Thermo Mechanical Modelling of Friction Stir Welding

Abstract

Friction stir welding (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 to develop of three dimensional thermal model. The early part of the thesis describes the process, the modelling problem and why finite element analysis package (ANSYS) was selected for the subsequent work.

Thermal modelling is the essential to obtain the peak temperature attainted during FSW. Residual stresses and microstructure can be predicted based on peak temperature data. In order to achieve good quality welds, weld input parameters such as tool rotational speed, translation velocity, heat input and tool dimensions have to be properly controlled.

As an initial step, a three-dimensional thermal model for Friction Stir Welding (FSW) is presented. The focus of this research is to develop a finite element simulation with improved capability to predict temperature evolution in aluminium alloy and 304 stainless steel. The simulation model is tested with existing experimental results obtained by Chao et al. [11], Zhu et al.[10] and Hwang et al.[26] The simulation carried out using finite element package ANSYS. The results of the simulation are in good agreement with that of experimental results obtained by Chao et al. [11], Zhu et al. [10] and Hwang et al.[26].

The thermal histories and temperature distributions in a workpiece during air and immersed friction stir welding (FSW) is explored experimentally process involving the butt joining of aluminium AA 8011. K- Type thermocouples are used to measure the temperature histories during FSW at different locations on the workpiece in the welding direction. Different types of thermocouple layouts used to measure the temperature histories during air and immersed FSW at different locations on the workpiece in the welding direction. Successful welding of aluminium plates is obtained controlling the maximum temperatures during the welding process.

Regression analyses by the least squares method are used to predict the temperatures at the joint line. One linear and two second-order models are used to describe the temperature distribution in the width direction.

To validate of three dimensional thermal model for FSW is aluminium AA 8011, temperature distribution is attempted by finite element simulation in ANSYS. Simulation result is compared with experimental result. The results of the simulation are in good agreement with that of results obtained by experimentally.