JP2016047556A - Rolling bearing unit for wheel support - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method by which a stepped columnar member to be used as a hub body of a rolling bearing unit for wheel support for instance can be manufactured, while occurrence of a chevron crack is prevented and increase in weight of the member is suppressed.SOLUTION: Material 28 formed by internally fitting core material 26 made of a light alloy such as an aluminum alloy in bottomed cylindrical surface layer material 27 by tight fit is utilized. Then, by inserting the material 28 into a cavity of a die and forming cold forging of pushing the material 28 into the cavity by a pressing punch, the stepped columnar member is formed.SELECTED DRAWING: Figure 1

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. Of 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 wheel bearing rolling bearing unit including a hub body made by the method of manufacturing the stepped columnar member. About.

  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. 12 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 arranged at two positions on the inner peripheral surface of the outer ring 2 at a part of the outer peripheral surface, slightly inwardly in the axial direction from the central part in the axial direction. Means the side that is the central side in the width direction of the vehicle body in the used state, and the right side of Fig. 12. Conversely, the left side in Fig. 12 that is the outside in the width direction of the vehicle body in the used state is referred to as the 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. Among these, the structure of the hub main 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. 13 has a radial rotation-side flange 7a near the outer peripheral portion of the outer peripheral surface in the axial direction, an inner ring raceway 8 at the middle portion, and a small-diameter step portion 12 at the inner end portion. , Each formed.
Such a hub main body 9a is manufactured by the process 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 a sizing process for forming seating surfaces 19 and 19 for contacting the axial side surface of the head 18 (see FIG. 12) of the stud 17 (FIG. The fourth intermediate material 20 shown in E) is used.

  In the axially inner end {the lower end of (E) in each figure} of the fourth intermediate material 20 is a male thread 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 a nut 11), or as shown in FIG. 15 (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.

  It is desired to reduce the weight of the hub body 9a manufactured as described above. That is, the wheel-supporting rolling bearing unit 1 (see FIG. 12) in which the hub body 9a is incorporated is a so-called unsprung load provided on the road surface side of the spring constituting the suspension device. In order to improve the driving performance centering on the characteristics, it is desirable to reduce the weight as much as possible. In the case of the manufacturing method described in Patent Document 4, generally, the hub body 9a is made by subjecting an iron-based alloy such as medium-carbon steel to cold forging, so that the weight of the hub body 9a is bulky. Thus, the weight of the wheel supporting rolling bearing unit 1 as a whole also increases.

  In the case of the manufacturing method described in Patent Document 4, the hub main body 9a is manufactured mainly by cold forging, with cutting and grinding being minimized. For this reason, while improving the yield of material, the processing time which these cutting processing and grinding processing require can be shortened, and the cost reduction of the wheel bearing rolling bearing unit 1 (refer FIG. 12) including the said hub main body 9a can be aimed at. . However, as shown in FIGS. 14 to 16 described above, when the hub main body 9a is manufactured by using the forward extrusion process in the cold, the axially 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 body 9a is manufactured as shown in FIGS. 14 to 16 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 generation 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.

  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

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 obtain a light-weight stepped columnar member while preventing the occurrence of chevron cracks, and the yield of the material is deteriorated, and the labor of processing is complicated. The invention has been invented to realize a manufacturing method that can prevent this from happening and a structure of a lightweight wheel-supporting rolling bearing unit.

The stepped columnar member that is the subject of the present invention includes a plurality of cylindrical surface portions having different outer diameters on the outer peripheral surface. And among these cylindrical surface parts, the adjacent cylindrical surface parts are made to continue by the step part.
In particular, the manufacturing method of the stepped columnar member described in claim 1 is made of a light alloy core material such as an aluminum alloy and an iron alloy material such as medium carbon steel, and the end of the core material is removed. A cold forging process is performed on a material composed of a bottomed cylindrical surface layer covering the outer portion.

When implementing the manufacturing method of the stepped columnar member of the present invention as described above, preferably, as in the invention described in claim 2, the raw material is used as the inner diameter side portion of the surface layer material. Made by an interference fit.
Further, when the invention described in claim 2 is carried out, preferably the height dimension of the core material is set to the depth dimension of the center hole of the surface layer material as in the invention described in claim 3. Smaller than.

  In addition, the invention described in claim 4 is such that the front end portion of the material (including the intermediate material of the previous stage obtained by subjecting this material to the previous step) is pushed into the die and subjected to forward extrusion processing. The outer diameter of the tip of the material 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. In particular, in the method of manufacturing the stepped columnar member according to claim 4, 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 is set to the inner diameter of the die. The front end portion of the material is pushed into the die while being pressed against the front end surface of the counter punch having a smaller diameter than the outer diameter of the cylindrical surface portion on the small diameter side. And by this pushing, the outer diameter of the tip portion of this material is reduced to form the cylindrical surface portion on the small diameter side and the stepped portion, and at the same time, at least in the portion near the tip of the central portion of the cylindrical surface portion on the small diameter side, A bottomed recessed hole is formed at the center of the distal end surface.

When implementing the manufacturing method of the stepped columnar member described in claim 4 as described above, for example, as in the invention described in claims 5 to 6, first, the columnar material is moved forward of the first step. By making the first intermediate material smaller in diameter than the proximal end portion by extruding, the second intermediate forward extrusion process is applied to the first intermediate material near the distal end. A second cylindrical surface portion having a smaller diameter than the cylindrical surface portion on the small diameter side at the distal end portion and a second step portion at the axial intermediate portion of the distal end portion are used as second intermediate materials.
In the case of the invention described in claim 5, while pressing the tip surface of the counter punch against the center portion of the tip surface of the material, the material has the concave hole in the center portion of the tip surface. The first intermediate material. Next, the first intermediate material is processed into the second intermediate material with a spacer fitted in the concave hole.
On the other hand, in the case of the invention described in claim 6, the concave hole is not formed when the material is the first intermediate material. Instead, the first intermediate material is used as the second intermediate material while the front surface of the counter punch is pressed against the center of the front surface of the first intermediate material to form the concave hole.

  According to a seventh aspect of the present invention, a concave hole is provided at the back end face of the central hole of the surface layer material, and a small diameter portion is provided at the base end portion of the core member to be engaged with the concave hole without a gap. Then, the core material is tightly fitted to the inner diameter side portion of the surface layer material to form the material, and the cylindrical surface portion and the stepped portion are formed on the material by cold forging to form an intermediate material. Then, a radial flange is provided on the outer peripheral surface of the intermediate material near the base end by subjecting the intermediate material to side extrusion.

The wheel support rolling bearing unit described in claim 8 includes an outer ring, a hub, and rolling elements.
Among these, the outer ring has a double row outer ring raceway on the inner peripheral surface, and does not rotate during use.
The hub rotates together with the wheel when in use, and includes a hub body and an inner ring. Of these, the hub body directly forms a radial rotation flange for supporting and fixing the wheel on the outer peripheral surface near the axially outer end, and an axially outer ring on the outer peripheral surface in the axial direction. doing. Further, the inner ring forms an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and is fitted and fixed to a small-diameter step portion formed at the inner end in the axial direction of the hub body.
Further, a plurality of rolling elements are provided between the inner ring raceways and the outer ring raceways so as to roll freely in each row.
In particular, in the case of the rolling bearing unit for supporting a wheel according to claim 8, the core portion of the hub body is made of a light alloy, and the surface portion covering the core portion is made of an iron-based alloy.

  According to the present invention configured as described above, a lightweight stepped columnar member is manufactured while preventing the occurrence of chevron cracks. For example, the wheel support using the stepped columnar member as a hub body is used. The rolling bearing unit can be reduced in weight. That is, since this stepped columnar member is made by cold forging a material made of a light alloy core material and a surface layer material made of an iron-based alloy and covering the outer portion of the core material, these cores are made. The sliding property between the material and the surface layer material can be improved, and the difference in the moving speed of the respective metal materials can be suppressed small inside the core material and the surface layer material, thereby preventing the occurrence of chevron cracks. Further, as compared with the case where the whole is made of an iron-based alloy such as medium carbon steel as in the conventional structure described above, it is possible to suppress an increase in the weight of the stepped columnar member.

