Laser Sharpens Grinding Wheels

Laurel M. Sheppard

Advances in the electronics industry have led to the development of new materials, such as Al₂O₃-TiC magnetic heads and special glasses for hard disks and liquid crystal screens. However, these materials are difficult to machine, requiring diamond grinding wheels, which dull quickly and must be sharpened to maintain their grinding performance.

Mechanical dressing (top) removes bonding materials and abrasives with a hone stick, requiring the grinding work to stop. Laser dressing (bottom) allows grinding to continue. Courtesy of Koji Matsumaru.

Researchers at Nagaoka University of Technology's School of Mechanical Engineering are working with the Applied Laser Engineering Center and Nano-Tem Co. Ltd. to develop a laser-based method that will resharpen (dress) the grinding wheels on the fly, removing bonding material more quickly and selectively than previous methods.

A conventional rotary dresser uses a hone stick that contains diamond abrasives. The stick is pressed against the grinding wheel as it rotates, removing the bonding material between the abrasive grains and exposing these grains. To do this, the machining process must be interrupted. This mechanical dressing method is relatively slow and can damage or even remove the diamond abrasive.

The researchers are using a frequency-doub led Nd:YAG laser from Continuum in Santa Clara, Calif., to evaporate the bonding material between the abrasives and penetrate the diamonds with minimal damage. (Diamond does not absorb its 532-nm wavelength.) Tests use a pulse rate of 8 ns, laser flux density of 0.03 to 0.48 J/mm² and laser beam diameter of 4 mm. Porous cast-iron bonded diamond grinding wheels from Nano-Tem rotate at 1.1 mm/s.

The researchers have analyzed the grinding wheel surface with scanning electron microscopy. Near the laser irradiation, the bonding material evaporates, so the diamonds protrude from the surface. The higher the laser flux density, the faster the dressing rate.

Laser dressing is about five times faster than mechanical dressing. Though the initial cost of the laser method is higher, costs would be offset by a faster removal rate and less wear on the grinding wheel, noted Koji Matsumaru and professor Kozo Ishizaki, principal investigators. "Since the laser dressing process can be done in process, total machining time is also reduced," Matsumaru added.

According to officials at Nano-Tem, the engineers have applied for a Japanese patent and plan to test the technique in a manufacturing environment.