Manufacturing method for press-molded products

Abstract

To provide a method for manufacturing a press-formed article in which crack generation during press molding is suppressed, in manufacturing a press-formed article having a top plate part and vertical wall parts that are continuous with the top plate part via ridge line parts.SOLUTION: Provided is a method for manufacturing a press-formed article which includes a top plate part with bent parts in top view, and vertical wall parts that are continuous from a part of the inside of the bends in the top plate part via ridge line parts. The method includes: a first molding step in which a metal plate blank is press-formed to an intermediate molding that has an intermediate top plate part, intermediate vertical wall parts, intermediate ridge line parts connecting the intermediate top plate part to the intermediate vertical wall parts, and that has a protrusion higher than a reference height of a top plate surface, at an end of the intermediate ridge line parts; and a second molding step in which the intermediate molding is press-formed to the press-formed article.SELECTED DRAWING: Figure 30

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a press-formed product having at least a top plate portion, a vertical wall portion, and a ridge portion that is a connection portion between the top plate portion and the vertical wall portion. [Background technology]

[0002] As automobile crashworthiness standards become stricter, progress is being made in improving the crashworthiness of vehicle bodies. At the same time, recent carbon dioxide emission regulations have made it necessary to reduce the weight of vehicle bodies. Therefore, to achieve both crashworthiness and vehicle weight reduction, metal plates with even higher strength than conventional ones are being used in vehicle bodies. Recently, efforts have been made to apply ultra-high-tensile steel plates with a strength of 1.5 GPa or higher. However, high-strength metal plates generally have poor ductility, so when press-formed parts are manufactured for vehicle body parts, cracks tend to occur at the edges during the press-forming process.

[0003] Conventionally, methods for preventing cracks in press-formed products have been employed. For example, Patent Document 1 discloses a method for preventing cracks from occurring at the connection portion between a wall portion continuing from a connecting side portion and a flange portion continuing from the wall portion when press-forming a T-shaped part having a T-shaped top plate portion in which a vertical side portion and a horizontal side portion are connected by a connecting side portion. Furthermore, Patent Document 2 discloses a method for preventing cracks from occurring during stretch flange forming of a press-formed product having a flat plate portion with a concave outer peripheral edge portion in which a portion of the outer peripheral edge is concave inward, and a flange portion bent along the concave outer peripheral edge portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-13952 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-104492 Summary of the Invention [Problem to be solved by the invention]

[0005] The method disclosed in Patent Document 1 involves first forming an intermediate part in a first forming step, which has a convex portion formed on the vertical side of the connecting side of the top plate, and a curved R portion formed by raising the bottom R portion connecting the wall portion continuing from the connecting side and the flange portion. Then, in a second forming step, the convex portion and the curved R portion of the intermediate part are crushed to form a T-shaped part of the target shape. This allows material to flow into the wall portion continuing from the connecting side, preventing cracks from occurring at the connection portion between the wall portion and the flange portion.

[0006] In addition, the method disclosed in Patent Document 2 involves applying plastic deformation to a portion of a blank material that corresponds to a flat portion, and drawing the material into the plastically deformed portion, thereby drawing the material toward a portion that corresponds to a bent portion of a flange, thereby providing excess material to the bent portion. The blank material with excess material is then bent to form a press-formed product having a flange. This is said to effectively suppress the occurrence of stretch flange cracking without reducing the formability of the bent portion of the flange of the press-formed product.

[0007] Thus, the methods disclosed in Patent Documents 1 and 2 prevent cracks in a press-formed product at a location subjected to stretch flange deformation. On the other hand, for example, in a press-formed product having a top plate portion that is generally T-shaped or L-shaped in top view and has horizontal and vertical sides, cracks may occur at the end of the ridge connecting the vertical wall portion and the horizontal side portion near the tip of the horizontal side portion, unlike cracks associated with stretch flange deformation. However, the methods disclosed in Patent Documents 1 and 2 above were unable to suppress cracks at the end of the ridge connecting the vertical wall portion and the horizontal side portion of a press-formed product having such a generally T-shaped or L-shaped top plate portion.

[0008] Furthermore, even in press molding of a press-molded product having a top plate portion, a vertical wall portion continuing to the top plate portion via a ridge portion, and a vertical flange portion continuing to the vertical wall portion, it was difficult to suppress cracks that occurred at the end of the ridge portion.

[0009] Furthermore, even in press molding of a press-molded product that has a top plate portion and a vertical wall portion that continues to the top plate portion via a ridge portion, where the top plate portion or a portion thereof is curved when viewed from above and the vertical wall portion continues to the inside of the curvature in the top plate portion, it has been difficult to suppress cracks that occur at the end of the ridge portion.

[0010] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a method for manufacturing a press-molded product having a top plate portion and a vertical wall portion connected to the top plate portion via a ridge portion, which suppresses the occurrence of cracks during press molding. [Means for solving the problem]

[0011] In order to solve the above problems and achieve the objectives, (1) The manufacturing method of a press-formed product of the present invention is a manufacturing method of a press-formed product having at least a top plate portion, a vertical wall portion, and a ridge portion which is the connecting portion between the top plate portion and the vertical wall portion, and includes a first forming process of press-forming a metal plate blank into an intermediate formed product having an intermediate top plate portion, an intermediate vertical wall portion, and an intermediate ridge portion connecting the intermediate top plate portion and the intermediate vertical wall portion, and having a convex portion higher than the reference height of the top plate surface at one or more locations on the intermediate top plate portion including the intermediate ridge portion, and a second forming process of press-forming the intermediate formed product into the press-formed product.

[0012] (2) The manufacturing method of the press-molded product according to the present invention is the method of manufacturing the press-molded product according to the invention of (1) above, wherein the shape of the press-molded product is such that the top plate portion has a horizontal side portion, a vertical side portion, and a connecting R portion where the horizontal side portion and the vertical side portion are connected, and is approximately T-shaped or approximately L-shaped in a top view, and the top plate portion is provided with the ridge portion connecting to the top plate portion from the horizontal side portion of the top plate portion across the connecting R portion and the vertical side portion, the vertical wall portion continuing via the ridge portion across the horizontal side portion of the top plate portion across the connecting R portion and the vertical side portion, and a bottom flange portion continuing from the vertical wall portion, and The plate portion has an intermediate horizontal side portion, an intermediate vertical side portion, and an intermediate connecting R portion connecting the intermediate horizontal side portion and the intermediate vertical side portion, and is approximately T-shaped or approximately L-shaped when viewed from above, and the height of the intermediate vertical side portion of the intermediate top plate portion is lower than the height of the vertical side portion in the target product shape.Furthermore, in the first molding process, the intermediate molded product is press-molded into an intermediate molded product having a convex portion higher than the height of the vertical side portion at the end of the intermediate horizontal side portion of the intermediate top plate portion including the intermediate ridge portion of the intermediate molded product and / or at the intermediate connecting R portion of the intermediate top plate portion including the intermediate ridge portion of the intermediate molded product.

[0013] (3) In the manufacturing method of the press-molded product of the present invention, in the invention (2) above, in the first molding step, the intermediate top plate portion including the intermediate ridge portion is press-molded into an intermediate molded product having a convex portion whose height gradually increases toward the tip side of the intermediate horizontal side portion.

[0014] (4) In the manufacturing method of the press-molded product of the present invention, in the invention (2) above, in the first molding process, the intermediate top plate portion including the intermediate ridge portion is press-molded into an intermediate molded product having a convex portion whose height is constant up to the tip side of the intermediate horizontal side portion.

[0015] (5) In the manufacturing method of the press-molded product of the present invention, in the invention (2) above, in the first molding step, the convex portion is formed in the intermediate connection R portion including the intermediate ridge portion, and further, the intermediate molded product is press-molded to have the intermediate horizontal side portion of the intermediate top plate portion whose height matches the height of the convex portion of the intermediate connection R portion.

[0016] (6) In the manufacturing method of the press-molded product of the present invention, in the invention (1) above, in the first molding process, the intermediate molded product is press-molded to have a convex portion higher than the reference height of the top plate surface at one or more locations of the intermediate top plate portion, including the end of the intermediate ridge portion.

[0017] (7) In the manufacturing method of a press-formed product according to the present invention, in the invention (6) above, the press-formed product has a vertical flange portion continuous with the vertical wall portion, and in the first forming process, the intermediate top plate portion including the intermediate ridge portion is press-formed into an intermediate formed product having the convex portion at the end portion on the vertical flange portion side of the press-formed product.

[0018] (8) The manufacturing method of the press-molded product of the present invention is the invention of (6) above, wherein the press-molded product has a top plate portion or a part of the top plate portion curved when viewed from above, and the vertical wall portion continues on the inside of the curvature in the top plate portion, and in the first molding step, the press-molded product is press-molded into an intermediate molded product having the convex portion on the intermediate top plate portion including the end of the intermediate ridge portion. [Effects of the Invention]

[0019] The present invention can suppress cracking during press molding in press-molded products having a top plate portion and a vertical wall portion connected to the top plate portion via a ridge line portion. In particular, in press-molded products having a top plate portion that is generally T-shaped or L-shaped in top view, including horizontal and vertical sides, cracking at the ridge line portion near the tip of the horizontal side can be suppressed. Furthermore, in press-molded products having a top plate portion, a vertical wall portion connected to the top plate portion via a ridge line portion, and a vertical flange portion connected to the vertical wall portion, cracking at the end of the ridge line portion near the vertical flange can be suppressed. Furthermore, in press-molded products having a top plate portion and a vertical wall portion connected to the top plate portion via a ridge line portion, the top plate portion or a portion thereof is curved in top view, and the vertical wall portion is connected to the inside of the curve of the top plate portion, cracking at the end of the ridge line can be suppressed. [Brief explanation of the drawings]

