A form of friction welding, where one of the workpieces is connected to a flywheel and accelerated to a pre-determined speed, thereby storing the energy required for the weld. The workpiece is then pushed against the second piece, which is restrained from rotating with a pre-determined force.

The kinetic energy in the flywheel is converted by friction into heat at the weld interface as the flywheel speed decreases. The welding force is maintained for a short period after rotation stops to complete the weld.