Numerical Simulation Studies On Tube Hydroforming For A Frame Side Rail

Tube hydroforming(THF) is an advanced process of forming closed-section, hollowparts with different cross sections by applying an internal hydraulic pressure andadditional axial compressive loads. In the past few years, it has been rapidlydeveloped as a remarkable research area. But it is still not fully implemented in thedomestic industry due to its complexity of process and short history. In particular,tubular hydroforming, which makes one step forming of complex closed hollow partspossible, is effectively used for high volum application in automotive industrybecause various closed sections resulting in the highest bending and torsional stiffnesssectional shape can be easily formed by use of this technology.In this paper, the hydroforming of straight tube with axial feeding andhydroforming of bended tube without axial feeding are classified, the hydroforming ofbended tube without axial feeding are studied deeply by plasticity theory, numericalsimulation and experiment, the forming rules and process control strategy arediscussed.Based on metal plasticity theory, the theoretical calculation formula of mainhydroforming process parameters such as friction condition, bulging pressure, limitpressure, axial feeding, loading path and counter force are proposed. According to theforming characteristics of the studied frame side rail, a finite element model of squaretube with bending axis is built up as the simplified mechanical model.Through finite element simulation, the influence of material flow as well as valuerange of main hydroforming process parameters. Four common loading paths arescreened by conventional testing optimization method, finally polygonal lines chosento be the loading path in this research. Based on the simulation results, hydroformingof bended tube without axial feeding processing rules and process control strategy arediscussed.Then, the typical pre-formed hydroforming part-frame side rail is also investigated, the FEA model of whole process including bending, pressing and hydroforming is setup and the influences of bending and pressing process are discussed. The Influencelaw main hydrofoming processing parameters such as material flow and tubethickness distribution, tube blank size, loading path are proposed.Aiming at the characteristic of profiled cross-section tube hydroforming, this paperpresent a per-loaded pressure loading path in pre-forming process. By this loadingpath, the forming result is better than that of conventional loading path. The formingpart can obtain smaller corner radius and uniform thickness distribution.Tube hydroforming is a multiple nonlinear process, the strain path is complicated,in forming process, always exist wrinkles, cracks. Hydroforming is a complicateddynamic process, the relationship between the internal pressure and axial feeding isdifficult to propose through explicit function. Currently, testing optimization methodis widely used in the study of traditional numerical simulation and the multi-objectiveoptimization method. In this paper, this method is still continued to work. A largenumber of simulations have been done to get an ideal forming result.Eventually, the mechanical properties of original frame side rail structure and newdesign of tubular frame side rail structure are coMPared to validate the feasibility ofthis design.