Furthermore, according to the invention described in claims 4 to 6, even when the outer surface shape of the stepped columnar member is limited, the generation of chevron cracks can be more effectively prevented, and the yield of the material is deteriorated. And troublesome processing can be prevented.
That is, in the case of the inventions described in claims 4 to 6, when the outer diameter of the leading end portion of the material is reduced, a bottomed concave hole is formed in the central portion of the cylindrical surface portion on the small diameter side by the counter punch. For this reason, the flow of the metallic material inside the material can be adjusted in the process of making the tip of the 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 that causes the chevron crack can be reduced. In particular, the difference in the moving speed of the metal material can be reduced at the surface layer portion made of an iron-based alloy, which is an important portion from the viewpoint of securing the strength. The fact that this difference can be reduced leads to a reduction in tensile stress generated in the material, particularly the surface layer material, and the generation of the chevron cracks can be suppressed. Furthermore, compressive stress is generated inside the material by forming the concave hole while crushing the center of the tip of the material. This compressive stress prevents a gap from being generated between the core material and the surface layer material. Further, as is well known in the field of metal processing, the compressive stress has an action of suppressing the generation of cracks, and therefore, the generation of cracks such as the chevron cracks can be suppressed based on the formation of the concave holes.

  In addition, the flow of the metallic material inside the material is arranged, and the counter punch is moved from the front end surface of the material to the inside of the front end portion of the material in order to make the inside of the material a compressive stress field or a state close thereto. Although the concave hole is formed by pushing, the force required for the pushing may be small. For this reason, the force required to form the cylindrical surface portion on the small diameter side at the tip end portion of the material is not significantly increased as compared with the case where the concave hole is not formed (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, the fragmentary sectional view which shows another example. Sectional drawing which shows the state immediately after processing a 1st intermediate material into a 2nd intermediate material with the metal mold apparatus. Sectional drawing which shows the state immediately after processing the 2nd intermediate material into the 3rd intermediate material with the metal mold apparatus. The figure similar to FIG. 12 which shows the 1st example of embodiment of this invention. The figure similar to FIG. 1 which shows the 2nd example. Similarly, the same figure as FIG. The figure similar to FIG. 1 which shows the 3rd example of embodiment of this invention. The figure similar to FIG. 1 which shows the 4th example. 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]
FIGS. 1-7 has shown the 1st example of embodiment of this invention corresponding to Claims 1-5,8. In the case of this example, first, in the first step, the core 26 made of an aluminum alloy such as A7075 or A6061 and the iron alloy such as medium carbon steel shown in FIG. The material 28 composed of the surface layer material 27 that covers the outer portion of the material 26 is cold-extruded forward. Such a material 28 is formed by fitting a columnar core material 26 into the inner diameter side portion of the bottomed cylindrical surface material 27 with an interference fit, and between the core material 26 and the surface material 27. Good slipperiness. In the case of this example, the height H of the core material 26 is made smaller than the depth D of the center hole of the surface layer material 27, and the step portion 29 is provided at the end of the material 28. The depth (DH) of the stepped portion 29 is such that the fluidity of the aluminum-based alloy constituting the core material 26 and the iron-based alloy constituting the surface layer material 27, and the first and second intermediate materials 33 described later. , 51 in consideration of the shape and aperture ratio. In the first step of cold forging the material 28, first, the material 28 is inserted into a cavity 31 of a die 30 formed by stacking a plurality of blocks as shown in FIG. Thereafter, the material 28 is pushed into the cavity 31 by a pressing punch 32 pressed by a ram of a pressing device (not shown). The material 28 is plastically deformed by the pushing operation, and the material 28 has an outer peripheral surface shape corresponding to the inner peripheral surface shape of the cavity 31 (the bus bar shape is the same and the unevenness is reversed). It becomes.

  In particular, in the case of the manufacturing method of this example, the upper end portion of the counter punch 34 is projected from the lower end center portion of the cavity 31. The lower end portion of the counter punch 34 is clamped and fixed between the upper surface of the lowermost block among the plurality of blocks constituting the die 30 and the next block. A cylindrical sleeve 35 is fitted around the counter punch 34 so as to be movable up and down. The lower portion of the cavity 31 is defined by the upper end surface of the sleeve 35, the outer surface of the upper end portion of the counter punch 34, and the inner peripheral surface of the uppermost block. Further, the lower end surfaces of the knockout pins 36, 36 each abutting the upper end surface against the lower end surface of the sleeve 35 are abutted against the upper surface of the elevating piece 37 fitted in the lowermost block.

  When the material 28 is pushed into the cavity 31 using the mold apparatus shown in FIG. 2 as described above, the outer peripheral surface of the tip (lower end) of the material 28 is brought to the inner peripheral surface of the cavity 31. The first intermediate material 33 is plastically deformed along the line. That is, at the distal end portion of the first intermediate material 33, a cylindrical surface portion 38 on the small diameter side, and an inclined step portion 39 that continues from the proximal end side of the cylindrical surface portion 38 on the small diameter side and continues to the larger diameter portion, Form. At the same time, the upper end portion of the counter punch 34 is pushed into the central portion of the first intermediate material 33 (the central portion of the core member 26) of the cylindrical surface portion 38 on the small diameter side, and this cylindrical surface portion on the small diameter side A bottomed concave hole 40 having a circular cross-sectional shape that opens at the front end surface of the first intermediate material 33 is formed at the center of the first intermediate material 33.

  The outer diameter and axial length of the counter punch 34 for forming the concave hole 40 are the same as those of the aluminum alloy and the surface layer material 27 constituting the core material 26 of the material 28 to the first intermediate material 33. This is determined by design consideration in consideration of the fluidity of the iron-based alloy to be constructed and the durability of the counter punch 34. The larger the outer diameter of the counter punch 34, the greater the degree of work hardening of the peripheral portion of the concave hole 40 at the tip of the first intermediate material 33, instead of improving its durability. Then, it becomes difficult to plastically deform (clamp and spread) the distal end portion (axially inner end portion) of the hub body 9b after completion in the radial direction. Considering these points, the outer diameter of the counter punch 34 is restricted to about 1/3 to 2/3, most preferably about 1/2 of the outer diameter of the cylindrical surface portion 38 on the small diameter side. Further, the depth of the concave hole 40 determined by the axial length of the counter punch 34 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 32 is lowered to the bottom dead center and the processing of the first intermediate material 33 is completed, the depth of the concave hole 40 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 34 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. Alternatively, as shown in FIG. 4, it is possible to employ a counter punch 34 in which an inclined surface portion 41 is provided at the tip portion, and a ring 42 made of a copper alloy such as brass is supported and fixed to the inclined surface portion 41 by a bolt 43. . When the tip of the counter punch 34 is pushed into the central portion of the cylindrical surface portion 38 on the small diameter side, as shown exaggeratedly in FIG. 4, along the inclined surface portion 41 due to the hydrostatic pressure of the core member 26. Thus, the diameter of the ring 42 is elastically expanded outward in the radial direction of the counter punch 34. As a result, when the counter punch 34 is pushed in, the core material 26 or the surface layer material 27 present in the outer peripheral surface of the ring 42 and the central portion of the first intermediate material 33 is slidably contacted without gaps, It is possible to prevent a part of the core material 26 from protruding from the inner peripheral surface of the concave hole 40 (this inner peripheral surface can be made smooth). Since this ring 42 is a copper-based alloy different from the aluminum-based alloy constituting the core material 26 and the iron-based alloy constituting the surface layer material 27 and the counter punch 34, the ring 42 and the first intermediate The slipperiness of the contact portion with the material 33 can be improved.

  In any case, if the pressing punch 32 is lowered to the bottom dead center and the first intermediate material 33 is formed, the raising / lowering piece that has been lowered until then is raised after the pressing punch 32 is raised. 37 is raised, and the sleeve 35 is raised via the knockout pins 36, 36. As a result, the first intermediate material 33 is pushed out of the cavity 31, so that the first intermediate material 33 is taken out from the die 30 and subjected to the next second step, so that the mold apparatus shown in FIG. It is inserted into the second cavity 45 of the floating die 44. The floating die 44 is supported by a plurality of springs 46 and 46 so as to be able to move up and down so as to descend when a large downward force is applied above the fixed block 47. The upper end portion of the second sleeve 48 placed and fixed on the upper surface of the fixed block 47 is fitted into the lower end portion of the floating die 44 so as to be capable of axial displacement (sliding in the vertical direction). Further, the upper end portion of the sleeve 35a, which is installed on the inner diameter side of the fixed block 47, is fitted into the lower end portion of the second sleeve 48 so as to be capable of axial displacement (up and down sliding). ing.

