Laser-based additive manufacturing of aqueous suspensions for fabricating large and dense ceramic components
HOMA J. 1, MUEHLER T. 2, ZIEGER Y. 1, MOHAMMADI M. 1, SCHWENTENWEIN M. 1
1 Lithoz GmbH, Vienna, Austria; 2 QEP3D GmbH, Stahnsdorf, Germany
Additive manufacturing (AM) technologies that can produce dense and strong parts from advanced ceramics are steadily gaining importance for a wide variety of applications. However, three challenges for an even more widespread use of these ceramics AM techniques are 1) relatively long post-processing times (especially debinding), 2) limitations to relatively small geometries, and 3) limited solutions for dark, non-oxide ultrahigh temperature ceramics (UHTCs) or refractory materials.
This contribution will focus on a recently industrialized AM approach, that addresses these challenges in ceramics AM. This method is called laser-induced slip casting (LIS) and it is based on the use of an aqueous slurry that allows printing and subsequent sintering of large and bulky components to full density and with mechanical properties on par with the ones established from conventional manufacturing processes. LIS is a so-called top-down process, so the building platform moves downwards the z-axis during printing. New suspension is coated on top of the building platform or the previously formed layers by means of a doctor blade. Via infrared light exposure through a laser, thermal energy is generated that partially dries the suspension and consolidates the structure with a high green density and low binder content (<3wt%). This approach makes the LIS method independent of the color or light absorption of the ceramic powders, allowing dark materials such as carbides and other UHTCs to be processed. By repeating this process layer-by-layer a three-dimensional green part is obtained. As a consequence of the low binder content in the green part, subsequent debinding is very straightforward and the combined debind and sintering times are typically <24hours. Using this protocol even for bulky objects with wall thicknesses >20 mm defect-free parts with relative densities of approximately 99 % can be obtained.
This contribution focuses on the application of LIS to alumina as well as solid-state sintered silicon carbide and presents the achieved materials strength, microstructure, and precision. It could be demonstrated that the resulting material properties are on one level with conventional forming methods such as slip-casting or pressing, making this technology interesting for prototyping or manufacturing of large ceramic components.