PRESS FORMING ANALYSIS METHOD, PRESS FORMING CRACK DETECTION METHOD FOR PRESS FORMED PRODUCT, MANUFACTURING METHOD FOR PRESS FORMED PRODUCT, PRESS FORMING ANALYSIS DEVICE, PRESS FORMING ANALYSIS PROGRAM

Abstract

To provide a press molding analysis method, a press molding breakage determination method, a press molding analyzer, and a press molding analysis program which can accurately analyze press molding by a finite element method, and to provide a manufacturing method of a press molding using the press molding breakage determination method.SOLUTION: A press molding analysis method includes a blank model creation step (S1) of creating a blank model, and a press molding analysis step (S2) of analyzing press molding using the created blank model. The blank model creation step (S1) includes a blank mesh creation step (S1-1) of creating a finite element mesh constituting the blank model, a grouping step (S1-2) of grouping the finite element constituting the finite element mesh into a plurality of groups, and a deformation condition setting step (S1-3) of setting different conditions relating to deformation for the finite elements of each of the grouped groups for every group.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a press forming analysis method using a finite element method, a press forming crack determination method for a press formed product using the press forming analysis method, a manufacturing method for a press formed product using the press forming crack determination method, a press forming analysis device, and a press forming analysis program. [Background technology]

[0002] The use of high-tensile steel sheets in automobile bodies is expanding due to the increasing need to reduce the weight of automobiles to improve fuel efficiency and collision safety. However, the low ductility of high-tensile steel sheets means that they are prone to fracture and other problems that hinder their application. For example, even if high-tensile steel is used, if fracture occurs during forming, it may be necessary to change the shape of the part, which is an obstacle to the use of high-tensile steel sheets. This issue can be addressed if fracture can be predicted in advance using forming analysis, and there is a demand for highly accurate prediction technology using forming analysis.

[0003] However, steel sheets are composed of various structures, and the size and orientation of crystal grains are not uniform, and deformation within the steel sheet has a non-uniform distribution, so there are cases where fracture cannot be predicted. As an analysis of non-uniform deformation within a material, Non-Patent Document 1 describes a case in which the generation of voids in a steel sheet containing ferrite and martensite was predicted using crystal plasticity finite element analysis. Furthermore, Non-Patent Document 2 describes a case in which a tensile test of aluminum was examined using crystal plasticity finite element analysis taking into account the crystal orientation. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Shigeru Yonemura, "Finite element analysis of deformation and fracture at the mesoscale," Nippon Steel & Sumitomo Metal Technical Review, 2018, No. 410, pp. 47-56

[0005] [Non-Patent Document 2] Kengo Yoshida, "Simulation of Sheet Metal Forming Using Crystal Plasticity Theory," Plasticity and Processing, Japan Society for Technology of Plasticity, March 2016, Vol. 57, No. 662, pp. 38-42 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the crystal plasticity finite element analysis applied in Non-Patent Documents 1 and 2 uses very small elements, which results in a huge calculation time, and therefore its application is limited to simple forming analysis such as tensile tests.

[0007] The present invention has been made to solve such problems, and aims to provide a press forming analysis method that can take into account the non-uniformity of deformation within a metal material by the finite element method in press forming using a metal plate, and can accurately predict cracks in a press-formed product. Another object of the present invention is to provide a press-molded crack determination method capable of determining cracks in press-molded products with high accuracy, and a manufacturing method for press-molded products using the press-molded crack determination method. Furthermore, an object of the present invention is to provide a press forming analysis device and a press forming analysis program capable of performing press forming analysis with high accuracy using the finite element method. [Means for solving the problem]

[0008] (1) The press molding analysis method according to the present invention is a press molding analysis method using a finite element method in which a computer executes each step, A blank model creation process of creating a blank model, and a press molding analysis process of performing a press molding analysis using the created blank model, The blank model creation step includes: a blank mesh creation step of creating a finite element mesh constituting a blank model; a grouping step of grouping finite elements constituting the finite element mesh into a plurality of groups; The method is characterized by including a deformation condition setting step of setting deformation-related conditions differently for each group of finite elements.

[0009] (2) In the above-mentioned (1), the deformation condition setting step is characterized in that mechanical properties or plate thicknesses are set differently for each group.

[0010] (3) In the method described in (1) above, the transformation condition setting step is characterized in that an element size is set differently for each group.

[0011] (4) In the above (1), the transformation condition setting step is characterized in that an element type is set differently for each group.

[0012] (5) Furthermore, in the above-mentioned (2), when the mechanical properties are set differently, the range of the set mechanical properties is set within the range of variation in the mechanical properties of each of the structures of the metal material used as the blank.

[0013] (6) Furthermore, in the case of the above-mentioned (2), when the mechanical properties are set differently, the range of the set mechanical properties is set within the range of variation of the mechanical properties of the metal material used as the blank.

[0014] (7) Furthermore, in the above-mentioned (6), the method further includes a blank characteristic variation range measurement step of measuring the variation range of the mechanical properties of a metal plate used as a blank, and in the blank characteristic variation range measurement step, a hardness distribution of the metal plate used as a blank is measured, and a range of variation in the mechanical properties is determined based on the hardness distribution.

[0015] (8) Furthermore, in the above-described (7), the blank characteristic variation range measuring process further comprises measuring the surface roughness of the front and back surfaces of the metal plate used as the blank, determining a plate thickness range based on the surface roughness of the metal plate, and randomly setting the plate thickness of the finite element mesh constituting the blank model within the plate thickness range.

[0016] (9) Furthermore, in the above-mentioned (2), when the plate thickness is set differently, the plate thickness range is set within a range of ±20% of the plate thickness of the metal material used as the blank.

