Manufacturing method of burring member

Abstract

To preferably burr a curved member.SOLUTION: In a method for manufacturing a burring member, a side wall projecting from the edge part of a first hole and a seating face expanding from the tip of the side wall are formed by pressing the inner peripheral face of a tabular curved part in a first direction. In the manufacturing method, a circular second hole is formed in the seating face, and a burring part projecting along the first direction from the edge part of the first hole is formed. The seating face has two apices positioned in the periphery of each edge part in the circumferential direction and inclines so that the seat face height may be smaller as it proceeds almost to the center in the peripheral direction of each apex part.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a burring member. [Background technology]

[0002] There is a known technology for forming a wall portion (hereinafter, burred portion) that surrounds a hole in a metal plate and protrudes from the edge of the hole by burring the metal plate. As an example, in the technology disclosed in Patent Document 1, a metal plate is pressed with a die to form a cylindrical portion with a bottom, and then a circular pilot hole that penetrates the center of the bottom surface (hereinafter, seat surface) of the cylindrical portion is formed to perform burring.

[0003] However, when a burring portion that protrudes from the outer peripheral surface of a cylindrical pipe in the radial direction of the pipe is formed by burring, the radial length (hereinafter, height) of the burring portion may not be constant. That is, when the top of the burring portion is formed along a plane parallel to the axis of the pipe, the outer peripheral surface of the pipe is curved, so that the burring portion becomes higher from the center toward the end in the circumferential direction of the pipe. When such a burring portion is formed, there is a risk of cracks occurring in the portion of the burring portion around the end in the axial direction of the pipe (hereinafter, peripheral end portion), and further, the possibility of such cracks occurring increases as the burring portion becomes higher. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-94580 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to avoid this, it is conceivable to perform burring by forming a circular seating surface protruding radially from the outer circumferential surface and forming an elliptical pilot hole in the seating surface whose major axis direction coincides with the axis of the pipe. As a result, the portion of the seating surface where the pilot hole is formed around the end of the pipe in the circumferential direction becomes relatively wide, so that it is possible to suppress the occurrence of cracks in the peripheral end portion during burring.

[0006] On the other hand, the curvature of the periphery of each end of the long axis at the edge of the pilot hole (hereinafter referred to as the small R part) becomes high. Therefore, during burring, stress is concentrated around the small R part on the bearing surface, which may cause cracks.

[0007] In one aspect of the present disclosure, it is desirable to perform successful burring on curved members. [Means for solving the problem]

[0008] One aspect of the present disclosure is a method for manufacturing a burring member, the method comprising: pressing an inner peripheral surface of a plate-shaped curved portion having a curved cross section perpendicular to an axis in a first direction to form a side wall protruding from an edge portion surrounding a first hole in the curved portion along the first direction and a seating surface expanding from a tip of the side wall; forming a circular second hole penetrating the seating surface, and forming a burring portion that protrudes from an edge portion of the first hole along the first direction and is a wall-like portion surrounding the first hole. The direction in which the cross section of the curved portion extends is defined as the circumferential direction. The portion of the seating surface surrounding the outer edge is defined as the outer edge. The seating surface has two apexes located around each end portion in the circumferential direction. The seating surface is inclined so that the seating surface height decreases from each apex toward approximately the center in the circumferential direction, and the seating surface height is the length in the first direction between the seating surface and a reference surface, and the reference surface is a virtual surface that is perpendicular to the first direction and located on the inner peripheral surface side of the seating surface.

[0009] According to the above configuration, the two apexes of the seating surface can prevent cracks from occurring in the circumferential end portion of the burred portion when the burred portion is formed, so that the shape of the second hole can be made closer to a circle. This prevents the curvature of the outer edge of the second hole from becoming partially high, and further prevents cracks from occurring when the burred portion is formed. Therefore, burring can be performed well on curved members.

[0010] In one aspect of the present disclosure, the second hole may be formed by pressing the seat in a second direction opposite the first direction. According to the above configuration, it is possible to suppress the occurrence of cracks when the burring portion is formed.

[0011] In one embodiment of the present disclosure, an inner mold and an outer mold may be used in the manufacturing method of the burring member. The inner mold may have a hole and an outer edge pressing surface. The hole is accessible to the outer mold. The outer edge pressing surface surrounds the hole. The inner edge pressing surface of the inner mold may press the inner circumferential surface of the curved portion in a first direction to form a seat and two apexes of the seat. In addition, the outer edge pressing surface of the inner mold may support a portion of the inner circumferential surface of the curved portion opposite to the seat, while the outer mold may press the seat and displace the outer mold toward the hole of the inner mold to form a second hole.

[0012] According to the above configuration, burring can be performed satisfactorily on a curved member. In one embodiment of the present disclosure, an inner mold and an outer mold may be used in the manufacturing method of the burring member. The inner mold may have a hole and an outer edge pressing surface. The hole is accessible to the outer mold. The outer edge pressing surface surrounds the hole. The inner edge pressing surface of the inner mold may press the inner circumferential surface of the curved portion in a first direction to form a seating surface. In addition, the outer edge pressing surface of the inner mold may support a portion of the inner circumferential surface of the curved portion opposite to the seating surface, while the outer mold may press the seating surface to form two apexes of the seating surface, and the outer mold may be displaced toward the hole of the inner mold to form a second hole.

