Method of manufacturing constant speed drive shaft

Abstract

The invention aims to provide a manufacturing method of a constant-speed driving shaft, which can be used for efficiently, stably and precisely manufacturing the driving shaft, especially the constant-speed driving shaft. A method of manufacturing a constant speed drive shaft by fully closed die cold forging, the fully closed die cold forging comprising a metal die pair, the metal die pair comprising an upper metal die and a lower metal die, the method includes: an annealing step of partially annealing a molding material at positions at which a first large-diameter member and a second large-diameter member included in the constant-speed drive shaft are molded, respectively; a cooling step of cooling the molding material partially annealed in the first step; and a molding step of molding, in one step, the first large-diameter member, the second large-diameter member, and the third large-diameter member in the molding material cooled in the second step by extruding using a metal mold and extruding from both directions of the molding material.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a constant velocity drive shaft for a vehicle by fully enclosed die cold forging. Background Art

[0002] Traditionally, the shaft of a vehicle is used as part of the power transmission path of the engine, that is, the rotational motion of the engine is transmitted as rotational driving force to the drive wheels or similar structures. For such a shaft, it is necessary to reduce the weight to improve the fuel efficiency of the vehicle, and it is necessary to increase the stiffness to reduce vibration and improve the quietness effect.

[0003] As a method for manufacturing a vehicle shaft, vehicle shafts are generally manufactured by machining methods such as cutting, and thus there are problems that cutting causes a large amount of material loss and manufacturing takes a long time.

[0004] As a method for manufacturing a vehicle shaft without machining the material, a cold forging manufacturing method (Patent Document 1) has been proposed.

[0005] Patent Document 1 discloses: a block-shaped base member integrally provided with a drive member of a window regulator, a cylindrical shaft member extending from the base member and formed in a direction perpendicular to the base member, and a horizontally wide and flat member formed at the distal end portion of the shaft member. An inner diameter bearing member is provided inside the horizontally wide and flat member and on the same axial line as the axial center of the shaft member. All these members are molded by cold forging.

[0006] [List of Cited References]

[0007] [Patent Documents]

[0008] [Patent Document 1] Japanese Unexamined Patent No. 7-12115. Summary of the Invention

[0009] [Technical Problem]

[0010] However, the drive shaft molded by the cold forging method described in Patent Document 1 has the following problems: it is difficult to prevent burrs from appearing in the processed part, and the process of removing burrs is inefficient in manufacturing the drive shaft, increasing the manufacturing cost. When the shaft structure to be manufactured is complex, cold forging requires multiple processes, which also brings the problem of increased manufacturing cost.

[0011] The present invention is proposed in view of these problems, and its object is to provide a method for manufacturing a constant velocity drive shaft that can manufacture a drive shaft, especially a constant velocity drive shaft, efficiently, stably and with high precision.

[0012] [Solution to the Problem]

[0013] 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 full-closed die cold forging, the full-closed die cold forging including a pair of metal dies, the pair of metal dies including an upper metal die and a lower metal die, the method including: an annealing step: partially annealing a molding material at positions where a first large-diameter member and a second large-diameter member included in the constant velocity drive shaft are respectively molded; a cooling step: cooling the molding material partially annealed in the first step; and a molding step: molding the first large-diameter member, the second large-diameter member, and a third large-diameter member in the molding material cooled in the second step in one step by squeezing using the pair of metal dies and squeezing from two directions of the molding material.

[0014] 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 full-closed die cold forging, the full-closed die cold forging including a pair of metal dies, the pair of metal dies including an upper metal die and a lower metal die, the method including: a heating step: heat-treating a molding material at positions where a first large-diameter member and a second large-diameter member included in the constant velocity drive shaft are respectively molded; and a molding step: molding the first large-diameter member, the second large-diameter member, and a third large-diameter member in the molding material heat-treated in the first step in one step by squeezing using the pair of metal dies and squeezing from two directions of the molding material.

[0015] In the method for manufacturing a constant velocity drive shaft according to the present invention, the constant velocity drive shaft includes a shaft member and a first large-diameter member, a second large-diameter member, and a third large-diameter member that are larger in diameter than the shaft member from the center of the shaft member toward both ends.

[0016] In the method for manufacturing a constant velocity drive shaft according to the present invention, the pair of metal dies includes a first cavity for molding the first large-diameter member, a second cavity for molding the second large-diameter member, and a third cavity for molding the third large-diameter member.

[0017] In the method for manufacturing a constant velocity drive shaft according to the present invention, the annealing step includes annealing a first position where the first large-diameter member of the molding material is molded and a second position where the second large-diameter member of the molding material is molded, and maintaining these positions at substantially the same temperature for a predetermined period of time.

