Burring device and burring method

Abstract

To provide a burring device which molds two facing cylindrical flanges.SOLUTION: A burring device (100) includes a first die (1), a second die (2), a first support shaft (6), a second support shaft (7), a first elastic member (8), a second elastic member (9), a cam member (3), a first punch (4), and a second punch. The first die (1) includes a first semi-cylinder recessed surface (11) and is rotatably supported by the first support shaft (6) and the first elastic member (8). The second die (2) is disposed adjacent to the first die (1), includes a second semi-cylinder recessed surface (21) and a lever part (22) protruding beyond the first die (1) to the side, and is rotatably supported by the second support shaft (7) and the second elastic member (9). The cam member (3) holds a state that the first semi-cylinder recessed surface (11) and the second semi-cylinder recessed surface (21) are closest to each other and define a cylindrical hole at an end of its downward movement. The first punch (4) and the second punch are provided so as to be insertable into the cylindrical hole.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a burring apparatus and a burring method. [Background technology]

[0002] Chassis parts used in automobiles are connected to other parts. The connection is configured by welding a collar to the chassis part, or by pressing a bush into a burring part formed in the chassis part. Here, chassis parts are required to reduce costs, improve fatigue properties, and ensure rust prevention performance. Considering the merits and demerits of welding a collar and pressing a bush based on these requirements, pressing a bush is preferable. This is because, compared to pressing a bush, welding a collar makes the entire chassis part heavier, the welding cost is higher, and the welded part is more susceptible to rust. For this reason, it is desirable to adopt pressing a bush rather than welding a collar for chassis parts whenever possible.

[0003] For example, in chassis parts such as upper arms and lower arms, the connection parts with other parts may be formed by pressing a cylindrical bush into a burred part without welding. In chassis parts, the bush press-in part (burred part) can be made of two opposing cylindrical flanges. The opposing cylindrical flanges can be formed by a method in which a flat plate-like member is burred to form two burred parts, and then bending is performed so that the axial centers of the burred parts are aligned. The opposing cylindrical flanges can also be formed by a method in which a flat plate-like member is bent and then burred, that is, two plate parts opposed to each other by bending are burred to form cylindrical flanges protruding inward from each plate part. In the former method, a high degree of bending is required because the axial centers of the burred parts must be aligned by bending. Therefore, the latter method is preferred.

[0004] Japanese Patent Laid-Open Publication No. 11-207412 (Patent Document 1) describes a burring device for forming two opposing burring holes (cylindrical flanges). This burring device forms burring holes in each of the flange parts of a linear workpiece including a web and two opposing flange parts (plate parts) continuously provided on both sides of the web. The burring device of Patent Document 1 includes a pair of slide dies divided into two in the longitudinal direction of the workpiece and two burring punches in order to form the burring holes. The divided surfaces of each slide die are formed with a recess corresponding to, for example, the half shape of the die hole into which the burring punch is inserted.

[0005] In the burring process of Patent Document 1, a workpiece in which pilot holes for burring holes are formed in each flange portion is placed in a burring device. At this time, slide dies separated from each other are placed between the flange portions of the workpiece, and the axis of the pilot hole is placed between the divided surfaces of the slide dies. From this state, the slide dies slide closer to each other, and the divided surfaces of the slide dies come into contact with each other. As a result, a die hole is defined by the recesses of the pair of slide dies. The die hole is placed at a position corresponding to the pilot hole of the workpiece, and two burring punches are inserted into this die hole. One burring punch is inserted from one end side of the die hole, and the other burring punch is inserted from the other end side of the die hole. As a result, opposing burring holes (cylindrical flanges) are formed between the flange portions of the workpiece. After the burring holes are formed, the two burring punches are pulled out of the die holes, and the slide dies slide away from each other. As a result, the burring punch and the slide die are separated from the burring holes, and the molded product having the burring holes can be removed from the burring device.

[0006] Japanese Patent Laid-Open Publication No. 6-312227 (Patent Document 2) describes a processing method for a bush mounting part in which burring is performed on a pair of wall parts (plate parts) facing each other with a specified gap therebetween to form a protrusion part (cylindrical flange) on each wall part. In this processing method, a collar is fitted between the wall parts, and the protrusion part formed by burring is brought into contact with the inner peripheral surface of the collar. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-207412 [Patent Document 2] Japanese Patent Application Publication No. 6-312227 Summary of the Invention [Problem to be solved by the invention]

[0008] In the burring device of Patent Document 1, the die holes for forming two opposing cylindrical flanges are defined by the recesses of a pair of dies. The pair of dies are configured to be slidable in the longitudinal direction of the workpiece. In this case, a large space is required to allow the dies to slide. This makes the burring device larger. In addition, the burring device of Patent Document 1 can also be used for chassis parts with simple shapes in which a cylindrical portion is provided at an end. However, in the case of chassis parts with complex shapes in which a cylindrical portion is protruded at a position away from an end, such as a front lower arm, there is substantially no space to allow the dies to slide, making it difficult to form cylindrical flanges.

[0009] In the processing method of Patent Document 2, the collar remains in the press-fit portion of the bush. In other words, the collar is integrated with the workpiece after processing. In this case, the weight of the chassis part increases by at least the weight of the collar. Furthermore, the gap between the collar and the workpiece may cause rust.

[0010] An object of the present disclosure is to provide a burring apparatus and a burring method that are capable of forming two opposing cylindrical flanges while minimizing the space required to allow the die to move, and that are capable of producing chassis parts with reduced weight increase and reduced rusting. [Means for solving the problem]

