Press mold

Abstract

To provide a press molding method and a press die for the same which can decrease cracking due to elongation of a press part and improve shape freezing property when one side wall part of a hat-shaped cross section shape part of the press part is elongated at a curvature ratio larger than that of the other side wall part to be curved in a direction for flange formation.SOLUTION: A press molding method comprises: a punch 21 which includes a first side wall formation part 211 forming one side wall part of a hat-shaped cross section, a second side wall formation part 212 forming the other side wall part, and a flange formation part 212H forming a flange part extending from the other side wall part; a cushion 22 with a wrinkle pressing part 221 which forms a flange part extending from the one side wall part; a pad 23; and a die 24. The die and the punch approach each other while the pad presses a material W on a top plate formation part 213 of the punch and the wrinkle pressing part of the cushion and the die sandwich the material, so that the one side wall part and the flange part of the same are drawn, and the other side wall part and the flange part of the same are bended.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a press forming method and a press die therefor, and more particularly to a press forming method and a press die therefor for forming a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction, and one side wall portion of the hat-shaped cross-sectional shape portion being curved in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion. [Background technology]

[0002] 14(A), the press part 100 having a hat-shaped cross-sectional shape that is continuous in the longitudinal direction is generally known to be obtained by a press-forming method in which a raw material (steel plate) SS is bent into a top plate 101 and left and right side wall portions 102, 103 with a hat-shaped cross section. That is, the press part 100 can be obtained by a press-forming method that includes a lower punch 201 having a hat-shaped cross-sectional forming surface, a pad 202 that presses the raw material SS against the top plate forming portion of the lower punch 201, and an upper die 203 that is located on the outer periphery of the pad 202 and has bending blades 203D that are formed along the left and right side wall portions of the hat cross section. The upper die 203 is lowered with the pad 202 pressing the raw material SS against the lower punch 201, and the bending blades 203D press the raw material SS against the lower punch 201 to bend the raw material SS into a shape that conforms to the forming surface of the lower punch 201.

[0003] However, in a pressed part 100 having a hat-shaped cross-sectional shape, the hat-shaped cross-sectional shape is often curved in the longitudinal direction, and in such cases, one side wall 102 of the hat cross section is often stretch-flanged and the other side wall 103 is often shrink-flanged. If this pressed part 100 is formed by a bending method, tensile stress remains in the stretch-flanged side wall 102, and compressive stress remains in the shrink-flanged side wall 103.

[0004] As a result, as shown in Figure 14(B), after release from the mold, the side wall 102 of the press part 100, which was formed by stretch flange forming, deforms inward (in the direction of arrow X1) due to residual tensile stress, and the side wall 103 of the press part 100, which was formed by shrink flange forming, deforms outward (in the direction of arrow X2) due to residual compressive stress, making it difficult to freeze into a regular shape. Furthermore, because the left and right side walls 102 and 103 deform in the same direction (X1 and X2), the entire hat-shaped cross-sectional shape portion is twisted, making it difficult to set the mold for the next process. Furthermore, when the raw material SS is a so-called high-tensile steel plate (e.g., a steel plate with a tensile strength of approximately 1 to 1.2 GPa), the amount of twist in the press part 100 after bending increases, necessitating repeated corrections to the forming surface of the press mold.

[0005] To address this problem, one possible method is to form the above-mentioned pressed part 100 using a drawing method to improve the shape fixability into the normal shape. However, this method poses the problem that, particularly in the case of high-tensile steel sheets, the elongation rate decreases, making it more likely that stretch cracks will occur in the side wall portion 102 during stretch flange forming.

[0006] In this regard, Patent Document 1 discloses a press-forming method for forming a press part 400, which includes a lower punch 301, a pad 302 for pressing a material SS against the lower punch 301, and an upper die 303 having a forming surface on the outer periphery of the pad 302, and has a substantially hat-shaped cross section that continues in the longitudinal direction, with a stretch flange-formed portion 402 and a shrink flange-formed portion 403 formed at positions facing each other across a top plate portion 401, as shown in Figs. 15 and 16, by cold bending a blanked material SS. Thus, a press forming method is disclosed in which, while the pad 302 presses the material portion SS1A of the top plate portion 401 at a position away from the stretch flange forming portion 402 and the shrink flange forming portion 403, the upper die 303 rotates and moves the material portions SS2 and SS3 that form the stretch flange forming portion 402 and the shrink flange forming portion 403 close to the lower punch 301 from the shrink flange forming side to the stretch flange forming side relative to the lower punch 301, and then presses them against the lower punch 301.

[0007] According to this press forming method, the raw material SS can be supplied from the shrink flange forming section 403 side to the stretch flange forming section 402 side, which has the effect of reducing stretch cracks in the stretch flange forming section 402. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-6926 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the press forming method disclosed in the above Patent Document 1, if the stretch flange forming portion 402 and the shrink flange forming portion 403 are not formed in opposing positions across the top plate portion 401, the material portions SS2 and SS3 that form the stretch flange forming portion 402 and the shrink flange forming portion 403 cannot be moved from the shrink flange forming side to the stretch flange forming side relative to the lower punch 301.

[0010] Therefore, in the case of a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction and one side wall portion of the hat-shaped cross-sectional shape portion is curved in the direction of stretch flange forming at a curvature greater than the curvature of the other side wall portion (for example, when one side wall portion of the hat-shaped cross-sectional shape portion is curved at a large curvature in the direction of stretch flange forming, but the other side wall portion is extended in a straight line or is curved at a small curvature so as to result in slight shrinkage flange forming), there is a problem that the supply of material to one side wall portion for stretch flange forming is insufficient, and stretch cracks occur in one side wall portion for stretch flange forming.

[0011] The present invention has been made to solve the above problems, and aims to provide a press forming method and a press die therefor that can improve shape fixability while reducing stretch cracking in a press part in which one side wall portion of a hat-shaped cross-sectional shape portion is bent in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion. [Means for solving the problem]

[0012] In order to achieve the above object, the press molding method and press mold according to the present invention have the following configurations. (1) A press forming method for forming a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction, in which one side wall portion of the hat-shaped cross-sectional shape portion is curved in a direction that results in stretch flange forming at a curvature rate that is greater than the curvature rate of the other side wall portion, a punch having a top plate forming portion that forms a top plate portion having a hat-shaped cross section, a first side wall forming portion that forms the one side wall portion, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion having a wrinkle suppressor portion that is separated from the first side wall molding portion and forms a flange portion extending from one of the side wall portions, and that is formed to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die having die molding portions disposed along an outer peripheral edge of the pad and facing the punch and the cushion, the die molding portions forming the side wall portions and the flange portions; a cushion pressurizing device that presses the cushion against the die with a pressure equal to or greater than the pressing force of the pad, The pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, and the die and the punch approach each other, thereby drawing and forming one side wall portion and the flange portion extending from the one side wall portion, and bending and forming the other side wall portion and the flange portion extending from the other side wall portion.

[0013] In the present invention, a punch having a top plate forming portion that forms a top plate portion with a hat-shaped cross section, a first side wall forming portion that forms one side wall portion, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion, a cushion that is separated from the first side wall forming portion and has a wrinkle suppressor portion that forms the flange portion extending from one side wall portion and is formed so as to be movable up and down relative to the punch, a pad that presses the material against the top plate forming portion of the punch, a die that is opposite the punch and cushion and is arranged along the outer periphery of the pad and has die forming portions that form both side wall portions and both flange portions, and a pressurizing force that is equal to or greater than the pressing force of the pad against the die. The die and punch are brought into close proximity with each other in a state in which the pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, thereby drawing and forming one side wall portion and a flange portion extending from that side wall portion, and bending and forming the other side wall portion and a flange portion extending from the other side wall portion.This makes it possible to reduce stretch cracking in one side wall portion of a press part that has a hat-shaped cross-sectional shape that is continuous in the longitudinal direction and is bent in a direction that results in stretch flange forming at a curvature rate that is greater than the curvature rate of the other side wall portion, while improving the ability to fix the shape into a normal shape.

