Method for manufacturing ring-shaped member

Abstract

There is provided a method for manufacturing ring-shaped members at a good yield and high production efficiency. To achieve this object, the following is performed. A single (a sequence of) forging produces a joined body formed by radially coupling four cylindrical portions with different inner diameter sizes. A cylindrical member that has the largest inner diameter size and a cylindrical member that has the third largest inner diameter size after the forging are employed as ring-shaped members without change. A rolling process is performed on respective cylindrical member that has the smallest inner diameter size and cylindrical member that has the second largest inner diameter size to obtain ring-shaped members. Thus, two sets of ring-shaped members are obtained as two sets of inner rings and outer rings.

Claims

1. A method for manufacturing a ring-shaped member, comprising: a forging step of forming a joined body from a round bar material, the joined body comprising a plurality of circular-shaped cylindrical portions coupled with each other; a cutting and separating step of cutting and separating the joined body to obtain a plurality of cylindrical members; and a rolling step of expanding an inner diameter size of a part of the plurality of cylindrical members to obtain a ring-shaped member, wherein the joined body comprising a first cylindrical portion, a third cylindrical portion, a second cylindrical portion, and a fourth cylindrical portion, by radially coupling each other, the third cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the first cylindrical portion, the second cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the third cylindrical portion, the fourth cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the second cylindrical portion, the rolling step comprises expanding an inner diameter size of a third cylindrical member such that the third cylindrical member has an inner diameter size identical to an inner diameter size of a first cylindrical member to obtain a third ring-shaped member, and expanding an inner diameter size of a fourth cylindrical member such that the fourth cylindrical member has an inner diameter size identical to an inner diameter size of a second cylindrical member to obtain a fourth ring-shaped member, and wherein the forging step comprises forming the joined body by radially coupling of a bottom end of an inner surface of the first cylindrical portion and an upper end of an outer surface of the third cylindrical portion, an upper end of an inner surface of the third cylindrical portion and a bottom end of an outer surface of the second cylindrical portion, and a bottom end of an inner surface of the second cylindrical portion and an upper end of an outer surface of the fourth cylindrical portion.

2. The method for manufacturing the ring-shaped member according to claim 1, wherein the rolling step includes expanding an inner diameter size of at least one of the third cylindrical member or the fourth cylindrical member while reducing a height of one of the third cylindrical member and/or fourth cylindrical member in an axial direction.

3. The method for manufacturing the ring-shaped member according to claim 1, wherein during the cutting and separating step or after the cutting and separating step, at least one of the third cylindrical member and the fourth cylindrical member is upset.

4. The method for manufacturing the ring-shaped member according to claim 1, wherein the rolling step includes a step of expanding an inner diameter size of the second cylindrical member.

5. The method for manufacturing the ring-shaped member according to claim 2, wherein the rolling step includes a step of expanding an inner diameter size of the second cylindrical member.

6. The method for manufacturing the ring-shaped member according to claim 3, wherein the rolling step includes a step of expanding an inner diameter size of the second cylindrical member.

7. A method for manufacturing a bearing, the method comprising: a forging step of forming a joined body from a round bar material, the joined body comprising a plurality of circular-shaped cylindrical portions coupled with each other; a cutting and separating step of cutting and separating the joined body to obtain a plurality of cylindrical members; and a rolling step of expanding an inner diameter size of a part of the plurality of cylindrical members to obtain a ring-shaped member, wherein the joined body comprising a first cylindrical portion, a third cylindrical portion, a second cylindrical portion, and a fourth cylindrical portion, by radially coupling each other, the third cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the first cylindrical portion, the second cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the third cylindrical portion, the fourth cylindrical portion having an outer diameter size configured to be identical to an inner diameter size of the second cylindrical portion, the rolling step comprises expanding an inner diameter size of a third cylindrical member such that the third cylindrical member has an inner diameter size identical to an inner diameter size of a first cylindrical member to obtain a third ring-shaped member, and expanding an inner diameter size of a fourth cylindrical member such that the fourth cylindrical member has an inner diameter size identical to an inner diameter size of a second cylindrical member to obtain a fourth ring-shaped member, and wherein the forging step comprises forming the joined body by radially coupling of a bottom end of an inner surface of the first cylindrical portion and an upper end of an outer surface of the third cylindrical portion, an upper end of an inner surface of the third cylindrical portion and a bottom end of an outer surface of the second cylindrical portion, and a bottom end of an inner surface of the second cylindrical portion and an upper end of an outer surface of the fourth cylindrical portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates cross-sectional views (a) to (g) of a processing outline of a ring-shaped member in a method for manufacturing the ring-shaped member in a first embodiment;

