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Chemnitz, Germany

Schnick M.,TU Dresden | Fuessel U.,TU Dresden | Hertel M.,TU Dresden | Spille-Kohoff A.,CFX Berlin Software GmbH | Murphy A.B.,CSIRO
Frontiers of Materials Science | Year: 2011

Current numerical models of gas metal arc welding (GMAW) are trying to combine magnetohydrodynamics (MHD) models of the arc and volume of fluid (VoF) models of metal transfer. They neglect vaporization and assume an argon atmosphere for the arc region, as it is common practice for models of gas tungsten arc welding. These models predict temperatures above 20 000 K and a temperature distribution similar to tungsten inert gas (TIG) arcs. However, current spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to TIG arcs they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapor and which is in a very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the work piece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapor in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2000 to 5000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, and the evaporation rate relative to the wire feed. Finally the model predictions are compared with the measuring results of Zielińska et al. © Higher Education Press and Springer-Verlag Berlin Heidelberg 2011. Source


Spille-Kohoff A.,CFX Berlin Software GmbH | Preuss E.,TU Berlin | Bottcher K.,Leibniz Institute for Crystal Growth
International Journal of Heat and Mass Transfer | Year: 2012

In Böttcher [K. Böttcher, Numerical solution of a multi-component species transport problem combining diffusion and fluid flow as engineering benchmark, Int. J. Heat Mass Transfer 53 (1-3) (2010) pp. 231-240], one of us described an implementation of ternary multi-component species transport by diffusion and convection and presented benchmark cases and simulation results for these cases computed with software ENTWIFE. In this paper, an implementation of the Stefan-Maxwell equation into the ANSYS CFX software is described in combination with a procedure to numerically calculate the ordinary multi-component diffusion coefficients in gases at any total number of components. Finally, the benchmark for ternary mixtures is extended to a quarternary one. A comparsion to the benchmark results of Böttcher revealed an implementation mistake in Böttcher's paper leading to wrong results in case of largely different molar masses. The correct benchmark results are presented here and furthermore compared to two different kinds of effective binary diffusion approaches in multi-component gas mixtures. © 2012 Elsevier Ltd. All rights reserved. Source


Schnick M.,TU Dresden | Fussel U.,TU Dresden | Spille-Kohoff A.,CFX Berlin Software GmbH
Welding in the World | Year: 2010

Plasma Tungsten Arc Welding (PTAW) compared with TIG Welding enables an increased welding speed, a reduced energy input per unit length and butt joint welding of plates without preparation of the welded seam due to keyhole effect. However, because of missed profound understanding of effects in plasma arcs, the indisputable advantages of this process increase demands on education and especially on the experience of developers and operators. In this paper, process parameters, properties of the plasma jet and the molten pool are derived from the numerical modelling of arc and sheath layer under consideration of the process gas properties and the effects of demixing. Basics of the model and the testing site are introduced in this paper. Additionally, influences of current intensity, plasma gas quantity, process gases and their specific properties, torch geometry on plasma jet and energy input into work piece is shown by an exemplary torch. Model and numerical results have been validated by impact pressure measurements at the surface of the work piece and penetration profiles (cross section). Source


Schnick M.,TU Dresden | Fuessel U.,TU Dresden | Hertel M.,TU Dresden | Haessler M.,TU Dresden | And 2 more authors.
Journal of Physics D: Applied Physics | Year: 2010

The most advanced numerical models of gas-metal arc welding (GMAW) neglect vaporization of metal, and assume an argon atmosphere for the arc region, as is also common practice for models of gas-tungsten arc welding (GTAW). These models predict temperatures above 20 000K and a temperature distribution similar to GTAW arcs. However, spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to measurements of GTAW arcs, they have shown the presence of a central local minimum of the radial temperature distribution. This paper presents a GMAW model that takes into account metal vapour and that is able to predict the local central minimum in the radial distributions of temperature and electric current density. The influence of different values for the net radiative emission coefficient of iron vapour, which vary by up to a factor of hundred, is examined. It is shown that these net emission coefficients cause differences in the magnitudes, but not in the overall trends, of the radial distribution of temperature and current density. Further, the influence of the metal vaporization rate is investigated. We present evidence that, for higher vaporization rates, the central flow velocity inside the arc is decreased and can even change direction so that it is directed from the workpiece towards the wire, although the outer plasma flow is still directed towards the workpiece. In support of this thesis, we have attempted to reproduce the measurements of Zielińska et al for spray-transfer mode GMAW numerically, and have obtained reasonable agreement. © 2010 IOP Publishing Ltd. Source


Schnick M.,TU Dresden | Fussel U.,TU Dresden | Hertel M.,TU Dresden | Spille-Kohoff A.,CFX Berlin Software GmbH | Murphy A.B.,CSIRO
Journal of Physics D: Applied Physics | Year: 2010

A computational model of the argon arc plasma in gas-metal arc welding (GMAW) that includes the influence of metal vapour from the electrode is presented. The occurrence of a central minimum in the radial distributions of temperature and current density is demonstrated. This is in agreement with some recent measurements of arc temperatures in GMAW, but contradicts other measurements and also the predictions of previous models, which do not take metal vapour into account. It is shown that the central minimum is a consequence of the strong radiative emission from the metal vapour. Other effects of the metal vapour, such as the flux of relatively cold vapour from the electrode and the increased electrical conductivity, are found to be less significant. The different effects of metal vapour in gas-tungsten arc welding and GMAW are explained. © 2010 IOP Publishing Ltd. Source

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