Serration machining device, serration machining method, and bolt

Abstract

To provide a serration machining device, a serration machining method, and a bolt enabling easy execution of serration machining on the outer surface of a blank material through forging.SOLUTION: A serration machining device 1 comprises: a punch 10 that applies striking force to a blank material 41; a die 20 that forms a serration 45 on the outer surface of the blank material 41; and a holder 30 that receives and supports the die 20. The die 20 is provided with a hole 21 into which the blank material 41 is driven; and a machining tooth 22 disposed in the hole 21. The holder 30 is provided with a floating structure 31 that moves the die 20 to which shock has been applied in a shock direction, and a shock absorption structure 32 that absorbs the shock. The die 20 receives the shock applied by the striking force of the punch 10 in a state where the blank material 41 abuts against an abutment 23 against which the blank material 41 abuts, and the shock is absorbed by the floating structure 31 and the shock absorption structure 32.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a serration processing apparatus, a serration processing method, and a bolt for forging serrations on a blank material made of metal such as a bolt.

Background Art

[0002] Bolts, sleeves, etc. may be subjected to serration processing in which serrated longitudinal grooves are formed on the outer surface or inner surface in order to prevent slipping due to torsional torque with respect to a mating object and fix it. Examples of bolts subjected to serration processing include hub bolts that are inserted through and attached to the mounting holes of a hub with the hub for mounting a tire in an automobile as a mating object. The hub bolt has a shaft-shaped main body portion. When one end portion on the tip side in the insertion direction into the mounting hole of the hub among both end portions of the main body portion is defined as the tip portion and the other end portion is defined as the base end portion, a plurality of serrations (45) are formed on the outer surface of the base end portion (see, for example, FIG. 2(e)). The hub bolt formed with the serrations (45) is press-fitted into the mounting hole of the hub, fitted with the hub, and exhibits an anti-rotation function that prevents the rotation of the hub bolt and the wheel nut when the wheel nut is tightened on the hub bolt during tire mounting. The base end portion of the serration is an incomplete serration portion (47) formed in an incomplete shape, such as having a narrower width and a shallower groove depth compared to the tip portion and the like. If there are dimensional variations in the width length (for example, indicated by the width length W in FIG. 2(d)) in the extending direction of the serrations between the plurality of serrations in the incomplete serration portion (47), the bolt cannot be sufficiently fitted with a mating object such as a hub, and the anti-rotation function cannot be satisfied and exhibited. Therefore, in serration processing, processing accuracy is required such that the error generated when forming the incomplete serration portion (47) with a predetermined width length is within a predetermined range. Generally, the serration processing on the outer surface of a blank material made of a material such as a bolt is performed by rolling from the perspective of production efficiency. Rolling is a processing method in which the blank material is pressed against a rolling die, which is a forming die, while rotating the blank material around its axis, and the outer surface of the blank material is plastically deformed. On the other hand, the serration processing on the inner surface of a blank material such as a sleeve cannot be performed by rolling, so it is performed by forging. Patent Document 1 discloses a forging technique for forming serrations on the inner surface of a blank material composed of a tubular body such as a sleeve.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although the serration processing by rolling is a processing method suitable for mass production, when the blank material rolls against the rolling die, an error tends to occur in the width length of the incomplete serration part of each formed serration. In recent serration processing, there are cases where it is required to suppress dimensional variations by suppressing the width length of the incomplete serration part to a very small width. In that case, it becomes difficult to meet the required quality in the serration processing by rolling. When a high level of processing accuracy is required, such as suppressing the width length of the incomplete serration part to a very small width, the serration processing by forging is more likely to improve the processing accuracy compared to rolling and is a desirable processing method. Patent Document 1 describes the serration processing on the inner surface of a blank material such as a sleeve, but does not describe the serration processing on the outer surface of a blank material such as a bolt. Also, even in the serration processing by forging, always suppressing the width length of the incomplete serration part to a very small width is strict and complicated in terms of management.

[0005] Therefore, an object of the present invention is to provide a serration processing apparatus, a serration processing method, and a bolt that can easily perform serration processing on the outer surface of a blank material by forging.

