Papers by Author: Shinichi Ninomiya

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: 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: 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: To improve the characteristic of the floating nozzle method, a new coolant supply method using a coolant flow guided flexible sheet was developed. In this method, all the coolant supplied from the nozzle outlet can surely be directed immediately to the grinding point, because the coolant flow guided flexible sheet made of a thin sheet material is attracted to the wheel surface automatically, and confines the coolant between the wheel surface and the sheet. Therefore, the coolant can be completely prevented from deviating away from the grinding point. In fact, when the coolant flow rate of 4 l/min was supplied from the upper part of the wheel by using this method, the amount of coolant that reached the grinding point was 18 times higher than the case of only the floating nozzle method. It was clarified that this method had the effect to improve the grinding performance. Furthermore, this new method has a possibility of the wide application such as in profile grinding and cam grinding.

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.

Abstract: Electrically conductive cutting edges diamond grinding wheels (EC-cutting edges D wheels) have properties such as, 1) convenient precise forming by EDM, 2) realization of high cutting edge density, 3) sufficiently large chip pockets along with fine cutting edges on large diamond grits, 4) contact sensing of the cutting edges with workpiece due to electrical conductivity, 5) expected application to the grinding of various types of steels due to high thermal resistance. Until now, the grinding ability of the sharp edges generated on the electrically conductive CVD diamond thick film wheel by electrodischarge trueing (ED trueing) was confirmed by grinding experiments using a small diameter lapping wheel and a small diameter disk wheel. In this research work, metal bonded diamond wheels containing boron doped electrically conductive diamond (EC diamond) grits, which possess high oxidation temperature, were trial manufactured. From the results of grinding test for an optical glass (BK7), it was found that the wear and grinding force for the EC diamond grits wheel were significantly low compared to a conventional diamond grits wheel. Furthermore, from the results of the investigation on ED trueing performance, a high trueing efficiency along with the possibility of cutting edge tip formation was confirmed.