bulk metal forming i - rwth aachen university metal forming i simulation techniques in manufacturing...

© WZL/Fraunhofer IPT

Bulk Metal Forming I

Simulation Techniques in Manufacturing Technology

Lecture 1

Laboratory for Machine Tools and Production Enginee ring

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 understanding of the mechanisms during metal forming

� Elastic and plastic material behaviour and its influence on the process results in forming technology

� Mathematical models for a description of the elastic and plastic material behaviour

� Introduction of processes in cold and warm bulk forming as 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 electrons

positive 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-centred cubic(fcc)

body-centred cubic(bcc)

hexagonal(hex)

examples:

sliding planes:

sliding directions:

sliding systems:

formability:

γ-Fe, Al, Cu

4

3

12

very good

α-Fe, Cr, Mo

6

2

12

good

Mg, Zn, Be

1

3

3

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

load

displacement

F1

F2

l1l1 = l2


Elastic Deformation

Stress-Strain Curve of Elastic Behaviour

00

01l

l 00 l∆l

l

ll

ldl

ε ldl

d1

0

=−==⇒= ∫ε

AF

0

=σ

tanel

el

εσα =

stre

ss

strain

F

F

Re

σel

eel

l0

∆l

lA0

A

engineering strain:

engineering stress:

α

For elastic behaviour:

Eel

el

εσ=

σ ≤ Re

E = Young‘s Modulus

specimenno. 1≙ no. 2


tensile test compression test shear test

F

F

l0

A0

l1

A1

A0

F

F

A1

l1

l0

0AF=σ

0AF−=σ

Elastic Deformation

Stress Determination Depending on Load

0AF=τ

F

Fa

l

q

A0

tensile stress compression stress shear stress


unloaded tensile-loaded

σ - nominal stressε - strainE - Young‘s Modulus

l0 l1

s

s

Elastic Deformation

Atomic Representation of Pure Elastic-Tensile Defor mation

00

01el l

∆l

lll

ε =−= Eel

el

εσ=

� elastic strain based on tensile load


τγ

τ

unloaded shear-loaded

γ - shear angleτ - shear stressG - shear modulusν - Poisson‘s ratioE - Young‘s modulus

Elastic Deformation

Atomic Representation of Pure Elastic-Shear Deforma tion

)2(1

Gel µγ

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

stre

ss

strain

engineering stress:(related to starting section)

F

F

Rm

Re ,se

eelepl

l0

∆l

lA0

A

load relieving reload

AF

=′σ

true tensile stress:(related to real section)

σ‘σ


Plastic Deformation

Strain Determination of an Idealized Upsetting Proc ess

00

01

00

1

0

ll

lll

ldl

ldl

dl

lxx

∆=−==⇒= ∫εε

0

1

0

1

0

1 ln ;ln ;lnhh

bb

ll

zyx === ϕϕϕ

0

1ln1

0ll

ldl

ldl

dl

l

==ϕ ⇒ =ϕ ∫

engineering strain (elastic)

true strain (plastic)

including of volume constancy

)1( ln ll

ll

ln l

ll ln

lul

ln ll

ln 0

0

00

0

0

x0

0

1 +=

+∆=

∆+=

+=

= xx εϕ

const. 111000 =⋅⋅=⋅⋅ bhlbhl

0 =++ zyx ϕϕϕ

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

flow

str

ess

effective strain

required stress to breakthe strain hardening

required stress for plastic deformation


Flow Stress

Strain Hardening Depends on Dislocationsschematic 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 > T Recrystallisation

- impact time

Schematic course of recrystallisation of cold formed structure

duct

ile y

ield

A10

, te

nsile

str

engt

h R

m

crys

tal

rege

nera

tion

large increaseof A 10

small decreaseof Rm

temperature, °C


RecrystallisationStress Curve of Cold Forming as a Result of Static Recrystallisation

flow

str

ess

effective strain

anne

alin

g fo

r re

crys

talli

satio

n

ϕϕϕϕvBr ϕϕϕϕvBr

ϕϕϕϕvBr - effective strain at time of fracture

� annealing for recrystallisation increases effective strain and decreases flow stress