Means for Solving the Problems

[0006] In order to solve the above problems, the invention according to claim 1 is a serration processing apparatus for forging serrations on a metal blank material, comprising: a punch for applying an impact force to the blank material; a die for forming the serrations on the blank material; a holder for accommodating and supporting the die, and the gist is that the die includes a hole portion into which the blank material is driven and processing teeth arranged in the hole portion; the holder includes a floating structure for moving the die, to which an impact due to the impact force is applied, in the direction of the impact, and an impact absorption structure for absorbing the impact. The invention according to claim 2 is characterized in that, in the description of claim 1, the floating structure includes a support member for supporting the die and a guide member for guiding the moving direction of the die. The invention according to claim 3 is characterized in that, in the description of claim 1, the impact absorption structure includes an elastic member disposed between the die and the holder. The invention according to claim 4 is characterized in that, in the description of claim 1, the die includes a contact portion with which the blank material comes into contact, and the impact due to the impact force of the punch is applied to the die in a state where the blank material is in contact with the contact portion. The invention according to claim 5 is characterized in that, in the description of claim 4, the distance between the contact portion and the processing teeth is 0.1 mm or more and 5 mm or less. The invention according to claim 6 is a serration processing method for forging serrations on a metal blank material, comprising: A forging process for forming the serration is provided by punching the blank material struck by a punch into a die to cause plastic deformation. The forging process includes: A first step of moving the die in the direction in which the impact is applied when the die is impacted by the punching of the punch; and A second step of absorbing the impact applied to the die. The invention according to claim 7, in the description of claim 6, is characterized in that the first step and the second step are executed at a stage of ending the forging process. The invention according to claim 8, in the description of claim 6, is characterized in that the first step includes: A step of bringing the blank material punched into the die into contact with the die; and A step of applying the impact caused by the punching of the punch to the die by the blank material in contact with the die. The invention according to claim 9 is a bolt manufactured by forging serrations on a metal blank material using the serration processing apparatus according to claim 1, the bolt comprising: A shaft-shaped main body portion; and a head portion provided at one end of the main body portion. The main body portion has, on the outer surface of one end portion, a serration portion composed of a plurality of the serrations, and an incomplete serration portion provided with a plurality of serrations having an incomplete shape between the serration portion and the head portion. The invention according to claim 10, in the description of claim 9, is characterized in that the width length of the incomplete serration portion is 0.1 mm or more and 5 mm or less. The invention according to claim 11, in the description of claim 9, is characterized in that the head portion has a concave groove at a position close to the main body portion of the seating surface. The invention according to claim 12, in the description of claim 11, is characterized in that the depth of the concave groove is 0.1 mm or more.

Advantages of the Invention

[0007] Since the present invention includes a floating structure in which a holder moves a die, which has been subjected to an impact due to the striking force of a punch, in the direction of the impact, and a shock absorption structure that absorbs the impact, it is possible to easily perform serration processing on the outer surface of a blank material by forging.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] The matters shown here are exemplary and for exemplarily explaining embodiments of the present invention, and are described for the purpose of providing an explanation that is considered to be the most effective and easy to understand for the principles and conceptual features of the present invention. In this regard, it is not intended to show the structural details of the present invention to a greater extent than necessary for a fundamental understanding of the present invention, and it is to clarify for those skilled in the art how some forms of the present invention are actually embodied by the description in combination with the drawings.

[0010] 〔1〕Serration Processing Apparatus The serration processing device of the present invention is a device for forging serrations on a metal blank material. As shown in FIG. 1, the serration processing device 1 includes a movable punch 10 that applies an impact force to the blank material 41, a fixed die 20 that forms serrations 45 on the blank material 41, and a holder 30 that houses and supports the die 20. Unless otherwise specified, the blank material is, as a specific example, one having the shape shown in FIG. 2(c), that is, a substantially bolt-shaped blank material 41 having a shaft-shaped main body portion 42 and a head portion 43 provided at one end (base end) of the main body portion 42. In this blank material 41, the main body portion 42 has a base end portion 44, which is one end portion, formed with a larger diameter than other portions, and the serration 45 is formed on the outer surface of the base end portion 44 as shown in FIG. 2(d).

[0011] The punch 10 is not particularly limited in terms of its configuration as long as it can apply an impact force to the blank material 41. Usually, an existing punch used in forging can be used. The direction in which the punch 10 applies an impact force to the blank material 41 is not particularly limited, but usually, it can be a direction along the axial direction of the blank material 41. For example, the serration processing device 1 shown in FIG. 1 is arranged horizontally, and the direction in which the punch 10 applies an impact force to the blank material 41 can be a horizontal direction along the axial direction of the blank material 41 from the left side in FIG. 1. Alternatively, the direction in which the impact force is applied can be a horizontal direction along the axial direction of the blank material 41 from the right side. Or, when the serration processing device 1 is arranged vertically, the direction in which the impact force is applied can be a vertical direction along the axial direction of the blank material 41 from the upper side.

[0012] The die 20 is for forming serrations 45 on the blank material 41. The die 20 is formed in a cylindrical shape such as a cylindrical shape or a polygonal cylindrical shape, and includes a hole portion 21 into which the blank material 41 is driven and a processing tooth 22 disposed in the hole portion 21 (see FIG. 1). The hole portion 21 extends in the axial direction of the die 20, and its axis center coincides with the axis of the die 20. The inner diameter of the opening 21a of the hole portion 21 is substantially the same as or slightly larger than the maximum diameter of the main body portion 42 of the blank material 41, that is, the diameter of the base end portion 44, and is smaller than the diameter of the head portion 43 of the blank material 41. For this reason, the entire main body portion 42 of the blank material 41 including the base end portion 44 is inserted into the hole portion 21, but the head portion 43 is not inserted into the hole portion 21 and is held outside the hole portion 21. Also, the hole portion 21 is provided so that the axis centers of the blank material 41 (main body portion 42) coincide with each other. As a result, the axis of the die 20 and the axis of the blank material 41 are on the same line and coincide. Note that the peripheral corner portion 21b of the opening 21a of the hole portion 21 is formed in an arc shape or a tapered shape in order to facilitate the insertion of the blank material 41.

[0013] The machining teeth 22 are fitted into the opening on the base end side of the die 20 so that the tooth tips 22a project into the hole portion 21. The outer surface of the base end portion 44 of the main body portion 42 of the blank material 41 inserted into the hole portion 21 is pressed against the tooth tips 22a of the machining teeth 22. The machining teeth 22 are formed harder than the material used for the blank material 41 by using a tool steel material such as die steel. As the main body portion 42 of the blank material 41 is driven (inserted) into the hole portion 21 of the die 20 by the impact of the punch 10, the tooth tips 22a plastically deform the outer surface of the base end portion 44 of the main body portion 42 into a groove shape to form a plurality of serrations 45.

