"Spin forging" just looks like welding.
It is. It is actually a form of welding called Friction Welding. Previously being a welder, and still working in the industry, finally a topic I know at least a bit about, ha ha.
Borrowed from Wikipedia:
"Friction welding (FW) is a class of solid-state welding processes that generates heat through mechanical friction between a moving workpiece and a stationary component, with the addition of a lateral force called "upset" to plastically displace and fuse the materials. Technically, because no melt occurs, friction welding is not actually a welding process in the traditional sense, but a forging technique. However, due to the similarities between these techniques and traditional welding, the term has become common. Friction welding is used with metals and thermoplastics in a wide variety of aviation and automotive applications."
