Sheet Metal Forming I
Simulation Techniques in Manufacturing Technology
Lecture 3
Laboratory for Machine Tools and Production Engineering
Chair of Manufacturing Technology
Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke
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Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 1
Introduction
Methods of Forming – Classification DIN 8580 ff
Manufacturing processes
Casting
Compressive
forming
Open die forging
Closed die forging
Cold extrusion
Rod extrusion
Rolling
Upsetting
Hobbing
Thread rolling
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Forming
Tension
compressive
forming
Deep drawing
Ironing
Spinning
Hydroforming
Wire drawing
Pipe drawing
Collar forming
Cutting
Tensil forming
Stretch forming
Extending
Expending
Embossing
Joining
Bending
With linear
tool
movement
With
rotatory tool
movement
Coating
Shear forming
Translate
Twist
Intersperse
Changing of
material properties
severing
Shearing
Fine Blanking
Cutting with a
single blade
Cutting with two
approaching blades
Splitting
Tearing
Seite 2
Techniques of Metal Forming: Bulk Forming – Sheet Metal Forming
Bulk forming:
Sheet metal forming:
High changes in diameter and
No or low unwanted changes of the
dimensions
original wall thickness
High deformation
Lower deformation
High material hardening
Lower material hardening
High forces
Lower forces
High tool stresses
than in bulk forming
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Seite 3
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 4
Sheet Material
Difference Between Sheet Material and Bulk Material
sheet
coil (width, length » thickness)
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bulk
slab (460 x 1400 x 3400)
Seite 5
Sheet Material
Manufacturing of Sheet by Flat Longitudinal Rolling
Coil velocity is considerably higher than
slab velocity
(v1 ≈ 400 v0)
Roller
l1 >> l0
Strip
The lenghtwise extension of the sheet leads to
directionally dependent material properties.
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Seite 6
Sheet Material
Definition of Anisotropy Values
Rolling
direction
Direction of pattern:
Strip
Impact of anisotropy
Perpendicular anisotropy r
Examination of anisotropy
Angle to rolling direction / °
The term ‘anisotropy’ describes:
The material properties’ dependance on the orientation to the rolling direction.
In sheet metal processing:
perpendicular anisotropy r (depending on sheet thickness) and
plane anisotropy ∆r (depending on sheet plane) are encountered.
Anisotropy has to be considered in the dimensioning of forming processes
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Seite 7
Sheet Material
Forming Property: Measuring Grid Technique
ϕb = ln
b1
d0
ϕl = ln
l1
d0
Deformation of the measuring grid because of tensile and compression stresses inside
the sheet metal while forming
The effective strain can be derived from the grid deformation = maximum deformation
(forming limit)
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Seite 8
Sheet Material
Forming Property: Forming Limit Curve
Definition: φ1 > φ2
Test conditions:
deep drawing test with hemispherical
stamp and straight strip
Strain φ1
“Failure “
Tensocompressive
“Well“
Quelle: ThyssenKrupp
Tenso-tenso
Variable strip thickness to vary φ2 (one test
corresponds with one value of φ2)
Material: RR St 1403
Sheet thickness : 1 mm
Strain φ2
Determination of forming limit curve
to predict failure by using FEM
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Seite 9
Sheet Material
Delivery Possibilities for Sheet
Hot rolled strip
thin sheet
thick plate
Cold rolled strip
thin sheet
thick plate
Surface finished sheet
Tailored blanks
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Seite 10
Sheet Material
Development of High Strength Sheet Materials
Elongation at Fracture A80 / %
Soft
High
strength
Higher strength
Highest strength
80
60
IF
40
20
0
0
200
400
600
800
1000
1200
1400
Tensile Strength Rm / MPa
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Seite 11
Material Sheet
Production of „Tailored Blanks“
Quelle: ThyssenKrupp
Door of
passenger car
Floor of
passenger car
Coil material can be made of sheets differing in
thickness and strength. Ulterior motive is the
production of sheet components with differing
sheet thickness considering feasible loadings .
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Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 13
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 14
Sheet Metal Forming
Deep Drawing
Stretch forming
Spinning
Deep drawing
Ironing
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Bending
Hydroforming
Seite 15
Deep Drawing Process
Deep Drawing of a Plane Round Sheet Plate
Punch
Blank holder
Sheet
metal
Drawing die
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Seite 16
Deep Drawing Process
Material Flow – from Flange to Cup Wall
a = Material to be bend
b = Material to be displaced
Before forming
After forming
Material displacement in circumferential
direction causes tangential compressive
stresses in the flange region.
