Press forming method

Abstract

The press forming method of the present application is a press forming method of press forming a press formed product (120) in which a flange portion (115) of a reverse-bent pre-press formed product (110) having a hat-shaped cross-sectional shape is bent in a reverse direction to become part of a vertical wall portion (123), using a punch (11) having a punch-side first inclined surface portion (11b), a punch-side second inclined surface portion (11c), and the punch-side first inclined surface portion (11b) and the punch-side second inclined surface portion (11c) being in a mountain shape protruding outward and a punch ridge line portion (11d) being formed at a connecting portion thereof, and a die (13) having a flange reverse-bent portion (13d). The press forming method makes the punch ridge line portion (11d) abut against an inner surface side of the vertical wall portion (113) and bends the flange portion (115) of the reverse-bent pre-press formed product (110) in a reverse direction by the flange reverse-bent portion (13d) of the die (13), thereby forming part of the vertical wall portion (123) of the press formed product (120).

Description

Technical Field

[0001] This invention relates to a press forming method, and more particularly to a press forming method for forming a press forming part with a high forming height of the flange portion of a press forming part before unbending a hat-shaped cross section. Background Technology

[0002] Most automotive parts are manufactured by stamping metal sheets. In recent years, to balance weight reduction and collision safety, higher-strength metal sheets have been used in automotive parts. Among the stamped products resulting from the stamping of such automotive parts are... Figure 12 The stamped product 120 with the U-shaped cross section as illustrated is an example. Figure 12 (a) Stamped product with a hat-shaped cross-section 130 ( Figure 12 (b)).

[0003] As in Figure 12 As shown as an example in (a), the U-shaped stamped article 120 includes: a top portion 121; a longitudinal wall portion 123 that extends continuously from both ends of the top portion 121 and slopes outward within a range of 1 to 10° relative to the press forming direction; and a shoulder part of apunch 125 that connects the top portion 121 and the longitudinal wall portion 123. Furthermore, as in... Figure 12 As shown as an example in (b), the stamped article 130 with a hat-shaped cross-section includes: a top plate portion 131; a longitudinal wall portion 133 that is continuous from both ends of the top plate portion 131 and inclined outward relative to the stamping direction; a flange portion 135 that is continuous from the lower end of the longitudinal wall portion 133; a punch shoulder R portion 137 that connects the top plate portion 131 and the longitudinal wall portion 133; and a die shoulder R portion (shoulder part of a die) 139 that connects the longitudinal wall portion 133 and the flange portion 135.

[0004] These stamped parts are manufactured through crash forming (bend forming) or deep drawing (draw forming) and are mainly used as reinforcing members in automobiles, thus utilizing high-strength metal sheets. However, the higher the strength of the metal sheet, the lower the formability indicators, such as ductility and stretch-flange ability. Therefore, especially in stamping processes aiming to achieve a target shape for U-shaped stamped parts with a curved portion that is approximately L-shaped or T-shaped when viewed from above, the longitudinal wall portion of the curved portion is prone to fracture due to stretching flange deformation. Furthermore, in stamped parts with a concave curve along the length and a cap-shaped cross-section, the flange portion of the curved portion is stretched along the bending direction, making it prone to fracture. Based on this, as a reaction force for forming the concave curved longitudinal wall, shrinkage deformation occurs in the top plate and punch shoulder R part of the curved part along the bending direction, which easily produces wrinkles.

[0005] On the other hand, in the stamping of stamped articles with a U-shaped or hat-shaped cross-section having a curved portion that is convex along its length when viewed from above, the longitudinal wall portion and the flange portion in the curved portion are compressed along the bending direction, resulting in shrinkage flanging, and the longitudinal wall portion tends to wrinkle easily. Furthermore, as a reaction force for forming the convexly curved longitudinal wall portion, it is stretched outward along the bend in the punch shoulder R portion, which easily leads to breakage.

[0006] Therefore, in stamped products with U-shaped or hat-shaped cross-sections that are concave or convex when viewed from above, especially stamped products with long longitudinal wall lengths and high forming heights, stamping is generally performed in multiple processes to mitigate the tensile stress and compressive stress generated during the stamping process and prevent breakage and wrinkling.

[0007] For example, in the case of Figure 12 (a) As shown in the figure, if the U-shaped cross-section of the stamped product 120 is the target shape, then... Figure 3As shown, firstly, through the first forming process, the length of the longitudinal wall portion 113 is shortened, that is, the hat-shaped cross-section with a low forming height is formed by stamping (shallow drawing forming) to create a reverse-bending pre-stamped product 110 with a short forming height (shallow drawing forming) without causing breakage or wrinkles. Figure 3 (a)). Then, through the next second forming process, the stamped part 120 with a high forming height of the longitudinal wall portion 123, which is formed by bending the flange portion 115 of the stamped part 110 before bending to achieve the desired longitudinal wall length, is stamped (forming) through a stamping process. Figure 3 (b)).

[0008] Furthermore, in the case of Figure 12 (b) The same applies when the stamped product 130 with the hat-shaped cross-section shown is set as the target shape, such as Figure 11 As shown, firstly, through the first forming process, the reverse-bending pre-stamped part 110 with a low forming height and a hat-shaped cross-section is formed (shallow drawing). Figure 11 (a)). Then, in the next second forming process, the stamped product 130, which has its flange portion 115 bent backwards to the desired longitudinal wall length by the longitudinal wall portion 133 and flange portion 135, is stamped (restrike forming) through the following second forming process. Figure 11 (b)). In this way, by performing stamping in multiple processes of shallow extrusion forming and shaping, the generation of fractures and wrinkles in stamped products can be suppressed.

[0009] However, when the flange 115 is bent backwards in the second forming process, it is not possible to achieve a sufficiently flat backward bend, for example... Figure 13 As shown, localized irregularities, i.e., bending crease portions 127 (or bending crease portions 141), remain in the longitudinal wall portion 123 (or longitudinal wall portion 133). The presence of bending crease portions 127 and 141 is particularly noticeable in high-tensile steel sheets with a thickness of 1.0 mm or more and a pressure greater than 440 MPa.

[0010] If such curved folds 127 and 141 remain, then as Figure 14As shown, resistance spot welding can become difficult. Specifically, resistance spot welding involves aligning the longitudinal wall portion 123 of the stamped part 120 or the longitudinal wall portion 133 of the stamped part 130 with the flat surface portion 151 of another flat component. By applying pressure from both sides using electrodes 153 and clamping them in place, a large current is flowed for a short time to create a weld part 155 (weld nugget), thereby joining the metals together. However, if curved or wrinkled portions 127 and 141 remain in the longitudinal wall portions 123 and 133, gaps are created between the flat surface portions 151 that are welded to the longitudinal wall portions 123 and 133. If these gaps are larger than the weldable gap, the welding current becomes difficult to flow, thus making welding difficult. Therefore, reducing the size of the curved or wrinkled portions 127 and 141 is important.

[0011] To address this problem, techniques have been proposed to straighten the bending wrinkles that remain after flattening a longitudinal wall portion subjected to bending processing. For example, Patent Document 1 discloses a technique that uses three punches with first convex portions arranged side by side at predetermined intervals and two dies with second convex portions arranged opposite each other in two concave forming spaces between the three first convex portions. The punches are pressed close to the die sides with the central first convex portion of the three first convex portions abutting against the convex side of the bending wrinkle. The bending wrinkles are straightened by applying small local deformations to the bending wrinkles using the first convex portions of the punches and the second convex portions of the dies.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent Application Publication No. 2013-103226 Summary of the Invention

[0015] The technical problem that the invention aims to solve

[0016] However, the technology disclosed in Patent Document 1 uses a special device to correct the bending wrinkles generated in stamped articles. In addition to the forming process of stamped articles, other processes are required to correct the bending wrinkles, which leads to a decrease in productivity.

