Ball joint and method for manufacturing ball joint

Abstract

The invention provides a ball joint capable of improving rigidity of a columnar part and a method for manufacturing the ball joint. A ball joint (100) is provided with a columnar section (110) and a housing (120). The columnar section (110) is provided with: a connection section (111) that is connected to an object to be connected (10); a flange-shaped receiving part 115 on which the object 10 to be connected is placed; and a ball part 114 having a spherical surface. A male thread part 112 for fastening the mounting nut 12 is formed on the connecting part 111. The flange-shaped receiving section (115) is formed so as to protrude radially outward from the connecting section (111) in a flange-shaped manner. A surface hardening layer 118 for hardening the surface layer is formed at a boundary portion 117 between the connecting portion 111 and the flange-shaped receiving portion 115.

Description

TECHNICAL FIELD

[0001] The present application relates to a ball joint for a suspension mechanism or a steering mechanism in a vehicle and a manufacturing method of the ball joint. BACKGROUND

[0002] In the past, in a suspension mechanism (suspension device) or a steering mechanism (steering device) of a vehicle such as an automobile, a ball joint has been used in order to movably link each component in a shaft shape to each other. For example, a ball joint is disclosed in Patent Literature 1, in which a ball portion formed at an end of a rod-shaped columnar portion is held in a slideable state inside a bottomed cylindrical housing. In this case, an outer thread linking a suspension device or a stabilizer bar or the like as a linking object is formed in the columnar portion, and a flange portion protruding in a flange shape and accommodating the linking object is formed between the outer thread and the ball portion.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2020-98011 SUMMARY

[0006] However, in the ball joint described in Patent Literature 1, when the linking object is linked to the linking portion on which the outer thread is formed, there is a problem that stress is easily concentrated in the boundary portion between the linking portion and the flange portion, and it is difficult to ensure rigidity.

[0007] The present application is proposed in order to address the above problem, and aims to provide a ball joint and a manufacturing method of the ball joint capable of improving the rigidity of the columnar portion.

[0008] To achieve the above object, the present application is characterized by a ball joint including: a columnar portion in which a flange-shaped receiving portion protruding in a flange shape and accommodating a linking object is formed between a linking portion linking the linking object and a ball portion formed in a rod shape; and a housing accommodating the ball portion of the columnar portion in a slideable state, in which a surface-hardened layer is formed in a boundary portion between the linking portion and the flange-shaped receiving portion.

[0009] According to this, the ball joint has the surface-hardened layer formed in the boundary portion between the linking portion and the flange-shaped receiving portion, and thus the rigidity (wear resistance or fatigue strength) of this boundary portion can be improved. In addition, the ball joint can reduce the outer diameter of the entire columnar portion by improving the rigidity of the boundary portion between the linking portion and the flange-shaped receiving portion, and thus the columnar portion can be miniaturized, and it is also easier to form a concave retreat portion in the boundary portion, and the tightness with the linking object can be improved.

[0010] Further, another feature of the present application is that, in the ball joint, the surface-hardened layer is formed by a shot mark.

[0011] Accordingly, the ball joint can easily form the surface-hardened layer because the surface-hardened layer is formed by the shot mark.

[0012] Further, another feature of the present application is that, in the ball joint, the boundary portion is recessed in a concave shape on the inner side of the columnar portion, and the surface-hardened layer is formed on the surface of the boundary portion of the concave recess.

[0013] Accordingly, the ball joint can improve the close contact with the object to be joined while securing the rigidity of the columnar portion because the surface-hardened layer is formed on the boundary portion of the concave recess.

[0014] Further, another feature of the present application is that, in the ball joint, the surface-hardened layer is further formed on the outer peripheral portion of the flange-shaped receiving portion.

[0015] Accordingly, the ball joint can improve the close contact with the object to be joined while securing the rigidity of the columnar portion because the surface-hardened layer is formed on the boundary portion of the concave recess.

[0016] In addition, the present application can be implemented not only as the invention of the ball joint but also as the invention of the manufacturing method of the ball joint.

[0017] Specifically, a manufacturing method of a ball joint that has a columnar portion in which a flange-shaped receiving portion that protrudes in a flange shape and that houses an object to be joined is formed between a columnar portion that has a joining portion that is joined to the object to be joined and that is formed in a rod shape and a spherical portion that has a spherical surface, and a housing that slidably houses the spherical portion of the columnar portion can include a surface-hardened layer forming step of forming a surface-hardened layer on a boundary portion of the joining portion and the flange-shaped receiving portion. Accordingly, the manufacturing method of the ball joint can expect the same effects as the above-described ball joint.

