Method for obtaining a wrinkle occurrence determination index of a press-formed product, method for determining occurrence of a wrinkle, apparatus for determining occurrence of a wrinkle, and program for determining occurrence of a wrinkle

Abstract

In a method for determining wrinkle generation of a press-formed product, in a biaxial stress test in which a load in an in-plane biaxial direction is applied to a cross-shaped plate-shaped test piece (100) to induce out-of-plane buckling at a measurement portion (101), a relationship between a strain in the in-plane biaxial direction and a load generated in a process of inducing the out-of-plane buckling at the measurement portion (101) is obtained for each load ratio in the in-plane biaxial direction (S1), a strain in the in-plane biaxial direction at a point where a first differential of a strain in an in-plane one-axis direction under a compression load becomes maximum is obtained as a stable behavior limit strain for each load ratio (S3), the stable behavior limit strains obtained for each load ratio are plotted on a two-dimensional coordinate, and a stable behavior limit line that becomes an index of wrinkle generation in a biaxial stress state is obtained (S5).

Description

Technical Field

[0001] This invention relates to a method for obtaining a wrinkle generation determination index for press-formed parts, which is used to determine the presence or absence of wrinkles under a biaxial stress condition during the press-forming process; a wrinkle generation determination method, a wrinkle generation determination device, and a wrinkle generation determination procedure based on the index to determine the presence or absence of wrinkles in the press-formed parts. Background Technology

[0002] Conventionally, as a material test for metal sheets, the Forming Limit Diagram (FLD) test has been conducted to determine the area that can be stamped without causing the metal sheet to fracture (Non-Patent Literature 1, etc.). Furthermore, by using the forming limit diagram obtained from this FLD test, the risk of bulging fractures, drawing fractures, and other defects during the stamping of metal sheets can be objectively and quantitatively evaluated.

[0003] Furthermore, as a material testing method for metallic materials, compressive loads are applied to thin metal sheets (Patent Document 1, Patent Document 2, Patent Document 3, etc.). For example, in the material test disclosed in Patent Document 3, it is believed that by applying an in-plane biaxial compressive load to a thin sheet test piece, the mechanical properties of the thin metal sheet under a biaxial compressive stress condition can be determined with high precision. It is also anticipated that by utilizing these material tests that apply compressive loads to thin metal sheets to determine the material properties of thin metal sheets under compressive stress conditions, it will contribute to improving the prediction accuracy of CAE (computer-aided engineering) analysis (press forming simulation) of the stamping process.

[0004] Generally, if a sheet metal is subjected to a compressive load during stamping, the sheet metal will suddenly deform out of plane from the target shape of the stamped product, resulting in out-of-plane buckling. Sometimes, wrinkles will be generated in the stamped product (hereinafter, sometimes referred to as "press wrinkles"). The mechanisms of such press wrinkles are classified as (1) buckling behavior of the sheet metal, and (2) excess metal or thickening caused by excess or uneven material inflow of the sheet metal.

[0005] Regarding the elastic or plastic buckling phenomenon in (1), there are cases such as compressive stress generated in the flange portion due to shrinkage flanging during the stamping process of a stamped article having a punch-bottom portion, a side wall portion, and a flange portion and having a hat-shaped cross section, and cases caused by uneven deformation of the metal sheet due to uneven loads, non-axisymmetric loads, etc. On the other hand, regarding the excess material or material accumulation in (2), it is believed that it will occur in the parts where the shape of the stamped article changes drastically (see Non-Patent Document 2).

[0006] Furthermore, the thinner the sheet metal and the lower its material strength, the easier it is for stamping wrinkles to form. In bulge forming, excess metal on the bulge surface caused by material flowing from the periphery of the processing section into the processing section is a direct cause, thus making it difficult to prevent the formation of stamping wrinkles and obtain stamped products of the desired shape.

[0007] Therefore, in order to obtain stamped parts that prevent the formation of stamping wrinkles, it is necessary to identify the causes of wrinkle formation during the stamping process and determine the stamping conditions based on the material properties of the metal sheet and the target shape of the stamped part.

[0008] As a method for predicting the generation of stamping wrinkles, the following techniques exist: performing stamping simulation based on the elasto-plastic finite element method, etc., and when displaying the stamped product obtained through the stamping simulation during and after the forming process on the computer screen, shading is applied according to the degree of compressive stress and compressive strain, and the presence or absence of wrinkles is determined by visual inspection.

[0009] Furthermore, some techniques have been proposed to infer the mechanism of wrinkle formation and to determine quantitative indicators for judging the presence or absence of wrinkles by using strain and stress calculated through stamping simulation. For example, Patent Document 4 discloses the following technique: by simulating the stamping of sheet material based on the elastoplastic finite element method, the equivalent stress and equivalent strain of each element in the stamping process are calculated. If the difference between the equivalent stress obtained from the workhardening curve of the sheet material and the equivalent stress calculated through stamping simulation is large relative to the calculated equivalent strain, buckling is considered to have occurred at the location of that element. This difference is used as a wrinkle evaluation parameter to determine and evaluate the presence or absence of wrinkles. Furthermore, Patent Document 5 discloses the following technique: when a stamped article having a top plate portion and an outwardly curved longitudinal wall portion is subjected to shrink flange forming through crash forming, the presence or absence of wrinkles in the stamped article is determined in advance based on whether the compressive strain generated at the top of the longitudinal wall portion exceeds the wrinkle generation limit strain. Moreover, Patent Document 6 discloses the following technique: based on the bending stress in the thickness direction section of the formed material at the bottom dead center during stamping, the curvature radius or curvature after load removal (die release) is estimated, and the presence or absence of wrinkles in the formed material during stamping is predicted based on this estimated curvature radius or curvature.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent No. 6246074

[0013] Patent Document 2: Japanese Patent Application Publication No. 2016-3951

[0014] Patent Document 3: Japanese Patent Application Publication No. 2019-35603

[0015] Patent Document 4: Japanese Patent Application Publication No. 11-319971

[0016] Patent Document 5: Japanese Patent Application Publication No. 2017-100165

[0017] Patent Document 6: Japanese Patent Application Publication No. 2007-229761

[0018] Non-patent literature

[0019] Non-patent document 1: ISO 12004-2:2008, "Metallic materials-Sheet and strip-Determination of forming-limit curves-Part 2: Determination of forming-limit curves in the laboratory", 2008.

[0020] Non-patent document 2: Compiled by the Thin Steel Sheet Forming Technology Research Association, The Difficulty and Easy Processing of Steel Forming, 4th Edition, p.226, Nikkan Kogyo Shimbun, (2017) Summary of the Invention

[0021] The problem that the invention aims to solve

[0022] The technologies disclosed in Patent Documents 4 through 6 all presuppose a mechanism for wrinkle formation and derive judgment indicators related to the presence or absence of wrinkles based on this mechanism. However, the boundary values ​​(critical values) for these judgment indicators, and the determination of the presence or absence of wrinkles in stamped products based on experiments or stamping simulations, are based on visual sensory judgment, thus lacking objectivity. Furthermore, the technologies disclosed in Patent Documents 4 through 6 target specific stamping methods (such as impact forming) and stamped products of specific shapes. Therefore, if the stamping method and the shape of the stamped product differ, the state of strain and stress will also differ, resulting in a lack of universality in the judgment indicators for the presence or absence of wrinkles derived from these technologies.

[0023] Therefore, there is a pursuit of material testing methods that, like the aforementioned fracture-related FLD test, can easily and quantitatively determine the presence or absence of wrinkles, and can determine indices for wrinkle formation that are universally applicable regardless of the stamping method or the shape of the stamped product. However, while the FLD test determines the initiation point (ultimate strain, etc.) of fracture (crack) in the sheet metal during stamping, it fails to determine indices for wrinkle formation caused by out-of-plane buckling resulting from compressive loads applied to the sheet metal during stamping.

[0024] Furthermore, in stamping with sheet metal as raw material (blank), most of the deformation experienced by the blank occurs under a biaxial stress state with compressive load acting in at least one of the in-plane biaxial directions. Therefore, in order to determine whether wrinkles are generated in stamping, it is necessary to determine the criteria for wrinkle generation under a biaxial stress state with compressive load acting in at least one of the in-plane directions.

[0025] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for obtaining wrinkle generation determination index of stamped products under biaxial stress state during the stamping process by applying a compressive load in at least one in-plane axial direction to a biaxial stress test of a cross-shaped plate test piece, a wrinkle generation determination method, a wrinkle generation determination device and a wrinkle generation determination procedure for determining the presence or absence of wrinkle generation under biaxial stress state based on the determined index.

[0026] Methods for solving problems

[0027] In the method for obtaining a wrinkle generation determination index for stamped products according to the first aspect of the present invention, a biaxial stress test is used to determine the presence or absence of wrinkle generation under biaxial stress state during the stamping process of the stamped product. The biaxial stress test involves applying an in-plane biaxial load (including at least an in-plane uniaxial compressive load) to a cross-shaped measuring portion of a cross-shaped plate test piece, inducing out-of-plane buckling at the measuring portion. The method for obtaining the wrinkle generation determination index for the stamped product includes: a step of obtaining an in-plane biaxial strain-load relationship, changing the in-plane biaxial load ratio acting on the measuring portion during the biaxial stress test, and for each load ratio, obtaining the relationship between the in-plane biaxial strain generated at the measuring portion and the load during the out-of-plane buckling induced at the measuring portion; and a step of obtaining a stable behavior limit strain, for each load ratio, calculating the first differential of the in-plane uniaxial strain under the larger compressive load. The process involves determining the stability limit point, which is the point where the first derivative of the calculated strain becomes the local maximum, and taking it as the starting point of out-of-plane buckling. The strain in the biaxial direction of the measuring part at the stability limit point is taken as the stability limit strain. The process also involves obtaining the stability limit line by plotting the in-plane biaxial stability limit strains obtained for each load ratio on a two-dimensional coordinate system and connecting the plotted stability limit strains to obtain the stability limit line, which is an indicator of the wrinkle generation under biaxial stress.

