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Hydroforming process of thin-walled tubular components with multiple local bulges

Cui Xiao-Lei, Guo Ju, Zhao Yuanyang, Lin Peng

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e169, 2023

EN

In the hydroforming process of a thin-walled tubular component with multiple local bulges, the bulge in the middle position is almost impossible to be formed with a conventional one-step hydroforming process because of the difficult axial feeding. To solve this problem, a novel method is proposed by preforming wrinkles using selective induction heating at different positions of tube blank to aggregate materials in advance for the subsequent hydroforming of tubular component with multiple local bulges. In this paper, the wrinkling behavior of 5052 aluminum alloy tube blank under different conditions and the deformation behavior of the wrinkled tube blank in subsequent hydroforming process of tubular component with three bulges are analyzed. It is shown that the existence of wrinkles is beneficial to increase the ultimate expansion ratio of the tube blank. Moreover, the instability behavior of multiple wrinkles on 5052 aluminum alloy tube blanks under different conditions was investigated by experiments. The process parameters for prefabricating two or three wrinkles, including temperature, spacing between wrinkles, and internal pressure, were determined through a detailed experimental investigation. Finally, the defects including splitting and undercut that occur in the hydroforming of tubular component with three bulges are analyzed, and the thin-walled tubular component with three bulges was hydroformed successfully using a wrinkled tube blank obtained under the process parameters of 250 °C, 4 mm, 5.5 MPa/350 °C, 10 mm, 2 MPa/400 °C, 6 mm, 1.33 MPa. These results provide insights for the manufacturing of tubular component with multiple local bulges from hard-to-form materials.

2

Analysis of thickness variation and stress state in hydroforming of complex T-shaped tubular part of nickel-based superalloy

Cui Xiao-Lei, Yuan Shijian

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

458--471

EN

Stress states on a multi-branch tubular part are the most complicated change in all types of hydroforming process, which result in severe variation of thickness. In this paper, an experimental and numerical research was conducted on a multi-step hydroforming process including intermediate annealing treatment to obtain effect of stress state on the thickness variation of a superalloy GH4169 complex T-shaped tubular part with expanded diameter, which corresponds to a real product used in aerospace industry. The material flow behavior at typical points on hydroformed tube blank was first analyzed. Then, the thickness variation on the hydroformed GH4169 tube blanks was discussed in every step. It is shown that the materials have different flow directions to form the side branch, where the thickness is always thinned during the four-step hydroforming process. Large axial feeding induces a continuous thickening between transition areas and tube ends. The thickness invariant dividing line in the side branch zone moves toward the tube ends with forming going on. However, in the hemisphere zone, it moves slightly towards the center of the side branch. Moreover, the stress states at three typical positions, as well as their effect on the thickness variation, were analyzed based on a sequential correspondence law between stress and strain components. On this basis, the mechanism of thickening in the left transition area, thinning at the top of side branch and thickness variation at the hemispheric pole was revealed. These results are very important for obtaining the thickness distribution of a complex T-shaped tubular part in multi-step hydroforming, and revealing the thickness variation mechanism by using engineering plasticity theory.

3

Effects of superimposed hydrostatic pressure on bulging deformation and fracture of tubes in double-sided hydroforming

Cui Xiao-Lei, Yuan Shi-Jian

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 2

569--583

EN

Finite element analysis and scanning electron microscope were conducted to investigate the bulging deformation and fracture of tubes in double-sided hydroforming. The effect of the external pressure imposed on the tube, which determines the magnitude of superimposed hydrostatic pressure, on the stress state, yield locus, fracture surface formation, and fracture strain was evaluated. The simulation results revealed that sufficiently high external pressure can change the stress state of the tube in double-sided hydroforming from an in-plane biaxial tensile stress state to a three-dimensional stress state, and it can increase its hydrostatic pressure in a superimposed manner. Moreover, double-sided free bulging and corner filling experiments were conducted on 5A02 aluminum alloy and 2A12 aluminum alloy tubes. It was found that the external pressure has a significant impact on the fracture behavior of these tubes. The increasing external pressure could change the type, number, size, and proportion of the dimples on the fractured surface, and transform the fracture mode from a void accumulation fracture to a pure shear fracture, which significantly improves the fracture limit of the tubes. These results are significant for the consolidation of the theoretical and numerical simulation prediction of the superimposed hydrostatic pressure effect in the hydroforming process.