Key Engineering Materials Vols. 523-524

Abstract: Single-phase (binder-less) nano-polycrystalline diamond (NPD) has been synthesized by direct conversion sintering from graphite under high pressure and high temperature. NPD is characterized by extremely high hardness compared with single crystal diamond (SCD), even at high temperature. In addition, NPD has high wear resistance, no anisotropic mechanical properties, no cleavages, and high thermal stability. These characteristics suggest that NPD has high potential for use in precision cutting tools for various hard works. In order to evaluate the cutting performance of NPD, cutting tests for various cemented carbides were conducted under various conditions and the results compared with those of single crystal diamond (SCD) and conventional polycrystalline diamond containing metal binder (PCD). The results revealed that NPD has outstanding potential for precision cutting and processing of diverse hard and brittle materials.

Abstract: The BTA tool is a tool for deep-hole drilling. The deep-hole which be machined by this tool has the excellent straightness and roughness. However, it's use a lot of cutting oil. Therefore, it will lead to environmental destruction. Thereupon, in this study, it is applied the near-dry system to the deep-hole drilling with BTA tool. In the previously, it was designed the experimental device with a double tube system, and the cutting experiments was carried out. In this system, the chip is discharged through inside of the inner tube. Frequently, the chip is cannot be divided by the adhesion on the cutting edge during drilling. Thereby, the chip was jammed into the inside of tool’s tube. It is tried experiments of various cutting conditions, cutting speed and feed rate, by tools with different geometry, height and width, of the chip-breaker. And, it is observed the discharge condition of chips, the chip’s shape and the situation of adhesion. As a result, it can be found the optimum cutting condition and tool’s geometry for a continuous chip’s discharge while the deep-hole is drilling by a BTA tool in near-dry system.

Abstract: Tungsten carbide is a crucial material for glass molding in optical industry. The present study investigated a feasibility of ductile machining of sintered tungsten carbide for glass molding by applying ultrasonic elliptical vibration cutting technology with single crystal diamond tool. Grain size and binder material of sintered tungsten carbide have an influence on hardness and/or toughness of the material. Binder material also has a chemical affinity to diamond. In order to examine the influence of material composition on ductile machining of tungsten carbide, a series of grooving and planing experiments were conducted to several different tungsten carbide workpieces with the different binder phase and the different grain size. The experimental results indicated that micro grooving in a ductile mode can be attained successfully by applying ultrasonic elliptical vibration cutting, while finished surface deteriorates with brittle fractures in ordinary cutting. It was also clarified that grain size and binder material have significant influence on the deteriorations in the surface quality, the tool shape and the cutting forces.

Abstract: Recently, in accordance with the technical development and miniaturization of the information equipments, the demand of optic elements with high precision and miniaturization is increased. The mold is used in the manufacture of the optic elements. Thus, it is needed to machine the mold with high efficiency and high precision. As the material of mold, hard material including cemented carbide and ceramics is used. However, it is a problem of the occurrence of severe tool wear when hard material is machined. To solve this problem, the cutting point swivel machining by using the diamond tool with special chamfer was proposed, which has the ability to suppress tool wear and to realize ultraprecise machining. It is confirmed that the cutting point swivel machining has the ability to suppress tool wear by the microgrooving experiment of SiC. This study aims at investigating the effect of the cutting point swivel machining, and making clear the relationship between tool rotation speed and tool wear. As a result, it is known that the actual cutting direction can be changed by using the cutting point swivel machining, and that the chipping of tool becomes conspicuous with increasing tool rotation speed.

Abstract: In this research, the temperature rise of the machined layer during surface grinding using a fluid supplying system from inside of grinding wheel is measured. Compared with the conventional fluid supply from an external nozzle, the grinding fluid is expected to be reached surely to the grinding point if this fluid supplying system is used. Thus the amount of supplying fluid can be reduced keeping the comparable cooling efficiency. Two or more thermocouples are continuously set to the machining layer from its back side through the small hole. Then the temperature change was measured during the continuous reciprocating grinding (round trip) with small depth of cut. As a result, even if the amount of the grinding fluid supply is decreased to 0. 5 L/min, the temperature rise in the machining layer is not very different from the case that the supplying amount is 10 L/min. In addition, by the result of the series of the experiments, the relationship between the temperature rise of the machining layer and the state of the supply of the grinding fluid and the grinding energy is inspected.

