阅读说明：本技术 回弹量偏差主因部位确定方法及装置 (Method and device for determining main cause part of springback value deviation ) 是由 小川刚史 卜部正树 饭塚荣治 于 2020-04-16 设计创作，主要内容包括：本发明提供一种确定出CAE分析与实际的成形品的回弹量偏差主因部位的回弹量偏差主因部位确定方法及装置。本发明具备：取得冲压成形品的驱动应力分布的成形品驱动应力分布取得步骤、取得回弹分析的驱动应力分布的分析驱动应力分布取得步骤、对下止点的成形品形状设定分析驱动应力分布和成形品驱动应力分布的应力差分布的应力差分布设定步骤、取得基于该应力差分布的回弹量的应力差回弹量取得步骤、对应力差分布的一部分区域的值进行变更并取得回弹量的变更应力差回弹量取得步骤、以及、对取得的回弹量进行比较并确定出成为回弹量产生偏差的主因的部位的回弹量偏差主因部位确定步骤。(The invention provides a method and a device for determining a springback value deviation main factor part of a formed product, which determine CAE analysis and actual forming. The present invention is provided with: a molded product drive stress distribution acquisition step of acquiring a drive stress distribution of a press molded product, an analysis drive stress distribution acquisition step of acquiring a drive stress distribution of springback analysis, a stress difference distribution setting step of setting a stress difference distribution of the analysis drive stress distribution and the molded product drive stress distribution for a molded product shape at a bottom dead center, a stress difference springback amount acquisition step of acquiring a springback amount based on the stress difference distribution, a changed stress difference springback amount acquisition step of acquiring a springback amount by changing a value of a partial region of the stress difference distribution, and a springback amount deviation main cause portion determination step of comparing the acquired springback amounts and determining a portion which becomes a main cause of a deviation of the springback amount.)

1. A method for determining a location of a main cause of a deviation in springback value, which, when a deviation occurs between a springback value of a press-formed product obtained by press-forming an actual plate and a springback value obtained when a springback analysis is performed on an analysis model having the same shape as that of the press-formed product, determines a location of the shape of the press-formed product, which is a main cause of the deviation,

the method for determining the main cause of the springback value deviation comprises the following steps:

a molded product drive stress distribution acquisition step of creating a press-molded product model from three-dimensional shape measurement data obtained by measuring a surface shape of the press-molded product after the press-molding is released, performing a mechanical analysis in a state where the press-molded product model is sandwiched between bottom dead centers by a mold model, and acquiring a stress distribution at the bottom dead center as a drive stress distribution contributing to springback of the press-molded product;

an analysis driving stress distribution acquisition step of acquiring a bottom dead center stress distribution in the springback analysis and a residual stress distribution after mold release, and acquiring a difference between the bottom dead center stress distribution and the residual stress distribution after mold release as a driving stress distribution for the springback analysis;

a stress difference distribution setting step of obtaining a stress difference distribution from a difference between the analyzed driving stress distribution obtained in the analyzed driving stress distribution obtaining step and the molded product driving stress distribution obtained in the molded product driving stress distribution obtaining step, and setting the stress difference distribution for a shape of the molded product at a bottom dead center of the springback analysis;

a stress difference rebound amount obtaining step of performing a rebound analysis based on the set stress difference distribution to obtain a rebound amount;

a modified stress difference springback amount obtaining step of modifying a value of a stress difference in a partial region in the stress difference distribution set in the stress difference distribution setting step, and obtaining a springback amount by performing springback analysis based on the modified stress difference distribution; and

a springback amount deviation main cause portion specifying step of comparing the springback amounts obtained in the changing stress difference springback amount obtaining step and the stress difference springback amount obtaining step to specify a portion of the formed product shape that becomes a main cause of the deviation in the springback amount between the press formed product and the springback analysis.

2. The method for determining a location of a main cause of a spring-back amount deviation according to claim 1,

the changing of the value of the stress difference in the changing stress difference rebound amount obtaining step is to perform any one of the following processes on the component in at least one direction with respect to the stress difference distribution: the average value in the thickness direction of the workpiece is replaced by the elimination, the constant times, the addition of a constant and the multiplication of the constant, and the replacement by the median in the thickness direction of the workpiece.

3. A springback value deviation main cause part determining device for determining a part of a shape of a formed product, which is a main cause of deviation, when the springback value of a press-formed product obtained by press-forming an actual plate member is deviated from the springback value of an analysis model having the same shape as the press-formed product in springback analysis,

the springback value deviation main factor position determination device comprises:

a molded product drive stress distribution acquisition means for creating a press-molded product model from three-dimensional shape measurement data obtained by measuring a surface shape of the press-molded product after the press-molding is released, performing a mechanical analysis in a state where the press-molded product model is sandwiched between bottom dead centers by a mold model, and acquiring a stress distribution at the bottom dead center as a drive stress distribution contributing to springback of the press-molded product;

