Arc Plasma Flow Research Articles

Phase denoising and unwrapping method for moiré fringes based on multiresolution analysis

Phase unwrapping for moiré fringes plays a crucial role in moiré tomography, and the precision of its outcomes deeply influences the detection results concerning high-temperature complex flow fields. In this paper, a phase denoising and unwrapping technique grounded in multiresolution analysis (MRA) is presented, and it is effectively applied to extract phase information from moiré fringes for propane-air flame and argon arc plasma flow fields. Firstly, the wrapped phase undergoes a wavelet packet decomposition for overall denoising. Subsequently, MRA is conducted to refine the denoising process and unwrap phase, involving layered wavelet packet decomposition and iterative unwrapping on different levels of approximate components. Following the hierarchical structure of MRA, the results from different levels are systematically combined and summarized. In order to ascertain the feasibility and applicability of this approach, a comparison is conducted between the results obtained from our proposed method and those obtained from three representative traditional methods. And then, the outcomes obtained from various unwrapping methods in scenarios involving noise and discontinuity, as well as the results between diverse wavelet basis functions, different decomposition layers and distinct iterations, are meticulously analyzed and compared. The findings indicate that our proposed method outperforms traditional phase unwrapping techniques in terms of continuity and smoothness, particularly when exposed to severe noise. Unlike the three classic methods, our proposed method maintains consistent results even in the presence of noise, thereby highlighting its advantages in terms of resilience against noise. In a word, this research serves as a crucial reference for the accurate detection of complex high-temperature flow fields by moiré tomography.

A novel magnetic field assisted powder arc additive manufacturing for Ti60 titanium alloy: Method, microstructure and mechanical properties

Due to the rapid heating-cooling process and unstable keyhole, pore defects are easily formed during the high energy beam-powder additive manufacturing (AM) process, posing great challenges to the high-performance manufacturing of aerospace components. Using an arc with lower energy density as a heat source can effectively avoid these defects, but its matching raw materials are limited to wire. In this paper, a novel magnetic field assisted powder arc additive manufacturing (MFA-PAAM) method has been proposed, which combines arc heat source and powder raw material to achieve dense metal parts. A transverse magnetic field (TMF) was introduced to solve the powder spattering problem which impacts the stability of the PAAM process, by regulating the direction of the arc plasma flow and the arc pressure. The unique melting behavior of the powder under arc heating was captured by a high-speed camera, which can be summarized into two steps: balling and adsorption by the molten pool. And the well-formed and fully dense Ti60 high-temperature titanium alloy wall components were successfully manufactured using the self-developed equipment. The microstructure of the thin-wall component is dominated by basket-weave distributed α laths and few β sheets remaining at their boundaries. A layered periodic distribution along the building direction was observed, which is mainly distinguished from the content and morphology of the β phase. The average ultimate tensile strength (UTS) and elongation to failure in the travelling direction are 1003.2 MPa and 15.1%, while the average UTS and elongation along the building direction are 1009.3 MPa and 16.6%, respectively. The fracture morphologies in both directions are characterized by ductile fracture. The MFA-PAAM technique shows great potential for fabricating materials that are difficult to be drawn into wires with high efficiency and performance.

Numerical analysis of arc physics and energy transfer under circumferential gas constraint effect

Energy dispersion and easy instability associated with arcs, the traditional metal processing heat source, restrict its development and application in the modern high-precision welding and additive manufacturing. This work aims to study the characteristics of a novel arc under circumferential gas constraint effect which can improve the arc stability and processing accuracy. A magnetohydrodynamics model was established to calculate the arc physics and heat transfer, considering the electron emission characteristics of tungsten and the effect of metal vapor. It indicates that the annular flexible constrained gas flow can significantly increase the physical characteristics such as arc temperature, plasma flow velocity and current density compared with traditional free arc which is named GTA. The arc heat generation increasement of the novel arc makes the heat transfer from arc to base metal higher than that of GTA. The additional annular gas flow inhibits the diffusion of metal vapor, stabilizing the arc and protecting the tungsten electrode from contamination. However, as the arc length decreases, eddy of arc plasma flow appears inside the arc, which can cause metal vapor to contaminate the tungsten. It's found that this novel gas flow constrained arc needs to be applied with a small current when welding with small arc length to avoid the eddy. Finally, the accuracy of the calculation model is verified by experimental detection of arc temperature.

