Press molded product manufacturing method, and press device

Abstract

To suppress concentration of residual stress near a notch in a press molded product.SOLUTION: A press molded product manufacturing method includes: a process in which metal mold set including a first metal mold 1 having a protrusion of a shoulder 1b includes a curved part 1bw-1 that curves convexly outward when viewed from a press direction, a second metal mold 2 having a recess, and a guide 3 is prepared; a process in which a material W1 to be molded having a notch between the first metal mold 1 and the second metal mold 2 is arranged; and a process in which the material to be molded is press-molded. Press molding includes shrink flanging that is performed in such a manner that the material W1 to be molded contacts the shoulder of the curved part 1bw-1 of the protrusion of the first metal mold 1 and is pressed. In the press molding, the guide 3 contacts a notch Wn at a position where the notch Wn can be prevented from shrinking by the shrink flanging.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a press molding technique using a mold. [Background technology]

[0002] Press-formed products are manufactured by pressing metal sheets. Press-formed products are manufactured by drawing or bending metal sheets using dies. Various measures are taken to reduce residual stress in press-formed products.

[0003] For example, Japanese Patent Application Laid-Open Publication No. 2019-150882 (Patent Document 1) discloses a shearing method in which a workpiece is placed on a die and sheared with a punch in the thickness direction of the workpiece to obtain a punched material and a processed material. In this method, a push-in punch is positioned opposite the punch. The push-in punch pushes the punched material into a punching hole in the processed material while it is still in the punched state, and presses the end face of the punched material against the sheared surface of the processed material. This reduces tensile residual stress in the sheared surface of the processed material.

[0004] In the press forming method disclosed in Japanese Patent Laid-Open Publication No. 2001-233019 (Patent Document 2), the locations of residual stress in a metal plate are identified in advance, and irradiation holes corresponding to those locations are drilled in a mold in advance. When the metal plate is pressed to the bottom dead center during press forming, a high-energy beam is irradiated onto the metal plate through the irradiation holes. This heats the locations of the metal plate irradiated with the high-energy beam, releasing the distortion at those locations. As a result, the residual stress is eliminated.

[0005] Japanese Patent Application Laid-Open Publication No. 2022-139470 (Patent Document 3) discloses a press apparatus. This press apparatus includes a punch, a pad disposed above the punch so as to face the top surface of the punch, a die disposed above the punch and to the side of the pad, and a holder disposed to the side of the punch and below the die. When performing press forming, a metal sheet material is placed on the top surface of the punch. The pad first presses the material on the top surface of the punch from above, and then the die reaches its bottom dead center. When the die descends, the die lower surface contacts the material before the first die shoulder and die side surface, and together with the holder upper surface, clamps the end of the material. Because the material is previously pressed down by the pad, tension is applied to the material by clamping the end of the material between the die lower surface and the holder upper surface. By bending the material under tension in this manner, residual tensile stress occurring on the inside of the bent portion of the press-formed product can be reduced. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-150882 [Patent Document 2] Japanese Patent Application Publication No. 1-233019 [Patent Document 3] Japanese Patent Publication No. 2022-139470 Summary of the Invention [Problem to be solved by the invention]

[0007] In press forming, it is sometimes necessary to reduce residual stress in a press-formed product and suppress stress concentration. The inventors studied a situation in which residual stress concentrates in a part of a press-formed product. As a result of the study, they found that when a metal plate having a notch is press-formed, tensile residual stress tends to become apparent near the notch.

[0008] Therefore, the present disclosure discloses a method for manufacturing a press-formed product and a press device that can suppress the concentration of residual stress near the notch in a press-formed product obtained by press-forming a metal plate having a notch. [Means for solving the problem]

[0009] A method for manufacturing a press-molded product according to an embodiment of the present invention includes: preparing a die set including a first die having a convex portion that protrudes in the pressing direction, wherein a shoulder of the convex portion includes a curved portion that curves convexly outward when viewed from the pressing direction; a second die having a concave portion that has a shape corresponding to the convex portion of the first die; and a guide; placing a workpiece having a notch between the first mold and the second mold; and a step of moving at least one of the first mold and the second mold from a molding start position in a pressing direction to a bottom dead center, thereby press-molding the workpiece. The press forming includes shrink flange forming by pressing the workpiece against a curved portion of a shoulder of the convex portion of the first die. During the press molding, during at least part of the process in which the first mold and the second mold move from the molding start position to the bottom dead center, the guide contacts the notch at a position that prevents the notch from shrinking due to shrink flange molding. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of press-forming a workpiece having a notch. [Figure 2] FIG. 2 shows the analysis results of press forming. [Figure 3] FIG. 3 is a perspective view showing an example of the configuration of the press device of this embodiment. [Figure 4] FIG. 4 is a diagram showing an example of each step in the method for manufacturing a press-formed product according to this embodiment. [Figure 5] FIG. 5 is a diagram for explaining how to determine the radius of curvature of the curved ridge line of the curved portion. [Figure 6] FIG. 6 is a diagram for explaining the positional relationship between the first mold 1 and the guide 3. As shown in FIG. [Figure 7] FIG. 7 is a diagram for explaining a configuration example and a modified example of the guide 3. In FIG. [Figure 8] FIG. 8 is a diagram for explaining an example of the arrangement of guides relative to the notches. [Figure 9] FIG. 9 is a diagram for explaining the coefficients in the calculation formula. [Figure 10] FIG. 10 is a perspective view showing a modified example of the mold set. [Figure 11] FIG. 11 shows an example of each step of a method for producing a press-molded product using the die set shown in FIG. [Figure 12] FIG. 12 is a diagram showing a modified example of the mold set. [Figure 13] FIG. 13 is a diagram showing an example of the arrangement of the bottom dead center and the start of forming in press forming using the die set shown in FIG. [Figure 14] FIG. 14 is a diagram showing a region Ra1 of the workpiece W1 that is subjected to shrink flange forming in the press forming shown in FIG. [Figure 15] FIG. 15 is a diagram showing an example of a mold set in which a guide 3 is provided on the top surface 1a of the protrusion 1A of the first mold 1. [Figure 16] FIG. 16 is a diagram showing a modified example of the mold set. [Figure 17] FIG. 17 is a diagram showing a modified example of the mold set. [Figure 18] FIG. 18 is a diagram showing a modified example of the mold set. [Figure 19] FIG. 19 is a diagram showing the model used in the analysis. [Figure 20] FIG. 20 is a diagram showing the model used in the analysis. [Figure 21] FIG. 21 is a diagram showing the analysis results of press forming of a workpiece having a notch. [Figure 22] FIG. 22 is a diagram showing the analysis results of press forming of a workpiece having a notch. DETAILED DESCRIPTION OF THE INVENTION

[0011] The inventors performed a CAE analysis of press forming to deep-draw a metal disk A1 having a notch at its edge, as shown in FIG. 1. The analysis revealed that, as shown in FIG. 2, press forming causes deformation such that the width of the notch narrows. Furthermore, as shown in the upper right diagram of FIG. 2, during press forming, a higher compressive stress is generated at the bottom of the notch (the innermost part of the notch) in a direction along the edge of the notch than in other parts. In the upper right diagram of FIG. 2, the darker shaded areas indicate areas with higher compressive stress. After demolding, springback (SB) causes tensile residual stress to become particularly large near the bottom of the notch, as shown in the lower diagram of FIG. 2. In the lower diagram of FIG. 2, the darker shaded areas indicate areas with higher tensile stress.

[0012] Based on the above tests and analyses, the following mechanism is considered. For example, as shown in Figure 1, when a press-formed product includes a curved ridgeline, the wall and flange portions adjacent to the ridgeline undergo shrink flange forming during press forming. During press forming involving shrink flanging, a portion of the material being pressed (the workpiece) (the wall, flange, and the portion forming the ridgeline between them) undergoes compressive deformation in the circumferential direction, i.e., parallel to the ridgeline of the die corresponding to the ridgeline between the wall and flange. This results in compressive stress in the material, compressing it in the circumferential direction. If there is a notch in the part that is compressed in the circumferential direction during shrink flanging, material flows in to narrow the circumferential width of the notch to relieve the circumferential compressive stress. This inflow deforms the notch, narrowing its circumferential width. The bottom of the notch (the notched portion of the workpiece edge) undergoes significant in-plane bending deformation. In-plane bending is bending deformation in a direction parallel to the plate surface. Therefore, at the bottom of the notch, a larger compressive stress is generated in the direction along the shape of the notch than in other parts that are subjected to the above-mentioned shrink flange deformation.Incidentally, because the effect of material constraint is small at the bottom of the notch (strictly speaking, the entire notch including the bottom), the direction of the generated tensile residual stress is in the direction along the shape of the notch, i.e., along the end face.

[0013] After release from the mold, the workpiece, i.e., the press-formed product, attempts to return to its original shape by springback, which causes circumferential tensile residual stress to occur in the area where circumferential compressive stress occurred during shrink flange forming. This tensile residual stress caused by springback is particularly large near the bottom of the notch, and is thought to be a cause of hydrogen embrittlement.

[0014] The inventors sought a method for reducing tensile residual stress near the bottom of a notch during a press forming process. After extensive investigation, they came up with the idea of ​​providing a guide in the mold that restricts the movement of the notch in the workpiece during and at the initial stage of forming, thereby suppressing the inflow of material circumferentially into the notch due to shrinkage flange forming. This suppresses plastic deformation caused by the inflow of material circumferentially into the notch due to shrinkage flange forming. Therefore, residual tensile stress due to plastic deformation after mold release is suppressed. As a result, it is possible to suppress the concentration of tensile residual stress near the notch. The following embodiments are based on this finding.

[0015] (Method 1) A method for manufacturing a press-molded product according to an embodiment of the present invention includes: preparing a die set including a first die having a convex portion that protrudes in the pressing direction, wherein a shoulder of the convex portion includes a curved portion that curves convexly outward when viewed from the pressing direction; a second die having a concave portion that has a shape corresponding to the convex portion of the first die; and a guide; placing a workpiece having a notch between the first mold and the second mold; and a step of moving at least one of the first mold and the second mold from a molding start position in a pressing direction to a bottom dead center, thereby press-molding the workpiece. The press forming includes shrink flange forming by pressing the workpiece against a curved portion of a shoulder of the convex portion of the first die. During the press molding, during at least part of the process in which the first mold and the second mold move from the molding start position to the bottom dead center, the guide contacts the notch at a position that prevents the notch from shrinking due to shrink flange molding.

