i

A STUDY ON TOOL DEFLECTION DURING DEEP POCKETING CYCLE

ZIKRULHAKIM BIN MUHD ZAHID

Report submitted in fulfilment of the requirementsfor the award of the degree of

Bachelor of Manufacturing Engineering

FACULTY OF MANUFACTURING ENGINEERINGUNIVERSITI MALAYSIA PAHANG

JUNE 2013

v

ABSTRACT

Tool deflection during deep pocketing cycle will cause tapper in mould and die. This

problem can cause defect on final product and also increases cost and time wasting in

manufacturing process. This study basically shows a detailed study to overcome tapper

problem in deep pocket. Dimensional accuracy due to tapper problem was analyzed in order to

obtain optimum cutting parameters. The pocket part was drawn by using CATIA software.

The data collected during experiment was analyzed using signal to noise ratio through Minitab

software. From the analysis, it was found that depth of cut has gives the most effect on tapper

problem, followed by feed rate and spindle speed. From the result, it is shown that level 1 of

depth of cut which is 0.3mm, level 1 of feed rate which is 64mm and level 2 of spindle speed

which is 1280rpm was the best cutting parameter. Hence, from these cutting parameters, the

tapper problem cause by tool deflection during deep pocketing cycle can be overcome.

vi

ABSTRAK

Pembiasan alat semasa pusingan pempoketan dalam akan menyebabkan ketidakrataan

di dalam acuan. Masalah ini akan menyebabkan kecacatan pada produk akhir yang akan

meningkatkan kos dan pembaziran masa ketika proses penghasilan. Kajian ini pada asasnya

menunjukkan kajian terperinci untuk menangani masalah ketidakrataan di dalam poket.

Ketepatan ukuran pada masalah ketidakrataan akan dianalisis untuk mendapatkan rujukan

pemotongan paling optimum. Bahagian poket dilukis dengan menggunakan perisian CATIA.

Data yang diambil semasa eksperimen telah dianalisis menggunakan nisbah signal kepada

noise melalui perisian Minitab. Daripada analisis, ia telah mendapati bahawa kedalaman

potongan telah member kesan yang paling tinggi terhadap masalah ketidakrataan, diikuti oleh

kadar memotong dan kelajuan mata. Daripada keputusan analisis, ia telah menunjukkan

bahawa kedalaman potongan pada tahap 1 iaitu 0.3mm, kadar memotong pada tahap1 iaitu

64mm/min dan kelajuan mata pada tahap 2 iaitu 1280rpm adalah rujukan pemotongan terbaik.

Maka, daripada rujukan pemotongan ini, masalah ketidakrataan yang disebabkan oleh

pembiasan alat semasa pusingan pempoketan boleh diselesaikan.

vii

TABLE OF CONTENT

Page

SUPERVISOR’S DECLARATION i

STUDENT’S DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vii

TABLE OF FIGURES x

TABLE OF TABLES xii

APPENDICES xiv

CHAPTER 1

Introduction

1.0 Project Title 1

1.1 Project Objectives 1

viii

1.2 Project Scopes 1

1.3 Project Background 2

1.4 Problem Statement 2

CHAPTER 2

Literature Review

2.0 Introduction 4

2.1 Milling Machine 4

2.2 Milling Parameter 5

2.2.1 Feed Rates 6

2.2.2 Cutting Speed 8

2.3 Tool Path 9

2.3.1 Spiral Tool Path 10

2.3.2 Zigzag Tool Path 10

2.3.3 Zigzag Tool Path Requirement 11

2.4 Machining Strategy 12

2.4.1 Pocketing Strategy 13

2.4.2 Process Planning 15

ix

2.5 Cutting Tools 16

2.5.1 Uncoated Carbides 16

2.5.2 Coated Carbides 17

2.6 Mild Steel 18

CHAPTER 3

Methodology

3.1 Flow Chart 21

3.2 Selection Of Cutting Parameters 22

3.2.1 Calculation 23

3.3 Work Piece Material Used 24

3.4 Cutting Tool Used 25

3.5 Design of Experiment 27

3.5.1 Experimental Procedure 29

3.6 Recommendation 31

3.7 Conclusion 31

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CHAPTER 4

Result and Discussion

4.1 Introduction 29

4.2 Data analysis 29

4.2.1 Measuring process 30

4.2.2 Collecting data 34

4.2.3 Data analysis 35

4.2.3.1 Spindle speed 37

4.2.3.2 Depth of cut 39

4.2.3.3 Feed rate 41

4.2.4 Surface plot 42

4.2.4.1 Dimension vs spindle speed and depth of cut 43

4.2.4.2 Dimension vs spindle speed and feed rate 44

4.2.4.3 Dimension vs depth of cut and feed rate 45

4.2.5 Optimum parameters 46

4.3 Summary 47

xi

CHAPTER 5

Conclusion

5.1 Conclusion 49

5.2 Recommendation 50

REFERENCES 51

TABLE OF FIGURE

CHAPTER 1

Figure No.