[0011] The burring device according to the present disclosure forms a first cylindrical flange protruding toward the second vertical plate portion on a workpiece including a first vertical plate portion and a second vertical plate portion opposed to the first vertical plate portion, and forms a second cylindrical flange opposed to the first cylindrical flange on the second vertical plate portion. The burring device includes a first die, a second die, a first support shaft, a second support shaft, a first elastic member, a second elastic member, a cam member, a first punch, and a second punch. The first die includes a first semi-cylindrical concave surface. The first semi-cylindrical concave surface corresponds to a vertically split half of the outer circumferential surfaces of the first cylindrical flange and the second cylindrical flange. The second die is disposed adjacent to the first die, and includes a second semi-cylindrical concave surface and a lever portion. The second semi-cylindrical concave surface corresponds to the other half of the outer circumferential surfaces of the first cylindrical flange and the second cylindrical flange. The lever portion is positioned below the second semi-cylindrical concave surface and protrudes laterally beyond the first die. The first support shaft is disposed below the first semi-cylindrical concave surface. The first support shaft rotatably supports the first die such that the first semi-cylindrical concave surface approaches or moves away from the second semi-cylindrical concave surface. The second support shaft is disposed below the second semi-cylindrical concave surface. The second support shaft rotatably supports the second die such that the second semi-cylindrical concave surface approaches or moves away from the first semi-cylindrical concave surface. The first elastic member urges the first die in a direction in which the first semi-cylindrical concave surface moves away from the second semi-cylindrical concave surface. The second elastic member urges the second die in a direction in which the second semi-cylindrical concave surface moves away from the first semi-cylindrical concave surface. The cam member is movable in the up and down directions. As the cam member moves downward, it comes into contact with the first die and the lever portion, and rotates the first die about the first support shaft while sliding against the first die, and rotates the second die about the second support shaft while sliding against the lever portion, and holds the first semi-cylindrical concave surface and the second semi-cylindrical concave surface in a state where they are closest to each other at the end of the downward movement. The first punch is provided so as to be insertable into a cylindrical hole defined by the closest first and second semi-cylindrical concave surfaces. The second punch is provided so as to be insertable into the cylindrical hole from the opposite side to the first punch.

[0012] The burring method according to the present disclosure uses the burring device according to the present disclosure described above to form the first cylindrical flange and the second cylindrical flange on the workpiece. The burring method includes steps (a), (b), (c), and (d). Step (a) is to prepare a workpiece including a first vertical plate portion having a first pilot hole and a second vertical plate portion having a second pilot hole facing the first pilot hole. Step (b) is to place the workpiece with respect to the burring device such that the first semi-cylindrical concave surface of the first die and the second semi-cylindrical concave surface of the second die are located between the first vertical plate portion and the second vertical plate portion. Step (c) is to move a cam member downward to hold the first semi-cylindrical concave surface and the second semi-cylindrical concave surface in the closest position at positions corresponding to the first pilot hole and the second pilot hole. In step (d), the first punch is moved toward the first pilot hole, and the second punch is moved toward the second pilot hole to form a first cylindrical flange and a second cylindrical flange. Effect of the Invention

[0013] The burring apparatus and burring method of the present disclosure make it possible to form two opposing cylindrical flanges while minimizing the space required to allow the die to move, and also to manufacture chassis parts with reduced weight and reduced rusting. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a chassis part obtained using a burring device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram showing a workpiece to be shaped by the burring device according to the embodiment of the present disclosure. [Diagram 3] FIG. 3 is a front view of the burring device according to the first embodiment. [Figure 4] FIG. 4 is a side view of the burring device according to the first embodiment. [Diagram 5] FIG. 5 is a schematic diagram showing a state in which the first punch and the second punch have reached the end of their movements in the burring device according to the first embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a state in which the first die is rotated in the burring device according to the first embodiment. [Figure 7] FIG. 7 is a schematic diagram showing a state in which the cam member has reached the end of its movement in the burring device according to the first embodiment. [Figure 8] FIG. 8 is a front view of a modified example of the burring device according to the first embodiment. [Figure 9] FIG. 9 is a front view of the burring device according to the second embodiment. [Figure 10] FIG. 10 is a schematic diagram showing a state in which the first punch and the second punch have reached the end of their movements in the burring device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present disclosure will be described. In the following description, the embodiment of the present disclosure will be described by way of examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and specific materials may be exemplified, but the present disclosure is not limited to these examples.

[0016] The burring device according to the present embodiment forms a first cylindrical flange protruding toward the second vertical plate portion on the first vertical plate portion of a workpiece including a first vertical plate portion and a second vertical plate portion opposed to the first vertical plate portion, and forms a second cylindrical flange opposing the first cylindrical flange on the second vertical plate portion. The burring device includes a first die, a second die, a first support shaft, a second support shaft, a first elastic member, a second elastic member, a cam member, a first punch, and a second punch. The first die includes a first semi-cylindrical concave surface. The first semi-cylindrical concave surface corresponds to a vertically divided half circumference of the outer circumferential surfaces of the first cylindrical flange and the second cylindrical flange. The second die is disposed adjacent to the first die, and includes a second semi-cylindrical concave surface and a lever portion. The second semi-cylindrical concave surface corresponds to the other half circumference of the outer circumferential surfaces of the first cylindrical flange and the second cylindrical flange. The lever portion is positioned below the second semi-cylindrical concave surface and protrudes laterally beyond the first die. The first support shaft is disposed below the first semi-cylindrical concave surface. The first support shaft rotatably supports the first die such that the first semi-cylindrical concave surface approaches or moves away from the second semi-cylindrical concave surface. The second support shaft is disposed below the second semi-cylindrical concave surface. The second support shaft rotatably supports the second die such that the second semi-cylindrical concave surface approaches or moves away from the first semi-cylindrical concave surface. The first elastic member urges the first die in a direction in which the first semi-cylindrical concave surface moves away from the second semi-cylindrical concave surface. The second elastic member urges the second die in a direction in which the second semi-cylindrical concave surface moves away from the first semi-cylindrical concave surface. The cam member is movable in the up and down directions. As the cam member moves downward, it comes into contact with the first die and the lever portion, and rotates the first die about the first support shaft while sliding against the first die, and rotates the second die about the second support shaft while sliding against the lever portion, and holds the first semi-cylindrical concave surface and the second semi-cylindrical concave surface in a state where they are closest to each other at the end of the downward movement. The first punch is provided so as to be insertable into a cylindrical hole defined by the closest first and second semi-cylindrical concave surfaces. The second punch is provided so as to be insertable into the cylindrical hole from the side opposite to the first punch (first configuration).

[0017] In the first configuration, the first die includes a first semi-cylindrical concave surface, and the second die includes a second semi-cylindrical concave surface. The die hole for forming the opposing first and second cylindrical flanges is a cylindrical hole defined by the closest first and second semi-cylindrical concave surfaces, and the first and second dies are arranged adjacent to each other. The first die is configured to be rotatable around a first support shaft while being biased by a first elastic member. The second die is configured to be rotatable around a second support shaft while being biased by a second elastic member. When one cam member moves downward, the cam member comes into contact with and slides against the lever portions of the first and second dies, and the first and second dies rotate around the corresponding support shafts. Furthermore, the cam member located at the end of the movement holds the first and second dies in a state where the first and second semi-cylindrical concave surfaces are closest to each other. Then, the first and second punches are inserted into the die holes defined by the first and second semi-cylindrical concave surfaces, thereby forming the first and second cylindrical flanges. The space that allows the first and second dies to rotate is smaller than, for example, the space that allows the slide die to move. Therefore, according to the burring device of the first configuration, the space that allows the dies (first and second dies) to move (rotate) can be reduced. Therefore, even if the chassis part has a complex shape in which the space that allows the dies to move is limited, two opposing cylindrical flanges (the first and second cylindrical flanges) can be formed. In addition, no collar is required for forming the cylindrical flanges, and no collar is present in the manufactured chassis part. Since there is no collar, it is possible to suppress an increase in the weight of the chassis part and also to suppress rusting.

