Powder stream thermal dynamics in directed energy deposition for high aggregation and thermal efficiency using computational fluid dynamics modeling

Exactly converging the metal powder flux at a given substrate position is of great importance for additively manufacturing high-quality metallic products, and it essentially depends on the geometric structure and thermal dynamics of powder streams. In this study, we developed a 3D numerical model to elucidate the interactions between powder, gas, and laser beam in a coaxial nozzle during laser directed energy deposition (DED). The numerical simulation indicates that the waist-shaped powder stream converges approximately 11.2 mm below the nozzle outlet, where the minimum nominal radius is achieved. Within the laser irradiation area, the powder particle temperature increases dramatically and reaches the maximum average value at approximately 20 mm away from the nozzle outlet. Furthermore, optimal powder stream convergence and high thermal efficiency can be achieved when the powder stream driven by low inner gas flow rate converges 4 mm below the laser beam focal plane. The results of high-speed and infrared imaging analysis demonstrate that the proposed model has good predictability for the mean particle velocity and temperature, with average R 2 of 0.91 and 0.96, respectively. This study provides an effective approach to achieve desired metal-powder stream convergence and high thermal efficiency for DED powder feeding.