3D Printing of Clay Paste Enhanced by Scrap Polymer from Powder Bed Processes

Purpose: Powder bed additive manufacturing processes are widespread due to their many technical and economic advantages. Nevertheless, the disposal of leftover powder poses a problem in terms of process sustainability. The purpose of this research is to provide an alternative solution to recycle waste PA12 powder from HP Multi Jet Fusion. In particular, the opportunity to use this material as a dispersion in 3D printed clay is investigated. Design/methodology/approach: A commercial fused deposition modelling printer was re-adapted to extrude a viscous paste composed of clay, PA12 and water. Once printed, parts were dried and then put in an oven to melt the polymer fraction. Four compositions with different PA12 concentration were studied. Firstly, the extrudability of the paste was observed by testing different extrusion lengths. Then, the surface porosities were evaluated through microscopical observations of the manufactured parts. Finally, benchmarks with different geometries were digitalised via three-dimensional scanning to analyse the dimensional alterations arising at each stage of the process. Findings: Overall, the feasibility of the process is demonstrated. Extrusion tests revealed that the composition of the paste has a minor influence on the volumetric flow rate, exhibiting a better consistency in the case of long extrusions. The percentage of surface cavities was proportional to the polymer fraction contained in the mix. From dimensional analyses, it was possible to conclude that PA12 had a positive influence on the shrinkage effect in the drying phase, while it increased dimensional alterations occurring in the melting phase. The results showed that the dimensional error measured in Z direction was always higher than that of the XY plane. Practical implications: The method proposed in this article provides an alternative solution to reuse leftover powders from powder bed fusion processes via another additive manufacturing process. Originality/value: The article presents an innovative additive manufactur- ing solution for powder reuse. Unlike the recycling methods in the body of literature, this solution does not require any intermediate transformation process, such as filament fabrication. Also, the cold material deposition enables the adoption of very inexpensive equipment for the extrusion. This preliminary study demonstrates the feasibility and the benefits of this process, paving the way for numerous future studies.