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: 2 : Mechanical Engg. _ ESE MAINS


01(a).

Sol: Tool geometry of single point cutting tool:

Cutting using single point cutting tool can be

affected by six angles of tool and the nose

radius of tool. The arrangement of all these in

a particular order is called single point cutting

tool nomenclature or designation. The two

systems are widely used in this context

1. ASA system (American Standards

Association System)

2. Orthogonal Rake System (ORS).

1. ASA system:

In this system, the angles defined are

measured with respect to three mutually

perpendicular planes.

According to ASA system, the single point

cutting tool can be designated as

b s e s Ce Cs r

Advantages:

Because the angles specified in the A.S.A

system are measured with respect to three

mutually perpendicular planes, the

understanding of angles and measurement of

angles are easier.

Disadvantage:

In A.S.A system the angles specified are

measured with respect to three mutually

perpendicular planes. Hence if the tool is

designated in A.S.A system, the analysis of

machining will be difficult.

To overcome the disadvantage of A.S.A

system, the O.R.S has been defined.

2. O.R.S (orthogonal rake system):

In this system, the angles defined are

measured with respect to plane containing

principal or side cutting edge and the plane

normal to it.

According to ORS the single point cutting

tool can be designated as

i – s e Ce – r

i = inclination angle

= side rake/orthogonal rake/effective rake

angle,

S = side relief angle

e = end relief angle

Ce = End cutting edge angle

= approach/ entering/principal cutting edge

angle

r = nose radius

Most commonly used method of designation

of single point cutting tool is A.S.A system

The conversion between angles of A.S.A and

O.R.S are given below

(1)

S

b

tan

tan

sincos

cossin

tan

itan

It can be written as

tani = sintanb costanS

tan = costanb + sintanS

tan

itan

sincos

cossin

tan

tan

S

b

: 3 : Conventional Test – 6


(2)

'e

'S

e

S

tan

cot

sincos

cossin

cot

cot and

e

s

'e

'S

cot

cot

sincos

cossin

tan

cot

Ce =End cutting edge angle is same in A.S.A

and O.R.S

= 90 Cs

r = Nose radius is same in A.S.A and O.R.S

system.

01(b).

Sol:

In the conventional method of operating

machine tools, the machinist turns the

controls, moves levers, and makes other

adjustments by hand to set power feeds in

motion. He also selects the proper speed, feed

and depth of cut, such as for the spindle of the

milling machine, drill press, boring mill, jig

boring machine, or the engine lathe. The

machinist does this in order to follow the

instructions given on the job operation sheet

or job blueprint, or simply on the basis of his

experience. In numerical control, a tape takes

the place of the machinist and his experience.

The tape controls the speed and feed of the

cutting tool, the movement of the table, the

flow of coolant, and the variety of other

operations required to machine a particular

job. A machine directed by numerical control

can machine workpieces to the highest degree

of accuracy, within the accuracy of the

machine tool itself. Each spindle, lead screw,

cross feed screw, and other machine tool

member that moves is provided with its own

motor-drive unit. Each movement to a spindle

or lead screw, for example, comes from the

motor attached for moving these members.

Such motors are called servomotors or

servomechanisms.

In manual control of machine, the required

optimum spindle speed is not available hence

nearby speed will be selected. Due to this the

loss of productivity will takes place. Whereas

in NC machines due to usage of stepper

motors or servomotors, it is possible to get

exact optimum speed hence no loss of

productivity will takes place.

Accuracy of the dimensions produced

depends on the machine operator in case of

manual controlled machine tool whereas

consistently accurate parts are possible to

produce in the NC machines.

Complex shapes of the components is

difficult to produce on manual controlled

machines whereas it is easy to produce on NC

machines.

Cost of NC machines is higher than the

manual controlled machines.



01(c).

Sol:

(i) Bite angle: The angle made by the

deformation zone with respect to the centre

of the rollers is called deformation angle (or)

Angle of bite. This depends on the reduction

in thickness and diameter of rollers.

(ii) Percentage reduction in thickness: The

percentage reduction in thickness with

respect to the original thickness is called

percentage reduction in thickness.

% reduction in thickness = (H0 – H1) / H0

(iii) Forward slip: The maximum % slip taking

place in the leading zone is called as

“forward slip”.Forward slip = (V – V0) / V, where V, V0

are the surface velocity of rollers and

velocity of strip respectively at entry.

