Method for acquiring material property, method for manufacturing press-formed article, punching device, and press-formed article manufacturing equipment

Abstract

Provided is technology that makes it possible to easily and accurately acquire material properties that affect the dimensional accuracy of a press, even within a press line. This method for acquiring a material property, for obtaining a material property of a metal plate for press working, involves: punching the metal plate; measuring the maximum punching load and the plate thickness of the metal plate during punching; and obtaining the breaking stress of the metal plate from the measured maximum load and plate thickness.

Description

Method for acquiring material properties, method for manufacturing press-molded products, punching device, and manufacturing equipment for press-molded products

[0001] The present invention relates to a technique for obtaining material properties of a metal plate for press working from measurements made during punching. In the present invention, the material properties are those related to breaking stress. The present invention also relates to a punching device for measuring the material properties, and a method and equipment for manufacturing a press-formed product equipped with the device.

[0002] From the viewpoint of improving collision safety and fuel economy, performance requirements for automotive parts include light weight, high strength, and high rigidity. To improve these performance requirements, it is necessary to address the increasing complexity of part shapes and to increase the strength of the materials used in the parts. As part shapes become more complex and the materials used become stronger, issues arise. One of these issues is the dimensional accuracy of the part shape. For example, as part shapes become more complex, more precise combinations with other parts are required. For this reason, high dimensional accuracy is required for press-formed products. Press-formed products are, for example, products or parts that are processed into products.

[0003] Furthermore, with steel materials, the range of variation in material properties increases as the strength of the material increases. This variation in material properties can occur even within the same coil. Therefore, even when press forming is performed on the same lot under the same press conditions, the amount of springback may vary. This is one of the causes of the variation in material properties. As a result, the dimensions of the press-formed product may also vary, resulting in a deterioration in accuracy. Furthermore, in some cases, the variation in material properties may cause forming defects such as cracks in the press-formed product.

[0004] To address these issues, methods for measuring material properties within a press line have been proposed. For example, Patent Document 1 describes measuring material properties within a press line. Patent Document 1 also describes feeding back the measured material properties to the press conditions. Patent Document 2 discloses a metal processing method in which a predetermined process is performed on a portion of the material that will not be used in the final product, followed by a material property test. In Patent Document 2, the portion that will not be used in the final product refers to a portion of the material that will not be used in the final product within the press line. Patent Document 3 also discloses a technique in which the weight of scrap is measured after forming and the weight is compared with a threshold value. Based on this comparison, the quality of a press-formed product is evaluated.

[0005] International Publication No. 2022 / 186337 Japanese Patent Application Laid-Open No. 2024-14479 Japanese Patent Application Laid-Open No. 2009-202178

[0006] As mentioned above, the range of variation in material properties of steel materials increases as the material strength increases. Furthermore, the greater the range of variation in material properties, the greater the impact on press forming results. The methods described in Patent Documents 1 and 2 provide feedback of material properties to press conditions. This approach is believed to be able to avoid these problems. Here, feedback of material properties corresponds to adjustment of press conditions. However, this feedback requires correlation between material properties and press conditions and press forming results. One possible method for achieving this is to perform press forming using a material with known material properties and then determine the correlation based on the results. Another possible method is to link various data acquired on the press line with the forming results in a big data manner. However, acquiring various numerical values ​​on the press line and then providing feedback to press conditions based on these values ​​presents the following challenges. Specifically, the former requires precise prediction of material properties from numerical values ​​obtained on the press line. Meanwhile, the latter requires control of the press line until mass production has progressed to a certain level and sufficient data has been accumulated to enable predictions using big data.

[0007] The inventors discovered that one of the challenges in accurately predicting material properties is thickness variation. Similar to the aforementioned variation in material strength, thickness also varies within a coil and between coils. To normalize this thickness variation, typical tensile tests convert the load into stress by dividing it by the cross-sectional area, and output this converted value as the material property. The cross-sectional area is the product of the test piece's width and thickness. Even for materials with the same breaking stress, a thicker plate will require a higher breaking load. Similarly, a thinner plate will require a lower breaking load. Similarly, even if the same load is applied at the time of breaking, different plate thicknesses will result in different breaking stresses.

