METHOD FOR MANUFACTURING CONSTANT VELOCITY DRIVE SHAFT

Abstract

A constant velocity drive shaft manufacturing method capable of manufacturing a constant velocity drive shaft among drive shafts with high efficiency and with stable and high accuracy. A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold includes an annealing step of partially annealing a molding material at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded, a cooling step of cooling the molding material partially annealed in the first step, and a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material cooled in the second step by pressing with the metal mold pair and pressing from both directions of the molding material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2023-207097, filed on Dec. 7, 2023, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a constant velocity drive shaft for vehicle by full enclosed die cold forging.

BACKGROUND ART

Conventionally, a shaft for vehicle has been used as a part of a power transmission path from an engine, that is, has transmitted rotational motion of the engine as a rotational driving force to a driving wheel or the like. For this shaft, a reduction in weight has been required to improve the fuel efficiency of a vehicle, and an increase in rigidity has been required to reduce vibration and improve quietness.

As a method for manufacturing a shaft for vehicle, the shaft for vehicle has been often manufactured generally by machining such as cutting processing, thereby presenting problems that there occur respective losses of a large number of materials by a cutting process and it takes time for the manufacturing.

As a method for manufacturing a shaft for vehicle without subjecting a material to cutting processing, a manufacturing method by cold forging has been proposed (Patent Literature 1).

Patent Literature 1 discloses that a block-shaped base part connected to a driving part of a window regulator, a cylindrical shaft part continued from the base part and formed in a direction perpendicular to the base part, and a width across flat part formed in a distal end portion of the shaft part are integrally provided, an inner-diameter bearing part is provided inside the width across flat part and on the same axial line as an axial center of the shaft part, and all these components are molded by cold forging means.

CITATION LIST

Patent Literature

[Patent Literature 1] Japanese Patent Laid-Open No. 7-12115

SUMMARY

Technical Problem

However, a drive shaft molded by the cold forging means described in Patent Literature 1 has problems that it is difficult to prevent a burr from occurring in a processed portion and a process for removing the burr is inefficient in manufacturing the drive shaft and increases a manufacturing cost. When a shaft to be manufactured has a complicated structure, cold forging needs to be performed in a plurality of processes, thereby also presenting a problem that a manufacturing cost increases.

The present invention has been made in view of such problems, and has as its object to provide a constant velocity drive shaft manufacturing method capable of manufacturing particularly a constant velocity drive shaft among drive shafts with high efficiency and with stable and high accuracy.

Solution to Problem

To attain the above-described object, a constant velocity drive shaft manufacturing method according to the present invention is a method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method including an annealing step of partially annealing a molding material at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded, a cooling step of cooling the molding material partially annealed in the first step, and a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material cooled in the second step by pressing with the metal mold pair and pressing from both directions of the molding material.

A constant velocity drive shaft manufacturing method according to the present invention is a method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method including a heating step of subjecting a molding material to heat treatment at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded, and a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material subjected to the heat treatment in the first step by pressing with the metal mold pair and pressing from both directions of the molding material.

In the method for manufacturing the constant velocity drive shaft according to the present invention, the constant velocity drive shaft includes a shaft part and the first large-diameter part, the second large-diameter part, and the third large-diameter part respectively having larger diameters than the diameter of the shaft part toward both end portions from the center of the shaft part.

In the method for manufacturing the constant velocity drive shaft according to the present invention, the metal mold pair includes a first cavity for molding the first large-diameter part, a second cavity for molding the second large-diameter part, and a third cavity for molding the third large-diameter part.

In the method for manufacturing the constant velocity drive shaft according to the present invention, the annealing step includes subjecting a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material to annealing treatment while holding the positions, respectively, at substantially the same temperatures for a predetermined time period.

In the method for manufacturing the constant velocity drive shaft according to the present invention, respective timings at which cooling is started at the first position and the second position are simultaneous in the cooling step, but one of the positions is cooled for a longer cooling time period than the other position while being repeatedly cooled and heated.

In the method for manufacturing the constant velocity drive shaft according to the present invention, temperatures at which a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material are respectively heated differ from each other in the heating step.

Advantageous Effect

According to the present invention, it is possible to manufacture a constant velocity drive shaft that can be reduced in cost and is highly accurate by being subjected to press molding using full enclosed die cold forging in each step using a plurality of metal mold pairs that differ in shape to prevent a burr from occurring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a configuration of a constant velocity drive shaft manufactured in the present invention.

