Die design method, die manufacturing method, program, and press part manufacturing method

Abstract

To provide a design method of a mold improving dimensional accuracy of a mold model through an easier processing method.SOLUTION: A design method of a mold is used in a first process of producing an intermediate component and a second process of press-forming the intermediate component to a product shape. The design method of the mold includes: a mold model creating process of creating a mold model based on the product shape; a press analysis process of obtaining a releasing shape; a difference calculation process of obtaining a shape difference between the releasing shape and the product shape; a forming surface shape correction process of correcting a forming surface shape of the mold model based on the shape difference; and a mold shape determination process of determining the forming surface shape of each mold. The forming surface shape correction process temporarily changes definition of physical properties of the mold model to be produced to those of an elastic body or an elastoplastic body, and deforms a forming surface of the changed mold model by loading a weight thereon with distribution corresponding to the shape difference with respect to the forming surface so as to set the deformed forming surface as the forming surface shape of the mold model for the first process.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a technique for designing and manufacturing dies by computer-assisted analysis (FEM analysis). The present invention is a technique suitable for, for example, a simulation analysis method for simulating and analyzing press molding for manufacturing automobile bodies, and a method for designing dies used in press machines for this press molding. Furthermore, the present invention relates to a technique for manufacturing panel parts and other pressed parts using the dies. [Background technology]

[0002] Many of the components that make up an automobile are manufactured by press molding. In recent years, as the materials used in automobiles have become stronger, the amount of deformation caused by springback after release from the mold of press molded components has become larger. Before deciding on the shape of the mold, prototypes are made using a press machine to evaluate whether the mold shape is the target shape, but as the strength of the materials increases, there has been a tendency to increase the number of times prototypes are made and tests are repeated.

[0003] However, the above-mentioned methods increase the number of steps and lead time required for mold manufacturing. For this reason, in recent years, molds have been designed and manufactured using simulation analysis (FEM analysis) using CAE. For example, Patent Document 1 discloses a method in which a panel component that has been subjected to springback analysis is placed on a measurement jig model that is also generated in the analysis space, the difference between the panel component and a target shape is determined under its own weight, and a mold model is modified based on this difference, and the mold model is modified until the difference between the newly obtained panel component and the target shape falls within an acceptable range.

[0004] Additionally, Patent Document 2 proposes a method for reducing camber back by preforming a hat part, which has a curvature in the longitudinal direction, with a smaller radius of curvature than the product shape and then forming it in order to lower the bottom dead point stress. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-221253 A [Patent Document 2] Patent Publication No. 2017-141603 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 is inefficient because it requires the creation of a measuring jig for each shape of the component to be analyzed. In addition, the method described in Patent Document 2 is useful for frame parts that have a relatively monotonous shape, but is difficult to apply to parts with complex design shapes such as doors, where the radius of curvature varies partially.

[0007] The present invention has been made in consideration of the above-mentioned points, and has an object to provide a technique capable of improving the dimensional accuracy of a die model using a simpler processing method. [Means for solving the problem]

[0008] The inventors have found that when a press process is performed in multiple steps, it is possible to easily generate each die model shape (forming surface shape) for each process by converting the shape difference, which is the difference between the work shape and the target shape obtained by simulation analysis, into a load distribution and applying the load distribution to the forming surface of a die model that is temporarily made into an elastic body or an elasto-plastic body. Based on this finding, the present invention has been developed.

[0009] That is, in order to solve the problem, one aspect of the present invention is a method for designing a die used in a manufacturing process for a press part, the method having a first step of press-molding a workpiece to produce an intermediate part having a preformed shape, and a second step of press-molding the intermediate part into a product shape to produce a final molded product, the method including a die model generation step of modeling a molding surface of the die based on the product shape to generate a die model, a press analysis step of simulating and analyzing press molding of the workpiece using the die model to obtain a demolded shape, which is the shape of the workpiece after demolding, a difference calculation step of obtaining a shape difference between the demolded shape obtained in the press analysis step and the product shape, and a calculation step of calculating a shape difference based on the shape difference obtained in the difference calculation step. The method comprises a molding surface shape modification process for modifying the molding surface shape of the mold model based on the above-mentioned molding surface shape modification process, and a mold shape determination process for setting the molding surface shape of the mold model modified in the molding surface shape modification process as the molding surface shape of the mold for the first process and setting the molding surface shape of the mold model before modification in the molding surface shape modification process as the molding surface shape of the mold for the second process, wherein the molding surface shape modification process temporarily changes the physical property definition of the mold model to be generated to an elastic body or an elasto-plastic body, and deforms the molding surface by applying a load to the molding surface of the modified mold model with a distribution corresponding to the shape difference, and sets the molding surface after the deformation as the molding surface shape of the mold model for the first process. Effect of the Invention

