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Bulk metal forming
Simulation Techniques in Manufacturing Technology
Lecture 4
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
Contents
1
Introduction and basics of bulk metal forming
2
Chronology of FE simulation
3
Simulation of hammer forging process
4
Simulation of deep rolling process
5
Summary
© WZL/Fraunhofer IPT
Seite 2
Overview of bulk metal forming processes
What is cold forming?
 The temperature of the workpiece amounts room temperature before forming
 No external heating of the workpiece (TBegin = 20 °C < TR)
 Process-related temperature increase of the workpiece because of dissipated
deformation energy (TEnd up to 350 °C)
Source: ThyssenKrupp Presta
© WZL/Fraunhofer IPT
Seite 3
Overview of bulk metal forming processes
Material properties (carbon steel)
T0: Room temperature
 Flow stress and fracture strain
 For cold forming applies:
– Flow stress decreases because
of increase of temperature
– Fracture strain can be assumed
as constant
Strain
Fracture strain φvf [-]
– Strain rate
– Forming temperature
– Material
Flow stress
Flow stress kf [MPa]
are a function of:
Temperature T [°C]
© WZL/Fraunhofer IPT
Seite 4
Overview of bulk metal forming processes
What is warm forming?
 External heating of the workpiece before forming
 Standard VDI 3166: Forming process with material strain hardening despite
heating
 Forming temperature between 500 °C and 900 °C
Source: Infostelle Industrieverband Massivumformung e.V.
© WZL/Fraunhofer IPT
Seite 5
Overview of bulk metal forming processes
Material properties
Tmin
Increase of stability and
decrease of ductility at non
alloyed and low alloyed steels
between 300 and 500 °C
Blue brittleness
© WZL/Fraunhofer IPT
Strain
Fracture strain φvf [-]
 Blue brittleness:
Flow stress
Flow stress kf [MPa]
 For the warm forming applies:
– Flow stress does not decrease
steadily because of blue
brittleness
– Fraction strain increases not
steadily because of blue
brittleness
Tmax
Temperature T [°C]
Seite 6
Overview of bulk metal forming processes
What is forging?
 Workpiece gets an external heating before forming
 Forming temperature is higher than recrystallization temperature TR = 0,4·TMelting
Source: Infostelle Industrieverband Massivumformung e.V.
© WZL/Fraunhofer IPT
Seite 7
Overview of bulk metal forming processes
Material Properties
surface after 500 °C
 Scaling: Oxidation above
500°C. Aerial oxygen reacts
with base material to Fe2O3
Flow stress
Blue brittleness
© WZL/Fraunhofer IPT
Strain
Fracture strain φvf [-]
 Scaling at the materials
T0: Room temperature
Flow stress kf [MPa]
 For forging applies:
– Flow stress decreases
steadily
– Fracture strain increases
steadily
Tmin
Temperature T [°C]
Seite 8
Contents
1
Introduction and basics of bulk metal forming
2
Chronology of FE simulation
3
Simulation of hammer forging process
4
Simulation of deep rolling process
5
Summary
© WZL/Fraunhofer IPT
Seite 9
Simulation of bulk metal forming processes
Considerations prior to a simulation study
Definition of the simulation problem
 Objective of the simulation study
 Relevant physical mechanisms:
– Mechanical, thermal, electro-magnetic…
 Type of the problem:
– Linear
– Non-linear
 Time dependency:
– Static
– Dynamic
 Simulation software & hardware:
– Solvers for the intended objectives
– Element types
– Specific numerical technologies
© WZL/Fraunhofer IPT
Constituents of a model
 Geometry
– Accurate form reproduction
– Stock or special FE mesh generator
– Critical areas, complex shapes
 Material
– Material model formulation
– Elasticity and Poisson’s ratio
– Density, hardening
– Thermal properties
 Boundary conditions
– Process parameters
– Process kinematics
– Process steps
Seite 10
Simulation of bulk metal forming processes
FE Study process
CAD model
Idealization
Discretization
Boundary conditions
Material modeling
FE-Analyses
Evaluation
© WZL/Fraunhofer IPT
Geometry of a workpiece and a tool.
Often available as CAD Data.
Universal formats for 3D data (STEP, STP, STL…)
Simplification of the real geometry for a more structured mesh
Meshing of an object into discrete domains
Numerical reproduction of mechanic, kinematic, contact,
electro-magnetic, thermal conditions of a real process
Numerical formulation of relevant material properties
(elasticity, plasticity, shear etc.)
Calculation of elementary matrices, definition of the
system matrix and a vector of outer forces, solution of
linear equation systems for every integration point
Analysis of the results and answering the objective
of the study
Seite 11
Simulation of bulk metal forming processes
Chronology of FEM-Simulation: Material modeling
 Description of material behavior using
mathematical material models
CAD model
 Use of ideal-plastic material model is sufficient for