[0028] In the second aspect of the present invention, a method for obtaining a wrinkle generation determination index for stamped products involves using a biaxial stress test to determine the presence or absence of wrinkles under biaxial stress during the stamping process. The biaxial stress test involves applying an in-plane biaxial load (including at least an in-plane compressive load in one axis) to a cross-shaped measuring portion of a cruciform test specimen for biaxial testing, inducing out-of-plane buckling at the measuring portion. The method for obtaining the wrinkle generation determination index includes: a step of obtaining an in-plane biaxial strain-load relationship, where the ratio of the in-plane biaxial load acting on the measuring portion during the biaxial stress test is changed, and for each load ratio, the relationship between the in-plane biaxial strain and load generated at the measuring portion during the out-of-plane buckling induced at the measuring portion is obtained; and a step of obtaining the wrinkle generation initiation strain, where for each load ratio, the larger compressive load is... The point where the polarity of the strain increment relative to the compressive load increment reverses in the relationship between strain and load in the in-plane uniaxial direction is determined as the wrinkle generation start point. The strain in the in-plane biaxial direction of the measuring part at the wrinkle generation start point is obtained as the wrinkle generation start strain. In the wrinkle generation start line acquisition process, the wrinkle generation start strain in the in-plane biaxial direction obtained for each load ratio is plotted on a two-dimensional coordinate, and the wrinkle generation start line under biaxial stress state is obtained by connecting the plotted wrinkle generation start strains.

[0029] The present invention relates to a method for determining wrinkle formation in stamped products, which uses the stable behavior limit line obtained by the method for obtaining wrinkle formation determination index of stamped products according to the first aspect of the present invention and the wrinkle formation start line obtained by the method for obtaining wrinkle formation determination index of stamped products according to the second aspect of the present invention to determine whether wrinkles are generated during the stamping process of the stamped product. The method for determining wrinkle formation in stamped products includes: a process for calculating the in-plane biaxial strain of the stamped product, performing a stamping simulation of the stamped product, and calculating the in-plane biaxial strain during the stamping process of the stamped product; and a wrinkle formation determination mapping acquisition process. The process involves obtaining a wrinkle generation determination map, which represents the stability behavior limit line and the wrinkle generation start line on a two-dimensional coordinate system with strain in the in-plane biaxial direction as the coordinate axis; and a wrinkle generation determination process for stamped products, in which the strain in the in-plane biaxial direction at a specified location of the stamped product is plotted on the obtained wrinkle generation determination map. If the plotted area is located between the stability behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamped product is high. If the plotted area is located closer to the compression side than the wrinkle generation start line, it is determined that wrinkle generation occurs at the specified location of the stamped product.

[0030] The present invention relates to a wrinkle generation determination device for stamped products, which uses a biaxial stress test to determine an index for determining the presence or absence of wrinkle generation under biaxial stress during the stamping process of the stamped product. The biaxial stress test involves applying an in-plane biaxial load (including at least an in-plane compressive load in one axis) to a cross-shaped measuring portion of a cross-shaped plate test piece, inducing out-of-plane buckling at the measuring portion. The device further includes an in-plane biaxial strain-load relationship acquisition unit, which modifies the operation of the biaxial stress test. For the load ratio in the in-plane biaxial direction of the measuring unit, for each load ratio, the relationship between the strain in the in-plane biaxial direction generated in the measuring unit during the out-of-plane buckling induced by the measuring unit and the load is obtained; the stability behavior limit strain acquisition unit, for each load ratio, calculates the first derivative of the strain in the in-plane uniaxial direction under the action of the larger compressive load, and obtains the stability behavior limit point as the point where the first derivative of the calculated strain is maximized, which is the starting point of out-of-plane buckling; the strain in the in-plane biaxial direction of the measuring unit at the stability behavior limit point is obtained as the stability behavior limit strain; the stability behavior limit line acquisition unit, for... The in-plane biaxial stability limit strain obtained for each load ratio is plotted on a two-dimensional coordinate system. By connecting these plotted stability limit strains, a stability limit line, which serves as an indicator of wrinkle formation under biaxial stress, is obtained. For the wrinkle formation initiation strain acquisition section, for each load ratio, the point where the polarity of the strain increment relative to the compressive load increment in the in-plane uniaxial direction of the larger compressive load reverses is determined as the wrinkle formation initiation point. The in-plane biaxial strain at this wrinkle formation initiation point is then obtained as the wrinkle formation initiation strain. The initiation line acquisition unit plots the in-plane biaxial strain at the start of wrinkle generation for each load ratio on a two-dimensional coordinate system, and obtains the wrinkle generation initiation line under biaxial stress state by connecting the plotted initiation strains. The in-plane biaxial strain calculation unit for stamped products performs a stamping simulation of the stamped product and calculates the in-plane biaxial strain during the stamping process. The wrinkle generation determination mapping acquisition unit obtains a wrinkle generation determination mapping, which represents the stability behavior limit line and the wrinkle generation initiation line on a two-dimensional coordinate system with the in-plane biaxial strain as the coordinate axis.The stamped product wrinkle generation determination unit plots the in-plane biaxial strain at a specified location of the stamped product onto the obtained wrinkle generation determination mapping. If the plot is located in the region between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamped product is high. If the plot is located closer to the compression side than the wrinkle generation start line, it is determined that wrinkle generation has occurred at the specified location of the stamped product.

[0031] In the wrinkle generation determination procedure for stamped articles disclosed in this invention, a biaxial stress test is used to determine the presence or absence of wrinkles under biaxial stress during the stamping process of the stamped article. The biaxial stress test involves applying an in-plane biaxial load, including at least an in-plane compressive load in one axis direction, to a cross-shaped measuring portion of a cross-shaped plate test piece, inducing out-of-plane buckling at the measuring portion. A computer functions as the following components: an in-plane biaxial strain-load relationship acquisition unit, which modifies the load applied during the biaxial stress test... The load ratio in the in-plane biaxial direction of the measuring unit is used to obtain the relationship between the strain in the in-plane biaxial direction generated in the measuring unit and the load during the out-of-plane buckling induced by the measuring unit for each load ratio. The stability behavior limit strain acquisition unit calculates the first derivative of the strain in the in-plane uniaxial direction under the larger compressive load for each load ratio, and obtains the stability behavior limit point as the point where the first derivative of the calculated strain is maximized, which is the starting point of out-of-plane buckling. The strain in the in-plane biaxial direction of the measuring unit at the stability behavior limit point is obtained as the stability behavior limit strain. The stability behavior limit line acquisition unit obtains the strain in the in-plane biaxial direction of the measuring unit for each load ratio. The in-plane biaxial stability limit strains obtained from the load ratios are plotted on a two-dimensional coordinate system. By connecting these plotted stability limit strains, a stability limit line, which serves as an indicator of wrinkle formation under biaxial stress, is obtained. For the wrinkle formation initiation strain acquisition section, for each load ratio, the point where the polarity of the strain increment relative to the compressive load increment in the in-plane uniaxial direction under the larger compressive load is reversed is determined as the wrinkle formation initiation point. The in-plane biaxial strain at this wrinkle formation initiation point is then obtained as the wrinkle formation initiation strain. The initiation line acquisition unit plots the in-plane biaxial strain at the start of wrinkle generation for each load ratio on a two-dimensional coordinate system, and obtains the wrinkle generation initiation line under biaxial stress state by connecting the plotted initiation strains. The in-plane biaxial strain calculation unit for stamped products performs a stamping simulation of the stamped product and calculates the in-plane biaxial strain during the stamping process. The wrinkle generation determination mapping acquisition unit obtains a wrinkle generation determination mapping, which represents the stability behavior limit line and the wrinkle generation initiation line on a two-dimensional coordinate system with the in-plane biaxial strain as the coordinate axis.The stamped product wrinkle generation determination unit plots the in-plane biaxial strain at a specified location of the stamped product onto the obtained wrinkle generation determination mapping. If the plot is located in the region between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamped product is high. If the plot is located closer to the compression side than the wrinkle generation start line, it is determined that wrinkle generation has occurred at the specified location of the stamped product.

[0032] Invention Effects

[0033] In this invention, a biaxial stress test is conducted on a cross-shaped plate specimen by applying a compressive load in at least one in-plane axis direction to obtain the relationship between strain and load in the biaxial in-plane direction. Based on this strain-load relationship, the stable behavior limit strain, which becomes the starting point for out-of-plane buckling, is determined. The determined stable behavior limit strain is plotted on a two-dimensional coordinate system with the strain in the biaxial in-plane direction as the coordinate axis. The plotted stable behavior limit strains are connected to obtain the stable behavior limit line. Thus, an index for determining the presence or absence of slight wrinkles under biaxial stress state during the stamping process of stamped products can be obtained.

[0034] Furthermore, in this invention, based on the relationship between the strain in the in-plane uniaxial direction of the compressive load and the load during the biaxial stress test, the strain at which wrinkles begin to form due to abrupt out-of-plane buckling is determined. This determined strain at which wrinkles begin to form is plotted on a two-dimensional coordinate system with the strain in the in-plane biaxial direction as the coordinate axis. The plotted strain at which wrinkles begin to form is connected to obtain the wrinkle initiation line. Thus, an index for determining the presence or absence of clear wrinkles under biaxial stress during the stamping process of a stamped product can be obtained.

