Research And Control Of Keyhole Feature And Weld Formation Stability In Variable Polarity Plasma Arc Welding

The stable transition of the keyhole weld pool in starting process seriously influences on the formation of weld during plasma arc welding. This keyhole establishing process is very complex and is not researched diffusely recently. By investigating the temperature field distribution'influence on the stable transition, as the main subject investigated, how to control the process parameters to complete the stable keyhole transition will be studied in this paper.By analysis of the establishing process of the keyhole weld pool, the regularities of the welding parameters are obtained. The welding current mainly influences on the heating rate and the temperature distribution in the establishing of the keyhole. The plasma gas flow rate, which also affects the heating process by changing the occurrence time of the keyhole, can influences on the rate of excavating the keyhole and the geometrical size of the keyhole severely. The wire feed time can change the formation of weld in the starting process, but it doesn't have any effect on the temperature.Owing to the complexity of the keyhole establishing process, a new control mode, heating the weld pool by weak process parameters and excavating the keyhole by strong process parameters, is adopted. This control mode can reduce the difficulty of the control, improve the accuracy by making the heating process independent of the excavating process relatively.Based on the above results, make sure the temperature filed distribution near the keyhole close to that near the satisfactory weld at the occurrence time of the keyhole by controlling the process parameters, the uniform formation of weld in the starting process is finished at last. The conclusion that the temperature fired distribution near the keyhole at the occurrence time of the keyhole is the decisive effect of the uniform formation of weld in starting process is proved. To keep the keyhole weld pool's thermal and mechanical conditions balance respectively at the occurrence time of the keyhole, which aim is to shorten the keyhole's self-regulating process seriously, is the essential of success.