General presswork and stampings manufacture, with pressings produced up to 6mm thick and made in the UK.
General Presswork, Pressings and Stampings,produced on a range of power presses up to 150 tonnes.
Materials processed are, most grades of mild steel, copper, aluminium and stainless steel.
Light stampings produced at A & R.
Press tools are made in house, from either blanking and forming tools to complete progression tooling. Components are made from mild steel, stainless steel and aluminium in all grades and thicknesses, from 0.3mm aluminium up to 6mm mild steel.
A selection of pressed out components fromA & R Engineering Ltd.
Please also see the presswork tooling and design section for more examples of general press tooling and opened up progression tools.
Heavy presswork made at A & R.
In the heavy pressings section, we have power presses up to 150 tonnes. See the companies plant list for more information on our machinery. Some of the metal pressing brackets shown above, are 6mm thick.
Shown above, are grain cooling floor panels.
These louvered pressings are produced with custom made tooling at A & R Engineering Ltd. The heavy duty drive over floor panels are use in agriculture, for cooling various cereal crops. They are positioned in concrete trenches where air is blown through. The air is passes through the trench and up through the louvered panel, where it cools the grain stored above. These panels are suitable for storage of oil seed rape, coffee, and all grain cereal crops..
Thin press work. Above is a lighting louver stamping produced at A & R Engineering Ltd.
Click here, for the lighting louver department, and more information on these type of products.
Fax: 01255 427743 E-mail: sales@arengineering.co.uk Tel: 01255 434261
A & R Engineering Ltd., home of pressings and presswork manufacture.
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SCRAP STRIP LAYOUT
SCRAP – STRIP LAYOUT
In the design of blanking parts from strip
material, the first step is to prepare blanking layout,
that is, to layout the position of the workpieces in the
strip and their orientation with respect to one another.
While doing so, the major consideration is the economy
of material.
Another important consideration in strip layout is
the distance between the blanks and the strip edge and
distance between blank to blank. To prevent the scrap
from twisting and wedging between the punch and the
die. The distance must increase with material thickness.
A general rule of thumb is to keep this distance equal
to from 1 to 1.5times the material thickness. The following
figure are example of strip layouts.
A – Front scrap
B – Bridge thickness
(space between parts and strip edge,and part to parts)
C – the distance from a point on one part to the
corresponding point on the next part.
H – Part width
l - Length of part
W – Width of strip
Y – Scrap recovery at end
N – Number of blanks
t– thickness of strip
L – Length of strip
B= 1.25t, when C is less than 2inch
= 1.5t, when C is more than 2inch
C = l + B
W = H + 2B
A = t + 0.015H
Y =L – Nc +B
N = L – B /C
PERCENTAGE OF UTILIZATION
Strip layout is important to have economy of press
tool operation. Scrap strip layout gives an idea on the
positioning of various punches, stops and pilots.
It ensures the ideal location of blanks in the stock strip.
Several trial layouts have to be made to confirm the
maximum percentage of utilization of stock strip. The
goal should be to have at least 75% utilization.
The percentage of stock used to calculated by the
formula:
% of utilization = Area of one blank X 100 /Lead X Width
Where, Lead = Length of component + Bridge thickness
Width= Breadth of component + 2 X Bridge thickness
-----------------------------
EXAMPLE 1: FOR STRIP LAYOUT CALCULATION
Length of part = 20mm : Breadth of part = 10mm
Thickness of part =1.5mm
Bridge thickness = one times of sheet thickness taken
= 1.0 X 1.5 = 1.50mm
Width of strip W = H + 2B
= 20 + 2 X 1.5 =23mm
Front scrap “a” = t + 0.015H
= 1.5 + 0.015 X 20
= 1.8mm
C =l + B = 10+1.5 =11.5mm
tool operation. Scrap strip layout gives an idea on the
positioning of various punches, stops and pilots.
It ensures the ideal location of blanks in the stock strip.
Several trial layouts have to be made to confirm the
maximum percentage of utilization of stock strip. The
goal should be to have at least 75% utilization.
