MFDP2 - L04 - Deep Drawing and Stretch Drawing - ENIM 2021-22

Mise en forme par déformation plastique 2
MECA 2
Lecture 04: Deep drawing and stretch forming
2021-22
Prof. Dr.-Ing. habil. Sami Chatti
Content
L02 – Deep drawing and stretch forming

Deep drawing
Principle and process parameters
Stresses and process forces
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
2022 Sami Chatti MFDP2 L4: Deep Drawing and Stretch Forming 4.2
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2
Comparison deep drawing vs. stretch forming
Deep drawing Stretch forming
Tensile-Compression stress in No wrinkles (pure tensile stress)

flange area (risk of wrinkles) Thickness reduction
Standard process for large Low springback
production scale Oversize parts
Constant sheet thickness is
aimed
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
2
4
Principle of deep drawing
FP
Punch
FBH FBH Blankholder
Sheet
Die
Definition according to DIN 8584:

Deep drawing belongs to the process of tensile-compressive forming of a sheet metal blank
(blank, circular blank) into a hollow part or of a hollow part to a hollow part with a smaller
circumference without an intended change of the sheet thickness
Deep drawing – process
Insert blank
Blankholder closing Punch

Blankholder
Punch in contact
with sheet Blank
Die
Deep drawing
Ejection of sheet
metal part
3
6
Insert blank
Blankholder closing
Punch
Blankholder
Punch in contact
with sheet Blank
Die
Deep drawing
Ejection of sheet
metal part
Insert blank
Blankholder closing Punch

Blankholder
Punch in contact
with sheet Blank
Die
Deep drawing
Ejection of sheet
metal part
4
8
Insert blank
Blankholder closing
Punch
Blankholder
Punch in contact
with sheet Blank
Die
Deep drawing
Ejection of sheet
metal part
Insert blank
Blankholder closing
Punch in contact
with sheet
Deep drawing
Ejection of sheet
metal part
5
10
Process parameters deep drawing
Blankholder
FP
FBH
• Initial diameter of blank d0 Die
• Actual blank diameter d Punch
• Punch diameter dp rp
rd
• Punch radius rp
dp
• Die diameter dd dd
• Die radius rd d
d0
• Punch force FP
• Blankholder force FBH
• Drawing ratio:
• Clearance u = (dd – dp)/2 = 1.2...1.35 t0
d0
• Sheet thickness t0 0 
dp
11
Dimensioning of (circular) blanks for round

deep drawing components
2
D0  2d1  4h 2
2022 Sami Chatti MFDP2 L4: Deep Drawing and Stretch Forming Cb_0124_pta 4.12
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12
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
13
Stresses in deep drawing
7
14
Deep drawing according to DIN 8587
Main group 2
Forming
Subgroup 2.1 Subgroup 2.2 Subgroup 2.3 Subgroup 2.4 Subgroup 2.5
Tensile-
Compressive Tensile Bend Shear
compressive
forming forming forming forming
forming
DIN 8583 DIN 8584 DIN 8585 DIN 8586 DIN 8587
Subgroup 2.2.1 Subgroup 2.2.2 Subgroup 2.2.3 Subgroup 2.2.4 Subgroup 2.2.5
Stripping Deep drawing Spinning Flanging Wrinkle bulging

DIN 8584 sheet 2 DIN 8584 sheet 3 DIN 8584 sheet 4 DIN 8584 sheet 5 DIN 8584 sheet 6
15
Forming area of a deep drawing part with

rotational symmetry
Flange
Deformation occurs in the flange area
s0
Wall
Bottom
s1 s 0
s1 s 0
8
16
Stresses during deep drawing
Flange
s Z  s id  s B  s F
Ideal stress (proportion) Wall
s id  1 .1  k fm  ln d
DP Bottom
Bending (proportion) dx
s B  f (k f , s 0 , rM ) st
x
Friction force (proportion)
s F  s FN  s FZ sr + sr
dj
ds r
between tool and blank
DP
s FN  f (m , s N ) RP =
2 st
due to the deflection at the die radius
p
R=D
2
m
s FZ  e 2  f (s id , s B , s FN )
17
Drawing force
second peak if
clearance too small
r '0r' 0,0.77
77  r0r
0 0
 
