COMMON BENDING TOOL DESIGN FOR TWO SHEET METAL COMPONENTS (LEFT & RIGHT)

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A
PROJECT REPORT
ON
COMMON BENDING TOOL DESIGN
FOR TWO SHEET METAL COMPONENTS (LEFT & RIGHT)
SUBMITTED BY
GAURAV KUMAR SINGH
Branch- Mechanical
Reg. No - 1201298388
UNDER THE GUIDANCE OF
PROF. R.K SAHU (Deptt. Of Mech. Engg.)
SUBMITTEDTO
Biju Patnaik University of Technology (BPUT), Rourkela
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF
BACHELOR OF TECHNOLOGY (B.TECH) IN MECHANICAL ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
GANDHI INSTITUTE FOR TECHNOLOGY
GRAMADHIA, GANGAPADA
BHUBANESWAR, ODISHA

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CONTENTS
CHAPTER NO. PAGES
1. CHAPTER 1 4
ABSTRACT 5
2. CHAPTER 2 6
HISTORY 7
3.CHAPTER 3 8
3.1 Press Tool ……………………………………………………………………………………….9
3.2 Compound Tool………………………………………………………………………………….9
3.3 Basic die components ………………………………………………………………………10
3.4 Part Details of Compound Tool………………………………………………………….11
3.5 Types of Press Tool and Operations ………………………………………………….12
4. CHAPTER 4 16
4.1 Metal-Cutting Process ………………………………………………………………17
4.2 Principle of Metal Cutting………………………………………………………….18
4.3 Forces Involved In the Metal-Cutting Process ……………………………19
4.4 Alignment Of Cutting Tools ………………………………………………………22
4.5 Cutting Clearances …………………………………………………………………...23
4.6 Stripping Pressure……………………………………………………………………25
4.7 Major Operation by Compound Tool………………………………………….26
5. CHAPTER 5 31
Practical blanking and piercing die design
5.1 Basic Approach to Die Design…………………………………………………..32
5.2Types of blanking dies …………………………………………………………….32
5.2.1 General Types Of Blanking Dies………………………………..32
5.2.2 Die- Block ……………………………………………………………33

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5.2.3 Die Block Thickness……………………………………………….34
5.2.4 Die Opening…………………………………………………………..35
5.2.5 Punch……………………………………………………………………35
5.2.6 Back Up Plate………………………………………………………...35
5.2.7 Methods Of Holding Punches………………………………….36
5.2.8 Centre Of Pressure…………………………………………………36
5.2.9 Strippers……………………………………………………………….36
5.2.10 Stock Stop……………………………………………………………...37
5.2.11 Strip Feeding…………………………………………………………38
5.2.12 Knockouts……………………………………………………………..38
5.2.13 The Die Shoe………………………………………………………….39
5.2.14 Bolster Plate………………………………………………………….39
5.2.15 Stops……………………………………………………………………..39
5.2.16 Ejecting Of Parts…………………………………………………….40
6. CHAPTER 6 41
STRIP LAYOUT
6.1 Strip layout ………………………………………………………………….42
6.1.1 Economy of material…………………………………………….42
6.1.2 Direction of material grain or fiber………………………..44
6.1.3 Strip or coiled stock……………………………………………...44
6.1.4 Direction of burr…………………………………………………..45
6.1.5 Press used……………………………………………………………45
6.1.6 Production required……………………………………………..45
6.1.7 Die cost………………………………………………………………..46
6.2 Press Capacity…………………………………………………………………....48

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6.3 Cutting Forces……………………………………………………………………49
7.CHAPTER 7…………………………………………………………………………….50
7.1 Advantages………………………………………………………………………………..51
7.2 Disadvantages……………………………………………………………………………51
7.3 Applications………………………………………………………………………………51
8. CHAPTER 8……………………………………………………………………………52
8.1 References & conclusion………………………………………………………………….53

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CHAPTER ONE

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ABSTRACT
ress tools are tools, used to produce a particular component in
large quantity, out of sheet metals by using presses. The most
common group of metal working operations is that which includes
blanking and piercing. More and more industrial sectors today look to
blanking and piercing for production of the components they need, from
small accurate parts to massively rigid ones. To deal with such a broad
range of requirements a considerable knowhow in the technology of both
tool-design and of pressing is necessary. Blanking is a process of producing
flat components. The entire periphery is cut. The cut-out piece is called
blank. This process is called blanking and tool used is called as blanking
tool. For producing any sheet metal components, blanking operation is the
primary process to carry-out. Similarly in case of piercing operation the cut
hole is the requirement, the cut-out piece is the scrap. In this project, a real
time design of a blanking and piercing tool is presented with the help of
Auto-CAD and the hard copy printsout.
P

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CHAPTER TWO

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HISTORY
istorically, metal was shaped by hand using a hammer. Later,
larger hammers were constructed to press more metal at once,
or to press thicker materials. Often a smith would employ a
helper or apprentice to swing the sledgehammer while the smith
concentrated on positioning the work piece.
Adding windmill or steam power yielded still larger hammers such
as steam hammers. Most modern machine presses use a combination of
electric motors and hydraulics to achieve the necessary pressure. Along
with the evolution of presses came the evolution of the dies used within
them.
H

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CHAPTER THREE

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INTRODUCTION
3.1 PRESS TOOL
A machine press, commonly shortened to press, is a machine tool that
changes the shape of a work piece.Press tools are commonly used
in hydraulic and mechanical presses to produce components at a high
productivity rate. Generally press tools are categorized by the types of
operation performed using the tool, such as blanking,
piercing, bending, forming, forging, trimming etc. The press tool will also be
specified as blankingtool, piercing tool, bendingtool etc.
3.2 COMPOUND TOOL
A die designed to simultaneously perform morethan oneoperation with
each stroke of the press. For example, a compound diemay blank and
pierce in a single stroke.

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(COPMOUND PRESS)
3.3Basic die components
In this tool two or more operations may be performed at on station. Such
dies are considered as cutting tools since, only cutting operations are
carried out. Simple compound die in which a washer is made by one stroke
of the press. The washer is produced by simultaneous blanking and
piercing operations. Compound die are more accurate and economical in
mass production ascompared to single operation dies.