[0018] In this case, the manufacturing method of the ball joint can be shot peening. Accordingly, the manufacturing method of the ball joint can expect the same effects as the above-described ball joint.

[0019] Furthermore, in these cases, the manufacturing method of the ball joint includes a thread forming step for forming external threads at the connecting portion, and a surface hardening layer forming step is performed before the thread forming step. Accordingly, the manufacturing method of the ball joint can form external threads that smooth the unevenness of the surface formed by shot peening in the surface hardening layer forming step.

[0020] Furthermore, in these cases, in the manufacturing method of the ball joint, the surface hardening layer forming process can further form a surface hardening layer on the outer periphery of the flange-shaped receiving portion. Accordingly, the manufacturing method of the ball joint can be expected to have the same functional effect as the ball joint described above. Attached Figure Description

[0021] [ Figure 1 [A partial fracture sectional view is shown to schematically represent the longitudinal section of a ball joint according to an embodiment of the present invention.]

[0022] [ Figure 2 To indicate Figure 1 A partially enlarged cross-sectional view showing the details of the formation state of the surface hardening layer within the dashed circle 2.

[0023] [ Figure 3 ] is used to indicate composition Figure 1 The flowchart shows the manufacturing process of the columnar part of the ball joint shown.

[0024] [ Figure 4 [A partially enlarged cross-sectional view showing details of the formation state of the surface hardening layer in a modified example of the present invention.]

[0025] [ Figure 5 [A partially enlarged cross-sectional view showing details of the formation state of the surface hardening layer involved in other variations of the present invention.]

[0026] [ Figure 6 [A partially enlarged cross-sectional view showing details of the formation state of the surface hardening layer involved in other variations of the present invention.] Detailed Implementation

[0027] Hereinafter, an embodiment of the ball joint according to the present invention will be described with reference to the accompanying drawings. Figure 1 This is a partial fracture sectional view of the longitudinal section of the ball joint 100 according to the present invention, presented schematically. Furthermore, the figures referenced in this specification are exaggerated or schematic representations of some constituent elements for ease of understanding of the invention. Therefore, the dimensions or proportions of the constituent elements may differ.

[0028] (Composition of ball joint 100)

[0029] This ball joint 100 is a joint member that links members of a suspension mechanism (suspension device) or a steering mechanism (steering device) employed in a vehicle such as an automobile, while allowing an angle change between the members. In the present embodiment, a member that constitutes the suspension mechanism or the steering mechanism and is directly linked to the ball joint 100 is taken as a linking object 10. This linking object 10 is formed in a plate shape, and a through-hole 11 for mounting the ball joint 100 is formed. The ball joint 100 is mainly composed of a cylindrical portion 110, a housing 120, a ball seat 123, and a dust cover 124.

[0030] The cylindrical portion 110 is a member for movably linking the linking object 10 to the housing 120, and is composed of a metal material in a round bar shape. This cylindrical portion 110 is formed with a linking portion 111 at one end (upper side in the drawing), and a ball portion 114 at the end of the other end (lower side in the drawing).

[0031] The linking portion 111 is a portion that penetrates the through-hole 11 of the linking object 10, and is mainly composed of an externally threaded portion 112 and a non-threaded portion 113. The externally threaded portion 112 is a portion that is threadedly engaged with a mounting nut 12 in a state of penetrating the through-hole 11 of the linking object 10, and is composed of an external thread for threadedly engaging with the mounting nut 12. This linking portion 111 is formed from the end of the one end toward the end of the other end of the cylindrical portion 110.

[0032] The non-threaded portion 113 is a portion that is disposed inside the through-hole 11 of the linking object 10, and is formed in a round bar shape that is smaller in diameter than the through-hole 11 and is not formed with an external thread. In the present embodiment, the non-threaded portion 113 is formed to such a degree that a gap is generated with respect to the inner peripheral surface of the through-hole 11 in the outer diameter, and is formed to be shorter in length than the length (depth) of the through-hole 11.

