METHOD OF MANUFACTURING A FORMED COMPONENT

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2024-084142 filed on May 23, 2024 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to a method of manufacturing a formed product.

WO2017/006793 describes a method of manufacturing a press-formed product, in which a blank is press-formed with a die and a punch to produce a product having a curved portion curved orthogonally to a top plate, in plan view. In this manufacturing method, the formed product is manufactured such that a material of the blank is invited by a material inflow facilitating portion to flow into an inner circumference of the curved portion, where a so-called stretch flange is to be formed. The material inflow facilitating portion has a shape formed by a raised portion of the blank, allowing the material of the blank to locally flow into the inner circumference of the curved portion.

SUMMARY

However, according to the manufacturing method described above, inviting the material of the blank to flow into the inner circumference of the curved portion is possible only when manufacturing a component such as an L-shaped component in which the curved portion is only partially formed in the entire component. In other words, when manufacturing a component that is curved orthogonally to the top plate portion in side view, such as a mostly curved component, there is a problem such that cracks easily occur in an area where a stretch flange is formed because the material is flowed in only a part of the area where the stretch flange is formed.

In one aspect of the present disclosure, in the press-formed product, it is preferable to provide a technique to inhibit occurrence of cracks in the area where the stretch flange is formed.

One aspect of the present disclosure is manufacturing a formed product by pressing a blank with a first press mold and a second press mold. The method comprising: arranging the blank between the first press mold and the second press mold spaced apart from each other; and forming a top plate portion, a vertical wall portion, and a flange portion while forming a fold on an extension portion by bringing the first press mold and the second press mold close to each other in a state where the blank is arranged between the first press mold and the second press mold to thereby press the blank by the first press mold and the second press mold. The blank includes a top plate corresponding portion that corresponds to the top plate portion of the formed product, a vertical wall corresponding portion that corresponds to the vertical wall portion of the formed product, and the extension portion. The extension portion is an area extending to an outer side from an outer-side edge of a vertical wall corresponding portion. The outer side is a downstream side in a direction from the vertical wall corresponding portion to a side opposite where a top plate corresponding portion is located, in a plane parallel to the blank. The flange portion is a portion that is formed of the extension portion and that extends from an outer-side edge of the vertical wall portion in a direction intersecting with the vertical wall portion, the flange portion having a shape curved to form a stretch flange. The fold extends along a longitudinal direction of an outer-side edge of the flange portion.

Here, in the flange portion having a shape curved to form the stretch flange, tensile stress is generated during its forming step, and cracks may occur. However, the aforementioned configuration makes it possible to obtain the following actions and effects. Specifically, the fold extends along a longitudinal direction of the outer-side edge of the flange portion and is thus curved in the same way as the flange portion. Therefore, the extension portion on the outer side relative to the fold is also a portion where the stretch flange is formed. Since tensile stress is also generated in the extension portion, as a reaction to this, compressive stress is generated in proximity to the fold. Compressive stress may relieve tensile stress in the flange portion. Accordingly, it is possible to inhibit the occurrence of cracks in the area where the stretch flange is formed.

In one aspect of the present disclosure, the method may include removing a portion of the extension portion that is on the outer side relative to the fold after forming the flange portion. According to this configuration, a part that is no longer required has been removed in the formed product, so that it is easy to perform an optional processing on the formed product in subsequent steps.

In one aspect of the present disclosure, the top plate portion may include a recessed portion recessed in a thickness direction of the top plate portion. This configuration makes it possible to manufacture various formed products.

In one aspect of the present disclosure, the recessed portion may be formed in advance in the blank before arranging the blank between the first press mold and the second press mold spaced apart from each other. This configuration makes it possible to manufacture various formed products.

