During forming, the workpiece is stressed beyond its elastic limit and thus plastically deformed. A distinction is made between the following process groups:
  • Forming under compressive conditions according to DIN 8583 (rolling, free-forming, swaging, indenting, pushing through),
  • Forming under a combination of tensile and compressive conditions according to DIN 8584 (drawing through constricted tool orifices, deep drawing, spinning, forming by raising, upset bulging, hydroforming),
  • Forming under tensile conditions according to DIN 8585 (stretch reducing, bulge forming, stretch forming),
  • Forming by bending according to DIN 8586 (with straight-line or with rotating tool movement),
  • Forming under sheering conditions according to DIN 8587 (twisting, shifting).

In addition, there are other forming processes such as vault structuring, crumpling, high-pressure torsion and the Guerin process.

Cold and hot forming

In sheet metal working, a distinction is made between cold forming and hot forming.

In cold forming, the deformation takes place well below the recrystallization temperature of the material, usually at room temperature. This means that higher forming forces are required. The dislocations and residual stresses in the metal lattice caused by cold forming result not only in an increase in hardness and yield strength but also in a change in the magnetic and electrical properties. The initial permeability and electrical conductivity are reduced. In the case of steel, permanent magnetization is possible. Other advantages of cold forming are:

  • Possibility to achieve tight dimensional tolerances,
  • Increase in the strength of the material,
  • Reduction of ductility, and
  • No scaling of the surface.

The main cold forming processes include:

  • Cold rolling,
  • Deep drawing,
  • Bending,
  • Drifting,
  • Peening,
  • Hammering, and
  • Pressing.

Hot forming comprises all forming steps which take place above the recrystallization temperature of the material. The hardening that takes place during forming is accompanied by recovery and softening processes in the material. As a result, high degrees of forming are possible despite low forming forces. The following points must be taken into account during hot forming:

  • Hot forming has poorer dimensional tolerances and surface finishes than cold forming,
  • Hot forming leads to slightly scaled surfaces.

Methods of hot forming include:

  • Forging,
  • Hot rolling,
  • Mold hardening,
  • Extrusion.