Method for predicting shape change of a press-formed part

Abstract

The present invention relates to a method for predicting a shape change of a press-formed product, which predicts a shape change of a lengthwise end portion side twist caused by stress relaxation with the passage of time after ejection from a mold and springback, for a press-formed product (1) having a U-shaped cross-sectional shape having a ceiling portion (3) and a pair of lengthwise wall portions (5) and including a shape curved along a lengthwise direction in plan view, including: a process (S1) of acquiring a shape and a residual stress of the press-formed product (1) immediately after springback; a process (S3) of setting a value of a stress that is less than a residual stress immediately after springback, for either one of the pair of lengthwise wall portions (5) of the press-formed product (1) immediately after springback; and a process (S5) of finding a shape of a force moment balance for the press-formed product (1) for which the value of the stress that is less than the residual stress immediately after springback is set.

Description

Technical Field

[0001] This invention relates to a method for predicting the shape change of press-formed parts, and particularly to a method for predicting the shape change of press-formed parts that have a U-shaped or Z-shaped cross-sectional shape and include a shape that is curved along the length direction in top view, and for predicting the shape change of press-formed parts over time after die release and springback. Background Technology

[0002] Stamping is a manufacturing method that can produce metal parts in a low-cost and short-time manner, and it is used in the manufacture of many automotive parts. In recent years, in order to balance collision safety and weight reduction of the automotive body, higher-strength metal sheets have been used in the stamping of automotive parts.

[0003] One of the main challenges in stamping high-strength metal sheets is the reduction in dimensional accuracy caused by springback. Springback is the phenomenon where the residual stress generated in the stamped part during the deformation of the metal sheet becomes a driving force, causing the stamped part to instantly return to the shape of the metal sheet before stamping, just like a spring.

[0004] The higher the strength of the metal sheet (e.g., high-strength steel sheet), the greater the residual stress generated during stamping, and therefore the greater the shape change caused by springback. Consequently, the higher the strength of the metal sheet, the more difficult it is to control the shape within specified dimensions after springback. Therefore, technology for accurately predicting the shape changes of stamped parts caused by springback is crucial.

[0005] In predicting shape changes caused by springback, stamping simulation based on the finite element method is typically used. This stamping simulation is divided into two stages: a first stage, which involves performing a press forming analysis of the process of stamping a metal sheet to the bottom dead center, predicting the residual stress at the bottom dead center (e.g., Patent Document 1); and a second stage, which involves a springback analysis of the shape of the stamped part after demolding (removal) due to springback, predicting the shape that achieves a balance between the moment of force and residual stress in the demolded stamped part (e.g., Patent Document 2).

[0006] Patent Document 1: Japanese Patent No. 5795151

[0007] Patent Document 2: Japanese Patent No. 5866892

[0008] Patent Document 3: Japanese Patent Application Publication No. 2013-113144

[0009] To date, stamping simulations that integrate the first stage of stamping analysis and the second stage of springback analysis have been used to predict the shape of the stamped part immediately following demolding and springback. However, when comparing the shape of the stamped part predicted by the stamping simulation with the shape of the actual stamped part, the inventors have noticed that there are stamped parts with lower shape prediction accuracy based on the stamping simulation.

[0010] Therefore, in investigating stamped parts with decreasing shape prediction accuracy based on stamping simulation, it was found that: Figure 2 As an example, a stamped part 1, having a U-shaped cross-section with a top portion 3 and a pair of sidewall portions 5, and bent along its length when viewed from above (from the direction of the top portion), or Figure 5 As an example, in a stamped part 11 with a Z-shaped cross-section having a top plate portion 13, a longitudinal wall portion 15, and a flange portion 17, and bent along the length direction when viewed from above, after demolding and several days have passed, a deformation occurs in which the end side in the length direction twists relative to the middle portion in the length direction, and the shape is different immediately after stamping and several days later.

[0011] The shape change of such stamped parts over time is considered to be similar to the phenomenon of structural members gradually deforming under continuous high external pressure, such as creep (e.g., Patent Document 3). However, the shape change of stamped parts not subjected to external pressure is unknown until now.

[0012] Furthermore, the second stage (springback analysis) in previous stamping simulations predicted the shape of the stamped part immediately after springback following removal from the die. Therefore, no research has been conducted to date regarding the shape change of springbacked stamped parts, which is the target of this application, for example, after several days. Moreover, as mentioned above, the time-unit-based shape change of the springbacked stamped part is a shape change not caused by external loads. Therefore, even if attempts are made to predict the time-unit-based shape change of the stamped part, analytical methods for handling shape changes caused by creep cannot be applied. Summary of the Invention

[0013] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for predicting the shape change of a stamped part that has a U-shaped or Z-shaped cross-section and includes a shape that bends along the length direction when viewed from above, and predicts the shape change of the stamped part based on the time unit after springback at the moment of demolding.

[0014] The first aspect of the present invention relates to a method for predicting the shape change of a stamped part. This method is for a stamped part having a U-shaped cross-section with a top plate and a pair of longitudinal walls continuous from the top plate, and including a shape that bends along its length in plan view. The method predicts the shape change of the stamped part after springback from the die, caused by stress relaxation over time. The method includes: a shape / residual stress acquisition step, in which the shape and residual stress of the stamped part after springback are acquired through springback analysis; a residual stress relaxation and reduction setting step, in which a stress value that is more relaxed and reduced than the residual stress after springback is set for at least one of the pair of longitudinal walls of the stamped part after springback; and a residual stress relaxation shape analysis step. In the residual stress mitigation shape analysis process, the shape of the force torque balance of the stamped part is determined for the set value of the mitigated stress.

[0015] The second aspect of the present invention relates to a method for predicting the shape change of a stamped part. This method targets a stamped part having a Z-shaped cross-sectional shape, including a top plate portion, a longitudinal wall portion continuous from the top plate portion, and a flange portion continuous from the longitudinal wall portion, and including a shape that bends along its length in plan view. The method predicts the shape change of the stamped part after springback from the die, caused by stress relief over time. The method includes a shape / residual stress acquisition step after springback. In this process, the shape and residual stress of the stamped part after springback are obtained through springback analysis of the stamped part; a residual stress mitigation and reduction setting process is performed, in which a stress value that is reduced by the residual stress after springback is set for at least the top plate portion and / or the flange portion of the stamped part after springback; and a residual stress mitigation shape analysis process is performed, in which the shape of the force torque balance is determined for the stamped part with the set mitigation and reduction stress value.

[0016] In the above-mentioned residual stress mitigation and reduction setting process, a stress value that reduces the residual stress by more than 5% compared to the stress after rebound can be set.

[0017] The blank for stamping the above-mentioned stamped parts can be a metal sheet with a tensile strength of 150 MPa grade or higher and 2000 MPa grade or lower.

[0018] According to the present invention, for stamped parts with a U-shaped or Z-shaped cross-section and including a shape that bends along the length direction when viewed from above, it is possible to predict with high accuracy the shape change of the longitudinal end of the stamped part as time passes after it is demolded and springs back from the die. As a result, in the manufacturing processes of automotive parts, automotive bodies, etc., stamped parts with better dimensional accuracy than before can be obtained, and manufacturing efficiency can be greatly improved. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the processing flow of the shape change prediction method for stamped parts according to Embodiment 1 of the present invention.

[0020] Figure 2 This is a diagram illustrating an example of a stamped part, as described in Embodiment 1 of the present invention, which has a U-shaped cross-section and is bent along its length when viewed from above. Figure 2 (a) is a 3D diagram. Figure 2 (b) is a top view.

[0021] Figure 3 This diagram illustrates the stress relaxation phenomenon, where stress decreases over time when the stress remains constant after being subjected to strain.

[0022] Figure 4 Yes Figure 2 The figure illustrates the shape changes of a pair of longitudinal walls in a U-shaped cross-section stamped part caused by stress relief. Figure 4 (a) is the bottom stop point of the stamping process after forming. Figure 4 (b) is after the springback is tight, Figure 4 (c) is after time has passed.

[0023] Figure 5 This is a diagram illustrating an example of a stamped part, as described in Embodiment 2 of the present invention, which has a Z-shaped cross-section and is bent along its length when viewed from above. Figure 5 (a) is a 3D diagram. Figure 5(b) is a top view.

[0024] Figure 6 Yes Figure 5 The figure illustrates the shape changes of the top plate and flange portions of the stamped part with a Z-shaped cross-section caused by stress relief. Figure 6 (a) is the bottom stop point of the stamping process after forming. Figure 6 (b) is after the springback is tight, Figure 6 (c) is after time has passed.

[0025] Figure 7 This is a diagram illustrating another example of a stamped part, as described in Embodiment 2 of the present invention, which has a Z-shaped cross-section and is bent along its length when viewed from above. Figure 7 (a) is a 3D diagram. Figure 7 (b) is a top view.

[0026] Figure 8 Yes Figure 7 The figure illustrates the shape changes of the flange and top plate portions of the stamped part with a Z-shaped cross-section caused by stress relief. Figure 8 (a) is the bottom stop point of the stamping process after forming. Figure 8 (b) is after the springback is tight, Figure 8 (c) is after time has passed. Detailed Implementation

[0027] [Implementation Method 1]

[0028] The method for predicting the shape change of stamped parts according to Embodiment 1 of the present invention is taken as an example. Figure 2 As shown, for a stamped part 1 with a U-shaped cross-section and including a shape that bends along its length when viewed from above, the shape change of the end-side torsion in the length direction caused by stress relief over time after demolding and springback is predicted, as shown in the figure. Figure 1 As shown, it includes the following steps: shape / residual stress acquisition process S1 after springback tightening, residual stress mitigation and reduction setting process S3, and residual stress mitigation shape analysis process S5.

[0029] Before explaining each of the above processes, the reason for the shape change of the stamped part 1, which is the object of shape prediction in Embodiment 1, is explained as follows: the shape changes of the end side twisting in the length direction occur as time passes after the moment of springback from the mold.

[0030] <Shape changes of U-shaped stamped parts over time>

[0031] like Figure 2As shown as an example, the stamped part 1 in this embodiment 1 has a U-shaped cross-section with a top plate portion 3 and a pair of longitudinal wall portions 5 continuous from the top plate portion 3, and includes a shape that bends along the length direction when viewed from above. Furthermore, the top plate portion 3 and the longitudinal wall portions 5 are continuous by a punch shoulder R portion 7. Additionally, the pair of longitudinal wall portions 5 are composed of a longitudinal wall portion 5a located on the inner side of the bend and a longitudinal wall portion 5b located on the outer side of the bend. Moreover, the inner side of the bend is the side that is the same as the center of curvature of the bend when viewed from above, and the outer side of the bend is the side that is opposite to the center of curvature of the bend when viewed from above (the same applies below).

[0032] The results of studying the shape change of such a stamped part 1 over time after springback are as follows: Figure 3 As shown in the stress-strain diagram, the inventors focused on the stress easing phenomenon, which maintains a constant stress after strain is applied and gradually eases over time. Furthermore, it was found that in the stamped part 1 after springback, the residual stress in the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend also gradually eases over time, thereby changing the shape that balances the torque of the force on the stamped part 1.

[0033] use Figure 4 The schematic diagram illustrates the shape change of the stamped part 1 caused by the mitigation of residual stress. Furthermore, in Figure 4 (b) of (ii) and Figure 4 In (c) and (ii), the solid line represents the shape of the A1-A1' section at the end of the stamped part 1 in the longitudinal direction, and the dashed line represents the shape of the A0-A0' section in the central part of the stamped part 1 in the longitudinal direction.

[0034] In the stamping process of stamped part 1, the metal sheet (blank) is as follows: Figure 2 The shape is bent into a curved shape when viewed from above. Therefore, at the bottom of the forming point, as shown... Figure 4 As shown in (a) and (i), tensile stress is generated in the longitudinal wall portion 5a on the inner side of the bend due to stretch flange deformation, which causes the line length of the blank end to extend, and compressive stress is generated in the longitudinal wall portion 5b on the outer side of the bend due to shrink flange deformation, which causes the line length of the blank end to shrink.

[0035] Next, if the stamped part 1 is removed from the die, the residual stress generated during stamping will act as a driving force to produce springback. During this springback, the inner longitudinal wall portion 5a tends to shrink, while the outer longitudinal wall portion 5b tends to extend. However, in-plane deformations such as shrinkage of the longitudinal wall portion 5a and stretching of the longitudinal wall portion 5b are difficult to occur due to the high stiffness. Therefore, as... Figure 4 As shown in (b) and (ii), torsion occurs at the longitudinal end relative to the central portion in the longitudinal direction of the stamped part 1. Furthermore, residual stress is generated at the bottom of the forming point on the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend. Figure 4 The absolute values ​​of the tensile stress and compressive stress shown in (a) and (i) decrease, or, depending on the circumstances, as Figure 4 As shown in (b) of (i), the residual stress and the bottom stop of the forming are reversed, and the shape becomes a force torque balance.

[0036] Then, the residual stress in the longitudinal wall portion 5a on the inner side of the springback bend (in) Figure 4 (b) of (i) represents compressive stress) and residual stress at the longitudinal wall portion 5b on the outer side of the bend (in Figure 4 In (b) of (i), the tensile stress gradually eases and decreases over time without being forced by external forces. Consequently, the shape in equilibrium with the torque of the force changes, thus as... Figure 4 As shown in (c) and (ii), further torsion occurs at the longitudinal end of the stamped part 1.

[0037] Thus, the following insight was obtained: In the stamped part 1 with a U-shaped cross-section and a curved shape when viewed from above, as time passes after stamping and springback, the residual stress in the longitudinal wall portion 5a on the inner side of the curve and the longitudinal wall portion 5b on the outer side of the curve is relieved, thus generating torsion at the end side in the length direction, resulting in a shape from the bottom stop of the forming ( Figure 4 (a)(ii)) further deviates from the shape.

[0038] Therefore, based on the above-mentioned new insights, the inventors studied a method for predicting the shape change of the stamped part 1 over time due to stress relief after springback. The result was that by further performing a third-stage analysis that relieves the residual stress in at least the longitudinal wall portion 5a on the inner side of the bend and / or the longitudinal wall portion 5b on the outer side of the bend of the stamped part 1 immediately after springback obtained in the second stage (springback analysis) of the above-mentioned stamping simulation, and determines the shape that balances the torque of the force on the stamped part 1, it is possible to predict the shape change of the stamped part 1 over time (torsion at the end side in the length direction) as described above.

[0039] <Method for Predicting Shape Changes in Stamped Parts>

[0040] Next, we will discuss the method for predicting the shape change of stamped parts involved in Embodiment 1. Figure 1 The following steps are explained: Step S1 for obtaining the shape / residual stress after springback, Step S3 for setting the residual stress mitigation and reduction, and Step S5 for analyzing the residual stress mitigation shape.

[0041] "Shape after springback / Residual stress acquisition process"

[0042] The springback shape / residual stress acquisition process S1 is a process of acquiring the shape and residual stress of the springback stamped part 1 by analyzing the springback of the stamped part 1.

[0043] As an example of the specific processing to obtain the shape and residual stress of the stamped part 1 after springback, a stamping simulation based on the finite element method can be given. The stamping simulation has the following steps: First, using a die model obtained by modeling the die used in the actual stamping of the stamped part 1, a stamping analysis is performed on the process of stamping a metal sheet to the lower limit of forming, and the shape and residual stress of the stamped part 1 at the lower limit of forming are obtained; Second, a springback analysis is performed to determine the shape and residual stress of the stamped part 1 after it is demolded from the die model at the lower limit of forming.

[0044] Residual stress mitigation and reduction setting procedures

[0045] The residual stress mitigation and reduction setting step S3 is a step of setting a value of stress that is more than the residual stress mitigation and reduction after springback on either of at least one pair of longitudinal wall portions 5 of the springback stamped part 1 obtained in the springback shape / residual stress acquisition step S1.

[0046] Here, the residual stress in the residual stress mitigation and reduction setting step S3 refers to the tensile and compressive stresses remaining in the springback stamped part 1. Furthermore, as described above, the pair of longitudinal wall portions 5 are referred to as the inner curved longitudinal wall portion 5a and the outer curved longitudinal wall portion 5b. Moreover, the stress value obtained by mitigating and reducing residual stress in the residual stress mitigation and reduction setting step S3 refers to the value obtained by mitigating and reducing the absolute values ​​of the compressive stress (negative value) remaining in the inner curved longitudinal wall portion 5a and the tensile stress (positive value) remaining in the outer curved longitudinal wall portion 5b in the springback stamped part 1, respectively.

[0047] Residual Stress Relief Shape Analysis Process

[0048] The residual stress relief shape analysis process S5 is a process that analyzes the shape of the stamped part 1 for which the value of the stress relief reduction was set in the residual stress relief reduction setting process S3 to determine the force torque balance.

[0049] In the residual stress relief shape analysis process S5, by applying the same analysis method as the springback analysis in the springback shape / residual stress acquisition process S1, the shape and residual stress of the stamped part 1 after setting the stress value to reduce residual stress can be obtained.

[0050] In this way, according to the shape change prediction method of the stamped part according to Embodiment 1, a stress value that is reduced in intensity than the residual stress after springback is set for either the longitudinal wall portion 5a on the inner side of the bend or the longitudinal wall portion 5b on the outer side of the bend of the stamped part 1 after springback, which is obtained through springback analysis. An analysis is performed to determine the shape of the stamped part 1 that is balanced with the torque of the force for the stamped part 1 with the set value of reduced intensity. As a result, it is possible to simulate the stress easing and shape change over time in the actual stamped part 1, and predict the shape change of the stamped part 1 after demolding and springback in the length direction end-side torsion over time.

[0051] Furthermore, in the above description, the residual stress mitigation and reduction setting step S3 sets a stress value for either the longitudinal wall portion 5a on the inner side of the bend or the longitudinal wall portion 5b on the outer side of the bend in the stamped part 1, that is, at least the longitudinal wall portion 5a and / or the longitudinal wall portion 5b, such that the residual stress in the above-mentioned portions is mitigated and reduced.

[0052] However, in this embodiment 1, for the parts of the stamped part 1 other than the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend, the residual stress mitigation and reduction setting process S3 can either directly set the residual stress after springback, or set the stress value obtained by mitigating and reducing the residual stress. Alternatively, the stress value obtained by mitigating and reducing the residual stress can be set for the entire stamped part 1. Furthermore, the residual stress mitigation and reduction setting process S3 can also change the proportion and value of residual stress mitigation and reduction for each part, such as the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend.

[0053] [Implementation Method 2]

[0054] The method for predicting the shape change of stamped parts according to Embodiment 2 of the present invention is taken as an example. Figure 5 As shown, for a stamped part 11 with a Z-shaped cross-section and including a shape that bends along the length direction when viewed from above, the shape change of the end-side torsion in the length direction caused by stress relief over time after demolding and springback is predicted, similar to Embodiment 1 described above (see also Embodiment 1). Figure 1 This includes the process of obtaining the shape / residual stress after springback, the process of setting the residual stress mitigation and reduction, and the process of analyzing the residual stress mitigation shape.

[0055] Before explaining each of the above processes, the reason for the shape change of the stamped part 11, which is the object of shape prediction in this embodiment 2, is explained as follows: the shape changes of the end side twisting in the length direction occur as time passes after the moment of springback from the mold.

[0056] <Shape changes of stamped parts with Z-shaped cross-sections over time (part 1)>

[0057] like Figure 5 As shown, the stamped part 11 in this embodiment 2 has a Z-shaped cross-section having a top plate portion 13, a longitudinal wall portion 15 continuous from the top plate portion 13, and a flange portion 17 continuous from the longitudinal wall portion 15, and includes a shape that bends along the length direction when viewed from above. Furthermore, the top plate portion 13 and the longitudinal wall portion 15 are continuous by a punch shoulder R portion 19, and the longitudinal wall portion 15 and the flange portion 17 are continuous by a die shoulder R portion 21. Moreover, the flange portion 17 is located on the inner side of the bend, and the top plate portion 13 is located on the outer side of the bend.

[0058] For such a stamped part 11, the same considerations as in Embodiment 1 described above are taken into account. Figure 3The stress relief phenomenon shown was investigated to explain the reason for the shape change over time. It was found that in the stamped part 11 after springback, the residual stress on the inner flange portion 17 and the outer top plate portion 13 gradually eased over time, thereby changing the shape to balance the torque of the force on the stamped part 11.

[0059] use Figure 6 The schematic diagram illustrates the shape change caused by the mitigation of residual stress in the stamped part 11. Furthermore, in Figure 6 (b) of (ii) and Figure 6 In (c) and (ii), the solid line represents the shape of the B1-B1' section at the end of the stamped part 11 in the longitudinal direction, and the dashed line represents the shape of the B0-B0' section in the central part of the stamped part 11 in the longitudinal direction.

[0060] In the stamping process of stamped part 11, the metal sheet (blank) is as follows: Figure 5 The shape is bent into a curved shape when viewed from above. Therefore, at the bottom of the forming point, as shown... Figure 6 As shown in (a) and (i), tensile stress is generated in the flange portion 17 on the inner side of the bend due to the extension flange deformation that causes the line length of the blank end to extend, and compressive stress is generated in the top plate portion 13 on the outer side of the bend due to the contraction flange deformation that causes the line length of the blank end to contract.

[0061] Next, if the stamped part 11 is removed from the die, the residual stress generated during stamping will act as a driving force to produce springback. During this springback, the inner flange portion 17 tends to contract, while the outer top plate portion 13 tends to extend. However, such in-plane deformation as the contraction of the flange portion 17 and the extension of the top plate portion 13 is difficult to occur due to its high rigidity. Therefore, as... Figure 6 As shown in (b) and (ii), torsion occurs at the longitudinal end relative to the central portion of the stamped part 11 in the longitudinal direction. Furthermore, residual stress is generated at the bottom of the forming point on the flange portion 17 on the inner side of the bend and the top plate portion 13 on the outer side of the bend. Figure 6 The absolute values ​​of the tensile and compressive stresses shown in (a) and (i) decrease, or, depending on the circumstances, as Figure 6 As shown in (b) of (i), the residual stress and the bottom stop of the forming are reversed, and the shape becomes a force torque balance.

[0062] Then, the residual stress in the flange portion 17 on the tightly bent side after springback (in) Figure 6 (b) of (i) represents compressive stress) and residual stress in the top plate portion 13 on the outer side of the bend (in Figure 6In (b) of (i), the tensile stress gradually eases and decreases over time without being forced by external forces. Consequently, the shape in equilibrium with the torque of the force changes, thus as... Figure 6 As shown in (c) and (ii), further torsion occurs at the longitudinal end of the stamped part 11.

[0063] In this way, in the stamped part 11 with a Z-shaped cross-section bent in top view, as time passes after stamping and springback, the residual stress in the flange portion 17 on the inner side of the bend and the top plate portion 13 on the outer side of the bend is relieved, thus generating torsion at the end side in the length direction, resulting in a shape from the bottom stop of forming ( Figure 6 (a)(ii)) further deviates from the shape.

[0064] Therefore, similar to Embodiment 1 described above, the inventors have discovered that by further performing a third-stage analysis that alleviates the residual stress in at least the inner flange portion 17 and / or the outer top plate portion 13 of the stamped part 11 after springback obtained in the second stage (springback analysis) of the stamping simulation, and determines the shape that is in equilibrium with the torque of the force on the stamped part 11, it is possible to predict the shape change (torsion at the end in the length direction) of the stamped part 11 over time.

[0065] <Method for Predicting Shape Changes in Stamped Parts>

[0066] Next, the springback-fed shape / residual stress acquisition process, the residual stress mitigation and reduction setting process, and the residual stress mitigation shape analysis process in the shape change prediction method for stamped parts according to Embodiment 2 of the present invention will be described.

[0067] "Shape after springback / Residual stress acquisition process"

[0068] The springback shape / residual stress acquisition process is a process of obtaining the shape and residual stress of the springback stamped part 11 by analyzing the springback of the stamped part 11.

[0069] Residual stress mitigation and reduction setting procedures

[0070] The residual stress mitigation and reduction setting process is a process of setting at least the flange portion 17 and / or the top plate portion 13 of the springback stamped part 11, which is obtained in the springback shape / residual stress acquisition process, a value that is more than the residual stress mitigation and reduction after springback.

[0071] Residual Stress Relief Shape Analysis Process

[0072] The residual stress relief shape analysis process is a process that analyzes the shape of a stamped part 11 for which the value of the stress relief reduction is set in the residual stress relief reduction setting process to determine the force torque balance.

[0073] In this way, according to the shape change prediction method for stamped parts according to Embodiment 2, a stress value that is reduced in intensity than the residual stress after springback is set for at least the flange portion 17 and / or the top plate portion 13 of the springback stamped part 11 obtained through springback analysis, and an analysis is performed to determine the shape balanced with the torque of the force for the stamped part 11 with the set reduced stress value. Therefore, it is possible to simulate the stress easing and shape change over time in the actual stamped part 11, and predict the shape change of the end-side torsion in the length direction of the stamped part 11 after demolding and springback over time.

[0074] The above description of this embodiment 2 is as follows: a stamped part with a Z-shaped cross-section and bent when viewed from above. Figure 5 As an example, a stamped part 11 having a flange portion 17 located on the inside of the bend and a top plate portion 13 located on the outside of the bend is taken as an example.

[0075] However, the shape change prediction method for stamped parts involved in Embodiment 2 only needs to take stamped parts with a Z-shaped cross-section and bent when viewed from above as the object, such as Figure 7 As shown in other examples, a stamped part 31 with a Z-shaped cross-section having a top plate portion 33 with a curved inner side and a flange portion 37 with a curved outer side can be used as an object.

[0076] <Shape changes of stamped parts with Z-shaped cross sections over time (part 2)>

[0077] like Figure 7 As shown, the stamped part 31 has a Z-shaped cross-section having a top plate portion 33, a longitudinal wall portion 35 continuous from the top plate portion 33, and a flange portion 37 continuous from the longitudinal wall portion 35, and includes a shape that is curved along the length direction when viewed from above. Furthermore, the top plate portion 33 and the longitudinal wall portion 35 are continuous by a punch shoulder R portion 39, and the longitudinal wall portion 35 and the flange portion 37 are continuous by a die shoulder R portion 41. Moreover, the top plate portion 33 and the flange portion 37 are connected to... Figure 5 The top plate portion 13 and the flange portion 17 of the stamped part 11 shown have opposite positions on the inner and outer sides of the bend.

[0078] Furthermore, for such a stamped part 31, as described above Figure 3 As shown in the stress relief phenomenon, the residual stress in the top plate portion 33 on the inner side of the bend and the flange portion 37 on the outer side of the bend also gradually eases over time, thus... Figure 8 As shown, the shape change that causes the longitudinal end-side twist of the stamped part 31 can be explained. Furthermore, in Figure 8 (b) of (ii) and Figure 8 In (c) and (ii), the solid line represents the shape of the C1-C1' section at the end of the stamped part 31 in the longitudinal direction, and the dashed line represents the shape of the C0-C0' section at the center of the stamped part 31 in the longitudinal direction.

[0079] like Figure 8 As shown in (a) and (i), if the stamped part 31 formed to the bottom stop of forming is demolded from the mold, springback occurs, resulting in residual stress in the inner bending top plate portion 33 and the outer bending flange portion 37. Figure 8 The absolute values ​​of the compressive and tensile stresses shown in (a) and (i) decrease, or, depending on the circumstances, as Figure 8 As shown in (b) of (i), the residual stress and the forming bottom dead center are reversed, resulting in a shape where the forces are in equilibrium. Thus, as... Figure 8 As shown in (b) and (ii), a twist is generated at the end of the length direction relative to the central portion of the stamped part 31 in the length direction.

[0080] Then, the residual stress in the top plate portion 33 on the tightly bent inner side after the rebound (in) Figure 8 (b) of (i) represents compressive stress) and residual stress in the flange 37 on the outer side of the bend (in Figure 8 In (b) of (i), the tensile stress gradually decreases over time without being forced by external forces. Consequently, the shape in equilibrium with the torque of the force changes, thus... Figure 8 As shown in (c) and (ii), further torsion occurs at the longitudinal end of the stamped part 31.

[0081] In this way, in the stamped part 31 with a Z-shaped cross-section having a top plate portion 33 with a curved inner side and a flange portion 37 with a curved outer side, the residual stress in the top plate portion 33 and the flange portion 37 is also relieved as time passes after stamping and springback, resulting in a shape change with end-side torsion in the length direction, becoming a shape from the bottom stop of forming ( Figure 8 (a) and (ii) are further deviated from the shape.

[0082] Therefore, when predicting the shape change of the stamped part 31 over time, the aforementioned shape / residual stress acquisition process after springback, residual stress mitigation and reduction setting process, and residual stress mitigation shape analysis process are also performed on the stamped part 31 as the object. This allows for the prediction of the shape change of the end-side torsion in the length direction caused by stress mitigation over time after the stamped part 31 has been demolded and springbacked from the die. Here, the residual stress mitigation and reduction setting process sets a stress value for at least the flange portion 37 and / or the top plate portion 33 of the springbacked stamped part 31 that is reduced by the residual stress mitigation after springback.

[0083] Furthermore, in this embodiment 2, the analysis in the springback analysis and residual stress relief shape analysis steps in the springback shape / residual stress acquisition process can be performed using the methods described in embodiment 1.

[0084] Furthermore, in this embodiment 2, for example, when the stamped part 11 with a Z-shaped cross-section is taken as the object, for parts other than the flange portion 17 and the top plate portion 13, the residual stress mitigation and reduction setting process can either directly set the residual stress immediately following springback, or set the stress value obtained by mitigating and reducing residual stress. Alternatively, the stress value obtained by mitigating and reducing residual stress can be set for the stamped part 11 as a whole. Moreover, the residual stress mitigation and reduction setting process can also change the proportion and value of mitigating and reducing residual stress for each part such as the flange portion and the top plate portion.

[0085] In addition, in stamped parts with U-shaped cross-sections ( Figure 2 Stamped parts with a Z-shaped cross-section () or Figure 5 and Figure 7 In any case, during the residual stress mitigation and reduction setting process, the present invention sets a stress value that is at least 5% lower than the residual stress mitigation after springback, thereby enabling good prediction of shape changes after time has passed, which is therefore preferred.

[0086] Furthermore, the above description refers to stamped parts that, although their cross-sectional shapes differ, are curved along their entire length when viewed from above. However, for the present invention, any stamped part that is curved along its length when viewed from above, except for a portion thereof, is acceptable. For example, a stamped part that includes a curved portion and a sideport extending linearly from the curved end of the curved portion to one or both sides of the sideport in the length direction is acceptable.

[0087] Furthermore, in the method for predicting the shape change of stamped parts involved in this invention, there are no particular limitations on the blank (metal sheet) used for stamping, the shape of the stamped part, or its type, but it is more effective for automotive parts stamped from metal sheets with high residual stress.

[0088] Specifically, regarding the thickness of the billet, it is preferably 0.5 mm or more and 4.0 mm or less. Furthermore, regarding the tensile strength of the billet, it is preferably 150 MPa or more and 2000 MPa or less, more preferably 440 MPa or more and 1470 MPa or less.

[0089] In stamping, the use of metal sheets with a tensile strength of less than 150 MPa is relatively rare, thus limiting the advantages of the shape change prediction method for stamping components described in this invention. However, for low-rigidity components such as automotive exterior panels that use metal sheets with a tensile strength of 150 MPa or higher, which are susceptible to shape changes caused by variations in residual stress, the advantages of this invention are greater, making it suitable for appropriate application.

[0090] On the other hand, metal sheets with tensile strengths exceeding 2000 MPa lack ductility, therefore, for example, in... Figure 2 The punch shoulder R 7 of the stamped part 1 with a U-shaped cross-section as shown. Figure 5 In the punch shoulder R portion 19 and die shoulder R portion 21 of the stamped part 11 with the Z-shaped cross section shown, cracks are easily generated during the stamping process, and there are cases where stamping cannot be performed.

[0091] Furthermore, as a type of stamped part, structural parts with U-shaped or Z-shaped cross-sections that are bent when viewed from above, such as roof side rails and front pillar uppers, are preferred. This invention can be widely used in automotive parts that have U-shaped or Z-shaped cross-sections and include shapes that are bent when viewed from above, and whose dimensional accuracy decreases due to torsion at the ends in the length direction caused by the passage of time after stamping.

[0092] Furthermore, the stamping method for the stamped part to which this invention is intended is not particularly limited to bending forming, crash forming, or deep drawing.

[0093] Example 1

[0094] <Stamped parts with U-shaped cross-section>

[0095] In Example 1, as Figure 2 As shown, for a stamped part 1 with a U-shaped cross-section and bent along its length when viewed from above, the shape change over time after demolding and springback is predicted and its validity is verified.

[0096] The stamped part 1 has a top plate portion 3 and a pair of longitudinal wall portions 5. In a top view, the longitudinal wall portion 5a is located on the inner side of the bend, and the longitudinal wall portion 5b is located on the outer side of the bend. Moreover, the forming bottom stop shape of the stamped part 1 sets the curvature radius of the bend at the boundary between the longitudinal wall portion 5b and the punch shoulder R portion 7 to 540 mm on the outer side of the bend and 490 mm on the inner side of the bend, and sets the longitudinal wall height of the longitudinal wall portion 5 in the stamping direction to 50 mm.

[0097] In Example 1, firstly, as an example of a metal sheet, a stamped part 1 was formed by stamping a steel sheet A having mechanical properties shown as an example in Table 1.

[0098] [Table 1]

[0099] (Table 1)

[0100] Plate thickness / mm Yield strength / MPa Tensile strength / MPa stretch / % Steel Plate A 1.2 690 1030 15

[0101] Furthermore, after the stamping process reaches the bottom stop point, the part is ejected from the mold and springs back for 3 days. The shape of the stamped part 1 is measured, and the inclination of the top plate portion 3 at the end of the length direction, with the top plate portion 3 at the center of the length direction as the reference, is measured as the torsion angle.

[0102] Next, an analysis was performed to predict the torsion of the long-direction end of the stamped part 1 based on the passage of time. In the analysis, firstly, a stamping analysis was performed on the process of stamping steel sheet A to the lower limit of forming using a die model that modeled the die used for stamping. The shape and residual stress of the stamped part 1 at the lower limit of forming were then determined.

[0103] Next, a springback analysis was performed to determine the shape and residual stress of the stamped part 1 immediately after it was demolded from the mold at the bottom stop of the forming process.

[0104] Furthermore, for the longitudinal wall portion 5a on the inner side of the bend and / or the longitudinal wall portion 5b on the outer side of the bend of the stamped part 1 obtained through springback analysis, a stress value is set to reduce the absolute value of the residual stress by a predetermined ratio. Moreover, an analysis is performed on the shape of the force moment balance of the stamped part 1 with reduced residual stress, and a predicted value of the inclination angle, i.e., the torsion angle, of the top plate portion 3 at the end of the length direction with the top plate portion 3 at the center of the length direction as a reference is obtained.

[0105] In Example 1, the case where the stress value obtained by reducing the residual stress after springback by a predetermined ratio (stress reduction rate) is set only for the longitudinal wall portion 5b on the outer side of the bent stamped part 1 obtained by springback analysis, or for both the longitudinal wall portion 5a on the inner side of the bent and the longitudinal wall portion 5b on the outer side of the bent, is referred to as Example 1 to Example 3.

[0106] In addition, as a comparison, Comparative Example 1 is a case in which stamping analysis and springback analysis of stamped part 1 were performed in the same way as in Examples 1 to 3 of the Invention, but no analysis was performed to determine the shape of the force torque balance by setting the stress value obtained to reduce residual stress.

[0107] Table 2 summarizes the results of the residual stress mitigation rate and the deviation of the torsion angle at the longitudinal end of the top plate portion 3 from the measured value in Examples 1 to 3 of the Invention and Comparative Example 1. Here, the measured value of the inclination angle, i.e., the torsion angle, of the top plate portion 3 at the longitudinal end with the central top plate portion 3 as the reference is 5.8°.

[0108] [Table 2]

[0109] (Table 2)

[0110]

[0111] In Table 2, the predicted value is the predicted value of the inclination, i.e., the torsion angle, of the top plate portion 3 at the end of the length direction, with the top plate portion 3 at the center of the length direction as the reference. In addition, the difference between the measured value and the predicted value, as well as the error of the predicted value relative to the measured value, are calculated and recorded.

[0112] In Comparative Example 1, the predicted value of the torsion angle was 4.6°, the difference between the measured value and the predicted value was 1.2°, and the error of the predicted value was 20.7%.

[0113] In Invention Example 1, a stress value was set only for the longitudinal wall portion 5b on the outer side of the bend, reducing the residual stress by 5%. The predicted value increased to 5.2°, the difference between the measured value and the predicted value became 0.6°, and the error of the predicted value became 10.3%, resulting in a result that is closer to the measured value than that of Comparative Example 1.

[0114] In Invention Example 2, a stress value was set for both the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend, which reduced the residual stress by 5%. The predicted value increased to 5.6°, the difference between the measured value and the predicted value became 0.2°, and the error of the predicted value became 3.4%. This result is closer to the measured value than that of Comparative Example 1 and Invention Example 1, and is therefore better.

[0115] In Invention Example 3, a stress value was set for both the longitudinal wall portion 5a on the inner side of the bend and the longitudinal wall portion 5b on the outer side of the bend, reducing the residual stress by 10%. The predicted value increased to 6.1°, the difference between the measured value and the predicted value became -0.3°, and the error of the predicted value became -5.2%. Although all are negative values, when compared using absolute values, they are better than those of Comparative Example 1 and Invention Example 1.

[0116] Example 2

[0117] <Stamped parts with Z-shaped cross-section (Part 1)>

[0118] In Example 2, as Figure 5 As shown, for a stamped part 11 with a Z-shaped cross-section and bent along its length when viewed from above, the shape change over time after demolding and springback is predicted, verifying its validity.

[0119] The stamped part 11 has a top plate portion 13, a longitudinal wall portion 15, and a flange portion 17. In a top view, the flange portion 17 is located on the inner side of the bend, and the top plate portion 13 is located on the outer side of the bend. Furthermore, the forming bottom stop shape of the stamped part 11 has a bending radius of 600 mm at the boundary between the longitudinal wall portion 15 and the punch shoulder R portion 19, and a longitudinal wall height of the longitudinal wall portion 5 in the stamping direction of 80 mm.

[0120] In Example 2, firstly, as an example of a metal sheet, a stamped part 11 was formed by stamping a steel sheet A having the mechanical properties shown as an example in Table 1 above.

[0121] Furthermore, after the stamped part 11 is stamped to the lower limit of the forming, immediately after it is demolded from the mold and springs back, and after springing back for 3 days, the shape of the stamped part 11 is measured, and the inclination of the top plate portion 13 at the end of the length direction with the top plate portion 13 at the center of the length direction as the torsion angle is measured.

[0122] Next, an analysis was performed to predict the torsion of the long-direction end of the stamped part 11 based on the passage of time. In the analysis, firstly, a stamping analysis was performed on the process of stamping the steel sheet A to the lower limit of forming using a die model that modeled the die used for stamping. The shape and residual stress of the stamped part 11 at the lower limit of forming were then determined.

[0123] Next, a springback analysis was performed to determine the shape and residual stress of the stamped part 11 immediately after it was demolded from the die model at the bottom stop of the forming process.

[0124] Furthermore, for the flange portion 17 on the inner side of the bend and / or the top plate portion 13 on the outer side of the bend of the springback stamped part 11, obtained through springback analysis, stress values ​​are set to reduce the absolute value of residual stress by a predetermined proportion. Moreover, an analysis is performed on the shape of the force moment balance of the stamped part 11 with reduced residual stress, and a predicted value of the inclination angle, i.e., the torsion angle, of the top plate portion 13 at the end of the length direction with the top plate portion 13 at the center of the length direction as a reference is obtained.

[0125] In Example 2, the case where the stress value obtained by reducing the residual stress after springback by a predetermined ratio (stress reduction rate) is set only for the flange portion 17 on the inner side of the bent stamped part 11 obtained by springback analysis, or for the top plate portion 13 on the outer side of the bent part and the flange portion 17 on the inner side of the bent part, is referred to as Example 4 to Example 6.

[0126] In addition, as a comparison, Comparative Example 2 is a case in which stamping analysis and springback analysis of the stamped part 11 were performed in the same way as in Examples 4 to 6 of the Invention, but no analysis was performed to determine the shape of the force torque balance by setting the stress value obtained to reduce residual stress.

[0127] Table 3 summarizes the results of the residual stress mitigation rate and the deviation of the torsion angle at the longitudinal end of the top plate portion 13 from the measured value in Invention Examples 4 to 6 and Comparative Example 2. Here, the measured value of the inclination angle, i.e., the torsion angle, of the top plate portion 13 at the longitudinal end with the central top plate portion 13 as the reference is 7.7°.

[0128] [Table 3]

[0129] (Table 3)

[0130]

[0131] In Table 3, the predicted value is the value obtained by predicting the inclination angle, or torsion angle, of the top plate portion 13 at the end of the length direction with the center of the top plate portion 13 as the reference. In addition, the difference between the measured value and the predicted value, as well as the error of the predicted value relative to the measured value, are calculated and recorded.

[0132] In Comparative Example 2, the predicted value of the torsion angle was 6.8°, the difference between the measured value and the predicted value was 0.9°, and the error of the predicted value was 11.7%.

[0133] In Invention Example 4, only the flange portion 17 on the inner side of the bend was set with a stress value that reduced the residual stress by 10%. The predicted value increased to 7.0°, the difference between the measured value and the predicted value became 0.7°, and the error of the predicted value became 9.1%, which is a result that is closer to the measured value than that of Comparative Example 2.

[0134] In Invention Example 5, a stress value was set for both the top plate portion 13 on the outer side of the bend and the flange portion 17 on the inner side of the bend, which reduced the residual stress by 10%. The predicted value increased to 7.4°, the difference between the measured value and the predicted value became 0.3°, and the error of the predicted value became 3.9%. This result is closer to the measured value than that of Comparative Example 2 and Invention Example 4, and is therefore better.

[0135] In Invention Example 6, stress values ​​were set for both the top plate portion 13 on the outer side of the bend and the flange portion 17 on the inner side of the bend, resulting in a 20% reduction in residual stress. The predicted value increased to 8.0°, the difference between the measured value and the predicted value became -0.3°, and the error of the predicted value became -3.9%. Although all were negative values, when compared using absolute values, they showed improvement compared to Comparative Example 2 and Invention Example 4, and were as good as Invention Example 5.

[0136] Example 3

[0137] <Stamped parts with Z-shaped cross-section (Part 2)>

[0138] In Example 3, for Figure 7 The Z-shaped cross-section of the stamped part 31, which is bent along its length when viewed from above, is shown. The shape change over time after demolding and springback is predicted, which verifies its validity.

[0139] like Figure 7 As shown, the stamped part 31 has a top plate portion 33, a longitudinal wall portion 35, and a flange portion 37. In a top view, the top plate portion 33 is located on the inner side of the bend, and the flange portion 37 is located on the outer side of the bend. Furthermore, the forming bottom stop shape of the stamped part 31 sets the radius of curvature of the bend at the boundary between the longitudinal wall portion 35 and the punch shoulder R portion 39 to 800 mm, and sets the longitudinal wall height of the longitudinal wall portion 5 in the stamping direction to 60 mm.

[0140] In Example 3, firstly, as an example of a metal sheet, a stamped part 31 was formed by stamping a steel sheet A having the mechanical properties shown as an example in Table 1 above.

[0141] Furthermore, after the stamped part 31 is stamped to the lower limit of the forming process, immediately after demolding from the mold and springing back, and after springing back for 3 days, the shape of the stamped part 31 is measured, and the inclination of the top plate portion 33 at the end of the length direction with the top plate portion 33 at the center of the length direction as the torsion angle is measured.

[0142] Next, an analysis was performed to predict the torsion of the long-direction end of the stamped part 31 based on the passage of time. In the analysis, firstly, a stamping analysis was performed on the process of stamping the steel sheet A to the lower limit of forming using a die model that modeled the die used for stamping. The shape and residual stress of the stamped part 31 at the lower limit of forming were then determined.

[0143] Next, a springback analysis was performed to determine the shape of the stamped part 31 after it was demolded from the mold at the bottom stop of the forming process and to assess the residual stress.

[0144] Furthermore, for the top plate portion 33 on the inner side of the bend and / or the flange portion 37 on the outer side of the bend of the springback stamped part 31, obtained through springback analysis, stress values ​​are set to reduce the absolute value of residual stress by a predetermined proportion. Moreover, an analysis is performed on the shape of the stamped part 31 for which the force torque balance is obtained, and the predicted value of the inclination angle, i.e., the torsion angle, of the top plate portion 33 at the end of the length direction with the top plate portion 33 at the center of the length direction as a reference is obtained.

[0145] In Example 3, the case in which the stress value obtained by reducing the residual stress after springback by a predetermined ratio (stress reduction rate) is set only for the flange portion 37 on the outer side of the bent stamped part 31 obtained by springback analysis, or for both the flange portion 37 on the outer side of the bent and the top plate portion 33 on the inner side of the bent, is described as Example 7 to Example 9.

[0146] In addition, as a comparison, Comparative Example 3 is a case in which stamping analysis and springback analysis of the stamped part 31 were performed in the same way as in Examples 7 to 9 of the Invention, but no analysis was performed to determine the shape of the force torque balance by setting the stress value obtained to reduce residual stress.

[0147] Table 4 summarizes the results of the residual stress mitigation reduction rate and the deviation of the torsion angle at the longitudinal end of the top plate portion 33 from the measured value in Examples 7 to 9 of the Invention and Comparative Example 3. Here, the measured value of the inclination angle, i.e., the torsion angle, of the top plate portion 33 at the longitudinal end with the central top plate portion 33 as the reference is 7.8°.

[0148] [Table 4]

[0149] (Table 4)

[0150]

[0151] In Table 4, the predicted value is the value obtained by predicting the inclination angle, or torsion angle, of the top plate portion 33 at the end of the length direction with the top plate portion 33 at the center of the length direction as a reference. In addition, the difference between the measured value and the predicted value, as well as the error of the predicted value relative to the measured value, are calculated and recorded.

[0152] In Comparative Example 3, the predicted value of the torsion angle was 7.2°, the difference between the measured value and the predicted value was 0.6°, and the error of the predicted value was 7.7%.

[0153] In Invention Example 7, only the flange 37 on the outer side of the bend was set with a stress value that reduced the residual stress by 10%. The predicted value increased to 7.6°, the difference between the measured value and the predicted value became 0.2°, and the error of the predicted value became 2.6%, which is a result that is closer to the measured value than that of Comparative Example 3.

[0154] In Invention Example 8, a stress value was set for the flange portion 37 on the outer side of the bend, reducing the residual stress by 10%, and a stress value was set for the top plate portion 33 on the inner side of the bend, reducing the residual stress by 5%. The predicted value increased to 7.9°, the difference between the measured value and the predicted value became -0.1°, and the error of the predicted value became -1.3%. Although all are negative values, when compared using absolute values, they are better than those of Comparative Example 3 and Invention Example 7.

[0155] In Invention Example 9, a stress value was set for the flange portion 37 on the outer side of the bend, reducing the residual stress by 20%, and a stress value was set for the top plate portion 33 on the inner side of the bend, reducing the residual stress by 10%. The predicted value increased to 8.2°, the difference between the measured value and the predicted value became -0.4°, and the error of the predicted value became -5.1%. Although both were negative values, when compared using absolute values, they showed improvement compared to Comparative Example 3, which is better.

[0156] Industrial availability

[0157] According to the present invention, a method for predicting the shape change of a stamped part that has a U-shaped or Z-shaped cross-section and includes a shape that bends along the length direction when viewed from above is provided. This method predicts the shape change of the stamped part based on a time unit after springback at the instant of demolding.

[0158] Explanation of reference numerals in the attached figures

[0159] 1…Stamped part; 3…Top plate portion; 5…Longitudinal wall portion; 5a…Longitudinal wall portion (inner curved side); 5b…Longitudinal wall portion (outer curved side); 7…Punch shoulder R portion; 11…Stamped part; 13…Top plate portion (outer curved side); 15…Longitudinal wall portion; 17…Flange portion (inner curved side); 19…Punch shoulder R portion; 21…Die shoulder R portion; 31…Stamped part; 33…Top plate portion (inner curved side); 35…Longitudinal wall portion; 37…Flange portion (outer curved side); 39…Punch shoulder R portion; 41…Die shoulder R portion.

Claims

1. A method for predicting the shape change of a stamped part, for a stamped part having a U-shaped cross-sectional shape having a top plate portion and a pair of longitudinal walls continuous from the top plate portion, and including a shape that bends along the length direction when viewed from above, predicting the shape change of the end-side torsion in the length direction caused by stress relief over time after springback at the instant of demolding from the die. The method for predicting the shape change of stamped parts is characterized by including: The springback shape / residual stress acquisition process involves obtaining the shape and residual stress of the springback stamped part through springback analysis. The residual stress mitigation and reduction setting process involves setting a stress value that is more mitigated than the residual stress after springback for either of the pair of longitudinal wall portions of the stamped part following springback. as well as The residual stress relief shape analysis process involves determining the shape of the force torque balance for the stamped part with a set value for the stress relief and reduction.

2. A method for predicting the shape change of a stamped part, for a stamped part having a Z-shaped cross-sectional shape having a top plate portion, a longitudinal wall portion continuous from the top plate portion, and a flange portion continuous from the longitudinal wall portion, and including a shape that bends along the length direction when viewed from above, predicting the shape change of the end-side torsion in the length direction caused by stress relief over time after springback at the instant of demolding from the die. The method for predicting the shape change of stamped parts is characterized by including: The springback shape / residual stress acquisition process involves obtaining the shape and residual stress of the springback stamped part through springback analysis. The residual stress mitigation and reduction setting process involves setting a stress value for at least the top plate portion and / or the flange portion of the springback stamped part that is less than the residual stress mitigation and reduction value after springback. as well as The residual stress relief shape analysis process involves determining the shape of the force torque balance for the stamped part with a set value for the stress relief and reduction.

3. The method for predicting the shape change of stamped parts according to claim 1 or 2, characterized in that, In the residual stress mitigation and reduction setting process, a value is set that reduces the residual stress by more than 5% compared to the stress after the rebound.

4. The method for predicting the shape change of stamped parts according to claim 1 or 2, characterized in that, The blank for stamping the stamped part is a metal sheet with a tensile strength of 150 MPa or higher and 2000 MPa or lower.

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