[0010] According to an aspect of the present invention, the difference between the workpiece shape (molded shape) after analytical press molding and demolding and the reference shape is converted into a load distribution, and the mold model is made an elastic or elasto-plastic body, so that the molding surface shape is automatically and smoothly corrected and can be made closer to the actual modified shape through simple processing.

[0011] Furthermore, by performing convergent calculations until the difference from the reference shape falls within an allowable range, the same preforming die shape can be derived regardless of the user of the analysis. [Brief description of the drawings]

[0012] [Figure 1]1A to 1C are diagrams illustrating an example of a manufacturing process for a pressed part according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a processing configuration according to an embodiment of the present invention. [Diagram 3] 1 is a process flowchart of a die design procedure according to the present invention. [Figure 4] FIG. 2 is a perspective view showing an example of product data. [Diagram 5] FIG. 2 is a cross-sectional view showing an example of the configuration of a die model for molding product data. [Figure 6] FIG. 2 is a perspective view showing an example of the configuration of a die model for molding product data. [Figure 7] FIG. 13 is a diagram for explaining a shape difference. [Figure 8] FIG. 13 is a diagram for explaining a pressure load. [Figure 9] 11A and 11B are diagrams for explaining pressure loads when a metal mold model is a surface model. [Figure 10] FIG. 13 is a diagram showing another example of converting a shape difference into a pressure. [Figure 11] FIG. 13 is a diagram for explaining a tension load. [Figure 12] 13 is a perspective view showing an example of the configuration of a metal mold model after a molding surface has been corrected; FIG. [Figure 13] FIG. 2 is a conceptual diagram of two-step molding including a first step and a second step. [Figure 14] FIG. 11 is a contour display of an example of a shape difference between product data and a workpiece formed using an initial die model. [Figure 15] FIG. 11 is a contour display of an example of the shape difference between the product data and a workpiece formed by the die model for the first process that has been subjected to shape modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. This embodiment is an invention relating to a die used in a manufacturing process for a pressed part 64 having a first step 60 and a second step 61, as shown in FIG.

[0014] The first step 60 is a step of press-molding a workpiece 62 to produce an intermediate part 63 having a preformed shape. The second step 61 is a step of press-molding the intermediate part 63 into a product shape to produce a final product 64.

[0015] (composition) The design of the die of this embodiment is performed by a simulation analysis using a computer. The simulation analysis is a CAE analysis using the finite element method (FEM). As in the conventional analysis method, the software (program) includes CAD software 100 and analysis software 110 (preprocessor 110A, solver 110B, and postprocessor 110C) as shown in FIG. 2. As the basic configuration of the CAD software 100 and analysis software 110, a known software configuration may be adopted. The analysis software 110 corresponds to the analysis program of the present disclosure.

[0016] The analysis software of this embodiment is software for determining, in other words, performing a design process, the molding surface shape (die shape) of a die used when press-molding a workpiece into a product of a desired shape.

[0017] As shown in FIG. 3, the analysis software includes a product data generation process S1 (product data generation means), an analysis process setting process S2 (analysis process setting means), a die model generation process S3 (die model generation means), a press forming analysis process S4 (press forming analysis means), a springback analysis process S5 (springback analysis means), a difference calculation process S6 (difference calculation means), an evaluation process S7 (evaluation means), a die model correction analysis process S8 (die model analysis means), and a die shape determination process S9 (die shape determination means).

