Experimental metrics of the powder layer quality in the selective laser sintering process

According to the literature, the microscopic quality of the powder layer produced in the Selective Laser Sintering (SLS) process is related to the onset of macroscopic defects of the produced powder. This study proposes an experimental procedure able to quantify the quality of the powder layer obtained in the spreading step of the SLS process. A dedicated experimental set-up was developed, able to mimic the powder spreading step of the SLS process and to allow the photographic analysis of its surface. Four commercial polymeric powders for SLS applications were tested at two different speeds of the recoater. An image processing analysis was developed, converting a series of microscopic images of layer surface in grey level profiles along the spreading direction. The grey level profiles were further analysed with a wavelet analysis tool, and the major features of the wavelet powder spectral density were used to calculate specific indicators of the powder layer quality. The different indicators provide consistent results comparing the tested powders and the testing conditions. The powder ranking according to spreadability indexes differs from the one obtained using flowability indexes. This finding confirms that spreadability cannot be directly related to flowability.