WO2024047968A1

WO2024047968A1 - Method for manufacturing press-molded article

Info

Publication number: WO2024047968A1
Application number: PCT/JP2023/019071
Authority: WO
Inventors: 裕之田中
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-08-29
Filing date: 2023-05-23
Publication date: 2024-03-07
Also published as: JPWO2024047968A1

Abstract

This method for manufacturing a press-molded article 1 is a method for manufacturing a press-molded article 1 having a main body part 11, which has a top plate part 5 and vertical wall parts 7 formed with ridgeline parts 9 interposed therebetween, and an outer flange part 3 formed on an end of the main body part 11 so as to be continuous from the top plate part 5, the ridgeline parts 9, and the vertical wall parts 7, the method including: an intermediate molding step for molding an intermediate molded article 24 that has the top plate part 5 and the vertical wall parts 7 formed with the ridgeline parts 9 interposed therebetween and that has a step formation part 27 at a root section of an outward-flange-equivalent part 25 so that the outward-flange-equivalent part 25 bulges outwards; and a target shape molding step for folding the outward-flange-equivalent part 25 of the intermediate molded article 24 outwards, forming an outward flange part 3, and molding a target shape.

Description

Manufacturing method of press molded products

The present invention relates to a method for manufacturing a press-formed product, and particularly includes a top plate portion and a vertical wall portion continuous to the top plate portion via a ridgeline portion, and includes a top plate portion, a ridgeline portion, and an end portion of the vertical wall portion. The present invention relates to a method of manufacturing a press-formed product having a continuously formed outward flange portion.

Due to stricter collision safety standards for automobiles, the collision safety of car bodies is being improved, and in response to carbon dioxide emission regulations, it is also necessary to reduce the weight of car bodies in order to improve fuel efficiency and shift to electric vehicles. In order to simultaneously improve the collision safety and reduce the weight of these vehicle bodies, high-strength steel plates (also referred to as high-tensile steel materials) with a tensile strength of 590 MPa or higher are increasingly being applied to vehicle body structural parts.

For example, as shown in FIG. 4, an automobile part, such as a floor cross member, includes a top plate part 5, a vertical wall part 7, and a ridgeline part 9 connecting the top plate part 5 and the vertical wall part 7. There is a press-formed product 1 having an outward flange portion 3 continuously formed at the end of a plate portion 5, a ridgeline portion 9, and a vertical wall portion 7.

When such a press-formed product 1 is press-formed, the portion of the outward flange portion 3 that is continuous with the ridgeline portion 9 (hereinafter referred to as the “corner flange portion”) undergoes stretch flange deformation, causing the corner flange portion 3b to deform. Cracks are more likely to occur at the tip.

Conventionally, regarding a method for manufacturing a press-formed product having an outward flange portion continuously formed at the end of the vertical wall portion 7, Patent Document 1 discloses a method for manufacturing a saddle-shaped press-formed product. ing. In Patent Document 1, the top plate constituent parts of the blank are curved, a first force directed from the inner surface side to the outer face side of the blank is applied, and a second force is applied to each of the outer face sides of the vertical wall constituent parts in the direction facing each other. Press forming is performed by applying a composite force of a force and a third force in the opposite direction to the first force. The method disclosed in Patent Document 1 is a method of molding the top plate portion, the vertical wall portion, and the outward flange portion at the same time.

Additionally, Patent Document 2 discloses, as another press forming method, a press forming method in which a metal plate is formed into a U-shaped cross section and then the outward flange portion is bent. In the method disclosed in Patent Document 2, when bending and raising the outward flange, forming of the flange starts from the top plate and the vertical wall, thereby reducing strain in the outward flange. It is said that it can be dispersed on the vertical wall side.

Patent Document 3 discloses that an outward flange is formed by a shearing step of forming a stepped portion in a workpiece having a top plate, a vertical wall, and a flange, and a cutting step of removing an unnecessary portion near the stepped portion. A press molding method is disclosed.