[0014] That is, the punch has a top plate forming portion that forms a top plate portion with a hat-shaped cross section, a first side wall forming portion that forms one of the side wall portions, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion that is separated from the first side wall forming portion and has a wrinkle suppression portion that forms the flange portion extending from one of the side wall portions and is formed so as to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die that faces the punch and cushion and is arranged along the outer peripheral edge of the pad and has die forming portions that form both side wall portions and both flange portions; and a cushion pressure device that presses the cushion against the die with a pressure force greater than or equal to the pressing force of the pad.Therefore, the punch and pad hold the material on the top plate side, and the cushion and die hold the material on one of the side wall portions, and the punch and die come close to each other, thereby enabling one side wall portion and a flange portion extending from one of the side wall portions to be stretch flanged. Furthermore, by sandwiching the material on the top plate side between the punch and the pad and bringing the punch and the die close to each other, the other side wall portion and the flange portion extending from the other side wall portion can be bent and formed.

[0015] In addition, in the early stages of the drawing process in which the punch, cushion, pad, and die cooperate to draw one side wall portion to be stretch-flanged and the flange portion extending from that side wall portion, the punch and die hardly bend the material on the other side wall portion. Therefore, by pressing the cushion against the die with a pressure greater than or equal to the pressing force of the pad, the cushion pressure device can suppress the amount of material on the one side wall portion to be stretch-flanged flowing into the punch while allowing the material to flow from the other side wall portion to the one side wall portion to be stretch-flanged.

[0016] In addition, the pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, and the die and punch approach each other, thereby drawing one side wall portion and the flange portion extending from that side wall, and bending the other side wall portion and the flange portion extending from that side wall. Therefore, by drawing the one side wall portion and the flange portion extending from that side wall while receiving material from the other side wall portion to the one side wall, the elongation of the one side wall portion and the flange portion extending from that side wall is reduced, and the reduced elongation also reduces tensile residual stress. As a result, stretch cracking of the one side wall portion and the flange portion extending from that side wall can be reduced, and shape fixability can be improved.

[0017] Therefore, according to the present invention, a press forming method can be provided that can improve shape fixability while reducing stretch cracking in a press part in which one side wall portion of a hat-shaped cross-sectional shape portion is bent in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion.

[0018] (2) In the press molding method described in (1), The other side wall portion is formed so that its bending angle relative to the top plate portion is smaller than the normal bending angle, and is then formed to the normal bending angle in a subsequent process.

[0019] In the present invention, the other side wall portion is formed at a bend angle relative to the top plate portion smaller than the normal bend angle and then formed to the normal bend angle in a subsequent process. Therefore, when drawing one side wall portion and the flange portion extending from one side wall portion, the other side wall portion is formed at a bend angle relative to the top plate portion smaller than the normal bend angle. Therefore, when drawing one side wall portion and the flange portion extending from one side wall portion, the material on the other side wall portion side can easily pass through the gap between the pad and the top plate forming portion of the punch, allowing more material to flow from the other side wall portion side to the one side wall portion side that will be stretch flanged. As a result, stretch cracking can be further reduced when drawing one side wall portion and the flange portion extending from one side wall portion, and shape fixability can be further improved.

[0020] (3) In the press molding method described in (1) or (2), The pad is divided into a plurality of sections corresponding to a region in the one side wall portion where the elongation rate of stretch flange forming is large and a region in the one side wall portion where the elongation rate is small, The pressing force of the pad corresponding to the region with the larger elongation rate is smaller than the pressing force of the pad corresponding to the region with the smaller elongation rate.

[0021] In the present invention, the pad is divided into multiple sections corresponding to the regions of high elongation and low elongation in one side wall portion, and the pressing force of the pad corresponding to the regions of high elongation is smaller than the pressing force of the pad corresponding to the regions of low elongation, so that when drawing one side wall portion and the flange portion extending from one side wall portion, the amount of material flowing from the other side wall portion to the one side wall portion can be further increased in the region of high elongation in stretch flange forming of one side wall portion. Therefore, during drawing, stretch cracking in the region of high elongation in stretch flange forming and the flange portion extending from one side wall portion can be further reduced, and shape fixability can be further improved.

[0022] Furthermore, when one side wall portion and the flange portion extending from the one side wall portion are drawn, the pressing force of the pad becomes relatively large in the region of the one side wall portion where the elongation rate of stretch flange forming is small, so the amount of material flowing from the other side wall portion to the one side wall portion can be reduced. As a result, deformation of the other side wall portion and the flange portion extending from the other side wall portion due to the flow of material can be suppressed, and shape fixability can be improved.

[0023] (4) A press die for forming a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction, and one side wall portion of the hat-shaped cross-sectional shape portion is curved in a direction that is stretch flange forming at a curvature rate greater than the curvature rate of the other side wall portion, a punch having a top plate forming portion that forms a top plate portion having a hat-shaped cross section, a first side wall forming portion that forms the one side wall portion, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion having a wrinkle suppressor portion that is separated from the first side wall molding portion and forms a flange portion extending from one of the side wall portions, and that is formed to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die having die molding portions disposed along an outer peripheral edge of the pad and facing the punch and the cushion, the die molding portions forming the side wall portions and the flange portions; a cushion pressurizing device that presses the cushion against the die with a pressure equal to or greater than the pressing force of the pad, The pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, and the die and the punch approach each other, thereby drawing and forming one side wall portion and the flange portion extending from the one side wall portion, and bending and forming the other side wall portion and the flange portion extending from the other side wall portion.

[0024] In the present invention, there is provided a punch having a top plate forming portion that forms a top plate portion having a hat-shaped cross section, a first side wall forming portion that forms one side wall portion, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion that is separated from the first side wall forming portion and has a wrinkle suppressor portion that forms the flange portion extending from one side wall portion and is formed so as to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die that is opposed to the punch and cushion and is arranged along the outer periphery of the pad and has die forming portions that form both side wall portions and both flange portions; and a pressing force that is applied to the die with a pressure force equal to or greater than the pressing force of the pad. The die and punch are brought into close proximity with each other in a state in which the pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, thereby drawing-forming one side wall portion and a flange portion extending from the one side wall portion, and bending-forming the other side wall portion and a flange portion extending from the other side wall portion.This makes it possible to improve shape fixability while reducing stretch cracking in one side wall portion of a press part that has a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction and is bent in a direction that results in stretch flange forming at a curvature rate greater than the curvature rate of the other side wall portion.

[0025] That is, the punch has a top plate forming portion that forms a top plate portion with a hat-shaped cross section, a first side wall forming portion that forms one of the side wall portions, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion that is separated from the first side wall forming portion and has a wrinkle suppression portion that forms the flange portion extending from one of the side wall portions and is formed so as to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die that faces the punch and cushion and is arranged along the outer peripheral edge of the pad and has die forming portions that form both side wall portions and both flange portions; and a cushion pressure device that presses the cushion against the die with a pressure force greater than or equal to the pressing force of the pad.Therefore, the punch and pad hold the material on the top plate side, and the cushion and die hold the material on one of the side wall portions, and the punch and die come close to each other, thereby enabling one side wall portion and a flange portion extending from one of the side wall portions to be stretch flanged. Furthermore, by sandwiching the material on the top plate side between the punch and the pad and bringing the punch and the die close to each other, the other side wall portion and the flange portion extending from the other side wall portion can be bent and formed.

[0026] In addition, in the early stages of the drawing process in which the punch, cushion, pad, and die cooperate to draw one side wall portion and the flange portion extending from that side wall portion to be stretch flanged, the punch and die hardly bend the material on the other side wall portion side. Therefore, by pressing the cushion against the die with a pressure greater than or equal to the pressing force of the pad, the cushion pressure device can suppress the amount of material flowing into the punch on the one side wall portion to be stretch flanged, while allowing the material to flow from the other side wall portion side to the one side wall portion to be stretch flanged.

[0027] In addition, the pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, and the die and punch approach each other, thereby drawing one side wall portion and the flange portion extending from that side wall, and bending the other side wall portion and the flange portion extending from that side wall. Therefore, by drawing the one side wall portion and the flange portion extending from that side wall while receiving material from the other side wall portion to the one side wall, the elongation of the one side wall portion and the flange portion extending from that side wall is reduced, and the reduced elongation also reduces tensile residual stress. As a result, stretch cracking of the one side wall portion and the flange portion extending from that side wall can be reduced, and shape fixability can be improved.

[0028] Therefore, according to the present invention, a press mold can be provided that can improve shape fixability while reducing stretch cracking in a press part in which one side wall portion of a hat-shaped cross-sectional shape portion is bent in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion.

[0029] (5) In the press mold described in (4), The cushion includes a connecting portion disposed on an outer circumferential side of the flange forming portion, and the connecting portion and the wrinkle suppressor are connected in a ring shape surrounding the punch, The connecting portion or the die is characterized in that a distance block is attached to abut against a seat portion of the opposing die or a seat portion of the connecting portion.