[0018] In the burring device according to the first configuration, the cam member preferably includes a side surface along the moving direction of the cam member, an end surface preceding the downward movement of the cam member, and an inclined surface continuing from the side surface and the end surface and inclined with respect to the moving direction. In this case, the first die may include a corner portion that comes into contact with and slides against the inclined surface of the cam member as the cam member moves downward, and a side surface that comes into contact with and slides against the side surface of the cam member as the cam member moves further downward and maintains contact with the side surface of the cam member when the cam member reaches its end terminal. The lever portion of the second die may include a corner portion that comes into contact with and slides against the end surface of the cam member as the cam member moves downward, and a flat surface that comes into contact with the end surface of the cam member when the cam member reaches its end terminal (second configuration).

[0019] The burring device of the first or second configuration may further include a first plate holder and a second plate holder. The first plate holder is arranged coaxially with the first punch and is urged toward the first and second dies relative to the first punch. The second plate holder is arranged coaxially with the second punch and is urged toward the first and second dies relative to the second punch (third configuration). In this case, during the period when the first cylindrical flange is formed by the first punch, the first vertical plate portion is sandwiched and restrained between the first plate holder and the first die (second die), and further during the period when the second cylindrical flange is formed by the second punch, the second vertical plate portion is sandwiched and restrained between the second plate holder and the first die (second die). Therefore, the dimensional accuracy of the formed first and second cylindrical flanges is improved.

[0020] The burring method according to the present embodiment uses a burring device according to any one of the first to third configurations to form the first cylindrical flange and the second cylindrical flange on the workpiece. The burring method includes steps (a), (b), (c), and (d). Step (a) is to prepare a workpiece including a first vertical plate portion having a first pilot hole and a second vertical plate portion having a second pilot hole facing the first pilot hole. Step (b) is to place the workpiece with respect to the burring device such that the first semi-cylindrical concave surface of the first die and the second semi-cylindrical concave surface of the second die are located between the first vertical plate portion and the second vertical plate portion. Step (c) is to move a cam member downward to hold the first semi-cylindrical concave surface and the second semi-cylindrical concave surface in the closest position at positions corresponding to the first pilot hole and the second pilot hole. In step (d), the first punch is moved toward the first pilot hole, and the second punch is moved toward the second pilot hole to form the first cylindrical flange and the second cylindrical flange (fourth configuration). In this case, since the burring method uses the burring device according to the first configuration, it is possible to form two opposing cylindrical flanges (the first cylindrical flange and the second cylindrical flange) while suppressing the space that allows the dies (the first die and the second die) to move (rotate). In addition, since no collar is required to form the cylindrical flanges and no collar is present in the manufactured chassis part, it is possible to suppress an increase in the weight of the chassis part and also to suppress rusting.

[0021] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0022] <Chassis parts> First, with reference to FIG. 1, a chassis part 200 obtained by using a burring device according to an embodiment of the present disclosure will be described. FIG. 1 is a schematic diagram showing an example of the chassis part 200. FIG. 1 shows a perspective view of the chassis part 200. The chassis part 200 shown in FIG. 1 is made of a single steel plate member. That is, the chassis part 200 is formed by using, for example, a blank cut out from a steel plate as a material, and by press forming, trimming, drilling, burring, and the like. In other words, the chassis part 200 is not made by welding a plurality of members together.

[0023] The chassis part 200 shown in FIG. 1 is a front lower arm. In an automobile, this chassis part 200 connects the vehicle body (specifically, the suspension) and the wheels. The chassis part 200 includes a main body 201, a wheel attachment part 202, a first vehicle body attachment part 203, and a second vehicle body attachment part 204. The main body 201 has a shape that extends while curving in an arch shape or an L shape in a plan view. The wheel attachment part 202 is provided at one end of the main body 201 in the extending direction. The first vehicle body attachment part 203 is provided at the other end of the main body 201 in the extending direction. The second vehicle body attachment part 204 is provided between the wheel attachment part 202 and the first vehicle body attachment part 203. The second vehicle body attachment part 204 protrudes from the main body 201 to the outside of the curve.

[0024] The second vehicle body mounting portion 204 has a cylindrical portion for receiving a bushing used for connection to the vehicle body. When connecting the chassis component 200 to the vehicle body, a cylindrical bushing is press-fitted into the cylindrical portion. The second vehicle body mounting portion 204 includes a first vertical plate portion 241 and a second vertical plate portion 242. Both vertical plate portions 241, 242 protrude from the main body 201 to the outside of the curve. The first vertical plate portion 241 and the second vertical plate portion 242 are arranged at an interval in the extending direction of the curved main body 201. The second vertical plate portion 242 is arranged parallel to the first vertical plate portion 241 and faces the first vertical plate portion 241. The first vertical plate portion 241 has a first cylindrical flange 251, and the second vertical plate portion 242 has a second cylindrical flange 252. The first cylindrical flange 251 protrudes from the first vertical plate portion 241 toward the second vertical plate portion 242. The second cylindrical flange 252 protrudes from the second vertical plate portion 242 toward the first vertical plate portion 241 and faces the first cylindrical flange 251. The first cylindrical flange 251 and the second cylindrical flange 252 protrude inward from the corresponding first vertical plate portion 241 and second vertical plate portion 242 and share a central axis. The inner and outer diameters of both cylindrical flanges 251, 252 are the same. In the second vehicle body mounting portion 204, the opposing first cylindrical flange 251 and second cylindrical flange 252 form a cylindrical portion.

[0025] The first cylindrical flange 251 and the second cylindrical flange 252 are formed by the burring device according to the embodiment of the present disclosure. In other words, the first cylindrical flange 251 and the second cylindrical flange 252 are burring parts. FIG. 2 shows an example of a workpiece 210 to be formed by the burring device. FIG. 2 shows a perspective view of the workpiece 210 corresponding to the chassis part 200 shown in FIG. 1. In the example shown in FIG. 2, the workpiece 210 is composed of a single steel plate member. In this case, the workpiece 210 is formed by press forming, trimming, punching, etc., using, for example, a blank cut out from a steel plate as a material. However, the workpiece 210 may be composed of a plurality of members. In short, the workpiece 210 only needs to have a first vertical plate portion 241 and a second vertical plate portion 242 facing each other.

