Papers by Author: Manabu Iwai

Abstract: For a purpose to improve electric discharge machinability of PCD composed of coarse (25μm) diamond particles, which has been thought to be extremely difficult to EDM, in this study, a method (US-EDM) to give an ultrasonic vibration to an electrode in axial direction, flexural direction and complex direction that couples axial and flexural directions was attempted. As a result, it was found that EDM efficiency could be improved to 6 times higher (0.065mm³/min) than a standard efficiency (0.011mm³/min) obtained in machining conventional PCD (C-PCD) and the electrode wear could be reduced to 1/2 by giving vibrations to the electrode in axial direction (frequency f=28kHz, amplitude δ=18μm). Further, this method (US-EDM) was applied also to a new PCD (EC-PCD) composed of electrically conductive diamond particles. As a result, it was made clear that EDM efficiency could be improved to 0.22mm³/min. This value is equivalent to approximately 5 times higher efficiency obtained in the machining of ordinary die steel and cemented carbide materials.

Abstract: Grinding experiments were carried out in wet, with MQL, in dry, with a spray of dry ice particles and various gases to examine influence of grinding atmospheres on the grinding performance in the combination surface grinding of steel and WC with a diamond wheel. From the experimental results, it was found that the grinding with inert gas injection which reduces an oxygen concentration at the grinding point would proceed a processing at more stable grinding force, resulting in less wear of the diamond abrasives.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD) material, which consists of electrically conductive diamond particles, has recently been developed for the purpose of providing the material with both excellent tool properties and machinability. This paper deals with effects of giving ultrasonic vibrations to an electrode on the EDM characteristics of EC-PCD with a view to achieve a great improvement in electro-discharge performance. In this series of EDM experiments, three types of ultrasonic vibration modes were selected (axial vibration, flexural vibration and complex vibration). The result showed that the removal efficiency of EC-PCD increased in any vibration modes. Especially when axial vibration with large amplitude and complex vibration composed of axial mode and flexural mode were given to the electrode, removal efficiency became four times higher than that obtained when no vibration was given. And, electrode wear rate was reduced to one third or 68% against the value of 187% obtained when no vibration was given. Furthermore it was shown that the effects resulted from not only the cavitation action of the working fluid but also the vibrational action of the electrode itself.

Abstract: With its high grit retention and easiness to true and dress, the vitrified bond is widely used as a bond material for cBN and diamond grinding wheels. By giving electrical conductivity to the vitrified bond, application of electrical discharge trueing/dressing and detection of a workpiece position by electrical contact sensing will become possible. And moreover, application of the vitrified bonded wheels to various types of electro-assisted grinding processes (electrochemical or electro discharge assisted methods) is expected. In this study, vitrified bonded diamond segments with electrical conductivity were manufactured experimentally by mixing the fine copper powders in the vitrified bond matrix. As a result of investigation into the electro discharge trueing performance in the die sinking and wire electro discharge machining, it was found that a vitrified bonded wheel could be formed by electro discharge machining only because the bond was electrically conductive. In addition, the electro discharge complex grinding utilizing electric discharge machining was applied to the PCD cutting tool materials using the electrically conductive vitrified bonded wheel, and confirmed that the grinding could be continued for a long time maintaining a stable grinding force.

Abstract: A vitrified bonded diamond wheel having electrical conductivity was manufactured on a trial basis. The electrically conductive (EC) vitrified bonded diamond wheel has enabled an electrodischarge truing and an electrical contact sensing. In this study, the EC vitrified bonded diamond wheel is applied to the EDM (Electro Discharge Machining) assisted grinding of PCD materials. The result shows that a lower and more stable grinding force can be realized and a better surface finish is attained compared with those achievable with a metal bonded diamond wheel.

Abstract: This paper deals with a new surface finishing method of electrically conductive diamond materials by making efficient use of an electrically conductive nature of the workpiece material, instead of conventional methods such as grinding, lapping and polishing using diamond abrasives. The authors focused on the electrolytic machining method and not on the electro discharge machining method for the two advantageous features of the electrolytic machining in addition to the general view that a better surface roughness could be obtained. One of those features is that no higher heat is generated at the machining point. This can eliminate a risk of the film delamination in the case where a workpiece is the CVD diamond coated tool. The other is that a wider machining gap is available between an electrode and a workpiece. This was thought to allow the electrolytic machining to be applied to a tool with a complex shape such as a drill and an endmill. Based on these concepts, electrolytic machining experiments were conducted on the electrically conductive diamond materials. From the results, it was found that the surface of the electrically conductive diamond could be smoothened enough by electrolytic machining though relatively long period of time was required.

Abstract: EDM machinability of PCD was investigated using a copper electrode giving ultrasonic vibrations. In this series of EDM experiments, three types of ultrasonic vibration modes were selected (axial vibration, flexural vibration and complex vibration). From the experimental results, it was found that EDM efficiency became 3 times higher than the ordinary EDM (no vibration given to the electrode) under the two specific vibration modes, namely, 1) the axial vibration (large) mode and 2) the complex vibration (axial vibration: large + flexural vibration: small) mode. Furthermore, it was shown that the effects resulted from not only the cavitation effect of the working fluid but also the vibrational action of the electrode itself.

Abstract: In grinding processes, water-soluble working fluid is in heavy usage to maintain and improve a grinding performance. In this paper, effects of the water quality (soft or hard) were studied in a new filter-less purification system using commercially available Polyglutamic acid based flocculants and the microbubble coolant at the same time. As a result of the experiments, it was found that the collection rate of the suspended matters by the magnetic adsorption removal for the hard water became lower compared to the soft water, due to the Ca component contained in rich. It has also been made clear that by removing the suspended matters in the fluid flocked by the flocculant using the magnetic adsorption method and overflowing the residue with the microbubbles after that, the collection rate of the suspended matters in the soft water fluid would become higher than 99%. In the case of the hard water as well, improvement of the collection rate by the microbubbles was confirmed.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD), which consists of electrically conductive diamond particles manufactured by doping boron atoms, has recently been developed for the purpose of providing material with both excellent tool properties and good machinability. This paper deals with an investigation into the machinability of EC-PCD by EDM with a copper electrode. As a result, it was found that the material removal rate of EC-PCD made up of diamond particles of 10 and 25 µm in diameter respectively was far higher than that of the conventional PCD. Furthermore, it was confirmed in the single pulse EDM experiment with a needle electrode that the EC diamond region in the EC-PCD was removed together with the cobalt region whereas only the cobalt region of C-PCD was removed when the electrode was set at plus polarity.

Abstract: This paper deals with prediction of improvement in surface roughness in helical scan grinding by simulation of virtual ground surface with a 3D-CAD model. It has been found that, by choosing the value of parameters of several grit conditions such as grit arrangement, protrusion height, inclination angle and so on, randomly for a real wheel, the maximum unevenness of the virtual ground surface and tendency of its change with feed angle nearly coincide with the surface roughness in the experiment of helical scan grinding. It is found that this simulation method is effective for the prediction of a surface ground by helical scan grinding.