Fundamentals of Press Tool

Technology
Introduction :
It is related with press working
Chip less manufacturing process
 It works with sheet metal
 Also known as cold stamping.
 What is Sheet Metal?
• whose thickness is between 0.006(0.15 mm) and
0.25 inches(6.35 mm).
• Anything thinner is referred to as a foil and
thicker is considered as a plate.
• Sheet thickness is generally measured in gauge.
Greater the gauge number, thinner the sheet of
metal.
• Sheet metal can be cut, bent and stretched into
nearly any shape.
• Generally two types of operations are performed-
forming and cutting.
 Fundamentals of Press Tool
Technology
• Foil : Thickness is less than 0.20mm (0.006”)
t < 0.20mm
• Sheet : Thickness is from 0.20mm (0.006”)
to 6mm (0.25”)
0.20 < t < 6mm
• Plate : Above 6mm (0.25”)
t> 6mm
 Fundamentals of Press Tool
Technology
• Sheet and plate metal parts for consumer and
industrial products such as
– Automobiles and trucks
– Airplanes
– Railway cars and locomotives
– Farm and construction equipment
– Small and large appliances
– Office furniture
– Computers and office equipment
Advantages of Sheet Metal Parts

• High strength.
• Good dimensional accuracy.
• Good surface finish.
• Relatively low cost.
• Economical mass production for large quantities.
Sheet Metalworking Terminology
• Punch-and-die
- tooling to perform cutting, bending, and drawing
• Stamping press
- machine tool that performs most sheet metal
operations
• Stampings
- sheet metal products
 Sheet Metal Operations: -

 Bending  PerforaTing
 Shearing  niBBling
 Blanking  emBoSSing
 Punching  Shaving
 Trimming  cuToff
 ParTing  dinking
 SliTTing  coining
 lancing  deeP drawing
 noTching  STreTch forming
 roll forming
 Equipments Required
 Mechanical Press –
The ram is actuated using a flywheel.
 Stroke motion is not uniform.
 Hydraulic Press –
Longer strokes than mechanical presses, and
develop full force throughout the stroke.
Stroke motion is of uniform speed,
especially adapted to deep drawing operations
 PRESSES FOR SHEET METAL WORKING

• Classification of presses. Types of presses for sheet

metal working can be classified by one or a
combination of characteristics, such as

– source of power,
– number of slides,
– type of frame and construction,
– type of drive, and
– intended applications.
 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 arbour 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. These presses have better performance
and reliability than mechanical presses.
Classification on the basis of source of power.

• 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.
• The press has a fixed bed.
• 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.
• For this reason, its two slides are generally referred to
as outer blank holder slide and the inner draw slide.
 Classification on the basis of number of slides.

• The blank holder slide is a hollow rectangle, while the

inner slide is a solid rectangle that reciprocates within
the blank holder.
• The blank holder slide has a shorter stroke and dwells
at the bottom end of its stroke, before the punch
mounted on the inner slide touches the workpiece.
• In this way, practically the complete capacity of the
press is available for drawing operation.
 Classification on the basis of number of slides.
• Triple Action Presses. A triple action press has three
moving slides.
• Two slides (the blank holder and the inner slide) 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.
• Cycle time for a triple – action press is longer than for a
double – action press because of the time required for
the third action.
 Classification according to slides actuation
• The most common method of actuating the press slide
is with a ‘Crankshaft’.
• ‘Double Cranks’ are employed for wider presses and
some large presses have ‘Multiple cranks’.
• ‘Eccentrics’ are used where only short strokes of the
slide are needed.
• ‘Knuckle joints’ are used where short, powerful strokes
are needed.
Classification on the basis of frame & construction
• According to type of frame:
– Open Frame Presses.
– Closed Frame Presses.
• Open Frame Presses:
– This press is also known as ‘Gap Frame’ or ‘C’ frame press.
– The most common type press is ‘Open back inclinable C-type
frame press’ commonly known as OBI press.
– Its frame is inclined backward which facilitates removal of
scrap or parts by gravity through the open back.
– It ranges from 1 tonne bench press to floor presses upto 200
tonnes with strokes 90 to 120 per minute.
– Owing to their construction, open frame presses are less rigid
and strong and are useful mainly for operations on smaller
work.
Classification on the basis of frame & construction

• Closed Frame Presses:

– These presses have two upright columns on each side of the
die.
– They are stronger, more rigid and balanced than C-type frame
presses.
– These are suitable for heavier work.
– Work is fed either from the front or from the back of the
press into the die are.
– These presses can be of two designs :
• Arch frame press and
• Straight side frame press.
 Classification on the basis of frame & 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.
Classification on the basis of frame & construction
• 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 on the basis of type of Drive
• Press drives refer to the means of supplying power to the ram,
which can be Belts, Gears or Hydraulics.
• If belts are used, it is non-geared and is flywheel driven.
• If geared, it may have several arrangements, from single gear
drives to multiple-reduction gear drives that are used on the very
large presses.
 Classification on the basis of Suspension
Nearly every mechanical press transmits force from a
crankshaft, eccentric shaft or eccentric gear through
connecting rods to the press slide. The attachment of the
connecting rods to the slide is commonly referred to as the
suspension point

• ‘Suspension’ refers to the number of points of

attachment from the drive to the press slide.

• On small presses, there is only one from the crankshaft

to the slide.

• On large presses, there may be as many as four.

 CNC Turret Presses
• Numerically Controlled (NC) and Computerised
Numerical Control (CNC) punching machinery differs
from the conventional mechanical, hydraulic or
pneumatic presses in that the workpiece is
automatically placed under a basic punch that is
gripped by a turret bushing or adapter in a single
station.
• CNC manipulates the punch controlling number
electronically, performing such tasks as optimisation of
punching instructions and other kinds of number
juggling that earlier technology could not do.
 CNC Turret Presses
• The operation of a turret press FMS (Flexible Machining
Systems) consists of the following steps:
– Selecting the tooling for the job;
– Computerised nesting of the parts;
– Loading material;
– Loading tools into the storage carousel.
• The automatic tool changer has a capacity of up to 22
different tools of any size or shape.
• Tools return and retrieval are performed along with the
punching sequence.
• After parts are punched and cut, a trap door in the
machine table unloads all parts upto 45 cms x 67 cms
into the bins for convenient handling and sorting.
 Press Selection
• Important factors affecting the selection of a press are size,
force, energy and speed requirements.

• Size. Bed and slide areas of the press should be of enough

size so as to accommodate the dies to be used and to make
available adequate space for die changing and maintenance.
• Stroke requirements are related to the height of the parts to
be produced.
• Press with short stroke should be preferred because it would
permit faster operation, thus increasing productivity.
• Size and type of press to be selected also depends upon the
method and nature of part feeding, the type of operation,
and the material being formed.
 Press Selection
• Force and Energy. Press selected should have the
capacity to provide the force and energy necessary for
carrying out the operation.
• The major source of energy in mechanical presses is the
flywheel, and the energy available is a function of mass
of flywheel and square of its speed.
• Press Speed. Fast speeds are generally desirable, but
they are limited by the operations performed.
• High speed may not, however, be most productive or
efficient.
• 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.
 Mechanical versus Hydraulic Presses
Characteristic Mechanical Presses Hydraulic Presses
Does not depend upon slide
Force Depends upon slide position.
position. Relatively constant.
Stroke length Short strokes Long strokes,even as much as 3 m.
Slow. Rapid advance and
High. Highest at mid-stroke.
Slide speed retraction. Variable speeds uniform
Can be variable
throughout stroke.
Capacity About 50 MN (maximum) About 500 MN, or even more.
Full stroke generally required Adjustable, slide reversal
Control
before reversel. possible from any position.
Operations requiring maximum Operations requiring steady
pressure near bottom of stroke. pressure through-out stoke. Deep
Cutting operations(blanking, drawing. Drawing irregular shaped
Application
shearing, piercing, Forming and parts. Straightening. Operations
drawing ) to depths of about 100 requiring variable forces and /or
mm. strokes.
Advantages of Mechanical Presses over Hydraulic

• Lower capital cost.

• Lower maintenance cost.

• Faster operation.

• Higher punch slides speeds.

 Advantages of Hydraulic Presses

• Constant pressure can be maintained throughout the

stroke.
• Force and speed can be adjusted throughout the stroke.
• More versatile and easier to operate.
• More powerful than mechanical presses.
• Tonnage adjustable from zero to maximum.
• It is safe since it stops at a pressure setting.
 Press Feeding Devices
• Safety is an important consideration in press operation
and every precaution must be taken to protect the
operator.

• Material must be tried to be fed to the press that

eliminates any chance of the operator having his or her
hands near the dies.