In one aspect of the present disclosure, the formed product may be an automobile component.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which:

FIG. 1A is a schematic perspective view of a press-formed product;

FIG. 1B is a schematic plan view of the press-formed product;

FIG. 1C is a schematic side view of the press-formed product;

FIG. 2A is a schematic perspective view of an intermediate product;

FIG. 2B is a schematic plan view of the intermediate product;

FIG. 2C is a schematic side view of the intermediate product;

FIG. 3 is a flow chart showing a method of manufacturing the press-formed product;

FIG. 4A is a cross-sectional view of a blank and its surrounding structure along a pressing direction thereof in an intermediate forming step;

FIG. 4B is another cross-sectional view of the blank and its surrounding structure along the pressing direction thereof in a forming step;

FIG. 5A is a schematic perspective view of an upper press mold;

FIG. 5B is a schematic perspective view of a lower press mold;

FIG. 6 is a diagram illustrating how a blank material moves; and

FIG. 7 is a schematic perspective view of another press-formed product.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

1. Embodiment

[1-1. Press-Formed Product]

A press-formed product 1 shown in FIGS. 1A to 1C is formed by press forming a blank 10. The press-formed product 1 is used, as one example, as a rear floor side member mounted on a vehicle. The manufacturing method according to the present embodiment can be used for manufacturing press-formed products of various shapes without being limited to the press-formed product 1 shown in FIGS. 1A to 1C. For example, the manufacturing method according to the present embodiment can be used for manufacturing press-formed products of any shape having a stretch flange. The stretch flange is a part of a flange where tensile stress is generated and a material is stretched. For example, the flange including the stretch flange has a shape formed by bending the blank in which a ridge line, that is a bent portion, has a concave arc shape relative to the blank.

As one example, the blank 10 is made of high-tensile steel. However, without being limited to high-tensile steel, the blank 10 may be made of stainless steel or iron, for example.

The press-formed product 1 includes a top plate portion 2, a first vertical wall portion 3, a second vertical wall portion 4, a first flange portion 5, and a second flange portion 6.

The top plate portion 2 is a plate-shaped portion where many of its portions, except for small ones, extend in the same plane. When describing the press-formed product 1 below, a thickness direction of the top plate portion 2 is referred to as an up-down direction. The top plate portion 2 is curved in the thickness direction. Specifically, the top plate portion 2 is curved so as to recess downward. The top plate portion 2 is curved also in plan view. More specifically, the top plate portion 2 is curved such that the first vertical wall portion 3 is recessed toward the second vertical wall portion 4.

The top plate portion 2 includes a first downward recessed portion 21b, an upward recessed portion 22a, and a second downward recessed portion 22b.

The upward recessed portion 22a is a portion on the top plate portion 2 that is recessed upward when the top plate portion 2 is viewed from below. The first downward recessed portion 21b and the second downward recessed portion 22b are portions on the top plate portion 2 that are recessed downward when the top plate portion 2 is viewed from above. Positions where the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b are arranged are not particularly limited as long as they are on the top plate portion 2.

The first vertical wall portion 3 is a plate-shaped portion extending from an end of the top plate portion 2 in a direction intersecting with the top plate portion 2. In the present embodiment, the first vertical wall portion 3 extends substantially downward from the end of the top plate portion 2. A portion where the top plate portion 2 and the first vertical wall portion 3 are joined to each other forms a first ridge line 3a. The first ridge line 3a has a concave arc shape recessed downward and has a partially curved arc shape in plan view. The first vertical wall portion 3 is curved along the first ridge line 3a.

The second vertical wall portion 4 is a plate-shaped portion extending from the other end of the top plate portion 2, which is opposite to the end from which the first vertical wall portion 3 extends, in a direction intersecting with the top plate portion 2. In the present embodiment, the second vertical wall portion 4 extends substantially downward from the other end of the top plate portion 2. A portion where the top plate portion 2 and the second vertical wall portion 4 are joined to each other forms a second ridge line 3b. The second ridge line 3b has a concave arc shape recessed downward. The second vertical wall portion 4 is curved along the second ridge line 3b. The term “along” as used herein refers not only to cases where there is complete alignment, but also to cases where there is substantial alignment. For example, a direction in which the second vertical wall portion 4 extends may be completely aligned with a direction in which the second ridge line 3b extends, or it may be approximately aligned a direction in which the second ridge line 3b extends.

The first flange portion 5 is a plate-shaped portion extending from an end of the first vertical wall portion 3 on the side opposite where the first ridge line 3a is, in a direction intersecting with the first vertical wall portion 3. The first flange portion 5 extends in a direction opposite to a direction in which the top plate portion 2 extends relative to the first vertical wall portion 3. The portion where the first vertical wall portion 3 and the first flange portion 5 are joined to each other forms a third ridge line 4a. The third ridge line 4a has a concave arc shape recessed downward and has a partially curved arc shape in plan view. The first flange portion 5 is curved along the third ridge line 4a. In other words, the first flange portion 5 is formed to have a stretch flange having a shape that is curved in a thickness direction of the first flange portion 5 and curved in plan view. The first flange portion 5 is substantially parallel to the top plate portion 2.

