Press-forming analysis method, press-forming analysis device, and press-forming analysis program

Abstract

A press forming analysis method according to the present invention uses a finite element method, and predicts a press forming load using a die model 9 having an upper die model 11 and a lower die model 17 modeled by shell elements. The press forming analysis method comprises: an elastic body element-imparted lower die model creation step S1 in which a lower structure 7 of a press device is modeled by an elastic body element 15 and imparted to the lower die model 17 to create an elastic body element-imparted lower die model 13; an elastic coefficient determination step S3 of determining an elastic coefficient to be imparted to the elastic body element 15; and a press forming load acquisition step S5 of performing press forming analysis using the die model 9 including the elastic body element-imparted lower die model 13 modeled in the elastic body element-imparted lower die model creation step S1, to acquire the press forming load.

Description

Press forming analysis method, press forming analysis device, and press forming analysis program

[0001] The present invention relates to a press forming analysis method, a press forming analysis device, and a press forming analysis program that can predict press forming loads acting on a press die during press working of a metal member. The metal member may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a galvanized steel sheet that has been subjected to a surface treatment (such as electro-galvanizing, hot-dip galvanizing, or organic coating treatment), or may be a sheet made of various metals such as SUS, aluminum, or magnesium.

[0002] The use of high-tensile steel sheets in automobile bodies is expanding due to the growing need for lighter automobiles to improve fuel efficiency and collision safety. However, the application of high-tensile steel sheets faces challenges such as poor formability due to its low ductility and poor dimensional accuracy due to its high material strength.

[0003] Furthermore, since press forming of high-tensile steel sheets requires an increased press forming load, which requires changes to the press line or division of parts, this increased press forming load is also a factor hindering the application of high-tensile steel sheets. Therefore, a press forming analysis method that can accurately predict the press forming load in advance is required.

[0004] It is also known that the forming state of a metal member using a press die varies depending on the structure of the press device. The inventors have confirmed that even when the same press die is used for press forming, the press forming load varies depending on the structure of the press device. Therefore, in order to accurately predict the press forming load, it is necessary to take into account the structure of the press device.

[0005] In this regard, Patent Document 1 proposes a method of calculating the press forming load from an approximation formula by calculating the correlation between the forming load at the bottom dead center of a press in an actual machine and the forming load at a stroke before the bottom dead center in a forming analysis. Also, Patent Document 2 proposes a press forming analysis method that takes into account the elastic deformation of a press device.

[0006] Japanese Patent No. 5610574 Japanese Patent Application Laid-Open No. 2022-121024

[0007] However, the method described in Patent Document 1 requires results of press forming loads on an actual machine, and is unable to predict press forming loads for new part shapes and materials in advance. Furthermore, the method described in Patent Document 2 is a method in which the elastic deformation of the press machine when a constant load is applied is applied to the forming analysis as deformation of the shape of the press die, and is unable to predict press forming loads.

[0008] The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a press forming analysis method, a press forming analysis device, and a press forming analysis program that can predict press forming loads in advance, even for new part shapes and materials.

[0009] The press forming analysis method according to the present invention is a method for predicting a press forming load using a die model having an upper die model and a lower die model modeled with shell elements, using the finite element method, and includes an elastic body element-added lower die model creation step of modeling the lower structure of a press device with elastic body elements and adding them to the lower die model to create an elastic body element-added lower die model, an elastic coefficient determination step of determining an elastic coefficient to be applied to the elastic body element, and a press forming load acquisition step of performing press forming analysis using a die model including the elastic body element-added lower die model modeled in the elastic body element-added lower die model creation step to acquire the press forming load.

[0010] In the elastic modulus determination step, the elastic modulus may be determined by measuring the distribution of reaction forces and displacements of an actual press due to a load applied to the press, by modeling the press using three-dimensional solid elements and determining the distribution of reaction forces and displacements by rigidity analysis of the displacements due to the load, or by modeling the press using two-dimensional shell elements and determining the distribution of reaction forces and displacements by rigidity analysis of the displacements due to the load.

[0011] The elastic coefficient may be calculated from the distribution of reaction forces obtained in the elastic coefficient determination step, and set to the elastic element at the corresponding position.

