Improved equipment reliability• Reduced equipment downtime• Increased plant capacity• Extended machine line• Lower maintenance and production costs• Approaching zero equipment - caused defects

• Improved team work between operators andmaintenance people

• Enhanced job satisfaction

• Improved return on investment

• Improved safety

Total Productive Maintenance (TPM)TPM is system oriented structured approach towardsexcellence in all spheres of Industrial Management andpowerful means to achieve high level product quality andproductivity through efficient utilization of all resources like,man, Machine, Material, Money, Minute, space andopportunity by Total employee participation through groupactivities and Autonomous Maintenance.

TPM implementation calls for change in attitude ofoperational personnel. It requires patience, perseveranceand persuasion to encourage workmen to think.

It is my machine and I have to maintain it : I operate thismachine and someone else maintains it" though changeof attitude is slow to achieve but has dramatic effect on


116

Types of TPM• Corrective or Breakdown Maintenance• Scheduled or routine maintenance• Preventive Maintenance• Predictive Maintenance

1 Corrective or Breakdown MaintenanceCorrective maintenance implies that repairs are made afterthe failure of machine or equipment. It says wait until afailure occurs and then remedy the situation as quickly aspossible. For example, replacing gears in a machine onlyafter the gears get failed and become inoperative.

2 Scheduled or Routine MaintenanceScheduled maintenance is a stitch-in-time procedureaimed at avoiding breakdowns. This includes all workundertaken to keep the production equipment in efficientcondition. It may cover periodic inspection, cleaning,lubrication, overhaul, repair, replacement etc.

3 Preventive MaintenancePreventive maintenance is carried out before the failurearises or prior to the equipment actually breaks down. It isa safety measure designed to minimize the possibility ofunanticipated breakdowns and interruptions in production

It involves repetitive and periodic upkeep, overhauling,servicing to the equipment to prevent breakdown.


117


Parting off Operation in a CNCObjectives : At the end of this lesson you shall be able to• understand what is G75 command• learn the parting off operation• aware of latest techniques in parting off.

Out of all the turning operation like turing, facing, grooving,taper turning etc, parting off operation is the one whichcauses trouble to most operators. ‘Parting off’ is definitelya challenging operation when you look at it mechanically,because the cutting tool is fairly thin, plunging deep into thematerial.

Once the tool tip is deep down in the parting groove of thematerial, getting chips out & lubrication of cutting tool, isa real program. If the lathe is sturdier, and has good rigidityparting may be easier. In manual parting, the operator withdraws the tool from the groove whenever he hears asqueaks. The parting tool should be set to exact centre ofthe job, otherwise there is a definite possibility of anaccident, involving tool breakage, or job getting damaged.

But parting in CNC is different where the “touchs” of manualmachining is absent, hence the idea of “Peck Parting” wasdeveloped.

Most machinist will be familar with peck drilling cylces,where the drill bit is retracted a little to break a chip or a lotto help extract chips from a deep hole over and over again.In parting off also we get the benefit if the tool retaces forevery advances.

Many of the machine controls have a peck option on G75grooving code, which is used for parting off. In conventionalCNC mode, there is a provision for “Parting off with peck”option Fanuc’s G75 is newer control uses a two line format:

G75 R0.002

G75 X1.0 P0.125 F10 (Refer Fig 1)

Where R is the amount of retraction after each peck (X1.0,Z-10.0) is the lower left corner of the grooving to itsreference point and the grooving is being done from right toleft. P is the depth of cut for each peck at a feed rate of F.So each peck cuts a distance of P retracts a distance R,Then re-engages the material and does another peck ofdistance p and cycle goes on till the bottom is reached.

If ‘Q’ value is specified with a Z value, then it means thegroove is wider than tool widths


118


Bar Feeding System through Bar FeederObjectives : At the end of this lesson you shall be able to• learn about the bar feeding operation• learn the advantages of bar feeding mechanism• learn the limitations of the system.

The Bar feeding mechanism is a metal cutting machine tooldesigned to feed the metal. This machine is exclusivelyintended for mass production and they represent faster andmore efficient way to feed a stock. Automatic Bar Feedingmechanism (ABF) consists of three major blocks. Theyare:

• Metal feed mechanism

• Bar clamping mechanism

• IR sensor unit

The IR unit determines the dimension for cutting the barclamping is through pneumatic system, which is highlyreliable and effective.

Need for Automation of Bar feeding

• To achieve mass production in manufacturing process.

• To reduce man power employed.

• To increase the efficiency of the machine.

• To reduce the workload & production cost.

• To reduce material handling & production time.

• To reduce the fatique of workers.

• To achieve good product quality.

• To reduce maintenance cost.

The motor will be rotated, so that the bar is moving frominitial position to the determined position.

IR sensor unit is used to deternmine the bar dimension tobe cut.

The compressed air from the compressor reaches thesolenoid valve. The solenoid valve changes the direction offlow according to the signal from the sensor unit.

The pneumatic cylinder is used to clamp the work pieceautomatically with the help of IR sensor unit.

Advantage1 Simple in construction than mechanical hacksaw.

2 It is a compact one

3 Less maintenance

4 Fast production

Limitation

• Additional cost is required to do the automation.

• Leakage of air affects the working of the unit.

Application

• Small and medium scale industries Application.

• Metal Cutting Industries and Work Shops.


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Input and Output of dataObjectives : At the end of this lesson you shall be able to• understand the importance of input/output data for a CNC• learn about output data, CNC parameter• learn about pitch error, custom macro variables.

The Input/Output data is very important elements in a CNCmachine. The CNC stores parameters like pitch errorcompensation PMC parameter CNC parameters, tookcompensation amount etc. The conrtrol of input and outputdatas through set of keys and commands are indicatedbelow.

Setting procedure of parameters

Parameter writing is enabled with following steps 1 to 3.

1 Set to MDI mode or emergency stop state.

2 Press function key several times or press soft key[SETTING] to display SETTING (HANDY) screen.

3 Set the cursor to PARAMETER WRITE and, press andkeys in this order. Here alarm 100 will be displayed.

4 Press function key several times to display the followingscreen.

<3> Soft key [OFF : 0] :Item with cursor position is set to 0 (bit parameter)

<4> Soft key [+INPUT] :Input value is added to the value at cursor

<5> Soft key [INPUT] :Input value is replaced with the value at cursor

<6> Soft key [F INPUT] :Parameters are input from reader/puncherinterface.

<7> Soft key [F OUTPUT] :Parameters are output to reader/puncher interface.

6 After the parameters have been input, set PARAMETERWRITE on the SETTING screen to 0. Press key torelease alarm 100.

7 Convenient method

<1> To change parameters in bit unit, press cursorkey or , then the cursor becomes bit length andyou can set parameters bit by bit (Bit parameteronly).

<2> To set data consecutively, use key.

(Ex.1)

This key sequence sets data as follows:

0 12340 ⇒ 45670 99990 0

(Ex.2)

This key sequence sets data as follows:

0 12340

⇒

00 99990 0

<3> To set the same data sequentially, press = .(Ex.1)

This key sequence sets data as follows:0 12340

⇒

12340 12340 0

<4> Bit parameters can be set as follows:

PARAMETER (SETTING) 1234 N12345

0000 SEQ INI ISO TVC0 0 0 0 0 0 0 0 0

0001 FCV0 0 0 0 0 0 0 0 0

0012RMV MIRX 0 0 0 0 0 0 0 0 0Y 0 0 0 0 0 0 0 0 0Z 0 0 0 0 0 0 0 0 0B 0 0 0 0 0 0 0 0 00020 I/O CHANNEL

S 0 T0000

REF **** *** *** 10: 15: 30[PARAM][DGNOS][ ][SYSTEM][(OPRT)]

To make the cursor display in bit unit, press the cursor key

⇒

or

⇐

.

5 Press soft key [(OPRT)] and the following operationmenu is displayed.

<1> Soft key [NO. SRH] :Searched by number.Examination) Parameter number

→

[NO. SRH].

<2> Soft key [ON : 1] :Item with cursor position is set to 1 (bit parameter)


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(Ex.1)This key sequence sets data as follows:

0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 00 0 0 0 0 0 0 0 0 0 0 1 1 0 0 00 0 0 0 0 0 0 0 0 0 0 1 1 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

8 After the required parameters are set, setPARAMETER WRITE to 0.

Inputting/ Oupputting Data

The CNC memorized the following data.

Outputting the data I/O device while the CNC is runningnormally.

1 CNC parameter

2 PMC parameter

3 Pitch error compensation amount

4 Custom macro variable values

5 Tool compensation amount

6 Part program (machining program, custom macroprogram)

Conforming the Parameters Reqiured for Data Input/Output

Be sure that data output cannot be done in an alarmstatus.

The following parameters are needed to input/output datawith a reader or puncher:

In addition, (*) indicates the standard setting for input/output devices made by FANUC. Change these settingsaccording to the unit you actually use.

(Parameter can be changed in MDI mode or emergencystop status.)

NFD 0: Feed is output when data is output.1: Feed is not output when data is output.

ASI (*) 0: EIA or ISO code is used for input/outputdata.(input: automatic detection, output: settingof bit 1 (ISO) of parameter No. 0000)

1: ASCII code is used.(To use the ASCII code, set bit 1 (ISO) ofparameter No. 0000 to 1. )

SB2 0: No. of stop bits is 1.(*) 1: No. of stop bits is 2.

#7 #6 #5 #4 #3 #2 #1 #00000 ISO

0020 Selection of I/O channel

#7 #6 #5 #4 #3 #2 #1 #00101 NFD ASI SB2

0102 Number specified for the input/output device

Set value Input/output device0 RS-232-C (Used control codes DC1 to DC4)1 FANUC CASSETTE ADAPTOR 1 (FANUC

CASSETEE B1/B2)2 FANUC CASSETTE ADAPTOR 3 (FANUC

CASSETEE F1)FANUC PROGRAM FILE Mate, FANUC FACard Adaptor

3 FANUC FLOPPY CASSETTE ADAPTOR,FANUC Handy FileFANUC SYSTEM P-MODEL H

4 RS-232-C (Not used control codes DC1 toDC4)

5 Portable tape reader6 FANUC PPR

FANUC SYSTEM P-MODEL G, FANUCSYSTEM P-MODEL H

ISO 0: ASCII code input/output1: ISO code input/output (with Data Server)

Outputting CNC Parameters

1 Enter EDIT mode or the emergency stop condition.

2 Press function key and soft key [PARAMETER] toselect a parameter screen.

ISO 0: Output with EIA code1: Output with ISO code (for RS-232-C serial

port 1 or 2)

(*) 0: Channel 1 (RS-232-C serial port 1: JD36Aof mainboard)

1: Channel 1 (RS-232-C serial port 1: JD36Aof main board)

2: Channel 2 (RS-232-C serial port 2: JD36Bof main board)

4: Memory card interface5: Data Server interface

NOTEIn the operation examples in this chapter, data in-put/output is done with an I/O device connected toJD36A. (I/O channel = 0)

0103 Baud Rate

#7 #6 #5 #4 #3 #2 #1 #00139 ISO

1: 50 7: 600 11: 96003: 110 8: 1200 12: 19200 [BPS]4: 150 9: 24006: 300 (*)10: 4800

#7 #6 #5 #4 #3 #2 #1 #00908 ISO

ISO 0: ASCII code input/output1: ISO code input/output (with memory card)


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3 Press soft key [(OPRT)] and continuous menu key .

4 Press soft keys [F OUTPUT] and [EXEC], and theparameters are started to be output.

Outputting Pitch Error Compensation Amount

If pitch error compensation is enabled, a pitch errorcompensation amount is output.

1 Select EDIT mode.

2 Press the function key .

3 Press continuous menu key several times, then presssoft key [PITCH] to select the pitch error compensationsetting screen.


5 Press soft keys [F OUTPUT] and [EXEC], then pitcherror compensation amount is started to be output.

Outputting Custom Macro Variable Values

When custom macro function is valid, values of variableNo. 500 and later are output.

1 Press function key .

2 Press continuous menu key several times, then presssoft key [MACRO] to select custom macro variablescreen.

3 Press soft key [(OPRT)] and then continuous menukey.

4 Press soft keys [F OUTPUT] and [EXEC], then custommacro variable values are output.

Outputting Tool Compensation Amount

1 Select EDIT mode.

2 Press function key and soft key [OFFSET] to displaythe tool compensation amount screen.


4 Press soft keys [F OUTPUT] and [EXEC], and thetool compensation amount is started to be output.

Outputting Part Program

1 Confirm the following parameters. If their setting doesnot match those indicated with the asterisk, selectthe MDI mode and re-set them and keep them re-setonly while this work is being done.

However, if you changed the parameter setting, restorethe original value after finishing this work.

NE8 (*) 0: Programs of 8000s are edited.1: Programs of 8000s can be protected.

(Protected programs are not output.)

2 Select EDIT mode.

3 Press the function key and then the soft key[PROGRM] to select the program content displayscreen.

4 Press soft key [(OPRT)] and press continuous menukey .

5 Input a program number to be output. To output allprograms input as:

6 Press soft keys [F OUTPUT] and [EXEC], then programoutput is started.

Inputting CNC Parameters

1 Set to the emergency stop state.

2 Press the function key and then the soft key [SETTING]to select the setting screen. Confirm “PARAMETERWRITE=1” on the setting screen.

3 Press function key and soft key [PARAMETER] toselect the parameter screen.


5 Press soft keys [F INPUT] and [EXEC]. Then input ofparameters are started.

6 Upon completion of parameter input, turn off the powerthen turn on the power again.

7 Alarm 300 is issued if the system employs an absolutepulse coder. In such a case, perform reference positionreturn again.

Inputting Pitch Error Compensation Amount

If pitch error compensation is enabled, a pitch errorcompensation amount is input.

1 Select EDIT mode.

2 Confirm that PARAMETER WRITE=1 on the settingscreen.


4 Press continuous menu key several times, then presssoft key [PITCH] to select the pitch error compensationsetting screen.

5 Press soft key [(OPRT)] and continuous menu key.

6 Press soft keys [F INPUT] and [EXEC], then pitcherror compensation amount is started to be input.

7 After a pitch error compensation amount is input,display the setting screen and reset “PARAMETERWRITE” to “0” on the setting screen.

Inputting Custom Macro Variable Values

When custom macro function is valid, input the variablevalues.

#7 #6 #5 #4 #3 #2 #1 #03202 NE9 NE8

NE9 (*) 0: Programs of 9000s are edited.1: Programs of 9000s can be protected.

(Protected programs are not output.)


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1 Select EDIT mode.

2 Turn off the program protect (KEY2=1).


4 Press continuous menu key several times, then presssoft key [MACRO] to select the custom macro variablescreen.


6 Press soft keys [F INPUT] and [EXEC], then custommacro variable values is started to be input.

Inputting Tool Compensation Amount

1 Select EDIT mode.

2 Turn off the program protect (KEY=1).


4 Press soft key [OFFSET] to display the toolcompensation amount display screen.


6 Press soft keys [F INPUT] and [EXEC], then toolcompensation amount is started to be input.

Inputting Part Programs

1 Confirm the following parameters. If their setting doesnot match those indicated with the asterisk, selectthe MDI mode and re-set them and keep them re-setonly while this work is being done.

#7 #6 #5 #4 #3 #2 #1 #03201 NPE RAL

#7 #6 #5 #4 #3 #2 #1 #03202 NE9 NE8

NE9 (*) 0: Programs of 9000s can be edited.1: Programs of 9000s are protected.

NE8 (*) 0: Programs of 8000s can be edited.1: Programs of 8000s are protected.

2 Select EDIT mode.

3 Turn off the program protect (KEY3=1).

4 Press the function key and then the soft key[PROGRM] to select the program content displayscreen.

5 Press soft key [(OPRT)] and press continuous menukey .

6 Press soft keys [F INPUT] and [EXEC], then programinput is started.

However, if you changed the parameter setting, restorethe original value after finishing this work.

NPE When programs are registered in part programstorage area, M02,M30 and M99 are:

0: Regarded as the end of program.(*) 1: Not regarded as the end of program.

RAL When programs are registered:(*) 0: All programs are registered.

1: Only one program is registered.


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DNC systemObjectives : At the end of this lesson you shall be able to• learn about the DNC system• learn type the DNC system• understand the advantage of DNC.

DNC System

It is a manufacturing system in which number of machinesare controlled by a computer through direct-connectionand in realtime. It is also a system connecting to a set ofNC. Machines to common memory for a part programmeor machine programme storage with provision ofon-demand distribution of data to machines.

The main components of a DNC are;

1 Central computer.

2 Bulk memory with storage of part programme.

3 Telecommunication lines and set of NC machine tools.

A schematic sketch indicating a set of NC machineconnected to a DNC is shown below:

There are two types of DNC machines namely 1. Behindthe Tape Reader System (BTR), 2. Special MachineControl Unit (MCU). In BTR system computer is linkeddirectly to NC controler unit the operation of the system isvery similar to conventional NC. The controler unit, usestwo temporery storage buffer to receive instruction fromDNC computer and convert them in to machine action. Onebuffer receives Data the other is providing controlling

instruction to machine tools. The cost of BTR system isvery less. The special machine control unit replace aregular controler, with the control unit capable of facilatingcommunication between machine tool and computer. Thissystem achives very high accuracy of interpolation and fastmetal removal rate.

Functions of DNCThe function of DNc system is to perform.

1 NC with out punched tape.

2 NC part programme storage.

3 Data collection, processing and reporting.

4 Communication.

A communication Network accomplishes the previousfunctios of DNC. This links DNC with central computer andmachine tools, Central computer and NC part programmerterminal, central computer and Bulk Memory.

Advantages of DNC system

It eliminates punched tape and tape reader.

It is convenient to store are NC part programme in computerfiles.

It has greater computational capability and flexibility.

It can report the shop performance at the click of a button.

DNC’s are very convenient in editing and dignoistic feature.

DNC is a first step in the development of production plantautomated with computer.


124


Use of CAM ProgrammeObjectives : At the end of this lesson you shall be able to• understand usefulness of CAM in manufacturing process• learn the output format of CAM programe• understand terms like CAD/CAE/DNC etc.

Introduction:Computer-aided manufacturing (CAM) is the use of asoftware to control machines and the related devices &equipment in the manufacture of components. CAM softwarealso assist in all operations such as process planning,production management, product transportation within theplant, storage of semi finished/finished product.

The purpose of CAM is to increase productivity and improvetooling, to enhance greater consistency of quality,minimising raw material wastage. CAM software is alsouseful for training & academic educational purposes.

CAM process has come out of CAD and sometimes CAEcomputer aided engineering, as a model generated byCAD, verfied by CAE and put into CAM software, whichcontrols the CNC machine tool

CAM is a numerical control (NC) programming tool, for 2D/3D models generated in CAD. CAM does not eliminate theneed for skilled professionals, but assists manufacturingpersonnel in building skills through visualisation, simulationand optimization tools. Integration of CAD with othercomponents of CAD/CAM/CAE, Product Life Cycle (PLC)management environment requires an effective CAD dataexchange, such as IGES/STL/ Parasolid formats. Theoutput from CAM is usually a text file of G-code/M-code,adthousands of commands, which can be transfered to aDNC programme.

CAM is specifically effective in typical areas like.

• High speed machining, streamlining tool paths.

• Multifunction machining.

• 5-axis machining & Automatic machining.

A finished components has to undergo different machiningprocess in its conversion from raw material i.e,

a Rough machining: From raw stock,raw casting passesthrough zig-zag clearing, plunge roughing, rest roughing,trohoidal milling aiming at maximum material removalin the least amount of time, maintaining dimensionalaccuracy.

b Semi-finishing: In this process, small amount of materialonly removed, to enable the tool to cut accurately suchas Raster passes, constant step-over process, pencilmilling etc.

c Finishing machining: It involve very light material removalto produce polished finish product. The feed is increasedto target SFM with high speed refered as highspeedmachining (HSM) CAM is mainly useful for contourmilling on four or more axis.

Usefulness of CAMGood CAM software is equally as important to manufacturersas the powerful machines and tool they use to cut desiredparts. Machine shops of all sizes and budgets are reapingbenefits of good CAM software beyond efficiencyprogramming their machining jobs. Users can structuretheir job, set their Toolpath, then use the simulationfunction to make sure their plan goes accordingly. Partgouges or collisions can potentially ruin a very crucial andexpensive CNC machine, threatening to affect that shop’sprofitablilty or ability to take on additional projects. It ismuch easier to readjust a Toolpath in the CAM softwarethan it is to fix or repalce a CNC machine!

Structuring your job with CAM SoftwareLet’s take s sprocket for example. You created yoursprocket using CAD software, now how will you make it?CAM software looks at what designed& determines how tomachine it out of materials. For starters, most CAMsoftware products provide a standard “Job Tree” formachining strategy organization. Then you will need to setup and save the features of the machine from your shopwithin the CAM software. This is important for developingprograms that are specific to your machine, allowing youto easily machine future projects, editing machine settingas needed. Next, you will identify your stock, allowing youto set initial work cooridinates, material type and the toolsto be used during machining. Lastly, you set your cuttingconditions, tool patterns, tool crib and tool holder for error-free CNC programming. One of the greatest benefits ofCAM software is the ability to save the information you putin the system, making future projects much more easilyprogrammed.