The second flange portion 6 is a plate-shaped portion extending from an end of the second vertical wall portion 4 on the side opposite where the second ridge line 3b is, in a direction intersecting with the second vertical wall portion 4. The second flange portion 6 extends in a direction opposite to a direction in which the top plate portion 2 extends relative to the second vertical wall portion 4. The portion where the second vertical wall portion 4 and the second flange portion 6 are joined to each other forms a fourth ridge line 4b. The fourth ridge line 4b has a concave arc shape recessed downward. The second flange portion 6 is curved along the fourth ridge line 4b. The second flange portion 6 is substantially parallel to the top plate portion 2.

In summary, the press-formed product 1 is substantially U-shaped and is curved so as to recess downward as a whole, as shown in FIG. 1C. In addition, the press-formed product 1 is partially curved in plan view. For example, the press-formed product 1 may have an L-like curve in plan view.

[1-2. Intermediate Product]

An intermediate product 1A shown in FIGS. 2A to 2C includes a preliminary top plate portion 2A, a preliminary first vertical wall portion 3A, a preliminary second vertical wall portion 4A, a preliminary first flange portion 5A, a preliminary second flange portion 6A, and an excess portion 7A. The press-formed product 1 is a formed product obtained by performing, on the intermediate product 1A, processing in a trimming step and a forming step, which are described in detail below. The preliminary top plate portion 2A, the preliminary first vertical wall portion 3A, the preliminary second vertical wall portion 4A, the preliminary first flange portion 5A, and the preliminary second flange portion 6A of the intermediate product 1A respectively correspond to the top plate portion 2, the first vertical wall portion 3, the second vertical wall portion 4, the first flange portion 5, and the second flange portion 6 of the press-formed product 1. In addition, a fifth ridge line 3Aa formed by the preliminary top plate portion 2A and the preliminary first vertical wall portion 3A, a sixth ridge line 3Ab formed by the preliminary top plate portion 2A and the preliminary second vertical wall portion 4A, a seventh ridge line 4Aa formed by the preliminary first vertical wall portion 3A and the preliminary first flange portion 5A, and an eighth ridge line 4Ab formed by the preliminary second vertical wall portion 4A and the preliminary second flange portion 6A respectively correspond to the first ridge line 3a, the second ridge line 3b, the third ridge line 4a, and the fourth ridge line 4b of the press-formed product 1.

The preliminary top plate portion 2A, the preliminary first vertical wall portion 3A, the preliminary second vertical wall portion 4A, the preliminary first flange portion 5A, and the preliminary second flange portion 6A of the intermediate product 1A have substantially the same configurations as the top plate portion 2, the first vertical wall portion 3, the second vertical wall portion 4, the first flange portion 5, and the second flange portion 6 of the press-formed product 1, respectively. Similarly to the press-formed product 1, the intermediate product 1A is also substantially U-shaped and is curved so as to recess downward as a whole, as shown in FIG. 2C. In addition, the intermediate product 1A is also partially curved in plan view. For example, the intermediate product 1A may have an L-like curve in plan view.

Similarly to the top plate portion 2, the preliminary top plate portion 2A includes the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b.

Hereinafter a description will be given of differences between the intermediate product 1A and the press-formed product 1.