International Publication No. 2019/216317 International Publication No. 2022/049916 International Publication No. 2016/194963

In the method disclosed in Patent Document 1, the mold structure is quite complicated and the manufacturing cost of the mold increases. Furthermore, since a combined force of a third force opposite to the first force is applied, it is difficult to sufficiently and evenly press the blank to press-form it, and it is also difficult to obtain a press-formed product with good dimensional accuracy.

In this regard, as disclosed in Patent Document 2, a press molding method in which a metal plate is molded into a U-shaped cross section and then the outward flange portion is bent can use a simple mold and improve dimensional accuracy. However, when press-forming high-strength materials with even higher strength, the connection between the ridgeline and the corner flange of the outward flange (hereinafter sometimes simply referred to as the "corner flange connection") may buckle ( A problem arose in that wrinkles and creases were more likely to occur.

Furthermore, the method disclosed in Patent Document 3 has a problem in that the mold structure is complicated and a cutting step is required.

The present invention has been made in view of the above problems, and an object of the present invention is to include a top plate portion and a vertical wall portion continuous to the top plate portion via a ridgeline portion, and to When manufacturing a press-formed product that has an outward flange that is continuously formed at the end of a vertical wall, there is no need to use a mold with a complicated structure, and buckling does not occur at the connection of the corner flange. Another object of the present invention is to provide a method for manufacturing a press-formed product that can stably produce a press-formed product with good dimensional accuracy.

In order to solve the above-mentioned problems and achieve the objectives,
(1) The method for manufacturing a press-formed product according to the present invention includes a main body portion having at least a top plate portion and a vertical wall portion formed via a ridgeline portion, and an end portion of the main body portion having the top plate. A method for manufacturing a press-molded product having an outward flange portion formed continuously on the ridgeline portion and the vertical wall portion, the method comprising: a top plate portion and a vertical wall portion formed via the ridgeline portion; an intermediate molding step of molding an intermediate molded product having an outwardly swollen stepped portion at the root of a portion corresponding to the outward flange molded into the outward flange portion; The present invention is characterized by comprising a target shape forming step of bending the outer flange portion outward and forming the outward flange portion into a target shape.

(2) In the method for manufacturing a press-formed product according to the present invention, in the invention described in (1) above, the intermediate forming step includes forming the top plate portion, the ridgeline portion, the vertical wall portion, and the step-shaped portion. , which is characterized by press molding in one step.

(3) In the method for manufacturing a press-formed product according to the present invention, in the invention described in (1) above, the intermediate forming step is performed after press-forming the top plate portion, the ridgeline portion, and the vertical wall portion. , the step-shaped portion is press-molded.

The method for manufacturing a press-formed product according to the present invention includes a top plate portion and a vertical wall portion continuous to the top plate portion via a ridgeline portion, and a vertical wall portion continuous to the top plate portion, the ridgeline portion, and the end portion of the vertical wall portion. When manufacturing press-formed products with outward-facing flanges, we can produce press-formed products with high dimensional accuracy without using a mold with a complicated structure and without buckling at the corner flange connections. This has the effect that products can be manufactured stably.

FIG. 1 is an explanatory diagram of a method for manufacturing a press-formed product according to an embodiment. FIG. 2 is a diagram showing an analysis result of the forming process of the target shape forming process according to the embodiment. FIG. 3 is a diagram schematically showing the forming process of the target shape forming process according to the embodiment. FIG. 4 is an explanatory diagram of an example of a press-formed product targeted by the present invention. FIG. 5 is an explanatory diagram of a conventional method for manufacturing a press-molded product. FIG. 6 is a diagram showing an analysis result of a molding process for molding an outward flange portion in a conventional example. FIG. 7 is a diagram schematically showing a molding process for molding an outward flange portion in a conventional example.

Below, embodiments of the method for manufacturing a press-formed product according to the present invention will be described. Note that the present invention is not limited to this embodiment.

