Study Of Plasma Cloud Sensing Of Keyhole Signal In PAW

During keyhole plasma arc welding, the stability of keyhole is of criticalimportance. The quality of the welding joint and the stability of the welding processdepend strongly on the keyhole stability. It is pivotal to sense and control thekeyhole status in real time to improve the welding quality during welding process.By using the developed multi-channel signal acquisition and processing system,this paper has systematically studied the plasma cloud phenomena, analyzed themechanism and requirement of the plasma cloud's appearance. It was founded thatthe shape change of the plasma cloud is strongly correlated with the keyhole status,and by sensing the shape change of the plasma cloud, the keyhole status could bedetected. Then the paper did systematically study on the principle and influencefactor of sensing the plasma cloud's shape change using the metal probe. It wasfounded that no matter in DC or pulse current keyhole plasma arc welding process,during the formation and close of the keyhole, the plasma cloud will swingperiodically, and the plasma cloud signal detected will accordingly produce aundershoot This undershoot could be used as the criterion of the keyhole status, andalso the frequency of the undershoot could be used as the criterion to judge whetherthe pulse welding is one-pulse-one-keyhole. On the basis of the above study, thepaper developed an applied multi-probe plasma cloud charge sensor, and tested thereliability and precision of it comparing with the designed efflux plasma chargesensor.At last, based on the developed plasma cloud sensor, the paper studied theclose-loop penetration control of the plasma arc welding. It was shown that theplasma cloud signal detected can reflect the information of the penetration andkeyhole. All the above research concerning the plasma cloud has shown that theplasma cloud sensing is a promising and applied sensing technology in keyholeplasma arc welding.