bulk metal forming processes
Idealization
Material modeling
Evaluation
Nominal strain ε
Plastic with
hardening
Nominal strain ε
© WZL/Fraunhofer IPT
Ideal plastic
Nominal strain ε
Stress σ
Stress σ
Postpro. Solver
FE-Analyses
Elastic
Stress σ
simulation of sheet metal forming processes
Stress σ
Boundary conditions
Preprocessor
Discretization
 Use of elastoplastic material models for
Elasto-plastic
with hardening
Nominal strain ε
Seite 12
Simulation of bulk metal forming processes
Chronology of FEM-Simulation: FE-Analysis
 Implicit solution method:
CAD model
Discretization
Boundary conditions
Preprocessor
Idealization
– Small number of time steps
(respectively long time increments)
– Higher effort for iterations compared to explicit
solution method
– Often less computation time then with explicit
solution method
– Applicable especially for static and
quasi-static problems
 Explicit solution method:
FE-Analyses
Evaluation
© WZL/Fraunhofer IPT
Postpro. Solver
Material modeling
– Length of increment depends on the speed of
sound c, Young‘s modulus E and material
density ρ; this requires a high number of
increments
– Longer computation time compared to implicit
solution method
– Applicable especially for highly dynamic
problems (e.g. crash-simulations)
Seite 13
Simulation of bulk metal forming processes
Movie: FEM-Simulation cross joint
Degree of damage
Effective stress
Mean stress
True strain
Velocity field
CAD model
Idealization
Discretization
Boundary conditions
Material modeling
FE-Analyses
Evaluation
 Typical evaluation variables are stress-strain-profiles or
characteristic values such as the degree of damage.
© WZL/Fraunhofer IPT
Seite 14
Contents
1
Introduction and basics of bulk metal forming
2
Chronology of FE simulation
3
Simulation of hammer forging process
4
Simulation of deep rolling process
5
Summary
© WZL/Fraunhofer IPT
Seite 15
Simulation of hammer forging process
Tool concept
Forge finishing process with balance in two steps
Closing plate
Forging blank
Pre-stamping
Radii according to drawings
or experience based values
Mandrel
Die
Ejector
1. Upsetting
(remove scale and
pre-stamping, if necessary)
2. Forge finishing
(gearing)
Source: The hammer forging simulation procedure is courtesy of Buderus
© WZL/Fraunhofer IPT
Seite 16
Simulation of hammer forging process
Abstract of the process chain for FE model
Real process chain of press line 3 by Buderus
Heating
Transportation
Waiting time in
air
Waiting time
after forging
die
Transport to
forging die
Waiting time
before forging
die
Preforming and
ejection
Waiting time
and
transportation
Forging and
ejection
Transportation
and waiting
time in
upsetting press
Transport und
waiting time at
interstage
position
Cooling
Transport und
waiting time
preforming die
Derived process chain for FEM-model
Heating,
transport and
waiting time
© WZL/Fraunhofer IPT
Preforming and
ejection
Waiting time
and
transportation
Forging and
ejection
Cooling
Seite 17
Simulation of hammer forging process
Simulation of process chain…
… with rigid tool on a half section
© WZL/Fraunhofer IPT
… with rigid tool in complete view
Seite 18
Simulation of hammer forging process
Overview on the model structure
Material model
 Time discretization:
Forming: explicit
Heating, spring back, cooling: implicit
 Geometrical interpolation: Linear
 Element type: 3D
 Element shape: Hexahedra
 Thermally coupled
 Reduced integration
400
350
300
250
200
150
100
50
0
1200
[1]
[2]
[3]
[4]
0
Contact and boundary conditions
 Coulomb friction model: µ = 0.2
 Normal contact: no penetration
 Contact type: Surface-to-Surface,
thermally coupled
 BCs depend on the process step, e. g.
temperature at the interstage position
or forming velocity of forging punch
Tool: X40CrMoV5
Workpiece: 16MnCr5
Flow stress σ [MPa]
–
–
0.5
1
True strain φ [-]
Flow stress σ [MPa]
Element definition
[5]
[6]
[7]
[8]
1000
800
600
400
200
0
1.5
0
16MnCr5
0.5
1
True strain φ [-]
1.5
X40CrMoV5
 Thermal conductivity λ
[W/m K]
43,39
 Specific heat capacity
cpm [kJ/kg K]
 Thermal expansion
coefficient αm
 E-modulus E [GPa]
< 30,25
474,14 < cpm < 685,71
11,04
[K−1]
 Density ρ [kg/m3]
<λ
< αm < 15,94
7821,8 < ρ
213,0
< 7373,0
< E < 46,5
22,95
<λ
< 25,77
428,40 < cpm < 715,72
10,08
< αm < 27,70
7755,6 < ρ
213,8
< 6982,0
< E < 50,7
Legend: [1]  = 500  −1 @ = 800° [2] [email protected] [3] [email protected] [4] [email protected] [5] [email protected] [6] [email protected] [7] [email protected] [8] [email protected] Source: Landolt-Börnstein DB
© WZL/Fraunhofer IPT
Seite 19
Simulation of hammer forging process
Reduction of the model to a two teeth concept
Heating,
transportation and
waiting
Forging blank
Preforming and
ejection
Preforming punch
Waiting time and
transportation
Forging blank
Forging and ejection
Forging punch / Mandrel
Cooling in air
Forging blank
