Comprehensive study of the cold-temperature directed energy deposition: Multi-physics modelling and experimental validation

Currently almost all the directed energy deposition (DED) processes are performed under ideal lab conditions with the room temperature close to 20 C. By contrast, the cold-temperature DED has potentially onsite use in cold environments, such as the winter in the Northern Hemisphere, where the ambient temperatures are often near or below freezing point temperature (0 C). However, there is a lack of study on the cold-temperature DED process due to its unique temperature conditions. To fill this gap, the authors employed both multi-physics modelling and experimental approaches to study the DED process at cold temperature (CT) -3 C-degrees, and compare to the room temperature (RT) 20(degrees) C DED process. Stainless Steel 316L (SS316L) was selected as powder material. The multiple physics in the DED process involving laser heat source, local melting, rapid cooling, solidification, phase change, evaporation, and fluid-gas interactions were modeled using the computational fluid dynamics (CFD) - volume of fluid (VOF) approach. To validate the model, the DED experiments were conducted using a cryogenic DED platform in which the DED process was chilled to customized low temperatures. This highfidelity model predicted accurate thermal results and deposit geometries for both the CT and RT DED cases. The results show that under sub-freezing conditions, the deposit size of the CT-DED is similar to 62.1 % bigger than the RTDED in the mean area throughout the length of the single-track thin wall. Furthermore, the CT-DED results show a steeper thermal gradient and at the same time a lower heat flux near the substrate. This high-fidelity modelling framework can be effectively expanded to study more cold-temperature additive manufacturing cases, like the Arctic exploration and in-Space manufacturing.