[0017] The present invention was made in view of the above-mentioned problems, and its object is to provide a stamping method that can reduce the size of the bending wrinkles remaining in the longitudinal wall of the stamped article that has been reverse-bent before the flange portion of the stamped article is reverse-bent to become the longitudinal wall portion, without the need for a special device to correct the bending wrinkles.

[0018] Technical solutions for solving technical problems

[0019] The stamping forming method of the present invention is a stamping forming method for forming a pre-bending stamped product with a cap-shaped cross-section, having a top plate portion, a longitudinal wall portion that is continuously inclined relative to the stamping forming direction from the top plate portion, and a flange portion that is continuous from the longitudinal wall portion via a die shoulder R portion. The method involves using a punch and a die to stamp the pre-bending stamped product by bending the flange portion to form the longitudinal wall portion. The punch has a top forming surface portion that has the same shape as the top plate portion of the pre-bending stamped product and a side-wall forming surface portion that forms the longitudinal wall portion. The side-wall forming surface portion is continuously inclined outward from the top forming surface portion and has a punch-side first sloped surface with an inclination angle relative to the stamping forming direction equal to the inclination angle of the longitudinal wall portion of the pre-bending stamped product. The die has a punch side second sloped surface portion that slopes continuously from the lower end of the punch side first sloped surface portion towards the inner side of the punch side first sloped surface portion. The punch side first sloped surface portion and the punch side second sloped surface portion are convex outwards in a mountain shape and a punch side ridge line portion is formed at their connection. The die has a flange unbending portion that causes the flange portion of the stamped article placed on the punch to bend in reverse. The die moves relative to the punch side when the stamped article is placed on the punch, so that the punch ridge line portion abuts against the inner surface of the longitudinal wall portion and the flange portion is bent in reverse by the flange unbending portion, thereby forming the longitudinal wall portion of the stamped article.

[0020] The die may have an inner surface shape that maintains a distance parallel to the outer surface of the punch.

[0021] The punch ridge can be formed at a position that satisfies the following formula.

[0022] h1-R1(1-sinα)-R1 / 2≤h2≤h1-R1(1-sinα)+2πR1(90-α) / 360+R1 / 2

[0023] Wherein, h2 represents the distance (mm) from the forming surface of the top plate of the punch to the punch ridge in the stamping direction, h1 represents the forming height (mm) of the stamped part before reverse bending, R1 represents the bending radius (mm) of the die shoulder R portion of the stamped part before reverse bending, and α represents the tilt angle (°) of the longitudinal wall portion of the stamped part before reverse bending relative to the stamping direction.

[0024] Beneficial effects

[0025] In this invention, when a punch having a first inclined facet, a second inclined facet, and a punch ridge portion, and a die having a flange reverse bending portion are used to reverse bend the flange portion of a cap-shaped pre-bending stamped article to form a longitudinal wall portion, the flange portion is reverse bent by abutting the punch ridge portion against the inner surface of the longitudinal wall portion in the pre-bending stamped article and by using the flange reverse bending portion of the die. This allows for a process-wise reduction in the size of the bent wrinkle portion without the need for additional special equipment, thereby improving productivity. Attached Figure Description

[0026] Figure 1 The figures illustrate the stamping method according to an embodiment of the present invention ((a) forming start position, (b) forming bottom dead center position).

[0027] Figure 2 This diagram illustrates the positional relationship between the tool ofpress forming used in the stamping forming method according to an embodiment of the present invention and the curved wrinkles generated in the longitudinal wall portion.

[0028] Figure 3 The figure illustrates the shapes of a cap-shaped pre-bending stamped article, which is the subject of this invention, a U-shaped pre-bending stamped article in which the flange portion of the pre-bending stamped article is bent in reverse to become a longitudinal wall portion, and in the embodiments thereof.

[0029] Figure 4 The figures illustrate the process of forming a U-shaped stamped part with a high forming height by bending the flange portion of the stamped part before bending the hat-shaped cross-section in the conventional stamping forming method ((a) forming start position, (b) forming bottom stop position).

[0030] Figure 5 The figures illustrate the formation of bending wrinkles during the process of shaping a pre-bent stamped part into a stamped part ((a) configuration of the stamping die, (b) before forming begins, (c) at the start of forming, (d) the bottom stop of forming, (e) after die release, (f) the bending wrinkle).

[0031] Figure 6 The figures illustrate the definition of the bending crease height in the longitudinal wall portion of a stamped article ((a) a cross-sectional view of the stamped article, (b) an enlarged view of the bending crease).

[0032] Figure 7 The figures illustrate the height of the bending wrinkle peaks in the longitudinal wall portion of the stamped article produced in the stamping forming method of this embodiment ((a) surface shape outline of the bending wrinkle, (b) enlarged view of the bending wrinkle).

[0033] Figure 8 The diagram schematically illustrates the cross-sectional shape of the longitudinal wall portion of the stamped product when the position of the punch ridge portion is changed in the stamping forming method of this embodiment ((a) conventional method, (b) in the present invention, the punch ridge portion abuts against the die shoulder R portion (11d), (c) in the present invention, the punch ridge portion abuts against the longitudinal wall portion side at the curved and wrinkled portion (11d), (d) in the present invention, the punch ridge portion abuts against the flange portion side at the curved and wrinkled portion (11d)).

[0034] Figure 9 The figures illustrate the preferred positions of the punch ridge in the stamping forming method of this embodiment ((a) forming start position, (b) forming bottom stop position).

[0035] Figure 10 This indicates that in the stamping method of this embodiment, the position of the punch ridge and the inclination angle β of the second inclined surface on the punch side have been changed. Figure 2(a) The ratio of the bending wrinkle peak height in the present invention to the bending wrinkle peak height produced by conventional methods, (b) The surface shape profile of the bending wrinkle when the punch ridge portion abuts against the die shoulder R portion in the present invention, (c) The surface shape profile of the bending wrinkle when the punch ridge portion abuts against the plastic bending deformation region on the longitudinal wall side in the present invention, (d) The surface shape profile of the bending wrinkle when the punch ridge portion abuts against the plastic bending deformation region on the flange side in the present invention).

[0036] Figure 11 Figure ((a) stamped article before reverse bending, (b) stamped article with hat-shaped cross-section, is shown as an example of a stamped article with hat-shaped cross-section, in which the flange portion of the stamped article is reverse bent to become the longitudinal wall portion by the stamping forming method of this embodiment.

[0037] Figure 12 Figures illustrating stamped articles with U-shaped and hat-shaped cross-sections are shown ((a) stamped article with U-shaped cross-section, (b) stamped article with hat-shaped cross-section).

[0038] Figure 13 The figures illustrate the bending wrinkles that occur in the longitudinal wall of a stamped article with a U-shaped or hat-shaped cross-section, where the flange portion of the stamped article with a low forming height is bent backwards to become the longitudinal wall portion. ((a) Stamped article with a U-shaped cross-section, (b) Stamped article with a hat-shaped cross-section, (c) Bending wrinkle).

[0039] Figure 14 This is a schematic diagram illustrating the problems encountered when joining the longitudinal wall of a stamped part with curved wrinkles to the flat surface of other components using resistance spot welding. Detailed Implementation

[0040] Before describing the stamping method according to the embodiments of the present invention, as part of the process of completing the present invention, research related to the principle of generating bending wrinkles and the method of reducing bending wrinkles will be described.

[0041] <Principle of Curved Wrinkle Generation>

[0042] Inventors used such Figure 4 The stamping die 40 shown, equipped with a punch 41 and a die 43, enables the stamping process to... Figure 3 As shown as an example in (a), the flange portion 115 of the pre-stamped article 110 with a hat-shaped cross-section having a top plate portion 111, a longitudinal wall portion 113, and a flange portion 115 is reverse-bent to obtain the shape. Figure 3 (b) As an example, the process of shaping the stamped product 120, which is part of the longitudinal wall portion 123 as shown in the example, is taken as an example, and the bending wrinkles 127 (see reference) generated in the longitudinal wall portion 123 are also taken as an example. Figure 13 The principle of (a) was studied.

