CN113573823B - Method for evaluating stretch flanging crack and method for selecting metal plate - Google Patents
Method for evaluating stretch flanging crack and method for selecting metal plate Download PDFInfo
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- CN113573823B CN113573823B CN202080020881.7A CN202080020881A CN113573823B CN 113573823 B CN113573823 B CN 113573823B CN 202080020881 A CN202080020881 A CN 202080020881A CN 113573823 B CN113573823 B CN 113573823B
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Abstract
Provided is a technique for evaluating stretch flanging cracks in a sheared end face of a metal plate for evaluation more easily. The metal plate 2 selected arbitrarily is subjected to a molding analysis of a hole expansion test under predetermined molding conditions, and the molding conditions are changed to have at least 2 pieces of reference strain gradient information (10 c) which is a relationship between the strain of the hole edge and the strain gradient along the radial direction obtained by converting the hole expansion ratio into the strain of the hole edge including the true strain. Under the same molding conditions as those corresponding to at least 2 pieces of reference strain gradient information (10 c), the metal plate for evaluation is subjected to hole expansion molding, the limiting hole expansion ratio at the time of the hole expansion limit of at least 2 pieces of metal plate for evaluation is obtained, and the moldable region (ARA) of the metal plate for evaluation is obtained from the at least 2 pieces of reference strain gradient information (10 c) and the obtained limiting hole expansion ratio at the time of at least 2 pieces of hole expansion limit. The stretch flanging crack at the shearing end face in the metal plate for evaluation was evaluated by the obtained formable area (ARA).
Description
Technical Field
The present application relates to a method for evaluating a stretch flanging crack at a sheared end face of a metal plate during press forming, a method for selecting a metal plate, a method for designing a press mold, a method for designing a part shape, and a method for manufacturing a press part.
Background
The steel sheet used for automobile parts has been developed to have higher strength, and one of the problems in press forming of the steel sheet is stretch flangings. However, the stretch flangings at the sheared end face are difficult to predict using a crack prediction method such as FLD.
Here, as described in non-patent document 1, it is known that the strain gradient in the vicinity of the fracture portion greatly affects the fracture limit of the stretch flanger crack. In this way, in the methods described in patent documents 1 to 3, for example, the relationship between the stretch flangings crack limit and the strain gradient is determined by an actual test for evaluating the stretch flangings deformation limit of the sheared end face, which is represented by a hole expansion test of a plurality of materials, and by a molding analysis thereof. And predicting the stretch flangings based on the relation between the determined stretch flangings crack limit and the strain gradient and the press forming analysis result.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 2009-204427
Patent document 2: japanese patent application laid-open No. 2017-140653
Patent document 3: international publication No. 2016/002880
Non-patent literature
Non-patent document 1: meal, rong Zhi, etc.: plasticity and working, 51-594 (2007), 700-705
Disclosure of Invention
Problems to be solved by the application
The problem of cracking of the sheared edge face in the stretch flanger forming during the press forming of the high-strength steel sheet is remarkable. Therefore, in order to prevent the occurrence of stretch flangings, it is important to evaluate the stretch flangings of the sheared end face of a metal sheet, particularly a high-strength steel sheet.
However, in the methods described in patent documents 1 to 3, it is necessary to perform molding analysis corresponding to an actual test every time the evaluated metal plate is changed, and therefore it takes time to obtain analysis data of the stretch flanging crack limit.
As described in patent document 3, there is also a method of directly calculating a strain gradient from a material test. However, this method requires a special device for determining the strain distribution in the material test. In addition, in the conical reaming molding, since the metal plate is warped, it is difficult to measure strain, and it is not practical.
As described above, in the conventional evaluation method, when selecting a metal plate to be used for processing, a step of performing a molding analysis for calculating a strain gradient required for stretch flanging crack prediction is required for each metal plate to be evaluated. Therefore, there is a problem that it takes time to determine an index (information of a strain gradient corresponding to a metal sheet to be evaluated) for evaluating the forming limit of the stretch flanger crack.
The present application has been made to solve the above-described problems, and an object of the present application is to provide a technique for evaluating stretch flangings on a sheared end face of a metal plate more easily so as to be able to determine press forming conditions.
The press forming conditions include, in addition to selecting a metal plate to be used for press forming, determining the shape of a press member, and the like.
Means for solving the problems
The inventors of the present application repeatedly studied a lot of stretch flares in a sheared edge, and found that, when 2 or more kinds of hole expansion forming analyses are performed on 1 metal plate selected arbitrarily, the obtained hole expansion ratio is used as analysis data when evaluating the strain gradient, irrespective of the material condition (strip) of the metal plate to be evaluated, and the "relationship between the strain at the hole edge and the strain gradient in the radial direction from the hole edge" obtained by converting the hole edge into the true strain is obtained.
