Study On Magnetorheological Polishing Technology By Using Of Large Polishing Tool For Single Crystal Silicon Carbide

With the continuous development of technology,the commonly used single crystal silicon can not meet its needs.The single crystal silicon carbide material is very suitable for the manufacture of high temperature,high frequency,high power and high integration electronic devices due to its wide band gap,high thermal conductivity,high critical breakdown electric field and good chemical stability.However,due to its high hardness and high brittleness,single-crystal silicon carbide is difficult to achieve highefficiency,high-precision,damage-free polishing by traditional polishing methods.Magnetorheological polishing is an advanced polishing method that can achieve ultrasmooth and damage-free processing.Therefore,this thesis proposes the application of magnetorheological polishing in the polishing process of single crystal silicon carbide,and the main conclusions have been summarized as the following aspects:(1)An electromagnetic excitation device based on the principle of gap leakage was designed.According to the principle of magnetorheological polishing of the large polishing die,the structure of the excitation device has been designed and the appropriate material has been selected.The number of coil turns of the excitation device was calculated based on the principle of gap leakage and the law of magnetic circuit.(2)Maxwell software has been used to simulate the magnetic field generated by the excitation device and optimize its size structure.Three-dimensional software has been used to make models of different sizes,and magnetic field simulations have been performed separately.The arc-edge protrusion array magnetic pole head structure is used to replace the traditional linear magnetic pole head,thereby improving the strength and range of the magnetic field.Through comparing the magnetic field obtained before and after optimization,the changes of magnetic induction intensity and magnetic field range have been analyzed.(3)Magnetorheological polishing experiment equipment have been built to conduct single crystal silicon carbide polishing experiment.Through single-factor experiment,the effect of different working gap,current and working time on the magnetorheological polishing effect of single crystal silicon carbide was analyzed.It was found that the processing of single-crystal silicon carbide materials using a large polishing die-type magnetorheological polishing method using electromagnetic field excitation can obtain sub-nanometer-level surface roughness.The surface roughness value of the material decreases with the increase of the energizing current and increases with the increase of the working gap.After polishing for 40 minutes,the roughness of the processed surface reached Ra 0.6nm.