Arc Pressure Research Articles

Electric Arc Recoil–A Novel Method for Reducing Lightning Strike Potential Difference for Transmission Line

Increasing arc pressure by tens of times with fine pouring tube, a positive shock wave by the pouring arc entering the closed space of the thin tube (electric arc recoil wave). The pressure of electric arc recoil wave is 8 to 23 times than that of the arc tube pouring wave. Since the recoil wave has more pressure than the arc tube pouring wave, and their directions are opposite, the tube poring arc is driven away from the tube channel by the recoil wave. The arc completely emptying and a large scale truncation to the electric arc are formed. Therefore, the truncation arc interrupts the lightning current, and recombusts to form a new tube pouring wave and backwash wave. The arc truncation and recombustion are caused by arc tube pouring and electric arc recoil alternately, and forming the intermittent lightning discharge, a large decrease in the amplitude of lightning current, steepness and discharge time. The results show that the amplitude of lightning current can reduce from 67.14 kA to 35.1 kA, and the lightning current steepness can decrease 77.3%. This attenuation method of lightning current amplitude could significantly reduce the lightning current flowing into the ground, the induced overvoltage and the ohm potential difference. Additionally, the problem of lightning strike step voltage in high soil specific resistivity areas and electromagnetic induced overvoltage can be solved by the method in this paper. The probability of original fault is reduced, and the operation reliability is enhanced. The method can lower the cost of ground network and improve the lightning protection performance.

Physical mechanism of material flow in variable polarity plasma arc keyhole welding revealed by in situ x-ray imaging

Lightweight manufacturing reduces energy consumption and protects the environment; therefore, it offers an important direction of development in engineering. Variable polarity plasma arc (VPPA) welding is a light gauge aluminum and magnesium alloy joining technology capable of the highly efficient welding of medium-thickness metals via the keyhole effect, and without the complex pre-processing required by traditional methods. However, the stability of the keyhole weld pool is easily lost, resulting in a much narrower parameter window than that of conventional methods. Here, through keyhole morphology analysis and x-ray in situ imaging experiments, we reveal the material flow behavior, the mechanism behind the stability of the keyhole weld pool, and the reason for the very narrow process parameter window in VPPA welding processes. We discovered that the polarity pressure difference of the plasma arc, which is induced by the keyhole boundary shape and plasma arc intensity, drives the flow pattern to the top side of the keyhole, which is beneficial for keyhole filling and the formation of a stable weld bead. The influence of the difference in plasma arc pressure and the keyhole boundary on the flow field revealed in this study may guide the optimization process of light metal joining to achieve the highly efficient and defect-free manufacturing of large and complex structures.

An improved heat transfer and fluid flow model of wire-arc additive manufacturing

Wire-arc additive manufacturing provides the fastest metal printing rate among all printing processes. Heat transfer and fluid flow models offer a usable connection between process variables and the parameters that affect the structure and properties of parts. Here we develop a computationally efficient, three-dimensional, transient, heat transfer and fluid flow model to calculate temperature and velocity fields, deposit geometry, cooling rates, and solidification parameters that affect the microstructure, properties, and defect formation. Calculations are done for multi-track depositions of a tool steel H13 and a titanium alloy Ti-6Al-4V and the computed results are tested using experimental data for different processing conditions. It is found that convective flow and arc pressure are the two most important factors that govern the width and depth of penetration, respectively. An adaptive grid technique proposed here enhances the computational speed by as much as by 50% without affecting the accuracy of the computed results. For the same processing conditions, Ti-6Al-4V exhibits a larger fusion zone than that for H13 steel attributed to the lower density of Ti-6Al-4V. In addition, Ti-6Al-4V exhibits faster cooling rates during solidification than H13 steel because of the lower difference between the liquidus and solidus temperatures for Ti-6Al-4V. A smaller hatch spacing results in a larger pool and slower cooling rates during the solidification of both alloys.

