These inertia friction welding videos are sooooo satisfying

Inertia friction welding joins two metal objects by spinning one at high rates of speed, then pressing it against the stationary piece. The friction heats both pieces and makes a weld sturdy enough for drive shafts, jet engines, spacecraft, and other machinery where joined pieces will endure tremendous stresses.

Here's some others (skipping to the good stuff):

This vintage video shows the process around the time it was first invented in 1960, though the film has a jump in it right at the best part!

Inertia Friction Welder for Aerospace Component – Model 480B (YouTube / MTI)