Method for specifying location of main cause of increase in molding load, method for manufacturing press-molded article, device for specifying location of main cause of increase in molding load, and program for specifying location of main cause of increase in molding load

Abstract

The present invention relates to a method for specifying a location of a main cause of an increase in a molding load, comprising: a step (S1) of setting an evaluation region in a mold model (15); a step (S3) for calculating the molding load distribution of the mold model (15); a step (S5) of calculating a load evaluation value for each evaluation region; a step (S7) for changing the deformation resistance of one evaluation region in the mold model and calculating a load evaluation value of the evaluation region in which the deformation resistance has been changed; and a step (S9) for specifying an evaluation region in which the load evaluation value changes before and after the deformation resistance of the mold model is changed, and specifying a site of the press-molded article (1) corresponding to the specified evaluation region as a site that is the main cause of an increase in the molding load.

Description

Technical Field

[0001] The present invention relates to a method, device and program for identifying a portion of a press formed part that is the main cause of an increase in forming load. In addition, the present invention relates to a method for manufacturing a press formed part that is the main cause of an increase in forming load and reduces the forming load associated with press forming by identifying a portion of the press formed part that is the main cause of an increase in forming load. Background Art

[0002] With the increasing demand for improvement of fuel efficiency and collision safety achieved by lightweighting of automobiles, the application of high-tensile steel sheets in automotive bodies is expanding. For high-tensile steel sheets, the reduction of formability due to its low ductility and the deterioration of dimensional accuracy caused by high material strength have become application issues. On the other hand, the increase in forming loads required for the forming of parts has also become a big problem, requiring changes in the press line and the division of parts, which have become the main reasons hindering the application of high-tensile steel sheets. Therefore, measures are sought to reduce the forming loads associated with stamping.

[0003] The forming load required for stamping can be predicted in advance using CAE analysis (computer aided engineering analysis). When studying the shape of parts and dies, CAE analysis has been used to predict the defects of press forming and poor appearance caused by cracks, wrinkles, springback, etc. generated during the forming of the parts. The forming load required for stamping can also be calculated using this CAE analysis. In addition, when a large forming load is predicted, the forming load can be reduced by changing the shape of the parts and dies, or studying the stamping process, etc.

[0004] For example, the forming load required for stamping varies depending on whether the part is trimmed (trimming) simultaneously with forming or before or after forming. Therefore, at the stamping site, the timing of trimming (cutting) the part is studied so that the forming load does not exceed the capacity of the press machine.

[0005] In addition, Patent Document 1 discloses a method of reducing the forming load by performing incremental forming by making the mold division movable.

[0006] Furthermore, Non-Patent Document 1 discloses a method for predicting forming loads by treating a die model as an elastic body. Non-Patent Document 1 also proposes a method for designing a stamping process by studying the effects of the gap between the slide part and the mold part of a stamping machine, and a method for designing a stamping process based on contact pressure distribution calculated by CAE analysis (see Non-Patent Document 1). Fig. 9 ) is a method to evaluate the die contact status of the stamping die and determine the die gap, poor contact, etc.

[0007] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2010-207907

[0008] Non-patent literature Non-patented document 1: Katsuichiro Omachi, "Study on loads and its application in stamping CAE using 3DSimSTAMP", Stamping Technology, Japan-Korea Industrial News, March 2015, Vol. 53, No. 3, P62-65 Summary of the invention

[0009] Problems to be solved by the invention

[0010] One of the main reasons for the increase in forming load is poor conformity between the blank and the die during forming (poor conformity to the die). The so-called conformity between the blank and the die during forming refers to the extent to which the blank is deformed along the surface profile of the die just before reaching the forming bottom dead center. When a part of the blank does not conform to the die during forming, that is, the part is hardly deformed into a shape along the surface profile of the die and reaches the end of forming, the forming load increases sharply when the upper and lower dies clamp the part at the forming bottom dead center to form the target shape.

[0011] In addition, other main reasons for the increase in forming load include buckling and wrinkles generated during forming. If buckling and wrinkles occur during the forming process, the apparent plate thickness of the portion becomes thicker, so the blank and the die are no longer in uniform contact. Therefore, when the upper and lower dies clamp the blank at the bottom dead point of the forming, the wrinkles are flattened, so the forming load increases.

[0012] Since the above two phenomena that increase the forming load are greatly affected by the shape of the component, when the forming load increases due to these factors, it is effective to take countermeasures by correcting the shape of the component.

[0013] In this regard, in the method of Patent Document 1, it is necessary to determine the location that is the main reason for increasing the forming load during the stamping process, that is, the location where the blank does not fit the mold during the forming process, and the location where buckling and wrinkles are predicted to occur, in the mold design stage to study the component shape and reflect it on the mold shape. However, in the past, when a large forming load was predicted, there was no method to clearly determine the location that was the main cause, so the component shape was corrected based on the designer's experience. In addition, it is necessary to create a mold model corresponding to the corrected component shape to perform CAE analysis to confirm the effect of the correction. In addition, when the result of the analysis is that the effect of reducing the forming load cannot be obtained, the above-mentioned component shape correction, mold model creation, and analysis must be repeated, resulting in greater trouble caused by trial and error.

[0014] In this regard, as described in non-patent document 1, there is also a method of determining the area with high surface pressure as the main cause of the increase in forming load (the main cause of the increase in forming load) based on the surface pressure distribution calculated by CAE analysis. However, the area with high surface pressure is not necessarily the area where the blank does not fit the mold during the forming process. For example, sometimes the surface pressure increases due to interference between molds, the rigidity of the mold and the stamping machine, etc. Therefore, even if the shape of the part where the surface pressure increases due to these reasons is corrected, the effect of reducing the forming load cannot be obtained. Therefore, in the case of determining the main cause of the increase in forming load based on the surface pressure distribution, it is necessary to distinguish the main causes of the increase in surface pressure. In the case where there are a large number of areas with high surface pressure, a lot of time is required before determining the main cause of the increase in load.

