Arc Pressure Distribution Research Articles

Investigation of humping defect in high speed gas tungsten arc welding by numerical modelling

Humping defect which commonly occurs in high current and high speed welding seriously deteriorates weld property. The periodical humping formation in high speed GTAW is investigated by a transient three-dimensional numerical model. A double-ellipse arc shear stress model is proposed. The arc heat flux and arc pressure distributions are modelled varying with molten pool surface evolution self-adaptively. The temperature, liquid metal velocity and resultant weld bead formation are simulated. The molten pool behaviors and their effects on humping formation are discussed. The numerical results show that the deformation of molten pool surface and the elongation of gouging region are two initial requirements for humping formation. The instant solidification, inertia force, surface tension, Marangoni shear stress and gravity also have significant effects on fluid flow in lateral peripheries of molten pool, which influences the humping formation correspondingly. This model gives a preliminary explanation to the tendency of humping in high current and high speed welding condition and the susceptibility of humping to workpiece thickness, active element concentration and workpiece inclination. The simulated weld bead profile, molten pool flow pattern and temperature history are validated with experimental weld appearance, high speed CCD images and temperature measurement, respectively, and good agreements are obtained.

Simulation of the influences of surface topography of deposited layer on arc shape and state in arc based additive forming

The stacking deposition and the overlapping deposition are usually employed in arc based additive forming process, which will result in different surface topographies of deposited layer. Consequently, the shape and state, heat and mass transfer of electric arc will be affected by the surface topography of deposited layer. A three-dimensional numerical model of electric arc based on magnetic fluid dynamics, local thermodynamic equilibrium and optical thin assumption for arc based additive forming process with pure argon shielding gas is presented. Simultaneously, four kinds of deposited layer model with different surface topographies are established, which are the deposited layer models of planar substrate, namely the substrate without weld bead, deposited layer model of single-pass single-layer, deposited layer model of single-pass two-layers, and deposited layer model of overlapping. The numerical calculation is performed on condition that deposition current and the distance between the electrodes are constant. And the simulation results include the profile of electric arc, corresponding temperature field, flow field, current density, electromagnetic force, and the arc pressure distribution. The temperature field of planar substrate accords well with other researcher's experimental result, and the profiles of electric arc are in good agreement with images captured by high-speed camera. Surface topography of deposited layer plays a decisive role in determining the profile of electric arc under the same process conditions. The comparison of evolvement among the distributions on specified paths shows that the electric arc of planar substrate has higher temperature, velocity, current density and pressure in the arc center, arising from completely symmetrical deposition layer model and smaller contact area between the arc and the substrate; the number of layers of single-pass multi-layer deposited layer has little influence on various parameters of electric arc, but because the deposited layer height changes, the temperature and pressure on the outside of deposited layer have small deviation; asymmetric arc profile will form when the overlapping deposition is performed. There is a relatively low temperature in the arc center, resulting from larger contact area between the arc and the surface of deposited layer. In addition, the distributions of current density, electromagnetic force and pressure deflect to the deposited layer. The above conclusions can provide a theoretical basis for basic research and process decision of arc based additive forming, and it can also provide the parameters for the subsequent weld pool dynamics and metal transfer simulation.

Anti-gravity gradient unique arc behavior in the longitudinal electric magnetic field hybrid tungsten inert gas arc welding

An external magnetic field applied in arc welding process results in electro-magnetic stirring (EMS) welding. The added longitudinal magnetic field (LMF) provides an effective method to control the arc behavior and affect the resultant welds. However, few studies have addressed arc behaviors in LMF-TIG hybrid welding, i.e., tungsten inert gas arc (TIG) hybrid welding with an external LMF; the LMF direction is the same as or parallel to the symmetric axis of welding arc. In this paper, a three dimensional (3D) multiphysics field model was established to analyze arc behavior in LMF-TIG hybrid welding. This model is formed by fluid dynamics equations coupled with Maxwell equations. The fields of temperature, velocity, and electric current field were obtained from this model through numerical simulation using the finite volume method (FVM). It was found that the arc changes from its free to strong electromagnetic field controlled status in three stages. After the applied electromagnetic field exceeds a critical value, mutation is induced in the arc resulting in an arc behavior completely different from that of the normal free arc. The arc pressure and temperature distributions shift their centers, where the peak pressure and temperature occur, from the tungsten axis. In addition, the arc exhibits negative pressure (i.e., anti-gravity gradient behavior) below the cathode and a tornado-style behavior. The arc plasma flow reverses, a circular area occurs, and a low-temperature zone forms in the center of the arc. The highest flow speed takes place on both sides of the arc symmetry axis. The unique appearance of the negative arc pressure and its formation mechanism are discussed.