[0030] In the present invention, the cushion includes a connecting portion disposed on the outer periphery of the flange-forming portion, and the connecting portion and the blank holder are connected in a ring shape surrounding the punch. The connecting portion or the die is fitted with a distance block that abuts against the seat of the opposing die or the seat of the connecting portion. Therefore, when the blank holder of the cushion and the die-forming portion of the die hold the material therebetween, the distance block attached to the connecting portion or the die can abut against the seat of the opposing die or the seat of the connecting portion. Therefore, when drawing one side wall portion and the flange portion extending from the one side wall portion, the cushion is prevented from tilting vertically relative to the punch, and the clearance between the blank holder of the cushion and the die-forming portion of the die can be maintained at a predetermined value. This can more stably reduce stretch cracking associated with drawing the one side wall portion and the flange portion extending from the one side wall portion, thereby improving shape fixability.

[0031] (6) In the press mold described in (4) or (5), The cushion pressure device is a fluid cylinder device in which a cylinder case is attached to the mold base of the punch and a cylinder rod that extends and retracts relative to the cylinder case presses the cushion, and is characterized by having a locking mechanism that stops the extension of the cylinder rod from the time press molding is completed until the pad separates from the top plate portion.

[0032] In the present invention, the cushion pressure device is a fluid cylinder device in which a cylinder case is attached to a punch die base and a cylinder rod that extends and retracts relative to the cylinder case presses the cushion. The device has a locking mechanism that stops the extension of the cylinder rod from the time press forming is completed until the pad separates from the top plate. Therefore, the pressed part can be released from the press die without deformation after press forming is completed, without using a die cushion pin with a locking mechanism of the press machine. Therefore, the press die can be installed in a general-purpose press machine that does not have a die cushion pin with a locking mechanism. This allows for increased productivity in press forming while maintaining the product precision of the pressed part after shape is frozen. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a press forming method and a press die for the same that can improve shape fixability while reducing stretch cracking in a press part in which one side wall portion of a hat-shaped cross-sectional shape portion is bent in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic perspective view of a pressed part formed by a press-molding method according to an embodiment of the present invention. [Figure 2] 2A and 2B are cross-sectional views of the press part shown in FIG. 1, in which (A) shows a C1-C1 cross-sectional view shown in FIG. 1, (B) shows a C2-C2 cross-sectional view shown in FIG. 1, and (C) shows a C3-C3 cross-sectional view shown in FIG. 1. [Figure 3] 2(A) are cross-sectional views of the essential part when the press part shown in FIG. 1 is press-formed to the cross section shown in FIG. 2(A), where (A) shows a cross-sectional view of the essential part during press-forming, and (B) shows a cross-sectional view of the essential part upon completion of press-forming. [Figure 4] 1A and 1B are distribution diagrams of the sheet thickness increase / decrease rate in region A of the press part shown in FIG. 1, where (A) shows a distribution diagram of the sheet thickness increase / decrease rate in region A when the flow of material from the other side wall side to one side wall side is prevented in the press forming method shown in FIG. 3, and (B) shows a distribution diagram of the sheet thickness increase / decrease rate in region A when the flow of material from the other side wall side to one side wall side is allowed in the press forming method shown in FIG. [Figure 5] 4A and 4B are cross-sectional views of essential parts of a first modified example of the press-forming method shown in FIG. 3, in which (A) shows a cross-sectional view of essential parts at the completion of press-forming in a first step in which the bending angle of the other side wall portion is formed to be small, and (B) shows a cross-sectional view of essential parts at the completion of press-forming in a second step in which the bending angle of the other side wall portion is formed to be the normal bending angle. [Figure 6] FIG. 4 is a plan view of a main part of a second modified example of the press-forming method shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view of a main part taken along the line DD shown in FIG. 6. [Figure 8] 2 is a cross-sectional view of a press die that press-forms the press part (C1-C1 cross section) shown in FIG. 1 at the start of forming. [Figure 9] FIG. 9 is a cross-sectional view of the press die shown in FIG. 8 during molding. [Figure 10] FIG. 9 is a cross-sectional view of the press die shown in FIG. 8 when molding is completed. [Figure 11] FIG. 9 is a cross-sectional view of the press die shown in FIG. 8 after the pressed part has been released. [Figure 12] FIG. 9 is a cross-sectional view of a modified example of the press die shown in FIG. 8 at the start of molding. [Figure 13] FIG. 13 is a cross-sectional view of the press die shown in FIG. 12 during molding. [Figure 14] 1A and 1B are cross-sectional views of a main part of a press part having a conventional hat-shaped cross-sectional shape, in which (A) shows a cross-sectional view of a main part in a press forming method using bending, and (B) shows a cross-sectional view of a main part of a bent press part after it has been released from the mold. [Figure 15] FIG. 1 is a plan view of the press molding method described in Patent Document 1. [Figure 16] FIG. 16 is a cross-sectional view of a main part during forming in the press forming method shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0035] Next, a press-forming method and a press die according to an embodiment of the present invention will be described in detail with reference to the drawings. First, a press part formed by the press-forming method according to the present embodiment and the press-forming method will be described, followed by a CAE analysis result of the plate thickness distribution state after press-forming. Next, a press die used in this press-forming method will be described.

[0036] <Pressed parts formed using this press molding method> First, a pressed part formed by the press-molding method according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 shows a schematic perspective view of a pressed part formed by the press-molding method according to this embodiment. Figure 2 shows cross-sectional views of the pressed part shown in Figure 1, where (A) shows the C1-C1 cross-sectional view shown in Figure 1, (B) shows the C2-C2 cross-sectional view shown in Figure 1, and (C) shows the C3-C3 cross-sectional view shown in Figure 1.

[0037] 1 and 2, a pressed part 10 formed by the press-forming method according to this embodiment has a hat-shaped cross-sectional portion 1 that is continuous in the longitudinal direction, and one side wall portion 11 of the hat-shaped cross-sectional portion 1 is curved in a direction that allows stretch flange forming at a curvature radius X1 that is greater than the curvature radius X2 of the other side wall portion 12. This pressed part 10 is used, for example, in floor members that constitute the body of an automobile, and in such cases, it is preferable to use a high-tensile steel sheet as the raw material W. For example, a high-tensile steel sheet having a tensile strength of 980 MPa or more can be used as the raw material W.

[0038] Here, one side wall 11 of the hat-shaped cross-sectional shape portion 1 is curved at a large curvature X1 in the direction of stretch flange forming, and the other side wall 12 is curved at a small curvature X2 in the direction of slight shrink flange forming, but this is not necessarily limited to this. The other side wall 12 may, for example, be curved at a small curvature X2 in the direction of slight stretch flange forming, or may extend in a substantially straight line. Note that the curvatures X1 and X2 are percentages of the reciprocals of the radii R1 and R2 that form the curved surfaces extended in the longitudinal direction of the side wall portions 11 and 12. If the side wall portions 11 and 12 are formed with curved surfaces of multiple curvatures X1 and X2, the curvatures X1 and X2 refer to the largest one.

[0039] The hat-shaped cross-sectional shape portion 1 also includes a top plate portion 13, side wall portions 11 and 12 that bend inward from both widthwise ends of the top plate portion 13, and flange portions 11H and 12H that bend outward from the tips of the side wall portions 11 and 12. In Figures 2(A) and 2(B), the other side wall portion 12 and flange portion 12H shown by solid lines are bent at a normal bending angle α0 relative to the top plate portion 13, while the other side wall portion 12a and flange portion 12Ha shown by imaginary lines are bent at a bending angle α that is smaller than the normal bending angle α0 relative to the top plate portion 13. This is formed in multiple steps, which will be described in detail in a modified example of this press forming method.

[0040] Furthermore, one side wall portion 11 is formed in region A, which is approximately half the longitudinal length of the top plate portion 13, and the other side wall portion 12 is formed in region B, which is the entire longitudinal length of the top plate portion 13, but the ranges of regions A and B are not necessarily limited to this. Also, as shown in Figure 2(C), the top plate portion 13 is bent outward at an obtuse angle θ at the midpoint in the longitudinal direction, resulting in a gentle warpage, but this warpage shape is not limited to this. Note that in this press forming method, which will be described later, region A is drawn and region B is bent.

