Manufacturing method for press-formed products
The method addresses cracking and positioning issues in press-formed products by rearranging pilot pins and pads in the press-forming die, enhancing material movement and reducing mold complexity for improved yield and defect-free manufacturing.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2025-06-23
- Publication Date
- 2026-05-19
AI Technical Summary
Existing methods for manufacturing press-formed products using high-tensile materials face issues such as cracking due to reduced elongation, complex mold structures, and difficulties in blank positioning, especially when forming parts with small vertical wall portions.
A method involving a press-forming die with rearranged pilot pins and pads to facilitate material movement from the top plate to the vertical wall portions, using a punch and die setup with pilot pins positioned to avoid the stretch flange area and employing a deeper vertical wall forming surface for one vertical wall portion to initiate forming before the other.
Reduces the risk of elongation flange cracking, simplifies mold structure, and improves yield by enabling easy blank positioning and material supply, resulting in defect-free press-formed products.
Smart Images
Figure 0007861896000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a press-formed product having a top plate portion extending in the longitudinal direction and a pair of vertical wall portions provided on both sides in the width direction of the top plate portion, and having an extended flange portion that becomes an extended flange forming on one of the vertical wall portions.
Background Art
[0002] In recent years, in order to achieve both improved collision safety and weight reduction of automobile bodies, the application of high-tensile materials of 590 MPa or more to body structure parts has been progressing. Since high-tensile materials tend to have reduced elongation, forming defects such as cracking become an issue in performing press forming.
[0003] Among press-formed products used in automobile parts, there are parts having a U-shaped cross-section with a top plate portion extending in the longitudinal direction and a pair of vertical wall portions formed on both sides in the longitudinal direction of the top plate portion. In such parts, when the punch shoulder ridge line portion connecting the top plate portion and the vertical wall portion is curved so as to be concave in a top view, the forming of the vertical wall portion formed in that portion becomes extended flange forming. Therefore, when manufacturing parts as described above by press-forming a metal plate, cracking is likely to occur at the punch shoulder portion of the curved portion and the lower end of the vertical wall portion. In particular, when press-forming ultra-high-tensile materials, the elongation of the material decreases, so the occurrence of cracking becomes more prominent.
[0004] Many methods for suppressing such extended flange cracking have been proposed conventionally. For example, Patent Document 1 discloses a method for manufacturing a press part having a hat cross-section and an L-shaped shape that is curved in the longitudinal direction in a top view. In the method of Patent Document 1, the inner side of the curve is first bent and then the outer side of the curve is drawn to suppress extended flange cracking.
[0005] Patent Document 2 discloses a method for manufacturing a part in which a part of the outer peripheral edge is curved so as to be concave. In the method described in Patent Document 2, stretch flange cracking is suppressed by delaying the timing of the completion of molding of the vertical wall portion continuous with the concave outer edge portion compared to the timing of the completion of molding of the vertical wall portions on both sides of that vertical wall portion. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] WO2018 / 003755 publication [Patent Document 2] Japanese Patent Publication No. 2023-130636 [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] The method described in Patent Document 1 may result in high production costs due to the complex mold structure. The method described in Patent Document 2 involves forming the concave vertical wall portion by dividing the vertical wall portion continuous with the concave outer edge into a concave vertical wall portion and the vertical wall portions on both sides of the concave vertical wall portion into side vertical wall portions, thereby dispersing the strain generated in the concave vertical wall portion. Therefore, if the width of the side vertical wall portions is small, the strain may not be sufficiently dispersed, and stretch flange cracking may occur.
[0008] Furthermore, when mass-producing parts, it is common practice to provide pilot pins in the mold to facilitate blank positioning, but Patent Documents 1 and 2 do not mention pilot pins. If pilot pins are not provided in the mold, positioning the blanks will take time, making mass production difficult, and the blanks may become unstable, potentially leading to sporadic cracking.
[0009] The present invention was made to solve the above-mentioned problems, and aims to provide a method for manufacturing press-formed products that has a simple mold structure, allows for easy blank positioning, and can suppress stretch flange cracking even in press-formed products where the width of the vertical wall portion other than the stretch flange portion is small. [Means for solving the problem]
[0010] (1) A method for manufacturing a press-formed product according to the present invention is a method for manufacturing a press-formed product having a top plate portion extending in the longitudinal direction and a pair of vertical wall portions provided on both sides of the top plate portion in the width direction, wherein a part of one of the punch shoulder ridges connecting one of the vertical wall portions and the top plate portion is curved in a recessed manner, thereby creating a stretch flange portion on one of the vertical wall portions, and the press-formed product is manufactured using a press-forming die comprising a punch, a die, and a plurality of pilot pins for holding a blank on the top plate forming surface of the punch, When the portion of the top plate corresponding to the extension flange portion is designated as the top plate extension flange corresponding portion, The plurality of pilot pins are arranged on one side, avoiding the portion corresponding to the extension flange of the top plate, and not straddling the portion corresponding to the extension flange of the top plate in the longitudinal direction of the top plate. The method is characterized by enabling the movement of material from the top plate portion of the blank to one of the vertical wall portions, thereby forming the press-formed product.
[0011] (2) Furthermore, in the case described in (1) above, a pad is provided in the area where the pilot pin is located, which cooperates with the punch to clamp the blank.
[0012] (3) Furthermore, in the present invention, the height of the vertical wall forming surface portion for forming one of the vertical wall portions having the stretch flange portion in the press forming die is made deeper than the height of the vertical wall forming surface portion for forming the other vertical wall portion, so that the forming of one of the vertical wall portions begins before the forming of the other vertical wall portion. [Effects of the Invention]
[0013] In the present invention, by arranging the pilot pins, which were conventionally arranged on both sides across the corresponding part of the top plate extension flange, so as not to cross the corresponding part of the top plate extension flange, it is possible to transfer the material from the corresponding part of the top plate of the blank to the corresponding part of one vertical wall, and thus a press-molded product can be formed. As a result, the risk of elongation flange cracking in the press-molded product can be greatly reduced, and a press-molded product without molding defects can be manufactured, contributing to an improvement in yield.
