Two Metals Enter, One Leaves: The Miracle of Friction Stir Welding

The typical images of welding—a robotic arm burping sparks or a masked Jesse James hovering over

a glowing metal puddle—don’t apply to friction stir welding (FSW). The metal-joining technique was developed in 1991 by The Welding Institute, an industrial research center near Cambridge, England. In the mid-1990s, two Scandinavian aluminum-extrusion companies became the first to use the technique commercially. Since then, it has been widely adopted by the aerospace industry and has slowly trickled into the automotive realm.

Sparks and eye shields are part of fusion welding, where an electric current heats two pieces of metal to a molten state. When the metal pool cools, a single, solid joint results. In contrast, FSW is a solid-state weld involving no molten metal. Heat generated by pressure and friction is all that’s needed to ensure a strong metal bond.

The benefits are numerous. Most notably, FSW works with dissimilar ­metals. Not only can it weld different aluminum alloys, but it can also weld steel to aluminum. Before FSW, this was time consuming, costly, and often resulted in brittle bonds not suitable for load-bearing applications.