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Springback in metal forming process often results in undesirable shape changes in formed parts and leads to deterioration in product quality. Even though springback can be predicted and compensated for through the theories or methodologies established thus far, an increase in manufacturing cost accompanied by a change in die shape is inevitable. In the present paper, it is suggested that the cost accompanied with springback compensation can be minimized while allowing the processing of various three-dimensional curved surfaces by using a flexible die composed of multiple punches. With the die being very flexible, the iterative trial-and-error method can be readily applied to compensate for the springback. Thus, repeated designing and redesigning of solid or matched dies can be avoided, effectively saving considerable time. Only some adjustments of punch height are required. Detailed designs of the flexible die as well as two core algorithms to control the respective punch heights are described in this paper. In addition, a closed-loop system for the springback compensation using the flexible die is proposed. The amount of springback was simulated by a finite element analysis and the modified displacement adjustment (DA) method as the springback compensation model was used in the closed-loop system. This system was applied to a two-dimensional quadratic shape problem, and its robustness was verified by an experiment.

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important for developing energy systems such as fuel cells and metal–air batteries. Precious metal catalysts, such as Pt and IrO2, have been considered electrochemical catalysts because of their excellent activity for the ORR and OER. However, their disadvantages, such as low durability for long-term operation and high price, necessitate the development of alternative electrochemical catalysts. Transition metal oxides with excellent electrical conductivity, high efficiency, and stability have been considered alternative electrochemical catalysts owing to their ORR and OER activities, which are similar to those of precious metal catalysts. Therefore, in this study, composite catalyst materials comprising Co3O4 and CoFe2O4 spinel oxides were synthesized via hydrothermal synthesis. The synthesized composite oxides exhibit bi-functional electrochemical catalytic activity for ORR and OER owing to the large active surface area and increased number of oxygen vacancies via the nanostrain in Co3O4 nanoparticles.

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