To create the new iMac, Apple's thinnest desktop yet, the designers used friction-stir welding to join the aluminum body. Unlike arc welding, the more standard way to fuse metal plates, a friction stir just needs a good rubbing—and a few thousand pounds of pressure—to stick together.
The top and bottom parts of this image are the bulkhead and the nosecone of the Orion spacecraft. The machine on the left is welding them without melting the metal. How? Using MAGIC! OK, I lied. It's not magic.