Method for manufacturing ring-shaped member

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.

TECHNICAL FIELD

The present invention relates to methods for manufacturing ring-shaped members, and, for example, relates to a method for manufacturing a ring-shaped member applied to an inner ring and an outer ring for a rolling bearing and a similar member.

BACKGROUND ART

There has been conventionally known a method for manufacturing two bearing rings (ring-shaped members), which are an inner ring and an outer ring for a rolling bearing, from one column-shaped material (so-called parent-child taking) (for example, see PTL 1). This manufacturing method includes the following first step to fifth step.

First step: through upsetting in hot working, a disk-shaped intermediate formed product202having an arc-shaped generating line of an outer circumferential surface illustrated in (b) ofFIG. 14is formed from a column-shaped material201illustrated in (a) ofFIG. 14.

Second step: through closed die forging, a stepped cylindrically-shaped formed product203illustrated in (c) ofFIG. 14is formed from the intermediate formed product202. In this formed product203, an outer periphery on one end of a small-diameter inner ring205is coupled to an inner periphery on one end of a large-diameter outer ring204. A bottom206is formed on an inner periphery on the other end of the inner ring205.

Third step: the formed product203is cut at the coupled site of the outer ring204and the inner ring205to separate the formed product203into the outer ring204and the inner ring205as illustrated in (d) ofFIG. 14.

Fourth step: as illustrated in (e) ofFIG. 14, the bottom206is punched from the separated inner ring205.

Fifth step: the outer ring204and the inner ring205are formed into a predetermined shape by a rolling process.

PTL 2 discloses the method of producing a ring-shaped member. In this method, a large-diameter cylindrical member and a small-diameter cylindrical member before cold rolling are made to have identical weights, and only the small-diameter cylindrical member is cold-rolled. Thus, the method produces a ring-shaped member with a diameter and a shape identical to those of the large-diameter cylindrical member (Since the large-diameter cylindrical member is not to be rolled, the large-diameter cylindrical member becomes the ring-shaped member without change).

The above-described PTL 1 discloses the method of producing a large-diameter cylindrical member and a small-diameter cylindrical member by a single forging process. The small-diameter cylindrical member is upset, and is then subject to a rolling process. Thus, in the method, the large-diameter cylindrical member in forging is produced to be a ring-shaped member serving as an inner ring, and the small-diameter cylindrical member in the forging is produced to be the ring-shaped member serving as an outer ring.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the technique disclosed in PTL 1, however, firstly, to manufacture lots of cylindrical members with identical diameters at once, a diameter expansion rate when a cylindrical member with the smallest diameter is cold-rolled needs to be substantially large, and a crack may easily occur. This leaves room for improvement.

Secondly, cylindrical members other than the outermost cylindrical member always need to be cold-rolled. This causes a problem of necessitating lots of cold rolling processes, which takes much processing time (The rolling process needs to be performed three times for producing four ring-shaped members). That is, although forging a large number of pieces at once improves a yield, a degree of difficulty in the cold rolling process increases (The crack is likely to occur.) as the number of pieces to be produced increases, and also necessitating an increase in the number of processes. This leaves room for improvement.

The technique disclosed in PTL 2 is a method of ensuring a scrap produced through the inner diameter punching to have a smaller size than that of a scrap produced through a so-called conventional parent-child taking process. However, to finish the small-diameter cylindrical member as an outer ring by the rolling process, a large diameter expansion rate is needed, and may lead to a longer processing time for the rolling process. This also leaves room for improvement.

Especially, further cost reduction is demanded these years, so there is an increased demand for a method for higher productivity.

The present invention has been made to solve the above-described conventional techniques, and an object of the present invention is to provide a method for manufacturing ring-shaped members at a good yield and a high production efficiency.

Solution to Problem

To solve the problems, there is provided a method for manufacturing a ring-shaped member, including:

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.

The joined body including 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 almost identical to an inner diameter size of the first cylindrical portion, the second cylindrical portion having an outer diameter size configured to be almost identical to an inner diameter size of the third cylindrical portion, the fourth cylindrical portion having an outer diameter size configured to be almost identical to an inner diameter size of the second cylindrical portion.

The rolling step includes expanding an inner diameter size of a third cylindrical member such that the third cylindrical member has an inner diameter size almost 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 almost identical to an inner diameter size of a second cylindrical member to obtain a fourth ring-shaped member.

