Investigation of Techniques for Online Path Compensation In Robotic Friction Stir Welding

Reducing weight is one of the enablers to design more environmentally friendly constructions. Friction Stir Welding (FSW) supports low weight design through its capability to join different combinations of light weight materials, e.g. different aluminium alloys, but also through its possibilities in producing continuous joints. StiRoLight is an ongoing national project in Sweden for robotic FSW for joining of light weight materials emphasising on the automotive and aerospace industry. During welding operations, there are relatively high forces applied on the FSW tool. These forces will cause deflections in robot joints, due to a lack of robot stiffness, and thus a deviation from the original (programmed) path. These deviations are dependent on the welding direction and the position of the welded part. Depending on the process window and specific application, these deflections might have a severe effect on the weld quality.

In this paper, a laser measurement system and a camera based system for path deviation measurement are investigated and compared. Furthermore, microscopic images of start and stop positions of the welds are investigated and compared with the online measurements and force sensor information. The main purpose of these tests is to find a robust system for online path compensation. The results from several FSW tests in AA-7020 aluminium in different welding directions and locations are presented and analyzed. Based on this analyze the two deviation measurement techniques are evaluated. The evaluation also includes the demands, process windows, for specific application from one of the industrial partners in the project within the aerospace industry. Finally, models of the deviations versus side forces, based on the simultaneously logged data, are presented.