Peripheral structure for through-hole of metal plate, blank, and automobile component

Abstract

The metal plate (200) has a flat plate section (102) and a machined section (204) having a through-hole (104a) formed in the center thereof. The machined section (204) comprises: a flat surface (406) formed on one side of the flat surface (102a) of the flat plate section (102) in the thickness direction (A); and an inclined surface (408) which extends from the flat surface (406) toward the flat surface (102a), and which satisfies the following conditions: 1.0 < = W < =-3.8314 * (R / t) + 11.47 < = 5.0, and 0.1 < = H < =-0.6604 * (R / t) + 2.0489 < = 1.0. Wherein, in the formula, W is the length (mm) of the inclined surface (408) in a direction orthogonal to the thickness direction (A), R is the radius of curvature (mm) of the through hole (104a) when viewed from the thickness direction (A), t is the thickness (mm) of the metal plate (200), and H is the distance (mm) between the flat surface (102a) and the flat surface (406) in the thickness direction (A).

Description

Technical Field

[0001] The present invention relates to a peripheral structure of a through-hole in a metal plate, a blank, and an automotive component. Background Art

[0002] In recent years, due to the tightening of carbon dioxide emission restrictions, there has been a demand for lighter automotive bodies. Along with this, the high-strength and thin-walling of metal plates used as automotive components have been continuously developed. On the other hand, excellent fatigue durability is required for automotive components.

[0003] There are cases where punching is performed on a metal plate used as a blank for an automotive component. When deformation is applied to an automotive component made of such a metal plate, stress concentration occurs around the punching portion (hole edge). As a result, there are cases where cracks and fatigue failures occur from the punching portion. Therefore, in order to improve the fatigue durability of automotive components, it is important to prevent fatigue cracks from occurring in the punching portion.

[0004] Conventionally, methods for preventing the occurrence of cracks in the punching portion have been proposed. For example, Patent Document 1 discloses a punching method for improving the stretch flange property of the punching end face. The punching die used in the punching method disclosed in Patent Document 1 has a cutting edge provided at a position that has descended a predetermined distance from the flat portion of the upper surface of the punching die along the punching direction, and the cutting edge portion is chamfered.

[0005] In the metal plate punched by the method of Patent Document 1, at the moment of punching completion, the workpiece bends in the punching direction. Therefore, when flanging is performed upward in the same direction as the punching direction after punching, the punching end face becomes a shape that has been flanged to a certain extent at the initial moment of upward flanging. In this case, when performing upward flanging, the plastic strain amount of the end face due to stretch flange deformation can be reduced. As a result, the stretch flange property of the punching end face can be improved, and the occurrence of cracks at the punching end face can be prevented.

[0006] Prior art documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-255167 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] In Patent Document 1, as described above, research has been conducted on improving stretch flangeability. However, no research has been conducted on the stress concentration generated around the punching section when deformation is applied to the entire metal plate. That is, no research has been conducted on the fatigue durability of a metal plate having a punching section.

[0011] Therefore, an object of the present invention is to improve the fatigue durability of a metal plate having a through-hole formed by punching.

[0012] Means for Solving the Problem

[0013] The present invention is directed to the peripheral structure, blank, and automotive component of a through-hole in a metal plate as described below.

[0014] (1) A peripheral structure of a through-hole in a metal plate, which is a structure around a through-hole formed in a metal plate, and has:

[0015] A flat plate portion; and a processing portion that stands up from the flat plate portion to one side in the thickness direction of the flat plate portion and has the through-hole formed at the center,

[0016] The flat plate portion includes a first flat surface that surrounds the periphery of the processing portion on the one side of the flat plate portion,

[0017] The processing portion includes: a wall surface that extends in the thickness direction and constitutes the inner wall of the through-hole; an annular second flat surface that is located inside the first flat surface when viewed from the thickness direction and extends in a direction crossing the thickness direction from the edge on the one side of the wall surface at a position on the one side of the first flat surface in the thickness direction; and an inclined surface that connects the outer edge of the second flat surface and the inner edge of the first flat surface and is inclined with respect to the thickness direction,

[0018] When viewed from the thickness direction, the through-hole includes a curved portion that is curved in an arc shape so as to bulge toward the outside of the through-hole,

[0019] In a cross-section of the processing portion that is parallel to the thickness direction and passes through the center of the through-hole and the curved portion, the following equations (i) and (ii) are satisfied,

[0020] 1.0 ≤ W ≤ -3.8314×(R / t) + 11.47 ≤ 5.0 ··· (i)

[0021] 0.1 ≤ H ≤ -0.6604×(R / t) + 2.0489 ≤ 1.0 ··· (ii)

[0022] Among them, in the above formulas (i) and (ii), W is the length (mm) of the inclined surface in the direction orthogonal to the thickness direction, R is the radius of curvature (mm) of the portion corresponding to the cross-section in the bent portion, t is the thickness (mm) of the metal plate, and H is the distance (mm) in the thickness direction between the first flat surface and the second flat surface.

[0023] (2) The peripheral structure of the through-hole of the metal plate according to (1) above, wherein the second flat surface extends in the direction orthogonal to the thickness direction.

[0024] (3) The peripheral structure of the through-hole of the metal plate according to (1) or (2) above, wherein the wall surface includes a shear surface extending in the direction orthogonal to the first flat surface.

[0025] (4) The peripheral structure of the through-hole of the metal plate according to (3) above, wherein in the cross-section, the portion of the wall surface located between the shear surface and the second flat surface is arranged to be positioned outside the shear surface in the direction orthogonal to the central axis of the through-hole, and the inclined surface is arranged to be positioned outside the outer edge of the second flat surface in the orthogonal direction.