Here, the method for manufacturing the ring-shaped member may be configured as follows. The forging step forms the joined body by radial coupling of one ends of a first cylindrical portion and a second cylindrical portion in an axial direction and the other ends of a third cylindrical portion and a fourth cylindrical portion in an axial direction.

The method for manufacturing the ring-shaped member may be configured as follows. The rolling step expands an inner diameter size of at least anyone of a third cylindrical member and a fourth cylindrical member while reducing a height of any one of the third cylindrical member and the fourth cylindrical member in an axial direction.

The method for manufacturing the ring-shaped member may be configured as follows. During the cutting and separating step or after the cutting and separating step, at least one of a third cylindrical member and a fourth cylindrical member is upset.

The method for manufacturing the ring-shaped member may be configured as follows. The rolling step includes a step of expanding an inner diameter size of a second cylindrical member.

Advantageous Effects of Invention

According to one aspect of the present invention, a method for manufacturing ring-shaped members at good yield and high production efficiency can be provided.

DESCRIPTION OF EMBODIMENTS

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.

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

FIG. 1illustrates 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.

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

Forging Step

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.

First, a cut billet2illustrated in (b) ofFIG. 1is produced using a round bar member1illustrated in (a) ofFIG. 1in a method of any one of press cutting, saw cutting, or cutting off. At this time, the cut billet2cut 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 billet2is upset or an end surface of the cut billet2is corrected. The cut billet2produced 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.

Next, the cut billet2is forged to obtain an intermediate formed body3as illustrated in (c) ofFIG. 1. Then, a joined body4, which is as illustrated in (d) ofFIG. 1, is formed by coupling a first cylindrical portion4A1, a second cylindrical portion4B1, a third cylindrical portion4A2, and a fourth cylindrical portion4B2in a radial direction.

Joined Body

As illustrated inFIG. 2, in the joined body4, an outer diameter size r2of the third cylindrical portion4A2is configured to be almost identical to an inner diameter size r2of the first cylindrical portion4A1. An outer diameter size r3of the second cylindrical portion4B1is configured to be almost identical to an inner diameter size r3of the third cylindrical portion4A2. An outer diameter size r4of the fourth cylindrical portion4B2is configured to be almost identical to an inner diameter size r4of the second cylindrical portion4B1.

One ends of the first cylindrical portion4A1and the second cylindrical portion4B1in the axial direction are radially coupled to the other ends of the third cylindrical portion4A2and the fourth cylindrical portion4B2in the axial direction. The respective inner diameter sizes and outer diameter sizes of the first cylindrical portion4A1, the second cylindrical portion4B1, the third cylindrical portion4A2, and the fourth cylindrical portion4B2are 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.

An outer diameter size r1of the first cylindrical portion4A1, the outer diameter size of the third cylindrical portion4A2(the inner diameter size of the first cylindrical portion4A1) r2, the outer diameter size of the second cylindrical portion4B1(the inner diameter size of the third cylindrical portion4A2) r3, the outer diameter size of the fourth cylindrical portion4B2(the inner diameter size of the second cylindrical portion4B1) r4, a height size h1of the first cylindrical portion4A1, and the height size h1of the second cylindrical portion4B1are restricted by product sizes.

A weight of the first cylindrical portion4A1is configured to be almost identical to a weight of the third cylindrical portion4A2. A weight of the second cylindrical portion4B1is configured to be almost identical to a weight of the fourth cylindrical portion4B2.

Thus, the joined body4is configured such that the fourth cylindrical portion4B2, the second cylindrical portion4B1, the third cylindrical portion4A2, and the first cylindrical portion4A1continuously 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 member5, which is produced by separation in the cutting and separating step described later, can be easily punched.

Cutting and Separating Step

As illustrated in (e) to (g) ofFIG. 1, the cutting and separating step is a step of cutting and separating the four cylindrical portions4A1,4B1,4A2, and4B2to obtain respective four cylindrical members5A1,5B1,5A2, and5B2. 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.

Rolling Process Step

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 member5A1and the second cylindrical member5B1as ring-shaped members6A1and6B1without change, and rolling the third cylindrical member5A2and the fourth cylindrical member5B2with a well-known rolling mill to expand the inner diameter sizes. This rolling step expands the inner diameter size of the third cylindrical member5A2so as to make the inner diameter size almost identical to that of the first cylindrical member5A1, and produce a third ring-shaped member6A2. Additionally, the inner diameter size of the fourth cylindrical member5B2is expanded so as to make the inner diameter size almost identical to that of the second cylindrical member5B1, and produce a fourth ring-shaped member6B2.

