Effect of stamping dimensional deviations on residual stresses and deformation of resistance spot welded steel sheets

Direct finite element analysis that takes stamping dimensional deviations into account was achieved based on coupled electro-thermo-mechanical method and reverse engineering in the current research. The two continuous resistance spot welding processes of the reverse established back side panel were simulated. Its residual stresses and deformation were compared with those of the ideal back side panel. Large distortion presents in the reverse back side panel while only slight deformation exists in the ideal one. The former is validated to be closer to the deformation of the actual welded back side panel. The peak residual stresses after processes 1 and 2 remain almost unchanged in the reverse back side panel while those in the ideal one show an increasing trend. The final residual stresses of the reverse and the ideal back side panel are both high but the former is lower than the later. The stamping dimensional deviations are responsible for these differences. They lead to obvious attenuation of geometric features and large assembly clearances in the reverse back side panel. These assembly clearances allow large deformations of the stamping parts during the welding process. Meanwhile, these clearances make it relatively freer for the heated sheet metal to expand thermally in the thickness direction, resulting in less or even no residual stress in this direction. These clearances also promote the release of the thickness-direction component of the tensile residual stress in the extension direction of sheet by allowing deformation in the thickness direction.