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3.4 PART DETAILS OF COMPOUNDTOOL

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3.5 Types of Press Tool and Operations
3.5.1 Blanking tool
When a component is produced with one single punch and die where the
entire outer profile is cut in single stoke is called Blanking.Blanking is the
operation of cutting flat shapes from sheet metal.The hole and metal
remained after blanking operation is discarded as a waste.Size of blank or
product is the size of the die & clearance is given on punch.It is a metal
cutting operation.It is fast process and generally used for medium and mass
production volumes.Itischeapest processin manufacturing.
3.5.2 Piercing Tool
Piercing involves cutting of clean holes with resulting scrape slug. The
operation is often called piercing, in general the term piercing is used to
describe die cut holes regardless of size and shape. Piecing is performed in
a press with the die. The piercing tool is used to pierce the holes as
secondary tool such as after bendingof componentetc.
3.5.3 Cut off tool
Cut off operations are those in which a strip of suitable width is cut to
lengthen single. Cut-off tools can produce many parts. The required length
of strip can be cut off for bending and formingoperationsusingthis tool.
3.5.4 Parting off tool
Parting off is an operation that involves two cut off operations to produce
blank from the strip. During parting some scrape is produced. Therefore
parting is the next best method for cutting blanks. It is used when blanks
will not rest perfectly. It is similar to cut off operation except the cut is in

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double line. This is done for components with two straight surfaces and
two profilesurfaces.
3.5.5 Trimming tool
When cups and shells are drawn from flat sheet metal the edge is left wavy
and irregular, due to uneven flow of metal. This irregular edge is trimmed
in a trimming die. Shown is flanged shell, as well as the trimmed ring
removed from around the edge. While a small amount of Material is
removed from the side of a componentin trimmingtool.
3.5.6 Shaving tool
Shaving removes a small amount of material around the edges of a
previously blanked stampings or piercing. A straight, smooth edge is
provided and therefore shaving is frequently performed on instrument
parts, watch and clock parts and the like. Shaving is accomplished in
shaving tools especially designed for the purpose.
3.5.7 Bending tool
Bending tools apply simple bends to stampings. A simple bend is done in
which the line of bend is straight. One or more bends may be involved, and
bendingtools are a large importantclass of press tools.
3.5.8 Forming tool
Forming tools apply more complex forms to work pieces. The line of bend
is curved instead of straight and the metal is subjected to plastic flow or
deformation.
3.5.9 Drawing tool
Drawing tools transform flat sheets of metal into cups, shells or other
drawn shapes by subjecting the material to severe plastic deformation.
Shown in fig is a rather deep shell that has been drawn from a flat

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sheet.This type of Press tools are used to perform only one particular
operation.
3.5.10 Progressive tool
Progressive tool differsfrom the stage tool by the followingaspect, in
progressive tool the final component is obtained by progressing the sheet
metal or strip in many stages. In each and every stage the component will
get its shape stage by stage the fullshape will be obtained at the finalstage.
3.5.11 Compound tool
The compound tool differs from progressive and stage tool by the
arrangement of punch and die. It is an inverted tool were blanking and
piercing takes place in a single stage and also blanking punch will act as
piercing die.
3.5.12 Combination tool
In combination tool two or more operations will be performed
simultaneously such as bending and trimming takes place in a single stage.
IN combination tool two or more operations such as forming, drawing,
extruding, embossing may be combined on the component with various
cutting operationslike blanking, piercing, broaching and cut off takes place.
3.5.13 Notching
This is cutting operation by which metal pieces are cut from the edge of a
sheet, strip or blank.
3.5.14 Perforating
This is a process by which multiple holes are very small and close together
are cut in flat work material.
3.5.15 Slitting
It refers to the operations of makingincomplete holes in a work piece.

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3.5.16 Lancing
This is a cutting in which a hole is partially cut and then one side is bent
down to form a sort of tab or louver. Since no metal is actually removed,
there will be no scrap.
3.5.17 Nibbling
The nibbling operation which is used for only for small quantities of
component is designed for cutting out flat parts from sheet metal. The flat
parts range from simple to complex contours. This operation is generally
substituted for blanking. The part is usually moved and guided by hand as
the continuously operating punch cuts away at the edge of the desired
contour.
3.5.18 Squeezing
Under the operations, the metal is caused to flow to all portions of a die
cavity under the action of compressiveforce.

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CHAPTER FOUR

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THEORY
4.1 Metal-Cutting Process
Metal cutting is a process used for separating a piece of material of
predetermined shape and size from the remaining portion of a strip or
sheet of metal. It is one of the most extensively used processes throughout
die and sheet-metal work. It consists of several different material-parting
operations, such a piercing, perforating, shearing, notching, cutoff, and
blanking.
In blanking, the piece is cut off from the sheet, and it becomes a finished
part. In piercing,the cutout portion is scrap which gets disposed off while
the product part travels on through the remainder of the die. The

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terminology is different here, though both processes are basically the same
and therefore belong to the same category, which is the process of metal
cutting (Fig. 4-1).
The actual task of cutting is subject to many concerns. The quality of
surface of the cut, condition of the remaining part, straightness of the edge,
amount of burr, dimensional stability—all these are quite complex areas of
interest, well known to those involved in sheet-metal work.
Most of these concerns are based upon the condition of the tooling and its
geometry,material thickness per metal-cutting clearance, material
composition, amount of press force, accurate locating under proper tooling,
and a host of additional minor criteria. These all may affect the production
of thousands and thousands of metal-stamped parts. With correct
clearances between the punch and die, almost perfect edge surface may be
obtained. This, however, will drastically change when the clearance amount
increases, and a production run of rough-edged parts with excessive burrs
will emerge from the die.
Highly ductile materials, or those with greater strength and lower ductility,
lesser thicknesses or greater thicknesses—these all were found similarly
susceptible to the detrimental effect of greater than necessary clearances.
The literature recommends different tolerance amounts for cutting tools.
Some claim 0.06t (t = material thickness) to be sufficient for almost all
applications. Others promotea 0.08t range, with 0.1t toppingitoff.