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Seite 17
Deep Drawing Process
Problem: Formation of Wrinkles in the Flange
By exceeding buckling instability
of the sheet material, the tangential
compressive stresses produce
wrinkles in the flange
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Deep Drawing Process
Failures in Deep Drawing
Earing
Plane anisotropy
Eccentric position
of circular blank
Mistake of user
Cup base fracture
Exceeding of tensile
strength of the material
Lip formation
Increased strain
hardening of the
material in edge
region
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Seite 19
Deep Drawing Process
Redrawing (Multi-Station Die)
Punch
Blank holder
Predrawed
cup
Back-up ring
Drawing die
Production of
rotationally symmetrical
components by
redrawing to reduce
loadings on tools and
workpiece
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Seite 20
Deep Drawing Process
Use of Brake and Drawing Beads
Deep drawn engine bonnet
Blank holder
Die
Punch
Draw bead
Use of brake or drawing beads to manage the material
flow during drawing
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Seite 21
Deep Drawing Process
Deep Drawn Mudguard
Avoidance of buckling during the forming of asymmetrical components by the use of
symmetrical geometry arrangement
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Seite 22
Deep Drawing Process
Deep Drawing of Car Body Components
Quelle: Daimler
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Seite 23
Deep Drawing Process
Deep Drawing with Elastic Tools and Liquid Media
Punch
Deep drawing
with rubber
stamp
Rubber
Workpiece
Deep
drawing with
rubber pad
Membrane
Water
Liquid
Workpiece
Deep
drawing
with water
bag
Rubber core
Deep drawing
with
membrane
The application of a rubber pad or a membrane, which is filled with a liquid medium, is universal
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Deep Drawing Process
Deep Drawing with Elastic Tools and Liquid Media
Deep drawing
with fluid
pressure on
one side
Workpiece
Deep drawing
with fluid
pressure on both
sides
Membrane
Vacuum
Deep drawing
with
positive pressure
on one side
Vacuum
Deep drawing
with
negative pressure
Workpiece
The process limits of deep drawing with rigid dies can be enlarged or
circumvented
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Seite 25
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 26
Sheet Metal Forming
Ironing
Strech forming
Spinning
Ironing
Deep drawing
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Bending
Hydroforming
Seite 27
Ironing Process
Schematical Description of Ironing
Punch
Sheet forming = Production of plane hollow
bodies without required change of wall
thickness
Ironing = Bulk forming
Workpiece
Ironing die
Ironing is applied for a defined reduction of the wall
thickness of a deep drawn workpiece
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Seite 28
Ironing Process
Multi-stage Ironing – Influence of workpiece velocity
Achievement of high wall
thickness proportions by multistation ironing
Because of the difference in
Punch
velocity between intake and
runout, the workpiece should
have left the first ironing die
before running into the next
ν
2
Distance
ν
1
Workpiece
Ironing dies
νS
t
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Seite 29
Ironing Process
Progression of Force for Different Distances of Ironing Dies
Drawing Force
1,2,3: Single drawings
4: Triple drawing
Ironing die
4
Ød2 az
Zwischenring
Distance ring
Abstreckring
Ironing die
1
2
Increase of resulting force in triple
drawing,
Risk of cup base fracture.
Punch Displacement
Ironing die
Ød2
4
4
Ironing die
3
2
az
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az
Large distance between ironing dies:
Ød1
1,2,3: Single drawings
4: Triple drawing
Distance ring
1
Low distance between ironing dies:
3
az az
Drawing Force
Ød1
az
Decrease of resulting force in
triple drawing,
Large stroke of punch required.
Punch Displacement
Seite 30
Ironing Process
Production of a Beverage Can
High strains can be reached by the use of
several ironing steps
Source: Visypack, Ball Europe
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Seite 31
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 32
Sheet Metal Forming
Bending Process
Stretch forming
Spinning
Bending
Deep drawing
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Ironing
Hydroforming
Seite 33
Bending Process
Classification of Bending Techniques
Forming by bending
Forming by bending with linear tool movement
Drawing by a
sliding action
Open bending
Die bending
Straightening
Radial die
forming
Open circular b.
