TWI Industrial Member Report Summary 1002/2011
By J Martin
In late 2004 - early 2005 TWI developed an innovative technique called stationary shoulder friction stir welding (SSFSW). SSFSW employs a rotating pin located in a non-rotating shoulder component, which slides over the surface of the material during welding. The SSFSW technique offered the potential to overcome one of the limitations of conventional friction stir welding (FSW); the inability to join plates which are positioned in different angular planes such as corners. This joint configuration is used extensively in transport industries for adding rib stiffeners to body skins.
Initially TWI demonstrated the feasibility of applying the SSFSW technique to corner joints using internal and Yorkshire Forward regional funding. The welding mechanism developed consisted of a rotating pin located in a non-rotating shoulder shaped to the internal corner of the plates to be welded. Figure 1 shows a schematic diagram of the technique applied to an unreinforced T-butt weld configuration and Figure 2 shows a fabricated T-component.
Trial samples showed successful T-joint welds with all the benefits of the SSFSW technique; very smooth weld surfaces, no reduction in cross-section and small heat affected zones (HAZs). However, the sharp internal corner was considered detrimental to the joint properties, particularly with regards to fatigue performance
This report details more recent feasibility trials to produce a fillet radius weld between abutting plates to make fillet reinforced T-butt joints. The principle of the technique is to convert a chamfer into a fillet by shaping the exit of the stationary shoulder. Figure 3 shows the shape of the pre and post welded components. Two 45° chamfers were machined into the leg of the T and this additional material was stirred during the welding process and then extruded into the fillet shape on exit from the shoulder. A schematic diagram of the weld is shown in Figure 4. This FSW technique is novel and potentially represents a major advancement in developing a new variant of the FSW process.
The objectives of this project were to:
- Develop welding procedures and demonstrate the feasibility of joining a range of similar and dissimilar aluminium alloys in a fillet reinforced T-butt joint configuration.
- Compare the mechanical joint strength of fillet reinforced and unreinforced T-butt welds in a range of similar and dissimilar aluminium alloys.