Abstract: Aiming at a previously conceived combined process of stamping & cold forging for stepped hole of thin sheet metal, by using DEFORM-3D software, numerical simulation of the deformation of this combined process is carried out by use of key technologies of finite element simulation for metal plastic working which includes geometrical model, material fracture damage and meshing technology, etc. Distributions of effective strain and effective stress, velocity field and force-stroke curve are obtained. A conclusion is drawn that the minute deformation can be divided into 3 stages, including punching with punch small-diameter side, concaving with punch big-diameter side and closed die forging. The technological features of this combined process and the material forming performance are analyzed. Technological experiments using AL-1100 sheet with a material thickness of 2.35 mm are carried out and clear profile of stepped hole is obtained, which verifies the above conclusion.

Key words: Finite element method, Material flow, Minute deformation, Stepped hole, forward-curved blades, impeller diameter, numerical simulation, reverse running, Keywords: hydraulic turbine