Metal vapour causes a central minimum in arc temperature in gas–metal arc welding through increased radiative emission

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The paper presents a transient three-dimensional model of an anti-phase-synchronized pulsed tandem gasmetal arc welding process, which is used to analyze arc interactions and their influence on the gas shield flow. The shielding gases considered are pure argon and a mixture of argon with 18% CO 2. Comparison of the temperature fields predicted by the model with high-speed images indicates that the essential features of the interactions between the arcs are captured. The paper demonstrates strong arc deflection and kinking, especially during the low-current phase of the pulse, in agreement with experimental observations. These effects are more distinct for the argon mixture with 18% CO 2 . The second part of the paper demonstrates the effects of arc deflection and instabilities on the shielding gas flow and the occurrence of air contamination in the process region. The results allow an improved understanding of the causes of periodic instabilities and weld seam imperfections such as porosity, spatter, heat-tint oxidation and fume deposits.

“…Therefore the use of a turbulence model is in fact not necessary, and will not influence our results; this is in accordance with the findings for modelling of a single gas-metal arc [37].…”

Section: Arc Behaviour and Interactionssupporting

confidence: 89%

Section: Arc Behaviour and Interactionsmentioning

confidence: 86%

Section: Arc Behaviour and Interactionsmentioning

confidence: 99%

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Three-dimensional modelling of arc behaviour and gas shield quality in tandem gas–metal arc welding using anti-phase pulse synchronization

Schnick¹,

Wilhelm²,

Lohse³

et al. 2011

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“…The analysis was performed by means of a magneto-hydrodynamic arc model previously developed by Schnick et al [22][23][24]. This model was originally applied for the simulation of the arc behaviour during pure arc welding processes such as tungsten inert-gas (TIG) and gas metal-arc (GMA) welding and implemented using the commercial software package Ansys CFX.…”

Section: Numerical Analysis Of Particular Laser-arc Interaction Phenomentioning

confidence: 99%

Process characteristics of fibre-laser-assisted plasma arc welding

Mahrle¹,

Schnick²,

Rose³

et al. 2011

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Abstract. Experimental and theoretical investigations on fibre-laser assisted plasma arc welding (LAPW) have been performed. Welding experiments were carried out on aluminium and steel sheets. In case of a highly focused laser beam and a separate arrangement of plasma torch and laser beam, high-speed video recordings of the plasma arc and corresponding measurements of the time-dependent arc voltage revealed differences in the process behaviour for both materials. In case of aluminium welding, a sharp decline in arc voltage and stabilization and guiding of the anodic arc root was observed whereas in steel welding the arc voltage was slightly increased after the laser beam was switched on. However, significant improvement of the melting efficiency with the combined action of plasma arc and laser beam was achieved for both types of material. Theoretical results of additional numerical simulations of the arc behaviour suggest that the properties of the arc plasma are mainly influenced not by a direct interaction with the laser radiation but by the laser induced evaporation of metal. Arc stabilization with increased current densities is predicted for moderate rates of evaporated metal only whereas metal vapour rates above a certain threshold causes a destabilization of the arc and reduced current densities along the arc axis.

“…Thus net emission coefficients remain important input data for numerical modelling of welding arcs as done by e.g. Lowke et al [4] and Schnick et al [5]. The use of net emission coefficients in such models has the drawback that it does not take into account the inhomogeneity of the temperature and the spatial distribution of the elements in experimental arcs.…”

Section: Introductionmentioning

confidence: 99%

Net emission coefficients of argon iron plasmas with electron Stark widths scaled to experiments

Wendt¹

2011

The net emission coefficient of plasmas containing argon and iron at atmospheric pressure is calculated and analysed for the case of cylindrical geometry. Its values are obtained by integrating the monochromatic net emission coefficient taking into account continuous and line radiation. The width of the spectral lines is determined by Doppler broadening, natural, resonance, van der Waals, electron and ion Stark broadening. As Stark broadening is the most important broadening mechanism in the considered pressure and temperature range, the electron Stark widths are calculated following the semi-empirical Stark broadening theory. Additionally, the electron Stark widths of Ar, Ar+, Fe and Fe+ are multiplied by scaling factors in order to reproduce experimental electron Stark widths. The scaling factor is determined for each species separately. For small plasma radii the net emission coefficient determined here shows good agreement with literature values where spherical geometry is considered while they decrease faster with increasing plasma radius. This behaviour is caused by the increase of the irradiation of the symmetry axis when cylindrical instead of spherical geometry is considered. For radii and temperatures typical of the metal filled core of arcs occurring in gas metal arc welding processes, i.e. radii between 1 and 2 × 10−3 m and temperatures between 5000 and 10 000 K, the scaling of the Stark widths increases the net emission coefficient of iron plasmas by between 2% and 23%. In this parameter range the net emission coefficient of iron plasmas for cylindrical geometry is between 30% and 37% smaller than values calculated for spherical geometry.