[0008] In Patent Documents 1 and 2, the values ​​obtained by measurement are the molding reaction force and deformation amount during a specified molding process. In other words, Patent Documents 1 and 2 do not directly obtain material properties. Therefore, to obtain material property values ​​as numerical values, some kind of conversion is required. However, Patent Documents 1 and 2 do not describe such a method. Furthermore, according to the inventor's study, it is preferable to use plate thickness as a parameter, but Patent Documents 1 and 2 do not calculate plate thickness. Therefore, Patent Documents 1 and 2 may not be able to accurately predict material properties. Furthermore, the technology described in Patent Document 3 allows for evaluation of molded products within the production line. However, when a defect is detected, it is not possible to identify the cause of the defect.

[0009] The present invention has been made in light of the above points, and one of its objects is to provide a technology that makes it possible to easily and accurately obtain material properties that affect the dimensional accuracy of a press even within a press line.

[0010] In order to solve the problem, one aspect of the present invention is a method for obtaining material properties of a metal plate for press processing, which comprises performing a punching process on the metal plate, measuring the maximum punching load during the punching process and measuring the thickness of the metal plate, and obtaining the breaking stress of the metal plate from the measured maximum load and thickness.

[0011] According to an aspect of the present invention, by correcting the measured maximum load by the plate thickness, it is possible to easily and accurately determine the breaking stress (maximum stress) even within a press line. That is, according to an aspect of the present invention, it is possible to easily and accurately obtain the breaking stress, which is a material property that affects the dimensional accuracy of press forming. Furthermore, in an aspect of the present invention, measurements for determining the above material properties are obtained from a metal plate (blank) for pressing. Therefore, the obtained material properties are also high. As a result, it is possible to adjust the press conditions for forming a press-formed product using the measured material properties. Furthermore, by using an aspect of the present invention, it is possible to suppress deterioration of dimensional accuracy and the occurrence of forming defects.

[0012] FIG. 1 is a diagram illustrating a processing step according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a punching device according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example in which a punching device according to an embodiment of the present invention is integrally provided in a blanking die of a blanking device. FIG. 4 is a diagram illustrating a difference in punching load history due to differences in plate thickness of a metal plate. FIG. 5 is a diagram illustrating a punching load. FIG. 6 is a diagram illustrating an example of a correlation between a maximum punching load and a maximum stress (TS). FIG. 7 is a diagram illustrating an example of a correlation between a maximum punching load corrected by plate thickness and a maximum stress (TS).

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to a press line for press manufacturing. Therefore, in this embodiment, a portion of a metal plate near the area that will become a press-formed part (product) is punched for measurement. In this embodiment, this improves press accuracy. However, the present invention can also be used simply to measure the breaking stress (maximum stress) of a material. As will be described later, one of the features of the present invention is that the plate thickness is also taken into account as a parameter when calculating the breaking stress.

[0014] (Configuration) In the manufacturing equipment (manufacturing method) for press-formed products according to this embodiment, a press line includes a material property acquisition process 30 and a main forming process 32, as shown in FIG. 1 . The main forming process 32 is a process in which a metal plate to be pressed is press-formed into a target part shape (product shape) using a press device (press die). The press condition adjustment process 31 in FIG. 1 is a process in which the material properties acquired in the material property acquisition process 30 are fed back to the press conditions in the main forming process 32. The press condition adjustment process 31 is a process in which the press conditions in the main forming process 32 are adjusted using a known method. Note that the processing of each process, such as the press condition adjustment process 31, is controlled by a control unit (not shown).

[0015] <Material property acquisition process 30> As shown in Fig. 1, the material property acquisition process 30 includes a punching process 30A and a material property calculation process 30B. The processing of the material property acquisition process 30 is controlled by a control unit (not shown). That is, the device is configured such that the processing of each process is controlled by a control unit (not shown).

