Electromagnetic composite rheological polishing (EMRP) is a new ultra-precision machining technology that combines electro-rheological polishing (ERP) and magneto-rheological polishing (MRP). The key technology of the polishing method is the preparation of electromagnetic composite rheological fluid (EMRF) with both electro- and magneto-rheological properties, especially the preparation of composite particles with electro- and magneto-rheological effects. In this study, the EMRF was prepared by using electromagnetic two-phase particles with abrasive characteristics. The electromagnetic two-phase composite particles are synthesized in two steps: the coupling method and sol-gel method. The two-step method successfully prepared the electromagnetic two-phase composite particles with nano-diamond particles embedded randomly on the surface. The electro-rheological shear stress of EMRF can reach 160.7 Pa when the test parameter voltage is 2.5 kV, and magneto-rheological shear stress of EMRF can reach 4076 Pa when the electromagnet excitation current is 3 A. When a fused silica glass is polished under a single magnetic field, the material removal depth reaches a maximum of 2.7 μm at a radius of 13.5 mm. Under the action of the electromagnetic compound field, the removal profile of the work-piece is smoother, and the material removal depth reaches the maximum value of 2.1 μm at a radius of 10.5 mm. This proves that the stiffness distribution of the polishing pad under the electromagnetic composite field is more dispersed than that under a single field. Therefore, the distribution of electromagnetic two-phase composite particles can be controlled by applying an electromagnetic composite field, which provides a good foundation for the abrasive control technology of EMRP.
Cluster magnetorheological finishing is a novel machining method for attaining super-smooth and even surfaces. The aim of the research is to strengthen the role of cluster magnetorheological polishing pads and improve the material removal rate (MRR) while attaining smooth and undamaged surfaces. To this end, a novel polishing disk with three-dimensional (3D) microstructures was formed by machining an array of holes on the surface of a polishing disk. The influences of the type of abrasives, geometric parameters of the holes, and polishing time on the roughness and MRR of the machined surface were explored. The test result showed that a polishing disk with multiple holes contributes to a higher MRR and a lower surface roughness relative to a smooth polishing disk, significantly improving the polishing effect; the diameter and distribution of multiple holes on the surface of the polishing disk exhibit a significant effect on the polishing process. The polishing effect with silica sols is most remarkably improved. The solid-state chemical reaction between sapphire and silica sols promotes material removal; relative to a smooth polishing disk, the MRR is increased by 107% and the surface roughness is decreased by 11%. The surface roughness is reduced from Ra 5.14 nm to Ra 0.24 nm by utilising the optimised technological parameters. Under the synergistic action of mechanical removal enhancement of polishing disks with multiple holes and chemical removal of silica sol sapphire can obtain super smooth undamaged surfaces efficiently.
Both the magnetorheological effect and the electrorheological effect can effectively constrain and clamp abrasives for polishing processing. This paper proposes a magneto-electric synergy rheological finishing (MERF) method. Based on a magnetoelectric composite field simulation, magnetoelectric synergistic rheological finishing equipment is built. A polishing slurry with both electrorheological and magnetorheological effects is prepared for processing a 2-inch single-crystal silicon wafer. Comb-type electrodes and cylindrical flat-bottomed magnetic poles are used to construct magnetoelectric composite fields. Under the action of a magnetoelectric composite field, a hemispherical polishing pad with abrasives distributed in strips can be obtained. By conducting a test, a smooth and gentle arc cross section of the removed contour can be obtained. The removal rate of MERF was 4.04 mg/h, which was between those of electrorheological finishing (ERF) and magnetorheological finishing (MRF). The surface roughness Ra reached 1.80 nm, and the depth and width of the machining traces were the largest. Magnetoelectric synergistic rheological finishing equipment can realize processing under electric fields, magnetic fields, and magnetoelectric composite fields. The MERF method can effectively enhance the semifixed binding force and distributional uniformity of the abrasive and achieve a more efficient and uniform planarization process.
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