1. Metal Cutting, Metal Forming & Metrology
Theory for IES, GATE & PSUs
Section‐I: Theory of Metal Cutting
Chapter-1: Basics of Metal Cutting
Chapter-2: Force & Power in Metal Cutting
Chapter-3: Tool life, Tool Wear, Economics and Machinability
Note down in the class
Note down in the class
Page-1
Section‐II: Metal Forming
Chapter-4: Cold Working, Recrystalization and Hot Working
Chapter-5: Rolling
Chapter-6: Forging
Chapter-7: Extrusion & Drawing
Chapter-8: Sheet Metal Operation
Chapter-9: Powder Metallurgy
Page-6
Page-8
Page-13
Page-16
Page-21
Page-30
Section‐III: Metrology
Chapter-10: Limit, Tolerance & Fits
Chapter-11: Measurement of Lines & Surfaces
Chapter-12: Miscellaneous of Metrology
Page-34
Page-38
Page-45
For‐2013 (IES, GATE & PSUs)
For IES, GATE, PSUs
Page 1 of 49
Bhopal -2014

2. Tool Failure
Tool Wear, Tool Life & Machinability
Tool Wear, Tool Life & M hi bili
T lW
T l Lif & Machinability
By S K Mondal
l
Tool Wear
Tool failure is two types
1. Slow‐death: The gradual or progressive wearing
g
p g
g
away of rake face (crater wear) or flank (flank wear) of
g
the cutting tool or both.
2. Sudden‐death: Failures leading to premature end
of the tool
The sudden‐death type of tool failure is difficult to
predict. Tool failure mechanisms include plastic
deformation, brittle fracture, fatigue fracture or edge
pp g
p
chipping. However it is difficult to predict which of
these processes will dominate and when tool failure
will occur.
Flank Wear: (Wear land)
Reason
Abrasion b h d particles and i l i
Ab i
by hard
i l
d inclusions i the work
in h
k
piece.
Shearing off the micro welds between tool and work
material.
material
Abrasion by fragments of built‐up‐edge ploughing
against the clearance f
i
h l
face of the tool.
f h
l
At low speed flank wear predominates.
p
p
If MRR increased flank wear increased.
Flank Wear: (Wear land)
Stages
Flank Wear
Fl k W occurs i three stages of varying wear rates
in h
f
i
Flank Wear: (Wear land)
Primary wear
The
Th region where the sharp cutting edge i quickly
i
h
h h
i
d
is
i kl
broken down and a finite wear land is established.
Secondary wear
y
The region where the wear progresses at a uniform rate.
For IES, GATE, PSUs
Page 2 of 49
Tool Wear
(a) Flank Wear
( ) Fl k W
( )
(b) Crater Wear
(c) Chipping off of the cutting edge
Flank Wear: (Wear land)
Effect
Flank
Fl k wear di
directly affect the component di
l ff
h
dimensions
i
produced.
Flank wear is usually the most common determinant of
tool life
life.
Flank Wear: (Wear land)
Tertiary wear
The
Th region where wear progresses at a gradually
i
h
d ll
increasing rate.
In the tertiary region the wear of the cutting tool has
become sensitive to increased tool temperature due to
high wear land.
Re‐grinding i recommended b f
R
i di
is
d d before they enter this
h
hi
region.
Bhopal -2014

3. Crater wear
Tool life criteria ISO
(A certain width of flank wear (VB) is the most common
(A
i id h f fl k
(VB) i h
criterion)
Uniform wear: 0.3 mm averaged over all past
Localized wear: 0.5 mm on any individual past
Localized wear: 0 5 mm on any individual past
More common in ductile materials which produce
continuous chip.
h
Crater wear Contd…..
Crater depth exhibits linear increase with time.
It increases with MRR
MRR.
Crater wear occurs on the rake f
C
h
k face.
At very hi h speed crater wear predominates
high
d
t
d i t
For crater wear temperature is main culprit and tool
defuse into the chip material & tool temperature is
maximum at some distance from the tool tip.
Wear Mechanism
1. Abrasion wear
2. Adhesion wear
3.
3 Diffusion wear
4. Chemical or oxidation wear
Why chipping off or fine cracks
developed at the cutting edge
d l
d
h
d
Tool material is too brittle
Crater wear has little or no influence on cutting forces
forces,
work piece tolerance or surface finish.
Notch Wear
Notch wear on the trailing edge is to a great extent an
oxidation wear mechanism occurring where th cutting
id ti
h i
i
h
the tti
edge leaves the machined workpiece material in the feed
Weak design of tool, such as high positive rake angle
direction.
As a result of crack that is already in the tool
But abrasion and adhesion wear in a combined effect can
contribute to the formation of one or several notches.
Excessive static or shock l di of the tool.
E
i
i
h k loading f h
l
List the important properties of cutting tool
materials and explain why each is important.
t i l
d
l i h
hi i
t t
Hardness at high temperatures ‐ this provides longer
life of the cutting tool and allows higher cutting speeds.
Toughness ‐ to provide the structural strength needed
to resist impacts and cutting forces
Wear resistance ‐ to prolong usage before replacement
doesn’t chemically react ‐ another wear factor
Formable/manufacturable ‐ can be manufactured in a
useful geometry
For IES, GATE, PSUs
Tool Life Criteria
Tool life criteria can be defined as a predetermined
numerical value of any type of tool deterioration which
can be measured.
Some of
the ways
Actual cutting time to failure.
Volume of metal removed.
Volume of metal removed
Number of parts produced.
p
p
Cutting speed for a given time
Length of work machined.
Page 3 of 49
Taylor’s Tool Life Equation
based on Flank Wear
Causes
Sliding of the tool along the machined surface
Temperature rise
VT n = C
Where, V = cutting speed (m/min)
T = Time (min)
T Time (min)
n = exponent depends on tool material
C = constant based on tool and work material and cutting
condition.
Bhopal -2014

4. Values of Exponent ‘n’
Tool Life Curve
l f
Extended or Modified Taylor’s equation
n = 0.08 to 0.2 for HSS tool
= 0.1 to 0.15 for Cast Alloys
= 0.2 to 0.4 f carbide tool
for
bid
l
[IAS 1999; IES 2006]
[IAS‐1999; IES‐2006]
= 0.5 to 0.7 for ceramic tool
5
7
[NTPC‐2003]
i.e Cutting speed has the greater effect followed by feed
g p
g
y
and depth of cut respectively.
Cutting speed used for different
tool materials
Effect of Rake angle on tool life
ChipEquivalent(q) =
Engaged cutting edge length
Plan area of cut
It is
I i used f controlling the tool temperature.
d for
lli
h
l
2. Carbide
3. Ceramic
Effect of Clearance angle on tool life
If clearance angle increased it reduces flank wear but
weaken the cutting edge so best compromise is 80 for
edge,
HSS and 50 for carbide tool.
HSS (min) 30 m/min < Cast alloy < Carbide
< Cemented carbide 150 m/min < Cermets
< Ceramics or sintered oxide (max) 600
m/min
Chip Equivalent
1. HSS
Effect of work piece on tool life
With hard micro‐constituents in the matrix gives poor
tool life.
With larger grain size tool life is better.
• The SCEA alters the length of the engaged cutting
E
i
f
t l tti
Economics of metal cutting
edge without affecting the area of cut. As a result, the
chip equivalent changed. When the SCEA is increased,
the chip equivalent is increased, without significantly
h h
l
d
h
f
l
changing th cutting f
h
i the tti forces.
• I
Increase i nose radius also i
in
di
l increases th value of th
the l
f the
chip equivalent and improve tool life
life.
For IES, GATE, PSUs
Page 4 of 49
Bhopal -2014

5. l
Formula
Vo To = C
n
Optimum tool life for minimum cost
⎛
C ⎞⎛ 1− n ⎞
To = ⎜ Tc + t ⎟ ⎜
⎟
Cm ⎠ ⎝ n ⎠
⎝
C ⎛ 1− n ⎞
= t ⎜
⎟
Cm ⎝ n ⎠
if Tc , Ct & Cm given
if Ct & Cm given
g
Optimum tool life for Maximum Productivity
p
y
(minimum production time)
⎛ 1− n ⎞
To = Tc ⎜
⎟
⎝ n ⎠
g g
Units:Tc – min (Tool changing time)
Ct – Rs./ servicing or replacement (Tooling
cost)
Cm – Rs/min (Machining cost)
V – m/min (Cutting speed)
Tooling cost (Ct) = tool regrind cost
+ tool depreciation per service/ replacement
Machining cost (Cm) labour cost + over head cost per
) = labour
min
Minimum Cost Vs Production Rate
Machinability‐Definition
Machinability can be tentatively defined as ‘ability of
M hi bili
b
i l d fi d
‘ bili
f
being machined’ and more reasonably as ‘ease of
machining’.
Such ease of machining or machining characters
h
f
h
h
h
of any tool‐work pair is to be judged by:
y
p
j g
y
Tool wear or tool life
Magnitude of the cutting forces
Surface finish
Magnitude of cutting temperature
g
g
p
Chip forms.
Vmax.production > Vmax.profit > Vmin. cost
Machinability‐‐‐‐‐‐‐‐‐‐‐‐‐Contd…….
Machinability will be high when cutting forces,
M hi bilit
ill b hi h
h
tti
f
temperature, surfaces roughness and tool wear are less,
tool life is long and chips are id ll uniform and short.
t l lif i l
d hi
ideally if
d h t
The addition of sulphur lead and tellurium to non‐
sulphur,
ferrous and steel improves machinability.
Sulphur i added t steel only if th
S l h
is dd d to t l
l
there i sufficient
is
ffi i t
manganese in it. Sulphur forms manganese sulphide
which exists as an i l t d phase and act as i t
hi h i t
isolated h
d t
internal
l
lubrication and chip breaker.
If insufficient manganese is there a low melting iron
sulphide will formed around the austenite grain
boundary. Such steel is very weak and brittle.
For IES, GATE, PSUs
Free Cutting steels
Addition of lead in low carbon re‐sulphurised steels and
also in aluminium copper and their alloys help reduce
aluminium,
their τs. The dispersed lead particles act as discontinuity
and solid lubricants and thus improve machinability by
reducing friction, cutting forces and temperature, tool
wear and BUE f
d
formation.
i
It contains less than 0.35% lead by weight .
35
y
g
A free cutting steel contains
C‐0.07%, Si
C
% Si‐0.03%, M
% Mn‐0.9%, P
% P‐0.04%, S
% S‐0.22%, Pb
% Pb‐0.15%
%
Page 5 of 49
Machinability Index
Or Machinability Rating
The machinability index KM is defined by
KM = V6 /V6 R
60
60R
Where V60 is the cutting speed for the target material
that ensures tool lif of 6 min, V60R i the same f the
h
l life f 60 i
is h
for h
reference material.
If KM > 1, the machinability of the target material is
better that this of the reference material and vice versa
material,
Bhopal -2014

6. Role of microstructure on Machinability
Coarse microstructure leads to lesser value of τs.
C
i
l d l
l f
Therefore, τs can be desirably reduced by
Proper heat treatment like annealing of steels
P
h
lik
li f
l
Controlled addition of materials like sulphur (S), lead
p
( ),
(Pb), Tellerium etc leading to free cutting of soft ductile
metals and alloys.
metals and alloys
ff
f
l
k
l ( )
Effects of tool rake angle(s) on
machinability
As Rake angle increases machinability increases.
But too much increase in rake weakens the cutting edge.
Effects of Cutting Edge angle(s) on
machinability
The
Th variation i th cutting edge angles d
i ti in the tti
d
l does not affect
t ff t
cutting force or specific energy requirement for cutting
cutting.
Increase in SCEA and reduction in ECEA improves
surface finish sizeably in continuous chip formation
hence Machinability.
Brittle materials are relatively more machinable.
Effects of clearance angle on machinability
Proper tool nose radiusing improves machinability to
some extent through
increase in tool life by increasing mechanical strength
and reducing temperature at the tool tip
d d i
h
l i
reduction of surface roughness, hmax
g
,
Inadequate clearance angle reduces tool life and surface
finish by tool – work rubbing, and again too large
clearance reduces the tool strength and tool life hence
g
machinability.
Cutting fluid
Cutting fluid
The cutting fluid acts primarily as a coolant and
secondly as a lubricant, reducing the friction effects at
dl
l bi
t
d i th f i ti
ff t t
the tool‐chip interface and the work‐blank regions.
Cast Iron: Machined dry or compressed air, Soluble oil
for high speed machining and grinding
Brass: Machined dry or straight mineral oil with or
without EPA
ih
EPA.
Aluminium: Machined dry or kerosene oil mixed with
y
mineral oil or soluble oil
Stainless steel and Heat resistant alloy: High
performance soluble oil or neat oil with high
concentration with chlorinated EP additive.
i
i h hl i
d
ddi i
For IES, GATE, PSUs
Surface Roughness
Effects of Nose Radius on machinability
hmax
f2
=
8R
8R
Ideal Surface ( Zero nose radius)
f
tan SCEA + cot ECEA
h
f
and (Ra) =
=
4 4 ( tan SCEA + cot ECEA )
Peak to valley roughness (h) =
Practical Surface ( with nose radius = R)
h=
f2
8R
and
Ra =
f2
18 3R
Change in feed (f) is more important than a change in nose radius
g
( )
p
g
(R) and depth of cut has no effect on surface roughness.
IAS 2009 Main
IAS ‐2009 Main
What are extreme pressure lubricants?
What are extreme‐pressure lubricants?
[ 3 – marks]
Where hi h pressures and rubbing action are
Wh
high
d
bbi
i
encountered, hydrodynamic lubrication cannot be
maintained; so E
i i d
Extreme P
Pressure (EP) additives must b
ddi i
be
added to the lubricant. EP lubrication is provided by a
number of chemical components such as b
b
f h i l
h
boron,
phosphorus, sulfur, chlorine, or combination of these.
The
Th compounds are activated b the hi h temperature
d
i
d by h higher
resulting from extreme pressure. As the temperature
rises, EP molecules b
i
l
l
become reactive and release
i
d
l
derivatives such as iron chloride or iron sulfide and
forms a solid protective coating.
f
lid
i
i
Page 6 of 49
Bhopal -2014