Thus, as the ring-shaped members for outer rings, two ring-shaped members6, the first ring-shaped member6A1, and the third ring-shaped member6A2can be produced. As the ring-shaped members for inner rings, the two ring-shaped members6, the second ring-shaped member6B1, and the fourth ring-shaped member6B2can be produced.

With the method for manufacturing the ring-shaped member according to the embodiment, as illustrated in (d) ofFIG. 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.

To produce two sets of the two ring-shaped members with identical sizes, since a difference in size between the first cylindrical portion4A1and the third cylindrical portion4A2, and a difference in size between the second cylindrical portion4B1and the fourth cylindrical portion4B2are 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.

To produce the four ring-shaped members6(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

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. 4illustrates 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.

As illustrated in (a) to (f) ofFIG. 4, in the first embodiment, the plural cylindrical portions included in the joined body4are axially coupled in the ascending order of inner diameters. Specifically, below the first cylindrical portion4A1, the second cylindrical portion4B1, which has the inner diameter size larger than the inner diameter size of the first cylindrical portion4A1, is concentrically coupled. Furthermore, below the second cylindrical portion4B1, the third cylindrical portion4A2, which has the inner diameter size larger than the inner diameter size of the second cylindrical portion4B1, 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.

In the second embodiment, the joined body4having 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

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. 5illustrates 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. 6illustrates 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. 7illustrates 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. 8illustrates 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.

As illustrated inFIG. 5, in the joined body4in the third embodiment, the height dimension (an axial dimension) h1of the first cylindrical portion4A1, a height dimension h2of the third cylindrical portion4A2, and a height dimension h3of the fourth cylindrical portion4B2meet a relationship of h2>h1and h2<h3. The height dimension h1of the second cylindrical portion4B1is assumed to be identical to the height dimension h1of the first cylindrical portion4A1.

In the above-described first and second embodiments, the four ring-shaped members6are obtainable while the height dimensions hardly change in the rolling step.

However, the actual dimensions of the ring-shaped members6as 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 inFIG. 5.

This often results in h2>h1when attempting to make a weight of the cylindrical portion4A1, which will be the ring-shaped member6A1, and a weight of the cylindrical portion4A2, which will be the ring-shaped member6A2, to be identical. Similarly, this often results in h3>h1when attempting to make a weight of the cylindrical portion4B1, which will be the ring-shaped member6B1, and a weight of the cylindrical portion4B2, which will be the ring-shaped member6B2, to be identical.

In the third embodiment, a rolling step that expands the inner diameter size of at least any one of the third cylindrical member4A2or the fourth cylindrical member4B2while reducing the height dimension is included, in the case where the respective height dimensions of the cylindrical portions4A1,4A2,4B1, and4B2meet at least any one of h2>h1or h3>h1.

As a modification of the third embodiment, the cutting and separating step may upset the cylindrical portions4A1,4A2,4B1, and4B2so as to each have the identical height dimension. In the case where the respective height dimensions of the cylindrical portions4A1,4A2, and4B1meet h2<h1, the height dimensions can be extended without restraining the height dimensions up to a predetermined dimension in the rolling step.

Specifically, as “the forging step”, firstly, the cut billet2illustrated in (b) ofFIG. 6is produced by using the round bar member1illustrated in (a) ofFIG. 6in any of methods of the press cutting, the saw cutting, or the cutting off.

Next, the cut billet2is forged to produce the intermediate formed body3as illustrated in (c) ofFIG. 6. Then, the joined body4, which is as illustrated in (d) ofFIG. 6, is formed by radial coupling of the first cylindrical portion4A1, the second cylindrical portion4B1, the third cylindrical portion4A2, and the fourth cylindrical portion4B2. Here, as described above, in the joined body4in the third embodiment, since the height dimension h2of the third cylindrical portion4A2is shorter than the height dimension h3of the fourth cylindrical portion4B2, an end surface of the fourth cylindrical portion4B2in the axial direction projects with respect to an end surface of the third cylindrical portion4A2in the axial direction.

Subsequently, as illustrated in (e) to (g) ofFIG. 6, “the cutting and separating step” according to the embodiment cut and separate the four cylindrical portions4A1,4B1,4A2, and4B2to obtain the respective four cylindrical members5A1,5B1,5A2, and5B2.

Next, “the rolling step” in the third embodiment employs the first cylindrical member5A1and the second cylindrical member5B1as the ring-shaped members6A1and6B1without change and performs the rolling process on the third cylindrical member5A2and the fourth cylindrical member5B2with 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 member5A2and the fourth cylindrical member5B2is performed while reducing the axial heights.

