| Mask projection Stereolithography technology is a rapid prototyping technology by mask imaging with ultraviolet, which developed on the basis of Stereo lithography Appearance(SLA, now stand for laser scanning curing usually). Compared with SLA, it not only has a lower equipment cost, faster speed, and better surface quality of formed parts, so Mask projection Stereolithography has became an important develop direction of stereolithography technology. The research work at domestic and abroad mainly focused on the small deflection of aspects generated during free-surface curing process, but relatively few studies on the behavior of the resin in constrain-surface system. With the development of resin materials, wax-containing resin has occurred, the form parts can directly applied to lost wax casting field, the shrinkage mechanism of this new type during curing process is also not clear. Therefore, the device structure, process control and optimization, different kinds of resin form mechanism in Mask projection Stereolithography have yet to be depth research. In view of the above problems, this paper mainly study the system equipment and shrinkage deformation in Mask projection Stereolithography with wax-containing resin.The forming principle and process characteristics of the constraint surface Mask projection Stereolithography were introduced, a machine based on DLP(Digital Light Procession) technology was designed. Exposure time is an important process parameter,the experiment of cured thickness in free surface was carried out, and the effect of exposure time to thin wall、recess and cantilever deformation was researched. Stress distributions of forming part in constrain-surface were studied, in order to reduce the adhesion between curing layer and resin bath, the relationship of curing layer and silicone film thickness was tested, it showed the optimum thickness is about 2mm.This paper discussed the requirement of photo initiator concentration in waxcontaining resin. Through experiments on the basic performance of the wax-containing resin, It showed that the light absorption rate is lower, the wax powders particle sizes concentrate 80-100μm. The melting point of the paraffin wax is generally 55-65 ℃, if the temperature is too high, wax melting will increase the viscosity of the resin, and the flow property becomes worse, which will affect the quality of the formed parts. This system used partial 405 nm UV LED cold light source, while controlling the light power, the maximum temperature of curing layer could be controlled within 50 ℃.The factors affect forming parts in Mask projection Stereolithography were classified, they were the error caused by data processing, generated during exposure forming and post-processing after the parts were formed. Each influencing factors were discussed in detail, compared the shrinkage behavior of normal resin and waxcontaining resin in the curing and post-processing combined with experiments, there were quite differences.The mechanism of shrinkage deformation was analyzed, the relationships between stress and strain and thermal stress of curing layer were obtained by mathematical deduction. Designed the corresponding three-dimensional models to studied typical deformation in curing process, determined the warp distortion affected by the length of the cantilever and the exposure time, and H4 standard model was tested to analyzed deformation on both ends of the support legs caused by shrinkage of cantilever structure. Provided a reference when adding support and determining suitable parameters for curing complex models. |