(2) FIG. 2 illustrates a cross-sectional view of a configuration of a joined body after a forging step in the method for manufacturing the ring-shaped member in the first embodiment;

(3) FIG. 3 illustrates cross-sectional views of configurations of cylindrical members and the ring-shaped members before and after a rolling step in the method for manufacturing the ring-shaped member in the first embodiment;

(4) FIG. 4 illustrates cross-sectional views (a) to (f) of a processing outline of the ring-shaped member in a method for manufacturing the ring-shaped member in a second embodiment;

(5) FIG. 5 illustrates a cross-sectional view of a configuration of a joined body after a forging step in a method for manufacturing a ring-shaped member in a third embodiment;

(6) FIG. 6 illustrates cross-sectional views (a) to (g) of a processing outline of the ring-shaped member in the method for manufacturing the ring-shaped member in the third embodiment;

(7) FIG. 7 illustrates cross-sectional views of configurations of cylindrical members and the ring-shaped members before and after a rolling step in the method for manufacturing the ring-shaped member in the third embodiment;

(8) FIG. 8 illustrates schematic views (a) and (b) of a processing outline of a rolling step in a method for manufacturing a ring-shaped member in one variation of the third embodiment;

(9) FIG. 9 illustrates a cross-sectional view of a configuration of a joined body after a forging step in a method for manufacturing a ring-shaped member in a fourth embodiment;

(10) FIG. 10 illustrates cross-sectional views (a) to (g) of a processing outline of a ring-shaped member in the method for manufacturing the ring-shaped member in the fourth embodiment;

(11) FIG. 11 illustrates cross-sectional views (a) to (c) of a processing outline of a cutting and separating step in a method for manufacturing a ring-shaped member in one variation of the fourth embodiment;

(12) FIG. 12 illustrates a cross-sectional view of a configuration of a joined body after a forging step in a method for manufacturing a ring-shaped member in a fifth embodiment;

(13) FIG. 13 illustrates cross-sectional views (a) to (g) of a processing outline of the ring-shaped member in the method for manufacturing the ring-shaped member in the fifth embodiment; and

(14) FIG. 14 illustrates cross-sectional views of a processing outline of ring-shaped members in a conventional method for manufacturing the ring-shaped member.

DESCRIPTION OF EMBODIMENTS

(15) The following detailed description will describe specific details for complete understanding of embodiments of the present invention. However, it is apparent that one or more embodiments and aspects can be embodied even without the specific details. In addition, for simplification, the drawings abbreviate illustrations of well-known structures and devices.

(16) Hereinafter, a method for manufacturing a ring-shaped member in some embodiment of the present invention will be described with reference to the drawings.

First Embodiment

(17) FIG. 1 illustrates cross-sectional views (a) to (g) of a processing outline of a ring-shaped member in a method for manufacturing the ring-shaped member in the first embodiment.

(18) The method for manufacturing the ring-shaped member in the first embodiment includes a forging step ((a) to (d) of FIG. 1), a cutting and separating step ((e) to (g) of FIG. 1), and a rolling forming step. In the first embodiment, a special technical feature can be found in this forging step.

(19) Forging Step

(20) The forging step is a step of forming a joined body where plural circular-shaped cylindrical members, which are made of a round bar material, are coupled together.

(21) First, a cut billet 2 illustrated in (b) of FIG. 1 is produced using a round bar member 1 illustrated in (a) of FIG. 1 in a method of any one of press cutting, saw cutting, or cutting off. At this time, the cut billet 2 cut out by the press cutting yields poor surface roughness on a cut surface. This may cause a crack or may produce poor squareness of the cut surface in an axial direction, and therefore the cut billet 2 is upset or an end surface of the cut billet 2 is corrected. The cut billet 2 produced by the saw cutting or the cutting off has good roughness on the cut surface and good squareness of the cut surface in the axial direction of the billet. Therefore, the upsetting and the end surface correction may not be performed.