FIG. 2 is a diagram illustrating a configuration of a metal mold used in an embodiment of the present invention.

FIGS. 3(A) to 3(D) are schematic views illustrating a method for manufacturing the constant velocity drive shaft.

FIG. 4 is a flowchart illustrating steps in a forging method using a hardness difference.

FIG. 5 is a schematic view for illustrating a holding temperature in heat treatment.

FIGS. 6(A) to 6(B) are diagrams illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

FIGS. 7(A) to 7(B) are diagrams illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

FIGS. 8(A) to 8(D) are diagrams illustrating an outline of a forging method using a temperature difference.

FIG. 9 is a flowchart illustrating steps in the forging method using a temperature difference.

FIGS. 10(A) to 10(B) are diagrams illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

FIGS. 11(A) to 11(B) are diagrams illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

DESCRIPTION OF PREFERRED EMBODIMENTS

Then, a method for manufacturing a constant velocity drive shaft according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view illustrating a configuration of the constant velocity drive shaft manufactured in the present invention.

As illustrated, a constant velocity drive shaft 100 includes a pair of constant velocity universal joints generally arranged away from each other in an axial direction and an intermediate shaft provided between both the constant velocity universal joints and rotating integrally with respective inner joint members of both the constant velocity universal joints, and includes a shaft part 101 and a first large-diameter part 102, a second large-diameter part 103, and a third large-diameter part 104 that are formed toward each of ends in the axial direction from the center of the shaft part 101. In the constant velocity drive shaft 100, a solid rod-shaped material is subjected to heat treatment, and the shaft part 101, the first large-diameter part 102, the second large-diameter part 103, and the third large-diameter part 104 are then molded by full enclosed die cold forging.

The shaft part 101 has a rod shape having a diameter that is the same as or slightly smaller than the diameter of the solid rod-shaped material before the constant velocity drive shaft 100 is molded.

The first large-diameter part 102 is molded by the full enclosed die cold forging after the heat treatment in the vicinity of the center of a main body of the constant velocity drive shaft 100. The first large-diameter part 102 has a columnar shape having a larger diameter than the diameter of the shaft part 101, and has tapered parts 102a and 102b, respectively, in both its upper and lower end portions.

The second large-diameter part 103 has a columnar shape having substantially the same diameter as that of the first large-diameter part 102, and has tapered parts 103a and 103b, respectively, in both its upper and lower end portions. The third large-diameter part 104 is formed in each of both end portions of the constant velocity drive shaft 100, and has a diameter that is larger than the diameter of the shaft part 101 and is substantially the same as those of the first large-diameter part 102 and the second large-diameter part 103. The third large-diameter part 104 has a columnar shape, and has tapered parts 104a and 104b, respectively, in its end portions on the center side of the constant velocity drive shaft 100.

For Configuration of Metal Mold

FIG. 2 is a diagram illustrating a configuration of a metal mold used in the embodiment of the present invention.

As illustrated, a metal mold 200 is for molding the shaft part 101, the first large-diameter part 102, the second large-diameter part 103, and the third large-diameter part 104, which constitute the constant velocity drive shaft 100, from the material subjected to the heat treatment, and includes an upper metal mold 201 and a lower metal mold 202.

The upper metal mold 201 is of a liftably movable type, and is composed of a mechanism that is lifted up and down by a hydraulic mechanism or a gas pressure mechanism, for example. The lower metal mold 202 is of a fixed type. The upper metal mold 201 and the lower metal mold 202 are arranged to oppose each other.

Each of the upper metal mold 201 and the lower metal mold 202 included in the metal mold 200 has cavities for respectively molding the first large-diameter part 101, the second large-diameter part 102, and the third large-diameter part 103 in a material X.

The upper metal mold 201 and the lower metal mold 202 respectively include first cavities 201a and 202a for molding the first large-diameter part 102, second cavities 201b and 202b for molding the second large-diameter part 103, and third cavities 201c and 202c for molding the third large-diameter part 104.

The first cavities 201a and 202a respectively included in the upper metal mold 201 and the lower metal mold 202 each have a concave shape and have a tapered shape on both sides. The second cavities 201b and 202b also each have the same shape as that of the first cavities 201a and 202a. On the other hand, the third cavities 201c and 202c each have a concave shape and have a tapered shape on one side.