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) ofFIG. 8, the rolling mill that includes a main roll12, a mandrel13, axial rolls14, and a tracer roll15can be used. The main roll12is secured and has a function to rotate the cylindrical member5A2(5B2), which is a rolled material, at a constant outer circumferential speed while rotating itself at a constant speed. The mandrel13is driven and disposed at the inner diameter side of the cylindrical member5A2(5B2). The mandrel13sandwiches the cylindrical member5A2(5B2) with the main roll12and moves in the main roll12direction to press the cylindrical member5A2(5B2) in a thickness direction.

The axial rolls14are generally positioned symmetrically with respect to centers of the main roll12and the cylindrical member5A2(5B2), and conical-shaped rolls re arranged on the upper and lower side to sandwich the cylindrical member5A2(5B2). One or both of the rolls are driven, and usually, the upper roll moves downward to press the cylindrical member5A2(5B2) in a height direction. The axial rolls14are formed into the cone shape because a peripheral velocity of the cylindrical member5A2(5B2) 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 rolls14are disposed such that the distal ends of the conical-shaped rolls match the center of the cylindrical member5A2(5B2). This horizontally (a diameter-expanding side) moves a pressing position of roll circumferential surfaces with respect to the cylindrical member5A2(5B2) as the diameter of the cylindrical member5A2(5B2) expands.

The tracer roll15rollingly contacts the outer circumferential surface of the cylindrical member5A2(5B2) at a position where the main roll12and the cylindrical member5A2(5B2) are symmetrical with respect to their centers. Bt the movement of the tracer roll15, the outer diameter size of the cylindrical member5A2(5B2) can be considered to be respective dimensions between rolling contact surfaces of the tracer roll15and the main roll12with respect to the rolled material.

The rolling mill configured as described above radially rolls the cylindrical member5A2(5B2) by the main roll12and the mandrel13while detecting the diameter of the cylindrical member5A2(5B2) by the tracer roll15. Thus, the rolling mill rolls the cylindrical member5A2(5B2) in the height direction of the cylindrical member5A2(5B2) and in the axial direction with the axial rolls14, which are disposed on the upper side and lower side.

Thus, as the ring-shaped members for outer rings, the two ring-shaped members6, the first ring-shaped member6A1, and the third ring-shaped member6A2can be produced. As the ring-shaped members for inner rings, the two ring-shaped members6, the second ring-shaped member6B1, and the fourth ring-shaped member6B2can be produced. Especially, in the third embodiment, the rolling step expands the inner diameter size of at least any one of the third cylindrical member5A2or the fourth cylindrical member5B2, while reducing the height dimension. This ensures performing the forging step without considering the height dimension.

Fourth Embodiment

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 inFIG. 9, in the joined body4used in the fourth embodiment, the height dimension (the axial dimension) h1of the first cylindrical portion4A1, the height dimension h2of the third cylindrical portion4A2, and the height dimension h3of the fourth cylindrical portion4B2meet a relationship of h2>h1and h2<h3. The height dimension h1of the second cylindrical portion4B1is assumed to be identical to the height dimension h1of the first cylindrical portion4A1.

In the fourth embodiment, a rolling step of expanding the inner diameter size of at least any one of the third cylindrical member4A2or the fourth cylindrical member4B2is included while reducing the height dimension simultaneously or separately, when the third cylindrical member5A2and the fourth cylindrical member5B2to be subject to the rolling process are cut and separated from the joined body4.

Specifically, as “the forging step”, the cut billet2illustrated in (b) ofFIG. 10is produced by using the round bar member1illustrated in (a) ofFIG. 10in any of methods of the press cutting, the saw cutting, or the cutting off.

Next, the cut billet2is forged to produce the intermediate formed body3as illustrated in (c) ofFIG. 10. Then, the joined body4illustrated in (d) ofFIG. 10is formed by radial coupling of the first cylindrical portion4A1, the second cylindrical portion4B1, the third cylindrical portion4A2, and the fourth cylindrical portion4B2. Here, as described above, in the joined body4in the fourth embodiment, since the height dimension h2of the third cylindrical portion4A2is shorter than the height dimension h3of the fourth cylindrical portion4B2, an end surface of the fourth cylindrical portion4B2in the axial direction projects with respect to an end surface of the third cylindrical portion4A2in the axial direction.