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(Fig. 4-1).
Naturally, a different type of separation must occur with a softer material
than with its harder counterpart. The carbon content certainly has an
influenceon this process as well.
Therefore, the tolerance range must have a provision to change not only
with the stock thickness but with its composition as well.
As already mentioned, good condition of tooling is absolutely essential to
the cutting process. We may have the most proper tolerance range between
the punch and die, and yet the cut will suffer from imperfections if worn-
out tools are used.
4.2 Principle of Metal Cutting
The metal is brought to the plastic stage by pressing the sheet between two
shearing blades so that fracture is initiated with the movement of the upper
shear, finally result in the separation of the slug from the parent strip. The
metal under the upper shear is subjected to both compressive and tensile
stresses. In an ideal shearing operation,the upper shear pushesthe metal to
a depth equal to about the third of its thickness. Because of pushing the
material into the lower shear the area of cross-section of the metal between
the cutting edge of the shear decreases and causes the initiation of the
fracture. The portion of the metal which is forced into the lower shear is
lightly burnished and would appear as a bright band around the blank
lower portion. The fractures which are initiated at both the cutting points
would progress further with the movement of the upper shear and if the
clearance is sufficient, would meet, thus completing the shearing action.The
two shearing elements of the press tool are the hardened punch and the die
plate having sharp edges and a certain shearing clearance. Both the shapes
of the punch and the die opening conform to the required shape of the
component. The punch is connected to the ram of the power press and
while descending contacts the stock, exerts pressure over the stock around
the cutting edges and shears it through. Exactly the same phenomenon that
takes place where in blanking (or) in piercing (or) in any other shearing
operation. In the process of shearing four important stages are usually
distinguished according to the observation.
1. STAGE I: Plastic Deformation The stock material has been placed on the
die and the punch is driven towards the die. The punch contacts the stock
material and exerts pressure upon it. When the elastic limit of the stock material
is exceeded, plastic deformation takes place.

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2. STAGE II: Penetration As the driving force of the ram continues, the punch
is forced to penetrate the stock material and the blank or slug is displaced into
the die opening a corresponding amount. This is true shearing part in of the
cutting cycle, from which the term “shearing action” is derived.
3. STAGE III: Fracture Further continuation of the punching pressure that
causes fractures to start at the cutting edges of the punch and the die. Under
proper cutting conditions, the fractures extended toward each other and meet.
When this occurs, the fracture is complete and the blank or slug is separated
from the original stock material. The punch then enters the die opening, pushing
the blank or slug slightly below the die cutting edge.
4. STAGE IV: As the punch completes the down stroke up to the lower point, the
component of slug is pushed through the die opening. Strictly speaking this
action is a consequence of the dynamic fracture at the stage III and only in
certain case the push through takes place where the punch takes place where the
punch travels beyond the land of the die. This is the simplest approach on the
shearing action. Before dealing with the details of the phenomenon, the attention
is drawn on the same other allied factors which calls for deeper deliberations on
the shearing process.
4.3 Forces Involved In the Metal-Cutting Process
Aside from the press force acting upon the ram and applying vertical
pressure to the die and subsequently to the steel-metal material, additional
forces are involved in the metal-cutting process. As the punch enters the
material, it pushesthe bulk of it down throughthe openingin the die.
However, a small portion of metal is forced sideways, as seen inFig. 4-
2.This flow, directed away from the cutting tool, is guided by the action of
tensile and compressiveforces which develops within the cutmetal,andis
thusGrain dependent: A different pattern of flow is seen along the grain than
against it.

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(Fig. 4-2)
Such movement of material affects the structure of the sheet, especially in
the immediate vicinity of the cutting station. Forced aside, the material
becomes too crowded by such expansion in its content and it resorts to
bulging through the only available outlet, through the surface of the sheet,
which it deforms. In areas where piercing is more congested, the
deformation progress is so widespread that the whole sheet becomes
distorted, displaying either an excessive camber or waviness or any other

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Variation from straightness. The expanding material pushes also against
the body of a punch, applying a side oriented or thrust force toward it. The
punch is suddenly restricted in its movements by the squeeze of bulging
material, which is accompanied by changes in friction, as well as increased
heat. The stability of the punch is often threatened and slim and fragile
tools can often break under such a load. The deformation of the cutoff
portion of metal is often not so pronounced, which is probably due to its
usually smaller size. It is obvious that the flow of tensile and compressive
forces resulting in the development of side-oriented and expansive shifts
within the material is also a great contributor to the emergence of wear of
the working surfaces. According to some, a side-oriented force generated
by the cut material may amount to 2 to 20 percent of the total blanking
force, with its marked dependency on the material thickness, its
composition, and the amountof clearance between the cutting surfaces.
Additionally, forces within the cut material further influence the size of a
sheared opening. On the complete retrieval of the punch, the bulging
material slightly flattens out, its movement being oriented toward the
empty space, which subsequently gets reduced in size. Cutting clearances of
up to 0.05t have been found to produce openings smaller than the size of
the cutting punch.
As already mentioned, the punch on its way out of the cut material is
restricted in movement by the emergence of frictional forces originating
within the structurally altered material. For the punch to progress, a
considerable force is needed to overcome this influence. This force, called a
stripping force, may be calculated with regard to the material composition,
its strength and thickness, the size of tooling, and its clearance. Naturally,
with increasing clearance between the punch and die arrangement, the
amount of stripping force decreases. But the quality of the cut decreases
along with it.
4.4 Alignment Of Cutting Tools
Punches entering the material must be absolutely concentric with the die
opening below.But sometimes a shift from the mutual axis may be due to
the assembly procedures; sometimesa minute movement in the frame of a
press may cause a slight offset of the two centerlines, which ideally should

