Evolutional Friction Law in the Numerical Simulation of the Deep Drawing of a Rail

Abstract

One of the most relevant technological parameters for the accurate numerical simulation of the deep drawing process is friction, since the contact between the blank sheet and tools develops friction forces that act as supplementary boundary conditions that determine the final part shape. Most applications reported in literature are still restricted to Coulomb’s law with a constant friction coefficient over the entire process. Although it is consensual that state conditions of contact surfaces and consequently the friction behaviour are influenced by a large number of parameters, there is no agreement about a wide-ranging law to accurately describe the friction evolution. One possibility is to use phenomenological laws that accurately fit experimental data. A Voce type law is used in this work to describe the evolution of the friction coefficient over the entire process as function of the contact pressure. This type of law guarantees a good correlation with experimental data and also numerical stability. The Voce type law was implemented in the static implicit code DD3IMP. The analysis of the relevance of considering the evolutional friction law in the numerical simulation is performed for a U-rail. This shape was selected for this study due to the simple deformation mechanisms that are involved, but also because it is a rail specially conceived to emphasize 2-D springback defects. The blank sheet material selected is a 6016-T4 aluminium alloy. The plastic behaviour is modelled using the 1948 Hill’s criterion with isotropic and kinematic hardening. The numerical results obtained considering the evolutional friction law are compared with two other results obtained with: (i) a constant friction value of 0.10, normally used for this material in industrial practice and (ii) three constant friction coefficients for each contact zone (flat, die radius and punch radius).