Analysis of the turbulence influence in the electric ARC plasma flow by the laboratory study method

Analysis of the turbulence influence in the electric ARC plasma flow by the laboratory study method

EVAPORATION OF MICRO-DROPLETS IN CATHODE ARC PLASMA COATING UNDER FORMED ELECTRON BEAM

Evaporation of micro-droplets in an arc plasma flow under the action of a self-consistency electron beam and the condition of direct heating of micro-droplets by fast electrons are considered. It is shown that the plasma is heated under the influence of the beam, even taking into account the fact that the electrons and ions of the plasma lose energy for the evaporation of micro-droplets. It is demonstrated that small micro-droplets evaporate more intensively. It is shown that the plasma electron density should be optimal. For the destruction of macro-particles in a plasma with a higher concentration, more powerful beams are required than in a case of plasma with a lower concentration.

Numerical investigation on the influence of current waveform on droplet transfer in pulsed gas metal arc welding

A numerical model for pulsed gas metal arc welding (P-GMAW) was established to investigate the influence of the welding current on the fluid flow of arc plasma and filler metal in P-GMAW. Three sets of welding current waveforms with identical peak and base current but different median currents at the drop stage of current were used to conduct the experiment and numerical simulation. Bead-on-plate welding experiments under different current waveforms were conducted and the results showed that the waveform with a median current of 140 A had the best tolerance of the welding speed amongst the three current waveforms. Based on the mathematical modelling, the temperature profile and fluid flow of arc plasma and filler metal under different current waveforms were obtained and compared. The results showed that the waveform with a median current of 140 A could lead to lower droplet temperature and velocity when the droplet reached the workpiece compared with the other two waveforms. The simulated droplet shapes at different moments were compared with the captured images by a high-speed camera and they exhibited good agreements.

Computer Intelligent Numerical Simulation of TIG Welding Using Platy Tungsten Electrode

In order to reveal the law of arc plasma flow and heat transfer in the process of flat tungsten electrode TIG welding as auxiliary heat source for hardfacing of cast iron surface. According to the free burning TIG arc using platy tungsten electrode, A three dimensional (3D) model for tungsten inert gas welding using platy tungsten electrode has been developed. The whole region of platy tungsten TIG arc, namely, platy tungsten cathode, arc plasma and anode surface is treated in a unified numerical model. By using fluent software to do the second development of equations source and solve these equations, the distribution of temperature, velocity and current density are obtained. The simulation results show that the current of flat tungsten electrode is more dispersed, and the heat generation of arc is more dispersed, which leads to the decrease of arc temperature; The current density on the cathode is much higher than that on the anode.

Arc Plasma Flow Variation by Obstruction Structures between Anode and Cathode

Arc plasma flow between electrodes has been investigated in several studies. However, in the industrial field, arc plasma flow between electrodes is hindered by interfering materials such as filler metal in arc welding, substrates in chemical vapor deposition, and powders in sintering. Therefore, in this study, high temperature arc plasma flow analysis via three obstruction structure shapes was performed to understand the inter-electrode interference phenomena. COMSOL Multiphysics was used for the analysis; COMSOL interface such as electric field, magnetic field, heat transfer, and fluid flow (laminar flow) was applied and Multiphysics such as plasma heat source and temperature coupling were considered. The temperature and velocity of the arc plasma were determined and the energy transfer between the electrodes was analyzed. We confirmed that the concave shape has a lower average heat flux than the other shapes, with the arc pressure evenly distributed in the anode. It is concluded that the concave shape can reduce the flow of the plasma from the anode and obtain even distribution of the arc plasma in the radial direction.