(iv) Neutral point: At the neutral point the

relative velocity and slip becomes equal to

zero.

(v) Backward slip: The maximum % of slip

taking place in the lagging zone is called as

“backward slip”.backward slip = (V1 – V) / V, where V, V1

are the surface velocity of rollers and

velocity of strip at exit respectively.

01(d).

Sol: Carburizing is one of the method of giving

making case hardening to a piece of steel.

The piece of work is placed is heated in

presence of carbon monoxide. So that the

carbon reacts with steel surface and give

much more rapid and direct absorption of

carbon by steel. The process consists of

increasing the carbon content of the case so

that it responds to hardening and keeping the

core soft and ductile. The carbon is

introduced by the process of diffusion from

carbon monoxide gas. This is achieved by

holding the component in an atmosphere of

mixture of CO and CO2, Hydrogen and other

gasses so proportioned that the maximum

rate of carbon absorption is attained.

Components of simple shape are suspended

from hooks in the atmosphere controlled gas

furnace tank. By suitable release or

suspension, the components can be

quenched directly from the surface finish

impossible to obtain by other methods.

Advantages of carburizing

Case depth can be obtained accurately.

Process is rapid

Laborious operations are eliminated

Less floor space.

Carburized steel is recommended for work

requiring a hard surface and a tough core.

This method is applicable for components

made by low and medium carbon steels.

Examples are gears, bearing surfaces, cam

shafts and wear resistant surfaces.

01(e).

Sol: Architecture of Microcontroller

The below figure shows a block diagram for

a typical fully-featured microcontroller,

indicating also the lists of typical external



devices that might interface to the

microcontroller.

The components of a microcontroller include the

CPU, RAM, ROM, digital I/O ports, a serial

communication interface, timers, A/D converters,

and D/A converters.

The RAM is used to store settings and values

used by an executing program.

The ROM is used to store the program and

any permanent data. A designer can have a

program and data permanently stored in ROM

by the chip manufacturer, or the ROM can be

in the form of EPROM or EEPROM, which

can be reprogrammed by the user.

Software permanently stored in ROM is

referred to as firmware.

Microcontroller manufacturers offer

programming devices that can download a

compiled machine code the file from a PC

directly to the EPROM of the microcontroller,

usually via the PC serial port and special-

purpose pins on the microcontroller. These

pins can usually be used for other purposes

once the device is programmed. Additional

EEPROM may also be available and used by

the program to store settings and parameters

generated or modified during execution. The

data in EEPROM is nonvolatile, which means

the program can access the data when the

microcontroller power is turned off and back

on again.

The digital I/O ports allow binary data to be

transferred to and from the microcontroller

using external pins on the IC. These pins can

CPU RAM(Volatile data)

ROM, EPROM or EEPROM(Nonvolatile software and data)

DigitalI/O ports

Serial communication(SPI, IC, UART, USART)

Timers

A/D D/A

Analog sensorsPotentiometersMonitored voltage

Analog actuatorsAmplifiersAnalog displays

External EPROMOther microcontrollersHost computer

SwitchesOn-of sensorsExternal A/D or D/AOn-off actuatorsDigital displays

MICROCONTROLLER

Fig: Block diagram for typical full-featured microcontroller

Fig: Microcontroller

CPU RAM ROM

I/O TimerSerialCOMPort



be used to read the state of switches and on-

off sensors, to interface to external analog-to-

digital and digital-to-analog converters, to

control digital displays, and to control on-off

actuators.

The I/O ports can be used to transmit signals

to and from other microcontrollers to

coordinate various functions.

The microcontroller can also use a serial port

to transmit to and from external devices,

provided these devices support the same serial

communication protocol. There are various

standards or protocols for serial

communication including SPI (Serial

Peripheral Interface), IC (Integrated Circuit),

UART (Universal Asynchronous Receiver-

Transmitter).

The A/D converter allows the microcontroller

to convert an external analog voltage (e.g.,

from a sensor) to a digital value that can be

processed or stored by the CPU. The D/A

converter allows the microcontroller to output

an analog voltage to a non digital device e.g.,

a motor amplifier.



02(a).

