An Investigation On One-step And Two-steps Tube Hydroforming(THF) Using Finite Element Method

The traditional manufacturing of cars components is producing them apartly. The technique results in a low precision of assemble and a waste of welding working procedure. With the development of motor industry it is more important to cut the cost by lightening the cargoes with less materials and high stiffness components. The occurrence of new technique using tube hydroforming(THF) can make it come true. The THF can not only lighten the cargoes significantly, but also help saving the materials. This new technology benefits the modern motors manufacturers.THF has lots of advantages such as: cut down the cost of the manufacturing, use less materials to get a lighter component and achieve components with complicated shape. The working procedures are less and the production has a high precision. The component obtained by this method is a whole structure, thus the strength and the stiffness of the components get better. Quasi-static process improves the useful life of the moulds. The number of moulds is also less than before. But in the process of manufacture, there exists lots of defects such as wrinkle, bursting, buckling and folding which should be paid attention to. To probe a optimum processing conditions is a main task of this thesis. In this study, geometrical models were prepared with Unigraphics (EDS Inc., USA), Non-linear analyses were performed using ANSYS/LS-DYNA (ANSYS Inc., USA) finite element package.The effect of some factors like length-diameter ratio and the thickness of the tube was discussed in this paper. The results shown that there were some regulation in the extent of the factors. Thereafter, the loading path was optimized by matching the stroke curve of extrude rod and pressure curve of inner liquid rationally.In this paper, the technique of two-steps method to process tube was applied to replace the one-step method in order to improve the forming limit of the components. The simulation of THF was performed by two steps according to explicit-to-implicit and implicit-to-explicit algorithms. Between the two steps springback should be taken into account. The results proved that the two-steps THF could compare with the one-step THF for producing components with improved forming quality.The distribution of deformation extend in two-step methods of THF was carefully determined. Five simulation experiments with different deformation extents were compared and analyzed and the concluded that there would be a most suitable condition in the extent of the first step which made the propoties of the tube be the optimization.