Manufacturing method of cylindrical collar and cylindrical collar heading device

Abstract

To form a knurled part in a complicated pattern on an outer peripheral surface of a cylindrical collar without using a special device other than a heading device.SOLUTION: The invention relates to a method of manufacturing a cylindrical collar by which the cylindrical collar including a knurled part on an outer peripheral surface is formed by using a multistage heading device. The manufacturing method of the invention uses, in a knurled part forming step, a split die D53, which comprises a plurality of split type dies D53a arranged around an axis and each having a knurled die D532a on its inner surface, and a die case D52, which converts a pressing force applied to the split die D53 into an inward force perpendicular to the axis, to press an outer peripheral surface of a cylindrical blank with the split die D53 and thereby form the knurled part on the outer peripheral surface of the cylindrical blank.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a manufacturing method for manufacturing a cylindrical collar to be embedded in a resin molding or the like using a pressing device, and more particularly to a manufacturing method for a cylindrical collar in which a knurling is provided on the outer peripheral surface of the cylindrical collar without using a dedicated machine other than the pressing device. [Background technology]

[0002] Conventionally, cylindrical collars that are embedded in resin molded products and used to connect bolts have widely been provided with knurling such as iris or flat grooves on the peripheral surface to prevent them from being detached from the resin molded product or from rotating around their axis. However, to form this knurling, in addition to the heading device that presses the cylindrical collar into that shape, a rolling device for forming the knurling and a transport device for transporting the workpiece from the heading device to the rolling device are required, which poses the problem of higher labor and equipment costs compared to when processing is completed using only the heading device.

[0003] Therefore, Patent Document 1 proposes a method for manufacturing a nut using a pressing device to press a metal hexagonal nut into a cylindrical die with an uneven shape on the inner peripheral surface for slip prevention, and to provide multiple triangular pyramid-shaped bulges on the ridges of the hexagonal nut. The nut in Patent Document 1 is prevented from rotating around the axis by the ridges of the hexagonal column and the triangular pyramid-shaped bulges.

[0004] Furthermore, Patent Document 2 proposes an insert fitting in which, when a workpiece is formed into a cylindrical shape by changing the orientation of a rod-shaped member using a forging device, annular flanges are provided on both axial ends and linear concave and convex portions extending axially therebetween are arranged alternately in the circumferential direction. The insert fitting in Patent Document 2 was proposed to enhance the anti-rotation and anti-slip effects of Patent Document 1, and is said to have an even greater anti-slip effect than the insert fitting with an iris knurled groove.

[0005] The present applicants also disclose in Patent Document 3 a method of providing a flat knurl on the outer circumferential surface of a cylindrical collar having enlarged diameter portions at both ends when a blank is pressed into a cylindrical die. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-315538 A [Patent Document 2] JP 2011-098357 A [Patent Document 3] Patent No. 7224077 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the manufacturing methods of Patent Documents 1 to 3, the workpiece is pressed into a cylindrical die with an uneven shape on the inside to process the uneven pattern for slip prevention, so there is a problem that there is a limit to the uneven pattern that can be formed and it is not possible to form an uneven pattern with a complex shape such as an iris knurling. The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing a cylindrical collar that is capable of forming a complex pattern of knurling, such as an iris knurling, on the outer surface of the cylindrical collar without using a dedicated device such as a rolling device other than a pressing device. [Means for solving the problem]

