Material extrusion additive manufacturing of AISI 316L pastes

Material extrusion (MEX) processes that employ metal-polymer composites to 3D print "green"parts offer an economical and user-friendly alternative to melt-based additive manufacturing. Leveraging existing powder metallurgy knowledge permits the fabrication of functional parts with predictable microstructures and properties. However, the large fractions of binder, typically 45 to 55 vol%, introduce the need for specialized debinding procedures that significantly prolong the total manufacturing time, limit geometrical capabilities, and negatively affect mechanical properties if not adequately removed. To address these limitations, this paper presents a MEX framework that involves (1) synthesis of a 316L stainless steel paste with just 3.2 vol% binder, (2) design and implementation of a synchronized two-stage extrusion mechanism, (3) an experimentally-driven approach to evaluate the effects of MEX parameters on extrudate morphology, density, and surface roughness, (4) multi-objective optimization, and (5) evaluation of thermal post-processing strategies. The as-printed samples displayed densities of 4.67 g/cm3 and 21.54 mu m areal surface roughness. The framework permitted the fabrication of increasingly complex geometries and sintered densities measuring 91.8-97.9%TD after just 22 h of thermal post-processing (including approx. ten hours of cooling time in the furnace).