Setting your Toolpaths within the CAM software:Once you have your starting points clearly identified(machine, tools and stock), you can move into the nextphase of developing your machining operations. Start withyour stock. Decide the toolpaths for your roughing andfinishing cycles that will ultimately determine your desiredpart design. Your Job Tree comes into play now, keepingyour machining operations organized and correctlysequenced. CAD-CAM software, like that from BobCAD-CAM, used wizard guides that act as a series of dialogboxes that walk you through the process step-by-step untilyour Toolpath is properly created. Wizards are sort of afool-proof way to make sure all your information is enteredin correctly, reducing programming time significantly forusers.


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After you created a Toolpath for each of your operations,you can move into most critical aspect of CAM software;simulation. This allows you to see your machine createyour part in a digital environment. There are three majorthings that are being accomplished during the time:

1 Part deviation analysis- the CAM software identifiedwhat’s not cut by the tool or where the tool went toodeep using multiple colors to represent different levelsof deviation.

2 Costly gauges or collisions are digitally detected priorto engaging your shop’s machine.

3 Cycle time can be easily calculated.

After you structure your job, creat your Toolpath and runsimulations to satisfaction, you are ready for postprocessing. This is the final step before your part ismachined. G-code is created by the CAM software, whichis the NC file that is read by the CNC machine. Think of theG-code as the GPS in your car; it basically tells themachine where to go. Each machine’s G-code can vary, soit’s important you have the proper post processor added toyour CAM software.


126

Production & Manufacturing Related Theory for Exercise 4.6.149Turner - Advanced Turning

Setting of tool for taper threads calculation of taper setting and thread depth.Objectives : At the end of this lesson you shall be able to• state the application of taper thread• state the methods of producing taper threads• describe methods of turning tapers on a lathe with its merits and demerits.

Taper thread

Taper threads are used on fasteners and pipe. Acommon example of a fastener with a taper thread is woodscrew. The threaded pipes used in some plumbinginstallations for the delivery of fluids under pressure havea threaded section that is slightly conical. Examples areNPT and BSP series. The seal provided by a threadedpipe joint is created when a tapered externally threadedinto an end with internal threads.

Inside tapered threads

- Insert the pipe into the chuck of the lathe and tightendown the chucks with an Allen wrench. Install the tapin the opposite chuck of the lathe. Move the ram forwarduntil the tapping tool reaches the inside of the pipe.Center the tapping tool to the interior of the pipe.

- Start the ram and slowly close the tapping tool.Lubricate the tapping tool periodically with metal cuttingfluid as it machines the tapered threads. Reverse theram of the lathe and slowly back the tapping tool out ofthe interior of the pipe. Check the tapered threads witha thread gauge.

- Set the steel plate, with holes drill holes, on the baseplate of the drill press and secure it in place. Insert atapping tool in the chuck of the drill press and securewith a chuck tool. Fill the drilled hole with metal cuttingfluid and slowly lower the tapping tool. Align the tappingtool before machining the tapered threads.

Outside tapered threads

- Insert the pipe in the lathe's chuck and secure it inplace, similar to the way you secured the pipe whenmachining inside tapered threads. Open the mouth ofthe opposite chuck and insert a threading die, insteadof attaching a tapping tool to the opposite chuck.Tighten down the chuck. Align the threading die withthe outside of the pipe.

- Cover both the end of the pipe and the interior of thedie with metal cutting fluid .Start the lathe and closethe ram slowly until it starts machining the taperedthreads. Pour more cutting fluid on the end of the pipeas you continue to close the ram of the lathe. Reversethe lathe ram after reaching the desired thread depth.Checks the threads with the thread gauge.

- Insert the screw, bold or rod in the chuck of the lathe.Install a threading die in the opposite chuck of the latheand machine the tapers threads, similar to the wayyou cut the threads on the outside of the pipe.

Cutting taper thread

Whereas the axial moment required for pitch feed isprovided by the machine, the radial moment required inaddition for producing a tapered thread is obtained by thetool slide feed. Do not clamp the slide by tightening lockingscrew .During thread cutting both the machine feed andthe feed of the head must be in continuous engagement.

Same as per taper turning ,the sensitiveness to release ofretaining pin must be reduced to the minimum by meansof regulating screw stop rod must not be displaced bychanging over from clockwise to anti-clockwise rotationfrom the position held.

Depending on the pitch of thread, taper angles will varywith varying cross feeds. The tool mounting and depthadjustment are same as taper turning attachment method.

The method of operation is the same as for straight threadcutting.

The taper for the taper thread is prepared by using normaltaper turning attachment methods.

Tapers may be produced by any conventional methodsaccording to the requirement and die sets are also usedfor producing taper threads.

Tailstock offset method (Fig 1)


127

In this method the job is held at an angle and the toolmoves parallel to the axis. The body of the tailstock isshifted on its base to an amount corresponding to theangle of taper.

Tail stock set over (Fig 2)

TaperTapers may be produced by any conventional methodsaccording to the requirement and die sets are also usedfor producing taper threads.

The taper can be turned between centres only and thismethod is not suitable for producing steep tapers.Theamount of offset is found by the formula. (Fig 3)

Offset = 2lXLd)(D −

where D = big dia. of taper

d = small dia. of taper

l = taper length

L = total length of job

AdvantagesPower feed can be given

good surface finish can be obtained

maximum length of the taper can be produced

external thread on taper portion can be produced

duplicate tapers can be produced

Disadvantagesonly external taper can be turned

accurate setting of the offset is difficult

taper turning is possible when work is held between cen-tres only.

damages the centre drilled holes of the work.

the alignment of the lathe centres will be disturbed

steep tapers cannot be turned

Calculation of Thread depth formula.BSN - 0.6403 x Pitch

Metric - 0.6134 x Pitch

Square - 0.5 x Pitch

Acme - 0.5 x Pitch

B.A - 0.6134 x Pitch

Buttress - 0.75 x Pitch

Worm thread - 0.68 x Pitch

Taper turning by attachment (Fig 3)

This attachment is provided on a few modern lathes. Herethe job is held parallel to the axis and the tool moves at anangle. The movement of the tool is guided by theattachment.

Taper angle is found by formula (Fig 3)

2l

dDTanφ

−=

AdvantagesBoth internal and external tapers can be produced.

Threads on both internal and external taper portions canbe cut.

Power feed can be given.

lengthy taper can be produced.

Good surface finish is obtained

The alignment of the lathe centres is not disturbed.

It is most suitable for producing duplicate tapers becausethe change in length of the job does not affect the taper.

The job can be held either in chuck or in between centres

Disadvantageonly limited taper angles can be turned.


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Heat treatment of plain carbon steelsObjectives : At the end of this lesson you shall be able to• state the purpose of heat treatment of steel• state the types of structure, constituents and properties of plain carbon steels.

Structure of steel when heated (Fig 2)

If steel is heated, a change in its structure commencesfrom 723° C. The new structure formed is called‘AUSTENITE’. Austenite is non-magnetic. If the hot steelis cooled slowly, the old structure is retained and it will havefine grains which makes it easily machinable.

If the hot steel is cooled rapidly the austenite changes intoa new structure called “MARTENSITE’. This structure isvery fine grained, very hard and magnetic. It is extremelywear-resistant and can cut other metals.

Heat treatment processes and purpose

Because steel undergoes changes in structure on heatingand cooling, its properties may be greatly altered bysuitable heat treatment.

The following are the various heat treatments and theirpurposes.

Hardening To add cutting ability

To increase wear resistance

Tempering: To remove extreme brittlenesscaused by hardening to an extent.

To induce toughness and shockresistance

Annealing: To relieve strain andstress

To eliminate strain/hardness

To improve machinability

To soften the steel

Normalising: To refine the grain structure ofthe steel

Heat treatment and its purpose

The properties of steel depend upon its composition and itsstructure. These properties can be changed to aconsiderable extent, by changing either its composition orits structure. The structure of steel can be changed byheating it to a particular temperature, and then, allowing itto cool at a definite rate. The process of changing thestructure and thus changing the properties of steel, byheating and cooling, is called ‘heat treatment of steel’.

Types of structure of steel (Fig 1)

The structure of steel becomes visible when a piece of themetal is broken. The exact grain size and structure can beseen through a microscope. Steel is classified accordingto its structure.

steel is an alloy of iron and carbon. But the carbon contentin steel does not exceed 1.7%.

Ferrite

Pig iron or steel with 0% carbon is FERRITE which isrelatively soft and ductile but comparatively weak.

Cementite

When carbon exists in steel as a chemical compound ofiron and carbon it is called ‘iron carbide’or CEMENTITE.Thisalloy is very hard and brittle but it is not strong.

Eutectoid/Pearlite steel

A 0.84% carbon steel or eutectoid steel is known asPEARLITE steel. This is much stronger than ferrite orcementite.

Hypereutectoid steel

More than 0.84% carbon steel or hypereutectoid steel ispearlite and cementite.


129

Hardening of carbon steelObjectives : At the end of this lesson you shall be able to• state the hardening of steel• state the purpose of hardening steel• state the process of hardening.

What is hardening?Hardening is a heart-treatment process in which steel isheated to 30-50° C above the critical range, smoking timeis allowed to enable the steel to obtain a uniformtemperature throughout its cross-section. Then the steelis rapidly cooled through a cooling medium.

Purpose of hardeningTo develop high hardness and wear-resistance properties.

Hardening affects the mechanical properties of steel-likestrength, toughness, ductility etc.

Hardening adds cutting ability.

Process of hardeningSteel with a carbon content above 0.4% is heated to 30-50°C above the upper critical temperature. (Fig1) A soakingtime of 5mts./10 mm thickness of steel is allowed. (Fig 1)

Then the steel is cooled rapidly in a suitable medium.Water, oil, brine or air is used as a cooling medium,depending upon the composition of the steel and thehardness required.

Tempering the hardened steelObjectives : At the end of this lesson you shall be able to• state what is tempering• state the purpose of tempering• relate the tempering colours and temperatures with the tools to be tempered• state the process of tempering of steels.

What is tempering?Tempering is a heat-treatment process consisting ofreheating the hardened steel to a temperature below 400°C,followed by cooling.

Purpose of tempering the steelSteel in its hardened condition is generally too brittle to beused for certain functions. Therefore, it is tempered.

The aims of tempering are:

- to relieve the internal stresses

- to regulate the hardness and toughness

- to decrease the brittleness

- to restore some ductility

- to induce shock resistance

Process of tempering the steelThe tempering process consists of heating the hardenedsteel to the appropriate tempering temperature and soakingat this temperature, for a definite period.

The period is determined from the experience that the fulleffect of the tempering process can be ensured only, if thetempering period is kept sufficiently long. Table 1 showsthe tempering temperature and the colour for different tools.


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Annealing of steelObjectives : At the end of this lesson you shall be able to• state the purpose of annealing• state the process of annealing.

The annealing process is carried out by heating the steelabove the critical range, soaking it for sufficient time toallow the necessary changes to occur, and cooling at apredetermined rate, usually very slowly, within the furnace.

Purpose

- To soften the steel

- To improve the machinability

- To increase the ductility

- To relieve the internal stresses

- To refine the grain size and to prepare the steel forsubsequent heat treatment process

Annealing process

Annealing consists of heating of hypoeutectoid steels to 30to 50°C above the upper critical temperature and 50°Cabove the lower critical temperature for hypereutectoidsteels. (Fig 1)

Soaking is holding at the heating temperature for 5 mts/10mm of thickness for carbon steels.

The cooling rate for carbon steel is 100 to 150°C/hr

Steel, heated for annealing, is either cooled in the furnaceitselfby switching off the furnance or its covered with drysand, dry lime or dry ash.

Turning tools 230 Pale strawDrills andmilling cutters 240 Dark strawTaps and shear 250 BrownbladesPunches,reamers, twistdrills 260 Reddish brownRivets,snaps 270 Brown purplePress tools,cold chisels 280 Dark purpleCold set forcutting steels 290 Light blueSprings, screwdrivers 300 Dark blue

320 Very dark blue340 Greyish blue

For tougheningwithout unduehardness 450-700 No colour

TABLE 1

Tools or Temperature Colourarticles in degrees (ºC)


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Normalising of steelObjectives : At the end of this lesson you shall be able to• state the meaning of normalising steel and its purpose• state the process of normalising steel• state the precaution to be taken while normalising steel.

The process of removing the internal defects or to refine thestructure of steel component is called normalising.

Purpose

- To produce fine grain size in the metal

- To remove stresses and strains formed in the internalstructure due to repeated heating and uneven cooling orhammering

- To reduce ductility

- To prevent warping

Process

To get the best results from normalising, the parts shouldbe heated uniformly to a temperature of 30 to 40°C abovethe upper critical temperature (Fig1), followed by cooling instill air, free from drought, to room temperature. Normalizingshould be done in all forgings, castings and work-hardenedpieces.

Precautions

Avoid placing the component in a wet place or wet air,thereby restricting the natural circulation of air around thecomponent. Avoid placing the component on a surface thatwill chill it.

Heating / Quenching steel for heat treatmentObjectives : At the end of this lesson you shall be able to• differentiate between the lower critical and the upper critical temperatures• state the three stages in the heat treatment process• determine the upper critical temperature for different carbon steels from the diagram.

Critical Temperatures

Lower critical temperature

The temperature, at which the change of structure toaustenite starts-723°C, is called the lower criticaltemperature for all plain carbon steels.

Upper critical temperature

The temperature at which the structure of steel completelychanges to AUSTENITE is called the upper criticaltemperature. This varies depending on the percentage ofcarbon in the steel. (Fig 1)

Example

0.57% and 1.15% carbon steel: In these cases the lowercritical temperature is 723°C and the upper criticaltemperature is 800°C.

For 0.84% carbon steel, both LCT and UCT are 723°C. Thissteels is called eutectoid steel.

Three stages of heat treatment

- Heating

- Soaking

- Quenching


132

When the steel on being heated reaches the requiredtemperature, it is held in the same temperature for a periodof time. This allows the heating to take place throughout thesection uniformly. This process is called soaking.

Soaking time

This depends upon the cross-section of the steel, itschemical composition, the volume of the change in thefurnace and the arrangement of the charger in the furnace.A good general guide for soaking time in normal conditionsis five minutes per 10mm of thickness for carbon and lowalloy steels, and 10 minutes per 10 mm of thickness forhigh alloy steels.

Heating steel

This depends on the selection of the furnace, the fuel usedfor heating, the time interval and the regulation in bringingthe part up to the required temperature. The heating rateand the heating time also depend on the composition of thesteel, its structure, the shape and size of the part to beheat-treated etc.

Preheating

Steel should be preheated at low temperature up to 600°Cas slowly as possible.

Quenching

Depending on the severity of the cooling required, differentquenching media are used.

The most widely used quenching media are:

- brine solution

- water

- oil

- air

Brine solution gives a faster rate of cooling while air coolinghas the slowest rate of cooling.

Brine solution (Sodium chloride) gives severe quenchingbecause it has a higher boiling point than pure water, andthe salt content removes the scales formed on the metalsurfaces due to heating. This provides a better contact withthe quenching medium and the metal being heat-treated.

Water is very commonly used for plain carbon steels.While using water as a quenching medium, the workshould be agitated. This can increase the rate of cooling.

The quenching oil used should be of a low viscosity.Ordinary lubricating oils should not be used for thispurpose. Special quenching oils, which can give rapid anduniform cooling with less fuming and reduced fire risks, arecommercially available. Oil is widely used for alloy steelswhere the cooling rate is slower than plain carbon steels.

Cold air is used for hardening some special alloy steels.

Induction hardeningObjectives : At the end of this lesson you shall be able to• state the process of the induction hardening method• state the advantages of the induction hardening process.

Induction hardening

This is a production method of surface-hardening in whichthe part to be surface-hardened is placed within an inductioncoil through which a high frequency current is passed.(Fig 1) The depth of penetration of the heating becomesless, as the frequency increases.

The depth of hardening for high frequency current to1.0mm. The depth of hardening for medium frequencycurrent is 1.5 to 2.0 mm. Special steels and unalloyedsteels with a carbon content of 0.35 to 0.7% are used.

After induction-hardening of the workpieces, stressrelieving is necessary.

The following are the advantages of this type of hardening

- The depth of hardening, distribution in width and thetemperature are easily controllable.

- The time required and distortion due to hardening arevery small.

- The surface remains free from scales.

- This type of hardening can easily be incorporated inmass production.


133

Carburising of steelObjectives: At the end of this lesson you shall be able to• state the process of pack carburising• state the process of liquid carbursing• state the process of gas carburising.

Pack carburising (Fig.1)

The parts are packed in a suitable metal box in which theyare surrounded by the carburising medium, such as wood,bone, leather or charcoal, with barium carbonate as anenergiser.

The lid is fitted to the box and sealed with fireclay and tiedwith a piece of wire so that no carbon gas can escape andno air can enter the box to cause de-carburisation.

Liquid carburising

Carburising can be done in a heated salt bath. (Sodiumcarbonatte,sodium cyanide and barium chloride are typicalcarburising salts). For a constant time and temperature ofcarburising, the depth of the case depends on the cyanidecontent.

This is suitable for a thin case, about 0.25 mm deep. Itsadvantage is that heating is rapid and distortion is minimised,and it is suitable for batch production.

Gas carburising

The work is placed in a gas-tight container which can beheated in a suitable furnace, or the furnace itself may be thecontainer.

The carburising gas ‘methane or propane’s is admitted tothe container, and the exit gas is vented.

Fig 2 illustrates the appearance of the structure across itssection produced by carburising.

Heat treatment

After carburising has been done, the case will contain

Owing to the prolonged heating, the core will be coarse andin order to produce a reasonable toughness, it must berefined.

To refine the core, the carburised steel is reheat about 870°C and held at that temperature long enough to produce auniformitly of structure, and is then rapidly to prevent graingrowth during cooling.

The temperature of this heating is much higher the suitablefor the case, therefore, an extremly brittle martensite will beproduced.

The case and the outer layers of the core must be refined.

The refining is done by reheating the steel about 760º to suitthe case, and quenching it.

Tempering

Finally the case is tempered at about 200° C to relivequenching stresses.

Fig 3 illustrates the apperance of the structure across itssection produced by case hardening.

about 0.9% carbon, and the core will still contain 0.15%carbon. There will be a gradual transition carbon contentbetween the case and the core. (Fig 2)


134

NitridingObjectives: At the end of this lesson you shall be able to• state the process of case hardening by gas nitriding• state the process of case hardening by nitriding in a salt bath.

In the nitriding process, the surface is enriched not withcarbon, but with nitrogen. There are two systems incommon use, gas nitriding and salt bath nitriding.

Gas nitriding

The gas nitriding process consists of heating the parts at500°C in a constant circualtion of ammonia gas for up to100 hours and cooling them in air.

Nitriding in salt bath

Special nitriding baths are used for salt-bath nitriding. Thisprocess is suitable for all alloyed and unalloyed types ofsteel, annealed or not annealed, and also for cast iron.

Process

The completely stress-relieved workpieces are preheated(about 400°C) before being put in the salt bath (about 520-570°C). A layer 0.01to 0.02mm thick is formed on thesurface which consists of a carbon and nitrogen compound.The duration of nitriding depends on the cross-section ofthe workpieces (half an hour to three hours). It is muchshorter than for gas nitriding. After being taken out of the

bath, the workpieces are quenched and washed water anddried.

Advantages

The parts can be finish-machined before nitriding becauseno quenching is done after nitriding, and, therefore, they willnot suffer from quenching distortion.

In this process, the parts are not heated above the criticaltemperature, and, hence warping or distortion does notoccur.

The hardness and wear-resistance are exceptional. Thereis a slight improvement in corrosion resistance as well.

Since the alloy steels, used are inherently strong whenproperly heat-treated, remarkable combinations of strengthand wear-resistance are obtained.


135

Production & Manufacturing Related Theory for Exercise 4.6.150Turner - Advanced TurningInterchangeability meaning, procedure for adoption,quality control procedurefor quality productionObjectives : At the end of this lesson you shall be able to• state the terms used under the BIS system of limits and fits• define each term under the BIS system of limits and fits.SizeIt is a number expressed in a particualr unit in themeasurement of length.

Basic sizeIt is the size based on which the dimensional deviationsare given. (Fig 1)

Actual sizeIt is the size of the component by actual measurementafter it is manufactured. It should be lie between the twolimits of size if the component is to be accepted.