an analysis drive stress distribution acquisition means for acquiring a bottom dead center stress distribution of the springback analysis and a residual stress distribution after the mold release, and acquiring a difference between the bottom dead center stress distribution and the residual stress distribution after the mold release as a drive stress distribution of the springback analysis;

stress difference distribution setting means for obtaining a stress difference distribution based on a difference between the analysis drive stress distribution obtained by the analysis drive stress distribution obtaining means and the molded article drive stress distribution obtained by the molded article drive stress distribution obtaining means, and setting the stress difference distribution for the molded article shape at the bottom dead center of the springback analysis;

a stress difference springback amount obtaining unit that performs springback analysis based on the set stress difference distribution to obtain a springback amount;

a modified stress difference springback amount obtaining means for modifying the value of the stress difference in a partial region in the stress difference distribution set by the stress difference distribution setting means, and performing springback analysis based on the modified stress difference distribution to obtain a springback amount; and

and a springback amount deviation main factor position specifying means for comparing the springback amounts obtained by the change stress difference springback amount obtaining means and the stress difference springback amount obtaining means, and specifying a position in the shape of the formed product, which is a main factor of the deviation in the springback amount between the press formed product and the springback analysis.

4. The device for determining a location of a main cause of a spring back amount deviation according to claim 3,

the change of the value of the stress difference of the change stress difference rebound quantity obtaining means is to perform any one of the following processes on the component in at least one direction of the stress difference distribution: the average value in the thickness direction of the workpiece is replaced by the elimination, the constant times, the addition of a constant and the multiplication of the constant, and the replacement by the median in the thickness direction of the workpiece.

Technical Field

The present invention relates to a method and an apparatus for determining a springback value deviation factor portion of a press-formed product, which determines a portion of the press-formed product that is a factor causing a deviation between a springback value of the press-formed product in an actual plate and a springback value analyzed by CAE.

Background

A press-formed product of a metal plate is required to have high shape accuracy. In order to satisfy the required shape accuracy, it is important to reduce springback caused by elastic deformation of a molded article taken out from a die after press molding.

Since the internal stress at the bottom dead center of the molded article affects the behavior of springback, it is effective to take measures against springback by grasping what influence the stress at which portion of the molded article affects springback.

As such a method, in the press-forming analysis method disclosed in patent document 1, analysis is performed by analysis using a finite element method.

According to the press forming analysis method of patent document 1, "how a certain defined amount related to springback changes before and after changing the distribution of residual stress in a certain region of a forming object that is a press formed product is calculated, and therefore, the influence of residual stress in a certain region of the forming object before mold release on springback can be predicted based on the result thereof" (see the effect of the invention).

By using the method disclosed in patent document 1, it is possible to investigate the springback countermeasure before the actual die is manufactured, and it is possible to significantly reduce the die adjustment work for ensuring the shape accuracy.

As another principal factor analysis method of springback using CAE analysis, patent document 2 discloses a method of: the Springback (SB) effective stress is calculated from the residual stress before and after the mold release, and the SB effective stress is used to perform a cause analysis, thereby performing a more appropriate evaluation.

The method described above performs a springback analysis using a stress state calculated from data settings of the CAE analysis. In contrast, patent document 3 discloses a method of: a measured three-dimensional shape obtained by measuring the surface shape of a molded article actually press-molded is substituted into CAE analysis, and a mechanical analysis is performed in a state where the measured three-dimensional shape is clamped to a molding bottom dead center by a mold model to obtain a stress distribution state, and a principal factor analysis is performed using the stress distribution state, thereby performing more accurate evaluation.

Patent document 1: japanese patent laid-open No. 2007 and 229724

Patent document 2: japanese patent laid-open publication No. 2012-206158

Patent document 3: japanese patent laid-open publication No. 2013-71120

However, even if a die is manufactured and press-formed with a springback countermeasure based on CAE analysis, the shape may be different from a shape expected by a countermeasure taken for an actual press-formed product.

This is because, depending on the shape of the die used for press forming and various forming conditions, there is a possibility that a forming load assumed in CAE analysis is not applied to the metal plate, or that the stress state before mold release cannot be accurately reproduced by CAE analysis. In such a case, it is necessary to adjust a die and a forming condition used for press forming, or to modify a setting in CAE analysis and a die shape.

In such an adjustment operation, it is required to specify a position of a molded article where a deviation between a result of springback analysis by CAE analysis and an actual springback value of the molded article occurs. The methods disclosed in patent documents 1 to 3 specify a site that is a cause of occurrence of springback itself, and do not specify a site that is a cause of deviation between CAE analysis and an actual springback amount.

In order to ensure the usefulness of the springback countermeasure using CAE analysis, it is required to improve the reproducibility of springback analysis so as not to deviate from the springback of an actual molded product. Therefore, it is also necessary to identify a portion of the molded product which is a main cause of the variation.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object thereof is to provide a method and a device for determining a position of a main cause of a deviation in a springback value of a portion of a press-formed product, which is a main cause of a deviation between a springback value of the press-formed product of an actual plate member and a springback value of a CAE analysis.

