Welding is widely used for joining materials. Residual stress remains near welded joints because of the high temperature attained during welding. Tensile residual stress on the surface of the material degrades its fatigue strength. Some methods of reducing residual stress such as heat treatment and shot peening can be used. These methods require special equipment and are time-consuming. On the other hand, ultrasonic vibration can be used to improve the precision of the machined surface and to cut hard metals. In this paper, we propose a new method of reducing residual stress using ultrasonic vibration during welding. The proposed method is applied to objects such as a car wheel. The transmission of ultrasonic vibration is an important factor in curved structures. An effective transmission device of ultrasonic vibration is developed. It is found that residual stress is reduced by about 20∼30% when ultrasonic vibration is used during welding. The effectiveness of the proposed method is demonstrated by an analytical method using a model considering elastoplastic characteristics.

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Processes for reducing the number of stages and adjusting wheel sizes in one-piece press forming of automobile steel wheels without welding were proposed. The number of stages was considerably reduced from 16 stages to only 9 stages by combining the deep drawing and ironing stages and by adding a holding die in the flaring stages. The width of the rim was adjusted by the length of punches in the redrawing stages, and the offset of the attachment of the disk to the rim was adjusted by the punch stroke in the disk finishing. In addition, the humps of the rim flange for fixing the tire were formed in the flaring and flanging stages. The proposed forming sequence of the one-piece wheels was evaluated by both finite element simulation and miniature experiment.

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Tubes with an internal rib have a high strength in comparison with those without a rib. These tubes can be used, for example, as structural parts, heat sinks, and impact absorbers. The existence of some holes at the rib enhances the function and value of the tubes. The appropriate positioning of holes at the rib reduces the weight of structural parts while preserving strength. In the case of heat sinks, holes change the fluid flow and realize effective heat transfer. In this research, a new extrusion method is proposed for manufacturing tubes with a holed rib. The method involves the use of a unique mandrel that has a slit along its axis and two guides at the slit exit. A holed plate is fed through the slit and made into a holed rib of the tube. The flow of the billet is investigated. In particular, the effect of the guide height is clarified in this study.

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