Forming – Metallurgical Basics in Plastic Deformation · Why is it Important to Distinguish Plastic and Elastic Strain? Advantage : By using the plastic strain it is possible to

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Forming – Metallurgical Basics in Plastic Deformation

Manufacturing Technology II

Lecture 3

Laboratory for Machine Tools and Production Engineering

Chair of Manufacturing Technology

Prof. Dr.-Ing. Dr.-Ing. E. h. F. Klocke

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Outline

Introduction

Chemical Constitution of Metals

Elastic Deformation

Plastic Deformation

Flow Stress

Occurring of fractures

Recrystallisation

Influences on Flow Stress

Typical Materials in Forming Technologies

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IntroductionWhat is Manufacturing Technology?

Manufacturing Technology is the teachings of economical production of finished products from raw materials according to given

geometrical properties.

raw material Manufacturing Tech. finished product

geometrically undefined geometrically defined

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IntroductionWhat is Forming?

semi-finished product finished product

plastic forming

forming

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Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation



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Chemical Constitution of Metals4 Basic Chemical Bonds

+ + + + + + + + + ++ + + + + + + + + ++ + + + + + + + + ++ + + + + + + + + +

electron gas (e-)

positive chargedmetal ions

ionic bond

metal bond

+

-

-

--

-

-

--

---

-

--+

++

++

++

++

++

+

+

metal bond

ionic bond

covalent bond

Van-der-Waals bond

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Chemical Constitution of MetalsThe 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

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Chemical Constitution of MetalsLattice 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

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Chemical Constitution of MetalsAtomic 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

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Chemical Constitution of MetalsComparison of Load-displacement Curves of Mono- and Multi-Crystal

load

displacement

body-centred cubic lattice

favourable loading direction

unfavourable loading direction

mono-crystal with unfavourable

orientation

mono-crystal with favourable orientation

multi-crystal

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Chemical Constitution of MetalsPunctual Lattice Errors

vacancy intermediate-lattice atom FRENKEL-matching

substituting atom emplacement atom

The foreign atoms induce stress to the crystal lattice. This stress effects crystal strengthening of the material.


Chemical Constitution of MetalsDislocations

screw dislocationedge dislocation

dislocations are linear errors in the lattice.

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Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation




Elastic DeformationTensile 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

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Elastic DeformationStress-Strain Curve of Elastic Behaviour

00

01l

l 00 l∆l

lll

ldl ε

ldl d

1

0

=−

==⇒=ε ∫

AF

0

=σ

tanelε∆

σ∆=α e

stre

ss

strain

F

F

Re

∆σe

∆εel

l0

∆l

lA0

A

engineering strain:

engineering stress:

α

For elastic behaviour:

Eelε

σ=

σ ≤ Re

E = Young‘s Modulus

specimen1=2


tensile test compression test shear test

F

F

l0

A0

l1

A1

A0

F

F

A1

l1

l0

AF

=σAF−

=σ

Elastic DeformationStress Determination Depending on Load

AF

=τ

F

Fa

l

θ

A

tensile stress compression stress shear stress

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unloaded tensile-loaded

σ - nominal stressε - strainE - Young‘s Modulus

l0 l

σ

σ

Elastic DeformationAtomic Representation of Pure Elastic-Tensile Deformation

00

01

l∆l

lll ε =

−= E

elεσ

=

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 DeformationAtomic Representation of Pure Elastic-Shear Deformation

Gelγτ

=

elastic shearing based on shear load

1- 2GE =υ

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Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation




Plastic DeformationStress-Strain Curve up to the Uniform Elongation

AF

0

=σ

stre

ss

strain

engineering stress:(related to starting section)

F

F

Rm

Re ,σe

εelεpl

l0

∆l

lA0

A

load relieving reload

AF =σ′

true tensile stress:(related to real section)

σ‘σ

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Plastic DeformationTypes of Plastic Deformation

dislocation movement

low power requirements

sliding

high power requirements

before

after


Plastic DeformationSliding and Dislocation Movement

dislocation movementsliding

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Plastic DeformationVideo Clip – Recordings of Dislocation Movements on Infrared Camera

F

tensile specimen of tempered aluminium with reflective surface

F


twinning

Plastic DeformationPlastic Deformation Based on Twinning

200 µm

Inconel 718,austenitic structure

twinningMechanical twinning especially appears, if the use of sliding systems is no longer possible or if deformation velocity reaches a critical value.