[0018] <Product data generation process S1> The product data generation step S1 executes a process for generating data on the product shape. Here, the product manufactured by the die is a draw panel 11 simulating an automobile door panel (panel part) as shown in Fig. 4. The draw panel 11 is a large panel manufactured by press-forming a steel plate, and has a shape with a curvature in one direction at the protruding portion 12 and a curvature that is relatively flat in the direction perpendicular to the protruding portion. The product also has a flange portion 13 formed around the entire outer periphery.

[0019] Here, automotive panel parts refer to exterior panel parts called outer parts (roof panel parts, door panel parts, etc.) and interior panel parts (panel parts arranged inside the vehicle) such as the floor and dash lower. Such automotive panel parts are a group of parts with a large projected area. Therefore, the amount of weight reduction achieved by reducing the plate thickness of automotive panel parts is significantly greater than that of other frame parts.

[0020] Moreover, automotive panel parts as exterior plate parts generally have a gently curved and wide curved surface. The surface of the exterior plate part is exposed to the user's eyes. For this reason, the exterior plate parts are required to have a high level of surface appearance quality. In this case, the thinner the exterior plate part is made to reduce the weight of the vehicle body, the lower the surface rigidity of the panel part, which is called tension rigidity. With such a decrease in surface rigidity of the panel part, the exterior plate part may undergo out-of-plane deformation. This out-of-plane deformation is called surface sink. The present disclosure is suitable for manufacturing such panel parts.

[0021] <Analysis process setting process S2> The analysis process setting step S2 executes a process of setting a molding mode (molding conditions) for press molding.

[0022] <Mold model generation process S3> In the die model generation step S3, the die is modeled. For example, the die model generating step S3 designs a die model consisting of a die 20, a holder 21, and a punch 22, as shown in Figures 5 and 6. Reference numeral 23 denotes a workpiece model of a workpiece (blank) to be molded. The shape of the molding surface of the mold produced here is the same as the shape of the molding surface of the mold used in the second step 61.

[0023] <Press molding analysis process S4> In the press forming analysis step S4, the press forming of the workpiece using the die model is simulated and analyzed by a known method. That is, in the press forming analysis step S4, the workpiece is modeled to generate a workpiece model 23, and the press forming of the workpiece model 23 is simulated and analyzed.

[0024] <Springback analysis process S5> The springback analysis step S5 performs a simulation analysis of springback due to press forming. That is, the springback analysis step S5 performs a simulation analysis of springback that occurs when the press-formed workpiece model 23 is released from a die.

[0025] Here, the thinner the workpiece or product, the lower the surface rigidity becomes, and there is a possibility that dimensional errors beyond the allowable limit may occur. For this reason, a condition in which the weight of the workpiece or product is applied to the surface may also be set and a simulation analysis may be performed.

[0026] <Difference calculation step S6> In the difference calculation step S6, the shape difference δ between the workpiece model after springback and the product data is calculated. For example, the springback phenomenon causes the protruding portion 31 of the workpiece model 30 to shrink in a direction in which the curvature is short-circuited, and as shown in Fig. 7, the surface-to-surface distance between the product data 11 and the workpiece model 30 increases due to demolding. This difference is calculated as the shape difference δ.

[0027] This shape difference δ is obtained as a distribution along the forming surface. Specifically, the shape difference δ between the product data 11 and the workpiece model 30 after springback is obtained for each node to obtain the distribution of the shape difference δ along the forming surface. The direction of each shape difference δ may be a direction perpendicular to the surface of the product data 11 or the workpiece model 30, or may be the pressing direction (the vertical direction in FIG. 7). It is also preferable to obtain the shape difference δ for the nodes of the surface of the protruding portion 31 to be bulged.

[0028] <Evaluation process S7> It is determined whether the total shape difference δ calculated in the difference calculation step S6 is within an allowable range. For example, it is determined whether or not the shape difference δ at all nodes is within a preset allowable range. If this determination is satisfied, the process proceeds to a die shape determination step S9. If molding is performed using only the mold generated in the mold model generation process S3 for manufacturing the product shape, the work shape will be frozen due to springback, which deviates from the product shape. For this reason, the optimal pre-molding shape is determined in the next process, the mold model correction analysis process S8, and molding is performed in two processes using the generated pre-molding shape and mold (mold for the first process) and the product shape mold (mold for the second process) generated in advance in the mold model generation process S3, so that the shape after final demolding is within the tolerance range of the product shape.