[0016] According to the above-mentioned manufacturing method 1, in press molding, the first and second dies contact the workpiece, and the workpiece is molded into a shape corresponding to the shapes of the first and second dies. The workpiece is shrunk and flanged by the curved shoulders of the convex portion of the first die. In press molding, the guide contacts the notch of the workpiece at a position that prevents the notch from shrinking during shrunk flange forming. The guide prevents material from flowing into the notch during shrunk flange forming. This prevents plastic deformation of the workpiece due to the flow of material into the notch. Therefore, residual tensile stress near the notch after demolding is suppressed. In other words, it is possible to suppress the concentration of tensile residual stress near the notch.

[0017] The curved shoulder portion of the convex portion of the first die is curved convexly outward from the convex portion when viewed from the pressing direction. The form in which the guide contacts the notch at a position that prevents the notch from shrinking due to shrinkage flange forming may be, for example, a form in which the guide contacts the notch at a position that prevents the circumferential width of the notch from shrinking. The circumferential direction is the direction of the ridge formed by the curved portion of the shoulder of the convex portion of the first mold as viewed from the pressing direction. Note that the form in which the guide contacts the notch at a position that prevents the notch from shrinking due to shrinkage flange forming may be a form in which the guide contacts the notch and applies a circumferential force to the notch. Furthermore, the guide may be positioned relative to the notch so that the circumferential width of the notch does not increase compared to when it was at the forming start position during the process in which the first and second molds move from the forming start position to the bottom dead center.

[0018] The forming start position is the position where the first and second dies contact the workpiece and apply force to it, thereby starting to deform the workpiece. At the forming start position, the first and second dies are spaced apart in the press direction. For example, the forming start position is the position at which at least one of the first and second dies moves in the press direction from a position where only one of them contacts the workpiece, until both the first and second dies contact the workpiece. The entire process of the first and second dies from the forming start position to the bottom dead center is sometimes referred to as the full stroke. Press forming begins when the first and second dies are at the forming start position, and ends at the bottom dead center.

[0019] In the press molding, in at least a portion (section) where the distance in the press direction between the first mold and the second mold changes during the process in which the first mold and the second mold move from the molding start position to the bottom dead center, the guide may contact the notch at a position that prevents the notch from shrinking due to shrink flange molding.

[0020] It is preferable that the guide contact the notch at a position that prevents the notch from shrinking due to shrink flange forming over at least one-third of the distance that the first mold moves relative to the second mold from the forming start position to the bottom dead center, i.e., at least one-third of the total stroke from the forming start position to the bottom dead center. This enhances the effect of the guide in suppressing the inflow of material into the notch due to shrink flange forming. From the same perspective, it is more preferable that the guide contact the notch at a position that prevents the notch from shrinking due to shrink flange forming over at least two-thirds of the distance that the first mold moves relative to the second mold from the forming start position to the bottom dead center, i.e., at least two-thirds of the total stroke from the forming start position to the bottom dead center.

[0021] (Method 2) In the above-mentioned manufacturing method 1, the guide may contact the notch at a position that prevents shrinkage due to shrink flange forming at a portion that includes the forming start position and where the distance between the first and second dies in the press direction changes during the process in which the first and second dies move from the forming start position to the bottom dead center. This allows the guide to effectively prevent material from flowing into the notch.

[0022] In addition, during the process in which the first mold and the second mold move from the molding start position to the bottom dead center, it is preferable that the guide contacts the notch at a position that includes the molding start position and that prevents the notch from shrinking due to shrink flange molding, at a portion that is at least one-third (more preferably at least two-thirds) of the movement distance of the first mold relative to the second mold from the molding start position to the bottom dead center.

[0023] At the forming start position, the proportion of the portion of the guide that contacts the notch relative to the entire notch is preferably as high as possible, for example, preferably 50% or more, more preferably 70% or more, and even more preferably 100%.

[0024] (Method 3) In the above-mentioned manufacturing method 1 or 2, the guide may contact the notch at a portion where the distance between the first mold and the second mold in the pressing direction changes, the portion including the bottom dead center, during the process in which the first mold and the second mold move from the forming start position to the bottom dead center. This makes it possible to more effectively prevent the flow of material into the notch by the guide.

[0025] In addition, it is preferable that the guide contacts the notch at a position that prevents the notch from shrinking due to shrink flange forming, in a portion that includes the bottom dead center and that is one-third or more (more preferably two-thirds or more) of the movement distance of the first mold relative to the second mold from the forming start position to the bottom dead center during the process in which the first mold and the second mold reach the bottom dead center from the forming start position. For example, the first mold and the second mold may be arranged so that the guide contacts the notch continuously from the forming start position to the bottom dead center.

[0026] At bottom dead center, the proportion of the area of ​​the guide that is in contact with the notch relative to the entire notch is preferably as high as possible, for example, preferably 50% or more, more preferably 70% or more, and even more preferably 100%.

[0027] (Method 4) In any of the above manufacturing methods 1 to 3, the guide may be provided in the first mold and may be fixed to the first mold during the process in which the first mold and the second mold move from the molding start position to bottom dead center. That is, the guide may be configured so that its relative position with respect to the first mold does not change, at least during the process from the molding start position to bottom dead center. This allows the guide and the first mold to move in conjunction with each other relative to the workpiece during press molding. Therefore, during press molding, it is possible to make the guide follow the notch in conjunction with the movement of the first mold relative to the workpiece.

[0028] (Method 5) In any of the above manufacturing methods 1 to 3, the guide may be provided in the second mold and may be fixed to the second mold during the process in which the first mold and the second mold move from the molding start position to bottom dead center. That is, the guide may be configured so that its relative position with respect to the second mold does not change at least during the process in which the first mold and the second mold move from the molding start position to bottom dead center. This simplifies the configuration of the guide.

[0029] (Method 6) In any one of the above manufacturing methods 1 to 5, the press forming may be performed by moving at least one of the first and second dies in a pressing direction while the workpiece is held between either the first or second die and a holder during the process of the first and second dies reaching the bottom dead center from the forming start position, thereby facilitating the draw forming of the workpiece.

[0030] (Method 7) In the above-mentioned manufacturing method 6, the guide may be provided on the holder and fixed to the holder while the first mold and the second mold are moving from the molding start position to the bottom dead center. That is, the guide may be configured so that its relative position with respect to the holder does not change at least during the movement from the molding start position to the bottom dead center. This simplifies the configuration of the guide.

[0031] (Recipe 8) In any of the above manufacturing methods 1 to 7, the workpiece may be positioned so that the entire notch is located outside the curved shoulder portion of the convex portion of the first mold as viewed from the press direction. For example, the workpiece may be positioned so that the entire notch is located outside the curved shoulder portion of the convex portion of the first mold as viewed from the press direction at both the forming start position and bottom dead center. In this case, the guide may also be positioned outside the curved shoulder portion of the convex portion of the first mold as viewed from the press direction. In this case, the entire notch is located in the portion of the workpiece that will be subjected to shrink flange forming. This effectively reduces the tensile residual stress around the notch that occurs during shrink flange forming. For example, the workpiece may be positioned so that the entire notch is located outside the curved shoulder portion of the convex portion of the first mold as viewed from the press direction during the process from the forming start position to bottom dead center.

[0032] (Configuration 1) The press device according to an embodiment of the present invention comprises: a first die having a convex portion that protrudes in the pressing direction, wherein a shoulder of the convex portion includes a curved portion that is curved convexly outward when viewed from the pressing direction; a second mold having a recessed portion having a shape corresponding to the protruding portion of the first mold; It is equipped with a guide. At least one of the first die and the second die is movable in the pressing direction from a forming start position where the first die and the second die are spaced apart to a bottom dead center. The guide is positioned to prevent the notch in the workpiece placed between the first and second molds from shrinking due to shrink flange molding during at least part of the process in which the first and second molds move from the molding start position to the bottom dead center.

[0033] In the above-mentioned configuration 1, the shoulder of the convex portion of the first mold, where the workpiece is press-molded between the convex portion of the first mold and the concave portion of the second mold, includes a curved portion that is convex outward. Therefore, the workpiece is shrink-flanged by the curved portion of the convex portion. The guide is positioned in a position that prevents the notch from shrinking during shrink-flanging during press molding. The guide prevents material from flowing into the notch during shrink-flanging. This prevents plastic deformation near the notch in the workpiece. Therefore, residual tensile stress near the notch after demolding is reduced.

[0034] The configuration in which the guide is provided at a position that prevents the notch from shrinking due to shrinkage flange forming may be a configuration in which the guide is provided at a position that prevents the circumferential width of the notch from shrinking in the circumferential direction. For example, the guide may be configured to contact the notch at at least two points that are circumferentially spaced apart as viewed from the pressing direction during at least a portion of the process from the forming start position to the bottom dead center. That is, the guide may be configured to contact a portion of the notch that includes at least two points that are circumferentially spaced apart. For example, the guide may be configured to contact a portion of the notch that includes at least two points that are circumferentially spaced apart in the part where the distance in the pressing direction between the first mold and the second mold changes during the process from the forming start position to the bottom dead center, continuously.

[0035] As an example, the guides may be positioned so that the maximum width of the guides between the notches at the forming start position, as viewed from the press direction, is 80 to 100% of the maximum width of the notches. This allows the guides to be positioned to prevent the notches from shrinking due to shrink flange forming during at least part of the process from the forming start position to the bottom dead center. From the same perspective, the maximum width of the guides between the notches at the forming start position, as viewed from the press direction, is more preferably 90 to 100%, and even more preferably 95 to 100%.

