Additive manufacturing techniques for ultraviolet (UV) curable silicones are investigated using a high-pressure extrusion apparatus. Manufacturing challenges encountered include the silicone slumping under its own weight, electrostatic repulsion between the printed part and the extrudate, clogging due to in-nozzle UV curing, and nozzle material accumulation. One of the silicones tested significantly slumped under its own weight and had a height decrease of 25% over 60 s if not in situ cured. Repulsion effects were observed due to tribocharging of the silicone and the UV curing process. Carbon black (CB) was added to the silicone to minimize repulsion effects, alleviate in-nozzle curing, and nozzle material accumulation. Durometer and tensile testing were used to compare mechanical properties of the silicone under different CB loading conditions. Higher loadings of CB abated repulsion effects and also significantly reduced the durometer and 100% secant modulus of elasticity of ASTM D638 Type 1 dogbone printed parts due to inhibition of UV curing depth. Postoven curing of samples increased the durometer and modulus of all samples tested. It was found that 0.15 wt% CB was optimal to reduce repulsion effects and to maintain durometer and secant modulus within −2.6% and −1.3% of bulk cast properties, respectively.
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