[0014] Here, the serrations 45 formed by the machining teeth 22 of the die 20 have a serration portion 46 and an incomplete serration portion 47 (see FIG. 2(d)). The incomplete serration portion 47 is provided at the base end edge (one end edge) of the base end portion 44 of the main body portion 42 and forms the base end portion (one end portion) of the serration 45. The serration 45 is formed by the serration portion 46 at all other portions except the incomplete serration portion 47 at the base end portion (one end portion). The serration portion 46 can be a serration formed in a complete state, that is, a serration formed in a groove shape or valley shape having a desired or conforming width and groove depth. The incomplete serration portion 47 can be a serration formed in an incomplete state, that is, a serration not formed in a groove shape or valley shape having a desired width and groove depth. Note that the incomplete serration portion 47 is not formed in a groove shape or valley shape, for example, is formed in a substantially planar shape or the like, or is formed in a groove shape or valley shape that is narrower in width and shallower in groove depth than that of the serration portion 46.

[0015] The die 20 is provided with an abutting portion 23 on the periphery of the opening 21a of the hole portion 21 against which the seating surface 43a of the head portion 43 of the blank material 41 can abut (see FIGS. 1 and 3). In a state where the blank material 41 is not in contact with the abutting portion 23, the blank material 41 to which an impact force is applied by the punch 10 receives the impact force only by the blank material 41 itself, and thereby propels the main body portion 42 inwardly of the hole portion 21 in its axial direction (see FIG. 3(b)). In this state (the state shown in FIG. 3(b)), only the tooth tips of the machining teeth 22 of the die 20 are in contact with the blank material 41, and substantially all of the impact force of the punch 10 applied to the blank material 41 is utilized for the plastic deformation of the blank material 41 by the machining teeth 22. In a state where the seating surface 43a of the head portion 43 of the blank material 41 abuts against the abutting portion 23, the blank material 41 stops the propulsion of the main body portion 42 into the inner part of the hole portion 21 of the die 20 (see FIG. 3(c)). In this state (the state shown in FIG. 3(c)), since the head portion 43 of the blank material 41 is in contact with the die 20 via the abutting portion 23, the impact force of the punch 10 applied to the blank material 41 can be applied to the die 20 as an impact. Note that a part of the impact force of the punch 10 applied to the blank material 41 can be utilized for the plastic deformation of the blank material 41 by the machining teeth 22.

[0016] The above-mentioned holder 30 is for accommodating and supporting the die 20. This holder 30 is formed in a cylindrical shape such as a cylindrical shape or a polygonal cylindrical shape, and the die 20 is accommodated inside the opening on the base end side (see FIG. 1). Further, the opening on the tip end side of the holder 30 is closed by a lid body 30A. The holder 30 includes a floating structure 31 that moves the die 20 to which an impact is applied in the direction of the impact, and a shock absorption structure 32 that absorbs the impact. The holder 30 has a hole portion that extends in the axial direction of the holder 30 with the axis of the holder 30 as the axis center. This hole portion communicates with the hole portion 21 of the die 20 and extends the hole portion 21 to the tip end side. The hole portion of the holder 30 is, for example, when the blank material is a long object such as the material of a shaft (axial member) and protrudes outward (tip end side) from the hole portion 21 of the die 20, for accommodating (inserting) the protruding portion from the hole portion 21.

[0017] As described above, when the impact force of the punch 10 is applied to the die 20 as an impact through the blank material 41 by the blank material 41 abutting against the abutting portion 23, the floating structure 31 has a function of releasing the impact by moving the die 20 in the impact direction. The impact direction when an impact is applied to the die 20 is the direction in which the punch 10 applies an impact force to the blank material 41 along the axial direction of the blank material 41. Since the axis of the blank material 41 inserted into the hole portion 21 of the die 20 coincides with the axis of the die 20 on the same line, it can be the axial direction of the die 20. For example, in the serration processing apparatus 1 shown in FIG. 1, the impact direction is the same direction as the direction in which the punch 10 applies an impact force to the blank material 41, and is the direction from the left side (base end side) to the right side (tip end side) along the axial direction of the blank material 41.

[0018] By functioning to release the impact applied to the die 20, the floating structure 31 can prevent deformation of the blank material 41 such as crushing of the head 43 due to the impact force of the punch 10 and breakage of the die 20 such as breakage of the processing teeth 22. That is, when the blank material 41 is driven into the hole 21 of the die 20 by utilizing the striking force of the punch 10 and serration is formed by forging, as in the above-described serration processing apparatus 1, there is a concern that due to the striking force of the punch 10, the head 43 of the blank material 41 may be crushed, resulting in molding defects, or the processing teeth 22 may break, causing the die 20 to be damaged. To prevent such problems, it is desirable to stop the striking by the punch 10 at a position slightly in front of the seating surface 43a of the head 43 of the blank material 41 being slightly separated from the front surface 24 (base end surface) of the die 20. However, it is extremely difficult to manage the working process so as to always keep the gap between the seating surface 43a of the head 43 of the blank material 41 and the front surface 24 of the die 20 constant. Also, due to the provision of the gap, the width length W of the incomplete serration portion 47 becomes longer, and the error generated during serration processing also becomes larger. Therefore, the above-described serration processing apparatus 1 simplifies the management of the working process by daringly bringing the head 43 of the blank material 41 into contact with the contact portion 23 of the die 20, and further, by providing a floating structure 31 and the like, it releases the striking force of the punch 10 and the impact applied to the die 20 to prevent problems from occurring.

