Stationary Gas Tungsten Arc Welding Research Articles

Modeling of Melt Flow and Heat Transfer in Stationary Gas Tungsten Arc Welding with Vertical and Tilted Torches.

A 3D numerical simulation was conducted to study the transient development of temperature distribution in stationary gas tungsten arc welding with filler wire. Heat transfer to the filler wire and the workpiece was investigated with vertical (90°) and titled (70°) torches. Heat flux, current flux, and gas drag force were calculated from the steady-state simulation of the arc. The temperature in the filler wire was determined at three different time intervals: 0.12 s, 0.24 s, and 0.36 s. The filler wire was assumed not to deform during this short time, and was therefore simulated as solid. The temperature in the workpiece was calculated at the same intervals using heat flux, current flux, gas drag force, Marangoni convection, and buoyancy. It should be noted that heat transfer to the filler wire was faster with the titled torch compared to the vertical torch. Heat flux to the workpiece was asymmetrical with both the vertical and tilted torches when the filler wire was fully inserted into the arc. It was found that the overall trends of temperature contours for both the arc and the workpiece were in good agreement. It was also observed that more heat was transferred to the filler wire with the 70° torch compared with the 90° torch. The melted volume of the filler wire (volume above 1750 °K) was 12 mm3 with the 70° torch, compared to 9.2 mm3 with the 90° torch.

The transient behaviours of free surface in a fully penetrated weld pool in gas tungsten arc welding

In order to study the phenomenon of the weld pool free surface evolution from partial to full penetration in gas tungsten arc welding (GTAW), the measurement method based on the lattice laser reflection on the weld pool surface was designed. Lattice lasers information and the concavity-convexity in the weld pool free surface were analyzed. Based on the volume of fluid method and the basic principle of fluid mechanics, temperature field and the flow field model which considered the free surface in a fully penetrated weld pool in GTAW were established. Fluid flow including the factor of buoyancy force, electromagnetic force and surface tension gradient was numerically analyzed for a fully penetrated weld pool in stationary GTAW. The result shows that: thermal expansion of metals is the main reason for the convex surface of weld pool at partial penetration. When fully penetrated, the concave surface of the lower surface is greater than that of the upper surface.

Effect of different electrode tip angles with tilted torch in stationary gas tungsten arc welding: A 3D simulation

In this study, the effect of different tip angles (30°, 60°, 90° and 120°) on the arc and weld pool behavior is analyzed in 2 mm and 5 mm arc lengths with tilted (70°) torch. Arc temperature, velocity, current density, heat flux and gas shear are investigated in the arc region and pool convection and puddle shapes are studied in the weld pool region. The arc temperature at the tungsten electrode is found the maximum with sharp tip and decreases as the tip angle increases. The arc temperature on the anode (workpiece) surface becomes concentrated with increase in tip angle. The arc velocity and gas shear stress are observed large with sharp tip and decreasing as the tip angle increases. Current density on the anode surface does not change with tip angle and observed almost the same in all the tip angles in both 2 mm and 5 mm arc lengths. Heat flux due to conduction and convection is observed more sensitive to the tip angle and decreases as the tip angle increases. The electromagnetic force is slightly observed increasing and the buoyancy force is observed slightly decreasing with increase in tip angle. Analyzing each driving force in the weld pool individually shows that the gas drag and Marangoni forces are much stronger than the electromagnetic and buoyancy forces. The weld pool shape is observed wide and shallow in sharp and narrow and deep in large tip angle. Increasing the arc length does not change the weld pool width; however, the weld pool depth significantly changes with arc length and is observed deep in short arc length. The arc properties and weld pool shapes are observed wide ahead of the electrode tip in the weld direction due to 70° torch angle. Good agreement is observed between the numerical and experimental weld pool shapes.

Effect of Torch Angle on Arc Properties and Weld Pool Shape in Stationary GTAW

In this paper, a three dimensional numerical simulation is performed on a stationary arc to study the effect of torch angle in gas tungsten arc welding (GTAW) of SS304 stainless steel. A comparison has been made to investigate 90o and 70o torch angles and analyze the effect on arc and weld pool shape. Current density, heat flux and gas shear stress are calculated in the arc region and are used as input to the workpiece to determine the weld pool. Buoyancy and Marangoni shear also affect the weld pool shape and are taken into account. The computed and experimental results are observed symmetric for 90o torch angle. For 70o torch angle, current density and hence the heat flux due to electron contribution is found the maximum behind and heat flux due to conduction and convection is found the maximum ahead of the electrode tip in the welding direction. This makes the maximum of total heat flux symmetric along the arc center. Heat flux due to conduction and convection decreases as the torch angle decreases resulting in a shallow weld pool. The nonsymmetric “w” shaped weld pool is developed by the combined effect of the gas shear and Marangoni convection. It is found that for 70o torch angle, the weld pool becomes non-symmetric, shallow and wide ahead of the electrode tip in the welding direction. The numerical weld pool shapes are verified through experiments.

