99992012 amu.pdf

Unit-II
• Machine tools and machining operations for
Turning
Boring
Shaping
Milling
Grinding
– Calculation of MRR, Power required and Cutting time
•Finishing operations
•Surface treatment
•Coating and cleaning
•Design of Jigs and Fixtures
•Design of press working tools

1. A cylindrical stainless steel rod with length L=150 mm,
diameter Do = 12 mm is being reduced in diameter to Df =11
mm by turning on a lathe. The spindle rotates at N = 400
rpm, and the tool is travelling at an axial speed of υ=200
mm/min
Calculate:
a. The cutting speed V (maximum and minimum)
b. The material removal rate MRR
c. The cutting time t
d. The power required if the unit power is estimated to 4
w.s/mm3

SOLUTION:
a. The maximum cutting speed is at the outer diameter Do
and is obtained from the expression V = π DoN
Thus,
Vmax = (π) (12) (400) = 15072 mm/min
The cutting speed at the inner diameter Df is
Vmin = (π) (11) (400) = 13816 mm/min
b. From the information given, the depth of cut is
d = (12 – 11) / 2 = 0.5 mm , and the feed is f = υ / Ν
f = 200 / 400 = 0.5 mm/rev
thus the material removal rate is calculated as
MRR = (π) (Davg) (d) (f) (N) = (π) (11.5) (0.5) (0.5) (400) = 3611 mm3
/min = 60.2 mm3 /s
c. The cutting time is
t = l / (f. N) = (150) / (0.5) (400) = 0.75 min
d. The power required is
Power = (4) (60.2) = 240,8 W

2. The part shown below will be turned in two machining steps.
In the first step a length of (50 + 50) = 100 mm will be reduced
from Ø100 mm to Ø80 mm and in the second step a length of
50 mm will be reduced from Ø80 mm to Ø60 mm. Calculate
the required total machining time T with the following cutting
conditions:
Cutting speed V=80 m/min,
Feed is f=0.8 mm/rev,
Depth of cut = 3 mm per pass.

SOLUTION:
V=80 m/min
f=0.8 mm/rev
The turning will be done in 2 steps. In first step a
length of (50 + 50) = 100 mm will be reduced from
Ø100 mm to Ø80 mm and in second step a length
of 50 mm will be reduced from Ø80 mm to Ø60 mm

3. The shaft shown in the figure below is to be
machined on a lathe from a Ø 25mm bar.
Calculate the machining time if speed V is 60
m/min., turning feed is 0.2mm/rev, drilling
feed is 0.08 mm/rev and knurling feed is 0.3
mm/rev.

Step 2
Turn Ø20 mm from Ø25 mm
Tm = L/FN
= 45/0.2 x 764
= 0.29 min

4. A batch of 800 workpieces is to be produced on a
turning machine. Each workpiece with length
L=120mm and diameter D=10mm is to be
machined from a raw material of L=120mm and
D=12mm using a cutting speed V=32 m/min and a
feed rate f=0.8 mm/rev. How many times we have
to resharpen or regrind the cutting tool?
In the Taylor’s expression, use constants as n=1.25
and C=175.

Slab-milling operation, in which a rotating cutting
tool removes a layer of material from the surface
of workpiece.
End-milling operation, in which a rotating cutter
travels along a certain depth in the workpiece and
produces a cavity.

Up milling and
down milling
• When the feed and the cutting
action is in the opposite direction
the operation is called up milling.
• When the feed and cutting
action are in the same
direction the operation is
called down milling.
• In down milling there is
tendency of the job being
dragged into the cutter, up
milling is safer and commonly
done.
• However down milling results
in a better surface finish and
longer tool life.