(1) A method for determining a location of a main cause of a deviation in springback value deviation according to the present invention is a method for determining a location of a main cause of a deviation in a shape of a press-formed product when a deviation occurs between a springback value generated in the press-formed product obtained by press-forming an actual plate and a springback value obtained when a springback analysis is performed on an analysis model having the same shape as the press-formed product, the method including: a molded product drive stress distribution acquisition step of creating a press-molded product model from three-dimensional shape measurement data obtained by measuring a surface shape of the press-molded product after the press-molding is released, performing a mechanical analysis in a state where the press-molded product model is sandwiched between bottom dead centers by a mold model, and acquiring a stress distribution at the bottom dead center as a drive stress distribution contributing to springback of the press-molded product; an analysis driving stress distribution acquisition step of acquiring a bottom dead center stress distribution in the springback analysis and a residual stress distribution after mold release, and acquiring a difference between the bottom dead center stress distribution and the residual stress distribution after mold release as a driving stress distribution for the springback analysis; a stress difference distribution setting step of obtaining a stress difference distribution from a difference between the analyzed driving stress distribution obtained in the analyzed driving stress distribution obtaining step and the molded product driving stress distribution obtained in the molded product driving stress distribution obtaining step, and setting the stress difference distribution for a shape of the molded product at a bottom dead center of the springback analysis; a stress difference rebound amount obtaining step of performing a rebound analysis based on the set stress difference distribution to obtain a rebound amount; a modified stress difference springback amount obtaining step of modifying a value of a stress difference in a partial region in the stress difference distribution set in the stress difference distribution setting step, and obtaining a springback amount by performing springback analysis based on the modified stress difference distribution; and a springback amount deviation main cause portion specifying step of comparing the springback amounts obtained in the change stress difference springback amount obtaining step and the stress difference springback amount obtaining step, and specifying a portion of the formed product shape that becomes a main cause of the deviation in the springback amount between the press formed product and the springback analysis.

(2) Further, according to the method described in the above (1), the changing of the value of the stress difference in the changing stress difference rebound amount obtaining step is performed by performing any one of the following processes on a component in at least one direction with respect to the stress difference distribution: the average value in the thickness direction of the workpiece is replaced by the elimination, the constant times, the addition of a constant and the multiplication of the constant, and the replacement by the median in the thickness direction of the workpiece.

(3) A springback value deviation main cause portion specifying device according to the present invention specifies a portion of a formed product shape that is a main cause of a deviation between a springback value of a press-formed product obtained by press-forming an actual plate and a springback value obtained by performing springback analysis on an analysis model having the same shape as the press-formed product, the springback value deviation main cause portion specifying device including: a molded product drive stress distribution acquisition means for creating a press-molded product model from three-dimensional shape measurement data obtained by measuring a surface shape of the press-molded product after the press-molding is released, performing a mechanical analysis in a state where the press-molded product model is sandwiched to a bottom dead center by a mold model, and acquiring a stress distribution at the bottom dead center as a drive stress distribution contributing to springback of the press-molded product; an analysis drive stress distribution acquisition means for acquiring a bottom dead center stress distribution of the springback analysis and a residual stress distribution after the mold release, and acquiring a difference between the bottom dead center stress distribution and the residual stress distribution after the mold release as a drive stress distribution of the springback analysis; stress difference distribution setting means for obtaining a stress difference distribution based on a difference between the analysis drive stress distribution obtained by the analysis drive stress distribution obtaining means and the molded article drive stress distribution obtained by the molded article drive stress distribution obtaining means, and setting the stress difference distribution for the molded article shape at the bottom dead center of the springback analysis; a stress difference springback amount obtaining unit that performs springback analysis based on the set stress difference distribution to obtain a springback amount; a modified stress difference springback amount obtaining means for modifying the value of the stress difference in a partial region in the stress difference distribution set by the stress difference distribution setting means, and performing springback analysis based on the modified stress difference distribution to obtain a springback amount; and a springback amount deviation main cause portion specifying means for comparing the springback amounts obtained by the change stress difference springback amount obtaining means and the stress difference springback amount obtaining means, and specifying a portion of the formed product shape which becomes a main cause of the springback amount deviation between the press formed product and the springback analysis.

(4) Further, according to the apparatus described in (3) above, the changing of the value of the stress difference by the stress difference rebound amount obtaining means is performed by subjecting the component in at least one direction to any one of the following processes with respect to the stress difference distribution: the average value in the thickness direction of the workpiece is replaced by the elimination, the constant times, the addition of a constant and the multiplication of the constant, and the replacement by the median in the thickness direction of the workpiece.

According to the present invention, since a portion that becomes a main cause of a deviation between the springback amount of the springback analysis by the CAE analysis and the springback amount of the actual formed product can be specified, the load of the work for adjusting the actual press-forming die and the forming conditions can be reduced, and the usefulness of the springback countermeasure using the CAE analysis can be improved.

Drawings

Fig. 1 is a flowchart showing a process flow of the springback value deviation main factor portion specifying method according to embodiment 1.

