l01 bulk metal forming 1

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© WZL/Fraunhofer IPT

Bulk Metal Forming ISimulation Techniques in Manufacturing Technology

Lecture 1

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



Seite 1 © WZL/Fraunhofer IPT

Lecture objectives

Basic knowledge in metallurgy for a better understandingof the mechanisms during metal forming

Elastic and plastic material behaviour and its influence onthe process results in forming technology

Mathematical models for a description of the elastic andplastic material behaviour

Introduction of processes in cold and warm bulk formingas well as in forging




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4

Plastic Deformation3

Elastic Deformation2

Metallurgical Basics1

Outline




Metallurgical Basics

4 Basic Chemical Bonds

+ + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + +electron gas (e-)

positive chargedmetal ions

ionic bond

metal bond

+

-

-

--

-

-

--

---

-

-

-+

+

+

+

+

++

+

+

+

+

+

+

metal bond

ionic bond

covalent bond

Van-der-Waals bond





The Metal Bond

metal atoms basically emit electronspositive charged ions

in pure metals no electron-absorbing atoms do existun-combined electrons (outer electrons) form an electron gas

outer electrons in metals can freely movegood electrical and thermal conductivity

in absolute pure metals all atoms are totally equalplastic deformation

+ + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + +

electron gas (e-)

positive chargedmetal ions

metal bond





Lattice Types of an Unit Cell

face-centredcubic(fcc)

body-centredcubic(bcc)

hexagonal(hex)

examples:

sliding planes:

sliding directions:sliding systems:

formability:

γ-Fe, Al, Cu

4

312

very good

α-Fe, Cr, Mo

6

212

good

Mg, Zn, Be

1

33

poor





Atomic and Macroscopic View of Metal Structures

idealcrystal

structure

special agglomeration of crystals

section plane

a

crystal latticeunit cell

2D – Cutof the microstructure

microstructure

schematically photograph

realcrystal

structure




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline




Elastic Deformation

Tensile Test – Load-Displacement Diagram

specimen 1

specimen 2

A1 = 2 • A2

follows:F1 = 2 • F2

relate force to cross section surface

tensile specimen

l o a d

displacement

F1

F2

l1l1 = l2




Elastic Deformation

Stress-Strain Curve of Elastic Behaviour

00

01

l

l 00 l

∆l

l

ll

l

dl ε

l

dl d

1

0

=−

==⇒= ∫ε

A

F

0

=σ

tanel

el

ε

σ α =

s t r e s s

strain

F

F

Re

σel

eel

l0

∆l

l

A0

A

engineering strain:

engineering stress:

α

For elastic behaviour:

Eel

el

ε

σ =

σ ≤ Re

E = Young‘s Modulus

specimenno. 1≙ no. 2




tensile test compression test shear test

F

F

l 0

A0

l 1

A1

A0

F

F

A1

l 1

l 0

0A

F =σ

0A

F −=σ

Elastic Deformation

Stress Determination Depending on Load

0A

F

=τ

F

Fa

l

q

A0

tensile stress compression stress shear stress




unloaded tensile-loaded

σ - nominal stress

ε - strainE - Young‘s Modulus

l0 l1

s

s

Elastic Deformation

Atomic Representation of Pure Elastic-Tensile Deformation

00

01el

l∆l

lll ε =−= E

el

el

ε σ =

elastic strain based on tensile load




τ

γ

τ

unloaded shear-loaded

γ - shear angle

τ - shear stressG - shear modulus

ν - Poisson‘s ratio

E - Young‘s modulus

Elastic Deformation

Atomic Representation of Pure Elastic-Shear Deformation

)2(1

Gel µ γ

τ

+== E

elastic shearing based on shear load




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline




Plastic Deformation

Stress-Strain Curve up to the Uniform Elongation

AF

0

=σ

s t

r e s s

strain

engineering stress:(related to starting section)

F

F

Rm

Re ,se

eelepl

l0

∆l

l

A0

A

loadrelieving reload

A

F =′σ

true tensile stress:(related to real section)

