Method for designing preforming shape, method for manufacturing press-molded article, and program

Abstract

The present invention provides technology that makes it possible to more easily design a preforming shape. Provided is a method for designing a preforming shape of an intermediate component. The method comprises: a position identification step (20) for identifying a crack occurrence position at which a crack is estimated to occur in a press-molded article that is obtained from molding when, in a single instance of press molding, a metal plate is press-molded to the bottom dead center of a die that enables molding to a target shape; a first surface area calculation step (21) for finding the surface area (A1) of the target shape that is positioned in a first region within a pre-set distance (L0) from the crack occurrence position; a basic shape setting step (22) for setting a basic shape of a preforming shape on the basis of the target shape; a second surface area calculation step (23) for determining a surface area (A2) of the basic shape that is positioned in a second region within the distance (L0) from a position corresponding to the crack occurrence position; and a basic shape modification step (24) for modifying the basic shape so as to satisfy expression (1).　Expression (1): 0.9×A1<A2<1.1×A1

Description

Preformed shape design method, press-formed product manufacturing method, and program

[0001] The present invention relates to a technology for manufacturing difficult-to-form parts. A difficult-to-form part is a press-formed product that may crack if formed into a target shape in a single press forming operation. In particular, the present invention relates to a technology for designing a preformed shape, which is the shape of an intermediate part, to realize the formation of difficult-to-form parts. The present invention also relates to a method for manufacturing a press-formed product using the preformed shape design technology.

[0002] From the viewpoint of improving vehicle crash safety and fuel economy, performance requirements for automotive parts include light weight, high strength, and high rigidity. To improve these performance requirements, part shapes must be more complex. Furthermore, the materials used must also be stronger. For this reason, automotive parts tend to be difficult to form. As a result, there is a problem in that it can be difficult to manufacture automotive parts by press forming.

[0003] To solve the above problems, various press forming methods have been developed, such as those described in Patent Documents 1 and 2. Patent Document 1 discloses a method for improving formability by dividing the process into steps to form a target shape and optimizing the shape of each step. Patent Document 2 deals with deep drawing of square tubes. Patent Document 2 also discloses a method for improving formability by optimizing the shape of each step or the blank shape.

[0004] Patent No. 5867657 Patent No. 7070820

[0005] Here, cracking during forming is a frequent issue when manufacturing complex-shaped parts by press forming or when manufacturing products by press forming high-strength materials. Cracks occur due to localized strain concentration in the material. Therefore, suppressing strain concentration is an effective way to prevent this.

[0006] Therefore, in the methods described in Patent Documents 1 and 2, the press working process is divided into two or more steps. Furthermore, in the methods described in Patent Documents 1 and 2, an appropriate intermediate part shape is formed in a step prior to the final step. Patent Documents 1 and 2 disclose a technique for effectively dispersing strain and improving formability. However, in these disclosed techniques, the line lengths of a specific cross section are compared between preforming and final forming. Then, design is performed based on this comparison. However, the position, direction, and number of the cross sections are arbitrary. Therefore, the formability improvement effect may vary significantly depending on how and how many cross sections are taken. Furthermore, countless preforming shapes with the same cross-sectional line lengths but different cross-sectional shapes can be designed. Therefore, repeated calculations are required to determine the appropriate shape from among them. Furthermore, each time, the preforming shape must be designed across almost the entire part shape. Therefore, the conventional approach to preforming shape design has a significant time and cost cost.

[0007] The present invention has been made in light of the above-mentioned points, and aims to provide a technique that enables a preformed shape to be designed more easily, and a technique related to the manufacture of a press-formed product using the preformed shape design.

[0008] The inventors investigated preform shape design methods to solve the above problems. They discovered the following: (1) When press-forming a target shape, there is no need to design a preform shape for areas where cracks are not likely to occur. Based on this idea, the preform shape design can be considered by limiting it to the area where cracks are likely to occur and the surrounding area. (2) When comparing cross-sectional line lengths, the results are affected by how the cross sections are taken. However, if the intervals between cross sections are made infinitely small, the sum of the cross-sectional line lengths becomes equal to or can approximate the surface area. Furthermore, once the area for calculating the surface area is determined, the same value can be obtained regardless of who calculates it. (3) The necessary surface area is secured by preforming in areas where cracks are likely to occur. This alleviates the strain concentration in the material that occurs during actual forming, making it possible to suppress cracks.

[0009] The feature of the above finding is that once the area for designing the preformed shape and the method for adjusting the surface area are determined, the result is uniquely determined. Therefore, the feature of the above finding is that the same result can be obtained regardless of who designs it. Therefore, the feature of the above finding is that, for example, once a program for designing the preformed shape is created, the preformed shape can be designed automatically.

[0010] In order to solve the problem, one aspect of the present invention is a method for designing a preformed shape when manufacturing a press-formed product of a target shape by press working, the method including a preforming step of press-forming a metal plate into a preformed shape, and a main forming step of press-forming an intermediate part of the preformed shape into a target shape. The method includes a position identification step of identifying a crack occurrence position where a crack is estimated to occur in the press-formed product when the metal plate is press-formed to bottom dead center in a single press forming operation using a mold that can form the target shape; a first surface area calculation step of calculating a surface area A1 in the target shape that is located in a first region within a predetermined distance L0 from the crack occurrence position; a basic shape setting step of setting a basic shape of the preformed shape based on the target shape; a second surface area calculation step of calculating a surface area A2 in the basic shape that is located in a second region within the distance L0 from a position corresponding to the crack occurrence position; and a basic shape deformation step of deforming the basic shape so as to satisfy the following equation (1): 0.9×A1<A2<1.1×A1 (1) The first and second regions have the same shape and are the same large region.

[0011] According to the aspects of the present invention, it is possible to more easily design a preformed shape, and as a result, according to the aspects of the present invention, it is possible to more easily manufacture a press-formed product.

[0012] FIG. 1 is a diagram showing an example of a flow for manufacturing a press-formed product according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a processing configuration for designing a preformed shape according to an embodiment of the present invention. FIG. 3 is a conceptual diagram showing transitions in designing a preformed shape according to an embodiment of the present invention. FIG. 4 is a diagram explaining a second shape setting process. FIG. 5 is a diagram explaining a second shape setting process. FIG. 6 is a diagram showing the relationship between each edge and dividing line 42 of a single shape and a target shape 41, as viewed from above. FIG. 7 is a diagram explaining changes to faces within a second region. FIG. 8 is an example explaining an example of a function f(L). FIG. 9 is a diagram showing an example of a program configuration. FIG. 10 is a diagram showing an example of a processing configuration for designing a preformed shape according to an embodiment of the present invention. FIG. 11 is a diagram showing an example of a program configuration. FIG. 12 is a diagram showing a target shape and crack positions in an example. FIG. 13 is a diagram showing a basic shape in an example. FIG. 14 is a diagram showing a preformed shape in an example. FIG. 15 is a diagram showing a press-formed product in an example.

