Magnetorheological Finishing Key Technologies

Magnetorheological Finishing(MRF) is an advanced optical manufacturing technology, which has evolved over the past decade. It utilizes micro-sized magnetic particle, nonmagnetic polishing abrasives, carrier fluid and hydrodynamic flow in a magnetic field to remove material from a part surface. It is a kind of deterministic process. Base of it, Aspherical parts can be surfaced by computer controlled with high form accuracy and the low surface roughness and the high efficiency. It conquer the defections such as low-efficiency and low-grade surface quality of the traditional method, so it is significant to develop this technology. The main aspect of the thesis is as following:1. Based of analyzing the property of MR fluid and the influence of the constituent to the polished optical surface, the components of the MR fluid are determined. The "standard" MR fluid consists of 30 vol% carbonyl iron as the magnetic component, 60 vol% water as the carrier fluid, 6 vol % cerium oxide as the abrasive and 4 vol% fluid stabilizers.2. Stability of the MR fluid is tested and a new type of magnetorheometer is developed to measure the yield stress of an MR fluid in the same field orientation used in polishing. It is shown that the MR fluid that is suitable for finishing of optical parts.3. Deduced from the hydrodynamic lubrication theory of the Bingham plastic flow, the material removal model of MRF is established. The reliability of the model is verified by the experiment.4. The effect on magnetorheological finishing by several parameters is researched by experiments on the MRF prototype machine tool. Those parameters include intensity of magnetic field, the density of polishing abrasive, polishing wheel rotation speed, size of the gap between the optical parts and the polishing wheel. By the use of orthogonal experiment, the influence to the removal efficiency and the surface quality by those parameters is analyzed. The principle of the optimized parameters selecting is deduced. At last, we get an optical part which RMS roughness is 0.66nm.