Simulation and optimization of the free bending process of aluminum alloy 6061 pipe

Metal pipes are the important components of structural load-bearing and conveying gas or liquid in the industrial field. However, the final forming profile obtained with the traditional bending process highly depends on the forming mold; the forming profile is simple, but the mold cost is relatively expensive. Thus, it is difficult for wide promotion on the bent pipe with a complex profile, especially for small batch production. The free bending process as a method of solving this problem is attracting a lot of attention. This process can achieve precision forming of the pipe without a forming mold. The pipe can be bent into different radii by adjusting the relative positions of the fixed die and mobile die. This process not only reduces the manufacturing cost but also improves the forming quality. The development of the free bending process will help to achieve high precision, high performance, high efficiency, and digitization of the industrial production of the metal pipes. In this study, an aluminum alloy 6061 pipe with a diameter of 30 mm and wall thickness of 2.0 mm was chosen. Its mechanical parameters were obtained by a tensile test of the axial and circumferential specimens of the pipe, and the obtained parameters were used for the parameter characterization of the chosen constitutive model. Meanwhile, a press bending test was carried out to validate the chosen model. Afterward, the pipe space free bending process was simulated by the finite element method, and the results were analyzed. Finally, the optimal values of the process parameters, including the shape of the mobile die, the size of the clearance of the mobile die and pipe, the frictional coefficient, and the feed speed of the pipe, were determined. This study has a great significance in the application of pipe space free bending forming process.