[0035] Furthermore, in this invention, based on the stable behavior limit line obtained as an indicator for determining the presence or absence of slight wrinkles under biaxial stress and the wrinkle generation start line obtained as an indicator for determining the presence or absence of clear wrinkles under biaxial stress, it is possible to objectively and accurately determine the presence or absence of wrinkles under biaxial stress during the stamping process of the stamped product. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the process of obtaining the wrinkle generation determination index of the stamped product according to this embodiment.

[0037] Figure 2 This is a diagram illustrating an example of a cross-shaped plate-shaped test piece used in the method for obtaining wrinkle generation determination index of stamped articles according to this embodiment.

[0038] Figure 3 This is a diagram illustrating an example of a biaxial stress testing apparatus used in a biaxial stress test of a cross-shaped plate test piece in the method for obtaining wrinkle generation determination index of stamped articles according to this embodiment.

[0039] Figure 4 The figure illustrates the pressing mechanism of the central tool and side tool of the biaxial stress testing apparatus according to an embodiment of the present invention ((a) shows the state in which the pressing mechanism is provided in the central tool and side tool, and (b) shows the pressing mechanism).

[0040] Figure 5 This is an example of a strain-load graph when a compressive load in the biaxial direction (x-axis direction and y-axis direction) is applied to a cross-shaped plate test piece in the method for obtaining the wrinkle generation determination index of stamped products according to this embodiment.

[0041] Figure 6 This is a graph showing the relationship between strain, load, and fold height in the in-plane uniaxial direction under compressive load in a biaxial stress test in which out-of-plane buckling is induced by the measuring section of a cross-shaped plate test piece, as an example in this embodiment, and a graph illustrating the limit point of stable behavior obtained from the relationship between strain and load.

[0042] Figure 7 This is a graph illustrating that, in this embodiment, the stable behavior strain and the strain at which wrinkle formation begins, obtained by a biaxial stress test with a changed load ratio in the in-plane biaxial direction acting on a cross-shaped plate test piece, are plotted on a two-dimensional coordinate system. The stable behavior limit line is obtained by connecting the stable behavior strains, and the wrinkle formation start line is obtained by connecting the wrinkle formation start strains.

[0043] Figure 8 This is a flowchart illustrating the process of obtaining the wrinkle generation determination index of stamped products according to other embodiments of this invention.

[0044] Figure 9 This diagram illustrates the wrinkle generation start point determined in other embodiments of this invention based on the relationship between the strain in the in-plane axial direction of the measuring portion of the plate-shaped test piece subjected to compressive load and the load.

[0045] Figure 10 This is a flowchart illustrating the process of the wrinkle generation determination method for stamped products according to this embodiment.

[0046] Figure 11This diagram illustrates an example of a wrinkle generation determination mapping that uses in-plane biaxial strain obtained through stamping simulation to determine the presence or absence of wrinkles in the wrinkle generation determination method for stamped articles according to this embodiment.

[0047] Figure 12 This is a diagram showing the stamped article that is the object of forming in the embodiment and the mold used in the stamping of the stamped article.

[0048] Figure 13 In the embodiment, the in-plane biaxial strain at the side portion of the stamped article with a forming height of 25 mm is plotted on the wrinkle generation determination map (a) and the shaded map of the stamped article and the position (○ and ●) where the wrinkle generation determination was made (b).

[0049] Figure 14 In the embodiment, the in-plane biaxial strain at the side portion of the stamped article with a forming height of 30 mm is plotted on the wrinkle generation determination map (a) and the shaded map of the stamped article and the position (○ and ●) where the wrinkle generation determination was made (b).

[0050] Figure 15 In the embodiment, the in-plane biaxial strain at the side portion of the stamped article with a forming height of 40 mm is plotted on the wrinkle generation determination map (a) and the shaded map of the stamped article and the position (○ and ●) where the wrinkle generation determination was made (b).

[0051] Figure 16 In the embodiment, the in-plane biaxial strain at the side portion of the stamped article with a forming height of 50 mm is plotted on the wrinkle generation determination map (a) and the shaded map of the stamped article and the position (○ and ●) where the wrinkle generation determination was made (b).

[0052] Figure 17 In the embodiments, the distribution of in-plane biaxial strain at the side surface of stamped articles with forming heights of 25mm, 30mm, 40mm and 50mm is represented by a diagram of wrinkle generation determination mapping based on the stability behavior limit line.

[0053] Figure 18 In the embodiments, the distribution of in-plane biaxial strain at the side surface of stamped articles with forming heights of 25mm, 30mm, 40mm and 50mm is represented in a diagram of wrinkle generation determination mapping based on the wrinkle generation start line.

[0054] Figure 19This is a block diagram of a wrinkle generation determination device for stamped products according to an embodiment of the present invention, and a diagram illustrating the function of a wrinkle generation determination procedure for stamped products according to an embodiment of the present invention. Detailed Implementation

[0055] Before describing the method for obtaining wrinkle generation determination index, wrinkle generation determination method, wrinkle generation determination device and wrinkle generation determination procedure of the stamped product according to the embodiments of the present invention (Embodiment 1), the plate-shaped test piece used as the object of the biaxial stress test in the present invention will be described below.

[0056] <Plate-shaped test piece>

[0057] As in Figure 2 As an example, the plate-shaped test piece 100 is cross-shaped in the in-plane biaxial direction, and has a measuring part 101 that is a rectangle in the center of the cross shape and four piece parts 103 that extend from the four sides of the measuring part 101 in the in-plane biaxial direction.

[0058] The measuring section 101 is a portion that, during biaxial stress testing, induces out-of-plane buckling at the location facing the opening 17 of the central portion 13a of the central mold 11a (described later), thus becoming the object of strain and stress measurement. It should be noted that... Figure 2 The rectangular measuring section 101 is shown as a square, but in this invention, the measuring section can also be rectangular.

[0059] The plate portion 103 is composed of a pair of plate portions 103a and a pair of plate portions 103b that are opposite to and sandwich the measuring portion 101. The direction in which the pair of plate portions 103a extend sandwiching the measuring portion 101 is ( Figure 2 (x-axis direction) and the direction extending from the measuring part 101 sandwiched by a pair of plates 103b ( Figure 2 The y-axis direction in the measurement section 101 is orthogonal to the measurement section 101, and these directions correspond to the in-plane biaxial direction of the measurement section 101 that applies the specified load to the plate-shaped test piece 100.

[0060] That is, by applying an in-plane biaxial compressive load to the measuring unit 101 via a pair of plates 103a and a pair of plates 103b, a biaxial compression test can be performed to make the measuring unit 101 biaxially compressed.

[0061] Alternatively, by applying a compressive load toward the measuring unit 101 via one plate 103a and applying a tensile load to the measuring unit 101 via another plate 103b, a uniaxial compression-uniaxial tension test can be performed, which puts the measuring unit 101 into a uniaxial compression-uniaxial tension condition.

[0062] Furthermore, by not applying load to a pair of plates 103a (or a pair of plates 103b) and applying compressive load to another plate 103b (or a pair of plates 103a), a uniaxial compression test can be performed to make the measuring section a uniaxial compression condition.

[0063] Furthermore, by attaching strain gauges to the measuring unit 101, the strain of the measuring unit 101 under biaxial stress conditions (biaxial compression condition, uniaxial compression and uniaxial tension condition, uniaxial compression condition) can be measured.

[0064] It should be noted that, Figure 2 The plate-shaped test piece 100 shown, as described in the following reference, has circular cut portions 105 obtained by cutting each corner of the cross shape into a circular shape, and a plurality of hole-shaped portions 107 provided on each line surrounding the measuring portion 101 and connecting the centers of adjacent circular cut portions 105 (reference: Japanese Patent Application Publication No. 2019-35603).

[0065] The circular cutout 105 prevents the plates 103a and 103b from bulging and folding at the corners when in-plane biaxial compressive loads are applied to the measuring section 101 via the plates 103a and 103b respectively, thus enabling the measuring section 101 to generate the compressive strain required for measuring material properties.

[0066] The hole-shaped portion 107 is used to disperse the localized stress concentration at the measuring portion 101 and reduce stress deviation.

[0067] However, the biaxial stress test in this invention is not limited to the use of Figure 2The shape of the plate-shaped test piece 100 shown is independent of the presence or absence of the circular cut portion 105 and the hole-shaped portion 107. The shape and size of the plate-shaped test piece can be appropriately changed according to the conditions of the biaxial stress test (load ratio, etc.).

[0068] [Method for Obtaining Indicators for Determining Wrinkle Formation in Stamped Parts]

[0069] The present invention relates to a method for obtaining a wrinkle generation determination index for stamped articles. This method uses a biaxial stress test to determine the presence or absence of wrinkles under biaxial stress during the stamping process of the stamped article. The biaxial stress test involves applying an in-plane biaxial load, including at least a compressive load in one in-plane axis, to an object, for example... Figure 2 The plate-shaped test piece 100 shown has a cross-shaped measuring section 101 in the in-plane biaxial direction, and the measuring section 101 induces out-of-plane buckling. For example... Figure 1 As shown, the method for obtaining wrinkle generation determination index of stamped products according to the embodiments of the present invention includes a process S1 for obtaining the strain-load relationship in the biaxial direction of the plane, a process S3 for obtaining the stable behavior limit strain, and a process S5 for obtaining the stable behavior limit line. The following describes each of the above processes.

