Method for evaluating buckling, device for evaluating buckling, program, and method for manufacturing panel component

Abstract

The present invention makes it possible to evaluate buckling of a panel component before assembly to another component through simple molding analysis. Provided is a method for evaluating buckling in which buckling prior to assembly of a panel component obtained by press molding a plate material into a three-dimensional form is evaluated through molding analysis using a computer. This method for evaluating buckling comprises: a press molding analysis step (20A) for performing press-molding analysis in which the plate material is formed into the panel component, and acquiring the panel shape after mold release as a reference panel shape (10); a self-weight analysis step (20B) for performing self-weight analysis with respect to the reference panel shape (10) in a condition in which the panel component is placed on a flat surface, and acquiring the panel shape after deformation resulting from the weight of the panel component as an evaluation panel shape (11); and a buckling evaluation step (20C) for evaluating buckling of the panel component having the evaluation panel shape (11).

Description

Detachment evaluation method, detachment evaluation device, program, and panel component manufacturing method

[0001] The present invention relates to a technology for evaluating the presence or absence of dents in a panel component formed by press-forming a sheet material into a three-dimensional shape, prior to assembly with other components, through computer-assisted forming analysis. Hereinafter, computer-assisted forming analysis will also be referred to as CAE analysis. The panel component targeted by the present invention is not limited to automobile components. The present invention can be applied to any panel component manufactured by press-forming a sheet material into a three-dimensional shape. Furthermore, the material of the panel component is not limited to steel. The present invention can also be applied to panel components made of iron alloys such as stainless steel, as well as non-ferrous and non-metallic materials.

[0002] A conventional method for analyzing dents is described in, for example, Patent Document 1. The method described in Patent Document 1 obtains the tension stiffness distribution by applying a load toward the back side of an evaluation panel. Then, the position of dents on the panel surface is identified from the tension stiffness distribution. Patent Document 1 also describes estimating the position of dents based on the product shape when predicting the stiffness of panel components during transport. It also describes using this method to predict whether dents will occur when the panel surface is gripped and transported by a suction device.

[0003] Japanese Patent Application Laid-Open No. 2020-201827

[0004] Before assembly, panel components may develop dents during transport. If dents develop in a panel component, this may result in plastic deformation (permanent distortion) of the panel component. If plastic deformation occurs, the panel component will no longer meet the required surface precision for a product, and the panel component may need to be disposed of or otherwise treated. However, in Patent Document 1, the panel shape used to predict dents is the product shape or the panel shape after springback. Note that in Patent Document 1, the panel shape used to predict dents is the panel shape of the panel component as it is transported by the suction means.

[0005] However, the inventors' investigations have led to the following findings regarding the occurrence of dents in thin panel components. The above-mentioned thin panel components are, for example, panel components with dimensions exceeding 1000 mm x 1000 mm, or panel components with a thickness of 1.5 mm or less. In other words, the inventors have found that the dent analysis results for the product shape and the panel shape after springback based on press forming analysis may differ from the dent conditions that occur in actual panel components on-site. Furthermore, the dent evaluation itself would be complicated if the actual shape of each panel immediately before transport were to be measured and evaluated individually in a storage area immediately before transport.

[0006] The present invention focuses on the above points and aims to make it possible to evaluate the occurrence of dents in panel components before assembly through a simple molding analysis.

[0007] In order to solve the problem, one aspect of the present invention is a dent evaluation method that evaluates dents in a panel component formed by press-molding a sheet material before assembly to another component by forming analysis using a computer, the dent evaluation method comprising: a press-molding analysis step that performs a press-molding analysis using the sheet material as the panel component and obtains the panel shape after release from the mold as a reference panel shape; a weight analysis step that performs a weight analysis of the reference panel shape under conditions where the panel component is placed on a flat surface and obtains the panel shape after deformation due to its weight as an evaluation panel shape; and a dent evaluation step that evaluates dents in the panel component with the evaluation panel shape.

[0008] According to an aspect of the present invention, simply by adding a weight analysis, it is possible to easily and in advance evaluate the likelihood of dents in a panel component before assembly using computer-based CAE analysis. The dent evaluation in this specification is performed, for example, by applying a load from the back side to the front side. The load for evaluation may also be applied from the front side to the back side. However, if the dents in an actual panel component after pressing before assembly cannot be reproduced using CAE analysis, the following problem arises. That is, if it is estimated that dents will occur, it is necessary to modify the panel shape by taking measures such as adding a shape to the estimated position. However, in the past, it was not easy to determine whether the modified panel shape would actually suppress dents. In this case, there is a risk that repeated die modifications and press molding would be necessary, resulting in significant losses in cost and time. In contrast, an aspect of the present invention can solve this problem.