The percentage of stock used to calculated by the
formula:
% of utilization = Area of one blank X 100 /Lead X Width
Where, Lead = Length of component + Bridge thickness
Width= Breadth of component + 2 X Bridge thickness
-----------------------------
EXAMPLE 1: FOR STRIP LAYOUT CALCULATION
Length of part = 20mm : Breadth of part = 10mm
Thickness of part =1.5mm
Bridge thickness = one times of sheet thickness taken
= 1.0 X 1.5 = 1.50mm
Width of strip W = H + 2B
= 20 + 2 X 1.5 =23mm
Front scrap “a” = t + 0.015H
= 1.5 + 0.015 X 20
= 1.8mm
C =l + B = 10+1.5 =11.5mm
FUNDEMENTALS FOR DESIGNING PRESS TOOLS:
-----------------------------------------------------------------------
CLEARANCE:
Clearance is the intentional space(gap)
between the punch and die cutting edges.
Proper clearances between the punch and die cutting
edges enables the fracture to meet, and the fracture portion
of the sheared edge has a clean appearance.
For improper clearances, cracks donot meet and
ragged edge results due to the material being dragged and
torn through the die.
Clearances are calculated by depending upon the
materials thickness and their cutting allowances. The usual
clearances preside of the die for various materials are
given below, in terms of the stock thickness “t”.
For copper, aluminium, brass and soft steel = 3 to 5% of t
For medium steel = 6% of t
For hard steel = 7% of t
Excessive cutting clearance provides larger burr
on the components and gives long tool life. Insufficient
cutting clearance prevents a clear break. It also increase
pressure on punch and die, thereby reduces the tool life.
Correct cutting clearance will allow the fractures
to meet evently resulting in a clear break and the sheared
edge as a clear appearance and minimum burr.
HOW TO APPLY CUTTING CLEARANCE
PIERCING OPERATION:
In piercing operation, clearance is given to the die.
The component size is equal to the punch .
Here slug is a scrap.
Die opening size = Hole to be pierced +2C.
BLANKING OPERATION:
In blanking operation, clearance is given to the punch.
The component size is equal to the die.
Here slug is desired part.
Blank punch size = Hole to be blanked – 2C
PUNCH AND DIE CLEARANCE AFTER CONSIDERING
THE ELASTIC RECOVERY OF THE MATERIAL:
In blanking operation, after the release of blanking
pressure, the blank expands slightly. The blanked part is
actually larger than the die opening that has produced it.
Similarly in piercing operation, after the strip is
stripped off the punch, the material recovers and the hole
contracts. Thus, the hole is actually small then the size of
the punch which produced it.
Thus to produce correct hole and blank sizes,
the punch size should be increase and the die opening
size should be decreased by an amount fo elastic recovery.
The elastic recovery will depend upon blank size,
stock thickness and material. It may be taken as between
0.0125mm to0.075mm.
For stock thickness upto 0.25mm,
this difference may be taken as zero.
For stock thickness 0.25mm to 0.75mm
—It may be equal to 0.025mm.
For stock thickness more than 0.75mm
—It may be taken as 0.05mm.
EXAMPLE: 1 FOR APPLICATION OF CLEARANCE:
A washer component has outer diameter is 30mm and
inner diameter is 10mm and stock thickness is 1.0mm .
material grade is mild steel.(soft steel)
Solution:
Cutting clearance = material thickness X cutting allowance
= 1.0 X 5%
= 1.0 X 5 / 100
=0.05mm per side.
Here elastic recovery taken as 0.05mm.
In blanking:
blank die opening size = part size – elastic recovery
= 30 – 0.05
= 29.95mm.
blank punch size = die opening size – 2C
= 29.95 – 2 X 0.05
= 29.85mm.
In piercing:
piercing punch size = part hole size + elastic recovery
= 10 +0.05
= 10.05mm.
piercing die opening size = punch size + 2C
= 10.05 + 2 X 0.05
= 10.15mm
----------------------------------------------------------------------
EXAMPLE 2: APPLICATION OF CLEARANCE:
inner diameter is 10mm and stock thickness is 1.0mm .
material grade is mild steel.(soft steel)
Solution:
Cutting clearance = material thickness X cutting allowance
= 1.0 X 5%
= 1.0 X 5 / 100
=0.05mm per side.