σ‘σ




Plastic Deformation

Strain Determination of an Idealized Upsetting Process

00

01

00

1

0

l

l

l

l l

l

dl

l

dl d

l

l

x x

∆=

−==⇒= ∫ε ε

0

1

0

1

0

1 ln ;ln ;lnh h

b b

l l z y x === ϕ ϕ ϕ

0

1ln1

0l

l

l

dl

l

dl d

l

l

==ϕ ⇒ =ϕ ∫

engineering strain (elastic)

true strain (plastic)

including of volume constancy

)1(ln l

l

l

l ln

l

ll ln

l

ul ln

l

l ln

0

0

00

0

0

x0

0

1 +=

+

∆=

∆+=

+=

= x x ε ϕ

const. 111000 =⋅⋅=⋅⋅ b h l b h l

0 =++ z y x ϕ ϕ ϕ

connection between true strain - engineering strain




Plastic Deformation

Types of Plastic Deformation

dislocation movement

low energy required

sliding

high energy required

before

after




Plastic Deformation

Sliding and Dislocation Movement

dislocation movementsliding




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline




Flow Stress

Flow Curve

f l o w

s t r e s s

effective strain

required stress to break

the strain hardening

required stress forplastic deformation




Flow Stress

Strain Hardening Depends on Dislocations

schematic diagramdislocation movement

sliding planes

dislocation origingrain boundary

moving direction

grain boundary

piled up dislocations at boundary grainsdislocation structure of little-formed copper




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline




Recrystallisation

Static Recrystallisation

requirements:

- ϕϕϕϕv > 0

- T > TRecrystallisation

- impact time

Schematic course of recrystallisation of cold formed structure

d u

c t i l e y i e l d A 1 0 ,

t e n s

i l e s t r e n g t h R m

c r y s t a l

r e g e n e r a t i o n

large increase

of A10

small decreaseof Rm

temperature, °C




Recrystallisation

Stress Curve of Cold Forming as a Result of Static Recrystallisation

f l o w

s t r e s s

effective strain

a n n e a l i n g f o r

r e c r y s

t a l l i s a t i o n

ϕϕϕϕvBr ϕϕϕϕvBr

ϕϕϕϕvBr - effective strainat time of fracture

annealing for recrystallisation increases effective strain and decreases flow stress

a n n e a l i n g f o r

r e c r y s

t a l l i s a t i o n




Recrystallisation

Effective Strain and Temperature Influence the Grain Size

g r a i n

s i z e

effective strain

range ofrecrystallisation




Recrystallisation

Forming Temperature and Velocity Influence the Flow Stress

forming temperature belowrecrystallisation temperature

high forming velocity

low forming velocity

forming temperature above

recrystallisation temperature

effective strain

f l o w

s t r e s s




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline




Bulk forming

massivesemi-finished material

component

Cold forming

What is Bulk Forming?




semi-finished part component

Cutting

1,3 kg

Introduction

Advantages of Bulk Forming

Forming

0,4 kg

componentbasic workpiece

C




fcc

bcc

Recrystallization

Cold forming

Iron-Carbon Phase Diagram

Carbon content in weight percent

Cermentite content in weight percent

δ-Fe

δ- + γ -Fe

T e m p e r a t u r e

i n ° C

Liquid + δ-Fe

Liquid

Fe3C(Cementite)

Liquid +

Fe3C

Liquid + γ -Fe

γ -Fe + Fe3C

γ -Fe(Austenite)

α-Fe (Ferrite)

γ - + α-Fe

α-Fe + Fe3C

C ld f i




Workpiece temperature / °C

S t r a i n ϕ

F l o w

s t r e s

s k f / M P a

L a y e r o f s c a l e / µ m

Cold forming

Material Properties

high flow stresses and low achievable strains by classic steel materials

C ld f i




Cold forming

Advantages and Disadvantages of Cold Forming

Cold Forming Advantages:

low tool material costs

low influence of forming velocity

no energy costs for heating no dimension faults caused by dwindling

high surface quality

increasing strength of the component

Disadvantages:

high forces

limited plastic strain

Cold forming




Forming process IT-Grade according to DIN ISO 286

5 6 7 8 9 10 11 12 13 14 15 16

Cold extrusion

Warm extrusion

Hot extrusion

Centerline average Ra / µm

0,5 1 2 3 4 6 8 10 12 15 20 25 30

achievable with special proceedings achievable without special proceedings

Cold forming

Efficiency

small shape, dimension and position tolerances as well as

good surface qualities are possible

Cold forming




forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.

