Arc Current Waveforms Research Articles

Effect of current waveform in MIG arc on weld bead formation in plasma-MIG hybrid welding

Plasma-metal inert gas (MIG) hybrid welding enables to join thick steel plates in single pass. However, arc coupling occurring between the plasma and MIG arcs disturbs its heat source characteristics, lowering the welding quality. This arc coupling phenomenon is not yet understood due to the complexity. This study aims to clarify the effect of current waveform of arc on weld bead formation according to the arc coupling in plasma-MIG hybrid welding. The metal transfer characteristics and bottom side weld pool were observed for direct current (DC) and pulse-MIG current waveforms. In addition, Ni element was used for visualizing the transport process of high-temperature molten metal provided by MIG welding within the weld pool. From these results, the effects of differences in MIG arc current waveforms on heat and mass transport processes within the weld pool and also on weld bead formation on the bottom side through changes in the occurrence of arc coupling were discussed. As a result, it was clarified that the droplets after detachment from the wire were transferred to the weld pool surface under the wire tip for DC MIG current, while those were transferred along the wire axis to the weld pool surface behind the keyhole for pulse-MIG current. When the droplet was transferred to the weld pool region with the forward flow such as the pulse-MIG current case, the heat was transported to the bottom side together with the counter-clockwise eddy behind the keyhole, strongly contributing to increasing the penetration depth. In the case of pulse-MIG current, the plasma arc is oscillated due to the arc coupling. According to this oscillation, the accumulation of molten metal behind the keyhole is prevented to suppress the humping bead formation. Consequently, pulse-MIG current was found to be suitable for increasing the penetration depth and suppressing humping bead formation on the bottom side comparing with DC MIG current.

Spectral diagnosis of underwater microsecond high-current pulsed discharge plasma

Underwater microsecond high-current pulsed discharge can generate powerful shock waves and a significant number of active ions, offering a wide range of applications. To analyse the characteristics of plasma channel formed by the discharge, this study established a comprehensive test platform and conducted spectral diagnosis for underwater high-current pulsed discharge. Considering the randomness of the pulsed arc discharge, the voltage and current waveforms under different discharge cases were measured, and the images and emission spectra of the plasma channel were obtained. The origin of the continuous emission of the initial spectra was analysed. A spectral fitting algorithm was proposed, which could separate the spectral lines into line emission of Hα and continuous background, and correct the self-absorption. The time-varying characteristics of electron density were obtained under three typical discharge cases, the possible errors caused by baseline shift were considered, and the influencing factors of line broadening were analysed. Under the test conditions of this study, the electron density of plasma channel was in the order of 1024–1025 m−3.

Non-Intrusive Arc Fault Detection and Localization Method Based on the Mann–Kendall Test and Current Decomposition

In recent years, electrical fires caused by arc faults have been increasing, seriously affecting the safety of people’s lives and property. Considering the complex arc fault characteristics of actual low-voltage users, the non-intrusive arc fault detection and localization method is studied. First, the characteristics of arc current waveforms are analyzed, and event detection based on the Mann–Kendall Test is performed for the difference between the current waveforms of two adjacent cycles, rather than using the current waveforms directly. Then, the current waveforms of the two segments are calculated via subtraction to obtain the current waveform of the electric appliances causing the event. A current feature parameter database of the normal and arc currents is constructed via harmonic analysis, and a multi-appliance current decomposition model considering the sparse operation characteristics of appliances is established; thus, the arc localization problem is transformed into an optimization problem. Finally, a genetic algorithm is used to optimize the differential current decomposition results, and then, locate the arc fault. A household arc fault simulation experiment is carried out for the common electric appliances of actual low-voltage users. The experimental results show that the proposed non-intrusive arc fault detection and localization method is effective.

