Research On Arc Interaction And Factors Affecting Weld Formation In Tandem P-GMAW

The traditional high speed and current GMAW is susceptible to weld defects, such as humping and undercutting. So researcher developed the technology of Tandem P-GMAW which could acquire sound weld bead even in high speed welding. But when welding the low carbon steel, the welding process was unstable with a bad weld formation. In this paper, tandem P-GMAW was applied to the welding of low carbon steel. The arc interaction, welding stability and factors affecting weld formation were researched to provide theoretical basis and empirical data for the popularization of this technology.The tandem welding torch fixture was designed and built. The synchronization acquisition system of images and electrical parameters was improved. The phase difference of two pulse current was defined. The effect of phase difference on arc shape and arc interaction were investigated. Three modes of arc interruption, i.e. background arc interruption, pulse rise arc interruption and short-circuiting arc interruption are observed. As the phase difference increased, the arc interrupted more frequently with a unstable welding process. Analysis showed that the over elongation of background arc was the major reason for arc interruption. The greater the phase difference is, the longer the time in which the background arc interacts with the peak arc, thus the more heavily the arc interrupted. When the value of background current increased, the stiffness of background was improved, then the arc interruption frequency decreased. Under the larger phase difference, as the welding speed increased, the leading arc interrupted more and the trailing arc interrupted less affected by the the backward movement of plasma caused by the high welding speed.Using the synchronization acquisition system of images and electrical parameters, the relationship between arc interactions, weld pool dynamics and weld shape was researched. Under different phase difference, the welding pool showed different dynamic behaviors. As the phase difference increased, the molten metal between two wires and the rear welding pool both appeared different changes, leading to a increased weld penetration and reinforcement, a decreased weld width. The effect of phase difference acting on weld shape almost stay the same under different welding speed, but the increased speed weakened the effect of phase difference.The weld appearance under different welding conditions were analyzed. As the phase difference increased, the weld appearance became worse. As the average current increased, the influence that phase difference affected weld appearance became weak. And the weld appearance was better than the weld of lower average current under the larger phase difference. As the welding speed increased, the molten metal of weld pool on a per unit length became less. So when arc interrupted, the weld pool was more susceptible to lack enough molten metal to wet the weld toe area, aggravating the unevenness of weld width.