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ACE Engineering Academy Hyderabad|Delhi|Bhopal|Pune|Bhubaneswar| Lucknow|Patna|Bengaluru|Chennai|Vijayawada|Vizag|Tirupati|Kukatpally |Kolkata
: 2 : Mechanical Engg. _ ESE MAINS
ACE Engineering Academy Hyderabad|Delhi|Bhopal|Pune|Bhubaneswar| Lucknow|Patna|Bengaluru|Chennai|Vijayawada|Vizag|Tirupati|Kukatpally |Kolkata
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
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(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.
: 4 : Mechanical Engg. _ ESE MAINS
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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
: 5 : Conventional Test – 6
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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
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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.
: 7 : Conventional Test – 6
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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
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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
: 9 : Conventional Test – 6
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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
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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.
: 11 : Conventional Test – 6
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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
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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
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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
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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.
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(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
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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
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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’
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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
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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
1SS1
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
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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
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