In-flight thermal control of molten metal droplet streams

Precision droplet manufacturing (PDM) is a process that builds complex 3D parts one nano-liter molten metal droplet at a time from a CAD file without the need for tooling. One method to control the droplet temperature when it arrives at the target is to heat the droplets in-flight. This note describes such a heater that uses helium and nitrogen as the convective heat transfer medium. Heating rates up to 11,000 °C/s are attained. The effect of droplet spacing on the heat transfer coefficient is experimentally detailed and a nascent-turbulent effect is observed to bring the heating rate for nitrogen close to that for helium. In addition, the experimental values are consistent with those from multi-droplet numerical simulations reported in the literature.