Stabilization and tribological properties of magnetorheological (MR) fluids: A review

To achieve the efficient and high-quality machining of hard and brittle ceramics used in various industries, in addition to other materials that are difficult to process, a magnetic-field enhanced shear thickening polishing technology was developed in this study. Based on the coupling effect of the magnetization enhancement and shear thickening, the proposed processing technology can improve the rheological properties of the shear thickening fluid, thus realizing an adaptive and efficient removal of microscopic materials. Herein, the microscopic material removal mechanism of this technology was analysed and the rheological properties of a magnetic shear thickening polishing fluid were studied. Based on the Preston's equation, the dynamic pressure of non-Newtonian fluids and the magnetorheological polishing theory, a material removal rate prediction model was established and it had a maximum relative error of 7.56%. The influences of the polishing head rotational speed, abrasive particle concentration and carbonyl iron powder particle concentration on the material removal function were investigated and the stability of the prediction model was verified. After polishing a zirconia workpiece for 20 min, a low-damage machining surface was obtained and the surface roughness was 8.3 nm. Therefore, the effectiveness of the material removal prediction model was verified and the findings of this study provide a theoretical basis for the realization of deterministic polishing. Moreover, the feasibility of the magnetic-field enhanced shear thickening polishing method for the ultra-precision machining of hard-to-machine materials, such as hard and brittle ceramics, was verified.

Material removal characteristics of magnetic-field enhanced shear thickening polishing technology

The normal positioning error hinders the use of magnetorheological finishing (MRF) in robotic polishing. In this paper, the influence of robotic normal positioning error on the MRF removal rate is revealed, and a force-controlled end-effector for the robotic MRF process is presented. The developed end-effector is integrated into a six-axis industrial robot, and the robot positions the end-effector while the end-effector realizes the constant force control. A fused silicon mirror is polished, and the result shows that the proposed device effectively compensates for robotic normal positioning error and simultaneously maintains the stability of the polishing process. After deterministic polishing, the PV (peak to valley) of the figure is reduced from 126.56nm to 56.95nm, and the RMS (root mean square) is reduced from 22.15 nm to 7.59 nm.

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Robotic Magnetorheological Finishing Technology Based on Constant Polishing Force Control

A line contact ring magnetorheological finishing (RMRF) process is conceptualized and developed for the finishing of precision optical surfaces. This tool is analogous to the cup wheel tool widely used in the optical industry for forming and fine grinding but semi-rigid in nature, thus removing high irregularities preferentially. This paper presents detailed simulations of the development of the new, to the best of our knowledge, RMRF tool and its experimental use and suitability in the polishing process. The line contact interaction between the workpiece and magnetorheological fluid present in the annular region is responsible for the finishing mechanism. The material removal rate and influence function of the RMRF process were calculated, which is essential and used for corrective polishing. The volumetric material removal rate was 0.0010406mm3/min with surface roughness of 5.94 nm; however, it can be increased with optimization of machine parameters such as gap, tool rotation, current, etc. Using this RMRF process, a polishing experiment was done over an NBK-7 glass workpiece of 40 mm aperture having 70 mm radius of curvature. Surface roughness improved down to 7 nm from 28.5 nm, and figure error improved down to 295 nm from 849 nm after four cycles of polishing. This investigation demonstrates the suitability of the RMRF process for precision polishing technology for glass optics.

Line contact ring magnetorheological finishing process for precision polishing of optics.

Synthesis characterization and functional analysis of magneto rheological fluid – A critical review

Owing to some specific advantages, magnetorheological fluid (MRF) has drawn significant attention in a broad range of modern precision machining field. With the diversification and improvement of demands, many novel structure configurations and processing methods have been applied to mechanical machining equipment. Although different applications with MRF have been proposed in existing literature, the classification, latest approaches and further trend are not involved clearly for machining field. Thus, the current applications used MRF are summarized from 2016 to 2020, which include machining auxiliary equipment and surface polishing equipment in this work. Especially, some detailed structures of equipment are investigated and relative limitations are analyzed based on the characteristics of MRF. Finally, in view of the current equipment, advantages and defects are briefly reported; the developing trends of modern precision machining with MRF are discussed. Therefore, in the state-of-the-art review, increasingly important role of MRF are emphasized for the machining field, which are conducive to innovative developments and market selection.

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Baiyi Wang

Papers

The Roles of Magnetorheological Fluid in Modern Precision Machining Field: A Review