[0016] [Punching Process 30A] In the punching process 30A, a punching process is performed on a metal plate using a punching device. During the punching process, the maximum punching load is measured. In addition, a process for measuring the thickness of the metal plate is performed. In this embodiment, information on the maximum punching load and plate thickness is measured using a punching device, which will be described later. The punching process in this embodiment is preferably performed on a metal plate portion in a non-pressing region of the metal plate to be pressed. The non-pressing region is a region other than the region that will become the press-formed product (product). However, it is preferable that the non-pressing region is a region close to the region that will become the press-formed product (product). For this reason, a portion to be punched is selected from the metal plate (blank) to be used for this press forming.

[0017] For example, it is desirable to perform the punching process for measurement in a blanking process. The blanking process is a process in which a metal plate is blanked (trimmed) and shaped before the main forming process 32. The punching process for measurement is performed on the material of the portion discarded by blanking. This makes it possible to measure the punching load without deteriorating the yield. The portion discarded by blanking is a non-press area. Furthermore, the blanking process usually occurs before the press forming process. Therefore, the measured load can also be used to adjust the press conditions in subsequent processes. However, the punching process 30A performed for measurement is not limited to the blanking process. If there is a process that includes a portion that will not remain in the final product, it is possible to perform the measurement of this embodiment using that portion that will not remain in the final product.

[0018] <Punching Apparatus 1> The punching apparatus 1 will be described with reference to Figure 2. The punching apparatus 1 is an apparatus for punching a metal plate used in the punching process 30A. As shown in Figure 2, the punching apparatus 1 of this embodiment includes a lower mold 2 and an upper mold 3 arranged opposite each other in the punching direction, a load measuring unit 5, and a plate thickness measuring device 7. The lower mold 2 has an installation surface 2a on its upper surface. The installation surface 2a is a flat surface on which the metal plate is placed. The lower mold 2 has an opening 2A for punching. The opening 2A is a through hole that opens into the installation surface 2a. The corners of the opening 2A serve as lower blades for punching.

[0019] The metal plate 20 placed on the installation surface 2a is restrained by a plate holder (not shown). For ease of understanding, the plate holder is omitted from Figure 2 and other figures. The plate holder is intended to hold the material so that it does not move during punching. Therefore, any means of plate holder is acceptable as long as the purpose can be achieved. For example, the punching device 1 of this embodiment may be incorporated into the blanking die 42 in the blanking process (see Figure 3). In this case, the plate holder of the punching device 1 and the plate holder of the blanking die may be integrated into a single structure.

[0020] The upper die 3 is disposed opposite the lower die 2 in the punching direction. The upper die 3 is equipped with a punch 3A for punching. The punch 3A is disposed coaxially with the opening 2A and is capable of advancing and retreating toward the opening 2A. The upper end of the punch 3A is connected to an upper die body 3B. A load measuring unit 5 is interposed between the upper end of the punch 3A and the upper die body 3B. Reference numeral 4 denotes a retainer. The retainer 4 adjusts the gap between the upper end of the punch 3A and the upper die body 3B. In this example, the retainer 4 is disposed between the load measuring unit 5 and the upper die body 3B. Reference numeral 3C denotes a pilot pin.

[0021] The load measuring unit 5 is a load meter that measures the load applied to the punch 3A during punching. In this embodiment, the load measuring unit 5 is configured with a load cell. The load measuring unit 5 is capable of supplying measurement information to the calculation unit 10. The installation position, device configuration, and measurement means of the load measuring unit 5 are not important as long as the purpose can be achieved. Furthermore, the upper mold 3 has an extension portion 6 located to the side of the punch 3A. A plate thickness measuring device 7 is provided at the lower end of the extension portion 6. Note that the plate thickness measuring device 7 is attached to the upper mold 3 so that the lower part of the plate thickness measuring device 7 is located above the insertion portion on the tip side of the punch 3A when the punch 3A is inserted into the opening 2A.