[0026] As shown in FIG. 2, in the second vehicle body mounting portion 204 of the workpiece 210, the first vertical plate portion 241 has a first pilot hole 261, and the second vertical plate portion 242 has a second pilot hole 262. The first pilot hole 261 is provided in a portion of the first vertical plate portion 241 that corresponds to the first cylindrical flange 251 (FIG. 1). The second pilot hole 262 is provided in a portion of the second vertical plate portion 242 that corresponds to the second cylindrical flange 252 (FIG. 1). Both pilot holes 261, 262 have a circular shape, and their diameters are smaller than the inner diameters of the first cylindrical flange 251 and the second cylindrical flange 252 of the chassis part 200. Half the difference between the outer diameter of the first cylindrical flange 251 and the diameter of the first pilot hole 261 is substantially the height of the first cylindrical flange 251. Similarly, half the difference between the outer diameter of the second cylindrical flange 252 and the diameter of the second pilot hole 262 is substantially the height of the second cylindrical flange 252 .

[0027] [First embodiment] <Burring device> The burring device 100 according to the first embodiment will be described with reference to Figs. 3 to 7. Figs. 3 and 4 are schematic diagrams of the burring device 100 according to the first embodiment. Fig. 3 is a front view of the burring device 100. Fig. 4 is a side view of the burring device 100, and is a view of the burring device 100 shown in Fig. 3 as viewed from the right side of the paper. Fig. 3 shows the second vehicle body mounting portion 204 as viewed from the outside of the curve, assuming that the workpiece 210 is placed in the burring device 100. Fig. 4 shows the second vehicle body mounting portion 204 as viewed along the central axes of the first prepared hole 261 and the second prepared hole 262, assuming that the workpiece 210 is placed in the burring device 100. However, in both Figs. 3 and 4, the workpiece 210 is omitted from illustration.

[0028] As shown in FIG. 3, the burring apparatus 100 includes a first die 1, a second die 2, a cam member 3, a first support shaft 6, a second support shaft 7, a first punch 4, and a second punch 5. As shown in FIG. 4, the burring apparatus 100 further includes a first elastic member 8 and a second elastic member 9. In FIG. 3, the cam member 3 is indicated by a two-dot chain line. In FIG. 3, the first elastic member 8 and the second elastic member 9 are omitted from illustration. A press machine can be used as the burring apparatus 100. In this case, the burring apparatus 100 includes a fixed bed and a ram that is above the bed and can be raised and lowered relative to the bed, neither of which is shown.

[0029] 3, the first punch 4 and the second punch 5 are disposed above the bed. The second punch 5 is disposed so as to face the first punch 4. The second punch 5 is disposed at a distance from the first punch 4 that is at least equal to or greater than the distance between the first vertical plate portion 241 and the second vertical plate portion 242 of the workpiece 210. Both punches 4, 5 have a cylindrical shape. The diameters of both punches 4, 5 are substantially the same as the inner diameters of the first cylindrical flange 251 and the second cylindrical flange 252 of the chassis part 200.

[0030] The first punch 4 is fixed to a first holder 41. The second punch 5 is fixed to a second holder 51. The first holder 41 is attached on the bed of the press machine so as to be slidable toward the second holder 51. This allows the first punch 4 to be slidable toward the second punch 5. The second holder 51 is attached on the bed of the press machine so as to be slidable toward the first holder 41. This allows the second punch 5 to be slidable toward the first punch 4.

[0031] A first punch cam member 42 is disposed above the first holder 41 to which the first punch 4 is fixed. The first punch cam member 42 is attached to the ram of the press machine. A second punch cam member 52 is disposed above the second holder 51 to which the second punch 5 is fixed. The second punch cam member 52 is attached to the ram of the press machine.

[0032] The first punch cam member 42 has a slope 42a whose distance from the second punch cam member 52 increases toward the bottom. The first holder 41 has a slope 41a corresponding to the slope 42a of the first punch cam member 42. The second punch cam member 52 has a slope 52a whose distance from the first punch cam member 42 increases toward the bottom. The second holder 51 has a slope 51a corresponding to the slope 52a of the second punch cam member 52.

[0033] When the ram of the press machine descends, the first punch cam member 42 moves downward. The downward movement of the first punch cam member 42 causes the inclined surface 42a of the first punch cam member 42 to come into contact with the inclined surface 41a of the first holder 41. As the first punch cam member 42 moves further, the inclined surface 41a of the first holder 41 slides against the inclined surface 42a of the first punch cam member 42, and the first holder 41 slides together with the first punch 4 toward the second holder 51. As a result, the first punch 4 moves toward the second punch 5.

[0034] When the ram of the press machine descends, the second punch cam member 52 moves downward. The downward movement of the second punch cam member 52 brings the inclined surface 52a of the second punch cam member 52 into contact with the inclined surface 51a of the second holder 51. As the second punch cam member 52 moves further, the inclined surface 51a of the second holder 51 slides against the inclined surface 52a of the second punch cam member 52, and the second holder 51 slides together with the second punch 5 toward the first holder 41. As a result, the second punch 5 moves toward the first punch 4.

[0035] Fig. 5 is a schematic diagram showing a state in which the first punch 4 and the second punch 5 reach the end of their movement in the burring device 100 according to the first embodiment. In other words, Fig. 5 is a front view in a state in which the first punch cam member 42 and the second punch cam member 52 reach the end of their downward movement (bottom dead center). As shown in Fig. 5, when the first punch cam member 42 and the second punch cam member 52 reach the bottom dead center and the first holder 41 and the second holder 51 reach the movement end of the slide, the first punch 4 is in a state in which it faces the second punch 5 and is close to it.

[0036] Returning to FIG. 3, the first die 1 , the second die 2 , the cam member 3 , the first support shaft 6 , and the second support shaft 7 are disposed between the first punch 4 and the second punch 5 .

[0037] Referring to FIG. 4, the first die 1 is rotatably supported by a first support shaft 6. The second die 2 is disposed adjacent to the first die 1 and rotatably supported by a second support shaft 7. The first support shaft 6 and the second support shaft 7 extend parallel to the moving direction of the first punch 4 and the second punch 5 (FIG. 3). In this embodiment, the first support shaft 6 is also used as the second support shaft 7. That is, the first support shaft 6 and the second support shaft 7 are a single member. The first support shaft 6 and the second support shaft 7 are fixed to the bed of the press machine via support members 61, 61 (FIG. 3). However, the first support shaft 6 may be provided separately from the second support shaft 7.

