Laser-Assisted Machining Will Make Ceramic Parts Less Costly

The technique could be especially critical for certain kinds of ceramic components that are not produced in large enough quantities to justify the expense of designing costly molds called dies. Components made in small lot sizes might be produced far more economically by machining instead of being formed with dies. But there has been no practical way to machine the brittle ceramic materials economically with the high precision needed for many components.

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The new technique, which could be in commercial use within a year, was developed by Yung C. Shin, a professor of mechanical engineering at Purdue University.

"I think we are past the experimental stage," Shin says. "We are hoping to reduce current manufacturing costs at least by 50 percent."

A paper about the work will appear in the April issue of the industry trade publication, Abrasives Magazine.

As the ceramic part is being machined, the laser heats the material to more than 1,000 degrees centigrade, or about 1,800 Fahrenheit, making it softer and more ductile. But the position and strength of the laser must be controlled precisely so that it heats only a tiny portion of material just before it is machined. The soft, red-hot ceramic is then removed with a cutting tool made out of an ultra-hard, diamond-like material called cubic boronitride, Shin says.

"We heat a very small, shallow layer of the surface, and then we remove it immediately so that the interior is not damaged by heat," Shin says.

Advanced ceramics are used in a wide range of applications, from engine parts to electronics, chemical processing to artificial human joints; the materials are exceptionally hard, can withstand high temperatures and do not wear out as quickly as metals.

The estimated world market for advanced ceramics this year is $25 billion, which represents a growth of almost 50 percent from the 1994 market of $16.7 billion, according to The Freedonia Group Inc., a forecasting company based in Cleveland. In the United States alone, the market for ceramic components is expected to be $10.9 billion by 2003, compared with about $7.4 billion in 1998, according to The Business Communications Co. in Norwalk, Conn.

Growth in some applications for advanced ceramics has been tempered by a major obstacle; the high cost of machining ceramic parts. With conventional methods, using diamond tools to grind ceramics is extremely expensive, sometimes amounting to more than 75 percent of the total cost of making a part.

"Right now that's the biggest problem." Shin says. "One of the advantages of this technique is that you might be able to produce complex geometry in one single cut. Currently, when people do diamond grinding, they have to go through multiple stations to get the geometry they need.

"Each diamond-grinding machine costs about $1 million. It's not unusual to need seven or eight of those machines to make one part. If we can machine this part using a single laser-assisted machining system that will cost less than half a million dollars, then that's a significant saving."

Ongoing research by Shin's team will include efforts to understand the details of how ceramics deform while being subjected to high heat, an important factor in future advances.

"We are trying to understand what we call the thermo-mechanical behavior of ceramics, and it's a very challenging issue," Shin says.