When faced with an especially complex design challenge, the benefits of using ceramics should be considered. Modern technical ceramics offer unique material properties and features, compared to metals and plastics. Ceramics typically offer high hardness, good wear resistance, high compressive strength, as well as minimal susceptibility to extreme chemistry.
Some ceramics, such as a chemical vapor deposition (CVD)-produced silicon carbide, exhibit high thermal conductivity, along with electrical conductivity, which allows for EDM machining. In contrast, aluminum nitride also has high thermal conductivity but acts as an electrical insulator.
When developing an application for ceramics, working with material experts early in the design process to understand these properties is critical. Insaco’s Designer’s Guide (www.insaco.com/designers_guide) is a resource for designers to explore the properties of common ceramics.
Technical ceramic challenges
Technical ceramics, such as alumina or zirconia can be produced by pressing powders and firing to create a “green fired” ceramic. This “green fired” material is quite soft, so adding holes, flats, or other features is quite simple and cost-effective using single point
The next step is sintering. This process causes the part to shrink, making it difficult to hold high accuracy tolerances or sizes. If high precision is required, machining must be done after the material has been fully fired. This is typically tolerance- and feature-driven and can add considerably to the cost.
Fully-fired technical ceramics are machined by grinding with tools or wheels that have diamonds embedded into a matrix of metal or glass. Grinding is a time-consuming process, but tight tolerances are possible. Surface finish improvements and polished surfaces can be achieved by using diamond suspended in a liquid (slurry).
Aerospace, defense applications
Aerospace and defense applications can have severe environments. These environments push the envelope of what most materials can withstand. Sapphire and ceramics are often considered where high-temperature strength, wear resistance, and inertness are required. For example, sapphire can be polished to a transparent condition for use in such products as windows, shields, and lenses.
Insaco has been working with these materials for more than 70 years. Our experience suggests that these materials are selected because of need, given the design considerations. While we recommend alternative materials be considered, a design engineer always needs to keep technical ceramics in mind. The material properties of ceramics often make them the only possible choice.