Journal of Materials Processing Technology 211 (2011) 1553–1562 Contents lists available at ScienceDirect Journal of Materials Processing Technology jou rnal h om epa g e: www.elsevier.com/locate/jmatprotec A computational investigation of different helium supplying methods for the improvement of GTA welding A. Traidia a,b,∗ , F. Roger a a ENSTA ParisTech, Department of Mechanical Engineering, Chemin de la Hunière, 91761 Palaiseau Cedex, France b AREVA NP, Technical Center, BP 40001 Saint Marcel, 71328 Chalon sur Saône, France a r t i c l e i n f o Article history: Received 16 December 2010 Received in revised form 11 April 2011 Accepted 15 April 2011 Available online 27 April 2011 Keywords: Thermal plasmas GTAW Marangoni flow Shielding gas Alternate supply Helium arcs a b s t r a c t A transient arc and weld pool model is developed, to study the effect of helium addition on the weld pool properties. Supplying mixtures of argon–helium, and alternate supply of pure argon and pure helium, are both studied. The arc characteristics are found to be highly dependent on the shielding gas composition. The addition of helium to argon increases the main governing forces in the weld pool, and more particularly the electromagnetic forces. This leads to the appearing of an electromagnetically induced vortex in the molten pool, which itself leads to an increase in the weld penetration by a factor that goes up to 3. The comparison between the numerical predictions and the experimental macrographs shows a good agreement as well as shape as dimensions. The numerical results reveal two main advantages of alternate supply of shielding gases; compared to the conventional mixtures supplying, the alternate method is more cost saving, and reduces the heat transfer to the workpiece for an equivalent weld penetration. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The extensive use of Gas Tungsten Arc Welding (GTAW) in the manufacturing industry has lead engineers to optimize welding parameters to increase productivity and improve welding qual- ity. An important trend introduced in the early 1970s, is the use of gas mixtures as a shielding gas (hereafter called conventional method), each mixture has its own thermophysical properties and produces unique arc characteristics. Due to its high thermal con- ductivity, helium (He) gas is often mixed with argon (Ar), which permits to improve the weld penetration and then to increase the welding speed. More recently Novikov (1992) proposed for the first time the method of alternate supply of shielding gases (hereafter called alternate method): instead of supplying a mixed Ar–He gas, pure Ar and pure He are supplied successively in the weld zone which gives a higher efficiency and a better weld quality. Kang et al. (2009b) investigated this new supplying method on austenitic stainless steels and found that it permits to increase the weld- ing speed, reduce the distortions after cooling, and is cost saving compared to the conventional method of supplying gas mixtures. ∗ Corresponding author at: ENSTA ParisTech, Department of Mechanical Engi- neering, Chemin de la Hunière, 91761 Palaiseau Cedex, France. Tel.: +33 169 319 735; fax: +33 169 319 906. E-mail address: traidia@ensta-paristech.fr (A. Traidia). Recent investigations conducted on GMA welding of aluminum by Kang et al. (2009a) showed the same conclusions. However, this method is still under study and is not used in industrial applications yet. For the commonly used conventional method, the ratio of each gas in the mixture is always determined by experimental tests and is dependent on the welding conditions, and the welded materials (austenitic stainless steel, nonferrous materials, etc.). The numeri- cal simulation is the main alternative to study the impact of such input parameters on the arc properties and weld shape character- istics. Currently, the numerical simulation of Gas Tungsten Arc Weld- ing (GTAW) is under great development. Many numerical models have been developed to study the behavior of GTA arcs; Fan et al. (1997) proposed a transient model to deal with pulsed current GTAW, Lu et al. (2009) studied the behavior of GTA arcs with nitro- gen and argon shielding gases, Gonzalez et al. (2005) proposed a three dimensional model to study moving arc welding. But, one of the most sophisticated models was proposed by Lowke et al. (1997); it deals with the cathode, arc plasma and anode together in a unified formalism. This makes the plasma–electrodes inter- faces as internal boundaries, and then, no assumptions are made on their temperature values. The boundary conditions are directly applied at the external frontiers and are more realistic than the most available models. 0924-0136/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2011.04.008