Although the excess portion 7A is formed in the intermediate product 1, the excess portion 7A is cut off when the intermediate product 1A is processed into the press-formed product 1, and thus the excess portion 7A does not exist in the press-formed product 1. The excess portion 7A is a plate-shaped portion extending from an end of the preliminary first flange portion 5A on the side opposite where the seventh ridge line 4Aa is. The end of the preliminary first flange portion 5A opposite to the seventh ridge line 4Aa corresponds to a trim line 50, which is shown in a dashed line. The trim line 50 is an outer-side edge of the preliminary first flange portion 5A and indicates a reference position when cutting the intermediate product 1A in the trimming step, which will be described in detail later. The excess portion 7A has a fold 8A that extends along a longitudinal direction of the outer-side edge of the preliminary first flange portion 5A. In other words, the fold 8A is formed in the excess portion 7A and extends along the longitudinal direction of the trim line 50. In short, the fold 8A extends along the preliminary first flange portion 5A where the stretch flange is formed. The fold 8A is formed to be a mountain fold. In the present embodiment, the fold 8A extends to a position that is approximately the same distance from the preliminary first vertical wall portion 3A, thus forming a ridge line along the seventh ridge line 4Aa. From the outer-side edge of the preliminary first flange portion 5A to the fold 8A, the excess portion 7A extends in a curved shape substantially identical with a shape of the preliminary first flange portion 5A, and then extends downward in a slope from the fold 8A. In other words, the fold 8A is formed on an outer side relative to the preliminary first flange portion 5A and the trim line 50. The fold 8A has a concave arc shape recessed downward, that is, an arc shape partially curved in plan view. The fold 8A may have a gentle ridge line. It is sufficient for the fold 8A to be formed in a way suitable for a material of the blank 10.

In addition, the fifth ridge line 3Aa, the sixth ridge line 3Ab, the seventh ridge line 4Aa, and the eighth ridge line 4Ab of the intermediate product 1A are formed in a slightly gentler shape than the first ridge line 3a, the second ridge line 3b, the third ridge line 4a, and the fourth ridge line 4b of the press-formed product 1, respectively. The press-formed product 1 is slightly larger in the up-down direction than the intermediate product 1A.

[1-3. Method of Manufacturing Press-Formed Product]

As shown in FIG. 3, the method of manufacturing the press-formed product 1 includes an intermediate forming step, the trimming step, and the forming step.

[1-3-1. Intermediate Forming Step]

The intermediate forming step in S10 is a step for press forming the blank 10 to form the intermediate product 1A. As shown in FIG. 4, the blank 10 used for the present manufacturing method includes a top plate corresponding portion 2B, a first vertical wall corresponding portion 3B, a second vertical wall corresponding portion 4B, and an extension portion 9B.

The top plate corresponding portion 2B is a portion corresponding to the preliminary top plate portion 2A of the intermediate product 1A. Specifically, the top plate corresponding portion 2B is an area in the blank 10 where the preliminary top plate portion 2A is to be formed when the intermediate product 1A is formed.

The first vertical wall corresponding portion 3B is a portion corresponding to the preliminary first vertical wall portion 3A of the intermediate product 1A. Specifically, the first vertical wall corresponding portion 3B is an area in the blank 1 where the preliminary first vertical wall portion 3A is to be formed when the intermediate product 1A is formed.

The second vertical wall corresponding portion 4B is a portion corresponding to the preliminary second vertical wall portion 4A of the intermediate product 1A. Specifically, the second vertical wall corresponding portion 4B is an area in the blank 10 where the preliminary second vertical wall portion 4A is to be formed when the intermediate product 1A is formed.

In the present embodiment, in the blank 10, the first vertical wall corresponding portion 3B and the second vertical wall corresponding portion 4B extend with the top plate corresponding portion 2B between them. Hereinafter, on a plane parallel to the blank 10, a downstream side in directions from the first vertical wall corresponding portion 3B and the second vertical wall corresponding portion 4B to the top plate corresponding portion 2B is referred to as an inner side, and a downstream side in directions from the first vertical wall corresponding portion 3B and the second vertical wall corresponding portion 4B to a side opposite where the top plate corresponding portion 2B is located is referred to as an outer side.

The extension portion 9B is an area extending further outward from an outer-side edge of the first vertical wall corresponding portion 3B.

In the intermediate forming step in S10, a press forming device is used. The press forming device includes an upper press mold 61, an upper pad 62, a gas cushion 63, and a lower press mold 71.

The upper press mold 61 shown in FIGS. 4A and 5A is a press mold for press forming. The upper press mold 61 includes a ceiling face 61a, an upper first wall forming portion 61b, an upper second wall forming portion 61c, an upper first flange forming portion 61d, an upper second flange forming portion 61e, and an upper fold forming portion 61f. In FIG. 5A, only a shape of a lower face of the upper press mold 61 is shown schematically and the ceiling face 61a is omitted.

The ceiling face 61a is a face facing down in the upper press mold 61 and extends in a direction perpendicular to the up-down direction.

