Papers by Author: Wataru Natsu

Abstract: In this report, our attention was paid on the tool wear due to the stop of tool-feed, caused by change from the automatic operation to the manual one in the lathe work, because it was thought that skill level of workers influences the tool wear significantly. First, the workers gaze-point movement was recorded with an eye camera and analyzed with the application software. The results showed that the stop time of the tool-feed for skilled workers was very shorter than that of beginners. Then, the relationship between the tool-feed stop time and the tool wear was investigated by using an NC lathe. It was found that the shorter the stop time is, the smaller the tool wear becomes. Based on the above findings, the influence of the skill level on the tool wear due to the tool-feed stop in lathe work was revealed and key issues in the skill transfer of lathe work were confirmed.

Abstract: The analysis of the ECM model expressed by an equivalent circuit is helpful to understand the ECM characteristics, such as the removal rate and machining accuracy. However, the parameters in the ECM equivalent circuit have not been determined yet, although several kinds of equivalent circuits were proposed. In this research, the parameters of the ECM equivalent circuit were determined experimentally, and the determination reliability was discussed.

Abstract: In this paper, the gap-width in pulse ECM was detected by measuring the peak current responsive to the applied pulse voltage, and the influences of machining conditions on the detection sensitivity were investigated. It was found from experimental results that the sensitivity is increased by using the lower concentration electrolyte and electrolyte height. In addition, the machining experiment also showed that the sensitivity can be kept constant by removing by-products timely from the gap area.

Abstract: The existence of debris in the inter-electrode area in micro-EDM interrupts the machining process. Applying ultrasonic vibration to the machining fluid helps circulate the machining fluid and remove the debris from the gap area, and thus reduce short-circuits and abnormal discharges. In this study, the effect of applying ultrasonic vibration to machining fluid in micro-EDM was experimentally investigated. It was found that a significant increase in the machining speed was realized by applying ultrasonic vibration. Also, with the vibration of the machining fluid, micro-hole drilling with ultra-small discharge energy became possible.

Abstract: In ECM process, insulating by-products exists in the inter-electrode area. These by-products disturb the current flow between the tool and workpiece electrodes, and thus affect the machining accuracy. As one of the ways to remove the by-products, a method was proposed to apply ultrasonic vibration to the tool electrode. However, the influence of the electrolyte concentration and the effect of ultrasonic vibration on the machining characteristics of the WC alloy have not been investigated yet. Therefore in this study, these influences were experimentally investigated. It was found that the machining accuracy is increased by using the low concentration electrolyte. Also, machining of the tungsten carbide (WC) alloy when applying the ultrasonic vibration to the tool electrode becomes possible.

Abstract: It is well-known that using pulse voltage could improve the machining accuracy in ECM process. However, the tool electrode wear occurs under some machining conditions in pulse ECM. In order to acquire the high machining accuracy, a method to eliminate the electrode wear by raising the low-level voltage was proposed and the relation between the low-level voltage and the machining accuracy was experimentally investigated in this research. It was found that the low-level voltage of 2V could not only prevent the tool electrode wear, but also improve the machining accuracy and the machining speed. In addition to the low-level voltage, the influence of the pulse duty ratio on the tool wear, the machining speed and accuracy was investigated. It was found that the raised low-level voltage was also effective when the duty ratio was increased and the increased duty ratio itself reduced the tool electrode wear.

Abstract: In this study, in order to keep the feed rate of the tool electrode the same as the dissolution rate of the workpiece material in the pulse ECM, a method was proposed to detect and control the gap-width according to the relationship between the current waveform and the gap-width. First, the relationship between the current waveform and the gap-width was investigated experimentally. It was found that there is a correlation in the transient overshoot of the current waveform and the gap-width. Based on this correlation, a system used to detect and control the gap width during machining was developed. This system is composed of the circuit that detects the change in the current waveform and the algorithm that processes the detected signals from the circuit. The effectiveness of the gap-width detecting and controlling method was verified by experimental results.

Abstract: Ring-shaped oil seals used in automobiles are usually manufactured by the press drawing and the press blanking considering the shape and the use application. In this process of manufacturing, the material availability is quite low because the central region part is cut from the product and becomes the waste material. We propose the forming method by the press drawing using a ring-shaped blank for the metallic part of the oil seal in order to improve the material availability and reduce the number of processes. In this research, the forming accuracy using the ring-shaped blank was investigated by the forming simulation. As the result, when the knockout was fixed in order to generate the sufficient bottoming by the punch, it was found that the bottom part can be formed flatly and the angle part can be formed almost right. Furthermore, it was found that the inside diameter of the formed product is proportional to the inside diameter of the blank except the case when the bottom part of the formed product is small. Hence, the required inside diameter of the ring-shaped blank can be calculated with the proportional relationship.

Abstract: In this paper the influence of machining liquid on the processing characteristics, such as the tool electrode wear and the tool actual feed were discussed. Micro EDM drilling was carried out using deionized water and oil dielectric as the machining liquid. It was found that using deionized water reduced the tool electrode wear. Also, occurrence of short-circuits during the processing is one of the reasons for causing large electrode wear. In the case of using oil dielectric, processed depth influences the tool electrode wear greatly and causes the change in the actual feed rate. While using deionized water, processed depth also causes the change in the actual feed rate, but nearly had no influence on the tool electrode wear. Meanwhile, when using deionized water, although the small electrode wear and high machining speed can be obtained, electrolytic dissolution may occur. Therefore, the effective method of decreasing the open voltage and increasing the feed rate to prevent the electrolytic dissolution was mentioned and experimentally verified.

Abstract: The purpose of this research is to establish a way to realize the axisymmetric free-form polishing by controlling the scanning speed of the rotating polishing tool. The scanning speed was determined by comparing the measured result of the polished shape with the target shape. Experiments with the proposed method were carried out and the effectiveness of the method was verified.