Abstract Laser powder blown directed energy deposition (DED-LB) is a metal additive manufacturing technique which uses a nozzle to transport metal powder particles to a melt pool created by a laser. Flow from the nozzle typically consists of powder particles transported by carrier gas and additional shield gas to prevent oxidation. While incorporation of powders, powder flow distribution, melt pool morphology, and process parameter mapping has been well studied for powder DED-LB, investigation of the effect of shield gas flow during deposition has been limited. To better understand the role of shield gas flow rate in process stability, in situ high-speed Schlieren imaging was used to visualize gas flow. Competition between the impinging particle-laden flow and melt pool emissions was observed, which created a vapor dome at the stagnation point and boundary layer that flowed across the substrate. It was found that lack of shield gas flow promotes melt pool instability, and that sufficient shield gas flow rate is process parameter dependent. The median plume height ranged from 2.5 mm to 4.9 mm across stable gas flow conditions with a standard deviation up to 0.85 mm. Oscillations in the plume height were found to be driven by the thermal mass of the melt pool, and shorter standoff distance appears to exacerbate plume instabilities. In all, high-speed Schlieren observations provide insight into the local gas flow phenomenon in powder DED-LB and highlights the importance of shield gas flow rate in process stability.
Webster et al. (2026) studied this question.