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. Consider press forming in which a metal sheet is press-formed to the bottom dead center in a single press using a die capable of forming the metal sheet into a target shape. There are cases in which cracks are expected to occur in the press-formed product formed during the press forming. This embodiment is a technology that takes such cases into consideration. The die capable of forming the metal sheet into a press-formed product of the target shape is, for example, a die whose forming surface is the same as or similar to the target shape.

[0014] In this embodiment, as shown in FIG. 1 , a press working 2 including a preforming step 2A and a main forming step 2B is used. In this embodiment, a technique for manufacturing a press-formed product 11 having a target shape by the press working 2 is described. The preforming step 2A is a step of press-forming a metal plate into an intermediate part 10 having a preformed shape. The main forming step 2B is a step of press-forming the intermediate part 10 having the preformed shape into a press-formed product 11 having a target shape. The present disclosure particularly relates to a technique related to the design of the preformed shape involved in the manufacture of the press-formed product.

[0015] "First embodiment" (method of designing a preformed shape) In the first embodiment, a basic shape of the preformed shape, which is the shape of the intermediate part 10, is provisionally set. Then, a partial area of ​​the provisionally set basic shape is changed as a design area. In this way, the preformed shape design in the first embodiment designs the preformed shape. Note that in this embodiment, after the basic shape is provisionally set, only the design area needs to be changed. However, the present invention also includes changing the shapes of other areas in conjunction with a change in the shape of the design area. The design area is the crack generation area and the outer peripheral area of ​​that area. The outer peripheral area is, for example, a part that is affected by cracks.

[0016] As shown in Fig. 2, the preform shape design method of this embodiment includes a position identification step 20, a first surface area calculation step 21, a basic shape setting step 22, a second surface area calculation step 23, a basic shape deformation step 24, and a shape evaluation step 25. Also, as shown in Fig. 2, the preform shape design method of this embodiment includes a basic shape resetting step 26. Note that it does not matter which of the first surface area calculation step 21 and the basic shape setting step 22 is executed first. Also, it does not matter which of the first surface area calculation step 21 and the basic shape setting step 22 is executed first.

[0017] The preform shape design of this embodiment is processed according to the following procedure. As will be described below, this process can be performed by a known forming analysis method. The known forming analysis method may be a forming analysis method using CAE with a computer. In other words, the process of the preform shape design method of this embodiment can be configured as a program executed by a computer.

[0018] <Position Identification Step 20> The position identification step 20 assumes that a metal plate is press-formed to the bottom dead center using a mold capable of forming the target shape in a single press forming operation. Based on this assumption, the position identification step 20 performs a process to identify a crack occurrence position W where a crack is estimated to occur in the press-formed product (see FIG. 3( a)). In the position identification step 20 of this embodiment, a forming analysis of press-forming the metal plate into the target shape is performed by finite element analysis using CAE. The position identification step 20 then identifies the region where a crack will occur based on the analysis results.

[0019] In this process, if the target shape, the material properties of the target metal plate, and the fracture limit line of the material are known in advance, the crack occurrence position W can be automatically determined using conventional general knowledge. It is also possible to identify the crack occurrence position W by performing actual press forming. Here, the detected crack occurrence position W is not limited to one location. As shown in FIG. 3( a), there may be multiple crack occurrence positions W. In this case, the processes of the first surface area calculation process 21 and the second surface area calculation process 23 described below, and the associated process of the basic shape deformation process 24, may be performed for each crack occurrence position W. The following process description basically describes the case where the processes are performed individually for each crack occurrence position W.

[0020] <First Surface Area Calculation Step 21> The first surface area calculation step 21 performs a process of calculating a surface area A1 based on the crack occurrence position W calculated in the position identification step 20 (see FIG. 3B). The surface area A1 is the surface area located within a first region within a predetermined distance L0 from the crack occurrence position W in the target shape. For example, the center position of the crack is used as the crack occurrence position W. In this case, the first region is an area surrounded by a sphere with a radius L0 and centered at the center position of the crack. The same applies to the second region described below. Note that the first region and the second region are, for example, regions of the same size. Note that the crack occurrence position W may be an area of ​​a predetermined size, and a position a predetermined distance away from the outer circumferential contour position of that area may be set as the outer edge of the first region. However, the above method is simpler.

[0021] In the first surface area calculation step 21 of this embodiment, the sum of the surface areas (surface area A1) of the meshes that represent the target shape (press-molded shape) that exist within the first region is calculated from the molding analysis information. This step can be performed automatically in conjunction with the results of the position identification step 20 if the distance L0 is determined in advance. The area of ​​each mesh can be calculated, for example, using Heron's formula or the like from the coordinate information of each node that makes up the mesh. However, other methods may also be used.

[0022] [Regarding distance L0] Distance L0 is set as follows. For example, distance L0 is set to a size that ensures that the crack area and its entire outer periphery are included within the first area defined by distance L0. This setting may be based on, for example, experiments or past empirical values. For example, distance L0 (mm) may be set to satisfy the following formula (3) when the tensile strength of the metal plate to be processed is TS (MPa): 0.5 × (TS ０．５ )≦L0(mm)≦3×(TS ０．５ ) ... (3)

[0023] Here, the outer edge of the first region defined by the distance L0 is generally designed closer to the crack generation region to achieve a greater crack suppression effect. However, if the distance L0 is less than 0.5 × (TS^0.5), the defined region may become too narrow. In this case, the preformed shape designed to match the surface area may become too steep, making it difficult to form the preformed shape. On the other hand, if the distance L0 exceeds 3 × (TS^0.5), the first region defined by the distance L0 becomes too large, reducing the crack suppression effect.

[0024] The reason why the tensile strength TS is included in the definition of the distance L0 in Equation (3) is as follows: Ultra-high tensile steel is generally more prone to strain concentration and cracking than mild steel. Therefore, the higher the tensile strength, the more widely preforming is required to disperse strain. Furthermore, if the preforming shape is too steep, the preforming shape cannot be fully formed into the target shape in the main forming step 2B, and marks are likely to remain.

[0025] <Basic Shape Setting Step 22> The basic shape setting step 22 involves setting a basic shape 30, which serves as the basis for the preformed shape, which is the shape of the intermediate part 10, based on the target shape (see FIG. 3(c)). It is preferable that the basic shape 30 be a shape that is close to the target shape as a whole. Examples of the basic shape setting step 22 include the following first shape setting step and second shape setting step. However, cases where the basic shape 30 is determined by other known methods for determining a preformed shape also fall within the scope of the present disclosure. However, it is preferable to set the basic shape 30 of the preformed shape using a simple process.

[0026] [First Shape Setting Step] In the first shape setting step, one formed shape selected from the plurality of formed shapes before the crack occurs is set as the basic shape 30 of the preformed shape. Each of the plurality of formed shapes is a shape selected from the formed shapes during forming of the metal plate to the bottom dead center using a mold that can form the target shape. In the first shape setting step of this embodiment, the basic shape 30 of the preformed shape is set in the forming analysis in the position identification step 20. At this time, the shape of the forming stage before the crack occurs is set as the basic shape 30 of the preformed shape.

