JP5776365B2 - Method and apparatus for manufacturing stepped cylindrical member - Google Patents

Description

The present invention provides, for example, a plurality of cylindrical surface portions that are concentric to the outer peripheral surface and have different diameters, such as a bearing ring member that constitutes a wheel bearing rolling bearing unit, that is, a hub body that constitutes a hub in combination with an inner ring. And a method for manufacturing a stepped columnar member in which adjacent cylindrical surface portions are made continuous with each other by a stepped portion, and an improvement of a manufacturing apparatus used in this manufacturing method . Specifically, when such a stepped columnar member is made by cold forging, which is plastic working in the cold, damage called a chevron crack does not occur inside, and a stepped columnar shape with good quality It is intended to realize a manufacturing method in which members can be stably obtained (yield can be improved).

  2. Description of the Related Art A wheel bearing rolling bearing unit is widely used to rotatably support a wheel constituting a wheel of an automobile and a disk or drum which is a rotating member for braking on a knuckle constituting a suspension device. FIG. 8 shows an example of a wheel bearing rolling bearing unit 1 for a driven wheel (a front wheel of an FR vehicle and an MR vehicle, a rear wheel of an FF vehicle) that has been widely known. The wheel supporting rolling bearing unit 1 supports a hub 3 on the inner diameter side of an outer ring 2 via a plurality of rolling elements 4 and 4 in a freely rotatable manner. In the state of use, the outer ring 2 is coupled and fixed to the knuckle, and the wheel and the brake rotating member are supported and fixed to the hub 3. Then, these wheels and the brake rotating member are rotatably supported with respect to the knuckle.

  For this purpose, double-row outer ring raceways 5 and 5 are disposed at two positions on the inner peripheral surface of the outer ring 2 and are part of the outer peripheral surface slightly inwardly in the axial direction (inside of the axial direction inside). Means the side that is the central side in the width direction of the vehicle body in use, and is the right side of Fig. 8. Conversely, the left side of Fig. 8 that is the outside in the width direction of the vehicle body in use is called outside in the axial direction. The same applies to the entire specification), and the stationary side flanges 6 are respectively formed. On the other hand, the outer peripheral surface of the hub 3 is provided with a rotation-side flange 7 for supporting and fixing the wheel and the brake rotating member on a portion near the outer end protruding outward in the axial direction from the outer ring 2. Double-row inner ring raceways 8 and 8 are formed on the portion near the inner end. A plurality of rolling elements 4, 4 are arranged between the inner ring raceways 8, 8 in both rows and the outer ring raceways 5, 5 in both rows, and the inner diameter of the outer race 2 is set. The hub 3 can freely rotate on the side.

  The hub 3 includes a hub body 9, an inner ring 10, and a nut 11, and the inner ring raceways 8 and 8 are formed in an intermediate portion of the hub body 9 and an outer peripheral surface of the inner ring 10. Further, the inner ring 10 is fixed to the hub body 9 by the nut 11 in a state where the inner ring 10 is externally fitted to a small-diameter step portion 12 formed near the inner end of the hub body 9 in the axial direction. A structure in which the inner ring 10 is fixed to the hub body 9 by a caulking portion formed at the inner end of the hub body 9 in the axial direction is also widely known.

  The hub body 9 constituting the wheel support rolling bearing unit 1 as described above is manufactured by subjecting a metal material such as carbon steel to plastic working. The structure of the hub body produced by such plastic working and the method of such plastic working have been widely known, for example, as described in Patent Documents 1 to 4. Of these, the structure of the hub body and the manufacturing method thereof described in Patent Document 4 will be described with reference to FIGS.

Of these, the hub main body 9a shown in FIG. 9 has a radial rotation side flange 7a on the outer peripheral portion of the outer peripheral surface in the axial direction, an inner ring raceway 8 in the middle portion, and a small diameter step portion 12 in the inner end portion. , Each formed.
Such a hub main body 9a is manufactured by the steps shown in FIGS. First, a long raw material made by extrusion molding, rolling molding, or the like is cut into a predetermined length to obtain a columnar material 13 as shown in FIG. Next, a first intermediate material 14 shown in (B) of each figure is produced by subjecting this material 13 to a first-stage forward extrusion process, which is a kind of cold forging process. Next, a second intermediate material 15 shown in (C) of each figure is obtained by subjecting the first intermediate material 14 to a second-stage forward extrusion process, which is also a kind of cold forging. Next, the shaft of the second intermediate material 15 is set in a state where the second intermediate material 15 is set in a split die having a predetermined inner peripheral surface shape as described in Patent Document 4. A punch is pressed against the direction end face {the upper end face of (C) in each figure}. And each figure is given by carrying out the side extrusion processing which is a kind of cold forging which makes the metal material which constitutes this 2nd intermediate material 15 flow radially outward while making this axial direction end face concave. A third intermediate material 16 having a rotation-side flange 7a as shown in FIG. Next, the third intermediate material 16 is subjected to sizing for forming seating surfaces 19 and 19 for contacting the axial side surface of the head 18 of the stud 17 (see FIG. 8). The fourth intermediate material 20 shown in E) is used.

