High speed tandem gas tungsten arc welding process of thin stainless steel plate

•A high speed tandem GTA welding experimental system has been established.•Tandem GTA welding can increase welding speed significantly.•High mechanical properties of tandem GTA weld was obtained.•Humping weld can be suppressed by the heat and force effects of assistant arc.

A high speed tandem gas tungsten arc welding process involving an assistant arc following the main arc to suppress the formation of undercut and humping defects is proposed. The influences of assistant electrode parameters and welding current combinations on weld appearance were studied through statistical design-of-experiment. The welding speed of 1.5 mm thick 409 L stainless steel plate was increased to 3 m/min without sacrificing weld appearance quality. Good mechanical properties and a fine microstructure of welded joint were obtained compared with the single arc weld at the equivalent heat input. The assistant arc prolonged the presence of liquid metal accumulated at the trailing region of molten pool. The main and assistant arcs formed a stable swelling under dynamic force balance preventing the liquid metal flowing backwards. Both the heat and force effects suppressed the formations of undercut and humping to improve the final weld appearance.