Method for forming hollow shaft to plate material

Abstract

To provide a processing method capable of forming a hollow shaft having desired height and / or wall thickness by handle burring by surely moving a wall around an opening formed in a plate material in a projection direction.SOLUTION: A peripheral edge part adjacent to an opening formed in a plate material is not pressed, but an area (opening periphery part) separated outward from the opening by a prescribed distance is pressed. Then, the plate material is sandwiched and pressed between a punch and a die, a material constituting the plate material is filled in a recessed part formed around an insertion hole of the die, and the material is brought into close contact with an inner peripheral surface being an outer wall surface of the recessed part in a radial direction. Thus, a portion of the material constituting the plate material is made to effectively flow from between a bottom surface of the recessed part and a top surface of a projection part toward a space (insertion space) formed by making a punch insertion hole, a die insertion hole and the opening with one another, and the material constituting the hollow shaft formed by handle burring is effectively increased.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for forming a hollow shaft in a plate material. [Background technology]

[0002] In this technical field, for example, in the case of hollow shafts and / or gears, it is common to integrally form a flange portion and a hollow shaft (shaft portion, i.e., burring portion) for use as a stopper and / or fastening portion or for use as a gear portion by forming teeth on the flange portion. It is also common to integrally form a hollow shaft for fitting a separate shaft to the member in the bottom plate portion of a bottomed cylindrical member (also called a "bowl-shaped member") such as a large-diameter motor shaft and / or a clutch case (within which an internal component such as a clutch is placed).

[0003] From the viewpoint of strength, it is desirable to integrally form such a hollow shaft from a plate material by plastic processing such as burring, but it is difficult to form a hollow shaft having a desired height and plate thickness by moving the material around the hole. Fig. 15 is a schematic cross-sectional view illustrating how a hollow shaft is formed in a plate material in a burring process by so-called "striking" according to the conventional technology. Note that Fig. 15 shows only the left side of the axis AXp of the punch 004 in the portion where the punch 004 strikes the vicinity of the opening 003a of the plate material 003 held between the die 001 and the pad 002, but the right side of the axis AXp is the same.

[0004] As illustrated in FIG. 15, in the burring process by the conventional technique, the corner C of the die 001 is the base point from the start of forming, so if the corner R of the corner C is small (the radius R of the roundness is small and sharp), there is a risk that the plate material 003 will crack. In addition, when a burring tool (also called a "burring punch") is pressed against a small hole 003a drilled in the plate material 003, a pressing force acts in the lateral direction of the small hole 003a, so that the material (also simply called "meat") constituting the plate material 003 is pressed in the lateral direction. As a result, a protrusion is formed around the burring tool, which causes a problem that a predetermined flatness cannot be obtained. Furthermore, since the meat escapes in the lateral direction, the meat forming the hollow shaft is reduced, which causes a problem that it is difficult to obtain a hollow shaft having a desired height.

[0005] Therefore, Patent Document 1 (JP Patent Publication No. 2000-317542) proposes a method in which, as shown in Fig. 16, the material around the edge of a small hole 6 drilled in a plate material 1 in the (a) drilling step is pressed by a pressing tool 7 in the next (b) pressing step to move (offset) it in the axial direction in advance, and the moved material is subjected to a milling process in the next (c) burring step to form a cylindrical part (hollow shaft) 2. As a second embodiment, as shown in Fig. 16(d) in the (b) pressing step, a pressing tool 9 having a tip surface formed in a roughly mortar shape is used to gather the material toward the center of the shaft by a taper effect when forming the recessed part 4 and the protruding part 8, thereby reducing lateral escape, and increasing the shaft length or thickness of the hollow shaft 2 formed in the next (c) burring step (see paragraph

[0017] in Patent Document 1).

[0006] However, in the (b) pressing step, there is no member (means for preventing the movement of material) capable of reducing the escape of material from the plate material in the axial upward and radial outward directions. Therefore, as shown by the black arrows in (d) of Fig. 16, the escape of material in these directions cannot be sufficiently prevented, and it is difficult to form a hollow shaft having a desired shaft length and / or wall thickness in the (c) burring step.

[0007] In addition, in the (b) pressing step, a pressing tool 7 having a protruding shaft 7a formed at the center of the tip surface is used to press the peripheral portion adjacent to the small hole 6 drilled in the plate material 1, so that stress is concentrated in a portion of the plate material 1 facing the corner C of the die 21. If the (b) pressing step is performed in such a state, work hardening of the plate material 1 progresses, which may cause problems such as cracks in the plate material 1 and / or wear of the die 21, or the plate material 1 may break in the following (c) burring step. For this reason, in the method disclosed in Patent Document 1, it becomes difficult to increase the working rate in the (c) burring step, and the shaft length and / or wall thickness of the hollow shaft to be formed is restricted.

[0008] As described above, there is a need in the art for a processing method that can reliably move the wall around the edge of an opening formed in a plate material in a protruding direction to form a hollow shaft having a desired height and / or thickness by burring. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2000-317542 A Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, there is a need in the art for a processing method that can reliably move the wall around the edge of an opening formed in a plate material in a protruding direction to form a hollow shaft having a desired height and / or wall thickness by burring. [Means for solving the problem]

[0011] In view of the above problems, the present inventors conducted intensive research and discovered that the above problems can be solved by pressing an area a predetermined distance outward from the opening, rather than pressing the peripheral portion adjacent to the opening formed in the sheet metal as in the prior art described above, to cause the material constituting the sheet metal to flow toward the center of the opening, and then performing a burring process using a punching process (hereinafter sometimes referred to as "punching burring").

[0012] Specifically, the method of forming a hollow shaft in a plate material according to the present invention (hereinafter, sometimes referred to as the "method of the present invention") includes the first to fourth steps listed below.

[0013] The first step is to set a plate material having an opening smaller than the cross-section of the die insertion hole into a die having a die insertion hole which is an insertion hole and a ring-shaped recess formed around the periphery of the opening of the die insertion hole, so that the die insertion hole and the opening are arranged coaxially.