[0026] (5) The peripheral structure of the through-hole of the metal plate according to any one of (1) to (4) above, wherein in the cross-section, the following formula (iii) is satisfied,

[0027] H ≤ 0.0975×(R / t) + 0.3009 ··· (iii)

[0028] Among them, in the above formula (iii), H is the distance (mm) in the thickness direction between the first flat surface and the second flat surface, R is the radius of curvature (mm) of the portion corresponding to the cross-section in the bent portion, and t is the thickness (mm) of the metal plate.

[0029] (6) The peripheral structure of the through-hole of the metal plate according to (5) above, wherein in the cross-section, the following formula (iv) is satisfied,

[0030] H ≤ 0.0975×(R / t) + 0.2381 ··· (iv)

[0031] Among them, in the above formula (iv), H is the distance (mm) in the thickness direction between the first flat surface and the second flat surface, R is the radius of curvature (mm) of the portion corresponding to the cross-section in the bent portion, and t is the thickness (mm) of the metal plate.

[0032] (7) The peripheral structure of the through-hole of the metal plate according to any one of (1) to (6) above, wherein the through-hole has a circular shape when viewed in the thickness direction.

[0033] (8) A blank having the peripheral structure of the through-hole of the metal plate according to any one of (1) to (7) above.

[0034] (9) An automotive component having the peripheral structure of the through-hole of the metal plate according to any one of (1) to (7) above.

[0035] Effects of the Invention

[0036] According to the present invention, it is possible to improve the fatigue durability of the metal plate formed with the through-hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. is an example of a metal plate formed with a through-hole by punching.

[0038] Figure 2 FIG. is another example of a metal plate formed with a through-hole by punching.

[0039] Figure 3 FIG. is a diagram showing an analysis model of the metal plate used in the simulation.

[0040] Figure 4 FIG. is a diagram showing another example of the analysis model of the metal plate.

[0041] Figure 5 FIG. is a diagram showing an analysis model of the metal plate of the comparison object.

[0042] Figure 6 FIG. is a diagram showing the analysis result.

[0043] Figure 7 FIG. is a diagram showing the analysis result.

[0044] Figure 8 FIG. is a schematic diagram of an example of a die for punching.

[0045] Figure 9 FIG. is a diagram showing the state of the die and the blank just before cutting the blank.

[0046] Figure 10 FIG. is a diagram for explaining the condition of forming burrs when cutting the blank.

[0047] Figure 11 FIG. is a diagram showing the analysis result.

[0048] Figure 12This is a diagram showing another example of a metal plate with a through-hole formed by punching.

[0049] Figure 13 This is a diagram showing a modified example of a die.

[0050] Figure 14 This is a diagram showing a modified example of a die. Detailed implementation

[0051] (Research conducted by the present inventor)

[0052] Figure 1 This is a diagram showing an example of a metal plate with a through-hole formed by punching. Figure 1 (a) of which is a perspective view of the metal plate. Figure 1 (b) of which is a cross-sectional view of the portion surrounded by the dashed line in Figure 1 (a). Figure 1 The metal plate 100 shown has a flat portion 102 and a processed portion 104. In addition, in Figure 1 , the thickness direction of the flat portion 102 is indicated by the arrow A. Hereinafter, the thickness direction of the flat portion 102 will also be simply referred to as the thickness direction A.

[0053] The processed portion 104 is formed by punching so as to stand up from the flat portion 102 to one side in the thickness direction A. A through-hole 104a is formed in the center of the processed portion 104. When viewed from the thickness direction A, the through-hole 104a has a circular shape.

[0054] The flat portion 102 has a flat surface 102a provided on one side in the thickness direction A and a flat surface 102b provided on the other side in the thickness direction A. The flat surfaces 102a and 102b are respectively provided so as to surround the periphery of the processed portion 104.

[0055] As Figure 1 (b) shows, the processed portion 104 has a wall surface 400, an inclined surface 402, and an inclined surface 404. The wall surface 400 extends in the thickness direction A and constitutes the inner wall of the through-hole 104a. The wall surface 400 includes a shear surface 400a and a fracture surface 400b. The inclined surface 402 is formed in a ring shape when viewed from the thickness direction A so as to connect the edge on one side in the thickness direction A of the wall surface 400 and the inner edge of the flat surface 102a. The inclined surface 404 is a burr and is formed in a ring shape when viewed from the thickness direction A so as to connect the edge on the other side in the thickness direction A of the wall surface 400 and the inner edge of the flat surface 102b.

[0056] In automotive components or the like using the above-described metal plate 100 as a blank, there are cases where bending deformation indicated by arrow B is applied around the processing portion 104. As a result of the research by the present inventor, it has been found that when such bending deformation is applied to the metal plate 100, stress concentration occurs at the edge of the through-hole 104a.

[0057] Therefore, the present inventor has conducted research to suppress the generation of such stress concentration. Specifically, the relationship between the shape of the end portion of the processing portion and the stress generated at the edge of the through-hole has been investigated.

[0058] Figure 2 FIG. is a diagram showing another example of a metal plate in which a through-hole is formed by punching. Figure 2 (a) is a perspective view showing the metal plate. Figure 2 (b) is a cross-sectional view of the portion surrounded by the chain line in Figure 2 (a). In addition, the manufacturing method of the metal plate shown in Figure 2 will be described later.

[0059] Figure 2 The difference between the metal plate 200 shown in Figure 1 and the metal plate 100 shown in

[0060] (Simulation)

[0061] The present inventor has studied the stress generated at the edge of the through-hole 104a when bending deformation is applied to the metal plate 100 and the metal plate 200. Specifically, the present inventor has conducted a simulation based on FEM analysis using a computer to investigate the stress generated at the edge of the through-hole 104a.