[0036] The width of the notch and guide as viewed from the press direction is the width in a direction perpendicular to the normal to the curved ridge formed by the curved portion of the shoulder of the convex portion of the first mold, which passes through the bottom of the notch. The bottom of the notch is the point at which the distance from the curved ridge of the curved portion of the notch in the workpiece at the starting position of forming is smallest as viewed from the press direction. The distance between a point on the notch and the curved ridge is the distance on the normal to the curved ridge. The maximum width of the guide between the notches is the maximum width of the portion between the guide notches, i.e., the portion sandwiched between the guides. The portion between the guide notches is at the same height as the notches. In other words, the portion between the guide notches overlaps with the notches as viewed from a direction perpendicular to the press direction.

[0037] The guide may be positioned so that the distance between both corners of the notch and the guide is 0.5 mm or less when viewed from the press direction at the forming start position. This allows the guide to be provided at a position that prevents the notch from shrinking due to flange forming during at least part of the process from the forming start position to the bottom dead center.

[0038] It is preferable that the shape of the guide as viewed from the press direction at the forming start position be formed so as to include the shapes of each cross section perpendicular to the press direction in the range where the guide contacts the workpiece from the forming start position to the bottom dead center. For example, the shape of the cross section (start cross section) perpendicular to the press direction of the guide at the same height as the notch in the workpiece at the forming start position may be the same as the shape of the cross section (bottom dead center cross section) perpendicular to the press direction of the guide at the same height as the notch in the workpiece at the bottom dead center. Furthermore, the cross section of the guide between these start cross section and bottom dead center cross section may also have the same shape as the start cross section.

[0039] For example, the start cross section of the guide can have the same shape as the notch at the forming start position, and further, the shapes of each cross section perpendicular to the press direction in the range that contacts the workpiece from the forming start position to the bottom dead center can also be the same shape as the notch at the forming start position. Alternatively, the width of the portion between the notches at the bottom dead center cross section of the guide can be smaller than the width of the portion between the notches at the start cross section of the guide. For example, the width of the cross section of the guide between the start cross section and the bottom dead center cross section can monotonically decrease as it approaches the bottom dead center cross section from the start cross section.

[0040] The corners of the notch are the portions that extend into the edge of the workpiece when viewed from the pressing direction, i.e., the corners at both ends of the notch. In other words, when viewed from the pressing direction, both ends of the notch are angular. The corners of the notch may also be rounded and curved when viewed from the pressing direction. In other words, the corners of the notch may have an R (roundness). In this case, the positions of the corners of the notch are based on the inner R end of the R of both corners.

[0041] The first mold may have a bottom surface and a convex portion protruding from the bottom surface in the pressing direction. The reentrant angle between the convex portion and the bottom surface has a curved portion that curves convexly outward when viewed from the pressing direction. The workpiece is pressed against the curved portion of the reentrant angle between the convex portion and the bottom surface of the first mold, thereby forming a shrink flange. In this case, the reentrant portion of the second mold has a shoulder of the reentrant portion that corresponds to the reentrant angle between the convex portion and the bottom surface. The shoulder of the reentrant portion has a curved portion that curves convexly outward when viewed from the pressing direction.

[0042] (Configuration 2) In the above-mentioned configuration 1, the guide may be provided at a position where, as viewed from the pressing direction, it intersects with a normal line to part of the curved ridge line formed by the curved portion of the shoulder of the convex portion of the first die. That is, the guide may be provided in part of an area where, as viewed from the pressing direction, all of the normal lines to the curved ridge line formed by the curved portion of the shoulder of the convex portion of the first die pass. This allows the guide to be positioned at a position where it is more likely to achieve the effect of preventing the notch from shrinking due to shrink flange forming.

[0043] When the first mold has a bottom surface and the protrusion protruding from the bottom surface in the pressing direction, the guide may be provided at a position intersecting, as viewed from the pressing direction, a normal to a part of a curved ridgeline formed by a curved portion of a reentrant angle between the protrusion and the bottom surface of the first mold. That is, the guide may be provided at a position intersecting with a normal to a part of a curved ridgeline formed by a curved portion of a shoulder of a recess of the second mold.

[0044] (Configuration 3) In the above-mentioned configuration 1 or 2, the guide may be provided at a position that is inside the notch of the workpiece as viewed from the pressing direction during at least a part of the process in which the first and second dies move from the forming start position to the bottom dead center, thereby making it possible to arrange the guide at a position that is more likely to achieve the effect of preventing the notch from shrinking due to shrink flange forming.

[0045] (Configuration 4) In any of the above configurations 1 to 3, the guide may be disposed so as to contact the notch at a position that prevents the notch from shrinking, in a portion where the distance between the first and second dies in the pressing direction changes, including the forming start position, during the process in which the first and second dies move from the forming start position to bottom dead center. This allows the guide to effectively prevent material from flowing into the notch.

[0046] (Configuration 5) In any of the above configurations 1 to 4, the guide may be disposed so as to contact the notch at a position that prevents the notch from shrinking, at a portion where the distance between the first and second dies in the pressing direction changes, including the bottom dead center, during the process in which the first and second dies reach the forming start position and bottom dead center. This makes it possible to more effectively prevent the flow of material into the notch by the guide.

[0047] (Configuration 6) In any one of the above configurations 1 to 5, the guide may be provided in the first mold and fixed to the first mold while the first and second molds move from the molding start position to the bottom dead center. This makes it possible to make the guide follow the notch in conjunction with the movement of the first mold relative to the workpiece during press molding.

[0048] (Configuration 7) In any one of the above configurations 1 to 6, the guide may be provided in the second mold and fixed to the second mold while the first mold and the second mold move from the molding start position to the bottom dead center, thereby simplifying the guide configuration.

[0049] (Configuration 8) In any one of the above configurations 1 to 7, the press apparatus may further include a holder for holding the workpiece. The holder may be configured to hold the workpiece between the first die or the second die and the holder while the first die and the second die move from the forming start position to the bottom dead center. This makes it easier to draw the workpiece.

[0050] (Configuration 9) In the above-mentioned configuration 8, the guide may be provided to the holder and fixed to the holder while the first mold and the second mold move from the molding start position to the bottom dead center. This simplifies the configuration of the guide.

[0051] (Configuration 10) In any of the above configurations 1 to 9, the guide may be disposed so as to be positioned outside the curved portion of the shoulder of the convex portion of the first die when viewed from the pressing direction, thereby further simplifying the configuration of the guide.

[0052] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0053] FIG. 3 is a perspective view showing an example of the configuration of a press machine according to this embodiment. In the example shown in FIG. 3, the press machine includes a die set consisting of a first die 1 having a convex portion 1A, a second die 2 having a concave portion 2A shaped to correspond to the convex portion 1A, and a guide 3. At least one of the first die 1 and the second die 2 is configured to be movable in the press direction FP from a forming start position to a bottom dead center. The convex portion 1A of the first die 1 protrudes in the press direction FP. The shoulder 1b of the convex portion 1A includes a curved portion that curves convexly outward as viewed from the press direction FP. A workpiece W1 is placed between the first die 1, which is at the forming start position, and the second die. As at least one of the first die 1 and the second die moves from the forming start position to the bottom dead center, the workpiece W1 is press-formed into a shape corresponding to the convex portion 1A and the concave portion 2A. During press forming, at least one of the first die 1 and the second die moves so that the first die 1 and the second die approach each other in the press direction. In press forming, the workpiece W1 is pressed against the curved shoulder portion of the protruding portion 1A of the first die 1, thereby shrinking and forming a flange. The workpiece W1 has a notch Wn.

[0054] The guide 3 is provided at a position corresponding to the notch Wn of the workpiece W1. The guide 3 contacts the notch Wn during press forming and prevents the width of the notch Wn from shrinking due to shrink flange forming. Specifically, the guide 3 is provided at a position that prevents the notch Wn of the workpiece W1, which is placed between the first mold 1 and the second mold 2, from shrinking due to shrink flange forming during at least a part of the process in which the first mold 1 and the second mold 2 move from the forming start position to the bottom dead center.

[0055] In the example of FIG. 3, the guide 3 is provided on the first mold 1 and is fixed to the first mold 1 during press molding. That is, during press molding, the guide 3 moves in conjunction with the first mold 1. In this example, the guide 3 is formed integrally with the first mold 1. That is, the guide 3 and the first mold 1 are formed from a single continuous metal body. This simplifies the structure of the mold set. Note that the guide 3 may also be formed from a metal body attached to the first mold 1.

[0056] In the example of Figure 3, the convex portion 1A of the first mold 1 has a top surface 1a, a shoulder 1b continuous with the top surface 1a, and a side surface 1c extending continuously from the shoulder 1b. The concave portion 2A of the second mold 2 has a bottom surface 2a corresponding to the top surface 1a of the convex portion 1A, a reentrant corner 2b continuing with the bottom surface 2a, a side surface 2c extending from the reentrant corner 2b, and a shoulder 2d continuing with the side surface 2c. The reentrant corner 2b of the concave portion 2A corresponds to the shoulder 1b of the convex portion 1A. The reentrant corner 2b of the concave portion 2A has a curved portion that curves convexly outward from the convex portion 1A when viewed from the pressing direction. The curved portion of the reentrant corner 2b of the concave portion 2A corresponds to the curved portion of the shoulder 1b of the convex portion 1A. The side surface 2c of the concave portion 2A corresponds to the side surface 1c of the convex portion 1A.

[0057] The curved portion of the shoulder 1b of the protrusion 1A is curved convexly outward when viewed from the pressing direction. In the example of Fig. 3, the curved ridge formed by the curved portion of the shoulder 1b of the protrusion 1A is curved convexly from the top surface 1a of the protrusion 1A toward the side surface 1c, that is, toward the outside of the protrusion 1A, when viewed from the pressing direction (see the right diagram in Fig. 4(a)). The curved ridge formed by the curved portion of the reentrant corner 2b of the recess 2A is curved convexly from the bottom surface 2a of the recess 2A toward the side surface 2c.

