Chapter 3 Chapter 3 THE STRUCTURE AND THE STRUCTURE AND DESIGN OF PRESS DIESDESIGN 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 pointKey point

• Classification of dies

• Structure and design of critical parts

• Center of die pressure

• Grammar:the use of prepositions

New wordsNew 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

1. Die Classifications 1.1 Manufacturing processes1.2 Number of operations 1.3 Number of stations 1.4 Die structure1.5 Die material1.6 Production quantities of pieces

2. Basic die components2.1 Technological components2.2 The structural components

§3.1 Typical structures and their characteristics of press dies

1. Die Classifications1. 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

1.3 Number of stationsSingle 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

1. Die Classifications

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

Die with guide plate

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

2. Basic die components

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

2. Basic die components

1. Introduction

2. Die blocks

3. Punches

4. Stripper plates

5. Die components for guiding and stopping

§§3.2 Structure and design of critical parts3.2 Structure and design of critical parts

1. Introduction1. Introduction

• A blanking dieCheaper to make and faster in operation• return-blank die:sheared blank returns upword

• drop-blank die

• A punching dieMay be manually or automatically fed

2. Die blocks2. 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 blocks2. 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.

2. Die blocks2. Die blocks

a)

2.2 fastening to the die shoea) 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

2. Die blocks2. Die blocks

2.3 sectioned dieworkpiece- large, die opening - complicated, contours - difficult to machine

2. Die blocks2. 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

3. 3. PunchesPunches

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

3. 3. PunchesPunches

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

3. 3. PunchesPunches

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

max UTSLT

EIl

)8.0(4min

2

max UTSLT

EIl

4. Stripper plates4. Stripper plates

• Solid stripperThe force of the press is used for stripping operation.

• Elastic stripperUsage:very accurate, thin material, thin punches.How: hold the scrap strip in a flat position before the punchmakes contact with the workpiece.

5. Die components for guiding and stopping5. 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 rails5.2 Die stops and french notch punch5.3 Positioning the individual blank5.4 Pilots

5. Die components for guiding and 5. Die components for guiding and stoppingstopping

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

5. Die components for guiding and 5. Die components for guiding and stoppingstopping

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 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 5. Die components for guiding and stoppingstopping

5.3 Positioning the individual blanka) Three dowels

b) A ring

c) A combination of dowels and guide-rails

5. Die components for guiding and 5. Die components for guiding and stoppingstopping

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.

§§3.3 Steps and contents of die design3.3 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 analysis1. 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 pressure2. 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

xi,yi=coordinates of the center

of gravity of a partial length

of cut edge

Li=partial length of cut edges

n

nnn

ii

n

iii

LLL

xLxLxL

L

xLX

...

...

21

2211

1

1

n

nnn

ii

n

iii

LLL

yLyLyL

L

yLY

...

...

21

2211

1

1

2. Center of die pressure2. 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 height3. Close height

mm10mm5 minmax HHH

ram

frame

plate

4. 4. General procedureGeneral procedure4.1 According to the technique analysis , select die type

and 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 height4.4 Draw up the technological plan