[0018] In the method for manufacturing a constant velocity drive shaft according to the present invention, the respective times when the first position and the second position start to cool are simultaneous in the cooling step, but the cooling time of one position is longer than the cooling time of the other position, and cooling and heating are repeated simultaneously.

[0019] In the method of manufacturing a constant velocity drive shaft according to the present invention, the temperatures at which the first position for molding the first large-diameter member of the molding material and the second position for molding the second large-diameter member are heated are different from each other in the heating step.

[0020] [Advantages of the Invention]

[0021] According to the present invention, by using a plurality of pairs of metal molds with different shapes and performing extrusion molding using full-closed die cold forging in each step to prevent the generation of burrs, a constant velocity drive shaft with low cost and high precision can be manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a plan view of the structure of the constant velocity drive shaft manufactured by the present invention.

[0023] Figure 2 is a schematic diagram of the structure of the metal mold used in an embodiment of the present invention.

[0024] Figure 3 is a schematic diagram of the method for manufacturing a constant velocity drive shaft.

[0025] Figure 4 is a flowchart of the steps of the forging method using a hardness difference.

[0026] Figure 5 is a schematic diagram for explaining the holding temperature in the heat treatment.

[0027] Figure 6 is a schematic diagram of the process for molding a constant velocity drive shaft by full-closed die cold forging.

[0028] Figure 7 is a schematic diagram of the process for molding a constant velocity drive shaft by full-closed die cold forging.

[0029] Figure 8 is a schematic overview of the forging method using a temperature difference.

[0030] Figure 9 is a flowchart of the steps of the forging method using a temperature difference.

[0031] Figure 10 is a schematic diagram of the process for molding a constant velocity drive shaft by full-closed die cold forging.

[0032] Figure 11 is a schematic diagram of the process for molding a constant velocity drive shaft by full-closed die cold forging. DETAILED DESCRIPTION OF THE INVENTION

[0033] Next, a method for manufacturing a constant velocity drive shaft according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0034] Figure 1 This is a plan view of the structure of the constant velocity drive shaft manufactured by the present invention.

[0035] As shown in the figure, the constant velocity drive shaft 100 includes a pair of constant velocity universal joints arranged substantially away from each other in the axial direction, and an intermediate shaft provided between the two constant velocity universal joints and integrally rotating with the corresponding inner joint members of the two constant velocity universal joints, and includes a shaft member 101 and a first large-diameter member 102, a second large-diameter member 103, and a third large-diameter member 104 formed axially from the center of the shaft member 101 toward each end. In the constant velocity drive shaft 100, a solid bar-shaped material is heat-treated and then the shaft member 101, the first large-diameter member 102, the second large-diameter member 103, and the third large-diameter member 104 are molded by fully enclosed die cold forging.

[0036] The shaft member 101 is rod-shaped, and its diameter is the same as or slightly smaller than the diameter of the solid bar-shaped material before the constant velocity drive shaft 100 is molded.

[0037] After heat treatment near the center of the main body of the constant velocity drive shaft 100, the first large-diameter member 102 is molded by fully enclosed die cold forging. The first large-diameter member 102 is columnar, its diameter is larger than the diameter of the shaft member 101, and it has tapered members 102a and 102b at its upper end portion and lower end portion, respectively.

[0038] The second large-diameter member 103 is columnar, its diameter is substantially the same as the diameter of the first large-diameter member 102, and it has tapered members 103a and 103b at its upper end portion and lower end portion, respectively. The third large-diameter member 104 is formed at each end portion of the two end portions of the constant velocity drive shaft 100, its diameter is larger than the diameter of the shaft member 101, and it is substantially the same as the diameters of the first large-diameter member 102 and the second large-diameter member 103. The third large-diameter member 104 is columnar and has tapered members 104a and 104b at its end portion on the center side of the constant velocity drive shaft 100, respectively.

[0039] <For die structure>

[0040] Figure 2 This is a schematic view of the structure of the die used in an embodiment of the present invention.

[0041] As shown in the figure, the die 200 is used to mold the shaft member 101, the first large-diameter member 102, the second large-diameter member 103, and the third large-diameter member 104 that constitute the constant velocity drive shaft 100 from a heat-treated material, and includes an upper die 201 and a lower die 202.

[0042] The upper metal mold 201 is vertically movable and includes, for example, a mechanism that moves up and down by a hydraulic mechanism or a pneumatic mechanism. The lower metal mold 202 is fixed. The upper metal mold 201 and the lower metal mold 202 are arranged opposite to each other.

