Press molding method

Abstract

A press molding method is provided that can suppress the occurrence of cracks and wrinkles in press parts having a T-shaped portion. [Solution] The press molding method of the present invention comprises a first molding process in which an intermediate part 21 having an intermediate horizontal side portion 23, an intermediate connection portion 25, and an intermediate vertical side portion 27 is press-molded, and a second molding process in which the intermediate part 21 is molded into a press part 1 having a target shape, wherein the intermediate connection portion 25 and the intermediate vertical side portion 27 have the same shape as the target shape, and the intermediate vertical wall portions 25w on both sides to which the intermediate connection portion 25 is connected are formed via intermediate R portions 29 having a larger radius of curvature than the target shape, and there is no vertical wall on the side to which the intermediate connection portion 25 is not connected.

Description

[Technical Field]

[0001] The present invention relates to a press-forming method for press-forming a press part from a metal plate, the press part having a horizontal side portion and a T-shaped portion formed by connecting a vertical side portion to the horizontal side portion via a connecting portion. Here, the metal plate may be a hot-rolled steel plate, a cold-rolled steel plate, or a surface-treated steel plate obtained by subjecting a steel plate to a surface treatment (electrogalvanizing, hot-dip galvanizing, organic coating treatment, etc.), or may be a plate made of various metals such as SUS, aluminum, magnesium, etc. [Background technology]

[0002] Due to the growing need to improve fuel efficiency by reducing the weight of automobiles, and from the perspective of reducing manufacturing costs, the integration of multiple metal component parts in automobile bodies is being considered. Integration is expected to reduce weight by eliminating joints between parts, and reduce manufacturing costs by reducing the number of molds required when manufacturing parts.

[0003] In particular, among automobile parts, the integration of parts called door ring 61 and rear member 63, shown in black in FIG. 8, has been attracting attention. A characteristic feature of the shapes of these parts is that they have a hat-shaped cross section with a T-shaped portion 9 formed by connecting a horizontal side portion 3 to a vertical side portion 7 via a connecting portion 5 that curves to the horizontal side portion 3, as in the door ring 61 shown in Fig. 9. In Fig. 9, dashed lines are drawn at the boundaries between the portion that constitutes the T-shaped portion 9 and other portions to make the T-shaped portion 9 easier to understand.

[0004] When automotive parts of such shapes are press-formed into a single unit, molding defects such as stretch flange cracks and wrinkles tend to occur at the joints, which are considered to be a problem.

[0005] As a conventional method for integrating parts, Patent Document 1 proposes a method for manufacturing an integrated part by casting aluminum. Furthermore, Patent Document 2 proposes a method for avoiding stretch flange cracking by supplying raw material by sliding the material located on the opposite side of the stretch flange forming portion on the top plate portion of the part. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] W / O / 2022 / 031991

[0007] [Patent Document 2] Patent No. 5168429 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the method of Patent Document 1 requires a minimum plate thickness of about 3 mm due to limitations in castability, which is thicker than pressed parts and does not reduce weight. In addition, it requires equipment with a large clamping force, making it difficult to reduce manufacturing costs.

[0009] Furthermore, in Patent Document 2, the blank, which is the material, moves beyond the top plate portion, so the amount of movement of the material differs greatly between the curved portion and other portions, which poses a problem that wrinkles are likely to occur in the top plate portion. Furthermore, because the amount of material movement is large, if the part corresponding to the horizontal side of the T is long, the material will come off the mold during the molding process, so there is a limit to the length of the horizontal side of the T that can be molded.

[0010] The present invention has been made to solve such problems, and aims to provide a press-molding method that can suppress the occurrence of cracks and wrinkles in press parts having T-shaped portions. [Means for solving the problem]

