Method and device for determining main cause parts of springback deviation

Abstract

The present invention provides a method and device for determining the main cause part of the springback amount deviation between CAE analysis and the actual formed product. The present invention includes: a formed product driving stress distribution acquisition step of acquiring the driving stress distribution of the stamping formed product, an analysis driving stress distribution acquisition step of acquiring the driving stress distribution of the springback analysis, a formed product springback amount acquisition step of acquiring the springback amount of the formed product based on the driving stress distribution of the formed product, a stress replacement springback amount acquisition step of replacing the value of the analysis driving stress in a part of the region with the driving stress value of the formed product corresponding to the above part of the region and acquiring the springback amount based on the stress replacement distribution after the replacement, and a springback amount deviation main cause part determination step of calculating the difference between the springback amount of the formed product and the stress replacement springback amount and determining the part that becomes the main cause of the springback amount deviation based on the calculated difference.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for determining a portion that is the main cause of the deviation between the springback amount of a stamped product in an actual sheet and the springback amount in a CAE analysis, which is the main cause of the deviation in the springback amount of the stamped product in the actual sheet Background Art

[0002] For a formed product obtained by stamping a metal sheet, high shape accuracy is required. In order to meet the required shape accuracy, it is important to reduce the springback generated by elastic deformation of the formed product taken out of the mold after stamping

[0003] The internal stress at the bottom dead center of the formed product affects the springback behavior. Therefore, it is effective for taking springback countermeasures to grasp which part of the formed product has what kind of influence on the springback

[0004] As such a method, in the stamping analysis method disclosed in Patent Document 1, analysis is performed by using an analysis using the finite element method

[0005] According to the stamping analysis method of Patent Document 1, "calculate how a certain defined quantity related to springback changes before and after changing the residual stress distribution in a certain area of the formed object that is the formed object of the stamped product. Therefore, based on the result, the influence of the residual stress in a certain area of the formed object before demolding on the springback can be predicted" (see the effect of the invention)

[0006] By using the method disclosed in Patent Document 1, it is possible to study springback countermeasures before manufacturing an actual mold, and it is possible to greatly reduce the mold adjustment work for ensuring shape accuracy

[0007] As another main cause analysis method of springback using CAE analysis, Patent Document 2 discloses a method of calculating the springback (SB) effective stress based on the residual stress before demolding and the residual stress after demolding, and using the SB effective stress for main cause analysis to perform a more appropriate evaluation

[0008] The above method performs springback analysis using the stress state calculated based on the data setting of the CAE analysis. On the other hand, in Patent Document 3, a method is disclosed in which the measured three-dimensional shape created by measuring the surface shape of an actually stamped formed product is substituted into the CAE analysis, and a mechanical analysis is performed in a state where the measured three-dimensional shape is clamped to the bottom dead center state by the mold model, and the stress distribution state is obtained, and the stress distribution state is used for main cause analysis to perform a more accurate evaluation

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-229724

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-206158

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2013-71120

[0012] However, even when a die is manufactured with springback countermeasures based on CAE analysis for stamping, the shape sometimes becomes different from the shape expected by the countermeasures taken with the actual stamped product.

[0013] This is because, depending on the shape of the die used for stamping and various forming conditions, there may be cases where the forming load assumed in the CAE analysis is not applied to the metal sheet, or cases where the stress state before demolding cannot be accurately reproduced by the CAE analysis. In such cases, it is necessary to adjust the die and forming conditions used for stamping, or modify the settings or die shape in the CAE analysis.

[0014] For such adjustment operations, it is required to determine at which part of the formed product the main cause of the deviation between the springback analysis result obtained by CAE analysis and the springback amount of the actual formed product occurs. The methods disclosed in Patent Documents 1 to 3 determine the part that is the main cause of the generation of springback itself, rather than the part that is the main cause of the deviation between the CAE analysis and the actual springback amount.

[0015] In addition, in order to ensure the effectiveness of the springback countermeasures using CAE analysis, it is required to improve the reproducibility of the springback analysis so as not to deviate from the springback of the actual formed product. For this purpose, it is also necessary to determine the part that is the main cause of the deviation of the formed product. Summary of the Invention

[0016] The present invention has been completed to solve the above problems, and an object thereof is to provide a method and device for determining the main cause part of the springback amount deviation that causes a deviation between the springback amount of the above-mentioned stamped product of the actual sheet and the springback amount of the CAE analysis of the stamped product.

[0017] <Process of Completing the Present Invention>

[0018] Regarding Figure 2The stamping of the stamped product 10 shown as an example in the text sometimes results in a difference (deviation) between the springback amount calculated by the springback analysis (also known as CAE analysis) performed before stamping and the springback amount of the actually stamped product (also known as the actual sheet metal). Moreover, the part that is the main cause of the deviation in the springback amount between such CAE analysis and the actual sheet metal is sometimes different from the part that is the main cause of the springback itself. Therefore, there is a problem that even if certain countermeasures are taken on the part that is the main cause of the springback to reduce the springback, the deviation in the springback amount between the CAE analysis and the actual sheet metal cannot be reduced.