[0008] The invention made to solve the above problems is a manufacturing method for a cylindrical collar using a multi-stage forging device equipped with movable dies and fixed dies that move toward and away from each other along an axis at each station that is connected in a row corresponding to each forging process, to form a cylindrical collar with a knurled outer surface. The manufacturing method of a tubular collar of the present invention includes a columnar blank forming process in which the outer shape of a linear material cut from a metal wire is adjusted into a columnar shape to form a columnar blank, a tubular blank forming process in which the columnar blank formed in the columnar blank forming process is formed into a cylindrical shape, and a knurling forming process in which a knurling is formed on the outer peripheral surface of the tubular blank, wherein the knurling forming process uses a splitting die consisting of a plurality of split dies arranged around an axis and having a knurling pattern on its inner surface, and a cylindrical die case that receives the splitting die when a pressing force in the axial direction is applied to the splitting die and converts the pressing force applied to the splitting die into an inward direction perpendicular to the axis, and the outer peripheral surface of the tubular blank is pressed by the splitting die to form a knurling on the outer peripheral surface of the tubular blank. Here, the term "knurling" refers to any shape of uneven pattern provided on the outer peripheral surface of a cylindrical collar to prevent the cylindrical collar from coming loose in the axial direction and / or to prevent the cylindrical collar from rotating in the circumferential direction.

[0009] Generally, in the pressing process of a tubular collar, a split die as described above is used as an auxiliary means to restrain the blank for forming the tubular collar from expanding radially outward due to the axial pressing force, and is not used to stamp a specific outer shape into the blank. In the manufacturing method of the tubular collar of the present invention, a knurling mold is provided on the inner surface of the split die, and this is used to press the outer surface of the tubular blank to form a knurl on the outer surface of the tubular collar.Therefore, without using any dedicated machine other than a heading machine, it is possible to form a knurl with a more complex pattern on the outer surface of the tubular collar than the knurling formed by the conventional method of forcing a blank into a cylindrical die.

[0010] In the columnar blank forming process, it is preferable that the columnar blank is formed into a non-circular shape in an axial cross section perpendicular to the axis, having a low portion that is closer to the axis than the periphery and a high portion that is farther from the axis than the periphery, and that in the knurling forming process, the columnar blank is pressed so that the low portion is located at the boundary between adjacent split dies and the high portion is located midway in the circumferential direction of the inner surface of the split dies. When a columnar blank having a circular cross section is used, there is a problem that the material of the columnar blank gets into the gap between adjacent split dies, leaving streaky marks of the split dies on the outer peripheral surface of the cylindrical collar. In the columnar blank forming process, a low portion is provided on the outer surface of the columnar blank facing the boundary of the split mold, which is closer to the axis than the periphery, and a high portion is provided in the circumferential middle portion of the inner surface of the split mold, which is farther from the axis than the periphery, and then the knurling process is performed.When the cylindrical die is pressed with the split die in the knurling forming process, the blank material can be moved from the high portion to the low portion to such an extent that it does not protrude into the gap of the split mold, thereby preventing traces of the boundary of the split mold from remaining on the outer surface of the cylindrical collar.

[0011] In the manufacturing method of the cylindrical collar according to the present invention, in the columnar blank forming step, it is preferable to form the axis perpendicular cross section of the columnar blank into a polygonal shape having sides as the low parts and corners as the high parts, and having a number of corners equal to the number of split dies of the split die. By providing three or more split dies in the split die, pressure from the split die can be applied more evenly to the peripheral surface of the columnar blank compared to the case where only two split dies are provided, so that a more uniform knurling pattern can be formed. In addition, by forming the shape of the cross section perpendicular to the axis of the columnar blank into a polygon having corners equal to the number of split dies, a load can be applied evenly around the axis of the columnar blank, and the blank can be symmetrically pressed together to form a more uniform knurling on the outer peripheral surface of the tubular collar.

[0012] In the case where the cross section perpendicular to the axis of the columnar blank is formed into a polygonal shape, it is preferable that the polygonal shape is a polygon with rounded corners, which allows the corners to be evenly distributed on both sides in the circumferential direction, thereby forming a more uniform knurl on the outer circumferential surface of the cylindrical collar.

[0013] When the cross section perpendicular to the axis of the columnar blank is formed into a polygonal shape, the polygonal shape is preferably a square shape. By forming the split dies of the split die with four symmetrical parts about the axis and forming the columnar blank into a square shape, the cross section of the cylindrical collar can be made closer to a circle than when the split dies are formed into three parts and the cross section perpendicular to the axis of the columnar blank is made into a triangle. In addition, compared to when five or more split dies are provided, the distance between the bottom of the cylindrical workpiece and the boundary between the split dies can be made larger, so that the marks caused by the gaps between the split dies can be suppressed from remaining on the outer peripheral surface of the cylindrical workpiece.