The scheme of chip formation during plain slab milling using a straight
cutter is shown in the figure.
D= Diameter of the cutter N= rpm of the cutter
d=depth of the cut f= feed velocity

Since all the cutting
edges take part in
machining, a study of the
process is facilitated by
considering the action of
only a single tooth.
If
f= feed velocity of a
table in mm/min
Then effective feed per
tooth in mm is f/NZ
N= cutter rpm
Z= number of teeth in
the cutter
Material removal rate per unit width= f d
λ
λ

It is seen from the figure
that the thickness of the
uncut material in front of
the cutting edge
increases gradually,
reaching a maximum
near the surface, and
again drops to zero
quickly.
If feed velocity is small as
compared with the
circumferential velocity
of the cutter then,
AB=AC Sin λ or
t1max = (f/NZ) Sin λ
Where
λ =angle included by the contact arc at
the cutter center O in radians
λ
λ

Consider triangle
OAT
Cos λ = OT/OA =
(D/2 – d)/ D/2
Hence
Sin λ = (1- Cos2 λ)1/2
= [1- (1-2d/D)2]1/2
= 2 (d/D) 1/2
Neglecting the higher order terms in d/D as it is normally very small.
Using this value of Sin λ in the expression of maximum uncut thickness we get
t1max = (f/NZ) Sin λ
t1max = 2f/NZ (d/D) 1/2
λ
λ

The cutting force
components FC and FT not
only change in direction
but also in magnitude as
the cutting edge moves
along the cutting surface.
When cutting with straight
cutter, there is no
component of the cutting
force along the cutter axis.
The average uncut
thickness can be taken as
half of the maximum value.
t1max = 2f/NZ (d/D) 1/2
t1av = f/NZ (d/D) 1/2

The average values FC
and FT can be
approximately found
using the average value
of uncut chip thickness.
Since FT acts in the
radial direction , it does
not produce any torque
and the arbor toque is
due to the component
FC.
Mmax = FC (D/2).
M= torque due to one
cutting tooth and varies
approximately as FC.
• The above figure shows the variation of
arbor torque with arbor rotation for the
action of only one single tooth.
• Now to get the over all torque (M ), the
moments due to all the teeth should be
properly superimposed. This leads to
three different possibilities.
1) λ<2π/Z 2) λ =2π/Z 3) λ >2π/Z
λ
λ

The figure shows the three
different possibilities, the
arbor torque corresponding
to each of the these are
shown.
The machining power can
be calculated by taking the
product of the arbor speed
and the average overall
arbor torque.
The average thrust force can
be considered to be acting
along the midradial line of
the work-cutter contact arc.
λ
λ
λ
λ
λ
λ

tm=Machining time = (lw +a)/f
lw = Length of the workpiece
a= approach length= [d(D-d)] 1/2

• Q: A mild steel block of 20mm width is being milled
using a straight slab milling cutter with 20 teeth,
50mm diameter and 10 degree radial rake. The feed
velocity of the table is 15mm/min and the cutter
rotates at 60 rpm. If the depth of cut of 1mm is used,
what will be power consumption. (Assume
coefficient of friction=0.5, and shear stress=400
N/mm2 .

• Q: Estimate the power required during the up
milling of a mild steel block of 20mm width using
straight slab milling cutter with 10 teeth, 75mm
diameter, and 10 degree radial rake. The feed
velocity of the table is 100mm/min, the cutter
rotates at 60 rpm and the depth of cut is 5mm.

The cutting operation
in shaper is
intermittent in nature
and takes place during
the forward stroke.
During the return of
the tool the feed
motion is is provided
when there is no
cutting action.
In an actual cutting
operation the major
parameters are:
N= Stroke per unit
time
S= Stroke length
R= Quick return ratio (displacement/stroke)
D= depth of cut and the tool angles.

The uncut thickness
and width of the cut
is given by the
relations
t1 = f cosψ
w=d / cosψ
Ψ = primary
principal cutting
edge angle
α = normal rake
angle

The figure shows the
cutting and thrust
components of the
force.
The cutting
components Fc
acts against v and FT
acts perpendicular to
the transient surface.
FT can be resolved into
two components Ff
(feed component) and
Fn (component normal
to the machined
surface)
Ff =FT cosψ
Fn =FT sinψ
MRR= LdfN
L= length of the job
N= number of cutting strokes per unit time

The cutting time is given by
Tm H/d x B/f x 1/N
B=breadth of the job
H= the total depth by which the work surface to be lowered
d= depth of cut
f=feed
N=cutting stroke per unit time
Since the cutting speed changes during the cutting stroke, the average
cutting speed v is given by
v=[NS(1+R)]/2
where
S=stroke length
R= quick return ratio
N= number of strokes per unit time

• Q: Determine the three components of the
machining force when shaping a cast iron block
with depth of cut = 4mm, feed= 0.25 mm/stroke,
normal rake angle of the tool= 10 degree,
principal cutting edge angle=30 degree,
coefficient of friction between chip and tool=0.6,
and ultimate shear stress of cast iron=340N/mm2
.If the operation takes place with 60
stroke/min,what will be the power consumption if
the length of the job is 200mm.