  At the inner end in the axial direction of the fourth intermediate material 20 (the lower end of (E) in each figure), an external thread is formed on the outer peripheral surface (as shown in FIG. (In the case of a structure in which the fitted inner ring 10 is prevented by the nut 11), or as shown in FIG. 11 (F), a bottomed and circular concave hole 21 that opens to the inner end surface in the axial direction is formed. A peripheral portion of the concave hole 21 is a cylindrical portion 22 and is a fifth intermediate material 23. Such a cylindrical portion 22 is plastically deformed radially outward (clamped) in a state in which the inner ring 10 is externally fitted to the small-diameter stepped portion 12, and the axial inner end face of the inner ring 10 is suppressed. The inner ring 10 is prevented from coming out of the small diameter step portion 12. Further, predetermined cutting processing such as drilling for forming a circular hole for inserting the stud 17 in the fourth intermediate material 20 to the fifth intermediate material 23, deburring, and processing of the inner ring raceway 8; The hub body 9a is obtained by grinding.

  As described above, if the hub main body 9a is manufactured with the cold forging as the main, and cutting and grinding are minimized, the processing time required for these cutting and grinding is improved. The cost of the wheel bearing rolling bearing unit 1 (see FIG. 8) including the hub body 9a can be reduced. However, as shown in FIGS. 10 to 12 described above, when the hub main body 9a is made by using the forward extrusion process in the cold, the axial direction intermediate portion through the shaft portion 24 constituting the hub main body 9a. There is a possibility that a crack called a chevron crack, which is widely known in the technical field of cold forging due to the description in Non-Patent Document 1 or the like, occurs in the inner end portion and the strength of the shaft portion 24 is lowered. is there. In particular, when the hub main body 9a is manufactured as shown in FIGS. 10 to 12 described above, the first intermediate material 14 is replaced with the second intermediate material 15 as shown in FIGS. During the processing, the chevron crack is likely to occur in a region extending from the step portion 25 described below to the inner end surface in the axial direction.

  As described above, the first reason why chevron cracks are likely to occur is the process shown in (A) → (B) of each of the drawings, in which the material 13 is subjected to forward extrusion processing to form the first intermediate material 14. A metal material (generally, medium carbon steel having a carbon concentration of about 0.3 to 0.7% by weight) is further subjected to forward extrusion to form the second intermediate material 15. Because of that. The second reason is that the difference in moving speed when the metal material passes through the step portion 25 during the forward extrusion process is large between the radially outer portion and the central portion. It is to become. In particular, depending on the inclination angle of the step portion 25 and the width dimension (step size) in the radial direction, the moving speed of the metal material during the forward extrusion process is slow at the radially outer portion and at the central portion. The tendency to increase becomes remarkable (the difference between the speeds of these two parts increases), the tensile stress generated inside the shaft part 24 increases, and the chevron crack is likely to occur.

  In order to prevent the occurrence of such chevron cracks, after obtaining the first intermediate material 14, the first intermediate material 14 is subjected to an annealing treatment, and then the second intermediate material 15 is obtained. It is effective to perform the second-stage forward extrusion. However, in this case, it is difficult to ensure the necessary hardness for each part including the part where the inner ring raceway 8 should be formed at the axially intermediate part of the hub body 9a. Further, at the time of the second-stage forward extrusion process shown in (B) → (C) of each figure, the first intermediate material 14 to the second intermediate material 15 are strongly pressed, for example, from both axial sides (high) If a hydrostatic pressure is applied and the inside of the first intermediate material 14 to the second intermediate material 15 is made a compressive stress field, the occurrence of the chevron crack can be prevented. However, in such a method, it is necessary to use a mold having a sufficient strength and rigidity as a mold (punch and die) used for the forward extrusion process, and the production cost of this mold increases. Furthermore, it is necessary to use a large press machine having a large capacity, and this also increases the equipment cost. On the other hand, if the first intermediate material 14 to the second intermediate material 15 have a hollow structure (if the shaft portion 24 has a hollow cylindrical shape), the difference in the moving speed of the metal material during forward extrusion processing. The occurrence of the chevron crack can be suppressed. Such a method is effective when building a hub having a spline hole at the center, which is incorporated in a wheel bearing rolling bearing unit for a drive wheel, but a solid hub body 9a for a driven wheel. In some cases, it is not always preferable. That is, by making the hub body hollow, it is possible to reduce the weight, but by forming a center hole (through hole) that is essentially unnecessary, sealing to prevent foreign matter such as muddy water from entering the center hole. A structure is required, which is disadvantageous in terms of cost reduction.