anne

alin

g fo

r re

crys

talli

satio

n


Recrystallisation

Effective Strain and Temperature Influence the Grai n Sizegr

ain

size

effective strain

range of recrystallisation


Recrystallisation

Forming Temperature and Velocity Influence the Flow Stress

forming temperature below recrystallisation temperature

high forming velocity

low forming velocity

forming temperature above recrystallisation temperature

effective strain

flow

str

ess


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


fcc

bcc

Recrystallization

Cold forming

Iron-Carbon Phase Diagram

Carbon content in weight percent

Cermentite content in weight percent

δ-Fe

δ- + γ-Fe

Tem

pera

ture

in °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


Workpiece temperature / °C

Str

ain

ϕ

Flo

w s

tres

s k f

/ MP

a

Laye

r of

sca

le /

µm

Cold forming

Material Properties

� high flow stresses and low achievable strains by classic steel materials


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


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


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


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


workpieceinsertion

compression extrusion ejection

punch

workpiece

cavity

ejector

die

Cold forming

Full Forward Extrusion: pin production


workpiece insertion

compression extrusion ejection

punch

workpiece

die

ejector

Cold forming

Cup Backward Extrusion: cup production


workpieceinsertion

closing ofthe die

extrusion ejection

upper punch

workpiece

lower die

lower punch

upper die

Cold forming

Radial Extrusion of a Cardan Joint


Cold forming

Mechanical Loads in Full Forward Extrusion Processe s

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

Reinforcement of extrusion dies

without internal pressure

with internal pressure

reinforcement 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 Str esses

punchgasketdieworkpiecepressure 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

Chevron Cracks by Full Forward Extrusion


3. forming step real workpiece

Cold forming

Chevron Cracks by Full Forward Extrusion

an unfavourable distribution of the interior material generates cracks

Chevrons

FEM-Simulation

DEFORM


bucking upsetting indirect cup extrusion

cutting radial extrusion burr cutting calibration

recrystallization recrystallization recrystallization

Cold forming

Phases of Production of a Bevel Gear

achievable deformation can be increased by recrystallization


Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline


Warm forming

Iron-Carbon Phase Diagram

fcc

bcc

Recrystallization



δ-Fe

δ- + γ-Fe

Tem

pera

ture

in °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


reduction of flow stress and increase of the achievable strain

Str

ain

ϕ

Flo

w s

tres

s k f

/ MP

a

Laye

r of

sca

le /

µm


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


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

semi-finished part cold forming

warmforming

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


Warm forming

Efficiency

medium shape, dimension and position tolerances as well as

medium surface quality are possible


Warm forming

Typical Warm Formed Components

slide hinge flange cylinder injector

Hirschvogel Hirschvogel

Audi


Forging8

Warm Forming7

Cold Forming6

Recrystallisation5

Flow Stress4




Outline


Forging

Iron-Carbon Diagram

fcc

bcc

Recrystallization



δ-Fe

δ- + γ-Fe

Tem

pera

ture

in °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


Forging

Material Properties


low flow stress and high achievable strain

Str

ain

j

Flo

w s

tres

s k f

/ MP

a

Laye

r of

sca

le /

µm


Forging

Advantages and Disadvantages of Forging

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


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


Forging

Efficiency

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 and

convection

� Heating by induction:� heat in the workpiece rim is generated by

electromagnetic induction by eddy current formation

� Conductive heating:� heating by high-frequency current with direct workpiece

contact

Furnace

Inductive heating facility

inductive and conductive heating reduces the production of primary tinder 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


upsetting

stretching

flat back gage acuminate back gage round back gage

Forging

Processes – Open Die Forging

Saarstahl

Saarstahl

simple tool geometries are used for open die forging processes

workpiece manipulator

upper die

lower die

work-piece


Freiformschmieden

Forging

Process cycle

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


Upper die

Lower die

Lower die

Upper die

Forging part

Forging part

Burr cavity

Forging

Closed Die Forging

� 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


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

Forging

Die Wear

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


Summary

� Influence of the metallurgical composion on the formability of metals

� Basic understanding of the elastic and plastic material behaviour and it‘s characterization

� Introduction of processes in cold and warm bulk forming as well as in forging

tanelε∆

σ∆=α

Eelε

σ=S

pann

ung σ

Nenndehnung ε0,2 %

α

Rp0,2

∆εel

∆σ

ReS

εel εpl

εel

bulk metal forming i - rwth aachen university metal forming i simulation techniques in manufacturing...

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