Abstract: The low current auxiliary TIG arc assisted high speed MIG process is carried out to analyze the suppression mechanism of undercut defect from the aspects of heat transfer, mass transfer and force field. The influence of the welding parameters on undercut defect is also analyzed. The low current auxiliary TIG arc can effectively reduce the temperature gradient around the edge of the weld pool during high speed MIG, which prolongs the existence time of the molten pool and promotes the filler metal to the edge of the weld to prevent undercut defect. The arc force and the droplet impact play major roles in the formation of the undercut defect. The auxiliary of low current TIG presents slight influence on MIG droplet, however, it can reduce the arc static and dynamic pressure obviously to mitigate or even inhibit undercut defect during the high-speed welding process. The orthogonal test shows that the inclination angle of welding torch, and the spacing of wire-pole are the important parameters affecting the formation of undercut defect compared with TIG current and tungsten distance workpiece distance. Optimizing torch angle and wire-pole spacing is a fast and economical way to improve low current auxiliary TIG-MIG hybrid welding to suppress undercut defect.

Key words: process optimization, suppression mechanism, TIG-MIG, undercut defect