Brief Description of the Drawings
[0014] [Figure 1] It is a plan view of a blank according to Embodiment 1. [Figure 2] It is an explanatory view of a press molding die used in Embodiment 1, and is a view corresponding to the A-A' cross section of FIG. 3. [Figure 3] It is a plan view of a punch and a pad used in Embodiment 1. [Figure 4] It is the FEM analysis result when the manufacturing method of the press-molded product according to Embodiment 1 is used. [Figure 5] It is a view for explaining the mechanism by which elongation flange cracking is suppressed in the manufacturing method of the press-molded product according to Embodiment 1. [Figure 6] It is a plan view of a punch and a pad used in Embodiment 2. [Figure 7] It is the FEM analysis result when the manufacturing method of the press-molded product according to Embodiment 2 is used. [Figure 8] It is a view for explaining the mechanism by which elongation flange cracking is suppressed in the manufacturing method of the press-molded product according to Embodiment 2. [Figure 9] It is an explanatory view of a press molding die used in Embodiment 3. [Figure 10] It is the FEM analysis result when the manufacturing method of the press-molded product according to Embodiment 3 is used. [Figure 11] It is a view for explaining the mechanism by which elongation flange cracking is suppressed in the manufacturing method of the press-molded product according to Embodiment 3 (Part 1). [Figure 12] It is a diagram (part 2) for explaining the mechanism by which elongation flange cracking is suppressed in the method for manufacturing a press-formed product according to Embodiment 3. [Figure 13] It is an explanatory diagram of the press-formed product to be manufactured in Embodiments 1 to 3. [Figure 14] It is a diagram for explaining a press mold when manufacturing the press-formed product of FIG. 13 by a conventional method. [Figure 15] It is a plan view of a blank according to the conventional method. [Figure 16] It is a result of FEM analysis when using the conventional method. [Figure 17] It is a diagram for explaining the mechanism by which elongation flange cracking occurs in the conventional method.
Embodiments for Carrying Out the Invention
[0015] [Embodiment 1] In the method for manufacturing a press-formed product according to Embodiment 1 of the present invention, the press-formed product 1 to be manufactured is shown in FIG. 13. FIGS. 13(a) to 13(c) are a perspective view, a top view, and a side view of the press-formed product 1. As shown in FIGS. 13(a) to 13(c), the press-formed product 1 is a component having a top plate portion 3 extending in the longitudinal direction and a pair of vertical wall portions (first vertical wall portion 5, second vertical wall portion 7) provided on both sides in the width direction of the top plate portion 3, and having a U-shaped cross section. The first vertical wall portion 5 corresponds to one vertical wall portion of the present invention, and the second vertical wall portion 7 corresponds to the other vertical wall portion of the present invention. As shown in FIGS. 13(b) and 13(c), the press-formed product 1 has a shape that is curved in a top view and upwardly warped in a side view.
[0016] A first punch shoulder ridge line portion 9 connecting the first vertical wall portion 5 and the top plate portion 3 is curved so that a part thereof is recessed inward in a plan view. Thereby, the forming of the first vertical wall portion 5 becomes elongation flange forming. On the other hand, the second punch shoulder ridge 11 connecting the second vertical wall 7 and the top plate 3 is curved such that a portion of it protrudes outward in a plan view. As a result, the second vertical wall 7 is formed using shrink flange forming. Thus, press-formed product 1 is a part manufactured by forming that involves stretch flange forming and shrink flange forming. Since the second punch shoulder ridge 11 has a gentle curve, the shrinkage flange forming of the second vertical wall 7 can be ignored, and in the following explanation, only the stretching flange forming of the first vertical wall 5 will be described.
[0017] Before describing the manufacturing method for press-formed products according to this embodiment, we will explain a conventional general manufacturing method for producing parts such as press-formed product 1, and the problems associated with this manufacturing method. As mentioned above, when mass-producing press-formed products 1, it is common practice to provide pilot pins in the mold to facilitate blank positioning. Therefore, the following explanation will use the case of manufacturing press-formed products 1 with a mold equipped with pilot pins as an example. In conventional manufacturing methods, a press-formed product 1 is produced by bending a blank 13, which is a metal sheet, using a press-forming die 31 as shown in Figure 14.
[0018] The press forming die 31 includes a punch 15 and a die 17 that cooperate with each other to form the blank 13 into a press-formed product 1, a pad 19 that cooperates with the punch 15 to hold the blank 13, and a pilot pin 21 attached to the upper surface of the punch 15 (the top forming surface 15a, which will be described later). Note that in Figure 14, only the shapes of the upper surface of the punch 15 and the lower surface of the die 17 are shown in order to make the shapes of the forming surfaces of the punch 15 and die 17 easier to understand. The molding surfaces of the punch 15 and die 17 will be described in detail in the embodiments described later.
[0019] The pad 19 is formed to be substantially the same shape as the top plate forming surface 15a of the punch 15, and by sandwiching the portion of the blank 13 that will become the top plate portion 3 (hereinafter referred to as the top plate equivalent portion) between the pad 19 and the punch 15, molding defects of the top plate portion 3 are suppressed. In particular, in the case of a part having an upward curved shape, such as the press-formed product 1, it is preferable to use the pad 19 to suppress wrinkles that occur on the top plate portion 3.
[0020] Two pilot pins 21 are provided on the top forming surface 15a of the punch 15. The pilot pins 21 position the blank 13 at a predetermined location on the punch 15 and are members that hold the blank 13 on the top forming surface 15a of the punch 15 so that the blank 13 does not shift during forming. The blank 13 has two pilot holes 23 (see Figures 14 and 15) that correspond to the pilot pins 21. By inserting the pilot pins 21 into these pilot holes 23 and setting the blank 13 in the punch 15, the positioning of the blank 13 is easily completed, and the blank 13 is held in place by the top forming surface 15a of the punch 15. From the viewpoint of positioning the blank 13 and preventing misalignment during molding, two or more pilot pins 21 are usually provided.
