Friction stir welding (FSW) is a technology that has crept quietly onto the scene over the years with a niche play in the aerospace industry, welding aluminum components together. FSW was developed in 1991 by The Welding Institute and consists of an innovative mechanical principle—heating two adjoining pieces to their plastic state by plunging a rotating tool head into them and mixing them together.
The FSW technique offers several advantages over conventional welding methods, including lower cost operation since it requires no consumables, a more consistent/stronger weld, and a better quality weld due to the weld being formed at a lower temperature.
The Airbus Group is on the forefront of this technology and developed a new head design that is proving to be a game changer. The technology is called DeltaN FS and consists of both mechanical and controls related innovations. The DeltaN FS technology features a compact head with a stationary shoulder, the piece used to support and guide the rotating tool head.
With traditional FSW, the shoulder rotates with the tool head, and since the shoulder comes into contact with the materials being welded, excess heat is generated at the top of the materials being welded. This contact point and excess heat cause issues with weld quality and limit its welding capabilities. With excess heat comes deformation and solidifications concerns. That point of excess heat is also the limiting factor on how deep you can weld and the types of joints you can weld, and eliminates the ability to weld materials of varying thickness. As such, traditional FSW is limited to welding butt joints of like material, of the same thickness, on either flat parts, or parts with a large radius. Think airplane fuselages and rocket booster tanks.
The stationary shoulder design opens a whole new world for FSW due to its ability to precisely control the heating point and not having excess heat generated at the shoulder, at the top of the material. Specific advantages include:
- Other joint geometries can be considered in addition to butt joints: T, corner, fillet, spot, edge, and lap joints;
- Welding of dissimilar materials that include aluminum, iron, copper, magnesium, lithium, thermoplastics;
- Welding of materials with varying thickness, .3 mm to 10 mm on robot mounted applications, and .3 mm to 100 mm on traditional CNC mounted applications; and
- Better weld quality, so good that secondary machining is rarely required.
The stationary shoulder principle allows for different shoulder designs to be considered, which is important for the different joint configurations, as well as welding curved surfaces. With the DeltaN FS technology curved surfaces as tight as 15 mm can be welded.
Since lower process forces are required, it is well suited to be mounted on a robot with force/position control capabilities. Couple this with the flexibility in the shoulder design discussed above and you have an FSW system uniquely suited to weld complex, three-dimensional shapes, something simply not possible with traditional FSW technologies.
Most product managers know the frustration of having the manufacturing process define the materials they use in their products; such compromises happen all the time. It is exciting to be able to offer a technology that allows manufacturers to reconsider the materials they use to comprise their products and make them better, lighter and more cost effective.