Sol: Cutting velocity = 100051850

100DN

= 49.95 m/min

Cutting power = cutting velocity (Vc) × Fc

= 49.95 × 1450/60

= 1207 W

Feed speed = minm

10002.0318

1000fN

= 0.0636 m/min = 0.00106m/sec

Feed power = Ff × Feed speed

= 450 × 0.00106 Nm/min = 0.477 W

The power due to radial force is negligible.

Therefore total power being consumed at the

cutting at the cutting point = 1207 + 0.44

= 1207.477 W

Rate of energy going with chip

= 1207.477× 0.9 = 1086.7 W

MRR = f.d.V = 0.2 4 49.95/ 60

= 0.666 cc/sec

Mass of chip produced

= 0.666 × 7.87 gm/sec

= 5.24 g/sec

Temperature rise of chip

= 1207.447 / (0.44 × 5.24)

= 523.57C

02(b).

Sol: Boring: The operation of enlarging the

existing hole by some extent by using

internal turning operation is called boring

operation. It is done on the lathe machine

and it is done by using single point cutting

tool.

Counter boring: The operation of enlarging

the end of an existing hole by internal

turning operation is called counter boring

operation.

Counter sinking: The operation of making

conical enlargement at the end of an existing

hole is called counter sinking. This is done

by using large size drill bit.

Spot facing: The operation of making the

surface of hole flat and square is called spot

facing. This is done by using end mill cutter

with drilling machine.

Data given:

Feed = 0.1mm/rev,

Width of work = 100mm,

L = stroke length = 140mm

Approach = over travel = 5mm width wise

B = 100 + 5 + 5 = 110 mm,

V = 25m/min, M = 0.67

BoringCounter sinking

Counter boring

spots

Spot facing



M+L

V=(N)strokesofno

1.

67.01140

25000

= 106.9 rpm

Time per cut N

1

f

B

= min10.3106.90.1

110=

02(c).

Sol:

Roughness: The very small size or

microscopic irregularities present on the work

piece is called Roughness. The reasons are

These are the irregularities caused by

machining itself due to variation in

process parameters.

These are the irregularities arising from

method of rupturing of the material during

the separation of the chip.

Waviness: Waviness is the longer wavelength

irregularities upon which roughness is super

imposed. Waviness may be induced due to

These are the irregularities arising because of:

Inaccuracies in the machine tool.

Ex: lack of straightness in the guide ways.

Deformation of work under cutting force

Deformation of work due to its own

weight.

These are the irregularities caused by

vibration of any kind, for example tool

chatter.

Talyserf ( Taylor Hobgon Talysurf ) :

This method uses E-type stamping with

primary winding is provided on the central

arm and two secondary windings are

provided on the two extreme arms. A

horizontal arm is provided which is pivoted

at the center. The distance present between

the arm and secondary winding will control

the emf generated. The two secondary

windings are connected to the voltmeter

such that voltmeter reads the difference in

emf generated in two secondary windings.

When the arm is perfectly horizontal, the

distance at S1 and S2 will be equal hence,

emf generated is same in both the secondary

winding and the voltmeter shows zero

reading. As the work piece is moving, the

stylus is finding the peaks and valleys, so

that the arm is tilting and the distance at S1

and S2 are changing, emf generated is

changing and hence the difference in emf

generated will be measured by using

voltmeter.

In this heights of irregularities is directly

proportional to the difference in emf , hence

S2S1

pivotedarm

W.P

V

Stylus



it is also called as voltage modulating type

or current modulating type equipment.

By taking the voltmeter readings the height

of irregularities can be measured and using

this the values Ra , Rz and Rt can be

estimated. This is the commonly used

method in industry. By connecting

amplifiers to the voltmeter the

magnifications can be increased.

03(a).

Sol: Riser: A riser is acting as reservoir to

supply molten metal to the casting cavity for

compensating liquid shrinkages taking place

during solidification. This avoids the

formation of cavities due to shrinkage. Most

metals are less dense as a liquid than as a

solid so castings shrink upon cooling, which

can leave a void at the last point to solidify.

Risers prevent this by providing molten

metal to the casting as it solidifies, so that

the cavity forms in the riser and not the

casting.

Requirements of riser

Volume of riser is at least equal to three

times the shrinkage volume of riser

Solidification time of riser is at least equal

to solidification time of casting metal.

