Chapter 3 THE STRUCTURE AND
DESIGN OF PRESS DIES
Main contents:
• Die classifications;
• Basic die components;
• Structure and design of critical parts;
• Center of die pressure;
• Steps and contents of die design.
Key point
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Classification of dies
Structure and design of critical parts
Center of die pressure
Grammar:the use of prepositions
New words
simple/plain die 简单模；die block 凹模块
compound/combination die 复合模
Progressive die 连续模/级进模；punch 凸模
die set 模架；die shoe下模座；guide plate 导板
shank holder上模座；punch holder 凸模固定板
guide rails导尺；stripper 卸料板；pilot 导正销
guide post/bushing 导柱/导套；screw 螺钉/栓
knock-out 顶件块/推件块；dowel 销钉
backing plate 垫板；blank holder承料板
§3.1 Typical structures and their
characteristics of press dies
1. Die Classifications
1.1 Manufacturing processes
1.2 Number of operations
1.3 Number of stations
1.4 Die structure
1.5 Die material
1.6 Production quantities of pieces
2. Basic die components
2.1 Technological components
2.2 The structural components
1. Die Classifications
1.1 Manufacturing processes
blanking dies, punching dies,
bending dies, drawing dies, et al.
1.2 Number of operations
single-operation dies----simple/plain dies
multi-operation dies----combination/compound dies
----progressive dies
1. Die Classifications
1.3 Number of stations
Single station dies
Multi-station dies----progressive dies
Single station dies may be :
Combination (a die in which both cutting and
noncutting operations are accomplished at one
press stroke) or
Compound (a die in which two or more cutting
operations are accomplished at every press
stroke).
1. Die Classifications
Progressive dies are made with two or more
stations. Each station performs an operation
on the workpiece or provides an idler station
(空位) so that the workpiece is completed
when the last operation has been
accomplished. After the first part has traveled
through all the stations, each subsequent
strokes(冲击)of the press produces another
finished part.
What’s different and common features
between progressive dies and compound
dies?
1. Die Classifications
1.4 Die structure
Guiding(导向及导料):
plain, with guide plate, with guide posts ；
stock guide, guide rails, guide pins (elastic and
solid), pilots
Stripper: movable elastic and solid
Stop pin(挡料): solid and elastic,
finger stops(始用挡料销), adjustable and fixed
1. Die Classifications
1.5 Die material
carbide(硬质合金),rubber, polyester (聚酯),
polyurethane (聚胺酯), zinc alloy, etc
1.6 Production quantities of pieces
Class A—high, best of materials
Class B—medium, cheaper materials, die cost
Class C—low-volume, cheapest
Temporary dies—small, lowest cost
2. Basic die components
2.1 Technological components
Directly participate in forming the work piece and have direct
contact with a material.
Punches, die block, form block, guide rails, stripper, drawing
die, blank holder
2.2 The structural components
Securely fasten all components to the subset and die set.
punch holder, die shoe, shank，guideposts, guide post
bushings , springs, screws , dowels
2. Basic die components
1 -shank
2 -shank holder
3 -backing plate
4 -punch holder
5 -punch
9 -guide rail
10-die block
11-die shoe
13-guide plate
Die with guide plate
2. Basic die components
1 -shank
2 -shank holder
3 -backing plate
4 -punch holder
5 -punch
6 -guide post bushing
7 -guide post
8 -stripper
9 -guide rail
10-die block
11-die shoe
Die with guide post and guide post bushing
§3.2 Structure and design of critical
parts
1. Introduction
2. Die blocks
3. Punches
4. Stripper plates
5. Die components for guiding and stopping
1. Introduction
• A blanking die
Cheaper to make and faster in operation
• return-blank die:sheared blank returns upword
• drop-blank die
• A punching die
May be manually or automatically fed
2. Die blocks
• Construction component housing the opening
and receiving punches.
2.1 die opening profile
2.2 fastening to the die shoe
2.3 sectioned die
2.4 calculation of die block dimensions
2. Die blocks
2.1 die opening profile
a) gives the highest quality workpiece, the most expensive. blanking
parts having complex contours with greater accuracy.
b) making small parts with low accuracy.
c) the simplest,making relatively large parts.
d) to punch small-diame ter (d < 5 mm) holes.