[0015] The present invention is completed to solve the above-mentioned problems, and its purpose is to provide a method, device and program for determining the main cause of the increase in forming load, which can easily determine the part of the stamped product that is the main cause of the increase in forming load. In addition, another purpose of the present invention is to provide a method for manufacturing a stamped product, which can reduce the forming load to manufacture the stamped product by using the above-mentioned method for determining the main cause of the increase in forming load.

[0016] Technical solutions to solve problems

[0017] <How the Invention Was Arrived>

[0018] In order to solve the above-mentioned problem, the inventors have conducted in-depth research on the phenomenon of increased forming load. As described above, when there is a part where the blank does not match the surface shape of the die halfway to the forming bottom dead point, the forming load at the end of the forming (just before reaching the forming bottom dead point) rises sharply. In addition, this phenomenon of the blank not matching the surface shape of the die is likely to occur in the shoulder part of a punch and the convex (or concave) shape part of the part shape.

[0019] Therefore, the inventors have further studied the phenomenon occurring near the bottom dead point of a stamped product having a convex shape. In actual stamping, near the bottom dead point of the stamping, a large surface pressure is applied to the surface of the punch and the die due to contact with the blank, and the surface of the punch and the die is slightly elastically deformed and becomes flat (squeezed).

[0020] If the die side is elastically deformed, the shape difference between the die shape and the blank shape becomes smaller, so the blank is easy to fit the die. However, for the convex part, even if the die side is slightly elastically deformed, the shape difference between the blank shape and the die shape is still large, so it is necessary to press the punch into the die, and use the force of the press to make the blank fit the die (deform along the die shape), so the load becomes higher. This is one of the main reasons for the increase in forming load when forming a stamped product with a convex part.

[0021] The reason why the forming load increases due to the forming of the convex shape is as described above, but the amount of load increase at this time is affected by the degree of elastic deformation ease of the mold. For example, when the mold is difficult to elastically deform, the mold is difficult to fit the blank, and the shape difference between the blank shape and the mold shape will not decrease. Therefore, it is necessary to increase the forming load and forcibly deform the blank, and the forming load is likely to increase. On the other hand, when the mold is easy to elastically deform, the mold is easy to fit the blank, and the shape difference between the blank shape and the mold shape decreases, so the forming load is difficult to increase.

[0022] As mentioned above, the degree of ease of elastic deformation of the mold (deformation resistance) affects the forming load. In addition, the influence of the mold deformation resistance becomes greater in the parts where the blank is difficult to fit with the mold during the forming process, that is, the parts where the shape difference between the blank shape and the mold shape during the forming process is large. On the other hand, the influence of the mold deformation resistance becomes smaller in the parts where the blank is easy to fit with the mold during the forming process. Before reaching the lower dead point of the forming, in the parts where the blank fits with the mold even if the mold does not deform elastically, even if the mold deforms elastically, the degree of fit between the blank and the mold will not change, so there is no effect on the increase in the forming load.

[0023] In addition, when the apparent sheet thickness increases due to wrinkles generated during forming and the forming load increases, it is difficult to increase the forming load even if the deformation resistance of the mold is reduced. If the deformation resistance of the mold is low, the mold elastically deforms in response to the increase in local load when flattening wrinkles, and the gap between the molds that clamp the blank is partially opened, and the phenomenon of a significant increase in the forming load before reaching the lower dead point of the forming is alleviated. Therefore, for the wrinkle-generating area such as the above, the degree of ease of elastic deformation of the mold, that is, the deformation resistance of the mold, will also affect the increase in the forming load. On the other hand, in areas where wrinkles do not occur, the apparent sheet thickness will not become thicker, so the elastic deformation of the mold will not have a significant impact on the forming load.

[0024] Based on the above situation, the inventors have obtained the following insight: only in the part of the stamped product that is the main cause of the increase in forming load, the degree of the ease of deformation of the die surface affects the increase in forming load. In addition, it is thought that by changing the deformation resistance only for a part of the die model in CAE analysis, as long as the change in the forming load before and after the deformation resistance is changed is observed, it is possible to evaluate whether the part is the main cause of the increase in forming load.

[0025] The present invention has been completed based on such a concept, and specifically comprises the following structures.

[0026] In the method for determining the location of the main cause of the increase in forming load involved in the present invention, a computer executes each process to determine the location of the stamped product that is the main cause of the increase in forming load, wherein the method for determining the location of the main cause of the increase in forming load includes: a setting step, setting at least two or more evaluation areas in a die model, the die model is obtained by forming the upper die and / or the lower die as an integral part and stamping the stamped product into a die model; a forming analysis step, using the die model, performing finite element method analysis on the stamping of the stamped product, and calculating the forming load distribution of the die model at the forming bottom dead point; a first calculation step, based on the forming load distribution calculated in the forming analysis step, calculating the load evaluation value of each evaluation area of ​​the die model; a second calculation step, using a deformation resistance change die model obtained by changing the deformation resistance of one evaluation area in the evaluation area of ​​the die model to a lower or higher value, to perform finite element method analysis on the stamping of the stamped product (finite element analysis), calculating the forming load distribution of the mold model for changing the deformation resistance at the forming lower dead point, and calculating the load evaluation value of the evaluation area in which the deformation resistance is changed based on the forming load distribution; and a determination step, determining the evaluation area in which the load evaluation value changes before and after the deformation resistance of the mold model is changed based on the load evaluation value calculated in the first calculation step and the load evaluation value calculated in the second calculation step, and determining the part of the stamped product corresponding to the determined evaluation area as the part of the stamped product that is the main cause of the increase in forming load.

[0027] The deformation resistance of the mold model 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 therefrom.

[0028] The load evaluation value of each evaluation area of ​​the mold model may be the load of each evaluation area, the maximum load or the average load.