[0021] In conventional construction methods, it is common to place one pilot pin 21 on each side of the portion of the top plate 3 in the longitudinal direction of the top plate 3 so as to avoid the portion of the top plate 3 that is continuous with the curved portion of the first punch shoulder ridge 9 (see Figure 15). Although not shown in Figure 14, pilot holes into which pilot pins 21 are inserted are provided in the pad 19 and die 17 as needed.
[0022] In the conventional manufacturing method using the press molding die 31 as described above, the punch 15 is positioned on the lower side and the die 17 on the upper side, facing each other, and the two pilot pins 21 attached to the punch 15 are inserted into the pilot holes 23 of the blank 13 to set the blank 13 on the punch 15. This ensures that the top plate portion of the blank 13 is correctly set on the top plate forming surface portion 15a of the punch 15. Subsequently, a pad 19 is placed on the blank 13, and the die 17 is lowered while the blank 13 is held between the punch 15 and the pad 19, thereby bending the blank 13 and forming it into the shape of the press-formed product 1.
[0023] Figure 16 shows the results of a finite element method (FEM) analysis of the plate thickness change rate of the first vertical wall section 5 when the press-formed product 1 is manufactured using this conventional method. For the analysis, the blank 13 was a metal plate of the 1470 MPa class, and the length L of the press-formed product 1 was set to 500 mm, the width W to 140 mm, and the height H to 60 mm (see Figure 13). The target plate thickness change rate (plate thickness change rate at which the risk of elongation flange cracking is considered low) when using 1470MPa material is -6.5%.
[0024] As shown in Figure 16, the FEM analysis revealed a significant reduction in plate thickness at the lower end of the first vertical wall section 5, specifically at the lower end of the portion continuous with the curved section of the first punch shoulder ridge. The maximum plate thickness change rate at this time was -6.8%, raising concerns about elongation flange cracking.
[0025] The factors causing stretch flange cracking when manufacturing press-formed product 1 using conventional methods will be explained using Figure 17. Figure 17 shows the molding process when a blank 13 is formed into a press-formed product 1 using a press molding die 31. The values such as "bottom dead center 50mm up" in the figure indicate the distance until the die 17 reaches the molding bottom dead center. When the die 17 is lowered while the top plate portion of the blank 13 is held between the punch 15 and the pad 19, the die 17 comes into contact with the blank 13, and deformation of the blank 13 begins as shown in Figure 17(b).
[0026] Further lowering the die 17 advances the forming of the first vertical wall portion 5 and the second vertical wall portion 7. At this time, as indicated by the arrows in Figures 17(c) and 17(d), the portion of the first vertical wall portion 5 that is continuous with the curved portion of the first punch shoulder ridge portion 9 is deformed as if being pulled to the left and right (stretch flange deformation). This deformation causes the material in that portion to be stretched, reducing the plate thickness and resulting in cracking. Hereafter, the portion where the plate thickness decreases due to this elongation flange deformation will be referred to as the elongation flange portion 5a.
[0027] The inventors reasoned that the placement of the pilot pin 21 in the top plate portion of the blank 13 made it difficult for the material in the top plate portion to move. If the pilot pin 21 were not provided in the mold, the material in the top plate portion would move, making it easier to supply material to the first vertical wall portion 5 and suppressing the reduction in plate thickness of the stretch flange portion 5a. However, in that case, positioning the blank 13 would take more time, making mass production of parts difficult. Therefore, the inventor conceived of changing the position of the pilot pin 21 used in the conventional press molding die 31, thereby enabling the positioning of the blank 13 while promoting the movement of the material in the top plate equivalent portion, making it easier to supply material to the stretch flange portion 5a. The present invention is based on the above findings and will be described in detail below based on specific embodiments.
[0028] The method for manufacturing a press-formed product according to this embodiment 1 uses the punch 15, die 17, pad 19, and pilot pin 21 of a conventional press molding die 31 shown in Figure 14, but only the arrangement of the pilot pin 21 is changed from the conventional general arrangement.
[0029] The press molding die 25 used in the manufacturing method of this embodiment will be described in more detail with reference to Figures 1 to 3. Figure 1 is a top view of the blank 13 in the state where it is set on the pilot pin 21. Figure 2 is a diagram corresponding to the AA' cross-section in Figure 3, and Figure 3 is a top view of the blank 13 and punch 15 at the bottom dead center of forming. The pad 19 is not shown in Figure 2, and the area where the pad 19 is placed is indicated by a black line in Figure 3.
[0030] As shown in Figure 2, the punch 15 includes a top plate forming surface 15a for forming the top plate portion 3 of the press-formed product 1, a first vertical wall forming surface 15b for forming the first vertical wall portion 5, and a second vertical wall forming surface 15c for forming the second vertical wall portion 7. Similarly, the die 17 also includes a top plate molding surface 17a, a first vertical wall molding surface 17b, and a second vertical wall molding surface 17c, all shaped to correspond to the molding surfaces of the punch 15. The height Hi of the first vertical wall forming surfaces 15b and 17b corresponds to the height of the first vertical wall 5 of the press-formed product 1, and the height Ho of the second vertical wall forming surfaces 15c and 17c corresponds to the height of the second vertical wall 7 of the press-formed product 1. Since both the first vertical wall 5 and the second vertical wall 7 have a height of H, Hi = Ho (≒H).
[0031] As shown in Figure 3, the pad 19 is formed to be substantially the same shape as the top plate forming surface 15a of the punch 15, and is positioned to clamp the entire top plate-equivalent portion of the blank 13. The punch 15, die 17, and pad 19 described above are the same as those in the conventional press molding die 31 described above.