2. Die blocks
2.2 fastening to the die shoe
a) socket head screws are inserted from the bottom
of the die shoe into threaded holes in the die
block.Dowels are used to prevent a shift in the
position of the block.
b) held in the retainer (has a shoulder)
c) pressed into the retainer (has no shoulder)
d) fastened into the retainer with a ball and screw
e) a bushing is used at the bottom
a)
2. Die blocks
2.3 sectioned die
workpiece- large,
die opening - complicated,
contours - difficult to machine
2. Die blocks
2.4 calculation of die block dimensions
A=a+2e,
B=b+2e.
Rectangular:
Fl
 s  0.75
  sd
2
( B  b) H
Circular:
2.5F 
2d 
1 
   sd
s 
H  3d 0 
3. Punches
Main consideration when design:
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do not buckle;
be strong enough to withstand the stripping force;
not be able to rotate as a result of the cutting action.
3.1 punch face geometry
3.2 methods for assembling punches
3.3 punch calculations
3. Punches
3.1 punch face geometry
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Flat punch-double bevel die
Concave punch-flat die
Bevel punch-flat die
Flat punch-concave die
a) flat,b) concave,c)bevel, d) double bevel
3. Punches
3.2 methods for assembling punches
Backing plate: P=F/A>Pd
3.3 punch calculations
• Compression stress:
• Buckling calculation:
 2 EI min
lmax 
4 LT (0.8UTS )
lmax  2.8
 2 EI min
4 LT (0.8UTS )
4. Stripper plates
• Solid stripper
The force of the press is used for stripping operation.
• Elastic stripper
Usage:very accurate,
thin material,
thin punches.
How: hold the scrap strip in a
flat position before the punch
makes contact with the
workpiece.
5. Die components for guiding and stopping
The group of die components known as guides
and stops includes the following components:
5.1 Stock guide and guide rails
5.2 Die stops and french notch punch
5.3 Positioning the individual blank
5.4 Pilots
5. Die components for guiding and
stopping
5.1 Stock guide and guide rails
Guide rails: Used to guide the work strip through the die.
Be placed between the stock shelf of die block
and the stripper plate or guide plate.
Types: solid and elastic
5. Die components for guiding and
stopping
5.2 Die stops and french notch punch
Die stops: Used to stop the material strip after each feed movement is
completed.
French notch punch: Used for trimming away a length of work strip that
is equal to the progression of the die.
Finger stops: Used to stop new strips in the proper location in a die.
5. Die components for guiding and
stopping
5.3 Positioning the individual blank
a)
b)
c)
Three dowels
A ring
A combination of dowels and guide-rails
5. Die components for guiding and
stopping
5.3 Pilots
Used in progressive and compound dies to position the work strip so
that the relationships between stations or previously punched holes
and the outside blanked contours of work pieces may be maintained.
§3.3 Steps and contents of die design
1. Technological property analysis
2. Center of die pressure
3. Close height
4. General procedure
Homework: 3 supplements on center calculation
of die pressure.
1. Technological property analysis
• Structure of work-piece
• Dimensional tolerance(尺寸公差),
geometrical tolerance(形位公差),
and surface roughness(表面粗糙度)
• Dimension base
2. Center of die pressure
The die pressure should be centered on a
vertical line passing through the specific point
that defines the resultant force of the punching
and blanking forces.
• Mathematical solution
X,Y=coordinates of the center
•
of the die pressure
n
X 
L x
i
i 1
n
i
L
L x  L2 x2  ...  Ln xn
 1 1
xi,yi=coordinates of the center
L1  L2  ...  Ln
i
i 1
n
Y 
L y
i 1
n
i
L
i 1
i
i

L1 y1  L2 y2  ...  Ln yn
L1  L2  ...  Ln
of gravity of a partial length
of cut edge
Li=partial length of cut edges
2. Center of die pressure
• Graphical solution
Use the force polygon and
link polygon closed to
determine the main forces
LRx and LRy operating in
any two directions
(preferably at right angles).
The point of intersection of
the lines of application will
indicate the position of the
center of die pressure.
3. Close height
H max  5 mm  H  H min  10 mm
ram
frame
plate
4. General procedure
4.1 According to the technique analysis , select die type
and determine die structure
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structure of die----simple, compound, combination, et al.
operation way----manual, automatic or self-automatic
removal of blanks or scraps
stripper----elastic or solid
accuracy of die
4.2 Center of die pressure
Calculation/determination
4.3 Close height
4.4 Draw up the technological plan