Measurement and Modeling of Forces in Extrusion-Based Additive Manufacturing of Flexible Silicone Elastomer With Thin Wall Structures

Flexible thin wall silicone parts fabricated via extrusion-based additive manufacturing (AM) tend to deform due to the AM forces, limiting the maximum build height. The tangential and normal forces in AM were measured to investigate effects of three key process parameters (volumetric flow rate Q, nozzle tip inner diameter di, and layer height t) on the build height. The interaction between the nozzle tip and the extruded silicone bead is controlled to prevent interaction, flatten the top surface of the extruded silicone, or immerse the nozzle in the extruded silicone. Results show that tangential and normal forces in AM strongly depend on this interaction. Specifically, the AM forces remained low (less than 0.2 mN) if the nozzle tip did not contact the extruded silicone bead. Once the nozzle interaction with extruded silicone came into effect, the AM forces quickly grew to over 1 mN. The single wall tower configuration was developed to determine a predictive deflection resistance approach based on the measured AM forces and the resultant bending moment of inertia. This approach shows that a smaller di can produce taller towers, while a larger di is better at bridging and overhangs. These results are applied to the AM of a hollow thin wall silicone prosthetic hand.