Mechanisms of gap bridging and hump suppression in oscillating laser-arc hybrid welding of thick plate steel under variable gap conditions

Welding thick plates with variable gaps is an essential and critical process for large-scale component manufacturing in many industrial fields. Key challenges include insufficient penetration or humping in small gaps and collapse in wide gaps. This study elucidated the characteristics of the variable-gap oscillating laser-arc hybrid welding (LAHW) of weathering steel by examining the arc behavior, molten pool flow, and hump formation process. The gap tolerance and hump defect suppression across the entire weld of thick-plate steel were investigated, and the associated mechanisms were elucidated. With an optimized oscillating amplitude of 1.5 mm and a frequency of 200 Hz, satisfactory weld formation was achieved, free of hump defects and collapse, at both 0 mm and 2.5 mm gaps. After applying the oscillating laser, the arc burnt stably, and the arc deflection degree decreased significantly owing to the improved arc conductive channel. Hump suppression is linked to keyhole size and stability and sufficient molten pool fluidity. The findings of this study provide a valuable reference for eliminating hump defects at small gaps while simultaneously improving the gap-bridging capability at larger gaps in thick-plate steel LAHW for large-scale component. Moreover, this study contributes to the advancement of oscillating LAHW technology and promotes its application in large-scale component welding in various manufacturing fields, including high-speed trains, shipbuilding, and energy equipment.