COLD-FORGING MODELIZATION - COMPARISON BETWEEN FORGE2 AND ABAQUS

Forge2 and Abaqus FEM softwares are regularly used at Irsid and CREAS for the simulation of cold forging processes. Abaqus is a development software, widely known as a reference for non linear simulations, wher eas Forge2 is specifically adapted to 2D forming simulations, using au tomatic remeshing of 6-node quadratic elements. The aim of this paper is to compare the results of these two approaches in the specific case of cold forging : the influence of element definition, automatic reme shing, formulation and resolution discrepancies are discussed. Two axi symmetric geometries have been chosen for this study : a tensile speci men (simple test with no tool contact and no need of remeshing) and a wheel spindle (more complex test of multi stage forging with direct ex trusion and heading). The different simulations use 6-node quadratic e lements (Forge2) and 4-node linear elements (Abaqus). In order to stud y the influence of the element geometry the tensile test simulation ha s also been performed by Abaqus with the 6-node quadratic element mesh . All the simulations have been carried out at constant strain rate an d isothermal conditions. Input data are rigorously the same for the tw o softwares. Moreover in both cases, the material behaviour and the gr owth of ductile damage have been defined with user subroutines. Compre ssion and axisymmetric notched tensile tests have been used to determi ne the parameters of the mechanical behaviour and ductile damage model , respectively. For each selected geometry, we have compared : - the f orce-displacement curves; - the geometry of the specimens; - the conto ur lines of plastic strain, hydrostatic pressure, equivalent stress an d ductile damage (before and after spring back). The results of the si mulations show that, in each case, the force evolutions are comparable . The geometries of the tensile specimens for different elongation val ues are identical. A comparison of the wheel spindle geometry at the f inal forging stage shows that the enclosed parts are also identical. W eak discrepancies can be observed only on the free surfaces, e.g. on t he shape of the head. These discrepancies, explained by the difference s in the contact formulation, are small enough to guarantee the indust rial tolerances. These two observations imply that the calculated mate rial flow is independent of the FEM software (Abaqus or Forge2) and of the element geometry (6-node quadratic or 4-node linear elements). Ex cept in the regions of the wheel spindle where Abaqus mesh is very dis torted (no automatic remeshing), the contour lines of the different si mulations are very similar. The most important discrepancies can be ob served in the calculation of the hydrostatic pressure. The simulations indicate the regions of highest ductile damage, which correspond perf ectly with the experimental fracture zones. Moreover, further wheel sp indle simulations have been made incorporating the elastic response of the tools. Once more, the simulations give comparable results, includ ing the hydrostatic pressure in the tools. By comparison with the refe rence calculation using Abaqus code, Forge2 has been shown to provide valid results in the specific case of 2D axisymmetric cold forging. Th is software is already in industrial usage for the optimization of for ging schedules.