[0062] Figure 3 FIG. is a diagram showing Figure 1 the analysis model of the metal plate 100. Figure 4 FIG. is a diagram showing Figure 2 the analysis model of the metal plate 200. Figure 3 (a) of Figure 4 and Figure 3 (a) of Figure 4The front view of the analysis model in (b). Figure 3 In (c) of Figure 4 In (c) of Figure 3 In (a) of Figure 4 The sectional view of the part surrounded by the dash-dotted line in (a) of . In addition, in the analysis models 300 and 310, for the parts having a structure corresponding to the structure of the metal plates 100 and 200, the same reference numerals as those of the metal plates 100 and 200 are used. However, as shown in Figure 3 In (c) of Figure 4 In (c) of , in the analysis models 300 and 310, the shapes of the machining parts 104 and 204 are simplified. The material properties of a hot-rolled steel sheet with a tensile strength of 780 MPa grade are set in the analysis models 300 and 310 and the analysis model 350 described later.

[0063] In Figure 3 And Figure 4 In , W represents the length (mm) in the direction orthogonal to the thickness direction A of the inclined surfaces 402 and 408, R represents the radius of curvature (mm) of the through-hole 104a as observed from the thickness direction A, and t represents the thickness (mm) of the flat part 102 (metal plate). In addition, in Figure 3 In , H represents the distance (mm) in the thickness direction A between the flat surface 102a and the top end of the machining part 104. In Figure 4 In , H represents the distance (mm) in the thickness direction A between the flat surface 102a and the flat surface 406. In addition, in Figure 4 In , F represents the length in the direction orthogonal to the thickness direction A of the flat surface 406. In this simulation, multiple analysis models 300 and 310 were created by changing the ratio of the length W, the radius of curvature R to the thickness t, i.e., R / t, and the distance H, and FEM analysis was performed. The length and width of the analysis models 300 and 310 were set to 90 mm and 30 mm. In addition, in the analysis model 300, the length W was set to 1.0 - 3.0 mm, the ratio R / t was set to 1.56 - 2.17, and the distance H was set to 0.1 - 1.0 mm. In the analysis model 310, the length W was set to 1.0 - 5.0 mm, the ratio R / t was set to 1.25 - 3.13, and the distance H was set to 0.1 - 1.0 mm. In addition, in the analysis model 310, the length F was set to 0.1 mm.

[0064] In addition, in this simulation, an analysis model for comparison was created. Figure 5 The figure showing the analysis model for comparison. Figure 5 The top view of the analysis model in (a) of Figure 5 The sectional view showing the b-b part of (a) of Figure 5 In (a) of Figure 5As shown, the analysis model 350 has a structure in which only a through-hole 350a is formed in the central portion of the metal plate, and no inclined surface is formed around the through-hole 350a. That is, the analysis model 350 has a flat shape as a whole. In addition, similar to the analysis models 300 and 310, a plurality of analysis models 350 were fabricated by changing the ratio R / t of the radius of curvature R to the thickness t of the through-hole 350a. The length and width of the analysis model 350 are the same as those of the analysis models 300 and 310, which are 90 mm and 30 mm.

[0065] In the FEM analysis, a 25 mm × 30 mm region 300a (hereinafter referred to as one end portion 300a) on one end side in the length direction and a 25 mm × 30 mm region 300b (hereinafter referred to as the other end portion 300b) on the other end side of the analysis models 300, 310, and 350 were constrained. In addition, as indicated by the arrow C in (b) of Figure 3 (b), Figure 4 (b), and Figure 5 (b), while fixing the position of the one end portion 300a, the position of the other end portion 300b was moved to apply a bending deformation to the analysis models 300, 310, and 350. And, when the other end portion 300b was rotated 2° with respect to the center of the analysis models 300, 310, and 350, the stress generated at the edge of the through-holes 104a and 350a on the outer surface side of the bending of the analysis models 300, 310, and 350 was investigated.

[0066] Specifically, first, the present inventors compared the stresses (the maximum value of the maximum principal stress) generated at the edges of the through-holes 104a and 350a for the analysis models 310 and 350 having equal ratios R / t. And, the length W and the distance H were determined when the stress generated at the edge of the through-hole 104a was lower than the stress generated at the edge of the through-hole 350a. The investigation results are shown in Tables 1 and 2 below. In addition, in Tables 1 and 2, "A" and "B" indicate cases where the stress generated at the edge of the through-hole 104a is lower than the stress generated at the edge of the through-hole 350a. In particular, "A" indicates a case where the stress generated at the edge of the through-hole 104a becomes 90% or less of the stress generated at the edge of the through-hole 350a. In addition, "C" indicates a case where the stress generated at the edge of the through-hole 104a is equal to or higher than the stress generated at the edge of the through-hole 350a.

[0067] [Table 1]

[0068] Table 1

[0069]

[0070] [Table 2]

[0071] Table 2

[0072]

[0073] Based on the results shown in Table 1 and Table 2, the present inventor obtained the upper limit values of the length W and the distance H for making the stress generated at the edge of the through hole 104a in the analysis model 310 lower than the stress generated at the edge of the through hole 350a in the analysis model 350. The upper limit values of the length W and the distance H for each ratio R / t are shown in Table 3 below.

