Influence of Bead Geometry on Weld Distortion in Laser Micro-welding of Thin Stainless Steel Sheet with High-speed Scanning

In this study, the thermal deformation of thin stainless steel sheet was investigated in bead-on-plate welding by using a single-mode fiber laser with Galvano scanning system. The numerical simulation was carried out to calculate temperature and stress fields, and its deformation characteristics were discussed. It was suggested that a specimen firstly deformed downward in the same direction of laser irradiation, and then deformed in the reversed direction after laser scanning. The final distortion angle in the negative direction, which is concave shape from the view direction of laser irradiation, was generated under the heat conduction and quasi-penetration welding mode, and the positive angle was obtained as the final distortion angle under the full-penetration welding mode. On the other hand, a small distortion could be achieved by the proper weld bead geometry in micro-welding of thin sheet, but the welding mode of minimum distortion conditions varied with specimen thickness. However, these relationships obtaining a small distortion could be understood by the relationship between aspect ratio of weld bead and distortion angle. Minimum angle of distortion could be achieved around maximum aspect ratio of weld bead regardless of specimen thickness and spot diameter, when an inflection point appeared in relationship between aspect ratio of weld bead geometry and distortion angle.