Spin Welding as the name implies, is a friction welding technique to join thermoplastic parts. It is essential for the parts to be joined or at least their joint areas must be circular for this method. A shallow Machining groove (tongue & groove) is desirable to index the two parts and to provide a uniform bearing surface.

With one part held stationary, either vertically or horizontally in a special fixture, the other is rotated at 100-4000 rpm with enough pressure applied to keep the parts in contact with each other. The heat generated in friction is used to bring the surfaces to a sealing temperature. When sufficient melt is obtained, the spinning stops, and the pressure is increased to distribute the melt and also to squeeze out excessive melt, completing the general process.