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match each other. Even with perfect positioning, a long, unsupported, and
unguided punch may be swayed aside by the movement of metal during the
cutting operation or by its own off-center punching, or by an action of some
other demanding operation within the die. To alleviate this problem,
punches should be guided in their movement unless their bulk is so great
that they actually constitute the major portion of the die. The guidance can
be provided through inserts in the stripper plate, which are appropriately
called guide bushings. Slim punches should be further protected by punch
sleeves, or wraps, and similar arrangements. Punches that have irregular
shapes or those having their face area ground to an angle often utilize
heels, which guidetheir progressduringthe cutting operation (Fig. 4-3).
Multipart retainers are an additional punch-guiding provision to a die. They
resemble small, self-contained punch plates, and they come in various sizes
and shapes and with different tool-retaining openings (Fig. 4-4). The whole
unit, along with the punch or punches it holds, is secured to the holding
plate with dowels and locked in this position by screws. The punch,
equipped with a ball-retaining groove, is precision-located by a pressure of
the spring-loaded ball.
Another help with tool guidance is that in which die shoes are aligned with
precision guide pins. Four-pillar die sets were found to be the most
accurately aligned instruments, surpassed only by subpress dies, which are
actually considered small, self-contained, and self-aligned press units.Guide
pin and pillar die sets are described in Sec. 3-1-2 and 3-1-3. Guide pins
areprecision-ground and fit into bushings of equal quality. Their tolerance
ranges are 0.0002 to 0.0004 in. (0.005 to 0.010 mm), and their smooth function
is aided by the lubricants retained in the grooves in the bushing. Self-lubricating
bushings are made of high-strength bronze material, where a lubricant is
embedded throughout its structure. Such a lubricating arrangement usually lasts
the entire life of the bushing.

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(Fig. 4-3 )
However, the absolute of the die alignmentsis the ball-bearing bushing
(Figs. 6-8 and 6-9), which runsso tight that the effect of the side-oriented
force on the tooling is almost eliminated.
4.5 Cutting Clearances
The amountof cutting clearance between the punchand the die is of great
importancein allnsheet-metal work. It is usually given as a percentage of
the thickness of cut material, as shown in Table 6-3.

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(Fig. 4- 4)
The cutting clearance is always added to the die bushing of the particular
cutting station. The punch, as stated previously, hasthe exact size of the
hole to be cut and a tolerance of
+0.0002 in. (+0.005 mm)
–0.0000 in. (−0.000 mm)

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The die opening, which is to contain the punch, will use its size, add the
amount of cutting clearance to it, and attach a tolerance range, often similar
to that of the punch, or
+0.0002in. (+0.005mm)
–0.0000in. (−0.000mm)
As an example, with the punch size of in metric, this becomes the die
opening at 8 percent cutting clearance for fabrication of 1/16 in. (1.6 mm)
thick material will be and in metric, Even though the correct cutting
clearance is recommended to be somewhere between 0.08t and 0.10t per
side, some manufacturers use clearances much broader, with up to 0.16t
per side. Such a gap may often be excessive and the cuts it will produce are
frequently rough and uneven. Yet, with larger-size punches and with
thicker material, greater cutting clearances can be chosen with no
detrimentaleffect on the outcome.
At the same token, manufacturers of tooling for automatic NC machinery
(so-called turret presses) sometimes use extremely small clearances with
impressive results. The trick is in the total guidance of the punch, which is
restricted from any deviation by its precisionmade sleeve, and ultimately
aligned with the die, both components being firmly retained within the
heavy ring of a turret. This type of tooling is built as separate little dies with
small spring-loaded strippersincluded in every assembly.
4.6 StrippingPressure
A stripping pressure calculation helps to determine the correct amount of
the spring pressure a spring-loaded stripper must produce. It usually varies
between 3 and 20 percent of the blanking pressure and can be figured out
usingEq.
Ps = 3.5 Lt
where all values are the same as with the blanking pressure. The amount of
delivered stripping pressure depends mainly on the proper design and
proper function of springs, which are supporting the stripper’s mass. The
second influential factor is the thickness of processed material, which
governs the demand for stripping pressure approximately as shown in
Table 6-5.

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The calculation above is but an approximation of the actual pressure
needed to strip the part. The precise amount is very difficult to establish,
since it is influenced by too manyvariables. The condition of the tooling,
cutting clearance, type of material, and lubrication of tooling are just
several out of many factors influencing the amount of stripping pressure
needed. Sheared punches may reduce the blanking pressure, but they have
no effect on the stripping pressure requirements. However, staged
punching, where the height of cutting tools is offset, will produce a
decrease in demand for stripping pressure. Two levels of punches would
halve the amount of stripping pressure otherwise needed. Three levels of
punches will useup one-third of the pressure, and so on.
4.7 Major Operation by Compound Tool
4.7.1 Blanking
When a component is produced with one single punch and die where the
entire outer profile is cut in single stoke is called Blanking.Blanking is the
operation of cutting flat shapes from sheet metal.The hole and metal
remained after blankingoperation is discarded as a waste.Size of blank or

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(Blanking operation)
product is the size of the die & clearance is given on punch.It is a metal
cutting operation.It is fast process and generally used for medium and mass
production volumes.It is cheapest process in manufacturing.It is used to
produce blanks of desired contour and size by cutting them out of the stock
strip. Blank is the desired ‘piece part’ made by blanking die. The material
remainingafter blanking is called as scrap.
Critical stages of shearing action in blanking:-
First stage: Plastic deformation
Second stage: Penetration
Third stage: fracture
4.7.2 Piercing
Piercing involves cutting of clean holes with resulting scrape slug. The
operation is called piercing, in general the term piercing is used to describe
die cut holes regardless of size and shape. Piecing is performed in a press
with the die. The piercing tool is used to pierce the holes as secondary tool
such as after bendingof component.

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This operation consists of simplehole punching. It differsfrom blankingin
that the punching(or material cut from stock) is the scrap and the strip is
the work piece. Piercing is nearly alwaysaccompanied by a blanking
operation before, after or at the same time.
Critical stages of shearing action in piercing:
First stage: Plastic deformation
Second stage: Penetration
Third stage: fracture
4.7.3 CLEARANCE
It is defined as the intentional space between the punch cutting edge and
die cutting edge. Theoretically clearance is necessary to allow the fractures
to meet when break occurs. The amount of clearance depends upon the
kind, thickness and hardness of the work material.In piercing the work
material is placed between the die and punch, where the punch should be
exact and the die requiresa clearance for the action to be performed.
The die opening must be sufficiently larger than the punch to permit a
clean fracture of the metal. This dimension between the mating members of
a die set is called clearance.
In the blanking operation, where the slug or blank is the desired part and
gas to be held to size, the die opening size equals the blank size and punch
size is obtained by subtracting the clearance from the die openingsize.