Limits of sizeThese are the extreme permissible sizes within which theoperator is expected to make the component. (Maximumand minimum limits) (Fig 2)

Maximum limit of sizeIt is the greater of the two limits of sizes.(Fig 2) (Table 1)

Minimum limit of sizeIt is the smaller of the two limits of size.(Fig 2) (Table 1)

Table 1(Examples)

Sl. Size of Upper Lower Max.limit Min limit No. component deviation deviation of size of size

+.0081 20

-.005 + 0.008 - 0.005 20.008 19.995

+.0282 20

+.007 + 0.028 - 0.007 20.028 20.007

-.0123 20

-.021 + 0.012 - 0.021 19.988 19.979

HoleIn ths BIS system of limits and fits, all internal features ofa component including those which are not cylindricalare designated as hole. (Fig 3)

ShaftIn the BIS system of limits and fits, all external featuresof a component including those which are not cylindricalare designated as shaft (Fig 3)

DeviationIt is the algebraic difference between a size and itscorresponding basic size. It may be positive, negative orzero.(Fig 2)


136

Upper deviation

It is the algebraic difference between the maximum limitof size and its corresponding basic size.(Fig 2) (Table 1)

Lower deviation

It is the algebraic difference between the minimum limit ofsize and its corresponding basic size.(Fig 2) (Table 1)

Upper deviation is the deviation which gives the maximumlimit of size. Lower deviation is the deviation which givesthe minimum limit of size.

Actual deviation

It is the algebraic difference between the actual size andits corresponding basic size. (Fig 2)

Tolerance

It is the difference between the maximum limit of size andthe minimum limit of size. It is always positive and isexpressed only as a number without a sign.(Fig 2)

Zero line

In the graphical representation of the above terms, thezero line represents the basic size. This lines is also calledthe line of zero deviation .(Figs1 and 2)

Fundamental deviation

There are 25 fundamental deviations in the BIS systemrepresented by letter symbols (capital letters for holesand small letters for shafts),i.e. for holes-ABCD----Zexcluding I,L,O,Q and W. (Fig 4)

In addition to the above, four sets of letters JS, ZA, ZB andZC are included.

For shafts, the same 25 letter symbols but in small lettersare used.(Fig 5)

The fundamental deviations are for achieving the differentclasses of fits.(Figs 8 & 9)

The position of tolerance zone with respect to the zeroline is shown in Figs 6 and 7.


137

Fundamental toleranceThis is also called ‘grade of tolerance’. In the B.I.S. system,there are 18 grades of tolerances represented by numbersymbols both for hole and shaft, denoted as IT01, IT0, IT1,IT2 ______ IT16 (Fig 10)

A higher number gives a larger tolerance.

Grade tolerance refers to the accuracy ofmanufacture.

In a standard chart, the upper and lower deviations foreach combination of fundamental deviation andfundamental tolerance are indicated for sizes ranging upto 500mm. (Refer to IS 919). An extract up to 500 mm isgien in Table 2.

Tolerance sizeThis includes the basic size, the fundamental deviationand the grade of tolerance.

Examples25H7-is the tolerance size of a hole whose basic size is25. The fundamental deviation is represented by the lettersymbol H and the grade of tolerance is represented bythe number symbol 7.(Fig 11)

25 e8 - is the tolerance size of a shaft whose basic size is25. The fundamental deviation is represented by the lettersymbol and the grade of tolerance is represented by thenumber 8. (Fig 12)

A very wide range of selection can be made by thecombination of the 25 fundamental deviation and grades oftolerance.

ExampleIn figure 13, a hole is shown as 25± 0.2which means that25mm is the basic dimension and ± 0.2 is the deviation.

As pointed out earlier, the permissible variation from thebasic dimension is called ‘DEVIATION’.

The deviation is mostly given on the drawing withdimensions.

In the example, 25± 0.2 is the deviation of the hole of 25mmdiameter. (Fig 13) This means that the hole is of acceptablesize if its dimension is between.

25±0.2=25.2 mm; or 25-0.2=24.8 mm

25.2mm is the maximum limit. (Fig 14)


138

24.8 mm is the minimum limit (Fig 15)

The difference between the maximum and minimum limitsis the TOLERANCE. Tolerance here is 0.4 mm. (Fig 16)

All dimensions of the hole within the tolerance zone are ofan acceptable size as shown in Fig 17.

As per IS 696, while dimensioning the components as adrawing convention, the deviations are expressed astolerance.

Fits and their classification as per the Indian standardObjectives : At the end of this lesson you shall be able to• define ‘fit’ as per the Indian standard• list out the terms used in limits and fits as per the Indian standard• state examples for each class of fit• define the graphical representation of different classess of fits.

Fit

It is the relationship exists between two mating parts, ahole and a shaft, with respect to their dimensionaldifferences before assembly.

Expression of a fit

A fit is expressed by writing the basic size of the fit first,(the basic size which is common to both the hole and theshaft) followed by the symbol for the hole, and the symbolfor the shaft.

Example

30 H7 / g6 or 30 H7 - g6 or 30 g6H7

Clearance

In a fit the clearance is the difference between the size ofthe hole and the size of the shaft, when the hole is biggerthan the shaft.

Clearance fit

It is a fit which always provides clearnace. Here thetolerance zone of the hole will be above the tolerance zoneof the shaft. (Fig 1)

Example20 H7 / g6

With the fit given, we can find the deviations from the chart.

For a hole 20 H7 we find in table 2, + 21.

These numbers indicate the deviations in microns.(1 micrometer = 0.001 mm)

The limits of the hole are 20+0.021=20.021mm and20+0=20.000mm. (Fig 2)

for a shaft 20 g6 we find in the Table - 7- 20


139

So the limits of the shaft are

20 - 0.007 = 19.993 mm

and 20 - 0.020 = 19.980 mm. (Fig 3)

Maximum clearanceIn a clearance fit or transition fit, the maximum clearanceis the difference between the maximum size hole and theminimum size shaft. (Fig 4)

Minimum clearanceIn a clearance fit, the minimum clearance is the differencebetween the minimum hole and the maximum shaft. (Fig.4)

The maximum clearance is 20.000 - 19.993 = 0.007mm.(Fig. 4)

The maximum clearance is 20.021 - 19.980 = 0.041mm.(Fig. 4)

There is always a clearance between the hole and theshaft. This is the clearance fit.

InterferenceIt is the difference between the size of the hole and theshaft before assembly, and this is negative. In this case,the shaft is always larger than the hole size.

Interference fitIt is fit which always provides interference. Here thetolerance zone of the the hole will be below the tolerancezone of the shaft. (Fig 5)

ExampleFit 25 H7 / p6 (Fig 6)


The limits of the hole are 25.000 and 25.035mm. and thelimits of the shaft are 25.022 and 25.035. The shaft isalways bigger than the hole. This is an interference fit.

Maximum interferenceIn an interference fit, it is the algebraic difference betweenthe minimum hole and the maximum shaft. (Fig 7)


140

Minimum interferenceIn an interference fit, it is the algebraic difference betweenthe maximum hole and minimum shaft. (Figs 7 and 8).

In the example shown in figure 6.

the maximum interference is = 25.035-25.000

= 0.035

the minimum interference is = 25.022-25.021

= 0.001

Transition fitIt is a fit which may sometimes provide clearance, andsometimes interference. When this class of fit isrepresented graphically, the tolerance zones of the holeand shaft will overlap each other. (Fig 8)

ExampleFit 75 H8 / j7 (Fig 9)

The limits of the hole are 75.000 and 75.046 mm and thoseof the shaft are 75.018 and 74.988 mm.

Maximum clearance = 75.046 - 74.988= 0.058 mm.

If the hole is 75.000 and the shaft 75.018 mm, the shaft is0.018mm bigger than the hole. This results in interference.This is a transition fit because it can result in a clearancefit or an interference fit.

Hole basis systemIf a standard system of limits and fits, where the size ofthe hole is kept constant and the size of the shaft is variedto get the different classes of fits, it is known as the holebasis system.

The fundamental deviation symbol ‘H’ is chosen for theholes, when the hole basis system is followed. This isbecause the lower deviation of the ‘H’ hole is zero. It isknown as the “basic hole”. (Fig 10)

Shaft basis systemIn a standard system of limits and fits, where the size ofthe shaft is kept constant and the variations are given tothe hole for obtaining different classes of fits, then it isknown as shaft basis system. The fundamental deviationsymbol ‘h’ is chosen for the shaft when the shaft basis isfollowed. This is because the upper deviation of the ‘h’shaft is zero. It is known as the ‘basic shaft’. (Fig 11)

The hole basis system is removed mostly. This is because,depending upon the class of fit, it will be always easier toalter the size of the shaft as it is external, but it is difficultto do minor alterations to a hole. Moreover the hole can beproduced by using standard toolings.

The three classes of fits, both under the hole basis andthe shaft basis, are illustrated in Fig 12.


141

The B. I. S system of limits and fits - reading the standard chartObjective : At the end of this lesson you shall be able to• refer to the standard limit system chart and determine the limits of sizes.

The standard chart covers sizes up to 500 mm (I.S.919 of1963) for both holes and shafts. It specifies the upper andlower deviations for a certain range of sizes for allcombinations of the 25 fundamental deviations, and 18fundamental tolerances.

The upper deviation of the hole is denoted as ES and thelower deviation of the hole is denoted as EI. The upperdeviation of the shaft is denoted as ‘es’ and the lowerdeviation of shaft is denoted as ‘ei’.

es is expanded as ECART SUPERIOR and ei asECART INFERIOR.

Determining the limits from the chartNote whether it is an internal measurement or an externalmeasurement.

Note the basic size.

Note the combination of the fundamental deviation andthe grade of tolerance.

The deviations which are given in microns, with the sign.Accordingly add or subtract from the basic size anddetermine the limits of size of the compnents.

Example30H7 (Fig 1)

It is an internal measurement. So we must refer to thechart for ‘holes’.

Look for es, and ei values in microns for H7 combinationfor 30mm basic size.

It is given as + 25 + 0

Therefore, the maximum limit of the hole is 30 + 0.025 =30.025 mm

The minimum limit of the hole is 30 + 0.000 = 30.000 mm.

Refer to the chart and note the values of 40 g6.

The table for tolerance zones and limits as perIS2709 is attached. (Table 1)


142

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10+7

10 E

up to

140

+92

+63

-450

-510

-710

-117

-88

+200

+260

+460

mm

Ove

r14

0+1

25+9

0+6

8+5

2+2

8+1

2.5

00

00

-14

-43

-85

-145

-210

-280

-520

-85

-50

-28

-12

+12

+20

+40

+63

+100

+250

+54

+106

+185

+305

+460

+530

+770

up to

160

+100

+65

+43

+27

+3-1

2.5

-25

-40

-100

-250

-39

-83

-148

-245

-460

-530

-770

-125

-90

-68

-52

-28

-20

00

00

+14

+43

+85

+145

+210

+280

+520

Ove

r16

0+1

33+9

3-2

30-3

10-5

80-9

3-5

3+4

80+5

60+8

30up

to18

0+1

08+6

8-4

80-5

60-8

30-1

33-9

3+2

30+3

10+5

80

Ove

r18

0+1

51+1

06-2

40-3

40-6

60-1

05-6

0+5

30


143

Mass production and interchangeable manufactureObjectives: At the end of this lesson you shall be able to• state the advantages and disadvantages of mass production• outline the meaning of the term, interchangeability• state the necessity for the limit system.

Mass production

Mass production means production of a unit, componentor part in large numbers.

Advantages of mass production

Time for the manufacture of components is reduced

The cost of a piece is reduced

Spare parts can be made available quickly

Gauges are used to check the components

Even unskilled workers can be employed for checking

Measuring time is saved

Disadvantages of mass production

Special purpose machines are necessary

Jigs and fixtures are needed

Gauges are to be used, hence the initial expenditure willbe high

Selective assembly

Figures 1&2 illustrate the difference between a selectiveassembly and a non-selective assembly. It will be seen inFig 1 that each nut fits only one bolt. Such an assemblyis slow and costly, and maintenance is difficult becausespares must be individually manufactured. spares mustbe individually manufactured.

Non-selective assembly provides interchangeabilitybetween the components.

In modern engineering production, i.e. mass production,there is no room for selective assembly. However, insomespecial circumstances, selective assembly is still justified.

Interchangeability

When components are mass-produced, unless they areinterchangeable, the purpose of mass production is notfulfilled. By interchangeability, we mean that identicalcomponents, manufactured by different personnel underdifferent environments, can be assembled and replacedwithout any rectification during the assembly stage andwithout affecting the functioning of the component whenassembled.

Necessity of the limit system

If components are to be interchangeable, they need to bemanufactured to the same identical size which is notpossible, when they are mass-produced. Hence, itbecomes necessary to permit the operator to deviate by asmall margin from the exact size which he is not able tomaintain for all the components. At the same time, thedeviated size should not affect the quality of the assembly.This sort of dimensioning is known as limit dimensioning.

A system of limits is to be followed as a standard for thelimit dimensioning of components.Non-selective assembly

Any nut fits any bolt of the same size and thread type.Such an assembly is rapid, and costs are reduced.

Maintenance is simpler because spares are easilyavailable. (Fig 2)


144

Quality controlObjectives : At the end of this lesson you shall be able to• state the features of quality control• state the meaning of quality control• sate the different factors of quality control• state the recent trends in quality control• state the different levels of inspection.

Quality control

The quality of a product is generally defined as itsusefulness towards the purpose for which it ismanufactured. In other words 'Fitness for use'.

In olden days, the manufacture of a product was in batchesie., in smaller quantities, not exceeding say 10 or 100.In this case, the components were made to fit each otherthrough an inspection process, where the good ones weresegregated from the bad.

With the advent of mass production, this method ofinspection caused a lot of rejections and themanufacturers started to use preventive inspection wherein measures were taken to reduce the rejection to almostzero.

Thus, one started hearing about the concept of `zerodefects'. The aim of the inspection is to prevent rejection.This new approach towards producing products fit for use,without the rejection losses and re–work called for theimposition of controls at different stages of the manufactureof a component. These controls ensured the requiredquality, and thus quality control became an importantactivity in the industries.

It is thoroughly understood today that quality starts fromthe customer and ends with the customer. Thus, thecustomer has become a very important person in the mindsof the manufacturers of consumables and other products.So the quality of a product has to be built into the productat the following stages. (Fig 1)

Product specification

The details regarding the product in question are collectedfrom the probable consumers (users) by the staff of themarketing and sales departments.

These details should truly reflect the requirements andaspirations of the users. Thus, the conformance of thereal use with the product specification is the first step ofquality control.

Technical specificationThe product specifications are scrutinized by variousexperts from the production and product servicedepartments. Based on the recommendations of theseexperts the technical specifications are prepared to veryminute details.

The correspondence between the product specification andthe technical specification is the second quality step.

Manufacturing the product, including packing andforwarding to the customerFor the manufacture of the product the right type of rawmaterial, machinery and manpower should be involved sothat the end product conforms to the technicalspecifications. Moreover, the product thus produced shouldreach the consumer without any damage.

This forms the third quality step.

Thus, quality control is the culmination of all these activitiesrequired for defining, quantifying, effecting and measuringthe quality of the product. The main objective of qualitycontrol is to achieve fitness for use at the lowest cost.

This calls for an understanding of the following points.

- There is always an optimum quality level.

- All personnel in an enterprise are responsible for thequality of a product.

- The quality must be controlled and built in at thevarious stages planned. This requires well organisedcooperation between all the departments in theenterprise.

- There is one quality level that strikes the optimumlevel between the utility and cost of product, as shownin Fig 2.

The two parameters, utility and cost in the graph, conformto the following basic laws.

Utility increases with increase in quality but the trend isdecreasing beyond the optimum quality level. This is thelaw of the decreasing marginal utility.


145

The cost does also increase with increasing quality. Theincrease is progressive.

This is the law of increasing marginal cost.

When the design is finalised and production starts, thecost of the product quality can be illustrated as in thegraph. (Fig.3) A well controlled and efficient productionrequires less inspection effort and vice versa. It is the totalcost of the production and the inspection/rejection thathas to be kept at a minimum. It is hence important toavoid sub-optimising ie., keeping one or the otherparameter at a minimum. It is hence important to avoidthis. From the graph it is also evident that too high or toolow a quality is uneconomical.

The optimum quality should be estimated from the totalcost.

Total costs cannot be precisely computed, due to practicallimitations in estimating and accounting, but it is obviousthat the cost should include more than that of the qualityand inspection function. In fact, it should include all thefunctions.

If all the functions are influencing the optimum quality,they are also responsible for the quality.

The old concept of quality control was that the inspectionor quality department was responsible for the quality. Thisconcept still persists to a considerable extent.

This concept is wrong and is emanating from thesecondary duty of inspection. Namely, to sort out faulty

component or products and ensure an economical qualitylevel after the inspection. This is however a postmortemactivity and the primary duty of the inspection is to helpother functions to prevent mistakes.

This is done by monitoring the quality in the differentsteps and at different stages, and feed back thisinformation to the concerned functions.

This monitoring should be based on costs, and penetratedown to processes and operations so that detailedinformation on quality costs are obtained.

Quality costs are mostly classified as follows.

Quality costs are often quite substantial and surveys ofthe European and American markets have found thataspect.

The quality costs are collected and presented to theconcerned parties. This is the ground for improvementand control. (Fig.4)

It must be possible to apply control of quality in all phasesof market use, design and production and a good qualitycost reporting system will indicate where the costs arehigher.

When the weak quality spots (where failure costs are high)are located, all the concerned parties must work togetherand find solutions for correcting and controlling the problemwith the drastic developments in technology, the user ie.the consumer is better placed today to demand reliabilityof the product (ie. failure-free performance of the productover a period of time). So the manufacturer has to widenthe sphere of quality control activities to quality assuranceand reliability, due to the stiff competition amongst themanufacturers.The concept 'Looks first and functionforemost', is one way to stress the need for improving thelooks of a product. The importance of appearance of theproduct and its dependable function is today being stressedand realized all over. Only then, can one compete in theinternational market.

Inspection costs Rejection costs

Labour, equipment Internal External and overhead for

Preventive Segregation Rejections Guarantee

Inspection Re-work Service

Delay Distance

Consequen- goodwilltial costs, etc. loss, etc.

Quality costs


146

We may find in the near future that quality control hasgiven way to the new concept namely Quality Engineeringwherein, the emphasis would be on the usefulness of aproduct, not only for the individuals but also for theentire humanity.

The occurance of non–florification trading on nuclearweapons is an apt example of such an understandingwith regard to the quality of a product.

Quality control

What is quality control?Quality control is a set of methods used by organizationsto achieve quality parameters or quality goals andcontinually improve the organization 's ability to ensurethat a software product will meet quality goals.

Quality control process (Fig.5)

The three class parameters that control software qualityare:

– Products– Processes– Resources

The total quality control process consists of :

– Plan - It is the stage where the quality control processesare planned.

– Do- Use a defined parameter to develop the quality.

– Check- Stage to verify of the quality of the parametersare met.

– Act- Take corrective action if needed and repeat thework.

Quality control characteristics– Process adopted to deliver a quality product to the

clients at best cost.

– Goal is to learn from other organizations so that qualitywould be better each time.

– To avoid making errors by proper planning andexecution with correct review process.

Quality control basic conceptsIn this article I explain three fundamental concepts thatevery buyer should be familiar with when it comes to qualityinspections:

1 Inspection levels

2 The AQL

3 When to inspect?

After 10 minutes, you will be able to understand thereliability of an inspector's findings and take more informeddecisions based on an inspection report.

If you have not started doing professional quality control,you will need to understand these 3 concepts to makesure the inspection plan meets your needs.

1 Inspection levelsWhy use random sampling?Shipments often represent thousands of products.Checking 100% of the quality would be long and expensive.A solution is to select samples at random and inspectthem, instead of checking the whole lot.

But how many samples to select? On the one hand.Checking only a few pieces might prevent the inspectorfrom noticing quality issues; on the other hand, theobjective is to keep the inspection short by reducing thenumber of samples to check.

The relevant standards purpose a standard severity, called"normal level", which is designed to balance these twoimperatives in the most efficient manner.

Within this normal severity, there are three general levels:I, II, and III. Level II is used for more than 90% ofinspections. For example, for an order of 8.000 products,only 200 samples are checked.

Military Standard 105 was created by the US Departmentof Defence to control their procurements more efficiently.In 1994 they decided to relay on non-governmentalorganizations to maintain this type of standard. The ANSI,ISO, and other institutes have created their own standard,but in essence they are similar. The major third -party QCfirms use the same standards and the same statisticaltables.

When to adopt a different level

Suppose you source a product from a factory that oftenships substandard quality. You know that the risk is higherthan average. How to increase the Discriminating powerof the inspection? You can opt for level III, and moresamples will be checked.

Similarly, if a supplier has consistently delivered acceptableproducts in the past and keeps its organization unchanged,you can choose level I. As fewer samples have to bechecked, the inspection might take less time and becheaper.

The relevant standards give no indication about when toswitch inspection levels, so most importers rely on their"gut feeling".

The "special levels"Inspectors frequently have to perform some special testson the products they are checking. In some cases thetests can only be performed on very few samples, for tworeasons:


147

1 They might take a long time (e.g. doing a full functiontest as per claims on the retail box).

2 They end up in product destruction. (E.g. unstitching ajacket to check the lining fabric).

For these situations only, the inspector can choose a"special level".

So we have three "general" inspection levels, and four"special levels". For a given order quantity, each level givesa different number of samples to check. Let's see how itplays in two examples.

2 The AQL (acceptance quality limit)In part 1, we explained the different inspection levels thatcan be used. Another basic concept rings familiar to manyimporters, but is often not clearly understood: the AQL(Acceptance Quality Limit).

