In this study, the closing behavior of internal voids was examined by deformation analysis involving the 2-D finite element method (FEM) that imitated voids in steel ingots in the compression process (upset process). In the compression process, a model experiment that uses internal voids is carried out to confirm the accuracy of deformation analysis. By comparing the model experiment with an analytical result, it was confirmed to imitate the internal void behavior by this analysis. The relationship between reduction ratio and void shape/void position was investigated by the analysis. In the forging process, the closing evaluation value of internal voids (Q value) was calculated by a model experiment and 3-D FEM. Using the analysis result, a limited value of the closing behavior of void is quantified, and it is now understood that the void closes at more than Q = 0.21. In addition, the forging process of filling the above-mentioned value was designed by the Taguchi method. The predicted Q value in the case of using the Taguchi method almost corresponds to the value calculated by deformation analysis. It was clarified that the process is capable of being designed simply.
