MCTD Lab

AMITY SCHOOL OF ENGINEERING

AND TECHNOLOGY

DEPARTMENT OF MECHANICAL

AND AUTOMATION ENGINEERING

METAL CUTTING AND TOOL DESIGN

LAB MANUAL

AMITY SCHOOL OF ENGINEERING AND TECHNOLOGY

DEPARTMENT OF MECHANICAL AND AUTOMATION

ENGINEERING

METAL CUTTING AND TOOL DESIGN LAB

Course Code: BTM: 623

Credit Unit: 01

LIST OF THE EXPERIMENTS

S.No NAME OF THE EXPERIMENTS

1. Step and taper turning on Lathe machine

2. To make a hexagonal headed bolt on a milling machine.

3. To make a job on a shaper machine.

4. To study the Kinematics design of workshop machine.

5. To make a job on drilling machine as per given specifications.

6. To measure cutting forces on a single point cutting tool.

7. To study of jig and fixture.

8.. Study of formation of chips during turning and shaping operations

on a sample of C.I,M.S,Brass,Cu & Aluminium

9. Determination of the life of the cutting tool used on Lathe for

various cutting speeds, feeds and different work piece materials.

Experiment No. 1

Aim: Step and Taper turning on lathe machine.

Apparatus:

(a) Round nose tool

(b) Parting tool

(d) Steel rule and outside caliper.

Theory:

Turning operation is performed by the lathe machine to generate/produce the required diameters,

faces and tapers on the product. The above required diameters, faces and tapes can be produced by

generating or forming processes.

a. Generating

Generating requires the movement of tool and Work piece to get the required shapes on the

product.

These are three main generating operations:

(a) Flat faces and shoulders

(b) Cylindrical surfaces - external diameters and internal bores

(c) Tapers and chamfers: Internal and external

b. Forming

It is the process of reproducing the tool shape in the Work piece.

Taper Turning Methods:

The Compound Slide

The compound slide is used to turn both large and small tapers. It has a limited accuracy and hand

folding must be used, but it is a quicker method of turning a wide ranger of tapers.

The Offset Tailstock

The method is used to turn shallow tapers with a high degree of accuracy. The machine feed may

be used, producing a good surface finish. The offset must be calculated using half the included

angle of the taper, and the length between centers. The taper i s calculated as offset per unit length,

and the tailstock, adjusted using a mandrel and dial test indicator.

Forming Tool

A rapid method of forming tapers, but the surface finish may be poor. Accurate tapers require the

tool to be accurately produced and set, with consequent cost. General purpose chamfers can be

made quickly and cheaply using knife tools.

Procedure:

(a) The round nose tool is centered for facing operations.

(b) The given raw material (here rod) is fixed in the 3-jaw chuck, such that, about 65 mm is

projecting from the 3-jaw chuck.

(c) The end of the raw material is faced and checked for the centering of the tool.

(d) Then turn the job for required dimensions that is 30 rnm diameters to a length of slightly more

than 60 mm.

(e) Now turn the step of 20 x 30 mm in. stage.

(f) Now measure the step lengths, 30 + 30 = 60 mm.

(g) If any extra size i s there, it i s cut off by using the parting tool.

(h) Hold the job in the reversed position, facing of the other end i s completed such that, the total

length i s exactly 6 0 mm.

(i)The taper angle is calculated, using the formula, where, D = Diameter at the big end of the

taper,

d = Diameter at the small end of the taper, and

L = Length of the taper.

(j) The compound rest is set to the taper angle.

(k) The taper is turned in stager using the compound slide feed feeding and cutting from right to

left.

Experiment No. 2

Aim: To make a hexagonal headed bolt on a milling machine.

Apparatus: Milling machine, milling tool, work piece, scale, measuring instruments.

Theory: Milling is the process of machining flat, curved, or irregular surfaces by mounting the

work piece to a slotted table and feeding against a rotating cutter containing a multiple cutting

edges. The milling machine consists basically of a motor driven spindle, which mounts and

revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the

work piece. Milling machines are basically classified as vertical or horizontal. These machines

are also classified as knee-type, ram-type, and bed type.

Two views of a common milling cutter with its parts and angles are identified. These parts

and angles in some form are common to all cutter types.

The pitch refers to the angular distance between like or adjacent teeth.

The pitch is determined by the number of teeth. The tooth face is the forward facing

surface of the tooth that forms the cutting edge.

The cutting edge is the angle on each tooth that performs the cutting.

The land is the narrow surface behind the cutting edge on each tooth.

The rake angle is the angle formed between the face of the tooth and the centerline

of the cutter. The rake angle defines the cutting edge and provides a path for chips

that are cut from the workpiece.

The primary clearance angle is the angle of the land of each tooth measured from a

line tangent to the centerline of the cutter at the cutting edge. This angle prevents

each tooth from rubbing against the workpiece after it makes its cut.

This angle defines the land of each tooth and provides additional clearance for

passage of cutting oil and chips.

The hole diameter determines the size of the arbor necessary to mount the milling

cutter.

