Combined surface-based and density-based spreadability assessment of metal and polymeric powders for Powder Bed Fusion

The quality of Powder Bed Fusion (PBF) parts relies on the quality of deposition of each powder layer. Despite powder spreadability being a key factor, no standard definition or universal Spreadability Index is currently available. Literature indices are typically based on static layer features, such as density and surface quality, or on dynamic behaviour, such as avalanche angle. Density-based indices are mainly used for metal powders, while surface-based indices are common for polymers, although they are often treated as equivalent. This study compares density- and surface-based spreadability for two metals, Ti6Al4V and AlSi10Mg, and two polymers, PA6 and PA6 Black, spread at 50, 75, and 100 mm/s. Powder layers were characterised by imaging, laser profilometry, and gravimetry. Three spreadability indices were computed, while surface parameters were obtained from profilometry maps as a reference. Images and profilometer scans were processed by wavelet transform to generate power spectra and extract a characteristic wavelength from the dominant peak. Layer density was calculated by weighing the collected powder and using the pocket area with the tool–surface gap to define the layer volume. The influence of spreading speed was strongly index- and material-dependent. For Ti6Al4V, SIimg, SIprof, and SIdens varied by 10%, 37%, and 3%, respectively; for AlSi10Mg by 20%, 0%, and 24%; for PA6 by <1%, 20%, and 14%; and for PA6 Black by 13%, 25%, and 3%. These results show that spreadability rankings depend on the selected index and, in some cases, on spreading speed.