(22) Next, the cut billet 2 is forged to obtain an intermediate formed body 3 as illustrated in (c) of FIG. 1. Then, a joined body 4, which is as illustrated in (d) of FIG. 1, is formed by coupling a first cylindrical portion 4A.sub.1, a second cylindrical portion 4B.sub.1, a third cylindrical portion 4A.sub.2, and a fourth cylindrical portion 4B.sub.2 in a radial direction.

(23) Joined Body

(24) As illustrated in FIG. 2, in the joined body 4, an outer diameter size r.sub.2 of the third cylindrical portion 4A.sub.2 is configured to be almost identical to an inner diameter size r.sub.2 of the first cylindrical portion 4A.sub.1. An outer diameter size r.sub.3 of the second cylindrical portion 4B.sub.1 is configured to be almost identical to an inner diameter size r.sub.3 of the third cylindrical portion 4A.sub.2. An outer diameter size r.sub.4 of the fourth cylindrical portion 4B.sub.2 is configured to be almost identical to an inner diameter size r.sub.4 of the second cylindrical portion 4B.sub.1.

(25) One ends of the first cylindrical portion 4A.sub.1 and the second cylindrical portion 4B.sub.1 in the axial direction are radially coupled to the other ends of the third cylindrical portion 4A.sub.2 and the fourth cylindrical portion 4B.sub.2 in the axial direction. The respective inner diameter sizes and outer diameter sizes of the first cylindrical portion 4A.sub.1, the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, and the fourth cylindrical portion 4B.sub.2 are configured to include machining allowances for a cutting and separating step, which will be described later, in a size of a rolling bearing as a product.

(26) An outer diameter size r.sub.1 of the first cylindrical portion 4A.sub.1, the outer diameter size of the third cylindrical portion 4A.sub.2 (the inner diameter size of the first cylindrical portion 4A.sub.1) r.sub.2, the outer diameter size of the second cylindrical portion 4B.sub.1 (the inner diameter size of the third cylindrical portion 4A.sub.2) r.sub.3, the outer diameter size of the fourth cylindrical portion 4B.sub.2 (the inner diameter size of the second cylindrical portion 4B.sub.1) r.sub.4, a height size h.sub.1 of the first cylindrical portion 4A.sub.1, and the height size h.sub.1 of the second cylindrical portion 4B.sub.1 are restricted by product sizes.

(27) A weight of the first cylindrical portion 4A.sub.1 is configured to be almost identical to a weight of the third cylindrical portion 4A.sub.2. A weight of the second cylindrical portion 4B.sub.1 is configured to be almost identical to a weight of the fourth cylindrical portion 4B.sub.2.

(28) Thus, the joined body 4 is configured such that the fourth cylindrical portion 4B.sub.2, the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, and the first cylindrical portion 4A.sub.1 continuously in this order from the inner diameter side. This ensures an efficient forming process with the four cylindrical portions coupled in the forging. The parts corresponding to the respective cylindrical portions are configured in a stepwise manner, because a cut length can be shortened and a cylindrical member 5, which is produced by separation in the cutting and separating step described later, can be easily punched.

(29) Cutting and Separating Step

(30) As illustrated in (e) to (g) of FIG. 1, the cutting and separating step is a step of cutting and separating the four cylindrical portions 4A.sub.1, 4B.sub.1, 4A.sub.2, and 4B.sub.2 to obtain respective four cylindrical members 5A.sub.1, 5B.sub.1, 5A.sub.2, and 5B.sub.2. In the cutting and separating, the plural cylindrical portions may be cut and separated in one step, or an inner diameter punching step may be performed simultaneously with the cutting and separating step.

(31) Rolling Process Step

(32) The rolling step is a step of expanding the inner diameter sizes of parts of the plural cylindrical members produced through the cutting and separating step. Specifically, the rolling step is a step of employing the first cylindrical member 5A.sub.1 and the second cylindrical member 5B.sub.1 as ring-shaped members 6A.sub.1 and 6B.sub.1 without change, and rolling the third cylindrical member 5A.sub.2 and the fourth cylindrical member 5B.sub.2 with a well-known rolling mill to expand the inner diameter sizes. This rolling step expands the inner diameter size of the third cylindrical member 5A.sub.2 so as to make the inner diameter size almost identical to that of the first cylindrical member 5A.sub.1, and produce a third ring-shaped member 6A.sub.2. Additionally, the inner diameter size of the fourth cylindrical member 5B.sub.2 is expanded so as to make the inner diameter size almost identical to that of the second cylindrical member 5B.sub.1, and produce a fourth ring-shaped member 6B.sub.2.