7. Four Important forming techniques are:
Rolling
Metal Forming
Sheet Metal Operation
Sh t M t l O
ti
Powder Metallurgy
P d M ll
Forging
g g
Extrusion
Drawing
D
i
By S K Mondal
Terminology
Ingot
Plastic Deformation
Mill product
Deformation beyond elastic limits.
Plate is the product with thickness > 5 mm
Sheet is the product with thickness < 5 mm and width > 600
Due to slip, grain fragmentation, movement of atoms
p, g
g
,
and lattice distortion.
mm
Strip is the product with a thickness < 5 mm and width <
600 mm
Rx depends on the amount of cold work a material has
already received. The higher the cold work, the lower
would b the Rx.
ld be h
Terminology
Semi‐finished product
Ingot: is the first solid form of steel.
I
i h fi
lid f
f
l
Bloom: is the product of first breakdown of ingot has square
p
g
q
cross section 6 x 6 in. or larger
Billet: is hot rolled from a bloom and is square 1 5 in on a
square, 1.5 in.
side or larger.
Slab: is the hot ll d ingot or bl
Sl b i th h t rolled i
t
bloom rectangular cross
t
l
section 10 in. or more wide and 1.5 in. or more thick.
Billet
slab
Recrystallisation Temperature (Rx)
“The minimum temperature at which the completed
“Th
i i
hi h h
l d
recrystallisation of a cold worked metal occurs within a
specified period of approximately one hour”.
Rx decreases strength and increases ductility
ductility.
If working above Rx, hot‐working process whereas
working b l
ki below are cold‐working process.
ld
ki
It involves replacement of cold‐worked structure by a
t vo ves ep ace e t o co d o ed st uctu e
new set of strain‐free, approximately equi‐axed grains to
replace all the deformed crystals
crystals.
Contd.
Contd
Grain growth
h
Grain growth follows complete crystallization if the materials
left at elevated temperatures.
p
Bloom
Strain Hardening
Strain Hardening
When metal is formed in cold state there is no
state,
Grain growth does not need to be preceded by recovery and
recrystallization; it may occur in all polycrystalline materials.
ll
ll l
ll
l
Rx = 0 4 x Melting temp (Kelvin)
0.4
temp. (Kelvin).
Rx of lead and Tin is below room temp.
p
recrystalization of grains and thus recovery from
y
g
y
In contrary to recovery and recrystallization, driving force
for this process is reduction in grain boundary energy.
Rx varies between 1/3 to ½ melting paint
paint.
place.
grain distortion or fragmentation does not take
In practical applications, grain growth is not desirable.
As grain deformation proceeds, greater resistance
to this ti
t thi action results i i
lt in increased h d
d hardness and
d
Rx of Iron is 450oC and for steels around 1000°C
Incorporation of impurity atoms and insoluble second phase
particles are effective in retarding grain growth.
Finer is the initial grain size; lower will be the Rx
Grain growth is very strongly dependent on temperature.
Rx of Cadmium and Zinc is room temp.
For IES, GATE, PSUs
Contd.
Page 7 of 49
strength i.e. strain hardening.
Bhopal -2014

8. Strain Hardening
St i H d i
Malleability
ll b l
Strain hardening (cold Working)
Malleability is the property of a material whereby it can
σ o = Kε n
be h
b shaped when cold b h
d h
ld by hammering or rolling.
ll
Strain rate effect (hot Working)
(
g)
σ o = Cε
Where
ε=
A malleable material i capable of undergoing plastic
ll bl
i l is
bl f
d
i
l i
m
deformation without fracture
fracture.
A malleable material should be plastic but it is not
1 dh v
Platen Velocity
= =
h dt h Instantaneous height
g
Cold Working
Working below recrystalization temp.
W ki b l
li i
essential to be so strong.
g
Lead, soft steel, wrought iron, copper and aluminium are
some materials in order of diminishing malleability.
Advantages of Cold Working
d
f ld
k
Disadvantages of Cold Working
d
f ld
k
Equipment of higher forces and power required
1. Better accuracy, closer tolerances
1.
2. Better surface finish
Hot Working
2. S f
Surfaces of starting work piece must be free of scale and
f t ti
k i
t b f f l d
3. Strain hardening increases strength and hardness
4. Grain flow during deformation can cause desirable
directional properties in product
5.
5 No heating of work required (less total energy)
dirt
3. Ductility and strain hardening limit the amount of forming
that can be done
4. In some operations, metal must be annealed to allow
further deformation
5
5. Some metals are simply not ductile enough to be cold
py
g
Working above recrystalization temp.
Working above recrystalization temp
worked.
Advantages of Hot Working
Dis‐advantages of Hot Working
1. The porosity of the metal is largely eliminated.
2.
2 The grain structure of the metal is refined
refined.
3. The impurities like slag are squeezed into fibers and
distributed h
di ib d throughout the metal.
h
h
l
4
4. The mechanical properties such as toughness,
p p
g
,
percentage elongation, percentage reduction in area, and
resistance to shock and vibration are improved due to
the refinement of grains.
1. It requires expensive tools.
2.
2 It produces poor surface finish due to the rapid
finish,
oxidation and scale formation on the metal surface.
3. D
Due to the poor surface fi i h close tolerance
h
f
finish, l
l
cannot be maintained.
For IES, GATE, PSUs
Page 8 of 49
Micro‐Structural Changes in a Hot
Mi
St t l Ch
i H t
Working Process (Rolling)
Working Process (Rolling)
Bhopal -2014

9. Annealing
g
•Annealing relieves the stresses from cold working – three
stages: recovery, recrystallization and grain growth.
recovery
growth
•During recovery, physical properties of the cold‐worked
material are restored without any observable change i
i l
d ih
b
bl h
in
microstructure.
Warm Forming
Isothermal Forming
h
l
Deformation produced at temperatures intermediate to
During hot forming, cooler surfaces surround a hotter
hot d ld forming is k
h and cold f
known as warm f
forming.
interior,
interior and the variations in strength can result in non
non‐
Compared to cold f
C
d
ld forming, i reduces l d i
i
it d
loads, increase
material ductility
ductility.
uniform deformation and cracking of the surface.
For temp.‐sensitive materials deformation is performed
under isothermal conditions.
Compared to hot forming it produce less scaling and
forming,
The dies or tooling must b h
Th di
li
be heated to the workpiece
d
h
k i
decarburization, better dimensional precision and
p
temperature, sacrificing die life for product quality.
p
,
g
p
q
y
smoother surfaces.
Close tolerances, low residual stresses and uniform metal
flow.
Rolling
Definition: The process of plastically deforming metal
by
b passing it b
between rolls.
ll
g
Rolling
Most id l
M widely used, hi h production and close tolerance.
d high
d i
d l
l
Friction b t
F i ti
between th rolls and th metal surface
the
ll
d the
t l
f
produces high compressive stress
stress.
Hot working
Hot‐working (unless mentioned cold rolling.
By S K Mondal
Metal will undergo bi‐axial compression.
g
p
Hot Rolling
Done above the recrystallization temp.
Results fine grained structure.
Surface quality and fi l di
S f
lit
d final dimensions are l accurate.
i
less
t
Breakdown of ingots into blooms and billets is done by
hot‐rolling. This is followed by further hot‐rolling into
g
y
g
plate, sheet, rod, bar, pipe, rail.
Hot rolling is terminated when the temp. falls to about
For IES, GATE, PSUs
(50 to 100°C) above the recrystallization temp.
Page 9 of 49
Bhopal -2014

10. Cold Rolling
Ring Rolling
Done below the recrystallization temp..
Ring rolls are used for tube rolling, ring rolling.
Products are sheet, strip, foil etc. with good surface
As the rolls squeeze and rotate, the wall thickness is
finish
fi i h and i
d increased mechanical strength with close
d
h i l
h ih l
reduced and the di
d d d h diameter of the ring i
f h i increases.
product dimensions
dimensions.
Shaped rolls can b used t produce a wide variety of
Sh
d ll
be
d to
d
id
i t f
Performed on four‐high or cluster‐type rolling mills
four high
cluster type
mills.
cross section profiles.
cross‐section profiles
(
(Due to high force and power)
g
p
)
Ring rolls are made of spheroidized graphite bainitic and
pearlitic matrix or alloy cast steel base.
Sheet rolling
In sheet rolling we are only attempting to reduce the
cross section thickness of a material.
h k
f
l
Roll Forming
Roll Bending
A continuous form of three‐point bending is roll
bending, where plates, sheets, and rolled shapes can
be bent to a desired curvature on forming rolls.
Upper roll being adjustable to control the degree of
curvature.
t
For IES, GATE, PSUs
Page 10 of 49
Bhopal -2014

11. Shape rolling
Pack rolling
Thread rolling
Pack rolling involves hot rolling multiple sheets of
Used to produce threads in substantial quantities.
material at once, such as aluminium f l
l
h
l
foil.
This is a cold‐forming process in which the threads are
A thin surface oxide fil prevents their welding.
hi
f
id film
h i
ldi
formed b rolling a thread bl k b
f
d by lli
h d blank between h d
hardened di
d dies
that cause the metal to flow radially into the desired
shape.
p
No metal is removed, greater strength, smoother, harder,
g
g
and more wear‐resistant surface than cut threads.
Thread rolling contd….
Manufacture of gears by rolling
Major diameter is always greater than the diameter of the
The straight and helical teeth of disc or rod type external
blank
bl k (
steel gears of small to medium d
l
f
ll
d
diameter and module are
d
d l
Blank diameter i li l l
Bl k di
is little larger than the pitch di
h
h i h diameter of
f
generated by cold rolling
rolling.
the thread
thread.
High accuracy and surface integrity
integrity.
Restricted to ductile materials
materials.
Employed for high productivity and high quality (costly
quality.
machine)
)
Larger size gears are formed by hot rolling and then
finished by machining.
Roll piercing
ll
Fig. Production of teeth of spur gears by rolling
For IES, GATE, PSUs
Page 11 of 49
It is a variation of rolling called roll piercing.
,
The billet or round stock is rolled between two rolls,
both of them rotating in the same direction with their
axes at an angle of 4.5 to 6.5 degree.
These rolls have a central cylindrical portion with the
sides tapering slightly There are two small side rolls
slightly.
rolls,
which help in guiding the metal.
Because of the angle at which the roll meets the metal,
it gets in addition to a rotary motion, an additional
axial advance, which brings the metal into the rolls.
This cross‐rolling action makes the metal friable at the
g
centre which is then easily pierced and given a
cylindrical shape by the central‐piercing mandrel.
central piercing
Bhopal -2014

