Springback prediction of AL6061 pipe in free bending process based on finite element and analytic methods

The free bending process is a promising process for forming metal pipes. It can be achieved without the frequent replacement of mould. This process has attracted considerable attention of researchers. However, its springback after unloading is a key issue that influences the final formed shapes of the pipe. In this study, finite element (FE) and analytic methods are used to predict the springback phenomena of the AL6061 pipe. The analytic model is enhanced by considering the neutral layer offset. Furthermore, to better investigate the springback process, the FE model of the free bending process is established. The influence of process parameters (e.g. friction, clearance, and mobile die section shape) on bending springback is investigated after the free bending process. The springback angle generally varies in the range of 2–2.5°, and the influence of process parameters on the final springback of the pipe in the free bending process is also discussed. Results showed that the neutral layer offset has a tendency to move towards the material tensile direction in the free bending process, which is different from the traditional rotary bending. Thus, the analytic model of pipe bending springback is optimised with the addition of the neutral layer offset. This study contributes to reinforcing the understanding of the springback mechanism and has a guiding significance for free bending process quality.