Finite element simulation of magnesium alloys laser beam welding

The authors are grateful to FONDERIE MESSIER (HONSEL group) that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Morraru of the IMS Laboratory, ARTS ET MÉTIERS PARISTECH, Aix En Provence, France.In this paper, a three-dimensional finite element model is developed to simulate thermal history magnesium-based alloys during laser beam welding. Space–time temperature distributions in weldments are predicted from the beginning of welding to the final cooling. The finite element calculations were performed using Cast3M code with which the heat equation is solved considering a non-linear transient behaviour. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam dimensions and welding speed, and it is associated to moving boundary conditions. Experiments were carried out to determine temperature evolution during welding and to measure the laser weld width. By comparing the thermal model answers with the measurements, it is found that numerical simulations results are in a good agreement with the experimental data

Three-Dimensional Numerical Simulation of a Gas Tungsten Arc Welding Process

Welding processes are widely used in many industries. The determination of welding parameters and the study of their influence on the mechanical and metallurgical behavior of materials require multiple experiments, and the relevant studies are costly in terms of time and resources. Thus, numerical simulations can serve as a solution when it comes to choosing the appropriate welding process and optimizing its parameters while minimizing costs. The present work contributes to the development of a finite element code, using MATLAB software, for the prediction of thermo-mechanical and metallurgical behavior during the Tungsten inert gas (TIG) welding process. Numerical computation is based on the mathematical formulation of physical phenomena and thermal exchanges. In this paper, results dealing with the prediction of the temperature field evolution during the C50 steel TIG-welding process are presented. In this case, the thermal problem is solved numerically using the finite element method. The memory and computation time problems are solved using optimal stocking and resolution algorithms. To validate the developed computation code, numerical results are first compared with other published numerical results, then with our experimental data. A satisfactory concordance between simulated temperature evolutions and those measured with thermocouples implanted in the welded sheets was found

CO2 laser beam welding of AM60 magnesium-based alloy

The authors are grateful to FONDERIE MESSIER HONSEL group that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Moraru of the LSIS Laboratory-Arts et Métiers ParisTech-Aix En Provence-France.Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal

Finite element simulation of magnesium alloys laser beam welding

The authors are grateful to FONDERIE MESSIER (HONSEL group) that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Morraru of the IMS Laboratory, ARTS ET MÉTIERS PARISTECH, Aix En Provence, France.In this paper, a three-dimensional finite element model is developed to simulate thermal history magnesium-based alloys during laser beam welding. Space–time temperature distributions in weldments are predicted from the beginning of welding to the final cooling. The finite element calculations were performed using Cast3M code with which the heat equation is solved considering a non-linear transient behaviour. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam dimensions and welding speed, and it is associated to moving boundary conditions. Experiments were carried out to determine temperature evolution during welding and to measure the laser weld width. By comparing the thermal model answers with the measurements, it is found that numerical simulations results are in a good agreement with the experimental data

CO2 laser beam welding of AM60 magnesium-based alloy

The authors are grateful to FONDERIE MESSIER HONSEL group that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Moraru of the LSIS Laboratory-Arts et Métiers ParisTech-Aix En Provence-France.Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal

A centralised Wi-Fi management framework for D2D communications in dense Wi-Fi networks

In Wi-Fi networks, Device-to-Device (D2D) communications aim to improve the efficiency of the network by supporting direct communication between users in close proximity. However, in a congested Wi-Fi network, establishing D2D connections through a locally managed self-organising approach will intensify the congestion and reduce the scalability of the solution. Therefore, a centralised management approach must be involved in orchestrating those actions to guarantee the sufficiency of D2D communications. In this paper, we propose a novel management framework for D2D communications in dense Wi-Fi networks. The proposed framework employs a Software-Defined Networking (SDN) based centralised controller in synergy with a novel Access Point (AP) channel assignment process. This framework is designed to proactively establish and manage D2D connections in Wi-Fi networks considering the available radio resources and the effect of the subsequent interference. Thus, improving the overall performance of the network and providing users with higher data rate. Through simulation, we validate the effectiveness of the proposed framework and demonstrate how D2D deployment considerably improves the Wi-Fi network efficiency especially when the data rate requirements are high. Furthermore, we show that our proposed framework achieves better performance than the widely deployed Least Congested Channel selection strategy (LCC)

Contribution à l etude expérimentale et numérique du soudage laser (application aux alliages de magnésium)

