Research On The Key Technologies Of Ultrasonic-Magnetorheological Compound Finishing

With the rapid development of modern optical technology, more and more aspheric lens have been applied for many new requirements of the optical systems presented. Aspheric lens can adjust many kinds of aberrations, improve the image quality of the instruments and simplify the structure of the system. Aspheric lens have been widely applied in many fields, such as military, aeronautics and aviation, electronics and so on. Most existing technologies for optical fabrication can not be applied in the machining of concave aspheres with small radius for the restriction of their machining conditions. The ultraprecision machining technology for concave aspheric elements with small radius is the great puzzle facing with optical fabrication. Therefore, it is urgent for the optical fabrication field to explore new ultraprecision machining technology suitable for aspheres with small radius and freeform surfaces.Ultrasonic-magnetorheological compound finishing (UMC finishing), which is first presented by the dissertation in both domestics and overseas, is a new kind of polishing technology for the ultraprecision machining of concave aspheres with small radius and freeform surfaces. The key technologies of UMC finishing are studied in the dissertation. The main aspects of the study are including:First, the general status of optical polishing technology for aspheres, especially magnetorheological finishing (MRF) in both domestic and overseas is reviewed. The review could be used as references for the study of UMC finishing technology.Second, the principle and the mechanism of UMC finishing method are studied. The magnetorheological polishing head is formed by the magnetic field, and the ultrasonic acts on it in UMC finishing. The magnetic field is not affected by the ultrasonic. The ultrasonic in UMC finishing can increase both the mechanical action and the chemical action in polishing, therefore, not only the polishing efficiency is increased, but also the material removal characteristic is reformed. The experimental results show that the material removal efficiency in UMC finishing is 3.1 times higher than that of in MRF, although the surface quality in UMC finishing is a little less than that of in MRF. The experiment also testifies that the material is removed by the coaction of the ultrasonic and the magnetic field in the process of UMC finishing.Third, the mathematical material removal models in UMC finishing when the workpiece is stationary, the workpiece is rotatory and the polishing head is oblique are established respectively. The mathematical models are established based on the study of the principle and the mechanism of UMC finishing. The mathematical models are got by the analysis of the ultrasonic stress, the magnetic stress and the hydrokinetic stress on the workpiece in the polishing zone according to the Preston empirical equation. The validity of the models is examined by the experimental results. The model established will be the theoeretical basis for the surface shape figuring in computer-controlled UMC finishing.Fourth, the experimental set-up of UMC finishing is developed independently based on the theoretical analysis of UMC finishing. The effect of the distribution forms of the magnetic field on the polishing results are studied in UMC finishing. The rotary ultrasonic equipment and the circulating and the viscosity-controlling system for magnetorheological fluid are developed. The experimental set-up of UMC finishing is the basis for further processing experiments.Fifth, many processing experiments are carried out on the experimental set-up of UMC finishing. The effects on both the material removal rate and the surface roughness in UMC finishing by the main processing parameters, such as the magnetic flux density, the ultrasonic vibration amplitude, the gap between the polishing head and the workpiece, the rotational speed of polishing head and the rotational speed of the workpiece are studied preliminarily. The processing parameters combination is achieved to get better polishing result in UMC finishing optical glass. The study will be the basis for the further application of UMC finishing technology.