[0012] The elastic coefficient may be a value calculated from the average of the distribution of the reaction forces determined in the elastic coefficient determination step, and set in the elastic element.

[0013] When the mold is an insert type, it is preferable that only the insert block in the lower mold model that is involved in the actual molding be modeled by adding elastic elements in the elastic element-adding lower mold model creation process.

[0014] The press forming analysis device according to the present invention predicts press forming loads using a mold model having an upper mold model and a lower mold model modeled with shell elements, and comprises an elastic element-added lower mold model creation unit that models the lower structure of the press device with elastic elements and adds them to the lower mold model to create an elastic element-added lower mold model, an elastic coefficient determination unit that determines the elastic coefficient to be applied to the elastic elements, and a press forming load acquisition unit that performs press forming analysis using a mold model including the elastic element-added lower mold model and acquires the press forming load.

[0015] The press forming analysis program according to the present invention causes a computer to function as the press forming analysis device according to the present invention.

[0016] According to the present invention, press forming loads can be predicted in advance by press forming analysis, even for new part shapes and materials, which in turn makes it possible to appropriately allocate the part forming processes and select the appropriate press equipment for producing the part.

[0017] FIG. 1 is a flowchart of a press forming analysis method according to a first embodiment. FIG. 2 is a diagram schematically illustrating a press apparatus and a die. FIG. 3 is a diagram illustrating a die model obtained by modeling the press apparatus and die shown in FIG. 2. FIG. 4 is an explanatory diagram of die types and corresponding lower die models with elastic elements. FIG. 5 is an explanatory diagram of a method for determining an elastic coefficient. FIG. 6 is a block diagram illustrating the configuration of a press forming analysis device according to a second embodiment. FIG. 7 is an explanatory diagram of a part shape to be formed in Example 1. FIG. 8 is an explanatory diagram of a die model used as a conventional example in Example 1. FIG. 9 is an explanatory diagram of a part shape to be formed in Example 2. FIG. 10 is an explanatory diagram of an actual die used in Example 2. FIG. 11 is an explanatory diagram of a die model obtained by modeling the actual die shown in FIG. 10.

[0018] <Background to the Invention> When the inventors were studying a press forming analysis method that can predict press forming loads taking into account the structure of a press device using press forming analysis with the finite element method, they first studied the phenomenon in which the press forming loads differ depending on the structure of the press device.

[0019] Through press forming tests using actual machines and investigations using press forming analysis, we found that the difference in press forming load depending on the structure of the press machine is due to the difference in the amount of elastic deformation during press forming of the lower structure of the press machine on which the lower die is installed. In other words, when the press die elastically deforms due to the reaction force during press forming, the lower structure of the press machine on which the press die is installed also elastically deforms, but the amount of elastic deformation of this lower structure differs depending on the structure of the press machine, and this is the cause of the difference in press forming load. We also found that the upper structure of the press machine also elastically deforms, but the effect is smaller than that of the lower structure.

[0020] Regarding the elastic deformation of the press machine, press forming analysis has been carried out in which the structure of the press machine is represented using non-rigid solid elements (three-dimensional elements) and the deformation of the press machine is taken into account, but this requires enormous calculation time and is not suitable for practical use.On the other hand, analysis using shell elements, which has a fast calculation time and is used in practice, models only the surface of the die, so it is not possible to reproduce the actual state where the die and the lower structure of the press machine come into contact, and it is not possible to take the elastic deformation of the press machine into account.

[0021] Therefore, in order to shorten the calculation time and to express the difference in elastic deformation of the lower structure, we concluded that it would be best to model the lower structure of the press device as an elastic body, set an appropriate elastic coefficient using boundary conditions, and assign it to the shell element mold model.

[0022] The present invention has been made based on the results of the above investigation, and specific embodiments thereof will be described below.

[0023] [Embodiment 1] A press-forming analysis method according to this embodiment is a press-forming analysis method for predicting a press-forming load using a die model having an upper die model and a lower die model modeled with shell elements, and includes an elastic element-applied lower die model creation step (S1), an elastic coefficient determination step (S3), and a press-forming load acquisition step (S5), as shown in Fig. 1. Each step will be described in detail below.