12. Planetary mill
Consist of a pair of heavy backing rolls surrounded by a large
number of planetary rolls.
Each planetary roll gives an almost constant reduction to the
slab as it sweeps out a circular path between the backing rolls
and the slab.
As each pair of planetary rolls ceases to have contact with the
work piece, another pair of rolls makes contact and repeat
that reduction.
h
d i
The overall reduction is the summation of a series of small
reductions b each pair of rolls. Th f
d ti
by
h i f ll Therefore, th planetary mill
the l
t
ill
can reduce a slab directly to strip in one pass through the
mill.
mill
The operation requires feed rolls to introduce the slab into
the mill, and a pair of planishing rolls on the exit to improve
the surface finish.
Camber
Defects in Rolling
Lubrication for Rolling
Hot rolling of ferrous metals is done without a lubricant.
Hot rolling of non‐ferrous metals a wide variety of
Defects
f
Surface
Defects
compounded oils, emulsions and f
d d il
l i
d fatty acids are used.
id
d
Cold
C ld rolling l b i
lli
lubricants are water‐soluble oils, l
t
t
l bl
il low‐
Wavy edges
viscosity lubricants such as mineral oils emulsions
lubricants,
oils, emulsions,
Alligatoring
p
paraffin and fatty acids.
y
What is
h
Cause
Scale,
rust,
scratches,
pits,
cracks
Strip is thinner
along its edges
than at its centre.
Edge breaks
Inclusions
and
impurities
in
the
materials
Due to roll bending
edges elongates more
and buckle.
Non‐uniform
deformation
Camber can be used to correct the roll deflection (at only
one value of the roll force).
Geometry of Rolling Process
Draft
Total reduction or “draft” taken in rolling.
T l d i “d f ” k i lli
Δh=h - h =2(R- Rcos α) =D(1- cos α)
0 f
Usually, the reduction in blooming mills is about 100
y,
g
mm and in slabbing mills, about 50 to 60 mm.
Maximum Draft Possible
For IES, GATE, PSUs
( ΔhPage 12 of = μ 2 R
)max 49
Torque and Power
The power is spent principally in four ways
Th
i
i i ll i f
)
gy
1) The energy needed to deform the metal.
2) The energy needed to overcome the frictional force.
3) Th power l
) The
lost i the pinions and power‐transmission
in h i i
d
i i
system.
4) Electrical losses in the various motors and generators.
Remarks: Losses in the windup reel and uncoiler must
p
also be considered.
Bhopal -2014

13. Torque and Power
Assumptions in Rolling
1. Rolls are straight, rigid cylinders.
R ll
i h i id li d
2. Strip is wide compared with its thickness, so that no
p
p
,
[For IES Conventional Only]
Will
be
b
discussed
in class
Stress Equilibrium of an Element in Rolling
Considering the thickness of the element perpendicular to
the plane of paper to be unity We get equilibrium
unity,
equation in - σ x h + (σ x +dσ x ) (h + dh) - 2pR dθ sin θ
x‐direction as,
+ 2 τ x R dθ cos θ = 0
I=
2Rθdθ
=
2
f + Rθ
∫h
∫
Now h / R =
or
2Rθdθ
=
h
2θdθ
∫h/R
⎛h⎞
= ln ⎜ ⎟
⎝R⎠
hf
+ θ2
R
d ⎛h⎞
= 2θ
θ
dθ ⎜ R ⎟
⎝ ⎠
2Rμ
R
II = ∫
dθ
h f + Rθ2
2μ
dθ
=∫
h f / R + θ2
= 2μ
⎛ R
⎞
R
.tan −1 ⎜
.θ ⎟
⎜ h
⎟
hf
f
⎝
⎠
For IES, GATE, PSUs
For sliding friction, τ x = μp Simplifying and neglecting
second order terms, sin θ ≅ θ and cos θ = 1 we get
d d t
i
d
1,
t
d (σ x h )
= 2 pR (θ ∓ μ )
dθ
2
p −σ x =
σ 0 = σ 0'
3
d
'
⎡ h ( p − σ 0 ) ⎤ = 2 pR (θ ∓ μ )
⎦
dθ ⎣
⎞⎤
d ⎡ ' ⎛ p
⎢σ 0 h ⎜ ' − 1 ⎟ ⎥ = 2 pR (θ ∓ μ )
dθ ⎣
⎝σ0
⎠⎦
∴
⎛h⎞
ln p / σ '0 = ln ⎜ ⎟ ∓ 2μ
⎝R⎠
(
)
R
.tan −1
hf
R
.tan −1
hf
'
d ( p /σ0 )
( p /σ )
'
0
⎛ R ⎞
.θ ⎟ + ln C
⎜
⎜ h
⎟
f
⎝
⎠
⎛ R ⎞
.θ ⎟
⎜
⎜
⎟
⎝ hf ⎠
Now at entry ,θ = α
Hence H = H0 with θ replaced by ∝ in above equation
At exit θ = 0
Therefor p = σ '0
Page 13 of 49
'
thus σ 0 h nearly a constant and itsderivative zero.
h = h f + 2 R (1 − cos θ ) ≈ h f + Rθ 2
⎛h⎞
p = C σ '0 ⎜ ⎟ e∓ μH
⎝R⎠
where H = 2
'
Due to cold rolling, σ 0 increases as h decreases,
d
( p / σ 0' ) 2R
dθ
=
(θ ∓ μ )
'
p /σ0
h
⎞ d
d ⎛ p ⎞ ⎛ p
σ 0' h
(σ 0' h ) = 2 pR (θ ∓ μ )
⎜ ' ⎟ + ⎜ ' − 1⎟
dθ ⎝ σ 0 ⎠ ⎝ σ 0
⎠ dθ
∴
widening of strip occurs (plane strain conditions).
3.
3 The arc of contact is circular with a radius greater than
the radius of the roll.
4. The material is rigid perfectly plastic (constant yield
st e gt ).
strength).
5. The co‐efficient of friction is constant over the tool‐
work i t f
k interface.
=
2R
(θ ∓ μ ) dθ
h f + Rθ 2
Integrating both side
2 Rθ dθ
'
ln ( p / σ 0 ) = ∫
∓
h f + Rθ 2
∫h
2 Rμ
dθ = I ∓ II ( say )
2
f + Rθ
⎛h ⎞
In the entry zone, p = C.σ '0 ⎜ o ⎟ e− μHo
y
,
⎝R⎠
R μHo
and C =
.e
ho
p = σ '0
h
μ H −H
. e ( 0 )
h0
In the it
I th exit zone
⎛ h ⎞
p = σ '0 ⎜ ⎟ .eμH
⎝ hf ⎠
At the neutral po int above equations
will give same results
Bhopal -2014

14. hn
h
μ H −H
. e ( 0 n ) = n . eμ Hn
h0
hf
or
p = ( σ′ − σ b )
o
ho
μ H − 2H
= e ( 0 n)
hf
or Hn =
⎛ h0 ⎞ ⎤
1⎡
1
⎢H0 − ln ⎜ ⎟ ⎥
2⎢
μ
⎝ hf ⎠⎥
⎣
⎦
⎛ R ⎞
.θ ⎟
⎜
⎜ h
⎟
f
⎝
⎠
⎛ h f Hn ⎞
hf
∴ θn =
.tan ⎜
.
⎜ R 2 ⎟
⎟
R
⎝
⎠
and h n = h f + 2R (1 − cos θn )
From H = 2
If back tension σ b is there at Entry
Entry,
R
.tan −1
hf
h
μ H −H
. e ( 0 )
h0
Forging
If front tension σ f is there at Exit,
p = ( σ′ − σ f )
o
h
. eμ H
hf
By S K Mondal
y
Forging
Draft
f
Because of the manipulative ability of the forging
B
f h
i l i
bili
f h f i
process, it is possible to closely control the grain flow in
the specific direction, such that the best mechanical
p p
properties can be obtained based on the specific
p
application.
The draft provided on the sides for withdrawal of the
forging.
Adequate draft should be provided‐at least 3o for
provided at
aluminum and 5 to 7o for steel
steel.
Internal surfaces require more draft than external
surfaces.
Flash
l h
The excess metal added to the stock to ensure complete
Th
l dd d
h
k
l
filling of the die cavity in the finishing impression is
called Flash.
For IES, GATE, PSUs
Flash
l h
Contd…
A flash acts as a cushion for impact blows from the
fl h
hi
f i
bl
f
h
finishing impression and also helps to restrict the
outward flow of metal, thus helping in filling of thin ribs
and bosses in the upper die.
pp
The amount of flash depends on the forging size and
may ar
ma vary from 10 to 50 per cent
0
cent.
The forging load can be decreased by increasing the
flash thickness.
Page 14 of 49
Gutter
In addition to the flash, provision should be made in the
I ddi i
h fl h
i i
h ld b
d i h
die for additional space so that any excess metal can flow
and help in the complete closing of the die. This is called
g
gutter.
Bhopal -2014

15. Gutter
Contd….
Without a gutter, a flash may become excessively thick,
not allowing the d to close completely.
ll
h dies
l
l l
Gutter d h and width should b sufficient to
G
depth
d
id h h ld be
ffi i
accommodate the extra material
extra, material.
Fullering or swaging Contd…
ll
A forging method for
f i
h d f
reducing the diameter of a
bar and in the process
making it longer is termed
g
g
as Fullering.
Operations involved in forging
l d f
Steps involved in hammer forging
S
i
l d i h
f i
Fullering or swaging
g
g g
Edging or rolling
Bending
B di
Drawing or cogging
g
gg g
Flattening
Blocking
l k
Finishing operation
Trimming or cut off
Edging or rolling
d
ll
Fullering or swaging
ll
It is the operation of reducing the stock between the two
I i h
i
f d i
h
kb
h
ends of the stock at a central place, so as to increase its
length.
Edging or rolling
d
ll
Contd….
Gathers the material as required in the final forging.
The pre‐form shape also helps in proper location of stock
in h blocking impressions.
i the bl ki i
i
The
Th area at any cross section should b same as th t of
t
ti
h ld be
that f
the corresponding section in the component and the
flash allowance.
Bending
d
Bending operation makes the longitudinal axis of the
stock in two or more places. This operation is d
k
l
h
done after
f
Blocking
l k
Imparts to the forging it’s general but not exact or final
I
h f i i’
lb
fi l
shape. This operation is done just prior to finishing
operation.
Flattening
l
This operation is used to flatten the stock so that it fits
Thi
i i
d
fl
h
k
h i fi
properly into the finishing impression of a closed die.
the stock has been edged or fullered and edged so that
the stock is brought into a proper relation with the shape
of the finishing impression.
For IES, GATE, PSUs
Page 15 of 49
Bhopal -2014

16. Finishing
h
Drop Forging
The dimensions of the finishing impression are same as
The drop forging die consists of two halves. The lower
that of the f l f
h
f h final forging d
desired with the necessary
d
h h
half f h die fixed
h lf of the d is f d to the anvil of the machine, while
h
l f h
h
hl
allowances and tolerances
tolerances.
the upper half is fixed to the ram The heated stock is
ram.
A gutter should be provided in the finishing impression
impression.
kept in the lower die while the ram delivers four to five
Cut off
Cut‐off
blows on the metal, in quick succession so that the metal
A pair of blades used to cut away a forging from the bar
after the finishing blow.
spreads and completely fills the die cavity. When the two
die halves close, the complete cavity is formed.
Drop forging is used to produce small components.
Press Forging
Advantages of Press Forging over Drop Forging
Force is a continuous squeezing type applied by the
Press forging is faster than drop forging
hydraulic
h d l presses.
Alignment of the two die halves can be more easily
Die Materials Should have
l h ld h
Good hardness, toughness and ductility at low and
Good hardness toughness and ductility at low and
elevated temperatures
p
Adequate fatigue resistance
Sufficient hardenability
Low thermal conductivity
Amenability to weld repair
A
bili ld
i
Good machinability
Material: Cr‐Mo‐V‐alloyed steel and Cr‐Ni‐Mo‐alloyed
y
y
steel.
Machine Forging
g g
p
g g
Unlike the drop or p
press forging where the material is
drawn out, in machine forging, the material is only upset
to get the desired shape.
Upset Forging
i
maintained than with h
i i d h
i h hammering.
i
Structural
St t l quality of th product i superior t d
lit
f the
d t is
i to drop
Increasing the diameter of a material by compressing its
forging.
forging
length.
l
th
With ejectors in the top and bottom dies, it is possible to
Employs split dies that contain multiple positions or
handle reduced die drafts.
cavities.
Roll Forging
ll
When the rolls are in the open position, the heated stock
Roll Forging Contd….
ll
A rapid process.
id
Forging Defects
f
Unfilled Sections: Die cavity is not
is advanced up to a stop. As the rolls rotate, they grip and
d
d
h
ll
h
d
completely f ll d d
l l filled, due to improper
roll down the stock The stock is transferred to a second
stock.
design of die
set of grooves. The rolls turn again and so on until the
Cold Shut or fold: A small crack at
piece is finished.
the corners of the forging. Cause:
g g
improper design of the die
For IES, GATE, PSUs
Page 16 of 49
Bhopal -2014