(33) Thus, as the ring-shaped members for outer rings, two ring-shaped members 6, the first ring-shaped member 6A.sub.1, and the third ring-shaped member 6A.sub.2 can be produced. As the ring-shaped members for inner rings, the two ring-shaped members 6, the second ring-shaped member 6B.sub.1, and the fourth ring-shaped member 6B.sub.2 can be produced.

(34) With the method for manufacturing the ring-shaped member according to the embodiment, as illustrated in (d) of FIG. 1, the number of scraps S, which are generated when the inner diameters are punched in the forging step, is only one for every four cylindrical portions. This substantially improves a yield compared with one piece of scrap generated for every two cylindrical portions by a so-called conventional parent-child taking process. Similarly, the yield can be substantially improved as compared to PTL 1 and PTL 2.

(35) To produce two sets of the two ring-shaped members with identical sizes, since a difference in size between the first cylindrical portion 4A.sub.1 and the third cylindrical portion 4A.sub.2, and a difference in size between the second cylindrical portion 4B.sub.1 and the fourth cylindrical portion 4B.sub.2 are small, the diameter expansion rate in the cold rolling process can be made small. Consequently, the four cylindrical members (the ring-shaped members) can be manufactured without a possibility of a crack. The small diameter expansion rate provides an effect of shortening the processing time, accordingly.

(36) To produce the four ring-shaped members 6 (two for each of the inner and the outer rings), performing the rolling process twice is sufficient. This configuration brings an effect of reducing the number of the steps in the rolling process, which especially takes much processing time.

Second Embodiment

(37) A method for manufacturing a ring-shaped member in the second embodiment will be described with reference to the drawings. In the second embodiment, the configuration of the joined body is different from the first embodiment. Therefore, like reference numerals designate corresponding or identical elements throughout the above-described embodiment and the second embodiment, and such elements may be omitted. FIG. 4 illustrates cross-sectional views (a) to (f) of a processing outline of a ring-shaped member in a method for manufacturing the ring-shaped member in the second embodiment.

(38) As illustrated in (a) to (f) of FIG. 4, in the first embodiment, the plural cylindrical portions included in the joined body 4 are axially coupled in the ascending order of inner diameters. Specifically, below the first cylindrical portion 4A.sub.1, the second cylindrical portion 4B.sub.1, which has the inner diameter size larger than the inner diameter size of the first cylindrical portion 4A.sub.1, is concentrically coupled. Furthermore, below the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, which has the inner diameter size larger than the inner diameter size of the second cylindrical portion 4B.sub.1, is concentrically coupled. Subsequently, as they are arranged lower, below a cylindrical portion having a larger inner diameter size is concentrically coupled with another cylindrical portion than a smaller inner diameter size.

(39) In the second embodiment, the joined body 4 having such a configuration eliminates a need for a thin mold, when compared with the shape of the first embodiment, and provides an effect of improvement in product life of the mold.

Third Embodiment

(40) A method for manufacturing a ring-shaped member in the third embodiment will be described with reference to the drawings. In the thirds embodiment, the rolling process is different from the first embodiment. Therefore, like reference numerals designate corresponding or identical elements throughout the above-described embodiments and the third embodiment, and therefore such elements may be omitted. FIG. 5 illustrates a cross-sectional view of a configuration of a joined body after a forging step in a method for manufacturing a ring-shaped member in the third embodiment. FIG. 6 illustrates cross-sectional views (a) to (g) of a processing outline of the ring-shaped member in the method for manufacturing the ring-shaped member in the third embodiment. FIG. 7 illustrates cross-sectional views of configurations of cylindrical members and the ring-shaped members before and after the rolling step in the method for manufacturing the ring-shaped member according to the third embodiment. FIG. 8 illustrates schematic views (a) and (b) of a processing outline of a rolling step in a method for manufacturing a ring-shaped member in one variation of the third embodiment.

(41) As illustrated in FIG. 5, in the joined body 4 in the third embodiment, the height dimension (an axial dimension) h.sub.1 of the first cylindrical portion 4A.sub.1, a height dimension h.sub.2 of the third cylindrical portion 4A.sub.2, and a height dimension h.sub.3 of the fourth cylindrical portion 4B.sub.2 meet a relationship of h.sub.2>h.sub.1 and h.sub.2<h.sub.3. The height dimension h.sub.1 of the second cylindrical portion 4B.sub.1 is assumed to be identical to the height dimension h.sub.1 of the first cylindrical portion 4A.sub.1.

