Measurement of Flowability and Layer Spreadability of Polymeric Powders for Powder Bed Fusion Processes at Ambient and Process Conditions

Powder Bed Fusion processes, such as Selective Laser Sintering (SLS), are additive manufacturing techniques that involve spreading powders in thin layers during the process. Using fine powders can enhance the final artefact’s quality by improving the definition of details. However, the cohesion of fine powders poses challenges for the spreading process. To address this, spreading is often performed at high temperatures to minimize defects caused by temperature peaks during the selective sintering/melting phases, which alternate with powder spreading. In this study, we conducted an extensive experimental campaign on the flowability and spreadability of commercial SLS polymeric powders at both ambient and high temperatures. We measured powder flowability using an Anton Paar Shear Cell at varying temperatures. Spreading tests were performed with an experimental setup that simulated the powder spreading process at different temperatures. We analyzed the quality of the powder spread using image analysis techniques on macroscopic and microscopic images of the spread powder layer. Macroscopic images provided indications of layer defects and uncovered areas, while wavelet analysis offered spectral power densities related to characteristic wavelengths of surface roughness, serving as a valuable tool for characterizing and validating DEM simulations of the powder spreading process. The results indicate that powder flowability and spreadability are only partially related. Notably, the effects of temperature on powder flowability become evident in the spreading process under conditions where powder f lowability is only marginally affected.