Short Arc Discharge Research Articles

Effects of non-electrical parameters on the characteristics of discharge craters and machining performance in short electrical arc milling

During electrical discharge machining (EDM), the process parameters greatly influence the discharge characteristics and machining performance, including electrical and non-electrical parameters. As a new EDM method, short electrical arc milling (SEAM) is plagued by frequent short circuits, poor debris removal, and low energy-transfer efficiency. Therefore, this paper investigated the influence of non-electrical parameters (electrode material, working medium, and electrode rotation) on the crater characteristics, machining efficiency, and electrode wear. The micromorphological characteristics of the workpiece were explored. The results suggested that non-electrical parameters compressed and fractured the plasma channels, thus changing the effect of EDM. The air-tap water medium and electrode rotation promoted debris removal and arc breaking, which prevented the arc from ablating the workpiece. When GH4099 alloy was machined with a copper electrode, the workpiece surface quality and machining efficiency were high, and the thickness of the heat-affected zone was small. This work reveals the characteristics of short electric arc discharge and provided a theoretical basis for the efficient and high-quality machining of difficult-to-cut materials by SEAM.

Research on Nondestructive Testing Signal Processing Method for Intermittent Fault of Circuit Structure

In the process of nondestructive testing of circuit structural units, considering that the eddy current intensity and distribution formed under the action of electromagnetic coupling will inevitably cause the change of voltage or impedance of electromagnetic induction testing coil, this kind of phenomenon reflects the signal change information caused by defects such as insulation wear, corrosion, cavitation and so on. In order to fully avoid the sudden faults such as short circuit, open circuit or arc discharge caused by hidden dangers, which force the equipment to stop for maintenance, this paper studies the principle of intermittent fault detection system of circuit structure, designs the circuit structure of typical modules, and establishes the defect prediction model based on Smoothing Technology. It provides a theoretical basis for effectively detecting intermittent fault signals, analyzing the propagation trend of intermittent faults and identifying defect modes, and can be extended to the acquisition and processing of intermittent fault signals of electronic equipment.

Study on discharge state detection of micro-EDM based on wavelet transform method

Micro electrical discharge machining (micro-EDM) is considered as one of the most effective methods for micro manufacturing. However, in micro-EDM, since the discharge energy is small and the discharge space is narrow, it is difficult to evacuate the discharge-generated debris from the discharge gap, which causes the frequent occurrence of short circuit and arc discharge resulting in low machining efficiency. To realize high efficiency and stability in micro-EDM, precise discharge state detection is necessary. In this paper, wavelet transform method was used to detect the discharge state under the transistor type pulse generator to achieve real-time detection with high accuracy. The discharge state detection method based on wavelet transform was theoretically analyzed and was realized with the field programmable gate array (FPGA) due to its high computation speed. Experimental investigations in micro-EDM were conducted, and the effectiveness of the discharge state detection method based on wavelet transform was verified.

Discharge characteristics of W-Cu electrode in short electrical arc discharge machining of Inconel 718

The current application of short electrical arc discharge machining (SEAM) for cemented carbide removal is limited by its surface quality. In this study, tungsten-copper (W-Cu) alloy materials with different proportions as electrodes were studied by experimental methods. The mechanism of electrical parameters and composition content affecting the processing performance of SEAM was investigated, including surface roughness (Ra), material removal rate (MRR), micro-morphology, and the recast layer thickness (RLT). The results showed that the maximum MRR with W50-Cu electrode was 41 g/min, and the processing performance was the best with W90-Cu electrode in the U of 25 V, F of 2.3 KHz, and D of 55%. The W90-Cu electrode could provide good processing, and a thinner and more uniform recast layer was found on the workpiece surface. Therefore, W-Cu alloy tools are recommended when the hard surface materials machined by SEAM requires higher accuracy and surface finish.

