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

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…)

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

Main goal Predicting the residual deformation in the structure

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

Step 3, Underbody Simulation results Residual deformations after 4000 seconds

Step 3, Underbody Simulation results Deformation history

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’

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!

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 …..