Study On The Key Technologies Of Belt Magnetorheological Finishing

Optical processing can be divided into contact processing and non-contact processing,contact processing mainly rely on various types of "grinding" to remove the material generated from the workpiece surface by the shear stress,so in general the head wear,the pressure will lead to uncontrollable factors such as processing uncertainty is not high,easy to produce the sub surface damage layer etc..Magnetorheological finishing(MRF)is a flexible grinding head processing method,and has the characteristics of complete recovery of magnetorheological fluid and stable state of grinding head.Therefore,it improves the machining accuracy greatly compared with traditional contact machining.However,for the most widely used large aperture optical elements in the field of space optics,especially for the SiC reflector,the problem of material removal is not enough,especially for the 2m reflector.In this thesis,the technology of belt magnetorheological finishing is put forward.It can improve the removal rate by increasing the area of the removal function and ensuring the accuracy and certainty of the process,thus shortening the processing cycle and reducing the processing cost.Based on the national project of large aspheric rapid and low-cost manufacturing needs,and taking aspheric magnetorheological finishing as the main line,this thesis start the research on the key technology of BMRF in the polishing process.We finally developed the belt magnetorheological finishing device and after integrating it with the machine tool we complete the high precision and deterministic processing of a SiC mirror with the diameter of 235 mm.It has laid a theoretical foundation for the application of Belt magnetorheological in large aperture aspheric surface rapid and low-cost manufacturing,provides technical support.The main work in the thesis as follow:1.System hardware technology research.In view of the problems existing in the prototype of the previous experimental principle prototype,we put forward and realized a lot of new designs.For example,designed and manufactured a new type belt,decreased the large friction between the belt and the magnetic box based on the air lubricating solution;the design and manufacture of a permanent magnet can satisfy the demand of processing area and magnetic field at the nozzle and recovery,improve the peak removal rate so as to improve the material removal rate;in the rising position of magnetorheological fluid using peristaltic pump to realize recovery of MR fluid,solved the problem of easy to be heat and be oxidized.2.Removal function distribution model.It is of great significance to study the material removal rate distribution in the long axis because of the greater length of the belt magnetorheological finishing removal function.After studying various factors affecting the removal rate of magnetorheological finishing(MRF),we selected the parameter of the gap slope as the main variable.Combined with the theory of virtual ribbon proposed by us,a large number of experimental data have been used to find a model for the distribution of the belt magnetorheological finishing removal function.This model can guide the design and selection of the Belt-MRF removal function,and can realize the prediction of variable removal function.3.Belt magnetorheological process experiments.Because of the shape of removal function,the removal function of belt magnetorheological is different from traditional magnetorheologica l in terms of edge effect and components for different materials and different curvatures of the workpiece.From the point of ensuring the removal of function stability,we have carried out several sets of process experiments,improved the Technology Library of belt magnetorheological finishing,and provided technical support for subsequent practical processing.4.Belt magnetorheological polishing capability verification.The application of belt magnetorheological finishing(MRF)to actual processing needs to take into account the edge effect,the direction of the feed,the limited attitude of the machining element in the length direction and so on.After combining the existing algorithm of the laboratory and the characteristic of the strip magnetorheological removal function,we completed the processing of the SiC plane mirror with a diameter of 235 mm,and achieved good results.It also verified that the belt magnetorheological finishing can be applied to the rapid processing and manufacturing of large aperture optical components.