Fig. 2 is a diagram illustrating a press-formed product according to embodiment 1.

Fig. 3 is a diagram showing a driving stress distribution of CAE analysis in embodiment 1.

Fig. 4 is a diagram showing a driving stress distribution of an actual plate member in embodiment 1.

Fig. 5 is a diagram showing a drive stress distribution (a) of CAE analysis, a drive stress distribution (b) of an actual plate, and a drive stress difference distribution (c) between CAE analysis and an actual plate in embodiment 1.

Fig. 6 is a diagram showing a driving stress difference distribution (a) between the CAE analysis and the actual plate and a displacement (b) calculated by the springback analysis based on the driving stress difference distribution.

Fig. 7 is a diagram showing the fixed point of the springback analysis and the analysis result of the displacement obtained by the springback analysis in embodiment 1.

Fig. 8 is a diagram for explaining a method of calculating an end swing amount and a bounce amount as a rebound amount in embodiment 1.

Fig. 9 is a diagram illustrating division of a molded article into regions in embodiment 1.

Fig. 10 is (one of) a graph showing a region (a) in which the stress difference is changed and a displacement (b) calculated by a springback analysis by changing the stress difference in the region in embodiment 1.

Fig. 11 is a diagram (second drawing) showing a region (a) in which the stress difference is changed and a displacement (b) calculated by springback analysis by changing the stress difference in this region in embodiment 1.

Fig. 12 is a diagram (third) showing a region (a) in which the stress difference is changed and a displacement (b) calculated by springback analysis by changing the stress difference in the region in embodiment 1.

Fig. 13 is a diagram (fourth) showing a region (a) in which the stress difference is changed and a displacement (b) calculated by springback analysis by changing the stress difference in the region in embodiment 1.

Fig. 14 is a graph showing the relationship between the region where the stress difference is eliminated and the amount of end swing due to springback when the stress difference is eliminated in embodiment 1.

Fig. 15 is a graph showing the relationship between the region where the stress difference is eliminated and the amount of bounce due to springback when the stress difference is eliminated in embodiment 1.

Fig. 16 is a graph showing a region in which the stress distribution at the forming bottom dead center of the CAE analysis is replaced with the stress distribution of the actual plate, and the amount of deviation between the CAE analysis and the end swing of the actual plate when the stress distribution is changed.

Fig. 17 is a graph showing a region in which the stress distribution at the forming bottom dead center of the CAE analysis is replaced with the stress distribution of the actual plate, and the deviation amount between the CAE analysis and the bounce of the actual plate when the stress distribution is changed.

Fig. 18 is a block diagram for explaining the configuration of the springback value deviation main factor portion specifying device according to embodiment 2.

Detailed Description

Before describing the method for determining the location of the main factor of the springback value deviation according to the embodiment of the present invention, the process of the present invention will be described.

< go to the invention

In press forming of the press-formed product 10 shown as an example in fig. 2, there may be a difference (deviation) between the springback amount calculated by springback analysis (also referred to as CAE analysis) performed before the press forming and the springback amount of the press-formed product (also referred to as actual plate) actually press-formed. A portion that becomes a main cause of the deviation of the springback amount between the CAE analysis and the actual plate may be different from a portion that becomes a main cause of the springback itself. Therefore, there is a problem that: even if some measures are taken to reduce springback at a portion that is a main cause of springback, it is not possible to reduce the deviation of the springback amount generated between the CAE analysis and the actual plate.

Therefore, the inventors have earnestly studied to solve such problems. As a result, it is thought that the main cause of the deviation of the spring back amount may be due to the difference between the stress contributing to the spring back in the CAE analysis and the stress contributing to the spring back in the actual plate member.

Therefore, in order to verify the validity of this concept, the stress contributing to springback (hereinafter, also referred to as a driving stress distribution) is obtained for the CAE analysis of the press-formed product 10 having a hat-shaped cross-sectional shape shown in fig. 2 and the actual plate, the difference between the driving stress distribution in the CAE analysis and the driving stress distribution in the actual plate (hereinafter, also referred to as a stress difference distribution) is calculated, and the springback analysis is performed by replacing the stress difference distribution with the stress distribution at the forming bottom dead center in the CAE analysis (a driving stress calculation method will be described in detail in the embodiment described later).

As the springback amount, the end swing amount, which is the amount of displacement in the plate width direction of the end portion in the longitudinal direction, and the springback amount, which is the amount of displacement in the forming stroke direction, were calculated (see fig. 8), and compared with the difference (deviation amount) between the CAE analysis and the springback amount of the actual plate member, and the results thereof are shown in table 1.

[ Table 1]

As shown in table 1, it can be seen that: the difference between the amount of springback of the CAE analysis and the actual plate member and the amount of springback obtained by the springback analysis in which the stress difference distribution is set are almost the same. Namely, the following findings were obtained: it is considered that the difference in the CAE analysis from the driving stress distribution of the actual plate, i.e., the stress difference, is the cause of the deviation in the spring back amount.

