Papers by Author: Manabu Iwai

Abstract: The authors have been conducting a research to apply strong alkali ion water (pH12 or so) to a working fluid for material removal processing. This is to cope with various problems relating to the existing water-soluble working fluid such as coolant putridity and the associated deterioration of factory environments and increased disposal costs of working fluids as well as to improve machining efficiency and tool life. In this study, the strong alkali ion water was applied to the tapping (M10) of stainless steel (SUS440C). As a result, use of the strong alkali ion water was found to contribute to the tool life improvement.

Abstract: In this study, a polycrystalline composite diamond (PCD) was adopted instead of a single crystal diamond as a burnishing tool. At first, EDM machinability was compared between two kinds of PCDs (10μm grain size), i.e. standard PCD (S-PCD) and electrically conductive PCD (EC-PCD (which was made of boron doped diamond particles). EDM machining time to make a hemispherical shape was 17 minutes for EC-PCD and 37 minutes for S-PCD. Further experiments were conducted with EC-PCD of different grain sizes such as 2μm and 5μm. As a result, the smaller the grain size of EC-PCD the higher the machining efficiency was. Surface roughness values of the EC-PCD after finish EDM were Rz=1.7μm for EC-PCD010, Rz=1.4μm for EC-PCD005, and Rz=1.2μm for EC-PCD002. As a result of burnishing a carbon steel bar (S45C, φ30mm) with the EC-PCD tool, the surface roughness value after machining was improved from 10μm to 1μm.

Abstract: As a measure to perform a burnishing process easily on an NC lathe, the authors propose a new method using a flank face positioned in a few millimeters lower part of the nose cutting edge of a tool. In the experiment, giving a fixed depth of burnishing (t=1, 2 and 4μm/pass), the carbon steel workpiece (S45C) of φ30mm which had been turned at V=200m/min and f=0.15mm/rev was burnished by predefined number of times. As a result, the surface roughness improved in nearly proportion to the total depth of burnishing and the roughness value of Rz≈10μm measured after turning could be improved to Rz≈2.5μm. Utilizing the feed control with an accuracy level of micron meters of the NC lathe, an attempt to control the dimensional accuracy of the workpiece diameter in the order of micron meters was also made. As a result, the workpiece radius came down constantly by 0.6~0.8 times in proportion to the tool depth of burnishing (t=1μm/pass), which reveals that the dimensional accuracy of the workpiece diameter could be controlled by the proposed burnishing process utilizing a fixed depth of burnishing system. Using the same burnishing process, circularity of the workpiece Δr could be improved to Δr≈2μm from Δr≈4μm measured after turning.

Abstract: For the purpose of improving the electric discharge machinability of PCD, the authors have proposed a method using an electrode made of a specific transition metal which is easy to react with diamond. As a result, Ti, Nb, Ta, Mo, and W among various reactive metals brought very high efficiency, higher than 3 times of existing electrode materials (Cu, CuW) in the EDM of PCD. It was thought that the higher removal efficiency was due to the material properties such as mixing enthalpy between transition metal atom and carbon atom and a crystal structure of body centered cubic (bcc) lattice.

Abstract: Recent years, use of the strong alkali ion water produced by electrolyzing high purity water (RO water) with addition of a small amount of electrolyte (potassium carbonate) is becoming widely used as a substitutable cleaning liquid in place of organic solvent which is said to exert a bad influence on the environment. The authors have been conducting a research to apply this strong alkali ion water (pH12 or so) to a working fluid for material removal processing. This is to cope with various problems relating to the existing water-soluble working fluid such as coolant putridity and the associated deterioration of factory environments and increased disposal costs of working fluids as well as to improve machining efficiency and tool life. In this study, the authors would like to describe how the working fluid consisting of water-soluble lubricant diluted with the strong alkali ion water contributes to an improvement of the factory environment and verify experimentally that the said fluid could improve the tool life by 1.2 to several times. In addition, a factor contributing to the improvement of material removal characteristics has been found to be the fact that the friction resistance of the said fluid containing the strong alkali ion water is as low as 2/3~1/2 of that of the fluid diluted with the city water.

Abstract: The authors developed “Dynamic Friction Polishing (DF polishing) Method” utilizing a thermochemical reaction between a diamond workpiece and a metal. This method enables high efficiency abrasive-free polishing of single crystal and polycrystalline diamonds (PCD) by simply pressing them against a stainless steel (SUS304) disc rotating at a high peripheral speed (V_S>2500m/min). In the authors’ previous paper, a top of the diamond test piece (0.6mm×0.6mm, (100) plane) was removed at a rate of 2.6mm/min (0.94mm³/min) under the polishing condition of sliding speed V_S=4000m/min, loading pressure P=130MPa and polishing time t=10s. A bottleneck for practical use of this method is a high pressure over 100MPa required for pressing a diamond workpiece against a rotating stainless steel disc. In this paper, a high efficiency tool was manufactured by electro-spark deposition of highly reactive special metals on a base disc tool. Among various reactive metals Nb and W brought very high efficiency in the polishing of a single crystal diamond.