[0020] [Figure 1] Figure 1 shows an example of a method for manufacturing a press-formed product according to embodiment 1 of the present invention, in which the ridge line at the tip of the horizontal side and the entire horizontal side of the top plate are made higher as convex portions, and illustrates a first forming process in which the press-formed product is press-formed into an intermediate shape in which the vertical wall height at the vertical side of the top plate is lower than the target shape, a second forming process in which the press-formed product has the vertical wall height of the target shape, and the reason why cracks at the end of the ridge line on the horizontal side of the press-formed product in the target shape can be suppressed ((a) first forming process, (b) second forming process). [Figure 2] Figure 2 shows an example of a manufacturing method for a press-formed product according to embodiment 1 of the present invention, in which the convex portion is only the connecting R portion, and illustrates a first forming process in which the press-formed product is press-formed into an intermediate shape in which the vertical wall height at the vertical side portion of the top plate is lower than the target shape, a second forming process in which the press-formed product has the vertical wall height of the target shape, and the reason why cracks at the end of the ridge portion on the horizontal side of the press-formed product in the target shape can be suppressed ((a) first forming process, (b) second forming process). [Figure 3]FIG. 3 is a diagram showing an example of a press-formed product having a top plate portion that is substantially T-shaped when viewed from above, which is an object to be manufactured in the present invention, in which the roundness of the tip of the horizontal side portion of the top plate is small. [Figure 4] FIG. 4 is a diagram showing an example of a press-formed product having a top plate portion that is substantially T-shaped when viewed from above, which is an object to be manufactured in the present invention, in which the tips of the horizontal sides of the top plate are largely rounded. [Figure 5] FIG. 5 is a diagram showing an example of a press-formed product to be manufactured in the present invention, which has a top plate portion that is substantially L-shaped when viewed from above. [Figure 6] FIG. 6 is a diagram illustrating a conventional manufacturing method for press-forming a press-formed product having a substantially T-shape in top view through two steps ((a) first forming step, (b) second forming step). [Figure 7] FIG. 7 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a roughly T-shaped press-formed product press-formed in two conventional steps ((a) intermediate shape, (b) target shape). [Figure 8] FIG. 8 is a diagram illustrating the locations where cracks occur in a press-formed product having a generally T-shaped top plate portion press-formed by a conventional manufacturing method, and the reasons for this. [Figure 9] Figure 9 is a diagram showing an example of a punch used in press-forming an intermediate-shaped press-formed product in which a convex portion is formed on the top plate portion in the first forming process in the manufacturing method for a press-formed product according to embodiment 1 of the present invention. It is a diagram showing a specific example of a punch that forms a ``convex portion'' of uniform height on the ridge portion that continues from the position where the horizontal side portion of the top plate extends, and further forms an intermediate-shaped product having a top plate horizontal side portion whose height matches the height of the convex portion. [Figure 10] Figure 10 is a diagram showing an example of a punch used in press-forming an intermediate-shaped press-formed product in which a convex portion is formed in the top plate portion in the first forming step in the manufacturing method for a press-formed product according to embodiment 1 of the present invention. It is a diagram showing a specific example of a punch that forms a ``convex portion'' on the ridge portion that continues from the position where the lateral side portion of the top plate extends, so that the height gradually increases toward the tip of the ridge portion, and further forms an intermediate-shaped product having a top plate lateral side portion that has a height that matches the height of the convex portion. [Figure 11] Figure 11 is a diagram showing an example of a punch used in press-forming an intermediate-shaped press-formed product in which a convex portion is formed on the top plate portion in the first forming process in the manufacturing method of a press-formed product according to embodiment 1 of the present invention, and is a diagram showing a specific example of a punch that forms a convex portion on the joint R portion of the top plate portion. [Figure 12] FIG. 12 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of forming for each of the intermediate shape and the target shape of an approximately T-shaped press-formed product press-formed by the manufacturing method of the press-formed product using the punch shown in FIG. 10(a) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). [Figure 13] FIG. 13 is a contour diagram showing the results of calculating the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a roughly T-shaped press-formed product press-formed in two conventional steps when the product target shape is as shown in FIG. 4 ((a) intermediate shape, (b) target shape). [Figure 14] FIG. 14 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of forming for each of the intermediate shape and the target shape of a substantially T-shaped press-formed product press-formed by the manufacturing method of the press-formed product using the punch (convex portion) shown in FIG. 11(a) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). [Figure 15] FIG. 15 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of forming for each of the intermediate shape and the target shape of a substantially T-shaped press-formed product press-formed by the manufacturing method of the press-formed product using the punch (height of the convex portion + horizontal side portion Up) shown in FIG. 11(b) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). [Figure 16] FIG. 16 shows the results of the plate thickness change rate obtained for the intermediate shape and the target shape of a press-formed product having an approximately L-shaped top plate portion press-formed by a conventional method ((a) intermediate shape, (b) target shape). [Figure 17]FIG. 17 shows the results of the plate thickness change rate obtained for the intermediate shape and the target shape of a press-formed product having an approximately L-shaped top plate portion press-formed by the method according to embodiment 1 of the present invention ((a) intermediate shape, (b) target shape). [Figure 18] FIG. 18 is an explanatory diagram of a method for manufacturing a press-formed product according to the second embodiment of the present invention. [Figure 19] FIG. 19 is an explanatory diagram of an intermediate punch used in a method for manufacturing a press-formed product according to the second embodiment of the present invention. [Figure 20] FIG. 20 is an explanatory view of an intermediate molded product according to the second embodiment of the present invention. [Figure 21] FIG. 21 is a diagram illustrating the thickness reduction rate of a press-formed product formed according to the second embodiment of the present invention. [Figure 22] FIG. 22 is an explanatory view of another aspect of the intermediate punch according to the second embodiment of the present invention. [Figure 23] FIG. 23 is an explanatory diagram of a press-formed product having a target shape according to the second embodiment of the present invention. [Figure 24] FIG. 24 is an explanatory diagram of a conventional method for press-forming the press-formed product shown in FIG. 23 in one step. [Figure 25] FIG. 25 is an explanatory diagram of the sheet thickness reduction rate when press-forming is performed using the conventional method shown in FIG. [Figure 26] FIG. 26 is an explanatory diagram of a method for manufacturing a press-formed product according to the third embodiment of the present invention. [Figure 27] FIG. 27 is an explanatory diagram of an intermediate punch used in a method for manufacturing a press-formed product according to a third embodiment of the present invention. [Figure 28] FIG. 28 is an explanatory diagram of an intermediate molded product according to the third embodiment of the present invention. [Figure 29] FIG. 29 is a diagram illustrating the sheet thickness reduction rate of a press-formed product formed according to the third embodiment of the present invention. [Figure 30] FIG. 30 is an explanatory diagram of a press-formed product having a target shape according to the third embodiment of the present invention. [Figure 31]FIG. 31 is an explanatory diagram of a conventional method for press-forming the press-formed product shown in FIG. 30 in one step. [Figure 32] FIG. 32 is an explanatory diagram of the sheet thickness reduction rate when press-forming is performed using the conventional method shown in FIG. [Figure 33] FIG. 33 is an explanatory diagram illustrating the mechanism by which cracks occur in a press-formed product press-formed by the conventional method shown in FIG. [Figure 34] FIG. 34 is a diagram illustrating the inclination angle of the tip end of the horizontal side portion in the press-formed product of the intermediate shape in Example 1. [Figure 35] FIG. 35 is a diagram illustrating a height increment for uniformly increasing the height of the tip end portion of the horizontal side portion of the press-formed product in the intermediate shape in Example 1. In FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] (Embodiment 1) Before describing the method for manufacturing a press-formed product according to the first embodiment of the present invention, the press-formed product to which the present invention is applied and the occurrence of cracks in the press-formed product will be described below. Note that the same or similar components are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0022] <Press-molded products targeted by the present invention> FIG. 3 shows a press-formed product 1 having a top plate portion 3, a vertical wall portion 5, and a bottom flange portion 7 as an example of a press-formed product to be manufactured in the present invention.

[0023] 3, the top panel 3 has a horizontal side 3a and a vertical side 3b and is generally T-shaped when viewed from above. Furthermore, the top panel 3 has an arc-shaped connecting R portion 3c extending from the horizontal side 3a to the vertical side 3b.

[0024] 3, the vertical wall portion 5 is continuous from the horizontal side portion 3a to the vertical side portion 3b of the top panel portion 3 via a ridge portion 9. The vertical wall portion 5 has a horizontal side vertical wall portion 5a that is continuous from the horizontal side portion 3a via the horizontal side ridge portion 9a, and a vertical side vertical wall portion 5b that is continuous from the vertical side portion 3b via the vertical side ridge portion 9b. Furthermore, the vertical wall portion 5 has a connecting R-side vertical wall portion 5c that is continuous from the connecting R-portion 3c via the connecting R-side ridge portion 9c and connects the horizontal side vertical wall portion 5a and the vertical side vertical wall portion 5b.

[0025] As shown in Figure 3, the bottom flange portion 7 is continuous with the vertical wall portion 5, and is formed continuously with each of the horizontal side vertical wall portion 5a, the vertical side vertical wall portion 5b, and the connecting R side vertical wall portion 5c.

[0026] Conventionally, such a press-formed product 1 has been press-formed in two steps, a first forming step and a second forming step, as shown in FIG.

[0027] First, in the first forming step, as shown in Fig. 6(a), a blank 11, which is a metal plate, is sandwiched between a punch 13 and a pad 15, and a die 17 is moved relatively toward the punch 13 to press-form a press-formed product 21 (see Fig. 6(b)) of an intermediate shape whose vertical wall height is lower than that of the target shape. Here, a top plate portion 23 of the press-formed product 21 of the intermediate shape is press-formed into the same shape as the top plate portion 3 (see Fig. 3) of the press-formed product 1 of the target shape.

[0028] Then, in the subsequent second forming process, as shown in Figure 6(b), the top plate portion 23 of the intermediate-shaped press-formed product 21 is clamped between a punch 31 and a pad 33, and the die 35 is moved relatively toward the punch 31 to press-form a press-formed product 1 of the target shape with a vertical wall height higher than that of the intermediate shape.

[0029] However, when the press-formed product 21 in the intermediate shape is press-formed into the press-formed product 1 in the target shape (FIG. 3) in the second forming step, cracks may occur at the end of the horizontal edge ridge 9a connecting the horizontal edge 3a and the horizontal edge vertical wall 5a. The end of the horizontal edge ridge 9a refers to the portion on the tip side of the horizontal edge ridge 9a in the direction in which the horizontal edge 3a extends.

[0030] In order to determine the cause of cracks occurring at the end of the horizontal edge ridge portion 9a of the press-formed product 1 having such an approximately T-shaped top plate portion 3, an analysis using the finite element method (FEM analysis) was performed on each of the two steps used to press-form the press-formed product 1 into the target shape, as shown in Figure 6.

