Influencing the Evolution of Damage in Cold Extrusion

Funding: German Research Foundation (DFG)
Project: CRC/TRR 188 • Subproject A02
Contact: Dr.-Ing. Oliver Hering

Damage in terms of microscopic voids influences the performance of cold extruded components.

It has already been shown that the influence of geometric parameters, such as extrusion strain or shoulder opening angle, on the load path leads to a change in the microscopically measurable damage. The separated influence of damage on the performance of the components was determined by means of measurements of the stiffness E, impact energy, and the number of cycles to failure in fatigue tests. Damage evolution is reduced by systematic stress superposition using a counter punch in forward rod extrusion without changing the geometry of the produced component (see Figure a). Furthermore, shafts with multiple stages and varying process routes are investigated. The occurring counter pressure pc reduces the triaxiality η during forming, resulting in a reduced damage evolution and, thus, improved product properties. By changing the process route, the damage distribution can be affected locally (see Figure b).

Impact of counter pressure and process route on damage evolution and resulting product performance