[0043] Each of the upper metal mold 201 and the lower metal mold 202 included in the metal mold 200 has cavities for molding the first large-diameter part 101, the second large-diameter part 102, and the third large-diameter part 103 in the material X, respectively.

[0044] The upper metal mold 201 and the lower metal mold 202 include a first cavity 201a and 202a for molding the first large-diameter part 102, a second cavity 201b and 202b for molding the second large-diameter part 103, and a third cavity 201c and 202c for molding the third large-diameter part 104, respectively.

[0045] The first cavities 201a and 202a included in the upper metal mold 201 and the lower metal mold 202 are each concave and tapered on both sides. The shapes of the second cavities 201b and 202b are also the same as those of the first cavities 201a and 202a. On the other hand, the third cavities 201c and 202c are both concave and tapered on one side.

[0046] <Forging method using hardness difference>

[0047] Figure 3 is a schematic diagram illustrating a method of manufacturing a constant velocity drive shaft, Figure 4 is a flowchart illustrating a forging method using hardness difference, Figure 5 is a schematic diagram illustrating the holding temperature in heat treatment, Figure 6 and Figure 7 are illustrations respectively showing the process of molding a constant velocity drive shaft by fully enclosed die cold forging.

[0048] A method of manufacturing a constant velocity drive shaft will be described with reference to the accompanying drawings.

[0049] <Heat treatment process>

[0050] As Figure 3 the material X shown in (a), a suitable material can be selected from iron, stainless steel, brass, copper, nickel-chromium steel, chromium-molybdenum steel, and similar materials. The solid bar-shaped material X is heat-treated (annealed) (step S100).

[0051] As the heat treatment to be performed here, the material X is partially annealed at the positions where the first large-diameter member 102 and the second large-diameter member 103 are respectively formed. The partial annealing can be achieved by induction hardening using, for example, an induction hardening coil. A conventional method can also be employed, such as a method of locally heating by laser irradiation.

[0052] As Figure 3 As shown in (b), the positions (annealing positions A and B) of the material X where the first large-diameter member 102 and the second large-diameter member 103 are respectively formed are subjected to partial annealing. Specifically, the material X is inserted into a high-frequency heating coil (not shown) in a non-contact state, and the high-frequency heating coil is matched with the annealing positions A and B of the material X.

[0053] Then, a high-frequency current is passed through the high-frequency heating coil to perform induction heating and partial annealing on the annealing positions A and B. The heating temperatures between the annealing positions A and B can be the same or different. Specifically, the annealing positions A and B of the material X are both subjected to partial annealing at a heating temperature of 700°C to 900°C. The corresponding start and stop times of the induction heating of the annealing positions A and B are simultaneous.

[0054] As Figure 5 As shown, first, the high-frequency heating coil is operated to heat the annealing positions A and B to a predetermined temperature Ta (°C). Each of the annealing positions A and B is heated to a temperature of 700 to 900°C and the heating temperature is maintained for a predetermined period of time.

[0055] After the corresponding processed portions at the annealing positions A and B are heated for a predetermined period of time, the high-frequency heating coil is stopped. Then, the processed portion at the annealing position B is air-cooled to the 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.

[0056] That is, the processed portion at the annealing position A undergoes a process of alternately repeating heating and cooling and is cooled to the target temperature in a longer period of time (ta (min)) than the processed portion at the annealing position B, as Figure 4 shown. Specifically, at the start of cooling, the high-frequency heating coil is turned off and maintained for a cooling period, and after a predetermined period of time, the high-frequency heating coil is turned on for heat treatment. The heat treatment does not require a long enough period of time to soften the processed portion, and only needs to heat the processed portion for a short enough period of time to raise its temperature from the temperature during the cooling process by several degrees Celsius to several tens of degrees Celsius.

[0057] The processed part at annealing position A cools to the target temperature in a longer time period (tb (min)) than the processed part at annealing position B, while cooling and heating are repeated.

[0058] Therefore, the processed part at annealing position A cools for a longer time period than the processed part at annealing position B, resulting in a hardness difference between the corresponding processed parts at annealing positions A and B. That is, the processed part at annealing position A, which cools in a long time period through repeated cooling and heating, has a lower hardness than the processed part at annealing position B, which cools only by air cooling. Therefore, a hardness difference occurs between the corresponding processed parts at annealing positions A and B, and then the program proceeds to perform full-closed die cold forging using the hardness difference as a subsequent step.

[0059] In the heat treatment described here, the heating temperature, the cooling temperature, and the corresponding time periods required for heating and cooling can be changed according to the type of material.