[0022] The plate thickness measuring device 7 is a device for measuring the plate thickness of the metal plate 20 placed on the installation surface 2a of the lower mold 2. The plate thickness measuring device 7 of this embodiment consists of two displacement meters, a first displacement meter 7A and a second displacement meter 7B. The displacement meters are distance meters. The two displacement meters 7A and 7B are synchronized to measure a first distance L1 and a second distance L2, respectively. The first distance L1 is the distance to the metal plate 20. The second distance L2 is the distance to the installation surface 2a of the lower mold 2. The measurement direction is a direction perpendicular to the installation surface 2a. It is preferable that the two displacement meters 7A and 7B are set so that the distances to the installation surface 2a are equal to each other.

[0023] The first displacement gauge 7A is arranged to face the area of ​​the installation surface 2a where the metal plate 20 is placed. The second displacement gauge 7B is arranged to face the area of ​​the installation surface 2a other than the area where the metal plate 20 is placed. A plurality of first displacement gauges 7A and a plurality of second displacement gauges 7B may be provided. In this case, the average value of the measurements of the plurality of displacement gauges may be used for each of the first displacement gauges 7A and the second displacement gauges 7B. The distance between the upper mold 3 and the lower mold 2 and the distance between the upper mold 3 and the metal plate 20 are measured synchronously. The difference between these distances can then be calculated as the plate thickness. Each of the displacement gauges 7A and 7B supplies the measured measurement information to the calculation unit 10. Here, the displacement gauges 7A and 7B may be of either a contact type or a non-contact type.

[0024] Note that if one displacement meter can measure the first distance L1 and the second distance L2, only one displacement meter may be used. For example, it is possible to measure the distance L1 before the metal plate 20 is installed and the distance L2 after the metal plate 20 is installed, and determine the plate thickness from the difference between the two distances L1 and L2. Furthermore, the plate thickness measuring device 7 may be separate from the upper die 3. Here, the punching device 1 of this embodiment is configured so that the upper die body 3B moves toward the lower die 2 by a known load application device (not shown). The punching device 1 is configured so that punching is performed by this movement.

[0025] It is desirable that the punching shape is circular. A circular shape reduces bias in the load during punching. This allows for more precise measurement of the punching load. Furthermore, if the punching shape is circular, a uniform load is applied to the punch 3A during punching. Therefore, it is possible to prevent chipping of the punch 3A. However, the punching shape is not limited to a circular shape. The punching shape can be changed as needed.

[0026] The corners of the opening 2A of the lower die 2 function as a lower blade during punching. When the punched shape is circular, the opening 2A has a circular cross section. The opening 2A also has a specified clearance with respect to the punch 3A used for punching. The clearance is set, for example, to about 2% to 20% of the plate thickness. The clearance is preferably set to 5% to 15%. Regarding the lower die 2, consider the case where the punching device 1 of this embodiment is incorporated into a blanking die in a blanking process (see FIG. 3). In this case, the lower die 2 may be configured integrally with the lower die 40 of the blanking die.

[0027] FIG. 3 shows an example in which the punching apparatus 1 of this embodiment is integrated into a blanking die. In FIG. 3, reference numeral 40 denotes the lower die of the blanking die 42. Reference numeral 41 denotes the upper die of the blanking die 42. Reference numeral 41A denotes the upper blade of the blanking die 42. Reference numeral 43 denotes a common plate connecting the upper die 41 of the blanking die 42 and the upper die 3 of the punching apparatus 1 of this embodiment. Reference numeral 20A denotes the press area where pressing is performed in the main forming process 32. Reference numeral 20B denotes the non-press area. The load measurement by the load measuring unit 5 is triggered, for example, when the gap between the upper die 3 and the lower die 2 falls below a first threshold. Furthermore, measurement is terminated, for example, when the gap falls below a second threshold that is smaller than the first threshold. This enables measurement of the load during punching for each shot.

[0028] Here, it is assumed that the initial standby position of punch 3A is constant. In this case, the distance from punch 3A to the material surface is longer for thinner materials and shorter for thicker materials. Therefore, for thinner materials, the time from when the measurement start trigger is activated until punch 3A contacts the material is long. In other words, the time until a load is generated on punch 3A is long. Furthermore, this time is shorter for thicker materials (see Figure 4). This time difference is a value correlated with the plate thickness. Therefore, it can be used to correct the plate thickness. The relationship between time and punch 3A load is schematically shown in Figure 4. In other words, the time it takes for the load to rise varies depending on the plate thickness. This time difference is a parameter that represents the variation in plate thickness. Therefore, it can be used to correct the maximum plate thickness. However, to ensure prediction accuracy, it is desirable to directly measure the distances L1 and L2.

