Method of manufacturing drive shaft for constant velocity

Abstract

To provide a method of manufacturing a drive shaft for contant velocity, with which a drive shaft for constant velocity in particular, among drive shafts, can be manufactured efficiently and with stable and high accuracy.SOLUTION: A method of manufacturing a drive shaft for constant velocity according to closed cold-forging comprising a die pair constituted by an upper die and a lower die includes: an annealing process for applying partial annealing to a molding raw material at a position for molding a first large diameter part and a second large diameter part constituting the drive shaft for constant velocity; a cooling process for cooling the molding raw material subjected to partial annealing in the first process; and a molding process for molding a first large diameter part, a second large diameter part, and a third large diameter part in a molding raw material in one process by applying pressing force by the die pair and pressing force from both directions to the molding raw material cooled in the second step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a manufacturing method of a constant velocity drive shaft for a vehicle by closed die cold forging.

Background Art

[0002] Conventionally, a shaft for a vehicle is used as part of a power transmission path from an engine, that is, it transmits the rotational motion of the engine as a rotational driving force to a driving wheel or the like. For this shaft, weight reduction is required to improve the fuel efficiency of the vehicle, and high rigidity is required to reduce vibration and improve quietness.

[0003] As a manufacturing method of a shaft for a vehicle, it is generally manufactured by machining such as cutting, and there are problems such as a large loss of material due to the cutting process and time required for manufacturing. Therefore, as a method of manufacturing a shaft for a vehicle without cutting the material, a manufacturing method by cold forging has been proposed (Patent Document 1).

[0004] According to Patent Document 1, a block-shaped base portion connected to a drive portion of a window regulator, a cylindrical shaft portion continuously formed with the base portion and formed in a direction perpendicular to the base portion, and a double-width portion formed at a tip portion of the shaft portion are integrally provided, and an inner diameter bearing portion is provided on the same axis as the axis of the shaft portion inside the double-width portion, and it is described that all these constituent portions are formed by cold forging means.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of a drive shaft formed by the cold forging means described in Patent Document 1, it is difficult to prevent burrs from occurring in the processed portion, and the process of removing these burrs is inefficient in manufacturing the drive shaft and increases the manufacturing cost. Further, when the shaft to be manufactured has a complex structure, there is also a problem that the manufacturing cost increases because cold forging needs to be performed in a plurality of steps.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a method for manufacturing a constant velocity drive shaft that can efficiently and stably manufacture a constant velocity drive shaft, particularly with high precision.

Means for Solving the Problems

[0008] To achieve the above object, a method for manufacturing a constant velocity drive shaft according to the present invention is a method for manufacturing a constant velocity drive shaft by closed die cold forging including a die pair composed of an upper die and a lower die, the method including: an annealing step of partially annealing a forming material at a position where a first large-diameter portion and a second large-diameter portion constituting the constant velocity drive shaft are formed; a cooling step of cooling the forming material partially annealed in the first step; and a forming step of forming a first large-diameter portion, a second large-diameter portion, and a third large-diameter portion in the forming material in one step by pressing the forming material cooled in the second step with the die pair and pressing from both directions.

[0009] Further, a method for manufacturing a constant velocity drive shaft according to the present invention is a method for manufacturing a constant velocity drive shaft by closed die cold forging including a die pair composed of an upper die and a lower die, the method including: a heating step of heat-treating a forming material at a position where a first large-diameter portion and a second large-diameter portion constituting the constant velocity drive shaft are formed; and a forming step of forming a first large-diameter portion, a second large-diameter portion, and a third large-diameter portion in the forming material in one step by pressing the forming material heat-treated in the first step with the die pair and pressing from both directions.

[0010] In addition, the manufacturing method of the constant velocity drive shaft of the present invention is characterized in that the constant velocity drive shaft has a shaft portion, a first large-diameter portion larger than the diameter of the shaft portion from the center of the shaft portion toward both ends, a second large-diameter portion, and a third large-diameter portion.

[0011] In addition, the manufacturing method of the constant velocity drive shaft of the present invention is characterized in that the mold pair has a first cavity for molding the first large-diameter portion, a second cavity for molding the second large-diameter portion, and a third cavity for molding the third large-diameter portion.

