Melting Mode Thresholds in Laser Powder Bed Fusion and Their Application Towards Process Parameter Development

Depending on processing conditions, laser powder bed fusion (LPBF) has broadly two different processing regimes, conduction and keyhole mode. Heat conduction governs the melt pool morphology observed in conduction mode melting. In contrast, keyhole mode melting is observed when the morphology of the molten pool is controlled by thermo-capillary convection and recoil momentum pressure generated by vaporization of a given material. Additionally, there exists another melting mode called transition mode wherein the dominance of conduction or convection depends on processing conditions. In this work, we use an analytical temperature prediction model, along with normalized processing diagrams, to obtain a processing window for achieving highdensity three-dimensional Ti-6Al-4V parts on a continuous beam exposure LPBF system. The normalized processing diagrams in this work help visualize the three melting modes - conduction, transition, and keyhole mode. The temperature prediction model can be used to predict the thresholds between the three melting modes. This work can be used for understanding the physical origins of defects in three-dimensional LPBF parts, as well as lower the risk of costly experimentation to go from powder to near fully dense products.Mechanical Engineerin