[0019] The floating structure 31 is not particularly limited in terms of its configuration as long as it has a function of moving the die 20 in the impact direction to release the impact. Specifically, it can have a configuration having a support member 33 and a guide member 34 (see FIG. 1). The support member 33 is formed in a cylindrical shape such as a cylindrical shape or a polygonal cylindrical shape. The support member 33 is arranged on the tip side (cover body 30A side) of the die 20 so that its axis is on the same line as the axis of the die 20 and is accommodated in the holder 30. Also, the support member 33 supports the die 20 from the side by bringing its front surface (the surface on the base end side) into contact with the rear surface 25 of the die 20. The guide member 34 is formed in a cylindrical shape such as a cylindrical shape or a polygonal cylindrical shape. The guide member 34 is accommodated in the holder 30 so as to enclose the support member 33 inside and have its axis coincide with the axis of the support member 33. The guide member 34 can move the support member 33 inside it, and the moving direction when the support member 33 moves can be the direction along the axis by the inner surface of the guide member 34 being in sliding contact with the outer surface of the support member 33.

[0020] In the floating structure 31, when an impact is applied to the die 20, the support member 33 is pushed by the die 20 and moves toward the inner back side (tip side) of the holder 30 together with the die 20 (see FIGS. 1 and 3(c)). When the die 20 and the support member 33 move, the moving direction of the support member 33 is guided by the guide member 34 in the axial direction of the die 20, which is the impact direction. The die 20 to which an impact is applied can be guided by the support member 33 and the guide member 34 of the floating structure 31 in the axial direction of the die 20, which is the impact direction, and move toward the inner back side (tip side) of the holder 30. That is, the floating structure 31 changes the force of the impact applied to the die 20 into a propulsive force that moves the die 20 toward the inner back side (tip side) of the holder 30 and dissipates the impact.

[0021] As described above, the shock absorption structure 32 has a function of absorbing the impact from the die 20 that is moved in the impact direction by the floating structure 31 and eliminating the impact. The shock absorption structure 32 is not particularly limited in terms of its configuration as long as it can absorb the impact applied to the die 20. Specifically, it can have a configuration having an elastic member 35 disposed between the die 20 and the holder 30 (see FIG. 1). Alternatively, the shock absorption structure 32 can have a configuration having a telescopic structure such as a cylinder, a rod, or a gas shock, not limited to the elastic member 35.

[0022] As the shock absorption structure 32, the elastic member 35 (a telescopic structure) is disposed between the support member 33 that supports the die 20 and the lid body 30A of the holder 30. When the die 20 moves together with the support member 33 by the floating structure 31 described above, the shock that the die 20 has can be applied to the elastic member 35 (telescopic structure) via the support member 33. The elastic member 35 (telescopic structure) to which the shock from the die 20 is applied can absorb the shock by being compressed between the support member 33 and the lid body 30A against its biasing force. That is, the elastic member 35 (telescopic structure) absorbs the shock converted from the driving force of the die 20 by the floating structure 31 by elastically deforming (telescoping) and receiving it (see FIGS. 1 and 3(c)). Further, after absorbing the shock, the elastic member 35 (telescopic structure) can push back the die 20 and the support member 33 by its biasing force and return them to their original positions.

[0023] The elastic member 35 is not particularly limited as long as it has a biasing force capable of absorbing shock, and examples thereof include a disc spring, a leaf spring, a coil spring, and elastic rubber. Among these, the disc spring can easily adjust the biasing force according to the number of sheets arranged, and is useful as the elastic member 35 used for the shock absorption structure 32. For example, in the serration processing apparatus 1 shown in FIG. 1, a plurality of disc springs 36 are used as the elastic member 35 used for the shock absorption structure 32. The disc spring 36 is formed in a disc shape with the central portion bulging in a curved shape on one surface side, and deforms into a planar shape when the applied load reaches the limit value. The limit value of the load applied to each disc spring 36 is determined, and the biasing force can be easily adjusted by increasing or decreasing the number of sheets used according to the magnitude of the shock applied to the die 20.

[0024] The biasing force of the elastic member 35 is preferably adjusted such that its lower limit value is equal to or greater than the forming load of the serration 45 and its upper limit value is equal to or less than the deformation load of the blank material 41. For example, when the forming load of the serration 45 is 1 t and the deformation load of the head 43 of the blank material 41 is 8 t, the biasing force of the elastic member 35 is preferably 1 t or more and 8 t or less, more preferably 1.2 t or more and 5 t or less, and even more preferably 1.5 t or more and 2.5 t or less. When a disc spring 36 is used as the elastic member 35, for example, when the load limit value of one disc spring 36 is 200 kg, the number of disc springs 36 is preferably 5 or more and 40 or less, more preferably 6 or more and 25 or less, and even more preferably 8 or more and 12 or less. Note that the disc springs 36 are not necessarily limited to using a plurality of disc springs with the same load limit value, and a plurality of disc springs with different load limit values combined can also be used.

