The process monitoring of the top side and the evaluation of surface quality were applied in adjustable ring mode (ARM) laser welding of 316 stainless steel by using visual monitoring and confocal sensor technology. Experiments were conducted in different power arrangements of an ARM laser. In this study, the process status was evaluated based on the area of keyhole entrance and the width of the pool. The geometric characteristics of the topside weld were measured by a confocal sensor. The shape of the fusion zone was analyzed based on its cross section. The process mechanism of a different mode of ARM laser welding was investigated by analyzing the process status and geometric characteristics of the surface bead. Experimental results showed that dual-mode laser welding could stabilize the keyhole entrance with a uniform weld surface formation in comparison to the pure ring-mode laser weld. The dual-mode laser also generated a wider molten pool with a wider fusion zone than the pure center laser weld.

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This paper studied the effects of two welding modes, i.e., keyhole penetration and full penetration, on laser welding of two zinc-coated steel stack ups of same total sheet thickness but different sheet thickness combinations. The effects of welding modes on keyhole and spatter behavior were studied via laser stitch welding with zigzag oscillation. It was found that keyhole penetration welding led to little spatter and mass loss for a thick-gage stack-up of same top and bottom sheet thickness (two 1.5mm zinc-coated steel sheets, viz., Stack-up S). This was confirmed by numerically calculated low Zout values which indicate a low potential of spatter due to zinc outgassing insufficiency. On the other hand, for a stack-up of thin top and thick bottom sheet combination (1.1mm/1.9mm, viz., Stack-up D), full penetration mode is more preferred generating significantly less spatter than the keyhole penetration mode. This was attributed to an enlarged keyhole size at the faying interface in the full penetration mode and the relatively thinner top sheet (1.1mm thick) compared to the bottom sheet (1.9mm thick). It was confirmed by the low average and maximum values of Zout. Lastly, for the thin top and thick bottom stack-up, the zigzag oscillation amplitude of full penetration mode was experimentally studied based upon numerical calculations of Zout and Zp to achieve a robust weld quality with minimum spatter.