TALAT Lecture 3705: Drawing of Automotive Sheet Metal Parts

TALAT Lecture 3705

Drawing of Automotive Sheet Metal Parts
30 pages, 37 figures

Advanced Level

prepared by Klaus Siegert, Institut für Umformtechnik, Universität Stuttgart

Objectives:

− to describe the special requirements for the successful fabrication of automotive alu-
minium sheet metal parts with respect to material properties, machinery and drawing
equipment and tools

Prerequisites:

− General production engineering background
− Background in sheet metal forming principles
− TALAT Lectures 3701 - 3704

Date of Issue: 1996
© EAA – European Aluminium Association

3705 Drawing of Automotive Sheet Metal Parts

Table of Contents

3705 Drawing of Automotive Sheet Metal Parts.............................................2
3705.01 Introduction................................................................................................ 3
3705.02 Characteristic Materials Parameters ....................................................... 4
Effect of Paint Bake Cycle on Strength ...................................................................4
Anisotropy................................................................................................................4
3705.03 The Drawing Process ................................................................................. 6
Stretch Forming .......................................................................................................6
Stretch Forming a Bulge with a Spherical Punch ....................................................7
Hydraulic Stretch Forming.......................................................................................8
Deep Drawing with a Hemispherical Punch ..........................................................10
Deep Drawing and Stretch Forming ......................................................................11
Drawing Irregular Sheet Shapes of Large Areas....................................................12
3705.04 Possibilities of Controlling the Material Flow....................................... 13
Control of Material Flow under Blankholder ........................................................13
Arrangement of Draw Beads..................................................................................15
3705.05 Adjusting the Die Cushion ....................................................................... 15
Mechanical vs. Hydraulic Press Equipment ..........................................................15
Four-Point Die Cushion .........................................................................................16
Desired and Actual Curves for Blankholder Force ................................................17
Advantages of a Servo-Hydraulic Die Cushion in the Press Table .......................17
Four-Point Die Cushion in the Press Table............................................................18
Four-Point Die Cushion in the Press Table with Adjustable Spindle Sleeves.......19
Functional Principle of a Spindle Sleeve Adjustment ...........................................20
Experimental Construction of a Single Action Hydraulic Press (10-Point) ..........20
Blankholder and Spindle Sleeve Forces.................................................................21
Force Displacement Curves ...................................................................................21
Demonstration Case of the Multi-Point Drawing Arrangement ............................24
3705.06 Tool Materials for Drawing of Aluminium Sheet Metal Parts ............ 25
Tool Materials........................................................................................................25
Surface Coatings for Drawing Tools .....................................................................26
3705.07 Examples................................................................................................... 27
3705.08 List of Figures............................................................................................ 29

TALAT 3705 2

3705.01 Introduction

Forecasts for the year 2000 predict that the proportion of steel used in cars will shrink
compared to 1984. At the same time the proportion of high strength steel will increase
sharply as will the share of automotive aluminium, see Figure 3705.01.01.

Forecast for the Year 2000
%
65
Steel
Steel
60
high-strength
50 and
higher strength
40 steel

30

20
Plastics

10 Plastics Aluminium Aluminium

0
1984 2000

Source: Thyssen technical reports 2/86

alu

Training in Aluminium Application Technologies
Forecast for the Year 2000 3705.01.01

Among other applications in the car, aluminium alloys will be used to substitute steel in
carbody sheet components. Previous experience with the production of aluminium sheet
metal components for cars has demonstrated that special attention has to be given to the
peculiarities of aluminium carbody sheet in the fabrication of car components. The fab-
rication process of carbody sheet metal components is a mixture of deep drawing and
stretch forming. Aluminium and steel behave differently with regard to these two basic
forming operations. It is, therefore, necessary to consider the basic technology of sheet
metal drawing for aluminium carbody components in view of the material properties,
the behaviour during the drawing process and the special requirements with respect to
the drawing equipment and the tooling.

TALAT 3705 3

3705.02 Characteristic Materials Parameters

Effect of Paint Bake Cycle on Strength

Figure 3705.02.01 shows the influence of cold forming and paint stoving on the yield
stress Rp0,2 of typical aluminium carbody sheet alloys. It is apparent that age-hardening
alloys profit from the baking cycle while strain-hardening alloys may suffer a reduction
in yield strength values.