Machining performance of titanium alloy in short electric arc milling

In order to solve the high-efficiency removal of difficult-to-cut materials such as titanium alloys, this paper conducts a in-depth research on the process characteristics of short electric arc milling machining (SEAM). The effects of processing conditions on material removal rate (MRR), tool wear ratio (TWR) and surface roughness (Ra) are studied. DeWesoft high-speed acquisition system, scanning electron microscope (SEM) and energy spectrometer (EDS) are used to characterize the machining performance of Ti-6Al-4V in SEAM. The results show that the surface of the machined Ti-6Al-4V has an obvious central depressions, surrounded by edge bumps and wrinkles caused by the melt. The effective number of short electric arc discharge is high, and the discharge rate can be maintained at a high level, increasing utilization rate of electric energy. The peak current of normal discharge reaches more than 900 A, which can generate a higher MRR. In addition, the surface morphology, re-solidified layer, and particle morphology of Ti-6Al-4V used for SEAM are also studied. These results lay a theoretical and technical foundation for the industrial application of SEAM.

Investigation of Short-Arc High-Pressure Xenon Discharge: Effect of Electrode Material Evaporation on Discharge Properties and Pulse Operation

This paper presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources.

Моделирование плазмы короткодугового ксенонового разряда сверхвысокого давления

AbstractWe have studied a high- (ultrahigh-) pressure short-arc discharge in xenon with thoriated tungsten cathodes. A system of equations formulated based on earlier experimental data indicating possible emission of cathode material (thorium) into the discharge gap has made it possible to determine the electric field strength, plasma temperature, and concentration of thorium atoms as well as thorium and xenon ions in the plasma. The problem has been solved for a model discharge between planar electrodes. The results indicate the key role of thorium atoms in the cathode region. Thorium atoms determine the ionization balance and other electrokinetic properties of plasma. Emission of thorium atoms reduces the plasma temperature at the cathode, which turns out to be noticeably lower than the plasma temperature near the anode; this is a new result that agrees with experimental data. Other electrokinetic characteristics of the plasma (in particular, charged particle concentration and electric field strength) are also in good agreement with the experiment.

Experimental study in SEAM machining performance of W-Cu alloy electrode materials

To solve problems such as insufficient energy and effective arc burning during the injection of a working medium in a short arc discharge channel, the application of a W-Cu alloy as the electrode material in short electrical arc machining (SEAM) is explored in this paper. Using the surface roughness, material removal rate, and tool electrode wear rate as technical indices, the effects of voltage, frequency, and duty cycle on W-Cu alloy materials are studied to explore machining characteristics in SEAM. Contrast experiments on a graphite electrode were conducted using a SU8010 scanning electron microscope and energy spectrum analysis to study the erosion mechanism of the W-Cu alloy material. This paper addresses applications of copper-based composites in SEAM and provides a theoretical basis for the development of electrode materials in the SEAM.

Temperature field simulation of the molten pool in SEAM

Short electric arc machining (SEAM) technology is a complex process involving arc physics, heat and mass transfer, metal melting, and solidification, which is characterized by locality, instantaneity, and unsteady states. The energy distribution as well as both the shape and size of the molten pool has an important influence on the quality of surfaces machined with SEAM. This paper presented a mathematical model of the short electric arc molten pool built via scientific method to conduct a quantitative analysis of the heat transfer of the molten pool. The model was conducted via discretization based on ANSYS and obtained change pattern of the quasi-steady state temperature field in the short electric arc molten pool via solving the set up mathematical model. Furthermore, the short electric arc discharge removal process was simulated via element birth and death technology. The temperature increase in SEAM was monitored with the A40 infrared thermal image instrument, the thermal cycling curves of the three critical nodes were analyzed, and the result shows that the maximum error between the simulated and the actual values was smaller. This verified that the setup model and adopted software method are appropriate and feasible. The surface microstructure of the nickel-based super-alloy GH4169 shows that the strong thermal effect of the arc in the molten pool causes the material near the eroded zone to instantaneously reach the melting point, and cool rapidly. This resulted in a strong temperature gradient, which had a significant effect on the microstructure, properties, and residual stress of the erosion zone.

A Magnetic Suspension Spindle System for Micro EDM

As an important manufacturing technology, micro EDM is widely applied in many industry fields. However, the slow response speed of servo system often leads to short circuit and arc discharge. To deal this problem, a magnetic suspension spindle system is used to improve the response frequency. This paper introduces the structure and principle of the magnetic suspension spindle device used for micro EDM, hardware and software solutions of the control system are illuminated by schematic diagram or flow chart. Using incremental PID algorithm, the axial (Z) response frequency reaches 150Hz, the radial and axial position accuracy is achieved with 5μm and 2μm. And the micro EDM is realized through the magnetic suspension spindle in 1.3mm stroke.

