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 © WZL/Fraunhofer IPT

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 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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 4

Sheet Material

Difference Between Sheet Material and Bulk Material


sheet coil (width, length » thickness) © WZL/Fraunhofer IPT


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. © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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) © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 . © WZL/Fraunhofer IPT

Seite 12

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 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

© WZL/Fraunhofer IPT

Seite 14

Sheet Metal Forming

Deep Drawing

Stretch forming

Spinning

Deep drawing

Ironing © WZL/Fraunhofer IPT

Bending

Hydroforming Seite 15

Deep Drawing Process

Deep Drawing of a Plane Round Sheet Plate Punch

Blank holder

Sheet metal

Drawing die

© WZL/Fraunhofer IPT

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. © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 18

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 21

Deep Drawing Process

Deep Drawn Mudguard


Avoidance of buckling during the forming of asymmetrical components by the use of

symmetrical geometry arrangement © WZL/Fraunhofer IPT

Seite 22

Deep Drawing Process

Deep Drawing of Car Body Components

Quelle: Daimler © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 24

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 © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 26

Sheet Metal Forming

Ironing

Strech forming

Spinning

Ironing

Deep drawing © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 32

Sheet Metal Forming

Bending Process

Stretch forming

Spinning

Bending

Deep drawing © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 36

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 38

Bending Process

Examples of Operation Steps using Die Bending

1. and 2. Step

1. Step © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 41

Sheet Metal Forming

Stretch Forming

Stretch forming

Bending

Deep drawing © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 44

Stretch Forming Process

Stretch Forming Failures Constriction with following crack

Brittle fracture


Cracks near to collet chucks © WZL/Fraunhofer IPT


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) © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

Seite 48

Sheet Metal Forming

Spinning

Bending

Stretch forming

Spinning

Deep drawing © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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. © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 54

Spinning Process

Force Components at Spinning Process

Ft

F a

Fr

Fr

Fa = Axial force © WZL/Fraunhofer IPT

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. © WZL/Fraunhofer IPT

Seite 56

Spinning Process

Spinning Process by Manual Work

Source: MetalSpinners

© WZL/Fraunhofer IPT

Seite 57

Spinning Process

Roll Spinning Pulley

Source: Leico

© WZL/Fraunhofer IPT

Seite 58

Spinning Process

Components

Aluminium reflectors

Rocket tank bottom

Aluminium-car-rim Source: Leifeld

© WZL/Fraunhofer IPT

Seite 59

Spinning Process

Laser Aided Spinning Machine Set-Up

Process


Increase of forming limit because of local heat input © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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. © WZL/Fraunhofer IPT

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

© WZL/Fraunhofer IPT

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 © WZL/Fraunhofer IPT

Seite 67