[0013] According to the above configuration, burring can be performed satisfactorily on a curved member. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a perspective view of a shell according to the first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die of the first embodiment before start of seating out, as viewed in the axial direction. [Diagram 3] FIG. 2 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die during seat removal in the first embodiment, as viewed in the axial direction. [Figure 4] FIG. 11 is an explanatory view of a curved portion and an inner die during seat ejection in the first embodiment, as viewed in the circumferential direction. [Diagram 5] FIG. 2 is a perspective view of an inner mold according to the first embodiment. [Figure 6] FIG. 2 is a front view of the inner mold according to the first embodiment. [Figure 7] FIG. 2 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die when punching a hole in the first embodiment, viewed in the axial direction. [Figure 8] FIG. 4 is a front view of a seat surface in which a second hole is formed in the first embodiment. [Figure 9] FIG. 2 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die during burring in the first embodiment, as viewed in the axial direction. [Figure 10] FIG. 11 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die during seat ejection in the second embodiment, as viewed in the axial direction. [Figure 11] FIG. 11 is an explanatory diagram of a curved portion, an inner die, an outer die, an inner horizontal die, and an outer horizontal die when punching a hole in a second embodiment, as viewed in the axial direction. [Figure 12] FIG. 11 is a perspective view of an outer mold according to a second embodiment. [Figure 13] FIG. 11 is a side view of an outer mold according to the second embodiment. [Figure 14]FIG. 11 is a front view of an outer mold according to a second embodiment. [Figure 15] FIG. 11 is an explanatory diagram of a curved portion, a die, a seating punch, and a pad during seating in the third embodiment, as viewed in the axial direction. [Figure 16] FIG. 11 is an explanatory diagram of a curved portion, a hole punch, a hole punching die, a pad, and a die when punching a hole in the third embodiment, as viewed in the axial direction. [Figure 17] FIG. 11 is an explanatory diagram of a curved portion, a hole punch, a hole punching die, a pad, and a die when punching a hole in the third embodiment, as viewed in the axial direction. [Figure 18] FIG. 11 is an explanatory diagram of a curved portion, an outer die, an inner punch, and a pad during burring in the third embodiment, as viewed in the axial direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the embodiments of the present disclosure are not limited to the following embodiments, and various forms may be adopted as long as they fall within the technical scope of the present disclosure.

[0016] [1. First embodiment] [(1) Overview] In the manufacturing method of the first embodiment, a shell 1 of a muffler to be mounted on a vehicle is manufactured (see FIG. 1). The shell 1 is a cylindrical member formed by bending a plate-like member, extends along an axis A, and has an elliptical cross section (hereinafter simply referred to as a cross section) perpendicular to the axis A. End plates are joined to both ends of the shell 1, and a sound-absorbing space is formed inside the shell 1.

[0017] The shell 1 has a configuration as a burring member, and has a burring hole 14 penetrating the shell 1, and a burring portion 13 which is a wall-like portion surrounding the burring hole 14 and protrudes outward from an edge portion surrounding the burring hole 14 on the outer circumferential surface 12 of the shell 1. More specifically, the burring portion 13 is located at a curved portion 10 which is a portion of the shell 1 having a curved cross section. Moreover, the burring portion 13 is located, for example, near the end portion in the major axis direction of the elliptical cross section.

[0018] The manufacturing method of the shell 1 of the first embodiment has a plurality of steps including seat setting, punching, and burring, and these steps form a burred portion 13 in the curved portion 10 of the shell 1. The plate thickness of the curved portion 10 is appropriately determined, and the thinner the plate thickness, the easier the curved portion 10 is to deform during seat setting. The curved portion 10 may also be configured by stacking a plurality of plate materials (for example, double winding).

[0019] This manufacturing method can be applied to the manufacture of burred members for various applications, which have a burred portion at a curved portion that is a plate-shaped portion with a curved cross section. Specifically, the burred member may be, for example, an exhaust pipe of a vehicle, an on-vehicle part other than an exhaust pipe, or a part that is not mounted on a vehicle.

[0020] [(2) About molds] The seating, punching and burring are performed, for example, by using an inner die 3, an outer die 4, an inner horizontal die 5 and an outer horizontal die 6 (see Figs. 2 to 7 and 9).

[0021] The inner horizontal die 5 is configured to come into contact with a portion of the inner circumferential surface 11 of the shell 1 other than the portion where the burring portion 13 is to be formed (see FIGS. 2, 3, 7, and 9). The inner horizontal die 5 is provided with a cylindrical arrangement space 50 for arranging the inner metal mold 3.

[0022] The outer horizontal die 6 is configured to come into contact with a portion of the outer peripheral surface 12 of the shell 1 other than the portion where the burring portion 13 is to be formed (see Figs. 2, 3, 7 and 9). The outer horizontal die 6 is provided with a cylindrical arrangement space 60 for arranging the inner die 3 and the outer die 4.