Elucidation of arc coupling mechanism in plasma-MIG hybrid welding process through spectroscopic measurement of 3D distributions of plasma temperature and iron vapor concentration

This study aims to clarify the mechanism of arc coupling phenomenon in plasma-MIG hybrid welding through the tomographically spectroscopic measurement of 3D distributions of plasma temperature and iron vapor concentration. The arc coupling strongly depends on arc current waveforms, so both the cases using DC MIG current and pulse MIG current were performed for the comparison. As a result, in the case using DC MIG current, two arcs were regularly connected, because the high temperature region between two arcs with an enough electrical conductivity was widely formed, retaining the current conduction between arcs. In the case using pulse MIG current, the two arcs were strongly connected only in the upslope duration of pulse MIG current. Both arcs were weakly connected or disconnected in other durations. The arc connection is thought to be governed by the balance between the stiffness and deflection of both arcs. In the case using pulse MIG current, two arcs were not connected in the downslope duration of pulse MIG current, although the pulse MIG current was similar with that in the upslope duration. In the upslope duration, the MIG arc is thought to be constricted because of the thermal pinch effect to increase the current density, which enhances the stiffness of MIG arc to prompt the arc connection. In contrast, the pulse MIG current density becomes lower in the downslope duration, which deflects the MIG arc backward to disconnect the arcs. The plasma current increased by 35 A during the arc connection, which increased the plasma arc temperature below the nozzle by 1000 K. The result implies that the arc coupling affects the distributions of the arc pressure and shear force by plasma arc acting on the keyhole inner wall, governing the keyhole stability as well as the weld pool formation process.

Low current arc ignition stability in micro-TIG welding

Micro‑tungsten inert gas (TIG) welding is widely used in electronic component manufacturing. Arc ignition under low current should be employed to avoid burning the micro-component. However, it is relatively complex to manipulate. To improve the stability and reliability of the arc ignition under low current, the effect of the ignition method, cathode spot motion (CSM), and welding circuit inductance is investigated. High voltage arc ignition (HVAI) experiments are carried out with different inductances under various CSM amplitudes. A high-speed digital camera is employed to record the arc image, while a digital oscilloscope is used to simultaneously detect the arc voltage and current waveforms. The results show that HVAI can achieve smooth arc ignition with the low current in a relatively long discharge gap. The inductance in the welding circuit plays an effective role in maintaining the burning of the micro-arc. However, overly high inductance prevents arc formation just after the breakdown of the gap. When a traditional TIG welding torch is used, cathode spots move violently at the beginning of the low current arc ignition. This results in arc oscillation in the space or even rapid extinguishing. By placing an insulating ceramic tube on the tungsten electrode, the emission of electrons can be limited to the electrode tip. This, in turn, restricts the range of motion of the cathode spots to the tip region. Consequently, low-current arc ignition performance is improved.

A high-performance WAAM process for Al–Mg–Mn using controlled short-circuiting metal transfer at increased wire feed rate and increased travel speed

Wire Arc Additive Manufacturing (WAAM) is a method for manufacturing high-scale metal objects. This method utilizes recent developments in welding to achieve better performance and higher process rates. Higher performance requires higher metal deposition rates, which implies higher heat input that negatively affects the manufacturing process. In the present study, a high-performance controlled short-circuiting metal transfer process at a wire feed rate of 12 m/min for WAAM with an Al–Mg–Mn alloying system was developed. The arc current and voltage waveforms were studied by oscillogram processing and then modified to reduce the energy input in comparison with a self-regulated gas metal arc welding process. The newly developed process was implemented to manufacture sample parts at a travel speed of up to 150 cm/min. The modified waveforms in combination with an increased travel speed led to a decrease in heat input, which appeared to be 16% lower than that of a conventional self-regulated process. Decreased heat input led to an improved geometry preservation stability at high process rates (up to 2.2 kg/h). Study of the mechanical properties showed that the elongation of the tensile samples was up to 41%. This increase in elongation was explained through macro- and microstructure analysis.

An overview on the cold wire pulsed gas metal arc welding

The demand to join newer and higher strength materials has motivated the development of controlled arc current waveforms in order to control deposition and heat input. Controlled waveforms in pulsed gas metal arc welding (P-GMAW) where the current is pulsed result in reduced nominal heat input, distortion, and residual stresses. A method to further improve these is by cold wire pulsed gas metal arc welding (CW-P-GMAW) to enhance P-GMAW with a cold wire (non-energized) fed into the weld pool. In this work, the feasibility of the process is reported and the influence of cold wire feeding on pulse parameters for low and high background to peak current ratios (Ib/Ip) were investigated through high-speed cinematography with synchronized current and voltage sampling; as well as evaluation of cross-sections via metallography. Moreover, it appears that the cold wire diminishes the heat transferred across the heat-affected zone (HAZ) for low current ratios.