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‘C’ is the amount of clearance per side of the die opening. The clearance is a
function of the kind, thickness and temper of the work material, harder
materials requiring larger clearance then the soft material, the exception
being aluminum. The usual clearance per side of the die, for various metals,
is given below in terms of the stock thickness, t:
For brass and soft steel, c= 5% of t
For medium steel, c= 6% of t
For hard steel, c= 7% of t
For aluminum c=10% of t
The clearance may be determined also with the help of the following
relations:
c = 0.0032 t √{shear strength of the material (in N/mm2) }
In blanking operation, the die size is taken as the blank size and the punch
is made smaller giving the necessary clearance between the die and the
punch.
Die size = blank size
Punchsize = blank size – 2 x clearance
Clearance = k .t . 
Where t is the shear strength of material, t is the thickness of sheet metal
stock, and k is a constant whose valuemay be taken as 0.003.
In a piercing operation, thefollowingequations hold.
Punchsize = blank size
Die size = blank size + 2 x clearance
Clearance = k. t. 

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CHAPTER FIVE

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ACTUAL/PRACTICAL COMPOUND DIE DESIGN
5.1 BASIC APPROACH TO DIE DESIGN
With every new part produced, a complete evaluation of the stamping
method and parameters must be performed. Based on the part’s flat layout,
the sequence of tooling must be designed, which in turn dictates the size of
the die. The economies of the strip must be assessed before the rest of the
design is finalized. Seemingly small details such as the availability of strip
material, the predetermined width, and its thickness and tolerance ranges
may turn out to be of tremendous importance when it comes to production.
For selection of the proper press, tonnage requirements must be calculated.
Further, the amount of stroke, shut height, mounting arrangement, and
other press- and productonrelated data must be compared to the capacities
of the selected press equipment. Only then may the actual design be
started, which always begins with the strip layout and its projection into
the cross section of a die. Such a sequence of work process is intentional, as
the cross-sectional view provides control of the placement of punches
within the assembly. Where punch bodies or heads may be too large to fit
the predetermined sequence of operations, or where an additional station
may need to be added later on, one of the stations must be skipped with
subsequent enlargement of the die. This can be readily assessed by
comparing the cross-sectional view with the layout of the strip, whereas by
looking only at the strip this may pass undetected. Both strip layout and
cross-sectional view should be drawn to size or scaled. With accurately
drawn punches and dies, the need for further detailing may often be
eliminated. In questionable areas, some dimensions may be added instead
of separate sketching or verbal explanations.

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5.2 Types of blanking dies:
5.2.1 There are two general types of blanking dies:
(a) Drop-throughdie- In this die, The die block assembly is mounted on
thebolster plate or the press bed and the punch assembly on the
press slide. The blank drops of its weight through the die opening
and the clearance provided in the bolster plate and press bed. This
design economical to build and maintain and is fast in working.
However, this design is not suitable under the followingcondition:
1. When the blank is too thin and fragile to be dropped very far.
2. When the blank is too heavy to be dropped for any appreciable
distance.
3. When the blank is too awkward to be removed from below
press. When the blank is larger than the press bed opening.
(b)Inverted type die: in this design, the punch becomes the lower
stationary part and the die is mounted on the ram. This type is somewhat
more complicated, more costly and slower in operation. The scrap disposal
is much easier but removal of blank freom the die opening is used
wherethe blank is large.
5.2.2 Die- block

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The dieblock is female half of two mated tools which carry the cutting
edges. It is subjected to extreme pressure and conditions. Hence the die
block is made of a superior quality of tool steel. A simple layout of die block
is shown in the fig 5-1. The die block may be of solid or sectional
construction, depending upon the size and contour of the die opening. If the
die opening is small and its contour is simple, asolid die block is the choice.
Sectional dies are made up of accurately ground matching components
which may be assembled together easily.
(Fig. 5-1)
5.2.3 Die blockthickness
The minimum thickness of the die block depends upon the strength
required to resist the cutting forces, and it will depend upon the type and
thickness of the material being cut. The determination of the die block
thickness is usually based on the experienceand thumb rule,
Accordingto thumb rule, the die thickness may be obtained as follows:
Dia thickness= 19 mm, for blank perimeter>=75mm
Die thickness= 25mm, for blank perimeter= 75mm to 250mm

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Die thickness= 31mm, for blank perimeter > 250mm.
5.2.4 Die opening
The side walls of the die block opening should be provided with sufficient
relief or taper so that the blank drops clear through. The taper can either
start from the top surface itself or softer a straight land from the surface of
the die, where the filling and grinding of the die is done by the machine, the
fullytapered cavity is quicker to produce and is thereforecheaper. But if the
die has to be finished on bench, the land is easier to file and sandstone.Soft
metals such as cupper brass and aluminum tend to swell more rapidly
softer being cut. This may be due to a slide spring back return of the
material along the lines in which it which it which it has been stressed in
compression. So, for such metals, the die cavity should be fully tapered. But
for the steel, the taper or relief should start afterthe straight land from the
die surface. The chipsadvantages of the straight land are that the original
dimensions of the die are retained softenreportedregrinding. With fully
tapered die cavity design, the die opening size increases after each
regrinding. This increase, however, is very negligible to cause any
appreciable effect on the blank dimensions.
5.2.5 Punch
The punch must be a perfect mate to the die block opening the size of the
working surface of punch is obtained by subtracting the total clearance
from the desire size of the blank. As shear is provided on the surface for
blanking operation. The punch is provided with awide flange or shoulder to
facilitate mounting and prevent its deflection under load. The minimum
length of punch should be such that it extends far enough into the die block
opening to ensure complete shearing of the blank. The punch length must
also providefor the anticipated number of regrinds.
5.2.6 Back up Plate
For small punches, back up plates or pressureplatesare often provided