[0023] The inner mold 3 is a cylindrical mold, and is configured so that an end portion of the inner mold 3 presses an inner circumferential surface 11 of a curved portion 10 of the shell 1 (see FIGS. 2 to 7 and 9). The inner mold 3 has an outer edge pressing surface 30 and a hole portion 33.

[0024] The outer edge pressing surface 30 is a band-like surface located around the outer edge of the end portion of the inner mold 3 that presses the curved portion 10, and extends along the outer edge of the end portion so as to surround the hole portion 33. The hole 33 is formed in the end of the inner mold 3 and communicates with the internal space of the cylindrical inner mold 3. The outer mold 4 is capable of entering the inside of the hole 33.

[0025] The outer mold 4 is a cylindrical mold, and presses the outer peripheral surface 12 of the curved portion 10 of the shell 1 with a pressing surface 40 located at the end (see Figs. 2, 3, 7 and 9). The pressing surface 40 is a substantially flat surface that is substantially perpendicular to the extension direction of the outer mold 4.

[0026] [(3) Seat out] In the seating, the inner peripheral surface 11 of the curved portion 10 of the shell 1 is pressed by the above-mentioned mold, thereby forming the seating portion 2 having a cylindrical shape with a bottom (see Figs. 2 to 4).

[0027] In the seating out process, first, the shell 1 is fixed by the inner horizontal die 5 and the outer horizontal die 6. Specifically, the inner horizontal die 5 is disposed inside the shell 1 and abuts against the periphery of a portion of the inner peripheral surface 11 where the burred portion 13 is to be formed, and the outer horizontal die 6 is disposed outside the shell 1 and abuts against the periphery of a portion of the outer peripheral surface 12 where the burred portion 13 is to be formed. Then, the shell 1 is sandwiched between the inner horizontal die 5 and the outer horizontal die 6 to fix the shell 1 (see FIG. 2).

[0028] In this case, as an example, the inner horizontal die 5 is disposed on the lower side and the outer horizontal die 6 is disposed on the upper side. However, this is not limiting, and the positions of the inner horizontal die 5 and the outer horizontal die 6 can be determined appropriately.

[0029] The inner mold 3 is disposed in the arrangement space 50 of the inner horizontal mold 5. At this time, the extension direction of the inner mold 3 coincides with the first direction D1, and the inner mold 3 is displaceable in the first and second directions D1 and D2. The first direction D1 is a direction from the inside to the outside of the shell 1, and may be, for example, a direction that substantially coincides with the radial direction of the cross section of the curved portion 10. The second direction D2 is the opposite direction to the first direction D1. The first and second directions D1 and D2 may be, for example, parallel to the vertical direction.

[0030] Then, by displacing the inner die 3 in the first direction D0, the inner peripheral surface 11 of the curved portion 10 of the shell 1 is pressed by the outer edge pressing surface 30. This causes the seating to be performed, and the seating portion 2 is formed in the curved portion 10 (see FIGS. 3 and 4).

[0031] [(4) Seat projection] The seat portion 2 has a side wall 21 and a seat portion 22 (see FIGS. 3 and 4). The side wall 21 is a wall-like portion that protrudes in the first direction D1 (in other words, outward) from an edge portion that surrounds the circular first hole 20 in the curved portion 10, and is a cylindrical portion that surrounds the first hole 20. In other words, the first hole 20 corresponds to an opening surrounded by the boundary between the end portion of the cylindrical side wall 21 and the curved portion 10. In addition, the circular shape means, for example, a circle, an approximately circle, an ellipse, or an approximately ellipse, etc.

[0032] The seat portion 22 is a wall-like portion covering the outer end of the side wall 21. The outer surface of the seat portion 22 forms a seat surface 23. The seat surface 23 is a circular surface that spreads out from the tip of the side wall 21, and protrudes outward from the surrounding portion of the seat projection 2 on the outer circumferential surface 12 of the shell 1. The seat surface 23 has an outer edge portion 24, two apexes 25, and a central portion 26.

[0033] In the first embodiment, the inclination of the seating surface 23, that is, the two apexes 25 and the central portion 26, are formed by pressing with the outer edge pressing surface 30 of the inner die 3 during seating. In other words, the seating surface 23 has a shape according to the outer edge pressing surface 30. Hereinafter, the direction in which the cross section of the curved portion 10 extends is defined as the circumferential direction D3. In other words, the direction that is approximately the same as the direction in which the arc centered on the axis A extends is defined as the circumferential direction D3. In addition, a virtual surface that is perpendicular to the first direction D1 and is located closer to the inner circumferential surface 11 than the seating surface 23 is defined as the reference surface R. In addition, the length in the first direction D1 between the seating surface 23 and the reference surface R is defined as the seating surface height H0.