[0033] The ball portion 114 is a portion that slides inside the ball seat 123, and is formed in a smooth convex spherical shape so as to smoothly slide with respect to the inner peripheral surface of the ball seat 123. The surface of this ball portion 114 is formed in a smooth spherical shape by polishing processing in order to ensure smooth sliding with the ball seat 123. Between these linking portion 111 and the ball portion 114, a flange-shaped receiving portion 115 is formed.

[0034] The flange-shaped receiving portion 115 is a portion that accommodates the linking object 10, and is formed in a round plate shape that protrudes in a flange shape on the outer side in the radial direction of the cylindrical portion 110. As shown in FIG. 1, this flange-shaped receiving portion 115 is mainly composed of a linking portion side surface 115a, a ball portion side surface 115b, and an outer peripheral portion 115c. Figure 2

[0035] ​The joint portion side surface 115a is a portion formed on the side of the joint portion 111 to receive the joint object 10, and is formed in a flat plate ring shape in plan view. The ball portion side surface 115b is a surface (a surface on the opposite side of the joint portion side surface) formed on the side of the ball portion 114, and is formed in a flat plate ring shape in bottom view. The outer peripheral portion 115c is an end surface of the outermost peripheral portion of the flange-shaped receiving portion 115, and is formed in a ring shape extending in the circumferential direction of the flange-shaped receiving portion 115. A surface-hardened layer 116 is formed on the outer peripheral portion 115c.

[0036] The surface-hardened layer 116 is a portion for improving the rigidity of the outer peripheral portion 115c, and is formed to have a higher hardness than the hardness of a more internal portion of the surface-hardened layer 116. In the present embodiment, the surface-hardened layer 116 is composed of a shot blast mark (a collection of innumerable pits). Further, the depth and hardness of the hardened layer in the surface-hardened layer 116 are appropriately determined in accordance with the specifications of the ball joint 100. Further, a surface-hardened layer 118 is also formed on a boundary portion 117 between the flange-shaped receiving portion 115 and the columnar portion 110.

[0037] The boundary portion 117 is a portion of the boundary between the flange-shaped receiving portion 115 and the columnar portion 110, and is a portion in a circular ring shape in the circumferential direction of the columnar portion 110. In the present embodiment, the boundary portion 117 is a portion where the flange-shaped receiving portion 115 and the columnar portion 110 intersect at substantially right angles and a portion in the vicinity thereof.

[0038] The surface-hardened layer 118 is the same as the surface-hardened layer 116, and is a portion for improving the rigidity of the boundary portion 117, and is formed to have a higher hardness than the hardness of an internal portion of the surface-hardened layer 118. In the present embodiment, the surface-hardened layer 118 is composed of the same shot blast mark (a collection of innumerable pits) as the surface-hardened layer 116. Further, the depth and hardness of the hardened layer in the surface-hardened layer 118 are appropriately determined in accordance with the specifications of the ball joint 100.

[0039] Between the flange-shaped receiving portion 115 and the ball portion 114, a ball support portion 119 extending in a circular rod shape is formed. In this case, a constricted portion 119a in which the outer diameter is constricted is formed on the ball support portion 119, and the ball portion 114 is connected by the constricted portion 119a.

[0040] The housing 120 is a portion that holds the ball portion 114, and is formed in a substantially cylindrical shape by casting processing or forging processing of a non-ferrous metal such as a steel material or an aluminum material. In this case, the housing 120 is formed on a front end portion of an arm portion extending in a rod shape in order to be connected to each of the constituent elements in a steering mechanism or a suspension mechanism, not shown.

[0041] The housing 120 is formed with an opening 121 that opens upward in the drawing at the end of one end of the cylindrical body (the upper end in the drawing), and is closed by a plug 122 at the end of the other end (the lower end in the drawing). The plug 122 is a plate-like member that closes the end of the other end of the housing 120 formed in a cylindrical shape, and is a substantially circular plate shape in which a steel material is formed with a recessed central portion. A ball seat 123 that is a bearing seat is housed in the interior of the housing 120.