1.1. Dimensional different between upper part and lower part 3

1.2. Tool deflection during deep pocketing cycle 4

CHAPTER 2

Figure No.

2.1. Spiral in and spiral out 10

xii

2.2. One-way and zigzag 11

2.3. Pocket shape and tool path pattern 14

2.4. Pocket shape and semi-finishing strategy 15

CHAPTER 3

Figure No.

3.1. Dimension for raw material 22

3.2. Design of end mill 23

3.4. Cross section of the pocket 27

CHAPTER 4

Figure No.

4.1: Deep pocket part 30

4.2: Upper part measurement 31

4.3: Lower part measurement 32

4.4: Wall measurement 33

4.5: SN ratio graph for spindle speed (A) 37

4.6: Line graph for dimension against spindle speed 38

xiii

4.7: SN ratio graph for depth of cut (B) 39

4.8: Line graph for dimension against depth of cut 40

4.9: SN ratio graph for feed rate (C) 41

4.10: Line graph for dimension against feed rate 42

4.11: Surface plot for dimension versus A and B 43

4.12: Surface plot for dimension versus A and C 44

4.13: Surface plot for dimension versus B and C 45

4.14: Graph dimension against depth of cut 47

TABLE OF TABLE

CHAPTER 2

Table No.

2.1. Recommended feed rate 7

2.2. Recommended cutting speed 9

CHAPTER 3

Table No.

xiv

3.1. TiAIN end mill properties 23

3.2. Experimental variables 25

CHAPTER 4

Table No.

4.1. Domain of the experiment 30

4.2: Table of result 34

4.3: SN ratio of dimension 36

4.4: Optimum parameters 46

APPENDICES

APPENDIX A 52

Appendix A1 53

Appendix A2 54

APPENDIX B 55

Appendix B1

1

CHAPTER 1

INTRODUCTION

1.0 Project Title

A study of tool deflection during deep pocketing cycle.

1.1 Project Objectives

To overcome tool deflection during deep pocketing cycle

Come out with best cutting parameter

1.2 Project Scopes

In order to achieve the project objective, this project needs a proper plan. The

project scopes as shown below.

i. Study on cutting tools in milling process for pocketing.

ii. Initial study about cutting parameters in milling.

iii. Study on tool path during pocketing process.

2

1.3 Project Background

Pocketing process is widely used in producing mould and die. The advance of

modern technology and a new generation of manufacturing equipment, particularly

computer numerical control (CNC) machine, have brought enormous changes to the

manufacturing sector. Generally, the handbook or human experience is used to select

convenient machine parameters in manufacturing industry. In process planning of

pocketing process, selecting reasonable milling parameters is necessary to satisfy

requirements involving machining economics, quality and safety.

In every machining process, defects on final product always occur either surface

roughness or dimensional accuracy. Meanwhile in pocketing process, tool deflection

will occur during the process and will affect dimensional accuracy of final product.

Hence, this study is to overcome the tool deflection problem and come out with the best

machining parameters at the end of this project.

The machining parameters in milling operations consists of cutting speed, depth

of cut, feed rate and number of passes. These machining parameters significantly impact

on the cost, productivity and quality of machining parts. The effective optimizations of

these parameters affect dramatically the cost and production time of machined

components as well as the quality of final products.

1.4 Problem Statement

One of the milling processes is pocketing. It is usually to machined mould and

die. But it is always comes with tool deflection problem (Figure 1.1 and Figure 1.2).

This problem logically can affect entire product that being produce. The defect on

products can be costly for manufacturers and its need the best solution to overcome the

tool deflection problem. Establishment of efficient machining parameters has been a

problem that has confronted manufacturing industries for nearly a century, and is still

3

the subject of many studies. Optimum machining parameters are of great concern in

manufacturing environments, where economy of machining operation plays a key role in

competitiveness in the market.