Abstract: PcBN cutting tools have excellent characteristics such as high degree of hardness and low chemical reactivity, so they have potential to replace high precision grinding of hardened steel with high precision cutting. PcBN might be more efficient tool material if improvement in formability, and good surface modification can be achieved. In order to solve these problems, Pulsed Laser Grinding (PLG) is applied to a shape cutting edge and to finish a rake face. After processing by the PLG, shaped cutting edges were observed with a scanning electron microscope (SEM) and measured with contact- type profilometer. As a result, cutting edges processed by the PLG are similar or shaper than that by conventional diamond grinding. In addition, as a one of effects of surface modification, The Vickers microhardness of rake faces increases by about 10 present after PLG. On the other hand, according to frictional test with lateral force microscopy, the coefficient of friction of rake face decreases by half of ordinary surface. Depending on these advantages of PLG, high precision turning of hardened steel with 58HRC in hardness by use of the tool processed by PLG can demonstrate good performance rather than a commercial tool with diamond grinding finish.

Abstract: This paper presents a mechanism for the formation of grain cutting edges in the micro dressing of coarse-grain polycrystalline cubic boron nitrite (cBN) grinding wheels using a fine-grain diamond dresser. Many grain cutting edges having a flat surface consisting of ductile smooth surfaces as well as many brittle micro dents, are formed on the working surface of the coarse-grain (#80 mesh) cBN wheel by micro dressing using a fine-grain (#1200 mesh) diamond dresser. This result shows that the flat surfaces of cutting edges on the wheel surface are formed on the basis of a ductile removal process as well as a brittle micro-fracturing of cBN grains by the diamond cutting edges. Moreover, cylindrical grinding experiments with these wheel working surfaces were conducted to clarify the feasibilyty of creating a ground mirror-like surface. As a result, it was confirmed that high-quality mirror surfaces with roughness less than 0.03 m Ra can be efficiently formed using the working surface prepared by this micro dressing method.

Abstract: Superalloys, used for turbine blades and jet engines for airplanes, have low heat conduction and high strength at elevated temperature. These properties make it very difficult to obtain effective grinding processes with high accuracy. Superalloys with fine performance under high temperature circumstances attract great attention to be used as the material for turbine blades. It has been expected to establish reliable efficient grinding of superalloys at the final grinding process. In this study, the influence of wheel wear, grinding ratio, and surface roughness, with the grinding process of superalloys, using metal bonded CBN wheel were carefully observed. Since superalloys have lower heat conduction and they cause a severe wheel wear, which leads to low grinding ratio. However, the high grinding ratio of about 800 and the stable figure of surface roughness of Rz=2μm were obtained when Co-base PWA647 and X45 were ground by using metal-bonded CBN wheel. Consequently, the Co-base superalloys perform rather well producing finer grinding process than the intensive Ni-base or Fe-base superalloys.

Abstract: In order to improve the efficiency of high-hardness laser strengthening mold polishing, especially to the free-form surface, a new precision finishing method based on soft-consolidation abrasives pneumatic wheel is brought forward. The pneumatic wheel is constituded by flexible rubber maxtrix, combined with the robbet control. The abrasives group is bond to the rubber matrix by the polymer binder. In the way, compared with those free abrasives used in other polishing method, the soft-consolidation abrasives can get more stable surpport from nearby polymer to form effective cutting. On the other hand, it is unlike the abrasive of rigid grinding wheel because the flexibility of pneumatic wheel can have self-adaptation according to the changes in local curvature and achieve large scale copying contact between tools and work piece. Combined with the lay elastic system theory and Preston equation and coefficients, the mechanics model of polishing is given. The results of experiment shows the Ra of workpiece can be reached to 0.09um and the efficiency of process can be improved three times more than free abrasive machining. It will show its wild prospects in the process of polishing.

Abstract: Ultrasonic vibration assisted processing is well known for the improvement in machined surface quality and processing efficiency due to the reduced forces and tribology-generated heating when grinding hard-brittle materials. We transplanted this philosophy to chemo-mechanical fixed abrasive polishing of optical glass, namely fused silica, in an attempt to improve surface roughness and/or material removal rate. Experiments were conducted to elucidate the fundamental characteristics of chemo-mechanical fixed abrasive polishing of fused silica in the presence and absence of ultrasonic vibration on a setup with an in-house built gadget. The experimental results show that ultrasonic vibration assisted chemo-mechanical fixed abrasive polishing can yield increased material removal rate while maintaining the surface roughness of manufactured optics compared to conventional fixed abrasive polishing without ultrasonic vibration. The mechanism of material removal in fixed abrasive polishing was also delved. We found that the glass material is removed through the synergic effects of chemical and mechanical actions between abrasives and glass and the resultant grinding swarf contains ample Si element as well as Ce element, standing in stark contrast to the polisher that contains abundant Ce element and minor Si element.