[0038] The first die 1 includes a first semi-cylindrical concave surface 11. The first semi-cylindrical concave surface 11 is formed on the surface on the side of the second die 2. The first semi-cylindrical concave surface 11 corresponds to a vertically split half of the outer circumferential surfaces of a first cylindrical flange 251 and a second cylindrical flange 252 of the chassis part 200 shown in FIG.

[0039] The second die 2 includes a second semi-cylindrical concave surface 21. The second semi-cylindrical concave surface 21 is formed on the surface on the first die 1 side. The second semi-cylindrical concave surface 21 corresponds to the other half of the outer circumferential surfaces of the first cylindrical flange 251 and the second cylindrical flange 252 of the chassis part 200 shown in FIG. 1 . In other words, the second semi-cylindrical concave surface 21, when combined with the first semi-cylindrical concave surface 11, corresponds to one circumference of the outer circumferential surfaces of the first cylindrical flange 251 and the second cylindrical flange 252.

[0040] The second die 2 further includes a lever portion 22. The lever portion 22 is positioned below the second semi-cylindrical concave surface 21. The lever portion 22 protrudes laterally beyond the first die 1. Specifically, the lever portion 22 protrudes obliquely upward from the lower portion of the second die 2. For this reason, the first die 1 is provided with a recess 12 to allow the lever portion 22 to pass therethrough.

[0041] As described above, the first die 1 is rotatably supported by the first support shaft 6, and the second die 2 is rotatably supported by the second support shaft 7. Specifically, the first support shaft 6 is disposed below the first semi-cylindrical concave surface 11. The first die 1 is rotatably supported around the first support shaft 6 so that the first semi-cylindrical concave surface 11 approaches or moves away from the second semi-cylindrical concave surface 21. The second support shaft 7 is disposed below the second semi-cylindrical concave surface 21. The second die 2 is rotatably supported around the second support shaft 7 so that the second semi-cylindrical concave surface 21 approaches or moves away from the first semi-cylindrical concave surface 11.

[0042] The first elastic member 8 biases the first die 1 in a direction in which the first semi-cylindrical concave surface 11 moves away from the second semi-cylindrical concave surface 21. In other words, the first elastic member 8 biases the first die 1, which is rotatable around the first support shaft 6, in a direction in which it moves away from the second die 2. The first elastic member 8 is fixed to the bed of the press. The first elastic member 8 is provided on the second die 2 side with respect to the first support shaft 6 (second support shaft 7). For example, a coil spring can be used as the first elastic member 8. A fluid pressure cylinder or a resin such as urethane can also be used as the first elastic member 8.

[0043] The second elastic member 9 biases the second die 2 in a direction in which the second semi-cylindrical concave surface 21 moves away from the first semi-cylindrical concave surface 11. In other words, the second elastic member 9 biases the second die 2, which is rotatable around the second support shaft 7, in a direction in which it moves away from the first die 1. The second elastic member 9 is fixed to the bed of the press. The second elastic member 9 is provided on the first die 1 side with respect to the second support shaft 7 (first support shaft 6). In this embodiment, the second elastic member 9 is attached to the lever portion 22 of the second die 2. For example, a coil spring can be used as the second elastic member 9. A fluid pressure cylinder or a resin such as urethane can be used as the second elastic member 9.

[0044] The cam member 3 is attached to the ram of the press machine via an elastic member (not shown). This elastic member is, for example, a coil spring or a fluid pressure cylinder. The cam member 3 is disposed so that a portion of it overlaps with the lever portions 22 of the first die 1 and the second die 2 when viewed in the vertical direction. The cam member 3 is movable in the vertical direction in association with the movement of the ram of the press machine.

[0045] When the ram of the press machine descends, the cam member 3 moves downward. As the cam member 3 moves downward, it comes into contact with the first die 1 and the lever portion 22, and rotates the first die 1 around the first support shaft 6 while sliding against the first die 1, and rotates the second die 2 around the second support shaft 7 while sliding against the lever portion 22. Then, at the end of the downward movement (bottom dead center of the cam member 3), the cam member 3 holds the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21 in the closest state. An example of a specific configuration that causes such an operation will be described below.

[0046] The cam member 3 has a side surface 3a, an end surface 3b, and a slope 3c. In the cam member 3, the side surface 3a is located on the second die 2 side. The side surface 3a is a surface along the moving direction of the cam member 3. That is, the side surface 3a is a surface along the vertical direction. In the cam member 3, the end surface 3b is a surface that precedes the downward movement of the cam member 3. That is, the end surface 3b is the lower surface of the cam member 3. In the example of this embodiment, the end surface 3b is a surface perpendicular to the side surface 3a. In the cam member 3, the slope 3c is continuous with the side surface 3a and the end surface 3b, and is inclined with respect to the moving direction of the cam member 3. That is, the slope 3c is inclined with respect to the side surface 3a and the end surface 3b.

[0047] The first die 1 has a corner 1a and a side surface 1b. In the first die 1, the corner 1a is an upper corner located near the cam member 3. The corner 1a comes into contact with the inclined surface 3c of the cam member 3 as the cam member 3 moves downward, and slides against the inclined surface 3c of the cam member 3 as the cam member 3 moves further. As the first die 1 slides, it rotates around the first support shaft 6. The corner 1a of the first die 1 is preferably rounded to prevent the corner 1a from biting against the inclined surface 3c of the cam member 3. However, the corner 1a may be angular.

[0048] In the first die 1, the side surface 1b is a side surface located close to the cam member 3. In other words, the side surface 1b is a side surface located opposite to the surface on which the first semi-cylindrical concave surface 11 is formed. As the cam member 3 slides against the corner portion 1a and moves downward, the side surface 1b comes into contact with the side surface 3a of the cam member 3, and slides against the side surface 3a of the cam member 3 as the cam member 3 moves further.

[0049] Fig. 6 is a schematic diagram showing a state in which the first die has rotated in the burring device 100 according to the first embodiment. In other words, Fig. 6 is a side view of the first die 1 in a state in which the side surface 1b of the first die 1 slides against the side surface 3a of the cam member 3. As shown in Fig. 6, when the side surface 1b of the first die 1 slides against the side surface 3a of the cam member 3, the first die 1 has finished rotating around the first support shaft 6. In the example shown in Fig. 6, the second die 2 remains in the initial state.