[0029] [Material property calculation process 30B] The material property calculation process 30B executes a process of calculating the breaking stress (maximum stress) of the metal plate 20 near the press from punching load information and plate thickness information. The punching load information and plate thickness information are calculated from the information measured in the punching processing process 30A. The material property calculation process 30B is executed by the calculation unit 10. As shown in FIG. 2, the calculation unit 10 includes a plate thickness calculation unit 10A, a maximum load calculation unit 10B, and a breaking stress calculation unit 10C. The plate thickness calculation unit 10A calculates the plate thickness from the difference between the distance information L1 and L2 measured synchronously by the first displacement meter 7A and the second displacement meter 7B. The maximum load calculation unit 10B calculates the maximum punching load from the load information continuously measured by the load measurement unit 5 during punching. The breaking stress calculation unit 10C performs processing to calculate the breaking stress (maximum stress) of the metal plate 20 from the plate thickness calculated by the plate thickness calculation unit 10A and the maximum punching load calculated by the maximum load calculation unit 10B.

[0030] In this embodiment, a punching test is performed on a metal plate 20 made of a material whose plate thickness and breaking stress are known in advance, and the punching load relative to the breaking stress is measured. Then, statistical processing is performed on the measurement information to obtain a correlation between the maximum punching load and plate thickness and the breaking stress. The breaking stress calculation unit 10C then references the correlation to obtain the breaking stress corresponding to the obtained maximum load and plate thickness.

[0031] The punching process for generating a correlation does not necessarily have to be performed within a press line. The punching process for generating a correlation can be performed in an independent test. For example, the punching process for a material with a known breaking stress can be performed as follows: Rectangular samples of approximately 200 mm x 200 mm are taken from multiple locations on multiple coils. Tensile test pieces and punched test pieces are taken from each of the rectangular samples. The tensile test pieces and punched test pieces taken from the same rectangular sample are then subjected to respective tests, assuming that they have the same material properties. The results can then be compared. However, the punching process for generating a correlation is not limited to this method.

[0032] Furthermore, in the punching test for generating the correlation, all plate thicknesses are measured before the test. Any method for measuring plate thickness can be used. For example, plate thickness can be measured directly using a micrometer or using an ultrasonic plate thickness gauge. Alternatively, the same method as the measurement method used in the press line can be used. For example, the breaking stress TS (maximum stress) obtained in the tensile test is used as the objective variable. Furthermore, the maximum load F during shear and plate thickness t obtained in the punching test are used as explanatory variables. Then, a calibration curve that constitutes the correlation between the two is created. For example, the calibration curve formula is expressed as the following formula (1): TS = αF / t + β (1)

[0033] Here, TS is the breaking stress (maximum stress). F is the maximum load during shearing. t is the plate thickness. α and β are numerical values ​​(coefficients) specific to each material. Furthermore, α and β in equation (1) are determined from the results of tensile tests and punching tests of materials whose material properties are known. This makes it possible to create a calibration curve. Using the calibration curve, it is possible to determine the maximum stress (breaking stress) of the material from the plate thickness measured using a mechanism installed in the press line and the maximum load during shearing. Note that the correlation is not limited to the calibration curve described above. A learning model is created by machine learning, using the maximum load and plate thickness as input data and breaking stress information as output data. This learning model may then be used as the correlation. A known learning method may be applied to machine learning.

[0034] <Pressing Condition Adjustment Step 31> The relationship between the maximum stress, the pressing conditions, and the dimensional accuracy of the pressed product is determined separately. Then, in the pressing condition adjustment step 31, the relationship is referenced, and the determined maximum stress is fed back to the pressing conditions to adjust the pressing conditions used in the main forming step 32. This makes it possible to improve the dimensional accuracy of the press-formed product. Possible pressing conditions to be adjusted include, for example, cushion pressure, pad pressure, and die standby position. However, the pressing conditions to be adjusted are not limited to these.

