Finite element analysis of tube inward curling process by conical dies

This paper combines the volume incompressible condition, Levy-Mises equation, and die profile description, to examine whether inward curling really takes place or not, and how much influence die angle, tube size (initial thickness/initial mean diameter of tube) and material property has on inward curling mode. When a cylindrical guide is used to prevent a tube from outward buckling, tubes can be inward-curled for the die angle below the critical one of 123°. An elasto-plastic finite-element method using updated Lagrangian formulation is developed to investigate the deformation behavior of tube end. The high non-linearity of the process was taken into account in an incremental manner and extended γmin technique was used to limit the size of each increment within a linear relation. The frictional force in the contact region between the tube and the tools is computed by the application of Coulomb's friction law. Tube inward curling predicted by FEM also shows the same trend as the experimental results. Moreover, the analytical expressions can provide a good reference guide for the tube inward curling forming in the industrial sector.