  In addition, a spacer 49 having substantially the same outer shape as the counter punch 34 is provided inside the sleeve 35a so as to be able to move up and down independently of the sleeve 35a. In the case of this example, a spring 50 is provided between the lower end surface of the spacer 49 and the fixing plate that constitutes the fixing block 47, and an upward elasticity is applied to the spacer 49. With the first intermediate material 33 (see FIG. 1B and FIG. 2) inserted into the second cavity 45, the upper end surface of the spacer 49 abuts against the inner end surface of the concave hole 40. Then, the upper end surface of the spacer 49 is kept in contact with the inner end surface of the concave hole 40 during the progress of the second step for processing the first intermediate material 33 into the second intermediate material 51. The inner surface shape of the lower portion of the second cavity 45 is defined by the inner peripheral surface and the front end surface (upper end surface) of the second sleeve 48, the upper end surface of the sleeve 35a, and the outer peripheral surface and front end surface of the spacer 49. Made. Further, by pushing the lower end portion of the pressing punch 32 a into the floating die 44, the outer surface shape of the first intermediate material 33 can be plastically deformed (forward extrusion molding) in accordance with the inner surface shape of the second cavity 45. It is said.

  When the first intermediate material 33 is pushed into the second cavity 45 with a large force using the mold apparatus shown in FIG. 5 as described above, the lower portion of the first intermediate material 33 is moved to the second intermediate material 33. The second intermediate material 51 is plastically deformed along the inner surface of the cavity 45. That is, the distal end portion or the axial intermediate portion of the cylindrical surface portion 38 on the small diameter side of the distal end portion of the first intermediate material 33 exists between the inner peripheral surface of the second sleeve 48 and the outer peripheral surface of the spacer 49. 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 38 on the small diameter side. Further, in a state where the pressing punch 32a is lowered to the bottom dead center, the portion pressed by the tip surface (upper end surface) of the second sleeve 48 is the inner ring 10a (see FIG. 7) in a state where the hub 3a is assembled. It becomes the step part 25a for abutting the axial direction outer end surface. The spacer 49 is lowered until the lower end surface of the spacer 49 comes into contact with the upper surface of a part of the fixed block 47 while compressing the spring 50 with the progress of the second step as described above. To do. Accordingly, while the second step proceeds, the tip end surface of the spacer 49 remains pressed against the back end surface of the concave hole 40. With the progress of the second step, 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 38 on the small diameter side that should become the small diameter step portion 12a. And the depth of the concave hole 40 is increased accordingly.

  When the second intermediate material 51 is formed as described above, the pressing punch 32a is raised. Then, the floating die 44 is slightly raised by the elasticity of the springs 46 and 46, and the spacer 49 is slightly raised by the elasticity of the spring 50. Therefore, following the ascent of these members 44, 49, the elevating piece 37a that has been lowered is raised, and the sleeve 35a is raised via the knockout pins 36a, 36a. As a result, since the second intermediate material 51 is pushed out from the second cavity 45, the second intermediate material 51 is taken out from the floating die 44 and subjected to the next third step. The device is inserted into the third cavity 53 of the die 52. Further, the front end portion (upper end portion side) of the spacer 49a biased upward by the spring 50a is fitted into the concave hole 40 without any gap. The second intermediate material 51 is crushed in the axial direction by the pressing punch 32b while the second intermediate material 51 is suppressed by the floating die 44a disposed around the pressing punch 32b. And it is set as the 3rd intermediate material 54 as shown to (D) of FIG. 1, and FIG. 6 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 44a remains pressed against the upper surface of the die 52 by the elasticity of the springs 46a and 46a.

When the third intermediate material 54 is formed as described above, the pressing punch 32b is raised, and then the raising / lowering piece 37b that has been lowered is raised and the knockout pins 36b and 36b are interposed. The sleeve 35b is raised. As a result, the third intermediate material 54 is pushed out from the third cavity 53, and the third intermediate material 54 is taken out of the die 52 and sent to the next step.
In this next step, in the third intermediate material 54, the inner diameter of the portion near the opening of the concave hole 40 is expanded by a cutting process such as turning, and this part is used as another concave hole 40a. A fourth intermediate material 55 as shown in (E) of FIG.
The fourth intermediate material 55 is further sent to the next step, and subjected to necessary processing such as surface pressing, cutting, and grinding to complete the hub body 9b. 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. However, in this example, the inner peripheral surface of the circular hole 56 through which the stud 17 is inserted is covered with a sealant to prevent electrolytic corrosion.

  Then, the inner ring 10a is externally fitted to the small-diameter step portion 12a of the hub main body 9b manufactured in this way, a jig is inserted into the another concave hole 40a, and the axial inner end portion of the small-diameter step portion 12a is inserted. The caulking portion 57 is formed by caulking outward in the radial direction. Thus, the hub 3a is formed by supporting and fixing the inner ring 10a to the inner end of the hub body 9b in the axial direction. By supporting the hub 3a on the outer ring 2 via the rolling elements 4 and 4, a wheel support rolling bearing unit 1a is configured. The inner ring opening of the outer ring 2 is closed with a bottomed cylindrical cover (not shown) to prevent infiltration of dust and rain water into the inner diameter side space of the outer ring 2, and the inner diameter side space. Prevent leakage of grease filled in the outside.

  According to the hub body manufacturing method of this example as described above, an increase in the weight of the hub body 9b to be manufactured can be suppressed, and the entire wheel support rolling bearing unit 1a incorporating the hub body 9b can be reduced in weight. That is, since the core portion of the hub body 9b is made of a light alloy and the outer portion is made of an iron alloy, the hub body is made of only an iron alloy as in the conventional structure described above. The hub body 9b can be reduced in weight. Further, in the hub main body 9b, the same iron system as that constituting the respective members 4, 10a is formed on the surface portion which is a portion in contact with the rolling elements 4, 4 and the inner ring 10a constituting the wheel supporting rolling bearing unit 1a. Since the alloy is used, it is possible to ensure the required hardness for the surface portion and to prevent the surface portion from being damaged by electrolytic corrosion. The inner end of the hub body 9b in the axial direction is shielded from the external space by a cap that closes the inner end opening of the outer ring 2 in use, as in the known conventional structure. Absent.

  Further, in the case of this example, when the outer diameter of the tip end portion (lower end portion in FIG. 1) of the material 28 is reduced to form the first intermediate material 33, the counter punch 34 causes the cylindrical surface portion 38 on the small diameter side. A bottomed recessed hole 40 is formed at the center of the substrate. At this time, since the height H of the core material 26 is smaller than the depth D of the surface layer material 27 and the step portion 29 is provided, the fluidity is higher than the iron-based alloy constituting the surface layer material 27. It can prevent that the light alloy which comprises the said core material 26 protrudes from the front end surface (lower end surface of FIG. 1, 2) of said 1st intermediate raw material 33. FIG. In addition, since the core material 26 is made of a light alloy and the surface layer material 27 is made of an iron-based alloy, the sliding property between the core material 26 and the surface layer material 27 can be improved. In the material 27, the difference in the moving speed of the respective metal materials can be suppressed small, and the above-mentioned chevron crack can be prevented. Further, in the process of making the tip portion of the material 28 into the cylindrical surface portion 38 on the small diameter side, the flow of the metal material inside the material 28 can be rectified, causing the chevron crack to occur. 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 28 to the first intermediate material 33 is reduced, and the occurrence of the chevron crack can be suppressed. Further, by forming the concave hole 40 while crushing the central portion of the distal end portion of the material 28, a compressive stress is generated in the first intermediate material 33 obtained by plastic deformation of the material 28. Arise. This compressive stress can prevent a gap from being generated between the core material 26 and the surface layer material 27. Further, as is well known in the field of metalworking, 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 40. The compressive stress generated in the first intermediate material 33 in the first step contributes to prevention of cracks in the second step, and the second intermediate material 51 of the second step 51 Prevents chevron cracks from occurring inside.

