Ceramic Machining: An Overview
Ceramic machining is not new. The first ceramic machinists can be traced back to the stone age. When the first pre-historic man picked up a rock and decided to change its shape by banging it against another rock, he was setting the stage for a technology that would become today's ceramic machining. The text-book definition of ceramics is the manufacture of any product made essentially from a nonmetallic mineral by firing at high temperatures. Chances are that the rocks our ancestors pounded on were actually ceramics.
Thanks to modern technology, today's methods of ceramic machining are somewhat less primitive. With the advent of diamond grinding wheels came the ability to efficiently grind the new ceramic materials as they appear in our present state of technology. For all practical purposes, the ceramic machining that takes place today is grinding with a tubular shaped diamond wheel. Ultrasonic drilling can be simplified as grinding or lapping as well.
Today's materials require a variety of diamond wheel configurations and compositions for successful grinding.
Aluminum oxide (A1203) is one of the most widely known ceramic materials. Aluminum oxide is a tough wear-resistant material that requires either a metal bond diamond wheel with high diamond concentration or a resin bond wheel for efficient grinding. The super tough silicon nitrides call for a resin bonded wheel that will break down as it grinds, therefore limiting any damage done to the material during the grinding operation. Softer materials such as Hafnium Carbide may require a wheel that is of high diamond concentration but sturdy metal bond to prevent wheel loading.
The need for ceramic machining is greater today than it has ever been. To understand why this is true, you must first examine why someone might require a ceramic part to be machined.
There are several reasons. The main reason is for flexibility of design and manufacturing. This is most useful in prototyping, where research and development designs can be tested and revised prior to any major tooling expenditures. This gives the designer/engineer a chance to exhaust any and all alternate designs and refine successful ones.
Another reason is precision. Today's injection molding is far better to anything we have known in the past, but it has its limitations. In the firing cycle, ceramics shrink a calculated percentage. During this shrinking, which is not always exact, some distortion of dimensions can also occur. Ceramic machining can carry through the prototype stage into production, if the tolerance requirement of a design warrants the precision that only machining can provide.
Many times both pressing/molding and ceramic machining will be utilized together. For example, a simple washer can be pressed out much cheaper than it can be machined, but if there is a tight flatness requirement, warping during firing may take the pieces out of specification. They can be ground to exact flatness and parallelism specifications after firing.
As tolerances and surface finish requirements continue to become more critical, the need for ceramic machining will expand. Recent developments in revolutionary new ceramic materials make possible configurations that were previously not able to be produced. Ellis Ceramtek, Inc. has developed a method of machining an actual spring from Zircoa's "Zycron" material. hese springs demonstrate some of the incredible properties now available in these materials.
When I look at the accelerated rate at which the ceramic machining technology is developing, I can't help wondering if future generations will look back on our machines and methods, as we do the caveman and his rocks.
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