[0074] [Table 3]

[0075] Table 3

[0076]

[0077] In addition, at each ratio R / t, if the length W and the distance H are respectively below specific values, then in the above Tables 1 and 2, all comparison results become either "A" or "B". Such specific values are referred to as upper limit values. For example, for the analysis model 310 with a ratio R / t of 1.92, as shown in Table 2, when the length W is 4.0 mm, the comparison result becomes "B" within the range where the distance H is from 0.1 to 0.9 mm. However, as shown in Table 1, when the length W is 1.0 mm and the distance H is 0.9 mm, the comparison result becomes "C". Therefore, the upper limit values of the length W and the distance H for the analysis model 310 with a ratio R / t of 1.92 are not 4.0 mm (length W) and 0.9 mm (distance H), but rather 4.0 mm (length W) and 0.8 mm (distance H).

[0078] In addition, the upper limit values of the length W and the distance H were determined in such a way that the total number of "A" and "B" in the comparison results is the largest. For example, in the case of a ratio R / t of 2.17, the combination of the upper limit value of the length W and the upper limit value of the distance H with the largest total number of "A" and "B" in the comparison results is as follows: the upper limit value of the length W is 3.0 mm, and the upper limit value of the distance H is 0.6 mm. Therefore, the upper limit values of the length W and the distance H in the case of a ratio R / t of 2.17 are 3.0 mm and 0.6 mm respectively.

[0079] In Figure 6 the relationship between the upper limit value of the length W and the ratio R / t is shown, and in Figure 7 the relationship between the upper limit value of the distance H and the ratio R / t is shown. In Figure 6 and Figure 7An approximate curve obtained by using the least squares method from a plurality of data (length W and distance H) obtained through analysis is shown. In addition, as described above, in the analysis using the analysis model 310, the length W is set to 1.0 to 5.0 mm, and the distance H is set to 0.1 to 1.0 mm. Here, in the case where the combination of the upper limit value of the length W and the upper limit value of the distance H becomes 5.0 mm (the maximum set value of the length W) and 1.0 mm (the maximum set value of the distance H) (that is, the combination when R / t = 1.25 and R / t = 1.56), there is a possibility of inappropriately representing the combination of the upper limit value of the length W and the upper limit value of the distance H. Specifically, as shown in Table 1 and Table 2, when the ratio R / t is 1.25 and 1.56, within the range where the length W is 1.0 to 5.0 mm and the distance H is 0.1 to 1.0 mm, all comparison results become "B" or "A". Considering this point, when the ratio R / t is 1.25 and 1.56, even if the length W is greater than 5.0 mm or the distance H is greater than 1.0 mm, there is a possibility that the comparison result becomes "B" or "A". In addition, in the case where the combination of the upper limit value of the length W and the upper limit value of the distance H becomes 1.0 mm (the minimum set value of the length W) and 0.1 mm (the minimum set value of the distance H) (that is, the combination when R / t = 3.13), there is also a possibility of inappropriately representing the combination of the upper limit value of the length W and the upper limit value of the distance H. Specifically, there is a possibility that the combination of the upper limit value of the length W and the upper limit value of the distance H is determined by values below the minimum set values of the length W and the distance H. Considering these points, the data for the cases where the ratio R / t is 1.25, 1.56, and 3.13 are excluded and obtained Figure 6 and Figure 7 the approximate curve shown.

[0080] According to this simulation result, it can be known that: in Figure 2 the metal plate 200 shown, by satisfying the following equations (i) and (ii), the stress generated at the edge of the through hole 104a can be reduced. In this case, even if the metal plate 200 is subjected to bending deformation, stress concentration generated at the edge of the through hole 104a can be suppressed. Therefore, it is possible to prevent cracks from occurring at the edge of the through hole 104a. As a result, the fatigue durability of the metal plate 200 can be improved.

[0081] 1.0 ≤ W ≤ -3.8314×(R / t) + 11.47 ≤ 5.0 ··· (i)

[0082] 0.1 ≤ H ≤ -0.6604×(R / t) + 2.0489 ≤ 1.0 ··· (ii)

[0083] Next, the present inventors compared the stresses (the maximum value of the maximum principal stress) generated at the edges of the through-holes 104a and 350a for the analysis models 300 and 350 where the ratios R / t are equal to each other. And, in the same manner as described above, the upper limit values of the length W and the distance H were obtained such that the stress generated at the edge of the through-hole 104a in the analysis model 300 is lower than the stress generated at the edge of the through-hole 350a in the analysis model 350. As a result, the upper limit values of the length W and the distance H of the analysis model 300 when the ratio R / t is 2.17 are 1.0 mm and 0.1 mm, respectively. In addition, the upper limit values of the length W and the distance H of the analysis model 300 when the ratio R / t is 1.56 are 1.0 mm and 1.0 mm, respectively. If these upper limit values are compared with the upper limit values of the analysis model 310 shown in Table 3, it can be seen that: for the ranges of the length W and the distance H that can make the stress generated at the edge of the through-hole 104a lower than the stress generated at the edge of the through-hole 350a in the analysis model 350, the analysis model 310 is larger than the analysis model 300.

[0084] From the results, it can be seen that: the analysis model 310 (refer to Figure 4 ) in which a flat surface 406 is formed at the tip of the processing portion 204 and the analysis model 300 (refer to Figure 3 ) in which the flat surface 406 is not formed can reduce the value of the stress generated at the edge of the through-hole 104a.

[0085] In addition, as can be seen by comparing Figure 3 and Figure 4 , the angle between the wall surface 400 and the inclined surface 402 of the analysis model 300 becomes significantly smaller compared to the angle between the wall surface 400 and the flat surface 406 of the analysis model 310. In other words, in the analysis model 300, the tip of the processing portion 104 has a more pointed shape compared to the analysis model 310. Therefore, it is considered that: in the analysis model 300, stress concentration is more likely to occur at the edge of the through-hole 104a (the tip of the processing portion 104) compared to the analysis model 310. From the above results, it can be seen that by providing the flat surface 406 at the tip of the processing portion 204 as in the metal plate 200 such as Figure 2 , stress concentration at the edge of the through-hole 104a can be suppressed.