Grinding
• It is the process of removing material by the abrasive action of
revolving wheel from the surface of the work piece, in order to
achieve required dimension and surface finish.
• The wheel used for this purpose is called grinding wheel.
• Grinding wheel consists of sharp grains called abrasives held
together by bonding material.
• The grains actually taking part in the material removal process
are called the active grains.
• Generally the sharp edges of the grains wear out and become
blunt.
• This results in large forces on the active grains during
machining.
• When the cutting edge is too blunt and the force is sufficiently
high, the grain may either get fractured or break away from the
wheel.

Mechanics of grinding
• In the analysis of grinding process, all grains are assumed to be
identical.
• Two different types of grinding operations namely plunge grinding
and surface grinding will be considered for analysis.
• In plunge grinding operation a job of rectangular cross-section is
being fed radially at the feed rate f (mm/min).
• The uncut chip thickness per grit ( t1 ) can be expressed as
t1 = f/ZN.
Z=number of active grains per revolution in one line
N=rpm of the wheel

b‘ = average grain width of cut in mm
t1 = uncut thickness per grit

The number of grains /revolution/line (Z) is given
by:
Z=πDC b'
D = diameter of the grinding wheel
b‘ = average grain width of cut in mm
C = the surface density of active grains (mm-2
Also
t1 = f/πDC b‘ N
t1 = [f/πDNC rg]1/2
rg can take the value between 10 and 20
The uncut sections have approximately triangular cross
section. The ratio rg =b‘/ t1 since b‘= t1 rg

Once t1 is estimated, the value of specific energy UC can
be determined and the power consumption is
W= A f UC /60
• A= cross section area of the job (mm2)
Force per single grit
Fc = 60000 W/ πDACN
Fc = [1000 f UC / πDCN] N
Uc = Uo t1
-0.4 Uo depends on materials, for
steel it is 1.4.
MRR= lxbxf mm3

• Q: Estimate the power requirement during plunge
grinding of a mild steel prismatic bar (20mmx15mm)
using a grinding wheel with 3 grits/ mm2. The
diameter of the wheel is 250 mm and the wheel
rotates at 2000 rpm. The plunge feed rate is
5mm/min.

Surface grinding The uncut
thickness and
width vary and
the maximum
value are:
t1max and
b'max
The average
values may be
taken as one-
half of these.
λ

The average length of
the chip is given as:
l=(D/2) λ
But
Cos λ = (D/2 –d)/D/2
Cos λ =1-(2d/D)
d=depth of cut
λ
Cos λ can be
expanded
(keeping only
two terms
since λ is
generally
small) as
Cos λ =1- λ2 /2
Hence
λ = 2 (d/D)1/2
Substituting
this in the
value of l we
obtain
l= (dD)1/2

The total volume of material removed per unit time = fdB
Where: f=feed, D=depth of cut, b=width of cut in mm
The average volume per chip can be approximately taken as:
1/6 (l t1max b’ max )
The number of chips produced per unit time is: πNDBC
Taking rg = b’ max / t1max
We have
(πNDBC) x (1/6 rg l t 2
1max ) = fdB
or
t1max = [6f/πNDCrg(d/D)1/2 ] 1/2
One half of this value is to be taken as the mean uncut thickness.

The power consumption can be taken as:
W = (BfDUc )/60 W
Total Tangential Force
Fc = 60000 W/ π DN
Fc = 60000 BfdUc / πDN 60
Fc = 1000 BfdUc/ πDN
N= wheel RPM
The number of grit actively engaged is: CBl=CB(Dd)1/2
The average force per grit is given by:
F’c = 60000 W/ π DNCB(Dd)1/2

Q. Estimate the grinding force during surface grinding of a
25mm wide mild steel block with a depth of cut of 0.05
mm. The diameter of the wheel is 200 mm and the wheel
rotates at 3000 rpm. The number of grits/mm2 is measured
and found to be 3. The feed velocity of the table is
100mm/min.

