Direct modeling of material deposit and identification of energy transfer in gas metal arc welding

International audiencePurpose - The purpose of this paper is to present original methods related to the modeling of material deposit and associated heat sources for finite element simulation of gas metal arc welding (GMAW). Design/methodology/approach - The filler deposition results from high-frequency impingements of melted droplets. The present modeling approach consists of a time-averaged source term in the mass equation for selected finite elements in the fusion zone. The associated expansion of the mesh is controlled by means of adaptive remeshing. The heat input includes a volume source corresponding to the droplets energy, for which a model from the literature is expressed in coherency with mass supply. Finally, an inverse technique has been developed to identify different model parameters. The objective function includes the differences between calculations and experiments in terms of temperature, but also shape of the fusion zone. Findings - The proposed approach for the modeling of metal deposition results in a direct calculation of the formation of the weld bead, without any a priori definition of its shape. Application is shown on GMAW of steel 316LN, for which parameters of the model have been identified by the inverse method. They are in agreement with literature and simulation results are found quite close to experimental measurements. Originality/value - The proposed algorithm for material deposit offers an alternative to the element activation techniques that are commonly used to simulate the deposition of filler metal. The proposed inverse method for parameter identification is original in that it encompasses an efficient and convenient technique to take into account the shape of the fusion zone

Adaptive anisotropic mesh technique for coupled problems: application to welding simulation

International audienceA major problem arising in finite element analysis of coupled problems, such as welding for instance, is the control of the mesh, that is an appropriate mastering of the spatial discretization to get accurate results in a minimum computer time. The present anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. Error indicators are derived to define an anisotropic mesh metric field, which is an input of the pre existing 3D remeshing procedure. The mesh metric consists of a combination of several metrics, each corresponding to the error estimation associated with a selected field of the solution produced (temperature, phase fraction, stress component). Mesh modifications are used to anisotropically and continuously adapt the mesh. We demonstrate the efficiency of the method by applying it to a coupled thermal-mechanical-metallurgical simulation of arc welding. We demonstrate that the use of an anisotropic adaptive finite element method can result in an order of magnitude reduction in computing time with no loss of accuracy compared to analyses obtained with isotropic meshes

New Numerical Technologies for the Simulation of Arc Welding Processes

International audienceThe paper presents the main concepts of a newly-developed numerical code for arc welding simulation and analysis. The new numerical technologies essentially consist first of original methods for the modeling of material deposit allowing a direct simulation of joint formation, instead of usual element birth techniques. Second, a dynamic mesh optimization procedure, allowing error control. And third, a multivariable finite element inverse method for identification of heat sources

A coupled approach for the modelling of arc welding processes

International audienceA 3D finite element model is presented, addressing some major phenomena arising in arc welding as well as their interaction: heat input, metal deposit, solidification, phase transformations in the solid state and material behavior. As a result of a simulation, the shape of the weld bead, the phase distribution, residual stresses and distortions are obtained. Some application and validation cases are discussed

Experimental validation of finite element codes for welding deformations

International audienceA single pass metal inert gas welding on an austenitic steel plate has been presented for the purpose of providing controlled experimental data against which numerical codes quantifying welding stresses can be validated. It includes a moving heat source with material deposit, and completes thus existing validation data. The experiment has been addressed by a numerical code, WeldSimS, reproducing qualitatively the distortion during welding quite well. Quantitative differences between the numerical and experimental results, however, indicate the need for more accurate modelling tools than those presently available, which are all based on commonly accepted modelling principles and input data

