Methods and results concerning the shielding gas flow in GMAW
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RESEARCH PAPER
Methods and results concerning the shielding gas flow in GMAW M. Dreher & U. Füssel & S. Rose & M. Häßler & M. Hertel & M. Schnick
Received: 23 October 2012 / Accepted: 22 February 2013 / Published online: 15 March 2013 # International Institute of Welding 2013
Abstract Gas metal arc welding (GMAW) of aluminium, high alloyed steel or titanium requires a shielding gas cover in order to provide preferably low parts per million concentration of oxygen at the joint. Consequently, it is necessary to be able to describe and to analyse the flow of shielding gas. The paper presents numerical and diagnostic investigations concerning the shielding gas flow in gas metal arc welding. Therefore, a numerical model and several diagnostic methods have been developed. The model used is based on ANSYS CFX and includes the effects of magneto hydrodynamic, turbulence and diffusion depending on temperature. The model is verified by Particle Image Velocimetry, Schlieren-technique, and gauging the oxygen concentration. Advantages and disadvantages of these particular methods and the potential of their combined application to analyse welding processes and torch design are shown. The methods introduced were used for the precise analysis of the shielding gas flow and the construction of torches in GMAW. The formation of turbulence by actual concepts of gas distributors and the advantages of optimised and innovative torch constructions are demonstrated. Furthermore the interaction between the process and the shielding gas flow is described and the explicit dependency of the gas cover based on the current profile employed (pulse welding) is visualised. Based on these results, the way in which different gas nozzles influence the shielding gas flow and what happens if the position of the torch or the type of joint changes is explained. In summary, the paper details the profound physical correlations between the construction of Doc. IIW-2355, recommended for publication by Commission XII “Arc Welding Processes and Production Systems”. M. Dreher (*) : U. Füssel : S. Rose : M. Häßler : M. Hertel Technische Universität Dresden, Dresden, Germany e-mail: [email protected] M. Schnick Teknoholt GmbH, Finsterwalde, Germany
the torch and the shielding gas cover as well giving concrete advice for users of the GMAW processes. Keywords (IIW Thesaurus) GMA welding . Shielding gas . Gas flow . Gas cover . Torch construction . Measurement . PIV . Schlieren . Oxygen . Numerical simulation
1 Introduction Gas metal arc (GMA) welding is used as a semi-automatic or automatic arc welding process in many applications. The arc burns between a consumable wire electrode and the work piece. The aim is a clean, defined (stable) and reproducible process. The shielding gas is mainly important in order to cool the torch, stabilise the arc, and to protect the wire and weld pool from oxidation. Particularly, the joining of aluminium, high alloyed steels or titanium requires an excellent cover of shielding gas to provide a low concentration of oxyge
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