Prediction of Weld Geometry and Size in Low-Frequency Laser Wobble Welding of Dissimilar Automotive Steels

A stable welding mode within the oscillating path is a complex challenge in wobble welding. The formation of a fusion zone involves a complex laser energy distribution along the oscillating path, which is governed by both oscillation (frequency, amplitude) and laser (laser power, welding speed) parameters. In this study, a coupled thermo-fluid dynamical model was developed to investigate the combined effects of oscillation and laser parameters on seam formation during low-frequency laser wobble welding. An experimental result showed the effectiveness of a circular wobble path to bridge the gaps within the plates of dissimilar automotive steels. The microstructure of the fusion zone and heat-affected zone underwent self-tempering along the circular path, resulting in the tempered martensite structure with quasi-uniform microhardness distribution. According to numerical data, the oscillating amplitude and welding speed were found to be the primary factors influencing the distribution of laser energy density, which in turn defines the final shape of the fusion zone. The periodic depth and shape of the weld seam were fixed along the oscillation path. A low amplitude resulted in a concentration of laser energy density at the centerline of the linear motion, leading to the formation of a typical U-shaped seam. Higher welding speed led to the spread of the peak laser energy density along the oscillation path, thereby promoting a more stable weld pool shape even at larger amplitudes. Conversely, lower welding speeds result in strong variations in weld seams with a W-shaped fusion zone.