  In the case of this example, since the core material 26 is softer than the iron-based alloy and is made of a light alloy such as an aluminum-based alloy, the force required for cold forging the material 28 is the same as that of the conventional structure described above. In this way, the material can be made smaller compared to the case where the material is made of only an iron alloy. Further, the force required to form the concave hole 40 by pushing the counter punch 34 from the front end surface of the material 28 into the front end portion of the material 28 may be small. Accordingly, the force required to form the small-diameter cylindrical surface portion 38 at the distal end portion of the material 28 is not significantly increased compared to the case where the concave hole 40 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 38 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 main body 9b manufactured by the manufacturing apparatus can be prevented from increasing.

[Second Example of Embodiment]
FIGS. 8-9 has shown the 2nd example of embodiment of this invention corresponding to Claims 1-5,7,8. In the case of this example, a small-diameter portion 58 having a smaller outer diameter than the middle portion is provided at the back end portion (upper end portion in FIG. 8) of the core material 26a of the material 28a. Accordingly, when the radial rotation side flange 7b is provided on the outer peripheral surface in the third step {(C) → (D)} in FIG. 8 in which the second intermediate material 51a is processed into the third intermediate material 54a, the stud 17 is provided. It is possible to prevent the light alloy constituting the core material 26a from entering the portion where the circular hole 56 is inserted. As a result, it is possible to prevent the light alloy from being exposed to the inner diameter side of the circular hole 56 after the circular hole 56 is formed. Therefore, it is troublesome to apply a sealing agent to the circular hole 56 portion in order to prevent electrolytic corrosion. Is no longer necessary.
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.

[Third example of embodiment]
FIG. 10 shows a third example of an embodiment of the present invention corresponding to claims 1 to 5. In the case of this example, in the first step {(A) → (B)} in FIG. 10) of processing the material 28 into the first intermediate material 33a, the concave hole 40b formed at the tip of the first intermediate material 33a. 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. 10}, in which the first intermediate material 33a is the second intermediate material 51b, the axial position of the back end surface of the concave hole 40b 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. In the case of this example, of the surface layer material 27 of the first intermediate material 33a, a portion that exists on the outer diameter side of the portion that forms the recessed hole 40b (is located on the outer side in the axial direction than the portion that forms the step portion 25a). The inner peripheral surface (up to the part) is cylindrical. As a result, the core member 26 can be made difficult to protrude from the inner peripheral surface of the concave hole 40b. Particularly, by making the shape of the tip of the counter punch 34 as shown in FIG. 4 described above, the protruding amount of the core material 26 can be further suppressed.
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.

[Fourth Example of Embodiment]
FIG. 11 shows a fourth example of an embodiment of the present invention corresponding to claims 1 to 4 and 6. In the case of this example, the first step {(A) → (B)} in FIG. 11 for processing the material 28 into the first intermediate material 33b is performed in the same manner as the conventional method shown in FIGS. . Then, in the second step {(B) → (C)} in FIG. 11) in which the first intermediate material 33b is used as the second intermediate material 51c, the second step is performed by the counter punch 34 (see FIG. 2). A concave hole 40 is formed in the center of the tip of the intermediate material 51c. Further, a small-diameter step portion 12a is formed near the tip of the second intermediate material 51c, and a step portion 25a is formed at an axially intermediate portion (base end portion of the small-diameter step portion 12a) near the tip.

At the time of the first step, since the material 28 is not yet work hardened, chevron cracks do not occur inside the obtained first intermediate material 33b. On the other hand, in the second step of obtaining the second intermediate material 51c, the outer diameter of the tip of the first intermediate material 33b 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 example, the concave hole 40 is formed in the front end surface of the first intermediate material 33b in such a second step so as to prevent the occurrence of the chevron crack.
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.

  In each example of the embodiment of the present invention described above, the forward extrusion processing for providing a plurality of cylindrical surface portions having different outer diameters is performed in two stages of the first process and the second process. However, when the value (drawing rate) obtained by dividing the outer diameter of the smallest cylindrical surface portion by the outer diameter of the raw material before processing is 1/2 or more among the processed cylindrical surface portions, the front where the respective cylindrical surface portions are provided. Extrusion can also be performed in one step.

  Moreover, the wheel support which applies the manufacturing method of the stepped cylindrical member as described in any one of Claims 1-3 among the manufacturing method of the stepped cylindrical member of this invention, and the rolling bearing unit for wheel support. The manufacturing method of the hub main body constituting the rolling bearing unit for use is not limited to the manufacturing method of each example of the embodiment of the present invention described above. That is, if the generation of chevron cracks is not a problem, or if the generation of chevron cracks can be prevented by another method, the conventional hub body manufacturing method described above is incorporated in the stepped cylindrical shape of the present invention. The manufacturing method of a member can also be applied.

  Moreover, the manufacturing method of the stepped columnar member of the present invention can provide a remarkable effect when a hub body constituting a wheel support rolling bearing unit for a driven wheel is manufactured. However, as long as it is an article in which a portion that overlaps in a plurality of stages is subjected to forward extrusion and the part has a stepped shape, the present invention can be applied not only to the hub body but also to the manufacture of the article.

DESCRIPTION OF SYMBOLS 1, 1a Rolling bearing unit for wheel support 2 Outer ring 3, 3a Hub 4 Rolling element 5 Outer ring raceway 6 Stationary side flange 7, 7a, 7b Rotation side flange 8 Inner ring raceway 9, 9a Hub body 10, 10a Inner ring 11 Nut 12, 12a Small diameter step portion 13 Material 14 First intermediate material 15 Second intermediate material 16 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 part 26, 26a Core material 27 Surface layer material 28, 28a Material 29 Step part 30 Dies 31 Cavity 32, 32a, 32b Press punch 33, 33a, 33b First intermediate material 34 Counter punch 35, 35a Sleeve 36, 36a, 36b Knockout pin 37, 37a, 37b Elevating piece 38 Cylindrical surface portion 3 on the small diameter side 3 9 Inclined step 40, 40a Recessed hole 41 Inclined surface 42 Ring 43 Bolt 44, 44a Floating die 45 Second cavity 46, 46a Spring 47 Fixed block 48 Second sleeve 49, 49a Spacer 50, 50a Spring 51, 51a-51c First Second intermediate material 52 Die 53 Third cavity 54, 54a Third intermediate material 55 Fourth intermediate material 56 Circular hole 57 Caulking portion 58 Small diameter portion

This invention relates to an improvement in a wheel supporting rolling bearing unit comprising a hub body.

  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. 12 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 arranged at two positions on the inner peripheral surface of the outer ring 2 at a part of the outer peripheral surface, slightly inwardly in the axial direction from the central part in the axial direction. Means the side that is the central side in the width direction of the vehicle body in the used state, and the right side of Fig. 12. Conversely, the left side in Fig. 12 that is the outside in the width direction of the vehicle body in the used state is referred to as the 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. Among these, the structure of the hub main 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. 13 has a radial rotation-side flange 7a near the outer peripheral portion of the outer peripheral surface in the axial direction, an inner ring raceway 8 at the middle portion, and a small-diameter step portion 12 at the inner end portion. , Each formed.
Such a hub main body 9a is manufactured by the process 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 a sizing process for forming seating surfaces 19 and 19 for contacting the axial side surface of the head 18 (see FIG. 12) of the stud 17 (FIG. The fourth intermediate material 20 shown in E) is used.

  In the axially inner end {the lower end of (E) in each figure} of the fourth intermediate material 20 is a male thread 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 a nut 11), or as shown in FIG. 15 (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.

  It is desired to reduce the weight of the hub body 9a manufactured as described above. That is, the wheel-supporting rolling bearing unit 1 (see FIG. 12) in which the hub body 9a is incorporated is a so-called unsprung load provided on the road surface side of the spring constituting the suspension device. In order to improve the driving performance centering on the characteristics, it is desirable to reduce the weight as much as possible. In the case of the manufacturing method described in Patent Document 4, generally, the hub body 9a is made by subjecting an iron-based alloy such as medium-carbon steel to cold forging, so that the weight of the hub body 9a is bulky. Thus, the weight of the wheel supporting rolling bearing unit 1 as a whole also increases.

  In the case of the manufacturing method described in Patent Document 4, the hub main body 9a is manufactured mainly by cold forging, with cutting and grinding being minimized. For this reason, while improving the yield of material, the processing time which these cutting processing and grinding processing require can be shortened, and the cost reduction of the wheel bearing rolling bearing unit 1 (refer FIG. 12) including the said hub main body 9a can be aimed at. . However, as shown in FIGS. 14 to 16 described above, when the hub main body 9a is manufactured by using the forward extrusion process in the cold, the axially 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 body 9a is manufactured as shown in FIGS. 14 to 16 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 generation 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.

