Electrostatic Induction Feeding Research Articles

Research of micro EDM/ECM method in same electrolyte with running wire tool electrode

A micro rod machining method which can switch between electrical discharge machining (EDM) and electrochemical machining (ECM) by attaching/detaching a diode to/from a bipolar pulse generator in parallel to the working gap was newly developed using a wire electrode made of tungsten. The problem of the wire electrode wear was eliminated by the use of the wire electrochemical turning (WECT) method in which the tungsten wire electrode is continuously running. The ultra-short bipolar pulse current was generated by the electrostatic induction feeding method where a pulse voltage is coupled to the working gap through a feeding capacitance. The machining characteristics of three types of wire guide; disk-shaped WC guide, laminated wire guide and cylindrical acrylic guide, were studied. The experimental results showed that the cylindrical acrylic guide has the best machining characteristics without the influence of guide wear and with less stray current flowing through the working gap. Using the cylindrical acrylic guide, the influences of the feeding capacitance C1, and the total amplitude of the pulse voltage on the machining characteristics were studied. Finally, a stainless steel SUS 304 micro-rod with a high aspect ratio of 14 was fabricated efficiently by using the EDM and ECM modes for rough and finish machining in sequence with the same setup, pulse generator, and neutral electrolyte.

A novel method to switch machining mode between Micro-ECM and Micro-EDM using oxide film on surface of tungsten electrode

A novel method to switch the machining mode between micro-EDM and micro-ECM in the same electrolyte using the same tool electrode and pulse generator circuit was proposed in this research. This method uses the electrostatic induction feeding method where a pulse voltage is coupled to the working gap through a capacitance. The switch between the EDM and ECM modes was realized by utilizing the oxide film formed on the surface of the tungsten electrode. To switch the ECM mode to the EDM mode, the polarity of the diode attached in parallel to the working gap was changed to control the generation of the oxide film. In the ECM mode, the diode was connected so that it is forwardly biased when the polarity of the tool electrode is positive, thereby the oxide film was not formed on the tungsten electrode. In the EDM mode, since the polarity of the diode was reversed, the oxide film was formed, thereby discharge could be ignited. The switching ability was verified from the waveforms of gap current and voltage which showed that discharge occurred in the EDM mode, whereas there was no discharge waveform observed in the ECM mode. In the ECM mode, the influences of total amplitude and rise/fall time of pulse voltage were investigated. In the EDM mode, the discharge probability with different concentrations of electrolyte was researched first. Then, the influence of the feeding capacitance C1 on the EDM mode was investigated. Finally, through-holes were machined by conducting the EDM and ECM modes in this order to obtain higher material removal rate in rough machining and better surface roughness without residual stress in finish machining.

Wire Electrochemical Grinding of Tungsten Micro-rod with Electrostatic Induction Feeding Method

In this study, tungsten was machined successfully with the neutral electrolyte NaNO3 aqueous solution and bipolar current because the nonconductive oxide layer on the surface, which interrupts the electrochemical dissolution process, was removed by the NaOH generated when the polarity of the tungsten is negative. However, the tool electrode was worn due to the bipolar current. Although the tool wear ratio was decreased when the platinum sheet was used as tool electrode than that with the stainless steel plate used as tool electrode, the platinum tool was also slightly worn. Hence, to avoid the influence of the tool wear, a new method, WECG (wire electrochemical grinding), for tungsten machining with neutral electrolyte and bipolar current is proposed, and the running brass wire is used as the tool electrode. Thereby, the problem of tool wear inevitable due to the bipolar current was eliminated because the running wire tool was used in this method.

Research on improvement of machining accuracy of micro-rods with electrostatic induction feeding ECM

Micro-rods were machined by electrochemical machining using the electrostatic induction feeding method, with which ultra-short current pulse duration of several tens of ns can easily be obtained. A tungsten plate and stainless steel (SUS304) rod were used as the tool electrode and workpiece, respectively. To improve the machining accuracy, the machining characteristics when the workpiece is fed in the axial and radial directions were investigated using NaCl aqueous solution as the electrolyte. When fed in the axial direction, the machinable length of the micro-rods was found to peak at the optimum feed speed because of the influence of pitting corrosion and collision between electrodes. When the workpiece was fed in the radial direction, the influence of pitting corrosion decreased, however, the micro-rod was shortened with increasing feed distance in the radial direction because of the stray current flowing through the end of the micro-rod. The simulation results of the material removal process agreed qualitatively with experimental results. Next, machining characteristics were compared between the electrolytes, NaCl and NaNO3 aqueous solutions, by feeding the workpiece in the axial direction. It was found that the influence of pitting corrosion was eliminated with the NaNO3 aqueous solution, and there was no machinable length limitation with suitable feed speeds. In addition, the taper angle and gap width were smaller with the NaNO3 aqueous solution, compared with those of the NaCl aqueous solution. Stainless steel micro-rods of 100μm in diameter with a high aspect ratio of 20 were fabricated with the NaNO3 aqueous solution. According to the preliminary research results, the machinable minimum diameter of the micro-rods was investigated and micro-rods with an average diameter of 9μm and length of 78μm were machined successfully.