[0012] In addition, the manufacturing method of the constant velocity drive shaft of the present invention is characterized in that in the annealing process, annealing is performed while maintaining the temperature at the same level for a certain period of time at a first position for molding the first large-diameter portion of the molded material and at a second position for molding the second large-diameter portion.

[0013] In addition, the manufacturing method of the constant velocity drive shaft of the present invention is characterized in that in the cooling process, the timing of starting cooling at the first position and the second position is the same, but for one position, cooling is performed while repeating cooling and heating, and the cooling time is made longer than that of the other position.

[0014] In addition, the manufacturing method of the constant velocity drive shaft of the present invention is characterized in that in the heating process, the temperatures for heating the first position for molding the first large-diameter portion of the molded material and the second position for molding the second large-diameter portion are different.

Advantages of the Invention

[0015] According to the present invention, by using a plurality of mold pairs with different shapes and performing press molding by closed-die cold forging in each process, the generation of burrs can be prevented, the cost can be reduced, and a high-precision constant velocity drive shaft can be manufactured.

Brief Description of the Drawings

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Best Mode for Carrying Out the Invention

[0017] Next, a manufacturing method of a constant velocity drive shaft according to an embodiment of the present invention will be described with reference to the drawings. Figure 1 is a plan view showing the configuration of a constant velocity drive shaft manufactured by the present invention. As shown in the figure, the constant velocity drive shaft 100 is generally provided between a pair of constant velocity joints arranged axially spaced apart and both constant velocity joints, and includes an intermediate shaft that rotates integrally with the inner joint members of both constant velocity joints. It is composed of a shaft portion 101, a first large-diameter portion 102 formed from the center of the shaft portion 101 toward each end in the axial direction, a second large-diameter portion 103, and a third large-diameter portion 104. The constant velocity drive shaft 100 is formed by subjecting a solid bar-shaped material to heat treatment and then performing closed die cold forging to form the shaft portion 101, the first large-diameter portion 102, the second large-diameter portion 103, and the third large-diameter portion 104.

[0018] The shaft portion 101 has a rod shape with a diameter that is the same as or slightly smaller than the diameter of the solid bar-shaped material before forming the constant velocity drive shaft 100. The first large-diameter portion 102 is formed by closed die cold forging after heat treatment near the center of the main body of the constant velocity drive shaft 100. The diameter of the first large-diameter portion 102 is larger than the diameter of the shaft portion 101 and is cylindrical, and has tapered portions 102a and 102b at both upper and lower ends.

[0019] The second large-diameter portion 103 has a cylindrical shape with a diameter substantially the same as that of the first large-diameter portion 102 and has tapered portions 103a and 103b at both upper and lower ends. The third large-diameter portion 104 is formed at both ends of the constant velocity drive shaft 100, has a diameter larger than that of the shaft portion 101 and substantially the same diameter as the first large-diameter portion 102 and the second large-diameter portion 103. The third large-diameter portion 104 has a cylindrical shape and has tapered portions 104a and 104b at the end on the center side of the constant velocity drive shaft 100.

[0020] <Regarding the configuration of the mold> Figure 2 is a diagram showing the configuration of the mold used in the embodiment of the present invention. As shown in the figure, the mold 200 is for molding the shaft portion 101, the first large-diameter portion 102, the second large-diameter portion 103, and the third large-diameter portion 104 that constitute the constant velocity drive shaft 100 from a heat-treated material, and is composed of an upper mold 201 and a lower mold 202.

[0021] The upper die 201 is a movable type that can move up and down, and is composed of a mechanism that moves up and down by, for example, a hydraulic mechanism or a gas pressure mechanism. The lower die 202 is a fixed type, and the two are arranged to face each other.

[0022] The upper die 201 and the lower die 202 that make up the die 200 have cavities for forming the first large-diameter portion 101, the second large-diameter portion 102, and the third large-diameter portion 103 with respect to the material X. The upper die 201 and the lower die 202 have a first cavity 201a, 202a for forming the first large-diameter portion 102, a second cavity 201b, 202b for forming the second large-diameter portion 103, and a third cavity 201c, 202c for forming the third large-diameter portion 104.

[0023] The first cavities 201a, 202a of the upper die 201 and the lower die 202 are concave, and both sides are tapered. The second cavities 201b, 202b also have the same shape as the first cavities 201a, 202a. On the other hand, the third cavities 201c, 202c are concave, and one side is tapered.