The lower press mold 71 as shown in FIGS. 4A and 5B is also a press mold for press forming. The lower press mold 71 includes a lower top plate forming portion 71a, a lower first wall forming portion 71b, a lower second wall forming portion 71c, a lower first flange forming portion 71d, a lower second flange forming portion 71e, and a lower fold forming portion 71f. In FIG. 5B, only a shape of an upper face of the lower press mold 71 is shown schematically and portions to be arranged on the lower top plate forming portion 71a, such as recesses, are omitted.

The lower top plate forming portion 71a is a portion for forming the preliminary top plate portion 2A. An upper side of the lower top plate forming portion 71a is provided with recesses and protrusions each corresponding to the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b. The lower top plate forming portion 71a is curved to so as to recess downward.

The upper first wall forming portion 61b and the lower first wall forming portion 71b have shapes similar to that of the preliminary first vertical wall portion 3A of the intermediate product 1A, and are portions for forming the preliminary first vertical wall portion 3A. The upper second wall forming portion 61c and the lower second wall forming portion 71c have shapes similar to that of the preliminary second vertical wall portion 4A of the intermediate product 1A, and are portions to form the preliminary second vertical wall portion 4A.

The upper first flange forming portion 61d and the lower first flange forming portion 71d have shapes similar to that of the preliminary first flange portion 5A of the intermediate product 1A, and are portions for forming the preliminary first flange portion 5A. The upper second flange forming portion 61e and the lower second flange forming portion 71e have shapes similar to that of the preliminary second flange portion 6A of the intermediate product 1A, and are portions for forming the preliminary second flange portion 6A.

The upper fold forming portion 61f is a portion for forming the excess portion 7A. The upper fold forming portion 61f is a portion extending from an end of the upper first flange forming portion 61d. A fold 61g is formed in the upper fold forming portion 61f and extends along a longitudinal direction of an outer-side edge of the upper first flange forming portion 61d. More specifically, the fold 61g extends along the upper first flange forming portion 61d for forming the preliminary first flange portion 5A where the stretch flange is formed. The fold 61g is formed to be a valley fold. From the outer-side edge of the upper first flange forming portion 61d to the fold 61g, the upper fold forming portion 61f extends in a curved shape substantially identical with a shape of the upper first flange forming portion 61d, and then extends downward in a slope from the fold 61g. In other words, the fold 61g is formed on the outer side relative to the upper first flange forming portion 61d. An angle formed by the upper first flange forming portion 61d and the upper fold forming portion 61f is substantially coincident with an angle formed by the preliminary first flange portion 5A and the excess portion 7A in the intermediate product 1A.

The lower fold forming portion 71f is also a portion for forming the excess portion 7A. The lower fold forming portion 71f is a portion extending from an end of the lower first flange forming portion 71d. A fold 71g is formed in the lower fold forming portion 71 and extends along a longitudinal direction of an outer-side edge of the lower first flange forming portion 71d. Specifically, the fold 71g extends along the lower first flange forming portion 71d for forming the preliminary first flange portion 5A where the stretch flange is formed. The fold 71g is formed to be a mountain fold. From the outer-side edge of the lower first flange forming portion 71d to the fold 71g, the lower fold forming portion 71f extends in a curved shape substantially identical with a shape of the lower first flange forming portion 71d, and then extends downward in a slope from the fold 71g. In other words, the fold 71g is formed on the outer side relative to the lower first flange forming portion 71d. An angle formed by the lower first flange forming portion 71d and the lower fold forming portion 71f is substantially coincident with the angle formed by the preliminary first flange portion 5A and the excess portion 7A in the intermediate product 1A.

The upper pad 62 is a pad for press forming. In the present embodiment, a cross section of the upper pad 62 along its up-down directions is substantially rectangular in shape. Recesses corresponding to the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b are provided on a lower surface of the upper pad 62.

The gas cushion 63 is a cushion utilizing a reaction force of compressed gas. The gas cushion 63 expands or contracts in its up-down direction according to pressure.

An upper surface of the gas cushion 63 comes in contact with a lower surface of the ceiling face 61a. A lower surface of the gas cushion 63 comes in contact with an upper surface of the upper pad 62.