[0034] The outer edge portion 24 is a band-shaped portion located around the outer edge of the seating surface 23 and extends around the center of the seating surface 23 along the outer edge. Each apex 25 is located around each end of the seating surface 23 in the circumferential direction D3. As an example, each apex 25 is provided at a position slightly away from the outer edge of the seating surface 23. However, this is not limited, and the apex 25 may be provided on the outer edge of the seating surface 23. Each apex 25 has a seating surface height H0 higher than the portion of the seating surface 23 other than the two apexes 25. The two apexes 25 may have the same seating surface height H0 or may have different seating surface heights H0.

[0035] The central portion 26 is a portion that is located approximately in the center of the seat 23 in the circumferential direction D3 and extends along the axis A. Note that the seat height H0 of the central portion 26 may be approximately constant, for example, or may be lower than other portions of the seat 23.

[0036] The seat 23 is inclined such that the seat height H0 decreases from each apex 25 toward the center 26 in a side view (see FIG. 3). That is, the seat 23 is V-shaped protruding in the second direction D2 when viewed in the direction of the axis A. Also, in a side view, the outer edge 24 of the seat 23 is inclined such that the seat height H0 decreases from each apex 25 toward the end along the outer edge of the seat 23 in the direction of the axis A (see FIG. 4). The seat 23 is curved so as to protrude in the first direction D1 when viewed in the circumferential direction D3.

[0037] [(5) Inner mold] The inclination of the seating surface 23 is formed by pressing the outer edge pressing surface 30 of the inner mold 3 against the inner peripheral surface 11 of the curved portion 10, and the outer edge 24 of the seating surface 23 has the same shape as the outer edge pressing surface 30 (see Figs. 3 to 6). That is, the outer edge pressing surface 30 of the inner mold 3 has two apexes 31 and a central portion 32. Each apex 31 and central portion 32 are portions for forming each apex 25 and central portion 26 of the seating surface 23, respectively. Below, the outer edge pressing surface 30 will be described based on the position at the time of seating out.

[0038] Each apex 31 is located around each end of the outer edge pressing surface 30 in the circumferential direction D3. As an example, each apex 31 is provided at a position slightly away from the outer edge of the outer edge pressing surface 30. However, this is not limited, and the apex 31 may be provided on the outer edge of the outer edge pressing surface 30. Furthermore, each apex 31 has a length in the first direction D1 relative to the reference plane R (hereinafter, the inner die height H1) greater than the portion of the outer edge pressing surface 30 other than the two apexes 31. The two apexes 31 may have the same inner die height H1 or may have different inner die heights H1.

[0039] The central portion 32 is located at approximately the center of the outer edge pressing surface 30 in the circumferential direction D3, and extends along the axis A. Note that the inner die height H1 of the central portion 32 may be approximately constant, for example, or may be lower than other portions of the outer edge pressing surface 30.

[0040] The outer edge pressing surface 30, like the seating surface 23, is inclined so that the inner die height H1 decreases from each apex 31 toward the central portion 32. That is, when viewed in the direction of the axis A, the outer edge pressing surface 30 also has a V-shape protruding in the second direction D2. Similarly to the outer edge 24 of the seating surface 23, the outer edge pressing surface 30 is inclined so that the inner die height H1 decreases from each apex 31 toward the end in the direction of the axis A along the outer edge of the outer edge pressing surface 30. That is, when viewed in the circumferential direction D3, the outer edge pressing surface 30 is also curved so as to protrude in the first direction D1.

[0041] [(6) Punching and burring] Hole punching is performed following the seating, and in the hole punching, the above-mentioned die is used to first form a circular second hole 27 penetrating the seat surface 23 of the seating portion 2 (see Figs. 7 and 8). Then, burring is performed, and the above-mentioned die is used to press the seating portion 2 in which the second hole 27 is formed, thereby forming a burred portion 13 at the edge of the first hole 20 (in other words, burred hole 14) (see Fig. 9).

[0042] In punching, the shell 1 is fixed by the inner horizontal die 5 and the outer horizontal die 6 in the same manner as in the seating out, and the outer peripheral pressing surface 30 of the inner die 3 is in contact with the inner peripheral surface 11 of the seating out portion 2. The outer die 4 is arranged so that its extension direction coincides with the second direction D2, and displaces in the second direction D2 through the arrangement space 60 of the outer horizontal die 6. At this time, the inner peripheral surface 11 of the seating out portion 2 is supported by the outer peripheral pressing surface 30 of the inner die 3. As a result, the pressing surface 40 of the outer die 4 presses the seating surface 23 of the seating out portion 2 in the second direction D2, and then penetrates the seating portion 22 and enters the hole portion 33 of the inner die 3. As a result, the second hole 27 (in other words, a pilot hole) penetrating the seating surface 23 is formed. At this time, the scrap S generated when the second hole 27 is formed falls into the hole portion 33 of the inner die 3. Alternatively, the second hole 27 may be formed by, for example, pressing the inner circumferential surface 11 of the seating portion 2 in the first direction D1 with a die.