[0058] In the example of FIG. 3, the first mold 1 has a bottom surface 1e and a protruding portion 1A protruding from the bottom surface 1e in the pressing direction. The reentrant angle 1d between the protruding portion 1A and the bottom surface 1e, i.e., the reentrant angle 1d between the side surface 1c and the bottom surface 1e, has a curved portion that curves convexly outward when viewed in the pressing direction. The recessed portion 2A of the second mold 2 has a shoulder 2d of the recessed portion 2A that corresponds to the reentrant angle 1d between the protruding portion 1A and the bottom surface 1e. The shoulder 2d of the recessed portion 2A has a curved portion that curves convexly outward when viewed in the pressing direction. The shoulder 2d of the recessed portion 2A is continuous with the side surface 2c of the recessed portion 2A. The outer surface 2e of the recessed portion 2A extends outward, continuing from the shoulder 2d of the recessed portion 2A. The outer surface 2e of the recessed portion 2A corresponds to the bottom surface 1e of the recessed portion 1A.

[0059] In the example of Fig. 3, the pad 4 is provided at a position sandwiched between the bottom surfaces 2a of the recessed portions 2A of the second mold 2. In other words, the pad 4 is provided at a position facing the top surfaces 1a of the protruding portions 1A of the first mold in the pressing direction. The pad 4 is attached so as to be movable in the pressing direction relative to the second mold 2. The second mold 2 is disposed to the side of the pad 4.

[0060] Although not shown, the press device may include a first support section that supports the first mold, a second support section that supports the second mold, and a movement mechanism that moves at least one of the first support section and the second support section in the pressing direction. The first support section may be, for example, a die set for the first mold. The second support section may be, for example, a die set for the second mold. The movement mechanism may be, for example, a slider.

[0061] FIG. 4 is a diagram showing an example of each step in the manufacturing method of a press-formed product in this embodiment. FIG. 4 shows an example of press forming using the press apparatus shown in FIG. 3. In the example of FIG. 4, a die set including the first die 1, second die 2, and guide 3 shown in FIG. 3 is prepared. As shown in FIG. 4(a), a workpiece W1 having a notch Wn is placed between the first die 1 and the second die 2. The left views of FIGS. 4(a) and (c) and FIG. 4(b) are cross-sectional views of the die set, and the right views of FIGS. 4(a) and (c) are views of the first die 1 and workpiece W1 as viewed from the pressing direction (above).

[0062] In the example shown on the left in Figure 4(a), the workpiece W1 is placed on the top surface 1a of the convex portion 1A of the first mold 1. A pad 4 presses the surface of the workpiece W1 opposite the convex portion 1A. Figure 4(a) shows an example in which the first mold 1 and the second mold 2 are in the molding start position. Both the first mold 1 and the second mold 2 in the molding start position are in contact with the workpiece W1. The molding start position is the position where the change of the workpiece W1 begins as both the first mold 1 and the second mold 2 come into contact with the workpiece W1 and apply force to it.

[0063] As shown in the right diagram of FIG. 4(a), the ridge line formed by the shoulder 1b of the protruding portion 1A of the first mold 1 has curved portions 1bw-1 and 1bw-2 that curve when viewed from the pressing direction. In the example shown in the right diagram of FIG. 4(a), the shoulder 1b has two ridge lines. The curved portion 1bw-1 of one of the two ridge lines curves convexly outward from the protruding portion 1A when viewed from the pressing direction. The curved portion 1bw-2 of the other ridge line curves convexly inward from the protruding portion 1A. The reentrant angle 1d between the shoulder 1b and the bottom surface 1e has two ridge lines. The curved portion 1dw-1 of one of the two ridge lines curves convexly outward from the protruding portion 1A when viewed from the pressing direction. The curved portion 1dw-2 of the other ridge line curves convexly inward from the protruding portion 1A. In press forming, the portion of the workpiece W1 that contacts the surface of the first mold 1 outside the curved portion 1bw-1 that curves convexly outward (see region Ra1 in FIG. 6) is subjected to shrink flange forming. The configuration of the curved portion is not limited to the example shown in FIG. 4(a). For example, both of the two ridges of the shoulder 1b of the convex portion 1A may have a curved portion that curves convexly outward from the convex portion 1A when viewed from the pressing direction. In the example shown in FIG. 4(a), the normal to the curved ridge of the curved portion 1bw-1 of the shoulder 1b coincides with the normal at the intersection of the normal to the curved portion 1bw-1 and the curved ridge of the curved portion 1dw-1 of the reentrant angle 1d, but these may differ.

[0064] In the example of FIG. 4(a), the protrusion 1A has a longitudinal direction. The curved shoulder portion of the protrusion is curved convexly in a direction perpendicular to the longitudinal direction of 1A when viewed from the pressing direction. As a modified example, the curved shoulder portion of the protrusion may be curved convexly outward in the longitudinal direction at the longitudinal end of the protrusion 1A. In this case, the longitudinal direction of the protrusion corresponds to the longitudinal direction of the workpiece. A notch may be provided at the longitudinal end of the workpiece.

[0065] The radius of curvature of the curved ridge formed by the curved portion of the shoulder of the protrusion 1A as viewed from the pressing direction is not particularly limited, but is preferably 2000 mm or less. When the radius of curvature of the curved portion is relatively small, the guide is more effective in suppressing deformation of the notch due to shrinkage during flange forming. From a similar perspective, the radius of curvature is preferably 1000 mm or less, and more preferably 100 mm or less. From a similar perspective, the radius of curvature of the curved portion of the reentrant angle 1d between the protrusion 1A and the bottom surface 1e, the radius of curvature of the reentrant angle 2b of the recess 2A, and the radius of curvature of the shoulder 2d of the recess 2A are also preferably 2000 mm or less, more preferably 1000 mm or less, and even more preferably 100 mm or less. The lower limit of these radii of curvature is not particularly limited, but may be, for example, 25 mm or more.

[0066] FIG. 5 is a diagram illustrating how to determine the radius of curvature of the curved ridgeline of the shoulder of the convex portion of the first die, as viewed from the press direction. As shown in FIG. 5, the radius of curvature of the curved ridgeline of the curved portion 1bw-1 is determined based on the point on the curved ridgeline that is closest to the notch Wn as viewed from the press direction at the start of forming. Point nb, where the distance between the curved ridgeline of the curved portion 1bw-1 and the notch Wn in the workpiece W1 at the start of forming as viewed from the press direction, is the smallest, and is defined as the bottom of the notch. Point nb is the point where the distance between the curved ridgeline on the normal and the notch Wn is smallest. Point b0, which is the intersection point between the normal V0 of the curved ridgeline of the curved portion 1bw-1 and the curved ridgeline, passing through point nb, is defined as the first reference point b0 for the radius of curvature. Points b1 and b2 on the curved ridgeline at both ends of a region 1.5 times the width p1 of the notch Wn in a direction perpendicular to the normal line V0 and centered on the first reference point b0 are defined as the second and third reference points b1 and b2. The radius of a circle passing through these first to third reference points b0, b1, and b2 is defined as the radius of curvature of the curved ridgeline of the curved portion 1bw-1. Similarly, the radii of curvature of the curved portion of the reentrant angle 1d between the convex portion 1A and the bottom surface 1e, the reentrant angle 2b of the recessed portion 2A, and the shoulder 2d of the recessed portion 2A are also determined based on the point on the curved ridgeline that is closest to the notch at the forming start position. If the workpiece has multiple notches, multiple radii of curvature of the curved ridgelines corresponding to each of the multiple notches are defined. In this case, it is preferable that at least one of the radii of curvature of the multiple curved ridgelines be within the above range.

[0067] In the example shown on the right in FIG. 4(a), the guide 3 contacts the notch Wn at the forming start position. The guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming. As an example, the guide 3 contacts the notch Wn at at least two points spaced apart in the circumferential direction when viewed from the pressing direction. Here, the circumferential direction is defined as the direction parallel to the direction of the ridge formed by the curved portion of the shoulder 1b of the protruding portion 1A of the first mold 1.

[0068] At least one of the first mold 1 and the second mold 2 moves from the forming start position to the bottom dead center in the press direction, thereby press-forming the workpiece W1. FIG. 4(b) shows the state of the first mold 1 and the second mold 2 on their way from the forming start position to the bottom dead center, and FIG. 4(c) shows the state at the bottom dead center. As the first mold 1 and the second mold 2 move from the forming start position to the bottom dead center, the distance of the second mold 2 from the first mold 1 in the press direction changes. The guide 3 may contact the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming, somewhere along the way from the forming start position to the bottom dead center. For example, the guide 3 may be configured to contact the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming, over at least one-third of the movement distance of the second mold 2 from the forming start position to the bottom dead center relative to the first mold 1, i.e., over at least one-third of the total stroke. At the bottom dead center, one surface of the workpiece W1 contacts the top surface 1a, shoulder 1b, and side surface 1c of the convex portion 1A of the first mold 1, and the other surface of the workpiece W1 contacts the bottom surface 2a, recessed corner 2b, and side surface 2c of the concave portion 2A of the second mold 2.

[0069] In press forming, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming during at least a part of the process in which the first die 1 and the second die 2 move from the start of forming to the bottom dead center. In the example of Fig. 4, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking when both the first die 1 and the second die 2 start contacting the workpiece W1, that is, when they are at the forming start position. Furthermore, the guide 3 is configured so that it contacts the notch Wn at a position that prevents the notch Wn from shrinking continuously throughout the first die 1 and the second die 2 from the forming start position to the bottom dead center.

[0070] In the example shown on the right in FIG. 4(c), the guide 3 prevents the notch Wn from shrinking due to shrink flanging. During press forming, compressive stress due to shrink flanging is generated in the workpiece W1. The direction Fp of the compressive stress is parallel to the ridge line of the shoulder 1b of the protruding portion 1A of the first mold 1 (the circumferential direction). Due to the compressive stress, the notch Wn tries to deform so as to narrow its circumferential width, i.e., shrink. The guide 3 suppresses deformation of the notch Wn that reduces its circumferential width. During press forming, the guide 3 prevents the notch Wn from shrinking in the circumferential direction or reduces the degree of shrinkage. In the example of FIG. 4(c), the guide 3 contacts the notch Wn at at least two points spaced apart circumferentially as viewed from the pressing direction at the bottom dead center. As a result, the guide 3 contacts the notch Wn at positions that prevent the notch Wn from shrinking.

