Rod-shaped semi-finished products are used to produce cold forged components which are manufactured by continuous or block casting and a subsequent rolling process. As a result, the semi-finished products already contain damage (e.g. pores) which evolves further by the cold forging process. The mechanical properties of forged components are, thus, the result of residual stress, strain hardening, and the damage occurring along the process chain. The load path occurring during the process (sequence of stress, strain, temperature, and strain rate) influences these properties. Accurate and general knowledge of the influence of a load path change, e.g. by a variation of the process parameters or an alternative process route, on the evolution of damage have not yet been developed sufficiently and systematically according to the state of the art. For this reason, the process chain-related development of damage in the design of products and process routes has so far not been considered.

The aim of this project is to analyze, predict, and control the damage evolution in cold forging. Damage control requires the design of modified and possibly novel process routes, based on the analysis of the causal relationships between the process and damage, as well as the development of new cold forging technologies that enable the production of forged components with defined, use-adapted damage.

In the first funding period the influence of differently applied stress states as well as their sequence and their superposition on damage evolution are analyzed based on basic tests (compression, tension, and torsion tests). In addition, it will be investigated to what extent the load path can be influenced during cold forging and how the load path change affects the damage. For this purpose, the influence of geometric and process parameters (extrusion strain, shoulder opening angle, transition radii, friction) as well as the influence of different process routes (for example multi-stage extrusion and / or with back pressure) on the load path and on the resulting damage are analyzed by forward rod extrusion. At the beginning of the first funding period the relationship between load path and damage is qualitatively analyzed on the basis of existing damage models (Lemaitre and Gurson-Tvergaard-Needleman) and validated by experiments. In the further course of the project the models will be replaced by the models developed in project area C in cooperation with project S01.

Based on this, the transferability of the gained findings to other cold forging processes will be examined in the second funding period. The focus of this period is also on technology development in the form of novel or modified cold forging process routes. In the third funding period thermal influences on the forging process, e.g. integrated local heating, are studied. In addition, the knowledge from the previous funding periods is used to derive a damage-reduced process chain for the production of industrially forged components.

Project leader
Prof. Dr.-Ing. Dr.-Ing. E. h. A. Erman Tekkaya
Institute of Forming Technology and Lightweight Components (IUL), TU Dortmund University

Project coordinator
Oliver Hering M. Sc.
Institute of Forming Technology and Lightweight Components (IUL), TU Dortmund University