Method for Producing Outer Ring Member of Constant Velocity Universal Joint

Abstract

A primary product is formed by performing forward extrusion of a work in the first step, and a secondary product is formed by performing swaging in the second step. In the third step, preliminary pushing of the upper surface of the secondary product is performed to obtain a tertiary product where a recess generally matching the longitudinal section in the axial direction of the bottom wall of a cup portion of the final product is formed in the upper surface. In the fourth step, a quaternary product having a cup portion provided with a ball rolling groove in the inner wall is formed by performing backward extrusion of the tertiary product by using a punch having a tip shape generally matching the longitudinal section of the recess. Finally, in the fifth step, an outer ring member is produced as a final product by performing ironing of the cup portion of the quaternary product.

Description

TECHNICAL FIELD

The present invention relates to an outer race (ring) for use in a constant velocity universal joint for transmitting rotational drive power, and more particularly to a method of manufacturing (producing) an outer race for use in a constant velocity universal joint by forging, the outer race comprising a cup member having a plurality of guide grooves defined in an inner circumferential surface thereof and a shank integrally formed with the cup member.

BACKGROUND ART

Heretofore, there has been manufactured an outer race (outer cup) for use in a constant velocity universal joint for driving axles of an automobile, for example, by placing a forging blank in a cavity defined in upper and lower dies that are joined to each other and pressing the forging blank with a punch.

The outer race comprises a cup member and a shank integrally formed with the cup member. The cup member has a plurality of axially extending ball rolling grooves defined in an inner circumferential surface thereof and spaced at equal intervals in the circumferential direction. Balls are disposed for rolling movement along the ball rolling grooves.

Patent Document 1 discloses a method of manufacturing such an outer race for use in a constant velocity universal joint by upsetting a preform to form a recess having a semicircular cross-sectional shape in the upper surface of the cup member. According to Patent Document 1, the recess defined in the upper surface of the cup member and having the semicircular cross-sectional shape causes a smooth plastic flow in a subsequent backward extrusion process for increased accuracy of the completed product.

Patent Document 2 discloses that forward and backward extrusion is performed on a hot-machined workpiece having a head and a barrel to form a recess on the upper surface of the head.

Patent Document 3 shows that the central region of an end face of a large-diameter portion is pressed to form a recess therein.

According to the technical ideas disclosed in Patent Documents 1 through 3, however, the recess is formed in the head of the intermediate form solely for the purpose of producing a smooth material flow in the subsequent process, e.g., a backward extrusion process. When ball rolling grooves are formed in the inner wall surface of the cup member by the backward extrusion process, the amount of deformation (material elongation) is still large, resulting in a greater amount of work (forming percentage) than in other processes.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-178090

Patent Document 2: Japanese Laid-Open Patent Publication No. 58-050149

Patent Document 3: Japanese Laid-Open Patent Publication No. 55-005120

DISCLOSURE OF THE INVENTION

It is a general object of the present invention to provide a method of manufacturing an outer race for use in a constant velocity universal joint by assigning a portion of the amount of work in a fourth step to a third step which precedes the fourth step for reducing the forming percentage of the fourth step for forming ball rolling grooves, thereby to optimally distribute work among the steps.

According to the present invention, the following first through fifth steps are carried out.

In the first step, forward extrusion is performed on a cylindrical workpiece which has been cut to a predetermined length to form a first form having a shank.

Then, in the second step, an upper portion of the first form exclusive of the shank is upset to compress and diametrically enlarge the upper portion of the first form to form a second form.

Then, in the third step, an upper surface of the second form is preliminarily pushed in to form a third form having a recess formed in the upper surface which is essentially identical in axial vertical cross-sectional shape to a bottom wall of a cup member of a final product. The bottom wall of the cup member would originally be formed in the fourth step next to the third step, but its formation is assigned to the third step.

Then, in the fourth step, backward extrusion is performed on the third form, using a punch whose distal end is shaped substantially identically to the vertical cross-sectional shape of the recess, to form a fourth form having a cup member with ball rolling grooves formed in an inner wall thereof.

