Micro-EDM has its potential in micro tools and parts manufacturing. However, the machining speed is quite low due to short-circuits and abnormal discharges, because of the difficult debris removal from the narrow gap-width. Especially, hole drilling process becomes impossible under an ultra-small discharge energy condition, such as a low open voltage and the stray capacitor in the RC discharge circuit. In this study, the effect of applying ultrasonic vibration to the machining fluid in micro-EDM was experimentally investigated, in order to realize a higher machining speed in the deep hole drilling process. Furthermore, the effect of vibration on the machining characteristics of micro-hole drilling under the ultra-small discharge energy condition was investigated. It was found that a significant increase in the machining speed was realized by applying ultrasonic vibration to the machining fluid. Also, with the vibration to the machining fluid, micro-hole drilling with ultra-small discharge energy became possible. Additionally, the experimental results show that the lateral gap-width between the tool electrode and workpiece was shortened, and the tool wear ratio became smaller.
This paper describes a new electrical discharge truing (ED-truing) method for an electroplated diamond tool. This new ED-truing method can straighten a conventional electroplated diamond tool by EDMing the tips of diamond grains, which have no electrical conductivity. The appropriate EDM conditions and the electrode material for ED-truing of the electroplated diamond tool are discussed. A grinding test using the ED-trued diamond tool is also examined. It is found that a short discharge pulse is effective in EDMing diamond grains. Moreover, it is found that a Cu-W alloy electrode, which can form a conductive carbon layer uniformly on the diamond surface, is suitable for the ED-truing. It is also confirmed that there is almost a 70% reduction in surface roughness as a result of ED-truing the electroplated diamond tool.
This study aims to develop a simulation tool to analyze the influence of wire structure, workpiece material, and workpiece thickness on the discharge current and wire vibration caused by the electromagnetic force observed in wire electrical discharge machining (WEDM), taking into consideration the electromagnetic field around the electrodes. The distribution of current density and magnetic flux density, electromagnetic force acting on the wire, and wire vibration were analyzed by coupling the equation for the entire discharge circuit with the Poisson's equation of the magnetic vector potential around the wire. Monolithic brass wire showed higher discharge current than coated steel wire, resulting in larger electromagnetic force acting on the wire. A copper workpiece exhibits smaller but reversed phase wire vibration compared with steel workpiece. Thicker workpieces cause larger wire vibration because the electromagnetic force acts on the wire electrode along a greater distance.
This paper describes a new method to electrochemically machine cemented tungsten carbide using electrolyte jet machining (EJM). NaNO3 aqueous solution was used as the electrolyte instead of a mixed aqueous solution of NaNO3 and NaOH, which is normally used for the conventional electrochemical machining (ECM) of cemented tungsten carbide, but has hazardous characteristics. The machining was carried out successfully with both alternating current (AC) and direct current(DC). However, AC enabled more localized dissolution under the jet than DC. An insulator nozzle was employed for AC machining to prevent the nozzle wear. It was also useful for DC machining because dissolution was more localized.
A titanium carbide (TiC) layer formed by electrical discharge coating has high hardness and excellent wear resistance. Therefore, this layer has been applied to molds, jigs and tools to extend the lives of these devices. On the other hand, depending on prospective application, it may be difficult to apply the layer because of defects and roughness on its surface. In this study, to reduce the number of defects and roughness, an improved TiC layer was formed using a TiC electrode containing silicon (Si), and the characteristics of the layer were investigated. It was found that the defects of the improved TiC layer were fewer than those of the TiC layer. The more Si the electrode contained, the fewer the defects in the improved TiC layer. The roughness of the improved TiC layer was lower than that of the TiC layer, and the hardness of the improved TiC layer was higher than that of the Si layer by electrical discharge coating. The more Si the electrode contained, the lower the roughness and hardness of the improved TiC layer. Furthermore, the improved TiC layer had higher corrosion, erosion and oxidation resistance than the TiC layer, the same as the Si layer.
This paper describes the machining characteristics of insulating ceramics by EDM (electrical discharge machining) with a piezoelectric device. A piezo scanner that can carry out drive control independently in the X-, Y-, and Z-directions was used for the piezoelectric device. Using the Z-axis as the main axis, dual servo control with a motor drive was applied, with oscillation in the X- and Y-axes, and the effects of these oscillations were examined. In addition to adding these controls to the piezo scanner, the removal rate was considerably improved by independently controlling the gain of the up-and-down motion based on the electrical discharge state of the high-resistance surface. Furthermore, to transmit rotation to the oscillation tool electrode, a magnetic non-contact transfer drive was utilized. Using this combination of controls, we effectively improved the removal rate in micro-hole machining.
In the wire EDM using a thin wire electrode, the reduction of wire vibration is important to achieve a high-precision machining, since the large amplitude of wire vibration leads to large kerf width, low shape accuracy, rough machined surface, low cutting speed and high risk of wire breakage. In this study, the movements of thin wire electrode during the process were directly observed by using a high-speed video camera in order to clarify the wire movement in fine wire EDM. The effects of machining conditions on the wire movement in the direction perpendicular to the machining direction were experimentally investigated. The results showed that the wire vibration amplitude in fine fire EDM increased with the wire running speed and flow rate of jet flushing but decreased with the wire tension. Also, the wire vibration during the process includes various frequency vibrations with 1st order string vibration. Furthermore, the wire vibration frequency increased not only with the wire tension but also the discharge pulse frequency.
Scribing characteristics of sapphire by using THG:YAG laser were experimentally investigated. The influence of polarization plane of laser beam on the curved shape at the tip of groove was also discussed. The absorptivity of laser beam at a high pulse repetition rate was still kept at higher order, although the feed rate became high. Therefore, a high pulse repetition rate condition is very effective for laser scribing of sapphire. The curved shape at the tip of groove was greatly influenced by the direction of polarization plane of laser beam. This phenomenon occurred not randomly but regularly depending on the angle of polarization plane. The laser beam was strongly reflected in the direction of curved shape generation, in other words, in the perpendicular direction to the polarization plane of laser beam. Therefore, a suitable setting of polarization plane could make a straight groove without the occurrence of curved shape.