Local figure correction of diamond turned aluminum substrates by Magnetorheological Finishing (MRF)

As demonstrated in the present work, the surface irregularity of diamond turned aluminum surfaces can be improved by a magnetorheological finishing process (MRF). The removal behavior of rapidly solidified Al6061 (RSA Al6061) based on standard MR fluids and adapted finishing parameters is investigated. Typical polishing functions (spots) and resulting removal rates are described. The material removal for an iterative figure correction is discussed versus the surface micro-roughness characteristics. The given micro-roughness values (rms) are related to the spatial frequency range: f ~ (10-2500) 1/mm which are relevant in terms of stray light requirements for the mentioned optical applications. Results are given for representative components. The effectivity of the approach is shown on mirrors for a cryogenic application.