The riser is located based two conditions.

During casting of uniform cross

sectioned castings the riser is provided

at top most point of casting cavity.

During casting of non-uniform

castings the riser is provided near to

the thickest portion than the thinnest

portion.

Shape of riser is selected such that the

surface area of riser exposed for heat

transfer must be as min as possible.

Riser design methods

(i) Caine’s methodFreezing Ratio

‘X’ =casting

riser

castings

risers

M

M

AV

AV

---------(1)

Freezing ratio X cby

a=

----------(2)

a, b, c are constants taken from casting table

corresponding to metal to be casted

Y = volumetric ratio =C

r

V

V-----------(3)

Equate (1) and (2)

c

bV

V

a

M

M

c

rc

r

Solve for ‘D’(ii) Modulus Method:

= Solidification time,

M = Modulus = (V/As) = (Volume/ surface

area)

r c

2C

2r MM

Mr MC

According to standard condition, modulus of

riser is taken as 20% higher than modulus of

casting



Mr = 1.2 MC

CM1.2=6

D

D = 7.2 MC

(iii) Novel Research Method:

Shape factor of casting (S.F) =t

W+L

L = Length of casting

W = width of casting

t = thickness of casting

Using SF value the value of ‘y’ can be taken

from tables, henceC

r

V

V=y

Vr = y Vc = the value of D & H can

calculated.

(iv) Shrinkage Volume consideration Method:

If % shrinkage of metal is given

Volume of riser = 3 shrinkage volume,

and calculate the D & H of riser.

And then check again so that the

(s)riser (s)casting

If the above condition satisfies, the

dimensions of riser are final.

If the above equation is not satisfied then

Assume that (s)riser = (s)casting, and

determine the size of riser.



03(b).

Sol: Solid state welding is a group of welding

processes which produces coalescence at

temperatures essentially below the melting

point of the base materials being joined,

without the addition of filler metal.

Advantages of Solid State Welding:

Weld (bonding) is free from microstructure

defects (pores, non-metallic inclusions,

segregation of alloying elements)

Mechanical properties of the weld are similar

to those of the parent metals

No consumable materials (filler material,

fluxes, shielding gases) are required

Dissimilar metals may be joined (steel -

aluminum alloy steel - copper alloy).

Types of sold state welding processes

(i) Cold Welding

Cold welding is a solid state welding process

which uses pressure at room temperature to

produce coalescence of metals with

substantial deformation at the weld.

Welding is accomplished by using

extremely high pressures on extremely clean

interfacing materials. Sufficiently high

pressure can be obtained with simple hand

tools when extremely thin materials are being

joined. When cold welding heavier sections a

press is usually required to exert sufficient

pressure to make a successful weld.

Indentations are usually made in the parts

being cold welded. The process is readily

adaptable to joining ductile metals.

Aluminum and copper are readily cold

welded. Aluminum and copper can be joined

together by cold welding.

(ii) Diffusion Welding (DFW)

Diffusion welding is a solid state welding

process which produces coalescence of the

faying surfaces by the application of

pressure and elevated temperatures. The

process does not involve microscopic

deformation melting or relative motion of

the parts. Filler metal may or may not be

used. This may be in the form of

electroplated surfaces.

The process is used for joining refractory

metals at temperatures that do not affect

their metallurgical properties. Heating is

usually accomplished by induction,

resistance, or furnace. Atmosphere and

vacuum furnaces are used and for most

refractory metals a protective inert

atmosphere is desirable.

Successful welds have been made on

refractory metals at temperatures slightly

over half the normal melting temperature of

the metal. To accomplish this type of joining

extremely close tolerance joint preparation

is required and a vacuum or inert

atmosphere is used. The process is used

quite extensively for joining dissimilar

metals. The process is considered diffusion

brazing when a layer of filler material is



placed between the faying surfaces of the

parts being joined. These processes are used

primarily by the aircraft and aerospace

industries.

(iii) Explosion Welding (EXW)

Explosion welding is a solid state welding

process in which coalescence is effected by

high-velocity movement together of the

parts to be joined produced by a controlled

detonation. Even though heat is not applied

in making an explosion weld it appears that

the metal at the interface is molten during

welding.

This heat comes from several sources,

from the shock wave associated with impact

and from the energy expended in collision.

