Manufacturing method of press-molded product and press-molded product

Abstract

The present invention provides a technology for improving productivity while suppressing defects during forming of high-strength steel sheets. The method for manufacturing a press-formed product of the present invention is a method for manufacturing a press-formed product by press-forming a blank material, the press-formed product having a top plate portion having an outer peripheral edge portion including a curved portion, a vertical wall portion continuous with the outer peripheral edge portion of the top plate portion, and a flange portion continuous with the vertical wall portion, wherein the process for forming the curved vertical wall portion continuous with the curved portion of the vertical wall portion includes a pre-forming process for generating a stepped curved vertical wall portion in which a lower vertical wall portion from a step portion provided at a predetermined position in the height direction of the curved vertical wall portion to the flange portion protrudes toward the flange portion relative to an upper vertical wall portion from the step portion to the top plate portion, and a main forming process for smoothing the stepped curved vertical wall portion into a flat curved vertical wall portion using a die having a cam structure.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a press-molded product. and Press molding Product Regarding. [Background technology]

[0002] There is a demand for reducing the weight of automotive parts from the viewpoints of countermeasures against environmental pollution, improving fuel efficiency, and the like. Efforts to reduce the weight of automotive parts have been made, for example, by reducing the thickness of automotive parts or by using high-strength steel sheets with higher strength than conventional steel sheets. High-strength steel sheets have a lower elongation amount than low-strength steel sheets, and are known to have inferior formability. Therefore, when attempting to realize a part shape that can be formed with conventional steel sheets using high-strength steel sheets, there is a risk of forming defects such as cracks and wrinkles. Patent Documents 1 and 2, for example, are cited as methods for suppressing defects such as cracks and wrinkles that occur during the forming of high-strength steel sheets.

[0003] Patent Document 1 discloses a method for improving formability by performing press molding in multiple forming steps, while Patent Document 2 discloses a method for manufacturing high-strength, sophisticatedly designed parts by press-molding a material softened by heating, and then quenching the material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5867657 [Patent Document 2] Japanese Patent Application Laid-Open No. 5952881 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in the case of a generally L-shaped part used in the lower part of a front pillar, when forming a curved vertical wall portion (hereinafter referred to as the curved vertical wall portion), wrinkles and cracks are likely to occur at the boundary between the top plate portion and the curved vertical wall portion, or at the boundary between the flange portion and the curved vertical wall portion. For example, to prevent cracks from occurring at the die shoulder, it is effective to move the material toward the die shoulder to suppress elongation of the material along the die shoulder. Specific countermeasures include draw forming or adjusting the mold shape to promote material rotation during forming. However, these countermeasures may cause the material to move toward not only the die shoulder used to form the curved vertical wall portion but also the punch shoulder, resulting in wrinkles at the punch shoulder. In particular, when forming high-strength steel sheets, a high pad pressure is required to prevent wrinkles. However, given the mold shape and pad size, it is generally difficult to set a high pad pressure. Furthermore, measures to prevent wrinkles at the punch shoulder and measures to prevent cracks at the die shoulder are mutually exclusive. Therefore, it is difficult to simultaneously implement measures to prevent wrinkles at the punch shoulder and cracks at the die shoulder.

[0006] Incidentally, the method described in Patent Document 1 above makes it possible to improve formability by appropriately designing the shape of each process. However, the method described in Patent Document 1 has problems in that productivity decreases or mold-related costs increase as the number of forming processes increases. Furthermore, the method described in Patent Document 2 not only requires heating the blank material to a transformation point or higher before press forming, but also requires quenching after press forming. Therefore, the method described in Patent Document 2 also has limitations in improving productivity.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a technique that can improve productivity in press forming while suppressing defects such as cracks and wrinkles that occur during the forming of high-strength steel sheets. [Means for solving the problem]

[0008] A manufacturing method for a press-formed product from one aspect is a method for manufacturing a press-formed product having a top plate portion having an outer peripheral edge portion including a curved portion, a vertical wall portion continuous with the outer peripheral edge portion of the top plate portion, and a flange portion continuous with the vertical wall portion by press-forming a blank material made of a metal plate, wherein the process of forming the curved vertical wall portion of the vertical wall portion that is continuous with the curved portion includes a first forming process in which a lower vertical wall portion from a step portion provided at a predetermined position in the height direction of the curved vertical wall portion to the flange portion generates a step-shaped curved vertical wall portion that protrudes toward the flange portion relative to an upper vertical wall portion from the step portion to the top plate portion, and a second forming process in which the step-shaped curved vertical wall portion is flattened into a flat curved vertical wall portion using a mold having a cam structure.

