(125c) The Thin Film Dynamics of Iclip: A New Vat Polymerization Process

We describe the non-Newtonian fluid mechanics of a new VAT polymerization process for Advanced Manufacturing that we name “iCLIP”, for Direct Injection Continuous Liquid Interface Production^1,2. The process builds on the existing CLIP process which relies on resin renewal at the build surface through the creation of a continuous liquid interface—the dead zone—that enables resin to be drawn into the gap through suction forces created as the curing part is gradually pulled away from the window. The dead zone is created and maintained by a constant supply of oxygen—a polymerization inhibitor—that is fed through the highly oxygen-permeable window at the bottom of the resin reservoir. Since the appropriate Damkohler numbers for the process are quite large the dead zone is a thin liquid film of 50-100 microns. The resin is cured by a rapid sequence of UV images that are projected at the build surface from a digital light projection system located underneath the reservoir. The CLIP process, while already used for numerous commercial products, is limited to single resins and is too slow to compete with injection molding in many applications. Print speeds in CLIP are limited – usually through unacceptable print defects at higher speeds - by the suction or Stefan forces created by flow in the thin dead zone where photocuring takes place. We remove this limitation by injecting resin through the molded part as it is being produced. Thus, the new process is entirely dependent on understanding the thin film flow in the dead zone with injection. Successfully engineering a network of the resin injection channels or “residucts”, as well as the injection rates through them as the part is being printed, we require computer simulation of the lubrication flow connecting the physical properties of the appropriate resin (e.g. its nonNewtonian rheology), the geometry of the network, the printing speed, and, finally, the footprint of the part in the plane of UV exposure. An order of magnitude increase in print speed has already been demonstrated. Moreover, the injection of resins through residucts offers the exciting new opportunity for multi-material, VAT polymerization at high speeds and resolution, through computer simulation-driven generative design of complex residuct structures administering multiple resins simultaneously. Our most recent work includes computer modeling closely coupled to printing experiments employing the newly designed residuct networks in iCLIP.

¹Lipkowitz, G., T. Samuelsen, K. Hsiao, B. Lee, M. Dulay, I. Coates, H. Lin, W. Pan, G. Toth, L. Tate, E.S.G. Shaqfeh, J. DeSimone, Science Advances 8 (39), eabq3917 (2022)

²Lipkowitz, G., I.A. Coates, N. Krishna, E.S.G. Shaqfeh, J.M. DeSimone, “Methods for modeling and real-time visualization of CLIP and iCLIP-based 3D printing”, Giant, 17, 2024, 100239