production technology...planer, etc. are single point tools. a multi-point tool has two or more than...

Production technology

B.E VI SEMESTER

DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING

B.E. - SEMESTER – VI

PRODUCTION TECHNOLOGY (2161909)

INDEX

Sr.

No. Experiment

Page

Number Dates

Sign. Grades/

Remarks Start End Start End

1. To study about single and multi-

point cutting tools.

2. To study about the different types

dies and press tool design.

3.

To study and practicing about jigs

and fixtures for various machining

operations.

4. Study About Various Thermal

Aspects In Machining.

5. To study about different types of

gears manufacturing processes.

6. To study about various non-

conventional machining process.

7. Prepare press tool design based on

given data.

8. Prepare Jig Design And Drawing

For Given Components.

9. To Study And Construct

Merchant’s Force Circle.

10.

To study various types of chip by

changing cutting parameters and

work material on lathe.

11.

To study about different thread

manufacturing processes and

demonstration on single and multi-

start thread manufacturing.

SINGLE AND MULTIPOINT CUTTING TOOL

PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 1

Date: ___ /___ /______

EXPERIMENT NO.1

AIM: STUDY OF SINGLE POINT AND MULTI POINT CUTTING TOOL.

1.1 Types of Cutting Tools

The cutting tools may be classified in different ways. Depending upon the number of cutting

points on the tool, the cutting tools are of two types:

1. Single-point cutting tools,

2. Multi-point cutting tools.

A single-point cutting tool has only one cutting point or edge. The tools used for turning,

boring, shaping, or planning operations, that is, tools used on lathes, boring machines, shaper,

planer, etc. are single point tools. A multi-point tool has two or more than two cutting [for

example, tools used on drilling machines, milling machines, broaching machines etc.] multi-

point tool can be considered to be basically a series of single-point tools.

Depending upon the construction of the cutting tool, it is classified as :

1. Solid tools,

2. Tipped cutting tools.

The solid cutting tools are made entirely of the same material, whereas, in a tipped cutting tool,

an insert of cutting tool material is brazed or held mechanically to the shank of another material.

1.1.1 Single Point Cutting Tools

The solid single point cutting tools have been discussed here.

1.1.2 Tipped Single Point Cutting Tools.

As already discussed the carbides, ceramics, cast alloys, diamond, CBN and UCON are used

as tips or inserts which are either brazed into a prepared seat machined on a tough steel tool

shank or are clamped to the shank, The second type of tips or inserts are known as indexable

inserts or throwaway tips.

1.1.2 Brazed Tipped Tools.

Fig. 1.1 Brazed Tipped Tools



Suitable shapes of tool material tips or inserts gets worm out are brazed in a steel shank. When

the tip or insert gets worn out, it is resharpened with the help of special grinding wheels. For

resharpening purposes, the tool wheel has to be removed from the machine involving a resetting

operation. The main drawback of a brazed tip is that of difference in co-efficient of expansion

of tip material and tool shank material, the brazing has to be done very carefully.

Fig.1.2 Single point cutting tool nomenclature

1.1.3 Mechanically Clamped Tip Tools.

In these tools, the tips or inserts are clamped mechanically on to the tool shank. These tips arc

known as index able because these have more than one cutting edges which are used one by

one by indexing. The tip and these tips are known as throwaway type because once all the edges

of the tip have been used, the tip or insert is removed from the tool shank and thrown away or

is disposal off (disposable tip). The most common shapes in which these tips are available are

: Square, triangular and diamond. The edges of the inserts may be at 90° to the tip face, or the

edges may be at a small angle to the face, In the first case, the tips will provide negative rake

angle because these will have to be clamped on to shank with the seating slopping downwards

to provide a clearance angle. Here, the number of cutting points will be twice the number of

edges, because when all the edges on the lop face have been used, the insert can be turned over

to give an additional equal number of cutting edges.

In the second case, positive rake is obtained on the tip. Here, the insert cannot be turned over

to use the cutting edges on the bottom face, because the small angles provided on the sides of

the tip will prevent this.

When a cutting edge on the tip gets worn, the clamp is released and the tip is (indexed) to bring

a new cutting edge into the cutting position. When all the edges have been used the tip is

thrown away and a new tip is substituted.



The various methods for fastening the tip are:

(i) Screw fastening

(ii) Bridge type clamp

(iii) Pin type clamp.

1.2 Multipoint Cutting Tools

1.2.1 Milling Cutters

Milling cutters are multi-point cylindrical cutting tools with cutting teeth spaced around the

periphery. The most appropriate way to classifying the milling cutters is on the method of

providing relief on the tools. According to this, the milling cutters are classified into two

categories:

1. Profile relieved cutters.

2. Form relieved cutters.

Fig. 1.2 Milling Cutters

The profile-relieved cutters are obtained by sharpening a narrow land behind the cutting edge.

This narrow land is re sharpened by grinding when the cutting edge become dull, relieved

cutters have a curved relief behind the cutting edge and these cutters have a curved relief behind

the cutting edge and these cutters are sharpened by grinding the tool face. There is greater

flexibility in adjusting relief angles in profile-relieved cutters since it is fixed in the

manufacture of the cutter. However, this type is more suitable for cutters with intricate

shapes/profile since the relief is not changed during re sharpening.



Fig.1.3 Milling Cutter Nomenclature

The milling cutters can also be classified according to the method of their mounting, example,

arbor type, shank type 'or spindle mounted type'. Most milling cutters are made as solid of

H.S.S., but they are also a\ a liable with carl tipped teeth or with disposable tips of various tool

materials.

The milling process is divided into two main types:

1. Peripheral milling, and

2. Face milling.

In peripheral milling, the finished surface is parallel to the axis of the cutter and is machined

by cutter teeth located on the periphery of the cutter, In face milling, the finished surface is at

right angle to the cutter axis and it is obtained by teeth on the periphery and the flat end of the

cutter.

1.2.2 Broach Tool

A broach is a multi-point cutting tool consisting of a bar having a surface containing a series

of cutting teeth or edges which gradually increase in size from the starting or entering end to

the rear end. Broaches are used for machining either internal or external surfaces .The surfaces

produced may be flat, circular or of any intricate shape. In broaching, the broach is

Fig.1. 3 Broaches.



Fig.1.4 Broach Nomenclature

pushed or pulled over or through a surface of a workpiece. Each tooth of the tool takes a thin

slice from the surface. Broaching of inside surface is called 'Internal or hole broaching' and

outside surfaces as "Surface broaching".

1.2.3 Drills

Drilling is the process of cutting or originating a round hole from the solid material. The tool

(drill) and not the workpiece is revolved and is fed into the material along its axis. There are

many ways of classifying drills, for example, according to: material, number and type of flutes,

drill size, type of shank (straight or taper) and cutting point geometry, etc.

Fig.1. 4 Drill bits

However the most common type of drill is the fluted twist drill, It is made from a round bar of

tool material, and has three principal parts: the point, the body and the shank. The drill is held

and rotated by its shank. The point comprises the cutting elements while the body guides the

drill in operation. The body of the drill has two helical grooves called "flutes" cut into its

surface. The flutes form the cutting surface and also assist in removing chips out of the drilled

hole. The two cutting edges are straight and are separated by web thickness of the drill which

is provided to strengthen the drill structure. The body of the drill is made slightly less in

circumference leaving a narrow "margin" at Ml nominal diameter along the edge of each flute.

This reduces rubbing action between the drill and the hole wall and allows the cutting fluid to

reach the point of the drill. The metal cut away to form the margin is known as "body diameter

clearance". To help further in reducing the rubbing action, drill bodies are given a slight back

taper (About 0.0075 mm per cm of length). The shank can be either straight or tapered (for big



drills). Straight shanks are provided for small drills (upto 10 to 12 mm diameter) and are held

in chucks.

1.2.3.1 Nomenclature of Drill Bits.

1. Axis: It is the imaginary longitudinal centre line of the drill.

2. Body: It is the portion of the drill extending from the outer corners of the cutting lips up to

the commencement of neck (if present) or shank.

3. Back taper: A slight decrease in diameter of the drill from the front end to the back in the

body of the drill.

Fig.1.5 Drill Bits Nomenclature

4. Flutes: Straight or helical grooves cut or formed in the body of the drill to provide cutting

edges, to allow chip removal, and to allow cutting fluid to reach the cutting edges.

5. Land: The peripheral portion of the drill body between adjacent flutes.

6. Body clearance: It is the space provided to eliminate undesirable contact between the drill

and the workpiece.

7. Margin: It is the cylindrical portion of the land which is not cut away to provide body

clearance. It is ground to the diameter of drill. There are 2 margins. Drill guidance and friction

losses in drilling depend on the margins.

8. Drill diameter. It is the diameter of the drill over the margins measured at the point.

9. Clearance diameter. It is the diameter over the cutaway portion of the drill lands.



10. Web. It is the central portion of the drill body that connects the lands. The extreme of the

web forms the chiesel edge on the two-flute drill.

11. Point. It is the cutting end of a drill formed by the ends of the lands and the web.

12. Lips or cutting edges. These are the cutting edges of a two-flute drill extending from the

chiesel edge to the periphery.

13. Chiesel edge. It is the edge at the end of the web that connects the cutting edges.

14. Shank. The part of the drill by which it is held and rotated.

15. Tang. The flattened end of a taper shank which fits a driving slot in a socket.

16. Lip relief. It is the axial relief on the drill point.

17. Lip relief angle. It is the axial relief angle at the outer comer of the lip. It is the angle by

the flank and a plane at right angles to drill axis.

18. Face. It is the portion of the flute surface adjacent to the lip on which the cut chips impinge.

19. Flank. It is the surface on a drill point which extends behind the lip to the following Pate.

20. Heel. The edges formed by the intersection of flute surface and body clearance. It is the

trailing edge of the land.

21. Point angle. It is the included angle of the cone formed by the cutting lips.

22. Helix angle. It is the angle made by the leading edge of the land with a plane containing

the axis of the drill.

23. Chiesel edge angle. It is the angle included between the chiesel edge and the cutting lip as

viewed from the end of the drill.

24. Web thickness. Thickness of web at the point, unless another location is indicated

25. Neck. It is a section of reduced diameter between the body and shank.

1.2.4 REAMERS

A reamer is a rotary cutting tool generally of cylindrical shape, which is used to enlarge and

finish holes to accurate dimensions to a previously formed hole. It is a multiple edge cutting

tool, having the cutting edges on its periphery. A reamer consists of three main parts : fluted

section, neck and shank, The fluted part consists of chamfer l1 starting taper l2, sizing section

l3 and the back taper L4. Chamfer length or bevel lead length L1, ensures proper and easy entry

of the reamer into the hole. The main cutting action of reamer is done by starting taper l2. The

sizing section serves to guide the reamer and also smooths or sizes the hole. The back taper l4

(with a difference between the maximum and minimum diameters of from 0.01 to 0.08 mm)

reduces friction between the reamer and the hole surface.



1.2.4.1 Types of Reamers

1. Hand reamers. These reamers are operated by hand with a tap wrench fitted on the square

end of the reamer. The work is held in the vise or vice versa. The flutes may be straight or

helical. The shank is straight with a square tang for the wrench.

2. Machine reamers. These are similar to hand reamers except that the shank is tapered.

3. Chucking reamers. These are machine reamers with shorter flutes. These may be either of

the type known as Rose reamers or Fluted reamers. Rose reamers do not cut on the

circumference of the flutes but are beveled off and clearanced to cut on their ends. These are

used for heavy roughing cuts, for example, for clearing out cored holes.

4. Floating reamers. Here the holders are not rigid but are floating. This permits the reamer to

follow the previously made hole naturally and without restraint resulting in a better hole.

5. Expanding reamers. These reamers allow slight increase in their size to allow for wear or

to remove an extra amount of material. For this, the body of the reamer is bored taper and is

slitted. A taper plug runs through the hole and is operated by a screw so that it acts as the

expander. The possible variation is generally between 0.15 to 0.50 mm.

Fig. 1.6 Reamers

6. Adjustable reamers. In these reamers, separate blades are inserted into the grooves provided

in the body of the reamer. The blades can be moved up or down to increase or decrease the size

of the reamer.

7. Taper reamers. These reamers are used to finish the taper holes for cutting the taper pins

used to secure the collars, pulleys etc. to the shafts.



Fig 1.7 Reamers

8. Shell reamers. Solid reamers (up to about 20 mm diameter) are usually made of H.S.S. To

reduce the cost of larger reamers, the cutting portion is made as separate shells which are

mounted on standard shanks made of lower cost sheels. These reamers, are, however, not very

rigid and accurate. Inserted teeth or blades in shells will further reduce the cost of the reamer.

To increase their production capacity, the reamers can be tipped with cemented carbides.

1.2.4.2 Nomenclature:

1. Axis. It is the longitudinal centre line of the reamer.

2. Back Taper. It is a slight decrease in diameter from front to back, in the flute length of the

reamer. As pointed out above, it is provided to reduce friction between the reamer and the hole

surface. It is also called "longitudinal relief.

3. Blade. It is the tooth or cutting element inserted in the reamer body. It may be adjustable

and/or replaceable.

4. Body. It is the fluted portion of the reamer, inclusive of the chamfer, taper and bevel.

5. Flutes. These are the longitudinal channels formed in the body of the reamer to provide

cutting edges, permit passage of chips and allow cutting fluid to reach the cutting edges.

6. Helix angle. Reamers may have straight flutes or helical flutes. Straight flutes are easy to

cut and resharpened. A helical flute or a spiral flute is formed in a helical path around the axis

of a reamer. Helix angle is the angle which a helical cutting edge at a given point makes with

an axial plane through the same point.

7. Land. It is the section of the reamer between adjacent flutes.

8. Cutting edge. It is the leading edge of the land in the direction of rotation for cutting.



9. Face. It is the portion of the flute surface adjacent to the cutting edge on which the chips

impinge after they are cut from the work.

10. Heel. It is the trailing edge of the land in the direction of rotation for cutting.

11. Chamfer. It is the angular cutting portion at the entering end of the reamer. It is also called

"Bevel" or "Bevel lead".

12. Neck. It is the section of reduced diameter connecting the reamer body to the shank.

13. Shank. It is the portion of the reamer by which it is held and driven.

14. Squared Shank. A cylindrical shank having a driving square on the back end.

15. Tang. It is the flattened end of a shank which fits a slot in the socket.

16. Periphery. It is the outside circumference of a reamer.

Fig.1.8 Reamer Nomenclature

17. Chamfer angle. It is the angle between the axis and the cutting edges of the chamfer

measured in an axial plane at the cutting edge. It is also called "Bevel Lead Angle".



18. Pilot. A cylindrical portion ahead of the entering end of the reamer body, which is

sometimes provided to maintain alignment.