[0014] The method for producing a tubular collar of the present invention includes one in which the knurling is an iris knurling.

[0015] The present invention includes a cylindrical collar forging device that is composed of a multi-stage forging device having movable dies and fixed dies that move toward and away from each other along an axis at each station that is lined up corresponding to each forging process, and that forms a cylindrical collar with a knurled outer surface. The cylindrical collar heading device of the present invention comprises first and second heading stations which shape the outer shape of a linear material cut from a metal wire into a columnar shape to form a columnar blank, third and fourth heading stations which form the columnar blank formed in the columnar blank forming process into a cylindrical shape, and a fifth heading station which forms a knurl on the outer peripheral surface of the cylindrical blank, wherein the fifth heading station comprises a splitting die which is arranged around an axis and consists of a plurality of split dies having a knurled shape on its inner surface, and a cylindrical die case which receives the splitting die when a pressing force in the axial direction is applied to the splitting die and converts the pressing force applied to the splitting die into an inward direction perpendicular to the axis, and is configured so that the inner surface of the splitting die presses against the outer peripheral surface of the cylindrical blank to form a knurl on the outer peripheral surface of the cylindrical blank. Effect of the Invention

[0016] As described above, the manufacturing method for a cylindrical collar and the multi-stage heading device according to the present invention can form a knurl having a complex shape, such as an iris knurl, on the peripheral surface of a cylindrical collar. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of a multi-stage heading device for manufacturing a cylindrical collar according to one embodiment of the present invention; [Diagram 2] FIG. 1 is a perspective view of a tubular collar made in accordance with one embodiment of the present invention. [Diagram 3] 3 is a perspective view of a second tubular blank used in manufacturing the tubular collar shown in FIG. 2. FIG. [Figure 4] 2 is a cross-sectional view of a main portion showing how a first columnar blank forming step is carried out in the first forging station of FIG. 1. [Diagram 5] 1. FIG. 4 is a cross-sectional view of a main portion showing how a second columnar blank forming step is carried out in the second forging station of FIG. [Figure 6] 1. FIG. 4 is a cross-sectional view of a main portion showing a state in which a first cylindrical blank forming step is carried out in the third forging station in FIG. [Figure 7] 1. FIG. 4 is a cross-sectional view of a main portion showing a state in which a second cylindrical blank forming step is carried out in the fourth forging station of FIG. [Figure 8] 2A is a longitudinal cross-sectional view of the periphery of a cylindrical blank before a knurling process in a fifth forging station in FIG. 1, and FIG. 2B is a cross-sectional view perpendicular to the axis thereof. [Figure 9] 1. FIG. 4A is a longitudinal cross-sectional view of the periphery of a cylindrical blank during a knurling process in a fifth forging station in FIG. 1, and FIG. [Figure 10] 1 after the knurling process in the fifth forging station in FIG. 1, (a) is a longitudinal cross-sectional view of the tubular collar and its periphery, and (f) is a cross-sectional view perpendicular to the axis thereof. [Figure 11] 10A is a front view of a main portion, FIG. 10B is a sectional perspective view of a main portion, and FIG. 10C is a vertical end view of a main portion during the knurling process shown in FIG. [Figure 12] 11A is a front view of the main part after the knurling process shown in FIG. 10, FIG. 11B is a sectional perspective view of the main part, and FIG. [Figure 13] FIG. 2 is an explanatory diagram showing changes in the shape of a blank in each process until a linear material is formed into a cylindrical collar in the first embodiment of the present invention. [Figure 14] FIG. 13 is a schematic diagram showing another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiment.

[0019] Fig. 1 shows a schematic diagram of a cylindrical collar forging device (hereinafter, also simply referred to as "forging device") 100 according to one embodiment of the present invention. The forging device 100 is a so-called multi-stage forging device, and is used to manufacture a cylindrical collar A shown in Fig. 2 from a linear material W obtained by cutting a coil material (not shown) to a predetermined length.