[0017] (10) Furthermore, in the above-mentioned (9), the method further includes a blank characteristic variation range measurement step for measuring the range of thickness of a metal plate used as a blank, and in the blank characteristic variation range measurement step, the surface roughness of the front and back surfaces of the metal plate used as the blank are measured, and the range of thickness is determined based on the surface roughness of the metal plate.

[0018] (11) A press molding analysis method according to the present invention is a press molding analysis method using a finite element method in which a computer executes each step, A blank model creation process of creating a blank model, and a press molding analysis process of performing a press molding analysis using the created blank model, The blank model creation step includes: A region setting step of setting a plurality of regions inside a contour line representing the shape of the blank; and a mesh creation step of creating a finite element mesh having a different element size, which is a condition related to the deformation, for each of the set regions.

[0019] (12) In addition, in the above (3) or (11), the range of the element size to be set is at least half the thickness of the metal plate used as the blank.

[0020] (13) A method for determining press-forming cracks in a press-formed product according to the present invention is characterized in that it includes a press-forming analysis of a press-formed product using the press-forming analysis method described in any one of (1) to (12) above, and further includes a press-forming crack determination step of determining whether or not cracks have occurred during press forming of the press-formed product based on a forming limit diagram (FLD) of a metal plate used for the press-formed product.

[0021] (14) A method for manufacturing a press-molded product according to the present invention is a method for manufacturing a press-molded product that suppresses press molding cracks, and includes a press molding crack determination step, a press condition adjustment step, and a press-molded product manufacturing step, The press molding crack determination step determines whether or not a crack occurs during press molding of the press-molded product by the press molding crack determination method described in (13) above, The press condition adjustment step changes press forming conditions including a blank shape and a die shape in the press forming analysis until it is determined that no cracks have occurred in all parts of the press-formed product when it is determined that a crack has occurred in the crack determination step, The press-formed product manufacturing process is characterized by producing a press-formed product by press-forming a metal plate under the press-forming conditions of the press-forming analysis when it is determined in the press condition adjustment process that no cracks will occur.

[0022] (15) A press molding analysis device according to the present invention performs press molding analysis of a press-molded product, A blank model creation unit that creates a blank model, and a press molding analysis unit that performs press molding analysis using the created blank model, The blank model creation unit includes: a blank mesh creation unit that creates a finite element mesh that constitutes a blank model; a grouping unit that groups finite elements constituting the finite element mesh into a plurality of groups; The method is characterized by including a deformation condition setting section for setting the mechanical properties, element size or element type as deformation conditions differently for each group of finite elements divided into groups.

[0023] (16) A press molding analysis device for performing a press molding analysis of a press-molded product, comprising: A blank model creation unit that creates a blank model, and a press molding analysis unit that performs press molding analysis using the created blank model, The blank model creation unit includes: a region setting unit that sets a plurality of regions inside a contour line that represents the shape of the blank; and a mesh creation unit that creates a finite element mesh having a different element size, which is a condition related to the deformation, for each of the set regions.

[0024] (17) A press molding analysis program according to the present invention is characterized in that it causes a computer to function as the press molding analysis device according to (15) or (16) above. Effect of the Invention

[0025] According to the present invention, in press forming using a metal plate, it is possible to perform an appropriate press forming analysis that takes into account the non-uniformity of deformation in a metal material. In addition, it is possible to improve the accuracy of determining press forming cracks during press forming. Furthermore, by determining press forming cracks based on the results of the press forming analysis of the present invention and performing press forming under press forming conditions that take measures against cracks, it is possible to suppress defects in press formed products. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a flowchart showing a process flow of the press forming analysis method according to the first embodiment. [Diagram 2] FIG. 11 is a flowchart showing a process flow of another aspect of the press forming analysis method according to the first embodiment. [Diagram 3]FIG. 11 is a flowchart showing a process flow of a press forming analysis method according to the second embodiment. [Figure 4] FIG. 11 is a flowchart showing a process flow of a press forming analysis method according to the third embodiment. [Diagram 5] FIG. 11 is a block diagram showing a configuration of a press molding analysis device according to a fourth embodiment. [Figure 6] FIG. 11 is a block diagram showing the configuration of another aspect of the press molding analysis device according to the fourth embodiment. [Figure 7] FIG. 2 is an explanatory diagram of a part shape that is an analysis target in the first embodiment. [Figure 8] FIG. 2 is an explanatory diagram of a blank mesh in Example 1. [Figure 9] FIG. 2 is an explanatory diagram of a state after press forming of an actual part having the same shape as the part that was the subject of analysis in Example 1. [Figure 10] FIG. 2 is an explanatory diagram of the analysis results of the first embodiment. [Figure 11] FIG. 11 is a flowchart showing a process flow of a press-molding analysis method according to another aspect of the first embodiment. [Figure 12] FIG. 11 is a flowchart showing a process flow of a press-molding crack determination method according to another aspect of the second embodiment. [Figure 13] FIG. 11 is a flow chart showing a process flow of a manufacturing method of a press-molded product according to another aspect of the third embodiment. [Figure 14] FIG. 1 is an explanatory diagram of a mold used in Example 2. [Figure 15] FIG. 11 is an explanatory diagram of the analysis results of Example 2. [Figure 16] FIG. 11 is an explanatory diagram of a state after press forming of an actual part having the same shape as the part that was the subject of analysis in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] [Embodiment 1] Before describing the embodiments, the background to the invention will be described. The inventors have studied the deformation of metal materials in order to reproduce the non-uniform deformation in metal materials using finite element analysis.

