Ball joint and method for manufacturing ball joint

Abstract

To provide a ball joint capable of improving rigidity of a stud part, and a method for manufacturing a ball joint.SOLUTION: A ball joint 100 comprises a stud part 110 and a housing 120. The stud part 110 comprises a connection part 111 that is connected to an object to be connected 10, a flange-shaped receiving part 115 to which the object to be connected 10 is fitted, and a ball part 114 having a spherical surface. The connection part 111 is provided with a male screw part 112 to which a mounting nut 12 is fastened. The flange-shaped receiving part 115 is formed to protrude radially outward with respect to the connection part 111 in a flange manner. A surface hardened layer 118 is formed at a boundary portion 117 between the connection part 111 and the flange-shaped receiving part 115, where a surface layer is hardened.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a ball joint used in a suspension mechanism or a steering mechanism of a vehicle, and a method for manufacturing the ball joint. [Background technology]

[0002] Conventionally, ball joints have been used in suspension mechanisms (suspension devices) and steering mechanisms (steering devices) in vehicles such as automobiles to movably connect shaft-shaped components to each other. For example, the following Patent Document 1 discloses a ball joint in which a ball portion formed on one end of a rod-shaped stud portion is held in a bottomed cylindrical housing in a slidable state. In this case, the stud portion is formed with a male thread to which a connection object such as a suspension or stabilizer is connected, and a flange portion is formed between the male thread and the ball portion, protruding like a flange and to which the connection object is assigned. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-98011 A Summary of the Invention

[0004] However, the ball joint described in Patent Document 1 above had a problem in that when an object to be connected was connected to a connecting part having a male thread, stress was likely to concentrate at the boundary between the connecting part and the flange, making it difficult to ensure rigidity.

[0005] The present invention has been made to address the above-mentioned problems, and its object is to provide a ball joint and a method for manufacturing a ball joint that can improve the rigidity of the stud portion.

[0006] In order to achieve the above-mentioned object, the present invention is characterized in that in a ball joint comprising a stud portion formed in a rod shape having a connecting portion that is connected to an object to be connected, and a ball portion formed with a spherical surface, a stud portion having a flange-like protruding flange-like receiving portion to which the object to be connected is placed, and a housing that slidably accommodates the ball portion of the stud portion, a surface-hardened layer is formed at the boundary between the connecting portion and the flange-like receiving portion.

[0007] According to this, because the ball joint has a surface-hardened layer formed at the boundary between the connecting part and the flange-shaped receiving part, the rigidity (wear resistance or fatigue strength) of this boundary can be improved. Also, because the ball joint can improve the rigidity of the boundary between the connecting part and the flange-shaped receiving part, the outer diameter of the entire stud part can be reduced, making the stud part more compact, and it is easier to form a concave relief part at the boundary, improving the adhesion to the object to be connected.

[0008] Another feature of the present invention is that in the ball joint, the surface hardened layer is formed by shot peening marks.

[0009] According to this, since the surface hardened layer of the ball joint is formed by shot peening marks, the surface hardened layer can be easily formed.

[0010] Another feature of the present invention is that, in the ball joint, the boundary portion is formed so as to be concavely recessed toward the inside of the stud portion, and a surface hardened layer is formed on the surface of the concavely recessed boundary portion.

[0011] According to this, since the ball joint has a surface-hardened layer formed at the concave boundary portion, it is possible to improve adhesion to the object to be connected while ensuring the rigidity of the stud portion.

[0012] Another feature of the present invention is that in the ball joint, a surface hardened layer is further formed on the outer periphery of the flange-shaped receiving portion.

[0013] According to this, since the ball joint has a surface-hardened layer formed on the outer periphery of the flange-shaped receiving portion, when the outer edge of the flange-shaped receiving portion is pressed into the object to be connected, deformation of the outer periphery can be suppressed and the connecting force can be increased. Also, in this case, the ball joint can improve the connecting force between the flange-shaped receiving portion and the object to be connected by forming the surface-hardened layer with shot peening marks.

