Methods for identifying forming load factors, methods for manufacturing press-formed parts, forming load factor identification devices, and forming load factor identification programs.

Abstract

DEPCT68 The method for identifying the portion of the forming load-increasing factor according to this invention includes step S1. The evaluation area settings in the template model are generated by pressing 15, step S3 of the calculation. Load distribution for molding of a 15-stage press molding model, step S5 of the calculation. Load assessment for each assessment zone, step S7 of the resistance change. Deformation of the evaluation district in one of the model templates, forming a press, and calculating the evaluation value. The load of the evaluation region where the deformation resistance changes, and step S9 of region identification. The assessment shows that the load assessment values ​​changed before and after the change in resistance. Deformation of the mold template and identification of the corresponding mold section 1. With regard to the assessment area identified as the part that causes an increase in forming load;

Description

Method for identifying part causing an increase in forming load, method for manufacturing press-molded product, device for identifying part causing an increase in forming load, and program for identifying part causing an increase in forming load

[0001] The present invention relates to a method, an apparatus, and a program for identifying a part of a press-formed part that causes an increase in forming load, and also to a method for manufacturing a press-formed part that identifies a part of the press-formed part that causes an increase in forming load and reduces the forming load associated with press forming.

[0002] The growing need for improved fuel efficiency and collision safety through weight reduction in automobiles has led to an expansion in the use of high-tensile steel sheets in automobile bodies. However, the application of high-tensile steel sheets has been hindered by issues such as poor formability due to their low ductility and poor dimensional accuracy due to their high material strength. On the other hand, the increased forming load required for part forming has also become a major issue, necessitating changes to press lines and the division of parts, hindering the application of high-tensile steel sheets. Therefore, a method for reducing the forming load associated with press forming is needed.

[0003] The forming load required for press forming can be predicted in advance using computer-aided engineering (CAE) analysis. CAE analysis has traditionally been used to predict defects of press forming and poor appearance due to fractures, wrinkles, springback, and other issues that occur during part forming when considering the shape of a part or press-forming die. The forming load required for press forming can also be calculated using CAE analysis. When a large forming load is predicted, attempts have been made to reduce the forming load by changing the shape of the part or die or by reviewing the stamping process.

[0004] For example, the forming load required for press forming varies depending on whether trimming of parts is performed simultaneously with forming or before or after forming. Therefore, at press sites, consideration is given to the timing of trimming parts so that the forming load does not exceed the capacity of the press machine.

[0005] Furthermore, Patent Document 1 discloses a method of reducing the forming load by performing incremental forming by dividing and moving a mold.

[0006] Furthermore, Non-Patent Document 1 discloses a method for predicting a forming load using a die model as an elastic body. Non-Patent Document 1 also proposes a method for designing a press process by considering the influence of gaps in the slide parts and mold parts of a press machine, and a method for evaluating the die contact state of a press die based on a contact pressure distribution calculated by CAE analysis (see Figure 9 in Non-Patent Document 1) and determining die gaps, poor contact, etc.

[0007] Japanese Patent Application Laid-Open No. 2010-207907

[0008] Katsuichiro Omachi, "Load Study of Press Forming CAE Using 3DSimSTAMP and Its Application," Press Technology, Japan-Korea Industrial Newspaper, March 2015, Vol. 53, No. 3, pp. 62-65

[0009] One of the factors that increases the forming load is poor conformity between the blank and the die during forming (not conforming to the die). The conformity between the blank and the die during forming refers to the extent to which the blank deforms to fit the surface profile of the die just before reaching the forming bottom dead center. If a part of the blank does not conform to the die during forming, that is, if that part reaches the end of forming in a state where it has barely deformed to fit the surface profile of the die, the forming load will increase sharply when the upper and lower dies sandwich that part at the forming bottom dead center and form it into the target shape.

[0010] Another factor that increases the forming load is buckling and wrinkles that occur during forming. When buckling or wrinkles occur during forming, the apparent thickness of the affected area increases, causing uneven contact between the blank and the die. As a result, when the upper and lower dies clamp the blank at the bottom dead center of the forming process, the wrinkles are crushed, which increases the forming load.

[0011] The above two phenomena that increase the forming load are greatly influenced by the part shape, so if the forming load increases due to these factors, it is effective to take measures by modifying the part shape.

[0012] In contrast, the method of Patent Document 1 requires that the part shape be considered and reflected in the die design stage by identifying areas that may increase the forming load during press forming, i.e., areas where the blank does not fit into the die during forming or areas where buckling or wrinkling is predicted. However, in the past, when a large forming load was predicted, there was no method for clearly identifying the areas that caused the increase, so the part shape was modified based on the designer's experience. Then, a die model corresponding to the modified part shape had to be created and subjected to CAE analysis to confirm whether the modification was effective. Furthermore, if the analysis did not result in a reduction in the forming load, the above-mentioned part shape modification, die model creation, and analysis had to be repeated, resulting in a significant amount of time and effort due to trial and error.

