A force controlled grinding-milling technique for quartz-glass micromachining

This paper presents a novel approach to the micromachining of quartz glass using an intellectualized grinding-milling technique to overcome the difficulties in machining hard-brittle materials. A bench-type linear 3-axis CNC machine tool providing grinding-milling at depths of several nanometers is constructed to realize ductile-regime material removal during quartz-glass milling. Finite element analysis (PEA) is conducted on the deformation and resonant frequency of the developed machine tool. A micro-tipped grinding-tool made of boron-doped polycrystalline composite diamond (BD-PCD) and designed with a double-negative back rake angle (DN-BRA) to create compressive stress grinding-milling is proposed and employed. To sense the force at which grinding-milling is conducted and provide real-time feedback on the milling tool's feed-rate, load-cells are devised on 3 axes. Using an appropriate grinding-milling technique in combination with proper feedback to control the machining feed-rate, quartz glass is machined layer-by-layer under a ductile regime. A miniature 3-step-shaped pyramid made of quartz glass of 0.3 mm in height and of Ra0.66 mu m surface roughness with very little brittle fracturing is achieved. The optimum grinding depth, milling speed and corresponding grinding-milling force are 1 mu m, 50-70 m/min, and 0.4 N, respectively. A comprehensive examination of the quantitative and qualitative properties of the BD-PCD tool was undertaken. Experimental confirmation of the proposed approach is presented. Additionally, the following aspects are discussed in detail: the spark erosion rate of the machined diamond tool, milling feed-rate, grinding depth, graphitization of diamond, and tool wear. (C) 2014 Elsevier B.V. All rights reserved.