Soft variable polarity plasma arc horizontal welding technology and weld asymmetry

Soft variable polarity plasma arc welding technology has been proposed to solve the problems in horizontal position welding for aluminium alloys. Arc thermal field shape, arc pressure distribution and the characteristic of the weld pool, which are important for keyhole stability, have been changed compared with the ordinary variable polarity plasma arc. Its stability in application can be evaluated by the operational window. The thermal cycle curves, microstructures and microhardness of the horizontal position weld indicate the weld asymmetry. The influence of asymmetry as well as welding defects on tensile strength and fracture behaviour has been studied. The fundamental reason for the asymmetry was considered as the asymmetric fluid flow around the keyhole in the weld pool.

Numerical simulation of plasma arc welding with keyhole-dependent heat source and arc pressure distribution

A three-dimensional and transient model with keyhole geometry-dependent heat source and arc pressure distribution is developed for plasma arc welding process. The influence of the keyhole evolution on heat flux and arc pressure distribution on the keyhole wall is taken into consideration. The dynamic variation of the temperature field and fluid flow in the weld pool as well as the keyhole shape and size are quantitatively analyzed. The experimentally observed phenomena, i.e., the backward curved keyhole channel and the very thin layer of molten metal at the front edge of weld pool, are first demonstrated with numerical simulation. The predicted establishment time of open keyhole, displacement of keyhole exit, and fusion line generally agree with the experimental ones.

Electrode tips geometry and penetrating in narrow gap welding

The problem of sidewall incomplete fusion in narrow gap tungsten inert gas (TIG) welding could be well solved when the proper magnetic field was added. However, the various tungsten electrode tips seriously affect the distribution of arc pressure and the quality of welding seams. In addition, it is a 350 A GTA, as this is in a regime in which finger penetration is common. This paper studies the distribution of arc pressure of five different styles of tungsten electrode tips: 30° circular cone, 60° circular cone, 60° circular cone with truncated cone of 2 mm diameter, terrace of 2×2 mm and terrace of 2×0·8 mm with the same welding parameters. The character of arc pressure is verified by assaying the seam cross-section under the controlling magnetic field condition in narrow gap welding. The measuring equipment that we designed independently is creative and applicative in narrow gap TIG welding under magnetic fields.

Characterization of welding arc and weld pool formation in vacuum gas hollow tungsten arc welding

An experimental method is suggested to obtain the effective arc radii for various welding conditions in vacuum gas hollow tungsten arc welding. The irradiance distribution of welding arc next above the anode workpiece is obtained by applying Abel inversion algorithm to the CCD arc image, and then used to determine the distribution of arc heat flux, arc pressure and current density from the physical relations of arc irradiance, temperature and current density in gas tungsten arc welding. The resultant arc models are then adopted to simulate the gas hollow tungsten arc welding process for various gas flow rates.

Measurement of arc pressure and shield gas pressure effect on surface of molten pool in TIG welding

Tungsten inert gas (TIG) welding is most frequently used for arc study because it is clean and easy to control welding factor. Many researchers have been focused on the plasma stream to find out the relationship between vertex angle and penetration of the tungsten electrode in TIG welding. Moreover, researchers studied the characteristics of vertex angle and arc pressure and heat flux distribution of the tungsten electrode. In addition, they have carried out factors that have influence on the behaviour of the molten pool. Previous studies assumed that arc pressure was dominant for the force that physically works on the surface of the molten pool, neglecting the shield gas pressure. In addition, they have been focused on the protection of molten weld pool from exposure to the atmosphere. The object of this study is to investigate the effect of shield gas pressure on the surface of the molten pool by measuring the distribution of arc pressure and shield gas pressure compared with arc physical results of previous researches. In this study, we measured the distribution of arc pressure and shield gas pressure on the water cooled copper plate by changing the setting shield gas pressure and shield gas cup inside diameter. As the setting shield gas pressure increased and the shield gas cup diameter decreased, the arc radius got narrower due to the thermal pinch effect. Maximum arc pressure was slightly affected by setting the shield gas pressure and shield gas cup diameter. However, the shield gas pressure on arc surroundings was raised with the increasing setting shield gas pressure and the decreasing gas cup inside diameter. Orbital welding with convex back bead was successfully performed through molten pool control by shield gas pressure adjustment.

