the structure and design of press dies

8/13/2019 The Structure and Design of Press Dies

1/35

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.


2/35


3/35


4/35

New words

simple/plain diedie block

compound/combination die

Progressive die/punchdie setdie shoeguide plate

shank holderpunch holder

guide railsstripperpilot

guide post/bushing/screw/

knock-out /dowel

backing plateblank holder


5/35

1. Die Classifications

1.1 Manufacturing processes

1.2 Number of operations1.3 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

3.1 Typical structures and their

characteristics of press dies


6/35


7/35

1.3 Number of stations

Single station dies

Multi-station dies----progressive diesSingle stat ion d iesmay be :

Combinat ion (a die in which both cutting and

noncutting operations are accomplished at one

press stroke)orCompound (a die in which two or more cutting

operations are accomplished at every press

stroke).



8/35

Progress ive diesare made with two or morestations. Each station performs an operationon the workpiece or provides an idler station

() so that the workpiece is completedwhen the last operation has beenaccomplished. After the first part has traveledthrough all the stations, each subsequentstrokes()of the press produces anotherfinished part.

Whats di f ferent and common featuresbetween progress ive dies and compounddies?



9/35

1.4 Die structure

Guiding:plain, with guide plate, with guide postsstock guide, guide rails, guide pins (elastic and

solid), pilots

Stripper:movable elastic and solid

Stop pin():solid and elastic,

finger stops(), adjustable and fixed



10/35

1.5 Die materialcarbide(),rubber, polyester(),

polyurethane(), zinc alloy, etc1.6 Production quantities of pieces

Class Ahigh, best of materials

Class B

medium, cheaper materials, die costClass Clow-volume, cheapest

Temporary diessmall, lowest cost



11/35

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,shankguideposts, guide postbushings, springs, screws,dowels



12/35

Die with guide plate

1 -shank

2 -shank holder3 -backing plate

4 -punch holder

5 -punch

9 -guide rail

10-die block

11-die shoe

13-guide plate



13/35

Die with guide post and guide post bushing

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



14/35

1. Introduction

2. Die blocks3. Punches

4. Stripper plates

5. Die components for guiding and stopping

3.2 Structure and design of criticalparts


15/35

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


16/35

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


17/35

2. Die blocks

2.1 die opening profilea) 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.


18/35

2. Die blocks

a)

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


19/35

2. Die blocks

2.3 sectioned dieworkpiece- large,

die opening - complicated,

contours - difficult to machine


20/35

2. Die blocks

2.4 calculation of die block dimensions

A=a+2e,

B=b+2e.Rectangular:

Circular:

sds

HbB

Fl

2

)(

75.0

sds

d

d

H

F

03

21

5.2


21/35

3. Punches

Main consideration when design:

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


22/35

3. Punches

3.1 punch face geometry

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


23/35

3. Punches

3.2 methods for assembling punches

Backing plate:P=F/A>Pd

3.3 punch calculations Compression stress:

Buckling calculation:

)8.0(48.2 min

2

maxUTSLT

EIl

)8.0(4min

2

maxUTSLT

EIl


24/35

4. Stripper plates

Solid stripperThe 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 punchmakes contact with the

workpiece.


25/35

5. Die components for guiding and stopping

The group ofdie 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


26/35

5. Die components for guiding and

stopping

5.1 Stock guide and guide railsGuide 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


27/35


stopping

5.2 Die stops and french notch punchDie 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 thatis equal to the progression of the die.

Finger stops:Used to stop new strips in the proper location in a die.


28/35


stopping

5.3 Positioning the individual blank

a) Three dowels

b) A ring

c) A combination of dowels and guide-rails


29/35


stopping

5.3 PilotsUsed 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.


30/35

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.


31/35

1. Technological property analysis

Structure of work-piece

Dimensional tolerance(),

geometrical tolerance(

),and surface roughness()

Dimension base


32/35


The die pressure should be centered on avertical 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

xi,yi=coordinates of the center

of gravity of a partial length

of cut edge

Li=partial length of cut edges

n

nn

n

ii

n

i

ii

LLL

xLxLxL

L

xL

X

...

...

21

2211

1

1

n

nn

n

i

i

n

i

ii

LLL

yLyLyL

L

yL

Y

...

...

21

2211

1

1


33/35


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 ofthe lines of application will

indicate the position of the

center of die pressure.


34/35

3. Close height

mm10mm5 minmax HHH

ram

frame

plate


35/35

4. General procedure

4.1 According to the technique analysis , select die typeand determine die structure

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

the structure and design of press dies

Documents