[0014] Furthermore, the present invention can be embodied not only as an invention of a ball joint, but also as an invention of a manufacturing method of a ball joint.

[0015] Specifically, in a method for manufacturing a ball joint comprising a stud portion formed in a rod shape having a connecting portion connected to an object to be connected, a ball portion formed with a spherical surface, a stud portion having a flange-like protruding flange-like receiving portion to which the object to be connected is fitted, and a housing for slidably receiving the ball portion of the stud portion, the method may include a surface-hardened layer forming step of forming a surface-hardened layer at the boundary between the connecting portion and the flange-like receiving portion, whereby the method for manufacturing the ball joint can be expected to achieve the same effects as the above-mentioned ball joint.

[0016] In this case, in the method for manufacturing the ball joint, the surface hardened layer forming step may be a shot peening process, whereby the method for manufacturing the ball joint can be expected to achieve the same effects as the above-mentioned ball joint.

[0017] In these cases, the method for manufacturing a ball joint includes a thread forming step of forming a male thread on the connecting portion, and the surface hardened layer forming step is performed before the thread forming step. In this way, the method for manufacturing a ball joint can form a male thread in which the surface irregularities formed by the shot peening process in the surface hardened layer forming step are smoothed out.

[0018] In these cases, the ball joint manufacturing method may further include forming a surface-hardened layer on the outer periphery of the flange-shaped receiving portion in the surface-hardened layer forming step, whereby the ball joint manufacturing method can be expected to achieve the same effects as the ball joint described above. [Brief description of the drawings]

[0019] [Figure 1] 1 is a partially cutaway cross-sectional view that illustrates a longitudinal section of a ball joint according to an embodiment of the present invention. [Diagram 2] 2 is a partially enlarged cross-sectional view showing in detail the state of formation of a surface-hardened layer within a dashed circle 2 shown in FIG. 1. [Diagram 3] 2 is a flowchart showing steps in a manufacturing process of a stud portion that constitutes the ball joint shown in FIG. 1. [Figure 4] FIG. 11 is a partially enlarged cross-sectional view showing in detail a state in which a surface hardened layer is formed according to a modified example of the present invention. [Diagram 5] FIG. 11 is a partially enlarged cross-sectional view showing in detail a state in which a surface hardened layer is formed according to another modified example of the present invention. [Figure 6] FIG. 11 is a partially enlarged cross-sectional view showing in detail a state in which a surface hardened layer is formed according to another modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of a ball joint according to the present invention will be described with reference to the drawings. Fig. 1 is a partially cutaway cross-sectional view showing a longitudinal section of a ball joint 100 according to the present invention. Note that each drawing referred to in this specification is a schematic representation in which some of the components are exaggerated in order to facilitate understanding of the present invention. For this reason, the dimensions and ratios between the components may differ.

[0021] (Configuration of ball joint 100) This ball joint 100 is a joint member that connects components to each other in a suspension mechanism (suspension device) or steering mechanism (steering device) used in vehicles such as automobiles while allowing angular change between the components. In this embodiment, a member that configures the suspension mechanism or steering mechanism and is directly connected to ball joint 100 is referred to as a connection object 10. This connection object 10 is formed in a plate shape and has a through hole 11 for attaching ball joint 100. Ball joint 100 is mainly composed of a stud portion 110, a housing 120, a ball seat 123, and a dust cover 124.

[0022] The stud portion 110 is a component for movably connecting the connection object 10 to the housing 120, and is configured by forming a metal material into a round bar shape. The stud portion 110 has a connecting portion 111 formed at one end (upper side in the figure) and a ball portion 114 formed at the other end (lower side in the figure).

[0023] The connecting portion 111 is a portion that passes through the through hole 11 of the object to be connected 10, and is mainly composed of a male thread portion 112 and a non-thread portion 113. The male thread portion 112 is a portion into which the mounting nut 12 is screwed when it passes through the through hole 11 of the object to be connected 10, and is composed of a male thread into which the mounting nut 12 is screwed. The connecting portion 111 is formed from the one end of the stud portion 110 toward the other end.

