Papers by Author: Tetsutaro Uematsu

Abstract: This paper deals with a new PCD named EC-PCD which is made up of boron doped diamond particles and its properties related to EDM machinability. For the purpose of improving various properties of standard PCD including resistance to heat, wear and reactivity, a new PCD (EC-PCD) was manufactured on a trial basis using electrically conductive diamond particle as a basic ingredient. Grain size, resistivity and thermal conductivity of the boron doped diamond used are 10μm, 5~37×10Ω•m and 440~580W/m•K. In this report, machinability of newly developed PCD (EC-PCD) by wire EDM was investigated in comparison with that of standard PCD. In wire cutting of 2 types of PCD in water under the condition of open gap voltage: ue=80V, set peak current: iP=0.8A and pulse condition: te/to=20/20μs, it was found that roughness of the first cut surface of standard PCD was approximately 8μm Rz, while that of EC-PCD was far better such as 3μm. Also in finish cut (7th cut), the latter achieved the value of Rz=1.7μm while the former achieved only the value of Rz=2.7μm. Expecting better performance, EC-PCD was tested also in oil. As a result, the best achieved roughness was improved to Rz=0.4μm with no chipping on the edge. To explore a reason for such a good roughness obtained, the cut samples were observed on the SEM, which revealed that the diamond particles in EC-PCD were flattened by electro discharge.

Abstract: The authors have proposed a new coolant named “micro bubble coolant” in which micro bubbles (20-50µm in diameter) are included. In the previous study, it was clarified that the tool life is improved by applying this new coolant to various machining such as boring, turning and grinding. This paper deals with purification effect of the micro bubble coolant. It has been found from the experiments that bacteria which cause putrefaction of the conventional water soluble coolant are eliminated by generating micro bubbles in the coolant. It has also been clarified that the micro bubble coolant isolates minute machined chips and machine oil from the coolant.

Abstract: This paper proposes a new dynamic friction polishing method which utilizes resistance heating for solving a problem of too high pressure on a workpiece in the previous dynamic friction polishing method proposed by the authors. In the new method, an electrically conductive diamond workpiece (which has proper electric resistance) is heated by an electrical current flowing from a stainless steel disc tool to the diamond workpiece during the dynamic friction polishing and the polishing efficiency increases remarkably even at a very low pressure on the workpiece. For example, polishing efficiencies of 233 and 800 µm/min are attained at low pressures of 2 and 5 MPa, respectively, at a disc sliding speed of 2500 m/min.

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 four grit conditions such as grit arrangement, protrusion height, apex angle and inclination angle randomly to 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. Furthermore, it is demonstrated that this analyzing method can be applied to R-shaped groove grinding and suggested that helical scan grinding is effective in grinding bearing grooves.

Abstract: In order to apply the floating nozzle method to an angular grinding on the external cylindrical grinding, basic experiments on V-groove grinding with the wheel edge were performed on the surface-grinding machine. The results showed that the floating nozzle method could maintain a good control of the wheel edge wear, leading to improved surface roughness compared with a conventional nozzle.

Abstract: In order to realize electrochemical finishing in tap water, an ultrasonic vibration using a transducer enabling three kinds of vibration modes, i.e., axial, bending, and complex, was given to the electrode. During the test finishing, it was observed that with electrode without ultrasonic vibration, the workpiece surface was simply covered with the rust. On the contrary, by applying the ultrasonic vibration of bending vibration mode or complex vibration mode with an appropriate amplitude, the material removal rate was increased and the surface roughness was improved.

Abstract: Estimation of mechanism of surface finish improvement in helical scan grinding, a method in which a good surface finish is obtained besides keeping a high grinding efficiency, is performed based on the virtual grinding trace using a 3D-CAD model. In three grit models, (a) a single grit on a wheel, (b) plural grits arrangement on a helical line on the wheel circumference, and (c) multiple grit arrangement in a triangular pattern, virtual grinding traces and their unevenness or surface roughness are investigated. The virtual grinding trace in helical scan grinding is made by interference of grit trajectories, and the results of the analysis are very similar to experimental results.

Abstract: It has been reported in our previous report that electrically conductive CVD diamond (hereafter, EC-CVD diamond) having specific resistance of the order of 1x10-3 Ω⋅m shows almost zero electrode wear even at the short pulse duration of 3μs on a die-sinking EDM machine. In this research EDM properties are investigated in the context of the pulse on time in oil and water. It is found that the electrode polarity has an effect on the electrode wear of the EC-CVD diamond electrode in oil. In the test in oil, EC-CVD diamond shows zero wear at positive [+] electrode polarity but a higher wear at negative [-] electrode polarity than that of the copper electrode. Furthermore, the EC-CVD diamond electrode showed very less wear than copper even in water. These results in oil and water may be due to the high thermal diffusivity, an increased rate of carbon adhesion and the high thermal stability of the EC-CVD diamond electrode. Workpiece surface roughness using the EC-CVD diamond electrode is about 20~50% lower than using the copper electrode under the same EDM conditions. From the single pulse discharge experiment with EC-CVD diamond and copper electrodes, the improvement in roughness is explained by the dispersion of the discharge in the case of EC-CVD diamond due to its rather high specific resistance.

Abstract: In order to improve the floating nozzle method, a new coolant supply method using a coolant flow guided flexible sheet has been developed. In this paper, basic properties of the coolant supply when the coolant flow guided flexible sheet method is used are investigated. At first, the phenomenon of automatic adherence of the flexible sheet to the wheel surface is observed with a high-speed camera. Next, the effect of the clearance between the sheet and the wheel surface is experimentally investigated. It is found that the thickness of the coolant flow in this clearance is very small as about 0.1mm, and can be controlled to some extent by controlling the coolant flow rate and wheel rotation speed. Furthermore, it is clarified that the influence of the flexible sheet on the electric power consumption of the main spindle motor is small.

Abstract: Polycrystalline diamond (PCD) exhibits a thermal conductivity similar to that of the electrically conductive chemical vapor deposition diamond (EC-CVD diamond) found to function as zero-wear electrodes at short pulse duration. In this study, PCD was used as electrodes applied to EDM on tungsten carbide. Two kinds of PCD (CTB-010 and CTH-025) with a flat surface were used. The wear of the PCD electrodes was about 1.5% for very short pulse duration such as te=1μs, but it was zero wear at te=30μs, though the wear of a Cu-W electrode was 10% even on the machine recommended conditions for the low wear. EDM experiment using a V-shaped PCD electrode with an included angle of 45° was also carried out and the performance was compared with the case using a V-shaped Cu-W electrode. Under the conditions of a no load voltage of 60V, a set peak current of 2A, and a medium pulse duration of te=15μs, there was no wear on PCD electrodes when observed under the SEM, whereas a 50μm-deep wear on the Cu-W electrodes even under the machine recommended condition for the low wear was observed.