[0029] <Mold model correction analysis process S8> The die model correction analysis process S8 is started when the evaluation process S7 results in an NG evaluation. In the die model correction analysis process S8, the physical properties of the die model are changed to an elastic body, and then pressure is applied to the molding surface of the die model to correct the molding surface. That is, a simulation analysis is performed to generate a molding surface shape (premolding shape) for the first process 60.

[0030] Specifically, the physical property definition of the die 20 in the mold model is temporarily changed to an elastic body to create a die 40, and the distribution of the shape difference δ calculated in the difference calculation process S6 is converted into a pressure distribution. After that, a simulation analysis is performed on the die 40 by applying the calculated pressure distribution to the molding surface of the elastic mold model, as shown in Figure 8, to deform the molding surface.

[0031] Here, in Fig. 8, the die 40 made of an elastic body is illustrated as a model having a certain thickness, but is not limited to this. For example, as shown in Fig. 9, the die 40 may be a plate model having only a molding surface, and the model may be a condition made of an elastic body.

[0032] The distribution of the shape difference δ can be converted into a pressure distribution by converting the shape difference δ of each node into a pressure value individually, or by converting it into an average pressure distribution for each element, as shown in FIG.

[0033] The method of converting the shape difference δ to pressure uses, for example, a preset function or table information. The relationship between the shape difference δ and the pressure is preferably linear, but may be nonlinear. However, the relationship is set so that the larger the shape difference δ, the greater the pressure. The range of pressure to be converted may be set according to the elastic coefficient of the die 40. Note that when the shape difference δ is a negative value, the pressure also becomes a negative value. In the state of FIG. 7, the shape difference δ is a positive value, so the pressure is converted to a positive value (the force pressing against the molding surface). In this manner, the die 40, which is an elastic mold model, is determined as the surface shape of the preforming mold based on the set pressure distribution.

[0034] Then, as shown in FIG. 12, the generated corrected die 50 of the metal mold is modeled into a holder 51 and a punch 52 required for molding by processing similar to that in the metal mold model generating step S3.

[0035] Here, the elastic modulus of the elastic body is set so that the line length of a representative cross section of the die 50 deformed by the pressure distribution is greater than the cross-sectional line length at the same position in the product shape. For example, a convergent calculation is performed using the elastic coefficient as a variable so that the line length ratio of the representative cross section of the die 50 deformed by pressure distribution to the cross section line length at the same position in the product shape is within the range of +0.01% to +0.1%.

[0036] If the line length were to be determined over the entire molding surface, calculations would be required. For this reason, in this embodiment, the line length is determined based on the line length at a representative cross section. The representative cross section is, for example, the line length at the center of the molding surface of the die. When the die model correction analysis process S8 ends, the process proceeds to step S4.

[0037] <Mold shape determination process S9> The mold shape determination process S9 determines the molding surface shape of the mold for the first process 60 and the molding surface shape of the mold for the second process 61. Specifically, the mold shape determination process S9 determines the molding surface shape of the mold model corrected in the mold model correction analysis process S8 as the molding surface shape of the mold for the first process 60. In addition, the molding surface shape of the mold model set in the mold model generation process S3 is determined as the molding surface shape of the mold for the second process 61. Then, the design process of the die model is completed.

[0038] (Modification) In the above explanation, the case of pressure has been exemplified as an example of converting the shape difference δ (distribution) into a load (distribution) in the die model correction analysis process S8. The load converted from the shape difference δ does not have to be pressure. For example, as shown in Fig. 11, it may be converted into tension, which is a force in the direction in which the molding surface of the die 40 expands (pulls up).

[0039] In the above description, the physical property definition of the die model is set to an elastic body in the die model correction analysis step S8, but this is not limited to this. The physical property definition of the die model may be set to an elastoplastic body. It is sufficient to set the physical property definition of at least the forming surface or the vicinity of the forming surface to an elastic body or an elastoplastic body.

[0040] In addition, the load may be applied only to one point in the center of the forming surface. Even if the load is applied only to one point in the center of the forming surface, it is effective for dimensional errors of the work surface.