[0050] 4 and 6, the lever portion 22 of the second die 2 has a corner 22a and a flat surface 22b. In the lever portion 22, the corner 22a is an upper corner located near the cam member 3. As the cam member 3 slides against the side surface 1b of the first die 1 and moves downward, the corner 22a comes into contact with the end surface 3b of the cam member 3, and slides against the end surface 3b of the cam member 3 as the cam member 3 moves further. As the cam member 3 slides, the second die 2 rotates together with the lever portion 22 around the second support shaft 7. The corner 22a of the lever portion 22 is preferably rounded to prevent the corner 22a from biting against the end surface 3b of the cam member 3. However, the corner 22a may be angular.

[0051] In the lever portion 22, the plane 22b is an upper surface located near the cam member 3. The plane 22b is continuous with the corner portion 22a. FIG. 7 is a schematic diagram showing a state in which the cam member 3 reaches the end of its movement in the burring device 100 according to the first embodiment. In other words, FIG. 7 is a side view of the cam member 3 when it reaches the end of its downward movement (bottom dead center). As shown in FIG. 7, when the cam member 3 reaches the bottom dead center, the plane 22b of the lever portion 22 is in contact with the end surface 3b of the cam member 3. In this state, the side surface 1b of the first die 1 is maintained in contact with the side surface 3a of the cam member 3.

[0052] In this case, the cam member 3 is in contact with both the side surface 1b of the first die 1 and the flat surface 22b of the lever portion 22, so that the downward movement of the cam member 3 is restricted. This also ends the rotation of the second die 2 around the second support shaft 7. As a result, the first semi-cylindrical concave surface 11 of the first die 1 and the second semi-cylindrical concave surface 21 of the second die 2 are held in the closest state. A cylindrical hole is defined by the closest first semi-cylindrical concave surface 11 and second semi-cylindrical concave surface 21, and this cylindrical hole becomes a die hole for forming the opposing first cylindrical flange 251 and second cylindrical flange 252.

[0053] It is preferable that the portions of the cam member 3 that slide against the first die 1 and the second die 2, i.e., the side surface 3a, the end surface 3b, and the inclined surface 3c, are treated to prevent galling. This treatment is, for example, a surface treatment using gunmetal. Similarly, it is preferable that the portions of the first die 1 that slide against the cam member 3, i.e., the corners 1a and the side surfaces 1b, are also treated to prevent galling. It is preferable that the portions of the lever portion 22 of the second die 2 that slide against the cam member 3, i.e., the corners 22a, are also treated to prevent galling.

[0054] The die hole must be a cylindrical hole without any chipping. If the die hole is partially chipped, such as in the shape of the letter C, the accuracy of the inner diameter of the burred part (cylindrical flange) formed by burring will be reduced. If the accuracy of the inner diameter of the burred part is reduced, it will be impossible to press a bush into the burred part. Even if the bush can be pressed into the burred part, the pull-out load of the bush will be reduced.

[0055] As described above, in this embodiment, after the operation of the first die 1 by contact and sliding with the cam member 3 is completed, the cam member 3 contacts the lever portion 22 of the second die 2 to operate the second die 2. However, the second die 2 may operate while the first die 1 is operating. Also, the second die 2 may operate simultaneously with the first die 1. Also, operation may start from the second die 2.

[0056] In this embodiment, a stopper 10 is provided below the lever portion 22. The stopper 10 also serves to stably limit the downward movement of the cam member 3.

[0057] After the cam member 3 reaches the bottom dead center, the ram of the press continues to descend in order to slide the above-mentioned first punch 4 and second punch 5. As the ram continues to descend, the elastic member supporting the cam member 3 contracts. This makes it possible to continue to hold the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21 in the closest position.

[0058] As described above, the first punch 4 moves toward the second punch 5, and the second punch 5 moves toward the first punch 4. During this movement, a cylindrical hole defined by the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21, i.e., a die hole, is disposed between the first punch 4 and the second punch 5. Therefore, the first punch 4 can be inserted into the cylindrical hole (die hole). On the other hand, the second punch 5 can be inserted into the cylindrical hole from the side opposite to the first punch 4.

[0059] <Burring method> The burring method according to this embodiment is carried out by using the burring apparatus 100. In the burring method, a first cylindrical flange 251 and a second cylindrical flange 252 are formed on the above-mentioned workpiece 210. In this way, the chassis part 200 is obtained. Specifically, the burring method includes steps (a), (b), (c), and (d) in this order.

[0060] 2, in step (a), as described above, the workpiece 210 including the first vertical plate portion 241 having the first pilot hole 261 and the second vertical plate portion 242 having the second pilot hole 262 is prepared. The second vertical plate portion 242 faces the first vertical plate portion 241. The second pilot hole 262 faces the first pilot hole 261.

[0061] Next, in step (b), the workpiece 210 is placed in the burring device 100 in the state shown in Fig. 4. At this time, the workpiece 210 is placed with respect to the burring device 100 so that the first semi-cylindrical concave surface 11 of the first die 1 and the second semi-cylindrical concave surface 21 of the second die 2 are positioned between the first vertical plate portion 241 and the second vertical plate portion 242.

[0062] Subsequently, in step (c), the ram is lowered to move the cam member 3 downward. As a result, as described above with reference to Fig. 6, the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21 are held in the closest state, and a cylindrical hole that becomes a die hole is formed by the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21. At this time, the cylindrical hole is disposed at a position corresponding to the first pilot hole 261 and the second pilot hole 262.

[0063] Next, in step (d), the ram is further lowered to move the first punch cam member 42 and the second punch cam member 52 downward. As a result, as described above with reference to FIG. 5, the first punch 4 is moved toward the first prepared hole 261, and the second punch 5 is moved toward the second prepared hole 262. The movement of the first punch 4 and the second punch 5 performs burring on the first vertical plate portion 241 and the second vertical plate portion 242. This burring forms the first cylindrical flange 251 protruding toward the second vertical plate portion 242 on the first vertical plate portion 241, and the second cylindrical flange 252 protruding toward the first vertical plate portion 241 on the second vertical plate portion 242. As a result, the opposing first cylindrical flange 251 and second cylindrical flange 252 are formed.

[0064] After the first cylindrical flange 251 and the second cylindrical flange 252 are formed, the ram is raised. As the ram is raised, the first punch cam member 42 and the second punch cam member 52 first move upward. As the first punch cam member 42 and the second punch cam member 52 move upward, the first punch 4 and the second punch 5 are released from the constraint by the first punch cam member 42 and the second punch cam member 52 and move away from each other. At this time, the first punch 4 and the second punch 5 move away from each other due to the elastic force from an elastic member (e.g., a coil spring) provided between the first holder 41 to which the first punch 4 is fixed and the second holder 51 to which the second punch 5 is fixed, for example. As a result, the first punch 4 and the second punch 5 move away from the first cylindrical flange 251 and the second cylindrical flange 252.