[0041] <Press forming method> Next, the press-forming method according to this embodiment will be described with reference to Figures 1 to 3. Figure 3 shows cross-sectional views of the essential parts when the pressed part shown in Figure 1 is press-formed to the cross section shown in Figure 2(A), where (A) shows the cross-sectional view of the essential parts during press-forming, and (B) shows the cross-sectional view of the essential parts when press-forming is completed.

[0042] As shown in Figures 1 to 3, this press-forming method is a press-forming method for forming a press part 10 having a hat-shaped cross-sectional shape portion 1 continuous in the longitudinal direction, in which one side wall portion 11 of the hat-shaped cross-sectional shape portion 1 is curved in a direction that results in stretch flange forming at a curvature rate X1 that is greater than the curvature rate X2 of the other side wall portion 12.The press-forming method includes a punch 21, a cushion 22, a pad 23, a die 24, and a cushion pressure device 25.The pad 23 presses a material W against a top plate forming portion 213 of the punch 21, and the material W is sandwiched between the wrinkle holder 221 of the cushion 22 and the die forming portion 241 of the die 24.When the die 24 and the punch 21 approach each other, the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 are drawn and the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 are bent.

[0043] Here, the punch 21 has a top plate forming portion 213 that forms the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that forms the flange portion 12H extending from the other side wall portion 12. The cushion 22 is separated from the first side wall forming portion 211 of the punch 21 and has a wrinkle suppression portion 221 that forms the flange portion 11H extending from one side wall portion 11, and is formed to be movable up and down relative to the punch 21. At the start of forming, the cushion 22 is raised to a position where the wrinkle suppression portion 221 and the top plate forming portion 213 of the punch 21 are at approximately the same height. Therefore, simultaneously with or slightly after the pad 23 presses the material W against the top plate forming portion 213 of the punch 21, the material W is sandwiched between the wrinkle holder 221 of the cushion 22 and the die forming portion 241 of the die 24.

[0044] The pad 23 is configured to press the material W against the top plate forming portion 213 of the punch 21 with a predetermined pressing force P1. A pressing device 26 for the pad 23 is attached to a mold stand that supports the die 24. The die 24 faces the punch 21 and the cushion 22 and has a die forming portion 241 that is arranged along the outer periphery of the pad 23 and forms both side wall portions 11, 12 and both flange portions 11H, 12H. The cushion pressurizing device 25 is configured to press the cushion 22 against the die 24 with a pressing force P2 that is equal to or greater than the pressing force P1 of the pad 23. The cushion pressurizing device 25 is equipped with a locking mechanism that stops the operation (rising) of the cushion 22 from the time when press-forming is completed until the pad 23 separates from the top plate portion 13.

[0045] According to the above press forming method, in a press part 10 having a hat-shaped cross-sectional shape portion 1 that is continuous in the longitudinal direction, one side wall portion 11 of the hat-shaped cross-sectional shape portion 1 being bent in a direction that results in stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12, stretch cracking of one side wall portion 11 can be reduced while improving the ability to fix the shape into a normal shape.

[0046] That is, the punch 21 has a top plate forming portion 213 that forms the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that forms the flange portion 12H extending from the other side wall portion 12, a cushion 22 that is separated from the first side wall forming portion 211 and has a wrinkle suppression portion 221 that forms the flange portion 11H extending from one side wall portion 11 and is formed so as to be movable up and down relative to the punch 21, a pad 23 that presses the material W against the top plate forming portion 213 of the punch 21, and a pad that faces the punch 21 and the cushion 22 and The die 24 is disposed along the outer periphery of the pad 23 and has a die forming portion 241 that forms both side wall portions 11, 12 and both flange portions 11H, 12H, and a cushion pressurizing device 25 that presses the cushion 22 against the die 24 with a pressure P2 that is equal to or greater than the pressing force P1 of the pad 23. Therefore, the punch 21 and the pad 23 sandwich the material W on the top plate portion 13 side, and the cushion 22 and the die 24 sandwich the material W on one side wall portion 11 side, and the punch 21 and the die 24 come close to each other, thereby enabling one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 to be stretch-flanged. In addition, the punch 21 and the pad 23 sandwich the material W on the top plate portion 13 side, and the punch 21 and the die 24 come close to each other, enabling the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 to be bent.

[0047] Furthermore, in the early stages of the drawing process in which the punch 21, cushion 22, pad 23, and die 24 cooperate to draw one side wall 11 and the flange 11H extending from one side wall 11 to be stretch-flanged, the punch 21 and die 24 barely bend the material W on the other side wall 12. Therefore, by the cushion pressure device 25 pressing the cushion 22 against the die 24 with a pressure P2 equal to or greater than the pressing force P1 of the pad 23, the material W on the one side wall 11 to be stretch-flanged can be caused to flow from the other side wall 12 to the one side wall 11 to be stretch-flanged. Furthermore, by suppressing the amount of material W on the one side wall 11 flowing into the punch 21, the amount of stretch in the direction of stretch-flanging can also be suppressed.

[0048] Furthermore, the amount of material W flowing into the punch 21 and the amount of stretch in the direction of stretch flange forming are suppressed for one side wall 11 to be stretch flanged. By drawing one side wall 11 and the flange 11H extending from one side wall 11 while receiving material W from the other side wall 12 to one side wall 11, the elongation of one side wall 11 and the flange 11H extending from one side wall 11 is reduced, and the reduced elongation also reduces tensile residual stress. As a result, stretch cracking of one side wall 11 to be stretch flanged and the flange 11H extending from one side wall 11 can be reduced, and the shape can be fixed to the normal shape more easily.

[0049] Therefore, according to this press-forming method, it is possible to provide a press-forming method that can reduce stretch cracks in a press part 10 in which one side wall portion 11 of a hat-shaped cross-sectional shape portion 1 is bent in a direction that results in stretch flange forming at a curvature rate X1 that is greater than the curvature rate X2 of the other side wall portion 12, while improving shape fixability.

[0050] <Thickness distribution after press forming> Next, the results of CAE analysis of the thickness distribution after press forming will be explained using Fig. 4. Fig. 4 shows distribution maps of the thickness increase / decrease rate in region A of the press part shown in Fig. 1, where (A) shows the distribution map of the thickness increase / decrease rate in region A when the flow of material from the other side wall side to one side wall side is blocked in the press forming method shown in Fig. 3, and (B) shows the distribution map of the thickness increase / decrease rate in region A when the flow of material from the other side wall side to one side wall side is allowed in the press forming method shown in Fig. 3.

[0051] In Figure 4, the rate of thickness increase or decrease is displayed by the distribution density of dots. Areas with a high dot distribution density have a large rate of thickness decrease, and areas with a low dot distribution density have a large rate of thickness increase. Here, if the rate of thickness decrease exceeds 10%, it is determined that stretch cracking has occurred. The areas where stretch cracking has occurred are displayed in white. Furthermore, if the rate of thickness increase exceeds 10%, it is determined that wrinkles have occurred. Here, no wrinkles have occurred.

[0052] As shown in Figure 4(A), when the flow of raw material W from the other side wall portion 12 to one side wall portion 11 is prevented in the press-forming method shown in Figure 3, the thickness reduction rate exceeds 10% at multiple locations in region A of one side wall portion 11 (including the flange portion) to be stretch-flanged, and stretch cracks occur. In contrast, as shown in Figure 4(B), when the flow of raw material W from the other side wall portion 12 to one side wall portion 11 is allowed in the press-forming method shown in Figure 3, the thickness reduction rate does not exceed 10% in region A of one side wall portion 11 (including the flange portion) to be stretch-flanged, and stretch cracks do not occur.

[0053] Therefore, from the distribution of the sheet thickness increase / decrease rates shown in Figure 4, it can be inferred that this press-forming method can reduce stretch cracking and improve shape fixability in a press part 10 in which one side wall portion 11 of the hat-shaped cross-sectional shape portion 1 is bent in the direction of stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12.

[0054] <Modification of this press molding method> Next, modified examples of the press-forming method will be described with reference to Figures 5 to 7. Figure 5 is a cross-sectional view of a main part of a first modified example of the press-forming method shown in Figure 3, where (A) shows a cross-sectional view of the main part at the completion of press-forming in the first step of forming the other side wall portion into a smaller bending angle, and (B) shows a cross-sectional view of the main part at the completion of press-forming in the second step of forming the other side wall portion into a normal bending angle. Figure 6 shows a plan view of a main part of a second modified example of the press-forming method shown in Figure 3. Figure 7 shows a cross-sectional view of the main part in the DD cross section shown in Figure 6.

