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.
The process used by NASA's Michoud Assembly Facility is called friction stir welding. This type of welding doesn't melt the metal or apply any heat to it. It's all about friction and pressure, and it's used when engineers need to put two metal parts together—usually aluminum—but they need to keep the original characteristics of the metal unchanged.
Friction stir welding uses a cylindrical-shouldered tool rotated at a constant speed and traverse rate between the two pieces of metal. The pieces of metal should be pressed so tight that they can't be deformed. The friction causes enough heat to soften the metal without melting it. The tool then pushes the plasticized metal from the two pieces, which solidify together into the new part. [NASA and Wikipedia]