Synthesis of Carbon Nanotubes and Nano-onions Using Electric Field Induced Needle-Pulsed Arc Discharge Plasma

Carbon nano-onions and multi-walled carbon nanotubes (MWCNTs) are synthesized by needle-pulsed arc discharge plasma. In a simple production apparatus, a needle pulsed plasma is applied between two graphite electrodes in the presence of an electric field between anode and cathode. The possibility of carbon nanotube production by short pulsed arc discharge technique is investigated in this article. The pulse width is 0.3 μsec. Acetone vapor as carbon source is introduced to plasma. A magnetic field, perpendicular to the plasma path, is provided. The advantages of using short pulsed plasma are studied in this work. The results show that applying a DC electric field between electrodes, increases plasma tendency toward cathode, enhances the chance of plasma-hydrocarbon interaction, prevents carbon ions from dispersion and finally makes it possible to produce CNTs by low-power short pulses in an arc-discharge plasma reactor. The products are examined using SPM techniques. In this work, adding an electric field to the pulsed plasma techniques, suggests a new method to produce carbon nano particles (CNPs) by short current pulses with lifetime of below one microsecond.

Model of Short Vacuum Arc at Collision Free Motion of Ions

A 2-D mathematical model of the short vacuum arc discharge is developed that considers a hydrodynamic mode of electron motion and collision-free mode for motion of fast cathode ions in a 2-D electric field. The model takes into consideration an angle distribution of ions on the cathode plasma boundary. A method of calculation of plasma density distribution in the gap is proposed. 2-D distributions of discharge current density, plasma density, and electric field in an external longitudinal magnetic field are calculated. It is shown that intersections of ion trajectories take place and a part of ion trajectories returns to the cathode. As the value of the external magnetic field decreases, the number of ion trajectories returning to the cathode increases and the number of ion trajectories reaching the anode decreases.

Electric field induced needle-pulsed arc discharge carbon nanotube production apparatus: Circuitry and mechanical design

A simple and low cost apparatus is reported to produce multiwall carbon nanotubes and carbon nano-onions by a low power short pulsed arc discharge reactor. The electric circuitry and the mechanical design details and a micro-filtering assembly are described. The pulsed-plasma is generated and applied between two graphite electrodes. The pulse width is 0.3 μs. A strong dc electric field is established along side the electrodes. The repetitive discharges occur in less than 1 mm distance between a sharp tip graphite rod as anode, and a tubular graphite as cathode. A hydrocarbon vapor, as carbon source, is introduced through the graphite nozzle in the cathode assembly. The pressure of the chamber is controlled by a vacuum pump. A magnetic field, perpendicular to the plasma path, is provided. The results show that the synergetic use of a pulsed-current and a dc power supply enables us to synthesize carbon nanoparticles with short pulsed plasma. The simplicity and inexpensiveness of this plan is noticeable. Pulsed nature of plasma provides some extra degrees of freedom that make the production more controllable. Effects of some design parameters such as electric field, pulse frequency, and cathode shape are discussed. The products are examined using scanning probe microscopy techniques.

A multiscale technique for the validation of a numerical code for predicting the pressure field induced by a high-power spark

A more precise knowledge of the pressure field induced by a high-power spark is essential to estimate the mechanical damage that a lightning strike can induce near the impact point. In this work we propose a multiscale approach to validate a numerical magnetohydro-dynamic model that can predict the pressure field when a very high-power discharge is considered. Two simplified models for the arc resistance are considered and their respective results are compared. A brief analysis regarding the numerical issues involved in the solution of a very high temperature gas is included. The numerical code has been validated against the experimental data of a short-arc discharge using a current waveform prescribed by the aeronautical standards. Our study shows that a strong shock wave is generated in the first power peak and this travels away from the arc column maintaining a relatively high strength a few tens of centimetres away. The pressure in the arc region remains high for the whole discharge period.

