Tube Hydroforming Experiments Research Articles

Comparison of Constitutive Relationships of Tubes Established Using Uniaxial Tensile Tests and Tube Hydroforming Experiments

The aim of the present paper is to evaluate existing constitutive models and to fitting hardening laws of SS304 tubes for the accurate prediction of the deformation behaviors of the tubes in hydroforming. Uniaxial tensile test (UTT) and free hydro-bugling (FHB) experiments were conducted on SS304 tubes, and a hi-speed three-dimensional (3D) digital image correlation (DIC) system was applied to obtain the deformation data of the samples. Eight constitutive relationships of the tubes were then established by fitting the equivalent stress and strain data with the four existing constitutive models of Hollomon, Ghosh, Voce and Ghosh/Voce, and the fitting accuracy of the obtained constitutive relationships were analyzed and compared. The results show that Ghosh/Voce model holds the highest accuracy in describing the deformation behaviors of the tubes in UTT and FHB, followed by the Ghosh model and then the Hollomon model. The Voce model holds the lowest accuracy. A distinct discrepancy between the constitutive relationships obtained using UTT and FHB experiments are observed in present research conditions.

Adaptive simulations in T-shape tube hydroforming with different outlet diameters

A successful tube hydroforming process depends largely on the loading paths for controlling the relationship between the internal pressure, axial feeding and the counter punch. The objective of this article is to propose an adaptive control algorithm to determine appropriate loading paths in T-shaped protrusion hydroforming with different outlet diameters. The finite element analysis is used to simulate the flow pattern of the tube during tube hydroforming process. The analytical flow line net configuration of the tube is utilized to determine the speed ratio of the counter punch to the axial feeding at the protrusion stage. Appropriate loading paths for different outlet diameters are determined using the proposed adaptive control algorithm. Different pressurization profiles are used in the tube hydroforming experiments. Experimental results show that a sound product is obtained using the pressurization profile determined by the proposed adaptive simulation algorithm. From the comparisons of the product shape and flow line net configurations between the analytical and experimental values, the validity of the proposed control algorithms is verified.

Preform Design for Tube Hydroforming Based on Wrinkle Formation

A two-stage preforming process based on wrinkle formation is developed for the tube hydroforming process to accumulate material in the forming zone, thus reducing the thinning rate and improving the formability. In preforming stage one, the wrinkle onset is triggered with limited axial compression. In preforming stage two, the wrinkle grows stably and uniformly to a certain height. Then, the preformed wrinkles are flattened to conform to the die shape in the final tube hydroforming process. An analytical model based on bifurcation analysis and postbuckling analysis of the elastic-plastic circular cylinder under axial compression and internal pressure is used to study the wrinkle evolution characteristics in tube hydroforming. The analytical results offer valuable guidance to the process design of the two-stage preforming process. To validate this methodology, preform die sets for two axisymmetric parts were designed and tube hydroforming experiments were carried out on SS 304 tubing. Through this methodology, an expansion rate of 71% was achieved.

Analytical model for planar tube hydroforming: Prediction of formed shape, corner fill, wall thinning, and forming pressure

An analytical model for planar tube hydroforming based on deformation theory has been developed. This analytical model can be used to predict hydroformed shape, corner fill, wall thinning, and forming pressure. As the model is based on a mechanistic approach with bending effects included, local strain and stress distribution across the wall thickness can be determined. This includes strain and stress distributions for the outer layer, inside layer, and middle layer. The model is validated using finite element analysis and tube hydroforming experiments on irregular triangular, irregular quadrilateral, and pentagonal hydroformed shapes.

Estimating the Strain-Based FLC of a Tube from Straight Tube Hydroforming Experiments and Numerical Models

Estimating the Strain-Based FLC of a Tube from Straight Tube Hydroforming Experiments and Numerical Models

Tube-hydroforming experiments on an Al 7003 extruded tube

Tube hydroforming (THF) is a valid alternative technique for the production of parts with enhanced performance in terms of resistance and feasibility of complex shapes.The present paper shows the results of the first tests conducted at the Brescia University Laboratory where experimental equipment, able to run THF experiments, is available. This equipment can be used to conduct experiments to validate the correct process parameters derived from simulations in order to obtain defect-free components and to realize pre-series parts. In particular, in the present research, the feasibility of forming a motorbike suspension arm, obtained from an Al 7003 extruded tube, was analyzed. The experimental thinning values were compared to the simulation ones in order to validate the FE model of the process. The good agreement obtained confirms that FE analysis is a valid tool for virtual prototyping of new processes such as THF.