1. The right partner in process simulation
Arcweld FE simulation of large 3D structures using MSC.Marc for Volvo Car Corporation
MSC.Software
The right partner in process simulation

2. Problem definition thermo-mechanical coupling
non-linear material properties at high temperatures
material properties depending on strain and strain rate
Definition of a moving heat source with input from ROBCAD
multiple welding heads
modelling of clamping conditions
weld geometry (FE-modeling)
FE-modelling strategy (solid, shell, beam…)

3. Problem definition (contd.)
User subroutines are standard features of MSC.Marc
User subroutines are used for controlling flux distribution and work hardening
Programming of arbitrary shaped moving heat source is done with user subroutine FLUX
Material behaviour is programmed with user subroutine WKSLP

4. Main goal
Predicting the residual deformation in the structure

5. Project phases Step 1 Step 2 Step 3 Simple T-node geometry
Development of welding routines
Verification against welding tests
Step 2
Ladderframe structure with same topology as the underbody
Development of routines for multiple weldingheads
Verification agains welding tests (in progress)
Step 3
Complete underbody structure
Model reduction to save computational time
Verification against welding tests (in progress)

6. Step 1, T-node Decision to go for a shell model
One robot welding 4 seams
Good agreements reached on both temperatures and deformations

7. Step 1, T-node Modelling of welding seams using shell elements
Thickness of shells in the seam have been set so that the correct cross section area is reached
Modeling of butt joint weld
Modeling of a fillet joint weld
Cross-section of
fillet joint welding seam
Base material
butt joint welding seam

8. Step 1, T-node Clamping modelling using stiff springs
Fixed clamping
(locked transl xy & rot z)
(locked transl yz & rot x)
Guide pin
(locked transl xyz)
Section of actual clamping unit.
T-node beam structure

9. Step 1, T-node Some simulation statistics 6500 elements
2.5mm elm size along seam
10-15mm global elm size
4 consecutive welding seams
weld data input from ROBCAD files
total simulation time is 200 seconds including 150 seconds cooling
365 increments total in simulation
computer time equals to appr. 50 hours on a single CPU ws

10. Step 1, T-node Simplified model to reduce calculation times
Replace parts of the structure with beam elements
Model size reduced to 1/3rd
Calculation times reduced to appr 20% of original
Correct principal behaviour can still be found with a much simpler model

11. Step 2, Ladderframe Modification to handle multiple welding robots
Two robots welding 16 seams each
A graphical `pre-step` was performed to verify welding data before simulation
Parallel execution necessary

12. Step 2, Ladderframe Some simulation statistics 27000 elements
2.5mm elm size along seam
15 mm global elm. Size
2 welding heads welding in parallell
each welding head is welding 16 seams
weld data input directly from ROBCAD files, one file per welding head
total simulation time is 4000 seconds including 3674 seconds cooling to reach room temperature
3673 increments total in simulation
computer time equals to 155 hours elapsed on a 8 cpu HP V-2250

13. Step 2, Ladderframe
Graphical pre-step to verify orientation of welding flame and welding power

14. Step 2, Ladderframe
Graphical pre-step to verify orientation of welding flame and welding power

15. Step 2, Ladderframe Simulation results Graphical results available
Avi-movies showing temperatures and deformations
Curve-plots showing measurement location displacements as function of time
Stress- and deformation fringe plots after cooling period

16. Step 2, Ladderframe Simulation results
Avi-movie showing temperatures and deformations

17. Step 2, Ladderframe Simulation results
Curve-plots showing measurement location displacements as function of time

18. Step 2, Ladderframe Simulation results
Residual stresses and deformations available on fringe plots

19. Step 2, Ladderframe Simulation summary
The FE-model is heated up faster then the verifying object
The cooling is to rapid in the FE-model
Correct principal behaviour in the FE-model

20. Step 3, Underbody
Simplification of FE-model to reduce calculation time
Two robots welding 9 seams each
A `pre-step` was performed to verify welding data before start of simulation

21. Step 3, Underbody Some simulation statistics 11000 elements
2.5mm elm size along seam
15 mm global elm. size
equivalent beam sections have replaced parts between welding locations
2 welding heads welding 9 seams each
weld data input directly from ROBCAD files, one file per welding head
total simulation time is 4000 seconds including 3745 seconds cooling to reach room temperature
1839 increments total in simulation
computer time equals to 27 hours on a 4P SGI O2000 (R10k/250Mhz)

22. Step 3, Underbody Simulation results Graphical results available
Avi-movies showing temperatures and deformations
Curve-plots showing measurement location displacements as function of time
Stress- and deformation fringe plots after cooling period

23. Step 3, Underbody Simulation results
Avi-movie showing node 1 right side

24. Step 3, Underbody Simulation results
Avi-movie showing node 2 right side

25. Step 3, Underbody Simulation results
Avi-movie showing node 3 right side

26. Step 3, Underbody Simulation results
Avi-movie showing node 4 right side

27. Step 3, Underbody Simulation results
Residual deformations after 4000 seconds

28. Step 3, Underbody
Simulation results
Deformation history

29. Step 3, Underbody Simulation summary
Simulations are to be verified against welding tests
Interesting behaviour on residual deformation due to clamping geometry seen from simulations
Welding simulations possible to perform ‘overnight’

30. Conclusions
All the features necessary for performing the complete welding simulation are available
Correct principal structural behavior compared to measurements
Welding of large 3D structures can be simulated with reasonable computing times
Short loop times are possible with automation of simulations
It is now possible to draw conclusions from different welding layouts before the prototype exists!

31. Future actions Simulation performance Use existing FE-models
Material data
Automation of simulation steps
Clamping modelling
Residual stress as input for fatigue analysis
Activate weld elements automatically
Consider deformations of structure before welding
…..