Improvement of figure and finish of diamond turned surfaces with magneto-rheological finishing (MRF)

Abstract

Single point diamond turning (SPDT) has been a cost effective technique to achieve the required figure and roughness specification on a wide range of IR optics. SPDT is one of the few technologies that can efficiently generate aspherical surfaces, and as recent developments such as fast-tool servos mature, "free-form" surfaces are becoming feasible as well. Optical end-user requirements for a wide range of industries are continuing to tighten, driven, for example by multi-spectral systems that require good performance at shorter wavelengths in addn. to IR. In many cases, specified shape tolerances can exceed SPDT capabilities. Addnl., SPDT typically leaves "turning marks" (affecting micro-roughness) that can be detrimental to performance. In some cases, surface integrity (e.g. sub-surface damage) can also be of concern. Magneto-rheol. finishing (MRF) has the proven ability to simultaneously improve roughness, figure, and surface integrity in a fast and cost effective manner. MRF is a deterministic, sub-aperture polishing technol., and is typically employed as the last manufg. step. MRF can deterministically remove from tens of nanometers to microns worth of material, while efficiently "converging" to the specified requirements. Conversely, SPDT has proven to be very effective in removing the hundreds of microns (if not mm) sometimes required to "pre-shape" an aspheric surface before its final polish. After a brief introduction of MRF, this paper will discuss how SPDT and MRF processes can complement one another very effectively. Examples of MRF results on a wide range of IR materials will be presented. [on SciFinder (R)]