[0029] The manufacturing method of a stamped product involved in the present invention is a method for manufacturing a stamped product, wherein the manufacturing method of the stamped product includes: a determination step, using the method for determining the main cause of the increase in forming load involved in the present invention, to determine the part of the stamped product that is the main cause of the increase in forming load; a shape correction step, correcting the shape of the stamped product at the determined part and the shape of the corresponding mold model; a determination step, repeatedly performing the determination step and the shape correction step until the change in the load evaluation value of the mold model before and after the deformation resistance of the mold model in the evaluation area of ​​the mold model is within a specified range, and determining the shape of the stamped product and the shape of the corresponding mold model; and a stamping step, making a mold based on the determined shape of the mold model, and using the made mold to stamp the stamped product.

[0030] In the device for determining the main cause of the increase in forming load involved in the present invention, the part of the stamping product that is the main cause of the increase in forming load is determined, wherein the device for determining the main cause of the increase in forming load comprises: a setting unit, which sets at least two evaluation areas in a mold model, and the mold model is obtained by forming the upper mold and / or the lower mold as an integral part and stamping the stamping product into a mold model; a forming analysis unit, which uses the mold model to perform finite element analysis on the stamping of the stamping product and calculates the forming load distribution of the mold model at the lower dead point of the forming; a first calculation unit, which calculates the load evaluation value of each evaluation area of ​​the mold model based on the forming load distribution calculated by the forming analysis unit; and a second calculation unit, which uses a through A deformation resistance changed die model is obtained by changing the deformation resistance of one of the evaluation areas of the die model to be lower or higher, a finite element method analysis is performed on the stamping forming of the stamped product, the forming load distribution of the deformation resistance changed die model at the forming lower dead point is calculated, and the load evaluation value of the evaluation area with the changed deformation resistance is calculated based on the forming load distribution; and a determination unit determines the evaluation area where the load evaluation value changes before and after the deformation resistance of the die model is changed based on the load evaluation value calculated by the first calculation unit and the load evaluation value calculated by the second calculation unit, and determines the part of the stamped product corresponding to the determined evaluation area as the part of the stamped product that is the main reason for the increase in forming load.

[0031] The forming load increase factor location identifying program according to the present invention causes a computer to function as the forming load increase factor location identifying device according to the present invention.

[0032] Effects of the Invention

[0033] According to the present invention, the location that is the main cause of the increase in forming load can be identified by a simple method such as changing the setting conditions related to the deformation resistance of the mold model in the finite element method (FEM) analysis. Since there is no need to correct the CAD data (computer-aided design data) of the part shape or the shape of the mold model as in the past, the time required for designing the part shape and the mold shape can be greatly shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flowchart showing the flow of the method for identifying a forming load increase factor location according to the first embodiment. Figure 2 This is an appearance diagram of the components used in the first embodiment. Figure 3 yes Figure 2 A cross-sectional view of the components shown, Figure 3 (a) is Figure 2 AA section view, Figure 3 (b) is Figure 2 BB cross-sectional view. Figure 4 This is a diagram for explaining the evaluation area set for the mold model in the first embodiment. Figure 5 It is a comparison expression in Figure 4 The graphs shown are load evaluation values ​​before and after the change when the deformation resistance of the die model is changed for each evaluation area. Figure 6 Yes means Figure 5 Graph showing the rate of change of load before and after the deformation resistance of the die model is changed (all evaluation areas). Figure 7 Only extracted Figure 6 Chart of evaluation areas G and M. Figure 8 This is a graph showing the change rate of the load before and after the deformation resistance of the mold model in another form of the first embodiment is changed (all evaluation areas). Fig. 9 This is a flowchart showing the flow of a method for manufacturing a press-formed product according to the second embodiment. Fig.10 This is a block diagram for explaining the structure of the forming load increase factor location identification device involved in the third embodiment. Fig.11This is a surface pressure distribution diagram used in a conventional method of identifying a location causing an increase in forming load. DETAILED DESCRIPTION

[0035] [Implementation Method 1]

[0036] The method for identifying the main cause of the forming load increase according to the first embodiment identifies the part of the stamped product that is the main cause of the forming load increase. Figure 2 .

[0037] Figure 2 The stamped product 1 is an example of a component obtained by simulating a front pillar of an automotive part, and is generally J-shaped and bent in the longitudinal direction when viewed from above. In addition, the stamped product 1 has a planar first top plate portion 3 and a second top plate portion 5 composed of a plane and an inclined surface on the upper surface of the area approximately one-third of the distance from the two ends in the longitudinal direction. In addition, a longitudinal wall portion 7 is formed on both sides of these first top plate portion 3 and the second top plate portion 5 via a shoulder R portion, and a flange portion 9 is formed on the longitudinal wall portion 7 via a shoulder R portion, and this area becomes a hat-shaped cross section.

[0038] In addition, the upper surface portion 10 connecting the first top plate portion 3 and the second top plate portion 5 is a mountain-shaped shape that gradually protrudes toward the center, and a longitudinal wall portion 7 is formed on both sides thereof, which is continuous from the first top plate portion 3 and the second top plate portion 5. In addition, a flange portion 9 is formed at the lower end of the longitudinal wall portion 7 over its entire length.

[0039] A first protrusion 11 that protrudes in a convex shape is formed on the first top plate portion 3. Also, a second protrusion 13 that protrudes in a convex shape is similarly formed on the flat surface portion of the second top plate portion 5. Figure 3 (a) means Figure 2 The AA cross-sectional shape, Figure 3 (b) means Figure 2 The BB cross-sectional shape. Figure 3 As shown, the protruding heights of the first protrusion 11 and the second protrusion 13 are substantially equal.

