Process Research Of Magnetorheological Finishing With A Small Permanent Magnet Ball-end Tool

With the development of technology, more and more precision components withsmall but complex shape are used. They play a pivotal role in apparatus which may beused in national defense and aerospace. Because of their small size and special shape, itis hard to find an effective processing method, especially polishing method, to ensuretheir high machining accuracy. Many of the polishing processes are polished by handburnishing, whose processing efficiency and yield is poor. Furthermore the processingquality depends on the skill of the worker.In order to meet the need of polishing components with complex small shape, anew polishing method based on the theory of magnetorheological finishing (MRF) isproposed. Its difference from other MRF finishing methods for the polishing tool is asmall ball-end permanent magnet, which helps to fit the complex shape of smallworkpieces. The small polishing tool is developed and the circulatory system formagnetorheological fluid (MRF) is built. The magnet field around the polishing tool isstudied to find out the stress situation of the carbonyl iron (CI) power. The result showsthat a stable polishing lap will form on the surface of polishing tool. The new toolshows excellent processing capability with peak removal rate3.3μm/min and surfaceroughness Ra10nm when it is immersed in MR fluid to polishing fused quartz.A3-D mathematical model of hydrodynamic lubrication is built based on thetheory of grease lubrication of sleeve bearing. Reynolds equation is solved by2-D finitedifference method and SSOR. Hydrodynamic pressure has been obtained thoughiteration method. Shear stress on work piece is obtained after that. The impact of normalstress and shear stress on the removal rate is studied. It shows that material removal ratehas positive correlation with shear stress but independent with normal stress. Hence, asensitive method is put forward by building a mathematical function of materialremoval rate though the relation between shear stress and polishing relative speed.The effect of several parameters on the polishing of plat and axis-symmetricalsurface is studied by single factor experiment. The orthogonal experiment is used instudying the impact factor of these parameters. Several rod lens are polished, and thefinal surface roughness is about Ra0.15nm. A1.5×1.5mm2fused quartz plate is polished,and its surface roughness decreases from Ra97nm to about Ra0.612nm. Besides, theconcave of a stainless slice is polished, and its surface roughness decreases fromRa0.2311μm to about Ra20nm.