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Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation




plastic strain ϕ

Flow StressUsing the Tensile Test as an Example of Flow Stress Determination

F

F

l0

∆l

lA0

A

stre

ss

σ‘

strain

Rm

Re ,σe

ϕ / εpl Ag – uniform elongation

fracture

σ

uniaxial stressσ1

elastic strain ε

lateral contraction

εel

triaxial stressσ1, σ2, σ3

true flow stress increases with increasing plastic deformation

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Flow StressUsing the Tensile Test as an Example of Flow Stress Determination

strain

AF

=σ´true tensile stress:F

F

Rm

Re ,σe

εel ϕ / εpl Ag

fracture

σ0

σ‘

kf

l0

∆l

lA0

A

ϕ⋅== eAF

AFk

0fflow stress:

useable region to determinate flow stress

stre

ss


Flow StressFlow Curve

flow

str

ess

effective strain

required strain to breakthe strain hardening

required strain for plastic deformation

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Flow StressStrain 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


Flow StressYield Conditions According Tresca and von Mises

σIσIIIσII σIσII

σIII

Tresca: τmax = σv = max (I σI – σII I;I σI – σIII I;I σII – σIII I)

von Mises: σv = [(σI – σII)² + (σI – σIII)² + (σII – σIII)²]

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12

12

τmax

ττ

σσ

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Flow StressStrain Determination of an Idealized Upsetting Process

00

01

0

1

0

ll

lll

ldl

ldld

l

l

∆=

−==⇒= ∫εε

0

1z

0

1y

0

1x h

h bb

ll ln;ln;ln =ϕ=ϕ=ϕ

0

1ln1

0ll

ldl

ldld

l

l

==ϕ ⇒ =ϕ ∫

engineering strain (elastic)

true strain (plastic)

including of volume constancy

)(lnlnlnln 1 ll

ll

lll

ll

0

0

00

0

0

1 +=

+

∆=

∆+=

= ϕ ε

konst. 111000 =⋅⋅=⋅⋅ bhlbhl

0 zyx =ϕ+ϕ+ϕ

connection between true strain - engineering strain


as an example a cylinder has to be halved and/or doubled around its length

0

1

llln=ϕ

0

01

lll −

=ε

compression forming tensile formingl l1 0 2= / l l1 02=

+1.0

+0.693-0.693

-0.5

Flow StressWhy is it Important to Distinguish Plastic and Elastic Strain?

Advantage: By using the plastic strain it is possible to sum deformation values of successive forming steps.

elasticstrain

plasticstrain

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Flow StressStrain Calculation of Successive Forming Steps

0

1

HHln=ϕ

0

01

HHH −

=ε

elastic strain

plastic strain

H0 = 30mm H1 = 25mm H2 = 20mm H3 = 15mm

0 1 2 3

0 1-16,6%

1 2-20%

0 2-33,3%

2 3-25%

0 3-50%

0 1-0,18

1 2-0,22

0 2-0,40

2 3-0,29

0 3-0,69


Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation



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Occurring of FracturesFracture as a result of Radial Extrusion

fractures depending on passing a critical deformation value


Occurring of FracturesFracture Shape in Longitudinal Direction

Effective strain detected by the simulation

The fracture shape depends on the present stress conditions.

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Occurring of fracturesFracture Shape in Crossing Direction

Effective strain detected by the simulation

The fracture shape depends on the present stress conditions.


