Abstract: In order to improve the quality of the product and reduce the cost, the appropriate shape of the blank must be determined. However, if using the conventional method, not only lots of time and man-power would be wasted but also the high accuracy, quality and efficiency could not be achieved. Based on the electric analog method for blank unfold which has already exist, a new reverse educing method about bulge-blank unfold based on equipotential field is introduced. The appropri-ate shape of the bulge-blank is obtained through the reverse educing method, which is based on the minimum energy theory and the minimum resistance pressure theory, and utilize the similarity between the blank flow law and the isopotential line of the electrostatic field. The superplasticity bulging process for Ti-6Al-4V blank is studied by using this method, a variety of parameter and the strain distribution of the blank are calculated, and the stress and the atmospheric pressure for the bulging are analysed. This method avoid the complex analytic calculation of the geometry and the time-consuming iteration solution, and improve the efficiency by composed to the FEM (Finite element method). This method is feasible and its result is credible.

Key words: Bulge-blank, Equipotential field, Isoparametric element, Reverse educing method, Affecting characteristic, Geometrical configuration, Non-tilting friction stir welding, Tool pin