[0014] The second step is a step of setting a first punch, which is a punch having a punch insertion hole, which is an insertion hole having a cross-section larger than the opening, and a ring-shaped protrusion formed on the periphery of the opening of the punch insertion hole, so that the top surface of the protrusion faces the bottom surface of the recess with the plate material sandwiched therebetween and the punch insertion hole, die insertion hole, and opening are arranged coaxially.

[0015] The third step is to drive the first punch and the die so that they approach each other. As a result, the peripheral area of ​​the opening, which is an area a predetermined distance outward from the opening in the plate material, is pressed toward the recessed portion by the protrusion, thereby bending the peripheral edge of the opening. Furthermore, the plate material is clamped between the first punch and the die, and the material constituting the plate material is filled into the recessed portion and adhered to the inner peripheral surface, which is the radially outer wall surface of the recessed portion. In addition, a part of the material is caused to flow from between the top surface of the protrusion and the bottom surface of the recessed portion toward the insertion space, which is a space formed by the punch insertion hole, the die insertion hole, and the opening communicating with each other.

[0016] The fourth process is a process in which a second punch, which is a burring punch separate from the first punch, is inserted into the insertion space from the first punch side toward the die side to perform a burring process on the sheet material, thereby forming a hollow shaft that stands upright from the sheet material toward the die side. Effect of the Invention

[0017] As described above, in the method of the present invention, unlike the conventional technique described above, the peripheral portion adjacent to the opening formed in the plate material is pressed, but the region (periphery of the opening) a predetermined distance outward from the opening is pressed by the annular protrusion of the punch. Then, the plate material is clamped between the punch and the die, and the material constituting the plate material is filled in the recess formed on the peripheral edge of the die insertion hole, and is brought into close contact with the inner peripheral surface, which is the radially outer wall surface of the recess. This allows a part of the material constituting the plate material to effectively flow from between the top surface of the protrusion and the bottom surface of the recess toward the space (insertion space) formed by the mutual communication of the punch insertion hole, the die insertion hole, and the opening. As a result, the material constituting the hollow shaft formed by performing the burring process (strike burring) can be effectively increased. That is, according to the method of the present invention, the material of the peripheral edge of the opening formed in the plate material can be reliably moved in the protruding direction to form a hollow shaft having a desired height and / or thickness.

[0018] Other objects, features and attendant advantages of the present invention will become readily apparent from the following description of the embodiments of the present invention which are given with reference to the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 is a flowchart showing an example of the flow of each step included in a method (first method) for forming a hollow shaft in a plate material according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an example of a method for preparing a plate material having openings formed therein. [Diagram 3]4 is a schematic cross-sectional view illustrating a die and a plate material arranged to have a predetermined positional relationship by performing a first step. FIG. [Figure 4] 10 is a schematic cross-sectional view illustrating a first punch, a die, and a plate material arranged to have a predetermined positional relationship by performing a second step. FIG. [Diagram 5] 10A to 10C are schematic cross-sectional views showing an example of the positional relationship between a first punch and a die and the shape of a plate material when a third step is performed. [Figure 6] FIG. 11 is a schematic cross-sectional view for illustrating the difference in the movement of the material (meat) constituting the plate material between the pressing step included in the method disclosed in Patent Document 1 and the third step included in the first method. [Figure 7] 11 is a schematic cross-sectional view illustrating the second punch, the first punch, the die, and the plate material in a state where the formation of the hollow shaft is completed by carrying out a fourth step. FIG. [Figure 8] (a) A schematic cross-sectional view showing an example of the positional relationship between the first punch, die and sheet material and the shape of the sheet material at the completion of the third step, (b) a schematic cross-sectional view showing an example of the positional relationship between the second punch, die and sheet material at the start of the fourth step, and (c) a schematic enlarged cross-sectional view showing an example of how the sheet material is pressed between the second punch and die at the start of the fourth step.

[0020] [Figure 9] 5A to 5C are schematic cross-sectional views showing some examples of the configuration of a first punch and a die used in a method (second method) for forming a hollow shaft in a plate material according to a second embodiment of the present invention. [Figure 10] 11 is a schematic cross-sectional view showing a further example of the configuration of a first punch and a die used in the second method. FIG. [Figure 11] FIG. 1 is a schematic oblique view showing an example of the configuration of a product including a molded product having a hollow shaft formed by a method for forming a hollow shaft in a plate material according to an embodiment of the present invention (hereinafter, may be referred to as the "embodiment method"). [Figure 12] FIG. 12 is a schematic perspective view showing the configuration of a cup-shaped body that is the base of the molded product shown in FIG. [Figure 13] 1 is a photograph showing a molded body formed from a cup-shaped body by the method of this embodiment. [Figure 14] 4 is a photograph, substituted for a drawing, showing a cross section near a hollow shaft formed at the bottom of a cup-shaped body by the method of this embodiment. [Figure 15] 1 is a schematic cross-sectional view illustrating a state in which a hollow shaft is formed in a plate material in a burring process by so-called "boring" according to a conventional technique. [Figure 16] 1A to 1C are schematic cross-sectional views showing the movement of each tool and the material constituting the plate material in each process included in the method described in Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] First Embodiment Hereinafter, a method for forming a hollow shaft in a plate material according to a first embodiment of the present invention (hereinafter, sometimes referred to as "first method") will be described with reference to the drawings.

[0022] <composition> Fig. 1 is a flow chart showing an example of the flow of each step included in the first method. As shown in Fig. 1, the first method includes the first to fourth steps listed below.

[0023] The first process performed in step S01 is to set a plate material having an opening smaller than the cross-section of the die insertion hole into a die having a die insertion hole which is an insertion hole and a ring-shaped recess formed on the periphery of the opening of the die insertion hole, so that the die insertion hole and the opening are arranged coaxially.

[0024] The method for preparing a plate material with an opening formed therein is not particularly limited. For example, as illustrated in FIG. 2, the plate material 100 is sandwiched between a punching die 210 having an insertion hole with the same cross-section and a punching pad 220, and by inserting a punching punch 230 into the insertion hole as indicated by the white arrow, an opening having a desired size and shape can be formed in the plate material 100. Note that the plate material to which the first method is applied does not necessarily have to be a member having a flat shape throughout. For example, as described above, the plate material 100 may be a plate-like portion constituting the bottom of a bottomed cylindrical body (also referred to as a "bowl-shaped body") such as a large-diameter motor shaft and / or a clutch case (where dirt such as a clutch enters).