19. Starting Taper. It is a slight relieved taper on the front end of the reamer. It facilitate.'

cutting and finishing of the hole. It is also called 'Taper Lead'.

20. Rake Angle. It is the angle between the face and a radical line from the cutting edge. It can

be zero, Negative or Positive,

21. Hook. It is the concave condition of a cutting face. The rake angle of a hooked cutting face

must be determined at a given point.

22. Clearance Angle. Practically, all the cutting action of the reamer is confined to the front

tapered portion. Suitable relief angles should be provided to ensure proper cutting action

without rubbing. Clearance angles are the angles formed by the primary or secondary

clearances and the tangent to the periphery of the reamer at the cutting edge,

23. Taper Lead Length. It is the length of the taper lead measured axially.

24. Taper Lead Angle. It is the angle formed by the cutting edges of the taper lead with the

reamer axis.

25. Bevel Lead Length. It is the length of the bevel lead measured axially.

26. Bevel Lead Angle. It is the angle formed by the cutting edges of the bevel lead

With I the reamer axis.

27. Margin or circular land. It is the cylindrically ground surface adjacent to the cutting edge

on the leading edge of the land.

__________

References: Production Engineering -by P.C. SHARMA

Manufacturing Processes I - by Prof. Pradeep Kumar (IIT ROORKEE)

http://www.iitr.ac.in/departments/ME/pages/People+Faculty+kumarfme.html

PRESSES AND PRESS WORK


Date: ___ /___ /______

EXPERIMENT NO.2

AIM: TO STUDY ABOUT DIFFERENT TYPES DIES AND PRESS TOOL DESIGN.

2.1 Classification of presses

Types of presses for sheet metal working can be classified by one or a combination of

characteristics, such as source of power, number of slides, type of frame and construction, type

of drive, and intended applications.

2.1.1 Classification on the basis of source of power

Manual Presses. These are either hand or foot operated through levers, screws or gears.

A common press of this type is the arbor press used for assembly operations.

Mechanical presses. These presses utilize flywheel energy which is transferred to the

work piece by gears, cranks, eccentrics, or levers.

Hydraulic Presses. These presses provide working force through the application of fluid

pressure on a piston by means of pumps, valves, intensifiers, and accumulators. These

presses have better performance and reliability than mechanical presses.

Pneumatic Presses. These presses utilize air cylinders to exert the required force. These

are generally smaller in size and capacity than hydraulic or mechanical presses, and

therefore find use for light duty operations only.

2.1.2 Classification on the basis of number of slides

Single Action Presses. A single action press has one reciprocation slide that carries the

tool for the metal forming operation. The press has a fixed bed. It is the most widely

used press for operations like blanking, coining, embossing, and drawing.

Double Action Presses. A double action press has two slides moving in the same

direction against a fixed bed. It is more suitable for drawing operations, especially deep

drawing, than single action press. For this reason, its two slides are generally referred

to as outer blank holder slide and the inner draw slide. The blank holder slide is a hollow

rectangle, while the inner slide is a solid rectangle that reciprocates within the blank

holder. The blank holder slide has a shorter stroke and dwells at the bottom end of its

stroke, before the punch mounted on the inner slide touches the work piece. In this way,

practically the complete capacity of the press is available for drawing operation.

Another advantage of double action press is that the four corners of the blank holder

are individually adjustable. This permits the application of non-uniform forces on the

work if needed. A double action press is widely used for deep drawing operations and

irregular shaped stampings.

Triple Action Presses. A triple action press has three moving slides. Two slides (the

blank holder and the inner slide) move in the same direction as in a double – action

press and the third or lower slide moves upward through the fixed bed in a direction

opposite to that of the other two slides. This action allows reverse – drawing, forming

or bending operations against the inner slide while both upper actions are dwelling.



Cycle time for a triple – action press is longer than for a double – action press because

of the time required for the third action.

2.1.3 Classification on the basis of frame and construction

Arch – Frame Presses. These presses have their frame in the shape of an arch. These

are not common.

Gap Frame Presses. These presses have a C-shaped frame. These are most versatile and

common in use, as they provide un – obstructed access to the dies from three sides and

their backs are usually open for the ejection of stampings and / or scrap.

Straight Side Presses. These presses are stronger since the heavy loads can be taken in

a vertical direction by the massive side frame and there is little tendency for the punch

and die alignment to be affected by the strain. The capacity of these presses is usually

greater than 10 MN.

Horn Presses. These presses generally have a heavy shaft projecting from the machine

frame instead of the usual bed. This press is used mainly on cylindrical parts involving

punching, riveting, embossing, and flanging edges.

Fig. 2.1 Typical frame designs used for power presses.



2.2 Press Working Terminology

Base The all machine tool, base is the one of the parts of a press. It is main supporting member for work

piece holding dies and different controlling mechanisms of press. Size of the table limits the size of

work piece that can be processed on a press. In case of some special presses the base carries mechanism

for tilting the frame in any desirable inclined position too.

Frame Frame constitutes main body of the press located at one edge of its base. It houses support for ram,

driving mechanism and control mechanisms. Some of the press have column shaped frame.

Ram This is main operating part of the press which works directly during processing of a work piece. Ram

reciprocates to and fro within its guide ways with prescribed stroke length and power. The stroke length

and power transferred can be adjusted as per the requirements. Ram at its bottom end carries punch to

process the work piece.

Pitman It is the part which connects the ram and crankshaft or ram eccentric.

Driving Mechanism Different types of driving mechanisms are used in different types of presses like cylinder and piston

arrangement in hydraulic press, crankshaft and eccentric mechanisms in mechanical press, etc. these

mechanisms are used to drive ram by transferring power from motor to ram.

Controlling Mechanisms Controlling mechanisms are used to operate a press under predetermined controlled conditions.

Normally two parameters are adjusted by controlling mechanisms length of stroke of ram and power of

stroke. Transfer of power can be disengaged with the help of clutch provided with driving mechanisms

as per need. In most of the presses controlling mechanisms is in built with the driving mechanisms.

Now-a-days compute controlled presses are being used in which controlling is guided by

microprocessor. These presses provide reliable and accurate control with automation.

Flywheel In most of the presses driven gear or driven pulley is made of the shape of flywheel, which is used for

storing the energy reserve wire of energy) for maintaining constant speed of ram when punch is pressed

against the work piece. Flywheel is placed in the driving mechanism just before the clutch is sequence

of power transmission.

Brakes Brakes are very urgent in any mobile system. Generally two types of brakes are used normal brake,

which can bring the driven shaft to rest quickly after disengaging it from flywheel. Other is emergency

brakes which are provided as foot brake to any machine. These brakes include power off switch along

with normal stronger braking to bring all motions to rest quickly.

Balster Plate It is a thick plate attached to the bed or base of the press. It is used to clamp the die assembly rigidly to

support the work piece. The die used in press working may have more than one part that is why the

phrase die assembly is being used at the place of die.



Die Set It is the unit assembly which incorporates a top shoe and bottom shoe, two or more guide

pillars and guide bushings.

Advantages: 1) It aligns the punch and dies members.

2) It reduces the setup time in the press to a minimum.

3) This facilitates resharpening of punch and die without removing from the

die set.

Fig. 2.2 Simple Cutting Die

Top shoe

this is the upper part of the die set which contains guide bushings and punch holding

assembly. It is directly fastened to the press ram with the help of shank.

Bottom shoe

this is the lower part of the die set which contains guide pillars. It is generally mounted on the

press bed. The die block is mounted on the bottom shoe.

Punch

punch is the male part of the die assembly, which is directly or indirectly moved by and

fastened

to the press ram. Punches are made from good grade of tool steel or high carbon high

chromium steel material and it is hardened. Punch is the master of piercing.

Die

die is the female part of the die assembly, which is mounted on the lower shoe. Dies are made

from tool steels or high carbon high chromium steel and it is hardened. Die is the master of

blanking.

Backup plate

Backup plate or pressure plate placed between the top plate and punch holder plate. It is a

hardened one. It is used to prevent the punch making any impression on the soft top plate.

The plate distributes the pressure over a wide area and the intensity of pressure on the punch



holder is reduced to avoid crushing. Backup plates are made from oil hardened non-shrinkage

steel materials and carbon steels (c45) and it is hardened and ground parallel. The thickness

of the backup plate depends upon the stock thickness.

For up to 2mm stock thickness, 3mm thickness backup plate is used.

For about 3mm stock thickness, 6mm thickness backup plate is used.

Punch holder plate

it is fastened to the top plate through the backup plate. It is used to hold the punch correctly.

These plates are made from mild steel material.

Guide pillars and guide bushings guide pillars are mounted on the bottom shoe and guide bushings are mounted on the top

shoe. Both they are press fitted on their plates. Pillar and bush have a slide fit to them. They

are help in obtaining alignment of the punch and die. These are made from carbon steels and

hardened and ground.

Stripper Plate

This plate is mounted on the die plate. It is called as fixed stripper plate. A channel is

provided in this plate for feeding the metal strip. It is used to strip out the strip from the

punch during the return stroke of the press. It is also helps to correctly guide the punch into

the die opening. In some cases, it is mounted to the punch assembly. It is called as spring

loaded stripper.

2.3 Specification of press

Expressing size of a machine (press) includes expressing each of the parameters pertaining to it

quantitatively in appropriate units. Expressing size in the above mentioned way is the specifications of

press. The following parameters are expressed as specifications of a press.

(a) Maximum Force: Maximum force that its ram can exert on the work piece, this is

expressed in tones and called tonnage. It varies from 5 to 4000 tons for mechanical

press. It may be up to 50,000 tons by hydraulic press.

(b) Maximum Stroke Length: Maximum distance traveled by the ram from its top most

position to extreme down position. It is expressed in mm. the stroke length is adjustable

so different values that can be obtained between minimum and maximum of stroke

length, these are also the part of specifications.

(c) Die Space: Total (maximum) surface area, along with (b x d), of bed, base, ram base.

This the area in which dies can be maintained.

(d) Shut Height: Total opening between the ram and base when ram is at its extreme down

position. This is the minimum height of the processed work piece.

(e) Press Adjustments: Different stroke lengths (already covered in point number 2).

Different tonnage that can be set as per the requirement.



(f) Ram Speed: It is expressed as number of strokes per minute. Generally it can be 5 to

5000 strokes per minute.

(g) Stroke: The stroke of press is distance of ram movement from its up position to its

down position.

2.4 Classification of Die

There is a broader classification of single operation dies and multi-operation dies.

(a) Single operation dies are designed to perform only a single operation in each stroke of ram.

(b) Multi operation dies are designed to perform more than one operation in each stroke of ram.

Single operation dies are further classified as described below.

Cutting Dies These dies are meant to cut sheet metal into blanks. The operation performed so is named as blanking

operation. These dies and concerned punches are given specific angles to their edges. These are used

for operation based on cutting of metal by shearing action.

Forming Dies These dies are used to change two shape of work piece material by deforming action. No cutting takes

place in these dies. These dies are used to change the shape and size related configuration of metal

blanks.

As there is a classification of single operation dies, multi-operation dies are can also be classified

(further) as described below.

Compound Dies

Fig. 4.3 Compound die

In these dies two or more cutting actions (operations) can be executed in a single stroke of the ram.



Transfer Die It is also like a progressive die having more than one working points. It is different form progressive

die as it has feeding fingers in the die which transfer the work piece from one work station to other. In

some cases feeding fingers are attached to press, and then the press is called transfer press.

Combination Dies

Fig. 4.3 Combination dies

As indicated by their names these dies are meant to do combination of two or more operations

simultaneously. This may be cutting action followed by forming operation. All the operations are done

in a single action of ram.

Progressing Dies

Fig. 4.4 Progressing Dies

These dies are able to do progressive actions (operations) on the work piece like one operation followed

by another operation and so on. An operation is performed at one point and then work piece is shifted

to another working point in each stroke of ram.



2.5 Principle of metal cutting:

The cutting of sheet metal in press work is a shearing process. The punch and die have same

shape of the part.

The sheet metal is held between punch and die. The punch moves down and presses the metal

into the opening of the die. There is a gap between the punch and die opening. This is called as

“Clearance”.

Fig. 4.5 Principle of Metal Cutting

The amount of clearance depends upon the type and thickness of the material. The punch

touches the metal and travels downward.

The material is subjected to both tensile and compressive stresses. By this pressure, the metal

is deformed plastically. The plastic deformation takes place in small area between punch and

die cutting edges. So the metal in this area is highly stressed. When the stress exceeds the

ultimate strength of the material, fracture takes place. The cutting edge of the punch starts the

fracture, in the metal from the bottom. The cutting edge of the die starts the fracture from the

top.

These fractures meet at center of the plate. As the punch continuous to move down, the metal

under the die is completely cutoff from the sheet metal. The cut out portion of the metal drops

down through the die opening. To make the metal to drop down freely, a die relief is given in

the die block. If the clearance is too large or too small cracks do not meet and a ragged edge

results due to the material being dragged and torn through the die.



2.6 Clearance

Clearance is the intentional space (gap) between the punch and die cutting edges.

Proper clearances between the punch and die cutting edges enable the fracture to meet, and the

fracture portion of the sheared edge has a clean appearance.

For improper clearances, cracks do not meet and ragged edge results due to the material being

dragged and torn through the die.

Clearances are calculated by depending upon the materials thickness and their cutting

allowances.

The usual clearances preside of the die for various materials are given below, in terms of the

stock thickness “t”.

For copper, aluminum, brass and soft steel = 3 to 5% of t

for medium steel = 6% of t

for hard steel = 7% of t

Excessive cutting clearance provides larger burr on the components and gives long tool life.

Insufficient cutting clearance prevents a clear break. It also increases pressure on punch and

dies, thereby reduces the tool life.

Correct cutting clearance will allow the fractures to meet evenly resulting in a clear break and

the sheared edge as a clear appearance and minimum burr.

2.6.1 How to Apply Cutting Clearance

Piercing Operation:

Fig. 2.6 Piercing Operation

In piercing operation, clearance is given to

the die.

The component size is equal to the punch.

Here slug is a scrap.

Die opening size = Hole to be pierced +2C.

Blanking Operation

Fig.2.7 Blanking Operation

In blanking operation, clearance is given to

the punch.

The component size is equal to the die.

Here slug is desired part.

Blank punch size = Hole to be blanked – 2C



2.7 Punch and Die Clearance after Considering the Elastic Recovery of the

Material.

In blanking operation, after the release of blanking pressure, the blank expands slightly. The

blanked part is actually larger than the die opening that has produced it.

Similarly in piercing operation, after the strip is stripped off the punch, the material recovers

and the hole contracts. Thus, the hole is actually small then the size of the punch which

produced it. Thus to produce correct hole and blank sizes, the punch size should be increase

and the die opening size should be decreased by an amount for elastic recovery.