Abstract: In order to cope with various problems associated with machining of PCD, development of a new PCD possessing excellent tool properties and good machinability at the same time has been demanded. From this point of view, the authors have developed a new PCD, “EC-PCD (Electrically Conductive PCD)”, composed of boron doped diamond particles in place of the standard non-conductive diamond. In this research, investigation into material properties of the newly developed EC-PCD is made. Through the tests, it was found that the boron doped diamond particles (the source material of the new PCD) had an electrical resistivity of 1.6×10^-4Ω·m and the thermal conductivity after sintering was lower than that of the standard PCD. In addition, it was confirmed that the electrical conductivity of the source diamond particles of the EC-PCD had not been lost even under the condition of high temperature and high pressure during the manufacture. As a result of the heat test, EC-PCD’s high resistance to oxidation at high temperatures was confirmed showing no changes in the surface condition even at 675oC while the surface of the S-PCD was largely changed at the same temperature. One of the reasons for this is guessed to be that EC-PCD is hard to react with the cobalt contained as a catalyst metal. Further, it was found in the friction tests using a steel ball that the friction coefficient of the EC-PCD was 50% higher than that of S-PCD at the room temperature though it dropped by 10-30% at the temperature of 80oC.

Abstract: In order to achieve a high efficient and high quality EDM of PCD, the authors have developed a new PCD having superior electrical conductivity by using boron diamond as a source material. On the other hand they applied a method to give ultrasonic vibrations to the electrode, and have made it clear that even the standard PCD could be machined at the similar level of efficiency to the cases of EDMing die steels and cemented carbides. With a purpose to obtain a good surface roughness on the PCD at high efficiency, various EDM conditions and methods were compared in this paper. Firstly, influence of discharge duration time was examined, and it was found that a shorter pulse duration time as t_e=0.5μs showed high efficiency and smaller electrode wear rate. Secondary, influence of bipolar pulse current method was examined, and it was found that the method effected higher efficiency but rather large amount of electrode wear resulted. Thirdly, ultrasonic assisted EDM was conducted, and it was found that the method showed superior result regarding efficiency and wear rate on both standard PCD and EC-PCD. A combination use of ultrasonic assisted and bipolar pulse current EDM methods was also attempted in this research. On the contrary to the expectation, efficiency and electrode wear rate became worse in EDM of standard and EC-PCD in comparison with other methods tested before.

Abstract: Electrically conductive PCD (EC-PCD), which was made of electrically conductive diamond particles, was applied to an electrode for EDM. In this study, properties of EC-PCD electrode in the EDM of cemented carbide were investigated and the results were compared with those of copper-tungsten (Cu-W) electrode and standard PCD (S-PCD) electrode. In terms of EDM speed, 35μm/min with Cu-W electrode, 15μm/min with S-PCD electrode and 22μm/min with EC-PCD were recorded. As for the electrode wear rate, though Cu-W electrode wore by 20-30%, S-PCD and EC-PCD did not wear at all and even the electrode length became longer by several micro meters. Roughness value of the EDMed surface was Rz=8μm with both Cu-W and S-PCD, while it was Rz=3μm in the case of EC-PCD. From the above, it was found that EC-PCD showed excellent performance in the electrode wear rate and the roughness of the EDMed surface, though EDM speed was 0.7 times of Cu-W electrode.

Abstract: It has been made clear that the EC-PCD composed of boron doped diamond particles improves the performance in the die sinking EDM and wire EDM in comparison with the existing standard PCD (S-PCD). However, the effect of the property improvement could not been evaluated quantitatively in the research reports in the past. Therefore, in this study, wire EDM cutting tests were conducted on the specimens of S-PCD and EC-PCD, in addition to the evaluation of cutting efficiency and cutting PCD surface, a detailed investigation of the cut surface properties of the PCD has been performed under the color 3D laser scanning microscope. In order to investigate effects of a grain size of the source diamond, EDM cutting experiments were conducted on the EC-PCD specimens of 4 different grain sizes. As a result, it was found that the cutting speed was higher in the case of EC-PCD than the case of S-PCD, e.g., by 20% and 40% respectively in the sample of 10μm and 25μm particle size. Also, in the case of the cut S-PCD surface, a groove due to the discharge is formed in the boundary of the tungsten carbide layer and the PCD layer. However, in the case of the cut EC-PCD surface, the groove did not appear in the boundary.