[0024] <Process for creating a lower mold model with elastic elements> The process S1 for creating a lower mold model with elastic elements is a process for creating a lower mold model with elastic elements by adding the lower structure of a press device as an elastic element to a lower mold model modeled with shell elements.

[0025] The actual devices involved in the elastic element-imparted lower die model creation step S1 are the lower structure of a press machine and the lower die of a die, and these will be described with reference to Figure 2, which schematically shows an actual die 1 and lower structure 7 of the press machine. The die 1 is composed of an upper die 3 and a lower die 5. As shown in Figure 2, the press machine includes a lower structure 7 and an upper structure (not shown), and the lower structure 7 has a riser 7b provided on a bolster 7a, the lower die 5 is installed on the riser 7b, and the upper die 3 is attached to the upper structure.

[0026] Figure 3 is a model of the press machine and mold shown in Figure 2, and the color coding of the dashed lines in Figure 2 corresponds to the color of the dashed lines in Figure 2. That is, the light gray dashed line indicates the mold 1 (mold model 9), and the black dashed line indicates the lower structure 7 of the press machine (elastic elements 15). As shown in Figure 3, the mold model 9 is composed of an upper mold model 11 and a lower mold model 13 with elastic elements, and the lower structure 7 is modeled with elastic elements 15 as an elastic body and is attached to a lower mold model 17 modeled with shell elements.

[0027] The differences in the setting method of the elastic element 15 due to differences in the shape of the lower mold 5 will be explained with reference to Fig. 4. Fig. 4(a) is a diagram showing the front surface of the lower mold 5 of an actual mold 1, and Fig. 4(b) shows the shape of the back surface side. In Fig. 4(b), (b-A) shows mold A (solid) whose back surface side is solid, and (b-B) shows mold B (hollow) whose back surface side is hollow.

[0028] 4(c) is a schematic diagram showing the cross-sectional shapes of mold A and mold B, with thick black lines indicating the areas between the lower structure 7 and the lower mold 5 where the elastic elements 15 are applied. As shown in (c-A) of FIG. 4(c), in the case of mold A, the lower mold 5 comes into contact with the lower structure 7 of the press device over the entire surface, so the elastic elements 15 are applied to the entire back surface. On the other hand, as shown in (c-B) of FIG. 4(c), in the case of mold B, the lower mold 5 comes into contact with the lower structure 7 only at the bottoms of the peripheral and central groove-shaped portions, so the elastic elements 15 are applied only to the areas of contact.

[0029] Fig. 4(d) shows the back surface of the elastic element-added lower mold model 13 to which the elastic elements 15 have been added in the areas shown in Fig. 4(c). In (d-A) of Fig. 4(d), it can be seen that the elastic elements 15 have been added to the entire back surface of the elastic element-added lower mold model 13, and in (d-B), it can be seen that the elastic elements 15 have been added to the periphery and central groove bottom back surface areas of the elastic element-added lower mold model 13.

[0030] <Elastic Coefficient Determination Step> The elastic coefficient determination step S3 is a step of determining an elastic coefficient to be applied to the elastic element 15 that models the lower structure 7. The elastic coefficient may be determined by measuring the distribution of reaction forces and displacements generated in the lower structure 7 of the press due to a load applied to the actual press. Alternatively, the press may be modeled using three-dimensional solid elements, the displacement due to the load applied is determined by rigidity analysis, and the distribution of reaction forces and displacements at that time is determined. In this case, as shown in FIG. 5 , one example of a specific method for calculating the elastic coefficient is to model the lower structure 7 of the press using solid elements, and the elastic coefficient is calculated by dividing the sum of reaction forces generated by forcibly pressing the lower mold 5 within the range of the press using a displacement by the area of ​​contact between the lower mold 5 and the lower structure 7. Alternatively, the press may be modeled using two-dimensional shell elements, and the distribution of reaction forces and displacements due to the load applied is determined by rigidity analysis.

[0031] Regarding the setting of the elastic coefficients to the elastic body elements 15, the elastic coefficients calculated from the reaction forces and displacements at each measurement position when a load is applied to the press device may be set to the elastic body elements 15 at the corresponding positions. Alternatively, the elastic coefficients calculated from the average reaction forces, which are obtained by dividing the sum of the reaction forces generated when a load is applied to the press device by the area on which the load is applied, and the displacement may be set to all the elastic body elements 15.

