Surface roughness and material-removal rate with magnetorheological finishing without subsurface damage of the surface

A new processing technique called magnetorheological finishing (MRF) is described, based on computer-controlled processing of optical surfaces and combining the features of ordinary processing using free abrasive with the characteristics provided by a polishing wheel and magnetization. Based on theoretical grounds, experiments to determine the material-removal rate on a parabolic mirror have been developed and carried out in order to clarify the influence of the control parameters: the gap between the workpiece and the polishing wheel, the rotation rate of the polishing wheel, the concentration of the volume fraction of nonmagnetic particles, and the polishing time. Experiments have been carried out to study the surface microstructure of the workpiece and the final surface roughness, brought from an initial rms value of 10.98 to 1.22 nm after 20 min of MRF, and this is evidence that the process rapidly reaches the nanometer level. The absence of subsurface damage of the polished surface confirms that the MRF technique is expedient in practice.