[0070] Procedure for Obtaining In-Plane Biaxial Strain-Load Relationship

[0071] In the process of obtaining the strain-load relationship in the biaxial direction of the plane, the load ratio in the biaxial direction of the plane acting on the measuring unit 101 during the biaxial stress test is changed. For each load ratio, the relationship between the strain and the load generated in the biaxial direction of the measuring unit 101 during the out-of-plane buckling process induced by the measuring unit 101 is obtained.

[0072] In step S1, which obtains the in-plane biaxial strain-load relationship, it is best to use, for example, [example]. Figure 3 and Figure 4 The biaxial stress testing apparatus 1 shown, which includes a central mold 11, a side mold 21 and a pressing mechanism 31, is used to perform biaxial stress testing on the plate-shaped test piece 100.

[0073] like Figure 3 As shown, the central mold 11 has a rectangular central portion 13 facing the measuring portion 101 that intersects the cross shape of the plate-shaped test piece 100, and a comb-shaped first comb-shaped part 15 formed on the edges of the four sides of the central portion 13. It is composed of a pair of central molds 11a and central molds 11b that clamp the two sides of the plate-shaped test piece 100.

[0074] The first comb tooth portion 15 is composed of a pair of first comb tooth portions 15a and a pair of first comb tooth portions 15b formed on opposite edges of a rectangular central mold 11. The directions of the opposing pair of first comb tooth portions 15a and the directions of the opposing pair of first comb tooth portions 15b are orthogonal at the central portion 13. Furthermore, as... Figure 2 As shown, these directions are biaxial in-plane directions through which compressive or tensile loads are applied to the measuring section 101 via a pair of plates 103a or a pair of plates 103b of the plate-shaped test piece 100. Figure 2 (corresponding to the x-axis and y-axis directions in the text).

[0075] Furthermore, an opening 17 is formed in the central portion 13a of one of the pair of central molds 11, the central mold 11a, which allows the measuring part 101 to have a degree of freedom in shape deformation, thereby inducing out-of-plane buckling. Additionally, the central mold 11 is designed to prevent in-plane movement of the plate-shaped test piece 100, such as... Figure 3 As shown, its four corners are connected to the pressing mechanism 31 by bolts 19. Figure 4 The base part 33 is fixed.

[0076] like Figure 3 As shown, the side mold 21 has: a comb-shaped second comb tooth portion 23 disposed on the sides of the four sides of the central mold 11 and engaging with the first comb tooth portion 15, and a holding portion 25 holding the cross-shaped piece portion 103 of the plate-shaped test piece 100, and is composed of a pair of side molds 21a and a pair of side molds 21b disposed between the central mold 11.

[0077] The side mold 21a has a second comb tooth 23a that engages with the first comb tooth 15a of the central mold 11 in a pluggable manner and a holding part 25a that holds the plate portion 103a of the plate-shaped test piece 100.

[0078] The side mold 21b has a second comb tooth 23b that engages with the first comb tooth 15b of the central mold 11 in a pluggable manner, and a holding part 25b that holds the plate portion 103b of the plate-shaped test piece 100.

[0079] In this way, by engaging the second comb tooth 23 with the first comb tooth 15 and moving the side mold 21, buckling at the plate portion 103 can be suppressed during the process of applying a compressive load to the plate-shaped test piece 100 via the plate portion 103.

[0080] It should be noted that, in this embodiment, as Figure 4As shown, the side molds 21a and 21b are respectively disposed on rollers 27a and 27b disposed on the upper surface of the base portion 33 of the pressing mechanism 31, and can move in the plane along a single axis while the second comb portions 23a and 23b are respectively engaged with the first comb portions 15a and 15b of the central mold 11.

[0081] The pressing mechanism 31, acting as a clamping force applying unit, applies a predetermined clamping force in the thickness direction of the plate-shaped test piece 100 in a manner that allows for insertion and extraction of the second comb tooth portion 23a, which engages with the first comb tooth portion 15a, and the second comb tooth portion 23b, which engages with the first comb tooth portion 15b. Figure 4 As shown, it has a base portion 33, a top plate portion 35, and a guide pin 37.

[0082] In the pressing mechanism 31, by applying a pressing force to the base portion 33 at the four corners using guide pins 37 from above the top plate portion 35, a predetermined clamping force can be applied in the thickness direction of the plate-shaped test piece 100 in a manner that allows the first comb portion 15 and the second comb portion 23 to be inserted and removed. This reliably prevents buckling distortion at the piece portion 103, which is preferable. It should be noted that at least one of the clamping force in the thickness direction applied by the bolt 19 and the clamping force in the thickness direction applied by the top plate portion 35 can also be used.

[0083] exist Figure 5 The diagram shows the use of a biaxial stress testing apparatus 1 to test the measuring section 101 of a plate-shaped test piece 100 in a biaxial in-plane direction. Figure 2 An example of a biaxial stress test with a load ratio of -1:-1 in the x-axis and y-axis directions, and a curve showing the relationship between strain and load generated in the in-plane biaxial direction in the measuring unit 101 during out-of-plane buckling induced by the measuring unit 101.

[0084] Procedures for Obtaining Stable Behavior Limits and Responses

[0085] The stable behavior limit strain acquisition process S3 is based on the relationship between the strain and load in the in-plane biaxial direction obtained in the strain-load relationship acquisition process S1 for each load ratio. For each load ratio, the first derivative of the strain in the in-plane uniaxial direction under the compressive load is calculated. The point where the first derivative of the calculated strain becomes the maximum is taken as the stable behavior limit point, which is the starting point of out-of-plane buckling. The strain in the in-plane biaxial direction of the measuring unit 101 at the stable behavior limit point is taken as the stable behavior limit strain.

[0086] exist Figure 6 The diagram shows the biaxial direction in the plane ( Figure 2(a) This is an example of a biaxial stress test where the load ratio in the x-axis and y-axis directions is -1:-1. The result is obtained by calculating the first derivative of the in-plane strain in the y-axis direction under compressive load, and taking the point where the first derivative of the calculated strain is maximized as the limit point of stable behavior. Figure 6 In the diagram, the horizontal axis represents the load acting on the plate-shaped test piece 100 (positive for tensile load, negative for compressive load), the left vertical axis represents the measured strain based on the strain gauge (positive for tensile strain, negative for compressive strain) and the first derivative of the strain with respect to the compressive load, and the right vertical axis represents the fold height, which is the amount of deformation in the thickness direction (out-of-plane direction) of the measuring part 101.

[0087] In a biaxial stress test, if a compressive load of at least one in-plane axial direction is gradually applied to the measuring portion 101 of the plate-shaped test piece 100, compressive strain accumulates at the measuring portion 101. However, shortly afterward, the accumulation of compressive strain relative to the compressive load becomes sluggish, and out-of-plane deformation occurs at the measuring portion 101. The stable behavior limit point represents the point at which the accumulation of compressive strain relative to the compressive load begins to slow down, and can be understood as the starting point indicating the first signs of out-of-plane buckling at the measuring portion 101. That is, if a compressive load is applied to the measuring portion 101 of the plate-shaped test piece 100 and the strain of the measuring portion 101 reaches the stable behavior limit point, slight wrinkles, although not clearly visible to the naked eye, are produced at the measuring portion 101, but the degree of wrinkle formation can be confirmed by palpation.

[0088] It should be noted that, as Figure 5 As shown, in a biaxial stress test, when a compressive load in the biaxial direction in the plane is applied to the measuring unit 101, the point where the absolute value of the strain is smaller and the first derivative of the strain becomes the largest can be used as the limit point of stable behavior in the relationship between strain and load in the biaxial direction in the plane. Alternatively, the limit point of stable behavior can be obtained by averaging or summing the strain and load in the biaxial direction in the plane.

[0089] Procedures for Obtaining the Limits of Stable Behavior

[0090] The stable behavior limit line acquisition process S5 plots the in-plane biaxial stable behavior limit strains obtained for each load ratio in the stable behavior limit strain acquisition process S3 on a two-dimensional coordinate system. By connecting the plotted stable behavior limit strains, the stable behavior limit line, which is the index of wrinkle generation under biaxial stress state, is obtained.

[0091] exist Figure 7The image shows an example of how the stability behavior limit strain in the in-plane biaxial direction obtained for each load ratio through a biaxial stress test using a plate-shaped test piece 100 was plotted on a two-dimensional coordinate system and the stability behavior limit line was obtained.

[0092] exist Figure 7 In the diagram, the origin represents the strain (ε) of the measuring unit 101 at the start of the biaxial stress test. x =0, ε y =0), regarding ε x and ε y Negative values ​​represent compressive strain, and positive values ​​represent tensile strain. Furthermore, in Figure 7 In the two-dimensional coordinate system shown, the negative region (ε) on the horizontal axis x <0, ε y =0) and the negative region on the vertical axis (ε) x =0, ε y <0 indicates uniaxial compression state, first quadrant (ε) x >0, ε y >0) indicates a tensile-tensile condition, in the third quadrant (ε x <0, ε y <0 indicates biaxial compression state, second quadrant (ε) x <0, ε y >0) and the fourth quadrant (ε x >0, ε y <0 indicates a tensile-compression condition. Furthermore, in Figure 7 In the diagram, the dashed line represents a straight path (strain path) where the plastic strain ratio remains constant under each load ratio when the plate specimen 100 is subjected to in-plane biaxial loads with a constant load ratio in a biaxial stress test.

[0093] Here, if we observe the relationship between the stability limit strain and the load ratio, the strain of the out-of-plane buckling of the measuring unit 101 in the biaxial in-plane direction extends from the second quadrant to the fourth quadrant, i.e., ε x and ε y At least one of them is produced under compressive strain, in the first quadrant, i.e., ε x and ε y No strain occurs when both sides are under tensile strain.