[0019] Therefore, the inventor conducted intensive research to solve such problems. As a result, it was conceived that the main cause of the deviation in the springback amount might be due to the difference between the stress contributing to the springback in the CAE analysis (hereinafter, also referred to as the driving stress distribution) and the stress contributing to the springback in the actual sheet metal (driving stress distribution).

[0020] Based on this idea, the inventor further conducted research and found that the deviation amount of the springback amount between the CAE analysis and the actual sheet metal is affected not only by the difference in the magnitude of the above-mentioned driving stress but also by the different parts where the driving stress is generated.

[0021] Moreover, the inventor obtained the following insight: Regarding the determination of the part that is the main cause of the deviation in the springback amount, it is effective to divide the driving stress distribution into multiple regions and study the degree of influence of the above-mentioned deviation amount for each divided region.

[0022] The present invention was completed based on the above insights. Specifically, it is composed of the following structure.

[0023] (1) The method for determining the main cause part of springback amount deviation of the present invention determines the part in the shape of the formed product that is the main cause of the deviation when there is a deviation in the springback amount generated by the stamping formed product obtained by stamping an actual sheet metal and the springback amount when performing springback analysis on an analysis model having the same shape as the above stamping formed product. The method for determining the main cause part of springback amount deviation includes: a formed product driving stress distribution obtaining step, in which, based on the three-dimensional shape measurement data obtained by measuring the surface shape of the above stamping formed product after demolding, a stamping formed product model is made, and mechanical analysis is performed in a state where the stamping formed product model is clamped to the bottom dead center by a die model, and the stress distribution at the forming bottom dead center is obtained as the formed product driving stress distribution of the above stamping formed product contributing to springback; an analysis driving stress distribution obtaining step, in which, the bottom dead center stress distribution and the residual stress distribution after demolding in the above springback analysis are obtained, and the difference between the bottom dead center stress distribution and the residual stress distribution after demolding is obtained as the analysis driving stress distribution in the springback analysis; a formed product springback amount obtaining step, in which, the formed product driving stress distribution is set for the formed product shape at the bottom dead center in the above springback analysis, and springback analysis is performed based on the set formed product driving stress distribution to obtain the springback amount; a stress replacement springback amount obtaining step, in which, the analysis driving stress distribution is set for the formed product shape at the bottom dead center, and the value of the analysis driving stress in a part of the area in the set analysis driving stress distribution is replaced with the value of the formed product driving stress in the area corresponding to the above part of the area in the formed product driving stress distribution, and springback analysis is performed based on the replaced stress replacement distribution to obtain the springback amount; and a springback amount deviation main cause part determining step, in which, the difference between the springback amount obtained in the stress replacement springback amount obtaining step and the springback amount obtained in the above formed product springback amount obtaining step is obtained, and based on the obtained difference, the part in the formed product shape that is the main cause of the above deviation is determined.

[0024] (2) Further, in the method described in the above (1), a stress replacement area selection step is included, in which, based on the difference between the analysis driving stress distribution obtained in the analysis driving stress distribution obtaining step and the formed product driving stress distribution obtained in the formed product driving stress distribution obtaining step, a stress difference distribution is obtained, and an area with a relatively large difference is selected as the above part of the area where stress replacement should be performed according to the stress difference distribution.

[0025] (3) When there is a deviation in the springback amount between the springback amount generated in the stamping product obtained by stamping a real plate and the springback amount obtained by performing a springback analysis on an analysis model having the same shape as the above stamping product, the device for determining the main cause part of the springback amount deviation of the present invention determines the part in the shape of the formed product that is the main cause of this deviation. The device for determining the main cause part of the springback amount deviation includes: a formed product driving stress distribution obtaining unit that makes a stamping product model based on the three-dimensional shape measurement data obtained by measuring the surface shape of the above stamping product after demolding, performs a mechanical analysis in a state where the stamping product model is clamped to the bottom dead center by a die model, and obtains the stress distribution at the forming bottom dead center as the formed product driving stress distribution of the above stamping product that contributes to springback; an analysis driving stress distribution obtaining unit that obtains the bottom dead center stress distribution and the residual stress distribution after demolding in the above springback analysis, and obtains the difference between the bottom dead center stress distribution and the residual stress distribution after demolding as the analysis driving stress distribution in the springback analysis; a formed product springback amount obtaining unit that sets the formed product driving stress distribution for the formed product shape at the bottom dead center in the above springback analysis, and performs a springback analysis based on the set formed product driving stress distribution to obtain the springback amount; a stress replacement springback amount obtaining unit that sets the above analysis driving stress distribution for the formed product shape at the bottom dead center, replaces the value of the analysis driving stress in a part of the area in the set analysis driving stress distribution with the formed product driving stress value of the area corresponding to the above part of the area in the formed product driving stress distribution, and performs a springback analysis based on the replaced stress replacement distribution to obtain the springback amount; and a springback amount deviation main cause part determining unit that obtains the difference between the springback amount obtained in the stress replacement springback amount obtaining unit and the springback amount obtained in the above formed product springback amount obtaining unit, and based on the obtained difference, determines the part in the shape of the formed product that is the main cause of the deviation in the springback amount between the above stamping product and the springback analysis.