The elastic recovery will depend upon blank size, stock thickness and material. It may be taken

as between 0.0125mm to0.075mm.

For stock thickness up to 0.25mm, this difference may be taken as zero.

For stock thickness 0.25mm to 0.75mm it may be equal to 0.025mm.

For stock thickness more than 0.75mm it may be taken as 0.05mm.

2.8 Press Selection Proper selection of a press is necessary for successful and economical operation. Press is a

costly machine, and the return on investment depends upon how well it performs the job.

There is no press that can provide maximum productively and economy for all application so,

when a press is required to be used for several widely varying jobs, compromise is generally

made between economy and productivity. Important factors affecting the selection of a press

are size, force, energy and speed requirements.

Size. Bed and slide areas of the press should be of enough size so as to accommodate the dies

to be used and to make available adequate space for die changing and maintenance. Stroke

requirements are related to the height of the parts to be produced. Press with short stroke should

be preferred because it would permit faster operation, thus increasing productivity. Size and

type of press to be selected also depends upon the method and nature of part feeding, the type

of operation, and the material being formed.

Force and Energy. Press selected should have the capacity to provide the force and energy

necessary for carrying out the operation. The major source of energy in mechanical presses is

the flywheel, and the energy available is a function of mass of flywheel and square of its speed.

Press Speed. Fast speeds are generally desirable, but they are limited by the operations

performed. High speed may not, however, be most productive or efficient. Size, shape and

material of work piece, die life, maintenance costs, and other factors should be considered

while attempting to achieve the highest production rate at the lowest cost per piece.



2.9 Mechanical versus Hydraulic Presses

Mechanical presses are very widely used for blanking, forming and drawing operations

required to be done on sheet metal. For certain operations which require very high force, for

example, hydraulic presses are more advantageous. Table 2.1 gives a comparison of

characteristics and preferred application of the two types of press.

Characteristic Mechanical Presses Hydraulic Presses

Force Depends upon slide

position. Dose not depends upon slide position. Relatively constant.

Stroke length Short strokes Long strokes, even as much as 3 m.

Slide speed High. Highest at mid-

stroke. Can be variable

Slow. Rapid advance and retraction. Variable speeds

uniform throughout stroke.

Capacity About 50 MN (maximum) About 500 MN, or even more.

Control Full stroke generally

required before reversel. Adjustable, slide reversal possible from any position.

Application

Operations requiring

maximum pressure near

bottom of stroke. Cutting

operations(blanking,

shearing, piercing, Forming

and drawing to depths of

about 100 mm.

Operations requiring steady pressure through-out stoke.

Deep drawing. Drawing irregular shaped parts.

Straightening. Operations requiring variable forces and /or

strokes.

2.10 Press Feeding Devices

Safety is an important consideration in press operation and every precaution must be taken to

protect the operator. Material must be tried to be fed to the press that eliminates any chance of

the operator having his or her hands near the dies. The use of feeding device allows faster and

uniform press feeding in addition to the safety features.

• Blank and Stamping Feeds.

Feeding of blanks or previously formed stampings to presses can be done in several ways.

Selection of a specific method depends upon factors like production rate needed, cost, and

safety considerations.

Manual feeding

Feeding of blanks or stampings by hand is generally limited to low production rate

requirements which do not warrant the cost of automatic or semi- automatic feeding devices.

Manual feeding, however, is accomplished with the use of a guard or, if a guard is not possible,

hand feeding tools and a point – of – operation safety device. Some commonly used hand

feeding tools are special pliers, tongs, tweezes, vacuum lifters and magnetic pick – ups.

http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT-ROORKEE/MANUFACTURING-PROCESSES/Metal%20Forming%20&%20Powder%20metallurgy/lecture7/lecture7.htm



Push feeds

These feeds are used when blanks need orientation in specific relation to the die. Work piece

is manually placed in a nest in a slide, one at a time, and the slide pushed until the piece falls

into the die nest. An interlock is provided so that the press cannot be operation until the slide

has correctly located the part in the die. To increase production rate, push feeds can be

automated by actuating the feed slide through mechanical attachment to the press slide.

Lift and transfer devices.

In some automatic installations vacuum or suction cups are used for lifting of blanks one at a

time from stacks and then moved to the die by transfer units. Separation of the top blank from

a stack is achieved by devices which are operated magnetically, pneumatically or mechanically.

• Dial Feeds.

Dial feeds consist of rotary indexing tables (or turntables) having fixtures for holding work

pieces as they are taken to the press tooling. Parts are placed in the fixtures at the loading station

(which are located away from the place of press operation) manually or by other means like

chutes, hoppers, vibratory feeders, robots etc. Such feeds are being increasingly used because

of higher safety and productivity associated with them.

• Coil Stock Feed.

Two main classifications of automatic press feeds for coil stock are slide (or gripper) and roll

feeds. Both of these may be press or independently driven.

Mechanical slide feeds.

Press – driven slide feeds have a gripper arrangement which clamps and feeds the stock during

its forward movement and releases it on the return stroke. Material is prevented from backing

up during the return stroke of the gripper by a drag unit like a frictional brake. Grippers

reciprocate on rods or slides between adjustable positive stops to ensure accuracy. Slide feeds

are available in a variety of sizes and designs. These are generally best for narrow coil stock

and short feed lengths.

Hitch – type feed.

This feed differs from press – driven mechanical slide feed in that actuation is by a simple flat

cam attached to the ram or punch holder instead of by the press. On the downward stroke of

the ram, one or more springs are compressed by the cam action, then on the upstroke, the

springs provide the force to feed stock into the die.

These feeds are best suited for coil stock of small to medium thickness and for relatively short

feed progression. These are one of the oldest and least expensive feeding devices still used vary



widely. Due to their low cost, they are generally left permanently attached to the dies, thus

reducing setup time.

Pneumatic slide feeds.

These feeds are similar to mechanical slide feeds in that they have grippers or clamps that

reciprocate on guide rails or slides between adjustable positive stops to push and / or pull stock

into a die. However, these differ in that they are powered by an air cylinder, with actuation and

timing of valves by cam – operated limit switches.

These feeds are best for short progression, and find wide applications in job shops because of

their low cost and versatility.

Roll feeds.

In these feeds, coil stock is advanced by pressure exerted between intermittently driven,

opposed rolls which allow the stock to dwell during the working part of the press cycle.

Intermittent rotation (or indexing) of the feed rolls, with the rolls rotating in only one direction,

is accomplished in many ways. In one common design, the rolls are indexed through a one –

way clutch by a rack – and – pinion mechanism that is actuated by an adjustable eccentric on

the press – crankshaft.

These feeds are available in several types and sizes to suit almost any width and thickness of

stock. Though their initial cost is slightly higher, their greater durability and lower maintenance

cost account for their extensive use.



2.11 Mounting Methods of Punches and Dies

Fig. 2.8 Mounting and holding of punches



Fig. 2.9 mounting of dies



Punch mounting methods

Type Mounting method Remarks

a Flange

fixing

The position and perpendicularity of the

punch are maintained by the shank, and

the head prevents the punch from coming

off.

Standard type for round punches. Reliable in

preventing the punch from coming off.

B Flange

(positioning

with a key

flat)



the head prevents the punch from coming

off.

The position is determined by a key flat

shank machined by WEDM and inserted

into a hole.

C Locating

with

dowel pin

Positional accuracy is achieved with the

dowel pin, and the head fastens the punch

in place.

The dowel hole is created by NC machining,

allowing easy positioning. This type is often

used for automobile dies.

D Fixing with

adjustment

pins



the head is fastened with a bolt.

This type allows the punch to be replaced

easily.

E Bolt fixing

(tapping)


punch are maintained by the punch plate,

and the bolt prevents the punch from

coming off.

Highly accurate and also reliable in

preventing the punch from coming off. Not

suitable for thin punches or punching for

heavy load.

F Key fixing The groove of the punch is fixed in place

with a key.

This type allows the punch to be installed

and replaced easily. This type is often used

for precision dies based on the stripper

plates.

G Holder

fixing

The head of the punch is screwed in place

with a holder.

This type allows the punch to be replaced

easily. This type is used in cases when the

clearance between the punch plate and

stripper plate is small.

H Ball lock A steel ball inside a special retainer locks

the punch groove to fasten the punch in

place.

The punch can be mounted and removed

easily by lifting up the steel ball with a pin.

This type is often used for automobile dies.

I Taper fixing A tapered part prevents the punch from

coming off.

This type is inexpensive because the head is

produced by upsetting. This type is often

used for quill punches.

J Taper+ring A special ring supports the tapered part. The special ring allows tapered head

punches with high strength heads to be

easily installed.



2.11.1 Punch holding methods

·Based on punch plate (fig.2.8)

This is the most commonly-used method, and because the punch is press-fit into the

punch plate, dies can be produced easily.

If the punch concentricity (fig.4.8) or accuracy of hole machining is poor, variation is

likely to occur in the clearance between the punch and die. As a result, this method is

not suitable for cases when clearance between the punch and die is small.

·Based on stripper plate (fig.2.9)

This method is primarily used for thin, high-precision dies (fig.4.9).

The punch tip is guided by the stripper plate, which is located close to the punch and

die, making it possible to minimize precision error. The punch is held in the punch

plate by a clearance

2.12 Strip Layout

Since, the components are to be ultimately blanked out of a stock strip; hence, precaution is to

be taken while designing the dies for utilizing as much of stock as possible.

It is also necessary in progressive dies, to ensure continuous handling of the scrap on the die

block, which means that the scrap strip should have sufficient strength.

Fig 2.5 strip layout terms

The distance between the blank and edge of strip known as back scrap

a = t + 0.015 h

Feed or advance or length of one piece of stock

S= w + b

The number of black which can be produced from one length of stock can be found out



N = (L – b) / s

The scrap remaining at end of length of strip may be calculated

Y = L – (Ns + b)

Measure of material of utilization

Ƞm = area of black to be cut / area of material available

Ƞm = (B/A) X 100

Percentage of scrap = [(A – B)/A] x 100

Where

a = Lead End

t = strip thickness

h = stock width

L = length of strip

W = black length

On material thickness the scrap bridge may be taken as

Material Thickness (mm) Scrap Bridge (mm)

0.8 0.8

0.8 to 3.2 t

Over 3.2 3.2

__________________

References:

Production Engineering -by P.C. SHARMA



JIGS AND FIXTURES


Date: ___ /___ /______

EXPERIMENT NO.3

AIM: TO STUDY AND PRACTICING ABOUT JIGS AND FIXTURES FOR VARIOUS

MACHINING OPERATIONS.

3.1 Fixture and Jig

3.1.1 Fixtures

Fixtures being used in machine shop are strong and rigid mechanical devices which enable

easy, quick and consistently accurate locating, supporting and clamping, blanks against cutting

tool(s) and result faster and accurate machining with consistent quality, functional ability and

interchangeability.

3.1.2 Jig

Jig is a fixture with an additional feature of tool guidance.

3.2 Purpose of Using Fixtures and Jigs

For a machining work, like drilling a through hole of given diameter eccentrically in a

premachined mild steel disk as shown in Fig. 3.1

Fig. 3.1 A through hole has to be drilled in a pre-machined mild steel disc.

In conventional drilling machine the following steps are followed with using jigs and fixtures.

cleaning and deburring the blank (disc)

marking on the blank showing the location of the hole and its axis on the blank

punch the centre at the desired location and prick punch the periphery of the hole to be

made in the disc

mount the blank in a drilling vice using parallel block, a small Vee block etc. to provide

support and clamp the blank firmly

position the vice along with the marked blank to bring the hole axis in alignment with the

drill axis by

JIGS AND FIXTURES


- either adjusting the vise position w.r.t. the fixed drill axis or moving the drilling

machine table and then locking the table position or moving the radial arm and the

drilling head, if it is a radial drilling machine

after fixing the blank, vise and the table, alignment is checked again

if error, like eccentricity, is found to occur then readjustment of location of the hole – axis

is to be done before and even after starting drilling

Drilling is accomplished.

Therefore it appears that so many operations are needed to be carried out carefully and skillfully

by the machinist or operator for such a simple job. Even after that there may be inaccuracies in

machining. Such tedious and time consuming manual work are eliminated or drastically reduced in

mass production by automatic or special purpose machine tools. But such machine tools are quite

expensive and hence are economically justified for only huge or mass production and not viable

for small lot or batch production. For batch production proper design and use of simple but effective

jigs and fixtures are appropriate and economically justified. This is schematically illustrated in Fig.

3.2.

The basic purposes of developing and using suitable jigs and fixtures for batch production in

machine shops are:

• To eliminate marking, punching, positioning, alignments etc.

• easy, quick and consistently accurate locating, supporting and clamping the blank in

alignment of the cutting tool

• Guidance to the cutting tool like drill, reamer etc.

• increase in productivity and maintain product quality consistently

• to reduce operator’s labour and skill – requirement

• to reduce measurement and its cost

• enhancing technological capacity of the machine tools

• Reduction of overall machining cost and also increases in interchangeability.

W – without using jig & fixture P – piece production

M – mass production B – batch production

F – using jig and fixture A – automatic (special purpose) machine

Fig. 3.2 Role of Jigs and Fixtures on machining cost

JIGS AND FIXTURES


3.3 Design Considerations for Jigs and Fixtures

Jigs and fixtures are manually or partially power operated devices. To fulfill their basic purposes,

jigs and fixtures are comprised of several elements (as indicated in Fig. 3.3):

• Base and body or frame with clamping features

• locating elements for proper positioning and orientation of the blank

• supporting surfaces and base

• clamping elements

• Tool guiding frame and bushes (for jig)

• Indexing plates or systems, if necessary

• Auxiliary elements

• fastening parts

Fig 3.3 Major Elements of jig and fixtures.

Therefore keeping in view increase in productivity, product quality, repeatability i.e.

interchangeability and overall economy in batch production by machining, the following factors

are essentially considered during design, fabrication and assembly of jigs and fixtures:

• easy, quick and consistently accurate locating of the blank in the jig or fixture in reference

to the cutting tool

• providing strong, rigid and stable support to the blank

• quick, strong and rigid clamping of the blank in the jig or fixture without interrupting any

other operations

• tool guidance for slender cutting tools like drills and reamers

• easy and quick loading and unloading the job to and from the jig or fixture

• use of minimum number of parts for making the jig or fixture

• use of standard parts as much as possible

• Reasonable amount of flexibility or adjustability, if feasible, to accommodate slight

variation in the job - dimensions.

• prevention of jamming of chips, i.e. wide chips-space and easy chip disposal

• Easy, quick and accurate indexing system if required.

