Robotic 3D friction stir welding : T-butt joint

Abstract: This Master Thesis was performed in terms of robotic three dimensional friction stir welding with T-butt joint. Friction stir welding (FSW) is a solid state welding method that achieves the weld temperature by friction of a rotating non-consumable tool with the workpiece. Science and technology fast developing requires for higher seam quality and more complex welding joint geometry like 3D welds. In order to acquire high productivity, capacity and flexibility with acceptable cost, robotic FSW solution have been proposed. Instead of the standard FSW machine, using a robot to perform complicated welds such as, three-dimensional. In this report, a solution for weld a 3D T-butt joint, which located in an aluminium cylinder with 1.5 mm thickness using a robot, was developed. Moreover, two new paths were investigated in order to avoid the use of two welds to perform this type of joint. The paths were tested on 2D and on 3D (with a 5050 curvature radius) geometries. Both paths had good results. What is more, the parameter developing methods of FSW process, which is composed of necessary parameter setting, positional compensation was introduced. Specially,the study demonstrates how complicate geometry can be welded using a robot. Also,it shows that TWT temperature control is able to acquire high quality 3D welds. In addition, an analysis of the 2D welding and 3D welding was performed, which exposed that, keeping exactly the same welding conditions, higher lateral forces on the tool were found during 3D welding. Basis on the special case in this paper, when the tool goes like "climbing" the sample, the suffering force of tool decreasing with increasing the height(Z position); nevertheless, when the tool goes like "downhill", the suffering force of tool decreasing with decreasing the height (Z position). What is more, in 2D weld, increasing the downforce (Fz) results increasing the lateral forces which can be Fx and/or Fy. Finally, the future works suggestions were presented in terms of (1) performing the new paths into a real cylinder, (2) performing tensile test on the paths and comparing it with conventional path which weld twice, (3) researching how the downforce (Fz) influence the Fx and Fy during welding of different 3D geometries, (4) how the cooling rate of backing bar influence the seam quality when it is use the same welding parameters and (5) the effect of performing welds in the same welding temperature achieved with different combination of the tool rotational speed and downforce on the material properties