FP  Fid  FR  Fbending   e
 μ Ø: cup angle
 
ideal force flange friction     die-ring friction
 bending/unbending 
9
18
Blankholder force
The blankholder force to prevent wrinkling

corresponds to an average pressure on the
flange of 1 to 2 % of the flow stress. Letting
this fraction to be l, we get:
FBH  l  k f  p ( r0 )  ( rm ) 
2 2
 
Since the blankholder force is usually

constant:
FBH  l  k f  p ( r0 )  ( rm ) 
2 2
r0  
where 0.01  l  0.02
𝑟 = 𝑟 + 𝑠 /2
19
Total drawing force
   r0  m  FBH k fm ,die-ring  s0  μ 

2
FP  2p rm    k fm ,flange  s0 ln       e   sin 

   rm  p  r0 2  rfd  s0  
 r 
ln  0 
 rm 
s fm 𝑟 : 𝐷𝑖𝑒 𝑝𝑟𝑜𝑓𝑖𝑙𝑒 𝑟𝑎𝑑𝑖𝑢𝑠
∅: Cup angle (e.g. )
𝛼: Die angle (e.g. )
r0  0.77  r0
10
20
Deep drawing component with and without
earing formation
Source: Deutsches Kupferinstitut

21
Determination of anisotropies in thin sheet

metal
Vertical anisotropy Horizontal anisotropy:
rm = 1/4 ( r0 + r90 + 2 r45 ) r = 1/2 ( r0 + r 90 - 2 r45 )
For deep drawing sheet metals a For deep drawing sheet metals a
value as high as possible is desired value as small as possible is desired
Determination of r -value:
sampling for tension test
0°, 45° and 90° to the
rolling direction
Rolling direction
Effect on deep drawing:
Large
Largelevel
levelanisotropy
anisotropy= =large
largeearing
earingformation
formation
11
22
Example 1: Punch force
1) A non-hardening aluminum blank of 120 mm diameter and 1.2 mm

thickness has a flow stress of 300 MPa. It is deep drawn to a
cylindrical cup of 60 mm mid-wall diameter. What is the final height of
the product? (assume constant material thickness)
2) For the deep drawing process mentioned above, the blankholder

force is 40 kN and the friction coefficient is 0.1. What is the value of
the maximum punch force? (Use the equation given below).
𝑟 μ𝐹 μπ
𝐹 = 2π 𝑟 σ 𝑡 ln + exp
𝑟 π𝑟 2
23
Solution example 1
12
24
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
25
Failure modes (1)
Wrinkles of 1st order

Description: Undesirable wrinkling which can occur in
deep drawing in that part of the blank which hast not
entered the drawing die
Possible counter measures:

Increase blankholder force
Increase friction in flange area
Wrinkles of 2nd order
Description: Undesirable wrinkling in that part of the wall of
a drawn shape which has passed over the radius of the die

Increase blankholder force
Increase blank diameter
Use of drawbeads
Decrease die clearance
Decrease die and punch radii
Source: CIRP dictionary
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26
Failure modes (2)
Bottom tear
Description: A split or failure near the bottom portion of a
drawn cup

Reduce blankholder force
Increase die and / or punch radii
Increase of die clearance
Earing
Description: A regular variation in length of a cup or
ironed part which results from the anisotropic properties
of the initial workpiece

Use of isotropic material
27
Failure modes (3)
Spring back
Description: The amount by which a workpiece reverts
towards its original shape after removal of forming load

Adjustment of blankholder force
Modification of tool geometry
Modification of part design
Source: Simon, H.: Rechnergestützte Ziehteilauslegung mit elementaren Berechnungs-

Methoden, Universtät Hannover, Dr,-Ing. Dissertation, 1989
14
28
Influence of geometrical parameters
Die radius
Radius too small  Bottom tear

Fp
FBH
Radius too large  Reduction of flange area
Blankholder
Punch radius Punch
Radius too small  Punch cuts the sheet Die
Die clearance
Die clearance too large  Cup is widened  Wrinkles of 2nd order

Die clearance too small  Iroining, increased punch force; bottom tear; galling possible
29
Design of Deep Drawing Tools
Die clearance u z
uz = 1.2t ......1.35t t: blank thickness
(According to Lange)
Depth of draw hz Punch Blankholder

