Master thesis : Design and Development of a Resin-Switching System for Multi-Material MSLA 3D Printing

Abstract

Multi-material fabrication through vat photopolymerisation requires the ability to switch between different photosensitive resins within a single print cycle, a capability that re- mains unavailable in commercial Masked Stereolithography Apparatus (MSLA) printers. This work addresses that gap by designing, developing, and characterising a complete resin-switching subsystem integrated into the custom-built MSLA printer of the Microsys laboratory at the University of Liège. The proposed solution adopts a single-vat architecture with dynamic fluid delivery. Peri- staltic pumps are used to fill and evacuate the resin in the vat through dedicated inlet and outlet apertures, while an isopropyl alcohol (IPA) sprinkler system, mounted directly on the vat, performs the intermediate cleaning of both the vat and the printed part be- tween successive resin changes. The mechanical system is composed of a custom resin vat, tubing layout, pinch valves, resin storage tanks, and a splash protection enclosure. The associated electronics consist of a reworked power supply board and a newly designed resin control board, which integrates motor drivers, analogue sensing circuitry, and an STM32 microcontroller. Experimental validation was conducted across three principal capabilities. The resin pumping step achieves a removal efficiency of approximately 98% for resins of viscosities up to 350 cP, provided that spontaneous film dewetting is achieved on the non Fluorinated Ethylene Propylene (nFEP) surface. The vat cleaning step, assessed by spectrometric measurement of residual contamination, demonstrates that a single 25 second IPA spray- ing cycle reduces cross-contamination to 0.65% when starting from a fully filled vat of 350 cP resin. Part cleaning, evaluated through optical microscopy and profilometer mea- surements on microfluidic test structures, shows that two consecutive 25 second spraying cycles deliver a cleaning performance comparable to that of a stand-alone four-minute ultrasonic bath. The results confirm that the system constitutes a viable proof-of-concept for autonomous multi-material MSLA printing. Several directions for future improvement are identified, including motorised vat tilting, additional inlet apertures, and the integration of film- directed cleaning nozzles to extend performance to higher-viscosity resins and deeper geometrical features.