  Conventionally, techniques described in Patent Documents 5 to 7 are known as other methods for preventing the occurrence of chevron cracks as described above. Among them, the conventional technique described in Patent Document 5 uses a material that can suppress the deformation resistance ratio, and the conventional technique described in Patent Document 6 includes a work hardening index of the material and an area reduction rate at each stage. The conventional technology described in Patent Document 7 regulates the manganese equivalent and the area reduction rate. In the case of these conventional techniques described in Patent Documents 5 to 7, it is considered that the generation of the chevron cracks can be prevented if even the conditions can be satisfied. However, in any case, the type of metal material (steel material) and the area reduction rate are limited. In the case of the hub main body 9a that is the object of the manufacturing method of the present invention, the types of metal materials that can be used are limited (in many cases, medium carbon steel is used), and the shaft area of the hub main body 9a is also reduced in terms of area reduction. It is difficult to satisfy the condition because the ratio between the outer diameter of the intermediate portion in the direction and the outer diameter of the small diameter step portion 12 cannot be made too small. Therefore, with respect to the hub body 9a, it is difficult to prevent the occurrence of chevron cracks by the conventional techniques as described in Patent Documents 5 to 7.

  In order to prevent the occurrence of the chevron crack in the shaft portion 24 of the hub main body 9a, the steps shown in FIGS. It is conceivable to perform a side extrusion process for forming the rotation side flange 7a. By adopting such a manufacturing method, it is not necessary to further extrude the first intermediate material 14 after work hardening, so that the occurrence of the chevron crack can be prevented. However, in such a method, it is necessary to form the entire small-diameter step 12 at the inner end in the axial direction of the hub main body 9a by shaving. For this reason, not only the yield of the material is deteriorated, but also the manufacturing cost of the hub body 9a is increased more than the cost of the mold is reduced by one process due to an increase in the amount of machining that requires machining time. Unavoidable.

JP 2006-111070 A JP 2006-142983 A JP 2008-296694 A JP 2009-255751 A Japanese Patent Laid-Open No. 2000-042676 Japanese Patent Laid-Open No. 2000-312947 JP 2007-130661 A

Shuji Kinoshita, Atsushi Inoue, Shoji Akita, “Samurai and Steel: Nippon Steel Cooperative Society, 62 (4)”, Japan Iron and Steel Institute, March 10, 1976, p. 165

  In view of the circumstances as described above, the present invention can prevent the occurrence of chevron cracks even when the metal material and shape to be used are limited, and the yield of the material is deteriorated, and the labor of processing is complicated. Invented to realize a method for manufacturing a stepped columnar member that can be prevented.

The manufacturing method of the stepped columnar member of the present invention is an intermediate material for a hub main body constituting a wheel bearing rolling bearing unit, and is provided with a plurality of cylindrical surface portions having different outer diameters on the outer peripheral surface, and adjacent cylinders. Pushing the tip of the material or the intermediate material at the previous stage (obtained by the previous process) into the die in order to produce a stepped cylindrical member with the surface parts continuous by the step part by cold forging. By processing, the outer diameter of the tip of this material or the intermediate material at the previous stage is reduced. A small-diameter cylindrical surface portion is formed at the distal end portion, and a step portion is formed at the proximal end portion of the small-diameter side cylindrical surface portion.
Particularly, in the case of the manufacturing method of the stepped columnar member of the present invention, when forming the cylindrical surface portion and the step portion on the small diameter side, the central portion of the tip surface of the material or the intermediate material of the previous stage, While pressing against the tip end surface of the counter punch having a smaller diameter than the outer diameter of the cylindrical surface portion on the small diameter side disposed on the inner diameter side of the die, the tip portion of the material or the intermediate material at the previous stage is pushed into the die. And by this pushing, the outer diameter of the tip of this material or the intermediate material of the previous stage is reduced to form the cylindrical surface portion and the stepped portion on the small diameter side, and at the same time, the central portion of the cylindrical surface portion on the small diameter side A bottomed recessed hole that opens at the center of the tip surface is formed at least at a portion near the tip.

