Analysis of characteristics of molten pool using cast shadow during high-power disk laser welding

On-line monitoring and control of laser welding process play an important role in welding quality assessment. The morphology of molten pool during welding process influences welding quality. Volume, tilt, and height were characteristics of molten pool, but they cannot be measured directly during the welding process. An experiment of surfacing weld of Type 304 austenitic stainless steel with high-power disk laser welding was implemented. An active vision system with an auxiliary laser light source was designed to acquire the images of molten pool and its shadow during the welding process. The images were pre-processed to analyze the characteristics of the casting shadow of molten pool instead of analyzing the characteristics of the molten pool itself. The area, maximal distance between the shadow and keyhole, maximal width, and the tilt of the shadow were selected as the characteristics to analyze the relationship between the morphology of molten pool and welding quality by linear and 10th non-linear fitting. The results indicated that the welding quality could be dynamically detected by observing these characteristics. A different welding process was also conducted to confirm the proposed method. The research in this paper provides a method for on-line monitoring and control during high-power disk laser welding.