Ce travail s intéresse à l étude du soudage par faisceau laser de l alliage de magnésium de désignation AM60. Il concerne un volet expérimental et un autre numérique. L étude expérimentale vise l investigation des conséquences métallurgiques et mécaniques du procédé sur l alliage utilisé et la validation des résultats numériques du modèle thermique développé. En premier lieu, une étude paramétrique a permis de déterminer les paramètres du soudage par faisceau laser CO2 de plaques en alliage AM60 de 3 mm d épaisseur. En deuxième lieu, la mise en œuvre d une chaîne d acquisition de la température, par des thermocouples implantés à proximité du cordon, a permis l enregistrement de la température en fonction du temps au cours du soudage. En troisième lieu, l étude métallographique de l assemblage, a révélé que la structure à gros grain du métal de base est transformée en une structure dendritique au niveau de la zone fondue. Alors qu au niveau de la zone affectée thermiquement de faible taille, une diminution de la taille de grain de la phase primaire est remarquée. En dernier lieu, la détermination expérimentale des caractéristiques mécaniques a montré une augmentation de la dureté dans la zone fondue et une diminution de l allongement maximal pour l assemblage. Mais par contre les caractéristiques de résistance dans la soudure et dans le métal de base sont semblables. L étude numérique a pour objectif de prédire l histoire thermique et l évolution des caractéristiques mécaniques des tôles soudées par faisceau laser. Nous avons développé, sur un code de calcul par éléments finis Cast3M, deux modèles numériques, tridimensionnels non stationnaires et non linéaires. Le premier a permis de simuler la distribution spatio temporelle de la température. Dans ce cas, le chargement appliqué est dépendant des paramètres du procédé et des caractéristiques du faisceau laser et il est associé à des conditions aux limites mobiles. Les résultats du modèle thermique développé ont été en accord avec les évolutions de la température mesurée expérimentalement. Le deuxième modèle a permis de déterminer la distribution des contraintes et des déformations résiduelles. Pour le modèle mécanique, nous avons considéré un comportement élasto-plastique avec un chargement thermique transitoire qui est le résultat du modèle thermique. L analyse transitoire non linéaire a permis de prédire l évolution des contraintes et des déformations en fonction du temps ainsi que la distribution des contraintes et des déformations résiduelles générées dans les pièces soudées par faisceau laser. La comparaison du profil de contraintes résiduelles simulées avec des résultats bibliographiques a conduit à une validation qualitative de valider qualitativement la réponse du modèle mécanique développé.This work deals with laser beam welding of AM60 magnesium alloy. It concerns experimental investigations and numerical simulations. The experimental study aims to investigate metallurgical and mechanical process consequences on studied alloy and to validate thermal model results. Firstly, a parametric study allows the determination of the CO2 laser beam welding parameters of plates with 3 mm thickness. Secondly, temperature evolution according time during welding are monitored using thermocouples fixed in the vicinity of the weld. Then, metallographic investigations are performed to reveal that the coarse grains of base metal are transformed into dendritic structure in the molten zone. Whereas, in the heat affected zone, a reduction in primary phase grain size is observed. Finally, mechanical characterisations show an increase in hardness in molten zone and a reduction in total elongation for the weld. But, strength properties are similar in the weld and base metal. The numerical study aims to predict thermal history and mechanical characteristics evolution of weldment during laser welding. Within the Finite Element (FE) code Cast3M, two three-dimensional nonstationary and nonlinear models are developed. The first allows the simulation of the space-time temperature distribution. In this case, the applied loading depends on process parameters and laser beam characteristics. It is associated to mobile boundary conditions. The thermal model results are in agreement with monitored temperature evolutions. In the second simulation, residual stresses and strains distributions are determined during welding. For the mechanical model, an elastoplastic behaviour with a transitory thermal loading is assumed, resulting from the thermal model. The nonlinear transitory analysis is able to predict stresses and strains evolutions according time as well as residual stress and strain distribution generated in the laser beam welded parts. The comparison of the residual stresses simulated profile with results from the literature enables a qualitative validation of the mechanical model.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Numerical simulation of heat transfer during leaf spring industrial quenching process

This study is carried out in partnership with the company CAVEO, manufacturer of leaf springs for vehicles. It concerns the development of a numerical model intended to follow the space-time temperature evolution of a leaf during two processing operations: hot cambering and quenching. This leaf is of a parabolic profile, made of EN-51CrV4 steel (AISI-6150). After austenitization, it passes through a cambering operation to confer it the desired deflection and then a quenching operation. This quenching is carried out in an oil bath to achieve better mechanical properties. The prediction of the temperature during quenching involves determining the heat transfer coefficient between the leaf and the oil bath. This coefficient is determined by quenching, under the same conditions as the leaf, using a standard probe of the same steel. The numerical model is based on the resolution of the transient heat equation by considering the heat loss flows towards the heterogeneous environment (ambient air, press contact and quenching oil). The results obtained by this model give the space-time temperature evolution of the leaf from the exit of the heating furnace to the exit of the oil bath. The numerical results are compared to the experimental profiles obtained through thermographic images throughout cambering and quenching operations. These results are consistent with experimental results

A centralised Wi-Fi management framework for D2D communications in dense Wi-Fi networks

In Wi-Fi networks, Device-to-Device (D2D) communications aim to improve the efficiency of the network by supporting direct communication between users in close proximity. However, in a congested Wi-Fi network, establishing D2D connections through a locally managed self-organising approach will intensify the congestion and reduce the scalability of the solution. Therefore, a centralised management approach must be involved in orchestrating those actions to guarantee the sufficiency of D2D communications. In this paper, we propose a novel management framework for D2D communications in dense Wi-Fi networks. The proposed framework employs a Software-Defined Networking (SDN) based centralised controller in synergy with a novel Access Point (AP) channel assignment process. This framework is designed to proactively establish and manage D2D connections in Wi-Fi networks considering the available radio resources and the effect of the subsequent interference. Thus, improving the overall performance of the network and providing users with higher data rate. Through simulation, we validate the effectiveness of the proposed framework and demonstrate how D2D deployment considerably improves the Wi-Fi network efficiency especially when the data rate requirements are high. Furthermore, we show that our proposed framework achieves better performance than the widely deployed Least Congested Channel selection strategy (LCC)