[0027] At this time, strain may have already begun to concentrate in the formed shape immediately before cracks occur. For this reason, it is desirable to use a formed shape that is 2 mm or more shallower than the forming depth at which cracks occur as the basic shape 30. Here, the minimum value of the forming depth is 0 mm. In other words, the present disclosure also includes using the shape of the metal sheet before forming as the basic shape 30.

[0028] [Second Shape Setting Step] In the second shape setting step, a basic shape 30 is set by the following first to fifth steps. Here, the shape of the metal plate is represented by a set of multiple elements from before forming through to during forming. The shape is represented, for example, by a mesh of multiple elements (see FIG. 4(a)). FIG. 4(a) shows the state in which the sides of all elements are expressed as equations and A mm, B mm, and C mm are calculated for all elements.

[0029] First, in the first setting step, a reference plane 40 is assumed, which is a plane perpendicular to the pressing direction in the main forming step 2B (see FIG. 5( a)). Then, polygonal single shapes 40A are arranged so as to be continuously aligned on the reference plane 40. In this way, the reference plane 40 is set as a plane partitioned by a repetition of a plurality of single shapes 40A (see FIG. 5( b)). It is preferable that the plurality of single shapes 40A are arranged two-dimensionally so as to be aligned linearly in the same direction.

[0030] FIG. 5B shows an example in which the single shape 40A is a quadrangle. The quadrangle may be a rectangle or a diamond. For example, the reference plane 40 may be divided into a grid of lines, and multiple single shapes 40A may be arranged on the reference plane 40. In this case, the reference plane 40 can be easily divided into multiple single shapes 40A simply by dividing it into a grid. In other words, it is possible to define a reference plane 40 consisting of multiple single shapes 40A simply and easily. Examples of single shapes include a quadrangle, a triangle, and a hexagon. However, it is preferable that the sides of multiple adjacent single shapes 40A arranged in a two-dimensional direction are linearly continuous along the extension direction of the sides (see FIGS. 5B and 6).

[0031] Next, a reference plane 40 is defined by a plurality of single shapes 40A. The reference plane 40 is moved in the press direction toward the target shape 41, and a state in which the reference plane 40 intersects with the target shape 41 is assumed. That is, a state in which each side of each single shape 40A arranged on the reference plane 40 intersects with the target shape 41 is assumed. Then, in the second setting process, a process is performed to divide the surface of the target shape 41 along division lines 42 formed on the surface of the target shape 41 by the above intersection (see FIG. 6 ). FIG. 4B shows an example of the relationship between the division lines 42 and the mesh. Next, in the third setting process, three or more nodes 45 are arranged on each division line 42 corresponding to each side of each single shape 40A. The three or more nodes 45 are arranged at a distance from each other. The multiple nodes 45 are arranged, for example, at equal intervals when viewed from the press direction.

[0032] Next, in the fourth setting step, multiple smooth curves 43 are set by connecting the multiple nodes 45 arranged along the extension direction of each parting line 42 (see FIG. 4( c)). Consider the case viewed from the pressing direction (e.g., from above) as shown in FIG. 6. In this case, the parting lines 42 connecting the sides of the single shape 40A and the smooth curves 43 based on the parting lines have the same straight line shape. However, when viewed from a side perpendicular to the pressing direction, the curves 43 are smooth and have no corners. On the other hand, the parting lines 42 are lines connecting the sides of the single shape 40A. Therefore, when viewed from a side perpendicular to the pressing direction, the parting lines 42 may have corners in some parts. Furthermore, the parting lines 42 may have portions with a sharper curvature than the curves 43.

[0033] Next, in the fifth setting step, a surface shape is formed by smoothly extending a surface in each region 44 (see FIG. 6) surrounded by the set curves 43. This surface shape is set as the basic shape 30 (see FIG. 4(d)). Note that it is preferable that the surfaces extended in each region 44 be connected smoothly.

[0034] Here, cracks in the press-formed product occur due to concentrated deformation in areas where the shape is sharply deformed. The basic shape 30 designed by this second shape setting process is roughly similar to the target shape. However, the surface shapes in various locations are moderately smooth, making the basic shape 30 a shape that is easy to form. This shape is used as the basic shape 30 of the preform shape, and the preform shape is designed in a later process. Note that the shape designed in this process may also be used as the preform shape for actual forming. If no cracks occur as a result, the design of the preform shape is completed in this process. Furthermore, it is preferable to set the spacing between adjacent parting lines 42 to be 1 / 10 or less of the line length of the target shape. The line length of the target shape is the line length in the direction in which adjacent parting lines 42 are arranged.

[0035] <Second Surface Area Calculation Step 23> The second surface area calculation step 23 performs a process of calculating a surface area A2 based on the crack occurrence position W determined in the position identification step 20 (see FIG. 3(d)). The surface area A2 is the surface area located in a second region within a distance L0 from the position corresponding to the crack occurrence position W in the basic shape 30. In the second surface area calculation step 23 of this embodiment, the basic shape 30 determined in the basic shape setting step 22 is defined by a mesh based on known forming analysis. Then, the sum of the surface areas of the meshes present in the second region (surface area A2) is calculated. The mesh conditions may be, for example, the same conditions as the mesh conditions that define the target shape.

[0036] In this step, the second region can be determined by, for example, determining the region as consisting of elements with the same element numbers as the elements included in the first region determined in the first surface area calculation step 21. In the case of an analysis method in which the element numbers change during molding, a mark is added to the outer edge of the first region in the analysis software. Then, a method can be considered in which the molding analysis is rewound to the shape that is the basis of the preformed shape, and the region is defined as the region surrounded by the mark. However, any method may be used.

[0037] <Basic Shape Deformation Step 24> Here, the area of ​​basic shape 30 that exists within the second region becomes the design region of the preformed shape for basic shape 30. Then, in basic shape deformation step 24, the second region of basic shape 30 is deformed to change the surface area within the second region so that the above-mentioned cracks do not occur in main forming step 2B. In this way, a shape 31 obtained by deforming basic shape 30 is designed as a candidate for the preformed shape (see FIG. 3( e)).

[0038] In the basic shape deformation process 24 of this embodiment, a process is performed to deform the shape of the basic shape 30 so as to satisfy the following equation (1): 0.9×A1<A2<1.1×A1 (1) As described above, A1 represents the surface area present in the first region of the target shape 41. A2 represents the surface area present in the second region of the basic shape 30.

[0039] Here, if the surface area A2 is too small, the preforming effect will be ineffective and cracks may occur. Also, if the surface area A2 is too large, cracks may occur during preforming. Also, if the surface area A2 is too large, even if no cracks occur during preforming, excess material may remain during main forming, potentially resulting in wrinkles. For these reasons, it is more desirable to have "0.95 x A1 < A2 < 1.05 x A1."

[0040] In the basic shape deformation process 24, for example, as shown in Figure 7, the nodes of the mesh in the second region are moved up and down (in the pressing direction or plate thickness direction). This adjusts the surface area A2 of the basic shape present in the second region. At this time, the amount of movement (amount of displacement in the up and down direction) is adjusted according to the distance from the crack occurrence position W. In addition, the area to be changed in the second region is adjusted so that it is smoothly connected to the area surrounding the second region.

