A Study of Preforming Design in the Tube-Hydroforming Process
Date Issued
2011
Date
2011
Author(s)
Chiang, Yen-Hui
Abstract
Nowadays, Tube hydroforming (THF) technique has been popularly applied to the car body structural components. The advantages of employing THF process over the conventional stamping and welding process have been lightweight and high strength for the car body structure. There are three operations in a complete THF process, which are tube bending, preforming, and hydro-forming. In the present study, the preforming die design and the loading path adopted in the hydroforming operation for manufacturing a twist beam used in a real axle were examined. In addition, the punch shape for hydro-piercing a scrap-attached hole was also investigated. Both the finite element simulations and the experimental approaches were employed to complete the analysis and die design.
Since the twist beam bears a relatively small curvature in one plane, it is difficult to bend the tube by a bending machine and needs to produce the bend in a preforming die. Also due to the deep V-shaped cavity along the curved axis of the twist beam, one or two more preforming operations are required to provide an appropriate preformed tube to the subsequent hydroforming operation. In the present study, the number of preforming operations and the geometry of each prefoming die are determined by the finite element analysis. It is found that three preforming operations are required for hydroforming this curved twist beam if a cam mechanism is not involved in the preforming operation. In addition, different loading paths are designed for the hydroforming operation to investigate the formability of this twist beam using the finite element simulations. Based on the finite element analysis, an optimum single-step loading path was established. However, a two-step loading path that would improve the maximum thinning a little bit was also developed.
As for the hydro-piercing operation, different punch shapes were designed to investigate the hole-piercing performance. The hole-piercing experiments were conducted first in a stamping process without hydraulic pressure acting on the opposite side of the sheet. The appropriate geometry of the punch shape was then applied to the hydro-piercing operation. The finite element simulation results indicate that the proposed punch shape could pierce the hole with the scrap remained in the tube that is required by the part design. The developed preforming die design concept, the loading path used in the hydroforming operation, and the punch shape for the hydro-piercing process could provide a valuable reference to the future study in the tube-hydroforming research field.
Subjects
tube-hydroforming
twist beam
rear axle
preforming die design
hydro-piercing
loading path
Type
thesis
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