Here elastic recovery taken as 0.05mm.
In blanking:
blank die opening size = part size – elastic recovery
= 30 – 0.05
= 29.95mm.
blank punch size = die opening size – 2C
= 29.95 – 2 X 0.05
= 29.85mm.
In piercing:
piercing punch size = part hole size + elastic recovery
= 10 +0.05
= 10.05mm.
piercing die opening size = punch size + 2C
= 10.05 + 2 X 0.05
= 10.15mm
----------------------------------------------------------------------
EXAMPLE 2: APPLICATION OF CLEARANCE:
Here a rectangular part has 50mm length, 30mm width
and material thickness is 1.5mm. It has dia 5mm holes
at 4 corners and a center hole is dia 15mm.
Solution:
Cutting clearance = material thickness X cutting allowance
=1.5 X 6%
=0.09mm preside.
Here, elastic recovery taken as 0.05mm.
Piercing-1: 4 Holes at corners
Punch size = 5.0 +0 .05 = 5.05mm
Piercing die size =5.05 + 2 X 0.09 = 5.23mm.
Piercing –2: center hole
Punch size = 15 + 0.05 = 15.05mm
Piercing die size = 15.05 + 2 X 0.09 =15.23mm.
Blanking
Die opening size = lenth is 50 – 0.05 = 49.95mm
=width is 30 – 0.05 = 29.95mm.
Blank punch size = 49.95 – 2 X 0.09 = 49.77mm.
= 29.95 – 2 X 0.09 =29.77mm.
and material thickness is 1.5mm. It has dia 5mm holes
at 4 corners and a center hole is dia 15mm.
Solution:
Cutting clearance = material thickness X cutting allowance
=1.5 X 6%
=0.09mm preside.
Here, elastic recovery taken as 0.05mm.
Piercing-1: 4 Holes at corners
Punch size = 5.0 +0 .05 = 5.05mm
Piercing die size =5.05 + 2 X 0.09 = 5.23mm.
Piercing –2: center hole
Punch size = 15 + 0.05 = 15.05mm
Piercing die size = 15.05 + 2 X 0.09 =15.23mm.
Blanking
Die opening size = lenth is 50 – 0.05 = 49.95mm
=width is 30 – 0.05 = 29.95mm.
Blank punch size = 49.95 – 2 X 0.09 = 49.77mm.
= 29.95 – 2 X 0.09 =29.77mm.
PRESS TOOL ACCESSORIES:
DIE SET:
It is the unit assembly which incorporates a topshoe
and bottom shoe, two or more guide pillars and guide
bushings.
Advantages: 1) It aligns the punch and die members.
2) It reduces the setup time in the press
to a minimum.
3) This facilitates resharpening of punch
and die without removing from
the dieset.
TOP SHOE:
This is the upper part of the dieset which contains
guidebushings and punch holding assembly. It is directly
fastened to the press ram with the help of shank.
BOTTOM SHOE:
This is the lower part of the dieset which contains
guide pillars.
It is generally mounted on the press bed. The die block
is mounted on the bottomshoe.
PUNCH:
Punch is the male part of the die assembly,
which is directly or indirectly moved by and fastened
to the press ram.
Punches are made from good grade of tool steel
or high carbon high chromium steel material and it is
hardened.
Punch is the master of piercing.
DIE:
Die is the female part of the die assembly, which
is mounted on the lower shoe.
Dies are made from tool steels or high carbon high
chromium steel and it is hardened.
Die is the master of blanking.
BACKUP PLATE:
Backup plate or pressure plate placed between the
top plate and punch holder plate.It is a hardened one.
It is used to prevent the punch making any impression
on the soft top plate.
The plate distributes the pressure over a wide area
and the intensity of pressure on the punch holder is reduced
to avoid crushing.Backup plates are made from OHNS
materials and carbon steels(C45) and it is hardened and
ground parallel.
(OHNS-Oil hardened non-shrinkage steel)
The thickness of the backup plate depends upon
the stock thickness.
For upto 2mm stock thickness, 3mm thickness
backup plate is used.