[0026] (4) Further, in the method described in the above (3), there is provided a stress replacement area selection unit that obtains a stress difference distribution based on the difference between the analysis driving stress distribution obtained in the above analysis driving stress distribution obtaining unit and the formed product driving stress distribution obtained in the above formed product driving stress distribution obtaining unit, and selects an area with a relatively large difference as the above part of the area where stress replacement should be performed according to the stress difference distribution.

[0027] According to the present invention, it is possible to determine the part that is the main cause of the deviation in the springback amount between the springback analysis performed by CAE analysis and the springback amount generated in the actual stamping product. Therefore, it is possible to reduce the workload of adjusting the actual stamping die and forming conditions, and thus improve the effectiveness of the springback countermeasure using CAE analysis. Description of the Drawings

[0028] Figure 1 It is a flowchart showing the processing flow of the method for determining the main cause part of the springback amount deviation in the first embodiment.

[0029] Figure 2 It is a diagram showing the stamped product in the first embodiment.

[0030] Figure 3 It is a diagram showing the driving stress distribution of the CAE analysis in the first embodiment.

[0031] Figure 4 It is a diagram showing the driving stress distribution (a) of the actual sheet and the displacement (b) calculated by the springback analysis based on the driving stress distribution in the first embodiment.

[0032] Figure 5 It is a diagram showing the fixed points of the springback analysis and the analysis results of the displacement obtained by the springback analysis in the first embodiment.

[0033] Figure 6 It is a diagram showing the calculation method of the end swing amount and the spring-up amount as the springback amount in the first embodiment.

[0034] Figure 7 It is a diagram showing the driving stress distribution (a) of the CAE analysis, the driving stress distribution (b) of the actual sheet, and the stress difference distribution (c) between the CAE analysis and the actual sheet in the first embodiment.

[0035] Figure 8 It is a diagram showing the region division of the stress difference distribution and the region with a relatively large stress difference in the first embodiment.

[0036] Figure 9 It is a diagram showing the region division (a) of the driving stress distribution of the CAE analysis and the region division (b) of the driving stress distribution of the actual sheet in the first embodiment.

[0037] Figure 10 It is a diagram showing the regions (a)(b) for replacing the driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in the region (c) (region B-1) in the first embodiment.

[0038] Figure 11 It is a diagram showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on the stress replacement distribution (region B-1) in the first embodiment.

[0039] Figure 12 It is a diagram showing the regions (a)(b) for replacing the driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in the region (c) (region B-2) in the first embodiment.

[0040] Figure 13 It is a diagram (region B-2) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on this stress replacement distribution in Embodiment 1.

[0041] Figure 14 It is a diagram (region C-3) showing the regions (a)(b) of the replacement driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in this region (c) in Embodiment 1.

[0042] Figure 15 It is a diagram (region C-3) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on this stress replacement distribution in Embodiment 1.

[0043] Figure 16 It is a diagram (region D-2) showing the regions (a)(b) of the replacement driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in this region (c) in Embodiment 1.

[0044] Figure 17 It is a diagram (region D-2) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on this stress replacement distribution in Embodiment 1.

[0045] Figure 18 It is a diagram (region E-2) showing the regions (a)(b) of the replacement driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in this region (c) in Embodiment 1.

[0046] Figure 19 It is a diagram (region E-2) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on this stress replacement distribution in Embodiment 1.

[0047] Figure 20 It is a diagram (region D-2 / E-2) showing the regions (a)(b) of the replacement driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in this region (c) in Embodiment 1.

[0048] Figure 21 It is a diagram (region D-2 / E-2) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on this stress replacement distribution in Embodiment 1.

[0049] Figure 22 It is a diagram (region F-2) showing the regions (a)(b) of the replacement driving stress and the stress distribution (stress replacement distribution) after replacing the driving stress in this region (c) in Embodiment 1.

[0050] Figure 23 It is a diagram (region F-2) showing the stress replacement distribution (a) and the displacement (b) calculated by the springback analysis based on the stress replacement distribution in the first embodiment.

[0051] Figure 24 It is a graph showing the relationship between the region where the driving stress is replaced and the deviation amount of the end swing generated by the springback when the driving stress is replaced in the first embodiment.

[0052] Figure 25 It is a graph showing the relationship between the region where the driving stress is replaced and the deviation amount of the bounce generated by the springback when the driving stress is replaced in the first embodiment.

[0053] Figure 26 It is a block diagram for explaining the structure of the springback amount deviation main cause part determination device according to the second embodiment. Detailed Embodiment

[0054] [Embodiment 1]

[0055] In the springback amount deviation main cause part determination method according to the first embodiment of the present invention, when there is a deviation between the springback amount generated in a stamping product obtained by stamping an actual sheet metal and the springback amount obtained by performing a springback analysis on an analysis model having the same shape as the stamping product, the part in the shape of the formed product that is the main cause of the deviation is determined. As Figure 1 shown, the springback amount deviation main cause part determination method according to the first embodiment of the present invention includes: a formed product driving stress distribution acquisition step S1, an analysis driving stress distribution acquisition step S3, a formed product springback amount acquisition step S5, a stress replacement region selection step S7, a stress replacement springback amount acquisition step S9, and a springback amount deviation main cause part determination step S11.