There is no such thing as zero defectFirst, as a buyer, you have to know what proportion ofdefects is tolerated on your market. If you are in the aviationbusiness, any defective part might cause a disaster, soyour tolerance will be very, very low. But you will have toaccept a higher percentage of defects if you sourceconsumer products that are assembled by hand in chinaor in India.

An objective limit is necessarySo, how many defects are too many? It is up to you, as abuyer, to make this decision. There are two reasons whyyou should not leave this to the inspector's judgment:

1 When it comes to giving instruction to an inspector,you should never leave gray areas-as they might openthe door to corruption.

2 Your supplier should have clear criteria for acceptability,or they will see rejections as unfair.

The AQL is the proportion of defects allowed by the buyer.It should be communicated to the supplier in advance.

The three categories of defectsSome defects are much worse than others. Threecategories are typically distinguished:

- Critical defects might harm a user or cause a wholeshipment to be blocked by the customs.

- Major defects are not accepted by most consumers,who decide not to buy the product.

- Minor defects also represent a departure fromspecifications, but some consumers would still buythe product.

For most consumer products, critical defects are notallowed, and the AQL for major defects and minor defectsare 2.5% and 4.0% respectively.

Some important remarks- A professional inspector will notice defects and evaluate

their category by himself. But it is better if the buyerhimself describes the most frequent defects andassigns categories to each one.

- Defects can be on the product itself, on the labeling oron the packaging.

- If one sample presents several defects, only the mostsevere one is counted.

How to read the AQL tablesThe master tables included in the relevant standards arecommonly called AQL tables. Let's take an example.You buy 8.000 widgets from a factory, and you chooseinspection level II. In the table below (which is only validfor single sampling plans), you see that the correspondingletter is L.Now let's turn to the next table (which is only appropriatefor normal-severity inspections). The letter L gives you thenumber of samples to draw at random: 200 pcs.And what about the AQL? Let's say you follow the usualpractice of tolerating 0% of critical defects, 2.5% of majordefects, and 4.0% of minor defects. The maximumacceptable number of defects is 10 major and 14 minor.In other words, the inspection is failed if you find at least 1critical defect and /or at least 11 major defects and /or atleast 15 minor defects.

3 When to inspect?The first two parts focused on the different inspection levelsand on the AQL tables. So you Know how to set the numberof samples to check and how many defects have to beaccepted. With these setting and your detailed productspecifications, a QC inspector can check your productsand reach a conclusion (passed or failed).

But importers face one more question when should theproducts be inspected? This is an extremely importantissue for buyers willing to secure their supply chain.Spending a few hundreds of dollars to check and fix issuesearly can be an excellent investment; if might save youweeks of delay, shipments by air, and /or lower qualityproducts that you have to accept and deliver to your owncustomers.

Four types of inspectionsLet's picture the simplified model where one factory turnsraw materials into finished products. (If you also have tomanage the quality of sub = suppliers' products, the samemodel can be applied to them)

Pre-production inspectionThis type of inspection is necessary if you want to checkthe raw materials or components that will be used inproduction. Buying cheaper materials can increase afactory's margin considerably, so you should keep an eyeon this risk. It can also be used to monitor the processesfollowed by the operators.

During production inspectionThis inspection allows you to get a good idea of averageproduct quality, and to ask for corrections if problems arefound. It can take place as soon as the first finishedproducts get off the line, but these samples might not berepresentative of the whole. So usually an inspection duringproduction is done after 10-30% of the products are finished.


148

DATE BY ACCEPTED REJECTED

INSPECTION RECORD

ACCEPTED

Customer _______________________

W.O No __________________________

No PCB __________________________

Part No. __________________________

Inspector __________________________

Commented _______________________

INSPECTED

READYTO USE

SIGNED BY ___________________

DATE ______________

Final (pre-shipment) inspectionInspecting the goods after they are made and packed isthe standard QC solution of most importers. The inspectorcan really check every detail, including counting the totalquantity and confirming the packaging. Final inspectionsare usually performed in a hurry, just before shipment. Toavoid creating delays, inspectors can usually start afterall products are finished and 80% + of the shipment quantityis packed.

Loading supervisionIn some cases, a buyer wants to make sure the factoryships the right products, in the right quantity, and with theright loading plan.

Records maintained in shop floor by a workerJob card: Each and every job is accompanied by jobcard in a industry. The job card is very important documentto be maintained by an operator. It include the followingdetails.

1 Document No

2 Date

3 Customer Name

4 Work order No

5 Operator Name

6 Time Record

7 Operation Name / Number

8 Quantity etc

Inspection recordThe record is used for inspecting the workpiece by theoperator or quality inspector.

1 Date of Inspection

2 Name of the component

3 Inspected by (Operator/ Inspector)

4 Quantity accepted/Rejected

5 Rework details if any

Accepted / Rejected / Rework tag : After inspecting thework piece, accepted tag is enclosed with sign and date ifthe work pieced are accepted and rejected tag is enclosedis the pieces are rejected. If there is any rework, reworktag is enclosed. The rework tag has the details of reworkto be done.


149

Surface qualityObjectives: At the end of this lesson you shall be able to• state the meaning of roughness value• state the parameters on which surface quality depends• state the method of measuring roughness• define the symbols for surface roughness.

When components are produced either by machining or byhand processes, the movement of the cutting tool leavescertain lines or patterns on the work surface. This is knownas surface texture. These are, in fact, irregularities, causedby the production process with regular or irregular spacingwhich tend to form a pattern on the workpiece.(Fig 1)

The components of surface texture

Roughness (Primary texture)

The irregularities in the surface texture result from theinherent action of the production process. These willinclude traverse feed marks and irregularities within them.(Fig 2a)

Waviness (Figs 2b & 2c)

This is the component of the surface texture upon whichroughness is superimposed. Waviness may result frommachine or work deflections, vibrations, chatter, heattreatment or warping strain.

The requirement of surface quality depends on the actualuse to which the component is put.

Examples

In the case of slip gauges (Fig 3) the surface texture hasto be extremely fine with practically no waviness. This willhelp the slip gauges to adhere to each other firmly whenwrung together.


150

‘Ra’ ValuesThe most commonly used method of expressing thesurface texture quality numerically is by using Ra value.This is also known as centre line average (CLA).

The graphical representation of Ra value is shown inFigures 6 & 7. In Figure 6 a mean line is placed cuttingthrough the surface profile making the cavities below andthe material above equal.

The cylinder bore of an engine (Fig 4) may require a certaindegree of roughness for assisting the lubrication needed forthe movement of the piston.

For sliding surfaces the quality of surface texture is veryimportant.

When two sliding surfaces are placed one over the other,initially the contact will be only on the high spots. (Fig 5)These high spots will wear away gradually. This wearingaway depends on the quality of the surface texture.

Due to this reason it is important to indicate the surfacequality of components to be manufactured.

The surface texture quality can be expressed and assessednumerically.

The profile curve is then drawn along the average line so thatthe profile below this is brought above.

A new mean line (Fig 7) is then calculated for the curveobtained after folding the bottom half of the original profile.

The distance between the two lines is the ‘Ra’ value of thesurface.

The ‘Ra’ value is expressed in terms of micrometre(0.000001) or (m); this also can be indicated in thecorresponding roughness grade number, ranging from N1 toN12.

When only one ‘Ra’ value is specified, it represents themaximum permissible value of surface roughness.


151

Example showing

__ Lay approximately parallel to the __ line representing the surface to

which, the symbol is applied.

⊥ Lay approximately perpendicularto the line representing the surfaceto which the symbol is applied

X Lay angular in both direction to linerepresenting the surface to whichthe symbol is applied.

M Lay multidirectional.

Lay: Symbols for designating the direction of lay are shown and interpreted in table 1.

TABLE 1

Direction of tool marksInterpretation

C Lay approximately circular relative to thecentre of the surface to which the symbolis applied.

R Lay approximately radial relative to thecentre of the surface of which the symbolis applied.

P Lay particulate, non-directional, orprotuberant.


152

Surface texture measuring instrumentsObjectives: At the end of this lesson you shall be able to• distinguish the features of mechanical and electronic surface indicators• name the parts of a mechanical surface indicator• brief the features of electronic surface indicators (taly-surf).

The use of surface finish standards which we have seenearlier is only a method of comparing and determining thequality of surface. The result of such measurement verymuch depends on the sense of touch and cannot be usedwhen a higher degree of accuracy is needed.

The instruments used for measuring the surface texturecan be of a mechanical type or with electronic sensingdevice.

Mechanical surface indicator

This instrument consists of the following features. (Fig 1)

1 Measuring stylus

2 Skids

3 Indicator scale

4 Adjustment screw

The stylus is made of diamond, and its contact point willhave a light radius.

When the stylus is slowly traversed across the test surfacethe stylus moves upward or downward depending on theprofile of the surface. (Fig 2) This movement is amplifiedand transferred to the dial of the surface indicator.Thepointer movement indicates the surface irregularities.

When using a mechanical surface indicator, measurementmust be read as it is moved over the surface, and then aprofile curve is drawn manually to compute the mean value.

There are different types of electronic surface measuringdevices; one type of such an instrument used in workshopsis the taly-surf.

Taly-surf (Electronic surface indicator): This is anelectronic instrument for measuring surface texture. Thisinstrument can be used for factory and laboratory use.(Fig 3)

The measuring head of this unit consists of a stylus (a)and a motor race (b) which controls the movement of theinstrument head across the surface. The movement of thestylus is converted to electrical signals. These signalsare amplified in the surface analyser/amplifier (c) whichcalculates the surface parameter and presents the resulton a digital or in the form of a diagram through a recorder(d).


153

Machining symbolsObjectives: At the end of this lesson you shall be able to• state the values of surface roughness• state the indication of surface roughness.

Surface symbol indication1 The basic symbol consists of two legs of unequal length

inclined at approximately 60°.

2 If the material removal by machining is required, a baris added to the basic symbol.

3 If the material removal is not permitted, a circle is addedto the basic symbol.

4 If some special characteristics have to be indicated, aline is added to the larger leg.

Letter symbols for tolerancesIndication of surface roughness values.

S. No. Roughness value Roughness grade Roughness Manufacturing processRa in microns Number Symbol

1. 50 N12 Flame cutting, hacksaw cut, bandsawcut, shot blast etc.

2. 25.0 N11 Sand casting, planning, shapingfilling etc.

3. 6.3 N9 Milling, drilling, die casting, turning,3.2 N8 forging, boring etc.1.6 N7

4. 0.8 N6 Centreless grinding, cylindrical grinding,0.4 N5 cold rolling, internal grinding, extrusion,0.2 N4 surface grinding, broaching, hobbing

EDM, reaming etc.

5. 0.1 N3 0.05 N2 Super finishing, lapping honning etc.

0.025 N1


154

5 Indication of surface roughness

a. Surface roughness obtained by any productionmethod.

b. Surface roughness obtained by removal of materialby matching.

b. Surface roughness obtained by removal of materialby matching.

6 Indication of special surface roughness characteristics

a. Indicating the production method.

b. Indicating the surface treatment or coating. Unlessotherwise stated, the numerical value of theroughness, applies to the surface roughness aftertreatment of coating.

c. Indicating the sampling length.

d. Direction of lay, surface pattern by the productionmethod employed.

e. Indication of allowance in mm.

Surface texture


155

LappingObjectives: At the end of this lesson you shall be able to• state the purpose of lapping• state the features of a flat lapping plate• state the use of charging a flat lapping plate• state the method of charging a cast iron plate• explain between wet lapping and dry lapping.

Lapping is a precision finishing operation carried out usingfine abrasive materials.

Purpose: This process

– improves geometrical accuracy

– refines surface finish

– assists in achieving a high degree of dimensionalaccuracy

– improve the quality of fit between the matingcomponents.

Lapping process: In the lapping process small amount ofmaterial are removed by rubbing the work against a lapcharged with a lapping compound. (Fig 1)

Lap materials and lapping compounds

The material used for making laps should be softer than theworkpiece being lapped. This helps to charge the abrasiveson the lap. If the lap is harder than the workpiece, theworkpiece will get charged with the abrasives and cut thelap instead of the workpiece being lapped.

Laps are usually made of:

– close grained iron

– copper

– brass or lead

The best material used for making lap is cast iron, but thiscannot be used for all applications.

When there is excessive lapping allowance, copper andbrass laps are preferred as they can be charged moreeasily and cut more rapidly than cast iron.

Lead is an inexpensive form of lap commonly used forholes. Lead is cast to the required size on steel arbor.These laps can be expanded when they are worn out.Charging the lap is much quicker.

Lapping abrasives: Abrasives of different types are usedfor lapping.

The commonly used abrasives are:

– Silicon Carbide

– Aluminium Oxide

– Boron Carbide and

– Diamond

Silicon carbide: This is an extremely hard abrasive. Itsgrit is sharp and brittle. While lapping, the sharp cuttingedges continuously break down exposing new cuttingedges. Due to this reason this is considered as very idealfor lapping hardened steel and cast iron, particularly whereheavy stock removal is required.

Aluminium oxide: Aluminium oxide is sharp and tougherthan silicon carbide. Aluminium oxide is used in un-fusedand fused forms. Un-fused alumina (aluminium oxide)removes stock effectively and is capable of obtaining highquality finish.

Fused alumina is used for lapping soft steels and non-ferrous metals.

Boron carbide: This is an expensive abrasive materialwhich is next to diamond in hardness. It has excellentcutting properties. Because of the high cost, it is used onlyin specialised application like dies and gauges.

Diamond: This being the hardest of all materials, it is usedfor lapping tungsten carbide. Rotary diamond laps are alsoprepared for accurately finishing very small holes whichcannot be ground.

Lapping vehicles: In the preparation of lapping compoundsthe abrasive particles are suspended in vehicles. Thishelps to prevent concentration of abrasives on the lappingsurfaces and regulates the cutting action and lubricatesthe surfaces.

The commonly used vehicles are

– water soluble cutting oils

– vegetable oil

– machine oils

– petroleum jelly or grease

– vehicles with oil or grease base used for lapping ferrousmetals.

Metals like copper and its alloys and other non-ferrousmetals are lapped using soluble oil, bentomite etc.

In addition to the vehicles used in making the lappingcompound, solvents like water, kerosene, etc. are alsoused at the time of lapping.


156

Abrasive of varying grain sizes from 50 to 800are used for lapping, depending on the surfacefinish required on the component.

The lapping compound consists of fine abrasive particlessuspended in a ‘vehicle’ such as oil, paraffin, grease etc.

The lapping compound which is introduced between theworkpiece and the lap chips away the material from theworkpiece. Light pressure is applied when both are movedagainst each other. The lapping can be carried out manuallyor by machine.

Hand lapping of flat surfaces: Flat surfaces are hand-lapped using lapping plate made out of close grained castiron. (Fig.2) The surface of the plate should be in a trueplane for accurate results in lapping.

The lapping plate generally used in tool rooms will havenarrow grooves cut on its surface both lengthwise andcrosswise forming a series of squares.

While lapping, the lapping compound collects in theserrations and rolls in and out as the work is moved.

Before commencing lapping of the component, the castiron plate should be CHARGED with abrasive particles.

This is a process by which the abrasive particles areembedded on to the surfaces of the laps which arecomparatively softer than the component being lapped.For charging the cast iron lap, apply a thin coating of theabrasive compound over the surface of the lapping plate.

Use a finished hard steel block and press the cuttingparticles into the lap. While doing so, rubbing should bekept to the minimum. When the entire surface of thelapping plate is charged, the surface will have a uniformgray appearance. If the surface is not fully charged, brightspots will be visible here and there.

Excessive application of the abrasive compoundwill result in the rolling action of the abrasivebetween the work and the plate developinginaccuracies.

The surface of the flat lap should be finished true byscraping before charging. After charging the plate, wash offall the loose abrasive using kerosene.

Then place the workpiece on the plate and move along andacross, covering the entire surface area of the plate. Whencarrying out fine lapping, the surface should be kept moistwith the help of kerosene.

Wet and dry lapping : Lapping can be carried out eitherwet or dry.

In wet lapping there is surplus oil and abrasives on thesurface of the lap. As the workpiece, which is being lapped,is moved on the lap, there is movement of the abrasiveparticles also.

In dry method the lap is first charged by rubbing theabrasives on the surface of the lap. The surplus oil andabrasives are then washed off. The abrasives embedded onthe surface of the lap will only be remaining. The embeddedabrasives act like a fine oilstone when metal pins to belapped are moved over the surface with light pressure.However, while lapping, the surface being lapped is keptmoistened with kerosene or petrol. Surfaces finished bythe dry method will have better finish and appearance.Some prefer to do rough lapping by wet method and finishby dry lapping.

Honing

Honing is a finishing process, in which a tool called honecarries out a combined rotary and reciprocating motionwhile the work piece does not perform any working motion.Most honing is done on internal cylindrical surface, such asautomobile cylindrical walls. The honing stones are heldagainst the work piece with controlled light pressure. Thehoning head is not guided externally but, instead, floats inthe hole, being guided by the work surface (Fig.3) It isdesired that

1 Honing stones should not leave the work surface2 Stroke length must cover the entire work length.

In honing rotary and oscillatory motions are combined toproduce a cross hatched lay pattern as illustrated in Fig.3.


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Honing tool

Lay pattern produced by combination of rotary and oscillatorymotion. (Fig.4)

The honing stones are given a complex motion so as toprevent every single grit from repeating its path over thework surface.

The critical process parameters are

1 Rotation speed

2 Oscillation speed

3 Length and position of the stroke

4 Honing stick pressure

With conventional abrasive stick, several strokes arenecessary to obtain the desired finish on the work piece.However, with introduction of high performance diamondand CBN grits it is now possible to perform the honingoperation in just one complete stroke. Advent of preciselyengineered microcrystalline CBN grit has enhanced thecapability further. Honing stick with microcrystalline CBNgrit can maintain sharp cutting condition with consistentresults over long duration.

Super abrasive honing stick with monolayer configuration,where a layer of CBN grits are attached to stick by agalvanically deposited metal layer, is typically found insingle stroke honing application.

With the advent of precision brazing technique, efforts canbe made to manufacture honing stick with single layerconfiguration with a brazed metal bond. Like brazedgrinding wheel such single layer brazed honing stick areexpected to provide controlled grit density, larger gritprotrusion leading to higher material removal rate andlonger life compared to what can be obtained with agalvanically bonded counterpart.

The important parameters that affect material removal rate(MRR) and surface roughness (R) are:

1 Unit pressure, P

2 Peripheral honing speed, Vc

3 Honing time, T


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Production & Manufacturing Related Theory for Exercise 4.6.151-152Turner - Advanced Turning

Importance of Technical term used in IndustryObjectives : At the end of this lesson you shall be able to• state the meaning of different terms used in industry• calculate the machine time in turning.

Engineering terminology

Broach (v) to finish the inside of a hole to a shape otherthan round, as in a keyway (n) The tool for the process,which has serrated edges and is pushed or pulled throughthe hole to produce the required shape.

Bushing (n) a smooth walled bearing (AKA a plainbearing). Also a tool guide in a jig or fixture.

Cam (n) A mechanical device consisting of an eccentricor multiply curved wheel mounted on a rotating shaft, usedto produce variable or reciprocating motion in anotherengaged for contacted part (Cam follower). Also Camshaft

Casting (n) any object made by pouring molten metal intoa mold.

Chamfer (n) a flat surface made by cutting off the edge orcorner of a object (bevel) (v) the process of creating achamfer.

Clevis (n) A U-shaped piece with holes into which a link isinserted and through which a pin or bolt is run. It is usedas a fastening device which allows rotational motion.

Collar (n) A Cylindrical feature on a part fitted on a shaftused to prevent sliding (axial) movement.

Collet (n) a cone-shaped sleeve used for holding circularor rod like pieces in a lathe or other machine.

Core (v) to form the hollow part of a casting, using a solidform placed in the mould (n) the solid form used in thecoring process, often made of wood, sand, or metal. Mouldwith core is final cast manifold.

Counter bore (n) a cylindrical flat-bottomed hole, whichenlarges the diameter of an existing pilot hole. (v) Theprocess used to create that feature.

Countersink (n) a conical depression added to an existinghole to accommodate and the conic head of a fastenerrecessing it below the surface of a face. (v) The processused to create that feature.

Coupling (n) A device used to connect two shafts togetherat their ends for the purpose of transmitting power. Maybe used to account for minor misalignment or for mitigatingshock loads.

Die (n) one of a pair of hardened metal plates or impressingor forming desired shape. Also, a tool for cutting externalthreads.

Face (v) to machine a flat surface perpendicular to theaxis of rotation of a piece.

Fillet (n) A rounded surface filling the internal anglebetween two intersection surfaces. Also Rounds

Fit (n) The class of contact between two machinedsurfaces, based upon their respective specified sizetolerances (Clearances, transitional, interference)

Fixture (n) A device used to hold a work piece whilemanufacturing operations are performed upon that workpiece.

Flange (See bushing example) (n) a projecting rim oredge for fastening, stiffening or positioning.

Gauge (n) A device used for determining the accuracy ofspecified manufactured parts by direct comparison.

Gear Hobbing (v) A special form of manufacturing thatcuts gear tooth geometrices. It is the major industrialprocess for cutting involute form spur gears.

