Reuse of green parts for metal material extrusion: A recycling approach for improved sustainability

In the recent years, a novel variant of Material Extrusion technique has been developed. This proved additive technology has been combined with an innovative filament loaded with metallic powder dispersed into a polymeric matrix. The parts printed with this metal/polymer composite filament by means of the Material Extrusion process are called “green parts”. After debinding and sintering treatments, the green parts became completely made by metal. As a novel technology, Metal Material Extrusion is still not a fully optimized and, therefore, efficient process and this leads to the generation of a great number of scraps due to the wasted products and to still existing process inefficiencies, which also increase the total costs of fabrication and undermine its economic competitiveness. In this paper, a circular approach for this new additive process has been proposed with a focus on the reuse and the remanufacture of the wasted products. Particularly, the reuse of defective green parts of Metal Material Extrusion technique was investigated to assess a circular manufacture of metallic parts. A new filament was fabricated starting from wasted green parts as raw feedstock with a commercial extrusion system. A comparison between commercial and recycled filaments was conducted. The polymeric content was studied by means of macrographic and thermogravimetric analysis, while a particle size distribution analysis was proposed to evaluate any change in metal powder sizes. Sequentially, secondary green parts were produced and underwent a debinding and sintering process to obtain near fully dense metallic parts. Furthermore, preliminary structural and mechanical evaluations of the secondary metallic samples were proposed in terms of apparent density, microstructure, and Vickers hardness. The resulting properties were compared to those of the virgin de-bound and sintered samples to assess the feasibility of the suggested circular fabrication process.