[0041] (Operation etc.) In this embodiment, when generating the shape of the die used in the first step 60, the difference between the work shape (molded shape) after press molding and demolding by analysis and the reference shape (product shape) is converted into a load distribution (pressure distribution, etc.), and the die model is made into an elastic body or an elastoplastic body. Then, the shape of the die model used in the first step 60 can be obtained by a simple process of applying the load distribution to the molding surface of the die model.

[0042] At this time, when generating the mold shape to be used in the first step 60, the load of the load distribution is applied discretely, but by making the mold model an elastic or elasto-plastic body, the molding surface is automatically corrected to a smooth surface. Furthermore, by performing convergent calculations until the difference from the product shape falls within an allowable range, the same die shape for the first process 60 can be derived regardless of the user of the analysis. Note that the load is preferably in the direction perpendicular to the surface, like pressure.

[0043] Through the above processing, the molding surface shape of the die model for the first process 60 is determined.

[0044] (Mold manufacturing) Then, based on the information about the mold determined in the above mold design, a mold for the first process 60 and a mold for the second process 61 are manufactured.

[0045] (Manufacture of press parts 64) 1, the manufacturing process of a pressed part 64 in this embodiment includes a first step 60 (preforming step) and a second step 61 (main forming step). In the first step 60, a workpiece 62 is press-formed with a die for the first step 60 to produce an intermediate part 63 having a preformed shape. In the second step 61, the intermediate part 63 produced in the first step 60 is press-formed with a die for the second step 61 into a product shape to produce a final molded product 64.

[0046] In the manufacture of this pressed part 64, in a first step 60, an intermediate part 63 is produced in a preformed shape that protrudes slightly more convexly than the product shape (FIG. 13(a)). Then, in a second step 61, the intermediate part 63 is press-formed in a die for the second step 61 that has the same molding surface as the actual product shape (FIGS. 13(b)(c)). As a result, in the manufacture of the pressed part 64 of this embodiment, it is possible to manufacture a final molded product with improved dimensional accuracy.

[0047] Here, from the viewpoint of improving dimensional accuracy, it is preferable that the cross-sectional line length of the preformed shape is slightly longer than the cross-sectional line length at the same position in the product shape. For example, the cross-sectional line length of the molding surface for the second process 61 is set to be within the range of +0.01% to +0.1% in terms of the ratio to the cross-sectional line length at the same position in the product shape. By setting it in this way, the dimensional accuracy of the pressed part 64 is improved.

[0048] In this case, in the press forming in the second step 61, as shown in FIG. 13(b), a compression load is applied to the surface, and the driving force of the springback can be reduced. In particular, when the press part 64 as the final formed product is a panel part having a large surface, out-of-plane deformation can be a problem, but by applying the manufacturing method of the present disclosure, it is possible to suppress the out-of-plane deformation.

[0049] Here, the press molding analysis step S4 and the springback analysis step S5 constitute a press analysis step (press analysis means). The die model correction analysis step S8 constitutes a molding surface shape correction step (molding surface shape correction means). EXAMPLES

[0050] 14 is a contour display of the shape difference δ between the product data (product shape) and the workpiece model formed using the initial die model (corresponding to only the second step 61) before correction in the die model correction analysis step S8. In the workpiece model formed using only the product shape die, the protruding part deforms by springback so as to short-circuit the curvature, so that the surface distance between the workpiece model and the product data was about 1.5 mm at maximum.

[0051] FIG. 15 is a contour display of the shape difference δ between the product data and the work model press-formed through a first process 60 and a second process 61, obtained by performing convergent calculation of the die shape based on the difference between the product data and the press-formed work model as shown in FIG. 14 and based on this embodiment, as shown in FIG. 3.

[0052] In the example of FIG. 15, good results were obtained with a maximum inter-face distance of about ±0.5 mm with respect to the product data.

[0053] As described above, by performing press molding using a die for the first process 60 obtained based on the present disclosure, the dimensional accuracy of the part is improved compared to when press molding is performed using only a die with the molding surface of the product shape.