[0043] exist Figure 5 The diagram illustrates the principle of creating curved wrinkles 127 in the longitudinal wall portion 123 of the stamped product 120. Here, Figure 5 (a) is a diagram showing the relative positional relationship between the punch 41 and the die 43 of the stamping die 40. Figure 5 (b) to Figure 5 (d) is a diagram showing the deformation action of the die shoulder R119 and its surrounding area of ​​the pre-stamped part 110 during the forming process from the forming start position to the forming bottom stop position. Figure 5 (e) is a cross-sectional view showing the longitudinal wall portion 123 of the stamped product 120 after it has been demolded from the stamping die 40. Figure 5 (f) is a magnified view of the curved folds 127 produced in the longitudinal wall portion 123. (See diagram for example.) Figure 5 As shown, if the die 43 is moved in the stamping direction for stamping, then at the starting position of stamping, the punch 41 and the die 43 are inclined relative to the stamping direction. Therefore, the vertical distance between the forming surface 41a of the punch side longitudinal wall and the forming surface 43a of the die side longitudinal wall is the gap. Figure 5 In (a) and (c), d1) is the gap at the moment when the forming bottom stop position is reached. Figure 5 The width of d2 in (a) and (d) is 1 / 2.

[0044] If the reverse-bending portion 43b of the flange of the die 43 abuts against the flange portion 115 of the stamped part 110 before reverse bending and reverse bending begins, then as Figure 5 As shown in (c), unbending deformation begins, such that the die shoulder R portion 119 becomes flat.

[0045] At this time, due to the vertical distance between the forming surface 41a of the punch side longitudinal wall and the forming surface 43a of the die side longitudinal wall during the forming process, i.e., the gap ( Figure 5 (c) d1) is wider than the sheet thickness of the pre-bending stamped product 110, thus creating space for the longitudinal wall portion 113 and the flange portion 115 of the pre-bending stamped product 110 to deform freely.

[0046] Therefore, the reaction force accompanying the reverse bending deformation of the die shoulder R portion 119 is applied to the longitudinal wall portion 113 and the flange portion 115 adjacent to the die shoulder R portion 119, and additional plastic bending deformation is added in the direction opposite to the shape of the die shoulder R portion 119 protruding towards the punch 41. Here, the regions on the longitudinal wall portion 113 side and the flange portion 115 side before and after the die shoulder R portion 119 are respectively referred to as the longitudinal wall side plastic bending deformation region 113a and the flange side plastic bending deformation region 115a.

[0047] Then, at the bottom stop position of the forming, as Figure 5 As shown in (d), the vertical distance between the forming surface 41a of the punch side longitudinal wall and the forming surface 43a of the die side longitudinal wall is the gap. Figure 5 (d) d2) narrows to approximately equal to the thickness of the stamped product 120, and the longitudinal wall portion 113 and flange portion 115 of the stamped product 110 before reverse bending are clamped and formed into the longitudinal wall portion 123 of the stamped product 120.

[0048] Here, the lower stop position of the forming ( Figure 5 The vertical distance d2 between the punch side longitudinal wall forming surface 41a and the die side longitudinal wall forming surface 43a in (d) and the difference between the thickness of the longitudinal wall portion 123 of the stamped product 120 and the thickness of the plate, multiplied by 100, is defined as the clearance.

[0049] At the bottom stop position of the forming ( Figure 5 (d) If the interval between the punch side longitudinal wall forming surface 41a and the die side longitudinal wall forming surface 43a is set to zero, that is, the curved wrinkle portion 127 generated in the longitudinal wall portion 123 of the stamped product 120 is squeezed by the flat punch side longitudinal wall forming surface 41a and die side longitudinal wall forming surface 43a, it is considered that the curved wrinkle portion 127 becomes flat and can be corrected in appearance.

[0050] However, in the stamped product 120, if it is demolded from the stamping die 40, then as Figure 5 As shown in (e), due to springback, the curved wrinkle 127 cannot be completely corrected to a flat shape, and localized irregularities, i.e., curved wrinkles 127, remain on the longitudinal wall 123. Figure 5 (f) shows an enlarged view of the curved wrinkles 127 remaining in the longitudinal wall portion 123 of the stamped part 120 after demolding.

[0051] like Figure 5As shown in (f), in the longitudinal wall portion 123 of the stamped product 120 after demolding, the portion corresponding to the shoulder part of a die 127a, the portion receiving plastic bending deformation 127b corresponding to the longitudinal wall side plastic bending deformation region 113a, and the flange side plastic bending deformation region 115a corresponding to the flange side plastic bending deformation region 115a are retained as bending wrinkles 127.

[0052]

[0053] Based on the above research related to the principle of generating curved wrinkles 127 in the longitudinal wall portion 123 of the stamped product 120 formed by bending the flange portion 115 of the stamped product 110 before bending, the inventors further studied a method to reduce the size (bending wrinkle peak height) of the curved wrinkles 127 generated in the stamped product 120.

[0054] Here, as an indicator for quantitatively evaluating the size of the curved fold 127, such as Figure 6 As shown, the vertical distance from the junction 127d of the longitudinal wall portion 123 on the inner surface side of the stamped product 120 and the junction 127e of the plastic bending deformation portion 127b on the longitudinal wall side and the junction 127e of the plastic bending deformation portion 127c on the flange side and the longitudinal wall portion 123 to the top of the protrusion of the bending wrinkle portion 127 is defined as the bending wrinkle peak height.

[0055] like Figure 5 As shown in (f), in the bent wrinkle portion 127, since the warping in the direction of the curvature direction (convex toward the punch 41 side) opposite to the warping in the direction of the curvature direction of the die shoulder R equivalent portion 127a remaining after the reverse bending of the die shoulder R portion 119 is completed, is applied to the longitudinal wall side plastic bending deformation portion 127b and the flange side plastic bending deformation portion 127c, the longitudinal wall side plastic bending deformation portion 127b and the flange side plastic bending deformation portion 127c are concave on the punch 41 side. Therefore, it can be seen that the bending wrinkle peak height of the bent wrinkle portion 127 which is convex on the punch 41 side is increased.

[0056] Therefore, based on the results of press forming simulation, the range of the plastic bending deformation portion 127b on the longitudinal wall side and the plastic bending deformation portion 127c on the flange side was studied in detail. The results showed that both the plastic bending deformation portion 127b on the longitudinal wall side and the plastic bending deformation portion 127c on the flange side become wider as the bending radius R1 of the die shoulder R portion 119 of the stamped part 110 before reverse bending increases, and are approximately half the bending radius R1 of the die shoulder R portion 119.

[0057] Based on these insights, the inventors conducted in-depth research on methods for reducing the height of the bending wrinkle peak in the bending wrinkle portion 127. As a result, it was discovered that when the flange portion 115 of the pre-bent stamped article 110 is reverse-bent, the height of the bending wrinkle peak can be reduced by bending the area where the bending wrinkle portion 127 occurs towards the side opposite to the bending wrinkle portion 127. This invention was made based on the above research, and its structure will be described below.

[0058] <Stamping Forming Method>

[0059] like Figure 3 As shown in (a), the stamping method of this embodiment of the invention is used for a cap-shaped pre-bending stamped article 110 having a top plate portion 111, a longitudinal wall portion 113 that is continuously inclined relative to the stamping direction from the top plate portion 111, and a flange portion 115 that is continuous from the longitudinal wall portion 113 via a die shoulder R portion 119. Figure 1 and Figure 2 As an example, the stamping die 10, which includes a punch 11 and a die 13, bends the flange portion 115 in reverse, thereby shaping the flange portion 115. Figure 3 (b) shows a stamped article 120 with a longitudinal wall portion 123 formed as an example, which is stamped.

[0060] The reverse bending pre-stamped part 110 has a punch shoulder R portion 117 that connects the top plate portion 111 and the longitudinal wall portion 113 and a die shoulder R portion 119 that connects the longitudinal wall portion 113 and the flange portion 115.