Plain milling cutters that are more than 3/4 inch in width are usually made with

spiral or helical teeth. A plain spiral-tooth milling cutter produces a better and

smoother finish and requires less power to operate. A plain helical-tooth milling

cutter is especially desirable when milling an uneven surface or one with holes in it

Indexing:

The indexing plate is a round plate with a series of six or more circles of equally spaced

holes; the index pin on the crank can be inserted in any hole in any circle. With the

interchangeable plates regularly furnished with most index heads, the spacing necessary for

most gears, bolt heads, milling cutters, splines, and so forth can be obtained. The following

sets of plates are standard equipment: Brown and Sharpe type consists of 3 plates of 6

circles each drilled as follows:

Plate I - 15, 16, 17, 18, 19, 20 holes

Plate 2 - 21, 23, 27, 29, 31, 33 holes

Plate 3 - 37, 39, 41, 43, 47, 49 holes

Cincinnati type consists of one plate drilled on both sides with circles divided as follows:

First side - 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43 holes

Second side - 46, 47, 49, 51, 53, 54, 57, 58, 59, 62, 66 holes

The following examples show how the index plate is used to obtain any desired part of a

whole spindle turn by plain indexing.

Milling a hexagon: Using the rule previously given, divide 40 by 6 which equals 6 2/3

turns, or six full turns plus 2/3 of a turn or any circle whose number is divisible by 3. Take

the denominator which is 3 into which of the available hole circles it can be evenly divided.

In this case, 3 can be divided into the available 18-hole circle exactly 6 times. Use this

result 6 as a multiplier to generate the proportional fraction required.

Example:

Therefore, 6 full turns of the crank plus 12 spaces on an 18-hole circle is the correct

indexing for 6 divisions.

The formula for calculating spindle speed in revolutions per minute is as follows:

Where RPM = Spindle speed (in revolutions per minute)., CS = cutting speed of milling

cutter (in SFPM), D = diameter of milling cutter (in inches)

Procedure:

Milling has many useful applications in production machining. Parallel slots of equal depth

can be milled by using straddle mills of equal diameters. Figure 8-29 illustrates a typical

example of straddle milling. In this case a hexagon is being cut, but the same operation

may be applied to cutting squares or splines on the end of a cylindrical work piece. The

work piece is usually mounted between centers in the indexing fixture or mounted

vertically in a swivel vise. The two side milling cutters are separated by spacers, washers,

and shims so that the distance between the cutting teeth of each cutter is exactly equal to

the width of the work piece area required.

Precautions:

Before setting up a job, be sure that the workpiece, table, the taper in the

spindle, and the arbor or cutter shank are free from chips, nicks, or burrs.

Do not select a milling cutter of larger diameter than is necessary.

Check the machine to see if it is in good running order and properly

lubricated, and that it moves freely, but not too freely in all directions.

Consider direction of rotation. Many cutters can be reversed on the arbor,

so be sure you know whether the spindle is to rotate clockwise or

counterclockwise.

Feed the workpiece in a direction opposite the rotation of the milling

cutter (conventional milling).

Do not change feeds or speeds while the milling machine is in operation.

When using clamps to secure a workpiece, be sure that they are tight and

that the piece is held so it will not spring or vibrate under cut.

Use recommended cutting oil liberally.

Use good judgment and common sense in planning every job, and profit

from previous mistakes.

Set up every job as close to the milling machine spindle as circumstances

will permit.

Experiment No. 3

Aim: To make a job on a shaper machine.

Apparatus:

Shaper machine, work piece, cutting tool, Vernier calipers, scale, marking tool.

Theory:

A shaper has a reciprocating ram that carries a cutting tool. The tool cuts only on the

forward stroke of the ram. The work is held in a vise or on the worktable, which moves at a

right angle to the line of motion of the ram, permitting the cuts to progress across the

surface being machined. A shaper is identified by the maximum size of a cube it can

machine; thus, a 24 -inch shaper will machine a 24-inch cube.

TABLE FEED MECHANISM— The table feed mechanism consists of a ratchet wheel

and pawl, a rocker, and a feed drive wheel. The feed drive wheel is driven by the main

crank. It operates similarly to the ram drive mechanism and converts rotary motion to

reciprocating motion. As the feed drive wheel rotates, the crankpin (which can be adjusted

off center) causes the rocker to oscillate. The straight face of the pawl pushes on the back

side of a tooth on the ratchet wheel, turning the ratchet wheel and the feed

screw. The back face of the pawl is cut at an angle to ride over one or more teeth as it is

rocked in the opposite direction. To change the direction of feed, lift the pawl and rotate it

one-half turn. To increase the rate of feed, increase the distance between the feed drive

wheel crankpin and the center of the feed drive wheel. The ratchet wheel and pawl method

of feeding crank-type shapers has been used for many years. Relatively late model

machines still use similar principles. Procedures used to operate feed mechanisms vary, so

consult manufacturers’ technical manuals for explicit instructions.

Procedure:

To machine a rectangular block from a rough casting, use the following sequence of

operations:

1. Clamp the casting in the vise so a face is horizontally level and slightly above the top of

the vise jaws. Allow one end to extend out of the side of the vise jaws enough so you can

take a cut on the end without unclamping the casting. Now feed the cutting tool down to

the required depth and take a horizontal cut across the face. After you have machined the

face, readjust the cutting tool so it will cut across the surface of the end that extends from

the vise. Use the horizontal motion of the ram and the vertical adjustment of the tool head

to move the tool across and down the surface of the end. When you have machined the end,

check to be sure it is square with the machined face. If it is not square, adjust the tool head

swivel to correct the inaccuracy and take another light finishing cut down the end.

