Not all welding is done with a blowtorch. With linear friction welding, metals can become hot enough to fuse just by rubbing them together at extremely high speeds.
This video from the technology engineering company TWI depicts the linear friction welding of two pieces of titanium in slow motion. The upper slab of metal moves rapidly back and forth as the lower slab remains stationary, producing temperatures between 1100 and 2200°F. Titanium melts at a considerably higher 3051°F, so while friction isn't enough to melt the metals, it does make them hot enough to forge into one.
The process is commonly used in aerospace engineering as a low-cost method for welding the bladed discs used in turbine engines. And while the video above goes on for about a minute, linear friction welding can take as little as a second to complete.
Header/banner images courtesy of TWI via YouTube.