[0055] (First modified example of the present press forming method) This press-forming method can be modified in various ways without departing from the spirit of the present invention. For example, in a first modification of this press-forming method, as shown in Fig. 5, the other side wall portion 12 is formed so that its bending angle α relative to the top plate portion 13 is smaller than the normal bending angle α0, and is then formed to the normal bending angle α in a subsequent process.

[0056] Here, in a first process using a press die 20B shown in Fig. 5(A), one side wall portion 11 and a flange portion 11H extending from the one side wall portion 11 are drawn, and at the same time, the other side wall portion 12 is formed so that the bending angle α relative to the top plate portion 13 is smaller than the normal bending angle α0. In a second process using a press die 30 shown in Fig. 5(B), the other side wall portion 12 is formed so that the bending angle α relative to the top plate portion 13 is the normal bending angle α0.

[0057] The press die 20B of the first step, like the press die 20 used in the press-forming method described above, includes a punch 21B, a cushion 22, a pad 23, a die 24B, and a cushion pressurizing device 25. The punch 21B and the die 24B are formed along the other side wall portion 12a and flange portion 12Ha bent at a bending angle α with respect to the top plate portion 13. The press die 30 of the second step includes a punch 31 formed with a hat-shaped cross section, a pad 33 that presses the material W against the punch 31, and a die 32 that forms the other side wall portion 12 and its flange portion 12H.

[0058] In this case, when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are drawn, the other side wall portion 12 is drawn at a bending angle α relative to the top plate portion 13 that is smaller than the normal bending angle α0. Therefore, when drawing one side wall portion 11 and the flange portion 11H extending from one side wall portion 11, the material W on the other side wall portion 12 side can more easily pass through the gap between the pad 23 and the punch 21, allowing more material W to flow from the other side wall portion 12 side to the one side wall portion 11 side that will be stretch flanged. As a result, stretch cracking can be further reduced when drawing one side wall portion 11 and the flange portion 11H extending from one side wall portion 11, and shape fixability can be further improved.

[0059] (Second modified example of the present press forming method) In a second modification of the press-forming method, as shown in FIGS. 6 and 7, the pad 23 is divided into multiple sections (e.g., two sections) corresponding to a region Y1 in one sidewall portion 11 where the elongation rate β (β1) is high and a region Y2 in one sidewall portion 11 where the elongation rate β (β2) is low. The pressing force P11 of the pad 23a corresponding to the region Y1 where the elongation rate β (β1) is high is smaller than the pressing force P12 of the pad 23b corresponding to the region Y2 where the elongation rate β (β2) is low. Note that the press die 20C used in the second modification of the press-forming method includes different pad pressing devices 26a and 26b corresponding to the pressing forces P11 and P12. The pressing forces P11 and P12 of the pads 23a and 23b refer to the loads per unit area on the top plate forming portion 213 of the punch 21.

[0060] In this case, when drawing one side wall portion 11 and the flange portion 11H extending from one side wall portion 11, the pressing force P11 of the pad 23a becomes relatively small in the region Y1 where the elongation rate β1 (β) of stretch flange forming of one side wall portion 11 is large, so the frictional force of the raw material W sandwiched between the pad 23a and the top plate forming portion 213 of the punch 21 decreases, and the inflow amount γ1 of the raw material W flowing from the other side wall portion 12 to one side wall portion 11 can be further increased. Therefore, during drawing, stretch cracking of the one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 in the region Y1 where the elongation rate β1 (β) of stretch flange forming is high can be further reduced, and shape fixability can be further improved.

[0061] Furthermore, when drawing one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11, the pressing force P12 of the pad 23b becomes relatively large in a region Y2 where the elongation rate β2 (β) of the stretch flange forming of the one side wall portion 11 is small, and the frictional force of the raw material W sandwiched between the pad 23b and the top plate forming portion 213 of the punch 21 increases, thereby reducing the inflow amount γ2 of the raw material W flowing from the other side wall portion 12 to the one side wall portion 11. Therefore, deformation of the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 due to the inflow of the raw material W can be suppressed, and shape fixability can be improved.

[0062] <Main press mold> Next, a press die according to this other embodiment will be described with reference to Fig. 1 and Figs. 8 to 11. Fig. 8 shows a cross-sectional view of the press die that press-forms the press part (C1-C1 cross section) shown in Fig. 1 at the start of forming. Fig. 9 shows a cross-sectional view of the press die shown in Fig. 8 during forming. Fig. 10 shows a cross-sectional view of the press die shown in Fig. 8 at the completion of forming. Fig. 11 shows a cross-sectional view of the press die shown in Fig. 8 after the press part has been released.

[0063] As shown in FIGS. 1 and 8 to 11 , a press die 20 according to this other embodiment has a hat-shaped cross-sectional shape portion 1 that is continuous in the longitudinal direction, and one side wall portion 11 of the hat-shaped cross-sectional shape portion 1 is curved in a direction that results in stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12. a punch 21 having a top plate forming portion 213 that forms a top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that forms a flange portion 12H extending from the other side wall portion 12; a cushion 22 that is separated from the first side wall forming portion 211 and has a wrinkle suppression portion 221 that forms a flange portion 11H extending from one side wall portion 11, and is formed so as to be movable up and down relative to the punch 21; a pad 23 for pressing the material W against the top plate forming portion 213 of the punch 21; a die 24 having a die molding portion 241 disposed along the outer periphery of the pad 23 and facing the punch 21 and the cushion 22, and forming both side wall portions 11 and 12 and both flange portions 11H and 12H; a cushion pressurizing device 25 that presses the cushion 22 against the die 24 with a pressure P2 that is equal to or greater than the pressing force P1 of the pad 23; The pad 23 presses the material W against the top plate forming portion 213 of the punch 21, and the material W is sandwiched between the wrinkle holder 221 of the cushion 22 and the die forming portion 241 of the die 24, and the die 24 and the punch 21 come close to each other, thereby drawing and forming one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11, and bending and forming the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12.

[0064] Here, the punch 21, cushion 22, pad 23, die 24, and cushion pressure device 25 of this press mold 20 will be explained in detail, with the points that are common to those already explained in this press molding method being omitted, and the explanation will focus on the points that have not been explained in this press molding method.

[0065] The press die 20 includes a die base 28 that supports the punch 21 and a die base 29 that supports the die 24. The cushion pressure device 25 also includes a pressure pin 251 that presses the cushion 22 toward the die 24, and a support plate 252 that supports the pressure pin 251 so that it can move up and down.

[0066] The pressure pin 251 and the support plate 252 are housed in the die base 28 of the punch 21 so as to be movable up and down. A drop stopper 253 is attached to the die base 28 of the punch 21 to catch the support plate 252 when it is in a lowered position. The support plate 252 is formed to abut against the die cushion pin 3 of the press machine and transmit the pressure force of the die cushion pin 3 to the pressure pin 251. The pressure pin 251 has an enlarged head portion 251T, and when the support plate 252 is in the lowered position, the head portion 251T is housed in a seat 281 of the die base 28. The press machine is equipped with a locking mechanism that temporarily stops the die cushion pin 3 at its bottom dead center.

[0067] Furthermore, a steel bending blade 24M is inserted into the die 24 at a position of a die forming portion 241 that forms the other side wall portion 12 and a flange portion 12H extending from the other side wall portion 12. Furthermore, a pressing device 26 for the pad 23 that presses the pad 23 toward the punch 21 is attached to a mold stand 29 of the die 24. The pressing device 26 for the pad 23 is composed of, for example, a gas pressure cylinder whose cylinder rod 261 extends and contracts in the vertical direction from a cylinder case filled with nitrogen gas. Furthermore, the cylinder rod 261 of the pressing device 26 for the pad 23 is extended so that the pad 23 comes into contact with the material W before the die forming portion 241 at the start of forming.

[0068] The press die 20 operates as follows: First, as shown in Fig. 8, the die cushion pins 3 of the press machine are operated to raise the pressure pins 251 of the cushion pressure device 25 to their raised positions, and the wrinkle suppression portion 221 of the cushion 22 is moved to approximately the same height as the top plate forming portion 213 of the punch 21. Then, the material W is placed on the wrinkle suppression portion 221 and the top plate forming portion 213, and the die 24 and punch 21 are brought close to each other, whereby the pad 23 presses the material W against the top plate forming portion 213 of the punch 21 with a predetermined pressing force P1.