(42) In the above-described first and second embodiments, the four ring-shaped members 6 are obtainable while the height dimensions hardly change in the rolling step.

(43) However, the actual dimensions of the ring-shaped members 6 as bearing rings (the inner rings and the outer rings) for rolling bearings are determined as a product. Therefore, even if the forging step performs the four-piece forming, the height dimensions often have the relationship as illustrated in FIG. 5.

(44) This often results in h.sub.2>h.sub.1 when attempting to make a weight of the cylindrical portion 4A.sub.1, which will be the ring-shaped member 6A.sub.1, and a weight of the cylindrical portion 4A.sub.2, which will be the ring-shaped member 6A.sub.2, to be identical. Similarly, this often results in h.sub.3>h.sub.1 when attempting to make a weight of the cylindrical portion 4B.sub.1, which will be the ring-shaped member 6B.sub.1, and a weight of the cylindrical portion 4B.sub.2, which will be the ring-shaped member 6B.sub.2, to be identical.

(45) In the third embodiment, a rolling step that expands the inner diameter size of at least any one of the third cylindrical member 4A.sub.2 or the fourth cylindrical member 4B.sub.2 while reducing the height dimension is included, in the case where the respective height dimensions of the cylindrical portions 4A.sub.1, 4A.sub.2, 4B.sub.1, and 4B.sub.2 meet at least any one of h.sub.2>h.sub.1 or h.sub.3>h.sub.1.

(46) As a modification of the third embodiment, the cutting and separating step may upset the cylindrical portions 4A.sub.1, 4A.sub.2, 4B.sub.1, and 4B.sub.2 so as to each have the identical height dimension. In the case where the respective height dimensions of the cylindrical portions 4A.sub.1, 4A.sub.2, and 4B.sub.1 meet h.sub.2<h.sub.1, the height dimensions can be extended without restraining the height dimensions up to a predetermined dimension in the rolling step.

(47) Specifically, as the forging step, firstly, the cut billet 2 illustrated in (b) of FIG. 6 is produced by using the round bar member 1 illustrated in (a) of FIG. 6 in any of methods of the press cutting, the saw cutting, or the cutting off.

(48) Next, the cut billet 2 is forged to produce the intermediate formed body 3 as illustrated in (c) of FIG. 6. Then, the joined body 4, which is as illustrated in (d) of FIG. 6, is formed by radial coupling of the first cylindrical portion 4A.sub.1, the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, and the fourth cylindrical portion 4B.sub.2. Here, as described above, in the joined body 4 in the third embodiment, since the height dimension h.sub.2 of the third cylindrical portion 4A.sub.2 is shorter than the height dimension h.sub.3 of the fourth cylindrical portion 4B.sub.2, an end surface of the fourth cylindrical portion 4B.sub.2 in the axial direction projects with respect to an end surface of the third cylindrical portion 4A.sub.2 in the axial direction.

(49) Subsequently, as illustrated in (e) to (g) of FIG. 6, the cutting and separating step according to the embodiment cut and separate the four cylindrical portions 4A.sub.1, 4B.sub.1, 4A.sub.2, and 4B.sub.2 to obtain the respective four cylindrical members 5A.sub.1, 5B.sub.1, 5A.sub.2, and 5B.sub.2.

(50) Next, the rolling step in the third embodiment employs the first cylindrical member 5A.sub.1 and the second cylindrical member 5B.sub.1 as the ring-shaped members 6A.sub.1 and 6B.sub.1 without change and performs the rolling process on the third cylindrical member 5A.sub.2 and the fourth cylindrical member 5B.sub.2 with the well-known rolling mill to expand the inner diameter sizes. Then, the rolling process of expanding the inner diameter sizes of at least any one of the third cylindrical member 5A.sub.2 and the fourth cylindrical member 5B.sub.2 is performed while reducing the axial heights.