[0040] exist Figure 2In the case of such a stamped product 1, the main reason is that the blank and the die are difficult to match (poor die matching) during the forming process at the convex-shaped parts such as the first convex part 11 and the second convex part 13, and there is a concern about the increase in the forming load. In this case, the shape of the part can be corrected to achieve a reduction in the forming load. In the previous method, it is necessary to perform shape correction on a large number of parts where there is a concern of poor die matching and wrinkles, and try to see if the forming load can be reduced. As a result, it is necessary to repeatedly correct the part shape CAD data and create a die model for finite element method (FEM) analysis, and the research takes time.

[0041] In addition, in the conventional method, the main cause of the increase in forming load (the part where the forming load can be expected to be reduced by shape correction) is estimated based on the surface pressure distribution, but the main cause of the increase in forming load cannot be easily determined based on the surface pressure distribution. Fig.11 The surface pressure distribution is described below.

[0042] Fig.11 The surface pressure distribution of the stamping part 1 is represented by the depth of the color at the bottom dead point of the forming process. Regarding the surface pressure value, + (positive) represents the surface pressure acting in the tensile direction, and - (negative) represents the surface pressure acting in the compression direction. In addition, the part with greater pressure in the tensile direction is represented by a light color, and the part with greater pressure in the compression direction is represented by a dark color.

[0043] exist Fig.11 In the figure, the area with the largest surface pressure in the compression direction (negative symbol) (lower limit area of ​​surface pressure) is surrounded by a white solid line, and the area with the largest surface pressure in the tension direction (positive symbol) (upper limit area of ​​surface pressure) is surrounded by a white dotted line. When observing the surface pressure distribution of the first convex portion 11 and the second convex portion 13, which may cause poor mold fit during the forming process, as shown in FIG. Fig.11 As shown in the figure, the upper surface of the first convex portion 11 and the second convex portion 13 and the boundary peripheral portion between the first top plate portion 3 and the second top plate portion 5 are displayed in a darker color, so it can be seen that a large compressive stress is applied. However, the stress greater than the stress generated in the first convex portion 11 and the second convex portion 13 is dispersed in other parts such as the side wall portion 7 and the flange portion 9, and it is impossible to determine which of the first convex portion 11 and the second convex portion 13 should be corrected in order to reduce the stamping load.

[0044] In contrast, the method for identifying the main cause of the increase in forming load in the present embodiment does not require the modification of the component shape CAD data or the die model, and can identify the main cause of the increase in forming load in a simple manner. Figure 2Which part of the press-formed product 1 becomes the main cause of the increase in forming load? The following is a specific description.

[0045] like Figure 1 As shown, the forming load increase main cause location identification method of this embodiment includes die model evaluation area setting step S1 to forming load increase main cause location identification step S9. Each process of die model evaluation area setting step S1 to forming load increase main cause location identification step S9 is executed by a computer.

[0046] <Mold model evaluation area setting procedure>

[0047] The die model evaluation area setting step (hereinafter referred to as the setting step) S1 is a step of setting at least two or more evaluation areas in a die model obtained by modeling a die for stamping a stamped product 1. In this embodiment, a die in which an upper die and / or a lower die are respectively composed of an integral component is used as an object.

[0048] In the setting step S1, similarly to the conventional procedure 1 described above, a mold model (mesh model) for finite element method (FEM) analysis is created based on the component shape CAD data. Then, the mold model is divided into a plurality of regions, and at least two or more evaluation regions are set. Examples of the set evaluation regions are shown in FIG. Figure 4 .

[0049] like Figure 4 As shown, in this embodiment, Figure 2 The mold model 15 of the shape corresponding to the stamped product 1 sets 19 evaluation areas A to S. Evaluation areas A to E and O to S correspond to the two flange portions 9 of the stamped product 1. Evaluation area G corresponds to the first convex portion 11 of the stamped product 1, and evaluation area M corresponds to the second convex portion 13 of the stamped product 1. In addition, evaluation area F corresponds to the first top plate portion 3 of the stamped product 1, and evaluation area L corresponds to the plane of the second top plate portion 5 of the stamped product 1. Furthermore, evaluation areas H to K and N correspond to the upper surface portion 10 of the stamped product 1 and the inclined surface of the second top plate portion 5.

[0050] The reason for evaluating the flange portion 9 of the press-formed product 1 is that there is a concern that wrinkles may be generated in the flange portion 9. Figure 2 In the case of the stamped product 1, the flange portion 9 undergoes shrink flange forming during the forming process, and the material is locally concentrated, which may cause wrinkles. As mentioned above, the part where wrinkles are generated during the forming process may also become the main cause of the increase in forming load, so the flange portion 9 is taken as the evaluation object.

[0051] The vertical wall portion 7 of the stamped product 1 and the curved portion (shoulder fillet portion) connecting the vertical wall portion 7 to other portions (flange portion 9, first top plate portion 3, etc.) are difficult to add shape, and even if it is assumed that it is the main cause of the increase in forming load, there is almost no room for shape change, so it is excluded from the evaluation object. In this way, the evaluation area does not necessarily need to be set to the entire die model 15, as long as it is set to a portion where there is a concern about poor fit between the blank and the die, a portion where there is a concern about wrinkles, a portion where there is room for shape correction, etc.

[0052] <Press forming analysis steps>

[0053] The forming analysis step S3 is a step of performing finite element method (FEM) analysis on the press forming of the press-formed product 1 using the die model 15 in which the evaluation region is set, and calculating a forming load distribution (not shown) of the die model 15 at the forming bottom dead point.

[0054] <Calculation procedure for die model load evaluation value>

[0055] The mold model load evaluation value calculation step (hereinafter referred to as the first calculation step) S5 is a step of calculating the load evaluation value of each evaluation area A to S based on the forming load distribution calculated in the forming analysis step S3. The load evaluation value is an index value used to evaluate the load required for forming for each evaluation area. In the present embodiment, the load applied to each evaluation area, that is, the reaction force (reaction force) received by the mold in each evaluation area is calculated as a value obtained by summing up the load data of each finite element mesh (finite element mesh) in the evaluation area, and is set as the load evaluation value. The load evaluation value can be set as the maximum load of each evaluation area (the maximum value of the load data of each finite element mesh in the evaluation area), or it can be set as the average load of each evaluation area (the value obtained by dividing the total value of the load data of each finite element mesh in the evaluation area by the area of ​​the evaluation area).