plasticity φ < 1,6 r<4 r<6

finishing effort less low high

semi-finished part cold forming

Cold forming

Efficiency

(for classic forming steels)

by the aid of cold forming processes a good workpiece quality can be reached

Cold forming




extrusion full extrusion hollow extrusion cup extrusion

forwardextrusion

backwardextrusion

radialextrusion

before after

Cold forming

Forming Processes

a: punch, b: die, c: workpiece, d: ejector, e: counter punch, f: spike

Cold forming




workpieceinsertion

compression extrusion ejection

punch

workpiece

cavity

ejector

die

Cold forming

Full Forward Extrusion: pin production

Cold forming




workpieceinsertion

compression extrusion ejection

punch

workpiece

die

ejector

Cold forming

Cup Backward Extrusion: cup production

Cold forming




workpieceinsertion

closing ofthe die

extrusion ejection

upper punch

workpiece

lower die

lower punch

upper die

Co d o g

Radial Extrusion of a Cardan Joint

Cold forming




g

Mechanical Loads in Full Forward Extrusion Processes

mechanical surface loads in a range of several 1000 MPa

material: QST 32-3 effective strain: φ = 1,4

radial stresses σr / MPa axial stresses σz / MPa

angle of shoulder :

Cold forming




g

Reinforcement of extrusion dies

without internal pressure

with internal pressurereinforcement creates compression stresses in the die, in order to reduce process-related

tensile stresses

compression

tensile

Cold forming




Typical Cold Formed Components

gear shafts

tubes

denticulations

screws

Hirschvogel Hirschvogel

FuchsSchraubenwerk

Flow Stress




Fracture as a result of Radial Extrusion

fractures depending on passing a critical deformation value

Cold forming




Crack Reduction by Superposition of Compressive Stresses

punchgasket

die

workpiece

pressure mediumrelief pressure valve

tearing could effectively be shift to higher strains by superposition

of compressive stresses

(superposition of compressive stresses)

(conventional cold forming)

Crack

Crack

Cold forming

Ch C k b F ll F d E i




Chevron Cracks by Full Forward Extrusion

Cold forming

Ch C k b F ll F d E t i




3. forming step real workpiece

Chevron Cracks by Full Forward Extrusion

an unfavourable distribution of the interior material generates cracks

Chevrons

FEM-Simulation

DEFORM

Cold forming

Ph f P d ti f B l G




bucking upsetting indirect

cup extrusion

cutting radial extrusion burr cutting calibration

recrystallization recrystallization recrystallization

Phases of Production of a Bevel Gear

achievable deformation can be increased by recrystallization

Outline




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline

Warm forming

Iron Carbon Phase Diagram




Iron-Carbon Phase Diagram

fcc

bcc

Recrystallization



δ-Fe

δ- + γ -Fe

T e m p e r a t u r e i n ° C

Liquid + δ-Fe

Liquid

Fe3C(Cementite)

Liquid +

Fe3C

Liquid + γ -Fe

γ -Fe + Fe3C

γ -Fe(Austenite)

α-Fe (Ferrite)

γ - + α-Fe

α-Fe + Fe3C

Warm forming

Material properties




Material properties

Workpiece

temperature / °C

reduction of flow stress and increase of the achievable strain

S t r a i n ϕ

F l o w

s t r e s s k f / M P a

L a y e r o f s

c a l e / µ m

Warm forming

Advantages and Disadvantages of Warm Forming




Advantages and Disadvantages of Warm Forming

Warm forming Advantages:

strengthening of the workpiece

small range of tolerance caused by dwindling

good surface quality

Disadvantages:

energy input for heating

high flow stresses

Hirschvogel

Warm forming

Efficiency




forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.500 kg

plasticity φ < 1,6 φ < 4 j < 6

finishing effort less low high

semi-finished part coldforming

warmforming

Efficiency

Warm forming

Efficiency





5 6 7 8 9 10 11 12 13 14 15 16

Cold extrusion

Warm extrusion

Hot extrusion


0,5 1 2 3 4 6 8 10 12 15 20 25 30


Efficiency

medium shape, dimension and position tolerances as well as

medium surface quality are possible

Warm forming

Typical Warm Formed Components




Typical Warm Formed Components

slide hinge flange cylinder injector

Hirschvogel Hirschvogel

Audi

Outline




Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline

Forging

Iron-Carbon Diagram




g

fcc

bcc

Recrystallization



δ-Fe

δ- + γ -Fe

T e m p e r a t u r

e i n ° C

Liquid + δ-Fe

Liquid

Fe3C(Cementite)