17. Forging Defects
f
Contd….
Scale Pits: Irregular depressions on the surface due to
S l Pi
I
l d
i
h
f
d
improper cleaning of the stock.
Die Shift: Due to Misalignment of the two die halves or
making the two halves of the forging to be of improper
shape.
Flakes: Internal ruptures caused b the improper
l k
l
d by h
cooling.
Improper Grain Flow: This is caused by the improper
design of the die which makes the flow of metal not
die,
flowing the final intended directions.
Forging Defects
f
Lubrication for Forging
b
f
Contd….
Forging Laps: These are folds of metal squeezed
Lubricants influence: friction, wear, deforming forces
together d
h during f
forging. They h
h have irregular contours
l
and fl
d flow of material in d
f
l
die‐cavities, non‐sticking,
k
and occur at right angles to the direction of metal flow
flow.
thermal barrier
barrier.
Hot tears and thermal cracking: These are surface
For hot forging: graphite MoS2 and sometimes molten
graphite,
cracks occurring due to non‐uniform cooling from the
g
g
g
glass.
forging stage or during heat treatment.
For cold forging: mineral oil and soaps.
g g
p
In hot forging, the lubricant is applied to the dies, but in
cold forging, it is applied to the workpiece.
Assumption
Extrusion & Drawing
Forging force is maximum at the end of the forging.
forging
Coefficient of friction is constant between workpiece and
dies (platens).
IES Conventional Only
Details will be discussed in the Class
Extrusion
The extrusion process is like squeezing toothpaste out of
a tube.
For IES, GATE, PSUs
Thickness of the workpiece i small compared with other
Thi k
f h
k i
is
ll
d ih h
dimensions, and the variation of stress field along y‐
,
g y
direction is negligible.
Length is much more than width, problem is plain strain
type.
type
The entire workpiece is in the plastic state during the
p
p
g
process.
Metal is compressed and forced to flow through a
suitably shaped die to form a product with reduced but
constant cross section.
Metal will undergo tri‐axial compression.
Hot extrusion is commonly employed
employed.
Lead, copper, aluminum, magnesium, and alloys of these
metals are commonly extruded.
Steels,
Steels stainless steels and nickel based alloys are
steels,
nickel‐based
difficult to extrude. (high yield strengths, welding with
wall). Use phosphate‐based and molten glass
lubricants .
Page 17 of 49
By S K Mondal
Extrusion Ratio
Ratio of the cross‐sectional area of the billet to the cross‐
sectional area of the product.
l
f h
d
about 40: 1 f h extrusion of steel
b
for hot
i
f
l
400: 1 f aluminium
for l i i
Bhopal -2014

18. Advantages of Extrusion
d
f
Any cross‐sectional shape can be extruded from the
nonferrous metals.
f
t l
Limitation of Extrusion
Limitation of Extrusion
Cross section must be uniform for the entire length of
the product.
p
Many shapes (than rolling)
No draft
od a t
Huge reduction in cross section.
Conversion from one product to another requires only a
single die change
Good dimensional precision.
Hot Extrusion Process
The temperature range for hot extrusion of aluminum is
430‐480°C
Used
U d to produce curtain rods made of aluminum.
d
i
d
d f l i
Application
A li ti
Working of poorly plastic and non ferrous metals and
alloys.
Manufacture of sections and pipes of complex
co gu a o .
configuration.
Medium and small batch production.
Manufacture of parts of h h d
f
f
f high dimensional accuracy.
l
Direct Extrusion
A solid ram drives the entire billet to and through a
lid
di
h
i
bill
d h
h
stationary die and must provide additional power to
overcome the f
h frictional resistance b
l
between the surface of the
h
f
f h
moving billet and the confining chamber.
Indirect Extrusion
Indirect Extrusion
A hollow ram drives the die back through a stationary,
confined billet.
billet
Design f die is
D i of di i a problem.
bl
Either direct or indirect method used
used.
Since no relative motion, friction between the billet and the
chamber i eliminated.
h b is li i t d
Required force is lower (25 to 30% less)
Low process waste
Cold Extrusion
ld
Backward cold extrusion
k
d ld
Used with low‐strength metals such as lead, tin, zinc,
The metal is extruded through the gap between the
and aluminum to produce collapsible tubes f
d l
d
ll
bl
b
for
punch and d opposite to the punch movement.
h d die
h
h
toothpaste, medications,
toothpaste medications and other creams; small "cans"
cans
For f
F softer materials such as aluminium and i alloys.
i l
h
l i i
d its ll
for shielding electronic components and larger cans for
Used for
U d f making collapsible t b
ki
ll ibl tubes, cans f li id and
for liquids d
food and beverages.
Impact Extrusion
similar articles
articles.
Now‐a‐days also been used for forming mild steel parts.
For IES, GATE, PSUs
Page 18 of 49
The extruded parts are stripped by the use of a stripper
plate, because they tend to stick to the punch.
Bhopal -2014

19. Hooker Method
k
h d
Hooker Method
k
h d
The ram/punch has a shoulder and acts as a mandrel.
Th
/
hh
h ld
d t
d l
A flat blank of specified diameter and thickness is placed in a
suitable di and i f
i bl die d is forced through the opening of the di with
d h
h h
i
f h die i h
the punch
when the punch starts d
h
h
h
downward movement. P
d
Pressure i
is
exerted by the shoulder of the punch, the metal being forced
to flow th
t fl
through th restricted annular space b t
h the
ti t d
l
between th
the
punch and the opening in the bottom of the die.
In l
I place of a fl solid bl k a h ll slug can also b used.
f flat lid blank, hollow l
l be
d
If the tube sticks to the punch on its upward stroke, a
stripper will strip it f
ll
from the punch.
h
h
Small copper tubes and cartridge cases are extruded by this
method.
Hydrostatic Extrusion Contd….
d
Hydrostatic Extrusion Contd….
d
Temperature is limited since the fluid acts as a heat sink
T
i li i d i
h fl id
h
i k
and the common fluids (light hydrocarbons and oils)
burn or decomposes at moderately low temperatures.
The metal deformation is performed in a high‐
high
compression environment. Crack formation is
suppressed,
suppressed leading to a phenomenon kno n as
known
pressure‐induced ductility.
Relatively brittle materials like cast iron, stainless steel,
molybdenum, tungsten and various inter‐metallic
inter metallic
compounds can be plastically deformed without
fracture,
fracture and materials with limited ductility become
highly plastic.
Lubrication for Extrusion
b
f
For hot extrusion glass is an excellent lubricant with
F h
i
l
i
ll
l bi
ih
steels, stainless steels and high temperature metals and
alloys.
For cold extrusion lubrication is critical especially with
extrusion,
critical,
steels, because of the possibility of sticking (seizure)
between
bet een the workpiece and the tooling if the lubrication
orkpiece
breaks down. Most effective lubricant is a phosphate
conversion coating on the workpiece.
h
k
Wire Drawing
Hydrostatic Extrusion
d
Another type of cold extrusion process.
High‐pressure fluid applies the force to the workpiece
through a di
h
h die.
It i f
is forward extrusion, b t th fl id pressure
d
t i
but the fluid
surrounding the billet prevents upsetting
upsetting.
Billet chamber
Billet‐chamber
friction
is
eliminated,
and the die.
Application
Extrusion of nuclear reactor fuel rod
E t i f
l
t f l d
Cladding of metals
Making wires for less ductile materials
Wire Drawing Contd….
A cold working process to obtain wires from rods of
bigger d
b
diameters through a d
h
h die.
Same process as b d
S
bar drawing except that i i
i
h it involves
l
smaller‐diameter material
material.
At the start of wire drawing the end of the rod or wire to
drawing,
enters the die orifice and sticks out behind the die.
Page 19 of 49
the
pressurized fluid acts as a lubricant between the billet
be drawn is pointed (by swaging etc.) so that it freely
p
( y
g g
)
y
For IES, GATE, PSUs
and
Bhopal -2014

20. Wire Drawing Contd….
Wire getting continuously wound on the reel.
Cleaning and Lubrication in wire Drawing
Wire Drawing Die
Cleaning is done to remove scale and rust by acid pickling.
Cleaning is done to remove scale and rust by acid pickling
Lubrication boxes precede the individual dies to help reduce
For fine wire, the material may be passed through a
friction drag and prevent wear of the dies.
number of di
b
f dies, receiving successive reductions i
i i
i
d i
in
Sulling: The wire is coated with a thin coat of ferrous
diameter,
diameter before being coiled
coiled.
hydroxide which when combined with lime acts as filler for
The wire is subjected to tension only But when it is in
only.
contact with dies then a combination of tensile,
the lubricant.
Phosphating: A thin film of Mn, Fe or Zn phosphate is
applied on the wire
wire.
compressive and shear stresses will be there in that
Electrolytic coating: For very thin wires, electrolytic coating
y
g
y
,
y
g
portion only.
of copper is used to reduce friction.
Rod and Tube Drawing
d d b
Die materials: tool steels or tungsten carbides or
polycrystalline diamond (for fine wire)
Rod and Tube Drawing Contd…
d d b
Rod drawing is similar to wire drawing except for the fact
R dd
i i i il
i d
i
f h f
that the dies are bigger because of the rod size being
larger than the wire.
The tubes are also first pointed and then entered
through the die where the point is gripped in a similar
way as the bar dra ing and pulled through in the form
a
drawing
desired along a straight line.
When the final size is obtained, the tube may be
annealed and straightened.
The practice of drawing tubes without the help of an
internal mandrel i called t b sinking.
i t
l
d l is ll d tube i ki
Swaging or kneading Contd…
k
d
Moving Mandrel
Extrusion Load
Approximate method (Uniform deformation, no friction)
A
i
h d (U if
d f
i f i i )
“work – formula”
The hammering of a rod or tube to reduce its diameter
where the d itself acts as the h
h
h die
lf
h hammer.
⎛A
P = Aoσ o ln ⎜ o
⎜A
⎝ f
Repeated bl
R
d blows are d li
delivered f
d from various angles,
i
l
causing the metal to flow inward and assume the shape
⎞
⎟
⎟
⎠
For real conditions
F l
di i
⎛A
P = KAo ln ⎜ o
⎜A
⎝ f
of the die.
It is cold working. The term swaging is also applied to
g
g g
pp
processes where material is forced into a confining die to
reduce its diameter.
For IES, GATE, PSUs
Fixed Plug Drawing
Floating plug Drawing
Swaging or kneading
k
d
Tube Sinking
⎞
⎟
⎟
⎠
K = extrusion constant.
Page 20 of 49
Bhopal -2014

21. Wire Drawing
Wire Drawing
Force required in Wire or Tube drawing
Approximate method (Uniform deformation, no friction)
Approximate method (Uniform deformation no friction)
“work – formula”
⎛A
P = Af σ o ln ⎜ o
⎜A
⎝ f
σd =
σ o (1 + B ) ⎡
⎛r ⎞ ⎤ ⎛r ⎞
⎢1 − ⎜ f ⎟ ⎥ + ⎜ f ⎟ .σ b
⎢ ⎝ ro ⎠ ⎥ ⎝ ro ⎠
⎣
⎦
B
2B
2B
Maximum Reduction per pass
With back stress, σ b
σo =
⎞
⎟
⎟
⎠
σ o (1 + B ) ⎡
2B
2B
⎛ rf ⎞ ⎤ ⎛ rf ⎞
⎢1 − ⎜ ⎟ ⎥ + ⎜ ⎟ .σ b
⎢ ⎝ ro ⎠ ⎥ ⎝ ro ⎠
⎣
⎦
B
Without back stress, σ b
σo =
f
Wire Drawing Analysis (Home Work)
Wire Drawing Analysis (Home Work)
The equilibrium equation in x-direction will be
(σ x + dσ x ) π ( r + dr )
2
dx ⎞
⎛
− σ xπ r 2 + τ x cos α ⎜ 2π r
⎟
cos α ⎠
⎝
dx ⎞
⎛
+ Px sin α ⎜ 2π r
⎟=0
cos α ⎠
⎝
or Bσ x − (1 + B ) σ o = ( rC )
2B
B.C at r = ro ,σ x = σ b
σ o (1 + B ) ⎡
Dividing by r 2 dr and taking dx/dr = cotα we get
dσ x 2
2τ
+ (σ x + Px ) + x cotα = 0
dr r
r
Vertical component of Px ≅ Px due to small half di
i l
f
d
ll h lf die
angles and that of τ x can be neglected
neglected.
Thefore,
Thefore two principal stresses are σ x and − Px
Both Tresca's and Von-Mises criteria will give
g
σ x + Px = σ o
and τ x = μ Px = μ (σ o − σ x )
Extrusion Analysis (Home Work)
Extrusion Analysis (Home Work)
∴ Bσ x − (1 + B ) σ o = ( rC )
⎤ ⎛ r ⎞2 B
⎥ + ⎜ ⎟ .σ b
or σ x =
B
⎥ r
⎦ ⎝ o⎠
2B
2B
σ o (1 + B ) ⎡ ⎛ rf ⎞ ⎤ ⎛ rf ⎞
⎢1 − ⎜ ⎟ ⎥ + ⎜ ⎟ .σ b
∴ Drawing stress (σ d ) =
B
⎢ ⎝ ro ⎠ ⎥ ⎝ ro ⎠
⎣
⎦
⎛r⎞
⎢1 − ⎜ ⎟
r
⎢
⎣ ⎝ o⎠
dσ x 2σ o 2 μ (σ o − σ x )
+
+
cotα = 0
dr
r
r
Let μ cotα = B
dσ x 2
= ⎡ Bσ x − (1 + B ) σ o ⎤
⎦
dr
r⎣
dσ x
2
or
= dr
⎡ Bσ x − (1 + B ) σ o ⎤ r
⎣
⎦
Integrating both side
ln ⎡ Bσ x − (1 + B ) σ o ⎤ ×
⎣
⎦
σ xo =
same equation except B.Cs
1
2B
2B
For IES, GATE, PSUs
B
2B
⎛r ⎞ ⎤
⎢1 − ⎜ f ⎟ ⎥
⎢ ⎝ ro ⎠ ⎥
⎣
⎦
1
= 2 ln ( rC )
B
{Cis integration cont.}
at r = ro
For a round bar both wire drawing and extrusion will give
g
g
s
⎡ Bσ b − (1 + B ) σ o ⎤
⎦
∴C = ⎣
ro
or σ x 2rdr + dσ x r 2 + 2rτ x dx + Px 2rdx tan α = 0
σ o (1 + B ) ⎡
B.C s at r = rf , σ x = 0
⎡ − (1 + B ) σ o ⎦
⎤
∴C = ⎣
rf
or σ x =
σ o (1 + B ) ⎡
B
2B
(at exit stress is zero)
σ o (1 + B ) ⎡
B
⎞
⎟
⎟
⎠
2B
⎤
⎥
⎥
⎦
2
A ⎛r ⎞
Extrusion ratio, R = o = ⎜ o ⎟ for round bar
,
A f ⎜ rf ⎟
⎝ ⎠
1
2B
2B
⎛r ⎞ ⎤
⎢1 − ⎜ ⎟ ⎥
⎜ ⎟
⎢ ⎝ rf ⎠ ⎥
⎣ Page 21 of 49
⎦
⎛r
⎢1 − ⎜ o
⎢ ⎜r
⎣ ⎝ f
σ xo =
σ o (1 + B )
B
⎛h
=⎜ o
⎜h
⎝ f
⎞
⎟ for flat stock
⎟
⎠
⎡1 − R 2 B ⎤
⎣
⎦
Bhopal -2014

