Extrusion-based polymer 3D printing induces shear strains within the material, influencing its rheological and mechanical properties. In materials like polyvinylidene difluoride (PVDF), these strains stretch polymer chains, leading to increased crystallinity and improved piezoelectric properties. This study demonstrates a 400% enhancement in the piezoelectric property of extrusion-printed PVDF by introducing additional shear strains during the printing process. The continuous torsional shear strains, imposed via a rotating extrusion nozzle, results in additional crystalline β-phases, directly impacting the piezoelectric behavior of the printed parts. The effect of the nozzle’s rotational speed on the amount of β-phase formation is characterized using FTIR. This research introduces a new direction in the development of polymer and composite 3D printing, where in-process shear strains are used to control the alignment of polymer chains and/or in-fill phases and the overall properties of printed parts.

Material extrusion-based polymer 3D printing, one of the most commonly used additive manufacturing processes for thermoplastics and composites, has drawn extensive attention due to its capability and cost effectiveness. However, the low surface finish quality of the printed parts remains a drawback due to the nature of stacking successive layers along one direction and the nature of rastering of the extruded tracks of material. In this work, an in-process thermal radiation-assisted, surface reflow method is demonstrated that significantly improves the surface finish of the sidewalls of printed parts. It is observed that the surface finish of the printed part is drastically improved for both flat and curved surfaces. The effect of surface reflow on roughness reduction was characterized using optical profilometry and scanning electron microscopy (SEM), while the local heated spot temperature was quantified using a thermal camera.

This work examines how feedstock composition and process settings influence the performance of Al-6061 parts made through material extrusion (MEX). A feedstock with 57 vol% (78 wt%) solids loading was selected based on torque rheometry, showing stable flow and shear-thinning behavior with a measured viscosity of 710.9 ± 3.2 Pa·s. Filaments produced from this material had a consistent diameter of 1.74 ± 0.0064 mm and were used to print specimens at extrusion multipliers of 0.9, 0.95, and 1.0. Debinding and sintering procedures, guided by thermal analysis, resulted in a peak density over 97% of the theoretical value. Among the conditions tested, the 0.95 extrusion multiplier produced the most favorable mechanical properties, with an ultimate tensile strength of 153.5 ± 3 MPa, a yield strength of 68.2 ± 11.7 MPa, and elongation reaching 28 ± 3%, which aligns with values reported for annealed Al-6061. Fractographic analysis showed a ductile fracture mode, confirming good interlayer adhesion and consistent sintering. These results show that MEX is a reliable method for fabricating Al-6061 parts with complex geometries and stable mechanical performance.