Methods for shaft manufacturing.

Abstract

Provided is a shaft manufacturing method that enables a wider selection of materials for a pipe member, and also improves mass productivity. This method for manufacturing a shaft 1 for which coupling members 3 are provided on the ends of a cylindrical member 2 carries out: a polishing step in which the end surfaces of a metal plate material are polished; a bending step in which the metal plate material is bent into a cylindrical shape or an arc shape; a diffusion bonding step in which the polished end surfaces which are of the metal plate bent into the cylindrical shape and are opposed to each other are abutted against each other or in which a plurality of the metal plate materials which have been bent into the arc shape are arranged in a cylindrical shape and the polished end surfaces thereof are abutted against each other, and the abutting portions are heated to carry out diffusing bonding, thereby forming the cylindrical member 2; a cooling step in which the cylindrical member 2 is cooled after the diffusion bonding step; and a coupling member joining step in which coupling members 3 are joined to the ends of the cylindrical member 2.

Description

Shaft manufacturing method

[0001] The present invention relates to a method for manufacturing a shaft.

[0002] Hollow shafts, in which connecting members provided with gears and splines are joined by friction welding to both ends of a prefabricated pipe member, are sometimes used as shafts for motors and the like (see Patent Document 1). For example, hollow shafts are often used when there is a strong demand for weight reduction, such as the shafts of motors for electric vehicles (EVs).

[0003] Japanese Patent Application Laid-Open No. 2006-258236

[0004] However, when using ready-made pipe members, the material must be selected from among the ready-made products prepared in advance by the manufacturer, and there are limitations on the materials that can be selected.

[0005] The present invention has been made in consideration of the current situation as described above, and aims to provide an unprecedented method for manufacturing a shaft, which allows for a wider range of choices for the material of the pipe member and also improves mass productivity.

[0006] The gist of the present invention will be explained with reference to the accompanying drawings.

[0007] A first aspect of the present invention relates to a method for manufacturing a shaft 1 having a connecting member 3 provided at the end of a cylindrical member 2, the method comprising: a polishing step of polishing the end faces of a metal plate; a bending step of bending the metal plate into a cylindrical or arc shape; a diffusion bonding step of butting the polished end faces of the metal plates facing each other in a cylindrically bent state, or of arranging a plurality of the metal plates bent into an arc shape in a cylindrical form and butting the polished end faces together, and heating the butted portions to form the cylindrical member 2; a cooling step of cooling the cylindrical member 2 after the diffusion bonding step; and a connecting member joining step of joining the connecting member 3 to the end of the cylindrical member 2.

[0008] A second aspect of the present invention relates to a method for manufacturing a shaft according to the first aspect, characterized in that the polishing step polishes the end face of the metal plate material so that the surface roughness Ra of the end face is 2 μm or less.

[0009] Furthermore, a third aspect of the present invention relates to a shaft manufacturing method characterized in that, in either the first or second aspect, it includes an outer finishing step of finishing the outer surface of the connecting portion between the cylindrical member 2 and the connecting member 3.

[0010] Furthermore, a fourth aspect of the present invention relates to a method for manufacturing a shaft according to any one of the first to third aspects, characterized in that it includes an inner finishing step of finishing the inner surface of the butted portion of the cylindrical member 2.

[0011] A fifth aspect of the present invention relates to a method for manufacturing a shaft according to any one of the first to fourth aspects, wherein the connecting member joining step is performed by friction welding or shrink fitting.

[0012] A sixth aspect of the present invention relates to the method for manufacturing a shaft according to the fifth aspect, characterized in that the connecting member joining step is carried out during the cooling step.

[0013] A seventh aspect of the present invention relates to a method for manufacturing a shaft according to any one of the first to sixth aspects, characterized in that in the bending step, the metal plate material is bent into a semi-cylindrical shape, and in the diffusion bonding step, the polished end faces of a pair of the semi-cylindrical metal plates are butted together and diffusion bonded.

