Numerical Investigation of Thermo-Mechanical Response, Tool Contact Stress, and Heat Generation Mechanisms in FSW of AISI 304 Stainless Steel Across Plunge, Dwell, and Travel Phases

Friction stir welding (FSW) is now widely acknowledged as an effective method for joining high-strength steels. Numerical simulation of FSW has become a vital tool for optimizing process parameters. In the present study, a 3-D numerical model based on the Coupled Eulerian–Lagrangian (CEL) formulation is developed to simulate the plunge, dwell, and travel phases during the FSW of 304 stainless steel under various rotational speeds, plunge rates, dwell times, and welding speeds. The model is validated using the experimental plunge force data across all three process phases, demonstrating good agreement. The numerical findings indicate that the tool rotational speed exerts a more pronounced influence on the peak temperature, plastic strain, stir zone (SZ) geometry and heat-affected zone (HAZ) profile compared to welding speed. A favorable balance between peak tool thermal levels and surface contact stress is achieved at 300 rpm and 1.25 mm/s welding speed. Furthermore, plastic deformation heat accounts for 18.8% and 43.5% of the total heat generation at 200 and 500 rpm, respectively. The developed model provides a robust baseline tool for FSW process optimization.