Internal high-pressure forming is a process for manufacturing lightweight components, especially automotive parts, with advantages of lower cost and weight reduction, better structural integrity and increased strength and sti ness over the conventional stamping process. One of the typical failure modes, including wrinkling, buckling and splitting, will occur through an unreasonable combination of the control parameters: the internal pressure and the axial punch feeding. In most previous papers, wrinkling is considered to be a failure mode. However, not all wrinkles are defects. The collection of materials in an expanding area by the formation of wrinkles is an alternative method for obtaining a preformed shape in the hydroforming die. In this case, the key point is to obtain`useful' wrinkles instead of`bad' wrinkles. In this paper, an investigation will be conducted on how to control the shape of the wrinkle waves and its e ect on the thickness distribution after hydroforming by using ®nite element simulation. LS-DYNA ®nite element software is used in this paper. An experiment has been carried out and the results obtained from experiment and simulation are in good agreement.

Due to the requirement of lightweight in the automotive industry, aluminum alloy components with irregular cross sections have been used for body-in-white parts. In order to obtain an aluminum alloy cross member with uniform thickness distribution and acceptable dimension accuracy, a hydro-forming process of a 6063-T4 aluminum alloy cross member was studied by experimental research and numerical simulation. To avoid severe thinning and bursting during hydro-forming, the design of experiments according to a central composite design method was carried out, and the significance of pre-form structural parameters was discussed on thinning. According to the optimum pre-form shape, experimental researches were then conducted on thickness distribution of typical sectional profiles and dimension accuracy. It is shown that the maximum thinning is 14 %, which is located on sectional profile B-B. The deviation of circumferential dimension accuracy along the axial direction is 0.33 %. The maximum dimensional deviation at sectional profiles A-A and B-B is 0.19 and 0.22 mm, respectively; accordingly, the dimension accuracy along the width direction is 0.4 and 0.31 %, respectively. Finally, a sound hydro-formed cross member is obtained.

Friction stir welding (FSW), as a solid state joining technique, has emerged as an efficient method for manufacturing tailor-welded blanks to optimize weight or performance in the final component. As the basic design of lightweight frame structures in the automotive and aircraft industry is frequently based on tubular profiles, the joining strategies and forming technologies have to be developed accordingly. In the present study, FSW tube was produced by a novel processing sequence. The plastic deformation characteristics during hydroforming were experimentally and numerically investigated with two types of end condition. The hydroforming performance of the FSW tubes was mainly investigated by die-bulge forming with fixed ends, and the wrinkling behavior during hydroforming was analyzed by employing axial feed on the tube ends. It is found that hydroforming FSW tube is a new deal and does show a few peculiarities. The FSW tube exhibits a spiral weld and the basin-shaped nugget. Finegrained structure is retained during tube forming. The thinning of the tube in axial direction shows M-shaped distribution during hydroforming. The severe thinning is observed at one quarter of the expansion zone from symmetry plane. In the hoop direction, the base material near the weld suffers severe thinning due to the high hoop and axial tensile stress. The thickness distribution greatly depends on the sequence of the contacting die and the variations of the curvature radius of the tube during hydroforming. Moreover, the weld shows an inhibitory effect for the generation of the wrinkles and decreases the number of the wrinkles as compared to the seamless tube during hydroforming. This effect is more obvious when the forming pressure is lower.

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