Two-dimensional finite element approximation of the hexagonal bolt forming process

In cold forging industry, it is well known that deformation mechanism of the billet and forming tools should be known during forging to properly design the dies and estimate the tool life. Since three-dimensional simulations of forging the geometrically complex forged parts involve with large computation time and effort, two-dimensional (2D) axi-symmetric approximation might be beneficial for an initial die design and selection of the machine capacity and die material. In the present study such an approximation was made for the two-stage hexagonal bolt forming process of two different carbon steels for comparative study. For simulations, in-house rigid-viscoplastic finite element (FE) programs were used for the deformation analysis with 2D and 3D approaches with hexahedral and tetrahedral elements to compare computation time, load requirement, distributions of the effective strain and stress, and interface boundary die force among three cases. The elastic analysis of tools was also carried out for comparison. It was found out that the load values and strain distributions were similar between 2D and 3D simulation results. However, elastic stress distributions in lower dies for 2D and 3D cases showed a relatively reasonable difference incurring the variation of tool life. For 3D simulations hexahedral element was more effective under the present investigation condition.