[0041] In the basic shape transformation step 24, such adjustment is performed based on an equation such as the following equation (2). Setting equation (2) enables the processing of the basic shape transformation step 24 to be more automated. The surface shape within the second region is changed to, for example, a surface shape expressed by equation (2). P(q, L) = q × f(L) (2) where the function f(L) represents a smooth curve. The function f(L) is a function equation that satisfies f(L0) = 0, f'(0) = 0, and f'(L0) = 0. Note that L is the shortest distance from a position corresponding to the crack occurrence position W. The shortest distance from the crack occurrence position W to the boundary of the second region is L0. An example of the function f(L) is shown in FIG. 8. Then, the value of q is adjusted using q as a variable. As a result, the surface area A2 of the portion of the basic shape 30 located within the second region is determined to satisfy equation (1).

[0042] An example of equation (2) is shown below: P(q, L)=q×(-(cos(2π×L / L0)-1) / 2) (2)' In this example, f(L) is set to "(-(cos(2π×L / L0)-1) / 2)."

[0043] Next, consider the second region of the finite element analysis model, which is used to design the shape of the basic shape 30 that serves as the basis for preforming. The number represented by P(q, L) corresponding to the L of each node is added to the z coordinates of all nodes in the second region. This process calculates the surface area A2. At this time, one possible method is to adjust the basic shape 30 by increasing or decreasing the value of q until equation (1) is satisfied.

[0044] The reason for using a trigonometric function in equation (2)' is as follows. That is, the differential value of equation (2)' is 0 at positions L = 0 and L = L0, and P(L) is 0 at position L = L0. Furthermore, if the above conditions are not met, the connection between the second region where shape design is performed and the outside of the second region becomes discontinuous. As a result, it becomes difficult to establish the mold shape (molding surface shape). However, as long as the above conditions are met, f(L) may be, for example, a combination of trigonometric functions or another equation such as a polynomial function.

[0045] <Shape Evaluation Step 25> In the shape evaluation step 25, first, the basic shape 30 obtained in the basic shape modification step 24 is set as the preforming shape. Then, using this preforming shape and the target shape, a forming analysis is performed that simulates the preforming step 2A and the main forming step 2B (see FIG. 3(f)). Then, in the shape evaluation step 25, it is determined whether or not cracks will occur in the forming analysis. If it is determined that no cracks will occur in the forming analysis, the design process is terminated (see FIG. 3(g)).

[0046] If it is determined that cracks will occur, the process proceeds to basic shape resetting step 26. Then, the basic shape 30 is changed, and the processing of second surface area calculation step 23 and basic shape deformation step 24 is repeatedly executed until the cracks are contained. Even if cracks have occurred, it is possible to terminate the design at any time if it is determined that the cracks can be avoided by minor correction of the preformed shape by other means.

[0047] <Basic Shape Resetting Step 26> If a crack occurs in the main forming step 2B, the basic shape resetting step 26 updates the modified basic shape 30 determined in the basic shape deformation step 24 to a new basic shape 30. Note that the corresponding location in the processing of the second surface area calculation step 23 and the basic shape deformation step 24 is limited to the location where a crack occurred in the above-mentioned shape evaluation step 25. Furthermore, if the location where the crack occurred has changed, the shape evaluation step 25 is treated as processing of the position identification step 20, and the first surface area calculation step 21 is also executed again. Regardless of whether the location where the crack occurred has changed, the processing of the shape evaluation step 25 may be treated as processing of the position identification step 20, and the first surface area calculation step 21 may also be executed again.

[0048] If it is determined that a crack has occurred in the preforming step 2A, the basic shape resetting step 26 increases the safety margin against cracks compared to the previous step. Then, the same process as the basic shape setting step 22 is performed to reset the basic shape 30. In the first shape setting step, increasing the safety margin means, for example, making the forming depth shallower.

[0049] (Program) Here, it is desirable that the above processing be performed automatically using a computer. Once formula (2) and the distance L0 are determined, the other conditions can be determined mechanically. Therefore, it is possible to automatically process the calculations for designing the preformed shape using a computer. In this case, it is possible to achieve even greater efficiency. That is, the design processing of this embodiment is configured as a program. Then, the program may be stored in a storage unit and executed by a computer.

[0050] For example, a program 50 to be executed by a computer may be configured to include a position identification step 50A, a first surface area calculation step 50B, a basic shape setting step 50C, a second surface area calculation step 50D, a basic shape transformation step 50E, and a shape evaluation step 50F, as shown in Figure 9.

[0051] The position specifying step 50A performs forming analysis up to the bottom dead center of forming under analysis conditions for press-forming a metal plate into a target shape in one press forming operation. This performs a process for specifying the location where a crack will occur. The first surface area calculation step 50B performs a process for calculating a surface area A1 located within a region within a set distance L0 from the crack location specified in the position specifying step 50A in the target shape.

[0052] The basic shape setting step 50C executes a process of provisionally setting the basic shape 30 of the preforming shape based on the target shape. The second surface area calculation step 50D executes a process of calculating the surface area A2 located within a second region in the basic shape 30. The second region is an area within the distance L0 from the position corresponding to the crack occurrence position identified in the position identification step 50A. The basic shape deformation step 50E executes a process of deforming the shape of at least the second region in the basic shape 30 so that the shape within the second region in the basic shape 30 satisfies 0.9×A1<A2<1.1×A1.

[0053] In this case, when only the shape within the second region is deformed, it is preferable to set the conditions that the deformation is zero at the outer peripheral position of the second region and that the deformation is performed so as to smoothly connect to the outside of the second region. In the shape evaluation step 50F, the modified basic shape 30 obtained in the basic shape deformation step 50E is used as the preformed shape, and a forming analysis is performed to form the preformed shape and perform actual forming. Then, the presence or absence of cracks is evaluated. If it is determined that no cracks will occur, the processing ends. If it is determined that cracks will occur, the modified basic shape 30 obtained in the basic shape deformation step 50E is changed to the basic shape 30. Then, the process returns to the first surface area calculation step 50B and the subsequent steps are repeatedly performed until the cracks are eliminated.

[0054] The program consisting of the above steps can be created by a known forming analysis method using a computer-aided CAE. Examples of inputs to the program include the target shape, the material properties of the target metal sheet, and the fracture limit of the material. The program may also be configured to execute each process described in the above-mentioned preformed shape design.

[0055] (Method for Manufacturing Press-Formed Product) As shown in FIG. 1 , the method for manufacturing a press-formed product according to this embodiment includes a preformed shape design step 1, a preformed shape design step 2A, and a main forming step 2B. In the preformed shape design step 1, a preformed shape is determined using the preformed shape design method described above. In the preformed shape design step 2A, a metal plate is press-formed into the determined preformed shape to manufacture an intermediate part 10. In the main forming step 2B, the intermediate part 10 having the preformed shape is press-formed into a target shape. Through the above-described processes, a preformed shape is designed using a simple method, making it possible to more reliably manufacture press-formed products that are free from cracks.