Finishing operations
Honing operation
– The honing operation is used for finishing the inside surface
of a hole.
– The honing tool consists of a set of aluminum–oxide or
silicon- carbide bonded abrasives called stones.
– Abrasives in the form of sticks are mounted on the mandrel
which is then given reciprocating (along the hole axis)
superimposed on a uniform rotary motion.
– The grit size varies from 80 mesh to 600 mesh.
– Depending on the work material, the honing speed may vary
from 15 m/min to 60 m/min, and the honing pressure lies in
the range 1-3 N/mm2.

• The tolerance and finish achieved in this operation are of the
order of 0.0025mm and 0.25μm respectively.
• Honing is also done external cylindrical or flat surfaces and to
remove sharp edges on cutting tools and inserts.
• A fluid is used to remove chips and to keep temperatures.
• If not done properly, honing can produce holes that are
neither straight nor cylindrical , but with shapes that are
bellmouthed wavy or tapered.

Lapping operation
• Lapping is another operation for improving the accuracy and
finish.
• It is accomplished by abrasives in the range of 120-1200 mesh.
• A lap is made of material softer than the work material.
• In this process straight, narrow groves are cut at 90 degree on
the lap surface and this surface is charged by sprinkling the
abrasive powder.
• The workpiece is then held against the lap and moved in
unrepeated paths.
• The material removal about 0.0025 mm and the lapping
pressure is generally kept in the range of 0.01-02 N/mm2
depending upon the hardness of the work material

Polishing
• Polishing is a process that produces a smooth, lustrous surface finish.
• Two basic mechanism are involved in the polishing process.
• a) Fine-scale abrasive removal and b) softening and smearing of the surface
layers by frictional heating during polishing.
• Polishing is done with disks or belts made of fabric, leather that are coated
with fine powder of aluminum oxide or diamond.
• Buffing is similar to polishing , with the exception that very fine abrasives
are used on soft disks made of cloth.
• The abrasives are supplied externally from the stick of abrasive compound.
• Polished parts may subsequently be buffed to obtain an even finer surface
finish.

Electropolishing
• Mirror like finishes can be obtained on metal surface by
electropolishing, a process that that is the reverse of
electroplating.
• Because there is no mechanical contact with the workpiece,
this process is particularly suitable for polishing irregular
shapes.
• The electrolyte attacks projections and peaks on the workpiece
surface at a higher rate than the rest of the surface, producing a
smooth surface.

Surface treatment, coating and cleaning
Surface treatments are performed in order to:
• Improve resistance to wear, erosion, and indentation.
• Control friction
• Reduce adhesion (electrical contacts)
• Improve lubrication
• Improve resistance to corrosion and oxidation
• Improve fatigue resistance
• Rebuild surfaces on worn components
• Modify surface texture
• Impart decorative features (color)
Several techniques are used to impart these characteristics to
various types materials.

Mechanical surface treatment and coating
• Several techniques are used to improve the properties of
finished components.
Shot peening:
• The workpiece surface is hit repeatedly with a large large
number of cast steel glass or ceramic balls.
• This action causes plastic surface deformation, at a depth up to
1.25mm using ball size ranging from 0.125mm to 5mm in
diameter.
• Shot peening causes compressive residual stresses on the
surface, thus improving the fatigue life of the component.
• This process is used extensively on shafts, gears, springs etc.

Water jet peening
• A water jet of water at a pressure as high as 400MPa
impinges on the surface of the workpiece, inducing
compressive residual stresses.
• The water jet peening process has been used successfully
on steels and aluminum alloys.
Laser peening
• In laser peening the workpiece surface is subjected to laser
shocks from high powered lasers.
• This surface treatment process produces compressive
residual stress layers that are typically 1 mm.
• Laser peening has been applied successfully to jet engine
fan blades and material such as titanium and nickel alloys.
• The laser intensities necessary for this process are on the
order of 100 to 300 J/cm2

Roller burnishing
• Also called surface rolling, the surface of the component is cold worked
by a hard and highly polished roller or rollers.
• This process is used on various flat , cylindrical or conical surfaces.
• Roller burnishing improves surface finish by removing scratches, tool
marks and pits.
• All types of metals, soft or hard can be roller burnished.
Cladding
• In cladding , metals are bonded with a thin layer of corrosion-resistant
metal through the application of pressure, using rolls.
• Atypical application is cladding of aluminum (Alcad), in which a corrosion
–resistant layer of aluminum alloy is clad over aluminum alloy body,
usually in sheet or tubular form.
• Other applications are steel clad with stainless steel or nickel alloys.

