Effect of the laser-induced vapor in the keyhole on the weld surface roughness in fiber laser welding

Weld surface roughness is an important criterion for evaluating weld quality. The main factors that affect weld surface roughness in fiber laser keyhole welding are identified by an in situ observation of the dynamic behavior of a keyhole mouth and by analyzing the eruption characteristics of the laser-induced vapor on the front keyhole wall (FKW). In fiber laser keyhole welding, the weld surface roughness first decreases and then increases with the increase in welding speed. Both the distortion rate of the keyhole mouth and its range of fluctuation will increase as the welding speed increases. The fluctuation in the distortion rate of the keyhole mouth diameter can reflect the stability of fiber laser keyhole welding. The laser-induced vapor at the FKW can erupt to impact the rear keyhole wall, and this is the main factor that affects the distortion rate of keyhole mouth diameter and weld surface roughness in fiber laser keyhole welding. In fiber laser-arc hybrid welding or in CO2 laser keyhole welding, plasma can suppress the effect of laser-induced vapor impacting the keyhole and reduce the weld surface roughness.