Experimental Study of Powder-mixed Near Dry Electrical Discharge Machining

The powder-mixed near dry electrical discharge machining (EDM) technology is presented; its dielectric medium is gas-liquid-solid three phase mixtures. Experiment result shows that the material removal rate (MRR) and surface roughness increases with the increase of pulse duration, peak current and layer thickness, while pulse interval has the opposite effect. Raising air pressure can increase MRR and improve surface quality. Electrode consumption decreases with the increase of pulse duration. When pulse duration is large, electrode consumption is near zero. Due to the presence of droplet and powder, dielectric strength of gas medium reduces, thus discharging gap increases, the eroded particles are easily removed, and the probability of short circuit and arc discharge is reduced, working stability is improved, thus MRR is improved. Due to discharge disperse effect of powder, electric erosion pit depth is reduced, thus surface roughness is reduced.

High-irradiance reactors with unfolded aplanatic optics

Reconstituting the intense irradiance of short-arc discharge lamps at a remote target, at high radiative efficiency, represents a central challenge in the design of high-temperature chemical reactors, heightened by the need for high numerical aperture at both the target and the source. Separating the optical system from both the source and the reactor allows pragmatic operation, monitoring, and control. We explore near-field unfolded aplanats as feasible solutions and report measurements for a prototype that constitutes a double-ellipsoid mirror. We also propose compound unfolded aplanats that collect lamp emission over all angles (in lieu of light recycling optics) and irradiate the reactor over nearly its full circumference.

Radiometric characterization of ultrahigh radiance xenon short-arc discharge lamps

Xenon short-arc discharge lamps exhibit ultrahigh radiance with substantial emission beyond the visible, primarily in the near infrared. Their radiance distributions are spatially and angularly inhomogeneous due to both the structure of the plasma arc and the infrared radiation from the electrodes. These characteristics are favorable for high-irradiance biomedical and high-temperature reactor applications that exploit both visible light and infrared radiation. For the affiliated optical designs, full-spectrum radiometry, rather than just visible photometry, is needed and not extensively available. We present experimental measurements for the spectral, spatial, and angular distributions of such 150 W lamps and relate the consequences for such novel applications.

Effectiveness of recycling light in ultra-bright short-arc discharge lamps

Recycling light back into a plasma lamp's radiant zone can enhance its radiance. Measurements are reported for the effectiveness, spectral properties and modified plasma radiance maps that result from light recycling with a specular hemispherical mirror in commercial 150 W ultrabright Xenon short-arc discharge lamps, motivated by projection, biomedical and high-temperature furnace applications. For certain spectral windows and plasma arc regions, radiance can be heightened by up to 70%. However, the overall light recycling efficiency is reduced to about half this value due to lamp geometry. The manner in which light-plasma interactions affect light recycling efficacy is also elucidated.

A simplified arc discharge set-up for high adhesion of DLC coatings

An extremely simple arc discharge unit for producing high-energy carbon plasma ions for the deposition of the adhesion layer of high-quality diamond-like carbon (DLC) coatings is presented. The system contains only a simplistic anode–cathode arrangement and the anode–cathode and ignition circuits. The high-ion energies result from high current rise rates of the short arc discharge pulses. In our current system a sufficient rise rate (5·10 9 A/s) is achieved with 6 kV anode–cathode voltages. However, much lower voltages can be used if low inductance circuits are used. The presented arc discharge set-up has no particle filtering system. The number of particles in a sufficiently thick adhesion layer was 40/mm 2, which is acceptable for most applications.

ショートアーク形放電ランプを用いた多点露光光造形システム

A new method of making 3-D objects by stereolithography is proposed. To reduce the cost and the size of the system, a short arc discharge lamp is used as a light source instead of the UV laser. To make the fabrication time shorter, multiple spots exposure using optical fibers is employed. Interface software between CAD and stereolithography was developed. The software transforms the 3-D figure data made by CAD to the pixel data for multiple spots exposure. The light beams scan over the surface of the resin using a x-y auto stage and are turned on and off based on the pixel data by shutters. As the result of the basic curing test and the fabrication of 3-D models, the practicality of the system was proved.