[0013] In this regard, as described in Non-Patent Document 1, there is a method for identifying areas with high surface pressure as areas causing an increase in forming load (forming load increase factor areas) based on the surface pressure distribution calculated by CAE analysis. However, areas with high surface pressure are not necessarily areas where the blank does not fit into the die during forming. For example, high surface pressure can also be caused by interference between dies or the stiffness of the die and press machine. Therefore, modifying the part shape in areas where surface pressure is high due to these reasons may not be effective in reducing the forming load. Therefore, when identifying areas causing an increase in forming load based on the surface pressure distribution, it is necessary to isolate the factors causing the increase in surface pressure. When there are many areas with high surface pressure, it takes a long time to identify the load increase factor areas.

[0014] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method, an apparatus, and a program for identifying a forming load increase factor portion, which can easily identify a portion of a press-formed product that causes an increase in the forming load. Another object of the present invention is to provide a method for manufacturing a press-formed product, which can manufacture a press-formed product while reducing the forming load by using the method for identifying a forming load increase factor portion.

[0015] <Background to the Invention> The inventors conducted extensive research into the phenomenon of increased forming load in order to solve the above-mentioned problems. As described above, if there is a portion of the blank that does not conform to the surface shape of the die on the way to the bottom dead center of forming, the forming load increases rapidly at the end of forming (just before the bottom dead center of forming). This phenomenon of the blank not conforming to the surface shape of the die is likely to occur at the punch shoulder part or a convex (or concave) portion of the part shape.

[0016] Therefore, the inventors have further studied in detail the phenomenon that occurs near the bottom dead center in forming a press-formed product having a convex portion. In actual press forming, near the bottom dead center, a large surface pressure acts on the surfaces of the punch and die due to contact with the blank, causing the surfaces of the punch and die to undergo slight elastic deformation and flatten (be crushed).

[0017] If the die side is elastically deformed, the difference in shape between the die shape and the blank shape is reduced, making it easier for the blank to fit the die. However, for convex-shaped portions, even if the die side is slightly elastically deformed, the difference in shape between the blank and die shape remains large, so a punch must be pressed into the die and the pressing force must be used to make the blank fit the die (deform it to fit the die shape), which increases the load. This is one of the reasons why the forming load increases when forming press-formed products with convex-shaped portions.

[0018] The reason why the forming load increases due to the formation of the convex portion is as described above, but the amount of load increase at that time is affected by the degree of elastic deformation of the mold. For example, if the mold is not easily elastically deformable, the mold will not easily conform to the blank and the difference in shape between the blank shape and the mold shape will not decrease, so it is necessary to increase the forming load to forcibly deform the blank, which tends to increase the forming load. On the other hand, if the mold is easily elastically deformable, the mold will easily conform to the blank and the difference in shape between the blank shape and the mold shape will decrease, so the forming load is less likely to increase.

[0019] As described above, the degree of elastic deformation of the die (deformation resistance) affects the forming load. Furthermore, in areas where the blank does not easily conform to the die during forming, i.e., areas where the difference between the blank shape and the die shape during forming is large, the effect of the die's deformation resistance is greater. On the other hand, in areas where the blank easily conforms to the die during forming, the effect of the die's deformation resistance is smaller. In areas where the blank conforms to the die even without elastic deformation of the die before reaching the bottom dead center of forming, the degree of conformity between the blank and the die does not change even if the die elastically deforms, so there is no effect on the increase in the forming load.

[0020] Furthermore, even when wrinkles generated during forming increase the apparent sheet thickness and the forming load, reducing the deformation resistance of the die reduces the increase in the forming load. Low die deformation resistance reduces the increase in the forming load due to the localized increase in load when crushing the wrinkles, causing the die to elastically deform in response to the localized increase in load, thereby opening the gap between the dies sandwiching the blank. This reduces the phenomenon of a large increase in the forming load before reaching the bottom dead center of forming. Therefore, even in areas where wrinkles occur, the degree of elastic deformation of the die, i.e., the deformation resistance of the die, affects the amount of increase in the forming load. On the other hand, in areas where wrinkles do not occur, the apparent sheet thickness does not increase, so the elastic deformation of the die does not significantly affect the forming load.

[0021] From the above, the inventors have found that the degree of deformability of the die surface affects the increase in forming load only in the area that causes the increase in forming load in a press-formed product, and have come up with the idea that by changing the deformation resistance of only a part of the die model in a CAE analysis and observing the change in forming load before and after changing the deformation resistance, it is possible to evaluate whether that part is the part that causes the increase in forming load.

[0022] The present invention has been made based on this idea, and specifically comprises the following components.

[0023] The method for identifying a part that causes an increase in forming load according to the present invention is a method in which a computer executes each step to identify a part of a press-formed product that causes an increase in forming load, the method including a setting step of setting at least two or more evaluation areas in a die model that models a die that press-forms the press-formed product, wherein an upper die and / or a lower die are configured as an integral part; a forming analysis step of using the die model to analyze the press-forming of the press-formed product using the finite element method and calculate a forming load distribution of the die model at the bottom dead center of forming; a first calculation step of calculating a load evaluation value for each evaluation area of ​​the die model based on the forming load distribution calculated in the forming analysis step; and a second calculation step of using a deformation resistance-change die model in which the deformation resistance of one evaluation area of ​​the die model is changed to be lower or higher and the press-forming of the press-formed product is analyzed using the finite element method. a second calculation step of calculating a forming load distribution of the deformation resistance-modified die model at the bottom dead center of forming and calculating a load evaluation value of the evaluation area in which the deformation resistance has been modified based on the forming load distribution; and an identification step of identifying the evaluation area in which the load evaluation value changes before and after the modification of the deformation resistance of the die model based on the load evaluation value calculated in the first calculation step and the load evaluation value calculated in the second calculation step, and identifying a portion of the press-molded product corresponding to the identified evaluation area as a portion of the press-molded product that causes an increase in the forming load.

