Aging due to successive reuse of polyamide 12 powder during laser sintering: extrinsic powder properties and quality of sintered parts

The effects of cumulative build time during the reuse of polyamide 12 (PA 12) for laser sintering (LS) on the morphology, size and shape distribution of the feedstock powder and quality of printed parts were investigated in this study. Both the virgin and reused powders contain potato-shaped, elongated, and relatively few near-spherical particles. In agreement with the scanning electron microscope images, the circularity-roundness plots also indicate presence of near-spherical, potato-shape, and elongated particles in the virgin and reused powders. Particle size distributions of the powders revealed an increase in the proportion of fine particles at higher reuse cycles, which is due to cracking and fragmenting during repeated exposure to the high processing temperature during LS. Mild orange peel was observed at a cumulative build time of 36.4 h, which becomes more evident with increase of the build time. Moreover, the presence of surface defects could be observed at cumulative build times greater than 36.4 h, and all the parts exhibit deviation in average thickness and width from the desired values.