Operational behavior of the switchback GMAW process using a mechanized rig for arc movement

Abstract

Switchback Gas Metal Arc Welding (GMAW) consists of a forward and backward periodic oscillation of the welding torch in the longitudinal direction of the joint. The present work has two objectives, to evaluate the use of a simple and practical device proposed for the switchback manipulation of the torch and to analyze the effect of the switchback parameters on the operational characteristic of the process. Two series of bead-on-plate depositions were planned, using the GMAW process with or without the switchback technique. To find an operational envelope, two levels of equivalent welding speeds were used for covering ranges of oscillation frequency and amplitude. A Ni superalloy was employed as deposition material, aiming at simulating weld overlays. Wire feeding speed, set voltage and contact tip-to-work distance (CTWD) were kept constant. The proposed device was evaluated and proved to be able to make the overlays with all combinations of planned parameters. It was demonstrated that if the backward length (B) is larger than half of the forward’s (F), the torch passes more often over the same point of the deposit, and the oftener the torch passes over the same point, the lower the incidence of intermittent narrowing of the bead. By evaluating the surface aspect of the beads, the greater the F, the higher the likelihood of this irregularity. Penetration is shallower with switchback (reason demonstrated based on the fraction of stroke length that the arc is over the subtract), yet the bead surface presents more ripples. Another incident non-geometric conformity is the "dragon back" aspect of the bead, which is favored by faster equivalent welding speeds and high values of forward and backward speeds. The found operational envelope for the GMAW process with switchback was stablished with low-values of speeds and lengths of forward and backward strokes.