Namely, the inventors of the present application have obtained the following findings: the relationship between the strain at the hole edge, which is obtained by converting the true strain in the molding in the above-described hole expansion molding analysis, and the strain gradient in the radial direction from the hole edge in the hole expansion molding is determined by the initial pore diameter of the metal plate and the shape of the molding tool for performing the hole expansion test, and is not affected by the mechanical properties such as the material strength, the plate thickness, and the R value. Accordingly, the inventors of the present application have found that, when performing hole-enlarging analysis on a metal plate having a certain mechanical property, a relationship between a strain at a hole edge obtained by performing true strain conversion on a hole-enlarging ratio in forming in the hole-enlarging analysis and a strain gradient in a radial direction from the hole edge in the hole-enlarging forming is obtained, it is possible to easily obtain a relationship between a strain at a hole edge at a hole-enlarging limit required for stretch flanging crack prediction and a strain gradient in a radial direction from the hole edge at a hole-enlarging limit even if forming analysis is not performed on each metal plate made of a different material.
In order to solve the problems, a method for evaluating a stretch flangings crack in a metal sheet for evaluation formed of a metal sheet having a sheared end face according to an aspect of the present application is characterized in that a molding analysis of a hole expansion test under a set molding condition is performed on a 2 nd metal sheet having a arbitrarily selected plate condition and selected independently of the metal sheet for evaluation, and the molding condition is changed to have 2 or more pieces of reference strain gradient information represented by a relationship between a strain at the hole end edge and a strain gradient in a radial direction from the hole end edge, the relationship being obtained by converting a hole expansion ratio into a strain at the hole end edge including a true strain, under the same molding conditions as those corresponding to at least 2 pieces of the reference strain gradient information of the above 2 pieces or more, performing hole-enlarging molding on the metal plate for evaluation, respectively, determining a limit hole-enlarging ratio at least for 2 hole-enlarging limits of the metal plate for evaluation, determining a moldable region of the metal plate for evaluation from the at least 2 pieces of the reference strain gradient information and the determined limit hole-enlarging ratio at least for 2 hole-enlarging limits, and evaluating a stretch-flanging crack at a sheared end face of the metal plate for evaluation from the determined moldable region
Another aspect of the present application is a method for selecting a metal sheet to be formed into a punched part, wherein the method for selecting a metal sheet is characterized in that a stretch flanging crack at a sheared end face is evaluated by the method for evaluating a stretch flanging crack in one aspect, and a metal sheet in which a stretch flanging crack at a sheared end face does not occur is selected based on the evaluation.
Another aspect of the present application is a method for designing a press die for press forming a metal plate, wherein the method for designing a press die is characterized in that a stretch-flanging crack at a shear end face in press forming the metal plate is evaluated by the method for evaluating a stretch-flanging crack in one aspect, and a press die capable of suppressing a stretch-flanging crack at a shear end face is obtained based on the evaluation.
Another aspect of the present application is a method for designing a part shape of a press-formed part obtained by press-forming a metal plate, wherein the method for evaluating a stretch flanging crack is characterized in that the method for evaluating a stretch flanging crack at a sheared end face in press-forming a metal plate is used to evaluate the stretch flanging crack at the sheared end face, and the part shape capable of suppressing the stretch flanging crack at the sheared end face is obtained based on the evaluation.
Another aspect of the present application is a method for manufacturing a punched member by punching a metal plate, wherein the method is characterized in that a stretch flanging crack at a shearing end face is evaluated by the stretch flanging crack evaluation method of the first aspect.
Another aspect of the present application is a method for manufacturing a press-formed member by press-forming a metal plate, wherein the press-forming condition is determined by the stretch flanger crack evaluating method according to the first aspect.
Effects of the application
According to the embodiment of the present application, data for evaluating (predicting) the stretch flangings of the sheared edge face can be obtained more easily.
That is, according to the aspect of the present application, for example, data for stretch flangingcrack prediction of a sheared end face of a metal plate can be easily obtained. Therefore, for example, it is possible to rapidly and accurately predict whether or not the selection of press molding conditions such as a metal plate, a press mold, and a part shape used in press molding various parts such as a panel part, a structure, and a skeleton part of an automobile is appropriate.
As a result, according to the aspect of the present application, the press-molded article can be stably manufactured by press molding, and the defective rate of the press-molded article can be greatly reduced. In addition, the shape of the press mold can be predicted with high accuracy in the design stage, contributing to shortening the manufacturing period of the press mold.
Drawings
Fig. 1 is a diagram illustrating a process of a stretch flanging crack evaluation method according to an embodiment of the present application.
Fig. 2 is a diagram showing an example of data of the preliminary information.
Fig. 3 is a diagram illustrating a process of the stretch flanger crack evaluation method.