For about 3mm stock thickness, 6mm thickness
backup plate is used.
PUNCH HOLDER PLATE:
It is fastened to the top plate through the backup plate.
It is used to hold the punch correctly.These plates are made
from mild steel material.
GUIDE PILLARS AND GUIDE BUSHINGS:
Guide pillars are mounted on the bottom shoe and
guide bushings are mounted on the top shoe.Both they are
press fitted on their plates. Pillar and bush have a slide
fit to them. They are help in obtaining alignment of the
punch and die. These are made from carbon steels and
hardened and ground.
STRIPPER PLATE:
This plate is mounted on the die plate.It is called
as fixed stripper plate. A channel is provided in this plate
for feeding the metal strip.It is used to stripout the strip
from the punch during the return stroke of the press.
It is also helps to correctly guide the punch into the
dieopening. In some cases, it is mounted to the punch
assembly. It is called as spring loaded stripper.
PRINCIPLE OF METAL CUTTING
PRINCIPLE OF METAL CUTTING:
The cutting of sheet metal in press work is a shearing
process.The punch and die have same shape of the part.
The sheet metal is held between punch and die.The punch
moves down and presses the metal into the opening of the
die.
There is a gap between the punch and die opening.This is
called as “Clearance”. The amount of clearance depends
upon the type and thickness of the material.
The punch touches the metal and travels downward.
The material is subjected to both tensile and compressive
stresses. By this pressure, the metal is deformed plastically.
The plastic deformation takes place in small area between
punch and die cutting edges. So the metal in this area is
highly stressed. When the stress exceeds the ultimate
strength of the material,fracture takes place.
The cutting edge of the punch starts the fracture,
in the metal from the bottom.The cutting edge of the die
starts the fracture from the top. These fractures meet at
center of the plate.
As the punch continuous tomove down, the metal
under the die is completely cutoff from the sheet metal.
The cut out portion of the metal drops down through
the die opening.To make the metal to drop down freely,
a die relief is given in the die block.
If the clearance is too large or too small cracks
do not meet and a ragged edge results due to the
material being dragged and torn through the die.
The cutting of sheet metal in press work is a shearing
process.The punch and die have same shape of the part.
The sheet metal is held between punch and die.The punch
moves down and presses the metal into the opening of the
die.
There is a gap between the punch and die opening.This is
called as “Clearance”. The amount of clearance depends
upon the type and thickness of the material.
The punch touches the metal and travels downward.
The material is subjected to both tensile and compressive
stresses. By this pressure, the metal is deformed plastically.
The plastic deformation takes place in small area between
punch and die cutting edges. So the metal in this area is
highly stressed. When the stress exceeds the ultimate
strength of the material,fracture takes place.
The cutting edge of the punch starts the fracture,
in the metal from the bottom.The cutting edge of the die
starts the fracture from the top. These fractures meet at
center of the plate.
As the punch continuous tomove down, the metal
under the die is completely cutoff from the sheet metal.
The cut out portion of the metal drops down through
the die opening.To make the metal to drop down freely,
a die relief is given in the die block.
If the clearance is too large or too small cracks
do not meet and a ragged edge results due to the
material being dragged and torn through the die.
TYPES OF DIES BASED ON CONSTRUCTION
TYPES OF DIES BASED ON CONSTRUCTION
1 SIMPLE DIES:
Simple dies or single action dies perform single
operation for each stroke of the press slide. The operation
may be any one of the operations listed under cutting or
forming dies.
2.COMPOUND DIES:
In compound dies,two or more cutting operations
may be performed at one station by one stroke of the press.
Compound dies are more accurate and economical in mass
production as compared to single operartion dies.
For example, a washer component is made by one
stroke of the press in compound die. The washer is produced
by simultaneous blanking and Piercing operations.
Die construction:
Here the blank punch cum piercing die is
mounted on the bottom of the bottom plate which
is bolsted with machine bed. Blank die and piercing
punch are mounted on the top plate which is mounted
on the press ram. A knockout is placed between
blankdie and piercing punch which is used for to
eject the component from the die. A stripper plate is
held with blank punch which is to strip out strip from
the punch after the operation completed.
