Optimisation of open die forging condition and tool design for ensuring both internal quality and dimensional precision by three-dimensional rigid–plastic finite element analysis

Focusing on the rough forging stage of the hot open die forging process, the influences of anvil design and pass schedule on the internal quality of forged billet have been numerically analysed using a three dimensional rigid-plastic finite element method. By analysing the strain distribution newly added by one forging stroke, it has been clarified that the region where a workpiece contacts an anvil can be divided into four zones according to the deformation and, in the zone where a dead metal region arises at the surface, high strain is obtained at the centre. As a result, as regards the anvil edge shape design, it was found that it is effective to select an arc of small radius to obtain high strain at the centre. Moreover, in order to ensure both internal quality and dimensional precision of a forged surface, it has been revealed that it is effective to apply a small curvature to the flat surface of an anvil. The results have enabled a fundamental scheme to optimise tool design for ensuring both internal quality and dimensional precision to be established.