Gas metal arc welding (GMAW) is one of the most widely used method to assemble parts together in various industries. Argon and helium are the most common shielding gases used in GMAW to protect the molten metal from oxidization. The shielding gas composition is a critical parameter in the GMAW process, which affects the efficiency, quality, and overall performance of the welding operation. In this project, a numerical investigation was conducted to study the transport phenomena in the GMAW arc under the shielding environments of pure Ar and three Ar-He mixtures. The detailed description of the transient arc plasma generation and interactions with moving droplets and weld pool surface provides insights into how the thermal physical properties of the two shielding gases affect the arc characteristics.