• The use of feeding device allows faster and uniform

press feeding in addition to the safety features.
 Blank and Stamping Feeds

• Feeding of blanks or previously formed stampings to

presses can be done in several ways.
• Selection of a specific method depends upon factors like
production rate needed, cost, and safety considerations.

• Manual feeding . Feeding of blanks or stampings by hand is

generally limited to low production rate requirements which
do not warrant the cost of automatic or semi- automatic
feeding devices.
• Manual feeding, however, is accomplished with the use of a
guard or, if a guard is not possible, hand feeding tools and a
point – of – operation safety device.
• Some commonly used hand feeding tools are special pliers,
tongs, tweezes, vacuum lifters and magnetic pick – ups.
 Blank and Stamping Feeds
• Chute feeds . For feeding small blanks or stampings, simple
chutes are often used.
• The blank slides by gravity along rails in the bottom of the
chute.
• Slide chutes are designed for a specific die and blank and are
generally attached permanently to the die so as to reduce
setup time.
• Slide angle of 200 - 300 is sufficient in most cases.
• Chute feeds need barrier guard enclosure for operation
protection, with just enough opening in the enclosure for the
blanks to slide through to the die.
 Blank and Stamping Feeds
• Push feeds . These feeds are used when blanks need orientation in
specific relation to the die.
• Work piece is manually placed in a nest in a slide, one at a time,
and the slide pushed until the piece falls into the die nest.
• An interlock is provided so that the press cannot be operation
until the slide has correctly located the part in the die.
• To increase production rate, push feeds can be automated by
actuating the feed slide through mechanical attachment to the
press slide.
• Lift and transfer devices . In some automatic installations
vacuum or suction cups are used for lifting of blanks one at a time
from stacks and then moved to the die by transfer units.
• Separation of the top blank from a stack is achieved by devices
which are operated magnetically, pneumatically or mechanically.
 Dial Feeds
• Dial feeds consist of rotary indexing tables (or
turntables) having fixtures for holding workpieces as
they are taken to the press tooling.

• Parts are placed in the fixtures at the loading station

(which are located away from the place of press
operation) manually or by other means like chutes,
hoppers, vibratory feeders, robots etc.

• Such feeds are being increasingly used because of

higher safety and productivity associated with them.
 Coil Stock Feed
• Two main classifications of automatic press feeds for coil
stock are slide (or gripper) and roll feeds. Both of these may
be press or independently driven.

• Mechanical slide feeds. Press – driven slide feeds have a

gripper arrangement which clamps and feeds the stock
during its forward movement and releases it on the return
stroke.
• Material is prevented from backing up during the return
stroke of the gripper by a drag unit like a frictional brake.
• Grippers reciprocate on rods or slides between adjustable
positive stops to ensure accuracy.
• Slide feeds are available in a variety of sizes and designs.
These are generally best for narrow coil stock and short feed
lengths.
 Coil Stock Feed
• Hitch – type feed. This feed differs from press – driven
mechanical slide feed in that actuation is by a simple flat
cam attached to the ram or punch holder instead of by the
press.
• On the downward stroke of the ram, one or more springs
are compressed by the cam action, then on the upstroke, the
springs provide the force to feed stock into the die.
• These feeds are best suited for coil stock of small to medium
thickness and for relatively short feed progression.
• These are one of the oldest and least expensive feeding
devices still used very widely. Due to their low cost, they are
generally left permanently attached to the dies, thus
reducing setup time.
 Coil Stock Feed
• Pneumatic slide feeds. These feeds are similar to mechanical
slide feeds in that they have grippers or clamps that
reciprocate on guide rails or slides between adjustable
positive stops to push and / or pull stock into a die.
• However, these differ in that they are powered by an air
cylinder, with actuation and timing of valves by cam –
operated limit switches.