[0024] The deformation resistance of the mold model to be changed in the second calculation step may be any one of displacement restraint, Young's modulus, plate thickness, density, mass, and yield strength, or a combination of two or more selected from these.

[0025] The load evaluation value for each evaluation region of the die model may be the load, maximum load, or average load for each evaluation region.

[0026] The method for manufacturing a press-molded product according to the present invention is a method for manufacturing a press-molded product, and includes: an identification step for identifying a portion of the press-molded product that causes an increase in forming load using the method for identifying a portion that causes an increase in forming load according to the present invention; a shape modification step for modifying the shape of the press-molded product at the identified portion and the shape of the corresponding die model; a determination step for determining the shape of the press-molded product and the shape of the corresponding die model by repeating the identification step and the shape modification step until the change in the load evaluation value before and after changing the deformation resistance of the die model in the evaluation area of ​​the die model falls within a predetermined range; and a press molding step for manufacturing a die based on the determined shape of the die model and press-molding the press-molded product using the manufactured die.

[0027] The forming load increase factor portion identifying device according to the present invention is a device for identifying a portion of a press-molded product that causes an increase in forming load, and includes a setting unit that sets at least two or more evaluation regions in a die model that models a die that press-moldes the press-molded product, wherein an upper die and / or a lower die are configured as an integral part; a forming analysis unit that uses the die model to perform a finite element method analysis of the press-molding of the press-molded product and calculates a forming load distribution of the die model at the bottom dead center of forming; a first calculation unit that calculates a load evaluation value for each evaluation region of the die model based on the forming load distribution calculated by the forming analysis unit; and a calculation unit that calculates a load evaluation value for one of the evaluation regions of the die model. a second calculation unit that performs a finite element analysis of the press forming of the press-formed product using a deformation resistance-changed mold model in which the deformation resistance of the mold model is changed to be lower or higher, calculates the forming load distribution of the deformation resistance-changed mold model at the bottom dead center of forming, and calculates a load evaluation value of an evaluation area in which the deformation resistance has been changed based on the forming load distribution; and an identification unit that identifies the evaluation area in which the load evaluation value changes before and after the change in deformation resistance of the mold model based on the load evaluation value calculated by the first calculation unit and the load evaluation value calculated by the second calculation unit, and identifies a portion of the press-formed product corresponding to the identified evaluation area as a portion of the press-formed product that causes an increase in the forming load.

[0028] The forming load increase factor portion identifying program according to the present invention causes a computer to function as the forming load increase factor portion identifying device according to the present invention.

[0029] According to the present invention, it is possible to identify the areas that cause an increase in forming load by simply changing the settings for the deformation resistance of the die model in finite element method (FEM) analysis. Since there is no need to modify the CAD data (computer-aided design data) of the part shape or the shape of the die model as in the past, the time required to design the part shape and die shape can be significantly reduced.

[0030] FIG. 1 is a flow diagram showing the flow of a method for identifying a forming load increase factor portion according to the first embodiment. FIG. 2 is an external view of a part targeted in the first embodiment. FIG. 3 is a cross-sectional view of the part shown in FIG. 2, where FIG. 3(a) is a cross-sectional view taken along line A-A in FIG. 2 and FIG. 3(b) is a cross-sectional view taken along line B-B in FIG. 2. FIG. 4 is a diagram illustrating evaluation regions set in a die model according to the first embodiment. FIG. 5 is a graph showing a comparison of load evaluation values ​​before and after a change in the deformation resistance of the die model for each evaluation region shown in FIG. 4 when the deformation resistance is changed. FIG. 6 is a graph showing the rate of change in load before and after a change in the deformation resistance of the die model shown in FIG. 5 (all evaluation regions). FIG. 7 is a graph showing only evaluation regions G and M in FIG. 6. FIG. 8 is a graph showing the rate of change in load before and after a change in the deformation resistance of a die model according to another aspect of the first embodiment (all evaluation regions). FIG. 9 is a flow diagram showing the flow of a method for manufacturing a press-formed product according to the second embodiment. FIG. 10 is a block diagram for explaining the configuration of a forming load increase factor portion identifying device according to the third embodiment. FIG. 11 is a surface pressure distribution diagram used in a conventional method for identifying a forming load increasing factor portion.

[0031] A method for identifying a forming load increase factor portion according to a first embodiment identifies a portion of a press-formed product that causes an increase in forming load. An example of a part that is a target of this embodiment is shown in FIG. 2.

[0032] The press-formed product 1 in Figure 2 is an example of a part simulating a front pillar of an automotive part, and has a generally J-shaped, longitudinally curved shape in plan view. The press-formed product 1 has a planar first top portion 3 and a second top portion 5 consisting of a flat surface and an inclined surface on the upper surface of approximately one-third of the region from each longitudinal end. Vertical wall portions 7 are formed on both sides of the first top portion 3 and the second top portion 5 via shoulder R portions. Flange portions 9 are formed on the vertical wall portions 7 via the shoulder R portions, giving the respective regions a hat-shaped cross section.