Case hardening and Hard facing
Case hardening
• Case hardening processes induce residual stress on surface.
• The formation of martensite during case hardening cause s
compressive residual stress on surface.
• Such stress are desirable, because they improve the fatigue life
of components by delaying the initiation of fatigue cracks. Etc.
• Some of the case harding process are carburizing,
carbonnitriding, cyaniding, nitriding, flame hardening
Hard facing
• In hard facing, a relatively thick layer , edge or point wear
resistant hard metal is deposited on the surface using any of the
welding technique.
• Hard coting of tungsten, carbide or chromuium and
molybdenum carbide can be deposited by using electric arc.
• Hard facing alloys can be used as electrode, rod wire or powder.
• Typical application for these alloys are valve seats, oil well
drilling tools, and dies for hot metalworking.

Thermal spraying
• In thermal spraying processes coating (various metals
and alloys, carbides and ceramics) are applied to metal
surfaces by a spray gun with a stream of oxyfuel flame,
electric arc plasma arc.
• The coating material can be in the form of wire, rod, or
powder and the droplets or particles impact the
surface at speeds in the range of 100 to 1200 m/s.
• Typical application includes aircraft engine
components,, structures, storage tanks, and
components which require resistance to wear and
corrosion.

Vapor deposition
• Vapor deposition is a process in which the work
surface is subjected to chemical reaction by gases
that contain chemical compounds of the material
to be deposited.
• The coating thickness is usually a few μm.
• The deposited material can consist of metals,
alloys, carbides, nitrides, borides, ceramics, or
oxides.
• The surface may be metals, plastic, glass or paper.
• Typical application of vapor deposition are the
coating of cutting tools , drills, milling cutters,
punches, dies and wear surface.

Anodizing
• Anodizing is an oxidation process in which the
workpiece surface are converted to hard and porous
oxide that provides corrosion resistance and decorative
finish.
• The workpiece is an anode in an electrolytic cell
immersed in an acid bath, which results in a chemical
adsorption of oxygen from the bath.
• Organic dyes of various color can be used to produce
stable, durable surface finish.
• Typical application of for anodizing are aluminum
furniture, and utensils, architectural shapes, picture
frames, etc.

Diffusion coating
• Diffusion coating is a process in which an alloying
element is diffused in the surface thus altering its
properties.
• The alloying elements can be supplied in solid,
liquid, or gaseous state.

Electroplating, electroless plating and
electroforming
• In electroplating, the workpiece (cathode) is plated with different
metal (anode)while both are suspended in a bath containing a
water base electrolyte solution.
• All metals can be electroplated; electrolyte thickness can range
from few atomic layers to a maximum of about 0.05mm.
• Chromium, nickel, cadmium, copper, zinc, and tin are the common
plating materials.
• Electroplating is used copper plating aluminum wire, chrome
plating hardware, tin plating copper electric terminals.
• Electroless plating is done by chemical reaction and without the
use of an external source of electricity.

• The most common application utilizes nickel although copper is
also used.
• In electroless nickel plating, nickel chloride is reduced using
sodium hypophosphite as a reducing agent, to nickel metal, which
is then deposited on the workpiece.
• Cavities, recesses, and the inner surfaces of tubes can be plated
successfully.
• A variation of electroplating is electroforming, which actually is a
metal forming process.
• Metal is electrodeposited on a mandrel, also called mould or
matrix , which is then removed, thus coating itself becomes the
product.
• The electroforming process is particularly suitable for low
production quantities and is suitable for aerospace, electronic
applications.