Supersonic Flow of Vacuum Arc Plasma in a Magnetic Field

We have investigated the supersonic flow of dense plasma, formed by a pulsed vacuum arc, in a magnetic field of about 1 T using probe and optical diagnostics. Two separate magnetic field configurations were examined—an axial field with either converging or diverging lines of force. We find that for a low-current arc of from 0.4 to 1 kA and pulse duration of 270 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , the diverging magnetic field leads to increased plasma flow velocity by about a factor of 2.5, whereas the converging magnetic field reduces the velocity by about the same amount. For a high-current arc of from 5 to 30 kA and pulse duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\mu \text{s}$ </tex-math></inline-formula> , the plasma flow velocity increases, although the effect of increased field strength on flow velocity is less significant. Here, we describe these observations and other effects of magnetic field on the parameters of the vacuum arc plasma flow.

Development of Executive Equipment Design for Implementing the Process of Generating of Drops of Microand Nanoscale Range

Modeling of velocities and temperatures processes distribution in the plasma-forming channel determining the design features and optimal parameters of the plasma torch nozzle is one of promising directions in development of plasma technologies. The aim of this work was to simulate the processes of velocities and temperature distribution in the plasma-forming channel and to determine the design features and optimal geometric parameters of the plasmatron nozzle which ensures the formation of necessary direction of plasma flows for generation of surface waves on the surface of a liquid metal droplet under the influence of the investigated instabilities.One of the main tasks is to consider the process of plasma jet formation and the flow of electric arc plasma. For obtaining small-sized particles one of the main parameters is the plasma flow velocity. It is necessary that the plasma outflow velocity be close to supersonic. An increase of the supersonic speed is possible due to design of the plasmatron nozzle especially the design feature and dimensions of the gas channel in which the plasma is formed. Also the modeling took into account dimensions of the plasma torch nozzle, i. e. the device should provide a supersonic plasma flow with the smallest possible geometric dimensions.As a result models of velocities and temperatures distribution in the plasma-forming channel at the minimum and maximum diameters of the channel were obtained. The design features and optimal geometric parameters of the plasmatron have been determined: the inlet diameter is 3 mm, the outlet diameter is 2 mm.The design of the executive equipment has been developed and designed which implements the investigated process of generating droplets of the micro- and nanoscale range. A plasmatron nozzle was manufactured which forms the necessary directions of plasma flows for the formation of surface waves on the metal droplet surface under the influence of instabilities. An algorithm has been developed for controlling of executive equipment that implements the process of generating drops of micro- and nanoscale range.

Investigation of the effect of torch tilt and external magnetic field on arc during overlapping deposition of wire arc additive manufacturing

PurposeThe purpose of this paper is to find a theoretical reference to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition in wire arc additive manufacturing (WAAM) and ensure the effect of the gas shielding and stable heat and mass transfer in deposition process. The multiphysical numerical simulation and physical experiment are used for validation.Design/methodology/approachIn this study, welding torch tilt deposition and external parallel magnetic field–assisted deposition are presented to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition, and a three-dimensional numerical model is developed to simulate the arc of torch tilt overlapping deposition and external parallel magnetic field–assisted overlapping deposition.FindingsThe comparison of simulated results indicate that the angle of welding torch tilt equal to 20° and the magnetic flux density of external transverse magnetic field equal to 0.001 Tesla are capable of balancing the electric arc and shielding gas effectively, respectively. The arc profiles captured by a high-speed camera match well with simulated results.Originality/valueThese studies of this paper can provide a theoretical basis and reference for the calibration and optimization of WAAM process parameters.

Numerical analysis of internal flow of molten pool in pulsed gas tungsten arc welding using a fully coupled model with free surface

A fully electromagnetic, fluid flow and heat transfer coupled model with free surface is proposed to analyze the internal flow of weld pool with the strong interaction of arc plasma in pulsed gas tungsten arc welding. Governing equations are solved in the whole domain including the tungsten cathode, arc plasma and weld pool without simplifications; the level set method, the Marangoni effect and the local thermodynamic equilibrium (LTE) diffusion approximation are used to treat the interface between the plasma arc and weld pool. The originality of this paper is providing a fully coupled model both with free surface and varying surface tension gradient to reveal the oscillating behaviour of arc plasma and internal flow of molten pool in a pulsed - GTAW process, especially with high peak current and low frequency. By considering the pulsed current ranging from 80 A to 400 A with oscillating frequency of 10 Hz and validating the model with experiments, the fully coupled model shows that the multiphysics-based simulation methodology could reveal the physical essence of periodically expansion and compression of arc plasma and fluctuations of molten pool subjected to pulsed current, The dynamic variations (the current density, electric potential, magnetic flux density, temperature, arc flow and internal flow of weld pool) and driving mechanisms of internal melt flow (The Marangoni effect due to varying surface tension gradient, Lorentz force, arc pressure, shear stress) are quantitatively analyzed, the computed arc plasma behaviour and molten pool profiles are in reasonable agreement with the corresponding experimental and calculating results, revealing that the arc plasma and the molten pool both have a very fast response to the varying current as a whole electromagneto-hydrodynamic system, while the internal flow of molten pool also exhibits nonlinear characteristics as a result of the Marangoni effect.

