Plasma chemical vaporization machining (CVM) has been proposed as a high-precision chemical shaping method, which uses rf plasma generated in the proximity of an electrode in an atmospheric environment. Based on the principle of plasma CVM, a computer numerically controlled plasma CVM device with a pipe electrode was proposed for optical fabrication. This paper reviews the plasma CVM device, its removal characteristics, and the fabrication results of glass optics by use of the device
Sintered polycrystalline diamond (PCD) is widely employed for cutting tools because of its high wear resistance. However, it is extremely difficult to shape PCD micro tools by conventional machining methods. We describe the truing of a PCD micro tool by electrical discharge machining (EDM). The EDM mechanism and the EDM machinability for PCD are discussed. It is confirmed that the insulated diamond grains in the PCD can be directly processed by EDM, because they are covered with an electrically conductive layer generated by applying discharge to the binder metal around them. Moreover, a short discharge duration is effective for improving the material removal rate and the surface roughness of PCD.
In this paper, a new method of electrochemical machining (ECM), where high-voltage pulses are intermittently supplied to electrodes during low-voltage pulsed ECM, is presented. The properties of this method are compared with those of a conventional low-voltage pulsed ECM method using a 0.3 mm φ electrode. We found that this method enables us to machine a workpiece using ECM conditions, that are difficult to use in the conventional ECM method, such as low electrolyte concentration and low pulse duty ratio. This method also enables us to machine a workpiece without strong flushing. The machining speed of this method is increased almost 3-6 times that of the conventional ECM method. A small side gap width comparable to the gap width by EDM is achieved using a low-density NaNO3 electrolyte.
In this study, the authors aimed to decrease tool wear ratio in non-contact electrostatic induction feeding for micro electrical discharge machining (EDM). Since this electrostatic induction feeding method is capable of non-contact electric feeding to the tool electrode, the tool electrode can be rotated at a high speeds of 50,000rpm or more. Accordingly, both material removal rate and machining accuracy can be improved. With this method however, since discharges occur with alternating polarity, the tool electrode wear rate is higher than conventional unipolarity pulse discharge where the polarity of the workpiece is positive. Thus, in this study, circuit impedance was switched alternately to decrease the tool wear ratio, so that the discharge peak current becomes high when the workpiece is negatively charged, and low when positively charged. As a result, the tool wear ratio equivalent to conventional unipolarity discharge was achieved.
This paper discusses the effect of the carbon fiber orientation on machining phenomena such as short-circuiting in the electrical discharge machining (EDM) of carbon fiber reinforced plastics (CFRP). Sinking EDM was carried out for a CFRP, where the carbon fiber orientation in each prepreg was even but different among the prepregs, in a configuration in which many prepregs were concurrently machined, and top and cross-section views of the machined surfaces were observed. It was found that the relative frequency of short-circuiting due to the fraying of carbon fibers decreases when the gap width is narrower. It was also found that the machined surface became uneven because of the different local material removal rates and electrode wear ratios among the prepregs.
This study describes a method to fabricate tungsten carbide alloy pins of diameters from 14 to 60 μm with the machining time about 12 min by environment-responsive electrochemical machining (ECM) using an ultra-low concentration electrolyte. To improve machining accuracy, pin rotation and ultrasonic washing during machining were adopted. It was realized that thinner pins with better axial symmetry were obtained with the rotation and ultrasonic washing. Furthermore, the effect of electrolyte concentration was investigated by using a NaNO3 aqueous solution. It was observed that by-product adhesion to pins reduced by using a NaNO3 aqueous solution over a certain concentration and the machining speed was improved by increasing the current, which increased electrical conductivity.