Study On High Efficiency And Ultra-precision Grinding Process And Machining Damage Of Sapphire

Sapphire single crystal (α-Al₂O₃) combines many good optical, physical and chemical properties, so sapphire is widely used in a range of applications such as optoelectronics, microelectronics, military, and superconductivity. With the rapid development of technology, increasingly stringent requirements for the machining precision and surface quality of sapphire substrate are demanded, and high efficiency and low damage machining technology has become the main obstacle for its industrial application. As a typical material difficult to machine, there is no mature machining technology for sapphire crystal, and the traditional technology machining the optical accessory is still mainly used for it. However, with increasing of the sapphire substrate dimension, problems such as unstable machining precision and surface quality, low machining efficiency etc. become severer, when adapting the traditional technology to machine sapphire substrate.From the status quo and trend of overseas and domestic ultra-precision machining technology for hard-brittle crystal material, ultra-precision machining with diamond grinding wheel (DGW) combines many priorities, such as high efficiency, low cost, high precision, good surface quality etc, and it indicates the direction of the development of ultra-precision machining technology for hard-brittle crystal material. However, damage layer and scratches are still caused by DGW, following process must be adapted to erase them in order to obtain super-smooth and non-damage surface. Therefore, decreasing grinded surface damage and scratches as much as possible is becoming more and more important for reducing following machining amount and time. For these, high efficiency and ultra-precision grinding process and machining damage detecting technology of sapphire must studied to provide technical support for Sapphire single crystal flattening.In this paper, according to relative motion between the cup grinding wheel and the sapphire substrate, a kinematic model of the substrate rotation grinding was established, the kinematic equation of the grit trajectory was derived based on the concept of pitch point and pitch circle etc. The influence of the interval and the density of the grinding marks, formed on the substrate surface by the many grits, on surface quality of the grinded substrate were analyzed. Simulation of the grinding marks on the substrate surface was developed by Matlab, the results of simulation and theoretical analyses were verified by grinding experiments. Aiming at the surface quality and material removal rate, an innovative ultra-precision machining process for sapphire, which is a procedure processing system, integrating the rough grinding with #325 DGW, fine grinding with #600 DGW, on a precision grinding machine based on substrate rotating grinding method, was put forward. The orthogonal test program of three factors, including the wheel speed, substrate speed, the feed rate, was designed. The optimum process parameters of the substrate rotation grinding were obtained and determined according to the different wheels, and prominent factors were analyzed meanwhile.Grinded sapphire surface quality by DGW was measured by Olympus optical microscope and Newview5022 surface profiler, the categories and the caused reasons were concluded and analyzed. Cross section method were used to detect sub-surface damage of DGW grinded sapphire surface, and the problems of choosing corrosive liquid was resolved. Based on the above, sub-surface damage was assessed.