[0025] FIG. 3 is a schematic cross-sectional view illustrating a die 310 and a plate material 100 arranged to have a predetermined positional relationship by executing the first step. As illustrated in FIG. 3, the die 310 has a die insertion hole 310a which is an insertion hole and an annular recess 310c formed at the periphery of the opening of the die insertion hole 310a. On the other hand, the plate material 100 has an opening 100a smaller than the cross-section of the die insertion hole 310a. In the example shown in FIG. 3, the inner diameter DIw of the opening 100a is smaller than the inner diameter DId of the die insertion hole 310a (DIw < DId). Then, the plate material 100 is set on the die 310 such that the die insertion hole 310a and the opening 100a are coaxially arranged (the die insertion hole 310a and the opening 100a have a common axis AX).

[0026] The second step executed in step S02 is a step of setting a first punch, which is a punch having a punch insertion hole with a cross-section larger than the opening and an annular protrusion formed at the periphery of the opening of the punch insertion hole, with the plate material sandwiched therebetween such that the top surface of the protrusion faces the bottom surface of the recess and the punch insertion hole, the die insertion hole, and the opening are coaxially arranged.

[0027] FIG. 4 is a schematic cross-sectional view illustrating a first punch 410, a die 310, and a plate material 100 arranged to have a predetermined positional relationship by the execution of the second step. As illustrated in FIG. 4, the first punch 410 has a punch insertion hole 410a, which is an insertion hole, and an annular protrusion 410b formed at the periphery of the opening of the punch insertion hole 410a. The punch insertion hole 410a has a cross-section larger than that of the opening 100a formed in the plate material 100. Typically, the punch insertion hole 410a has the same cross-section as the die insertion hole 310a.

[0028] In the example shown in FIG. 4, the inner diameter DIp of the punch insertion hole 410a is larger than the inner diameter DIw of the opening 100a (DIp > DIw). Also, as described above, typically, the inner diameter DIp of the punch insertion hole 410a is equal to the inner diameter DId of the die insertion hole 310a (DIp = DId). And the outer diameter DOb of the protrusion 410b (the diameter of the outer peripheral surface, which is the outer wall surface in the radial direction) is smaller than the inner diameter DIc of the recess 310c (the diameter of the inner peripheral surface, which is the outer wall surface in the radial direction) (DOb < DIc). That is, with the plate material 100 interposed therebetween, the top surface of the protrusion 410b faces the bottom surface of the recess 310c. Further, the first punch 410 is set in the set of the die 310 and the plate material 100 so that the punch insertion hole 410a, the die insertion hole 310a, and the opening 100a are coaxially arranged (the punch insertion hole 410a, the die insertion hole 310a, and the opening 100a have a common axis AX).

[0029] Incidentally, in the example shown in FIG. 4, the top surface at the tip of the protrusion 410b provided on the first punch 410 is in contact with the plate material 100, but it is not necessarily required to bring the top surface of the protrusion 410b into contact with the plate material 100 in the second step, and the top surface of the protrusion 410b and the plate material 100 may be separated.

[0030] The third process, which is executed in step S03, is a process of driving the first punch and the die so as to approach each other. As a result, the peripheral area of ​​the opening, which is an area a predetermined distance outward from the opening in the plate material, is pressed toward the recessed portion by the protrusion, thereby bending the peripheral edge of the opening. Furthermore, the plate material is clamped between the first punch and the die, and the material constituting the plate material is filled into the recessed portion and brought into close contact with the inner peripheral surface, which is the radially outer wall surface of the recessed portion. In addition, a part of the material is caused to flow from between the top surface of the protrusion and the bottom surface of the recessed portion toward the insertion space, which is a space formed by the punch insertion hole, the die insertion hole, and the opening communicating with each other.

[0031] FIG. 5 is a schematic cross-sectional view showing an example of the positional relationship between the first punch 410 and the die 310 and the shape of the sheet material 100 accompanying the execution of the third step. FIG. 5(a) illustrates the state of each member at the time when the third step is started. In the example shown in FIG. 5, the first punch 410 is driven to approach the die 310 as shown in the figure by the white arrow, but the die 310 may be driven to approach the first punch 410 in the opposite manner, or both the first punch 410 and the die 310 may be driven to approach each other. In addition, a mechanism for driving either one or both of the first punch 410 and the die 310 is omitted in FIG. 5, and is not particularly limited as long as the effect of the present invention can be achieved. Typically, a driving mechanism widely used in the technical field, such as a hydraulic press, can be adopted.

[0032] FIG. 5B illustrates a state in which the first punch 410 approaches the die 310 and the peripheral portion of the opening 100a of the sheet material 100, which is a region that is a predetermined distance outward from the opening 100a, is pressed toward the recessed portion 310c by the protrusion 410b (see the portion surrounded by the thick dashed line), and the peripheral portion of the opening 100a is pressed and bent. After that, when the first punch 410 approaches the die 310 further, as illustrated in FIG. 5C, the sheet material 100 is sandwiched between the first punch 410 and the die 310, and the recessed portion 310c is filled with the material constituting the sheet material 100, and the material constituting the sheet material 100 adheres to the inner peripheral surface, which is the outer wall surface in the radial direction of the recessed portion 310c (see the portion surrounded by the thick dashed line). This makes it difficult for the material constituting the sheet material 100 to flow outward in the radial direction. On the other hand, there is nothing on the inside in the radial direction (i.e., on the side of the opening 100a) that impedes the flow of the material constituting the sheet material 100. As a result, part of the material constituting the sheet material 100 flows from between the top surface of the protrusion 410b and the bottom surface of the recess 310c toward the insertion space, which is a space formed by the punch insertion hole, the die insertion hole, and the opening communicating with each other.