[0011] (1) The press-forming method according to the present invention is a method for press-forming a press part having a T-shaped portion as a target shape, the method comprising the steps of: a first forming step of press-forming an intermediate part; and a second forming step of press-forming the intermediate part into the press part having a target shape, The press part having the target shape is It has a T-shape having a horizontal side portion and a vertical side portion connected via a connecting portion, The horizontal side portion has a top plate portion, and vertical wall portions and flange portions formed continuously with the vertical wall portions on both sides of the top plate portion to which the connecting portion is connected, and has at least a vertical wall portion on the side of the top plate portion to which the connecting portion is not connected, The connection portion has a top plate portion, a curved vertical wall portion formed continuously with the top plate portion and curved from the horizontal side portion to the vertical side portion, and a curved flange portion formed continuously with the curved vertical wall portion, the vertical side portion includes a top plate portion, a vertical wall portion formed continuously with the top plate portion, and a flange portion formed continuously with the vertical wall portion, The intermediate part is The intermediate horizontal side portion and the intermediate vertical side portion are connected via an intermediate connecting portion to form a substantially T-shape. the intermediate connection portion and the intermediate vertical side portion have substantially the same shape as the target shape, The intermediate vertical wall portions on both sides of the intermediate horizontal side portion to which the intermediate connection portion is connected are formed via an intermediate R portion having a larger radius of curvature than the target shape, and the side to which the intermediate connection portion is not connected does not have a vertical wall.

[0012] (2) In addition, in the above (1), the radius of curvature of the intermediate R portion is equal to the height of the vertical wall.

[0013] (3) Furthermore, in the above-described (1) or (2), the first molding process forms a constraining shape for constraining the flange portion of the intermediate part in the second molding process, and the second molding process forms the constraining shape by pressing it with a pad.

[0014] (4) In addition, in the above (1) or (2), the second molding step is characterized in that a restraining shape for restraining the flange portion of the intermediate part is formed by a pad. [Effects of the Invention]

[0015] According to the present invention, it is possible to suppress the occurrence of cracks and wrinkles in a press part having a T-shaped portion, thereby enabling the integration of metal member parts having a T-shaped portion by press forming, thereby reducing the weight of the part and the manufacturing cost. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are explanatory diagrams of the press forming method of the present embodiment, showing an intermediate part (FIG. 1A) and a pressed part having a target shape (FIG. 1B). [Figure 2] FIG. 1 is an explanatory diagram (part 1) of a mold for a first molding step in an embodiment. [Figure 3] FIG. 2 is an explanatory diagram (part 2) of a mold for a first molding step in the embodiment. [Figure 4] FIG. 10 is an explanatory diagram (part 1) of a mold for a second molding step in the embodiment. [Figure 5] FIG. 10 is an explanatory diagram (part 2) of a mold for a second molding step in the embodiment. [Figure 6] 6(a) and 6(b) are diagrams showing the state of stretch flange cracking (FIG. 6(a)) and the state of wrinkles (FIG. 6(b)) of the intermediate part in the example. [Figure 7] 7(a) and 7(b) are diagrams showing the state of stretch flange cracks (FIG. 7(a)) and the state of wrinkles (FIG. 7(b)) of a press part having a target shape in an example. [Figure 8] 1 is a diagram illustrating an automobile part that is the subject of the present invention. [Figure 9] FIG. 9 is a view showing a door ring extracted from the parts shown in FIG. 8. [Figure 10] 1 is an explanatory diagram of a T-shaped portion that is the subject of the present invention. [Figure 11] FIG. 1 is an explanatory diagram of the target shape used in explaining the process leading to the invention (part 1). [Figure 12] FIG. 2 is an explanatory diagram of the target shape used in the explanation of the process leading to the invention (part 2). [Figure 13] FIG. 1 is an explanatory diagram of a conventional mold used in explaining the process leading to the invention (part 1). [Figure 14] FIG. 2 is an explanatory diagram of the conventional mold used in explaining the process leading to the invention (part 2). [Figure 15] 15(a) and 15(b) are diagrams showing the state of stretch flange cracks (FIG. 15(a)) and the state of wrinkles (FIG. 15(b)) of a part pressed using a conventional die. DETAILED DESCRIPTION OF THE INVENTION

[0017] As shown in FIG. 10 , the press part 1 that is the subject of the present invention has a horizontal side portion 3 and a T-shaped portion 9 formed by connecting a vertical side portion 7 to the horizontal side portion 3 via a connecting portion 5 that curves. First, the components that make up this T-shaped portion 9 will be described with reference to FIG. 10 . In addition, when the term "T-shaped portion" is used in this application, it does not only mean an exact T-shape in which the horizontal and vertical sides form a right angle, but also means a shape in which the horizontal and vertical sides are connected via a connecting portion. In this specification, when referring to the top plate portion, vertical wall portion, and flange portion, the letters "t," "w," and "f" are added after the numbers indicating each portion, respectively.