Influence of nozzle orifice diameter in keyhole plasma arc welding

Keyhole welding with the plasma arc welding process occurs when the engineered nozzle and the plasma gas flowrate impart the arc pressure and heat distribution necessary for the formation of a keyhole weld pool. Experimental investigations were conducted to determine the influence of nozzle orifice diameter on weld width and weld stability for a range of substrate thicknesses in Ti-6Al-4V. The experimental results are compared with a semianalytical heat flow model. Both the experimental results and the semianalytical model show that the nozzle orifice diameter can significantly influence the top width and penetration for a given parameter set, particularly in relatively thin substrates.

Numerical analysis of the heat source characteristics of a two-electrode TIG arc

Various kinds of multi-electrode welding processes are used to ensure high productivity in industrial fields such as shipbuilding, automotive manufacturing and pipe fabrication. However, it is difficult to obtain the optimum welding conditions for a specific product, because there are many operating parameters, and because welding phenomena are very complicated. In the present research, the heat source characteristics of a two-electrode TIG arc were numerically investigated using a 3D arc plasma model with a focus on the distance between the two electrodes. The arc plasma shape changed significantly, depending on the electrode spacing. The heat source characteristics, such as the heat input density and the arc pressure distribution, changed significantly when the electrode separation was varied. The maximum arc pressure of the two-electrode TIG arc was much lower than that of a single-electrode TIG. However, the total heat input of the two-electrode TIG arc was nearly constant and was independent of the electrode spacing. These heat source characteristics of the two-electrode TIG arc are useful for controlling the heat input distribution at a low arc pressure. Therefore, these results indicate the possibility of a heat source based on a two-electrode TIG arc that is capable of high heat input at low pressures.

Numerical simulation of pulsed current tungesteninert gas (TIG) welding arc

A two-dimensional axisymmetric model of free burning tangsten inert gas (TIG) arc under the action of pulsed current is developed. Using the FLUENT software and choosing appropriate boundary conditions and strongly coupling control equations, a pulsed TIG arc is simulated. The variations of arc form, temperature field, temperature and velocity on the arc axis and surface pressure distribution of the workpiece are obtained and analyzed in the periodic current process; under the action of different values of peak current, duty ratio and pulse frequency, the arc pressure distributions are obtained and analyzed. The results show that they lag behind the variation of pulse current, the variation from base current to peak current is faster, then eventually reaches a relativly stable state; with the increase of peak current, the arc pressure increase greatly; with the increase of duty ratio, the arc pressure increases slowly; with the increase of pulse frequency, the arc pressure cannot reach a stable state gradually, and the max arc pressure tends to decrease.

Modeling of the transport phenomena in GMAW using argon–helium mixtures. Part I – The arc

This article presents a numerical investigation on the transient transport phenomena in the arc which include the arc plasma generation and interactions with moving droplets and workpiece for pure argon and three argon–helium mixtures (75% Ar + 25% He, 50% Ar + 50% He, and 25% Ar + 75% He) during the gas metal arc welding (GMAW) process. The results indicate that the arcs in various shielding gases behave very differently due to the significant differences in thermophysical properties, including the ionization potential and the electrical conductivity, thermal conductivity, specific heat, and viscosity at high temperatures. For the same welding power input, it was found the increase of helium content in the mixtures results in (1) the change of plasma arc shape from bell-like to cone-like and (2) the change of arc pressure distribution along the workpiece surface from Gaussian-like to flat-top with decreasing peak value. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.

