Friction stir welding development for aluminum aircraft structures

There's mechanical energy. In fact, the only new welding process developed in the last twenty-five years is friction stir welding. If you look at the two hundred welding and cutting processes listed in the back of the welding handbook, you'll find that 150 of them were developed between 1875 and 1925. Another fifty were developed between 1925 and 1975. From 1975 to 2000, there was one new welding process developed. They call it friction stir welding. They take a metal electrode basically like a milling machine, ram it into the surface of the plate between two plates, and forge them together at room temperature. It generates a little friction so it gets warm, but it's a solid-state welding process — there's no melting and almost no distortion. Boeing put in a $10 million facility to weld aluminum plates.