[0024] The non-threaded portion 113 is a portion that is placed inside the through hole 11 of the connection object 10, and is formed in the shape of a round bar with a smaller diameter than the through hole 11 and no male threads. In this embodiment, the non-threaded portion 113 is formed with an outer diameter that leaves a gap with the inner circumferential surface of the through hole 11, and is formed with a length that is shorter than the length (depth) of the through hole 11.

[0025] Ball portion 114 is a portion that slides within ball seat 123, and is formed into a smooth, convex spherical shape so as to slide smoothly against the inner peripheral surface of ball seat 123. The surface of ball portion 114 is formed into a smooth spherical surface by grinding to ensure smooth sliding with ball seat 123. A brim-shaped receiving portion 115 is formed between connecting portion 111 and ball portion 114.

[0026] The flange-shaped receiving portion 115 is a portion to which the connection object 10 is fitted, and is formed in a disk shape that protrudes like a flange radially outward from the stud portion 110. As shown in Fig. 2, the flange-shaped receiving portion 115 is mainly configured to have a connecting portion side surface 115a, a ball portion side surface 115b, and an outer circumferential portion 115c.

[0027] The connecting portion side surface 115a is a portion formed on the connecting portion 111 side for receiving the connection target object 10, and is formed in a flat ring shape in a plan view. The ball portion side surface 115b is a surface formed on the ball portion 114 side (the surface opposite to the connecting portion side surface), and is formed in a flat ring shape in a bottom view. The outer peripheral portion 115c is an end face of the outermost periphery of the flange-shaped receiving portion 115, and is formed to extend in a ring shape in the circumferential direction of the flange-shaped receiving portion 115. A surface-hardened layer 116 is formed on this outer peripheral portion 115c.

[0028] The surface-hardened layer 116 is a portion for increasing the rigidity of the outer peripheral portion 115c, and is formed to have a higher hardness than the inner portion of the surface-hardened layer 116. In this embodiment, the surface-hardened layer 116 is composed of shot peening marks (a collection of countless dents). The depth and hardness of the hardened layer in the surface-hardened layer 116 are appropriately determined depending on the specifications of the ball joint 100. In addition, a surface-hardened layer 118 is also formed in a boundary portion 117 between the flange-shaped receiving portion 115 and the stud portion 110.

[0029] Boundary portion 117 is a boundary portion between flange-shaped receiving portion 115 and stud portion 110, and is an annular portion in the circumferential direction of stud portion 110. In this embodiment, boundary portion 117 is a portion where flange-shaped receiving portion 115 and stud portion 110 intersect at a substantially right angle and the surrounding area.

[0030] Similar to the surface-hardened layer 116, the surface-hardened layer 118 is a portion for increasing the rigidity of the boundary portion 117, and is formed to have a higher hardness than the hardness of the inner portion of the surface-hardened layer 118. In the present embodiment, the surface-hardened layer 118 is formed of shot peening marks (a collection of countless dents) similar to the surface-hardened layer 116. The depth and hardness of the hardened layer in the surface-hardened layer 118 are appropriately determined depending on the specifications of the ball joint 100.

[0031] A ball support portion 119 extending in a round bar shape is formed between this flange-shaped receiving portion 115 and the ball portion 114. In this case, a constricted portion 119a having a narrowed outer diameter is formed in the ball support portion 119, and the ball portion 114 is connected via this constricted portion 119a.

[0032] Housing 120 is a portion that holds ball portion 114, and is formed into a substantially cylindrical shape by casting or forging steel or non-ferrous metal such as aluminum. In this case, housing 120 is formed at the tip of a rod-shaped extending arm portion for connection to each component of a steering mechanism or suspension mechanism (not shown).