[0028] Metallic materials are made up of a group of crystal grains with the same crystal slip deformation direction, and are formed by a group of crystal grains with different deformation directions. It is believed that the difference in the deformation direction and magnitude of each crystal grain causes the non-uniformity of deformation in the metallic material. Due to the non-uniformity of deformation in the metallic material, areas with large microscopic strain and areas with small strain are distributed in the metallic material. In metallic materials with high ductility, the amount of deformation until fracture is large, so the strain distribution caused by the non-uniformity of deformation in the metallic material is small compared to the overall strain of the metallic material and does not have a significant effect on cracking of press-formed products. However, in high-tensile steel sheets with low ductility, the strain distribution caused by the non-uniformity of deformation in the metallic material can be large compared to the overall strain of the metallic material, and may affect cracking of press-formed products. Here, the size of the crystal grains in metal materials is on the order of several tens of microns, whereas the mesh size of the finite elements generally used in press forming analysis is much larger, on the order of several millimeters, making it difficult to reproduce the conditions related to the deformation of individual crystal grains in conventional press forming analysis.

[0029] Therefore, focusing on the fact that the conditions related to the deformation of actual metal materials are determined by the shape, size, and distribution of crystal grains, the finite element meshes are regarded as an aggregate of crystal grains of about several millimeters each in press forming analysis using the finite element method, and the conditions related to deformation are handled for each finite element mesh. In the past, all finite element meshes were treated as having uniform properties with regard to the conditions related to deformation, but the idea was reached that by performing press forming analysis with non-uniform properties for each finite element mesh, non-uniform deformation of the finite element meshes can be generated, and cracks in press formed products caused by non-uniform deformation in metal materials can be reproduced. The researchers then discovered that when performing press forming analysis, it would be possible to group the finite element mesh that constitutes the blank and set different deformation-related conditions for each group. The present invention is based on these findings, and is specifically described in the following embodiments.

[0030] The press forming analysis method according to this embodiment is based on the finite element method in which a computer executes each step, and includes a blank model creation step (S1) of creating a blank model, and a press forming analysis step (S2) of performing press forming analysis using the created blank model, as shown in FIG. 1. Each step will be described in detail below.

[0031] <Blank model creation process> The blank model creation step (S1) is a step of creating a blank model by modeling a metal plate that will serve as a blank using finite elements. Here, the metal member may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a surface-treated steel sheet obtained by subjecting a steel sheet to a surface treatment (electrolytic galvanization, hot-dip galvanization, organic coating treatment, etc.), or a sheet made of various metals such as SUS, aluminum, magnesium, etc.

[0032] The blank model creation process (S1) includes a blank mesh creation process (S1-1), a grouping process (S1-2), and a transformation condition setting process (S1-3).

[0033] <Blank mesh creation process> The blank mesh creation step (S1-1) is a step of creating a finite element mesh that constitutes a blank model.

[0034] Grouping process The grouping step (S1-2) is a step of grouping the finite elements that make up the finite element mesh into a plurality of groups. For example, if there are 1000 finite elements, the 1000 finite elements are divided into three groups, for example, A, B, and C. It is possible to arbitrarily determine which finite elements belong to which group. The finite element mesh that constitutes the blank is divided into multiple groups in order to set different deformation conditions for each group in order to reproduce the non-uniform deformation within the metal material. The number of groups should be at least two.

[0035] <<Deformation condition setting process>> In the deformation condition setting step (S1-3), a deformation-related condition is set for each group of finite elements, the conditions being different for each group. Here, examples of the conditions related to deformation include mechanical properties, plate thickness, element size, and element type.

[0036] Mechanical properties include yield strength, tensile strength, strain hardening index (n value), plastic strain ratio (r value), friction coefficient, stress-strain relationship, etc., and are characteristics related to deformation, such as ease of deformation during press forming. Plate thickness is also a condition related to deformation; if the plate is thick, it is difficult to deform, and if it is thin, it is easy to deform. In addition, in forming analysis using the finite element method, the calculated stress and strain differ depending on the element size and element type, so the element size and element type are also conditions related to deformation. The element type may be a triangle or a quadrangle in terms of shape, and the integration method may be a complete integration type or a selective reduced integration type.

[0037] In addition, when the mechanical properties are set to different values, it is preferable that the range of the set mechanical properties is within the range of variation in the mechanical properties of each structure of the metal material used as the blank. For example, in the case of a dual-phase steel mainly composed of ferrite and martensite, the tensile strength of the ferrite is set in the range of 210 to 300 MPa, and the tensile strength of the martensite is set in the range of 1200 to 1800 MPa for each mesh.

[0038] Moreover, it is preferable that the range of the mechanical properties to be set is within the range of variation in the mechanical properties of the metal material used as the blank. For example, in the case of a 1180 MPa-class high tensile material, the tensile strength is set within the range of 1180 to 1300 MPa for each mesh.

[0039] As described above, when setting different mechanical properties, by keeping them within the range of properties that the actual metal material has, it is possible to obtain analysis results that are suitable for the metal material actually used.

[0040] In addition, when the plate thickness is set differently, it is preferable that the plate thickness range is within a range of ±20% of the plate thickness of the metal material used as the blank. For example, when the metal material is a cold-rolled steel plate, the thickness tolerance (Tables 15 and 16) shown in JIS G 3141 (cold-rolled steel plate and steel strip) is a maximum of ±20%, and the plate thickness may be set differently within this range.

[0041] When setting different element sizes, it is preferable to set the range of element sizes to at least half the thickness of the metal plate used as the blank. The definition of shell elements requires that the element size be sufficiently large compared to the plate thickness, but in actual analysis, up to about half the plate thickness is used, so it is sufficient to set different element sizes within this range.