Closing plate
3
2
1
Transportation and
waiting plates
Preforming plate
© WZL/Fraunhofer IPT
Transportation and
waiting plates
Ejector
Die
Forging plate
Seite 20
Simulation of hammer forging process
Model structure: heating and transportation
Data of the real process
Volumes of forging blanks
FE-model
Forging
blank
(16MnCr5)
Elastic,
implicit,
thermally
coupled
 Heating
–
ϑWSK = 1270 °C
 Waiting time in air
–
t1 = 8 s, ϑair = 30 °C, ϑcontact = 50 °C
 Transportation to upsetting press
–
t2 = 7 s, ϑair = 30 °C, ϑcontact = adiabat
t3 = 4 s, ϑair = 30 °C, ϑcontact = 120 °C
 Transportation to the interstage position
–
ϑair
t5 = 5,5 s, ϑair = 30 °C, ϑcontact = adiabat
 Waiting time at the interstage position
–
ΔV16MnCr5,Δt = 1250 = -5,21 %
VFT,kalt = 13 177 458,06 mm³
ΔVZunder = +0,5 %
VFT,kalt,korr = 13 243 345,35 mm³
–
–
dmax,Ofen = 210 mm
hESM = 382,36 mm
 Determination of the scale conditioned
AESM = 321 526,32 mm²
Dzowv = 0,205 mm
 Final geometry of the billet for the
t7 = 5,5 s, ϑair = 30 °C, ϑcontact = adiabat
t8 = 5 s, ϑair = 45 °C, ϑcontact = 170 °C
–
–
–
–
t6 = 2,5 s, ϑair = 30 °C, ϑcontact = 50 °C
 Waiting time before preforming die
–
 Consideration of thermal expansion
surficial material loss (zowv)
 Transportation to the main press
–
VFT,warm = 13 863 688,62 mm³
 Determination of the billet height (ESM)
hESM,Sim
t4 = 3,5 s, ϑair = 30 °C, ϑcontact = 120 °C
–
–
–
ϑWSK
 Waiting time after upsetting press
–
ideal form filling according to the tool
 Consideration of scale loss
 Waiting time before upsetting press
–
 Finished part (FT) in a hot state after
3
2
ϑcontact
1
simulated model
–
–
hESM,Sim = 382,3 – 2*0,205 = 381,95 mm
dESM,Sim = 210,0 – 2*0,205 = 209,59 mm
Waiting plates
Legend: WSK = workpiece, ESM = billet, zowv = scale conditioned surficial material loss
© WZL/Fraunhofer IPT
Seite 21
Simulation of hammer forging process
Analysis of the resulting temperature distribution
Video: 01 – Heating
Before the
upsetting press
After the
furnace
Before the
preforming
t1-8 = 42 s
t1-2 = 16 s
t3-8 = 26 s
ϑWSK,OF = 1100 °C
Temp [°C]
+1270
3
2
ϑWSK = 1270 °C
+1110
1
ϑWSK,min = 976 °C
ΔϑWSK = -294 °C
+950
Legend: Temp = Designation according to Abaqus  Temperature in °C; OF = surface
© WZL/Fraunhofer IPT
Seite 22
Simulation of hammer forging process
Analysis of thermal expansion
After the furnace
radial direction
hESM,Sim = 381,95 mm
Before the
furnace
U [mm]
+8,398
3
2
t1-8 = 42 s
Δ½d = +2,05 mm
+4,199
1
After the furnace
axial direction
hESM,Sim = 389,75 mm
Video: 01 - Heating
+0
t1-8 = 42 s
Δh = +7,8 mm
Legend: U = Designation according to Abaqus; U = value of the displacement vector in all three coordinates 1, 2, 3  length change in mm
© WZL/Fraunhofer IPT
Seite 23
Simulation of hammer forging process
Model structure: preforming and ejection
Data of the real process
FE-Modell
 Preforming
–
–
–
Press force FVSP = 1200 t
stroke length h = 600 mm
Engine power Eengine = 2x200 KW
Preforming punch
(X40CrMoV5)
Elastic, thermally coupled
 Waiting time after preforming die
–
–
–
t1 = 4 s,
ϑair = 45 °C,
ϑcontact = 170 °C
 Transport to the mail forging die
–
–
–
t2 = 3 s,
ϑair = 45 °C,
ϑcontact = adiabat
ϑWSK
Forging blank
(16MnCr5)
Elastic-plastic, thermally coupled
(Explicit, ALE)
ϑair
 Waiting time before the mail forging die
–
–
–
t3 = 5 s,
ϑair = 45 °C,
ϑcontact = 170 °C
ϑcontact
Preforming plate
(X40CrMoV5)
Elastic, thermally coupled
3
2
1
Legend: ALE = Arbitrary Lagrangian Eulerian
© WZL/Fraunhofer IPT
Seite 24
Simulation of hammer forging process
Calculation of punch force for preforming
Model: 02-preforming
Calculation of the punch force for preforming
70
60
(1)
(3)
Force3 [t]
50
(1) Application of punch
360°-model
(2) Application of billet
on the plate
40
Two-teeth-model
30
20
10
(3) Application of generated surface
on the shoulders
0
Process time during preforming Δt [s]
(2)
3
3
2
2
1
© WZL/Fraunhofer IPT
1
Seite 25
Simulation of hammer forging process
Analysis of stress distribution in the workpiece
Video: 02-preforming
25 % stroke
75 % stroke
S [MPa]
100 % stroke
σmax = 283 MPa
+308
3
2
+154
1
+0
Δt = 0,32 s
Legend: S = Designation according to Abaqus; S = Stress von Mises  von Mises equivalent stress σV in MPa
© WZL/Fraunhofer IPT
Seite 26
Simulation of hammer forging process
Analysis of stress distribution in the billet
Video: 02-Preforming
25 % stroke
S [MPa]
75 % stroke
100 % stroke
σmax = 118 MPa
+129
3
2
+65
1
+0
Δt = 0,32 s
Legend: S = Relation according to Abaqus; S = Stress von Mises  von Mises equivalent stress σV in MPa
© WZL/Fraunhofer IPT
Seite 27
Simulation of hammer forging process
Analysis of stress distribution in the preforming punch
Video: 02-Preforming
25 % stroke
S [MPa]
75 % stroke
100 % stroke
σmax = 158 MPa
+173
3
2
+87
1
+0
Δt = 0,32 s
