Experimental Investigation of Surface Roughness in Ultra-Precision Cutting of Plastics

Abstract

The plastic optical components have recently been increasingly used as one of the key parts of the high precision equipments and machines such as over head projector, compact disk player, projection TV, copy machine. The present research aims to clarify the influence of cutting conditions on the surface roughness formed by ultra-precision cutting of plastics and as the result find the best plastic for ultra-precision cutting. For the purpose, the plastics of polymethyl methacrylate (PMMA), polycarbonate (PC) and cycliic olefin polymer (ZEONEX), which are the representative plastics used as the optical parts, are face-turned at various cutting conditions with single crystal diamond bite attached on the ultra-precision turning machine. Then the face-turned plastic surfaces are observed with a Nomarski differential interference microscope and measured with AFM (NanoScope III). The best surface roughness formed by dry ultra-precision cutting is about 20nm(Ry) for the PMMA plastic while it is over 100nm for the PC and ZEONEX. The cutting fluid supply is useful for improving the surface roughness and the best surface roughness formed by wet ultra-precision cutting of the PMMA plastic is about 10nm (Ry). The best surface roughness obtained in the wet cutting of the PMMA plastic is almost the same for the different bite nose radius. The depth of cut and cutting speed in the wet cutting of the PMMA plastic have little influence on surface roughness.