Simulation And Experimental Study On Ultrasonic Assisted Electrochemical Machanical Polishing

Silicon carbide material belong to the third generation of semiconductor materials,with excellent electrical properties,including wide bandgap,high breakdown electric field,high saturation drift speed and high thermal conductivity.These features can make SiC devices work in high temperature,high power and high frequency conditions,but at the same time high hardness,high brittleness,poor impact resistance,strong chemical inertness and other characteristics of silicon carbide make its processing extremely difficult,and the existing processing methods have the disadvantages of low efficiency and poor surface quality.Ultrasonic assisted electromechanical mechanical polishing is a composite polishing technology that combines the effects of ultrasonic vibration,electrochemistry and abrasive mechanical action.The influence of different process parameters on the polishing of the specimen was studied by analyzing the flow,temperature and electric field to provide important theoretical guidance for the efficient ultra precision machining of silicon carbide.Firstly,the simulation model of flow field is established.The effects of ultrasonic vibration amplitude,frequency,flow field thickness and polishing pad on the absolute pressure,flow rate,vapor volume fraction and wear are studied.The results show that the cavitation takes place mainly on the surface of the specimen.The amplitude,frequency and film thickness have important influence on the flow field performance.The results show that the abrasive wear is affected by the type,diameter and concentration and the perforated polishing pad can play a buffer effect which makes the flow field more stable and conducive to the improvement of the processing quality.As far the temperature and electrochemical simulation,the temperature affects the saturated vapor pressure directly and the electric field voltage,current density,energy density distribution affect the process of chemical reaction rate.The results show that the effect of friction heat on the temperature field is weaker than that of the impact heat of the polishing fluid.The temperature of the cavitation region,that is,the temperature of the polishing fluid at the surface of the specimen is fluctuating during the rising process.The use of perforated polishing pad makes the conductivity of the flow field decrease and the electric field parameter form a cyclic distribution,that is,the electric voltage is low and the current density is large at the small hole;the concentration of liquid is has a significant effect on the parameters of the electric field.When the applied voltage is small,surface of the specimen is susceptible to passivation and the sufficient applied voltage can accelerate the chemical reaction of the surface.Finally,the experimental data that recorded by real-time data acquisition system were obtained and analyzed,including pressure,friction,flow field resistance and temperature.Experimental results have shown that: The increase of loading force can greatly improve the mechanical action and the removal rate is greatly increased,but the surface quality can not be guaranteed.Secondly,applying catalyst,electric field and ultrasonic can make the removal rate and the surface quality of the specimen improved obviously.The surface quality of the specimen was significantly improved by using polishing pad,but the removal rate was reduced significantly.