Legend: S = Relation according to Abaqus; S = Stress von Mises  von Mises equivalent stress σV in MPa
© WZL/Fraunhofer IPT
Seite 28
Simulation of hammer forging process
Analysis of stress distribution in the preforming plate
Video: 02-Preforming
25 % stroke
75 % stroke
100 % stroke
σmax = 309 MPa
S [MPa]
+309
3
2
+180
1
+0
Δt = 0,32 s
Legend: S = Relation according to Abaqus; S = Stress von Mises  von Mises equivalent stress σV in MPa
© WZL/Fraunhofer IPT
Seite 29
Simulation of hammer forging process
Analysis of temperature distribution in the billet
Video: 02-preforming
25 % stroke
75 % stroke
100 % stroke
Δϑ = 308 °C
ϑmin = 983 °C
ϑmax = 1291 °C
Temp [°C]
+1291
3
2
+1163
1
+983
Δt = 0,32 s
Legend: Temp = Designation according to Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 30
Simulation of hammer forging process
Analysis of the absolute radial strains in the billet
Video: 02-preforming
25 % stroke
75 % stroke
100 % stroke
U1 [mm]
+47
3
2
Δd = +31,24 mm
+24
1
+0
Δd = +46,86 mm
Legend: U1 = Designation according to Abaqus; U1 = value of the first component of the displacement vector U  radial length change in mm
© WZL/Fraunhofer IPT
Seite 31
Simulation of hammer forging process
Analysis of the absolute radial strains in VS-plate
Video: 02-preforming
75 % stroke
25 % stroke
100 % stroke
Δh = -0,066 mm
Mandrel of the
preforming plate
Application of the ESM
on the plate.
U3 [mm]
+0
3
2
Δh = -0,066 mm
-0,031
1
-0,066
Δh = -0,054 mm
Legend: U3 = Designation according to Abaqus; U3 = value of the third component of the displacement vector U  axial length change in mm; VS = preforming
© WZL/Fraunhofer IPT
Seite 32
Simulation of hammer forging process
Model structure: forging and ejection
Data of the real process
FE-model
 Spindle forging press
–
–
–
–
–
Forging punch / mandrel
(X40CrMoV5)
Elastic, thermally coupled
FSP = 10 000 t
hstroke = 800 mm
Eengine = 1050 kW
vAuftreff = 583 mm/s
FPrellschlag = 131 485 kN
Forging blank
(16MnCr5)
Elastic-plastic, thermally coupled
(Explicit, ALE + CEL)
 Ejector
–
–
htable = 200 mm
hStößel = 30 mm
ϑWSK
ϑair
 Temperatures
–
–
ϑair = 45 °C,
ϑcontact = 170 °C
Die with the tooth geometry
(X40CrMoV5)
Elastic, thermally coupled
 Friction [MESS02]
–
Closing plate by means of spring
(X40CrMoV5)
Elastic, thermally coupled
depends on pressure : 0.1 < µ < 0.2
ϑcontact
Ejector
(X40CrMoV5)
Elastic, thermally coupled
3
2
Forging plate
(X40CrMoV5)
Elastic, thermally coupled
1
Source: [MESS02] Messner, C.: Reibung und Wärmeübergang beim Schmieden, 2002; CEL = Coupled Eulerian Lagrangian Method
© WZL/Fraunhofer IPT
Seite 33
Simulation of hammer forging process
Calculation of the punch force for the forging
Model: 04-Forging
Calculation of the punch force for the forging
ALE: 1927 t
2000
1800
CEL: 1939 t
(1) Application of the forging punch/ mandrel
(2) Application of the first mandrel platform
1600
(3)
(1)
1400
Force F3 [t]
(2)
1200
(3) Application of the second
mandrel platform
LAG: 1664 t
1000
800
600
400
LAG
200
CEL
0
ALE
-200
Process time during forging Δt [s]
3
3
2
2
1
1
Legend: LAG = Lagrange calculation method, Standard; CEL = Coupled Eulerian Lagrangian Method, ALE = Arbitrary Lagrangian Eulerian Method
© WZL/Fraunhofer IPT
Seite 34
Simulation of hammer forging process
Calculation of the closing plate force for the forging
Model: 04-Forging
Calculation of the closing plate force
300
250
(3)
Force F3 [t]
200
150
LAG: 273 t
(1) Application of the billet on the closing plate
(2) Closing force due to mandrel movement
(3) Forging punch in completely applied
(4) Overcoming of the die inner pressure
100
50
(1) (2)
0
-50
-100
Process time during forging Δt [s]
3
3
2
2
1
© WZL/Fraunhofer IPT
1
Seite 35
Simulation of hammer forging process
Analysis of the power requirements of the ejector
Modell: 04-Forging
Power requirements of the ejector
100
(1) Beginning of the ejection (adhesion)
90
80
LAG: 89 t
(2) Stick-Slip effect
(adhesion > sliding friction)
Force F3 [t]
70
60
(3) Decreasing contact surface
between the billet and the die
50
40
30
20
10
(1)
(3)
(0) Forging
0
(2)
-10
Process time during forging Δt [s]
3
3
2
2
1
© WZL/Fraunhofer IPT
1
Seite 36
Simulation of hammer forging process
Analysis of stress distribution in the tool
Video: 04-Forging
25 % stroke
75 % stroke
S [MPa]
100 % stroke
σmax = 700 MPa
+700
3
2
+350
1
+0
Δ t = 0,32 s
Legend: S = Designation according to Abaqus; S = Stress von Mises  von Mises equivalent stress σV in MPa
© WZL/Fraunhofer IPT
Seite 37
Simulation of hammer forging process
Analysis of the temperature distribution in the billet
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
ϑ25,min = 917°C
Δϑ = 288 °C
ϑmin = 1035 °C
ϑmax = 1323 °C
Temp [°C]
+1323
3
2
+1121
1
+917
Δt = 0,32 s
Legend: Temp = Designation according to Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 38
Simulation of hammer forging process
