For most people, ceramics are hard, fragile materials primarily associated with tiles, bricks and pottery. These functional and largely clay-based materials are the most common ceramics in everyday use. More specialized technical ceramics used in extreme environments and demanding applications are less common, but have properties that make them unique. A small percentage of these technical ceramics are categorized as having the rarer ability to be machined.

Machinable is a term used to describe ceramic materials that can be machined with conventional metalworking machines after sintering. That is, they can be turned, milled, drilled and sawed without the need for diamond tools. The vast majority of technical ceramics are non-machinable and can only be machined with diamond tools after sintering because the material is almost as hard as diamond. Machinable ceramics balance this loss with a range of other benefits at the expense of the superpower of hardness.

Machinable ceramics tend to be manufactured in large blocks (also known as billets) for consistency and ease of fabrication. The more technically complex of these machinable materials control their structure through hot pressing (also known as HIPing). The hot pressing process is not cheap, but it gives engineers the consistency they so appreciate. Pressing materials at high temperatures restricts the crystal growth of the material and prevents the formation of large crystals, leaving a fine structure. Fine particles can be pulled from the surface of the material by carbide tools, leaving a smooth surface during the process.

In most cases, the dimensions of the blanks for machinable ceramics are significantly larger than the typical dimensions of ceramic blocks for sintered non-machinable technologies.

Non-machinable ceramics achieve their hardness by densification during sintering and by shrinking in size in the furnace. The larger the part, the more it has to shrink, and this shrinkage is not completely controllable. These ceramics are manufactured to estimated dimensions and any tight tolerances require diamond grinding after sintering.

For machinable ceramics, shrinkage and associated shrinkage tolerances are not an issue because the parts are machined from already sintered blanks to their final dimensions. The machining process can be time consuming. However, in small quantities, it is usually more economical and less time-consuming than manufacturing non-machinable ceramics, especially if diamond grinding to final size is required.

Hot pressing is not the only way to obtain workable ceramics. A machinable glass-ceramic was developed in the formulation of a material designed to mimic the natural properties of mica. The material, known as Macor, quickly gained favor in NASA's space shuttle program, where large pieces were machined to precise dimensions to help insulate the cabin from the alternating heat and cold to which the orbiting spacecraft was subjected.

Machinable ceramics cover a range of materials. macor, the machinable glass-ceramic highlighted above, and Shapal Hi-M Soft, a machinable aluminum nitride. But there are also a variety of boron nitride grades and natural materials, such as mica and lava, each of which offers unique and often quick solutions to challenges that may be difficult to solve.

You may not realize it, but machining precision ceramics has become a challenge because of their ultra-high hardness. In order to consistently produce high-quality ceramic parts at a reasonable cost, you must have the right machining tools, in-depth knowledge of the material, and the right design of the ceramic structure.

To Good Ceramics has many years of experience in developing high quality precision ceramic parts. We utilize our experienced team and in-depth knowledge of ceramic materials to create the best precision ceramic products for our customers at competitive prices.