[0060] For example, the hardness at annealing position A is 10 HRB, and the hardness at annealing position B is 5 HRB. The hardness varies depending on the material and the cooling time period, and the hardness difference between the two also varies depending on the material and the cooling time period.

[0061] <Full-closed die cold forging process>

[0062] Then, the heat-treated material X is molded in the full-closed die cold forging process.

[0063] During the heat treatment, the material X in a state where there is a hardness difference between annealing positions A and B is placed on the lower die 202 included in the die 200, as Figure 6 shown in (a) (step S101), and then the upper die 201 is lowered by a hydraulic cylinder (not shown) to closely contact the material X, forming a closed state as Figure 6 shown in (b).

[0064] While maintaining the closed state, the upper die 201 applies a predetermined load to the material X and applies pressure to the material X from both sides in the axial direction by a piston, as Figure 7 shown in (a). The load applied by the upper die 201 to the material X in the downward direction is 2000 kN to 5000 kN, and the load applied by the piston to the material X in the axial direction is 2000 kN to 3000 kN.

[0065] Under the loads applied by the upper metal die 201 and the piston, during the heat treatment process, the metal material with the lowest hardness in contact with the machined part at the annealing position A flows into the first cavity 201a of the upper metal die 201 and the first cavity 202a of the lower metal die 202. The metal material with the second lowest hardness in contact with the machined part at the annealing position B flows into the second cavity 201b in the upper metal die 201 and the second cavity 202b in the lower metal die 202. Finally, the non-heat-treated metal material at each end portion of the two end portions of the material X flows into the third cavity 201c of the upper metal die 201 and the third cavity 202c of the lower metal die 202.

[0066] In this way, the hardness of the parts of the large-diameter component expected to be molded by heat treatment is reduced, and a hardness difference appears between the parts. Thus, the material first starts to flow into the part with the lowest hardness, and thus a one-step compression process can be carried out by cold forging.

[0067] On the other hand, when no heat treatment is carried out or there is no hardness difference between the parts even though heat treatment has been carried out, and when the compression process has been carried out by cold forging, the metal material at each end portion of the two end portions of the material X will flow first, so that the large-diameter component is molded, and the metal material in the other part is prevented from flowing. Therefore, the parts of the large-diameter component expected to be molded are heat-treated, and a hardness difference is generated between the parts, so that multiple large-diameter components can be molded simultaneously by a one-step compression process.

[0068] <Forging method using temperature difference>

[0069] Next, a forging method using temperature difference will be introduced.

[0070] Figure 8 (a) to Figure 8 (c) are schematic diagrams showing the outline of the forging method using temperature difference, Figure 9 is a flowchart showing the forging method using temperature difference, Figure 10 and Figure 11 are diagrams respectively showing the process of molding a constant speed drive shaft by full-closed die cold forging.

[0071] <Heat treatment process>

[0072] As Figure 8 (a) shows, the solid rod-shaped material X is heat-treated (step S200). During the heat treatment process in the forging process using temperature difference, at the positions where the first large-diameter component 102 and the second large-diameter component 103 are respectively formed, the material X is heated to a predetermined temperature. For example, heating methods such as induction quenching coils and laser irradiation and traditional methods are used.

[0073] AsFigure 8 As shown in (b), heat treatment is performed on the positions (heating positions A and B) where the first large-diameter component 102 and the second large-diameter component 103 of material X are respectively formed. Specifically, material X is inserted into a high-frequency heating coil (not shown) in a non-contact state, and the high-frequency heating coil is matched with heating positions A and B of material X.

[0074] Next, a high-frequency current is passed through the high-frequency heating coil to inductively heat heating positions A and B. The heating temperature at heating position A is 400°C to 600°C, and the heating temperature at heating position B is 600°C to 800°C. The heating temperatures described here are only examples and can be changed according to the material type.

[0075] <Fully enclosed die cold forging process>

[0076] As Figure 8 shown in (c), when heating positions A and B are respectively heated to 700°C and 500°C by heat treatment, the program will then enter the cold forging process.

[0077] In the cold forging process, the heat-treated material X is placed on the lower metal die 202 included in the metal die 200, as Figure 10 shown in (a) (step S201), and the upper metal die 201 is lowered by a hydraulic cylinder (not shown) to make it in close contact with material X, forming a closed state ( Figure 10 b).

[0078] While maintaining the closed state, the upper metal die 201 applies a predetermined load to material X, and pressure is applied to both sides of material X in the axial direction by a piston, as Figure 11 shown in (a).