• These feeds are best for short progression, and find wide
applications in job shops because of their low cost and
versatility
 Roll Feed
• Roll feeds. In these feeds, coil stock is advanced by pressure
exerted between intermittently driven, opposed rolls which allow
the stock to dwell during the working part of the press cycle.
• Intermittent rotation (or indexing) of the feed rolls, with the
rolls rotating in only one direction, is accomplished in many ways.
• In one common design, the rolls are indexed through a one –
way clutch by a rack – and – pinion mechanism that is actuated by
an adjustable eccentric on the press – crankshaft.
• These feeds are available in several types and sizes to suit
almost any width and thickness of stock.
• Though their initial cost is slightly higher, their greater
durability and lower maintenance cost account for their extensive
use.
•
 Press Operations
 Sheet Metal operations done on a Press &
 Grouped in Two Categories
 Cutting and Forming
 Cutting: Stresses are above Ultimate Strength of
the sheet metal.
Forming : Stresses are below Ultimate Strength.
of the sheet metal.
LOAD Vs PUNCH
DISPLACEMENT
ZONES OF EDGES
 ZONES OF PART EDGES
• Prefered edges on cutting edge:
• Large Shear Zone with small burrs
• Rollover Zone (Zr):Caused by Plastic material deformation
• Shear Zone (Zs): Smooth and shiny area caused during
shearing
• Fracture Zone (Zf): Rough surface results, after material cracks
• Burrs Zone (Zb): Caused by plastic deformation
• Depth of Crack Penetration (Dcp) : Angle of fractured zone
depends mainly on clearance
• Secondary Crack: If cracks do not run towards each other, and
Material is sheared again
PUNCH & DIE
 EFFECT OF CLEARANCE
• Excessive Clearance:
– Reduces shear zone, increases fracture zone, will
result in tapered cut edge
• Less Clearance:
– Reduces fracure zone, increases shear zone, result in
less tapered cut edge (FINE BLANKING)
• Proper Clearance : Shear zone will be 1/3 of material
thickness , fracture zone (approx 2/3) will result less
tapered cut edge, little bit is roll over zone
 EFFECT OF CLEARANCE
• Excessive clearance will result in tapered cut
edge because for any cutting operation, the
opposite side of the material that the punch
enters after cutting, will be the same size as the
die opening.
• The width of the burnish zone is an indication
of the hardness of the material. Provided that
the die clearance and material thickness are
constant, the softer the material the wider will
be the burnish zone.
 Press Operations
 Cutting or Shearing :
 Blanking : Article punched out of sheet metal
 Punching: Hole is the desired product
 Notching : Cut from a edge of a Sheet
 Perforating : Generation of multiple holes on a sheet
 Trimming : Cutting unwanted material from the
periphery of previously formed component.
 Shaving : To have accurate dimensions by removing thin
strips
 Slitting : To produce lines in sheet & no scrape produced
 Lancing : It is a piercing operation in which the workpiece
is sheared and bent with one strike of the die.
Shearing

• Shearing is defined
as separating
material into two
parts.
• It utilizes shearing
force to cut sheet
metal.
Blanking
• A piece of sheet
metal is removed
from a larger piece
of stock.
• This removed piece
is not scrap, it is the
useful part.
Fine Blanking
• A second force is
applied underneath the
sheet, directly opposite
the punch, by a
"cushion".
• This technique
produces a part with
better flatness and
smoother edges.
Dies: -

Made up of tool
steel and used to cut
or shape material.
1. Simple die
2. Compound die
3. Combination die
4. Progressive die
 Dies and Punches
• Simple- single operation with a single stroke

• Compound- two operations with a single stroke

• Combination- two operations at two stations

• Progressive- two or more operations at two or

more stations with each press stroke, creates
what is called a strip development
Simple Die
• Simple dies or single
action dies perform
single operation for
each stroke of the
press slide.
• The operation may be
one of the cutting or
forming operations.
Compound Die
• In these dies, two or
more operations may
be performed at one
station.
• Such dies are
considered as cutting
tools since, only
cutting operations are
carried out.
Combination Die
• In this die also , more
than one operation may
be performed at one
station.
• It is different from
compound die in that in
this die, a cutting
operation is combined
with a bending or
drawing operation, due
to that it is called
combination die.
Progressive Die

• A progressive
has a series of
operations.
• At each station ,
an operation is
performed on a
work piece
during a stroke
of the press.
Cutting Die
 Press Operations-Cutting
 Blanking : Article punched out of sheet metal
Punching: Hole is the desired product
Press Operations-Cutting
Press Operations-Cutting
Notching : Cut from a edge of a Sheet
Press Operations-Cutting
Generation of multiple holes on a sheet
Press Operations-Cutting
Press Operations-Cutting
Press Operations-Cutting
Press Operations-Cutting
 Press Operations-Cutting
To produce lines in sheet & no scrape produced
Press Operations-Cutting
 Press Operations-Cutting
Nibbling : Punching a series of small holes along the path
to generate a large cut-out shape.
Lancing