[0042] The ball seat 123 is a member that holds the ball portion 114 formed on the cylindrical portion 110 in a state of being able to rotate and slide freely inside the housing 120, and is constituted in a shape in which a synthetic resin material (for example, polyether ether ketone resin) is formed in a cup shape in which the longitudinal cross-sectional shape is substantially U-shaped. In the upper side opening portion and the lower side opening portion of the ball seat 123, a lubricating grease that is not shown is applied, and this is used to ensure lubricity between the inner peripheral surface of the ball seat 123 and the outer peripheral surface of the ball portion 114. On the other hand, in the outer peripheral portion of the housing 120, a cover receiving portion 120a is formed in a state of protruding to the outside in the radial direction of the housing 120, and a dust cover 124 is held on the cover receiving portion 120a.

[0043] The dust cover 124 is a member for preventing foreign matter from entering the interior of the housing 120, and is formed in a substantially cylindrical shape in which a rubber material or a soft synthetic resin material that is elastically deformable is formed with a bulged central portion. The opening portion of one end (the upper side in the drawing) of the dust cover 124 is elastically fitted to the root portion of the ball portion 114 side of the flange-like receiving portion 115 of the cylindrical portion 110, and the opening portion of the other end is fitted to the outer peripheral portion of the housing 120 on the cover receiving portion 120a by a metal snap ring 125.

[0044] (Manufacture of the ball joint 100)

[0045] Next, the manufacture of the ball joint 100 configured as such will be described. Furthermore, in the description of the manufacturing process of the ball joint 100, the manufacture of the cylindrical portion 110 directly related to the present application will be described with reference to the drawings, and the manufacturing process not directly related to the present application will be appropriately omitted. Figure 3

[0046] First, a worker manufactures the cylindrical portion 110. The cylindrical portion 110 is mainly manufactured through a bulk forming process (S1), a heat treatment process (S2), a surface hardening layer forming process (S3), a thread portion forming process (S4), and a ball portion forming process (S5). Specifically, in the bulk forming process, the worker performs forging processing on a round bar material composed of carbon steel or alloy steel by a forging machine that is not shown, thereby integrally forming the joint portion 111, the non-thread portion 113, the flange-like receiving portion 115, the ball support portion 119, and the ball portion 114, respectively.

[0047] ​In this forging process, the cylindrical portion 110 is gradually shaped by periodically plastically deforming the round bar material. In this case, the ball portion 114 and the ball support portion 119 in the cylindrical portion 110 are processed in so-called rough shaping that leaves a predetermined cutting allowance. Further, this bulk shaping process can of course be performed by cutting instead of forging or in addition to forging.

[0048] Next, the worker performs a heat treatment process. Specifically, the worker applies heat treatment consisting of quenching and tempering to the semi-finished product of the cylindrical portion 110 shaped in the bulk shaping process to increase the hardness of the entire cylindrical portion 110.

[0049] Next, the worker performs a surface hardening layer forming process. Specifically, the worker masks the remaining portions (the joint portion side surface 115a and the ball portion side surface 115b) of the flange-shaped receiving portion 115 of the semi-finished product of the cylindrical portion 110 subjected to the heat treatment with masking tape (not shown) in a state in which the outer peripheral portion 115c and the boundary portion 117 are exposed, and then performs shot blasting on the entire cylindrical portion 110.

[0050] As a result, the worker can work harden each surface layer of the joint portion 111, the ball portion 114, the outer peripheral portion 115c, the boundary portion 117, and the ball support portion 119 in the cylindrical portion 110 except the portions that have been masked. Further, the processing specifications such as the medium diameter in the shot blasting are appropriately determined in accordance with the specifications of the ball joint 100.

[0051] Next, the worker performs a thread forming process. Specifically, the worker performs roll forming on the semi-finished product of the cylindrical portion 110 by a roll forming machine (not shown) to form an external thread in the joint portion 111. As a result, the worker can form the external thread portion 112 in a part of the joint portion 111 in the semi-finished product of the cylindrical portion 110. In this case, the rough surface formed by the shot blasting before the external thread is formed is smoothed by the roll forming.

[0052] Next, the worker performs a ball portion forming process. Specifically, the worker performs cutting on the outer peripheral surface of the ball portion 114 including the ball support portion 119 using a work machine tool such as an NC (numerical control) lathe (not shown) for the semi-finished product of the cylindrical portion 110. Further, the worker performs grinding on the ball portion 114 using a grinding machine (not shown) to complete the ball portion 114. Through these processes, the worker can manufacture the cylindrical portion 110.

[0053] Next, the worker shapes the housing 120. Specifically, the worker prepares the plug 122 and the socket 123 in addition to the cylindrical portion 110. In this case, the plug 122 is previously formed into a circular plate shape by press working. Further, the socket 123 is previously formed into a cylindrical shape by injection molding.

[0054] The worker sets the respective components of the cylindrical portion 110, the plug 122, and the socket 123 in an unillustrated mold for shaping the housing 120. In this case, the worker sets the ball portion 114 of the cylindrical portion 110 in the mold in a state in which the ball portion 114 can rotate and slide within the socket 123.

[0055] Next, the worker casts an aluminum alloy (aluminum die casting) into the mold in which the cylindrical portion 110, the plug 122, and the socket 123 have been set. Thus, the housing 120 is shaped, which integrally has the cylindrical portion 110, the plug 122, and the socket 123. Further, in the present embodiment, the housing 120 is shaped in a state in which an unillustrated arm portion extending in a bar shape is integrally formed in the outer peripheral portion of the housing 120. Further, the housing 120 can be cast together with the cylindrical portion 110, the plug 122, and the socket 123, or can be shaped separately and then assembled with the cylindrical portion 110, the plug 122, and the socket 123.

[0056] Next, the worker installs the dust cover 124 to the housing 120 having the cylindrical portion 110, the plug 122, and the socket 123. Specifically, the worker prepares the dust cover 124 and the snap ring 125, and then inserts an opening portion of one end (upper side in the drawing) of the dust cover 124 into the outer peripheral portion of the ball support portion 119 in the cylindrical portion 110, and inserts the other end (lower side in the drawing) of the dust cover 124 into the cover receiving portion 120a of the housing 120.

[0057] Then, the worker inserts the snap ring 125 into the outer peripheral surface of the dust cover 124. Through the installation of the dust cover 124 to the housing 120, the ball joint 100 is completed. Further, the worker coats an unillustrated lubricant on the inner peripheral surface of the socket 123, the outer peripheral surface of the ball portion 114 exposed from the opening portion of the housing 120, and between the ball portion 114 of the cylindrical portion 110 and the plug 122 before casting the housing 120 and installing the dust cover 124, so that the ball portion 114 can smoothly rotate and slide.

[0058] (Assembly of the ball joint 100)

[0059] The assembly of the ball joint 100 to the connection object 10 will be described. Further, in the description of the assembly process of the ball joint 100, the manufacturing process not directly related to the present application will be appropriately omitted.

[0060] After the worker passes the coupling portion 111 of the cylindrical portion 110 through the through-hole 11 of the coupling target object 10, the worker fastens the mounting nut 12 to the external thread portion 112, and thereby the cylindrical portion 110 of the ball joint 100 is mounted to the coupling target object 10. In this case, the boundary portion 117 in the cylindrical portion 110 collides with the edge portion of the through-hole 11 when the coupling portion 111 is passed through the through-hole 11, or is subjected to a tensile force due to the fastening of the mounting nut 12, but the damage to the boundary portion 117 is suppressed by the surface-hardened layer 118 formed in the boundary portion 117.

[0061] Further, the flange-shaped receiving portion 115 is subjected to a shearing force in the outer edge portion of the flange-shaped receiving portion 115 (the coupling portion side surface 115a) due to the strong pressing of the coupling target object 10, and the outer edge portion sinks into the inside of the coupling target object 10, and thereby the deformed portion 13 in which a portion of the surface layer of the coupling target object 10 is plastically deformed like a circular ring-shaped bulge is tightly attached to the outer peripheral portion 115c. However, the outer peripheral portion 115c of the flange-shaped receiving portion 115 is suppressed from being plastically deformed and the like due to the strong attachment of the coupling target object 10, because the surface-hardened layer 116 is formed in the outer peripheral portion 115c. Further, the flange-shaped receiving portion 115 improves the frictional resistance between the coupling target object 10 by the uneven surface of the surface-hardened layer 116, and thereby the tightness is improved.

[0062] Further, the worker couples the housing 120 to other constituent elements in the steering mechanism or the suspension mechanism, which are not shown, by the arm portion (not shown) extending from the housing 120. Thereby, the worker can mount the ball joint 100 to the steering mechanism or the suspension mechanism.

[0063] (Action of the ball joint 100)

[0064] The action of the ball joint 100 configured as described above will be described. The ball joint 100 is used as a joint member in the suspension mechanism or the steering mechanism in a vehicle, which is not shown. Then, various stresses and vibrations such as bending, stretching, compression, shearing, and the like, according to the load of the wheel action or the vehicle posture, act on the ball joint 100 when the vehicle is running.