[0043] The center of the second hole 27 substantially coincides with the center of the seating surface 23 (see FIG. 8). Note that it is preferable that the second hole 27 has a shape that is as close to a perfect circle as possible. When the second hole 27 is formed in the seating surface 23 by punching, the displacement of the outer die 4 in the second direction D2 stops. At this time, the pressing surface 40 of the outer die 4 is located inside the hole portion 33 of the inner die 3. Then, burring is performed, and the inner horizontal die 5 and the outer horizontal die 6 are displaced in the second direction D2, and the shell 1 is also displaced in the second direction D2 accordingly. As a result, the outer edge portion 24 surrounding the second hole 27 in the seating portion 22 is sandwiched and pressed between the inner peripheral surface 61 surrounding the arrangement space 60 of the outer horizontal die 6 and the outer peripheral surface 34 of the inner die 3 (see FIG. 9). As a result, the side wall 21 and the outer edge portion 24 are extended along the first and second directions D1 and D2, and the portion is formed into the burring portion 13 surrounding the burring hole 14 (in other words, the first hole 20).

[0044] [2. Second embodiment] [(1) Overview] The manufacturing method of the shell 1 of the second embodiment is similar to that of the first embodiment in that a burred portion 13 is formed in the curved portion 10 of the shell 1 by seating, punching, and burring. However, the manufacturing method of the second embodiment differs from that of the first embodiment in the configuration of the outer mold 4 and the timing at which the inclination is formed on the seating surface 23. The differences between the manufacturing method of the second embodiment and the first embodiment will be described below.

[0045] [(2) Seat out] In the seating of the second embodiment, the curved portion 10 of the shell 1 is pressed by the above-mentioned mold to form the seating portion 2 having a bottomed cylindrical shape (see FIG. 10). At this time, if the plate thickness of the curved portion 10 is thick, there is a possibility that the inclination is not formed on the seating surface 23, and the second embodiment illustrates, as an example, a case where the inclination is not formed on the seating surface 23.

[0046] That is, in the seating out process, first, in the same manner as in the first embodiment, the shell 1 is fixed by the inner horizontal die 5 and the outer horizontal die 6, and the inner die 3 is placed in the arrangement space 50 of the inner horizontal die 5. Then, by displacing the inner die 3 in the first direction D0, the inner circumferential surface 11 of the curved portion 10 of the shell 1 is pressed by the outer edge pressing surface 30. In this way, seating out is performed, and the seating out portion 2 is formed in the curved portion 10.

[0047] In the second embodiment, the seating surface 23 of the seating portion 2 formed by seating is a substantially flat surface substantially perpendicular to the first direction D0. That is, the inner die 3 used in the second embodiment has a configuration similar to that of the first embodiment, and the outer edge pressing surface 30 is inclined. However, if the plate thickness of the curved portion 10 is thicker than that of the first embodiment, the seating surface 23 may not be deformed into a shape corresponding to the outer edge pressing surface 30. The second embodiment illustrates such a case, and as an example, the seating surface 23 is substantially flat. Note that the inner die 3 of the second embodiment may not have an inclination and may be substantially flat substantially perpendicular to the first direction D1.

[0048] [(3) Punching and burring] In the hole punching following the seating, an inclination similar to that in the first embodiment is formed on the seating surface 23 of the seating portion 2, and then a circular second hole 27 penetrating the seating surface 23 is formed (see FIG. 11). Then, by pressing the seating portion 2 with the second hole 27 formed therein, a burring portion 13 is formed on the edge of the first hole 20 by burring similar to that in the first embodiment.

[0049] In punching, the shell 1 is fixed by the inner horizontal die 5 and the outer horizontal die 6 in the same manner as in the seating out, and the outer edge pressing surface 30 of the inner die 3 is in contact with the inner peripheral surface 11 of the seating portion 2. The outer die 4 is arranged so that its extension direction coincides with the second direction D2, and passes through the arrangement space 60 of the outer horizontal die 6 and is displaced in the second direction D2 to reach the hole portion 33 of the inner die 3. At this time, the inner peripheral surface 11 of the seating portion 2 is supported by the outer edge pressing surface 30 of the inner die 3.

[0050] In addition, the pressing surface 40 of the outer mold 4 in the second embodiment is formed with an inclination, which will be described later. Therefore, the pressing surface 40 of the outer mold 4 displaced in the second direction D2 comes into contact with the seating surface 23 of the seat projection portion 2 and presses the seating surface 23, whereby the seating portion 22 sandwiched between the pressing surface 40 and the outer edge pressing surface 30 is deformed, and the seating surface 23 is formed with an inclination similar to that of the first embodiment. In other words, the seating surface 23 is formed into a shape corresponding to the pressing surface 40 and the outer edge pressing surface 30, and the seating surface 23 is formed with two apexes 25 and a central portion 26 similar to those of the first embodiment.

[0051] Then, the pressing surface 40 of the outer die 4 penetrates the seat portion 22, and the outer die 4 enters the hole portion 33 of the inner die 3. As a result, a second hole 27 penetrating the seat surface 23 is formed. Note that scrap S generated when the second hole 27 is formed falls into the hole portion 33 of the inner die 3. Also, the second hole 27 of the second embodiment has the same shape as that of the first embodiment.