[0069] 9, the die 24 and the punch 21 are brought closer to each other, and the die forming portion 241 of the die 24 and the blank holder 221 of the cushion 22 hold the material W on one side wall 11 at a predetermined pressure P2, and then the one side wall 11 and the flange 11T extending from the one side wall 11 are drawn. At the initial stage of this drawing, the gap between the die forming portion 241 and the second side wall forming portion 212 and the flange forming portion 212H of the punch 21 is large, and the material W on the other side wall 12 is slightly bent. The pressure P2 with which the die forming portion 241 of the die 24 and the blank holder 221 of the cushion 22 hold the material W on one side wall 11 is greater than the pressure P1 with which the pad 23 presses the material W against the top plate forming portion 213 of the punch 21.

[0070] Therefore, the amount of material W flowing into the punch 21 on the one side wall 11 side to be stretch flanged can be suppressed, while the material W can be made to flow from the other side wall 12 side to the one side wall 11 side to be stretch flanged. Furthermore, by suppressing the amount of material W flowing into the punch 21 on the one side wall 11 side, the amount of stretch in the direction to be stretch flanged can also be suppressed.

[0071] 10, the die 24 and punch 21 are brought close to the bottom dead center to complete the drawing of region A consisting of one side wall portion 11 and the flange portion 11H extending from that side wall portion 11, and the bending of region B consisting of the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12. At this bottom dead center, the locking mechanism of the die cushion pins 3 of the press machine is activated to temporarily stop the upward movement.

[0072] 11, when the die 24 separates from the punch 21 and moves to the top dead center, the locking mechanism of the die cushion pin 3 is released, and the pressure pin 251 moves to the raised position. At this time, the cushion 22 releases the formed press part 10, which is in contact with the blank holder 221, from the punch 21. Note that by attaching a lift device 4 to the punch 21 and using the lift pins 41 of the lift device 4 to lift the flange 12H extending from the other side wall 12, the formed press part 10 can be released from the punch 21 in a well-balanced manner without deformation.

[0073] As described above, in this press die 20, the pad 23 presses the material W against the top plate forming portion 213 of the punch 21, and the die 24 and the punch 21 approach each other in a state in which the material W is sandwiched between the clamping portion 221 of the cushion 22 and the die forming portion 241 of the die 24, thereby drawing-forming one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11, and bending-forming the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12. Therefore, by drawing-forming one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 while receiving material W from the other side wall portion 12 side to the one side wall portion 11 side, the elongation rate of the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 is reduced, and the reduction in elongation rate also reduces tensile residual stress. As a result, stretch cracks in one side wall portion 11 and flange portion 11H extending from one side wall portion 11 that are stretch flanged can be reduced, and shape fixability can be improved.

[0074] Therefore, according to the present press die 20, it is possible to provide a press die 20 that can improve shape fixability while reducing stretch cracking in a press part 10 in which one side wall portion 11 of the hat-shaped cross-sectional shape portion 1 is bent in the direction of stretch flange forming at a curvature rate X1 that is greater than the curvature rate X2 of the other side wall portion 12.

[0075] 8 to 11, in the press die 20, the cushion 22 is provided with a connecting portion 222 arranged on the outer periphery of the flange forming portion 212H, the connecting portion 222 and the wrinkle suppressor 221 are connected in a ring shape surrounding the punch 21, and a distance block 27 is preferably attached to the connecting portion 222 or the die 24, and is in contact with the seat 242 of the opposing die 24 or the seat 223 of the connecting portion 222. Furthermore, it is preferable that the pressure positions (positions of the pressure pins 251) of the cushion pressure device 25 for the cushion 22 be provided at both the positions of the wrinkle suppressor 221 and the positions of the connecting portion 222.

[0076] In this case, with the blank W sandwiched between the clamping portion 221 of the cushion 22 and the die forming portion 241 of the die 24, the distance block 27 attached to the connecting portion 222 or the die 24 can abut against the opposing seat portion 242 of the die 24 or the seat portion 223 of the connecting portion 222. Therefore, when drawing-forming one side wall portion 11 and the flange portion 11H extending from one side wall portion 11, the cushion 22 is prevented from tilting in the vertical direction with respect to the punch 21, and the clearance between the clamping portion 221 of the cushion 22 and the die forming portion 241 of the die 24 can be maintained at a predetermined value. Therefore, stretch cracks caused by drawing-forming one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 can be more stably reduced, and shape fixability can be improved.

[0077] <Modifications of this press die> Next, a modified example of the press die will be described with reference to Figures 12 and 13. Figure 12 shows a cross-sectional view of the modified press die shown in Figure 8 at the start of molding. Figure 13 shows a cross-sectional view of the press die shown in Figure 12 during molding.

[0078] The press die 20 can be modified in various ways without departing from the spirit and scope of the present invention. For example, the cushion pressure device 25 described above includes pressure pins 251 that press the cushion 22 toward the die 24 and a support plate 252 that supports the pressure pins 251 so that the pressure pins 251 can move up and down. The support plate 252 is configured to abut against the die cushion pins 3 of the press machine and transmit the pressure force of the die cushion pins 3 to the pressure pins 251. However, the cushion pressure device 25 is not necessarily limited to this.

[0079] For example, as shown in Figures 12 and 13, the cushion pressure device 25D is a fluid cylinder device 25D in which a cylinder case 252D is attached to a mold stand 28D of a punch 21D and a cylinder rod 251D that extends and retracts relative to the cylinder case 252D presses against the cushion 22D, and may have a locking mechanism 25DR that stops the extension of the cylinder rod 251D from the time when press molding is completed until the pad 23 separates from the top plate portion 13.

[0080] In this case, the pressed part 10 can be released from the press die 20D after press forming is completed without deformation, without using die cushion pins 3 with locking mechanisms of the press machine. Therefore, the press die 20D can be installed in a general-purpose press machine that does not have die cushion pins 3 with locking mechanisms. This makes it possible to improve productivity in press forming while maintaining the product precision after the shape of the pressed part 10 is frozen.

[0081] Furthermore, by positioning the fluid cylinder device 25D in a balanced manner relative to the cushion 22D, it is possible to prevent the cushion 22 from tilting in the vertical direction relative to the punch 21 when squeezing one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11, and it is preferable to maintain the clearance between the wrinkle suppression portion 221 of the cushion 22 and the die forming portion 241 of the die 24 at a predetermined value.

[0082] As described above, the cushion 22D is provided with the connecting portion 222 arranged on the outer periphery of the flange forming portion 212H, and the connecting portion 222 and the blank holder 221D are connected in a ring shape surrounding the punch 21, and the connecting portion 222 or the die 24 may be fitted with a distance block 27 that abuts against the seat 242 of the opposing die 24 or the seat 223 of the connecting portion 222. In this case as well, the pressure position (position of the cylinder rod 251D) of the cushion pressure device 25D for the cushion 22D is preferably set at the position of the blank holder 221D and the position of the connecting portion 222. This makes it possible to more stably reduce stretch cracks that occur during drawing of one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11, thereby improving shape fixability.

[0083] <Action and effect> As described above in detail, according to the press forming method of this embodiment, punches 21, 21B, 21D each having a top plate forming portion 213 that forms the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that forms the flange portion 12H extending from the other side wall portion 12, are used. cushions 22, 22D having wrinkle suppression portions 221, 221D and formed to be movable up and down relative to the punches 21, 21B, 21D; pads 23, 23C for pressing the material W against the top plate forming portions 213 of the punches 21, 21B, 21D; dies 24, 24B facing the punches 21, 21B, 21D and the cushions 22, 22D and disposed along the outer periphery of the pads 23, 23C and having die forming portions 241 for forming both side wall portions 11, 12 and both flange portions 11H, 12H; and a cushion pressure device 25, 25D for pressing the cushion 22, 22D against the die 24, 24B with a pressure P2 equal to or greater than the pressing force P1 of the pad 23, 23C. The pad 23, 23C presses the material W against the top plate forming portion 213 of the punch 21, 21B, 21D, and the die 24, 24B and the punch 21, 21B, 21D approach each other in a state where the material W is sandwiched between the wrinkle holder 221 of the cushion 22, 22D and the die forming portion 241 of the die 24, 24B. The flange portion 11H extending from one side wall portion 11 is drawn, and the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 are bent. This reduces stretch cracking of one side wall portion 11 in the press part 10, which has a hat-shaped cross-sectional shape portion 1 that is continuous in the longitudinal direction and is bent in a direction that results in stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12, while improving the shape preservability into a normal shape.