[0031] FIG. 7 shows the thickness change rates at the bottom dead center of the intermediate-shape press-formed product 21 and the target-shape press-formed product 1, calculated by FEM analysis, for the first and second forming processes, respectively. The results shown in FIG. 7 are for a case where a steel plate having a thickness of 1.2 mm and a tensile strength of 780 MPa was used as the blank 11, the vertical wall height of the intermediate-shape press-formed product 21 was 20 mm, and the vertical wall height of the target-shape press-formed product 1 was 30 mm. The thickness change rates shown in FIG. 7 are calculated by dividing the difference between the thickness of each portion of the intermediate-shape press-formed product 21 or the press-formed product 1 and the thickness of the metal plate that is the blank 11 by the thickness of the blank 11. In this specification and the drawings, a positive value for the thickness change rate is referred to as a thickness increase rate, and a negative value for the thickness change rate is referred to as a thickness decrease rate. The greater the absolute value of the thickness decrease rate, the more likely cracks are to occur.

[0032] Figure 7(a) shows the thickness change rate at the bottom dead center of the intermediate-shape press-formed product 21 press-formed in the first forming step shown in Figure 6(a), where the thickness reduction rate at the end of the horizontal edge ridge 29a was -4.7%. Figure 7(b) shows the thickness change rate at the bottom dead center of the press-formed product 1 of the target shape press-formed in the second forming step shown in Figure 6(b), where the thickness reduction rate at the end of the horizontal edge ridge 9a was -16.9%. As such, the absolute value of the thickness reduction rate at the end of the horizontal edge ridge 9a of the target shape is large. As a result, the thickness at the end of the horizontal edge ridge 9a in the second forming step is significantly reduced, making it more likely to crack.

[0033] The reason why the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the press-formed product 1 having the target shape is large will be explained with reference to FIG. 8. Conventionally, as described above, in the first forming step, a press-formed product 21 having an intermediate shape with a vertical wall height lower than that of the target shape is press-formed, and then in the second forming step, the intermediate shape press-formed product 21 is press-formed into a press-formed product 1 having the vertical wall height of the target shape. In this case, in the second forming step, as shown in FIG. 8, the horizontal edge ridge portion 29a is stretched, and a large tensile force acts on the horizontal edge ridge portion 9a. As a result, this large tensile force increases the absolute value of the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the target shape, as shown in FIG. 7(b) described above, leading to the occurrence of cracks.

[0034] Therefore, the inventors have studied methods for reducing the tensile force acting on the horizontal edge ridge 9a during the two-step press-forming of a press-formed product 1 having a target shape. As a result, as shown in Figures 1 and 2, the inventors came up with the idea of ​​forming a vertical wall height at the tip of the horizontal edge 23a of the top plate 23 of the press-formed product 21 having an intermediate shape (Figure 1) higher than the vertical wall height of the vertical edge 23b in the first forming step, and forming an upwardly raised convex portion 23d in the region extending from the horizontal edge 23a to the vertical edge 23b, including the connecting round portion 23c, in the top plate 23 of the press-formed product 21 having an intermediate shape (Figure 2). As shown in Figure 2, when the upwardly raised convex portion 23d is crushed in the subsequent second forming step to form the connecting round portion 3c that becomes the top plate portion of the target shape, material flows from the upwardly raised convex portion 23d toward the tip of the horizontal edge ridge 9a. It was found that this reduces the tensile force acting on the horizontal edge ridge portion 9 a and suppresses cracks at the end of the horizontal edge ridge portion 9 a. The present invention has been made based on the above-mentioned findings, and the specific configuration is as follows.

[0035] <Method of manufacturing press-molded products> The manufacturing method of the press-molded product according to the first embodiment is such that the press-molded product 1 shown in FIG. 2 described above is press-molded into an intermediate shape in which the vertical wall height of the vertical side portion of the top plate is lower than the target shape in a first molding process, and then press-molded to the vertical wall height of the target shape in a subsequent second molding process.

[0036] In the method for manufacturing a press-formed product according to the first embodiment, in the first forming step, as shown in FIG. 1(a), the vertical wall height of the horizontal side portion 23a of the top plate portion 23 of the press-formed product 21 in an intermediate shape is formed to include a "protrusion" that is higher than the vertical wall height of the vertical side portion. In the first forming step, as shown in FIGS. 9 and 10, a punch 71 including a region that is higher in the region forming the horizontal side portion 23a of the top plate portion 23 than the region forming the vertical side portion 23b may be used to press-form the press-formed product 21 in an intermediate shape. Alternatively, in the method for manufacturing a press-formed product according to the first embodiment, as shown in FIG. 2(a), a protrusion 23d that is higher than the surrounding height (the reference height of the top plate surface) is formed in the region from the horizontal side portion 23a to the vertical side portion 23b, including the connecting round portion 23c. Here, the protrusion 23d is formed to be higher than the vertical side portion 23b of the top plate portion 23 in the intermediate shape. In the first forming step, as illustrated in Fig. 11(a), a punch 71 having a convex portion forming portion 73d formed in a region extending from a horizontal side forming portion 73a including a connection R forming portion 73c of a top plate forming portion 73 to a vertical side forming portion 73b may be used to press-form the intermediate-shaped press-formed product 21. In the first forming step, as illustrated in Fig. 11(b), a punch 61 having a convex portion forming portion formed in a region extending from a convex portion forming portion 63d of the top plate forming portion to a horizontal side tip side forming portion 63a1 may also be used to press-form the intermediate-shaped press-formed product 21.

[0037] Furthermore, in the method for manufacturing a press-formed product according to the first embodiment, in the subsequent second forming step, the intermediate formed product formed in the first forming step is press-formed into the top plate portion 3 having the target shape.

[0038] <Reasons why cracking can be suppressed> The reason why the method for manufacturing a press-formed product according to the first embodiment can suppress the occurrence of cracks at the ends of the horizontal edge ridges 9a of the press-formed product 1 having a target shape will be described with reference to FIGS.

[0039] In the first embodiment, as described above, in the first forming step, press-molding is performed to form an intermediate-shaped press-molded product 21 including a "protrusion" in which the horizontal side 23a of the intermediate-shaped top plate portion 23 is higher than the vertical side 23b (FIG. 1(a)). Alternatively, in the first forming step, press-molding is performed to form an intermediate-shaped press-molded product 21 in which a protrusion 23d is formed on the top plate portion 23 that is higher than the vertical side 23b of the intermediate-shaped top plate portion 23 (FIG. 2(a)).

[0040] When this intermediate-shape press-formed product 21 is press-formed into the target-shape press-formed product 1 in the second forming step, material flows from the higher parts of the intermediate shape to the horizontal edge ridges 9a, as shown in Figures 1(b) and 2(b). This reduces the tensile force acting on the horizontal edge ridges 9a in the target-shape press-formed product 1. As a result, the reduction in plate thickness at the ends of the horizontal edge ridges 9a is reduced, and cracking can be suppressed.

[0041] <Mode of horizontal side> In the above description, the first forming step was described as a step of uniformly raising the tip end portion of the horizontal side portion 23a of the intermediate press-formed product 21 in the direction of extension of the horizontal side portion 23a, as shown in FIG. 1(a). Examples of this step are shown in FIGS. 9(a) and 9(b). FIG. 9(a) is a schematic diagram of a punch (die) that uniformly raises the tip end portion of the horizontal side portion 73a relative to the boundary line between the region of the top plate forming portion 73 where the vertical side portion 73b of the top plate forming portion 73 extends toward the horizontal side portion 73a and the horizontal side portion 73a. FIG. 9(b) is a schematic diagram of a punch (die) that uniformly raises the region from the boundary line between the region of the top plate forming portion 73 where the vertical side portion 73b of the top plate forming portion 73 extends toward the horizontal side portion 73a and the horizontal side portion 73a to the tip. Thus, the range over which the tip end portion of the horizontal side portion 73a is uniformly raised is not particularly limited. However, from the viewpoint of suppressing wrinkles in the vicinity of the connecting R portion 3c in the second forming step, it is preferable to make the tip end portion of the intermediate horizontal side forming portion 73a higher than the boundary line with the region where the vertical side forming portion 73b is extended. Therefore, only the tip end portion of the horizontal side forming portion 73a may be made uniformly higher than that shown in Figure 9(a) (not shown).

[0042] Furthermore, when the tip end portion of the horizontal side portion 23a is uniformly elevated in the first forming step, the increment in height of the tip end portion is preferably 0.05 or more and 0.5 or less in ratio to the vertical wall height of the horizontal side vertical wall portion 25a of the intermediate-shaped press-formed product 21. If the increment in height of the tip end portion of the horizontal side portion 23a is less than 0.05, the height of the horizontal side portion 23a (see FIG. 8) is insufficient, resulting in only a slight decrease in the absolute value of the thickness reduction rate at the end of the horizontal side ridge portion 9a of the target shape, which may make it difficult to prevent cracks. If the increment in height of the tip end portion of the horizontal side portion 23a is more than 0.5, the vertical wall height at the tip end of the horizontal side portion 23a becomes too high in the first forming step, which stretches the horizontal side ridge portion 29a and increases the absolute value of the thickness reduction rate, which may increase the risk of cracks occurring in the first forming step.

[0043] Furthermore, in the present invention, in the first forming step, as exemplified in FIG. 10, the intermediate shaped horizontal side forming portion 73a may be inclined so as to gradually become higher toward the tip end in the extending direction.

[0044] Fig. 12 shows the results of calculating the plate thickness change rate for each of the intermediate-shaped press-formed product 21 and the target-shaped press-formed product 1, in which an intermediate-shaped press-formed product 21 having horizontal side portions 23a that are inclined so that the leading end is gradually higher in the first forming process. The results shown in Fig. 12 are for a blank 11 made of a steel plate having a plate thickness of 1.2 mm and a tensile strength of 780 MPa. Furthermore, the vertical wall height of the intermediate-shaped press-formed product 21 was 20 mm, the vertical wall height of the target shape was 30 mm, the inclination angle on the leading end side of the horizontal side portions 23a in the intermediate-shaped press-formed product 21 was 15.4°, and the height increment at the leading end was 5.5 mm.

[0045] As shown in Figure 12(a), in the press-formed product 21 of the intermediate shape, the thickness reduction rate at the tip of the horizontal edge ridge portion 29a was -9.1%, an absolute value that was greater than the -4.7% obtained by the conventional method shown in Figure 7(a) described above. However, as shown in Figure 12(b), in the press-formed product 1 of the target shape, the thickness reduction rate at the tip of the horizontal edge ridge portion 9a was -11.9%, an absolute value that was less than the -16.9% obtained by the conventional method shown in Figure 7(b) described above. This result indicates that even when the tip side of the horizontal edge portion 23a is inclined in the press-formed product 21 of the intermediate shape, cracks at the end of the horizontal edge ridge portion 9a of the press-formed product 1 of the target shape can be suppressed.