[0018] The horizontal side portion 3 has a top plate portion 3t, a vertical wall portion 3w on the side of the top plate portion 3t where the connecting portion 5 is connected, and a flange portion 3f formed continuously with the vertical wall portion 3w. The top plate portion 3t also has a vertical wall portion 3w and a flange portion 3f on the side to which the connection portion 5 is not connected. However, the T-shaped portion 9 targeted by the present invention may have only a vertical wall portion 3w on the side to which the connecting portion 5 is not connected, and may not have a flange portion. In the following description, the side of the top panel 3t to which the connection portion 5 is connected will be simply referred to as the "connection portion side," and the side to which the connection portion 5 is not connected will be simply referred to as the "non-connection portion side."

[0019] The connection portion 5 is the area surrounded by a dashed line in Figure 10, and has a top plate portion 5t, curved vertical wall portions 5w formed on both sides of the top plate portion 5t and curved from the horizontal side portion 3 toward the vertical side portion 7, and a curved flange portion 5f formed continuously with the curved vertical wall portion 5w.

[0020] The vertical side portion 7 has a top plate portion 7t, vertical wall portions 7w formed on both sides of the top plate portion 7t, and flange portions 7f formed continuously with the vertical wall portions 7w.

[0021] <Background to the invention> Before describing the embodiments, the background to the invention will be described. When examining a press molding method for a press part having the above-mentioned T-shaped portion 9, the inventors first conducted a press molding analysis using the finite element method to specifically examine the movement of material that causes molding defects.

[0022] FIG. 11 shows a perspective view of the pressed part 1 that was the subject of the study, and FIG. 12 shows a cross-sectional view taken along line AA in FIG. 11, with the dimensions of each part shown in the figure. 13 and 14 are explanatory diagrams of the conventional die 51 used in the analysis, which is equipped with a punch 53, a pad 55, and a die 57, and the sheet pressing load of the pad that holds down the blank 11 was set to 10 tonf for forming. The analysis was carried out by press-forming the blank 11 in one process using the conventional die 51, and accurately determining the locations and positions where stretch flange cracks and wrinkles occur. The blank 11 is made of a cold-rolled 980 MPa high-tensile steel plate having a thickness of 1.4 mm.

[0023] Figure 15 shows a contour diagram of the analysis results. Figure 15(a) shows the analysis results for stretch flange cracking, showing the state at the bottom dead center of forming. As shown in Figure 15(a), stretch flange cracking occurred at the flange end of the connection portion 5, and it was found that cracking was also a concern in the curved vertical wall portion 5w that continues to the curved flange portion 5f. 15(b) shows the analysis results of wrinkles, showing the shape 5 mm before the bottom dead center of forming. As shown in FIG. 15(b), it was found that wrinkles occurred near the vertical side 7 of the top plate 5t of the connection part 5.

[0024] From the press forming analysis, it was found that stretch flange cracking, which is one of the forming defects, occurs when the material is pulled into the curved vertical wall portion 5w when forming the curved portion of the connection portion 5. More specifically, it occurs when the material at the end edge of the curved flange portion 5f, which is formed continuously with the curved vertical wall portion 5w, is pulled toward the curved vertical wall portion 5w and then pulled to both the left and right sides of the curved vertical wall portion 5w.

[0025] The causes of wrinkles are considered to be as follows. On the non-connection side of the top panel portion 3t of the horizontal side portion 3, there is a vertical wall portion 3w that extends over the entire length of the horizontal side portion 3. Also, on the connection side of the horizontal side portion 3, as shown in Fig. 10, there are paired vertical wall portions 3w on both sides of the connection portion 5, similar to the connection portion side. In other words, on both sides of the connection portion 5 on the top panel portion 3t of the horizontal side portion 3, there are vertical wall portions 3w on both sides of the top panel portion 5t.

[0026] However, in the area where the connection portion 5 is formed, a vertical wall portion 3w exists on the non-connection side of the top plate portion 3t, but there is no corresponding vertical wall portion 3w on the connection side, resulting in a curved vertical wall portion 5w. Therefore, when focusing on the top plate portion 3t, the amount of material movement is less in the region where the connection portion 5 is formed, particularly in the region close to the vertical side portion 7, than in other regions. Therefore, due to the difference in the amount of material movement between these regions, it is thought that wrinkles occur in the top plate portion 5t of the connection portion 5, which has the least amount of material movement, particularly in the region close to the vertical side portion 7.