[0025] In the above serration processing apparatus 1, in a state where the head 43 of the blank material 41 is not in contact with the contact portion 23 of the die 20, that is, in a state where substantially all of the impact force of the punch 10 is utilized for the plastic deformation of the blank material 41 by the processing teeth 22 (see Fig. 3(b)), the serration portion 46 of the serration 45 can be formed. Also, in the serration processing apparatus 1, in a state immediately before the head 43 of the blank material 41 comes into contact with the contact portion 23 of the die 20 (see Fig. 3(c)), an incomplete serration portion 47 of the serration 45 can be formed.

[0026] That is, the serration portion 46 is formed by completely plastically deforming the outer surface of the base end portion 44 in the main body portion 42 of the blank material 41 to which the impact force of the punch 10 is applied. When the serration portion 46 is formed, surplus material is generated by plastically deforming the outer surface of the base end portion 44. However, this surplus material is gathered toward the base end edge of the base end portion 44 as the main body portion 42 is driven into the hole portion 21. When the head 43 of the blank material 41 comes into contact with the contact portion 23 of the die 20, the surplus material is constricted (compressed and consolidated) by the tooth tips 22a of the processing teeth 22, thereby forming the incomplete serration portion 47.

[0027] The width W of the incomplete shaving portion 47 (see FIG. 2(d)) can be adjusted by the distance L (see FIG. 1) between the contact portion 23 and the tooth tip 22a of the machined tooth 22. The distance L can be appropriately set according to the desired width W of the incomplete shaving portion 47 and is not particularly limited. Specifically, the distance L can be 0.1 mm or more at the lower limit value, preferably 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 0.7 mm or more. Also, the distance L can be 5 mm or less at the upper limit value, preferably 3.5 mm or less, more preferably 2.5 mm or less, and even more preferably 1.5 mm or less.

[0028] The above-described shaving processing apparatus 1 can be provided with a position adjustment structure for adjusting the position of the die 20 inside the holder 30 (see FIG. 1). Specifically, the position adjustment structure adjusts the position of the die 20 with respect to the holder 30 so that the front surface 24 of the die 20 is substantially flush with the front surface 38 of the holder 30. The position adjustment structure has a plurality of coil springs 37 disposed between the guide member 34 of the floating structure 31 and the rear surface 25 on the tip side of the die 20. The plurality of coil springs 37 are arranged at equal intervals in the circumferential direction of the guide member 34. The coil spring 37 aligns the front surface 24 of the die 20 with the front surface 38 of the holder 30 and makes them flush by biasing the die 20 toward the base end side (punch 10 side). Also, the coil spring 37 forms a gap S between the guide member 34 and the die 20. This gap S can be used as a margin for moving the die 20 by the floating structure 31.

[0029] Note that the position adjustment structure is not limited to a configuration having the coil spring 37, and as long as the position of the die 20 inside the holder 30 can be adjusted, it can be a configuration having an elastic member such as a leaf spring, a disc spring, or elastic rubber, or an expansion and contraction structure such as a cylinder, a rod, or a gas shock. Alternatively, in addition to configuring the position adjustment structure to include an elastic member such as a coil spring 37 or a telescopic structure, etc., it can be realized by the shape (structure) of the die 20, the holder 30, the support member 33, the guide member 34, etc. As a specific example of the position adjustment structure by such a shape (structure), as shown in FIG. 1, an example can be given in which unevenness 37A is formed on the outer peripheral surface of the die 20 and the inner peripheral surface of the holder 30, respectively. In this case, the die 20 and the holder 30 can be arranged such that the front surface 24 of the die 20 is flush with the front surface 38 of the holder 30 in a state where the unevenness 37A of each other is engaged, and a gap S can be formed between the guide member 34 and the die 20.

[0030] In the above-described serration processing apparatus 1, as shown in FIG. 4, a convex portion 26 can be provided around the hole portion 21 on the contact surface 23 of the die 20. The shape of the convex portion 26 is not particularly limited, and can be, for example, a polygonal shape such as a triangular shape or a trapezoidal shape in a cross-sectional view, a semi-circular shape or a semi-elliptical shape, etc., and a continuous annular shape such as an annular shape or a polygonal ring shape in a plan view, or an intermittent annular shape in which a plurality of arcs, curves, or straight lines draw a circular shape or a polygonal shape. Note that the convex portion 26 shown in FIG. 4 is formed in a semi-circular shape in a cross-sectional view and an annular shape in a plan view. When the convex portion 26 is provided on the contact surface 23 of the die 20, a concave groove 48 can be formed by forging on the seating surface 43a of the head portion 43 of the blank material 41 (see FIG. 4). As will be described later, this concave groove 48 is for accommodating shaving chips 61 generated when the bolt 40 (hub bolt) obtained from the blank material 41 is press-fitted into the mounting hole of the mating member 60 (hub) (see FIG. 5). The height (projection amount) of the convex portion 26 from the contact surface 23 of the die 20 can be appropriately set according to the size of the concave groove 48 to be formed, and is not particularly limited. For example, the height (projection amount) of the convex portion 26 from the front surface 24 of the die 20 can be 0.1 mm or more at the lower limit value, preferably 0.15 mm or more, more preferably 0.2 mm or more. Usually, the upper limit value of the height (projection amount) of the convex portion 26 from the front surface 24 of the die 20 can be 5 mm or less.

