Impact of the vapor plume on fluctuations of capillary shape and depth during deep-penetration laser welding of stainless steel

In deep-penetration laser welding, the associated vapor plume leads to an attenuation of the laser beam and deformation of the phase front. These effects dynamically modify the intensity distribution on the workpiece, resulting in significant fluctuations of the weld penetration depth. In this study, high-speed X-ray imaging was used to quantify the effect of the fluctuations of the vapor plume on the capillary depth during welding. Identical welding parameters for stainless steel (1.4301) were applied in two cases: one without a cross-jet and one with a cross-jet positioned 20 mm above the capillary to remove the plume. The results show that with a cross-jet, the capillary geometry experienced only negligible fluctuations, and its depth remained largely constant. In contrast, without a cross-jet and with increasing plume formation, the welding depth decreased significantly, occasionally leading to complete capillary collapse. These findings highlight the direct impact of the plume on the laser beam and its connection to the penetration stability and resulting welding depth.