Analysis of temperature distribution in the forging punch
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δϑ = 86 °C
ϑmin = 170 °C
ϑmax = 256 °C
Temp [°C]
+256
3
2
+225
1
+170
Δt = 0,32 s
Legend: Temp = Designation according Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 39
Simulation of hammer forging process
Analysis of temperature distribution in the closing plate
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δϑ = 253 °C
ϑmin = 170 °C
ϑmax = 423 °C
Temp [°C]
+423
3
2
+275
1
+170
Δt = 0,32 s
Legend: Temp = Designation according Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 40
Simulation of hammer forging process
Analysis of temperature distribution in the die
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δϑ = 130 °C
ϑmin = 170 °C
ϑmax = 300 °C
Temp [°C]
+300
3
2
+235
1
+170
Δt = 0,32 s
Legend: Temp = Designation according Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 41
Simulation of hammer forging process
Analysis of temperature distribution in the forging plate
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δϑ = 35 °C
ϑmin = 170 °C
Temp [°C]
ϑmax = 205 °C
+205
3
2
+187
1
+170
Δt = 0,32 s
Legend: Temp = Designation according Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 42
Simulation of hammer forging process
Analysis of the temperature distribution in the ejector
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δϑ = 22 °C
ϑmax = 192 °C
ϑmin = 170 °C
Δh = 200 mm
Temp [°C]
+192
3
2
+181
1
+170
Δt = 1 s
Legend: Temp = Designation according Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 43
Simulation of hammer forging process
Analysis of the absolute radial strains in the forging punch
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δ½d = 1,31 mm
U1 [mm]
+1.31
3
2
+0,5
1
-0,48
Δt = 0,32 s
Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U  radial length change in mm
© WZL/Fraunhofer IPT
Seite 44
Simulation of hammer forging process
Analysis of the absolute radial strains in the closing plate
Video: 04-Forging
25 % stroke
U1 [mm]
75 % stroke
100 % stroke
Δ½d = 0,42 mm
+0,42
3
2
+0,18
1
+0
Δt = 0,32 s
Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U  radial length change in mm
© WZL/Fraunhofer IPT
Seite 45
Simulation of hammer forging process
Analysis of the thermal expansion in the die
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δ½d = 1,08 mm
U1 [mm]
+1,08
3
2
+0,52
1
+0
Δt = 0,32 s
Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U  radial length change in mm
© WZL/Fraunhofer IPT
Seite 46
Simulation of hammer forging process
Analysis of the thermal expansion of the forging plate
Video: 04-Forging
25 % stroke
75 % stroke
100 % stroke
Δh = -0,32 mm
Mandrel of the
forging plate
U3 [mm]
Δh = -0,32 mm
+0
3
2
-0,18
1
-0,32
Δ t = 0,32 s
Legend: U3 = Designation according to Abaqus; U3 = value of the third component of the displacement vector U  axial length change in mm
© WZL/Fraunhofer IPT
Seite 47
Simulation of hammer forging process
FE-model structure: cooling
Main data of the real process
FE-model
 Cooling
–
–
ϑair = 30 °C,
t = 24 h
Forging blank
(16MnCr5)
Elastic, thermally coupled,
implicit
ϑWSK
ϑair
ϑcontact
3
2
© WZL/Fraunhofer IPT
1
Seite 48
Simulation of hammer forging process
Analysis of the temperature distribution in the billet
Video: 05-Cooling
24h
0h
ϑ = 1312 °C
ϑ = 20 °C
ϑ = 20 °C
Temp [°C]
+1312
3
2
Δt = 4h
+660
1
+20
Δt = 24h
Legend: Temp = Designation according to Abaqus  Temperature in °C
© WZL/Fraunhofer IPT
Seite 49
Simulation of hammer forging process
Deviations from the nominal values of the finish part
Nominal geometry of the
hot tooth acc. to the tool
drawing
Real geometry after forging (FEM)
24 h cooling
hs,Ist = 32,84 mm (+0,84 mm)
½ dist = 202,72 mm (+0,72 mm)
After
cooling
U1 [mm]
hz,ist = 183,3 mm (+0,3 mm)
½ d24h = 199,3 mm
(-3,42 mm)
hTraganteil = 66,67 mm
(-116,33 mm)
hs,soll = 32 mm
hz,soll = hTraganteil = 183 mm
½ dsoll = 202 mm
+92,37
3
2
msoll = 101,67 kg
1
Vsoll = 184,85 ∙ 106 mm3
+46,63
0
mist = 101,71 kg (+0,04%)
hz,24h = 180,22 mm
(-3,1 mm)
hs,24h = 32,28 mm
(-0,56 mm)
Finished part
(acc. drawing)
½ dEnd = 196,8 mm
(+2,5 mm)
hz,End = 175,3 mm
(+4,92 mm)
Vist = 185,97 ∙ 106 mm3 (+0,6%)
Legend: + X mm = Oversize due to the tool elongation, - X mm = th. shrinkage due to cooling; + X mm = machining allowance for finished part
© WZL/Fraunhofer IPT
Seite 50
Simulation of hammer forging process
Iterative increase of the billet mass (V = 103%)
Boundary conditions
Real geometry after forging (FEM)
 Nominal geometry
Compensation
region
½ dist = 202,42 mm (+0,42 mm)
hs,Ist = 32,61 mm (+0,61 mm)
U1 [mm]
+92,37
Burr
hz,ist = 183,0 mm (+0,0 mm)
Model
Tool: rigid body
Billet: elastic-plastic
 volumes 103%,
 optimized meshing
102%, 102,5% do not
reach 100% form
filling.
developed to 100% at
103% billet.