[0086] (Manufacturing method of the metal plate)

[0087] Next, the manufacturing method of the metal plate 200 will be described. Figure 8 is a schematic diagram showing an example of a mold for manufacturing the metal plate 200. As shown in Figure 8As shown, the die 10 includes a punch 12, a die 14, and a blank holder 16. The punch 12 is formed in a columnar shape (a cylindrical shape in this embodiment) and is arranged to be able to move forward and backward in the vertical direction (the stamping direction).

[0088] The die 14 has a hollow shape so that the punch 12 can be inserted therein. In this embodiment, the die 14 has: a flat and annular support surface 40 that supports a blank (metal plate) 18; a cylindrical (a cylindrical shape in this embodiment) inner peripheral surface 42 that extends downward from the inner peripheral edge of the support surface 40; a flat and annular (a circular shape in this embodiment) flange surface 44 that extends from the lower edge of the inner peripheral surface 42 toward the inside of the inner peripheral surface 42; and a cylindrical (a cylindrical shape in this embodiment) inner peripheral surface 46 that extends downward from the inner peripheral edge of the flange surface 44. The blank holder 16 is formed in a hollow shape so that the punch 12 can be inserted therein and has an annular lower surface 60 that faces the support surface 40 of the die 14. In this embodiment, the inner peripheral edges of the support surface 40 and the flange surface 44 are each circular in shape.

[0089] As Figure 8 shown, in the case of punching the blank 18, first, the blank 18 is placed on the support surface 40 of the die 14. After that, with the blank 18 pressed by the blank holder 16, the punch 12 is moved downward to cut a predetermined area of the blank 18 (shearing process) using the punch 12 and the die 14. Thus, as Figure 2 shown, a metal plate 200 having a through hole 104a can be obtained.

[0090] Figure 9 is a view showing the state of the die 10 and the blank 18 immediately before cutting the blank 18. As Figure 9 shown, when cutting a predetermined area of the blank 18 using the die 10, the blank 18 is cut with the shoulder of the punch 12 and the inner peripheral edge of the flange surface 44 of the die 14 as the cutting tools respectively.

[0091] Here, in this embodiment, a step is provided between the support surface 40 and the flange surface 44. Therefore, the portion of the blank 18 located inside the inner peripheral edge of the support surface 40 is pressed toward the flange surface 44 side. Thus, as Figure 2 shown, a processed portion 204 is formed so as to stand up from a flat plate portion 102 in the thickness direction A.

[0092] In addition, as Figure 9 shown, when cutting the blank 18, a part of the blank 18 is pressed against the flange surface 44 to undergo plastic deformation. Thus, as Figure 2 shown, a flat surface 406 can be formed on the processed portion 204.

[0093] In addition, in the metal plate 200, the distance H in the thickness direction A between the flat surface 102a and the flat surface 406 (see Figure 2 ) is substantially equal to the distance h in the stamping direction (vertical direction) of the die 10 between the support surface 40 and the flange surface 44 (see Figure 8 ). Therefore, the distance H in the thickness direction A between the flat surface 102a and the flat surface 406 can be adjusted by adjusting the distance h between the support surface 40 and the flange surface 44. Further, in the metal plate 200, the length W in the direction orthogonal to the thickness direction A of the inclined surface 408 can be adjusted by adjusting the length w in the direction orthogonal to the stamping direction of the flange surface 44 with respect to the die 10 (see Figure 8 ). In addition, the clearance CL between the punch 12 and the die 14 (the inner peripheral edge of the flange surface 44) (see Figure 2 ) may be made appropriate according to the thickness of the blank 18. For example, it is set to 18% or less of the thickness of the blank 18, and preferably set to 15% or less. Figure 9

[0094] Regarding the manufacturing method of the metal plate 200, the present inventors further conducted research and found that: in the die 10, if the distance h in the stamping direction between the support surface 40 and the flange surface 44 becomes large, burrs are likely to be generated. Figure 10 FIG. is a view for explaining the situation of forming burrs when cutting the blank 18.

[0095] As Figure 10 shown, as a result of the research by the present inventors, it is found that: when cutting the blank 18, an inflection point P is generated on the lower surface of the blank 18 between the support surface 40 and the flange surface 44, and there is a case where the portion of the blank 18 between the inflection point P and the flange surface 44 deforms in a manner of bulging outward. In this case, it is found that a fracture occurs between the inflection point P and the shoulder of the punch 12 (the portion indicated by the single-dot chain line), and it may not be possible to properly form the flat surface 406 (see Figure 2 ), or excessive burrs may be generated.

[0096] Therefore, the present inventors created an axisymmetric model of two-dimensional solid elements for the die 10 and the blank 18 and performed FEM analysis to investigate the generation conditions of the inflection point P. Specifically, multiple analysis models were created by changing the ratio R1 / t1 of the radius of curvature R1 of the outer peripheral surface of the punch 12 (not shown) to the thickness t1 of the blank 18, and FEM analysis was performed. And in each analysis model, the distance d in the stamping direction between the inflection point P and the support surface 40 was investigated. In addition, the ratio R1 / t1 was set to 1.25 to 6.25, the distance h was set to 1.0 mm, and the length w in the direction orthogonal to the stamping direction of the flange surface 44 was set to 1.0 mm. The clearance CL between the punch 12 and the die 14 (see Figure 9 ​)The ratio CL / t1 with respect to the thickness t1 of the blank 18 is set to 12.5%. In addition, the material properties of the blank 18 are set in the same manner as the material properties of the above-described analysis model 300.