[0079] The load is similar to the forging method using the hardness difference described above, so it will not be elaborated here.

[0080] Next, under the action of the load applied by the upper metal die 201 and the load applied by the piston, a part of material X flows into the concave portions of each of the first to third cavities 201a to 201c formed in the upper metal die 201 and the first to third cavities 202a to 202c formed in the lower metal die 202 by compression processing, as Figure 11 shown in (b), and the first to third large-diameter components 102 to 104 are molded by one-step compression processing.

[0081] Under the loads applied by the upper metal mold 201 and the piston, the metal material that has been heated to the highest temperature at the heating position A flows into the first cavity 201a of the upper metal mold 201 and the first cavity 202a of the lower metal mold 202 during the heat treatment process. The metal material at the heating position B with the second highest temperature flows into the second cavity 201b of the upper metal mold 201 and the second cavity 202b of the lower metal mold 202. Finally, the unheat-treated metal material at each of the two end portions of the material X flows into the third cavity 201c of the upper metal mold 201 and the third cavity 202c of the lower metal mold 202.

[0082] Therefore, in the forging method using the temperature difference, the positions for separately molding the large-diameter components have been heated by heat treatment before the cold forging process, so that multiple large-diameter components can be simultaneously molded by one-step compression processing in the cold forging. Although the positions for separately molding the large-diameter components of the material X are heated, by changing the heating temperatures of the respective heating positions, a temperature difference is formed between the respective heating positions, resulting in a softening difference between the respective heating positions.

[0083] Therefore, the softest metal material at the heating position A will first flow into the cavities of each of the upper metal mold 201 and the lower metal mold 202 according to the difference in softening degree, thereby molding the first large-diameter component 102 and the second large-diameter component 103, and each of the two end portions of the unheat-treated material X will finally be molded into the shape of the third large-diameter component 104.

[0084] The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope and spirit of the present invention.

[0085] [List of Reference Numerals]

[0086] 100 Constant-speed drive shaft

[0087] 101 Shaft component

[0088] 102 First large-diameter component

[0089] 102a, 102b, 103a, 103b, 104a, 104b Tapered component

[0090] 103 Second large-diameter component

[0091] 104 Third large-diameter component

[0092] 200 Metal mold

[0093] 201 Upper metal mold

[0094] 202 Lower metal mold

[0095] The first cavities 201a and 202a

[0096] The second cavities 201b and 202b

[0097] The third cavities 201c and 202c.

Claims

1. A method for manufacturing a constant speed drive shaft by fully closed die cold forging, the fully closed die cold forging comprising a metal die pair, the metal die pair comprising an upper metal die and a lower metal die, the method comprising: An annealing step of partially annealing the molding material at positions where a first large diameter component and a second large diameter component included in the constant speed drive shaft are respectively molded; Cooling step: cooling the molded material partially annealed in the first step; as well as Molding step: molding the first large diameter component, the second large diameter component, and the third large diameter component in the molding material cooled in the second step in one step by extruding with a metal mold and extruding from two directions of the molding material.

2. A method for manufacturing a constant speed drive shaft by fully closed die cold forging, the fully closed die cold forging comprising a metal die pair, the metal die pair comprising an upper metal die and a lower metal die, the method comprising: A heating step of heat-treating the molding material at positions where a first large-diameter component and a second large-diameter component included in the constant speed drive shaft are respectively molded; as well as Molding step: molding the first large diameter member, the second large diameter member, and the third large diameter member in the molding material subjected to the heat treatment in the first step in one step by extruding with a metal mold and extruding from two directions of the molding material.

3. The method for manufacturing a constant speed drive shaft according to claim 1 or 2, wherein the constant speed drive shaft comprises a shaft member and a first large diameter member, a second large diameter member and a third large diameter member having a diameter larger than that of the shaft member from the center toward both ends of the shaft member.

4. The method for manufacturing a constant speed drive shaft according to claim 1 or 2, wherein the metal mold pair includes a first cavity for molding the first large diameter component, a second cavity for molding the second large diameter component, and a third cavity for molding the third large diameter component.

5. The method of manufacturing a constant speed drive shaft according to claim 1, wherein the annealing step includes annealing a first position of the molded material where the first large diameter component is molded and a second position where the second large diameter component is molded while maintaining the positions at approximately the same temperature for a predetermined period of time.

6. The method for manufacturing a constant speed drive shaft according to claim 5, wherein the respective times at which the first position and the second position start cooling are simultaneous in the cooling step, but the cooling time of one position is longer than the cooling time of the other position, and cooling and heating are repeated.

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

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