Influencing Residual Stress in PBF-LB/M Processes Through In-Process Microstructure Assessment and Selective Laser Heat Treatment

In powder bed fusion by laser beam melting of metal (PBFLB/M), residual stresses form in the fabricated layers and affect the process by promoting deformations and cracks. Certain tool steels are especially prone to such defects. This paper presents a concept to reduce residual stresses in the PBF-LB/M manufacturing process of H13 tool steel through selective laser heat treatment, inducing solid-state phase transformations. These directly influence residual stresses due to the associated volume change of the crystal lattice. To assess the microstructure, an eddy current sensor is attached to the coating unit. Local temperature conditions are recorded using a high-speed thermographic camera. The captured data is translated into models using Bayesian optimization and gaussian process regression. Initial results show the successful detection of microstructural changes through in-process laser heat treatments. Subsequently, these measurements and models are utilized determine process parameters for local laser heat treatment. The targeted outcome is a technology that reduces residual stresses, thereby minimizing deformations and cracks in additively manufactured components.