Monitoring of welding status by molten pool morphology during high-power disk laser welding

Behavior of a molten pool is closely related to the welding status and weld appearance, but it is difficult to directly observe and measure the morphology of a molten pool due to its quick and dynamic variation. An active vision system was designed to obtain the molten pool morphology information using its shadow during high-power disk laser welding of Type 304 austenitic stainless steel plates. In this study, a diode laser was employed to illuminate a molten pool and form its shadow. A high-speed camera equipped with a narrow band pass filter was utilized to record the morphology of molten pool and its shadow during laser welding. A narrow band filter was used to eliminate the optical interference of spatters, welding laser beam and plume, and allowed the camera only to receive the radiation of diode laser illuminant. An algorithm was developed to segment the shadow of molten pool. By defining and analyzing the parameters of molten pool shadow, the relationship between the morphology of molten pool and the stability of the laser welding process was characterized in quantitative way, which provides a basic understanding of a molten pool behavior for real-time monitoring of high-power disk laser welding status.