Precision finishing with magnetorheological (MR) jet technology

Abstract

As optical components' shape becomes more complex, and requirements on the precision get tighter, new, and more versatile polishing processes are required. Conformal, free form or steep concave optics are important examples of optics that are difficult to finish using conventional techniques due to mechanical interferences and steep local slopes. One suitable way to polish such shapes is by using a jet of abrasive/fluid mixture. A fundamental property of a fluid jet is that it begins to lose its coherence as the jet exits a nozzle resulting in instability of the material removal rate, and is therefore unsuitable for deterministic finishing. A method of jet stabilization has been proposed, developed and demonstrated whereby the jet of magnetorheological fluid is magnetized by an axial magnetic field when it flows from the nozzle. It has been shown that a magnetically stabilized jet of MR polishing fluid generates a reproducible material removal function (polishing spot) at a distance of several tens of centimeters from the nozzle. The technology is most attractive for the finishing of complex shapes like free form optics, steep concaves and cavities. Results will be presented showing the ability to use this technique to finish a variety of optical components.