Abstract: An automotive-structural-part joint structure is formed by bending one metal sheet, includes a groove portion including a top portion and a pair of side wall portions, is provided at an end part of one automotive structural part in a longitudinal direction, and is configured to join the one automotive structural part to another automotive structural part in an intersecting direction. The automotive-structural-part joint structure includes: a pair of vertical rib portions configured to stand upward from both side ends of the top portion; and an outward-directed flange portion configured to extend outward from three side edges of the groove portion on an end part side where the other automotive structural part is joined, the flange portion being continuously formed along the three side edges.

Abstract: A method for identifying a variation factor portion of a springback amount, including: performing press forming analysis under first press forming conditions, and calculating a residual stress distribution in a press formed part; performing springback analysis on the press formed part, and calculating a first springback amount; performing press forming analysis under second press forming conditions, and calculating a residual stress distribution in the press formed part; replacing a value of residual stress in a partial area of the residual stress distribution; performing springback analysis on the press formed part for which the value of the residual stress has been replaced, and calculating a second springback amount; obtaining a difference between the second springback amount and the first springback amount; and identifying a portion in the press formed part that is a factor for variation in springback amount of the press formed part based on the obtained difference.

Abstract: A shape change prediction method of a press formed part predicts a shape change in which an end side in a longitudinal direction is twisted due to stress relaxation with a lapse of time after springback at a moment of die release from a tool of press forming with respect to the press formed part having a U-shaped cross-sectional shape including a top portion and side wall portions, and includes: acquiring a shape and a residual stress of the press formed part immediately after the springback by a springback analysis of the press formed part; setting a value of stress relaxed and reduced compared to the residual stress immediately after the springback for at least one of the side wall portions; and acquiring a shape with which moment of force is balanced for the press formed part in which the value of the relaxed and reduced stress is set.

Abstract: A press forming part includes: a top portion; a side wall portion continuous from the top portion via a punch shoulder; and a flange portion continuous from the side wall portion via a die shoulder, the press forming part having a curved portion curved in a recessed manner in a top view, wherein a bending radius of the die shoulder in the curved portion is increased from an end side toward a middle portion of the curve.

Abstract: A press forming method of press forming a press forming part that includes a top portion, a side wall portion continuous from the top portion via a punch shoulder, and a flange portion continuous from the side wall portion via a die shoulder, the press forming part having a curved portion curved in a recessed manner in a top view, the press forming method includes: making a bending radius of the die shoulder in the curved portion increased from an end side toward a middle portion of the curve.

Abstract: A method for identifying a necking limit strain of a metal sheet includes a step of measuring the distribution of strain in a tensile orthogonal direction in a tensile deformation process of a notch root for two or more types of sheet specimens having a notch geometry in a portion of a sheet edge; a step of obtaining a strain increment ratio of the notch root in the tensile deformation process and a strain gradient in the tensile orthogonal direction; a step of obtaining necking limit strain at which necking occurs in the notch root based on the strain increment ratio in the tensile deformation process; and a step of identifying the necking limit strain as a function of the strain gradient from the relation between the necking limit strain obtained for the two or more types of sheet specimens and the strain gradient at that time.

Abstract: A press forming method includes: press forming a press formed product including a top portion, a side wall portion continuous from the top portion through a punch shoulder portion, and a flange portion continuous from the side wall portion through a die shoulder portion, the press formed product including a curved portion that is concave and curved in a top view; and increasing a bending radius of the punch shoulder portion in the curved portion from a center of a curve toward an end side of the curve.

Abstract: A shape change prediction method for a press formed part predicts a shape change of the press formed part over time after springback at a moment of a release from a press-forming die, and includes: a shape/residual stress immediately after the springback acquisition step of acquiring a shape and a residual stress of the press formed part immediately after the springback by a springback analysis of the press formed part; a residual stress relaxation/reduction setting step of setting a value of a residual stress relaxed and reduced from the acquired residual stress to all bent portions or a part of the bent portions in the press formed part immediately after the springback; and a shape analysis step of determining a shape in which moments of force are balanced for the press formed part in which the value of the residual stress relaxed and reduced in the bent portions is set.

Abstract: A press forming method for controlling a shape change of a press formed part over time after the press formed part springs back at a moment of a release from a press-forming die includes: a press forming step of press forming a metal sheet into the press formed part by using the press-forming die; a die releasing step of releasing the press formed part, which is press-formed, from the press-forming die; and a post-release die holding step of holding the released press formed part in a forming bottom dead center shape for 30 minutes or more by using the press-forming die.

Abstract: A shape change prediction method for a press formed part for predicting a shape change of the press formed part with a lapse of time units after springback at a moment of a release from a die includes: a shape/residual stress immediately after springback acquisition step of acquiring a shape and a residual stress of the press formed part immediately after the springback by a springback analysis of the press formed part; a residual stress relaxation/reduction setting step of setting a value of a residual stress relaxed and reduced from the acquired residual stress to the press formed part immediately after the springback; and a shape analysis step of determining a shape, in which moments of force are balanced, for the press formed part to which the value of the relaxed and reduced residual stress is set.

