A Method of Evaluating the Driving Force and Stresses During Tube Die Expansion

In this study, an analytical approach based on the energy method is used to estimate the force required to expand tubes for different die shapes. The proposed method calculates the driving force by the volume energy change and working effect ratio instead of depending on the contact pressure and the shape of the contact surface in the previous studies. The new approach greatly reduces the difficulty of the analysis and simplifies the calculation. Since the accurate stress distribution in the transition zone is essential for determining the working effect factor, a new analytical approach with self-adaption is also introduced to estimate the strain and stress distribution in the transition zone of an expanding tube, and the contact position between die and tube can also be obtained by this approach. In this study, three finite element models as a numerical approach are used to develop an axisymmetric model including multiple linear kinematic hardening behavior to confirm the approach. Additionally, copper and steel 3/8 inch tubes are expanded with oval dies on a designed test workbench with different boundary conditions. The tangential, longitudinal strains and driving force are monitored and recorded during the expansion process. Finally, the results from the three approaches show a very good agreement.