F
BH
hz is limited by maximum drawing ratio
F
P
Punch radius rP
Die
rP > r
D
r rP
Die radius rD D
0.04 D0
rP  (50  D0  DP )t
DP100 2
h
D z
t Blank thickness P

100 maximum drawing ratio u
z
(According to Romanowski)
15
30
Variables in deep drawing -blankholder force-
Blankholder force too high
FP
FBH
Blankholder force too low Adequate blankholder force
31
Process limits of deep drawing process
F
BHmax
Tears
BH
Blankholder force F
Working area
Wrinkles
Depth of draw h
16
32
Process control of the deep drawing process
Disturbance variable
Characteristics of semifinished products
Lubricant (amount, type, distribution,...)
Tool characteristics (surface, wearout,...)
Deep drawing process Result
Control manipulated
variable Reference variable
Blankholder force Drawing force
(global or for several Height of wrinkles
force transmission
Flange feed-in
points)
Controller Friction force
(dependent on the displacement
of the punch)
Strategy /
set values
33
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
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34
Drawing ratio β in first draw and second draw
35
Influence of the punch diameter on the

maximum drawing ratio
2.2
2.1
St 1403, Ms 63B, Ns 180
Maximum drawing ratio  0,max
St 1203, Ms 63A
St 1303
2.0
1.9
1.8
AL 99.5
AlMn
1.7
0 100 200 300 400
Punch diameter DP
t0
18
36
Increasing the drawing ratio (1)
Direct successive drawing Reverse drawing
Outer surface remains outer Inner surface from the first drawing
surface of the formed cup becomes the outer surface in the second
drawing
N. Bay (2002)
37
Increasing the drawing ratio (2)
Conventional Increased drawing ratio
N. Bay (2002)
19
38
Deep drawing and Ironing
VAW Aluminium AG (2001)
Ironing process: force at end cross section:
 2m m  tan  
Ftotal  A1  k fm 1    jmax 
 sin 2 tan   2 
39
Example 2: Drawing ratio
A cylindrical cup as shown in the figure is manufactured from St 1303

steel blank. The permissible draw ratio for this material is 2.05.
Determine:
(1) the blank diameter d0.
(2) the actual drawing ratio.
(3) the minimum number of draws required in order to produce the part.
20
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Solution example 2: Drawing ratio
41
Example 3: Process design
From a 1 mm thick blank of sheet metal material number 1.0338 (St

14) a hollow cylindrical part with a diameter of 45 mm and a can body
height of 90 mm is to be drawn. The limiting draw ratio βmax of the
material is 2.
1) Calculate the initial diameter D of the circular blank.

2) Calculate the total drawing ratio βtot.
3) If βtot is greater than the limiting drawing ratio βmax, several
drawing operations are needed. In order to have a robust and
reproducible production sequence, the maximum permitted
drawing ratios should not be fully utilized. Design a process with
three operations whereby β1 may have a maximum value close to
2, and all following β values are less than 1.3. Determine the
values of the punch diameters.
21
42
Solution example 3
43
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
22
44
Movie: Deep Drawing
Principle: Real Process:

FP
FBH FBH
Placing the blank
Closing the blankholder
Movement of the punch
Deep Drawing
Ejection of the workpiece
45
Drawbeads for drawing irregular parts
Drawbeads
• Drawbeads are used for parts of a
plane, rectangular, irregular or
complex geometry
• In general, drawbeads are placed
at side walls and are used to slow
down the material flow
• In corner radii the material flow is
undisturbed
Blankholder Punch
Drawbeads
Die
23
46
Deep drawing: applications in automotive sector
47
Variation of steel material used in the car body
60
Mild steels, Structural steels
50 Isotropic steels
Total elongation A 80 in %
Higher-strength IF-steels
40 Dual-phase steels (DP)
TRIP steels
TRIP 1000
30
20 Bake-hardening
steels DP800 / 1000
Work hardening Hot-formed steels
10 Micro-alloyed
steels
steels Complexphase
steels (CP) CP1000
0
200 400 600 800 1000 1200
Einleitung
Tensile strength R m in MPa

(Source: ThyssenKrupp Steel Europe)
24
48
Material used in the car body – Mercedes C-class
Mild steel
High strength steel
Highest strength steel
Ultra high strength steel
Hot-formed steel
Aluminium
Plastic
Highest strength steel (11%)
High strength Ultra high strength steel (3 %)

steel (50%)
Hot-formed steel 6%
Aluminium (3%)
Source: Mercedes-Benz
Mild steel Plastic (2%)
Source: ATZ extra „Die neue C-Klasse von Mercedes-Benz“, April 2007 (25%)
49
Material used in the car body – Volkswagen VW up!