Occurring of Fractures

Ductile Fracture

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Occurring of Fractures

Brittle Fracture


Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation



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RecrystallisationGrain Origin and Grain Deformation Regarding Primary Shaping and Forming

1. nucleation 2. nucleic growth 3. grain origin

grain deformation

prim

ary

shap

ing

form

ing


RecrystallisationStatic Recrystallisation

requirements:

- ϕv > 0

- T > T recrystallisation

- impact time

schematic course of recrystallisation of cold formed structure

temperature

crys

tal

rege

nata

tion

duct

ileyi

eld

tens

ilest

reng

th

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RecrystallisationStress Curve of Cold Forming as a Result of Static Recrystallisation

flow

str

ess

effective strain

anne

alin

g fo

r re

crys

tallis

atio

n

ϕvBr ϕvBr

ϕvBr - effective strain at time of fracture

annealing for recrystallisation increases strain hardening and decreases flow stressan

neal

ing

for

recr

ysta

llisat

ion


Recrystallisation Recrystallisation of Brass

starting conditions 3 s at 580°C 4 s at 580°C

8 s at 580°C 15 min at 580°Cimwf Stuttgart

recrystallisation de-creases material‘s mechanical properties to the values of unformed materials

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RecrystallisationDynamic Recrystallisation

hot extrusion

T >> T recrystallisation


RecrystallisationForming Temperature and Velocity Influences the Flow Stress

forming temperature below recrystallisation temperature

high forming velocity

low forming velocity

forming temperature above recrystallisation temperature

effective strain

flow

str

ess

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RecrystallisationEffective Strain and Temperature Influences the Grain Size

grai

n si

ze

strain

range of recrystallisationtem

perature

recrys

tallis

ation


Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation



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Influences on Flow StressFlow Curves – Material Influence

grey cast iron

malleable cast iron

steel

stre

ss

strain

flow

str

ess

kf

effective strain ϕ

C15 16MnCr5 C35

soft annealed

normalized

0 0,4 0,8 1,2 0 0,4 0,8 1,2 0 0,4 0,8 1,2 1,60

400

600

200

800

1200

MPa

carbon content

carbon content

flow stress

soft annealedsoft annealed

normalized normalized


ϕ = 360 s-1

Influences on Flow StressFlow Curves – Forming Velocity Influence

flow

str

ess

kf

150

200

100

250

300

MPa

effective strain ϕ0 0,4 0,8 1,2 1,6 2,0

ϕ = 1000 s-1

ϕ = 40 s-1

C15 at 1100 °C

forming velocity

flow stress

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Influences on Flow StressFlow Curves – Temperature Influence

flow

str

ess

kf

4

6

2

10

200MPa

effective strain ϕ0 1,5 3,0 4,5 6,0 7,5 9,0

40

20

60

100

500°C

400°C

300°C

250°C

200°C

20°C

Al 99,9 at 10 s-1

temperature

flow stress


Outline

Introduction


Elastic Deformation

Plastic Deformation

Flow Stress


Recrystallisation

Influences of Flow Stress


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Typical Materials in Forming TechnologiesThe Iron-Carbon Diagram

martensite

bainite

austenite 0,8 % Cperlite

0,1 % C

ferrite

perlite

0,4 % C

ferrite

perlite

1,2 % C

cementite

perlite

Quelle: www.metallograf.de


Typical Materials in Forming TechnologiesSteels and Their Industrial Use

fcc

bcc

bcc

lattice

10

-

-

Ni

-

0,25

0,25

Si

-

0,35

1,15

Mn

18

1,5

0,95

Cr

0,05

1,0

0,16

C

X5CrNi1810

(austenite steel)

100Cr6

(heat-treated steel)

16MnCr5

(case-hardened steel)

steel

Because of the face-centred cubic lattice of austenite austenitic steels can be cold formed very easy.

Quelle: BOIE

Quelle: CIS

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Typical Materials in Forming TechnologiesNon-Iron Metals and Their Industrial Use

aluminium- and aluminium forgeable alloys(e.g. EN AW-AL99,98Mg1)

– fcc very good hot and cold forming properties

– alloying elements to increase mechanical strength (e.g. Cu, Mg, Si, Zn)

titan alloys(e.g. Ti6Al4V)

– bcc/hex moderate cold forming properties– alloying elements to favour hexagonal structure

(e.g. Al, Sn, O)– alloying elements to favour bcc structures (e.g. V, Cr, Fe)

more non-iron metals: copper, nickel, magnesium, zirconium, tin, zinc, lead

Documents

Forming – Metallurgical Basics in Plastic Deformation · Why is it Important to Distinguish Plastic and Elastic Strain? Advantage : By using the plastic strain it is possible to