Ultrasonic vibration–assisted magnetorheological hybrid finishing process for glass optics

This paper presents an experimental investigation on ultrasonic vibration–assisted magnetorheological finishing (VAMRF) process for improved material removal rate (MRR) and surface finishing on glass optics polishing. An additional process parameter, i.e., vibrating motion, is added in the magnetorheological finishing (MRF) process for corrective polishing of glass optics. Influence function, a material removal characteristic of the process and necessary for deterministic processing, was calculated experimentally for the VAMRF. The results show that hybrid VAMRF provides approximately 20% higher MRR (14.3 nm/min) as compared to that of conventional Ball End MRF (BEMRF), which is 11.9 nm/min. Better surface micro-roughness improvement observed in VAMRF process (3.05 nm) as compared to that in BEMRF process (5.1 nm) from initial value (7.06 nm) in surface of N-BK7 glass workpiece. The developed hybrid process is applied in corrective polishing of glass optics of 25 mm diameter, and it is demonstrated that the figure error (RMS) of the surface has reduced down to 34 nm from 131 nm. Experimental results show that the developed hybrid finishing process is a promising candidate for corrective polishing of optics.