This paper describes a high hardness coating by spark plasma sintered tungsten porous electrode with an electrical discharge machine utilizing the electrical discharge machining phenomenon. The effect of the electrical discharge machining conditions, the relative density of the sintered material used as the tool electrode, and the particle size on the coating properties were investigated. By using porous tungsten as the tool electrode, a processed surface with a higher hardness was achieved. In addition, the lower the relative density, the higher was the Vickers hardness of the processed surface. SPS sintered tungsten was used, the larger the discharge current, the higher was the Vickers hardness of the processed surface. The larger the powder particle size of the SPS sintered tungsten was, the higher was the Vickers hardness of the processed surface.
A multi-layered artificial skin, which is mainly consisted of three layers of silicone elastomer, printed paper, and resin plate, is expected as sealing material of facial defects. However, sweating phenomenon from the surface of missing parts results in insanitary conditions to the skin surface, and micro-drilled holes are required to improve the breathability of the multi-layered artificial skin as human’s sweat glands. High-efficiency processing is expected by using a high pulse repetition-rate laser. Although ultra-short pulsed laser is used, a continuous long time laser irradiation deteriorated the aesthetic quality of multi-layered artificial skin because of heat accumulation corresponding to the high pulse-repetition-rate. Therefore, laser irradiation method with the high-efficiency and good-aesthetic-quality was experimentally investigated by using picosecond pulsed laser of 1064 nm wavelength. The laser irradiation method, which can reduce the heat affected zone at the adhesion part between the print paper and the silicone elastomer, was effective in order to improve the esthetic quality of drilled hole for the multi-layered artificial skin. The discoloration area around drilled hole on multilayered artificial skin could be reduced by dividing method of laser shot number at the same irradiation point to provide non-irradiation time. A long non-irradiation time resulted in the reduction of discoloration area around drilled hole on multi-layered artificial skin under the similar heat input condition.
In pulse ECM, it has been found that the low-level voltage of the applied pulse influences the tool electrode wear and the machining accuracy. To attain a higher machining accuracy, the relationship between the low-level voltage and the machining accuracy was experimentally investigated in this study. It was found that a low-level voltage higher than 0V not only prevents tool electrode wear, but also improves the machining accuracy. In addition to the low-level voltage, the influence of the tool materials on the machining speed was also investigated. It was found that the different optimal low-level voltage depends on the tool material.
The machining accuracy of electrochemical machining (ECM) is low since zones that are far away from the tool electrode are also machined. Furthermore, the scattering of electrolyte solution during processing constitutes a severe environmental problem. To overcome these problems, this study set out to develop a novel method that not only limits the working area by sucking the electrolyte into the region between the tool tip and the workpiece, but also prevents the electrolyte from being scattered. In this paper, the processing characteristics of an electrolyte solution combined with the proposed suction method, especially in the depth direction, were investigated.
This paper aims to form a chromium carbide containing layer on metal mold steel by EDM finishing in chromium powder mixed working fluid in order to improve the surface characteristics for long life of metal mold, such as surface hardness, corrosion resistance and releasability of molded resin. The surface characteristics of carbon tool steel with low chromium content finished by EDM in chromium powder mixed working fluid were compared to those of alloy tool steel SKD11 with high chromium content. Experimental results shows that surface hardness, corrosion resistance and releasability of molded resin could be significantly improved to the same high level for both kinds of steel by EDM finishing in chromium powder mixed fluid.
The machining accuracy of Electrochemical Machining (ECM) is affected by the temperature and bubbles. The effect of bubbles in the simulation can be considered by first calculating the volume fraction of gas distribution (using bubbly flow approximation in this study) and then approximating the effective conductivity in the inter-electrode gap by using Bruggemann equation. Since, Bruggemann equation is independent of bubble diameter and distribution, its dependency on that was investigated in this study. Moreover, the effect of the bubbles generated on the machining accuracy of the axi-symmetric work piece with different flow rates was also investigated.
An electrochemical reaction is a complex phenomenon influenced by the materials of electrodes, electric field, and the solution. This paper reports a fundamental study of a nano-processing method based on electrochemical phenomena. In this study, reaction on the entire surface of the workpiece is inhibited by maintaining its electrode potential using a potentiostat. A minuscule tool electrode is made to approach the surface and a voltage is applied between the workpiece and the tool. The voltage enhances a strong electric field and induces a local reaction only in the region directly beneath the tool. A removal process in an acidic solution is developed and fundamental experiments are conducted using nickel as a processed material. The experimental results indicate that removal of metal at an extremely low rate can be realized by the proposed method.