Influence of Cold Work and Simulated
Lacquer Stoving (205 °C/ 30 min.) on Yield Strength
300
6009-T4 after stoving
2
N/mm

250
Yield strength Rp0,2

6009-T4 before stoving

200 5182-O

150
5182-O after stoving

100
0 1 2 3 4 5 6 7 % 8
Cold Work (Strain)
Source: IFU Stuttgart

alu Influence of Cold Work and Simulated
Training in Aluminium Application Technologies Lacquer Stoving on Yield Strength 3705.02.01

Anisotropy

Figure 3705.02.02 shows the yield criteria for a plane state of stress as a function of the
r value. A value of r = 1 indicates an isotropic behaviour.
Under a tensile-compressive state of stress, as in the flange of a deep drawn part, the
stress required to maintain a plastic state decreases with increasing values of r. This
means that increasing values of r result in lower drawing forces.
During tensile-tensile stressing, e.g. in the body of a deep drawn part, larger axial
stresses can be transmitted with increasing values of r.
By increasing the value of r, one can increase the strength of the body and at the same
time lower the strength in the flange. This explains why the limiting draw ratio increases
with increasing r values.

TALAT 3705 4

Aluminium sheet alloys in a state of good drawing quality generally have values of r ≤ 1
which vary with respect to the rolling direction.

Effects of Anisotropy
!"
I

! # %& r=5
IV
kf r=3
r = 1, ∆ r = 0
-kf r=0
!1
kf

-kf II

III

alu

Effect of r-Value on Yield Locus 3705.02.02

Figure 3705.02.03 illustrates the elongation values Ag and A80 for the alloy
AlMgSi1-ka (EN-AW 6082-T4) using polar coordinates.

Elongation Values for AlMgSi1-ka
in polar coordinates
Rolling direction (RD)
0° 22.5° 45°
%
30

%
15 67.5°

90°
to RD

Ag
A80mm

Source: IfU Stuttgart

alu

Elongation Values for AlMgSi1-ka in Polar Coordinates 3705.02.03

Figure 3705.02.04 shows the vertical anisotropy r for the alloy AlMg5Mn-w (EN-AW
5182-0) using polar coordinates.

TALAT 3705 5

Vertical Anisotropy r for AlMg5Mn w
as a function of rolling direction

Rolling direction (RD)

0° 22.5° 45°

1.0

67.5°
0.4

r90° = 0.640
90°
to RD
r0° = rmin' 0.592

r45° = rmax' 0.934

r value for ϕg = 0.11

alu Vertical Anisotropy r for AlMg5Mn w
Training in Aluminium Application Technologies as a Function of Rolling Direction
3705.02.04

The varying elongation behaviour and the varying values for anisotropy are a result of
the texture of the individual materials. The values shown here are exemplary and depend
on the material as well as on the processes of cold and warm rolling and on the heat
treatment.

3705.03 The Drawing Process

Stretch Forming

Basic elements of stretch forming are shown in Figure 3705.03.01. During stretch form-
ing, the sheet is clamped on two sides. As a result, the increase in the sheet surface area
due to the activation of the punch, is accompanied by a decrease in sheet thickness. A
tensile state of stress exists. The forming zone starts at the clamping grips and proceeds
to the punch middle. In order to ensure that, in spite of the hindering action of the fric-
tion, even this portion of the sheet is strained, it is desirable to keep the coefficient of
friction between sheet blank and punch low and to have a high strain hardening coeffi-
cient.

TALAT 3705 6

Stretch Forming
µ Sheet blank

Gripping jaws (clamps)

' Two-sided clamping Stretching forming punch

' Due to rigid clamping, increase of surface compensated for by decrease in sheet thickness
with little participation of parts not under tension.

' The forming zone spreads out, starting from the end of the gripping jaw to the middle
of the forming punch.

Aims:

' As small a coefficient of friction µ as possible between sheet and forming punch.

' A high strain hardening coefficient n


alu

Stretch Forming 3705.03.01

Stretch Forming a Bulge with a Spherical Punch

Figure 3705.03.02: During the stretch forming of a bulge with a spherical punch the
blank is clamped firmly under the blankholder so that no material can flow in from the
flange to supply material for the increasing surface area during drawing. The enlarge-
ment of the hemispherical surface area can only be achieved by a decrease in sheet
thickness.

Mechanical drawing
FSt + FK FSt + FK
µ

h Drawing ring

Blankholder
d0

FK FK
Drawing punch (forming block)
FSt
- Clamping force FK prevents flowing-in of sheet
- All-around clamping
- Forming zone spreads out from clamping location to punch dome
- Increase of surface area compensated for only by decrease in thickness.

Aims: - rmin large
- ∆r small
- n large
Coefficient of friction µ between sheet and punch should be kept small.

alu

Mechanical Drawing 3705.03.02

TALAT 3705 7

The forming zone starts at the clamping grips and proceeds to the spherical punch pole.
For this stretch forming process it is desirable to have as low a value of ∆r as possible
and as high a value of rmin and strain hardening coefficient n as possible. The coefficient
of friction between sheet and punch should be kept low.