[0097] The relationship between the ratio R1 / t1 and the distance d is shown in Figure 11 . In addition, in Figure 11 , an approximate curve obtained by the least squares method from the distance d obtained by analysis is represented by a dashed line. Moreover, in Figure 11 , a straight line parallel to the above approximate curve and passing through the point corresponding to the distance d when the ratio R1 / t1 is 1.25 is represented by a single-dot chain line.

[0098] It is considered that in order not to generate the inflection point P during punching, the distance h in the punching direction between the support surface 40 and the flange surface 44 may be set to be less than or equal to the distance d between the inflection point P obtained by the above-described FEM analysis and the support surface 40. Regarding this point, as described above, in the metal plate 200, the distance H in the thickness direction A between the flat surface 102a and the flat surface 406 is substantially equal to the distance h. Therefore, by performing punching in such a manner that the distance H in the thickness direction A between the flat surface 102a and the flat surface 406 is less than or equal to the distance d obtained by the above-described FEM analysis, the flat surface 406 can be formed more appropriately (see Figure 2 ), and the generation of excessive burrs can be sufficiently suppressed. In addition, when the through hole 104a of the metal plate 200 is formed by using the die 10, the curvature radius R of the through hole 104a is substantially equal to the curvature radius R1 of the outer peripheral surface of the punch 12. In addition, the thickness t of the flat plate portion 102 of the metal plate 200 is substantially equal to the thickness t1 of the blank 18. Therefore, by forming the through hole 104a in such a manner as to satisfy the following formula (iii), the flat surface 406 can be formed more appropriately (see Figure 2 ), and the generation of excessive burrs can be sufficiently suppressed. In addition, it is more preferable to form the through hole 104a in such a manner as to satisfy the following formula (iv). In this case, the area of the flat surface 406 can be made sufficiently large.

[0099] H ≤ 0.0975×(R / t) + 0.3009 ··· (iii)

[0100] H ≤ 0.0975×(R / t) + 0.2381 ··· (iv)

[0101] Among them, in the above formulas, H represents the distance (mm) in the thickness direction A between the flat surface 102a and the flat surface 406, R represents the curvature radius (mm) of the through hole 104a observed from the thickness direction A, and t represents the thickness (mm) of the flat plate portion 102 (metal plate).

[0102] (Description of Embodiments of the Present Invention)

[0103] The present invention has been made based on the above insights. Specifically, the peripheral structure of the through-hole of the metal plate according to an embodiment of the present invention is characterized in that in the peripheral structure of the through-hole 104a of the metal plate 200 shown in Figure 2 , the cross-sectional shape of the processing portion 204 that is parallel to the thickness direction A and passes through the center of the through-hole 104a satisfies the following formulas (i) and (ii).

[0104] 1.0 ≤ W ≤ -3.8314×(R / t) + 11.47 ≤ 5.0 ··· (i)

[0105] 0.1 ≤ H ≤ -0.6604×(R / t) + 2.0489 ≤ 1.0 ··· (ii)

[0106] Wherein, in the above formulas (i) and (ii), W is the length (mm) in the direction orthogonal to the thickness direction A of the inclined surface 408, R is the radius of curvature (mm) of the through-hole 104a, t is the thickness (mm) of the metal plate 200, and H is the distance (mm) in the thickness direction A between the flat surface 102a and the flat surface 406.

[0107] In addition, the peripheral structure of the through-hole of the metal plate according to the present embodiment is formed, for example, using a blank (such as a steel plate or an aluminum plate) with a thickness of 1.6 mm to 4.0 mm and a tensile strength of 590 MPa or more. However, a blank with a thickness less than 1.6 mm or greater than 4.0 mm can also be used, and a blank with a tensile strength less than 590 MPa can also be used.

[0108] In the present embodiment, the flat surface 102a corresponds to the first flat surface, the flat surface 406 corresponds to the second flat surface, and the wall surface 400 of the through-hole 104a corresponds to the bent portion. In addition, in the present embodiment, the radius of curvature of the through-hole 104a refers to the radius of curvature of the shear surface 400a observed from the thickness direction A. The radius of curvature of the through-hole 104a can be measured using a spherometer.

[0109] In addition, in the present embodiment, the flat surface 406 is formed so as to extend in the direction orthogonal to the thickness direction A. In this case, the tip portion of the processing portion 204 does not become a sharp shape, and thus, stress concentration at the edge of the through-hole 104a can be sufficiently prevented. In the cross-section of the processing portion 204 that is parallel to the thickness direction A and passes through the center of the through-hole 104a ( Figure 2 the cross-section shown), the length (corresponding to Figure 4 the length F of (c)) of the flat surface 406 in the direction orthogonal to the thickness direction A is preferably 0.1 mm or more. In addition, in Figure 2In the metal plate 200 shown, the flat surface 406 is provided in a direction orthogonal to the thickness direction A, but the flat surface 406 may not be strictly orthogonal to the thickness direction A. In this specification, the case where the flat surface is inclined 0 to 10° with respect to the direction orthogonal to the thickness direction A is included in "the flat surface extends in the direction orthogonal to the thickness direction A". Even in this case, stress concentration at the edge of the through hole 104a can be sufficiently prevented. Further, in the present embodiment, the flat surface 102a is also formed in a manner of extending in the direction orthogonal to the thickness direction A, similarly to the flat surface 406.

