Flashing light curing strategy for shape fidelity improvement in photopolymerization-based ceramic additive manufacturing

Abstract

We proposed a flashing mechanism as an alternative to continuous illumination to counter scattering-induced overcuring in photopolymerization-based ceramic additive manufacturing (AM). Unlike the conventional continuous illumination method, the flashing technique exposes the ceramic slurry to multiple flashes of ultraviolet (UV) light in stages. The duration of the flash determines the radical formation in the UV-exposed region and their degree of diffusion in the unexposed area due to scattering. Off-times between consecutive flashes ensure the complete radical utilization, reaction termination, and the formation of a prepolymerized layer with reduced scattering efficiency. The study investigates the effects of flash duration and off-time on slurry curability and overcuring for zirconia (ZrO₂), titania (TiO₂), and alumina (Al₂O₃), at various solid loadings and compared with continuous illumination. Furthermore, the degree of conversion (DoC) was calculated and compared for both illumination methods. Lattice structures printed using both methods were subjected to debinding and sintering for densification, followed by an evaluation of their material properties. The results demonstrate that the flashing effectively controls scattering-induced overcuring with shorter flash durations and longer off-times, enhancing the printing accuracy. Although, flashing irradiation led to slightly low monomer conversion, which affected the interlayer strength in green bodies, the final sintered structures exhibited comparable density and mechanical properties to those printed continuously. These findings suggest that the flashing technique is a viable alternative to continuous AM to achieve high-shape fidelity by mitigating scattering effects in photopolymerization-based ceramic AM without compromising material properties.