[0035] <Main Forming Step 32 > In the main forming step 32, the metal plate 20 is press-formed into a target part shape using a press die under the press conditions adjusted in the press condition adjustment step 31.

[0036] (Operation and Others) Here, when a coil of metal plate is shipped, a material property test such as a tensile test is usually performed. The material property of the coil is then obtained through this material property test. However, the material property test is not performed over the entire length of the coil, but rather samples are taken from representative locations. For this reason, conventionally, only the representative material property of the coil is known. However, in reality, the material property has a certain range of variation within the coil compared to the representative material property. Furthermore, there is also a range of variation in the plate thickness within the coil. For this reason, the plate thickness is not uniform over the entire length of the coil.

[0037] To measure the precise material properties of the material along the entire length of the coil, it is necessary to conduct material property tests, such as tensile tests, along the entire length of the coil. However, collecting samples and conducting tests along the entire length of the coil is not practical from the standpoint of yield and cost. It is also possible to use a representative value within the coil as the material properties of the metal plate 20 (blank) to be pressed. In this case, since the precise material properties are unknown, there is a risk of variations in the quality of the press-formed product. In particular, the higher the material strength, the greater the variation in material properties, and the greater the impact on the press-forming results.

[0038] In contrast, in this embodiment, the maximum stress is obtained as a material property from material near the product (press-formed product) within the press line. This makes it possible to measure the maximum stress TS of the metal sheet 20 to be pressed into the press-formed product without using special samples or conducting material tests. Although the thickness of the sheet is not constant within the coil, the thickness does not usually change sharply. In other words, the thickness of the metal sheet cut from the coil for pressing can be considered to be approximately constant. Consider the case where precise material properties are known. In this case, it is advisable to determine the relationship between the material properties, press conditions, and dimensional accuracy in advance. By referring to this relationship and adjusting the press conditions according to the material properties, it is believed possible to consistently achieve high dimensional accuracy.

[0039] Previous studies have reported on the correlation between shear load and maximum stress in materials. The inventors used coils with multiple strength levels, collected test specimens from multiple locations on each coil, and performed circular punch tests on each specimen. They then investigated the relationship between shear load and maximum stress from the punch tests. The results of the investigation revealed that shear load and maximum stress exhibit a high correlation, consistent with conventional knowledge. However, they concluded that a more accurate prediction was necessary to achieve the objectives of the present invention. The inventors then investigated methods to further improve prediction accuracy beyond predictions based solely on shear load and came up with the following hypothesis: Shear load is a load, i.e., a force. In contrast, stress is the load divided by the cross-sectional area. Therefore, the two are being compared in different dimensions. The cross-sectional area of ​​a punch in a circular punch test is expressed as the product of the circumferential length and the plate thickness. Note that when the same punching punch 3A is used, the circumferential length can be considered to be the same.

[0040] From the above, it is believed that the variable not reflected in the current measurement method using punching is the plate thickness. Therefore, it is believed that taking the plate thickness into account will enable more precise prediction of the maximum stress. In other words, it is believed that correcting the load using the plate thickness will enable more precise prediction of the maximum stress. That is, in this embodiment, the correlation between the shear load and the maximum stress of the material is corrected using the plate thickness. This makes it possible to determine the maximum stress of the material with higher accuracy. In addition, the plate thickness is determined from the material near the metal plate to be pressed, and the maximum stress is obtained. As a result, it is possible to obtain the material properties (maximum stress) of the metal plate that will become the press-formed product with high accuracy. Then, by adjusting the press conditions for forming the press-formed product using the measured material properties, it is possible to suppress deterioration of dimensional accuracy and the occurrence of forming defects.