[0056] Second Embodiment (Method for Designing Preformed Shape) The second embodiment is a forming method for directly determining a preformed shape, which is the shape of the intermediate part 10. As shown in FIG. 10 , the design of the preformed shape in the second embodiment includes a preformed shape setting step 60 and a shape evaluation step 25. In the preformed shape setting step 60, the preformed shape is designed by the following processing of a first setting step 60A to a fifth setting step 60E. First, in the first setting step 60A, a reference plane 40, which is a plane perpendicular to the pressing direction in the main forming step 2B, is assumed. Then, single polygonal shapes 40A are arranged in a continuous line on the reference plane 40. In this way, the reference plane 40 is set as a plane defined by a repetition of a plurality of the single shapes 40A.

[0057] In this case, in the first setting step 60A, it is preferable to arrange a plurality of single shapes 40A by making the single shape 40A a quadrangle and dividing the reference plane 40 with grid-like lines. It is also preferable to divide the reference plane 40 into a plurality of single shapes 40A. In this case, it is possible to simply and easily define the reference plane 40 consisting of a plurality of single shapes 40A.

[0058] Next, a reference plane 40 is imagined, which is partitioned by a plurality of single shapes 40A and is made up of the plurality of single shapes 40A. The reference plane 40 is moved in the press direction toward the target shape, and a state in which it intersects with the target shape is imagined. That is, a state in which each side of each single shape 40A arranged on the reference plane 40 intersects with the target shape is imagined. In a second setting process 60B, the surface of the target shape is divided by dividing lines 42 formed on the surface of the target shape by the intersecting state. Next, in a third setting process 60C, three or more nodes are arranged on each dividing line 42 corresponding to each side of each single shape 40A. The three or more nodes are arranged at equal intervals when viewed from the press direction.

[0059] Next, in a fourth setting step 60D, curves 43 are set that connect the plurality of nodes aligned along the extension direction of the parting lines 42. The curves 43 are set as smooth curves that do not have sharp curvatures (corners). A plurality of curves 43 are set for each extension direction of each parting line 42. Next, in a fifth setting step 60E, a surface shape is formed by smoothly extending a surface in each region surrounded by the plurality of set curves 43, and the surface shape is set as the preformed shape.

[0060] Here, cracks in press-formed products occur when deformation concentrates in areas where the shape is rapidly deformed. The preformed shape designed using the method of the second embodiment is roughly close to the target shape. However, the preformed shape has a moderately gentle shape in each area, making it easier to form. In addition, it is preferable to set the spacing between adjacent parting lines 42 to be 1 / 10 or less of the line length of the target shape. The line length of the target shape is the line length in the direction in which adjacent parting lines 42 are arranged.

[0061] <Shape Evaluation Step 61> In the shape evaluation step 61, first, a forming analysis is performed simulating the preforming step 2A and the main forming step 2B using the preforming shape and target shape determined in the preforming shape setting step. The shape evaluation step 61 then determines whether or not a crack will occur in the forming analysis. If it is determined that a crack will occur, the preforming shape is changed until the crack subsides. In other words, if a crack occurs in the preforming step 2A, the preforming shape setting step executes processing with a larger safety margin for cracks than the previous time. This resets the preforming shape. Note that even if a crack has occurred, the design can be terminated at any time if it is determined that the crack can be avoided by minor adjustments to the preforming shape using other means.

[0062] (Program) Here, it is desirable that the above processing be performed automatically using a computer. By determining the reference plane 40 consisting of a plurality of single shapes 40A, other conditions can be determined mechanically. Therefore, it is possible to further improve efficiency by automatically performing calculations using a computer. In other words, the design processing of this embodiment may be configured as a program, stored in a storage unit, and executed by a computer.

[0063] For example, a program 70 to be executed by a computer may be configured to include a first setting step 70A to a fifth setting step 70E, as shown in Figure 11. First, in the first setting step 70A, a reference plane 40 is assumed, which is a plane perpendicular to the pressing direction in the main forming process 2B. Then, polygonal single shapes 40A are arranged in a continuous line on the reference plane 40. In this way, the reference plane 40 is set as a plane partitioned by a repetition of a plurality of the single shapes 40A.

[0064] In this case, it is preferable that the single shape 40A is set to a quadrilateral shape in the first setting step 70A. Then, a plurality of single shapes 40A are arranged by dividing the reference plane 40 with grid-like lines. In this way, it is preferable that the reference plane 40 is divided into a plurality of single shapes 40A. In this case, it is possible to simply and easily define the reference plane 40 consisting of a plurality of single shapes 40A.

[0065] Next, in a second setting step 70B, a reference plane 40 is defined by a plurality of single shapes 40A, and the reference plane 40 is assumed to be composed of the plurality of single shapes 40A. The reference plane 40 is moved in the press direction toward the target shape, and a state in which it intersects with the target shape is assumed. The surface of the target shape is then divided by division lines 42 formed by the intersection of each side of each single shape 40A with the target shape. Next, in a third setting step 70C, three or more nodes are placed on each division line 42 corresponding to each side of each single shape 40A. The three or more nodes are placed at equal intervals as viewed from the press direction. Next, in a fourth setting step 70D, the plurality of nodes arranged along the extension direction of each division line 42 are connected. This results in the setting of multiple smooth curves 43.

[0066] Next, in a fifth setting step 70E, a surface shape is formed by smoothing each area surrounded by the set plurality of curves 43. This surface shape is set as the preforming shape. Next, in a shape evaluation step 70F, the preforming shape set in the fifth setting step 70E is set as the preforming shape. Then, forming analysis of preforming and main forming is performed. If it is determined that cracks will occur, the conditions are changed and then the process proceeds to the second setting step 70B. Then, the second setting step 70B to the fifth setting step 70E are repeatedly executed until the cracks are eliminated.

[0067] The program consisting of the above steps can be created by a known forming analysis method using a computer-aided engineering (CAE). The inputs to the program can include, for example, the target shape and the material properties of the target metal plate.

[0068] (Method for manufacturing a press-formed product) The method for manufacturing a press-formed product of this embodiment includes a preformed shape design step 1, a preformed shape design step 2A, and a main forming step 2B. In the preformed shape design step 1, a preformed shape is determined using the preformed shape design method described above. In the preformed shape design step 2A, a metal plate is press-formed into the determined preformed shape to manufacture an intermediate part 10. In the main forming step 2B, the intermediate part 10 with the preformed shape is press-formed into a target shape. Through the above processes, a preformed shape is designed using a simple method, making it possible to more reliably manufacture a press-formed product that does not generate cracks.

