JP2023177203A - Press molding method and method for manufacturing press molded article - Google Patents

Abstract

To provide a press molding method and a method for manufacturing a press molded article which do not require a trimming step after press molding, sufficiently suppress wrinkles of a flange part generated by shrinking flange deformation, and can be applied to bending molding.SOLUTION: A press molding method and a method for manufacturing a press molded article, which are methods for molding a press molded article 1 that has a top plate part 3 having a convex outer peripheral edge part 3a where an outer peripheral edge or a part thereof is curved outward in a convex shape, a vertical wall part 5 continuous to the top plate part 3, and a flange part 7 continuous to the vertical wall part 5, includes: a first molding step of molding a metal plate into an intermediate molded article 15; and a second molding step of molding the intermediate molded article 15 molded in the first molding step into the press molded article 1 having a target shape, wherein the intermediate molded article 15 has a height from the top plate part 3 in at least a part corresponding to the convex outer peripheral edge part 3a of the top plate part 3 to a flange part 25 lower than a height from the top plate part 3 to the flange part 7 of the press molded article 1 having the target shape.SELECTED DRAWING: Figure 1

Description

The present invention relates to a press-forming method for a press-formed product having a top plate portion, a vertical wall portion, and a flange portion, and a method for manufacturing a press-formed product, and particularly to a method for manufacturing a press-formed product, and in particular, to prevent shrinkage flange deformation when forming the press-formed product. The present invention relates to a press molding method that suppresses the occurrence of wrinkles and a method of manufacturing a press molded product.

As the collision safety of automobile bodies continues to improve due to stricter collision safety standards for automobiles, it is also necessary to reduce the weight of automobile bodies in order to improve fuel efficiency and shift to electric vehicles in response to carbon dioxide emission regulations. In order to both improve collision safety and reduce weight of these car bodies, the use of high-strength steel plates of 590 MPa or higher (also known as high-tensile steel) is progressing in car body structural parts. When press-forming high-strength materials into vehicle body structural parts, it is important to suppress wrinkles caused by shrinkage flange deformation.

For example, some automobile parts have a top plate, a vertical wall, and a flange, such as A-pillar uppers, A-pillar lowers, and bumper parts. In such parts, if the outer periphery of the top plate or a part of it is curved outward in a convex shape, the vertical wall or flange of the part will shrink during press forming and become a flange. Deformation may occur, and wrinkles may occur at the ends of the vertical walls and the ends of the flanges. Particularly in the case of high-tensile steel materials, increasing the strength makes them more likely to buckle and cause wrinkles.

Therefore, Patent Document 1 has a top plate part and a sloped wall part continuous to at least one side of the top plate part without a flange at the tip, and the whole or part of the sloped wall part is press-formed in plan view. When forming a press-formed product that is curved convexly toward the oblique wall portion in the longitudinal direction of the product using a concave die and a convex punch, the end portion of the blank material is lower than the portion corresponding to the oblique wall portion during forming. By holding the side parts between a die and a punch and forming the sloped wall part with the end side parts held, buckling of the blank material in the thickness direction is prevented, and the sloped wall part A method for suppressing the appearance of wrinkles is disclosed.

Further, in Patent Document 2, the top plate part and the flange part have a hat-shaped cross section that is continuous in the width direction via the side wall part, and the top plate part and the flange part are arranged on the top plate part side along the longitudinal direction. When manufacturing a press-formed product by press-forming a metal plate into a product shape having a convexly curved curved part, a wrinkle suppressing area is set to press the metal plate with a wrinkle suppressor at the outer circumferential part from the flange position. It has a step-drawing process that performs forming with step-drawing, and when forming with step-drawing, an additional area is set at a part of the flange position to be suppressed with a wrinkle suppressor, thereby eliminating wrinkles that occur at the flange. A method for suppressing this is disclosed.