[0020] (Cylindrical collar) As shown in Fig. 2, the cylindrical collar A is cylindrical with a through hole A1 penetrating along the central axis, and an iris knurling A3 is formed over the entire length and circumference of the outer circumferential surface A2. Tapered portions A4, A4, tapered portions A5, A5, and flat portions A6, A6 are provided at both ends of the through hole A1 and both ends of the outer circumferential surface A2, respectively. The cylindrical collar A is formed from a wire material W cut from a coil material such as iron, aluminum, stainless steel, brass, etc. The cylindrical collar A has a female thread formed inside and is used, for example, to be embedded in a resin molded product such as an interior panel of an automobile and to connect a bolt or the like thereto.

[0021] (Cylindrical collar forging device) As shown in Fig. 1, a first forging station 10 to a fifth forging station 50 are connected in this order to the forging apparatus 100. Each of the forging stations 10 to 50 includes movable units P1, P2, ... P5 (left side of Fig. 1) and fixed units D1, D2, ... D5 (right side of Fig. 1) which move toward and away from each other along imaginary axes m1 to m5 extending in the front-rear direction (left-right direction of Fig. 1). The movable units P1, P2, . . . P5 each include a ram P11, P21, . . . P51, and a movable die consisting of a movable punch P12, P22, P32 and a movable sleeve P42, P52 which are fitted to the ram P11, P21, . The fixed units D1, D2, ..., D5 each include a frame D11, D21, ..., D51 which is immovably fixed to the forging apparatus 100, and a fixed die consisting of dies D12, D22, ..., D42 which are fitted into the frames D11, D21, ..., D51, respectively, and a die case D52.

[0022] (First forging station) As shown in Figs. 1 and 4, the first forging station 10 includes a movable punch P12, a die D12, and a knockout pin D13. The die D12 includes a columnar inner chamber D12a that opens forward (left side in Fig. 4) to guide the movable punch P12 and for forging the first columnar blank B1, a guide hole D12b that is continuous with the rear side of the inner chamber D12a (right side in Fig. 4) to guide the knockout pin D13, and an inner chamber rear opening D12c that opens at the rear end of the inner chamber D12a to communicate with the inner chamber D12a and the guide hole D12b. The inner chamber D12a, the guide hole D12b, and the inner chamber rear opening D12c are provided with a rounded square cross section perpendicular to the axis. The movable punch P12 and the knockout pin D13 are also provided with a rounded square cross section perpendicular to the axis in accordance with the inner chamber D12a and the guide hole D12b.

[0023] (First columnar blank forming process S1) The first columnar blank forming step S1 is a step of forming a first columnar blank B1 from a linear material W using a first forging station 10. In the first columnar blank forming process S1, a linear material W (not shown in FIG. 4) accommodated in the inner chamber D12a of the first forging station 10 with its axial direction in the front-rear direction is supported from the rear side by a tip face of a knockout pin D13 inserted into the guide hole D12b so as to block the guide hole rear opening 12c, while the movable punch 12 is advanced into the inner chamber D12a to press the linear material W. As shown in FIG. 4, the linear material W has a tapered portion b5 on the outer periphery on one end side that is the rear side of the inner chamber 12a, and is formed into a first columnar blank B1 having a columnar shape with rounded corners and a cross section perpendicular to the axis being a square.

[0024] (Second forging station) As shown in Figs. 1 and 5, the second forging station 20 includes a movable punch P22, a die D22, and a knockout pin D23. The die D22 includes a columnar inner chamber D22a that opens forward (left side in Fig. 5) to guide the movable punch P22 and forge the second columnar blank B2, a guide hole D22b that is continuous with the rear side of the inner chamber D22a (right side in Fig. 5) to guide the knockout pin D23, and an inner chamber rear opening D22c that opens at the rear end of the inner chamber D22a to communicate with the inner chamber D22a and the guide hole D22b. The inner chamber D22a, the guide hole D22b, and the inner chamber rear opening D22c are provided with a rounded square cross section perpendicular to the axis. The movable punch P22 and the knockout pin D23 are also provided with a rounded square cross section perpendicular to the axis in accordance with the inner chamber D22a and the guide hole D22b.

