Research On The Method Of Lap Magnetorheological Finishing Based On Permanent Magnet Array

Magnetorheological finishing is an emerging high-end optical manufacturing technology that has been widely used in ultra-smooth surface processing in fields such as aerospace,national defense,information and microelectronics.Unlike traditional chemical mechanical polishing,magnetorheological finishing can adjust the magnetic field distribution to change the shape of the polishing pad to adapt to components of different shapes and sizes,achieving high-quality polishing with complex shapes and structural components.In response to the problems of large coil volume,difficult manufacturing,severe heating,and complex cooling system in the traditional layout of lap-magnetorheological finishing electromagnet clusters,this study proposes a lap-magnetorheological finishing method based on a permanent magnet array.Combining the dynamic changes of gradient magnetic fields with the structural morphology and motion mode of magnetorheological polishing pads to achieve ultra-smooth and low-damage flattening processing of wafers.The analytical models of the Halbach array magnetic field were established using the equivalent current method and the equivalent magnetic charge method,respectively.The magnetic induction distribution at different heights on the top of the Halbach array and the magnetic field gradient changes in the x and y directions were studied.The research shows that the equivalent current model does not have a logarithmic solution of complex values during the solving process,and it also avoids the functional solution of the variational equation by the traditional Maxwell model,which is an economical and effective method for the Halbach array magnetic field structures design.Based on the equivalent current analytical model of the Halbach array magnetic field,a dynamic magnetic field model for lap-magnetorheological finishing was established,and a quasi-Newton optimization design method for the model was proposed.A dynamic magnetic field device for lap-magnetorheological finishing was developed.Through simulation and experimental research of two different array forms,the optimal magnetic field layout scheme was determined in the form of a circular symmetric array.In addition,the effect of process parameters such as magnetic field speed,workpiece speed,and depth of workpiece immersion into the polishing pad on the surface roughness of the polished workpiece was experimentally studied.The research results indicate that the dynamic magnetic field device based on the Halbach array can achieve significant magnetic field intensity and gradient changes with fewer magnets,which provides a reference method for the small and lightweight design of magnetic field devices in magnetorheological finishing.Based on the lap-magnetorheological finishing process experiment,combined with the mechanical effects of micro removal and liquid dynamic pressure theory,the mechanical mechanism of material removal in magnetorheological finishing under a dynamic magnetic field was studied.The dynamic pressure load model,shear load model,and elastic load model during the magnetorheological plane polishing process were established using analytical methods.The experimental study investigated the influence of key parameters such as magnetic field speed,polishing fluid viscosity,and workpiece immersion depth in the polishing fluid on various loads in the model.The study shows that at a magnetic field speed of 40-60 r/min,iron powder volume fraction of 30%-40%,and workpiece immersion depth in the upper and middle layers of the polishing fluid,the processing system obtained the optimal polishing load.Through experimental research on the rheological properties of magnetorheological polishing fluids with different volume fractions of iron powder,a functional relationship between strain and storage modulus,loss modulus,and normal force under elastic load was established.This provides a new strategy for measuring the elastic load component contained in normal force in lap-magnetorheological finishing.Based on analyzing the mechanical effect of load on material removal in magnetorheological finishing,the effect of polishing fluid structure on the surface quality of workpiece was further studied.Si O₂-CI（Carbonyl Iron,CI）magnetic sensitive particles with villous coating structure were prepared by the St?ber method,and the physicochemical properties of the particle structure were characterized by SEM,VSM,FTIR,LPSA and other technologies.The Rheology characteristics of the modified magnetorheological polishing fluid were studied and the processing performance was tested.The research shows that within a polishing time of 1.5 hours,Si O₂-CI magnetorheological polishing fluid improves the surface roughness of the workpiece by 28.5%compared to CI magnetorheological polishing fluid.When using a magnetorheological polishing fluid coated with Si O₂ for CI,the volume content of additional abrasive particles can be reduced,and the surface magnetic field effect and applied pressure decrease more than pure CI fluid.Scratches on the workpiece surface can also be minimized.