The method for determining the location of the main cause of the springback value deviation according to the present invention is completed through the above-described process, and a specific method thereof will be described in the following embodiments.

In the following description, the "bottom dead center" indicates a state in which the punch and the die contact each other with the blank interposed therebetween (a state in which the forming is completed in the CAE analysis). "forming bottom dead center" means a state where forming is completed by an actual die. "analysis bottom dead center" indicates a state in which the forming is completed in the CAE analysis.

[ embodiment 1]

In the method for determining a springback value deviation main cause portion according to embodiment 1 of the present invention, when a press-formed product obtained by press-forming an actual plate member deviates from a springback value analyzed by springback, a portion of a shape of the press-formed product, which is a main cause of the deviation in the springback value, is determined. As shown in fig. 1, the present invention includes: a molded product drive stress distribution acquisition step S1, an analysis drive stress distribution acquisition step S3, a stress difference distribution setting step S5, a stress difference springback value acquisition step S7, a change stress difference springback value acquisition step S9, and a springback value deviation principal factor part determination step S11.

The above steps will be described by taking as an example a case where a press-formed article 10 having a hat-shaped cross-sectional shape as shown in fig. 2 is press-formed.

In the CAE analysis of the present embodiment, as shown in fig. 2, press forming analysis is performed in which a blank mold 9 as a workpiece (steel plate) is sandwiched by a die mold 3 composed of a die 5 and a punch 7. In the press forming analysis, as shown in fig. 2, the blank mold 9 was fixed by the positioning pin during the forming process, the element size of the blank mold 9 was about 1mm, the friction coefficient between the blank mold 9 and the die mold 3 was 0.15 as the analysis condition, and the forming bottom dead center position was a position where the clearance between the upper and lower dies was 1.45 mm. The processed material was a 980MPa grade GA steel plate with a plate thickness of 1.4 mm.

The actual plate member in the present embodiment is formed by press forming under the same forming conditions set in the CAE analysis.

< step of obtaining distribution of drive stress of molded article >

The molded product driving stress distribution obtaining step S1 is a step of obtaining a driving stress distribution of an actual plate.

Specifically, the actual plate member is press-formed under the same conditions as those set in the CAE analysis described above. Then, a press-formed product model is created from three-dimensional shape measurement data obtained by measuring the surface shape of the actual plate after the mold release, and a mechanical analysis is performed in a state where the press-formed product model is sandwiched to the bottom dead center of the molding by using the mold model 3 shown in fig. 2, so that a stress distribution as shown in fig. 4 is obtained.

As the mechanical analysis, elastic finite element analysis was performed. The stress distribution obtained by the elastic finite element analysis corresponds to the stress contributing to springback of the actual plate, i.e., the driving stress of the actual plate.

Here, as a specific method of measuring the three-dimensional shape of the actual plate member, making a press-formed product model, and elastic finite element analysis, for example, the method described in patent document 3 can be used.

< analyzing the driving stress distribution obtaining step >

The analysis driving stress distribution obtaining step S3 is a step of obtaining the bottom dead center stress distribution in the CAE analysis (springback analysis) and the residual stress after the mold release, and obtaining the driving stress of the CAE analysis from the difference between the two.

The stress at the bottom dead center of the press-formed article affects the behavior of springback, but the stress remains in the press-formed article after the press-formed article is released from the die. That is, it is considered that not all of the stress before the die release contributes to the spring back, and the stress remaining in the press-formed product after the die release where the spring back occurs does not contribute to the spring back.

In order to perform accurate comparative analysis with the driving stress (stress contributing to springback) acquired in the molded product driving stress distribution acquisition step S1, it is necessary to calculate the driving stress in the CAE analysis.

Therefore, in the analysis driving stress distribution obtaining step S3, CAE analysis is performed using the die model 3 and the blank model 9 shown in fig. 2, and the stress of the press-formed product before the die release (bottom dead center) and the residual stress of the press-formed product after the die release (after springback) are obtained, and the driving stress distribution (hereinafter, also simply referred to as stress distribution) in the CAE analysis as shown in fig. 3 is calculated by subtracting the residual stress after the die release from the stress at the bottom dead center.

In the analysis driving stress distribution obtaining step S3, CAE analysis is performed by a computer. The CAE analysis can use, for example, finite element analysis software. In the present embodiment, LS-DYNA ver.971, which is commercially available finite element analysis software, was executed on a computer to perform analysis, and a dynamic explicit method was applied to a solver.

The present invention is not limited to the use of the die mold 3 as shown in fig. 2 or the press-formed article 10 having a hat-shaped cross-sectional shape as a forming object, and the die mold, the press-formed article, and the like can be appropriately set according to the forming object.

In the case where the residual stress after the mold release is a small value that can be almost ignored, the stress distribution at bottom dead center may be analyzed as the stress distribution contributing to the springback.

