In-process measurement of the resin's conversion degree in micro-stereolithography using near-critical-angle reflection

Abstract

Micro-stereolithography is one of the most powerful manufacturing techniques to produce micro sized three-dimensional structure layer by layer. Its mechanism is essentially based on the curing (solidification) feature of photosensitive resin - resin in liquid state convert to the solid state under the irradiation in the specific wavelength range. In order to ensure each layer in fabrication is in enough curing degree and cured in the correct shape, the in-process measurement on distribution of resin′s curing degree is strongly required. In our investigation, a measurement method that detects the refractive index variation of resin using near-critical-angle reflection has been raised to achieve the in-process measurement in micro-stereolithography. Since the relation between refractive index and the curing degree of resin that is has been experimentally measured, the distribution of resin′s curing degree in fabrication process can be obtained once the refractive index variation is in-process measured by proposed method. This measurement method has been proved both theoretically and experimentally. The formation process of a single layer of cured resin in stereolithography has been successfully recorded.