Analysis of gas-solid multi-phase flow around a deposit in directed energy deposition

Although metal additive manufacturing (AM) gathers attention from various industries, the process stability in metal AM still remains in an important issue for ensuring the production quality. In particular, powder-based directed energy deposition (DED) is difficult to stabilize because large amount of metal is contentiously molten with a high-power heat source. Furthermore, the materia! powder flow needs to be precisely converged on the meltpool; otherwise the considerable amount of materials would be wasted. Against these challenges, this study aims to analyze the turbulent flow in the fabrication space for converging the powder trajectories on the meltpooi stably and accurately. By constructing a gas-solid multiphase-flow simulation for the coaxial nozzle for DED, the influence of carrier and shield gases on the powder flow is numerically calculated. According to the estimated particle distribution, the particle concentration on the top surface of deposit decreases in the higher-layer deposition. Moreover, the particle-flow convergence is enhanced with higher carrier gas-flow rate. These analyses highly agree with the experimental results on powder distribution measured with a laser light sheet system. As a conclusion, it is clarified that the carrier gas supply should be higher at higher layer deposition to keep the powder convergence stable in DED.