• easy and safe handling and moving the jig or fixture on the machine table, i.e., their shape,

size, weight and sharp edges and corners

• easy and quick removal and replacement of small parts

• manufacturability i.e. ease of manufacture

• durability and maintainability

• Service life and overall expenses.

JIGS AND FIXTURES


3.4 Principles and Methods of Locating, Supporting and Clamping Blanks

and Tool Guidance in Jigs and Fixtures

It is already emphasized that the main functions of the jigs and fixtures are:

(a) Easily, quickly, firmly and consistently accurately

• locating

• supporting and

• clamping

The blank (in the jig or fixture) in respect to the cutting tool(s)

(b) Providing guidance to the slender cutting tools using proper bushes

There are and can be several methods of locating, supporting and clamping depending upon the

size, shape and material of the job, cutting tool and the machining work required. But some basic

principles or rules are usually followed while designing for locating, supporting and clamping of

blank in fixtures.

Principles or rules of locating in jigs and fixtures

For accurate machining, the work piece is to be placed and held in correct position and orientation

in the fixture (or jig) which is again appropriately located and fixed with respect to the cutting tool

and the machine tool. It has to be assured that the blank, once fixed or clamped, does not move at

all.

Any solid body may have maximum twelve degrees of freedom as indicated in Fig. 3.4. By properly

locating, supporting and clamping the blank it’s all degrees of freedom are to be arrested as

typically shown in Fig.

Fig. 3.4 Possible degrees of freedom of a solid body.

JIGS AND FIXTURES


The three adjacent locating surfaces of the blank (work piece) are resting against 3, 2 and 1 pins

respectively, which prevent 9 degrees of freedom. The rest three degrees of freedom are arrested

by three external forces usually provided directly by clamping. Some of such forces may be attained

by friction.

Fig 3.5 Arresting all degree of freedom of blank in fixture

Some basic principles or rules need to be followed while planning for locating blanks in

fixtures, such as;

• One or more surfaces (preferably machined) and / or drilled / bored hole(s) are to be taken

for reference

• The reference surfaces should be significant and important feature(s) based on which most

of the dimensions are laid down

• Locating should be easy, quick and accurate

• In case of locating by pin, the pins and their mounting and contact points should be strong,

rigid and hard

• A minimum of three point must be used to locate a horizontal flat surface

• The locating pins should be as far apart as feasible

• Vee block and cones should be used for self-locating solid and hollow cylindrical jobs as

typically shown in Fig.

• Sight location is applicable to first – operation location of blank with irregular surfaces

produced by casting, forging etc. as indicated in Fig. when the bracket is first located on

two edges to machine the bottom surface which will be used for subsequent locating.

• Adjustable locating pin(s) as indicated in Fig. is to be used to accommodate limited part

size variation.

JIGS AND FIXTURES


Fig. 3.6 Locating by Vee block and cone.

• For locating large jobs by rough bottom surface one of the three pins may be replaced

by a pivoted arm as indicated in Fig. 3.6. The pivoted arm provides two contact

points.

Fig. 3.7 (a) Sight location and (b) location by pivoted points (equalizer)

3.4.1 General methods of locating

3.4.1.1 Locating blanks for machining in lathes

In lathes, where the job rotates, the blanks are located by

- fitting into self centering chuck

- fitting into 4 – independent jaw chuck and dead centre

- in self – centering collets

- in between live and dead centers

- by using mandrel fitted into the head stock – spindle

- Fitting in a separate fixture which is properly clamped on a driving plate which is

coaxially fitted into the lathe spindle.

JIGS AND FIXTURES


3.4.1.2 Locating for machining in other than lathes

In machine tools like drilling machine, boring machine, milling machine, planning machine,

broaching machine and surface grinding machine the job remains fixed on the bed or work table of

those machine tools.

Fixtures are mostly used in the aforesaid machine tools and jig specially for drilling, reaming etc.

for batch production.

For machining in those jigs and fixtures, the blank is located in several ways which include the

followings

3.4.1.3 Locating by flat surfaces

Fig. 3.8 typically shows locating jobs by their flat surfaces using various types of flat ended pins

and buttons.

Fig. 3.8 Locating by (a) flat surfaces and (b) types of pins used for that.

3.4.1.4 Locating by holes

JIGS AND FIXTURES


In several cases, work pieces are located by premachined (drilled, bored or pierced) holes, such as;

• Locating by two holes as shown in Fig. 3.9 (a) where one of the pins has to be

diamond shaped to accommodate tolerance on the distance between the holes and

their diameters

• Locating by one hole and an external pin which presents rotation of the blank around

the inner pin as indicated in Fig. 3.9 (b)

• Locating by one hole and one Vee-block as shown in Fig. 3.10

Fig. 3.9 Locating by holes.

Fig. 3.10 Locating by a pin and Vee block.

3.4.1.5 Locating on mandrel or plug

JIGS AND FIXTURES


Ring or disc type work pieces are conveniently located on mandrel or single plug as shown in Fig.

3.11.

However there may be several other ways of locating depending upon the machining conditions

and requirements.

Fig. 3.11 Locating by mandrel or plug.

3.4.2 Supporting – principles and methods

A work piece has to be properly placed in the jig or fixture not only for desired positioning and

orientation but also on strong and rigid support such that the blank does not elastically deflect or

deform under the actions of the clamping forces, cutting forces and even its own weight.

Basic principles or rules to be followed while designing or planning for supporting • supporting should be provided at least at three points

• supporting elements and system have to be enough strong and rigid to prevent deformation

due to clamping and cutting forces

• Unsupported span should not be large to cause sagging as indicated in fig.

• Supporting should keep the blank in stable condition under the forces as indicated in fig.

• for supporting large flat area proper recess is to be provided, as indicated in fig. for better

and stable support.

• round or cylindrical work pieces should be supported (along with locating) on strong vee

block of suitable size

• Heavy work pieces with pre-machined bottom surface should be supported on wide flat

areas, otherwise on flat ended strong pins or plugs.

• if more than three pins are required for supporting large work pieces then the additional

supporting pins are to be spring loaded or adjustable mandrel work piece job jig plate plug

• additional adjustable supporting pins need to be provided

- to compensate part size variation

- when the supporting surface is large and irregular

- when clamping and cutting forces are large

• ring or disc type jobs, specially requiring indexing should be supported (and located) in

mandrel

JIGS AND FIXTURES


Fig. 3.12 Deflection due to force(s) for wide gap in between supports.

Fig. 3.13 Stability in supporting.

Fig. 3.14 Recess in long span supporting.

Common methods of supporting job in fixtures

- supporting on vices

- supporting on flat surfaces / blocks (fig. 3.15 (a))

- supporting by fixed pins (fig. 3.15 (b))

- additional supporting by adjustable pins and plugs or jack screws as shown in fig. 3.16

- Supporting (and locating) on vee blocks and mandrels.

JIGS AND FIXTURES


Fig. 3.15 Supporting (a) by flat surface and (b) by pins

Fig. 3.16 Adjustable supporting pins.

JIGS AND FIXTURES


3.4.3 Clamping of work piece in fixtures

In jigs and fixtures the work piece or blank has to be strongly and rigidly clamped against the

supporting surfaces and also the locating features so that the blank does not get displaced at all

under the cutting forces during machining.

While designing for clamping the following factors essentially need to be considered.

clamping need to be strong and rigid enough to hold the blank firmly during machining

clamping should be easy, quick and consistently adequate

clamping should be such that it is not affected by vibration, chatter or heavy pressure

the way of clamping and unclamping should not hinder loading and unloading the blank in

the jig or fixture

the clamp and clamping force must not damage or deform the work piece

clamping operation should be very simple and quick acting when the jig or fixture is to be

used more frequently and for large volume of work

clamps, which move by slide or slip or tend to do so during applying clamping forces,

should be avoided

clamping system should comprise of less number of parts for ease of design, operation and

maintenance

the wearing parts should be hard or hardened and also be easily replaceable

clamping force should act on heavy part(s) and against supporting and locating surfaces

clamping force should be away from the machining thrust forces

clamping method should be fool proof and safe

Clamping must be reliable but also inexpensive.

3.4.4 Various methods of clamping Clamping method and system are basically of two categories:

3.4.4.1 General type without much consideration on speed of clamping operations

3.4.4.2 Quick acting types

3.4.4.1 General clamping methods of common use

Screw operated strap clamps as typically shown in Fig. 3.17. The clamping end of the strap is

pressed against a spring which enables quick unclamping

Fig. 3.17 Common strap type clamping

JIGS AND FIXTURES


Clamping from side for unobstructed through machining (like milling, planning and

broaching) of

the top surface. Some commonly used such clamping are shown in Fig. 3.18

Fig. 3.18 Clamping from side for free machining of the top surface.

Fig. 3.19 Clamping by swing plates.

JIGS AND FIXTURES


3.4.1.1 Clamping by swing plates

Such clamping, typically shown in Fig. 3.19, are simple and relatively quick in operation but is

suitable for jobs of relatively smaller size, simpler shape and requiring lesser clamping forces.

• Other conventional clamping methods include:

∗ Vices like drilling and milling vices

∗ Magnetic chucks

∗ Chucks and collets for lathe work.

3.4.1.2 Quick clamping methods and systems

Use of quick acting nut – a typical of such nut and its application is visualized schematically in

Fig. 3.20

Fig. 3.20 Quick acting nut for rapid clamping.

3.4.1.3 Cam clamping -

Quick clamping by cam is very effective and very simple in operation. Some popular methods and

systems of clamping by cam are shown in Fig. 3.21

The cam and screw type clamping system is used for clamping through some interior parts where

other simple system will not have access.

Fig. 3.21 Quick clamping by cams.

JIGS AND FIXTURES


Quick multiple clamping by pivoted clamps in series and parallel. This method shown in Fig. is

capable to simultaneously clamp number of rods even with slight diameter variation.

3.5 Locating Devices:

Pins of various designs and made of hardened steel are the most common locating devices used

to locate a work piece in z jig or fixture. The shank of the pin is press fitted or driven into the

body of the jig or fixture. The locating diameter Of the pin is made larger than the shank to

prevent it from being forced into the jig or fixture body due to the weight of the work piece or

the cutting forces. Depending upon the mutual relation between the work piece and pin, the

pins may be classified as:

1. Locating pins 2. Support pins 3. Jack pins

3.5.1 Locating pins: When reamed or finely finished holes are available in the workpiece,

these can be used for locating purposes. Depending upon their form, the locating pins are

classified as:

Fig.3.5.1 Locating Pins

JIGS AND FIXTURES


3.5.1.1 Conical locating pins

These pins are used to locate a work piece which is cylindrical and with or without a hole. Any

variation in the hole size will be easily accommodated due to the conical shape of the pin.

3.5.1.2 Cylindrical locating pins

In these pins, the locating diameter of the pin is made a push fit with the hole in the work piece,

with which it has to engage. The top portion of these pins is given a sufficient lead either by

chamfering or by means of radius to facilitate the loading of the work piece.

3.5.2 Support pins

With these pins (also known as rest pins, buttons or pads), work pieces with flat surfaces can

be supported at convenient points. In the fixed type of support pins, the locating surface is

either ground flat or is curved. Support pins with flat head are usually employed to provide

location and support to machined surfaces, because more contact area is available during

location. It would ensure accurate and stable location and would not indent the work. The

spherical head or rounded-head rest buttons are conventionally used for supporting rough

surfaces (unmachined and cast surfaces), because they provide a point support which may be

stable under these circumstances. Adjustable type support pins are used for work pieces whose

dimensions can vary, e.g., sand castings, forging or unmachined faces.

Fig. 3.5.2 support pin

JIGS AND FIXTURES


If the component is to be located in the jig/fixture body, without the aid of these support pins,

then the surface of the jig/ fixture body where the component will be supported will have to be

machined. This will involve unnecessary machining time. The use of support pins saves

machining time as only seats for the pins can be machined instead of the entire body of a large

fixture. For small work pieces, however, no support pins are necessary. The fixture body itself

can be machined suitably to provide the locating surfaces. An ample recess should be provided

in corners so that burr on the work piece corners or dirt and swarf do not obstruct proper

location through positive contact of the work piece with the locating surface. Support pins in

large fixtures automatically provide similar recesses.

3.5.3 Jack pins.

Fig. 3.5.3 jack pin

Jack pins or spring pins are also used to locate the work pieces whose dimensions are subject

to variation. The pin is allowed to come up under spring pressure or conversely is pressed down

by the work piece. When the location of the work piece is secured, the pin is locked in this

position by means of the locking screw.

3.5.4 Radial or Angular Location.

Work pieces such as connecting rod or lever, which have two previously machined and finished

holes at the two ends, may be located with the help of two pins projecting from the base surface

of a jig or fixture, which will fit into the two holes in the work piece. Assuming that the work

piece is effectively located on pin A, the only movement the work piece can have is that of

rotation about the pin A. Now, neither the work piece nor the jig or fixture can be made to the

exact dimensions. It means the centre distances between pins A and B and between holes A

and B is subject to variation. Let the tolerance for the centre distance between the holes A and

B be 'x' and that for the centre distance between the pins, A and B by 'y'. Then if the work piece

is effectively located on pin A and if the pin B is a complete cylinder, the allowance between

pin B and hole B will be x plus y. When the centre distance dimensions for the pins and holes

are at maximum and minimum conditions, a large allowance will result between the hole and

pin at B in the Y direction. Due to this, the work piece will have undesirable rotation about the

pin A and the pin B becomes useless. Therefore, to locate the component completely, location

faces opposed to this rotational movement should be provided at the hole B. This is achieved

by relieving the pin B on two sides perpendicular to the X-axis. This will allow for variations

JIGS AND FIXTURES


in the X-direction but will provide cylindrical locating surfaces in the Y-direction. This will

result in a flattened or diamond pin locator as shown in respectively.

The- important and accurate hole of the two holes should be used for principal cylindrical-

location with a full cylindrical pin. The diamond pin is used to constrain the pivoting of the

work piece around the principal location. The principal locator should be longer than the

diamond pin so that the work piece can be located and pivoted around it before engaging with

the diamond pin. This simplifies and speeds up locating of the work piece.

Fig. 3.5.4 flattened pin locator

A work piece with only one hole can also be fully located as shown in Fig. The principal

location is secured from pin A. The radial movement in both the directions of y-axis is restricted

by providing two pins B confining the periphery of the work piece. The basic principle for

radial locations so as to minimize deviations from true locations is to position the radial locators

as far from the axis of rotation as possible.

3.6 Types of Clamps

JIGS AND FIXTURES


While the types of clamps are numerous, they can be classified in seven basic groups: strap,

cam, screw, latch, wedge or key, toggle, and rack and pinion. Most clamping devices contain

one or more of these elements. In a combination, the name of the most prominent element is

given to the complete clamping device.