Heat is also released by plastic deformation

associated with jetting and ripple formation

at the interface between the parts being

welded. Plastic interaction between the

metal surfaces is especially pronounced

when surface jetting occurs. It is found

necessary to allow the metal to flow

plastically in order to provide a quality weld.

Explosion welding creates a strong weld

between almost all metals. It has been used

to weld dissimilar metals that were not

weldable by the arc processes. The weld

apparently does not disturb the effects of

cold work or other forms of mechanical or

thermal treatment. The process is self-

contained, it is portable, and welding can be

achieved quickly over large areas. The

strength of the weld joint is equal to or

greater than the strength of the weaker of the

two metals joined.

Explosion welding has not become too

widely used except in a few limited fields.

One of the most widely used applications of

explosion welding has been in the cladding

of base metals with thinner alloys. Another

application for explosion welding is in the

joining of tube-to-tube sheets for the

manufacture of heat exchangers. The

process is also used as a repair tool for

repairing leaking tube-to-tube sheet joints.

Another and new application has been the

joining of pipes in a socket joint. This

application will be of increasing importance

in the future.

(iv) Forge Welding (FOW)

Forge welding is a solid state welding

process which produces coalescence of

metals by heating them in a forge and by

applying pressure or blows sufficient to

cause permanent deformation at the

interface.

This is one of the older welding processes

and at one time was called hammer welding.

Forge welds made by blacksmiths were

made by heating the parts to be joined to a

red heat considerably below the molten

temperature. Normal practice was to apply

flux to the interface. The blacksmith by

skillful use of a hammer and an anvil was

able to create pressure at the faying surfaces



sufficient to cause coalescence. This process

is of minor industrial significance today.

(v) Friction Welding (FRW)

Friction welding is a solid state welding

process which produces coalescence of

materials by the heat obtained from

mechanically-induced sliding motion

between rubbing surfaces. The work parts

are held together under pressure. This

process usually involves the rotating of one

part against another to generate frictional

heat at the junction. When a suitable high

temperature has been reached, rotational

motion ceases and additional pressure is

applied and coalescence occurs.

There are two variations of the friction

welding process. In the original process one

part is held stationary and the other part is

rotated by a motor which maintains an

essentially constant rotational speed. The

two parts are brought in contact under

pressure for a specified period of time with a

specific pressure. Rotating power is

disengaged from the rotating piece and the

pressure is increased. When the rotating

piece stops the weld is completed. This

process can be accurately controlled when

speed, pressure, and time are closely

regulated.

The other variation is called inertia

welding. Here a flywheel is revolved by a

motor until a preset speed is reached. It, in

turn, rotates one of the pieces to be welded.

The motor is disengaged from the flywheel

and the other part to be welded is brought in

contact under pressure with the rotating

piece. During the predetermined time during

which the rotational speed of the part is

reduced the flywheel is brought to an

immediate stop and additional pressure is

provided to complete the weld.

Both methods utilize frictional heat and

produce welds of similar quality. Slightly

better control is claimed with the original

process. Among the advantages of friction

welding is the ability to produce high quality

welds in a short cycle time. No filler metal is

required and flux is not used. The process is

capable of welding most of the common

metals. It can also be used to join many

combinations of dissimilar metals.

Friction welding requires relatively expensive

apparatus similar to a machine tool. There are

three important factors involved in making a

friction weld: The rotational speed which is

related to the material to be welded and the

diameter of the weld at the interface.

1. The pressure between the two parts to be

welded. Pressure changes during the weld

sequence. At the start it is very low, but it is

increased to create the frictional heat. When

the rotation is stopped pressure is rapidly

increased so that forging takes place

immediately before or after rotation is

stopped.

2. The welding time. Time is related to the

shape and the type of metal and the surface



area. It is normally a matter of a few

seconds. The actual operation of the

machine is automatic and is controlled by a

sequence controller which can be set

according to the weld schedule established

for the parts to be joined.

Normally for friction welding one of the

parts to be welded is round in cross section;

however, this is not an absolute necessity.