39. 39 | P a g e
between the punch plate and punch holder. The punch plate or punch
retainer fits closely over the body of the punch and holds it in proper
relative position. It is attached to the punch holder. The back up plate is
provided to take the cutting force of the punch head, provide a base and
insurance against punch deflection when the punch does not have a flange
or shoulder and prevent the hardened punch from being pushed into the
softer punchholder, thus become loose.
5.2.7 Methods of Holding Punches
The mounting of a blanking punch in the punch in the punch holder does
not present any problems. Being relatively bigger, they are made with
flanges that are dowelsinto position and directly fastened to the punch
holder by screws without the use of punch plate and sometimes without
even a back up plate. When used, the thickness of punch plate should be 1.5
times the punchdiameter.
5.2.8 Centre of pressure
When the shape of blank to be cut is irregular. The summation of shear
forces about the Centre line of the press ram may not be symmetrical. Due
to this, bending moments will be introduced in the press ram, producing
misalignment and undesirable deflections. To avoid thisCentre of pressure
of the shearing action of the die must be found and while laying out the
punch position on the punch holder, it should be ensured that the Centre
line of press ram passes exactly through the Centre pressure of the blank. It
should be noted that it is not the centroid of the area of the blank.
5.2.9 Strippers
After a blank has been cut by the punch on its downward stroke the scrap
strip has a tendency to expand. On the return stroke of the punch, the scrap
strip has the tendency to adhere to the punch and be lifted by it. This action
interferes with the feeding of thestock through the die and some device
must be used to strip the scrap material from the punch as it clears up the
die block. Such a device is called stripper or stripper plate.It is two types,
1. Fixed stripper
Stripper is attached at a fixed height over the die block. The height should
be sufficient to permit the sheet metal to be fed freely between the upper
die surface and the under surface of the stripper plate. The stripper plate is

40. 40 | P a g e
usually of the same width and length as the die block. in simple dies, it is
fastened with the same screws and dowels which are used for die block. In
the complex dies, the strippers fastening willbe independent ofrefastening.
The thickness of the stripper plate should be sufficient to withstand the
forces needed to strip the scrap strip from the punch. The usual value 9.5
mm to 16mm.
2. Sprig loaded stripper
This type is used on large blanking operations and also on very thin and
highly ductile materials where to utilize the pad pressure to hold the
surrounding stock during the blanking operation. In this design the
stripper plate is mounted over the compression springsand suspended by
bolted from the punch holder, with the lower surface of the striper below
the cutting end of the punch. As the punch travels downward from the
blanking operation, the stripper plate contacts thestock strip first and hold
s it until the clears the strip on its return stroke. As the punch rises, spring
pressure holds the strip, stripping it forces may vary from 2.5 to 20% of
cutting force. However, the more common values for most of the
applications are 5 to 10%.
5.2.10 Stock Stop

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The strip of sheet metal is fed guide, or through a slot in the stripper plate.
After each blanking, the strip has to be advanced a correct distance. The
device used to achieve this is called stock stop. The simplest arrangement
may be dowel pin or a small block, against which an edge of the previously
blanked hole is pushed after each stroke of the press. On its upward stroke,
the punch carries the stock strip as so far as the underside of the stripper
plate. Due to this, the stock strip gets released from the stop. With constant
pressure exerted pushing the stock strip to the left, the stock will move as it
is lifted clear, then drop with the next hole over the stop as the scrap strip
is stripped from the punch.
5.2.11 StripFeeding
Stock strip may be fed into the die either manully or mechanically. Manual
feeding is suitable only for low production or with presses operating at low
values of stroke per minute. Modern presses operate 200 to 300 strokes
per minute. For such cases, manual feeding is not feasible and automatic
feeding is the only answer. For this, the strip is prepared in large coils. The
first step in the feeding of strip is the unwinding of coil. Two methods are in
use for the purpose:
1) Reel
2) Coil cradle
The reel is considered to be better as it does not damage the strip in any
way. The reel may be or may not be powerful driven. In the case of power
driven reels, a roller at a end of a long loop arm, rides on the uncoilingstrip.
When the sufficient coil has been unwound, the loop arm raised, the power
supply is switched on. In the case of unpowered reels, the coil is unwound
by an external power source, which may be feeding mechanism or
straightening rolls. When enough coilshave been unwound the reel is
stopped on from uncoilingby a manualor automatic brake.
After uncoilingand straighten, the final step is to feed the strip into the die.
The main two typesof feedingsystem are:
1) Roll Feed
2) Slide And Hitch Feed
5.2.12 knockouts
The function of the knockout is to shed or eject a work piece from within
the die cavity as the work piece may get jammed in the die cavity due to

42. 42 | P a g e
friction. A knockout may be actuated by springs or by a positive acting
knockout pin and bar arrangement. The knockout pin usually leads through
the shank. It may be single pin or a double pin fastened to a pad or collar
above the shank. The working of a positive knockout pin arrangement is
shown in the fig 2.3 for an inverted OBI press. On the return stroke of the
press, the knockout pin strikes the knockout bar. This makes the knockout
pin to accurate the knockout plate which forces the blank out of the die
opening. The function of the knockout plate is to support and guide fragile
punches.
5.2.13 the die shoe
The punch holder together with two or more guide posts constitutes a die.
The die shoe and the punch holder are made of CI, CS and rolled steel. For
smaller dies, CI is used, whereas for larger and special die sets, CS and
rolled tool are used. Bushing is assembled to the upper shoe by press fitting
and guide posts are press fitted in to lower shoe. The bushing and posts are
sized to provide a slip fit. For average range of die sets, the diameter of
guide posts varies from 2.5 cm to 7.5 cm. larger pins may be used if
extreme alignment is required. When die is fully closed, the upper end of
the guide posts should not project beyond the top surface of the upper
shoe.
5.2.14Bolster Plate
When many dies are to run in the same press at different times, the ware
occurring on the press bed is high. The bolster plate is incorporated to take
the wear, plate is made from boiler plate or tbp=1.75(for steel) to 2.00 (for
CI)* T. it is attached to the press bed and the die shore is then attached to it.
It is machined so that its surfaces are flat and parallel. Bolster plates are
relatively cheap and easy to replace. The other functions of a bolster plate
are:
1) To provide attachment holesfor the diesratherthandrilling these
holesin the press bed,
2) To support the die shoe when it is located over a large hole in the press
bed.
3) To take up space in the presswhen the pressshut height is too great for
the die shut height.
4) To provide chutesfor ejecting partsor scrap out the side of the press.