[0094] Furthermore, according to Figure 7The relationship between the stability limit line and the strain path at various load ratios is shown. Under biaxial compression (third quadrant), it is compared with uniaxial compression (on the horizontal axis (ε)). x ), on the vertical axis (ε) y Low compressive strain leads to out-of-plane buckling. Furthermore, under tension-compression conditions (second and fourth quadrants), out-of-plane buckling does not occur until the compressive strain is higher than that under uniaxial compression. Thus, by plotting the stability limit strain in the in-plane biaxial direction, obtained from biaxial stress tests, onto a two-dimensional coordinate system with the strain in the in-plane biaxial direction as the axis, and connecting the stability limit strains, a stability limit line, which serves as the starting point for out-of-plane buckling under various biaxial stress and uniaxial compression conditions, can be obtained.

[0095] It should be noted that, in the above explanation, a biaxial stress test was conducted using a cross-shaped plate test piece 100, and the stable behavior limit strain, which serves as the starting point for out-of-plane buckling at the measuring section 101, was used to determine the stable behavior limit line, which is an indicator of wrinkle formation. However, if compressive load is still applied to the measuring section 101 even if the strain at the measuring section 101 exceeds the stable behavior limit point, then... Figure 6 As shown, the compressive strain accumulated in the measuring section 101 is released all at once, resulting in out-of-plane buckling, and the compressive strain of the measuring section 101 is transformed into tensile strain.

[0096] Therefore, as another embodiment of this embodiment (Embodiment 2), the strain in the biaxial direction in the plane when the compressive strain accumulated in the measuring unit 101 is released all at once and the measuring unit 101 produces out-of-plane buckling can also be used as an indicator to determine whether a clear wrinkle is generated.

[0097] Other embodiments of this implementation involve methods for obtaining wrinkle generation determination indicators for stamped products that are similar to those in Embodiment 1, through... Figure 2 The measuring section 101 of the cross-shaped plate test piece 100 shown induces a biaxial stress test for out-of-plane buckling, and an index is obtained to determine the presence or absence of wrinkles under biaxial stress during the stamping process of stamped products. For example... Figure 8 As shown, other embodiments of this invention involve methods for obtaining wrinkle generation determination indicators for stamped products, including a process S1 for obtaining the in-plane biaxial strain-load relationship, a process S13 for obtaining the wrinkle generation initiation strain, and a process S15 for obtaining the wrinkle generation initiation line. Here, the process S1 for obtaining the in-plane biaxial strain-load relationship is the same as that in Embodiment 1 described above. Therefore, the process S13 for obtaining the wrinkle generation initiation strain and the process S15 for obtaining the wrinkle generation initiation line will be described below.

[0098] "The process of obtaining strain at the beginning of wrinkle formation"

[0099] The strain-load relationship obtained at the start of wrinkle generation in step S13 is based on the strain-load relationship obtained in the biaxial ...

[0100] exist Figure 9 The diagram illustrates an example of how the initiation point of wrinkle formation was determined based on the relationship between strain and load at the measuring section 101 of the plate-shaped test specimen 100 using a biaxial stress test with a load ratio of -1:-1. The initiation point of wrinkle formation corresponds to the moment when a slight change in wrinkle, which can be identified by palpation, abruptly transforms into a clear wrinkle.

[0101] Process for obtaining the wrinkle formation start line

[0102] The process S15, which obtains the wrinkle generation start line, plots the in-plane biaxial direction wrinkle generation start strain obtained for each load ratio on a two-dimensional coordinate system. By connecting the plotted wrinkle generation start strains, the wrinkle generation start line under biaxial stress is obtained.

[0103] In the above Figure 7 The diagram shows the result of plotting the in-plane biaxial strain for each load ratio onto a two-dimensional coordinate system to obtain the initiation line of the wrinkle formation.

[0104] As previously described, if an in-plane biaxial load is applied to the measuring section 101 of the cross-shaped plate test piece 100, the strain at the measuring section 101 reaches the stability behavior limit line along a straight path (strain path) with a constant strain ratio. Here, no out-of-plane buckling is observed in the strain path from the origin to the stability behavior limit line, and the measuring section 101 shows the initial signs of out-of-plane buckling at the point when the stability behavior limit line is reached.

[0105] If a biaxial in-plane load is applied to the measuring unit 101 after reaching the stability behavior limit line, the strain at the measuring unit 101 will cross the stability behavior limit line along the strain path and reach the wrinkle initiation line. Here, within the range between the stability behavior limit line and the wrinkle initiation line, compressive strain accumulates in the measuring unit, resulting in slight out-of-plane buckling (wrinkling) in the measuring unit 101 to a degree that is difficult to determine visually but can be confirmed by palpation.

[0106] Furthermore, at the point in time when the wrinkle generation initiation line is reached, the compressive strain accumulated in the measuring section 101 is released all at once, and the slight wrinkles generated in the measuring section 101 are transformed into clear wrinkles.

[0107] Thus, the method for obtaining the wrinkle generation determination index of stamped products according to other solutions of this embodiment serves as an index for determining the presence or absence of wrinkle generation under biaxial stress state during the stamping process of stamped products. It is possible to obtain the stability behavior limit line and the wrinkle generation start line on a two-dimensional coordinate system with strain in the biaxial direction in the plane as the coordinate axis.

[0108] [Method for determining the occurrence of wrinkles in stamped parts]

[0109] The wrinkle generation determination method for stamped products according to the embodiment (Embodiment 3) of the present invention uses the stable behavior limit line obtained by the wrinkle generation determination index acquisition method for stamped products of this embodiment (Embodiment 1) described above, and the wrinkle generation start line obtained by the wrinkle generation determination index acquisition method for stamped products of another scheme of this embodiment (Embodiment 2) described above, to determine whether wrinkles are generated during the stamping process of the stamped product. Figure 10 As shown, the wrinkle generation determination method for stamped products according to the embodiments of the present invention includes a biaxial strain calculation step S21, a wrinkle generation determination mapping acquisition step S23, and a wrinkle generation determination step S25. These steps will be described below.

[0110] Calculation Process for Biaxial Strain in Stamped Parts

[0111] The process S21, which calculates the in-plane biaxial strain of the stamped product, simulates the stamping process of the stamped product and calculates the in-plane biaxial strain of a specified part of the stamped product during the stamping process.

[0112] There are no particular restrictions on the specific location of the stamped part for obtaining in-plane biaxial strain, but it is best to choose the location where wrinkles are to be concerned during the stamping process.

[0113] "Process for Determining and Obtaining the Mapping of Wrinkle Generation"

[0114] The wrinkle generation determination mapping acquisition process S23 represents the stable behavior limit line and wrinkle generation start line obtained by the method described in Embodiment 1 and Embodiment 2 on a two-dimensional coordinate with strain in the biaxial direction in the plane as the coordinate axis, and obtains the wrinkle generation determination mapping that determines whether wrinkle generation occurs under biaxial stress state.

[0115] exist Figure 11The image shows an example of a wrinkle initiation determination mapping that represents the stability behavior limit line and the wrinkle initiation start line on a two-dimensional coordinate system with strain along two in-plane axes as the coordinate axes. Figure 11 In the figure, the region on the tensile side of the in-plane biaxial strain ratio relative to the stability behavior limit line represents the region of biaxial strain that does not produce out-of-plane buckling ("no wrinkling" in the figure). Additionally, in... Figure 11 In the diagram, the area enclosed by the stable behavior limit line and the wrinkle initiation line represents a region where slight wrinkles occur to a degree that cannot be visually confirmed (referred to as "wrinkle concern" in the figure). Furthermore, in... Figure 11 In the figure, the region on the compression side of the strain ratio in the biaxial direction within the plane represents the area where clear wrinkles are produced (“wrinkle production” in the figure).

[0116] "Stamping Forming Wrinkle Generation Judgment Process"

[0117] In the stamping part wrinkle generation determination process S25, the in-plane biaxial strain at a specified location of the stamping part, obtained in the in-plane biaxial strain calculation process S21, is plotted on the wrinkle generation determination mapping obtained in the wrinkle generation determination mapping acquisition process S23. If the plot on the wrinkle generation determination mapping is located in the area between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamping part is high. If the plot is closer to the compression side than the wrinkle generation start line, it is determined that wrinkle generation occurs at the specified location of the stamping part.

[0118] It should be noted that the effectiveness of the method for determining the generation of wrinkles in stamped products involved in Embodiment 2 is demonstrated in the embodiments described later.

[0119] [Wrinkle Generation Detection Device for Stamped Products]

[0120] The wrinkle generation determination device 41 (hereinafter referred to as "wrinkle generation determination device 41") of the present invention determines the presence or absence of wrinkle generation under biaxial stress state during the stamping process of the stamped article by using a biaxial stress test. The biaxial stress test involves applying an in-plane biaxial load, including at least a compressive load in one in-plane direction, to an object such as... Figure 2 The cross-shaped measuring portion 101 of the plate-shaped test piece 100, which is cross-shaped in the in-plane biaxial direction, induces out-of-plane buckling. For example... Figure 19As shown, the wrinkle generation determination device 41 includes an in-plane biaxial strain-load relationship acquisition unit 43, a stable behavior limit strain acquisition unit 45, a stable behavior limit line acquisition unit 47, a wrinkle generation start strain acquisition unit 49, a wrinkle generation start line acquisition unit 51, an in-plane biaxial strain calculation unit 53 for stamped products, a wrinkle generation determination mapping acquisition unit 55, and a stamped product wrinkle generation determination unit 57.