[0033] The third step is intended to increase the axial length or wall thickness of the hollow shaft by shifting (offsetting) the material (wall) for forming the hollow shaft in the axial direction in advance by the subsequent burring. This point is also the same as in the pressing step (b) included in the method disclosed in the above-mentioned Patent Document 1.

[0034] However, there is a big difference in the way the material (meat) constituting the plate material pressed by the pressing tool or punch moves between the pressing step included in the method disclosed in Patent Document 1 and the third step included in the first method described above with reference to Fig. 16. Fig. 6 is a schematic cross-sectional view for explaining such a difference, in which (a) illustrates the way the meat moves in the pressing step included in the method disclosed in Patent Document 1, and (b) illustrates the way the meat moves in the third step included in the first method. Note that (a) illustrates only the left side of the axis AXp of the pressing tool 7 in the part where the periphery of the small hole 6 (reference number omitted) drilled in the plate material 1 is pressed by the pressing tool 7, but the right side of the axis AXp is the same. In addition, in (b), only the left side of the drawing of the axis AX common to the punch insertion hole 410a and the opening 100a, where the area (the surrounding area) a predetermined distance outward from the opening 100a (symbol omitted) formed in the plate material 100 is pressed by the punch 410, is depicted, but the right side of the axis AX is similar.

[0035] First, in the pressing step shown in (a) included in the method disclosed in Patent Document 1, the peripheral portion adjacent to the small hole 6 (reference numeral omitted) drilled in the plate material 1 is pressed by the pressing tool 7 toward the hole 21a of the die 21 along the axis AXp (see the open arrow). As a result, the material of the peripheral portion adjacent to the small hole 6 is sandwiched between the pressing tool 7 and the die 21 and flows toward the inside in the radial direction, but is hindered by the protruding shaft 7a formed at the center of the tip face of the pressing tool 7, and flows in the direction of pressing by the pressing tool 7 along the axis AXp (see the filled arrow). In this way, in the pressing step included in the method disclosed in Patent Document 1, the flow of the material of the plate material 1 pressed by the pressing tool 7 is hindered (see the zigzag line), so that the work hardening of the plate material 1 progresses, and it is difficult to secure the amount of material required to form a hollow shaft having a desired shaft length and / or wall thickness.

[0036] As described above, in the pressing step, the pressing tool 7 having the protruding shaft 7a formed at the center of the tip surface is used to press the peripheral portion adjacent to the small hole 6 (reference number omitted) drilled in the plate material 1, so that stress is concentrated in the portion of the plate material 1 facing the corner C of the die 21. If the pressing step is performed in such a state, work hardening of the plate material 1 progresses, which may cause problems such as cracks in the plate material 1 and / or wear of the die 21, or the plate material 1 may break in the subsequent burring step. This makes it difficult to increase the work rate in the burring step, and limits the shaft length and / or wall thickness of the hollow shaft to be formed.

[0037] On the other hand, in the third step included in the first method shown in (b), instead of pressing the peripheral portion adjacent to the opening formed in the plate material as in the pressing step included in the method disclosed in Patent Document 1, an area (the area surrounding the opening) a predetermined distance outward from the opening is pressed toward the recessed portion 310c of the die 310 by the protrusion 410b of the first punch 410. Accordingly, as described above with reference to (b) and (c) of Figures 5, the sheet material 100 is clamped between the first punch 410 and the die 310 (see the zigzag line), the material constituting the sheet material 100 fills the recess 310c, and some of the material (meat) constituting the sheet material 100 flows from between the top surface of the protrusion 410b and the bottom surface of the recess 310c toward the insertion space, which is the space formed by the punch insertion hole 410a, the die insertion hole 310a, and the opening 100a communicating with each other (see the black arrow).

[0038] At this time, in the third step included in the first method, there is no member that hinders the flow of material, such as the protruding shaft 7a of the pressing tool 7 disclosed in Patent Document 1 (the first punch 410 does not have a portion corresponding to the protruding shaft 7a formed at the center of the tip surface of the pressing tool 7). As a result, the material of the plate material 100 can freely flow from between the top surface of the protrusion 410b and the bottom surface of the recessed portion 310c toward the insertion space. That is, in the third step included in the first method shown in (b), the flow of the material of the plate material 100 pressed between the first punch 410 and the die 310 is not hindered, so that the amount of material required to form a hollow shaft having a desired shaft length and / or thickness can be secured.

[0039] Furthermore, since the thickness of the plate material 100 flows into the insertion space before stress is concentrated on the portion of the plate material 100 facing the corner C of the die 310 as in the pressing step included in the method disclosed in Patent Document 1, it is possible to reduce the risk of problems such as cracks occurring in the plate material 100 due to work hardening and / or wear of the die 310, or breakage of the plate material 100 in the next fourth step (stretching burring). That is, according to the third step included in the first method, it is possible to increase the stretching rate in the next stretching burring, and a hollow shaft having the desired height and plate thickness can be formed.

[0040] The fourth process carried out in step S04 is a process in which a second punch, which is a burring punch separate from the first punch, is inserted into the insertion space from the first punch side toward the die side to perform burring on the sheet material, thereby forming a hollow shaft that stands upright from the sheet material toward the die side.

[0041] FIG. 7 is a schematic cross-sectional view illustrating the second punch 510, the first punch 410, the die 310, and the plate material 100 in a state where the formation of a predetermined hollow shaft is completed by the execution of the fourth step. As illustrated in FIG. 7, the second punch 510 is a burring punch separate from the first punch 410, and is a substantially columnar member having an outer diameter DOp that is smaller than the inner diameter DId of the die insertion hole 310a and larger than the inner diameter DIw of the opening 100a (DOp < DIp and DOp > DIw). By inserting the second punch 510 having such a configuration into the insertion space from the side of the first punch 410 toward the side of the die 310 and performing handling processing on the plate material 100 (see the white arrow), a hollow shaft 100s erected from the plate material 100 toward the side of the die 310 can be formed.

