Abstract: A press forming method reduces a time for chronological shape variation of a press formed part after occurrence of springback at a moment when the press formed part is released from a die, and includes: forming the press formed part by press forming with a metal sheet by using the die; releasing the press formed part formed by press forming, from the die; fitting the press formed part released from the die into the die and securing the press formed part in conformity with a shape at a bottom dead center of forming; heating the press formed part fitted into the die to a first temperature higher than room temperature and holding the press formed part at the first temperature for a predetermined time period of less than 30 minutes; and cooling the press formed part heated and held, to a second temperature lower than the first temperature.

Abstract: A method of calculating residual stress includes: measuring strain of a deformed portion of the metal sheet in a deformation process of plastically deforming the metal sheet and acquiring a strain history of the measured strain; calculating a stress increment of the deformed portion in the deformation process according to a material constitutive model using an acquired strain increment calculated from the acquired strain history and an assumed strain increment calculated, by assuming a deformation state of the deformed portion, from strain other than the strain from which the strain history is acquired, and sequentially updating stress from a start to an end of deformation of the deformed portion using the calculated stress increment; and determining, as residual stress of the deformed portion, the stress of the deformed portion at the end of the deformation in the deformation process among the sequentially updated stresses.

Abstract: Provided is a sheet material press forming method of press forming a formed part including a top portion with a protrusion having a blockage protrusive shape, the method including: preforming a high-strength steel sheet; and then forming it into a target shape without fractures or wrinkles, which is achieved by determining a shape in the preforming by press forming analysis according to the following steps: S1: the region of the protrusion having the target shape is discretized into two-dimensional elements and nodes for finite element analysis; and S2: the discretized portion are applied with internal stress in the normal directions of the two-dimensional elements from the inside of the discretized portion and deformed under the following conditions: (a) the two-dimensional elements are deformed within an elastic deformation range; and (b) adjacent ones of the two-dimensional elements have an angle therebetween which is free to change.

Abstract: A press forming method includes: a first forming step of press-forming a preformed part including: a top portion and flange portions having same shapes as a top portion and a flange portions in a target shape of a press-formed product; and side wall portions having projecting chevron shape in a cross-section in a press-forming direction as compared with side wall portions; and a second forming step of press-forming the preformed part into the target shape. Each side wall portions includes: a side wall portion adjacent to top connecting to the top portion; a side wall portion adjacent to flange connecting to the flange; and a bent portion between the side wall portion adjacent to top and the side wall portion adjacent to flange. An angle on an acute side formed by the side wall portion adjacent to top and a horizontal plane decreases toward an end portion from a center.

Abstract: Provided is a sheet material press forming method of press forming a formed part including a top portion with a protrusion having a blockage protrusive shape, the method including: preforming a high-strength steel sheet; and then forming it into a target shape without fractures or wrinkles, which is achieved by determining a shape in the preforming by press forming analysis according to the following steps: S1: the region of the protrusion having the target shape is discretized into two-dimensional elements and nodes for finite element analysis; and S2: the discretized portion are applied with internal stress in the normal directions of the two-dimensional elements from the inside of the discretized portion and deformed under the following conditions: (a) the two-dimensional elements are deformed within an elastic deformation range; and (b) adjacent ones of the two-dimensional elements have an angle therebetween which is free to change.

Abstract: A press forming method for forming a press-formed product having no flange portion from a blank by performing a crash forming process while using a die and a punch, the press-formed product including at least a top portion and a side wall portion continued from the top portion via a connecting portion and being structured so that either all or a part of the side wall portion curves toward an outside of the press-formed product to form a convex shape in a planar view, the press forming method including forming the side wall portion while keeping a tip end portion of the blank in continuous contact with a side wall forming portion of the die and causing the die to impose no restraint on any part other than the tip end portion of the blank.

Abstract: A method of press forming includes: forming a trench-shaped portion into a product shape with a die and a punch until reaching a first bottom dead center, and forms at least one of: a flange portion subject to shrink flange deformation such that a linear length of the flange portion subject to the shrink flange deformation in a longitudinal direction is shorter than a linear length of a flange portion in the product shape; and a flange portion subject to stretch flange deformation such that a linear length of the flange portion subject to the stretch flange deformation in the longitudinal direction is longer than the linear length of the flange portion in the product shape; and forming the formed flange portion into the product shape with the die and a flange forming die until reaching a second bottom dead center.

Abstract: Displacement or a load is applied to an elastic-plastic material to deform the elastic-plastic material plastically to acquire experimental values of a stress-strain relation. With a kinematic-hardening incremental vector d?ij of a yield surface in an elastic-plastic constitutive model as a predetermined first equation, the elastic-plastic constitutive model being defined as a function of stress and back stress, a computer identifies material constants contained in the elastic-plastic constitutive model with the acquired experimental values. The computer identifies material constants contained in a predetermined second equation on the basis of the acquired experimental values and the predetermined first equation into which the identified material constants are substituted.

