Short Discharge Pulses Research Articles

In-process measurement of mechanical loads during electrical discharge machining

In electrical discharge machining, in-process measurements of the induced mechanical stress are essential to develop process models for improving the fatigue strength of the machined part. For this purpose, high-speed digital speckle photography is introduced to measure the workpiece-side load fields with a lateral displacement resolution of 28 nm at a spatiotemporal resolution of 29 µm and 40 µs, respectively. As a result, the load effects of even individual 100 µs short discharge pulses are temporally resolved for the first time, and the occurring spatial load inhomogeneities and their dynamics are characterized to complement our understanding of the machining process.

Performance of a TR-iso-pulse generator in micro ED-drilling

This study describes a TR-iso-pulse generator which has better machining performance than an RC-pulse generator in micro-electrical discharge drilling (micro ED-drilling). Although machining with a TR-pulse generator is more efficient compared to when using a RC-pulse generator in macro-scale EDM, an RC-pulse generator is often used in micro EDM because it can generate the short discharge pulse necessary to minimize the discharge energy. However, to increase the machining efficiency, it is necessary to develop a TR-iso-pulse generator capable of generating a small amount of uniform discharge energy. In this research, a TR-iso-pulse generator was constructed for micro ED-drilling. For an accurate performance comparison between an RC-pulse generator and a TR-iso-pulse generator, each pulse generator was set up to generate the same discharge energy for a single discharge. Through micro ED-drilling, material removal rate (MRR) and relative wear ratio (RWR) were measured with respect to feed rate, and then the periphery of the machined hole, longitudinal section, lateral overcut, and surface roughness were compared for machining accuracy analyses. As a result, MRR was increased by 121% and RWR was decreased by 39% in the TR-iso-pulse generator compared with the RC-pulse generator. In addition, while lateral overcut was increased by 4.63%, less amounts of re-solidified material were deposited at the periphery of the machined hole and surface roughness was also reduced by 22% in the TR-iso-pulse generator.

Investigation of parameters of plasma generated by high-power impulse magnetron sputtering (HiPIMS) of graphite

High-power impulse magnetron sputtering (HiPIMS) of graphite is used for deposition of hard and wear-resistant amorphous carbon films, because tetragonal diamond-like carbon (DLC) bonds produced under subplantation mechanism at negative substrate bias voltage more intensive in the case of high-density plasma. In scientific literature one can find the fact that DLC films are more hard (37 GPa) in the case of short (7 μs) magnetron discharge pulses comparing to long (50 μs) ones (17 GPa) in HiPIMS of graphite. Likely, it is connected with denser plasma and more effective carbon subplantation in the case of short discharge pulses compared to long ones. To confirm this, it is necessary to investigate dependencies of plasma parameters (ion concentration, electron temperature, plasma and floating potentials) generated by HiPIMS of graphite on discharge pulse width. It was shown that electron temperature increased from 5.34 to 10.27 eV, and plasma density increased from 1.2⋅1010 to 2.2⋅1010 cm−3 while pulse width decreased from 100 to 15 μs. It can be explained by increase of plasma disequilibrium since pulse current and power density increased to 250 A and 39.4 W/cm2, respectively.

Time-resolved mass-spectral characterization of ion formation from a low-frequency, low-temperature plasma probe ambient ionization source

New-found interest in the development of ionization sources for mass spectrometry, inspired by the advent of ambient desorption/ionization mass spectrometry, has led to a resurgence in plasma-source development and characterization. Dielectric-barrier discharges, particularly the low-temperature plasma (LTP) probe format, have been at the forefront of this field due to their low power consumption and relatively simple design. However, better fundamental understanding of this desorption/ionization source is needed to improve the analytical capabilities of such a device. Here, we use relatively fast (2.5 ms per spectrum) time-resolved mass spectrometry to characterize the temporal reagent-ion distribution from a low-frequency LTP probe. Different voltage waveforms were found to heavily influence the discharge properties and, consequently, ion production. Ion signals from short discharge pulses, ca. 40 μs, were found to be significantly broadened, ca. 10 ms, prior to extraction into the mass spectrometer. Additionally, higher frequencies of a sine-wave LTP produced the largest flux of reagent ions, which existed for most of the voltage waveforms. Finally, temporal signals for reagent and analyte ions were measured and related to specific ionization processes: proton transfer and charge transfer.