[0009] Furthermore, in a planar view of the press-formed product, the curved portion has an arc shape, and the second forming process preferably smooths out the stepped curved vertical wall portion by abutting a mold having the cam structure against the lower vertical wall portion at an angle of 0 degrees or more and 75 degrees or less with respect to a plane parallel to the upper surface of the top plate portion along a straight line connecting the center point of the curved portion in a planar view of the press-formed product and the midpoint of the curved portion.

[0010] Furthermore, it is preferable that the process of forming the curved vertical wall portion is carried out before the first forming process and includes a third forming process of forming a boundary portion between the top plate portion and the curved vertical wall portion on the blank material.

[0011] A press-molded product from another aspect is manufactured by the above-described method for manufacturing a press-molded product.

[0012] Further, a press forming method from another viewpoint is a method for press-forming an intermediate formed product from a blank sheet by relative movement of a die and a punch, wherein the die has a top plate forming surface portion that forms a top plate portion of the intermediate formed product, a die-side vertical wall forming surface portion that forms a vertical wall portion that continues to an outer peripheral edge portion of the top plate portion, and a die-side flange forming surface portion that forms a flange portion that continues to the vertical wall portion, and the die-side vertical wall forming surface portion has a die-side step forming portion that, in a height direction of the vertical wall portion, forms a step portion that protrudes more toward the flange portion than an upper vertical wall portion from the top plate portion to the predetermined position on a curved vertical wall portion that continues to the curved portion provided on the outer peripheral edge portion of the top plate portion, The punch has a punch-side flange forming surface portion that forms the flange portion of the intermediate formed product, and a punch-side vertical wall forming surface portion that is equipped with a punch-side step forming portion that forms the step portion of the curved vertical wall portion between the punch and the die-side vertical wall forming surface portion when the punch and the die move relative to each other, and as the die and punch move relative to each other, the blank plate is bent and formed by the top plate forming surface portion and the die-side vertical wall forming surface portion of the die to form the top plate portion, and then the blank plate is sandwiched between the die-side step forming portion and the punch-side step forming portion to form the curved vertical wall portion having the step portion, and the blank plate is bent and formed by the die-side flange forming surface portion and the die-side vertical wall forming surface portion to form the flange portion. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to improve productivity in press forming while suppressing defects such as cracks and wrinkles during forming of high-strength steel sheets. In other words, according to the present disclosure, highly designed parts can be easily formed without reducing productivity. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic perspective view showing an example of the press-formed product of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the flow of the method for manufacturing a press-formed product. [Figure 3] FIG. 3 is a schematic end view showing the procedure of the preforming step. [Figure 4] FIG. 4 is a schematic perspective view showing an example of a preform. [Figure 5] FIG. 5 is a schematic end view showing the procedure of the main molding step. [Figure 6] FIG. 6 is a schematic diagram showing an example of the movement direction of the cam die. [Figure 7] FIG. 7 is a schematic diagram for determining the procedure for determining the moving direction of the cam die. [Figure 8] Figure 8(a) is a schematic diagram showing the area of wrinkles and cracks that occur when a press-formed product is manufactured by a single press molding, and Figure 8(b) is a schematic diagram showing the area of cracks that occur when a press-formed product is manufactured by performing the main molding process without using a cam mold. [Figure 9] FIG. 9 is a schematic perspective view showing an example of a blank material in which the boundary portion between the ceiling portion and the vertical wall portion is formed by press molding. [Figure 10] FIG. 10 is a schematic diagram showing the flow of material in a press-molded product when conventional press molding is performed. [Figure 11] FIG. 11(a) is a schematic end view showing the case where material flows in from the top plate portion when the punch is moved vertically in the main forming process, and FIG. 11(b) is a schematic end view showing the case where material flows in from the flange portion in the main forming process. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, this embodiment will be described with reference to the drawings. The press-formed product shown in this embodiment is, for example, a press-formed product used in a lower part of a front pillar lower of an automobile. The shape of the press-formed product is, for example, a substantially L-shape in a plan view of the press-formed product. Note that the shape of the press-formed product is not limited to a substantially L-shape in a plan view of the press-formed product, and may be a substantially T-shape or a cross shape.

