Eur. Phys. J. Appl. Phys. 43, 111–122 (2008) DOI: 10.1051/epjap:2008106 T HE EUROPEAN P HYSICAL JOURNAL APPLIED PHYSICS Gas influence on the arc shape in MIG-MAG welding S. Zielinska 1, 2 , S. Pellerin 2, a , F. Valensi 2 , K. Dzierzega 1 , K. Musiol 1 , Ch. de Izarra 2 , and F. Briand 3 1 Institute of Physics, Jagellonian University, ul. Reymonta 4, 30-459 Krakow, Poland 2 LASEP, Facult´ e des Sciences-Bourges, Universit´ e d’Orl´ eans, BP 4043, 18028 Bourges Cedex, France 3 CTAS - Air Liquide Welding, Rue d’Epluches, Saint-Ouen l’Aumˆone, France Received: 14 February 2008 / Accepted: 19 May 2008 Published online: 24 June 2008 – c  EDP Sciences Abstract. Composition of the applied shielding gas has a strong influence on physical properties of the plasma and parameters of the welding process. In particular, increase of the percentage of carbon dioxide in argon results in an increase of the transition current value while changing from the globular to spray mode of metal transfer during the welding process. In order to explain this phenomenon, the MIG/MAG welding arc plasma was investigated for different mixtures of argon and carbon dioxide in the shielding gas. Applying a fast camera, recording distribution of spectral lines of the plasma components, we noticed some phenomena not described yet in the literature. Especially, there is a limit in the percentage of relative concentration CO2/Ar beyond which the arc shape is significantly modified. PACS. 52.50.Dg Plasma sources – 52.50.Nr Plasma heating by DC fields; ohmic heating, arcs – 52.70.-m Plasma diagnostic techniques and instrumentation – 52.77.-j Plasma applications 1 Introduction In the Gas Metal Arc Welding (GMAW) processes an arc discharge between a consumable solid metal electrode and a weld pool is used. The wire-electrode, the liquid metal transferring inside the arc and the weld pool are protected against air by a shielding gas flux: an inert gas in the case of the MIG (Metal Inert Gas) welding or a chemically active one in the case of the MAG (Metal Active Gas) process. These welding methods are used in all sectors of activity to join all grades of metal (ferrous and non- ferrous). The schematic description of the welding torch is presented in Figure 1. The most frequently used gases or gas mixtures are ar- gon or/and helium in MIG welding and various mixtures of these gases with CO 2 ,H 2 ,O 2 ,N 2 in MAG welding. The MIG-MAG welding is usually performed with the melting electrode used as an anode, what assures better arc sta- bility. The wire electrode melting and the metal transfer in the arc can take place in three fundamental ways (modes) [1,2]: short-circuit transfer (“short-arc”), trans- fer by large drops (“globular transfer”) and axial spray transfer (“spray-arc”). The mode of the transfer depends on shielding gas type, dimension and composition of the electrode wire, electrode extension, wire feed speed, arc voltage and current. These three modes are character- ized by different arc stability, weld penetration, spatter of the melted metal, gas consumption and quantity of fume. a e-mail: stephane.pellerin@univ-orleans.fr Tip Torch Mettable electrode wire (anode) Shielding gas Weld bead Workpiece (cathode) Arc Fig. 1. The welding torch. Each of these modes has different applications, operating conditions and welding quality: • In the “short-arc” transfer, metal is deposited by series of short circuit resulting from regular contact between the electrode and weld pool (see Fig. 2a). This type of transfer occurs for low current intensity and relatively low arc voltage. After arc ignition, the tip of wire is being melt due to the resistance heating, and leads to the droplet formation. For these conditions, the elec- trode melting rate is not sufficient for the droplet de- tachment, and so melted metal is transferred from the Article published by EDP Sciences