[0056] In addition, in the following description, "bottom dead center" represents the state where the punch and the die are in contact with each other with the blank interposed therebetween (the state where forming is completed in CAE analysis). "Forming bottom dead center" represents the state where forming is completed by an actual stamping die. "Analysis bottom dead center" represents the state where forming is completed in CAE analysis.

[0057] Taking the case of stamping a stamping product 10 having a hat-shaped cross-sectional shape as Figure 2 shown as an example, the above steps will be described.

[0058] In the CAE analysis of the present embodiment, as Figure 2 shown, a stamping analysis is performed using a die model 3 composed of a die 5 and a punch 7 with a blank model 9 as the workpiece material (steel sheet) interposed therebetween. In addition, in the stamping analysis, asFigure 2 As shown in the figure, the blank model 9 is fixed by a positioning pin during the forming process. The key dimensions of the blank model 9 are approximately 1 mm. As an analysis condition, the friction coefficient between the blank model 9 and the die model 3 is 0.15, and the position of the lower dead point of forming is the position where the gap between the upper and lower die models is 1.45 mm. In addition, the material to be processed is a 980 MPa grade GA steel plate with a thickness of 1.4 mm.

[0059] The actual panel in this embodiment is formed by stamping under the same conditions as the forming conditions set in the CAE analysis.

[0060] <Forming product driving stress distribution obtaining step>

[0061] The forming product driving stress distribution obtaining step S1 is a step of obtaining the driving stress distribution of the actual panel.

[0062] Specifically, the actual panel is formed by stamping under the same conditions as the forming conditions set in the above CAE analysis. Based on the three-dimensional shape measurement data obtained by measuring the surface shape of the actual panel after demolding, a stamping product model is made. Then, a mechanical analysis is performed in the state where the stamping product model is clamped to the lower dead point of forming by the die model 3 shown in Figure 2 the figure, and the stress distribution shown in (a) of Figure 4 is obtained.

[0063] As the above mechanical analysis, an elastic finite element analysis is performed. The stress distribution obtained by this elastic finite element analysis corresponds to the stress of the actual panel that contributes to springback, that is, the driving stress of the actual panel.

[0064] Here, as a specific method for measuring the three-dimensional shape of the actual panel, making the stamping product model, and performing the elastic finite element analysis, for example, the method described in Patent Document 3 can be used.

[0065] <Analysis driving stress distribution obtaining step>

[0066] The analysis driving stress distribution obtaining step S3 is a step of separately obtaining the lower dead point stress distribution and the residual stress distribution after demolding in the CAE analysis (springback analysis), and obtaining the driving stress in the CAE analysis based on the difference between the two.

[0067] The stress at the lower dead point of the stamping product affects the springback behavior, but there is also stress remaining in the stamping product after demolding from the die. That is, it can be considered that not all of the stress before demolding contributes to springback, and the stress remaining in the stamping product that has undergone springback after demolding does not contribute to springback.

[0068] In order to correctly compare and analyze with the driving stress (the stress contributing to springback) obtained in the molded product driving stress distribution obtaining step S1, it is necessary to calculate the driving stress in the CAE analysis.

[0069] Therefore, in the analysis driving stress distribution obtaining step S3, the Figure 2 shown mold model 3 and blank model 9 are used to perform a CAE analysis to obtain the stress of the stamping molded product before demolding (bottom dead center) and the residual stress of the stamping molded product after demolding (after springback). Subtract the residual stress after demolding from the stress at the bottom dead center, thereby calculating the Figure 3 shown driving stress distribution in the CAE analysis (hereinafter, also simply referred to as stress distribution).

[0070] In addition, the analysis driving stress distribution obtaining step S3 performs a CAE analysis by a computer. The CAE analysis can use, for example, finite element method analysis software. In the present embodiment, the analysis is performed by executing LS-DYNA Ver.971, which is a commercially available finite element method analysis software, on a computer, and the dynamic explicit method is applied in the solver.

[0071] In addition, the present invention is not limited to using the Figure 2 shown mold model 3 or the stamping molded product 10 having a hat-shaped cross-sectional shape as the molding object, and the mold model, stamping molded product, etc. can be appropriately set according to the molding object.

[0072] In addition, when the residual stress after demolding is a relatively small value that can be almost ignored, it is also possible to regard the entire stress distribution at the bottom dead center of the analysis as contributing to springback, and use the stress distribution at the bottom dead center as the analysis driving stress distribution.

[0073] <Molded product springback amount obtaining step>

[0074] The molded product springback amount obtaining step S5 is a step of setting the molded product driving stress distribution obtained in the molded product driving stress distribution obtaining step S1 for the shape of the molded product at the bottom dead center in the CAE analysis, and performing a springback analysis based on the set molded product driving stress distribution to calculate the springback amount generated here.