[0069] "Others" The present disclosure may also take the following configurations: (1) A method for designing a preformed shape when manufacturing a press-formed product of a target shape by press working including a preforming step of press-forming a metal sheet into the preformed shape and a main forming step of press-forming an intermediate part of the preformed shape into a target shape, the method comprising: a position specifying step of specifying a crack occurrence position where a crack is estimated to occur in the press-formed product when the metal sheet is press-formed to bottom dead center in a single press forming operation using a mold that can form the target shape; a first surface area calculation step of calculating a surface area A1 in the target shape that is located in a first region within a predetermined distance L0 from the crack occurrence position; a basic shape setting step of setting a basic shape of the preformed shape based on the target shape; a second surface area calculation step of calculating a surface area A2 in the basic shape that is located in a second region within the distance L0 from a position corresponding to the crack occurrence position; and a basic shape deformation step of deforming the basic shape so as to satisfy the following formula (1): 0.9×A1<A2<1.1×A1...(1)

[0070] (2) The basic shape setting step sets one formed shape selected from a plurality of formed shapes that are formed in the middle of forming the metal plate to the bottom dead center with the die and that are formed before the crack occurs as the basic shape of the preformed shape. (3) The position specifying step specifies a position where the crack is estimated to occur by forming analysis by a computer that press-forms the metal plate into a target shape, and the basic shape setting step determines the formed shape before the crack occurs by forming analysis by a computer that press-forms the metal plate into the target shape.

[0071] (4) The basic shape setting process includes the steps of: arranging single polygonal shapes in a continuous line on a reference plane, which is a plane perpendicular to the press direction in this forming process, to partition the reference plane into a repetition of a plurality of the single shapes; when the partitioned reference plane is moved in the press direction toward the target shape, dividing the surface of the target shape with dividing lines formed on the surface of the target shape by intersecting each side of each single shape arranged on the reference plane with the target shape; arranging three or more nodes spaced apart from each other on each dividing line corresponding to each side of each of the single shapes; setting a plurality of smooth curves connecting the multiple nodes arranged along the extension direction of each dividing line; and setting the surface shape formed by smoothly extending a surface in each area surrounded by the set multiple curves as the basic shape.

[0072] (5) The single shape is a quadrangle, and the reference plane is divided by grid lines to arrange a plurality of single shapes on the reference plane. (6) The interval between adjacent dividing lines is set to 1 / 10 or less of the line length of the target shape in the direction of arrangement of the adjacent dividing lines.

[0073] (7) In the basic shape deformation step, for the surface shape within the crack occurrence region, which is the region within the distance L0 from the position corresponding to the crack occurrence position in the basic shape, the shape of the position at a distance L from the position corresponding to the crack occurrence position is determined using a function P(q, L) expressed by the following equation (2): P(q, L) = q × f(L) (2) where f(L) is a function equation that satisfies f(L0) = 0, f'(0) = 0, and f'(L0) = 0.

[0074] (8) The distance L0 is set to a value that can include the entire crack area within the first area. (9) When the tensile strength of the metal plate material is TS (MPa), the distance L0 is set to a value that satisfies the following formula (3): L0 < 3 × TS ０．５ ...(3)

[0075] (10) If the basic shape after deformation in the basic shape deformation process is used as the preformed shape and the preformed process and main forming process are performed and no crack reduction effect is observed, the basic shape after deformation in the basic shape deformation process is updated to the basic shape, and the second surface area calculation process and the basic shape deformation process are repeatedly performed to design the preformed shape until the crack reduction effect is observed.

[0076] (11) A method for designing the preformed shape when a press-formed product of a target shape is manufactured by press working, the method including a preforming step of press-forming a metal plate into the preformed shape and a main forming step of press-forming an intermediate part of the preformed shape into the target shape, the method comprising: arranging single polygonal shapes in a continuous line on a reference plane that is a plane perpendicular to the press direction, thereby partitioning the reference plane into a repetition of a plurality of the single shapes; dividing the surface of the target shape at division lines formed on the surface of the target shape by intersecting each side of each single shape arranged on the reference plane with the target shape when the partitioned reference plane is moved in the press direction toward the target shape; arranging three or more nodes spaced apart from each other on each division line corresponding to each side of each of the single shapes; setting a plurality of smooth curves connecting the plurality of nodes arranged along the extension direction of each division line; and defining a surface shape formed by smoothly stretching each area surrounded by the set curves as the preformed shape.

[0077] (12) The single shape is a quadrangle, and a plurality of single shapes are arranged on the reference plane by dividing the reference plane with grid lines. (13) The interval between adjacent parting lines is set to 1 / 10 or less of the line length of the target shape in the arrangement direction of the adjacent parting lines. (14) A method for manufacturing a press-formed product, comprising: determining a preformed shape by the preformed shape design method disclosed herein; and manufacturing a press-formed product of a target shape by a press working method including a preforming step of press-forming the metal plate into the preformed shape, and a main forming step of press-forming an intermediate part of the preformed shape into a target shape.

[0078] (15) A program for causing a computer to execute a design process for determining a preformed shape when a press-formed product of a target shape is manufactured by press working, which includes a preforming step of press-forming a metal plate into a preformed shape and a main forming step of press-forming an intermediate part of the preformed shape into the target shape, since cracks occur in the press-formed product when a metal plate is press-formed into a target shape in one press forming operation. The program includes: a position specifying step of specifying a position where a crack will occur by performing forming analysis up to the bottom dead center of forming under analysis conditions for press-forming a metal plate into the target shape in one press forming operation; a first surface area calculation step of calculating a surface area A1 located in a first region within a set distance L0 from the crack occurrence position in the target shape specified in the position specifying step; a basic shape setting step of provisionally setting a basic shape of the preformed shape based on the target shape; and a second surface area calculation step of calculating a surface area A2 located in a second region within the distance L0 from a position in the basic shape corresponding to the crack occurrence position specified in the position specifying step. a basic shape deformation step of deforming the basic shape so that the shape in the second region of the basic shape satisfies 0.9×A1<A2<1.1×A1.

[0079] (16) The basic shape setting step sets as the basic shape one of a plurality of formed shapes obtained by the same forming analysis as in the position specifying step, which is a formed shape during forming to the bottom dead center and before the crack occurs. (17) The basic shape setting step includes the steps of: arranging single polygonal shapes in a continuous line on a reference plane that is a plane perpendicular to the press direction, thereby partitioning the reference plane into a repetition of a plurality of the single shapes; determining a plurality of division lines formed on a surface of the target shape by each side of each single shape arranged on the reference plane intersecting with the target shape when the partitioned reference plane is moved in the press direction toward the target shape; arranging three or more nodes on each division line corresponding to each side of each of the single shapes at equal intervals as viewed from the press direction; setting a plurality of smooth curves connecting the plurality of nodes arranged along the extension direction of each division line; and setting a surface shape formed by smoothing surfaces in each region surrounded by the set plurality of curves as the basic shape.

[0080] (18) The single shape is made into a quadrangular shape, and a plurality of single shapes are arranged on the reference plane by dividing the reference plane with grid lines. (19) The basic shape deformation step determines a preformed shape at a position that is a distance L from the position corresponding to the crack occurrence position, for a surface shape in the crack occurrence region, which is the second region within the distance L0 from the position corresponding to the crack occurrence position in the basic shape, using P(q, L) expressed by the following formula: P(q, L) = q × f(L) where f(L) is a function formula that satisfies f(L0) = 0, f'(0) = 0, f'(L0) = 0. (20) When the tensile strength of the material of the metal plate is TS (MPa), the distance L0 is set to a value that satisfies the following formula: L0 < 3 × TS ０．５

[0081] ​(21) If it is determined that the effect of reducing cracks is not recognized when the pre-forming process and the main forming process are performed using the basic shape after deformation obtained in the basic shape deformation step as the pre-forming shape, the basic shape after deformation obtained in the basic shape deformation step is updated to the pre-forming shape, and the processing of the second surface area calculation step and the basic shape deformation step is repeatedly performed until the effect of reducing cracks is recognized.

