Dynamic interaction between a laser beam and keyhole front wall during fiber laser welding

A bright spot (laser beam spot-center-induced metal vapor) on the keyhole front wall (KFW) was observed during fiber laser keyhole welding of a 'sandwich' specimen to reveal the interaction between the laser beam and the KFW. The dynamic behavior of the bright spot shows that the keyhole formation is the result of periodical drilling of the laser beam spot center on the KFW during welding. Welding parameters have little effect on the drilling period. The drilling speed first increases and then decreases with the increase in the keyhole depth, and the next drilling process begins before the drilling speed reduces to 0 m s⁻¹. The average drilling speed can be increased by increasing the line energy or power density of the laser. (paper)