[0025] (Second columnar blank forming process S2) The second columnar blank forming step S2 is a step of forming a second columnar blank B2 from the first columnar blank B1 using a second forging station 20. In the second columnar blank forming process S2, a first columnar blank B1 (not shown in FIG. 5) is accommodated in the inner chamber D22a of the second forging station 20 with one end having the tapered portion b5 facing forward, and while the tip surface of a knockout pin D23 inserted into the guide hole 22a supports the first columnar blank B1 from the rear side so as to block the guide hole rear opening 22c, a movable punch P22 is inserted into the inner chamber D22a to press the first columnar blank B1. As shown in FIG. 5, the first columnar blank B1 is formed into a second columnar blank B2 having tapered portions b5 on both ends of its outer circumferential surface and a columnar shape with a rounded square cross section perpendicular to its axis.

[0026] (Third forging station) As shown in Figs. 1 and 6, the third forging station 30 includes a movable punch P32, a die D32, a fixed punch D33, and a fixed sleeve D34 arranged so that the fixed punch D33 passes through it. The die D32 has a cross section perpendicular to its axis that is a rounded square, and is provided with a forging hole D32a that penetrates in the front-rear direction (left-right direction in Fig. 6). The movable punch 32 has a cross section perpendicular to its axis that is a rounded square, a cross section perpendicular to its axis of a tip portion D33a that is a circle, and a main portion D33b that is a rounded square. The fixed sleeve D34 has both an outer peripheral surface and an inner peripheral surface that are rounded square. The tip portion D33a of the fixed punch D33 protrudes from the front end of the fixed sleeve D34 by the depth of a pilot hole B3a of a first cylindrical blank B3 described later.

[0027] (First cylindrical blank forming process S3) The first cylindrical blank forming step S3 is a step of forming a first cylindrical blank B3 from the second columnar blank B2 using a third forging station 30. In the first cylindrical blank forming process S3, the second columnar blank B2 (not shown in FIG. 6) is placed in the forging hole D32a of the third forging station 30 with the other end (right side in FIG. 6) abutting against the tip of the fixed punch D33, and is pressed by the movable punch P32 until the rear edge of the second columnar blank B2 abuts against the fixed sleeve D34. In this way, the tip portion D33a of the fixed punch D33 fits into the other end side of the second columnar blank B2, forming a pilot hole b11 in the second columnar blank B2, and the first cylindrical blank B3 is formed.

[0028] (4th forging station) As shown in Figs. 1 and 7, the fourth forging station 40 includes a movable sleeve P42, a die D42, a fixed punch D43, and a fixed sleeve D44 arranged so that the fixed punch D43 passes through it. The die D42 has a cross section perpendicular to its axis that is a rounded square, and is provided with a forging hole D42a that penetrates in the front-rear direction (left-right direction in Fig. 7). The movable sleeve P42 has both an outer peripheral surface and an inner peripheral surface that are rounded square in cross section perpendicular to its axis. The tip portion D43a of the fixed punch D43 has a circular cross section perpendicular to its axis, and is longer than the tip portion D33a of the fixed punch D33 of the third forging station 30. The main body portion D43b of the fixed punch D43 is provided in a rounded square shape. The fixed sleeve D44 has both an outer peripheral surface and an inner peripheral surface that are rounded square in cross section. The length by which the tip portion D43a of the fixed punch D43 protrudes from the front end of the fixed sleeve D44 is set to be longer than the axial length of a second cylindrical blank B4, which will be described later.