[0016] 1 is a schematic perspective view showing one embodiment of a press-formed product. The press-formed product 10 is produced by press-forming a blank material. The blank material is, for example, a high-strength steel plate (high-tension material) having a thickness of 1.2 mm and a tensile strength of 1180 MPa or more.

[0017] The press-formed product 10 has a top plate portion 20, a vertical wall portion 30, and a flange portion 40. The vertical wall portion 30 is a portion that connects the top plate portion 20 and the flange portion 40. The vertical wall portion 30 has a flat vertical wall portion 31 extending in one direction, a flat vertical wall portion 32 extending in a direction intersecting the one direction, and a curved vertical wall portion 33 connecting these flat vertical wall portions 31, 32. The curved vertical wall portion 33 is curved so as to be convex toward the top plate portion 20. In other words, the outer peripheral edge portion of the top plate portion 20 has a curved portion 34 that follows the curved vertical wall portion 33. In addition, in a plan view of the press-formed product 10, the curved portion 34 is curved, for example, in an arc shape.

[0018] Next, a method for manufacturing the press-formed product 10 will be described. As shown in Fig. 2, the press-formed product 10 is produced through two processes: a preforming process and a main forming process. The preforming process is a process in which a blank material cut into a predetermined shape is press-formed. The main forming process is a process in which the preformed product produced in the preforming process is formed using a cam die.

[0019] The above-mentioned preforming step and main molding step are preferably consecutive steps. Furthermore, the preforming step and main molding step do not necessarily have to be consecutive steps. For example, the preforming step may be performed in a specific factory, and then the main molding step may be performed on the resulting preformed product in another factory. Here, the preforming step corresponds to the first molding step recited in the claims. Furthermore, the main molding step corresponds to the second molding step recited in the claims.

[0020] (Preforming process) The preforming step will be described below with reference to Figures 3(a) and 3(b). The preforming step is a step in which the blank 100 is press-molded to produce a preformed product 150 (see Figure 4). Examples of press molding used to produce the preformed product 150 include form molding and draw molding.

[0021] First, the press-molding die 120 will be described. The press-molding die 120 used in the preforming step is composed of a die 121 and a punch 123. The die 121 is provided with a top plate forming surface portion 121a, a vertical wall forming surface portion 121b, and a flange forming surface portion 121c. The top plate forming surface portion 121a forms a top plate portion 151 of the preformed product 150 between itself and the punch 123. The vertical wall forming surface portion 121b forms a curved vertical wall portion 153 of the preformed product 150 between itself and the punch 123. The flange forming surface portion 121c forms a flange portion 152 of the preformed product 150 between itself and the punch 123.

[0022] A step forming portion 121d is provided at a predetermined position in the height direction of the vertical wall molding surface portion 121b. That is, the portion of the vertical wall molding surface portion 121b from the flange molding surface portion 121c to the step forming portion 121d protrudes more toward the flange molding surface portion 121c than the portion from the top plate molding surface portion 121a to the step forming portion 121d.

[0023] Here, the vertical wall molding surface portion 121b corresponds to the die-side vertical wall molding surface portion in the claims. The flange molding surface portion 121c corresponds to the die-side flange molding surface portion in the claims. The step forming portion 121d corresponds to the die-side step forming portion in the claims. The portion from the top plate molding surface portion 121a to the step forming portion 121d corresponds to the upper vertical wall portion in the claims. The portion from the flange molding surface portion 121c to the step forming portion 121d corresponds to the lower vertical wall portion in the claims.