[0024] <Forging method using hardness difference> Figure 3 is a schematic diagram showing a manufacturing method of a constant-velocity drive shaft, Figure 4 is a flowchart showing a forging method using a hardness difference, Figure 5 is a schematic diagram for explaining the holding temperature of heat treatment, and Figures 6 and 7 are diagrams showing the forming process of a constant-velocity drive shaft by closed-die cold forging. With reference to these drawings, the manufacturing method of the constant-velocity drive shaft will be described.

[0025] <Heat treatment process> The material X shown in Figure 3(a) can adopt an appropriate material from iron, stainless steel, brass, copper, nickel-chromium steel, chromium-molybdenum steel, etc. Heat treatment (annealing) is performed on this solid bar-shaped material X (step S100). The heat treatment performed here is to perform partial annealing on the positions where the first large-diameter portion 102 and the second large-diameter portion 103 are formed on the material X. The partial annealing is performed, for example, by high-frequency quenching using a high-frequency quenching coil. It is also possible to adopt conventional methods such as a method of partially heating by laser irradiation.

[0026] As shown in Fig. 3(b), partial annealing is performed at the positions (annealing position A and annealing position B) where the first large-diameter portion 102 and the second large-diameter portion 103 of the material X are formed. Specifically, the material X is inserted into the inside of a high-frequency heating coil (not shown) in a non-contact state, and the high-frequency heating coil is aligned with the annealing position A and the annealing position B of the material X.

[0027] Next, a high-frequency current is passed through the high-frequency heating coil to inductively heat the annealing position A and the annealing position B to perform partial annealing. The heating temperature may be the same or different for the annealing position A and the annealing position B. Specifically, the annealing position A and the annealing position B of the material X are partially annealed at a heating temperature of 700°C to 900°C. Note that the timing to start and the timing to stop the inductive heating of the annealing position A and the annealing position B are the same.

[0028] As shown in Fig. 5, first, the high-frequency heating coil is operated to heat the annealing position A and the annealing position B to a predetermined temperature Ta (°C). The annealing position A and the annealing position B are heated to a temperature of 700 to 900°C and the heating temperature is maintained for a certain period of time. After heating the processed portions at the annealing position A and the annealing position B for a certain period of time, the high-frequency heating coil is stopped. Next, for the processed portion at the annealing position B, it is cooled to the target temperature (for example, 300°C) by air cooling, and for the processed portion at the annealing position A, the high-frequency heating coil is intermittently turned on and off repeatedly to cool it to the target temperature (for example, 300°C).

[0029] That is, as shown in Fig. 4, a process of alternately repeating heating and cooling is performed on the processed portion at the annealing position A, and it is cooled to the target temperature over a longer time than the processed portion at the annealing position B (ta(min)). Specifically, when cooling starts, the high-frequency heating coil is turned off to maintain the cooling period, and after a certain period of time, the high-frequency heating coil is turned on to perform a heating process. This heating process does not require a time sufficient to soften the processed portion, and heating is performed for a time such that the temperature rises several degrees to several tens of degrees from the temperature during cooling.

[0030] While repeating cooling and heating, the processed portion at the annealing position A is cooled to the target temperature over a longer time (tb(min)) than the processed portion at the annealing position B. By cooling the processed portion at the annealing position A over a longer time than the processed portion at the annealing position B in this way, a hardness difference occurs between the processed portions at the annealing position A and the annealing position B. That is, the hardness of the processed portion at the annealing position A, which is cooled by repeatedly heating and cooling over a longer time than the processed portion at the annealing position B that is simply air-cooled, decreases. Therefore, a difference in hardness occurs between the processed portions at the annealing position A and the annealing position B, and the process proceeds to the next step of closed-die cold forging treatment that utilizes the hardness difference. Note that the heating temperature, cooling temperature, and time taken for heating and cooling shown here can be changed depending on the type of material. The hardness at the annealing position A is, for example, 10 HRB and the hardness at the annealing position B is 5 HRB. This hardness varies depending on the material and the cooling time, and the hardness difference between the two also varies depending on the material and the cooling time.