[0032] <Press-forming load acquisition step> The press-forming load acquisition step S5 is a step of performing a press-forming analysis using the die model 9 including the elastic element-applied lower die model 13, and acquiring the press-forming load.

[0033] According to the press forming analysis method of this embodiment, press forming loads can be predicted in advance even for new part shapes and materials. Furthermore, because the lower structure 7 of the press is modeled using elastic elements 15 and attached to the lower die model 17, which is modeled using shell elements, the calculation time is not as long as in press forming analysis, which represents the structure of the press using non-rigid solid elements (three-dimensional elements) and takes into account the deformation of the press. Furthermore, as a result of being able to predict press forming loads in advance, it becomes possible to appropriately allocate the processes for forming the part and select the appropriate press for producing the part.

[0034] [Embodiment 2] The press forming analysis method described in Embodiment 1 can be realized by causing a computer to execute a preset program. A press forming analysis device, which is an example of such a device, will be described in this embodiment. As shown in FIG. 6 , the press forming analysis device 21 according to this embodiment is configured by a computer such as a PC (personal computer), and includes a display device 23, an input device 25, a storage device 27, a working data memory 29, and a processing unit 31. The display device 23, the input device 25, the storage device 27, and the working data memory 29 are connected to the processing unit 31, and each function is executed in response to a command from the processing unit 31. Hereinafter, each component of the press forming analysis device 21 according to this embodiment will be described.

[0035] <Display Device> The display device 23 is used to display the analysis results and is configured with a liquid crystal monitor or the like.

[0036] <<Input Device>> The input device 25 is used for display instructions for blanks, press-molded products, etc., and for inputting conditions by an operator, and is composed of a keyboard, a mouse, etc.

[0037] <Storage Device> The storage device 27 is used to store various files such as die CAD data, shape files of blanks and press-molded products, and is configured with a hard disk or the like.

[0038] <Working Data Memory> The working data memory 29 is used for temporary storage of data used by the arithmetic processing unit 31 and for calculations, and is composed of RAM (Random Access Memory) and the like.

[0039] 6, the calculation processing unit 31 has an elastic body-applied lower die model creation unit 33, an elastic coefficient determination unit 35, and a press-forming load acquisition unit 37, and is configured by a CPU (Central Processing Unit). Each of these units functions when the CPU executes a predetermined program. The functions of each of the above units in the calculation processing unit 31 will be described below.

[0040] The elastic body-imparted lower die model creation unit 33 creates the elastic body element-imparted lower die model 13 by adding the lower structure 7 of the press device as the elastic body element 15 to the lower die model 17 modeled with shell elements, and executes the elastic body-imparted lower die model creation step S1 described in embodiment 1. The die model 9 consisting of the upper die 3 and the lower die 5 is created by the shell elements by a die model creation unit (not shown).

[0041] The elastic coefficient determination unit 35 determines the elastic coefficient to be applied to the elastic element 15 that models the lower structure 7, and executes the elastic coefficient determination step S3 described in the first embodiment.

[0042] The press forming load acquisition unit 37 performs press forming analysis using the mold model 9 including the elastic element-added lower mold model 13 to acquire the press forming load, and executes the press forming load acquisition process S5 described in embodiment 1.

[0043] According to the press forming analysis device 21 of this embodiment, as in the first embodiment, even for new part shapes and materials, the press forming load can be predicted in advance, and the calculation time does not become enormous.

[0044] As described above, the elastic body-applied lower die model creation unit 33, the elastic coefficient determination unit 35, and the press forming load acquisition unit 37 in the press forming analysis device 21 of this embodiment are realized by the CPU executing a predetermined program. Therefore, the press forming analysis program according to the present invention can be specified as causing a computer to function as the elastic body-applied lower die model creation unit 33, the elastic coefficient determination unit 35, and the press forming load acquisition unit 37.