3.COMBINATION DIES:
In combination dies more than one operations may be
performed at one station. It is differs from compound dies.
In combination dies cutting and non- cutting operations done
at one station by one stroke of the press.
1.BACKUP PLATE 2.PUNCH HOLDER PLATE
3.BLANK PUNCH CUM DRAW DIE 4.KNOCKOUT
5.STRIPPER PLATE 6.DIE PLATE 7.PRESSURE PAD
8.FORMING PUNCH 9.BASE PLATE.
A cup shaped component is produced in combination dies.
Blank punch cum draw die is mounted on the punch holder and
it is fastened to the press ram.Knockout is held inside the blank
punch which is push out the part from the draw die. A stripper
plate is also held with blank punch.
Blank die and inner size form punch are mounted on the
base plate which are held on the press bed. Pressure pad is
placed between blank die and form punch, which is used for
giving uniform drawing and also to eject the cup from the
form punch.
The sheet metal is placed between the blank punch
and die. During operation, the blank punch first cut
the outer of the blank in sheet metal and also
to form as a cup. Pressure pad helps the uniform and
rigid formation of cup. A diecushion is permanently
mounted under the press machine bed, which helps
uniform drawing and also to eject the part after return
stroke of ram.
4.PROGRESSIVE OR FOLLOW DIE:
Progressive die has a series of stations. At each station
, an operation is performed on a workpiece during a stroke of
the press.Between stroke, the piece in the metal strip is
transferred to the next station.A finished work is made at
each stroke of the press.
For example, in progressive die a rectangle blank part
have two round holes at corners and a one square hole at
the center.
Here the component is completed for three station.
At first station,two coner holes to be pierced on the sheet metal.
At second station,first the pilots are correctly guide the already
pierced holes and then center square hole is done one the
sheet metal.At that same time,two corner holes are pierced out
at first station for next component(second part).
Then the strip is moved at station-3. In this stage,
the component is blanked out from the sheet metal. At the
same time,in first stagte,third part corner holes are produced
and in second stage,the second part have center square
hole piercing.The above stage operations are done
simultaneously.
5.TRANSFER DIES:
Unlike the progressive die where the metal stock is fed
progressively from one station to another. But in transfer dies,
the already out blanks are fed mechanically from
station to station.
6.MULTIPLE DIES:
Multiple or gang dies produce two or more
workpieces at each stroke of the press. A gang or number
of simple dies and punches are ganged together to
produce two or more parts at each stroke of the press.
7.INVERTED DIES:
In generally, in punch holder plate punch is held,
which is fastened to the ram. Die is fitted with die holder,
which is held on press bed.
But in inverted dies, the punch and die are to be
interchanged. Punch is held in bed and the die is fastened
to the ram.
1 SIMPLE DIES:
Simple dies or single action dies perform single
operation for each stroke of the press slide. The operation
may be any one of the operations listed under cutting or
forming dies.
2.COMPOUND DIES:
In compound dies,two or more cutting operations
may be performed at one station by one stroke of the press.
Compound dies are more accurate and economical in mass
production as compared to single operartion dies.
For example, a washer component is made by one
stroke of the press in compound die. The washer is produced
by simultaneous blanking and Piercing operations.
Die construction:
Here the blank punch cum piercing die is
mounted on the bottom of the bottom plate which
is bolsted with machine bed. Blank die and piercing
punch are mounted on the top plate which is mounted
on the press ram. A knockout is placed between
blankdie and piercing punch which is used for to
eject the component from the die. A stripper plate is
held with blank punch which is to strip out strip from
the punch after the operation completed.
3.COMBINATION DIES:
In combination dies more than one operations may be
performed at one station. It is differs from compound dies.
In combination dies cutting and non- cutting operations done
at one station by one stroke of the press.
1.BACKUP PLATE 2.PUNCH HOLDER PLATE
3.BLANK PUNCH CUM DRAW DIE 4.KNOCKOUT
5.STRIPPER PLATE 6.DIE PLATE 7.PRESSURE PAD
8.FORMING PUNCH 9.BASE PLATE.