[0033] The top surface 10 connecting the first top plate 3 and the second top plate 5 has a mountain-like shape that gradually convexes toward the center, and on both sides of the top surface 10 are formed vertical wall portions 7 that continue from the first top plate 3 and the second top plate 5. A flange portion 9 is formed at the lower end of the vertical wall portion 7 over its entire length.

[0034] A first protruding protrusion 11 is formed on the first top plate 3. Similarly, a second protruding protrusion 13 is formed on the flat surface of the second top plate 5. Figure 3(a) shows the cross section A-A of Figure 2, and Figure 3(b) shows the cross section B-B of Figure 2. The protruding heights of the first protruding protrusion 11 and the second protruding protrusion 13 are approximately the same, as shown in Figure 3.

[0035] In the case of a press-formed product 1 shown in Figure 2, there is a concern that the forming load may increase due to poor fit between the blank and the die during forming at convex-shaped portions such as the first convex portion 11 and the second convex portion 13 (poor die fit). In this case, the forming load can be reduced by modifying the shape of the affected portion. Conventional methods require modifying the shape of many portions where poor die fit or wrinkles are a concern to determine whether the forming load can be reduced. This requires multiple revisions of the part shape CAD data and the creation of die models for finite element method (FEM) analysis, which is a time-consuming process.

[0036] Furthermore, in the conventional method, the forming load increasing factor portion (the portion where the forming load can be reduced by modifying the shape) is estimated based on the contact pressure distribution, but it is not possible to easily identify the forming load increasing factor portion from the contact pressure distribution. The reason for this will be explained based on the contact pressure distribution in Figure 11.

[0037] The surface pressure distribution in Figure 11 shows the magnitude of the surface pressure at the bottom dead center when the press-formed product 1 is formed, expressed as shades of color. The surface pressure values ​​indicate that the surface pressure acts in the tensile direction, and that the surface pressure acts in the compressive direction, with + (plus) indicating the surface pressure acting in the tensile direction, and - (minus) indicating the surface pressure acting in the compressive direction. Furthermore, areas where the surface pressure is greater in the tensile direction are shown in light colors, and areas where the surface pressure is greater in the compressive direction are shown in dark colors.

[0038] In Figure 11, the area where the surface pressure in the compression direction (negative sign) is the highest (lower limit of surface pressure), is indicated by a solid white line, and the area where the surface pressure in the tension direction (positive sign) is the highest (upper limit of surface pressure), is indicated by a dashed white line. Looking at the surface pressure distribution of the first convex portion 11 and the second convex portion 13, where poor mold fit during molding is a concern, as shown in Figure 11, the upper surfaces of the first convex portion 11 and the second convex portion 13 and the area around the boundary between the first top plate portion 3 and the second top plate portion 5 are displayed in dark colors, indicating that a large compressive stress is acting. However, stresses greater than those occurring in the first convex portion 11 and the second convex portion 13 are scattered in other areas, such as the side wall portion 7 and the flange portion 9, making it difficult to determine which of the shapes of the first convex portion 11 and the second convex portion 13 should be modified to reduce the press-molding load.

[0039] In contrast, the method for identifying a forming load increase factor portion according to the present embodiment can easily identify which portion of the press-formed product 1 in Fig. 2 is causing an increase in the forming load, without requiring modification of the part shape CAD data or the die model. A specific description will be given below.

[0040] The method for identifying a forming load increase factor portion of this embodiment includes a die model evaluation area setting step S1 to a forming load increase factor portion identifying step S9, as shown in Fig. 1. Each step from the die model evaluation area setting step S1 to the forming load increase factor portion identifying step S9 is executed by a computer.

[0041] <Die Model Evaluation Area Setting Step> The die model evaluation area setting step (hereinafter abbreviated as the setting step) S1 is a step of setting at least two or more evaluation areas in a die model that models a die that press-forms the press-formed product 1. In this embodiment, the target is a die in which the upper die and / or the lower die are each formed as an integral part.

[0042] In the setting step S1, a die model (mesh model) for finite element method (FEM) analysis is created from part shape CAD data, as in the conventional procedure 1 described above. Then, the die model is divided into a plurality of regions, and at least two or more evaluation regions are set. An example of the evaluation regions to be set is shown in FIG. 4.

[0043] As shown in Figure 4, in this embodiment, 19 evaluation areas A to S are set for a die model 15 having a shape corresponding to the press-formed product 1 in Figure 2. Evaluation areas A to E and O to S correspond to both flange portions 9 of the press-formed product 1. Evaluation area G corresponds to the first convex portion 11 of the press-formed product 1, and evaluation area M corresponds to the second convex portion 13 of the press-formed product 1. Furthermore, evaluation area F corresponds to the first top plate portion 3 of the press-formed product 1, and evaluation area L corresponds to the flat surface of the second top plate portion 5 of the press-formed product 1. Furthermore, evaluation areas H to K and N correspond to the top surface portion 10 of the press-formed product 1 and the inclined surface of the second top plate portion 5.