[0052] Thereafter, as the punching is completed, the displacement of the outer die 4 in the second direction D2 is stopped, and burring is performed in the same manner as in the first embodiment. That is, the inner horizontal die 5 and the outer horizontal die 6 are displaced in the second direction D2, thereby forming the burring portion 13.

[0053] [(4) Outer mold] The pressing surface 40 of the outer mold 4 has the same shape as the inclined seating surface 23 (see Figs. 11 to 14). That is, the pressing surface 40 has two apex forming portions 41 and a central portion 42. Each apex forming portion 41 and the central portion 42 are portions for forming each apex 25 and the central portion 26 of the seating surface 23, respectively. Below, the pressing surface 40 will be described based on the position at the time of seating.

[0054] Each apex forming portion 41 is located at each end of the pressing surface 40 in the circumferential direction D3. In other words, each apex forming portion 41 is located at the outer edge of the pressing surface 40. Each apex forming portion 41 has a length in the first direction D1 relative to the reference plane R (hereinafter, outer mold height H2) greater than the portions of the pressing surface 40 other than the two apex forming portions 41. The two apex forming portions 41 may have the same outer mold height H2 or may have different outer mold heights H2.

[0055] The central portion 42 is located at approximately the center of the pressing surface 40 in the circumferential direction D3, and extends along the axis A. Note that the outer die height H2 of the central portion 42 may be approximately constant, for example. The pressing surface 40 is inclined such that the outer mold height H2 decreases from each apex forming portion 41 toward the central portion 42. In other words, when viewed in the direction of the axis A, the pressing surface 40 has a V-shape with the central portion 42 protruding in the second direction D2.

[0056] [3. Third embodiment] [(1) Overview] The manufacturing method of the shell 1 of the third embodiment is similar to that of the first embodiment, in that the burring portion 13 is formed in the curved portion 10 of the shell 1 by seating, punching, and burring (see Figs. 15 to 18). However, the manufacturing method of the third embodiment differs from that of the first embodiment in the dies used in these steps. Specifically, a dedicated die is used in each step, which allows the seating surface 23 to be formed with high precision. The differences between the manufacturing method of the third embodiment and the first embodiment will be described below.

[0057] [(2) Seat out] In the seating process, a die 70, a seating punch 72, and a pad 74 are used, and the seating portion 2 is formed by pressing the inner surface 11 of the curved portion 10 of the shell 1, which is fixed by the die 70 and the pad 74, with the seating punch 72 (see Figure 15).

[0058] The seat punch 72 is a cylindrical member, and a pressing surface 73 having a shape corresponding to the seat portion 2 is provided at its end. The die 70 is disposed outside the shell 1 and comes into contact with the periphery of a portion of the outer circumferential surface 12 of the curved portion 10 of the shell 1 where the burring portion 13 is to be formed. At this time, a space is formed between that portion and a seating surface forming portion 71 of the die 70. The seating surface forming portion 71 is a recessed portion on the surface of the die 70 that comes into contact with the outer circumferential surface 12, and has a shape corresponding to the seating portion 2.

[0059] The pad 74 is configured similarly to the inner horizontal die 5, and has an arrangement space 75 similar to the inner horizontal die 5. The pad 74 is arranged inside the shell 1 and abuts against the periphery of a portion of the inner circumferential surface 11 of the shell 1 where the burring portion 13 is to be formed, with the arrangement space 75 facing said portion. Also, the seating punch 72 is arranged in the arrangement space 75.

[0060] The shell 1 is then fixed by being clamped between the die 70 and the pad 74. Also, the seat punch 72 arranged in the arrangement space 75 is displaced in the first direction D1, and the pressing surface 73 of the seat punch 72 presses the inner circumferential surface 11 of the curved portion 10 (see FIG. 15). At this time, the curved portion 10 is clamped and pressed between the pressing surface 73 of the seat punch 72 and the seat surface forming portion 71 of the die 70, thereby forming the seat portion 2.

[0061] (3) Hole Punching In punching, a punch 80, a punch die 82, a pad 85, and a die 88 are used. Then, the seat projection 2 in the curved portion 10 of the shell 1 is pressed by the punch 80 in the same manner as in the first embodiment, whereby a second hole 27 is formed in the seat surface 23 of the seat projection 2 (see Figures 16 and 17). The hole punch 80 is configured similarly to the outer die 4 of the first embodiment, and has a pressing surface 81 located at an end portion.

[0062] The hole punching die 82 is configured in the same manner as the inner mold 3 of the first embodiment, and includes an outer edge pressing surface 83 and a hole portion 84. The pad 85 is disposed on the outside of the shell 1 and abuts against the periphery of the protruding portion 2 on the outer circumferential surface 12 of the curved portion 10 of the shell 1. The pad 85 also has a through hole 86 penetrating the pad 85 and a peripheral portion 87 surrounding the through hole 86. The peripheral portion 87 has a shape corresponding to the outer edge portion 24 of the seating surface 23 of the protruding portion 2. When the pad 85 is disposed, the through hole 86 faces a portion of the seating surface 23 of the protruding portion 2 where the second hole 27 is formed, and the peripheral portion 87 abuts against the outer edge portion 24 of the seating surface 23.