Strain-Path Curves for Mechanical Drawing
Stretch forming with a hemispherical punch

Lubricant: uncompounded oil 300 cSt/ 40°C
50
point 18
point 15
point 12
40
point 9
P
FR point 6
12
30
9 Tear depth 36.5 mm
18 36.5 mm
15 15
ϕ1 [1]

Tear 12
20 30 mm
9
6 20 mm
18
10 6
10 mm

0
0 10 20 30 40 50
Source: W.Karsunke ϕ2 [1]
alu

Strain-Path Curves for Mechanical Drawing 3705.03.03

Figure 3705.03.03 illustrates the traces of the principal strains at different locations of
the drawn bulge during stretch forming with a hemispherical punch. The traces of strain
from locations 9 and 12 approach the forming limit curve closest. Not surprisingly, tear-
ing occurs at a location next to these points on the bulge.

Hydraulic Stretch Forming

During hydraulic drawing, the blank is clamped all around its edges so that the forming
zone is the portion within the drawing ring, see Figure 3705.03.04. Like in the previous
case, the increase in surface area has to be compensated for by a decrease in the sheet
thickness.

As far as the characteristic sheet values are concerned, large values for rmin and low
values for ∆r are desirable. The strain hardening coefficient n should be as high as pos-
sible.

TALAT 3705 8

Hydraulic FK + Fu
d0
FK + Fu

drawing
h Drawing ring

Base plate

πd0
2

PHydr. Fu = PHydr.
FN + Fu FN + Fu 4

- Clamping force FK prevents flowing-in of sheet
- All-around clamping
- Forming zone equal to sheet region included in drawing ring
- Increase of surface area compensated for only by decrease in thickness.

Aims: - rmin large
- ∆r small
-n large

Source:IFU Stuttgart

alu

Hydraulic Drawing 3705.03.04

Figure 3705.03.05 illustrates the traces of the principal strains at different locations on
the drawn part during hydraulic stretch forming. One notices that the differences be-
tween the individual measuring locations is much smaller than for mechanical buldge
drawing, indicating that the deformation strain is much more uniformly distributed over
the component.

Strain-Path Curves for Hydraulic Drawing

50
18 point 18
point 15
point 12
40
point 9
15 point 6

30 Tear
Tear depth 36.5 mm
18 36.5 mm
12 15
ϕ1 [1]

12
20 30 mm
9
9
20 mm
6
10 6
10 mm

0
0 10 20 30 40 50
Source: W.Karsunke ϕ2 [1]
alu

Strain-Path Curves for Hydraulic Drawing 3705.03.05

TALAT 3705 9

In Figure 3705.03.06, the principal strains ϕg for mechanical and hydraulic drawing are
compared.

Comparison of the Principal Strains ϕg
for Mechanical and Hydraulic Drawing
1.00

0.80 10 cSt/40°C
 Stretch forming
100 cSt/40°C  with hemispherical
300 cSt/40°C  punch
ϕg [1]

0.60
hydraulic drawing

0.40
18

0.20
30 mm
1 35
0
1 5 10 15 18 20 25 30 35
Location of measuring points over hemisphere 100

Source: W.Karsunke

alu Comparison of the Principal Strains ϕg
3705.03.06
Training in Aluminium Application Technologies for Mechanical and Hydraulic Drawing

Deep Drawing with a Hemispherical Punch

Figure 3705.03.07: In deep drawing with a hemispherical punch, the forming zone
covers the region between the flange outer edge and the location where the drawing part
leaves the drawing ring curvature. In contrast to stretch forming, the surface areas of the
blank and the drawn part are about the same, so that the sheet thickness remains almost
constant.

The blankholder force prevents the formation of „type 1“ folds. The base of the drawing
part is formed according to the principle of mechanical drawing.

As far as the characteristic sheet values are concerned, large values for rmin and low
values for ∆r are desirable. The strain hardening coefficient n should be as high as pos-
sible.

The coefficients of friction µ for the combinations punch/lubricant/sheet, blankholder/
lubricant/sheet, drawing ring/lubricant/sheet and drawing ring rounding/lubricant/sheet
should be as low as possible.

TALAT 3705 10

FSt + FN FSt + FN
Deep Drawing
with a
h Drawing ring
hemispherical punch
d0
D Blankholder

- blankholder force FN prevents
type 1 folds. FN FN
Drawing punch
- Forming zone is the sheet area between FSt
flange outer diameter (D = f(h))
and the location at which the sheet Aims: - rmin large
leaves the drawing ring curvature (d0). - ∆r small
- Surface area of drawn part is -n large
approximately equal to the surface area
of the original blank. Consequently, Coefficients of friction should be kept small
sheet thickness is almost constant. for the following combinations:
hemisspherical punch surface / lubricant / sheet,
- Dome (bottom of part) is formed
blankholder / lubricant / sheet,
by stretch forming
drawing ring / lubricant / sheet and
drawing ring rounding / lubricant / sheet.

alu

Deep Drawing with a Hemispherical Punch 3705.03.07

Deep Drawing and Stretch Forming

Figure 3705.03.08 shows two separate schematics for the comparison of the deep draw-
ing and stretch forming processes for a flat bottomed cup.

