Spark Generation Research Articles

The Application of Wire Electrical Discharge Machining (WEDM) in the Prototyping of Miniature Brass Gears

Due to its ability to cut complex shapes without the set-up times of conventional processes, wire electrical discharge machining (WEDM) lends itself to the prototyping or limited-run production of miniature gears with a low aspect ratio for use in small mechanisms. Cutting of very thin workpieces using WEDM presents a difficulty in terms of machining stability, and requires careful consideration of machining parameters.The recast layer that occurs in WEDM affects both the geometrical accuracy and hardness properties of the gears. For accurate motion transmission, this layer should be minimised. At the same time, the process should be optimised to produce gears in the minimum possible machining time. The production of very accurate, low aspect ratio gears is difficult in WEDM because the limited area for spark generation between wire and workpiece leads to unstable machining, resulting in poor machining rate and surface finish.This work focuses on reducing the depth of the recast layer and optimising surface finish whilst maintaining an acceptable machining rate. The effects of machining parameters have been investigated, establishing the suitability of the WEDM process for producing gears and gear dies. It is demonstrated that the Ra value for surface roughness in very thin workpieces can be reduced by approximately an order of magnitude (from 3.4 µm to 0.4 µm) using control of basic parameters.Building on this, a feasibility study has taken place cutting brass gears of a thickness of 0.3mm and altering rough and skim cut parameters such that the final depth of recast layer is minimised and a smooth surface finish is achieved. The gears were examined for recast layer depth and surface finish. The recast layer was investigated by polishing and etching, then measuring the depth using optical microscopy and a scanning electron microscope (SEM). SEM was also used to investigate surface topography, as different topographies are preferable from a tribological point of view.The results indicate that the depth of the recast layer can be reduced while maintaining a good material removal rate, by removing only the recast material with the second pass. Thus it is possible to increase the productivity of gear production with WEDM, while maintaining good surface characteristics. This work opens up possibilities for prototyping miniature gears.

Thermal Stress Analysis of XW-42 Steel Workpiece Using Finite Element Modeling

Electric discharge machine (EDM) is a non-conventional machining process, usually used for machining of hard materials. In this process, material removes due to spark generation between tool and workpiece. High heat generates at the spark zone radius, resulting in thermal stresses in the workpiece. If this thermal stress approaches the yield stress value of material, creates micro-cracks and catastrophic failure etc. XW-42 steel has been used as a workpiece for thermal analysis. ANSYS Workbench 15.0 is used for the analysis, in which coupled custom system is chosen for the calculation of stress concentration values. Also, this study reveals the influence of input parameters like current intensity, voltage gap and duty factor on equivalent stress. It is seen that equivalent stress occur in the central spark zone of the tool and workpiece. Response output parameters are prominently affected by the current density. By evaluating the optimum values of temperature, equivalent stress and strain, total deformation, the input process parameters can be controlled to the desired values, results in less stress concentration occurs, so that the damage to the workpiece can be reduced.

The Dependence of CNT Aerogel Synthesis on Sulfur-driven Catalyst Nucleation Processes and a Critical Catalyst Particle Mass Concentration

The floating catalyst chemical vapor deposition (FC-CVD) process permits macro-scale assembly of nanoscale materials, enabling continuous production of carbon nanotube (CNT) aerogels. Despite the intensive research in the field, fundamental uncertainties remain regarding how catalyst particle dynamics within the system influence the CNT aerogel formation, thus limiting effective scale-up. While aerogel formation in FC-CVD reactors requires a catalyst (typically iron, Fe) and a promotor (typically sulfur, S), their synergistic roles are not fully understood. This paper presents a paradigm shift in the understanding of the role of S in the process with new experimental studies identifying that S lowers the nucleation barrier of the catalyst nanoparticles. Furthermore, CNT aerogel formation requires a critical threshold of FexCy > 160 mg/m3, but is surprisingly independent of the initial catalyst diameter or number concentration. The robustness of the critical catalyst mass concentration principle is proved further by producing CNTs using alternative catalyst systems; Fe nanoparticles from a plasma spark generator and cobaltocene and nickelocene precursors. This finding provides evidence that low-cost and high throughput CNT aerogel routes may be achieved by decoupled and enhanced catalyst production and control, opening up new possibilities for large-scale CNT synthesis.

From plasma to nanoparticles: optical and particle emission of a spark discharge generator

The increased demand for high purity nanoparticles (NPs) of defined geometry necessitates the continuous development of generation routes. One of the most promising physical techniques for producing metal, semiconductor or alloy NPs in the gas phase is spark discharge NP generation. The technique has a great potential for up-scaling without altering the particles. Despite the simplicity of the setup, the formation of NPs in a spark discharge takes place via complex multi-scale processes, which greatly hinders the investigation via conventional NP measurement techniques. In the present work, time-resolved optical emission spectroscopy (OES) was used to provide information on the species present in the spark from as early as approximately 100 ns after the initiation of the discharge. We demonstrate that operando emission spectroscopy can deliver valuable insights into NP formation. The emission spectra of the spark are used to identify, among others, the main stages of material erosion and to calculate the quenching rate of the generated metal vapour. We demonstrate that the alteration of key control parameters, that are typically used to optimize NP generation, clearly affect the emission spectra. We report for Cu and Au NPs that the intensity of spectral lines emitted by metal atoms levels off when spark energy is increased above an energy threshold, suggesting that the maximum concentration of metal vapour produced in the generator is limited. This explains the size variation of the generated NPs. We report a strong correlation between the optical and particle emission of the spark discharge generator, which demonstrate the suitability of OES as a valuable characterization tool that will allow for the more deliberate optimization of spark-based NP generation.

Role of FK506-binding protein in Ca2+ spark regulation

The elementary Ca2+ release events, Ca2+ sparks, has been found for a quarter of century. However, the molecular regulation of the spark generator, the ryanodine receptor (RyR) on the sarcoplasmic reticulum, remains obscure. Although each subunit of the RyR homotetramer has a site for FK506-binding protein (FKBP), the role of FKBPs in modifying RyR Ca2+ sparks has been debated for long. One of the reasons behind the controversy is that most previous studies detect spontaneous sparks, where the mixture with out-of-focus events and local wavelets prevents an accurate characterization of Ca2+ sparks. In the present study, we detected Ca2+ sparks triggered by single L-type Ca2+ channels (LCCs) under loose-seal patch clamp conditions in FK506-treated or FKBP12.6 knockout cardiomyocytes. We found that FKBP dissociation both by FK506 and by rapamycin decreased the Ca2+ spark amplitude in ventricular cardiomyocytes. This change was neither due to decreased releasable Ca2+ in the sarcoplasmic reticulum, nor explained by changed RyR sensitivity. Actually FK506 increased the LCC-RyR coupling probability and curtailed the latency for an LCC to trigger a RyR Ca2+ spark. FKBP12.6 knockout had similar effects as FK506/rapamycin treatment, indicating that the decreased spark amplitude was attributable to the dissociation of FKBP12.6 rather than FKBP12. We also explained how decreased amplitude of spontaneous sparks after FKBP dissociation sometimes appears to be increased or unchanged due to inappropriate data processing. Our results provided firm evidence that without the inter-RyR coordination by functional FKBP12.6, the RyR recruitment during a Ca2+ spark would be compromised despite the sensitization of individual RyRs.

Analytical Simulation of Random Textures Generated in Electrical Discharge Texturing

Textured functional surfaces are finding applications in the fields of bioengineering, surface energy, hydrodynamics, lubrication, and optics. Electrical discharge machining (EDM), which is normally used to generate smoother surface finish on various automotive components and toolings, can also generate surfaces of rough finish, a desirable characteristic for texturing purposes. There is a lack of modeling efforts to predict the surface textures obtained under various EDM operating conditions. The aim of the current work is to capture the physics of the electrical discharge texturing (EDT) on a surface assuming random generation of multiple sparks with respect to (i) space, (ii) time, and (iii) energy. A uniform heat disk assumption is taken for each individual spark. The three-dimensional (3D) texture generated is utilized to evaluate a 3D roughness parameter namely arithmetic mean height, Sa. Surface textures obtained from the model are validated against experimentally obtained ones by comparison of distribution of Ra values taken along parallel sections along the surface. It was found that the distribution of simulated Ra values agrees with that of experimental Ra values.

線香花火の実験的考察 : 溶融 K_2Sn 中の石墨微結晶の構造的酸化反応

線香花火の実験的考察 : 溶融 K_2Sn 中の石墨微結晶の構造的酸化反応

Investigation of remelting and preheating in SLM of 18Ni300 maraging steel as corrective and preventive measures for porosity reduction

One of the most critical defects in selective laser melting (SLM) is the porosity formation. Optimization of process parameters for reducing the porosity levels to lower than <1% is possible in most of the cases. Susceptibility to porosity formation can be higher for different alloys as function of chemical composition due to higher spark generation and molten pool instabilities. On the other hand, the probability of porosity formation increases in larger components due to an extended processing time. Powder recoater wear, increase in thermal load, and accumulation of particles in the processing chamber become more relevant as the processing time increases. Hence, the use of integrated monitoring and correction strategies becomes crucially important. In this work, three different correction strategies are discussed for the correction of porosity during the SLM of 18Ni300 maraging steel. The main aim is to develop a possible correction and prevention scheme to be used within a fully monitored SLM process. The 18Ni300 maraging steel is susceptible to high levels of porosity due to the empirically observed melt-pool instabilities as well as high spark and vapor generation. The correction methods consisted of remelting of the defected layer employing different scan strategies namely “double pass,” “soft melting,” and “polishing.” As a preventive strategy, preheating at 170 °C was also evaluated. At an initial stage, all the strategies were tested throughout the part built in order to assess their general capacity in improving the part density. Surface roughness, geometrical error, and material microhardness were also evaluated to assess the impact of the strategies on the other quality aspects. The results indicate the capacity of improving the part density and reduce the part roughness effectively.

From pulsed to continuous wave emission in SLM with contemporary fiber laser sources: effect of temporal and spatial pulse overlap in part quality

In this work, the effect of pulse temporal and spatial overlapping is evaluated in selective laser melting (SLM). An SLM system operating with fiber laser in pulsed wave (PW) emission was employed. The test material was 18Ni300 maraging steel, which shows reduced process stability due to a high amount of vapour and spark generation during the process. The pulsation characteristics of contemporary power-modulated fiber lasers compared to previously employed Q-switched Nd:YAG systems are explained. Processing conditions are studied moving towards continuous wave (CW) by increasing the duty cycle with fixed fluence. The key quality aspects, namely part density and dimensional error, were evaluated and the robustness was assessed. The results demonstrate that with a limited amount of increase in duty cycle by 3%, part density can be improved, while the dimensional error increases. The results show that CW is preferable when fully dense large parts have to be obtained. On the other hand, operating in PW is convenient when thin struts as in lattice structure or micro and precise features are required.

Spectroanalytical Generators “Sharovaya Molniya”: Upgrading and Diversification

A brief overview of the new electric arc and spark discharge generators of ShM series (“Sharovaya Molniya”) developed at the “VMK-Optoelektro nika company” over a period of 2011 -2016 and designed for atomic-emission spectral analysis is presented. A number of hardware changes that improve characteristics of existing generators are considered. In addition to well-known ShM-40 and ShM-250 generators, lightweight modifications of ShM generators have been developed and manufactured (mainly for the laboratories of educational institutions). “Sharm” arc generators have the same parameters as ShM-40 with an arc current of up to 20 A. “SKAT” spark generators forms a spark discharge of a positive polarity with the parameters similar to those of ShM-250. ShM-20 arc generators form an ac arc discharge (frequency 25 kHz) and dc arc discharge with a current up to 20 A. The generator control system has been upgraded using advanced microcontrollers to extend the capabilities of the devices and improve their performance.

Steps towards green manufacturing through EDM process: A review

AbstractThis paper focuses on the current machining process initiatives, carried out by various researchers relevant to the environmental aspects, thereafter predicting EDM performances. electrical discharge machining (EDM) is widely used unconventional machining method, because of its ability to process very hard material with precision. In thermo-electric process, control spark generation between electrodes causes material removal; however, application of hydrocarbon oil based dielectric fluid is an issue of environmental disruption. Replacement of dielectric to rectify the problem is one of the main concerns in EDM research. This paper highlights dry-EDM, near-dry EDM and EDM in water, conceived as an environment friendly alteration in the oil EDM process referred as a green EDM process. The work provides a thorough review of dry, near-dry EDM and EDM in water as a process, where the target is to endeavor dielectric fluids which could be the alternative to replace hydrocarbon oil. It is perceived that ...

ELEKTROFULHURATOR FOR DENTAL INTERVENTIONS OF THE NORMALIZED OUTPUT VALUE

Spark generators find more and more application for medical practice at different surgical and therapeutic procedures, for example, in dentistry for removing tumors of different origin, for stopping bleeding, for root canals preparation etc. Invasions with using of such apparatus are called electrosurgery.The authors developed a block diagram of a spark generator that extends the functionality of the equipment for installation on the normalized setting power of spark discharge for performance of appropriate medical procedures: maximum power - for surgical removal (cutting) of biological tissues, reduced power - for coagulation; for desiccation- minimum power; at the same time high reliability in the work of spark generator is ensured.

Supression of laser breakdown by pulsed nonequilibrium ns discharge

The avalanche ionization induced by infrared laser pulses was investigated in a pre-ionized argon gas. Pre-ionization was created by a high-voltage pulsed nanosecond discharge developed in the form of a fast ionization wave. Then, behind the front of ionization wave additional avalanche ionization was initiated by the focused Nd-YAG laser pulse. It was shown that the gas pre-ionization inhibits the laser spark generation. It was demonstrated that the suppression of laser spark development in the case of strong gas pre-ionization is because of fast electron energy transfer from the laser beam focal region. The main mechanism of this energy transfer is free electrons diffusion.

Detection and removal of impurities in nitric oxide generated from air by pulsed electrical discharge

Inhalation of nitric oxide (NO) produces selective pulmonary vasodilation without dilating the systemic circulation. However, the current NO/N2 cylinder delivery system is cumbersome and expensive. We developed a lightweight, portable, and economical device to generate NO from air by pulsed electrical discharge. The objective of this study was to investigate and optimize the purity and safety of NO generated by this device. By using low temperature streamer discharges in the plasma generator, we produced therapeutic levels of NO with very low levels of nitrogen dioxide (NO2) and ozone. Despite the low temperature, spark generation eroded the surface of the electrodes, contaminating the gas stream with metal particles. During prolonged NO generation there was gradual loss of the iridium high-voltage tip (−90 μg/day) and the platinum-nickel ground electrode (−55 μg/day). Metal particles released from the electrodes were trapped by a high-efficiency particulate air (HEPA) filter. Quadrupole mass spectroscopy measurements of effluent gas during plasma NO generation showed that a single HEPA filter removed all of the metal particles. Mice were exposed to breathing 50 parts per million of electrically generated NO in air for 28 days with only a scavenger and no HEPA filter; the mice did not develop pulmonary inflammation or structural changes and iridium and platinum particles were not detected in the lungs of these mice. In conclusion, an electric plasma generator produced therapeutic levels of NO from air; scavenging and filtration effectively eliminated metallic impurities from the effluent gas.

Review of research work in die sinking EDM for machining curved hole

Manufacturing is one of the most important sectors. It involves various machining operations to be performed on the workpiece, through which the output can be achieved. Global competition calls for quick manufacturing in new product development. Electrical discharge machining (EDM) is one of the sustainable manufacturing techniques available for machining the complex workpieces. Recently EDM development is taking place rapidly. Many researchers have focused on spark generation in EDM for continuous improvement. Electrical discharge machining requires the tool (master pattern) and workpiece (replica of master pattern). It works on the principle of spark erosion process. The generation of spark erosion distinguishes this non-traditional manufacturing method from traditional one. Most of the EDM utilizes the linear travels of head during machining of the workpiece. So, constrained restricted to only horizontal or vertical machining surface irrespective of curved surface machining. This review paper explains the mechanisms and methods adopted for developing the curved hole machining. These mechanisms enhance the utility and applications in the field of aerospace, molding and automobile industries.

A stepper-piezo-based co-actuation paradigm for tool positioning in parallel spark micro-electro-discharge machining

We report a new method for tool positioning in micro-electro-discharge machining with multiple electrodes for generating parallel spark employing a combination of stepper motor and piezoactuator-based co-actuation method. The stepper motor was used for coarse positioning and the inequality arising due to difference in the tool size of multiple tools used in micro-electro-discharge machining was equated employing piezoactuation followed by electrical continuity test. Simultaneous sparks for two different electrodes could be observed employing this method. The voltage waveforms across the tool–workpiece interface also confirm the generation of simultaneous and parallel sparks across both the electrodes.

Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague–Dawley rats

BackgroundThe increasing use of silver nanoparticles (AgNPs) in consumer products is concerning. We examined the potential toxic effects when inhaled in Brown-Norway (BN) rats with a pre-inflammatory state compared to Sprague–Dawley (SD) rats.MethodsWe determined the effect of AgNPs generated from a spark generator (mass concentration: 600–800 μg/mm3; mean diameter: 13–16 nm; total lung doses: 8 [Low] and 26–28 [High] μg) inhaled by the nasal route in both rat strains. Rats were sacrificed at day 1 and day 7 after exposure and measurement of lung function.ResultsIn both strains, there was an increase in neutrophils in bronchoalveolar lavage (BAL) fluid at 24 h at the high dose, with concomitant eosinophilia in BN rats. While BAL inflammatory cells were mostly normalised by Day 7, lung inflammation scores remained increased although not the tissue eosinophil scores. Total protein levels were elevated at both lung doses in both strains. There was an increase in BAL IL-1β, KC, IL-17, CCL2 and CCL3 levels in both strains at Day 1, mostly at high dose. Phospholipid levels were increased at the high dose in SD rats at Day 1 and 7, while in BN rats, this was only seen at Day 1; surfactant protein D levels decreased at day 7 at the high dose in SD rats, but was increased at Day 1 at the low dose in BN rats. There was a transient increase in central airway resistance and in tissue elastance in BN rats at Day 1 but not in SD rats. Positive silver-staining was seen particularly in lung tissue macrophages in a dose and time-dependent response in both strains, maximal by day 7. Lung silver levels were relatively higher in BN rat and present at day 7 in both strains.ConclusionsPresence of cellular inflammation and increasing silver-positive macrophages in lungs at day 7, associated with significant levels of lung silver indicate that lung toxicity is persistent even with the absence of airway luminal inflammation at that time-point. The higher levels and persistence of lung silver in BN rats may be due to the pre-existing inflammatory state of the lungs.