Parameter identification of dc black‐box arc model using non‐linear least squares

The black-box arc model is known to be a useful technique to simulate dynamic arc-circuit interaction by reflecting arc characteristics. Existing researches have shown that the black-box model has been widely used to analyse the ac arc characteristics of SF6 and air circuit breakers. Due to the enormous energy and steep rise rate (di/dt) during dc fault, it is important to consider dc arc characteristics. However, there are no examples of black-box models for dc circuit breakers utilised in railway systems and dc microgrid. In this study, the applicability of the black-box model, which was applied to the existing ac arc analysis, was verified for the dc arc analysis. Black-box modelling is applied to datasheet of industrial low-voltage circuit breakers and parametric sweep method was used to select Schwarz model parameters considering the tendency of dc arc current waveform for the dc pole-to-pole fault. The authors also applied the Levenberg–Marquardt algorithm, which is the most extensively used for the optimisation of functional parameters, to the Schwarz model for accurate and reliable arc modelling. As a result, the dc arc feasibility of the black-box model was analysed through simulation results, and a model optimisation technique was proposed.

Electrical Lifespan Prediction of HVDC Relay Based on the Accumulated Arc Erosion Mass

Electrical lifespan prediction is one of the key problems for the designers of switching apparatus. It is of great necessity to develop empirical correlations between the design parameters and the electrical lifespan. In this paper, a novel method using the arc erosion mass as the prediction variable is proposed to predict the electrical lifespan of high-voltage direct-current (HVDC) relays. The arc current waveforms are measured, and the arc erosion mass during each breaking operation is calculated based on the relationship between the arc current and the arc erosion rate. The arc erosion mass is accumulated until it reaches a threshold value, which is determined by the electrical lifespan experimental results using HVDC products. It is found that the arc erosion mass linearly accumulates with the lifespan, which is very convenient in the electrical lifespan prediction. Experiments are carried out with a parameter-adjustable device similar to the actual HVDC relay structure. Effects of two key design parameters, the arc-blowing magnetic field flux density and the contact breaking speed, of the electrical lifespan are investigated. The magnetic field flux density is changed in the range from 40 to 80 mT, and the breaking speed is varied from 0.85 to 1.3 m/s. The relationships between the lifespan and the magnetic field flux density as well as the breaking speed are regressively constructed. It is shown that the developed relationships can be used for HVDC relay electrical lifespan prediction.

A Study on the Transient of Secondary Arc Current of UHV Transmission Lines

Secondary arcs are a type of alternating-current electric arc burning in open space, the arcing times of which are closely related to the transient of their currents. To elucidate the formation mechanism of the transient, the secondary current was first decomposed into the natural component and the forced component. Then, the corresponding circuit models were established and the formulas calculating these two components were derived. By means of the electromagnetic transients program simulation, the typical secondary arc current waveform is gotten, and its evolution is divided into three stages based on its characteristics. The influences of key factors (e.g., secondary arc resistance, shunt compensation degree, and neutral reactor) on the transient were investigated, and the most critical factor was obtained. It indicates that the transient of secondary arc current is mainly characterized by its natural component. Furthermore, using the Laplace transform method, and along with the simplification of the system circuit, the characteristic equation for the UHV transmission line was developed, and the damping factors and resonant frequencies of the natural component were solved. Compared with the previous steady-state analysis, the relationship between the decaying and oscillating processes with the system parameters is quantitatively explained. Rather than the line length, the neutral reactor, the decay of secondary arc current is directly proportional to the arc resistance, but inversely proportional to shunt reactor. The proposed methodology can be also applied to recovery voltage study. The results are essential for the transient analysis, the choice of neutral reactor, as well as the implementation of single-phase auto-reclosing strategy.

Arc location predictor on a 2D composite surface in vacuum

Conductors, insulators and semiconductors behave differently in the environment containing charged particles. For any sample substrate which consists either of these two or more has a specific charging property. In the charged environment, a differential potential is built up on metal and insulators kept adjacent to each other. If the surface potential exceeds the specified threshold voltage, a breakdown occurs on the substrate�s surface which results into release of heat and light energy. This is termed as an electrostatic discharge or an arc. Thus, discharges deteriorate the surface properties of the substrate and reduce its functional life. Hence, an understanding of such charging-arcing phenomenon on various substrate�s surface is essential. For this purpose, a dedicated facility for creating charged environment using electron gun and plasma source is developed and various parameters of discharge are measured and analyzed. As the size of the substrate is a major concern of performing experiments, an algorithm for predicting arc current waveform is developed simultaneously. This software is based on the basic details provided by the user. It is capable of generating a library of arc current waveforms on each arc favorable location. A dedicated database is obtained for each substrate having different geometrical shape. Generated arc waveform at any specified location is a function of its distance from substrate�s edges. It is based on 'arc image pixel manipulation technique'. Both experimental and simulated results are obtained for smaller sample substrates initially. Software generated waveform and actual waveform are quite comparable with each other. On successfully identifying arc location on the surface using the algorithm, use of CCD camera for the same can be avoided. A unique approach for reproducing a different waveform at each location by breaking the symmetry of the substrate is also discussed in the paper.