[0032] Here, the portion of the top plate portion 3 corresponding to the extension flange portion 5a of the first vertical wall portion 5 is defined as the top plate extension flange corresponding portion 3a. The top plate extension flange corresponding portion 3a can be defined as follows. First, the stretch flange portion 5a is set to include the part where the plate thickness decreases the most when press-formed product 1 is formed using a conventional method (the portion with the greatest plate thickness reduction). Specifically, the stretch flange portion 5a is defined as the range in which the plate thickness change rate exceeds a predetermined value. The above predetermined values can be set as appropriate, but here, the range in which the plate thickness change rate is 90% or more of the maximum plate thickness change rate (-6.8%) is defined as the elongated flange portion 5a. The rate of change in plate thickness when press-formed product 1 is formed using a conventional method may be determined by FEM analysis, or it may be determined from press-formed product 1 actually manufactured by press forming.
[0033] Next, as shown by the white dashed lines A1 and B1 attached to the first vertical wall portion 5 in Figure 16, lines are drawn from both ends of the extended flange portion 5a in the longitudinal direction of the part toward the first punch shoulder ridge portion 9. The dashed lines A1 and B1 should be perpendicular to the tangent at the intersection with the lower end edge of the first vertical wall portion 5.
[0034] Next, draw lines from the upper ends of dashed lines A1 and B1 toward the second punch shoulder ridge section 11, as shown by the white dashed lines A2 and B2 on the top plate section 3 in Figure 16. It is preferable that the dashed lines A2 and B2 are perpendicular to the tangent lines at the intersection with the first punch shoulder ridge section. The area between the dashed lines A2 and B2 drawn as described above will be designated as the top plate extension flange corresponding area 3a. Furthermore, the parts of the top plate portion 3 other than the top plate extension flange corresponding portion 3a, that is, the parts on both sides of the top plate extension flange corresponding portion 3a in the longitudinal direction of the component, are designated as the top plate non-extension flange corresponding portions 3b and 3c. When the top plate portion 3 is viewed from above, the portion 3a corresponding to the top plate extension flange, the portions 3b and 3c corresponding to the top plate non-extension flange, and the dashed lines A2 and B2 that form the boundary between them are as shown in Figure 13(b).
[0035] As described above, when the portion of the top plate 3 corresponding to the extension flange portion 5a is designated as the top plate extension flange compatible portion 3a, it was conventional to place one pilot pin 21 each in the top plate non-extension flange compatible portion 3b and the top plate non-extension flange compatible portion 3c, straddling the top plate extension flange compatible portion 3a (see Figures 13 to 15).
[0036] In contrast, in this embodiment, as shown in Figures 1 and 3, the pilot pin 21 is positioned on one side while avoiding the top plate extension flange corresponding portion 3a, and without straddling the top plate extension flange corresponding portion 3a in the longitudinal direction of the top plate portion 3. Specifically, no pilot pins 21 are placed in the top plate extension flange corresponding portion 3a and the top plate non-extension flange corresponding portion 3c, while two pilot pins 21 are placed in the top plate non-extension flange corresponding portion 3b.
[0037] Figure 4 shows the results of an FEM analysis performed under the same analysis conditions as in Figure 16 regarding the rate of change in the plate thickness of the first vertical wall portion 5 when the press-formed product 1 is manufactured with the pilot pins 21 arranged as described above. As shown in Figure 4, in the manufacturing method of this embodiment, the maximum plate thickness change rate of the stretched flange portion 5a was -6.0%, and the reduction in plate thickness was suppressed compared to before the position of the pilot pin 21 was changed (Figure 16). In other words, by simply changing the position of the pilot pin 21, it was possible to suppress the elongation flange deformation of the first vertical wall portion 5a.
[0038] The mechanism by which the expansion flange deformation can be suppressed by changing the position of the pilot pin 21 will be explained using Figure 5. Figure 5 shows the molding process when the blank 13 is formed into a press-formed product 1 using a press molding die 25. When the die 17 is lowered while the top plate portion of the blank 13 is held between the punch 15 and the pad 19, the die 17 comes into contact with the blank 13, and the forming of the first vertical wall portion 5 begins, as shown in Figure 5(b).
[0039] In molding involving stretch flange forming, when the molding of the first vertical wall portion 5 having the stretch flange portion 5a begins, the material of the portion corresponding to the top plate attempts to move toward the portion that will become the first vertical wall portion (hereinafter referred to as the first vertical wall portion). However, conventionally, pilot pins 21 were placed in the non-stretch flange corresponding parts 3b and 3c of the top plate, which suppressed material movement in these areas.
[0040] In contrast, in this embodiment, both pilot pins 21 are positioned in the non-stretch flange compatible portion 3b of the top plate, thereby enabling material movement in the non-stretch flange compatible portion 3c of the top plate. Therefore, as molding progresses as shown in Figures 5(b) to 5(d), the material in the non-stretch flange corresponding portion 3c of the top plate moves in the direction of the arrow in the figure, and material is supplied to the first vertical wall portion. This makes it easier to supply material to the stretch flange portion 5a, and suppresses the reduction in plate thickness of the stretch flange portion 5a.
[0041] In this embodiment, an example is shown in which two pilot pins 21 are placed in the non-extension flange compatible portion 3b of the top plate and no pilot pins 21 are placed in the non-extension flange compatible portion 3c of the top plate. However, the present invention is not limited to this, and two pilot pins 21 may be placed on the non-extension flange compatible portion 3c side of the top plate and no pilot pins 21 may be placed in the non-extension flange compatible portion 3b of the top plate. In this case as well, the material in the non-stretch flange portion 3b of the top plate portion can move more easily toward the first vertical wall portion, so that material can be supplied to the stretch flange portion 5a more easily than in the conventional method, and the reduction in plate thickness of the stretch flange portion 5a can be suppressed.
