Spark Formation Research Articles

Multi-criteria decision making for better quality indicators in µ-EDM using TiN-coated WC electrode

ABSTRACT It is highly essential to enhance the micro EDM process while machining titanium specimens. The utilization of coated electrode and adaptation of optimization algorithms in the process can enhance the material removal mechanism. In the present work, an attempt was made to find the influence of TiN coated tungsten carbide electrode in micro EDM process while machining titanium alloy specimens. It was also attempted to adopt DEAR-based optimization in the process. The TiN coating can produce lower TWR with better surface quality than uncoated tungsten carbide electrode. The capacitance has higher influential nature in µ-EDM since it controls the charging and discharging process during the spark formation across discharge gap. It was found that voltage (Level 3), capacitance (Level 3), and the tool rotation (Level 2) can create better quality measures under the prediction error of 2.3%. The optimal combination can enhance the machining accuracy with tiny craters formation.

Improvement of Methods and Devices for Multi-Parameter High-Voltage Testing of Dielectric Coatings

Currently, the high voltage testing method is widely used to detect pinholes and porosity defects in dielectric coatings. However, most modern coatings also have requirements for the minimum allowable coating thickness. Conducting tolerance tests on the thickness of dielectric coatings concurrently along with monitoring integrity within a single technological process appears promising. Additionally, mitigating the impact of various interfering parameters is crucial. This paper conducts a theoretical and experimental examination of spark formation processes in both gas and dielectrics. This analysis takes place during the identification of both through and non-through defects in dielectric coatings on conductive substrates. The principles of selecting the test voltage for the investigated dielectric coatings, considering the need to detect both through defects and inadmissible thinning, are theoretically and experimentally justified. It is suggested to utilize a probabilistic approach for evaluating the detectability of the mentioned defects. It is demonstrated that, when the dielectric strength of the coating is known, it is feasible to identify both through and non-through defects in coatings with a calculated probability under a specified test voltage. The conditions of occurrence of partial discharges in the process of testing are investigated, and measures to suppress their influence on the inspection results are proposed. The influence of the substrate surface roughness on the magnitude of the breakdown voltage during testing is considered.

Measurement of laminar burning speed at high pressures using plasma affected flame

Measurements of a propagating flame are crucial to the understanding and verification of important flame phenomena. Specifically, laminar, unstretched flame speed is desired to verify complex flame behavior such as turbulence or chemical kinetic models. This data is also necessary as advanced and more efficient combustion devices operate at these high pressures where this data is less reliable from the onset of flame instabilities. This research provides laminar burning speed (Suo) and Markstein length (Lb) measurements utilizing a novel technique which incorporates flame propagation during and just after the ignition phase. The analysis utilizes a constant pressure technique where the expansion of a spherical flame is visually measured. Flame propagation of stoichiometric flame from 1 to 50 atm are examined up to a radius of 20 mm. The inclusion of early flame propagation improves the measurement of Suo through the addition of a larger data set than usually possible in the conventional method. The measurement method utilizes electrical data of the spark formation with a thermodynamic model to predict the kernel velocity and temperature which result from plasma formation. In addition, morphology of the early kernel at high pressure is reported as well as comparisons to the conventional Suo measurement.

Experimental Evaluation of ND: YAG Laser Parameters and Sample Preparation Methods for Texturing Thin AISI 316L Steel Samples

In mechanical and material engineering, the effect of laser texturing depends on many factors besides device specification, primarily the properties of the materials being processed, and, secondly, the preparation of the sample. Laser texturing of thin (<5 mm) samples is mostly performed utilizing short-pulse lasers, but depending on the power of the laser beam, the process can also be performed by using continuous operation lasers. When using a laser beam to modify the surface layer, special attention should be paid to the surface preparation process. Engraving a shiny metal surface can lead to laser beam dispersion and energy loss. Some materials require special preparation and surface darkening in order to be effectively engraved. In the case of engraving, maximizing the efficiency and repeatability of the process is the key to obtaining the desired properties. The aim of the conducted study was to establish satisfying parameters and a sample preparation method for texturing thin AISI 316L samples. Appropriately selected laser parameters added to proper sample preparation. The sanding, etching, and darkening of the surface layer improved the quality of the weld and eliminated problems such as deformation and spark formation that often occur with raw samples during the texturing process.

FACTORS INFLUENCING THE EFFICIENCY OF MODERN ELECTRO-EROSION PROCESSING

The article describes the factors of increasing the efficiency of processing products on EDM equipment. due to the use of linear drives with high dynamic accuracy. Also, the inter-electrode gap in the processing zone, its influence on optimal energy regimes and maximum material removal was investigated in the work. The electrode is fed into the spark formation zone 5-10 times more often, the relative duration is several times longer than in machines with KGP drives. Sludge removal due to the pumping effect from rapid movements of the electrode instead of pumping. The use of linear motors, servo drives, precision linear position sensors, devices for automatic wire feeding, hole search, wire breakage prevention - will increase the productivity of wire-cutting processing by 40-100%.A comparative analysis of the performance of parts processing on equipment with the use of linear and KGP (ball-screw pairs) drives was carried out.

Analysis of thermal additive centrifugal abrasive flow machining process with improved electrode geometry

Thermal additive centrifugal abrasive flow machining (TACAFM) is a recent hybrid of abrasive flow machining to cater for its limitation of low material removal (MR) through spark formation and centrifugal action of centrifugal force generating (CFG) electrode. The geometry of the CFG electrode is a crucial parameter in determining the centrifugal action on media and spark formation. The present investigation proposed a novel triangular-shaped electrode for improving the efficiency of the TACAFM process. The validation of spark and flow parameters with the proposed electrode was analysed using ANSYS FLUENT@. The simulation results were further validated by experimentation and artificial neural network modelling. The effect of supply current, rotational speed of CFG electrode and number of cycles were analysed for MR and on percentage improvement in the surface finish (%ΔRa) on the brass workpiece by the proposed electrode. The experimental results show the average cumulative percentage absolute error obtained for MR is 0.33% and that for %ΔRa is 0.96%. The scanning electron microscopy images justify the machining performance through spark generation. The experimental results are in good confirmation of simulation results and highlight the suitability of the proposed electrode for the TACAFM process.

Kinetic mechanism and sub-ns measurements of the thermal spark in air

This experimental and numerical study is focused on the formation of fully ionized plasmas in ambient air by nanosecond pulsed discharges, namely the thermal spark. The first contribution of this article is the experimental characterization of the electron number density during the pulse. An increase of the electron number density up to 1019 cm−3 was measured with sub-nanosecond resolution via three techniques based on optical emission spectroscopy (OES): Stark broadening of H α , Stark broadening of N+/O+, and the continuum emission of electrons. The discharge diameter is measured with sub-nanosecond resolution using calibrated OES of the N+ and O+ lines. All measurements indicate a transition to a micrometric-size filament of fully ionized plasma in approximately 0.5 ns. The second main contribution of this work is the development of a 0D kinetic mechanism to explain this observation. The mechanism includes 100 reactions, 12 species, and 12 excited electronic states. Particular attention is paid to modeling the N2, N2 +, N, and O electronic state kinetics using the electronic states as additional pseudo-species. Our results show that including the electron-impact ionization of the excited electronic states of N and O, in addition to those of N2, is necessary to explain the experimental results, emphasizing the key role of excited state kinetics in the thermal spark formation.

IP3R activity increases propensity of RyR-mediated sparks by elevating dyadic [Ca2＋

Calcium (Ca2＋) plays a critical role in the excitation contraction coupling (ECC) process that mediates the contraction of cardiomyocytes during each heartbeat. While ryanodine receptors (RyRs) are the primary Ca2＋ channels responsible for generating the cell-wide Ca2＋ transients during ECC, Ca2＋ release, via inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) are also reported in cardiomyocytes to elicit ECC-modulating effects. Recent studies suggest that the localization of IP3Rs at dyads grant their ability to modify the occurrence of Ca2＋ sparks (elementary Ca2＋ release events that constitute cell wide Ca2＋ releases associated with ECC) which may underlie their modulatory influence on ECC. Here, we aim to uncover the mechanism by which dyad-localized IP3Rs influence Ca2＋ spark dynamics. To this end, we developed a mathematical model of the dyad that incorporates the behaviour of IP3Rs, in addition to RyRs, to reveal the impact of their activity on local Ca2＋ handling and consequent Ca2＋ spark occurrence and its properties. Consistent with published experimental data, our model predicts that the propensity for Ca2＋ spark formation increases in the presence of IP3R activity. Our simulations support the hypothesis that IP3Rs elevate Ca2＋ in the dyad, sensitizing proximal RyRs towards activation and hence Ca2＋ spark formation. The stochasticity of IP3R gating is an important aspect of this mechanism. However, dyadic IP3R activity lowers the Ca2＋ available in the junctional sarcoplasmic reticulum (JSR) for release, thus resulting in Ca2＋ sparks with similar durations but lower amplitudes.

Effect of inert gas on ignition ability of metal friction

For typical equipment used in the industries, such as conveyors, grinding and polishing machines, the potential hazard of friction sparks and hot surfaces as ignition sources should be considered. In this study, three representative metallic materials are selected to study the incendivity of the friction spark and hot surface in an inert gas environment. When the metal has a lower thermal conductivity, the heat energy is more likely to accumulate at the contact surface instead of being conducted. CO2 exhibits a better inhibitory effect on the spark formation and the temperature of sparks and hot surface than N2. When additional N2 content reaches 40%, the maximum temperatures of cast iron, 304 stainless steel, and 316 stainless steel decreased by 43.7%, 33.2%, and 35.6%. For 40% CO2, the maximum temperatures of the three metal friction surfaces are reduced by 48.1%, 47.7%, and 47.5%. The ignition test results are quantitatively analyzed, and the probability distributions of ignition and spark and friction surface temperatures are obtained. Compared with N2, the ignition probability of cast iron friction can be reduced by up to 57.8% with CO2. SEM, XPS and EDS analyses are performed for frictional products to examine the suppression effect of inert gas. The oxidation degree and the atomic percentage of oxygen in the friction products decrease with the increase of inert gas content.

Two-dimensional Configuration and Temporal Evolution of Spark Discharges in Pulsars

We report on our investigation of the evolution of a system of spark discharges in the inner acceleration region (IAR) above the pulsar polar cap. The surface of the polar cap is heated to temperatures of around 106 K and forms a partially screened gap (PSG), due to thermionic emission of positively charged ions from the stellar surface. The spark lags behind corotation speed during their lifetimes due to variable E × B drift. In a PSG, spark discharges arise in locations where the surface temperatures go below the critical level (T i ) for ions to freely flow from the surface. The spark commences due to the large drop in potential developing along the magnetic field lines in these lower temperature regions and subsequently back-streaming particles heat the surface to T i . Regulation of the temperature requires the polar cap to be tightly filled with sparks and a continuous presence of sparks is required around its boundary since no heating is possible from the closed field line region. We estimate the time evolution of the spark system in the IAR, which shows a gradual shift in the spark formation along two distinct directions resembling clockwise and anticlockwise motions in two halves of the polar cap. Due to the differential shift of the spark pattern in the two halves, a central spark develops representing the core emission. The temporal evolution of the spark process was simulated for different orientations of a non-dipolar polar cap and reproduced the diverse observational features associated with subpulse drifting.

Magnesium Ions Moderate Calcium-Induced Calcium Release in Cardiac Calcium Release Sites by Binding to Ryanodine Receptor Activation and Inhibition Sites.