  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

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

The present invention is, in view of the circumstances as described above, it is possible to prevent the occurrence of chevron cracks is obtained by the invention to realize a structure of lightweight wheel supporting rolling bearing unit.

The stepped columnar member including the hub body constituting the wheel bearing rolling bearing unit that is the subject of the present invention includes a plurality of cylindrical surface portions having different outer diameters on the outer peripheral surface. And among these cylindrical surface parts, the adjacent cylindrical surface parts are made to continue by the step part.
In addition, the manufacturing method of the stepped columnar member is made of a light alloy core material such as an aluminum alloy and an iron alloy material such as medium carbon steel, and covers the outer portion excluding the end of the core material. A material composed of a bottom cylindrical surface layer material is cold forged.

When implementing the manufacturing method of the stepped columnar member as described above, preferably , the material is made by fitting the core material to the inner diameter side portion of the surface layer material.
Also, if this, preferably, the height dimension of said core member, is smaller than the depth dimension of the center hole of the surface layer member.

Also, before SL material pushes the leading end of (the pre-obtained by subjecting a previous step to the material comprising the intermediate material) in the die, by applying a forward extrusion, the outer tip portion of said material Shrink the diameter. 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 . Then, when forming the cylindrical surface portion and the stepped portion of the small diameter side, the central portion of the front end surface of the material was placed on the inner diameter side of the die, the small diameter of the counter than the outer diameter of the cylindrical surface portion of the small diameter side While pressing against the front end surface of the punch, the front end portion of the material is pressed into the die. And by this pushing, the outer diameter of the tip portion of this material is reduced to form the cylindrical surface portion on the small diameter side and the stepped portion, and at the same time, at least in the portion near the tip of the central portion of the cylindrical surface portion on the small diameter side, A bottomed recessed hole is formed at the center of the distal end surface.

In this case, For example, first, by applying a forward extrusion of the first stage cylindrical material, after the first intermediate material has a smaller diameter than the proximal end portion near the distal end portion closer, the first A second-stage forward extrusion process is performed on the tip portion of the intermediate material, and a second cylindrical surface portion having a smaller diameter than the cylindrical surface portion on the small diameter side is provided at the tip portion, and an axially intermediate portion of the tip portion is provided. Let the second step part be a second intermediate material.
Then, before Symbol while pressing the distal end surface of the counter punch on the central portion of the front end surface of the material, the material, and the first intermediate material having a concave hole at the center portion of the distal end surface. Next, the first intermediate material is processed into the second intermediate material with a spacer fitted in the concave hole.
Alternatively , when the material is the first intermediate material, the concave hole is not formed. Instead, the first intermediate material is used as the second intermediate material while the front surface of the counter punch is pressed against the center of the front surface of the first intermediate material to form the concave hole.

Also, pre-Symbol a recessed holes in the back end surface of the center hole of the surface layer material, a small diameter portion which engages without gaps and the concave hole on the base end portion of the core member, respectively provided. Then, the core material is tightly fitted to the inner diameter side portion of the surface layer material to form the material, and the cylindrical surface portion and the stepped portion are formed on the material by cold forging to form an intermediate material. Then, a radial flange is provided on the outer peripheral surface of the intermediate material near the base end by subjecting the intermediate material to side extrusion.

According to the manufacturing method of the stepped columnar member configured as described above, a lightweight stepped columnar member is manufactured while preventing the occurrence of chevron cracks. It is possible to reduce the weight of the rolling bearing unit for wheel support according to the present invention. That is, since this stepped columnar member is made by cold forging a material made of a light alloy core material and a surface layer material made of an iron-based alloy and covering the outer portion of the core material, these cores are made. The sliding property between the material and the surface layer material can be improved, and the difference in the moving speed of the respective metal materials can be suppressed small inside the core material and the surface layer material, thereby preventing the occurrence of chevron cracks. Further, as compared with the case where the whole is made of an iron-based alloy such as medium carbon steel as in the conventional structure described above, it is possible to suppress an increase in the weight of the stepped columnar member.

Furthermore, if a bottomed concave hole is formed at the center of the cylindrical surface portion on the small diameter side, the occurrence of chevron cracks can be more effectively prevented even when the outer surface shape of the stepped columnar member is limited, It is possible to prevent the yield of the material from deteriorating and complication of processing.
That is, when the outer diameter of the tip of the material is reduced, a bottomed concave hole is formed in the central portion of the cylindrical surface portion on the small diameter side by the counter punch. For this reason, the flow of the metallic material inside the material can be adjusted in the process of making the tip of the 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 that causes the chevron crack can be reduced. In particular, the difference in the moving speed of the metal material can be reduced at the surface layer portion made of an iron-based alloy, which is an important portion from the viewpoint of securing the strength. The fact that this difference can be reduced leads to a reduction in tensile stress generated in the material, particularly the surface layer material, and the generation of the chevron cracks can be suppressed. Furthermore, compressive stress is generated inside the material by forming the concave hole while crushing the center of the tip of the material. This compressive stress prevents a gap from being generated between the core material and the surface layer material. Further, as is well known in the field of metal processing, the compressive stress has an action of suppressing the generation of cracks, and therefore, the generation of cracks such as the chevron cracks can be suppressed based on the formation of the concave holes.

In addition, the flow of the metallic material inside the material is arranged, and the counter punch is moved from the front end surface of the material to the inside of the front end portion of the material in order to make the inside of the material a compressive stress field or a state close thereto. Although the concave hole is formed by pushing, the force required for the pushing may be small. For this reason, the force required to form the cylindrical surface portion on the small diameter side at the tip end portion of the material is not significantly increased as compared with the case where the concave hole is not formed (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 rolling bearing unit for supporting a wheel according to the present invention includes an outer ring, a cover, a hub, and a rolling element.
Among these, the outer ring has a double row outer ring raceway on the inner peripheral surface, and does not rotate during use.
The cover closes the axially inner end opening of the outer ring.
The hub rotates together with the wheel when in use, and includes a hub body and an inner ring. Hub body of this, the outer peripheral surface of the axially outer end portion near the radial rotation side flange for supporting and fixing the wheel, an inner ring raceway of the axially outer axially intermediate portion outer peripheral surfaces, respectively directly Forming. Further, the inner ring forms an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and is fitted and fixed to a small-diameter step portion formed at the inner end in the axial direction of the hub body.
Further, a plurality of rolling elements are provided between the inner ring raceways and the outer ring raceways so as to roll freely in each row.
In particular, in the case of the rolling bearing unit for supporting a wheel according to the present invention, the core portion of the hub body is made of a light alloy, and the surface portion covering the core portion is made of an iron-based alloy. Furthermore, the core part of the rotation side flange is constituted by a part of a light alloy constituting the core part of the hub body.
When the rolling bearing unit for supporting a wheel according to the present invention as described above is implemented, a stud for supporting and fixing the wheel is preferably inserted into the rotation side flange as in the invention described in claim 2. For this purpose, a light alloy constituting the hub body is exposed on the inner peripheral surface of the circular hole, and the inner peripheral surface of the circular hole is covered with a sealant.

According to the wheel support rolling bearing unit of the present invention configured as described above, the core portion of the hub body is made of a light alloy and the outer portion is also made of an iron-based alloy. Compared with the case where the hub body is made of only an iron-based alloy, the hub body can be reduced in weight. In addition, the surface of the hub body that is in contact with the rolling elements and the inner ring constituting the rolling bearing unit for supporting the wheel is made of the same iron-based alloy as that constituting the rolling elements and the inner ring. It is possible to secure the hardness required for the portion and to prevent the surface portion from being damaged by electrolytic corrosion. The inner end of the hub body in the axial direction is shielded from the external space by a cover that closes the inner end opening of the outer ring in use, as in the known conventional structure, so that electric corrosion does not occur. . Further, since the hub body can be made by cold forging a material made of a light alloy core material and a surface layer material made of an iron-based alloy and covering the outer portion of the core material, these cores can be made. The sliding property between the material and the surface layer material can be improved, and the difference in the moving speed of the respective metal materials can be suppressed small inside the core material and the surface layer material, thereby preventing the occurrence of chevron cracks.