TIG 용접에서 열유속이 용융효율과 용입형상에 미치는 영향

The characteristics of arc pressure, current density and heat flux distribution are important factors in understanding physical arc phenomena, which will have a marked effect on the penetration, size and shape of a weld in TIG welding. The purpose of this study is to find out the effect of the heat flux on the melting efficiency and penetration shape in TIG welding using the results of the previous investigators. The conclusions obtained permit to draw a proper method which derived the heat flux distributions by arc pressure distribution measurements, but previous researchers calculated heat flux and current distribution with the heat intensity measurements by the calorimetry. Heat flux of Ar gas arc was concentrated at the central part and distributed low from the arc axis to the radial direction, that of He mixing arc was lower than that of Ar gas, and it was wide distributed to radial direction. That showed a similar characteristic with the Nestor's by calorimetry calculated values. Throughout heat flux drawn in this study was discussed melting efficiency and penetration shape on Ar gas and He mixing gas arc.

Numerical Modeling of Welding Arc with Complex System between Arc Plasma and Molten Electrode

It is important to consider the interaction between arc plasma and electrodes because melting of electrodes strongly affects arc plasma. Therefore, a GMA model will be developed, based on the unified model of TIG arc. As a first step, a TIG arc model with a calculation for molten cathode shape has been proposed. This model is calculated in two cases; molten W cathode and Calculation result of W cathode. In the case of W cathode, cathode shape change was found to affect the arc plasma property strongly. Calculated results of radial temperature distributions on electrode surface and arc pressure distributions at the anode surface are very similar to the experimental results.

Computational simulation for the constricted flow of argon plasma arc

A two-dimensional mathematical model has been developed to research the behavior of the transferred-type argon plasma arc constricted by a torch. The model includes a part of torch and tungsten electrode to achieve more reasonable results. Solving the model, the arc temperature and flow fields have been derived. And the distributions of the current density and electromagnetic force have been gotten, as well as the voltage drop of the plasma arc and the distributions of heat flux, pressure at the anode. The arc pressure and current density distributions at the anode are measured experimentally to show the simulated results believable. The influences of welding parameters on the distribution of the arc pressure at the anode have been studied. The result shows that the arc pressure is much dependent on the current and plasma gas flow rate, while is not sensitive to the arc length in the study range.

Selection of empirical equations for approximating the distribution of arc pressure

Selection of empirical equations for approximating the distribution of arc pressure

The characteristic of twin-electrode TIG coupling arc pressure

The coupling arc of twin-electrode TIG (T-TIG) is a particular kind of arc, which is achieved through the coupling of two arcs generated from two insulated electrodes in the same welding torch. It is therefore different from the single arc of conventional TIG in its physical characteristics. This paper studies the distribution of T-TIG coupling arc pressure, and analyses the influences of welding current, arc length, the distance between electrode tips and electrode shape upon arc pressure on the basis of experiment. It is expected that the T-TIG welding method can be applied in high efficiency welding according to its low arc pressure.

Derivation of current density distribution by arc pressure measurement in GTA welding

Arc pressure is an important factor in understanding physical arc phenomena, especially its effects on the penetration, size and shape of GTA welding. The purpose of the present study is to derive the current density distribution on the anode base metal from the measured arc pressure distribution in GTA welding using the results from previous investigators. Using the measured arc pressure distribution on the anode base metal in GTA welding from the central part to the circumference and the equations of Lin et al. and Maecker, the current density distribution was derived. Applying the derived equation from the present work, the current density distribution was calculated from the low current region to the high current region by means of shield gas mixing ratio. It is compared and discussed with the practical welding current and the derived current by numerical integration of the current density distribution from the central part to the circumference region.

Numerical simulation of the arc pressure in gas tungsten arc welding

A two-dimensional axisymmetric numerical model has been developed to describe the heat transfer and fluid flow in the gas tungsten welding arc. The electrode-tip geometry is considered in the model and the cathode and arc column regions are included in the solution of the current continuity equation. The magneto-hydrodynamics equations are solved using the SIMPLE algorithm. The prediction of the arc column temperatures is in fair agreement with experimental results; moreover, the computed results indicate that the distributions of arc parameters such as current density, electromagnetic force and velocities, reflect well the generating mechanism of the arc pressure. In addition, the effects of the current, the electrode-tip angle and the arc length on the arc pressure distribution are analyzed by the use of the arc model that has been developed.