Process Knowledge Press Tools
Pressing process
Pressing Moulding Casting Welding Forging Machining
Topics to be covered
Sheet metal Applications
Different sheet metal operations
Elements of a Press Tool
Functions of each element
Types of Press Tool
Cutting Clearance
Cutting Force
Invention of printing press
Sheet metal Processing
(Pressing process)
Pressing process
Definition of pressing process
It is the process by which the sheet metal is pressed (formed, pierced,
blanked, bent) to get the required shape and size
General press part application
2 WHEELER
WHEEL RIMS> PETROL TANKS >
FRAME >
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Pressing process
General press part application
Car body
Fenders
Doors
Gears
Cams
Links
Levers
Keys
Hinges etc.
Why Sheet metal & Pressing process ?
Ease of manufacture & less
process complexity
Thin sections can be produced as
low as 0.2 mm
High productivity & Cost effective
Can be easily fabricated by joining
technology
Superior strength and good
aesthetics if painted / plated
Shearing
It is a method of cutting sheets without forming chips
The material is stressed in a section which lies parallel to the forces
applied by SLITTING or SHEARING blades
SHEARING
SLITTING
7
Shearing
It is a method of cutting sheets without forming chips
The material is stressed in a section which lies parallel to the forces
applied ( by means of shearing blades or Punch & Die )
Punch
Punch
Sheet
Sheet
Die
Critical stages of shearing
There are three stages of
shearing
Penetration Fracture
Plastic deformation
Plastic
Penetration deformation
Fracture
Peak load
Punch
Stress
Sheet
Die
time
Types of Pressing operation
There are as many as 29 pressing operations.
Broadly classified as Cutting operation and Forming operation
Cutting operation Forming operation
Blanking Piercing Bending Forming
Fine blanking Cutting off Drawing Flaring
Parting off Trimming Embossing Coining
Shaving Perforating Extrusion Bulging
Lancing Dinking Curling Swaging
Broaching Notching Planishing Rolling
Nibbling Louvering Ironing Flaring
Flanging
Types of Pressing operation
Few general pressing operations are
Pressing process
Blanking Piercing Trimming Fine Parting
Blanking off
Bending Forming Drawing Embossing Flaring
Etc.,
What is Blanking ?
Blanking is a process of producing flat stampings. The entire
periphery is cut and cut out piece is called the blank
The material is stressed beyond its ultimate strength between two
cutting edges
Blanking
Punch punch
Sheet
Scrap
Die
Output
product
What is Piercing ?
It is also a shearing operation similar to the blanking process.
The difference between Blanking and piercing is,
In blanking, the cut out piece is the required material &
In piercing, the cut out piece is scrap material / slug.
Piercing Blanking
punch punch
Scrap
Scrap Required
part
Input Process - 1 Process - 2
raw material Piercing operation Blanking operation
What is Cutting off ?
A cutoff operation creates a part
from the sheet stock with a single
cut.
Each cut separates another part
Cutoff lines may be straight,
curved, or jagged
Why cutting off operation ?
No material scrap in Cutoff
operation
What is Cutting off ?
What is Parting off ?
Parting is very similar to a cutoff,
except two simultaneous cuts are
required instead of one.
A parting operation leaves a
small amount of scrap between
blanks
Why Parting off operation ?
Material saving at the sides
compared to Blanking operation
What is Parting off ?
Comparison
cutting off parting off
Slug
What is Shaving operation?
Shaving finishes a previously cut
edge by shearing off the small
amount of the remaining rough
portion
The cutting clearance between
punch and die will be less than the
ordinary blanking which lead to
shaving of metal.
Why Shaving operation ?
Shaving increases accuracy and
smoothness.
Alternate to fine blanking process
for certain parts
What is Trimming operation ?
It is a shearing operation which
removes the excess unwanted
material from a drawn part
Why Trimming operation ?
To remove the excess drawn part
to get desired shape and clean
finish part
What is Trimming operation ?
What is Trimming operation ?
Drawing Trimming
Scrap
What is the operation needed to produce this part?
What is Lancing operation?
Shearing an interior portion of the
sheet to create a bent tab that
remains attached on one end is
Lancing
What is Notching operation?
What is Notching operation ?
Notching
What is Notching operation?
Notching removes a portion of
metal from the side.
In this example, notch appears as
part of the outer edge of the final
blank.
What is Bending operation?