[0082] (22) A program for causing a computer to execute a design process for determining a preformed shape when a press-formed product of a target shape is manufactured by press working including a preforming process for press-forming a metal plate into a preformed shape and a main forming process for press-forming an intermediate part of the preformed shape into the target shape, since cracks occur in the press-formed product when a metal plate is press-formed into a target shape in one press forming. The program includes the steps of: arranging single polygonal shapes in a continuous line on a reference plane that is a plane perpendicular to the press direction, thereby partitioning the reference plane into a repetition of a plurality of the single shapes; determining a plurality of division lines formed on a surface of the target shape by each side of each single shape arranged on the reference plane intersecting with the target shape when the partitioned reference plane is moved in the press direction toward the target shape; arranging three or more nodes on each division line corresponding to each side of each of the single shapes at equal intervals as viewed from the press direction; and setting a plurality of smooth curves connecting the plurality of nodes arranged along the extension direction of each division line. and setting, as a preformed shape, a surface shape formed by smoothly applying a surface to each area surrounded by the set plurality of curves. (23) The single shape is set to a quadrangular shape, and the reference plane is partitioned by grid-like lines to arrange a plurality of single shapes on the reference plane.

[0083] "First Example" The first example will be described based on the first shape setting step in the first embodiment described above. In this example, a shape simulating a front pillar lower of an automobile, as shown in Fig. 12, was used as the target shape. A 1180 MPa-class hot-dip galvanized material (plate thickness 1.2 mm) was used as the metal plate.

[0084] At this time, when an attempt was made to form the target shape in a single press forming, a crack occurred at the position shown in FIG. 12. Therefore, based on the first embodiment employing the first shape setting process, a basic shape 81 serving as the basis for the preformed shape was set as shown in FIG. 13. Then, as shown in FIG. 14, the shape of the basic shape 81 near the crack occurrence position W was changed. The boxed area is the design portion of the shape. This process was repeated until the crack was eliminated, with the changed basic shape being used as the new basic shape 81, and the process of changing the shape near the crack was performed. In this example, the number of repetitions was four. The final target shape formed is shown in FIG. 15.

[0085] In this way, it was found that by adopting the design of the preform shape based on the present invention, it is possible to obtain a formed product of a good target shape without the occurrence of cracks. In this way, the use of the present invention makes it possible to easily design the preform shape.

[0086] "Second Example" In the second example, an example based on the second shape setting process in the first embodiment will be described. In this example, the preformed shape was designed under the same conditions as in the first example, except that the basic shape 81 was set using the second shape setting process. In this case, a preformed shape that eliminated cracks was obtained after three repetitions. In this way, it was found that by adopting the preformed shape design based on the present invention, it is possible to obtain a formed product with a good target shape without cracks. In this way, the use of the present invention makes it possible to easily design a preformed shape.

[0087] The entire contents of Japanese Patent Application No. 2023-197994 (filed November 22, 2023), from which this application claims priority, are incorporated herein by reference. While the present invention has been described with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

[0088] 1 Preformed shape design process 2 Press working 2A Preformed process 2B Main forming process 10 Intermediate part 11 Press-formed product 20 Position identification process 21 First surface area calculation process 22 Basic shape setting process 23 Second surface area calculation process 24 Basic shape deformation process 25 Shape evaluation process 26 Basic shape resetting process 30 Basic shape 40 Reference plane 40A Single shape 41 Target shape 42 Parting line 43 Curve 44 Area surrounded by curve 45 Node 50 Program 50A Position identification step 50B First surface area calculation step 50C Basic shape setting step 50D Second surface area calculation step 50E Basic shape deformation step 50F Shape evaluation step 60 Preformed shape setting process 61 Shape evaluation process 70 Program 70F Shape evaluation step A1 Surface area A2 Surface area W Location of occurrence

Claims

1. A method for designing a preformed shape when manufacturing a press-formed product of a target shape by press working including a preforming process of press-forming a metal plate into a preformed shape and a main forming process of press-forming an intermediate part of the preformed shape into a target shape, the method comprising: a position identification process for identifying a crack occurrence position where a crack is estimated to occur in the press-formed product when the metal plate is press-formed to the bottom dead center with a die capable of forming the preformed shape into the target shape in a single press forming; a first surface area calculation process for calculating a surface area A1 located in a first region within a preset distance L0 from the crack occurrence position in the target shape; a basic shape setting process for setting a basic shape of the preformed shape based on the target shape; a second surface area calculation process for calculating a surface area A2 located in a second region within the distance L0 from a position corresponding to the crack occurrence position in the basic shape; and a basic shape deformation process for deforming the basic shape so as to satisfy the following formula (1). 0.9×A1<A2<1.1×A1...(1) 2. A method for designing a preformed shape as described in claim 1, wherein the basic shape setting step selects one of a plurality of formed shapes which are formed in the middle of forming the metal plate to the bottom dead center with the die and before the crack occurs, as the basic shape of the preformed shape.

3. A method for designing a preformed shape as described in claim 1 or claim 2, wherein the position identifying step identifies a position where the crack is estimated to occur by a computer-based forming analysis in which the metal plate is press-formed into the target shape, and the basic shape setting step determines the formed shape before the crack occurs by a computer-based forming analysis in which the metal plate is press-formed into the target shape.

4. A method for designing a preformed shape as set forth in any one of claims 1 to 3, wherein the basic shape setting step comprises: arranging single polygonal shapes in succession on a reference plane, which is a plane perpendicular to the press direction in this forming step, to divide the reference plane into a repetition of a plurality of the single shapes; dividing the surface of the target shape at division lines formed on the surface of the target shape by intersecting each side of each single shape arranged on the reference plane with the target shape when the divided reference plane is moved in the press direction toward the target shape; arranging three or more nodes at a distance from each other on each division line corresponding to each side of each of the single shapes; setting a plurality of smooth curves by connecting the plurality of nodes arranged in the extension direction of each division line; and setting, as the basic shape, a surface shape formed by smoothing surfaces in each area surrounded by the set curves.

5. A method for designing a preformed shape according to claim 4, wherein the single shape is a quadrangle, and a plurality of single shapes are arranged on the reference plane by dividing the reference plane with grid-like lines.

6. A method for designing a preformed shape as described in claim 4 or claim 5, wherein the interval between adjacent parting lines is set to 1 / 10 or less of the line length of the target shape in the arrangement direction of the adjacent parting lines.

7. A method for designing a preformed shape according to any one of claims 1 to 6, wherein the basic shape transformation step determines the shape of a position at a distance L from the position corresponding to the crack occurrence position, for a surface shape within a crack occurrence region, which is a region within the distance L0 from the position corresponding to the crack occurrence position in the basic shape, using a function P(q, L) expressed by the following formula (2): P(q, L) = q x f(L) ... (2) where f(L) is a function formula that satisfies f(L0) = 0, f'(0) = 0, f'(L0) = 0.

