Bobbin tools were developed to overcome some of the difficulties encountered in conventional friction stir welding (FSW), such as the need for a backing bar and the potential to generate root defects in the weld. Along with the complete elimination of root flaws, lower distortion joints are produced compared with conventional FSW, due to a balanced weld profile. Process benefits are also realised through almost zero weld forging forces acting on the FSW machine and work-holding fixture. Elimination of the need for a backing bar also makes new joint designs possible and extends the range of FSW applications.
TWI’s floating-bobbin design, where the probe and shoulder combination of the tool is free to float in the tool holder, was developed to overcome some of the limitations of the fixed-bobbin tool. The innovative floating action of the tool compensates for misalignment between the tool and workpiece and also for workpiece dimensional and geometrical tolerances without the need for sophisticated machine control systems.