International audienceThis paper investigates some issues in physical modeling of metal inert gas/metal active gas (MIG/MAG) welding process in the short arc mode. In this mode, a metal supply is molten in the arc state and then transferred to the weld pool during the short-circuit state. A hybrid model having two distinct continuous states whose switchings are controlled by two guard conditions is proposed. Due to the complexity of the physical phenomena involved in the welding process, simplifications are used to obtain a model accounting for the main physical contributions but simple enough to yield an efficient, fast and numerically tractable simulator which can be used intensively for evaluating different control strategies. In an attempt to validate the proposed model, different measurements have been made including supply voltage and current sampled synchronously with high speed digital video. In order to extract some relevant quantities representative of the metal transfer from image sequences, an active contour algorithm is developed and tested. The effectiveness of the proposed model in the prediction of major tendencies of a welding process, especially in the arc state, is shown using experimental data. Some limitations of the model during the metal transfer are also stressed and possible remedies are then proposed
An experimental study on MIG-MAG welding in reverse polarity (anode wire) has been implemented to analyse the influence of the active gas type and composition on the welding process. The analysis of the arc column using optical emission spectroscopy and high speed imaging completed by µ-structural study of the electrode wire by EDS/XRD and EPMA methods have provided helpful explanations on the globular/spray mode transition depending of the active gas in the shielding gas. These results highlight the existence of an oxide layer (“gangue”) and the modification of the typology of this one in globular mode according to the active gas (Ar/CO2 or Ar/O2) probably responsible of the globular/spray mode transfer by modification of the electrical/thermal conductivities of the oxide layer. Spectroscopic analysis reveals modification by an arc constriction in Ar/O2 mixtures and linked to a more prominent drop of the electronic temperature along the arc column axis. With this active gas, analysis of the Fe I / Ar I emissivity ratio show a higher metal vapours content responsible for the temperature drop by their strong radiative emission along the arc column.
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