 Boundary conditions of FE–
–
 101%, 101,5%,
 Nominal geometry is
hTraganteil = 173,73 mm
(-0,10 mm)
hz,soll = 183 mm
h = 173,83 mm
hs,soll = 32 mm
½ dsoll = 202 mm
Conclusion
 For V = 103% will be
evaluated material
flow, contact surface
and forming force.
 For 103% the billet is
also calculated with
elastic tools.
+46,63
0
Legend: U1: radial displacement
© WZL/Fraunhofer IPT
Seite 51
Simulation of hammer forging process
Analysis of material flow with the rigid tools (V = 103%)
95% forming
97% forming
100% forming
VR [mm/s]
+450
+225
0
 Compensation region is already
filled, before the tooth top width is
completely formed
 There is a high resulting flow velocity
below ca. 45°, it means that the
material flows in the compensating
region and in the die
 The flowing velocity slightly increase
 Accordingly increases the material
flow in compensation region
 The material flow on the tooth top at
some places is almost zero, it means
that the tooth there is maximally filled
 The material flow is located in the
compensation region
 The tooth top width is under the
requested percentage contact area is
completely formed
 The flow velocity at the contact with
the tool is zero
Legend: VR = resulting velocity vector
© WZL/Fraunhofer IPT
Seite 52
Simulation of hammer forging process
Analysis of the forming force for the rigid tools (V = 103%)
Model: 04-Forging
Calculation of the punch force for the forging
V = 103%: 4437 t
4500
4000
(a)
(b) Application of the first mandrel platform
3500
Punch force F3 [t]
(b)
(c)
(a) Application of the forging punch/ mandrel
3000
2500
(c) Application of the second
mandrel platform
x2.67
2000
1500
1000
V = 100%: 1664 t
500
V=103%
V=103%(starr)
(rigid)
0
V=100%
V=100%(elastisch)
(elastic)
-500
Process time by forging Δt [s]
3
3
2
2
1
1
Legend: V=100% (elastic) : Result of the simulation; V=103% (rigid): result of the simulation with the rigid tool
© WZL/Fraunhofer IPT
Seite 53
Simulation of hammer forging process
Simulation of the forging steps in the case of el. tools (V = 103%)
Boundary conditions
Real geometry of the forging (FEM)
Conclusion
 Nominal geometry
 Form filling with elastic
Tools: elastic
Billet: Elastic-plastic
 Volumes 103%
 Optimized mesh
 Optimized punch stroke,
to compensate elastic
upsetting of the punch
(185 vs. 191 mm).
U1 [mm]
+92,37
hz,ist = 183,01 mm (+0,01 mm)
Model
hTraganteil = 128,53 mm
(-45,3 mm)
 Optimized punch stroke
 Boundary conditions of FE–
–
tools in comparison to
usage of rigid tools is
not complete
½ dist = 202,9 mm (+0,9 mm)
hs,Ist = 32,19 mm (+0,19 mm)
hz,soll = 183 mm
hs,soll = 32 mm
h = 173,83 mm
½ dsoll = 202 mm
compensates the
upsetting of the punch.
However the form filling
is not reached
 The compensation
region is already
partially filled.
Compensation
region
+46,63
0
Legend: U1: radial displacement
© WZL/Fraunhofer IPT
Seite 54
Simulation of hammer forging process
Simulation of the forging steps in the case of elastic tools (V = 104%)
Boundary conditions
Real geometry after forging (FEM)
Conclusions
 Nominal geometry
 An additional
Tools: elastic
Billet: elastic-plastic
 Volumes 104%
 Optimized meshing
 Optimized punch stroke
 Additional mesh
optimization in
compensation region
U1 [mm]
+92,37
hz,ist = 183,5 mm (+0,5 mm)
Model
hTraganteil = 142,24 mm
(-31,59 mm)
 The elastic strains in
 Boundary conditions of FE–
–
increase of the billet
mass to 104% as well
as local mesh
optimization of the
compensation region
do not lead to the
100% form filling
½ dist = 203,735 mm (+1,73 mm)
hs,Ist = 32,16 mm (+0,16 mm)
hz,soll = 183 mm
hs,soll = 32 mm
h = 173,83 mm
½ dsoll = 202 mm
the tool are too large
 The compensation
region is partially
filled also here
Compensation
region
+46,63
0
Additional mesh optimization in
compensation region
Contour V = 103 %
Legend: U1: radial displacement
© WZL/Fraunhofer IPT
Seite 55
Simulation of hammer forging process
Analysis of the material flow in the case of elastic tools (V = 104%)
95% Forming
97% Forming
100% Forming
VR [mm/s]
+450
+225
0
 The flow velocity with the elastic
tools is clearly smaller in comparison
to the rigid tools and moreover is
distributed within the whole part, but
not focused in the domain of the
compensated region.
 The flow diagram is hardly changed
by 97%. The material flow on the
tooth top is not zero, therefore there
is not available any form filling due to
distention of the tools.
 The compensation region is even at
104% billet mass not sufficiently
filled, so the 100% form filling is not
reached
 In the case of absence of the
compensation region, the material
situated there would flow in the die.
Legend: VR = resulting velocity vector
© WZL/Fraunhofer IPT
Seite 56
Simulation of hammer forging process
Analysis of the forming force in the case of elastic tools (V = 104%)
Modell: 04-Forging