[0027] From the above considerations, it was found that the following measures are effective in suppressing stretch flange cracking of the curved flange portion 5f and wrinkles of the top plate portion 5t. That is, stretch flange cracking can be suppressed by reducing the movement of material in the curved flange portion 5f and the curved vertical wall portion 5w. Furthermore, wrinkles in the top plate portion 5t are suppressed by reducing the difference in the amount of material movement between the region where the connection portion 5 is formed and other regions. Specifically, the amount of material movement in the region where the amount of material movement is large, i.e., the amount of material movement in the region other than the region where the connection portion 5 is formed, is reduced.

[0028] To achieve this material movement, the present invention performs press forming in two steps rather than one step. When forming the intermediate part 21 in the first step, the amount of material movement in the region other than the intermediate joint 25 in the intermediate top plate portion 23t of the intermediate horizontal side portion 23 is reduced to prevent wrinkles. In the second step, press forming is performed so as to reduce material movement in the curved flange portion 5f and the curved vertical wall portion w to prevent stretch flange cracking. The present invention is based on this finding, and specific embodiments will be described below.

[0029] [Embodiment Mode] The press-forming method according to this embodiment is a method for press-forming a press part 1 having the T-shaped portion 9 shown in FIG. 10 described above, The method includes a first forming step of press-forming an intermediate part 21 (see FIG. 1(a)) having an intermediate horizontal side portion 23, an intermediate connecting portion 25, and an intermediate vertical side portion 27, and a second forming step of forming the intermediate part 21 into a press part 1 (see FIG. 1(b)) having a target shape. Note that FIG. 1(b) shows a state in which unnecessary portions have been trimmed after forming. Each step will be described in detail below.

[0030] <1st molding process> The first molding process is a process for molding an intermediate part 21, which has an intermediate horizontal side portion 23, an intermediate connecting portion 25, and an intermediate vertical side portion 27, as shown in Figure 1(a), and the intermediate connecting portion 25 and the intermediate vertical side portion 27 have the same shape as the target shape. When we say the same shape here, we do not mean exactly the same shape, but rather include cases where, for example, there is a gradually changing portion at the boundary between the intermediate connection portion 25 and the intermediate horizontal side portion 23 where the shape gradually changes.

[0031] Furthermore, the connecting portion side of the intermediate top plate portion 23t of the intermediate horizontal side portion 23 has an intermediate vertical wall portion 23w formed via an intermediate R portion 29 having a larger radius of curvature than the target shape, and an intermediate flange portion 23f formed continuously with the intermediate vertical wall portion 23w. In addition, the intermediate flange portion 23f and the intermediate curved flange portion 23f have a step shape 30. Furthermore, the middle horizontal side portion 23 does not have a vertical wall on the non-connection side of the middle top panel portion 23t.

[0032] 1(a), the radius of curvature of the intermediate R portion 29 is equal to the vertical wall height, so the entire intermediate vertical wall portion 23w is the intermediate R portion 29, and has a curved shape as a whole.

[0033] 2 and 3, the intermediate part 21 as described above is formed using an intermediate molding die 31 consisting of a punch 33, a pad 35, and a die 37. The plate pressing load of the pad 35 is set to, for example, 10 tonf. The intermediate molding die 31 differs from the conventional die 51 shown in FIGS. 13 and 14 in the following three main points.

[0034] First, in the first forming step, no vertical wall is formed on the non-connection portion side of the intermediate top panel portion 23t, and therefore no die for forming the vertical wall exists.

[0035] Secondly, the intermediate vertical wall forming portions 33w and 37w that form the intermediate vertical wall portion 23w in the punch 33 and die 37 have a large radius of curvature R shape so that an intermediate R portion 29 having a larger radius of curvature than the R portion of the target shape can be formed. In the example shown in Figure 1(a), the radius of curvature of the intermediate R portion 29 is equal to the height of the vertical wall, so the intermediate R portion 29 is formed by the intermediate vertical wall forming portions 33w and 37w of the punch 33 and die 37. In this example, the radius of curvature of the intermediate vertical wall molding portions 33w and 37w is 70 mm.

