Well, you ruined that housing-you can't weld cast to mild steel." Jay Prosche-Jensen of Ultimate Driveline has heard that from "experts" for 30 years. Being the mild-mannered guy he is, his reply is ...

Welding. There’s something almost supernatural about being able to melt metal and use it to glue other pieces of metal together. It’s an experience you must have if you’ve never done it before.

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 ...