Liquid-metal capillary switch for electrical power application

Liquid-metal (LM) electrical switches have been desired for decades to overcome intrinsic shortcomings of traditional mechanical switches equipped with solid contacts. Existing LM electrical switches, functioning via solid-liquid wetting or liquid droplet actuation, mostly focus on low current and small signal switches. In this Letter, a LM switch aiming at a power-level current switch has been proposed. A proof-of-concept prototype was fabricated via encapsulating Galinstan droplets into a silicone matrix. The device switches on a circuit when LM droplets are squeezed into a capillary channel to coalesce. The switch-off process with arc burning is realized by capillary breakup of the LM bridge and high-speed contact separation driven by a pressure difference contributed by Laplace pressure, electrical arc pressure, and atmospheric pressure. Switching off 0.5 A–5 A current under DC 220 V within 0.13–1.69 ms, the device demonstrates a high-speed current interruption ability compared to two kinds of commercial push-button switches. A high-speed camera is utilized to visualize the LM switch's current interruption process. In such a situation, the LM contacts exhibit a separation speed up to 3.85 m/s. Apart from the pressure difference, a slip layer between the LM and capillary wall also plays an important role in driving LM contacts. The LM switch has potential for applications in communication and control equipment acquiring a fast switch of the electrical power signal. This paper offers a framework for designing the LM switch dealing with intense electrical discharge.

A Convenient Unified Model to Display the Mobile Keyhole-Mode Arc Welding Process

Keyhole-mode plasma arc welding (PAW) has a good prospect in the manufacturing industry. Unified models of plasma arc and workpiece help to reveal the physical mechanism in PAW for a better application. Previous unified models either deal with a constant keyhole situation or take too much computational time to display the dynamic keyhole process with a two-phase flow method. In view of the convenience for industrial application as well as good accuracy, a convenient unified model was developed to describe the mobile keyhole-mode PAW. With a simplified technique, the multiphase heat and force effect between plasma arc and workpiece was turned into a single-phase problem at each individual domain. Thus, it takes less computational time than previous unified models. The temperature field and weld pool during the mobile keyhole-mode PAW process were revealed, the arc flow and pool flow were displayed and the electric potential was predicted. The experiment was conducted on a stainless-steel plate, and the weld pool image and the measured arc pressure agree well with the calculated result. The calculated electric potential drop also coincides with the experiment. The model provides a convenient and accurate method to display the mobile keyhole-mode arc welding process.

Application of double electrode welding as the way to increase welding productivity of fillet welds of bridge structures

One of the ways to solve the task to increase productivity and obtain an enlarged leg in one pass is the use of two-electrode submerged arc welding (welding with a split electrode). When testing this welding method with respect to welding bridge metal structures, it was found that the quality of the welded joints and the productivity of the process substantially depend on the positioning of the electrodes relative to the groove. However, for the effective implementation of this method, a comprehensive study of its functionality for welding of bridge metal structures is necessary to conduct. An effective tool in solving such problems is physical and mathematical modeling, which allows without running a large number of experiments to study the features of the formation of fillet welds. To carry out this analysis, we used the previously developed physical and mathematical model of weld formation in single-arc submerged arc welding, added a description of the spatial position of the split electrode relative to the joint and defined the distribution of the heat flux and pressure of the double arc. It was found that the location of the electrodes with the lagging arc on the web provides better weld formation.