[0042] As is clear from the above description and FIG. 7, the inner diameter and the outer diameter of the hollow shaft 100s respectively correspond to the outer diameter DOp of the second punch 510 and the inner diameter DId of the die insertion hole 310a. Further, the wall thickness Ts of the hollow shaft 100s corresponds to the difference between the outer diameter DOp of the second punch 510 and the inner diameter DId of the die insertion hole 310a. Furthermore, the axial length of the hollow shaft 100s is the volume of the portion of the plate material 100 protruding into the space (insertion space) where the punch insertion hole 410a, the die insertion hole 310a, and the opening 100a communicate with each other when the execution of the second step is completed, and the bottom area of the hollow shaft 100s (that is, the difference between the cross-sectional area corresponding to the outer diameter DOp of the second punch 510 and the cross-sectional area corresponding to the inner diameter DId of the die insertion hole 310a).

[0043] In the fourth step included in the first method of forming the hollow shaft 100s as described above, the risks concerned in the handling burring according to the prior art described above are reduced with reference to FIG. 15. Specifically, as described above with reference to FIG. 15, in the handling burring according to the prior art, since the corner C of the die 001 is the starting point from the start of forming, if the corner R of the corner C is small (the radius R of the roundness is small and sharp), there is a risk that the plate material 003 will crack.

[0044] On the other hand, in the first method, as illustrated in Fig. 8(a), at the completion of the third step, the sheet material 100 protrudes along the corner C of the die 310 into the insertion space and becomes attached to the side surface of the die 310. Therefore, when the stamping burring is started in the next fourth step, the sheet material 100 is subjected to stamping in a state where it is sandwiched between the second punch 510, which is a stamping punch, and the side surface of the die 310, as illustrated in Fig. 8(b) and Fig. 8(c), which is an enlarged view of the part surrounded by the thick dashed line in Fig. 8(b) (see the hollow arrow in Fig. 8(c)).

[0045] As a result of the above, in the fourth step included in the first method, the load on the corner C of the die 310 can be reduced compared to the conventional rolling burring. In addition, even if the angle R of the corner C of the die 310 is made small, there is little stress concentration on the portion of the plate material 100 facing the corner C of the die 310, and problems such as cracks originating from the portion during rolling burring and / or wear of the die 310 are unlikely to occur. Therefore, in the fourth step included in the first method, it is possible to increase the rolling rate while reducing the occurrence of cracks in the plate material 100 and wear of the corner C of the die 310 compared to the conventional rolling burring.

[0046] In addition, in Figures 8(a) and (b), as in Figure 6(b) described above, only the left side of the axis AX where the second punch 510 is inserted into the insertion space from the first punch 410 side toward the die side 310 and the sheet metal 100 is subjected to the cutting process is depicted, but the same is true for the right side of the axis AX.

[0047] <effect> As described above, in the first method, the peripheral portion adjacent to the hole formed in the plate material is not pressed as in the conventional technique described above, but the region (periphery of the hole) a predetermined distance outward from the hole is pressed by the annular protrusion of the punch. Then, the plate material is clamped between the punch and the die, and the material constituting the plate material is filled in the recess formed on the peripheral edge of the die insertion hole, and is brought into close contact with the inner peripheral surface, which is the radially outer wall surface of the recess. This allows a part of the material constituting the plate material to effectively flow from between the top surface of the protrusion and the bottom surface of the recess toward the space (insertion space) formed by the mutual communication of the punch insertion hole, the die insertion hole, and the hole. As a result, the material constituting the hollow shaft formed by performing the burring process (strike burring) by burring can be effectively increased. That is, according to the first method, the material on the peripheral edge of the hole formed in the plate material can be reliably moved in the protruding direction to form a hollow shaft having a desired height and / or thickness.

[0048] Second Embodiment Hereinafter, a method for forming a hollow shaft in a plate material according to a second embodiment of the present invention (hereinafter, sometimes referred to as the "second method") will be described with reference to the drawings.

[0049] As described above, in the first method, the peripheral portion of the hole is pressed by the annular protrusion of the punch, the sheet material is clamped between the punch and the die, and the material constituting the sheet material is filled into the recess formed on the periphery of the insertion hole of the die and is brought into close contact with the inner peripheral surface of the recess. This effectively causes a portion of the material constituting the sheet material to flow from between the top surface of the protrusion and the bottom surface of the recess toward the insertion space, effectively increasing the material constituting the hollow shaft formed by the stroke burring.

[0050] In the second method, the first punch and die are configured so as to more reliably move the peripheral wall of the opening formed in the plate material in the protruding direction, thereby more reliably forming a hollow shaft having the desired height and / or thickness.

[0051] <composition> Specifically, the second method is the above-mentioned first method, which is a method for forming a hollow shaft in a sheet material, in which the first punch and the die are configured so that in at least a portion of the portion where the sheet material is clamped by the first punch and the die in the third step, the distance between the first punch and the die in the axial direction of the insertion space becomes larger the closer to the axis of the insertion space.

[0052] Fig. 9 is a schematic cross-sectional view illustrating the configuration of a first punch and a die used in the second method. For comparison, Fig. 9(a) shows a first punch 410 and a die 310 used in the first method illustrated in Fig. 5. In Fig. 9, the plate material 100 is omitted in order to clearly show the configuration of the first punch and the die.

[0053] First, in the first punch 410 and the die 310 used in the first method illustrated in FIG. 9(a), there is no portion configured such that the distance between the first punch 410 and the die 310 in the direction of the axis AX of the insertion space increases as the distance approaches the axis AX of the insertion space. Even in such a configuration, as described in the explanation of the first method, the material of the sheet material 100 pressed between the first punch 410 and the die 310 in the third step fills the recessed portion 310c and adheres to the inner peripheral surface (see the portion surrounded by the thick dashed line), which is the outer wall surface in the radial direction of the recessed portion 310c, so that the material of the sheet material 100 does not easily flow outward in the radial direction. On the other hand, there is nothing that hinders the flow of the material constituting the sheet material 100 on the inner side in the radial direction (i.e., the axis AX side of the insertion space). As a result, part of the material of the plate material 100 flows from between the top surface of the protrusion 410b and the bottom surface of the recess 310c toward the insertion space, increasing the amount of material that constitutes the hollow shaft formed by the boring performed in the fourth step.