[0031] The above-mentioned serration processing device 1 takes the blank material 41 having the head 43 as a specific example, and the floating structure 31 etc. operates when the head 43 abuts against the contact portion 23 of the die 20. On the other hand, in the case of a blank material having no head, for example, a blank material 51 made of a cylindrical body as a material of a metal sleeve 50, by using the serration processing device 2 as shown in FIG. 6, serration processing can be performed on the entire outer surface 52 of the blank material 51.

[0032] That is, as shown in FIG. 6, the serration processing device 2 has a stepped portion 27 in the hole portion 21 of the die 20. This stepped portion 27 functions as a contact portion that abuts against the inserted tip portion 53 of the blank material 51. That is, the above-mentioned serration processing device 1 has the contact portion 23 that abuts against the blank material 41 on the front surface 24 of the die 20 (in other words, outside the hole portion 21), while the serration processing device 2 has the stepped portion 27 as a contact portion that abuts against the blank material 51 inside the hole portion 21. However, the serration processing device 1 and the serration processing device 2 have substantially the same configuration except that the positions where the contact portions that abut against the blank material are provided are different.

[0033] FIG. 6(a) shows the state when the serration processing is started, and FIG. 6(b) shows the state at the end of the serration processing. When the blank material 51 is driven into the inner back side (tip side) of the hole portion 21 of the die 20 by the impact force of the punch 10, the inserted tip portion 53 of the blank material 51 abuts against the stepped portion 27 as the contact portion. When the impact force of the punch 10 is applied to the blank material 51 that abuts against the stepped portion 27, the impact force can be applied to the die 20 as an impact through the stepped portion 27. Then, the die 20 to which the impact is applied can move within the holder 30 by the floating structure 31, and the impact can be absorbed by the impact absorption structure 32.

[0034] 〔2〕Serration processing method The serration processing method of the present invention is a serration processing method for forging serrations on a metal blank material, and includes a forging process of forming the serrations by driving the blank material struck by a punch into a die to cause plastic deformation, wherein the forging process includes a first step of moving the die in the direction in which the impact is applied when the die is impacted by the strike of the punch, and a second step of absorbing the impact applied to the die.

[0035] The forging process can be executed using the above-described serration processing apparatus 1. That is, the forging process is a process of forming a plurality of serrations 45 by driving the blank material 41 struck by the punch 10 into the hole portion 21 of the die 20 and plastically deforming the outer surface of the main body portion 42 of the blank material 41.

[0036] Regarding the forging process, first, as shown in FIG. 3(a), the main body portion 42 of the blank material 41 is inserted into the hole portion 21 of the die 20 and set. Next, the strike on the head portion 43 of the blank material 41 by the punch 10 is started. At this time, the front surface 24 of the die 20 is positioned substantially on the same plane as the front surface 38 of the holder 30. Next, as shown in FIG. 3(b), a striking force is continuously applied to the head portion 43 of the blank material 41 by the punch 10. The main body portion 42 of the blank material 41 to which the striking force is applied to the head portion 43 is pushed into the hole portion 21 of the die 20 and moves in the inner back direction (right direction in FIG. 3(b)) of the hole portion 21. As the blank material 41 moves in the hole portion 21 of the die 20 along with the movement of the main body portion 42, since the machining teeth 22 are in pressure contact with the outer surface of the base end portion 44 of the main body portion 42, the outer surface of the base end portion 44 is rubbed against the tooth tips of the machining teeth 22 and plastically deformed, and a plurality of serrations 45 are formed.

[0037] In the forging process, the serration part 46 (not shown) of the serration 45 is formed by the serration processing device 1 before reaching from Fig. 3(b) to Fig. 3(c), and the incomplete serration part 47 (not shown) of the serration 45 is formed at the stage of completing the forging process of Fig. 3(c). The forging process includes a first process of moving the die 20 in the direction in which the impact is applied when an impact is applied to the die 20 by the strike of the punch 10, and a second process of absorbing the impact applied to the die 20. These first process and second process are executed at the stage of completing the forging process. Moreover, the first process has a process (process A) of bringing the blank material 41 driven into the die 20 into contact with the die 20, and a process (process B) of applying the strike force of the punch 10 to the blank material 41 as an impact to the die 20.

[0038] That is, when it comes to the stage of completing the above-mentioned forging process, as process A of the first process, the seating surface 43a of the head 43 of the blank material 41 is brought into contact with the contact part 23 of the die 20. The seating surface 43a of the head 43 and the contact part 23 of the die 20 are in surface-to-surface pressurization. Therefore, as process B of the first process, when the strike force of the punch 10 is applied to the blank material 41, the strike force is applied to the die 20 as an impact from the head 43 of the blank material 41. And when an impact is applied to the die 20, as the first process, the die 20 moves in the impact direction (the tip direction, the right direction in Fig. 3(c)) as shown in Fig. 3(c) by the floating structure 31.

[0039] When the die 20 moves in the impact direction, as the second process, the impact absorption structure 32 absorbs the impact applied to the die 20. Specifically, the die 20 moving in the impact direction resists the biasing force of the disc spring 36, compresses the disc spring 36 with the lid body 30A, and moves in the inner back direction (the direction of the lid body 30A side) of the holder 30 while being guided by the support member 33 and the guide member 34. Then, the compressed disc spring 36 receives the die 20 and absorbs and reduces the impact, and the forging process is completed. After the forging process is completed, when the punch 10 is retracted, the die 20 is returned to its original position by the biasing force of the disc spring 36 accordingly.