Effect of TMF and AMF Components on Expansion Process in Different Ignition Modes of Vacuum Arc Between Spiral-Type TMF Contacts

The drawn vacuum arc begins with a bridge column formed from the explosion of a liquid metal bridge after separating the contacts. The expansion process of the initial arc has an effect on arc motion or diffusion. In order to deeply study the influence of transverse magnetic field (TMF) and axial magnetic field (AMF) on the drawn arc characteristics in the initial expansion stage, in this article, arc ignition mode and appearance under two groups of contacts with different AMF and TMF components were experimentally studied. It was found that simultaneously reducing TMF and AMF components would end the expansion stage earlier, and the fluctuation of the arc column pressure during the expansion was larger. When TMF and AMF components were further reduced, the arc needs to take a longer time to extend across the slot gap due to insufficient Ampere force. When TMF was basically unchanged and AMF was reduced, the arc burned more intense, the diameter of the arc column was smaller, and the arc would merge earlier in multipoint ignition mode. The characteristics of arc voltage, pressure, and duration of expansion stage were analyzed, founding that the arc with a moderate TMF and AMF components had a smaller rising slope of arc voltage, a faster reducing speed of arc pressure, and a smaller range of the duration of expansion stage. In addition, the variation of magnetic field strength in different ignition modes and contact structures during the arc expansion stage was simulated to explain the mechanism of arc behavior.

The behavior of TIG welding arc in a high-frequency axial magnetic field

The effect of high-frequency axial magnetic field (HFAMF) on the shape of the welding arc and welding formation of tungsten inert gas (TIG) welding is analyzed theoretically and experimentally. The 316L stainless steel plate was welded with HFAMF produced by the excitation coil installed on the welding torch. The influence of the HFAMF on the welding process is studied by changing the magnetic frequency from 0 to 2000 Hz. The experimental results show that when the magnetic field frequency reaches 1500 Hz, the arc rotation radius is decreased to the minimum; the arc shape changes from cone to compressed cylinder; and the arc temperature, the arc pressure, and the depth-width ratio of the weld beam reached the maximum. Otherwise, the effect of applied HFAMF on the stress of arc and weld pool is discussed, and the mechanism of arc contraction is analyzed.

Numerical analysis of the heat-pressure characteristics in ultrasonic vibration assisted plasma arc

The ultrasonic vibration assisted plasma arc welding process was developed to enhance the welding efficiency while the underlying mechanism of ultrasonic interaction with plasma arc is not yet elucidated. In this study, a numerical model of ultrasonic vibration assisted plasma arc is proposed, which takes into account the influence of plasma flow velocity on the ultrasonic propagation as well as the macro- and micro-effects of ultrasound on the heat-pressure characteristics of the plasma arc. The calculation results show that the plasma flow velocity affects the ultrasonic field in the plasma arc, resulting in a significant increase in the sound pressure near the workpiece surface. Ultrasound can increase the thermal conductivity of plasma and reduce the electric conductivity of plasma. The acoustic radiation force is at the same order of electromagnetic force, while the acoustic energy is five orders of magnitude lower than Joule heat. Under the comprehensive action of ultrasonic vibration, the plasma arc pressure and current density on the anode surface are increased so that the keyholing/penetrating ability of the plasma arc is enhanced. The model is validated by comparison of predicted and measured arc pressure and current density on the anode surface.

Research status and future perspectives on ultrasonic arc welding technique

In recent years, ultrasonic arc welding technology, a novel and promising welding process, has been widely applied in the welding of steel, aluminum alloy, titanium alloy, nickel base alloy and composite materials to improve the welding efficiency and quality of the welded joints. This paper reviews the research status of ultrasonic arc welding technology, systematically classifies and summarizes the process of ultrasonic arc welding in terms of different ultrasonic energy forms, and evaluates the limitations of the processes. Based on the experiment and simulation results, this paper summarizes the effect mechanisms of ultrasonic on the arc characteristics and molten pool behaviors during arc welding, namely the theories of ultrasonic vibration and electromagnetic field, and briefly discusses the association mechanism of ultrasonic vibration and electromagnetic field. Finally, we summary the systematic results supporting the association mechanism. On the one hand, ultrasonic energy leads to arc compression, which can effectively improve the arc stiffness, arc pressure and energy density, thus improving the arc thermal efficiency and welding efficiency. On the other hand, the ultrasonic stirring and mixing effects as well as the high-frequency pulsed electromagnetic field force introduced by the ultrasonic energy accelerate the thermal convection circulation and the flow of the molten pool, and affect the solidification and crystallization behavior of the molten pool, thus improving the formation, microstructure and mechanical properties of the weld. The paper aims to comprehensively review the ultrasonic arc welding process and mechanisms, and provide guidance for the future research and development in ultrasonic arc welding technique.