[0029] (Second cylindrical blank forming process S4) The second tubular blank forming step S4 is a step of forming a second tubular blank B4 from the first tubular blank B3 using a fourth forging station 40. In the second tubular blank forming process S4, the tip portion D43a of the fixed punch D43 is inserted from the rear (right side in FIG. 7) into the pilot hole b11 of the first tubular blank B3 to fit the first tubular blank B3 (not shown in FIG. 7) into the forging hole D42a, and the first tubular blank B3 is pressed by the movable sleeve P42 until the periphery of the other end side (right side in FIG. 7) abuts against the fixed sleeve D44. In this way, the pilot hole b11 of the first tubular blank B3 penetrates to one end side, and the second tubular blank B4 is formed.

[0030] As shown in Fig. 3, the second cylindrical blank B4 has a through hole b1 penetrating in the axial direction, an outer peripheral surface b2, tapered portions b4, b4 provided at both ends of the through hole b1, tapered portions b5, b5 provided at both ends of the outer peripheral surface b2, and flat portions b6, b6 at both ends. The outer peripheral surface b2 is composed of four flat portions b21, ... and four corner portions b22, ..., and the cross section perpendicular to the axis is provided as a rounded square (non-circular shape). In the second cylindrical blank B4, the flat portions b21 of the outer peripheral surface b2 correspond to a low portion closer to the axis than the periphery, and the corner portions b22 correspond to a high portion farther from the axis than the periphery.

[0031] (5th forging station) As shown in FIGS. 1 and 8 to 10, the fifth forging station 50 includes a movable sleeve P52, a movable side support sleeve P53, a die case D52, a split die D53, a die side support sleeve D54, and a mandrel D55.

[0032] The movable sleeve P52 is cylindrical and configured to move forward and backward (up and down in FIG. 8(a)) to press the dividing die D53 from the front.

[0033] The die case D52 has a splitting die accommodating chamber D52a that penetrates in the front-rear direction (the up-down direction in FIG. 8(a)) and accommodates the splitting die D53. A peripheral surface D521 of the splitting die accommodating chamber D52a has a uniform diameter over its entire length in the front-rear direction and has first to fourth uniform diameter portions D521a to D521d with smaller diameters toward the rear, and has inclined portions D521e, D521f, and D521g between the uniform diameter portions D521a to D521d that decrease in diameter toward the rear.

[0034] The split die D53 has four split dies D53a, ... that are divided at equal intervals in the circumferential direction. As shown in Fig. 8(a) , an outer peripheral surface D531 of each split die D53a is provided with three equal-diameter portions D531a, D531b, D531c that are the same diameter over the entire length in the front-rear direction and have smaller diameters toward the rear, and between these are provided inclined portions D531d, D532e whose outer peripheral surface has a smaller diameter toward the rear.

[0035] The movable support sleeve P53 is cylindrical and slides inside the movable sleeve P52. The die support sleeve D54 is cylindrical and has the same diameter as the movable support sleeve P53, and cooperates with the movable support sleeve P53 to hold the second cylindrical blank B4 from the front and rear. The mandrel D55 is rod-shaped and slides inside the die support sleeve D54, the second cylindrical blank B4, and the movable support sleeve P53 to support the second cylindrical blank B4 from the inside.

[0036] (Knurling process S5) The knurling step S5 is a step of forming a cylindrical collar A from the second cylindrical blank B4 formed in the cylindrical blank forming step S4. In the knurling process S5, as shown in Figure 8(a), a mandrel D55 is inserted inside the second cylindrical blank B4 and clamped from the front and rear by the movable side support sleeve P53 and the die side support sleeve D54. In this state, the split die D53 is pressed from the front by the movable sleeve P52. As shown in Figures 9(a) and 9(b), the smallest diameter portion D531c on the outer circumferential surface D531 of the split die D53 rides on the same diameter portion D521c to the same diameter portion D521d on the inner circumferential surface D521 of the die case D52. The four split dies D53a,... are pressed radially inward, and the knurling die D532a provided on the inner circumferential surface D532 abuts against the corner portion b22 of the second cylindrical blank B4. Furthermore, when the split die D53 is pressed by the movable sleeve P52, the intermediate equal diameter portion D531b of the split die D53 rides on the equal diameter portion D521c to the equal diameter portion D521d of the die case D52, and the four split dies D53a, ... are pressed radially inward until they abut against each other, as shown in Figures 10(a) and 10(b). In this way, the second cylindrical blank B4 is formed with an iris knurl A3 on its entire circumference by the knurling die D532a, and is formed into a cylindrical collar A.

