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 (FEA) 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 μm surface roughness with very little brittle fracturing is achieved. The optimum grinding depth, milling speed and corresponding grinding-milling force are 1 μm, 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.