Study On Tray Type Magnetorheological Polishing Using Low-frequency Alternating Magnetic Field

In recent years,ultra-precision components such as optical lenses,sapphire substrates and silicon wafers,which are applied in high-end fields such as optical technology,LED lighting and semiconductor integrated circuits,are in great demand.These ultra-precision components have extremely high requirements for their surface quality.Traditional ultra-precision machining technology is out of the question to obtain high efficiency,high precision and no damage polishing.Magnetorheological polishing is an advanced ultra-precision polishing method which can achieve ultrasmooth and non-damaging machining.When the static magnetic field is excited,the abrasive is easy to accumulate,and when the dynamic magnetic field is used,the magnetic field line is constantly changing,and the magnetic particles have the dynamic property,so as to promote the uniform distribution of abrasive particles and improve the quality of workpiece surface processing.Considering the alternating current as the electromagnet excitation to generate dynamic magnetic field,but at high frequency,it is easy to damage the workpiece.Therefore,this paper proposed to use low-frequency alternating magnetic field for tray-type magnetorheological polishing,and carried out the following research:(1)The excitation device of groove pole electromagnet is designed.According to the principle of magnetorheological polishing,the construction of the electromagnet excitation equipment is designed,and appropriate materials are selected for each part according to the performance requirements.Based on the theory of electromagnetism and the law of magnetic circuit,the number of coil turns of the electromagnet excitation equipment satisfying the magnetic field requirements is calculated.(2)Maxwell software was used to simulate the magnetic field generated by the groove type electromagnet excitation device,and its size and structure were optimized.The characteristics of the alternating magnetic field are studied,and the excitation effect of the groove magnetic pole and the plane magnetic pole is compared.It is found that the magnetic fields generated by both can meet the polishing requirements in the machining area,and the groove magnetic pole can produce better excitation effect.So as to obtain the optimal structure size,the magnetic field simulation analysis of groove depth and groove width was carried out by single factor method.The results show that the effect of groove depth and groove width on magnetic induction intensity increases goes up and then goes down,and make no difference on the magnetic field distribution shape.(3)The magnetorheological polishing experiment platform with low frequency alternating magnetic field excitation was built,and the K9 glass polishing experiment was carried out.The effects of different current frequency,working gap,polishing groove speed,workpiece speed,polishing liquid volume and abrasive type on the surface roughness improvement rate and material removal rate of K9 glass were systematically analyzed by single factor experiment.The experiment results show that the effects of each factor on the surface roughness improvement rate and material removal rate of K9 glass were significant.The surface roughness improvement rate and material removal rate are 15.21 nm/min and 2.03 mg/min,respectively,after 30 min polishing with the optimal process parameters,which are 11% and 116% higher than the optimal values before the optimized process parameters.After polishing for 180 min,the roughness of the machined surface converges from Ra 580 nm to Ra 5.04 nm.