| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 98 === The application of tube hydroforming technology to improve the structure property in lightweight and high strength has drawn much attention from the automotive industry. In the present study, the hydroforming process for producing a trailing arm was examined.
A tube hydroforming process usually consists of three forming operations: tube bending, pre-forming and hydroforming. In the present study, the analysis of cross-sections was conducted first to examine the manufacturing feasibility according to the part shape design. The tube-bending processes were then investigated using the finite element analysis. The tube may be pre-bent by a bending machine or bent in the pre-form die, called die bending, depending on whether the centerline of the bent tube is planar or not. The effect of the tube bending method on the formability of hydroforming was analyzed. It is found that the tube bent in a die is apt to causing local expansion that may lead to fracture in the final product. However, most of the local expansions which appear near the tube ends could be formed without fracture with the assistance of axial feeding.
For a bent tube not being properly placed into the hydroforming die cavity, an additional pre-forming operation is required to avoid pinching at die closing. Two types of pre-forming dies were proposed in the present study to cope with the pinching problem. The efficiency of these two different pre-forming dies was also evaluated with the use of the finite element simulations.
For a part with complex shape, axial feed is usually required to provide sufficient material at the position where the expansion ratio is much higher. In the hydroforming process with axial feeding, an appropriate loading path of hydraulic pressure is fundamental to the process design. However, in an actual production process, a simple loading path is always preferred. In the present study, the effect of various loading path on the formability of hydrofoprming a trailing arm was also discussed. The finite element simulation results show that the trailing arm with complex part shape could be produced with a constant hydraulic pressure during the axial feeding. The results obtained in the present study could be valuable references to the future research in hydroforming a complex-shaped part with advanced technology.
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