Subsequently, as illustrated in (e) to (g) ofFIG. 10, in “the cutting and separating step” in the fourth embodiment, the four cylindrical portions4A1,4B1,4A2, and4B2are cut and separated to obtain the respective four cylindrical members5A1,5B1,5A2, and5B2.

Here, as illustrated in (e) ofFIG. 10, in the fourth embodiment, the cylindrical member5A2is separated from a joined body4′ from which the cylindrical member5A1has been cut and separated, and is also upset. Specifically, as illustrated in (a) ofFIG. 11, the joined body4′ from which the cylindrical member5A1has been cut and separated is installed to an upsetting die23, which is provided with a circular separation die22. The separation die22contacts bottom surfaces of the cylindrical portion4B1, the inner circumferential surfaces of the cylindrical portion4A2, and the outer circumferential surfaces of the cylindrical portion4B2. Thereafter, as illustrated in (b) ofFIG. 11, a circular punch21, which contacts the outer circumferential surfaces of the cylindrical portion4B1and the top surfaces of the cylindrical portion4A2, presses to the joined body4′ to separate the cylindrical member5A2. As illustrated in (c) ofFIG. 11, the punch21upsets the cylindrical member5A2to configure the height dimension h1from h3, thus obtaining the ring-shaped member6A2.

In the fourth embodiment, the cylindrical portion4A2may be separated and upset independently. However, the simultaneous separation and upset reduce the number of the processes.

Thus, in the fourth embodiment, by upsetting the cylindrical members5A2and5B2in the cutting and separating step, the height dimensions of the cylindrical members5A1and5B1can 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

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.

In the third embodiment and the fourth embodiment, the cylindrical member5A2is configured to have the height dimension h2to adjust its shape. However, depending on the dimension of the ring-shaped member6A2, there is a small difference Δr (seeFIG. 12) between the inner diameter (r3) and the outer diameter (r2) of the cylindrical portion4A2, and the ring-shaped member6A2may have a thin wall in the radial direction and may be large in the height direction. Consequently, when the height dimension of the cylindrical member5A2is reduced or when the cylindrical member5A2is subject to the rolling while reducing the height dimension, the cylindrical member5A2may buckle.

In the fifth embodiment, therefore, the outer diameter size of the ring-shaped member6B1is configured to be larger than the outer diameter size r3of the cylindrical portion4B1, and the cylindrical member5B1is also subject to the rolling process. Thus, through the expansion of the diameter, the dimensions of the ring-shaped member6B1as a product are finished to have predetermined dimensions.

Specifically, as “the forging step”, the cut billet2illustrated in (b) ofFIG. 13is produced by using the round bar member1illustrated in (a) ofFIG. 13in any of methods of the press cutting, the saw cutting, or the cutting off.

Next, the cut billet2is forged to obtain the intermediate formed body3as illustrated in (c) ofFIG. 13. Then, the joined body4illustrated in (d) ofFIG. 13is formed by radial coupling of the first cylindrical portion4A1, the second cylindrical portion4B1, the third cylindrical portion4A2, and the fourth cylindrical portion4B2.

Subsequently, as illustrated in (e) to (g) ofFIG. 13, in “the cutting and separating step” in the fifth embodiment, the four cylindrical portions4A1,4B1,4A2, and4B2is cut and separated to obtain the respective four cylindrical members5A1,5B1,5A2, and5B2.

Next, in “the rolling step” in the fifth embodiment, the first cylindrical member5A1is used as the ring-shaped member6A1without change, and the rolling is performed on the second cylindrical member5B1, the third cylindrical member5A2, and the fourth cylindrical member5B2with 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 member5B1to expand the inner diameter to produce the ring-shaped member6B1. The rolling process is performed on the fourth cylindrical member5B2to expand the inner diameter size so as to have the inner diameter size identical to that of the second cylindrical member5B1. Thus, the ring-shaped member6B2is produced.

Thus, as the ring-shaped members for outer rings, the two ring-shaped members6, the first ring-shaped member6A1, and the third ring-shaped member6A2can be obtained. As the ring-shaped members for inner rings, the two ring-shaped members6, the second ring-shaped member6B1, and the fourth ring-shaped member6B2can be obtained. Especially, in the fifth embodiment, even if the rolling process is performed on the second cylindrical member5B1, when compared with the third cylindrical member5A2and the fourth cylindrical member5B2, the diameter can be expanded by only a slight amount. Accordingly, the processing time taken for the rolling process on the second cylindrical member5B1can be small.

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.

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