[0065] In this case, the outer peripheral portion 115c and the boundary portion 117 in the ball joint 100 are also subjected to vibrations due to the above load. However, the damage is suppressed by the surface-hardened layers 116 and 118 formed in the outer peripheral portion 115c and the boundary portion 117, respectively.

[0066] As can be understood from the description of the above-described operation method, according to the above-described embodiment, the ball joint 100 is able to improve the rigidity of the outer peripheral portion 115c and the boundary portion 117 because the surface-hardened layers 116, 118 are formed in these portions, respectively. Further, the ball joint 100 is able to reduce the outer diameter of the entire cylindrical portion 110 and achieve the miniaturization of the cylindrical portion 110 by being able to improve the rigidity of the outer peripheral portion 115c and the boundary portion 117.

[0067] In addition, in implementing the present application, various modifications can be made without being limited to the above-described embodiments as long as the object of the present application is not deviated. Further, in each of the following modification examples, the same components as those of each of the above-described embodiments are attached with corresponding symbols and the description thereof is omitted.

[0068] For example, in the above-described embodiment, the ball joint 100 is formed with the surface-hardened layers 116, 118 in the outer peripheral portion 115c and the boundary portion 117, respectively. However, the ball joint 100 can be formed with the surface-hardened layer 118 in at least the boundary portion 117. Further, in a case where the surface-hardened layer 116 is required to be formed in the outer peripheral portion 115c of the flange-like receiving portion 115 without the surface-hardened layer 118 being required to be formed in the boundary portion 117, the surface-hardened layer 118 can be omitted from the boundary portion 117 and the surface-hardened layer 116 can be formed in the outer peripheral portion 115c of the flange-like receiving portion 115.

[0069] Further, in the above-described embodiment, the shot-blasting is performed after the portion (the joint portion side surface 115a and the ball portion side surface 115b in the flange-like receiving portion 115) of the cylindrical portion 110 is shielded in the surface-hardened layer forming process. However, in the surface-hardened layer forming process, the shot-blasting can be performed on at least the outer peripheral portion 115c and the boundary portion 117.

[0070] Therefore, in the surface-hardened layer forming process, the shot-blasting can be performed on the entire cylindrical portion 110, and thus the surface-hardened layers 116, 118 can be formed in the surface layer of the entire cylindrical portion 110. In this case, in the surface-hardened layer forming process, the shot-blasting can be performed after the portion other than the flange-like receiving portion 115 is shielded, and thus the surface-hardened layers 116, 118 can be formed only in the surface layer of the flange-like receiving portion 115. Further, in the surface-hardened layer forming process, the shot-blasting can be performed on the outer peripheral portion 115c and the boundary portion 117 and the like by using a nozzle of a blasting medium.

[0071] Further, in the above-described embodiment, the boundary portion 117 is configured to connect the non-threaded portion 113 and the flange-like receiving portion 115 at substantially right angles. However, the boundary portion 117 can be configured to connect the non-threaded portion 113 and the flange-like receiving portion 115 at an angle other than right angles. Figure 4As shown, the non-threaded portion 113 and the flange-like receiving portion 115 are connected with a curved surface. Further, the boundary portion 117 can also be formed as a curved surface as shown in FIG. 6B. Figure 5 As shown, the intersection of the non-threaded portion 113 and the flange-like receiving portion 115 is recessed on the inside of the cylindrical portion 110. Accordingly, the ball joint 100 can improve the rigidity of the cylindrical portion 110 while improving the tightness with the connecting object 10, because the surface-hardened layer 118 is formed in the boundary portion 117 of the recessed portion.

[0072] Further, in this case, the surface-hardened layer 118 can be formed only on the inside surface of the boundary portion 117 of the recessed portion, or can be formed to the outside of the boundary portion 117 to the peripheral portion (the non-threaded portion 113 and the connecting portion side surface 115a). In particular, when the inner peripheral surface of the through-hole 11 of the connecting object 10 is in contact with and fitted into the non-threaded portion 113 in the connecting portion 111, as shown in FIG. 6B, the surface-hardened layer 118 is formed on the surface layer of the non-threaded portion 113, so that the durability of the non-threaded portion 113 can be improved. Figure 6 As shown, the surface-hardened layer 118 is extended and formed on the surface layer of the non-threaded portion 113, so that the durability of the non-threaded portion 113 can be improved.

