1998-09-29

Towards Further Understanding of the Mechanics of Tube Hydroforming 982276

The objective of this work is to shed some further understanding into the mechanics of tube hydroforming. Initially this process was developed with the philosophy of forming the tube around the pure shear line, such that the deformation can be obtained with the least changes in thickness. To design a process to achieve this intent is very challenging, considering the complex shapes that are designed.
The work starts by examining some simple geometries to provide an understanding and a methodology for the process design. It is shown that by changing the amount of material feed in, the part can be made to split, wrinkle or form around the pure shear line, and hence with the least thinning at the areas of interest. The work also confirmed that the material r value has a major impact on the ability of the material to maintain its thickness in this process; the higher the r value, the better the formability and the less changes in thickness.
The mechanics of pre-bending are also examined to illustrate the physical material requirements during the preform stage. It is shown that the more constraints during tube bending, the more the energy requirements and the more buckling that can result.
The work uses a special version of the FTI/FAST_FORM3D program, for determining the strains and energies required to transform the tube to the pre-form or the final configuration.
The paper concludes by highlighting a methodology for the pre-form and final form design. In essence the original tube diameter and length are designed to optimize material content and minimize strains in the part, and hence establish a relationship between original tube diameter and amount of material feed in. The pre-form is then designed to ensure balance of material content in individual sections, as well as satisfy the least strain reversal from the pre-form to the final form.

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