Abstract: Single TIG welding is the key manufacturing technology of thin-walled stainless steel pipe for industrial application, but its production efficiency is lower. If the welding current and speed are simultaneously increased, the undercut and humping weld will appear. Based on the formation of weld appearance defects in high speed welding process, high speed tandem TIG welding process is proposed. The experimental results indicate that the welding speed of 409L ferritic stainless steel pipe with two specifications of 48 mm×1.2 mm and 42 mm×1.5 mm can reach up to 5.1 m/min and 3.2 m/min under the condition of good weld appearance, respectively. Compared with single TIG welding production, tandem TIG welding can improve the production efficiency by 240% and 140%, reduces energy consumption by 44% and 29%, respectively. The expansion ratios of the 409L ferritic stainless steel pipe with these two specifications reach 11.2% and 21.4%, which satisfy the requirement of production. The analysis of tandem TIG welding mechanism indicates that the assistant TIG arc following the main TIG arc, heats the liquid metal piled up at the rear of the molten pool formed by the main TIG arc, which prolong the existence time of liquid metal and improve its flowing backwards from both the thermal and force aspects. So the developed tandem TIG welding process can obtain the good weld appearance at high welding speed, which not only increase production efficiency, but also reduce the energy consumption.

Key words: high speed welding, tandem tungsten inert gas(TIG) welding, weld appearance, welding efficiency