[0054] On the other hand, in the second method, the first punch 410 and the die 320 are configured so that in at least a part of the portion where the sheet material 100 is clamped by the first punch 410 and the die 310 in the third step, the distance between the first punch 410 and the die 310 in the direction of the axis AX of the insertion space becomes larger as the sheet material 100 approaches the axis AX of the insertion space. In the portion where the first punch 410 and the die 320 are configured in this manner, the thickness of the sheet material 100 that flows toward the side where the distance between the first punch 410 and the die 310 in the direction of the axis AX of the insertion space becomes larger as the first punch 410 and the die 310 approach each other in the third step. That is, the thickness of the sheet material 100 that flows toward the axis AX of the insertion space increases. Therefore, according to the second method, the thickness of the peripheral edge of the opening formed in the sheet material 100 can be more reliably moved in the protruding direction to more reliably form a hollow shaft having a desired height and / or thickness.

[0055] Incidentally, the specific method for configuring the first punch 410 and the die 320 so that in at least a portion of the portion where the sheet material 100 is clamped by the first punch 410 and the die 310, the distance between the first punch 410 and the die 310 in the direction of the axis AX of the insertion space becomes larger as it approaches the axis AX of the insertion space, is not particularly limited.

[0056] For example, a second method according to one embodiment is a method for forming a hollow shaft in a plate material, in which at least a portion of the bottom surface of a recess in a die is configured to become deeper as it approaches the axis of the insertion space.

[0057] Fig. 9(b) is a schematic cross-sectional view illustrating the configuration of the first punch and die used in the second method having the above-mentioned configuration. In the example shown in Fig. 9(b), the entire bottom surface of the recessed portion 311c of the die 311 is configured to become deeper as it approaches the axis AX of the insertion space. Therefore, at least in the portion where the top surface of the protrusion 410b of the first punch 410 and the bottom surface of the recessed portion 311c face each other, the distance between the first punch 410 and the die 311 becomes larger as it approaches the axis AX of the insertion space.

[0058] As a result, in the above portion, as the first punch 410 and the die 311 approach each other in the third step, the thickness of the sheet material 100 flowing toward the side where the distance between the first punch 410 and the die 311 in the direction of the axis AX of the insertion space is larger increases. That is, the thickness of the sheet material 100 flowing toward the axis AX of the insertion space increases. Therefore, according to the above configuration, the thickness of the peripheral edge of the opening formed in the sheet material 100 can be more reliably moved in the protruding direction to more reliably form a hollow shaft having a desired height and / or thickness.

[0059] In the example shown in FIG. 9(b), the entire bottom surface of the recessed portion 311c is configured to become deeper as it approaches the axis AX of the insertion space, but the entire bottom surface of the recessed portion 311c does not necessarily have to be configured in this way, and a part of the bottom surface of the recessed portion 311c may be configured in this way. In the example shown in FIG. 9(b), the bottom surface of the recessed portion 311c is inclined at a constant angle so that it becomes deeper as it approaches the axis AX of the insertion space, so the bottom surface of the recessed portion 311c is drawn by a straight line. However, the bottom surface of the recessed portion 311c does not necessarily have to be inclined at a constant angle so that it becomes deeper as it approaches the axis AX of the insertion space, and for example, the angle at which the bottom surface of the recessed portion 311c becomes deeper as it approaches the axis AX of the insertion space may change continuously or discontinuously along the way. In the latter case, the bottom surface of the recessed portion 311c in the cross-sectional view such as FIG. 9 is drawn as a curved line or a line having a bend point.

[0060] Furthermore, in the die used in the second method according to this embodiment, at least a part of the surface facing the first punch, which is not the bottom surface of the recessed portion, may be configured to become deeper as it approaches the axis of the insertion space. For example, as illustrated in Fig. 9(c), a top surface 312p of a portion radially outward of the recessed portion 312c of the die 312 may be configured to become deeper as it approaches the axis AX of the insertion space.

[0061] In this case as well, in the above-mentioned portion, as the first punch 410 and the die 312 approach each other in the third step, the thickness of the sheet material 100 flowing toward the side where the distance between the first punch 410 and the die 312 in the direction of the axis AX of the insertion space is larger increases. That is, the thickness of the sheet material 100 flowing toward the axis AX of the insertion space increases. Therefore, with the above-mentioned configuration, the thickness of the peripheral edge of the opening formed in the sheet material 100 can be more reliably moved in the protruding direction to more reliably form a hollow shaft having a desired height and / or thickness.

[0062] In the example shown in FIG. 9(c), the entire top surface 312p is configured to become deeper as it approaches the axis AX of the insertion space, but the entire top surface 312p does not necessarily have to be configured in this way, and only a part of the top surface 312p may be configured in this way. In the example shown in FIG. 9(c), the top surface 312p is drawn as a straight line because it is inclined at a constant angle so that it becomes deeper as it approaches the axis AX of the insertion space. However, it is not necessarily required that the top surface 312p is inclined at a constant angle so that it becomes deeper as it approaches the axis AX of the insertion space, and for example, the angle at which the top surface 312p becomes deeper as it approaches the axis AX of the insertion space may change continuously or discontinuously along the way. In the latter case, the top surface 312p in the cross-sectional view such as FIG. 9 is drawn as a curve or a line having a bend point.

[0063] Furthermore, in the example shown in Figure 9(c), both the bottom surface of recess 310c and the top surface of the portion radially outer than recess 310c are configured to become deeper as they approach the axis AX of the insertion space, but it is not necessary that both of these surfaces are configured in this manner. As shown in Figure 9(b) as an example, only the bottom surface of recess 310c may be configured in this manner, or, although not shown, only the top surface of the portion radially outer than recess 310c may be configured in this manner.

[0064] In addition, for example, a second method according to another embodiment is a method for forming a hollow shaft in a sheet material, in which at least a portion of the top surface of the protrusion provided on the first punch is configured to become lower as it approaches the axis of the insertion space.