Creating a partial cut

in the sheet, so that
no material is
removed. The
material is left
attached to be bent
and form a shape,
such as a tab, vent,
or louver.
Shaving

Shearing away minimal

material from the edges of a
feature or part, using a
small die clearance. Used to
improve accuracy or finish.
Tolerances of ±0.025 mm
are possible.
Dinking

Dinking - A specialized
form of piercing used for
punching soft metals. A
hollow punch, called a
dinking die, with beveled,
sharpened edges presses
the sheet into a block of
wood or soft metal.
 PRESS TOOL DESIGN
• Requirements of Press Tool Design
– Dimensional accuracy and surface finish of
stampings should be as per DRAWING &
Specification
– Easy to replace while punch & die worn out
– Standard components to be used during assembly
– %age of Material Utilisation=
(Total area of blank cut / Area of uncut strip)x100
i.e. the value to be 70% - 80%
 STRIP LAYOUT
Bridge Gap (BG)= t + 0.015h, Here t= Sheet Thickness, h= Ht. of
Comp.
Pitch (s) = Component width + BG =D+BG
No of Blanks (N) can be produced from one length of stock
= (L – b) / s, Here ‘b’ is the front bridge.
Scrap remain at end (y) = L – (Ns+b)
Material Scrap bridge
Thickness (t) (b) mm
mm
Upto 0.8 0.8
0.8 to 3.2 t
above 3.2 3.2
TERMS USED IN STRIP LAYOUT
Pitch
Distance between two consecutive operations on a strip.

Scrap bridge
This is the portion of the material remaining after blanking
operation between one edge of the strip and the cutout portion.
The portion of material remaining between the two adjacent
openings after blanking is also called as the scrap bridge.

Front Scrap
This is the scrap bridge on that edge of the strip which is
towards the operator.

Back Scrap
This is the scrap bridge on that edge of the strip which is
away from the operator
EXAMPLE:

Calculate the economy factor to punch the mild steel

washer in single row feeding. Outside diameter is
30mm, Inside diameter is 18mm and Thickness is 2mm
Scrap bridge width (b) is = 1.2 s. , where s = sheet thickness
Scrap bridge width (b) = 1.2 x 2
=2.4 mm
Pitch = D + b = 30 + 2.4 = 32 mm
Strip width = D+ 2b = 30 + 4.8 = 34.8 mm
Number of rows = one
Area of blank = Л D²
4
= Л 30²
4
= 706.65 mm²

Area of blank x No. of rows x 100

pitch x strip width
=(706.65 x 1) / (32 x 34.8) = 63.45%
Calculate the economy factor to punch the same washer in
double row feeding
Single row one pass layout

• This is the most popular way of laying out the strip.

• The blanks are arranged in a single row.

• The strip is passed through the tool only once to punch

out the blanks from it.

• There are two possible ways of laying out this strip.

• Narrow run.

• Wide run.
WIDE RUN

• Wide run is more desirable due to the following reasons.

• Shorter advance distance of the strip feeding promotes easy
• More" blanks could be produced from a given length of strip
compared to narrow run.
• Fewer number of strips are to be handled to produce a given
number of blanks.
• Narrow run is used when the grain direction of the piece part has
importance.
BLANKS HAVING AT LEAST TWO STRAIGHT PARALLEL
EDGES.
• In such cases the strip width should be equal to the distance
between the parallel sides.
• The blanks are produced by a cut off or parting operation.
• If the blank has got two sets of parallel sides, a cut off operation is
sufficient to produce the blanks.
• But if the blank has got only one set of parallel sides, these sides
become the sides of the stock strip and the other non-parallel sides
are produced by a parting operation.
STRIP LAYOUT FOR CUT OFF AND PARTING
• Cut off punch cuts with only one edge.
• No scrap is produced.
• A parting punch cuts with two opposite edges thereby producing a
scrap.