[0042] <Press molding analysis process> The press forming analysis step (S2) is a step of performing a press forming analysis using the created blank model. In press forming analysis, the deformation state when a blank model is formed into a target shape using a die model is analyzed, and analytical results such as stress, strain, and plate thickness during the forming process and at the bottom dead point of forming are obtained. The analysis results using the created blank model reproduce the non-uniformity of deformation in metal sheets, and are close to the results of actual press forming. In this regard, as will be shown in the examples described later, when cracks are judged based on the press forming analysis results using the blank model of the present invention, results close to those of an actual press formed product are obtained. This proves that the press forming analysis results reproduce results close to those of actual press forming.

[0043] According to the present embodiment, in press forming analysis using the finite element method, it is possible to perform an appropriate forming analysis that takes into account the non-uniformity of deformation in a metal material. This makes it possible to improve the accuracy of determining press forming cracks during press forming. Therefore, by determining press molding cracks based on the results of the press molding analysis of the present invention and performing press molding under press molding conditions that take measures against cracks, defects in press molded products can be suppressed.

[0044] In the above description, the finite element meshes constituting the blank are divided into groups, and the conditions related to deformation are set differently for each group. However, when the condition relating to the deformation is the element size, as shown in FIG. 2, the blank model creating step (S11) may be configured by the following steps. That is, the embodiment includes a region setting process (S11-1) for setting multiple regions inside a contour line representing the shape of the blank, and a mesh creation process (S11-2) for creating finite element meshes having different element sizes, which are conditions related to deformation, for each of the multiple regions that have been set.

[0045] <Other aspects of the first embodiment> A press forming analysis method according to another aspect of this embodiment 1 includes, prior to the blank model creation step (S1) of the press forming analysis method according to this embodiment 1, a blank characteristic variation range measurement step (S0) for measuring the variation range of the mechanical properties of a metal plate used as a blank or the plate thickness range, as shown in FIG. 11 .

[0046] Then, in the deformation condition setting step (S1-3) in the blank model creation step S1 of the press molding analysis method of the above-mentioned embodiment 1, when different settings are made for the mechanical properties, in the blank characteristic variation range measurement step (S0), the range of the mechanical properties to be set is determined by measuring the hardness distribution of the metal plate used as the blank, and the range of variation in the mechanical properties is determined based on the measured hardness distribution.

[0047] For example, the hardness (Vickers hardness HV) distribution of the metal plate used as a blank is measured. It is known that the Vickers hardness HV corresponds to about 1 / 3 of the tensile strength (for example, JIS Handbook (1) Steel I, edited by the Japanese Standards Association, SAE-J-417 Hardness Conversion Table), and even if a tensile test piece (for example, JIS Z 2201) cannot be taken from the metal plate used as a blank, the distance between the centers of the indentations should be at least three times the diagonal distance of the indentations (20 μm or more) (for example, ISO 6507), and the range of variation in tensile strength can be obtained based on the Vickers hardness HV distribution of the metal plate.

[0048] In addition, in the deformation condition setting step (S1-3) in the blank model creation step S1 of the press forming analysis method of the above-mentioned embodiment 1, when the plate thickness is set differently, the plate thickness range to be set in the blank characteristic variation range measurement step (S0) may be determined based on the measured surface roughness by measuring the surface roughness of the front and back surfaces of the metal material used as the blank. For example, the arithmetic mean roughness Ra defined in JIS B0601 and the arithmetic mean height Sa defined in ISO25178 can be adopted as the plate thickness range of the metal material used as the blank.

[0049] In addition, when the hardness distribution of a metal plate used as a blank is measured, the range of variation in mechanical properties is determined based on the measured hardness distribution, and different tensile strengths are set for elements belonging to each group, the surface roughness of the front and back surfaces of the metal plate used as a blank may be measured, a range of plate thickness may be determined based on the surface roughness of the metal plate, and the plate thickness of the finite element mesh constituting the blank model may be set randomly within the range of plate thickness, regardless of the group.

[0050] According to a press molding analysis method relating to another aspect of this embodiment 1, the range of variation of the mechanical properties (tensile strength) of the metal plate used as a blank to be formed into a press-formed product, or the range of plate thickness, is determined based on the hardness distribution of the metal plate used as a blank to actually form into a press-formed product, and the measurement results of the surface roughness on the front and back surfaces of the metal plate, so that it is possible to further improve the reproduction accuracy of cracks in the press-formed product caused by uneven deformation in the metal material used as a blank to form into the press-formed product.

[0051] [Embodiment 2] By carrying out the press-molding analysis method according to the above-mentioned first embodiment and using the results, it is possible to determine whether or not cracks will occur during press molding of a press-molded product. Specifically, as shown in FIG. 3, the process includes a blank model creation step (S1, S11), a press-molding analysis step (S2), and a press-molding crack determination step (S3). The blank model creation steps (S1, S11) and the press molding analysis step (S2) are as described in the first embodiment. The press-forming crack determination step (S3) determines whether or not a crack occurs during press forming of the press-formed product based on a forming limit diagram (FLD) of a metal plate used for the press-formed product.

[0052] In addition, many commercial CAE (Computer Aided Engineering) solvers are equipped with a function that uses the results of a press forming simulation to determine whether or not cracks will occur through FLD. By using this function, it is possible to easily determine whether or not cracks will occur during press forming.

[0053] <Other aspects of the second embodiment> Another aspect of embodiment 2 relates to a press-molding crack determination method that performs a press-molding analysis method related to another aspect of embodiment 1 described above, and uses the results to determine whether or not cracks have occurred during press molding of a press-molded product. Another aspect of the press-molding crack determination method of this embodiment 2 includes a blank characteristic variation range measurement process (S0), a blank model creation process (S1, S11), a press-molding analysis process (S2), and a press-molding crack determination process (S3), as shown in Figure 12. The blank characteristic variation range measuring step (S0), the blank model creating step (S1, S11) and the press molding analyzing step (S2) are as described in the first embodiment.

