Effects of polyamide-11 powder refresh ratios in multi-jet fusion: A comparison of new and used powder

Abstract

Abstract Multi-jet fusion (MJF) is a polymer powder bed process increasingly explored for the commercial fabrication of final products. The most popular materials used in MJF are polyamide 12 (PA12) and polyamide 11 (PA11), and the recommendation is to recycle at most 70% of the used powder. This results in significant amounts of used powder being discarded. In this paper we explored what happens if different ratios of new-to-used powder are used. Therefore, this research offers an insight in the thermal, morphological, and mechanical characteristics of all new, the recommended 30:70 mixed ratio, and all used PA11 powder. The thermal properties were evaluated through thermogravimetric analysis and differential scanning calorimetry. The morphology of the powders was examined through powder size distribution, powder flowability, and qualitatively through scanning electron microscopy and their printability and performance was assessed through tensile testing and porosity analysis using X-ray microcomputed tomography. We found that the samples fabricated with all used powder performed worse in tension than the other powder ratios, but its thermal properties did not significantly vary. We found that the used powder exhibited the greatest surface fractal which affected the porosity of the fabricated specimens. This difference was identified as the possible cause for the decrease in the tensile strength from 45 MPa to 39 MPa.