Study On The Mechanism Of Magnetorheological Polishing Of Fused Silica Based On Electrolyte Modulation

Magnetorheological polishing as an advanced flexible polishing technology,its working principle is the magnetization of iron powder particles in the magnetorheological fluid under the action of magnetic field to form a layer of flexible polishing pad will be polished abrasive extrusion,driven by the polishing wheel to polish the surface of the workpiece,so magnetorheological polishing has the advantages of tangential force dominant,do not introduce new sub-surface damage,etc.,become an indispensable part of the processing process of high-quality optical components The important part of the process.With the development of modern science and technology,several major optical projects such as laser fusion systems,lithography,aerospace optical systems,etc.need a large number of different apertures of high-precision flat,spherical and aspheric optical components,which put forward increasingly demanding requirements on the accuracy and efficiency of magnetorheological polishing,so the study of magnetorheological polishing material removal mechanism and high stability of the polishing fluid is the key issue to determine the polishing accuracy and efficiency.At present,many scholars have prepared highly stable magnetorheological polishing solution by using electrolyte regulation,but the effect of the addition of electrolyte in the polishing solution on the polishing process and the material removal mechanism have rarely been studied,which directly limits the development of magnetorheological polishing technology.In this thesis,the most typical nanodiamond polishing solution for magnetorheological polishing is studied.The effect of electrolyte addition on the degree of agglomeration of abrasive particles and carbonyl iron powder in the polishing solution is systematically investigated,and the effect of particle agglomeration in the polishing solution on the polishing results and the mechanism of material removal is discussed,and finally the method of electrolyte regulation is proposed to prepare magnetorheological polishing solution with high stability and low surface defects.The specific research of this paper is as follows:(1)The effect of electrolyte addition on the agglomeration properties of particles in polishing solution was investigated.The results show that the addition of electrolyte affects the original bilayer structure of particles,making the absolute value of zeta potential decrease and the repulsive force between particles decrease,causing the agglomeration of particles in solution.As the concentration of electrolyte added to the polishing solution increases,the zeta potential and particle size of the particles in the polishing solution also increase,and the electrolyte with high metal cation chemistry has a greater effect on the zeta potential and particle size of the particles in the solution than the electrolyte with low metal cation chemistry.(2)The effect of particle agglomeration in magnetorheological polishing solutions on the processing of fused silica optical components was investigated.The results show that the degree of agglomeration of abrasive particles has a greater influence on the form of fused silica wear,with the increase of agglomeration,the wear is converted from adhesive wear to abrasive wear,and the degree of agglomeration of abrasive particles affects the material removal rate of fused silica and the form of damage to fused silica,the greater the degree of agglomeration of abrasive particles,the greater the material removal rate.When the size of the abrasive agglomerates is small,slight furrows appear on the wear surface and the material is removed in a plastic manner without significant damage to the fused silica subsurface;as the degree of abrasive agglomeration increases,significant Hertz cracks appear on the fused silica surface and are accompanied by brittle spalling.The degree of iron powder agglomeration is proportional to the viscosity of the magnetorheological polishing solution,and the agglomeration of iron powder causes its own volume fraction to increase,which affects the viscosity of the polishing solution,and the greater the degree of agglomeration the greater the viscosity of the polishing solution.And carbonyl iron powder agglomeration on the polishing solution of the sinkability and stability of the greater impact,the more serious carbonyl iron powder agglomeration iron powder particles of their own mass is also greater,resulting in sink more likely to occur.(3)In response to the problems of poor stability and low surface quality of processed optical components in traditional magnetorheological polishing solution,a nanodiamond magnetorheological polishing solution with good stability and high surface quality of processed optical components was developed by using electrolyte regulation method.The experimental results of magnetorheological polishing showed that the stability of nanodiamond magnetorheological polishing solution increased more than 7 times than that of conventional nanodiamond magnetorheological polishing solution,and also effectively improved the surface roughness of polished workpiece from 4 nm to less than 2 nm.In summary,this thesis provides a theoretical analysis of the shortcomings of existing magnetorheological polishing solutions guided by practical engineering needs,on the basis of which the nanodiamond magnetorheological polishing solution is optimized to provide ideas for the subsequent development of magnetorheological solutions.