Electrical Discharge Process Research Articles

超硬合金における気中創成加工に関する研究

In dry electric discharge machining of cemented carbide, short circuits frequently occur between work and tool electrodes, disrupting the process. In this study, to increase the efficiency of electric discharge frequency and increase work removal rate, we researched the effects of superposed voltage, ultrasonic vibration, high peak current, and mist supply. As a result, it was found that applying superposed voltage and ultrasonic vibration can increase work removal ratio. A long pulse and a low peak current are more appropriate than a short pulse and a high peak current for dry electric discharge. Moreover, by supplying mist into the working gas, the electric discharge process becomes more stable, the consumption of the electrode is lower, and a larger work removal ratio can be expected.

Teaching manufacturing processes using computer animation

This paper presents eight animation tools developed at École Polytechnique de Montréal. Two sets of animations were created. The first set is intended for teaching an advanced manufacturing course. Slide shows used during this course have been enhanced with animations and simulations. Six animations were created to demonstrate chip formation, cutting forces, machine tool rigidity, chip plastic deformation, tool thermal behavior, and the electrical discharge process. The second set of animations is used for the presentation of other related topics during scientific conferences. The project was carried out using Macromedia Flash MX and Corel Draw 12 software. Evaluation of the animations as a lecture tool showed that this new learning technology produces excellent results and enhances the teaching and learning process.

304 コロナ放電によるディーゼル排ガス中のPM,NOx,THCの同時除去特性(大気環境改善技術(1),大気・水保全技術)

Electrical discharge process using corona is effective in reducing particulate matter (PM), nitrogen oxides (NOx) and total hydrocarbon (THC) contained in diesel engine exhaust. We experimentally evaluate the application of DC corona discharge reactor to reduce the PM, NOx and THC from diesel exhaust. Particulate trapping in a corona reactor can be accomplished by electrostatic precipitation. The accumulated PM on a nichrome electrode of reactor can be regenerated by the controlled burning process. In a corona reactor, NO is oxidized to NO_2 and NO_2 reacts with H_2O contained in exhaust. NOx decreases as a result of HNO_3 formation in a reactor, and successively HNO_3 is neutralized on the filter paper contained alkali. A corona reactor consists of cylindrically-shaped outer electrode made of stainless steel and central electrode made of rolled nichrome wire. In this study, the effects of corona voltage, current and the space velocity of reactor on soot collection efficiency, NOx removal rate and THC reduction rate are investigated. Also discussed is the particle size distribution of soot collected by a reactor.

Электроразрядные процессы в плазменном окружении МКС

Электроразрядные процессы в плазменном окружении МКС

Methane conversion to C 2 hydrocarbons and hydrogen in atmospheric non-thermal plasmas generated by different electric discharge techniques

Methane conversion to C 2 hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C 2 products. Pulsed spark discharges gives the highest acetylene yield (54%) and H 2 yield (51%) with 69% of methane conversion in a pure methane system and at 10 SCCM of flow rate and 12 W of discharge power. In the two DBD processes, ethane is the major C 2 products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H 2 formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17 eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19 eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75 eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205 eV/molecule, respectively. The immersion of the γ-Al 2O 3 pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C 2 yield.

Electro discharge machining of nickel–titanium shape memory alloys

Electro discharge machining (EDM) is a common fabrication process for miniaturized components in medical technology and micro engineering today. As EDM induces material changes in the near surface zone, the surface integrity becomes ever more important, the smaller the components are. In order to characterize the influence of EDM on the near surface zone, basic metallurgical investigations on pseudo-elastic NiTi shape memory alloys (SMAs) were carried out. Material removal in EDM depends on the electric discharge processes between the tool and the workpiece electrode in a dielectric fluid. Material is removed by melting and vaporization in single sparks. This results in craters with varying size and depth depending on the discharge energy. The microstructure of this melting zone is characterized by hollows, cracks and precipitation. Cracks open at the surface in consequence of randomly and locally overlapping thermal shocks. The cracks grow vertically into the material, starting at the surface. In the melting zone, significant precipitations were detected and subsequently identified by EDX as titanium carbides. The material removal rate, which is an important process factor in manufacturing, approximately increases in linear proportion with the discharge energy, and achieves commercially interesting values by using an electrode made of copper and tungsten. The results of the microstructure analysis require the removal of the near surface zone to ensure the properties of the components. This is possible via a smooth EDM-process, followed by electrolytic polishing.

