Determination of shrink fitting ratio to improve fatigue life of 2-layer compound forging die by considering elasto-plastic deformation of outer ring

Abstract

The shrink fitting ratio is an important design parameter in assembling compound forging dies. However, the determination for the optimal parameter to prolong die life is often neglected in the industry. Thus, the authors propose a method to identify optimal shrink fitting ratio by the use of master fatigue diagram to achieve maximum fatigue life where the working conditions under multi-stress tension-compression mode and various oscillation amplitudes are considered. In this paper, a master fatigue diagram was made from experimental results obtained for the die insert material SKD11. The 0.2% yield stress and ultimate tensile stress boundaries of the shrink ring material SKD61 obtained from FEM are then superimposed onto the master fatigue diagram. The modified master fatigue diagram is applied to determine optimal shrink fitting ratio for the 2-layer compound forging die in axi-symmetric forging. The method shows the capability of improving fatigue life by increasing the shrink fitting ratio into the elasto-plastic region of the shrink ring material.