[0044] The reason why the flange portion 9 of the press-formed product 1 was evaluated was because there was a concern about wrinkles occurring in the flange portion 9. In the case of the press-formed product 1 shown in FIG. 2, the flange portion 9 may undergo shrink flange forming during forming, which may cause material to concentrate locally and cause wrinkles. As mentioned above, the area where wrinkles occur during forming may also be an area that increases the forming load, so the flange portion 9 was evaluated.

[0045] The vertical wall portion 7 of the press-formed product 1 and the curved portion (shoulder R portion) connecting the vertical wall portion 7 to other portions (flange portion 9, first top plate portion 3, etc.) were excluded from the evaluation because it is difficult to add shape to them and there is little room for changing the shape even if they are portions that cause an increase in the forming load. In this way, the evaluation region does not necessarily have to be set to the entire die model 15, but can be set to portions where there is concern about poor fit between the blank and die, portions where there is concern about the occurrence of wrinkles, portions where there is room for shape modification, etc.

[0046] <Press forming analysis step> The forming analysis step S3 is a step in which the press forming of the press-formed product 1 is analyzed using the die model 15 in which an evaluation area has been set, using the finite element method (FEM), and the forming load distribution (not shown) of the die model 15 at the bottom dead center of forming is calculated.

[0047] <Mold Model Load Evaluation Value Calculation Step> The mold model load evaluation value calculation step (hereinafter abbreviated as the first calculation step) S5 is a step of calculating a load evaluation value for each evaluation area A to S based on the molding load distribution calculated in the molding analysis step S3. The load evaluation value is an index value for evaluating the load required for molding for each evaluation area. In this embodiment, the load applied to each evaluation area, i.e., the reaction force received by the mold in each evaluation area, is calculated as the sum of the load data for each finite element mesh within the evaluation area, and this is used as the load evaluation value. The load evaluation value may be the maximum load for each evaluation area (the maximum value of the load data for each finite element mesh within the evaluation area) or the average load for each evaluation area (the sum of the load data for each finite element mesh within the evaluation area divided by the area of ​​the evaluation area).

[0048] The load evaluation value for each evaluation region calculated in the first calculation step S5 is shown by a black bar graph in Fig. 5. The load evaluation value displayed on the vertical axis in Fig. 5 is normalized using the load of evaluation region O as a reference value.

[0049] <Deformation Resistance-Changed Mold Model Load Evaluation Value Calculation Step> The deformation resistance-changed mold model load evaluation value calculation step (hereinafter abbreviated as second calculation step) S7 is a step in which the deformation resistance of the mold model 15 is changed in only one evaluation region out of the evaluation regions A to S, finite element method (FEM) analysis is performed, and a load evaluation value for the evaluation region in which the deformation resistance of the mold model 15 has been changed is calculated. Below, a specific description will be given using an example of changing the deformation resistance of the mold model 15 in evaluation region A.

[0050] First, the setting conditions for the mold model 15 used in the first calculation step S5 are changed so that the deformation resistance of the mold model 15 is lowered or increased only in the portion where the evaluation area A is set. For example, to lower the deformation resistance of the mold model 15, the setting conditions may be changed by relaxing the displacement constraint, reducing the elastic modulus, thinning the plate thickness, lowering the density, reducing the mass, or lowering the yield strength. Only one of the above setting conditions may be changed, or two or more may be changed in combination. In this embodiment, in order to lower the deformation resistance in the evaluation area A of the mold model 15, the elastic modulus of the portion where the evaluation area A is set of the mold model 15 is set to 0.05% (almost zero) of the initially set value.

[0051] Next, using a die model (hereinafter referred to as deformation resistance modified die model 17) in which the deformation resistance in evaluation region A of die model 15 is reduced as described above, the press forming of press-formed product 1 is analyzed by the finite element method (FEM) to calculate the forming load distribution at the bottom dead center of forming. Then, based on the calculated forming load distribution of deformation resistance modified die model 17, a load evaluation value for evaluation region A (here, load (reaction force received by the die in evaluation region A)) is calculated.

[0052] The same process as above is performed for evaluation areas B to S to calculate the load evaluation value after the deformation resistance change in each evaluation area of ​​the mold model 15. The load evaluation value for each evaluation area calculated in the second calculation step S7 is shown by a white bar graph in FIG.

[0053] <Step for identifying areas that cause an increase in forming load> The step for identifying areas that cause an increase in forming load (hereinafter abbreviated as the identification step) S9 is a step for identifying areas of the press-formed product 1 that cause an increase in forming load based on the load evaluation value calculated in the first calculation step S5 and the load evaluation value calculated in the second calculation step S7.

[0054] As described above, in Figure 5, the load evaluation value calculated in the first calculation step S5 is displayed as a black bar graph, and the load evaluation value calculated in the second calculation step S7 is displayed as a white bar graph, and the load evaluation value before and after the change in deformation resistance is compared for each evaluation area of ​​the mold model 15.

[0055] 5, before the deformation resistance was changed (black bars), the load evaluation value was the largest in evaluation region G corresponding to the first convex portion 11 of the press-formed product 1, and the load evaluation value was the next largest in evaluation region M corresponding to the second convex portion 13 of the press-formed product 1. As such, it can be seen that before the deformation resistance was changed, large loads were generated in the first convex portion 11 and the second convex portion 13, which are prone to mold fit problems during molding.