22. If effect of container friction is considered
Sheet Metal
p f = ram pressure required by container friction
τ i = uniform interface shear stress between
billet and container wall
2τ L
p f .π r0 = 2π r0τ i L or p f = i
ro
2
Product has light weight and versatile shape as
compared to forging/casting
Sheet Metal Operation
Most commonly used – low carbon steel sheet (cost,
strength, formability)
Aluminium and titanium for aircraft and aerospace
∴ Total Extrusion Pressure(Pt ) = σ xo + p f
Sheet metal has become a significant material for,
and Extrusion Load = pt .π r0
‐ automotive bodies and frames,
2
‐ office furniture
By S K Mondal
y
‐
frames for home appliances
Piercing (Punching) and Blanking
Piercing (Punching) and Blanking
(
h ) d l k
Piercing and blanking are shearing operations.
In blanking, the piece being punched out becomes
the workpiece and any major b
h
k i
d
j burrs or undesirable
d i bl
features should be left on the remaining strip
strip.
In piercing (Punching) the punch‐out is the scrap
(Punching),
punch out
and the remaining strip is the workpiece.
g
p
p
Both done on some form of mechanical press.
Clearance (VIMP)
l
(
)
Clearance Contd….
l
Die opening must be larger than punch and known as
Di
i
b l
h
h
d k
‘clearance’.
Punching
Punch = size of hole
Die = punch size +2 clearance
Remember: I punching punch i correct size.
R
b
In
hi
h is
t i
Blanking
Bl ki
Die = size of product
Punch = Die size ‐2 clearance
Blanking
Punching
Remember: In blanking die size will be correct.
For IES, GATE, PSUs
Page 22 of 49
Bhopal -2014

23. Punching Force and Blanking Force
h
d l k
Clearance in %
Clearance in %
If th allowance f th material i a = 0.075 given th
the ll
for the
t i l is
i
then
C = 0 075 x thickness of the sheet
0.075
Fm ax = Ltτ
Capacity of Press for Punching and Blanking
Press capacity will be =
F ax ×C
m
If clearance is 10 % given then
The punching force for holes which are smaller than the stock
thickness may be estimated as follows:
thi k
b ti t d f ll
C = 0 01 x thickness of the sheet
0.01
Fmax =
π dtσ
3
Minimum Diameter of Piercing
f
d
t
Energy and Power for Punching and Blanking
Ideal E
Id l Energy (E in J) = maximum force x punch travel = Fmax × ( p × t )
i
i
f
h
l
π
τs πd.t
Piercing pressure, = Strength of punch, σc × 4 d2
(Unit:Fmax in kN and t in mm othrwise use Fmax in N and t in m)
a
a
Where p is percentage penetration required for rupture
E×N
60
[Where N = actual number of stroke per minute]
Ideal power in press ( P inW ) =
Actual Energy ( E in J ) = Fmax × ( p × t ) × C
Where C is a constant and equal to 1.1 to 1.75 depending upon the profile
E×N
Actual power in press ( P i W ) =
A
l
i
inW
60 ×η
WhereE is actual energy and η is efficiency of the press
Force required with shear on Punch
F=
[Where C is a constant and equal to 1.1 to 1.75 depending
upon the profile]
th fil ]
Fmax (tp) Lτ t(tp)
=
S
S
Shear on Punch
h
h
To reduce shearing force, shear is ground on the face of
the d or punch.
h die
h
It distribute the cutting action over a period of time.
I di ib
h
i
i
i d f i
Shear only reduces th maximum f
Sh
l
d
the
i
force t b applied b t
to be
li d but
total work done remains same
same.
Fine Blanking
l k
Fine Blanking ‐ dies are designed that have small
Fi
Bl ki
di
d i
d h h
ll
clearances and pressure pads that hold the material
while it is sheared. The final result is blanks that have
extremely close tolerances.
y
Where p = penetration of punch as a fraction
S shear on the punch or die, mm
S = shear on the punch or die, mm
For IES, GATE, PSUs
Page 23 of 49
Bhopal -2014

24. Slitting ‐ moving rollers trace out complex paths during
Trimming ‐ Cutting unwanted excess material from the
Lancing – A hole is partially cut and then one side is bent
cutting (like a can opener).
periphery of a previously formed component.
down to form a sort of tab or louver. No metal removal, no
Shaving ‐ Accurate d
h
dimensions of the part are obtained b
f h
b
d by
scrap.
Perforating: Multiple holes which are very small and
close together are cut in flat work material.
removing a thin strip of metal along the edges
edges.
Notching: Metal pieces are cut from the edge of a sheet,
strip or bl k
ti
blank.
Squeezing ‐ Metal is caused to flow to all portions of a die
cavity under the action of compressive forces.
Dinking
k
Steel Rules ‐ soft materials are cut with a steel strip
shaped so that the edge is the pattern to b cut.
h
d
h h d
h
be
Nibbling
Nibbli ‐ a single punch i moved up and d
i l
h is
d
d down rapidly,
idl
Used to blank shapes from low‐strength materials, such as
U d
bl k h
f
l
h
i l
h
rubber, fiber, or cloth.
The shank of a die is either struck with a hammer or mallet or
the entire die is driven downward by some form of
y
mechanical press.
Elastic recovery or spring back
l
b k
Total deformation = elastic deformation + plastic
deformation.
d f
each time cutting off a small amount of material This
material.
At th end of a metal working operation, when th
the
d f
t l
ki
ti
h
the
allows a simple die to cut complex slots.
p
p
pressure is released there is an elastic recovery and the
released,
total deformation will get reduced a little. This
g
phenomenon is called as "spring back".
Elastic recovery or spring back Contd..
l
b k
More important in cold working.
Punch and Die material
Punching Press
h
Commonly used – tool steel
For high production ‐ carbides
It d
depends on th yield strength. Hi h th yield
d
the i ld t
th Higher the i ld
strength, greater spring back.
To compensate this, the cold deformation be carried
beyond the desired limit by an amount equal to the
spring back.
For IES, GATE, PSUs
Page 24 of 49
Bhopal -2014

25. Bolster plate
l
l
Bolster plate Contd....
l
l
Punch plate
h l
When many dies are to run in the same press at different
Used to locate and hold the
times, the wear occurring on the press b d is h h The
h
h
bed high. h
punch in position.
h
bolster plate is incorporated to take this wear
wear.
This is
Thi i a useful way of
f l
f
Relatively cheap and easy to replace
replace.
mounting,
mounting
Attached to the press bed and the die shoe is then
small punches.
p
especially
for
attached to it.
Stripper
Stripper Contd....
The stripper removes the stock from the punch after a
piercing or blanking operation.
Ps = KLt
Where Ps = stripping force, kN
stripping force kN
L = perimeter of cut, mm
t = stock thickness, mm
k hi k
Knockout
k
Knockout is a mechanism, usually connected to and
K
k
i
h i
ll
d
d
operated by the press ram, for freeing a work piece from
a die.
K = stripping constant,
= 0.0103 for low‐ carbon steels thinner than 1.5 mm with
the cut at the edge or near a preceding cut
= 0.0145 for same materials but for other cuts
f
i l b f h
= 0.0207 for low‐ carbon steels above 1.5‐mm thickness
= 0.0241 for harder materials
f h d
l
Pitman
Dowel pin
l
It is a connecting rod which is used to transmit motion
from the main d
f
h
drive shaft to the press slide.
h f
h
ld
Drawing
For IES, GATE, PSUs
Page 25 of 49
Bhopal -2014

26. Drawing
Drawing
Drawing is a plastic deformation process in which a flat
Hot drawing is used for thick‐walled parts of simple
sheet or plate is f
h
l
formed into a three‐dimensional part
d
h
d
l
geometries, thinning takes place.
h
k
l
with a depth more than several times the thickness of
Cold drawing uses relatively thin metal, changes the
C ld d
i
l i l hi
l h
h
the metal.
thickness very little or not at all and produces parts in a
all,
As a punch descends into a mating die, the metal
p
g
,
wide variety of shapes.
y
p
assumes the desired configuration.
Blank Size
Blank Size
D = d + 4dh
2
D = d 2 + 4dh − 0.5r
D=
Drawing Force
⎡D
⎤
P = π dtτ ⎢ − C ⎥
⎣d
⎦
When d > 20r
when15r ≤ d ≤ 20r
( d − 2r ) + 4d ( h − r ) + 2π r ( d − 0.7r )
2
when d < 10r
Deep drawing
d
Drawing when cup height is more than half the diameter is
termed deep drawing.
p
g
Easy with ductile materials.
Blank Holding Force
Blank holding force required depends on the
wrinkling t d
i kli
tendency of th cup. Th maximum
f the
The
i
g
y
g
limit is generally to be one‐third of the drawing
force.
Draw Cl
D
Clearance
Punch diameter = Die opening diameter – 2 5 t
2.5
Stresses on Deep Drawing
Stresses on Deep Drawing
In flange of blank:
Bi‐axial tension and
compression
A cylindrical vessel with flat bottom can be deep drawn by
The ratio of the maximum blank diameter to the
diameter of the cup d
d
f h
drawn . i.e. D/d.
d
There i a li i i d
Th
is limiting drawing ratio (LDR) after which the
i
i (LDR), f
hi h h
Due to the radial flow of material, the side walls increase in
thickness as the height is increased.
Deep Drawability
bl
punch will pierce a hole in the blank instead of drawing
drawing.
In wall of the cup:
simple
uni axial
uni‐axial
tension
This ratio depends upon material amount of friction
material,
double action deep drawing
drawing.
p
present, etc.
Deep drawing ‐ is a combination of drawing and stretching.
Limiting drawing ratio (LDR) is 1.6 to 2.3
For IES, GATE, PSUs
Page 26 of 49
Bhopal -2014