2. To machine the second face and end, turn the block over and set the previously

machined face on parallels (similar to the method used in step 1). Insert small strips of

paper between each corner of the block and the parallels. Clamp the block in the vise and

USC a soft-face mallet to tap the block down solidly on the parallels. When the block is

held securely in the vise, machine the second face and end to the correct thickness and

length dimensions of the block.

3. To machine a side, open the vise jaws so the jaws can be clamped on the ends of the

block. Now set the block on parallels in the vise with the side extending out of the jaws

enough to permit a cut using the down feed mechanism. Adjust the ram for length of stroke

and for position to machine the side and make the cut.

4. Set up and machine the other side as described in step 3

Precautions:

1. Wear safety glasses or face shield.

2. Wear hearing protection that is suitable for the level and frequency of the noise you are exposed to.

3. Use the cutter (and spindle speed / RPM) suited for the job.

4. Use sharp cutters only and keep them clean.

5. Remove all wrenches and tools used in the set up from the table.

6. Make sure all guards are in place.

Experiment No. 4

Aim: To study the kinematics design of workshop machines.

Apparatus: Center lathe machine, shaper machine, Bench drilling machine.

Theory:

Kinematics System Of Lathes

Amongst the various types of lathes, centre lathes are the most versatile and commonly used.

Figure schematically shows the typical kinematics system of a 12 speed centre lathe.

For machining in machine tools the job and the cutting tool need to be moved relative to each

other. The tool-work motions are :

• Formative motions : - cutting motion - feed motion

• Auxiliary motions: - indexing motion - relieving motion etc

In lathes

o Cutting motion is attained by rotating the job

o Feed motion by linear travel of the tool - either axially for longitudinal feed -or radially for cross

feed

It is noted, in general, from Figure

• The job gets rotation (and power) from the motor through the belt-pulley, clutch and then the

speed gear box which splits the input speed into a number (here 12) of speeds by operating the

cluster gears.

• The cutting tool derives its automatic feed motion(s) from the rotation of the spindle via the gear

quadrant, feed gear box and then the approx mechanism where the rotation of the feed rod is

transmitted

- either to the pinion which being rolled along the rack provides the longitudinal feed

- or to the screw of the cross slide for cross or transverse feed.

• While cutting screw threads the half nuts are engaged with the rotating lead screw to positively

cause travel of the carriage and hence the tool parallel to the lathe bed i.e., job axis.

• The feed-rate for both turning and threading is varied as needed by operating the Norton gear and

the Meander drive systems existing in the feed gear box (FGR). The range of feeds can be

augmented by changing the gear ratio in the gear quadrant connecting the FGB with the spindle

• As and when required, the tailstock is shifted along the lathe bed by operating the clamping bolt

and the tailstock quill is moved forward or backward or is kept locked in the desired location.

• The versatility or working range of the centre lathes is augmented by using several attachments

like

- Taper turning attachment

- Thread milling attachment

(iv) Machining Operations Usually Done In Centre Lathes

The machining operations generally carried out in centre lathes are :

• Facing

• Centering

• Rough and finish turning

• Chamfering, shouldering, grooving, recessing etc

• Axial drilling and reaming by holding the cutting tool in the tailstock barrel

• Taper turning by

-offsetting the tailstock

-swiveling the compound slide

-using form tool with taper over short length

-using taper turning attachment if available

-combining longitudinal feed and cross feed, if feasible.

• Boring (internal turning); straight and taper

• Forming; external and internal

• Cutting helical threads; external and internal

• Parting off

• Knurling

In addition to the aforesaid regular machining operations, some more operations are also

occasionally done, if desired, in centre lathes by mounting suitable attachments available in

the market, such as,

• Grinding, both external and internal by mounting a grinding attachment on the

saddle

• Copying (profiles) by using hydraulic copying attachment

• Machining long and large threads for lead screws, power-screws, worms etc. by

using thread milling attachment.

Kinematic system of milling machine

The kinematic system comprising of a number of kinematic chains of several mechanisms

enables transmission of motions (and power) from the motor to the cutting tool for its

rotation at varying speeds and to the work-table for its slow feed motions along X, Y and Z

directions. In some milling machines the vertical feed is given to the milling (cutter) head.

The more versatile milling machines additionally possess the provisions of rotating the

work table and tilting the vertical milling spindle about X and / or Y axes.

Figure typically shows the kinematic diagram of the most common and widely used milling

machine having rotation of the single horizontal spindle or arbor and three feed motions of

the work-table in X, Y and Z directions.