Figure 1.1: Dimensional different between upper part and lower part

Figure 1.2: Tool deflection during deep pocketing cycle

100mm

99.8mm

4

CHAPTER 2

LITERATURE REVIEW

2.0 Introduction

Milling is a process to remove material on work piece. There are several type of

milling process such as pocketing, drilling, and face milling. Pocketing clears an area

bounded by specified entities such as lines, arc, and free form curves, which constitute

outer periphery with or without island. There are rectangular shape, circular shape and

inclined shape of pocketing. During deep pocketing, tool deflection occurs and causes

the different in measurement between inner and outer part.

2.1 Milling Machine

Milling is the process of machining flat, curved, or irregular surfaces by feeding

the work piece against a rotating cutter containing a number of cutting edges. The usual

mill consists basically of a motor driven spindle, which mounts and revolves the milling

cutter, and a reciprocating adjustable worktable, which mounts and feeds the work piece.

5

Milling machines are basically classified as vertical or horizontal. These

machines are also classified as knee-type, ram-type, manufacturing or bed type, and

planer type. Most milling machines have self-contained electric drive motors, coolant

systems, variable spindle speeds, and power-operated table feeds. [1]

A milling machine is a machine tool that cuts metal with a multiple-tooth cutting

tool called a milling cutter. The work piece is fastened to the milling machine table and

is fed against the revolving milling cutter. The milling cutters can have cutting teeth on

the periphery or sides or both.

Milling machines can be classified under three main headings:

(i) General Purpose machines - these are mainly the column and knee type (horizontal &

vertical machines).

(ii) High Production types with fixed beds- (horizontal types).

(iii) Special Purpose machines such as duplicating, profiling, rise and fall, rotary table,

planetary and double end types.

Milling attachments can also be fitted to other machine tools including lathes

planning machines and drill bench presses can be used with milling cutters. Milling

machine is one of the most versatile conventional machine tools with a wide range of

metal cutting capability. Many complicated operations such as indexing, gang milling,

and straddle milling can be carried out on a milling machine. [2]

2.2 Milling Parameter

Optimum machining parameters are of great concern in manufacturing

environments, where economy of machining operation plays a key role in

competitiveness in the market. Due to high capital and machining costs of the NC

6

machines, there is an economic need to operate NC machine as efficiently as possible in

order to obtain the required pay back. The success of the machining operation will

depend on the selection of machining parameters. A human process planner selects the

proper machining parameters using his own experience or from the handbooks on the

part geometry, technological requirement, machine tool, a cutting tool and the part

material. These parameters do not give optimal result. The effective optimizations of

these parameters dramatically minimize the cost and production time of machined

components as well as the increase the quality of the final product. [3,4]

2.2.1 Feed Rate

Feed rate is the velocity at which the cutter is fed, that is, advanced against the

work piece. It can be expressed thus for milling also, but it is often expressed in units of

distance per time for milling (millimeters per minute), with considerations of how many

teeth (or flutes) the cutter has then determining what that means for each tooth.

Feed rate is dependent on the:

Type of tool

Surface finish desired

Power available at the spindle

Rigidity of the machine and tooling setup

Strength of the work piece

Characteristic of the material being cut, chip flow depends on material type and

feed rate. The ideal chip shape is small and breaks free early, carrying heat away

from the tool.

7

This formula can be used to figure out the feed rate that the cutter travels into or around

the work. This would apply to cutter on a milling machine (Table 2.1). [2]

= × ×Where:

FR = the calculated feed rate in inches per minute or mm per minute.

RPM = is the calculated speed for the cutter

T = number of teeth on the cutter

CL = the chip load or feed per tooth. This is the size of chip that each tooth of the

cutter takes.

Table 2.1: Recommended feed rate

Type of milling Feed rate (mm/min)

Face milling 50 – 400

Corner milling 50 – 500

Pocket milling 50 – 500

Slot milling 1 50 – 500

Slot milling 2 50 – 500(Source: Courtesy of N.Baskar, P. Asokan, R. Saravanan , G. Prabhaharan (2006). Selection of optimal

machining parameters for multi-tool milling operations using a memetic algorithm.)

(1)

8

2.2.2 Cutting Speed

Cutting speed may be defined as the rate (or speed) that the material moves past

the cutting edge of the tool, irrespective of the machining operation used – the surface

speed. A cutting speed for mild steel is 100ft/min (30meters/min). The hardness of the

cutting tool material has a great deal to with the recommended cutting speed. The harder

the cutting tool, the faster the cutting speed. The softer the cutting tool material, the

slower the recommended cutting speed. For a given material there will be an optimum

cutting speed for a certain set of machining conditions, and from this speed the spindle

speed (RPM) can be calculated.

Factors affecting the calculation of cutting speed are:

The material being machined

The material the cutter is made from.

