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Статья. Опубликована в журнале "LLE Review". – 2000. – Vol. 83 – P. 157-172.
Название на русском языке: Понимание механизма удаления стекла при магнитореологическом полировании (MRF).Авторы: A.B. Shorey, S.D. Jacobs, W.I. Kordonski, R.F. Gans.Аннотация к статье на английском языке: The mechanisms of material removal in MRF have been presented. Previous work describes how the shear stress due to the hydrodynamic flow of the MR fluid between the rotating wheel and the part surface controls the removal rate. The idea that material removal depends on the shear stress at the part surface is supported by the linear relation between removal rate and the total drag force shown here. It has also been shown previously that the nanohardness of the CI is important in material removal with nonaqueous MR fluids. We show here that as DI water is added to the MR fluid, the differences in the behavior of the hard and soft CI become less significant as the removal rate dramatically increases for both. This is due to either the presence of a hydrated layer or reduced fracture toughness of the glass in aqueous MR fluids. The addition of nonmagnetic nano-abrasives increases removal rates further since they move to the interface between the CI and the glass surface to control material removal. A transition from twobody to three-body removal is hypothesized. The relative increase in removal depends on the amount and type of the abrasive since different abrasives interact with the glass surface in different ways. This behavior of the abrasive is evident from both AFM scans as well as drag force measurements. More work should allow these results to be summarized in a modified Preston equation based on the local shear stress at the part surface.
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UNDERSTANDING THE MECHANISM OF GLASS REMOVAL IN MAGNETORHEOLOGICAL FINISHING (MRF)
Understanding the Mechanism of Glass Removal in Magnetorheological Finishing (MRF) Introduction Two magnetorheological (MR) fluids are currently in widespread industrial use for the commercial manufacture of highprecision optics using magnetorheological finishing (MRF). One composition, which consists of cerium oxide in an aqueous suspension of magnetic carbonyl iron (CI) powder, has been found appropriate for almost all soft and hard optical glasses and low-expansion glass-ceramics. The second composition, which uses nanodiamond powder as the polishing abrasive, is better suited to calcium fluoride, IR glasses, hard single crystals (i.e., silicon and sapphire), and very hard polycrystalline ceramics (i.e., silicon carbide). The extension of MRF to a vast array of materials is possible because of the unique nature of this finishing process. The magnetic carbonyl iron particles may be thought of as a form of variable compliance lap that supports the nonmagnetic polishing abrasives. Lap stiffness may be increased or decreased by adjusting the CI concentration and/or the magnetic field strength.
The mechanisms of material removal important to glass polishing have been an area of study for years. Cumbo1 describes the goals of precision polishing to be to shape the glass to within 0.1 µm of the desired form, to remove subsurface damage created by grinding operations, and to reduce the peak-to-valley (p–v) roughness to less than 5 nm. While there are several proposed mechanisms of material removal in polishing, none are widely accepted. Some authors describe polishing in terms of small-scale fracture,2,3 while others describe it as “plastic scratching” of a hydrated layer4 or a tribo-chemical wear process.5 The goal of this work is to try to use some of these existing theories to understand the mechanisms of material removal in the MRF of glass. Preston6 gave a classic theory of removal in glass polishing that is still being stu