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 with different die shapes. The proposed method calculates the driving force using the energy of deformation and the energy produced by friction. The new approach greatly reduces the difficulty of the analysis and simplifies the calculation. The stress distribution in the transition zone is also estimated using an analytical approach based on a self-adaption of the stress–strain curve. The approach is validated using four different numerical axisymmetric finite element models with different sizes, materials, and die shapes subjected to push and pull die expansion. Additionally, stainless steel and copper 3/8 in. tubes have been expanded with a prolate spheroid (oval) die in an experimental test bench under the two conditions of push and pull. The tangential and longitudinal strains and driving forces are monitored and recorded during the expansion process. Finally, the results from the three approaches show a very good agreement.