[0063] The die 88 is configured similarly to the inner horizontal die 5, and has an arrangement space 89 similar to that of the inner horizontal die 5. The die 88 is disposed inside the shell 1 and abuts against the periphery of the seating portion 2 on the inner circumferential surface 11 of the shell 1, with the arrangement space 89 facing the seating portion 2.

[0064] Further, the hole punching die 82 is disposed in the arrangement space 89. At this time, the hole portion 84 of the hole punching die 82 faces the portion of the seating portion 2 where the second hole 27 is to be formed, and the outer edge pressing surface 83 abuts against the outer edge portion 24.

[0065] During hole punching, similarly to the first embodiment, the hole punch 80 is displaced in the second direction toward the pad 85 and passes through the through hole 86 (see FIG. 17). Then, the pressing surface 81 of the hole punch 80 presses the seating surface 23 of the seating portion 2, then penetrates the seating portion 22 and enters the hole portion 84 of the hole punching die 82. As a result, the second hole 27 penetrating the seating surface 23 is formed. At this time, scrap S generated during the formation of the second hole 27 falls into the hole portion 33 of the inner die 3.

[0066] [(4) Burring] In boring, an outer die 90, an inner punch 92, and a pad 94 are used, and the boring portion 13 is formed by pressing the seat portion 2, in which the second hole 27 is formed, in the curved portion 10 of the shell 1 with the inner punch 92 (see Figure 18).

[0067] The inner punch 92 is a cylindrical member having a pressing end 93 with a flat end surface. The outer die 90 is disposed outside the shell 1 and abuts against the periphery of the seating portion 2 on the outer peripheral surface 12 of the curved portion 10 of the shell 1. A burring forming portion 91, which is a cylindrical hole, is formed on the abutting surface of the outer die 90 against the outer peripheral surface 12. When the outer die 90 is disposed, the seating portion 2 is accommodated in the burring forming portion 91.

[0068] The pad 94 is configured similarly to the inner horizontal die 5, and has an arrangement space 95 similar to the inner horizontal die 5. The pad 94 is disposed inside the shell 1 and abuts against the periphery of the seating portion 2 on the inner circumferential surface 11 of the shell 1, and the arrangement space 95 faces the seating portion 2. In addition, an inner punch 92 is disposed in the arrangement space 95.

[0069] Then, the shell 1 is fixed by being clamped between the outer die 90 and the pad 94. Also, the inner punch 92 arranged in the arrangement space 95 is displaced in the first direction D1, and the inner punch 92 passes through the second hole 27. At this time, the outer edge 24 of the seating portion 2 is clamped and pressed by the inner peripheral surface of the burring forming portion 91 of the outer die 90 and the outer peripheral surface around the pressing end 93 of the inner punch 92, thereby forming the burring portion 13.

[0070] [4. Effects] (1) According to the above embodiment, the two apexes 25 of the seating surface 23 can prevent cracks from occurring in the periphery of the end of the burring portion 13 in the circumferential direction D3 during burring, so that the shape of the second hole 27 can be made closer to a circle. This prevents the curvature of the outer edge of the second hole 27 from becoming partially high, and further prevents cracks from occurring during burring. Therefore, burring can be performed well on a curved member.

[0071] (2) The curved portion 10 is pressed in the first direction D1 to be seated, and the second hole 27 is formed by the outer die 4 displaced in the second direction D2, which is the opposite direction to the first direction D1, pressing the seating surface 23. When the second hole 27 is formed by the outer die 4 displaced in the first direction D1, a burr is formed on the edge of the second hole 27 so as to face the outside of the curved portion 10. Such a burr may be stretched further outward during burring, and as a result, cracks are likely to occur during burring. In contrast, when the second hole 27 is formed by the outer die 4 displaced in the second direction D2, a burr is formed on the edge of the second hole 27 so as to face the inside of the curved portion 10. Such a burr is unlikely to be stretched during burring, and as a result, cracks during burring can be suppressed. Furthermore, the outer die 4 displaced in the second direction D2 enters the hole 33 of the inner die 3. Therefore, the scraps S generated when the second holes 27 are formed fall into the hole portions 33 of the inner die 3, making it easier to collect the scraps S.

[0072] (3) In the first embodiment, the inclination of seating surface 23 provides a shear angle effect, which can suppress noise when second hole 27 is formed by pressing with outer die 4. In addition, the bending moment when second hole 27 is formed is reduced, which can suppress work hardening around second hole 27 and therefore cracks.

[0073] (4) Furthermore, the second hole 27 can be formed in the seating surface 23 by one pressing using the outer die 4. Moreover, the hole punching and burring are achieved by a series of operations of the inner die 3 and the outer die 4. Therefore, the occurrence of cracks during burring can be suppressed without increasing the number of steps.