[0056] Next, Fig. 6 shows the change in the load evaluation value, expressed as a percentage, before and after changing the deformation resistance in each evaluation region of the mold model 15. Fig. 7 also shows a comparison of graphs extracted from Fig. 6 for evaluation region G and evaluation region M. The vertical axis in Figs. 6 and 7 represents the change in the load evaluation value calculated from the formula: load evaluation value after changing the deformation resistance of the mold model / load evaluation value before changing the deformation resistance × 100, with the closer to 100%, the smaller the change, and the further from 100%, the larger the change.

[0057] As shown in Figures 6 and 7, the change in the load evaluation value before and after changing the deformation resistance was within ±10% in most evaluation areas, whereas in evaluation area G corresponding to the first convex portion 11 of the press-formed product 1, the load evaluation value decreased by approximately 75%.

[0058] As explained in the background to the invention, in areas where the blank does not conform to the die during forming, the ease of die deformation (i.e., the deformation resistance of the die model) affects the forming load. Therefore, areas where the load evaluation value changes significantly before and after changing the deformation resistance of the die model can be determined to be areas where poor die conformity occurs during forming, i.e., areas that cause an increase in the forming load (forming load increasing area). Therefore, in the identification step S9 of this embodiment, the area of ​​the press-formed product 1 corresponding to the evaluation area G, i.e., the first convex portion 11, can be identified as the forming load increasing area.

[0059] The reason why the first protruding portion 11, of the two protruding portions of the press-formed product 1, is a forming load increasing factor has been investigated and will be explained below. As explained with reference to FIG. 3 , the first protruding portion 11 and the second protruding portion 13 have approximately the same protruding height. However, the bulging formability of the protruding portions is not necessarily the same even if the protruding heights are the same, and is significantly affected by the metal flow from the surrounding areas of the protruding portion. Specifically, if material can easily flow into the protruding portion from the surrounding areas, the blank will be more easily deformed during forming of the protruding portion and will fit the mold more easily.

[0060] In the case of the first convex portion 11 and the second convex portion 13 of the press-formed product 1, as shown in FIG. 3 , the distance (a1, a2) from the second convex portion 13 to the outer periphery of the second top plate portion 5 is longer than the distance (b1, b2) from the first convex portion 11 to the outer periphery of the first top plate portion 3. Therefore, material from the second top plate portion 5 near the second convex portion 13 tends to flow toward the second convex portion 13, improving the blank's conformity to the mold during forming. On the other hand, because the first convex portion 11 and the outer periphery of the first top plate portion 3 are located close to each other, material from the first top plate portion 3 near the first convex portion 11 tends to flow toward the vertical wall portion 7, reducing material flow toward the first convex portion 11 and resulting in poor mold conformity of the blank. From the above, it can be said that the first convex portion 11 is a region more susceptible to poor mold conformity during forming than the second convex portion 13.

[0061] As described above, in this embodiment, it is possible to identify the forming load increasing factor portion by the simple method of changing the setting conditions related to the deformation resistance of the die model. Since it is possible to identify the portion with poor die fit or the portion with the risk of wrinkle formation without the need to modify the part shape CAD data or the shape of the die model used in the finite element method (FEM) analysis as in the past, it is possible to significantly reduce the time required to consider the part shape, which is efficient.

[0062] In the above-described embodiment, the deformation resistance of a die model in one evaluation region is changed, and based on the change in the load evaluation value of the die model in that region before and after the change, it is determined whether the portion of the press-formed product corresponding to that region is a forming load increase factor portion. Alternatively, for example, the deformation resistance of evaluation regions other than the one evaluation region in the die model may be changed, and the forming load increase factor portion may be identified based on the change in the load evaluation value of the entire die model before and after the change in deformation resistance. An example of the above is shown in FIG. 8 .

[0063] Figure 8 corresponds to the graph of Figure 6 described above and shows the change in load evaluation value for the entire mold model 15 before and after changing the deformation resistance. In this example, the deformation resistance is not changed in only one evaluation area of ​​the mold model 15, so the horizontal axis shows the evaluation area of ​​the mold model 15 for which the deformation resistance was not changed. The vertical axis shows the change in the sum of load evaluation values ​​(total load) for the entire mold model 15, and is a value calculated using the formula: total load for the entire mold model after changing the deformation resistance / total load for the entire mold model before changing the deformation resistance × 100. As in Figure 6, the closer to 100%, the smaller the change in total load, and the further from 100%, the larger the change in total load.

[0064] As shown in Figure 8, when the deformation resistance of only the evaluation region G in the die model 15 was not changed, the change in the total load before and after the change in deformation resistance was smaller than in the examples of the other evaluation regions. The results in Figure 8 show that the load is easily reduced when the deformation resistance of the evaluation region G in the die model 15 is changed, but is difficult to reduce when the deformation resistance of the evaluation region G is not changed. Therefore, in this case as well, the first convex portion 11, which is the portion of the press-formed product 1 corresponding to the evaluation region G in the die model 15, can be identified as the portion that increases the forming load.