Idler (n) A mechanism used to regulate the tension in beltor chain. Or, a gear used between a driver and followergear to maintain the direction of rotation.

Jig (n) A special device used to guide a cutting tool (drilljig) or to hold material in the correct position for cutting orfitting together (as in welding or brazing)

Journal (n) The part of a shaft that rotates within a bearingkey (woodruff key shown) (n) A small block or wedgeinserted between a shaft and hub to prevent circumferentialmovement.

Keyseat (n) A slot or groove cut in a shaft to fit a key. Akey rests in a keyseat.

Keyway (n) A slot cut into a hub to fit a key. A key slidesin a keyway.

Knurl (v) To roughen a turned surface, as in a handle or aknob.

Pinion (n) A plain gear, often the smallest gear in a gearset,often the driving gear, May be used in conjuction with agear rack (rack and pinion, see below)

Planetary Gears (n) A gear set characterized by one ormore planet gear (s) rotating around a sun gear. Epicyclicgearing systems include an outer ring gear (known as anplanetary system)

Rack (w/pinion gear) (n)A toothed bar acting on (or actedupon ) by a gear ( pinion)

Ratchet (n) A space mechanical device used to permitmotion in one direction only.


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shims (n) a thin strip of metal inserted between twosurfaces to adjust for fit. (v) The process of inserted shims

Spline (n) A cylindrical pattern of keyways. May beexternal (L) or Internal (R)

Tap (v) To cut internal machine threads in a hole, (n) thetool used to create that feature.

Undercut (n) A cut having inward sloping sides, (v) to cutleaving an overhanging edge.

Definitions of technical terms- CNC SYSTEM

Absolute co - ordinates: The distance (or dimensions ofthe current position from the origin (or zero point) of acoordinate system (or measuring system) measuredparallel to each axis of the system.

Address: A name (or label, or number) identifying a storagearea in a control system or computer memory.

Analog: The use of physical quantity (like voltage) whoseamplitude represents that of another quantity (like distance)

APT: Automatically programmed tools.

ASCII: American standard code for information interchange.

Auxiliary function: Another name for miscellanceousfunction.

Axis: When associated with machine tools, an axis is adirection in which a machine tool table or head can move.

Backlash: The maximum movement at one end of amechanical system (such as geartrain) which does notcause the other end to move.

Base number: A base number (or radix) is an impliednumber used when expressing a value numerically in thenormal decimal system, the base is 10 and 87 is a shortway to representing 8x101+7x10o=87 in binary notation1011 represents 1x23+0x22+1x21+1x20 = 8+2+1 = 11 indecimals

Binary coded decimal number (BCD): Therepresentation of a number by groups of four binary digitsfor each decimal digit in a number.

Binary digits: The characters 0 or 1 used in the binarysystem to express any value ( see Base number)

Bit: A binary digit or its representation.

Block: A collection of words in some agreed form. Usuallyon a control tape, and separated from succeeding blocksby an End of -Block code.

BIS - British Standards institution.

Buffer: A temporary storage area where information is helduntil it is moved into an operating area.

CCW: Counter clock wise.

Characters: The set of letters, decimal digits, signs (suchas + - :% etc)

Circular interpolation: A contour control system withcircular interpolation cuts an arc of a circle from one blockon a control tape.

Co -ordinate system: A series of intersecting planes, orplanes and cylinders ( usually three) which form a referencesystem.

CPU: Central processing unit. The controlling unit in adigital computer.

Cutter diameter compensation: Provision in the controlsystem to modify the cutter offset by entering a numericalcorrection to the cutting tool diameter.

Cutter offset: Position of reference point on the tool.

Cutting speed: The velocity of the cutting edge of the toolrelative to the work piece.

Cycle: A sequence of operations which frequently repeated.

Depth of cut: The amount of metal ( in mm or inch) removedperpendicularly to the direction of feed in one pass of thecutter over the work piece.

Digit: a character used in a numbering system.

Downtime: Time during which equipment is out of actionbecause of faults.

Dwell: A pause of programmed duration, usually to ensurethat a cutting action has time to be completed.

End-of-block mode: An agreed code which indicates thecompletion of a block of input information on punched tape.

Feed: The movement of a cutting tool into a work piece.

Feed rate: The rate, in mm/min or in. /min, at which thecutting tool is advanced into the work piece.

Format: An agreed order in which the various types ofwords will appear within a block,

Hardware: Equipment e.g., Machine tool, or Control, orcomputer.

Incremental co-ordinates: The distance of currentposition from the preceding position, measured in termsof axial movements in the co-ordinate system.

Interpolation: The process of supplying the positions ofa set of more closely spaced points between more widelyspaced points such as change points.

IPM: Inches per minute (in. /min).

IPR: Inches per revolution (in. /rev) of a cutter or workpiece.

ISO: International Organization for Standardization.

Machine language or machine instruction: Theinstructions and data for computers are based on patternsof bits.

Machine zero: The machine zero point is at the origin ofthe coordinate measuring system of the machine.

Manual data input (MDI): A means, on the control panel,of inserting numerical information into the control system.

Manuscript: Handwritten program.

Miscellaneous function: A control tape term for codessuch as M03 used to control machine tool functions suchas 'rotate spindle clockwise'.


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NC: Numerical control.

Preparatory function word: A word near the beginningof a control tape block which calls for a change in mode.

Preset tools: The setting of tools in special holders awayfrom the machine tool.

Program: A systematic arrangement of instructions orinformation to suit a piece of equipment.

RPM: Revolutions per minute (rev/min), a measure ofspindle speed.

Sequence number: The number allocated to a block orgroup of blocks to identify them. Commonly takes a formlike N 278.

Servomechanism: A closed-loop positioning-controlsystem.

Software: Programs, sequences of instructions, etc. Notequipment (see Hardware).

Spindle speed: the rotational speed in RPM of the spindleor shaft which supplies the cutting power.

Subroutine: A sequence of computer-programmingstatements or instructions which perform an operationfrequently required.

Word: An agreed arrangement of characters and digits(usually less than 10) which conveys one instruction, pieceof information, or idea.

Documentations - 1Objectives: At the end of this lesson you shall be able to• describe work organisation• name the aspects of organisation of work• state the common technical terms used in industry.

Work organisation

Work organisation is to arrange and distribute the workbetween the work teams in such a way that the best useis made of the available labour, materials, tools andequipment.

- to order the operations and activities of the work shouldfollow each other.

- to decide the various work teams.

- to decide the various work teams.

- to instruct and communicate correctly in order to avoidmisunderstandings.

Organisation of work

The organisation of work includes many aspects, such as

- Pace of work (speed of an assembly line, quotas).

- Work load.

- Number of people performing a job (staffing levels).

- Hours and days on the job.

- Length and number of rest breaks and days away fromwork.

- Layout of the work.

- Skill mix of those workers on the job.

- Assignment of tasks and responsibilities and

- Training for the tasks being performed.

Some common terms technically used in industry are asfollows:

- Lean production- Continuous improvement- Just-in-time production

- Work teams- Total productive maintenance- Total quality management- Outsourcing/ contracting out

Lean production

An overall approach to work organisation that focuses onelimination of any "waste" in the production / servicedelivery process. It often includes the following elements:"continuous improvement", "just-in-time production" andwork teams.

Continuous improvement

A process for continually increasing productivity andefficiency, often relying on information provided by employeeinvolvement groups or teams. Generally involvesstandardizing the work process and eliminating micro-breaks or any "wasted" time spent not producing/ serving.

Just-in-time production

Limiting or eliminating inventories, including work-in-progressinventories, using single piece production techniques oftenlinked with efforts to eliminate "waste" in the productionprocess, including any activity that does not add value tothe product.

Work teams

Work teams operate within a production or service deliveryprocess, taking responsibility for completing wholesegments of work product. Another type of team meetsseparately from the production process to "harvest" theknowledge of the workforce and generate develop andimplement ideas on how to improve quality, production andefficiency.


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Total productive maintenance

Designed to eliminate all nonstandard, non-plannedmaintenance with the goal of eliminating unscheduleddisruptions, simplifying (de-skilling) maintenanceprocedures and reducing the need for "just-in-case"maintenance employees.

Total quality management

This is aimed towards zero defect or elimination of poorquality in production. The quality concept of assuming thebest quality from inception to implementation throughoutthe production process.

Outsourcing/ Contracting out

Transfer of work formerly done by employees to outsideorganisations. In many workplaces undergoing restructuring,worker knowledge about the productive/ service process isgathered through "employee involvement" and then usedby management to "lean out" and standardize the workprocess, thereby reducing reliance on worker skill andcreativity. This restructuring has resulted in job loss forsome underperformed, while increasing the work load andwork pace for those who remain on the job. The result ofthese changes in work organisation is that it is no longerjust machines that are wearing out-it is the workersthemselves.

Different types of documentation as per industrial needsObjectives : At the end of this lesson you shall be able to• state the purpose of documentation• list the different types of documentation• explain the documents format - batch processing, BOM, cycle time, productivity report, manufacturing

inspection report.

Documentation

Documentation and records are used throughout themanufacturing process as well as supporting processes(quality control) must meet the basic requirements.Documentation is a set of documents provided on paper,or online, or on digital or analog media, such as audiotape or CDs. Examples are user guides, white papers,online help, quick reference guides.

The stages of recording the documents is to

- prepare, review, update and approve documents.- identify changes and current revision status of

documents.- use of applicable documents available at points of use

with the control documents of external origin- identify and distribute relevant versions to be identifiable

and remain legible.- prevent unintended use of obsolete documents and

archiving.

The different types of documentation as per industrialneeds includes

- Processing charts- Bill of materials (BOM)- Production cycle time format- Productivity reports- Manufacturing stage inspection report- Job cards format- Work activity log- Batch production record format- Estimation of work- Maintenace log format

Process chart

A process chart is a graphical representation of the activitiesperformed during manufacturing or servicing jobs. Graphicalrepresentation of the sequence of operations (workflow)constituting a process, from raw materials to finishedproduct.Process charts are used for examining the process in detailto identify areas of possible improvements.The different types of process charts they are- Operation process chart- Flow process chart (man/ material/ equipment type)- Operator chart (also called two handed process chart)- Multiple activity chart- Simo chart

Batch record forms

The documents used and prepared by the manufacturingdepartment provide step-by-step instructions for produc-tion-related tasks and activities, besides including areason the batch record itself for documenting such tasks.

Batch production record is prepared for each batch shouldinclude information on the production and control of eachbatch. The batch production record should confirm that itis the correct with standard operating procedure.

These records should be numbered with a unique batch oridentification number and dated and signed when issued.

The batch number should be immediately recorded in dataprocessing system. The record should include date ofallocation, product identity and size of batch.

Documentation of completion of each significant step inthe batch production records (batch produciton and con-trol records) should include :


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The batch processing record is signed with datementioning name of person responsible and theirdesignation. The remarks if any on the process should bealso mentioned then and there.Bill of materials (BOM) format - 2

The list of parts involved in manufacturing of an assemblyarranged in order is given in this format.

The format shown is as per bureau of Indian StandardsIS:11666-1985 as example for Engineering Componentdrawings.

The BOM in the form of tabular columns has thecomponent marked with item number, and its name is

given under description and number of is mentioned underquantity, with reference drawing ie., sub assembly/partdrawing number.

The material designation as per code of practice orstandards is mentioned, and any other specific notes aregiven under remarks column.

The BOM is placed on the manufacturing drawingcontaining with assembly and parts in standard sheet sizesof engineering drawing.

- Dates and when apporiate time.

- Major ewuipment used machinery and specified batchnumbers of raw materiala, reprocessed materials usedduring manufacturing.

- Critical process parameters records.

- Trial products or sample (if reqiured).

- Signatures of staff for sequence of operation.

- Laboratory test result and line inspection notes.

- Achieved production aganist target.

- Packaging and label (if any) details.

Batch processing record: (Sample format - 1)

The format 1 used in documentation of batch processingrecord has the description of the job, necessarilymentioned with part number and name of the part.A predetermined batch quantity with batch number allotedand identified with batch record number is documentation.The product reference is made with purchase order number.The production process is descriptively written about thesequence of operation to be carried out on the product.The manufacturer organization name, period of manufacturepreferably the year with starting date of manufacture andend date of manufacturer and number of pages of documentaccording to batch quantity processed, and total numberof pages of document, inclusive of inserted pages andmanufacturing facilities is provided with.


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BATCH PROCESSING RECORD - FORMAT - 1

Batch Processing Record

Description of job Batch no. :

Part no. : Batch quantity :

Name of part : Batch record no. :

Purchase order no. :

Description of process :

Manufacturing Organisation :

Period of manufacture (Year - Qtr): Start date of manufacture: End date of manufacture:

Number of pages according to batch: Inserted pages: Manufacturing facilities:

Total number of pages

1. Operator / TechnicianDate Name and signature

2. Production in-charge:Date Name and signature

3. Section managerDate Name and signature

4. Plant in-charge:Date Name and signature

5. Production in-charge:Date Name and signature

Remarks (if any)


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BILL OF MATERIAL (BOM) - FORMAT - 2 as per IS: 11666-1985

S.No Item No. Description Quantity Reference Material as Remark dwg no. per standard

Cycle timeCycle time is the total time from the beginning to the endof the process. Cycle time includes process time, duringwhich a raw material worked with to bring it closer torequired form output, and delay time, during which theworkpiece waiting for next operation.

The time taken to perform one operation repeatedlymeasured from “Start to Start” the starting point of oneproduct’s processing in a specified machine oroperationuntil the start of another similar product’sprocessing in the same machine or process. Cycle timeis commonly categorized into same machine/process.

Machine cycle timeThe processing time of the machine working on a part.

Auto cycle timeThe time a machine runs un-aided (automatically) withoutmanual intervention.

Overall cycle timeThe complete time it takes to produce a single unit. Thisterm is generally used when speaking of a single machineor process.

Total cycle timeThis includes all machines, processes, and classes ofcycle time through which a product must pass to becomea finished product. This is not lead time, but it does helpin determining it.

Production cycle time (Format - 3)This format 3 should contain mentioning the organizationname department / section name. The process which isbeing observed for analysing the cycle time is mentionedwith line in charge name and the date/time of theoperations, with operator name is indicated.

The time observation on each operation, sequence notedin the column, and lowest repeatable is also mentionedfor each operation. The times observation for machinecycle time is also noted, with any notes be recorded inrespective operations in sequence.


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PRODUCTION CYCLE TIME - FORMAT 3

Organisation Name: Process: Line Incharge: Date/Time:

Department / Section :

Operator : Machine NotesCycle Time

OperatorSequence Observed Times Lowest Repeatable

Productivity reportProductivity report to measure and review the efficiency ofa person, machine, factory, system, etc., in convertinginputs into useful outputs. Productivity report is computedby dividing average output per period by the total costsincurred or resources (capital, energy, material,personnel) consumed in that period.

The base document daily production report which revealsthe actual output against the target plan and on investmentcost incurred as mentioned above decides the costefficiency.

Daily production report (Format 4)The output of production is shown in the format, referringthe job order no quantity, material and size, every processinvolved, to produce a component, quality control,packing should contain the details of planned quantity andproduced quantity is recorded in the document. This isthe base details for arriving the productivity report.Theincurred cost is worked out considering infrastructure, rawmaterials and facilities.


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Manufacturing stage inspection report (Format 5)The format 5 is to monitor the production in various stagesfor which manufacturing stage inspection conducted fordocumentation to review the productivity. The format givesthe details of product being inspected showing the detailsof customer reference by purchase order (PO) number

and date, job order number and date, process involved inmanufacture of product, the quality submitted forinspection. The accepted and rejected quality recordedwith inspection record review date and the inspectionperson signature who conducted the stage inspection isrecorded date wise for mentioned /specified period withstart and end dates.


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Documentations - 2Objectives : At the end of this lesson you shall be able to• state the purpose of job card and its format details• explain work activity log format details• state the details of batch production format.

Job cardA job card is a document showing the details of a job to beperformed in a production shop. It is used to authorizeand instruct the work team to take up the production work.

Job card format - 1Job card has the details of commencing the job, customername, work order no, document number, reference numberand date.

The details which have to be recorded about the productline description showing the operations each into recordingof start time and total time of operation. The location timerecorded is to track if any delay/ reasons and necessaryactions if taken with remarks.

If the product has to be completed with any of the furtheroperations in sequence, this card will travel along with jobfor next workstations for further operations if any to completethe requirement of job, and recorded till finishing of thejob.

Doc No.

Job Card Rev No.

Date

Order Starting Date

Customer

Work Order No.

Details

S.No. Date Production Line Time (Minutes) Location Remarks Description Start Time End Time Total Time Time

JOB CARD - FORMAT-1


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Work activity log format - 2This document is to record the activity/operations performedby the operator from time to time (format) shows timeduration as one hour (For whole day shift). The operator

has to record every hour, activity description, equipment/machinery/instrument used to perform the job.

Any remarks may noted by the operator to complete thisrecord.

Organisation Name:

Department:

Section:

Employee Name:

Supervisor Name:

Date:

Start / Stop Operations Equipment / Machinery/ Remarksperformed Instruments used

8.00 to 9.00 a.m.

9.00 to 10.00 a.m.

10.00 to 11.00 a.m.

11.00 to 12.00 noon

12.00 to 1.00 p.m.

1.00 to 2.00 p.m.

2.00 to 3.00 p.m.

3.00 to 4.00 p.m.

4.00 to 5.00 p.m.

5.00 to 6.00 p.m.

WORK ACTIVITY LOG - FORMAT-2

Batch production record format - 3This document is for recording the details of productioncovering the processing steps with documented pagenumber with deviation against each in short description.

This document is to be prepared under heading descriptionof job part number, batch number, name of the part. Theprocessing steps number serially for each process withsequential operations in logical order with documentedpage number. The description of deviation are noted againsteach operations in sequence gives the detail of batchproduction record for every part.


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BATCH PRODUCTION RECORD - FORMAT-3

Batch Production Record in accordance with batch processing record

Manufacturing Organisation Name: _______________________

Description of job: ______________________

Name of part: __________________________

Batch No.: ____________________________

The following deviations have appeared (continued)

No. process Name of processing step Documented Short description step page no. of deviation

1 Raw material preparation:

Operation 1: Descaling 1. _____________

Operation 2: Degreasing 2. _____________

Operation 3: Wire brushing 3. _____________4. _____________

2 Sizing of material:

Operation 1: Shearing 1. _____________

Operation 2: Deburring 2. _____________3. _____________

Estimation and maintenance records• state the purpose of estimation• explain the details of formats for estimation sheet• explain the details of formats for maintenance log, history sheet of machinery and equipment and checklist

for preventive maintenance.

Estimation is the method of calculating the variousquantities and the expenditure to be incurred on a particularjob or process.

In case the funds available are less than the estimatedcost the work is done in part or by reducing it orspecifications are altered,

The following essential details are required for preparingan estimate.

Drawings like plan, elevation and sections of importantparts.

Detailed specifications about workmanship & propertiesof materials, etc.

Standard schedule of rates of the current year.

Estimating is the process of preparing an approximationof quantities which is a value used as input data and it isderived from the best information available.

An estimate that turns out to be incorrect will be anoverestimate if the estimate exceeded the actual result,and an underestimate if the estimate fell short of the actualresult.

A cost estimate contains approximate cost of a productprocess or operation. The cost estimate has a single totalvalue and it is inclusive of identifiable componentvalues.


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Part Name: Thumb Screw

Assembly: Dial gauge holder

Part No:3

Material:Fe 3 10

Stock S 12:45x30

01 Job setting on Lathe 10 min Steel rulefour jaw chuck

02 Facing Lathe 5 min

03 Centre drilling Lathe 15 min

04 Turning 39.7 mm Lathe 5 min Vernier caliper

05 Step turning Ø22 mm Lathe 5 min Vernier caliper

06 Form radius of 4mm Lathe 10 min Radius caliper

07 Space b/w,’div’ and ‘a’ hole Lathe 10 min

08 Cut a internal thread use Lathe 20 min thread a plug machine tap gauge

09 1 x 450

Champer Lathe 5 min

10 Reverse the hold the job true it Lathe 7 min

11 Facing Lathe 10 min Vernier caliper

12 turn 39.7mm and revolving Lathe 5 min Vernier caliper centre support Lathe 10 min

13 clamp the knurling tool Lathe 20 min and knur the

surface

14 1 x 450 chamfer of knur surface Lathe 15 min

Operation Operation Machine Estimated Rate / piece Instrument No description time per hr


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Maintenance log - Format 5This format is made with details of maintenance activities performed machinewise,

MAINTENANCE LOG - FORMAT - 5

Organisation Name :

Department:

Section:

Name of the machine:

S.No Date Nature of fault Details of rectification done Signature of in-charge

History sheet of machinery equipment - Format 6The document recorded with historical data about themachinery and equipment, contains all details aboutsupplier address, order no., date of receipt, installed andplaced, Date of commissioning and machine dimensions,

weight, cost, particulars of drive motor, spare parts details,belt specification, lubrication details, major repair/ overhaulsdone with dates recorded then and there for analysing thefunctional and frequency of breakdown etc.,


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MACHINERY AND EQUIPMENT RECORD FORMAT - 6

Organisation Name:

Department:

Section:

History sheet of machinery & Equipement

Description of equipment

Manufacturer’s address

Supplier’s address

Order No. and date

Date on which received

Date on which installed and place

Size : Length x Width x Height

Weight

Cost

Motor particular Watts/ H.P./ r.p.m: phase: Volts:

Bearings/ spares/ record

Belt specification

Lubrication details

Major repairs and overhauls carried out with dates

Checklist for preventive maintenance inspection -Format 7The very essential document required to observe, thefunctional aspects of each parts, defects and theremedial measures taken is recorded.

