Bulk Metal Forming I

Bulk Metal Forming I Simulation 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 © 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

© WZL/Fraunhofer IPT

Seite 1

Outline 1

Metallurgical Basics

2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 2


4 Basic Chemical Bonds metal bond ionic bond covalent bond

metal bond

Van-der-Waals bond positive charged metal ions electron gas (e-)

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

ionic bond -

+

-

+

-

+

-

-

+

-

-

+

-

+


-

+

+

-

+

-

+

+

-

-

+

+

+

Seite 3


The Metal Bond metal atoms basically emit electrons

positive charged ions in pure metals no electron-absorbing atoms do exist

un-combined electrons (outer electrons) form an electron gas outer electrons in metals can freely move

good electrical and thermal conductivity in absolute pure metals all atoms are totally equal

plastic deformation


positive charged metal ions

+

+

+

+

+

+

+

+

+

+

+

+ + + + metal bond + + + + +

electron gas (e-)

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+ Seite 4


Lattice Types of an Unit Cell face-centred cubic (fcc)

body-centred cubic (bcc)

hexagonal (hex)

γ-Fe, Al, Cu

α-Fe, Cr, Mo

Mg, Zn, Be

sliding planes:

4

6

1

sliding directions:

3

2

3

sliding systems:

12

12

3

very good

good

poor

examples:

formability: © WZL/Fraunhofer IPT

Seite 5


Atomic and Macroscopic View of Metal Structures crystal lattice

unit cell

ideal crystal structure

a real crystal structure microstructure

2D – Cut of the microstructure section plane special agglomeration of crystals schematically © WZL/Fraunhofer IPT

photograph Seite 6

Outline 1


2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 7

Elastic Deformation

Tensile Test – Load-Displacement Diagram load

specimen 1

F1

specimen 2 F2

A1 = 2 • A2 follows: F1 = 2 • F2

tensile specimen

l1 =l1l2

displacement relate force to cross section surface


Seite 8

Elastic Deformation

Stress-Strain Curve of Elastic Behaviour F

stress

engineering stress: Re

specimen no. 1 ≙ no. 2

∆l

l0

F A0

engineering strain: A

l

σ =

dl dε = l0

σel

⇒ ε =

A0

dl l1 − l0 ∆l = = ∫l l0 l0 l0 0 l1

α eel

strain

For elastic behaviour:

F © WZL/Fraunhofer IPT

tan α =

σ el ε el

E =

σ el ε el

σ ≤ Re E = Young‘s Modulus Seite 9

Elastic Deformation

Stress Determination Depending on Load tensile test

shear test

compression test

F

A1

F l1

A0

F

a

q

A1

l0

l0

l l1

F

A0

F σ = A0 tensile stress © WZL/Fraunhofer IPT

F

−F σ = A0 compression stress

F

A0

F τ= A0 shear stress Seite 10

Elastic Deformation

Atomic Representation of Pure Elastic-Tensile Deformation unloaded

tensile-loaded

s l0

l1 s

σ E = el ε el

l −l ∆l ε el = 1 0 = l0 l0

σ - nominal stress ε - strain E - Young‘s Modulus

elastic strain based on tensile load © WZL/Fraunhofer IPT

Seite 11

Elastic Deformation

Atomic Representation of Pure Elastic-Shear Deformation unloaded

shear-loaded

τ γ

τ

G =

τ E = γ el 2(1 + µ )

elastic shearing based on shear load © WZL/Fraunhofer IPT

γ - shear angle

τ - shear stress G - shear modulus ν - Poisson‘s ratio E - Young‘s modulus Seite 12

Outline 1


2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 13

Plastic Deformation

Stress-Strain Curve up to the Uniform Elongation true tensile stress:

F stress

(related to real section)

σ‘ σ

Rm

σ′ =

F A

∆l A

l

l0

Re ,se

engineering stress: load relieving

(related to starting section) reload

A0

σ =

epl

eel

F A0

strain

F © WZL/Fraunhofer IPT

Seite 14

Plastic Deformation

Strain Determination of an Idealized Upsetting Process true strain (plastic) l

1 dl dl l ⇒ ϕ = ∫ = ln 1 dϕ = l l l0 l0

l l0

ϕ x = ln 1 ; ϕ y = ln

b1 h ; ϕ z = ln 1 b0 h0

including of volume constancy l 0 ⋅ h0 ⋅ b0 = l1 ⋅ h1 ⋅ b1 = const.