Deep drawing and stretch forming

Deep drawing Stretch forming

alu

Deep Drawing and Stretch Forming 3705.03.08

TALAT 3705 11

Sheet metal parts with large surface areas are usually formed using a combination of
deep drawing and stretch forming.

A state of pure stretch forming exists only in very few cases. In such cases, the outer
edge of the blank is clamped so that the increase in surface area can only come out of
the sheet thickness.

Deep drawing is the other extreme in which the blankholder holds the sheet so that it
can flow in during forming. The sheet thickness remains approximately constant and the
surface areas of the shaped part and the starting blank are about the same.

Drawing Irregular Sheet Shapes of Large Areas

Two types of drawing beads are shown in the Figure 3705.03.09. The clamping beads
have a rectangular section and absolutely prevent any sheet material from flowing in.
Brake rolls serve only to create an additional forming work.

Drawing Irregular Sheet Shapes of Large Areas

Blank form

Drawing frame

alu
Drawing Irregular Sheet Shapes of Large Areas 3705.03.09

TALAT 3705 12

3705.04 Possibilities of Controlling the Material Flow

In processes which are not purely deep drawing but consist instead of a combination of
deep drawing and stretch forming, it is necessary to control the flow of material under
the blankholder. This can be achieved using different methods, individually or in com-
binations.

Control of Material Flow under Blankholder

Control of material flow
under the blankholder

Influence of
Blank form Lubricant Crimp frictional forces

Blankholder force
FN

drawing crimp

- type
- amount Draw path S
- distribution clamping crimp


alu

Control of Material Flow Under Blankholder 3705.04.01

Figure 3705.04.01 shows a number of possibilities for controlling material flow under a
blankholder:

Blank form
Large sheet blank areas under the blankholder require large forming forces.

Lubricants
One method is to use a blank with nonuniform lubrication, i.e, different lubrication con-
ditions at different locations of the blank, before drawing. Another method is to use a
blank with a uniform basic lubrication which is then locally enhanced at chosen places
by lubricating jets arranged in the tool, i.e., before each pressing stroke, an additional
local lubrication effect exists between sheet and work-piece.

TALAT 3705 13

Clamping crimps
Clamping crimps hinder the flowing in of the material to varying degrees, depending on
the form and size. It is thus possible to reduce the blankholder force, whereby the draw-
ing force is increased.

Influencing the frictional forces
By regulating the blankholder force, it is possible to enhance or hinder the flow of mate-
rial under it. This effect is obtained by locally varying the distance between blankholder
and drawing frame, so that higher contact pressures can be brought to bear where the
distance is smaller.

Another possibility of controlling the material flow and consequently the deformation
strain distribution during the drawing of irregular sheet shapes with varying draw
depths, is by using brake rolls and draw beads. These hinder the flow of material by
varying amounts, depending on their form and size. Again, it is possible to reduce the
blankholder force, whereby the drawing force increases.

As a result of the brake action of the draw beads, the material can no longer freely flow
over the draw ring radius into the draw gap during the forming process. Thus it is possi-
ble to reduce the stress differences between side walls and corner regions for compli-
cated irregular shapes as well as for square shaped drawn parts.

By optimally arranging the draw beads, one can control the material flow to create a
uniform stress distribution such as occurs while fabricating cylindrical shapes. Brake
rolls and draw beads ensure that the resistance of material flow over the draw ring radius
into the draw gap varies locally, thus simulating the effect of increasing blankholder
pressure.

Depending on the design and arrangement in the tool, one can differentiate between
draw beads and brake rolls.

Draw beads are arranged at some distance from the drawing ring radius and cause, to-
gether with the die radius, a three-fold directional change of the sheet. Draw beads can
be arranged in both slanting and straight blankholder surfaces.

Brake rolls are arranged at the die shoulder and create a two-fold directional change of
the sheet material. Brake rolls in the draw ring are used mostly for round or oval sheet
shapes with a parabolic or similar casing form.

TALAT 3705 14

Arrangement of Draw Beads

Figure 3705.04.02 shows the arrangement of draw beads for a drawn carbody compo-
nent.