[0054] According to this embodiment, the range of variation of the mechanical properties (tensile strength) of the metal plate used as a blank to be formed into a press-formed product, or the range of plate thickness, is determined based on the hardness distribution of the metal plate used as a blank to be actually formed into a press-formed product, and the measurement results of the surface roughness of the front and back surfaces of the metal plate, thereby making it possible to further improve the accuracy of determining cracks in the press-formed product.

[0055] [Embodiment 3] The third embodiment relates to a method for manufacturing a press-formed product by utilizing the press-forming crack determination method of the second embodiment. The manufacturing method of the press-molded product of this embodiment 3 includes a blank model creation process (S1, S11), a press molding analysis process (S2), a press molding crack determination process (S3), a press condition adjustment process (S4), and a press-molded product manufacturing process (S5), as shown in Figure 4.

[0056] The blank model creation steps (S1, S11) and the press molding analysis step (S2) are as described in the first embodiment. Moreover, in the press-molding crack determination step (S3), the presence or absence of a crack occurring during press-molding of the press-molded product is determined by the press-molding crack determination method of the second embodiment. In addition, in the press condition adjustment process (S4), when it is determined in the crack determination process that cracks have occurred, the press molding conditions, including the blank shape and mold shape in the press molding analysis, are changed until it is determined that no cracks have occurred in all parts of the press-molded product.

[0057] When a press-formed product is drawn using a press forming die consisting of a die, punch, and blank holder, the press forming conditions such as the blank holder force, die shoulder radius, punch shoulder radius, and lubrication of the blank in contact with the die surface and blank holder surface are changed. By changing the sheet pressure, the tension acting on the blank during press forming can be optimized to eliminate the occurrence of cracks.

[0058] At the die shoulder and punch shoulder, the blank is subjected to bending and unbending deformation while being subjected to tension, which accelerates the rapid reduction in thickness and easily leads to cracks. Therefore, by changing the shape of the press forming die to increase the die shoulder radius and punch shoulder radius, it is possible to eliminate cracks at the die shoulder and punch shoulder, promote the material flow through the die shoulder and punch shoulder, and eliminate cracks that occur near the die shoulder and punch shoulder. By lubricating the blank that comes into contact with the die face and the sheet pressing face, the drawing limit is improved and the occurrence of cracks can be eliminated.

[0059] In addition, the press-formed product manufacturing process (S5) produces a press-formed product by press-forming the metal plate under the press-forming conditions of the press-forming analysis when it is determined in the press condition adjustment process (S4) that no cracks will occur. When the plate clamping force is changed as a press forming condition in the press forming analysis, the setting value on the air pressure control panel of the pneumatic die cushion (auxiliary pressure device) of the press forming machine is changed, and the metal plate is press formed to produce a press-formed product.

[0060] When the shape of the press molding die is changed as a press molding condition for the press molding analysis, the shape data of the press molding die (model) used in the press molding analysis is input into a CAD / CAM program linked to an NC machine tool, and converted into NC data (NC program) for NC processing. The NC machine tool machines a polystyrene foam casting die model or a steel die using the full mold casting method (lost foam casting method). Then, using the NC data (NC program), the NC machine tool produces a polystyrene foam casting die model or a steel die. Then, the press molding die with the changed shape is used to press mold a metal plate to produce a press molded product. As press forming conditions for press forming analysis, when the lubrication of the blank in contact with the die surface and the sheet pressing surface is changed, the type of lubricant is changed (increasing viscosity, adding extreme pressure additives), or a polymer film such as a polyethylene film is inserted, the metal sheet is press formed to produce a press-formed product.

[0061] According to this embodiment, a press-formed product in which press-forming cracks are suppressed can be manufactured.

[0062] <Other aspects of the third embodiment> A manufacturing method of a press-molded product according to another aspect of the third embodiment may include a blank characteristic fluctuation range measuring step (S0) as shown in Fig. 13. The blank characteristic fluctuation range measuring step (S0) is as described in the first embodiment.

[0063] According to another aspect of embodiment 3, the variation range of the mechanical properties (tensile strength) of the metal plate used as a blank to be formed into a press-formed product, or the range of plate thickness, is determined based on the hardness distribution of the metal plate used as a blank to actually form into a press-formed product, and the measurement results of the surface roughness on the front and back surfaces of the metal plate. This makes it possible to further improve the accuracy of determining cracks in the press-formed product, and therefore makes it possible to manufacture press-formed products in which press-formed cracks are further suppressed.

[0064] [Embodiment 4] The present embodiment relates to a press forming analysis device that executes the press forming analysis method in the first embodiment. An example of the configuration of the press molding analysis device 1 according to the present embodiment is shown in Fig. 5. The press molding analysis device 1 is configured by a PC (personal computer) or the like, and has a display device 3, an input device 5, a storage device 7, a working data memory 9, and a calculation processing unit 11, as shown in Fig. 5. The display device 3, the input device 5, the storage device 7 and the working data memory 9 are connected to a processor 11, and each of the functions is executed in response to a command from the processor 11. The functions of the components of the optimization analysis device 1 according to this embodiment will be described below.

[0065] ≪Display device≫ The display device 3 is used to display the blank model, the analysis target model, and further the analysis results, and is composed of a liquid crystal monitor or the like.

[0066] Input Devices The input device 5 is used for inputting instructions from an operator, such as reading out the blank model file 13 (FIG. 5) and displaying the blank model or the analysis target model, and is composed of a keyboard, a mouse, and the like.

[0067] ≪Storage device≫ The storage device 7 is used for storing various files such as the Frank model file 13 and analysis results, and is composed of a hard disk or the like.