3D simulation of stationary gas tungsten arc welding of L-shape, V-shape and open-corner joints

This paper presents a three-dimensional simulation of stationary gas tungsten arc welding which studies the development of the arc and weld pool in three types of joints, namely L-shape, V-shape and open-corner. Temperature, heat flux, current density and gas shear stress are determined in the arc and are used as input to the workpiece to determine the heat, fluid flow and weld pool shape. Buoyancy and surface tension gradient which affect the pool shape are taken into consideration. It is observed that the current density, heat flux and gas shear distribution in the arc domain is the same in all the cases. The electromagnetic force is observed to be the same in L-shape and V-shape joints. In the case of the open-corner joint, some electromagnetic force is also observed on the bottom edge of the weld. The fluid flow and weld pool shape is found to be the same in the case of L-shape and V-shape joints which shows that the orientation of workpiece does not produce any gravity effect. Due to the sharp edge in the open-corner joint, the weld pool is observed to be shallow and wide. In all three cases, the molten metal flows from the sides and the weld pool is formed slightly upwards at the weld centre in the experimental results. This phenomenon is not considered in the numerical analysis and the weld pool depth near the weld centre is a little different from the experimental results; however, the remaining pool shapes are observed to be in good agreement.

Predictions of weld formation using gas tungsten arcs for various arc lengths from unified arc-electrode model

AbstractPredictions have been made of weld formation for stationary gas tungsten arc welding by making two-dimensional (2D) calculations of temperature and fluid flow velocity of the arc and the electrodes. The whole region of the arc system is modelled, including the tungsten cathode, the arc plasma and the workpiece anode, and convection within the weld pool. Predicted properties of the weld shape for 150 A arcs in argon and helium, for various arc lengths, are compared with experimental results of cross-sectional area of weld. Although total power to the anode increases with increasing arc length, for argon arcs the heat flux density at the axis of the anode becomes lower, with the result that the cross-sectional area of the weld becomes smaller with increasing arc length. For helium arcs total power to the anode also increases with increasing arc length, but the distribution of heat flux density to the anode is approximately constant, with the result that the cross-sectional area of the weld increases...

Vorticity based turbulence model for thermofluids modelling of welds

A comprehensive thermofluids model of stationary gas tungsten arc welding (GTAW) has been developed and used to examine the effects of thermofluids phenomena on the predicted temperatures and flow field in the weld pool, as well as their impact on the resultant weld pool dimensions in 304 stainless steel and 6061 aluminium plates. A dynamic numerical grid remapping technique was used within the finite element based model to model the geometry of the solid/liquid interface and free surface of the weld pool. Initial work showed that correlation between experimental and predicted weld pool dimensions was only possible provided that the effects of turbulence were modelled using a well posed k - ε turbulence model. However, the two-equation k - ε turbulence model introduces additional complexity and requires considerable additional computational effort. To overcome these shortcomings, a simpler vorticity based turbulence model has been developed in which the turbulent viscosity and thermal conductivity are based upon the magnitude of the vorticity in the flow field as predicted through solution of the continuity, momentum and energy equations. Excellent correlation was obtained between the weld pool dimensions predicted by the vorticity based turbulence model, the predictions from the k - ε turbulence model and the experimental data from welds made in 304 stainless steel with three different sulphur impurity concentrations and in 6061 aluminium. The advantage of the vorticity based turbulence model is that it is significantly less computationally intensive than the standard k - ε turbulence model and has, therefore, the potential of providing tractable and practical computations of fully three-dimensional welding processes.

Heat transfer and fluid flow in a partially or fully penetrated weld pool in gas tungsten arc welding

In this study, fluid flow driven by a combination of electromagnetic force, buoyancy force, arc drag force, and surface tension gradient is numerically analyzed for a partially or fully penetrated weld pool in stationary gas tungsten arc welding (GTAW). Irregular shape of the weld pool and the moving liquid–solid interface is handled by a boundary-fitted-coordinates technique. Surface tension on the top and the bottom free surfaces of the weld pool is found to play a critical role in determining the flow pattern in the weld pool. The calculated GTA weld bead geometry compares favorably with experimental results.

A theoretical model for gas metal arc welding and gas tungsten arc welding. I.

A recently developed theory for predicting arc and electrode properties in gas metal arc welding (GMAW) has been generalized to include arc–electrode interfaces, variation of surface tension pressure with temperature, Marangoni forces and handling of weld pool development in stationary gas tungsten arc welding (GTAW). The new theory is a unified treatment of the arc, the anode, and the cathode, and includes a detailed account of sheath effects near the electrodes. The electrodes are included as dynamic entities and the volume of fluid method is used to handle the movement of the free surface of the molten metal at one electrode. Predictions can be made of the formation and shape of the welding droplets as a function of time in GMAW and also of weld pool development in GTAW, accounting for effects of surface tension, inertia, gravity, arc pressure, viscous drag force of the plasma, Marangoni effect and magnetic forces, and also for wire feed rate in GMAW. Calculations are made of current densities, electric potential, temperatures, pressures and velocities in two dimensions, both in the arc and also within the molten metal and solid electrodes. Calculations are presented for GMAW and GTAW for an arc in argon and the results are compared with experimental temperature measurements for the plasma and the electrodes.

EFFECT OF VARIOUS DRIVING FORCES ON HEAT AND MASS TRANSFER IN ARC WELDING

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

A Study on Heat and Mass flow in Stationary Gas Tungsten arc Welding using the Numerical Mapping Method

The phase changing problem at the liquid-solid interface that occurs during stationary gas tungsten arc (GTA) welding has been studied by considering the four driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, the aerodynamic drag force and the surface tension force at the weld pool surface. In the numerical simulation, difficulties associated with the irregular shape of the moving interface have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the liquid-solid boundary. This method also has the capacity to handle the time-dependent changing solution domain of the moving boundary problem and could be applied effectively to this transient weld pool development problem with the moving boundary and phase change condition.