[0061] Furthermore, a punch shoulder R portion 125 connecting the top plate portion 121 and the longitudinal wall portion 123 is formed in the stamped product 120. Here, the top plate portion 121 and the punch shoulder R portion 125 have the same shape as the top plate portion 111 and the punch shoulder R portion 117 of the stamped product 110 before reverse bending, respectively. In addition, the inclination angle α of the longitudinal wall portion 113 of the stamped product 110 with respect to the stamping direction is set to be equal to the inclination angle α of the longitudinal wall portion 123 of the stamped product 120.

[0062] like Figure 1As shown, the punch 11 has a top plate forming surface 11e and a punch side longitudinal wall forming surface 11a.

[0063] The top plate forming surface 11e is formed with a top plate portion 121 having the same shape as the top plate portion 111 of the reverse-bending pre-stamped part 110.

[0064] The forming surface 11a of the punch side longitudinal wall shapes the longitudinal wall portion 113 of the reverse-bending pre-stamped part 110, such as... Figure 1 As shown, it has a first inclined surface 11b on the punch side, a second inclined surface 11c on the punch side, and a punch ridge portion 11d. It should be noted that the longitudinal wall forming surface 11a on the punch side corresponds to the "longitudinal wall forming surface" described in the claims of this application.

[0065] like Figure 2 As shown, the first inclined surface 11b on the punch side is continuously inclined outward from the top plate forming surface 11e, and the inclination angle relative to the stamping direction is equal to the inclination angle α of the longitudinal wall portion 113 of the stamped product 110 before reverse bending relative to the stamping direction.

[0066] like Figure 2 As shown, the second inclined surface 11c on the punch side continuously inclines inward from the lower end of the first inclined surface 11b on the punch side. In this embodiment, as... Figure 2 As shown, the second inclined surface 11c on the punch side is inclined inward toward the punch 11 side with an inclination angle β (0<β≤α) based on the first inclined surface 11b on the punch side.

[0067] like Figure 1 As shown, the punch ridge portion 11d is formed at the connection between the first inclined surface portion 11b and the second inclined surface portion 11c on the punch side. As a result, the punch side longitudinal wall forming surface portion 11a presents a mountain shape with the first inclined surface portion 11b and the second inclined surface portion 11c on the punch side protruding outward from the punch 11.

[0068] like Figure 1 As shown, the die 13 and the punch 11 are arranged opposite each other, and the die 13 has a die side longitudinal wall forming surface 13a and a flange reverse bending portion 13d.

[0069] The longitudinal wall forming surface 13a of the die side and the longitudinal wall forming surface 11a of the punch side cooperate to form the longitudinal wall portion 113 of the reverse-bending pre-stamped article 110, such as Figure 1 As shown, it has a first inclined face 13b on the die side and a second inclined face 13c on the die side.

[0070] like Figure 2 As shown, the first inclined surface 13b on the die side is inclined at an angle α relative to the stamping direction and is parallel to the first inclined surface 11b on the punch side.

[0071] like Figure 2 As shown, the second inclined portion 13c on the die side is continuously inclined towards the punch 11 from the lower end of the first inclined portion 13b on the die side relative to the stamping direction. In this embodiment, as... Figure 2 As shown, the second inclined surface 13c on the die side is inclined towards the punch 11 with an inclination angle β (0<β≤α) based on the first inclined surface 13b on the die side, and is parallel to the second inclined surface 11c on the punch side.

[0072] The flange reverse-bending portion 13d continues from the second inclined portion 13c on the die side and abuts against the flange portion 115 of the reverse-bending pre-stamped article 110 mounted on the punch 11, thus bending in reverse. In this embodiment, as... Figure 2 As shown, the flange reverse bending portion 13d has a flange forming face 13e that forms the flange portion 115 and a die shoulder 13f connected to the flange forming face 13e.

[0073] Furthermore, the reverse-bending pre-stamped article 110 is placed on the punch 11, and the die 13 is moved relative to the punch 11, so that the punch ridge portion 11d of the punch 11 abuts against the inner surface of the longitudinal wall portion 113, and all or part of the flange portion 115 is reverse-bent through the reverse-bending portion 13d of the flange of the die 13, thereby forming the longitudinal wall portion 123 of the stamped article 120. At this time, the top plate portion 121 is formed into the same shape as the top plate portion 111 of the reverse-bending pre-stamped article 110.

[0074] like Figure 2 As shown, the punch ridge 11d of the punch 11 can be configured to abut against the die shoulder R 119 of the reverse-bending stamped part 110, the longitudinal wall side plastic bending deformation region 113a, or the flange side plastic bending deformation region 115a, which corresponds to the region in the longitudinal wall 123 of the stamped part 120 that generates bending wrinkles 127 (see reference). Figure 5 (c)).

[0075] Moreover, such as Figure 1 As shown in (b), the die 13 is moved relative to the punch 11, as follows: Figure 2 As shown, the area where the punch ridge 11d of the punch 11 and the longitudinal wall 123 of the stamped product 120 produce bent wrinkles 127 ( Figure 5 (f) The inner sides of 127a, 127b, and 127c) abut against each other, and the flange 115 bends in the opposite direction.

[0076] Reasons for reducing the size of curved wrinkle peaks

[0077] Next, the reasons why the stamping method of this embodiment can reduce the size of the bending wrinkles 127 generated in the longitudinal wall portion 123 of the stamped product 120 will be explained.

[0078] exist Figure 7 The middle axis represents the outline of the surface shape of the punch 11 side of the longitudinal wall portion 123 of the stamped product 120. The horizontal axis represents the position of the longitudinal wall portion 123 of the stamped product 120 in the direction from the lower end to the upper end (X direction), and the vertical axis represents the distance (surface shape outline) from the surface of the punch 11 side of the longitudinal wall portion 123 to the surface of the curved and wrinkled portion 127 in the direction perpendicular to the longitudinal wall portion 123 (Y direction).

[0079] Figure 7 (a) shows A through an existing stamping die 40 ( Figure 4 The surface shape profile of the punch 41 side of the bent wrinkle portion 127 of the stamped product 120, which is formed by bending the flange portion 115 of the stamped product 110 before bending, is such that the height of the bent wrinkle peak is the maximum value of the distance to the surface of the bent wrinkle portion 127 in the direction perpendicular to the longitudinal wall portion 123. Figure 7 h in (a) a ).

[0080] Figure 7 (a) B is the surface shape profile of the punch 11 side of the bent wrinkle 127 when the longitudinal wall portion 123 of the stamped product 120 formed by stamping does not produce a bent wrinkle 127 when using the stamping die 10 of this embodiment. Figure 7 (a) C is the surface shape profile on the side of the punch 11 that produces the curved wrinkle portion 127 on the longitudinal wall portion 123 of the stamped product 120 by stamping using the stamping die 10 of this embodiment, and is the shape obtained by combining the surface shape profile A and the surface shape profile B.

[0081] like Figure 6 (b) As shown in the definition of the bending wrinkle peak height, the bending wrinkle peak height h in the surface shape profile C is... c It is from both ends of the curved pleats 127 ( Figure 7 An imaginary straight line connecting the region where the curved wrinkle 127 is generated in (b) and the boundary 127d of the longitudinal wall 123 corresponding to the longitudinal wall 113, and the boundary 127e of the region where the curved wrinkle 127 is generated and the boundary corresponding to the flange 115. Figure 7 The maximum vertical distance from the dashed line in (a) is ( Figure 7 h in (a) c), and the height h of the bending wrinkle peak of the surface shape profile A is greater than that when using the existing punch 31. a ( Figure 7 h in (a) a )Low.

[0082] Thus, according to the stamping method of this embodiment, by making the punch ridge 11d and the area in the stamped product 110 before reverse bending where the bending wrinkle 127 is generated ( Figure 6 (b) Figure 7 (a) Figure 7 (b) The boundary 127d and the boundary 127e of the flange 115 are abutted together, and the flange 115 is bent in reverse, which can be bent concavely towards the punch 11 side to change the surface shape profile of the bent wrinkle 127 and reduce the height of the bent wrinkle peak of the bent wrinkle 127.