When implementing the manufacturing method of the stepped columnar member of the present invention as described above, for example, first , the first-stage forward extrusion processing is performed on the columnar material so that the distal end portion becomes the proximal end portion. After the first intermediate material having a smaller diameter than the first intermediate material, the second intermediate portion of the first intermediate material is subjected to a second-stage forward extrusion process, and the front end portion has a smaller diameter than the cylindrical surface portion on the small diameter side. Let the 2nd cylindrical surface part be the 2nd intermediate material which has a 2nd step part in the axial direction intermediate part of this tip side part, respectively.
And while pressing the front end surface of the counter punch against the central portion of the front end surface of the raw material, this material is used as the first intermediate material having the concave hole in the central portion of the front end surface. Next, the first intermediate material is processed into the second intermediate material with a spacer fitted in the concave hole.
Further, when the present invention as described above is carried out, in addition, the length of the second cylindrical surface portion may be a part of the cylindrical surface portion on the small diameter side during the forward extrusion process in the second stage. It is possible to employ a configuration in which the second cylindrical surface portion extends more than the length in the axial direction and is plastically deformed so that the axial dimension of the concave hole is increased.
Further, although not within the technical scope of the present invention, when the material is the first intermediate material, the counter punch is not formed in the central portion of the front end surface of the first intermediate material without forming the concave hole. It is also possible to adopt a configuration in which the first intermediate material is used as the second intermediate material while the concave surface is formed by pressing the front end surface of the first intermediate material.
Furthermore, when implementing the present invention as described above, it is possible to additionally employ a configuration in which the spacer is provided in a state of being given upward elasticity.
In the case of adopting such a configuration, the second-stage forward extrusion process can be performed in a state where the upper end surface of the spacer is kept in contact with the inner end surface of the concave hole.

Moreover, the manufacturing apparatus of the stepped cylindrical member used for implementing the manufacturing method of the stepped cylindrical member of the present invention as described above includes a floating die, a sleeve, and the spacer.
Of these, the floating die is supported by the fixed block in a state where it can be raised and lowered so that it is lowered when a large downward force is applied.
The sleeve is fixed to the fixed block with the upper end thereof being fitted into the lower end of the cavity of the floating die so as to be vertically displaceable.
The spacer has substantially the same outer shape as the counter punch, and is installed inside the sleeve in a state where an upward elasticity is applied and in a state where it can be raised and lowered.
In the stepped columnar member manufacturing apparatus having the above-described configuration, the upper end surface of the spacer is brought into contact with the deep end surface of the concave hole of the first intermediate material during the second-stage forward extrusion processing. In this state, the portion close to the tip of the first intermediate material is pushed into the cavity of the floating die and the inside of the sleeve to form the second intermediate material.

According to the manufacturing method and manufacturing apparatus of the stepped columnar member of the present invention configured as described above, even when the metal material used and the outer surface shape of the stepped columnar member are limited, chevron cracks are generated. In addition, it is possible to prevent the yield of the material from deteriorating and complication of processing. In addition, equipment costs increase, or it is no longer necessary to incorporate extra members such as a seal plate into the finished product, and manufacture of stepped cylindrical members such as the hub body constituting the wheel bearing rolling bearing unit. Increase in cost can be suppressed.

  That is, in the case of the manufacturing method of the stepped columnar member of the present invention, when the outer diameter of the tip portion of the material or intermediate material is reduced, the bottomed concave hole is formed in the center portion of the cylindrical surface portion on the small diameter side by the counter punch. Form. For this reason, the flow of the metal material inside the material or intermediate material can be adjusted in the process of making the tip of the material or intermediate material the cylindrical surface portion on the small diameter side. In other words, the difference in the moving speed of the metal material between the portion near the outer diameter and the portion near the center of the material or intermediate material, which causes the chevron crack, can be reduced. The fact that this difference can be reduced leads to a reduction in tensile stress generated inside the material or intermediate material, and the occurrence of chevron cracks can be suppressed. Furthermore, compressive stress is generated inside the material or intermediate material by forming the concave hole while crushing the center of the tip of the material or intermediate material. As is well known in the field of metal processing, compressive stress has the effect of suppressing the occurrence of cracks, and therefore, the occurrence of cracks such as the chevron cracks can be suppressed based on the formation of the concave holes.

  Further, in order to arrange the flow of the metal material inside the material or intermediate material, and to bring the inside into a state of compressive stress or close to it, the counter punch is moved from the front end surface of the material or intermediate material. The concave hole is formed by being pushed into the front end portion of the material or intermediate material, but the force required for this pushing may be small. For this reason, the force required to form the cylindrical surface portion on the small diameter side at the tip portion of the material or intermediate material is not significantly increased as compared with the case where the concave hole is not formed (in the conventional method). Therefore, it is not necessary to use a mold having particularly high strength and rigidity as a mold used to form the cylindrical surface portion on the small diameter side, or to use a large-sized one having a large capacity as a pressing device. For this reason, the cost for a manufacturing apparatus can be suppressed and the processing cost of the stepped columnar member such as the hub body manufactured by the manufacturing apparatus can be prevented from increasing.