[0065] [Embodiment 2] A description will be given of a manufacturing method of the press-formed product 1 that was the subject of Embodiment 1. The manufacturing method of the press-formed product 1 of this embodiment uses the method of identifying a forming load increase factor portion of Embodiment 1 to identify a portion of the press-formed product 1 that causes an increase in the forming load, and modifies the part shape of that portion, thereby reducing the load required for press forming.

[0066] 9, the method for manufacturing the press-formed product 1 of this embodiment includes a forming load increase factor portion identifying step S11, a shape modifying step S13, a press-formed product / die model shape determining step S15, and a press forming step S17. Each step will be described in detail below.

[0067] <Step of Identifying Part of Forming Load Increase Factor> The step of identifying part of forming load increase factor (hereinafter abbreviated as identification step) S11 is a step of identifying a part of the press-formed product 1 that causes an increase in the forming load (forming load increase factor part) using the method of identifying part of forming load increase factor described in embodiment 1. The setting step S1 to identification step S9 described in embodiment 1 correspond to the identification step S11 in this embodiment 2.

[0068] In the case of the press-formed product 1 of FIG. 2, as explained in the first embodiment, the first convex portion 11 can be identified as the site causing the increase in forming load.

[0069] <Shape Modification Step> The shape modification step S13 is a step of modifying the shape of the press-formed product 1 at the portion identified in the identification step S11 and the shape of the corresponding evaluation region of the die model. As described above, since the first convex portion 11 of the press-formed product 1 has been identified as the forming load increasing factor portion, the part shape of the portion including the first convex portion 11 is first modified.

[0070] In this example, it is presumed that the increase in forming load is due to the blank not fitting well to the punch shoulder and die shoulder (shoulder part of a die) that form the first protrusion 11. Therefore, the part shape is modified so that these parts fit well to the die during forming.

[0071] To modify the part shape, for example, it is advisable to reduce the height of the first convex portion 11. By reducing the height of the convex portion and reducing the difference in height between the punch bottom (first top plate portion 3), the difference in shape with the flat portion is reduced, which is expected to reduce poor fit between the die and the blank during molding.

[0072] (Shape modification example 1) The original height of the first convex portion was 3 mm, but this was changed to 2 mm or 1.5 mm.

[0073] Also, for example, it is advisable to increase the shoulder radius of the punch shoulder R portion (see the white arrow in the enlarged view of FIG. 3 ) and the die shoulder R portion (see the black arrow in the enlarged view of FIG. 3 ) of the first convex portion 11. Increasing the shoulder radius of the convex-shaped portion is expected to have the effect of easing the shape change and reducing poor fit between the die and the blank during forming.

[0074] (Shape Modification Example 2) The initial shoulder radius of the punch shoulder R portion and die shoulder R portion of the first convex portion 11 was 7 mm, but this was changed to 10 mm or 15 mm.

[0075] After correcting the shape of the first convex portion 11 of the press-formed product 1, the shape of the corresponding die model is also corrected in the same way.

[0076] <Press-formed product / mold model shape determination step> The press-formed product / mold model shape determination step (hereinafter abbreviated as the determination step) S15 is a step in which the effect of the shape modification in the shape modification step S13 is confirmed and the shape of the press-formed product 1 and the shape of the corresponding mold model are determined.

[0077] First, in order to confirm the effect of modifying the part shape, an analysis similar to that in the identifying step S11 is performed using the mold model whose shape has been modified in the shape modifying step S13 (hereinafter referred to as the mold model after shape modification). Specifically, an evaluation region similar to that in Fig. 4 is set for the mold model after shape modification (setting step S1).

[0078] Next, the press forming of the press-formed product 1 in Figure 2 is analyzed using the shape-modified mold model in which the evaluation area has been set, using the finite element method (FEM), and the load evaluation value of the evaluation area G before the deformation resistance change is calculated (forming analysis step S3, first calculation step S5).

[0079] Next, the deformation resistance of the part corresponding to the evaluation area G of the mold model after the shape modification is changed, and a finite element method (FEM) analysis is performed again using the mold model to calculate the load evaluation value of the evaluation area G after the deformation resistance modification (second calculation step S7).

[0080] Then, the change in the load evaluation value before and after the change in deformation resistance in the evaluation region G in the shape-modified die model is confirmed. If the change in the load evaluation value before and after the change in deformation resistance becomes small and falls within a predetermined range, it can be determined that the forming load will be reduced by the modification of the part shape performed in shape modification step S13. Therefore, the shape of the press-formed product 1 and the shape of the die model are determined using the press-formed product shape modified in shape modification step S13 and the shape of the shape-modified die model.

[0081] The above-mentioned predetermined range may be defined by the difference in the load evaluation value before and after the change in deformation resistance, or may be defined by the rate of change in the load evaluation value before and after the change in deformation resistance.

[0082] Furthermore, if the change in the load evaluation value before and after changing the deformation resistance is large even after modifying the shape of the die model, it is determined that the effect of the shape modification is low, and the shape modification step S13 and the specification step S11 are performed again. In this way, the shape modification step S13 and the specification step S11 are repeated until the effect of the shape modification can be confirmed, and the shape of the press-molded product 1 and the shape of the die model are determined.

