Aging Dynamics in Polymer Powder Bed Fusion Systems: The Case of Selective Laser Sintering

• Characterization of Polyamide 12 powder degradation in Selective Laser Sintering. • Microscopic images and data from aged powder dictate minor differences induced by process. • Thermal stress influences Polyamide 12 Powder Aging. • Increased material shrinkage by 0.98 % is detected after six printing iterations. Additive manufacturing (AM) is an advanced production method for layer-by-layer fabrication, offering a paradigm shift in manufacturing. However, the sustainability of AM processes is poor, since suppliers recommend reusing 50 %-70 % of reprocessed powder, contributing to a significant increase in material disposal. To explore the possibility of fully reusing the polymeric material, we conduct a comprehensive characterisation of the powder particulates, in combination with analysis of the final prints. Utilizing optical and scanning electron microscopes, we statistically evaluate the size, morphology, and shape of the particles. Furthermore, tensile strength and deformation of printed bars is evaluated, showcasing the impact of aging on the print properties. The findings reveal that consecutive reuse of used powder significantly influences dimensional accuracy of the printed parts. We detect a 30.63 % relative value of shrinkage after six printing iterations, which corresponds to an absolute shrinkage increase by 0.98 %. This is significant considering the standard shrinkage for the material used is already 3.2 %. Additionally, parts that are printed with reused material exhibit a small increase in elongation at yield, as well as an unexpected rise in tensile strength. Significant agglomeration of small particles is observed in the aged powder, since there are particles of less than 10 µm, which are not found in the virgin powder. These results contribute to a better understanding of the issues related to the reusing of aged material, and offer invaluable insights for mitigating the environmental impact that is associated with material disposal in AM.