Development of an in-situ high-precision micro-hole finishing technique

This study presents the development of an in-situ hybrid micro-manufacturing process for making a novel micro-tool for the fabrication of a high-precision micro-hole of 200 μm in diameter in difficult-to-machine material. The hybrid approach consists of rotary micro-EDM, micro-EDM peck-drilling, co-deposition, reverse micro-w-EDM, and micro-honing. These techniques can all be conducted on a single machining center allowing for in-situ micro-manufacturing. On the basis of the concept of a 'machining center', a horizontal/vertical dual-usage high-precision headstock and a hybrid work-tank with modularized design are devised. A novel micro grinding-tool which has an invert-tapered forked microstructure with central-symmetry and radial-elasticity is designed and fabricated using the hybrid processes. By applying the principle of cantilever beam support, the micro grinding-tool is employed for honing a micro-hole on SKD11 cold-working steel, achieving micro-scale material removal. All working coordinates are recorded during the process, the micro-tool and-workpiece do not need to be unloaded and repositioned until all planned tasks are completed. Experimental results demonstrate that flatness of the hole-wall, circularity, and surface roughness of the honed micro-hole are 1 μm, 0.5 μm and Ra0.032 μm, respectively. Approaches to the factors influencing formation and accuracy of the micro-tool involving surface topography, current density in co-deposition, wire tension, rotation speed in honing, and tool longevity are all evaluated in detail.