Influence of helium content on a ternary-gas-shielded GMAW process

Abstract

Helium was added to the shielding gas for mild-steel gas metal arc welding. The influence of helium content in a ternary shielding gas (Ar–CO2–He) mixture on arc properties, metal transfer process, and weld bead profile was investigated by numerical simulation and experimental study. As the helium content increases, the arc temperature field becomes more constricted but the central high-temperature zone expands. The current density on the arc axis increases with increasing helium content. The heat flux density on the cathode increases as the helium content increases. The changes in the arc properties lead to the changes in the metal transfer. With increasing helium content, the droplet size increases and the transfer frequency decreases, with approximately linear dependence on helium content. When the helium content is increased from 0 to 25 vol%, the droplet diameter increases by about 80% and the transfer frequency decreases by about 77%, compared to the zero-helium case; this is attributed to changes in the forces on the detaching droplets. With the addition of helium, the base metal fusion area increases and has a more rounded profile; this is attributed to the increased droplet diameter and decreased droplet frequency.