Simulation And Experimental Study On Uitrasonic-Electrochemical Polishing Of Sillicon Carbide

Silicon carbide(SiC) is the third-generation semi-conductor, its electrical and physical properties are unique. However, SiC is also known as super-hard material, it is very hard to process for its high brittleness, low im Pact resistance and extremely low chemical inertness. Traditional processing methods get low-quality surface, the current ultra-precision polishing applied to silicon carbide is very limited because of the low material removal rate(MRR).Ultrasonic-electrochemical polishing(UECMP) combined electrochemical effect and ultrasonic vibration to polish workpiece, it has been proved effective in processing mold, but there is still no research on polishing silicon carbide through UECMP. By simulation and experimental studies on the polishing process, the influence of different process Parameters on polishing effect is investigated. This Paper tested the feasibility to obtain high-quality surface and achieve high MRR by UECMP, which has guiding significance to efficient ultra-precision machining of SiC.CFD simulation is firstly carried out, three kinds of simulating models are built to analyze the influence of ultrasonic wave, fluid film thickness and pores on polishing Pad. It turns out that ultrasonic wave can cause strong shear flow and high pressure at the polishing surface, the shear flow and pressure grow stronger with the decrease of film thickness. Pores on the Pad break the continuous fluid flow under workpiece, which turns velocity and pressure of fluid into stepwise rate and ultrasonic cavitation easier to observe.Ansoft Maxwell is employed to simulate the electric field distribution, the effect of slurry conductivity, fluid film thickness and workpiece material are studied. Results show that electric current Pass the workpiece through its faces instead of body, the current density on polishing surface rises with the growth of slurry conductivity and falls when film thickness increases. Com Pared with Fe and Cu, SiC consumes 20% of electric energy when it Pass the workpiece.At last, ultrasonic-electrochemical polishing tester is developed to achieve ultrasound assistance, electricity application and data collection. After a series of experiments, the influence rule of ultrasonic wave, voltage and slurry composition on polishing effect are obtained. Results of experiments reveal that the friction coefficient between the SiC workpiece and the polishing tool is determined by the slurry, diamond suspension provides highest MRR when used as slurry. MRR also rises when applying positive voltage or ultrasonic wave to the workpiece, and the influence of ultrasonic wave exceeds electricity, but the friction coefficient does not change with these two factors. Under the chosen experimental Parameters, the MRR of SiC reaches top to 15.7mg/h when applying both assisting factors and using diamond suspension as slurry.