The milling cutter mounted on the horizontal milling arbor, receives its rotary motion at

different speeds from the main motor through the speed gear box which with the help of

cluster gears splits the single speed into desirably large number(12, 16, 18, 24 etc) of

spindle speeds. Power is transmitted to the speed gear box through Vee-belts and a safety

clutch as shown in the diagram. For the feed motions of the workpiece (mounted on the

work-table) independently, the cutter speed, rotation of the input shaft of the speed gear

box is transmitted to the feed gear box through reduction (of speed) by worm and worm

wheels as shown. The cluster gears in the feed gear box enables provide a number of feed

rates desirably. The feeds of the job can be given both manually by rotating the respective

wheels by hand as well as automatically by engaging the respective clutches. The

directions of the longitudinal (X), cross (Y) and vertical (Z) feeds are controlled by

appropriately shifting the clutches. The system is so designed that the longitudinal feed can

be combined with the cross feed or vertical feed but cross feed and vertical feed cannot be

obtained simultaneously. This is done for safety purpose. A telescopic shaft with universal

joints at its ends is incorporated to transmit feed motion from the fixed position of the feed

gear box to the bed (and table) which moves up and down requiring change in length and

orientation of the shaft. The diagram also depicts that a separate small motor is provided

for quick traverse of the bed and table with the help of an over running clutch. During the

slow working feeds the rotation is transmitted from the worm and worm wheel to the inner

shaft through three equi-spaced rollers which get jammed into the tapering passage. During

quick unworking work-traverse, the shaft is directly rotated by that motor on-line without

stopping or slowing down the worm. Longer arbors can also be fitted, if needed, by

stretching the over-arm. The base of the milling machine is grouted on the concrete floor or

foundation.

Kinematic System of general purpose drilling machine and their principle of working:

Kinematic system in any machine tool is comprised of chain(s) of several mechanisms to

enable transform and transmit motion(s) from the power source(s) to the cutting tool and

the workpiece for the desired machining action. The kinematic structure varies from

machine tool to machine tool requiring different type and number of tool-work motions.

Even for the same type of machine tool, say column drilling machine, the designer may

take different kinematic structure depending upon productivity, process capability,

durability, compactness, overall cost etc targeted. Figure below shows a typical kinematic

system of a very general purpose drilling machine, i.e., a column drilling machine having

12 spindle speeds and 6 feeds.

The kinematic system enables the drilling machine the following essential works; Cutting

motion: The cutting motion in drilling machines is attained by rotating the drill at different speeds

(r.p.m.). Like centre lathes, milling machines etc, drilling machines also need to have a

reasonably large number of spindle speeds to cover the useful ranges of work material, tool

material, drill diameter, machining and machine tool conditions. It is shown in Fig. 4.2.10

that the drill gets its rotary motion from the motor through the speed gear box (SGB) and a

pair of bevel gears. For the same motor speed, the drill speed can be changed to any of the

12 speeds by shifting the cluster gears in the SGB. The direction of rotation of the drill can

be changed, if needed, by operating the clutch in the speed reversal mechanism, RM-s

shown in the figure.

• Feed motion

In drilling machines, generally both the cutting motion and feed motion are imparted to the

drill. Like cutting velocity or speed, the feed (rate) also needs varying (within a range)

depending upon the tool-work materials and other conditions and requirements.

Fig. 4.2.10 visualises that the drill receives its feed motion from the output shaft of the

SGB through the feed gear box (FGA), and the clutch. The feed rate can be changed to any

of the 6 rates by shifting the gears in the FGB. And the automatic feed direction can be

reversed, when required, by operating the speed reversal mechanism, RM-s as shown. The

slow rotation of the pinion causes the axial motion of the drill by moving the rack provided

on the quil.

The upper position of the spindle is reduced in diameter and splined to allow its passing

through the gear without hampering transmission of its rotation.

• Tool work mounting

The taper shank drills are fitted into the taper hole of the spindle either directly or through

taper socket(s). Small straight shank drills are fitted through a drill chuck having taper

shank. The workpiece is kept rigidly fixed on the bed (of the table). Small jobs are

generally held in vice and large or odd shaped jobs are directly mounted on the bed by

clamping tools using the T-slots made in the top and side surfaces of the bed

Schematic view of the drives of a drilling machine

Experiment No. 5

Aim: To make a job on drilling machine as per given specification.

Apparatus: Drill machine, drill bit, work holding devices, wire brush, Steel plate.

Theory:

Drilling Process

The drilling machine (drill press) is a single purpose machine for the production of holes.

Drilling is generally the best method of producing holes. The drill is a cylinderical bar

with helical flutes and radial cutting edges at one end. The drilling operation simply

consist of rotating the drill and feeding it into the workpiece being drilled.

The process is simple and reasonably accurate and the drill is easily controlled both in

cutting speed and feed rate. The drill is probably one of the original machining processes

and is the most widely used.

Drilling machine -important features/dimensions

Bench Drill

The most common form of drilling machine is the bench drill. As the name

implies this machine is normally bolted down to a bench. The workpiece can

be clamped onto the worktable or onto the base. Tee slots are normally

provided for this function. The worktable can be moved up and down the

vertical column. The worktable can be clamped at the selected height. The

drill is normally located in a three jaw chuck which is rotated by the drive

system. The figure below shows a belt drive. Modern bench drills are driven

by more sophisticated arrangements. The chuck is moved up and down by a

feed handle which drives rotating spindle via a rack and pinion mechanism.