Japanese Patent Application Publication No. 2016-221558 Japanese Patent Application Publication No. 2018-034176

However, in the press forming method described in Patent Document 1, since the inclined wall part is formed with the end part of the blank material being held between the die and the punch than the part corresponding to the inclined wall part, the die and the punch It is necessary to trim the sandwiched part in the next step.
Furthermore, the method of Patent Document 1 also has a problem in that it cannot be applied to a press-formed product having a flange portion continuous to a vertical wall portion (slanted wall portion).

In this regard, although the method for manufacturing a press-formed product described in Patent Document 2 can be applied to forming a press-formed product having a flange portion, it cannot be applied to press-forming by bending (form) forming because it uses a wrinkle suppressor. There is a problem.

The present invention has been made to solve this problem, and can sufficiently suppress wrinkles in the flange caused by shrinkage flange deformation without requiring a trimming process after press forming, and can also be applied to bending forming. The purpose of the present invention is to provide a possible press molding method and a method for manufacturing press molded products.

(1) The press molding method according to the present invention includes a top plate portion having a convex outer peripheral edge portion in which the outer peripheral edge or a portion thereof is curved outward in a convex shape, and a vertical wall continuous to the top plate portion. A method for forming a press-formed product having a flange portion and a flange portion continuous to the vertical wall portion, the method comprising: a first forming step of forming a metal plate into an intermediate molded product; a second forming step of forming the intermediate molded product into the press-formed product having the target shape, the intermediate molded product having a flange portion extending from the top plate portion at least in a portion corresponding to the convex outer peripheral edge of the top plate portion. The height from the top plate to the flange of the press-formed product having the target shape is lower than the height from the top plate to the flange.

(2) Furthermore, in the item described in (1) above, the first forming step is characterized by applying drawing forming or bending forming, and the second forming step is characterized by applying bending forming. be.

(3) Furthermore, in the method described in (1) or (2) above, the metal plate is a steel plate having a tensile strength of 590 MPa class or higher.

(4) Furthermore, the method for manufacturing a press-formed product according to the present invention includes: A method for producing a press-formed product having a vertical wall portion continuous to the vertical wall portion and a flange portion continuous to the vertical wall portion, the method comprising: a first forming step of forming a metal plate into an intermediate molded product; and the first forming step. a second molding step of molding the intermediate molded product into the press molded product having a target shape, the intermediate molded product having at least a portion of the top plate corresponding to the convex outer peripheral edge of the top plate portion; The height from the flange part to the flange part is lower than the height from the top plate part to the flange part of the press-formed product having the target shape.

(5) Furthermore, in the item described in (4) above, the first forming step applies drawing forming or bending forming, and the second forming step applies bending forming. be.

(6) Furthermore, in the method described in (4) or (5) above, the metal plate is a steel plate having a tensile strength of 590 MPa class or higher.

The present invention includes a first forming step of forming a metal plate into an intermediate molded product, and a second forming step of forming the intermediate molded product into a press-formed product having a target shape. The height from the top plate portion to the flange portion of the portion corresponding to the convex outer peripheral edge portion of the plate portion is lower than the height from the top plate portion to the flange portion of the press-formed product having the target shape. Thereby, in the first molding step, the intermediate molded product can be molded while reducing the amount of shrinkage flange deformation. In addition, in the second forming step, an intermediate molded product having higher rigidity than a flat blank is molded into the target shape, so material movement due to shrinkage flange deformation is less likely to occur and wrinkles are less likely to occur.
Therefore, it is possible to suppress an increase in the thickness of a molded product having a target shape, and a press-formed product with a good shape without wrinkles can be obtained, which leads to an improvement in yield in press molding.
Furthermore, since there is no need to clamp the ends of the blank between a punch and a die, the conventional trimming process is not essential.
Furthermore, since wrinkle suppression is not required, it can also be applied to bending.