[0042] As described above, the effects of the present invention can be expected regardless of whether the pilot pin 21 is placed in the non-stretch flange portion 3b or the non-stretch flange portion 3c of the top plate. However, in the case of a part having a straight portion (a portion where the shape of the top plate portion 3 is linear), such as the example press-formed product 1, it is more preferable to provide the pilot pin 21 in the straight portion. The reason for this is as follows. In the non-stretch flange portion 3b of the press-formed product 1, both the first punch shoulder ridge portion 9 and the second punch shoulder ridge portion 11 are straight, and the shape of the part in that portion is linear. Even without the pilot pin 21, it is thought that material movement in the top plate portion would be difficult during molding in such straight sections.
[0043] On the other hand, in the non-extended flange portion 3c of the top plate, the second punch shoulder ridge portion 11 has a gently curved shape, so it is considered that the material of the portion corresponding to the top plate is likely to move in the direction of the inward curve of the second punch shoulder ridge portion 11, that is, toward the portion corresponding to the first vertical wall. Therefore, by placing a pilot pin in the non-stretch flange-compatible section 3b of the top plate, where material movement is expected to be small, material movement becomes possible in the non-stretch flange-compatible section 3c of the top plate, where material movement is large, and more material is supplied to the section corresponding to the first vertical wall.
[0044] In this embodiment, an example is shown in which two pilot pins 21 are provided, but the number of pilot pins 21 is not particularly limited and may be three or more. From the viewpoint of promoting material movement, one pilot pin 21 may suffice, but from the viewpoint of positioning the blank 13 and preventing misalignment during molding, it is desirable to provide multiple pilot pins 21. Furthermore, even when three or more pilot pins 21 are provided, the pilot pins 21 are arranged on one side while avoiding the top plate extension flange compatible area 3a and without crossing over the top plate extension flange compatible area 3a. Specifically, all pilot pins are arranged in either the top plate non-extension flange compatible area 3b or the top plate non-extension flange compatible area 3c, and no pilot pins 21 are placed in the top plate extension flange compatible area 3a.
[0045] As described above, according to the manufacturing method of press-formed products of this embodiment, by arranging the pilot pin 21 in only one of the top plate non-stretch flange corresponding portion 3b or the top plate non-stretch flange corresponding portion 3c, material movement from the top plate equivalent portion of the blank 13 to the first vertical wall equivalent portion is made possible, thereby forming the press-formed product 1. Therefore, since press-molded products 1 without molding defects can be manufactured using conventional punches 15 and dies 17 of a general shape, equipment costs can be reduced and yield can be improved.
[0046] Furthermore, while Patent Document 2, mentioned above, disperses the strain generated in the stretch flange portion by starting the formation of the vertical wall portion from a portion other than the stretch flange portion, in this case, if the width of the portion other than the stretch flange portion is small, there is a possibility that the strain will not be sufficiently dispersed and stretch flange cracking cannot be suppressed. In this regard, the method of this embodiment is expected to be effective in the above case as well, since the material for the top plate portion is supplied to the first vertical wall portion during the molding process.
[0047] Although this embodiment describes an example using pad 19, pad 19 is not essential, and the present invention can also be applied to press forming performed without pad.
[0048] In this embodiment, the portion of the top plate 3 that does not straddle the pilot pin 21 was defined by starting from the extension flange portion 5a and setting the top plate extension flange corresponding portion 3a in correspondence with it. However, although the extension flange portion 5a is at the lower end of the first vertical wall portion 5, the first vertical wall portion 5 is continuous with the top plate portion 3 via the first punch shoulder ridge portion 9 and is closely related to the shape of the top plate portion 3. Therefore, a portion corresponding to the top plate extension flange corresponding portion 3a may be set based on the shape of the top plate portion 3. For example, the curved portion of the first punch shoulder ridge portion 9 in the top plate portion 3, specifically the region from one R-end to the other R-end in the curved portion, is defined as the top plate curved portion, and this top plate curved portion is defined as a portion that does not cross the pilot pin 21, similar to the top plate extension flange corresponding portion 3a. The boundary lines on both sides of the curved top plate can be determined by drawing perpendicular lines toward the second punch shoulder ridge section 11 to the tangent lines passing through one of the R-end points and the other R-end point.
[0049] [Embodiment 2] The method for manufacturing a press-formed product according to this second embodiment involves performing press forming with a smaller arrangement range for the pad 19 than in the first embodiment. The punch 15 and die 17 used in Embodiment 2 are the same as those in Embodiment 1 (see Figure 2), and the arrangement of the pilot pins 21 is also the same as in Embodiment 1. Figure 6 shows the arrangement range of the pad 19 in the press molding die 27 used in this embodiment.
[0050] As described above, the conventional method and Embodiment 1 involved using a pad 19 having the same shape as the top plate forming surface 15a of the punch 15, and pressing the entire top plate-equivalent portion of the blank 13.
[0051] In contrast, in this embodiment, as shown in Figure 6, the pad 19 is placed in the area where the pilot pin 21 is located (top plate non-stretch flange corresponding area 3b), and the pad 19 is not placed in the areas where the pilot pin 21 is not located (top plate stretch flange corresponding area 3a, top plate non-stretch flange corresponding area 3c), and press forming is performed by clamping only the top plate non-stretch flange corresponding area 3b of the top plate equivalent portion of the blank 13.
[0052] Figure 7 shows the results of an FEM analysis performed under the same analysis conditions as in Figure 4 regarding the rate of change in the plate thickness of the first vertical wall portion 5 when the pad 19 is arranged as described above and a press-formed product is manufactured. As shown in Figure 7, in the manufacturing method of this embodiment using the press molding die 27, the maximum plate thickness change rate of the stretched flange portion 5a was -4.2%, which further suppressed the reduction in plate thickness compared to Embodiment 1, in which the pad 19 was arranged to sandwich the entire portion equivalent to the top plate. In other words, by placing pads only in the area where the pilot pin 21 is located, and not in other areas, it was found that the elongation flange deformation of the first vertical wall portion 5 can be further suppressed.
