Friction welding is a technique used to bond materials – specifically metals and thermoplastics – with a strong bond using friction itself to heat the surfaces and join them.
This video gives you a great close-up look at the process as this automated machine joins the the axle ends to a rear end housing. As you can see, the ends are clamped into rotating chucks like you find on an industrial lathe, then moved into position near the ends of the housing. The chucks are spun up to a high rotational speed, then pressed inward, using the friction to both clean and heat the metal on both parts and create a clean, solid weld.
The pressure is applied inward after the rotation stops, allowing the weld to cure as the metals cool, before the chucks are released and moved back away from the housing. This method is often preferred over typical TIG or MIG welding because the heat is confined to a smaller area, which reduces stress on the metals. It’s also considerably faster and more repeatable.