Study of the Effect of Air-diffusion-channel on Separation Force in Constrained Surface Stereolithography

Although constrained surface vat photopolymerization possesses fast printing speed and unrestricted building height compared to free surface stereolithography, it usually suffers from large separation forces required to detach cured parts from constrained window. To reduce the separation forces, introducing oxygen inhibition layer has recently proven to be an efficient method. Apart from conventional constrained surface vat photopolymerization, a thin layer where polymerization is inhibited continuously exists during fabrication process, hence avoiding the formation of vacuum between cured parts and vat surfaces. As a result, continuous fabrication that otherwise is challenging can be achieved. However, current methods are still not favorable to maintain oxygen inhibition layer for sufficient fabrication time. Recently, air-diffusion-channel constrained surface has been proposed for improving the stability of oxygen inhibition. Specifically, a thin layer of polydimethylsiloxane is added to the porous acrylic surface, thereby continuous oxygen supply is obtained owing to high oxygen permeability through PDMS. To better understand the mechanics behind this method and further improve its capability, simulations of the separation force and oxygen inhibition are conducted using COMSOL, a finite element analysis software. Simulation results indicate that oxygen plays an important role on separation force and there is a relationship between channel area ratio and effective printing time. Specifically, oxygen inhibition mechanics, polymerization process and oxygen diffusion through the constrained surface are comprehensively considered for an optimal structure of constrained surfaces.