A METHOD FOR DETERMINING FREE SURFACES IN STEADY-STATE FINITE-ELEMENT COMPUTATIONS

Some forming processes mainly consist in steady-state phases, and should preferably be modelled by steady state approaches to save computing time. However, some difficulties occur as the geometry of free surfaces is not fixed: the domain on which the computation is to be performed is not known a priori. An optimal control method for determination of these free surfaces is presented and its inclusion in a finite element code is described. Validation of the technique is made on a classical problem: die swell in polymer extrusion, for which well established numerical solutions exist. It is shown that the proposed method correctly models this phenomenon. It is then applied to two cases of rolling operations: flat rolling of slabs, and shape rolling (square-oval pass), with comparison to simulation experiments on plasticine.