Lehrstuhl für Technologieder Fertigungsverfahren

Laboratoriumfür Werkzeugmaschinenund Betriebslehre

Manufacturing Technology II

Exercise 5

Drawing Processes

WerkzeugmaschinenlaborLehrstuhl für

Technologie der FertigungsverfahrenProf. Dr. - Ing. F. Klocke

RWTH - AachenSteinbachstraße 53

52065 Aachen

Inhaltsverzeichnis

Fertigungstechnik II - Übung 5 2

Table of Contents

1 Introduction .................................................................................................... 32 Collection of formulas..................................................................................... 43 Exercises........................................................................................................ 5

3.1 Deep drawing......................................................................................... 53.2 Ironing.................................................................................................... 73.3 Stretch drawing...................................................................................... 9

Introduction

Fertigungstechnik II - Übung 5 3

1 Introduction

The majority of thw work undertaken nowadays in the steel processing industry, is

in the field of sheet metal working. Sheet metal working processes are used in

order to manufacture three-dimensional parts from the sheet steel. The processes

most frequently used, are deep drawing, ironing , stretch drawing and bending.

The area of applications in deep drawing operations ranges from straightforward

cup-shaped components to complex free-form or sculptured parts like those used

in the automotive industry. Tool costs account for a large percentage of the

manufacturing cost. Consequently, deep drawing is used mainly for mass

production.

Ironing is used for axial tapering operations conducted on parts, generally

produced in a deep drawing operation. One example of the application of this

technique, is in the production of drinks cans.

In contrast, stretch drawing and bending processes rarely depend on the tools

used. They require a high level of manual use and are therefore used mainly for

form drawing in small series production.

However, all of the operations are very similar in terms of the states of stress

which produce plastic form change. The methods used to calculate forming forces

and deformation work, which form the basis of process and machine design, can

therefore be described together.

Collection of formulas

Fertigungstechnik II - Übung 5 4

2 Collection of formulas

Vertical anisotropy: r

bbss

b

s= =

�

��

�

��

�

��

�

��

ϕϕ

ln

ln

0

1

0

1

Average vertical anisotropy: ( )r r r r= + +° ° °

14

20 45 90

Maximum possible drawing force in deep

drawing operations: (base fracture)

F d s R KZ mmax = ⋅ ⋅ ⋅ ⋅π 1 0

Blank holder force in deep drawing

operations:

F A pn N N= ⋅

Ideal drawing force in deep drawing

operations:

F d s kddZid m fmm

= ⋅ ⋅ ⋅ ⋅�

��

�

��π 0 ln

Width of drawing gap in deep drawing

operations:

u s K sZ = + ⋅0 010

Exercises

Fertigungstechnik II - Übung 5 5

3 Exercises

3.1 Deep drawing

s 0

punch

blank holder

sheet metal

drawing die

Fig. 3.1: Principle underlying deep drawingA cylindrical cup without a flanged shoulder is to be deep drawn from a flat circular

blank in one draw.

Drawing ratio: β = 1,9

Cup diameter

(punch diameter): dst = 70 mm

Initial thickness: s0 = 1 mm

Radius of drawing ring: rR = 6 mm

Material (sheet metal): Rm = 340 N/mm²

1. The dimensions specified, necessitate the use of a clamp for holding down the

sheet steel required in order to prevent wrinkling. The rounding of the punch

edge and the change in the thickness of the sheet steel can be ignored in this

calculation.

2. Calculate the initial diameter of the circular blank d0

3. Calculate the height of the drawn part, h

4. The flange area of the sheet steel acted upon by the blank holder, is

AN = 7400 mm² before forming begins.

Exercises

Fertigungstechnik II - Übung 5 6

Blank holder pressure of pN = 1,0 N/mm² is required in order to give reliable

protection from wrinkling.

Specify the level of blank holder force required?

5. List two design options which can be used to apply blank holder pressure in

single-acting presses.

6. Describe briefly which operations conducted without a blank holder, result in

wrinkling.

7. State which numerical value must not, under any circumstances be exceeded

by the drawing force, if base fractures are to be avoided?

Ignore the material hardening during the forming operation.

8. The actual drawing force depends largely on the friction ratios which develop.

List the points at which friction occurs when the cup is deep drawn.

At what point is a higher level of friction desirable from the point of view of the

drawing force to be transferred?

9. The three presses available in your company are specified in detail in the Table

below.

Press A B C

double-acting x

single-acting x x

max. load:blank holder tappet

drawing tappet

10 kN

80kN

-

80kN

-

100 kN

press stroke: 50 mm 70 mm 70 mm

Investigate the suitability of these machines for the machining tasks in hand.

Assume that the drawing force is the maximum value determined in Item 6.

Exercises

Fertigungstechnik II - Übung 5 7

3.2 Ironing

D0

D1

Di

punch

workpiece drawing die

Fig. 3.2: Basic principle of the stretch drawing operation

Workpieces which are supposed to have thinner walls in the cup wall area, can be

produced in ironing operations. In the example in question, the wall thickness of a

cup made of Ck10, is to be reduced in one draw, from 2.5 mm to 1.6 mm.

Calculate the tappet force required for this stretch drawing process.

Dimensions specified

Exercises

Fertigungstechnik II - Übung 5 8

Cup diameter: d1 = 100 mm

Wall thickness before ironing: s1 = 2.5 mm

Wall thickness after ironing: s2 = 1.6 mm

Forming efficiency ηF = 0.4

mean yield strength

before the ironing process: kf0 = 240 N/mm²

The following applies to the

flow curve: kf (ϕ) = 690 ϕ0,252 N/mm²

Exercises

Fertigungstechnik II - Übung 5 9

3.3 Stretch drawing

Fig. 3.3: Principle underlying stretch drawing

Stretch drawing is an economically efficient process when the small to medium

quantities of curved sheet are required. The material is formed when the punch is

driven into the steel sheet which is held in clamping jaws. This process is used in

the aerospace industry as well as in the automotive industry and ship building.

A metal sheet made of Ck10, is drawn over a forming block as shown in

Fig. 4.3.1. Calculate the level of punch force required.

Dimensions specified

Length of sheet before forming: l0 = 1250 mm

Constant sheet width: b = 800 mm

Thickness of sheet before forming s0 = 3 mm

Exercises

Fertigungstechnik II - Übung 5 10

Forming efficiency: ηF = 0.7

Extension required: l1 - l0 = 350 mm

mean yield strength

before stretch drawing: kf0 = 240 N/mm²

The following applies to the

flow curve: kf (ϕ) = 690 ϕ0,252 N/mm²

Angle between punch and

clamping force at the collet chuck: γ = 0°