Abstract: A method of identifying a cause of springback includes a step of performing a press forming analysis, a step of performing a springback analysis on the basis of information acquired by the press forming analysis, a step of dividing a shape of a press forming product acquired by the press forming analysis into a plurality of regions, a step of changing Young's modulus in a designated direction in any region of the divided regions, a step of performing the springback analysis on the press forming product whose Young's modulus is changed, a step of acquiring springback amount differences on the basis of multiple springback analysis results, and a step of identifying the cause of the springback on the basis of the acquired springback amount differences.

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.

Abstract: A press forming method for forming a press-formed product having no flange portion from a blank by performing a crash forming process while using a die and a punch, the press-formed product including at least a top portion and a side wall portion continued from the top portion via a connecting portion and being structured so that either all or a part of the side wall portion curves toward an outside of the press-formed product to form a convex shape in a planar view, the press forming method including forming the side wall portion while keeping a tip end portion of the blank in continuous contact with a side wall forming portion of the die and causing the die to impose no restraint on any part other than the tip end portion of the blank.

Abstract: A method for press forming analysis includes (1) performing a coordinate transformation to calculate a distribution of stress (a) before a release from the press die in a local coordinate system; (2) performing a springback analysis which includes (i) calculating a distribution of residual stress after the release and performing the coordinate transformation to calculate a distribution of residual stress (b) in the local coordinate system, and (ii) calculating shape data (d) after the release; (3) calculating a difference (a-b) as SB effective stress, performing a coordinate transformation to calculate a distribution of SB effective stress in a global coordinate system, changing or removing the SB effective stress in an analysis target region and performing the springback analysis to calculate a shape data (c) after the release; and (4) calculating a difference (c-d) to determine a degree of influence of the analysis target region.

Abstract: A method of press forming includes: forming a trench-shaped portion into a product shape with a die and a punch until reaching a first bottom dead center, and forms at least one of: a flange portion subject to shrink flange deformation such that a linear length of the flange portion subject to the shrink flange deformation in a longitudinal direction is shorter than a linear length of a flange portion in the product shape; and a flange portion subject to stretch flange deformation such that a linear length of the flange portion subject to the stretch flange deformation in the longitudinal direction is longer than the linear length of the flange portion in the product shape; and forming the formed flange portion into the product shape with the die and a flange forming die until reaching a second bottom dead center.

Abstract: Displacement or a load is applied to an elastic-plastic material to deform the elastic-plastic material plastically to acquire experimental values of a stress-strain relation. With a kinematic-hardening incremental vector d?ij of a yield surface in an elastic-plastic constitutive model as a predetermined first equation, the elastic-plastic constitutive model being defined as a function of stress and back stress, a computer identifies material constants contained in the elastic-plastic constitutive model with the acquired experimental values. The computer identifies material constants contained in a predetermined second equation on the basis of the acquired experimental values and the predetermined first equation into which the identified material constants are substituted.

Abstract: A method for specifying stretch flange limit strain includes specifying stretch flange limit strain so as to satisfy a relation in the following formula by using: strain gradient in an inward direction directed from an end portion of a metal sheet at a time a press load is applied; and strain gradient in a sheet thickness direction of the metal sheet intersecting the loading direction: ??lim=A[a·???/?r+b·???/?t]+c where ??lim represents the stretch flange limit strain (tangential direction of the sheet edge), ???/?r represents the strain gradient in the inward 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.

Abstract: A method of identifying a cause of springback includes a step of performing a press forming analysis, a step of performing a springback analysis on the basis of information acquired by the press forming analysis, a step of dividing a shape of a press forming product acquired by the press forming analysis into a plurality of regions, a step of changing Young's modulus in a designated direction in any region of the divided regions, a step of performing the springback analysis on the press forming product whose Young's modulus is changed, a step of acquiring springback amount differences on the basis of multiple springback analysis results, and a step of identifying the cause of the springback on the basis of the acquired springback amount differences.

Abstract: The present invention provides a method and apparatus for easily and clearly identifying the effect of a countermeasure for reducing springback in press-forming. According to the invention, the method for identifying the effect of a countermeasure for reducing springback includes calculating a pre-release residual stress distribution in a press-formed part under a preset press-forming condition, calculating an after-release residual stress distribution in the press-formed part released from the die on the basis of the result of calculation, calculating the difference between the residual stress distributions on the basis of these results of calculation, calculating the difference between residual stress distributions similarly obtained under a changed press-forming condition, calculating a variation in the residual stress distribution caused by changing the press-forming condition on the basis of these differences between the residual stress distributions, and displaying the variation in contour plots.

Abstract: A method for press forming analysis includes (1) performing a coordinate transformation to calculate a distribution of stress (a) before a release from the press die in a local coordinate system; (2) performing a springback analysis which includes (i) calculating a distribution of residual stress after the release and performing the coordinate transformation to calculate a distribution of residual stress (b) in the local coordinate system, and (ii) calculating shape data (d) after the release; (3) calculating a difference (a-b) as SB effective stress, performing a coordinate transformation to calculate a distribution of SB effective stress in a global coordinate system, changing or removing the SB effective stress in an analysis target region and performing the springback analysis to calculate a shape data (c) after the release; and (4) calculating a difference (c-d) to determine a degree of influence of the analysis target region.