stamping fea model input review
Post on 05-Jul-2018
218 Views
Preview:
TRANSCRIPT
-
8/16/2019 Stamping Fea Model Input Review
1/20
2/18/20081
A Review of FEA Metal Forming Simulation Practices
in Automotive Industry
C. Q. Hu
-
8/16/2019 Stamping Fea Model Input Review
2/20
2/18/20082
Contents
• Factors affecting stamping feasibility
• Material model• Friction models
• Simulation methodology
• Parameters of current simulations and the
sensitivity
• Not quantified parameters• Summary
-
8/16/2019 Stamping Fea Model Input Review
3/20
2/18/20083
1. Factors affecting metal forming feasibility
Blank (sheet metal)
Tooling (punch and die)
Die face design (addendum)
Kinematics: tipping, binder wrap, punch contact progression
Draw beads design
Die material (hardness, rigidity & friction behaviour)
Blank location
Mechanical properties ( r, n, r, YS, UTS values)
Gauge (thickness)
Variation of the mechanical properties and gauge Blank size
Surface coating
Surface finish (topography)
Edge conditions
Aging and pre-strain conditions
-
8/16/2019 Stamping Fea Model Input Review
4/20
2/18/20084
1. Factors affecting metal forming feasibility
Press
Press type (hydraulic or mechanical)
Binder pressure (force)
Press speed
Lubrication ( type, viscosity, temperature and pressure sensitivity) quantity
Lubrication
Blank location
Tool wear
Dirt
Ambient temperature and humidity
Press counter balance pressure
Process noise
-
8/16/2019 Stamping Fea Model Input Review
5/20
2/18/20085
2. Material models
An accuracy of FEA prediction is dependant on plastic models, in which different yieldingcriteria and hardening laws are suitable different materials and stamping process.
r
Yielding CriteriaAutoform PamStamp 2G
Input requirements
current new current new
Von Mises
(isotropic)yes yes yes yes σy, r bar
Hill’s 48
(Planar anisotropic) yes yes yes yes
σy, r values at 0, 45 and
90 degrees
Hill’90 (introducing bi-axial
yield stress)no yes yes yes
σy, r values at more
than three angles or σyat a bi-axial stress state
6 component Barlat no no no yesUni, bi-axial, and shear
tests
Vegter no no no no
Uni, bi-axial, and shear
tests
-
8/16/2019 Stamping Fea Model Input Review
6/20
2/18/20086
2. Material models
Hardening Laws :
Hardening law
Autoform PamStamp 2G
Input requirements
current new current new
Isotropic yes yes yes yes σy, UTS, n
Kinematic no no yes yes σy, UTS, n
Kinematic hardening, not isotropic hardening, takes account of non-linear strain
path, such as bending/unbending, reverse drawing in a multi-stage forming
process
Hardening is represented by :
• A tensile test curve along the rolling direction
• The power law (Ludwik equation or Krupkowski equation ) for steels• The voce equation for Al alloys
-
8/16/2019 Stamping Fea Model Input Review
7/20
2/18/20087
3. Friction model
• In practice, coefficient of friction is dependant on contact pressure,
slide speed (static and kinetic), blank coating, lubrication and tool
surfaces, etc.
• Coulomb friction law, which assumes coefficient of fiction is
constant regardless kinetic factor, contact pressure and slide speed,
is the only option in both AutoForm and PamStamp 2G
• Other general FEA code, such as LS/Dyna, HKS/ABAQUS,
provide more detailed friction models
-
8/16/2019 Stamping Fea Model Input Review
8/20
2/18/20088
4. Simulation methodology
Press trial
Manufacture
Tool Design
Product design
CAE
Conceptfeasibility
CAE
tool maker
-
8/16/2019 Stamping Fea Model Input Review
9/20
2/18/20089
4. Simulation methodology
4.1 Simulation practices in concept stage
AutoForm for most panels:
To develop binder surface, addendum components To study feasibility, using:
Von Mises (or Hill 45) yielding criterion, isotropic
hardening law
Blank holder load: decided using empirical formula,Coefficient of friction: 0.14(steel), 0.12 or 0.17 (Al)
Using more conservative feasibility criteria
PamStamp 2G only for A panels (skin) for validation, using: Hill 45 yielding and isotropic hardening law
Coefficient of friction: 0.14(steel), 0.12 or 0.17 (Al)
Average mesh size : 10 mm, Adaptive mesh level, 2
-
8/16/2019 Stamping Fea Model Input Review
10/20
2/18/200810
4. Simulation methodology
4.2 Feasibility criteria in the concept stage
For necking failure, allowing 20% safety margin
For steel inner panels:Maximum thinning
-
8/16/2019 Stamping Fea Model Input Review
11/20
2/18/200811
4. Simulation methodology
4.3 The simulation practices in the tool maker sector
?4.3 Feasibility criteria in the tool maker sector
?
-
8/16/2019 Stamping Fea Model Input Review
12/20
2/18/200812
5. Parameters of current simulations and the sensitivity
5.1 Yielding criterion of Material model
• For mild steels, Hill 48 appears to be accurate enough
• For HSS, Hill 90 is more accurate than Hill 48
• For Aluminium, Barlat’s criterion is better than Hill 48 but need not only tensiletests but also bi-axial and shear tests.
• It has been claimed that Vegter criterion can describe yielding behaviour of HSS
and Al alloys, and material tests is easier compared with that for Barlat model.
• More sophisticated and practical yield criteria for Al alloys has been expecting
5.2 Hardening law of Material model
• Isotropic hardening for linear strain path• Kinematic hardening for nonlinear strain path
Details
Details
-
8/16/2019 Stamping Fea Model Input Review
13/20
2/18/200813
• Thickness: wrinkling tendency, FLD0, springback
• YS: material distribution, hardening exponent, springback
• UTS: (not a direct input parameter); hardening exponent, fracture strain
• n value: hardening, distribution of strain, FLD0
• r values: deep draw ability
• Hardening curve: Krupkowski equation , Ludwik equation or converted tensile curve
• Blank orientation
• Direction of a tensile test for mechanical property input (0, 45, 90 degree)
• Forming limit curve ( test methods)
• Blank mesh quality and adaptive mesh level
5.3 Material properties
5.4 Tools
• Tooling radius, size, punch type (flat or crown)
• The clearance between die and punch: material flow, wrinkling and springback
• Tool mesh design
5. Parameters of current simulations and the sensitivity
FLD0
Hardening
n effects
Tool geo
-
8/16/2019 Stamping Fea Model Input Review
14/20
2/18/200814
• Using a constant coefficient of friction to quantify
different coating of sheet steels and Al alloys, and
other tribological factors
5.4 Process
• Blank holding pressure or load
• Press type ( single or double action)
• Operation stages
• Artificial press speed setup including of type of curve and magnitude
• Boundary conditions, especially for springback prediction
5.5 Friction
5. Parameters of current simulations and the sensitivity
Example
-
8/16/2019 Stamping Fea Model Input Review
15/20
2/18/200815
5. Not included Parameters
5.1 Material properties
• Coating type (dipped and thickness or quantity
• Surface finish (topology)
• Material variation with a roll, or along the width of blank, especially for HSS
• Strain rate effect
5.2 Lubrication•Type (Fluid-film, solid, Extreme Pressure (EP) lubricants )
•Quantity and distribution
5.3 Process
• Temperature
-
8/16/2019 Stamping Fea Model Input Review
16/20
2/18/200816
• FEA code and CAE experience have been developed to deal with for
convention mild steel panels
• The accuracy of Wrinkling and springback prediction is considerablely
dependant on model setup• Regarding new materials, such as HSS and Al alloys, new material
model should be investigated
• Due to confidential issues, the publication about bench mark test for
commercial FEA codes is rare• Simulation validation researches, dealing with new materials, different
tool and complex forming process, is required
6. Summary
-
8/16/2019 Stamping Fea Model Input Review
17/20
2/18/200817
7. Appendix
7.1 Material models: Yielding criteria
Back
-
8/16/2019 Stamping Fea Model Input Review
18/20
-
8/16/2019 Stamping Fea Model Input Review
19/20
2/18/200819
7.3 Empirical formula: FLD0=min(n/0.24, 1.0)*(23.0+14.6t)%
7. Appendix
Back
7.4 Krupkowski equation: σ=K*(ε0 + εp)n , and K=UTS*(e/n)n Back
7.5 n effects on strain value
0
0.1
0.2
0.3
0.4
0.5
10 12 14 16 18 20 22 24
Punch depth (mm)
P e a k
s t r a i n
n=0.23
n=0.21
n=0.19
n=0.17
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
10 12 14 16 18 20 22 24
Punch depth (mm)
F l o o r s t r a i n
n=0.23
n=0.21
n=0.19
n=0.17
Back
-
8/16/2019 Stamping Fea Model Input Review
20/20
2/18/200820
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 50 100 150 200
Distance from centre (mm)
E n g . s t r a i n
-5
0
5
10
15
20
25
30
P u n c h H e i g h t ( m m )
strain, crown
strain, flat
Crown geo
Flat geo
7. Appendix
7.6 Tool geometry effects
Back
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20 22
Punch depth (mm)
S t r a i n a l o
n g w a l l
u=0.01
u=0.05
u=0.1
u=0.15
u=0.2
7.6 Friction effects
Back
top related