Research On The Model Of Force-Displacement-Controlled MPF For Bidirectional Curvature Blank

Because the contacting area between the basic group and the sheet metal has been greatly decreased in multi-point forming, lack of restrain along the thickness direction often appears, and forming defects is liable to occur. In this paper, a new method which can improve the forming quality of multi-point forming process was studied. The forming mode named force–displacement separated control was proposed. The aim of the study is to constrain the sheet metal between the die groups allover the forming process of the material, thus to improve the forming ability and quality. The reason to improve the forming quality under the new forming mode was discussed and the approach to realize this forming method was proposed. Numerical simulation method was adopted to study the springback and forming process of sphere surface, sail and saddle surfaces. The effect factors and regular pattern were discussed. Those results show that metal sheet thickness, deformation and forming force have effect on wrinkle defect. With metal sheet thickness and forming force increasing, deformation diminishing, wrinkle can be gradually weakened. The wrinkles of sphere and sail parts mainly centralize near the symmetrical axis. The wrinkles of saddle parts mainly centralize the center. In the multi-point forming, dimple may appear. The dimples mainly centralize in the edge. With thickness increasing, deformation and forming force diminishing, dimple can be gradually weakened. Springback was affected by the forming force, the thickness and the curvature. The springback ratio decreases with the increase of the forming force, the thickness and the curvature.Based on the geometric compensation method, the springback controlling in force–displacement separated control method are discussed by numerical simulation. The working surface constructed by element matrix is modified according to the prediction value. Through repeating the process of predicting and modifying working surface, springback will be controlled under tolerance. And the paper provides the ultimate punch's stroke to form precise surface by one-time.