A cup shaped component is produced in combination dies.
Blank punch cum draw die is mounted on the punch holder and
it is fastened to the press ram.Knockout is held inside the blank
punch which is push out the part from the draw die. A stripper
plate is also held with blank punch.
Blank die and inner size form punch are mounted on the
base plate which are held on the press bed. Pressure pad is
placed between blank die and form punch, which is used for
giving uniform drawing and also to eject the cup from the
form punch.
The sheet metal is placed between the blank punch
and die. During operation, the blank punch first cut
the outer of the blank in sheet metal and also
to form as a cup. Pressure pad helps the uniform and
rigid formation of cup. A diecushion is permanently
mounted under the press machine bed, which helps
uniform drawing and also to eject the part after return
stroke of ram.
4.PROGRESSIVE OR FOLLOW DIE:
Progressive die has a series of stations. At each station
, an operation is performed on a workpiece during a stroke of
the press.Between stroke, the piece in the metal strip is
transferred to the next station.A finished work is made at
each stroke of the press.
For example, in progressive die a rectangle blank part
have two round holes at corners and a one square hole at
the center.
Here the component is completed for three station.
At first station,two coner holes to be pierced on the sheet metal.
At second station,first the pilots are correctly guide the already
pierced holes and then center square hole is done one the
sheet metal.At that same time,two corner holes are pierced out
at first station for next component(second part).
Then the strip is moved at station-3. In this stage,
the component is blanked out from the sheet metal. At the
same time,in first stagte,third part corner holes are produced
and in second stage,the second part have center square
hole piercing.The above stage operations are done
simultaneously.
5.TRANSFER DIES:
Unlike the progressive die where the metal stock is fed
progressively from one station to another. But in transfer dies,
the already out blanks are fed mechanically from
station to station.
6.MULTIPLE DIES:
Multiple or gang dies produce two or more
workpieces at each stroke of the press. A gang or number
of simple dies and punches are ganged together to
produce two or more parts at each stroke of the press.
7.INVERTED DIES:
In generally, in punch holder plate punch is held,
which is fastened to the ram. Die is fitted with die holder,
which is held on press bed.
But in inverted dies, the punch and die are to be
interchanged. Punch is held in bed and the die is fastened
to the ram.
SOLVED EXAMPLE IN TOOL DESIGN
SOLVED EXAMPLE:-1
A washer with a 12.7mm internal hole and an
outside diameter of 25.4mm is to be made from 1.5mm
thickness of strip of 0.2% carbon steel. Considering the
elastic recovery of the material.
Find (a) the clearance
(b) blank die opening size
(c) blank punch size
(d) piercing punch size
(e) piercing dieopening size
Solution:
(a)clearance for soft steel is taken as
C = 5% of t
= 5/100 X 1.5
clearance = 0.075mm/side.
(b)Blank dieopening size is equal to the blank size.
but to allow for the expansion of the blank,the die
opening should be made smaller, Thus,
Blank dieopening = Blank size – Elastic recovery
= 25.40 – 0.05
= 25.35mm.
(c)Blank punch size = Blank dieopening size – 2C
= 25.35 – 2 X 0.075
= 25.20mm.
(d)Piercing punch size is equal to the hole size.
But to allow for the contraction of the hole due
to elastic recovery, the punch is made larger,
Thus,
Piercing punch size = hole size + elastic recovery
= 12.70 + 0.05
= 12.75mm.
(e)Piercing die opening = Piercing punch size + 2C
= 12.75 + 2 X 0.075
= 12.90mm.
SOLVED EXAMPLE:-2
The strip thickness is 2.0mm and the length of
blank is 10mm and height is 20mm. Strip length is 1.0m.
Find (a) the value for front scrap
(b) the value for scrap bridge
(c) width of strip
(d) length of one part of stock needed to produce
one part.
(e) Number of parts which canbe produced in strip.
(f) Scrap maintaining at the end of strip.