Hot-formed steel
Ultra high Mild steel
strength steel
Highest
strength steel High strength steel
Source: ATZ extra „Der neue VW up!“, September 2011
Source: Volkswagen
25
50
Deep drawing: applications in the household
51
Content

Deep drawing
Process limits
Drawing ratio
Applications
Machines
Stretch forming
Applications
26
52
Deep drawing of large sheet metal components:
Tools and large panel transfer press
2022 Sami Chatti MFDP2 L4: Deep Drawing and Stretch Forming Ck_0006_ba 4.53
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Double action hydraulic press
Slide cylinder
Press crown
Tie rod
Die
Punch
Slide cushion
Blankholder
Lifting cylinder
Draw cushion
Draw cushion
cylinder
27
54
Principle: double action press
55
28
56
57
29
58
59
30
60
Setup of a hybrid press
Clamp set for stroke adjustment Eccentric shaft
Feed drive Clutch-brake

combination with
compact drive
Hydraulic accumulator
Slide for bottom side
counter- Compressed air
balance accumulator for
Hydraulic slide counterbalance
cylinder mechanically actuated
top slide
Bed plate Hydraulic actuated
bottom slide
Bed plate
shift device Position sensing system
for the slide
Hydraulic Scrap chute

draw cushion
Damping element
61
Triple action hydraulic press

Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
31
62
Principle: triple action press
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
63

Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
32
64
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
65
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
33
66
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
67
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
34
68
Hydraulic in
block construction
Main motor
Slide cylinder
Blankholder
cylinder
Main pump
Blankholder
guide
Adjustment of
depth of draw
Pressure adjustment
Limit switch
Draw cushion
guide
Draw cushion
plate
69
Classification of deep drawing presses according to

the amount of degrees of freedom
Classification of deep drawing presses according to the amount of degrees of freedom
Corresponding to the amount of necessary degrees of freedom (acting axis) the following presses are
used:
- Single action press (movement of the main slide)
- Double action press (movement of main and blank holder slide or main slide and die
cushion)
- Triple action press (movement of main and blank holder slide and die cushion)
Classification of deep drawing presses according to the kind of movement generation
- Displacement-related (crank, eccentric, knuckle joint press) and

- Force-related (hydraulic) press
Advantages of hydraulic presses disadvantages of hydraulic presses

High nominal forces can be obtained lower number of strokes than with mechanical
presses
High nominal forces are available during the high energy consumption
whole forming procedure
precisely adjustable and controllable force and speed
simple and stepless adjustability of stroke and
dead centres of the slide
easier automation
protection against overloads
possibility to interrupt the slide stroke
35
70
Content

Deep drawing
Process limits
Drawing ratio
Blank
Case studies
Applications
Stretch forming
Applications
71
Definition of stretch forming
Definition according to DIN 8585:

Stretch forming is the forming of a sheet blank with a rigid
(one-piece) punch, whereby the blank is rigidly clamped at
the edges. The blank can be clamped between rigid tools,
corresponding to the upper and lower drawing frames of the
conventional tools, or be clamped in gripping jaws.
Types of Stretch Forming

Simple stretch forming
Tangential stretch forming
Stretch forming according to Cyril-Bath
Multi-sided stretch forming
36
72
Stretch forming – process principle
73
Stretch forming – process principle
37
74
Application example
75
Film: Stretch forming
Process principle: Real Process: Airplane side wall
Insert blank
Close collets
Move punch
Stretch forming
38
76
Stretch forming according to DIN 8585
Main Group 2
Forming
Subgroup 2.1 Subgroup 2.2 Subgroup 2.3 Subgroup 2.4 Subgroup 2.5
Tensile-
Compressive- Tensile- Bend Shear
compressive
forming forming forming forming
forming
DIN 8583 DIN 8584 DIN 8585 DIN 8586 DIN 8587
Subgroup 2.3.1 Subgroup 2.3.2 Subgroup 2.3.3

