Materials to be formed gives the first classification of forging processes between ferric and non-ferric materials forging, including in this last group mainly Al, Cu and Ti alloys.
From the point of view of forming temperature, forging processes can be divided between:
- Hot forging. When material forming is made above re-crystallising temperature and very near the fusion temperature of the material. For steel is about 1,100 ºC – 1,250 ºC.
- Cold forging. When material forming is made at ambient temperature (20 ºC). In the case of steel, this is limited to revolution parts.
- Warm forging. When material forming is produced at temperature below re-crystallising temperature, normally a little bit higher than half the fusion temperature. For steel is about 650 ºC – 900 ºC.
If we attend to the forging die type, forging processes can be divided between:
- Open die forging or Free forging, when forming is produced by means of a pair of flat dies or platens. Here it is also included rotary forging for big rings. Always it is performed at high temperature and forging is produced in a one-by-one basis or in very short series. It is used from a few kilograms to several tonnes.
- Closed die forging, when each of the dies has engraved half mirror shape of the part to be formed when both dies are closed giving the final part. The shape in the dies can include an area for allowing the excess of material to flow (flash forging) or not (flashless forging or closed die forging). This is applied to forging parts from several grammes to hundred of kilogrammes.