FIG. 2 is an explanatory diagram of a press molding method according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a component (target shape) targeted in the embodiment, with FIG. 2(a) being a perspective view and FIG. 2(b) being a plan view. It is a figure which shows the shaping|molding process in the 2nd shaping|molding process of embodiment. Thickness increase rate distribution of the intermediate molded product formed in the first forming process (Figure 4(a)) and plate thickness increase rate distribution of the press-formed product (target shape) formed in the second forming process (Figure 4(b)) ). It is an explanatory view of material inflow amount in a 1st molding process and a 2nd molding process. It is a graph showing the relationship between the height of the intermediate molded product and the amount of material inflow in each process. It is a figure which shows the board|plate thickness increase rate distribution and the maximum board|plate thickness increase rate of the intermediate molded article in the example of this invention of an Example. It is a figure which shows the plate|board thickness increase rate distribution and the maximum plate|board thickness increase rate of the molded article (press molded article) of the target shape in the example of this invention of an Example. FIG. 3 is a diagram showing a thickness increase rate distribution and a maximum thickness increase rate of a press-formed product formed by a conventional press-forming method. FIG. 3 is a diagram showing a forming process in a conventional press forming method.

A press-formed product targeted by the press-forming method and press-formed product manufacturing method according to the present embodiment will be described based on the example of FIG. 2. Note that FIG. 2 shows a part of the press-formed product. The press-formed product 1 shown in FIG. 2 has a top plate part 3, a vertical wall part 5, and a flange part 7, and a part of the outer peripheral edge of the top plate part 3 is convex outward. It has a curved portion (hereinafter referred to as "convex outer peripheral edge portion 3a"). The boundary between the convex outer circumferential edge 3a and other parts is, for example, up to the radius end of the convex outer circumferential edge 3a when the top plate part 3 is viewed in plan.
Further, in this example, the angle formed between the vertical wall portion 5 and the flange portion 7 of the press-formed product 1 was 90°.

The boundary between the top plate part 3 and the vertical wall part 5 in the press-formed product 1 has an R shape corresponding to the shape of the punch shoulder used in press forming, so this part is referred to as the "punch shoulder R part 9". It is called. Further, since the boundary between the vertical wall portion 5 and the flange portion 7 has an R shape corresponding to the shape of the die shoulder, it is referred to as a “die shoulder R portion 11”. Hereinafter, in this specification, when "punch shoulder R section 9" and "die shoulder R section 11" are simply expressed, they refer to the above-mentioned portions of the press-formed product 1, not the mold.

First, before explaining the press-forming method and the method for manufacturing a press-formed product according to the present embodiment, we will discuss the problems when press-forming a press-formed product 1 as shown in FIG. 2 by a conventional method. An example will be explained in which the height from the top plate part 3 to the flange part 7 is 16 mm.
FIG. 9 shows the results of FEM analysis for the case where the press-formed product 1 was press-formed by the conventional method, and shows the distribution of the plate thickness increase rate by color shading. The plate thickness increase rate was determined by calculating the difference (plate thickness increment) between the plate thickness of press-formed product 1 after press forming and the blank plate thickness before press forming, and expressed as a ratio (rate) to the blank plate thickness. The larger the value, the greater the plate thickness. Furthermore, as the plate thickness increases, wrinkles are more likely to occur in the region of the press-formed product. Furthermore, the more localized the increase in board thickness, the more likely it is that wrinkles will form.

When forming the press-formed product 1 as shown in FIG. 2 by a conventional method, a flat blank is formed into the target shape in one step using, for example, a punch and die having a shape corresponding to the target shape. In this case, the vertical wall portion 5 and the flange portion 7 corresponding to the convex outer peripheral edge portion 3a of the top plate portion 3 shrink and undergo flange deformation, material concentrates, and wrinkles are likely to occur. In the case of the press-formed product 1 shown in FIG. 2, the plate thickness increased the most at the end of the flange portion 7 shown by the arrow in FIG. 9, and the maximum plate thickness increase rate was +12.5%. As described above, the locally increased plate thickness causes wrinkles in the relevant portions, which has been a problem. The reason why the plate thickness of the flange portion 7 locally increases as shown in FIG. 9 will be explained using FIG. 10.