27. Limiting Drawing Ratio (LDR)
The average reduction in deep drawing
d
=05
0.5
D
d ⎞
⎛
Reduction = ⎜ 1 − ⎟ × 100% = 50%
D⎠
⎝
Thumb l
Th b rule:
First draw:Reduction = 50 %
Second draw:Reduction = 30 %
Third draw:Reduction = 25 %
Fourth draw:Reduction = 16 %
Fifth draw:Reduction = 13 %
Progressive piercing and blanking die for
making a simple washer.
making a simple washer
Defects in Drawing ‐ wrinkle
f
kl
An insufficient blank holder pressure causes wrinkles to
A i
ffi i
bl k h ld
i kl
develop on the flange, which may also extend to the wall
of the cup.
Flange Wrinkle
For IES, GATE, PSUs
Wall Wrinkle
Die Design
Progressive dies
Compound dies
Combination dies
Progressive dies
Perform two or more operations simultaneously in a single
stroke of a punch press, so that a complete component is
k f
h
h
l
obtained for each stroke.
Compound dies
All the necessary operations are carried out at a single
station, in a single stroke of the ram. To do more than one set
of operations, a compound die consists of the necessary sets
of punches and di
f
h
d dies.
Combination di
C
bi
i dies
A combination die is same as that of a compound die with
the
th main diff
i difference th t h
that here non‐cutting operations such as
tti
ti
h
bending and forming are also included as part of the
operation.
operation
Method for making a simple washer in a compound piercing and
blanking die. Part is blanked (a) and subsequently pierced
(b) The blanking punch contains the die for piercing.
Defects in Drawing ‐ Fracture
f
Further, too much of a blank holder pressure and friction
F h
h f bl k h ld
df i i
may cause a thinning of the walls and a fracture at the
flange, bottom, and the corners (if any).
Page 27 of 49
Lubrication
b
In drawing operation, proper lubrication is essential for
I d
i
i
l b i i i
i l f
p
1. To improve die life.
2. To reduce drawing forces.
3. T d
To reduce temperature.
4
4. To improve surface finish.
p
Defects in Drawing ‐earing
f
While drawing a rolled stock, ears or lobes tend to occur
Whil d
i
ll d
k
l b
d
because of the anisotropy induced by the rolling
operation.
Bhopal -2014

28. Defects in Drawing – miss strike
f
k
Defects in Drawing – Orange peel
f
l
Due to the misplacement of the stock, unsymmetrical
D
h
i l
f h
k
i l
flanges may result. This defect is known as miss strike.
A surface roughening (defect) encountered in forming
f
h i
(d f )
d i f
i
products from metal stock that has a coarse grain size.
It is due to uneven flow or to the appearance of the
overly large grains usually the result of annealing at too
high a temperature.
Stretcher strains (like Luders Lines)
St t h t i (lik L d Li )
Caused by plastic deformation due to inhomogeneous
C
d b
l ti d f
ti
d
t i h
yielding.
These lines can criss‐cross the surface of the workpiece and
p
may be visibly objectionable.
Low carbon steel and aluminium shows more stretcher
strains.
Surface scratches
Surface scratches
Spinning
Die or punch not having a smooth surface, insufficient
lubrication
Spinning
Spinning i a cold‐forming operation i which a
S i i
is
ld f
i
ti
in hi h
rotating disk of sheet metal is shaped over a male
form, or mandrel.
Localized pressure is applied through a simple
round‐ended wooden or metal tool or small roller,
which traverses the entire surface of the part
Spinning
1. A mandrel (or die for internal pieces) is placed on a
d l ( di f i
l i
)i l d
rotating axis (like a turning center).
2. A blank or tube is held to the face of the mandrel.
3.
3 A roller is pushed against the material near the
center of rotation, and slowly moved outwards, pushing
the bl k against the mandrel.
h blank
h
d l
4. The part conforms to the shape of the mandrel (with
e pa t co o s t e s ape o t e a d e ( t
some springback).
5. Th process i stopped, and th part i removed and
The
is t
d
d the
t is
d d
trimmed.
For IES, GATE, PSUs
tc = tb sinα
Page 28 of 49
Bhopal -2014

29. Underwater
explosions.
HERF
High Energy Rate Forming, also known as HERF or explosive
forming can b utilised t f
f
i
be tili d to form a wide variety of metals, f
id
i t f
t l from
g
gy
g(
)
High Energy Rate Forming(HERF)
aluminum to high strength alloys.
Applied a large amount of energy in a very sort time interval.
Electro‐magnetic
Electro magnetic
(the use of
rapidly formed
magnetic fields).
HERF
Underwater spark
discharge (electro‐
discharge (electro
hydraulic).
HERF makes it possible to form large work pieces and
difficult‐to‐form metals with less‐expensive equipment and
Internal
combustion of
g
gaseous
mixtures.
tooling required.
No
N springback
i b k
Underwater Explosions
U d
E l i
Underwater explosions
U d
l i
Electro‐hydraulic Forming
l
h d l
A shock wave in the fluid medium (normally water ) is
generated b d
d by detonating an explosive charge.
l
h
TNT and d
d dynamite f hi h energy and gun powder f
i for higher
d
d for
lower energy is used
used.
Used for parts of thick materials
materials.
Employed
in
Aerospace,
aircraft
industries
Pneumatic‐
P
i
mechanical
means
and
automobile related components.
An operation using electric discharge in the form of
sparks to generate a shock wave in a fluid is called
electrohydrulic forming.
A capacitor bank is charged through the charging circuit,
subsequently, a switch i closed, resulting i a spark
b
tl
it h is l d
lti
in
k
within the electrode gap to discharge the capacitors.
g p
g
p
Energy level and peak pressure is lower than underwater
explosions but easier and safer.
Used for bulging operations in small parts.
Electromagnetic or Magnetic Pulse Forming
Based on the principle that the electromagnetic field of
B d
h
i i l h h l
i fi ld f
an induced current always opposes the electromagnetic
field of the inducing current.
A large capacitor bank is discharged, producing a current
surge through a coiled conductor.
h
h
l d
d
For IES, GATE, PSUs
If the coil has been placed within a conductive cylinder,
around a cylinder, or adjacent th fl t sheet of metal, th
d
li d
dj
t the flat h t f
t l the
discharge induces a secondary current in the workpiece,
causing it to be repelled from the coil and conformed to
a die or mating workpiece.29 of 49
Page
Bhopal -2014

30. Stretch Forming
h
Electromagnetic or Magnetic Pulse Forming
The process is very rapid and is used primarily to expand
or contract tubing, or to permanently assemble
b
l
bl
component parts
parts.
This process is most effective for relatively thin materials
( 5
(0.25 to 1.25 mm thick).
5
)
Produce large sheet metal parts in low or limited
P d
l
h t
t l
t i l
li it d
quantities.
A sheet of metal is gripped by two or more sets of jaws
that stretch it and wrap it around a single form block.
Because most of the deformation is induced by the
g,
tensile stretching, the forces on the form block are far
less than those normally encountered in bending or
o
g.
forming.
There is very little springback, and the workpiece
conforms very closely to the shape of the tool
tool.
Because the forces are so low, the form blocks can often
be
b made of wood, l
d
f
d low‐melting‐point metal, or even
lti
i t
t l
plastic.
Stretch Forming Contd......
h
Stretch Forming Contd......
h
Popular in the aircraft industry and is frequently used to
form aluminum and stainless steel
f
l
d
l
l
Low‐carbon steel can b stretch f
L
b
l
be
h formed to produce l
d
d
large
panels for the automotive and truck industry
industry.
Stretch Forming Contd......
h
Ironing
The process of thinning the walls of a drawn cylinder by
passing it b
between a punch and d whose separation is
h d die h
less than the original wall thickness
thickness.
The walls are thinned and lengthened while the
lengthened,
thickness of the base remains unchanged.
g
Examples of ironed products include brass cartridge
p
p
g
cases and the thin‐walled beverage can.
Ironing Contd....
Embossing
b
Coining
It is a very shallow drawing operation where the depth of
Coining is essentially a cold‐forging operation except for
the d
h draw is l
limited to one to three times the thickness of
d
h
h h k
f
the f
h fact that the fl
h h flow of the metal occurs only at the top
f h
l
l
h
the metal and the material thickness remains largely
metal,
layers and not the entire volume
volume.
unchanged.
Coining is used for making coins medals and similar
coins,
articles.
For IES, GATE, PSUs
Page 30 of 49
Bhopal -2014

31. Bending
After basic shearing operation, we can bend a part to give it some
shape.
h
Bending parts depends upon material properties at the location of
the bend.
h b d
At bend, bi‐axial compression and bi‐axial tension is there.
Bending
Bending
The strain on the outermost fibers of the bend is
Bend allowance,
Lb = α(R+kt)
α(R+kt)
ε=
where
R = bend radius
k = constant (stretch factor)
k
(
h f
)
For R > 2t
k = 0.5
For R < 2t
1
2R
+1
+1
t
k = 0.33
t = thickness of material
hi k
f
i l
α = bend angle (in radian)
g (
Bending Force
Bending Force
Klσ ut t 2
F=
w
Where l =Bend length = width of the stock, mm
Powder Metallurgy
σ ut = Ulti t tensile strength, MPa (N/mm 2 )
Ultimate t il t
th MP (N/
t = blank thickness, mm
w = width of die-opening, mm
idth f di
i
K = die-opening factor , (can be used followin table)
Condition
V-Bending
U-Bending
Edge-Bending
W < 16t
1.33
2.67
0.67
W > = 16t
1.20
2.40
0.6
For U or channel bending force required is double than V
For U or channel bending force required is double than V – bending
For edge bending it will be about one‐half that for V ‐ bending
By S K Mondal
Manufacturing of Powder
Manufacturing of Powder
Atomization using a gas stream
Powder Metallurgy
Powder Metallurgy
Powder metallurgy is the name given to the
p
process by which fine powdered materials are
y
p
blended,
pressed
into
a
desired
shape
(compacted), and then heated (sintered) in a
controlled atmosphere to b d the contacting
ll d
h
bond h
surfaces of the particles and establish the desired
p p
properties.
For IES, GATE, PSUs
Molten metal is
forced th
f
d through a
h
small orifice and
is disintegrated by
a
jet
of
compressed air
air,
inert gas or water
jet,.
jet It is used for
low melting point
materials, brass,
materials brass
bronze, Zn, Tn,
Al, Pb etc.
Manufacturing of Powder
Manufacturing of Powder
Reduction
Metal oxides are turned to pure metal powder when
exposed to below melting point gases results in a
product of cake of sponge metal.
The i
h irregular sponge‐like particles are soft, readily
l
lik
i l
f
dil
compressible,
compressible and give compacts of good pre‐sinter
(“green”) strength
g
g
Used for iron, Cu, tungsten, molybdenum, Ni and
Page 31 of 49
Cobalt.
Bhopal -2014

32. Manufacturing of Powder
Manufacturing of Powder
Manufacturing of Powder
Electrolytic Deposition
Used for iron, copper, silver
Process is similar to electroplating
electroplating.
For making copper powder, copper plates are placed as
anode in the tank of electrolyte, whereas the aluminium
plates are placed i th electrolyte t act as cathode.
l t
l d in the l t l t to t
th d
p
pp g
p
When DC current is passed, the copper gets deposited
on cathode. The cathode plated are taken out and
powder i scrapped off. Th powder i washed, d i d and
d is
d ff The
d is
h d dried d
p
pulverized to the desired grain size.
g
The cost of manufacturing is high.
Granulations ‐ as metals are cooled they are stirred rapidly
Machining ‐ coarse powders such as magnesium
Milling ‐ crushers and rollers to break down metals. Used for
g
brittle materials.
Shooting ‐ drops of molten metal are dropped in water, used
for low melting point materials
materials.
Condensation – Metals are boiled to produce metal vapours
and then condensed to obtain metal powders. Used for Zn,
Characteristics of metal powder:
Ch
i i
f
l
d
Fineness: refers to particle size of powder, can be
p
p
,
determined either by pouring the powder through a sieve or
by microscopic testing A standard sieves with mesh size
testing.
varies between (100) and (325) are used to determine
particle size and particle size di t ib ti of powder i a
ti l i
d
ti l i distribution f
d in
certain range.
Particle size distribution: refers to amount of each particle
size in the powder and have a great effect in determining
flowability, apparent density and final porosity of product.
Mg, Cd.
Mg Cd
Blending
l d
Blending or mixing operations can be done either dry or wet.
Bl di
i i
ti
b d
ith d
t
Lubricants such as graphite or stearic acid improve the flow
characteristics and compressibility at the expense of reduced
strength.
Binders
produce
the
reverse
effect
of
lubricants.
Thermoplastics or a water‐soluble methylcellulose binder is
water soluble
used.
Most lubricants or binders are not wanted in the final
product and are removed ( volatilized or burned off)
Compacting
C
ti
Compacting
Sintering
Powder is pressed into a “green compact”
Controlled atmosphere: no oxygen
40 to 1650 MPa pressure (Depends on materials,
Heat to 0.75*T melt
Particles bind together, diffusion, recrystalization
P ti l bi d t th diff i
t li ti
product complexity)
and grain growth takes place.
g
g
p
Still very porous, ~70% density
Part shrinks in size
May be done cold or warm (higher density)
Density increases, up to 95%
Strength increases, Brittleness reduces, Porosity
St
th i
B ittl
d
P
it
decreases. Toughness increases.
g
For IES, GATE, PSUs
Page 32 of 49
Bhopal -2014

