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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°