Forging Method Using Hardness Difference

FIGS. 3(A) to 3(D) are schematic views illustrating a method for manufacturing the constant velocity drive shaft, FIG. 4 is a flowchart illustrating a forging method using a hardness difference, FIG. 5 is a schematic view for illustrating a holding temperature in heat treatment, and FIGS. 6(A) to 6(B) and 7(A) to 7(B) are diagrams each illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

The method for manufacturing the constant velocity drive shaft will be described with reference to the drawings.

Heat Treatment Process

As a material X illustrated in FIG. 3(A), an appropriate material can be adopted from among iron, stainless steel, brass, copper, nickel chromium steel, chromium molybdenum steel, and the like. The solid rod-shaped material X is subjected to heat treatment (annealing) (step S100).

As the heat treatment to be performed here, the material X is subjected to partial annealing at positions where the first large-diameter part 102 and the second large-diameter part 103 are respectively formed. The partial annealing is performed by induction hardening using an induction hardening coil, for example. A conventional method such as a method for performing partial heating by laser irradiation can also be adopted.

As illustrated in FIG. 3(B), the positions where the first large-diameter part 102 and the second large-diameter part 103 are respectively formed (an annealing position A and an annealing position B) of the material X are subjected to partial annealing. Specifically, the material X is inserted into a high-frequency heating coil (not illustrated) in a non-contact state, and the high-frequency heating coil is made to match the annealing position A and the annealing position B of the material X.

Then, a high-frequency current is made to flow through the high-frequency heating coil to inductively heat and partially anneal the annealing position A and the annealing position B. A heating temperature may be the same or different between the annealing position A and the annealing position B. Specifically, the annealing position A and the annealing position B of the material X are each partially annealed at a heating temperature from 700° C. to 900° C. Respective timings at which the inductive heating of the annealing position A and the annealing position B are started and stopped are simultaneous.

As illustrated in FIG. 5, the high-frequency heating coil is first operated to heat the annealing position A and the annealing position B to a predetermined temperature Ta (° C.). Each of the annealing position A and the annealing position B is heated to a temperature from 700 to 900° C., to hold the heating temperature for a predetermined time period.

After respective processed portions at the annealing position A and the annealing position B are each heated for a predetermined time period, the high-frequency heating coil is stopped. Then, the processed portion at the annealing position B is air-cooled to a target temperature (e.g., 300° C.), and the processed portion at the annealing position A is intermittently cooled to the target temperature (e.g., 300° C.) by repeatedly turning on and off the high-frequency heating coil.

That is, the processed portion at the annealing position A is subjected to processing for alternately repeating heating and cooling, to be cooled to the target temperature over a longer time period (ta (min)) than the processed portion at the annealing position B, as illustrated in FIG. 4. Specifically, the high-frequency heating coil is turned off and held for a cooling period when cooling is started, and the high-frequency heating coil is turned on to perform heat treatment after an elapse of a predetermined time period. The heat treatment does not require a time period long enough to soften the processed portion, to heat the processed portion for a time period short enough to rise by several degrees Celsius to several ten degrees Celsius from a temperature during cooling.

The processed portion at the annealing position A is cooled to the target temperature over a longer time period (tb (min)) than the processed portion at the annealing position B while being repeatedly cooled and heated.

Thus, the processed portion at the annealing position A is cooled over a longer time period than the processed portion at the annealing position B so that a hardness difference occurs between the respective processed portions at the annealing position A and the annealing position B. That is, the processed portion at the annealing position A cooled over a long time period by being repeatedly cooled and heated decreases in hardness than the processed portion at the annealing position B cooled only by air cooling. Therefore, a difference occurs in hardness between the respective processed portions at the annealing position A and the annealing position B, and the procedure proceeds to full enclosed die cold forging processing as a subsequent step using a hardness difference.

In the heat treatment illustrated here, a heating temperature and a cooling temperature, and respective time periods required for heating and cooling can be changed depending on the type of material.

A hardness at the annealing position A is 10 HRB, for example, and a hardness at the annealing position B is 5 HRB. The hardness differs depending on a material and a cooling time period, and a hardness difference therebetween also differs depending on the material and the cooling time period.

Full Enclosed Die Cold Forging Process

Then, the material X subjected to the heat treatment is molded in a full enclosed die cold forging process.