[0073] Further, in the above embodiment, the cylindrical portion 110 is integrally formed by the connecting portion 111, the ball portion 114, the flange-like receiving portion 115, and the ball support portion 119 with the same material. However, the cylindrical portion 110 can be formed by integrally forming the connecting portion 111, the ball portion 114, the flange-like receiving portion 115, and the ball support portion 119 with the same material. However, the cylindrical portion 110 can also be formed by integrally forming the ball portion 114 and then joining the ball support portion 119 using welding or the like.

[0074] Further, in the above embodiment, the surface-hardened layer forming process forms the surface-hardened layers 116, 118 on the peripheral portion 115c and the boundary portion 117 by shot peening. However, the surface-hardened layer forming process can form the surface-hardened layers 116, 118 on the peripheral portion 115c and the boundary portion 117 by any surface-hardening treatment (for example, various heat treatments such as high-frequency quenching treatment or flame quenching treatment, nitriding treatment, or carburizing treatment) other than shot peening.

[0075] Further, in the above-described embodiment, the surface-hardened layer forming step is performed before the thread portion forming step. However, the surface-hardened layer forming step can be performed after the thread portion forming step. In this case, the thread portion forming step can be performed before the heat treatment step, but can also be performed after the heat treatment step. Further, the thread portion forming step can also be formed by machining other than rolling, for example, cutting.

[0076] BRIEF DESCRIPTION OF DRAWINGS

[0077] 10: object to be joined

[0078] 11: through hole

[0079] 12: mounting nut

[0080] 100: ball joint

[0081] 110: cylindrical portion

[0082] 111: joining portion

[0083] 112: externally threaded portion

[0084] 113: non-threaded portion

[0085] 114: ball portion

[0086] 115: flange-like receiving portion

[0087] 115a: joining portion side surface

[0088] 115b: ball portion side surface

[0089] 115c: outer peripheral portion

[0090] 116: surface-hardened layer

[0091] 117: boundary portion

[0092] 118: surface-hardened layer

[0093] 119: ball support portion

[0094] 119a: constricted portion

[0095] 120: housing

[0096] 120a: cap receiving portion

[0097] 121: opening portion

[0098] 122: plug

[0099] 123: ball seat

[0100] 124: dust cap

[0101] 125: snap ring

Claims

1. A ball joint, characterized in that Possessing: a cylindrical portion in which a flange-shaped receiving portion protruding in a flange shape and accommodating a connection object is formed between a cylindrical portion having a connection portion connected to the connection object and formed in a rod shape and a ball portion formed with a spherical surface, and a housing accommodating the ball portion of the cylindrical portion in a slidable manner, a surface-hardened layer is formed at a boundary portion of the connection portion and the flange-shaped receiving portion.

2. The ball joint according to claim 1, wherein the surface-hardened layer is formed by a shot blast mark.

3. The ball joint according to claim 1, wherein the boundary portion is formed in a concave recess on an inner side of the cylindrical portion, the surface-hardened layer is formed on a surface of the boundary portion of the concave recess.

4. The ball joint according to claim 1, wherein a surface-hardened layer is further formed at an outer peripheral portion of the flange-shaped receiving portion.

5. A method of manufacturing a ball joint, characterized by The ball joint possesses: a cylindrical portion in which a flange-shaped receiving portion protruding in a flange shape and accommodating a connection object is formed between a cylindrical portion having a connection portion connected to the connection object and formed in a rod shape and a ball portion formed with a spherical surface, and a housing accommodating the ball portion of the cylindrical portion in a slidable manner, a surface-hardened layer is formed at a boundary portion of the connection portion and the flange-shaped receiving portion.

6. The manufacturing method of the ball joint according to claim 5, wherein the surface-hardened layer forming step is shot blast processing.

7. The method of manufacturing a ball joint according to claim 6, wherein including: a thread portion forming step in which an external thread is formed at the connection portion, the surface-hardened layer forming step is performed before the thread portion forming step.

8. The manufacturing method of the ball joint according to claim 5, wherein the surface-hardened layer forming step further forms the surface-hardened layer at an outer peripheral portion of the flange-shaped receiving portion.

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