Investigation on ultra-precision lapping of A-plane and C-plane sapphires

A series of lapping experiments on A-plane and C-plane sapphires were accomplished using a precision single side lapping machine. The differences in the material removal rate, surface topography, surface breakage and subsurface damage between the two sapphire orientations were explored. The influence of the lapping parameters, such as the abrasive disk speed, lapping time, lapping liquid flow rate and wander star wheel speed, were analysed for their effects on the material removal rate. The experimental results showed that the abrasive disk speed played the most prominent role in the material removal rate during sapphire lapping. Under the same lapping conditions, the removal rate of the C-plane sapphires could be 5.7 times higher than that of the A-plane sapphires. The main surface damage form of the A-plane sapphires after lapping was surface breakage, while that of the C-plane sapphires was surface scratching. After lapping, the A-plane sapphires had a greater subsurface damage depth than the C-plane sapphires. The subsurface cracks of the A-plane sapphires included transverse and radial cracks, while the subsurface cracks of the C-plane sapphires were mainly transverse cracks. The lapping surface quality of the C-plane sapphires was superior to the A-plane sapphires.