Numerical simulation of heat transfer and flow behavior in the melt pool of 304 stainless steel Joule hot melt wire additive manufacturing

A three-dimensional transient model was developed for 304 stainless steel fabricated via Joule Hot-wire Additive Manufacturing (JHAM), incorporating the key physical phenomena within the molten pool. This study investigated the heat transfer and flow behavior during the JHAM process. For single-track deposition, systematic analysis revealed that a lower printing velocity led to greater Joule heat input, resulting in a deeper penetration depth, enhanced fluid flow, and higher overall velocity within the molten pool. Conversely, increasing the printing velocity reduced the heat input per unit time, decreasing flow velocity and causing upward accumulation of molten metal, which increased the deposition height while decreasing its width. Good agreement between the simulated and experimental geometric dimensions of single tracks validated the model's accuracy.In multi-track deposition, the center distance was found to be a decisive factor for molten pool stability and final quality. A spacing of 0.30 mm facilitated the formation of a stable double-vortex flow pattern within the pool, promoting uniform heat and mass distribution. This optimal condition yielded the best surface quality with the lowest roughness (Ra = 3.654 µm) and the highest microhardness (peak value of 299 HV), the latter being attributed to enhanced grain refinement driven by a higher cooling rate. In contrast, a smaller center distance of 0.15 mm caused severe heat dissipation to the prior track and flow instability, while a larger center distance of 0.45 mm led to excessive heat concentration and a disordered flow regime. Both non-optimal conditions degraded surface finish and mechanical properties. The close correspondence between simulation and experimental results confirms that 0.30 mm is the optimized center distance under the investigated conditions.