[0031] <Closed-die cold forging process> Next, the heat-treated material X is formed in a closed-die cold forging process. In the heat treatment process, the material X with a hardness difference between the annealing position A and the annealing position B is placed on the lower die 202 that constitutes the die 200 as shown in Fig. 6(a) (step S101), and the upper die 201 is lowered by a hydraulic cylinder (not shown) as shown in Fig. 6(b) so that the upper die 201 is brought into close contact with the material X to form a closed state.

[0032] While maintaining this closed state, the upper die 201 applies a predetermined load to the material X and applies pressure from both sides in the axial direction of the material X by means of a piston as shown in Fig. 7(a). The load applied downward by the upper die 201 to the material X is 2000 kN to 5000 kN, and the load applied by the piston in the axial direction of the material X is 2000 kN to 3000 kN.

[0033] Due to the load by the upper die 201 and the load by the piston, first, the metal material corresponding to the processed portion of the annealing position A with the lowest hardness by the heat treatment process flows into the first cavity 201a of the upper die 201 and the first cavity 202a of the lower die 202. Then, next, the metal material corresponding to the processed portion of the annealing position B with a lower hardness flows into the second cavity 201b of the upper die 201 and the second cavity 202b of the lower die 202. Finally, the metal materials at both end portions of the non-heat-treated material X flow into the third cavity 201c of the upper die 201 and the third cavity 202c of the lower die 202.

[0034] In this way, the hardness of the portion where the large-diameter portion is to be formed is lowered by heat treatment, and due to the hardness difference for each portion, the material flow starts in order from the portion with the lowest hardness, enabling compression processing by cold forging in one step. Conversely, when compression processing by cold forging is performed without heat treatment or when there is no hardness difference for each portion even after heat treatment, the metal materials at both end portions of the material X flow first and the large-diameter portion is formed, and the flow of the metal material in other portions is blocked. Therefore, by performing heat treatment on the portion where the large-diameter portion is to be formed and providing a hardness difference for each portion, it becomes possible to simultaneously form a plurality of large-diameter portions by compression processing in one step.

[0035] <Forging Method Utilizing Temperature Difference> Next, a forging method utilizing temperature difference will be described. Figs. 8(a) to (c) are diagrams showing the outline of the forging method utilizing temperature difference, Fig. 9 is a flowchart showing the forging method utilizing temperature difference, and Figs. 10 and 11 are diagrams showing the molding process of a drive shaft for constant speed by closed-die cold forging.

[0036] <Heat treatment process> As shown in Fig. 8(a), heat treatment is performed on the solid bar-shaped material X (step S200). In the heat treatment process in the forging process using the temperature difference, the positions where the first large-diameter portion 102 and the second large-diameter portion 103 are formed on the material X are heated to a predetermined temperature. For example, a heating method using a high-frequency quenching coil or laser irradiation is adopted, and the conventional method is used.

[0037] As shown in Fig. 8(b), heat treatment is performed on the positions (heating positions A and B) where the first large-diameter portion 102 and the second large-diameter portion 103 of the material X are formed. Specifically, the material X is inserted into the inside of a high-frequency heating coil (not shown) in a non-contact state, and the high-frequency heating coil is aligned with the heating positions A and B of the material X.

[0038] Next, a high-frequency current is passed through the high-frequency heating coil to inductively heat the heating positions A and B. The heating temperature is 400°C to 600°C at the heating position A and 600°C to 800°C at the heating position B. Note that the heating temperatures shown here are examples and can be changed depending on the type of material.

[0039] <Closed die cold forging process> As shown in Fig. 8(c), when the heating position A is heated to 700°C and the heating position B is heated to 500°C by the heat treatment, the process then proceeds to the cold forging process. In the cold forging process, as shown in Fig. 10(a), the heat-treated material X is placed on the lower die 202 that constitutes the die 200 (step S201), and the upper die 201 is lowered by a hydraulic cylinder (not shown) to bring the upper die 201 into close contact with the material X to form a closed state (Fig. 10(b)).

[0040] While maintaining this closed state, the upper die 201 applies a predetermined load to the material X and, as shown in Fig. 11(a), applies pressure from both sides in the axial direction of the material X by a piston. Regarding the load, since the forging method using the hardness difference described above is the same, the explanation is omitted.

[0041] Next, as shown in FIG. 11(b), due to the load applied by the upper die 201 and the load applied by the piston, a part of the material X flows by material flow through compression processing into the concave portions constituting the first to third cavities 201a to 201c formed in the upper die 201 and the first to third cavities 202a to 202c formed in the lower die 202, and the first to third large-diameter portions 102 to 104 are formed by one-step compression processing.