[0084] That is, punches 21, 21B, 21D each having a top plate forming portion 213 for forming the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 for forming one side wall portion 11, a second side wall forming portion 212 for forming the other side wall portion 12, and a flange forming portion 212H for forming the flange portion 12H extending from the other side wall portion 12, cushions 22, 22D each having a wrinkle suppression portion 221 separated from the first side wall forming portion 211 and for forming the flange portion 11H extending from one side wall portion 11 and formed to be movable up and down relative to the punches 21, 21B, 21D, pads 23, 23C for pressing the material W against the top plate forming portion 213 of the punches 21, 21B, 21D, and pads 23, 23C facing the punches 21, 21B, 21D and the cushions 22, 22D. The die 24, 24B is arranged along the outer peripheral edge of die 3C and has a die forming portion 241 that forms both side wall portions 11, 12 and both flange portions 11H, 12H, and a cushion pressure device 25, 25D that presses the cushion 22, 22D against the die 24, 24B with a pressure P2 that is greater than or equal to the pressing force P1 of the pad 23, 23C.Therefore, the punch 21, 21B, 21D and the pad 23, 23C clamp the material W on the top plate portion 13 side, and the cushion 22, 22D and the die 24, 24B clamp the material W on one side wall portion 11 side, while the punch 21, 21B, 21D and the die 24, 24B come close to each other, thereby allowing one side wall portion 11 to be stretch flanged and the flange portion 11H extending from one side wall portion 11 to be draw-formed. In addition, punches 21, 21B, 21D and pads 23, 23C clamp the material W on the top plate portion 13 side, and punches 21, 21B, 21D and dies 24, 24B come close to each other, thereby enabling the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 to be bent and formed.

[0085] Furthermore, in the early stages of drawing the one side wall 11 to be stretch-flanged and the flange 11H extending from the one side wall 11 by cooperation of the punches 21, 21B, 21D, cushions 22, 22D, pads 23, 23C, and dies 24, 24B, the punches 21, 21B, 21D, and dies 24, 24B hardly bend the material W on the other side wall 12. Therefore, by the cushion pressure devices 25, 25D pressing the cushions 22, 22D against the dies 24, 24B with a pressure P2 that is equal to or greater than the pressing force P1 of the pads 23, 23C, the amount of material W on the one side wall 11 to be stretch-flanged that flows into the punch 21 is suppressed, while the material W can flow from the other side wall 12 into the one side wall 11 to be stretch-flanged.

[0086] In addition, the pads 23 and 23C press the material W against the top plate forming portions 213 of the punches 21, 21B, and 21D, and the dies 24 and 24B and the punches 21, 21B, and 21D approach each other in a state where the material W is sandwiched between the wrinkle holders 221 of the cushions 22 and 22D and the die forming portions 241 of the dies 24 and 24B. As a result, one side wall portion 11 and a flange portion 11H extending from one side wall portion 11 are drawn and formed, and the other side wall portion 11 is drawn and formed. 2 and the flange portion 12H extending from the other side wall portion 12 are bent. Therefore, by drawing the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 while receiving a supply of material W from the other side wall portion 12 to the one side wall portion 11, the elongation of the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 is reduced, and the reduced elongation also reduces the tensile residual stress. As a result, stretch cracking of the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 that is stretch flanged can be reduced, and the shape fixability into the normal shape can be improved.

[0087] Therefore, according to this embodiment, a press forming method can be provided that can reduce stretch cracks in a press part 10 in which one side wall portion 11 of a hat-shaped cross-sectional shape portion 1 is bent in a direction that results in stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12, while improving shape fixability.

[0088] Furthermore, according to this embodiment, the other side wall portion 12 is formed so that the bending angle α relative to the top plate portion 13 is smaller than the normal bending angle α0 and is then formed to the normal bending angle α in a subsequent process. Therefore, when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are draw-formed, the other side wall portion 12 is formed so that the bending angle α relative to the top plate portion 13 is smaller than the normal bending angle α0. Therefore, when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are draw-formed, the material W on the other side wall portion 12 side can more easily pass through the gap between the pad 23 and the top plate forming portion 213 of the punch 21B, allowing more material W to flow from the other side wall portion 12 side to the one side wall portion 11 side that will be stretch-flanged. As a result, it is possible to further reduce stretch cracks that may occur when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are draw-formed, and it is possible to further improve the shape fixability.

[0089] Furthermore, according to this embodiment, pad 23C is divided into multiple parts corresponding to the region Y1 in one side wall portion 11 where the elongation rate β (β1) of stretch flange forming is large and the region Y2 where the elongation rate β (β2) is small, and the pressing force P11 of pad 23a corresponding to the region Y1 where the elongation rate β (β1) is large is smaller than the pressing force P12 of pad 23b corresponding to the region Y2 where the elongation rate β (β2) is small. Therefore, when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are squeeze-formed, the inflow amount γ1 of material W flowing from the other side wall portion 12 side to one side wall portion 11 side can be further increased in the region Y1 in one side wall portion 11 where the elongation rate β1 (β) is large. Therefore, during drawing, stretch cracks in one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 in the region Y1 where the elongation rate β1 (β) of stretch flange forming is large can be further reduced, and shape fixability can be further improved.

[0090] Furthermore, when one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 are draw-formed, the pressing force P12 of the pad 23b becomes relatively large in the region Y2 where the elongation rate β2 (β) of the one side wall portion 11 is small, so that the inflow amount γ2 of the raw material W flowing from the other side wall portion 12 to the one side wall portion 11 can be reduced. Therefore, deformation of the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 due to the inflow of the raw material W can be suppressed, and shape fixability can be improved.

[0091] According to the press dies 20, 20B, 20C, and 20D of this other embodiment, punches 21, 21B, and 21D each have a top plate forming portion 213 that forms the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that forms the flange portion 12H extending from the other side wall portion 12; and punches 21, 21B, and 21D each have a top plate forming portion 213 that forms the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 that forms one side wall portion 11, a second side wall forming portion 212 that forms the other side wall portion 12, and a flange forming portion 212H that is separated from the first side wall forming portion 211 and forms the flange portion 11H extending from one side wall portion 11. cushions 22, 22D having wrinkle suppression portions 221 for pressing the blank W against the top plate forming portions 213 of the punches 21, 21B, 21D and formed to be movable up and down relative to the punches 21, 21B, 21D; pads 23, 23C for pressing the blank W against the top plate forming portions 213 of the punches 21, 21B, 21D; dies 24, 24B facing the punches 21, 21B, 21D and the cushions 22, 22D and arranged along the outer periphery of the pads 23, 23C and having die forming portions 241 for forming both side wall portions 11, 12 and both flange portions 11H, 12H; and a cushion pressure device 25, 25D for pressing the cushion 22, 22D against the die 24, 24B with a pressure P2 equal to or greater than the pressing force P1 of the pad 23, 23C, and the cushion 22, 22D presses the material W against the top plate forming portion 213 of the punch 21, 21B, 21D, and the die 24, 24B and the punch 21, 21B, 21D come close to each other in a state where the material W is sandwiched between the wrinkle holder 221 of the cushion 22, 22D and the die forming portion 241 of the die 24, 24B. The flange portion 11H extending from one side wall portion 11 is drawn, and the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 are bent. This reduces stretch cracking of one side wall portion 11 in the press part 10, which has a hat-shaped cross-sectional shape portion 1 that is continuous in the longitudinal direction and is bent in a direction that results in stretch flange forming at a curvature rate X1 that is larger than the curvature rate X2 of the other side wall portion 12, while improving the ability to fix the shape into a normal shape.