[0046] Specific examples of inclining the tip end of the horizontal side portion 23a of the intermediate shape are shown in Figures 10(a) and 10(b). In Figure 10(a), the vertical side molding portion 73b of the top plate molding portion 73 is inclined from the boundary between the region where the vertical side molding portion 73b extends toward the horizontal side molding portion 73a and the horizontal side molding portion 73a as the starting point, and gradually becomes higher toward the tip in the direction in which the horizontal side molding portion 73a extends. In Figure 10(b), the vertical side molding portion 73b is inclined from the extended region of the vertical side molding portion 73b closer to the boundary between the region where the vertical side molding portion 73b extends toward the horizontal side molding portion 73a and the horizontal side molding portion 73a as the starting point, and gradually becomes higher toward the tip in the direction in which the horizontal side molding portion 73a extends.

[0047] In this way, there is no particular limitation on the starting position for tilting the tip end portion of the horizontal side molding portion 73a, and the vertical side molding portion 73b may be tilted from the tip end side of the boundary line between the extended region and the horizontal side molding portion 73a (not shown).

[0048] Furthermore, as shown in Figures 10(a) and 10(b), when the tip side of the horizontal edge molding portion 73a is inclined in the intermediate-shaped press-formed product 21, the inclination angle based on the horizontal edge portion 3a of the target shape is preferably 3 degrees or more and 25 degrees or less.

[0049] If the inclination angle is less than 3 degrees, the absolute value of the thickness reduction rate of the horizontal edge ridge portion 9a in the press-formed product 1 of the target shape will only decrease slightly, and it may be difficult to prevent cracks. Also, if the inclination angle is more than 25 degrees, in the first forming step (see FIG. 12(a)), the horizontal edge ridge portion 29a between the horizontal edge portion 23a and the horizontal edge vertical wall portion 25a will be stretched, and the absolute value of the thickness reduction rate will increase, which may increase the risk of cracks occurring in the first forming step.

[0050] 9(a) and 9(b) and 10(a) and 10(b) illustrate specific shapes of the punch (die) that forms the horizontal side portion 23a of the intermediate-shaped press-formed product 21, but the present invention is not limited to these shapes. Any shape other than the horizontal side forming portion 73a shown in FIGS. 9 and 10 may be used as long as the punch (die) forms the height of the tip end of the horizontal side portion of the top plate portion of the intermediate shape higher than the vertical side portion of the top plate portion of the intermediate shape.

[0051] For example, in the first forming step, the height of the region of the horizontal side of the intermediate shape that is an extension of the vertical side may be made higher than the height of the vertical side of the intermediate shape.

[0052] The above description has been directed to the press-formed product 1 having a top plate portion 3 that is approximately T-shaped in top view. However, the present invention may also be directed to a press-formed product 41 that includes a top plate portion 43 that is approximately L-shaped in top view and has a horizontal side portion 43a and a vertical side portion 43b, a vertical wall portion 45, and a bottom flange portion 47, as shown in Fig. 5 .

[0053] Conventionally, a press-formed product 41 having a generally L-shaped top plate portion 43 is produced by press-forming it into an intermediate shape with a low vertical wall height in a first forming process, followed by press-forming it into the target vertical wall height in a second forming process, as shown in FIG. 16 . Therefore, similar to the press-formed product 1 having a generally T-shaped top plate portion 3, the horizontal-side vertical wall portion 55a of the press-formed product 51 in the intermediate shape shown in FIG. 16(a) is stretched in the vertical wall height direction in the second forming process shown in FIG. 16(b). This causes a large tensile force to act on the horizontal-side vertical wall portion 45a and the horizontal-side ridge portion 49a of the target shape. As a result, this large tensile force increases the absolute value of the thickness reduction rate at the end of the horizontal-side ridge portion 49a (17.7%), leading to cracking.

[0054] 17(a), in the first forming step, the tip end portion of the horizontal side portion 53a of the top plate portion is raised so that the tip end portion of the horizontal side portion 53a is higher than the vertical side portion. In the subsequent second forming step, the tip end portion of the horizontal side portion 53a of the intermediate shape is set to the height of the target shape.

[0055] As a result, as in the case of manufacturing a press-molded product 1 having the aforementioned approximately T-shaped top plate portion 3, the absolute value of the plate thickness reduction rate at the end of the horizontal side ridge portion 49a of the target shape can be reduced (-12.6%), thereby suppressing cracking.

[0056] 17(a), the height of the tip end portion of the horizontal side portion 53a of the top plate portion is uniformly higher than the tip end portion of the vertical side portion 53b of the top plate portion. However, even when manufacturing a substantially L-shaped press-formed product 41, the tip end portion of the horizontal side portion 53a of the intermediate shape may be inclined so that the height gradually increases toward the tip end in the direction in which the horizontal side portion 53a connects to the vertical wall portion and extends.

[0057] Next, FEM analysis was performed to verify that the reduction in plate thickness at the end of the horizontal edge ridge portion 9a is reduced by performing intermediate forming using the punch shape shown in Figure 11, for each process of press-forming the press-formed product 1 of the target shape through the first forming process and the second forming process.

[0058] Fig. 14 shows the results of determining the sheet thickness change rate at the bottom dead center of forming of the intermediate-shape press-formed product 21 and the target-shape press-formed product 1 by FEM analysis of the first forming step and the second forming step according to embodiment 1. The results shown in Fig. 14 are for a case where a 780 MPa-class steel plate is used as the blank 11, the vertical wall height of the intermediate-shape press-formed product 21 is 20 mm, and the vertical wall height of the target-shape press-formed product 1 is 30 mm. The sheet thickness change rate is a value obtained by dividing the difference between the sheet thickness at each portion of the press-formed product 1 or the intermediate-shape press-formed product 21 and the sheet thickness of the metal sheet that is the blank 11 by the sheet thickness of the blank 11.

[0059] In the intermediate-shaped press-formed product 21, the thickness reduction rate at the end of the horizontal edge ridge portion 29a was −1.8%, as shown in Fig. 14(a). The absolute value of this thickness reduction rate is slightly higher than the thickness reduction rate (−1.2%, see Fig. 13(a)) of the intermediate-shaped press-formed product 21 press-formed by the conventional method.

[0060] On the other hand, the thickness reduction rate of the press-formed product 1 of the target shape press-formed in the second forming step shown in Figure 14(b) was -8.1%. This value is smaller in absolute value than the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the press-formed product 1 press-formed by the conventional method (= -11.0%, see Figure 13(b)). As a result, it can be seen that cracks at the end of the horizontal edge ridge portion 9a of the press-formed product 1 of the target shape can be suppressed.

[0061] As described above, in the manufacturing method of the press-formed product according to the first embodiment, in the second forming step, the convex portion 23d is crushed to form the target shape of the top plate portion 3. This reduces the tensile force acting on the horizontal edge ridge portion 9a continuing from the horizontal edge portion 3a of the top plate portion 3 having the target shape, and makes it possible to suppress cracks at the end of the horizontal edge ridge portion 9a.

[0062] In addition, the height increment of the convex portion 23d formed on the intermediate-shaped top plate portion 23 in the first molding process (the height to the apex of the convex portion 23d when the vertical side portion 23b of the intermediate-shaped top plate portion 23 is used as the reference) should be 5% to 50% of the width of the horizontal side vertical wall portion 25a.

[0063] If the height increase of the protrusions 23d is less than 5%, the flow of material to the horizontal edge ridges 9a caused by crushing the protrusions 23d in the second molding step will be insufficient, and cracks may not be sufficiently suppressed. Also, if the height increase of the protrusions 23d exceeds 50%, the flow of material to the horizontal edge ridges 9a caused by crushing the protrusions 23d in the second molding step will be excessive, and although cracks can be suppressed, excess material may cause wrinkles, which may be a problem.

[0064] In the present invention, the projection may have a shape other than the projection 23d shown in FIG. 2(a) as long as the projection is formed at the connecting R portion connecting the horizontal side portion and the vertical side portion of the intermediate-shaped top plate portion.

[0065] In another aspect of the first embodiment, the first forming step may be a step of press-forming an intermediate-shaped press-formed product 21 as illustrated in FIG. 15(a). Here, the intermediate-shaped press-formed product 21 has a convex portion 23d formed on the top plate portion 23, and a tip portion 23a1 of the horizontal side portion 23a is higher than the vertical side portion 23b of the intermediate-shaped top plate portion 23. In this case, the first forming step may use, for example, a punch 61 having a convex portion forming portion 63d and a horizontal side tip forming portion 63a1 that forms the intermediate-shaped portion 23a1 uniformly higher than the vertical side portion 23b, as shown in FIG. 11(b). Then, in the subsequent second forming step, the convex portion 23d is crushed, and the intermediate-shaped portion 23a1 is adjusted to the height of the target shape.

[0066] 15(a) is a diagram showing the results of FEM analysis of the sheet thickness change rate at the bottom dead center of forming of an intermediate-shaped press-formed product 51 according to another aspect of the first embodiment. FIG. 15(b) is a diagram showing the results of FEM analysis of the sheet thickness change rate at the bottom dead center of forming of a target-shaped press-formed product 1 according to another aspect of the first embodiment. The results shown in FIG. 15 are for a case where a 780 MPa-class steel plate is used as the blank 11, the vertical wall height of the intermediate-shaped press-formed product 51 is 20 mm, and the vertical wall height of the target-shaped press-formed product 1 is 30 mm. The sheet thickness change rate shown in FIG. 15 is a value obtained by dividing the difference between the sheet thickness at each portion of the intermediate-shaped press-formed product 51 or the press-formed product 1 and the sheet thickness of the metal sheet that is the blank 11 by the sheet thickness of the blank 11.

[0067] In the intermediate-shaped press-formed product 51, the thickness reduction rate at the end of the horizontal edge ridge portion 29a was -2.5%, as shown in Fig. 15(a). The absolute value of this thickness reduction rate is larger than the thickness reduction rate (-1.2%) of the intermediate-shaped press-formed product 51 press-formed by the conventional method (see Fig. 13(a)).