It is the straining of metal
around a straight axis, with very
little change in thickness
During bending, the inside of the
bend compresses along the axis
of bend & the outside of the bend
stretches instead.
Metal flow is uniform along the
bend axis
What are the types of Bending operation?
Two main methods for sheet bending are
V-bending
Edge bending
What is Spring back?
Air bending V-Die bending U-Die bending Bottoming Coining
Wiping die bending Double die bending Rotary bending
Bending operations
Simple BENDING Complex
What is Forming operation?
It is similar to bending except the
line of bend is along the curved
axis instead in a straight line.
The metal flow is not uniform as
in bending and it depends on the
shape of the component.
What is Drawing operation ?
What is Drawing operation ?
It is the process used for making hollow cylindrical shapes from a
flat sheet metal
During drawing the sheet experiences a variety of forces and
severe plastic deformation
Blanking Drawing
Drawing Tool
What is Embossing operation?
Embossing compresses sheet
metal against a patterned die in
order to create a raised surface
In embossing the upper and lower
die shapes match
No thickness variation in part
Why Embossing operation ?
Creating ribs by embossing
add strength to the sheet metal
What is Coining operation?
It is similar to embossing
The key difference with embossing
is in the shape of the die. The
upper die and lower die shapes
does not match
The thickness of the part varies
Why Coining operation ?
To create different impressions
/ embossing on the part
Flanging/Collar Drawing
Flanging or collar drawing is a process in which a collar is formed so
that more number of threads can be provided.
The collar wall can also be used for as rivet when two sheets are to be
fastened together.
What is Planishing operation?
It is used to straighten the
blanked component.
Very fine serration points
penetrate all around the surface
Why Planishing operation ?
Releases stress and improves the
straightness of the component
What is Planishing operation?
General Pressing process terminologies
Tool related
Pillar / die set
Die & Punch
Cutting / Angular clearance
Stripper
Stopper
Guide plate
Part related
Nesting, RM utilization
Strip layout, pitch
Stock
Plant terminology : Root, Leaf, Seed, Stem …
Pressing process terminologies – Tool related
Pillar / Die set
It is a sub press unit consisting of a
bottom plate and top plate together
with the guide pillars and bushes
Some of the advantages are
Improve accuracy of the set
Alignment of punch & die
Minimum set up time
Improved quality and life
Pressing process terminologies – Tool related
Pillar / Die set
The following elements are considered before selecting the die set.
1. Make or manufacture,
2. Type,
3. Size,
4. Material,
5. Thickness of the die holder,
6. Type & length of the bushing,
7. Thickness of the punch holder,
8. Length of guide post,
9. Shank diameter,
10. Grade of precision.
DIE SET COMPONENTS:
Top plate.
Guide bushing.
Guide pillar.
Bottom plate.
Pressing process terminologies – Tool related
Pillar / Die set
It is a sub press unit consisting of a bottom plate and top plate
together with the guide pillars and bushes
Pressing process terminologies – Tool related
Pillar / Die set
• TOP PLATE:
• The upper working member of the die set is called the top plate.
• The upper surface of the top plate is bears against the under side of the
press ram.
• Punch components are fastened to the lower finished surface.
• The top plate is generally made out of M.S.
Pressing process terminologies – Tool related
Pillar / Die set
BOTTOM PLATE :
• The bottom plate is the lower working member of the die sets.
• Usually the bottom plate is made thicker than the top plate to
compensate the weakening effect of the slug and blank holes which
must be machined through it.
• Generally it is made up of M.S.
Pressing process terminologies – Tool related
Pillar / Die set
GUIDE PILLAR:
• Guide pillars are precision-ground pins which are press fitted into
accurately bored holes in the bottom plate. They aligns punch & die
components with the high degree of accuracy.
• Guide pillars are used for precision die sets are chromium plated to
provide high degree of accuracy of resistance to wear. The addition
of chromium reduce wear up to 50%.
• They are specified at least ¼ inch shorter than the shut height.
Pressing process terminologies – Tool related
Pillar / Die set
REMOVABLE GUIDE PILLAR:
• Pillars may be removed for die sharpening, specially in large dies.
• In first kind of removable pillar have an axial hole machined
through them are tapered at one end to engage a taper pin.
• In second type of removable pillar, the taper pin is advanced for
locking by means of a socket cap screw.
• In third type of removable pillar a socket head cap screw is
engaged In retaining cap to clamp the pillar to the bushing.