Die flanging
B. without radial
stress
Radial die forming
Edge rolling
Bending by
bulging
Winding
Crimping
Roll straightening
Corrugating
Roll forming to shape
Coiling
Rotary bending
Circular bending
Roll draw bending
Swing-folding
Roll bending
Forming by bending with rotatory tool movement
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Seite 34
Bending Process
Distribution of Stresses and Straines during Bending
y
εbl
εel
εpl
εpl
εel - Elastic elongation
s0 /
2
Neutral fiber
Yielding point
σx; εx
εpl - Plastic elongation
εbl - Permanent elongation
after springback
s0 /
2
State of stress under load
State of stress after springback
Ideal plastic material
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Seite 35
Bending Process
The Springback Issue
Residual stresses of
component lead to
springback
The state of residual
stresses after forming
depends on the reaction of
the material deformation
The flow behaviour at load
inversion depends on
history of deformation
(Bauschinger-Effect)
Stainless steel
Aluminium
Copper
High strength
steel
Steel
Quelle: IWM
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Bending Process
Deformation in Bending Zone
Workpiece
Reduction of cross section and
deformation along the bending edge
occurs when having thick sheets and
small bending radii
Clamping jaw
S : Sheet thickness
Ri: Inner radius
Ra: Outer radius
Fiber of no extension
Workpiece
Especially in case of open bending
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Middle fiber
(“Neutral fiber“)
Region of cross section reduction by
stretching
Seite 37
Bending Process
Roll Forming to Shape
Workpiece
Initial state
Distance
between
roller-pair
Upper roll
Final state
Lower roll
1. Step
4. Step
6. Step
5. Step
7. Step
2. Step
3. Step
Strips of optional length
can be formed
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Seite 38
Bending Process
Examples of Operation Steps using Die Bending
1. and 2.
Step
1. Step
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3. and 4.
Step
2. Step
5. and 6.
Step
3. Step
7. Step
4. Step
Seite 39
Bending Process
Arrangement of Rollers at Three-Roll Bending Machines
Symmetrical
three-roller bending machine
Roll bending is mainly used for rolling of thin, medium and
thick plates for producing tubes and tubular workpieces.
By variation of roll position non-rotationally symmetric
workpieces can be produced as well.
Quelle: Bergrohr
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Seite 40
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 41
Sheet Metal Forming
Stretch Forming
Stretch forming
Bending
Deep drawing
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Ironing
Spinning
Hydroforming
Seite 42
Stretch Forming Process
Difference Between Bending and Stretch Forming: The Neutral Fiber
Stretched zone
Neutral fiber
Stretch formed profile
Upset
zone
Stretched zone
Sheet thickness
Open bended profile
Reduction of springback by stretch
forming
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Neutral Fiber (outside of the sheet)
Seite 43
Stretch Forming Process
Sketch of a Stretch Forming Press
Workpiece
Forming punch
Collet chuck
Bottom plate
Piston
Hydraulic cylinder
Low tool and machine costs concerning the size of the work pieces being produced
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Seite 44
Stretch Forming Process
Stretch Forming Failures
Constriction with following
crack
Brittle fracture
Cracks near to collet chucks
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Cracks in vertex region
Seite 45
Stretch Forming Process
Stretch Forming Techniques
Workpiece
Waste
material
Lost end
Basic stretch forming (high amount of
waste material)
Waste
material
Workpiece
Tangential stretch forming (low amount of waste
material)
Tangential stretch forming (underdrawing possible, higher process flexibility)
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Seite 46
Stretch Forming (+ Deep Drawing)
Drawing of Car Body Panels
Drawing of car body panels
Stretch forming
Deep drawing
Drawing of car body panels
Punch
Blank holder
With break
bead
Source: PtU
Die
Real drawing of a car body panel is always a combination between stretch forming and
deep drawing
© WZL/Fraunhofer IPT
Seite 47
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
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Seite 48
Sheet Metal Forming
Spinning
Bending
Stretch forming
Spinning
Deep drawing
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Ironing
Hydroforming
Seite 49
Spinning Process
Spinning Process (Sketch) with Intermediate Stages
s0 : Sheet thickness of circular blank
do : Diameter of circular blank
0 : Basic shape
1-6 : Intermediate stages
7 : Final stage
Projizierstreckdrücken
Spinning roll
Spinning chuck
Counterholder
animated
animiert
Workpiece
Low tool costs and cycle times in comparison to alternative processes
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Seite 50
Spinning Process
Spinning Techniques
Gegenwerkzeug
Counter tool
Spinning roll
Drückwalze
Drückform
Spinning
form
Counterholder
Gegenhalter
Counterholder
Gegenhalter
Drückstab
Spinning bar
Engen durch
Drücken
Contracting
by spinning
Spinning of
external
flanges
Erzeugen
von
Außenborden
durch Drücken
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Aufweiten durch
Drücken
Expanding
by spinning
Erzeugen
von Innenborden
Spinning
of
durch
insideDrücken
beads
Drückwalze
Spinning
roll
Einhalsen
durch
Drücken
Necking by
spinning
Workpiece
Werkstück
Gewindedrücken
Thread spinning
Seite 51
Spinning Process
Ironing by Spinning in Same and Opposite Direction
Spinning
chuck
Drückfutter
Counterholder
Gegenhalter
Same direction process
Flow of material in direction of tool
movement
Drückrolle
Spinning
roll
Spinning chuck
Drückfutter
Opposite direction process
Flow of material in opposite
direction of tool movement
Drückrolle
Spinning roll
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Seite 52
Spinning Process
Defects in Production when Spinning a Cup
Radial cracks by tangential
compression and bending stresses
Formation of wrinkles by tangential
compression and bending stresses
Tangential cracks by
radial or axial tensile stresses
During spinning axial and radial tensile stresses occur as well
as tensile and compressive stresses in tangential direction.