Three dimensional dynamic study of a metal halide thallium iodine discharge plasma powered by a sinusoidal and square signal

The purpose of this paper is to study the dynamic of a metal halide thallium iodine discharge lamp fed by a sinusoidal and square power supply. For this, a chemical model under Local Thermodynamic Equilibrium conditions has been developed to compute the plasma composition and transport coefficients such as thermal conductivity, viscosity and electric conductivity. This is then coupled with a three-dimensional time-dependent code that solves the system of the mass, energy and momentum equations, as well as the Laplace equation for the plasma using Comsol Multiphysics with Matlab. After validation with the experimental results, this model was applied to analyze the influence of the key parameters on the discharge behavior such as frequency for an AC arc current and the atomic ratio for square arc-current wave form on the convective process.

Development of an In-Orbit High-Voltage Experimental Platform: HORYU-4

HORYU-4 is a 12-kg satellite currently under development at the Kyushu Institute of Technology. Its main mission is to perform an in-orbit high-voltage technology demonstration to evaluate state-of-the-art arc mitigation technologies in real space environments. The main objective is to perform a similar experiment as those on the ground for the validation of existing test methods. The obtained data (arc current waveforms, in particular) will be utilized to evaluate testing methods, as the waveforms on the ground must have some resemblance to those in space. To perform such an experiment in orbit, we have outfitted this satellite with typical laboratory equipment, such as oscilloscopes and video cameras and a high-voltage source (i.e., Sphelar solar cells, also used on HORYU-2). In fact, this satellite is a miniaturized in-orbit laboratory for high-voltage experiments. An oscilloscope and video camera have been designed and developed using commercial off-the-shelf components that provide sufficient measurement capabilities with a limited size and power range.

High Speed Video Camera and Electrical Signal Analyses of Arcs Behavior in a 3-Phase AC Arc Plasma Torch

A 3-phase AC plasma torch has been developed and aims at overcoming some limits of the classical DC torches in terms of efficiency, cost and reliability. However, the arc behavior in 3-phase plasma torch remains poorly explored. This paper is dedicated to the high speed video camera at 100,000 frames per second and electrical signal analyses of arcs behavior in a 3-phase AC arc plasma torch. First, a reference case at 150 A, in nitrogen as working gas, has been deeply analyzed. Afterwards, a parametric study based on current and inter-electrode gap has been carried out. Results show that only one arc can exist at a given time and arcs rotate by switching from a pair of electrodes to another one, following the maximal electrical gap potential. However, a particular “abnormal” arc behavior was sometimes observed. Indeed, the arc motion within the inter-electrode gap increases the heat exchange and stabilizes the 3-phase discharge whereas the system is unbalanced when the arc is in the periphery. The analysis highlights that the arc motion is strongly influenced by the electrode jet velocity and repulsive Lorentz forces. The parametric study shows that the current increases both jet velocity and arc discharge stability. Elsewhere, the increase of the inter-electrode gap can also stabilizes the electrical 3-phase arc discharge. Furthermore, the correlation between arc motion and current waveform is highlighted. This work is likely to open the way toward a better understanding of 3-phase discharges in the perspective of their further optimization.

Microstructure and process characterization of laser-cold metal transfer hybrid welding of AA6061 aluminum alloy

Fiber laser-cold metal transfer (CMT) hybrid welding of an AA6061 aluminum alloy thin sheet was carried out. The microstructure was analyzed by an optical microscope, scanning electron microscope, and energy-dispersive spectrometry. The cross-weld tensile strength and hardness were tested to evaluate the mechanical properties of the welded joint. Accepted joints with finer microstructure and free of defects were obtained. The tensile strength was up to 223 MPa, 10 % stronger than that of a laser-pulse metal inert gas (PMIG) hybrid welded joint. Due to the featured CMT arc current waveform, stronger constitutional supercooling and more heterogeneous nuclei were generated in the weld pool of laser-CMT hybrid welding in comparison with laser-PMIG hybrid welding. It led to the results that the laser-CMT joint has a finer microstructure and narrower columnar dendrite zone compared with the laser-PMIG joint. Because of the stabilization of the CMT arc on the laser-induced keyhole, spatters were seldom found during laser-CMT hybrid welding and few hydrogen pores appeared in the joint.