[0068] <Working data memory> The working data memory 9 is used for temporary storage of data used by the arithmetic processing unit 11 and for calculations, and is composed of a RAM (Random Access Memory) or the like.

[0069] <Calculation processing unit> 5, the calculation processing unit 11 includes a blank model creation unit 15 and a press molding analysis unit 17. The blank model creation unit 15 includes a blank mesh creation unit 19, a grouping unit 21, and a deformation condition setting unit 23. Each part of the arithmetic processing unit 11 functions when a CPU (Central Processing Unit) of a PC (Personal Computer) executes a predetermined program. The function of each part of the arithmetic processing unit 11 will be described below.

[0070] <Blank mesh creation section> The blank mesh creating unit 19 has a function of creating a finite element mesh that constitutes a blank model.

[0071] <Grouping section> The grouping unit 21 has a function of dividing the finite elements that make up the finite element mesh into a plurality of groups.

[0072] <Transformation condition setting section> The deformation condition setting unit 23 has a function of setting different mechanical properties, element sizes or element types as deformation conditions for the finite elements of each group.

[0073] According to the press forming analysis device 1 of this embodiment, in the same manner as described in the embodiment 1, it becomes possible to perform an appropriate forming analysis that takes into account the non-uniformity of deformation in the metal material in the press forming analysis using the finite element method. This makes it possible to improve the accuracy of determining press forming cracks during press forming.

[0074] When the deformation-related condition is element size, the blank model creation unit 27 may be configured by a region setting unit 29 and a mesh creation unit 31, as in the press molding analysis device 25 shown in FIG. The area setting section 29 has a function of setting a plurality of areas inside a contour line that represents the shape of the blank. The mesh creating unit 31 also has a function of creating a finite element mesh having a different element size, which is a condition related to deformation, for each of a plurality of set regions.

[0075] [Embodiment 5] The press molding analysis program according to this embodiment causes a computer to function as the press molding analysis devices 1 and 25 shown in the fourth embodiment. Specifically, the press forming analysis program is executed by the CPU to: The blank model creation unit 15 (blank mesh creation unit 19, grouping unit 21, deformation condition setting unit 23) and the press molding analysis unit 17 are put into operation. In another embodiment, the press molding analysis program is executed by the CPU to function as the blank model creation unit 27 (area setting unit 29, mesh creation unit 31). EXAMPLES

[0076] A simulation was carried out to confirm the effect of the present invention, which will be described below. Fig. 7 shows a part 33 which is the subject of this embodiment. As shown in Fig. 7, this part 33 has a top plate portion 35, both sides of the top plate portion 35, vertical wall portions 37, and a flange portion 39 at the lower end of the vertical wall portion 37, and the top plate portion 35 has an upwardly convex curved shape. In addition, both ends are bent downward to form an end flange portion 41 at the lower end. The width of the end flange portion 41 is 100 mm, the width between both vertical wall portions at the center of the part is 60 mm, and the R (radius) of the ridge portion connecting the top plate portion 35 and the vertical wall portion 37 at the center of the part is 10 mm (R10). The material of the part 33 is a cold-rolled 1180 MPa class high tensile steel plate with a plate thickness of 1.40 mm.

[0077] The blank mesh used in conventional press forming analysis is shown in FIG. 8(a), and the blank meshes according to the present invention are shown in FIG. 8(b), FIG. 8(c), and FIG. 8(d). The specifications shown in each figure are listed in Table 1.

[0078] [Table 1]

[0079] In the blank mesh shown in Fig. 8(a), all elements are the same, the element size is 1.20 mm, the element type is a quadrilateral full-integration shell element, the plate thickness is 1.40 mm, the yield stress is 886 MPa, and the tensile strength is 1234 MPa.

[0080] For the blank mesh shown in Fig. 8(b), the elements constituting the blank mesh were divided into three groups, and different plate thicknesses or tensile strengths were set for the elements in each group, while other setting conditions were the same. Specifically, case 1 was set to an element size of 1.20 mm, element type of quadrilateral full integral shell element, plate thicknesses of 1.35 mm, 1.40 mm, and 1.45 mm for each group, yield stress of 886 MPa, and tensile strength of 1234 MPa. Case 2 had an element size of 1.20 mm, element type of quadrilateral fully integrated shell element, plate thickness of 1.40 mm, yield stress of 886 MPa, and tensile strength of three types for each group: the standard of 1234 MPa, 1221 MPa (-1% of the standard), and 1246 MPa (+1% of the standard).

[0081] In the blank mesh shown in Fig. 8(c), the size of one side of the quadrilateral elements was arbitrarily changed between 0.70 mm and 1.80 mm, and the element type was a quadrilateral fully integrated shell element with a plate thickness of 1.40 mm, yield stress of 886 MPa, and tensile strength of 1234 MPa. In the embodiment, elements were created with a uniform size of 1.20 mm in both length and width, and then the coordinates of the nodes constituting the elements in the range (group) where the element size was changed were arbitrarily moved within the range of +0.30 mm and -0.25 mm in both length and width on the plane to change the element size.

[0082] In the blank mesh shown in FIG. 8(d), the elements constituting the blank mesh were divided into two groups, and the element types of the elements in each group were made different, with the other setting conditions being the same. Specifically, the element size was 1.20 mm, there were two element types: rectangular fully integrated shell element and triangular fully integrated shell element, the plate thickness was 1.40 mm, the yield stress was 886 MPa, and the tensile strength was 1234 MPa.

[0083] Fig. 9 shows an actual press-formed product 43 produced by actually press-forming a press-formed product having the same shape as that shown in Fig. 7. As shown in Fig. 9, in the actual press-formed product 43, a crack occurred in the width direction of the top plate portion 45 near the center of the part 33 in the longitudinal direction of the top plate portion 45.

[0084] Moreover, the results of a conventional forming analysis using a blank made of the blank mesh in Fig. 8(a) are shown in Fig. 10(a). In addition, the analysis results of case 1 for a blank made of the blank mesh of Figure 8(b) are shown in Figure 10(b-1), and the analysis results of case 2 for a blank made of the blank mesh of Figure 8(b) are shown in Figure 10(b-2). FIG. 10(c) shows the analysis results for a blank made of the blank mesh of FIG. 8(c), and FIG. 10(d) shows the analysis results for a blank made of the blank mesh of FIG. 8(d). The analysis results in Fig. 10 show that cracks were determined using FLD based on the results of press forming analysis, and the locations where cracks occurred are shown in black in the figure.

[0085] In Figure 10(a), which shows the results for the conventional example, no black lines indicating cracks appear, but in Figures 10(b) to (d), which show the results for the inventive example, black lines appear near the center of the top plate in all cases. In this way, while the conventional example was unable to determine the occurrence of cracks, the example of the present invention was able to determine the occurrence of cracks, and a result close to that of the actual press-formed product 43 shown in FIG. 9 was obtained. EXAMPLES

[0086] A press-formed product (part 33) according to the third embodiment was manufactured using a metal blank having a thickness of 1.4 mm, a yield stress of 1055 MPa, and a tensile strength of 1470 MPa for part 33 having the same shape as that of Example 1 shown in Fig. 7, and a press-formed die (lower die 47 in Fig. 14(a) and upper die 49 in Fig. 14(b)). The lower die is composed of a punch 47a and a plate holder 47b (blank holder), and the upper die 49 is composed of a die 49a.

[0087] The element size of the blank mesh used in the press forming analysis was 1.20 mm, and the element type was quadrilateral full integration shell element. As shown in Fig. 8(b), the elements constituting the blank mesh were divided into three groups, and different tensile strengths were set for the elements belonging to each group.

[0088] The range of tensile strength set for each element belonging to each group was set based on the range of variation in mechanical properties determined from the measured hardness distribution by measuring the Vickers hardness HV distribution of the metal plate used as a blank. Vickers hardness HV was measured at 1 mm intervals over the entire width of the metal plate, using an indenter specified in JIS B 7725, with a test force of 200 g and a test force holding time of 10 seconds. Based on the variation (1σ=3.8%) from the average value of Vickers hardness HV, three types of tensile strength were determined for each group: standard 1234 MPa, 1141 MPa, which is -7.6% (-2σ) from the standard, and 1327 MPa, which is +7.6% (=2σ) from the standard.

[0089] In addition, the surface roughness of the front and back surfaces of the metal material used as the blank was measured, and the range of blank thickness was determined based on the arithmetic mean height Sa defined in ISO 25178. Based on the average (Ave) of the measured Sa being 0.022 mm and the standard deviation (σ) being 0.0018 mm, the range of thickness (total of front and back surfaces) was set to 1.40 mm ± 0.0025 (= Ave + 2σ) mm, and the thickness of the finite element mesh that constitutes the blank was set randomly, regardless of each group.

[0090] A press forming analysis was then carried out with a press forming condition of 40 tons of sheet pressure (the force generated at the contact point between the sheet pressure and die). The analysis results are shown in Figure 15(a). The analysis results in Figure 15(a) show that cracks were determined using FLD based on the results of the press forming analysis, and the locations where cracks occurred are indicated by black lines in the figure. Figure 16(a) shows an actual press-formed product produced by actually press-forming a metal plate under the above press-forming conditions using the press-forming die of Figure 14. As shown in Figure 16(a), in the actual press-formed product, a crack occurred in the width direction of the top plate near the center of the part's longitudinal direction in the top plate.

[0091] Next, a press forming analysis was performed with a plate pressure of 30 tons as the press forming condition. The analysis results are shown in Figure 15(b). The analysis results in Figure 15(b) showed that the cracks in the top plate were eliminated, and it was determined that no cracks had occurred in any part of the press formed product.

[0092] Next, the setting value on the air pressure control panel of the pneumatic die cushion (auxiliary pressure device) of the press molding machine was changed so that the plate pressing force was 30 tons, which was the press molding condition for the press molding analysis in which it was determined that no cracks would occur. Then, the metal plate was actually press-formed using the press molding die in Figure 14 to produce a press-formed product. The actual press-formed product is shown in Fig. 16(b). As shown in Fig. 16(b), in the actual press-formed product, cracks in the width direction of the top plate near the center of the part's longitudinal direction in the top plate portion were suppressed, similar to the analysis results in Fig. 15(b).

[0093] As described above, it has been demonstrated that by performing press forming analysis using a blank model to which the present invention is applied, it is possible to obtain analysis results that are close to the actual press-formed product 43. That is, the present invention can improve the accuracy of determining press molding cracks during press molding. Therefore, by determining press molding cracks based on the results of the forming analysis of the present invention and performing press molding under press molding conditions that take measures against cracks, defects in press molded products can be suppressed. [Explanation of symbols]

[0094] 1 Press molding analysis device 3 Display device 5 Input Devices 7 Storage device 9 Working Data Memory 11 Processing unit 13 Blank Model File 15 Blank Model Creation Department 17 Press forming analysis section 19 Blank mesh creation section 21 Group Division 23 Transformation condition setting section 25 Press molding analysis device (other aspects) 27 Blank Model Creation Section (Other Forms) 29 Area setting section 31 Mesh Creation Section 33 parts 35 Top plate 37 Vertical wall section 39 Flange 41 End flange 43 Actual press-molded product 45 Top plate 47 Lower mold 47a Punch 47b Board Holder 49 Upper mold 49a Die

Claims

1. A press molding analysis method using a finite element method in which a computer executes each step, A blank model creation process of creating a blank model of a metal plate to be a blank, and a press forming analysis process of performing a press forming analysis using the created blank model, The blank model creation step includes: a blank mesh creation step of creating a finite element mesh constituting a blank model; a grouping step of setting a plurality of groups to which the finite elements constituting the finite element mesh belong, and arbitrarily determining which of the finite elements belong to which group, and grouping the finite elements; A press molding analysis method comprising: a deformation condition setting step of setting deformation-related conditions differently for each group of finite elements in order to reproduce non-uniform deformation due to the shape, size, and distribution of crystal grains in a metal material.

2. 2. The press forming analysis method according to claim 1, wherein the deformation condition setting step sets different mechanical properties or plate thicknesses for each group.

3. 2. The press forming analysis method according to claim 1, wherein the deformation condition setting step sets an element size differently for each group.

4. 2. The press forming analysis method according to claim 1, wherein the deformation condition setting step sets element types differently for each group.

5. The press forming analysis method according to claim 2, characterized in that, when the mechanical properties are set to different values, the range of the set mechanical properties is set within a range of variation in the mechanical properties of each structure of the metal material applied as the blank.

6. The press forming analysis method according to claim 2, characterized in that, in the case where the mechanical properties are set to different values, the range of the set mechanical properties is set within a range of variation in the mechanical properties of the metal material used as the blank.

7. 7. The press forming analysis method according to claim 6, further comprising a blank characteristic variation range measurement step of measuring a variation range of mechanical properties of a metal plate used as a blank, wherein in the blank characteristic variation range measurement step, a hardness distribution of the metal plate used as the blank is measured, and a range of variation in the mechanical properties is determined based on the hardness distribution.

8. The press forming analysis method according to claim 7, characterized in that in the blank characteristic variation range measurement process, the surface roughness of the front and back surfaces of the metal plate used as the blank is measured, a plate thickness range is determined based on the surface roughness of the metal plate, and the plate thickness of the finite element mesh constituting the blank model is randomly set within the plate thickness range.

9. The press forming analysis method according to claim 2, characterized in that, when the plate thickness is set differently, the plate thickness range is set within a range of ±20% of the plate thickness of the metal material applied as the blank.

10. The press forming analysis method according to claim 9, further comprising a blank characteristic variation range measurement step of measuring a range of thickness of a metal plate used as a blank, wherein in the blank characteristic variation range measurement step, surface roughnesses of the front and back surfaces of the metal plate used as the blank are measured, and the range of thickness is determined based on the surface roughness of the metal plate.

11. A press molding analysis method using a finite element method in which a computer executes each step, A blank model creation process of creating a blank model of a metal plate to be a blank, and a press forming analysis process of performing a press forming analysis using the created blank model, The blank model creation step includes: A region setting step of setting a plurality of regions inside a contour line representing the shape of the blank; a mesh creation process for creating, for each of a plurality of set regions, a finite element mesh with different element sizes, which are a deformation-related condition, in order to reproduce non-uniform deformation due to the shape, size, and distribution of crystal grains in the metal material.

12. 12. The press forming analysis method according to claim 3 or 11, wherein the range of the set element size is set to be equal to or greater than 1 / 2 of the sheet thickness of the metal sheet used as the blank.

13. A press-molding crack determination method for a press-molded product, comprising: performing a press-molding analysis of the press-molded product using the press-molding analysis method according to any one of claims 1 to 11; and further determining whether or not a crack has occurred in press molding of the press-molded product based on a forming limit diagram (FLD) of a metal plate used for the press-molded product.

14. A method for manufacturing a press-molded product that suppresses press molding cracks, the method including a press molding crack determination step, a press condition adjustment step, and a press-molded product manufacturing step, The press molding crack determination step determines whether or not a crack occurs during press molding of the press-molded product by the press molding crack determination method according to claim 13, The press condition adjustment step changes press forming conditions including a blank shape and a die shape in the press forming analysis until it is determined that no cracks have occurred in all parts of the press-formed product when it is determined that a crack has occurred in the crack determination step, The press-formed product manufacturing process is a method for manufacturing a press-formed product, characterized in that a metal plate is press-formed under the press forming conditions of the press forming analysis when it is determined in the press condition adjustment process that no cracks will occur, to manufacture a press-formed product.

15. A press molding analysis device for performing press molding analysis of a press-molded product, A blank model creation unit creates a blank model of a metal plate that serves as a blank, and a press forming analysis unit performs press forming analysis using the created blank model, The blank model creation unit includes: a blank mesh creation unit that creates a finite element mesh that constitutes a blank model; a grouping unit that sets a plurality of groups to which the finite elements constituting the finite element mesh belong, and arbitrarily determines which of the finite elements belong to which group, and groups the finite elements; A press molding analysis device characterized by including a deformation condition setting unit that sets different mechanical properties, element size or element type as deformation-related conditions for each group of finite elements in order to reproduce non-uniform deformation due to the shape, size and distribution of crystal grains in a metal material.

16. A press molding analysis device for performing press molding analysis of a press-molded product, A blank model creation unit creates a blank model of a metal plate that serves as a blank, and a press forming analysis unit performs press forming analysis using the created blank model, The blank model creation unit includes: a region setting unit that sets a plurality of regions inside a contour line that represents the shape of the blank; and a mesh creation unit that creates, for each of a plurality of set regions, a finite element mesh with different element sizes, which are conditions related to deformation, in order to reproduce non-uniform deformation due to the shape, size, and distribution of crystal grains in a metal material.

17. A press molding analysis program for causing a computer to function as the press molding analysis device according to claim 15 or 16.

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