Advanced Materials Research Vols. 76-78

Abstract: In die-sinking EDM, the electrode is moved only in the Z-axis direction, while in oscillating EDM, electrodes are oscillated in both the X-axis and Y-axis directions to realize high accuracy machining. There are many ways of designing electrodes for oscillating EDM. However, because the form of electrodes and subsequently the oscillating patterns of these electrodes depend on the shapes of the die/mold used, they become complicated when the die/mold shape is complicated, and electrode design takes hours in such cases. This paper therefore proposes a new approach of designing electrodes for oscillating EDM. Some oscillating patterns based on the proposed approach are also analyzed from the viewpoint of usefulness.

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: In recent years, to improve the electrical discharge machining properties, several trials have been applied with the ultrasonic vibration system which was combined on the sinking electrical discharge machine. In this paper, the effects of the ultrasonic vibration were investigated with the designed sinking EDM machine. Some experimental parameters of tool electrode polarity, rotational workpiece speed and directions were examined during the sinking EDM process on the cemented carbide material of G5. Material removal rate, electrode wear ratio and surface roughness were estimated as the machining properties under finishing machining conditions. The experiments were carried out on ultrasonic longitudinal frequency 59 kHz and electrode spindle till 1,000 rpm. Two rotational apparatuses were used simultaneously on the opposite rotational direction during discharge machining. The discharge conditions were estimated with the waveforms analysis. As the results, the EDM device system which was combined ultrasonic vibration, improved the material removal rate and surface roughness of the EDMed workpiece.

Abstract: In order to realize environmental-friendly machine tools, a linear-motor-driven table supported by constant-flow hydrostatic water bearings is developed. The table system is free from environmental pollution because the system needs no oil. For simplicity, a single-sided bearing system is chosen for the table-slide. To obtain a high sustaining force, preload is applied to the bearings using the attractive force of an iron core linear-motor’s magnets. The preload is effective in both the vertical and horizontal directions by inclined motor magnets. Miniature gear-pumps supply flow to the bearings without pump pulsation, and the bearings consume very small amounts of water and electric power. The measured table sustaining force was 3.0kN and static stiffness was 0.3kN/m under a flow rate Q=0.92mL/s per bearing and ideal bearing clearance h=16m.

Abstract: . Traditional diamond grits used for making resin bonded abrasives are monocrystalline in acicular shape and with smooth surface, so they are easy to fall off prematurely during grinding, the use effect is not good. Taking the powder graphite and the iron-base alloy catalyst as the raw material by adopting a new indirect heating craft, under the high pressure and high temperature conditions within cubic press, this project developed a new variety of diamond -- CSD abrasive with crumb structure. They have equi-axed shape and rough surface. It has been proved that the abrasive wheels made with CSD diamond have self-sharpening characteristics and high bondability. The grinding efficiency and service life of the abrasive wheels made with CSD can be doubled.

Abstract: The development of China as the world's manufacturing house is best exemplified in the industry of diamond superabrasives. Diamond is indispensable in the creation of industrial infrastructure, including the construction of roads and building of houses. The diamond market was previously dominated by countries outside China. However, a "great leap forward" has taken in China with rapid expansion in Chinese diamond-making capabilities from the enlargement of the equipment (cubic presses) and improvements in diamond yield and product quality in the end of last century. In the new millennium, China outpaced the rest world combined in the total diamond output, became the largest producer in the world indubitably. This paper presents the progress in recent years based on the statitics, and also an outlook of the future development of the Chinese superabrasives industry based on the Chinese macroeconomics and the recent data of the end-users as well as their future development trend.

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 residual stresses on the top surface and side face of the diamond layer of PDC with 25.4mm in diameter and 3.2mm in thickness were measured using Micro-Raman Spectroscopy, thus the stresses and their radial and vertical distributions were obtained. To evaluate the magnitude of the thermal residual microstress in the diamond layer of PDC, the tungsten carbide substrate of PDC was cut by electric discharge machining (EDM), and several Raman measurements were performed on the top surface of the diamond layer. The results show that 1) the stresses in the central part of the diamond surface are compressive, the biggest stress is about 600 MPa, the magnitude of the stress decreases from the center to the edge of PDC, and at about 2mm near the edge of PDC, the stress becomes tensile; 2) the stresses on the side face of the diamond layer are tensile, the maximum is about 580 MPa near the interface. These tensile stresses are thought to be one of the main factors to cause delamination of PDC used for cutting tools; 3) the measured value of the microstress in the diamond layer is 62.5MPa.

Abstract: . Micro ultrasonic machining (micro-USM) is an effective machining method for hard brittle materials. In the micro-USM process, the workpiece materials are machined through the accumulation of small brittle fractures generated by the impacts of abrasive grains. Therefore, it becomes difficult to obtain a smooth machined surface. In the proposed electrorheological fluid-assisted ultrasonic machining (ER fluid-assisted USM), the behavior of abrasive grains is controlled using the effect of dielectrophoretic force acting on the abrasive grains and the ER effect. The behavior of the abrasive grains can be controlled by changing the electric field distribution. In the present paper, the shape and position of the auxiliary electrode are arranged in order to control the abrasive grains to the side surface of the micro rectangular tool. By positioning the auxiliary electrode parallel to the micro rectangular tool, it becomes possible to concentrate abrasive grains to the side surface of the micro rectangular tool. Smoothing of the side surface of the workpiece by using the side surface of the micro rectangular tool is then investigated. As a result, the surface roughness of the side surface of the workpiece can be improved.

Abstract: This paper discuss a simple, low-cost method I detecting wear progress of bearing within audio frequency signals; f < 20 kHz. The technique is found to be suitable since it is sensitive to the surface degradation prior to the onset of severe wear. The wear test is conducted under pin-on-disc configuration in a lubricated sliding condition. The results show that the value of I-kaz coefficient Z∞ is represented by scattered data in an I-kaz 3D spaces in which the scattered areas underwent contraction with increased sliding distance. From this statistical analysis, a clear-cut correlation with the established Taylor Tool Life Curve is noted. Here, the lower value of Z∞ indicates severe wear which lies I the failure region of Taylor’s curve. Examination of worn microstructures is carried out using a secondary electron microscopy (SEM). Based on the morphology investigation, it is found that under lubricated test, parallel grooves and craters up to 2 µm in size are present indicating an abrasive wear mechanism has occurred. The surface damages are found to scale with the increasing sliding distance. However the wear resistance behaviour of the bearings seems to improve as the sliding distance is increased.