As manufacturers expand the use of aluminum, titanium, magnesium and other high-strength, lightweight alloys, interest in alternative joining technologies is increasing. One is friction stir welding (FSW), in which a cylindrical shouldered tool with a profiled pin is rotated at high speed and plunged into the joint area between two abutting metal plates or sheets. Frictional heat between the welding tool and workpieces causes the latter to soften without reaching their melting points.

The rotating tool then traverses along the joint line, transferring the softened material around itself as it moves and stirring material from each part together. Plasticized material is pressed downwards by the tool shoulder and transported from the front of the tool to the trailing edge where it is forged into a butt or lap joint.

Friction stir spot welding is performed like FSW, but enables more localized welding and can be readily implemented into robotic assembly systems. These benefits offer great appeal to manufacturers of appliances, trucks, trains, off-road equipment and airplanes.

Aerospace companies are equally interested in refill friction stir spot welding (RFSSW) because it eliminates the tool exit hole in joints. Boeing and GKN Aerospace, for example, are working closely with EWI in a project overseen by the LIFT Consortium called “Processing and Properties Database for Refill Friction Stir Spot Welding of Aerospace Materials.” Equipment designer and integrator Coldwater Machine Co. is also participating.

Begun in April 2017, the project will validate and further develop RFSSW using aerospace titanium and aluminum alloys. Conventional FSW has been performed with titanium using refractory metals, but, there is no literature related to performing RFSSW with titanium alloys.

As for aluminum, much RFSSW work has been done with AA 2000, 5000 and 6000 alloys. This project will include welding hard metals such as Ti-64, aluminum-lithium and 7000 series aluminum. Coldwater’s robot-mounted SpotMeld system is being used to weld 1000 to 7000 series aluminum, and document the data to improve process control.

The project will also produce an initial database of process parameters and mechanical properties, initial design guidelines based on this process data and demonstration articles of the proposed applications. Other industry and research partners include Lockheed Martin, Comau, Bond Technologies, the University of Tennessee-Knoxville, Oak Ridge National Laboratory and the University of Michigan. The project is expected to be completed by October 2018.

LIFT is operated by the American Lightweight Materials Manufacturing Innovation Institute, a public-private partnership focused on developing and deploying manufacturing technologies for advanced lightweight materials, and implementing education and training programs to prepare the workforce to assemble these materials. The institute is one of the founding members of Manufacturing USA, a federal initiative that creates regional hubs to quicken the development and adoption of cutting-edge manufacturing technologies.

SpotMeld is used by manufacturers in various industries to join aluminum, magnesium, nonferrous and dissimilar material sheets of varying thicknesses. The system is compatible with various brands of robots (including Fanuc, KUKA and ABB) and CNC machines. It is easy to fixture, energy efficient, and offers automated tool changeover. Welding programs can be called up on demand via the robot controller.

For more information on refill friction stir spot welding, call 419-678-4877 or visit