The Andrews University chapter of the Society of Automotive Engineers (SAE) took a field trip the shop of someone who designs friction stir welders. This welding process produces much less heat and doesn't produce an arc - watching the welding process is essentially like watching a pice of metal pass through a milling machine (the grandfather of friction stir welders) without sending off any chips.
a weld (approximately one inch wide and creating a depression of a few thousandths of an inch on a thick piece of aluminum alloy)
One of the welding tips - the screw-like point presses into the metal and between that and the plate above it exerting 100kN (about 11.2 tons) of force on the workpiece and spinning at somewhere between 200 and 1800 rpms creates enough friction to bring the workpiece just short of it's melting point and mixes material from both sides together creating a clean, uniform weld that is stronger than conventional methods for welding aluminum alloys, copper, and titanium.
They showed us a CAD (computer drawn) based video clip of how one of their machines will be used for a new rocket that NASA is building but were unable to show us the whole thing due to the fact that there were non-US citizens in our group and the tag of the video said "sensitive but unclassified". They also wouldn't let us take pictures of a number of parts they had in their shop that belonged to various customers. At one point I was asking some questions about the welding process on a particular part when one of the designers said he would show me one of his 'dirty tricks' . He took my notebook and began drawing, showing me how to take a particular bolt and, through use of a lathe, turn, drill, and tap it in a particular way making one of the welding tips (much like the one pictured above) that can be used even on a milling machine (given a big enough machine and some practice). He said that when customers wanted him to try out a new bit design this was how he did it, that way, when writing up his report he could just look up the Rockwell hardness of the bolt, give it's dimensions after turning and not mention how exactly he had made something with such a high tech job in twenty minutes from materials available at your hardware store... it wasn't 'till I was on the way home that I realized that this had absolutely nothing to do with the part I was asking about but rather had been a distraction from it.