[0065] Further elevation of the ram causes the cam member 3 to move upward. With the upward movement of the cam member 3, the first die 1 and the second die 2 are released from the restraint by the cam member 3. Then, the second die 2 rotates around the second support shaft 7 by the elastic force from the second elastic member 9 so that the second semi-cylindrical concave surface 21 moves away from the first semi-cylindrical concave surface 11, and the first die 1 rotates around the first support shaft 6 by the elastic force from the first elastic member 8 so that the first semi-cylindrical concave surface 11 moves away from the second semi-cylindrical concave surface 21. As a result, the first die 1 and the second die 2 move away from the first cylindrical flange 251 and the second cylindrical flange 252. Then, the molded product (chassis part 200) having the first cylindrical flange 251 and the second cylindrical flange 252 is removed from the burring device 100.

[0066] [effect] In this embodiment, the first die 1 includes a first semi-cylindrical concave surface 11, and the second die 2 includes a second semi-cylindrical concave surface 21. A die hole for forming the opposing first cylindrical flange 251 and second cylindrical flange 252 is a cylindrical hole defined by the closest first semi-cylindrical concave surface 11 and second semi-cylindrical concave surface 21. The first die 1 and second die 2 are arranged adjacent to each other. The first die 1 is configured to be rotatable around the first support shaft 6 while being biased by the first elastic member 8. The second die 2 is configured to be rotatable around the second support shaft 7 while being biased by the second elastic member 9. When one cam member 3 moves downward, the cam member 3 comes into contact with and slides against the lever portions 22 of the first die 1 and the second die 2, and the first die 1 and the second die 2 rotate around the corresponding support shafts 6 and 7. Furthermore, the cam member 3 located at the end of the movement holds the first die 1 and the second die 2 in a state where the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21 are closest to each other. Then, the first punch 4 and the second punch 5 are inserted into cylindrical holes (die holes) defined by the first semi-cylindrical concave surface 11 and the second semi-cylindrical concave surface 21, thereby forming the first cylindrical flange 251 and the second cylindrical flange 252.

[0067] The space that allows the first die 1 and the second die 2 to rotate is smaller than, for example, the space that allows the slide die to move. Therefore, according to the burring device and the burring method of this embodiment, the space that allows the dies (first die 1 and second die 2) to move (rotate) can be reduced. Therefore, even for a chassis part 200 with a complex shape in which the space that allows the die to move is limited, two opposing cylindrical flanges (the first cylindrical flange 251 and the second cylindrical flange 252) can be formed.

[0068] Furthermore, in the burring apparatus and burring method according to this embodiment, no collars are required for molding the first cylindrical flange 251 and the second cylindrical flange 252, and no collars are present in the manufactured chassis part 200. Since no collars are present, it is possible to suppress an increase in the weight of the chassis part 200, and it is also possible to suppress rusting.

[0069] <Modification> Fig. 8 is a front view of a modified example of the burring device 100 according to the first embodiment. Fig. 8 is a view corresponding to Fig. 3. As shown in Fig. 8, in the burring device 100A, the lever portion 22 of the second die 2 may be provided so as to penetrate the lower portion of the first die 1. In this case, the recess 12A is provided so as to cut out the lower portion of the first die 1.

[0070] [Second embodiment] The burring device 100B according to the second embodiment will be described with reference to Figs. 9 and 10. Fig. 9 is a front view of the burring device 100B according to the second embodiment. Fig. 9 shows the second vehicle body mounting portion 204 viewed from the outside of the curve, assuming that the workpiece 210 is placed in the burring device 100B. In other words, Fig. 9 is a view corresponding to Fig. 3. Fig. 10 is a schematic view showing a state in which the first punch 4 and the second punch 5 reach the end of their movements in the burring device 100B. In other words, Fig. 10 is a view corresponding to Fig. 5. The burring device 100B differs from the burring devices 100 and 100A according to the first embodiment in the configuration in which the burring device 100B includes the first plate holder 43 and the second plate holder 53.

[0071] As shown in FIG. 9, in the burring device 100B, the first plate holder 43 is provided near the first punch 4, and the second plate holder 53 is provided near the second punch 5. Specifically, the first plate holder 43 is, for example, a plate material having an annular shape, and is arranged coaxially with the first punch 4. The inner diameter of the first plate holder 43 is larger than the diameter of the first punch 4. In the initial state, the first plate holder 43 is arranged between the first punch 4 and the first die 1 (the second die 2). The first plate holder 43 is supported by the first holder 41 via the first plate holder elastic member 44. The first plate holder elastic member 44 biases the first plate holder 43 toward the first die 1 and the second die 2. In other words, the first plate holder 43 is biased toward the first die 1 and the second die 2 with respect to the first punch 4. As the first plate holder elastic member 44, for example, a coil spring can be used.

[0072] The second plate holder 53 is, for example, a plate having an annular shape, and is arranged coaxially with the second punch 5. The inner diameter of the second plate holder 53 is larger than the diameter of the second punch 5. In the initial state, the second plate holder 53 is arranged between the second punch 5 and the first die 1 (the second die 2). The second plate holder 53 faces the first plate holder 43. The second plate holder 53 is supported by the second holder 51 via a second plate holder elastic member 54. The second plate holder elastic member 54 biases the second plate holder 53 toward the first die 1 and the second die 2. In other words, the second plate holder 53 is biased toward the first die 1 and the second die 2 relative to the second punch 5. As the second plate holder elastic member 54, for example, a coil spring can be used.

[0073] The burring method using the burring apparatus 100B having such a configuration includes steps (a), (b), (c), and (d) as in the first embodiment. Specifically, in step (a), a workpiece 210 is prepared, and in step (b), the workpiece 210 is placed relative to the burring apparatus 100B. Next, in step (c), the cam member 3 is moved downward to rotate the first die 1 and the second die 2. As a result, a cylindrical hole that becomes a die hole is formed by the first semi-cylindrical concave surface 11 of the first die 1 and the second semi-cylindrical concave surface 21 of the second die 2. Then, in step (d), the first punch cam member 42 and the second punch cam member 52 are moved downward to move the first punch 4 toward the first pilot hole 261 of the first vertical plate portion 241, and the second punch 5 toward the second pilot hole 262 of the second vertical plate portion 242. As a result, the first vertical plate portion 241 and the second vertical plate portion 242 are subjected to burring, and as a result, the opposing first cylindrical flange 251 and second cylindrical flange 252 are formed.