Calculation of the punch force for the forging
V = 103%: 4437 t
4500
(b)
(c)
(a)
Punch force F3 [t]
4000
3500
3000
(a) Application of the forging punch/ mandrel
(b) Application of the first mandrel platform
(c) Application of the second mandrel platform
2500
V = 104%: 3173 t
2000
1500
1000
V = 100%: 1664 t
500
VV=100%
= 100% (elastisch)
(elastic)
0
(rigid)
VV=103%
= 103% (starr)
-500
(elastic)
VV=100%
= 104% (elastisch)
Process time during forging Δt [s]
3
3
2
2
1
1
Legend: V=100% (elastic) : Result of the simulation; V = 104% (elastic): result of the simulation in the case of elastic tool
© WZL/Fraunhofer IPT
Seite 57
Simulation of hammer forging process
Analysis of the tool loads in the punch at V=104%
Equivalent stress
σv [MPa]
Plot of the contact area
P [MPa]
+653,8
+1615
+356,6
+881,1
0
0
Legend: σv : von Mises equivalent stress; P = contact pressure per unit area
© WZL/Fraunhofer IPT
Seite 58
Simulation of hammer forging process
Analysis of the tool loads in the die at V = 104%
Equivalent stress
Plot of the contact area
99% Forming
100% Forming
σv [MPa]
P [MPa]
+471,3
+1354
+271,8
+676,8
0
0
Legend: σv : von Mises equivalent stress; P = contact pressure per unit area
© WZL/Fraunhofer IPT
Seite 59
Simulation of hammer forging process
Performed optimization process
Optimization process with the rigid tools
To analyze the tool
concept with the
rigid tool
Real
geometry
Mesh optimization
Iterative increase of
the billet mass until
the form filling is
reached
Nominal
geometry
The optimum in the case of the rigid tools is the initial situation
for the optimization for the case of the elastic tools
Optimization process with the elastic tools
To analyze the tool
concept with the
elastic tool
© WZL/Fraunhofer IPT
Optimization of the
punch stroke
Iterative increase of
the billet mass
Seite 60
Simulation of hammer forging process
Optimization process in the case of the rigid tool
 Form filling (FF) is not reached at the billet volume of V = 100% and application
To analyze the
tool concept
with the rigid
tool
of the rigid tool. Reasons are:
– Volume loss due to insufficient meshing at the tooth root (~1%)
– Volume loss in the burr due to adjusted tool geometry (0,5%)
 Meshing at the tooth root is optimized and billet mass is increased at 1,5%
 Form filling is not reached at volume of V = 101,5% with optimized mesh and
in the case of rigid tool. Reason is:
Mesh
optimization
– Precocious infilling of the compensation region prevents complete flow od the material in
the die. Thus, there is no 100% form filling.
 Billet mass is increased at 0,5%, until 100% form filling is reached
 Form filling is reached at V = 103%, optimized mesh and rigid tools.
Iterative
increase of the
billet mass until
the form filling
is reached
 Background:
– Compensation region is filled in the way, that the material through the required
percentage contact area of 100% is aligned to the die.
Legend:
© WZL/Fraunhofer IPT
Derived procedures to optimize the identified deficit
Seite 61
Simulation of hammer forging process
Optimization process in the case of the elastic tool
 Form filling in the case of the elastic tools and with the application of the
To analyze the
tool concept
with the elastic
tool
optimization steps of the rigid process chain is not reached. Reasons are:
– Elastic upsetting of the punch of about 6 mm, el. deflection of the die and the forging
plate as well as precocious infilling of the compensation region
 Elongated punch stroke should compensate given elastic upsetting
 Form filling is not reached in the case of the elastic tools, optimized punch
stroke, and the optimization procedures of the rigid proses. Reasons are:
Optimization of
the punch
stroke
– Elastic deflection of the tool and precocious infilling of the compensation region
 Iterative increase of the billet mass should fill the compensation region.
 Form filling is not reached at V = 104%, el. tools, optimized punch stroke,
and the optimization procedures of the rigid proses. Reasons are:
Iterative
increase of the
billet mass
– Even more strong deflection of the die (~ 2mm)
 Main influencing parameter on the form filling: el. strains of the tools
– Earlier infilling of the compensating region.
 Material in the compensating region could be used for the form filling
Legend:
© WZL/Fraunhofer IPT
Derived procedures to optimize the identified deficit
Seite 62
Contents
1
Introduction and basics of bulk metal forming
2
Chronology of FE simulation
3
Simulation of hammer forging process
4
Simulation of deep rolling process
5
Summary
© WZL/Fraunhofer IPT
Seite 63
Simulation of deep rolling process
Modelling and verification of material behavior
Baushinger
test of 42CrMo4
Bauschinger-Versuch
bei 42CrMo4
1200
0
-400
0 0 = 0 + ∞ (1 −  −
−
0
-1200
)
0
-2%
-1%
0%
1%
2%
3%
( − )


