Analysis of coupled residual stresses in stamping and welding processes by finite element methods

Residual stress distribution in an automotive component produced by forming and welding processes has been predicted by finite element methods. Multi-step process simulations have been synthesized to predict the coupled residual stresses. For the qualitative verification of the distribution, a neutron diffraction detection technique is adopted for residual stress measurement. Stamping simulation is carried out first and the results are mapped onto the mesh for welding simulation. Springback simulation is also performed to estimate the stamping residual stress distribution. Although the welding phenomenon is complex in the construction of a model, a simple simulation model is proposed with several assumptions and verified with experimental results. Temperature-dependent material properties are used for the welding simulation. Stress-strain relations on various temperatures are obtained from the Johnson-Cook model of SAPH380. Each process simulation result is compared with a measured one and a good correlation is achieved. The high residual stresses in the wall area of the sample can be successfully predicted with the sequential stamping and welding simulation. From simulation results, large weld residual stresses are obtained when the stamping effects are included, but not as large as the linear summation of weld and stamping residual stresses. The stamping or welding simulation alone cannot predict the large wall stress generation on the final product, but the sequential non-linear simulation successfully predicts the high stresses at the wall region.