Mapping 3D printed part density and filament flow characteristics in the material extrusion (MEX) process for filled and unfilled polymers

Material extrusion (MEX) 3D printing offers a promising avenue for fabricating metal and ceramic components, where highly loaded polymer filaments are 3D-printed and sintered. Achieving nearly 100% 3D-printed part density is critical in this process, as porosity during printing compromises part properties after sintering. However, challenges arise due to the unfavourable mechanical and rheological properties of MEX metal filaments, leading to slow print-speeds, filament breakage, and inconsistent extrusion. This work explores these process-property correlations by developing process maps for bound metal filaments and unfilled polymer systems. This study throws light on the significance of back-flow and back-pressure in calculating the pressure drop across the nozzle, especially in a diverse set of material systems represented by hard and stiff PLA, soft and flexible TPU, and brittle and fragile bronze filaments. Additionally, ANOVA identified the effect of print conditions on measured variables, while regression models helped predict the behaviour of a given material under different process conditions. Therefore, this study enables material design and discovery for bound-metal filaments while addressing critical knowledge gaps, thereby paving the way for high-density 3D-printed components.