8. A method for designing a preformed shape as described in any one of claims 1 to 7, wherein the distance L0 is set to a value that can include the entire area of ​​the crack within the first area.

9. The method for designing a preformed shape according to any one of claims 1 to 8, wherein the distance L0 is set to a value that satisfies the following formula (3) when the tensile strength of the material of the metal plate is TS (MPa): L0 < 3 × TS ０．５ ...(3) 10. A method for designing a preformed shape as described in any one of claims 1 to 9, wherein, if the basic shape after deformation in the basic shape deformation process is used as a preformed shape and the preformed process and main forming process are performed and no crack reduction effect is observed, the basic shape after deformation in the basic shape deformation process is updated to the basic shape, and the second surface area calculation process and the basic shape deformation process are repeatedly performed until a crack reduction effect is observed, thereby designing a preformed shape.

11. A method for designing a preformed shape when manufacturing a press-formed product of a target shape by press working including a preforming process in which a metal plate is press-formed into a preformed shape, and a main forming process in which an intermediate part of the preformed shape is press-formed into a target shape, the method comprising the steps of: arranging single polygonal shapes in a continuous line on a reference plane that is a plane perpendicular to the press direction, thereby dividing the reference plane into a repetition of a plurality of the single shapes; dividing the surface of the target shape at division lines formed on the surface of the target shape by each side of each single shape arranged on the reference plane intersecting with the target shape when the divided reference plane is moved in the press direction toward the target shape; arranging three or more nodes spaced apart from each other on each division line corresponding to each side of each of the single shapes; setting a plurality of smooth curves connecting the multiple nodes arranged in the extension direction of each division line; and defining a surface shape formed by smoothing each area surrounded by the set curves as the preformed shape.

12. The method for designing a preformed shape according to claim 11, wherein the single shape is a quadrangle, and a plurality of single shapes are arranged on the reference plane by dividing the reference plane with grid-like lines.

13. A method for designing a preformed shape as set forth in claim 11, wherein the interval between adjacent parting lines is set to 1 / 10 or less of the line length of the target shape in the arrangement direction of the adjacent parting lines.

14. A method for manufacturing a press-formed product, comprising: determining a preformed shape by the design method for a preformed shape according to any one of claims 1 to 13; and manufacturing a press-formed product having a target shape by a press processing method including a preforming step of press-forming the metal plate into the preformed shape; and a main forming step of press-forming an intermediate part having the preformed shape into a target shape.

15. A program for causing a computer to execute a design process for determining a preformed shape when a press-formed product of a target shape is manufactured by press working including a preforming process for press-forming a metal plate into a preformed shape and a main forming process for press-forming an intermediate part of the preformed shape into a target shape, since cracks will occur in the press-formed product if a metal plate is press-formed into a target shape in one press forming operation, the program comprising: a position specifying step for specifying a position where a crack will occur by performing forming analysis up to the bottom dead center of forming under analysis conditions for press-forming a metal plate into a target shape in one press forming operation; a first surface area calculation step for calculating a surface area A1 located within a first region within a set distance L0 from the crack occurrence position in the target shape specified in the position specifying step; a basic shape setting step for provisionally setting a basic shape of the preformed shape based on the target shape; and a second surface area calculation step for calculating a surface area A2 located within a second region within the distance L0 from a position in the basic shape corresponding to the crack occurrence position specified in the position specifying step. a basic shape deformation step of deforming the basic shape so that a shape within the second region in the basic shape satisfies 0.9×A1<A2<1.1×A1.

16. The program described in claim 15, wherein the basic shape setting step sets as the basic shape one of a plurality of formed shapes obtained by the same forming analysis as in the position identification step, which is a formed shape in the middle of forming to the bottom dead center and before the crack occurs.

17. The program according to claim 15 or 16, wherein the basic shape setting step comprises the steps of: dividing a reference plane, which is a plane perpendicular to the press direction, into a repetition of a plurality of the simple shapes by arranging simple shapes consisting of polygonal shapes in a continuous line on the reference plane; determining a plurality of division lines formed on the surface of the target shape by each side of each simple shape arranged on the reference plane intersecting with the target shape when the divided reference plane is moved in the press direction toward the target shape; arranging three or more nodes at equal intervals as viewed from the press direction on each division line corresponding to each side of each of the simple shapes; setting a plurality of smooth curves by connecting the multiple nodes arranged along the extension direction of each division line; and setting the surface shape formed by smoothly extending a surface in each area surrounded by the set multiple curves as the basic shape.

18. The program according to claim 17, wherein the single shape is a quadrangle, and a plurality of single shapes are arranged on the reference plane by dividing the reference plane with grid-like lines.

19. The program according to any one of claims 15 to 18, wherein the basic shape transformation step determines a preformed shape at a position a distance L from the position corresponding to the crack occurrence position for a surface shape in the crack occurrence region, which is the second region within the distance L0 from the position corresponding to the crack occurrence position in the basic shape, using P(q, L) expressed by the following formula: P(q, L) = q x f(L), where f(L) is a function formula that satisfies f(L0) = 0, f'(0) = 0, f'(L0) = 0.

20. The program according to any one of claims 15 to 19, wherein the distance L0 is set to a value that satisfies the following formula, where TS (MPa) is the tensile strength of the material of the metal plate: L0 < 3 × TS ０．５ 21. A program described in any one of claims 15 to 20, wherein if it is determined that the effect of reducing cracks is not recognized when the pre-forming process and main forming process are performed using the basic shape after deformation obtained in the basic shape deformation step as a pre-forming shape, the basic shape after deformation obtained in the basic shape deformation step is updated to the pre-forming shape, and the processing of the second surface area calculation step and the basic shape deformation step is repeatedly performed until the effect of reducing cracks is recognized.

22. A program for causing a computer to execute a design process for determining a preformed shape when a press-formed product of a target shape is manufactured by press working including a preforming process for press-forming a metal plate into a preformed shape and a main forming process for press-forming an intermediate part of the preformed shape into a target shape, since cracks will occur in the press-formed product if a metal plate is press-formed into a target shape in one press forming process. The program includes the steps of: arranging single polygonal shapes in a continuous line on a reference plane that is a plane perpendicular to the press direction, thereby partitioning the reference plane into a repetition of a plurality of the single shapes; determining a plurality of division lines formed on a surface of the target shape by each side of each single shape arranged on the reference plane intersecting with the target shape when the partitioned reference plane is moved in the press direction toward the target shape; arranging three or more nodes on each division line corresponding to each side of each of the single shapes at equal intervals as viewed from the press direction; and setting a plurality of smooth curves by connecting the multiple nodes arranged along the extension direction of each division line. and setting, as a preformed shape, a surface shape formed by smoothly applying a surface to each area surrounded by the set plurality of curved lines.

23. The program according to claim 22, further comprising: making the single shape a quadrangle; dividing the reference plane with grid lines to place a plurality of single shapes on the reference plane; and arranging a plurality of single shapes on the reference plane.

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