Rubber mandrel and internal pressure effects on thin-walled tube bending: a comparative study

Tube bending plays a crucial role in various industrial sectors, ranging from aerospace, military, and petrochemical to automotive manufacturing. However, a persistent challenge in this process is the occurrence of springback, which disrupts the intended shape of the bent tubes and affects product assembly. While previous research has primarily focused on predicting and managing springback using simplified biaxial stress assumptions, the influence of radial normal stress (internal pressure) has often been overlooked, particularly in modern bending techniques like hydroforming and rubber pad forming. In this study, a comprehensive investigation into the impact of internal pressure on springback during tube bending was undertaken, employing analytical, numerical, and experimental methodologies. The utilization of a rubber mandrel in thin-walled tube bending effectively reduces springback angles by up to 9.86% compared to bending without it. The numerical simulation demonstrates stronger agreement with experimental data, highlighting the importance of internal pressure generated by the mandrel's contact stress. This pressure contributes to increasing the plastic strain level, extending the plastic skin, and removing the elastic core, subsequently reducing springback.