The paper gives a review on studies on metal inert gas (MIG) and metal active gas (MAG) welding processes with the focus on diagnostics of the arc, the material transfer, and the temporal process behaviour in welding experiments. Recent findings with respect to an improved understanding of the main mechanisms in the welding arc and the welding process are summarized. This is linked to actual developments in welding arc and welding process modelling where measurements are indispensable for validation. Challenges of forthcoming studies are illustrated by means of methods under development for welding process control as well as remaining open questions with respect to arc-surface interaction and arc power balance.

The positive column plasma of dc glow discharges at low pressure in a mixture of helium and 2% xenon is studied. Such glow discharges are favored candidates for the design of mercury-free light sources. A self-consistent model of the column plasma is presented based on strict radially resolved treatment of the nonlocal non-equilibrium kinetics of the electron component, the space-charge potential and the densities of ions and excited atom states. A detailed reaction kinetic scheme of the low-lying xenon excited states has been developed and is included in the model. The model is validated by a comparison with measurements of the axial electric field and the densities of the lowest metastable and resonant xenon levels. The latter was obtained by tunable diode laser absorption and probe diagnostics. The initial results of the model show a pronounced radial structure of the rare-gas column plasma and nonlocal properties of the electron power budget caused by space-charge confinement. The impact of the uncertainty of atomic data used in the model on the quantitative results is investigated in detail. A large impact of the cross sections of electron-impact excitation of the xenon ground state and the excitation and ionization of the xenon excited states, which are known with insufficient reliability only, has been observed.

In this work, we present for the first time a unified model of a low-current short-length arc between copper electrodes. The model employs one-dimensional fluid description of the plasma in argon and copper vapour at atmospheric pressure and the heat transfer in the electrodes made of copper. The solution of the particle and energy conservation of electrons and heavy particles is coupled with the solution of the Poisson equation, from which the self-consistent electric field is obtained. The operation of the non-refractory cathode is based on thermo-field emission. Heat fluxes from the plasma to the electrodes are considered so that a phase change and evaporation from the cathode and a release of copper atoms into the plasma are taken into account. The influence of the copper atoms and ions on the plasma properties is analysed and discussed. The model’s predictions are compared with experimental data and a qualitative agreement is obtained besides the restrictions of the one-dimensional fluid model.

Electrical measurements and numerical modelling of dc tungsten-inert gas arcs are carried out in order to determine the electric field and the voltage, and to study their importance to the plasma-electrode interaction. The configuration under consideration is very typical for tungsten-inert gas welding processes and includes a conically shaped cathode made of doped tungsten and atmospheric pressure argon as a shielding gas. The studies analyze the effects of the inter-electrode distance and the electric current over wide ranges of variation—currents from below 10 A up to 200 A, and distances from 20 mm down to 2 mm in the modelling and to the short-circuit in the experiment. The comparison of the experimentally obtained and the computed current–voltage and arc length-voltage characteristics clearly prove the predictive capability of the advanced non-equilibrium model of the arc and the electrodes. Moreover, the self-consistent model yields the structure of the electric potential and the electric field and is capable of describing the peculiarities of the plasma-electrode interaction.