Most welding starts by melting metal. Friction stir welding never does — and that single fact is why it joins alloys that conventional fusion welding tears apart. Invented at The Welding Institute in Cambridge in 1991 by Wayne Thomas, FSW uses a rotating, non-consumable tool with a profiled pin and a broader shoulder. The pin plunges into the seam between two clamped plates while the shoulder rides on the surface. Rotation generates frictional and adiabatic heating that drives the material to roughly 0.8 of its absolute melting temperature — hot enough to go plastic, never hot enough to liquefy. The tool then traverses the joint, and the softened metal flows around the pin from the leading to the trailing edge, where it is forged together under the shoulder’s pressure. Because nothing melts, the defects that plague fusion welds simply don’t appear: - No solidification cracking, porosity, or hydrogen embrittlement - No filler metal, shielding gas, or fume - Minimal distortion, since ...