[0056] The load evaluation value of each evaluation area calculated in the first calculation step S5 is Figure 5 It is represented by a black bar graph. It should be noted that Figure 5 The numerical value of the load evaluation value shown on the vertical axis is obtained by normalizing the load of the evaluation area O as a reference value.

[0057] <Calculation procedure for load evaluation value of deformation resistance change die model>

[0058] The deformation resistance changed mold model load evaluation value calculation step (hereinafter referred to as the second calculation step) S7 is a step of performing finite element method (FEM) analysis by changing the deformation resistance of the mold model 15 in only one evaluation area of ​​the evaluation areas A to S, and calculating the load evaluation value of the evaluation area in which the deformation resistance of the mold model 15 is changed. Hereinafter, a case where the deformation resistance of the mold model 15 in the evaluation area A is changed will be specifically described as an example.

[0059] First, the setting conditions of the mold model 15 used in the first calculation step S5 are changed so that the deformation resistance of the mold model 15 is reduced or increased only in the portion where the evaluation area A is set. For example, in the case of reducing the deformation resistance of the mold model 15, the setting conditions are changed to relax the displacement constraint, reduce the elastic modulus, reduce the plate thickness, reduce the density, reduce the mass, and reduce the yield strength. In addition, 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 reduce the deformation resistance in the evaluation area A of the mold model 15, the elastic modulus of the portion of the mold model 15 where the evaluation area A is set is set to 0.05% (approximately 0) of the initially set value.

[0060] Next, using the die model that reduces the deformation resistance in the evaluation area A of the die model 15 as described above (hereinafter referred to as the deformation resistance change die model 17), the stamping of the stamped product 1 is analyzed by the finite element method (FEM) to calculate the forming load distribution at the forming bottom dead point. Then, based on the calculated forming load distribution of the deformation resistance change die model 17, the load evaluation value of the evaluation area A is calculated (here, the load (reaction force received by the die in the evaluation area A)).

[0061] The same process as above is performed for the evaluation areas B to S, and the load evaluation value after the deformation resistance change in each evaluation area of ​​the mold model 15 is calculated. The load evaluation value of each evaluation area calculated in the second calculation step S7 is calculated. Figure 5 Indicated by white bars in the graph.

[0062] <Steps to identify the main cause of increased forming load>

[0063] The step of determining the main cause of the increase in forming load (hereinafter referred to as the determination step) S9 is a step of determining the part of the stamped product 1 that is the main cause of the 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.

[0064] exist Figure 5In the figure, as described above, the load evaluation values ​​calculated in the first calculation step S5 are displayed in a black bar graph, and the load evaluation values ​​calculated in the second calculation step S7 are displayed in a white bar graph, and the load evaluation values ​​before and after the deformation resistance is changed are compared for each evaluation area of ​​the mold model 15.

[0065] like Figure 5 As shown, before the deformation resistance is changed (black bar graph), the load evaluation value of the evaluation area G corresponding to the first convex portion 11 of the stamped product 1 is the largest, and the load evaluation value of the evaluation area M corresponding to the second convex portion 13 of the stamped product 1 is the second largest. Thus, it can be seen that before the deformation resistance is changed, a large load is generated in the first convex portion 11 and the second convex portion 13, which are prone to poor mold fit during the forming process.

[0066] Next, a graph showing the change in the load evaluation value before and after the deformation resistance in each evaluation area of ​​the mold model 15 is changed in percentage is shown. Figure 6 In addition, Figure 6 The graphs of the evaluation area G and the evaluation area M are extracted and compared in FIG. Figure 7 . Figure 6 , Figure 7 The vertical axis in the figure is a value obtained by calculating the change in the load evaluation value according to the formula: load evaluation value after deformation resistance of the mold model is changed / load evaluation value before deformation resistance is changed×100, and it shows that the closer to 100%, the smaller the change, and the farther away from 100%, the larger the change.

[0067] like Figure 6 , Figure 7 As shown, in most evaluation areas, the change in the load evaluation value before and after the deformation resistance is changed is within ±10%. In contrast, in the evaluation area G corresponding to the first convex portion 11 of the stamped product 1, the load evaluation value is reduced by about 75%.

[0068] As described in the context of the present invention, the ease of deformation of the mold (i.e., the deformation resistance of the mold model) at the location where the blank does not fit the mold during the forming process affects the forming load. Therefore, it can be determined that the location where the load evaluation value changes significantly before and after the deformation resistance of the mold model is changed is the location where the mold fits poorly during the forming process, that is, the location that becomes the main cause of the increase in the forming load (the location where the forming load increases mainly). Therefore, in the determination step S9 of the present embodiment, the location of the stamped product 1 corresponding to the evaluation area G, i.e., the first convex portion 11, can be determined as the location where the forming load increases mainly.

[0069] The reason why the first convex portion 11 of the two convex portions of the stamped product 1 is the main cause of the increase in the forming load has been studied and described below. Figure 3 As described in , the protruding heights of the first convex portion 11 and the second convex portion 13 are substantially the same. However, even if the protruding heights are the same, the bulging properties of the convex portion are not necessarily the same, and are greatly affected by the metal flow from the peripheral portion of the convex portion. Specifically, if the material easily flows from the peripheral portion to the convex portion, the blank is easily deformed during the forming of the convex portion and is easily matched with the mold.

