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Influence of base material plastic behaviour and process parameters on friction stir weldability

Leitão, Carlos Miguel Almeida
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
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In current work the weldability in friction stir welding (FSW) of two aluminium alloys currently used in welding construction, the Al-Mg-Si (AA6082-T6) and the Al-Mg (AA5083-H111) alloys, is analysed and related with base materials plastic properties at high temperatures and strain rates. The weldability of both alloys was evaluated by performing a deep morphological, microestrutural and mechanical characterization of a large number of welds produced under a wide range of welding conditions. Simultaneously, the plastic behaviour of both base materials was characterized by accomplishing an extensive mechanical characterization program, which included performing uniaxial tests, under different temperatures and loading conditions, as well as a deep literature review on microestrutural and phenomenological modelling of aluminium alloys plasticity. The hardening behaviour of the aluminium alloys, at increasing temperatures and strain rates, was then related to base material weldability. It was found that the AA6082 alloy, which displays intense flow softening during tensile loading at high temperatures, and is sensitive to dynamic precipitation and overageing under intense non-uniform deformation, displays good weldability in FSW. Under the same welding conditions...

Influence de la géométrie de l’outil sur la robustesse du FSW robotisé; Influence of the tool geometry on the robustness of the robotized FSW process

JEMAL, Nejah; BEN ATTAR, Amarilys; LANGLOIS, Laurent; ZIMMER-CHEVRET, Sandra
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
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En soudage par friction malaxage (Friction Stir Welding, FSW), l’outil est l’acteur principal de l’opération. Dans sa configuration conventionnelle, l’outil FSW n’est pas considéré comme un consommable lors du soudage des alliages d’aluminium. Sa partie active constituée d’un épaulement et d’un pion permet l’échauffement et le malaxage de la matière. Dans cette étude, on s’intéresse tout d’abord à analyser l’influence de la géométrie de l’outil sur la qualité du cordon. En effet, pour plusieurs géométries d’outil de soudage, les domaines de soudabilités opératoires sont définis et comparés. À partir de ces résultats, la robustesse des différentes géométries d’outil vis-à-vis de la qualité du malaxage lors d’une variation des paramètres de soudage est évaluée. D’autre part, pendant le soudage l’interaction outil/matière évolue suivant la géométrie des surfaces actives de l’outil FSW. Aussi, l’outil FSW a une influence sur les efforts engendrés au cours du soudage. Ces derniers sont donc également analysés afin de définir l’influence de la géométrie sur leurs variations. Dans un objectif de robotisation du procédé, cette étude est une première étape dans l’optimisation de l’outil en trouvant le bon compromis entre qualité du joint soudé et amplitude des efforts.; In FSW the welding tool is a process major player. In its conventional configuration the FSW tool is not consumable. Its active part is composed by a shoulder and a pin and these elements allow two fundamental phenomena for FSW process: material warm up and material stirring. In this study the influence of the FSW tool geometry is analyzed and put in relation with the weld quality. Indeed for several FSW tool geometries the process window is established and compared. From these results the FSW tool geometries robustness is evaluated with regard to the weld quality when the welding parameters are evolving. On the other hand during the welding operation material/tool interaction evolves depending on the active welding tool surfaces. Therefore FSW tool influences forces values created during welding operation. These forces are analyzed in order to define the influence of the FSW tool geometries on their evolution. This study is a first step in the FSW tool optimization in finding a compromise between weld quality and welding forces in the aim to develop robotized FSW.; Agence Nationale de la Recherche...

Modelling and Visualisation of Material Flow in Friction Stir Spot Welding

Reilly, Aidan; Shercliff, Hugh; Chen, Yingchun; Prangnell, Philip
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
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This is the author accepted manuscript. The final version is available from Elsevier at http://dx.doi.org/10.1016/j.jmatprotec.2015.06.021; The material flow in friction stir spot welding of aluminium to both aluminium and steel has been investigated, using pinless tools in a lap joint geometry. The flow behaviour was revealed experimentally using dissimilar Al alloys of similar strength. The effect on the material flow of tool surface features, welding conditions (rotation speed, plunge depth, dwell time), and the surface state of the steel sheet (un-coated or galvanized) have been systematically studied. A novel kinematic flow model is presented, which successfully predicts the observed layering of the dissimilar Al alloys under a range of conditions. The model and the experimental observations provide a consistent interpretation of the stick-slip conditions at the tool-workpiece interface, addressing an elusive and long-standing issue in the modelling of heat generation in friction stir processing.; The authors wish to thank the EPSRC for funding this research through the following grants: Friction Joining ? Low Energy Manufacturing for Hybrid Structures in Fuel Efficient Transport Applications (EP/G022402/1 and EP/G022674/1); and LATEST2...

Modelling of friction stir welding

Colegrove, Paul Andrew
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
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This thesis investigates the modelling of friction stir welding (FSW). FSW is a relatively new welding process where a rotating non-consumable tool is used to join two materials through high temperature deformation. The aim of the thesis is the development of a numerical model to improve process understanding and to assist in the design of new tools. The early part of the thesis describes the process, defines the modelling problem and describes why a computational fluid dynamics package (FLUENT) was selected for the subsequent work. A systematic series of friction stir welding experiments in 7075 aluminium alloy, used to provide validation data for a numerical model of the process, are described in chapter 2. The trials examined how the welding conditions and tool type affected the weld temperature and heat input. From this data a thermal model of the welds was developed that included the convective heat flow due to material mixing. Chapters 3 to 6 describe the model development, from a preliminary model of a standard tool, to a detailed analysis of 2 dimensional profiles incorporating a novel slip boundary condition, and finally to a full 3 dimensional model of a new tool design, including material slip. The preliminary model with a standard tool assumed that the material stuck to the tool surface and included features such as the tool tilt...

Modelling of friction stir spot welding

Reilly, Aidan
Fonte: University of Cambridge; Department of Engineering; Sidney Sussex College; Trinity Hall Publicador: University of Cambridge; Department of Engineering; Sidney Sussex College; Trinity Hall
Tipo: Thesis; doctoral; PhD
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Friction stir spot welding (FSSW) is a solid-state welding process which is especially useful for joining precipitation-hardened aluminium alloys that undergo adverse property changes during fusion welding. It also has potential as an effective method for solid-state joining of dissimilar alloys. In FSSW, heat generation and plastic flow are strongly linked, and the scale of the process in time and space is such that it is difficult to separate and control the influence of all the relevant input parameters. The use of modelling is well-established in the field of welding research, and this thesis presents an analysis of the thermal and mechanical aspects of FSSW, principally using the finite element (FE) technique. Firstly, a thermal FE model is shown, which is subsequently validated by reference to experimental temperature data in both aluminium-to-aluminium and aluminium-to-steel welds. Correlations between high-quality welds and temperature fields are established, and predictions are made for peak temperatures reached under novel welding conditions. Deformation and heating are strongly linked in FSSW, but existing modelling tools are poorly suited to modelling flow processes in the conditions extant in FSSW. This thesis discusses the development and optimisation of two novel techniques to overcome the limitations of current approaches. The first of these uses greatly simplified constitutive behaviour to convert the problem into one defined purely by kinematics. In doing so...