Recently, the simple upsetting of high-strength steel has often been performed without heating and lubrication at a high compression ratio to improve the environment by sustainable manufacture and a productive automobile. Under these severe conditions, the extremely high pressure causes the tool to be elastically concaved. The shaped tool induces an increase in upsetting load and a decrease in the flatness of upset products. In this study, the convex tool with a small slope is investigated experimentally and analyzed by finite element method (FEM) to reduce the overload and improve the flatness. The obtained load (F_c = C₁CAY = C₁F_s) indicates a second correction factor C₁ for modifying the load F_s which is estimated by a conventional slab method as F_s = CAY, where the coefficient C is determined by friction coefficient and product height diameter ratio, and A and Y are the cross-sectional area and flow stress of the work, respectively. Additionally, the modified flatness α_t = C₂ (δ₀ - δ_R ) of the work is estimated by a combination of the elastic theory and FEM analysis, where the correction coefficient C₂ is determined by FEM analysis and δ₀ - δ_R is the elastic difference between the thickness δ₀ at the center and the thickness δ_R at the outer diameter of the work.

To design a drawing schedule for a wire with Fuchs' ovate section from a round wire, the effects of the cross-sectional shape and the reduction in cross-sectional area on underfilling have been investigated by experiments and numerical analyses. It has been found that under conditions where the axis ratio (major axis length/minor axis length) is less than 1.3, underfilling is suppressed when the area reduction is greater than 30 %. It has been confirmed that the lateral spread by drawing is very small, about 1 to 3 %, and not sensitive to the area reduction. Furthermore, the center position of the wire before drawing is distant from the center of gravity of Fuchs' ovate section when the area reduction is small, and the axis ratio is large. It has been determined that the center of gravity of the die hole almost matches that under conditions where underfilling is suppressed when the area reduction is large. The minimum initial wire diameter before drawing to suppress underfilling has been revealed.

In-process measurements using various sensors, including acoustic emission (AE) sensors and force sensors, in a cold forging process of bevel gears was performed in this study. Furthermore, metal flow in the forging process calculated by a simulation and the simulated results are fused with the results obtained from various sensors in a cold forging die set to evaluate the possible factors influencing the die life. The relationship between AE output and the influential factors is evaluated. As a result, it is found that there is a significant correlation between AE data and factors such as the change of the friction condition and the initiation and propagation of fatigue cracks. This result indicates that AE data can be used for evaluating the condition of dies during forging and have the potential to be a predictive indicator of die life.