In a heat treatment process, the material X in a state where there is a hardness difference between the annealing position A and the annealing position B is placed on the lower metal mold 202 included in the metal mold 200 as illustrated in FIG. 6(A) (step S101), and the upper metal mold 201 is lowered by a hydraulic cylinder (not illustrated) and is brought into close contact with the material X to form a closed state as illustrated in FIG. 6(B).

The upper metal mold 201 applies a predetermined load to the material X while maintaining the closed state, and applies a pressure from both sides in the axial direction of the material X by a piston as illustrated in FIG. 7(A). The load to be applied in a downward direction to the material X by the upper metal mold 201 is 2000 kN to 5000 kN, and the load to be applied in the axial direction of the material X by the piston is 2000 kN to 3000 kN.

With the load applied by the upper metal mold 201 and the load applied by the piston, a metal material that contacts the processed portion at the annealing position A having the lowest hardness flows into the first cavity 201a in the upper metal mold 201 and the first cavity 202a in the lower metal mold 202 in the heat treatment process. A metal material that contacts the processed portion at the annealing position B having the next lowest hardness flows into the second cavity 201b in the upper metal mold 201 and the second cavity 202b in the lower metal mold 202. Finally, a metal material in each of both end portions of the material X not subjected to heat treatment flows into the third cavity 201c in the upper metal mold 201 and the third cavity 202c in the lower metal mold 202.

Thus, respective hardnesses of portions where large-diameter parts are desired to be molded by heat treatment are reduced, and there is a hardness difference among the portions, whereby the material first starts to flow into the portion having the lowest hardness, thereby making it possible to perform one step of compression processing by cold forging.

On the other hand, when heat treatment is not performed or heat treatment has been performed but there is no hardness difference among the portions and when compression processing by cold forging has been performed, the metal material in each of both the end portions of the material X first flows so that the large-diameter part is molded and the metal material in the other portion is prevented from flowing. Accordingly, the portions where the large-diameter parts are desired to be molded are subjected to heat treatment and a hardness difference is provided among the portions, thereby making it possible to simultaneously mold a plurality of large-diameter parts by one step of compression processing.

Forging Method Using Temperature Difference

Then, a forging method using a temperature difference will be described.

FIGS. 8(A) to 8(D) are diagrams illustrating an outline of a forging method using a temperature difference, FIG. 9 is a flowchart illustrating the forging method using a temperature difference, and FIGS. 10(A) to 10(B) and 11(A) to 11(B) are diagrams each illustrating processes for molding the constant velocity drive shaft by full enclosed die cold forging.

Heat Treatment Process

As illustrated in FIG. 8(A), the solid rod-shaped material X is subjected to heat treatment (step S200). In a heat treatment process in a forging process using a temperature difference, the material X is heated to a predetermined temperature at the positions where the first large-diameter part 102 and the second large-diameter part 103 are respectively formed. For example, a heating method and conventional method using an induction hardening coil and laser irradiation is adopted.

As illustrated in FIG. 8(B), the positions where the first large-diameter part 102 and the second large-diameter part 103 are respectively formed (the heating position A and the heating position B) of the material X are subjected to heat treatment. Specifically, the material X is inserted into a high-frequency heating coil (not illustrated) in a non-contact state, and the high-frequency heating coil is made to match the heating position A and the heating position B of the material X.

Then, a high-frequency current is made to flow through the high-frequency heating coil, to inductively heat the heating position A and the heating position B. A heating temperature is 400° C. to 600° C. at the heating position A, and is 600° C. to 800° C. at the heating position B. The heating temperature illustrated here is an example, and is changeable depending on the type of material.

Full Enclosed Die Cold Forging Process

As illustrated in FIG. 8(C), when the heating position A and the heating position B are respectively heated to 700° C. and 500° C. by the heat treatment, the procedure then proceeds to a cold forging process.

In the cold forging process, the material X subjected to the heat treatment is placed on the lower metal mold 202 included in the metal mold 200 as illustrated in FIG. 10(A) (step S201), and the upper metal mold 201 is lowered by a hydraulic cylinder (not illustrated) and is brought into close contact with the material X to form a closed state (FIG. 10(B)).

The upper metal mold 201 applies a predetermined load to the material X while maintaining the closed state, and applies a pressure from both sides in the axial direction of the material X by a piston as illustrated in FIG. 11(A).

The load is similar to that in the forging method using a hardness difference described above, and hence description thereof is not repeated.