33. H t I t ti P
i (HIP)
Hot Isostatic Pressing (HIP)
Cold Isostatic Pressing (CIP)
ld
( )
Is carried out at high temperature and p
g
p
pressure using a
g
The powder is contained in a flexible mould made of
gas such as argon.
rubber or some other elastomer material
bb
h
l
l
The flexible mould is made of sheet metal. (Due to high
The flexible
Th fl ibl mould i then pressurized b means of
ld is h
i d by
f
temperature)
high‐pressure water or oil (same pressure in all
oil.
Compaction
C
i
directions)
)
simultaneously.
simultaneously
No lubricant is needed
U
Used in the production of billets of super‐alloys, high‐
p
p
y, g
High and uniform density can be achieved
speed steels, titanium, ceramics, etc, where the integrity
and
d
sintering
i
i
are
completed
l d
of the materials is a prime consideration
Features of PM products
f
d
For high tolerance parts, a sintering part is put back into
F hi h l
i
i
i
b ki
a die and repressed. In general this makes the part more
accurate with a better surface finish.
A part has many voids that can be impregnated One
impregnated.
method is to use an oil bath. Another method uses
vacuum first then impregnation
acuum first,
impregnation.
A part surface can be infiltrated with a low melting point
metal to increase density, strength, hardness, ductility
and impact resistance.
Plating, heat treating and machining operations can also
be
b used.
d
Advantages Contd….
d
Physical properties can be controlled
Variation from part to part is low
Hard to machine metals can be used easily
H d t
hi t l b d il
No molten metals
No need for many/any finishing operations
Permits high volume production of complex shapes
g
p
p
p
Production of magnets
d
f
50:50 Fe‐Al alloys is used for magnetic parts
F Al ll i d f
i
Al‐Ni‐Fe is used for permanent magnets
p
g
Sintering is done in a wire coil to align the magnetic
poles of the material
H2 is used to rapidly cool the part (to maintain magnetic
alignment)
Total shrinkage is approximately 3‐7% (for accurate parts
an extra sintering step may be added before magnetic
alignment)
li
t)
The sintering temperature is 600°C in H2
g
p
Disadvantages
d
Metal powders deteriorate quickly when stored
M l
d d
i
i kl h
d
improperly
Fixed and setup costs are high
Part size is limited by the press, and compression of the
Part size is limited by the press and compression of the
powder used.
Sharp corners and varying thickness can be hard to
p oduce
produce
Non‐moldable features are impossible to produce.
Allows non‐traditional alloy combinations
Good control of final density
For IES, GATE, PSUs
Page 33 of 49
Advantages
d
Good tolerances and surface finish
G d l
d f fi i h
Highly complex shapes made quickly
g y
p
p
q
y
Can produce porous parts and hard to manufacture
materials (e.g. cemented oxides)
materials (e g cemented oxides)
Pores in the metal can be filled with other
materials/metals
Surfaces can have high wear resistance
Porosity can be controlled
Low waste
Automation is easy
A li ti
Applications
Oil impregnated bearings made from either iron or
Oil‐impregnated
copper alloys for home appliance and automotive
applications
li ti
P/M filters can be made with pores of almost any size.
p
y
Pressure or flow regulators.
Small
S ll gears, cams etc.
t
Products where the combined properties of two or more
p p
metals (or both metals and nonmetals) are desired.
Cemented carbides are produced by the cold‐
Cemented carbides are produced by the cold
compaction of tungsten carbide powder in a binder, such
as cobalt ( 5 to 12%), followed by liquid‐phase sintering.
b lt ( t %) f ll
d b li id h i t i
Bhopal -2014

34. Pre ‐ Sintering
Repressing
Infiltration
fl
If a part made by PM needs some machining, it will be
Repressing is performed to increase the density and
Component is dipped into a low melting‐temperature
rather very d ff l if the material is very h d and
h
difficult f h
l
hard
d
improve the mechanical properties.
h
h
l
alloy l
ll liquid
d
strong.
strong These machining operations are made easier by
Further improvement i achieved b re‐sintering.
F h i
is hi d by
i
i
The liquid
Th li id would fl
ld flow i
into the voids simply b capillary
h
id i l by
ill
the pre‐sintering operation which is done before
pre sintering
action,
action thereby decreasing the porosity and improving
sintering operation.
the strength of the component.
g
p
The process is used quite extensively with ferrous parts
p
q
y
p
using copper as an infiltrate but to avoid erosion, an alloy
of copper containing iron and manganese is often used.
Impregnation
Oil‐impregnated Porous Bronze Bearings
Impregnation is similar to infiltration
I
i i i il
i fil
i
PM component is kept in an oil bath. The oil penetrates
p
p
p
into the voids by capillary forces and remains there.
The oil is used for lubrication of the component when
necessary. During the actual service conditions, the oil is
released slowly to provide the necessary l b
l
d l l
d h
lubrication.
The components can absorb between 12% and 30% oil by
e co po e ts ca abso b bet ee
%a d
o
volume.
It i b i
is being used on P/M self‐lubricating b
d
lf l b i ti
bearing
i
components since the late 1920's.
For IES, GATE, PSUs
Page 34 of 49
Bhopal -2014

35. Terminology
Nominal size: Size of a part specified in the drawing
Basic size: Size of a part to which all limits of
variation (i.e. tolerances) are applied.
(
)
pp
t, o e a ce & ts
Limit, Tolerance & Fits
Actual size: Actual measured dimension of the part.
p
The difference between the basic size and the actual
size should not exceed a certain limit, otherwise it will
interfere with the interchangeability of the mating
parts.
By S K Mondal
Terminology
Terminology C td
Contd....
Limits of sizes: There are two extreme permissible
sizes for a dimension of the part. The largest
permissible size for a dimension is called upper or high
or maximum limit, whereas the smallest size is known
as lower or minimum limit.
Tolerance
The difference between the upper limit and lower
limit.
It is the maximum permissible variation in a
dimension.
The tolerance may be unilateral or bilateral.
Terminology
Terminology C td
Contd....
g
p
g
Zero line: A straight line corresponding to the basic
size. The deviations are measured from this line.
Deviation: Is the algebraic difference between a size
(actual, max. etc.) and the corresponding basic size.
Actual deviation: Is the algebraic difference between
an actual size and the corresponding b i size.
l i
d h
di basic i
Upper d i i
U
deviation: I the algebraic diff
Is h l b i difference b
between
Terminology Contd....
e
o ogy
Unilateral Limits occurs when both maximum limit and
minimum limit are either above or below the basic size.
+0.18
e.g. Ø25 +0 18
+0.10
Basic Size = 25 00 mm
25.00
Upper Limit = 25.18 mm
Lower Limit = 25.10 mm
Tolerance = 0.08 mm
0.10
e.g.
e g Ø25 -0 10
-0.20
Basic Size = 25.00 mm
Upper Limit = 24.90 mm
Lower Limit = 24.80 mm
Tolerance = 0.10 mm
Terminology
Terminology C td
Contd....
Lower deviation: Is the algebraic difference between
the minimum size and the basic size.
Mean deviation: Is the arithmetical mean of upper
pp
and lower deviations.
Terminology
Terminology Contd
Contd....
For Unilateral Limits, a case may occur when one of the
Limits
limits coincides with the basic size,
e.g. Ø25 +0.20 , Ø25 0
0
‐0.10
0.10
Bilateral Limits occur when the maximum limit is above
and the minimum limit is below the basic size.
e.g. Ø25 ±0.04
Basic Size = 25 00 mm
25.00
Upper Limit = 25.04 mm
Lower Li it = 24.96 mm
L
Limit
6
Tolerance = 0.08 mm
Fit
Fits: (assembly condition between “Hole” & “Shaft”)
Hole – A feature engulfing a component
Shaft – A feature being engulfed by a
component
p
Fundamental deviation: This is the deviation, either
the upper or the lower deviation, which is nearest one
to zero line for either a hole or shaft.
the maximum size and the basic size
size.
For IES, GATE, PSUs
Page 35 of 49
Bhopal -2014

36. Transition Fits
Clearance Fits
Interference Fits
Hole
Hole
Max C
Hole
Max C
Min C
Tolerance zones never meet
T l
Tolerance zones always
overlap
Shaft
Max I
Shaft
Tolerance zones never meet
but crosses each other
Min I
Max I
Shaft
Max. C = UL of hole - LL of shaft
Min. C = LL of hole - UL of shaft
The clearance fits may be slide fit, easy sliding fit, running
Th l
fit
b lid fit
lidi fit
i
fit, slack running fit and loose running fit.
Max. C = UL of hole - LL of shaft
Max. I = LL of hole - UL of shaft
The transition fits may be force fit, tight fit and push fit.
Max. I = LL of hole - UL of shaft
Min.
Min I = UL of hole - LL of shaft
The interference fits may be shrink fit, heavy drive fit and
The interference fits may be shrink fit heavy drive fit and
light drive fit.
5. Basis of Fits ‐ Hole Basis
Tolerance Zone
µ
µm
• It is defined graphically
by the magnitude of the
Tolerance Zone tolerance and by its
position in relation to the
zero line.
55
20
Allowance
In this system, the basic
diameter of the hole is constant
while the shaft size varies
according to the type of fit.
It is Minimum clearance or maximum interference. It is
the intentional difference between the basic
dimensions of the mating parts. The allowance may be
gp
y
positive or negative.
I
T
C
Hole Basis Fits
Basic Size
Legends:
Hole
Shaft
Tolerance
C - Clearance
T-T
Transition
ii
I - Interference
• This system leads to greater
economy of production, as a single
drill or reamer size can be used to
produce a variety of fits by merely
altering the shaft limits
limits.
• The shaft can be accurately
produced to size by turning and
grinding.
• Generally it is usual to recommend
hole-base fits except where
fits,
temperature may have a
detrimental effect on large sizes.
Basis of Fits ‐ Shaft Basis
Limits and Fits
Limits and Fits
•Here the hole size is varied to
produce the required class of fit with a
basic-size shaft.
C
T
I
Shaft Basis Fits
Legends:
Hole
Shaft
Tolerance
C - Clearance
T-T
Transition
ii
I - Interference
A series of drills and reamers is
required for this system,
therefore it tends to be costly.
It may, however, be necessary
It may however be necessary
to use it where different fits are
required along a long shaft. For
example, in the case of driving
example in the case of driving
shafts where a single shaft may
have to accommodate to a
variety of accessories such as
couplings, bearings, collars,
etc., it is preferable to maintain
a constant diameter for the
permanent member, which is
the shaft, and vary the bore of
the accessories.
For IES, GATE, PSUs
Limits and fits comprises 18 grades of fundamental
tolerances for both shaft and hole, designated as IT01,
IT0 and IT1 to IT16. These are called standard
tolerances. (IS‐919) But ISO 286 specify 20 grades upto
IT18
There are 25 (IS 919) and 28 (ISO 286) types of
fundamental deviations
deviations.
Hole: A, B, C, CD, D, E, EF, F, FG, G, H, J, JS, K, M, N, P,
R, S, T, U, V, X, Y, Z, ZA, ZB, ZC.
R S T U V X Y Z ZA ZB ZC
Shaft : a, b, c, cd, d, e, ef, f, fg, g, h, j, js, k, m, n, p, r, s, t,
u, v, x, y, z, za, zb, zc.
A unilateral hole basis system is recommended but if
y
necessary a unilateral or bilateral shaft basis system may
Page 36 of 49
also be used
Tolerance Designation (ISO)
Tolerance on a shaft or a hole can also be calculated by
using the formulas provided by ISO
ISO.
T = K ×i
where,
where
T is the tolerance (in µm)
i = 0.453 D + 0.001D (unit tolerance, in µm)
D = D1D2
(D1 and D2 are the nominal sizes marking
the beginning and the end of a range of
g
g
g
sizes, in mm)
K = 10(1.6)( ITn − IT 6 )
[For IT6 to IT16]
Bhopal -2014

