Hierarchical effects of multi-layer powder spreading in the electron beam powder bed fusion additive manufacturing of pure tungsten material

Abstract

In multi-layer powder spreading process of electron beam powder bed fusion (PBF-EB) additive manufacturing, the quantitative correlation between characteristics (actual height of the deposited layer, packing density, average surface roughness) of each spread powder layer and corresponding process parameters (set thickness value of the layer, spreading velocity) has not been well established. And the underlying mechanism is still not clear. For this objective, PBF-EB additive manufacturing of pure tungsten component in physical experiment is numerically reproduced by a validated coupled discrete element method-computational fluid dynamics (DEM-CFD) model, where the cumulative effects of process parameters are comprehensively analyzed through systematic parametric studies. The results show that with the increase of set thickness value of the layer, the number of layers that reaching steady state first decreases and then increases. After stabilization, the packing density and the average surface roughness of the powder bed are mainly determined by spreading velocity, while the actual height of the deposited layer is determined by both the packing density and the set thickness value of the layer. The mechanism can be ascribed to different motion behaviors of particles located in the top and bottom regions of a new powder layer induced by the impediment of the melted region in the powder bed. The bottom particles can be squeezed by strong forces to form a dense structure, while the top particles escape from the force arches to the zone consisted of weak forces before they are spread and their motion behaviors are dependent on their residual velocity. The obtained highlighted results are not only of theoretical significance, but also of practical value for parameter setting and optimization in the actual electron beam powder bed fusion additive manufacturing of pure W and other materials.