Investigation Into Rheological Properity Of ER Polishing Fluid And ER Fluid-assisted Polishing

With the development of the photoelectron communications technology，largenumbers of micro-aspherical lenses with low surface roughness are applied into theoptical system of the medical, aerospace, defense and other fields. Highermanufacturing quality of optical lenses has been required, such as higher surfacequality, better surface accuracy, and lower surface roughness and so on. A newmethod utilizing field-assisted polishing has been widely applied in polishing process.Under financial support of the project named Program for Ministry of Education of PR China and Scientific Research Program for Excellent Youth of Jilin Province, P RChina, this thesis investigated the Electrorheological(ER) fluid-assisted polishingtechnique, and confirmed the validity of the presented model by polishingexperiments conducted on five-axis the ER fluid-assisted polishing machine withneedle-like tool electrode and circular-type integrated tool electrode system.In ER fluid-assisted polishing process, the ultra-fine abrasive particle is thepolishing media with high hardness and good dielectric properties. When the electricfield is applied, the microstructure and rheological properties of ER polishing fluidwill change, with its apparent viscosity and shear yield stress improve significantly.The microstructure formed by polarized particles perpendicular to the electrodes isobserved by CCD camera. In this thesis, simulation on microstructure of ER polishingfluid is completed by the motion equation of particles. The microstructure of ERpolishing fluid has been analyzed with the influencing factors such as abrasiveparticle size and volume fraction and so on. The combination structure of ER particleswith abrasive particles has four different types changing with the sizes of abrasiveparticles. On this basis, the rheological properties of ER polishing fluid is analyzed byintroducing the microstructure of ER polishing fluid, including the viscosity, shearstress and the shear yield stress of the ER polishing fluid under the external electricfield. In this thesis, the theoretical model of the static shear yield stress of the ERpolishing fluid is developed based on the combination structure of ER particles withabrasive particles and the attraction forces between particles in ER polishing fluid. Aseries of experiments are conducted to study the properties of ER polishing fluid onthe self-made cylinder rotational rheometer and the key factors of influence theproperties of ER polishing fluid are analyzed. The yield stress testing device isdeveloped to investigate the influential regularities of the species, sizes and volume fraction of abrasive particles on the shear yield stress of ER polishing fluid.In this thesis, the combination structure of ER particles with abrasive particlesand the forces exerted on the abrasive particles for material removal is discussed whenthe electric field is applied, a model for the prediction of surface roughness in ERfluid-assisted polishing of conductive materials is established. Polishing experimentswith different abrasive particles for different conductive materials are conducted andthe regularity for the key process parameters to the surface roughness and materialremoval in polishing region is acquired. The experimental results have goodagreement to theoretical model which confirm the validity of the presented model.This thesis designed and promoted integrated tool electrode system. A series ofexperiments are also conducted to polish glass-ceramic by a circular-type integratedtool electrode in the ER fluid-assisted polishing process and the influential regularitiesof polishing process parameters on the surface roughness are acquired. Based on thetheory of hydrodynamic lubrication, the formation of solid core in polishing process isinvestigated and a mathematical model taking into account the normal pressure isderived. The normal pressure of ER fluid-assisted polishing fluid in polishing area ismeasured by the dynamometer, which confirms the validity of the presented model.The influence of key process parameters such as voltage, rotational speed of electrodetool and gap on the normal pressure is investigated. The relationship between surfaceroughness and the normal pressure is analyzed by Preston’s equation.The research work has guiding significance for the promotion to the properties ofER polishing fluid, lower roughness surface and material removal.