Key Technologies Of Magnetorheological Polishing For K9 Glass And Simulation Study Of Single Grain Scratching

K9 optical glass is prone to sub-surface damage due to its high hardness and brittleness,which can cause micro-cracks and residual stresses in the process of machining.Magneto-rheological polishing technology,as a flexible polishing method,relies on the flexible polishing tape generated by the magneto-rheological polishing liquid under the action of a magnetic field to remove materials.It has the characteristics of high precision and no sub-surface damage,and can meet the processing requirements of K9 optical glass well.However,the current research on the polishing mechanism mainly includes mechanical grinding,chemical action,and surface flow theory,and there is no clear and unified understanding of the removal mechanism,so exploring the removal mechanism of materials is still the focus of current research.Based on the current research gaps,this article analyzes the magnetic field and rheological effect of magneto-rheological polishing through simulation,and conducts a series of simulation analyses on the material removal process from the perspective of a single polishing particle to explore the effects of different process parameters.The specific work is as follows:Due to the fact that magnetic field strength is one of the main factors affecting the magnetic abrasive polishing effect,the excitation device needs to be structurally optimized in order to obtain appropriate gradient magnetic fields.Through magnetic circuit simulation of the excitation device,including the number of magnets,magnetization method,magnet arrangement,and air gap width,different magnetic induction lines and magnetic induction strength distributions were obtained under different working conditions.The results showed that when the air gap width was 4mm,the magnetic induction strength generated by single permanent magnet axial magnetization was the highest,reaching 358.4 m T,theoretically making it possible to form an effective polishing tape in this area.Secondly,the magnetic field strength generated by the excitation device affects the magnetorheological effect of the magnetorheological fluid.Based on the magnetic field strength generated by the excitation device,the mechanical model of magnetic-sensitive particles was established using the theory of induced dipole moments.The magnetorheological effect of the magnetorheological fluid was numerically simulated.By simulating the chain formation process and shear process of the magnetorheological fluid,it was found that the magnetic-sensitive particles in the magnetorheological fluid were first magnetized under the action of the magnetic field,and then moved and completed the chain formation process,the degree of which was related to the magnetic field strength.When the magnetic chain was subjected to external shear,the magnetic chain tilted,broke,and recombined along the shear direction.Due to the dynamic equilibrium between the breakage of old chains and the recombination of new chains,the shear yield stress of the magnetorheological fluid remained basically stable.Finally,the material removal process of K9 glass by single abrasive grains was simulated and analyzed using orthogonal experimental design.The maximum residual stress and average residual stress on the machined surface were used as evaluation indicators to determine the optimal combination of factor levels.Simulation analysis was conducted on the material removal process using the optimal combination.The cutting force of the abrasive grain in the friction process was extracted and compared with the yield stress of the magnetorheological fluid,and the influence of each factor level was discussed.The results showed that the shape of the abrasive grain had the greatest impact on the residual stress on the surface,which was closely related to the edges of the grain.The cutting depth was the next factor,which was related to the diameter of the abrasive grain affecting the contact area between the grain and the material.The cutting speed had the least impact,mainly affecting the contact time between the grain and the material.Under the optimal combination,the removal of material by the abrasive grain was in the plastic domain,and the cutting force of the abrasive grain remained around 12 μN,which was lower than the shear yield stress of the magnetorheological fluid.