Influence of a modified drawing process on the resulting residual stress state of cold drawn wire

Torsion bars are used in automotive engineering as well as in other industrial applications. Such elements are produced by bending cold drawn wires. In conventional drawing processes tensile residual stresses occur near the surface of the wire. Small bending radii, which are required in limited assembly spaces, result in component failure due to reduced formability. Additional operations such as heat treatment or shot peening are necessary to influence the residual stress of the wire and to improve the dynamic stability of the torsion bar. The aim of the research is to reduce tensile residual stresses near the surface of the wire in order to eliminate process steps and to enhance formability. Therefore, a forming technology is developed by using a modified drawing die geometry on the basis of gradation extrusion. Finite element simulation is used to investigate the influences of element geometry, number of elements and process modification on the resulting residual stresses after wire drawing of a steel alloy. The results are evaluated and compared with the conventional wire drawing process. Furthermore, the requirements for the design of an experimental test device will be outlined as well as the measurement of the residual stresses by using X-ray diffraction.