[0121] The wrinkle generation determination device 41 can also be composed of the CPU (Central Processing Unit) of a computer (PC, etc.). In this case, the aforementioned components function by executing a prescribed program through the computer's CPU.

[0122] In-plane biaxial strain-load relationship acquisition section

[0123] The in-plane biaxial strain-load relationship acquisition unit 43 modifies the in-plane biaxial load ratio acting on the measuring unit 101 during the biaxial stress test, and for each load ratio, acquires the relationship between the strain and load generated in the measuring unit 101 in the in-plane biaxial direction during the out-of-plane buckling induced by the measuring unit 101. In this embodiment, the in-plane biaxial strain-load relationship acquisition unit 43 performs the aforementioned in-plane biaxial strain-load relationship acquisition step S1.

[0124] Stable Behavior Limit Response Acquisition Department

[0125] The stable behavior limit strain acquisition unit 45 calculates the first derivative of the strain in the in-plane biaxial direction under compressive load for each load ratio based on the relationship between strain and load obtained in the in-plane biaxial strain-load relationship acquisition unit 43 for each load ratio. The point where the first derivative of the calculated strain becomes maximum is taken as the stable behavior limit point, which is the starting point of out-of-plane buckling. The strain in the in-plane biaxial direction at the measurement unit 101 at the stable behavior limit point is obtained as the stable behavior limit strain. In this embodiment, the stable behavior limit strain acquisition unit 45 performs the aforementioned stable behavior limit strain acquisition step S3.

[0126] "Stable Behavior Limits Acquisition Section"

[0127] The stability behavior limit line acquisition unit 47 plots the in-plane biaxial stability behavior limit strains obtained in the stability behavior limit strain acquisition unit 45 for each load ratio on a two-dimensional coordinate system. By connecting the plotted stability behavior limit strains, the stability behavior limit line, which serves as an indicator of wrinkle formation under biaxial stress, is obtained. In this embodiment, the stability behavior limit line acquisition unit 47 performs the aforementioned stability behavior limit line acquisition step S5.

[0128] "Fold Generation Begins with Strain Acquisition"

[0129] The strain at which wrinkle generation begins to occur is obtained by the strain-load relationship obtained by the strain-load relationship acquisition unit 43 in the biaxial direction of the in-plane for each load ratio. For each load ratio, the point where the polarity of the strain increment relative to the compressive load increment in the strain-load relationship in the uniaxial direction of the in-plane under compressive load is reversed is determined as the wrinkle generation start point. The strain in the biaxial direction of the measurement unit 101 at the wrinkle generation start point is obtained as the wrinkle generation start strain. In this embodiment, the strain at which wrinkle generation begins to occur to occur is obtained by the strain at which wrinkle generation begins to occur to occur step S13 described above.

[0130] "The section on the starting line of wrinkle formation"

[0131] The wrinkle generation start line acquisition unit 51 plots the in-plane wrinkle generation start strain obtained for each load ratio in the biaxial direction on a two-dimensional coordinate system, and obtains the wrinkle generation start line under biaxial stress state by connecting the plotted wrinkle generation start strains. In this embodiment, the wrinkle generation start line acquisition unit 51 performs the aforementioned wrinkle generation start line acquisition step S15.

[0132] Calculation of Biaxial Strain in Stamped Parts

[0133] The in-plane biaxial strain calculation unit 53 of the stamped product performs a stamping simulation of the stamped product and calculates the in-plane biaxial strain of a specified part of the stamped product during the stamping process. In this embodiment, the in-plane biaxial strain calculation unit 53 of the stamped product performs the aforementioned in-plane biaxial strain calculation step S21 of the stamped product.

[0134] Wrinkle Generation Determination Mapping Acquisition Department

[0135] The wrinkle generation determination mapping acquisition unit 55 acquires a wrinkle generation determination mapping, which represents the stability behavior limit line obtained by the stability behavior limit line acquisition unit 47 and the wrinkle generation start line obtained by the wrinkle generation start line acquisition unit 51 on a two-dimensional coordinate system with strain in the biaxial direction as the coordinate axis, and determines whether wrinkles are generated under biaxial stress state. In this embodiment, the wrinkle generation determination mapping acquisition unit 55 performs the aforementioned wrinkle generation determination mapping acquisition step S23.

[0136] Stamping Part Wrinkle Generation Judgment Department

[0137] The stamped product wrinkle generation determination unit 57 plots the in-plane biaxial strain at a predetermined location of the stamped product, calculated by the in-plane biaxial strain calculation unit 53, onto a wrinkle generation determination mapping obtained in the wrinkle generation determination mapping acquisition unit 55. If the plot on the wrinkle generation determination mapping is located in the region between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the predetermined location of the stamped product is high. If the plot is located closer to the compression side than the wrinkle generation start line, it is determined that wrinkle generation has occurred at the predetermined location of the stamped product. In this embodiment, the stamped product wrinkle generation determination unit 57 performs the aforementioned stamped product wrinkle generation determination process S25.

[0138] [Procedure for Determining Wrinkle Formation in Stamped Parts]

[0139] The embodiments of the present invention can be configured as a wrinkle generation determination procedure for stamped products. Specifically, the wrinkle generation determination procedure for stamped products according to the embodiments of the present invention uses a biaxial stress test to determine an index for determining the presence or absence of wrinkle generation under biaxial stress during the stamping process of the stamped product, thereby determining whether wrinkle generation occurs during the stamping process. The biaxial stress test involves applying an in-plane biaxial load, including at least a compressive load in one in-plane axis, to an object, for example... Figure 2 The cross-shaped measuring portion 101 of the plate-shaped test piece 100, which is cross-shaped in the in-plane biaxial direction, induces out-of-plane buckling. For example... Figure 19 As shown, the wrinkle generation determination program for stamped products according to the embodiments of the present invention uses a computer as an in-plane biaxial strain-load relationship acquisition unit 43, a stable behavior limit strain acquisition unit 45, a stable behavior limit line acquisition unit 47, a wrinkle generation start strain acquisition unit 49, a wrinkle generation start line acquisition unit 51, an in-plane biaxial strain calculation unit 53 for stamped products, a wrinkle generation determination mapping acquisition unit 55, and a wrinkle generation determination unit 57 for stamped products.

[0140] In the above-described embodiment, the wrinkle generation determination device and wrinkle generation determination procedure for stamped products can, in the same manner as the wrinkle generation determination index acquisition method for stamped products according to Embodiment 1 of the present invention, serve as an index for determining the presence or absence of wrinkle generation under biaxial stress state during the stamping process of the stamped product, and calculate the stability behavior limit line and wrinkle generation start line on a two-dimensional coordinate system with strain in the biaxial direction as the coordinate axis. Furthermore, the same effect demonstrated in the embodiments described later can be obtained as in Embodiment 2 of the present invention.

[0141] Example

[0142] Since experiments and analyses were conducted to verify the effectiveness of the method for determining the wrinkle formation of stamped products involved in this invention, the following explanation is provided.

[0143] In this embodiment, the stability behavior limit line and wrinkle initiation line obtained by biaxial stress testing of a cross-shaped plate specimen under biaxial in-plane compressive loads are used to verify the stability behavior limit line and wrinkle initiation line. Figure 12 Determination of wrinkle generation in the stamping simulation of the stamped part 200 shown.

[0144] In this embodiment, firstly, as described in the aforementioned Implementation 1, for Figure 2 The measuring section 101 of the cross-shaped plate test piece 100 shown is used by... Figure 3 and Figure 4 The biaxial stress testing apparatus 1 shown induced out-of-plane buckling biaxial stress test in the measuring unit 101, and determined the stability limit line and the wrinkle initiation line under biaxial stress state. Then, using the determined stability limit line and wrinkle initiation line, the aforementioned [structure / equipment] was manufactured. Figure 11 The wrinkles shown generate a decision mapping.

[0145] It should be noted that in the biaxial stress test, for the plate-shaped test piece 100, steel sheets with a tensile strength of 270 MPa and a thickness of 1.2 mm are used as the test material. The size of the measuring part is 30 mm × 30 mm, and the opening 17 formed in the central mold 11a of the biaxial stress testing device 1 is a circle with a diameter of φ25 mm. In addition, the biaxial stress state acting on the measuring part 101 is uniaxial compression, biaxial compression, and tension-compression.

[0146] Next, proceed Figure 12 The stamping simulation based on FEM analysis of the stamped part 200 with convex face 201 and side face 203 shown determines the presence or absence of wrinkles in the stamped part 200. It should be noted that... Figure 12 In the image, only the left half of the stamped part 200 is shown to indicate the state of the punch 211. In the stamping simulation, the stamped part 200 covers the entire circumference of the die 213.

[0147] like Figure 12As shown, the stamped product 200 is obtained by bulging using a die 210 equipped with a punch 211, a die 213, and a blank holder 215. The blank used is a circular steel plate with a tensile strength of 270 MPa and a thickness of 1.2 mm. Furthermore, the forming height of the stamped product 200 is varied within the range of 20 mm to 50 mm, based on... Figure 11 The wrinkle generation determination mapping shown indicates whether wrinkles are generated at the side portion 203 of the stamped part 200 at each forming height. Table 1 shows the blank material, mold conditions, and FEM analysis conditions.

[0148] [Table 1]

[0149] (Table 1)

[0150]

[0151] exist Figures 13-16 The diagram shows the in-plane biaxial strain at the side portion 203, calculated through stamping simulations of stamped parts 200 with forming heights of 20mm, 30mm, 40mm, and 50mm, plotted on a wrinkle generation determination mapping and a shaded image of the stamped part 200. Figures 13-16 In the middle, ○ and ● indicate the location in the side part 203 where the determination of wrinkle generation is evaluated and the plotting of the strain in the in-plane biaxial direction at that location.

