Metal-bonded diamond wheel dressing by using wire electrical discharge: principle and prototype machine design

Metal-bonded grinding wheels offer particular benefits for the grinding of difficult-to-machine materials. Such wheels have superior dimensional and thermal stability, and more quickly dissipate the grinding heat. To in-process dress the metal-bonded diamond wheels of complex contours with the high-precision, wire electrical discharge dressing (WEDD) was used to remove the excess metal material on the surface. A prototype CNC machine tool based on the WEDD method was developed. Some novel designs were proposed to improve the dressing precision and performance. An air spindle with sub-micron runout was used to clamp the metal-bonded diamond wheels, which aims to decrease the runout of the dressed wheels. A specially designed wire guide was used to limit and minimize the positional fluctuations of wire electrodes. To dress the complex shape grinding wheel, the C-axis was designed to adjust the angle of the wire guide relative to the wheel to be dressed, which avoided motion interference between them. In addition, a high-low-voltage power supply was developed. By using the high ignition voltage, it is possible to form the discharge channel under a large gap, and thus the grinding wheel with the large diamond grain of the size 75 similar to 90 mu m could be dressed. WEDD of a metal-bonded diamond grinding wheel was performed on the developed prototype machine tool. The experimental results demonstrated that the developed prototype could realize the dressing of the grinding wheel with a runout of less than 2 mu m. The grinding experiments showed that a better grinding surface with Ra less than 0.8 mu m was obtained.