Pillar Drill

The pillar drill has the same features as the bench drill. This drill is however

free standing and is of a far heavier construction able to take larger drills. The

larger drills normally have taper shanks which are located within a taper bore

in the spindle end. These tapers are standardised as morse tapers.

Drills

There are two common types of twist drills, high-speed steel drills, and

carbide-tipped drills. The most common type used for normal workshop

practice is the high-speed steel twist drill because of its low cost. Carbide-

tipped metal drills are used in production work where the drill must remain

sharp for extended periods, such as in a numerically controlled drilling

machine. Other types of drills available include solid carbide drills, TiN

coated drills, diamond drills etc. etc.

Twist drills shanks are either straight shank or tapered shank (Morse taper).

Straight shank twist drills are usually 12mm or smaller and are gripped in the

drill chucks. Tapered shank drills are usually for the larger drills that need

more strength which is provided by the taper socket chucks.

Common twist drill sizes range from 0.3mm to 90mm in diameter. Larger

holes are cut by special drills that are not considered as twist drills.

Types of Drills Bits

Definitions

1. Cutting Speed (v):-

It’s the peripheral speed of the drill.The cutting speed depends upon the properties

of the material being drilled, drill material, drill diameter, rate of speed, coolant used etc…

v = *D*N where

D = dia of the drill in m

N = Speed of rotation in rpm

2. Feed Rate (f):-

It’s the movement of drill along the axis (rpm)

3. Depth of Cut (d):-

The distance from the machined surface to the drill axis.

d = D / 2

As the depth of hole increases, the chip ejection becomes more difficult and the

fresh cutting fluid is not able to cutting zone. Hence for machining the lengthy hole special

type of drill called ‘gun drill’ is used.

4. Material Removal Rate:-

It’s the volume of material removed by the drill per unit time

MRR = ( D2 / 4) * f * N mm3 / min

5. Machining Time (T) :-

It depends upon the length (l) of the hole to be drilled , to the Speed (N) and feed (f)

of the drill

t = L / f N min

EXPERIMENT NO.6

AIM: To measure cutting forces on a single point cutting tool.

APPARATUS: Lathe, Vernier caliper, Cutting tool, thread, ruler.

THEORY: Irrespective of basic nature of the chip obtained during machining of metal,

the main factor governing the formation of chips is the plastic deformation of the metal

by a shear process. The deformation of metal occurs along a plane just ahead of the tool

and running upto free work surface.

After passing out the shear plane, the deformed metal slides along the tool

face due to the velocity of cutting tool. The size of the shear zone is thick if the metal is

machined at low cutting speed and vice versa. The width of chip b2 does not correspond

to original width b1. During orthogonal cutting, the tool moves with a velocity Vc

against the work, thereby shears the metal along the shear plane AB. The out coming

chip of thickness t2 experiences two velocity components, Vf and Vs along the tool face

and shear plane.

The undeformed chip thickness is t1.

In ABC,

sin

1tAB

Where, Shear angle.

In ABD,

sin ( 90- + ) = AB

t 2

AB = )90(

2

Sin

t

AB = )(

2

Cos

t

Where, = rake angle.

Sin

t1 = )(

2

Cos

t

tt

2

1 = )(

Cos

Sin

rC =

)(

Cos

Sin

rC =

SinSinCosCos

Sin

r c

1 =

Sin

SinSinCosCos

r c

1 = SinCotCos

tan =

Sin

Cos

rr

c

c

1

Also, btlbtl 222111

Where, l2 = length of cut chip which had a length l1 before cutting.

bl = width of cut

a) CUTTING SPEED: If the cutting speed is low for machining a brittle workpiece

then discontinuous chips will be produced while if the cutting speed is high for

machining a ductile workpiece then continuous chips will be produced. These

chips have same thickness throughout their length.

b) RAKE ANGLE: For cutting at high speeds and then producing a continuous

chip, a large rake angle is required. If rake angle is small, the chips will be

discontinuous. Shear angle depends on rake angle as:

tan =

Sin

Cos

rr

c

c

1

c) FEED AND DEPTH OF CUT: Feed and depth of cut also affect the cutting

ratio and hence shear angle btlbtl 222111

tt

2

1 = lblb

11

22 = rC =

ll

1

2 ( if bb 21 )

l2 can be measured by using a thread.

So higher the value of b2 & l2, more will be the cutting ratio.

PROCEDURE:

1) Perform a turning operation on Lathe using a sharp tool, perform orthogonal

cutting.

2) Obtain the chip produced.

3) With the help of a thread and a ruler measure its length.

4) Using a Vernier find its breadth.

5) Calculate tl / t2 using above given relations, hence find rc.

6) Calculate using,

=

Sin

Cos

rr

c

c

1tan

1

7) Perform the above steps at different speeds, feed, and depth of cut.

RESULT: The effect of cutting speed, feed, depth of cut, and rake angle on cutting

ratio rc and shear angle has been studied.

DISCUSSION AND ANALYSIS: The quantities tl & t2 are easily obtained by direct

measurement, so can be calculated. Sometimes it is not practical to measure chip

thickness, so in such cases, shear plane angle can be directly obtained from

photomicrograph of chip but cannot be accurately determined by this method as it is

difficult to find the exact position of shear plane. To avoid all these difficulties rc can be

calculated first, as

rc = tl / t2 = ll / l2

Where, ll = 2 r

As the cutting speed is increased more and more continuous chips are produced, so l2

increases and hence rc decreases. With increase in depth of cut, the chip thickness

increases and hence longer chips can be produced without breaking. So rc will decrease.