These stresses can finally lead to an overload of the
workpiece.
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Radial cracks by
tangential tensile stresses
Seite 53
Spinning Process
Maximum Accepted Spinning Proportion
Spinning Proportion βmax
Material St 13
dW/d1 = 1,5
Related sheet thickness s0/d1
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Seite 54
Spinning Process
Force Components at Spinning Process
Ft
F
a
Fr
Fr
Fa = Axial force
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Fr = Radial force
Ft = Tangential force
Seite 55
Spinning Process
= 1.2
= 0.1
= 0.2
= 0,17 · 10-2
Material St 13
Diameter after
conditioning d1
Diameter of spinning roll dW
Specific Axial Force Fa / d12 / MPa
dW / d1
ρW / d1
ρW / d1
f / d1
Specific Radial Force Fr / d12 / MPa
Axial und Radial Force at Spinning Process
Axial Force
Curvature of roll ρW
Feed f
Spinning Proportion β = d0 / d1
Radial Force
Spinning Proportion β = d0 / d1
Forming forces increase when feed and initial sheet thickness are increased.
Axial and radial forces are influenced by spinning proportion β and curvature radius ρW of spinning
roll without reduction of sheet thickness.
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Spinning Process
Spinning Process by Manual Work
Source: MetalSpinners
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Seite 57
Spinning Process
Roll Spinning Pulley
Source: Leico
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Seite 58
Spinning Process
Components
Aluminium reflectors
Rocket tank bottom
Aluminium-car-rim
Source: Leifeld
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Seite 59
Spinning Process
Laser Aided Spinning
Machine Set-Up
Process
Increase of forming limit because of local heat input
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Seite 60
Outline
1
Introduction
2
Sheet Material
3
Sheet Metal Forming Techniques
3.1 Deep Drawing Process
3.2 Ironing Process
3.3 Bending Process
3.4 Stretch Forming Process
3.5 Spinning Process
3.6 Hydroforming
© WZL/Fraunhofer IPT
Seite 61
Sheet Metal Forming
Hydroforming
Strech forming
Spinning
Hydroforming
Deep drawing
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Ironing
Bending
Seite 62
Hydroforming
Principles of Hydroforming
ProzessInitiation
of
beginn
process
ProzessEnd of
ende
process
keine
externe
No external
Druckversorgung
pressure supply
Expanding in a closed tool
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Seite 63
Hydroforming
Production of a T-Part
Counterholder
Close press
Tube
Halves of formtool
Fill up with
fluid medium
Move horizontal
cylinder, adjust
water pressure,
direct counterholder
Open press,
eject part
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Seal stamp
Secondary form
T-part
Seite 64
Hydroforming
Production of a Engine Bracket
Hydroforming tool
Engine bracket with add-on parts
In comparison to conventional construction:
30 % lower weight,
20 % lower costs,
60 % lower tool costs.
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Seite 65
Hydroforming
Production of a Engine Bracket
Axial cylinders seal ends
of tubes
Preformed piece is flooded
by hydromedium
Forming with internal
pressure of 1.500 bar
Final shape of workpiece
depends on die cavity
Axial cylinders add
material by sliding
Punching after forming;
slugs are bend down
inside
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Seite 66
Hydroforming
Examples of Components in the Field of Car Body
Audi TT
Roof frame
lateral l./r.
Reinforcement
Eaves gutter l./r.
Transversal
bar of windscreen
Closure pipe
Main pipe
Control arm
Rear bottom
transversal bar
Sillboard l./r.
Transversal bar of seat l./r.
Audi A6
Production of high strength life and weight optimized components and units
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Seite 67