Study On Technique Of Magnetorheological Finishing

Magnetorheological finishing (MIRE) is an advanced optical manufacturing technology, which has evolved over the past decade. It fits for rapid polishing of medium or small size optical elements. In magnetorheological finishing, magnetically stiffened magnetorheological (MR) abrasive fluid flows through a preset converging gap that is formed by a workpiece surface and a moving rigid wall, to create precise material removal and polishing. A fundamental advantage of MRF over traditional polishing is that the polishing tool does not wear, since the recirculated fluid is continuously monitored and maintained. Therefore, during polishing, the material removal function is not changed, that is useful for us to control the polishing process. There are two preconditions before MIRE: One is presenting a suitable gradient magnetic field, the other is preparing magnetorheological polishing fluids (MRP fluids) with good rheology. In this thesis we first study on these two preconditions. On the one hand, we design a magnetic circuit, which is similar to that of Ferrograph. According to the analysis of the forces acting on magnetic particles in this magnetic field, we find that MRP fluids can form a ribbon that is regarded as 損olishing tool? It is true that MRP fluids really form a ribbon in our MIRE experiment. On the other hand, on the basis of studying on compositions, properties and rheology of MR.P fluids, we prepare several kinds of MRP fluids with good properties. By using them in our MIRE experiment, we get a good polishing result. Secondly, the mechanism of MIRE is studied. When MIRP fluidsis delivered to the vicinity of the gap formed by convex part and moving wall, it is pressed by the magnetic field gradient against the wall, so it stiffens, and becomes a plastic Bingham medium before it enters the gap. When plastic Bin~ham medium enters the gap, a core attaching to the moving wall is formed in 損olishing spot? So, a very small gap is formed between the upper surface of the core and the part surface. Thereafter, a shear flow occurs in this very small gap, resulting in the development of high pressure or high stress on surface of the part and thus, material removal a portion of the part surface. According to Preston equation, mathematics model of MIRE is established in this thesis. The III reliability of the mathematics model is verified by MRF experiment. At the end of the thesis, based on MIRE experiment, the curves and the laws of the effect on MRF by several parameters are given. These parameters include polishing time, velocity of moving wall, magnetic field intensity, size of the gap between the part and moving wall, hardness of the part and concentration of MIRP fluids. After polished, t microroughness and subsurface damage of the part are studied. Also, we explain how to correct figure of the workpiece.