Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Fabrication of Optical Surfaces on Polymethyl Methacrylate by Ultra-Precision Diamond Turning

Makitoshi Shimizu1 and Jiwang Yan1,a

1Department of mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan


In this study, we attempted to investigate the fundamental cutting mechanisms of PMMA in ultra-precision diamond turning. First, the effect of tool feed rate on material removal behavior was investigated. The flow-type chips, which indicate ductile mode cutting, were observed at all feed rates. However, chips with uneven widths occurred at low feed rates, indicating that machining became unstable. The relationship between surface roughness and feed rate was also explored by measuring surface roughness using a white-light interferometer. It was found that the surface roughness worsened as the feed rate decreased, which showed an opposite trend to the results of glass and metals cutting. Furthermore, the effect of cutting speed on surface formation mechanism was investigated. At a low feed rate (1 µm/rev), the surface finish was improved with decreasing the cutting speed. In contrast, when the feed rate was high (10 µm/rev), surface quality became worse as the cutting speed decreased. By observations of the machined surface and chips at different cutting speeds and feed rates, it was found that the thermoplasticity and brittleness of PMMA are two key factors that affect the machining characteristics. By optimizing the cutting parameters, a surface roughness of lower than 5 nm Sa was achieved, which meets the requirement of optical lenses. These results help to understand the ultra-preicison cutting characteristics of PMMA and are expected to contribute to the fast fabrication of high-quality optical polymer lenses.

Keywords: Diamond turning, Ultra-precision cutting, Optical polymer, Polymethyl methacrylate, PMMA

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