3.6.1 Lever of strap clamps

Fig. 3.22 Lever of strap clamps

This is the most popular clamping device used in workshops, and tool rooms of jigs and

fixtures.

Figs. B, C and D show lever type clamps in which the layout is based on fig A. In these, as the

nut is unscrewed the spring pushes the clamp upward. The clamp has a longitudinal slot so that

it can be speed up by using a threaded handle or a quick action locking cam in place of

hexagonal nut .Fig shows the hinge clamp, the sliding clamp, and the latch clamp. The fulcrum

is positioned so that clamp bar is parallel to the base of the tool at all times. Strap clamp can be

operated by either manual or power driven devices. Manual devices include hexagonal nuts,

hand knobs, and cams as shows in fig.3.22. The holding power of a strap clamp is determined

by the size of the threaded member binding the clamp.

JIGS AND FIXTURES


Fig. 3.22 Types of clamps

3.6.2 Screw clamps

These are widely used for jigs and fixtures. These have lover costs. However, their operating

speed is quite slow. The basic screw clamp uses the torque developed by a screw thread to hold

a part in place. This is done by direct pressure or by acting on another clamp.

Fig. 3.23 indirect clamping with a screw clamp.

There are variations of the screw type clamp. The efficiency of the screw clamp can be

improved by using swing clamps, hook clamps and quick acting knobs.

JIGS AND FIXTURES


3.6.3 Cam action clamps

Cam action clamps, when properly selected and used, provide a fast, efficient and simple way

to hold work, as shows in fig.

Fig 3.24 direct pressure cam clamps

Due to their construction and basic operating principles, the use of cam action clamps is limited

in some types of tools.

3.6.3 hinged clamps

These utilize hinged lids for loading and unloading the components. Generally the clamp is

made integral with the hinged lib.

Fig. 3.25 hinged clamped bolt

fig. shows an arrangement using combination of hinged clamps and hinged bolt. This type of

clamp is often required when it is necessary to move both the clamp and the bolt completely

out of the way for the loading of component. The casing is designed such that the lugs are

JIGS AND FIXTURES


provided for locating the hinge pins. In order to save the operator’s time, a coil spring is used

to hold the washer under the nut.

fig shows an arrangement in which a hook cam is fitted which permits the job to be handled

faster. it is only suitable for light clamping. The clamping lever is hinged on the clamping bar

which, in its turn, is hinged on the fixture. along the clamping bar is fitted a floating pad which

holds the work and the clamping lever is then forced against a pin or other abutment fitted to

the fixture.

3.6.4 two way clamps

Fig. shows an example of rapid clamping in two directions from one screw. Clamping force

is applied to the top and one side of the work piece.

Fig. 3.26 two way clamps

the clamp has a quick release action. in this arrangement, the length of the levers should be

approximately such that equal pressure is applied by each clamp at its clamping position. the

top clamp is slotted at the end so that the whole of its clamping mechanism could be swung

clear of the work.

3.6.5 Wedge operated clamps

Fig. shows the operation of wedge operated clamps in which the horizontal movement of the

wedge causes upward vertical clamping force on the work piece. the wedge could be operated

either manually by a screw or cam, or by pneumatic or hydraulic cylinder in which case

automatic clamping of the work piece as part of a fully automatic machine cycle is possible.

Wedges having angle of 1-4’ are self holding type and normally hold the work without

additional attachments. large angle wedges are used where large movement is required. in these

wedge clamps, another holding device is required to hold and wedge the work piece in place.

Fig. 3.28 wedge operated clamp

3.6.6 Cam operated clamps

JIGS AND FIXTURES


These provide a fast, efficient, and simple way to hold work. if cam clamps apply pressure

directly to work and work is subjected to vibration, then clamp may loosen and such clamp

should not be used. Direct pressure cam clamps must be positioned to resist the natural

tendencies of the clamp to shift or move the work when the clamp is engaged. to prevent this

movement, the clamp is always positioned such that work is pushed into the locaters when

pressure is applied.

Fig. 3.29 indirect pressure cam clamp

the advantages of cam action can be obtained in indirect clamping method by using cam action

rather than screw threads to bind strap clamps as shown in fig. in this method, the possibility

of loosening or shifting the work during clamping is decreased.

There are three basic type of cams used for clamping mechanisms: flat eccentric, flat spiral,

and cylindrical.

3.67 Toggle action clamps

These are fast acting clamps. These have the natural ability to move completely free of the

work, allowing for faster taking out of parts. The holding force to toggle clamps compared to

the application force is very high.

fig. shows the four basic clamping actions, viz. hold down, pull, squeeze, and straight line

action.

3.6.8 Power clamping:

Power activated clamps may operate under hydraulic power, pneumatic power, or with an air-

to-hydraulic booster.

The power clamps have better control of clamping pressures. Wear on moving parts of the

clamp is less, operating cycles becomes faster. Production speeds and efficiency are higher but

initial cost is high. Fig. shows a typical application of power clamp.

JIGS AND FIXTURES


Fig. 3.30 toggle clamps

Fig 3.31 power clamp

JIGS AND FIXTURES


3.7 Types of jig bushes

Depending upon nature of fitting, quick mounting and replacement, job requirement etc. jig bushes

are classified into several types.

• Bushes may be

⎯ Press fitted type

⎯ Slip type

⎯ Screwed type

Press fitted thin sleeve type bushes are generally used for shorter runs and are not renewable.

Renewable type slip bushes are used with liner. But screw bushes, though renewable may be used

without or with liner.

• Bushes may be

⎯ Without head

⎯ With head

⎯ With a flange being screwed on the bracket.

Fig. 3.32 Bushes (a) without head, (b) with head and (c) flange.

Fig. 3.32.1 Jig bushes

JIGS AND FIXTURES


Frequently replaceable bushes are provided with some locking system as shown in Fig. 3.33

Fig. 3.33 Locking of frequently replaceable bushes.

Some special jig bushings are often designed and used as and when required as indicated in Fig.

3.34

Fig. 3.34 Special jig – bushes for critical requirements.

Many other types are possible and made depending upon the working situation and critical

requirements.

JIGS AND FIXTURES


3.8 Types of jigs

3.8.1 Template jig

3.8.2 Plate type jig

3.8.3 Open type jig

3.8.4 Channel jig

3.8.5 Leaf Jig

3.8.6 Box type jig

3.8.1 Template Jig This is the simplest type of jig; It is simply a plate made to the shape and size of the work piece;

with the required number of holes made it. It is placed on the work piece and the hole will be

made by the drill; which will be guided through the holes in the template plate should be

hardened to avoid its frequent replacement this type of jig is suitable if only a few part are to

be made.

Fig.3.35 Template Jig

3.8.2 Plate Type Jig: This is an improvement of the template type of jig. In place of simple holes, drill bushes are

provided in the plate to guide the drill. The work piece can be clamped to the plate and holes

can be drilled. The plate jigs are employed to drill holes in large parts, maintaining accurate

spacing with each other.

Fig. 3.36 Plate type jig

http://2.bp.blogspot.com/_2_P6uqc8P3w/TN1-ki2uAnI/AAAAAAAAAH8/nrDqecpobFU/s1600/Template+jig.bmp

http://2.bp.blogspot.com/_2_P6uqc8P3w/TN1_0WxQlhI/AAAAAAAAAIA/RIpeDXnHia8/s1600/plate+jig.bmp

JIGS AND FIXTURES


3.8.3 Open Type Jig: In this jig the top of the jig is open; the work piece is placed on the top.

Fig. 3.37 Open type jig

3.8.4 Channel jig; The channel jig is a simple type of jig having channel like cross section. The component is

fitted within the channel is located and clamped by locating the knob. The tool is guided

through the drill bush.

Fig. 3.38 Channel jig

3.8.5 Leaf Jig It is also a sort of open type jig , in which the top plate is arrange to swing about a fulcrum

point , so that it is completely clears the jig for easy loading and unloading of the work piece.

The drill bushes are fitted into the plates, which are also known as leaf, latch or lid.

Fig. 3.37 Leaf Jig

http://4.bp.blogspot.com/_2_P6uqc8P3w/TN2BBWMHxaI/AAAAAAAAAIE/u_XFoZ59INM/s1600/open+type+jig.bmp

http://1.bp.blogspot.com/_2_P6uqc8P3w/TN2ClpDfboI/AAAAAAAAAII/N6ajnF5fNsE/s1600/channel+Jig.bmp

http://2.bp.blogspot.com/_2_P6uqc8P3w/TN2DaFx5AyI/AAAAAAAAAIM/FhhrrRKQClM/s1600/Leaf+jig.bmp

JIGS AND FIXTURES


3.8.6 Box Type Jig When the holes are to drill more than one plane of the work piece, the jig has to be provided

with equalant number of bush plates. For positioning jig on the machine table feet have to be

provided opposite each drilling bush plate. One side of the jig will be provided with a swinging

leaf for loading and unloading the work piece, such a jig would take the form of a box. Such a

jig should be as light as possible. Since it will have lifted again and again. Typical figure of

box type jig is shown:

Fig. 3.38 Box Type jig

3.8.7 Angular Jig

Fig. 3.39 Angular Jig

This type of jig is used when the hole is

drilled at an angle to the drilling bush axis.

These types of jigs are used to drill holes in

collars and hubs of pulleys and gears.

__________

References:

Production Engineering -by P.C. SHARMA



http://2.bp.blogspot.com/_2_P6uqc8P3w/TN2FDAypNzI/AAAAAAAAAIQ/X7kInjUC2Hw/s1600/box+type+jig.bmp

THERMAL ASPECTS IN MACHINING

PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING

DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 59

Date: ___ /___ /______

EXPERIMENT NO. 4

AIM: STUDY ABOUT VARIOUS THERMAL ASPECTS IN MACHINING

Introduction:

Temperature is the main limitation in the selection of process parameters such as cutting

speed and feed rate in the machinability and production of some advanced materials

such as titanium and nickel-based alloys.

In such materials due to their lower thermal conductivity, most of heat flows into tool

and which accelerates tool failure.

When a metal is deformed plastically as in cutting operations, the energy spent is

converted into heat, raising the temperature of chip, tool, and work piece.

The heat generated during machining operation depends on the rate of metal cutting,

cutting speed, specific heat and thermal conductivity of the work piece and tool

material.

Cutting speed has more influence on the temperature because as speed increases, the

time for heat dissipation decrease, thus temperature increase.

The total heat generated during operation is distributed between work piece, tool, chip

and surrounding. The amount of dissipated by surroundings is very small and can be

neglected. The heat distributed in metal cutting operation is approximately 70:15:15

between chips, tool and work piece.

4.1. Amount of heat Generation

The amount of heat generated in metal machining per unit time is equivalent to

mechanical work done given by,

Q Fc.V J/s

4.2. Effect of Cutting Temperature on tool and Workpiece

For cutting tool:

Plastic deformation of cutting edges if tool material is not enough hard.

Thermal fracturing of cutting edges.

Formation of built up edge.

Rapid tool wear.




For Workpiece:

Dimensional inaccuracy

Rapid corrosion due to surface damage by oxidation.

Burning

Micro-cracks at the surface.

4.3 Source of Heat generation in machining

During machining heat is generated at the cutting point from three sources Those

sources and causes of development of cutting temperature are:

• Primary shear zone, where the major part of the energy is converted into heat

• Secondary deformation zone at the chip – tool interface where further heat is

generated due to rubbing and / or shear

• At the worn out flanks due to rubbing between the tool and the finished surfaces.

4.4 Cutting Fluid:

Cutting fluid are those liquid and gases which are applied to cutting zone to facilitate

cutting operation by removing heat.




4.4.1 Characteristics of Good cutting Fluid:

High specific heat and thermal conductivity

Ability of spreading and wetting

High lubricity without gumming and foaming

Chemically stable and non corrosive

Non toxic, odorless and colorless

Easily available with low cost.

4.4.2 Method for application of cutting Fluid:

Flood cooling

Mist cooling

High pressure refrigerated cooling

Student Activity:

Prepare table for recommended cutting fluid for various engineering materials.

GEAR MANUFACTURING METHODS



Date: ___ /___ /______

EXPERIMENT NO. 5

AIM: STUDY OF GEAR MANUFACTURING METHODS.

Introduction:

The methods commonly used for gear manufacturing include the following:

4.1. Machining:

Gear cutting by machining may be done by the following methods:

• Form cutting

• Template process

• Generating processes

4.1.1. Form cutting:

In the form cutting process a tool or cutter having a profile corresponding to the tooth space is

used to cut each space.

The accuracy of the tooth space is, therefore, a function of the accuracy of the cutter.

The other factors that contribute to the accuracy are:

a) Centralized location of the cutter relative to the blank

b) Proper division of the blank while cutting successive tooth spaces.

c) Depth of tooth space.

d) Concentricity of the teeth with the axis of the gear.

The various machining processes that use form cutters include:

a) Form milling with a disc cutter

b) Cutting with a single point tool on a shaper or planer

c) Broaching

4.1.2. Template process:

In the template method of gear cutting, a single point tool guided by a template is used to cut

the form of the tooth instead of a form tool. The process is carried out on special machines

called gear planers. The template guides and reciprocates the tool while the gear blank is held

stationary. If a template many times larger than the size of the teeth to be cut is used, very high

accuracy of tooth form can be ensured. Normally three sets of templates are used to complete

the tooth, one set for producing rough form of the tooth and the other two sets for finishing one

side each. The method is suitable for cutting very large size teeth which are difficult to cut with

a form tool. It can also be used for cutting straight bevel gears but has been replaced by

generating methods which are much more accurate and faster. The method is frequently used

for finishing the gear teeth formed by other methods.




4.1.3. Gear generation:

In the generation processes the profile to be cut is produced by a combination of movements

co-ordinated in such a way that the kinematic principle upon which the surface depends is fully

realized. The turning operation on a centre lathe is a simple example of a generated surface.

The kinematic derivation of this shape is that of sweeping a straight line about a parallel axis.

The necessary movements are provided by a combination of straight line movement of a tool

and rotation of the workpiece by the spindle. As has already been illustrated in the discussion

of the tooth profile a fundamental basis for the system which can be produced easily and

accurately is the involute rack. The rack forms the basis for some of the important methods of

gear generation the generating methods commonly used include:

(i) By the use of a pinion cutter in a gear shaping machine

(ii) By the use of a rack cutter in a gear shaping machine.

(iii) By the use of a hob in a gear hobbing machine.

(iv) By the use of bevel gear generator.

Machining of gears is the most common method of producing accurate gears for high speed

and high duty applications.