Fig. 4 is a diagram showing an example of reference strain gradient information.
Fig. 5 is a diagram illustrating an example of a molding tool.
Fig. 6 is a diagram illustrating a process of the possible area setting step.
Fig. 7 is a diagram illustrating a process of the possible area setting step.
Fig. 8 is a diagram showing the shape of the punch member R in the embodiment.
Fig. 9 is a diagram illustrating evaluation of the embodiment.
Detailed Description
Next, an embodiment of the present application will be described with reference to the drawings.
(embodiment 1)
In the stretch flanging crack evaluation method of the present embodiment, as a step of evaluating a stretch flanging crack of an evaluation metal plate made of a metal plate having a sheared end face, which is manufactured by press forming, there are provided an actual test step 3, a limit strain gradient calculation step 4, a possible region setting step 5, and an evaluation determination step 6, as shown in fig. 1. In this specification, the "metal plate for evaluation" is also referred to as "metal plate to be evaluated".
The preliminary information 10 for stretch flangings crack evaluation is stored in advance in the database 2 (storage unit). The preliminary information 10 is acquired by performing the preliminary information acquisition step 1 in advance and stored in the database 2.
< preliminary information acquisition Process 1 >)
In the preliminary information acquiring step 1, processing is performed on the 2 nd metal plate having the same or different plate conditions as the metal plate for evaluation, specifically, the 2 nd metal plate having arbitrarily selected plate conditions regardless of the metal plate for evaluation. The preliminary information acquisition step 1 performs molding analysis of a hole expansion test under a set molding condition (hereinafter also referred to as hole expansion test condition) for an arbitrarily selected 2 nd metal plate.
The sheet metal component is usually a characteristic condition of a metal sheet set when analyzing the metal sheet. The plate conditions are, for example, material strength, mechanical properties of the plate, plate thickness, etc. The plate member of the 2 nd metal plate to be analyzed by molding is not particularly limited, and for example, an arbitrarily selected plate member may be used from among plate members of a plurality of metal plates which are assumed to be metal plates for evaluation. That is, the sheet metal plate 2 subjected to the above-described molding analysis can be arbitrarily selected and used irrespective of the sheet metal plate for evaluation (mechanical properties, plate thickness, etc.). Therefore, the sheet metal strip of the 2 nd sheet metal analyzed by the molding is usually a condition different from the sheet condition of the metal sheet for evaluation.
By the above-described molding analysis, the relationship between the hole expansion ratio and the strain gradient in the radial direction from the hole edge was obtained. The preliminary information obtaining step 1 converts the hole expansion ratio in the molding analysis into true strain as the strain of the hole edge. In the preliminary information obtaining step 1, the above-described processing is performed to obtain reference strain gradient information including a relationship between the strain and the strain gradient of the hole edge, corresponding to the molding conditions set in the reaming test. The process in the preliminary information acquisition step 1 was performed 2 times or more by changing the reaming test conditions. The plate conditions of the molding analysis 2 nd metal plate may be different or the same for each reaming test condition. The metal plate 2 may be a plate member that is easily analyzed by molding.
Thus, 2 or more pieces of data including the molding conditions (hole expansion test conditions) and the preliminary information 10 of the reference strain gradient information are acquired, and the acquired 2 or more pieces of data of the preliminary information 10 are stored in the database 2 in advance.
The molding conditions were expressed by 2 variables, that is, the initial pore diameter formed in the metal plate and the shape of the molding tool (punch shape) for performing the reaming test. The reaming test conditions were set to 2 or more molding conditions obtained by changing at least one of the initial pore diameter and the molding tool shape.
The data of the preliminary information 10 stored in the database 2 is in the form of data such as that shown in fig. 2. In the example shown in fig. 2, the data of the preliminary information 10 includes a data number 10a, a molding condition 10b for specifying the reaming test condition, and reference strain gradient information 10c corresponding to the molding condition. The reference strain gradient information 10c is information "relationship between hole expansion ratio and strain gradient in radial direction from hole end edge" represented by a curve 11 shown in fig. 3 and 4. The reference strain gradient information 10c is composed of, for example, a conversion formula showing the above-described relationship, table information containing 2 or more pieces of data (hole expansion ratio, strain gradient in the radial direction from the hole edge), and the like.
Here, since the strain gradient affects the stretch flanging deformation limit, it is preferable to obtain the stretch flanging deformation limit when the strain gradient is wide. Therefore, it is preferable to obtain the reference strain gradient information 10c by changing the initial pore diameter of the metal plate and the size of the molding tool in various ways. In general, in a plurality of kinds of hole expansion tests, in the case of hole expansion test molding using a molding tool (punch) of the same shape, the smaller the initial hole diameter of a metal plate, the larger the strain gradient in the radial direction of the hole from the hole edge at the time of molding at the same hole expansion rate in the plurality of kinds of hole expansion tests. The shape of the forming tool also affects the strain gradient, and tends to be large when the shape of the forming tool is a conical shape (see fig. 5 a) and small when the shape of the forming tool is a cylindrical shape (see fig. 5 b) for the same initial aperture of the metal plate.