[0024] The punch 123 is provided with a flange forming surface portion 123a and a vertical wall forming surface portion 123b. The flange forming surface portion 123a forms a flange portion 152 of the preform 150 between itself and the die 121. The vertical wall forming surface portion 123b forms a curved vertical wall portion 153 of the preform 150 between itself and the die 121.

[0025] Furthermore, a step forming portion 123c is provided at a predetermined position in the height direction of the vertical wall molding surface portion 123b. That is, the portion of the vertical wall molding surface portion 123b from the flange molding surface portion 123a to the step forming portion 123c is recessed more inward than the other portions.

[0026] Here, the flange forming surface portion 123a corresponds to the punch-side flange forming surface portion in the claims, the vertical wall forming surface portion 123b corresponds to the punch-side vertical wall forming surface portion in the claims, and the step forming portion 123c corresponds to the punch-side step forming portion in the claims.

[0027] As shown in Figure 3(a), when the preforming process starts, the punch 123 moves in the direction B in the figure, and the punch 123 presses the blank 100 held by the die 121. In other words, the direction B in Figure 3(a) is the pressing direction in the preforming process. The blank 100 is bent by the punch 123 moving in the pressing direction.

[0028] As described above, the punch 123 is provided with a step forming portion 123c corresponding to the curved vertical wall portion 153 of the preform 150. In addition, the die 121 is provided with a step forming portion 121d corresponding to the curved vertical wall portion 153 of the preform 150.

[0029] When the punch 123 moves in the pressing direction, the blank 100 is sandwiched between the die 121 and the punch 123. At this time, the flow of material from the flange portion 152 side and the top plate portion 151 side into the curved vertical wall portion 153 is ensured. This makes it difficult for cracks to occur, but also makes the curved vertical wall portion 153 more susceptible to slight wrinkles.

[0030] As shown in FIG. 3(b), as press forming continues, the blank 100 is sandwiched between the step forming portion 121d of the die 121 and the step forming portion 123c of the punch 123. This forms a curved vertical wall portion 153 having a step portion 153a. At this time, excess material that would cause wrinkles is absorbed by the formation of the step portion 153a. As a result, the occurrence of wrinkles is suppressed in the step portion 153a.

[0031] Furthermore, when the punch 123 moves in the pressing direction, the blank 100 is sandwiched between the flange forming surface 121c of the die 121 and the flange forming surface 123a of the punch 123. This forms the flange 152. At this time, a boundary portion 153d (see FIG. 4) between the top plate portion 151 and the curved vertical wall portion 153 in the press-formed product 10, and a boundary portion 153e (see FIG. 4) between the flange portion 152 and the curved vertical wall portion 153 are also formed.

[0032] As shown in Fig. 4, in the preform 150, the height H2 of the curved vertical wall portion 153 is set to be lower than the height H1 of the vertical wall portions 154, 155. The height H2 of the curved vertical wall portion 153 is set to a height that will not cause wrinkles or cracks. Specifically, the height H2 of the curved vertical wall portion 153 is preferably equal to or greater than the radius R2 (see Fig. 3(b)) of the shoulder of the punch 123, and more preferably equal to or greater than the sum of the radius R1 (see Fig. 3(b)) of the shoulder of the die 121 and the radius R2 of the shoulder of the punch 123. The preform 150 corresponds to an intermediate formed product as defined in the claims.

