A comparison of double shielded GMAW-P with conventional GMAW-P in the arc, droplet and bead formation

摘要

Double shielded pulsed gas metal arc welding (D-GMAW-P) was proposed to feed the shielding gas of Argon (Ar) and carbon dioxide (CO2) with two independent coaxial channels. The molten pool was protected from blow-holes by improving the flow rates of shielding gas in the inner channel and outer channel. The feeding of Ar in inner channel and CO2 in outer channel made the current density distribution of the double-shielded arc generate a strong electromagnetic pinch force at the necking positon of droplet, which was favorable for droplet transfer, thereby improving welding stability. In the case of avoiding short circuit and spatter, the content of CO2 in shielding gas could be increased to 50 % by the double-channel torch. Compared with the conventional GMAW-P arc, the outer ring of the double-shielded arc had a more significant thermal compression effect on its inner ring, which made the arc heat-pressure distribution more concentrated and the droplet impingement much weaker. It decreased the backward flow velocity of molten metal, thereby weakening its eroding action on the gouging region and weld toe. Both the finger penetration and undercut defect were suppressed. The weld fusion line varied from an S-type to a C-type, which could effectively alleviate stress concentration.