Effects of anisotropy in drawing and extrusion processes of bulk metal forming

The effects of anisotropy of axisymmetric materials (round bars, tubes) on metal forming processes are discussed. These effects are strongest for thin-walled hollow materials in metal forming processes when the wall thickness is not predetermined by the die (tube drawing without mandrel, free extrusion of hollow components). Similarly to the normal anisotropy of sheet metal, a high radial anisotropy increases the resistance against a variation of wall thickness in tube drawing. There are also effects in forming solid materials such as forward extrusion of bars whereby the buckling of cross sections is influenced through the variation of radial anisotropy with the distance from the axis. The favourable anisotropy properties depend on the actual priorities. If, for example, for a metal forming process the material anisotropy results in high compressive stresses this may be favourable for increasing the ductility of the material whereas the increase of the load acting on the tool reduces tool life.