Pressing process terminologies – Tool related
Pillar / Die set
GUIDE BUSHINGS:
Guide bushings are engaged with the guide pillars for aligning the top plate
with the bottom plate. Most bushings are made up of tool steel, they are
also available in bronze.
There are two types :
1. Plain bushing are simple sleeves, pressed into the top plate.
2. Shouldered bushings are turned down at one end and they are pressed
into the top plate against the shoulder thus formed.
Pressing process terminologies – Tool related
Pillar / Die set
BALL BEARING DIE SETS:
Some die sets are provided with ball bearing .Guide pillars are pressed into
the top plate and thy engage linear ball bearings.
Lubrication is provided by cup greasing and this is sufficient for entire run.
Ball bearings should take more place than conventional guiding and they
reduce die space a small extend.
Pressing process terminologies – Tool related
Die & Punch
Die
Die and Punch are the female and
male part of the complete die
respectively
Three categories of punches
Punch
Cutting punches
Piercing
( piercing, blanking, notching,
Piercing punch = Pierced hole size
trimming….).
Piercing die = Hole size + total clearance
Non-cutting punches
( forming, bending, drawing, Blanking
extruding…). Blanking punch =Blank size-total clearance
Hybrid punches Blanking die = Blank size
(shear & form, punch-trim…).
Pressing process terminologies – Tool related
Die & Punch
Die and Punch are the female and male part of the complete die
respectively
Pressing process terminologies – Tool related
Die & Punch
DIE BUSHES
These are inserted in Mild Steel retainer plate.
Advantages:
Easily replaceable.
Reduces cost of the die
manufacturing.
Applications:
In large piercing dies.
Pressing process terminologies – Tool related
Stripper
The main function of the
stripper is to strip the
stock material off the
punches after each stroke
Other functions :
Act as a guide to punches
Hold the strip flat and tight
during the pressing
operation
Pressing process terminologies – Tool related
Stripper
Pressing process terminologies – Tool related
Stripper
BOX STRIPPER
A typical box pin stripper is shown in figure.
The overall dimensions E and D are made the same as the die block.
Strippers are generally left soft. How ever when required the back gauge
should be hardened.
Pressing process terminologies – Tool related
Stripper
CLAMPING SPRING STRIPPERS
They are true pressure pads. They bears against the stock material,
applying pressure to it. The material is clamped between stripper
and die. Clearance must be large enough to ensure clamping.
Pressing process terminologies – Tool related
Strip guide
Pressing process terminologies – Tool related
Stopper
For each and every stroke of the
press the strip has to be feed
forward for one pitch length
Stopper is a part of tool, to arrest
the movement of the strip when it is
fed forward to one pitch length
Types of stopper : Solid stops,
Plain pin stop, Headed pin stop,
Trigger stopper, Finger stops,
Pusher stops etc.,
Pressing process terminologies – Tool related
Stopper
Pressing process terminologies – Tool related
Stopper
STOP POSITION
This is the location of the actual stopper position surface
against which the stock strip is halted.
Pressing process terminologies – Tool related
Stopper
Registry position.
• This is the exact location in which the stock strip must be established in
order to obtain dimensionally correct component.
• The work is located by the stop and is registered by the pilots.
• The registry position may or may not be the same as the stop position.
• When a stop functions as an approximation gauge the stop position does
not coincide with the registry position.
Pressing process terminologies – Tool related
EJECTORS
If the expulsion of the blank achieved by
forcing it upwards, the action is known
as "ejection". The element of the tool
which ejects the blank is called an
"ejector“.
Ejectors may be actuated by
compression springs. Rubber, pneumatic
devices or hydraulic devices.
Ejectors if used with spring strippers,
always return the blank into the strip due
to the simultaneous stripping and
ejecting action.
Pressing process terminologies – Tool related
EJECTORS
Pressing process terminologies – Tool related
SHEDDERS
In inverted tools, die becomes the upper member of the tool,
being clamped to the press ram. The expulsion of the blanks is
achieved by forcing them downwards. This action is generally
known as "shedding" and the element of the tool which sheds
the blanks is known as the "shedder".
Press tools
Tools - Used for Pressing process
Pressing tools are made in at least two sections called the punch
and the die.
