Directed Energy Deposition

This video showcases a special optical technique called Schlieren imaging to visualize thermal plumes created by directed energy deposition (DED). A conical nozzle points down to a surface and metal powder particles flow from the nozzle, as does a room temperature flow of shield gas. A laser (invisible in the video) heats and melts the surface, and the powder particles melt on contact and freeze to form a solid deposit. The shield gas interacts with the melt pool and heats up, forming turbulent wall jets that flow away in all directions from the melt pool. The heated gas becomes visible because the light used to form the image is bent by the density gradients existing between the hot wall jets and the cooler surroundings. 

The video also shows significant “spatter” of hot and possibly molten particles ejected away from the melt pool under the influence of the cold shield gas flow impinging the surface. Each ejected particle has its own little thermal plume. 

The visualization allows researchers to understand how laser power, shield gas flow rate, particle flow rate and stand off distance influence the gas flow environment as metal is deposited in this DED additive manufacturing process.