In order to improve the accuracy of stretch flangings crack prediction of the sheared edge face in the present embodiment, it is preferable to perform the molding analysis and the molding test under as many molding conditions as possible. Among them, considering the metal plate used in the actual test, it is preferable that the initial pore diameter formed on the metal plate is 5mm or more and 200mm or less. If the initial pore diameter is less than 5mm, the blanking tool is likely to be deformed during blanking of a metal plate to be described later, and thus the hole edge in a uniform shearing state cannot be obtained, and the experimental accuracy is lowered. If the initial pore diameter is larger than 100mm, the pore diameter is larger than that of a usual molding tool for punching, and accordingly, the equipment using the punching molding tool is also large and impractical. More preferably, the initial pore diameter of the metal plate is 10mm or more and 50mm or less.
The shape of the forming tool takes into account a conical shape, a cylindrical shape, a bulb shape, etc. The shape of the molding tool may be any shape as long as the molding tool can reproduce molding states of various strain gradients in molding analysis and can perform actual tests under the same molding conditions. The shape of the molding tool is preferably a conical shape having an angle of 60 ° at the tip of the punch as described in japanese industrial standard JISZ 2256.
In the analysis of the hole expansion in the preliminary information obtaining step 1, analysis of the molding conditions determined in consideration of the above is performed.
As a method of the molding analysis, a widely used finite element method is preferably used. In the method of the molding analysis, any molding analysis method may be employed as long as the molding conditions can be reproduced in analysis and the strain of the metal sheet during molding can be obtained. Hereinafter, a case of finite element analysis will be described as an example.
And (3) obtaining the maximum strain distribution at the hole end edge in any molding state and reducing along with the radial trend from the hole end edge through molding analysis of a reaming test. And, a strain gradient is calculated from the strain distribution. The strain is defined in various ways, and as the strain used, a strain that strongly reflects the circumferential strain of the hole is preferable. Such strain may be, for example, a maximum principal strain or an equivalent plastic strain, and the maximum principal strain is preferable.
By converting the hole expansion ratio into the strain of the hole edge obtained by performing the true strain conversion and using the same, the dependence of the reference strain gradient information 10c including the relationship between the strain of the hole edge and the strain gradient on the material characteristics of the metal plate can be suppressed.
That is, according to the findings obtained by the present inventors, the relationship between the strain of the hole edge obtained by converting the true strain from the hole expansion ratio during the hole expansion molding analysis and the strain gradient in the radial direction from the hole edge during the hole expansion molding is determined by the initial pore diameter of the metal plate and the shape of the molding tool for performing the hole expansion test, and is not affected by the mechanical properties of the material such as the material strength, the plate thickness, and the r value. Further, according to the findings obtained by the present inventors, by performing a hole-enlarging forming analysis on a metal plate having a certain mechanical property, a relationship between a strain of a hole edge obtained by performing a true strain conversion from a hole-enlarging ratio in forming in the hole-enlarging forming analysis and a strain gradient in a radial direction from the hole edge in the hole-enlarging forming is obtained, and thus, even if the forming analysis is not performed on a different material at a time, a relationship between a strain of the hole edge at a hole-enlarging limit and a strain gradient in a radial direction from the hole edge at a hole-enlarging limit, which are required for stretch-flanging crack prediction, can be easily obtained.
Fig. 4 shows an example of a curve (graph) 11 of the reference strain gradient information 10c. The initial hole diameter applied in this example and the punch shape as the molding tool shape 21 are shown in tables 1, 2 and fig. 5. In fig. 5, reference numeral 20 denotes a metal plate. Note that the curve (graph) of the reference strain gradient information 10c is also referred to as a master curve (master curve).
TABLE 1
TABLE 2
Fig. 4 (a) is a graph of reference strain gradient information 10c in the case of analysis under the reaming test condition in which the initial pore diameter is 10mm Φ and the molding tool shape 21 is a conical shape. Fig. 4 (b) is a graph of the reference strain gradient information 10c in the case of analysis under the reaming test condition in which the initial pore diameter is 25mm Φ and the molding tool shape 21 is a conical shape. Fig. 4 (c) is a graph of the reference strain gradient information 10c in the case of analysis under the reaming test condition in which the initial pore diameter is 50mm Φ and the shaping tool shape 21 is a conical shape. Fig. 4 (d) is a graph of the reference strain gradient information 10c in the case of analysis under the reaming test condition in which the initial pore diameter is 25mm Φ and the molding tool shape 21 is a cylindrical shape. Fig. 4 (e) is a graph of the reference strain gradient information 10c in the case of analysis under the reaming test condition in which the initial pore diameter is 50mm Φ and the molding tool shape 21 is a cylindrical shape.
