Performance of different material extrusion 3D printing strategies in improving density and dimensional properties

Material extrusion (MEX) 3D printing has shown significant potential for rapid manufacturing of metallic components exhibiting complex geometries. However, a key challenge intrinsically Linked with this additive manufacturing process is related to the formation of rhomboid interlayer voids, which refers to Linear voids formed at the interface of four deposited beads when no defect mitigation strategy is used. In this study, three defect mitigation approaches were compared with a benchmark standard printing strategy. The performance of these approaches were quantified using density measurements, microscopic observations, and laser scan dimensional measurements. Using a typical flow multiplier at 120% (i.e., typical value reported in the literature) completely mitigated the rhomboid voids commonly observed in standard printing but produced poorer dimensional properties with dimensional deviations (∆) up to ± 500 µm than those obtained using standard printing (i.e., 0 < ∆ < 75 µm). The second approach (all beads overlapped) confirmed that by modifying the tool path, it is possible to force the bead to overlap with the previous one (optimal overlap at 20%) to eliminate rhomboid voids and produce dimensionally accurate green parts (e.g., 0 < ∆ < 50 µm). However, the nozzle obstruction produced by this strategy led to the formation of macroscopic stacking defects which were systematically visible within printed parts. Using a similar overlap value set at 20%, the green parts produced with the third mitigation approach were free of such stacking defects, in addition to having a maximum dimensional deviation below 50 µm. The printing results obtained in this research confirm that the first bead overlapped strategy is suitable for producing a dimensionally accurate part that is free both of rhomboids and stacking defects.