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G. Mitteramskogler, R. Gmeiner, R. Felzmann, C. Hofstetter, S. Gruber, J. Stampfl, Ebert, W. Wachter, J. Laubersheimer:
"Light curing strategies for lithography-based additive manufacturing of customized ceramics";
Additive Manufacturing, 1 (2014), 1; 110 - 118.

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 m. 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.

Additive manufacturing; Ceramic; Zirconia; Photopolymerization; Digital light processing

http://dx.doi.org/10.1016/j.addma.2014.08.003