The blank 10 is arranged between the upper press mold 61 and the lower press mold 71 spaced apart from each other, although the illustration is omitted. More specifically, the blank 10 is arranged between the upper pad 62, which is arranged above the blank 10 and below the upper press mold 61, and the lower press mold 71, which is arranged below the blank 10. At this point of time, the upper first wall forming portion 61b, the upper second wall forming portion 61c, the upper first flange forming portion 61d, the upper second flange forming portion 61e, and the upper fold forming portion 61f of the upper press mold 61 are substantially parallel with the lower first wall forming portion 71b, the lower second wall forming portion 71c, the lower first flange forming portion 71d, the lower second flange forming portion 71e, and the lower fold forming portion 71f of the lower press mold 71, respectively.

The upper pad 62 comes in contact with an upper surface of the blank 10. The lower top plate forming portion 71a of the lower press mold 71 comes in contact with a lower surface of the blank 10. The blank 10 is clamped from above and below by and between the upper pad 62 and the lower press mold 71. Specifically, the top plate corresponding portion 2B of the blank 10 is clamped by and between the upper pad 62 and the lower press mold 71. Of the blank 10 clamped therebetween, the first vertical wall corresponding portion 3B, the second vertical wall corresponding portion 4B, and the extension portion 9B are not in contact with the upper pad 62 and the lower press mold 71.

The upper press mold 61 is moved from above the upper pad 62 downward to the blank 10 clamped by and between the upper pad 62 and the lower press mold 71 to perform press forming.

As shown in FIG. 4A, when the upper press mold 61 and the lower press mold 71 are brought close to each other, first of all, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b are formed in the top plate corresponding portion 2B.

Next, the upper fold forming portion 61f comes in contact with the blank 10. Specifically, the upper fold forming portion 61f comes in contact with the extension portion 9B. The extension portion 9B extends in a direction substantially perpendicular to a thickness thereof while the upper fold forming portion 61f slopes downward. Therefore, as the upper press mold 61 is brought closer to the lower press mold 71, a contact area between the extension portion 9B and the upper fold forming portion 61f becomes larger. As the extension portion 9B is gradually bent downward, the fold 8A is formed in the extension portion 9B.

When the upper press mold 61 is brought even closer to the lower press mold 71 to press the blank 10, the blank 10 is deformed to come in close contact with the upper first wall forming portion 61b, the upper second wall forming portion 61c, the upper first flange forming portion 61d, the upper second flange forming portion 61e, and the upper fold forming portion 61f. This results in forming the preliminary top plate portion 2A, the preliminary first vertical wall portion 3A, the preliminary second vertical wall portion 4A, the preliminary first flange portion 5A, the preliminary second flange portion 6A, and the excess portion 7A in the blank 10. More specifically, the preliminary top plate portion 2A is formed of the top plate corresponding portion 2B; the preliminary first vertical wall portion 3A is formed of the first vertical wall corresponding portion 3B; the preliminary second vertical wall portion 4A is formed of the second vertical wall corresponding portion 4B. Further, the preliminary first flange portion 5A and the excess portion 7A are formed of the extension portion 9B.

[1-3-2. Trimming Step]

The trimming step in S20 is a step for performing trimming on the intermediate product 1A that has been formed in the intermediate forming step in S10. In the trimming step, the intermediate product 1A is cut along the trim line 50. The trim line 50 is the outer-side edge of the preliminary first flange portion 5A. That is, the trim line 50 is a boundary between the preliminary first flange portion 5A and the excess portion 7A. In other words, in the trimming step, the excess portion 7A is removed from the intermediate product 1A.

[1-3-3. Forming Step]

The forming step in S30 is a step for press forming a formed product 1B obtained by removing the excess portion 7A in the trimming step in S20.

In the forming step, as shown in FIG. 4B, an optional processing is performed on the formed product 1B using an upper press mold 61B and a lower press mold 71B, which are different from the upper press mold 61 and the lower press mold 71, respectively, to form the press-formed product 1.

[1-4. Actions]

In an area where the stretch flange is formed, tensile stress is generated and a material of the stretch flange is stretched in the process of forming the stretch flange. The material stretch may result in cracks in the area where the stretch flange is formed. In addition, the material stretch may make a thickness of the area where the stretch flange is formed thinner than an original thickness of the blank.

Since the preliminary first flange portion 5A is curved to be recessed downward, and the preliminary first flange portion 5A is an area where the stretch flange is formed. Therefore, the preliminary first flange portion 5A is a portion where tensile stress is generated.