Finally, in the fifth step, the cup member of the fourth form is squeezed to manufacture a Barfield constant velocity universal joint having a shank and a cup member which are integrally formed with each other.

According to the present invention, an amount of work which would be involved in the formation of the bottom wall of the cup member in the fourth step is assigned to the third step which precedes the fourth step. Thus, the forming percentage of the fourth step for forming the ball rolling grooves is reduced.

According to the present invention, as a result, since the forming percentage of the fourth step is reduced, the amount of deformation (material elongation) of the forging blank is reduced to avoid the development of material cracks for thereby achieving a good die transcription rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method of manufacturing an outer race for use in a constant velocity universal joint according to an embodiment of the present invention;

FIGS. 2A through 2F are side elevational and partly vertical cross-sectional views showing shapes of the outer race for use in a constant velocity universal joint produced as a workpiece is forged into a completed product according to the manufacturing method shown in FIG. 1;

FIG. 3 is a vertical cross-sectional view of the outer race for use in a constant velocity universal joint as the completed product, the view being taken along the axial direction of the outer race;

FIG. 4 is a view as viewed in the direction indicated by the arrow Z in FIG. 3;

FIG. 5 is an enlarged fragmentary side elevational view of a ball rolling groove shown in FIG. 4; and

FIG. 6 is an enlarged fragmentary side elevational view of a rounded surface formed in the boundary between a recess and an upper surface of a third form shown in FIG. 2D.

BEST MODE FOR CARRYING OUT THE INVENTION

In a method of manufacturing an outer race for use in a constant velocity universal joint according to an embodiment of the present invention, as illustrated in a flowchart shown in FIG. 1, a workpiece 10 (see FIG. 2A) in the form of a cylinder (billet) of carbon steel is forged a total of five times into an outer race 12 for use in a Barfield constant velocity universal joint (hereinafter simply referred to as “outer race 12”) as a finally completed product.

As shown in FIGS. 3 and 4, the outer race 12 basically comprises a bottomed cylindrical cup member 16 joined to an end of a shaft, not shown, and having an opening 14, and a shank 18 integrally formed with the cup member 16.

The cup member 16 has an outer surface near the joint between the cup member 16 and the shank 18. The outer surface includes a curved surface 22 having a vertical cross section along the axial direction which becomes smaller in diameter to provide an arcuate cross-sectional shape extending from a side peripheral surface 20 toward the shank 18. The curved surface 22 is joined to the shank 18 by an annular step 24 extending in a direction perpendicular to the axial direction.

The cup member 16 of the outer race 12 has spherical inner surfaces 28 projecting from an inner wall surface thereof toward the center. A plurality of axially extending ball rolling grooves 30a through 30f are defined, each between adjacent two of the inner surfaces 28, at intervals of 60 degrees around the axis.

The ball rolling grooves 30a through 30f serve to allow balls, not shown, to roll smoothly therein, and extend along the inner wall surface of the outer race 12 to positions near terminal ends at the bottom of the cup member 16. As shown in FIG. 5, each of the ball rolling grooves 30a through 30f is of an arcuate cross-sectional shape having a single radius of curvature as viewed along the axial direction (the direction indicated by the arrow Z in FIG. 3) of the outer race 12.

The cup member 16 of the outer race 12 has a bottom wall 32 disposed on the deepest region of the inner wall surface of the cup member 16 and extending in a direction perpendicular to the axial direction (see an imaginary line F1 in FIG. 3). The bottom wall 32 is aligned with an intermediate position of the curved surface 22 on the outer surface of the cup member 16, and is spaced ΔP from an imaginary line F2 of the annular step 24 contiguous to the curved surface 22 along the axial direction (see FIG. 3).

