Service life of tools for precision forming

The tooling systems applied in production of cold forged components are repetitively subjected to very high loads. Despite of the high strength materials and prestressing applied to die inserts, these loads often cause local plastic deformation of the dies. Even though the plastic deformations caused by each forming cycle are relatively small they accumulate during the production and can eventually lead to the initiation of fatigue cracks. Once a fatigue crack is initiated it can grow and lead to the failure of tooling system. Statistical investigations show that more than eighty percent of cold forging tools fail in this way.

The designers are therefore interested in identifying and optimising those design parameters that have strong impact on the fatigue response of tooling systems. The response is modeled by an elasto-plastic constitutive model, which combines isotropic and kinematic hardening with continuum damage. This permits relatively precise modelling of stress/strain response of tool steels over large number of loading cycles and estimation of accumulated damage. A method for evaluating the sensitivity of damage to material parameters and optimisation can be combined with this approach.