[0068] On the other hand, when the intermediate-shaped press-formed product 51 shown in FIG. 15(a) was press-formed into the press-formed product 1 of the target shape in the second forming step, the thickness reduction rate at the end of the horizontal edge ridge 9a was −4.7%, as shown in FIG. 15(b). This value is significantly smaller in absolute value than the thickness reduction rate obtained by the conventional method (−11.0%, see FIG. 13(b)). Furthermore, the absolute value is smaller than the thickness reduction rate obtained when only the protrusion 23d is formed (−8.1%, see FIG. 14(b)). Therefore, by forming the protrusion 23d on the intermediate-shaped press-formed product 51 and raising the tip end portion 23a1 of the horizontal edge 23a in the first forming step, the thickness reduction at the end of the horizontal edge ridge 9a can be further suppressed, which is preferable.

[0069] When the intermediate-shaped press-formed product 21 is press-formed, if the portion 23a1 at the tip end of the horizontal side portion 23a is made taller, the height increase is preferably equal to or less than the height increase of the convex portion 23d. By making the convex portion 23d taller than the portion 23a1, the convex portion 23d can be crushed during the press-forming process into the target shape, causing material to flow to the horizontal side ridge portion 9a.

[0070] In addition, the intermediate-shaped press-molded product 21 shown in Figure 15 has the vertical side portion 23b higher from the extended area side of the vertical side portion 23b than the boundary line between the area extended toward the horizontal side portion 23a and the horizontal side portion 23a, and the portion 23a1 from the boundary line to the tip side of the horizontal side portion 23a is uniformly higher.

[0071] However, in the present invention, other than making the convex portion 23d higher than the portion 23a1, there are no particular limitations on the form or range in which the portion on the tip side of the horizontal side portion in the intermediate-shaped press-formed product press-formed in the first forming step is raised.

[0072] Furthermore, the present invention may be a press-molded product 41 having a top plate portion 43 that is approximately L-shaped when viewed from above and has a horizontal side portion 43a and a vertical side portion 43b, a vertical wall portion 45, and a bottom flange portion 47, as shown as an example in Figures 5 and 16(b).

[0073] In the case of a press-formed product 41 having an approximately L-shaped top plate portion 43, in the past, when the product was press-formed into an intermediate shape with a low vertical wall height in the first forming process and then press-formed to the target vertical wall height in the subsequent second forming process, cracks were likely to occur at the end of the horizontal edge ridge portion 49a.

[0074] Therefore, in the present invention, as with the above-described substantially T-shaped press-formed product 1, in the first forming step, a convex portion higher than the height (reference height of the top surface) of the vertical side portion 53b of the intermediate-shaped top plate portion 53 is formed at the connecting R portion connecting the horizontal side portion and the vertical side portion of the top plate portion. Then, in the subsequent second forming step, the convex portion is crushed to form the top plate portion in the target shape.

[0075] This makes it possible to reduce the reduction in plate thickness at the end of the horizontal edge ridge 49a of the target shape and suppress cracking, even when manufacturing a press-formed product 41 having a generally L-shaped top plate portion 43. Furthermore, in the first forming step, a convex portion may be formed on the top plate portion of the intermediate shape, and the portion on the tip side of the horizontal edge portion may be made higher than the vertical edge portion of the top plate portion of the intermediate shape.

[0076] According to the manufacturing method for a press-formed product of the first embodiment, even when a high-strength steel plate is used, cracks can be suppressed at the ends of the horizontal edge ridge portions 9a of the press-formed product 1 having a target shape. Therefore, the press-formed product 1 manufactured using a high-tensile steel plate by the manufacturing method for a press-formed product of the first embodiment can be manufactured as a vehicle body part.

[0077] (Embodiment 2) The target shape of the press-formed product targeted in embodiment 2 will be described with reference to Fig. 23. The press-formed product 101 includes a top plate portion 103, a top plate flange portion 105 extending from one longitudinal end of the top plate portion 103, and a vertical wall portion 109 continuing from the top plate portion 103 via a ridge portion 107. The press-formed product also includes a vertical flange portion 111 bent outward on one longitudinal end side of the vertical wall portion 109, and a horizontal flange portion 113 bent outward at the lower end of the vertical wall portion 109.

[0078] The process leading to the invention according to embodiment 2 will be described below using a press-formed product 101 as an example. Fig. 24 is an explanatory diagram of a conventional manufacturing method for press-forming the press-formed product 101 shown in Fig. 23 in one step.

[0079] The blank 115 to be formed into the press-molded product 101 shown in Figure 23 is made of a metal plate, and as shown in Figure 24, its overall shape is approximately rectangular, with a top plate flange equivalent portion 117 formed on one end and vertical flange equivalent portions 119 formed on both sides of the top plate flange equivalent portion 117.

[0080] Furthermore, a mold 121 used in a conventional method for manufacturing a press-formed product 101 includes a punch 123, a pad 125 that presses the blank 115, and a die 127 that cooperates with the punch 123 to form the top plate portion 103, the vertical wall portion 109, the horizontal flange portion 113, and the vertical flange portion 111. The punch 123 includes a top plate forming surface portion 129 that mainly forms the top plate portion 103. The punch 123 also includes a top plate horizontal edge forming surface portion 168 that forms the horizontal edges of the top plate forming surface portion 129, a punch-side vertical wall forming surface portion 131 that forms the vertical wall portion 109 continuous with the vertical edge, and a punch-side horizontal flange forming surface portion 133 that forms the flange portion continuous with the punch-side vertical wall forming surface portion 131. The punch 123 also includes a punch-side vertical flange forming surface portion 135 that forms the vertical flange portion 111 continuous with the horizontal edge of the top plate forming surface portion 129.

[0081] The pad 125 has a shape corresponding to the top plate forming surface portion 129 of the punch 123. The die 127 consists of a pair of left and right die portions, and is equipped with a die-side vertical wall forming surface portion 137, a die-side horizontal flange forming surface portion 139, and a die-side vertical flange forming surface portion 141.

[0082] In a conventional manufacturing method for a press-formed product 101, a blank 115 is sandwiched between a pad 125 and a punch 123, a die 127 is moved relative to the punch 123, and the top plate portion 103, vertical wall portion 109, and horizontal flange portion 113 are press-formed, and the vertical flange portion 111 is bent laterally to form the press-formed product into a target shape. With regard to this conventional manufacturing method for a press-formed product 101, a press forming analysis was performed using a finite element method (FEM) when a metal plate with a tensile strength of 1.5 GPa class was used, and the plate thickness reduction rate of the press-formed product 101 after forming was determined.

[0083] FIG. 25 shows the thickness reduction rate at the bottom dead center of forming as a contour, with lighter colored areas indicating larger thickness reduction rates. In the following explanation, the thickness reduction rate is expressed as a value (ratio) obtained by dividing the difference between the thickness of the metal plate that is the blank 115 and the thickness of each area after press forming by the thickness of the metal plate that is the blank 115. As the thickness reduction rate increases, cracks become more likely to occur. As shown in the partially enlarged view of FIG. 25, the end of the ridge line portion 107 on the side where the vertical flange portion 111 is formed (hereinafter simply referred to as "end portion 142 of ridge line portion 107") has a thickness reduction rate of 8.9%, which indicates that the thickness reduction rate is the largest and cracks are more likely to occur.

[0084] The reason why the thickness reduction rate at the end 142 of the ridge line portion 107 is large will be explained with reference to Figure 25. The arrows in Figure 25 indicate the tensile forces generated during the forming process. When the vertical wall portion 109 is formed via the ridge line portion 107, a tensile force as indicated by arrow (i) in Figure 25 acts on the plate surface of the ridge line portion 107. Furthermore, when the vertical flange portion 111 is bent laterally, an additional tensile force as indicated by arrow (ii) is applied to the end 142 of the ridge line portion 107. In this way, both the tensile force during the forming of the vertical wall portion 109 and the tensile force during the laterally bending of the vertical flange portion 111 act on the end 142 of the ridge line portion 107, which increases the thickness reduction rate and makes it more likely to crack.

[0085] Therefore, the inventors have investigated a method for reducing the tensile force acting on the end 142 of the ridgeline portion 107. As a result, when press-forming a press-formed product 101 having a target shape shown in FIG. 23 , press-forming is performed in two steps, a first forming step and a second forming step. In the first forming step, a convex portion higher than the surrounding height (the reference height of the top plate surface) is formed at the end of the ridgeline portion of the intermediate product formed near the intermediate vertical flange portion. In the second forming step, the convex portion is crushed to the height of the target product. It has been found that this reduces the tensile force acting on the end 142 of the ridgeline portion 107 and prevents wrinkles from forming in the top plate portion 103 or the vertical wall portion 109. The present invention is based on this finding, and a method for manufacturing a press-formed product 101 according to a second embodiment will be described with reference to FIG. 18 .

[0086] The manufacturing method of the press-formed product 101 according to the second embodiment includes a first forming step (FIG. 18(a)) and a second forming step (FIG. 18(b)). The first forming step is a step of press-forming an intermediate product 149 (see FIG. 20(a)) having an intermediate top plate portion 143, an intermediate vertical wall portion 145 continuing to the intermediate top plate portion 143 via an intermediate ridge portion 144, and a convex portion 147 formed on an end portion 142 of the intermediate ridge portion 144 closer to the intermediate vertical flange portion 153 and higher than the surrounding height (reference height of the top plate surface). The intermediate product 149 also has an intermediate horizontal flange portion 151 and an intermediate vertical flange portion 153. The second forming step is a step of press-forming the intermediate product 149 into the press-formed product 101 having the target shape. Each step will be described in detail below.

[0087] <1st molding process> 18(a), the first forming step is a step in which a blank 115 is press-formed using an intermediate punch 155, an intermediate pad 157, and an intermediate die 159 to produce an intermediate formed product 149 shown in FIG. 20. The blank 115 is the same as that shown in FIG. 24. As shown in FIGS. 18 and 19, the intermediate punch 155 has a T-shaped intermediate top plate forming surface portion 161 having vertical and horizontal sides in a plan view, a punch-side intermediate vertical wall forming surface portion 163 that forms the intermediate vertical wall portion 145, a punch-side intermediate horizontal flange forming surface portion 165 that forms the intermediate horizontal flange portion 151, and a punch-side intermediate vertical flange forming surface portion 167 that forms the intermediate vertical flange portion 153.

[0088] Convex portion forming portions 169 for forming the convex portions 147 are formed on both widthwise sides of the end of the intermediate top plate forming surface portion 161. In the intermediate punch 155 shown in FIG. 19, the convex portion forming portions 169 extend toward the top plate flange portion 105 (see FIG. 20), increasing the overall height of the intermediate top plate forming surface portion 161. The punch-side intermediate vertical wall forming surface portion 163 has a gentler inclination angle than the conventional punch-side vertical wall forming surface portion 131 shown in FIG. 24. In addition, the angle formed by the punch-side intermediate horizontal flange forming surface portion 165 and the punch-side intermediate vertical wall forming surface portion 163 is set to be the same angle as the angle formed by the vertical wall portion 109 of the target shape and the horizontal flange portion 113 of the target shape.

