Arc ignitability, bead protection and weld shape variations for He–Ar–O2 shielded GTA welding on SUS304 stainless steel

The influences of argon and oxygen in helium base shielded GTA welding on the arc ignitability, bead protection and weld penetration are systematically investigated by bead-on-plate welding on SUS304 stainless steel. Experimental results show that the critical electrode tip work distance for arc ignition is increased from 1 mm under pure He shielding to 5 mm under He–50%Ar shielding. Small addition of oxygen content to the He–Ar mixed shielding can significantly change the weld shape from a wide shallow type to a narrow deep one, and the weld depth/width ratio can be doubled due to the change in the Marangoni convection from an outward to an inward direction.