Selecting the suitable thermoplastic elastomer as the main component in the feedstock for metal material extrusion of aluminium

Abstract

Metal material extrusion (MMEX) involves the systematic deposition of material layer by layer, followed by debinding and sintering to produce fully dense metallic parts. The feedstocks, initially comprising metal powder and a binder system, are pivotal in determining processability and final properties. This study utilized polylactic acid (PLA) as the backbone and a thermoplastic elastomer (TPE) as the primary, solvent-debindable component in the binder system, with a 50 and 55 vol% aluminium (Al) powder content. PLA was selected due to its lower degradation temperature and to try to increase the sustainability of the MMEX process. An initial experimentation with various TPEs, employing thermal analysis (TGA and DSC), rheological behavior assessment, mechanical property testing, contact angle measurement, and solvent debinding processes, aimed to identify the most suitable TPE for this study. The results demonstrated that a very low interfacial tension between PLA and TPE is not desirable, as it may result in the removal of some powder particles during the solvent-debinding process. The TPE type with lower viscosity, optimum interfacial tension with PLA, low residue after degradation, adequate rigidity, and flexibility is proper for use as the soluble part of the binder system. After selecting of the appropriate TPE, the printability at a nozzle temperature of 270 °C was undertaken. The solvent debinding process for printed samples was conducted at room temperature. The results indicated that 90 wt% of the TPE was removed successfully from the samples printed with 30 vol% PLA in binder formulation without any defects during solvent debinding.