Reading the latest Popular Mechanics (May 2010), they mentioned something I have not heard of before called friction stir welding. It’s a process used to join metal, usually aluminum, without an arc. Instead, it uses a spinning rod, rotating at 15,000 rpm to heat the metal and high pressure to join the heated pieces together. It can move at 8 inches per minute and weld 1 inch thick plates in one pass instead of a dozen or so using conventional techniques.
It’s only used on large welding jobs at the moment because of the equipment necessary, it won’t be replacing your MIG welder anytime soon, but developments are coming which will allow it to join steel or different metals and a tool called a bobbin may allow quicker and smaller jobs. It’s currently used in the space program and in similar situations, knowing some of the visitors here, I bet a few of you are familiar with this technology already. Very cool.