Arrangement of draw beads
10°

10° 10°
a

b

a b

alu

Arrangement of Draw Beads 3705.04.02

3705.05 Adjusting the Die Cushion

Mechanical vs. Hydraulic Press Equipment

During drawing with a mechanical double-acting press (press with drawing punch ram
and blankholder ram), the blankholder can be locally adjusted at the four points under
the crank so that different contact pressures can be applied at the locations front left,
front right, rear left and rear right under the blankholder, Figure 3705.05.01. A regula-
tion, if at all possible, can only be carried out as far as the pressure is concerned.

With the double-acting hydraulic press it is possible, without any great effort, to regulate
the blankholder force during the draw path at each corner point, since each corner point
has its own hydraulic cylinder.

TALAT 3705 15

Double action press Single action press Single action press
with pneumatic drawing with hydraulic drawing
equipment in the press table equipment in the press table

a a a
b

c e e
d d d
e c c

f
f f
g
h

~ 20 x 4x

a) Ram b) Blankholder ram c) Drawing punch d) Blankholder e) Counter pressure
f) Mounting plate g)Hydraulic cylinder h) Air-cushion pins

alu

Drawing Equipment 3705.05.01

Four-Point Die Cushion

Four-point drawing equipment

press ram
tool top part
blank
bottom drawing frame
(blankholder)
drawing tool
tool plate
tool mounting plate
table plate
hydraulic cylinder (4x)
proportional valve


alu

Four-Point Drawing Equipment 3705.05.02

TALAT 3705 16

Figure 3705.05.02 together with the Figure 3705.05.01 illustrate that it is possible to
draw parts using a three-piece tool not only with a two-fold acting press but also with a
simple acting press. In these cases, the blankholder (lower drawing frame) is supported
on a drawing form plate (cushion) form with the help of a number of pressure bolts.
This drawing form plate is moved up and down or subjected to the blankholder force
with the help of pneumatic or hydraulic cylinders.

Desired and Actual Curves for Blankholder Force

When the top frame contacts the blank lying on the lower frame, an undesirable force
peak occurs, causing the lubricant film to break down, Figure 3705.05.03. In addition,
this causes an undesirable overloading of the tool and machine and is a cause of noise.
This undesirable force peak can be avoided by starting the drawing process with a lower
pressure in the cylinders and then increasing this pressure to a level which prevents the
formation of type-1 folds and allows the necessary material flow to be regulated.

1000 1000
900 900
Force [kN]

800 800
Force [kN]

700 Required curve 700 Required curve
600 600
500 500
400 400
300 300
200 200
100 100
0 0
1000 1000
900 900
Actual curve Actual curve
Force [kN]

800 800
Force [kN]

700 700
600 600
500 500
400 400
300 300
200 200
100 100
0 0
210 120 60 15 0 Ram path 210 120 60 15 0 Ram path
before UT [mm] before UT [mm]

120 135 150 165 180 Crank angle [°] 120 135 150 165 180 Crank angle [°]
Source: IfU, Stuttgart UT UT

alu

Desired and Actual Curves for Blankholder Force 3705.05.03

Advantages of a Servo-Hydraulic Die Cushion in the Press Table

Figure 3705.05.04 summarises the advantages of a die cushion in the press table of a
simple acting press over the mechanical double acting press with a drawing ram and a
blankholder ram:
− No overturning operations required between drawing press and trimming press
necessary.

TALAT 3705 17

− Reduction of the force peaks during initial contact between the top frame and the
sheet blank lying on the bottom frame.
− Control of the blankholder force, i.e., the material flow over the draw path.
− Reproducible press operation

Advantages of a Servo Hydraulic Die Cushion
in the Press Table

A servo hydraulic die cushion in the press table of a simply acting press table
has following advantages over a two-fold acting mechanical press with drawing
ram and blankholder ram :

1. No overturning operations required between drawing press and trimming press.

2. Reduction of the force peak during contaction of the top frame and sheet blank
lying on the bottom frame.

3. Control of the blankholder force, i.e., the material flow over the draw path.

4. Reproducible press operation.

alu Advantages of a Servo Hydraulic Die Cushion
Training in Aluminium Application Technologies in the Press Table 3705.05.04

Four-Point Die Cushion in the Press Table

Four-point die cushion in the press table with
individually controlled and regulated hydraulic cylinders
Tool mounting
plate

Table plate

Hydraulic
cylinder
Proportional valve


alu

Four-Point Die Cushion in the Press Table 3705.05.05

The present trend is to produce large one-piece pressed shapes, e.g. complete automo-
bile side walls. Conventional four-point die cushion is, however, unsuitable for large
parts. One method of developing the die cushion is the possibility of utilising many cyl-
inders instead of four corner cylinders, Figure 3705.05.05. In order to prevent the regu-

TALAT 3705 18

lating and control mechanism from getting too complicated, the cylinders can be joined
together in groups which are controlled in unison.