[0053] The mechanism by which stretch flange deformation can be suppressed by reducing the placement range of pad 19 will be explained using Figure 8. Figure 8 shows the molding process when the blank 13 is formed into a press-formed product 1 using the press molding die 27. When the die 17 is lowered while the punch 15 and pad 19 are gripping only the portion 3b corresponding to the non-stretch flange of the top plate of the blank 13, the die 17 comes into contact with the blank 13, and the forming of the first vertical wall portion 5 begins, as shown in Figure 8(b).
[0054] As mentioned above, when the molding of the first vertical wall section 5 begins, the material of the non-stretch flange corresponding portion 3c of the top plate section attempts to move in the direction of the arrow in the figure. In Embodiment 1, since the pilot pin 21 was not placed in the non-stretch flange corresponding portion 3c of the top plate, there was no suppression of material movement by the pilot pin 21. However, since the non-stretch flange corresponding portion 3c of the top plate was held by the pad 19, there was suppression of material movement by the pad 19.
[0055] In this respect, in this embodiment, since the non-stretch flange-compatible portion 3c of the top plate is not held in place by the pad 19, there is no suppression of material movement by the pad 19, and the material is even easier to move than in Embodiment 1. Therefore, as molding progresses as shown in Figures 8(b) to 8(d), the material in the non-stretch flange corresponding portion 3c of the top plate moves in the direction of the arrow in the figure, and more material is supplied to the first vertical wall portion 5. This makes it easier to supply material to the stretch flange portion 5a, further suppressing the reduction in plate thickness of the stretch flange portion 5a.
[0056] The above is an example where the pilot pin 21 is placed on the non-extension flange compatible area 3b of the top plate, but the same applies when the pilot pin 21 is placed on the non-extension flange compatible area 3c of the top plate. That is, when the pilot pin 21 is placed on the non-extension flange compatible area 3c of the top plate, the pad 19 is placed only on the non-extension flange compatible area 3c of the top plate, and the pad 19 is not placed on the extension flange compatible area 3a and the non-extension flange compatible area 3b of the top plate. Also in this case, since the material of the portion corresponding to the top plate 3b of the top plate non - elongation flange in the top plate equivalent portion easily moves toward the first vertical wall portion 5, the elongation flange deformation of the first vertical wall portion 5 can be further suppressed compared to the embodiment 1 in which the pads 19 are arranged over the entire top plate equivalent portion.
[0057] As described above, according to the manufacturing method of the press - formed product according to this embodiment, by arranging the pads 19 so as to sandwich only the portion where the pilot pins 21 are arranged, the reduction in the plate thickness of the elongation flange portion 5a can be further suppressed compared to the embodiment 1.
[0058] [Embodiment 3] The manufacturing method of the press - formed product according to this embodiment 3 performs press - forming by making the heights of the first vertical wall forming surfaces 15b and 17b of the punch 15 and the die 17 deeper than the heights of the second vertical wall forming surfaces 15c and 17c. Note that the arrangement of the pilot pins 21 is the same as that in the embodiment 1, and the arrangement range of the pads 19 is the same as that in the embodiment 2. A cross - sectional view of the press - forming die 29 used in this embodiment is shown in FIG. 9.
[0059] When the heights of the first vertical wall portion 5 and the second vertical wall portion 7 are the same, generally, the heights Hi of the first vertical wall forming surfaces 15b and 17b of the punch 15 and the die 17 and the heights Ho of the second vertical wall forming surfaces 15c and 17c are also set to be the same (see FIG. 2). And that height is not set to be excessively deeper than the height of the product shape, but is set to be about the same height. Therefore, in the punch 15 and the die 17 used in the conventional example, the embodiment 1, and the embodiment 2 of FIG. 14, as described above, Hi = Ho (≈H). If the heights of the first vertical wall portion 5 and the second vertical wall portion 7 are different, the height of the die is set according to the higher one. That is, when the height of the first vertical wall portion 5 is H1 and the height of the second vertical wall portion 7 is H2, when H1 < H2, Hi = Ho (≈H2), and when H1 > H2, Hi = Ho (≈H1).
[0060] In contrast, as shown in Figure 9, this embodiment sets the height Ho of the second vertical wall forming surfaces 15c and 17c to be approximately the same as the height H of the press-formed product 1, as in the conventional method (Ho ≈ H), and sets the height Hi of the first vertical wall forming surfaces 15b and 17b to be deeper than the height Ho of the second vertical wall forming surfaces 15c and 17c (Hi > Ho) before press forming is performed.
[0061] Figure 10 shows the results of an FEM analysis of the plate thickness change rate of the first vertical wall portion 5 when a press-formed product 1 is manufactured using the press-forming die 29 described above, under the same analysis conditions as in Figures 4 and 7. As shown in Figure 10, in the manufacturing method of this embodiment using the press forming die 29, the maximum plate thickness change rate of the stretched flange portion 5a was -3.6%, which further suppressed the plate thickness reduction compared to Embodiment 2 where Hi=Ho. In other words, the result showed that by setting Hi > Ho, the elongation flange deformation of the first vertical wall portion 5 can be further suppressed.
[0062] The mechanism by which extension flange deformation can be suppressed by setting Hi > Ho will be explained using Figures 11 and 12. Figures 11 and 12 show the state of the press molding die 29 and the blank 13 during the molding process when the blank 13 is formed into a press-formed product 1 using the press molding die 29, specifically the state of the press molding die 29 and the blank 13 when the molding of the first vertical wall portion 5 begins. Figure 11 is a cross-sectional view corresponding to AA' in Figure 3, and Figure 12 is a top view showing the state of the blank 13 at the time of Figure 11.