(51) Here, in the rolling step, a rolling mill that includes an axial roll disclosed in JP 2002-205103 A can be used. Specifically, as illustrated in (a) and (b) of FIG. 8, the rolling mill that includes a main roll 12, a mandrel 13, axial rolls 14, and a tracer roll 15 can be used. The main roll 12 is secured and has a function to rotate the cylindrical member 5A.sub.2 (5B.sub.2), which is a rolled material, at a constant outer circumferential speed while rotating itself at a constant speed. The mandrel 13 is driven and disposed at the inner diameter side of the cylindrical member 5A.sub.2 (5B.sub.2). The mandrel 13 sandwiches the cylindrical member 5A.sub.2 (5B.sub.2) with the main roll 12 and moves in the main roll 12 direction to press the cylindrical member 5A.sub.2 (5B.sub.2) in a thickness direction.

(52) The axial rolls 14 are generally positioned symmetrically with respect to centers of the main roll 12 and the cylindrical member 5A.sub.2 (5B.sub.2), and conical-shaped rolls re arranged on the upper and lower side to sandwich the cylindrical member 5A.sub.2 (5B.sub.2). One or both of the rolls are driven, and usually, the upper roll moves downward to press the cylindrical member 5A.sub.2 (5B.sub.2) in a height direction. The axial rolls 14 are formed into the cone shape because a peripheral velocity of the cylindrical member 5A.sub.2 (5B.sub.2) differs between the inner circumferential side and the outer circumferential side (the inner circumferential side< the outer circumferential side). Therefore, the difference in the circumferential velocity can be absorbed. Accordingly, the axial rolls 14 are disposed such that the distal ends of the conical-shaped rolls match the center of the cylindrical member 5A.sub.2 (5B.sub.2). This horizontally (a diameter-expanding side) moves a pressing position of roll circumferential surfaces with respect to the cylindrical member 5A.sub.2 (5B.sub.2) as the diameter of the cylindrical member 5A.sub.2 (5B.sub.2) expands.

(53) The tracer roll 15 rollingly contacts the outer circumferential surface of the cylindrical member 5A.sub.2 (5B.sub.2) at a position where the main roll 12 and the cylindrical member 5A.sub.2 (5B.sub.2) are symmetrical with respect to their centers. Bt the movement of the tracer roll 15, the outer diameter size of the cylindrical member 5A.sub.2 (5B.sub.2) can be considered to be respective dimensions between rolling contact surfaces of the tracer roll 15 and the main roll 12 with respect to the rolled material.

(54) The rolling mill configured as described above radially rolls the cylindrical member 5A.sub.2 (5B.sub.2) by the main roll 12 and the mandrel 13 while detecting the diameter of the cylindrical member 5A.sub.2 (5B.sub.2) by the tracer roll 15. Thus, the rolling mill rolls the cylindrical member 5A.sub.2 (5B.sub.2) in the height direction of the cylindrical member 5A.sub.2 (5B.sub.2) and in the axial direction with the axial rolls 14, which are disposed on the upper side and lower side.

(55) Thus, as the ring-shaped members for outer rings, the two ring-shaped members 6, the first ring-shaped member 6A.sub.1, and the third ring-shaped member 6A.sub.2 can be produced. As the ring-shaped members for inner rings, the two ring-shaped members 6, the second ring-shaped member 6B.sub.1, and the fourth ring-shaped member 6B.sub.2 can be produced. Especially, in the third embodiment, the rolling step expands the inner diameter size of at least any one of the third cylindrical member 5A.sub.2 or the fourth cylindrical member 5B.sub.2, while reducing the height dimension. This ensures performing the forging step without considering the height dimension.

Fourth Embodiment

(56) A method for manufacturing a ring-shaped member in the fourth embodiment will be described with reference to the drawings. In the fourth embodiment, the cutting and separating step is different from the third embodiment. Therefore, like reference numerals designate corresponding or identical elements throughout the above-described embodiments and the fourth embodiment, and such elements may be omitted. As illustrated in FIG. 9, in the joined body 4 used in the fourth embodiment, the height dimension (the axial dimension) h.sub.1 of the first cylindrical portion 4A.sub.1, the height dimension h.sub.2 of the third cylindrical portion 4A.sub.2, and the height dimension h.sub.3 of the fourth cylindrical portion 4B.sub.2 meet a relationship of h.sub.2>h.sub.1 and h.sub.2<h.sub.3. The height dimension h.sub.1 of the second cylindrical portion 4B.sub.1 is assumed to be identical to the height dimension h.sub.1 of the first cylindrical portion 4A.sub.1.