[0110] In addition, in the present embodiment, the wall surface 400 includes a shear surface 400a extending in a direction orthogonal to the flat surface 102a. Further, in Figure 2 In the metal plate 200 shown, the wall surface 400 is provided in a direction orthogonal to the flat surface 102a, but the wall surface 400 may not be strictly orthogonal to the normal direction of the flat surface 102a. In this specification, the case where the shear surface is inclined 0 to 10° with respect to the normal direction of the flat surface is included in "the shear surface extends in the direction orthogonal to the flat surface".

[0111] In addition, in the present embodiment, the portion of the wall surface 400 located between the shear surface 400a and the flat surface 406 (the fracture surface 400b in the present embodiment) is provided at a position outside the shear surface 400a in the radial direction D of the through hole 104a. In other words, the portion of the wall surface 400 located between the shear surface 400a and the flat surface 406 does not protrude to a position inside the through hole 104a beyond the shear surface 400a when viewed from the thickness direction A. Further, the inclined surface 408 is provided at a position outside the outer edge of the flat surface 406 in the radial direction D of the through hole 104a. In other words, the inclined surface 408 does not extend to a position on the through hole 104a side beyond the outer edge of the flat surface 406 when viewed from the thickness direction A. In this case, the shape of the periphery of the machining portion 204 becomes a smooth shape, and thus stress concentration around the through hole 104a can be sufficiently suppressed, and thereby the fatigue durability of the metal plate 200 can be improved. Further, as described in Figure 12 below, the shape of the through hole viewed from the thickness direction A is not limited to a circular shape. When the shape of the through hole viewed from the thickness direction A is not a circular shape, the radial direction of the through hole refers to the direction orthogonal to the central axis of the through hole.

[0112] In addition, in the present embodiment, the cross-sectional shape of the machining portion 204 parallel to the thickness direction A and passing through the center of the through hole 104a preferably satisfies the following formula (iii). In this case, the flat surface 406 can be more appropriately formed (refer to Figure 2 ), and the generation of excessive burrs can be sufficiently suppressed.

[0113] H ≤ 0.0975×(R / t) + 0.3009 ··· (iii)

[0114] Wherein, in the above formula (iii), H is the distance (mm) in the thickness direction A between the flat surface 102a and the flat surface 406, R is the radius of curvature (mm) of the through-hole 104a, and t is the thickness (mm) of the metal plate 200.

[0115] In addition, in all regions around the through-hole, it is preferable to satisfy the above formulas (i) and (ii), and it is also possible to satisfy the above formulas (i) and (ii) only in a part of the region around the through-hole. The same applies to the above formula (iii). In addition, if the above formulas (i) and (ii) are satisfied, it is also possible not to satisfy the above formula (iii).

[0116] In addition, in the above-described embodiment, the case where the present invention is applied to the metal plate 200 in which the through-hole 104a has a circular shape when viewed in the thickness direction A has been described, but the shape of the through-hole 104a is not limited to a circular shape. The through-hole formed in the processing portion may have one or more (four in this embodiment) straight portions and one or more bent portions when viewed in the thickness direction of the flat plate portion. For example, as Figure 12 shown in (a) of Figure 12 the through-hole 104a may have an oval shape. In addition, Figure 12 the through-hole 104a shown in (a) of Figure 12 has two straight portions 50 and two bent portions 52. In addition, as shown in (b) of Figure 12 and (c) of Figure 12 , the through-hole 104a may have a polygonal shape with a bent portion 52 provided at a corner. In addition, the bent portion 52 is bent in an arc shape so as to protrude toward the outside of the through-hole 104a. In this case, in a cross-section of the processing portion 204 that is parallel to the thickness direction A and passes through the center of the through-hole 104a and the bent portion 52, it is sufficient to satisfy the above formulas (i) and (ii). The same applies to the above formula (iii). In addition, in this case, R in the above formulas (i), (ii), (iii), and (iv) represents the radius of curvature (mm) of the portion of the bent portion 52 corresponding to the above cross-section.

[0117] In addition, the metal plate of the present invention includes not only flat metal plates but also various formed products (e.g., automotive parts) manufactured using flat metal plates as blanks. That is, the peripheral structure of the through-hole of the metal plate of the present invention can be utilized in blanks used as blanks for various formed products (automotive parts, etc.) and various formed products. For example, as automotive parts of the present invention, suspension parts (lower arms, upper arms, tie rods, subframes, etc.), body parts, and ladder frames having the above-described peripheral structure of the through-hole can be cited.

[0118] (Modified example of the mold)

[0119] In Figures 8 - 10 In the die 14 of the mold 10 shown, the support surface 40 and the inner peripheral surface 42 are connected orthogonally to each other, and the inner peripheral surface 42 and the flange surface 44 are connected orthogonally to each other, but the shape of the die 14 is not limited to the above example.

[0120] For example, as shown in (a) of Figure 13 , the connecting portion between the inner peripheral surface 42 and the flange surface 44 may also be bent into an arc shape. By rounding the connecting portion between the inner peripheral surface 42 and the flange surface 44 in this way, the durability of the die 14 can be improved.

[0121] In addition, for example, as shown in (b) of Figure 13 , the connecting portion between the support surface 40 and the inner peripheral surface 42 may also be bent into an arc shape. By rounding the portion forming the inclined surface 408 (see Figure 2 ), in the manufactured metal plate 200, the durability of the peripheral portion of the rising portion 408a of the inclined surface 408 (see (b) of Figure 2 ) can be improved.

[0122] In addition, for example, as shown in (c) of Figure 13 , the connecting portion between the support surface 40 and the inner peripheral surface 42 and the connecting portion between the inner peripheral surface 42 and the flange surface 44 may be bent into arc shapes respectively. In this case, the durability of the metal plate 200 and the die 14 can be improved.