[0063] When the die 17 is lowered while the punch 15 and pad 19 are gripping the non-stretch flange-corresponding portion 3b of the blank 13 corresponding to the top plate, the first vertical wall forming surface portion 17b of the die 17 contacts the blank 13 before the second vertical wall forming surface portion 17c. As a result, as shown in Figures 11 and 12, the forming of the first vertical wall portion 5 begins before the forming of the second vertical wall portion 7.
[0064] In this regard, in the case of Hi=Ho, as shown in Figure 5, the forming of the first vertical wall portion 5 and the forming of the second vertical wall portion 7 begin simultaneously. Therefore, when forming the first vertical wall portion 5, the material for the portion that will become the second vertical wall portion (hereinafter referred to as the second vertical wall equivalent portion) is sandwiched between the second vertical wall forming surfaces 15c and 17c of the punch 15 and die 17, making it difficult for the material for the second vertical wall equivalent portion to move.
[0065] In contrast, in this embodiment, when the molding of the first vertical wall portion 5 begins, the material of the portion corresponding to the second vertical wall is not sandwiched between the second vertical wall molding surfaces 15c and 17c, so the material of the portion corresponding to the second vertical wall is more easily moved than in Embodiment 2. Therefore, the materials for the top plate portion and the second vertical wall portion are in a state where they can move in the direction of the arrows shown in Figure 12, and the amount of material supplied to the first vertical wall portion increases. This makes it easier to supply material to the stretch flange portion 5a, further suppressing the reduction in plate thickness of the stretch flange portion 5a.
[0066] In this embodiment, the pad 19 is placed only in the area where the pilot pin is located, but the present invention is not limited to this, and the pad 19 may be placed to clamp the entire top plate portion, or the pad 19 may not be used at all.
[0067] Furthermore, while embodiments 1 to 3 were described using the example of manufacturing the press-formed product 1 shown in Figure 13, the press-formed products targeted by the present invention are not limited to this. The present invention is also effective for press-formed products of other shapes, as long as the product has a top plate portion extending in the longitudinal direction and a pair of vertical wall portions provided on both sides of the top plate portion in the width direction, and one of the punch shoulder ridges is curved in a recessed manner, thereby giving the other vertical wall portion an extended flange portion. For example, the present invention can also be applied to the manufacture of a hat-shaped cross-section component having a pair of flange portions continuous with the lower end of the vertical wall portion.
[0068] Furthermore, although the first punch shoulder ridge portion 9 of the example press-formed product 1 was curved in a concave manner in part and straight in other parts, other parts may be gently curved. That is, a part of the first punch shoulder ridge portion 9 may be curved with a bending radius x, and other parts may be curved with a bending radius greater than x. Furthermore, although the second punch shoulder ridge portion 11 of the example press-formed product 1 was gently curved in the same direction as the first punch shoulder ridge portion 9, the second punch shoulder ridge portion 11 may also be straight. [Examples]
[0069] We conducted specific verification tests to confirm the improvement in moldability by the press-molded product manufacturing method according to the present invention, and the results are described below.
[0070] (Example 1) In this embodiment 1, the press-formed product 1 shown in Figure 13 was used as the manufacturing target, and the maximum rate of change in the thickness of the first vertical wall portion 5 was determined by changing the position of the pilot pin 21, the arrangement range of the pad 19, and the height Hi of the first vertical wall forming surfaces 15b and 17b of the punch 15 and die 17 using FEM analysis. The dimensions of press-formed product 1 were a length L of 500 mm, a width W of 140 mm, and a height H of 60 mm. For the analysis, the blank was set to a steel plate with a thickness of t=1.4 mm and a tensile strength of 1470 MPa. As mentioned above, the target plate thickness change rate when using 1470MPa material is -6.5%. The experimental results in this embodiment are shown in Table 1.
[0071] [Table 1]
[0072] Table 1, No. 1, is a comparative example corresponding to the conventional construction method explained in Figure 14. In No. 1, the pilot pins 21 were placed one each in the top plate non-stretch flange compatible area 3b and top plate non-stretch flange compatible area 3c, the placement range of the pad 19 was set to the entire top plate, and the analysis was performed with the Hi and Ho values of the punch 15 and die 17 being the same. In analysis No. 1, the rate of change in plate thickness at the stretched flange portion 5a was -6.8%, which fell short of the target of -6.5%.
[0073] No. 2 is an example of the invention corresponding to Embodiment 1 described above. In No. 2, the pilot pins 21 were placed in the non-extension flange-compatible area 3b of the top plate, the placement range of the pads 19 was set to the entire top plate, and the Hi and Ho values of the punch 15 and die 17 were set to be the same for the analysis. In the analysis of No. 2, the rate of change in plate thickness at the stretched flange portion 5a was -6.0%, which suppressed the reduction in plate thickness more than in No. 1, thus achieving the target.
[0074] No. 3 is an example of the invention corresponding to Embodiment 2 described above. In No. 3, the pilot pins 21 were placed in the non-stretch flange area 3b of the top plate, the placement range of the pads 19 was limited to the non-stretch flange area 3b of the top plate, and the analysis was performed with Hi and Ho of the punch 15 and die 17 being the same. In the analysis of No. 3, the rate of change in plate thickness at the stretched flange portion 5a was -4.2%, indicating that the reduction in plate thickness was suppressed even further than in No. 2.
[0075] Examples No. 4 to No. 6 are examples of the invention corresponding to Embodiment 3 described above. In No. 4, the pilot pins 21 were placed in the non-stretch flange area 3b of the top plate, the placement range of the pads 19 was limited to the non-stretch flange area 3b of the top plate, and the Hi of the punch 15 and die 17 was made 20 mm deeper than Ho for the analysis. In No. 5, the Hi was made 40 mm deeper than Ho for the analysis, and in No. 6, the Hi was made 60 mm deeper than Ho for the analysis. In the analysis of No. 4 to No. 6, increasing the depth of Hi in punch 15 and die 17 suppressed the reduction in plate thickness of the elongation flange portion 5a, and in No. 6, it was reduced to -3.5%.