[0033] Here, it is preferable that the step portion 153a of the curved vertical wall portion 153 formed in the preforming step is set as follows. R1≧R3≧5mm (1) R2≧R4≧5mm (2) R1+R2≧R3+R4+L (3)

[0034] R1: Radius of curvature of the shoulder of the die (boundary between the top plate 151 and the upper vertical wall 153b) R2: radius of curvature of the shoulder of the punch (boundary between the lower vertical wall portion 153c and the flange portion 152) R3: Radius of curvature of the boundary (die side) between the step portion 153a and the upper vertical wall portion 153b R4: Radius of curvature of the boundary (punch side) between the step portion 153a and the lower vertical wall portion 153c L: Amount of protrusion of the lower vertical wall portion 153c from the upper vertical wall portion 153b

[0035] For example, if the curvature radii R3 and R4 are less than 5 mm, there is a high risk of cracks occurring when forming the step portion 153a. Also, if the curvature radius R3 exceeds the curvature radius R1, if the curvature radius R4 exceeds the curvature radius R2, or if the sum of the protrusion amount L, the curvature radius R3, and the curvature radius R4 exceeds the sum of the curvature radii R1 and R2, the step portion 153a becomes too large, increasing the possibility of wrinkles occurring at the top and bottom of the step portion 153a. Therefore, the above-mentioned formulas (1) to (3) are defined based on these factors.

[0036] Generally, the forming height H0 of the curved vertical wall portion can be obtained, for example, from the following equation (4). ε=(R0-tanθ) / (R0-H0 / cosθ) -1 ···(4) ε: Elongation along the curved vertical wall θ: Inclination of the curved vertical wall relative to the direction of punch movement H0: Forming height of curved vertical wall R0: Radius of curvature of the curved vertical wall

[0037] The maximum formable height is the formed height H0 of the curved vertical wall when the value of elongation ε is equal to the limit strain of the material in the plane strain state. The limit strain in the plane strain state can be obtained by known methods such as the Nakajima method or the Marciniak method.

[0038] (Main molding process) The main forming process is a process of performing press forming using a die (hereinafter referred to as a cam die) 162 having a cam mechanism on the stepped curved vertical wall portion 153 of the preform 150. By the main forming process, the stepped portion 153a of the curved vertical wall portion 153 becomes flat.

[0039] As shown in FIG. 5(a), the preform 150 is held by the die 160. When the main forming step is started, the cam die 162 moves in the direction C in FIG. 5(a). The direction C in FIG. 5(a) is the pressing direction in the main forming step. When the cam die 162 moves in the pressing direction, the stepped curved vertical wall portion 153 of the preform 150 is sandwiched between the cam die 162 and the die 160. As a result, the stepped portion 153a disappears, and the protrusion amount L of the lower vertical wall portion 153c becomes 0 (see FIG. 5(b)). When the cam die 162 moves in the pressing direction, the inflow of material from the top plate portion 151 to the curved vertical wall portion 153 and the inflow of material from the flange portion 152 to the curved vertical wall portion 153 are suppressed. As a result, occurrence of wrinkles at boundary portion 153d between top plate portion 151 and curved vertical wall portion 153 and occurrence of cracks at boundary portion 153e between flange portion 152 and curved vertical wall portion 153 are prevented.

[0040] Here, the movement direction (pressing direction) of the cam die 162 in the main forming step will be described. As shown in FIG. 6(a), for example, a case will be described in which the curved vertical wall portion 153 has an arc shape in a plan view of the preformed product 150. The pressing direction of the cam die 162 (reference symbol C in FIG. 6(a)) is a direction along a straight line L1 connecting a center point P1 of the curved vertical wall portion 153 and a midpoint P2 of the curved vertical wall portion 153 in a plan view of the preformed product 150. Furthermore, as shown in FIG. 6(b), the pressing direction of the cam die 162 is a direction inclined downward at a predetermined angle θ1 with respect to a plane including the upper surface of the top plate portion 151 in the D-D' cross section shown in FIG. 6(a).

[0041] The angle θ1 is set as follows: For example, if the angle θ1 is set to approximately 90°, the step portion 153a of the preform 150 may not be stretched well during molding using the cam die 162. In this case, material may flow from the flange portion 152 into the step portion 153a, causing cracks. Therefore, the angle θ is preferably in the range of 0°≦θ≦75°, and more preferably in the range of 0°≦θ1≦45°.