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5.2.15 Stops
Strip material, when first being guided into the die, must stop somewhere
for the sequence of die operations to begin successfully. It is obvious that
the strip should not go as far as the forming tool, which may need some
pre-blanking work performed at the beginning. Advancing the strip too far
may lead to greater than usual wear and tear of the tooling and its
subsequent misalignment and breakage.For that purpose, stops are
introduced in the die work. The first stop, which the strip meets on its way, is
usually the first pierce and blank locator, which navigates the strip in such a
way that all cutting is included prior to its arrival at forming and other
stations.The automatic stop is a device which slides up and down along with the
movement of the ram and either:
1) Forces the nose of the stop lever up, to release its engagement of the strip
for the latter’sProgression (during the downward movement of the ram)
2) Releases its pressure on the lever, thus allowing its nose to come down,
pushed by a forceof a spring. In such a position, the lever is ready for
registration and retainment of theadvancing strip (during the upward
movement of the ram).
5.2.16 Ejecting of Parts
Spring-loaded stock lifters, pressure pins, or pressure pads may all be used as
ejectors of finished parts, wherever these are not cut off in the last operation..

44. 44 | P a g e
CHAPTER SIX

45. 45 | P a g e
STRIP LAYOUT
6.1 Strip layout: It plays an important role especially in the case of the
design of the press tool. Strip decides the economic utilization of the work
piece and helps in the decrease of cost of the job and reduction in the
production time by increasing the number of components or layout the
position of the work pieces in the strip and their orientation with respect to
another. This is called ‘strip layout’. The factors which will influence the
stock layout are:
1) Economy of material,
2) Direction of material grain or fibre,
3) Strip or coiled stock,
4) Press used,
5) Production required,
6) Die cost.
6.1.1 Economy of material
In the above figure, the differentwaysof arrangingto blank the given work
piece are shown. The arrangementof Fig.(a), the strip would either have to
be fed twice,once for each row or doubleblanking willhave to be employed
The percent of material utilization may increase somewhat by the
arrangement of Fig.(b), that is , by having two rows of blanks. Fig.(c) shown

46. 46 | P a g e
in a single row, double pass strip. This is called “stock nesting”. Here, the
strip will have to be passed through the dies once, turned over and passed
through dies a second time. Nesting considerably reduces the scrap.
However the strip layout with maximum material saving may not be the
best strip layout, as the die construction may become more complex which
will offset the savings due to material economy unless a large number of
parts are to be produced.
Another important consideration in strip layout is the distance between the
nearest points of blanks and between blanks and the edges of the strip. To
prevent the scrap from twisting and wedging between blanks and the die,
the distance must increase with material thickness. A general rule of thumb
is to keep this distance, called web, at least 1.5 times the material thickness.
However other factors such as strip thickness, hardness of the material,
type of operation, shape of blank etc. may allow the web to be thinner. The
variousterms connected with strip layoutare shown in below figure.
The distancebetween the blank and edge of strip, known as back scrap may
be determined by the equation,
a= t + 0.015h
The distancebetween successive blanks and also the scrap bridge, b, is
given in below table.
Material thickness in mm b in mm
0.8 0.8
0.8 to 3.2 t
Over 3.2 3.2

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In general softer material s requires larger spacing and thinner materials require larger
spacing.
The feed or advance or the length of one piece of stock needed to produce oneblank is,
S = w + b
The number of blanks which can be produced from one length of stock can be found out
as, N = (L – b)/s
The scrap remaining at the end of one length of strip may be calculated from,
Y=L (Ns + b)
Measure of material utilization:
ηm=area of blank to be cut /area of material available
=B/A*100
% of scrap=
( 𝐴−𝐵)
𝐴
∗ 100
Now area of material available per blank=feed or advance * stock width
6.1.2 Directionof material grainor fibre
This factor is to be considered if the cut blanks have to undergo any
subsequent operation, such as, bending or deep drawing. When the sheet
metal strip is rolled in the mill, a fibre is produced in the direction of strip
length. During subsequent bending operation on the blank, to obtain
maximum strength from bend parts, the bend should be made across the
strip or at an angle of 90° to the fibre. Therefore some part prints specify
that the fibre is to run in the direction of an arrow shown on the print.
In such cases, the blanks may cannotbe tripped or rotated to just any
position desired.
6.1.3 Stripor coiled stock
Another importantconsideration in the strip layoutis whether the stock
used will be in the form of a strip or coil. Whereas, the stock strip may be
passed through the die morethan once, the coiled stock is usually passed
through the die only once.

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When coiled stock is used, recoiling and recoiling of the stock is expensive.
Thus coiled stocked is used when:
1) Production ishigh
2) Thinner metal sheets are employed.
3) The stock needsto be passed through the die only once.
4) Strip stock is used when:
5) Production islow
6) Thicker sheet metals are used
7) The stock needsto be passed through the die morethan once.
6.1.4 Directionof burr
When sheet metal is cut in a die, a burr is produced on the die side of the
scrap strip and on the punch side of the blank. If the burr has to be on the
hidden side, then the expensive operation of removing the burr need not be
done. For this, a note is often placed on the part drawing which reads “burr
down”. To control the position of the burr may limit the stock-layout
arrangement. Scrap may not be reduced to a minimum.
6.1.5 Press used
During production planning, a press has been assigned to the operation and
the die. Therefore, the stock layout has to be such that it allows the die to
be designed within the press capacity. Shear may have provided on punch
or die, to limit the maximum cuttingforce within the presscapacity.
Another factor is the bed area of the press. The relation of the press bed
area to the blank area is a definite factor controlling the stock layout. The
third factor is to have the cutting forces of the die evenly balanced around
the center line of the press ram.
6.1.6 Productionrequirement
The followingguidelines may be followed when the production is the main
consideration:
a) Low production –thin material:
I. Strip stock and a single-pass layout.
II. Cuttingof one or more blanks at a time.