Four-Point Die Cushion in the Press Table with Adjustable Spindle Sleeves

The Institut für Umformtechnik (institute for forming technology) of the University of
Stuttgart and the company Maschinenfabrik Müller-Weingarten have developed an al-
ternative method. In the construction shown in this Figure 3705.05.06 and Figure
3705.05.08, the force for the blankholder in the drawing frame is controlled by spindle
sleeves with integrated force gauges in which the spindle sleeves can be adjusted to dif-
ferent heights using a stored programme. The spindle sleeves are supported on a draw-
ing cushion which can be regulated and controlled by four hydraulic cylinders.

Spindle sleeve (pressure bolt)
Table plate
Spindle sleeve (presssure bolt)
adjustment

Die cushion plate
Guide for due cushion plate

Hydraulic cylinder

Proportional valve


alu Four-Point Die Cushion in a Press Table with
Training in Aluminium Application Technologies Adjustable Spindle Sleeves 3705.05.06

With this design it is possible to maintain the reliable adjustment of the force-path curve
for each corner cylinder. By choosing the spindle sleeve to be activated, an adjustment
can be made to suit the drawing frame form. The spindle sleeves not required can re-
main in their normal position. By choosing the optimal spindle sleeve lengths, the tool
can be elasticly bent to compensate for the flexure of the drawing frame and drawing
cushion plate as well as for regulating the material flow by locally adjusting the contact
pressure.

TALAT 3705 19

Functional Principle of a Spindle Sleeve Adjustment

Figure 3705.05.07: The adjustable spindle sleeves are supported against pressure
gauges fitted on the drawing cushion plate. The spindle sleeves are adjusted by hydro
motors, belt drive and spline shaft, whereby the height adjustment is recorded on a mo-
ment controller.

Functional principle of a spindle sleeve adjustment
Spindle sleeve (pressure bolt)
Table plate

Spindle sleeve adjusting spindle
Force gauge
Drawing cushion plate

Spline shaft

Toothed belt drive

Moment controller
Hydro motor
Source: IFU Stuttgart, Müller-Weingarten AG

alu

Functional Principle of a Spindle Sleeve Adjustment 3705.05.07

Experimental Construction of a Single Action Hydraulic Press (10-Point)

Figure 3705.05.08 shows the experimental construction of a single action hydraulic
press with a 10-point die cushion in the press table. For details refer to Figure
3705.05.06.

Experimental Construction of a
Single Action Hydraulic Press (10-Point)
extension gauges for
inductive path gauge punch force
with feeler pin for measurement
folds measurement

extension gauges for
flexure measurement

spindle sleeves (10)
force gauge for
measuring
blankholder force
drawing tool
hydraulic die
cushion
press table
Source: IfU Stuttgart fixing elements
Experimental Construction of a
alu
3705.05.08
Training in Aluminium Application Technologies Single Action Hydraulic Press (10-Point)

TALAT 3705 20

Blankholder and Spindle Sleeve Forces

Figure 3705.05.09 shows the blankholder and spindle sleeve forces acting on the draw-
ing cushion plate of a 10-point die cushion based on the principle of four corner point
cylinder forces Fvl (front left), Fvr (front right), Fhl (rear left) and Fhr (rear right). The
sum of these forces is equal to the sum of the active spindle sleeve forces FP1 to FP10.

Blankholder and spindle sleeve forces of a die
cushion plate of a 10-point drawing equipment
PN Lower drawing frame

FP10
FP6 FP7 FP8 FP9

FP5 FP4 FP3 FP2 FP1

Fhl Fhr
Die cushion plate
Fvl Fvr
FVl......Fhr : Controllable and adjustable blankholder forces
FP1.....FP10: Adjustable spindle sleeve forces

alu

Blankholder and Spindle Sleeve Forces 3705.05.09

Force Displacement Curves

Figure 3705.05.10 shows the force-displacement curves of the total blankholder force
FNtot (upper diagram) as well as for the four different blankholder forces (Fvr, Fhr, Fvl,
Fhl), which were pre-set in a five-step rising gradient, over the full drawing path. Fur-
thermore, it also shows the force-displacement curves for the four active spindle sleeves
( FP1, FP2, FP3, FP4) as a function of the drawing path. The formation of force peaks was
largely prevented by correctly pre-setting the individual force-displacement curves for
the four active spindles.