4.2. Casting:

Gears for low duty applications can be produced by casting processes. Large gears can be

produced by conventional dry sand or green sand processes but such gears are not accurate

dimensionally and have rough surfaces. They are generally used as cast and are found in

applications like concrete mixers, road rollers and gardening equipment where speeds are low

and noise and inaccuracy can be tolerated. Main advantage of casting is that the cost of

production is low. Hence the method is used mainly for production of large gears in which

inaccuracy of profile can be tolerated. More accurate gears in small size and large volume are

produced by die casting processes. They are generally made in nonferrous materials, are fairly

accurate and have good surface finish. Spur helical, bevel, worm and face gears can be

produced by this method. Die cast gears are used for light load conditions as in toys, hand tools,

gardening equipment etc. Gears required for transmitting heavier loads may be made by

investment casting.

Such gears are more accurate and have better surface characteristics. They also have more

strength. Gears made by die casting and investment casting processes, however, are limited to

low melting temperature metals and alloys and do not have the strength and wear characteristics

equal to those of heat treated steel gears.

4.3. Stamping:

Thin gears are sheared out of sheet stock upto 3mm thick by the use of punch and die sets. The

stock used in the gears is usually received as rolls. The stock is passed through a roll

straightener which irons out the stock and makes it flat. The stock then passes through the dies

and gears are sheared out. Because of the shearing action the cut edges tend to be rough and

the gears may be finished by passing them through shaving dies. If some other feature is to be

produced on the gear they are produced by the use of compound or progressive dies. A

compound die is preferable for better concentricity of centre hole with gear teeth as the entire

gear is produced in one stroke. Stamped gears are used in toys, clocks, watches, timer




mechanisms, water and electric meters etc. A wide variety of materials are used for the

production of these gears. They include plain carbon steels, stainless steels, aluminium alloys

and copper alloys. Although initial tooling costs are high, unit cost of production can be very

low when production quantities are large.It should be noted that a die set will be required for

each gear and the entire range of [ gears of a given module cannot be produced with one die.

4.4. Coining:

In this process gears are produced from blocks in a hydraulic press or forging hammers

applying heavy pressure. Gears produced by this process may be used as such or sometimes

may require light K machining.

4.5. Cold drawing:

In this process the gear tooth shape is produced progressively as the stock runs through several

dies. The final die gives the desired shape. The material is squeezed into the shape of the die

under pressure and hence the surface of the teeth is quite hard and smooth. Good drawing

quality materials like plain carbon steels, stainless steel, brass, bronze and aluminium can be

drawn. Gears produced by this process are used in clocks, type writers and other small

appliances.

4.6. Rolling:

In the rolling process, the workpiece is rolled between two cylindrical rollers of equal diameter

and having equal number of teeth (same module). The rollers are driven at the same pitch line

speed. During roll forming the rolls are gradually fed inwards till the gear teeth are produced.

The centre distance between the rollers is adjustable and the rollers are mounted in strong

bearings capable of taking heavy loads that occur during the process. Rolling of gears may be

done hot or cold. For hot rolling the gear stock is heated by induction heating and then rolled

while in the I plastic state. Large deformations are therefore possible in hot rolling. Hot rolled

gears may be finished by cold rolling to give a smooth finish to the gear teeth. Cold rolling of

gears is done without any heating and involves much higher pressures compared to hot rolling.

The gears produced by this process generally need no further finishing. The material also

becomes stronger and more fatigue resistant due to cold working. The rolling process is mainly

used for production of worms and involute splines. The produced teeth have good accuracy.

Since there is no metal cutting involved considerable material saving may result. The accuracy

of the finished gears depends upon the accuracy of the blank size provided. An approximation

to the blank size can be made by subtracting one depth from the finished outside diameter of

the gear. Plain carbon steels, alloy steels and brasses are the materials commonly used for rolled

gears. Because of the heavy equipment cost, rolled gears are economical only in large

quantities.

4.7. Extrusion:

Quite accurate gears of small size can be produced by the extrusion process. In this process

heated blocks of material to be extruded are placed in the extrusion cylinder and forced from

one end by a ram. Long lengths of rods having the cross section of the desired gear come out

from the die at the other end. These rods are then cut to required gear width with hack saws

and the resulting gears are finished. The materials that can be extruded include brass, bronze




and alloys of aluminium, magnesium and zinc. The method is used for production of spur gears

only.

4.8. Powder Metallurgy:

In this process raw material in the form of metal powders is mixed with a suitable binder and

forced under high pressure into a die cavity to take the desired shape of the gear. The compact

is then taken out and sintered in furnaces to produce the necessary bond. The gears so produced

may be further finished by coining. Coining helps remove any distortion due to the heat

treatment process and involves repressing the sintered gear in another die. The process also

improves gear accuracy and surface finish. Gears of Cast iron, steel, brass and other alloys can

be produced by this process. The process of producing gears by powder metallurgy is restricted

to small size gears not more than 25 mm diameter. Larger gears are produced by the Powder

Metallurgy Forging process. In this process powder metallurgy performs are forged to produce

the final gear form. This gives strength and durability to the gears. Gears produced by this

method also do not require further finishing. Gears produced by powder metallurgy have high

dimensional accuracy and surface finish and find applications in electrical appliances, small

motor drives, instruments and toys. Accurate gear pump rotors made of stainless steel can also

be produced by this method.

4.9. Plastic Moulding:

This process is used for mass production of plastic gears. These gears generally are lighter, run

quieter, have less friction and have smooth surfaces. They also do not need lubrication.

Thermoplastic materials like nylon are generally moulded by the injection moulding process

while thermosetting materials are handled by compression moulding. More accurate gears for

heavy duty applications may even be produced by machining from laminated plastics.

4.10. Gear Finishing Processes:

In order for gears to operate efficiently and without noise at a high speed for a reasonable life

span it is important that the profile of the gear teeth be accurate, smooth, without any

irregularities, projections or nicks. Gears produced by most processes with the possible

exception of roll forming are found not up to the mark in many cases. Gears produced by

milling may not have accurate tooth profile because of the use of a limited number of cutters.

Gear tooth surfaces produced by shaping or hobbing are composed of tiny flats which may not

be acceptable. The size of these flats can be reduced by reducing the feed rate but that increases

the cutting time. In many cases gears are hardened after cutting the teeth to improve their life.

This may introduce slight distortion or surface roughness. Use of gears with inaccurate or rough

profile leads to noisy operation, unequal loading of gear teeth, faster wear and early failure of

the gears. For economic production, it is considered more desirable to cut slightly inaccurate

gears at a fast rate and finish the tooth surfaces by a subsequent finishing operations.

The finishing operation is intended to perform the following functions :

(i) Correct any errors of profile and pitch

(ii) Eliminate any after effect of heat treatment.

(iii) Ensure proper concentricity of the pitch circle and the central hole.

The processes commonly used for gear finishing include.




1. Gear shaving

2. Gear burnishing

3. Gear grinding

4. Gear lapping

5. Honing

These processes remove very small amount of material from the tooth surface clearing any

irregularities, rectifying defects and producing a smooth, accurate surface for efficient

operation.

4.10.1. Gear Shaving:

Gear shaving is the most common method for gear finishing. In this method, the gear teeth are

finished by making the gear run at high speed in mesh and pressed against a hardened gear

shaving cutter. Sharp edges of the shaving cutter scrape small amount of metal from the surface

of the teeth removing any surface irregularities and correcting any errors. The axis of cutter

and gear are generally crossed at 5 to 15 degrees. This produces a small sliding action between

the gear and cutter teeth giving a smooth surface. Two types of gear shaving cutters are in

common use : rotary type and rack type. The rotary type of cutter is a gear with serrations or

grooves on its flanks. The edges of these grooves are sharpened to produce the cutting action.

The shaving operation with these cutters is carried out on rotary shaving machines. The cutter

is mounted on a mandrel and rotated at a surface speed of about 2 metres/second. The work

piece is loaded between live centres, raised to the level of the cutter and reciprocated at a slow

speed while being driven. The reciprocating action is to ensure that the shaving operation

extends over the entire length of the gear tooth.

During the shaving operation workpiece may be fed radialy or tangentially to the cutter. The

rack type shaving operation is carried out on rack type shaving machines using a rack type

cutter. The cutter is reciprocated at high speed in mesh with the workpiece. At the same time

the workpiece is reciprocated sideways and fed into the cutter. This type of cutter gives more

accurate gear teeth than the rotary cutter because an accurate rack is more easy to produce. It

also has a fuller contact with the workpiece compared to a rotary cutter. But rack type of

shaving cutters cannot be used for cluster type and very large size gears. Gear shaving is a fast

and rapid production process producing accurate teeth profiles on unhardened gears. If desired,

the process can also be used to crown gear teeth slightly at the centre to localize tooth contact

and provide better clearance during operation. Gear shaving corrects small errors in tooth

spacing, tooth profile, concentricity and helix angle. It also improves the surface finish.

4.10.2. Gear Burnishing:

Gear burnishing is a cold working process in which any high spots on unhardened gears are

plastically deformed to produce smooth and accurate surfaces. The gear to be finished is

mounted on a vertical floating spindle in mesh with three hardened burnishing gears. One of

these burnishing gears is power driven. During burnishing operation, the burnishing gears are

fed inwards towards workpiece and made to turn a few rotations in each direction. The surface

irregularity of the gear teeth are squeezed and a good surface finish obtained. The gear teeth

also get slightly hardened due to cold working. The process is however not recommended for

very precise gears because of hi localized residual stresses produced. Gear burnishing is used

for unhardened gears. The process can only improve the surface finish of the teeth and does

not correct t tooth profile or pitch of the teeth. As such the process is suitable only for gears

which do not require high accuracy.




4.10.3. Gear Grinding:

Gear grinding is the most accurate method of finishing gear teeth. It is most suitable for

finishing of hardened gears which cannot be finished by shavi: or burnishing. Heat treatment

often causes considerable distortion and oxide film formation whi needs deeper cuts for

complete removal. Grinding can accomplish this job easily because of the abrasive action and

is oft preferred to lapping because of the better accuracy obtained with grinding.

4.10.3.1. Form Wheel grinding:

Form wheel grinding shown at (a) is done with the help of a grinding wheel shaped to the exact

profile of a gear tooth space like a disc type form millii cutter. The workpiece is reciprocated

under the grinding wheel which is plunge fed in the work gear to the desired depth. The teeth

are finished one by one and after one tooth is finished to the desired si; the blank is indexed to

the next tooth space as in the form milling operation. Spur, helical, bevel and worm gears are

finished by this method.

4.10.3.2. Threaded wheel grinding :

Threaded wheel finishing operation uses a wheel on which a helical thread has been developed.

The wheel is rotated about its own axis to give a cutting speed of 20-30 m/second and also

given a feeding motion of 0.5 to 0.6 mm/rev. of the workpiece along the axis of the workpiece.

The work piece is also given a rotational movement in mesh with the wheel and a periodic in

feed towards the wheel. This method is very fast but a lot of time is required to prepare the

grinding wheel.

4.10.4. Lapping:

Lapping is often done on hardened gears (Hardness, > 45RC) to remove bun's, scales,

abrasions, nicks and irregularities from the surface and to remove small errors caused by heat

treatment. It is carried out by running the work gear in mesh with a mating gear or one or more

small cast iron toothed laps under a flow of fine abrasives in oil. The teeth on the lapping gear

are so formed that when the lap and the work gear are meshed together their centre lines are

not parallel. This creates a sliding action between the teeth all over the contact surface. The

sliding action causes the abrasive grains to remove irregularities form the tooth surface and

make it smooth. During lapping the work is turned first in one direction and then in the other

to finish both sides of the tooth. The work may be moved back and forth to cover the total face

with of the gear. Very small amount of material is removed during lapping. As such the process

can only correct minor errors but in many cases it proves faster and cheaper than form grinding.

4.10.5. Honning:

Like lapping, honing is also suitable for finishing heat treated gears. It is carried out with the

help of steel tools having abrasive or cemented carbide particles embedded in their surface.

Plastic tools, impregnated with abrasives are also used for honing. Plastic honing tools have

the advantage of being lighter and can be trued many times before being scrapped. The honing




tool is pushed with constant force along the tooth space but unlike the shaving tools (which are

rigid) the honing tools are allowed to float. An axial vibratory motion may also be provided to

the honing tool. Honing is done on machines similar to gear shaving machines but there is no

infeed mechanism in these machines. The honing tool and the work gear are mounted in relation

to each other such that honing tool rotates the work gear at a high speed. The work gear is also

provided with a reciprocating motion while rotating. Honing is done on internal and external

spur and helical gears to correct small error to produce smooth surfaces so that the finished

gears run quieter. The honing tools are costlier than lapping tools but the process is much faster.

As such honing is often preferred to lapping for large quantity operation.

NON CONVENTIONAL MACHINING PROCESSES



Date: ___ /___ /______

EXPERIMENT NO. 6

AIM: PROCESS PRINCIPLE, PROCESS PARAMETER AND APPLICATION OF

NON-CONVENTIONAL MACHINING.

5.1. Introduction:

With the development of technology, more and more challenging problems are faced by the

scientists and technologists in the field of manufacturing. The difficulty in adopting the

traditional manufacturing processes can be attributed mainly to the following three basic

sources:

1. New materials with a low machinability

2. Dimensional and accuracy requirements

3. A higher production rate and economy

Many new materials and alloys that have been developed for specific uses possess a very low

machinability. Producing complicated geometries in such materials becomes extremely

difficult with the usual methods. Also, sometimes the combination of the materials properties

and the job dimensions is such that it makes the use of the traditional processes impossible.

Examples of these types of jobs are machining a complicated turbine blade made of

superalloys, and producing holes and slots (both through and blind) in materials such as glass

and semiconductors. At times, the job becomes difficult because of the dimensional

complications. So, drilling a noncircular hole or a micro hole becomes problematic (and

sometimes impossible) if the traditional processes are used. Apart from the situations cited,

higher production rate and economic requirements may demand the use of nontraditional (or

unconventional) machining processes.

To take such difficult jobs, two approaches are possible, viz, (i) a modification of the traditional

processes e.g., hot machining) and (ii) the development of new processes. Here, we will discuss

the presently available common unconventional machining processes. Such processes are

becoming increasingly unavoidable and popular; therefore, knowledge of these is essential for

a mechanical engineer. The basic objective of all machining operations is to remove the excess

material to obtain the desired shape and size. These operations use various types of energies.

Table shows the possible machining processes using the different types of energies and various

methods of material removal.




5.2. Abrasive Jet Machining (AJM):

In AJM, the material removal takes places place due to the impingement of the fine abrasive

particles. These particles move with a high speed air (or gas) stream. The abrasive particles are

typically of 0.025 mm diameter and the air discharges at aj pressure of several atmospheres.

5.2.1. Mechanics of AJM:

When an abrasive particle impinges on the work surface at a high velocity, the impact causes

a tiny brittle fracture and the flowing air (or gas) carries away the dislodged small work piece

particle (wear particle). Thus, it is obvious that the process is more suitable when the work

material is brittle and fragile.

