Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining

Abstract

Achieving a smooth surface finish in optical components by machining requires wear resistant sharp cutting tools. Single crystal diamond as a cutting tool material has met this requirement so far, but at a cost disadvantage. An economical alternative, such as alumina single crystal(sapphire), with sufficient hardness, wear resistance, and chemical inertness, is explored in this work. A sapphire cutting tool with a zero rake, seven-degree clearance, and edge radius of about 430 nm is fabricated using lapping, polishing, and chemical mechanical polishing processes. The performance of the tool was evaluated via orthogonal cutting of OFHC copper, free-cutting brass, Al6061, and Stavax ESR steel. The influence of parameters, such as cutting speed and uncut chip thickness, on surface finish, cutting force, thrust force, friction coefficient, and chip morphology are analyzed. It was observed that the sapphire tool generates surfaces with average roughness ranging from 10–40 nm on copper and aluminum alloys. However, minimal tool wear observed in the machining of copper alloys and excessive in the aluminum alloy and Stavax. Furthermore, built-up edge was significant in Al6061, and edge chipping was dominant in Stavax during machining. Sapphire is a suitable alternative cutting tool material for machining copper alloys.