Development of a padless ultraprecision polishing method using electrorheological fluid

A new kind of polishing method for mirror surface using the electrorheological (ER) fluid is presented. ER fluid is colloidal suspension and stiffens into semi-solid when subjected to an electric field. In this study, the mixture of the ER fluid and abrasives is used as polishing slurry. When the ER fluid is placed at the interface between a part and a moving platen, the friction force increases with the applied voltage. Since the polymeric ER particles separating two surfaces attract neighboring fine abrasives along the electric field across the gap, making the abrasives participate in material removal, they replace roles of pad used in a common mirror polishing. This paper analyzes the friction characteristics of the ER fluid at the sliding interface experimentally, and the behavior of the ER particles at the interface with and without the application of an electric field is observed optically. In addition, material removal rate of single crystal silicon according to the electric field strength is evaluated using the mixture of the ER fluid and diamond powders for a few conditions of different velocities and normal pressures. At last, average surface roughness of 2.9 nm is obtained as a result of the polishing of silicon surface whose average roughness is about 50 nm with the 0.25 μm diamond-mixed ER fluid.