Ryanodine receptor channels at calcium release sites of cardiac myocytes operate on the principle of calcium-induced calcium release. In vitro experiments revealed competition of Ca2+ and Mg2+ in the activation of ryanodine receptors (RyRs) as well as inhibition of RyRs by Mg2+. The impact of RyR modulation by Mg2+ on calcium release is not well understood due to the technical limitations of in situ experiments. We turned instead to an in silico model of a calcium release site (CRS), based on a homotetrameric model of RyR gating with kinetic parameters determined from in vitro measurements. We inspected changes in the activity of the CRS model in response to a random opening of one of 20 realistically distributed RyRs, arising from Ca2+/Mg2+ interactions at RyR channels. Calcium release events (CREs) were simulated at a range of Mg2+-binding parameters at near-physiological Mg2+ and ATP concentrations. Facilitation of Mg2+ binding to the RyR activation site inhibited the formation of sparks and slowed down their activation. Impeding Mg-binding to the RyR activation site enhanced spark formation and speeded up their activation. Varying Mg2+ binding to the RyR inhibition site also dramatically affected calcium release events. Facilitation of Mg2+ binding to the RyR inhibition site reduced the amplitude, relative occurrence, and the time-to-end of sparks, and vice versa. The characteristics of CREs correlated dose-dependently with the effective coupling strength between RyRs, defined as a function of RyR vicinity, single-channel calcium current, and Mg-binding parameters of the RyR channels. These findings postulate the role of Mg2+ in calcium release as a negative modulator of the coupling strength among RyRs in a CRS, translating to damping of the positive feedback of the calcium-induced calcium-release mechanism.

Features of intensive evaporation of liquid-metal steel drops heated in a high-frequency inductor

The paper presents the results of experimental studies of the processes of intense melting in air of samples (solid balls) made of metals, primarily various steels. It is shown that the heating of some steels is accompanied by intense sparking - the ejection of small secondary droplets (sparks) from the primary droplet heated up to 2500 K into the surrounding space. A possible mechanism of this process is proposed and described at a qualitative level. Possible reasons for the explosive fragmentation of secondary droplets are indicated and experimentally confirmed. The vibration process of molten samples shell, caused by the vortex motion and evaporation of the melt inside the droplet, is described. The influence of spark formation on the stability of the induction melting process is demonstrated.

МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ЭЛЕКТРОИСКРОВОГО ФОРМИРОВАНИЯ ИЗНОСОСТОЙКИХ ПОКРЫТИЙ НА ОБРАБАТЫВАЕМЫХ ПОВЕРХНОСТЯХ

The article considers a new direction in optimizing the process of plasma hardening of the surfaces of cutting elements of agricultural machines based on the use of electric spark discharge energy. (Research purpose) The research purpose is in optimizing the technological process of hardening the surfaces of cutting elements of agricultural machines by the method of electric spark alloying of carbide material elements. (Materials and methods) A device under RF patent No. 2655420, developed by the scientific supervisor of the subject S. N. Sharifullin, was used for electric spark alloying. A tungsten-cobalt rod with a diameter of 4 millimeters, consisting of 94 percent tungsten and 6 percent cobalt, was used as the electrode material for this case. The processed sample of 65G steel, which is the main material of the working bodies of tillage equipment. The physical and chemical properties of the samples were studied with a scanning electron microscope EVO 50 XVP from Zeiss. (Results and discussion) After the electric spark treatment of the alloyed elements, there were about ten, while their spectra also appear at different irradiation energies. The alloyed elements in the surface layer are not only separate, but also in the form of compounds with other elements. Such alloying elements as carbon, cobalt and tungsten appeared in a noticeable amount in the surface layer. Electric spark treatment allows increasing the microhardness of the surfaces of cutting elements of tillage equipment up to three times. (Conclusions) When developing a mathematical model of the electric spark formation of wear-resistant coatings on the treated surfaces, it is necessary to use the energy conservation equations of the electron gas, the Maxwell equations, the continuity and momentum equations. The complex solution of these equations makes it possible to obtain the required output parameters depending on the input ones.

Increasing SERCA function promotes initiation of calcium sparks and breakup of calcium waves.

