Comparative evaluation of effect of shielding gas using gas mixer and shielding gas alternator for GMAW of tube to tube joints

Abstract

Gas Metal Arc Welding (GMAW) with alternating shielding gases is a method wherein two different shielding gases are alternatingly supplied to the torch for effectively protecting the weld pool from the atmospheric contamination. The alternating supply of two different shielding gases to the arc in GMAW produces an effect similar to pulsed current GMAW but dynamically more superior. GMAW with alternating shielding gases of argon and CO2 has been tried for welding of carbon and alloy steel tube butt joints. The properties of weldments with alternate shielding gas and conventional supply of shielding gases with mixing units have been evaluated. The arc experiences switching from globular transfer to short-circuiting within the weld puddle due to alternating shielding gases. This causes stirring in the molten weld pool and positively affects the weld pool thereby minimising spatter and porosity during welding. The bead characteristics of welds deposited with gas mixer have been compared to the characteristics obtained by welding with alternate shielding gas supply. The alternating supply of shielding gas in GMAW is found to consume less argon thereby provide significant cost savings in shielding gas.