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Type: Thesis
Title: 3 dimensional flow and thermal modelling of the friction stir welding process
Author: Colegrove, Paul
Issue Date: 2001
School/Discipline: School of Chemical Engineering & Advanced Materials
Abstract: Friction Stir V/elding (FSW) is a relatively new welding process, having being patented in 1991 by The Welding Institute, Cambridge. This process has great advantages in welding difficult to weld aluminium alloys. The process gives low post weld distortion, can weld thick sections in a single pass and produces welds with excellent mechanical properties. FS'W uses a rotating tool to generate heat by mechanical work and friction. A key feature of the process is the localised deformation and material flow around the FSW tool. Various authors have used analytical and numerical thermal models to predict the weld microstructure and residual stress and distortion. However these models have not yet been able to predict the conditions whereby a successful weld can be achieved. To fully understand the complete welding process flow modelling is required. Some preliminary flow models have been published, however the field is still largely in its infancy. Therefore, this thesis presents: o A thorough review of the thermal models that have been published to date. o A brief investigation into the related field of friction welding. o An investigation into the material properties that will be relevant to the process. o A theory for describing how the material flows around the pin. This is an area that is not fully understood and is necessary to the development of a successful flow model of the process. The work reviews the current literature in this area as well as presenting some new data to support the proposed theory. A theory for analysing the heat generated around the pin. This has been used in the thermal model described below. A basic thermal model of the process. This model is quasi-steady state and is solved using the finite element method. Features of this model are the inclusion of the tool and backing plate, and the inclusion of heat generation at the pin, which is particularly relevant to the welding of thick sections. This model has been validated for a weld with 12mm thick 5083 aluminium. The development of transient thermal models for thick plate aluminium. These models have shown how transient effects at the plate ends and the duration of the initial plunge have a drastic impact on the resulting thermal profile. 25mmthick 5083,7150 and a 1000 series aluminium alloy have been used in this modelling work. The development of an automatic meshing program for use in a finite element model for solving the flow around the pin. Two finite element packages have been used to predict the flow of material around the pin. The model is isothermal and has not included the effect of any slip between the tool and the workpiece material. This model is able to show the amount of heat generated, and the pressure and flow of material around the pin. An investigation into the microstructure produced from a 5083 Friction Stir Weld. This microstructure demonstrated stick slip flow around the pin through analysing the 'so-called' pin retraction defect. The flow features observed in the weld were compared against the weld travel and rotational An investigation into the evidence for and against surface melting during Friction Stir Welding. While microstructural evidence indicates that surface melting does not occur, some temperature measurements suggest otherwise. A balanced review is presented. It is believed that more data is required for a definitive answer. It is believed that the thesis lays the foundations for future thermal and flow modelling of the friction stir welding process.
Advisor: Painter, Mike
Graham, Denny
Wahab, M. A.
Dissertation Note: Thesis (M.Eng.Sc.)--University of Adelaide, Dept. of Mechanical Engineering, 2002
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