A strategy to eliminate interbead defects and improve dimensional accuracy in material extrusion 3D printing of highly filled polymer

Material extrusion 3D printing (MEX) of highly filled polymer has been demonstrated capable of prototyping or fabricating metallic parts with complex shapes. However, interlayer rhomboid voids produced during the production run directly impact the density of parts, while the widely used over-extrusion strategy negatively affects their overall dimensions. Using a high solid loading powder-binder feedstock, an overlapping strategy was proposed to fabricate full density and dimensional accurate green parts. Stainless steel powder was mixed with a wax-based binder to formulate a feedstock that was used to 3D print hollow square prisms with different overlapping ratios and layer heights. The influence of these printing parameters was quantified by Archimedes density, size/shape of interlayer voids, and CMM dimensional deviations. The results showed that the layer height had no influence on the defect size when an overlap is used; an overlap as low as 5 % already reduced the defects traditionally minimized by a smaller layer height. An overlap ratio ranging from 15 % to 20 % both eliminated the interlayer rhomboid voids and minimized dimensional deviations of parts fabricated by MEX. High overlapping (i.e., > 25 %) promoted the formation of macroscopic defects which decreased the part quality.