[0045] A specific press forming analysis was performed to verify the effects of the present invention, and is described below. Figure 7 shows the part geometry of Example 1. The part was made of cold-rolled 1180 MPa-class high-tensile steel plate with a thickness of 1.6 mm. As an example of the invention, a die model 9 including a lower die model 13 with elastic body elements, as shown in Figure 3, was used. Three different sizes of press machines (press machines (1), (2), and (3)) were assumed, and the die types used were a solid Type A (die A) and a hollow Type B (die B) shown in Figure 4. The elastic coefficients of the elastic body elements 15 of press machines (1), (2), and (3) were set as shown in Table 1. As described in Figure 5, the lower structure 7 of the press machine was modeled with solid elements, and the elastic coefficient was calculated by dividing the sum of the reaction forces generated by forcibly pressing the die 1 within its range by the area of ​​contact between the die 1 and the lower structure 7.

[0046]

[0047] As a conventional example, an analysis was performed using a die model 41 in which the upper die 3 and lower die 5 of a press die, which are currently commonly used in forming analysis of automobile presses, are modeled as rigid bodies made of shell elements. This conventional die model 41 is shown in Figure 8. The upper die model 43 and lower die model 45 are made of shell elements, and the lower structure model 47 is also modeled as a rigid body made of shell elements. A press forming test was also performed using an actual machine. The analysis results are shown in Table 2.

[0048]

[0049] <Press device (1)> In press device (1), the load in the actual press forming test of die A was 1630 kN, while the press forming load predicted by the conventional method was 4428 kN, resulting in an error of 171% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 1747 kN, resulting in an error of 7% from the actual press forming test.

[0050] Furthermore, while the actual press forming test load for die B was 1286kN, the press forming load predicted by the conventional method was 4428kN, with an error of 244% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 1382kN, with an error of 7% from the actual press forming test.

[0051] <Press device (2)> For press device (2), the actual press forming test load for die A was 2222kN, while the press forming load predicted by the conventional method was 4428kN, with an error of 99% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 2156kN, with an error of 3% from the actual press forming test.

[0052] Furthermore, while the actual press forming test load for die B was 1527kN, the press forming load predicted by the conventional method was 4428kN, with an error of 190% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 1619kN, with an error of 6% from the actual press forming test.

[0053] <Press device (3)> In press device (3), the load in the actual press forming test of die A was 1563kN, while the press forming load predicted by the conventional method was 4428kN, with an error of 183% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 1535kN, with an error of 2% from the actual press forming test.

[0054] Furthermore, while the actual press forming test load for die B was 1323kN, the press forming load predicted by the conventional method was 4428kN, with an error of 235% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 1296kN, with an error of 2% from the actual press forming test.

[0055] As described above, it can be seen that the proposed method (invention example) is extremely superior to the conventional method in all cases.

[0056] Figure 9 shows the part shape targeted in Example 2. The part is made of cold-rolled 1470 MPa-class high-tensile steel plate, with a thickness of 1.2 mm. Figure 10 shows the die structure of Example 2. The die of Example 2 has a divided structure using an insert method. Figure 10(a) shows the upper die 3, and the part to be formed is the insert block 49. Figure 10(b) shows the appearance of the insert block 49 portion of the punch, and Figure 10(c) shows cross sections of die C (c-C) when the punch is a solid block, and die D (c-D) when the punch is a hollow block.

[0057] Figure 11 shows a mold model 9 in which only the insert block 49 shown in Figure 10 is modeled. In Figure 11, parts corresponding to those in Figure 3, which shows the mold model 9 of Example 1, are given the same reference numerals. Figure 11(a) is a perspective view of the mold model 9 seen from above, and includes an upper mold model 11, a blank model 51, a blank holder model 53, and a lower mold model 13 with elastic elements. In Figure 11, each part of the upper mold model 11 is color-coded gray, but this is a specification of the software used and has no special meaning in relation to the present invention.

[0058] Figure 11(b) shows the mold model 9 as seen from below, Figure 11(b-C) shows mold C, which is a solid block, and Figure 11(b-D) shows mold D, which is a hollow block.

[0059] The elastic coefficient of the elastic element 15 representing the press device (4) used was determined by dividing the sum of the reaction forces when a displacement was applied to the lower structure 7 in the same analysis as in Example 1 by the installation area of ​​the holder of the insert block 49 of each of the molds C and D. The set elastic coefficients are shown in Table 3.