Painting
• Because of its decorative and functional properties (such as
environmental protection, low cost, relative ease of application and the
range of available colors), paint is widely used as a surface coating.
• The engineering application of painting range from machinery to
automobile parts.
Paints are classified as:
• i) Enamels: produces a smooth coat and dry with glossy or semi glossy
appearance.
• Ii) Lacquers: which form a film by evaporation of a solvent
• iii) Water based paints: which are easily applied but have a porous
surface and absorb water, making them more difficult to clean then the
first two.
• Selection of particular paints depends on resistance to mechanical
action (abrasion, impact etc.) or to chemical actions ( acids, solvents,
detergents etc.)
• Common methods of applying paints are dipping, brushing and
spraying).

Cleaning Surfaces
• Cleaning involves the removal of solid, semi solid or liquid
contamination from a surface.
• Basically there are two types of cleaning processes
mechanical and chemical.
• Mechanical cleaning consists of physically disturbing the
contaminants, often with wire or fibre brushing, abrasive
blasting or steam jets.
• Many of these processes are particularly effective in
removing rust, scale and other solid contamination.
• Chemical cleaning usually involves the removal oil and
greese from the surfaces

127
Accuracy of Machining process depends upon:
• The precision of mounting of
– Work
– Tool
• Their accurate movement
For repeated identical work (in mass production)
• Reduction in
– Set-up time
– Clamping time
• Minimizes production time
• Jigs and fixtures

128
A jig or fixtures needs to provide the following functionality
tobeaneffectiveproductiondevice:
• Location
• Clamping
• Support
• Resistance to cutting forces
• Safety

Jigs and fixtures both
• Hold the work
• Support the work
• Locate the work
Jigs in addition
• Guide the cutting tool
Fixtures have
• Reference point for setting the cutting tool with
reference to the workpiece
129

• Jigs are designed for specific operations.
• Jigs are commonly used for making parts that contains
holes.
• Jigs are used for operations like drilling, reaming,
counter boring and tapping.
• They are light in weight.

• Fixtures are workpiece supporting devices
• The are used for holding and locating the workpiece but
not for guiding the tool.
• The are designed on the basis of machines on which the
operations are to be performed.
• They are heavy in weight.
• Turning
• Milling
• Grinding
• Shaping
• Planning etc
Fixtures

141
Functional surfaces
• It is necessary to understand the functional surfaces
present in a component and their utility from the
standpoint of its manufacture.
• The essential reason for machining is that these surfaces
are to be mating with surfaces machined in the other
part.
• It is always necessary to consider the fact that machining
increases the final cost of the component and hence
should be minimized based on the following as far as
possible:
• Location surfaces
• Support surfaces
• Clamping (holding) surfaces

Location surfaces
– Required to be correctly identified
– Generally identified through
• Baselines in dimensioning
• Already finished surface
142

143
Support surfaces
– Surface in the end
– Not necessary to provide support for all operations
– May be provided through clamping at critical points
– Surface where maximum deflection under action
– Should not disturb the location/locators
– Should not interfere with loading/unloading

Clamping (holding) surfaces
– Surfaces should provide
• Easy clamping
• Shortest possible time
– Generally opposite to locating surface
– If not possible, alternate surfaces can be chosen
– Machined surfaces should be avoided
– Clamping surface area should be large
– Surfaces should have enough rigidity
100

• Press working has been defined as chipless
manufacturing process by which component are made
from sheet metal.
• Press working operations are caused out with help of a
metal forming machine called press which shear or
forms the component by applying force.
• The main features of the press include a stationary bed
and a powered ram can be driven towards the bed or
away from the bed to apply force or required pressure
for various metal forming operations.
• The ram is equipped with a punch or a set of punches
which have the shape of the job to be produced while
the die block is attached to the bed.

• Workpiece are produces or formed as the punch
descends onto the die block.
• Die – punch combination is used for the process to
impart the desired shape to the blank.
• Press tool operations of sheet metal is by far the
cheapest and fastest method to complete
manufacturing of component.
• Press working is used in large number of industries
like automobile industry, aircraft industry, lock
industry, telecommunication, electrical appliance,
utensils etc.

Classification of presses.
Classification on the basis of source of power.
• Manual Presses. These are either hand or foot operated
through levers, screws or gears. A common press of this
type is the arbor press used for assembly operations.
• Mechanical presses. These presses utilize flywheel
energy which is transferred to the work piece by gears,
cranks, eccentrics, or levers.
• Hydraulic Presses. These presses provide working force
through the application of fluid pressure on a piston by
means of pumps, valves, intensifiers, and accumulators.
• Pneumatic Presses. These presses utilize air cylinders to
exert the required force. These are generally smaller in
size and capacity than hydraulic or mechanical presses,
and therefore find use for light duty operations only.

Classification on the basis of number of slides
• Single Action Presses. A single action press has one
reciprocation slide that carries the tool for the metal
forming operation. It is the most widely used press for
operations like blanking, coining, embossing, and drawing.
• Double Action Presses. A double action press has two
slides moving in the same direction against a fixed bed. It
is more suitable for drawing operations, especially deep
drawing, than single action press.
• Triple Action Presses. A triple action press has three
moving slides. Two slides move in the same direction as in
a double – action press and the third or lower slide moves
upward through the fixed bed in a direction opposite to
that of the other two slides. This action allows reverse –
drawing, forming or bending operations against the inner
slide while both upper actions are dwelling.

Classification on the basis
of frame and construction
• Arch – Frame Presses.
These presses have their
frame in the shape of an
arch. These are not
common.
• Gap Frame Presses. These
presses have a C-shaped
frame. These are most
versatile and common in
use, as they provide un
obstructed access to the
dies from three sides and
their backs are usually open
for the ejection of
stampings and / or scrap.

Straight Side Presses. These
presses are stronger since the
heavy loads can be taken in a
vertical direction by the massive
side frame and there is little
tendency for the punch and die
alignment to be affected by the
strain.
Horn Presses. These presses
generally have a heavy shaft
projecting from the machine frame
instead of the usual bed. This press
is used mainly on cylindrical parts
involving punching, riveting,
embossing, and flanging edges.

Classification of dies
There is a broader classification of single operation dies and multi-
operation dies.
• (a) Single operation dies are designed to perform only a single
operation in each stroke of ram.
• (b) Multi operation dies are designed to perform more than one
operation in each stroke of ram.
Single operation dies are further classified as described below.
Cutting Dies
• These dies are meant to cut sheet metal into blanks. The
operation performed so is named as blanking operation.

Forming Dies
• These dies are used to change two shape of workpiece material by
deforming action. No cutting takes place in these dies.
Compound Dies
• In these dies two or more cutting actions (operations) can be
executed in a single stroke of the ram.
Combination Dies
• These dies are meant to do combination of two or more
operations simultaneously. This may be cutting action followed by
forming operation. All the operations are done in a single action of
ram.

Progressing Dies
• These dies are able to do progressive actions (operations) on the
workpiece like one operation followed by another operation and
so on. An operation is performed at one point and then workpiece
is shifted to another working point in each stroke of ram.

Press operations: Shearing
• Shearing is a cutting operation used to remove a blank of required
dimensions from a large sheet.
• A metal being sheared between a punch and a die.

• Shearing begins with formation of cracks on both sides of the
blank, which propagates with application of shear force.
• The fracture progresses downwards with the movement of upper
shear and finally results in separation from parent strip.
• Shearing a blank involves plastic deformation due to shear stress.
Therefore, the force required for shearing is theoretically equal to
the shear strength of blank material.

The shearing operations are:
• Punching
• Blanking
• Notching
• Piercing
• Perforating
• Parting
• Nibbling
• Trimming
• Shaving

Punching/Blanking
Punching or blanking is a process in
which the punch removes a
portion of material from the larger
piece or a strip of sheet metal.
If the small removed piece is
discarded, the operation is called
punching, whereas if the small
removed piece is the useful part
and the rest is scrap, the operation
is called blanking.

Notching
• Punching the edge of a sheet,
forming a notch in the shape of
a portion of the punch.
• It usually removes a small
portion from edge or side of a
sheet.

Piercing
The typical operation,
in which a cylindrical
punch pierces a hole
into the sheet.
Sometimes called
Punching.
Identical to Blanking,
only the punched out
portion which is coming
out through die is
scrap.
Normally Blanking
follows a piercing
operation

• Trimming:
When parts are produced by die casting or drop forging, a
small amount of extra metal gets spread out at the parting
plane. This extra metal, called flash, is cut – off before the
part is used, by an operation called trimming.
• Shaving:
Shaving operation is a finishing operation where a small
amount of metal is sheared away from an already blanked
part. Its main purpose is to obtain better dimensional
accuracy.

