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Nowadays, sapphire substrates are widely employed for GaN light emitting diodes (LEDs) due to their comparatively low cost, large diameter, high quality, optical transparency, and high temperature stability etc. However, in spite of its commercial importance and extended history, the machining of sapphire remains a challenge. In the manufacture of sapphire, chemical mechanical polishing (CMP) has been widely used to obtain a mirror surface on the sapphire substrate and minimize the subsurface damages. In this paper, published literature in the past decade on CMP of sapphire substrates is summarized. Recent investigations into material removal mechanism of CMP of sapphire substrates are introduced and advances in experimental studies are reviewed in terms of abrasives, sapphire crystal orientations, pad materials, and other process parameters (such as polishing pressure, pad rotational speed, and temperature etc.). Possible topics for future research are also discussed.

To suppress chatter is very important for ensuring processing quality and efficiency in ultrasonic-assisted grinding of thin-walled workpiece of SiCp/Al composites. Based on the chatter mechanism analysis, a stability analysis model is built and the analytical method is proposed. The cutting parameters can be selected reasonably based on the lobe diagram of stability, and the experiments were conducted using the parameters of selected points on lobe diagram. The experimental results show that the cutting force and surface roughness of unstable points are much larger than that of stable points, the vibration marks appear on the workpiece surface with unstable machining, and the surface quality is better in stable machining, which indicate that the chatter could be suppressed by this method to guarantee machining quality and efficiency.

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