In this paper, the effects of theoretical models of materials and dies on finite element (FE) predictions of a hot forging process are presented, to provide process design engineers and researchers with some useful insight into the theoretical approaches on which they rely. The material was assumed to be rigid-viscoplastic or rigid-thermoviscoplastic and the dies were assumed to be rigid or elastic. The problem of die fracture occurring during the hot forging of aluminum fixed scroll was studied. This process is particularly sensitive to theoretical models, mostly because the die-stress component causing the die fracture has a relatively weak relationship with the forming load. A fully thermo-mechanically coupled FE analysis considered die elastic deformation and was first conducted to reveal die fracture with emphasis on the maximum die stress and forming load. The predictions for four simulated cases using different theoretical assumptions of the material and die were then compared. These were also compared with experiments, undertaken to observe the relationship between maximum die stress component and forming load, to reveal the effects of material and die models in FE predictions. The differences in forming load, die stress and their variation with time among the four cases were clarified quantitatively for different die and material models, to provide some insight into metal forming for engineers and researchers.

Progressive shearing with blanking dies is commonly employed to produce large quantities of tiny sheet metal electronic parts. Sheet metal pins, which are narrow and long, that are sheared with a progressive die set are often twisted. The twist in the sheet metal pins, which usually occurs in the final shearing operation, generally decreases with increasing blank holding force. The blank holding forces in all shearing operations are not the same because of different shearing positions and areas.In the current study, the optimal layout of the springs in a progressive die set to minimize the twist of the sheet metal pin is proposed. In order to find the holding force acting on the tiny narrow blanks produced with the proposed springs during the shearing process, the equivalent area method is used in the structural analysis. The shearing of the sheet-metal pin was simulated to compute the twist angle associated with the blank holding force. The constraint condition satisfying the pre-set blank holding force from the previous shearing operations was imposed. A design of experiments (DOE) was numerically implemented by analyzing the progressive die structure and by simulating the shearing process. From the meta-model created from the experimental results and by using a quadratic response surface method (PQRSM), the optimal layout of the springs was determined. The twist of sheet metal pin associated with the optimal layout of the springs found in the current study was compared with that of an existing progressive die to obtain a minimal amount of twist.