Survey of whole air data from the second airborne Biomass Burning and Lightning Experiment using principal component analysis

Hydrocarbon and halocarbon measurements collected during the second airborne Biomass Burning and Lightning Experiment (BIBLE‐B) were subjected to a principal component analysis (PCA), to test the capability for identifying intercorrelated compounds within a large whole air data set. The BIBLE expeditions have sought to quantify and understand the products of burning, electrical discharge, and general atmospheric chemical processes during flights arrayed along the western edge of the Pacific. Principal component analysis was found to offer a compact method for identifying the major modes of composition encountered in the regional whole air data set. Transecting the continental monsoon, urban and industrial tracers (e.g., combustion byproducts, chlorinated methanes and ethanes, xylenes, and longer chain alkanes) dominated the observed variability. Pentane enhancements reflected vehicular emissions. In general, ethyl and propyl nitrate groupings indicated oxidation under nitrogen oxide (NOx) rich conditions and hence city or lightning influences. Over the tropical ocean, methyl nitrate grouped with brominated compounds and sometimes with dimethyl sulfide and methyl iodide. Biomass burning signatures were observed during flights over the Australian continent. Strong indications of wetland anaerobics (methane) or liquefied petroleum gas leakage (propane) were conspicuous by their absence. When all flights were considered together, sources attributable to human activity emerged as the most important. We suggest that factor reductions in general and PCA in particular may soon play a vital role in the analysis of regional whole air data sets, as a complement to more familiar methods.

Purification of single walled carbon nanotubes by thermal gas phase oxidation

Single walled carbon nanotubes (SWNT) have been produced in an electric arc discharge by using a graphite rod as anode which is filled with a powder mixture of graphite and metallic catalysts like nickel and yttrium. The soot material containing approximately a third of SWNT was collected from the cathode region as a soft, voluminous material. The main by-products in this process are amorphous carbon and graphitic nanoparticles which have to be removed by an appropriate purification process. The as-produced soot material was purified by gas phase oxidation in air at 355 °C. The oxidation of amorphous carbon in air is advantageous against wet chemical methods because it is better controllable. Thermogravimetric analysis and electron microscopy were used to investigate the oxidation behavior of the different kinds of carbon. Oxidation of SWNT and amorphous carbon occurs simultaneously even at moderate temperatures, whereas amorphous carbon is more rapidly oxidized than SWNT. For optimizing the purification procedure by gas phase oxidation, kinetic studies were used to determine the oxidation time for each component in the soot at a given temperature. So it is possible to remove the amorphous carbon quantitatively with minimal losses of SWNT. But it was found that graphitic nanoparticles have the highest stability against oxidation and could therefore not be quantitatively removed by this method without the complete destruction of SWNT. Therefore, the electric arc discharge process has to be a controlled process for minimum production of graphitic nanoparticles to obtain a material with a high content of SWNT.

Application of electric discharge process in joining aluminum and stainless steel sheets

By the process using electric energy, two-ply sheet laminates of aluminum (A1100)–stainless steel (SUS430) have been made without the reduction in the thickness of the both sheets. The A1100–SUS430 layered sheets were finally resistance-heated at 833 K for 0.4–3.6 ks under an applied pressure of 30 MPa after the pulsed electrical discharge for 0.7 ks. The true shear strength of the joined interface shows almost the constant value of 60–68 MPa to the holding time of 1.8 ks at 833 K. The true shear strength is close to that of A1100 sheet, which means satisfactory joining is achieved. After the holding time of 2.7 ks, the true shear strength is reduced to 30 MPa, due to the creation of a continuous intermetallic compound layer. The values of the joined area fraction at the A1100–SUS430 interface are changed from 25 to 70% for the laminates resistance-heated for 0.4–3.6 ks at 833 K. Little change of the joined area fraction are shown in the laminates resistance-heated for the holding times of more than 1.8 ks. It is suggested on the basis of the result of the thermal calculation that the maximum value (70%) of the joined area fraction is due to inhomogeneity of the surface-temperature on the SUS430 side at the A1100–SUS430 interface by the heat release because the SUS430 sheets is wider than the base surface of the graphite punch. For application of the process using the electric energy in joining the metallic sheets, it is important to avoid the inhomogeneities of electric current and temperature distribution through the interface between the sheets to be joined.