< stress difference distribution setting step >

As shown in fig. 5, the stress difference distribution setting step S5 is a step of: the difference between the stress distribution calculated in the analysis drive stress distribution acquisition step S3 (fig. 3 and 5 (a)) and the stress distribution calculated in the molded product drive stress distribution acquisition step S1 (fig. 4 and 5 (b)) is calculated as a stress difference distribution ((c) of fig. 5), and the calculated stress difference distribution is set as a stress distribution in the bottom dead center shape of the CAE analysis.

The stress distributions shown in fig. 5 show the difference in stress level by the shade of color. Fig. 5 (c) is a diagram in which the range width of the color display is set smaller than those of fig. 5 (a) and 5 (b). In this way, it is easier to distinguish between a portion where the stress difference is large (a portion near black or white) and a portion where the stress difference is small (a portion near a gray halftone on the right side in the figure).

< step of measuring differential stress rebound >

The stress difference springback amount obtaining step S7 is a step of performing springback analysis using the stress difference distribution set in the stress difference distribution setting step S5, and calculating the springback amount generated here.

In the present embodiment, the press-formed product 10 (fig. 6 (a)) having the bottom dead center shape in which the stress difference distribution is set is subjected to springback analysis, and the displacement after springback is calculated by the springback analysis (fig. 6 (b)). In the springback analysis, as shown in fig. 7, three points provided on one end side of the molded product were fixed at fixed points, and displacements due to springback were calculated.

Next, as shown in fig. 8, the end swing amount ((a) of fig. 8) and the bounce amount ((b) of fig. 8) are calculated based on the displacement calculated by the springback analysis. In the present embodiment, as shown in fig. 8 a, the end swing amount is a movement amount (positive in the direction of the arrow) in the direction of the arrow in the drawing due to springback at one of two evaluation points provided on the other end side of the press-formed product 10, and as shown in fig. 8 b, the springback amount is a displacement amount (positive in the direction away from the die 5) in the direction of the forming stroke at the midpoint between the two evaluation points.

< Change stress Difference rebound quantity obtaining step >

The step S9 of changing the stress difference elastic resilience amount is a step of: in the stress difference distribution set in the stress difference distribution setting step S5, the value of the stress difference at a certain portion of the press-formed product 10 is changed, springback analysis is performed based on the changed stress difference distribution (changed stress difference distribution), and the springback amount generated thereby is calculated.

In the present embodiment, as shown in fig. 9, the press-formed product 10 is divided into a plurality of regions (6 divisions a to F in the longitudinal direction and 3 divisions 1 to 3 in the width direction) and the stress difference in each region is eliminated, that is, the value of the stress difference is set to zero. The region for eliminating the stress difference is not necessarily one region, and the stress difference may be eliminated in a plurality of regions.

After the values in a certain region are eliminated, springback analysis is performed, and the end swing amount and the bounce amount shown in fig. 8 are calculated as springback amounts, respectively.

Fig. 10 shows a displacement calculated by eliminating the stress difference (making the value of the stress difference zero) in the region 1 (see fig. 10 a) from the stress difference distribution set in the stress difference distribution setting step S5 and performing springback analysis (see fig. 10 b). Based on the calculated displacement, the springback amount (end swing amount, bounce amount) is calculated. Similarly, the springback value (not shown) is calculated for the regions 2 and 3.

Similarly, fig. 11 shows a displacement calculated by eliminating the stress difference (making the value of the stress difference zero) in the region a (see fig. 11 a) from the stress difference distribution set in the stress difference distribution setting step S5 and performing springback analysis (see fig. 11 b). Based on the calculated displacement, the springback amount (end swing amount, bounce amount) is calculated. Similarly, the springback value (not shown) is calculated for the regions B to F.

Fig. 12 and 13 show displacements calculated by eliminating stress differences (making the stress difference zero) in the regions a-1 and a-3 (see fig. 12 a and 13 a) from the stress difference distribution set in the stress difference distribution setting step S5 and performing springback analysis (see fig. 12 b and 13 b). Based on the calculated displacement, the springback amount (end swing amount, bounce amount) is calculated. The springback values (not shown) were calculated similarly for the regions A-1 to F-3.

< determination of principal factor part of deviation of springback amount >

The springback amount deviation principal factor position determining step S11 is a step of: based on the springback amount calculated in the stress difference springback amount obtaining step S7 and the changed stress difference springback amount obtaining step S9, a portion that becomes a main cause of a deviation in the springback amount between the CAE analysis and the actual plate is specified.

Fig. 14 shows the results of the stress difference spring back amount obtaining step S7 and the results of changing the end swinging amount calculated in the stress difference spring back amount obtaining step S9. In fig. 14, the reference number is an end oscillation amount based on a stress difference distribution in which stress is not eliminated, and 1 to 3, a to F, A-1 to F-3 are end oscillation amounts based on a modified stress difference distribution in which stress differences in the respective regions are eliminated.

The swing amount (reference number) of the end portion without changing the stress difference was-10.7 mm. On the other hand, when observing the end swing amounts of the stress relief regions in the regions 1 to 3, it can be seen that: only the region 2 has a larger change from the reference number than the regions 1 and 3.

