A variation of friction welding that produces a weld between two butted workpieces by the friction heating and plastic material displacement caused by a high speed rotating tool that traverses along the weld joint.
A solid phase, autogenous welding method introduced in 1991 that has been used successfully in welding the 2000,5000, and 6000 series of aluminum sheet alloys.
Welding is accomplished by rotating a non-consumable probe and entering it into the abutting edges of the sheets to be welded. The frictional heat generated between the tool and the workpieces produces plastic deformation, then the tool is moved along the joint. The base material fills in behind the probe to complete the weld. No melting occurs during the operation, so the process is solid phase in nature. For certain aluminum alloys, no shielding gas is required.
The joining of aluminum alloys, especially those that are often difficult to weld, has been the initial target for developing and judging the performance of friction stir welding. As the technology for this process is developed, its use will be applied to other materials.
Applications
Friction stir welding has potential applications in major industries such as aerospace, aluminum production, automotive, construction, rail car manufacturing, refrigeration, shipbuilding, and storage tanks and pressure vessels.
Advantages
(1) The electromechanical machine tool equipment is energy efficient (a single pass 12.5 mm [0.5 in.] deep weld can be made in 6xxx alloy with a gross power of 3 kW), requires very little maintenance, and apart from welding tools and electric power, relies on no other consumable.
(2) A high level of operator skill and training is not required.
(3) The welding process requires neither filler metals nor weld pool shielding gas.
(4) Special joint edge profiling is unnecessary.
(5) Oxide removal immediately prior to welding is unnecessary.
(6) The technique is ideally suited to automation.
(7) If necessary, the welding operation can take place in all positions from flat to overhead.
Limitations
(1) Single-pass welding speeds in some sheet alloys are slower than for some mechanized arc welding techniques.
(2) The parts must be rigidly clamped against a backing bar to prevent weld metal breakout, if full penetrations are required.
(3) At the end of each weld run a hole is left where the tool pin is withdrawn. In many cases it may be necessary to fill the hole by an alternative process, such as
(4) Run-on/run-off plates are necessary where continuous welds are required from one edge of a plate to the other.
(5) Due to workpiece clamping and access requirements, applications where portable equipment could be used may be limited.