Optimizing Post Processing Techniques for Volumetric Additive Manufacturing (VAM)

Volumetric additive manufacturing (VAM) methods promise layer-less 3D structure fabrication with homogeneous material properties, however, current post-processing methods limit the quality of VAM parts due to the low crosslinking density in their green state. A systematic method of developing a post-processing protocol and characterizing the fidelity maintained throughout the entire printing and post-production process is explained here. The overlapping light patterns used to selectively cure layer-less 3D volumes in VAM leaves solidified parts suspended in the print volume and coated with uncured resin. Effective removal of this resin is critical before a final curing step to ensure the desired resolution and material properties are maintained. However, the hyper-green state of VAM parts - due to the nature of VAM’s layerless technique with no support structures and low degree of polymer crosslinking- results in a lower mechanical strength. This poses challenges by increasing the susceptibility of deformation, local damage from handling, solvent swelling, or shrinkage due to outswelling of uncured during post-cure. Thus, selecting appropriate post-processing solvents and techniques is crucial to maintaining part fidelity and mechanical integrity in VAM.

This study introduces a novel post-processing approach tailored to optimize part quality in VAM. A range of solvents with varying properties such as molecular weights, chain lengths, and volatilities were tested across multiple post-processing methods, including centrifugation and sonication on parts with different green strengths. The evaluation metrics include dimensional accuracy (overall and feature specific), solvent handleability, and potential local damage. From this analysis, an optimal solvent and processing method were identified. Additionally, the proposed post-processing strategy demonstrates applicability across other light-based 3D printing technologies, broadening material compatibility and expanding potential applications.