[0054] (others) The present disclosure may also have the following configuration. (1) A method for designing a die used in a manufacturing process for a pressed part, the manufacturing process including a first step of press-molding a workpiece to produce an intermediate part having a preformed shape, and a second step of press-molding the intermediate part into a product shape to produce a final product, the method comprising the steps of: a die model generating step of generating a die model by modeling a molding surface of a die based on the product shape; A press analysis process for simulating and analyzing press molding of a workpiece using the die model to obtain a release shape, which is the shape of the workpiece after release from the die; a difference calculation step of calculating a shape difference between the release shape calculated in the press analysis step and the product shape; a molding surface shape correction step of correcting a molding surface shape of the die model based on the shape difference calculated in the difference calculation step; a die shape determination process for determining the molding surface shape of the die model corrected in the molding surface shape correction process as the molding surface shape of the die for the first process, and the molding surface shape of the die model determined in the die model generation process as the molding surface shape of the die for the second process; Equipped with The molding surface shape modification process temporarily changes the physical property definition of the mold model to be generated to an elastic or elastoplastic body, and deforms the molding surface of the modified mold model by applying a load with a distribution corresponding to the shape difference, and sets the deformed molding surface as the molding surface shape of the mold model for the first process. (2) The press analysis step, the difference calculation step, and the molding surface shape correction step are repeatedly performed until the shape difference falls within a preset allowable range. (3) The cross-sectional line length of the forming surface after the above deformation is within the range of +0.01% to +0.1% in terms of the ratio to the cross-sectional line length at the same position in the above product shape. (4) The above pressed part is a panel part. (5) The load is pressure, which is a force in a direction pressing the forming surface, or tension, which is a force in a direction lifting the forming surface. (6) The above mold model is a surface model that represents only the above molding surface. (7) The above press analysis process is a press forming analysis step of performing a forming analysis of the press forming of a workpiece using the die model; and a springback analysis process for analyzing springback due to demolding after the press molding analysis process. (8) A method for manufacturing a mold, in which the molding surface shape of a mold for a first step and the molding surface shape of a mold for a second step are determined by the mold design method of the present disclosure. (9) A method for manufacturing a press part, comprising the steps of: manufacturing a press part using a die for a first step and a die for a second step according to the present disclosure. (10) A program for causing a computer to execute a process for determining a molding surface shape of a die for a first step and a molding surface shape of a die for a second step, which are used in a manufacturing process for a press part having a first step of press-forming a workpiece to produce an intermediate part having a preformed shape, and a second step of press-forming the intermediate part into a product shape to produce a final product, the program comprising: a die model generating means for generating a die model by modeling a molding surface of a die based on the product shape; A press analysis means for simulating and analyzing press molding of a workpiece using the die model to obtain a release shape of the workpiece after release from the die; a difference calculation means for calculating a shape difference between the release shape calculated by the press analysis means and the product shape; a molding surface shape correcting means for correcting a molding surface shape of the die model based on the shape difference calculated by the difference calculating means; a mold shape determining means for determining the molding surface shape of the mold model corrected by the molding surface shape correcting means as the molding surface shape of the mold for the first process, and the molding surface shape of the mold model before correction by the molding surface shape correcting means as the molding surface shape of the mold for the second process; Equipped with The molding surface shape modification means temporarily changes the physical property definition of the mold model to be generated to an elastic or elastoplastic body, deforms the molding surface of the modified mold model by applying a load with a distribution corresponding to the shape difference, and sets the deformed molding surface as the molding surface shape of the mold model for the first process. (11) The cross-sectional line length of the forming surface after the above deformation is within the range of +0.01% to +0.1% in terms of the ratio to the cross-sectional line length at the same position in the above product shape. (12) The load is set as a pressure, which is a force in a direction pressing the forming surface, or a tension, which is a force in a direction lifting the forming surface. [Explanation of symbols]

[0055] 60 First step 61 Second step 63 Intermediate parts 64 Press parts 100 CAD software 110 Analysis Software 110A Preprocessor 110B Solver 110C Post Processor S1 Product data generation process S2 Analysis process setting process S3 Mold model generation process S4 Press molding analysis process S5 Springback analysis process S6 Difference calculation process S7 Evaluation process S8 Mold model correction analysis process S9 Mold shape determination process