[0036] Third, the intermediate flange forming portions 33f, 37f of the punch 33 and die 37 that form the flange portions 23f, 27f and curved flange portion 25f of the intermediate part 21 have step forming portions 33fs, 37fs that form the step shape 30 with a height of 6 mm and a curvature radius of 5 mm.

[0037] The intermediate part 21 formed in the first forming step does not have a vertical wall on the non-connection side of the intermediate horizontal side portion 23, so the material is not pulled toward that side. In addition, the radius of curvature of the intermediate R portion 29 is large, and more specifically, the entire shape is gently curved, so the amount of material movement during the forming process of the intermediate vertical wall portion 23w is suppressed, and the difference in material movement between the area where the intermediate connection portion 25 is formed is small. Therefore, in the first forming step, no wrinkles are generated in the intermediate top panel portion 25t. Furthermore, in the first molding process, since the radius of curvature of the intermediate R portion 29 is large, no large tensile force is generated that pulls the intermediate flange portion 25f and the intermediate curved vertical wall portion 25w toward the intermediate horizontal side portion 23, and therefore no cracks occur in the intermediate curved flange portion 25f.

[0038] <Second forming process> As shown in FIGS. 4 and 5, the target shape mold 41 for the second molding step includes a punch 43, a die 47, and a pad 45.

[0039] The second forming step is a step of press-forming the intermediate part 21 into the press part 1 (see FIG. 1(b)) having the target shape. Specifically, a vertical wall portion w and a flange portion f are formed on the intermediate part 21 on the non-connecting side of the intermediate top plate portion 23t of the intermediate horizontal side portion 23, and the vertical wall portion w is formed by setting the intermediate R portion 29 of the intermediate part 21 as an R portion with a curvature radius of the target shape.

[0040] In the second forming step, press forming is performed while the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f are restrained. In this embodiment, since the step shape 30 is formed in the first forming step, in the second forming step, the step shape 30 is pressed by the pad 45.

[0041] Because the intermediate connection portion 25 is already formed into the same shape as the target shape in the first forming process, there is almost no material movement in that area in the second forming process. Also, because the vertical wall portion 23w is already formed on the connection portion side of the intermediate top plate portion 23t, there is little material movement in that area in the second forming process. For these reasons, no wrinkles are formed in the top plate portion 5t of the connection portion 5 after the second forming process.

[0042] Furthermore, because the shape of the intermediate connecting portion 25 has already been formed into the target shape, the flange end of the intermediate connecting portion 25 will not be pulled toward the curved vertical wall portion 25w in the second forming step and will not crack. Furthermore, in the second forming step, the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f are formed in a restrained state, which suppresses material movement, and also in this respect, the curved flange portion 5f of the connecting portion 5 will not be pulled and will not crack.

[0043] As described above, according to this embodiment, no stretch flange cracks or wrinkles occur in either the first forming step or the second forming step.

[0044] In the above description, the radius of curvature of the intermediate R portion 29 formed in the first forming step is the same as the height of the vertical wall portion 3w, but the radius of curvature of the intermediate R portion 29 of the present invention may be larger than the target shape, and may be smaller than the vertical wall height. In this case, a planar intermediate vertical wall portion 23w exists continuously with the intermediate R portion 29.

[0045] Furthermore, in the above explanation, the step shape 30 is given as an example of a restraining shape for restraining the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f, but the restraining shape of the present invention is not limited to this and may be any shape that can restrain the intermediate flange portions 23f, 27f and the curved flange portion 25f in the second molding process.

[0046] Furthermore, in the above description, a constraining shape is formed in the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f in the first molding step, but the present invention is not limited to this, and it is also possible to not form a constraining shape in the first molding step, but to constrain the relevant portions while forming the constraining shape using pad 45 in the second molding step. [Example]

[0047] The occurrence of stretch flange cracking and wrinkles when press-forming the target shape shown in Figure 11 using an example of the present invention was simulated by analysis. The dies used in the first and second forming steps were the same as those described in the embodiment.

[0048] Contour diagrams of the analysis results are shown in Fig. 6 and Fig. 7. 6(a) shows the analysis results of the intermediate part 21. The analysis results for stretch flange cracking are shown in Fig. 6(a), which shows the state at the bottom dead center of forming. As shown in Fig. 6(a), no stretch flange cracking occurred anywhere in the intermediate joint 25, including the flange end. Furthermore, Figure 6(b) shows the analysis results for wrinkles, showing the shape 5 mm before the bottom dead center of forming. As shown in Figure 6(b), no wrinkles were observed anywhere, including the intermediate top plate portion 25t.

