Discrete Element Method Analysis of the Spreading Mechanism and Its Influence on Powder Bed Characteristics in Additive Manufacturing

Abstract

Laser powder bed fusion additive manufacturing is among the most used industrial processes, allowing for the production of customizable and geometrically complex parts at relatively low cost. Although different aspects of the powder spreading process have been investigated, questions remain on the process repeatability on the actual beam–powder bed interaction. Given the influence of the formed bed on the quality of the final part, understanding the spreading mechanism is crucial for process optimization. In this work, a Discrete Element Method (DEM) model of the spreading process is adopted to investigate the spreading process and underline the physical phenomena occurring. With parameters validated through ad hoc experiments, two spreading velocities, accounting for two different flow regimes, are simulated. The powder distribution in both the accumulation and deposition zone is investigated. Attention is placed on how density, effective layer thickness, and particle size distribution vary throughout the powder bed. The physical mechanism leading to the observed characteristics is discussed, effectively defining the window for the process parameters.

Mechanical and microstructural characterization of titanium gr.5 parts produced by different manufacturing routes

“…In this context, the results reported in Fig. 13 indicate that, especially for E-PBF, for which the powder size distribution is usually larger compared to L-PBF, process criticisms may occur when considering thin walls due to the emphasized melt pool instabilities, and not sufficient powder bed packing [ 27 ]. These considerations justify the results obtained for the E-PBF parts, for which the density of the axisymmetric geometry part is less sensitive to variations than the T part.…”

Laser-Powder Bed Fusion of Inconel 718 Alloy: Effect of the Contour Strategy on Surface Quality and Sub-Surface Density

“…According to the aforementioned points, these experimental outcomes could be explained considering the following issues: i) the samples #5, despite the use of a higher scanning speed for the bulk region, has the lowest roughness due to the employment of a reduced contour scanning speed. This can be explained considering the balling phenomenon, for which an insufficient heat input implies an unstable melting track, determining the formation of separated molten balls that adversely affects the final surface quality [8]; ii) the samples #1 do suffer of the not advantageous position on the build platform: given the edges of the latter, the powder bed spreading process could be quite different in comparison with the inner part [24], determining therefore a different laser-matter interaction even at fixed laser process parameters; iii) the influence of the powder spreading process justifies also this point, considering also that feedstocks with a wide powder size distribution may induce, in the case of the bigger powders, the formation of an agglomerated front as the recoater moves across the platform. This effect, as expected, is more pronounced when considering the platform edges (see samples #1).…”

Mechanical and microstructural characterization of titanium gr.5 parts produced by different manufacturing routes

“…In this context, the results reported in Fig. 13 indicate that, especially for E-PBF, for which the powder size distribution is usually larger compared to L-PBF, process criticisms may occur when considering thin walls due to the emphasized melt pool instabilities, and not sufficient powder bed packing [28]. These considerations justify the results obtained for the E-PBF parts, for which the density of the axisymmetric geometry part is less sensitive to variations than the T part.…”