[0042] The pressing direction in the main forming step may be determined by the following method. For example, as shown in Fig. 7(a), in a plan view of the die 160 used in the main forming step, a line connecting a midpoint P3 of the curve-forming portion 161 of the die 160 to a center point P4 of the curve-forming portion 161 of the die 160 is defined as a line L2. As shown in Fig. 7(b), a line connecting a midpoint P5 of a boundary portion 160c between the side surface 160a and the bottom surface 160b of the die 160 to a center point P6 of the boundary portion 160c is defined as a line L3. The intersection of the line L2 and the line L3 is defined as an intersection point P7.

[0043] As shown in Fig. 7(c), in a plan view of the die 121 used in the preforming step, a line L4 connects a midpoint P8 of the curve-forming portion 122 of the die 121 to a center point P9 of the curve-forming portion 122. As shown in Fig. 7(d), a line L5 connects a midpoint P10 of a boundary portion 121e between the vertical wall forming surface portion 121b and the flange forming surface portion 121c of the die 121 to a center point P11 of the boundary portion 121e. The intersection of the line L4 and the line L5 is an intersection point P12.

[0044] As shown in FIG. 7(e), the direction from the intersection point P12 to the intersection point P7 is the moving direction of the cam die 162 (the pressing direction in the main forming process). In addition, when the pressing direction in the main forming process is the z direction, and the two directions perpendicular to the z direction are the x direction and the y direction, the coordinates of the point P12 (x P12 , y P12 ,z P12 ) and the coordinates of point P7 (x P7 , y P7 ,z P7), a vector v from point P12 to point P7 is calculated. Then, a range of ±30° around the z-axis and y-axis, centered on point P7 or point P12, from the direction of the calculated vector v is set as the pressing direction in the main forming process. Note that if the cam die 162 is moved beyond the range of ±30° around the z-axis and y-axis, it becomes difficult to form the stepped portion 153a.

[0045] In this embodiment, the movement direction of the cam die 162 is set to a range of ±30° around the z-axis and y-axis with point P7 or point P12 as the center from the direction of the calculated vector. However, the movement direction of the cam die 162 may also be set to a range of ±10° around the z-axis and y-axis with point P5 or point P8 as the center.

[0046] The occurrence of wrinkles and cracks will be described below. As shown in Fig. 8(a), in a press-molded product 200 produced by one press molding, the material flows from the top plate portion 201 toward the curved vertical wall portion 202 while leaning toward the top plate portion 201. The material also flows from the flange portion 204 toward the curved vertical wall portion 202 while spreading. As a result, wrinkles occur in a region 203a at a boundary portion 203 between the top plate portion 201 and the curved vertical wall portion 202. Cracks also occur in regions 205a and 205b at a boundary portion 205 between the flange portion 204 and the curved vertical wall portion 202.

[0047] 8(b), when the main forming step is performed without using a cam die after the preliminary forming step, wrinkles do not occur in the boundary portion 253 between the top surface portion 251 and the curved vertical wall portion 252 in the formed press-formed product 250. On the other hand, when the main forming step is performed without using a cam die, the material flows from the flange portion 254 to the curved vertical wall portion 252 while spreading. As a result, cracks occur in the region 255a of the boundary portion 255 of the flange portion 254.

[0048] In the main molding step of this embodiment, the step portion 153a of the preform 150 is stretched by a cam mold. Note that, in molding using a cam mold, material from the top plate portion 20 does not flow into the boundary portion 35 between the top plate portion 20 and the curved vertical wall portion 33. Furthermore, material from the flange portion 40 does not flow into the boundary portion 36 between the curved vertical wall portion 33 and the flange portion 40. As a result, the occurrence of wrinkles at the boundary portion 35 and cracks at the boundary portion 36 is suppressed.

