Preliminary assessment of material extrusion (MEX) for medical applications: The effect of hatch angle

Material extrusion (MEX) is one of the most widely used Additive Manufacturing (AM) technologies owing to its simplicity and accessible cost. The technique is based on the principle of extrusion of thermoplastic material, layer-by-layer, on a building platform through multiple head nozzles. Metal filled filaments, in combination with debinding and sintering cycles, may innovate and transform the traditional functioning of the MEX technique into a cost-effective alternative for the conventional metallic AM processes. In the present document, the optimal printing conditions characterizing LPBF technology were replicated on MEX technology, with the aim of assessing the effects of the printing parameter hatch angle over the material properties and, at the same time, providing a better understanding of the production of medical metal parts via MEX. Indeed, in this particular context, the use of Powder Bed Fusion (PBF) and Directed Energy Deposition (DED) prevails, requiring MEX-based technique extensive research for its applicability. The influence of a specific AM process parameter, the hatch angle, was assessed following a single factor Design of Experiment (DOE), varying over two levels: the optimal Laser Powder Bed Fusion (LPBF) scanning strategy (67°k) and the most common MEX deposition strategy (±45°). Specimens were manufactured, using MEX technology (Ultimaker S5) and AISI 316L filament (BASF Ultrafuse 316L) and tested. Results of the defect analysis, including closed and open porosity, and mechanical properties were collected and statistically compared to determine any difference in the two-deposition strategies. Furthermore, in the analysis, LPBF key characteristics are reported as benchmark values.