Recently, hydroforming technologies have been applied to complex-shaped auto mobile parts, so that the number of hydroforming parts after bending has increased. In this study, deformation behavior of a tube during hydroforming after bending is investigated. First, a tube is bent by 45 degrees by rotary draw bending. The bent tube is then introduced into a hydroforming die and expanded to a rectangular cross section at a 50% expanding ratio. We use several types of loading paths of internal pressure and axial feeding. Results show that, in the case of a high-initial pressure path, bursting occurs on the intermediate side of the tube during axial feeding. When the internal pressure is decreased to prevent bursting, bursting still occurs on the compression side in the case of high pressure during axial feeding. On the other hand, in the case of low internal pressure during axial feeding, wrinkles form after a maximum pressure increase. Finally, a sample that features no bursting or wrinkles is successfully obtained. It is found that the gap between the bent tube and the hydroforming die on the compression side should be small to prevent bursting or wrinkles from occurring, so that the bending radius before hydroforming should be large.
Recently, tube—hydroformed automobile parts have been appreciated for their features in improving fuel economy and crash safety. Hydroforming using conical tubes could be effective to obtain further complex shaped parts of cars. Generally, in hydroforming using conical tubes, it is difficult to obtain a large expansion ratio and a large work hardness because of difficulties in axial feeding. In this paper, two newly developed hydroforming technologies are proposed in order to enable axial feeding in hydroforming. Both technologies are relatively easy methods using special dies. Fundamental tests of the new hydroforming methods using conical tubes, which are made of high tension steel, are carried out. The expansion ratio and plastic strain after hydroforming are investigated. The effects of axial feeding on deformation are discussed.
Recently, tube hydroforming has been appreciated for its features in improving fuel economy and crash safety. Tubular hydroforming parts with a rectangular cross section are typical automotive parts. There are, however, problems in conventional hydroforming. The first problem is that a high internal pressure is necessary to obtain a small corner radius. The second problem is that thickness is largely reduced around corner portions. To solve these problems, the vertical double-action forming method is proposed. This method consists of two stages. The first stage is to form a tube into an elliptic cross-sectional shape. The second stage is to form a square cross-sectional shape by stamping under internal pressure. Experiments on the vertical double-action forming method are carried out. It is clear that, in this method, a small corner radius can be formed with a low internal pressure. The circumferential thickness deviations, furthermore, can be largely reduced by this method. By FE analysis the influences effects of equivalent stress and friction on thickness distribution are discussed in both methods.
Aluminum alloy sections have broad applications such as in general structures and automotive components. Owing to the increasing complexity of such components, there is an increasing demand for highly curved thin-walled sections. Therefore, reliable bending processes are required to manufacture such components without undesirable deformations such as wrinkling and folding, during bending. To prevent undesirable deformations and predict when they may occur, it is necessary to generate a significant amount of data from various forming configurations in which process parameters are varied. In this paper, we concentrated on the problem of bending square section thin-walled tubes and used finite element analysis to generate the data required for the prediction of working limits. Four different tube materials (A6063S-O, A6063S-T5, A6061S-O and A6061S-T6) were used to investigate the relationship between deformation behavior and material properties. Subsequently, the effect of using a wiper die on the working limit of extruded aluminum sections was investigated. The working limit was improved using a wiper die.
Extruded aluminum alloy sections are advanced materials composed of lightweight structural members. A secondary forming process such as bending is required when these materials are utilized for practical use. Some undesirable deformations such as flattening distortion, wrinkling and splitting occur during the bending process of light gauge tubes. Thus, the working limits for the shape and dimension of such sections are very important in designing lightweight constructions. In this study, a square tube, a square tube with a lateral direction rib, a square tube with a radial direction rib, an asymmetric channel, a hat channel and a channel were used in rotary draw bending with axial tension. Mandrels were selected to match the characteristics of the sections. The working limits for some thickness ratio and materials such as A6061S-O, A6061S-T6, A6063S-O and A6063S-T5 were introduced. This study shows that a working limit that depends on the type of cross section and on thickness ratio, and the application of axial tension to the draw bending of light gauge tubes are very effective in preventing wrinkling in rotary draw bending.
A novel semi-dieless metal bellows forming process with local induction heating and axial compression without using any conventional dies is proposed. Firstly, the thickening of a tube is induced by local heating and axial compressive force. Secondly, the buckling of the tube occurs, producing a convoluted shape. The seamless tubes used are stainless steel SUS304 with an outer diameter of 5 mm and a thickness of 0.5 mm and 0.3 mm. The effects of compression ratio on the profiles of the bellows such as convolution height, pitch and thickness are investigated experimentally. It is found that convolution height can be controlled by compression ratio. Additionally, the mechanism of this process for fabrication of the metal bellows can be clarified by loading curve during processing. Furthermore, the validity of a two-step compression technique for improving convolution height and pitch is verified. The fundamental of the proposed technique can be confirmed as a basic processing key to fabricating metal bellows with various dimensions and small quantities.