As described above, the reference strain gradient information 10c represented by the different curve 11 is obtained by changing at least one of the initial pore diameter and the molding condition of the molding tool shape.
Here, the inventors tried to obtain the reference strain gradient information 10c for each metal plate by using 4 steel grades having tensile strengths of 270MPA, 590MPA, 980MPA, 1470MPA under the conditions of a hole expansion test in which the initial pore diameter is 10mm Φ and the shape of the forming tool is a conical shape. In this case, it was confirmed that the reference strain gradient information 10c was 0.1mm at least at the strain gradient -1 The same curves are shown below. In addition, it was confirmed that when analysis was performed by making only the r values different, the reference strain gradient information 10c was still at a strain gradient of 0.1mm -1 The following curves are substantially the same (main curves). In addition, when the plate thickness was changed between 0.5mm and 4.0mm and confirmed, it was confirmed that the reference strain gradient information 10c had a strain gradient of 0.1mm -1 The following curves are substantially the same.
Here, in the finite element analysis, the reference strain gradient information 10c is preferably obtained so as to avoid local excessive deformation of the finite element.
From this point of view, when the reference strain gradient information 10c is obtained, it is preferable that the equivalent stress-equivalent plastic strain relationship of the 2 nd metal plate used for the molding analysis in the hole expansion test is analyzed under a condition that the material characteristics are soft, such as a uniaxial tensile test of a metal plate having a uniform elongation of 7.5% or more. In addition, it is preferable to use the equivalent stress-equivalent plastic strain relationship obtained by the uniaxial tensile test of the 2 nd metal plate or the approximation formula thereof for the molding analysis.
< actual test procedure 3 >)
In the actual test step 3, under the same molding conditions (hole expansion test conditions) as those corresponding to the 1 st reference strain gradient information selected from the plurality of reference strain gradient information 10c stored in the database 2, hole expansion molding is actually performed on a metal plate made of the same material as the metal plate for evaluation, and the limit hole expansion rate at the time of the hole expansion limit of the metal plate for evaluation is obtained.
< Limit Strain gradient calculation procedure 4 >)
In the limit strain gradient calculation step 4, a strain gradient in the radial direction from the hole edge corresponding to the limit strain is calculated based on the 1 st reference strain gradient information stored in the database 2 and the limit strain, which is the strain at the hole edge at the time of the hole edge at the limit expansion ratio corresponding to the limit expansion ratio obtained in the actual test step 3. That is, in the limit strain gradient calculation step 4, the reference strain gradient information 10c corresponding to the reaming test conditions used in the actual test step 3 is referred to, and as shown in fig. 3, the strain gradient corresponding to the strain of the hole edge obtained by converting the limit reaming ratio obtained in the actual test step 3 is obtained, and data at the time of the limit strain (strain of the hole edge, strain gradient) is obtained. In the example of fig. 3, the hole expansion ratio at the time of ultimate strain was changed to 0.58 at the hole edge, and 0.095 was obtained as a strain gradient corresponding to 0.58 at the hole edge from the curve 11 of the corresponding reference strain gradient information 10c.
The actual test step 3 and the ultimate strain gradient calculation step 4 were performed 2 times or more by changing the reaming test conditions stored in the database 2. Thus, 2 or more data (strain at the edge of the hole, strain gradient) corresponding to the limit strain are obtained.
< possible region setting Process 5 >)
In the possible region setting step 5, a formable region ARA as shown in fig. 7 is obtained from a set (see fig. 6) of data (strain at the edge of the hole, strain gradient) obtained by changing (the reaming test condition, the reference strain gradient information 10 c) data 2 times or more and at the time of limiting strain of 2 or more. The strain at the end edge of the hole corresponds to the data of the limit strain.
For example, the position of 2 or more groups (strain at the hole edge and strain gradient) obtained in the limit strain gradient calculation step 4 is set as the boundary value of the moldable region ARA, a straight line passing through the 2 or more groups (strain at the hole edge and strain gradient) is set as the molding limit line L, and a region below the line is set as the moldable region ARA.
< evaluation determination Process 6 >)
In the evaluation determination step 6, the stretch flanging crack at the sheared end face in the metal plate to be evaluated is evaluated based on the formable region ARA obtained in the possible region setting step 5. In the evaluation determination step 6, for example, a molding analysis is performed in which the press molding to be evaluated is simulated, and the evaluation is performed based on whether or not the relationship between the strain at the edge of the metal plate to be evaluated and the strain gradient in the direction from the edge toward the inside of the metal plate to be evaluated in the press molding analysis exists in the moldable region ARA. In the case of data in the formable region ARA, it is predicted that stretch flanging cracks at the sheared end face do not occur.