Here, the fold 8A has a concave arc shape recessed downward. Thus, the excess portion 7A is also an area where the stretch flange is formed. Since tensile stress is generated in the area where the stretch flange is formed, tensile stress is generated in the excess portion 7A. In particular, tensile stress is generated in a portion of the excess portion 7A that is on the outer side relative to the fold 8A. In FIG. 6, for the purpose of illustrating tensile stress that is generated in the excess portion 7A, directions of tensile stress are simplified and indicated by a double-headed arrow A. When tensile stress is generated, compressive stress is generated around tensile stress as a reaction to tensile stress. In other words, compressive stress is generated in proximity to the fold 8A. In FIG. 6, for the purpose of illustrating compressive stress that is generated in proximity to the fold 8A, directions of compressive stress are simplified and indicated by arrows B. The occurrence of compressive stress causes tensile stress of the preliminary first flange portion 5A to be relieved. In addition, the occurrence of compressive stress in proximity to the fold 8A causes a blank material of the excess portion 7A to flow into the preliminary first flange portion 5A and a reduction in the thickness of the blank to be relieved.

In summary, in the present embodiment, by forming the first flange portion 5A and the excess portion 7A while forming the fold 8A, tensile stress is intentionally induced in the excess portion 7A. As a result, the occurrence of compressive stress in proximity to the fold 8A is thought to relieve tensile stress of the preliminary first flange portion 5A.

[1-5. Effects]

The embodiment described in detail above produces the effects below.

(1a) In the aforementioned embodiment, while pressing the blank 10 with the upper press mold 61 and the lower press mold 71 and forming the fold 8A in the extension portion 9B, the preliminary top plate portion 2A, the preliminary first vertical wall portion 3A, the preliminary second vertical wall portion 4A, the preliminary first flange portion 5A, the preliminary second flange portion 6A, and the excess portion 7A are formed of the blank 10. The fold 8A extends along the longitudinal direction of the outer-side edge of the preliminary first flange portion 5A and has a concave arc shape recessed downward. This configuration helps to relieve tensile stress in the preliminary first flange portion 5A, as described in detail in [1-4. Actions]. As a result, it is possible to inhibit the occurrence of cracks in the area where the stretch flange is formed. Furthermore, this configuration helps to reduce a reduction in the plate thickness of the area where the stretch flange is formed.

(1b) In the aforementioned embodiment, the first flange portion 5 has the stretch flange formed in a shape that is bent in the thickness direction of the first flange portion 5 and curved in plan view. This configuration makes it possible to form the flange portion with higher strength than a flange portion where the stretch flange is not formed.

(1c) In the aforementioned embodiment, by using the upper pad 62 and the lower press mold 71, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b are formed. This configuration makes it possible to form the preliminary first flange portion 5A and each of the recessed portions in the same step.

(1d) In the aforementioned embodiment, in the intermediate forming step in S10, the preliminary top plate portion 2A, the preliminary first vertical wall portion 3A, the preliminary second vertical wall portion 4A, the preliminary first flange portion 5A, the preliminary second flange portion 6A, and the excess portion 7A are formed of the blank 10. This configuration makes it possible to form all of the respective portions of the intermediate product 1A in the same process.

(1e) In the aforementioned embodiment, the excess portion 7A is removed from the intermediate product 1A in the trimming step in S20 to form the formed product 1B. Specifically, the portion of the extension portion 9B that is on the outer side relative to the fold 8A is removed after the preliminary first flange portion 5A is formed. According to this configuration, a part that is no longer required has been removed from the intermediate product 1A, so that it is easier to perform an optional processing on the formed product 1B in the subsequent forming step in S30.

[1-6. Correspondence Relationship]

In the aforementioned embodiment, the upper press mold 61 corresponds to one example of a first press mold, the lower press mold 71 corresponds to one example of a second press mold. In addition, the intermediate product 1A corresponds to one example of the formed product, the preliminary top plate portion 2A corresponds to one example of the top plate portion, the preliminary first vertical wall portion 3A corresponds to one example of the vertical wall portion, the preliminary first flange portion 5A corresponds to one example of the flange portion, and the fold 8A corresponds to one example of the fold. In addition, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b each correspond to one example of the recessed portion.