[0071] The cross-sectional shape of the surface of the guide 3 perpendicular to the pressing direction is shaped to match the shape of the notch Wn. In the example of FIG. 4, the side wall 3a of the guide 3 is formed at a position corresponding to the path along which the notch Wn will pass from the start of press forming to the bottom dead center. The side wall 3a of the guide 3 has an inclined surface inclined with respect to the pressing direction. The inclined surface of the side wall 3a of the guide 3 slopes downward as it approaches the protrusion 1A. The shape of the inclined surface of the side wall 3a can be shaped to match the path along which the notch Wn will pass during press forming. The guide 3 is positioned inside the notch Wn as viewed from the pressing direction throughout the entire process in which the first mold 1 and the second mold 2 move from the pressing start position to the bottom dead center. As a result, the guide 3 contacts the notch Wn continuously from the start of press forming to the bottom dead center at a position that prevents the notch Wn from shrinking. In the example of FIG. 4, the cross-sectional shape of the side wall 3a of the guide 3, perpendicular to the pressing direction, is formed so as to contact the notch Wn at least two points spaced apart in the circumferential direction.

[0072] According to the manufacturing method shown in FIG. 4, the workpiece W1 is molded into a shape corresponding to the shapes of the first and second molds, resulting in a press-formed product. During press molding, the guide 3 prevents shrinkage of the notch Wn due to shrinkage flange forming. Plastic deformation due to compressive stress near the bottom of the notch Wn is particularly suppressed. This suppresses tensile residual stress near the notch after demolding. As a result, for example, in a press-formed product, hydrogen embrittlement can be suppressed even when hydrogen embrittlement is likely to occur due to tensile residual stress concentrating near the notch. Furthermore, when the tensile strength of the workpiece is 1180 MPa or higher, hydrogen embrittlement is more likely to occur due to the tensile residual stress concentrating in a certain area. Therefore, this embodiment is suitable for use when the tensile strength of the workpiece is 1180 MPa or higher. The manufacturing method shown in FIG. 4 is an example of a method for manufacturing a press-formed product by bending.

[0073] The guide 3 does not have to be configured to contact the notch Wn continuously from the start of forming to the bottom dead center. The guide 3 may be configured to contact the notch Wn at a position that prevents the notch Wn from shrinking during part of the process in which the first mold 1 and the second mold 2 move from the start of forming to the bottom dead center. For example, the side wall 3a of the guide 3 may be formed so that the guide 3 contacts the notch Wn at at least two points that are spaced apart in the circumferential direction as viewed from the pressing direction during at least part of the process in which the first mold 1 and the second mold 2 move from the start of forming to the bottom dead center. In this case, the side wall 3a of the guide 3 may be parallel to the pressing direction, i.e., not inclined relative to the pressing direction.

[0074] In the example of FIG. 4, as shown in FIG. 4(c), the press-formed product has a top surface portion wp, a side wall ws extending from the top surface portion wp, and a flange wf extending from the side wall ws. A ridgeline exists between the top surface portion wp and the side wall ws, and another ridgeline exists between the side wall ws and the flange wf. These ridgelines have curved portions corresponding to the curved portions 1bw-1 and 1bw-2 of the shoulder 1b of the protrusion 1A. The top surface portion wp is formed by being sandwiched between the top surface 1a of the protrusion 1A of the first mold 1 and the bottom surface 2a of the second mold 2 at the bottom dead center. The side wall ws is formed by being sandwiched between the side surface 1c of the protrusion 1A and the side surface 2c of the recess 2A at the bottom dead center. The flange wf is formed by being sandwiched between the outer surface 2e of the second mold 2 and the first mold 1 or holder 5 at the bottom dead center. 4, the notch Wn of the workpiece W is provided in a portion corresponding to the flange wf of the press-formed product. Note that the notch Wn may also be provided in a portion corresponding to the side wall ws or top surface wp of the press-formed product.

[0075] FIG. 6 is a diagram illustrating the positional relationship between the first mold 1 and the guide 3. FIG. 6 is a view of the first mold 1 as seen from the pressing direction (above). In FIG. 6, the area Ra1 indicated by dotted hatching on the surface of the first mold 1 corresponds to the area where the workpiece W1 is subjected to shrink flange forming. That is, during press forming, the portion of the workpiece W1 that contacts the area Ra1 is subjected to shrink flange forming. The guide 3 may be provided at a position corresponding to the notch Wn within the area Ra1. Furthermore, even if the guide 3 is outside the area Ra1, it may be provided at a position that prevents the notch Wn from shrinking due to shrink flange forming.

[0076] For example, the guide 3-1 shown in Fig. 6 is provided on the top surface 1a of the protrusion 1A. The top surface 1a is not in the region Ra1. In this way, when the cutout Wn of the workpiece W1 placed in the first mold 1 overlaps with the top surface 1a when viewed from the pressing direction, a guide may be provided on the top surface 1a, as in guide 3-1. Also, a guide 3 may be provided on the side surface 1c of the protrusion 1A, as in guide 3-2.

[0077] In the example of FIG. 6 , the guides 3, 3-1, and 3-2 are all provided at positions intersecting with normals V0, V1, and V1 of a portion of the curved ridgeline formed by the convex curved portion 1bw-1 on the outer side of the shoulder 1b of the convex portion 1A of the first mold 1. In this way, the positions at which the guides are provided can be positions at which, as viewed from the pressing direction, they intersect with the normals of a portion of the curved ridgeline formed by the convex curved portion on the outer side of the shoulder of the convex portion of the first mold, and can be positions corresponding to the notches. Here, the normals of the curved ridgeline formed by the curved portion of the shoulder of the convex portion as viewed from the pressing direction are imaginary lines perpendicular to the tangents of the curved ridgeline as viewed from the pressing direction. For example, the guides may be provided at positions at which, as viewed from the pressing direction, they intersect with the normals of a portion of the curved ridgeline formed by the convex curved portion on the outer side of the shoulder of the convex portion of the first mold, and on the top surface of the convex portion or on the outer side of the curved ridgeline. 6, the guides 3, 3-1, and 3-2 are all provided at positions where they intersect with a normal to a portion of the curved ridge formed by the convex curved portion 1dw-1 outside the reentrant angle 1d between the convex portion 1A and the bottom surface 1e of the first mold 1. In this way, the positions where the guides are provided can be positions where they intersect with a normal to a portion of the curved ridge formed by the convex curved portion outside the reentrant angle between the convex portion and the bottom surface of the first mold, as viewed from the pressing direction, and can be positions corresponding to the notches. In this case, for example, the guides may be provided outside the reentrant angle between the convex portion and the bottom surface of the first mold, as viewed from the pressing direction.

[0078] The shape of the guide 3 as viewed from the pressing direction corresponds to the notch. For example, as shown in Fig. 6, the guides 3, 3-1, and 3-2 are formed to extend in both directions of normals V0, V1, and V2 to the curved ridge of the curved portion 1bw-1 as viewed from the pressing direction. The guides 3, 3-1, and 3-2 are shaped to have a width in the direction parallel to the curved ridge of the curved portion 1bw-1.

[0079] The shoulder of the convex portion of the first mold may have an R in a cross section parallel to the pressing direction, i.e., a rounded, curved shape. When the shoulder of the convex portion has an R in this way, the position where the R ends on the inside of the shoulder of the convex portion is defined as the ridgeline of the shoulder. In other words, the boundary line between the top surface of the convex portion and the shoulder is defined as the ridgeline. The R end on the inside of the shoulder of the convex portion of the first mold is the boundary between the curved portion of the shoulder in a cross section parallel to the pressing direction and the flat portion (straight portion) of the inner top surface or the portion curved in the opposite direction. Note that, for example, in the above cross section, the top surface adjacent to the shoulder may be slightly curved in the same direction as the shoulder. In this case, the degree of curvature of the adjacent top surface is sufficiently smaller than the degree of curvature of the shoulder. In this case, the point where the degree of curvature changes in the above cross section is defined as the boundary between the shoulder and the adjacent top surface, i.e., the R end of the shoulder.

[0080] When the reentrant angle between the side and bottom surfaces of the convex portion of the first mold has an R in a cross section parallel to the press direction, the position where the R ends on the inside of the reentrant angle is defined as the ridgeline of the reentrant angle, as described above. When the reentrant angle or shoulder of the concave portion of the second mold has an R in a cross section parallel to the press direction, the position where the R ends on the inside of the reentrant angle or shoulder of the concave portion is defined as the ridgeline of the shoulder of the concave portion, as described above.

[0081] FIG. 7 is a diagram illustrating exemplary configurations and modifications of the guide 3. In each of FIGS. 7(a) to 7(d), the upper diagram shows an example of the arrangement of the guide 3 and the notch Wn at the start of forming, i.e., at the forming start position, and the lower diagram shows the positional relationship between the guide 3 and the notch Wn at bottom dead center. The upper diagram shows a start cross section of the guide 3, and the lower diagram shows a cross section of the guide 3 at bottom dead center. As shown in FIGS. 7(a) to 7(d), the notch Wn is formed in part of the end (edge) of the workpiece W1. When viewed from the thickness direction of the workpiece W1, both ends of the notch Wn form a corner nc. When viewed from the thickness direction, the portion of the notch Wn between the corners nc extends into the workpiece W1.

[0082] 7(a) shows the guide 3 in the example shown in FIG. 4. In the case of FIG. 7(a), the guide 3 contacts the entire notch Wn both at the start of forming and at bottom dead center. In this example, the width of the portion between the notches Wn at the bottom dead center cross section of the guide 3 is smaller than the width at the start cross section of the guide 3. The width of the portion between the notches Wn at each cross section between the start cross section and the bottom dead center cross section of the guide 3 may become smaller the closer to bottom dead center.

[0083] In the example of FIG. 7(b), the guide 3 is configured to contact the entire notch Wn at the start of forming, but not contact the notch Wn at the bottom dead center. In this case, the guide 3 also suppresses the flow of material into the notch Wn due to shrink flange forming. In this case, the guide 3 may be configured to extend in the pressing direction. That is, the surface of the side wall 3a of the guide 3 may be formed so as to be parallel to the pressing direction. In this example, the shape of the bottom dead center cross section of the guide 3 is the same as the start cross section. Furthermore, the start cross section of the guide 3 has the same shape as the notch Wn at the forming start position. In this case, the shapes of each cross section of the guide 3 between the start cross section and the bottom dead center cross section can also be the same as the start cross section.