[0089] 18 has a shape corresponding to the intermediate top plate forming surface portion 161 of the intermediate punch 155. The intermediate die 159 has a die-side intermediate vertical wall forming surface portion 171 shaped corresponding to the punch-side intermediate vertical wall forming surface portion 163, and a die-side intermediate horizontal flange forming surface portion 173 shaped corresponding to the punch-side intermediate horizontal flange forming surface portion 165. The intermediate die 159 also has a die-side intermediate vertical flange forming surface portion 175 shaped corresponding to the punch-side intermediate vertical flange forming surface portion 167.

[0090] 20(a) is manufactured using an intermediate punch 155, an intermediate pad 157, and an intermediate die 159. As described above, the intermediate product 149 has an intermediate top plate portion 143, an intermediate vertical wall portion 145, a top plate flange portion 105, an intermediate horizontal flange portion 151, and an intermediate vertical flange portion 153. In addition, a convex portion 147 is formed at an end portion 146 of an intermediate ridge portion 144 of the intermediate product 149.

[0091] 20(b) shows the AA cross section of the intermediate product 149 in FIG. 20(a) in comparison with the press-formed product 1 (FIG. 21) (two-dot chain line) of the target shape. As shown in FIG. 20(b), a convex portion 147 is formed at the end of the ridge portion of the intermediate product 149, causing the end 146 of the intermediate ridge portion 144 to bulge. This makes the bending radius of the top plate portion 103 and the vertical wall portion 109 larger than that of the target shape, thereby reducing the tensile force when bending the top plate portion 103 and the vertical wall portion 109 in the first forming step. As shown in FIG. 20(a), the thickness reduction rate of the end 146 of the intermediate ridge portion 144 was 2.8%, which was smaller than the 8.9% of the conventional press-formed product 101 shown in FIG. 25.

[0092] <Second forming process> The second forming step is a step of press-forming the intermediate formed product 149 into the target shape of the press-formed product 101. The punch 123, pad 125, and die 127 used in the second forming step have the same shapes as the conventional punch 123, pad 125, and die 127 shown in FIG.

[0093] In the second forming step, by crushing the convex portion 147 at the end 146 of the intermediate ridge portion 144 shown in Fig. 20 to form the target shape, material flows toward the end 146 of the intermediate ridge portion 144, reducing the tensile force and preventing cracking of the end 142 of the ridge portion 107 of the press-formed product 101, which has the target shape, as shown in Fig. 23. Furthermore, because the convex portion 147 is provided only to the end 146 of the intermediate ridge portion 144 and not to the entire area, no excess material flows in the second forming step, and wrinkles do not form in the top plate portion 103 or vertical wall portions 109 of the press-formed product 101, which has the target shape.

[0094] A press-formed product 101 formed by the second forming step is shown in Fig. 21. As shown in Fig. 21, the thickness reduction rate of the end 142 of the ridge line portion 107 in the press-formed product 101 formed by the second forming step after passing through the first forming step was 4.1%. As such, compared to the conventional thickness reduction rate of the end 142 of the ridge line portion 107 of 8.9% (see Fig. 25) shown in Fig. 25, it can be seen that the thickness reduction rate is smaller in the present invention, making it possible to prevent cracks.

[0095] The shape of the intermediate punch 155 in the first forming step is not limited to that shown in Fig. 19, and may be, for example, that shown in Fig. 22(a) and Fig. 22(b). In the one shown in Fig. 22(a), the convex portion forming portions 169 are formed only on both sides in the width direction of the end of the intermediate top plate forming surface portion 161, and in the one shown in Fig. 22(b), the convex portion forming portions 169 extend to the top plate side edge forming surface portion 168, but other areas of the side of the top plate side edge forming surface portion 168 are not raised.

[0096] Furthermore, the press-formed product 101 having the target shape in the second embodiment has a vertical flange portion 111, but the press-formed product having the target shape of the present invention also includes one that does not have a vertical flange.

[0097] (Embodiment 3) The target shape of the press-formed product targeted in embodiment 3 will be described with reference to Fig. 30. A press-formed product 177 has a top plate portion 179 having a curved portion when viewed from above, and a vertical wall portion 183 that continues from a part of the inside of the curve of the top plate portion 179 via a ridge portion 181, and an end portion 185 of the ridge portion 181 has an R-shape.

[0098] The process leading to the invention according to embodiment 3 will be described below using a press-formed product 177 as an example. Fig. 31 is an explanatory diagram of a conventional method for manufacturing a press-formed product 177 shown in Fig. 30, in which the press-formed product 177 is press-formed in one step.

[0099] Blank 187 formed into press-molded product 177 is made of a metal plate, and as shown in Fig. 31, top plate equivalent portion 189 formed into top plate portion 179 is curved in an arc shape. Vertical wall equivalent portions 191 are formed inside the curve of top plate equivalent portion 189, at positions extending inward in the longitudinal direction from both ends of top plate equivalent portion 189. Ends 193 of vertical wall equivalent portions 191 are formed in an R-shape.

[0100] In a conventional manufacturing method of the press-formed product 177, the blank 187 is sandwiched between a pad 199 and a punch 197 of a mold 195, and the die 201 is moved relative to the punch 197 to press-form the top plate portion 179 and the vertical wall portion 183 into a target shape. With regard to such a conventional manufacturing method of the press-formed product 177, a press-forming analysis was performed using the finite element method (FEM) when a metal plate having a tensile strength of 980 MPa class was used for the blank 187, and the plate thickness reduction rate of the press-formed product 177 after forming was obtained.

[0101] Figure 32 shows the thickness reduction rate at the bottom dead center of forming as a contour, with the lighter the color, the greater the thickness reduction rate. As shown in Figure 32, the thickness reduction rate at end 185 of ridge line 181 is 10.8%, which is the largest thickness reduction rate and is therefore more susceptible to cracking.

[0102] The reason why the thickness reduction rate at end 185 of ridge line portion 181 is large will be explained with reference to Figure 33. The arrows in Figure 33 indicate the tensile force generated during the forming process. When vertical wall portion 183 is formed via ridge line portion 181, a tensile force acts on the plate surface of ridge line portion 181 as shown by arrow (iii) in Figure 33. Furthermore, as shown by arrow (iv), a tensile force is generated at end 185 of the ridge line portion due to the vertical wall portion 183 being pulled inward. Furthermore, end 185 of the ridge line portion has a notch shape, and as shown by arrow (v), tensile force is concentrated and a large tensile force acts, resulting in a large thickness reduction rate and making cracks more likely to occur.

[0103] Therefore, the inventors have studied methods for reducing the tensile force acting on the edge 185 of the ridge line portion. As a result, they have decided to perform press molding in two steps: a first molding step and a second molding step. Then, in the first molding step, a convex portion higher than the surrounding height (the reference height of the top plate surface) is given to the edge of the ridge line portion of the intermediate molded product to be molded, and in the second molding step, the convex portion is crushed to the height of the target molded product. It has been found that this reduces the tensile force acting on the edge 185 of the ridge line portion 181 and prevents wrinkles from forming in the top plate portion 179 or the vertical wall portion 183. The present invention is based on this finding, and a method for manufacturing a press-molded product 177 according to a third embodiment will be described with reference to FIG. 26 .

[0104] The manufacturing method of the press-formed product 177 according to the third embodiment includes a first forming step (FIG. 26(a)) and a second forming step (FIG. 26(b)). The first forming step is a step of press-forming an intermediate product 211 (see FIG. 28) having an intermediate top plate portion 203, an intermediate vertical wall portion 207 continuing to the intermediate top plate portion 203 via an intermediate ridge portion 205, and a convex portion 209 formed at an end portion 206 of the intermediate ridge portion 205 and higher than the surrounding height (reference height of the top plate surface). The second forming step is a step of press-forming the intermediate product 211 into the press-formed product 177 (FIG. 29). Each step will be described in detail below.

[0105] <1st molding process> In the first forming step, as shown in Fig. 26(a), a blank 187 is press-formed using an intermediate punch 213, an intermediate pad 215, and an intermediate die 217 to produce an intermediate formed product 211 shown in Fig. 28. The blank 187 is similar to that shown in Fig. 31. As shown in Fig. 26(a) and Fig. 27 which schematically shows the intermediate punch 213 of Fig. 26(a), the intermediate punch 213 has an intermediate top plate forming surface portion 219 and a punch-side intermediate vertical wall forming surface portion 221 which forms the intermediate ridge portion 205.

[0106] Punch-side convexity forming portions 223 for forming the convexities 209 are formed on both widthwise sides of the end of the intermediate top plate forming surface portion 219. The punches shown in Figures 26(a) and 27 are arranged so that the central positions of the punch-side convexity forming portions 223 overlap with the end portions 206 of the intermediate ridge portions 205.

[0107] The intermediate pad 215 has a shape corresponding to the intermediate top plate forming surface portion 219 of the intermediate punch 213. The intermediate die 217 has a die side intermediate vertical wall forming surface portion 225 shaped corresponding to the punch side intermediate vertical wall forming surface portion 221, and a die side convex portion forming portion 226 shaped corresponding to the punch side convex portion forming portion 223.

[0108] Figure 28(b) shows the cross section BB in Figure 28(a) in comparison with the cross section of the target press-formed product shape (two-dot chain line). As shown in Figure 28(b), the end of the ridge line in the intermediate formed product 211 is formed with a convex portion 209, causing the end 206 of the intermediate ridge line portion 205 to bulge. This increases the bending radius of the intermediate top plate portion 203 and the intermediate vertical wall portion 207 compared to the target shape, thereby reducing the tensile force required to bend the intermediate top plate portion 203 and the intermediate vertical wall portion 207 in the first forming step. As shown in Figure 28(a), the thickness reduction rate at the end 206 of the intermediate ridge line portion 205 is 5.5%, which is smaller than the 10.8% reduction rate of the conventional press-formed product 177 shown in Figure 32.

[0109] <Second forming process> The second forming step is a step of press-forming the intermediate formed product 211 into a target shape, that is, a press-formed product 177. The punch 197, pad 199, and die 201 used in the second forming step have the same shapes as the conventional punch 197, pad 199, and die 201 shown in FIG.