[0074] 5. Other embodiments (1) In the first and second embodiments, the inner die 3, the outer die 4, the inner horizontal die 5, and the outer horizontal die 6 are used for seating, punching, and burring, with the inner die 3 and the inner horizontal die 5 arranged on the lower side and the outer die 4 and the outer horizontal die 6 arranged on the upper side. However, the dies used in these steps are not limited to this and can be appropriately determined, and the positions of each die can also be appropriately determined. Even in such a case, burring can be performed satisfactorily by forming two apexes 31 on the seating surface 23 during seating, as in the first embodiment, or by forming two apexes 31 on the seating surface 23 in parallel with the formation of the second hole 27, as in the second embodiment.

[0075] (2) In the first and second embodiments, the seating surface 23 protrudes outward from the peripheral portion of the seating portion 2 on the outer circumferential surface 12 of the shell 1. However, this is not limited thereto, and for example, the portion including the center of the seating surface 23 may be recessed inward from the peripheral portion.

[0076] (3) In the piercing and burring of the second embodiment, the same inner die 3 as in the first embodiment is used, and two apexes 31 are formed on the outer edge pressing surface 30. However, this is not limited thereto, and the outer edge pressing surface 30 of the inner die 3 may extend in a substantially flat shape in a direction substantially perpendicular to the first and second directions D1 and D2.

[0077] (4) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. [Explanation of symbols]

[0078] A...axis, R...reference surface, H0...seat height, H1...inner mold height, H2...outer mold height, D1...first direction, D2...second direction, D3...circumferential direction, 1...shell, 10...curved portion, 11...inner surface, 12...outer surface, 13...burring portion, 14...burring hole, 2...seat portion, 20...first hole, 21...side wall, 22...seat portion, 23...seat surface, 24...outer edge portion, 25...top, 26...center, 27...second hole, 3...inner mold, 30...outer edge pressing surface, 31...top, 32...center, 33...hole portion, 34...outer edge surface, 4...outer mold, 40...pressing surface, 41...top forming portion, 42...center, 5...inner horizontal mold, 50...arrangement space, 6...outer horizontal mold, 60...arrangement space, 61...inner surface.

Claims

1. A method for manufacturing a burring member, comprising the steps of: pressing an inner peripheral surface of a plate-shaped curved portion having a curved cross section perpendicular to an axis in a first direction to form a side wall protruding from an edge portion surrounding a first hole in the curved portion along the first direction and a seating surface expanding from a tip of the side wall; forming a circular second hole penetrating the seat surface, and forming a burring portion that is a wall-like portion that protrudes from the edge of the first hole along the first direction and surrounds the first hole, The direction in which the cross section of the curved portion extends is defined as a circumferential direction, The portion around the outer edge of the seat surface is defined as an outer edge portion, The seating surface has two apexes located around each end in the circumferential direction, The seating surface is inclined so that the seating surface height becomes smaller from each of the apexes toward the approximate center in the circumferential direction, and the outer edge portion is inclined so that the seating surface height becomes smaller from each of the apexes toward the end in the axial direction along the outer edge of the seating surface, and further, when viewed in the circumferential direction, the seating surface is curved so as to protrude in the first direction, The seat height is a length in the first direction between the seat and a reference surface, and the reference surface is a virtual surface that is perpendicular to the first direction and is located closer to the inner circumferential surface than the seat, In the manufacturing method of the burring member, an inner mold is used, The inner die has a pressing surface having a shape corresponding to the seating surface, The top of the seating surface is formed by the pressing surface of the inner die abutting against the inner circumferential surface of the curved portion. A method for manufacturing a burring member.

2. A method for manufacturing a burring member according to claim 1, The second hole is formed by pressing the seat surface in a second direction that is opposite to the first direction. A method for manufacturing a burring member.

3. A method for manufacturing a burring member according to claim 2, The manufacturing method of the burring member uses an inner mold and an outer mold, The inner mold has a hole into which the outer mold can enter and an outer edge pressing surface surrounding the hole, The inner circumferential surface of the curved portion is pressed in the first direction by the outer edge pressing surface of the inner mold, thereby forming the seat surface and the two apexes on the seat surface, The outer die presses the seating surface while supporting a portion of the inner circumferential surface of the curved portion opposite to the seating surface with the outer edge pressing surface of the inner die, and the outer die is displaced toward the hole portion of the inner die, thereby forming the second hole. A method for manufacturing a burring member.

4. A method for manufacturing a burring member according to claim 2, The manufacturing method of the burring member uses an inner mold and an outer mold, The inner mold has a hole into which the outer mold can enter and an outer edge pressing surface surrounding the hole, The seat surface is formed by pressing the inner circumferential surface of the curved portion in the first direction with the outer edge pressing surface of the inner mold, The outer edge pressing surface of the inner die supports a portion of the inner circumferential surface of the curved portion opposite to the seating surface, while the outer die presses the seating surface, thereby forming the two apexes of the seating surface, and further, the outer die is displaced toward the hole portion of the inner die to form the second hole. A method for manufacturing a burring member.

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