[0083] <Press Molding Step> The press molding step S17 is a step in which a mold is manufactured based on the shape of the mold model determined in the determination step S15, and the manufactured mold is used to press-form the press-molded product 1. Molds include those made of cast metal and those made of steel. For cast metal molds, a full mold casting method (evaporative pattern casting method) is used, in which a casting mold model is manufactured by NC machining using a numerically controlled machine (NC machine tool) from a material that dissipates at high temperatures, such as polystyrene foam. For steel press molds, the steel must be machined (cut, grind, and polished) by NC machining. The process of manufacturing a mold based on the shape of the mold model determined in the determination step S15 includes an NC data acquisition process and an NC machining process. The NC data acquisition process is a process of acquiring NC data for NC machining based on the shape of the mold model determined in the determination step S15. Data relating to the shape of the mold model is input into a CAD / CAM program linked to an NC machine tool and converted into NC data (numerical control data) (NC program) for NC machining. The NC machine tool machines a polystyrene foam casting mold pattern or a steel mold. The NC machining process is a process in which the NC machine tool actually produces a polystyrene foam casting mold pattern or a steel mold using the NC data (NC program) acquired in the NC data acquisition process.

[0084] As described above, in this embodiment, it is possible to easily identify the portion of the press-formed product 1 that causes an increase in the forming load and easily confirm the effect of shape modification on that portion, thereby significantly shortening the time required to determine the shapes of the press-formed product 1 and the mold. Furthermore, since the forming load can be efficiently reduced, this is also suitable for press forming of high-tensile steel sheets.

[0085] [Embodiment 3] The forming load increase factor location identifying method described in Embodiment 1 can be implemented by running a preset program on a PC (personal computer). An example of such an apparatus will be described in this embodiment. A forming load increase factor location identifying apparatus 19 according to this embodiment includes a display device 21, an input device 23, a main memory device 25, an auxiliary memory device 27, and an arithmetic processing unit 29, as shown in FIG. 10. The display device 21, the input device 23, the main memory device 25, and the auxiliary memory device 27 are connected to the arithmetic processing unit 29, and the arithmetic processing unit 29 performs each function in response to commands from the arithmetic processing unit 29.

[0086] The display device 21 is used to display execution results, etc., and is composed of a liquid crystal monitor (LCD monitor), etc. The input device 23 is used for input from the operator, etc., and is composed of a keyboard, mouse, etc. The main memory device 25 is used for temporary storage of data used by the calculation processing unit 29, calculations, etc., and is composed of a RAM (Random Access Memory), etc. The auxiliary memory device 27 is used for data storage, etc., and is composed of a hard disk, etc. The auxiliary memory device 27 stores at least various data necessary for finite element method (FEM) analysis of mold models, etc.

[0087] The calculation processing unit 29 is composed of a CPU (Central Processing Unit) such as a PC (Personal Computer), and by executing a program that has been set in advance in the calculation processing unit 29, a mold model evaluation area setting unit (hereinafter abbreviated as the setting unit) 31, a molding analysis unit 33, a mold model load evaluation value calculation unit (hereinafter abbreviated as the first calculation unit) 35, a deformation resistance changed mold model load evaluation value calculation unit (hereinafter abbreviated as the second calculation unit) 37, and a molding load increase factor part identification unit (hereinafter abbreviated as the identification unit) 39 are realized.

[0088] The setting unit 31 realizes the same processing as the setting step S1 described in embodiment 1. Similarly, the forming analysis unit 33 realizes the forming analysis step S3, the first calculation unit 35 realizes the first calculation step S5, the second calculation unit 37 realizes the second calculation step S7, and the identification unit 39 realizes the identification step S9.

[0089] As described above, according to this embodiment, it is possible to identify the forming load increasing factor portion by a simple method similar to that of Embodiment 1. Therefore, by modifying the part shape based on the identified portion, it is possible to efficiently take measures to reduce the forming load.

[0090] As described above, the setting unit 31, forming analysis unit 33, first calculation unit 35, second calculation unit 37, and identification unit 39 in the forming load increase factor location identifying device 19 of this embodiment are realized by the CPU executing a predetermined program. Therefore, the forming load increase factor location identifying program according to the present invention can be specified as causing a computer to function as the setting unit, forming analysis unit, first calculation unit, second calculation unit, and identification unit.

[0091] According to the present invention, it is possible to provide a method, an apparatus, and a program for identifying a forming load increase factor portion, which can easily identify a portion of a press-formed product that causes an increase in the forming load. Also, according to the present invention, it is possible to provide a method for manufacturing a press-formed product, which can manufacture a press-formed product with a reduced forming load by using the method for identifying a forming load increase factor portion.

[0092] REFERENCE SIGNS LIST 1 Press-molded product 3 First top plate portion 5 Second top plate portion 7 Vertical wall portion 9 Flange portion 10 Upper surface portion 11 First convex portion 13 Second convex portion 15 Mold model 17 Deformation resistance-modified mold model 19 Forming load increase factor portion identifying device 21 Display device 23 Input device 25 Main memory device 27 Auxiliary memory device 29 Arithmetic processing unit 31 Mold model evaluation area setting unit (setting unit) 33 Molding analysis unit 35 Mold model load evaluation value calculation unit (first calculation unit) 37 Deformation resistance-modified mold model load evaluation value calculation unit (second calculation unit) 39 Forming load increase factor portion identifying unit (identification unit)