[0065] Fig. 10 is a schematic cross-sectional view illustrating the configuration of the first punch and die used in the second method having the above-mentioned configuration. In the example shown in Fig. 10(a), the entire top surface of the protrusion 411b of the first punch 411 is configured to become lower as it approaches the axis AX of the insertion space. Therefore, at least in the portion where the top surface of the protrusion 411b of the first punch 411 and the bottom surface of the recess 310c face each other, the distance between the first punch 411 and the die 310 becomes larger as it approaches the axis AX of the insertion space.

[0066] As a result, in the above portion, as the first punch 411 and the die 310 approach each other in the third step, the thickness of the sheet material 100 flowing toward the side where the distance between the first punch 411 and the die 310 in the direction of the axis AX of the insertion space is larger increases. That is, the thickness of the sheet material 100 flowing toward the axis AX of the insertion space increases. Therefore, according to the above configuration, the thickness of the peripheral edge of the opening formed in the sheet material 100 can be more reliably moved in the protruding direction to more reliably form a hollow shaft having a desired height and / or thickness.

[0067] In the example shown in FIG. 10(a), the entire top surface of the protrusion 411b is configured to become lower as it approaches the axis AX of the insertion space, but the entire top surface of the protrusion 411b does not necessarily have to be configured in this way, and a part of the top surface of the protrusion 411b may be configured in this way. In addition, in the example shown in FIG. 10(a), the top surface of the protrusion 411b is configured to become lower at a certain angle as it approaches the axis AX of the insertion space, so the top surface of the protrusion 411b is drawn by a straight line. However, the top surface of the protrusion 411b does not necessarily have to be inclined so that it becomes lower as it approaches the axis AX of the insertion space at a certain angle, and for example, the angle at which the top surface of the protrusion 411b becomes lower as it approaches the axis AX of the insertion space may change continuously or discontinuously along the way. In the latter case, the top surface of the protrusion 411b in the cross-sectional view such as FIG. 10 is drawn as a curve or a line having a bend point.

[0068] Furthermore, in the second method according to this embodiment, various dies used in the second method according to the above embodiment may be used in combination. For example, in the example shown in Fig. 10(b), a first die 411 having a protrusion 411b with a top surface configured as described above is used in combination with the die 311 illustrated in Fig. 9(b). In addition, in the example shown in Fig. 10(c), a first die 411 having a top surface of the protrusion 411b configured as described above is used in combination with the die 312 illustrated in Fig. 9(c).

[0069] By using the first die 411 having the protrusion 411b having the top surface configured as described above in combination with various dies used in the second method according to the above-mentioned embodiment, it is possible to further increase the thickness of the sheet material 100 that flows toward the direction of the axis AX of the insertion space where the distance between the first punch 411 and the die 311 or 312 in the direction of the axis AX of the insertion space increases as the first punch 411 and the die 311 or 312 approach each other in the third step. That is, it is possible to further increase the thickness of the sheet material 100 that flows toward the axis AX of the insertion space. Therefore, according to these configurations, it is possible to more reliably and in a larger amount to move the thickness of the peripheral edge of the opening formed in the sheet material 100 in the protruding direction, thereby more reliably forming a hollow shaft having a desired height and / or thickness.

[0070] <effect> As described above, in the second method, the first punch and the die are configured so that in at least a part of the portion where the plate material is clamped by the first punch and the die in the third step, the distance between the first punch and the die in the axial direction of the insertion space becomes larger as the plate material approaches the axis of the insertion space. Therefore, as the first punch and the die approach each other in the third step, the thickness of the plate material that flows toward the side where the distance between the first punch and the die in the axial direction of the insertion space becomes larger increases. In other words, the thickness of the plate material that flows toward the axis of the insertion space increases. As a result, according to the second method, the thickness of the peripheral edge of the opening formed in the plate material can be more reliably moved in the protruding direction to more reliably form a hollow shaft having a desired height and / or thickness. EXAMPLES

[0071] The method for forming a hollow shaft in a plate material according to the present invention (the method of the present invention) will be described below with reference to the drawings. However, the examples described below are merely illustrative and do not limit the scope of the present invention.

[0072] FIG. 11 is a schematic perspective view showing an example of the configuration of a product including a molded body formed by a method for forming a hollow shaft in a plate material according to an embodiment of the present invention (hereinafter, sometimes referred to as the "embodiment method"). The molded body 610 shown in (a) is a bottomed tubular body (bowl-shaped body) in which a hollow shaft 610s is formed in the plate-shaped part constituting the bottom by the embodiment method, and a hollow shaft member 620 shown in (b) is fitted into the hollow shaft 610s of the molded body 610, and they are fixed to each other by a method such as caulking or laser welding. As a result, a clutch case 630 shown in (c) is assembled. (c) is a schematic perspective view showing a cross section of the clutch case 630 taken along a plane including the axis of the shaft member 620.

[0073] Incidentally, functional members such as a clutch (not shown) are housed inside the clutch case 630. Also, for the purpose of preventing misalignment between the molded body 610 and the shaft member 620 in the rotational direction, serrations or the like may be formed at the fitting portion between the hollow shaft 610s of the molded body 610 and the shaft member 620.

[0074] Next, a process of forming a hollow shaft 610s by the embodiment method at the bottom of a bottomed cylindrical body (bowl-shaped body) that is the base of the molded body 610 to obtain the molded body 610 will be described. Fig. 12 is a schematic perspective view showing the configuration of the bowl-shaped body that is the base of the molded body 610. As shown in Fig. 12, the central part excluding the peripheral part of the bottom 600b of the bowl-shaped body 600 that is the base of the molded body 610 has a flat plate shape. The bowl-shaped body 600 having such a shape was molded by pressing from a plate-shaped member (not shown).

[0075] In addition, an aperture 600a having a predetermined inner diameter is formed in advance at the center of the bottom portion 600b. The aperture 600a is formed by, for example, clamping the bottom portion 600b between a die and a punching pad, in which insertion holes having the same cross section are formed, and inserting a punch into the insertion hole, as described above with reference to Fig. 2. However, the aperture 600a may be formed by other processing methods, such as cutting.