This format enables to program the frequency ofmaintenance schedules so as to minimise frequentbreakdown of machinery/equipments.


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PREVENTIVE MAINTENANCE RECORD - FORMAT 7

Organisation Name :

Department :

Section :

Name of the Machine :

Machine Number :

Model No & Make :

Check list for machine inspection

Inspect the following items and tick in the appropriate column and list the remedial measures for the defective items.

Items to be checked Good working Satisfactory Defective Remedial measures

Level of the machine

Belt/chain and its tension

Bearing condition (Look, feel, Listen noise)

Driving clutch and brake

Exposed gears

Working in all the speeds

Working in all feeds

Lubrication and its system

Carriage & its travel

Cross-slide & its movement

Compound slide & its travel

Tailstock’s parallel movement

Electrical controls

Safety guards

Inspected by :

Signature :

Name :

Date : Signature of in-charge


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Production & Manufacturing Related Theory for Exercise 4.6.153Turner - Advanced TurningTerms used in part Drawings and Geometrical tolerances, and symbolsObjective: At the end of this lesson you shall be able to• state the meanings of various drawing terminology.

Glossary of drawing terminology

Abstraction: The reduction of an image or object to anessential aspect of its form or concept.

Acute angle: An angle lesser than 90 degrees.

Ascending planes: Flat surfaces not parallel to the groundor floor planes whose vanishing points appear above thehorizontal line.

Background: The most distance zone of space in athree-dimensional illusion.

Concave: A shape that is hollow and curved, like theinside portion of a bowl.

Convex: A shape that curved outward, like the surface ofa sphere.

Content: The subject matter of a work of art, including itsemotional, intellectual, symbolic, the matic , and narrativeconnotations, which together give the work its totalmeaning.

Descending planes: Flat surfaces not parallel to theground or floor planes whose vanishing points fall belowthe horizon line.

Descriptive drawing: Highly detailed renderings intendedto articulately define what is seen.

Design: A working plan or an arrangement of parts, form,color etc.

Drawing: The act by which an artist records what he orshe sees or feels; The fine art of making a descriptivevisual expression by dragging a tool across a receptivesurface-usually a piece of fine-quality, toothed paper.

Full range: A complete gradation of tonal values from thelightest to the darkest values whether black and white orin a color context.

Geometric shape: Shape created by mathematical lawsand measurements, such as a circle or a square.

Ground plane: The flat, horizontal plane on which theview stands that extends to the horizon.

Horizon line: A line corresponding to the eye level of theviewer in linear perspective; Contains the vanishing pointsin a one -point or two-point perspective drawing.

Horizontal: Parallel to the plane of the horizon; flat andeven, level.

Idealized drawing: A rendering which achieves asatisfactory resemblance to the subject whilesimultaneously eliminating imperfections.

Kneaded eraser: A soft, malleable eraser that is used tolighter values or as an aid in the creation of gradations.

Layout: The placement of an image within a two -dimensional format.

Life drawing: Drawing from live forms in order to gainvisual understanding of the movements, gestures, andphysical capabilities of live bodies as aesthetically pleasingart forms.

Line: The pathway of a moving point as in the trail of ascratch, a brush stroke, or the engraved deposition ofdrawing material resulting from dragging a tool over areceptive surface; visible by contrasts in value.

Line quality: The visual traits and /or expressive characterof lines.

Modeling: The change from light to dark across a surface;a technique for creating the illusion of form and/or space.

Multiple perspectives: Difference eye levels andperspectives used in the same drawing.

Oblique: A slanting line or plane that is not parallel to theedges of the picture plane.

Obtuse angle: An angle greater than 90 degrees.

Orthogonal line: In linear perspective, an oblique linethat is drawn using a vanishing point.

Parallel: Extending in the same direction at the samedistance a part, so as never to meet.

Pattern: A repeated compositional element or regularrepetition of a design or single shape.

Perpendicular: At right angles to a given plane or lineexactly upright or vertical.

Perspective: A mathematical method of representingforms as they recede in space and diminish in size usingconverging lines that meet a central vanishing point on thehorizon line.


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Pictorial: Refers to a picture, not only its actual two-dimensional space but also its potential for threedimensional illusion.

Picture plane: the actual flat surface, or opaque plane,on which drawing is produced. It also refers to theimaginary, transparent "windows of nature" that representsthe format of a drawing mentally super imposed over real-world subject matter.

Planer analysis: A structural description of a form in whichits complex curves are generalized into major plane zones.

Plane: A perfectly flat surface as a geometric plane, orfloor plane;

Profile: The shape of a head (or) face (i.e.) seen or drawnfrom the side.

Rectilinear shapes: Two-dimensional shapes that arecharacterized by having four sides that meet one anotherat right angles; shapes based upon rectangle and squares.

Render: To draw with an unusually high degree of detailedrepresentation.

Scale: Size and weight relationships between forms.

Sketch: A drawing, or an act of drawing done quickly withminimal or no elaboration, but effectively captures theessential form in space, with basic light and shadow.

Tangent: Touching a curved surface at one point but notintersecting it.

Taper: To decrease gradually in width or thickness.

Texture: The surface character or tactile qualitiesexperienced either through the sense of touch or throughthe imagination.

Three-dimensional: Having height, width and depth;synonymous with form.

Three-dimensional space: the illusion of volume orvolumetric space.

Three-point perspective: A system for depicting three-dimensional depth on a two dimensional surface. Inaddition to lines relending to two points on the horizon,lines parallel and vertical to the ground appear to convergeto a third vanishing point located either above or below thehorizon line.

Two -dimensional: Having height and width; synonymouswith shape.

Two dimensional space: Space that has height and widthwith little or no illusion of depth.

Two-point perspective: A form of linear perspective whichthe line receding into space converge at two vanishingpoints on the horizon line(eye level), one to the left of theobject being drawn and one to the right.

Unit of measure: A portion of a complex shape or three-dimensional form that is used to measure all of the orderelements within the shape or form-the head serves as agood unit of measure for determining proportionalrelationships within human figure.

Working drawings: The studies artists make inpreparation for a final work of art.

Geometrical tolerancingObjectives: At the end of this lesson you shall be able to• define geometrical tolerance• state the necessity of using geometrical tolerances• list the recommended symbols for tolerancing under the three groups of form, attitude and location.

Form i.e. straightness, flatness, roundness, cylindricityand profile of a line and a surface

Attitude i.e. parallelism, squareness and angularity

Location i.e. position, concentricity and symmetry

Definition of geometrical toleranceGeometrical tolerance is the maximum permissible overallvariation of form or position of a feature.

Reason for using geometrical tolerance

This will help the operator to produce the components,particularly those parts which must fit together precisely.

To have an international system which will overcome theusual language barrier. This is achieved by the use ofsymbols which represent geometrical characteristics.

General principles of geometrical tolerances

The geometrical tolerance consists of a frame whichcontains a symbol, representing the geometrical tolerancezone, in this instance 0.05 for the characteristic ofparallelism. The symbol for flatness is shownaccompanied by the tolerance zone figure of 0.02 in thelower frame. (Fig 1)

Notice that from each of the frames a leader is drawnso that it is normal, i.e. at 90° to the relevant face andending with an arrow-head against the face.


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Characteristic Symbol

Straightness

Flatness

Roundness


Cylindricity

Profile of a line

Profile of a surface

Notice also that from the ‘parallelism’ frame, anotherleader is drawn terminating in a blacked-in equilateraltriangle on a projection drawn out from the base line.The blacked-in triangle (about 4.5 mm high from base toapex) is the symbol used to represent a datum face orline.

An alternate method of arranging the frames and symbolsis shown in Fig 2 where the datum is given a letter and aframe of its own and an independent leader line endingin the blacked-in triangle, inverted and drawn againstthe actual component base line. The datum letter ‘A’ isthen added as an extra component in the geometricaltolerance frame.

Recommended symbols for geometrical tolerancingGeometrical tolerances are arranged into three groups.They are tolerances of form, of attitude and of location.

Tolerances of FORM are identified by the use of symbolsfor the following characteristics.

The application of symbols is indicated in fig 3, where(3a), (3b), (3c) & (3d) show the use of geometricaltolerances controlling the straightness of a circular

section part. In (3a) and (3b) the leader lines from thetolerance frame end in an arrow-head against the axisapplies to the full length of the part. The interpretationat (3a) shows that for functional acceptance, the entiremain axis must lie between two parallel straight lines0,1 apart in that plane. At (3b) the symbol for the diameter® precedes the tolerance. This means that the entiremain axis must lie within a cylindrical tolerance zone 0.1mm diameter.

Figures (3c) and (3d) show the same geometricaltolerance, applied this time to the diameter dimension ofthe smaller diameter of the part.

This means that the geometrical tolerance applies overthe length of the dimensional feature only.

Figure (3e) and figure (3f) deal with the geometricaltolerance for flatness of a surface, where the symbol forflatness is followed by the tolerance figure of 0.05. Thisfigure indicates that the actual surface (as previouslyshown in Figure 1) must be between two parallel planes0.05 apart. If a particular form of direction is prohibited,then this is stated in a note form against the toleranceframe. Eg. ‘Not concave’.


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Parallelism

Squareness

Angularity

The geometrical tolerance controlling roundness of a partis shown in figures (3g), (3h) and (3j). The interpretationfor (3g) and (3h) is that the true form of the periphery ofthe part at any cross-section perpendicular to the axismust lie between two concentric circles whose radialdistance apart is 0.02 for (3g) and 0.03 for (3h).

For the sphere shown in (3j) the geometrical toleranceapplies to concentric circles with the radial distance apart0.04 at the periphery at any section of maximum diameter.

Fig.5 shows the method of applying a geometrical toleranceto a curved surface. The symbol is followed by the tolerance0.05 which means that the actual surface must lie betweentwo surfaces enveloping a succession of sphere 0.05diameter whose centre lies on the theoretical surface.

In Fig.6 the geometrical tolerance is applied to lineardimensions controlling the profile. The rectangular ‘boxes’around the 250 centre dimension and the 50 radius is themethod used to indicate theoretical dimensions i.e. thedimensions relevant to perfect form.

The interpretation of the geometrical tolerance is that theactual profile must be between two lines which touch asuccession of circles 0.2 dia. whose centre lies on thetheoretical profile.

Tolerances of attitude are identified and indicated by theuse of symbols for the following.

The sphere controlling cylindricity is shown in Fig 4. Herethe interpretation shows, that for acceptance, the surfaceof the part must be within two coaxial cylinders, whoseradial distance apart is 0.05.

A typical application of tolerances for these threecharacteristics is shown in figures 7, 8 and 9. Fig. (7a)(7b) and (7c) show the application of tolerancing to control‘parallelism’. (7a) shows that the axis of the upper holemust lie between the two lines 0.08 apart which are parallelwith the datum axis, i.e., the axis of the lower hole, asindicated by the leader ending in the blacked-in triangle.In (7b) the method uses a separate datum letter ‘A’which is added to the frame after the tolerance of 0.05diameter. (Note the symbol Ø.) The requirement is thatthe upper hole axis must lie within a cylindrical zone0.05 diameter with its axis parallel with the axis of thedatum hole ‘A’. Fig (7c) shows a component whose upper


179

Examples of the application of the geometrical tolerancefor ‘squareness’ are shown in (8a) (8b) (8c) with (8a) (8b)and (8c) using the separate box method for indicating thedatum.

The interpretation is as follows.

The axis of the vertical hole must lie between two parallellines, 0.05 apart, which are perpendicular to the commondatum axis ‘A’ of the two horizontal wholes. (8a)

The axis of the upper cylindrical portion must lie withina cylindrical tolerance zone of 0.01 diameter, the axis ofwhich is perpendicular to the datum surface ‘A’. (8b)

surface must be between two parallel planes 0.05apart, parallel with the bottom datum surface. Whilethe overall tolerance zone is 0.05 as shown in theupper section of the frame, the figures in the lowersection of the frame stipulate that over any length of 100the parallelism tolerance is reduced to 0.02.

This shows that the right hand end face must lie betweentwo parallel planes 0.05 apart, which are perpendicular tothe datum axis. (8c)

Here the datum surface is indicated by a leader from theframe. The requirement is that the right hand face mustlie within the two parallel planes, 0.05 apart, which areperpendicular to the datum surface. (8d)

Geometrical tolerances for the control of ANGULARITYare shown in figures (9a) (9b) and (9c).

The figure (9a) shows that the requirement is the axis ofthe hole must lie within the cylindrical tolerance zone 0.1diameter, the axis of which must be included at thetheoretical angle of 60° to the datum surface A.

In (9b) the requirement is that the right hand end facemust lie within the two parallel planes 0.08 apart whichare inclined at the theoretical angle of 75° to the datumaxis A of the through hole.


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Position

Concentricity

Symmetry

Figure (9c) shows a component whose upper angleface, must lie between the two parallel planes 0.05apart which are inclined at the theoretical angle of 35°to the base, the datum surface. Notice that the theoreticalangle in each example is boxed.

Tolerances of location are identified and indicated bythe use of symbols for the following characteristics.

Figures (10), (11), (12) show typical examples of thesecharacteristics and symbols. In Figure (10a) the hole centredimensions of 25 and 30 are boxed to show that theseare the theoretical dimensions. The geometrical tolerancerequires that the hole centre must lie within a cylindricalzone 0.05 diameter. The use of theoretical positions, alsoknown as ‘true positions’, implies that the axis of thecylinder is square with the plane of the drawing.

Figure (10b) shows the hole with the same true positions,but with the geometrical tolerances arranged to give greatertolerance along the horizontal axis.The resultingrequirement is that the axis of the hole must lie within arectangular box whose sides are 0.03 and 0.06, and lengthequal to the width of the component.

In (10c) the two holes are shown with their true positionspaced at 45° on a 30mm pitch circle radius.Thegeometrical tolerance shows that each actual hole centremust lie within a cylindrical zone 0.08 diameter whoseaxis lies at the true centre position. The tolerance cylindersare disposed relative to the two datum features, namelythe axis of the smaller bore and the right hand end face.The datum letters are included in the tolerance frame.

Examples of geometrical tolerance for ‘CONCENTRICITY’are given in figures. (11a), (11b) and (11c). Theinterpretations are as follows.


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In figure (11a) the axis of the smaller diameter must liewithin the cylindrical zone 0.08 diameter which mustbe coaxial with the datum axis i.e. the axis of datumdiameter ‘A’.

In figure (11b) the axis of the two end portions must liewithin a cylindrical tolerance zone 0.08 dia.

Figure (11c) The axis of the large central portion mustlie within a cylindrical zone 0.1 diameter which is coaxialwith the mean axis of the datum diameters ‘A’ and ‘B’.(Notice that to indicate the requirement of the mean axisthe datum letters are separated by a hyphen and enclosedin the same compartment of the tolerance frame)

- (12a) the axis of the hole must lie between twoparallel planes, 0.08 apart which are symmetricallydisposed about the mean axial plane of datum width‘A’ and ‘B’

- (12b) the mean plane of the slot must be betweentwo parallel planes, 0.05 apart symmetricallydisposed about the mean plane of the datum width‘W’

The geometrical tolerance of ‘SYMMETRY’ follows infigures (12a), (12b) and (12c) where the interpretationsare:

- (12c) the median planes of the two end slots mustbe between two parallel planes, 0.06 apart.


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A detailed drawing which indicates geometrical tolerances. (Fig.13)


183

Geometric tolerance classes and typesA geometrical tolerance is the maximum permissible overallvariation of from or position from that shown in the drawing.

Geometrical tolerances are applied apart from dimensionaltolerances, where it is necessary to control more pre-cisely the form or shape of some feature of the part be-cause of its functional requirements.

Class Type Symbol Reference entry

Form Straightnes Surface of revolution, axis,straight edge

Flatness Plane surface (not datum plane)

Circularity Cylinder, cone, sphere

Cylindricity Cyclinder surface

Profile Line Edge

Surface Surface (not datum plane)

Orientation Angularity Plane, surface, axis

Parallelism Cyclinder, surface, axis

Perpendicularity Planar surface

Location Position Any

Concentricity Axis, surface of revolution

Symmetry Any

Run out Circular Cone, cylinder, sphere, plane

Total Cone, cylinder, sphere, plane


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Automatic lathes

Lathes, which are capable of automatically perform-ing a preset cycle of operations by presenting the workto the cutting tools and of ejecting the finished workpiece,are known as automatic lathes.

The various types of automatic lathes are:

- automatic turret lathes

- single spindle automatic lathes

- multi–spindle automatic lathes.

These machines are usually similar to their standardtypes with the addition of automatic features. The de-gree to which a lathe is made automatic is determinedby the purpose for which it is to be used.

Modern automatic lathes are available with the followingfeatures.

• Load the workpiece (manual).

• Start the machine (manual).

• Circulate the coolant (automatic).

• Perform all cutting operations (automatic).

• Change the speeds, feeds, and tools (automatic).

• Gauge and inspect the finished workpiece (manual).

• Unload the workpiece (automatic).

• Repeat the cycle without attention from theoperator (automatic).

Automatic turret lathes

The automatic turret lathe is sometimes called anautomatic chucking machine. It is similar in principle tothe standard turret lathe, and additionally, it is automaticin operation except for the insertion and removal of thework.

These lathes vary in size and range from heavy dutylathes for rapid and accurate production of componentsto lathes used to manufacture small items from barstock.

The feeding of tools, indexing of turret, movement ofturret slides and cross-slides and change of speedsand feeds are automatically controlled by cams or aplug board system.

Single spindle automatic lathes

There are many types of single spindle automatic lathesin use. (Fig 1 ) The automatic screw machine is apopular type. In a single spindle automatic machine,only one component at a time is machined and thismachine is used for a wide range of operations.These operations vary from cutting small screwthreads to machining castings and forgings.

Production & Manufacturing Related Theory for Exercise 4.6.154-156Turner - AdvancedTurningAutomatic lathe - types - parts, toolholders, theory of calculationObjectives: At the end of this exercise you shall be able to• differentiate between a centre lathe and a production lathe• list and name the parts of a capstan lathe• specify a capstan lathe• state the constructional features of a capstan lathe.

The control of feeds and speeds and the indexing of toolsmay be done by cams, plug boards or the numericalcontrol system.

Automatic screw machinesThese machines are used to produce screws, boltsand pins from bar stock. The cross slide, turret slide,and bar–feed mechanism are all operated automatically.

Multi-spindle automatic lathesMulti-spindle automatic lathes represent an extremelyfast method of producing work. The work may be bar–fed or held in a chuck. The bars are fed into the spindleswhich are located in a spindle carrier. The spindlesare positioned in a circular pattern in the carrier.The carrier which is being operated by an indexing mech-anism may accommodate 4, 6 or 8 spindles. The spin-dle rotates in the carrier and the carrier is indexed fromone tool station to the next tool station, according to thesequence.

The tooling set up for a six–spindle automatic lathe isshown in Fig 2.


185

Use of cams in automatic lathesObjectives: At the end of this exercise you shall be able to• classify the cams used on automatic lathes• state use of cams in automatic lathes.

Fully automatic or semi-automatic lathe machinesare often controlled with the help of drum cams andcam plates. The lathe tools necessary for productionare mounted in one or more supports ie. drum turret orhorizontal turret head. The drum cam or cam plate,

The tools are mounted in a cam or gear-operated toolslides, which operate at right angles and parallel to thespindle.

The difference in operation between multi-spindle and otherautomatic lathes is that in a multispindle machine therotating work is indexed from tool station to tool stationwhilst in the others the tools themselves are indexed.

The spindle–carrier assembly is a strong and preciselymade unit. It consists of a spindle carrier, work spindle,spindle stop and start, and the indexing mechanisms.

The nearly radial position of the cross slide directs allcutting thrusts towards the centre of the carrier. Thisarrangement permits heavy feeds, and provides extraroom for tooling without holder interference.

The Index error is minimized by the tangential cuttingaction.

Tools and equipments

A wide range of tools are available for use on automats.The tool-holders used are interchangeable betweenmachines of the same series and frequently betweenstations on the same machine.

Standard tool-holders and attachments are designed tocover most requirements, and when necessary, spe-cial holders are available to handle the less commonproduction processes.

Tools may be preset in their respective tool-holders orpresetting fixtures which are usually situated away fromthe machine. Change over from the manufacture of onetype of component to another type is confined tochange of tape and replacement of the preset tools,collets and the raw material for the new component.This is done when the machine is numerically controlled.

Circular form tools (Fig 3)

In any type of automatic lathes, turning concave,convex or any irregular shape on the component isachieved using form tools. These form tools are of twotypes, straight and circular. The straight types are usedfor wider surfaces and the circular types are used fornarrower surfaces. Fig 4 illustrates forming operationsperformed by straight and circular form tools.