[0084] In the example of FIG. 7(c), the guide 3 contacts both corners nc of the notch Wn at the start of forming. The guide 3 also contacts both corners nc of the notch at the bottom dead center. These are examples of the form in which the guide 3 contacts the notch at a position that prevents the notch from shrinking. Note that in the example of FIG. 7(c), the guide 3 may be configured to contact both corners of the notch throughout the entire process from the start of forming to the bottom dead center. In the example of FIG. 7(c), the guide 3 is configured not to contact the portion between the two corners nc of the notch Wn.

[0085] In the example of Figure 7(d), the guide 3 contacts both corners nc of the notch Wn at the start of forming. At the bottom dead center, the guide 3 does not contact both corners nc of the notch. In this case, too, the guide 3 suppresses the flow of material into the notch Wn due to shrinkage flange forming. In the example of Figure 7(d), the guide 3 is configured so as not to contact the portion between the two corners nc of the notch Wn. In this example, the shape of the bottom dead center cross section of the guide 3 is the same as the start cross section. In addition, the shapes of each cross section between the start cross section and the bottom dead center cross section of the guide 3 can also be the same as the start cross section.

[0086] 7(a) to 7(d) are examples in which the guide 3 contacts the notch Wn at at least two points spaced apart in the circumferential direction when viewed from the pressing direction. Note that the configuration in which the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking is not limited to the above examples.

[0087] FIG. 8 is a diagram illustrating an example of the arrangement of the guide 3 relative to the notch Wn. FIG. 8 is a diagram illustrating the guide 3 and a portion of the workpiece W including the notch Wn at the start of forming, as viewed from the pressing direction. At the start of forming (i.e., when the first mold and the second mold are in the forming start position), the maximum width W3 of the guide 3 between the notches as viewed from the pressing direction can be set to 80 to 100% of the maximum width Wn0 of the notch. This allows the guide 3 to prevent the notch Wn from shrinking in the circumferential direction at least in part of the process from the forming start position to the bottom dead center. The ratio of the maximum width W3 of the guide 3 between the notches to the maximum width Wn9 of the notch is more preferably 90 to 100%, and even more preferably 95 to 100%.

[0088] In the example of Fig. 8, the maximum width of the notch is the distance between lines V01 and V02 parallel to the normal line V0 passing through both corners nc of the notch when viewed from the pressing direction. In this case, the guide 3 may be arranged so that it overlaps 80 to 100% of the imaginary line between the two corners nc of the notch when viewed from the pressing direction. Furthermore, the proportion of the portion of the imaginary line between the two corners nc of the notch that the guide 3 overlaps is more preferably 90 to 100%, and even more preferably 95 to 100%.

[0089] The guide 3 may be positioned so that, at the forming start position, the distance between both corners nc of the notch Wn and the guide 3 is 5 mm or less when viewed from the pressing direction. In this case, too, the guide can be provided at a position that prevents the notch from shrinking due to flange forming during at least part of the process from the forming start position to the bottom dead center.

[0090] As a specific example, in at least a portion of the process from the forming start position to the bottom dead center, the maximum width w3 of the guide 3 between the notches in each stroke can be greater than the width Wn1 of the portion corresponding to the notch Wn in each stroke after shrinkage flange formation in the absence of the notch Wn (w3 > Wn1). In other words, in at least a portion of the process from the forming start position to the bottom dead center, the guide 3 may be configured to prevent the notch from shrinking more than the amount of shrinkage of the portion corresponding to the notch in the absence of the notch in each stroke. The width Wn1 of the portion corresponding to the notch in the absence of the notch in one stroke after shrinkage flange formation can be approximated, for example, by the following formula (1) or formula (2). Wn1=Wn0×(1 - Δr / r0) ···(1) Wn1=Wn0×{1 - (S / r0)×(1-sinθ) / cosθ} ···(2)

[0091] Figure 9 is a diagram illustrating w0, Δr, r0, S, and θ in the above equations (1) and (2). In Figure 9, W1a indicates the outer edge of the workpiece at the starting position of forming as viewed from the press direction. W1b indicates the outer edge of the workpiece during forming, i.e., after shrink flange forming. Wn0 is the width of the notch-equivalent portion of the workpiece at the starting position of forming (i.e., the width of the notch). Wn1 is the width of the notch-equivalent portion at a stroke point during forming, i.e., the width of the notch-equivalent portion after shrink flange forming at a stroke point. S indicates the stroke. The stroke S is expressed as the relative movement distance between the first and second dies, with the starting position of forming being set to 0. Δr is the radial inflow amount of the workpiece after shrink flange forming at a stroke point. Δr in the above equation (1) can be calculated, for example, by an approximation using the stroke S and θ, as in the above equation (2). rd is the radius of curvature of the curved ridge of the curved portion 1bw-1 of the shoulder of the convex portion of the first die as viewed from the press direction. r0 represents the radius of curvature of the workpiece. r0 can be approximated by adding the average of rnc1 and rnc2 to rd. That is, r0 = rd + (rnc1 + rnc2) / 2. rnc1 and rnc2 are the distances from each of the two corners nc of the notch to the curved ridge in the normal direction. That is, rnc1 is the distance between the curved ridge on the normal line passing through one corner nc of the notch and one corner nc. rnc2 is the distance between the curved ridge on the normal line passing through the other corner nc of the notch and the other corner nc. θ is the angle of the sidewall line relative to the press direction in the cross section of the workpiece after shrink flange forming at one stroke, parallel to the press direction. θ is not particularly limited, but is preferably 30 degrees or less. The line of the side wall in a cross section parallel to the pressing direction is a straight line connecting the end of the R on the side wall between the top surface and the side wall and the end of the R on the side wall between the side wall and the flange or the end of the side wall (if there is no flange). The side wall may be curved in the cross section. In this case, the radius of curvature of the side wall in the cross section is preferably 500 mm or more, for example.

[0092] The formula for calculating Wn1 is not limited to the above example. For example, rd may be the radius of curvature of the curved ridge of the curved portion 1dw-1 of the reentrant angle between the convex portion and the bottom surface of the first die as viewed from the pressing direction. The method for determining Δr is not limited to using the stroke and angle θ as in the example of formula (2) above. For example, an approximate value of Δr may be determined based on an actual measurement, or the value of Δr for each stroke may be determined based on Δr at the bottom dead center. Wn1 may also be calculated using CAE analysis. Alternatively, the deformation due to shrinkage flange forming of the notch without a guide can be calculated using CAE analysis, and the shape of the guide can be determined to prevent the calculated shrinkage of the notch.

[0093] FIG. 10 is a perspective view showing a modified die set. In the example of FIG. 10, the press machine includes a die set including a first die 1 having a convex portion 1A, a second die 2 having a concave portion 2A shaped to correspond to the convex portion 1A, a guide 3, and a holder 5. The holder 5 holds the workpiece W1 between the first die 1 or the second die 2 and the holder 5 while at least one of the first die 1 and the second die 2 moves from the forming start position to the bottom dead center. The convex portion 1A of the first die 1 can be configured similarly to the convex portion 1A of the first die 1 shown in FIG. 3. The shoulder 1b of the convex portion 1A has a curved portion that curves outwardly convexly when viewed from the pressing direction. The concave portion 2A of the second die 2 has a bottom surface 2a corresponding to the top surface 1a of the convex portion 1A, a reentrant corner 2b corresponding to the shoulder 1b of the convex portion 1A, a side surface 2c extending from the reentrant corner 2b, a shoulder 2d at the end of the side surface 2c, and an outer surface 2e extending outward from the shoulder 2d. The holder 5 has a pressing surface 5a that faces the outer surface 2e of the second die 2 in the pressing direction.

[0094] In the example of FIG. 10, the workpiece W1 is placed between the first mold 1 and the second mold. The workpiece W1 is also placed between the holder 5 and the second mold 2. With the workpiece W1 held between the holder 5 and the second mold 2, at least one of the first mold 1 and the second mold 2 moves from the forming start position to the bottom dead center, whereby the workpiece W1 is press-formed into a shape corresponding to the convex portion 1A and the concave portion 2A. In the press forming, the workpiece W1 is pressed against the curved portion of the shoulder of the convex portion 1A of the first mold 1, thereby shrinking and forming a flange. The workpiece W1 has a notch Wn.

[0095] The guide 3 is provided at a position corresponding to the notch Wn of the workpiece W1. The guide 3 contacts the notch Wn during press forming and prevents the width of the notch Wn from shrinking due to shrink flange forming. In the example of FIG. 3, the guide 3 is provided on the first mold 1 and is fixed to the first mold 1 during press forming. In other words, the guide 3 moves in conjunction with the first mold 1 during press forming. In this example, the guide 3 is formed integrally with the first mold 1.

[0096] In the mold set shown in FIG. 10, a pad may be provided on the bottom surface 2a of the recess 2A of the second mold 2, similar to the example in FIG.

[0097] FIG. 11 shows an example of each step of a manufacturing method for a press-molded product using the die set shown in FIG. 10. The left views of FIGS. 11(a) and (c) and FIG. 11(b) are cross-sectional views of the die set, and the right views of FIGS. 11(a) and (c) are views of the first die 1, holder 5, and workpiece W1 as viewed from the pressing direction (above). In the example of FIG. 11, as shown in the left view of FIG. 11(a), a workpiece W1 having a notch Wn is placed between the first die 1 and the second die 2. The holder 5 is placed to the side of the protrusion 1A of the first die 1. The holder 5 is configured to be movable in the pressing direction relative to the first die 1.

[0098] Figure 11(a) shows an example in which the first mold 1 and the second mold 2 are in the molding start position. In the example shown on the left in Figure 11(a), the workpiece W1 is placed on the pressing surface 5a of the holder 5. The pressing surface 5a of the holder 5 contacts one side of the workpiece W1, and the outer surface 2e of the recess 2A contacts the other side of the workpiece W1. The workpiece W1 is held by the holder 5 and the second mold 2 between the pressing surface 5a of the holder 5 and the outer surface 2e of the second mold 2. Furthermore, both the first mold 1 and the second mold 2, which are in the molding start position, are in contact with the workpiece W1.

