Multi-point forming of three-dimensional sheet metal and the control of the forming process

Multi-point forming (MPF) is a novel manufacturing technique for three-dimensional sheet metal. The discrete punches are composed of a pair of reconfigurable MPF dies and the shapes of the dies can be changed with requirement during the process of sheet forming. In this paper, three key problems concerning the control of the MPF process are discussed and the relevant numerical approaches are presented in detail. The determination of the three-dimensional surfaces of multi-point dies is based on the numerical representation of the objective shape, which describes a given geometry of sheet part by 18 d.o.f. high-precision triangular finite elements. To predict a sheet blank in MPF, a positive definite functional is proposed, and the variational problem is solved by an iterative scheme of FEM. On the basis of the assumption that the deformation of material follows the ideal forming path, a functional to compute the intermediate deformed shapes is formulated so that the difference is minimum in the least square sense between the deformation of configuration computed and the deformation of configuration in the ideal forming path. By minimizing the functional with membrane triangular elements, a series of intermediate configurations are obtained, consequently the forming path of sheet is described. Typical examples show the applicability of the proposed approaches. (C) 2002 Elsevier Science Ltd. All rights reserved.