[0075] In the present embodiment, a springback analysis is performed on the stamping molded product 10 ([[]] Figure 4 of (a)) with the shape of the bottom dead center where the molded product driving stress distribution is set, and the displacement after springback ( Figure 4 of (b)) is calculated through this springback analysis. In the springback analysis, as Figure 5 shown, three parts provided on one end side of the stamping molded product are fixed at the fixed points, and the displacement caused by springback is calculated.

[0076] Next, as Figure 6As shown, based on the displacement calculated through springback analysis, the end swing amount ( Figure 6 (a) of Figure 6 ) and the spring-up amount ( Figure 6 (b) of Figure 6 ) are calculated. In the present embodiment, as shown in

[0077]

[0078] Figure 7 Figure 3 Figure 7 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 6 Figure 6 the end swing amount is the movement amount in the direction of the arrow in the figure (positive in the direction of the arrow) caused by springback at any one of the two evaluation points provided on the other end side of the press-formed product 10, and as shown in

[0077] <Stress replacement area selection step>

[0078] Figure 7 Figure 3 Figure 7 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 As shown, in the stress replacement area selection step S7, the stress difference distribution ( Figure 3 Figure 7 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 is calculated as the difference between the stress distribution ( Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 3 Figure 7 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 obtained in the analysis driving stress distribution acquisition step S3) and the stress distribution ( Figure 4 Figure 7 Figure 7

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8

[0079]

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8

[0080] Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 7 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 7 Figure 7 Figure 7

[0081] Figure 8 Figure 7 Figure 7

[0081] Figure 8 Figure 7As shown, the stamping product 10 is divided into a plurality of regions (6-divided from A to F in the length direction and 3-divided from 1 to 3 in the width direction), and the stress differences of each region are compared, and the regions judged to have relatively large stress differences (regions including parts close to black or white) are selected.

[0082] In the stress replacement region selection step S7 of the present embodiment, six regions (B-1, B-2, C-3, D-2, E-2, F-2) indicated by dotted circles in the Figure 8 figure are selected.

[0083] In addition, the method of selecting the region with a relatively large stress difference as the stress replacement region is not limited to the above method. For example, in the case of being performed by a computer or the like, the magnitude of the stress difference is numerically valued for each divided region, and regions such as 1 / 2 and 1 / 3 of the total number of divided regions are selected in descending order of the numerical value. In addition, in the present embodiment, the regions judged to have relatively large stress differences are selected, but the selection criterion is not limited to this. For example, all regions with a stress difference greater than a preset value may be selected.

[0084] <Stress replacement springback amount acquisition step>

[0085] The stress replacement springback amount acquisition step S9 is to set the shape of the product at the bottom dead center to the analysis driving stress distribution obtained in the analysis driving stress distribution acquisition step S3, and replace the value of the analysis driving stress in the region selected in the stress replacement region selection step S7 in the set analysis driving stress distribution with the value of the product driving stress in the region corresponding to the selected region in the product driving stress distribution obtained in the product driving stress distribution acquisition step S1. The springback amount is obtained by performing springback analysis based on the replaced stress distribution (stress replacement distribution).

[0086] Figure 9 It shows the state where the driving stress distribution in the CAE analysis and the driving stress distribution in the actual sheet are regionally divided by the same method as the Figure 8 stress difference distribution. Using the driving stress distribution in the CAE analysis and the driving stress distribution in the actual sheet, stress replacement is first performed on region B-1, which is one of the regions selected in the stress replacement region selection step S7. Figure 10 (c) of Figure 10 shows the result of replacing the stress at region B-1 in the driving stress distribution of the CAE analysis ( Figure 10 (a) of

[0087] In addition, Figure 11This represents the result of displacement calculated through springback analysis based on the stress distribution after stress replacement in region B-1. Based on the calculated displacement, the end swing amount ( Figure 6 as shown in (a)) and the bounce amount ( Figure 6 as shown in (b)) of the springback amount are calculated respectively.

[0088] For other regions selected in the stress replacement region selection step S7, stress replacement is also carried out in the same way. The result of springback analysis based on this stress replacement distribution is as shown in Figures 12 to 23 . Based on the calculated displacement, the end swing amount and the bounce amount are also calculated for other regions respectively.

[0089] In addition, for region D-2 and region E-2, the parts with relatively large stress differences are confirmed in a way that straddles the two regions (refer to Figure 8 ). Therefore, in addition to stress replacement in each region, the springback amount in the case of stress replacement for both regions is also calculated (refer to Figure 20 , Figure 21 ). In this way, the region where stress replacement is carried out is not necessarily one region, and the stress of multiple regions can also be replaced.

[0090] <Main cause part determination step of springback amount deviation>

[0091] The main cause part determination step S11 of springback amount deviation is a step of finding the difference between the springback amount obtained in the stress replacement springback amount obtaining step S9 and the springback amount obtained in the molded product springback amount obtaining step S5, and determining the part that becomes the main cause of the deviation between the CAE analysis and the actual sheet metal springback amount based on the obtained difference.

