Parametric finite-element studies on the effect of tool shape in friction stir welding

The success of the Friction Stir Welding (FSW) process, and the weld quality produced, depends significantly on the design of the welding tool. In this paper the effect of variation in various tool geometry parameters on FSW process outcomes, during the plunge stage, were investigated. Specifically the tool shoulder surface angle and the ratio of the shoulder radius to pin radius on tool reaction force, tool torque, heat generation, temperature distribution and size of the weld zone were investigated. The studies were carried out numerically using the finite element method. The welding process used AA2024 aluminium alloy plates with a thickness of 3 mm. It was found that, in plunge stage, the larger the pin radius the higher force and torque the tool experiences and the greater heat generated. It is also found that the shoulder angle has very little effect on energy dissipation as well as little effect on temperature distribution

Residual Stress in Friction Stir Welding and Laser-Assisted Friction Stir Welding by Numerical Simulation and Experiments

The friction stir welding (FSW) has become an important welding technique to join materials that are difficult to weld by traditional fusion welding technology. In this technique, the material is not led to fusion, and the joint is the result of the rotation and movement along the welding line of the tool that causes softening of material due to frictional heat and the stirring of the same. In FSW, the temperature does not reach the fusion value of the materials, and this helps to decrease the residual stress values. However, due to the higher force involved in the weld and, thus, the rigid clamping used, the residual stresses are not low in general in this technique. As the presence of high residual stress values influences the post-weld mechanical properties, e.g. fatigue properties, it is important to investigate the residual stress distribution in the FSW welds. In this chapter, two numerical models that predict temperatures and residual stresses in friction stir welding and laser-assisted friction stir welding will be described. Experimental measurements of temperatures and residual stress will be carried out to validate the prediction of the models

Laser assisted friction stir welding: finite volume method and metaheuristic optimization

Friction Stir Welding (FSW) is a solid state joining process that uses a non-consumable rotating welding tool to generate frictional heat at the welding location. Large forces are required to produce friction between the welding tool and the work piece which increases the wear rate of the welding tool in welding materials with high melting temperature. Several different approaches have been developed to address this problem. This thesis focuses on a new modification of friction stir welding, called Laser Assisted Friction Stir Welding, a process developed in the last decade. This process uses laser energy to preheat the work piece at a localized area ahead of the rotating tool, thus softening a volume of the work piece ahead of the tool. The work piece is then joined by the rotating tool as in conventional FSW. The amount of heat generated during welding determines the quality of the weld. Hence understanding the temperature distribution is necessary in determining the optimum process parameters for the welding process. In this thesis, a three dimensional model of laser assisted friction stir welding is developed, using FLUENT which is based on finite volume method, to obtain the temperature distribution in the work piece. The developed model can be used to better understand the process, predict the process performance and to determine optimal process parameters. A comparison with pure friction stir welding without laser assistance is also made to show its potential benefits. Parametric studies are designed to understand the effect of variation of certain process parameters such as feed rate, tool rotational speed and laser heat input on temperature distribution in the work piece. Finally, optimal combinations of friction stir welding and laser parameters are determined by a metaheuristic - Ant Colony Optimization

Coupled Thermo Mechanical Modeling of Friction Stir Welding and Fatigue Life Improvement of Friction Stir Welding Structures

Friction- stir- welding (FSW) is comparatively a new welding process invented by The Welding Institute in 1991. Since no melting or fusion occurs during the welding process, FSW is free of high heat input and solidification defects. Two main objectives have been set forth in this work. The first object of this thesis is to develop thermomechanical models based on experimental knowledge and understanding the FSW process at a fundamental level. The quality of friction-stir-welding (FSW) joints depends on many critical weld process parameters. The main challenge for the FSW is in the selection of these critical process parameters that would produce a defect-free weld joint. For a particular pin tool, spindle rotational speed, welding speed, plunge rate and vertical plunge force are considered as key factors to generate heat during welding process. In this work, a temperature dependent friction coefficient is employed that takes into account both sticking and sliding friction conditions. Furthermore, both strain rate independent and strain rate dependent plasticity model was applied to develop FSW. Moreover, heat generation as a process in itself is modeled by accounting for friction heat and plastic deformation between tool/boundary conditions. To demonstrate the validity of the model, the model is applied to different weld schedules of Aluminum AA2219 alloys. Finally, the developed model is used to carry out parametric studies on the effect of process parameters such as rotational speed, welding speed, plunge rate and plunge force on heat generation during FSW. This parametric study helps to give an insight into creating defect free weld joints. Also the effect of process parameters on the quality of predictions using Coulomb and modified Coulomb models of FSW has been analyzed in this current work. A second objective of the research is to improve fatigue life of defect free AA2219 Friction welded joints by Post Weld Heat Treatment (PWHT). Later fatigue life was experimentally compared with base material, as welded specimen and post weld heat treated specimen. Post weld heat treated specimens have higher fatigue strength compare to as welded specimen

Development Of Multi-Component Loads, Torque And Temperature Measurement Device For Friction Stir Welding Process

Friction stir welding process is a solid state joining method that utilizes heat source from mechanical friction work of a rotational tool exerted on work material, producing joint without the use of filler material. Since its introduction, friction stir welding is still at infant stage compared to conventional fusion joining method. The welding process fundamental is still not well established, lack in standard practicing guideline and optimum operating conditions for typical material application as well as inability to definitively relate process variables to the produced joint properties. The basis of this study is regarding to the mechanical work principle of the welding process, which is devised through measurement method as a mean to look for the possible benefits of improved joint mechanical properties. This study presents the analysis of welding parameters responses via a metrology system which measure the dynamic and quasi-static multi components three dimensional loads, torque exerted and to capture the corresponding temperature profile. The measured loads and torque represent the acting reaction forces suggesting its influences on joint physical properties based on welding parameters variables. In addition, a mathematical model is derived to approximate the welding process based on the work material temperature-dependent material properties, employed to validate the metrology system. Contact mechanic principle is adapted into the model accounting both Coulomb’s friction and plastic deformation principle. Proceeding, heat transfer within the system is studied through experimental work. The relationship of the measured loads and torque with the corresponding temperature shows the possibility to control the process variables