< action etc. >)
As described in non-patent document 1, the deformation limit in stretch flanging is affected by the strain gradient in the vicinity of the end edge. This is because, when the strain gradient increases, even if the end edge reaches the strain localization condition, the condition is not reached in the interior thereof, and therefore the localization suppressing effect of the strain acts and the necking suppressing effect in the region where the strain is small increases. That is, for both reasons of expansion of the deformation limit of the material and improvement of uniformity of strain distribution at the hole edge, if the strain gradient increases, the deformation limit of stretch flanging is increased.
According to the present embodiment, a hole expansion forming analysis is performed on 1 metal plate selected arbitrarily, and a relation between a strain at a hole edge obtained by performing true strain conversion from a hole expansion ratio during forming and a strain gradient in a radial direction from the hole edge at the hole expansion ratio is obtained in advance in the forming analysis. In the present embodiment, the limit hole expansion ratio at the time of the hole expansion limit is obtained by performing an actual hole expansion test using the same initial hole diameter and the same molding tool as those used for the molding analysis, and the value of the strain gradient at the time of the hole expansion limit is calculated from the relationship between the strain at the hole edge during molding and the strain gradient in the radial direction from the hole edge during molding. The same method is used to determine the stretch-flanging moldable region ARA from the relationship between the strain of the hole end edge at the reaming limit and the strain gradient in the radial direction from the hole end edge at the reaming limit in at least 2 or more reaming tests.
Then, a forming analysis simulating press forming is performed, and the relation between the obtained formable region ARA of stretch flanger forming and the strain of the end edge of the metal plate for evaluation in the press forming analysis and the strain gradient in the metal plate for evaluation in the inward direction from the end edge is compared, and if the deformation state of the end edge in the press forming analysis is within the formable region ARA, stretch flanger cracking is predicted to be suppressed. That is, whether or not molding is possible at the time of press molding can be determined for the metal plate for evaluation.
When the reference strain gradient information 10c is obtained, by using the strain of the hole edge obtained by performing true strain conversion from the hole expansion ratio, the relationship between the strain of the hole edge and the strain gradient in the radial direction from the hole edge is determined by the initial pore diameter of the metal plate and the shape of the forming tool for performing the hole expansion test, and is not affected by the mechanical properties such as the material strength, the plate thickness, and the r value. As a result, in the present embodiment, it is not necessary to perform molding analysis on the metal plate for evaluation made of different materials each time, and it is possible to more easily obtain the relationship between the strain at the hole end edge at the hole expansion limit required for stretch flanging crack prediction and the strain gradient in the radial direction from the hole end edge at the hole expansion limit.
As described above, in the present embodiment, data for stretch flangingcrack prediction of the sheared edge face can be easily obtained.
As described above, according to the present embodiment, since the data for predicting the stretch-flanging crack of the sheared edge face of the metal plate to be evaluated can be easily obtained, it is possible to rapidly and accurately predict whether or not the metal plate used for press-molding various members such as the panel member, the structure and the skeleton member of the automobile is suitable. As a result, according to the present embodiment, press molding can be stably performed, and the reduction of the defective rate of the press-molded product can be greatly facilitated. In addition, the shape of the press mold can be predicted with high accuracy in the design stage, contributing to shortening the manufacturing period of the press mold.
(embodiment 2)
In embodiment 2, the stretch flanger crack is simply evaluated by the stretch flanger crack evaluation method described in embodiment 1, and selection of press forming conditions and design modification are performed based on the evaluation.
As the press forming conditions, for example, selection of a metal plate used in press forming, selection of a molding surface of a die used in press forming, determination of a press member to be manufactured, and the like are included.
For example, in the present embodiment, when a metal plate molded into a press member is selected, a stretch flanging crack at a sheared end face is evaluated by the stretch flanging crack evaluation method described in embodiment 1, and a metal plate in which a stretch flanging crack at a sheared end face does not occur is selected based on the evaluation.
In the present embodiment, for example, when designing a press die for press forming a metal plate, the stretch-flanging crack at the shear end face at the time of press forming the metal plate is evaluated by the stretch-flanging crack evaluation method described in embodiment 1, and a press die capable of suppressing the stretch-flanging crack at the shear end face is obtained based on the evaluation.
In the present embodiment, for example, when designing a component shape of a press-formed member obtained by press-forming a metal plate, the stretch flanger crack at the shear end face at the time of press-forming the metal plate is evaluated by the stretch flanger crack evaluation method described in embodiment 1, and the component shape in which the stretch flanger crack at the shear end face is suppressed is obtained based on the evaluation.