[0110] 28 is crushed to form the target shape, material flows toward the end 206 of the intermediate ridge line portion 205, reducing the tensile force and preventing cracking of the end 185 of the ridge line portion 181 of the press-formed product 177, which has the target shape. Furthermore, because the protrusion 209 is provided only to the end 206 of the intermediate ridge line portion 205, not the entire area, no excess material flows, and wrinkles are not formed in the top plate portion 179 or vertical wall portion 183 of the press-formed product 177, which has the target shape.

[0111] A press-formed product 177 formed by the second forming step is shown in Figure 29. As shown in Figure 29, the thickness reduction rate of end 185 of ridge line portion 181 in press-formed product 177 formed by the second forming step after passing through the first forming step was 7.0%. This is a significant reduction compared to the thickness reduction rate of 10.8% (see Figure 32) of end 185 of ridge line portion 181 when press-forming is performed in a conventional one step, and it is clear that cracks can be prevented.

[0112] The shape of the intermediate punch 213 in the first forming step is not limited to that shown in Fig. 27(a) and may be, for example, that shown in Fig. 27(b). In the one shown in Fig. 27(a), the top position of the punch side convex portion forming portion 223 is arranged so as to extend to the outside of the end portion 206 of the intermediate ridge portion 205, while in the one shown in Fig. 27(b), the punch side convex portion forming portion 223 extends along the ridge portion to the end of the intermediate top plate forming surface portion 219.

[0113] 29, the curvature of the ridgeline 181 of the top plate 179 and the vertical wall 183 does not necessarily have to be constant, and a portion of the ridgeline 181 may be straight. Also, the angle of the intermediate vertical wall 207 of the intermediate molded product 211 does not have to be the same as the angle of the target shape, and it may be less steep than the target shape, or may not be sloped at all. [Example]

[0114] An analysis was carried out to verify the effects of the present invention, which will be described below. Example 1 In Example 1, the targets were a press-formed product 1 having a generally T-shaped top plate portion 3 shown in Fig. 3 and a press-formed product 41 having a generally L-shaped top plate portion 43 shown in Fig. 5. Each of the press-formed product 1 and the press-formed product 41 was manufactured by the first forming step and the second forming step of the manufacturing method for a press-formed product according to the first embodiment described above.

[0115] In the analysis, a 1.2 mm thick steel sheet with a tensile strength of 780 MPa was used as the metal sheet blank. FEM analysis was then performed for each of the first and second forming processes to examine the effectiveness of suppressing cracking at the ends of the horizontal edge ridges 9a (approximately T-shaped press-formed product 1) and horizontal edge ridges 49a (approximately L-shaped press-formed product 41) in the target shape. The effectiveness of suppressing cracking was evaluated using the thickness reduction rate. As mentioned above, the thickness reduction rate is a negative value of the thickness change rate, calculated by dividing the difference between the thickness of each portion of the press-formed product in the intermediate or target shape and the thickness of the blank metal sheet by the thickness of the blank.

[0116] In Example 1, the height of the tip end of the horizontal side 23a of the top plate portion of the intermediate shape in the first forming step was made higher than the height of the vertical side end of the top plate portion of the intermediate shape, which was used as an example of the invention. In this example, the horizontal side forming portion of the top plate forming portion formed into the intermediate shape in the first forming step was shaped as shown in Figures 34 and 35. In Figure 34, the tip end of the horizontal side of the top plate portion of the intermediate shape is inclined so that it gradually becomes higher toward the tip in the direction in which the horizontal side extends. Here, the inclination angle of the press-formed product of the intermediate shape in which the tip end of the horizontal side is inclined was changed to various angles.

[0117] On the other hand, Figure 35 shows an intermediate shape top plate in which the horizontal side of the top plate is uniformly elevated in the direction in which the horizontal side extends. Furthermore, in the intermediate shape in which the horizontal side end is uniformly elevated, a protrusion 23d is formed that is elevated upward from the horizontal side to the vertical side so as to straddle the connecting curve of the approximately T-shaped or approximately L-shaped. Here, for the intermediate shape in which the horizontal side end is uniformly elevated, the height increment of the horizontal side end portion is varied in various ways, and the height of the protrusion 23d is made the same as the height of the horizontal side end portion.

[0118] 7(a) or 16(a) described above, a conventional example was used for comparison in Example 1, in which the height of the tip end of the horizontal side portions 23a, 53a of the top plate portions 23, 53 of the intermediate-shape press-formed products 21, 51 was set to the height of the top plate portions 3, 43 of the target shape. As with the inventive examples, FEM analysis was also performed on the conventional example for each of the first forming step and the second forming step, and the sheet thickness reduction rate was determined for each of the intermediate-shape and target-shape press-formed products at the bottom dead center of forming.

[0119] Table 1 shows the results of the inclination angle of the tip end portion of horizontal side portion 23a or the tip end portion of horizontal side portion 53a in the top plate portion of the intermediate shape, and the thickness reduction rate at the end of horizontal side ridge portion 9a of the press-formed product of the target shape or horizontal side ridge portion 49a of the press-formed product 41. Note that the greater the absolute value of the thickness reduction rate, the greater the thickness reduction.

[0120] [Table 1]

[0121] In the conventional example No. 1, the inclination of the tip end of horizontal side portion 23a (generally T-shaped) or horizontal side portion 53a (generally L-shaped) of the top plate portion of the intermediate shape is set to 0°. The thickness reduction rate at the end of horizontal side ridge portion 9a (generally T-shaped) of the target shape in No. 1 is -16.9%, and the thickness reduction rate at the end of horizontal side ridge portion 49a (generally L-shaped) is -17.7%. These absolute values ​​are large, and it is thought that cracks will occur.

[0122] In contrast, in Nos. 2 to 9, the inclination angle of the tip end of horizontal side portion 23a or horizontal side portion 53a of the top plate portion of the intermediate shape was set to 3.8° to 23.7°. It can be seen that the absolute value of the thickness reduction rate at the end of horizontal side ridge portion 9a or horizontal side ridge portion 49a of the target shape in Nos. 2 to 9 was reduced compared to the conventional example (-17.7%). In particular, in No. 7, where the inclination angle was 18.3°, the thickness reduction rate was -10.6%, which was a significant decrease in absolute value and was favorable.

[0123] Table 2 shows the height of the portion at the tip of the horizontal side portion 23a or the tip of the horizontal side portion 53a in the top plate portion of the intermediate shape, and the plate thickness reduction rate at the end of the horizontal side ridge portion 9a or the horizontal side ridge portion 49a of the press-formed product of the target shape.

[0124] [Table 2]

[0125] In the conventional example No. 1, the height increment at the tip of the horizontal side portion 23a (generally T-shaped) or the tip of the horizontal side portion 53a (generally L-shaped) in the top plate portion of the intermediate shape was set to 0 mm. The thickness reduction rate at the end of the horizontal side ridge portion 9a (generally T-shaped) of the target shape in No. 1 is -16.9%, and the thickness reduction rate at the end of the horizontal side ridge portion 49a (generally L-shaped) is -17.7%. These absolute values ​​are large, and it is thought that cracks will occur.

[0126] In contrast, in Nos. 11 to 17, the height increment of the tip of the horizontal side portion 23a (generally T-shaped) or the tip of the horizontal side portion 53a (generally L-shaped) of the top plate portion of the intermediate shape was set to 3 mm to 25 mm. It can be seen that the thickness reduction rate at the end of the horizontal side ridge portion 9a (generally T-shaped) or the horizontal side ridge portion 49a (generally L-shaped) of the target shape in Nos. 11 to 17 is reduced compared to the conventional example. In particular, in No. 17, where the height increment was 25 mm, the thickness reduction rate was -8.0%, and the absolute value was significantly reduced, which was favorable.

[0127] As described above, it has been shown that the method of the present invention can suppress cracks at the end of the ridge portion on the horizontal side when manufacturing a press-formed product having a top plate portion that is approximately T-shaped or approximately L-shaped by press-forming in two steps.

[0128] Example 2 In Example 2, a press-molded product 1 having an approximately T-shaped top plate portion 3 with the dimensions shown in Figure 4 was targeted, and was press-molded using the first and second molding steps of the manufacturing method for press-molded products according to the above-mentioned embodiment 1.

[0129] A steel sheet with a thickness of 1.2 mm and a tensile strength of 780 MPa was used as the blank. FEM analysis of the first and second forming processes was then performed to examine the effect of suppressing cracking at the end of the horizontal edge ridge portion 9a of the target shape. The effect of suppressing cracking was evaluated using the thickness reduction rate of the press-formed product of the target shape obtained by FEM analysis. As mentioned above, the thickness reduction rate is a negative value of the thickness change rate obtained by dividing the difference between the thickness of each portion of the press-formed product of the intermediate shape or target shape and the thickness of the metal sheet that is the blank by the thickness of the blank.

[0130] In the example of the invention, in the first forming process, the punch 71 shown in Figure 11(a) or the punch 61 shown in Figure 11(b) was used to press-form an intermediate-shaped press-formed product 21 (Figure 2(a)) or an intermediate-shaped press-formed product 51 (Figure 15(a)).

[0131] The height of the convex portion forming portion 73d of the punch 71 shown in FIG. 11(a) was changed to variously change the height increment of the convex portion 23d.

[0132] Moreover, the height of the convex portion forming portion 63d and the horizontal edge tip forming portion 63a1 of the punch 61 shown in FIG. 11(b) was made equal and the height was changed, thereby varying the height increment of the convex portion 23d.

[0133] For comparison, a conventional example was prepared in which no protrusion was formed on the connecting R portion 23c of the top plate portion 23 of the intermediate-shape press-formed product 21, as shown in Fig. 13. Similarly to the inventive example, FEM analysis was performed on the first and second forming steps of the conventional example to determine the thickness reduction rate of the press-formed product 1 of the target shape at the bottom dead center of forming. In this example, it was previously determined through actual press forming and press forming analysis that cracks would occur if the absolute value of the thickness reduction rate exceeded 10%.

[0134] Table 3 shows the height increment at the convex portion 23d of the press-formed product 21 of the intermediate shape shown in Fig. 2(a) or Fig. 13(a) and the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the press-formed product 1 of the target shape. Note that the greater the absolute value of the thickness reduction rate, the greater the thickness reduction.

[0135] [Table 3]

[0136] In the conventional example of No. 21, no protrusions were formed on the intermediate-shape press-formed product 21, and the height increase at the protrusions was set to 0 mm. The thickness reduction rate at the end of the horizontal edge ridge 9a of the target shape in No. 21 was -11.0%, and the absolute value was so large that cracks occurred.

