Effect of tool shoulder profile on the axial force and joint strength of friction stir spot welded aluminum alloys
In many industries, the use of articulated robots has proven to be an efficient and beneficial way in which to reduce manufacturing costs, e.g., by increasing productivity through automating repetitive processes. However, because of their limited payload capacity, articulated robotic arms have found limited use in processes like friction stir welding (FSW), which require precise position control under relatively high process loads. This limitation in payload has restricted the use of robots to low-loading operations in manufacturing. One way to increase the usefulness of robots for FSW is to reduce the process forces to which they are required to react. One potential area of robotic application is friction stir spot welding (FSSW), a variant of FSW. FSSW is typically used to join two overlapped sheet metal workpieces. A significant portion of the process cycle of FSSW is the plunge cycle. The axial (z) load generated in the process can be substantial depending on selection of the weld tool and process parameters. This study is a continuation of the work performed in the first phase on a gantry-style FSW machine to analyze the process feedback forces, mainly the axial force. In the first phase of this project, the level of the axial force required to produce FSSW in an AA2024-T3 bare aluminum sheet, was significantly lowered by reducing the weld tool shoulder diameter from 0.4 inches (10.2 mm) to 0.3 inches (7.6 mm). Results from the second phase of this project included the influence of three weld tool shoulder geometries, namely concave, convex scrolls, and flat scrolls, on the axial force, mechanical strength (shear strength), and macrostructural properties produced between AA7075-T6 (typical of stringers) and AA2024-T3 (typical of an aircraft skin). The effects of process parameters were analyzed using the design of experiments (DOE) approach. The results of this research suggest that basic and swept FSSW of dissimilar aerospace alloys can be successfully performed at an axial force that is suitable for robotic applications.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering