JP2024031803A - Press molding analysis method, press molding breakage determination method of press molding, manufacturing method of press molding, press molding analyzer, and press molding analysis program - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a press forming analysis method using the finite element method, a method for determining press molding cracks in a press molded product using the press forming analysis method, a method for manufacturing a press forming product using the press forming crack determining method, and a press forming analysis apparatus. and related to press forming analysis programs.

The use of high-tensile steel plates in automobile bodies is expanding due to the growing need for improved fuel efficiency and collision safety through lighter automobiles. However, due to its low ductility, high-strength steel plates have poor formability such as breakage, which is a problem in their application. For example, even if high-strength steel is used, if breakage occurs during forming, the shape of the part may need to be changed, which is a factor that inhibits the application of high-strength steel sheets. This point can be addressed if breakage can be predicted in advance using molding analysis, and highly accurate prediction technology using molding analysis is required.

However, steel plates are composed of various structures, and the size and direction of crystal grains are not uniform, and deformation within the steel plate has an uneven 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 an example in which the generation of voids within a steel plate containing ferrite and martensite was predicted using crystal plasticity finite element analysis.
Furthermore, Non-Patent Document 2 describes an example in which a tensile test of aluminum was examined using a crystal plasticity finite element analysis that takes into account crystal orientation.

Shigeru Yonemura, “Finite element analysis of mesoscale deformation and fracture, Nippon Steel & Sumikin Technical Report, 2018, No. 410, p. 47-56

Kengo Yoshida, “Simulation of forming metal sheets using crystal plasticity theory, plasticity and processing,” Japan Society for Plastic Processing, March 2016, Vol. 57, No. 662, p. 38-42

However, in the crystal plasticity finite element analysis applied in Non-Patent Documents 1 and 2, the elements used are very small and the calculation time is enormous, so its application is limited to simple forming analysis such as tensile tests. has been done.

The present invention has been made to solve such problems, and in press forming using a metal plate, it is possible to take into account the non-uniformity of deformation within the metal material by using the finite element method, and to prevent cracks in the press-formed product. The purpose is to provide a press forming analysis method that can predict accurately.
Another object of the present invention is to provide a press molding crack determination method that can accurately determine cracks in a press molded product, and a method for manufacturing a press molded product using the press molding crack determination method.
Furthermore, it is an object of the present invention to provide a press forming analysis device and a press forming analysis program that can perform press forming analysis with high precision using the finite element method.

(1) The press forming analysis method according to the present invention is a press forming analysis method using the finite element method in which a computer executes each step,
It includes a blank model creation step of creating a blank model, and a press forming analysis step of performing press forming analysis using the created blank model,
The blank model creation step includes:
a blank mesh creation process for creating a finite element mesh that constitutes a blank model;
a grouping step of grouping the finite elements constituting the finite element mesh into a plurality of groups;
The present invention is characterized in that it includes a deformation condition setting step in which conditions related to deformation are set differently for each group of finite elements divided into groups.

(2) Furthermore, in the method described in (1) above, the deformation condition setting step is characterized in that mechanical properties or plate thicknesses are set differently for each group.

(3) Furthermore, in the method described in (1) above, the deformation condition setting step is characterized in that the element size is set differently for each group.

(4) Furthermore, in the method described in (1) above, the deformation condition setting step is characterized in that element types are set differently for each group.

(5) In addition, in the case described in (2) above, if the mechanical properties are to be set differently, the range of mechanical properties to be set should be determined by the machine that has the structure of each metal material applied as a blank. It is characterized by the fact that it is within the range of variation in physical properties.

(6) In addition, in the case of the item described in (2) above, if the mechanical properties are to be set differently, the range of mechanical properties to be set shall be determined by the variation in mechanical properties of the metal material used as a blank. It is characterized by being within the range of .

(7) In addition, the method described in (6) above further includes a blank property variation range measurement step of measuring a variation range of mechanical properties of a metal plate applied as a blank, and in the blank property variation range measurement step, the blank The method is characterized in that the hardness distribution of a metal plate to be applied as a metal plate is measured, and the range of variation in mechanical properties is determined based on the hardness distribution.

(8) Further, in the item described in (7) above, in the blank characteristic variation range measuring step, the surface roughness of the front and back surfaces of the metal plate to be applied as a blank is further measured, and the surface roughness of the metal plate is The method is characterized in that a range of plate thicknesses is determined based on the above-described range of plate thicknesses, and the plate thicknesses of the finite element mesh constituting the blank model are randomly set within the range of plate thicknesses.

(9) In addition, in the case described in (2) above, if the plate thickness is to be set differently, the plate thickness of the metal material to be applied with the plate thickness range as a blank when setting the plate thickness. It is characterized by being within a range of ±20%.

(10) In addition, the method described in (9) above further includes a blank characteristic variation range measurement step of measuring the range of thickness of the metal plate to be applied as a blank, and in the blank property variation range measurement step, the metal plate is applied as a blank. The method is characterized in that the surface roughness of the front and back surfaces of the metal plate is measured, and the range of the plate thickness is determined based on the surface roughness of the metal plate.

(11) The press forming analysis method according to the present invention is a press forming analysis method using a finite element method in which a computer executes each step,
It includes a blank model creation step of creating a blank model, and a press forming analysis step of performing 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 an outline representing the shape of the blank;
The present invention is characterized in that it includes a mesh creation step of creating a finite element mesh having different element sizes, which are conditions related to deformation, for each of a plurality of set regions.

(12) Also, in the item described in (3) or (11) above, the range of the element size to be set is 1/2 or more of the thickness of the metal plate used as a blank. It is.

(13) The method for determining press molding cracks in a press molded product according to the present invention includes performing a press molding analysis of a press molded product using the press molding analysis method described in any one of (1) to (12) above. The method further includes a press molding crack determination step of determining whether or not cracks occur during press forming of the press molded product based on a forming limit diagram (FLD) of a metal plate used in the press molded product. be.

(14) The method for manufacturing a press-formed product according to the present invention is a method for manufacturing a press-formed product that suppresses press-forming cracks, and includes a press-molding crack determination step, a press condition adjustment step, and a press-formed product manufacturing step. including,
In the press molding crack determination step, the presence or absence of cracks in press molding of the press molded product is determined by the press molding crack determination method described in (13) above;
In the press condition adjustment step, when it is determined that cracks have occurred in the crack determination step, the blank shape and mold in the press forming analysis are adjusted until it is determined that no cracks have occurred in all parts of the press-formed product. By changing the press forming conditions including the shape,
The press-formed product manufacturing process is characterized by manufacturing a press-formed product by press-forming a metal plate under the press-forming conditions of the press-forming analysis when it is determined that no cracking occurs in the press condition adjustment step. It is something to do.

(15) The press forming analysis device according to the present invention performs press forming analysis of a press formed product,
It includes a blank model creation section that creates a blank model, and a press forming analysis section that performs press forming analysis using the created blank model,
The blank model creation section includes:
a blank mesh creation unit that creates a finite element mesh that constitutes a blank model;
a grouping unit that groups the finite elements constituting the finite element mesh into a plurality of groups;
The present invention is characterized in that it includes a deformation condition setting section for setting different mechanical properties, element sizes, or element types for each group as conditions related to deformation for the finite elements of each group.

(16) Also, a press forming analysis device that performs press forming analysis of a press formed product,
It includes a blank model creation section that creates a blank model, and a press forming analysis section that performs press forming analysis using the created blank model,
The blank model creation section includes:
an area setting section that sets multiple areas inside the outline representing the shape of the blank;
The present invention is characterized in that it includes a mesh creation unit that creates a finite element mesh having different element sizes, which are conditions related to deformation, for each of a plurality of set regions.

(17) A press forming analysis program according to the present invention is characterized in that it causes a computer to function as the press forming analysis apparatus described in (15) or (16) above.

According to the present invention, in press forming using a metal plate, it becomes possible to perform an appropriate press forming analysis that takes into account the non-uniformity of deformation within the metal material. Furthermore, the accuracy of determining press molding cracks during press molding can be improved. Further, 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, it is possible to suppress defects in press molded products.

FIG. 2 is a flowchart showing the process flow of the press forming analysis method according to the first embodiment. FIG. 3 is a flowchart showing the process flow of another aspect of the press forming analysis method according to the first embodiment. FIG. 3 is a flowchart showing a process flow of a press forming analysis method according to Embodiment 2. FIG. FIG. 7 is a flowchart showing a process flow of a press forming analysis method according to Embodiment 3; FIG. 3 is a block diagram showing the configuration of a press forming analysis device according to a fourth embodiment. FIG. 7 is a block diagram showing the configuration of another aspect of the press forming analysis device according to the fourth embodiment. FIG. 3 is an explanatory diagram of a component shape that was analyzed in Example 1. FIG. 3 is an explanatory diagram of a blank mesh in Example 1. FIG. 2 is an explanatory diagram of a state after press molding of an actual part having the same shape as the part analyzed in Example 1. FIG. 3 is an explanatory diagram of analysis results of Example 1. FIG. 3 is a flowchart showing a process flow of a press forming analysis method according to another aspect of the first embodiment. FIG. 7 is a flowchart showing a process flow of a press molding crack determination method according to another aspect of the second embodiment. 7 is a flowchart showing the process flow of a method for manufacturing a press-formed product according to another aspect of Embodiment 3. FIG. FIG. 3 is an explanatory diagram of a mold used in Example 2. FIG. 7 is an explanatory diagram of analysis results of Example 2. FIG. 7 is an explanatory diagram of a state of an actual part having the same shape as the part analyzed in Example 2 after press molding.

[Embodiment 1]
Prior to describing the embodiments, the circumstances leading to the invention will be described.
The inventors studied the deformation of a metal material in order to reproduce the non-uniformity of deformation within the metal material in finite element analysis.

Metal materials are made up of crystal grains with the same crystal sliding deformation direction, and multiple crystal grains with different deformation directions, and the differences in the deformation direction and size of each crystal grain are It is thought that this causes non-uniform deformation within the metal material. Due to the non-uniformity of deformation within the metal material, areas with large microscopic strain and areas with small strain are distributed in a mixed manner within the metal material. Metal materials with high ductility require a large amount of deformation before breaking, so the strain distribution caused by non-uniform deformation within the metal material is small compared to the overall strain of the metal material, and does not significantly affect cracks in press-formed products. . However, in high-strength steel sheets with low ductility, the strain distribution caused by non-uniform deformation within the metal material has a size that cannot be ignored relative to the overall strain of the metal material, and may affect cracking of press-formed products. .
The size of crystal grains in metal materials is on the order of tens of microns, whereas the mesh size of finite elements generally used for press forming analysis is much larger, on the order of several millimeters, and the deformation of individual crystal grains is The relevant conditions are difficult to reproduce in conventional press forming analysis.

Therefore, we focused on the fact that conditions related to the deformation of actual metal materials are determined by the shape, size, and distribution of crystal grains, and in press forming analysis using the finite element method, we created a finite element mesh of several millimeters each. We considered it as an aggregate of crystal grains and handled the conditions related to deformation for each finite element mesh. Regarding conditions related to deformation, conventionally all finite element meshes were treated as having uniform properties, but by performing press forming analysis in which non-uniform properties are given to each finite element mesh, We came up with the idea that by creating non-uniform deformation of the finite element mesh, it is possible to reproduce cracks in press-formed products caused by non-uniform deformation within the metal material.
They also discovered that when performing press forming analysis, the finite element mesh that makes up the blank can be divided into groups, and the conditions related to deformation can be set differently for each group.
The present invention is based on this knowledge, and is specifically shown in the following embodiments.

The press forming analysis method according to the present embodiment is based on the finite element method in which a computer executes each process, and as shown in FIG. and a press forming analysis step (S2) of performing press forming analysis using the blank model obtained.
Each step will be explained in detail below.

<Blank model creation process>
The blank model creation step (S1) is a step of creating a blank model in which a blank metal plate is modeled using finite elements.
Here, metal members include hot-rolled steel sheets, cold-rolled steel sheets, surface-treated steel sheets that have undergone surface treatment (electrogalvanization, hot-dip galvanization, organic coating treatment, etc.), SUS, aluminum, magnesium, etc. , a plate made of various metals may be used.

The blank model creation step (S1) includes a blank mesh creation step (S1-1), a grouping step (S1-2), and a deformation condition setting step (S1-3).

《Blank mesh creation process》
The blank mesh creation step (S1-1) is a step of creating a finite element mesh constituting a blank model.

《Group division process》
The grouping step (S1-2) is a step of grouping the finite elements constituting 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, A, B, and C, for example. It may be arbitrarily determined which finite element belongs to which group.
The reason why the finite element mesh constituting the blank is divided into multiple groups is to set different conditions regarding deformation for each group in order to reproduce the non-uniformity of deformation within the metal material, and the number of groups is at least 2. The above may be sufficient.

《Deformation condition setting process》
In the deformation condition setting step (S1-3), different conditions related to deformation are set for each group of finite elements.
Here, examples of conditions related to deformation include mechanical properties, plate thickness, element size, and element type.

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 important for deformation such as ease of deformation in press forming. It is a relevant characteristic.
Plate thickness is also a condition related to deformation; thicker plates are less likely to deform, while thinner plates are more likely 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.
Element types include triangles and quadrilateral shapes, and integral methods such as complete integral type, selective reduction integral type, and the like.

In addition, in the case where the mechanical properties are set differently, it is preferable that the range of the mechanical properties to be set 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 dual-phase steel mainly consisting of ferrite and martensite, the tensile strength of ferrite is set in the range of 210 to 300 MPa, and the tensile strength of martensite is set in the range of 1200 to 1800 MPa, respectively.

Further, it is preferable that the range of mechanical properties to be set be within the range of variations in mechanical properties of the metal material used as the blank.
For example, in the case of 1180 MPa class high tensile strength material, set the tensile strength for each mesh within the range of 1180 to 1300 MPa.

As described above, when setting the mechanical properties differently, by setting them within the range of the properties of the actual metal material, it is possible to obtain analysis results that are compatible with the metal material actually used.

Further, in the case where the plate thickness is set to be different, it is preferable that the plate thickness range is within ±20% of the plate thickness of the metal material used as a blank. For example, when the metal material is 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 within this range The plate thickness can be set differently.

In the case where the element sizes are set to be different, it is preferable that the range of element sizes to be set is 1/2 or more of the thickness of the metal plate used as a blank. The definition of a shell element requires that the element size be sufficiently large compared to the plate thickness, but in actual analysis, up to about 1/2 of the plate thickness is used, so the element size varies within this range. This can be set as a setting.

<Press forming analysis process>
The press forming analysis step (S2) is a step of performing press forming analysis using the created blank model.
In press forming analysis, a mold model is used to analyze the deformation state when a blank model is formed into a target shape, and analysis results such as stress, strain, and plate thickness during the forming process and at the bottom dead center of forming are obtained.
The analysis results using the created blank model reproduce the non-uniformity of deformation of the metal plate, and are close to the results of actual press forming.
Regarding this point, as will be shown in Examples below, when crack determination is performed based on the press forming analysis results using the blank model of the present invention, results close to those of the actual press formed product can be obtained. This confirms that the press forming analysis results reproduce results close to actual press forming.

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 within the metal material. Thereby, the accuracy of determining press molding cracks during press molding can be improved.
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, it is possible to suppress defects in press molded products.

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

<Other aspects of Embodiment 1>
As shown in FIG. 11, the press forming analysis method according to another aspect of the first embodiment is applied as a blank before the blank model creation step (S1) of the press forming analysis method according to the first embodiment. A blank characteristic variation range measuring step (S0) of measuring a variation range of mechanical properties or a range of plate thickness of a metal plate.

Then, in the deformation condition setting step (S1-3) in the blank model creation step S1 of the press forming analysis method of the first embodiment, if the mechanical properties are set differently, the blank property variation range measurement is performed. In step (S0), the range of mechanical properties to be set is determined by measuring the hardness distribution of a metal plate used as a blank, and determining the range of variation in mechanical properties based on the measured hardness distribution.

For example, the hardness (Vickers hardness HV) distribution of a metal plate used as a blank is measured. It is known that the Vickers hardness HV is equivalent 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 the blank Even if it is not possible to collect a tensile test piece (e.g. JIS Z 2201) from a metal plate to be applied as The range of variation in tensile strength can be obtained based on the Vickers hardness HV distribution of the plate.

In addition, in the case where the plate thickness is set differently in the deformation condition setting step (S1-3) in the blank model creation step S1 of the press forming analysis method of the above-described first embodiment, the blank characteristic variation range measurement step In (S0), the range of the plate thickness to be set may be determined by measuring the surface roughness of the front and back surfaces of the metal material used as a blank, and determining the range of the plate thickness based on the measured surface roughness. 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 range of thickness of the metal material used as the blank.

In addition, when measuring the hardness distribution of a metal plate to be applied as a blank, determining the range of variation in mechanical properties based on the measured hardness distribution, and setting different tensile strengths for each element belonging to each group, The surface roughness of the front and back surfaces of the metal plate to be applied as a blank is measured, the range of plate thickness 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 divided into groups. The plate thickness may be set randomly within the range of the plate thickness.

According to the press forming analysis method according to another aspect of the first embodiment, the variation range of mechanical properties (tensile strength) or the range of plate thickness of a metal plate applied as a blank to be formed into a press-formed product is determined. , is determined based on the hardness distribution of the metal plate to be used as a blank to be actually formed into a press-formed product and the surface roughness measurement results of the front and back surfaces of the metal plate, so the metal to be used as a blank to be formed into a press-formed product It is possible to further improve the reproduction accuracy of cracks in press-formed products caused by non-uniform deformation within the material.

[Embodiment 2]
By implementing the press forming analysis method of Embodiment 1 and using the results, it is possible to determine whether or not cracks occur during press forming of a press formed product.
Specifically, as shown in FIG. 3, it includes a blank model creation step (S1, S11), a press forming analysis step (S2), and a press forming crack determination step (S3).
The blank model creation process (S1, S11) and the press forming analysis process (S2) are as described in the first embodiment.
The press molding crack determination step (S3) determines whether or not cracks have occurred during press forming of the press molded product based on a forming limit diagram (FLD) of a metal plate used for the press molded product.

Note that many commercial CAE (Computer Aided Engineering) solvers are also equipped with a function to determine the presence or absence of cracking by FLD using the results obtained from press forming simulations, so by using such a function, , it is possible to easily determine whether or not cracks occur during press molding.

<Other aspects of Embodiment 2>
Another aspect of Embodiment 2 is to implement the press forming analysis method according to the other aspect of Embodiment 1 and use the results to determine whether or not cracks occur during press forming of a press formed product. The present invention relates to a method for determining press molding cracks.
As shown in FIG. 12, the press forming crack determination method according to another aspect of the second embodiment includes a blank characteristic variation range measurement step (S0), a blank model creation step (S1, S11), and a press forming analysis step. (S2) and a press molding crack determination step (S3).
The blank characteristic variation range measurement step (S0), the blank model creation step (S1, S11), and the press forming analysis step (S2) are as described in the first embodiment.

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

[Embodiment 3]
Embodiment 3 relates to a method of manufacturing a press-molded product using the press molding crack determination method of Embodiment 2.
As shown in FIG. 4, the method for manufacturing a press-formed product according to the third embodiment includes a blank model creation process (S1, S11), a press-forming analysis process (S2), and a press-forming crack determination process (S3). , a press condition adjustment step (S4), and a press-formed product manufacturing step (S5).

The blank model creation process (S1, S11) and the press forming analysis process (S2) are as described in the first embodiment.
Further, in the press molding crack determination step (S3), the presence or absence of cracks in the press molding of the press molded product is determined by the press molding crack determining method of the second embodiment.
In addition, in the press condition adjustment step (S4), when it is determined that cracks have occurred in the crack determination step, the blank shape in the press forming analysis is Change the press forming conditions including the mold shape and mold shape.

When drawing a press-formed product using a press mold consisting of a die, a punch, and a blank holder, there are various factors such as plate holding force, die shoulder radius, punch shoulder radius, die surface and plate holding surface. Change press forming conditions such as lubrication of contacting blanks.
By changing the plate holding force, it is possible to optimize the tension applied to the blank during press forming and eliminate the occurrence of cracks.

At the die shoulder and punch shoulder, the blank undergoes bending and unbending deformation under tension, which rapidly accelerates the reduction in plate thickness and easily leads to cracking. Therefore, by changing the shape of the press molding die so that the die shoulder radius and punch shoulder radius become larger, cracks at the die shoulder and punch shoulder can be eliminated, and the It also promotes material flow and eliminates cracks that occur near the die shoulder and punch shoulder.
By lubricating the blank that contacts the die surface and plate holding surface, the drawing limit can be improved and the occurrence of cracks can be eliminated.

In addition, in the press-formed product manufacturing process (S5), the metal plate is press-formed under the press-forming conditions of the press-forming analysis when it is determined that no cracking occurs in the press-condition adjustment process (S4). Manufacture.
When changing the plate holding force as a press forming condition for press forming analysis, change the setting value on the pneumatic control panel of the pneumatic die cushion (auxiliary pressure device) of the press forming machine, press form the metal plate, and press Manufacture molded products.

When changing the shape of a press forming die as a press forming condition for press forming analysis, input the shape data of the press forming die (model) used for press forming analysis into a CAD/CAM program linked to an NC machine tool. , convert to NC data (NC program) for NC processing. Note that the NC machine tool is used to machine a casting mold model made of polystyrene foam or a steel mold by a full mold casting method (vanishing model casting method). Then, using the NC data (NC program), a styrofoam casting mold model or a steel mold is manufactured using an NC machine tool. Then, the metal plate is press-molded using a press-molding die whose shape has been changed to produce a press-molded product.
As press forming conditions for press forming analysis, if you change the lubrication of the blank that contacts the die surface and plate holding surface, change the type of lubricant (increase in viscosity, add extreme pressure additives), change the type of lubricant (increase in viscosity, add extreme pressure additives), or A film is inserted and a metal plate is press-formed to produce a press-formed product.

According to this embodiment, it is possible to manufacture a press-molded product in which press-molding cracks are suppressed.

<Other aspects of Embodiment 3>
As shown in FIG. 13, a method for manufacturing a press-formed product according to another aspect of the third embodiment may include a blank characteristic variation range measuring step (S0). The blank characteristic variation range measuring step (S0) is as described in the first embodiment.

According to another aspect of the third embodiment, the range of variation in mechanical properties (tensile strength) or the range of plate thickness of a metal plate applied as a blank to be formed into a press-formed product is adjusted to actually form the press-formed product. The determination is made based on the hardness distribution of the metal plate used as the blank to be formed and the surface roughness of the front and back surfaces of the metal plate, and it is possible to improve the accuracy of determining cracks in press-formed products. It is possible to produce a press-molded product with more suppressed cracking.

[Embodiment 4]
The present embodiment relates to a press forming analysis apparatus that executes the press forming analysis method in the first embodiment.
FIG. 5 shows an example of the configuration of the press forming analysis apparatus 1 according to the present embodiment. The press forming analysis device 1 is constituted by a PC (personal computer) or the like, and as shown in FIG. There is.
The display device 3, the input device 5, the storage device 7, and the working data memory 9 are connected to the arithmetic processing section 11, and their respective functions are executed by instructions from the arithmetic processing section 11.
Hereinafter, the functions of each component of the optimization analysis device 1 according to the present embodiment will be explained.

≪Display device≫
The display device 3 is used to display a blank model, a model to be analyzed, analysis results, etc., and is composed of a liquid crystal monitor or the like.

≪Input device≫
The input device 5 is used for reading out the blank model file 13 (FIG. 5), inputting instructions by an operator such as displaying a blank model or a model to be analyzed, and is composed of a keyboard, a mouse, and the like.

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

≪Working data memory≫
The working data memory 9 is used for temporary storage of data used by the arithmetic processing unit 11 and for computation, and is composed of RAM (Random Access Memory) and the like.

≪Arithmetic processing unit≫
The calculation processing section 11 includes a blank model creation section 15 and a press forming analysis section 17, as shown in FIG. The blank model creation section 15 includes a blank mesh creation section 19, a grouping section 21, and a deformation condition setting section 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 functions of each part of the arithmetic processing section 11 will be explained below.

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

<Group section>
The grouping unit 21 has a function of dividing finite elements constituting a finite element mesh into a plurality of groups.

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

According to the press forming analysis apparatus 1 according to the present embodiment, in the same way as described in the first embodiment, in press forming analysis using the finite element method, an appropriate You will be able to perform detailed molding analysis. Thereby, the accuracy of determining press molding cracks during press molding can be improved.

Note that when the condition related to deformation is the element size, the blank model creation section 27 may be configured by the area setting section 29 and the mesh creation section 31, as in the press forming analysis device 25 shown in FIG. good.
The area setting unit 29 has a function of setting a plurality of areas inside the outline representing the shape of the blank.
Furthermore, the mesh creation unit 31 has a function of creating finite element meshes having different element sizes, which are conditions related to deformation, for each of a plurality of set regions.

[Embodiment 5]
The press forming analysis program according to the present embodiment causes a computer to function as the press forming analysis apparatuses 1 and 25 shown in the fourth embodiment.
Specifically, the press forming analysis program is executed by the CPU,
The blank model creation section 15 (blank mesh creation section 19, grouping section 21, deformation condition setting section 23) and press forming analysis section 17 are made to function.
In another aspect, the press forming analysis program is executed by the CPU to function as the blank model creation section 27 (area setting section 29, mesh creation section 31).

A simulation was conducted to confirm the effect of the present invention, and will be described below.
FIG. 7 shows a component 33 that is the object of this embodiment. As shown in FIG. 7, this component 33 has a top plate part 35, a vertical wall part 37 on both sides of the top plate part 35, and a flange part 39 at the lower end of the vertical wall part 37. 35 has an upwardly curved shape. Further, both ends are bent downward, and an end flange portion 41 is provided at the lower end. The width of the end flange portion 41 is 100 mm, the width between both vertical walls in the center of the component is 60 mm, and the R of the ridgeline connecting the top plate 35 and the vertical wall 37 in the center of the component is 10 mm (R10 ).
The material of the component 33 is a cold-rolled 1180 MPa class high tensile strength steel plate with a thickness of 1.40 mm.

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

The blank mesh shown in FIG. 8(a) has all the same elements, the element size is 1.20 mm, the element type is a rectangular complete integral shell element, the plate thickness is 1.40 mm, the yield stress is 886 MPa, and the tensile strength is 1234 MPa.

The blank mesh shown in Figure 8(b) was created by dividing the elements constituting the blank mesh into three groups, setting different plate thicknesses or tensile strengths for the elements belonging to each group, and keeping the other setting conditions the same. . Specifically, the element size was 1.20 mm, the element type was a rectangular fully integral shell element, the plate thickness was 1.35 mm, 1.40 mm, and 1.45 mm for each group, the yield stress was 886 MPa, and the tensile strength was 1234 MPa. This is case 1.
In addition, the element size is 1.20mm, the element type is a rectangular fully integral shell element, the plate thickness is 1.40mm, the yield stress is 886MPa, the tensile strength is 1234Mpa, which is the standard for each group, and 1221MPa, which is -1% compared to the standard. Case 2 was defined as three types of 1246MPa, which is +1% compared to the standard.

The blank mesh shown in Fig. 8(c) has a rectangular element whose side size is arbitrarily changed between 0.70 mm and 1.80 mm, and the element type is a rectangular fully integral shell element, plate thickness 1.40 mm, yield stress 886 MPa, and tensile strength. The strength was set to 1234MPa. In the example, after creating elements with a uniform size of 1.20 mm vertically and horizontally, the coordinates of the nodes that make up the elements of the range (group) in which the element size is changed are set to +0.30 mm and -0.25 mm in the vertical and horizontal plane, respectively. I moved it arbitrarily and changed the element size.

In the blank mesh shown in FIG. 8(d), the elements constituting the blank mesh were divided into two groups, and the element type was varied for each element belonging to each group, with other setting conditions being the same.
Specifically, the element size was 1.20 mm, the element types were two types: a rectangular fully integral shell element and a triangular fully integral shell element, the plate thickness was 1.40 mm, the yield stress was 886 MPa, and the tensile strength was 1234 MPa.

FIG. 9 shows an actual press-formed product 43 manufactured by actually press-molding 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 component 33 in the longitudinal direction.

Further, FIG. 10(a) shows the results of conventional molding analysis using the blank made of the blank mesh shown in FIG. 8(a).
In addition, Figure 10 (b-1) shows the analysis results of Case 1 with a blank made of the blank mesh in Figure 8 (b), and Figure 10 (b-1) shows the analysis results of Case 2 with a blank made of the blank mesh in Figure 8 (b). 10(b-2).
Further, the analysis results for the blank made of the blank mesh of FIG. 8(c) are shown in FIG. 10(c), and the analysis results for the blank made of the blank mesh of FIG. 8(d) are shown in FIG. 10(d).
The analysis results in FIG. 10 are obtained by performing crack determination using FLD based on the results of press forming analysis, and the locations where cracks occur are shown in black in the figure.

In FIG. 10(a), which is the result of the conventional example, no black line indicating the occurrence of cracks appears, but in FIGS. 10(b) to (d), which are the results of the invention example, the top plate part A black line appears near the center.
As described above, although crack occurrence cannot be determined in the conventional example, crack occurrence can be determined in the present invention example, and results close to those of the actual press-formed product 43 shown in FIG. 9 could be obtained.

For the part 33 having the same shape as Example 1 shown in FIG. ) A press-molded product (component 33) according to the third embodiment was manufactured using a lower mold 47 and an upper mold 49 (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.

The element size of the blank mesh used in the press forming analysis is 1.20 mm, the element type is a rectangular complete integral shell element, and the elements that make up the blank mesh are divided into three groups as shown in Figure 8 (b). A different tensile strength was set for each element.

The range of tensile strength set for each element belonging to each group is 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 to be applied as a blank. did.
Vickers hardness HV was determined by measuring the entire length of the metal plate in the width direction at 1 mm intervals, using an indenter specified in JIS B 7725, using a test force of 200 g, and a test force holding time of 10 seconds. Based on the variation (1σ = 3.8%) with respect to the average value of Vickers hardness HV, the tensile strength for each group is 1234 MPa as the standard, 1141 MPa -7.6% (-2σ) as compared to the standard, and +7.6 as compared to the standard. % (=2σ) of 1327MPa.

In addition, the surface roughness of the front and back surfaces of the metal material used as a blank was measured, and the range of the blank board thickness was determined based on the arithmetic mean height Sa defined in ISO25178. Based on the measured average Sa (Ave) of 0.022 mm and standard deviation (σ) of 0.0018 mm, the plate thickness range (total of front and back surfaces) was set to 1.40 mm ± 0.0025 (= Ave + 2 σ) mm, and the blank was constructed. The plate thickness of the finite element mesh was set randomly, regardless of each group.

Then, a press forming analysis was carried out using a plate holding force (force generated at the contact portion between the plate holding and the die) of 40 tons as a press forming condition. The analysis results are shown in FIG. 15(a). The analysis results in FIG. 15(a) are obtained by determining cracks using FLD based on the results of press forming analysis, and the crack occurrence sites are indicated by black lines in the figure.
FIG. 16(a) shows an actual press-formed product manufactured by actually press-forming a metal plate under the above-mentioned press-forming conditions using the press-forming die shown in FIG. 14. As shown in FIG. 16(a), in the actual press-formed product, a crack occurred in the width direction of the top plate near the center of the top plate in the longitudinal direction of the component.

Subsequently, press forming analysis was performed using a plate pressing force of 30 tons as press forming conditions. The analysis results are shown in FIG. 15(b). In the analysis results shown in FIG. 15(b), it was determined that the crack occurrence site in the top plate part was resolved and no cracks occurred in all parts of the press-formed product.

Next, the pneumatic control panel of the pneumatic die cushion (auxiliary pressure device) of the press forming machine was set so that the plate pressing force was 30 tons as the press forming condition for the press forming analysis that determined that no cracking occurred. The values were changed and a metal plate was actually press-molded using the press molding die shown in FIG. 14 to produce a press-molded product.
FIG. 16(b) shows an actual press-formed product. 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 top plate in the longitudinal direction of the component can be suppressed, similar to the analysis results in FIG. 15(b). was completed.

As described above, it has been demonstrated that the analysis result can be made close to the actual press-formed product 43 by performing press-forming analysis using a blank model to which the present invention is applied.
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 molding analysis of the present invention and performing press molding under press molding conditions that take measures against cracks, it is possible to suppress defects in press molded products.

1 Press forming analysis device 3 Display device 5 Input device 7 Storage device 9 Working data memory 11 Arithmetic processing section 13 Blank model file 15 Blank model creation section 17 Press forming analysis section 19 Blank mesh creation section 21 Grouping section 23 Deformation condition setting Part 25 Press forming analysis device (other aspects)
27 Blank model creation section (other aspects)
29 Area setting part 31 Mesh creation part 33 Parts 35 Top plate part 37 Vertical wall part 39 Flange part 41 End flange part 43 Actual press molded product 45 Top plate part 47 Lower die 47a Punch 47b Plate holder 49 Upper die 49a Die

Claims (17)

A press forming analysis method using the finite element method in which a computer executes each process,
It includes a blank model creation step of creating a blank model, and a press forming analysis step of performing press forming analysis using the created blank model,
The blank model creation step includes:
a blank mesh creation process for creating a finite element mesh that constitutes a blank model;
a grouping step of grouping the finite elements constituting the finite element mesh into a plurality of groups;
A press forming analysis method comprising the step of setting deformation conditions for each group of finite elements, in which conditions related to deformation are set differently for each group. 2. The press forming analysis method according to claim 1, wherein in the deformation condition setting step, mechanical properties or plate thickness are set differently for each group. 2. The press forming analysis method according to claim 1, wherein in the deformation condition setting step, element sizes are set differently for each group. 2. The press forming analysis method according to claim 1, wherein in the deformation condition setting step, element types are set differently for each group. In the case where mechanical properties are set differently, the range of mechanical properties to be set is within the range of variation in mechanical properties of each structure of the metal material applied as a blank. The press forming analysis method according to claim 2. In the case where the mechanical properties are set differently, the range of the mechanical properties to be set is within the range of variations in the mechanical properties of the metal material used as the blank. Press forming analysis method described. a blank property variation range measuring step of measuring a variation range of mechanical properties of a metal plate applied as a blank; in the blank property variation range measurement process, a hardness distribution of the metal plate used as a blank is measured; 7. The press forming analysis method according to claim 6, wherein the range of variation in mechanical properties is determined based on the following. In the blank characteristic variation range measuring step, further, the surface roughness of the front and back surfaces of the metal plate to be applied as a blank is measured, the range of plate thickness is determined based on the surface roughness of the metal plate, and a blank model is constructed. 8. The press forming analysis method according to claim 7, further comprising randomly setting the plate thickness of the finite element mesh within the range of the plate thickness. In the case where the plate thickness is set differently, the plate thickness is set within a range of ±20% of the plate thickness of the metal material to be applied as a blank. The press forming analysis method according to claim 2. a blank characteristic variation range measuring step of measuring the thickness range of a metal plate to be applied as a blank; 10. The press forming analysis method according to claim 9, wherein the range of plate thickness is determined based on the surface roughness of the metal plate. A press forming analysis method using the finite element method in which a computer executes each process,
It includes a blank model creation step of creating a blank model, and a press forming analysis step of performing 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 an outline representing the shape of the blank;
A press forming analysis method comprising: a mesh creation step of creating a finite element mesh having different element sizes, which are conditions related to deformation, for each of a plurality of set regions. 12. The press forming analysis method according to claim 3 or 11, wherein the range of the element size to be set is 1/2 or more of the thickness of the metal plate used as the blank. A press forming analysis method of a press formed product is performed using the press forming analysis method according to any one of claims 1 to 12, and further, a forming limit diagram (FLD) of a metal plate used for the press formed product is determined. A method for determining press molding cracks in a press molded product, the method comprising a press mold crack determining step of determining whether or not cracks have occurred during press molding of the press molded product. A method for manufacturing a press-formed product that suppresses press-molding cracks, comprising a press-molding crack determination step, a press condition adjustment step, and a press-formed product manufacturing step,
The press molding crack determination step determines whether or not cracks occur during press molding of the press molded product by the press molding crack determination method according to claim 13,
In the press condition adjustment step, when it is determined that cracks have occurred in the crack determination step, the blank shape and mold in the press forming analysis are adjusted until it is determined that no cracks have occurred in all parts of the press-formed product. By changing the press forming conditions including the shape,
The press-formed product manufacturing process is characterized by manufacturing a press-formed product by press-forming a metal plate under the press-forming conditions of the press-forming analysis when it is determined that no cracking occurs in the press condition adjustment step. A method for manufacturing press-formed products. A press forming analysis device that performs press forming analysis of press formed products,
It includes a blank model creation section that creates a blank model, and a press forming analysis section that performs press forming analysis using the created blank model,
The blank model creation section includes:
a blank mesh creation unit that creates a finite element mesh that constitutes a blank model;
a grouping unit that groups the finite elements constituting the finite element mesh into a plurality of groups;
A press forming analysis device comprising: a deformation condition setting section that sets different mechanical properties, element sizes, or element types as conditions related to deformation for each group of finite elements divided into groups. A press forming analysis device that performs press forming analysis of press formed products,
It includes a blank model creation section that creates a blank model, and a press forming analysis section that performs press forming analysis using the created blank model,
The blank model creation section includes:
an area setting section that sets multiple areas inside the outline representing the shape of the blank;
A press forming analysis device comprising: a mesh creation unit that creates a finite element mesh having different element sizes, which are conditions related to deformation, for each of a plurality of set regions. A press forming analysis program that causes a computer to function as the press forming analysis apparatus according to claim 15 or 16.

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