The axial vertical cross-sectional shape of the bottom wall 32 of the cup member 16 includes a circular flat surface 33 having a diameter D3 as viewed in plan and an annular slanted surface 35 extending continuously from the circular flat surface 33 to the opening and inclined at a tilt angle of θ3 to the circular flat surface 33. As described later, the vertical cross-sectional shape of the bottom wall 32 is essentially identical to the vertical cross-sectional shape of a recess 62 of a third form 60 and a bottom wall 76 of a fourth form 70.

The outer race 12 is manufactured by the following steps:

In a first preparatory step, a workpiece 10 (see FIG. 2A) cut into a cylinder (billet) having a predetermined length is treated by spheroidizing annealing. The workpiece 10 is softened to facilitate first through fifth forging steps to be described below.

In a second preparatory step, the workpiece 10 is coated with a lubricative chemical conversion coating. Specifically, a lubricative chemical conversion coating of such as zinc phosphate or the like, for example, is formed on the surface of the workpiece 10 by bonderizing to make the surface of the workpiece 10 lubricative. More specifically, the workpiece 10 may be dipped in a solvent with zinc phosphate or the like dissolved therein for a predetermined period of time to form a lubricative chemical conversion coating on the workpiece 10.

Then, in a first forging step S1, a first forging die, not shown, is used to perform forward extrusion on an end face of the workpiece 10 coated with the lubricative chemical conversion coating.

Specifically, the workpiece 10 is placed in the cavity of the first forging die, not shown, and the end face of the workpiece 10 is pressed by a punch, not shown. The other end face of the workpiece 10 is pressed into the cavity, producing a first form 40 having a tapered reduced-diameter portion 40a and a shank 40b on the other end face, as shown in FIG. 2B.

Then, in a second forging step S2, the first form 40 is upset. Specifically, the first form 40 is placed in the cavity of a second forging die, not shown. At this time, the shank 40b is inserted in a shank holder, not shown, provided in the second forging die.

While the tip end of the shank 40b inserted in the shank holder, not shown, is being supported by a stop member, not shown, the upper portion of the first form 40 is pressed by a punch. As the upper portion of the first form 40 is pressed, the upper portion is compressed vertically and expanded horizontally, thereby producing a second form 50 (see FIG. 2C).

Then, in a third forging step S3, the upper surface of the head of the second form 50 is preliminarily pressed in to produce a third form 60 with a recess 62 defined centrally in the upper surface of the head (see FIG. 2D).

Specifically, a third forging die, not shown, is used, and the upper surface of the second form 50 placed in the cavity of the third forging die is pressed by a punch, not shown, forming a recess 62 in which the upper surface of the head of the second form 50 is centrally depressed a predetermined depth in the axial direction.

As shown in FIG. 6, the recess 62 is defined by a circular flat surface 64 having a diameter D1 (see FIG. 2D) as viewed in plan and an annular slanted surface 66 extending continuously from the circular flat surface 64 to the opening and inclined at a tilt angle of θ1 to the circular flat surface 64.

The recess 62 has a depth T1 (see FIG. 2D) which may be set to a value equal to or smaller than a spaced distance T2 (see FIG. 2E) between a circular flat surface 72 which is formed deeply in the cup member of a fourth form 70 in a next step and the inner terminal ends of ball rolling grooves 74 along the axial direction (vertical direction) (T1≦T2).

In the third form 60, the vertical cross-sectional shape of the recess 62 that is defined by the circular flat surface 64 and the annular slanted surface 66 is essentially identical to the vertical cross-sectional shape of a bottom wall 76 formed deeply in the cup member of the fourth form 70 in the next step, and is also essentially identical to the vertical cross-sectional shape of the bottom wall 32 of the outer race 12 of the final produced along the axial direction.

A round surface 68 having a curved cross-sectional shape which is not of an angular shape and has a predetermined radius of curvature is circumferentially formed in the boundary between the upper surface of the head of the third form 60 and the opening of the recess 62 (see FIG. 6).

The round surface 68 at the open inlet of the recess 62 is effective to prevent creases from being formed around the opening of the recess 62, and is also effective to avoid cracks which would otherwise be produced due to creases when the third form 60 will be heated in a subsequent step.