Multi-Physics Modeling of Steel Ingot Melting by Electric Arc Plasma and its Application to Electric Arc Furnace

Arc melting is one of the commonly-used melting methods in modern material manufacturing. The present study established a numerical model coupling the electric arc plasma, solid melting, and liquid flow together to simulate the steel ingot melting process using the electric arc. The direct current (DC) electric arc behavioral characteristics with varying arc length generated by the moving electrode were analyzed based on the validated model. The effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were studied. A potential method was also proposed to apply the established model in simulating the electric arc furnace (EAF) scrap melting. The study reveals that a reasonable and stable arc length can provide higher instantaneous heat flux and current density and reduce the arc dissipation, meanwhile balance the electrode consumption rate and melting efficiency to achieve the highest economic benefit. In addition, the dynamic electrode movement during the melting process maintains the original arc performance near the ingot top surface, which also results in a positive impact on the melting efficiency.

Numerical Analysis of the Metal Transfer and Welding Arc Behaviors in Underwater Flux-cored Arc Welding

Based on the VOF method, a three-dimensional numerical analysis model coupling both droplets and arc behaviors is developed to simulate the metal transfer and arc plasma flow processes in underwater wet flux-cored arc welding. The relationships between several physical quantities such as droplet shape and temperature, electromagnetic force and current density of droplets and arc at different periods are analyzed. As it turns out, the special arc plasma component is the main reason why the arc concentrates on the bottom of the droplet, rather than being wrapped. As the volume of the droplet increases, the arc temperature decreases. The constriction of arc shape leads to the result that the welding current flow goes through from the droplet bottom–a small area to subjacent arc. Therefore, at the anode spot an intense electromagnetic spot force is formed. The droplets are also affected by the gas flow resistance inside the bubble. Under the combinative actions of the spot force and the gas flow resistance, the main mode of droplet transfer is large droplet repelled transfer. For verifying the reliability of the model, the real-time metal transfer process is captured by a high-speed camera, the experimental values and the simulated values are found to be in good agreement.

Modeling and simulation of muzzle flow field of railgun with metal vapor and arc

During the electromagnetic railgun launching process, there will be a complex flow field with high temperature in the muzzle area because of the high-speed friction, transition and secondary arc-ignition. This paper models the muzzle area of railgun when the projectile is far away from the muzzle, and the dynamic simulation of the flow field with secondary arc in the muzzle area is carried out based on the magneto hydrodynamic equations. Meanwhile, a multi-component plasma transport model is used to analyze the muzzle arc plasma flow process of the mixed gas of Al vapor and the air. Furthermore, the pressure boundary conditions are fitted by the dynamic mesh simulation results. The current and voltage of the muzzle are obtained through the emission experiment of the railgun experimental prototype. We load the current data into the simulation model and the voltage of experiments and simulations are compared, which proves the accuracy of the simulation. Then the plasma temperature and the composition of Al vapor in the muzzle flow process are analyzed in-depth.

Heat and pressure characteristics in hollow cathode centered negative pressure arc column

Arc characteristics are found greatly changed by the negative pressure from the hollow cathode. These changes affect the distribution of arc pressure, arc plasma flow and temperature along the arc column. The characteristics of HCCNPA (hollow cathode centered negative pressure arc) along the arc column were investigated in this study to understand the changes and influences. It was found that the negative pressure applied to the cathode reduced the arc pressure and the arc radius, and complicated the plasma flow distribution with a clear zero-speed dividing line in the arc column. Above the boundary line, the plasma in the middle of the arc column flowed to the cathode, and the peripheral plasma flowed to the anode, presenting two peak values in the arc pressure distribution. The inner negative pressure also could adjust the total arc force acting on the work-piece. Under the same inner negative pressure conditions, the difference in arc force between GTA (gas tungsten arc) and HCCNPA did not change at varying arc lengths.