[0099] As shown in the right diagram of Figure 11(a), the two ridges formed by the shoulder 1b of the protruding portion 1A of the first mold 1 have curved portions 1bw-1 and 1bw-2 that curve when viewed from the pressing direction. The curved portion 1bw-1 of one of the two ridges curves convexly outward. During press forming, the portion of the workpiece W1 outside the curved portion 1bw-1 that curves convexly outward is shrunk and flanged.

[0100] In the example shown on the right in Figure 11(a), the guide 3 contacts the notch Wn at the start of forming. The guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming. As an example, the guide 3 contacts the notch Wn at at least two points that are spaced apart in the circumferential direction when viewed from the pressing direction.

[0101] 11(b) shows the state on the way from the forming start position to the bottom dead center, and FIG. 11(c) shows the state at the bottom dead center. At the bottom dead center, one surface of the workpiece W1 contacts the top surface 1a, shoulder 1b, and side surface 1c of the protrusion 1A of the first mold 1, and the other surface of the workpiece W1 contacts the bottom surface 2a, reentrant corner 2b, and side surface 2c of the recess 2A of the second mold 2.

[0102] In the example shown on the right in Fig. 11(c), the guide 3 prevents the notch Wn from shrinking due to shrink flange forming. In the example in Fig. 11(c), the guide 3 contacts the notch Wn at at least two points spaced apart in the circumferential direction when viewed from the pressing direction. As a result, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking.

[0103] The cross-sectional shape of the surface of the guide 3 perpendicular to the pressing direction is shaped to match the shape of the notch Wn. In the example of FIG. 11, the side wall 3a of the guide 3 is formed at a position corresponding to the path along which the notch Wn will pass from the start of press forming to the bottom dead center. The side wall 3a of the guide 3 has an inclined surface inclined with respect to the pressing direction. The inclined surface of the side wall 3a of the guide 3 slopes downward as it approaches the protrusion 1A. The shape of the inclined surface of the side wall 3a can be shaped to match the path along which the notch Wn will pass during press forming. The guide 3 is positioned inside the notch Wn as viewed from the pressing direction throughout the entire process in which the first mold 1 and the second mold 2 move from the pressing start position to the bottom dead center. As a result, the guide 3 contacts the notch Wn continuously from the start of press forming to the bottom dead center at a position that prevents the notch Wn from shrinking. In the example of FIG. 11, the cross-sectional shape of the side wall 3a of the guide 3, perpendicular to the pressing direction, is formed so as to contact the notch Wn at at least two points spaced apart in the circumferential direction.

[0104] The guide 3 does not have to be configured to contact the notch Wn continuously from the start of molding to the bottom dead center. The guide 3 may be configured to contact the notch Wn at a position that prevents the notch Wn from shrinking during part of the process in which the first mold 1 and the second mold 2 reach the bottom dead center from the start of molding.

[0105] According to the manufacturing method shown in Fig. 11, the guide 3 prevents the shrinkage of the notch Wn due to shrink flange forming during press forming. Therefore, the residual tensile stress around the notch after demolding is suppressed. Note that the manufacturing method shown in Fig. 11 is an example of a method for manufacturing a press-formed product by drawing.

[0106] FIG. 12 is a diagram showing a modified die set. The die set shown in FIG. 12 is an example of a die set for producing a press-formed product by cylindrical drawing. The die set includes a first die 1, a second die 2, a guide 3, and a holder 5. In the example of FIG. 12, the convex portion 1A of the first die 1 is a cylinder whose axis is the pressing direction FP. A guide 3 extends obliquely from the side surface 1p of the cylinder. The guide 3 protrudes in the pressing direction FP beyond the top surface 1a of the cylinder of the convex portion 1A. The guide 3 moves in conjunction with the first die 1. The second die 2 is a cylinder whose axis is the pressing direction FP. The interior of the cylinder becomes the concave portion 2A. The cylinder forming the concave portion 2A and the cylinder forming the convex portion 1A are arranged coaxially, and the cylinder forming the convex portion 1A can be inserted into the cylinder that is the concave portion 2A. The workpiece W1 is a circular plate with a notch Wn. The guide 3 is provided at a position corresponding to the notch Wn. The holder 5 is a cylinder that surrounds the column of the first mold 1. One axial end face 5a (pressing surface) of the cylinder of the holder 5 faces the other axial end face 2e (outer face) of the cylinder of the second mold 2. A part of the wall that constitutes the cylinder of the holder 5 has been removed to form a space 5s through which the guide 3 passes.

[0107] Fig. 13 is a diagram showing an example of the arrangement of the start of forming and the bottom dead center in press forming of the die set shown in Fig. 12. The upper part of Fig. 13 is a perspective view, and the lower part is a view of the first die 1, holder 5, and workpiece W1 as viewed from the pressing direction FP.

[0108] In the example shown in FIG. 13 , at the start of molding, the pressing surface of the holder 5 contacts one side of the workpiece W1, and the outer surface of the second mold 2 contacts the other side. At the start of molding, the first mold 1 begins to contact one side of the workpiece W1 while the second mold 2 and holder 5 are holding the workpiece W1. At the start of molding, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange deformation. Even at bottom dead center, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange deformation. Alternatively, from the start of molding of the first mold 1 and the second mold 2 until they reach bottom dead center, the guide 3 may continuously contact the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange deformation.

[0109] FIG. 14 is a diagram showing the region Ra1 of the workpiece W1 where shrink flange forming is performed in the press forming shown in FIG. 13. In FIG. 14, the edge of the workpiece W1 is indicated by a dashed line, and the region Ra where shrink flange forming is performed is indicated by dots. In the example shown in FIG. 14, the region Ra1 where shrink flange forming is performed is the outside of the curved portion 1bw-1 that curves convexly outward from the shoulder 1b of the protruding portion 1A of the first mold 1 as viewed from the press direction. The guide 3 is located inside the notch Wn at a position where it intersects with a normal line (a line perpendicular to the tangent line) of a portion of the curved ridgeline formed by the curved portion 1bw-1. In the example of FIG. 14, the guide 3 is located outside the curved portion 1bw-1 as viewed from the press direction. If the notch Wn reaches the top surface 1a of the protruding portion 1A of the first mold 1 as viewed from the press direction, the guide 3 may be provided on the top surface 1a.

[0110] FIG. 15 is a diagram showing an example of a die set in which a guide 3 is provided on the top surface 1a of the convex portion 1A of the first die 1. In the example of FIG. 15, the guide 3 is provided on the top surface 1a of the first die 1. The guide 3 is formed so as to protrude from the top surface 1a in the pressing direction FP. The guide 3 may be formed integrally with the first die 1. The guide 3 may also be part of the first die 1. FIG. 15 shows the arrangement of the die set at the start of forming. The notch Wn of the workpiece W1 placed at the start of forming reaches the top surface 1a of the first die 1 when viewed from the pressing direction. At the start of forming, the guide 3 contacts the notch Wn at a position that prevents the notch Wn from shrinking due to shrink flange forming.

[0111] FIG. 16 is a diagram showing a modified example of a die set. In the example of FIG. 16, the guide 3 is provided independently of the first die 1, the second die 2, and the holder 5. For example, at the start of forming, the guide 3 may contact the notch Wn of the workpiece W1 held by the holder 5 and the second die 2 at at least two points spaced apart in the circumferential direction. This prevents the guide 3 from reducing the width of the notch Wn due to shrinkage flange deformation during press forming. The guide 3 may be configured to move or not move independently of any of the first die 1, the second die 2, and the holder 5. Alternatively, the guide 3 may be configured to move in conjunction with any of the first die 1, the second die 2, and the holder 5.

[0112] FIG. 17 is a diagram showing a modified example of a die set. In the example of FIG. 17, the guide 3 is provided on the holder 5. The left diagram of FIG. 17 is an exploded perspective view of the die set, and the right diagram is a diagram showing an example of the arrangement of the die set at the start of molding. In the example of FIG. 17, the guide 3 contacts the notch Wn of the workpiece W1 held by the holder 5 and the second die 2 at at least two points spaced apart in the circumferential direction at the start of molding. This allows the guide 3 to prevent the width of the notch Wn from shrinking due to flange deformation during press molding. The guide 3 may be formed to extend in the pressing direction FP. In other words, the side surface of the guide 3 may be formed parallel to the pressing direction FP.

[0113] FIG. 18 shows a modified mold set. In the example of FIG. 18, the guide 3 is provided in the second mold. The left diagram of FIG. 18 is an exploded perspective view of the mold set, and the right diagram shows an example of the arrangement of the mold set at the start of molding. The guide 3 protrudes in the pressing direction from the outer surface 2e of the recess 2A of the second mold 2, facing the first mold 1. The guide 3 is provided at a position corresponding to the notch Wn of the workpiece W1. In the example of the right diagram of FIG. 18, the guide 3 contacts the notch Wn of the workpiece W1 held by the holder 5 and the second mold 2 at at least two points spaced apart in the circumferential direction at the start of molding. This prevents the width of the notch Wn from shrinking due to flange deformation during press molding. The guide 3 may be formed to extend in the pressing direction. That is, the side surfaces of the guide 3 may be formed parallel to the pressing direction.

[0114] The workpiece may have multiple cutouts. In this case, a guide is provided for at least one of the multiple cutouts. That is, the guide may be provided so as to contact at least one of the multiple cutouts at a position that prevents at least one of the multiple cutouts from shrinking due to shrink flange forming during press forming. Examples of the workpiece having multiple cutouts include a case where a small cutout is included within a large cutout, and a case where multiple cutouts are formed side by side in the circumferential direction. In such cases, a guide is also provided for at least one of the multiple cutouts.