2. Other Embodiments

Although the embodiment of the present disclosure has been described so far, the present disclosure may take various forms without being limited to the aforementioned embodiment.

(2a) In the aforementioned embodiment, the preliminary first flange portion 5A has the stretch flange formed in a shape that is bent in the thickness direction of the preliminary first flange portion 5A and curved in plan view. However, the shape of the area where the stretch flange is formed is not limited thereto. For example, a stretch flange may be formed in a shape that is curved in the thickness direction of the preliminary first flange portion 5A, or a stretch flange may be formed in a shape that is curved in plan view. More specifically, the above manufacturing method can also be used when forming a press-formed product 100 shown in FIG. 7, which is not curved in plan view but is recessed in a thickness direction thereof.

In addition, the above manufacturing method can also be used, for example, when forming a press-formed product having a shape that is curved in a T-shape or Y-shape in plan view.

When forming an intermediate product having two or more curved portions, such an intermediate product may be formed while forming two or more folds, each corresponding to an individual one of the two or more curved portions, on the two or more curved portions. When forming an intermediate product for the press-formed product 100 shown in FIG. 7, such an intermediate product may be formed while forming, in addition to the fold 8A that extends along the longitudinal direction of the outer-side edge of the preliminary first flange portion 5A, another fold that extends along a longitudinal direction of an outer-side edge of the preliminary second flange portion 6A. With this manufacturing method, it is possible to relieve tensile stress that is generated in the preliminary first flange portion 5A; and at the same time, it is also possible to relieve tensile stress that is generated in the preliminary second flange portion 6A. Specifically, even for the intermediate product having the two or more curved portions, it is possible to simultaneously form the two or more curved portions such that tensile stress is relieved in each of the two or more curved portions, and it is also possible to inhibit the occurrence of cracks in each of the portions.

(2b) In the aforementioned embodiment, the single fold 8A that extends along the longitudinal direction of the outer-side edge of the preliminary first flange portion 5A is formed in the excess portion 7A. However, the number of the folds formed in the excess portion 7A is not limited thereto. Two or more folds may be formed in the excess portion 7A. For example, a second fold parallel to the fold 8A may be formed, in the excess portion 7A, on a side opposite to the outer-side edge of the preliminary first flange portion 5A across the fold 8A. In other words, the second fold may be formed such that the outer-side edge of the preliminary first flange portion 5A, the fold 8A, and the second fold parallel to the fold 8A are arranged in this order. A slope down from the second fold may be steeper than a slope down from the fold 8A. On the contrary, the slope down from the second fold may be gentler than the slope down from the fold 8A. A sloping surface to the fold 8A from the outer-side edge of the preliminary first flange portion 5A and a surface sloping downward from the second fold may be substantially parallel with each other. In other words, by forming two folds in the excess portion 7A with the fold 8A and the second fold, a stepped portion may be formed in the excess portion 7A. The stepped portion may be formed as a plurality of steps in a tiered manner.

Alternatively, the fold 8A does not necessarily have to be formed continuously. The fold may be partially discontinuous in its extending direction.

(2c) In the aforementioned embodiment, the fold 8A is formed to be a mountain fold. However, the shape of the fold is not limited thereto. The fold may be formed to be a valley fold. Specifically, from the outer-side edge of the preliminary first flange portion 5A to the fold 8A, the excess portion 7A may be formed to extend in a curved shape substantially identical with the shape of the preliminary first flange portion 5A, and then extend upward in a slope from the fold 8A.

(2d) In the aforementioned embodiment, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b are formed in the top plate corresponding portion 2B, using with the upper pad 62 and the lower press mold 71. However, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b may be formed in advance in the blank 10 before arranging the blank 10 between the upper press mold 61 and the lower press mold 71. For example, the first downward recessed portion 21b, the upward recessed portion 22a, and the second downward recessed portion 22b may be formed in advance in the blank 10 by using different press molds from the upper press mold 61 and the lower press mold 71.

(2e) A function performed by a single element in the above-described embodiments may be distributed among a plurality of elements, and a function performed by a plurality of elements may be integrated in a single element. Part of the configuration in the above-described embodiments may be omitted. Furthermore, at least part of the configuration of the above-described embodiments may be added to or replace a configuration of other embodiments.