Exploring the actual stacking height of metal powder bed in laser powder bed fusion additive manufacturing

Laser Powder Bed Fusion (LPBF) is an additive manufacturing process that builds parts by layer-by-layer spreading and selective laser melting of metal powders. The characteristics of the powder bed are closely related to laser parameters and the particle size distribution of the metal powder. However, the actual stacking height of the powder bed changes dynamically due to shrinkage during powder spreading, melting, and solidification. This study investigates the actual stacking height of metal powders by analyzing powder flow behavior during falling, spreading, melting, and solidification using the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). The results show that height shrinkage caused by powder spreading can be eliminated by increasing the gap between the blade and the working platform from 0 μm to 20 μm. The shrinkage rates due to solidification and liquid metal flow were found to be 8.5% and 31.5%, respectively. Furthermore, mathematical models relating the actual stacking height to layer thickness, number of layers, and solidification shrinkage were established, providing a theoretical foundation for LPBF processes with larger layer thicknesses, as well as for support structure design, printing accuracy, and allowance planning.