[0083] Preferred Position of the Punch Rib in a Punch

[0084] Figure 8 This is a schematic diagram showing the cross-sectional shape of the longitudinal wall portion 123 of the stamped product 120 when the position (11d) of the punch ridge portion 11d of the punch 11 used in the stamping method of this embodiment is changed. Here, Figure 8 (a) is the case of using the existing punch 41. Figure 8 (b) is the case where the punch ridge 11d of the punch 11 abuts against the die shoulder R 119. Figure 8 (c) and Figure 8 (d) is the case where the punch ridge 11d abuts against the outer side of the area where the bending wrinkle 127 is generated. Figure 8 (b) to Figure 8 The white arrow in (d) indicates the position where the punch ridge 11d abuts.

[0085] If the punch 11 of this embodiment is used (refer to...) Figure 1 The situation and the use of existing punch 41 (refer to) Figure 4 When comparing the surface shape profile of the curved wrinkle 127 under the condition of ), then as Figure 8 (a) and Figure 8 As shown in (b), the height of the bending wrinkle peak in the bending wrinkle portion 127 decreases (h). a >h b ).

[0086] Furthermore, if the position where the punch ridge 11d of the punch 11 abuts is located on the outer side of the area where the bent wrinkle 127 is generated, i.e., on the longitudinal wall 113 side or on the flange 115 side, such as Figure 8 (c) and Figure 8As shown in (d), if the punch ridge 11d is located in the area where the bending wrinkle 127 is generated ( Figure 8 Compared to (b), the bending wrinkle peak height is higher than that of the case using the existing punch 41. Figure 8 Compared to (a), the height of the bending fold peak was not improved.

[0087] according to Figure 8 (b) to Figure 8 (d) shows that, for the punch ridge 11d provided on the punch 11, there is a preferred position to reduce the size of the bent wrinkle 127. Therefore, based on Figure 9 The preferred position of the punch ridge 11d will be explained.

[0088] Figure 9 (a) is a diagram schematically showing the area where a bent wrinkle 127 is generated when the flange portion 115 of the stamped article 110 is bent backward.

[0089] Based on the geometric relationship between the angle α (°) of inclination of the longitudinal wall portion 113 relative to the stamping direction and the bending radius R1 of the die shoulder R portion 119, the length l1 of the region of the die shoulder R portion 119 of the stamped product 110 before reverse bending (refer to...) Figure 9 (a) can be calculated using equation (1).

[0090] l1=2πR1×(90°-α) / 360°…Equation (1)

[0091] Furthermore, the length l2 of the longitudinal wall side plastic bending deformation region 113a in the longitudinal wall portion 113 of the reverse bending pre-stamped product 110 and the length l3 of the flange side plastic bending deformation region 115a in the flange portion 115, as described above in the principle of bending wrinkle generation, are approximately 1 / 2 of the bending radius R1 of the die shoulder R portion 119 of the reverse bending pre-stamped product 110, and are therefore calculated by equations (2) and (3).

[0092] l2=R1×1 / 2…Equation (2)

[0093] l3=R1×1 / 2…Equation (3)

[0094] Therefore, the length of the region where the bending wrinkle 127 is generated can be calculated as the sum of the length l1 of the die shoulder R portion 119 of the reverse bending pre-stamped product 110, the length l2 of the plastic bending deformation region 113a on the longitudinal wall side, and the length l3 of the plastic bending deformation region 115a on the flange side.

[0095] For example, when the bending radius R1 of the die shoulder R portion 119 is 5 mm and the inclination angle α of the longitudinal wall portion 113 of the pre-bending stamped product 110 relative to the stamping direction is 3°, the length l1 of the die shoulder R portion 119 is 7.6 mm according to formula (1), and the length l2 of the plastic bending deformation region 113a on the longitudinal wall side and the length l3 of the plastic bending deformation region 115a on the flange side are both 2.5 mm according to formulas (2) and (3). In this case, the length of the region in the pre-bending stamped product 110 that generates the bending wrinkle portion 127 is their combined value of 12.6 mm (=7.6 mm + 2.5 mm + 2.5 mm).

[0096] If the inclination angle of the first inclined surface 11b on the punch side is set to be the same as the inclination angle α of the longitudinal wall portion 113 of the reverse-bending pre-stamped product 110, and the forming height of the reverse-bending pre-stamped product 110 is set to h1, then the distance h from the top plate forming surface 11e in the stamping direction at the junction of the die shoulder R portion 119 and the longitudinal wall side plastic bending deformation region 113a is... d according to Figure 9 The geometric relationship shown in (a) is derived from h d =h1-R1·(1-sinα)…Calculate using equation (4).

[0097] exist Figure 9 (b) shows the region where the bending wrinkle 127 is generated and the location of its boundary when the top plate portion 111 of the pre-bending stamped article 110 is taken as a reference. When the inclination angle α of the longitudinal wall portion 113 of the pre-bending stamped article 110 is in the range of 1 to 10°, it can be approximated as cosα≈1. Therefore, if equations (1) to (4) are used, the distance h from the top plate portion 111 in the stamping direction to the boundary of the longitudinal wall portion 113 side is... s The distance h from the junction of the flange portion 115 to the flange portion 115 e Calculated using equations (5) and (6) respectively.

[0098] h s =h1-R1·(1-sinα)-R1×1 / 2…Equation (5)

[0099] h e =h1-R1·(1-sinα)+2πR1×(90°-α) / 360°+R1×1 / 2…Equation (6)

[0100] Therefore, if the distance from the forming surface 11e of the top plate in the stamping direction of the punch ridge 11d is set to h2 (refer to...), Figure 2 If the position of the punch ridge 11d satisfies h, then s ≤h2≤h eThat is, the following formula (7) is used to determine that the punch ridge 11d can abut against the inner surface of the longitudinal wall 113 in the region where the bending wrinkle 127 is generated, and the flange 115 of the stamped product 110 before bending is bent in reverse, and the region where the bending wrinkle 127 is generated can be bent sharply to further reduce the bending wrinkle peak height, which is therefore preferred.

[0101] h1-R1(1-sinα)-R1 / 2≤h2≤h1-R1(1-sinα)+2πR1(90-α) / 360+R1 / 2...Equation (7)

[0102] Here, h2 represents the distance (mm) from the forming surface 11e of the top plate of the punch 11 to the punch ridge 11d in the stamping direction, and h1 represents the forming height (mm) of the stamped part 110 before reverse bending (refer to...). Figure 3 R1 represents the bending radius (mm) of the die shoulder R119 of the stamped part 110 before reverse bending (refer to...). Figure 3 ), α represents the inclination angle (°) of the longitudinal wall portion 113 of the stamped part 110 before reverse bending relative to the stamping direction (refer to...). Figure 3 ).

[0103] Inclination angle of the second inclined face on the punch side

[0104] Figure 10 (a) When the inclination angle α of the first inclined surface 11b on the punch side relative to the stamping direction is set to 10°, and the inclination angle β of the second inclined surface 11c on the punch side is set to 10°, or further to β×1 / 2 (=5°) and β×1 / 4 (=2.5°), the bending wrinkle peak height when the position of the punch ridge 11d is changed in the plastic bending deformation region 113a on the longitudinal wall side where the bending wrinkle occurs, the die shoulder R portion 119, and the plastic bending deformation region 115a on the flange side, is obtained by measuring the bending wrinkle peak height h of the bending wrinkle portion 127 in the stamped product 120 formed by stamping using the existing punch 41. a (Refer to Figure 7 (a) The surface shape profile A) is a graph representing the ratio when set to 100%. Figure 10 (b) to Figure 10 (d) indicates Figure 10 (a) is a drawing showing the surface shape profile of the punch side of the curved wrinkle 127 in (b) to (d). Furthermore, Figure 10 (b) to Figure 10 (d) The horizontal axis (X direction), vertical axis (Y direction), A, B, and C are related to the above. Figure 7 same.