5.2.2. Process Parameters:

The process characteristics can be evaluated by judging (i) the burr, (ii) the geometry of

the cut, (iii) the roughness of the surface produced, and (iv) the rate of nozzle wear. The

major parameters which control these quantities are

(i) The abrasive (composition, strength, size, and mass flow rate),

Energy type

Mechanics of

material removal

Energy source

Process

Mechanical erosion

Mechanical/fluid motion Abrasive jet machining (AJM)

Ultrasonic machining(USM)

Electrochemical Ion displacement

Electric current

Electrochemical machining(ECM)

Mechanical and

electrochemical

Plastic shear and

ion displacement

Electric current and

mechanical motion Electrochemical grinding(ECG)

Chemical Corrosive reaction Corrosive agent

Chemical machining(CHM)

Fusion and

vaporization

Electric spark

Electric discharge

machining(EDM)

High speed electrons

Electron beam machining(EBM)

Thermal

Powerful radiation

Laser beam machining(LBM)

Ionized substance

Ion beam machining(IBM)

Plasma arc machining(PAM)




(ii) The gas (composition, pressure, and velocity),

(iii) The nozzle (geometry, material, distance from and inclination to the work

surface).

5.2.3. Summary of AJM Characteristics:

Mechanics of material

removal

Media Abrasives

Velocity

Pressure

Nozzle

Critical parameters

Materials application

Shape (job) application

Limitations

Brittle fracture by impinging abrasive grains at high speed Air, CO2

AI203, SiC

0.025 mm diameter, 2-20 g/mm, non recirculating

150-300 m/sec

2-10 atm

WC, sapphire

Orifice area 0.05-0.2 mm2

Life 12-300 hr

Nozzle tip distance 0.25-75 mm

Abrasive flow rate and velocity, nozzle tip distance

from work surface, abrasive grain size and jet

inclination

Hard and brittle metals, alloys, and non-metallic materials

(e.g., germanium, silicon, glass, ceramics, and mica)

Specially suitable for thin sections

Drilling, cutting deburring, etching, cleaning

Low metal removal rate (40 mg/min, 15 mm3/rnin),

embedding of abrasive in work piece, tapering of

drilled holes, possibility of stray abrasive action

5.3. Ultrasonic Machining (USM):

The basic USM process involves a tool (made of a ductile and tough material) vibrating with a

very high frequency and a continuous flow of abrasive slurry in the small gap between the tool

and the work surface (figure) The tool is gradually fed with a uniform force. The impact of the

hard abrasive grains fractures the hard and brittle work surface, resulting in the removal of the

work material in the form of small wear particles which are carried away by the abrasive slurry.

The tool material, being tough and ductile, wears out at a much slower rate.

5.3.1. Mechanics of USM:-

The physics of ultrasonic machining is neither complete nor uncontroversial. The reasons of

material removal during USM are believed to be

(i) The hammering of the abrasive particles on the work surface by the tool,

(ii) The impact of the free abrasive particles on the work surface,

(iii) The erosion due to cavitation, and

(iv) The chemical action associated with the fluid used.

A number of researchers have tried to develop the theories to predict the characteristics of

ultrasonic machining. The model proposed by M.C. Shaw is generally well-accepted and

despite its limitations, explains the material removal process reasonably well. In this model,




the direct impact of the tool on the grains in contact with the work piece (which is responsible

for the major portion of the material removal) is taken into consideration. Also, the assumptions

made are that

(i) The rate of work material removal is proportional to the volume of work material per

impact,

(ii) The rate of work material removal is proportional to the number of particles making

impact per cycle,

(iii)The rate of work material removal is proportional to the frequency (number of cycles

per unit time),

(iv) All impacts are identical,

(v) All abrasive grains are identical and spherical in shape.

5.3.2. Process Parameters:

The important parameters which affect the process are the

(i) Frequency,

(ii) Amplitude,

(iii) Static loading (feed force).

(iv) Hardness ratio of the tool and the workpiece,

(v) Grain size,

(vi) Concentration of abrasive in the slurry.

5.3.3. Summary of USM Characteristics

Mechanics of material

removal

Medium

Absrasives

Vibration Frequency

Tool Material

Critical parameters


Shape application

Limitations

Brittle fracture caused by impact of abrasive grains due to tool

vibrating at high frequency

Slurry

B4C,SiC, AI2O3 ,

diamond 100-800 grit size 4

15-30 kHz, 25-100

Soft steel

Frequency, amplitude, tool material, grit size, abrasive

material, feed force, slurry concentration, slurry viscosity

Metals and alloys (particularly hard and brittle), semiconductors,

nonmetals, e.g., glass and ceramics

Round and irregular holes, impressions

Very low MRR, tool wear, depth of holes and cavities small

5.4. Electro-chemical Machining (ECM):

This process may be considered as the reverse of electroplating with some

modifications. Further, it is based on the principle of electrolysis. In a metal, electricity

conducted by the free electrons, but it has been established that in an electrolyte the conduction

of electricity is achieved through the movement of ions. Thus, the flow of current

through an electrolyte is always accompanied by the movement of matter. In electrochemical




machining the objective is to remove metal, the workpiece is connected to the positive,

and the tool to the negative, terminal. Figure shows a workpiece and a suitably-shaped tool, the

gap between the tool and the work being full of a suitable electrolyte. When the current is

passed, the dissolution of the anode occurs. However, the dissolution rate is more where the

gap is less and vice versa as the current density is inversely proportional to the gap. Now, if the

tool is given a downward motion, the work surface tends to take the same shape as that of the

tool, and at a steady state, the gap is uniform, as shown in figure. Thus, the shape of the tool is

reproduced in the job.

In an electrochemical machining process, the tool is provided with a constant feed motion. The

electrolyte is pumped at a high pressure through the tool and the small gap between the tool

and the workpiece (figure). The electrolyte is so chosen that the anode is dissolved but no

deposition takes place on the cathode (the tool). The order of the current and voltage are a few

thousand amperes and 8-20 volts. The gap is of the order of 0.1-0.2 mm.

5.4.1. Electrochemistry of ECM Process:

The electrolysis process is governed by the following two laws proposed by Faraday:

(i) The amount of chemical change produced by an electric current, that is the amount of

any material dissolved or deposited, is proportional to the quantity of electricity passed.

(ii) The amounts of different substances dissolved or deposited by the same quantity of

electricity are proportional to their chemical equivalent weights.

5.4.2. Summary of ECM Characteristics

Electrolysis

Critical parameters

Materials

application

Shape application

Limitations

Conducting electrolyte Cu, brass, steel

Voltage, current, feed rate, electrolyte, electrolyte conductivity

All conducting metals and alloys

Blind complex cavities, curved surfaces, through cutting, large

through cavities

High specific energy consumption (about 150 times that required for

conventional processes), not applicable with electrically

nonconducting materials and for jobs with very small dimension,

expensive machine

5.5. Electric Discharge Machining (EDM):

When discharge takes place between two points of the anode and the cathode, the intense heat

generated near the zone melts and evaporates the materials in the sparking zone. For improving

the effectiveness, the work-piece and the tool are submerged in a dielectric fluid

(hydrocarbon or mineral oils). It has been observed that if both the electrodes are made of the

same material, the electrode connected to the positive terminal generally erodes

at a faster rate. For this reason, the workpiece is normally made anode. A suitable gap, known

as the spark gap, is maintained between the tool and the workpiece surfaces. The sparks

are made to discharge at a high frequency with a suitable source. Since

the spark occurs at the spot where the tool and the workpiece surfaces are the closest and since

the spot changes after each spark (because of the material removal after each spark), the sparks




travel all over the surface. This result in a uniform material removal all over the surface, and

finally the work face conforms to the tool surface. Thus, the tool produces the required

impression in the workpiece. For maintaining the predetermined spark gap, a servocontrol unit

is generally used. The gap is sensed through the average voltage across it and this volt is

compared with a preset value. Sometimes, a stepper motor is used instead of a servo-motor. Of

course, for primitive operations, a solenoid control is also possible, and with this it becomes

extremely inexpensive and simple to construct. The spark frequency normally in the range 200-

500,000 Hz, the spark gap being of the order of 0.025-0 mm. The peak voltage across the gap

is kept in the range 30-250 volts. A MRR up 300mm3/min can be obtained with this process,

the specific power being of the order 10 W/mm3/min. The efficiency and the accuracy of

performance have been found improve when a forced circulation of the dielectric fluid is

provided. The most common used dielectric fluid is kerosene. The tool is generally made of

brass or a copper alloy.

5.5.1. EDM Circuits and Operating Principles:

Several basically different electric circuits are available to provide the pulsating across the

work-tool gap. Though the operational characteristics are different, in almost all such circuits

a capacitor is used for storing the electric charge before the discharge takes place across the

gap. The suitability of a circuit depends on the machining conditions and requirements. The

commonly-used principles for supplying the pulsating dc can be classified into the following

three groups:

(i) Resistance-capacitance relaxation circuit with a constant dc source

(ii) Rotary impulse generator

(iii) Controlled pulse circuit

5.5.2. Electrode Material:

The selection of the electrode material depends on the

(i) Material removal rate,

(ii) Wear ratio,

(iii) Ease of shaping the electrode,

(iv) Cost

The most commonly-used electrode materials are brass, copper, graphite, Al alloys, copper-

tungsten alloys, and silver-tungsten alloys.

The methods use for making the electrodes are:

(i) Conventional machining (used for copper, brass, Cu-W alloys, Ag-W alloys, and

graphite),

(ii) Casting (used for Zn base die casting alloys, Zn-Sn alloys, and Al alloys).

(iii) Metal spraying

(iv) Press forming

Flow holes are normally provided for the circuit of the dielectric, and three holes should be as

large as possible for rough cuts to allow large flow rates at a low pressure.

5.5.3. Dielectric Fluids:




The basic requirements of an ideal dielectric fluid are

(i) Low viscosity,

(ii) Absence of toxic vapours,

(iii) Chemical neutrality,

(iv) Absence of inflaming tendency

(v) Low cost

5.5.4. Summary of EDM Characteristics

Machanics of material

removal

Medium

Tool Materials

Material removal rate

Critical parameters


Shape application

Limitations

Melting and evaporation aided by cavitation

Dielectric fluid

Cu, brass, Cu-W alloy, Ag-W alloy, graphite 0.1-10

5xl03mm3 /min

Voltage, capacitance, spark gap, dielectric circulation, melting

temperature

All conducting metals and alloys

Blind complex cavities, micro holes for nozzles, through cutting of non

circular holes, narrow slots

High specific energy consumption (about 50 times that in conventional

machining); when forced circulation of dielectric is not possible,

removal rate is quite low; surface tends to be rough for larger removal

rates; not applicable to non-conducting materials

5.6. Electro Beam Machining (EBM):

Basically, electron beam machining is also a thermal process. Here, a stream of high speed

electrons impinges on the work surface whereby the kinetic energy, transferred to the work

material, produces intense heating. Depending on the intensity of the heat thus generated, the

material can melt or vaporize. The process of heating by an electron beam can n, depending on

the intensity, be used for annealing, welding, or metal removal.

5.6.1. Summary of EBM Characteristics: Mechanics of material removal

Medium

Tool

Maximum material removal rate

Specific power consumption

(typical)

Critical parameters


Shape application

Limitations

Melting , vaporization

Vacuum

Beam of electrons moving at very high

velocity

10mm3 /min

450W/mm3 -min

Accelerating voltage, beam current,

beam diameter, work speed, melting

temperature

All materials

Drilling fine holes, cutting contours in

sheets, cutting narrow slots

Very high specific energy consumption,

necessity of vacuum , expensive machine




5.7. Laser Beam Machining (LBM):

Like a beam of high velocity electrons, a laser beam is also capable of producing very high

power density. Laser is a highly coherent (in space and time) beam of electromagnetic

radiation.

5.7.1. Summary of LBM Characteristics:

Mechanics of material removal

Medium

Tool


Specific power consumption (typical)

Critical parameters


Shape application

Limitations

Melting, vaporization

Normal atmosphere

High power laser beam

5mm3/min

1000W/mm3/min

Beam power intensity, beam diameter,

melting temperature

All materials

Drilling fine holes

Very large power consumption, cannot cut

materials with high heat conductivity and high

reflectivity

5.8. Plasma Beam Machining (PBM):

A plasma is a high temperature ionized gas. The plasma arc machining is done with a high

speed jet of a high temperature plasma. The plasma jet heats up the workpiece (where the jet

impinges on it), causing a quick melting. PAM can be used on all materials which conduct

electricity, including those which are resistance to oxy-fuel gas cutting. This process is

extensively used for profile cutting of stainless steel, monel, and superalloy plates.

A plasma is generated by subjecting a flowing gas to the electron bombardment of an arc. For

this, the arc is set up between the electrode and the anodic nozzle; the gas is forced to flow

through this arc.

The high velocity electrons of the arc collide with the gas molecules, causing a dissociation of

the diatomic molecules or atoms into ions and electrons resulting in a substantial increase in

the conductivity of the gas which is now in plasma state. The free electrons, subsequently,

accelerate and cause more ionization and heating. Afterwards, a further increase in temperature

takes place when the ions and free electron recombine into atoms or when the atoms recombine

into molecules as thee are exothermic processes. So, a high temperature plasma is generated

which is forced through the nozzle in the form of a jet.

The mechanics of material removal is based on

(i) heating and melting

(ii) Removal of the molten metal by the blasting action of the plasma jet.




5.8.1. Summary of PBM Characteristics:

Mechanics of material removal

Medium

Tool

Maximum temperature

Maximum velocity of plasma jet


Specific energy

Power range

Maximum plate thickness

Cutting speed

Voltage

Current

Critical parameters


Shape application Limitation

Melting

Plasma

Plasma jet

16,000°C

500 m/sec

150cm3 /min

1000W/cm3 -min

2-200 kW

Up to 200 mm (depends on material)

0.1-7.5 m/min

30-250 V

Up to 600 amp

Voltage, current, electrode gap, flow rate, nozzle

dimensions, melting temperature

All conducting materials, Cutting plates

Low accuracy

PRESS TOOL DESIGN


Date: ___ /___ /______

EXPERIMENT NO.7

AIM: PREPARE PRESS TOOL DESIGN BASED ON GIVEN DATA.

A Washer with 12.7 mm internal hole and an outside diameter of 25.4 mm is to be made from 1.5 mm thick strip of 0.2% carbon steel. Considering the elastic recovery of the material Design the press tool and its various parameters.

JIG DESIGN


Date: ___ /___ /______

EXPERIMENT NO.8

AIM: PREPARE JIG DESIGN AND DRAWING FOR GIVEN COMPONENTS.