The figure which showed the end face shape about a part while showing the change of the cross-sectional shape regarding the virtual plane containing a central axis in order of a process regarding the 1st example of embodiment of this invention. Sectional drawing which shows the state immediately after processing a raw material into the 1st intermediate raw material with a metal mold apparatus. The partial side view which shows three examples of the shape of the front-end | tip part of a counter punch. Similarly, sectional drawing which shows the state immediately after processing a 1st intermediate material into a 2nd intermediate material with a metal mold apparatus. Similarly, sectional drawing which shows the state immediately after processing a 2nd intermediate material into the 3rd intermediate material by the metal mold apparatus. The figure similar to FIG. 1 which shows the 2nd example of embodiment of this invention. The figure similar to FIG. 1 which shows one example of the reference example relevant to this invention . Sectional drawing which shows an example of the rolling bearing unit for wheel support incorporating the hub main body used as the object of the manufacturing method of this invention. The end view (a) and side view (b) which show an example of the hub body known conventionally from the forging process by cold. The figure which showed the end surface shape about one part while showing the change of a side surface shape in order of a process regarding one example of the manufacturing method of the hub main body conventionally known. The figure which similarly shows the change of side surface shape thru | or cross-sectional shape. The perspective view which similarly shows the change of surface shape.

[First example of embodiment]
A first example of the embodiment of the present invention will be described with reference to FIGS. In the case of this example, first, in the first step, the material 13 made of a metal material such as medium carbon steel shown in FIG. B) and the first intermediate material 14a shown in FIG. In such a first step, first, the material 13 is inserted into a cavity 27 of a die 26 formed by overlapping a plurality of blocks as shown in FIG. Thereafter, the material 13 is pushed into the cavity 27 by a pressing punch 28 pressed by a ram of a pressing device (not shown). The material 13 is plastically deformed by the pushing operation, and the material 13 has an outer peripheral surface shape that matches the inner peripheral surface shape of the cavity 27 (the bus bar shape is the same and the unevenness is reversed). 14a.

  In particular, in the case of the manufacturing method of this example, the upper end portion of the counter punch 29 is protruded from the central portion of the lower end portion of the cavity 27. The lower end portion of the counter punch 29 is clamped and fixed between the upper surface of the lowermost block among the plurality of blocks constituting the die 26 and the next block. A cylindrical sleeve 30 is fitted around the counter punch 29 so as to be movable up and down. The lower end of the cavity 27 is defined by the upper end surface of the sleeve 30 and the outer surface of the upper end portion of the counter punch 29. Further, the lower end surfaces of the knockout pins 31, 31 having their respective upper end surfaces abutted against the lower end surface of the sleeve 30 are abutted against the upper surface of the elevating piece 32 fitted in the lowermost block.

  When the material 13 is pushed into the cavity 27 using the mold apparatus shown in FIG. 2 as described above, the outer peripheral surface of the tip (lower end) of the material 13 is brought to the inner peripheral surface of the cavity 27. A plastic deformation occurs along the first intermediate material 14a. That is, a cylindrical surface portion 33 on the small diameter side at the distal end portion of the first intermediate material 14a, and an inclined step portion 34 that continues from the base end side of the cylindrical surface portion 33 on the small diameter side and a larger diameter portion. Form. At the same time, the upper end portion of the counter punch 29 is pushed into the center portion of the cylindrical surface portion 33 on the small diameter side in the first intermediate material 14a, and the first portion of the cylindrical surface portion 33 on the small diameter side is A bottomed concave hole 35 having a circular cross-sectional shape is formed in the distal end surface of the intermediate material 14a. In addition, the said inclination step part 34 is corresponded to the step part described in Claim 1 of a claim.

  The outer diameter and axial length of the counter punch 29 for forming the concave hole 35 vary depending on the carbon content of the material 13, and the flow of the metal material constituting the material 13 to the first intermediate material 14a. In consideration of the characteristics and the durability of the counter punch 29, it is determined by design consideration. As the outer diameter of the counter punch 29 increases, the durability of the counter punch 29 increases, but the degree of work hardening of the peripheral portion of the concave hole 35 at the tip of the first intermediate material 14a becomes significant. Then, it becomes difficult to plastically deform (clamp and spread) the distal end portion (the inner end portion in the axial direction) of the hub body after completion in the radial direction. Considering these points, the outer diameter of the counter punch 29 is restricted to about 1/3 to 2/3, most preferably about 1/2 of the outer diameter of the cylindrical surface portion 33 on the small diameter side. Further, the depth of the concave hole 35 determined by the axial length of the counter punch 29 is determined in consideration of the durability and the degree of work hardening. In the case of this example, in the state where the pressing punch 28 is lowered to the bottom dead center and the processing of the first intermediate material 14a is completed, the depth of the concave hole 35 is set in the axial direction of the hub body after completion. It is made to correspond to the axial direction length of the small diameter step part 12a which exists in an edge part, or just to become slightly larger than this axial direction length. Further, the shape of the front end surface (upper end surface) of the counter punch 29 is determined in consideration of the durability and the degree of work hardening. For example, a simple flat surface as shown in FIG. 3A, a truncated trapezoidal shape as shown in FIG. 3B, or a hemispherical shape as shown in FIG.