Fabrication of tungsten micro-rods by ECM using ultra-short-pulse bipolar current

This paper describes tungsten micro-rod machining using a neutral electrolyte and ultra-short-pulse bipolar current supplied by the electrostatic induction feeding method. The tungsten oxide layer can be removed by NaOH generated when the polarity of tungsten electrode is negative. The machining accuracy improves with higher electrolyte concentration, and there is less tool wear when platinum tool electrode is used. A micro-rod with a diameter of 7.1μm and aspect ratio of 14 was fabricated successfully. The machinable minimum diameter was equivalent to that obtained by EDM. Furthermore, the current waveform could be optimized to increase the material removal rate.

Fabrication of micro-rods with electrostatic induction feeding ECM

Micro-rods were machined by electrochemical machining using the electrostatic induction feeding method, with which ultra-short current pulse duration of several tens of ns was obtained. A tungsten plate and stainless steel (SUS304) rod were used as the tool electrode and workpiece, respectively. The rotating workpiece rod was fed axially in the direction normal to the top surface of the tool electrode, thereby the diameter of micro-rod was determined by the depth of cut in the radial direction. The influences of voltage amplitude and the thickness and surface area of the tool electrode on machining characteristics were investigated from the aspects of machinable length limitation, straightness of the micro-rod, pitting corrosion, and surface finish to determine the optimum machining conditions. The results of machining experiments and current density simulation showed that the influence of stray current on machining accuracy markedly decreased with decreasing tool electrode thickness, allowing micro-rods with higher aspect ratio and better surface finish to be fabricated. On the other hand, the influence of the top surface area of the tool electrode on machining accuracy was small due to small changes in the current density on the frontal surface of workpiece, resulting in small changes in the material removal rate (MRR).

Research on servo feed control of electrostatic induction feeding micro-ECM

This paper researches about the machining characteristics and servo feeding control of micro electrochemical machining (ECM) with the electrostatic induction feeding method. Since current can flow only in the rising and falling time of pulse voltage, short pulses in the order of several tens of nanoseconds can easily be obtained, realizing significantly narrow gap widths. To avoid short circuit in the small working gap of several micrometers, a servo feeding control system based on monitoring the peak of gap voltage was developed. Compared with the old method, which monitors the average gap voltage, controllability of the working gap width with higher response was obtained because of the higher S/N ratio. The influence of the reference voltage on the material removal rate (MRR) and machining accuracy was investigated. The results showed that higher MRR and smoother surface can be obtained with lower reference voltages, due to the higher current density in the working gap obtained with higher current efficiency. However, the MRR decreased when the reference voltage was too low, as a result of the interruption of machining by the frequent retreat of the tool electrode due to short circuit. On the other hand, the MRR increased with increasing feeding capacitance C1, because electric charge per each pulse duration increased in proportion to C1. The inlet side gap width was independent of C1, due to the higher MRR and shorter machining time with larger C1. Based on the preliminary study, through-holes of 50μm in diameter were machined on a stainless steel (SUS304) plate with a thickness of 50μm to investigate the straightness of the holes. The diameter of the hole at the inlet and outlet sides was 58.5μm and 55.5μm, respectively.

Research on influence of electrolyte on micro-rod fabrication with the electrostatic induction feeding ECM

Research on influence of electrolyte on micro-rod fabrication with the electrostatic induction feeding ECM

Increasing Discharge Energy in Micro EDM of Non-contact Electrical Feeding using Electrostatic Induction Feeding Method by Re-designing the Feeding Electrode

Increasing Discharge Energy in Micro EDM of Non-contact Electrical Feeding using Electrostatic Induction Feeding Method by Re-designing the Feeding Electrode

Increasing discharge energy of micro-EDM with electrostatic induction feeding method through resonance in circuit

This paper describes the method to increase discharge energy in micro-EDM using electrostatic induction feeding as the pulse generator. In a previous study, controlled pulse train method was introduced to increase discharge energy and enlarge unit removal per discharge by allowing multiple discharges to occur at the same spot. During observation, it was found that the oscillation of discharge current is excited at higher amplitude even if the same capacitance is used. In this paper, the influence of frequency on discharge energy was investigated. It was found that higher discharge energy can be obtained when machining was done at the resonant frequency of the circuit. Influence of capacitance and inductance on resonant frequency was studied. Probability of discharge continuity at different frequencies was examined. The results confirmed that higher discharge continuity within the pre-determined pulse train duration can be achieved when machining is conducted at resonant frequency, leading to higher material removal rate (MRR).