The economical life of the cutter.

Cutting speeds are calculated on the assumption that optimum cutting condition exist

(Table 2.2), these include:

Metal removal rate

Full and constant flow of cutting fluid

Rigidity of the machine and tooling setup

Continuity of cut

Condition of material

9

Table 1.2: Recommended cutting speed

Type of milling Cutting speed (m/min)

Face milling 60 – 120

Corner milling 40 – 70

Pocket milling 40 – 70

Slot milling 1 30 – 50

Slot milling 2 30 – 50(Source: Courtesy of N.Baskar, P. Asokan, R. Saravanan , G. Prabhaharan (2006). Selection of optimal

machining parameters for multi-tool milling operations using a memetic algorithm.)

2.3 Tool Path

Milling is one of the most widely used metal removal processes. Pocket milling

clears an area bounded by a set of specified entities such as lines, arcs, and free-form

curves, which constitute outer periphery with or without islands. The machining

sequence may be either in the order of entities selected or in reverse order. Types of

pockets include rectangular, circular, and inclined.

Based on the contour shapes and machining methods, pocketing tool paths are

classified into spiraling and zigzag types. Although there are many possible ways of

planning a tool path in pocket-milling operation, traditionally contour augmentation

(spiral) and zigzag (or staircase) milling, have been the two standard procedures

practiced. Zigzag or staircase milling involves the movement of the tool in a number of

parallel passes to cover an entire area of the polygon to be machined.[3]

10

2.3.1 Spiral Tool Path

To generate spiral tool path, the boundary profile are streaked inwards while the

island profiles outwards using the appropriate steps. In spiral-out option, the tool paths

track from the centre of pocket to the outer boundary of the pocket, whereas in spiral-in

option, the tool-path track from the outer boundary of the pocket towards the centre

inwardly, as in Figure 2.1. Contour augmentation (spiral) milling method requires a

relatively larger tool overlap between successive passes to avoid the undercut

projections on the surface of the polygon. This results in an increased length of the tool

path, and consequently, machining time. [5]

Figure 2.1: Spiral in and spiral out

2.3.2 Zigzag Tool Path

In the zigzag method of pocketing, the tool paths generated are parallel to a

predefined vector direction and the tool moves back and forth. This method is used when

a machine tool has a preferred direction of cut, like along the major axis of machine or

the grain direction of the material calls for a particular direction of machining. One way

machining, the tool always cuts the material in one way, along or against the spindle

10

2.3.1 Spiral Tool Path

To generate spiral tool path, the boundary profile are streaked inwards while the

island profiles outwards using the appropriate steps. In spiral-out option, the tool paths

track from the centre of pocket to the outer boundary of the pocket, whereas in spiral-in

option, the tool-path track from the outer boundary of the pocket towards the centre

inwardly, as in Figure 2.1. Contour augmentation (spiral) milling method requires a

relatively larger tool overlap between successive passes to avoid the undercut

projections on the surface of the polygon. This results in an increased length of the tool

path, and consequently, machining time. [5]

Figure 2.1: Spiral in and spiral out

2.3.2 Zigzag Tool Path

In the zigzag method of pocketing, the tool paths generated are parallel to a

predefined vector direction and the tool moves back and forth. This method is used when

a machine tool has a preferred direction of cut, like along the major axis of machine or

the grain direction of the material calls for a particular direction of machining. One way

machining, the tool always cuts the material in one way, along or against the spindle

10

2.3.1 Spiral Tool Path

To generate spiral tool path, the boundary profile are streaked inwards while the

island profiles outwards using the appropriate steps. In spiral-out option, the tool paths

track from the centre of pocket to the outer boundary of the pocket, whereas in spiral-in

option, the tool-path track from the outer boundary of the pocket towards the centre

inwardly, as in Figure 2.1. Contour augmentation (spiral) milling method requires a

relatively larger tool overlap between successive passes to avoid the undercut

projections on the surface of the polygon. This results in an increased length of the tool

path, and consequently, machining time. [5]

Figure 2.1: Spiral in and spiral out

2.3.2 Zigzag Tool Path

In the zigzag method of pocketing, the tool paths generated are parallel to a

predefined vector direction and the tool moves back and forth. This method is used when

a machine tool has a preferred direction of cut, like along the major axis of machine or

the grain direction of the material calls for a particular direction of machining. One way

machining, the tool always cuts the material in one way, along or against the spindle

