Impact of Manufacturing processes on crash test results · PDF file– HPDC – LPDC – Investment casting ProCAST specific capabilities – Stress and deformation –...

SIXTH FRAMEWORK PROGRAMME PRIORITY [6.2] [SUSTAINABLE SURFACE TRANSPORT]012497 DEVELOPMENT OF BEST PRACTICES AND IDENTIFICAT ION OF BREAKTHROUGHTECHNOLOGIES IN AUTOMOTIVE ENGINEERING SIMULATION - AUTOSIM

Summary

Impact of Manufacturing processeson crash test results

Luděk Kovář, Mecas ESI s.r.o, Czech RepublicThe 18th of January, Barcelona, Spain

• Examples of Manufacturing processes impacting crash test results• Stamping simulation• Casting simulation• Welding simulation• 2G solution provided by ESI Group


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Manufacturing processes impactingcrash test results

VTOS


Casting• Rupture of casted parts strongly influence crash results

• High quality of casting process required

Spot-welding

• Rupture of spotwelds strongly influence crash results

• Source of crack initiation due to affected zone by welding (important for HSS)

Stamping

• New materials applied for new car designs

• Variable thickness distribution, wrinkling tendency and springback effectafter stamping introduces imperfections for buckling initiation

• Forming of the material influences Yield strength and risk of rupture


Summary

PAM-CRASH 2G

VTOS• Pam-Crash 2G – solution for crash test analysis, standard tool of virtual prototyping of new car designs


Crash Simulation: State of the Art Material Models:

– Elastic– Elastic-plastic (metal)– Foam– Rubber– Composite

Contacts:– Master - slave– Self– Friction and damping (option)

Kinematics:– Large Displacements– Large Rotations

Geometry: 3DDiscretization: Finite Elements

Formulation: Lagrangian

Analysis: Dynamic

Solution Scheme: ExplicitFinite Element:

– Solids

– Shells– Membranes

– Beams

– Bars/Dashpots

– Joints Standard Assumptions: • isotropic behaviour of the metal sheet material• part thickness as in the original sheet coil• stress- and strain-free state at the start of the crash simulation• yield stress und strain limit as in the original sheet• no springback after forming


Summary

Stamping simulation

VTOS• Pam-Stamp 2G – tool of virtual manuafacturing

– Check part formability– Die development with respect to formability– Validation & optimization of tools (drawbeads, ...)– Arbitrary process – single-action, double-action, triple-action

forming, hydroforming, rubber pad forming, gravity, trimming, springback, ...


Forming Simulation: State of the Art • Forming-Simulation enables the early detection and correction of forming

problems and is increasingly used for tool design

• Key features of the industrially applied programs:– 3D, non-linear FEM-Formulation– dynamic/quasi-statistic treatment– Lagrangian description– explicit/implicit integration of the system equations– automatic recognition and treatment of contact– Discretization of the sheet with brick/shell elements– anisotropic elasto-plastic models for the sheet

• Simulation Results: – stress/strain/thickness distributions– Remaining forming capacity/ rupture risk– Wrinkling tendency/Surface quality– Springback– Tool loads PAM-STAMP 2G


Deep-Drawing ExamplesWrinklingSpringback

High rupture risk

FLD-Analysis

ε2

ε1

FLC

tornintact

D

B11 ln=ε D

B22 ln=ε

D

B1

B2


Forming Influences: Increased Yield StrengthEffective Plastic Strain

• Local plastic strains of 30% can be reached, which corresponds to a doubledyield stress for typical sheet materials

0

50

100

150

200

250

300

350

400

450

0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4

Umformgrad

Str

eckg

renz

e (M

Pa)

Stress-Strain Diagram


Forming Influences: Springback

• The springback induced by forming can lead to changed dominant buckling modesduring the crash.

Displacement-magnitude [mm]

Exaggerated Representation of Springback Displacements


Deep-Drawn Longitudinal Member(PAM-STAMP/PAM-CRASH Coupling with Mapping)

With Forming Effects Without Forming Effects


Force-Displacement-Historywith forming influenceno forming influence

For

ce (

kN)

Displacement (mm)• The forming process strongly influences the buckling mode

and the absorbed energy

Deep-Drawn Longitudinal Member


Summary

Casting simulation

VTOS• ProCAST– tool of virtual manuafacturing

– Check of casting process– Validation & optimization of risers and chills placement– ...


Casting Simulation: State of the Art

ProCAST 2005Casting processes– Gravity casting

– Tilt casting

– Lost foam casting– HPDC

– LPDC

– Investment casting

ProCAST specific capabilities– Stress and deformation

– Porosity

– Hot tearing– Macrosegregation

– Grain structure&growth

– Inverse calculation

- Method of the Finite Elements is used (FEM)• Geometry description with high accuracy• Works with 2D and 3D elements

SimulationCasting

Aluminium hpdc casting (courtesy of Kovolit a.s.)


Kurz and Fisher

Mushy zone definition• Porosity is not restricted to shrinkage porosity (macroporosity),

which is due to entrapped liquid surrounded by solid.

• Porosity also occurs during solidification, within the interdendritic region. This si later represented by microporosity.


Microporosity/Macroporosity

Region B

REGION AThe free surface will go down by an amount corresponding to the density change calculated above (blue area).

REGION BA “void” of the corresponding volume is created at the highest most liquid point of the Region. This corresponds to a Macroporosity (blue area).

In zone 4 , the local change of density between the fraction of solid of MACROFS and fs=1 is transformed in Microporosity.

