High Removal Rate MRF (TM)

Magnetorheological Finishing (MRF) is a well-established process for precision optical finishing. The primary benefits of MRF are its determinism, ability to finish complex surface shapes and good removal rate. Higher removal rates can be desirable to reduce cycle times or increase the amount of material removal. Cases include but are not limited to aspherization, harder materials, correcting higher error amplitudes, polishing very large aperture optics, and subsurface damage removal. Novel developments have been made with the fluid nozzle, magnetic field, and wheel geometry to increase the removal rate. Custom nozzle shapes are used to create a very wide MRF ribbon resulting in a much wider removal function (spot). The increase in ribbon width requires the use of higher volumetric flow rates. The magnetic field must be shaped to ensure that the field passes through this wider ribbon. Radius of curvature of the MRF wheel parallel to the axis of rotation is increased to achieve a wider spot. Results show an order of magnitude increase in volumetric removal rate due to a much wider and longer spot. Spot width increases of 3x, and spot length increases of 2x, as compared to a traditional MRF spot, were achieved. Polishing shape corrections were conducted with these spots which resulted in convergence rates over 80%. This development allows MRF to be used in applications previously limited by cycle time.