Post on 20-Mar-2018
transcript
© 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
Seite 2© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 3© WZL/Fraunhofer IPT
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
Seite 4© WZL/Fraunhofer IPT
Metallurgical Basics
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
Seite 5© WZL/Fraunhofer IPT
Metallurgical Basics
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
Seite 6© WZL/Fraunhofer IPT
Metallurgical Basics
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
Seite 7© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 8© WZL/Fraunhofer IPT
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
Seite 9© WZL/Fraunhofer IPT
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
Seite 10© WZL/Fraunhofer IPT
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
Seite 11© WZL/Fraunhofer IPT
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
Seite 12© WZL/Fraunhofer IPT
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
Seite 13© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 14© WZL/Fraunhofer IPT
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
Seite 15© WZL/Fraunhofer IPT
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
Seite 16© WZL/Fraunhofer IPT
Plastic Deformation
Types of Plastic Deformation
dislocation movement
low energy required
sliding
high energy required
before
after
Seite 17© WZL/Fraunhofer IPT
Plastic Deformation
Sliding and Dislocation Movement
dislocation movementsliding
Seite 18© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 19© WZL/Fraunhofer IPT
Flow Stress
Flow Curve
flow
str
ess
effective strain
required stress to breakthe strain hardening
required stress for plastic deformation
Seite 20© WZL/Fraunhofer IPT
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
Seite 21© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 22© WZL/Fraunhofer IPT
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
Seite 23© WZL/Fraunhofer IPT
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
Seite 24© WZL/Fraunhofer IPT
Recrystallisation
Effective Strain and Temperature Influence the Grai n Sizegr
ain
size
effective strain
range of recrystallisation
Seite 25© WZL/Fraunhofer IPT
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
Seite 26© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 27© WZL/Fraunhofer IPT
Bulk forming
massivesemi-finished material
component
Cold forming
What is Bulk Forming?
Seite 28© WZL/Fraunhofer IPT
semi-finished part component
Cutting
1,3 kg
Introduction
Advantages of Bulk Forming
Forming
0,4 kg
componentbasic workpiece
Seite 29© WZL/Fraunhofer IPT
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
Seite 30© WZL/Fraunhofer IPT
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
Seite 31© WZL/Fraunhofer IPT
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 32© WZL/Fraunhofer IPT
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
Seite 33© WZL/Fraunhofer IPT
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
Seite 34© WZL/Fraunhofer IPT
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
Seite 35© WZL/Fraunhofer IPT
workpieceinsertion
compression extrusion ejection
punch
workpiece
cavity
ejector
die
Cold forming
Full Forward Extrusion: pin production
Seite 36© WZL/Fraunhofer IPT
workpiece insertion
compression extrusion ejection
punch
workpiece
die
ejector
Cold forming
Cup Backward Extrusion: cup production
Seite 37© WZL/Fraunhofer IPT
workpieceinsertion
closing ofthe die
extrusion ejection
upper punch
workpiece
lower die
lower punch
upper die
Cold forming
Radial Extrusion of a Cardan Joint
Seite 38© WZL/Fraunhofer IPT
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 :
Seite 39© WZL/Fraunhofer IPT
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
Seite 40© WZL/Fraunhofer IPT
Cold forming
Typical Cold Formed Components
gear shafts
tubes
denticulations
screws
Hirschvogel Hirschvogel
FuchsSchraubenwerk
Seite 41© WZL/Fraunhofer IPT
Flow Stress
Fracture as a result of Radial Extrusion
fractures depending on passing a critical deformation value
Seite 42© WZL/Fraunhofer IPT
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
Seite 43© WZL/Fraunhofer IPT
Cold forming
Chevron Cracks by Full Forward Extrusion
Seite 44© WZL/Fraunhofer IPT
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
Seite 45© WZL/Fraunhofer IPT
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
Seite 46© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 47© WZL/Fraunhofer IPT
Warm forming
Iron-Carbon Phase Diagram
fcc
bcc
Recrystallization
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
Seite 48© WZL/Fraunhofer IPT
Warm forming
Material properties
Workpiece temperature / °C
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
Seite 49© WZL/Fraunhofer IPT
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 50© WZL/Fraunhofer IPT
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
Seite 51© WZL/Fraunhofer IPT
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
Warm forming
Efficiency
medium shape, dimension and position tolerances as well as
medium surface quality are possible
Seite 52© WZL/Fraunhofer IPT
Warm forming
Typical Warm Formed Components
slide hinge flange cylinder injector
Hirschvogel Hirschvogel
Audi
Seite 53© WZL/Fraunhofer IPT
Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Seite 54© WZL/Fraunhofer IPT
Forging
Iron-Carbon Diagram
fcc
bcc
Recrystallization
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
Seite 55© WZL/Fraunhofer IPT
Forging
Material Properties
Workpiece temperature / °C
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
Seite 56© WZL/Fraunhofer IPT
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 57© WZL/Fraunhofer IPT
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
Seite 58© WZL/Fraunhofer IPT
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
Forging
Efficiency
low shape, dimension and position tolerances as well as
low surface quality possible
Seite 59© WZL/Fraunhofer IPT
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
Seite 60© WZL/Fraunhofer IPT
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 61© WZL/Fraunhofer IPT
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
Seite 62© WZL/Fraunhofer IPT
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
Seite 63© WZL/Fraunhofer IPT
Forging
Open Die Forging
Saarstahl
Seite 64© WZL/Fraunhofer IPT
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
Seite 65© WZL/Fraunhofer IPT
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
Seite 66© WZL/Fraunhofer IPT
Forging
Stages of Closed Die forging
crankshaft
connection rod
hinge bearing
� an effective preform production is the key for short production chains
Seite 67© WZL/Fraunhofer IPT
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