Variable Polarity Plasma Arc Welding Visual Signal Extraction And Keyhole Behaviors Research

The technology of variable polarity plasma arc vertical welding has broad prospect for development in the actual production. It is well known that the reliability characterization for keyhole of VPPAW is a technical problem in engineering field. Through visual information to characterize keyhole can be a direct method and it is of great significance to improve the stability of welding. This paper tries to study VPPAW through visual information, so that to get keyhole parameters of instantaneous change during welding process. The changing rule of the keyhole change and welding forming combined with visual information is summarize, then welding parameters is optimized. It will be a valuable research and application.A visual signal system is built up, which can get the double sides of visual messages. Tree part based model image processing algorithm is used for incomplete weld pool and linear scanning edge algorithm for full weld pool. Meanwhile, using canny edge extraction method to detect keyhole puddle from the backside. Research shows that image process algorithm can characterize the visual characteristics of signal accurately, and be applied in VPPAW under different process parameters, which has features of robustness and controllability.The formation quality of VPPAW is analyzed based on keyhole stability combined with visual method. Research shows that the stability of keyhole determines the formation quality of welding, welding current, welding speed and plasma gas flow rate are main influence factors of keyhole stability. The sensitivity of speed and plasma gas flow rate for keyhole stability is high. Under the condition of the abnormal keyhole behavior is usually difficult to restore. Through research on welding process behavior of keyhole, double-sided visual signal relationship can reflect punch time of keyhole, and in this way welding formation and quality can be predicted. Optimize welding process to ensure stable welding speed and plasma gas flow rate,then confirm set current system value for the first time. A small scale of dynamic adjustment guarantee the stability of the keyhole, eventually quality and process of welding can be improved.