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, the fragmentary sectional view which shows another example. Sectional drawing which shows the state immediately after processing a 1st intermediate material into a 2nd intermediate material with the metal mold apparatus. Sectional drawing which shows the state immediately after processing the 2nd intermediate material into the 3rd intermediate material with the metal mold apparatus. The figure similar to FIG. 12 which shows the 1st example of embodiment of this invention. The figure similar to FIG. 1 which shows the 2nd example. Similarly, the same figure as FIG. The figure similar to FIG. 1 which shows the 3rd example of embodiment of this invention. The figure similar to FIG. 1 which shows the 4th example. 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]
1 to 7 show a first example of an embodiment of the present invention. In the case of this example, first, in the first step, the core 26 made of an aluminum alloy such as A7075 or A6061 and the iron alloy such as medium carbon steel shown in FIG. The material 28 composed of the surface layer material 27 that covers the outer portion of the material 26 is cold-extruded forward. Such a material 28 is formed by fitting a columnar core material 26 into the inner diameter side portion of the bottomed cylindrical surface material 27 with an interference fit, and between the core material 26 and the surface material 27. Good slipperiness. In the case of this example, the height H of the core material 26 is made smaller than the depth D of the center hole of the surface layer material 27, and the step portion 29 is provided at the end of the material 28. The depth (DH) of the stepped portion 29 is such that the fluidity of the aluminum-based alloy constituting the core material 26 and the iron-based alloy constituting the surface layer material 27, and the first and second intermediate materials 33 described later. , 51 in consideration of the shape and aperture ratio. In the first step of cold forging the material 28, first, the material 28 is inserted into a cavity 31 of a die 30 formed by stacking a plurality of blocks as shown in FIG. Thereafter, the material 28 is pushed into the cavity 31 by a pressing punch 32 pressed by a ram of a pressing device (not shown). The material 28 is plastically deformed by the pushing operation, and the material 28 has an outer peripheral surface shape that matches the inner peripheral surface shape of the cavity 31 (the bus bar shape is the same and the concavity and convexity are reversed). It becomes.

  In particular, in the case of the manufacturing method of this example, the upper end portion of the counter punch 34 is projected from the lower end center portion of the cavity 31. The lower end portion of the counter punch 34 is clamped and fixed between the upper surface of the lowermost block among the plurality of blocks constituting the die 30 and the next block. A cylindrical sleeve 35 is fitted around the counter punch 34 so as to be movable up and down. The lower portion of the cavity 31 is defined by the upper end surface of the sleeve 35, the outer surface of the upper end portion of the counter punch 34, and the inner peripheral surface of the uppermost block. Further, the lower end surfaces of the knockout pins 36, 36 each abutting the upper end surface against the lower end surface of the sleeve 35 are abutted against the upper surface of the elevating piece 37 fitted in the lowermost block.

  When the material 28 is pushed into the cavity 31 using the mold apparatus shown in FIG. 2 as described above, the outer peripheral surface of the tip (lower end) of the material 28 is brought to the inner peripheral surface of the cavity 31. The first intermediate material 33 is plastically deformed along the line. That is, at the distal end portion of the first intermediate material 33, a cylindrical surface portion 38 on the small diameter side, and an inclined step portion 39 that continues from the base end side of the cylindrical surface portion 38 on the small diameter side and continues to the larger diameter portion Form. At the same time, the upper end portion of the counter punch 34 is pushed into the central portion of the first intermediate material 33 (the central portion of the core member 26) of the cylindrical surface portion 38 on the small diameter side, and this cylindrical surface portion on the small diameter side A bottomed concave hole 40 having a circular cross-sectional shape that opens at the front end surface of the first intermediate material 33 is formed at the center of the first intermediate material 33.

  The outer diameter and axial length of the counter punch 34 for forming the concave hole 40 are the same as those of the aluminum alloy and the surface layer material 27 constituting the core material 26 of the material 28 to the first intermediate material 33. This is determined by design consideration in consideration of the fluidity of the iron-based alloy to be constructed and the durability of the counter punch 34. The larger the outer diameter of the counter punch 34, the greater the degree of work hardening of the peripheral portion of the concave hole 40 at the tip of the first intermediate material 33, instead of improving its durability. Then, it becomes difficult to plastically deform (clamp and spread) the distal end portion (axially inner end portion) of the hub body 9b after completion in the radial direction. Considering these points, the outer diameter of the counter punch 34 is restricted to about 1/3 to 2/3, most preferably about 1/2 of the outer diameter of the cylindrical surface portion 38 on the small diameter side. Further, the depth of the concave hole 40 determined by the axial length of the counter punch 34 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 32 is lowered to the bottom dead center and the processing of the first intermediate material 33 is completed, the depth of the concave hole 40 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 34 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. Alternatively, as shown in FIG. 4, it is possible to employ a counter punch 34 in which an inclined surface portion 41 is provided at the tip portion, and a ring 42 made of a copper alloy such as brass is supported and fixed to the inclined surface portion 41 by a bolt 43. . When the tip of the counter punch 34 is pushed into the central portion of the cylindrical surface portion 38 on the small diameter side, as shown exaggeratedly in FIG. 4, along the inclined surface portion 41 due to the hydrostatic pressure of the core member 26. Thus, the diameter of the ring 42 is elastically expanded outward in the radial direction of the counter punch 34. As a result, when the counter punch 34 is pushed in, the core material 26 or the surface layer material 27 present in the outer peripheral surface of the ring 42 and the central portion of the first intermediate material 33 is slidably contacted without gaps, It is possible to prevent a part of the core material 26 from protruding from the inner peripheral surface of the concave hole 40 (this inner peripheral surface can be made smooth). Since this ring 42 is a copper-based alloy different from the aluminum-based alloy constituting the core material 26 and the iron-based alloy constituting the surface layer material 27 and the counter punch 34, the ring 42 and the first intermediate The slipperiness of the contact portion with the material 33 can be improved.

  In any case, if the pressing punch 32 is lowered to the bottom dead center and the first intermediate material 33 is formed, the raising / lowering piece that has been lowered until then is raised after the pressing punch 32 is raised. 37 is raised, and the sleeve 35 is raised via the knockout pins 36, 36. As a result, the first intermediate material 33 is pushed out of the cavity 31, so that the first intermediate material 33 is taken out from the die 30 and subjected to the next second step, so that the mold apparatus shown in FIG. It is inserted into the second cavity 45 of the floating die 44. The floating die 44 is supported by a plurality of springs 46 and 46 so as to be able to move up and down so as to descend when a large downward force is applied above the fixed block 47. The upper end portion of the second sleeve 48 placed and fixed on the upper surface of the fixed block 47 is fitted into the lower end portion of the floating die 44 so as to be capable of axial displacement (sliding in the vertical direction). Further, the upper end portion of the sleeve 35a, which is installed on the inner diameter side of the fixed block 47, is fitted into the lower end portion of the second sleeve 48 so as to be capable of axial displacement (up and down sliding). ing.

  In addition, a spacer 49 having substantially the same outer shape as the counter punch 34 is provided inside the sleeve 35a so as to be able to move up and down independently of the sleeve 35a. In the case of this example, a spring 50 is provided between the lower end surface of the spacer 49 and the fixing plate that constitutes the fixing block 47, and an upward elasticity is applied to the spacer 49. With the first intermediate material 33 (see FIG. 1B and FIG. 2) inserted into the second cavity 45, the upper end surface of the spacer 49 abuts against the inner end surface of the concave hole 40. Then, the upper end surface of the spacer 49 is kept in contact with the inner end surface of the concave hole 40 during the progress of the second step for processing the first intermediate material 33 into the second intermediate material 51. The inner surface shape of the lower portion of the second cavity 45 is defined by the inner peripheral surface and the front end surface (upper end surface) of the second sleeve 48, the upper end surface of the sleeve 35a, and the outer peripheral surface and front end surface of the spacer 49. Made. Further, by pushing the lower end portion of the pressing punch 32 a into the floating die 44, the outer surface shape of the first intermediate material 33 can be plastically deformed (forward extrusion molding) in accordance with the inner surface shape of the second cavity 45. It is said.

