Simulated inter-filament fusion in embedded 3D printing

Published

November 15, 2024

Author(s)

Leanne Friedrich, Ross Gunther

Abstract

In embedded 3D printing (EMB3D), a nozzle extrudes continuous filaments inside of a viscoelastic support bath. Compared to other extrusion processes, EMB3D enables softer structures and print paths that conform better to the shape of the part. However, strategies for high-quality dimensional accuracy and mechanical properties remain undocumented in EMB3D. This work uses computational fluid dynamics simulations in OpenFOAM to probe the underlying physics behind two processes: deformation of the printed part due to nearby nozzle motion and fusion between neighboring filaments during printing. By simulating different rheological models, we disentangle yielding from viscous dissipation, and we isolate interfacial tension effects from rheology effects, which are difficult to separate in experiments. Critically, these simulations find that disturbance and fusion are controlled by the flow of the support bath around the nozzle, and shape defects are most prominent when viscous dissipation dominates the system. Because the support fluid transmits stress from the nozzle to the existing part, the nozzle must remain far from existing parts during non-printing moves, moreso when traveling next to the part than above the part and especially when the interfacial tension between the ink and support is non-zero. Moreover, because support can become trapped between filaments at zero interfacial tension, the spacing between filaments must be tight enough to produce over-printing, or printing too much material for the designed space. Spacings for vertical walls must be even tighter than spacings for horizontal planes. At these spacings, printing a new filament creates shape defects in the old filament. While ink-support combinations at non-zero interfacial tension have better inter-filament fusion, they also produce shape defects. Slicing algorithms that consider these unique EMB3D defects are needed to improve mechanical properties and dimensional accuracy of fabricated parts.

Citation

Biofabrication

Volume

17

Issue

1

Pub Type

Journals

Download Paper

https://doi.org/10.1088/1758-5090/ad8fd5

Local Download

Keywords

3D-printing, extrusion, support-bath, Herschel Bulkley, rheology, capillarity

Citation

Friedrich, L. and Gunther, R. (2024), Simulated inter-filament fusion in embedded 3D printing, Biofabrication, [online], https://doi.org/10.1088/1758-5090/ad8fd5, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957157 (Accessed March 1, 2025)