With the aim of realizing ultra-small-diameter cutting tools with high performance, we have fabricated gun barrel drills 15μm in diameter made of superhard materials, such as sintered diamond (PCD) and cubic boron nitride (CBN). Electrical discharge machining was employed for fabrication, which enabled simple tool fabrication even for tools composed of superhard materials. Their drilling performance was also investigated and compared with that of cemented carbide drills. The increases in cutting force and tool wear for PCD drills were less than those for cemented carbide drills, although the tool life of some PCD drills, shown as the number of drilled holes until tool breakage, was shorter. The tool life of CBN drills was much shorter, probably because the grain size of CBN was larger than those of PCD and cemented carbide.

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In this paper, a simulation method for analysis of the surface texture taking motion error of the machine tool into consideration is proposed and the influence of tool run-out on the surface texture is examined. By comparing simulated results with the actual surface texture of a metal mold machined by a ball-end mill, the influence of tool run-out on the surface texture is evaluated. The tool run-out hardly affects the surface texture in cases in which the feed marks are made by only one edge of the ball-end mill. Furthermore, the surface roughness reaches a minimum at a certain tool tilting angle when a ball-end mill with large tool run-out is used. Finally, the machined surface roughness is calculated based on the cusp height commonly used for the machining of metal molds when the tool run-out is varied. From this relationship, the allowable tool run-out to obtain the required surface roughness can be effectively estimated.

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This paper presents the mechanism of formation of cutting edges in micro dressing of coarse-grained cBN vitrified bonded wheels using a fine-grained diamond dresser. A flat surface consisting of many micro brittle dents as well as ductile smooth surfaces is formed on top of the cBN grain cutting edge by micro dressing using a fine-grained diamond dresser with a grain size of #1200. A mirror surface with a roughness <0.035μm Ra can be formed efficiently using the cBN wheel working surface prepared by this micro dressing method.

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Polycrystalline diamond (PCD) has been widely used for various cutting tools and die components, taking advantage of its hardness and wear resistance properties. For wide application of PCD, methods to obtain a mirror-finish surface and for ultra-precision machining of PCD are required. In this study, UV-assisted polishing was applied to the final polishing of PCD. The removal rate of constant-pressure grinding was 10μm/h, and short-term UV-assisted polishing was able to remove the abrasion marks induced by the constant pressure of grinding. The micro-roughness after UV polishing finally reached 0.8 nmRa, and the roundness of sharp edges of PCD was 0.29μm. The curved surface of the PCD die mold was finished by UV-assisted polishing, and the effectiveness of this method was confirmed.

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Under optimum grinding conditions, constant grinding force is exerted on a workpiece during ductile-mode grinding of BK7 glass. The existence of such a constant force results in a ground surface without cracks, no residual stock removal, and a consistent number of successive grits. Based on the results, the cutting force, specific grinding energy, and depth of cut for a single grain could be calculated. The tangential force is <0.18 mN, specific grinding energy is <5 mJ, and depth of cut is <4 nm with a removal rate of 0.075 mm³/s. These results suggested that it is easy for a single grain to be removed in ductile mode. However, above 0.075 mm³/s, grinding is almost impossible because surface burning occurs on the workpiece. The continuous contact between the wheel and workpiece is thought to result in heat generation. Thus, to achieve a more intermittent machining process, the application of thrust force directional vibration was demonstrated.

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