FP5/GROWTH-COLT

Title: Improvement of Service Life and Reliability of Cold Forging Tools with Respect to Fatigue Damage due to Cyclic Plasticity

Partners: THYSSEN-KRUPP-PRESTA (LI), BÖHLER (AT), DANFOSS (DK), ROCKFIELD (UK), C3M(SI), Risoe National Laboratorie (DK), University of Erlangen-Nuernberg (DE)

Summary: Cold forging is the most efficient technology for mass production of high precision parts for transport, mechanical and electrical industries. There is a large potential for reducing the production costs in this industry by improving reliability of tools. The optimisation potential relies on enormous scatter of tool life which is currently encountered in the production. This is because cold forging tools operate under extreme conditions where slight variations in process load and material strength have a strong impact on tool failure. The main objective of this project is to develop a methodology to increase tool life and to reduce its scatter. Key problems are related to fundamental understanding of the deterioration mechanisms, identification of stochastically relevant process parameters and introduction of such technological modifications in steel making, tool manufacturing and cold forging which will lead to more economical production.

Description of the work: Since more than 80% of tools in cold forging fail because of fatigue damage due to cyclic plasticity the fundamental research will be focused on this deterioration phenomenon. Microstructural models will be developed to describe the relationship between microstructure and mechanical properties of tool steel materials while phenomenological models will be used to estimate their fatigue resistance under operating conditions. These phenomenological models will be implemented into Finite Element (FE) code for sensitivity analyses, inverse modelling, and optimisation of forming processes and tooling systems. The stochastic nature of cold forming processes will be taken into account by combining statistical interference analysis with Strength Versus Load (SVL) concept and FE models. This will provide a theoretical basis for developing a computer aided decision support system which will assist technology designers to identify those stochastically relevant parameters which have a strong impact on the reliability of tools and must therefore be more strictly controlled during steel making, tool manufacturing, and cold forging production. The investigations will be supported by experimental measurements and testing in laboratory environments, pilot plants and industrial mass production. This will include advanced mechanical and fatigue testing, assessment of internal stresses and structure details by neutron diffraction methods and high-energy synchrotron X-ray techniques as well as measurements of thermomechanical processing conditions.

Figure: Cold forging products