Metal vapour is formed in arc welding processes by the evaporation of molten metal in the weld pool, and in the case of gas–metal arc welding, in the wire electrode and droplets. The presence of metal vapour can have a major influence on the properties of the arc and the size and shape of the weld pool. Previous experimental and computational works on the production and transport of metal vapour in welding arcs, in particular those relevant to gas–metal arc welding and gas–tungsten arc welding, are reviewed. The influence of metal vapour on the thermodynamic, transport and radiative properties of plasmas is discussed. The effect of metal vapour on the distributions of temperature, current density and heat flux in arcs is examined in terms of these thermophysical properties. Different approaches to treating diffusion of metal vapour in plasmas, and the production of vapour from molten metal, are compared. The production of welding fume by the nucleation and subsequent condensation of metal vapour is considered. Recommendations are presented about subjects requiring further investigation, and the requirements for accurate computational modelling of welding arcs.

https://iopscience.iop.org/article/10.1088/0022-3727/43/43/434001/pdf

The effects of metal vapour in arc welding

The methods used to model thermal plasmas, including treatments of diffusion in arcs in gas mixtures, are reviewed. The influence of thermophysical properties on the parameters of tungsten–inert-gas (TIG) welding arcs, particularly those that affect the weld pool, is investigated using a two-dimensional model in which the arc, anode and cathode are included self-consistently. The effect of changing each of six thermophysical properties on the characteristics of an argon TIG arc is assessed. The influence of the product of specific heat and mass density is found to be particularly important in determining the arc constriction. By examining the influence of the different properties on the heat flux density, current density and shear stress at the anode, it is concluded that the weld pool depth can be increased by using shielding gases with high specific heat, thermal conductivity and viscosity. The effect of metal vapour on the arc and weld pool properties is assessed. The most important effect of the metal vapour is found to be the increased electrical conductivity at low temperatures, which leads to lower heat flux density and current density at the weld pool, implying a shallower weld pool.

https://iopscience.iop.org/article/10.1088/0022-3727/42/19/194006/pdf

Modelling of thermal plasmas for arc welding: the role of the shielding gas properties and of metal vapour

Tungsten?inert-gas welding arcs are modelled using a two-dimensional axisymmetric computational code. Both electrodes (the tungsten cathode and the metal anode workpiece) and the arc plasma are included self-consistently in the computational domain. The influence of adding helium, hydrogen and nitrogen to the argon shielding gas is investigated. It is found that addition of any of the gases increases the heat flow to and the current density at the anode. The shear stress and the arc pressure at the anode surface are increased by adding hydrogen or nitrogen or up to about 50?mol% helium, but decrease when more helium is added. It is predicted that the effect of adding any of the gases is to increase the depth of the weld pool, in agreement with the experimental evidence. The results are explained by referring to the thermodynamic and transport properties of the gas mixtures.

https://iopscience.iop.org/article/10.1088/0022-3727/42/11/115205/pdf

A computational investigation of the effectiveness of different shielding gas mixtures for arc welding

Shielding gases are of considerable significance in the protection of molten metal from atmospheric contamination during welding processes. These gases play an important role in a number of aspects of welding, including arc characteristics and the microstructure of weldments. Understanding of the influence of welding shielding gases on different materials is consequently important, and extensive studies and experiments have been performed by numerous researchers. Based on previous studies, the objective of the current study is to collate and summarize the most important findings and approaches of earlier research. This paper provides analysis of the influence of different combinations of process gases on welding of commonly used materials in manufacturing. The results presented can be used as guidelines to achieve higher quality and efficiency in welding practices. This study provides a good foundation for learning and creates enhanced awareness of shielding-gas-related issues among metal industry actors, permitting objective evaluation of welding productivity and quality.

Influence of shielding gases in the welding of metals

Predictions have been made of anode melting for free-burning arcs by making two-dimensional calculations of temperature profiles of the arc and the electrodes to make predictions of weld depth and weld shape in arc welding. Predicted properties at 150 A, for various arc lengths, are compared with experimental results of: 1) weld shape; 2) heat intensity as a function of radius; and 3) current density as a function of radius at the anode. The whole region of the arc system is modeled, including the tungsten cathode, the arc plasma and the solid and molten anode, including convection within the molten weld-pool. Theoretical and experimental results are also obtained for highand low-sulfur steel, which have markedly different surface tension properties of the molten liquid, resulting in weld depths that differ by a factor of three because of changed convective circulation properties in the weld pool. Although total power to the anode increases with increasing electrode separation, the current density becomes less, with the result that for electrode distances above 2 mm, for argon, the width and depth of the molten region become less, in agreement with experimental results that we have obtained.

Anode melting from free-burning argon arcs

An experimental investigation in gas tungsten arc welding with the hydrogen addition to argon was made. The hydrogen addition to argon makes the arc constrict and the energy concentrate in the arc, which produces increase in arc power. Experimental welding was carried out on three base metals, i.e., low-alloy steel, high-alloy stainless steel, and an aluminum alloy, using no filler material and in argon with the addition of 0.5-20% hydrogen. In welding of stainless steel with the addition of 20% hydrogen to argon, the quantity of the base metal melted increases by three to five times, with the other parameters remaining the same, in welding of low-alloy steel by three times, and in welding of aluminum by six to nine times. The experimentally obtained results were compared with the theoretical ones. With both steels, the experimental and theoretical results agreed well, but with aluminum, they differed very much.

J. Tusek

Papers

Experimental investigation of gas tungsten arc welding and comparison with theoretical predictions