It is a cold-working process, which means that it occurs well below the melting temperature of the metal being worked.
The male hub is generally hardened and the female die block softened by annealing to help form the impression.
As the metal flows the face of the die block is deformed, and, generally, must be machined flat.
The die block is often a cylinder that is reinforced with a surrounding steel ring during the hubbing process.
In the case of mild steel, a typical hubbing press exerts a pressure of approximately 1500 short tons-force per square inch (21 GPa) to transfer the image from a master hub into the master die.