<p>Tungsten inert gas welding, a widely used joining process, is particularly prevalent in industries such as heat exchangers where both copper and stainless steel play vital roles. This paper details the development of a numerical model using COMSOL Multiphysics to simulate the dissimilar welding process between pure copper (Cu) and 304 stainless steel (SS304). The model, based on a Gaussian heat source, considers convective and radiative heat loss and material phase change for a comprehensive analysis. The primary goal of this investigation is to analyze the temperature distribution curve, assess the isothermal profile, and scrutinize the bead geometry. Temperature-dependent material properties are considered, predicting maximum and minimum temperatures for both materials at different times. These predictions are compared with temperatures measured by a thermocouple inserted into the workpiece. Two cases are explored for each process: one with an arc shift and one without, considering differences in thermal conductivity and melting point between copper and stainless steel. Upon a meticulous comparative analysis between numerical model results and experimental data, a substantial congruence is observed in the shape of the bead and the contour depicting phase change, indicating robust consistency. Importantly, the simulated temperatures closely align with those measured thermocouple, offering additional validation to the simulation accuracy. Furthermore, intentional arc offset, directing heat to copper in Cu-SS welding, enhances penetration, fusion, and integrity. This deliberate adjustment impacts the controlled mixing of molten metals yielding a more homogeneous weld and improved joint performance.</p>