Before describing the embodiments of the present invention, the shape of a press-formed product targeted by the present invention will be described based on FIG. 4 showing an example thereof. As shown in FIG. 4, the object of the present invention is a press-molded product 1 having an outward flange portion 3, which includes a top plate portion 5, a vertical wall portion 7, and a top plate portion 5 and a vertical wall. The main body part 11 has a ridgeline part 9 connecting the parts 7. The press-formed product 1 has an outward flange portion 3 formed at an end of the main body portion 11 and continuous with the top plate portion 5, the ridgeline portion 9, and the vertical wall portion 7. In the example shown in FIG. 4, the press-formed product 1 includes a horizontal flange portion 13 at the lower end of the vertical wall portion 7. As shown in FIG. In the following description, the portions of the outward flange portion 3 that are continuous with the top plate portion 5, the ridgeline portion 9, and the vertical wall portion 7 will be referred to as the top plate flange portion 3a, the corner flange portion 3b, and the vertical wall flange, respectively. It is called part 3c.

FIG. 5 is a diagram showing a conventional method for forming the press-formed product 1. Conventionally, as shown in FIG. 5(a), first, an intermediate molded product having a top plate portion 5, a ridgeline portion 9, a vertical wall portion 7, and a horizontal flange portion 13 at the lower end of the vertical wall portion 7 is manufactured. 15 is formed. The intermediate molded product 15 has a top plate part 5, a ridgeline part 9, and a vertical wall part 7 extending from the end thereof, and these extension parts form the outward flange part 3 (top plate flange part 3a, top plate flange part 3a, They become a corner flange portion 3b and a vertical wall flange portion 3c). Therefore, in this embodiment, the extending portion is referred to as the outward flange equivalent portion 17. Each part of the intermediate molded product 15 may be press-molded at the same time, or each part may be press-molded individually. Thereafter, as shown in FIG. 5(b), the outward flange portion 17 of the intermediate molded product 15 is bent outward to form the outward flange portion 3, resulting in a press molded product 1 having the target shape.

As a forming method for bending the outward flange equivalent part 17, for example, as disclosed in Patent Document 2, a bending force is first inputted to the top plate flange equivalent part 17a and the vertical wall flange equivalent part 17c. . Then, in a subsequent forming method in which the outward flange equivalent portion 17 is bent, a bending force may be input to the corner flange equivalent portion 17b.

In Fig. 6, a steel plate with a thickness of 1.4 mm and a tensile strength of 590 MPa class is used, and the target shape is that the height of the outward flange part 3 is 18 mm, and the top plate part 5, ridge line part 9, vertical wall part 7 and the outward facing It is a figure which shows the result of FEM analysis about the case where R of the boundary part with the flange part 3 is 3 mm. In FIG. 6, the state of the intermediate molded product 15 before the outward flange portion 3 is molded (FIG. 6(a)) is changed to the state where the outward flange portion 3 is bent and raised to the bottom dead center of molding (FIG. 6(d)). ), including intermediate stages.

Tension is applied to the tip of the outward flange portion 3, reducing the plate thickness. On the other hand, a large compressive force acts on the connecting portion 35 (see FIG. 4) of the corner flange portion 3b. Therefore, the compressive force increases the plate thickness, and the maximum plate thickness increase rate at the bottom dead center of molding reaches 47%, causing wrinkles and folds (see FIG. 6(d)). Here, the plate thickness increase rate is calculated by determining the difference between the plate thickness at the relevant portion and the plate thickness of the blank metal plate, and calculating the ratio to the plate thickness of the blank metal plate.

FIG. 7 is a diagram schematically showing the results of a more detailed study of the process by which wrinkles and folds occur in conventional press forming. FIG. 7 shows a cut surface taken in the direction of arrow A along the ridgeline 9 of the press-formed product 1 shown in FIG. The state of the punch 19, die 20, lower pad 21, and metal plate 23 up to (FIG. 7(e)) is shown. Note that the numerical value such as [30 mmup] is the distance in the press forming direction in consideration of the plate thickness to the forming bottom dead center of the die 20 at the relevant position. Therefore, for example, the position of the die 20 at "30 mmup" is +30 mm in the opposite direction of press forming from the bottom dead center of the press.

As shown in FIG. 7, at [38mmup], the outward flange equivalent part 17, which is the end of the metal plate 23, starts to contact the punch 19, and at [30mmup], the outward flange equivalent part 17 of the metal plate 23 starts to contact the die 20. undergoes bending deformation in the direction. Thereafter, at [24mmup], the portion of the outward flange equivalent portion 17 away from the die 20 is bent, and the tip portion is folded so as to approach the die 20 side. Furthermore, as the molding progresses, a fold occurs between the lower pad 21 and the molding surface of the punch 19 at [10 mmup], and even when the molding progresses to [4 mmup], the fold remains as it is, and the bottom dead center of the molding is not reached. Cracks may appear or creases may remain.

This form of molding is possible because the corner flange equivalent part 17b, which is an extension of the ridgeline part 9, passes through the ridgeline part 9 and has high rigidity against bending, so it does not wrap around the die 20 and is separated from the die 20. One of the reasons is that it is folded in position (see FIG. 7(c)). Further, in this example, the vertical wall flange portion 3c (see FIG. 6) is not perpendicular to the surface of the top plate portion 5 of the press-formed product 1, but is inclined inward. This is because a large gap is created between the flange forming portion of the punch 19 and the flange forming portion of the die 20 at the initial stage of press forming.

When considering measures to prevent the connecting portion 35 of the corner flange equivalent portion 17b from folding, the inventor focused on the deformation of the metal plate 23 from [30 mm up] to [24 mm up] in FIG. Such deformation occurs because the ends of the metal plate 23 are free to deform, leading to folding, so in order to prevent this, it is possible to restrain the free deformation of the ends of the metal plate 23. However, since it is necessary to mold the corner flange equivalent portion 17b into the corner flange portion 3b, it is difficult to completely restrain the end portion of the metal plate 23 with a mold. Therefore, we came up with the idea that if the portion of the metal plate 23 corresponding to the root of the outward flange portion 3 could be wrapped around the die 20 at the initial stage of press forming, the above-mentioned folding could be prevented. The present invention is based on this idea, and specifically, is as shown below.

As an example is shown in FIG. 1(a), the root portions of the outward flange equivalent portions 25 (the top plate flange equivalent portion 25a, the corner flange equivalent portion 25b, and the vertical wall flange equivalent portion 25c) of the intermediate molded product 24 include: A step-shaped portion 27 that is a step that swells outward is provided. In such an intermediate molded product 24, the outward flange equivalent portion 25 is formed into the outward flange portion 3 (top plate flange portion 3a, corner flange portion 3b, and vertical wall flange portion 3c) to obtain the target shape. . In such an intermediate molded product 24, by providing the stepped portion 27, it becomes easier to wrap around the die 20 at the initial stage of press molding, and the above-mentioned folding can be prevented.

FIGS. 2(a) to 2(d) are diagrams showing the results of FEM analysis of the press forming process of the intermediate molded product 24 into the target shape. FIG. 2A shows an intermediate molded product 24 (before flange molding) in which a stepped portion 27 is formed. FIGS. 2(b) to 2(d) show the process of forming the flange portion.

Tension is applied to the tip of the outward flange portion 3, reducing the plate thickness. In addition, compressive force acts on the connecting portion 33 (see FIG. 1(b)) between the ridgeline portion 9 and the corner flange portion 3b, thereby increasing the plate thickness. On the other hand, the maximum plate thickness increase rate at the bottom dead center of forming is 28%, which is significantly lower than the maximum plate thickness increase rate of 47% in Fig. 6(d) showing the conventional example, and it is possible to prevent wrinkles. Recognize. One of the reasons why this maximum plate thickness increase rate is reduced is that in the present invention, in [10 mmup] shown in FIG. 2(c), compared to the conventional [10 mmup] shown in FIG. An example of this is that the increased thickness of the connecting portion 31 (see FIG. 1(a)) between the corner flange corresponding portion 25b and the corner flange equivalent portion 25b is dispersed.

FIG. 3 is a diagram schematically showing a molding process of molding the intermediate molded product 24 into a target shape in press molding of the present invention. 3 shows the punch 19, the die 20, the lower pad 21, and the metal during the process from [38mmup] to [4mmup] on a cut surface cut in the direction of arrow A along the ridgeline 9, as shown in FIG. The state of the board 23 is shown.

As shown in FIG. 3, from [38mmup] to [30mmup], the connection part 31 between the ridgeline part 9 and the corner flange equivalent part 25b has a step-shaped part 27 formed therein, so that it can be wrapped around the die 20. become. Subsequently, at [30 mmup], the outward flange equivalent portion 25 begins to contact the punch 19, and at [24 mmup], the tip of the metal plate 23 is bent toward the die 20 side. At this time, the tip of the outward flange equivalent portion 25 does not approach the die 20 side because the stepped portion 27 is formed. Therefore, the connecting portion 31 (see FIG. 1(a)) between the ridgeline portion 9 and the corner flange equivalent portion 25b is not bent at an acute angle. In this regard, in [24mmup] of FIG. 7 showing the conventional example, the tip of the outward flange equivalent part 25 approaches the die 20 side, and the connecting part 35 between the ridgeline part 9 and the corner flange part 3b (see FIG. 4) is bent at an acute angle.

Furthermore, as the press forming progresses, the outward flange equivalent portion 25 is formed without being folded in the gap between the die 20 and the punch 19 at [10 mm up]. Thereafter, the molding progresses to [4 mmup], and the outward flange portion 3 is formed at the bottom dead center of molding, and the connecting portion 33 (see FIG. 1(b)) between the ridgeline portion 9 and the corner flange portion 3b does not wrinkle. In this manner, in this embodiment, by providing the stepped portion 27, the connecting portion 31 between the ridgeline portion 9 and the corner flange equivalent portion 25b wraps around the die 20 in the initial stage of molding. As a result, the connecting portion does not get into the gap between the lower pad 21 and the punch 19 and become folded, and the occurrence of wrinkles is prevented.

Note that the step-shaped portion 27 formed in the intermediate forming step can be press-formed at the same time as the top plate portion 5, vertical wall portion 7, and ridgeline portion 9 are formed. Molding in one step makes manufacturing more efficient. Alternatively, the stepped portion 27 may be press-molded after the top plate portion 5, the vertical wall portion 7, and the ridgeline portion 9 are formed.

In addition, in the target shape forming step of forming the outward flange portion 3, as disclosed in Patent Document 2, a bending force is first input to the top plate flange equivalent portion 25a and the vertical wall flange equivalent portion 25c. do. After that, it is preferable to input bending force to the corner flange equivalent portion 25b. By doing so, it is possible to prevent cracks from occurring at the tip of the corner flange portion 3b.

In addition, in the above description, the orthogonal cross section of the ridgeline portion 9 having the vertical wall portions 7 on both sides of the top plate portion 5 and the horizontal flange portion 13 at the lower end of the vertical wall portion 7 is hat-shaped. However, the present invention is not limited thereto. That is, in the present invention, the orthogonal cross section of the ridgeline portion 9 without the horizontal flange portion 13 may be U-shaped, or a hat-shaped or U-shaped one is divided in half in the direction of the ridgeline portion 9 of the top plate portion 5. It may be shaped like a letter or L. In addition, bending or drawing is suitable for forming the outwardly bulging step-shaped portion of the present invention. Since the outward flange portion 3 is formed by bending the stepped portion, it becomes easy to form the outward flange portion 3 even when the width thereof is wide. On the other hand, if the stepped portion is formed by shear forming as described in Patent Document 3, the width of the flange portion may be restricted due to the fracture limit of the material, which may be undesirable.

In this example, in order to confirm the effects of the present invention, press forming analysis of the press-formed product 1 shown in FIG. 4, which is the object of the present invention, and press forming of the actual material were performed. As the high tensile strength material, a 980 MPa class steel plate with a plate thickness of 1.4 mm was used. The press-molded product 1 has a hat shape in which the width of the top plate portion 5 is 84 mm, the height of the vertical wall portion 7 is 100 mm, and the length of the ridge line portion 9 is 180 mm. Regarding the outward flange part 3, the outward flange width as defined in FIG. It was set to 3 mm.

In addition, in this example, as a conventional example and an invention example, a press is used to form an outward flange portion 3 on an intermediate molded product 15 (see FIG. 5(a)) press-formed using the blank model of the high tensile material. Molding analysis was performed. As a conventional example, as shown in FIGS. 5 and 6, a press forming analysis was conducted in which the outward flange portion 3 was formed without providing the stepped portion 27 at the root portion of the corner flange equivalent portion 17b. In addition, as an example of the invention, as shown in FIG. 1(a), a stepped portion 27 is provided at the root portion of the corner flange equivalent portion 25b on the intermediate molded product 24, and press molding is performed to form the outward flange portion 3. An analysis was performed. In addition, in the invention example, the height of the step-shaped portion 27, that is, the difference in height between the step-shaped portion 27 and the top plate portion 5, was changed from 1.0 mm to 2.5 mm, and the press forming analysis was performed. The influence of the height of 27 was also compared. The rate of increase in the thickness of the connection portion 33 or 35 between the ridgeline portion 9 and the corner flange portion 3b was determined from the thickness of the connection portion using the thickness of the blank model as a reference. The results of the analysis are shown in Table 1.

No. 1, which is a conventional example in which the stepped portion 27 is not provided. In the case of No. 1, the maximum plate thickness increase rate was as large as 47.6%. In the actual pressed material, buckling (wrinkling and folding) occurred at the connection portion 35 between the ridgeline portion 9 and the corner flange portion 3b. On the other hand, invention example No. 1 in which the stepped portion 27 was provided. 2~No. 5, the analysis results showed that the maximum plate thickness increase rate decreased significantly in both cases. Moreover, buckling did not occur in these actual pressed materials. In addition, No. When the height of the stepped portion 27 of No. 4 was 2.0 mm, the maximum plate thickness increase rate was the lowest at 25%, which was almost half of the 47.6% of the conventional example. As described above, it has been demonstrated that buckling of the connecting portion 33 between the ridgeline portion 9 and the corner flange portion 3b can be prevented by providing the stepped portion 27 in the intermediate molded product 24 of the present invention.

The present invention provides a press-formed product that can stably produce press-formed products with good dimensional accuracy without using a mold with a complicated structure and without causing buckling at the connection portion of the corner flange. A manufacturing method can be provided.

1 Press molded product 3 Outward flange portion 3a Top plate flange portion 3b Corner flange portion 3c Vertical wall flange portion 5 Top plate portion 7 Vertical wall portion 9 Ridge line portion 11 Main body portion 13 Horizontal flange portion 15 Intermediate molded product (conventional example)
17 Outward flange equivalent part (conventional example)
17a Part corresponding to the top plate flange (conventional example)
17b Corner flange equivalent part (conventional example)
17c Vertical wall flange equivalent part (conventional example)
19 Punch 20 Die 21 Lower pad 23 Metal plate 24 Intermediate molded product (invention example)
25 Outward flange equivalent part (invention example)
25a Part corresponding to top plate flange (invention example)
25b Corner flange equivalent part (invention example)
25c Vertical wall flange equivalent part (invention example)
27 Step-shaped portion 31 Connection portion between ridgeline portion and corner flange portion of intermediate molded product (invention example)
33 Connection part between ridgeline part and corner flange part of press-formed product (invention example)
35 Connection between ridgeline and corner flange (conventional example)

Claims

A main body portion having at least a top plate portion and a vertical wall portion formed via a ridgeline portion, and a main body portion formed at an end of the main body portion continuously to the top plate portion, the ridgeline portion, and the vertical wall portion. A method for manufacturing a press-formed product having an outwardly facing flange portion, the method comprising:
An intermediate molded product having a top plate portion and a vertical wall portion formed through a ridgeline portion, and having a stepped portion bulging outward at the root portion of a portion corresponding to the outward flange formed in the outward flange portion. An intermediate forming step to form the
A method for manufacturing a press-formed product, comprising a target shape forming step of bending and raising a portion corresponding to the outward flange of the intermediate molded product outward to form the outward flange portion into a target shape. .
The method for manufacturing a press-formed product according to claim 1, wherein in the intermediate forming step, the top plate portion, the ridgeline portion, the vertical wall portion, and the step-shaped portion are press-formed in one step.
Manufacturing the press-formed product according to claim 1, wherein the intermediate forming step includes press-forming the step-shaped portion after press-forming the top plate portion, the ridgeline portion, and the vertical wall portion. Method.