- THE MAGAZINE
The design and development of advanced ceramics for high-performance applications, such as those in medical or aerospace, is one of the most challenging tasks of modern engineering. The widespread use of ceramics, however, depends on the availability of industrial processing routes to fabricate parts that often have extremely complex geometries. Owing to the difficulty of conventional ceramic manufacturing methods to produce complex-shaped ceramic parts with the desired microstructures and properties, novel processing techniques, such as solid free form (SFF) and ceramic 3-D printing based on laser stereolithography, are becoming increasingly important.
Dimensional DefinitionThe development of ceramic 3-D printing methods has been mainly motivated by the need for shaping methods capable of producing functional yet complex ceramic parts with precise dimensional definition and without using tooling or costly secondary machining. Stereolithography involves laser polymerization of a curable system consisting of a suspension of ceramic particles in a photopolymer. Using computer-assisted design (CAD) information without breaking the digital design chain, the components are manufactured in successive layers with a laser that polymerizes a paste made of photosensitive resins and ceramic powders.
The preparation of this paste is a key component of the stereolithography process; it requires a suspension of ceramic particles (mean grain size of about 1 µm) in a UV-reactive organic system with a high powder loading. The paste must also maintain a suitable rheology for the spreading of thin layers (down to 10 µm) and a sufficient reactivity to UV for polymerization.
The paste is introduced in a piston, which delivers a controlled quantity onto the working area. A thin layer of suspension with a thickness varying from 10-200 µm, depending on the UV reactivity of the system and the desired dimensional resolution, is deposited by means of a specific device. Using CAD information, the laser beam radiation is focused on the top surface of the deposited paste and deflected by galvanometric mirrors to harden the cross-sectional pattern and bond with the underlying previous layer.
The elevator table is then moved down a layer thickness, and a subsequent layer is deposited to reiterate the UV curing process. This procedure is repeated until the part is built. About 95% of the curing process can be carried out in the stereolithography equipment. The cured part is removed, rinsed clean of excess uncured resin, and then heat treated in debinding and sintering cycles to eliminate the cured resin and sinter the ceramic to near theoretical densities.
After 3-D printing, the resulting ceramic parts do not require expensive secondary operations, like machining, to suit the intended applications. They exhibit the same properties as parts made by conventional die pressing or ceramic injection molding. No tooling or mold is necessary, so the manufacturing lead times are short. After short development periods, manufacturers are able to test and use a ceramic solution at lower costs.
This technology is increasingly used for both rapid prototyping and volume production of final parts. Its aim is not to replace standard parts made by extrusion, dry pressing or ceramic injection molding (CIM), but to rapidly make extremely complex shapes, in prototype quantity or medium-sized lots, up to several thousand units per run. The process is also able to produce components consisting of different materials (e.g., metal and ceramic). Ceramic 3-D printing also expands the functionality of components.
Application OpportunitiesAvailable materials include high-grade alumina, zirconias of different colors, aluminum nitride, hydroxyapatite (HAP), tri-calcium phosphates (TCP) and manufacturers' own powders (these must undergo a process development period to accommodate the properties of individual powders). 3-D printing can be applied to ceramics in multiple potential applications. In microelectronics, for example, 3-D printing can be used in the development of microwave devices (e.g., filters, resonators) with high dimensional resolution and pattern density. Another example is parts for the luxury industry, such as watches and jewelry.
Biomedical applications are proving to be particularly exciting. Hydroxyapatite ceramic implants enable the replacement of the large osseous defects of the skull dome and the jawbone area. The method is also used in reconstructive surgery for patients who carry, or are likely to carry, a loss of cranio-facial osseous substance after a surgery. As an alternative to osseous grafts that often must come from the patient, ceramic implants prevent additional surgery, costs and pain.
In biomedical applications, 3-D printing makes it possible to control the location, distribution and geometry of the ceramic substitutes pores, unlike implants that are made porous by adding organic foam or porogens. The porosity is structured in three dimensions, and the diameter of the fully interconnected pores is constant.
These unique features promote osteointegration and increase the substitute mechanical strength. Compressive mechanical strength is between three to five times higher than that of conventional porous structures. This production process can therefore significantly reduce the risk of post-operation inflammation caused by micro-debris that breaks when handling and positioning the implant.
Rapid PrototypingIt is well known that ceramics offer a variety of desirable mechanical, magnetic, thermal, chemical and electrical properties. These properties translate into qualities that fit the requirements of various industries, including telecommunications, electronics and aerospace, as well as research laboratories and manufacturers of video projection equipment, etc.
When 3-D printing technology is used for rapid prototyping, it is possible to produce nearly any shape-simple or complex-that has been developed by the ceramic manufacturer; only a CAD component file is necessary. The intrinsic quality of the prototype is the same as that of the products made from conventional high-volume production processes. The process has been industrialized, and production runs in excess of 10,000 units per year are cost effective.
For more information, contact 3DCeram USA/Euro Industries at 3578 Hartsel Dr., Unit E 356, Colorado Springs, CO 80920; call (719)264-6111; fax (719)264-6333; email email@example.com; or visit www.3dceram.com.