Solution:
A = front scrap ; b = back scrap(bridge thickness)
l = length of part ; h = height of part
T = thickness of part; w = width of scrap
C = distance from part to part
Y = end of scrap; L = total length of scrap
Solution:
Length of part l = 10mm
Height of part h = 20mm
Thickness of part = 2.0mm
Total length of scrap L = 1.0m (= 1000mm)
(a)Front scrap and back scrap
a = t + 0.015h
= 2.0 + 0.015 X 20
= 2.30mm.
(b)Scrap bridge thickness = It is taken as one times
of sheet thickness
= 1 X 2.0
= 2.0mm.
(C) Width of strip W = Height of part + 2bridgethick
= 20 + 2 X 2
= 24mm.
(d) Length of one piece of stock needed to produce one
blank is,
C = l + b
= 10 + 2
C = 12.0mm.
(e) Number of parts in the strip
N = Total length of strip – bridge thickness
C
= L – b
C
= 1000 –2
12
N = 83 blanks produced.
(f) Scrap remaining at the end
Y = L – (Nc+b)
= 1000 – (83 X 12 + 2)
= 2.0mm.
SOLVED EXAMPLE:-3
A washer with a12.7mm hole and an outside
diameter of 25.4mm is to be made from 1.50mm
hickness Of strip of 0.2% carbon steel. The ultimate
shearing Strength of the material is 2800Kg/C
(1) Find the total cutting force if both punches act at
the same time and no shear is applied to either
punch or die.
(2) What will be the cutting force if the punches are
staggered. So that only one punch acts at a time.
(3) Taking 60% penetration and shear on punch of
1.0mm. What will be the cutting force if both
punches act together.
Solution:
(1)Cutting force F = П(D + d)st
D=25.4mm; d=12.7mm; t=1.5mm
Shear strength S=2800Kg/Cm2 = 28Kg/mm2.
F = П(25.4+12.7)X1.5X28.0
= 5.027 tonnes.
(2)When the punches are staggered, the punch taking
the largest cut will require the greatest force.
F=ПDst
=П X 25.4 X 28 X 1.5
=3.35 tonnes.
(3) F = t X K X Fmax
K X t X I
K = percentage of penetration = 0.6
I = shear on punch = 1.0mm
Fmax = 5.027 tonnes.
F = 1.5 X 0.6 X 5.027
(0.6 X 1.5)+ 1.0
= 2.38tonnes.
SOLVED EXAMPLE:-4
A hole of 60mm diameter is to be produced in
steel plate 2.5mm thick. The ultimate shear strength
of the material is 45Kg/mm2. If the punching force
is reduced to half of the force using a punch without
shear. Estimate the amount of shear on the punch.
Take % of penetration as 40%.
Solution:
The punching force with non-sheared punch.
Fmax = ПDst
= П X 60 X 45 X 2.5
= 21.20 tonnes.
Work done = Fmax X penetration(punch travel)
= 21.20 X 0.4t
= 21.20 X 0.4 X 2.5
= 21.20tonnes.
Now workdone remains the same with a sheared and
A non-sheared punch,
Punch travel = penetration + shear
= K.t + I
If F is the blanking force, then comparing the workdone,
Fmax X K X t = F(K.t + I)
I= K X t (Fmax – F)
F
Now, F = ½ Fmax
= 10.6tonnes.
I = 0.4 X 2.5 X 10.6
10.6
I = 1.0mm
So the amount of shear on punch is 1.0mm.
A washer with a 12.7mm internal hole and an
outside diameter of 25.4mm is to be made from 1.5mm
thickness of strip of 0.2% carbon steel. Considering the
elastic recovery of the material.
Find (a) the clearance
(b) blank die opening size
(c) blank punch size
(d) piercing punch size
(e) piercing dieopening size
Solution:
(a)clearance for soft steel is taken as
C = 5% of t
= 5/100 X 1.5
clearance = 0.075mm/side.
(b)Blank dieopening size is equal to the blank size.
but to allow for the expansion of the blank,the die
opening should be made smaller, Thus,
Blank dieopening = Blank size – Elastic recovery
= 25.40 – 0.05
= 25.35mm.
(c)Blank punch size = Blank dieopening size – 2C
= 25.35 – 2 X 0.075
= 25.20mm.
(d)Piercing punch size is equal to the hole size.
