ADDITIVE MANUFACTURING OF STAINLESS STEEL VIA FUSED DEPOSITION

摘要

Conventionally, processes for additive manufacturing of metals use laser or electron beams and open powder. This makes them expensive and potentially hazardous to health. In contrast to that, fused deposition of metals (FDMet) represents a low cost and safe alternative for fabrication of near net-shape metal structures. Figure 1 illustrates the FDMet process used in this study. 316L stainless steel powder is mixed with a thermoplastic binder into a homogeneous feedstock. The feedstock was extruded into a filament, which is used for 3D printing in off-the-shelf, low cost, fused deposition modeling 3D printers. More than 60 wt% of the thermoplastic binder is removed in a solvent debinding step, leaving behind a porous structure consisting of metal powder and the insoluble backbone polymer. In a thermal step, the backbone is removed by pyrolysis. Finally, the metal powder is sintered into dense metallic structures. Optimization of the binder composition is essential to fulfill all the requirements imposed by the different process steps: compatibility, high flexibility and strength, low viscosity, high yield strength when molten, form stability and low residue. In this study, we perform an optimization of the binder composition to maximize the printability. We show that by reducing the filament viscosity and increasing the stiffness, the wear-out of the filament by the extruder gears can be prevented. Therefore, it is possible to reduce the nozzle diameter from 800 urn to 200 urn for increased print resolution. The sintered material is characterized by electron microscopy and nanoindentation mapping. Figure 2 a) shows a thin-walled structure in the as-printed state. The indentation maps report an elastic modulus scattering around 200 GPa (Fig. 2 b)) and a hardness of 5.75 GPa (Fig. 2 c)) of the sintered sample. Pores appear as regions of lower modulus and hardness.