In the present study, the loading path with constant internal fluid pressure during axial feeding to hydroform an automotive structural part with higher expansion ratio was investigated. The axial feedings employed at various internal fluid pressures were simulated by the finite element method. It is found that the axial feeding applied at a favorable internal fluid pressure, the production part with higher expansion ratio still could be made. Compared with other loading paths published in literature, which are mainly linear paths, the proposed loading path provides a simple approach to achieve better performance in the hydroforming process. The factors causing wrinkling fin the hydroforming process were also studied by analyzing the relationship between the die face shape and the material flow in the die cavity. An optimum die face design that avoided pinching at the die closing process was then proposed. The actual hydroforming process for manufacturing the automotive structural part was conducted as well in the present study to validate the proposed loading path and the optimum die face design. The consistent agreement between the production part and the finite element simulation results confirms not only the proposed loading path and die face design, but also the effectiveness of the finite element analysis employed in the tube-hydroforming process.

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