  When the first intermediate material 33 is pushed into the second cavity 45 with a large force using the mold apparatus shown in FIG. 5 as described above, the lower portion of the first intermediate material 33 is moved to the second intermediate material 33. The second intermediate material 51 is plastically deformed along the inner surface of the cavity 45. That is, the distal end portion or the axial intermediate portion of the cylindrical surface portion 38 on the small diameter side of the distal end portion of the first intermediate material 33 exists between the inner peripheral surface of the second sleeve 48 and the outer peripheral surface of the spacer 49. 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 38 on the small diameter side. Further, in a state where the pressing punch 32a is lowered to the bottom dead center, the portion pressed by the tip surface (upper end surface) of the second sleeve 48 is the inner ring 10a (see FIG. 7) in a state where the hub 3a is assembled. It becomes the step part 25a for abutting the axial direction outer end surface. The spacer 49 is lowered until the lower end surface of the spacer 49 comes into contact with the upper surface of a part of the fixed block 47 while compressing the spring 50 with the progress of the second step as described above. To do. Accordingly, while the second step proceeds, the tip end surface of the spacer 49 remains pressed against the back end surface of the concave hole 40. With the progress of the second step, 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 38 on the small diameter side that should become the small diameter step portion 12a. And the depth of the concave hole 40 is increased accordingly.

  When the second intermediate material 51 is formed as described above, the pressing punch 32a is raised. Then, the floating die 44 is slightly raised by the elasticity of the springs 46 and 46, and the spacer 49 is slightly raised by the elasticity of the spring 50. Therefore, following the ascent of these members 44, 49, the elevating piece 37a that has been lowered is raised, and the sleeve 35a is raised via the knockout pins 36a, 36a. As a result, since the second intermediate material 51 is pushed out from the second cavity 45, the second intermediate material 51 is taken out from the floating die 44 and subjected to the next third step. The device is inserted into the third cavity 53 of the die 52. Further, the front end portion (upper end portion side) of the spacer 49a biased upward by the spring 50a is fitted into the concave hole 40 without any gap. The second intermediate material 51 is crushed in the axial direction by the pressing punch 32b while the second intermediate material 51 is suppressed by the floating die 44a disposed around the pressing punch 32b. And it is set as the 3rd intermediate material 54 as shown to (D) of FIG. 1, and FIG. 6 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 44a remains pressed against the upper surface of the die 52 by the elasticity of the springs 46a and 46a.

When the third intermediate material 54 is formed as described above, the pressing punch 32b is raised, and then the raising / lowering piece 37b that has been lowered is raised and the knockout pins 36b and 36b are interposed. The sleeve 35b is raised. As a result, the third intermediate material 54 is pushed out from the third cavity 53, and the third intermediate material 54 is taken out of the die 52 and sent to the next step.
In this next step, in the third intermediate material 54, the inner diameter of the portion near the opening of the concave hole 40 is expanded by a cutting process such as turning, and this part is used as another concave hole 40a. A fourth intermediate material 55 as shown in (E) of FIG.
The fourth intermediate material 55 is further sent to the next step, and subjected to necessary processing such as surface pressing, cutting, and grinding to complete the hub body 9b. 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. However, in this example, the inner peripheral surface of the circular hole 56 through which the stud 17 is inserted is covered with a sealant to prevent electrolytic corrosion.

  Then, the inner ring 10a is externally fitted to the small-diameter step portion 12a of the hub main body 9b manufactured in this way, a jig is inserted into the another concave hole 40a, and the axial inner end portion of the small-diameter step portion 12a is inserted. The caulking portion 57 is formed by caulking outward in the radial direction. Thus, the hub 3a is formed by supporting and fixing the inner ring 10a to the inner end of the hub body 9b in the axial direction. By supporting the hub 3a on the outer ring 2 via the rolling elements 4 and 4, a wheel support rolling bearing unit 1a is configured. The inner ring opening of the outer ring 2 is closed with a bottomed cylindrical cover (not shown) to prevent infiltration of dust and rain water into the inner diameter side space of the outer ring 2, and the inner diameter side space. Prevent leakage of grease filled in the outside.

According to the hub body manufacturing method of this example as described above, an increase in the weight of the hub body 9b to be manufactured can be suppressed, and the entire wheel support rolling bearing unit 1a incorporating the hub body 9b can be reduced in weight. That is, since the core portion of the hub body 9b is made of a light alloy and the outer portion is made of an iron alloy, the hub body is made of only an iron alloy as in the conventional structure described above. The hub body 9b can be reduced in weight. Further, in the hub main body 9b, the same iron system as that constituting the respective members 4, 10a is formed on the surface portion which is a portion in contact with the rolling elements 4, 4 and the inner ring 10a constituting the wheel supporting rolling bearing unit 1a. Since the alloy is used, it is possible to ensure the required hardness for the surface portion and to prevent the surface portion from being damaged by electrolytic corrosion. The inner end of the hub body 9b in the axial direction is shielded from the outer space by a cover that closes the inner end opening of the outer ring 2 in use, as in the known conventional structure. Absent.

  Further, in the case of this example, when the outer diameter of the tip end portion (lower end portion in FIG. 1) of the material 28 is reduced to form the first intermediate material 33, the counter punch 34 causes the cylindrical surface portion 38 on the small diameter side. A bottomed recessed hole 40 is formed at the center of the substrate. At this time, since the height H of the core material 26 is smaller than the depth D of the surface layer material 27 and the step portion 29 is provided, the fluidity is higher than the iron-based alloy constituting the surface layer material 27. It can prevent that the light alloy which comprises the said core material 26 protrudes from the front end surface (lower end surface of FIG. 1, 2) of said 1st intermediate raw material 33. FIG. In addition, since the core material 26 is made of a light alloy and the surface layer material 27 is made of an iron-based alloy, the sliding property between the core material 26 and the surface layer material 27 can be improved. In the material 27, the difference in the moving speed of the respective metal materials can be suppressed small, and the above-mentioned chevron crack can be prevented. Further, in the process of making the tip portion of the material 28 into the cylindrical surface portion 38 on the small diameter side, the flow of the metal material inside the material 28 can be rectified, causing the chevron crack to occur. 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 28 to the first intermediate material 33 is reduced, and the occurrence of the chevron crack can be suppressed. Further, by forming the concave hole 40 while crushing the central portion of the distal end portion of the material 28, a compressive stress is generated in the first intermediate material 33 obtained by plastic deformation of the material 28. Arise. This compressive stress can prevent a gap from being generated between the core material 26 and the surface layer material 27. Further, as is well known in the field of metalworking, 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 40. The compressive stress generated in the first intermediate material 33 in the first step contributes to prevention of cracks in the second step, and the second intermediate material 51 of the second step 51 Prevents chevron cracks from occurring inside.

  In the case of this example, since the core material 26 is softer than the iron-based alloy and is made of a light alloy such as an aluminum-based alloy, the force required for cold forging the material 28 is the same as that of the conventional structure described above. In this way, the material can be made smaller compared to the case where the material is made of only an iron alloy. Further, the force required to form the concave hole 40 by pushing the counter punch 34 from the front end surface of the material 28 into the front end portion of the material 28 may be small. Accordingly, the force required to form the small-diameter cylindrical surface portion 38 at the distal end portion of the material 28 is not significantly increased compared to the case where the concave hole 40 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 38 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 main body 9b manufactured by the manufacturing apparatus can be prevented from increasing.

[Second Example of Embodiment]
8 to 9 show a second example of the embodiment of the present invention. In the case of this example, a small-diameter portion 58 having a smaller outer diameter than the middle portion is provided at the back end portion (upper end portion in FIG. 8) of the core material 26a of the material 28a. Accordingly, when the radial rotation side flange 7b is provided on the outer peripheral surface in the third step {(C) → (D)} in FIG. 8 in which the second intermediate material 51a is processed into the third intermediate material 54a, the stud 17 is provided. It is possible to prevent the light alloy constituting the core material 26a from entering the portion where the circular hole 56 is inserted. As a result, it is possible to prevent the light alloy from being exposed to the inner diameter side of the circular hole 56 after the circular hole 56 is formed. Therefore, it is troublesome to apply a sealing agent to the circular hole 56 portion in order to prevent electrolytic corrosion. Is no longer necessary.
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.

[Third example of embodiment]
FIG. 10 shows a third example of the embodiment of the present invention. In the case of this example, in the first step {(A) → (B)} in FIG. 10) of processing the material 28 into the first intermediate material 33a, the concave hole 40b formed at the tip of the first intermediate material 33a. 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. 10}, in which the first intermediate material 33a is the second intermediate material 51b, the axial position of the back end surface of the concave hole 40b 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. In the case of this example, of the surface layer material 27 of the first intermediate material 33a, a portion that exists on the outer diameter side of the portion that forms the recessed hole 40b (is located on the outer side in the axial direction than the portion that forms the step portion 25a). The inner peripheral surface (up to the part) is cylindrical. As a result, the core member 26 can be made difficult to protrude from the inner peripheral surface of the concave hole 40b. Particularly, by making the shape of the tip of the counter punch 34 as shown in FIG. 4 described above, the protruding amount of the core material 26 can be further suppressed.
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.