Similarly, when observing the swing amounts of the end portions of the regions a to F in the stress relief region, it can be seen that: the regions D and E have a larger change from the reference number than the other regions.

Then, when observing the end swing amounts in the case where the stresses in the regions a-1 to F-3, which are further subdivided regions, are eliminated, it is found that: the end swing amount of the region D-2 and the region E-2 is reduced compared to the reference number without stress relief. As such, the end swing amount is reduced in a certain region due to the elimination of the stress difference, which indicates that the deviation of the end swing amount in the region has a large influence.

This is also a suitable result because the variation is large in the region 2 and the region D, E, and it can be determined that the region D-2 and the region E-2 are portions where the CAE analysis deviates from the actual amount of swing of the end portion of the plate member.

Further, the end swing amounts of the regions other than the region D-2 and the region E-2 are about the same as the end swing amount (reference number) in the case where the stress difference is not changed, and thus it can be determined that these regions have a small influence on the deviation between the CAE analysis and the end swing amount of the actual plate.

The calculated results are also shown in fig. 15 for the pop-up amount.

The spring-up (reference number) without changing the stress difference was 4.2 mm. On the other hand, when the stress relief regions are observed for the spring-up amounts of the regions 1 to 3, it is found that: only zone 2(-8.3mm) showed a larger change from the reference number than zone 1(4.8mm) and zone 3(7.5 mm).

Similarly, when the stress relief region is observed as the amount of bounce of the regions a to F, it is found that: the region D (-2.9mm) and the region F (-0.9mm) have a larger change from the reference number than the other regions.

Then, when the spring-up amounts in the case where the stresses in the regions a-1 to F-3, which are further subdivided regions, were eliminated were observed, it was found that: the spring-up amount (0.1mm) of the region F-2 was greatly reduced as compared with the reference number without stress relief, and almost no spring-up occurred. As with the end swing amount, a region is reduced in the spring amount due to the elimination of the stress difference, which indicates that the region has a large influence on the deviation of the spring amount.

This is also a reasonable result because the variation in the amount of bounce is large in the region 2 and the region F, and it can be specified that the region F-2 is a portion where the CAE analysis deviates from the actual amount of bounce of the plate member.

Although the change of the area 2 and the area D from the reference number is large, when the stress of the subdivided area D-2 is removed, the spring-up amount is-4.6 mm, and the spring-up direction is opposite to the spring-up amount of 4.2mm which is the reference number without removing the stress, and the spring-up amount is increased.

This indicates that: in the case where the stress difference in the region D-2 is eliminated, the region is a portion where the spring-up amount is easily deviated. That is, it is determined that the region D-2 is a portion where the deviation of the pop-up amount is suppressed in the case where there is a stress difference, and is not a portion where the deviation occurs.

In the present embodiment, although the springback value is calculated when the stress is eliminated in all of the subdivided regions a-1 to F-3 as shown in fig. 14 and 15, a region expected to have a large influence can be selected from the results of the regions 1 to 3 and the regions a to F as described above, and therefore, the result of further subdivision can be obtained only for the region. In a press-formed product having a complicated shape, it is necessary to increase the number of divided regions and further divide the product into smaller pieces, and it takes time to obtain results in all the divided regions. Therefore, by selecting and analyzing a region that may affect the deviation from a large region division, it is possible to shorten the time until the deviation main cause region is identified.

Next, the validity of the determination that the portion identified by the springback amount deviation main factor portion identifying method of the present embodiment is a portion that becomes a main factor of the deviation between the CAE analysis and the springback amount of the actual plate member will be described.

As described above, when the press-formed product 10 shown in fig. 2 is formed, the regions D-2 and E-2 of the press-formed product 10 are identified as the portions that become the main cause of the deviation between the CAE analysis and the actual amount of end swinging of the plate member. Further, the region F-2 is identified as a portion that causes variation in the amount of bounce.

Therefore, the drive stress at each position specified in the drive stress distribution obtained by CAE analysis (see fig. 3) is replaced with the drive stress distribution at each position of the actual plate corresponding to the drive stress distribution, and springback analysis is performed to verify whether or not the variation in springback amount is small.

First, a result of verification as to whether the amount of deviation from the end swing of the actual plate member is reduced or not by the CAE analysis is shown in fig. 16.

Fig. 16 is a graph of the result (deviation amount) of subtracting the actual plate end swing amount from the CAE analyzed end swing amount, where the vertical axis represents the deviation amount and the horizontal axis represents the stress replacement region. "none" in the horizontal axis is the case where there is no stress replacement region, and in this case, the deviation amount is-11.6 mm which is the difference between the CAE analysis and the actual plate member. In addition, "all" is a case where all regions of the driving stress distribution of the CAE analysis are replaced with the driving stress distribution of the actual plate, and in this case, the amount of deviation is almost zero.

On the other hand, when the stress distribution of the actual plate member is replaced only for the region D-2 or the region E-2 specified in the present embodiment, as shown by "D-2" and "E-2" in fig. 16, the amount of swing deviation from the end portion of the actual plate member is reduced in any of them.