311 コロナ放電によるディーゼル PM、NOx の除去特性

Electrical discharge process using corona is effective in reducing particulate matter (PM) and nitrogen oxides (NOx) of diesel engine exhaust. We experimentally evaluate the application of DC corona discharge reactor to reduce the PM and NOx from diesel exhaust. Particulate trapping in a corona reactor can be accomplished by electrostatic precipitation. The accumulated PM on a nichrome electrode of reactor can be regenerated by the controlled burning process. In a corona reactor, NO is oxidized to NO_2 and NO_2 reacts with H_2O contained in exhaust. NOx decreases as a result of HNO_3 formation in a reactor. HNO_3 is neutralized on the filter paper contained alkali. A corona reactor consists of cylindrically-shaped outer electrode made of stainless steel and central electrode made of rolled nichrome wire. Dimensions of prototype reactors are ID×length=φ27×160,φ54×320,a flow rate of 14l/min, resulted in space velocity of about 9200 and 1250/hr. In this study, the effects of corona voltage, current and the space velocity of reactor on the soot collection efficiency and the NOx removal efficiency are investigated. Also discussed is the particle size distribution of soot collected by a reactor. Experimental results show that 1) a corona discharge reactor is capable of reducing both diesel particulates and NOx simultaneously, 2) Nano-particles less than φ0.5μm can be removed by a corona process.

Machining Characteristics of Insulated Si3N4 Ceramics by Electrical Discharge Method. Use of Powder-Mixed Machining Fluid.

To clarify the electrical discharge machining (EDM) mechanism of insulated ceramics with an assisting electrode method, the waveforms and displacement curve of tool electrode were investigated during electrical discharge process, with emphasis on the following factors: (1) The effects of EDM conditions on machining rate, wear of electrode, surface roughness and stability of discharge. (2) The variation of discharge stability corresponding to the machining process. From the obtained results, it appeared that an electrical conductive layer was created on the machined surface by the generation of both long pulse and concentration discharge pulses. The surface roughness decreased with increasing the ratio of these abnormal pulses. To decrease the generation of abnormal pulses, machining was carried out in carbon-powder-mixed machining fluid. As a result, the surface roughness was markedly improved according to on increase of the normal discharge ratio and discharge dispersion phenomena.

Methanol conversion from methane and water vapor by electric discharge (Effect of electric discharge process on methane conversion)

Methanol conversion from methane and water vapor by electric discharge (Effect of electric discharge process on methane conversion)

Methanol conversion from methane and water vapor by electric discharge (Effect of electric discharge process on methane conversion)

The possibility of methanol conversion from a methane and water-vapor gas mixture was investigated for a new and highly efficient energy conversion system. Reforming process of methanol to hydrogen can be used for low-temperature thermal energy utilization. Direct methanol production from a methane and water-vapor mixture by spark or glowlike discharges has been achieved experimentally. A high methanol mole fraction of 0.5% has been obtained by both discharges. The effects of applied high voltage time, total pressure, and ratio of gas mixture on the conversion efficiency have been clarified experimentally. The electric energy consumption for methanol production by the spark discharge method is 1/100 that by the glow discharge method. The methanol conversion process has also been analyzed theoretically by considering the dissociation of the initial mixture gas by electrons and 104 elementary reactions. The results suggest that a very short period energy input such as a spark discharge can effectively produce methanol compared with a steady-state discharge such as a glowlike discharge. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 404–417, 1999

Methanol conversion from methane and water vapor by electric discharge (Effect of electric discharge process on methane conversion)

The possibility of methanol conversion from a methane and water-vapor gas mixture was investigated for a new and highly efficient energy conversion system. Reforming process of methanol to hydrogen can be used for low-temperature thermal energy utilization. Direct methanol production from a methane and water-vapor mixture by spark or glowlike discharges has been achieved experimentally. A high methanol mole fraction of 0.5% has been obtained by both discharges. The effects of applied high voltage time, total pressure, and ratio of gas mixture on the conversion efficiency have been clarified experimentally. The electric energy consumption for methanol production by the spark discharge method is 1/100 that by the glow discharge method. The methanol conversion process has also been analyzed theoretically by considering the dissociation of the initial mixture gas by electrons and 104 elementary reactions. The results suggest that a very short period energy input such as a spark discharge can effectively produce methanol compared with a steady-state discharge such as a glowlike discharge. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 404–417, 1999

Evidence of a high-altitude discharge process responsible for radar echoes at 24.4 MHz

We present preliminary evidence of a high-altitude, electrical discharge process that can produce radar echoes at 24.38 MHz. This conclusion is drawn from pulsed-radar observations of near time-coincident occurrences of impulsive electromagnetic radiation with radar echoes that originated at altitudes well above those of mesoscale convective systems.