Claims

1. A method for designing a die used in a manufacturing process of a press part, the method comprising a first step of press-molding a workpiece to produce an intermediate part having a preformed shape, and a second step of press-molding the intermediate part into a product shape to produce a final product, the method comprising: a die model generating step of generating a die model by modeling a molding surface of a die based on the product shape; A press analysis process for simulating and analyzing press molding of a workpiece using the die model to obtain a release shape, which is the shape of the workpiece after release from the die; a difference calculation step of calculating a shape difference between the release shape calculated in the press analysis step and the product shape; a molding surface shape correction step of correcting a molding surface shape of the die model based on the shape difference calculated in the difference calculation step; a die shape determination process for determining the molding surface shape of the die model corrected in the molding surface shape correction process as the molding surface shape of the die for the first process, and the molding surface shape of the die model determined in the die model generation process as the molding surface shape of the die for the second process; Equipped with The molding surface shape modification process temporarily changes the physical property definition of the mold model to be generated to an elastic body or an elastoplastic body, and deforms the molding surface of the modified mold model by applying a load with a distribution corresponding to the shape difference, and sets the deformed molding surface as the molding surface shape of the mold model for the first process. A method for designing a mold.

2. repeating the processes of the press analysis step, the difference calculation step, and the molding surface shape correction step until the shape difference falls within a preset allowable range.

2. The method for designing a mold according to claim 1.

3. The cross-sectional line length of the forming surface after the deformation is within a range of +0.01% to +0.1% in terms of the ratio to the cross-sectional line length at the same position in the product shape.

2. The method for designing a mold according to claim 1.

4. 4. The die design method according to claim 3, wherein the press part is a panel part.

5. 2. The method for designing a die according to claim 1, wherein the load is a pressure which is a force in a direction pressing the molding surface, or a tension which is a force in a direction lifting the molding surface.

6. 6. The method for designing a mold according to claim 1, wherein the mold model is a surface model that represents only the molding surface.

7. The press analysis process is as follows: a press forming analysis step of performing a forming analysis of the press forming of a workpiece using the die model; A springback analysis process for analyzing springback due to demolding after the press molding analysis process; The method for designing a mold according to claim 1, further comprising:

8. A method for manufacturing a mold, in which a molding surface shape of a mold for a first process and a molding surface shape of a mold for a second process are determined by the mold design method described in any one of claims 1 to 7.

9. A method for manufacturing a pressed part, comprising the steps of: manufacturing the pressed part by using a die for a first process and a die for a second process as defined in claim 8.

10. A program for causing a computer to execute a process for determining a molding surface shape of a die for a first process and a molding surface shape of a die for a second process used in a manufacturing process for a press part, the process having a first process of press-molding a workpiece to produce an intermediate part having a preformed shape, and a second process of press-molding the intermediate part into a product shape to produce a final molded product, the program comprising: a die model generating means for generating a die model by modeling a molding surface of a die based on the product shape; A press analysis means for simulating and analyzing press molding of a workpiece using the die model to obtain a release shape of the workpiece after release from the die; a difference calculation means for calculating a shape difference between the release shape calculated by the press analysis means and the product shape; a molding surface shape correcting means for correcting a molding surface shape of the die model based on the shape difference calculated by the difference calculating means; a mold shape determining means for determining the molding surface shape of the mold model corrected by the molding surface shape correcting means as the molding surface shape of the mold for the first process, and the molding surface shape of the mold model before correction by the molding surface shape correcting means as the molding surface shape of the mold for the second process; Equipped with The molding surface shape correction means temporarily changes the physical property definition of the generated die model to an elastic body or an elastoplastic body, and applies a load to the molding surface of the changed die model with a distribution corresponding to the shape difference to deform the molding surface, and sets the deformed molding surface as the molding surface shape of the die model for the first process. A program characterized by:

11. The cross-sectional line length of the forming surface after the deformation is within a range of +0.01% to +0.1% in terms of the ratio to the cross-sectional line length at the same position in the product shape.

11. The program according to claim 10.

12. 12. The program according to claim 10, wherein the load is set as a pressure that is a force in a direction pressing the forming surface, or a tension that is a force in a direction lifting the forming surface.

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