Abstract: A method of press forming that forms a press-formed product into a target shape, the method including: forming a top portion; forming a side wall portion and a flange portion such that a side wall height of the side wall portion of the press-formed product becomes larger than a side wall height of the target shape, where the side wall height of the side wall portion is formed to be larger than the side wall height of the target shape by adding a value half or less of a radius of curvature of the ridge, in a longitudinal direction vertical cross section, of the target shape; and reforming a ridge between the side wall portion and the flange portion such that the side wall height of the side wall portion becomes the side wall height of the target shape.

Abstract: A method and apparatus for identifying a portion that is a factor causing a discrepancy in springback amount between a press-formed product and a CAE analysis.

Abstract: A method and device for specifying a portion causing a discrepancy in springback amount between CAE analysis and an actual formed product.

Abstract: An automotive-structural-part joint structure is formed by bending one metal sheet, includes a groove portion including a top portion and a pair of side wall portions, is provided at an end part of one automotive structural part in a longitudinal direction, and is configured to join the one automotive structural part to another automotive structural part in an intersecting direction. The automotive-structural-part joint structure includes: a pair of vertical rib portions configured to stand upward from both side ends of the top portion; and an outward-directed flange portion configured to extend outward from three side edges of the groove portion on an end part side where the other automotive structural part is joined, the flange portion being continuously formed along the three side edges.

Abstract: A method for identifying a variation factor portion of a springback amount, including: performing press forming analysis under first press forming conditions, and calculating a residual stress distribution in a press formed part; performing springback analysis on the press formed part, and calculating a first springback amount; performing press forming analysis under second press forming conditions, and calculating a residual stress distribution in the press formed part; replacing a value of residual stress in a partial area of the residual stress distribution; performing springback analysis on the press formed part for which the value of the residual stress has been replaced, and calculating a second springback amount; obtaining a difference between the second springback amount and the first springback amount; and identifying a portion in the press formed part that is a factor for variation in springback amount of the press formed part based on the obtained difference.

Abstract: A springback variation cause analysis method includes: calculating a first stress distribution in a press forming part; calculating a second stress distribution in the press forming part; calculating a difference between the second and the first stress distribution, and replacing and setting the first or the second stress distribution with the calculated stress difference distribution; calculating a first springback amount to be caused in the press forming part; changing a value of stress difference in a partial area of the press forming part in the stress difference distribution set for the press forming part; calculating a second springback amount; and analyzing a portion in the press forming part that is a cause of variation in springback amount in the press forming part due to scattering or variation in press forming conditions, based on the second springback amount and the first springback amount.

Abstract: A method of press forming that forms a press-formed product into a target shape, the method including: forming a top portion; forming a side wall portion and a flange portion such that a side wall height of the side wall portion of the press-formed product becomes larger than a side wall height of the target shape, where the side wall height of the side wall portion is formed to be larger than the side wall height of the target shape by adding a value half or less of a radius of curvature of the ridge, in a longitudinal direction vertical cross section, of the target shape; and reforming a ridge between the side wall portion and the flange portion such that the side wall height of the side wall portion becomes the side wall height of the target shape.

Abstract: A springback variation cause analysis method includes: calculating a first stress distribution in a press forming part; calculating a second stress distribution in the press forming part; calculating a difference between the second and the first stress distribution, and replacing and setting the first or the second stress distribution with the calculated stress difference distribution; calculating a first springback amount to be caused in the press forming part; changing a value of stress difference in a partial area of the press forming part in the stress difference distribution set for the press forming part; calculating a second springback amount; and analyzing a portion in the press forming part that is a cause of variation in springback amount in the press forming part due to scattering or variation in press forming conditions, based on the second springback amount and the first springback amount.

Abstract: A press forming method according to the present invention includes: a first forming step of forming the press formed part by using the first press forming tool having a line length in the cross-sectional direction of the joining portion contacting with a flange portion subjected to stretch flange deformation or a flange portion subjected to shrink flange deformation is a line length L1 in the cross-sectional direction that is shorter than a line length L2, where the line length L2 is a line length in a cross-sectional direction of the joining portion of the second press forming tool for making the product shape; and a second forming step of forming the press formed part in the product shape by crash forming by using the second press forming tool in which the line length in the cross-sectional direction of the joining portion is L2.

Abstract: A method for manufacturing a press formed part, the method including specifying stretch flange limit strain in a metal sheet by using strain gradient in a radial direction and strain gradient in a sheet thickness direction. The strain gradient in the radial direction being directed from an end portion of the metal sheet at a time a press load is applied. The strain gradient in the sheet thickness direction being a direction of the metal sheet that intersects a loading direction. Additionally, the stretch flange limit strain satisfies the formula ??lim=A[a·???/?r+b·???/?t]+c, where ??lim represents the stretch flange limit strain in a tangential direction of the sheet edge, ???/?r represents the strain gradient in the radial direction, ???/?t represents the strain gradient in the sheet thickness direction, A, a, and b represent influence coefficients, and c represents the limit strain at a time the strain gradient is zero.