After the third forging step S3 is finished, the third form 60 is subjected to a low-temperature annealing process for removing stresses from the third form 60, a shot blasting process for removing oxide scales, etc. that are produced by the low-temperature annealing process, and a bonderizing process for forming a lubricative chemical conversion coating such as of zinc phosphate or the like on the outer surface of the third form 60. These processes allow the third form 60 to be plastically deformed with ease.

Thereafter, a fourth forging die, not shown, is used to carry out a fourth forging step S4. The fourth forging step is performed on the third form 60 whose shank is inserted in a shank inserter of the fourth forging die, not shown, by a punch, not shown, whose distal end is shaped substantially identically to the vertical cross-sectional shape of the recess 62 of the third form 60, thereby producing a fourth form 70 (see FIG. 2E).

The vertical cross-sectional shape of a bottom wall 76 formed deeply in the cup member of the fourth form 70 includes a circular flat surface 72 having a diameter D2 as viewed in plan and an annular slanted surface 78 extending continuously from the circular flat surface 72 to the opening and inclined at a tilt angle of θ2 to the circular flat surface 72. As described above, the vertical cross-sectional shape of the bottom wall 76 is essentially identical to the vertical cross-sectional shape of the recess 62 of the third form 60.

Since the fourth forging step S4 is performed on the third form 60 using the punch, not shown, whose distal end is shaped substantially identically to the vertical cross-sectional shape of the recess 62 of the third form 60, the circular flat surface 64 of the recess 62 does not plastically flow, and only the annular slanted surface 66 as a plastically flowable region is pushed outwardly backwards of the cup member.

After the fourth forging step S4, a fifth cold forging step S5 is performed on the fourth form 70. Prior to the fifth forging step S5, at least one of the surfaces of the fourth form 70 and a fifth forging die, not shown, may be coated with a liquid lubricant. The liquid lubricant prevents the fourth form 70 or the fifth forging die from suffering seizure during the fifth forging step. The liquid lubricant may be a known liquid lubricant which has heretofore been used.

In the fifth forging step S5, the fifth forging die, not shown, is used, and a punch whose distal end is shaped substantially identically to the vertical cross-sectional shape of the recess 62 of the third form 60 is used for ironing (finally sizing) the inner and outer surfaces of the fourth form 70 to finish the cup member 16 into a final product configuration.

Specifically, the wall thickness of the cup member 16 and the width and depth of the ball rolling grooves 30a through 30f are processed to desired dimensional accuracy to produce an outer race 12 used in a Barfield constant velocity universal joint as a completed product with the desired dimensional accuracy of the cup member 16 including the shape of the ball rolling grooves 30a through 30f (see FIG. 2F).

While the fifth forging step S5 is carried out on the fourth form 70, the circular flat surface 72 of the bottom wall 76 of the cup member does not plastically flow, and only the annular slanted surface 78 as a plastically flowable region is subjected to ironing.

The vertical cross-sectional shape of the bottom wall 32 formed deeply in the cup member 16 of the outer ring 12 includes a circular flat surface 33 having a diameter D3 as viewed in plan and an annular slanted surface 35 extending continuously from the circular flat surface 33 to the opening and inclined at a tilt angle of θ3 to the circular flat surface 33. The vertical cross-sectional shape of the recess 62 of the third form 60 is essentially identical to the vertical cross-sectional shape of the bottom wall of the fourth form 70.

Stated otherwise, the circular flat surfaces 64, 72, 33 of the forms ranging from the third form to a fifth form (the outer race 12 as a final product) have substantially equal diameters D1≅D2≅D3, and the annular slanted surfaces 66, 78, 35 have equal tilt angles θ1=θ2=θ3 with respect to the circular flat surfaces 64, 72, 33. The tilt angles of the annular slanted surfaces 66, 78, 35 should preferably be set to about 45 degrees.