Visual inspection of weld quality can be

based on the flash, which occurs around the

outside perimeter of the weld. Normally this

flash will extend beyond the outside

diameter of the parts and will curl around

back toward the part but will have the joint

extending beyond the outside diameter of

the part. If the flash sticks out relatively

straight from the joint it is an indication that

the time was too short, the pressure was too

low, or the speed was too high. These joints

may crack. If the flash curls too far back on

the outside diameter it is an indication that

the time was too long and the pressure was

too high. Between these extremes is the

correct flash shape. The flash is normally

removed after welding.

(vi) Hot Pressure Welding (HPW)

Hot pressure welding is a solid state

welding process which produces

coalescence of materials with heat and the

application of pressure sufficient to produce

macro-deformation of the base metal. In this

process coalescence occurs at the interface

between the parts because of pressure and

heat which is accompanied by noticeable

deformation. The deformation of the surface

cracks the surface oxide film and increases

the areas of clean metal. Welding this metal

to the clean metal of the abutting part is

accomplished by diffusion across the

interface so that coalescence of the faying

surface occurs. This type of operation is

normally carried on in closed chambers

where vacuum or a shielding medium may

be used. It is used primarily in the

production of weldments for the aerospace

industry. A variation is the hot isostatic

pressure welding method. In this case, the

pressure is applied by means of a hot inert

gas in a pressure vessel.

(vii) Roll Welding (ROW)

Roll welding is a solid state welding process

which produces coalescence of metals by

heating and by applying pressure with rolls

sufficient to cause deformation at the faying

surfaces. This process is similar to forge

welding except that pressure is applied by

means of rolls rather than by means of

hammer blows. Coalescence occurs at the

interface between the two parts by means of

diffusion at the faying surfaces. One of the

major uses of this process is the cladding of

mild or low-alloy steel with a high-alloy

material such as stainless steel. It is also

used for making bimetallic materials for the

instrument industry.



(viii) Ultrasonic Welding (USW)

Ultrasonic welding is a solid state welding

process which produces coalescence by the

local application of high-frequency vibratory

energy as the work parts are held together

under pressure. Welding occurs when the

ultrasonic tip or electrode, the energy

coupling device, is clamped against the

work pieces and is made to oscillate in a

plane parallel to the weld interface.

The combined clamping pressure and

oscillating forces introduce dynamic stresses

in the base metal. This produces minute

deformations which create a moderate

temperature rise in the base metal at the

weld zone. This coupled with the clamping

pressure provides for coalescence across the

interface to produce the weld. Ultrasonic

energy will aid in cleaning the weld area by

breaking up oxide films and causing them to

be carried away.

The vibratory energy that produces the

minute deformation comes from a

transducer which converts high-frequency

alternating electrical energy into mechanical

energy. The transducer is coupled to the

work by various types of tooling which can

range from tips similar to resistance welding

tips to resistance roll welding electrode

wheels. The normal weld is the lap joint

weld.

The temperature at the weld is not raised

to the melting point and therefore there is no

nugget similar to resistance welding. Weld

strength is equal to the strength of the base

metal. Most ductile metals can be welded

together and there are many combinations of

dissimilar metals that can be welded. The

process is restricted to relatively thin

materials normally in the foil or extremely

thin gauge thicknesses.

This process is used extensively in the

electronics, aerospace, and instrument

industries. It is also used for producing

packages and containers and for sealing

them.

03(c).

Sol: Given data, t1 = 0.25 mm, t2 = 0.75 mm

b = 2.5 mm, = 0, Fc = 900 N, FT = 400 N

3

1

0.75

0.25

2

1 ==t

t=r

NF

tantanFF

c

t

0.44900

400tan =μ=β = 23.96

Shear angle

o11 18.44=3

1tan=

αsinr1

αcosrtan=

Shear force (Fs)

= Fccos ( + – )/ (cos( – α) = 727.25N

Ultimate shear stress

bt

sinF=

A

F=τ

1

s

s

s

=2.50.25

sin18.44727.251

MPaormm

N06.683=

2



04(a).Sol: Deformation of metals:

Metals or alloys get deformed when they are

stressed and the deformation causes change in

dimensions.

The deformation of metals is of two types:

(a) Elastic deformation:

Elastic deformation is a temporary

deformation which disappears after the load

applied is removed.

When the elastic deformation occurs, the

strain is nearly proportional to the applied

stress and the ratio between stress and strain

is known as Young’s modulus of elasticity E,

Where,strain

stress=E .

Young’s modulus gives an idea aboutelasticity of a metal.