[0049] In the above-described embodiment, the method for manufacturing the press-formed product 10 includes a preforming step in which the preformed product 150 is press-formed and a main forming step in which the stepped curved vertical wall portion 153 of the preformed product 150 is formed using a cam die. However, the method for manufacturing the press-formed product 10 is not limited to this. As shown in FIG. 9 , for example, it is also possible to perform the above-described preforming step after press-forming the blank 100 to preliminarily generate a boundary portion 303 between the top plate portion 301 and the curved vertical wall portion 302. In this case, by preliminarily generating the boundary portion 303 between the top plate portion 301 and the curved vertical wall portion 302, the above-described preforming step prevents material from the top plate portion 301 from flowing into the curved vertical wall portion when generating the stepped curved vertical wall portion. Therefore, the occurrence of wrinkles is suppressed at the boundary portion between the top plate portion and the vertical wall portion.

[0050] Furthermore, if the curved vertical wall portion is generated after the boundary portion 303 between the top plate portion 301 and the curved vertical wall portion 302 has been generated in advance, it is possible to form the curved vertical wall portion higher than if the curved vertical wall portion is generated without generating the boundary portion 303 between the top plate portion 301 and the vertical wall portion.

[0051] <Summary of effects> The manufacturing method of the press-molded product of the present invention is a method for manufacturing a press-molded product 10 having a top plate portion 20 with an outer peripheral edge portion including a curved portion, a vertical wall portion 30 continuous with the outer peripheral edge portion of the top plate portion 20, and a flange portion 40 continuous with the vertical wall portion 30 by press-molding a blank 100 made of a metal plate, and is characterized in that the process of forming the curved vertical wall portion 33 of the vertical wall portion 30 that is continuous with the curved portion includes a pre-forming process in which a lower vertical wall portion 153c from a step portion 153a provided at a predetermined position in the height direction of the curved vertical wall portion 33 to the flange portion 40 is formed to have a step-shaped curved vertical wall portion 153 that protrudes toward the flange portion 40 side relative to an upper vertical wall portion 153b from the step portion 153a to the top plate portion 20, and a main forming process in which the upper vertical wall portion 153b and the lower vertical wall portion 153c are smoothed using a cam mold 162.

[0052] For example, as shown in Fig. 10, when a press-formed product 400 is manufactured in a single forming step, at a ridge line 401a between a top plate portion 402 and a curved vertical wall portion 401, the material of the top plate portion 402 is pulled toward the curved vertical wall portion 401 (in the direction H in Fig. 9) while being pushed toward the curved vertical wall portion 401. At a ridge line 401b between the curved vertical wall portion 401 and a flange portion 403, the material of the flange portion 403 is pulled toward the curved vertical wall portion 401 (in the direction I in Fig. 10) while being pushed toward the curved vertical wall portion 401 while being pushed toward the curved vertical wall portion 401. Therefore, wrinkles are likely to occur at the ridge line 401a, and cracks are likely to occur at the ridge line 401b.

[0053] On the other hand, in the manufacturing method of the press-formed product 10 of this embodiment, first, a preformed product 150 having a stepped curved vertical wall portion 153 is produced in a preforming step. At this time, excess material flowing into the curved vertical wall portion 153 from the top plate portion 151 side and excess material flowing into the curved vertical wall portion 153 from the flange portion 152 are absorbed by the stepped portion 153a. Furthermore, in the main forming step, when the stepped curved vertical wall portion 153 is formed, the flow of material from the top plate portion 151 or the flange portion 152 into the curved vertical wall portion 153 is suppressed. As a result, the occurrence of wrinkles and cracks is prevented at a boundary portion 35 between the top plate portion 20 and the curved vertical wall portion 33 and a boundary portion 36 between the flange portion 40 and the curved vertical wall portion 33.

[0054] Furthermore, in a plan view of the press-formed product 10, the curved vertical wall portion 153 has an arc shape, and the main forming process forms the vertical wall portion 30 by abutting the cam die 162 against the lower vertical wall portion 153c at an angle of 0 degrees or more and 75 degrees or less with respect to a plane parallel to the upper surface of the top plate portion 20 along a straight line connecting the center point P1 of the curved vertical wall portion 153 and the midpoint P2 of the curved vertical wall portion 153 in a plan view of the press-formed product 10.

