Ceramic Stereolithography - Layer-By-Layer Fabrication

TA&T has adapted the commercial stereolithography process to make precise and intricate ceramics. Stereolithography was commercialized in the late 1980's by 3D Systems, Inc. and is primarily used for rapid prototyping (automated freeform fabrication) of plastic, three-dimensional (3D) parts automatically from a CAD file. In stereolithography, parts are built on a build platform situated in a vat of liquid photocurable resin. A UV-laser scans on the resin surface to selectively solidify the liquid by photopolymerization. 3D parts are built layer-by-layer with the laser solidifying each layer and bonding it to the previous one.

Thermal Processing and Material Options

TA&T has adapted the stereolithography process to fabricate high performance, net shape ceramic components by replacing the conventional epoxy-based resin with a ceramic-based resin consisting of fine, sinterable ceramic powder dispersed in a liquid photocurable resin. The stereolithography machine builds green-state ceramic parts to the desired shape. The green parts are then subjected to conventional ceramic binder burnout and firing steps to: 1) burnout the photocurable resin that serves as a binder for the ceramic particles; and 2) sinter the ceramic to high density. During sintering, the body shrinks in a predictable manner based on the difference between the green density and its final sintered density. The table below lists the ceramics materials that we use to make parts by stereolithography. In addition to these ceramics, we also have experience working with metal materials including silver for electronic conductor patterns and stainless steel.

Resolution and Accuracy

Minimum feature size is dependent on the beam diameter of stereolithography laser and to some extent on the scattering properties of the ceramic particles in the resin. Currently TA&T is using a laser system that provides a spot size of 100 microns (dia.) and minimum feature sizes in the plane parallel to the layers (X/Y) are 100 - 200 microns depending the ceramic material. In the plane perpendicular to the layers (Z), minimum feature size is determined by the layer thickness and control of laser cure depth. Minimum Z feature size ranges from 10 - 50 microns depending on the nature of the feature and the surrounding geometry. Aspect Ratio: Because of the layer-by-layer fabrication process and the minimal forces applied to features during fabrication, high aspect ratios can be achieved. To date, thin walls (150microns wide) have been built with aspect ratios of 20.

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