Investigation of thermal dynamics for different leading configuration in hybrid laser-MIG welding

For hybrid laser-MIG welding of aluminum alloy, the weld bead quality is decided by the thermal dynamics in the molten pool. In order to analyze the influence of leading configuration on thermal behavior and mass transfer, a three-dimensional numerical model is established. In the model, a combined model is utilized to simulate the multiple reflections and Fresnel absorption of laser beam. The laser-arc interaction is considered and the plasma is shrinked for arc-leading configuration. Surface tension, electromagnetic force, buoyancy are considered to investigate the fluid flow pattern, and droplet impact and arc pressure are taken into account to track the free surface. For different configurations, the temperature and velocity field, together with concentration distribution of magnesium and zinc are compared and analyzed. The results show that transport phenomena of the molten pool is strongly affected by the configuration. For arc-leading (AL) configuration, it is easier to get a larger penetration. Meanwhile, the concentration distribution of magnesium and zinc is more homogeneous for laser-leading (LL) configuration. Furthermore, the developed model can provide theoretical basis for processing experiments.

On the synthesis and structural evolution of artificial CrN/TiN nanocomposites

The synthesis of nanocomposites is limited to thermodynamically immiscible phases or to phase separation by exceeding the limits of solution. Hence, the formation of nanocomposites based on transition metals, revealing a nanocrystalline Metal-Nitride/nanocrystalline Metal-Nitride structure, is restricted. These restrictions can be overruled by a spatially separated synthesis of the two phases and a recombination during the deposition. With this approach, the limits of current systems can be expanded, enabling the synthesis of artificial nanocomposites based on a variety of materials. We demonstrate the synthesis of a composite of two nanocrystalline phases of the miscible transition metal-nitrides CrN and TiN. TiN nanoparticles were synthesized using an atmospheric-pressure arc reactor and in-situ injected into a growing CrN thin film. The thin films are analyzed regarding their physical- and microstructure using two-dimensional GIXRD, XPS based on synchrotron radiation and TEM. The CrTiN thin film reveals a two-phase structure consisting of nanocrystalline CrN and TiN phases with crystallite sizes of 9 nm and 4 nm according to GIXRD. XPS indicates bonding of Cr-N, Cr-Cr, and Ti-N. No hint for Cr-Ti bonding was found, excluding (Cr,Ti)N solid solution formation. Based on the TEM-investigations, TiN nanoparticles are embedded as agglomerates in the CrN matrix.

Evolution of anodic erosion components and heat transfer efficiency for W and W80Ag20 in atmospheric-pressure arcs

Based on the in situ diagnostic system and the digital image post-processing technique, quantifications of the anodic erosion components and heat transfer efficiency for tungsten and the W80Ag20 material in arcs of argon, helium, and nitrogen were achieved. The leading vaporization of silver has been found to result in evidently lower anodic heat transfer efficiency and much smaller molten pools compared with those of the tungsten anode, but the intensive generation of silver vapor under the melt layer causes higher splashing erosion of the W80Ag20 anode. However, these characteristics can be strongly changed by the cathodic blowing, which leads to a much higher splashing erosion of tungsten anode but a lower erosion rate of W80Ag20 anode. Through the visualization of the erosion behavior and the post microanalysis of the anode surface, the possible driving mechanisms for the generation of the splashing droplet were discussed. The result indicates that the local high pressure caused by the vapor blasting during the bubble explosion plays a key role in the detachment of splashing droplets. Furthermore, as for the tungsten-based anode, the comparison of erosion behavior between the W80Ag20 anode and the previous-studied W70Cu30 anode makes it clear that increasing the temperature difference between the melting point (MP) of tungsten and the boiling point (BP) of the other material has the pros and cons. It is effective for the decrease of the anode erosion when the anode heat energy is relatively weak, while it can promote the splashing erosion when the liquid tungsten layer has been formed on the anode tip. These results are beneficial for the optimal design of the electrode system in circuit breakers.

