NDLI: Magnetorheological (MR) Jet Finishing Technology

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	William, I. Kordonski Aric, B. Shorey Tricard, Marc
Copyright Year	2004
Abstract	Conformal (or freeform) and steep concave optics are important classes of optics that are difficult to finish using conventional techniques due to mechanical interferences and steep local slopes. One suitable way to polish these classes of optics is by using a jet of abrasive/fluid mixture. In doing so, the energy required for polishing may be supplied by the radial spread of a liquid jet, which impinges a surface to be polished. Such fluid flow may generate sufficient surface shear stress to provide material removal in the regime of chemical mechanical polishing. Once translated into a polishing technique, this unique tool may resolve a challenging problem of finishing steep concave surfaces and cavities. A fundamental property of a fluid jet is that it begins to lose its coherence as the jet exits a nozzle. This is due to a combination of abruptly imposed longitudinal and lateral pressure gradients, surface tension forces, and aerodynamic disturbance. This results in instability of the flow over the impact zone and consequently polishing spot instability. To be utilized in deterministic high precision finishing of remote objects, a stable, relatively high-speed, low viscosity fluid jet, which remains collimated and coherent before it impinges the surface to be polished, is required. A method of jet stabilization has been proposed, developed and demonstrated whereby the round jet of magnetorheological fluid is magnetized by an axial magnetic field when it flows out of the nozzle. It has been experimentally shown that a magnetically stabilized round jet of MR polishing fluid generates a reproducible material removal function (polishing spot) at a distance of several tens of centimeters from the nozzle. In doing so, the interferometrically derived distribution of material removal for an axisymmetric MR Jet, which impinges normal to a plane glass surface, coincides well with the radial distribution of rate of work calculated using computational fluid dynamics (CFD) modeling. Polishing results support the assertion that the MR Jet finishing process may produce high precision surfaces on glasses and single crystals. The technology is most attractive for the finishing of complex shapes like freeform optics, steep concaves and cavities.
Sponsorship	Fluids Engineering Division
Starting Page	77
Ending Page	84
Page Count	8
File Format	PDF
ISBN	0791847098
DOI	10.1115/IMECE2004-61214
Volume Number	Fluids Engineering
Conference Proceedings	ASME 2004 International Mechanical Engineering Congress and Exposition
Language	English
Publisher Date	2004-11-13
Publisher Place	Anaheim, California, USA
Access Restriction	Subscribed
Subject Keyword	Jet Sub-aperture Polishing Magnetorheological (mr) Optical Finishing
Content Type	Text
Resource Type	Article

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