[0049] Figure 7 shows the analysis results of the target shape, and Figure 7(a) shows the analysis results for stretch flange cracking, showing the state at the bottom dead center of forming. As shown in Figure 7(a), no stretch flange cracking occurred anywhere, including the flange end of the connection portion 5. Figure 7(b) shows the analysis results for wrinkles, showing the shape 5 mm before the bottom dead center of forming. As shown in Figure 7(b), no wrinkles were observed anywhere, including the top plate portion 5t.

[0050] As described above, it was confirmed that according to the present invention, stretch flange cracks and wrinkles did not occur in either the intermediate part 21 or the pressed part 1 having the target shape. [Explanation of symbols]

[0051] 1 Pressed parts 3 Side part 3t Top plate of horizontal side 3w Vertical wall of horizontal side 3f Flange part of horizontal edge 5 Connection 5t Top plate of connection 5w Curved vertical wall of connection 5f Curved flange at connection 7 Vertical Side 7t Top plate of vertical side 7w Vertical wall part of vertical side 7f Flange part of vertical side 9 T-shaped part 11 Blank 21 Intermediate parts 23 Middle horizontal part 23t Intermediate top plate of intermediate horizontal section 23w Intermediate vertical wall of intermediate horizontal side 23f Intermediate flange part of intermediate horizontal side 25 Intermediate joint 25t Intermediate top plate of intermediate connection 25w Intermediate curved vertical wall of intermediate connection 25f Intermediate curved flange part of intermediate connection 27 Middle vertical side 27t Intermediate top plate part of intermediate vertical side 27w Intermediate vertical wall of intermediate vertical side 27f Intermediate flange part of intermediate vertical side 29 Middle R section 30 Step shape 31 Intermediate molding die 33 Punch 33w Middle vertical wall molding part 33f Intermediate flange molding part 33fs Step molding section 35 pads 37 Die 37w Middle vertical wall molding part 37f Intermediate flange molding part 37fs Step molding section 41 Target shape mold 43 Punch 45 pads 47 Die 51 Conventional mold 53 Punch 55 Pad 57 Die 61 Door Ring 63 Rear member

Claims

1. A press forming method for press-forming a press part having a T-shaped portion into a target shape, comprising: a first forming step of press-forming an intermediate part; and a second forming step of press-forming the intermediate part into the press part having a target shape, The press part having the target shape is The connector is T-shaped and has a horizontal side portion and a vertical side portion connected via a connecting portion, The horizontal side portion has a top plate portion, and vertical wall portions and flange portions formed continuously with the vertical wall portions on both sides of the top plate portion to which the connecting portion is connected, and has at least a vertical wall portion on the side of the top plate portion to which the connecting portion is not connected, The connection portion has a top plate portion, a curved vertical wall portion formed continuously with the top plate portion and curved from the horizontal side portion to the vertical side portion, and a curved flange portion formed continuously with the curved vertical wall portion, the vertical side portion includes a top plate portion, a vertical wall portion formed continuously with the top plate portion, and a flange portion formed continuously with the vertical wall portion, The intermediate part is The intermediate horizontal side portion and the intermediate vertical side portion are connected via an intermediate connecting portion to form a substantially T-shape. the intermediate connection portion and the intermediate vertical side portion have substantially the same shape as the target shape, A press forming method characterized in that the intermediate vertical wall portions on both sides of the intermediate horizontal side portion to which the intermediate connection portion is connected are formed via an intermediate R portion having a larger radius of curvature than the target shape, and no vertical wall is present on the side to which the intermediate connection portion is not connected.

2. 2. The press forming method according to claim 1, wherein the radius of curvature of the intermediate R portion is equal to the height of the vertical wall.

3. 3. The press forming method according to claim 1, wherein the first forming step forms a constraining shape for constraining the flange portion of the intermediate part in the second forming step, and the second forming step forms the constraining shape by pressing with a pad.

4. 3. The press forming method according to claim 1, wherein the second forming step comprises forming a restraining shape for restraining the flange portion of the intermediate part with a pad.

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