UC Davis

In the Directed Energy Deposition (DED) realm, challenges persist concerning process stability and mechanical properties in as-built components. Facts like inconsistent laser head feed rate and accumulated heat during multi-layer deposition result in variations in melt pool energy, causing variant clad widths and heights. Moreover, significant residual stress in as-built DED parts can induce excessive distortions and cracking. To tackle these challenges, offline energy control systems that adjust laser power or feed rate have been implemented to manage melt pool energy and improve productivity. Additionally, an innovative online clad height compensation system has been developed to achieve global height geometry, further boosting productivity. However, the impact of these productive and quality control systems on the mechanical properties of austenitic stainless-steel parts, specifically residual stress, remains unexplored. In this research, residual stress measurements in as-built DED thin wall parts fabricated with energy and/or height control strategies using neutron diffraction have been investigated. The control of three key DED parameters influencing residual stress distribution and magnitude has been identified and discussed. Measurements indicate that neither offline energy control nor online height control adversely affects the quality of the thin wall parts and offline LP-based energy control can reduce residual stress magnitude and its variation. Additionally, the height control results in compressive residual stress with elevated magnitudes. Furthermore, aggressive DED parameters hold the potential for further improvement by pairing with an energy control strategy. This study establishes a foundation for further developing comprehensive control strategies designed to enhance the productivity and quality of DED systems.