| With the rapid development of modern science and technology,in the field of optics and micro-electronics,the requirements of surface shape accuracy,surface roughness and subsurface damage degree of key components are increasingly high,which requires the polishing equipment to have extremely high processing accuracy.Due to the low processing efficiency of traditional polishing equipment,the surface quality of the workpiece is difficult to meet the needs of high-precision equipment.Hence,researchers have proposed different polishing methods.Among the polishing methods,Lap-magnetorheological finishing(Lap-MRF)has the characteristics of high accuracy,flexible polishing,and no grinding head wear.At present,there are few studies on material removal models for LapMRF,which hinders the ultra-precision development of Lap-MRF.Therefore,in this study,the material removal function and mechanism of Lap-MRF are studied,and the following research contents are completed:(1)According to the working state of the MRF fluid,the model of MRF fluid is simplified as Bingham fluid,and combined with the working conditions of MRF fluid,the fluid dynamic pressure equation of Bingham fluid under certain conditions is deduced.The process of polishing is defined as mechanical action.Based on Preston equation,the material removal mathematical model of Lap-MRF equipment is established.(2)The magnetic field,velocity field and pressure field of the fluid are analyzed by COMSOL Multiphysics.To ensure that the magnetic particles form stable polishing grinding head during polishing,the stepped Halback Array structure is determined,which can effectively improve the local magnetic field intensity.The influence of magnetic field rotation velocity and magnetic particles bulk concentration on polishing pressure is simulated.(3)The material removal mechanism of MRF is explained.Based on the principle of molecular dynamics,the molecular dynamics model of polishing monocrystalline silicon workpiece by diamond abrasive particle is established.The simulation results show that it is easier to obtain high quality surface by polishing in liquid environment,which reveals the material removal mechanism from the microscopic perspective.In addition,according to the simulation results,the effect of linear polishing pressure on the subsurface damage layer and material removal of the workpiece is analyzed.(4)The process parameters of MRF are studied experimentally.Firstly,the influence law of each parameter on polishing pressure is analyzed by single factor experiment.Then,the orthogonal experiment is designed according to the influence law,and the influence degree of each process parameter on the polishing pressure is determined.In addition,the combination of the maximum and minimum process parameters is determined.Finally,a smooth surface with surface roughness Sa=0.068μm is obtained by polishing experiments with different polishing pressure parameters. |
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