[0037] 11 shows in detail the state during forming of the fleur-de-lis roll A3 on the second cylindrical blank B4 shown in FIG. 9(a) and (b), and at this stage, the four split dies D53a of the split die D53 have four gaps D533, ... at their boundaries. The corners b22 of the second cylindrical blank B4 first abut against the inner peripheral surface D532 of the split die D53a, and in this state, the flat surface b21 of the second cylindrical blank B4 has a gap D543 between it and the inner peripheral surface D532 of the split die D53a. This prevents the material of the flat surface b21 from being pinched by the gap D533, and therefore prevents the trace of the gap D533 from remaining on the outer peripheral surface of the cylindrical collar A. As shown by the arrows in FIG. 11(a), the corners b22 of the second cylindrical blank B4 flow into the adjacent flat surfaces b21 to fill the gaps D534, so that the cross section perpendicular to the axis of the second cylindrical blank B4 is formed into a circle.

[0038] Fig. 12 shows in detail the state of the cylindrical collar A after molding in the fleur-de-lis knurling forming step S5 shown in Fig. 10(a) and (b), in which the adjacent split molds D53a, D53a are completely abutted, the gap D533 disappears, the cylindrical collar A has a circular cross section perpendicular to its axis, and the fleur-de-lis knurling A3 is formed over the entire outer circumferential surface A2. After this, the split molds D53a, ... are opened, and the cylindrical collar A is carried out.

[0039] (Changes in blank shape) Fig. 13 shows how the shape of the linear material W cut from the coil changes with each process from the first columnar blank forming process S1 to the knurling process S5. In Fig. 13, the left-pointing arrow indicates that the linear material W or blank is handed over to the forging station where the next process is performed without being turned over, and the left-pointing arc-shaped arrow indicates that the blank is turned over and handed over to the forging station where the next process is performed. (CUT process) As shown on the right side of FIG. 13, the wire material W cut out from the coil has a cylindrical shape. (Process S1) The linear material W is formed into a first columnar blank B1 having a rectangular column shape and a tapered portion b5 on one end side in a first columnar blank forming step S1 by a first forging station. (Process S2) The first columnar blank B1 is inverted from one end to the other end by a chuck not shown, and is delivered to the second forging station 20 where the second columnar blank forming process S2 is performed, and is formed into a second columnar blank B2 having tapered portions b5, b5 on both ends. (Process S3) The second columnar blank B2 is transferred to the third forging station 30, where the first tubular blank forming process S3 is performed, with its axial orientation maintained by a chuck not shown, and is formed into a first tubular blank B3 having a pilot hole B3a on the other end side. (Process S4) The first cylindrical blank B3 is transferred to the fourth forging station 40, where the second cylindrical blank forming process S4 is performed, with the axial orientation maintained by a chuck not shown, and is formed into a second cylindrical blank B4 having a through hole b1 that penetrates the pilot hole B3a to one end. (Process S5) The second cylindrical blank B4 is handed over to the fifth forging station 50, where the knurling process S5 is performed, with its axial orientation kept unchanged by a chuck not shown, and is formed into a cylindrical collar A having a circular axial cross section and an iris knurling A3 formed on the outer peripheral surface A2.

