Metal additive manufacturing : a first comparison between SLM and sintered FDM parts

Metal additive manufacturing is currently reaching an important position in the metal manufacturing industry. A new process based on Fused Deposition Modelling is emerging. It relies on special filaments composed of metal powder and binder. This process is advertised as a cheap and reliable alternative to the well-known MAM processes but very few information is available about the process itself, the achievable results and their consistency in comparison with other processes. This thesis is based on the Ultrafuse 316LX filament designed by BASF to build 316L stainless steel parts through extrusion with a FDM machine, debinding of the green part then sintering. In this work samples were manufactured with a standard FDM machine at UCLouvain. Some samples underwent gaseous catalytic debinding and dry hydrogen atmosphere sintering in a factory that had the necessary facilities. The other samples were debinded with alternative methods and sintered under vacuum or argon atmosphere. The Ultrafuse 316LX filament was also experimentally characterised to complete the limited available data about its composition. It was found that thermal debinding can be a viable alternative to gaseous catalytic debinding and that other debinding processes might be developed. The best final samples reached a mean relative density of 83.81% under dry hydrogen atmosphere and 80.6% under argon atmosphere. It was also concluded that sintering in dry hydrogen is necessary to avoid unwanted oxidation. It was however discussed that the most critical parameters come from the FDM step that produces macroscopic defects and the much better density should be achievable. The results showed that the achieved density could exceed 97% if these defects are solved. The tensile strength tests on the final specimens achieved up to 82.41% of the SLM samples' ultimate strength which announces promising results from future denser samples. It was concluded that MFDM might not bring outstanding results but could still become an unavoidable process in metal additive manufacturing due to the potential achievable isotropy and the possible significant cost reduction.