In any case, if the pressing punch 28 is lowered to the bottom dead center and the first intermediate material 14a is formed, the raising / lowering piece which has been lowered until then is raised after the pressing punch 28 is raised. 32 is raised, and the sleeve 30 is raised via the knockout pins 31, 31. As a result, since the first intermediate material 14a is pushed out from the cavity 27, the first intermediate material 14a is taken out from the die 26 and subjected to the next second step, so that the mold apparatus shown in FIG. It is inserted into the second cavity 37 of the floating die 36. The floating die 36 is supported by a plurality of springs 38, 38 so as to be movable up and down so as to descend when a large downward force is applied above the fixed block 39. Further, the upper end of the second sleeve 40 (corresponding to the sleeve of the claims) placed and fixed on the upper surface of the fixed block 39 is displaced axially (sliding in the vertical direction ) to the lower end of the floating die 36. ) Is possible. Furthermore, the upper end of the sleeve 30a, which is installed on the inner diameter side of the fixed block 39, is fitted into the lower end of the second sleeve 40 so as to be capable of axial displacement (up and down sliding). ing.

  A spacer 41 having substantially the same outer shape as the counter punch 29 is installed inside the sleeve 30a so as to be able to move up and down independently of the sleeve 30a. In the case of this example, a spring 42 is provided between the lower end surface of the spacer 41 and the fixing plate constituting the fixing block 39, and an upward elasticity is applied to the spacer 41. With the first intermediate material 14a {see FIG. 1B and FIG. 2} inserted into the second cavity 37, the upper end surface of the spacer 41 abuts against the inner end surface of the concave hole 35. Then, the upper end surface of the spacer 41 continues to contact the inner end surface of the concave hole 35 during the progress of the second step for processing the first intermediate material 14a into the second intermediate material 15a. The inner surface shape of the lower portion of the second cavity 37 is defined by the inner peripheral surface and the front end surface (upper end surface) of the second sleeve 40, the upper end surface of the sleeve 30a, and the outer peripheral surface and front end surface of the spacer 41. Made. Further, by pushing the lower end of the pressing punch 28a into the floating die 36, the outer surface shape of the first intermediate material 14a can be plastically deformed (forward extrusion molding) in accordance with the inner surface shape of the second cavity 37. It is said.

When the mold apparatus shown in FIG. 4 as described above is used and the first intermediate material 14a is pushed into the second cavity 37 with a large force, the lower portion of the first intermediate material 14a becomes the second intermediate material 14a. It plastically deforms along the inner surface of the cavity 37 and becomes the second intermediate material 15a. That is, the distal end portion or the axial intermediate portion of the cylindrical surface portion 33 on the small diameter side of the distal end portion of the first intermediate material 14 a exists between the inner peripheral surface of the second sleeve 40 and the outer peripheral surface of the spacer 41. It is pushed into the cylindrical space. The outer peripheral surface of the pushed-in portion becomes a small-diameter step portion 12a having a smaller diameter than the cylindrical surface portion 33 on the small-diameter side. The small diameter step portion 12a corresponds to the second cylindrical surface portion described in the claims . Further, in a state where the pressing punch 28a is lowered to the bottom dead center, the portion pressed by the distal end surface (upper end surface) of the second sleeve 40 is the axially outer end surface of the inner ring 10 in a state where the hub 3 is assembled. Is a step portion 25a (see FIG. 8). The spacer 41 is lowered until the lower end surface of the spacer 41 comes into contact with the upper surface of a part of the fixed block 39 while compressing the spring 42 with the progress of the second step as described above. To do. Accordingly, while the second process proceeds, the tip end surface of the spacer 41 remains pressed against the back end surface of the concave hole 35. Further, as the second process proceeds, the axial length of the small diameter step portion 12a is larger than the axial length of the portion of the original cylindrical surface portion 33 on the small diameter side that should become the small diameter step portion 12a. And the depth of the concave hole 35 is increased accordingly. The step 25a corresponds to the second step described in the claims .

  When the second intermediate material 15a is formed as described above, the pressing punch 28a is raised. Then, the floating die 36 is slightly lifted by the elasticity of the springs 38, 38, and the spacer 41 is slightly lifted by the elasticity of the spring 42. Therefore, following the ascent of each of the members 36 and 41, the elevating piece 32a that has been lowered is raised and the sleeve 30a is raised via the knockout pins 31a and 31a. As a result, since the second intermediate material 15a is pushed out from the second cavity 37, the second intermediate material 15a is taken out from the floating die 36 and subjected to the next third step. The device is inserted into the third cavity 44 of the die 43. Further, the front end portion (upper end portion side) of the spacer 41a urged upward by the spring 42a is fitted into the concave hole 35 without a gap. The second intermediate material 15a is crushed in the axial direction by the pressing punch 28b while the second intermediate material 15a is suppressed by the floating die 45 disposed around the pressing punch 28b. And it is set as the 3rd intermediate raw material 16a as shown to (D) of FIG. 1, and FIG. 5 which provided the radial rotation side flange 7a in the outer peripheral surface. During the progress of such a third step, the lower surface of the floating die 45 remains pressed against the upper surface of the die 43 by the elasticity of the springs 46 and 46.

