Design of powder nozzle for high resource efficiency in directed energy deposition based on computational fluid dynamics simulation

Directed energy deposition (DED), an additive manufacturing process, is a suitable approach for freeform production with metallic materials. By generating a melt pool with a high-power laser beam, injected material powder is contentiously laminated on a baseplate by melting and solidifying. Although all supplied powder should be molten and solidified in order to reduce the material waste, powder distribution is difficult to converge owing to turbulence around the melt pool. Furthermore, an inappropriate powder supply easily leads to sputter generation, which also increases the material waste. In this study, the gas flow under a powder nozzle was analyzed by a computational fluid dynamics (CFD) simulation in order to achieve a high convergence in the powder supply. By measuring the powder distribution with a laser light sheet system and conducting deposition tests, the powder distribution and supply efficiency were experimentally evaluated. According to a gas-solid multiphase-flow simulation, the convergence distance of the powder flow should be shorter than the laser beam focus distance to improve the powder convergence with a lower gas-flow rate. Moreover, the powder nozzles were redesigned by taking the simulation results into consideration, and deposition tests were conducted to evaluate the powder supply efficiency, porosity rate, and penetration rate. The experimental result of the designed nozzle shows a clear improvement in the powder supply efficiency from 50.2 to 66.0%.