[0105] according to Figure 10(a) It can be seen that by placing the punch ridge portion 11d within the region (113a, 119, 115a) where the bending wrinkle portion is generated, the bending wrinkle peak height can be reduced. Furthermore, the bending wrinkle peak height is reduced most when the punch ridge portion 11d is located at the center of the region where the bending wrinkle portion is generated (see reference). Figure 10 (b) and Figure 10 (c) shows the surface shape profile C).

[0106] Furthermore, according to Figure 10 (a) It can be seen that by increasing the tilt angle β of the second tilted surface 11c on the punch side, the effect of reducing the height of the bending wrinkle peaks in the appearance is improved (refer to...). Figure 10 (b) and Figure 10 (d) shows the surface shape profile C). Therefore, in order to reduce the height of the bending wrinkle peak, it is preferable to increase the tilt angle β of the second tilted face 11c on the punch side.

[0107] However, if the tilt angle β of the second inclined surface 11c on the punch side is larger than the tilt angle α of the first inclined surface 11b on the punch side, then the second inclined surface 11c on the punch side is closer to the top plate forming surface 11e side than the punch ridge portion 11d. Therefore, when the die 13 of the stamping die 10 is moved relative to the stamping direction in parallel, the gap in the vertical direction between the second inclined surface 11c on the punch side and the second inclined surface 13c on the die side at the forming bottom stop position widens, and it is not possible to sufficiently restrict the reverse-bent flange portion 115. Therefore, the effect of reducing the bending wrinkle peak height of the bending wrinkle portion 127 is also saturated.

[0108] Therefore, when the die 13 moves relative to the punch 11 in parallel with the stamping direction, the inclination angle β of the second inclined surface 11c on the punch side can be set to be less than or equal to the inclination angle α of the first inclined surface 11b on the punch side (0 < β ≤ α).

[0109] However, when using a stamping die 10 equipped with a mechanism that moves the die 13 toward the punch 11 at an inclination relative to the stamping direction for insert bending, there is no upper limit for the inclination angle β of the second inclined surface 11c on the punch side, as described above, and it can be set appropriately.

[0110] Furthermore, if the stamped product 120 is demolded from the stamping die 10 after stamping, the longitudinal wall portion 123, formed by bending the flange portion 115 in the reverse direction, springs back convexly toward the punch 11 (see reference). Figure 5(e) Therefore, the tilt angle β of the second inclined surface 11c on the punch side is preferably kept within the range that the bending amount (concave towards the punch 11 side) of the longitudinal wall portion 123 of the stamped product 120 during the stamping process does not exceed the springback amount (convex towards the punch 11 side).

[0111] However, the springback of the longitudinal wall portion 123 after demolding is affected by various factors such as the cross-sectional shape and length direction shape of the stamped product 120, the tensile strength and thickness of the metal sheet used in the sheet metal 100, and the distribution of residual stress or strain generated in the stamped product 120, and therefore cannot be determined uniformly. Therefore, the springback of the longitudinal wall portion 123 is preferably determined in advance by numerical simulation using the finite element method or by preliminary experiments.

[0112] Furthermore, the die 13 preferably has an inner surface shape that is spaced parallel to the outer surface of the punch 11. Here, the inner surface shape of the die 13 refers to the shape of the first inclined portion 13b and the second inclined portion 13c on the die side. The outer surface of the punch 11 refers to the shape of the first inclined portion 11b and the second inclined portion 11c on the punch side. Preferably, the first inclined portion 13b on the die side is inclined at an angle α relative to the stamping direction and is parallel to the first inclined portion 11b on the punch side, and the second inclined portion 13c on the die side is inclined at an angle β toward the punch 11 with reference to the first inclined portion 13b on the die side and is parallel to the second inclined portion 11c on the punch side.

[0113] Furthermore, when the die 13 is moved parallel to the stamping direction and approaches the bottom stop position of the punch 11, the first inclined surface 13b and the second inclined surface 13c on the die side are preferably arranged opposite each other with a predetermined gap between them in the vertical direction relative to the first inclined surface 11b and the second inclined surface 11c on the punch side, respectively. This is because, as Figure 1 As shown in (b) at the bottom stop position of the forming, the longitudinal wall portion 113 can be restricted by reducing the space in which the longitudinal wall portion 113 between the punch 11 and the die 13 can freely deform, thus making it easy to transfer the shape of the first inclined surface portion 11b and the second inclined surface portion 11c on the punch side, the first inclined surface portion 13b on the die side, and the second inclined surface portion 13c on the die side.

[0114] The spacing between the punch and the die

[0115] Here, in Figure 1 and Figure 2In the stamping die 10 shown, it is preferable that the punch 11 and the die 13 are spaced apart by a distance of 0% to 50% of the sheet metal thickness. The distance between the punch 11 and the die 13 is a value (%) calculated by dividing the vertical distance between the first inclined surface of the punch side and the first inclined surface of the die side, and the vertical distance between the second inclined surface of the punch side and the second inclined surface of the die side, by the sheet metal thickness and multiplying by 100.

[0116] When the interval is less than 0%, it becomes a so-called "thinning" process, which carries the risk of abnormal sliding wear, or "galling," on the sliding surface, and is therefore not preferred. Furthermore, when the interval is greater than 50%, space is created where the sheet metal can move freely, making it difficult to achieve the desired effect of the invention, and is therefore also not preferred.

[0117] Especially when using sheet metal with a tensile strength exceeding 1600 MPa or a thickness of 3.6 mm that is prone to "wear" between the stamping die and the sheet metal, it becomes important to adjust the spacing appropriately.

[0118] It should be noted that the description of the stamping method in this embodiment pertains to the stamping of a U-shaped stamped article 120, in which the flange portion 115 of the stamped article 110 before the cap-shaped cross-section is reverse-bent completely to become part of the longitudinal wall portion 123, as in... Figure 11 As shown as an example, the present invention can also be used to stamp a stamped article 130 in which a portion of the flange portion 115 of the stamped article 110 is reverse-bent to become part of the longitudinal wall portion 133, and the remaining portion of the flange portion 115 becomes a cap-shaped cross-section of the new flange portion 135. In this case, it is also similar to the stamped article 130 in which a portion of the flange portion 115 is reverse-bent to become part of the longitudinal wall portion 133, and the remaining portion of the flange portion 115 becomes a cap-shaped cross-section of the new flange portion 135. Figure 4 The same applies to the stamping of the U-shaped cross-section stamped product 120. By making the punch ridge 11d of the punch 11 abut against the inner surface of the longitudinal wall 113 of the stamped product 110 before reverse bending and making the flange 115 reverse bend, the size (bending wrinkle peak height) of the remaining bending wrinkle 141 in the longitudinal wall 133 of the hat-shaped cross-section stamped product 130 can be reduced.

[0119] Furthermore, when the present invention sets the target shape of a stamped product that is bent along the length direction when viewed from above, it can not only reduce the size of the remaining bending wrinkles (bending wrinkle peak height) in the longitudinal wall portion of the stamped product, but also suppress the breakage caused by stretch flange forming and the wrinkles caused by shrink flange forming in the bent stamped product.

[0120] In this embodiment, the die 13 has a first inclined surface 13b and a second inclined surface 13c on the die side that are parallel to the first inclined surface 11b and the second inclined surface 11c on the punch side, respectively. The first inclined surface 13b and the second inclined surface 13c on the die side cooperate with the first inclined surface 11b and the second inclined surface 11c on the punch side to clamp the longitudinal wall portion 113 of the reverse bending pre-stamped product 110.

[0121] However, the present invention is not limited to the die 13 having a first inclined surface 13b and a second inclined surface 13c on the die side that are parallel to the first inclined surface 11b and the second inclined surface 11c on the punch side, respectively. Alternatively, the punch ridge portion may abut and the flange portion may be bent in reverse to form a longitudinal wall portion along the first inclined surface and the second inclined surface of the punch side.

