With the rapid development of the aviation and automobile industry, the multi-way tube hydroforming process has been the focus of research[1]. The principle of hydroforming process is to form various complicated thin-walled hollow section parts by the combined action of mechanical load and hydro-static internal pressure[2, 3]. Compared with the traditional forming technology, the part using hydroforming process has many advantages, such as lightweight, good structural integrity, avoiding secondary operation, and reducing waste[4].
In the hydroforming process, it is found that internal pressure, axial feed and friction are the main parameters that affect the forming effect[5]. Fvollertsen[6] has summarized the estimation formulas of various process parameters of high pressure forming in T-shaped tubes and specifically given the estimation formulas of clamping force, axial feed force, reverse thrust punch force, and shaping pressure. Manabe and Amino[7] confirmed with both finite element (FE) simulations and experiments that key process and material factors affect the tube wall thickness distribution. Optimizing the data in the hydroforming process to obtain higher branch height and more uniform wall thickness has always been the focus of research. Alaswad et al.[8] compared the research results between single and bi-layered hydroforming processes under the same conditions, and concluded that the loading path should be optimized for superior control of the process because of complexity of the hydroforming process. Jang et al.[9] found that internal pressure and axial feed determine the quality of deformed parts, and the equivalent static load method is used to optimize the loading path to prevent defects. Fiorentino et al. [10] formed a Y-shaped piece by creating asymmetric conditions in the feed zone of the tube hydroforming process and utilizing a quasi-free model. Jirathearanat et al.[11] evaluated the process design of hydroforming for Y-shaped tubes through finite element analysis (FEA) and experiment, and found that tube length is the important parameter affecting the formability of protrusion. In addition to the study of load path and internal pressure optimization, Xu et al.[12, 13] proposed to adjust the material flow by changing the friction coefficient in the asymmetric zone in the tube part, thereby avoiding wrinkling in T-shaped tube hydroforming. Moreover, Dong et al. investigated on the hydroforming process by mixing the hydroforming process with both artificial aging and heat treatment on aluminum alloys and obtained good results on formability issues[14].
At present, the research on four-way tubes has also achieved certain results, which can be divided into X-type four-way tubes and parallel double-branch type four-way tubes. Mehran and Kadkhodayan[15] studied the optimization of load path in hydroforming of angled tubes which include X- and Y-shaped tubes through statistical methods in conjunction with FEA and simulated annealing algorithms, and the quality of the final product containing the variance of tube thickness and height was improved significantly by using the optimization method. Olabi et al.[16] used the LS-DYNA preprocessor and solver to establish a finite element model for the hydroforming of copper X-shaped double-layer tubes, and simulated the failure modes of X-shaped tube rupture and wrinkles and verified them with experiments. Majzoobi et al. [17] study the effect of the branch end boundary condition on the product quality, and found the X-shape tube quality can be improved by application of a constraint such as spring in the branch of the hydroforming die.
However, some one-step forming of complex shape parts frequently appear the defects of wrinkling, cracking and uneven wall thickness in the hydroforming process. Therefore, the research of multi-step hydroforming is great significance. Cui et al.[18] studied the manufacture of GH4169 expanded diameter T-shaped tubular parts and used four-step hydroforming to successfully overcome the problem of severe thinning in the traditional one-step hydroforming. Peng et al.[19, 20] proposed a multi-step process with preform procedure to improve the stress states in the protrusion to avoid the wrinkling and cracking defects, and sound components were produced.
There are more studies on T-shaped tube and four-way tube, but few studies on five-way tube. In the past, five-way tube was formed by welding multiple T-shaped tubes together. Because the tube blank is relatively long and the structure is complex, it is difficult to form the five-way tube. This paper proposes a multi-step forming method of five-way tube to eliminate the defects of large-diameter branch breaking during one-step forming and optimize the wall thickness and branch height. Finally, the results obtained are verified through experiments to prove that the proposed method is effective.