[0014] In addition, an eighth aspect of the present invention relates to a method for manufacturing a shaft 1 having a connecting member 3 provided at an end of a cylindrical member 2, the method comprising: a bending step of bending a metal plate material into a cylindrical or arc shape; a diffusion bonding step of butting end faces of the metal plate materials facing each other in a cylindrically bent state, or arranging a plurality of the metal plate materials bent into a cylindrical shape and butting their end faces together, and heating the butted portions to form the cylindrical member 2; a cooling step of cooling the cylindrical member 2 after the diffusion bonding step; and a connecting member joining step of joining the connecting member 3 to the end of the cylindrical member 2 by friction welding or shrink fitting, wherein the connecting member joining step is performed during the cooling step.

[0015] A ninth aspect of the present invention relates to a method for manufacturing a shaft according to any one of the first to eighth aspects, characterized in that the shaft 1 is a shaft 1 for an EV motor.

[0016] As described above, the present invention provides a new shaft manufacturing method that can broaden the range of materials that can be selected for the pipe member and also improve mass productivity.

[0017] It is a schematic explanatory perspective view in which a part of a shaft is cut out. It is a schematic explanatory view of an EV motor. It is an explanatory view of a process of Example 1. It is an explanatory view of a process of Example 2.

[0018] A preferred embodiment of the present invention will be briefly described below, illustrating the operation of the present invention with reference to the drawings.

[0019] A metal plate is bent into a cylindrical shape, and the opposing ends are butted together and diffusion-bonded to produce a cylindrical member 2 that will become the body of the shaft 1. A connecting member 3, which has gears, splines, etc. formed thereon, is then bonded to the end of this cylindrical member 2 by friction welding, shrink fitting, etc., to obtain the shaft 1 for a rotating body, such as an EV motor.

[0020] In this case, the cylindrical member 2 is manufactured by bending a metal plate into a cylindrical shape and then diffusion bonding it, which allows for a wide range of material choices, making it possible to form hollow shafts made of materials suitable for a variety of applications. That is, diffusion bonding allows for the formation of cylindrical members without quench cracking, even from steels with a high carbon content (high carbon steel) or alloy steels with a high alloying element content (high alloy steel). In contrast, when welding metal plates bent into a cylindrical shape, for example, quench cracking is likely to occur during welding, and the materials that can be selected are limited to low carbon steel and low alloy steel.

[0021] Alternatively, a cylindrical member can be produced in the same manner as above by bending a metal plate into an arc, arranging multiple pieces of this arc-shaped metal plate into a cylindrical shape, and butting opposing ends together to form a diffusion bond.

[0022] Furthermore, diffusion welding does not require large-scale equipment (such as a forging machine), and can be achieved using relatively versatile equipment such as a vacuum furnace equipped with a heating device.

[0023] Furthermore, in the present invention, by polishing the edges of the metal plate material that will become the bonding surfaces through a polishing process before diffusion bonding, diffusion bonding can be performed more efficiently in a shorter time, thereby improving mass productivity.

[0024] Therefore, according to the present invention, by using high-strength alloy steel for the metal plate material, which cannot be selected for pre-fabricated pipe components, it is possible to manufacture a high-strength, lightweight shaft 1 that is ideal for use in EV motors.

[0025] Furthermore, for example, when the cylindrical member 2 is cooled after diffusion bonding, the connecting member 3 can be joined by friction welding or shrink fitting. In this case, the heat generated during diffusion bonding is utilized, and the connecting member 3 can be joined after diffusion bonding in the diffusion bonding equipment (vacuum chamber) without the heating step before joining the connecting member, making it possible to manufacture hollow shafts extremely efficiently.

[0026] A specific embodiment 1 of the present invention will be described with reference to the drawings.

[0027] This embodiment is a method for manufacturing a hollow shaft 1 having a cylindrical member 2 and a connecting member 3 attached to the end of the cylindrical member 2.