Modélisation numérique du soudage à l'arc des aciers

Welding is a highly used assembly technique. Welding simulation software would give access to residual stresses and information about the weld's microstructure, in order to evaluate the mechanical resistance of a weld. It would also permit to evaluate the process feasibility when complex geometrical components are to be made, and to optimize the welding sequences in order to minimize defects. This work deals with the numerical modelling of arc welding process of steels. After describing the industrial context and the state of art, the models implemented in TransWeld ( software developed at CEMEF) are presented. The set of macroscopic equations is followed by a discussion on their numerical implementation. Then, the theory of remeshing and our adaptive anisotropic remeshing strategy are explained. Two welding metal addition techniques are investigated and are compared in terms of the joint size and transient temperature and stresses. The accuracy of the finite element model is evaluated based on experimental results and the results of the analytical solution. Comparative analysis between experimental and numerical results allows the assessment of the ability of the numerical code to predict the thermomechanical and metallurgical response of the welded structure. The models limitations and the phenomena identified during this study are finally discussed and permit to define interesting orientations for future developments.Le soudage est un moyen d'assemblage très utilisé dans l'industrie. Disposer d'un logiciel de simulation permettrait d'évaluer les contraintes résiduelles et d'obtenir des informations sur la microstructure du joint de soudure, nécessaires à l'analyse de sa tenue mécanique; mais aussi d'évaluer la faisabilité du procédé pour la réalisation de pièces complexes et d'optimiser les séquences de soudage pour minimiser les défauts. Cette thèse porte sur le développement d'un outil de simulation numérique du soudage à l'arc des aciers. Après  avoir  décrit  le  contexte  tant  industriel que  bibliographique  de  ce  travail,  nous précisons  les  différents  modèles  implémentés  dans  le  code  de  calcul  TransWeld (le logiciel développé au CEMEF dans le cadre de ce travail). La description des équations macroscopiques employées  est  suivie  de leur mise en œuvre numérique.  Nous  abordons  ensuite  la  théorie  du  remaillage  adaptatif  et  nous décrivons  les  éléments  essentiels  de  la  stratégie  de  remaillage  développée  dans  le  cadre  de cette thèse. Ensuite, nous présentons les méthodes développées pour la modélisation de l'apport de métal et de la formation du cordon de soudage. Des simulations numériques conformes aux essais sont réalisées. L'analyse comparative entre résultats expérimentaux et numériques permet de juger de l'aptitude du code de calcul à prédire l'état thermomécanique et métallurgique de la structure soudée. Les limitations de notre modélisation et les phénomènes qu'elle a permis de mettre en évidence  sont  enfin  discutés  et  permettent  de  définir  quelques  orientations  intéressantes pour les développement futur de cette modélisation

Modélisation thermomécanique du soudage : apport de matière et adaptation de maillage

International audienceIn this paper, an adaptive remeshing strategy and a new technique for modelling of addition of filler material are presented. The anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error. The material deposit is modelled as a source term in the conservation equation. We show that the use of an anisotropic adaptive finite element method can result in an order of magnitude reduction in computing time. It also allows modelling joint formation.Dans ce papier, une stratégie d'adaptation de maillage et une approche de modéli-sation de l'apport de matière sont présentées. Nous avons développé ici une stratégie de re-maillage adaptatif anisotrope basée sur l'estimateur d'erreur d'interpolation. Nous présentons aussi une approche qui permet de modéliser l'apport de métal comme un terme de source dans l'équation de conservation. Les résultats numériques obtenus montrent que l'adaptation de maillage permet à la fois le temps de calcul (à precision identique), et de suivre l'évolution de la surface du cordon au cours de l'apport et du refroidissement

Adaptive mesh technique for thermal-metallurgical numerical simulation of arc welding processes

International audienceA major problem arising in finite element analysis of welding is the long computer times required for a complete three-dimensional analysis. In this study, an adaptative strategy for coupled thermometallurgical analysis of welding is proposed and applied in order to provide accurate results in a minimum computer time. The anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. The methodology is applied to the simulation of a gas-tungsten-arc fusion line processed on a steel plate. The temperature field and the phase distributions during the welding process are analyzed by the FEM method showing the benefits of dynamic mesh adaptation. A significant increase in accuracy is obtained with a reduced computational effort