Robot system for flexible 3D friction stir welding

Abstract: Applying Friction Stir Welding (FSW) on complex joint geometries requires not only a machine with 3-dimesional work space capacity, but also a sound definition of the part geometry as well as knowledge about the process. Having a joining process, such as FSW, with great characteristics from both seam quality and environmental perspective, but yet only a minor presence in the manufacturing industry may be related to flexibility and cost issues. The machines that are present in production today are mainly devoted towards one single task, with small if any possibility to apply changes. The use of FSW has therefore mainly been introduced in areas where there are extreme demands on the seam quality, or in large scale production. In order to truly challenge the existing solutions using fusion welding techniques, we propose a solution consisting of an industrial robot, which may solve the machine issues to a great extent as well as the flexibility issues by the implementation of planning and control algorithms.In this thesis we aim to develop a general methodology towards 3-dimensional FSW on complex objects. This include a robot prototype based on a standard industrial design, modified to carry out the process to a satisfactory extend. The prototype implementation includes software to control the motion of the welding tool, explicitly in the axial direction by the use of force feedback control and implicitly in the plane perpendicular to the axial direction to avoid path deviations. Other tools proposed in this thesis include planning software to create complex paths, both online and off-line, to consider not only the aspects regarding the robot's motion, but also including restraints due to the FSW process.The evaluation of the proposed system is conducted with an objective to define weldability, in term of alloys, thicknesses and speed, to verify the path planning algorithms for an online as well as an off-line scenario, and to verify the control algorithms response to path deviation due to manipulator compliance, and merge the results from those studies into a discussion on usability of the proposed system and application areas and operations suitable.