-1200
 -3%
= -2%
− 
0
-1%
0%
1%

2%
800
F
F
F
0
60
80
3%
60
80
GGG60 [2%]
1200
Initial state
400
40
Time t [s]
Simulation
Experiment
Dehnung [%]
1200
20
-400
-800
Dehnung
[%]
Strain
[%]
Baushinger
test of GGG60
Bauschinger-Versuch
bei GGG60
Spannung [MPa]
400
-800
 Kinematic part:
-800
-400
800
400
0
-400
-800
-1200
-800
-1200
-3%
800
-400
 Isotropic
hardening model:
400
400
-1200
-3%
42CrMo4 [2%]
1200
800
Spannung [MPa]
Spannung [MPa]
800
Simulation and verification
Stress σ [MPa]
 Bbb
Modelling
 Modelling of non-linear
isotropic/kinematic material
behavior by means of
constitutive material
descriptionBauschinger-Versuch
according tobei GGG60
1200
Lemaitre-Chaboche
Stress σ [MPa]
Experiment
 Tension-Compression-tests at
Karlsruhe Institute of
Technology (KIT) at 2%, 4%
and 6% strain
0
-2%
-1%
0%
1%
Dehnung [%]
2%
3%
Tension Compression Tension
20
40
Time t [s]
Strain [%]
© WZL/Fraunhofer IPT
Seite 64
Simulation of deep rolling process
Modelling of press kinematic by rotationally sym. deep drawing
Exemplary application
Process kinematic
Contact description

ωK



Kmax
Simplified deep drawing tool

r


ωk


, , 



r

Workpiece
© WZL/Fraunhofer IPT
ω
, , 



RP
Seite 65
Simulation of deep rolling process
Modelling of the chosen geometry element
B
Abstraction
Abstraction
C
Geometry variation
A
A

B

0

4
4


1
1

© WZL/Fraunhofer IPT
2
 2 = ∞
 
Mises [MPa]
C

+1200
+600
+0
Seite 66
Simulation of deep rolling process
Simulative evaluation of the residual stresses
Residual stresses in axial direction (y)
Eigenspannungen quer: S33(P)
400
Transverse residual stresses σ [MPa]
400
200
0
-200
-400
-600
-800
-1000
-1200
200
0
-200
-400
-600
-800
-1000
-1200
© WZL/Fraunhofer IPT
P=175
P=250
3.00
2.16
1.33
0.50
0.45
0.40
0.35
0.30
0.25
0.20
Edge depth t [mm]
Edge depth t [mm]
pressure P=100 bar
Walzdruck
0.15
0.10
0.05
3.00
2.16
1.33
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-1400
-1400
0.00
Longitudinal residual stresses σ [MPa]
Residual stresses in circumferential
Eigenspannungen
längs: S11(P)
direction
(x)
P=325
P=400
pressure P=100 bar
Walzdruck
P=175
P=250
P=325
P=400
Seite 67
Contents
1
Introduction and basics of bulk metal forming
2
Chronology of FE simulation
3
Simulation of hammer forging process
4
Simulation of deep rolling process
5
Summary
© WZL/Fraunhofer IPT
Seite 68
Summary
 Bulk metal forming besides sheet metal forming is
the most relevant group in metal forming
 In general, depending on the process temperature,
one can distinguish between three main groups:
– cold forming
– warm forming
– hot forming
 During product design one should consider
advantages and disadvantages of all these three
variants from technological point of view
 The detailed simulation procedures are presented
for the hammer forging and deep drawing processes
© WZL/Fraunhofer IPT
Seite 69
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