[Fourth Example of Embodiment]
FIG. 11 shows a fourth example of the embodiment of the present invention. In the case of this example, the first step {(A) → (B)} in FIG. 11 for processing the material 28 into the first intermediate material 33b is performed in the same manner as the conventional method shown in FIGS. . Then, in the second step {(B) → (C)} in FIG. 11) in which the first intermediate material 33b is used as the second intermediate material 51c, the second step is performed by the counter punch 34 (see FIG. 2). A concave hole 40 is formed in the center of the tip of the intermediate material 51c. Further, a small-diameter step portion 12a is formed near the tip of the second intermediate material 51c, and a step portion 25a is formed at an axially intermediate portion (base end portion of the small-diameter step portion 12a) near the tip.

At the time of the first step, since the material 28 is not yet work hardened, chevron cracks do not occur inside the obtained first intermediate material 33b. On the other hand, in the second step of obtaining the second intermediate material 51c, the outer diameter of the tip of the first intermediate material 33b 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 example, the concave hole 40 is formed in the front end surface of the first intermediate material 33b in such a second step so as to prevent the occurrence of the chevron crack.
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.

  In each example of the embodiment of the present invention described above, the forward extrusion processing for providing a plurality of cylindrical surface portions having different outer diameters is performed in two stages of the first process and the second process. However, when the value (drawing rate) obtained by dividing the outer diameter of the smallest cylindrical surface portion by the outer diameter of the raw material before processing is 1/2 or more among the processed cylindrical surface portions, the front where the respective cylindrical surface portions are provided. Extrusion can also be performed in one step.

Moreover , the manufacturing method of the hub main body which comprises the rolling bearing unit for wheel support of this invention is not restricted to the manufacturing method of each example of embodiment of this invention mentioned above. That is, if the generation of chevron cracks is not a problem, or if the generation of chevron cracks can be prevented by another method, a light alloy such as an aluminum alloy is added to the above-described conventional hub body manufacturing method. A step for cold forging a material consisting of a core material made of iron and an iron-based alloy such as medium carbon steel, and a bottomed cylindrical surface layer covering the outer portion excluding the end of the core material The manufacturing method of a cylindrical member can also be applied.

Moreover , the manufacturing method of the stepped columnar member can provide a remarkable effect when a hub body constituting a wheel bearing rolling bearing unit for a driven wheel is manufactured. However, as long as it is an article in which a portion that overlaps in a plurality of stages is subjected to forward extrusion and the part has a stepped shape, the present invention can be applied not only to the hub body but also to the manufacture of the article.

DESCRIPTION OF SYMBOLS 1, 1a Rolling bearing unit for wheel support 2 Outer ring 3, 3a Hub 4 Rolling element 5 Outer ring raceway 6 Stationary side flange 7, 7a, 7b Rotation side flange 8 Inner ring raceway 9, 9a Hub body 10, 10a Inner ring 11 Nut 12, 12a Small diameter step portion 13 Material 14 First intermediate material 15 Second intermediate material 16 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 part 26, 26a Core material 27 Surface layer material 28, 28a Material 29 Step part 30 Dies 31 Cavity 32, 32a, 32b Press punch 33, 33a, 33b First intermediate material 34 Counter punch 35, 35a Sleeve 36, 36a, 36b Knockout pin 37, 37a, 37b Elevating piece 38 Cylindrical surface portion 3 on the small diameter side 3 9 Inclined step 40, 40a Recessed hole 41 Inclined surface 42 Ring 43 Bolt 44, 44a Floating die 45 Second cavity 46, 46a Spring 47 Fixed block 48 Second sleeve 49, 49a Spacer 50, 50a Spring 51, 51a-51c First Second intermediate material 52 Die 53 Third cavity 54, 54a Third intermediate material 55 Fourth intermediate material 56 Circular hole 57 Caulking portion 58 Small diameter portion

Claims (8)

  A method of manufacturing a stepped columnar member in which a plurality of cylindrical surface portions having different outer diameters are provided on an outer peripheral surface, and adjacent cylindrical surface portions are continuous with each other by a step portion, comprising: a light alloy core material; A method for producing a stepped columnar member, characterized by cold forging a material made of an alloy and comprising a bottomed cylindrical surface layer material covering an outer portion excluding the end of the core material.   The method for producing a stepped columnar member according to claim 1, wherein the material is produced by tightly fitting the core material to an inner diameter side portion of the surface layer material.   The manufacturing method of the stepped columnar member of Claim 2 which makes the height dimension of the said core material smaller than the depth dimension of the center hole of the said surface layer material.   By pushing the distal end of the material into a die, the outer diameter of the distal end of the material is reduced, and a cylindrical surface portion on the small diameter side is formed on the distal end portion, and a stepped portion is formed on the proximal end portion of the cylindrical surface portion on the small diameter side. When forming each, while pressing the center portion of the tip surface of the material against the tip surface of the counter punch having a smaller diameter than the outer diameter of the cylindrical surface portion on the small diameter side, arranged on the inner diameter side of the die, By pushing the tip of the intermediate material into the die, the outer diameter of the tip of the material is reduced to form the cylindrical surface portion and the step portion on the small diameter side, and at the same time, the central portion of the cylindrical surface portion on the small diameter side The manufacturing method of the stepped columnar member according to any one of claims 2 to 3, wherein a bottomed recessed hole that opens at a central portion of the tip surface is formed at least at a portion near the tip.   By applying a first-stage forward extrusion process to the material, the first intermediate material having a smaller diameter than the proximal end portion is formed in the first intermediate material. A second intermediate having a second cylindrical surface portion with a smaller diameter than the cylindrical surface portion on the small diameter side at the front end portion and a second step portion at the axially intermediate portion of the front end portion. In the process of making the material, while pressing the tip surface of the counter punch against the center portion of the tip surface of the material, the material is the first intermediate material having the concave hole in the center portion of the tip surface, The manufacturing method of the stepped columnar member according to claim 4, wherein the first intermediate material is processed into the second intermediate material in a state where a spacer is fitted in the concave hole.   By applying a first-stage forward extrusion process to the material, the first intermediate material having a smaller diameter than the proximal end portion is formed in the first intermediate material. In the process of subjecting the first intermediate to the second intermediate material, which is subjected to forward extrusion processing, and the cylindrical surface portion on the small diameter side is provided at the tip end portion and the step portion is provided at the axial intermediate portion of the tip end portion. The manufacturing method of the stepped columnar member according to claim 4, wherein the first intermediate material is used as the second intermediate material while pressing the front surface of the counter punch against the front surface of the material.   A concave hole is provided in the back end surface of the center hole of the surface layer material, and a small diameter portion that engages with the concave hole without gap is provided in the base end portion of the core material, and the core material is provided on the inner diameter side portion of the surface material. By making an interference fit into the material, and forming the cylindrical surface portion and the stepped portion by cold forging into an intermediate material, and then subjecting the intermediate material to lateral extrusion, The method for manufacturing a stepped columnar member according to any one of claims 2 to 6, wherein a radial flange is provided on an outer peripheral surface of a portion near the base end of the intermediate material.   An outer ring having a double row outer ring raceway on the inner peripheral surface and not rotating during use, a hub having a double row inner ring raceway on the outer peripheral surface and rotating together with the wheels during use, both the inner ring raceways and the both outer rings A plurality of rolling elements provided in a freely movable manner for each row between the raceway and the hub, wherein the hub is formed by coupling and fixing a hub body and an inner ring, The hub body is formed by directly forming a radial rotation side flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and an inner ring track on the outer side in the axial direction on the outer peripheral surface in the axial direction. The inner ring is formed with an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and is a rolling bearing for wheel support that is externally fitted and fixed to a small-diameter step portion formed near the axial inner end of the hub body. In the unit, the core of the hub body is made of light alloy, and this core A surface portion of a ferrous alloy covering, the wheel support rolling bearing unit, characterized in that constitute respectively.

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