[0070] In the case of the first convex portion 11 and the second convex portion 13 of the stamped product 1, as Figure 3 As shown, the distance (a) from the second protrusion 13 to the outer periphery of the second top plate portion 5 1 、a 2 ) is greater than the distance (b) from the first protrusion 11 to the outer periphery of the first top plate 3 1 、b 2 ) is long. Therefore, the material of the second top plate portion 5 near the second convex portion 13 easily flows to the second convex portion 13 side, and the blank is easy to fit with the mold during forming. On the other hand, since the first convex portion 11 is close to the outer periphery of the first top plate portion 3, the material of the first top plate portion 3 near the first convex portion 11 is also easy to flow to the longitudinal wall portion 7 side, and the material flow to the first convex portion 11 side becomes less, and the mold fit of the blank becomes worse. Based on the above content, it can also be said that the first convex portion 11 is a part that is more likely to produce poor mold fit during the forming process than the second convex portion 13.

[0071] As described above, in this embodiment, the main cause of the increase in forming load can be determined by a simple method such as changing the setting conditions related to the deformation resistance of the mold model. It is possible to determine the location of poor mold fit and the location of concern for wrinkles without having to correct the part shape CAD data or the shape of the mold model used in the finite element method (FEM) analysis as in the past, so it is effective to significantly shorten the time required for studying the part shape.

[0072] In the above-mentioned embodiment, the deformation resistance of the mold model in an evaluation area is changed, and based on the change in the load evaluation value before and after the deformation resistance of the mold model in the area is changed, it is determined whether the part of the stamped product corresponding to the area is the main cause of the increase in the forming load. In contrast, for example, in the mold model, the deformation resistance of other evaluation areas other than one evaluation area can be changed, and the main cause of the increase in the forming load can be determined based on the change in the load evaluation value before and after the deformation resistance of the entire mold model is changed. The above example is shown in Figure 8 .

[0073] Figure 8 Equivalent to the aforementioned Figure 6The graph shows the change in the overall load evaluation value of the mold model 15 before and after the deformation resistance is changed. In this case, since the deformation resistance is not changed in only one evaluation area of ​​the mold model 15, the evaluation area of ​​the mold model 15 where the deformation resistance is not changed is displayed on the horizontal axis. In addition, the vertical axis shows the change in the sum of the overall load evaluation values ​​of the mold model 15 (load sum), which is a value calculated by the formula: total load of the mold model after the deformation resistance is changed / total load of the mold model before the deformation resistance is changed × 100. Figure 6 Likewise, it is shown that the closer to 100%, the smaller the change in the total load, and the farther away from 100%, the larger the change in the total load.

[0074] like Figure 8 As shown, when the deformation resistance is not changed in only the evaluation area G in the mold model 15, the change in the total load before and after the deformation resistance is changed is smaller than that in the examples of other evaluation areas. Figure 8 The results show that when the deformation resistance of the evaluation area G in the die model 15 is changed, the load is easy to reduce, and when the deformation resistance of the evaluation area G is not changed, the load is difficult to reduce. Therefore, in this case, the first convex portion 11, which is a portion of the stamped product 1 corresponding to the evaluation area G in the die model 15, can be determined as the portion mainly causing the increase in the forming load.

[0075] [Implementation Method 2]

[0076] The manufacturing method of the stamped product 1 used as the object in the first embodiment is described. The manufacturing method of the stamped product 1 of the present embodiment uses the method for determining the location of the main cause of the increase in the forming load in the first embodiment to determine the location of the stamped product 1 that is the main cause of the increase in the forming load, and by correcting the shape of the part at the location, the load required for stamping is reduced.

[0077] like Fig. 9 As shown, the manufacturing method of the stamped product 1 of this embodiment includes a forming load increase main cause location determination step S11, a shape correction step S13, a stamped product / die model shape determination step S15 and a stamping step S17. Each step will be described in detail below.

[0078] <Steps to identify the main cause of increased forming load>

[0079] The step of determining the main cause of the increase in forming load (hereinafter referred to as the determination step) S11 is a step of determining the part of the press-formed product 1 that is the main cause of the increase in forming load (the main cause of the increase in forming load part) using the method of determining the main cause of the increase in forming load described in Embodiment 1. The setting step S1 to the determination step S9 described in Embodiment 1 are equivalent to the determination step S11 of this Embodiment 2.

[0080] exist Figure 2 In the case of the press-formed product 1, as described in the first embodiment, it can be determined that the first convex portion 11 is the main cause of the increase in the forming load.

[0081] <Shape Correction Procedure>

[0082] The shape correction step S13 is a step of correcting the shape of the stamped product 1 at the position determined in the determination step S11 and the shape of the evaluation area of ​​the corresponding die model. As described above, since the first convex portion 11 of the stamped product 1 is determined as the main cause of the increase in the forming load, the component shape of the portion including the first convex portion 11 is first corrected.

[0083] In this example, it is presumed that the main reason for the increase in forming load is that the blank does not fit the punch shoulder and the die shoulder (shoulder part of a die) of the portion forming the first protrusion 11 during the forming process. Therefore, the part shape is corrected to improve the die fit during the forming process of this portion.

[0084] As a correction of the component shape, for example, the protruding height of the first protrusion 11 can be reduced. By reducing the protruding height of the convex portion, the height difference with the punch bottom (first top plate portion 3) is reduced, and the shape difference with the flat portion is reduced, which can be expected to reduce the effect of poor fit between the mold and the blank during the forming process.

[0085] (Shape Modification Example 1) The initial protrusion height of the first protrusion was 3 mm, so it was changed to 2 mm or 1.5 mm.

[0086] In addition, for example, the punch shoulder radius of the first protrusion 11 may be increased (see Figure 3 White arrow in the enlarged view), die shoulder radius (refer to Figure 3 By increasing the shoulder radius of the convex portion, it is expected that the shape change will be smoother and the mismatch between the die and the blank during the forming process will be reduced.

[0087] (Shape Modification Example 2) The initial shoulder radius of the punch shoulder fillet portion and the die shoulder fillet portion of the first convex portion 11 was 7 mm, so it was changed to 10 mm or 15 mm.