3D heat transfer, fluid flow and electromagnetic model for cold metal transfer wire arc additive manufacturing (Cmt-Waam)

Abstract In this paper, we present a 3D numerical model of Wire Arc Additive Manufacturing to simulate the material deposition and the temperature field from the operating parameters. This predictive model, applied to a Cold Metal Transfer (CMT) process, takes into account electromagnetism, fluid flow and heat transfer in all domains (wire, arc, melt pool, substrate). This model, developed using COMSOL Multiphysics® software, calculates the creation of the molten metal drop at the filler wire tip, the detachment of the drop when the filler material retracts during the short circuiting phase and the growth of the deposit. This innovative work describes for the first time the wire behaviour dynamically and its interaction with the melt pool in 3D in a fully coupled approach. The dynamics of the free surface are treated with the level set method, particularly efficient for strong topological changes. The Lorentz forces, shear stress, arc pressure, and Joule effect are calculated. This model requires only the knowledge of the operating parameters without any assumption on the arc distribution. It aims to simulate the build-up of a 304 stainless steel wall. To validate this model, the melt pool dimensions and shape of the deposit calculated for the first layer are compared to experimental data given by macrographs and high speed videos.

Arc Characteristics and Weld Bead Microstructure of Ti-6Al-4V Titanium Alloy in Ultra-high Frequency Pulse Gas Tungsten Arc Welding (UHFP-GTAW) Process

To resolve the problem of grain coarsening occurring in the fusion zone and the heat-affected zone during conventional gas tungsten arc welding(C-GTAW) welded titanium alloy, which severely restricts the improvement of weld mechanical properties, welding experiments on Ti-6Al-4V titanium alloy by adopting ultra-high frequency pulse gas tungsten arc welding (UHFP-GTAW) technique were carried out to study arc characteristics and weld bead microstructure. Combined with image processing technique, arc shapes during welding process were observed by high-speed camera. Meanwhile the average arc pressure under various welding parameters were obtained by adopting pressure measuring equipment with high-precision. In addition, the metallographic samples of the weld cross section were prepared for observing weld bead geometry and microstructure of the fusion zone. The experimental results show that, compared with C-GTAW, UHFP-GTAW process provides larger arc energy density and higher proportion of arc core region to the whole arc area. Moreover, UHFP-GTAW process has the obviously effect on grain refinement, which can decrease the grain size of the fusion zone. The results also revealed that a significant increase of arc pressure while increasing pulse frequency of UHFP-GTAW, which could improve the depth-to-width ratio of weld beads.

Numerical simulation for dynamic behavior of molten pool in tungsten inert gas welding with reserved gap

Abstract A 3-dimensional transient numerical analysis model of tungsten inert gas (TIG) welding with a reserved gap was established in this study. The loss of the total heat input and change in arc pressure due to the reserved gap were considered in this model. The dynamic variations of the flow field and deformation in weld pool were analyzed. Simulated results indicate that the maximum sag of weld pool is larger, and the top surface area of weld pool is smaller as the reserved gap increases. The flow tendency of the molten metal is mainly backward, and the top surface of the weld pool is higher in the front part and lower in the rear part. The liquid metal flows from both sides to the middle, bringing heat into the gap. The liquid metal in front of the weld pool flows to the back of weld pool through the gap, which facilitates weld penetration.

