Numerical investigation on effects of operating conditions and final dimension predictions in laser powder bed fusion of molybdenum

In this article, three-dimensional discrete element method (DEM) and computational fluid dynamics (CFD) coupled numerical simulations were carried out to investigate the single/multi-track and multi-layer printing of Molybdenum (Mo) powder using laser powder bed fusion (LPBF) approach at meso-scale. In the whole process, the effects of powder spreading and selective melting in multi-layer fabricating were analyzed, through which a mathematical correlation was derived to quantify the final stable dimensions of the powder bed and the printed region. Results show that appropriate laser scanning velocity, laser power and adequate powder bed density are indispensable for a smooth and continuous molten track. The scanning hatch distance should not exceed the molten pool width. The application of a certain preheating temperature can improve the inter-track connectivity. During multi-layer melting, the established quantitative correlations in the steady state between the set gap height (HN), actual layer thickness (hA), molten layer thickness (hM) and fusion ratio (ρF) are hA=HN/ρF and hM=HN, respectively, which have been verified by the results through both physical experiments and numerical simulations. The results obtained have both theoretical significance and practical value in optimizing the process parameters for Mo material in LPBF.