[0088] After the shape of the first convex portion 11 of the press-formed product 1 is corrected, the shape of the corresponding die model is also corrected in the same manner.

[0089] <Steps for determining the shape of stamped products / die models>

[0090] The stamped product / die model shape determination step (hereinafter referred to as determination step) S15 is a step of confirming the effect of the shape correction in the shape correction step S13 and determining the shape of the stamped product 1 and the shape of the die model corresponding thereto.

[0091] First, in order to confirm the effect of the correction of the component shape, the same analysis as in the determination step S11 is performed using the mold model that has been shape-corrected in the shape correction step S13 (hereinafter referred to as the shape-corrected mold model). Figure 4 The same evaluation area (setting step S1).

[0092] Next, the mold model after shape correction with evaluation area set is used to Figure 2 The press forming of the press-formed product 1 is analyzed by the finite element method (FEM), and the load evaluation value of the evaluation area G before the deformation resistance is changed is calculated (forming analysis step S3, first calculation step S5).

[0093] Next, the deformation resistance of the portion of the shape-corrected die model corresponding to the evaluation region G is changed, and the finite element method (FEM) analysis is performed again using the die model to calculate the load evaluation value of the evaluation region G after the deformation resistance is changed (second calculation step S7 ).

[0094] Then, the change of the load evaluation value before and after the deformation resistance of the evaluation area G in the die model after the shape correction is confirmed. When the change of the load evaluation value before and after the deformation resistance is changed becomes small and is within the prescribed range, it can be judged that the forming load is reduced by the correction of the part shape performed in the shape correction step S13. Therefore, the shape of the stamped product 1 and the shape of the die model are determined based on the shape of the stamped product corrected in the shape correction step S13 and the shape of the die model after the shape correction.

[0095] The above-mentioned predetermined range may be defined by the difference between the load evaluation values ​​before and after the deformation resistance is changed, or may be defined by the change ratio of the load evaluation values ​​before and after the deformation resistance is changed.

[0096] In addition, even if the shape of the die model is corrected, the change in the load evaluation value before and after the deformation resistance is changed is large, and it is determined that the effect of the shape correction is low, and the shape correction step S13 and the determination step S11 are performed again. In this way, the shape correction step S13 and the determination step S11 are repeated until the effect of the shape correction can be confirmed, and the shape of the stamped product 1 and the shape of the die model are determined.

[0097] <Stamping steps>

[0098] The stamping step S17 is a step of making a mold based on the shape of the mold model determined in the determination step S15, and using the made mold to perform stamping of the stamped product 1. The mold has a mold made of a casting and a mold made of steel. In the case of a mold made of a casting, the following full mold casting method (evaporative pattern casting method) is used: a casting mold model is made from a raw material that disappears at a high temperature such as expanded polystyrene by NC machining (NC machining) using an NC machine tool (numerically-controlled machine). In addition, in the case of a stamping mold made of steel, it is necessary to machine the steel (cutting, grinding, and polishing) by NC machining. The process of making 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 for acquiring NC data for NC machining based on the shape of the mold model determined in the determination step S15. The data related to the shape of the mold model is input into the CAD / CAM program that cooperates with the NC machine tool and converted into NC data (numerical control data) (NC program) for NC processing. The NC machine tool performs mechanical processing on the mold model for casting made of foamed polystyrene or the mold made of steel. The NC processing process is a process of actually making the mold model for casting made of foamed polystyrene or the mold made of steel using the NC machine tool using the NC data (NC program) obtained in the NC data acquisition process.

[0099] As described above, in this embodiment, the part of the press-formed product 1 that is the main cause of the increase in forming load can be easily determined, and the effect of the shape correction for this part can be easily confirmed, so the time until the shape of the press-formed product 1 and the die is determined can be greatly shortened. In addition, since the forming load can be effectively reduced, it is also suitable for the press forming of high-tensile steel plates.

[0100] [Implementation method 3]

[0101] The forming load increase main cause location identification method described in the first embodiment can be implemented by causing a PC (personal computer) to execute a preset program. In this embodiment, an example of such a device is described. The forming load increase main cause location identification device 19 involved in this embodiment has Fig.10 2 shows an example of a display device 21, an input device 23, a main storage device 25, an auxiliary storage device 27, and an arithmetic processing unit 29. The arithmetic processing unit 29 is connected to the display device 21, the input device 23, the main storage device 25, and the auxiliary storage device 27, and performs various functions according to instructions from the arithmetic processing unit 29.

[0102] The display device 21 is used to display the execution results, etc., and is composed of a liquid crystal monitor (LCD monitor) and the like. The input device 23 is used for input from the operator, etc., and is composed of a keyboard, a mouse, etc. The main storage device 25 is used for temporary storage and calculation of data used by the calculation processing unit 29, and is composed of a RAM (Random Access Memory) and the like. The auxiliary storage device 27 is used for data storage, etc., and is composed of a hard disk and the like. The auxiliary storage device 27 stores at least various data required for finite element method (FEM) analysis of mold models, etc.

[0103] The calculation processing unit 29 is composed of a CPU (Central Processing Unit) or the like of a PC (Personal Computer), and by executing a preset program by the calculation processing unit 29, a mold model evaluation area setting unit (hereinafter referred to as a setting unit) 31, a forming analysis unit 33, a mold model load evaluation value calculation unit (hereinafter referred to as a first calculation unit) 35, a deformation resistance change mold model load evaluation value calculation unit (hereinafter referred to as a second calculation unit) 37 and a forming load increase main cause location determination unit (hereinafter referred to as a determination unit) 39 are realized.

[0104] The setting unit 31 implements the same processing as the setting step S1 described in Embodiment 1. Similarly, the forming analysis unit 33 implements the forming analysis step S3, the first calculation unit 35 implements the first calculation step S5, the second calculation unit 37 implements the second calculation step S7, and the determination unit 39 implements the determination step S9.

