Experimental analysis of an extrusion system for additive manufacturing based on polymer pellets

One of the most popular additive manufacturing (AM) processes is based on polymer extrusion using a continuous filament as feedstock. However, the use of this type of feedstock increases costs and narrows the variety of materials that can be used. The development of technologies that allow polymer pellets to be processed as feedstock would increase the popularity of polymer extrusion by addressing these two issues. This work describes the development of a piston-driven extrusion head that can extrude polypropylene granules into a filament. The head was designed to minimize the volume of material fused during the extrusion process and reduce the effect of material degradation. Experiments were conducted to characterize the dimensions of the filaments generated. Material degradation inside the extrusion head was assessed by infrared spectroscopy, and its effect on filament strength was analyzed by tensile tests. The results showed that the system was able to produce a continuous filament. Spectroscopy revealed that degradation occurs inside the heated cylinder but does not greatly influence the strength of the extrudate. However, a flow variation along the length of the filament was observed. For the proposed system to be considered feasible for AM, this variation needs to be better understood and controlled.