I. Introduction
The essence of 3D printing technology is additive manufacturing technology. Compared with traditional large-scale subtractive manufacturing technology, 3D printing is an important technology to develop from mass manufacturing mode to personalized manufacturing mode. According to its raw materials and molding methods, 3D printing is mainly divided into the following types. Fused Deposition Modeling(FDM), Stereo Lithography Apparatus(SLA), Selective laser sintering(SLS).[1] The technology of SLA was first successfully commercialized by 3D Systems company, which produces ProJet series and iPro series 3D printing equipment using SLA technology. This technology has the characteristics of high automatization of forming process, good surface quality of making prototype, high dimensional accuracy and the realization of relatively fine forming dimension, which has become a widely used rapid prototyping technology.[2]