By using circular form tools many operations arecombined and performed, all in one stroke, by shapingthe circular form tools accordingly.

While using circular form tools, special attention isgiven for selecting the correct speeds and feeds. This isdue to the presence of a wider surface area comingin contact with the circular form tools during the ma-chining.

The cross feed ranges from 0.01 to 0.08mm per revolu-tion and the cutting speed is slightly less than that forlongitudinal turning.

which rotates at constant speed, controls the movementsof the tools. The turret head is indexed first and thenthe tool carriage and/or tool post is moved towards theworkpiece at the correct feed rate.


186

Cams are used to actuate various slides in the auto-matic lathes.

Cams may be classified according to their shapesand mechanical designs into several distinct groups withthe subdivisions numbering a dozen or more.

For practical purposes, all cams can be divided intothree classes; radial or plate (Fig 1), cylindrical or barrel(Fig 2) and pivot beam type (Fig 3) which is founduseful in fixture designs.

In fully automatic lathes (generally used for machin-ing bar stock) the workpiece feeding, clamping andcutting off are also governed by the cam control system.A layout of a cam design worksheet is appended in Fig4.

The various features considered at the time of preparingcam design worksheets are sequence of operation,speeds, feeds, depth of cuts, index of turret and otherslides (front, rear and top).

Fig 5 is the tool layout for the job shown in the worksheetof Fig 4.

Fig 6 is the cam layout for the job shown in Fig 4.


187

Feed stock Dwell 26 26 4 1/2

2/1 46262eno( terrut xednIstation)

Centre End of bar 3 0.15 20 29 5

Dwell To 16pu naelc

Index turret (one station) 26 26 4 1/2

TurnΦ8 and drill Φ 5.25 14.25 0.125 114 117 20Dwell To 16pu naelc

Index turret (one station) 26 26 4 1/2

Drill Φ 2.5 hole 6.5 0.07 93 93 162/1 19raelc oT kcab porD

Form (over lapped) 2.4 0.012 200 (204) (35)Dwell To 16pu naelc

0.005Index turret (one station) 26 26 4 1/2Cone bottom of Φ 5.25 3.2 0.07 46 50 8 1/2Dwell To )1(6pu naelC

Index turret (one station) 26 26 4 1/2Ream Φ 5.6 and cone 12.75 0.25 51 53 9Dwell To 16pu naelc

Index turret (over lapped) 26 26 (4 1/2)Cut off Cross-slide(R) 1.5 0.05 30 32 5 1/2Cut off Cross-slide(R) 0.5 0.07 7 3 1 1/2

221loot ffo tuc raelC

Totals before correction 2/1 7715%2/1 29

inportant SHEET Automatic screw machine Short stroke

Work spindle speeds rev/min. Cutting speed m/min.R.H 4995 Turning 150

Fast R.H Drilling 5.25 dia. 82Drilling 2.5 dia. 46

Distance between turret and chuck Sequence of operation Throw Feed Revs.of work spindle Hund-Minimum mmmm nilevarT for each over Correc reths

per opera- lapped tednepo noit.ver53 64

In an another type of single spindle automatic lathe theslides are operated by individual cams. Fig 7 show thevarious tools slides.

The cams used on such a machine are shown in figures 8and 9.

A single cam to control the various slide movementsis a complicated one for designing and manufacturing.

Whereas, when one cam is made to actuate one slide,the design part of it becomes easier. Only that particularcam may be replaced in case a defect is noted in thecomponent. Moreover a set of cams designed for aparticular component may be useful for the manufactureof components with the same shape and design, butwith slight dimensional variations.


188

Differences between centre lathe and production lathe

Centre lathe Production lathe(Capstan and turret lathe)

1 Single-way tool post holds only one tool. Four-way tool post accommodates different typesof tools in four ways.

2 At the end of every operation, the tool needs Pre-set tool can be indexed. It avoids tool setting time.to be changed. It requires more operation time.

3 Not suitable for production jobs. Suitable for production jobs

4 Most suitable for tool room jobs. Most suitable for mass production jobs.

5 High skill is necessary to operate a centre A semi-skilled person can operate, pre-set turrentlathe of a capstan or turret lathe

6 Combination cuts are employed Combination cuts can be given both on carriagewith difficulty. and turret head simultaneously.

7 By using a single point tool, various sizes of Tap and dies are used to form threads; sometimesthread can be cut short lead screw is provided to cut threads with

chasers

8 Tailstock is provided to hold cutting tools Turret is provided to hold six or more toolslike drills and support the job with centres.

9 There is no separate bed over the There is an auxiliary bed provided for productionmain bed for the tool movement (capstan) for the auxiliary slide.

10 Job cannot be fed continuously after Job can be fed by a bar -feed attachmentcompletion of operation.

11 Time taken is more for producing a Time taken is less for producing a workpieceworkpiece.

12 The cost of machine is low. The cost of machine is high.

13 Trips and stops are not provided for Trips and stops are provided for rapid stopping andstopping the tool slides. starting

14 Generally chuck work and in between Generally bar works can be carried out.centre work can be carried out.

15 The manufacturing cost of components is more. The manufacturing cost of components is compara-tively lower.


189

Tool-holding devicesThe wide variety of work performed in a capstan lathe inmass production necessitated designing of different typesof tools and tool-holders for holding the tools for typicaloperations. The tool-holders may be mounted on turretfaces or on crossslide tool post, and may be used forholding tools for bar and chuck work. Certain tool- holdersare used for holding tools for both bar and chuck workwhile box tools are particularly adopted in bar-work. In thecapstan or turret lathe practice, the whole assembly ofthe holder and its tool is designated according to the typeof the holder. Thus a slide tool holder with the tool mountedin it is called a 'Slide tool' and a knee tool-holder with thetool fitted into it is called a 'Knee tool'. Special tool-holdersare also sometimes designed for special purposes. Themost important and widely used tool-holders are listedbelow.

– Straight cutter-holder

– Plain or adjustable angle cutter-holder

– Roller steady turning tool-holder.

– Recessing tool-holder.

– Knee turning tool-holder.

– Stop and centre drill-holder.

– Combination tool-holder.

Stops and tripsOne of the features enabling the capstan and turret lathesto produce quantities of similar parts is the system ofstops and trips for controlling the movements of the cuttingtools.

The stops for controlling the travel of the saddle, and ofthe turret slide of a turret lathe, are carried on a shaftsuspended on brackets from the front of the machine bed.An illustration of this, as applied to the saddle on a smallcapstan lathe, is shown in Fig.1, where the stop shaft isat the bottom of the illustration.

the shaft is rotated by hand. On some of the moreelaborate turret lathes the stop shaft for the turret faceshas six sides with stops, and is automatically rotated tosynchronize with the turret.

A similar principle is adopted in respect of the cross -slide stops on most machines. A rotating bar is mountedon the side of the cross-slide and carries four adjustablestops at each end. Hand rotation of the shaft is used tobring the stop at each end and to position for any particulartool. To prevent swarfs from getting in the unit, it is generallyprovided with a cover.

Cutting speedSimilar to a centre lathe, the cutting speed in a capstanor turret lathe is the rate at which any point on the workpasses over the tool, and this is expressed in metres perminute.

FeedIt is the amount the tool moves per revolution of the work.This is expressed in mm per revolution.

Depth of cutIt is the perpendicular distance measured between amachined and an un-machined surface.

Bar-feeding mechanismThe capstan and turret lathes while working on bar workrequire some mechanism for bar-feeding. The long barswhich protrude out of the headstock spindle require to befed through the spindle up to the bar-stop after the firstpiece is completed and the collet chuck is opened. Insimple cases, the bar may be pushed by hand. But thisprocess unnecessarily increases the total operationaltime, because the spindle and the long

Principal parts of capstan and turret lathesThe capstan lathe has essentially the same parts as theengine lathe except that the turret complex mechanismincorporated in it makes it suitable for mass productionwork. The different parts of a capstan lathe are shown inFigs 1a,b and c.

1 Headstock

2 Cross-slide tool post

3 Hexagonal turret

4 Saddle for auxiliary slide

5 Auxiliary slide

6 Lathe bed

7 Feed rod

8 Saddle for crossslide

9 Feed stop rod for turret

10 Hand wheel for turret slide.Provision is made for four stops round the shaft so thatthe travel of four tools may be controlled at any particulartime. It is arranged that the stop first trips out the feedand then serves as a dead stop for the small handoperatedmovement necessary to complete the travel. For bringingeach stop in position, when all the four are being used,


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A capstan lathe is specified by providing the followingfeatures- The maximum diameter of rod that can be passed

through the headstock spindle.

- The swing diameter of the work that can be rotatedover the lathe bedways.

- The minimum and maximum spindle speeds.

- Number of feeds available to the carriage and turretsaddle.

- The capacity of the motor. (H.P. of the machine)

The capstan lathe: constructionA capstan lathe consists of a lathe bed, headstock,turret head or slide, saddle, carriage, cross-slide, toolposts and feed rod.

The lathe bed of a capstan lathe is quite similar inconstruction to that of a centre lathe, the only differenceis in the ways of the bed. The bed ways are provided flatinstead of in a combination (Vee and Flat) to receiveheavy loads during multiple cutting.

Generally an all-geared headstock is used for rapid changeof the spindle speeds. This should be selected prior toan operation by changing the lever or pressing thespeed-changing button. The spindle is hollow and the bar-stock should be passed through it.

On the right side of the capstan lathe there is a hexagonalturret head mounted on a vertical spindle. The turret facehas a bored hole on the centre which receives lengthytools like drills, reamers, holders for tools and split bushes.

A star wheel is provided in front of the machine whichoperates manually for the to and fro motion of the turrethead assembly. Power feed is also provided for the turrethead with suitable feed rate. The turret head is fullyretracted, and at the end of its travel a turret indexingmechanism is automatically operated for the next positionof the tool. Each movement of the tool will be controlledby adjustable stops. Each stop is set for correct travel ofthe tool movement, which will stop further movement ofthe tool.

The type of the cross-slide depends upon the size of themachine. The slide is positioned in between the headstockand turret head over the saddle. If it has two tool posts,one is at the front and the other is at the rear end of theslide. The front tool post is moving inward to bring thecutting tool into operation. The rear tool post is movinginward when the front tool post is moving outward. Therear tool post actually does the ending operation like partingoff, with or without chamfering. All the lateral movementsof the saddle and the cross - slide will be controlled bytrips and stoppers for correct movement of the tools inoperation.

The feed-rod controls the motion for the carriage in thesame way as in an engine lathe.

The stop-rod is mounted below the bed in between thegearbox housing and feed-rod housing. It has four splinesover the periphery to accommodate the stoppers inmeasuring positions with respect to the related turningoperations for the saddle movements.

bar must come to a dead stop before any adjustment canbe made. Thus in each case unnecessary long time iswasted in stopping, setting and starting the machines.Various types of bar-feeding mechanism have, therefore,been designed which push the bar forward immediatelyafter the collet releases the work without stopping themachine, and thereby enable the setting time to be re-duced to the minimum.

Working principle of the bar feeding mechanism(Fig 2)

The bar 6 is passed through the bar-chuck 3, throughthe spindle of the machine and then through the collectchuck. The bar-chuck 3 rotates in the sliding bracket body2 which is mounted on a long slide bar. The bar chuck 3grips the bar centrally by two set screws 5 and rotateswith the bar in the sliding bracket body 2. One end of the


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chain 8 is connected to the pin 9 fitted on the sliding bracket10 and the other end supports the weight 4, the chainrunning over to fixed pullys 7 and 11 mounted on the slidebar. The weight 4 constantly exerts an end thrust on thebar-chuck while it revolves on the sliding bracket and forcesthe bar through the spindle, the moment the collet chuckis released. Thus bar-feeding may be accomplishedwithout stopping the machine.

Turret headsObjectives : At the end of this lesson you shall be able to• state what is a turret head• list the types of turrets• state the constructional and functional features of a turret head.

The turret head

The turret head is also known as a tool head. The turretis a six sided (hexagonal) block mostly and it is carriedon the bed of the machine for accommodating andbringing forward the tools. Each of the faces of the hexagonis accurately machined, square to the axis of the latheand has four tapped holes to accommodate the clampingbolts of the tool-holders or attachments. At the centreof each face is a through hole into which the shanksof the tool-holders may be accommodated and clamped.A pad bolt is often employed for the purpose of clamping.(Fig 1)

Smaller types of capstan lathes have the turrets nothexagonal but circular. They have six holes foraccommodating the tools. During the cycle of operationit is necessary to bring each tool into position for itswork by indexing and locating the turret to thesuccessive position.

On the turret lathe, the turret head is supported on afree bearing. The turret can be pulled round easily byhand when the clamping arrangement has been released.

The turret is located in each of the six correct positionsby some hand-operated plunger. The machine operatorreleases the clamp and locates the plunger beforeindexing the turret manually.

On the capstan lathe, means are provided whereby theturret is automatically indexed to its next position, whenit reaches the extreme end of its withdrawal movementfrom the previous operation.


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This is movable along the bed-ways. The turret head canbe indexed by hand or automatically on the withdrawal ofthe turret slide. As this takes place, the fork (1) alongwith the cam (5) turns relative to the fixed stop (2). Thecam lifts the turret (9) through rollers (6). The flanges(7 and 8) of the claw clutch, which serve to lock theturret, come out of engagement.

As the fork turns further, the ratchet gearing (3) indexesthe turret into the next position.The lock pins (11) preventthe turret from overrun, performing a preliminary lockingfunction. When the slide is advanced the fork (1) turns inthe opposite direction, the cam (5) lowers the rollers (6)with turret (9) and flanges (7) and (8) of the claw clutchcome back into engagement, finally locking the turret inposition. The locking force is adjusted with the nut (10).The stopper roller (12) with adjustable stops, whose

number corresponds to the number of the turrets'tool position is indexed through a gear transmissionsimultaneously with the turret. The stops limit the travelof the turret relative to the saddle (A). The stops areadjusted when the machine is set up for operation.

In the capstan lathe turret head stops are fitted in thesaddle. The overhang increases as the turret movestowards the workpiece held in the headstock. Thisoverhang limits the strength and consequently thecapacity of the machine. In the turret lathe the overhangis constant, permitting a heavier work load. Slide stopsin this type are fitted in the lathe bed. (Fig 3)

In each machine the sliding movement of the turrethead is made by operating a handwheel. This turns thepinion which mashes with the rack in the bed.Movement of the turret head back from the headstockautomatically indexes the turret.

Types of turret heads

Turret heads are classified according to the axis of rotationwhich may be horizontal, vertical or inclined.

Turret lathes with turret heads of vertical and inclinedaxis are provided with cross-slides whereas those withhorizontal axis turrets have no cross-slides since the crossfeed of the tool is effected by the turret slide itself.

Constructional features of a turret head with verticalaxis (Fig 2)

Roller box turning toolsObjectives : At the end of this lesson you shall be able to• state the purpose of roller box turning tool• list the types of roller box turning tools• state the constructional features of each type• state the functional features of the each type.

Roller box turning tools

Plain turning operations may be performed on capstanand turret lathes by feeding the tool

- from the hexagonal turret- by the indexing tool post on crossslide- by feeding tools from both.

Turning operations carried out from the hexagon turretprovide rigid support to the tool for making heavy cuts.Tools used in the turret are of special design and are referredto as box turning tools. Box turning tools are of twotypes.


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- `V' steady turning tools- Roller steady turning tools

`V' Steady tool–holder (Fig 1)

These holders are for turning brass and for making lightcuts on other free cutting materials. A short length of theworkpiece is hand–machined to the required diameterand the steady is adjusted to this surface.

The cutting tool is set slightly ahead of the Veesteady. These tools may have single or multiple toolblocks.

A hardened adjustable Vee steady is positioned suchthat it just touches the workpiece.

The shank of the steady is mounted in an extensionarm in the turret.

Where good surface finish is needed on the turnedportion, it is preferable to have the cutting tool inadvance to the Vee steady, and where concentricity isof prime importance, the cutting tool may be set behindthe Vee steady.

The roller steady tool-holders (Fig 2)

These holders are used for most turning operations. Eachholder has a limited size capacity. A short length ofthe work is machined to the correct diameter. Therollers and tool are set on this diameter. The cutting actionforces the workpiece against the rollers, producing ahigh burnished finish on the work. The cutting tool isset in advance of the rollers for most turning operations.This set up produces a good surface finish. Somesteadies are available with rollers set ahead of the cuttingtool.

The roller steady tool-holders are of two types.

• The tangential type (Fig 3)

• The ending type (Fig 4)

In the tangential type the workpiece is supported bytwo rollers running on the diameter being cut (followingrollers). The tool can be retracted at the end of the cutby pulling the handle. By this, scoring of the workpiecesurface turned is avoided. Fine adjustment of the cuttingtool is achieved by the use of the micrometer dial. Thechips flow clear off the tool-holder ensuring that swarfdoes not become clogged around the work area. (Fig 3)


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In the ending type shown in figure 4 with leading orforward rollers, the workpiece is supported by two rollerson a previously cut diameter. Leading rollers ensurethat the diameter being turned is concentric to thepreviously turned diameter on which the rollers run.

The leading rollers may not produce the same standardof surface finish.

When using the ending type of roller steady tool-holder,the cutting is taking place on the end of the workpiece.This is made possible by the use of the leading rollers.(Fig 4)

Figure 5 shows the geometry of a roller box showingforces on the tool and the rollers.

Figure 6 shows the roller steady tool-holder adjustments.The forces F1, F2 and R1 are also illustrated.

Turret lathesObjectives: At the end of this lesson you shall be able to• specify a turret lathe• name the various attachments & accessories used on turret lathes• distinguish between horizontal and vertical types of turret lathes.

Specification of a turret lathe

A turret lathe is specified by giving the

- maximum diameter of a rod that can be held

- maximum spindle hole diameter

- maximum swing over the bed

- number of spindle speeds

- number of feeds (carriage) cross-slide and longitudinal

- number of feeds (turret carriage)

- power required for machine motor and coolant motors.

Accessories / attachments

Work-holding accessories

Self centering chuck, independent chuck, combinationchuck, air operated chuck, push-out type collet chuck,draw in type collet chuck, dead length type collet chuck.

Turret : Pentagon, hexagon or octagon type.

Tool-holders

Straight cutter holderPlain or adjustable angle cutter holderMultiple cutter holderOffset cutter holderCombination tool-holder or multiple turning headSlide tool-holderKnee tool-holderDrill holderBoring bar holder or extension holderReamer holderKnurling tool-holderRecessing tool-holderForm tool-holder- straight- circularTap-holder


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Die-holderBalanced tool-holder (box tool)- V-steady box tool-holderroller box tool-holderBar ending tool-holder

Attachments

Taper turning attachmentThread cutting attachment

Horizontal turret lathes are classified as:

- ram type turret lathes- saddle type turret lathes- chucking machine.

Saddle type turret lathes (Fig 1a)

The hexagonal turret is mounted directly on a saddle andthe whole unit moves back and forth on the bed ways toapply feed. This type of turret lathe is heavier in constructionand is particularly adopted for larger diameter bar worksand chuck works. The machine can accommodate longerworkpieces.

Ram type turret lathes (Fig 1b)

The ram type turret lathe carries the hexagonal turret on aram or a short slide. The ram slides longitudinally on asaddle positioned and clamped on lathe bedways. Thistype of machine is lighter in construction and is suitablefor machining bars of smaller diameters. The tools aremounted on the square turret and the six faces of thehexagonal turret. The feeding movement is obtained whenthe ram moves from the left to the right. When the ram ismoved backward the turret indexes automatically andthe tool mounted on the next face comes into operation.

Chucking machineThe chucking machines are used to machine castingsand forgings that must be held in chucks or fixtures. Thistype of machine handles a large variety of work which isbasically the same as that done on standard turret lathesequipped for chuck work.

Vertical turret lathesA vertical turret lathe is a machine with a vertical turrethead and a horizontal work table. Most of the operationsperformed on a regular turret lathe are also done on thistype of machine. It is preferred for large and heavy work.

The principal parts of a vertical turret lathe are the

- base- column- rail- table- saddle and turret head- side head

Many attachments are used on vertical turret lathes.

Dead stops and trips on capstan and turret lathesObjectives : At the end of this lesson you shall be able to• state the necessity of stops and trips• list the types of stops and trips• state the constructional and functional features of stops and trips• types of stop and trip arrangements.

