Damage-induced performance variations of cold forged parts

Forming processes play a key role in the manufacturing of metal components. They allow for the economical production of geometrical shapes with reproducibly high quality. Strain hardening and residual stresses affect the performance of the produced parts. These factors are controllable and can even be utilized to increase the performance of the component. This, however, does not apply to damage. Damage in metals describes the decrease of the load-bearing capacity due to the appearance and evolution of voids. The aim is to analyse, predict, and control the evolution of damage in cold forging, to allow for a production of cold forged components with a defined, load-adapted performance. It was investigated numerically to what extent the load path, which is responsible for the damage evolution, is affected in cold forging. Subsequently, the effect of load path changes on the product performance was determined experimentally in the region of the central axis where the load path is affected most by the extrusion parameters. Hereby, a correlation between the occurring triaxiality during forming and the product performance by means of number of cycles to failure in multi-step fatigue tests, impact energy and Young’s modulus was observed.