Novel synthesis of MoSi2 and MoSi2-Al203 ultrafine powders

Molybdenum disilicide (MoSi2) is a promising high temperature material with a high melting point (2032°C), low density (6.24 Mg m-3 ), excellent high temperature oxidation resistance (up to about 1900°C), and metal like thermal and electrical conductivities. For structural applications, the formation of composites can be benejicial. Alumina (Al2O3) has a thermal expansion coefficient close to that of MoSi2 in a wide temperature range from 200°C to 1400°C. Improvement in elevated temperature strength has been reported by the formation of a composite between MoSi2 and A1203. However, the brittle nature of MoSi2 based materials at medium to low temperatures remains an obstacle for their applications. One possible solution is to develop microstructures with ultrajine grains so that ductility can be improved through the grain boundary sliding mechanism. The present work gives preliminary results related to the synthesis ofultrajine MoSi2-Al203 composite powders. The MoSi2 powders (0.1–4 μm) were produced by an electric arc discharge process under varying voltage and capacitance. Three powder generating mechanisms have been identified. The influence of processing parameters (voltage, capacitance, and energy input) on the powder characteristics is discussed. Finally, the synthesis of MoSi2-A1203 composite powders by coating individual MoSi2 particles with an alumina gel through a sol-gel process is also demonstrated.

Observation of Complicated Surface Defects by Photoacoustic Microscopy and Nondestructive Evaluation

Simulated complicated surface defects fabricated on a metal specimen are detected by photoacoustic (PA) microscopy, and their signals are reconstructed as PA images. Two types of complicated defects with slit-type cross sections were fabricated on a metal specimen by electrical discharge processing and mechanical processing. The surface defect geometry of one type is a pair of mutually parallel defects, and that of the other type is a pair of defects which cross each other orthogonally. The PA image obtained, clearly shows the locations of the edges of the two defects. Furthermore, the results show that complicated defects composed of two sections can be detected separately as individual defects, and that the photoacoustic method is useful for detection of crossing surface defects which are difficult to detect using present NDE techniques.

Methanol Conversion from Methane and Water Vapor by Electric Discharge. Effect of Electric Discharge Process on Methane Conversion.

The possibility of methanol conversion from a methane and water vapor gas mixture was investigated for a new and highly efficient energy conversion system. Reforming process of methanol to hydrogen cas be used for a low-temperature thermal energy utilization. Direct methanol production from methane and wetar-vapor mixture by spark or glowlike discharges has been achieved experimentally. High methanol production rate of 0.5% has been obtained by both discharges. The effects of reaction time, total pressure and ratio of gas mixture on the conversion efficiency have been clarified experimentally. The electric energy consumption for the methanol production by the spark discharge is 0.01 times smaller than that by the glow discharge. The methanol conversion process has also been analyzed theoretically by considering 104 elementary reactions. The result suggests that a very short period energy input such as a spark discharge can effectively produce methanol.

Effect of Gas Temperature on Pulsed Corona Discharge Processing of Acetone, Benzene and Ethylene

AbstractExperiments on the plasma-assisted oxidation of dilute concentrations of acetone, benzene, and ethylene in atmospheric pressure gas streams by pulsed corona electrical discharge processing show that temperature influences the oxidation chemistry. In dry air mixtures, the main oxidation products are CO and CO

Observation of Surface Defects using Photoacoustic Microscope and Quantitative Evaluation of the Defect Depth

Quantitative trial of nondestructive evaluation (NDE) of a variable-depth defect using photoacoustic (PA) microscopy has been demonstrated. Two kinds of slit-type simulated defects, cross sections of which are rectangular and arc-shaped, were fabricated on a metal specimen by electrical discharge processing. Imaging of defects by PA microscopy enabled precise determination of both the location of edges and the shapes of defects. PA imaging of an artificially made vertical defect with linearly increasing depth showed that the best result agrees well with a model based on a line heat source along a metal wall in a defect.