Investigation on the Dynamic Behavior of Weld Pool and Weld Microstructure during DP-GMAW for Austenitic Stainless Steel

The influence of heat and droplet transfer into weld pool dynamic behavior and weld metal microstructure in double-pulsed gas metal arc welding (DP-GMAW) was investigated by the self-designed high-speed welding photography system. The heat input, the arc pressure, the droplet momentum and impingement pressure were measured and calculated. It was found that the arc pressure is far less than the droplet impingement pressure. The heat input and droplet impingement pressure per unit time acting on weld pool were proportional to the current pulse frequency, which fluctuated with thermal pulse. The size and oscillation amplitude of the weld pool had noticeable periodic changes synchronized with the process of heat input and droplet impingement. Compared to the microstructure of pulsed gas metal arc welding (P-GMAW) weld metal, that of DP-GMAW weld metal was significantly refined. High oscillation amplitude assisted the enhancement of weld pool convection, which leads to more constitutional supercooling. The heat input and shear force during the peak of thermal pulse causing dendrite fragmentation which provided sufficient crystal nucleus for the growth of equiaxed grains and the possibility of grain refinement. The effects of current parameters on welding behavior and weld metal grain size are investigated for further understanding of DP-GMAW.

Regulation of the welding current magnetic field during electric arc welding of pipes

ABSTRACT Mathematical models of magnetic field induction at welding plates and pipes are obtained. The influence of the product shape on induction is established by experiment-calculated way. Magnetic blast during pipe welding increases by more than 10 times due to the concentration of magnetic field lines in a ferromagnetic pipe with high magnetic permeability, the increase in induction by π (3.14) times, the electromagnetic force, acting on an arc and magnetic pressure. A method of one-sided high-speed welding of pipes is developed. In such a case, by passing a current opposite to the welding current inside a ferromagnetic pipe, the magnetic blast is prevented, the process stability is enhanced, upward electromagnetic force and magnetic pressure are created that keep the liquid metal from flowing out of the bath. It ensures the formation of quality seams on a flux cushion and an increase in the impact strength of welded joints by 2–2.5 times.

Effect of welding variables on GTAW arc stagnation pressure

This paper presents the influence of welding current, electrode-workpiece distance, electrode composition, electrode diameter, electrode tip angle, shielding gas composition, and pulsed current frequency over the arc stagnation pressure of gas tungsten arc welding (GTAW). In this study, arc application tests were carried out over a 1-mm diameter hole on a non-melting water-cooled copper plate. The hole was connected to a differential pressure sensor through an extension tube. As a result, the welding arc pressure was observed to be directly proportional to the square of the welding current and to the tungsten electrode diameter. Moreover, the pressure increases as the electrode-workpiece distance is reduced, and it is inversely proportional to the electrode tip angle, for angles greater than 45°. Also, the electrode composition, the pulsed current frequency, and the gas composition influence the welding arc stagnation pressure.

Influence of interwire angle on undercutting formation and arc behavior in pulsed tandem narrow-gap GMAW

The tandem narrow-gap gas metal arc welding was adopted in this study. The effects of interwire angle on the welding process stability and arc behavior were investigated. With the interwire angle increasing, the welding process stability gets improved. The arc interruptions which frequently occur in the leading arc are eliminated when the interwire angle is >0°. The mutual electromagnetic attraction between the two arcs decreases with the interwire angle increasing due to the increased arc distance. The two arcs move from the groove bottom to the sidewalls, which transfer more heat to the sidewalls resulting in increased weld width. This leads to serious undercutting defects especially when the interwire angle is 20°. The molten metal under the arcs flows to the rear of welding pool under the action of plasma drag force, arc pressure and droplet impingement. As a result, there is no adequate molten metal to fill the sidewalls, giving rise to undercutting defects. The undercutting at the groove sidewall close to the trailing arc is smaller. This is because the liquid metal under the trailing arc is more massive, which means more molten metal flows to the sidewall, alleviating the undercutting defect.