In the present embodiment, for example, in manufacturing a punched member in which a metal plate is punched to manufacture a punched member, a stretch flanging crack at a sheared end face is evaluated by the stretch flanging crack evaluation method described in embodiment 1.
In the present embodiment, for example, when manufacturing a press-formed member obtained by press-forming a metal plate to manufacture a press-formed member, the press-forming conditions are determined by the stretch flanging crack evaluation method described in embodiment 1.
According to the present embodiment, it is possible to rapidly and accurately predict whether or not the selection of press molding conditions such as a metal plate, a press mold, and a part shape used in press molding various parts such as a panel part, a structure, and a skeleton part of an automobile is appropriate.
As a result, according to the aspect of the present application, the press-molded article can be stably manufactured by press molding, and the defective rate of the press-molded article can be greatly reduced. In addition, the shape of the press mold can be predicted with high accuracy in the design stage, contributing to shortening the manufacturing period of the press mold.
Examples
A metal plate formed of a plate material shown in table 3 was press-formed, and an attempt was made to evaluate the case of obtaining a curved press member R shown in fig. 8.
TABLE 3
The metal plates formed of the plate materials shown in table 3 were subjected to a hole expansion test under the conditions of the initial hole diameters and press tools shown in tables 1 and 2, and the limiting hole expansion ratios shown in table 4 were obtained. The strain at the edge of the hole obtained by converting the true strain from the limiting hole expansion ratio was obtained, and the strain gradient was obtained by the method described in this embodiment on the basis of the curve (main curve) shown in fig. 4. The results are shown in Table 4.
TABLE 4
The molding limit line L and the moldable region ARA were obtained from the strain and the strain gradient of the hole edge shown in table 4, and the results are shown in fig. 9.
The shape analysis simulating press forming was performed on each part shape in which the curvature radius of the bending of the press part R in the longitudinal direction was changed. Then, the strain at the edge of the metal plate to be evaluated in the press forming analysis and the strain gradient in the metal plate to be evaluated in the inward direction from the edge were obtained, and whether or not the metal plate was located in the moldable region ARA shown in fig. 9 was confirmed. From the results of the above-described examination, it was predicted by molding analysis that stretch flangings did not occur when the radius of curvature was 300mm and 400mm, and stretch flangings occurred when the radius of curvature was 200mm or less.
On the other hand, in the test of press molding by actually changing the curvature radius of the bending of the press member R in the longitudinal direction, stretch flangings were not generated when the curvature radius was 300mm and 400mm, and stretch flangings were generated when the curvature radius was 200mm or less.
According to the evaluation results of this example, it can be evaluated that the radius of curvature of the bending of the press member R in the longitudinal direction needs to be 300mm or more.
As described above, it was confirmed that the evaluation of the stretch flangings according to the present application is consistent with the results in the actual press forming, and the prediction of the stretch flangings can be evaluated with high accuracy using the evaluation method of the stretch flangings according to the present application.
The entire contents of japanese patent application 2019-047363 (filed on date 14 at 3/2019), which claims priority to the present application, are hereby incorporated by reference as part of the present application. While the present application has been described with reference to a limited number of embodiments, the scope of the claims is not limited thereto, and variations of the embodiments based on the disclosure above will be apparent to those skilled in the art.
Description of the reference numerals
1. Preparation information acquisition step
2. Database for storing data
3. Actual test procedure
4. Ultimate strain gradient calculation step
5. Possible region setting step
6. Evaluation determination step
10. Preparation information
10a data numbering
10b molding conditions
10c reference strain gradient information
ARA formable area
L-shaped limit line
Claims (10)
1. A stretch-flanging crack evaluation method for evaluating a stretch-flanging crack of a metal plate for evaluation, which is formed of a metal plate having a sheared end face, characterized in that,
the molding analysis of the hole expansion test under the set molding conditions is performed on the 2 nd metal plate which is selected independently of the evaluation metal plate and has any selected plate condition, and the molding conditions are changed to have at least 2 pieces of reference strain gradient information which is obtained by converting the hole expansion ratio into the strain of the hole edge including the true strain and is represented by the relation between the strain of the hole edge and the strain gradient in the radial direction from the hole edge,
under the same molding conditions as those corresponding to at least 2 pieces of the reference strain gradient information out of the 2 pieces or more of the reference strain gradient information, performing hole expansion molding on the evaluation metal plate, respectively, to determine a limit hole expansion ratio at least at 2 hole expansion limits of the evaluation metal plate,
obtaining a formable region of the metal plate for evaluation based on the at least 2 pieces of reference strain gradient information and the obtained limit hole expansion ratio at least 2 hole expansion limits,
and evaluating the stretch flangings at the sheared end face of the evaluation metal plate by using the obtained moldable region.
