Bulk Metal Forming I

Transcription

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
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-)
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ionic bond
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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
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metal bond
+ + + + +
electron gas (e-)
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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:
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
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
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
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
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
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
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
low energy required
Seite 16
Plastic Deformation
Sliding and Dislocation Movement
sliding
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
Seite 19
Flow Stress
Strain Hardening Depends on Dislocations
schematic diagram
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
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
Seite 23
Recrystallisation
grain size
Effective Strain and Temperature Influence the Grain Size
range of
recrystallisation
effective strain
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
effective strain
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
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
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<4
less
low
hot
0,05 – 1.500 k
r<6
high
cold forming
by the aid of cold forming processes a good workpiece quality can be reached
Seite 33
Cold forming
Forming Processes
extrusion
full extrusion
before
hollow extrusion
cup extrusion
after
forward
extrusion
backward
extrusion
radial
extrusion
a: punch, b: die, c: workpiece, d: ejector, e: counter punch, f: spike
Seite 34
Cold forming
Full Forward Extrusion: pin production
workpiece
insertion
compression
extrusion
ejection
punch
workpiece
cavity
ejector
die
Seite 35
Cold forming
Cup Backward Extrusion: cup production
workpiece
insertion
compression
extrusion
ejection
punch
workpiece
die
ejector
Seite 36
Cold forming
Radial Extrusion of a Cardan Joint
workpiece
insertion
closing of
the die
extrusion
ejection
upper punch
upper die
workpiece
lower die
lower punch
Seite 37
Cold forming
Mechanical Loads in Full Forward Extrusion Processes
angle of shoulder :
radial stresses σr / MPa
material: QST 32-3
axial stresses σz / MPa
effective strain: φ = 1,4
mechanical surface loads in a range of several 1000 MPa
Seite 38
Cold forming
Reinforcement of extrusion dies
tensile
compression
without internal pressure
with internal pressure
reinforcement creates compression stresses in the die, in order to reduce process-related
tensile stresses
Seite 39
Cold forming
Typical Cold Formed Components
tubes
Hirschvogel
Hirschvogel
gear shafts
denticulations
screws
Fuchs
Schraubenwerk
Seite 40
Flow Stress
Fracture as a result of Radial Extrusion
fractures depending on passing a critical deformation value
Seite 41
Cold forming
Crack Reduction by Superposition of Compressive Stresses
punch
gasket
die
workpiece
pressure medium
relief pressure valve
(conventional cold forming)
Crack
(superposition of compressive stresses)
Crack
tearing could effectively be shift to higher strains by superposition
of compressive stresses
Seite 42
Cold forming
Chevron Cracks by Full Forward Extrusion
Seite 43
Cold forming
Chevron Cracks by Full Forward Extrusion
Chevrons
DEFORM
FEM-Simulation
3. forming step
real workpiece
an unfavourable distribution of the interior material generates cracks
Seite 44
Cold forming
Phases of Production of a Bevel Gear
bucking
upsetting
indirect
cup extrusion
recrystallization
cutting
radial extrusion
recrystallization
burr cutting
calibration
recrystallization
achievable deformation can be increased by recrystallization
Seite 45
Outline
1
2
Elastic Deformation
3
Plastic Deformation
4
Flow Stress
5
Recrystallisation
6
Cold Forming
7
Warm Forming
8
Forging
Seite 46
Warm 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
Seite 47
Warm forming
Strain ϕ
Material properties
Workpiece
temperature / °C
reduction of flow stress and increase of the achievable strain
Seite 48
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
Seite 49
Warm forming
Efficiency
forming
workpiece weight
plasticity
finishing effort
semi-finished part
cold
0,001 – 30 kg
φ < 1,6
less
cold
forming
warm
0,001 – 50 kg
φ<4
low
hot
0,05 – 1.500 kg
j<6
high
warm
forming
Seite 50
Warm forming
Efficiency
Forming process
5
6
7
8
9 10 11 12 13 14 15 16
0,5 1
2 3 4 6 8 10 12 15 20 25 30
Cold extrusion
Warm extrusion
Hot extrusion
medium shape, dimension and position tolerances as well as
medium surface quality are possible
Seite 51
Warm forming
Typical Warm Formed Components
Audi
Hirschvogel
Hirschvogel
slide hinge
flange cylinder injector
Seite 52
Outline
1
2
Elastic Deformation
3
Plastic Deformation
4
Flow Stress
5
Recrystallisation
6
Cold Forming
7
Warm Forming
8
Forging
Seite 53
Forging
Iron-Carbon 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
Seite 54
Forging
Strain j
Material Properties
Workpiece temperature / °C
low flow stress and high achievable strain
Seite 55
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
Seite 56
Forging
Efficiency
forming
workpiece weight
plasticity
finishing effort
initial state
cold
0,001 – 30 kg
φ < 1,6
less
cold
forming
warm
forming
warm
0,001 – 50 kg
φ<4
low
hot
0,05 – 1.500 kg
φ<6
high
forging
Seite 57
Forging
Efficiency
Forming process
5
6
7
8
9 10 11 12 13 14 15 16
0,5 1
2 3 4 6 8 10 12 15 20 25 30
Cold extrusion
Warm extrusion
Hot extrusion
low shape, dimension and position tolerances as well as
low surface quality possible
Seite 58
Forging
Heating Methods
Furnace
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
Inductive heating facility
Conductive heating:
heating by high-frequency current with direct workpiece
contact
inductive and conductive heating reduces the production of primary
tinder as a result of the heating rate
Seite 59
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
Seite 60
Forging
Processes – Open Die Forging
workpiece
manipulator
upsetting
Saarstahl
upper die
workpiece
stretching
Saarstahl
lower die
flat back gage
acuminate back gage
round back gage
simple tool geometries are used for open die forging processes
Seite 61
Forging
Process cycle
Freiformschmieden
round forging
blank
upsetting
wastage
forging and shearing
streching
forging a step
upsetting
streching
forging
forging a step
simple tool geometries can produce complex workpiece geometries
Seite 62
Forging
Open Die Forging
Saarstahl
Seite 63
Forging
Closed Die Forging
Forging without burr:
• low forming forces
• complete material utilization
• max. permitted volume fluctuation 0,5%
Upper die
• exact workpiece positioning required
Lower die
Forging part
Upper die
Burr cavity
Lower die
Forging part
Forging with burr:
• less standards on workpiece volume
fluctuation
• no exact workpiece positioning required
• the removal of the burr needs an extra
process step
Seite 64
Forging
Die Wear
1
2
1 - wear / abrasion
2 - thermal fatigue / crack formation
1/3/4
3 - mechanical fatigue / crack formation
1/4
4 - plastic deformation
1
3
2
1/4
the main reason for tool change is the abrasion on edges and cracks in cavitations
Seite 65
Forging
Stages of Closed Die forging
crankshaft
connection rod
hinge bearing
an effective preform production is the key for short production chains
Seite 66
Spannung σ
Summary
εel
Influence of the metallurgical composion on the
εpl
Rp0,2
ReS
formability of metals
∆εel
∆σ
∆σ
∆ ε el
tan α =
E =
σ
ε el
α
0,2 %
εel
Nenndehnung ε
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
Seite 67

Bulk Metal Forming I

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