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b) Low production of thin material:
I. Strip stock and a single or double-passlayout.
II. Cuttingone blank at a time.
c) High production –thin material:
I. Coiled stock and a single pass layout.
II. Cuttingof one or more blanks at a time.
d) High production – thick material:
I. Strip stock, and a single or double-passlayout.
II. Cuttingof morethan oneblank at a time.
6.1.7 Die-cost
A. Higher productions.
B. Cutting more than one time, particularly when cutting extremely
complicated blank shapes, or when cutting extremely accurate blank
sizes.
However, for simple round or square-edeged blanks, multiple cutting at
one time is often practical. Also, double-pass dies are less expensive than
cutting two at a time.
So, the designer has to decide while making the stock layout, as to which
is preferred: more operator time per blank or more machine time per
blank.
The first step in strip layout is defining the strip. This process involves
naming the strip assembly and the strip part and defining the width and
height of a station, the project shortcut, the number of stages, and an offset
before and after the strip. You can specify a prefix for the name that is
generated for parts placed inside the strip assembly. Parts include
instances of the article and stamp referenceparts.
Note: Termsused in a strip layout
1) Scrap bridge
a) this is the portion of the material remainingafter blanks operation
between oneedge of the strip and the cutout portion.
b) Thee portion of material remainingbetween the two adjacentopenings
after blanking is also called as the scrap bridge.
2) FrontScrap: This is the scrap bridge on that edge of the strip which is
towardsthe operator

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In the design of blanking part from strip material, the first step is to
prepare blanking layout, that is, to layout the position of the work pieces in
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 1.5timesthe material thickness.
6.1.8 STRIP ARRANGEMENT
Press tool design types may be categorized by layout as well as by motif or
style of pattern. The term layout refers to the arrangement of motifs in the
framework of the design plane. Unlike a painting or drawing, which
isdesigned in relation to its boundaries or edges, the elements in a
textiledesign are designed in relation only to each other. There are
no boundaries,

51. 51 | P a g e
When the pattern is printed it will continue over yards and yards of cloth.
For a textile design to be reproduced on fabric, it must eventually be
developed into one standard unit containing a specific arrangement of the
desired motifs. This one unit, called a repeat, will be repeated across the
width and length of the fabric in a continuousmanner.
6.2 CUTTINGFORCES
In the cutting operation, as the punchin its downward movemententers
the material, it need notpenetrate the thickness of the stock in order to
affect complete ruptureof the part. The distance which the punchenters
into the work material to cause raptureto take place called ‘penetration’
and is usually given as the percentage of the stock thickness.
The percentage of penetration depends on the material being cut and also
on the stock thickness. When a hard and strong material is being cut, Very
little penetration of the punch is necessary to caused fracture. With softer
materials, the penetration will greater. For example, for soft aluminum, it is
60% of ‘t’; for 0.15% carbon steel annealed, it is 38% of ‘t’; and only 24% of
thickness, being smaller for thicker sheets and greater for thinner sheets, as
shown in the below table i.e., it is inversely proportionalto stock thickness.
PENETRATION
Stock
thickness
‘t’ in mm
2
5
2
0
1
5
12.
5
1
0
8 6 5 3 2.
5
1.
6
Belo
w 1.6
Penetratio
n % of ‘t’
2
5
3
1
3
4
37 4
4
4
7
5
0
5
6
6
2
67 70 80
Cuttingforce is the force which has to act on the stock material in order to
cut out the blank or slug. This determines the capacity of the pressto be
used for the particular tool.
Calculation of cutting force,
Cuttingforce = l*s*T (max.)

52. 52 | P a g e
where,
l=length of periphery to be cut in mm
s=sheet thickness in mm
T max = shear strength of stock material in N/mm
Relationship between shearing action and cutting force the three critical
stages of shearing action are related to cutting force. Resistance begins
when the punch contacts the stock material. The load builds up rapidly
during the plastic deformation stage. It continues to increase while
penetration takes place. The accumulated load is suddenly released when
fractureoccurs. The curvelevels off near the bottom.
FORMULATION
F= A x Tß
F = Cuttingforce
S = Material thickness
L = Total cutting length
A = L x S = Shear area
Tß = Shear strength
Note : Shear strength = 80% of tensile strength
6.3 PRESS CAPACITY
The specified amount of force that a press is capable of exerting near the
bottom of its stroke in order to carry out a stampingoperation.
First get the Dia of material in inches = A
Get the thickness of material in inches = B
Now, Multiplier for M.sis 80 & for soft material like copper, brass,
aluminum is6 0.
now putthe A X B X MULTIPLIER = TONNAGE
Example,
1 inch dia
5mm thickness Material is M.S.
SO TONNAGE is: 1 x 0.1968 x80 = 15.75istonnagerequired

53. 53 | P a g e
CHAPTER SEVEN

54. 54 | P a g e
ADVANTAGES AND DISADVANTAGES:
7.1 Advantages
1) Requires minimalspace in the press.
2) Leaves all burrsin one direction.
3) Superior accuracy between holes and trim edges.
4) Moreeconomical to build than a progressivedie.
7.2 disadvantages
A disadvantage of building a compound blank die is the limited
space which ends to leave die components thin and weak. This
concentrates the load and shock on the punches and matrixes resulting
in tooling failures.
7.3 Applications
It is used in aerospace industries, house hold equipment’s, automobile
parts, ship parts, electronic appliances. The best examples are daily used
saving blade, drawingclips, cold rink bottle cap & cap opener, cane clip, etc.

55. 55 | P a g e
CHAPTER EIGHT

56. 56 | P a g e
8.1 Conclusion
In today’s scenario of latest new product development trends, where the
time to introduce a new product is under pressure, forming simulation for
each sheet metal component has become essential. Sheet metal simulation
help the tool designer to understand metal flow in a better way for complex
shapes, which in turn increases the component quality and reduce the
design cycle time and cost. It can be effectively used for optimizing the die
design in order to improve quality, optimizing process parameters without
any physical tool build.
8.2 References
1) Metal Cuttingand Tool Design by B.J.RANGANATH.
2) Mechanical EngineeringDesign by JOSEPH SHIGLEY &CHARLESM
ISCHKE.
3) EngineeringDesign by GEORGE DIETER AND LINDA SCHMIDT.
4) Fundamentals Of Tool Design By David Spitler, JeffLantrip, John N
ee and David A Smit
5) Production Engieeringby Dr.P.C.ShramaS
chandpublication/chapter2
6) Hand book of diedesign second edition by Ivanasuchy.