Tilting separation analysis of bottom-up mask projection stereolithography based on cohesive zone model

Compared with top-down stereolithography, bottom-up mask projection stereolithography can reduce the start filling volume of vat and is able to build components with high-viscosity materials. For general photosensitive materials, a separation process is required to detach the cured layer from the resin vat surface in order to accomplish the fabrication of current layer. The separation process can be achieved without damaging the part by utilizing appropriate platform motions including pulling-up, tilting and shearing, and covering inert film on the vat surface. The tilting separation is used in both industrial and academic area. However, there is a limited corresponding study compared with pulling-up separation. The mechanism of tilting separation and its effects on separation force and fabrication process are not clear. In this paper, an analytical model based on cohesive zone model was formed and a specialized experimental system was built. Experimental studies on the tilting effects on cohesive stiffness and fracture energy were conducted by collecting and analyzing separation force data. The results showed that changing exposure area function or the part fabrication orientation changed the cohesive stiffness, and increasing tilting separation velocity caused different increase in fracture energy when using different inert films. The results of this investigation can be used to choose the reasonable platform motion and process parameters by considering the part geometry and the characteristics of both inert film and materials.