Nov. 10, 2004 Tools so tiny that they are difficult to see, are solving the problems of carving patterns in glass, ceramics and other brittle materials, according to a Penn State engineer.
"Even very brittle materials like glass will cut smoothly at a micron level," says Dr. Eric R. Marsh, associate professor of mechanical engineering. "The tools we are making are small enough so that the brittle materials behave like a malleable material like aluminum, producing smooth curly chips of glass or ceramic."
Normally, brittle materials come apart in large uncontrolled chunks or they simply fracture completely. The researchers are trying to control the machining process so that well-defined, accurate, microscopic patterns can be created in brittle materials.
Demands for smaller channels in glass for micro fluids, dimples to create tiny chemical reservoirs and MEMs – microelectromechanical systems, fuel the need to find quick, inexpensive ways to create these tiny devices.
Marsh; Chris J. Morgan, graduate student at University of Kentucky, and R. Ryan Vallance, assistant professor, George Washington University, begin with polycrystalline diamond on Carborundum -- a commercially available product -- to create miniature drills and end mills using microelectro discharge machining. EDM removes parts of the millimeter diamond surface by sputtering them off to fashion the tool. They use this noncontact method because the tools are tiny and fragile. The Carborundum base becomes the shaft of the drill or mill end.
The researchers describe how the tools are created and used in an online edition of the Journal of Micromechanics and Microengineering, which will be available in hard copy on Dec. 10. The engineers take advantage of the uneven surface created by diamond removal at the microscopic level and use the rough surface for cutting.
The tools spin exceptionally fast to remove material to create dimples or channels. The fast spinning, however, does not mean that the carving takes place rapidly. The tools are so small and so fragile that only very slight pressure, about as much as a paperclip exerts, sculpts the surface. It can take as long as an hour to produce one dimple a half millimeter in diameter.
Slow as that may be, the process would be faster than the current process which employs photolithography. Tiny tools can be designed and manufactured in less than a day and used to create the desired surface immediately. Photolithography requires many more steps and much longer lead-time.
While photolithography is typically only used on silicon chips or wafers, the tiny tools will work on glass, emeralds, sapphires, ceramics of all kinds and calcium fluorite. There are applications in optics, DNA analysis and biocomputers on a chip.
Tiny tools can also create shapes that photolithography cannot. In photolithography, surface shapes have to be built up by layer after layer of material creating a stair-step surface. Tiny tools grind and shape smooth surfaces although they cannot yet achieve the nano-size structures available with photolithography.
"This really is a way to get shapes that we cannot get any other way," says Marsh.
Currently, the researchers are using existing machines designed for larger equipment to operate the tools, but they hope to develop a tabletop appliance. Equipment donations from Professional Instruments and Lion Precision in Minnesota and Panasonic supported this work. The National Science Foundation funded this research.
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