[0028] Specifically, the process includes a cutting process for cutting out a metal plate from a base material, a polishing process for polishing the end faces of the metal plate, a bending process for bending the metal plate into a cylindrical shape, a diffusion bonding process for butting the polished end faces of the metal plates facing each other in a cylindrically bent state and heating the butted parts to form the cylindrical member 2 by diffusion bonding, a cooling process for cooling the cylindrical member 2 after the diffusion bonding process, a connecting member joining process for joining the connecting member 3 to the end of the cylindrical member 2, and an external finishing process.

[0029] As shown in Fig. 1, the shaft 1 of this embodiment is formed by joining metal connecting members 3, which are provided with engaging portions such as gears and splines, to both ends of a metal cylindrical member 2, and is used as the shaft 1 of an EV motor, for example, as shown in Fig. 2. In Fig. 2, reference numeral 4 denotes a rotor, 5 denotes a stator, 6 denotes a housing, and 7 denotes a bearing.

[0030] The cylindrical member 2 is formed by bending a metal plate into a cylindrical shape and diffusion bonding the opposing ends. The metal plate can be a steel plate or a non-ferrous metal plate (such as a high-tensile steel plate, a stainless steel plate, or a titanium alloy plate) cut to a predetermined size.

[0031] Each step will be described in detail.

[0032] In the cutting step, a metal plate material B of a predetermined size is cut from a base material A (FIG. 3(a)).

[0033] In the polishing process, the opposing ends of the metal plate B that are bent into a cylindrical shape during the bending process are polished. Specifically, both ends are polished so that the surface roughness Ra of each end is 2 μm or less. This polishing facilitates favorable atomic diffusion at the bonding surface, resulting in strong diffusion bonding in a short period of time.

[0034] Next, in the bending process, the metal plate B with the polished edges is rolled into a cylindrical shape using a forging tool or a bending roll machine (FIG. 3(b)). In the case of high-strength or thick plates, the plate is rolled while being heated warm (approximately 300°C to 800°C) or hot (approximately 1000°C to 1300°C). The order of the polishing and bending processes may be reversed.

[0035] Next, in the diffusion bonding process, the metal plates are placed in a vacuum furnace (diffusion bonding furnace C), the polished end faces of the cylindrically rolled metal plates are butted together, a rod-shaped jig having an outer peripheral surface along the inner surface of the metal plate is placed inside, and a cylindrical jig having an inner peripheral surface along the outer surface of the metal plate is placed outside, and the butted parts are sandwiched from the inside and outside and pressed with a predetermined pressure (about 5 to 10 MPa), and heated to about 900 to 1000°C, and held for a predetermined time (several tens of minutes to several hours) (FIG. 3(c)). －６ Pa to 10 －３ A vacuum atmosphere of about Pa is maintained.

[0036] Diffusion bonding provides uniform strength and properties around the entire circumference compared to welding.

[0037] Subsequently, in the cooling step, the heating is stopped, and the cylindrical member 2 after the diffusion bonding step is allowed to cool naturally in the vacuum furnace.

[0038] Subsequently, in the connecting member joining step, the connecting member 3 having the gear portion and the spline portion formed thereon is joined by friction welding or shrink fitting (FIG. 3(d)).

[0039] Friction welding is performed using a general friction welding machine, and shrink fitting is performed at a temperature of, for example, 150°C to 180°C.

[0040] Subsequently, in an outer finishing step, finishing processes such as cutting and polishing are carried out to remove irregularities on the outer surface of the connecting portion between the cylindrical member 2 and the connecting member 3 (FIG. 3(e)).

[0041] The connecting member 3 is made by cold or hot forging a material into a hollow shape so that the diameter gradually decreases toward the outside, and then machining (cutting, gear machining, spline rolling, etc.) the outer surface to form gears and splines. The friction-welded surface with the cylindrical member 2 is formed by cutting.