In case of large rake angles or positive rake angle, continuous chips are produced with

long lengths. So increase in the rake angle increases the length of chip and hence

decrease in cutting ratio.

The shear angle depends indirectly on cutting ratio and rake angle. Less the

rake angle more will be shear angle. More the value of cutting ratio, more will be the

shear plane angle, as

tan =

Sin

Cos

rr

c

c

1

So for, low values of r, rc will be more and will also be more, hence with increase in

cutting velocity, feed, depth of cut, the cutting ratio as well as decrease. It has been

assumed that the cutting edge of tool is sharp and no built up edge is formed.

In case of side flow consideration, then chip thickness ratio is to be multiplied

by , the side flow factor.

Where = b1 / b2

In case of brittle material, with small tool rake angles, the discontinuous chips

will be produced, with very small length. In that case, the value of chip thickness ratio

will come out to be more than found in case of continuous chips. So ductile materials

give longer chips than the brittle materials. The chip length has to be carefully

measured here, by using a thread. This is done by putting the thread carefully upon the

chip, such that it just sticks to the surface. In this way, the length of thread, which sticks

to the chip surface, gives the length of chip l2.

Irrespective of the basic nature of the chips obtained during machining of

metal, the main factor governing, the formation of chips is the plastic deformation of

the metal by shear process.

The deformation of metal occurs along a plane just ahead of the tool and

running upto free work surface, without passing out of the shear plane of the deformed

metal slides along the tool face due to velocity of the cutting tool. The size of the shear

zone is thick if metal is machined at low cutting speeds and thin if metal is machined at

high cutting speeds. When the cutting velocity changes, width and thickness both vary

to a large extent. The chip width b2 and chip thickness t2 do not correspond to the initial

values of b1 & t1.

Continuous chips, in the form of long coils, have the same thickness throughout the

length of the coil. These chips are produced due to continuous plastic deformation of

the metal along the shear plane without any rupture. Continuous chips without built up

edge can be obtained only at high cutting speeds, when the surface finish and the tool

life improve and power consumption reduces.

For larger values of rake angle, the friction between tool face and chips also

reduces. For high values of rake angle and use of efficient cutting fluids, continuous

chips can be produced without any built up edge. For this the cutting edge of the tool

should be sharp enough. If the rake angle is small, built up edge may be formed and

chip thickness may not be uniform throughout the length of the chip. From graph a non-

linear relationship is obtained, showing 3 regions.

EFFECT OF CUTTING SPEED: The cutting ratio increases as the cutting speed is

increased. As the speed is increased the chip becomes thinner and area of shear plane is

reduced. The forces required to produce the chip becomes smaller as speed is increased.

So, as the speed is increased, specific cutting energy reduces, resulting in higher

efficiency.

EFFECT OF FEED: At larger feeds, the specific cutting energy ps and shear strength of

the work material s remains constant, but at low feeds, ps and s both increase. This is

due to “tool-nose” force.

EFFECT OF RAKE ANGLE: As the rake angle increases the shear angle also

increases. The specific cutting energy ps reduce as increases. This results in greater

efficiency at larger value of rake angle.

The friction angle also increases as is increased. As increases, the stress at the

tool chip interface decrease and since frictional stress remains constant, increases.

OBSERVATION:

Diameter of workpiece,D=

Slot width=

L1=π D-slot width

=

Feed=

When L1= , r = ,Depth =

N(rpm) L2(cm) rc =L2/ L1 Φ

1

2

3

When L1= , r = ,Depth =

Depth of cut(div) L2(cm) rc =L2/ L1 Φ

1

2

3

When L1= , r = ,Depth =

N(rpm) L2(cm) rc =L2/ L1 Φ

1

2

3

When L1= , r = ,Depth =

Depth of cut(div) L2(cm) rc =L2/ L1 Φ

1

2

3

Experiment No. 7

Aim: Study of Jigs and Fixtures.

Theory: Introduction:

Jigs and fixtures are production tools used to accurately manufacture duplicate and

interchangeable parts. Jigs and fixtures are specially designed so that large numbers of

components can be machined or assembled identically, and to ensure interchangeability of

components. The economical production of engineering components is greatly facilitated

by the provision of jigs and fixtures. The use of a jig or fixture makes a fairly simple

operation out of one which would otherwise require a lot of skill and time.

Both jigs and fixtures position components accurately; and hold components rigid and

prevent movement during working in order to impart greater productivity and part

accuracy. Jigs and fixtures hold or grip a work piece in the predetermined manner of

firmness and location, to perform on the work piece a manufacturing operation.

A jig or fixture is designed and built to hold, support and locate every component (part) to

ensure that each is drilled or machined within the specified limits.

The correct relationship and alignment between the tool and the work piece is maintained.

Jigs and fixtures may be large (air plane fuselages are built on picture frame fixtures) or

very small (as in watch making). Their use is limited only by job requirements and the

imagination of the designer.