[0042] Due to the load applied by the upper die 201 and the load applied by the piston, first, the metal material at the heating position A heated to the highest temperature by the heat treatment process flows into the first cavity 201a of the upper die 201 and the first cavity 202a of the lower die 202. Then, next, the metal material at the heating position B with a high temperature flows into the second cavity 201b of the upper die 201 and the second cavity 202b of the lower die 202. And finally, the metal materials at both end portions of the unheat-treated material X flow into the third cavity 201c of the upper die 201 and the third cavity 202c of the lower die 202.

[0043] Thus, in the forging method using the temperature difference, by heating the position where the large-diameter portion is to be formed by heat treatment before the cold forging process, it becomes possible to simultaneously form a plurality of large-diameter portions by the compression processing of one-step cold forging. Heating is performed on the position where the large-diameter portion of the material X is to be formed, and by changing the heating temperature according to the position to provide a temperature difference at the heating position, a difference in softening of the heating position occurs.

[0044] Therefore, by flowing in order from the metal material at the heating position A that is the most softened due to the difference in softening into the respective cavities of the upper die 201 and the lower die 202, the first large-diameter portion 102 and the second large-diameter portion 103 are formed, and finally, both end portions of the unheat-treated material X are formed into the shape of the third large-diameter portion 104. is

[0045] Note that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

Explanation of Reference Numerals

[0046] 100 Drive shaft for constant speed 101 Shaft portion 102 First large-diameter portion 102a, 102b, 103a, 103b, 104a, 104b Taper portion 103 Second large-diameter portion 104 Third large-diameter portion 200 Mold 201 Upper mold 202 Lower mold 201a, 202a First cavity 201b, 202b Second cavity 201c, 202c Third cavity

Claims

1. A method for manufacturing a constant velocity drive shaft by closed die cold forging, comprising a die pair composed of an upper die and a lower die, an annealing step of partially annealing the forming material at positions where a first large-diameter portion and a second large-diameter portion constituting the constant velocity drive shaft are formed with respect to the forming material, a cooling step of cooling the forming material partially annealed in the first step, a forming step of forming a first large-diameter portion, a second large-diameter portion, and a third large-diameter portion on the forming material in one step by pressing the forming material cooled in the second step with the die pair and pressing from both directions, A method for manufacturing a constant velocity drive shaft, characterized by comprising the above steps.

2. A method for manufacturing a constant velocity drive shaft by closed die cold forging, comprising a die pair composed of an upper die and a lower die, a heating step of heat-treating the forming material at positions where a first large-diameter portion and a second large-diameter portion constituting the constant velocity drive shaft are formed with respect to the forming material, a forming step of forming a first large-diameter portion, a second large-diameter portion, and a third large-diameter portion on the forming material in one step by pressing the forming material heat-treated in the first step with the die pair and pressing from both directions, A method for manufacturing a constant velocity drive shaft, characterized by comprising the above steps.

3. The constant velocity drive shaft according to claim 1 or 2, characterized in that it has a shaft portion, a first large-diameter portion larger than the diameter of the shaft portion from the center of the shaft portion toward both ends, a second large-diameter portion, and a third large-diameter portion.

4. The die pair according to claim 1 or 2, characterized in that it has a first cavity for forming a first large-diameter portion, a second cavity for forming a second large-diameter portion, and a third cavity for forming a third large-diameter portion. A method for manufacturing a constant velocity drive shaft, characterized by comprising the above steps.

5. The annealing process of the manufacturing method of the constant velocity drive shaft according to claim 1 is characterized in that annealing treatment is performed while maintaining the temperature at the same level for a certain period of time at the first position for forming the first large-diameter portion of the formed material and at the second position for forming the second large-diameter portion.

6. In the cooling process of the manufacturing method of the constant velocity drive shaft according to claim 5, the timing of starting cooling at the first position and the second position is the same. However, for one of the positions, cooling is performed while repeating cooling and heating, and the cooling time is made longer than that of the other position.

7. In the heating process of the manufacturing method of the constant velocity drive shaft according to claim 2, the heating temperatures for the first position for forming the first large-diameter portion of the formed material and the second position for forming the second large-diameter portion are different.

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