The dies and punches are normally made of OHNS, HC HCr or other
alloy steels. These tool steels have the strength, wear resistance,
and thermal shock resistance to withstand thousands cutting /
Forming operations
Pressing process terminologies – Tool related
Open Guide plate tool
Pressing process terminologies – Tool related
Guide plate
The guide plates are provided to
locate and guide the strip / coil Guide
plate
Pressing process terminologies – Tool related
Guide plate
The guide plates are provided to locate and guide the strip / coil
Types of tools used for Pressing process
Tools
Single Progressive Compound Combination
Station tool tool tool tool
Assembly Side cam
tool tool Etc.,
Types of Tools used for Pressing process
Single station tool
It performs only one operation at
a time like Blanking or Piercing or
Forming or trimming etc.,
Single station tool is made if the
options like progressive /
Compound / Combination tool is
not feasible (either for
Complication or Cost)
Types of Tools used for Pressing process
Progressive tool
It performs two or more
operations at different stages
every time the press ram
descends
The strip must move from the first
station through each succeeding
station to produce a complete
work piece
Types of Tools used for Pressing process
Progressive tool
Types of Tools used for Pressing process
Progressive tool operation
In progressive tool operation, the stock strip is advanced through a
series of stations that perform one or more distinct press working
operation in the work piece
Progressive Operation Next operation
- Bending
Station 1 Station 2 Station 3 Station 4 Station 5
Types of Tools used for Pressing process
Compound tool
In compound tool, two or more
cutting operations are performed
at the same stage carried out in a
single stroke of the press
The cutting operation should act in
the opposite direction
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Compound tool
Types of Tools used for Pressing process
Combination tool
In this type of tool, two or more
operations such as forming,
drawing, embossing may be
combined with one of the cutting
operations such as blanking,
piercing and cut off
The component is blanked first
and then formed
Types of Tools used for Pressing process
Assembly tool
Component parts are placed onto the centre pin
Rivets are continuously fed from a hopper to the riveting head, via
tracks which orientate the rivet correctly.
Pressing process terminologies – Part related
Stock material
The material out of which stampings are made is known as “Stock
material”
Stock strip : Stock strips are fed into the tool. They are advanced through the
required distance at each press stroke for a series of repetitive operations
Unit Stock : Stock materials which are fed individually into the tool for
processing are called unit stock.
Piece part : A piece part is a product of a tool. It may be a complete product in
itself one component of a product.
Pressing process terminologies – Tool related
Cutting clearance
Punch
Clearance
It is the gap between a side of a
punch and the corresponding side
of the die opening on one side of
the edge, when punch is entered
Die
into the die opening
Optimum clearance
If the cutting clearance is more Fracture
Cut band
Edge radius
than the specified limit, excessive Excess clearance Large burrs
Fracture
burrs will be present along the cut Large radius
Small Cut band
Insufficient clearance
General cutting clearance = 0.06 x t Fracture
Small burrs
Multiple
Small radius Cut band
Importance of Cutting clearance
Aid the life of the die.
Increase the quality of the piece part.
Improve the characteristics of piece part.
Reduces undue stress and wear on the cutting edges
DETERMINATION OF PUNCH AND DIE SIZE:
For Piercing:
Pierced hole size =Piercing punch size
Die = Hole size + 2 clearance.
For Blanking:
Blanking punch = Blanking size – 2 clearance.
Blanking size = Die size
For finding the cutting clearance following formula to be used.
Clearance = c X s X
for above 3 mm clearance =
(1.5x s) x (s-0.015) x
Pressing process terminologies – Tool related
Angular clearance
Punch Die
It is a draft or taper applied to the
side walls of the die opening in
order to relieve the internal
pressure of the blank or slug as it
Clearance
passes through the opening
Soft materials require greater
angular clearance than hard
Cutting Force:
“Cutting force is the force applied on the stock material in order to
cut out the blank or slug”. This determines the capacity of the
press to be used for particular tool. The area to be cut is found by
multiplying the length of cut by stock thickness.
Formula for calculating the cutting force:
Cutting force = L x S x T max
L = Length of periphery to be cut in ‘mm’.
S = Sheet thickness in ‘mm’
T max = Shear strength in N/mm2
Shear and tensile strengths for most materials are not the same.
Generally for calculation purposes Shear strength is
considered as 80% of tensile strength.
Methods to Reduce Cutting Force:
It sometimes becomes necessary to reduce the cutting force
to prevent press over loading .
Stepped punches to be used.
To grind the face of the punch or die to a small shear angle.
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