Study on Machining of Large Acrylic Lens

Abstract

An injection molding has generally been used in the production of plastic lenses. However, it is difficult to make the die and optimize the molding conditions for large-sized lenses. In this study, the cutting of a large-sized lens using ultraprecision lathe was attemped.Acrylic is easy to warp by cutting heat, which sometimes deteriorates the lens performance. So first, the fundamental cutting characteristics of acrylic were investigated to obtain a flat surface by face milling. Experimental results made it clear that the warp could be controlled and acrylic with the fine flatness was achieved by considering the cutting heat. Next, finishing condition for acrylic was examined with various kinds of cutting tools in the ultraprecision lathe. As a result, it was clear that the tool material affects optical characteristics such as the transmissivity and refractive index. But, by using a monocrystalline diamond tool with the suprior thermal characteristics, a large lens 430 mm in diameter could be cut, and the optical characteristics of acrylic material could be retained.