[0040] Also, when a convex portion 26 is provided around the hole portion 21 on the front surface 24 of the die 20, in the forging process, as shown in FIG. 4, a concave groove 48 can also be formed on the seating surface 43a of the head portion 43 of the blank material 41. That is, in the forging process, the convex portion 26 of the die 20 bites into the seating surface 43a of the head portion 43 of the blank material 41 by the impact force of the punch 10, thereby forming the concave groove 48.

[0041] 〔3〕 Bolt The bolt 40 of the present invention is manufactured by forging a serration 45 on a metal blank material 41 using the above-described serration processing apparatus 1 (see FIGS. 2 and 5). The bolt 40 includes a shaft-shaped main body portion 42 and a head portion 43 provided at one end (base end) of the main body portion 42. The main body portion 42 has a base end portion 44 having a larger diameter than other portions, and a plurality of serrations 45 are formed on the outer surface of the base end portion 44. Further, a male thread 40a is engraved on the outer surface of the main body portion 42 except for the base end portion 44 where the serration 45 is formed.

[0042] The blank material 41, which is the material of the bolt 40, is obtained by forging a round bar-shaped material shown in FIG. 2(a) through a shape having a large-diameter cylindrical portion 41a and a small-diameter cylindrical portion 41b shown in FIG. 2(b) into the shape shown in FIG. 2(c). For this blank material 41, using the above-described serration processing apparatus 1, as shown in FIG. 2(d), a serration 45 is formed on the outer surface of the base end portion 44 of the main body portion 42, and further, as shown in FIG. 2(e), a male thread 40a is formed on the outer surface of the main body portion 42 by roll forging or the like, thereby obtaining the bolt 40 from the blank material 41.

[0043] The serration 45 is formed in a groove shape extending in the axial direction of the main body portion 42 on the outer surface of the base end portion 44 of the main body portion 42. Further, a plurality of serrations 45 are formed on the outer surface of the base end portion 44 of the main body portion 42 at equal intervals in the circumferential direction. The blank material 41, which is the material of the bolt 40, is inserted into the serration processing device 1 from the tip end portion of the main body portion 42 with one end on the head portion 43 side of both ends in the axial direction of the main body portion 42 as the base end and the other end on the opposite side as the tip end and used. Note that the blank material 41 is not limited to the shape shown in FIG. 2(c). For example, it can also be shaped with a male thread 40a formed on the outer surface of the main body portion 42 as shown in FIG. 2(e). That is, FIGS. 2(c) to (e) show the process of manufacturing the bolt 40 by performing processing on the blank material 41 in the order of serration processing, upset forging processing, etc., but it is not limited to this. The bolt 40 can also be manufactured by performing processing on the blank material 41 in the order of upset forging processing, etc., before serration processing.

[0044] The material of the bolt 40 (or the blank material 41) is not particularly limited as long as it is a metal capable of plastic deformation by forging. Examples of such materials include iron, aluminum, copper, stainless steel, carbon steel, brass, aluminum alloy, titanium alloy, etc. The use of the bolt 40, etc. is not particularly limited. Usually, a bolt with serrations is press-fitted into the mounting hole of the mating object 60 and fitted with the mating object 60 to prevent slippage due to torsional torque with respect to the mating object 60. As a bolt used for such applications, a hub bolt for attaching the mating object 60 to a hub for mounting an automobile tire can be exemplified. Note that the shape of the head portion 43 can be appropriately set according to the use of the bolt 40, etc. and is not particularly limited. When the use of the bolt 40, etc. is a hub bolt, usually, the shape of the head portion 43 can be a dish shape (see FIGS. 2 and 5). Also, the shape of the head portion 43 can be a plate shape, a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, etc. Alternatively, the bolt 40 can be configured to include only an axial main body portion 42 without the head portion 43.

[0045] Here, the blank material 41 to be used in the above-described serration processing device 1 is not limited to the material for the bolt 40, and can be used as the material for a shaft, a sleeve, a bush, etc., as long as it has serrations on its outer surface. The shape of the blank material 41 is not particularly limited as long as it is a shape corresponding to the target object of the material. For example, when the blank material 41 is the material for a shaft, its shape can be rod-shaped, and when it is the material for a sleeve, a bush, etc., their shapes can be cylindrical, elliptical cylindrical, polygonal cylindrical.

[0046] The above-described serration 45 has a complete-shaped serration portion 46 and an incomplete-shaped incomplete serration portion 47. The serration portion 46 is formed as a valley shape or a groove shape concave that forms a V shape or a rounded shape in a cross-sectional view.

[0047] The incomplete serration portion 47 is formed in a substantially planar shape extending in the circumferential direction of the main body portion 42, and is provided at the base end edge of the base end portion 44 of the main body portion 42, which is the base end portion of the serration 45, so as to be located between the serration portion 46 and the head portion 43. The incomplete serration portion 47 is for fixing the bolt 40 to the mating object 60 by being fitted and locked into the mounting hole of the mating object 60. The width length W (see Fig. 2(d)) of the incomplete serration portion 47 is not particularly limited, but from the viewpoint of reducing the error generated during formation by reducing the width length W, the lower limit value can be 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, and still more preferably 0.7 mm or more. Also, from the viewpoint of making the width length W a predetermined size or more for fixing to the mating object 60, the upper limit value of the width length W can be 5 mm or less, preferably 3.5 mm or less, more preferably 2.5 mm or less, and still more preferably 1.5 mm or less.

