Shinichi Ninomiya

A New Complex Grinding Method for Ceramic Materials Combined with Ultrasonic Vibration and Electrodischarge Machining

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.

Prediction of Surface Roughness by 3D-CAD Model in Helical Scan Grinding and Groove Grinding

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.

Development of New PCD Made Up of Boron Doped Diamond Particles and its Machinability by EDM

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.

A New Diamond Wheel Containing Boron Doped Diamond Abrasives Enabling Electrically Conductive Cutting Edge and High Thermal Stability

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.

Effect of the Floating Nozzle in Grinding of Mild Steels with Vitrified CBN Wheel

In the case of grinding mild steels using a vitrified CBN wheel, considerable wheel wear is caused because ground chips accumulate in the chip pockets of the wheel and the CBN grains fall out from the wheel surface. In this study, in order to suppress the wear of vitrified CBN wheels, the floating nozzle developed by the authors was applied to the grinding of mild steel materials and the grinding performance was investigated experimentally. It was confirmed that, when the coolant was supplied with the floating nozzle, the wheel wear was reduced in half with a quantity only 1/12 times of the one with a conventional coolant nozzle. The surface roughness and surface quality of the ground workpiece were improved by using the floating nozzle. Moreover, by the use of emulsion type coolant combined with the floating nozzle, the wheel wear was smaller, compared with the one using the solution type coolant. Introduction CBN grinding wheels are widely used nowadays in various types of grinding operation. Hardness and thermal conductivity of CBN grains are extremely high next to diamond grains. Therefore, CBN wheels can correspond to the high efficiency grinding and the high precision grinding of hard materials such as heat treated steels [1]. However, in the case of grinding of mild steel materials using a vitrified CBN wheel, a considerable amount of wheel wear is caused because ground chips accumulate in the chip pockets of the wheel and the CBN grains fall out from the wheel surface [2]. Dr. Syoji et al reported that the wear of a vitrified CBN wheel can be suppressed by increasing wheel peripheral speed and supplying coolant jet at a high pressure [2,3]. On the other hand, the authors proposed a floating nozzle which can supply coolant effectively especially to profile grinding wheels of arbitrary shapes [4]. When coolant is supplied to a wheel with the floating nozzle, the grinding performance improves remarkably with a small amount of coolant compared with a conventional coolant nozzle [4-6]. The reason for this is that a necessary amount of coolant reaches the grinding point effectively by using the floating nozzle, resulting in effective cooling and lubrication. In this paper, the floating nozzle is applied to the grinding of mild steel materials in order to suppress the wear of a vitrified CBN wheel and the grinding performance is investigated experimentally.

Effect of Complex Electrodischarge Grinding for Electrically Conductive PCD

Polycrystalline Composite Diamond (PCD) is excellent in chipping resistance despite its very high hardness. However, it is not easy to EDM or grind PCD. To realize high efficiency and high quality processing of PCD simply and at low cost, the authors devised new PCD (EC-PCD) by using electrically conductive diamond particles and applied a complex electrodischarge grinding method. In this study, investigation is made on effective grinding condition to realize high efficiency, low and stable grinding force and low wheel wear in complex electrodischarge grinding. As a result, superior grinding property was obtained when the grinding wheel was set at minus polarity, and set peak current of iP = 4 and 6 A was applied. Furthermore it also became clear that additional conventional grinding process followed after complex electrodischarge grinding improved the surface condition.

Odor Suppression of Putrid Water-Soluble Coolant Using Home Ion Generator

This paper deals with a technique to easily suppress bad odor of water-soluble coolant (working fluid) by using a commercially available ion generator for home use. At the shop floor, water-soluble coolant is in heavy use, where putrid bad odor is apt to be generated from water since over 95% of the coolant component is water, leading to a short life of the coolant. Expecting an effect of suppressing putrid odor of water-soluble coolant, application of ion mixed air using an ion generator for house use was examined. As a result, bubbling with ion mixed air could achieve a drastic suppression of a bad odor generated from putrid water-soluble coolant, compared to a bubbling with air only. In addition, it was confirmed that by discharging ions into a machine emitting a bad odor, the odor level decreases drastically. From these results, a machine having an ion generator built-in can be proposed as an environmentally friendly machine tool.

EDM Properties of EC-PCD Using a Copper Electrode

Electrically conductive polycrystalline composite diamond (EC-PCD), which consists of electrically conductive diamond grits, has recently been developed for the purpose of providing the material with both excellent tool property and good machinability. This paper deals with an investigation of machinability of EC-PCD by EDM with a copper (Cu) electrode. As a result, it was found that the EDM speed (Material removal rate) for EC-PCD was higher than that of the standard PCD. Although the surface roughness of the standard PCD was 13µm Rzjis at set current ip=3A, the surface roughness of the EC-PCD was 5µm Rzjis at the same current condition. Furthermore, it was observed that the EC diamond particle in EC-PCD was machined by single discharge EDM. Moreover, it was confirmed that EC-PCD was able to be applied a fine discharge profiling or a making fine holes using a rotating electrode.

Complex Grinding Assisted with Electrical Discharge Machining for Electrically Conductive PCD

A new PCD material named EC-PCD (Electrically conductive polycrystalline composite diamond), which consists of electrically conductive diamond grits, has recently been developed. This paper deals with an investigation of a complex grinding assisted with electrical discharge machining (EDM) to realize high efficiency, low and stable grinding force and low wheel wear for the new EC-PCD. The effect of complex grinding assisted with EDM is compared experimentally with the standard PCD (S-PCD). The result shows that, in the complex grinding, lower and more stable grinding force is realized thanks to the material removal action in EDM and that lower wheel wear and better surface finish are attained, just when the EC-PCD is selected as a workpiece.

Purification Effect of Micro Bubble Coolant

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.