[0009] 1 is a diagram illustrating an example of the configuration of a dent evaluation device according to an embodiment of the present invention; FIG. 2 is a diagram illustrating an example of the configuration of an evaluation panel shape determination unit; FIG. 3 is a diagram illustrating an example of the configuration of a program for performing dent evaluation; FIG. 4 is a diagram illustrating the shape of an actual panel part in an embodiment; FIG. 5 is a diagram illustrating weight analysis; (a) is a side view showing the shape before weight analysis, and (b) is a side view showing the shape after weight analysis; FIG. 6 is a plan view showing a displacement application position F1 and evaluation points P1 and P2 in an embodiment; FIG. 7 is a diagram illustrating the amount of variation from a product (actual panel part); (a) is a diagram illustrating the amount of variation in an actual part; (b) is a diagram illustrating the amount of variation in a panel shape after springback; (c) is a diagram illustrating the amount of variation in a panel shape after weight analysis; and FIG. 8 is a diagram illustrating the results of a CAE analysis of dents at evaluation point P1; (a) is the CAE analysis result for the product shape; (b) is the analysis result for the actual part shape; (c) is the CAE analysis result for the panel shape after springback; and (d) is the CAE analysis result for the panel shape after weight analysis. 1 is a plan view showing an example of a shape after addressing the dent at evaluation point P1. FIG. 2 is a diagram showing the CAE analysis results for the dent at evaluation point P2. (a) is the CAE analysis result for the product shape. (b) is the analysis result for the actual part shape. (c) is the CAE analysis result for the panel shape after springback. (d) is the CAAE analysis result for the panel shape after weight analysis. FIG. 3 is a plan view showing an example of a shape after addressing the dent at evaluation point P2. FIG. 4 is a diagram showing the procedure of a manufacturing method for a panel component according to an embodiment based on the present invention.

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. The presence or absence of dents in an actual panel component after pressing is confirmed on a jig or at the assembly location of the pressed panel component. The inventors discovered that the on-site dent evaluation of the panel component before assembly with other components differs from the dent evaluation of the shape after springback calculated by CAE analysis. After repeated investigations, the inventors obtained the following findings: In thin, large panel components, the panel component deflects due to its own weight before assembly. This indicates that the panel shape after springback calculated by CAE analysis must be evaluated taking into account the effect of deflection due to its own weight. The above-mentioned thin, large panel components refer to panel components with dimensions exceeding 1000 mm x 1000 mm or panel components with a thickness of 1.5 mm or less.

[0011] Based on this knowledge, in this embodiment, it was considered to perform a dent analysis using CAE analysis on a panel shape that takes into account the influence of its own weight. This embodiment is designed to enable accurate determination of dents in panel components before assembly through such dent analysis. Furthermore, since this embodiment simply adds a weight analysis, evaluation can be easily performed using a computer-based forming analysis. Note that evaluation of dents in assembled panel components is performed, for example, assuming pressure when the outer periphery is constrained. In contrast, evaluation of dents in panel components before assembly is performed, for example, assuming vibration input during transportation when the outer periphery is not constrained.

[0012] (Detachment Evaluation Device 1) The dentation evaluation device 1 of this embodiment is a device that evaluates dents before assembly of a panel component formed by press-forming a sheet material into a three-dimensional shape. The dentation evaluation device 1 of this embodiment evaluates dents before assembly through forming analysis using a computer. Therefore, the processing of the dentation evaluation device 1 can be configured as a program executed by a computer. As shown in FIG. 1, the dentation evaluation device 1 of this embodiment includes a press-forming analysis unit 2, an evaluation panel shape determination unit 3, and a dent evaluation unit 4. The dentation evaluation device 1 may also include a panel shape modification unit 6 shown in FIG. 1.

[0013] <Press-forming analysis unit 2> The press-forming analysis unit 2 constitutes the press-forming analysis step. The press-forming analysis unit 2 acquires information on the sheet material to be evaluated and the press-forming conditions. The press-forming conditions include, for example, the target part shape and the press-forming method. The press-forming analysis unit 2 then performs press-forming analysis using a blank model of the sheet material to be evaluated and the set die model. The shape of the press-formed product after demolding is then defined as the reference panel shape 10.

[0014] The set die model is set using a known method based on the molding surface shape of an actual die that press-forms a blank made of plate material into a target part shape. For example, a die model that follows the target part shape is set as the set die model. However, a die model that is corrected for springback after demolding is preferred as the set die model. The above press molding analysis includes two analyses: an analysis that obtains the panel shape at the bottom dead center during press molding, and an analysis that obtains the shape after demolding, i.e., after springback.

[0015] Press forming analysis is usually performed using CAE analysis such as the finite element method (FEM). Therefore, the above press forming analysis can be performed using a computer-assisted structural analysis, such as a known CAE analysis. The reference panel shape 10 after demolding varies from the bottom dead center of the mold due to demolding. This variation can be determined by press forming analysis. Applicable press forming methods in this example include form forming and draw forming. The present invention can be applied to any of these press forming methods.

[0016] <Evaluation Panel Shape Determination Unit 3> The evaluation panel shape determination unit 3 is a processing unit that determines the evaluation panel shape 11. The evaluation panel shape 11 is a panel shape for evaluating bumps. As shown in FIG. 2, the evaluation panel shape determination unit 3 includes a dimension evaluation unit 3A and a shape modification unit 3C.

[0017] [Dimension Evaluation Unit 3A] The dimension evaluation unit 3A includes a first judgment unit 3Aa and a second judgment unit 3Ab. The first judgment unit 3Aa determines whether the dimensions of the reference panel shape 10 determined by the press forming analysis unit 2 are 1000 mm x 1000 mm or more in plan view. The second judgment unit 3Ab determines whether the plate thickness of the reference panel shape 10 is 1.5 mm or less. If the judgment by the first judgment unit 3Aa or the second judgment unit 3Ab is not satisfied, the dimension evaluation unit 3A proceeds to the shape setting unit 3B. The shape setting unit 3B sets the reference panel shape 10 determined by the press forming analysis unit 2 as the evaluation panel shape 11 for evaluating dents. Thereafter, the shape setting unit 3B terminates the processing of the evaluation panel shape determination unit 3. On the other hand, if the above judgment is satisfied, the dimension evaluation unit 3A proceeds to the shape modification unit 3C.

[0018] [Shape Modification Unit 3C] The shape modification unit 3C includes a dead weight analysis unit 3Ca and an evaluation panel setting unit 3Cb. The dead weight analysis unit 3Ca performs dead weight analysis on the panel part model of the reference panel shape 10 obtained by the press forming analysis unit 2. Then, through the dead weight analysis, the dead weight analysis unit 3Ca obtains the panel shape after deformation caused by the dead weight load. The dead weight analysis unit 3Ca constitutes a dead weight analysis step. Note that a known analysis method may be used for the dead weight analysis.

[0019] In this embodiment, the deadweight analysis is performed under the following conditions to analyze the deadweight load on a panel component of the reference panel shape 10. The conditions are that the panel component of the reference panel shape 10 is placed on a flat and rigid mounting surface 30 without constraining the outer periphery of the panel component, as shown in FIG. 5 . Under these conditions, the panel component abuts against the mounting surface 30 and does not further deform downward. The panel component of the reference panel shape 10 is a large panel component or a thin panel component. Therefore, depending on the three-dimensional shape formed by press molding, deformation occurs in the panel component. Typically, the center of the panel shape is more likely to deform downward in a planar view. The evaluation panel setting unit 3Cb sets the panel shape after deformation in the processing of the deadweight analysis unit 3Ca as the evaluation panel shape 11.

[0020] <Bump Evaluation Unit 4> The bump evaluation unit 4 constitutes a bump evaluation step. The bump evaluation unit 4 evaluates bumps on panel components of the evaluation panel shape 11. A known analysis method may be used for the bump evaluation method. The bump evaluation process includes, for example, checking for the presence or absence of bumps and estimating the bump location. In a typical bump evaluation, a load is applied from the front to the back of the panel component. The bump analysis is then performed based on information about the displacement of the panel surface due to the load. The bump evaluation of this embodiment may also be performed by applying a load from the front to the back of the panel. However, in this embodiment, the panel shape to be evaluated is a panel shape in which a load is applied from the front to the back side using gravity analysis. Therefore, in this embodiment, a bump analysis is performed under conditions in which a load is applied from the back to the front side of the panel.

[0021] However, for example, if the weight analysis determines that there is a bulging portion on the front side due to deformation of the panel shape, it is preferable to perform the following. That is, it is preferable to perform a bow analysis by applying a load from the front side of the panel to the back side at least to the bulging portion and its vicinity. In this case, the bow analysis is performed by applying a load from the front side of the panel to the back side. The load application direction may also be changed for each region of the panel. Furthermore, it is also possible to perform an evaluation in which a load is applied from the back side to the front side and an evaluation in which a load is applied from the front side to the back side for the same portion.

[0022] The dent evaluation unit 4 of this embodiment performs processing to estimate dent positions for a panel component consisting of an evaluation panel shape 11. As shown in FIG. 1, the dent evaluation unit 4 of this embodiment has a tension stiffness strength distribution acquisition unit 4A and a dent position evaluation unit 4B. This embodiment illustrates an example of adopting the dent evaluation described in Patent Document 1. However, it differs in that the load is applied from the back side.

[0023] [Tension stiffness distribution acquisition unit 4A] The tension stiffness distribution acquisition unit 4A applies a load from the rear surface of the panel to the front surface at a preset load application position on the panel surface of the evaluation panel shape 11. This load displaces the panel surface toward the front surface by a preset displacement amount. The tension stiffness distribution acquisition unit 4A then performs a process to determine the resulting tension stiffness distribution along the panel surface. Two or more levels of displacement are set as the set displacement amount. The tension stiffness distribution acquisition unit 4A then determines the tension stiffness distribution along the panel surface for each set displacement amount. In other words, it acquires multiple tension stiffness distributions along the panel surface. The tension stiffness distribution acquisition unit 4A determines the tension stiffness distribution (tension stiffness distribution) through a load application simulation.

[0024] The load simulation is performed, for example, under conditions that constrain the outer periphery of the panel component of the evaluation panel shape 11. For example, the panel surface is divided into multiple regions (nodes), and the reaction force (load) generated in each region due to the application of a load to the load application points is calculated by simulation. The reaction force (load) in each region is then calculated as a tension stiffness distribution along the panel surface (tension stiffness strength distribution). Furthermore, a load-displacement curve (load distribution) for each region (node) is calculated from the tension stiffness distribution (tension stiffness strength distribution) at multiple levels based on multiple displacement amounts. The load application position is set at a position on the evaluation panel shape 11 that is estimated to have the weakest tension stiffness. For example, the load application position is set to a load application point set within the center of the panel surface. The center of the panel surface is, for example, a region including the center point (e.g., the center of gravity) of the panel and having a radius of 10 mm from the center point.

[0025] Furthermore, as the displacement of the panel at the load application point, two or more displacement amounts are set, for example, selected from a range of 10 mm to 40 mm. Then, a simulation is performed to determine the distribution of tension stiffness for each level of displacement amount. It is preferable that three or more levels of the displacement amount are set. The reason for setting the displacement amount in the range of 10 mm to 40 mm is as follows: that is, to evaluate the cracks that would occur due to indentation that generates a displacement within this range. There is no problem with setting the displacement amount level to 10 levels or less, preferably 5 levels or less.

[0026] [Slippage Position Evaluation Unit 4B] The slippage position evaluation unit 4B determines whether or not a slippage position exists based on the distribution of multiple tension stiffnesses obtained by the tension stiffness strength distribution acquisition unit 4A. If a slippage position exists, the slippage position is determined. Here, the center of the panel is the furthest from the constraint points on the panel periphery, and therefore is presumed to have the weakest stiffness. The slippage position evaluation unit 4B determines whether or not there is an area where the load is lower than the center of the panel based on the strength of the load distribution (tension stiffness distribution) generated by the load applied to the center of the panel. An area where the load is lower than the center of the panel is defined as a low-load area. If it is determined that such a low-load area exists, it determines that the low-load area is a slippage position with a high risk of slippage.

[0027] Alternatively, the dent position evaluation unit 4B may determine a position where the load temporarily decreases as the displacement at the load-applied position increases as a dent position. Here, when a load is applied to the panel center, which is estimated to have weak tension stiffness, a flexure node occurs when the load is applied due to the propagation of tension along the surface. The flexure node moves along the surface. If the flexure node is located in a low-load region, the node is likely to move easily, making dents more likely to occur. That is, in this embodiment, a portion of the evaluation position where the load decreases as the displacement increases in the load-displacement curve (load distribution) is determined to be a dent position (low-load region). Alternatively, in this embodiment, a region where the load is lower than the panel center, which is estimated to have weak tension stiffness, is determined to be a dent position. On the other hand, if there is no low-load region, the panel component is determined to have no dent position.

[0028] Through the above processing, the dent evaluation unit 4 determines whether or not there is a dent position. If there is a dent, the dent position (low load area) is determined. If the third determination unit 5 determines that there is a dent based on the processing by the dent evaluation unit 4, it proceeds to the panel shape modification unit 6. On the other hand, if the third determination unit 5 determines that there is no dent position in the panel component, it ends the processing and, for example, sets the panel shape as the target component shape.

[0029] <Panel Shape Modification Unit 6> The panel shape modification unit 6 performs processing when it determines that a dent location exists. The panel shape modification unit 6 modifies the evaluation panel shape 11 to increase the rigidity of the panel before assembly. Measures for modifying the evaluation panel shape 11 to increase the rigidity of the panel include, for example, known methods and measures described in previously cited patent publications, published patent applications, etc. Examples of measures for increasing rigidity include changing the panel curvature, attaching a reinforcing sheet, and adding a bead or other shape. Here, if the part is in the design stage, the panel shape itself may be modified. The part design stage refers, for example, to a stage when a mold does not yet exist. If the part is in the prototype stage, the mold may be adjusted to correspond to the modified panel shape. Mold adjustments include adjusting the expected mold shape. After the panel shape modification unit 6 modifies the panel shape, the above-described processes are executed again to re-evaluate the dent location in the modified panel shape. The above-described processes are then repeated until it is determined that the panel rigidity before assembly is high based on the absence of a dent location.

[0030] (Program 20) The bump evaluation device 1 of this embodiment is configured as a program 20 as shown in Fig. 3. This program 20 can be executed by a computer CPU. The program 20 shown in Fig. 3 is a program for evaluating bumps in a panel component before assembly with other components through forming analysis. The panel component is, for example, a panel component manufactured by press-forming a plate material into a three-dimensional shape. This program 20 includes a press-forming analysis step 20A, a weight analysis step 20B, and a bump evaluation step 20C.

[0031] The press molding analysis step 20A is a step of performing press molding analysis of press molding using a plate material as a target panel part. Furthermore, a process is executed to obtain the panel part after demolding as a reference panel shape 10 from the analysis. The weight analysis step 20B is a step of performing weight analysis on the reference panel shape 10 under the condition that the panel part is placed on a flat surface. Furthermore, a process is executed to obtain the panel shape after deformation due to weight as an evaluation panel shape 11 from the analysis. The dent evaluation step 20C is a step of executing a process to evaluate dents of the panel part of the evaluation panel shape 11.

[0032] (Manufacturing Method of Panel Component) In the manufacturing method of the panel component of this embodiment, a panel component is manufactured by steps such as those shown in Fig. 12, and the manufactured panel component is transported to the next step, etc. The manufacturing method of the panel component of this embodiment includes a defect evaluation step S30 and a panel component manufacturing step S32.

[0033] <Detachment Evaluation Process S30> The dentation evaluation process S30 may be performed, for example, by the dentation evaluation device 1 described above. In the dentation evaluation process S30, first, a panel component having a target component shape is subjected to dentation evaluation using the dentation evaluation method described above. If the dentation evaluation determines that dents will occur, the target component shape is modified to eliminate the dents. The modification of the target component shape and the dentation evaluation are then repeated until it is determined that dents will not occur. If the dentation evaluation determines that dents will not occur, the process proceeds to the panel component manufacturing process S32.

[0034] <Panel Component Manufacturing Step S32> In the panel component manufacturing step S32, a panel component is manufactured by press-forming a plate material into the final target component shape. Any known press-forming method may be used.

[0035] <Transportation Step S34> The manufactured panel components are transported by a transport means to a warehouse or the next process. The panel components transported to the warehouse are temporarily stored on the floor of the warehouse or on a pallet. The panel components are then transported to the next process by the transport means as needed. The transport means transports the panel components by gripping the surface of the panel components, for example, by suction or magnetic attraction.

[0036] <Assembly Process S36> In the next process, the panel component is assembled to other components. The panel component may be, for example, an outer panel of an automobile door, a hood, or a roof. In the panel component manufacturing method of this embodiment, the panel component is manufactured in a shape that does not produce dents that may occur during transportation of the panel component. This improves product precision and also improves yield.

[0037] <Functions and Others> Conventionally, problems with dents would arise after prototyping, and mold modifications would be made through trial and error. In contrast, in this embodiment, the presence or absence of dents is examined through simulation. This makes it possible to suppress the occurrence of defects during the evaluation stage using the actual product, and contribute to reducing lost development man-hours.

[0038] This embodiment evaluates large-area, thin press-formed panels, such as exterior panels for automobile roofs, hoods, and doors. This evaluation makes it possible to predict in advance the occurrence of distortion (permanent deformation) due to dents in panel components, which is likely to occur during the transfer process in press forming. It is then possible to take measures to prevent this. As a result, this embodiment makes it possible to detect the risk of dents before a prototype vehicle is manufactured. As a result, it is possible to minimize losses in development and production preparation.

[0039] That is, according to this embodiment, panel dents can be easily predicted. Therefore, it is not necessary to actually produce a prototype vehicle for dent evaluation during the development stage of a car. Furthermore, from information on the panel shape of the product, it is possible to easily predict whether or not panel dents will occur, which are likely to occur during transportation after press processing. In other words, it is possible to consider countermeasures against dents occurring during transportation and other pre-assembly stages at the design stage of parts. As a result, this embodiment can reduce losses in, for example, new car development, and also enable efficient development and production without slowing down production speed even in mass production.

[0040] Next, an example of this embodiment will be described. FIG. 4 shows the panel shape of an actual panel component to be evaluated in this example. The target panel component shown in FIG. 4 is thin, with a plate thickness of 1.2 mm. The size of the panel component is 1400 x 1100 mm. In other words, the panel component of this example is a large component with a side length of over 1000 mm. When such a large panel component is held by hand, if the component's rigidity is low, the component itself will bend. The panel component of this example is made of steel with a material strength of 270 MPa.

[0041] First, a model of a flat plate (blank) made of steel with a thickness of 1.2 mm and a material strength of 270 MPa was generated. A press-forming analysis was performed using FEM analysis to press-form the blank model of the plate into a target panel shape. In this example, the target panel shape was the shape shown in FIG. 1 . From this analysis, a part model of a reference panel shape 10 was obtained. The reference panel shape 10 is the panel shape after demolding, i.e., the panel shape after springback. Next, a weight analysis was performed on the part model of the obtained reference panel shape 10 to obtain a part model of an evaluation panel shape 11. The evaluation panel shape 11 consists of the panel shape after deformation due to its own weight.

[0042] As shown in Figure 5, the deadweight analysis was performed under the condition that the panel component was placed on a flat, rigid support surface 30 without restraining the outer periphery of the panel component. The support surface 30 was made rigid to simulate the situation where a portion of the panel component that had sagged due to its own weight would contact the support surface 30 and prevent further sagging. The deadweight analysis in this example is a shape analysis that simulates the state in which the panel component is placed on the support surface 30, which is a flat surface simulating the ground. The shape analysis allows the component itself to bend until it naturally contacts the flat support surface 30. Thin, large panel components are prone to bending. Therefore, when checking for actual dents by tactile inspection, the inspection is performed on an inspection table or at the component assembly position. Therefore, the effects of the panel component's own weight are unavoidable. When performing this deadweight analysis on a panel component, the component often sags around its center.

[0043] Next, the analysis of the Bekotski evaluation will be described. Here, Fig. 6 shows the displacement applying position F1 and the evaluation points P1 and P2 in the Bekotski analysis.

[0044] <For Evaluation Point P1> First, evaluation was performed on evaluation point P1. Here, the crinkle analysis was performed under the following conditions (1) to (3). (1) The entire outer periphery of the panel was constrained in the press direction at 100 mm intervals along the circumferential direction. (2) The panel was displaced 40 mm from the back to the front (bottom to top in Figure 6) at displacement application position F1. Then, the displacement in the press direction of evaluation point P1 associated with the displacement at displacement application position F1 was obtained. (3) The displacement in the press direction and the acceleration (second-order derivative) of that displacement were then evaluated. Crinkle can be detected based on the acceleration. That is, when crinkle occurs, the velocity changes suddenly in the press direction or the opposite direction as the displacement at displacement application position F1 occurs. This change allows quantitative detection of crinkle. However, the presence or absence of crinkle can be determined based on the information on the displacement in the press direction (2) alone.

[0045] FIG. 7 shows an example of a press shape for a dent evaluation. As shown in FIG. 7(a), the actual part shape shows a sagging center portion due to its own weight. The actual part shape shows the amount of deformation when the product panel part is placed on the floor. In contrast, the reference panel shape 10 (see FIG. 7(b)) after springback, which was analyzed using CAE, shows no sagging center portion. On the other hand, the evaluation panel shape 11 (see FIG. 7(c)) that underwent a weight analysis was found to closely reproduce the actual part shape (see FIG. 7(a)).

[0046] FIG. 8 shows the results of the Bekozki analysis at the evaluation point P1 for each panel shape. FIG. 8(a) shows the CAE analysis results for the panel shape of the product shape. FIG. 8(b) shows the analysis results when an actual displacement load is applied to the displacement application position F1 for the actual part. The actual part is a panel part in the product shape actually placed on the floor. This panel shape is also referred to as the actual part shape. FIG. 8(c) shows the CAE analysis results for the reference panel shape 10 after springback, which simulates the product shape. FIG. 8(d) shows the CAE analysis results for the evaluation panel shape 11 after weight analysis. Each analysis result in FIG. 8 is expressed as displacement and acceleration data for the evaluation point P1. The horizontal axis shows the amount of displacement applied to the displacement application position F1. The vertical axis shows the amount of displacement and acceleration at the evaluation point P1 at that time. Note that all analysis results other than the actual part shape were obtained by CAE analysis.

[0047] The following was learned from Figure 8. For the panel shape of the product shape shown in Figure 4, the CAE analysis showed no collapse in the center, and as can be seen from Figure 8(a), there was no dent at evaluation point P1. The absence of dents means that, as shown in Figure 8(a), the displacement and acceleration at the evaluation point change in proportion to the applied displacement. Similarly, as can be seen from Figure 8(c), there was no dent at evaluation point P1 for the reference panel shape 10 after springback.

[0048] On the other hand, with the actual part shape, placing the panel part on the floor causes, for example, a sag in the center of the part. As shown in FIG. 8(b), when a displacement of about 15 mm was applied, the displacement and acceleration of evaluation point P1 changed suddenly. In other words, a sag occurred. Furthermore, the CAE analysis of evaluation panel shape 11 (FIG. 8(d)) also showed a similar shape to the sag in the center of the actual part. That is, with evaluation panel shape 11, the sag analysis also showed that when a displacement of about 15 mm was applied, the displacement and acceleration of the evaluation point changed suddenly, just like the actual part. In other words, a sag occurred.

[0049] Next, based on the results shown in Figure 8, a bead 14A was added to suppress dents. Figure 9 shows the improved panel shape 14. For the improved panel shape 14 shown in Figure 9, dents were evaluated for the evaluation panel shape 11 after weight analysis. From this evaluation, it was determined that sagging in the center of the part was suppressed and there was no dent at evaluation point P1. When an actual part with the improved panel shape was placed on the floor and dents were evaluated with a finger, no dents occurred at evaluation point P1. In other words, the countermeasure and its effectiveness were confirmed.

[0050] <For Evaluation Point P2> Next, a similar evaluation was performed using P2 as the evaluation point without changing the displacement application position F1. Evaluation point P2 is the position shown in FIG. 6. FIG. 10 shows the results of the dent evaluation at evaluation point P2. As can be seen from FIG. 10, the same results were obtained when the evaluation point was changed from P1 to P2. FIG. 10(a) shows the CAE analysis results for the panel shape of the product shape. FIG. 10(b) shows the analysis results when an actual displacement was applied to the displacement application position F1 of the actual part. The actual part is a panel part in the product shape actually placed on the floor. This panel shape is also referred to as the actual part shape. FIG. 10(c) shows the CAE analysis results for the reference panel shape 10 after springback, which simulates the product shape. FIG. 10(d) shows the CAE analysis results for the evaluation panel shape 11 after self-weight analysis.

[0051] As can be seen from Figure 10(a), when the panel shape used to evaluate the product shape was used, the CAE analysis showed no sagging in the center and no dents. On the other hand, the actual part shape showed dents in the center when placed on the floor. As shown in Figure 10(b), when a displacement of approximately 15 mm was applied, the displacement and acceleration at evaluation point P2 changed rapidly. In other words, dents occurred. The CAE analysis also showed that the evaluation panel shape 11, which was subjected to weight analysis, showed a similar shape to the dent in the center of the actual part. Therefore, the dent analysis shown in Figure 10(d) showed that when a displacement of approximately 15 mm was applied, similar to the actual part, the displacement and acceleration at the evaluation point changed rapidly. In other words, dents occurred. In contrast, the reference panel shape 10 after springback was evaluated as follows. That is, as shown in Figure 10(c), it was determined that there were no dents at evaluation point P2.

[0052] Next, to suppress dents at evaluation point P2, a bead 15A was added. The improved panel shape is shown in Figure 11. Using the improved panel shape 15 shown in Figure 11 as the reference panel shape 10, a dent analysis was performed on the evaluation panel after the weight analysis. The dent analysis determined that there were no dents at evaluation point 2. In addition, an actual part with the improved panel shape 15 was placed on the floor and evaluated for dents at evaluation point P2. This evaluation showed that no dents occurred, confirming the dent countermeasures and their effectiveness.

[0053] (Other) The present disclosure may also be configured as follows. (1) Disclosure 1 discloses a dent evaluation method for evaluating dents in a panel component formed by press-forming a sheet material before assembly with another component by forming analysis using a computer, the method comprising: a press-forming analysis step of performing a press-forming analysis using the sheet material as the panel component and acquiring the panel shape after release from the mold as a reference panel shape; a weight analysis step of performing a weight analysis on the reference panel shape under conditions in which the panel component is placed on a flat surface and acquiring the panel shape after deformation due to the weight as an evaluation panel shape; and a dent evaluation step of evaluating dents in the panel component having the evaluation panel shape. (2) Disclosure 2 discloses that the dent evaluation step applies a load to a set load application position to displace the panel surface from the back side to the front side, thereby determining a distribution of tension stiffness along the panel surface that occurs multiple times while changing the amount of displacement due to the load, and estimating the position of the dent on the panel surface from the determined multiple distributions of tension stiffness. (3) Disclosure 3 evaluates panel parts having dimensions of 1000 x 1000 mm or more in a plan view. (4) Disclosure 4 evaluates panel parts having a plate thickness of 1.5 mm or less. (5) Disclosure 5 describes the press molding as form molding or draw molding. (6) Disclosure 6 describes a dent evaluation device that evaluates dents in a panel part obtained by press molding a plate material before assembly with another part by forming analysis using a computer, the device comprising: a press molding analysis unit that performs press molding analysis using the plate material as the panel part and acquires the panel shape after demolding as a reference panel shape; a weight analysis unit that performs weight analysis on the reference panel shape under conditions where the panel part is placed on a flat surface and acquires the panel shape after deformation due to weight as an evaluation panel shape; and a dent evaluation unit that evaluates dents in the panel part having the evaluation panel shape.(7) Disclosure 7 is a program for evaluating dents in a panel component obtained by press-forming a sheet material by forming analysis before assembly to another component, the program causing a computer to execute the following steps: a press-forming analysis step of performing a press-forming analysis using the sheet material as the panel component and acquiring the panel component after release from the mold as a reference panel shape, a weight analysis step of performing a weight analysis on the reference panel shape under conditions in which the panel component is placed on a flat surface and acquiring the panel shape after deformation due to its weight as an evaluated panel shape, and a dent evaluation step of evaluating dents in the panel component of the evaluated panel shape. (8) Disclosure 8 is a method for manufacturing a panel component by press-forming a sheet material into a target component shape, the method comprising: evaluating the target component shape of the panel component by a dent evaluation method described in any of Disclosures 1 to 5 before press-forming, and, if the evaluation determines that dents will occur, changing the target component shape to a shape that can suppress the occurrence of dents.

[0054] The entire contents of Japanese Patent Application No. 2024-080361 (filed May 16, 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 would be obvious to those skilled in the art.

[0055] REFERENCE SIGNS LIST 1 Detachment evaluation device 2 Press forming analysis section 3 Evaluation panel shape determination section 3A Dimension evaluation section 3B Shape setting section 3C Shape modification section 3Ca Weight analysis section 3Cb Evaluation panel setting section 4 Detachment evaluation section 4A Tension stiffness strength distribution acquisition section 4B Detachment position evaluation section 6 Panel shape modification section 10 Reference panel shape 11 Evaluation panel shape 20 Program 20A Press forming analysis step 20B Weight analysis step 20C Detachment evaluation step 30 Placement surface F1 Displacement application position P1, P2 Evaluation point

Claims

1. A dent evaluation method for evaluating dents in a panel component formed by press-molding a sheet material by computer-assisted molding analysis before assembly to another component, the method comprising: a press-molding analysis step of performing a press-molding analysis using the sheet material as the panel component and obtaining the panel shape after release from the mold as a reference panel shape; a weight analysis step of performing a weight analysis on the reference panel shape under conditions where the panel component is placed on a flat surface and obtaining the panel shape after deformation due to its own weight as an evaluation panel shape; and a dent evaluation step of evaluating dents in the panel component with the evaluation panel shape.

2. A method for evaluating cavities as described in claim 1, wherein the step of evaluating cavities involves applying a load to a set load application position to displace the panel surface from the back side to the front side, thereby determining the distribution of tension stiffness along the panel surface multiple times by changing the amount of displacement caused by the load application, and estimating the position of cavities on the panel surface from the distribution of tension stiffness thus determined.

3. A method for evaluating the appearance of beaks as described in claim 1 or claim 2, wherein the evaluation targets panel components having dimensions in plan view of length x width = 1000 x 1000 mm or more.

4. A method for evaluating cracks and dents according to any one of claims 1 to 3, in which panel components having a thickness of 1.5 mm or less are evaluated.

5. A method for evaluating the degree of adhesion of a part according to any one of claims 1 to 4, wherein the press molding is form molding or draw molding.

6. A dent evaluation device that evaluates dents in a panel component formed by press-molding a sheet material by computer-assisted molding analysis before assembly to another component, comprising: a press molding analysis unit that performs press molding analysis using the sheet material as the panel component and obtains the panel shape after release from the mold as a reference panel shape; a weight analysis unit that performs a weight analysis of the reference panel shape under conditions where the panel component is placed on a flat surface and obtains the panel shape after deformation due to its weight as an evaluation panel shape; and a dent evaluation unit that evaluates dents in the panel component with the evaluation panel shape.

7. A program for evaluating, by forming analysis, the dents of a panel part formed by press-forming a sheet material before assembly to another part, comprising: a press-forming analysis step for performing a press-forming analysis of the sheet material as the panel part and obtaining the panel part after release from the mold as a reference panel shape; a weight analysis step for performing a weight analysis of the reference panel shape under the condition that the panel part is placed on a flat surface and obtaining the panel shape after deformation due to its own weight as an evaluation panel shape; and a dent evaluation step for evaluating the dents of the panel part with the evaluation panel shape.

8. A method for manufacturing a panel part in which a panel part is manufactured by press-molding a sheet material into a target part shape, the target part shape of the panel part is evaluated before press-molding using a cavity evaluation method described in any one of claims 1 to 5, and if the evaluation determines that cavity will occur, the target part shape is changed to a shape that can suppress the occurrence of cavity.

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