Evaluation of Polyethylene Terephthalate Powder in High Speed Sintering

Abstract

Laser Sintering (LS) was the first Powder Bed Fusion (PBF) method for polymers and it is now quite an established process for rapid prototyping and even for the production of functional parts. High Speed Sintering (HSS) is a variant of PBF which was later developed and it has the potential to be more scalable than LS. Most of the work for HSS and LS has been conducted with polyamide-12 (PA 12). This work reports the first effort to use polyethylene terephthalate (PET) in HSS. Well defined, simple and complex parts could be printed without any build failures. However, limitations were induced by current HSS machines which led to some curvature (warpage) in tensile bars after manufacturing. The reason for this was that all currently available machines for HSS are built for polymers such as polyamide 12, which means their maximum bed temperature is limited to 190 °C. This corresponds to the lower limit of processability of PET in PBF processes. The slightly curved tensile bars were straightened by heating them to 230 °C with a weight on top, and afterwards the mechanical properties were measured. The tensile modulus was similar to what was obtained with PET via LS but the strength and elongation-at-break (EAB) was lower. Microscopy showed that the reason for the lower strength and EAB was the incomplete melting of particles. This arose from the temperature limitation of the current generation of HSS machines. The porosity was established as 2.23% by helium pycnometry which is the same as for LS. The results of the thermal analysis indicated that the PET parts manufactured with HSS were semi-crystalline like the PET parts manufactured via LS.