37. Diameter Steps
Diameter Steps
Above
(mm)
(
)
Upto and including
(mm)
(
)
‐
‐
3 ‐
6
6 ‐
10 ‐
18 ‐
8
30 ‐
5
50 ‐
80 ‐
120 ‐
180 ‐
250 ‐
315 ‐
400 ‐
3
6
10
18
30
50
80
120
180
250
315
400
500
Fundamental Deviation
Value of the Tolerance
IT01
IT0
IT1
IT3
3
ar2
IT4
ar3
IT5
5
ar4 = 7i
IT7
IT8
0.3 + 0.008D 0.5 + 0.012D 0.8 + 0.02D
=a
10(1.6)(ITn -IT6)
(
)
= 16i
IT11
10(1.6)(ITn -IT6)
= 100i
IT15
10(1.6)(ITn -IT6)
= 640i
10(1.6)(IT
0( 6)
n
-IT6)
= 25i
IT12
10(1.6)(ITn -IT6)
= 160i
IT9
)
10(1.6)(
10(1 6)(ITn -IT6)
= 40i
IT13
10(1.6)(ITn -IT6)
= 250i
IT2
ar
r = 101/5
IT6
6
10(1.6)(ITn -IT6)
= 10i
Grades of Tolerance
It is an indication of the level of accuracy.
IT01 to IT4
measuring i
i instruments
IT10
IT6)
10(1.6)
10(1 6)(ITn -IT6)
= 64i
IT14
10(1.6)(ITn -IT6)
= 400i
IT16
‐ For production of gauges, plug gauges,
IT5 to
IT t IT 7 ‐ F fit i precision engineering applications
For fits in
i i
i
i
li ti
IT8 to IT11 – For General Engineering
IT12 to IT14 – For Sheet metal working or press working
IT15 to IT16 – For processes like casting general cutting
casting,
10(1.6)(ITn -IT6)
= 1000i
work
Fundamental Deviations
is chosen to locate the tolerance zone w.r.t. the zero line
Calculation for Upper and Lower Deviation
For Shaft
Holes are designated by capital letter:
Letters A to G - oversized holes
Letters P to ZC - undersized holes
ei = es – IT
es = ei + IT
For Hole
F H l
EI = ES – IT
ES = EI + IT
Shafts are designated by small letter:
Letters m to zc - oversized shafts
Letters a to g - undersized shafts
es = upper deviation of shaft
pp
ei = lower deviation of shaft
ES = upper deviation of hole
EI= lower deviation of hole
H is used for holes and h is used for shafts
whose fundamental deviation is zero
For hole, H stands for a dimension whose lower
deviation f
d i ti refers t th b i size. Th h l H f which
to the basic i The hole for hi h
the lower deviation is zero is called a basic hole.
Similarly, for shafts, h stands for a dimension whose
upper deviation refers to the basic size. The shaft h for
which the upper deviation is zero is called a basic
shaft.
A fit is designated by its basic size followed by symbols
representing the limits of each of its two components,
the hole being quoted first.
For example 100 H6/g5 means basic size is 100 mm
example,
and the tolerance grade for the hole is 6 and for the
shaft is 5
5.
For IES, GATE, PSUs
Recommended Selection of Fits
Basic size
Hole Tolerance Zone
Shaft Tolerance Zone
Fundamental Deviation
F d
t l D i ti
IT#
Page 37 of 49
Bhopal -2014

38. Interchangeability
Selective Assembly
All the parts (hole & shaft) produced are measured
and graded into a range of dimensions within the
tolerance groups.
Reduces the cost of production
d
h
f
d
Term employed for the mass production of identical
items within the prescribed limits of sizes.
If the variation of items are within certain limits, all
parts of equivalent size will be equally fit for operating in
machines and mechanisms and the mating parts will
give the required fitting.
This facilitates to select at random from a large number
of parts f an assembly and results i a considerable
f
for
bl
d
l in
id bl
g
p
saving in the cost of production.
Tolerance Sink
A design engineer keeps one section of the part blank
(without tolerance) so that production engineer can
dump all the tolerances on that section which b
d
ll h
l
h
i
hi h becomes
most inaccurate dimension of the part
part.
Position of sink can be changing the reference point
point.
Tolerance for the sink is the cumulative sum of all the
tolerances and only like minded tolerances can be added
i.e. either equally bilateral or equally unilateral.
Limit Gauges
Limit Gauges
Allocation of manufacturing tolerances
ll
i
f
f
i
l
holes.
Plug gauge: used to check the holes The GO plug gauge is
the size of the low limit of the hole while the NOT GO plug
gauge corresponds to the high limit of the hole
hole.
Snap, Gap or Ring gauge: used for gauging the shaft and
male components. Th G snap gauge i of a size
l
The Go
is f
i
corresponding to the high (maximum) limit of the shaft,
while the NOT GO gauge corresponds to the l
hil
h
d
h low
(minimum limit).
Unilateral system:
gauge tolerance zone lies
t l
li
entirely within the work tolerance zone.
work tolerance zone becomes smaller by the sum of the
gauge tolerance
tolerance.
Example
Size of the hole to be checked 25 ± 0.02 mm
Here, Hi h limit of hole = 25.02 mm
H
Higher li it f h l 25 02
Lower limit of hole = 24 98 mm
24.98
Work tolerance = 0.04 mm
∴ Gauge tolerance = 10% of work tolerance = 0.004 mm
+0.004
mm
−0 000
0.000
+0.000
0.000
Dimension of 'NOT GO' Plug gauge = 25.02
mm
−0.004
∴ Dimension of 'GO' Plug gauge = 24.98
Fig. Plug gauge
Fig. Ring and snap gauges
• Taking example of above:
• Bilateral system: in this
∴Wear Allowance = 5% of work tolerance = 0.002 mm
system, the GO and NO GO
gauge tolerance zones are
bisected by the high and
low limits of the work
f
tolerance zone.
Taking example as above:
∴ Dimension of 'GO' Plug gauge = 24.98
+0.002
−0 002
0.002
Dimension of 'NOT GO' Plug gauge = 25.02
For IES, GATE, PSUs
mm
+0.002
+0.002
mm
−0.002
g g
y
Wear allowance: GO gauges which constantly rub
against the surface of the parts in the inspection are
subjected to wear and loose their initial size.
The size of go plug gauge is reduced while that of go
snap gauge increases.
i
To increase service life of gauges wear allowance is
g g
added to the go gauge in the direction opposite to
wear. Wear allowance is usually taken as 5% of the
work tolerance.
Wear allowance is applied to a nominal diameter
W ll
i
li d
i l di
before gauge tolerance is applied.
Page 38 of 49
Nominal size of GO plug gauge = 24.98 + 0 002 mm
24 98 0.002
∴ Di
Dimension of 'GO' Plug gauge = 24.982
i
f
Pl
24 982
+0.004
mm
−0.000
gg g
Dimension of 'NOT GO' Plug gauge = 25.02
+0.000
−0 004
0.004
Bhopal -2014
mm

39. T l ’ Pi i l
Taylor’s Principle
Linear measurements
This principle states that the GO gauge should always be
so d
designed that it will cover the maximum metal
d h
ll
h
l
condition (MMC) of as many dimensions as possible in
the same limit gauges, whereas a NOT GO gauges to
Measurement of Lines & Surfaces
cover the minimum metal condition of one dimension
only.
Some of the i
S
f h instruments used f
d for the li
h linear
measurements are:
Rules
Vernier
Micrometer
Height gauge
Bore gauge
B
Dial indicator
Slip gauges or gauge blocks
By S K Mondal
Vernier Caliper
A vernier scale is an auxiliary scale that slides along the main
scale.
The vernier scale is that a certain number n of divisions on
the vernier scale is equal in length to a different number
(usually one less) of main‐scale divisions
main scale divisions.
nV = (n −1)S
where n = number of d
h
b
f divisions on the vernier scale
h
l
V = The length of one division on the vernier scale
g
and S = Length of the smallest main‐scale division
Least count is applied to the smallest value that can be read
directly by use of a vernier scale.
Least count = S − V = 1 S
n
M t i Mi
t
Metric Micrometer
A micrometer allows a measurement of the size of a
body. It is one of the most accurate mechanical devices
in common use.
It consists a main scale and a thimble
Method of Measurement
Step‐I: Find the whole number of mm in the barrel
Step‐I: Find the reading of barrel and multiply by 0.01
Vernier Caliper
Bore Gauge: used for measuring bores of different
g g
g
sizes ranging from small‐to‐large sizes.
Provided with various extension arms that can be
added for different sizes
sizes.
Micrometer
For IES, GATE, PSUs
Page 39 of 49
Step‐III: Add the value in Step‐I and Step‐II
Dial indicator: Converts a linear
displacement into a radial
movement to measure over a
small range of movement f the
ll
f
for h
plunger.
The typical least count that can be
obtained with suitable gearing
dial indicators is 0.01 mm to 0.001
mm.
mm
It is possible to use the dial
indicator as a comparator by
mounting it on a stand at any
g
y
suitable height.
Principle of a dial indicator
Bhopal -2014

40. pp cat o s o d a
d cato
c ude:
Applications of dial indicator include:
centering workpices to machine tool spindles
offsetting lathe tail stocks
aligning a vice on a milling machine
checking dimensions
To make up a Slip Gauge pile to 41.125 mm
A Slip Gauge pile is set up with the use of simple
Sli G
il i
t
ith th
f i l
maths.
Decide what height you want to set up, in this
g y
p
case 41.125mm.
Take away the thickness of the two wear gauges,
and then use the gauges in the set to remove
each place of decimal in turn starting with the
turn,
lowest.
A M t i li
t (88 Pi
)
A Metric slip gauge set (88 Pieces)
Slip gauges size or
range, mm
1.005
1.001 to 1.009
1.010 to 1.490
0.500 to 9.500
0 500 to 9 500
10 to 100
Increment, mm
Increment mm
‐
0.001
0.010
0.500
0 500
10.000
For IES, GATE, PSUs
Number of
Pieces
1
9
49
19
10
Slip Gauges or Gauge blocks
These are small bl k of alloy steel.
Th
ll blocks f ll
l
Used in the manufacturing shops as length standards.
g
p
g
Not to be used for regular and continuous
measurement.
measurement
Rectangular blocks with thickness representing the
dimension of the block. The cross‐section of the block
is usually 32 mm x 9 mm.
s usua y 3
.
Are hardened and finished to size. The measuring
surfaces of th gauge bl k are fi i h d t a very hi h
f
f the
blocks
finished to
high
degree of finish, flatness and accuracy.
Come in sets with different number of pieces in a given
set t suit th requirements of measurements.
t to it the
i
t f
t
A typical set consisting of 88 pieces for metric units is
yp
g
p
shown in.
To build
T b ild any given di
i
dimension, it i necessary t
i
is
to
y
,
p
g
identify a set of blocks, which are to be put together.
Number of blocks used should always be the smallest.
Generally the top and b
G
ll h
d bottom Sli G
Slip Gauges i the pile
in h il
g g
y
are 2 mm wear gauges. This is so that they will be the
only ones that will wear down, and it is much cheaper
to replace two gauges than a whole set.
l
h
h l
To make up a Slip Gauge pile to 41.125 mm
41.125
-4.000
______
37.125
-1.005
1 00
_______
36.120
-1.020
1 020
_______
35.100
-1.100
1 100
_______
34.000
-4.000
4 000
_______
30.000
-30.000
30 000
_______
0.000
Comparators
Comparator is another form of linear measuring
method, which is quick and more convenient for
checking l
h ki large number of id ti l di
b
f identical dimensions.
i
During the measurement, a comparator is able to give
g
p
g
the deviation of the dimension from the set dimension.
Cannot measure absolute dimension but can only
compare two dimensions.
Highly reliable.
To magnify the deviation, a number of principles are
used such as mechanical, optical, pneumatic and
electrical.
electrical
Page 40 of 49
Fig. Principle of a comparator
Bhopal -2014

41. Mechanical Comparators
Mechanical Comparators
Limit Gauges
Feeler Gauge
Gauge
Snap Gauge
External Dimensions
Plug Gauge
g
g
Internal Dimensions
Taper Plug Gauge
Taper hole
Ring Gauge
External Diameter
Gap Gauge
G G
Gaps and Grooves
G d G
Radius Gauge
Gauging radius
Thread pitch Gauge
p
g
The Mikrokator principle
greatly
magnifies
any
deviation i size so th t
d i ti
in i
that
even
small
deviations
produce l
d
large d fl
deflections of
f
the pointer over the scale.
p
For Measuring
External Thread
Sigma Mechanical Comparator
Mechanical Comparators
Mechanical Comparators
The Sigma Mechanical Comparator uses a partially
The Eden‐Rolt Reed system uses a
y
wrapped b d wrapped about a d
d band
d b
driving d
drum to turn a
pointer attached to the end of two
pointer needle The assembly provides a frictionless
needle.
reeds. One reed is pushed by a
movement with a resistant pressure provided by the
plunger, while the other is fixed. As
springs.
one reed moves relative t th other,
d
l ti to the th
the pointer that they are commonly
attached to will deflect.
Sigma Mechanical Comparator
Optical Comparators
These d i
devices use a plunger to rotate a mirror. A li h
light
Th
l
i
beam is reflected off that mirror, and simply by the
virtue of distance, the small rotation of the mirror can
be converted to a significant translation with little
g
friction.
Pneumatic Comparators
Pneumatic Comparators
Flow type:
The float height is essentially proportional to the air
that escapes f
h
from the gauge h d
h
head
Master
M t gauges are used t fi d calibration points on
d to find lib ti
i t
the scales
The
input
pressure
is
regulated
to
allow
magnification adjustment
For IES, GATE, PSUs
Page 41 of 49
Bhopal -2014