11

direction in the entire process as in Figure 2.2. The offset chains of pocket entities are

intersected with a sequence of equidistant parallel lines, curves and arcs, which are

oriented along the selected direction of cut. In successive zigzag method, machining

takes place bidirectional parallel to a selected axis. In bidirectional milling, the cutting

edge changes alternatively left and right sided, up milling and climb milling. Zigzag

(staircase) milling requires more number of stops and turns, requiring more machining

time. [5, 6]

Figure 2.2: One-way and Zigzag

2.3.3 Zigzag Tool Path Requirement

Generally accepted user requirements of a zigzag machining include efficient

machining using minimum machining time, fine surface quality without tool marks, and

no gouge against boundary curves. Considering the above functional requirements, tool-

path generation algorithm developed in this study includes the following [5]:

(i) Minimization of tool retractions.

Tool retractions cause non-cutting tool motions in the air and tool marks

on the machined surface. These types of motions have to be minimized.

11

direction in the entire process as in Figure 2.2. The offset chains of pocket entities are

intersected with a sequence of equidistant parallel lines, curves and arcs, which are

oriented along the selected direction of cut. In successive zigzag method, machining

takes place bidirectional parallel to a selected axis. In bidirectional milling, the cutting

edge changes alternatively left and right sided, up milling and climb milling. Zigzag

(staircase) milling requires more number of stops and turns, requiring more machining

time. [5, 6]

Figure 2.2: One-way and Zigzag

2.3.3 Zigzag Tool Path Requirement

Generally accepted user requirements of a zigzag machining include efficient

machining using minimum machining time, fine surface quality without tool marks, and

no gouge against boundary curves. Considering the above functional requirements, tool-

path generation algorithm developed in this study includes the following [5]:

(i) Minimization of tool retractions.

Tool retractions cause non-cutting tool motions in the air and tool marks

on the machined surface. These types of motions have to be minimized.

11

direction in the entire process as in Figure 2.2. The offset chains of pocket entities are

intersected with a sequence of equidistant parallel lines, curves and arcs, which are

oriented along the selected direction of cut. In successive zigzag method, machining

takes place bidirectional parallel to a selected axis. In bidirectional milling, the cutting

edge changes alternatively left and right sided, up milling and climb milling. Zigzag

(staircase) milling requires more number of stops and turns, requiring more machining

time. [5, 6]

Figure 2.2: One-way and Zigzag

2.3.3 Zigzag Tool Path Requirement

Generally accepted user requirements of a zigzag machining include efficient

machining using minimum machining time, fine surface quality without tool marks, and

no gouge against boundary curves. Considering the above functional requirements, tool-

path generation algorithm developed in this study includes the following [5]:

(i) Minimization of tool retractions.

Tool retractions cause non-cutting tool motions in the air and tool marks

on the machined surface. These types of motions have to be minimized.

12

(ii) Minimization of tool-path elements

At the end of tool path elements, the feed rate should be slowed to avoid

machining error caused by rapid change of feed direction. Minimizing the

number of tool-path elements improves both productivity and quality of

machined parts.

(iii) Maximization of average tool-path length

Tool-path elements having longer length allow constant feed rate and

direction, which in turn improves surface quality.

(iv) Technological requirements

The tool-path planning system should be able to adapt to the various

technological requirements or constraints such as one way milling or

zigzag milling and up or down milling.

(v) Motion along boundary curve

Linear tool motion between tool-path elements may cause gouging at the

sharp vertices of boundary curves and which has to be checked.

2.4 Machining Strategy

Most computer aided manufacturing (CAM) systems have predefined pocketing

routines which require selection of axial and radial depth of cut, and the starting point

and directions of the tool path for each layer of cut. Tool paths may start from the center

13

of the pocket towards walls with zigzag and lace paths which are all based on the

geometric relationship between the cutter and pocket features.

The material removal rate is defined by the product of depth and width of cut,

spindle speed and feed, which are presently selected based on trials and past experience.

Some researchers manipulated the feed rate to increase the material removal rate while

respecting cutting force and power limits along the tool path. However, incorrect spindle

speed, axial and radial depths of cut cause chatter vibrations and leaves poor surface

finish. [7]

2.4.1 Pocketing strategy

The pocketing requires identification of cutting conditions (radial and axial depth

of cut, spindle speed and feed) and tool path strategy to be used by the CAM system.

The objective is to determine the most time optimal strategy with highest material

removal rate (MRR) without violating the chatter, torque and power limit of the machine

tool. Although the pocket geometries vary significantly depending on the part and

die/mold features, two basic pocket shapes are considered here to develop a general

pocketing strategy [7].