The effects of pulse charging on cycling characteristics of commercial lithium-ion batteries

The effects of a pulse charging technique on charge–discharge behavior and cycling characteristics of commercial lithium-ion batteries were investigated by comparison with the conventional direct current (dc) charging. The impedance spectra and cycling voltammograms of Li-ion batteries cycled by both protocols have been measured. The individual electrodes in the batteries have also been examined using XRD and SEM. The results show that pulse charging is helpful in eliminating concentration polarization, increasing the power transfer rate, and lowering charge time by removing the need for constant voltage charging in the conventional protocol. Pulse charging interrupts dc charging with short relaxation periods and short discharge pulses during charging, and also improves the active material utilization giving the battery higher discharge capacity and longer cycle life. Impedance measurements show that the magnitude of the interfacial resistance of the batteries cycled both by pulse charging and dc charging is small. However, at the same number of cycles, the interfacial resistance of the pulse charged battery is larger than that of dc charged. The batteries after 300 cycles charged by pulse charging show higher peak currents during both forward and reverse scans indicating higher reversibility of the electrodes. XRD and SEM studies of the individual electrodes indicate that pulse charging maintains the stability of the LiCoO 2 cathode better than dc charging and inhibits the increase in the thickness of the passive film on the anode during cycling.

絶縁性セラミックスの放電加工における加工現象 コンデンサ放電の効果

Because of the high resistivity of insulating ceramics, there are some differences compared with the EDM of metallic materials. The secondary metal as an assisting electrode and a minus polarity of the electrode overcame the difficulties of machining for insulating ceramics. And the insertion of a condenser between the electrode and the workpiece improves the removal rate and the stability in electrical discharge machining for insulating ceramics. But there is no distinct explanation of the mechanisms. In this paper, we certified the mechanism and the effects of the condenser EDM for insulating ceramics as Si3N4, Sialon and SiC.There are two types of the electrical discharge waveforms in the condenser EDM of insulating ceramics. A high electrical resistance of the surface causes a discharge with longer pulse duration than the settled value of discharge duration, which produces a lot of carbon from the working oil by heating. The low electrical resistance generates short discharge pulses which waste the carbon gradually. These waveforms are affected by a discharge-detection voltage, an equivalent resistance of ceramics' surface, and electrical parameters of discharge circuits. An adequate balance of a long pulse and short pulses makes it possible to machine insulating ceramics with high removal rate and high stability.

Comparison of time-resolved H- density measurements in a hydrogen discharge and model calculations

Time-resolved mass spectrometry of negative ions and time-resolved Langmuir probe measurements are carried out in a pulsed hydrogen discharge. Both diagnostics show a strong increase of the H- density in the post-discharge. The measured transient shape of the H- density in the hydrogen post-discharge is compared with an advanced theoretical model. This comparison shows that the H- slope is mainly influenced by the density distribution of vibrationally excited molecules and the transient drop of the electron temperature in the post-discharge. In accordance with our model, no influence of positive ions and atomic hydrogen on the H- density is observed up to plasma densities of 1011 cm-3. Measurements of the maximum H- density in the post-discharge in dependence on the duration of the single pulse indicate the density evolution of vibrationally excited molecules during the discharge. At plasma densities between 1010 and 1011 cm-3 a saturation of the density distribution of the vibrationally excited molecules is observed after 200-500 mu s. By variation of the pause duration with a fixed short discharge pulse (40 mu s) the lifetime of the vibrational excited molecules in the post-discharge is found to be approximately 1-4 ms.

A Simple 100 MW Tunable CO2 TEA Laser Volumetrically Excited without Using Any Preionization

A CO2 TEA laser was built which is excited by a single short discharge pulse without using any preionizing devices. The laser is tunable to more than 80 lines between 9.1 IJIM and 10.9 pm. Maximum output energies of 20 .11 and peak powers in excess of 100 MW were obtained. Laser radiation was also generated using N20, CO and HF.

Elektronenverluste in einem abklingenden Wasserstoffplasma

The time dependence of the electron density in the afterglow period of an electrodeless discharge in hydrogen was measured by means of 4- and 8-mm microwave interferometry. An exponential decay was observed in the late afterglow permitting the evaluation of a time constant in the density range from 1012–1010 electrons per cm3. The decay time of the plasma was influenced by the discharge conditions. Electron losses could be explained by ambipolar diffusion and attachment to impurities. Two diffusion coefficients were found correlated to the discharge duration. The mobility value H0=10.1±1.0 cm2/V · sec calculated from the diffusion coefficient found for short discharge pulses agrees with Saporoschenkos mobility value μ0=10.2 cm2/V · sec for the H 3 + -ion. A second mobility value μ0=14.8±1.2cm2/V · sec found for longer discharge pulses might refer to the H+-ion.