Talks and Poster Presentations (without Proceedings-Entry):
R. Gmeiner, M. Pfaffinger, J. Stampfl:
"Dental ceramic restorations fabricated by lithography-based additive manufacturing";
Talk: 23rd European Dental Materials Conference,
Nürnberg, Deutschland (invited);
In contrast to various conventional manufacturing technologies like milling or casting the Additive Manufacturing (AM) of high performance materials offers superior properties like significantly increased design freedom. Furthermore, the near-net-shape production reduces waste material. This is of great interest especially for advanced ceramic materials.
Regarding different AM technologies for the production of ceramics, such as Selective Laser Sintering, 3D Printing, Inkjet Printing or Fused Deposition Modeling, Stereolithography provides the highest achievable precision and surface quality. Based on the principle of Digital Light Processing (DLP) a Digital Mirror Device (DMD) dynamically generates light masks for the selective curing of highly filled photopolymers. Thus a three dimensional structure is built layer by layer. The used LED light source emits visible blue light with a wavelength of 460 nm. By using the process of photopolymerisation, a photosensitive slurry, filled with ceramic powder particles, gets cured. Hence the generated organic matrix of the composites serves as mechanical support for the embedded ceramic powder particles. In order to get dense ceramic structures after the 3D-printing step a subsequent thermal processing of the so called green part is necessary. Herein the polymer-ceramic composite is heated up to 400°C for pyrolyzing the organic components. This is the most critical process. The burn out leads to a weight loss as well as a dimensional shrinkage of the part. Consequently, to avoid the destruction, the development of a precise temperature profile depending on the portion and composition of the organic components is necessary. The residual powder particles are attracted and stabilized in their three dimensional shape only by physical interactions. At temperatures up to 1500°C, depending on the ceramic material, the powder particles are sintered together to finally obtain a fully dense ceramic part.
At the TU Wien different kind of ceramics can be processed using stereolithography. To guarantee the flaw-less production of high quality products, for each ceramic material the modification and optimization of the slurry´s organic composition, the building parameters as well as the thermal processing is of crucial importance. The fields of application for ceramic parts fabricated by AM are various, ranging from industrial (e.g. machine components, casting cores) and aerospace to biomedical (e.g. scaffolds) or dental and even design applications (see Fig. 1).
For the DLP machines at TU Wien the building platform size of 110 x 70 mm² allows the parallel production of several parts at once independent on the number or complexity of the structures. The maximum volume of one part is 110 x 70 x 80 mm³. The maximum resolution is 1920 x 1200 pixels corresponding to an absolute resolution of 25 x 25 µm² in the building plane (x and y-direction) and a layer thickness of 25 µm (z-direction) as well.
Tab. 1 shows the properties of different ceramics produced at the TU Wien using the DLP process. Regarding the measured biaxial bending strength, the achieved values for AM are in the range given in literature for conventional manufacturing technologies or even higher.
Therefore this manufacturing process shows high potential for producing high quality ceramic parts for applications with special requirements on complexity, accuracy as well as reliability. The creation of nearly unconstraint complex geometries opens new possibilities in constructing machine parts or biomimetic elements. In particular for small lot sizes or prototypes, production costs are reduced because no molds or dies are necessary. Additionally, the time and costs for post-processing of the ceramic parts are lower compared to conventional manufacturing technologies. It also rules out the risk of damaging the ceramic during post-processing.
additive manufacturing, dental restorations, ceramics, stereolithography, bioactive glasses
Electronic version of the publication:
Created from the Publication Database of the Vienna University of Technology.