[0137] In contrast, in the invention examples Nos. 22 to 25, a convex portion 23d is formed on the top plate portion 23 of the intermediate shape, and the height increment is set to 3 mm to 10 mm. It can be seen that the absolute value of the thickness reduction rate at the end of the horizontal side ridge portion 9a of the target shape in Nos. 22 to 25 is reduced compared to the conventional example (-11.0%). In particular, in No. 25, where the height increment is 10 mm, the thickness reduction rate is -8.1%, and the absolute value is significantly reduced.

[0138] Table 4 shows the height increments at the protrusions 23d and the tip end portions 23a1 of the horizontal side portions 23a of the press-formed product 21 of the intermediate shape shown in Fig. 15 or 13, and the thickness reduction rates at the ends of the horizontal side ridge portions 9a of the press-formed product 1 of the target shape. As with Table 3, the greater the absolute value of the thickness reduction rate, the greater the thickness reduction.

[0139] [Table 4]

[0140] In the conventional example No. 21, as in Table 3 above, the thickness reduction rate at the end of the ridge line portion 9a on the horizontal side of the target shape was -11.0%, which was a large absolute value and caused cracks.

[0141] In contrast, in the invention examples Nos. 31 to 34, the height increments at the protrusions 23d of the intermediate shape and the tip end portions 23a1 of the horizontal side portions 23a were set to 3 mm to 10 mm. It can be seen that the absolute values ​​of the thickness reduction rates at the ends of the horizontal side ridge portions 9a of the target shapes in Nos. 31 to 34 were reduced compared to the conventional examples. In particular, in No. 34, where the height increment was 10 mm, the thickness reduction rate was -4.7%, which was favorable.

[0142] As described above, it has been shown that the method of the present invention can suppress cracks at the end of the ridge line on the horizontal side when manufacturing a press-formed product having an approximately T-shaped top plate portion by press-forming in two steps.

[0143] Example 3 In Example 3, a 1.2 mm thick 1.5 GPa grade material was used as the metal plate for the blank 115, and press-formed products 101 with target dimensions shown in FIG. 23 were press-formed by the method of the present invention, the comparative method, and the conventional method.

[0144] In the method of the present invention, an intermediate punch 155 shown in Figure 19 was used in the first forming step to change the height h of the convex portion forming portion 169 of the intermediate punch 155, thereby press-forming an intermediate formed product 149 in which the height increment Δh of the end 146 of the intermediate ridge portion 144 shown in Figure 20 was changed, and then in the second forming step, press-forming was performed to form the target press-formed product 101 shown in Figure 23. The comparative method is a method of manufacturing a press-formed product in two steps, but in which the convex portion 147 is not formed in the first step. The conventional method was press-formed in one step, as shown in Figure 24.

[0145] The thickness reduction rate of the end 142 of the ridgeline portion 107 (see FIG. 23) was determined by FEM analysis. The thickness reduction rate is the value (ratio) obtained by dividing the difference between the thickness of the metal plate that is the blank and the thickness of each portion of the formed product by the thickness of the metal plate that is the blank 115. Table 5 shows the ridgeline portion end height increment Δh and the maximum thickness reduction rate of the target press-formed product 101. Note that, based on actual press-forming and press-forming analysis, it was previously known that cracks would occur in the target press-formed product 101 of Example 3 when the maximum thickness reduction rate was 7.0% or more.

[0146] [Table 5]

[0147] In the conventional example No. 41, which was press-formed in one process, the height increment Δh at the edge of the ridge line was 0, and the maximum thickness reduction rate was as large as 8.9%, resulting in cracking. In addition, the comparative example No. 42, which was press-formed in two processes, had a height increment Δh at the edge of the ridge line of 0, and the maximum thickness reduction rate was as large as 7.2%, resulting in cracking. In contrast, Nos. 43 to 50 had reduced maximum thickness reduction rates, indicating that cracking was suppressed. In particular, No. 44 had a maximum thickness reduction rate of 3.9%, less than half the original value, which was remarkably good.

[0148] Example 4 In Example 4, a 1.4 mm thick 980 MPa grade blank metal plate was used. A press-formed product 177, the target dimensions of which are shown in Figure 30, was press-formed by the method of the present invention, the comparative method, and the conventional method. In the method of the present invention, the intermediate punch 213 shown in Figure 27(a) was used in the first forming step. The height H of the punch-side convex portion forming portion 223 of the intermediate punch 213 was changed to form an intermediate formed product 211 shown in Figure 28(a) in which the height increment ΔH of the end 206 of the intermediate ridge portion 205 was changed. Subsequently, in the second forming step, the target press-formed product 177 shown in Figure 30 was press-formed. The comparative method was press-formed in two steps, but is a manufacturing method for a press-formed product 101 in which the convex portion 209 was not formed in the first step. The conventional method was press-formed in one step, as shown in Figure 31.

[0149] The thickness reduction rate of the end 185 of the ridgeline portion 181 (see FIG. 30) was determined by FEM analysis. Table 6 shows the ridgeline portion end height increment ΔH and the maximum thickness reduction rate of the target press-formed product 177. Note that, based on actual press forming and press forming analysis, it was previously known that cracks would occur in the target press-formed product 229 of Example 4 when the maximum thickness reduction rate was 10.5% or more.

[0150] [Table 6]

[0151] In the conventional example No. 51, which was press-formed in one process, the height increment ΔH at the edge of the ridgeline was 0, and the maximum thickness reduction rate was as large as 10.8%, resulting in cracking. In addition, the comparative example No. 52, which was press-formed in two processes, had a height increment ΔH at the edge of the ridgeline was 0, and the maximum thickness reduction rate was as large as 10.5%, resulting in cracking. In contrast, Nos. 53 to 59 had reduced maximum thickness reduction rates, indicating that cracking was suppressed. In particular, No. 58 had a maximum thickness reduction rate of 4.6%, less than half the original value, which was remarkably good. [Industrial Applicability]

[0152] The present invention can provide a method for manufacturing a press-molded product that can suppress the occurrence of cracks when manufacturing a press-molded product having a generally T-shaped or generally L-shaped top plate portion by press molding. [Explanation of symbols]

[0153] 1 Press-molded products 3 Top plate 3a Side part 3b Vertical side 3c Connection R part 5 Vertical wall section 5a Vertical wall on horizontal side 5b Vertical wall on vertical side 5c Connection R side vertical wall 7 Bottom flange 9 Ridgeline 9a Horizontal side ridgeline part 9b Vertical side ridge 9c Connecting R-side ridge 11 Blank 13 Punch 15 pads 17 Die 21 Intermediate-shaped press-molded products 23 Top plate 23a Side part 23a1 Tip side 23b Vertical side 23c Connection R part 23d Convex part 25a Horizontal side vertical wall part 29a Lateral side ridgeline part 31 Punch 33 Pad 35 Die 41 Press-molded product (approximately L-shaped) 43 Top plate 43a Side part 43b Vertical side 45 Vertical wall section 45a Horizontal side vertical wall part 47 Bottom flange 49a Side ridgeline 51 Intermediate-shaped press-molded product (approximately L-shaped) 53 Top plate 53a Side part 53b Vertical side 55a Horizontal side vertical wall part 61 Punch 63a1 Side edge side molding part 63b Vertical side forming part 63d Convex forming part 71 Punch 73 Top plate molding section 73a Side molding part 73b Vertical side molding part 73c Connection R molding part 73d Convex forming section 101 Press-molded products 103 Top plate 105 Top plate flange 107 Ridge 109 Vertical wall section 111 Vertical flange 113 Horizontal flange 115 Blank 117 Top plate flange equivalent part 119 Vertical flange equivalent part 121 Mold 123 Punch 125 pads 127 Die 129 Top plate molding surface section 131 Punch side vertical wall forming surface part 133 Punch side horizontal flange forming surface 135 Vertical flange forming surface on punch side 137 Die side vertical wall forming surface 139 Die side horizontal flange forming surface 141 Die side vertical flange forming surface 142 Edge of ridge 143 Intermediate top plate 144 Middle Ridge 145 Intermediate vertical wall 146 End of intermediate ridge 147 Convex 149 Intermediate molded products 151 Intermediate horizontal flange 153 Intermediate vertical flange 155 Middle Punch 157 Intermediate Pad 159 Intermediate Die 161 Intermediate top plate molding surface section 163 Punch side intermediate vertical wall forming surface 165 Punch side intermediate horizontal flange forming surface 167 Punch side intermediate vertical flange forming surface 168 Top plate horizontal molding surface 169 Convex forming section 171 Die side intermediate vertical wall forming surface 173 Die side intermediate horizontal flange forming surface 175 Die side intermediate vertical flange forming surface 177 Press-molded products 179 Top plate 181 Ridge 183 Vertical wall section 185 Edge of ridge 187 Blank 189 Top plate equivalent part 191 Vertical wall equivalent section 193 End of vertical wall equivalent 195 molds 197 Punch 199 pads 201 Die 203 Intermediate top plate 205 Middle ridge 206 End of intermediate ridge 207 Intermediate vertical wall 209 Convex 211 Intermediate molded products 213 Middle Punch 215 Intermediate Pad 217 Intermediate Die 219 Intermediate top plate molding surface section 221 Punch side intermediate vertical wall forming surface 223 Punch side convex forming section 225 Die side intermediate vertical wall forming surface 226 Die side convex forming section 229 Press-molded products

Claims

[Claim 1] A method for manufacturing a press-formed product having a top plate portion having a curved portion in top view and a vertical wall portion continuing from a part of the inner side of the curve of the top plate portion via a ridge portion, a first forming step of press-forming the metal plate blank into an intermediate formed product having an intermediate top plate portion, an intermediate vertical wall portion, and an intermediate ridge portion connecting the intermediate top plate portion and the intermediate vertical wall portion, and having a convex portion at an end of the intermediate ridge portion that is higher than a reference height of the top plate surface; a second forming step of press-forming the intermediate formed product into the press-formed product; It is equipped with The intermediate punch used in the first forming step is The punch includes an intermediate top plate forming surface portion and a punch-side intermediate vertical wall forming surface portion that forms the intermediate ridge line portion, a punch-side convex portion forming portion for forming the convex portion is formed on both sides of the end of the intermediate top plate forming surface portion in the width direction, the punch-side convex-portion-forming portion is disposed so that a central portion thereof overlaps an end portion of the intermediate ridge portion; Manufacturing method for press-molded products.

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