Advances in finishing using magnetorheological (MR) jet technology

Abstract

Modern optical designs often include components with shapes more complicated than simple spherical and plano surfaces. These shapes, which include conformal, steep concave, stepped and free form surfaces, are often difficult to finish with conventional techniques due to mechanical interference and steep local slopes. A suitable approach to polishing these shapes is to use a jet of fluid containing an appropriate abrasive. However, a fundamental property of a fluid jet is that it will begin to lose its coherence once it exits the nozzle. This instability results in an unpredictable removal rate of the fluid jet, which makes it unsuitable for use in a deterministic finishing process. A method of jet stabilization whereby a jet of magnetorheological (MR) fluid is magnetized by an axial magnetic field when it flows from the nozzle has been demonstrated and implemented into the Magnetorheological Jet (MR JetTM) finishing process. The magnetically stabilized jet of MR polishing fluid produces a stable and reproducible material removal function (polishing spot) at a distance of several tens of centimeters from the nozzle making MR Jet an attractive technology for the finishing of complex shapes such as free form optics, steep concaves, and cavities. Recent results will be presented showing the ability to use this technology to finish a variety of shapes and materials including glass, metals, and ceramics.