[0048] The bolt 40 can have a concave groove 48 at a position where the head 43 is close to the main body 42 of the seating surface 43a (see Fig. 5). When the bolt 40 is a hub bolt, the concave groove 48 can accommodate the shaving chips 61 generated when the bolt 40 is press-fitted into the mounting hole of the mating member 60 (hub). That is, when the bolt 40 is press-fitted into the mounting hole of the mating member 60 (hub), the bolt 40 may shave off the inner surface of the mounting hole of the hub, etc., and powdery or filamentous shaving chips 61 may be generated. Such shaving chips 61 may be sandwiched between the bolt 40 and the mounting hole of the mating member 60 (hub), etc., and may impair the fixing of the bolt 40 to the mating member 60 (hub). The concave groove 48 formed in the seating surface 43a of the head 43 of the bolt 40 can accommodate the shaving chips 61, and thereby the bolt 40 can be stably and firmly fixed to the mounting hole of the mating member 60 (hub).

[0049] The depth of the concave groove 48 is not particularly limited as long as it can accommodate the shaving chips 61. However, from the viewpoint of preferably accommodating the shaving chips 61, the lower limit value can be 0.1 mm or more, preferably 0.15 mm or more, and more preferably 0.2 mm or more. Usually, the upper limit value of the depth of the concave groove 48 can be 5 mm or less. The concave groove 48 can be formed by providing a convex portion 26 on the contact surface 23 of the die 20 in the above-mentioned serration processing device 1 (see Fig. 4). Alternatively, the concave groove 48 is not limited to being formed by providing a convex portion 26 on the die 20 of the serration processing device 1. For example, it can be formed in the process of forming the head 43 when obtaining the blank material 41 having the shape shown in Fig. 2(c) by forging, or the seating surface 43a of the head 43 of the blank material 41 having the shape shown in Fig. 2(c) can be formed by cutting or the like, or the seating surface 43a of the head 43 of the blank material 41 having the shape shown in Fig. 2(d) can be formed by forging, cutting or the like.

Explanation of Reference Numerals

[0050] 1, 2; Serrating processing device, 10; Punch, 20; Die, 21; Hole portion, 22; Processing teeth, 23; Contact portion, 27; Step portion, 30; Holder, 31; Floating structure, 32; Impact absorption structure, 33; Support member, 34; Guide member, 35; Elastic member, 40; Bolt, 41; Blank material, 42; Main body portion, 43; Head portion, 43a; Seat surface, 44; Base end portion, 45; Serrating, 46; Serrated portion, 47; Incomplete serrated portion, 51; Blank material, L; Distance between one end (tooth tip) of the processing teeth and the contact portion, S; Gap between the rear surface of the die and the opposing surface of the holder, W; Width length of the incomplete serrated portion.

Claims

1. A serration processing device for forging serrations on a metal blank material, comprising: A punch for applying an impact force to the blank material; A die for forming the serrations on the blank material; A holder for accommodating and supporting the die, and The die includes a hole portion into which the blank material is driven and processing teeth disposed within the hole portion, The holder includes a floating structure for moving the die, to which an impact due to the impact force has been applied, in the direction of the impact, and an impact absorbing structure for absorbing the impact. The serration processing device is characterized by this.

2. The serration processing device according to claim 1, wherein the floating structure includes a support member for supporting the die and a guide member for guiding the moving direction of the die.

3. The serration processing device according to claim 1, wherein the impact absorbing structure includes an elastic member disposed between the die and the holder.

4. The die includes a contact portion against which the blank material abuts, The serration processing device according to claim 1, wherein an impact due to the impact force of the punch is applied to the die in a state where the blank material abuts against the contact portion.

5. The serration processing device according to claim 4, wherein the distance between the contact portion and the processing teeth is 0.1 mm or more and 5 mm or less.

6. A serration processing method for forging serrations on a metal blank material, comprising: A forging step of forming the serrations by driving the blank material struck by a punch into a die and plastically deforming it, The forging step includes: A first step of moving the die in the direction of the impact when an impact is applied to the die by the impact of the punch. A serration processing method characterized by including a second step of absorbing the impact applied to the die.

7. The serration processing method according to claim 6, wherein the first step and the second step are executed at a stage where the forging step is completed.

8. The first step includes: a step of bringing the blank material driven into the die into contact with the die; The serration processing method according to claim 6, further including a step of applying, as the impact, the impact of the punch on the blank material in contact with the die to the die.

9. A bolt manufactured by forging serrations on a metal blank material using the serration processing apparatus according to claim 1, the bolt comprising: a shaft-shaped main body portion; and a head portion provided at one end of the main body portion. The main body portion has, on the outer surface of one end portion, a serration portion composed of a plurality of the serrations, and an incomplete serration portion provided with a plurality of incomplete-shaped serrations between the serration portion and the head portion.

10. The bolt according to claim 9, wherein the width length of the incomplete serration portion is 0.1 mm or more and 5 mm or less.

11. The bolt according to claim 9, wherein the head portion has a concave groove at a position close to the main body portion of the seating surface.

12. The bolt according to claim 11, wherein the depth of the concave groove is 0.1 mm or more.

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