[0122] Furthermore, the present invention is not limited to a single step of bending the flange portion of a pre-prepared cap-shaped cross-section pre-bent stamped article in reverse, but includes two steps to stamp a target-shaped stamped article: a first forming step of stamping a cap-shaped cross-section pre-bent stamped article and a second forming step of forming a longitudinal wall portion by bending the flange portion of the pre-bent stamped article in reverse.

[0123] It should be noted that when the stamped product being formed in this invention is an automotive part, examples of automotive parts that can be exemplified by using high-strength metal sheets include A-pillars, B-pillars, roof rails, side rails, front side members, rear side members, cross members, and other frame components.

[0124] Example 1

[0125] In this embodiment 1, stamping simulations were performed on the first forming process and the second forming process respectively to determine the height of the bending wrinkle peaks in the bending wrinkles generated in the longitudinal wall portion 123 of the stamped product 120. The first forming process is used for... Figure 3(a) The reverse-bending pre-stamped article 110 with the hat-shaped cross-section shown is stamped, and the second forming process described above causes the flange portion 115 of the reverse-bending pre-stamped article 110 to bend in reverse. Figure 3 (b) shows the stamped part being stamped.

[0126] In the first forming process, a metal sheet with a thickness of 1.2 mm and a tensile strength of 1180 MPa is used as sheet material 100. A stamping die (not shown) equipped with a punch, a die, and a sheet holder is used to form the sheet material. Figure 3 (a) shows a top plate portion 111, longitudinal wall portion 113 and flange portion 115, which are stamped before reverse bending.

[0127] For the target shape of the reverse bending pre-stamped part 110, the forming height h is set to 50mm, and the length l of the top plate part 111 is set to... T Set the inclination angle α of the longitudinal wall portion 113 to 3°, and set the width W of the flange portion 115 to 50mm. F The bending radius of the punch shoulder R117 and the bending radius of the die shoulder R119 are both set to 10 mm. Furthermore, the dimensions of the punch and die used in the first forming process are set to correspond to the target shape of the stamped part before reverse bending.

[0128] In the next second forming process, such as Figure 1 As shown, a stamping die 10 with a punch 11 and a die 13 is used to completely reverse bend the flange portion 115 of the stamped product 110 before reverse bending, thereby stamping the stamped product 120 with a U-shaped cross-section having a top plate portion 121 and a longitudinal wall portion 123.

[0129] For the target shape of the stamped product 120, the length of the top plate portion 121 and the bending radius of the punch shoulder R portion 125 are set to be the same as those of the stamped product 110 before reverse bending.

[0130] For the dimensions of the stamping die 10, the width of the top plate forming surface 11e of the punch 11 is set to 50mm, and the first inclined surface 11b on the punch side and the first inclined surface 13b on the die side are both set to 3°, which is equal to the inclination angle α of the longitudinal wall portion 113 of the stamped product 110 before reverse bending.

[0131] Furthermore, the distance h2 between the punch ridge 11d and the top plate forming surface 11e is set to 50mm, the inclination angle of the first inclined surface 11b on the punch side is set to α = 3°, the inclination angle of the second inclined surface 11c on the punch side with the first inclined surface 11b on the punch side as a reference is set to β = 0~3°, the bending radius of the die shoulder R 119 is set to 10mm, and the interval between the first inclined surface 11b on the punch side and the first inclined surface 13b on the die side at the forming bottom stop, and the interval between the second inclined surface 11c on the punch side and the second inclined surface 13c on the die side are both set to 3% of the plate thickness of the sheet metal 100.

[0132] Then, the height of the bending wrinkle peak of the bending wrinkle portion 127 generated in the longitudinal wall portion 123 of the stamped product 120 formed in the second forming process is calculated. Here, the bending wrinkle peak height is set as the maximum value of the distance to the surface of the bending wrinkle portion 127 in the direction perpendicular to the longitudinal wall portion 123.

[0133] In this embodiment 1, as shown below, the stamping simulation was performed by changing the inclination angle β of the second inclined surface portion 11c of the punch side of the punch 11 used in the stamping of the stamped article 120 and the position of the punch ridge portion 11d, and the effect of reducing the height of the bending wrinkle peak was studied.

[0134] [The tilt angle of the second tilted face on the punch side]

[0135] In this embodiment, firstly, the tilt angle β of the second tilted surface 11c of the punch side of the punch 11 used in the second forming process is changed, and the height of the bending wrinkle peak of the bending wrinkle portion is studied.

[0136] The inclination angle of the second inclined surface 11c on the punch side, from the first inclined surface 11b on the punch side, is set to β = 1°, 2°, or 3° within a range of inclination angle α (=3°) or less on the outer side from the stamping direction. These cases are examples of Invention Examples 1-1, 1-2, and 1-3, respectively, to determine the height of the bending wrinkle peak in the bending wrinkle portion 127. Furthermore, as a comparison, a... Figure 4 As a comparative example 1, the case of a stamped product 120 formed by stamping with a conventional stamping die 40, in which the flange portion 115 of the stamped product 110 before reverse bending is reverse bent to become part of the longitudinal wall portion 123 is shown. Similar to Invention Examples 1-1 to 1-3, the height of the bending wrinkle peak of the bending wrinkle portion 127 is determined.

[0137] Table 1 shows the results of the bending wrinkle peak height of the stamped articles 120 in Examples 1-1 to 1-3 of the Invention and Comparative Example 1.

[0138] [Table 1]

[0139]

[0140] The bending wrinkle peak height in Comparative Example 1 is 1.72 mm. In contrast, the bending wrinkle peak heights in Invention Examples 1-1, 1-2, and 1-3 are 1.24 mm, 1.35 mm, and 1.52 mm, respectively, all lower than those in Comparative Example 1. This demonstrates that by using a punch 11 with a punch ridge portion 11d, the bending wrinkle peak height of the bending wrinkle portion 127 can be reduced.

[0141] Furthermore, based on the results of Invention Examples 1-1 to 1-3, it was shown that increasing the tilt angle β of the second tilted surface portion 11c on the punch side increases the effect of reducing the height of the bending wrinkle peak. This is because, when the flange portion of the stamped article 110 is reverse-bent, deformation that causes the die shoulder R portion 119 to bend in the opposite direction is promoted.

[0142] It should be noted that a stamping simulation was also performed when the tilt angle β of the second tilted surface 11c on the punch side was set to be 4° larger than the tilt angle α of the first tilted surface 11b on the punch side.

[0143] In this case, the die 13 can also be moved horizontally, and the insert bending is performed on the punch 11 side. Even if the inclination angle of the second inclined surface 11c on the punch side is greater than the inclination angle α of the first inclined surface 11b on the punch side, the flange portion of the stamped product 110 before reverse bending can be reverse bent to stamp the stamped product 120.

[0144] [The Influence of the Position of the Punch Ridge]

[0145] Next, a stamping simulation was performed on the case where the position of the punch ridge portion 11d of the punch 11 used in the second forming process was changed within the preferred scope of the present invention, and the height of the bending wrinkle peak of the bending wrinkle portion was determined.

[0146] Here, as an example of the invention, the case where the inclination angle of the second inclined surface 11c on the punch side is set to β = 3° within the range of an inclination angle α on the outer side of the first inclined surface 11b on the punch side from the stamping direction, is taken as Example 2-1 to Example 2-5.

[0147] Table 2 shows the results of the bending wrinkle peak heights of the stamped articles 120 in Invention Examples 2-1 to 2-5 and Comparative Example 1 above.

[0148] [Table 2]

[0149]

[0150] In Invention Example 2-1, the position of the punch ridge portion 11d is set within the preferred range of the present invention. In Invention Example 2-2, the position of the punch ridge portion 11d is set within the range of the plastic bending deformation region 113a on the longitudinal wall side. In Invention Example 2-2, the position of the punch ridge portion 11d is set within the range of the die shoulder R portion 119. In Invention Example 2-3, the position of the punch ridge portion 11d is set within the range of the plastic bending deformation region 115a on the flange side. The bending wrinkle peak heights in Invention Examples 2-1, 2-2, and 2-3 are 1.24 mm, 1.23 mm, and 1.24 mm, respectively, which are significantly reduced compared to the bending wrinkle peak height in Comparative Example 1.

