Laser Aims to Reduce Ceramic Costs
WEST LAFAYETTE, Ind. -- Because of their exceptional hardness, resistance to wear and stability at high temperatures, advanced ceramics are becoming popular for precision parts in aerospace, automotive and manufacturing industries. They are also well-suited to medical applications such as parts for artificial joints.
However, the same properties that make precision ceramics popular also make them difficult to manufacture. Machining accounts for as much as 75 percent of the production costs. A new technique that uses a laser to soften ceramics before machining could reduce costs by half or more.
High-precision shaping of ceramic parts is generally a multistep process requiring several diamond grinding machines that cost more than $1 million each. The new technique, developed by Yung C. Shin, professor of mechanical engineering at Purdue University, combines these steps into one machining operation, with a cost of $400,000.
A laser rapidly heats a thin layer of the ceramic to 1300 to 1400 °C immediately before its removal with an ultrahard cubic boronitride tool. This softens a layer of the material to a glassy phase that the cutting tool can remove, substantially reducing the compressive forces of grinding that can cause cracks, Shin said.
A machined ceramic part first softened by a laser shows that damage extends only a few microns. The technique avoids the subsurface cracking characteristic of grinding processes.
The Purdue lab uses a 1.5-kW CO2 laser, usually at 300 to 400 W, but Shin believes that other lasers, such as an Nd:YAG, could also be used. The critical factor for precise machining is to focus the beam to a 2-mm-diameter spot. Typically, the heating depth is about 1 mm, but this can be adjusted for maximum precision. Cutting tool wear is reduced, so lathing speed can be increased by an order of magnitude and tool life is extended.
One potential drawback to the process is that it may not be applicable to all types of ceramic materials. Most of the work so far has used silicon nitride, and current experiments are establishing operating conditions for zirconia and alumina/silica ceramics.
Although commercialization plans are still in preliminary stages, Shin is working with potential partners to develop the machine. He hopes that a system capable of producing 10,000 parts per day will be available within a year.
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