Investigation of Laser Welding Processes for Automotive Structural Applications

The motive behind this study was to investigate the autogenous laser welding (ALW), and Hybrid laser arc welding (HLAW) processes in the aspects of productivity and quality for the application in automotive industries. Presently, Gas metal arc welding (GMAW) process is being used for the manufacturing of two-wheeler frame. Low power density of GMAW process limits the depth of penetration and productivity of the process which are the two key concerns in automotive industries. Therefore, GMAW process was compared with advanced laser welding processes in the aspects of productivity, heat input, weld bead geometries and gap bridgeability. Effects of these welding methods on distortion and mechanical properties were also evaluated. The trade-off between productivity and quality were interpreted in each processes. Low carbon steel (S275) of 2 mm, 4 mm and 8 mm thick materials with square butt joint configuration were used for the evaluation. Better weld quality with complete penetration was achieved in autogenous laser welding and hybrid laser arc welding processes with improved productivity by a factor of 8 times compared to GMAW in 2 mm and 4 mm thick materials and in 8 mm thick material, complete penetration with an improvement of productivity by a factor of 3 times was achieved. High power density of ALW and HLAW processes provided complete penetration even at ~70% to 80% less heat input than GMAW process which eventually reduces the fusion zone area by ~ 50% to 70%. Therefore, these processes control the metallurgical damage to the base material. Moreover, high power density of HLAW and ALW processes results in ~75% and ~85% less distortion than GMAW process respectively. HLAW process improved the productivity with considerably less increase in hardness than ALW process. For instance, in 2 mm thick material, productivity was improved by 8 times than GMAW process with 55% and 17% increase in average fusion zone hardness in ALW and HLAW processes respectively. In mechanical strength standpoint, all three welding processes produced weld region stronger than base material. Negligible increase in strain was observed on weld metal in DIC test. Therefore, fracture occurred in the base material during tensile test. Lack of bead reinforcement and poor gap bridgeability were found to be the critical concerns in autogenous laser welding process. However, hybridization of laser and arc resolved these issues. Overall, HLAW process found to be superior to GMAW and ALW processes in the aspect of productivity and quality.