As described above, when the third intermediate material 16a is formed, the pressing punch 28b is raised, and then the raising / lowering piece 32b that has been lowered is raised and the knockout pins 31b and 31b are interposed. The sleeve 30b is raised. As a result, since the third intermediate material 16a is pushed out from the third cavity 44, the third intermediate material 16a is taken out from the die 43 and sent to the next step.
In this next step, in the third intermediate material 16a, the inner diameter of the portion near the opening of the concave hole 35 is expanded by a cutting process such as turning, and this part is used as another concave hole 21a. A fourth intermediate material 47 as shown in (E) of FIG. The peripheral portion of the other concave hole 21a is used to form a caulking portion for suppressing the inner end surface in the axial direction of the inner ring fitted on the small diameter step portion 12a.
The fourth intermediate material 47 is further sent to the next step and subjected to necessary processing such as surface pressing, cutting, and grinding to complete the hub body. Since these processes are the same as those in the conventional manufacturing method and are well known to those skilled in the art, illustration and description are omitted.

  As described above, in the case of the hub body manufacturing method of this example, when the outer diameter of the tip portion (lower end portion in FIG. 1) of the material 13 is reduced to form the first intermediate material 14a, the counter punch 29, a bottomed concave hole 35 is formed in the center of the cylindrical surface portion 33 on the small diameter side. For this reason, the flow of the metal material inside the material 13 can be rectified in the process of making the tip of the material 13 the cylindrical surface portion 33 on the small diameter side, and this material 13 causes the chevron crack. The difference in the moving speed of the metal material between the outer diameter portion and the center portion can be reduced. As a result, the tensile stress generated inside the material 13 to the first intermediate material 14a is reduced, and the occurrence of the chevron crack can be suppressed. Further, by compressing the material 13 by plastically deforming the material 13 by forming the concave hole 35 while crushing the central portion of the tip of the material 13, a compressive stress is applied. Occurs. As is well known in the field of metal processing, the compressive stress has the effect of suppressing the occurrence of cracks, and therefore, the generation of cracks such as the chevron cracks can be suppressed based on the formation of the concave holes 35. The compressive stress generated in the first intermediate material 14a in the first step contributes to prevention of cracking in the second step, and the second intermediate material 15a in the second step. Prevents chevron cracks from occurring inside.

  Further, the force required to form the concave hole 35 by pushing the counter punch 29 from the front end surface of the raw material 13 into the inner end of the raw material 13 may be small. Therefore, the force required to form the small-diameter cylindrical surface portion 33 at the distal end portion of the material 13 is not significantly increased compared to the case where the concave hole 35 is not formed (in the conventional method). Accordingly, it is not necessary to use a mold having particularly high strength and rigidity as a mold used to form the cylindrical surface portion 33 on the small diameter side, or to use a large-sized one having a large capacity as a pressing device. For this reason, the cost for a manufacturing apparatus can be suppressed and the processing cost of the stepped columnar member such as the hub body manufactured by the manufacturing apparatus can be prevented from increasing.

[Second Example of Embodiment]
FIG. 6 shows a second example of the embodiment of the present invention . In the case of this example, in the first step {(A) → (B)} in FIG. 6 which processes the material 13 into the first intermediate material 14a, the concave hole 35a formed at the tip of the first intermediate material 14a. Is made shallower than in the first example of the embodiment described above. Then, in the state where the second step {(B) → (C)} in FIG. 6}, in which the first intermediate material 14a is the second intermediate material 15a, the axial position of the back end surface of the concave hole 35a is The axial position of the step portion 25a existing at the base end portion of the small-diameter step portion 12a is substantially matched.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, the description regarding the equivalent parts is omitted.

[ One Reference Example Related to the Present Invention ]
FIG. 7 shows an example of a reference example related to the present invention . In the case of this reference example , the first process {(A) → (B)} in FIG. 7 for processing the material 13 into the first intermediate material 14 is the same as the conventional method shown in FIGS. Do. Then, in the second step {the step (B) → (C)} in FIG. 7) in which the first intermediate material 14 is used as the second intermediate material 15a, the second step is performed by the counter punch 29 (see FIG. 2). A concave hole 35 is formed in the center of the tip of the intermediate material 15a. Further , a small-diameter step portion 12a is formed at the tip portion of the second intermediate material 15a, and a step portion 35a is formed at the axially intermediate portion (base end portion of the small-diameter step portion 12a) near the tip portion. Yes.