[0076] As described above, in this embodiment 1, it was confirmed that the reduction in plate thickness of the stretch flange portion 5a can be suppressed by placing the pilot pin 21 only in the non-stretch flange portion 3b of the top plate. Furthermore, in addition to the above, it was confirmed that by limiting the placement range of the pad 19 to only the non-stretch flange compatible area 3b of the top plate, the reduction in plate thickness of the stretch flange area 5a can be further reduced. Furthermore, in addition to the above, it was confirmed that the reduction in plate thickness of the stretched flange portion 5a can be further suppressed by making the height Hi of the first vertical wall molded surface portions 15b and 17b deeper than the height Ho of the second vertical wall molded surface portions 15c and 17c.
[0077] (Example 2) In the case of the press-formed product 1 shown in Figure 13, it is common to use a pad 19 during press forming to suppress wrinkles in the top plate portion 3 caused by the upward curvature. However, depending on the shape of the press-formed product, press forming may be performed without using the pad 19. Therefore, in this second embodiment, we investigated the effects of the present invention when press forming is performed without using a pad.
[0078] In this second embodiment, the target of production was a press-formed product (not shown) that had the same shape as press-formed product 1 in Figure 13 when viewed from above, and no upward curvature when viewed from the side. Using FEM analysis, the position of the pilot pin and the height Hi of the first vertical wall forming surface of the punch and die were changed to determine the maximum rate of change in the first vertical wall. As mentioned above, no pads were placed. The dimensions of the press-formed product were set to a length L of 500 mm, a width W of 140 mm, and a height H of 60 mm. For the analysis, the blank was set to a steel plate with a thickness of t=1.4 mm and a tensile strength of 1470 MPa. As mentioned above, the target plate thickness change rate when using 1470MPa material is -6.5%. The experimental results in this example are shown in Table 2.
[0079] [Table 2]
[0080] Table 2, No. 11, is a comparative example that corresponds to the conventional construction method. In No. 11, the pilot pins were positioned one on each side of the top plate in the non-extended flange area, and the analysis was performed with the Hi and Ho values of the punch and die being the same. In the analysis of No. 11, the rate of change in plate thickness at the stretched flange portion was -4.0%.
[0081] No. 12 is an example of the invention corresponding to Embodiment 1. In No. 12, the pilot pins were arranged in a configuration of two in the non-extended flange area of one side of the top plate, and the analysis was performed with the Hi and Ho values of the punch and die being the same. In the analysis of No. 12, the rate of change in plate thickness at the stretched flange portion was -3.8%, indicating that the reduction in plate thickness was suppressed compared to No. 11.
[0082] No. 13 is an example of the invention corresponding to Embodiment 3. In No. 13, two pilot pins were placed in the non-extended flange area of one side of the top plate, and the punch and die Hi were made 40 mm deeper than Ho for the analysis. In the analysis of No. 13, the rate of change in plate thickness at the stretched flange portion was -3.6%, indicating that the reduction in plate thickness was suppressed even further than in No. 12.
[0083] As described above, in this Example 2, which investigated molding without using a pad, both the comparative example and the inventive example achieved the target rate of change in sheet thickness. However, it was confirmed that the inventive example could suppress the reduction in sheet thickness even more effectively than the comparative example. Furthermore, even in molding without using pads, it was confirmed that the reduction in plate thickness at the stretched flange portion can be further reduced by making the height Hi of the first vertical wall molding surface deeper than the height Ho of the second vertical wall molding surface. [Explanation of Symbols]
[0084] 1 Press-formed product 3. Top panel 3a Area compatible with top plate extension flange 3b Non-extension flange compatible area on top panel 3c Top panel non-extension flange compatible area 5 First vertical wall section 5a Stretch flange portion 7 Second vertical wall section 9. First punch shoulder ridge section 11. Second punch shoulder ridge section 13 Blank 15 punches 15a Top plate molding surface part 15b 1st vertical wall molding surface part 15c 2nd vertical wall molding surface part 17 Dies 17a Top plate molding surface part 17b 1st vertical wall molding surface part 17c 2nd vertical wall molding surface part 19 pads 21 Pilot Pins 23 pilot holes 25 Press molding die (Embodiment 1) 27 Press molding die (Embodiment 2) 29 Press molding die (Embodiment 3) 31. Press molding die (conventional)
Claims
1. A method for manufacturing a press-formed product, comprising a punch, a die, and a plurality of pilot pins for holding a blank on the top-formed surface of the punch, wherein the press-formed product has a top plate portion extending in the longitudinal direction and a pair of vertical wall portions provided on both sides of the top plate portion in the width direction, and a portion of one of the punch shoulder ridges connecting one of the vertical wall portions and the top plate portion is curved in a recessed manner, thereby creating an elongated flange portion on one of the vertical wall portions, the press-formed product having an elongated flange portion, the press-formed product being manufactured using a press-forming die comprising a punch, a die, and a plurality of pilot pins for holding a blank on the top-formed surface of the punch, When the portion of the top plate corresponding to the extension flange portion is designated as the top plate extension flange corresponding portion, The plurality of pilot pins are arranged on one side, avoiding the portion corresponding to the extension flange of the top plate, and not straddling the portion corresponding to the extension flange of the top plate in the longitudinal direction of the top plate. A method for manufacturing a press-formed product, characterized by enabling the movement of material from the top plate portion of the blank to one of the vertical walls portions, thereby forming the press-formed product.
2. The method for manufacturing a press-formed product according to claim 1, characterized in that a pad that cooperates with the punch to clamp the blank is placed in the area where the pilot pin is positioned.
3. A method for manufacturing a press-formed product according to claim 1 or 2, characterized in that the height of the vertical wall forming surface portion for forming one of the vertical wall portions having the stretch flange portion in the press forming die is made deeper than the height of the vertical wall forming surface portion for forming the other vertical wall portion, so that the forming of one of the vertical wall portions begins before the forming of the other vertical wall portion.