[0041] (Other) The present disclosure may also have the following configurations. (1) Disclosure 1 is a method for acquiring material properties of a metal plate for press working, comprising: performing a punching process on the metal plate, measuring a maximum punching load and a thickness of the metal plate during the punching process, and determining the breaking stress of the metal plate from the measured maximum load and thickness. (2) Disclosure 2 is a method for acquiring material properties of a metal plate for press working when the metal plate for press working is press-formed into a press-formed product, comprising: performing a punching process on a region of the metal plate other than a region that will become the press-formed product, measuring a maximum punching load and a thickness of the metal plate during the punching process, and determining the breaking stress of the metal plate from the measured maximum load and thickness. (3) Disclosure 3 discloses a method for acquiring material properties, which includes punching a metal plate made of a material whose thickness and breaking stress are known in advance, measuring the punching load relative to the breaking stress, determining a correlation between the maximum punching load and thickness and the breaking stress based on the measurement results, and determining the breaking stress corresponding to the measured maximum load and thickness by referring to the correlation. (4) Disclosure 4 discloses a method for generating a learning model using machine learning to determine the correlation, with the maximum punching load and thickness as input data and information on the breaking stress as output data. (5) Disclosure 5 discloses a method for manufacturing a press-formed product by press-forming a metal plate, in which, before the press forming, the breaking stress of the metal plate is determined using a metal plate portion other than the region that will become the press-formed product, using the method for acquiring material properties of Disclosure 2. (6) Disclosure 6 discloses a method for manufacturing a metal plate for press forming, which includes a blanking process before press forming the metal plate for press forming, in which the punching process is performed in the blanking process. (7) Disclosure 7 discloses a method for adjusting the press conditions for the press forming based on the determined breaking stress.(8) Disclosure 8 discloses a punching apparatus for punching a metal plate for press processing, the punching apparatus comprising: a lower die having a punching opening on an installation surface 2a on which the metal plate is placed; an upper die having a punch that can advance and retreat toward the opening; a load measuring unit that measures the load applied to the punch; and a thickness measuring device that measures the thickness of the metal plate placed on the lower die. (9) Disclosure 9 discloses the thickness measuring device, which is provided on the upper die, and measures a first distance to a surface of the metal plate placed on the installation surface and a second distance to the installation surface, and calculates the thickness of the metal plate from the first distance and the second distance. (10) Disclosure 10 discloses a manufacturing facility for press-formed products, the manufacturing facility comprising a press apparatus that press-forms a metal plate, the punching process being performed on the metal plate before press-forming. (11) Disclosure 11 discloses a non-pressed region of the metal plate other than the region that will become the press-formed product, which is set as the target for punching. (12) A blanking device is provided for blanking the metal plate before press forming, and the punching device is provided in a die of the blanking device.

[0042] An example according to this embodiment will be described. In the example, a punching test was performed using the punching device 1 of this embodiment. The test materials were materials with the strength levels and surface treatments shown in Table 1. Eight samples for each material were cut out for tensile tests and punching tests from various locations within the coil. This allowed for the representation of material variations within the coil. Samples cut out from the same location were assumed to have the same material properties, and the tensile test results were matched with the punching test results. This allowed for the tensile properties to be predicted through the punching test.

[0043]

[0044] Figure 5 shows an example of the measurement of the load of a certain sample. The punching load changes as shown in Figure 5. The maximum punching load during punching can be obtained from the continuously measured loads. Figure 6 also shows the relationship between the maximum punching load obtained from the punching test results and the maximum stress TS obtained from the tensile test. As mentioned above, it has long been known that there is a correlation between the parameters of the maximum punching load and the breaking stress (maximum stress). Figure 6 shows that a relatively good correlation is obtained between materials with different strength levels. However, it is difficult to say that the strength variation of materials with the same strength level can be accurately predicted. Therefore, it is clear that further improvement in accuracy is necessary for purposes such as improving dimensional accuracy.

