Introduction to subpressure-driven soft deformation method for removing inherent voids in green components manufactured by material extrusion.

This study introduces a post-treatment process, the subpressure-driven soft deformation method, to reduce inherent voids in Material Extrusion (MEX) components. By subjecting printed green components to heat treatment under subpressure, the process enhances viscosity, effectively filling voids formed between deposited tracks. The average porosities of the samples sintered from the green components without and with soft deformation are calculated to be 3.55% and 2.36%, respectively. A comparison of the tensile strengths and fracture surfaces of the sintered samples with and without soft deformation treatment indicated that the sintered samples with soft deformation treatment exhibited narrower standard deviation for the various mechanical properties. Capillary rheometer calculations indicate feedstock viscosity to be between 450.34 and 1018.31 Pa s under subpressure, diminishing inter-track voids without sizeable dimensional changes. Molecular dynamics simulation demonstrates a 3.7-fold increase in bond strength, indicating intertrack voids effectively eliminated. Reduced inter-particle distances facilitate necking, grain growth, and improved sintered density.

Study of solid loading of feedstock using trimodal iron powders for extrusion based additive manufacturing.

Volume loading of feedstock using trimodal iron (Fe) powders was investigated for the application of extrusion-based additive manufacturing (AM). Fe trimodal powder composed of nano, sub-nano, and micro particles was manufactured via the powder metallurgy process where small particles behave as rolling bearings among large particles, and thereby improving the flow characteristics of feedstock by minimizing friction among the particles. The flow behavior and microstructures of the monomodal feedstock were compared with those of the trimodal feedstock. We have confirmed that the critical powder loading of monomodal powder was measured to be 70 vol.% while trimodal powder showed up to 74 vol.%. Furthermore, trimodal feedstocks of 60, 65, 70, 75, and 80 vol.% Fe powder were prepared to determine the optimal powder content for sintering. As a result, the feedstock with powder content of 70 vol.% gave the highest sintered density of 92.32%, the highest Vickers hardness of 80.67 HV, with the smallest dimensional variation in shrinkage, proposing 70 vol.% of trimodal feedstock to be the suitable powder content for AM. Finally, its microstructural and mechanical comparison with 70 vol.% sintered part using monomodal Fe powder, showed that the sintered part using trimodal feedstock displayed higher hardness, uniform shrinkage as well as smaller grain size, confirming trimodal feedstock to be favorable for the application of extrusion-based AM.