Influence of Machining Conditions on Machining Characteristics of Micro-rods by Micro-ECM with Electrostatic Induction Feeding Method

This paper describes a machining method of micro-rod using electrochemical machining (ECM) with the electrostatic induction feeding method developed by the authors. The influences of the feeding directions of workpiece rod on the machining characteristics were investigated. Higher voltage amplitude was needed to keep the same feed speed with the radial feeding method due to the larger machining area, and longer micro-rod was easier to be machined with the axial feeding method, because the jetting of electrolyte into the surface gap was easy. The influence of pitting corrosion on the machining accuracy was insignificant with the radial feeding method, because the side of the micro-rod is machined at the same time.

Development of a New Generator for Electrochemical Micro-machining

One of the great advantages in Electrochemical Machining (ECM) is that there is practically no affected zone generated on the machined surface. Also, compared to the electro-discharge machining (EDM), there is no wear on the electrode. Nevertheless, the disadvantage of this process is the relatively poor accuracy, due to the dissolution that occur in the gap, generated by gas bubbles that increase the current density at the side gap. To prevent this drawback, it has been demonstrated that using ultra-short current pulses (100ns and less) at high frequency (around the MHz), the result is an effective method that improve remarkably the machining accuracy [1]. In order to achieve ultra-short current pulses, the method of electrostatic induction feeding has been used that allows the generation of current pulses shorter than several tens of nano-seconds [1]. This technic is very simple and low cost but suffers from the following inconvenient: the pulse duration and the peak current depends on the size of the electrode (capacitance between the electrode and the machining piece) and on the machining conditions.The purpose of our development is to reach the same objectives in terms of simplicity and inexpensive generator but with a high flexibility.By changing peak current and duration, one can adapt very precisely the power and consequently the machining rate and the accuracy, adapting the generator to a multiple kind of applications. Moreover, for stable machining, we have identified and used an electrical signal allowing the process control.

Fabrication of micro-rods by micro-electrochemical machining with the electrostatic induction feeding method

Fabrication of micro-rods by micro-electrochemical machining with the electrostatic induction feeding method

Comparison between Electrostatic Induction Feeding with Controlled Pulse Train Method and Relaxation Pulse Generator for Micro EDM

Comparison between Electrostatic Induction Feeding with Controlled Pulse Train Method and Relaxation Pulse Generator for Micro EDM

Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.

Improving Discharge Energy in Micro-EDM with Electrostatic Induction Feeding by Controlled Pulse Train Method

Improving Discharge Energy in Micro-EDM with Electrostatic Induction Feeding by Controlled Pulse Train Method

Micro Drilling EDM with Electrostatic Induction Feeding by Controlling the Duration of High Frequency Discharge

Micro Drilling EDM with Electrostatic Induction Feeding by Controlling the Duration of High Frequency Discharge

静電誘導給電法を用いた電解加工における工具電極消耗の研究

静電誘導給電法を用いた電解加工における工具電極消耗の研究

Micro electrochemical machining using electrostatic induction feeding method

This paper describes a micro ECM system using the electrostatic induction feeding method. With this method, since the pulse voltage is coupled to the tool electrode by capacitance, the pulse duration of the electrolytic current is determined by the rise and fall time of the voltage pulse and is thus significantly short, realizing short gap width. A servo feed system was also developed based on the measurement of the gap voltage. Wear of the tungsten tool was negligibly small because of the oxide layer formed on the tool, allowing micro-holes with sharp edges and straight walls to be drilled.

Ultra-Short Pulse ECM using Electrostatic Induction Feeding Method

This paper describes micro electrochemical machining (ECM) using the electrostatic induction feeding method. In ECM, gap distance can be decr eased to several micro meters by using pulse durations shorter than several tens of nano seconds. With the electrostatic induction feeding method which has been developed by the authors, since the pulse power supply is coupled to th e tool electrode by capacitance, the current pulse duration is nearly equal to the rise time and fall time of the pulse voltage regardless of the pulse-on time of the pulse voltage. Thus ultra-short current pulses can easily be obtained without a need to use an expensive ultra-short pulse generator. M achining results of micro-hole drilling with current pulse duration of several ns showed that significantly small side gap of 1μm could be obtained.