At the time of the first step, since the material 13 is not yet work hardened, chevron cracks do not occur in the obtained first intermediate material 14. On the other hand, in the second step of obtaining the second intermediate material 15a, the outer diameter of the tip of the first intermediate material 14 that has already been hardened is reduced by forward extrusion processing, so that chevron cracks are likely to occur. . Therefore, in the case of this reference example, the concave hole 35 is formed in the front end surface of the first intermediate material 14 during the second step, so that the chevron crack is prevented from occurring.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, the description regarding the equivalent parts is omitted.

The manufacturing method of the stepped columnar member of the present invention is intended for a hub body constituting a wheel bearing rolling bearing unit for a driven wheel . However, although it is not within the technical scope of the present invention, the article is not limited to the hub body as long as it is an article that is subjected to forward extrusion processing in a plurality of stages and the part is stepped. Applicable to.

DESCRIPTION OF SYMBOLS 1 Rolling bearing unit for wheel support 2 Outer ring 3 Hub 4 Rolling body 5 Outer ring raceway 6 Stationary side flange 7, 7a Rotation side flange 8 Inner ring raceway 9, 9a Hub body 10 Inner ring 11 Nut 12, 12a Small diameter step part 13 Material 14, 14a First intermediate material 15, 15a Second intermediate material 16, 16a Third intermediate material 17 Stud 18 Head 19 Seat surface 20 Fourth intermediate material 21, 21a Recessed hole 22 Cylindrical portion 23 Fifth intermediate material 24 Shaft portion 25, 25a Step portion 26 Dies 27 Cavity 28, 28a Press punch 29 Counter punch 30, 30a, 30b Sleeve 31, 31a, 31b Knockout pin 32, 32a, 32b Lifting piece 33 Small diameter cylindrical surface portion 34 Inclined step portion 35 Recessed hole 36 Floating die 37 Second cavity 38 Spring 39 Fixed block 0 second sleeve 41,41a spacer 42 spring 43 die 44 third cavity 45 floating die 46 spring 47 fourth intermediate material

Claims (3)

Stepped columnar shape that is an intermediate material for the hub body that constitutes a wheel bearing rolling bearing unit, and is provided with a plurality of cylindrical surface portions with different outer diameters on the outer peripheral surface, and the adjacent cylindrical surface portions are continued by stepped portions. In order to build a member by cold forging, the outer diameter of the tip of this material is reduced by pushing the tip of the columnar material into a die, and the cylindrical surface portion on the small diameter side is connected to the tip of this small diameter side. A cylindrical portion on the small diameter side, in which a central portion of the distal end surface of the material is disposed on the inner diameter side of the die during the first-stage forward extrusion process for forming a step portion at the base end portion of the cylindrical surface portion while pressed against the front end surface of the small diameter of the counter punch than the outer diameter of the surface portion, by pushing the tip of the material within the die, and shrink the outer diameter of the distal end portion of the material, the cylindrical surface portion of the small diameter side and Simultaneously with forming the step After this the small diameter side at least the tip portion near the central portion of the cylindrical surface portion of, to form a first intermediate material to form a concave hole with a bottom opening to a center portion of the tip surface,
In a state in which a spacer is fitted in the concave hole, a second-stage forward extrusion process is performed on the portion near the tip of the first intermediate material, and the portion near the tip has a smaller diameter than the cylindrical surface portion on the small diameter side. In the process of forming a second intermediate material having a second cylindrical surface portion and a second intermediate portion having a second step portion at the axially intermediate portion near the tip, the length of the second cylindrical surface portion is the cylindrical surface portion on the small diameter side. A stepped columnar member that is plastically deformed so that the axial dimension of the concave hole is larger than the length in the axial direction of the portion that should become the second cylindrical surface portion . The spacer is provided in a state of being given upward elasticity.
The method of manufacturing a stepped columnar member according to claim 1, wherein the second-stage forward extrusion processing is performed in a state in which an upper end surface of the spacer is kept in contact with a rear end surface of the concave hole. It is used for carrying out the manufacturing method of the stepped columnar member according to any one of claims 1 and 2.
A floating die, a sleeve, and the spacer;
Of these, the floating die is supported by the fixed block so that it can be raised and lowered so that it falls when a large downward force is applied.
The sleeve is fixed to the fixed block in a state where the upper end of the sleeve is fitted into the lower end of the cavity of the floating die so as to allow vertical displacement.
The spacer has substantially the same outer shape as the counter punch, and is installed inside the sleeve in a state in which an upward elasticity is applied and in a state where it can be raised and lowered,
In the second stage of forward extrusion, the upper end surface of the spacer is in contact with the back end surface of the concave hole of the first intermediate material, and the portion near the tip of the first intermediate material is placed on the floating die. An apparatus for manufacturing a stepped columnar member as the second intermediate material by being pushed into the cavity and the inside of the sleeve.

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