Design and Draw Drilling Jigs for drilling holes in given components by using any CAD software.

Figure No.1 For Batch No. 1

Figure No. 2 For Batch NO.2

JIG DESIGN


Figure No. 3 for Batch No. 3

________________

MERCHANT’S FORCE CIRCLE


Date: ___ /___ /______

EXPERIMENT NO.9

AIM: TO STUDY AND CONSTRUCT MERCHANT’S FORCE CIRCLE.

9.1 Cutting Forces and Parameters affecting on it 9.1.1 Force Relation

Here the analysis is limited to two dimensional or orthogonal cutting which is simpler to understand as compared to the complicated three dimensional cutting process when a cut is made. The force acting on metal chip are,

Fig. 9.1 Force Relationship Fs = which is resistance to shear of the metal is forming the chip its act along shear plane. Fn = Which is Normal to the shear plane. This is backing up force on the chip provided by the work piece. F = It is the frictional resistance of the tool acting on chip. It acts downward against the motion of the chip as it glides upwards along the tool face. N = It is the force subjected at the tool chip interface acting normal to the cutting face of the tool and is provided by the tool. In figure free body diagram showing the forces acting on chip. R is the resultant force of F and N and R’ that of Fs and Fn, Neglecting the couple which curl the chip. Considering the equilibrium of the chip, R and R’ are equal in magnitude opposite in direction and collinear as shown. All this force can be represented with the help of a circle known as the ‘merchant force circle’. In figure the two force triangle have been superimposed by placing the two equal forces R and R’ together. In the figure β is the angle of friction. In this diagram for convenience, the resultant force have been moved to the point of the tool. Since the



forces Fs and Fn are at right angle to each other, their intersection lies on circle with diameter R’. The two orthogonal components (horizontal and vertical) Fc and Ft of the resultant force R’ can be measured by using tool dynamometer. The thrust force Ft does not contribute the work done it holds the tool against the work piece. By knowing Fc, Ft, α,∅ all the component force acting on the chip can be determined with help for merchant force circle.

Fig. 9.2 Merchant Force Circle Diagram

First we will find out resultant force R with the help of Fc and Ft which are already find in tool dynamometer.

R = √𝐹𝑐2 + 𝐹𝑡2 N By knowing Fc, Ft, α, ∅ and R all the component force acting on the chip can be determined below.



Determination of Fs Fs = AB = AQ – QB Considering ∆ AQR and finding AQ = Fc cos ∅ ∆ REC and finding QB = RE = Ft sin ∅ Fs = Fc cos ∅ - Ft sin ∅ … … … … … … … … … … … … … … … … … … … (i) Determination of Fn Fn = BC = BE + EC Considering ∆ AQR and finding BE = RQ = Fc sin ∅ ∆ REC and finding EC = Ft cos ∅ Fn = Fc sin ∅ + Ft cos ∅ … … … … … … … … … … … … … … … … … … … (ii) Determination of F F = AD = AP + PD = AP + SC Considering ∆ RPA and finding AP= Fc sin α ∆ RSC and finding SC = Ft sin (90 – α) = Ft cos α F = Fc sin α + Ft cos α … … … … … … … … … … … … … … … … … … … (iii) Determination of N N = CD = PS = PR – RS Considering ∆ RPA and finding RP= Fc cos α ∆ RSC and finding RS = Ft cos (90 – α) = Ft sin α N = Fc cos α - Ft sin α … … … … … … … … … … … … … … … … … … … (iv) Fc and Fs can be find out another way as per merchant’s diagram triangle Fc = R cos (β – α) And Fs = R cos {∅ + (β – α)}

9.2 Procedure for Construct Merchant’s Circle Diagram.

Suppose, in a simple turning under orthogonal condition given speed, feed, depth of cut and tool geometry, the only two force components FC Ft are known by experiment i.e., direct measurement, then how can one determine the other relevant forces and machining characteristics easily and quickly without going into much equations and calculations but simply constructing a circle-diagram. This can be done by taking the following sequential steps.

- Determine Fc and Ft by using Tool Dynamometer and other parameters feed, speed, depth of cut, chip thickness and rake angle respectively.

- Determine the resultant force by using R = √𝐹𝑐2 + 𝐹𝑡2 equation. - Take Suitable scale for Fc, Ft and R in cm or mm.



- Draw one vertical and horizontal line and draw rake angle from intersection of two lines upper side.

- Mark Fc on horizontal line from that intersection of two line with suitable scale and draw perpendicular line downward side and mark Ft with suitable scale.

- Line which joining Ft and Fc will give a value of R. - Now draw circle by taking R as diameter. - For determining Fs and Fn the value of shear angle has be evaluated. - Draw the shear plane with the value of shear angle and then Fs and Fn

intercepts. - Get F

and N as intercepts in the circle by extending the tool rake surface get

the value of F and N. - Get friction angle and other angle by measuring angle in diagram.

9.3 Experimental Data for Merchant’s Force Circle Diagram. The following data has been observed during orthogonal cutting

- Uncut chip thickness = 0.125 mm - Chip thickness = 0.250 mm - Cutting Speed = 100 m/min - Rake Angle = 10° - Cutting Force = 70 N - Thrust Force = 25 N

Construct Merchant Force Circle Diagram and find out all forces and angles which are subjected during machining process. (Take suitable scale)

__________

References: Production Engineering -by P.C. SHARMA Manufacturing Processes I - by Prof. T Jagadeesha (NIT, Calicut)

CHIP FORMATION


Date: ___ /___ /______

EXPERIMENT NO.10

AIM: TO STUDY VARIOUS TYPES OF CHIP BY CHANGING CUTTING

PARAMETERS AND WORK MATERIAL ON LATHE.

10.1 Types of chips Whatever the cutting conditions can be, the chips produced may belong to one of the following three types. 1. Discontinuous chips: 2. Continuous chips. 3. Continuous chips with buildup edge (BUE).

Fig. 1.20 Types of chips

Discontinuous Chips These types of chips are usually produced when cutting more brittle materials like grey cast iron, bronze and hard brass. These materials lack the ductility necessary for appreciable plastic chips formation. The material ahead of the tool edge fails in a brittle fracture manner along the shear zone. This produces small fragments of discontinuous chips. Since the chips break up into small segments, the friction between the tool and the chips reduces, resulting in better surface finish. These chips are convenient to collect, handle and dispose of. Discontinuous chips are also produced when cutting more ductile materials under the following conditions:

(i) Large chip thickness.

CHIP FORMATION


(ii) Low cutting speed. (iii) Cutting with the use of a cutting fluid. (iv) Small rake angle of the tool.

Continuous Chips. These types of chips are produced when, machining more ductile materials. Due to large plastic deformations possible with ductile materials, longer continuous chips are produced. This type of chip is the most desirable, since it is stable cutting, resulting in generally good surface finish. On the other hand, these chips are difficult to handle and dispose of. The chips coil in a helix (chip curl) and curl around the work and the tool and may injure the operator when break loose. Also, this type of chip remains in contact with the tool face for a longer period, resulting in more frictional heat. These difficulties are usually avoided by attaching to the tool face or machine on the tool face, a 'chip breaker', the function of chip breaker is to reduce 1 curvature of the chip and thus break it. The following cutting conditions also help in the production of continuous chips:

Small chip thickness.

High cutting speed.

Large rake angle of the cutting tool.

Reducing the friction of the chip along the tool face, by: imparting high surface

finish to the tool face, use of tool material with low co-efficient of friction, and use

of good cutting fluid.

Continuous chips with built up edge (BUE). - When machining ductile materials, conditions of high local temperature and

extreme pressure in the cutting zone and also high friction in the tool-chip interface,

may cause the work material to adhere or weld to the cutting edge of then tool

forming the built-up edge.

- Successive layers of work material are then added to the built up edge. When this

edge becomes larger and unstable, it breaks up and part of it is carried up the face of

the tool along with the chip while the remaining is left over the surface being

machined, which contributes to the roughness of the surface.

- The built-up edge changes its size during the cutting operation. It first increases,

then decreases, then again increases etc. This cycle is a source of vibration and poor

surface finish.

- Although, the built-up edge protects the cutting edge of the tool, changes the

geometry of the cutting tool. Low cutting speed also contributes to the formation of

the built-up edge.

CHIP FORMATION


- Increasing the cutting speed, increasing the rake angle and using a cutting fluid

contribute to the reduction or elimination of the built-up edge.

Observation Table

Sr. No

Material Cutting Speed

(m/min)

Depth of cut

(mm)

feed (mm/rev)

observed types of chips

1

2

3

4

Conclusion: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

__________

References: Production Engineering -by P.C. SHARMA

THREAD MANUFACTURING


Date: ___ /___ /______

EXPERIMENT NO.11

AIM: TO STUDY ABOUT DIFFERENT THREAD MANUFACTURING PROCESSES

AND DEMONSTRATION ON SINGLE AND MULTI-START THREAD

MANUFACTURING.

11.1 General Applications of Screw Threads

1. Fastening

2. Joining

3. Clamping: strongly holding an object by a threaded rod

4. Controlled linear movement

5. Transmission: of motion and power

6. Converting rotary motion to translation

7. Position control in instruments

8. Precision measurement of length

9. Acting as worm for obtaining slow rotation of gear or worm wheel

10. Exerting heavy force

11. Conveying and squeezing materials

12. Controlled automatic feeding in mass production assembly etc.

11.2 Classification of Screw Threads

Screw threads having various applications can be classified as follows

According to location

External screw thread

Internal screw thread

According to configuration

Straight (helical) – most common, e.g., bolts, studs etc.

Taper (helical), e.g., in drill chuck

Radial (scroll) as in self centring chuck

According to the direction of the helix

Right hand (common)

Left hand (occasionally)

According to form

Vee thread (600

or 550

angle) – most common



Acme thread (290)

Square thread (generally in power screws)

Buttress thread (45o)

Worm thread (290

~ 400)

Semi-circular (groove section) thread being used in recirculating type bolts, screws.

According to standard

BSW (British Standard Whitworth); thread – size is designated by TPI

(threads per inch)

Metric thread; thread size is specified by pitch or lead (in mm)

According to number of start

Single start – most common

Multi-start (2 to 4)

According to spacing of threads

TPI (no. of threads per inch), e.g. 12 TPI

Pitch (or lead) – distance between two successive threads (or length of travel of the

nut for one rotation of the screw), in mm

According to compactness or fineness of threads

General threads (with usually wide thread spacing), pipe threads

Fine threads (generally for leak proof)

According to segmentation

Full threads (common)

Half turns as in half nuts

Sector thread – e.g., in the jaws of lathe chucks.

11.3 Production of Screw Threads – Possible Methods and Their

Characteristics.

The various methods, which are more or less widely employed for producing screw threads are:

Casting

Characteristics;

o Only a few threads over short length

o Less accuracy and poor finish

o Example – threads at the mouth of glass bottles, spun cast iron pipes etc.



Forming (Rolling) characteristics;

o Blanks of strong ductile metals like steels are rolled between threaded dies

o Large threads are hot rolled followed by finishing and smaller threads are straight

cold rolled to desired finish

o Cold rolling attributes more strength and toughness to the threaded parts

o Widely used for mass production of fasteners like bolts, screws etc.

Removal process (Machining)

o Accomplished by various cutting tools in different machine tools like lathes, milling

machines, drilling machines (with tapping attachment) etc.

o Widely used for high accuracy and finish

o Employed for wide ranges of threads and volume of production; from piece to

mass production.

Semi finishing and finishing (Grinding)

Characteristics:

o Usually done for finishing (accuracy and surface) after performing by machining

or hot rolling but are often employed for direct threading on rods

o Precision threads on hard or surface hardened components are finished or directly

produced by grinding only

o Employed for wide ranges of type and size of threads and volume of production

Precision forming to near – net – shape

Characteristics

o No machining is required, slight grinding is often done, if needed for high accuracy

and finish

Non-conventional process (EDM, ECM etc.)

Characteristics:

o When conventional methods are not feasible

o High precision and micro threads are needed

o Material is as such difficult – to – process

11.4 Production of screw threads by machining Machining is basically a removal process where jobs of desired size and shape are

produced by gradually removing the excess material in the form of chips with the help of sharp cutting edges or tools. Screw threads can be produced by such removal process both manually using taps and dies as well as in machine tools of different types and degree of automation. In respect of process, machine and tool, machining of screw threads are done by several ways



10.4.1 Thread cutting by hand operated tools

Usually small threads in few pieces of relatively soft ductile materials, if required, are made manually in fitting, repair or maintenance shops.

External screw threads

Machine screws, bolts or studs are made by different types of dies which look and apparently behave like nuts but made of hardened tool steel and having sharp internal cutting edges. Fig. 1 shows the hand operated dies of common use, which are coaxially rotated around the premachined rod like blank with the help of handle or die stock.

Solid or button die: used for making threads of usually small pitch and diameter in one pass.

Spring die: the die ring is provided with a slit, the width of which is adjustable by a screw to enable elastically slight reduction in the bore and thus cut the thread in number of passes with lesser force on hands.

Split die: the die is made in two pieces, one fixed and one movable (adjustable) within the cavity of the handle or wrench to enable cut relatively larger threads or fine threads on harder blanks easily in number of passes, the die pieces can be replaced by another pair for cutting different threads within small range of variation in size and pitch.

Pipe die: pipe threads of large diameter but smaller pitch are cut by manually rotating the large wrench (stock) in which the die is fitted through a guide bush as shown in Fig. 1

Fig 11.1 - Different types of thread cutting dies.

Internal screw threads : Internal screw threads of usually small size are cut manually, if needed, in plates, blocks, machine parts etc. by using taps which look and behave like a screw but made of tool steel or HSS and have sharp cutting edges produced by axial grooving over the threads as shown in Fig. 2. Three taps namely, taper tap, plug tap and bottoming tap are used consecutively



after drilling a tap size hole through which the taps are axially pushed helically with the help of a handle or wrench.

Fig.11 2 - Hand operated taps for cutting internal threads.

11.4.2 Machining screw threads in machine tools

Threads of fasteners in large quantity and precision threads in batches or lots are produced in different machine tools mainly lathes, by various cutting tools made of HSS or often cemented carbide tools.

Machining screw threads in lathes

Screw threads in wide ranges of size, form, precision and volume are produced in lathes ranging from centre lathes to single spindle automats. Threads are also produced in special purpose lathes and CNC lathes including turning centres.

In centre lathes

Single point and multipoint chasing, as schematically shown in Fig. 3. This process is slow but can provide high quality. Multipoint chasing gives more productivity but at the cost of quality to some extent

Fig. 11.3 - External threading in lathe by chasing.

_____________________

production technology...planer, etc. are single point tools. a multi-point tool has two or more than...

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