Research On Hydroforming Of Profiled Cross-section Hollow Component

Tube hydroforming (THF) is an advanced process of forming closed-section, hollow parts with different cross sections by applying an internal hydraulic pressure and additional axial compressive loads. In the past few years, it has been rapidly developed as a remarkable research area. But it is still not fully implemented in the domestic industry due to its complexity of process and short history. In particular, tubular hydroforming, which makes onestep forming of complex closed hollow parts possible, is effectively used for high volume application in automotive industry because various closed sections resulting in the highest bending and torsional stiffness sectional shape can be easily formed by use of this technology. In this paper, the hydroforming of straight tube with axial feeding and hydroforming of bended tube without axial feeding are studied by plasticity theory, numerical simulation and experiment, the forming rules and process control strategy are discussed.Based on metal plasticity theory, the stress strain state and process control principles of two types of hydroforming are proposed. The non-symmetry T-shaped tube is simulated, and the material flow, stress strain state and thickness distribution of non-symmetry T-shaped tube are analysised, the influence of process parameters such as axial feeding, limit pressure, loading path, friction condition and counter force are discussed.Then the process control strategy of this kind of hydroforming parts is delivered. The typical bended hydroforming part—front transom is also investigated, the FEA model of whole process including bending and hydroforming is set up and the influence of bending process is discussed. Aim at the characteristic of profiled cross-section tube hydroforming, this paper present a per-loaded pressure loading path. By this loading path, the forming result is better than that of conventional loading path. The forming part can obtain smaller corner radius and uniform thickness distribution.The strain-based forming limit diagram (FLD) as an effective criterion of sheet forming quality has been extensively applied in THF research. But the traditional strain-based FLD is a function of strain history. Strain path effects undermine the utility of the traditional FLD for formability assessment of processes that are inherently non-linear, such as hydroforming of tubes. In this paper, the stress-based forming limit diagram (FLSD) is introduced in the forming limit investigate of tube hydroforming. The forming limit of LF21 Aluminum alloy sheet was tested and its forming limit diagram (FLD) was determined. Then the FLSD of LF21 was constituted by transformation formulas between limit strain and limit stress and Hill'79 yield model. This FLSD was used in conjunction with finite element simulations to predict the onset of fracture and limit forming pressure in tube hydroforming. Results indicate that the simulation result compares well with the theoretics analysis and experimental result and the FLSD is able to predict the forming limit of tube hydroforming with remarkable accuracy.In order to overcome the disadvantages of conventional optimization methods, a feedback optimization methods consist of fuzzy logic control algorithm and adaptive simulation is proposed. By failure control rule constituted, failure indicators obtained from the simulation results are used as the input of the fuzzy logical control, and the output sets of the fuzzy logical control are used for adjusting the loading path. In this way, a reasonable loading path for hydroforming parts can be obtained. Its validity is verified by the optimization results of T-shaped tube and front transom.At last, on the basis of simulation and optimization results, the experiment equipment and forming die are produced and a series of experiments of front transom are performed. From the experimental results, the influence of pressure loading path pattern and friction condition are investigated. Then, the results from experiments are compared with the results from the FEA simulation and optimization, the percentage error between experiment and simulation results is not exceeding 10%, validated the veracity of FEA results.