[0045] FIG. 7 shows the results of correction made to the results shown in FIG. 6 . The correction results are the results of correcting the maximum punching load using the measured plate thickness based on the present disclosure. Comparing FIG. 6 and FIG. 7 reveals the following: By correcting for plate thickness, the overall correlation coefficient in FIG. 7 improved. At the same time, prediction accuracy improved even for materials with the same strength level. Therefore, the breaking strength (maximum stress) calculated from the measured maximum punching load and plate thickness is more accurate than in the past. Therefore, it was found that the breaking strength of the metal plate 20 for press work can be predicted with greater accuracy. Furthermore, the correlation accuracy of the calibration curves and other correlations between the maximum punching load and plate thickness and breaking strength, which were previously calculated, was high. Therefore, it was found that the breaking strength can be predicted with greater accuracy by using the calculated calibration curves and other correlations.

[0046] The entire contents of Japanese Patent Application No. 2024-101954 (filed June 25, 2024), from which this application claims priority, are incorporated herein by reference. While the present invention has been described with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

[0047] REFERENCE SIGNS LIST 1 punching device 2 lower die 2A opening 3 upper die 3A punch 5 load measurement unit 7 plate thickness measurement device 7A first displacement meter 7B second displacement meter 10 calculation unit 10A plate thickness calculation unit 10B maximum load calculation unit 10C breaking stress calculation unit 20 metal plate 30 material property acquisition process 30A punching process 30B material property calculation process 31 press condition adjustment process 32 main forming process 42 blanking die L1 first distance L2 second distance TS maximum stress (breaking stress)

Claims

1. A method for obtaining material properties of a metal plate for press working, comprising the steps of: punching the metal plate; measuring the maximum punching load during the punching process; and measuring the thickness of the metal plate; and obtaining the breaking stress of the metal plate from the measured maximum load and thickness.

2. A method for obtaining material properties to determine the breaking stress of a metal plate when the metal plate for press processing is press-formed into a press-formed product, comprising the steps of: punching an area of ​​the metal plate other than the area that will become the press-formed product; measuring the maximum punching load during the punching process; and measuring the thickness of the metal plate; and determining the breaking stress of the metal plate from the measured maximum load and thickness.

3. A method for acquiring material properties as described in claim 1 or claim 2, which comprises punching a metal plate made of a material whose thickness and breaking stress are known in advance, measuring the punching load relative to the breaking stress, determining the correlation between the maximum punching load and plate thickness and the breaking stress based on the measurement results, and then determining the breaking stress corresponding to the measured maximum load and plate thickness by referring to the correlation.

4. A method for acquiring material properties as described in claim 3, wherein a learning model is generated using machine learning to obtain the correlation, with the maximum punching load and plate thickness as input data and information on breaking stress as output data.

5. A method for manufacturing a press-molded product in which a press-molded product is manufactured by press-molding a metal plate, and before the press-molding, the breaking stress of the metal plate is obtained by the method for obtaining material properties set forth in any one of claims 1 to 4 using a metal plate portion in an area other than the area that will become the press-molded product.

6. A method for manufacturing a press-formed product according to claim 5, further comprising a blanking step prior to press-forming the metal plate for press-forming, wherein the punching step is carried out in the blanking step.

7. A method for producing a press-molded product according to claim 5 or claim 6, wherein the press conditions for the press molding are adjusted according to the determined breaking stress.

8. A punching device for punching a metal plate for press processing, comprising: a lower die having a punching opening on its installation surface on which the metal plate is placed; an upper die having a punch that can advance and retreat toward the opening; a load measuring unit that measures the load applied to the punch; and a thickness measuring device that measures the thickness of the metal plate placed on the lower die.

9. A punching device according to claim 8, wherein the plate thickness measuring device is provided on the upper die, measures a first distance to the surface of a metal plate placed on the installation surface, and measures a second distance to the installation surface, and calculates the thickness of the metal plate from the first distance and the second distance.

10. A manufacturing facility for press-formed products, comprising a press device for press-forming metal plates, and the punching device according to claim 8 or 9 for punching the metal plates before press-forming.

11. The press-formed product manufacturing equipment according to claim 10, wherein a non-press area of ​​the metal plate other than the area that will become the press-formed product is set as the target for punching.

12. The press-molded product manufacturing equipment according to claim 10, further comprising a blanking device for blanking the metal plate before press-molding, and the punching device is provided in a die of the blanking device.

Images