Furthermore, as shown by "D-2/E-2", it was revealed that: by replacing the stress distribution of the actual plate member for both the regions D-2, E-2, the amount of swing deviation from the end portion of the actual plate member can be further reduced.

Likewise, a result of verification as to whether the amount of deviation of the CAE analysis from the bounce of the actual plate member is reduced is shown in fig. 17. As for the deviation of the pop-up amount, as shown by "F-2", the stress distribution in the region F-2 of the forming bottom dead center is replaced with the stress distribution of the actual plate, so that the pop-up deviation amount from the actual plate is reduced.

The results show that: the site identified by the springback amount deviation main factor site identification method of the present embodiment is appropriate as a site that becomes a main factor of the deviation of the springback amount from the actual plate by the CAE analysis.

As described above, according to the method of the present embodiment, it is possible to accurately specify a portion that becomes a main cause of the deviation between the CAE analysis and the springback amount of the actual plate.

By identifying the portion that becomes the main cause of the deviation in the spring back amount in this manner, it is possible to efficiently perform adjustment work of the die, the molding conditions, and the like for bringing the CAE analysis close to the actual post-mold shape of the plate.

Further, by modifying the settings and the die shape in the CAE analysis with the specified portion as the center, the reproducibility of the springback analysis can be improved, and the usefulness of the springback countermeasure using the CAE analysis can be ensured.

The change of the stress difference distribution performed in the present embodiment is to eliminate the stress difference in at least a certain partial region (make all the components zero), but the method of changing the stress difference distribution is not limited to this, and the change may be performed by eliminating the components in at least one direction, multiplying the components by a constant, adding the constant to the components, multiplying the components by the constant, replacing the components by the average value in the thickness direction of the workpiece, and replacing the components by the median in the thickness direction of the workpiece.

[ embodiment 2]

The method for determining the location of the main factor of the springback value deviation described in embodiment 1 can be realized by a PC (personal computer) executing a preset program. In this embodiment, an example of such a device will be described.

The springback value deviation main factor location determining device 11 of the present embodiment includes 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 fig. 18 as 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 in accordance with an instruction from the arithmetic processing unit 21.

The display device 13 is used for displaying results and the like, and is constituted by a liquid crystal display or the like. The input device 15 is used for input by an operator and is constituted by a keyboard, a mouse, and the like. The main storage device 17 is used for temporary storage, calculation, and the like of data used by the arithmetic processing unit 21, and is constituted by a RAM and the like. The auxiliary storage device 19 is used for storing data and the like, and is constituted by a hard disk or the like.

At least various data necessary for CAE analysis, such as the three-dimensional shape measurement data 23 and the mold model 25, are stored in the auxiliary storage device 19.

The arithmetic processing unit 21 is constituted by a CPU such as a PC. The molded product driving stress distribution obtaining means 27, the analysis driving stress distribution obtaining means 29, the stress difference distribution setting means 31, the stress difference springback amount obtaining means 33, the change stress difference springback amount obtaining means 35, and the springback amount deviation main factor part specifying means 37 are realized by executing a program set in advance by the arithmetic processing unit 21.

The molded article driving stress distribution obtaining means 27 realizes the same processing as the molded article driving stress distribution obtaining step S1 described in embodiment 1. Similarly, the analysis drive stress distribution obtaining means 29 realizes the analysis drive stress distribution obtaining step S3, the stress difference distribution setting means 31 realizes the stress difference distribution setting step S5, the stress difference springback amount obtaining means 33 realizes the stress difference springback amount obtaining step S7, the change stress difference springback amount obtaining means 35 realizes the change stress difference springback amount obtaining step S9, and the springback amount deviation principal factor portion determining means 37 realizes the springback amount deviation principal factor portion determining step S11.

According to the present embodiment as described above, as in embodiment 1, it is possible to accurately specify a portion that is a main cause of a deviation between the CAE analysis and the springback amount of the actual plate member.

Accordingly, various adjustment operations for approximating the CAE analysis to the actual post-die-release shape of the plate can be efficiently performed based on the specified portion, and the usefulness of the springback countermeasure can be ensured.

The present invention is not limited to the final molded product (product shape), and can be applied to a halfway molded product even in the case of press-molded products in which the molding process is performed in stages. In the above embodiment, an example in which a steel sheet is used as a workpiece is described, but the present invention can also be applied to an aluminum sheet.

Description of the reference numerals

A mold model; stamping a die; a punch; a blank mold; 10.. a press-formed article; a rebound quantity deviation main factor position determining device; a display device; an input device; main storage; a secondary storage device; a calculation processing unit; three-dimensional shape measurement data; a mold model; a molded product driving stress distribution acquisition unit; an analysis drive stress distribution acquisition unit; a stress difference distribution setting unit; a stress difference rebound amount obtaining unit; a unit for obtaining the rebound quantity by changing the stress difference; a springback value deviation main cause position determining unit.