[0092] Figure 24 This represents the result of finding the difference between the end swing amount (end swing amount in CAE analysis) obtained in the stress replacement springback amount obtaining step S9 and the actual sheet metal end swing amount obtained in the molded product springback amount obtaining step S5, that is, the end swing deviation amount.

[0093] "None" on the horizontal axis of the chart is the case without stress replacement. In this case, the deviation amount is -11.6 mm, which is the difference between the CAE analysis and the actual sheet metal. In addition, "ALL" is the case where all regions of the driving stress distribution in the CAE analysis are replaced with the driving stress distribution of the actual sheet metal. In this case, the deviation amount is approximately zero.

[0094] "B-1" to "F-2" on the horizontal axis are the end swing deviation amounts in the case of stress replacement of the driving stress in the CAE analysis for the 6 regions selected in the stress replacement region selection step S7.

[0095] It can be seen that, compared with the deviation amount between the CAE analysis shown as "none" and the actual plate, when stress replacement is performed on "D-2" or "E-2" in the selected 6 regions, the end swing deviation amount is reduced.

[0096] In addition, as shown by "D-2 / E-2", it can be seen that by replacing the driving stress distribution of the actual plate for both regions D-2 and E-2, the end swing deviation amount is further reduced.

[0097] Therefore, based on Figure 24 the results, it can be determined that regions D-2 and E-2 are the parts where the end swing amount between the CAE analysis and the actual plate shows a deviation.

[0098] Similarly, Figure 25 it shows the results of obtaining the deviation amount of springback between the CAE analysis and the actual plate. Regarding the deviation amount of springback, it can be seen that, compared with the deviation amount between the CAE analysis shown as "none" and the actual plate, when stress replacement is performed on "F-2" in the selected 6 regions, the deviation amount of springback is reduced.

[0099] Therefore, based on Figure 25 the results, it can be determined that region F-2 is the part where the springback amount between the CAE analysis and the actual plate shows a deviation.

[0100] On the other hand, even when stress replacement is performed, the regions with the same deviation amount as that of "none" indicate the parts that have a relatively small influence on the deviation between the CAE analysis and the actual plate.

[0101] That is, if such regions are assumed to be the main cause of deviation, it is indicated that even if certain countermeasures are implemented for stamping forming, the springback deviation amount between the CAE analysis and the actual plate will hardly change. Therefore, in the present invention, when the springback deviation amount after replacing the driving stress of a part of the regions is at the same level as the springback deviation amount between the CAE analysis without stress replacement and the actual plate, this part of the region is not the main cause of the deviation of the springback amount between the CAE analysis and the actual plate.

[0102] As described above, according to the method of the present embodiment, it is shown that the part that is the main cause of the springback amount deviation between the CAE analysis and the actual plate can be determined with high precision.

[0103] By determining the part that is the main cause of the springback amount deviation in this way, it is possible to effectively perform adjustment operations such as molds and forming conditions in order to make the shape of the actual plate after demolding close to the CAE analysis.

[0104] In addition, by modifying the settings and die shape in the CAE analysis with the determined part as the center, the reproducibility of the springback analysis can be improved, and the effectiveness of the springback countermeasure using the CAE analysis can be ensured.

[0105] In this embodiment, a method of dividing a stamping product into 18 regions has been described. However, for stamping products with complex shapes, the number of divided regions needs to be increased for further refinement, so it takes time to obtain results for all the refined regions. Using the stress replacement region selection step S7 of this embodiment to narrow down the regions assumed to have a greater impact is effective in shortening the time until the main cause part of the deviation is determined.

[0106] That being said, the present invention is not limited to this. It is also possible not to execute the stress replacement region selection step S7, but to execute the stress replacement springback amount acquisition step S9 by taking each of the divided regions as a part of the region where stress replacement should be performed.

[0107] [Embodiment 2]

[0108] The method for determining the main cause part of the springback amount deviation described in Embodiment 1 can be implemented by causing a PC (personal computer) to execute a pre-set program. An example of such a device is described in this embodiment.

[0109] The springback amount deviation main cause part determination device 11 of this embodiment has Figure 26 a display device 13, an input device 15, a main storage device 17, an auxiliary storage device 19, and an arithmetic processing unit 21 as shown in an example. The arithmetic processing unit 21 is connected to the display device 13, the input device 15, the main storage device 17, and the auxiliary storage device 19, and executes each function according to the instructions of the arithmetic processing unit 21.

[0110] The display device 13 is used for displaying results and the like, and is composed of a liquid crystal monitor or the like. The input device 15 is used for input by an operator and is composed of a keyboard, a mouse, etc. The main storage device 17 is used for temporarily storing and operating data used in the arithmetic processing unit 21 and is composed of a RAM or the like. The auxiliary storage device 19 is used for storing data and is composed of a hard disk or the like.

[0111] In the auxiliary storage device 19, at least various data required for CAE analysis such as three-dimensional shape measurement data 23 and die models 25 are stored.

