Preparation Of MR Polishing Fluid And Study On The Stability Of Removal Function

With the development of science and technology, modern optical systems make a higher demand for surface accuracy and surface quality optics. The high-precision aspheric mirrors are especially used more and more widely. The manufacturing technology of aspheric mirrors is always the difficult and hot issue. Because traditional processing methods exist pad aging, mismatch of workpiece- lap, removal function instability and other shortcomings which result in the process uncontrolled, lower processing efficiency. It is difficult to obtain high-precision aspheric mirrors. As a new generation of high deterministic optical processing technology, magnetorheological finishing(MRF) can overcome the shortcomings of traditional processing and become the ideal method for aspheric manufacture.The key factor to achieve high efficiency and deterministic MRF is to ensure the efficient and stability of removal function in manufacture process. Efficient and stability removal function depends on three factors. Firstly is the performance of magnetorheological polishing fluid, secondly is the stability and accuracy of the loop control system; thirdly is the rationality of processing parameter selection. Therefore, this paper carried deeply study on these three aspects and applied of research results to the actual processing of an aspheric mirror.The main contents of this article:1. High performance MR polishing fluid development and testing.Through the study of the mechanism of solid particles dispersion and combining with the needs of the actual optical processing, we developed the excellent performance MR polishing fluid, proposed MR polishing fluid preparation process and established the MR fluid performance testing platform. The off- field viscosity, dispersion properties and rheological properties of MR polishing fluid are tested with the testing equipment. The results show that the prepared MR polishing fluid possesses low off- field viscosity, good anti-settling property and rheology property which meet the demand of polishing. Finally, the material removal rate and shape are improved by preparing MR polishing fluid as a flocculation system in dispersion.2. MRF circulatory system and its impact on the removal functionThe advantages and disadvantages of several structural forms of MRF equipment are discussed. We develop MR polishing fluid circulatory system based on the inverted form MRF equipment developed by ourselves, combining with requirement of flu id composition control in actual polishing and fluid clean up after finishing. The circulatory system monitors the viscosity of MR polishing fluid by test the pressure along the channel of circulatory system and supply the fluid in real time. The temperature of MR polishing fluid is controlled by cooling water system. The influences of temperature and viscosity changes on flow and removal function are also studied. Finally, the precision and reliability of circulatory system and the stability of prepared MR polishing fluid are verified by the removal function stability experiment.3. The influences of main process parameters on the force in process and removal function in manufacture processThe influences of main process parameters changes on the force in manufacture process are studied by using KISTLER force sensor by selecting two kinds of common used material BK7 and RB-Si C. The influences of the changes on removal function are also studied. The similarities and differences of influences are compared between processing two kinds of material. Finally, the relationship between normal force, pressure, shear force, shear stress and material removal rate are studied.4. The actual machining asphericThe removal mechanism of MRF on RB-Si C material and roughness after polishing are studied. An aspheric RB-Si C reflective mirror is manufactured with self-developed MR polishing fluid and apparatus. The surface accuracy and roughness meet the surface requirement before modification. A kind of MR polishing fluid suitable for polishing silicon modified layer was developed. The influence abrasive concentration change in MR polishing fluid on removal function is also studied. The silicon modified of aspheric RB-Si C reflective mirror is polished by using two kind of MR polishing fluid with high material removal rate and low material removal rate. After polishing the surface accuracy reaches λ/50(λ=632.8nm).In this paper, the preparation of MR polishing fluid and the factors that influence the stability of removal function are deeply studied. Few kinds of MR polishing fluid are developed respectively for the material commonly used in optical engineering. MRF circulatory system is established based on self-developed polishing apparatus to control ensure the removal function stab ility of during polishing. The influences of main process parameters on removal function are analyzed. The efficient and stable removal function obtained by select reasonable process parameters which are applied to actual aspheric element manufacture successfully and desirable result achieved.