Hubbing is a process to make recessed cavities in female tooling dies.
The process begins with a male tool, the hub, which is made with the desired profile then hardened. The hub is then slowly pressed (using hydraulic force) into the desired tooling cavity hole to reproduce the inverse of the profiles.
The metal displaced from the cavity is removed by machining, using a fly cutter on a milling machine or grinding it on a surface grinder.
This is a good alternative to the conventional die sinking process where the female tool cavity is machined. In hubbing, the male tool is machined and external machining is easier than internal machining.
This is often used to produce plastic extrusion dies economically.