[0074] 10, in step (d), the first punch 4 moves, and the first plate holder 43 contacts the portion of the first vertical plate portion 241 surrounding the first pilot hole 261 before the first punch 4, and the first plate holder 43 and the first die 1 (second die 2) sandwich the first vertical plate portion 241. In addition, the second punch 5 moves, and the second plate holder 53 contacts the portion of the second vertical plate portion 242 surrounding the second pilot hole 262 before the second punch 5, and the second plate holder 53 and the first die 1 (second die 2) sandwich the second vertical plate portion 242. The first punch 4 moves further, and the first plate holder elastic member 44 contracts in a state in which the first plate holder 43 and the first die 1 (second die 2) sandwich the first vertical plate portion 241, and burring is performed to form the first cylindrical flange 251. As the second punch 5 moves further, the second plate holder elastic member 54 contracts while the second plate holder 53 and the first die 1 (second die 2) are sandwiching the second vertical plate portion 242, and burring is performed to form the second cylindrical flange 252. In this case, during the burring by the first punch 4, the portion of the first vertical plate portion 241 surrounding the first pilot hole 261 is sandwiched and restrained between the first plate holder 43 and the first die 1 (second die 2). Furthermore, during the burring by the second punch 5, the portion of the second vertical plate portion 242 surrounding the second pilot hole 262 is sandwiched and restrained between the second plate holder 53 and the first die 1 (second die 2). Therefore, the dimensional accuracy of the formed first cylindrical flange 251 and second cylindrical flange 252 is improved.

[0075] The above describes the embodiments according to the present disclosure. However, the above-described embodiments are merely examples. Therefore, the present disclosure is not limited to the above-described embodiments, and the above-described embodiments may be appropriately modified and implemented within the scope of the present disclosure. For example, the chassis component 200 is not limited to a front lower arm, and may be another component such as a rear lower arm, a front upper arm, a front lower arm, a front subframe, a rear subframe, or a trailing arm. [Explanation of symbols]

[0076] 100, 100A, 100B: Burring device 1: First die 11: First semi-cylindrical concave surface 1a: corner 1b: Side 2: Second die 21: Second semi-cylindrical concave surface 22: Lever section 22a: corner 22b: Plane 3: Cam parts 3a: Side 3b: End face 3c: slope 4: First punch 43: First board holder 5: Second punch 53: Second board holder 6: 1st spindle 7:Second spindle 8: First elastic member 9: Second elastic member 200: Chassis parts 210: Workpiece 241: 1st vertical plate part 242:Second vertical plate part 251: First cylindrical flange 252: 2nd cylindrical flange 261:First hole 262:Second pilot hole

Claims

1. A burring device for forming a first cylindrical flange on a workpiece including a first vertical plate portion and a second vertical plate portion opposed to the first vertical plate portion, the first cylindrical flange protruding toward the second vertical plate portion, and the second cylindrical flange opposed to the first cylindrical flange, the burring device comprising: a first die including a first semi-cylindrical concave surface corresponding to a half circumference of a vertical split of an outer peripheral surface of the first cylindrical flange and the second cylindrical flange; a second die disposed adjacent to the first die, the second die including a second semi-cylindrical concave surface corresponding to another half of the outer circumferential surfaces of the first cylindrical flange and the second cylindrical flange, and a lever portion positioned below the second semi-cylindrical concave surface and protruding laterally beyond the first die; a first support shaft disposed below the first semi-cylindrical concave surface and configured to rotatably support the first die such that the first semi-cylindrical concave surface approaches or moves away from the second semi-cylindrical concave surface; a second support shaft disposed below the second semi-cylindrical concave surface and configured to rotatably support the second die such that the second semi-cylindrical concave surface approaches or moves away from the first semi-cylindrical concave surface; a first elastic member that biases the first die in a direction in which the first semi-cylindrical concave surface moves away from the second semi-cylindrical concave surface; a second elastic member that biases the second die in a direction in which the second semi-cylindrical concave surface moves away from the first semi-cylindrical concave surface; a cam member that is movable in a vertical direction, the cam member coming into contact with the first die and the lever portion as it moves downward, rotating the first die around the first support shaft while sliding against the first die, and rotating the second die around the second support shaft while sliding against the lever portion, and holding the first semi-cylindrical concave surface and the second semi-cylindrical concave surface in a state where they are closest to each other at a terminal end of the downward movement; a first punch that is insertable into a cylindrical hole defined by the first semi-cylindrical concave surface and the second semi-cylindrical concave surface that are closest to each other; a second punch that is insertable into the cylindrical hole from the side opposite the first punch.

2. The burring device according to claim 1, the cam member includes a side surface along a moving direction of the cam member, an end surface preceding a downward movement of the cam member, and an inclined surface continuing to the side surface and the end surface and inclined with respect to the moving direction, the first die includes a corner portion that contacts and slides against the inclined surface of the cam member as the cam member moves downward, and a side portion that contacts and slides against the side surface of the cam member as the cam member moves further downward and maintains contact with the side surface of the cam member when the cam member reaches the end terminal; a lever portion of the second die including a corner portion that contacts and slides against the end face of the cam member as the cam member moves downward, and a flat surface that contacts the end face of the cam member when the cam member reaches the terminal end.

3. The burring device according to claim 1, further comprising: a first plate holder arranged coaxially with the first punch and biased toward the first die and the second die relative to the first punch; a second plate holder arranged coaxially with the second punch and biased toward the first die and the second die relative to the second punch.

4. A burring method for a workpiece including a first vertical plate portion and a second vertical plate portion opposed to the first vertical plate portion, comprising forming a first cylindrical flange on the first vertical plate portion protruding toward the second vertical plate portion and forming a second cylindrical flange on the second vertical plate portion opposed to the first cylindrical flange, using the burring device according to any one of claims 1 to 3, (a) preparing the workpiece including the first vertical plate portion having a first pilot hole and the second vertical plate portion having a second pilot hole opposite the first pilot hole; (b) disposing the workpiece relative to the burring device such that the first semi-cylindrical concave surface of the first die and the second semi-cylindrical concave surface of the second die are positioned between the first vertical plate portion and the second vertical plate portion; a step (c) of moving the cam member downward so that the first semi-cylindrical concave surface and the second semi-cylindrical concave surface are held in closest proximity to each other at positions corresponding to the first pilot hole and the second pilot hole; and (d) moving the first punch toward the first pilot hole and moving the second punch toward the second pilot hole to form the first cylindrical flange and the second cylindrical flange.

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