[0092] That is, punches 21, 21B, 21D each having a top plate forming portion 213 for forming the top plate portion 13 having a hat-shaped cross section, a first side wall forming portion 211 for forming one side wall portion 11, a second side wall forming portion 212 for forming the other side wall portion 12, and a flange forming portion 212H for forming the flange portion 12H extending from the other side wall portion 12, cushions 22, 22D each having wrinkle suppression portions 221, 221D separated from the first side wall forming portion 211 and forming the flange portion 11H extending from one side wall portion 11 and formed to be movable up and down relative to the punches 21, 21B, 21D, pads 23, 23C for pressing the material W against the top plate forming portions 213 of the punches 21, 21B, 21D, and pads 23, 23C facing the punches 21, 21B, 21D and the cushions 22, 22D. The die 24, 24B is arranged along the outer peripheral edges of the pads 23, 23C and has a die forming portion 241 that forms both side wall portions 11, 12 and both flange portions 11H, 12H, and a cushion pressure device 25, 25D that presses the cushion 22, 22D against the die 24, 24B with a pressure P2 that is equal to or greater than the pressing force P1 of the pads 23, 23C.Therefore, the punch 21, 21B, 21D and the pad 23, 23C clamp the material W on the top plate portion 13 side, and the cushion 22, 22D and the die 24, 24B clamp the material W on one side wall portion 11 side, while the punch 21, 21B, 21D and the die 24, 24B come close to each other, thereby allowing the one side wall portion 11 to be stretch flanged and the flange portion 11H extending from the one side wall portion 11 to be draw-formed. In addition, punches 21, 21B, 21D and pads 23, 23C clamp the material W on the top plate portion 13 side, and punches 21, 21B, 21D and dies 24, 24B come close to each other, thereby enabling the other side wall portion 12 and the flange portion 12H extending from the other side wall portion 12 to be bent and formed.

[0093] Furthermore, in the early stages of drawing the one side wall 11 to be stretch-flanged and the flange 11H extending from the one side wall 11 by cooperation of the punches 21, 21B, 21D, cushions 22, 22D, pads 23, 23C, and dies 24, 24B, the punches 21, 21B, 21D, and dies 24, 24B hardly bend the material W on the other side wall 12. Therefore, by the cushion pressure devices 25, 25D pressing the cushions 22, 22D against the dies 24, 24B with a pressure P2 that is equal to or greater than the pressing force P1 of the pads 23, 23C, the material W on the one side wall 11 to be stretch-flanged can be made to flow from the other side wall 12 to the one side wall 11 to be stretch-flanged while suppressing the amount of material W flowing into the punches 21, 21B, 21D.

[0094] In addition, the pads 23 and 23C press the material W against the top plate forming portions 213 of the punches 21, 21B, and 21D, and the dies 24 and 24B and the punches 21, 21B, and 21D approach each other in a state where the material W is sandwiched between the wrinkle holders 221 of the cushions 22 and 22D and the die forming portions 241 of the dies 24 and 24B. As a result, one side wall portion 11 and a flange portion 11H extending from one side wall portion 11 are drawn and formed, and the other side wall portion 11 is drawn and formed. 2 and the flange portion 12H extending from the other side wall portion 12 are bent. Therefore, by drawing the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 while receiving a supply of material W from the other side wall portion 12 to the one side wall portion 11, the elongation of the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 is reduced, and the reduced elongation also reduces the tensile residual stress. As a result, stretch cracking of the one side wall portion 11 and the flange portion 11H extending from the one side wall portion 11 that is stretch flanged can be reduced, and the shape fixability into the normal shape can be improved.

[0095] Therefore, according to this other embodiment, it is possible to provide press dies 20, 20B, 20C, and 20D that can improve shape fixability while reducing stretch cracking in a press part 10 in which one side wall portion 11 of a hat-shaped cross-sectional shape portion 1 is bent in a direction that results in stretch flange forming at a curvature rate X1 that is greater than the curvature rate X2 of the other side wall portion 12.

[0096] Furthermore, according to this other embodiment, the cushion 22 is provided with a connecting portion 222 arranged on the outer periphery of the flange forming portion 212H, and the connecting portion 222 and the wrinkle suppression portion 221 are connected in a ring shape surrounding the punch 21, and a distance block 27 is attached to the connecting portion 222 or the die 24, 24B, which abuts against the seat portion 242 of the opposing die 24, 24B or the seat portion 223 of the connecting portion 222.Therefore, when the wrinkle suppression portion 221 of the cushion 22 and the die forming portion 241 of the die 24, 24B clamp the material W, the distance block 27 attached to the connecting portion 222 or the die 24, 24B can abut against the seat portion 242 of the opposing die 24, 24B or the seat portion 223 of the connecting portion 222. Therefore, when one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 are draw-formed, the cushion 22 is prevented from tilting in the vertical direction relative to the punches 21, 21B, and the clearance between the wrinkle holder 221 of the cushion 22 and the die forming portion 241 of the dies 24, 24B can be maintained at a predetermined value. Therefore, stretch cracks that occur during the draw-formation of one side wall portion 11 and the flange portion 11H extending from one side wall portion 11 can be more stably reduced, and shape fixability can be improved.

[0097] Furthermore, according to this other embodiment, the cushion pressure device 25D is a fluid cylinder device 25D in which a cylinder case 252D is attached to the die base 28D of the punch 21D, and a cylinder rod 251D that extends and retracts relative to the cylinder case 252D presses the cushion 22D. The fluid cylinder device 25D includes a locking mechanism 25DR that stops the extension of the cylinder rod 251D from the time press molding is completed until the pad 23 separates from the top plate portion 13. This allows the pressed part 10 to be released from the press die 20D after press molding is completed without deformation, without using die cushion pins 3 with locking mechanisms of the press machine. Therefore, the press die 20D can be installed in a general-purpose press machine that does not have die cushion pins 3 with locking mechanisms. This allows for increased productivity in press molding while maintaining the product precision of the pressed part 10 after the shape is frozen. [Industrial Applicability]

[0098] The present invention can be used as a press molding method and a press mold for molding a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction, and one side wall portion of the hat-shaped cross-sectional shape portion is curved in a direction that results in stretch flange forming at a curvature greater than the curvature of the other side wall portion. [Explanation of symbols]

[0099] 1 Hat-shaped cross-sectional section 10 Pressed parts 11, 12, 12a Side wall part 11H, 12H, 12Ha flange 13 Top plate 20, 20B, 20C, 20D press molds 21, 21B, 21D Punch 22, 22D cushion 23, 23C, 23a, 23b pads 24, 24B die 25, 25D cushion pressure device 25D Fluid Cylinder Device 25DR locking mechanism 27 Distance Block 28, 28D type stand 211 1st side wall molding part 212 2nd side wall molding part 213 Top plate molding section 212H flange forming part 221, 221D Wrinkle holding part 222 Connecting part 223 Seat area 241 Die forming section 242 Seat area 251D Cylinder Rod 252D Cylinder Case P1, P11, P12 pressing force P2 pressure W material X1, X2 Curvature Y1, Y2 area α, α0 bending angle β, β1, β2 elongation rate

Claims

1. A press die for forming a press part having a hat-shaped cross-sectional shape portion that is continuous in the longitudinal direction, one side wall portion of the hat-shaped cross-sectional shape portion being curved in a direction that becomes stretch flange forming at a curvature rate that is greater than the curvature rate of the other side wall portion, a punch having a top plate forming portion that forms a top plate portion having a hat-shaped cross section, a first side wall forming portion that forms the one side wall portion, a second side wall forming portion that forms the other side wall portion, and a flange forming portion that forms a flange portion extending from the other side wall portion; a cushion having a wrinkle suppressor portion that is separated from the first side wall molding portion and forms a flange portion extending from one of the side wall portions, and that is formed to be movable up and down relative to the punch; a pad that presses the material against the top plate forming portion of the punch; a die having die molding portions disposed along an outer peripheral edge of the pad and facing the punch and the cushion, the die molding portions forming the side wall portions and the flange portions; a cushion pressurizing device that presses the cushion against the die with a pressure equal to or greater than the pressing force of the pad, the die and the punch approach each other in a state in which the pad presses the material against the top plate forming portion of the punch, and the material is sandwiched between the wrinkle holder of the cushion and the die forming portion of the die, thereby drawing-forming the one side wall portion and the flange portion extending from the one side wall portion, and bending-forming the other side wall portion and the flange portion extending from the other side wall portion; The cushion includes a connecting portion disposed on an outer circumferential side of the flange forming portion, and the connecting portion and the wrinkle suppressor are connected in a ring shape surrounding the punch, A press mold characterized in that a distance block is attached to the connecting portion or the die, and abuts against the seat portion of the opposing die or the seat portion of the connecting portion.

2. The press die according to claim 1, The cushion pressure device is a fluid cylinder device in which a cylinder case is attached to the mold base of the punch and a cylinder rod that extends and retracts relative to the cylinder case presses the cushion, and the press mold is characterized in that it has a locking mechanism that stops the extension of the cylinder rod from the time press molding is completed until the time the pad separates from the top plate portion.

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