(b) Plastic deformation:

Plastic deformation is a permanent

deformation which remains even after the

deforming load is removed.

When the stresses in the metal specimen cross

the elastic limit the specimen gets deformed

permanently.

This permanent deformation is called as

plastic deformation and causes the distortion

of the crystal structure which is irreversible.

Plastic deformation plays a vital role in metal

shaping processes such as drawing forging,

bending, extrusion, stamping, rolling etc.

Mechanisms of Plastic Deformation

There are two important mechanisms:

(a) Plastic deformation by slip and

(b) Plastic deformation by twinning

These two mechanisms occur by pure shear

stresses.

(a) Plastic deformation by slip:

If a tangential force is applied on lattice, the

top atomic planes will move with respect to

bottom atomic planes, known as displacement

of atomic planes, also known as slip

phenomenon.

Here the entire plane of atoms are moving,

hence it is called as line defect or planar

defect. Ex: Forging process in materials.

When a material is operated at low

temperature, the slip phenomenon is difficult

but when it is operated at a high temperature,

it will be easy because if a material is

operated at high temperature, the

displacement of atomic planes is easy. Hence

plastic strain can be produced. The shape

change will be easy.

(b) Plastic deformation by twinning:

If an angled force is applied on the lattice a

single lattice splits into two identical sub

lattices, known as twinning phenomenon.

F

Before deformation After deformation



With respect to the plane of force I and I’ arethe mirror images (twins). In this

phenomenon limited atomic planes will

undergo displacement in a particular

direction.

Twinning is also a slip phenomenon limited to

particular atomic plane.

Example: Super conductivity materials

(Zero electrical resistance in materials)

04(b).

Sol:

Micro constituents of iron and steel:

Austenite (-iron): It is solid solution of

ferrite and iron carbide in gamma iron which

is formed when steel contains carbon up to

1.8% at 1130oC. On cooling below 723oC it

starts transforming into pearlite and ferrite.

Austenite is non-magnetic and soft. It exists

in FCC crystal structure.

Ferrite: It is a BCC iron phase with very

limited solubility of carbon. The solubility of

carbon in ferrite is 0.008% at room

temperature. Ferrite does not harden when

cooled rapidly. It is very soft and highly

magnetic. At room temperature ferrite

contains maximum 0.0025% C only.

Cementite: Cementite is actually Fe3C,

which contains 6.67%C by weight, which is

extremely hard and brittle in nature.

Cementite increases gradually with increase

in carbon percentage. It is magnetic at below

200oC.Cementite contains orthorhombic

crystal structure.

Pearlite: It is combination of about 87% of

ferrite and 13% of Cementite. Steel with 0.8%

carbon is wholly Pearlite, less than 0.8% is

hypo eutectoid contains ferrite and Pearlite

and is soft. More than 0.8% is hyper eutectoid

steel which contains Pearlite and Cementite

which is hard and brittle. It is having a pearl

like lusture when viewed through microscope.

Bainite: It is the product of isothermal

decomposition of austenite and it cannot be

produced by continuous cooling Bainite is

aggregate of ferrite and carbide. Also it is

tougher.

Martensite: This is obtained by rapid cooling

of austenite. It is extremely hard and possess

acicular needle like structure. It is magnetic

and has carbon content up to 2%. It is

extremely hard and brittle. The decomposition

of austenite below 320oC starts the formation

of martensite.

Troosite: It differs from pearlite only in the

degree of fineness of structure and carbon

content. It is produced by transformation of

tempered martensite. Troosite is weaker than

martensite.

Sorbite: Sorbite microstructure constitute a

mixture of ferrite and finely divided cementite

F

Before deformation After deformation

I I’



produced on tempering martensite above

450oC. Pearlite, Troosite and Sorbite all are

ferrite cementite mixture having a lamellar

structure.

Ledeburite: Ledeburite is the product of

eutectic reaction. Thus Ledeburite is a

eutectic mixture; consist of alternate layers of

austenite and cementite. It contains 4.3

percent carbon and is formed at about

1130C.

04 (c) (i).

Sol:

(a) Hole Basis System:

Lower limit of hole = Basic size =200 mm

Maximum interference = difference between

the maximum material limits of hole and

shaft.

