Debris exclusion from the wire EDM gap has been conventionally done by jet flushing using nozzles but the debris stagnation area always presents near the wire with the conventional method. In this study, a new flushing method using tilting nozzle to wire running direction to reduce the debris stagnation in the kerf was proposed on the base of simulation results by computational fluid dynamics (CFD) analysis. The simulations and experiments clarified that the tilting jet flushing nozzle could decrease the debris stagnation area in the kerf and leads to smoother debris exclusion, resulting in higher removal rate. Furthermore, the wire deflection caused by hydrodynamic force due to the jet flushing was calculated by a structural analysis using the distributions of pressure acting on the wire surface by jet flushing flow obtained by the CFD analysis.
In this study, the thermal deformation of thin stainless steel sheet was investigated in bead-on-plate welding by using a single-mode fiber laser with Galvano scanning system. The numerical simulation was carried out to calculate temperature and stress fields, and its deformation characteristics were discussed. It was suggested that a specimen firstly deformed downward in the same direction of laser irradiation, and then deformed in the reversed direction after laser scanning. The final distortion angle in the negative direction, which is concave shape from the view direction of laser irradiation, was generated under the heat conduction and quasi-penetration welding mode, and the positive angle was obtained as the final distortion angle under the full-penetration welding mode. On the other hand, a small distortion could be achieved by the proper weld bead geometry in micro-welding of thin sheet, but the welding mode of minimum distortion conditions varied with specimen thickness. However, these relationships obtaining a small distortion could be understood by the relationship between aspect ratio of weld bead and distortion angle. Minimum angle of distortion could be achieved around maximum aspect ratio of weld bead regardless of specimen thickness and spot diameter, when an inflection point appeared in relationship between aspect ratio of weld bead geometry and distortion angle.
In recent years, ceramics materials have found increased use in industry. However, some of them are insulating ceramics that cannot be machined by conventional electrical discharge machining. In this study, we developed a special wire EDM machine for investigating the machining characteristics of insulating ceramics. The machining characteristics of Si3N4 insulating ceramics, especially surface roughness, are described. It was confirmed that long pulse discharges are minimally generated under the second cutting conditions where small discharge craters are uniformly formed on the machined surface. The resulting surface roughness was improved down to 4 μmRz. In addition, a unique process of machining with insulating ceramics, in which the threshold level becomes almost of the same as the voltage between the discharge and power supply positions, was observed.
The birth, growth, and separation of bubbles are microscopically observed in the electrodeposition of nickel in a nickel sulfamate bath. Bubbles repeatedly nucleate and grow at the same locations on the electrode used in the electrodeposition. The bubbles disturb ion transportation to the electrode surface for a long duration, causing the formation of holes, because electrodeposition only occurs outside the areas where bubbles are generated. Scanning electron microscopy (SEM) observation revealed that the surface texture of the bubble traces is smoother than that of the other areas and that there are many cracks and fragments in the bubble traces, which cause local changes in the characteristics of the electrodeposited film.
The effects of carbon nanotube (CNT) composites on the elastic modulus of nickel-based CNT composite coating were investigated using the indentation method. The elastic moduli of the coating at CNT concentrations of 0-40 vol.% were evaluated by experimentation and numerical calculations. The elastic modulus was changed by the addition of CNTs because of changes in CNT composites and nickel crystal. The structure of the matrix changed from the columnar crystal to random crystal due to the addition of the CNTs. The elastic modulus of the coatings with low concentration of CNTs can be calculated by the rule of mixtures from the percentage of each crystal orientation and the value of elastic moduli of each crystal orientation, and were almost the same as the experimental value. The measured elastic moduli agree well with the predictions of Halpin-Tsai equations at low CNT concentrations in the matrix. The high-CNT-concentration layer, which is approximately 40 vol.%, can be prepared by periodic reverse electroplating. The coatings with a surface layer of high CNT concentration have a higher elastic modulus. Although the moduli increase with increasing CNT concentrations, the determined values are lower than the predicted values of elastic modulus derived from the Halpin-Tsai equations.
Electroplating is used for corrosion protection, surface hardening, metal thin film manufacturing, etc. In conventional electroplating, the workpiece is immersed in the plating solution, and the whole contact surface is plated. Therefore, the mask operation and the removal of unnecessary plating film are needed for local plating in the case of ornament plating and so on. However, these additional processes would lead to a substantial increase in processing time and cost. In this research, a novel approach to realize local electroplating by using a suction tool, with which the electrolyte is confined in the area between the tool electrode and workpiece, was proposed. The results of the verification experiment showed that the maskless local electroplating can be performed, and pattern plating such as characters is possible with the proposed method.
Micro EDM with electrostatic induction feeding method can stimulate minimum discharge energy per pulse. With this pulse generator, since there is no contact between the pulse power supply and the tool, the tool electrode can be rotated at very high speed and significantly improve the cooling of the tool electrode. However, since the feeding capacitance which is formed between the feeding electrode and tool electrode is extremely small, it is difficult to conduct rough machining. Therefore, controlled pulse train method is introduced to increase the discharge energy. With this method, discharge energy can be enlarged even if the machining is done with the same small capacitance. Results show that material removal rate (MRR) can be increased with the increase in pulse train duration and higher MRR and lower tool wear ratio (TWR) can be achieved compared to the conventional method.
In this paper, multiple discharge phenomena in electrical discharge machining were observed directly through a transparent electrode using a high speed video camera. Multiple discharges occurred with a probability of about 2% in a steady state of normal sinking EDM. The probability was high when the gap width between electrodes was narrowed by the servo feed control and where debris particles were densely-distributed. Moreover, we investigated the change in gap voltage and discharge current waveforms and relative distance between the locations of consecutive discharges, when multiple discharges occurred.