Feasibility study of silicone stereolithography with an optically created dead zone
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abstract
2019 Elsevier B.V. Vat photopolymerization (VP) of silicone can produce better finish and higher resolution than the conventional extrusion-based method. One challenge in the current bottom-up VP processes is the separation that forms between the cured part and vat at each layer. Oxygen-inhibition is commonly adopted as a solution (i.e. dead zone), but it is limited by the size, material, and environment. Herein, a method to optically create the dead zone by low one photon polymerization (LOPP) is investigated. LOPP is achieved by a low-absorbance wavelength and a gradient light beam. In this study, two sets of the experiments, stationary exposure and moving exposure, were conducted with two low-absorbance wavelengths (375 nm and 385 nm) for a formulated UV-curable silicone. The first experiment measured the effect of beam power; the second experiment measured the effect of scanning speed. The results show that the lower-absorbance wavelength (385 nm) generates a larger, more stable dead zone and a smaller curing spot in both experiments, while the 375 nm wavelength produces a rapidly changed dead zone in the stationary condition and nearly no dead zone in the moving condition. The curing speed of 385 nm at the same power level was 10 times slower than 375 nm, but could be scaled up non-linearly by the beam power. A tripled light power of 385 nm can accelerate the process by a factor of 7 and be comparable to that of 375 nm. Thus, this study confirms the feasibility of an optically created dead zone and also uncovers the necessity of high-power light source for this application.