= H-shaft – L-hole

Upper limit of shaft = Lower limit of hole +

Maximum interference

= 200 + 0.12 = 200.12 mm

Hole tolerance = T = H-hole – L-hole

= H-hole – 200

Shaft tolerance = T = H-shaft – L-shaft

= 200.12 – L-shaft

Because tolerance on hole and shaft are equal

H-hole – 200 = 200.12 – L-shaft

H-hole = 200 + 200.12 – L-shaft

= 400.12 – L-shaft

Minimum interference = 0.05 = difference

between minimum material limits of hole

and shaft

= L-shaft – H-hole

= L-shaft – (400.12 – L-shaft)

= L-shaft – 400.12 + L-shaft

= 2 L-shaft – 400.12

2 L-shaft = 400.12 + 0.05 = 400.17

L-shaft = 400.17/2 = 200.085mm

H-hole = 400.12 – 200.085 = 200.035mm

(b) Shaft Basis System:

Upper limit of shaft = Basic size = 200 mm

Maximum interference = difference between

the maximum material limits of hole and

shaft.

= H-shaft – L-hole

L-hole = H-shaft – Maximum interference

= 200 – 0.12 = 199.88 mm

Hole tolerance = T = H-hole – L-hole

= H-hole – 199.88

Shaft tolerance = T = H-shaft – L-shaft

= 200 – L-shaft

Because tolerance on hole and shaft are equal

H-hole – 199.88 = 200 – L-shaft

H-hole = 200 + 199.88 – L-shaft

= 399.88 – L-shaft

Minimum interference = 0.05 = difference

between minimum material limits of hole

and shaft

= L.shaft – H.hole = L.shaft – (399.88 –L.shaft)

= L.shaft – 399.88 + L.shaft

= 2 L.shaft – 399.88

2 L-shaft = 399.88 + 0.05 = 399.93

L-shaft = 399.93/2 = 199.965mm

H-hole = 399.88 – 199.965 = 199.915mm



04 (c) (ii)

Sol: Given that ht = 1500 + 100 = 1600mm,

h2 = 1500mm

To avoid aspiration effect

A1 / A2 = [(ht – h2 )/ ht ]0.5

= [(1600 – 1500 ) / 1600]0.5

= (d1/d2)2

(d1/d2) = 1/2

05 (a).

Sol:

h0 = 300 mm,

h = 50 mm,

w0 = 600 mm

R = 500 mm

w = 5 mm,

wf = w0 + 5 = 600 + 5 = 605 mm

.32170.150050

tan °=α==R

Δh=α

% Reduction in thickness = 100h

h

0

= %67.1610030050

Coefficient of elongation0

L

L=λ f

250605

300600=

hw

hw=

L

LhwL=hwL

ff

00

0

ffff000

= 1.19

05 (b)

Sol:

Tank 1:1i

1

S1

1

q

q

Tank 2:21

o

S1

1

q

q

Then, 12i

1

1

o

i

o

S11

S11

qq

qq

qq

1SS1

qq

212

21i

o

------ (1)

(ii) ?q

h

i

2

2

2

2

2

2

2o R

hg

R

P

R

hq

1SSR

qh

212

21

2

i

2

(or) 1SSg/R

212

21

2

qi

q1

qo

h2

h1



05 (c).

Sol: 100 LPM = 100 10–3 m3/60sec

= sec/m600

1 3

dc = 100 mm = 0.1 m,

dr = 40 mm = 0.04 m,

p = 10 bar = 10 105 Pa

= 106 Pa = 106 N/m2

(a) Extension Speed = 2c

in

1.04

600

1

A

Q

00785.0

00166.0 = 0.21219 m/sec

(b) Retraction speed

=

4

0.040.1

4

π600

1

=AA

Q22

rc

in

0.001649

0.00166= = 1.010 m/sec

(c) Extension Load capacity (Newtons)

cext aP=F = 26 0.14

π10 = 7853.98 N

(d) Retraction,

rcretraction AAPF

226 0.040.14

π10=

= 6597.34 N

(e) Power (kW) :

Power = Force velocity

QP=A

QAP=

cc

263 m/N10/secm600

1=

= kW1.6=W6

104

ACE Engineering Academy … · ACE Engineering Academy Hyderabad|Delhi|Bhopal|Pune|Bhubaneswar|...

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