Papers by Author: Sadao Sano

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: 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: 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.

Abstract: This paper proposes a new PCD (polycrystalline diamond) wheel with porous skeleton structure realized by removing the cobalt binder from PCD by EDM (electrodischarge machining), and investigates the grinding characteristics of the wheel. The pores are made successfully on PCD by adopting appropriate EDM conditions. The efficiency of making the pores is found to be higher, when the size of the diamond grains in the PCD material is small, and jumping motion to the copper electrode is not given during the EDM. A porous PCD grinding wheel made by this method using a rotating circular PCD (grain size of 10'm) disc of 20mm diameter has a good skeleton structure with sufficient projections on the wheel surface. A satisfactory grinding characteristics with a surface finish of Ra=0.02'm in grinding on a tungsten carbide work is achieved.

Abstract: A new complex grinding method named Ultrasonic Electrodischarging Grinding Method (US-ED-G in short) is described. In the US-ED-G, ultrasonic grinding and ED grinding are simultaneously carried out on an electrically conductive workpiece with a metal bond grinding wheel. When compared with other complex grinding methods, the US-ED-G is remarkably effective in reducing grinding force a great deal and maintaining grinding ability of a wheel for a long time in efficient grinding of extremely hard-to-grind ceramic materials like TiB2. A stock removal rate of 200mm3/min and a grinding ratio of 110 have been attained by selecting appropriate conditions in US-ED-G of TiB2. A compact and rigid ultrasonic attachment is also described, which was developed as a removable tool for carrying out US grinding and US-ED-grinding on a machining center or a grinding center.

Abstract: Electrically conductive CVD diamond having a high thermal diffusivity, when used as an electrode for micro EDM, revealed very low wear compared to copper and Cu-W electrodes in the case of finish EDM condition, where the short pulse duration is adopted. In this research work polycrystalline diamond (PCD), which has a thermal conductivity similar to that of the electrically conductive CVD diamond, is introduced as a new composite electrode material for EDM. Various properties of PCD with respect to EDM of die-steel (SKD11) and tungsten carbide (G5) have been studied and compared with those of the electrically conductive CVD diamond, copper and copper-tungsten electrode materials. It is found that electrode wear and material removal rate decreased with an increase in thermal conductivity depending on the type of the PCD material when very short pulse duration of te=1µs is applied. Extremely low wear, 1/20~1/50 times of the Cu-W electrode in the case of EDM of tungsten carbide workpiece at short pulse duration and zero wear in the case of EDM at short and long pulse duration of SKD11 can be realized.

Abstract: The performance of electrically conductive CVD (called EC-CVD) diamond thick film possessing a high thermal diffusivity has been examined as an electrode for fine electrical discharge machining (EDM). The results indicate a possibility of zero wear in EDM as compared to copper and copper-tungsten (Cu-W) electrodes. It is particularly significant at short pulse EDM conditions, where the EC-CVD diamond electrodes showed increased machining efficiency and a remarkably low wear. In EDM of tungsten carbide, a very low electrode wear ratio of 0.3% was realized with the EC-CVD diamond electrode. Zero wear EDM could be achieved even for sharp V-shapes with included angles of 15 and 30° with V-shaped EC-CVD diamond electrodes. Thermal FEM analysis to examine the relation between the thermal diffusivity and temperature distribution at short pulse duration indicated lowest temperature on EC-CVD diamond electrode surface.

Abstract: Electro-discharge grinding (hereafter called ED-grinding) was carried out with a trial manufactured metal bond diamond wheel containing electrically conductive diamond grits (hereafter called EC-D-grits-wheel). In this research two effects i.e. removal action of workpiece by electrical discharge machining, and an in-process dressing action of the cutting edges on the grits are expected to take place. The results of ED-grinding with EC-D-grits-wheel (f100mm, SDE120Q80M) on tungsten carbide indicated a significant decrease of 21% in the grinding force, when the set discharge current was increased from 0A to 12A. It was also clarified from the alternative-grinding test with and without an electro-discharge action that stable grinding characteristics along with a reduced grinding force could be achieved in the case of the EC-D-grits-wheel with the electro-discharge action. High-speed camera photographs indicated that a stable discharge condition was achieved.