[0123] In addition, for example, as shown in (a) of Figure 14 , the inner peripheral surface 42 may be inclined with respect to the support surface 40 and the flange surface 44. In this case, the durability of the metal plate 200 and the die 14 can also be improved. In addition, as shown in (b) and (d) of Figure 14 , by bending the connecting portion between the inner peripheral surface 42 and the flange surface 44 into an arc shape, the durability of the die 14 can be further improved. In addition, by Figure 14By bending the connecting portion between the support surface 40 and the inner peripheral surface 42 into an arc shape as shown in (c) and (d), the durability of the metal plate 200 (the raised portion of the inclined surface 408) can be further improved.

[0124] In addition, if the metal plate 200 (the processed portion 204) can satisfy the above-mentioned equations (i) and (ii), the die may not be provided with a blank holder. In addition, the manufacturing method of the metal plate 200 is not limited to the above method. If the metal plate 200 (the processed portion 204) can satisfy the above-mentioned equations (i) and (ii), a die with a shape and size different from the shape and size of the above die can also be used to manufacture the metal plate 200. Therefore, the shape and size of the die can be appropriately changed according to the blank and size of the metal plate 200 so that the metal plate 200 (the processed portion 204) satisfies the above-mentioned equations (i) and (ii).

[0125] Industrial Applicability

[0126] According to the present invention, the fatigue durability of a metal plate formed with a through hole can be improved. Therefore, the present invention can be suitably used in the blank metal plates of various automotive parts.

[0127] Description of Reference Numerals

[0128] 102, flat plate portion; 102a, flat surface (first flat surface); 104a, through hole; 200, metal plate; 204, processed portion; 400, wall surface; 400a, shear surface; 400b, fracture surface; 406, flat surface (second flat surface); 408, inclined surface.

Claims

1. A peripheral structure of a through-hole in a metal plate, which is a structure around a through-hole formed in the metal plate, having: A flat plate portion; and a processing portion that stands up from the flat plate portion to one side in the thickness direction of the flat plate portion and has the through-hole formed at the center, The flat plate portion includes a first flat surface that surrounds the periphery of the processing portion on the one side of the flat plate portion, The processing portion includes: a wall surface that extends in the thickness direction and constitutes the inner wall of the through-hole; an annular second flat surface that is located on the inner side of the first flat surface when viewed in the thickness direction and extends in a direction intersecting the thickness direction from the edge on the one side of the wall surface at a position on the one side of the first flat surface in the thickness direction; and an inclined surface that connects the outer edge of the second flat surface and the inner edge of the first flat surface and is inclined with respect to the thickness direction, When viewed in the thickness direction, the through-hole includes a bent portion that is bent in an arc shape so as to bulge toward the outside of the through-hole, In a cross-section of the processing portion that is parallel to the thickness direction and passes through the center of the through-hole and the bent portion, the following formulas (i) and (ii) are satisfied, 1.0 ≤ W ≤ -3.8314×(R / t) + 11.47 ≤ 5.0 ··· (i), 0.1 ≤ H ≤ -0.6604×(R / t) + 2.0489 ≤ 1.0 ··· (ii), wherein, In the above equations (i) and (ii), W is the length of the inclined surface in the direction orthogonal to the thickness direction, R is the radius of curvature of the portion corresponding to the cross-section in the bent portion, t is the thickness of the metal plate, H is the distance in the thickness direction between the first flat surface and the second flat surface, the unit of W is mm, the unit of R is mm, the unit of t is mm, and the unit of H is mm.

2. The peripheral structure of the through-hole in the metal plate according to claim 1, wherein, The second flat surface extends in the direction orthogonal to the thickness direction.

3. The peripheral structure of the through-hole in the metal plate according to claim 1 or 2, wherein, The wall surface includes a shear surface extending in the direction orthogonal to the first flat surface.

4. The peripheral structure of the through-hole in the metal plate according to claim 3, wherein, In the cross-section, the portion of the wall surface located between the shear surface and the second flat surface is arranged to be positioned outside the shear surface in the direction orthogonal to the central axis of the through-hole, and the inclined surface is arranged to be positioned outside the outer edge of the second flat surface in the orthogonal direction.

5. The peripheral structure of the through-hole in the metal plate according to any one of claims 1 to 4, wherein, In the cross-section, the following equation (iii) is satisfied. H ≤ 0.0975×(R / t) + 0.3009 ··· (iii), where, in the above equation (iii), H is the distance in the thickness direction between the first flat surface and the second flat surface, R is the radius of curvature of the portion corresponding to the cross-section in the bent portion, t is the thickness of the metal plate, the unit of H is mm, the unit of R is mm, and the unit of t is mm.

6. The peripheral structure of the through-hole in the metal plate according to claim 5, wherein, In the cross-section, the following equation (iv) is satisfied. H ≤ 0.0975×(R / t) + 0.2381 ··· (iv), where, in the above equation (iv), H is the distance in the thickness direction between the first flat surface and the second flat surface, R is the radius of curvature of the portion corresponding to the cross-section in the bent portion, t is the thickness of the metal plate, the unit of H is mm, the unit of R is mm, and the unit of t is mm.

7. The peripheral structure of the through-hole of the metal plate according to any one of claims 1 to 6, wherein, The through-hole has a circular shape when viewed from the thickness direction.

8. A blank having the peripheral structure of the through-hole of the metal plate according to any one of claims 1 to 7.

9. An automotive component having the peripheral structure of the through-hole of the metal plate according to any one of claims 1 to 7.

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