Diamond cutting of a large off-axis Fresnel lens Mold

The oxygen-free copper (OFC) is often used for the substrate material of the molds for the hot hydraulic press, the injection, and the light guide plate. The diamond cutting is usually used for the high precision finish process of the nonferrous metals. In this article, an OFC mold, which is used for testing the hot hydraulic press process of the large segmental double-side polymethyl methacrylate (PMMA) Fresnel lens, was designed. The rotary radius of this mold is about 1000 mm and the mold must be fabricated to the high form accuracy and the low surface roughness. According to the conventional machining method, a rotary table with the radius larger than 1000 mm is necessary for fabricating this mold. However, this mold is justly used for the first test of the hot hydraulic press of the large segmental double-side PMMA Fresnel lens. Thus, the fabrication of this mold should be carried out at the lower cost using the holding machine tool. In order to cut this mold on an ultraprecision air hydrostatic bearing rotary table of 500 mm in diameter, a special method was proposed by the authors of this article. In this experiment, the diamond cutting process of the mold was investigated. The single crystal diamond cutting tool with the tip radius of 1 mu m was used at the depth of cut 1 mu m for the finish process in order to get the mold with the very small groove corner. After the finish cutting process, the surface has a very low roughness.