Liquid +Fe

3C

Liquid + γ -Fe

γ -Fe + Fe3C

γ -Fe(Austenite)

α-Fe (Ferrite)

γ - + α-Fe

α-Fe + Fe3C

Forging

Material Properties




p

Workpiece temperature / °C

low flow stress and high achievable strain

S t r a i n j

F l o w

s t r e s s k f / M P a

L a y e r o f s

c a l e / µ m

Forging

Advantages and Disadvantages of Forging




g g g g

Forging Advantages:

less effort

high plasticity

Disadvantages:

high energy input for heating

high material costs for tools

dimension faults by shrinkage

material loss and finishing caused by tinder

Forging

Efficiency




forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.500 kgplasticity φ < 1,6 φ < 4 φ < 6finishing effort less low high

initial state coldforming warmforming forging

Forging

Efficiency





5 6 7 8 9 10 11 12 13 14 15 16

Cold extrusion

Warm extrusion

Hot extrusion


0,5 1 2 3 4 6 8 10 12 15 20 25 30


low shape, dimension and position tolerances as well as

low surface quality possible

Forging

Heating Methods




Heating in furnaces:

furnaces are heated by gas, oil or electricity

heat transmission to the workpiece by radiation andconvection

Heating by induction:

heat in the workpiece rim is generated byelectromagnetic induction by eddy current formation

Conductive heating:

heating by high-frequency current with direct workpiececontact

Furnace

Inductive heating facility

inductive and conductive heating reduces the production of primarytinder as a result of the heating rate

Forging

Tinder




If iron-based materials are heated above 500 °C

under the influence of oxygen, iron oxide (Fe3O2)

will be generated on the surface, which is called

tinder. Tinder peels away off the workpiece during the

forming process.

This results in loss of material, surface marking

and tool wear.

Saarstahl

Forging

Processes – Open Die Forging




upsetting

stretching

flat back gage acuminate back gage round back gage

Saarstahl

Saarstahl

simple tool geometries are used for open die forging processes

workpiece manipulator

upper die

lower die

work-

piece

Forging

Process cycle




Freiformschmieden

simple tool geometries can produce complex workpiece geometries

round forging

upsetting

streching

upsetting

strechingforging

forging and shearingwastage

blank

forging a step

forging a step

Forging

Open Die Forging




Saarstahl

Forging

Closed Die Forging




Upper die

Lower die

Lower die

Upper die

Forging part

Forging part

Burr cavity

Forging without burr:

• low forming forces

• complete material utilization

• max. permitted volume fluctuation 0,5%

• exact workpiece positioning required

Forging with burr:

• less standards on workpiece volume

fluctuation

• no exact workpiece positioning required

• the removal of the burr needs an extra

process step

Forging

Die Wear




1 - wear / abrasion

2 - thermal fatigue / crack formation

3 - mechanical fatigue / crack formation

4 - plastic deformation

2

1/3/4

1/4

1

3 1/41 2

the main reason for tool change is the abrasion on edges and cracks in cavitations

Forging

Stages of Closed Die forging




crankshaft

connection rod

hinge bearing

an effective preform production is the key for short production chains

Summaryg

σ




Influence of the metallurgical composion on the

formability of metals

Basic understanding of the elastic and plastic materialbehaviour and it‘s characterization

Introduction of processes in cold and warm bulk formingas well as in forging

tanelε∆

σ∆=α

Eelε

σ=

S p a n n u n g

Nenndehnung ε0,2 %

α

Rp0,2

∆εel

∆σ

ReS

εel εpl

εel

l01 bulk metal forming 1

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