[0042] The shaft 1 can be formed through the above steps, but an inner finishing step may be included if necessary. The inner finishing step is performed after the diffusion bonding step and before the connecting member joining step, and is a finishing process such as cutting and polishing to remove irregularities on the inner surface of the butted portion of the cylindrical member 2.

[0043] If necessary, the connecting member joining step may be performed during the cooling step.

[0044] Specifically, when the cylindrical member 2 reaches a predetermined temperature during the cooling process after diffusion bonding, friction welding or shrink fitting may be used to join the connecting member 3 to the end of the cylindrical member 2. For example, to prevent oxidation, the cylindrical member 2 is kept in a vacuum furnace until the temperature reaches about 200°C, and then removed from the vacuum furnace and shrink fitting or the like is performed. In this case, the connecting member 3 can be joined by utilizing the heat generated during diffusion bonding. Then, the cylindrical member 2 is naturally cooled to room temperature.

[0045] The diffusion bonding step, cooling step, and connecting member bonding step may be performed in the same vacuum furnace. That is, after the diffusion bonding, the cylindrical member 2 may not be removed from the vacuum furnace, but the connecting member 3 may be bonded when the cylindrical member 2 reaches a predetermined temperature, and the joined cylindrical member 2 and connecting member 3 may be removed after cooling is complete.

[0046] As described above, this embodiment allows for a wide range of material selection, making it possible to form the shaft 1 using materials suitable for a variety of applications. That is, by using diffusion bonding, a cylindrical member can be formed without generating quench cracks even when using high carbon steel or high alloy steel.

[0047] Furthermore, diffusion welding does not require large-scale equipment and can be achieved using relatively versatile equipment such as a vacuum furnace equipped with a heating device.

[0048] Furthermore, by polishing the edges of the metal plates that will be the bonding surfaces in a polishing step before diffusion bonding, the diffusion bonding can be carried out more efficiently in a shorter time, thereby improving mass productivity.

[0049] Therefore, by using high-strength alloy steel, which cannot be selected for pre-made pipe components, for the metal plate material, it becomes possible to manufacture a high-strength, lightweight shaft 1 that is ideal for use in EV motors.

[0050] Therefore, this embodiment provides a shaft manufacturing method that allows for a wider range of choices for the material of the pipe member and also improves mass productivity.

[0051] In this embodiment, whereas in the first embodiment, a single metal plate is rolled into a cylindrical shape and diffusion bonded to obtain the cylindrical member 2, a plurality of metal plates are bent into an arc shape (so that each metal plate forms a part of the cylindrical member), arranged in a cylindrical shape, and diffusion bonded to obtain the cylindrical member 2.

[0052] Specifically, in this embodiment, two metal plates B cut from a base material A as shown in Fig. 4(a) are sandwiched between an upper die D (convex die) and a lower die E (concave die) in the bending process, and are bent into semi-cylindrical shapes by conforming to the concave and convex shapes of the upper and lower dies (Fig. 4(b)). Therefore, the number of bending steps can be reduced, and fewer dies are required.

[0053] Then, a pair of semi-cylindrical metal plates B are butted together with their end faces facing each other, and the butted ends are diffusion-bonded to obtain a cylindrical member 2 (FIG. 4(c)).

[0054] Thereafter, similar to Example 1, the connecting members 3 having gear portions and spline portions formed thereon are joined to both ends of the cylindrical member 2 by friction welding or shrink fitting (FIG. 4(d)). Next, finishing processes such as cutting and polishing are performed to remove irregularities on the outer surface of the connecting portion between the cylindrical member 2 and the connecting member 3 (FIG. 4(e)).

[0055] In the diffusion bonding process of this example, two semi-cylindrical metal plates are arranged facing each other to form a cylindrical shape, and are clamped and pressed from above and below with jigs, so that the butted end faces are held together under pressure and heat for a predetermined period of time. The jigs used for clamping and pressing from above and below are a pair of upper and lower jigs, each with a concave curved surface that conforms to the outer circumferential surface (convex curved surface) of each semi-cylindrical metal plate.