The first forging step S1 through the third forging step S3 may be carried out according to a warm forging process or a hot forging process, and the fourth forging step S4 and the fifth forging step S5 may be carried out according to a cold forging process. Alternatively, all the first forging step S1 through the fifth forging step S5 may be carried out according to a cold forging process.

According to the present embodiment, an amount of work which would originally be involved in the formation of the bottom wall of the cup member in the fourth forging step S4 is assigned to the third forging step S3 which precedes the fourth forging step S4 to form the recess 62 in the upper surface of the third form 60. Thus, the forming percentage of the fourth forging step S4 for forming the ball rolling grooves 30a through 30f is reduced.

According to the present embodiment, as a result, since the forming percentage of the fourth forging step S4 is reduced, the amount of deformation (material elongation) of the forging blank is reduced to avoid the development of material cracks for thereby achieving a good die transcription rate.

According to the present embodiment, furthermore, the circular flat surface of the recess 62 formed in the third form 60 does not plastically flow, and is excluded from a plastically flowable region. Therefore, when the ball rolling grooves 74, 30a through 30f are to be formed in the fourth forging step and the fifth forging step, the plastic flow (material flow) becomes smoother to form the ball rolling grooves 74, 30a through 30f with higher accuracy.

According to the present embodiment, furthermore, as part of the amount of work involved in the fourth forging step is assigned to the third forging step which precedes the fourth forging step, the forming percentage of the fourth forging step for forming the ball rolling grooves 74 is reduced to optimally distribute work among the steps. As a consequence, the production of defective products suffering material cracks, etc. is suppressed for an increased yield.

Claims

1. A method of manufacturing an outer race for use in a Barfield constant velocity universal joint having a shank and a cup member which are integrally formed with each other by forging, comprising:

a first step of performing forward extrusion on a cylindrical workpiece which has been cut to a predetermined length to form a first form having a shank;

a second step of upsetting an upper portion of the first form exclusive of said shank to compress and diametrically enlarge the upper portion of the first form to form a second;

a third step of preliminarily pushing in an upper surface of said second form to form a third form having a recess formed in the upper surface which is essentially identical in axial vertical cross-sectional shape to a bottom wall of a cup member of a final product;

a fourth step of performing backward extrusion on said third form, using a punch whose distal end is shaped substantially identically to the vertical cross-sectional shape of said recess, to form a fourth form having a cup member with ball rolling grooves formed in an inner wall thereof; and

a fifth step of ironing the cup member of said fourth form.

2. A method according to claim 1, wherein a round surface having a curved cross-sectional shape is circumferentially formed in a boundary between an upper surface of a head of said third form and an opening of said recess.

3. A method according to claim 1, wherein said recess of said third form is defined by a circular flat surface having a diameter D1 as viewed in plan and an annular slanted surface extending continuously from said circular flat surface to the opening and inclined at a tilt angle of θ1 to said circular flat surface.

4. A method according to claim 3, wherein the vertical cross-sectional shape of a bottom wall formed deeply in the cup member of said fourth form includes a circular flat surface having a diameter D2 as viewed in plan and an annular slanted surface extending continuously from said circular flat surface to the opening and inclined at a tilt angle of θ2 to said circular flat surface, and is essentially identical to the vertical cross-sectional shape of the recess of said third form (D1≅D2, θ1=θ2).

5. A method according to claim 4, wherein the vertical cross-sectional shape of the bottom wall formed deeply in the cup member of said outer race includes a circular flat surface having a diameter D3 as viewed in plan and an annular slanted surface extending continuously from said circular flat surface to the opening and inclined at a tilt angle of θ3 to said circular flat surface, and is essentially identical to the vertical cross-sectional shapes of the recess of said third form and the bottom wall of said fourth form (70) (D1≅D2≅D3, θ1=θ2=θ3).

6. A method according to claim 1, wherein the recess of said third form has an axial depth T1 equal to or smaller than an axially spaced distance T2 (T1≦T2) between a circular flat surface formed deeply in the cup member of said fourth form and inner terminal ends of said ball rolling grooves.