FIG. 10 shows a molding process when the press-formed product 1 is molded by the conventional press-forming method described above. FIG. 10 shows the process in which the blank 13 deforms, including a front view (upper view, view seen from the direction of the arrow in FIG. 2(b)) and a cross-sectional view (corresponding to the AA′ cross section in FIG. 2(b)). (Figure below).
Note that numerical values such as "5 mmup" in the figure indicate the distance between the punch 21 and the die 23 in the press forming direction (excluding the plate thickness). Therefore, in the case of "5 mmup", the gap in the press forming direction between the part of the punch 21 that forms the flange part 7 of the press-formed product 1 and the part of the die 23 that forms the flange part 7 is +5 mm to the thickness of the blank 13. This shows that the figure includes the following. Further, "0mmup" indicates the state at the bottom dead center of molding.

As shown in FIG. 10, when the vertical wall portion 5 corresponding to the convex outer peripheral edge 3a of the top plate portion 3 begins to be formed, the flange shrinks and deforms as shown in the front view (upper view) of “10 mm up”. This causes, for example, two large mountain-shaped wrinkles to form at the end of the blank 13. These two large mountain-shaped wrinkles become concentrated in the center of the convex outer periphery and become clearer as the shrinkage flange deformation progresses (see the front view of "5mmup" and "3mmup").

As the molding progresses, when the bottom surface of the die 23 reaches the top of the mountain, the molding progresses so that the die 23 crushes the wrinkles, but when the molding progresses to "1 mm up", the blank 13 remains with the wrinkles. It is restrained and reaches the bottom dead center of molding (see "0mmup").

As mentioned above, in the conventional forming process, large wrinkles occur in the gap between the punch 21 and the die 23, and the flange portion 7 is formed without completely crushing these wrinkles, so the wrinkles remain in the press-formed product 1. , the thickness of the plate increased locally in the area where the wrinkles occurred.

As a means to prevent wrinkles from forming during the forming process, it is preferable to use a wrinkle suppressor at a portion corresponding to the flange portion 7, but this cannot be applied in bending forming because there is no wrinkle suppressor.

Therefore, the press forming method of this embodiment takes measures that can be applied to bend forming while reducing the occurrence of wrinkles in the flange portion 7 compared to the conventional method.

Specifically, the press molding method according to the present embodiment has a convex outer peripheral edge 3a in which a part of the outer peripheral edge is curved outward in a convex shape, as shown in FIG. Press molding having a top plate part 3, a vertical wall part 5 continuous to the top plate part 3 via a punch shoulder R part 9, and a flange part 7 continuous to the vertical wall part 5 via a die shoulder R part 11. As shown in FIG. 1, the method includes a first forming step of forming a blank 13, which is a metal plate, into an intermediate molded product 15, and converting the intermediate molded product 15 into a press-formed product 1 having a target shape. A second molding step is provided.
Note that since the press-formed product 1 is manufactured by executing the press-forming method, the invention of the press-forming method can be constituted as the invention of the method of manufacturing a press-formed product. Therefore, the embodiment of the press molding method described below is common to the embodiment of the method of manufacturing a press molded product.

FIG. 1(a) is a perspective view of the punch 17, die 19, and blank 13 in a state before forming in the first forming step, and FIG. 1(b) is a cross-sectional view of B in FIG. 1(a).
Further, FIG. 1(c) is a perspective view of the punch 21, die 23, and intermediate molded product 15 before forming in the second forming process, and FIG. 1(d) is a cross-sectional view of C in FIG. 1(c). be.
Note that for each of the molds in FIGS. 1(a) to 1(d), only the shape of the molding surface portion is shown as a plate, ignoring the thick wall portion.
Further, in the intermediate molded product 15 shown in FIG. 1(d), the same parts as those in the press-formed product 1 are given the same reference numerals.
Each step will be explained in detail below.

<First molding process>
The first forming step is a step of press-forming a blank 13, which is a metal plate, into an intermediate molded product 15, as shown in FIGS. 1(a) and 1(b).
The punch 17 and the die 19 are punches 21 used in the second forming process for forming the intermediate molded product 15 into a target shape, such that the height hd1 from the forming surface portion corresponding to the top plate portion 3 to the forming surface portion corresponding to the flange portion 25 of the intermediate molded product 15 is The height hd0 of the die 23 from the molding surface portion corresponding to the top plate portion 3 of the press-formed product 1 to the molding surface portion corresponding to the flange portion 7 is lower than the height hd0 (hd1<hd0).

In the first forming step, as shown in FIG. 1(b), the die 19 is lowered with a part of the blank 13 being held between the upper surface of the top plate forming surface of the punch 17 and the pad 27, and the flange is formed from the top plate 3. 25 (hereinafter simply referred to as "the height of the intermediate molded product 15") hd1 is the height from the top plate part 3 of the press-formed product 1 having the target shape to the flange part 7 (hereinafter simply referred to as "the height of the press-formed product 15"). An intermediate molded product 15 (see FIG. 1(d)) having a height lower than hd0 (referred to as "height of molded product 1") is molded.
The angle formed between the vertical wall portion 29 and the flange portion 25 of the intermediate molded product 15 in this example is 90°, which is the same as the angle formed between the vertical wall portion 5 and the flange portion 7 of the target shape.
Shrinkage flange deformation occurs when forming the vertical wall portion 29 of the intermediate molded product 15 in the first molding process, but as described above, the height of the intermediate molded product 15 is higher than the height of the press-formed product 1 having the target shape. Since the amount of shrinkage flange deformation is also low, the amount of shrinkage flange deformation is small compared to the conventional case where a flat plate blank 13 is formed into a target shape.
Therefore, in the first molding step, the thickness of the flange portion 25 of the intermediate molded product 15 is less likely to increase, and wrinkles are less likely to occur.

<Second molding process>
The second molding step is a step of molding the intermediate molded product 15 molded in the first molding step into the press molded product 1 having the target shape. The punch 21 and die 23 in the second forming process have shapes corresponding to the target shape and are the same as the conventional mold shown in FIG. 10, so they are given the same reference numerals.

In the second forming process, as shown in FIG. 1(d), the punch shoulder R portion 9 of the intermediate molded product 15 is set to match the shoulder of the punch 21, and the punch 21 and pad 27 are used to form the top of the intermediate molded product 15. The die 23 is relatively moved while holding the plate portion 3, and the intermediate molded product 15 is molded into the target shape.
FIG. 3 shows the molding process in the second molding step.
3 shows the deformation process of the blank 13 in the same way as FIG. Each is shown in a cross-sectional view (bottom view). The meanings of numerical values such as "5mmup" are also the same as in FIG. Note that the height of the intermediate molded product 15 was 12 mm, and the height of the press molded product 1 (target shape) was 16 mm.

When the die 23 is lowered from the state shown in FIG. 1(d), the die 23 contacts the flange portion 25 of the intermediate molded product 15 at "5 mm up". Thereafter, the die 23 bends back the die shoulder R portion 31 of the intermediate molded product 15, and the lower part of the vertical wall portion 5 begins to be molded. Although this molding is accompanied by shrinkage flange deformation, the intermediate molded product 15 is work-hardened, so it has higher rigidity than the flat blank 13 and the material is less likely to move. Therefore, with "5mmup", even if wrinkles are generated as shown in the front view of "3mmup" instead of two local peaks as in the conventional case, the press forming direction of the die 23 and punch 21 is Since the gap is very small (board thickness + 3 mm), the wrinkles are crushed by the die 23 without becoming large and reach the bottom dead center of the molding.
As described above, the high rigidity of the intermediate molded product 15 makes it difficult for wrinkles to occur during the forming process, and the thickness of the flange portion 7 of the press-formed product 1 is difficult to increase in the second molding process, so that wrinkles do not occur easily. Hard to occur.

FIG. 4 shows the distribution of the plate thickness increase rate of the intermediate molded product 15 and the press-formed product 1 in the above-described example.
FIG. 4(a) shows the distribution of the plate thickness increase rate of the intermediate molded product 15 at the molding bottom dead center in the first molding step. Moreover, FIG. 4(b) shows the distribution of the plate thickness increase rate of the press-formed product 1 at the bottom dead center of forming in the second forming process. Note that the distribution of the plate thickness increase rate in FIGS. 4(a) and 4(b) is shown in a smaller range than in the conventional example shown in FIG.

As can be seen by comparing FIG. 4(a) and FIG. 4(b), the press-formed product 1 formed in the second forming process has a wider range of plate thickness increase than the intermediate formed product 15 formed in the first forming process. are distributed in This shows that the strain caused by the shrinkage flange deformation during the second forming process is dispersed over a wider range than the strain caused by the shrinkage flange deformation during the first forming process, and this figure also shows that the strain caused by the shrinkage flange deformation during the second forming process It can be seen that the plate thickness does not increase locally and wrinkles do not easily occur.

As described above, in the first molding step of the present embodiment, the intermediate molded product 15 whose height from the top plate portion 3 to the flange portion 25 is lower than the target shape is molded, and in the second molding step, the intermediate molded product 15 is molded. By molding the molded product 15 into the target shape, the problem of local increase in plate thickness can be solved and wrinkles generated in the flange portion 7 of the press-formed product 1 can be suppressed.
Furthermore, since there is no need to clamp the end of the blank between a punch and a die, there is no need for a trimming process as in the conventional example shown in Patent Document 1.
In addition, by performing the first forming step and the second forming step of the above-mentioned press forming method, the target press-formed product can be manufactured, and the manufactured press-formed product has suppressed wrinkles as described above. becomes.

Further, the press molding method and the method for manufacturing a press molded product of the present embodiment can suppress wrinkles in the flange portion 7 without using a wrinkle suppressor, and therefore can be applied to press molding by bending (form) forming. That is, it is particularly effective when drawing or bending is applied in the first forming step of forming the intermediate molded product 15, and bending is applied in the second forming step of forming the target shape.

Further, the press-forming method and the method for manufacturing a press-formed product of the present embodiment are particularly effective when using a high-strength steel plate that is prone to wrinkles due to shrinkage flange deformation. For example, the metal plate (blank) may be a steel plate having a tensile strength of 590 MPa or higher, and in that case as well, sufficient wrinkle reduction effects can be achieved.

Note that in the press forming method and the method for manufacturing a press formed product of the present embodiment, the height from the top plate portion 3 to the flange portion 25 is lower than the target shape by forming the intermediate molded product 15. This makes it possible to reduce the amount of wrinkles that occur on the product compared to the conventional method, and this point will be further explained.

FIG. 5A shows the cross-sectional shape of the blank 13 before molding in the first molding step with a broken line, and the cross-sectional shape of the intermediate molded product 15 at the bottom dead center of molding after molding with a solid line. Here, the distance from the end of the blank 13 to the end of the flange portion 25 of the intermediate molded product 15 in FIG. 5(a) is defined as the material inflow amount in the first molding step.
The amount of material flowing in this first molding step becomes smaller as the height of the intermediate molded product 15 becomes lower. If the amount of material inflow is small, the amount of shrinkage flange deformation in the first forming process will be small, so by lowering the height of the intermediate molded product 15, the increase in plate thickness due to the first forming process (increase in plate thickness from the blank 13) can be reduced. Can be reduced.

FIG. 5(b) shows the cross-sectional shape of the intermediate molded product 15 at the bottom dead center of the first molding process as a broken line, and the solid line represents the cross-sectional shape of the press-formed product 1 at the bottom dead center of the second molding process. It is. Here, the distance from the end of the flange part 25 of the intermediate molded product 15 to the end of the flange part 7 of the press-formed product 1 in FIG. 5(b) is defined as the material inflow amount in the second molding process.
The amount of material inflow in this second molding step increases as the height of the intermediate molded product 15 decreases. If the amount of material inflow is large, the shrinkage flange deformation amount in the second forming process will be large, so by lowering the height of the intermediate molded product 15, the plate thickness will be increased in the second forming process (plate thickness increase from the intermediate molded product 15). ) becomes larger.
In addition, the lower the height of the intermediate molded product 15, the larger the wrinkles will be in the molding process because the vertical wall portion 5 will start molding when the gap between the punch 21 and the die 23 in the press molding direction is large in the second molding process. This can easily lead to an increase in the thickness of the molded product with the target shape.

As described above, the lower the height of the intermediate molded product, the smaller the amount of material flowing in the first molding step, and the larger the amount of material flowing in the second molding step. As an example of the above relationship, FIG. 6 shows the relationship between the height of the intermediate molded product 15 and the amount of material inflow in each process when the height from the top plate part to the flange part of the target shape is 16 mm.

If the height of the intermediate molded product 15 is lowered, the amount of material flowing in the first forming process can be reduced and the increase in plate thickness can be reduced, but the amount of material flowing in the second forming process increases and the increase in plate thickness increases. In some cases, it may not be possible to sufficiently reduce the final plate thickness increase. Therefore, the present invention becomes more effective by setting the height of the intermediate molded product 15 so as to reduce the increase in plate thickness in a well-balanced manner in both the first molding step and the second molding step. For example, it is preferable to set the height of the intermediate molded product to about 50% to 90% of the height of the target shape, since the amount of material flowing in each process is well balanced. This point will be specifically explained in the following examples as well as the effects of the present invention.

The effect of suppressing wrinkles due to shrinkage flange deformation in the press-forming method and press-formed product manufacturing method of the present invention was specifically investigated using FEM analysis, and the results will be described below.
In this example, a case was confirmed in which a steel plate with a thickness of 1.0 mm and a tensile strength of 980 MPa class was used as a blank, and the press-formed product 1 of FIG. 2 was press-formed into the target shape. Note that the height of the target shape is 16 mm.
FEM analysis was conducted for a conventional example in which a steel plate is formed into a target shape in one process and an example of the present invention in which a steel plate is formed into a target shape in two processes, and the maximum plate thickness increase rate at the shrinkage flange deformation site was determined. Note that since the analysis results of the conventional example are as explained with reference to FIG. 9, the analysis results of the example of the present invention will be explained below.

In the example of the present invention, FEM analysis was performed on four examples in which the height of the intermediate molded product 15 was 14 mm, 12 mm, 10 mm, and 8 mm. Figure 7 shows the plate thickness increase rate distribution at the bottom dead center of the intermediate molded product 15 in the first forming process, and Figure 8 shows the distribution of the plate thickness increase rate at the bottom dead center of the molded product with the target shape (press-formed product 1) in the second forming process. The distribution of plate thickness increase rate is shown. In FIGS. 7 and 8, numerical values such as "14 mm" indicate the height of the intermediate molded product 15, and numerical values such as "7.4%" indicate the maximum plate thickness increase rate. Further, the maximum plate thickness increase rates in FIGS. 7 and 8 both indicate the rate of increase based on the plate thickness of the blank 13. Table 1 summarizes the results of FIGS. 7 to 9.

As shown in FIGS. 7 to 9 and Table 1, in the conventional example, the maximum plate thickness increase rate of the molded product with the target shape (press-formed product 1) was 12.5%, whereas in the example of the present invention (No. .2 to No.5), the maximum plate thickness increase rate of the molded product with the target shape was all lower than the conventional example. As a result, as described above, this example showed that the present invention can suppress flange wrinkles due to shrinkage flange deformation more than before.
Note that, as described above, wrinkles can be suppressed more effectively by setting the height of the intermediate molded product 15 so that the increase in plate thickness can be reduced in a well-balanced manner in both the first molding process and the second molding process. be able to. This point will be specifically explained below.

As can be seen by comparing the maximum plate thickness increase rate of the intermediate molded products 15 of No. 2 to No. 5, the lower the height of the intermediate molded product 15 in the first forming process, the more the intermediate molded product in the first forming process increases. The maximum plate thickness increase rate of product 15 decreases. This is because the lower the height of the intermediate molded product 15, the lower the amount of material flowing in the first molding process (see FIG. 5(a)).

On the other hand, in the second forming process, as can be seen by comparing the maximum plate thickness increase rate of molded products with the target shape of No. 2 to No. 5, No. 3 has the smallest maximum plate thickness increase rate, No. 4 and No. 5, in which the height of the intermediate molded product 15 is lower than No. 3, have a higher maximum plate thickness increase rate than No. 3. This is because the lower the height of the intermediate molded product 15 is, the earlier the molding start time of the vertical wall portion 5 becomes, and the amount of material flowing in the second molding step (see FIG. 5(b)) increases.

Therefore, as in example No. 3 in Table 1, if the height of the intermediate molded product 15 is set to minimize the increase in thickness after the second molding process, the wrinkle suppression effect can be maximized. It is possible and effective.

1 Press-formed product (target shape)
3 Top plate portion 3a Convex outer peripheral edge portion 5 Vertical wall portion (press molded product)
7 Flange part (press molded product)
9 Punch shoulder R part 11 Die shoulder R part (press molded product)
13 Blank (metal plate)
15 Intermediate molded product 17 Punch (first molding process)
19 Die (first molding process)
21 Punch (second forming process, conventional example)
23 Die (second forming process, conventional example)
25 Flange part (intermediate molded product)
27 Pad 29 Vertical wall part (intermediate molded product)
31 Die shoulder R part (intermediate molded product)

Claims (6)

A top plate portion having a convex outer peripheral edge portion where the outer peripheral edge or a portion thereof is curved outward in a convex shape, a vertical wall portion continuous to the top plate portion, and a flange portion continuous to the vertical wall portion. A press molding method for forming a press molded product having
a first forming step of forming a metal plate into an intermediate molded product;
a second molding step of molding the intermediate molded product molded in the first molding step into the press molded product having a target shape;
The intermediate molded product has a height from the top plate portion to the flange portion of at least a portion corresponding to the convex outer peripheral edge of the top plate portion that is equal to the height from the top plate portion to the flange portion of the press molded product having the target shape. A press forming method characterized by being lower than the height. The first forming step applies drawing forming or bending forming,
2. The press forming method according to claim 1, wherein the second forming step applies bending forming. 3. The press forming method according to claim 1, wherein the metal plate is a steel plate having a tensile strength of 590 MPa or higher. A top plate portion having a convex outer peripheral edge portion where the outer peripheral edge or a portion thereof is curved outward in a convex shape, a vertical wall portion continuous to the top plate portion, and a flange portion continuous to the vertical wall portion. A method for manufacturing a press-formed product comprising:
a first forming step of forming a metal plate into an intermediate molded product;
a second molding step of molding the intermediate molded product molded in the first molding step into the press molded product having a target shape;
The intermediate molded product has a height from the top plate portion to the flange portion of at least a portion corresponding to the convex outer peripheral edge of the top plate portion that is equal to the height from the top plate portion to the flange portion of the press molded product having the target shape. A method for manufacturing a press-formed product characterized by being lower than its height. The first forming step applies drawing forming or bending forming,
5. The method of manufacturing a press-formed product according to claim 4, wherein the second forming step applies bending forming. 6. The method for manufacturing a press-formed product according to claim 4, wherein the metal plate is a steel plate having a tensile strength of 590 MPa or higher.

Images