[0056] When clamping and pressing the metal plate material from above and below with jigs, a cylindrical (or columnar) jig may be placed inside the semi-cylindrical metal plate material to support the metal plate material from the inside.

[0057] Furthermore, by using two semi-cylindrical metal plates, when finishing the butted end faces, the parallel end faces can be butted together simply by making them horizontal (no need to calculate the angle of the end faces), making polishing and other processes easier and less costly. Furthermore, the vector for applying pressure during diffusion bonding can be vertical (a direction perpendicular to the butted end faces), making it easier to apply pressure (and maintain it) (the jig structure can be simplified).

[0058] In this embodiment, the cylindrical member 2 is formed from two metal plates (of approximately the same shape) bent into semi-cylindrical shapes, but the cylindrical member 2 may also be formed from three or more metal plates (of approximately the same shape) bent into an arc shape.

[0059] The rest is the same as in Example 1.

Claims

DEPCT661. Method for the production of shafts in which the linking parts are arranged at the ends of a cylindrical part. This method is characterized by the inclusion of a polishing step for polishing the end surfaces of the metal sheets to achieve a surface roughness Ra of 2 micrometers or less; a bending step for bending the metal sheets into a hemispherical shape; a diffusion connection step for arranging the pair of metal sheets, which have been bent into hemispherical shapes, to create a cylindrical shape and butt-joining them. The polished end surfaces of the metal sheets are then heated at the butt-joined parts so that the butt-joined parts are diffused, in this way creating the cylindrical part; a cooling step for cooling the cylindrical part after the diffusion connection step; a linking part connection step for connecting the linking parts to the ends of the cylindrical part; and a final internal finishing step for cutting or polishing the inner surfaces of the butt-joined parts of the cylindrical part after the diffusion connection step.

1. A method for manufacturing shafts under claim 1, characterized by the inclusion of an external final finishing step for the final finishing of the outer surfaces of the linked sections of the cylindrical sections and the linked parts.

3. A method for manufacturing shafts under claim 1 or 2, characterized by the joining of the linked parts being performed via friction welding or compression fitting.

4. A method for manufacturing shafts under claim 3, characterized by the joining of the linked parts being performed during the cooling process.

5. A method for manufacturing shafts under any of claims 1 through 4, characterized by the use of the shafts in electric vehicle (EV) motors.

6. A method for manufacturing shafts in which the linked parts are attached to the ends of cylindrical sections.This method is characterized by the inclusion of a polishing step for polishing the end surfaces of the metal sheets, a bending step for bending the metal sheets into a hemispherical shape, a diffusion connection step for arranging pairs of the bent metal sheets to create a cylindrical shape and butt-joining them. The polished end surfaces of the metal sheets are then heated at the butt-joint points to create a diffusion connection, thereby creating a cylindrical part. A cooling step is used to cool the cylindrical part after the diffusion connection step, and a linking step is used to connect the linking parts to the ends of the cylindrical part via friction welding or compression fitting during the cooling step of the diffusion connection.

7. A method for the fabrication of shafts under claim 6, which is characterized by a polishing step involving polishing the end surfaces of the metal sheets to a surface roughness Ra of 2 micrometers or less.

8. A method for the fabrication of shafts under claim 6 or 7, which is characterized by the inclusion of an external final finishing step for the final finishing of the outer surfaces of the linked sections of the cylindrical and linked parts.

9. A method for the fabrication of shafts under any of claims 6 through 8, which is characterized by the inclusion of an internal final finishing step for the final finishing of the inner surfaces of the linked sections of the cylindrical parts.

10. A method for the fabrication of shafts under any of claims 6 through 9, which is characterized by the use of shafts in electric vehicle (EV) motors.

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