Investigating the production of polypropylene powder suitable for processing through laser sinter additive manufacturing

Abstract

Additive Manufacturing (AM) has become a promising technology supporting the 4th Industrial Revolution. The Laser Powder Bed Fusion (L-PBF) process is one of the AM technologies with the potential to use metallic, ceramic, and polymeric materials in powder form to produce end-usable parts. Medical, aerospace, and automobile industries are the major applications of this technology. Despite good mechanical performances obtained from laser-sintered components using polyamide powders, the high cost of these materials limits the widespread adoption of the L-PBF technology by industry. There is a need to increase the number of feedstock polymeric materials suitable for the L-PBF process to reduce the cost of producing parts through this technology. In recent years, Polypropylene (PP) powder suitable for L-PBF has become available, but the cost is similar to that of polyamide powders. This study investigated the possibility of using PP pellets intended for the injection moulding industry supplied by South African company Sasol Limited to produce powder suitable for L-PBF. Through experimentation, the precipitation of two isotactic PP grades, HNR100 (70%) and HTV145 (20%), mixed with talc (10%) into m-Xylene produced powder with the required particle size and morphology. A cost analysis showed that producing the new composite powder at a much-reduced cost compared to similar commercially available powder was possible. The new PP composite powder was characterized through Differential Scanning Calorimetry (DSC), Thermogravimetry (TGA), Scanning Electron Microscope (SEM), Fourier Transform Infra-Red (FTIR), and X-ray diffraction (XRD). Results from these tests showed that the newly developed composite powder is well suited to the L-PBF process and compared well to commercial PP powder, which was acquired as a benchmark for developing the new material. Process parameters were developed for successfully printing the newly developed composite powder on a Sintratec S1 L-PBF machine. The mechanical properties of the produced tensile test pieces showed results comparable to what could be achieved with the commercially available powder. Similarly, dimensional accuracy and surface roughness measurements showed comparable results. It could be concluded from the study that it is worthwhile and profitable to promote the production of PP powder using locally produced PP pellets. Not only could powder suitable for L-PBF be produced that delivers parts similar to commercially available powder but at a much-reduced cost, whilst stimulating local industry development and countering costly imported materials.