Then, a part of the material X flows by compression processing to a concave portion constituting each of the first to third cavities 201a to 201c formed in the upper metal mold 201 and the first to third cavities 202a to 202c formed in the lower metal mold 202 with the load applied by the upper metal mold 201 and the load applied by the piston, as illustrated in FIG. 11(B), and the first to third large-diameter parts 102 to 104 are molded by one step of compression processing.

With the load applied by the upper metal mold 201 and the load applied by the piston, a metal material at the heating position A that has been heated to the highest temperature flows into the first cavity 201a in the upper metal mold 201 and the first cavity 202a in the lower metal mold 202 in the heat treatment process. A metal material at the heating position B having the next highest temperature flows into the second cavity 201b in the upper metal mold 201 and the second cavity 202b in the lower metal mold 202. Finally, a metal material in each of both end portions of the material X not subjected to heat treatment flows into the third cavity 201c in the upper metal mold 201 and the third cavity 202c in the lower metal mold 202.

Thus, in the forging method using a temperature difference, positions where large-diameter parts are respectively molded have been heated by the heat treatment before the cold forging process, thereby making it possible to simultaneously mold a plurality of large-diameter parts by one step of compression processing in cold forging. Although positions where large-diameter parts are respectively molded of the material X are heated, a temperature difference is provided among heating positions by changing a heating temperature depending on each of the positions so that there occurs a difference in softening among the heating positions.

Therefore, the metal material at the heating position A most softened first flows into the cavities in each of the upper metal mold 201 and the lower metal mold 202 depending on the difference in softening, whereby the first large-diameter part 102 and the second large-diameter part 103 are molded, and each of both the end portions of the material X not subjected to heat treatment is finally molded into a shape of the third large-diameter part 104.

The present invention is not limited to the above-described embodiment, but various modifications are possible without departing from the scope and spirit of the invention.

REFERENCE SIGNS LIST

• • 100 constant velocity drive shaft
  • 101 shaft part
  • 102 first large-diameter part
  • 102 a, 102 b, 103 a, 103 b, 104 a, 104 b tapered part
  • 103 second large-diameter part
  • 104 third large-diameter part
  • 200 metal mold
  • 201 upper metal mold
  • 202 lower metal mold
  • 201 a, 202 a first cavity
  • 201 b, 202 b second cavity
  • 201 c, 202 c third cavity

Claims

1. A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method comprising: an annealing step of partially annealing a molding material at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded;a cooling step of cooling the molding material partially annealed in the first step; anda molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material cooled in the second step by pressing with the metal mold pair and pressing from both directions of the molding material.

2. A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method comprising: a heating step of subjecting a molding material to heat treatment at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded; anda molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material subjected to the heat treatment in the first step by pressing with the metal mold pair and pressing from both directions of the molding material.

3. The method for manufacturing the constant velocity drive shaft according to claim 1, wherein the constant velocity drive shaft includes a shaft part and the first large-diameter part, the second large-diameter part, and the third large-diameter part respectively having larger diameters than the diameter of the shaft part toward both end portions from the center of the shaft part.

4. The method for manufacturing the constant velocity drive shaft according to claim 1, wherein the metal mold pair includes a first cavity for molding the first large-diameter part, a second cavity for molding the second large-diameter part, and a third cavity for molding the third large-diameter part.

5. The method for manufacturing the constant velocity drive shaft according to claim 1, wherein the annealing step includes subjecting a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material to annealing treatment while holding the positions, respectively, at substantially the same temperatures for a predetermined time period.

6. The method for manufacturing the constant velocity drive shaft according to claim 5, wherein respective timings at which cooling is started at the first position and the second position are simultaneous in the cooling step, but one of the positions is cooled for a longer cooling time period than the other position while being repeatedly cooled and heated.

7. The method for manufacturing the constant velocity drive shaft according to claim 2, wherein temperatures at which a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material are respectively heated differ from each other in the heating step.

8. The method for manufacturing the constant velocity drive shaft according to claim 2, wherein the constant velocity drive shaft includes a shaft part and the first large-diameter part, the second large-diameter part, and the third large-diameter part respectively having larger diameters than the diameter of the shaft part toward both end portions from the center of the shaft part.

9. The method for manufacturing the constant velocity drive shaft according to claim 2, wherein the metal mold pair includes a first cavity for molding the first large-diameter part, a second cavity for molding the second large-diameter part, and a third cavity for molding the third large-diameter part.