[0112] The arithmetic processing unit 21 is composed of a CPU such as a PC. The molded product driving stress distribution acquisition unit 27, the analysis driving stress distribution acquisition unit 29, the molded product springback amount acquisition unit 31, the stress replacement area selection unit 33, the stress replacement springback amount acquisition unit 35, and the springback amount deviation main cause part determination unit 37 are realized by executing a preset program by the arithmetic processing unit 21.

[0113] The molded product driving stress distribution acquisition unit 27 implements the same processing as the molded product driving stress distribution acquisition step S1 described in the first embodiment. Similarly, the analysis driving stress distribution acquisition unit 29 implements the analysis driving stress distribution acquisition step S3, the molded product springback amount acquisition unit 31 implements the molded product springback amount acquisition step S5, the stress replacement area selection unit 33 implements the stress replacement area selection step S7, the stress replacement springback amount acquisition unit 35 implements the stress replacement springback amount acquisition step S9, and the springback amount deviation main cause part determination unit 37 implements the springback amount deviation main cause part determination step S11.

[0114] According to the present embodiment described above, it is possible to determine with the same high accuracy as in the first embodiment the part that is the main cause of the springback amount deviation between the CAE analysis and the actual sheet metal.

[0115] Therefore, it is possible to effectively perform various adjustment operations for making the post-demolding shape of the CAE analysis close to that of the actual sheet metal based on the determined part, and the effectiveness of the springback countermeasure can be ensured.

[0116] An example in which the springback amount deviation main cause part determination device 11 in the present embodiment has the stress replacement area selection unit 33 has been described, but similar to the case described in the first embodiment, the present invention is not limited thereto, and the stress replacement area selection unit 33 may not be provided, and the stress replacement springback amount acquisition unit 35 performs stress replacement on all the divided regions as part of the regions where stress replacement should be performed.

[0117] The present invention is not limited to the final molded product (product shape), and can also be applied to intermediate molded products in the case of stamping molded products where the molding process is carried out in stages. In addition, in the above embodiment, an example in which a steel sheet is used as the work material has been described, but it can also be applied to aluminum sheets.

[0118] Description of reference numerals

[0119] 3... Die model; 5... Die; 7... Punch; 9... Blank model; 10... Stamped product; 11... Device for determining main cause parts of springback amount deviation; 13... Display device; 15... Input device; 17... Main storage device; 19... Auxiliary storage device; 21... Arithmetic processing unit; 23... Three-dimensional shape measurement data; 25... Die model; 27... Unit for obtaining driving stress distribution of formed product; 29... Unit for obtaining analyzed driving stress distribution; 31... Unit for obtaining springback amount of formed product; 33... Unit for selecting stress replacement area; 35... Unit for obtaining springback amount of stress replacement; 37... Unit for determining main cause parts of springback amount deviation.

Claims

1. A method for determining the main cause part of springback deviation, which determines the part in the shape of the formed product that is the main cause of the deviation when there is a deviation in the springback amount generated by the stamping product obtained by stamping an actual sheet metal and the springback amount when performing springback analysis on an analysis model with the same shape as the stamping product. Among them, the method for determining the main cause part of springback deviation includes: A step of obtaining the forming product driving stress distribution. In this step, a stamping product model is made based on the three-dimensional shape measurement data obtained by measuring the surface shape of the stamping product after demolding, and mechanical analysis is performed in a state where the stamping product model is clamped to the bottom dead center by a die model, and the stress distribution at the forming bottom dead center is obtained as the forming product driving stress distribution of the stamping product that contributes to springback. A step of obtaining the analysis driving stress distribution. In this step, the bottom dead center stress distribution and the residual stress distribution after demolding in the springback analysis are obtained, and the difference between the bottom dead center stress distribution and the residual stress distribution after demolding is obtained as the analysis driving stress distribution in the springback analysis. A step of obtaining the springback amount of the forming product. In this step, the forming product driving stress distribution is set for the shape of the forming product at the bottom dead center in the springback analysis, and springback analysis is performed based on the set forming product driving stress distribution to obtain the springback amount. A step of obtaining the stress replacement springback amount. In this step, the analysis driving stress distribution is set for the shape of the forming product at the bottom dead center, and the value of the analysis driving stress in a part of the area in the set analysis driving stress distribution is replaced with the value of the forming product driving stress in the area corresponding to the part of the area in the forming product driving stress distribution, and springback analysis is performed based on the replaced stress replacement distribution to obtain the springback amount; and A step of determining the main cause part of springback deviation. In this step, the difference between the springback amount obtained in the stress replacement springback amount obtaining step and the springback amount obtained in the forming product springback amount obtaining step is calculated, and based on the calculated difference, the part in the shape of the forming product that is the main cause of the deviation is determined.

2. The method for determining the main cause part of springback deviation according to claim 1, Among them, it includes a stress replacement area selection step. In this step, a stress difference distribution is obtained based on the difference between the analysis driving stress distribution obtained in the analysis driving stress distribution obtaining step and the forming product driving stress distribution obtained in the forming product driving stress distribution obtaining step, and an area with a relatively large difference is selected as the part of the area where stress replacement should be performed according to the stress difference distribution.