[0076] By applying the method for forming a hollow shaft in a plate material according to the first embodiment of the present invention (first method) as an example method to the bottom 600b of the bowl-shaped body 600 in which the opening 600a is formed as described above, a molded body 610 having a hollow shaft 610s standing from the bottom 600b toward the outside of the bowl-shaped body 600 in the axial direction as shown in Fig. 11 was obtained. That is, the central part having a flat plate shape of the bottom 600b of the bowl-shaped body 600 corresponds to the "plate material" in the method of the present invention. Note that the details of the example method have been described in detail with reference to Figs. 1 to 8 in the explanation of the first method, so that the explanation here will be omitted.

[0077] Fig. 13 is a photograph showing a molded body 610 formed from a bowl-shaped body 600 by the method of this embodiment described above. (a) shows the molded body 610 observed from the bottom 600b side, and (b) shows the molded body 610 observed from the opening side opposite to the bottom 600b. Fig. 14 is a photograph showing a cross section near the hollow shaft formed at the bottom of the bowl-shaped body by the method of this embodiment.

[0078] As shown in FIG. 14(b), in forming the formed body 610 by the embodiment method, the thickness Tp of the part pressed by the protrusion of the first punch due to the clamping pressure between the first punch and the die in the third step was 62% of the thickness of the corresponding part of the cup-shaped body 600 (the original thickness To shown in FIG. 12(b)). That is, the crushing rate of that part was 38%, and the wall of the crushed part (the part surrounded by the thick dashed line in FIG. 14(b)) was added as material constituting the hollow shaft 610s. Also, the wall thickness Ts of the hollow shaft 610s was 48% of the original thickness To. That is, the crushing rate in the crushing burring performed in the fourth step was 52%.

[0079] As a result of the above, the shaft length of the hollow shaft could be extended by 2 mm compared to the case where a hollow shaft was formed by the conventional burring. In other words, it was confirmed that the method of the embodiment in which the plate material is clamped and pressed by the first punch having an annular protrusion and the die having an annular recess before burring can effectively increase the material (wall) constituting the hollow shaft and form a hollow shaft having a desired height and / or wall thickness.

[0080] For the purpose of explaining the present invention, several embodiments and modifications having specific configurations have been described above, sometimes with reference to the attached drawings. However, the scope of the present invention should not be construed as being limited to these exemplary embodiments and modifications, and it goes without saying that appropriate modifications can be made within the scope of the claims and the matters described in the specification.

[0081] For example, the method of forming a hollow shaft in a plate material according to the present invention (the method of the present invention) can be applied not only to the formation of a hollow shaft in a cup-shaped body as described above, but also to the formation of a flange portion for connecting an exhaust pipe, construction piping, etc. In this case, as can be seen from Figures 7 and 14, the portion pressed by the annular protrusion of the first die in the third step included in the method of the present invention becomes an annular recess, and this recess can be used as a portion for accommodating a member for achieving airtightness and / or liquid-tightness, such as a gasket. [Explanation of symbols]

[0082] 100...plate material, 100a...hole, 100s...hollow shaft, 210...hole punching die, 220...hole punching pad, 230...hole punching punch, 310, 311, 312...die, 310a...die insertion hole, 310c, 311c, 312c...recessed portion, 312p...top surface of outer portion of recessed portion, 410, 411...first punch, 410b, 411b...projection portion, 510...second punch, 600...cup-shaped body, 600b...bottom portion, 600a...opening, 610...molded body, 610s...hollow shaft, 620...shaft member, 630...clutch case, AX...common shaft, C...corner of die, DIw...inner diameter of opening, DIc...inner diameter of recess, DId...inner diameter of die insertion hole, DIp...inner diameter of punch insertion hole, DOb...outer diameter of protrusion, DOp...outer diameter of second punch, To...original plate thickness, Tp...plate thickness of portion pressed by protrusion, Ts...wall thickness of hollow shaft.

Claims

1. a first step of setting a plate material having an opening smaller than a cross section of the die insertion hole in a die having a die insertion hole serving as an insertion hole and an annular recess formed around an opening of the die insertion hole, such that the die insertion hole and the opening are coaxially arranged; a second step of setting a first punch, which is a punch having a punch insertion hole that is an insertion hole having a cross section larger than the opening and a ring-shaped protrusion formed on the periphery of the opening of the punch insertion hole, such that the top surface of the protrusion faces the bottom surface of the recessed portion with the plate material sandwiched therebetween and the punch insertion hole, the die insertion hole, and the opening are coaxially arranged; a third step of driving the first punch and the die toward each other to press the peripheral portion of the opening, which is a region a predetermined distance outward from the opening of the plate material, toward the recessed portion with the protrusion, thereby bending the peripheral portion of the opening, and clamping the plate material between the first punch and the die to fill the recessed portion with material constituting the plate material and bring it into close contact with an inner peripheral surface, which is a radially outer wall surface of the recessed portion, and causing a portion of the material to flow from between the top surface of the protrusion and the bottom surface of the recessed portion toward an insertion space, which is a space formed by the punch insertion hole, the die insertion hole, and the opening communicating with each other; a fourth step of inserting a second punch, which is a burring punch separate from the first punch, into the insertion space from the first punch side toward the die side to perform a burring process on the plate material, thereby forming a hollow shaft standing from the plate material toward the die side; A method for forming a hollow shaft in a plate material, comprising:

2. A method for forming a hollow shaft in a plate material according to claim 1, comprising the steps of: The first punch and the die are configured so that in at least a portion of the portion where the plate material is clamped by the first punch and the die in the third step, the distance between the first punch and the die in the axial direction of the insertion space becomes larger as the distance approaches the axis of the insertion space. A method for forming a hollow shaft in a plate material.

3. A method for forming a hollow shaft in a plate material according to claim 2, comprising the steps of: At least a portion of the bottom surface of the recess is configured to become deeper as it approaches the axis of the insertion space. A method for forming a hollow shaft in a plate material.

4. A method for forming a hollow shaft in a plate material according to claim 2 or 3, comprising the steps of: At least a portion of the top surface of the protrusion is configured to become lower as it approaches the axis of the insertion space. A method for forming a hollow shaft in a plate material.

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