Forming, which is the changing of the shape of solid bodies by use of force, is one of the main finishing processes in metalworking. Metals are crystalline bodies that contain so-called "slip planes" along which the metal can be moved at high pressure. This movement leads, however, to a change in the grain structure, the results of which depend on the temperature during forming:
- During cold working at room temperature (i.e. without any heat input), dislocations pile up and lead to an increase in strength. By annealing the material, a heat treatment, the strengthening is removed again. Heat treatment at a temperature above the recrystallisation temperature causes new grains to form.
- Hot working requires smaller forces because strength, and with it resistance to deformation, decreases with increasing temperature.
Cold working of aluminium and its alloys is possible at room temperature, which is why it is an important method of processing aluminium. One differentiates between two processes:
- Forming requires high pressures and alloys capable of being wrought and includes impact extrusion, stamping, extrusion, forging, rolling and drawing.
- Sheet metal forming using strip and sheet includes folding, crimping, spinning (without any large shape change), embossing, roll forming, deep drawing and beating (using a hammer).