TALAT 3705 21

Force-Stroke Curves

Total blankholder force Spindle sleeve force
FNges FP2
kN FP9
800
200 FP4
kN
100 FP7
600

50 100 150 mm 200
400 Blankholder force
Fvr
kN
200 Fhr
200
Fvl
100
Fhl
0
50 100 150 mm 200 50 100 150 mm 200
Stroke Stroke

Source: IFU, Stuttgart

alu

Force-Stroke Curves 3705.05.10

Figure 3705.05.11 shows the hydraulic simple-acting 4,000 kN press supplemented by a
10-point die cushion at the Institute of Forming Technology (IFU) of the University of
Stuttgart.

Hydraulic 4.000 kN
Sheet Forming Press
at the
Institut für Umformtechnik,
University of Stuttgart

Source: Müller-Weingarten Co.

alu
Hydraulic 4.000 kN Sheet Forming Press 3705.05.11

TALAT 3705 22

The characteristics of a multi-point die cushion in the press table of a simple-acting
press with respect to the drawing process are summarised in Figure 3705.05.12.

Four-Point Die Cushion in the Press Table
of a Simple Acting Press

' Force application to the blankholder can be adjusted to be
most suitable for the tool.

' Material flow controlled by a defined elastic flexure of the
blankholder using a stored programmable height adjustment
of the spindle sleeves.

' Control and regulation of the blankholder force over the
stroke using four hydraulic cylinders and the proportional
valve technology.

' Reproducible operational behaviour of the die cushion.

alu Four-Point Die Cushion in the Press Table of a
Training in Aluminium Application Technologies Simple Acting Press 3705.05.12

Figure 3705.05.13 gives an example of a lower drawing frame.

Lower drawing frame ( I )
1700
840


alu

Lower Drawing Frame ( I ) 3705.05.13

TALAT 3705 23

Demonstration Case of the Multi-Point Drawing Arrangement

Figure 3705.05.14 shows the lower drawing frame with a four-point force transmission
for the forming of a rectangular cup. The flexural elastic deformation of this four-point
drawing frame can of course be simulated by FE-calculations.

Lower Drawing Frame (II)


alu

Lower Drawing Frame (II) 3705.05.14

1200
Tears
KN
FP6 FP7 FP8 FP9
FP10
1000
FP5 FP4 FP3 FP2 FP1
900 Extension
uniform optimal spindle of the
800 force level sleeve height
working
700 range
Total blankholder force

600

500

400
Working range
300
for good parts
200

100 Type 1 folds
0
0 20 40 60 80 100 120 140 mm 180
punch stroke

alu
Optimal Working Range for Deep Drawing 3705.05.15

Figure 3705.05.15 shows that the working range for deep drawing can be extended con-
siderably by the adjustment of the local blankholder pressure with the aid of the spindle

TALAT 3705 24

sleeves in a multi-point die cushion. The necessary adjustment of the blankholder force
distribution depends on the specific tool geometry and can be determined for each draw-
ing tool. The lower limit of the working range is a consequence of the formation of
„type 1“ folds in the draw part flange. The upper limit of the working range is a conse-
quence of the formation of tears in the region of the drawn part body. This working
range has to be determined anew for each sheet-lubricant combination.

With an optimal adjustment of the spindle sleeves in a multiple point die cushion, it is
possible to widen the working range for deep drawing and increase the draw depth.

3705.06 Tool Materials for Drawing of Aluminium Sheet Metal Parts

Tool Materials

Figure 3705.06.01 lists typical tool materials for drawing automotive steel and alumin-
ium sheet metal parts. As in the case of steel, the drawing tools for aluminium are of
grey cast iron quality. Experience has shown, however, that the surfaces of such materi-
als are not suitable for forming aluminium. The materials 1.0443 (GS 45) as well as
1.2769 (GS 45 Cr Ni Mo 4 2) are more suitable, since better surface finishes can be ob-
tained, which in turn reduce the tendency for wear and cold weld adhesion. The alumin-
ium bronze AMPCO also has very good gliding properties.

Tool Materials

Steel sheet:
0.6025 (GG 25 Cr Mo)
1.2080 (X 210 Cr 12)
1.2379 (X 155 Cr V Mo 12 1)

Aluminium:
1.0443 (Gs 45)
1.2769 (G 45 Cr Ni Mo 42)

The tool materials listed for aluminium allow a better surface finishing
so that the tendency for cold welding is reduced.

Source: Haller

alu

Tool Materials 3705.06.01

TALAT 3705 25

Surface Coatings for Drawing Tools

Surface treatments are being increasingly used to improve the wear resistance and to
prevent or reduce the possibility of cold welding as well as to improve the gliding char-
acteristics. In addition to the classical processes of hardening, case hardening, nitriding,
boriding and hard chromium plating, there is an increasing tendency to use hard com-
pound layers based on titanium nitride (TiN) and titanium carbide (TiC). Such layers are
applied using either the chemical vapour deposition (CVD) or the physical vapour depo-
sition (PVD) process, see Figure 3705.06.02. Coatings deposited using the PVD proc-
ess are gaining in popularity, since the process reaction temperature of maximum 550
°C is far below the tempering temperature of the tool steel used.

