The operating principle of friction stir welding is shown in the illustration. A rotating tool with a central probe is pressed into the joint and traversed along the weld line. Frictional heat, generated mostly under the tool's shoulder, softens the material. The shoulder also acts to contain the softened material which is forced to the back of the tool, in the process becoming consolidated to form a solid phase weld. Providing the components are adequately restrained, a high quality solid phase weld is formed following considerable hot working of the material at the joint.
The process has demonstrated a number of advantages over competing and established conventional arc welding processes. Some of the more widely proclaimed advantages for aluminium alloys are as follows:
- Solid phase process, therefore no problems with hot cracking, porosity, etc
- Low distortion
- No filler wire or shielding gas requirement for aluminium alloys
- No fume, no spatter, no UV radiation, therefore environmentally friendly
- Uses machine tool technology, therefore easy to automate, and reduces need for skilled welders
- Can work in any position
- Good mechanical properties, which for aluminium alloys typically equals or exceeds those obtainable by competing processes
- Energy efficient
- Can weld 'unweldable' aluminium alloys
There are a number of limitations and the most commonly cited are:
- Exit hole left after withdrawing tool
- Significant down force and traversing forces required, therefore clamping is more substantial than for arc welds
- Lacks the flexibility of manual and arc processes, for example, FSW cannot be used where metal deposition is required.
Friction Stir welding is without doubt one of the most significant developments in welding technology to have emerged.
The time span from its invention and first patent in December 1991 to industrial production in the mid 1990s is almost certainly the shortest for any totally new welding process.
For further information see our friction stir welding or please contact us.