1

2

3

4


Parameters of the porosity model

f s=

PIP

EF

S

f s=

MA

CR

OF

S f s

= 1

f s=

0

Dendritiesnucleation

Dendrities growth,

Formation of solid network throug liquidmetal can flow

Dendrities growth,

Liquid metal can not flow through the solid network without anadditional pressure


ProCAST 2005 - increase of casting process efectivity

� Optimalization of filling&gating layout

� Prediction of cold junctions and misrunning

� Optimalization of number and location of risers

� Check of effectivity of chills (cooling channels)

� Optimalization of venting

� Prediction of macroporosity and microporosity

� Calculation of stress, deformation and cracks&tearing

�

Residual porosity level affects mechanical properties of casted parts


ProCAST 2005

GRAVITY CASTING EXAMPLE

MATERIAL : cast ALCu5MgTimold Sand_silica

INITIAL TEMPERATURE : cast 730°Cmold 25°C

Advance porosity calculationsare performed as post-processing of standard therma l casting results

Methodology:

1. Standard thermal casting calculation is performed first.2. Based on previous results the macro- and micro-por osity, as well as the pipe shrinkage are calculated on finer

grid. Finer grid is superimposed to calculate the press ure drop in the mushy zone and nucleation and growth o f pores are computed (ProCAST v2005 is needed).


Calcosoft – mesh, advanced porosity calculation

Standard thermal castingcalculation is performed first on coarse grid. Calculation of macro-

and micro-porosity –finer grid

Macro- and micro-porosity – contour


PAM-CRASH/ProCAST coupling• The part influenced by porosity after casting process is more sensitive to damage

Displcement of upper free edgeWith Casting Effects

Without Casting Effects


Summary

Welding simulation

VTOS• SYSWELD – tool of virtual manufacturing

– Check of heat treatment processes– Check of hardening processes– Check of welding processes


Welding Simulation: State of the ArtSYSWELD simulates all physical effects that are related to:

Welding and Heat treatment

Courtesy GM• With/without wire material

• With mechanical contact(friction/spot)

• Without mechanical contact(laser, MIG, electron beam....)

• High speed / thin walled

• Low speed / thick walled

Characterization of welding processes

Typical applicationsMIG (metal inert gas) weldingWIG / TIG weldingLaser weldingElectron beam weldingSpot welding

SYSWELD


Physics of Welding

Fusion zone (FZ)– melting / solidification of material, solid state phase transformations

Heat affected zone (HAZ) – recrystallization, solid state phase transformations

HAZ

FZ

base material

Macrograph of a spot-weld

In FZ and HAZ, there occurs due to welding process:

– structural changes of material due to phase transfo rmations– volume changes of material due to thermal expansion

There appear permanent deformations and residual stresses and mechanical properties of the original material are changed.


Phase Transformations and Volume Changes

T [°C]

εT [ - ]austenitization

Martenzitictransformation

γγγγ

γγγγαααα Dissolution of

carbides ⇒austenite + carbon

γγγγ + interstitial carbon

αααα + external carbides

Tetragonal distorted grid

Initial grid


Definition of material properties

Material properties show strong dependence on temperature and material phase

T [°C]

σY [MPa]

austenite

martenzite

bainite

ferite

Yield stress vs. temperature

Strain hardening at room temperature

εp [ - ]

σH [MPa]


Modelling of Phase Transformations

Continuous cooling transformation diagram

t [s]

T [°C] v [°C·s -1] ∈ {-1000;-1}

martenzite

bainite

feriteDetermination of material properties

of welded joints ⇒ evaluation of shift of yield strength due to phase transformations

Determination of residual stresses and plastic strains ⇒ evaluation of shift of yield strength andfracture strain

Determination of distortions due to welding ⇒ evaluation of initial geometrical imperfections of welded parts

Simulation of Welding and Heat Treatment


Example of spot-welded metal sheets (shear test)

Area of the weld joint

Mesh of symmetrical part of a specimen

Symmetrical constraints

One quarter of a specimen formed by 2 spot-welded metal plates, th=2 mm, standard deep-drawing steel


Resulting Yield Stress [MPa] after weldingYield stress of basic material = 235 MPa


Resulting Distribution of Matenzite [-]


Shear Test (PAM-CRASH 2G)– Case A

• Original material– Case B

• Material with phases– Case C

• Material with phases• Mapping of plastic deformations

Loading

Fixed

Shear Test: Force vs. Deformation


Shear Test: Von Mises Stress [GPa]

A B

C

Without Welding Effects With Welding Effects

With Welding Effects

PAM-CRASH/SYSWELD coupling


Summary

Conclusion

VTOS• From PAM-Stamp/PAM-crash coupling,• ProCAST/PAM-crash coupling,• and SYSWELD/PAM-crash coupling• Towards 3G integrated solution …


ESI Group Strategy:‘1G / 2G / 3G’1G single trade applications

�� To understand and improve physical tests:To understand and improve physical tests: better testsbetter tests

3G multidisciplinary spaceglobal decision making process: global decision making process: Full virtual prototyping for Full virtual prototyping for ““Simulation Based DesignSimulation Based Design””

2G multi trade solutionsTo allow onTo allow on--line design improvements: line design improvements: less physical prototypesless physical prototypesTo include the effects of fabricating processes on design perforTo include the effects of fabricating processes on design performance: mance: as built as testedas built as tested

Impact of Manufacturing processes on crash test results · PDF file– HPDC – LPDC – Investment casting ProCAST specific capabilities – Stress and deformation –...

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