Surface Treatment Processes
Powder-
Salt bath
Nitriding Gas-
(Nitrocarburising) Plasma-
Reaction
Boriding Powder-
layers
Pastes-
Vanadising
TD process
Ion implanting VD process
Coatings
mainly N

W2C
Applied Hard chromium
TiC
layers plating
TiN
CVD process TiC + TiN
CrxCy
PVD process
TiN

alu

Surface Treatment Processes 3705.06.02

Through the use of coatings, it is possible to utilise the properties of both the protective
coating and the base material. The protective coating increases the wear resistance and
the base material absorbs the mechanical stresses without affecting the coating.

TALAT 3705 26

3705.07 Examples

Figure 3705.07.01: CAD depiction of a coupè door planking

CAD illustration of a coupé door planking


alu
CAD Illustration of a Coupé Door Planking 3705.07.01

Figure 3705.07.02: Designing surfaces

Designing surfaces


alu
Designing Surfaces 3705.07.02

TALAT 3705 27

Figure 3705.07.03: CAD depiction of edge "B" of the drawing punch surface

CAD illustration of edge ''B''
of the drawing punch surface


alu
CAD Illustration of edge ''B'' of the Drawing Punch Surface 3705.07.03

Figure 3705.07.04: Considering springback in the design

Considering springback in the design


alu

Considering Springback in the Design 3705.07.04

The a.m. Figures are all examples of computer assisted designing of body parts.

TALAT 3705 28

3705.08 List of Figures

Figure No. Figure Title (Overhead)
3705.01.01 Forecast for the Year 2000

3705.02.01 Influence of Cold Work and Simulated Lacquer Stoving on Yield
Strength
3705.02.02 Effect of r-Value on Yield Locus
3705.02.03 Elongation Values for AlMgSi1-ka in Polar Coordinates
3705.02.04 Vertical Anisotropy r for AlMg5Mn-w as a Function of Rolling Direction

3705.03.01 Stretch Forming
3705.03.02 Mechanical Drawing
3705.03.03 Strain-Path Curves for Mechanical Drawing
3705.03.04 Hydraulic Drawing
3705.03.05 Strain-Path Curves for Hydraulic Drawing
3705.03.06 Comparison of the Principal Strains ϕg for Mechanical and Hydraulic
Drawing
3705.03.07 Deep Drawing with a Hemispherical Punch
3705.03.08 Deep Drawing and Stretch Forming
3705.03.09 Drawing Irregular Sheet Shapes of Large Areas

3705.04.01 Control of Material Flow under Blankholder
3705.04.02 Arrangement of Draw Beads

3705.05.01 Drawing Equipment
3705.05.02 Four-Point Drawing Equipment
3705.05.03 Desired and Actual Curves for Blankholder Force
3705.05.04 Advantages of a Servo Hydraulic Die Cushion in the Press Table
3705.05.05 Four-Point Die Cushion in the Press Table
3705.05.06 Four-Point Die Cushion in a Press Table with Adjustable Spindle Sleeves
3705.05.07 Functional Principle of a Spindle Sleeve Adjustment
3705.05.08 Experimental Construction of a Simple Acting Hydraulic Press (10-
Point))
3705.05.09 Blankholder and Spindle Sleeve Forces
3705.05.10 Force-Stroke Curves
3705.05.11 A Hydraulic 4,000 kN Sheet Forming Press
3705.05.12 Four-Point Die Cushion in the Press Table of a Simple Acting Press
3705.05.13 Lower Drawing Frame (I))
3705.05.14 Lower Drawing Frame (II)
3705.05.15 Optimal Working Range for Deep Drawing

3705.06.01 Tool Materials

TALAT 3705 29

Figure No. Figure Title (Overhead)
3705.06.02 Surface Treatment Processes

3705.07.01 CAD Illustration of a Coupè Door Planking
3705.07.02 Designing Surfaces
3705.07.03 CAD Illustration of Edge "B" of the Drawing Punch Surface
3705.07.04 Considering Springback in the Design

TALAT 3705 30

TALAT Lecture 3705: Drawing of Automotive Sheet Metal Parts

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (16)

Destacado

Destacado (20)

Similar a TALAT Lecture 3705: Drawing of Automotive Sheet Metal Parts

Similar a TALAT Lecture 3705: Drawing of Automotive Sheet Metal Parts (20)

Más de CORE-Materials

Más de CORE-Materials (20)

Último

Último (20)

TALAT Lecture 3705: Drawing of Automotive Sheet Metal Parts