Increasing sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) pump activity enhances sarcoplasmic reticulum calcium (Ca) load, which increases both ryanodine receptor opening and driving force of Ca release flux. Both of these effects promote Ca spark formation and wave propagation. However, increasing SERCA activity also accelerates local cytosolic Ca decay as the wave front travels to the next cluster, which limits wave propagation. As a result, increasing SERCA pump activity has a biphasic effect on the propensity of arrhythmogenic Ca waves, but a monotonic effect to increase Ca spark frequency and amplitude. Waves of sarcoplasmic reticulum (SR) calcium (Ca) release can cause arrhythmogenic afterdepolarizations in cardiac myocytes. Ca waves propagate when Ca sparks at one Ca release unit (CRU) recruit new Ca sparks in neighbouring CRUs. Under normal conditions, Ca sparks are too small to recruit neighbouring Ca sparks where Ca sensitivity is also low. However, under pathological conditions such as a Ca overload or ryanodine receptor (RyR) sensitization, Ca sparks can be larger and propagate more readily as macro-sparks or full Ca waves. Increasing SERCA pump activity promotes SR Ca load, which promotes RyR opening and increases driving force of the Ca release flux from SR to cytosol, promoting Ca waves. However, high sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) activity can also decrease local cytosolic [Ca] as it approaches the next CRU, thereby reducing wave appearance and propagation. In this study, we use a physiologically detailed model of subcellular Ca cycling and experiments in phospholamban-knockout mice, to show how Ca waves are initiated and propagate and how different conditions contribute to the generation and propagation of Ca waves. We show that reducing diffusive coupling between Ca sparks by increasing SERCA activity prevents Ca waves by reducing [Ca] at the next CRU, as do Ca buffers, low intra-SR Ca diffusion and distance between CRUs. Increasing SR Ca uptake rate has a biphasic effect on Ca wave propagation; initially it enhances Ca spark probability and amplitude and CRU coupling, thereby promoting arrhythmogenic Ca wave propagation, but at higher levels SR Ca uptake can abort those arrhythmogenic Ca waves.

Simulation and experimental investigation of tool wear rate in dry and near-dry EDM process

Purpose Many engineering applications in this era require new age materials; however, some classic alloys like spring steel are still used in critical applications such as aerospace, defense and automobile. To machine spring steel material, there exist various difficulties such as rapid tool wear rate, the rough surface formation of a workpiece and higher power consumption. The purpose of this paper is to address these issues, various approaches in addition to electrical discharge machines (EDM) are used such as dry EDM (DEDM) and near dry EDM (NDEDM). Design/methodology/approach This study focuses on these two approaches and their comparative analysis with respect to tool wear during machining of spring steel material. For this study, current, gap voltage, cycle time and dielectric medium pressure are considered input variables. This study shows that the near dry EDM approach yields better results. Hence, the thermo-electrical model for this approach is developed using ANSYS workbench, which is further validated by comparing with experimental results. This thermo-electrical model covers spark radius variation and formation of temperature profile due to electric discharge. Transient thermal analysis is used to simulate the electric discharge machining. Findings It is observed from this study that discharge environment parameters such as debris concentration and fluid viscosity largely influences the dielectric fluid pressure value. Experimental results revealed that NDEDM yields better results in comparison with DEDM as it shows a 25% lesser tool wear rate in NDEDM. Originality/value The range of predicted results and the experimental results are in close agreement, authenticating the model.