3. A device for determining the main cause part of springback deviation, which determines the part in the shape of the formed product that is the main cause of the deviation when there is a deviation in the springback amount generated by the stamping product obtained by stamping an actual sheet metal and the springback amount when performing springback analysis on an analysis model with the same shape as the stamping product. Among them, the device for determining the main cause part of springback deviation includes: A molded product driving stress distribution obtaining unit fabricates a stamping molded product model based on three-dimensional shape measurement data obtained by measuring the surface shape of the stamping molded product after demolding, performs a mechanical analysis in a state where the stamping molded product model is clamped to the bottom dead center using a die model, and obtains the stress distribution at the forming bottom dead center as the molded product driving stress distribution of the stamping molded product that contributes to springback; An analysis driving stress distribution obtaining unit obtains the bottom dead center stress distribution and the residual stress distribution after demolding in the springback analysis, and obtains the difference between the bottom dead center stress distribution and the residual stress distribution after demolding as the analysis driving stress distribution in the springback analysis; A molded product springback amount obtaining unit sets the molded product driving stress distribution for the shape of the molded product at the bottom dead center in the springback analysis, and performs a springback analysis based on the set molded product driving stress distribution to obtain the springback amount; A stress replacement springback amount obtaining unit sets the analysis driving stress distribution for the shape of the molded product at the bottom dead center, replaces the value of the analysis driving stress in a part of the regions in the set analysis driving stress distribution with the value of the molded product driving stress in the region corresponding to the part of the regions in the molded product driving stress distribution, and performs a springback analysis based on the replaced stress replacement distribution to obtain the springback amount; and A springback amount deviation main cause part determination unit calculates the difference between the springback amount obtained in the stress replacement springback amount obtaining unit and the springback amount obtained in the molded product springback amount obtaining unit, and based on the calculated difference, determines the part in the molded product shape that is the main cause of the deviation in the springback amount between the stamping molded product and the springback analysis.

4. The springback amount deviation main cause part determination device according to claim 3, wherein, it includes a stress replacement region selection unit, and the stress replacement region selection unit obtains a stress difference distribution based on the difference between the analysis driving stress distribution obtained in the analysis driving stress distribution obtaining unit and the molded product driving stress distribution obtained in the molded product driving stress distribution obtaining unit, and selects a region with a relatively large difference as the part of the regions where stress replacement should be performed according to the stress difference distribution.

5. A storage medium stores a springback amount deviation main cause part determination program. The springback amount deviation main cause part determination program determines the part in the molded product shape that is the main cause of the deviation when there is a deviation between the springback amount generated by a stamping molded product obtained by stamping an actual sheet metal and the springback amount when a springback analysis is performed on an analysis model having the same shape as the stamping molded product, wherein, the springback amount deviation main cause part determination program is executed by the arithmetic processing unit of a computer, and the springback amount deviation main cause part determination program causes the computer to implement the following units: A molded product driving stress distribution obtaining unit manufactures a stamping molded product model based on three-dimensional shape measurement data obtained by measuring the surface shape of the stamping molded product after demolding, performs a mechanical analysis in a state where the stamping molded product model is clamped to the bottom dead center using a die model, and obtains the stress distribution at the forming bottom dead center as the molded product driving stress distribution that contributes to springback of the stamping molded product; An analysis driving stress distribution obtaining unit obtains the bottom dead center stress distribution and the residual stress distribution after demolding in the springback analysis, and obtains the difference between the bottom dead center stress distribution and the residual stress distribution after demolding as the analysis driving stress distribution in the springback analysis; A molded product springback amount obtaining unit sets the molded product driving stress distribution for the shape of the molded product at the bottom dead center in the springback analysis, and performs a springback analysis based on the set molded product driving stress distribution to obtain a springback amount; A stress replacement springback amount obtaining unit sets the analysis driving stress distribution for the shape of the molded product at the bottom dead center, replaces the value of the analysis driving stress in a part of the regions in the set analysis driving stress distribution with the value of the molded product driving stress in the region corresponding to the part of the regions in the molded product driving stress distribution, and performs a springback analysis based on the stress replacement distribution after replacement to obtain a springback amount; and A springback amount deviation main cause part determination unit obtains the difference between the springback amount obtained in the stress replacement springback amount obtaining unit and the springback amount obtained in the molded product springback amount obtaining unit, and based on the obtained difference, determines the part in the shape of the molded product that is the main cause of the deviation in the springback amount between the stamping molded product and the springback analysis.

6. The storage medium according to claim 5, wherein, the springback amount deviation main cause part determination program causes a computer to implement a stress replacement region selection unit, and the stress replacement region selection unit obtains a stress difference distribution based on the difference between the analysis driving stress distribution obtained in the analysis driving stress distribution obtaining unit and the molded product driving stress distribution obtained in the molded product driving stress distribution obtaining unit, and selects a region with a relatively large difference as the part of the regions where stress replacement should be performed according to the stress difference distribution.

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