[0152] At a forming height of 25mm ( Figure 13 ) and 30mm ( Figure 14 In the stamped product 200, wrinkles at the side portion 203 could not be visually confirmed. Furthermore, in the wrinkle formation determination mapping, the in-plane biaxial strain at the side portion 203 was located in the region to the upper right of the stability behavior limit line (the in-plane biaxial strain is on the tensile side), and was therefore determined not to have wrinkles. Thus, it can be concluded that the presence or absence of wrinkles can be determined in stamped products 200 with forming heights of 25mm and 30mm.

[0153] It should be noted that the above determination pertains to the presence or absence of wrinkles at the ○ and ● positions of the side portion 203. However, the range shown, in which the in-plane biaxial strain of the entire side portion 203 is plotted, is within... Figure 13 (a) and Figure 14 (a) shows the area represented in gray in the wrinkle generation determination map. Based on this result, it is determined that no wrinkles are generated at any location on the side surface of the stamped part 200 with forming heights of 25 mm and 30 mm, which is consistent with the determination of wrinkle generation based on visual observation.

[0154] At a forming height of 40mm ( Figure 15 In the stamped product 200, the formation of wrinkles at the ○ and ● positions of the side portion 203 could not be visually confirmed. On the other hand, in the wrinkle formation determination mapping, the in-plane biaxial strain at the ○ and ● positions of the side portion 203 is located in the region to the upper right of the stable behavior limit line, and it is determined that no wrinkles have been formed, which is consistent with the wrinkle formation determination based on visual inspection.

[0155] However, the range obtained by plotting the in-plane biaxial strain of the side portion 203 as a whole, which was obtained through stamping simulation, is... Figure 15 (a) shows the gray area in the wrinkle generation determination map, which is located beyond the stable behavior limit line and the wrinkle generation start line. Therefore, it is determined that a wrinkle has occurred in the lower part of the side portion 203. Figure 15 In the shaded view of the stamped article 200 shown in (a), the shadow representing wrinkles can also be seen on the lower part of the side portion 203.

[0156] At a forming height of 50mm ( Figure 16 In the stamped product 200, no wrinkles were observed at the ○ position on the side portion 203, while wrinkles were confirmed at the ● position. Similarly, in the wrinkle generation determination mapping, the in-plane biaxial strain plot at the ○ position is located to the upper right of the stable behavior limit line, therefore it is determined that no wrinkles have occurred. Conversely, the in-plane biaxial strain plot at the ● position is located to the lower left of the wrinkle generation start line (the in-plane biaxial strain is on the compression side), therefore it is determined that clear wrinkles have occurred, consistent with the visual wrinkle generation determination.

[0157] Furthermore, the range of in-plane biaxial strain in the entire side portion 203, obtained through stamping simulation, was plotted and is as follows: Figure 16 (a) shows the area represented in gray in the wrinkle generation determination map, which corresponds to the case with a forming height of 40 mm. Figure 15 Compared to (a), the wrinkles are more widely distributed, crossing both the stability behavior limit line and the wrinkle generation initiation line. Therefore, by increasing the forming height from 40mm to 50mm, the area where wrinkles are determined to occur at the side portion 203 is wider, compared to... Figure 16 (b) The shaded view of the stamped article 200 shows a consistent area of ​​wrinkles generated on the side portion 203.

[0158] exist Figure 17The diagram shows the positional relationship between the range of in-plane biaxial strain in the entire side portion 203 and the stability behavior limit line, obtained by plotting the strain in the biaxial direction throughout the entire side portion 203 when the forming height of the stamped part 200 is 25mm, 30mm, 40mm, and 50mm. Figure 17 It can be seen that by increasing the forming height, the range of strain in the biaxial direction in the plane becomes wider, extending beyond the stable behavior limit line at forming heights of 40mm and 50mm. Furthermore, it is determined that at a forming height of 50mm, slight wrinkles will occur over a wider area on the side surface.

[0159] exist Figure 18 The diagram shows the positional relationship between the range of in-plane biaxial strain in the entire side portion 203 and the wrinkle initiation line, obtained by plotting the strain when the forming height of the stamped article 200 is 25mm, 30mm, 40mm, and 50mm. Figure 18 It can be seen that by increasing the forming height, the range of strain in the biaxial direction within the plane becomes wider, extending beyond the area where wrinkles begin to form at forming heights of 40mm and 50mm. Furthermore, it is determined that at a forming height of 50mm, clear wrinkles will form over a wider area on the side surface.

[0160] Table 2 shows the results of visually determining the formation of wrinkles for the stamped product 200, in which the forming height has been varied within the range of 20mm to 50mm, and the results of determining the presence or absence of wrinkles using the stability behavior limit line and the wrinkle formation start line in the method of the present invention.

[0161] [Table 2]

[0162] (Table 2)

[0163] Forming height / mm Based on visual judgment Determination based on the limit line of stable behavior Determination of the starting line of wrinkle formation 20 ○ ○ ○ 21 ○ ○ ○ 22 ○ ○ ○ 23 ○ ○ ○ 24 ○ ○ ○ 25 ○ ○ ○ 26 ○ ○ ○ 27 ○ ○ ○ 28 ○ ○ ○ 29 ○ ○ ○ 30 ○ ○ ○ 31 × × ○ 32 × × ○ 33 × × ○ 34 × × ○ 35 × × ○ 36 × × ○ 37 × × ○ 38 × × ○ 39 × × ○ 40 × × ○ 41 × × ○ 42 × × ○ 43 × × × 44 × × × 45 × × × 46 × × × 47 × × × 48 × × × 49 × × × 50 × × ×

[0164] (No wrinkles: ○, Wrinkles: ×)

[0165] The determination of wrinkle formation based on visual inspection involves illuminating the side portion 203 of the stamped article 200 with light from various directions and conducting detailed visual observation to determine the presence or absence of slight wrinkles. This determination is consistent with the result of determining the presence or absence of wrinkles using the stability behavior limit line of the present invention. Furthermore, while the determination of wrinkle formation based on visual inspection does not distinguish between slight and distinct wrinkles, the result of determining wrinkle formation using the wrinkle formation start line of the present invention indicates that if the forming height of the stamped article is 43 mm or more greater than the forming height of the stamped article that was determined to have slight wrinkles using the stability behavior limit line, then distinct wrinkles are determined to have occurred.

[0166] The above indicates that the wrinkle generation determination method for stamped articles according to the present invention can accurately determine the presence or absence of wrinkles under biaxial stress during the stamping process of stamped articles based on objective indicators. Furthermore, according to the present invention, it is possible to distinguish between minor wrinkles and prominent wrinkles for determination.

[0167] It should be noted that the above embodiments show the results for 270MPa grade cold rolled steel sheet, but the present invention is not limited to 270MPa grade steel sheet, nor is it limited to cold rolled steel sheet. It can also be ultra-high tensile strength steel sheet such as 1180MPa grade steel sheet, hot rolled steel sheet, or other materials.

[0168] Industrial applicability

[0169] According to the present invention, a method for obtaining wrinkle generation determination index of stamped products, a wrinkle generation determination method, a wrinkle generation determination device, and a wrinkle generation determination procedure are provided. These methods are capable of determining the presence or absence of wrinkles under biaxial stress state during the stamping process of stamped products by applying a compressive load in at least one in-plane axial direction to a cross-shaped plate test piece through a biaxial stress test, and are further capable of determining the presence or absence of wrinkles under biaxial stress state based on the determined index.

[0170] Label Explanation

[0171] 1. Biaxial stress testing apparatus

[0172] 11 Central Mold

[0173] 11a Central Mold

[0174] 11b Central Mold

[0175] 13 Central Department

[0176] 13a Central Department

[0177] 15 First comb teeth

[0178] 15a First comb teeth

[0179] 15b First comb teeth

[0180] 17. Opening

[0181] 19 bolts

[0182] 21 Side mold

[0183] 21a Side mold

[0184] 21b Side mold

[0185] 23 Second comb teeth

[0186] 23a Second comb teeth

[0187] 23b Second comb teeth

[0188] 25. Maintenance section

[0189] 25a Holding section

[0190] 25b Holding section

[0191] 27a Roller

[0192] 27b Roller

[0193] 31 Pressing Mechanism

[0194] 33. Base section

[0195] 35 Top Plate Section

[0196] 37 Guide pins

[0197] 41. Wrinkle Generation Detection Device

[0198] 43. In-plane biaxial strain-load relationship acquisition section

[0199] 45 Stable Behavior Limit Strain Acquisition Section

[0200] 47. Stable Behavior Limit Line Acquisition Section

[0201] 49. Wrinkle formation begins with strain acquisition.

[0202] 51. The starting line for wrinkle formation is obtained.

[0203] 53. In-plane biaxial strain calculation unit for stamped parts

[0204] 55. Wrinkle Generation Determination Mapping Acquisition Unit

[0205] 57. Stamping forming part wrinkle generation judgment section

[0206] 100 plate test pieces

[0207] 101 Measurement Department

[0208] 103 pieces

[0209] 103a Film Section

[0210] 103b film section

[0211] 105 Circular cut

[0212] 107 Hole Shape Section

[0213] 200 stamped parts

[0214] 201 Bulging-up Face

[0215] 203 Side profile

[0216] 210 mold

[0217] 211 Punch

[0218] 213 Stamping Die

[0219] 215 bracket.