Discrete Fireworks Algorithm for Single Machine Scheduling Problems

Over the recent years, Fireworks Algorithm has recorded an increasing success on solving continuous optimization problems, due to its efficiency, simplicity and more importantly its rapid convergence to good optimums. Thus, the Fireworks Algorithm performance is now widely comparable with the most popular methods in the optimization field such as evolutionary computation and swarm intelligence techniques. This paper introduces a discrete Fireworks Algorithm for combinatorial single machine scheduling problems. Taking advantage of the robust design of the original Fireworks Algorithm, a new adaptation of sparks generation is proposed with a novel use of the control parameters. To verify the explorative performance of the algorithm, a hybridization with Variable Neighborhood Search heuristic is implemented. To validate it, the proposed method is tested with several benchmarks instances of the single machine total weighted tardiness. A comparison with other optimization algorithms is also included. The obtained results exhibit the high performance of the proposed method.

Role of Mitochondria in Cerebral Vascular Function: Energy Production, Cellular Protection, and Regulation of Vascular Tone.

Mitochondria not only produce energy in the form of ATP to support the activities of cells comprising the neurovascular unit, but mitochondrial events, such as depolarization and/or ROS release, also initiate signaling events which protect the endothelium and neurons against lethal stresses via pre-/postconditioning as well as promote changes in cerebral vascular tone. Mitochondrial depolarization in vascular smooth muscle (VSM), via pharmacological activation of the ATP-dependent potassium channels on the inner mitochondrial membrane (mitoKATP channels), leads to vasorelaxation through generation of calcium sparks by the sarcoplasmic reticulum and subsequent downstream signaling mechanisms. Increased release of ROS by mitochondria has similar effects. Relaxation of VSM can also be indirectly achieved via actions of nitric oxide (NO) and other vasoactive agents produced by endothelium, perivascular and parenchymal nerves, and astroglia following mitochondrial activation. Additionally, NO production following mitochondrial activation is involved in neuronal preconditioning. Cerebral arteries from female rats have greater mitochondrial mass and respiration and enhanced cerebral arterial dilation to mitochondrial activators. Preexisting chronic conditions such as insulin resistance and/or diabetes impair mitoKATP channel relaxation of cerebral arteries and preconditioning. Surprisingly, mitoKATP channel function after transient ischemia appears to be retained in the endothelium of large cerebral arteries despite generalized cerebral vascular dysfunction. Thus, mitochondrial mechanisms may represent the elusive signaling link between metabolic rate and blood flow as well as mediators of vascular change according to physiological status. Mitochondrial mechanisms are an important, but underutilized target for improving vascular function and decreasing brain injury in stroke patients. © 2016 American Physiological Society. Compr Physiol 6:1529-1548, 2016.

Signal analysis of an actively generated cavitation bubble in pressurized pipes for detection of wall stiffness drops

Due to the increasing production of volatile new renewable energies as solar and wind, storage hydropower plants have to operate under harsh operation conditions in order to stabilize the electricity grid. As a result, highly transient water pressures occur in pressure tunnels and shafts more frequently. Non-intrusive monitoring techniques are therefore of special interest for these critical infrastructures. The propagation of a pressure wave generated actively by a cavitation bubble was experimentally investigated in a steel test pipe divided in several reaches. A local wall stiffness drop was simulated by replacing steel pipe reaches with less stiff materials as aluminum and PVC. Through the analysis of the pressure wave reflections due to the cavitation bubble explosion, recorded by two hydrophones placed at the extremities of the test pipe, the location of the weak reaches could be detected. An underwater spark generator was developed to produce cavitation bubbles in the pipe resulting in very steep shock waves. This allowed identifying very precisely the wave front and correspondingly the wave speed and the weak reach location. Compared to the wave analysis from water-hammer signals, the active cavitation bubble generation in the pipe is an innovative method that significantly increased the effectiveness of the detection of wall stiffness drops.