[0060]

[0061] As a conventional example, an analysis was performed using a die model in which the upper and lower insert blocks 49 of a press die were modeled as rigid bodies made of shell elements, which is currently commonly used in forming analysis of automobile presses. Furthermore, a press forming test was also performed using an actual machine, as in Example 1. The analysis results are shown in Table 4.

[0062]

[0063] The actual press forming test load for die C in press device (4) was 1976kN, while the press forming load predicted by the conventional method was 6214kN, with an error of 314% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 2065kN, with an error of 5% from the actual press forming test.

[0064] Furthermore, while the actual press forming test load for die D was 1885kN, the press forming load predicted by the conventional method was 6214kN, with an error of 330% from the actual press forming test. In contrast, the press forming load predicted by the proposed method (invention example) was 2017kN, with an error of 7% from the actual press forming test.

[0065] As described above, under all conditions, the press forming load predicted by the proposed method (example of the invention) had a smaller error with the actual press forming test than the press forming load predicted by the conventional method, demonstrating that the accuracy of press forming load prediction was improved.

[0066] According to the present invention, it is possible to provide a press forming analysis method, a press forming analysis device, and a press forming analysis program that can predict the press forming load in advance even for new part shapes and materials.

[0067] REFERENCE SIGNS LIST 1 Die 3 Upper die 5 Lower die 7 Lower structure 7a Bolster 7b Riser 9 Die model 11 Upper die model 13 Lower die model with elastic element 15 Elastic element 17 Lower die model 21 Press forming analysis device 23 Display device 25 Input device 27 Storage device 29 Working data memory 31 Arithmetic processing unit 33 Lower die model with elastic element creation unit 35 Elastic coefficient determination unit 37 Press forming load acquisition unit 41 Die model (conventional example) 43 Upper die model (conventional example) 45 Lower die model (conventional example) 47 Lower structure model (conventional example) 49 Insert block 51 Blank model 53 Blank folder model

Claims

1. A press forming analysis method for predicting press forming loads using a die model having an upper die model and a lower die model modeled with shell elements, using the finite element method, comprising: an elastic-element-added lower die model creation step of modeling a lower structure of a press device with elastic elements and adding the elastic elements to the lower die model to create an elastic-element-added lower die model; an elastic coefficient determination step of determining an elastic coefficient to be applied to the elastic elements; and a press forming load acquisition step of performing press forming analysis using a die model including the elastic-element-added lower die model modeled in the elastic-element-added lower die model creation step to acquire the press forming load.

2. The press forming analysis method according to claim 1, wherein in the elastic coefficient determination step, the elastic coefficient is determined by one of the following: measuring the distribution of reaction force and displacement of the press due to the load applied to the actual press; modeling the press using three-dimensional solid elements, determining the displacement due to the load applied by rigidity analysis, and determining the distribution of reaction force and displacement at this time; or modeling the press using two-dimensional shell elements, determining the displacement due to the load applied by rigidity analysis, and determining the distribution of reaction force and displacement at this time.

3. The press forming analysis method according to claim 2, wherein the elastic coefficient is calculated from the distribution of reaction forces obtained in the elastic coefficient determination step and set in the elastic body element at the corresponding position.

4. A press forming analysis method according to claim 2, wherein the elastic coefficient is a value calculated from the average of the distribution of reaction forces obtained in the elastic coefficient determination step, and is set in the elastic body element.

5. A press molding analysis method as described in claim 1, in which, when the mold is an insert type, only the insert block involved in the actual molding in the lower mold model is modeled by adding elastic elements in the elastic element-added lower mold model creation process.

6. A press forming analysis device that predicts press forming loads using a die model having an upper die model and a lower die model modeled with shell elements, comprising: an elastic element-added lower die model creation unit that models a lower structure of a press device with elastic elements and adds them to the lower die model to create an elastic element-added lower die model; an elastic coefficient determination unit that determines the elastic coefficient to be applied to the elastic elements; and a press forming load acquisition unit that performs press forming analysis using a die model including the elastic element-added lower die model and acquires the press forming load.

7. A press forming analysis program that causes a computer to function as the press forming analysis device according to claim 6.

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