Droplet transfer in arcing-wire GTAW

In arcing-wire GTAW process, the wire melting speed and weld penetration are decoupled. To well study the arcing-wire GTAW, especially the droplet transfer mode, the forces imposed on the droplet are analyzed firstly and compared with those in conventional GMAW. Then the experiments have been carefully designed and conducted. High-speed images uncover desirable stable droplet transfer mode: touching transfer and free transfer.In touching transfer, the droplet formed by the melted wire touches and transfers into the weld pool but the wire is separated from the weld pool each time after the transfer. This is similar to short-circuiting transfer in conventional GMAW except for there is no short-circuiting because the wire and work-piece is not in series in a same circuit. Experimental results show that the touching transfer produces stable arcs and spatter-free welds. By analyzing the high-speed images, the distance from the initial position of the wire to the weld pool and the wire feed speed should be the major parameters determining the transfer period and the droplet size.In free transfer, similarly as in GMAW, when the droplet grows large enough, then it separates from the wire and transfer freely into the weld pool. The transfer period and mass for the detachment both reduce as the current or the wire feed speed increases. The whole transfer is smooth and spatter free.With the pulse current adding into the wire, the droplets can easily transfer into the weld pool, the period is determined by the pulse cycle.