[0151] In Invention Examples 2-4 and 2-5, the position of the punch ridge portion 11d is outside the preferred range of the present invention. In Invention Example 2-4, the punch ridge portion 11d is positioned closer to the punch shoulder R portion 117 than the plastic bending deformation region 113a on the longitudinal wall side. In Invention Example 2-5, the punch ridge portion 11d is positioned closer to the top of the flange portion 115 than the plastic bending deformation region 115a on the flange side. The bending wrinkle peak height in Invention Examples 2-4 and 2-5 is 1.45 mm, which is smaller than the bending wrinkle peak height in Comparative Example 1, but larger than that in Invention Examples 2-1 to 2-3.

[0152] Example 2

[0153] In this embodiment 2, stamping simulations were performed on the first forming process and the second forming process, and the size of the curved wrinkles 141 generated in the longitudinal wall portion 133 of the stamped product 130 was studied. The first forming process described above... Figure 11 (a) The reverse-bending pre-stamped article 110 with the hat-shaped cross-section shown is stamped, and the second forming process described above causes the flange portion 115 of the reverse-bending pre-stamped article 110 to bend in reverse. Figure 11 (b) The stamped product 130 with the hat-shaped cross-section shown is stamped.

[0154] In this stamping simulation, similar to Embodiment 1 above, Embodiment 3 uses a stamping die (not shown) that includes a punch having a first inclined face on the punch side, a second inclined face on the punch side, and a punch ridge portion, and a die having a flange reverse bending portion. The stamping is performed on a stamping product 130 that has a cap-shaped cross-section that reverse bends a portion of the longitudinal wall portion 113 side of the flange portion 115 of the stamping product 110 before reverse bending to become a longitudinal wall portion 133 and makes the portion of the flange portion 115 opposite to the longitudinal wall portion 113 become the flange portion 135.

[0155] For the target shape of the stamped article 130, the forming height is set to H = 80 mm, and the width of the flange portion 135 is set to WF = 20 mm. Furthermore, for the punch used in the stamping of the stamped article 130, the inclination angle of the first inclined surface on the punch side is set to α = 3°, and the inclination angle of the second inclined surface on the punch side is set to β = 3°. Moreover, other conditions regarding the target shape of the stamped article 130 and the dimensions of the stamping die are the same as in Embodiment 1 described above.

[0156] Furthermore, in Example 2, a case in which the flange portion 115 of the stamped product 110 is bent backwards before being stamped and the stamped product 130 is stamped using an existing stamping die 40 is used as a comparative example.

[0157] Then, for both Invention Example 3 and Comparative Example 2, the height of the bending wrinkle peaks of the remaining bending wrinkles 141 in the longitudinal wall portion 133 of the stamped article 130 with a hat-shaped cross-section was determined. The bending wrinkle peak heights were determined in the same manner as in the above-described embodiment (see [reference]). Figure 6 Table 3 shows the results of the bending wrinkle peak heights in Invention Example 3 and Comparative Example 2.

[0158] [Table 3]

[0159]

[0160] The bending wrinkle peak height in Comparative Example 2 was 1.71 mm. In contrast, the bending wrinkle peak height in Invention Example 3 was 1.24 mm, which is lower than that in Comparative Example 2. Thus, according to the stamping method of the present invention, it is shown that even when the stamped product 130 with a hat-shaped cross-section is made into the target shape, the bending wrinkle peak height of the bending wrinkle portion 141 can be reduced.

[0161] Industrial applicability

[0162] According to the present invention, a stamping method can be provided that eliminates the need for a special device to correct bending wrinkles, thereby reducing the size of the bending wrinkles remaining in the longitudinal wall portion of a stamped article whose flange portion has been bent backwards to become a longitudinal wall portion before the reverse bending of the hat-shaped cross-section.

[0163] Explanation of reference numerals in the attached figures

[0164] 10: Stamping die; 11: Punch; 11a: Forming surface of the longitudinal wall of the punch; 11b: First inclined surface of the punch; 11c: Second inclined surface of the punch; 11d: Punch ridge; 11e: Forming surface of the top plate; 13: Die; 13a: Forming surface of the longitudinal wall of the die; 13b: First inclined surface of the die; 13c: Second inclined surface of the die; 13d: Flange reverse bending portion; 13e: Flange forming surface; 13f: Die shoulder; 40: Stamping die; 41: Punch; 41a: Forming surface of the longitudinal wall of the punch; 43: Die; 43a: Forming surface of the longitudinal wall of the die; 43b: Flange reverse bending portion; 110: Stamped part before reverse bending; 111: Top plate portion; 113: Longitudinal wall portion; 113 a: Longitudinal wall side plastic bending deformation area; 115: Flange portion; 115a: Flange side plastic bending deformation area; 117: Punch shoulder R portion; 119: Die shoulder R portion; 120: Stamped part; 121: Top plate portion; 123: Longitudinal wall portion; 125: Punch shoulder R portion; 127: Bending and wrinkled portion; 127a: Die shoulder R equivalent portion; 127b: Longitudinal wall side plastic bending deformation portion; 127c: Flange side plastic bending deformation portion; 127d: Interface; 127e: Interface; 130: Stamped part; 131: Top plate portion; 133: Longitudinal wall portion; 135: Flange portion; 137: Punch shoulder R portion; 139: Die shoulder R portion; 141: Bending and wrinkled portion; 151: Flat surface portion; 153: Electrode; 155: Welding portion.

Claims

1. A stamping forming method, which is a stamping forming article having a hat-shaped cross-section having a top plate portion, a longitudinal wall portion that is continuously inclined from the top plate portion with respect to the stamping forming direction, and a flange portion that is continuous from the longitudinal wall portion via a die shoulder R portion, wherein the flange portion is reverse-bent to form the longitudinal wall portion, characterized in that, For the aforementioned punch The stamped article has a top plate forming surface that forms the top plate portion of the stamped article, having the same shape as the top plate portion of the stamped article before bending, and a longitudinal wall forming surface that forms the longitudinal wall portion. The longitudinal wall forming surface continuously slopes outward from the top plate forming surface and has a first inclined surface on the punch side with an inclination angle relative to the stamping direction equal to the inclination angle of the longitudinal wall portion of the stamped article before reverse bending. It also has a second inclined surface on the punch side that continuously slopes inward from the lower end of the first inclined surface on the punch side, which is more inward than the first inclined surface on the punch side. The first and second inclined surfaces on the punch side form an outwardly convex mountain shape, and a punch ridge is formed at their connection point. For the aforementioned die... The flange has a reverse bending portion that causes the flange portion of the reverse-bending pre-stamped article, which is placed on the punch, to bend in reverse. Before the reverse-bending stamping article is placed on the punch, the die is moved relative to the punch side, so that the punch ridge portion abuts against the inner surface side of the longitudinal wall portion and the flange portion is reverse-bent through the flange reverse-bending portion, thereby forming the longitudinal wall portion of the stamping article.

2. The stamping forming method according to claim 1, The concave die has an inner surface shape that is spaced parallel to the outer surface of the convex die.

3. The stamping forming method according to claim 1 or 2, The punch ridge is formed at a position that satisfies the following formula. h1-R1(1-sinα)-R1 / 2 ≤ h2≤ h1-R1(1-sinα)+2πR1(90-α) / 360+R1 / 2 in, h2 represents the distance in the stamping direction from the forming surface of the top plate of the punch to the punch ridge, in mm; h1 represents the forming height of the stamped part before reverse bending, in mm; R1 represents the bending radius of the die shoulder R of the stamped part before reverse bending, in mm; and α represents the inclination angle of the longitudinal wall of the stamped part before reverse bending relative to the stamping direction, in °.

Images