ϕ x + ϕy + ϕz = 0 engineering strain (elastic) 1 dl dl l − l ∆l dε x = ⇒ εx = ∫ = 1 0 = l0 l l0 l0 l0 0

l


connection between true strain - engineering strain

 l1   l0 + ux   l0 + ∆l   ∆l l0        ϕx = ln   = ln  = ln  = ln  +  = ln (ε x + 1)    l0   l0   l0   l0 l0  Seite 15

Plastic Deformation

Types of Plastic Deformation sliding

dislocation movement before

after

high energy required © WZL/Fraunhofer IPT

low energy required Seite 16

Plastic Deformation

Sliding and Dislocation Movement sliding


dislocation movement

Seite 17

Outline 1


2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 18

Flow Stress

flow stress

Flow Curve

required stress to break the strain hardening

required stress for plastic deformation

effective strain © WZL/Fraunhofer IPT

Seite 19

Flow Stress

Strain Hardening Depends on Dislocations schematic diagram dislocation movement grain boundary

dislocation origin

sliding planes

moving direction

dislocation structure of little-formed copper piled up dislocations at boundary grains grain boundary


Seite 20

Outline 1


2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 21

Recrystallisation

Static Recrystallisation

- ϕv > 0 - T > T Recrystallisation - impact time © WZL/Fraunhofer IPT

crystal regeneration

requirements:

ductile yield A10, tensile strength Rm

Schematic course of recrystallisation of cold formed structure

small decrease of Rm

large increase of A10

temperature, °C Seite 22

Recrystallisation

ϕvBr

ϕvBr - effective strain at time of fracture

annealing for recrystallisation

annealing for recrystallisation

flow stress

Stress Curve of Cold Forming as a Result of Static Recrystallisation

ϕvBr

effective strain

annealing for recrystallisation increases effective strain and decreases flow stress © WZL/Fraunhofer IPT

Seite 23

Recrystallisation

grain size

Effective Strain and Temperature Influence the Grain Size

range of recrystallisation


Seite 24

Recrystallisation

flow stress

Forming Temperature and Velocity Influence the Flow Stress forming temperature below recrystallisation temperature

high forming velocity forming temperature above recrystallisation temperature

low forming velocity


Seite 25

Outline 1


2

Elastic Deformation

3

Plastic Deformation

4

Flow Stress

5

Recrystallisation

6

Cold Forming

7

Warm Forming

8

Forging


Seite 26

Cold forming

What is Bulk Forming?

Bulk forming

massive semi-finished material


component

Seite 27

Introduction

Advantages of Bulk Forming

Forming

Cutting

1,3 kg

0,4 kg

basic workpiece


component

semi-finished part

component

Seite 28

Cold forming

Iron-Carbon Phase Diagram δ-Fe

Liquid + δ-Fe

fcc

Temperature in °C

δ- + γ-Fe

Liquid

Liquid + γ-Fe

Fe3C (Cementite)

Liquid + Fe3C

γ-Fe (Austenite)

γ-Fe + Fe3C

γ- + α-Fe α-Fe (Ferrite)

Recrystallization α-Fe + Fe3C

bcc

Carbon content in weight percent Cermentite content in weight percent


Seite 29

Cold forming

Flow stress kf / MPa

Strain ϕ

Layer of scale / µm

Material Properties

Workpiece temperature / °C high flow stresses and low achievable strains by classic steel materials © WZL/Fraunhofer IPT

Seite 30

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


Seite 31

Cold forming

Efficiency

IT-Grade according to DIN ISO 286

Forming process 5

6

7

8

9 10 11 12 13 14 15 16

Centerline average Ra / µm 0,5 1

2 3 4 6 8 10 12 15 20 25 30

Cold extrusion Warm extrusion Hot extrusion achievable with special proceedings

achievable without special proceedings

small shape, dimension and position tolerances as well as good surface qualities are possible © WZL/Fraunhofer IPT

Seite 32

Cold forming

Efficiency forming workpiece weight plasticity finishing effort

semi-finished part

cold warm 0,001 – 30 kg 0,001 – 50 kg forming steels) φ < 1,6 (for classicr