The forming operations are:
• Lancing
• Drawing
• Bending
• Embossing

Drawing
It is a cold drawing operation.
A process of making utensils, pressure
vessels, gas cylinders, cans, shells,
kitchen sinks, etc from blanks.
Similar to blanking except that the
punch and die are provided with the
necessary rounding at the corners to
allow smooth flow of metal during
drawing & to avoid shearing.
One of the widely used sheet metal
forming operations.
Cupping and Deep Drawing are two
operations.
Press operations: Forming

• Proper selection of a press is necessary for successful and
economical operation.
• Press is a costly machine, and the return on investment depends
upon how well it performs the job.
• There is no press that can provide maximum productively and
economy for all application.
• Hence when a press is required to be used for varying jobs,
compromise is generally made between economy and
productivity.
Important factors affecting the selection of a press are:
Size
• Bed and slide areas of the press should be of enough size so as to
accommodate the dies to be used.
• Stroke requirements are related to the height of the parts to be
produced.

Force and Energy
• Press selected should have the capacity to provide
the force and energy necessary for carrying out the
operation.
Press Speed
• Fast speeds are generally desirable, but they are
limited by the operations performed.
• Size, shape and material of workpiece, die life,
maintenance costs, and other factors should be
considered while attempting to achieve the highest
production rate at the lowest cost per piece.

Press selection
• Required force f for: blanking, piercing,
lancing, etc., is given by
» h = gage thickness, m
» ls = length to be sheared, m
» U= ultimate tensile strength 181

Press selection
Example:
Circular disks 50 cm in diameter are to be blanked from No. 6 gage commercial-
quality, low-carbon steel.
– thickness of 6 gage steel = 5.08 x 10-3 m
– ultimate tensile strength, U = 330 x103 kN/m2
required blanking force
f = 0.5 x (330 x 103) x (5.08 x 10-3) x (π x 50 x 10-2) = 1316.6kN
Table 9.3: 1750kN press
182

The clearance between the die and punch can be determined as
c = 0.003 t. p
where
t is the sheet thickness
p is the shear strength of sheet material
For blanking operation, die size = blank size, and the punch is made
smaller, by considering the clearance.
The maximum force, F required to be exerted by the punch to shear
out a blank from the sheet can be estimated as
F = t. L. p
where
t is the sheet thickness,
L is the total length sheared
p is the shear strength of the sheet material.

• Stripping force.
Two actions take place in the punching process–
punching and stripping. Stripping means extracting the
punch. A stripping force develops due to the spring
back of the punched material that grips the punch. This
force is generally expressed as a percentage of the force
required to punch the hole, although it varies with the
type of material being punched and the amount of
clearance between the cutting edges. The following
simple empirical relation can be used to find this force.
SF = 0.02 L.t
where
SF = stripping force, kN
L = length of cut, mm
t = thickness of material, mm

Example: A circular blank of 30 mm diameter is to be cut from 2 mm
thick 0.1 C steel sheet. Determine the die and punch sizes. Also
estimate the punch force and the stripping force needed. You may
assume the following for the steel : Tensile strength: 410 MPa ; shear
strength : 310 MPa
Solution:- For cutting a blank, die size = blank size = 30mm
Clearance = c = 0.003 t. p = 0.003 x t x p = 0.003 x 2 x 310 = 1.86 mm
Punch size = blank size – 2 clearance
= 30 – 2 x 1.86 = 26.28 mm
Punch force needed = L. t. p = π x 30 x 2 x 310 (L= πD)
= 58.5 kN
Stripping force needed = 0.02 L. t
= 0.02 x p x 30 x 2
= 3.77 kN

Important consideration for design of a die set
The following important points should be considered while designing
a die set:
• Cost of manufacturing depends on the life of die set, so
selection of material should be done carefully keeping
strength and wear resistant properties in mind.
• Die is normally hardened by heat treatment so design
should accommodate all precautions and allowances to
overcome the ill effects of heat treatment.
• Accuracy of production done by a die set directly
depends on the accuracy of die set components.
• Standardized components should be used as much as
possible.
• Easy maintenance should be considered. Replacement
of parts should be easy.

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