Patent Document ID: 10089422
Application ID: 14765208
Patent Flag: 1

Claim One:
1. A springback-amount prediction method comprising: determining a spring-back amount of a press-formed product including: (i) an experimental-value acquisition step of plastically deforming an elastic-plastic material to acquire experimental values of a stress-strain relation; (ii) a first material-constant identification step of, by a computer, with a kinematic-hardening incremental vector dα ij of a yield surface in an elastic-plastic constitutive model as Equation (1), the elastic-plastic constitutive model being defined as a function of stress and back stress, identifying material constants contained in the elastic-plastic constitutive model using the experimental values acquired at the experimental-value acquisition step; (iii) a second material-constant identification step of, by the computer, based on the Equation (1) into which the material constants identified at the first material-constant identification step are substituted and based on the experimental values acquired at the experimental-value acquisition step, identifying material constants contained in Equation (2); and (iv) a step of, by the computer, predicting the springback amount with the Equation (1) and the Equation (2) into which the material constants identified are substituted, and the elastic-plastic constitutive model, modifying a die based upon the determined spring-back amount, and pressing the die onto a metal sheet to produce the press-formed product, wherein Equation (1) is defined as follows: d ⁢ ⁢ α i ⁢ ⁢ j = [ C ⁡ ( a Y ) ⁢ ( σ i ⁢ ⁢ j - α i ⁢ ⁢ j ) - C 0 ⁢ ρ ⁢ ⁢ X i ⁢ ⁢ j ] ⁢ d ⁢ ⁢ ɛ eq p Equation (2) is defined as follows: C = C a + C c ⁢ exp ⁡ ( - X eq n A ) ⁢ where: a: maximum value of movement of yield surface Y: yield stress α ij : movement vector of yield surface σ ij : stress vector X ij : yield—surface kinematic—hardening amount after stress reversal X eq : equivalent value of X ij dε p eq : equivalent plastic—strain increment C 0 , C C , A, n: material constants ρ: variable such that ρ=1 or ½.