Energy Parameters of Weld Formation Process in MIG-MAG Welding

The article presents results of an experimental study and simulation of the effect of welding arc energy characteristics on the nature of electrode metal transfer in MIG-MAG welding. Based on the research results, a method has been developed for determining the coefficient of welding arc plasma flow pressure. The method makes it possible to take into account the dependence of the electrode metal transfer pattern and plasma flow pressure on geometrical dimensions of a welded joint.

Simulation and analysis of heat transfer and fluid flow characteristics of arc plasma in longitudinal magnetic field-tungsten inert gas hybrid welding

In the present work, an axisymmetrical model based on the magnetohydrodynamics (MHD) is established to investigate the effect of external longitudinal magnetic field (LMF) on arc characteristics during the gas tungsten arc welding (GTAW) process. The profiles of temperature and voltage drop, distributions of axial velocity, shear stress, and arc pressure, etc., in the cases of different applied LMF strengths ranging from 0 to 0.06 T are simulated by utilizing the fluid dynamic theory coupled with Maxwell equations. In order to achieve more accurate values of heat transfer and fluid flow of arc plasma, we take the boundary layer of electrodes into consideration. The results show that the applied LMF could drive particles to rotate and expand the arc, and a negative pressure area appears at the center and induces an upward streaming of gas (i.e., anti-gravity flow) through the arc core with the effects of centrifugal force, concentrating the anodic energy to the cathode. When the magnetic induction strength is 0.06 T, vortexes are dramatically formed around the arc axis by the interaction between the anti-gravity flow from the arc center and outside downward flow from the arc fringes. Thus, the distribution of current density, anodic heat flux, and arc pressure shifts from the arc center to the periphery and forms a bimodal pattern. The various thermal fluxes and subsequent thermal efficiency are also quantitatively investigated for a better understanding of the effects of LMF on arc behaviors and the theoretical predictions show good agreement with the experimental results.

Modelling of fluid flow phenomenon in laser+GMAW hybrid welding of aluminum alloy considering three phase coupling and arc plasma shear stress

The present study aims to develop a unified three dimensional numerical model for fiber laser+GMAW hybrid welding, which is used to study the fluid flow phenomena in hybrid welding of aluminum alloy and the influence of laser power on weld pool dynamic behavior. This model takes into account the coupling of gas, liquid and metal phases. Laser heat input is described using a cone heat source model with changing peak power density, its height being determined based on the keyhole size. Arc heat input is modeled as a double ellipsoid heat source. The arc plasma flow and droplet transfer are simulated through the two simplified models. The temperature and velocity fields for different laser powers are calculated. The computed results are in general agreement with the experimental data. Both the peak and average values of fluid flow velocity during hybrid welding are much higher than those of GMAW. At a low level of laser power, both the arc force and droplet impingement force play a relatively large role on fluid flow in the hybrid welding. Keyhole depth always oscillates within a range. With an increase in laser power, the weld pool behavior becomes more complex. An anti-clockwise vortex is generated and the stability of keyhole depth is improved. Besides, the effects of laser power on different driving forces of fluid flow in weld pool are also discussed.

Complex analysis of microparticles deposited from arc-discharge plasma on vacuum-chamber walls

A complex study of the microparticles and condensate in the form of films deposited from an arcplasma flow on vacuum-chamber walls is performed. The study includes determination of the chemical and phase composition of the particles, their morphology, differential thermal analysis, electron microscopy, and also electron paramagnetic resonance and infrared spectroscopy. The plasma flow propagates in electric and magnetic fields. The formed structures are a result of the interaction of particles emitted from the cathode spot. In this case, the formation and existence of current layers in the plasma flow are assumed. The retrograde rotation of the cathode spot and plasma flow are analyzed. The conditions for the formation of fractal structures from plasma are determined.