Evaluation of polymeric binders in 316L stainless steel manufacturing by filament-based MEX

Recently, the use of filament 3D printers to produce metal parts has significantly increased, requiring filaments with a high metal powder content suitable for extrusion, printing, debinding, and sintering. However, the high metal content leads to increase brittleness, complicating handling and printing, and no international standards exist to assess the printability. This study focuses on 316L stainless steel filaments composed of 60 vol.% solid loading and a binder of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA) and paraffin wax (PW). Taguchi method was employed to assess the impact of varying binder compositions. PW is the dominant factor, with increases in PW reducing flexibility, stiffness and hardness, while increasing brittleness. EVA is the dominant factor increasing buckling resistance. The filaments exhibit shear-thinning behaviour, with increased PW content reducing complex viscosity and significantly increasing the melt flow rate. The optimal compositions are identified as LDPE:EVA:PW ratios of 50:20:30, 50:30:20, 40:40:20 and 40:40:20 vol.%. All compositions were successfully printed, debound, and sintered, producing parts with a relative density exceeding 94%. The tensile properties achieve an ultimate tensile strength of 456 ± 21 MPa, a yield strength of 156 ± 3 MPa, and an elongation of 38.9 ± 4%. However, adjusting the LDPE and EVA contents within the range of 20–40 vol.% in the binders insignificantly affects the mechanical properties of the filament and as-sintered parts. Furthermore, a boundary for assessing the printability of 316L-loaded filaments is proposed based on the relationship between flexibility, buckling resistance and stiffness.