Laser-assisted machining will make
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.
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.
Source: Yung C. Shin, (765) 494-9775, firstname.lastname@example.org
Writer: Emil Venere, (765) 494-4709, email@example.com
Purdue News Service: (765) 494-2096; firstname.lastname@example.org
NOTE TO JOURNALISTS: A copy of the research paper referred to in this news release is available from Emil Venere, Purdue News Service, (765) 494-4709, email@example.com
Purdue doctoral student Frank E. Pfefferkorn adjusts a lathe used in research into laser-assisted machining of ceramic parts. (Purdue News Service Photo by David Umberger)
The surface of a ceramic cylinder is heated by a laser so that the brittle cylinder can be machined by a lathe without cracking or splintering. (Purdue Mechanical Engineering Photo by Michael Black)A publication-quality photograph is available at the News Service Web site and at the ftp site. Photo ID: Shin.Ceramic2
Its Potential and Future
Recent years have seen a substantial growth in the use of advanced materials to obtain improved properties such as high hardness, thermal stability and wear resistance, which are required to meet the stringent specifications of modern products. Such materials include ceramics, high-temperature alloys, and composites. Due to their superior mechanical properties and wear resistance, use of these advanced materials has steadily increased over the years.
Currently, advanced materials are fabricated into products by a broad range of manufacturing processes. While forming processes can produce various shapes with a high production rate, the attendant dimensional accuracy and surface finish are often lacking and a finishing operation is usually performed to achieve a high dimensional tolerance and/or a very fine surface finish. Due to the expanding use of such materials in automotive, aerospace, medical and other engineering applications, there is an increasing need for cost-effective finishing processes.
Machining processes have been most commonly used when high accuracy or flexibility is required. In addition, various shapes can be achieved on a single CNC machine, without requiring specifically tailored tools, as in forming. Therefore, when various parts are to be produced in small lot sizes, machining processes become more economical than forming processes, the costs of which are very high due to the requisite dies. However, many advanced materials are known to be very difficult to machine and in some cases are considered unmachinable by conventional techniques.
Hence, there exists a definite need for new and more efficient machining techniques, particularly for ceramics and high-temperature alloys. As more advanced materials are developed, development of pertinent cost-effective fabrication processes for precision parts becomes a more critical issue. A promising technique in machining of these difficult-to-machine materials is thermally assisted machining processes, particularly laser or plasma assisted machining processes.