(57) In the fourth embodiment, a rolling step of expanding the inner diameter size of at least any one of the third cylindrical member 4A.sub.2 or the fourth cylindrical member 4B.sub.2 is included while reducing the height dimension simultaneously or separately, when the third cylindrical member 5A.sub.2 and the fourth cylindrical member 5B.sub.2 to be subject to the rolling process are cut and separated from the joined body 4.

(58) Specifically, as the forging step, the cut billet 2 illustrated in (b) of FIG. 10 is produced by using the round bar member 1 illustrated in (a) of FIG. 10 in any of methods of the press cutting, the saw cutting, or the cutting off.

(59) Next, the cut billet 2 is forged to produce the intermediate formed body 3 as illustrated in (c) of FIG. 10. Then, the joined body 4 illustrated in (d) of FIG. 10 is formed by radial coupling of the first cylindrical portion 4A.sub.1, the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, and the fourth cylindrical portion 4B.sub.2. Here, as described above, in the joined body 4 in the fourth embodiment, since the height dimension h.sub.2 of the third cylindrical portion 4A.sub.2 is shorter than the height dimension h.sub.3 of the fourth cylindrical portion 4B.sub.2, an end surface of the fourth cylindrical portion 4B.sub.2 in the axial direction projects with respect to an end surface of the third cylindrical portion 4A.sub.2 in the axial direction.

(60) Subsequently, as illustrated in (e) to (g) of FIG. 10, in the cutting and separating step in the fourth embodiment, the four cylindrical portions 4A.sub.1, 4B.sub.1, 4A.sub.2, and 4B.sub.2 are cut and separated to obtain the respective four cylindrical members 5A.sub.1, 5B.sub.1, 5A.sub.2, and 5B.sub.2.

(61) Here, as illustrated in (e) of FIG. 10, in the fourth embodiment, the cylindrical member 5A.sub.2 is separated from a joined body 4 from which the cylindrical member 5A.sub.1 has been cut and separated, and is also upset. Specifically, as illustrated in (a) of FIG. 11, the joined body 4 from which the cylindrical member 5A.sub.1 has been cut and separated is installed to an upsetting die 23, which is provided with a circular separation die 22. The separation die 22 contacts bottom surfaces of the cylindrical portion 4B.sub.1, the inner circumferential surfaces of the cylindrical portion 4A.sub.2, and the outer circumferential surfaces of the cylindrical portion 4B.sub.2. Thereafter, as illustrated in (b) of FIG. 11, a circular punch 21, which contacts the outer circumferential surfaces of the cylindrical portion 4B.sub.1 and the top surfaces of the cylindrical portion 4A.sub.2, presses to the joined body 4 to separate the cylindrical member 5A.sub.2. As illustrated in (c) of FIG. 11, the punch 21 upsets the cylindrical member 5A.sub.2 to configure the height dimension h.sub.1 from h.sub.3, thus obtaining the ring-shaped member 6A.sub.2.

(62) In the fourth embodiment, the cylindrical portion 4A.sub.2 may be separated and upset independently. However, the simultaneous separation and upset reduce the number of the processes.

(63) Thus, in the fourth embodiment, by upsetting the cylindrical members 5A.sub.2 and 5B.sub.2 in the cutting and separating step, the height dimensions of the cylindrical members 5A.sub.1 and 5B.sub.1 can be identical before the rolling step. Consequently, in the rolling step in the fourth embodiment, only the dimension of the diameter can be expanded without reducing the height dimension. This configuration achieves the rolling step with simpler facilities without an axial roll.

Fifth Embodiment

(64) A method for manufacturing a ring-shaped member in the fifth embodiment will be described with reference to the drawings. In the fifth embodiment, only the rolling step is different from the third embodiment and the fourth embodiment. Therefore, like reference numerals designate corresponding or identical elements throughout the above-described embodiments and the fifth embodiment, and such elements may be omitted.

(65) In the third embodiment and the fourth embodiment, the cylindrical member 5A.sub.2 is configured to have the height dimension h.sub.2 to adjust its shape. However, depending on the dimension of the ring-shaped member 6A.sub.2, there is a small difference r (see FIG. 12) between the inner diameter (r.sub.3) and the outer diameter (r.sub.2) of the cylindrical portion 4A.sub.2, and the ring-shaped member 6A.sub.2 may have a thin wall in the radial direction and may be large in the height direction. Consequently, when the height dimension of the cylindrical member 5A.sub.2 is reduced or when the cylindrical member 5A.sub.2 is subject to the rolling while reducing the height dimension, the cylindrical member 5A.sub.2 may buckle.

