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Free expansion of straight tubes is the simplest test to evaluate tube properties for hydroforming applications and to provide basic understanding of the mechanics of tube hydroforming. A circular cylindrical tube is sealed at both ends and fluid, usually water, is pumped into the tube to increase its internal pressure to bulge and burst the tube. Previous numerical simulations of the free expansion tube test were limited to modeling the midsection of the tube under various assumptions of deformation path. The simulation results obtained deviated from the experimental results under all simulation conditions considered. A new model is developed in this paper in which the whole tube is simulated instead of considering only its mid-section. Judged by the pressure-expansion relations, the model accurately predicted free expansion hydroforming tests results.

Sheet metal forming of automobile body panel consists of two processes performed in series: binder forming and punch forming. Due to differences in deformation characteristics of the two forming processes, their analysis methods are different. The binder wrap surface shape and formed part shape are calculated using different mathematical models and different finite element codes, e.g., WRAPFORM and PANELFORM, respectively. The output of the binder forming analysis may not be directly applicable to the subsequent punch forming analysis. Interpolation, or approximation, of the calculated binder wrap surface geometry is needed. This surface representation requirement is carried out using computer aided geometric design tools. This paper discusses the use of such a tool, SURFPLAN, to link WRAPFORM and PANELFORM calculations.

Corner fill is a simple benchmark conceived to gain knowledge of tube hydroforming. In corner fill of tube hydroforming, an originally long round tube is positioned in a cylindrical die with square cross-section and expands under applied internal pressure to fill the corners of the die. In order to ensure burst of the tubes, the cross-sectional dimension of the square die is chosen to be greater than the outer diameter of the tube. A two-dimensional plane strain finite element model has been developed to study the tube behaviors under applied internal pressure. This model treats the corner fill process more realistically than shell elements models because thickness stress and distortions of a normal segment through the thickness of the tube can be simulated [Chen, 2004]. The calculated results of stress and strain and the change of tube geometry as functions of pressure are presented.

A computational procedure is presented to evaluate the static dent resistance at the center of a steel door panel. Using the design parameters of geometric shape, thickness and the stress-strain relations of the steel, the static dent initiation load can be calculated. The method is based on the concept of plastic work which is the non-recoverable energy dissipated in the panel by the applied load. A threshold value of plastic work of 0.02 joule is used to signal the dent initiation. A comparison of the computed and measured dent initiation loads of ten experimental panels shows the maximum deviation is less than 20 newtons.

A simple problem of tube expansion to fill the die corners in the hydroforming process is studied. Based on a two-dimensional plane stress model the tube is simulated numerically using a static implicit finite element analysis, particularly, the commercial finite element code ABAQUS. Similar to the development and application of two-dimensional finite element codes for sheet metal forming, this two-dimensional model provides insight of the detailed deformation and stress/strain development otherwise lost in a more complex three-dimensional model. To facilitate discussions, high friction is assumed such that the tube does not slide on the die surface after contact. The calculated results predict the requirement to form sharp corners and demonstrate the development of the deformation, strain and stress states in the tube.

WRAPFORM is a mathematical model and computer program for calculating binder wrap surface shape. It employs punch-opening line of the die as a geometric input and does not use the complete binder surface. This paper presents WRAPFORM-II, an improvement of the WRAPFORM model by including the binder surface geometry in the simulation. The new model has been applied to several dies and results are compared to those of the base WRAPFORM model. For a decklid die reported in the literature, whose simulated binder wrap showed bifurcation possibilities, straightforward application of WRAPFORM-II predicts a more plausible result which is consistent with the original design intent. In another case, WRAPFORM-II predicted the feasibility of a design to put more material into the die cavity. Other applications show slightly improved simulation results by using WRAPFORM-II.