Slurry Conditions for Reaction-Induced Slurry-Assisted Grinding of Optical Glass Lens
Tappei Kawasato*,, Hinata Takamaru*, Kazuhisa Hamazono**, Masahiko Fukuta**, Katsutoshi Tanaka**, Yusuke Chiba***, Mikinori Nagano***, Hidebumi Kato***, and Yasuhiro Kakinuma*
*Department of System Design Engineering, Faculty of Science and Technology, Keio University
3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
**Nano Processing System Division, Shibaura Machine Co., Ltd., Numazu, Japan
***Production Headquarters, Nikon Corporation, Sagamihara, Japan
The demand for optical glass lenses is rising owing to the increase in image resolution. Optical glass is a hard and brittle material. Thus, an efficient and precise grinding method is required for optical glass to improve lens quality and productivity. There are a few methods of producing crack-free machined surfaces; however, they provide only limited grinding efficiency. To resolve this issue, the authors’ group has proposed the reaction-induced slurry-assisted (RISA) grinding method, which expands the range of ductile-regime grinding by utilizing the chemical–mechanical action of a cerium oxide slurry. In this study, the grinding performance of RISA grinding is experimentally evaluated for different pH levels. The results are compared using Tukey’s test, where surface roughness is considered as the characteristic value and the pH value as the analyzed factor. The result shows that RISA grinding efficiently produces a high-quality surface when the slurry is alkaline. The adhesion of cerium oxide abrasives to the wheel in RISA grinding follows the same mechanism as slurry aggregation. In addition, adhesion is more likely to occur when the alkalization of the slurry promotes aggregation. The tank in the slurry supply unit is replaced with a rotating tank to ensure stable RISA grinding with a highly aggregable slurry while preventing aggregation. The performance evaluation shows that a high-quality surface with a surface roughness of less than 10 nm in most parts is obtained. Moreover, the critical depth of cut stably increases by a factor of 5.8.
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