Light curing strategies for lithography-based additive manufacturing of customized ceramics

Lithography-based additive manufacturing (AM) is increasingly becoming the technology of choice for the small series or single unit production. At the TU Vienna a digital light processing (DLP) system was developed for the fabrication of complex technical ceramics, requiring high levels of detail and accuracy. The DLP-system used in this study creates a ceramic green part by stacking up layers of a photo-curable resin with a solid loading of around 45 vol.% zirconia. After a thermal debinding and sintering step the part turns into a dense ceramic and gains its final properties. The native resolution of the DLP process depends on the light engine's DMD (digital mirror device) chip and the optics employed. Currently it is possible to print 3D-structures with a spatial resolution down to 40 μm. A modification of the light source allows for the customization of the light curing strategy for each pixel of the exposed layers. This work presents methods to improve the geometrical accuracy as well as the structural properties of the final 3D-printed ceramic part by using the full capabilities of the light source. On the one hand, the feasibility to control the dimensional overgrowth to gain resolution below the native resolution of the light engine-a sub-pixel resolution-was evaluated. Overgrowth occurs due to light scattering and was found to be sensitive to both exposure time and exposed area. On the other hand, different light curing strategies (LCSs) and depths of cure (Cd) were used for the 3D-printing of ceramic green parts and their influence on cracks in the final ceramic was evaluated. It was concluded that softstart LCSs, as well as higher values for Cd, reduce cracks in the final ceramic. Applying these findings within the 3D-printing process may be another step toward flawless and highly accurate ceramic parts.