[0115] (Analysis results) The inventors conducted forming analysis and springback analysis of notched cylindrical drawing using computer simulations. Figure 19(a) shows a notched workpiece model WM used in the analysis. The workpiece model WM was a circular plate with a diameter of 90 mm and a center axis along the Z axis. This circular plate had a circular notch with a diameter of 30 mm when viewed from the axial direction. The material used was a steel plate with a tensile strength of 1470 MPa and a thickness of 1.4 mm. Figure 19(b) shows the shapes and dimensions of die models 1M and 2M, holder model 5M, and guide model 3M used in the forming analysis. Die model 1M corresponds to the first die 1. Die model 2M corresponds to the second die 2. Holder model 5M corresponds to the holder 5. Guide model 3M corresponds to the guide 3. In Figure 19(b), the unit of dimensions is mm. The forming height (drawing height, stroke) from the forming start position to the bottom dead center was 4 mm and 6 mm. The blank holder load applied to the workpiece WM by the die model 2M and holder model 5M was 80 kN. The pressing direction was the Z direction, i.e., the axial direction of the disk of the workpiece model. In the model of Figure 19(b), the shoulder R (radius of curvature) of the die models 1M and 2M was both 5 mm, and the drawing heights (4 mm, 6 mm) were both less than the sum of these shoulder R, 10 mm, so ironing was not performed.

[0116] FIG. 20 is a diagram showing the guide models used in the analysis. Forming analysis was performed using guide models 3M1 and 3M2 shown in FIGS. 20(a) and 20(b), respectively, and a forming analysis without a guide as shown in FIG. 20(c). The press forming using guide model 3M1 in FIG. 20(a) is Example 1. The press forming using guide model 3M2 in FIG. 20(b) is Example 2. The press forming without a guide in FIG. 20(c) is a comparative example.

[0117] Figure 20(a) shows a guide model 3M1 in which the guide contacts the entire notch from the forming start position to the bottom dead center. The shape of the guide model 3M1 was determined using the following procedure. First, as shown in Figure 20(c), the notch shape at each stroke stage (0, 4, and 6 mm) was obtained from the results of a forming analysis without a guide. To ensure that the guide was wider than the width of the notch shape obtained from the analysis results, the radii of the guide circle in the cross section perpendicular to the pressing direction at strokes of 0, 4, and 6 mm were set to 15 mm (the same radius as the notch in the workpiece), 14 mm, and 13 mm, respectively. Based on the relationship between the guide radius and stroke at these three stages, the guide radius r was approximated by a quadratic function of the stroke Xz to determine the guide radius for each stroke. The coefficients of this quadratic function were obtained using regression analysis. The guide was positioned so that the guide arc contacted the bottom of the notch when no guide was used. In this way, the shape of the guide model 3M1 in Figure 20(a) was determined. A molding analysis was carried out using this guide model 3M1. Figure 21 shows the results of this analysis. Figure 21 shows the shapes of the molded model WM and the guide model 3M1 at each stroke stage (0, 2, 4, 6 mm). In the results shown in Figure 21, the guide continuously contacts the notch from the molding start position to the bottom dead center. The shape of the guide model 3M1 shown in Figure 20(a) is called a follow-up type. Note that Example 1 corresponds to the mold structure of Figure 12 and the contact mode of Figure 7(a).

[0118] The shape of the guide model 3M2 in Figure 20(b) is a shape that contacts the entire notch at the forming start position. This shape maintains the shape contacting the notch at the forming start position in the press direction (Z direction). In other words, the cross-sectional shape of the guide model 3M2 perpendicular to the Z axis is the same at all positions in the Z direction. The surface of the guide model 3M2 in Figure 20(b) is the surface obtained by extending the notch shape at the forming start position in the press direction (Z direction). A forming analysis was performed using this guide model 3M2. Figure 22 shows the results of this analysis. Figure 22 shows the shapes of the formed model WM and the guide model 3M2 at each stroke stage (0, 2, 4, and 6 mm). In the results shown in Figure 22, after the start of forming, the guide contacts only a portion of the notch (including the corners of the notch) rather than the entire notch. The shape of the guide model shown in Figure 20(b) is referred to as the initial maintenance type. Example 2 corresponds to the mold structure of Figs. 16 and 17, the contact state at the molding start position corresponds to Fig. 7(a), and the contact state at the bottom dead center (during molding) corresponds to Fig. 7(c).

[0119] Table 1 below shows the analysis results for Examples 1 and 2 and Comparative Example. In Table 1 below, the stress after demolding corresponds to the residual stress of the press-molded product. Note that positive values ​​indicate tensile stress and negative values ​​indicate compressive stress. The directions of the maximum principal stress and minimum principal stress were along the edge of the bottom of the notch. Note that the notch width (linear distance) at a molding height of 0 mm was 28.1 mm in all of Comparative Example, Example 1, and Example 2. [Table 1]

[0120] The results shown in Table 1 above show that the residual stress at the center of the notch, i.e., the bottom of the notch, is significantly lower in Examples 1 and 2, which have a guide, than in the comparative example, which does not have a guide. This suggests that Examples 1 and 2 can suppress the concentration of residual stress near the center (bottom) of the notch, compared to the comparative example, which does not have a guide.

[0121] The results shown in Table 1 above show that Example 1, which used a follow-up type guide, had lower residual stress in the center of the notch than Example 2, which used an initial-maintenance type guide. This is thought to be because the guide was in continuous contact with the entire notch from the start of forming to the bottom dead center, which more reliably prevented the guide from flowing material into the notch, and as a result, the residual stress near the bottom of the notch was further reduced.

[0122] Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and carried out within the scope of the spirit of the present invention. [Explanation of symbols]

[0123] 1: First mold, 2: Second mold, 3: Guide, 4: Pad, 5: Holder, W1: Molded material, Wn: Notch

Claims

1. preparing a die set including: a first die having a convex portion that protrudes in the pressing direction, wherein a shoulder of the convex portion includes a curved portion that curves convexly outward when viewed from the pressing direction; a second die having a concave portion that has a shape corresponding to the convex portion of the first die; and a guide; placing a workpiece having a notch between the first mold and the second mold; and a step of moving at least one of the first mold and the second mold in a press direction from a molding start position to a bottom dead center, and press-molding the workpiece, the press forming includes shrink flange forming by pressing the workpiece against a curved portion of a shoulder of the convex portion of the first die, In the press molding, during at least a part of the process in which the first mold and the second mold reach bottom dead center from the molding start position, the guide contacts the notch at a position that prevents the notch from shrinking due to shrink flange molding.

2. A method for manufacturing a press-molded product according to claim 1, A method for manufacturing a press-molded product, wherein the guide contacts the notch at a position that prevents shrinkage due to the shrink flange molding at a portion where the distance in the press direction between the first mold and the second mold changes, including the molding start position, during the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

3. The method for manufacturing a press-molded product according to claim 1 or 2, A method for manufacturing a press-molded product, wherein the guide contacts the notch at a position that prevents shrinkage due to the shrink flange molding at a portion including the bottom dead center where the distance in the press direction between the first mold and the second mold changes during the process in which the first mold and the second mold reach the molding start position and bottom dead center.

4. The method for manufacturing a press-molded product according to claim 1 or 2, A method for manufacturing a press-molded product, wherein the guide is provided on the first mold and is fixed relative to the first mold during the process in which the first mold and the second mold move from the molding start position to the bottom dead center.

5. The method for manufacturing a press-molded product according to claim 1 or 2, A method for manufacturing a press-molded product, wherein the guide is provided on the second mold and is fixed relative to the second mold during the process in which the first mold and the second mold move from the molding start position to the bottom dead center.

6. The method for manufacturing a press-molded product according to claim 1 or 2, The press molding is performed by moving at least one of the first mold and the second mold in the press direction while the workpiece is held between either the first mold or the second mold and a holder during the process in which the first mold and the second mold move from the molding start position to the bottom dead center.

7. The method for manufacturing a press-molded product according to claim 6, A method for manufacturing a press-molded product, wherein the guide is provided on the holder and the first mold and second mold are fixed to the holder during the process from the molding start position to the bottom dead center.

8. The method for manufacturing a press-molded product according to claim 1 or 2, A method for manufacturing a press-molded product, in which the workpiece is positioned so that the entire cutout is located outside the curved portion of the shoulder of the convex portion of the first mold when viewed from the press direction.

9. a first die having a convex portion that protrudes in a pressing direction, wherein a shoulder of the convex portion includes a curved portion that is curved convexly outward when viewed from the pressing direction; a second mold having a recessed portion having a shape corresponding to the protruding portion of the first mold; With guides and At least one of the first mold and the second mold is movable in a press direction from a molding start position where the first mold and the second mold are separated to a bottom dead center, The guide is provided in a position that prevents a notch in the workpiece placed between the first mold and the second mold from shrinking due to shrink flange molding during at least part of the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

10. The press device according to claim 9, A press device, wherein the guide is provided at a position where, when viewed from the pressing direction, it intersects with a normal to a part of a curved ridge line formed by a curved portion of a shoulder of the convex portion of the first die.

11. The press device according to claim 9, A press device in which the guide is provided at a position that is inside the cutout of the workpiece when viewed from the pressing direction during at least part of the process in which the first mold and the second mold move from the molding start position to the bottom dead center.

12. The press device according to any one of claims 9 to 11, the guide is arranged so as to contact the notch at a position that prevents the notch from shrinking, at a portion where the distance in the press direction between the first mold and the second mold changes, including the molding start position, during the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

13. The press device according to any one of claims 9 to 11, the guide is arranged to contact the notch at a position that prevents the notch from shrinking, at a portion where the distance in the press direction between the first mold and the second mold changes, including the bottom dead center, during the process in which the first mold and the second mold reach the molding start position to the bottom dead center.

14. The press device according to any one of claims 9 to 11, A press apparatus, wherein the guide is provided on the first mold and is fixed relative to the first mold during the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

15. The press device according to any one of claims 9 to 11, A press apparatus, wherein the guide is provided on the second mold and is fixed relative to the second mold during the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

16. The press device according to any one of claims 9 to 11, Further, a holder for holding the workpiece is provided, A press device wherein the holder is configured to hold the workpiece between either the first mold or the second mold and the holder during the process in which the first mold and the second mold reach the bottom dead center from the molding start position.

17. 17. The press device according to claim 16, The guide is provided on the holder, and the first mold and the second mold are fixed to the holder during the process from the molding start position to the bottom dead center.

18. The press device according to any one of claims 9 to 11, a press device, wherein the guide is disposed so as to be located outside a curved portion of a shoulder of the convex portion of the first die when viewed from the pressing direction.

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