Extending Expanding Stretch identing
DIN 8585 DIN 8585 DIN 8585
Subgroup Subgroup
2.3.3.1.1.1 2.3.3.1.1.2
Stretch drawing Embossing
DIN 8585 DIN 8585
77
Deformation area during stretch forming
Plastic deformation only in

the inner area of the blank
F
Punching force F
s0
F
max
s1< s0
Displacement of the punch
Inhibit the flange feed-in

e.g. with the help of clamping
elements in the tool
39
78
Content

Deep drawing
Process limits
Drawing ratio
Blank
Case studies
Applications
Stretch forming
Applications
79
Simple stretch forming
Punch
Source: Müller-Weingarten Co.
40
80
Example of simple stretch forming
Airplane wings
Stretch forming at TAI
81
Tangential stretch forming
Punch
Source: Müller-Weingarten Co.
41
82
Flexible stretch forming
Punch
Four gripper stretch

forming machine
Source: IFU Stuttgart
83
Surface failure by stretch forming

Reason: Yield-Point Elongation
Stretch formed part with Lueder‘s bands
Source: S. Kalpakjian
42
84
Film: The crossbar transfer press by Schuler
85
Appendix: English for Production Engineers
English Français English Français

Emboutissage
Deep Drawing Earing Formation d'oreilles
profond
Rapport
Punch Poinçon Drawing Ratio
d’emboutissage
Blankholder/Binder Serre-flan Limiting Drawing Rapport limite
Die Matrice Ratio (LDR) d’emboutissage
Profondeur
Die Radius Rayon de matrice Depth of Draw
d'emboutissage
Clearance Jeu d’emboutissage Wall (of a cup) Paroi
Drawbead Jonc de retenue Flange (of a cup) Collerette
Formage par
Fracture Fracture Stretch forming
extension
Fracture à la base de
Bottom Tear
la coupelle
Wrinkling Plissement
43
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Mise en forme par déformation plastique 2

Lecture 04: Deep drawing and stretch forming

Prof. Dr.-Ing. habil. Sami Chatti

L02 – Deep drawing and stretch forming

Deep drawing Stretch forming

Tensile-Compression stress in No wrinkles (pure tensile stress)

L02 – Deep drawing and stretch forming

FBH FBH Blankholder

Definition according to DIN 8584:

Deep drawing – process

Blankholder closing Punch

Deep drawing – process

Blankholder closing Punch

Deep drawing – process

• Actual blank diameter d Punch

Dimensioning of (circular) blanks for round

L02 – Deep drawing and stretch forming

Stresses in deep drawing

Stripping Deep drawing Spinning Flanging Wrinkle bulging

Forming area of a deep drawing part with

Ideal stress (proportion) Wall

The blankholder force to prevent wrinkling

Since the blankholder force is usually

Total drawing force

   r0  m  FBH k fm ,die-ring  s0  μ 

FP  2p rm    k fm ,flange  s0 ln       e   sin 

Source: Deutsches Kupferinstitut

Determination of anisotropies in thin sheet

Effect on deep drawing:

1) A non-hardening aluminum blank of 120 mm diameter and 1.2 mm

2) For the deep drawing process mentioned above, the blankholder

L02 – Deep drawing and stretch forming

Failure modes (1)

Wrinkles of 1st order

Possible counter measures:

Possible counter measures:

Possible counter measures:

Possible counter measures:

Source: CIRP dictionary

Failure modes (3)

Possible counter measures:

Source: Simon, H.: Rechnergestützte Ziehteilauslegung mit elementaren Berechnungs-

Radius too small  Bottom tear

Radius too small  Punch cuts the sheet Die

Die clearance too large  Cup is widened  Wrinkles of 2nd order

Design of Deep Drawing Tools

Depth of draw hz Punch Blankholder

Blankholder force too high

Blankholder force too low Adequate blankholder force

Process limits of deep drawing process

Deep drawing process Result

L02 – Deep drawing and stretch forming

Influence of the punch diameter on the

Direct successive drawing Reverse drawing

Increasing the drawing ratio (2)

Conventional Increased drawing ratio

VAW Aluminium AG (2001)

Ironing process: force at end cross section: