JP7509278B1 - Press molding method, manufacturing method of press molded product, intermediate molded product, and press molding die - Google Patents

Abstract

A technology is provided that can prevent wrinkles in a press-formed product that has a top plate portion and a vertical wall portion and has a stepped surface in the longitudinal direction of the top plate portion.
[Solution] A press-forming method for a press-formed product comprising a top plate portion and a vertical wall portion connected to the top plate portion in the width direction of the top plate portion via a ridge portion, wherein the top plate portion has a first top plate surface on the upper side, a step surface and a second top plate surface on the lower side by convex and concave bending in the longitudinal direction, the method including a first forming process in which a metal plate blank is press-formed into an intermediate formed product of an intermediate shape, and a second forming process in which the intermediate formed product is formed into the press-formed product, wherein the intermediate formed product has an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion of the press-formed product, and a base line of the step surface has moved toward the first top plate surface in the press direction.
[Selected Figure] Figure 1

Description

The present invention relates to a press molding method for a press molded product having a top plate portion and a vertical wall portion, in which the top plate portion has a step due to uneven bending in the longitudinal direction, a manufacturing method for the press molded product, an intermediate molded product, and a press molding die used for press molding.

When press-molding a metal part having a convex portion and a concave portion at the boundary between the top plate surface and the vertical wall, a problem occurs in that wrinkles occur near the convex portion and the concave portion. For example, when press-molding a metal part (press-molded product 1) having a step surface 12 on the top plate portion 10 as shown in Figures 4 and 5, a form molding is generally used to mold the vertical wall portion 20 and further the flange 30 while the top plate portion 10 is held down with a pad. At this time, as shown in the enlarged view of Figure 4 (b), the material bent at the boundary (upper ridge line 11a) between the upper top plate surface 11 and the vertical wall portion 20 and the material bent at the boundary (side ridge line 21a) between the step surface 12 and the vertical wall portion 20 gather in the vertical wall portion 20 near the convex bend 2 and the concave bend 3. The flow direction M of the material is indicated by an arrow. Therefore, wrinkles D occur in the vertical wall portion 20. This is also the case with a metal part (press-molded product 1) as shown in Figure 5 without a flange.

When press-molding a metal part (press-molded product 1) in which continuous convex bends 2 and concave bends 3 as shown in Figure 6 are formed across the top plate portion 10 and vertical wall portion 20, draw molding is often used, in which the top plate portion 10 and vertical wall portion 20 are molded while the flange portion 30 is first clamped and restrained by a mold. At this time, the material bent at the boundary (apex line 12a) between the upper top plate surface 11 and the step surface 12 and the material bent at the boundary (side ridge line 21a) between the front vertical wall surface 21 and the step surface 12 gather on the step surface 12 near the convex bend 2 and concave bend 3, causing wrinkles. The flow direction M of the material is indicated by an arrow. As a result, wrinkles D occur on the step surface 12.

Technologies for preventing such wrinkles have been developed in the past. For example, Patent Document 1 discloses a technique for increasing the rigidity of the top plate surface by forming a bead in advance at the boundary between the top plate surface and the vertical wall, thereby preventing material from collecting in the wrinkle-prone area. Patent Document 2 discloses a technique for suppressing wrinkles by press-forming the metal plate in the wrinkle-prone area while it is held between dies. Patent Document 3 discloses a technique for preventing wrinkles by intentionally providing a convex shape in the wrinkle-prone area to absorb excess material and then crushing it in the next process.

International Publication No. WO 2021/181982 International Publication No. WO 2020/105647 JP 2019-013952 A

However, the above-mentioned conventional techniques have the following problems.
That is, the technology described in Patent Document 1 prevents wrinkles by increasing the rigidity of areas where the material does not need to be deformed, such as the top plate surface and flanges, and preventing the material from gathering in those areas. However, the wrinkles that the present invention targets occur in the process of deforming and forming materials such as vertical walls and step surfaces, so this is not an effective measure.

The technology described in Patent Document 2 makes it easy to mold a relatively flat part such as a flange while constraining the material with a die. However, the wrinkles targeted by this invention are three-dimensional vertical walls or stepped surfaces, so they cannot be constrained with a die during press molding.

The technology described in Patent Document 3 is effective because providing a convex shape in an area where wrinkles are likely to occur can absorb excess material. However, it can be difficult to flatten the convex shape. Metal plates with a thickness of about a few millimeters easily buckle when compressed and deformed within the plate surface, so in order to flatten it, it is necessary to draw out the absorbed material to the surrounding area. However, in general press molding, the metal plate is molded by sliding the die in the height direction of the product, so while it is easy to move the material in the height direction, it is difficult to move the material in a direction different from the height direction. Therefore, when there is excess material in a direction different from the height direction, such as the wrinkles that this invention targets, it is difficult to flatten it.

The present invention has been made in consideration of the above, and aims to provide a technology that can prevent wrinkles in press-molded products that have a top plate portion and a vertical wall portion and have a stepped surface in the longitudinal direction of the top plate portion.

The press forming method of the present invention, which advantageously solves the above problem, is a press forming method for a press-formed product comprising a top plate portion and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, the top plate portion having a first top plate surface on the upper side, a step surface, and a second top plate surface on the lower side by longitudinal convex bending and concave bending, the method including a first forming step of press-forming a metal sheet blank into an intermediate formed product having an intermediate shape, and a second forming step of forming the intermediate formed product into the press-formed product, the intermediate formed product having an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion, and a foot line of the step surface of the press-formed product has been moved toward the first top plate surface in the press direction.

In addition, the press molding method according to the present invention is
(a) the intermediate molded product has the first intersection point moved to a side edge line formed by the step surface and the vertical wall surface;
(b) Furthermore, the vertical wall portion of the press-molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the rear side due to convex and concave bendings that are continuous with the convex and concave bendings of the top plate portion, respectively, and the intermediate molded product has an additional shape in which a first intersection between a lower ridge line that is the boundary between the second top plate surface and the second vertical wall surface and a foot line of the step surface is further moved to a position on the step surface on an extension surface of the second vertical wall surface, or to a position on the step surface further away from the first vertical wall surface.
(c) the additional shape further has a second intersection point on the lower ridge line and a third intersection point on the foothill line;
(d) a ratio ΔH of a press direction movement distance h of the first intersection in the intermediate molded product to a distance H in the press direction between the first top plate surface and the second top plate surface near the step surface is in the range of 9 to 100%;
This may be a more preferable solution.

The method for producing a press-formed product according to the present invention, which advantageously solves the above problem, is characterized in that a press-formed product is obtained by press-forming a metal blank using any of the press-forming methods described above.

The intermediate molded product of the present invention, which advantageously solves the above problem, is an intermediate molded product of a press-molded product, which comprises a top plate portion and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, and the top plate portion has a first top plate surface on the upper side, a step surface, and a second top plate surface on the lower side due to convex and concave bending in the longitudinal direction, and is characterized in that the press-molded product has an additional shape in which a first intersection between the lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion, and the foot line of the step surface has moved toward the first top plate surface in the press direction.

The intermediate molded product according to the present invention is
(e) the moved first intersection point is on a side edge line formed by the step surface and the vertical wall surface;
(f) Furthermore, the vertical wall portion of the press-molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the back side due to convex and concave bendings that are continuous with the convex and concave bendings of the top plate portion, and the first intersection between the lower ridge line formed by the second top plate surface and the second vertical wall portion and the foot line of the step surface is further moved to a position on the step surface on the extension plane of the second vertical wall surface, or to a position on the step surface further away from the first vertical wall surface,
This may be a more preferable solution.

The press-molding die according to the present invention, which advantageously solves the above-mentioned problems, comprises a top plate portion and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, and the top plate portion has a first top plate surface on the upper side, a step surface, and a second top plate surface on the lower side by convex bending and concave bending in the longitudinal direction. The press-molding die is used for press-molding a metal blank into an intermediate molded product having an intermediate shape when manufacturing a press-molded product,
The intermediate molded product is characterized in that it is formed to have an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion of the press-molded product, and a foot line of the step surface is moved toward the first top plate surface in the press direction.

In addition, the press molding die according to the present invention is
(g) the intermediate molded product has the first intersection point moved to a side edge line formed by the step surface and the vertical wall surface;
(h) further, the vertical wall portion of the press-molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the rear side, which are formed by convex and concave bendings respectively continuing from the convex and concave bendings of the top plate portion, and the intermediate molded product is formed to have an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the second vertical wall surface, and a base line of the step surface is further moved to a position on the step surface on an extension surface of the second vertical wall surface, or to a position on the step surface further away from the first vertical wall surface;
This may be a more preferable solution.

The press molding method, manufacturing method for press molded products, intermediate molded products, and press molding dies of the present invention can prevent wrinkles in the vertical wall portions and step surfaces near the step portions where the height of the top plate changes.

Schematic diagrams for explaining a press molding method for product shape 1 according to one embodiment of the present invention, in which (a) is a schematic oblique view of an intermediate molded product of product shape 1 after a first molding process, (b) is a side view thereof, (c) is an enlarged view of the side portion, and (d) is a schematic oblique view of a press molded product of product shape 1 after a second molding process. Schematic diagrams for explaining the press molding method of pattern 1 of product shape 3 in the above embodiment, where (a) is a schematic oblique view of an intermediate molded product of pattern 1 of product shape 3 after a first molding process, (b) is a side view thereof, and (c) is a schematic oblique view of a press molded product of product shape 3 after a second molding process. Schematic diagrams for explaining the press molding method of pattern 2 of product shape 3 in the above embodiment, where (a) is a schematic oblique view of an intermediate molded product of pattern 2 of product shape 3 after a first molding process, (b) is a side view thereof, and (c) is a schematic oblique view of a press molded product of product shape 3 after a second molding process. FIG. 1 is a schematic diagram for explaining a conventional press molding method for product shape 1, in which (a) is a schematic oblique view of a press molded product for product shape 1, (b) is a partially enlarged oblique view thereof, and (c) is a side view. 1 is a schematic perspective view of a press-molded product of product shape 2. FIG. FIG. 1 is a schematic diagram for explaining a conventional press molding method for a product shape 3, in which (a) is a schematic oblique view of a press molded product for the product shape 3, (b) is a partially enlarged oblique view thereof, and (c) is a side view. 1 is a schematic diagram illustrating the wrinkle suppression effect of the press molding method for product shape 1 according to this embodiment. FIG. 1A and 1B are perspective views showing examples of dimensions of press-molded products in the examples, in which FIG. 1A shows a product shape 1, and FIG. 1B shows a product shape 3. 1A and 1B are perspective views showing the thickness distribution of press-formed products in Examples, where FIG. 1A shows the case of Test No. 1 and FIG. 1B shows the case of Test No. 2.

The following describes in detail the embodiments of the present invention with reference to the drawings. Note that the following embodiments are merely examples of shapes and methods for embodying the technical ideas of the present invention, and do not limit the configuration to those described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

Figure 1 is a schematic diagram for explaining the press molding method of product shape 1 according to this embodiment. Figure 2 is a schematic diagram for explaining the press molding method of pattern 1 of product shape 3 according to this embodiment. Figure 3 is a schematic diagram for explaining the press molding method of pattern 2 of product shape 3 according to this embodiment. Product shape 2 is product shape 1 without flange portion 30 as shown in Figure 5. Also included is product shape 3 without flange portion 30.

In this embodiment, the press-molded product 1 of the product shape 1 comprises a top plate portion 10, a vertical wall portion 20 connected to the top plate portion 10 via a ridge portion in the width direction of the top plate portion 10, and a flange portion 30 connected to and extending from an edge of the vertical wall portion 20 different from the top plate portion. The top plate portion 10 has an upper top plate surface 11, a step surface 12, and a lower top plate surface 13 due to a convex bend 2 and a concave bend 3 in its longitudinal direction. The top plate surface 10 has a top line 12a at the boundary between the upper top plate surface 11 and the step surface 12, and a base line 12b at the boundary between the step surface 12 and the lower top plate surface 13. The top plate surface 11 has an upper ridge line 11a at the boundary between the upper top plate surface 11 and the vertical wall portion 20. The step surface 12 has a side ridge line 21a at the boundary between the step surface 12 and the vertical wall portion 20. The lower ridge line 13a at the boundary between the lower top plate surface 11 and the vertical wall portion 20.

In this embodiment, in addition to the shape of the top plate portion 10 of the product shape 1, the press-molded product 1 of the product shape 3 has a vertical wall portion 20 with a front vertical wall surface 21, a common step surface 12, and a rear vertical wall surface 22 due to a convex bend 2 and a concave bend 3 that are continuous with the convex bend 2 and the concave bend 3 of the top plate portion 10, respectively. A side ridge 21a is present at the boundary between the front vertical wall surface 21 and the step surface 12, and a valley line 22a is present at the boundary between the step surface 12 and the rear vertical wall surface 22. The upper ridge 11a is the boundary between the upper top plate surface 11 and the front vertical wall surface 21, and the lower ridge 13a is the boundary between the lower top plate surface 13 and the rear vertical wall surface 22.

In the press forming method of this embodiment, a metal sheet blank is press formed through two steps, an intermediate forming step (first forming step) and a product forming step (second forming step). Then, a press-formed product 1 having the product shape is manufactured. Examples of an intermediate-shaped intermediate product 100 are shown in Figures 1(a), 2(a), and 3(a).

In each figure showing this embodiment, the boundaries between the surfaces that represent the shape are shown by lines, but the actual press-formed product 1 is rounded. The roundness may be determined arbitrarily, taking into consideration the roundness of the product shape, for example, by making the radius of curvature of the curved surface that is the boundary small as long as the metal plate does not crack. For metal plates with a tensile strength of 590 MPa or less, it is preferable to set the radius of curvature to 2 mm or more on the inner surface of the curved surface, as this makes it difficult for cracks to occur. On the other hand, for metal plates with a tensile strength of more than 590 MPa, it is also preferable to set the radius of curvature to 4 mm or more, as this makes it difficult for cracks to occur. There is no particular upper limit for the radius of curvature, but if the radius of curvature exceeds 10 mm, the portion (additional shape 9) of the intermediate shape (intermediate molded product 100) that is changed from the shape of the metal part (press-formed product 1) will be wide, and there is a risk of interference with functionally necessary portions such as the seat.

In this embodiment, the intersection of the lower ridge 13a and the foot line 12b of the press-formed product 1 is the first intersection 5. At this first intersection 5, a convex bend occurs in the width direction and a concave bend occurs in the longitudinal direction. In the intermediate product 100, an additional shape 9 is formed including a first intersection 6 in which this intersection is moved toward the upper top plate surface 11 in the press direction, that is, in the product height direction HD. Specifically, in the case of product shape 1, as shown in Figures 1 (a) to (c), the additional shape 9 can be composed of a line segment connecting the first intersection 6 of the intermediate product 100 in which the first intersection 5 of the press-formed product 1 is moved toward the upper top plate surface 11 on the side ridge 21a, the second intersection 7 on the lower ridge 13a, and the third intersection 8 on the foot line 12b. The line segment may be a straight line or a curve, and the first intersection may be on the step surface 12 near the side ridge. Product shape 2 differs from product shape 1 in that it does not have a flange, so the additional shape 9 of the intermediate molded product 100 can be formed in the same way.

In addition, in pattern 1 of product shape 3, as shown in Figures 2(a) and (b), the additional shape 9 can be formed by a line segment connecting the first intersection 6 of the intermediate molded product 100 obtained by moving the first intersection 5 of the press-molded product 1 to the upper top plate surface 11 side and the front vertical wall surface 21 side within the step surface 12, the second intersection 7 on the lower ridge line 13a, and the third intersection 8 on the foot line 12b. The line segment may be a straight line or a curved line. The additional shape 9 is also formed by a concave bend 3 on the step surface 12 that includes the first intersection 6 on the step surface 12 and is parallel to the front vertical wall surface 21, and a concave bend 3 on the rear vertical wall surface 22 that includes the second intersection 7 and is parallel to the step surface.

Furthermore, in pattern 2 of product shape 3, as shown in Figures 3(a) and (b), the additional shape 9 can be composed of a line segment connecting the first intersection 6 of the intermediate molded product 100 obtained by moving the first intersection 5 of the press-molded product 1 toward the upper top plate surface 11 side parallel to the rear vertical wall surface 22 within the step surface 12, the second intersection 7 on the lower ridge line 13a, and the third intersection 8 on the foot line 12b. The line segment may be a straight line, a curved line, or a combination of straight lines and curves. Straight lines are more preferable because they are easier to design and easier to manage the shape of the mold.

The ratio ΔH (%) of the product height direction HD of the moving first intersection 6, i.e., the distance h in the press direction, to the press direction distance H between the top plate surfaces 11, 13 near the step surface 12 is preferably in the range of 9 to 100%. ΔH of 100% indicates that the first intersection 6 of the added shape 9 is at the ridge convex portion 4 of the upper top plate surface 11, i.e., the intersection of the upper ridge 11a and the apex line 12a. Here, the press direction distance H between the top plate surfaces 11, 13 can be the difference in height between the apex line 12a and the base line 12b of the intermediate molded product 100.

Even if the press direction distance H between the top plate surfaces 11, 13 of the press-molded product 1 and the intermediate molded product 100 is not the same, this is acceptable as long as there are no wrinkles or cracks in the press-molded product. If the H of the intermediate molded product 100 is too large compared to the H of the press-molded product 1, it is likely to wrinkle during the product molding process. On the other hand, if the H of the intermediate molded product 100 is too small compared to the H of the press-molded product 1, it is likely to crack.

In this embodiment, the height position of the flange portion 30 of the intermediate molded product 100 can be selected in the product height direction from a height position equal to the height of the lower top plate surface of the intermediate molded product 100 to a height position that becomes the flange portion 30 of the press molded product 1. Actual pressed parts have more complex shapes, and can be appropriately selected to distribute the press load per press or to form other shapes near the flange portion, such as beads and seats, without wrinkles or cracks.

The inventors believe that the mechanism of wrinkle suppression according to this embodiment is as follows.
<Product shape 1>
Taking the metal part (press-formed product 1) of the product shape 1 shown in FIG. 1(d) as an example, the intermediate product 100 of the intermediate shape shown in FIG. 1(a) has a ridge line portion connecting the first intersection 6 and the second intersection 7 of the additional shape 9, instead of the recess at the first intersection 5 of the press-formed product 1 formed by the concave bending 3. As a result, when the press-formed product 1 is formed in one process from a blank of a metal plate, the material flow M that causes wrinkles in the vertical wall portion 20 is pulled to the ridge line portion of this additional shape 9 in the intermediate forming process, and the material flow M is distributed to the ridge line portion of the additional shape 9. This additional shape 9 is subjected to the concave bending 3 up to the first intersection 5 of the press-formed product 1 in the subsequent product forming process. Compared to the case where the press-formed product 1 is formed from a blank of a metal plate in one process, the above-mentioned two-process forming process is expected to have the following wrinkle suppression effect.

First, the length of material in the ridge direction is compared between the intermediate product 100 and the press-formed product 1 using FIG. 7. The length Y1-Y1' of the ridge of the additional shape 9 of the intermediate product 100 is shorter than the corresponding length Y2-X2-Y2' of the press-formed product 1 after processing. Therefore, the material is stretched and no excess material is generated. As described in the problem points of Patent Document 3, the direction of this ridge is different from the height direction (press direction HD), so it is difficult to deal with wrinkles in the conventional method. On the other hand, when comparing the cross section in the press direction HD, the line segment X1-X1"-X1' of the additional shape 9 of the intermediate product 100 is longer than X2-X2' of the press-formed product 1. However, this direction is a direction in which the material is easily pulled in press forming, so it is easy to disperse the excess material. These advantages are also the same for the metal part (press-formed product) of product shape 2 in FIG. 5 that does not have a flange.

<Product shape 3>
The same is true for the metal part (press-molded product) of the product shape 3 shown in FIG. 2(c) or FIG. 3(c). By forming the intermediate molded product 100 of the intermediate shape shown in FIG. 2(a) or FIG. 3(a) in the intermediate molding process, wrinkles can be suppressed. The first intersection 6 of the additional shape 9 of the intermediate molded product 100 may be located in a position moved toward the upper top plate surface 11 side from the first intersection 5 of the press-molded product 1 in the height direction (press direction HD) of the metal part. Pattern 1 may be a pattern in which the first intersection of the additional shape is placed on a line connecting the first intersection 5 of the press-molded product and the ridgeline convex portion 4, or pattern 2 may be a pattern in which the first intersection 6 of the additional shape is simply provided on a step surface above the first intersection 5 of the press-molded product 1 (in the height direction of the metal part). The wrinkle suppression effect of patterns 1 and 2 is the same as that of the above-mentioned product shape 1. Pattern 1 is preferable as a wrinkle countermeasure. On the other hand, it is necessary to note that the shape of the rear vertical wall surface 22 and the flange portion 30 also changes in pattern 1. For example, if the flange portion has spot welds and high dimensional accuracy is required, it should be avoided to form the flange portion in two processes. If possible, the shape of the metal part (press-formed product) may be the intermediate shape of Pattern 1 or 2 itself.

<Steel type and plate thickness>
The metal plate used in this embodiment is preferably a steel plate having a tensile strength in the range of 270 to 1800 MPa and a plate thickness in the range of 0.6 to 4.0 mm. This does not deny the application of this embodiment to metal materials having a tensile strength of less than 270 MPa or a plate thickness of less than 0.6 mm. However, there are few metal parts in general automobiles and home appliances whose tensile strength and plate thickness are below the above. Metal plates with a tensile strength exceeding 1800 MPa have poor ductility, so there is a risk that cracks will easily occur when the ridgeline portion is reshaped into the product shape in the second forming step of this embodiment. Metal plates with a plate thickness exceeding 4.0 mm will be subject to a high processing load in the second forming step of this embodiment, so there is a risk that the mold will be easily damaged, such as being dented.

Figure 8 shows an example of the dimensions of the press-formed product used in the study. In order to prevent cracks in the metal plate, the boundaries of each surface were curved such that the convex boundaries on the outside of the product had an inner surface curvature radius of 5 mm, and the concave boundaries had an outer surface curvature radius of 6 mm. The boundaries of each surface of the intermediate formed product also had the same radius of curvature. The plate thickness and mechanical properties of the materials used are summarized in Table 1.

In the comparative example, a metal sheet blank was formed into a press-formed product of the product shape in a single forming process. In the invention example, a press-formed product of the product shape was formed in two forming processes, the intermediate forming process and the product forming process shown in the above embodiment. In the intermediate forming process, product shapes 1 and 2 were formed by foam forming, and product shape 3 was drawn by drawing. In addition, in the product forming process, all product shapes were formed by foam forming.

The results of the study on product shapes 1 and 2 are summarized in Table 2. The step of the top plate, i.e., the distance H in the press direction between the upper top plate surface 11 and the lower top plate surface 13, was set to two levels, 10 mm and 8 mm. Press molding was performed by changing the ratio ΔH (%) of the movement distance h in the press direction from the first intersection 5 of the press-molded product 1 of the first intersection 6 of the intermediate molded product 100 to H, using the values shown in Table 2. LA in Table 2 is the distance between the first intersection 5 of the press-molded product 1 and the second intersection 7 of the intermediate molded product, and LB is the distance between the first intersection 5 of the press-molded product 1 and the third intersection 8 of the intermediate molded product.

Wrinkles were evaluated based on two criteria. The first was the increase in thickness of the area where wrinkles were likely to occur after the final process. A thickness increase rate of 35% or more was deemed unacceptable. When forming a metal plate using a press die, a gap (clearance) equal to the thickness of the metal plate is provided between the upper and lower dies, and it is common to avoid compressing the metal plate in the thickness direction. If the plate thickness increases, it will be thicker than the gap provided in the die, so if the thickness becomes too large, problems may occur with the die. If the increase is less than 35%, the strength of the die is sufficiently large compared to the force compressing the metal plate, so problems such as denting or damage to the die are unlikely to occur. On the other hand, if the increase is 35% or more, such problems are likely to occur. The second was an evaluation of the product appearance after the final process. If the metal plate buckles outside the plate surface and the wrinkles fold over, or if buckling occurs without overlapping, it is marked as ×, and otherwise as ○.

Tests No. 1 and 5 showed significant wrinkles and overlapped wrinkles. As a result, the thickness increase rate could not be measured, and appearance evaluation was also impossible. In the invention examples, the wrinkles were minor in all cases, and the appearance evaluation was satisfactory. The larger ΔH was, the smaller the thickness increase rate was, and the better the wrinkle evaluation was.

Figure 9 shows the results of an FEM (finite element method) analysis of the distribution of the plate thickness increase/decrease rate (%) for Test No. 1 and Test No. 2. Figure 9(a) shows the plate thickness distribution for Test No. 1. It can be seen that wrinkles D overlap. Figure 9(b) shows the plate thickness distribution for Test No. 2. No wrinkles were observed, and the plate thickness increase rate was a maximum of 25%.

The results of the study on product shape 3 are summarized in Tables 3 and 4. Table 3 shows the case where the intermediate shape is pattern 1, and Table 4 shows the case where the intermediate shape is pattern 2. The specifications in the tables are the same as those in Table 2. In Tables 3 and 4, LC is the distance projected onto the base line 12b between the first intersection point 5 of the press-formed product 1 and the first intersection point 6 of the intermediate molded product.

In tests No. 9 and 13, ΔH was 0, the sheet thickness increase rate was large at 35% or more, and wrinkles occurred. On the other hand, in tests where ΔH was 9% or more, the sheet thickness increase rate was kept low and no wrinkles occurred.

The press molding method, manufacturing method for press molded products, intermediate molded products, and press molding dies of the present invention can prevent wrinkles on the vertical wall portions and step surfaces near the step portions where the height of the top plate changes, improving the yield of press molded products and productivity, making them industrially useful.

1 Press-molded product 100 Intermediate molded product 10 Top plate portion 11 Upper top plate surface 11a Upper ridge line 12 Step surface 12a Crest line 12b Base line 13 Lower top plate surface 13a Lower ridge line 20 Vertical wall portion 21 Front vertical wall surface 21a Side ridge line 22 Back vertical wall surface 22a Valley line 30 Flange 2 Convex bend 3 Concave bend 4 Ridge convex portion (intersection of upper ridge line and ridge line)
5 First intersection (between the foot line and the lower ridge line of the press molded product) 6 First intersection (of the added shape of the intermediate molded product) 7 Second intersection 8 (on the lower ridge line of the added shape of the intermediate molded product) Third intersection 9 (on the foot line of the added shape of the intermediate molded product) Added shape D (of the intermediate molded product) Wrinkles M Flow direction (of material) HD Product height direction (press direction)

Claims (12)

A press-molding method for a press-molded product, comprising: a top plate portion; and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, the top plate portion having a first top plate surface on an upper stage side, a step surface, and a second top plate surface on a lower stage side by convex bending and concave bending in the longitudinal direction,
A first forming step of press-forming a metal sheet blank into an intermediate formed product having an intermediate shape;
A second molding step of molding the intermediate molded product into the press-molded product,
A press molding method in which the intermediate molded product has an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion of the press molded product, and a foot line of the step surface has been moved toward the first top plate surface in the press direction. The press molding method according to claim 1, wherein the intermediate molded product is such that the first intersection point is located on a side edge formed by the step surface and the vertical wall surface. The vertical wall portion of the press -molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the back side, each of which is formed by a convex bend and a concave bend that are continuous with the convex bend and the concave bend of the top plate portion,
The press molding method according to claim 1, wherein the intermediate molded product has an additional shape in which a first intersection between a lower ridge line, which is a boundary between the second top plate surface and the second vertical wall surface, and a base line of the step surface is located at a position on the step surface that is on an extension of the second vertical wall surface , or at a position on the step surface that is closer to the first vertical wall surface than on the extension of the second vertical wall surface. The press forming method according to any one of claims 1 to 3, wherein the additional shape has a second intersection point on the lower ridge line and a third intersection point on the foot line. The press molding method according to any one of claims 1 to 3, wherein the ratio ΔH of the distance moved in the press direction h of the first intersection point in the intermediate molded product to the distance H in the press direction between the first top plate surface and the second top plate surface near the step surface is in the range of 9 to 100%. Using the press molding method according to any one of claims 1 to 3,
A method for producing a press-molded product, comprising press-molding a metal blank to obtain a press-molded product. An intermediate press-molded product comprising a top plate portion and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, the top plate portion having a first top plate surface on the upper side, a step surface, and a second top plate surface on the lower side by convex bending and concave bending in the longitudinal direction,
An intermediate molded product having an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion, and a foot line of the step surface of the press molded product has been moved toward the first top plate surface in the press direction. The intermediate molded product according to claim 7, wherein the moved first intersection point is on a side edge formed by the step surface and the vertical wall surface. The vertical wall portion of the press -molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the back side, each of which is formed by a convex bend and a concave bend that are continuous with the convex bend and the concave bend of the top plate portion,
The intermediate molded product according to claim 7 or 8, wherein the first intersection between a lower ridge line formed by the second top panel surface and the second vertical wall portion and a base line of the step surface has an additional shape located at a position on the step surface that is on an extension of the second vertical wall surface, or at a position on the step surface that is closer to the first vertical wall surface than on the extension of the second vertical wall surface. A press-molding die for press-molding a metal blank into an intermediate molded product having an intermediate shape when manufacturing a press-molded product, the press-molding die comprising: a top plate portion; and a vertical wall portion connected to the top plate portion via a ridge portion in the width direction of the top plate portion, the top plate portion having a first top plate surface on an upper stage side, a step surface, and a second top plate surface on a lower stage side by longitudinal convex bending and concave bending,
A press molding die in which the intermediate molded product is formed to have an additional shape in which a first intersection between a lower ridge line, which is the boundary between the second top plate surface and the vertical wall portion of the press molded product, and a foot line of the step surface is moved toward the first top plate surface in the press direction. The press molding die according to claim 10, wherein the intermediate molded product is such that the first intersection point is located on a side edge formed by the step surface and the vertical wall surface. The vertical wall portion of the press -molded product has a first vertical wall surface on the front side, a step surface common to the top plate portion, and a second vertical wall surface on the back side, each of which is formed by a convex bend and a concave bend that are continuous with the convex bend and the concave bend of the top plate portion,
The press molding die according to claim 10 or 11, wherein the intermediate molded product is formed to have an additional shape in which a first intersection between a lower ridge line, which is a boundary between the second top plate surface and the second vertical wall surface, and a base line of the step surface is located at a position on the step surface that is on an extension of the second vertical wall surface, or at a position on the step surface that is closer to the first vertical wall surface than on the extension of the second vertical wall surface.

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