[0040] (Other embodiments) FIG. 14 shows another embodiment of the present invention. The splitting die in the present invention is not limited to being split into four parts, but may be split into two parts as in the splitting die D253 in FIG. 14(a), split into three parts as in the splitting die D353 in FIG. 14(b), or split into five parts as in the splitting die D453 in FIG. 12(c). When using the splitting die D253 in two parts, it is preferable that the cylindrical die B20 has two flat parts B20a facing the gaps of the splitting die 253 and has a track-shaped (non-circular) cross section perpendicular to the axis. When using the splitting die D353 in three parts, it is preferable that the cylindrical die B30 has three flat parts B30a facing the gaps of the splitting die D352 and has a rounded equilateral triangle (non-circular) cross section perpendicular to the axis. When using the five-part split die D453, it is preferable that the cylindrical die B40 has five flat portions B40a facing the gaps of the split die 452 and has an axial cross section formed into a regular pentagon with rounded corners (non-circular shape). [Explanation of symbols]

[0041] Cylindrical collar forging device 100 First forging station 10 Second forging station 20 3rd forging station 30 Fourth forging station 40 5th forging station 50 Dice Case D52 Splitting die D53 Knurled type D532a Split type D53a Inner peripheral surface D532 Cylindrical Collar A Knurling A3 First columnar blank B1 Second columnar blank B2 First cylindrical blank B3 Second cylindrical blank B4 Lower part (flat part) b21 High part (corner) b22 Axis line m1,m2,m3,m4,m5 Linear material W

Claims

1. A method for manufacturing a cylindrical collar, which uses a multi-stage heading device having movable dies and fixed dies which move toward and away from each other along an axis for each station that is connected in a row corresponding to each step of heading, to form a cylindrical collar having a knurled outer surface, a columnar blank forming process in which an outer shape of the linear material cut out from the metal wire is adjusted to a columnar shape to form a columnar blank; a cylindrical blank forming step of forming the columnar blank formed in the columnar blank forming step into a cylindrical shape; a knurling forming step of forming a knurl on an outer peripheral surface of the cylindrical blank; Equipped with In the knurling process, A split die including a plurality of split dies arranged around an axis and having a knurled inner surface; a die case that is cylindrical and receives the split die when a pressing force in the axial direction is applied to the split die and converts the pressing force applied to the split die into an inward direction perpendicular to the axial line; A method for manufacturing a tubular collar, characterized in that the outer peripheral surface of the tubular blank is pressed by the split die to form a knurl on the outer peripheral surface of the tubular blank.

2. In the columnar blank forming step, the columnar blank is formed into a non-circular shape in an axial vertical cross section having a lower portion closer to the axis than a periphery and a higher portion farther from the axis than a periphery, A method for manufacturing a cylindrical collar as described in claim 1, wherein in the knurling process, the columnar blank is pressed so that the low portion is located at the boundary between adjacent split dies and the high portion is located in the middle in the circumferential direction of the inner surface of the split dies.

3. 3. The method for manufacturing a cylindrical collar according to claim 2, wherein in the columnar blank forming process, the axial perpendicular cross section of the columnar blank is formed into a polygonal shape having sides as the low parts and corners as the high parts, and having a number of corners equal to the number of split dies of the split die.

4. 4. The method for manufacturing a tubular collar according to claim 3, wherein said polygonal shape is a polygon with rounded corners.

5. 4. The method of claim 3, wherein said polygonal shape is a square.

6. 5. The method for producing a tubular collar according to claim 4, wherein the knurling is an iris knurling.

7. A cylindrical collar forging device that is provided with a movable die and a fixed die that move toward and away from each other along an axis for each station that is aligned in a row corresponding to each step of forging, and that forms a cylindrical collar with a knurl on its outer circumferential surface, a first and a second forging station for forming a columnar blank by adjusting the outer shape of a linear material cut out from a metal wire into a columnar shape; a third and fourth forging stations for forming the columnar blank formed in the columnar blank forming step into a cylindrical shape; a fifth forging station for forming a knurl on an outer peripheral surface of the cylindrical blank; Equipped with The fifth forging station comprises: A split die including a plurality of split dies arranged around an axis and having a knurled inner surface; a die case that is cylindrical and receives the split die when a pressing force is applied to the split die in the axial direction, and converts the pressing force applied to the split die into an inward direction perpendicular to the axial line; A cylindrical collar heading device characterized in that the inner surface of the split die is configured to press the outer peripheral surface of the cylindrical blank to form a knurl on the outer peripheral surface of the cylindrical blank.

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