2. A stretch-flanging crack evaluation method for evaluating a stretch-flanging crack of a metal plate for evaluation, which is formed of a metal plate having a sheared end face, characterized in that,
the device comprises a storage unit for associating and storing reference strain gradient information, which is information represented by a relation between a strain at the hole edge and a strain gradient in a radial direction from the hole edge, obtained by converting a hole-edge strain including true strain into a strain at the hole edge, and performing molding analysis of a hole-expansion test under the set molding conditions, for a 2 nd metal plate selected independently of the metal plate for evaluation and having an arbitrarily selected plate condition,
the memory unit stores at least 2 pieces of reference strain gradient information having different molding conditions,
the step of evaluating the stretch flangings of the metal plate for evaluation includes the steps of:
a practical test step of performing hole expansion molding on the evaluation metal plate under molding conditions identical to molding conditions corresponding to the 1 st reference strain gradient information selected from the plurality of reference strain gradient information stored in the storage unit, to determine a limit hole expansion rate at the time of a hole expansion limit of the evaluation metal plate;
a limit strain gradient calculation step of calculating a radial strain gradient from the hole edge corresponding to the limit strain, based on the 1 st reference strain gradient information and the limit strain, which is the strain at the hole edge at the time of the reaming limit corresponding to the limit hole expansion rate obtained in the actual test step; and
a possible region setting step of obtaining a moldable region from 2 or more sets of data including the limit strain and the strain gradient, the data being obtained by changing the reference strain gradient information so as to perform the actual test step and the limit strain gradient calculation step 2 or more times,
the stretch flanging crack at the shearing end face in the metal plate for evaluation is evaluated by the formable region obtained in the possible region setting step.
3. The stretch-flanging crack evaluating method according to claim 1 or 2, wherein the plate condition is at least one of mechanical properties and plate thickness of the 2 nd metal plate.
4. The stretch-flanging crack-evaluating method according to claim 1 or 2, wherein in the evaluation based on the formable region, a forming analysis simulating press forming is performed, and the determination is made based on whether or not a relationship between a strain of an end edge of the evaluation metal plate in the forming analysis and a strain gradient in an inward direction from the end edge in the evaluation metal plate exists in the formable region.
5. The stretch flanging crack evaluating method according to claim 1 or 2, wherein the equivalent stress-equivalent plastic strain relationship of the 2 nd metal plate used in the molding analysis of the hole expansion test is obtained by a uniaxial tensile test of a metal plate having a uniform elongation of 7.5% or more when the reference strain gradient information is obtained, and the equivalent stress-equivalent plastic strain relationship obtained by the uniaxial tensile test of the 2 nd metal plate or an approximation thereof is used in the molding analysis.
6. A method of selecting a metal plate, which is a method of selecting a metal plate to be formed into a punched part, the method characterized in that,
the stretch-flanging crack evaluating method according to any one of claims 1 to 5, wherein the stretch-flanging crack at the shearing end face is evaluated when the metal sheet is formed into the press member, and the metal sheet on which the stretch-flanging crack at the shearing end face does not occur is selected based on the evaluation.
7. A method for designing a stamping die for stamping a metal plate, the method being characterized in that,
the stretch-flanging crack evaluating method according to any one of claims 1 to 5, wherein the stretch-flanging crack at the shearing end face is evaluated when the metal plate is press-formed, and a press die capable of suppressing the stretch-flanging crack at the shearing end face is obtained based on the evaluation.
8. A method for designing a part shape of a punched part obtained by punching a metal plate, characterized in that,
the stretch-flanging crack evaluating method according to any one of claims 1 to 5, wherein the stretch-flanging crack at the shearing end face is evaluated when the metal plate is press-formed, and the shape of the member in which the stretch-flanging crack at the shearing end face is suppressed is obtained based on the evaluation.
9. A method for manufacturing a punched member by punching a metal plate to manufacture a punched member, characterized by,
the stretch-flanging crack evaluating method according to any one of claims 1 to 5, wherein the stretch-flanging crack at the shearing end face is evaluated when the metal plate is press-formed into the press-formed member.
10. A method for manufacturing a punched member by punching a metal plate to manufacture a punched member, characterized by,
the press forming condition is determined by the stretch flanger crack evaluation method of any one of claims 1 to 5.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2019047363 | 2019-03-14 | ||
| JP2019-047363 | 2019-03-14 | ||
| PCT/JP2020/011189 WO2020184712A1 (en) | 2019-03-14 | 2020-03-13 | Stretch flange crack evaluation method, metal sheet selection method, press die design method, component shape design method, and pressed component manufacturing method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN113573823A CN113573823A (en) | 2021-10-29 |
| CN113573823B true CN113573823B (en) | 2023-09-05 |
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