The jigs and fixtures must. be accurately made and the material used must' be able to

withstand wear and the operational (cutting) forces experienced during metal cutting

Jigs and fixtures must be clean, undamaged and free from swarf and grit Components must

not be forced into a jig or fixture.

Jigs and fixtures are precision tools. They are expensive to produce because they are made

to fine limits from materials with good resistance to wear. They must be properly stored or

isolated to prevent accidental damage, and they must be numbered for identification for

future use.

General Classification

The terms "jigs" and "fixtures" are rather loosely used by shopmen. While this is

necessarily so in some cases, in most instances it is more correct to apply the term jig to a

device which holds the work and automatically locates the cutting tool so that each piece

produced is a duplicate of all the others. Fixtures, on the other hand, do not automatically

locate the cutting tool. While fixtures may be used to produce duplicates, this result is

usually gained by means of a cutting tool locating jig separated from the fixture itself.

Fixtures are essentially work-holding devices.

Object of These Tools. While several effects are gained by using jigs and fixtures, they all

reduce to one thing, namely, production. For example, by the proper use of jigs and

fixtures, production is made more uniform, giving interchangeability of parts. If jigs and

fixtures are properly used, production is attended by a reduction of labor cost, both when

the machine parts are being produced, and when the parts are assembled to produce the

completed machine.

Importance

That jigs and fixtures are an important factor in modern production is clearly shown by a

study of the various production cuts in this book. These illustrations for the most part show

the machine in a working condition, and in nearly every case some special fixture or jig

is holding the work or is guiding the tool. In some cases, the special work-holding device is

a simple work chuck or a magnetic work chuck, in others the special devices are rather

elaborate.

Fundamental Principles Of Design

Use of Jig. In jig design it is usual to first consider the uses to which it is to be put. If, for

example, the piece for which the jig is made is to finally bear a fixed relation to some other

machine part, it becomes necessary to consider not only the part being jigged, but also its

relation to the other parts with which it is to be assembled. Again, if the piece being jigged

is of special accuracy, the jig design may be different from that of a machine part in which

no special accuracy is required. In one case, the jig is both a rapid production tool and an

interchangeability tool. In the other case, the jig is merely a convenient tool for getting

rapid production. As a Work Holder. It is usual in the design of jigs to next consider how

the piece shall be held in the prospective jig. The points or surfaces upon the piece which

are those best suited for location points and surfaces are decided upon. If the piece has been

previously machined, the surface machined usually offers the best location to work from.

If, on the other hand, the surfaces of the stock are rough, as in an ordinary casting, the

selection of the locating surfaces or surface is usually a more difficult one. Usually some

surface or hole will be essentially more important than all the remaining surfaces or holes.

In such a case, the jig designer uses location points which will position the important hole

or surface, afterward considering the points of lesser importance. This he terms "working to

or working from the important point". A flat surface, if it has previously been machined, is

usually located against a flat surface; if not previously machined, a flat surface should be

given line or point contact. It is customary to locate a curved surface against a V or against

points.

Clamping

This refers to the particular devices which hold the piece being jigged against the location

points or surfaces. The design should be such that the least number of clamping devices

may be used, so that no unnecessary time is consumed in charging the jig, as this limits

production unless the jigs are charged as a separate job.

All clamping devices should exert their pressure, wherever possible, directly in line with

the supporting points. If this is done the piece clamped will not be sprung out of shape. As

an aid in understanding the already mentioned points, a simple jig will be illustrated and its

construction described.

Drill Jigs

While a study of the illustrations in this book will show the student that jigs are an

important factor in all production machines, perhaps in no other machine is their

importance so complete as in the drilling of holes. For this reason a drill jig will be used to

illustrate jig construction. In the line drawing, Figs. 375 and 376, are shown the top and

bottom views of a simple jig of the open box type designed to rapidly produce duplicate

work. In Fig. 377 are shown two views'of a jig of the closed box type for rapid production

of duplicate parts. While neither of these jigs are elaborate in either design or construction,

they fairly represent their types.

Types of Drill Jigs. Drill jigs are of three forms (a) plate jigs; (b) open box; (c) closed box.

The plate jig usually consists of a flat plate with located bushings which is positioned on

the work and clamped to it. The open box type, as shown, consists of a casting provided

with legs or feet. The piece jigged is clamped to the lower or under surface of the jig body.

Two Views of Closed Box Drill Jig

Experiment No.8

Aim: To study the formation of chips in turning and shaping of C.I., M.S., Brass, Cu and

Aluminium.

Apparatus: V tool, Engine Lathe, Work-pieces of different materials diameter 40-50 length 75-

80mm, Center drill.

Theory: Properties of materials being machined give different types of chips and the cutting

conditions also prevail. The length of chip depends on ductility of material. More the ductility

longer will be the chip. Harder and less ductile materials produce shorter chips. The built-up edge

(BUE) formation is due to low cutting speeds, low feed rates, high depth of cuts and machining

without coolant. This increases roughness of newly manufactured surface finish. The chip carries

about 80% heat away and 10% is heat is carried away by tool and 10% heat is absorbed by work

piece.

