Effects of process parameters on weld bead defects in oscillating laser-GMA hybrid welding of lap joints

The oscillating laser-GMA hybrid welding tests with lap joint configuration were conducted to observe the behaviour of welding arc, metal transfer and weld pool. Temperature distribution in the resultant lap joint was monitored. Based on the observations and the resultant morphology and geometry of weld bead, effects of three important process parameters, i.e. welding speed, laser beam oscillation and lateral distance of hybrid heat source relative to top sheet edge (LDHS), on the weld bead defects were examined. Consequently, occurrence mechanisms of the weld defects were proposed. LDHS influenced the defects such as non-uniform weld bead width, discontinuity and lack of fusion at top sheet, whilst the undercutting defect occurred at the top sheet if welding speed exceeded 6 m min(-1). The laser beam oscillation could disperse the high concentrated power density of single-mode laser to avoid deep penetration channel through bottom sheet, but had little effect on the weld geometry.