Study on a magneto-rheological removal process of periodic turning marks

Single Point Diamond Turning (SPDT) has the potential to cost-effectively manufacture optical materials such as metals and plastic types. However, SPDT generally leaves tool marks on the machined surfaces, which creates problems that can deteriorate the optical performance. Several processes have been studied to eliminate the tool marks caused by SPDT, but it was difficult to carry out without the additional defects like sub-surface damages and other tool marks. To overcome this weakness, we investigated the Magneto-Rheological Finishing (MRF) process to effectively remove the periodic micro structures without surface deterioration for optical performance. The workpiece used in the experiment is a mirror plated with electroless nickel-phosphorus. Through the processing of the SPDT, an initial surface gets periodic tool marks, which have a height of 1.1 μm and a pitch of 20 μm. We studied on the reduction rate of the turning marks by the MRF process with some different conditions of uniform removal. The quantitative analysis of the surface roughness and residual marks was performed using a scanning low-coherence interferometer and through the Power Spectral Density (PSD) respectively. The results showed that reduction rates of tool marks depend on the angles (0, 45, and 90 degs) between the turning direction of the tool marks and the rotation direction of MR wheel. In the case of 45 degs, it indicated the fastest reduction rate.