Claims

1. A method for obtaining a wrinkle generation determination index for a stamped product, comprising determining, through a biaxial stress test, an index for determining the presence or absence of wrinkle generation under biaxial stress during the stamping process of the stamped product, wherein the biaxial stress test applies an in-plane biaxial load, including at least an in-plane compressive load in one axis direction, to a cross-shaped measuring portion of a cross-shaped plate test piece, thereby inducing out-of-plane buckling at the measuring portion, wherein... The method for obtaining the wrinkle generation determination index of the stamped product includes: The process of obtaining the strain-load relationship in the in-plane biaxial direction involves changing the load ratio in the in-plane biaxial direction acting on the measuring part during the biaxial stress test, and for each load ratio, obtaining the relationship between the strain and load generated in the in-plane biaxial direction in the measuring part during the out-of-plane buckling induced by the measuring part. The process for obtaining the stable behavior limit strain involves, for each load ratio, calculating the first derivative of the in-plane strain in one axis direction under the compressive load of the larger party, determining the point where this first derivative of the calculated strain is maximized as the stable behavior limit point, which is the starting point of out-of-plane buckling, and obtaining the stable behavior limit strain as the strain in the biaxial direction of the measuring part at the stable behavior limit point; and The process of obtaining the stability behavior limit line involves plotting the stability behavior limit strain in the biaxial direction of the plane for each load ratio on a two-dimensional coordinate system. By connecting the plotted stability behavior limit strains, the stability behavior limit line, which serves as an indicator of wrinkle generation under biaxial stress, is obtained.

2. A method for obtaining a wrinkle generation index for a stamped product, comprising determining, through a biaxial stress test, an index for determining the presence or absence of wrinkle generation under biaxial stress during the stamping process of the stamped product, wherein the biaxial stress test applies an in-plane biaxial load, including at least an in-plane compressive load in one axis direction, to a cross-shaped measuring portion of a cross-shaped plate test piece, thereby inducing out-of-plane buckling at the measuring portion, wherein... The method for obtaining the wrinkle generation determination index of the stamped product includes: The process of obtaining the strain-load relationship in the in-plane biaxial direction involves changing the load ratio in the in-plane biaxial direction acting on the measuring part during the biaxial stress test, and for each load ratio, obtaining the relationship between the strain and load generated in the in-plane biaxial direction in the measuring part during the out-of-plane buckling induced by the measuring part. In the process of obtaining the strain at the start of wrinkle formation, for each load ratio, the point where the polarity of the strain increment relative to the compressive load increment in the relationship between strain and load in the in-plane uniaxial direction under the action of the larger compressive load is reversed is determined as the wrinkle formation start point. The strain in the in-plane biaxial direction of the measuring part at this wrinkle formation start point is obtained as the wrinkle formation start strain; and The process of obtaining the wrinkle initiation line involves plotting the in-plane biaxial strains for each load ratio on a two-dimensional coordinate system and then connecting these plotted in-plane strains to determine the wrinkle initiation line under biaxial stress.

3. A method for determining the presence or absence of wrinkles in a stamped product, comprising using the stable behavior limit line obtained by the method for obtaining the wrinkle generation determination index of a stamped product according to claim 1 and the wrinkle generation start line obtained by the method for obtaining the wrinkle generation determination index of a stamped product according to claim 2, wherein, The method for determining the wrinkle generation of the stamped product includes: The process of calculating the in-plane biaxial strain of the stamped product involves simulating the stamping process of the stamped product and determining the in-plane biaxial strain during the stamping process. The process of obtaining a wrinkle generation determination map involves acquiring a wrinkle generation determination map, which represents the stability behavior limit line and the wrinkle generation start line on a two-dimensional coordinate system with strain along two in-plane axes as the coordinate axes; and In the process of determining the occurrence of wrinkles in stamped products, the in-plane biaxial strain at a specified location of the stamped product is plotted on the obtained wrinkle occurrence determination map. If the plot is located in the region between the stable behavior limit line and the wrinkle occurrence start line, it is determined that the risk of wrinkles occurring at the specified location of the stamped product is high. If the plot is located on the compressive strain side closer to the wrinkle occurrence start line, it is determined that wrinkles have occurred at the specified location of the stamped product.

4. A wrinkle generation determination device for a stamped product, which uses a biaxial stress test to determine an index for determining the presence or absence of wrinkle generation under biaxial stress during the stamping process of the stamped product, wherein the biaxial stress test applies an in-plane biaxial load, including at least an in-plane compressive load in one axis direction, to a cross-shaped measuring portion of a cross-shaped plate test piece, thereby inducing out-of-plane buckling at the measuring portion, wherein... The wrinkle generation determination device for the stamped product includes: The in-plane biaxial strain-load relationship acquisition unit changes the in-plane biaxial load ratio acting on the measuring unit during the biaxial stress test, and for each load ratio, obtains the relationship between the in-plane biaxial strain and the load generated in the measuring unit during the out-of-plane buckling induced by the measuring unit. The stability behavior limit strain acquisition unit calculates the first derivative of the in-plane strain in the uniaxial direction of the compressive load acting on the larger of the load ratios for each load ratio. The point where the first derivative of the calculated strain is maximized is taken as the stability behavior limit point, which is the starting point of out-of-plane buckling. The in-plane biaxial strain of the measurement unit at the stability behavior limit point is obtained as the stability behavior limit strain. The stability behavior limit line acquisition section plots the stability behavior limit strain in the biaxial direction in the plane for each load ratio on a two-dimensional coordinate system, and obtains the stability behavior limit line, which is an index of wrinkle generation under biaxial stress state, by connecting the plotted stability behavior limit strains. The strain acquisition unit at the start of wrinkle generation determines the point where, for each load ratio, the polarity of the strain increment relative to the compressive load increment in the relationship between the strain and the load in the in-plane uniaxial direction under the action of the larger compressive load is reversed as the wrinkle generation start point, and the strain in the in-plane biaxial direction of the measurement unit at the wrinkle generation start point is obtained as the wrinkle generation start strain. The wrinkle generation start line acquisition section plots the in-plane biaxial strain of wrinkle generation start in each load ratio on a two-dimensional coordinate system, and obtains the wrinkle generation start line under biaxial stress state by connecting the plotted wrinkle generation start strains. The in-plane biaxial strain calculation unit of the stamped product performs a stamping simulation of the stamped product and calculates the in-plane biaxial strain during the stamping process of the stamped product. The wrinkle generation determination mapping acquisition unit acquires the wrinkle generation determination mapping, which represents the stability behavior limit line and the wrinkle generation start line on a two-dimensional coordinate system with strain in the in-plane biaxial direction as the coordinate axis. and The stamped product wrinkle generation determination unit plots the in-plane biaxial strain at a specified location of the stamped product onto the obtained wrinkle generation determination mapping. If the plot is located in the region between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamped product is high. If the plot is located on the compressive strain side closer to the wrinkle generation start line, it is determined that wrinkle generation occurs at the specified location of the stamped product.

5. A procedure for determining wrinkle formation in a stamped article, comprising determining, through a biaxial stress test, an index for determining the presence or absence of wrinkle formation under biaxial stress during the stamping process of the stamped article, wherein the biaxial stress test applies an in-plane biaxial load, including at least an in-plane compressive load in one axis direction, to a cross-shaped measuring portion of a cross-shaped plate test piece, thereby inducing out-of-plane buckling at the measuring portion, wherein... To enable the computer to function as the following components: The in-plane biaxial strain-load relationship acquisition unit changes the in-plane biaxial load ratio acting on the measuring unit during the biaxial stress test, and for each load ratio, obtains the relationship between the in-plane biaxial strain and the load generated in the measuring unit during the out-of-plane buckling induced by the measuring unit. The stability behavior limit strain acquisition unit calculates the first derivative of the in-plane strain in the uniaxial direction of the compressive load acting on the larger of the load ratios for each load ratio. The point where the first derivative of the calculated strain is maximized is taken as the stability behavior limit point, which is the starting point of out-of-plane buckling. The in-plane biaxial strain of the measurement unit at the stability behavior limit point is obtained as the stability behavior limit strain. The stability behavior limit line acquisition section plots the stability behavior limit strain in the biaxial direction in the plane for each load ratio on a two-dimensional coordinate system, and obtains the stability behavior limit line, which is an index of wrinkle generation under biaxial stress state, by connecting the plotted stability behavior limit strains. The strain acquisition unit at the start of wrinkle generation determines the point where, for each load ratio, the polarity of the strain increment relative to the compressive load increment in the relationship between the strain and the load in the in-plane uniaxial direction under the action of the larger compressive load is reversed as the wrinkle generation start point, and the strain in the in-plane biaxial direction of the measurement unit at the wrinkle generation start point is obtained as the wrinkle generation start strain. The wrinkle generation start line acquisition section plots the in-plane biaxial strain of wrinkle generation start in each load ratio on a two-dimensional coordinate system, and obtains the wrinkle generation start line under biaxial stress state by connecting the plotted wrinkle generation start strains. The in-plane biaxial strain calculation unit of the stamped product performs a stamping simulation of the stamped product and calculates the in-plane biaxial strain during the stamping process of the stamped product. The wrinkle generation determination mapping acquisition unit acquires the wrinkle generation determination mapping, which represents the stability behavior limit line and the wrinkle generation start line on a two-dimensional coordinate system with strain in the in-plane biaxial direction as the coordinate axis. and The stamped product wrinkle generation determination unit plots the in-plane biaxial strain at a specified location of the stamped product onto the obtained wrinkle generation determination mapping. If the plot is located in the region between the stable behavior limit line and the wrinkle generation start line, it is determined that the risk of wrinkle generation at the specified location of the stamped product is high. If the plot is located on the compressive strain side closer to the wrinkle generation start line, it is determined that wrinkle generation occurs at the specified location of the stamped product.

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