Method for determining thickness reduction amount of sheet material, and thickness-reduced component

Abstract

[Problem] To prevent a sheet material from cracking even when the thickness of the sheet material is reduced. [Solution] A method for determining a reduction in thickness of a sheet material according to the present invention involves estimating, in a first simulation, a first reduction rate of the sheet thickness when a workpiece 10A is molded into a component shape in a state where the original sheet thickness thereof is maintained. The method also involves: predicting, in a second simulation, the thickness reduction amount of the sheet material from the first reduction rate and a molding limit of the sheet material; and, when the sheet thickness is reduced by pulling the sheet material so as to achieve the predicted thickness reduction amount and the sheet material is press-molded into the shape of a component 10D, confirming whether a second reduction rate of the sheet thickness falls within the range of the molding limit of the sheet material.

Description

Method for determining thickness reduction amount of plate material and thickness reduction part

[0001] The present invention relates to a method for determining the amount of thinning of a plate material and a part with thinning.

[0002] Parts used in automobile suspensions and other applications are formed by pressing steel material. The price of these parts affects the price of the automobile itself, so research into weight reduction is often conducted while taking into account factors such as weight and strength.

[0003] The technology for reducing the weight of press-molded parts describes a method for forming thin-walled sections by restraining a plate material with a restraining means that restrains the plate material at at least two different points, and then pulling the plate material by moving the restraining means relatively away from each other as a pair of press dies move closer to each other.

[0004] JP 2011-235289 A

[0005] The present inventors have focused on the fact that when the thinning technique as disclosed in Patent Document 1 is actually used, there is a risk of cracks occurring in the workpiece during press forming, and have been conducting extensive research.

[0006] Therefore, an object of the present invention is to prevent cracks from occurring in a workpiece material during press forming even when the material is thinned.

[0007] One aspect of the present invention is a method for determining the amount of metal loss in a sheet material, comprising a first simulation and a second simulation. The first simulation predicts a first reduction rate of the sheet material thickness when the sheet material is formed into the shape of a part from its original thickness. The second simulation predicts the amount of metal loss from the forming limit of the sheet material and the first reduction rate, and determines the second reduction rate of the sheet material thickness when the sheet material is pulled to reduce its thickness to the predicted amount and then formed into the shape of the part. The second reduction rate is determined by confirming that the second reduction rate is within the range of the forming limit of the workpiece.

[0008] Fig. 5 is a diagram showing an example of the configuration of elongation of a press-molded product in a stress-strain curve. Fig. 6 is a schematic diagram showing a first simulation in the method for determining the amount of metal loss in a plate material according to an embodiment of the present invention. Fig. 7 is a schematic diagram showing a second simulation in the method for determining the amount of metal loss in a plate material according to an embodiment. Fig. 8 is a flowchart showing the method for determining the amount of metal loss in a plate material according to an embodiment. Fig. 9 is a diagram showing a case where the method for determining the amount of metal loss in a plate material is applied to a part different from that in Fig. 1. Fig. 10 is a diagram showing the part according to Fig. 5 alone.

[0009] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following description does not limit the technical scope or meaning of terms described in the claims. Also, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0010] FIG. 1 is a diagram showing an example of the elongation configuration of a press-formed product on a stress-strain curve. FIG. 2 is a schematic diagram showing a first simulation of a method for determining the amount of metal loss in a sheet material according to an embodiment. FIG. 3 is a schematic diagram showing a second simulation of a method for determining the amount of metal loss in a sheet material according to an embodiment. FIG. 4 is a flowchart showing a method for determining the amount of metal loss in a sheet material. The method for determining the amount of metal loss in a workpiece 10A according to an embodiment of the present invention can be used, for example, to determine the amount of metal loss in a workpiece when manufacturing a front suspension member such as a metal-reduced part 10F shown in FIG. 2.

[0011] The above-described thinned part 10F is formed by a press, and a characteristic of the press is that the thickness of the workpiece (plate material) becomes thinner during drawing, etc. The inventors have considered the following method for determining the amount of thinning of the workpiece material 10A, since strength is required for the part to be designed and the plate thickness becomes thinner during processing.