But to allow for the contraction of the hole due
to elastic recovery, the punch is made larger,
Thus,
Piercing punch size = hole size + elastic recovery
= 12.70 + 0.05
= 12.75mm.
(e)Piercing die opening = Piercing punch size + 2C
= 12.75 + 2 X 0.075
= 12.90mm.
SOLVED EXAMPLE:-2
The strip thickness is 2.0mm and the length of
blank is 10mm and height is 20mm. Strip length is 1.0m.
Find (a) the value for front scrap
(b) the value for scrap bridge
(c) width of strip
(d) length of one part of stock needed to produce
one part.
(e) Number of parts which canbe produced in strip.
(f) Scrap maintaining at the end of strip.
Solution:
A = front scrap ; b = back scrap(bridge thickness)
l = length of part ; h = height of part
T = thickness of part; w = width of scrap
C = distance from part to part
Y = end of scrap; L = total length of scrap
Solution:
Length of part l = 10mm
Height of part h = 20mm
Thickness of part = 2.0mm
Total length of scrap L = 1.0m (= 1000mm)
(a)Front scrap and back scrap
a = t + 0.015h
= 2.0 + 0.015 X 20
= 2.30mm.
(b)Scrap bridge thickness = It is taken as one times
of sheet thickness
= 1 X 2.0
= 2.0mm.
(C) Width of strip W = Height of part + 2bridgethick
= 20 + 2 X 2
= 24mm.
(d) Length of one piece of stock needed to produce one
blank is,
C = l + b
= 10 + 2
C = 12.0mm.
(e) Number of parts in the strip
N = Total length of strip – bridge thickness
C
= L – b
C
= 1000 –2
12
N = 83 blanks produced.
(f) Scrap remaining at the end
Y = L – (Nc+b)
= 1000 – (83 X 12 + 2)
= 2.0mm.
SOLVED EXAMPLE:-3
A washer with a12.7mm hole and an outside
diameter of 25.4mm is to be made from 1.50mm
hickness Of strip of 0.2% carbon steel. The ultimate
shearing Strength of the material is 2800Kg/C
(1) Find the total cutting force if both punches act at
the same time and no shear is applied to either
punch or die.
(2) What will be the cutting force if the punches are
staggered. So that only one punch acts at a time.
(3) Taking 60% penetration and shear on punch of
1.0mm. What will be the cutting force if both
punches act together.
Solution:
(1)Cutting force F = П(D + d)st
D=25.4mm; d=12.7mm; t=1.5mm
Shear strength S=2800Kg/Cm2 = 28Kg/mm2.
F = П(25.4+12.7)X1.5X28.0
= 5.027 tonnes.
(2)When the punches are staggered, the punch taking
the largest cut will require the greatest force.
F=ПDst
=П X 25.4 X 28 X 1.5
=3.35 tonnes.
(3) F = t X K X Fmax
K X t X I
K = percentage of penetration = 0.6
I = shear on punch = 1.0mm
Fmax = 5.027 tonnes.
F = 1.5 X 0.6 X 5.027
(0.6 X 1.5)+ 1.0
= 2.38tonnes.
SOLVED EXAMPLE:-4
A hole of 60mm diameter is to be produced in
steel plate 2.5mm thick. The ultimate shear strength
of the material is 45Kg/mm2. If the punching force
is reduced to half of the force using a punch without
shear. Estimate the amount of shear on the punch.
Take % of penetration as 40%.
Solution:
The punching force with non-sheared punch.
Fmax = ПDst
= П X 60 X 45 X 2.5
= 21.20 tonnes.
Work done = Fmax X penetration(punch travel)
= 21.20 X 0.4t
= 21.20 X 0.4 X 2.5
= 21.20tonnes.
Now workdone remains the same with a sheared and
A non-sheared punch,
Punch travel = penetration + shear
= K.t + I
If F is the blanking force, then comparing the workdone,
Fmax X K X t = F(K.t + I)
I= K X t (Fmax – F)
F
Now, F = ½ Fmax
= 10.6tonnes.
I = 0.4 X 2.5 X 10.6
10.6
I = 1.0mm
So the amount of shear on punch is 1.0mm.
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