Analysis of TIG Welding Arc Using Boundary-Fitted Coordinates

Abstract

The characteristics of argon arc in tungsten inert gas (TIG) welding have been studied by considering the electrode shape which has an effect on the current density distribution near the electrode tip. For including the electrode surface configuration into the solution domain, the boundary-fitted coordinate system was employed. Then, a non-rectangular computational region in the physical domain was transformed into a rectangular area with uniformly spaced grids in the computational domain using the second-order central difference method. With the geometric transformation coefficients, the finite difference equations were derived in the computational transformed domain. As the most critical boundary condition, the normal current density distribution entering an electrode surface was postulated by the Gaussian distribution in consideration of the geometry of the electrode shape. For examining the simulated results, the temperature profile was compared with the experimental measurement of the previous research. The transferring phenomena on the base plate, such as current density, heat flux, arc pressure and drag force, were also calculated, because they are necessary data for analysing the molten pool during welding.

Derivation of Forces Acting on the Liquid Weld Metal Based on Arc Pressure Measurements Produced Using Alternating Shielding Gases in the GTAW Process

“…The maximum shear stress was found to occur 1 mm from the arc centreline; and for argon and helium this was found to be ~80 N/m 2 and ~240 N/m 2 respectively. For argon, this was in agreement with data published by Lee and Na [14] and Hu and Tsai [15] for GTAW and GMAW respectively. The results show that helium produces a considerably larger plasma shear stress, thus encouraging the liquid weld metal to flow radially outwards at the weld pool surface.…”

“…The benefits of using alternating shielding gases are linked to three independent phenomenon [1]: a) variation in arc pressure, b) arc pressure peaking and c) variation in weld pool fluidity, and are said to result in flow vectors opposite in direction for argon and helium [2]. Arc pressure measurements conducted when using argon have been published whilst investigating the effects of a variety of welding parameters including welding current [7][8][9][10][11], tungsten electrode geometry [10][11][12], arc length [10], nozzle outlet diameter [13] and shielding gas pressure [13]. The shielding gas composition is also known to have a considerable effect on the arc pressure [9,10], however, the availability of data for helium and argon-helium mixtures is extremely limited and that for alternating shielding gases is non-existent.…”

“…The plasma shear stress is a result of the arc plasma moving radially outward creating a drag force on the liquid weld pool surface. Previous publications on plasma shear are based on numerical modelling techniques; Lee and Na [14] presented data for GTAW, whilst Hu and Tsai [15] simulated the gas metal arc welding (GMAW) process. The arc force is defined as the force of the arc plasma impinging on the weld pool surface; Burleigh and Eagar [16] measured the arc force using a torsion bar and displacement transducer, whilst Lin and Eagar [17] numerically integrated the arc pressure over the impingement area of the arc.…”

Derivation of Forces Acting on the Liquid Weld Metal Based on Arc Pressure Measurements Produced Using Alternating Shielding Gases in the Gtaw Process

“…For argon, this was in agreement with data published by Lee and Na [14] and Hu and Tsai [15] for GTAW and GMAW respectively. The results show that helium produces a considerably larger plasma shear stress, thus encouraging the liquid weld metal to flow radially outwards at the weld pool surface.…”

Arc pressure and weld metal fluid flow while using alternating shielding gases. Part 1: arc pressure measurement

“…Studies [5][6][7] have shown that the current density increases approximately linearly with increasing current, while Fan and Shi 8 stated that the electromagnetic force is the driving force for fluid flow in the arc plasma and increases with increasing current density; thus the electromagnetic force will increase with increasing arc pressure.…”