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J. Stampfl, G. Mitteramskogler, S. Springer, S. Gruber, A. Ovsianikov, R. Liska:
"Lithography-based Additive Manufacturing of Cellular Ceramic and Composite Structures";
Talk: Euromat 2011, Montpellier; 09-12-2011 - 09-15-2011; in: "Euromat 2011", (2011), Paper ID B33-O21H, 1 pages.

Additive Manufacturing Technologies (AMT) allow the fabrication of three-dimensional parts with high geometric complexity. Several AMTs (e.g. selective laser sintering, 3D-Printing, stereolithography, ..) are capable of processing powder-based ceramic materials. The focus of this work is the use of lithography-based AMT for the structuring of ceramic filled photopolymers and hybrid resins..

In a first approach, a light engine based on a digital mirror device with 1920x1080 pixels is used to selectively expose photosensitive resins with blue light (460nm). By stacking up multiple layers, three dimensional parts can be built up. The utilized AMT device has been modified to facilitate the processing of filled photopolymers with high viscosity. Using this approach, it is possible to structure ceramics as well as ceramic filled polymers with a resolution of 40m. In the case of cellular geometries, pore sizes down to 200m are feasible.

One key advantage of using ceramic filled photopolymers is the high achievable solid loading (up to 55vol% ceramics) which facilitates the manufacturing of fully dense (>99.5% of the theoretical density) ceramic parts. Alumina, tricalcium phosphates and silicon nitride have been investigated regarding their processability with lithography based AMT. Cellular structures are especially appealing for the use as scaffolds in biomedical engineering. Examples of bioceramic and (filled) biopolymer structures are presented and evaluated regarding mechanical properties, biodegradability and biocompatibility.

In a second approach, photosensitive hybrid resins are structured using a femtosecond-laser (800nm) which triggers two photon polymerization (2PP). 2PP only takes place in the focal area of the laser beam. Outside the focal area the laser intensity is too low to trigger polymerization. Due to this fact, 2PP does not require a layered deposition of material, and therefore the resolution in z-direction is significantly higher than with other AMTs. Using 2PP a feature resolution down to 100nm in xy-direction and 200nm in z-direction is achievable. In order to achieve sufficiently stiff cellular structures, sol-gel-derived organic-inorganic hybrid resins are used in this approach.

Project Head Jürgen Stampfl:
Photopolymerbasierte generative Fertigungsverfahren für kundenspezifische Produkte