[0012] As shown in Figure 1, materials such as steel are Ｕ It undergoes elastic deformation up to the yield point of σ, but once the yield stress is exceeded, plastic deformation occurs, and σ ｍａｘ The inventors have calculated the elongation (total elongation δ Ｔ) is due to the elongation caused by the part molding (part B), and there is also room for elongation caused by the reduction in the thickness of the material by stretching the material (part A). Therefore, the following method for determining the amount of thinning was devised. Part C in Figure 1 shows the stage where roughness appears on the surface of the material just before the material breaks, and δ Ｕ The range of δ Ｌ The range indicates local elongation.

[0013] First, a workpiece 10A having a predetermined thickness is selected (S1 in FIG. 4). Then, as shown in FIG. 2, a simulation is performed in which the workpiece 10A is formed into a predetermined part shape while maintaining the predetermined thickness (S2). This simulation is referred to as the "first simulation" in this specification. The first simulation can use various software used in CAE (Computer Aided Engineering) for press molding, and aims to confirm the thickness reduction rate using a blank shape (part blank shape) obtained by trimming a workpiece of normal thickness.

[0014] The workpiece has a limit to the thickness reduction that can be achieved depending on the material. Therefore, the thickness of the workpiece 10A when formed into a predetermined shape is determined, and the reduction rate of the thickness (referred to as the first reduction rate) is checked to see if the first reduction rate when the workpiece 10A is formed exceeds the forming limit. If the first reduction rate exceeds the forming limit (S3: NO), the part shape is reconsidered (S4).

[0015] If the thickness reduction rate is within the forming limit (S3: YES), the designer predicts the amount of thickness reduction of the workpiece 10A from the forming limit of the workpiece 10A and the first reduction rate, and sets the pulling amount of the workpiece 10C (S5). Then, the sizes of a rectangular blank, which is an example of the shape of the workpiece 10C before pulling, and a reduced-thickness blank after pulling are determined (S6). Next, the workpiece 10C is pulled to achieve the predicted amount of thickness reduction, thereby forming a reduced-thickness blank 10D in which a portion of the workpiece 10C has been reduced in thickness.

[0016] The thin-walled blank 10D has original thickness portions d1, which are provided at sheet holding portions such as both ends and have the same thickness as the sheet thickness before thinning, gradual-change portions d2, where the sheet thickness gradually changes, and thin-walled portions d3, where the sheet thickness is thinner (see FIG. 3). The thin-walled portions d3 are portions where the sheet thickness has decreased to a value targeted by the designer, and the gradual-change portions d2 are provided between the original thickness portions d1 and the thin-walled portions d3 and refer to portions where the sheet thickness gradually changes, for example, monotonically.

[0017] The term "monotonic" as used herein includes cases where the thickness changes linearly between the original thickness portion d1 and the thinned portion d3, and cases where the thickness changes curvilinearly, convex outward or inward, but does not include cases where the thickness increases and decreases, such as in a sine wave. By connecting the thinned portion d3 and the original thickness portion d1 with the gradually changing portion d2, there is no sudden change in thickness, and this configuration prevents stress concentration. While the original thickness portion d1 has been described as being located at both ends of the workpiece 10A in a predetermined direction, the original thickness portion d1 may be located at any location other than both ends as long as the thickness remains unchanged from before the thinning.

[0018] Next, it is confirmed whether the size of the reduced-metal blank 10D is larger than the size of the component blank 10E (S7). If the size of the reduced-metal blank 10D is not larger than the size of the component blank 10E (S7: NO), the pulling amount is reset, or the sizes of the rectangular blank and the reduced-metal blank 10D are redetermined, and then the rectangular blank is pulled (S8).

[0019] If the size of the reduced-metal blank 10D is larger than the size of the component blank 10E (S7: YES), the reduced-metal blank 10D is formed into the component blank 10E in the trimming process. Then, a simulation is performed to form this component blank 10E into the reduced-metal part 10F (S9). This simulation is referred to as a second simulation in this specification. The designer then confirms whether the sum of the thickness reduction rate when the workpiece 10C is formed into the reduced-metal blank 10D and the thickness reduction rate when the reduced-metal blank 10D is formed into the reduced-metal part 10F (referred to as a second reduction rate) is within the forming limit.

[0020] If the second reduction rate exceeds the forming limit (S10: NO), the amount of stretching of the workpiece 10C is adjusted to remake the reduced-metal blank 10D (S5). The sizes of the rectangular blank and the stretched reduced-metal blank 10D are then determined (S6). After confirming that the reduced-metal blank 10D is not smaller than the shape of the part blank 10E (S7), a second simulation is performed in which the part blank 10E is formed by a trimming process, and the new part blank 10E is formed into the reduced-metal part 10F (S9).

[0021] If the second reduction rate of the thinned part 10F is within the forming limit (S10: YES), the shape is adopted as the official shape. Note that work hardening occurs during the forming of the workpiece. Therefore, even if the forming limit of the workpiece is determined numerically, it is necessary to take into account the influence of work hardening when predicting the second reduction rate in step S10 from the first reduction rate in step S3.

[0022] As described above, in this embodiment, the amount of metal loss in the workpiece is determined from the first and second simulations. In the first simulation, the reduction rate of the thickness of the workpiece 10A when the workpiece 10A is formed into the shape of a part from its original thickness is predicted as the first reduction rate. Then, in the second simulation, the amount of metal loss is predicted from the forming limit of the workpiece 10A and the first reduction rate. Then, the workpiece 10C is pulled to reduce its thickness to achieve the predicted amount of metal loss, and the reduction rate of the thickness when the workpiece 10C is formed into the shape of the metal-reduced part 10F is determined as the second reduction rate. It is confirmed that the second reduction rate is within the range of the forming limit of the workpiece 10A.

[0023] This configuration allows for appropriate thinning molding according to the part shape. Furthermore, weight reduction is possible by thinning only areas that do not affect part performance. Furthermore, since the thinned part 10F is reproduced using the thinned blank 10D, the cost of input materials can be reduced.

[0024] In the first simulation, the size of the workpiece 10A is set, the workpiece 10A is formed into a part 10B, and the first reduction rate of the workpiece 10A is estimated by determining the thickness of the formed part 10B. By configuring in this manner, it is possible to obtain information necessary to form the workpiece 10A into a reduced-wall shape without breaking it.

[0025] In the second simulation, the maximum thickness reduction rate of the thinned part 10F formed after the workpiece 10C is pulled to reduce its thickness is set as the second reduction rate, and it is confirmed whether the second reduction rate is within the forming limit of the workpiece 10C. By configuring in this way, it is possible to prevent cracks from occurring when the workpiece 10C is actually press-formed.

[0026] In the second simulation, the amount of tension of the workpiece 10C is set based on the forming limit of the workpiece 10C and the part forming amount based on the original thickness, and the shape of the workpiece 10C after tensioning is trimmed to the part shape. This configuration improves the accuracy of determining whether cracks will occur when the reduced-thickness workpiece is formed into the actual shape.

[0027] Furthermore, the second reduction rate is set by taking into consideration the reduction in elongation due to work hardening of the workpiece 10C. In reality, work hardening occurs during press working, which may reduce the maximum reduction rate in thickness at which cracks occur in the workpiece. Therefore, by configuring in this way, it is possible to prevent cracks from occurring even when the workpiece 10C is actually press-formed into the simulated shape.

[0028] Furthermore, when manufacturing the metal-reduced part 10F according to the above-described process, the weight of the metal-reduced part 10F can be reduced by determining the amount of metal-reduced part 10F from the plate material.

[0029] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the claims. Figures 5 and 6 are diagrams illustrating a case where the metal-reduction amount determination method according to the present invention is applied to a part different from that shown in Figure 2. In the above description, the metal-reduction part 10F applied to the embodiment is a front suspension member. However, as shown in Figures 5 and 6, the metal-reduction amount determination method may also be applied to a part 10G, such as a torsion beam of a torsion beam suspension located at the rear, as long as the part has a reduced thickness due to press forming.

[0030] The present invention encompasses the following aspects and configurations.

[0031] 1. A method for determining an amount of metal reduction of a plate material, comprising: a first simulation and a second simulation; wherein in the first simulation, a rate of reduction in plate thickness when a plate material is formed into the shape of a part from a state of its original thickness is predicted as a first reduction rate; in the second simulation, an amount of metal reduction is predicted from the forming limit of the plate material and the first reduction rate; the plate material is pulled to reduce its thickness to achieve the predicted amount of metal reduction, and then the rate of reduction in plate thickness when the plate material is formed into the shape of the part is set as a second reduction rate; and the amount of metal reduction of the plate material is determined by confirming that the second reduction rate is within the range of the forming limit of the plate material.

[0032] 2. The method for determining a metal loss reduction amount of a plate material according to 1., wherein in the first simulation, a size of the plate material is set, the plate material is formed into a part shape, and the plate thickness of the formed part is determined to thereby estimate the first reduction rate of the plate material.

[0033] 3. The method for determining a metal loss reduction amount of a plate material according to 1. or 2., wherein in the second simulation, a maximum plate thickness reduction rate of the part formed after the plate thickness is reduced by pulling the plate material is set as the second reduction rate, and it is confirmed whether the second reduction rate is within a range of a forming limit of the plate material.

[0034] 4. The method for determining an amount of thinning of a plate material according to any one of 1. to 3., wherein in the second simulation, a forming limit amount of the plate material is set as an amount of tension of the plate material from a part forming amount based on the original plate thickness, and the shape of the plate material after tensioning is trimmed to the shape of the part.

[0035] 5. The method for determining the amount of thinning of a plate material according to any one of 1. to 4., wherein when setting the second reduction rate, a reduction in elongation due to work hardening of the plate material is taken into consideration.

[0036] 6. A metal-reduced part in which the amount of metal-reducing of the plate material is set by the method according to any one of 1. to 5.

[0037] 7. The metal-thickness-reduced part according to 6., having an original thickness portion whose thickness is the same as the thickness before metal-thickness reduction, a metal-thickness-reduced portion whose thickness has been reduced to a set value, and a gradually changing portion provided between the metal-thickness-reduced portion and the original metal-thickness portion, whose thickness changes.

[0038] 10A work material, 10B parts.

Claims

1. A method for determining an amount of metal reduction in a sheet material, comprising: a first simulation and a second simulation; wherein in the first simulation, a rate of reduction in thickness when a sheet material is formed into the shape of a part from a state of its original thickness is predicted as a first reduction rate; in the second simulation, an amount of metal reduction is predicted from the forming limit of the sheet material and the first reduction rate; the sheet material is pulled to reduce its thickness to achieve the predicted amount of metal reduction, and then the rate of reduction in thickness when the sheet material is formed into the shape of the part is defined as a second reduction rate; and the amount of metal reduction in the sheet material is determined by confirming that the second reduction rate is within the range of the forming limit of the sheet material.

2. A method for determining the amount of thinning of a plate material as described in claim 1, wherein in the first simulation, the size of the plate material is set, the plate material is formed into a part shape, and the first reduction rate of the plate material is estimated by determining the plate thickness of the formed part.

3. A method for determining the amount of thinning of a plate material according to claim 1 or claim 2, wherein in the second simulation, the maximum thickness reduction rate of the part formed after the plate material is pulled to reduce its thickness is set as the second reduction rate, and it is confirmed whether the second reduction rate is within the forming limit range of the plate material.

4. A method for determining the amount of thinning of a plate material according to claim 1, wherein in the second simulation, the forming limit amount of the plate material is set to the amount of tension of the plate material from the part forming amount based on the original plate thickness, and the shape of the plate material after tension is trimmed to the shape of the part.

5. A method for determining the amount of thinning of a plate material according to claim 1, wherein the second reduction rate is set taking into consideration the reduction in elongation due to work hardening of the plate material.

6. A metal-reduced part in which the amount of metal-reducing of the plate material is set by the method according to claim 1.

7. A metal-reduced part according to claim 6, having an original thickness portion whose thickness is the same as the thickness before metal-reducing, a metal-reduced portion whose thickness has been reduced to a set value, and a gradually changing portion provided between the metal-reduced portion and the original thickness portion, in which the thickness changes.

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