Igor Krivtsun

Numerical study of the anode boundary layer in atmospheric pressure arc discharges

The anode boundary layer in atmospheric pressure arc discharges is studied numerically on the basis of the hydrodynamic (diffusion) equations for plasma components. The governing equations are formulated in a unified manner without the assumptions of thermal equilibrium, ionization equilibrium or quasi-neutrality. For comparison, a quasi-neutral model of the anode layer is also considered. The numerical computations are performed for an argon arc at typical values of the current density in anode layers (500–2000 A cm−2). The results of numerical modelling show that the common collisionless model of the sheath fails to describe the sheath region for the problem under consideration. For this reason, a detailed analysis of the anode sheath is performed using the results of unified modelling. In addition, the distributions of plasma parameters in the anode layer are analysed and the basic characteristics of the layer (anode voltage drop, sheath voltage drop, anode layer thickness, sheath thickness, heat flux to the anode) are calculated. Our results are found to be in good agreement with the existing theoretical predictions and experimental data. The dependence of the anode layer characteristics on the current density is also discussed.

Modelling of binary alloy (Al–Mg) anode evaporation in arc welding

A simple analytical model of binary alloy anode evaporation in gas–tungsten arc and gas–metal arc welding is proposed. The model comprises the model of evaporation in convective and diffusive regimes, model of anode processes and allows one to calculate basic physical properties of multicomponent arc plasma near the anode surface as functions of the anode surface temperature, anode chemical composition, electron temperature and electric current density at the anode surface. Evaporation of binary Al–Mg alloys with different magnesium mass fraction into argon plasma is considered on the basis of the proposed model. The dependences of the alloy boiling temperature on the magnesium mass fraction and electron temperature are presented. Several physical parameters, which are important from the technological point of view (magnesium mass flux, heat loss due to evaporation, anode potential drop, anode heat flux), are calculated for a wide range of anode surface temperature and different values of the magnesium mass fraction. In addition, the influence of heat loss due to evaporation on the total heat flux coming to the anode surface is demonstrated.

A dynamic model of droplet formation in GMA welding

A comparative analysis of different approaches is carried out, which mathematically describes the metal droplet formation process in an electrode during gas metal arc (GMA) welding. It was shown that a hydrostatical model of the droplets free surface could not correctly describe the formation and transfer of electrode metal droplets. The complete hydrodynamic model, which uses the whole system of Navier–Stokes equations, requires significant computer resources for numerical realization. This limits its application to small computational experiments. As an alternative for this model, the approximate hydrodynamic model adapted to GMA welding conditions is considered. It is shown that this model allows the prediction of droplet geometry right up to its detachment. The influence of the welding current and magnetic pressure on the droplet size and detachment frequency is studied.

Modeling of weld pool phenomena in tungsten inert gas, CO2-laser and hybrid (TIG+CO2-laser) welding

The efficiency of the welding process in terms of weld penetration and weld width is greatly determined by the heat, mass, and charge transfer phenomena in the weld pool. These phenomena, in turn, depend on the thermal and electromagnetic interaction of the heat source used with the metal being welded. The most adequate models of the welding processes should consider the interaction of the phenomena in the heat source, on the base metal surface and inside its volume by a self-consistent way. This paper is devoted to the development of a self-consistent model of weld pool dynamics in tungsten inert gas (TIG), laser and hybrid (laser + TIG) spot welding without a keyhole formation. The proposed model allows simulation of processes taking place in the weld pool and on its surface. The model takes into account free surface deformation, influence of plasma shear stress, thermocapillary Marangoni effect, and Lorentz forces on the weld pool, as well as of the processes in the arc plasma including laser-arc inter...

Interaction of CO2-laser beam with argon plasma of gas tungsten arc

A self-consisted mathematical model was proposed for energy, mass, and charge transfer processes in the arc column plasma and anode region of gas tungsten arc (GTA) with water-cooled anode under the influence of a focused laser beam, propagating along the arc column. This model was the basis for performing detailed numerical analysis of the interaction processes between Gaussian beam radiation emitted by a continuous-wave CO2-laser and the argon plasma of a stationary GTA. It was determined that additional local heating by focused laser radiation changes the thermal and electromagnetic characteristics of the arc column plasma. The influence of laser radiation absorption and refraction in the arc plasma on the characteristics of the laser beam and its thermal effect on the anode metal surface was studied. Laser heating of the arc plasma also leads to a rearrangement of spatial distributions of temperature, electric potential and current density in the near-anode arc plasma, thus changing the distributed and integral characteristics of its thermal impact on the anode surface.

Task of volumetrical evaporation and behaviour of droplets in pulsed MIG welding of AlMg alloys

The mainly used aluminium alloys in automobile industry are AlMg alloys. Because of the significant difference in the evaporation temperatures of aluminium and magnesium, the process of metal transfer through the welding arc is often very unstable. This has an influence on the droplet behaviour as well as on the physical properties of arc plasma. Understanding the physical phenomena in AlMg droplets in MIG welding helps to have a better control of the welding process. This paper presents the results of study of a task concerning volumetrical evaporation and behaviour of droplets in pulsed MIG welding of AlMg alloys.