디지털 제어를 이용한 알루미늄 아크 용접기의 기술현황

Recently, welding technology of nonferrous metals which were difficult to implement by arc welder has become available through digitalization of arc welding machine. Among them, the welding quality improvement of aluminum welding is very noticeable. These results increase the arc stability by controlling arc current and voltage waveform precisely, and control wire feed speed by synchronizing with arc current which the feed rate of filler wire is controlled by a precise motor control of servomotor and not by a simple constant speed feeding. Not only through the hardware digitalization of arc welding machine but also through advance of software of arc welding, it became possible to implement a certain level of welding quality by a simple operation. These led to CMT welding process implementation which requires low heat input than current arc welding and highly increased the applicability of the aluminum welding.

Ion velocities in a micro-cathode arc thruster

Ion velocities in the plasma jet generated by the micro-cathode arc thruster are studied by means of time-of-flight method using enhanced ion detection system (EIDS). The EIDS triggers perturbations (spikes) on arc current waveform, and the larger current in the spike generates denser plasma bunches propagating along with the mainstream plasma. The EIDS utilizes double electrostatic probes rather than single probes. The average Ti ion velocity is measured to be around 2×104 m/s without a magnetic field. It was found that the application of a magnetic field does not change ion velocities in the interelectrode region while leads to ion acceleration in the free expanding plasma plume by a factor of about 2. Ion velocities of about 3.5×104 m/s were detected for the magnetic field of about 300 mT at distance of about 100–200 mm from the cathode. It is proposed that plasma is accelerated due to Lorentz force. The average thrust is calculated using the ion velocity measurements and the cathode mass consumption rate, and its increase with the magnetic field is demonstrated.

基于光电触发的瞬态电弧测量及分析

A single-phase metal welding arc circuit was built in this paper.The transient arc lasted too short to measurement.According to the arc optical characteristics,the photodiode-based oscilloscope external trigger circuit was designed.It met the requirements through the tests.Three different materials were used in welding arc test,the voltage and current waveforms were recorded by oscilloscope and the influence of material difference on the arc was analyzed.

펄스 GMA 위빙 용접에서 그루브형상에 따른 아크특성에 관한 연구

In this paper, arc characteristics of V groove joints using pulsed GMA welding were found out. The bevel angles of <TEX>$22.5^{\circ}$</TEX> and <TEX>$30.0^{\circ}$</TEX> were chose to make the V groove configuration with the groove angles of <TEX>$45^{\circ}$</TEX> and <TEX>$60.0^{\circ}$</TEX>, respectively. In the experiment, the arc current waveform measurement and the high speed photography were taken to investigate the arc characteristics for a single-beveled asymmetric workpiece. Consequently, the welding current was changed abnormally around the edge of groove. As the arc moved close to the groove face, the welding current was increased rapidly because the welding arc was affected by the inclined surface. Also the welding current waveforms were measured for the double-sided symmetric workpiece to verify the previous measurements for the single-beveled workpiece, and similar current waveforms were found.

Emission Spectra of Arc Plasmas

Emission spectra of arc plasmas contain valuable information regarding arc sites, plasma parameters and composition, and temporal dynamics of plasma expansion. Emission spectra within the range of 200-800 nm were measured for trigger arcs on triple junctions and sustained arcs between solar array strings. Spectra were recorded from arcs on several different brands of conventionally designed solar array samples immersed in simulated low-Earth-orbit plasma. The arc sites and cathode materials were determined for plasmas generated by primary discharges and sustained arcs. Comparative analysis of temporal dynamics of arc current pulse waveforms with spectral line intensities allowed obtaining estimates for plasma expansion rates. Statistical processing of spectral line intensities resulted in calculations of arc plasma electron temperatures and surface densities of some atomic species. The presence of a flux of energetic electrons (above 100 eV) was confirmed by analysis of the structure of the excited atom and ion energy levels.