Mechanism of chip formation in machining ductile materials:

During continuous machining the uncut layer of the work material just ahead of the cutting tool

(edge) is subjected to almost all sided compression. The force exerted by the tool on the chip arises

out of the normal force, N and frictional force, F Due to such compression, shear stress develops,

within that compressed region, in different magnitude, in different directions and rapidly increases

in magnitude. Whenever and wherever the value of the shear stress reaches or exceeds the shear

strength of that work material in the deformation region, yielding or slip takes place resulting shear

deformation in that region and the plane of maximum shear stress. But the forces causing the shear

stresses in the region of the chip quickly diminishes and finally disappears while that region moves

along the tool rake surface towards and then goes beyond the point of chip-tool engagement. As a

result the slip or shear stops propagating long before total separation takes place. In the mean time

the succeeding portion of the chip starts undergoing compression followed by yielding and shear.

This phenomenon repeats rapidly resulting in formation and removal of chips in thin layer by layer.

Mechanism of chip formation in machining brittle materials:

The basic two mechanisms involved in chip formation are

• Yielding – generally for ductile materials

• Brittle fracture – generally for brittle materials

During machining, first a small crack develops at the tool tip due to wedging action of the cutting

edge. At the sharp crack-tip stress concentration takes place. In case of ductile materials

immediately yielding takes place at the crack-tip and reduces the effect of stress concentration and

prevents its propagation as crack. But in case of brittle materials the initiated crack quickly

propagates, under stressing action, and total separation takes place from the parent work piece

through the minimum resistance path Machining of brittle material produces discontinuous chips

and mostly of irregular size and shape.

Chip Formation in Turning:

Chip Formation during shaping:

Experiment No.9

Aim: To study the life of a cutting tool used on the lathe machine.

Theory: The cutting tools need to be capable to meet the growing demands for higher productivity

and economy as well as to machine the exotic materials which are coming up with the rapid

progress in science and technology.

The cutting tool material of the day and future essentially require the following properties to resist

or retard the phenomena leading to random or early tool failure:

i) High mechanical strength; compressive, tensile, and TRA

ii) Fracture toughness – high or at least adequate

iii) High hardness for abrasion resistance

iv) High hot hardness to resist plastic deformation and reduce wear rate at elevated temperature

v) Chemical stability or inertness against work material, atmospheric gases and cutting fluids

vi) Resistance to adhesion and diffusion

vii) Thermal conductivity – low at the surface to resist incoming of heat and high at the core to

quickly dissipate the heat entered

viii) High heat resistance and stiffness

ix) Manufacturability, availability and low cost.

Tool Life Tool life generally indicates the amount of satisfactory performance or service rendered by a fresh

tool or a cutting point till it is declared failed.

Tool life is defined in two ways:

(a) In R & D: Actual machining time (period) by which a fresh cutting tool (or point)

satisfactorily works after which it needs replacement or reconditioning.

The modern tools hardly fail prematurely or abruptly by mechanical breakage or rapid plastic

deformation. Those fail mostly by wearing process which systematically grows slowly with

machining time. In that case, tool life means the span of actual machining time by which a fresh

tool can work before attaining the specified limit of tool wear. Mostly tool life is decided by the

machining time till flank wear, VB reaches 0.3 mm or crater wear, KT reaches

0.15 mm.

(b) In industries or shop floor: The length of time of satisfactory service or amount of acceptable

output provided by a fresh tool prior to it is required to replace or recondition.

Assessment of tool life For R & D purposes, tool life is always assessed or expressed by span of

machining time in minutes, whereas, in industries besides machining time in minutes some other

means are also used to assess tool life, depending upon the situation, such as

• No. of pieces of work machined

• Total volume of material removed

• Total length of cut.

Measurement of tool wear

The various methods are:

i) By loss of tool material in volume or weight, in one life time – this method is crude and is

generally applicable for critical tools like grinding wheels.

ii) By grooving and indentation method – in this approximate method wear depth is measured

indirectly by the difference in length of the groove or the indentation outside and inside the worn

area

iii) Using optical microscope fitted with micrometer – very common and effective method

iv) Using scanning electron microscope (SEM) – used generally, for detailed study; both qualitative

and quantitative

Taylor’s tool life equation

Wear and hence tool life of any tool for any work material is governed mainly by the level of the

machining parameters i.e., cutting velocity, (VC), feed, (so) and depth of cut (t). Cutting velocity

affects maximum and depth of cut minimum. The usual pattern of growth of cutting tool wear

(mainly VB), principle of assessing tool life and its dependence on cutting velocity are

schematically shown in Fig

The tool life obviously decreases with the increase in cutting velocity keeping other conditions

unaltered as indicated in Fig. If the tool lives, etc are plotted against the

corresponding cutting velocities, etc as shown in Fig a smooth curve like a

rectangular hyperbola is found to appear. When F. W. Taylor plotted the same figure taking both

V and T in log-scale, a more distinct linear relationship appeared as schematically shown in Fig.

With the slope, n and intercept, c, Taylor derived the simple equation as

Where, n is called, Taylor’s tool life exponent. The values of both ‘n’ and ‘c’ depend mainly upon

the tool-work materials and the cutting environment (cutting fluid application). The value of C

depends also on the limiting value of V undertaken (i.e., 0.3 mm, 0.4 mm, 0.6 mm etc.).