Development and Optimization of an Innovative Double Chamber Nozzle for Highly Efficient DMD

Injection nozzles design in Direct Metal Deposition (DMD) critically affects the performances of the process in terms of powder deposition efficiency. In fact, the fluid-dynamic behavior of the powder particles falling into the molten pool strongly depends both on the internal geometry of the deposition nozzle and on the geometry of the nozzle outlet. This efficiency, for commercial nozzles, is usually under 50%, thus implying an unaffordable powder waste. SUPSI implemented an innovative nozzle concept, designed as a coaxial double chamber that enables the concurrent flow of the powder-carrier gas mixture and of the shielding gas. In this configuration, the shielding gas allows to reduce the spread of the blown powder particles, constraining the carrier gas flow and limiting its divergence. Such innovative design also enables the integration of various modules - different in shape - to be nested to the bottom end of the nozzle, in order to adapt its outlet geometry. The main objective of the design is to influence the shape of the powder flux ejected from the nozzle outlet by exploiting the shielding gas while limiting oxidation processes. In order to assess the influence of the feeding parameters on the flow geometry, different concepts and shapes of nozzle outlet have been tested and investigated against the deposition efficiency, both numerically and experimentally. The testing campaign relies upon an image analysis performed on a demonstration setup where the powder flux is tracked using a high-speed camera. Experimental results demonstrate improved deposition efficiency through a significant (up to 18%) spread reduction.