Application of Circuit Modeling in the Study of Spark Formation During Electroerosion Treatment

Electrical discharge machining (EDM) of a workpiece is a complex, fast-flowing process characterized by alternating (intermittent) states: short circuit, idle and spark formation. The discontinuity of the EDM process means that the processing is carried out in single pulses, which are formed by a special pulse generator. The parameters of the generator pulses can be divided into time and electrical. The time period and duration of the pulses, as well as the difference between these two parameters (the “silence” interval), are considered temporary. The electric ones include the amplitude value of the voltage, the maximum permissible current, and the polarity of the pulses. in addition, depending on the device of the generator, the pulses can be composite, for example, have an igniting pulse with a higher voltage and a lower current than the main (working) pulse. In this work, we have developed a interelectrode gap model that allows not only to obtain values of electrical parameters, but also to evaluate and to optimize the electrical parameters of materials being processed with known electrical properties. The key advantage of this model is its modularity, which allows to add new functional blocks, which describe external and internal influences, for example, the concentration of erosion products, uneven electrical conductivity of the workpiece, and others, without changing its structure.

Simplified Spark Pulser for Nanoparticles Generation

This article studies the possibility to design high-voltage pulser to sustain spark discharges in dielectric liquid using cheap and simple design. A spark pulser based on a zero-voltage switch oscillating circuit is used to power a high-voltage transformer. Sparks are ignited between copper electrodes in deionized water. The influence of input voltage and electrode gap on voltage and delay before breakdown, deposited charge, and energy is discussed. The effect of a spark gap device is also studied. Parameters of electric discharge are used to determine the capacitance and inductance of generator, through modeling of the equivalent electrical circuit. The utilization of the pulser in nanoparticles synthesis is evaluated by estimating the electrode erosion rate. In addition, the cavitation bubble generated by the spark is used to determine the pressure of the medium in which the spark and nanoparticles formation occur. Results show that the operation is similar to other setups.

Color‐Changing Sparks from Rare Earth Metal Powders

Commonly, sparks emit light according to the well‐known black (gray) body radiation. Recently, we reported on color‐changing sparks based on erbium powder, which switch their light emission between black body emission (surface combustion) and element‐specific emission (vapor phase combustion). Herein, we investigated the spark formation from the adjacent rare‐earth elements. The corresponding boiling points are significantly below (Yb, Sm, Tm) or above (Y, Lu) the boiling point of Er. While Yb and Sm evaporate too fast to form longer sparks, Y, Lu and Tm form color‐changing sparks with varying length of the element‐specific emission phase. The sparks were investigated by time‐resolved emission spectroscopy, long‐time exposures, and NIR/MIR imaging. The same basic pyrotechnic formulation containing one of these metal powders reveals a strongly differing burning behavior depending on the boiling point of the metal. The burning characteristics change from a green strobe (Yb) to intense colorful crackling (Tm) and finally a sparkling fountain with long‐flying sparks (Lu, Y, Er).

Cardiac ryanodine receptor distribution is dynamic and changed by auxiliary proteins and post-translational modification.

The effects of the immunophilins, FKBP12 and FKBP12.6, and phosphorylation on type II ryanodine receptor (RyR2) arrangement and function were examined using correlation microscopy (line scan confocal imaging of Ca2+ sparks and dual-tilt electron tomography) and dSTORM imaging of permeabilized Wistar rat ventricular myocytes. Saturating concentrations (10 µmol/L) of either FKBP12 or 12.6 significantly reduced the frequency, spread, amplitude and Ca2+ spark mass relative to control, while the tomograms revealed both proteins shifted the tetramers into a largely side-by-side configuration. Phosphorylation of immunophilin-saturated RyR2 resulted in structural and functional changes largely comparable to phosphorylation alone. dSTORM images of myocyte surfaces demonstrated that both FKBP12 and 12.6 significantly reduced RyR2 cluster sizes, while phosphorylation, even of immunophilin-saturated RyR2, increased them. We conclude that both RyR2 cluster size and the arrangement of tetramers within clusters is dynamic and respond to changes in the cellular environment. Further, these changes affect Ca2+ spark formation.

Promising algorithm for diagnosing vehicle ignition coils

The principle of performance of all elements, and their interconnection are described. A failure in one element causes a failure in the entire system and impossibility of movement. The analysis of key processes was carried out. Conclusions about responsible elements were drawn. An ignition coil that generates high voltage during the spark formation is one of the elements. Its technical state was studied; its regular monitoring was suggested.