Stop and tripsStops and trips are meant for controlling the movement ofthe cutting tool on the crossslide and on the hexagonalturret. They serve the purpose of providing dimensionalaccuracy on identical components produced in largequantities. They minimize delays for measuring andgauging. The stops for controlling the travel of the saddleand of the turret of a turret lathe are carried on a shaft

suspended on brackets from the front of the machine bed.It is arranged that the stop first trips out the feed, and thenserves as dead stop for the small handoperatedmovement necessary to complete the travel. For bringingeach stop into position, when several of them are beingused, the shaft is rotated by a hand wheel provided. Onsome of the most elaborate turret lathes the stops forsaddle movement, which are four in number are provided on


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a shaft below the headstock. (Fig 1) The stop shaft forthe turret has six stops which are automatically rotatedto synchronize with the turret. (Fig 2)

Dead stopsA dead stop terminates the tool travel at a point wherea workpiece diameter or depth is correct to the drawingspecification. (Fig 6)

The cross-slide is also provided with a shaft with stopsto control the depth of cuts of each tool on thecross-slide tool post. (Fig 3)

Finger stopsA finger stop is positioned radially on the hand wheel andis aligned with a mark on the graduated scales whenthe relevant dimension on the workpiece is down to size.There may be three or four finger stops, each alignedto a different mark on the graduated scale. (Fig 4)

Feed tripsA feed trip switches off the power feed to the tool whenthe workpiece is almost to size. When the trip devicetouches the stop, it trips the power feed. A furthermanual movement of the slide, through a previouslydetermined distance will bring the slide to the dead stopas shown. (Fig 5)


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Collets used on capstan and turret lathesObjectives : At the end of this lesson you shall be able to• list the collets used for bar work on the capstan and turret lathes• state the constructional and functional features of each type of collet.

Indexing a stop-bar or rollA ̀ stop-bar' is indexed to the position in conjunction withthe relevant tool. This may be carried out manually byindexing the bar to present a letter, a record being madeof which letter goes with each tool.In the case of a turret,thestop-bar will be indexed automatically with the turret and,therefore, each stop is always presented for the sameturret station. (Fig 7)

The collet chuck

Collets provide a means of holding cold-drawn barmaterials or previously machined parts to undergo asecond operation. They maintain an accurate alignmentof the component to be machined with the rotating spindleaxis of the lathe.

The working principle of the collet chuck is illustrated inFig 1.

The common constructional features of collets have alreadybeen dealt with in the previous exercises.

Types of collets

Dead length type (Fig 2)

The workpiece does not move when this type of colletis operated; and, therefore, an accurate length of work-piece can be maintained.

Draw back type (Fig 3)


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Their range of adjustment is much greater than with solidcollets, usually about 1.5 mm. The collet pads are usuallynot suitable for gripping short workpieces. These pads areavailable in sets of three or four pieces. The pads areavailable to accommodate hexagonal bars also. Whenhexagonal bars are held, the bar must be rotated afterinserting so as to get the corners properly engaged.(Fig 6)

Sometimes the collet pads are provided with springspacers to keep the collet pads apart when the chuck isopened making the workpiece loading easier. (Fig 7)

This is also referred to as draw in collet. This collet isusually screwed to a draw bar or tube which draws thecollet into the sleeve causing it to grip the bar. A keywaylocated in the body of the collet accommodates the keyin the sleeve preventing rotation of the collet, whichultimately prevents the collet getting unscrewed fromthe draw bar during operation. This type of collet is notsuitable for accurate length workpiece as it tends topull the workpiece away from the bar-stop when closing.

Pushout type (Fig 4)

When this type of collet is closed by pushing againstthe taper of the accommodating sleeve, it tends the baralso to be pushed along with the collet against the bar-stop. Unless the turret hand wheel is held by pressing inthe anticlockwise direction, the component length mayshow variations.

Master collet with interchangeable liners (Fig 5)

The master piece is of collet shape. This has a taperedbore into which liners or pads, mostly three in number,can be fitted. When the pads are fitted to the internal taperof the master piece, the inner bore that results by theassembly of the pads accommodates the bar. Themasterpiece controls the grip. The pads are assembledto the master piece by means of stop screws.

The collet pads are used in most of the larger sizes ofbar work.

Points to be remembered during selecting a solidcolletThe above type of collets accommodates only onesize of bar for which they are manufactured. If the bardiameter differs by even 0.1 mm from the nominal size,the operation of the collet will not be proper and theaccuracy of the collet will be lost.

Production : Turner (NSQF Level-5) : RT for Ex No. 4.6.154 - 4.6.156Copyright @ NIMI Not to be Republished

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Clean and deburr the workpiece and form a good chamferon the end face of the bar which enters the collet.

Check that the collet just fits on the workpiece withoutforcing.

A round bar having a scaly unmachinedouter surface must never be held in a colletchuck.

Checking the collet tensionIndex the bar-stop into position and apply force to the barusing the star wheel of the turret slide. (Fig 8)

If the bar moves under pressure, open the chuck andreadjust the knurled cap.

Feed for correct adjustment on a manually operated chuck,by feeling for resistance when closing the chuck. (Fig 9)

If long heavy bars are to be held, put the machine inmotion and check that the bar does not move in the colletwhen accelerated up to the cutting speed.

When soft materials and thin walled tubes are to beheld, check that no excessive damage has been causedby the grip of the collet to the surface of the soft bar orthe diameter of the thin tube.

Turret lathesComparison between turret and capstan lathes

Turret lathe Capstan lathe

The turret is mounted on an auxiliary slide which slideson the saddle.

The auxiliary bed feeds the tools into the work. Theoverhanging of the auxiliary bed from the stationarysaddle presents a non-rigid construction which issubjected to bending, deflection or vibration under heavycutting loads.

The capstan lathe can be operated under light cuttingconditions, accommodating workpieces with high cuttingspeeds, feeds and less depth of cuts.

The capstan lathes are capable of turning bars up to amaximum of 60 mm diameter only.

Smaller and lighter bar work can be done on a capstanlathe.

On a capstan lathe, the hexagonal turret can be movedback and forth rapidly without having to move the entiresaddle unit.

1 The turret is mounted on the saddle which slidesdirectly on the bed.

2 The construction provides utmost rigidity to the toolsupport as the entire cutting load is taken up by thelathe bed directly.

3 The turret lathe can operate under severe cuttingconditions, accommodating heavier workpieces withhigh cutting speeds, feeds and depth of cuts.

4 The turret lathes are capable of turning bars up to 200mm in diameter.

5 Larger and heavier works can be done on turret lathes.

6 In the turret lathe, the hand feeding is a laboriousprocess due to the movement of the entire saddleunit.


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The constructional features of a turret latheA turret lathe consists of a bed, an all-geared headstock,and a crossslide on which a four-way tool post is mountedto hold four different, single point tools. A tool post fittedat the rear of the cross-slide holds a parting tool inan inverted position. The tool post mounted on thecross-slide is indexed by hand. In a turret lathe there isno tailstock but in its place a hexagonal turret is mountedon a saddle which is sliding on the bed. The six faces ofthe turret can hold six different tools. The turret may beindexed automatically or manually and each tool may bebrought in line with the lathe axis in a regular sequence.The workpieces are held in collets or on chucks.The longitudinal movements of the turret and cross-feedmovement of the crossslide are controlled by adjustablestops. These stops enable different tools set at differentpositions to move by a predetermined amount forperforming different operations on repetitive workpieceswithout measuring the length (or) diameter of the machinedsurfaces in each case.

These special characteristics of the turret lathe enable itto perform a series of operations such as turning, drilling,boring, reaming, thread cutting, necking, chamfering,cutting off and many other operations in a regularsequence to produce a large number of identical piecesin a minimum time.

Types of turret lathesTurret lathes can be classified into two main groups

- Horizontal type turret lathe.- Vertical type turret lathe.

Horizontal type turret lathesThey are lathes which perform all the operations in ahorizontal position with the help of a cross-slide tool postand turret head. These operations include turning, drilling,boring, reaming, thread cutting, necking, chamfering andcutting off.

Vertical turret lathesThese are lathes with a vertical turret head and a horizontalwork table. All the operations performed on a regular turretlathe can be done on this type of machine also. It ispreferred for large and heavy workpieces.

Parts of a horizontal turret lathe. (Fig 1)


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Types of tool - holders in capstan and turretObjective: At the end of this lesson you shall be able to• state the different types of tool-holders and their uses.

The following are the different types of tool-holders.

Single cutter turner tool-holderRoller steady turning tool-holderMultiple cutter turner tool-holderCombination end face and turner tool-holderQuickacting slide tool-holderCentre drilling tool-holder and bar-stopAdjustable knee toolDie headClutch type tap and die-holderFloating tool-holderCombination facing and spotting drill-holderTaper shankdrill socket-holderDrill chuck (drill-holder)Combination stock stop and centre-holderFlanged tool-holderKnee turning tool-holderRecessing and boring tool-holder for boringRecessing tool-holder.

Uses of the common tool holders used on turret lathes

Knee turning tool-holder (Fig 1)

A knee turning tool is used while the job is held rigidlyin a chuck or fixture. It is used for machining componentsby combined operations. The rigidity of this tool-holdercan be increased by using the overhead support barprotruding from the headstock.

Roller steady turning tool - holder (Fig 2)

Roller steady turning tool-holder is used mainly for turningexternal diameters while a fairly good finish is needed onthe component. The roller steady supports the job whena lengthier job is to be turned.

Recessing and boring tool-holders (Fig 3)

Recessing and boring tool-holders are used in combinationfor internal recessing and boring.

Bar-stop and centre drill tool-holder (Fig 4)

A bar-stop is used for setting the bar stock protrudingto the required length to a preset position from the chuck.A centre drill tool-holder is used for centre drilling wheredrilling is to be done in a job.


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Knee turning - holder and combination tool - holderObjective : At the end of this lesson you shall be able to• state the constructional features of a knee turning tool-holder and a combination tool-holder.

Floating reamer-holder (Fig 5)

Where reaming is to be done in a turret lathe, a floatingreamer-holder is used to ream a drilled hole. The floatingholder facilitates by aligning itself with the axis of the drilledhole without causing much load on the reamer.

Combination facing and start drilling holder (Fig 6)

Combination facing and start drilling holder is used to facethe end of the job and to provide a small hole for shortdepth ready for a drilling operation.

Knee turning tool-holder (Figs 1a and 1b)

Work which is held in a chuck or in a turning fixture isfairly rigid, and needs no additional support while machiningtakes place. If the tool-holder mounted on the turret headis meant for combined operations, like turning and forming,the tool-holder must also be rigid and well supported. Itis also essential that some arrangement should be providedto take up the heavy load which comes on the turret head.Such combination of operations is usually carried out witha knee tool-holder. The rigidity of this type of tool-holdercan be increased by using the overhead support barprotruding from the headstock. This engages the guidebush on the tool-holder and maintains the alignment ofthe turret and the spindle axis, preventing deflection of theturret by the cutting force applied.

A boring bar can also be fitted so that a hole can bemachined at the same time as the external surface isbeing machined. The chuck or fixture should be fitted witha guide bush to pilot the end of the boring bar, and againmaintain the geometry of the tool by reducing tooldeflections.

Combination tool-holder (Figs 2a and 2b)


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Methods of producing external threads on capstan lathesObjectives : At the end of this lesson you shall be able to• state various methods of producing external threads on capstan lathes• state the construction and function of a self-opening die head• state the types of self-opening die heads• list and name the parts of a die insert.

ie. by two combination tool-holders, one in the machineand the other out for tool maintenance. When the toolshave been reground they are preset in position and thecomplete tool-holder is changed. Presetting of boring toolsis facilitated by the use of a boring bar cutter micrometer.(Fig 3)

The knee turning tool-holder has provision for only oneturning tool, and it has a greater range of adjustment.But the adjustment for positioning the turning tool headin the combination type tool-holder is merely that of a tooloverhang in the tool post.

External threads are generally manufactured- by using a single point tool with self opening die heads- by thread rolling heads.

Self-opening die heads (Fig 1)

A further development of the knee tool-holder is thecombination tool-holder which can be fitted with two turningtools and a boring bar. Thus simultaneous machiningoperations are possible. By increasing the number of toolsin the boring bar, multi diameter bores can be machinedat the same time.

Such set ups involve more complex and time consumingtool setting and are only economic where the time savedin machining outweigh the setting time. The machine downtime for setting can be reduced by the use of pre-set tooling,

Self-opening die heads are most commonly used in thethread manufacturing process. They are made in a widerange of sizes for producing threads up to about 100 mmdiameter.

In addition to dies/chasers for standard threads, manydies/chasers for special threads are also available.

The die head is fed to the work by the operator who thenallows it to feed itself along the work, and follows upwith the turret. The turret stop is set slightly short to thethread length. When the die head movement is stoppedby the turret stop, the front portion of the die head continuesto feed forward under the self-feeding action until it ispulled clear of the detent pin.

Long accurate threads need a positive method of feedingthe die head over the work. On capstan lathes this isachieved with a hexagon turret, leadon attachment. If themachine is equipped with a crossslide and the threadchasing attachment, the crossslide is linked to thehexagon turret to provide positive lead.

Advantages when using a self-opening die headThe direction of workpiece rotation does not have to bereversed.

A roughing and finishing arrangement enables two cuts tobe made.


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An adjusting screw permits variations to be made fromthe standard size, or enables several cuts to be made oncoarse threads.

The cutting stresses maintain the die in the correctposition, preventing errors caused by die tilt or movement.

The two types of die heads in use are the radial dieheads and the tangential die heads.

Radial die head (Fig 2)

This die head uses radial cutting chasers. Adjustmentcan be made to the thread cutting size and also forroughing and finishing cuts to be made on the workpiece.

Tangential die head (Fig 3)

These die heads use chasers of tangential type. Thesechasers can be sharpened quite often. This gives thema long life.

Thread rolling heads (Fig 4)

Thread rolling is a modern method of producing threadson turret lathes and automatic machines. They producethreads with excellent grain flow, and the pitch, the formand the accuracy of the threads are made to closetolerances.

The dies (Fig 5)

The markings on the die piece indicate the

- die type- thread diameter- die number- thread relieved on the leading side- slots to locate the die in the die head.


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Accessories for capstan and turret latheObjectives: At the end of this lesson you shall be able to• state the use of the knurling tool-holder• state the use of the multiple-cutter holder• state the use of the drill-holder• state the use of the boring bar-holder• state the use of the reamer-holder.

Knurling tool-holder (Fig 1)

The knurling can also be performed by the tooling fromthe turret head. The knurling tool-holder shown in Fig 1 ismounted on the turret head. The position of the knurlscan be adjusted with the screw to accommodate differentdiameters of the work. Different patterns of knurled surfacesare obtained by tilting the knurls.(Figs 2 and 3)

Multiple-cutter holder (Fig 4)

The multiple-cutter holder accommodates more than onetool. The one shown in Fig 4 enables turning of two differentdiameters simultaneously. Turning and boring tools orturning and facing tools can also be set in the holderto perform multiple operations simultaneously.

Drill holder (Fig 5)

The twist drills having morse taper shanks are usuallyheld in a socket which is parallel outside and taperedinside. These sockets are inserted in the bracket of aflange tool-holder and clamped to it by set screws. Straightshank drills are mounted on Jacob's drill chuck, which inturn is held by the flanged tool-holder and socket.

Boring bar-holder (Fig 6)

This holder is also called an extension holder or a flangedtool-holder. These holders are intended for holding drills,reamers, boring bars, etc.


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Reamer-holderThe standard practice of holding reamers in a capstan/turret lathe is in some form of floating holder which permitssome amount of end movement of the reamer to alignitself with the work.

Fault analysis production turningObjectives: At the end of this lesson you shall be able to• list the common faults and state their causes and effects• state the remedies for avoiding repetition of the faults.

Common faults

Figure Cause Remedy

Collet not gripping the bar

The workpiece insecurely supported

Play in the spindle bearings or toolslideways

Spindle speed too high

Incorrect feed rate

Incorrect tool height

Incorrect tool geometry or a worn outtool bit.

Play in the tool slideways

Incorrect or insufficient flow of cutting oil

Overhang of the tool in the tool-holder toogreat

Tool loose in the tool-holder

Play in the spindle bearings

Ensure collet tension is correct

Hold the workpiece rigidly

Inform the supervisor, maintenance section

Reduce the spindle speed

Adjust the feed rate suitably

Check the centre height of the tool and setto correct height.

Regrind the tool to the specification

Inform the supervisor

Change or adjust the flow of cutting oil

Set the tool back in the tool-holder with aminimum overhang.

Clamp the tool rigidly

Inform the supervisor, maintenance section.

Chatter (Fig 1)

Lateral grooves andridges formed on theworkpiece giving amoulted appearance.

Incorrect tool geometry or worn out toolbit

Insufficient coolant.

Tool point too keen.

Incorrect spindle speed, feed rate,material or tool material.

Regrind the tool bit to specification.

Increase the coolant supply.

Hone small radius on to the tool point unlessa sharp corner is specified.

Check each against the specification andadjust according to the requirement.

Poor surface texture(Fig.2)

The cutting tool markswidely spaced and / or tornsurface of the workpiece.


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Figure Cause Remedy

Dirty collect and collet sleeve

Worn out collect.

Remove, clean and lubricate the collect sleeve.

Replace the collect.

Eccentricity (Fig.3)

Breakage of tool (Fig 4) Reset the tool with a minimum overhang.

Reset the tool to the centre height.

Reset the tool as near as possible to the collet.

Set the speeds and feed to thoserecommended.

Tool overhang too great.

Tool set below centre.

The part-off too is too far from the collet.

Incorrect spindle speed and feed rate.

Bar feed defective (Fig 5) Reset the collet tension and clean, if necessary.Increase the feed cord weight.Examine the feed cord line and the pulleys.

Loose or dirty collet.

Insufficient feed cord weight.

Jammed feed cord.

Bell-mouthed hold (Fig.6) Regrind or replace the centering tool.Reset the centering tool or drill centrally.

Chipped centering tool.

The centering tool or the drill misaligned.

Pip leftout after partingoff (Fig 7)

Regrind the part-off tool to the specification.

Reset the centre height of the tool.

Worn out part-off tool, or incorrect toolgeometry.

Centre height of tool too high or too low.


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Methods of producing internal threads on capstan / turret lathesObjectives: At the end of this lesson you shall be able to• state various methods of producing internal threads• state construction details of a collapsible tap• state the functional features of a collapsible tap.

Internal threads are cut using 2 types of tools– Single point thread cutting tool– Solid tap

Internal threading by using a single point threadcutting tool (Fig 1)

Threading with a single point tool is usually carried out onlarge workpieces or when special threads are required.

The tool may be mounted either on the hexagon turret oron the square turret fitted to the cross-slide. A threadingdrive accessory is fitted to the lathe, which enables thetool to be fed along the work at the appropriate rate forthe desired pitch.Several cuts are normally made, eachslightly deeper than the previous cut, until the thread depthappropriate to the selected pitch is obtained. The threadingtool is normally held in a bar mounted in a slide tool-holder.

Solid taps

Solid taps are used for small diameter threads. They areusually spiral fluted.

The tap is fitted to the hexagon turret in a special tap-holder. The holder is designed to release the tapautomatically at the end of the cut, permitting the tap torotate along with the workpiece. (Fig 2)

The procedure for cutting the thread is as follows

Move the turret to the workpiece.

Start the tap in the hole by exerting pressure on the turretdrive hand wheel.

Keep slight forward pressure on the turret drive to preventthe tap from pulling the turret along as the threadcutting operation progresses.

This precaution will prevent distortion of the thread.

Excessive forward drive pressure will also distort thethread.

Forward motion of the tap should be stopped first beforeit reaches the end of the hole being threaded. When usingthe hexagon turret this distance is set with the turret stop.When the stop is reached by the advancing turret, theautomatic release operates, releasing the tap and allowingit to revolve with the workpiece.

Reverse the headstock spindle rotation to drive the tapback out of the threaded hole.

Collapsible tap (Fig 3)

The collapsible tap is a mechanism in which thread cuttingchaser inserts, normally six in number, are positioned inthe slots provided in the head. These inserts are broughtto the cutting position by pulling the lever provided. At theend of the threading operation, the tap collapses. Thetap may then be drawn directly out of the work withoutreversing the rotation of the headstock spindle. Thisreduces the production time. This facility is applicable


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only for cutting threads in holes of larger diameter due tothe presence of collapsible mechanism. For cuttingthreads in successive pieces, the lever is again broughtto the engaging position so that the thread cutting insertsare brought back from the collapsed or released stateto the cutting position.

Threading attachment

To produce accurately pitched threads, when using a singlepoint thread cutting tool, the tool must be advanced intothe work at a rate determined by the thread pitch. Thetechnique for producing correct rate differs in the followingtwo set ups anyone of which may be provided in thecapstan or turret lathe.

A thread lead attachment is used most commonly todrive the turret of the capstan lathe and a thread chasingattachment is used to drive the saddle of the turret lathe.

Threading lead attachment (Fig 4)

This attachment is used on capstan lathes.

A thread lead (lead screw) of the required pitch is fitted tothe turret drive. The turret is moved by the action of thehalf nut engaging the lead screw. (Fig 4)

The thread lead attachment includes a release mechanismwhich is operated by the turret stops. The length of thethread cut may be set automatically by adjusting theposition of the turret stops.

Thread chasing attachment (Fig 5)

This attachment is used on the turret lathes to drive thesaddle at the required rate for the threading operation.

A threaded sleeve is fitted on the feed shaft and a meshingthreaded collar is fixed to the saddle. The collar drawsthe saddle along the threaded sleeve.

The pitch of the thread on the sleeve determines the pitchof the thread cut on the workpiece.


turner(iv) preface the national instructional media institute (nimi) was established in 1986 at...

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