NOTCHING
• Notching is a cutting operation for cutting off small portions from
the edge of a strip or a pre blanked component.
STRIP LAYOUT FOR CUT OFF
• Cut off punch cuts with only one edge.
• No scrap is produced.
• A parting punch cuts with two opposite edges thereby
producing a scrap.
 CUTTING FORCE
• Max cutting force Fmax in Newton needed to
shear the material is equal to the product of
sheared area and shear strength of material
Τs. For a circular blank diameter D mm and of
thickness t mm,
• the cutting force Fmax = πDt x Ts N
= P.t x Ts N
 2. Center of die pressure

The die pressure should be centered on a vertical

line passing through the specific point that defines
the resultant force of the punching and blanking
forces.
• Mathematical solution
n
X,Y=coordinates of the center
•  Li xi
L x  L 2 x 2  ...  L n x n
of the die pressure
X  i 1
 1 1 xi,yi=coordinates of the center
n
L 1  L 2  ...  L n

i 1
Li
of gravity of a partial length
n of cut edge
 Li yi
L 1 y 1  L 2 y 2  ...  L n y n Li=partial length of cut edges
Y  i 1

n
L 1  L 2  ...  L n
i 1
Li
 CENTER OF PRESSURE
• X & Y are the distance to centre of pressure from x & y axis
• Therefore , Center of pressure (CP) will be
Element l x y lx ly
1 10 5 0 50 0
2 1.25 10 0.625 12.5 .781
3 6.25 6.875 1.25 42.968 7.812
4 7.5 3.75 5 28.125 37.5
5 1.25 3.125 8.75 3.906 10.935
6 7.5 2.5 5 18.75 37.5
7 2.5 1.25 1.25 3.125 3.125
8 1.25 0 0.625 0 0.781

Ʃl = 37.5, Ʃlx = 159.375, Ʃly = 98.437, Therefore,

X = (Ʃlx / Ʃl) = 159.375/37.5 = 4.25cm =42.5mm
Y = (Ʃly / Ʃl) = 98.437/37.5 = 2.625cm =26.25mm
Bending

• Bending is a metal
forming process in which
a force is applied to a
piece of sheet metal,
causing it to bend at an
angle and form the
desired shape.
 BENDING
• METAL MOVEMENT : Movement of unstressed
sheet metal from one plane to another plane.
• Grain Direction :
• Bend Axis:
• Position of Bend Axis:
– Parallel to Grain Direction
• Moderate bend with larger bend radius.
• Perpendicular to Grain Direction
• Sharp bend with narrow radius (upto sheet
thickness)
 BLANK LENGTH
• Flat Blank Length Calculation
– Neutral Plane Method
– Subtracting Constant Method “X”
– Correction Factor Method “Y”
 BLANK LENGTH
• Flat Blank Length Calculation
– Neutral Plane Method
• Position of NP (Ci) from inner surfce based Bend
Radius (Rb)
• Rb is smaller than 2T, then Ci = 0.33T
• Rb is btw 2T to 4T, then Ci = 0.40T
• Rb is greater than 4T, then Ci = 0.50T
– First find position of Ci , then calculate the overall
length
NEUTRAL PLANE METHOD
 SUBSTRCTING CONSTNT METHOD
“X”
• In the Table
– Sheet Thickness is at Horizontal Axis
– Bend Radius at Vertical Axis
• Let Bend Radius is 2mm nd sheet thickness is
1.5mm, then from table “X” = 2.9
• Add the outer length, then subtract factor “X”
SUBSTRCTING CONSTNT METHOD
 CORRECTION FACTOR “Y”
• To find factor “Y” three things to find
• First find out the ratio of Rb /T, placed in
Horizontal Axis
• Then find out the factor “Y” from Vertical Axis
• Exmple : Let Rb = 2.1mm and T= 1.5, then Rb
/T=1.4 then “Y” = 0.9
• The Table is made after extensive
experimentation
CORRECTION METHOD “Y”
Drawing
Deep Drawing
• Deep drawing is a
metal forming process
in which sheet metal is
stretched into the
desired shape.
• A tool pushes
downward on the sheet
metal, forcing it into a
die cavity in the shape
of the desired part.
 Drawing
• Radius of Draw die (Rd): 4 to 10 times of sheet
thickness.
• While Rd is small leads to resistance to flow of
metal, tearing of it
• While Rd is large leads to wrinkle in the
component
• Radius of Draw punch (Rp): 4 times of sheet
thickness. Excessive leads to buckel of sheet
material
• Draw Clearance: 1.1 to 1.25 times the sheet
thickness
 Drawing
• Drawing Speed of Punch:
– Punch travels downwards to force the blank into
the die cavity
• Ram speed is critical because:
– It initiate plastic deformation
– Internal inertia of the work material must be
overcome
– Sufficient punch travel time to be given to
overcome rupture of material.