(66) In the fifth embodiment, therefore, the outer diameter size of the ring-shaped member 6B.sub.1 is configured to be larger than the outer diameter size r.sub.3 of the cylindrical portion 4B.sub.1, and the cylindrical member 5B.sub.1 is also subject to the rolling process. Thus, through the expansion of the diameter, the dimensions of the ring-shaped member 6B.sub.1 as a product are finished to have predetermined dimensions.

(67) Specifically, as the forging step, the cut billet 2 illustrated in (b) of FIG. 13 is produced by using the round bar member 1 illustrated in (a) of FIG. 13 in any of methods of the press cutting, the saw cutting, or the cutting off.

(68) Next, the cut billet 2 is forged to obtain the intermediate formed body 3 as illustrated in (c) of FIG. 13. Then, the joined body 4 illustrated in (d) of FIG. 13 is formed by radial coupling of the first cylindrical portion 4A.sub.1, the second cylindrical portion 4B.sub.1, the third cylindrical portion 4A.sub.2, and the fourth cylindrical portion 4B.sub.2.

(69) Subsequently, as illustrated in (e) to (g) of FIG. 13, in the cutting and separating step in the fifth embodiment, the four cylindrical portions 4A.sub.1, 4B.sub.1, 4A.sub.2, and 4B.sub.2 is cut and separated to obtain the respective four cylindrical members 5A.sub.1, 5B.sub.1, 5A.sub.2, and 5B.sub.2.

(70) Next, in the rolling step in the fifth embodiment, the first cylindrical member 5A.sub.1 is used as the ring-shaped member 6A.sub.1 without change, and the rolling is performed on the second cylindrical member 5B.sub.1, the third cylindrical member 5A.sub.2, and the fourth cylindrical member 5B.sub.2 with the well-known rolling mill to expand the inner diameter sizes. That is, unlike the above-described embodiments, the rolling process is performed on the second cylindrical member 5B.sub.1 to expand the inner diameter to produce the ring-shaped member 6B.sub.1. The rolling process is performed on the fourth cylindrical member 5B.sub.2 to expand the inner diameter size so as to have the inner diameter size identical to that of the second cylindrical member 5B.sub.1. Thus, the ring-shaped member 6B.sub.2 is produced.

(71) Thus, as the ring-shaped members for outer rings, the two ring-shaped members 6, the first ring-shaped member 6A.sub.1, and the third ring-shaped member 6A.sub.2 can be obtained. As the ring-shaped members for inner rings, the two ring-shaped members 6, the second ring-shaped member 6B.sub.1, and the fourth ring-shaped member 6B.sub.2 can be obtained. Especially, in the fifth embodiment, even if the rolling process is performed on the second cylindrical member 5B.sub.1, when compared with the third cylindrical member 5A.sub.2 and the fourth cylindrical member 5B.sub.2, the diameter can be expanded by only a slight amount. Accordingly, the processing time taken for the rolling process on the second cylindrical member 5B.sub.1 can be small.

(72) Accordingly, while a loss of productivity is minimized, the scraps S generated through the inner diameter punch in the forging step are the one scrap S for every four ring-shaped members. This contributes to a good yield, which is advantageous of the four-piece forming process.

(73) Although the present invention has been described with reference to the specific embodiments, this does not intend to limit the invention by the explanations. The person skilled in the art clearly understands various modifications of the disclosed embodiments and other embodiments of the present invention through reference of the descriptions of the present invention. Accordingly, it should be understood that the claims also cover these modifications or embodiments included in the scope and the gist of the present invention.

REFERENCE SIGNS LIST

(74) 1 round bar member 2 cut billet 3 intermediate formed body 4 joined body 4A.sub.1 first cylindrical portion 4B.sub.1 second cylindrical portion 4A.sub.2 third cylindrical portion 4B.sub.2 fourth cylindrical portion 5 cylindrical member 5A.sub.1 first cylindrical member 5B.sub.1 second cylindrical member 5A.sub.2 third cylindrical member 5B.sub.2 fourth cylindrical member 6 ring-shaped member 6A.sub.1 first ring-shaped member 6B.sub.1 second ring-shaped member 6A.sub.2 third ring-shaped member 6B.sub.2 fourth ring-shaped member