Patent Document ID: 9868145
Application ID: 13119656
Patent Flag: 1

Claim One:
1. A forming method of an elastic-plastic material based on a forming simulation of the elastic-plastic material using one or a plurality of upper or lower tools having one tool configuration which is not modified during the forming simulation, the forming method comprising: calculating an element equivalent nodal force vector {f} e , from a stress tensor σ obtained using a computer to perform a finite element method, for a plurality of finite elements of a first target configuration of the elastic-plastic material based on Equation (3), { f } e = ∫ Ve ⁢ [ L ] t ⁡ [ B ] t ⁢ { σ } ⁢ dV = { ⋮ N x i N y i N z i M x i M y i M z i ⋮ } ( 3 ) where [L] represents a coordinate transform matrix and [B] represents a relationship matrix between displacement and strain, the coordinate transform matrix [L] is a transformation matrix for converting the element equivalent nodal force vector in an element coordinate system into a vector in a global coordinate system, the coordinate transform matrix [L] is calculated by using a direction cosine with respect to an element coordinate system (X′, Y′ and Z′) of the X-, Y- and Z-axes of the global coordinate system; calculating a total equivalent nodal force vector {f} of areas by integrating the element equivalent nodal force vector {f} e for the plurality of finite elements for at least a portion of the elastic-plastic material as represented in Equation (4), 
 {f}=∫ V {f} e dV  (4) wherein the calculated total equivalent nodal force vector is obtained by converting stress at bottom dead point of the tool into an equivalent nodal force, the total equivalent nodal force vector consists of a cross-sectional force component (Nx, Ny and Nz) and a bending moment component (Mx, My and Mz) in the global coordinate system; calculating an amount of only the bending moment component of the total equivalent nodal force vector; displaying the amount of the bending moment of the total equivalent nodal force vector, which does not include the cross-sectional force component, as an image corresponding to a configuration of the elastic-plastic material; setting a bending moment threshold, and specifying, among the at least a portion of the elastic-plastic material, a part having the bending moment component of the total equivalent nodal force vector that is larger than the bending moment threshold, as a springback-inducing area, referring to the calculated total equivalent nodal force vector; and forming a subject elastic-plastic material into a modified target configuration that is modified from the first target configuration at the specified springback-inducing area.