[0055] For example, when the cam die 162 is moved in the direction J in FIG. 11(a) in the main molding process, it may be difficult for the cam die 162 to properly stretch the step portion 153a. In this case, for example, the material of the top plate portion 151 flows into the curved vertical wall portion 153, causing wrinkles to form at the boundary between the top plate portion 151 and the curved vertical wall portion 153. Also, as shown in FIG. 11(b), when the cam die 162 is moved in the direction J in FIG. 11(b), the curved vertical wall portion 153 stretches and then gets caught on the cam die 162, causing the material of the flange portion 152 to flow into the curved vertical wall portion 153. In this case, cracks form at the boundary between the curved vertical wall portion 153 and the flange portion 152.

[0056] On the other hand, in this embodiment, in the main forming step, the cam die 162 is moved in the direction C in Figure 5(a). The movement of the cam die 162 in the direction C in Figure 5(a) prevents material from flowing from the top plate portion 151 into the curved vertical wall portion 153, and from the flange portion 152 into the curved vertical wall portion 153. This makes it possible to prevent wrinkles from occurring at the boundary between the top plate portion 151 and the curved vertical wall portion 153, and cracks from occurring at the boundary between the flange portion 152 and the curved vertical wall portion 153.

[0057] In addition, the process of forming the vertical wall portion 30 is carried out before the preforming process, and includes a third forming process of forming the boundary portion between the top plate portion 20 and the vertical wall portion 30 on the blank material 100.

[0058] According to this, in the third forming step, the blank 100 is press-formed to form a boundary portion 303 between the top plate portion 301 and the vertical wall portion. The boundary portion 303 formed in the third forming step prevents material from flowing from the top plate portion 301 into the vertical wall portion when the vertical wall portion is formed by press forming. As a result, the occurrence of wrinkles is suppressed at the boundary portion between the top plate portion 301 and the vertical wall portion.

[0059] Furthermore, when the vertical wall portion is formed by press molding, the material is prevented from flowing into the vertical wall portion from the top plate portion 301. As a result, the height of the curved vertical wall portion 401 can be made higher than the height of the curved vertical wall portion when the curved vertical wall portion 401 is formed without forming the boundary portion 303 between the top plate portion 301 and the vertical wall portion. [Explanation of symbols]

[0060] 10 Press-molded products 20 Top plate 30 Vertical wall section 33 Curved vertical wall 40 flange 100 blanks 150 preforms 153 Curved vertical wall 153a Step 153b Upper vertical wall 153c Lower vertical wall

Claims

1. A method for manufacturing a press-formed product having a top plate portion having an outer peripheral edge portion including a curved portion, a vertical wall portion continuous with the outer peripheral edge portion of the top plate portion, and a flange portion continuous with the vertical wall portion by press-forming a blank material made of a metal plate, The step of forming a curved vertical wall portion continuous with the curved portion among the vertical wall portions includes: a first molding process for generating a curved vertical wall portion having a step shape in which a lower vertical wall portion from a step portion provided at a predetermined position in a height direction of the curved vertical wall portion to a flange portion protrudes toward the flange portion relative to an upper vertical wall portion from the step portion to the top plate portion; a second molding step of smoothing the stepped curved vertical wall portion into a flat curved vertical wall portion using a mold having a cam structure; A method for producing a press-molded product, comprising:

2. In a plan view of the press-formed product, the curved portion has an arc shape, The second molding step includes: The die having the cam structure is abutted against the lower vertical wall portion at an angle of 0 degrees or more and 75 degrees or less with respect to a plane parallel to the upper surface of the top plate portion along a straight line connecting the center point of the curved portion and the midpoint of the curved portion in a plan view of the press-molded product, thereby smoothing the curved vertical wall portion having a step shape. The method for manufacturing a press-formed product according to claim 1 .

3. The step of forming the curved vertical wall portion includes: a third forming step that is performed before the first forming step and forms a boundary portion between the top plate portion and the curved vertical wall portion in the blank material; The method for manufacturing a press-formed product according to claim 1 .

4. A press-formed product manufactured by the method for manufacturing a press-formed product according to any one of claims 1 to 3.

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