[0105] As described above, according to this embodiment, the location that is the main cause of the forming load increase can be identified by a simple method similar to Embodiment 1. Therefore, if the component shape is corrected based on the identified location, measures for reducing the forming load can be effectively taken.

[0106] As described above, the setting unit 31, the forming analysis unit 33, the first calculation unit 35, the second calculation unit 37, and the determination unit 39 in the forming load increase main cause location identification device 19 of the present embodiment are implemented by the CPU executing a predetermined program. Therefore, the forming load increase main cause location identification program involved in the present invention can be determined so that a computer functions as the setting unit, the forming analysis unit, the first calculation unit, the second calculation unit, and the determination unit.

[0107] Industrial Applicability

[0108] According to the present invention, a method, device and program for determining the main cause of the increase in forming load can be provided, which can easily determine the part of the stamped product that is the main cause of the increase in forming load. In addition, according to the present invention, a method for manufacturing a stamped product can be provided, and by using the above-mentioned method for determining the main cause of the increase in forming load, the stamped product can be manufactured with a reduced forming load.

[0109] Description of symbols 1 Stamping products 3. First top plate 5 Second top plate 7 Vertical wall 9 Flange 10 upper surface 11 First convex part 13 Second convex part 15 Mold Model 17 Deformation resistance change mold model 19 Device for determining the main cause of increased forming load 21 Display device 23 Input Devices 25 Main storage device 27 Auxiliary storage device 29 Calculation Processing Unit 31 Mold model evaluation area setting unit (setting unit) 33 Forming Analysis Department 35 Die model load evaluation value calculation unit (first calculation unit) 37 Deformation resistance change die model load evaluation value calculation unit (second calculation unit) 39 Determination of the main cause of the increase in forming load (determination part).

Claims

1. A method for determining a location of a main cause of an increase in forming load, wherein a computer executes each process to determine a location of a stamped product that is a main cause of an increase in forming load, wherein: The method for determining the location of the main cause of the increase in forming load includes: A setting step of setting at least two evaluation areas in a die model, wherein the die model is obtained by modeling a die in which an upper die and / or a lower die are formed of an integral component and the stamped product is stamped; A forming analysis step, using the die model to perform a finite element method analysis on the stamping forming of the stamped product, and calculating the forming load distribution of the die model at the forming bottom dead point; A first calculation step of calculating a load evaluation value for each evaluation area of ​​the mold model based on the forming load distribution calculated in the forming analysis step; a second calculation step, using a deformation resistance changed die model obtained by changing the deformation resistance of one evaluation area in the evaluation areas of the die model to be lower or higher, performing finite element method analysis on the stamping of the stamped product, calculating the forming load distribution of the deformation resistance changed die model at the forming bottom dead point, and calculating the load evaluation value of the evaluation area in which the deformation resistance is changed based on the forming load distribution; and A determination step, based on the load evaluation value calculated in the first calculation step and the load evaluation value calculated in the second calculation step, determines the evaluation area where the load evaluation value changes before and after the deformation resistance of the mold model is changed, and determines the part of the stamped product corresponding to the determined evaluation area as the part of the stamped product that is the main reason for the increase in forming load.

2. The method for determining the location of the main cause of the forming load increase according to claim 1, wherein: The deformation resistance of the mold model changed in the second calculation step is any one of displacement constraint, elastic modulus, plate thickness, density, mass, and yield strength, or a combination of two or more selected therefrom.

3. The method for determining the location of the main cause of the forming load increase according to claim 1, wherein: The load evaluation value of each evaluation area of ​​the mold model is the load of each evaluation area, the maximum load, or the average load.

4. A method for manufacturing a stamped product, wherein: The method for manufacturing the stamped product comprises: A determination step of determining a portion of the press-formed product that is a major cause of increased forming load using the method for determining a portion that is a major cause of increased forming load according to any one of claims 1 to 3; A shape correction step of correcting the shape of the stamped product at the determined location and the shape of the corresponding die model; a determining step, repeatedly performing the determining step and the shape correcting step until a change in the load evaluation value of the mold model before and after the deformation resistance of the mold model in the evaluation area of ​​the mold model is within a prescribed range, thereby determining the shape of the stamped product and the shape of the corresponding mold model; and The press forming step is to prepare a die based on the determined shape of the die model, and to press form the press-formed product using the prepared die.

5. A device for determining a location of a main cause of an increase in forming load, which determines a location of a stamped product that is a main cause of an increase in forming load, wherein: The device for determining the location of the main cause of the increase in forming load comprises: A setting unit that sets at least two evaluation areas in a die model, wherein the die model is obtained by modeling a die that is used to stamp the stamped product, wherein the upper die and / or the lower die are formed of an integral component; A forming analysis unit, using the die model, performs a finite element method analysis on the stamping of the stamped product, and calculates a forming load distribution of the die model at a forming bottom dead point; a first calculation unit that calculates a load evaluation value for each evaluation area of ​​the mold model based on the forming load distribution calculated by the forming analysis unit; a second calculation unit, using a deformation resistance-changed die model obtained by changing the deformation resistance of one evaluation area of ​​the die model to be lower or higher, performing finite element method analysis on the stamping of the stamped product, calculating a forming load distribution of the deformation resistance-changed die model at a forming bottom dead point, and calculating a load evaluation value of the evaluation area in which the deformation resistance is changed based on the forming load distribution; and The determination unit determines the evaluation area where the load evaluation value changes before and after the deformation resistance of the mold model is changed, based on the load evaluation value calculated by the first calculation unit and the load evaluation value calculated by the second calculation unit, and determines the part of the stamped product corresponding to the determined evaluation area as the part of the stamped product that is the main reason for the increase in forming load.

6. A forming load increase main cause location identifying program, causing a computer to function as the forming load increase main cause location identifying device according to claim 5.

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