[0033] This housing 120 has an opening 121 formed at one end (upper end in the figure) of a cylindrical body that opens upward in the figure, and the other end (lower end in the figure) is closed by a plug 122. The plug 122 is a plate-like member that closes the other end of the cylindrical housing 120, and is made of steel and formed into a roughly circular plate shape with a recessed center. A ball seat 123 is accommodated inside the housing 120 as a bearing seat.

[0034] The ball seat 123 is a component that holds the ball portion 114 formed on the stud portion 110 in a rotatable and slidable state within the housing 120, and is configured by forming a synthetic resin material (e.g., PEEK resin) into a cup shape having a substantially U-shaped vertical cross section. Grease (not shown) is applied to the upper and lower openings of the ball seat 123 to ensure lubrication between the inner peripheral surface of the ball seat 123 and the outer peripheral surface of the ball portion 114. Meanwhile, a cover receiving portion 120a is formed on the outer peripheral portion of the housing 120 in a state of protruding radially outward from the housing 120, and a dust cover 124 is held on the cover receiving portion 120a.

[0035] Dust cover 124 is a component for preventing foreign matter from entering housing 120, and is made of elastically deformable rubber or soft synthetic resin material in a generally cylindrical shape with a bulge in the center. One opening of dust cover 124 (upper side in the figure) is elastically fitted into the base portion of ball portion 114 side of flange-shaped receiving portion 115 of stud portion 110, and the other opening is fitted via a metallic circlip 125 into the outer periphery of housing 120 on cover receiving portion 120a.

[0036] (Manufacturing of ball joints 100) Next, a description will be given of the manufacture of ball joint 100 configured as described above. In describing the manufacturing process of ball joint 100, the manufacturing process of stud portion 110, which is directly related to the present invention, will be mainly described with reference to Figure 3, and manufacturing processes that are not directly related to the present invention will be omitted as appropriate.

[0037] First, an operator manufactures the stud portion 110. The stud portion 110 is manufactured mainly through an overall forming step (S1), a heat treatment step (S2), a surface hardened layer forming step (S3), a threaded portion forming step (S4), and a ball portion forming step (S5). Specifically, in the overall forming step, an operator forges a round bar material made of carbon steel or alloy steel using a forging machine (not shown) to integrally form the connecting portion 111, the non-threaded portion 113, the flange-shaped receiving portion 115, the ball support portion 119, and the ball portion 114.

[0038] In this forging process, the stud portion 110 is gradually formed by plastically deforming a round bar material in stages. In this case, the ball portion 114 and ball support portion 119 of the stud portion 110 are processed by so-called rough forming, leaving a certain amount of cutting allowance. It is of course possible to perform this overall forming process by cutting instead of or in addition to the forging process.

[0039] Next, the worker performs a heat treatment process. Specifically, the worker performs a heat treatment consisting of quenching and tempering on the semi-finished product of the stud portion 110 formed in the overall forming process, thereby improving the hardness of the entire stud portion 110.

[0040] Next, the worker performs the surface hardening layer forming process. Specifically, the worker masks the remaining parts (the connecting part side surface 115a and the ball part side surface 115b) with masking tape (not shown) while exposing the outer periphery 115c and the boundary part 117 of the flange-shaped receiving part 115 in the semi-finished product of the stud part 110 that has been heat treated, and then performs a shot peening process (also called "shot blasting") on the entire stud part 110.

[0041] This allows the worker to work-harden the surface layers of connecting portion 111, ball portion 114, outer circumferential portion 115c, boundary portion 117, and ball support portion 119, which are portions of stud portion 110 other than the masked portion. The processing specifications for the shot peening process, such as the media diameter, are determined appropriately according to the specifications of ball joint 100.

[0042] Next, the worker performs a thread forming process. Specifically, the worker forms a male thread in the connecting portion 111 by rolling the semi-finished stud portion 110 with a thread rolling machine (not shown). This allows the worker to form the male thread 112 in part of the connecting portion 111 in the semi-finished stud portion 110. In this case, the rough surface of the male thread 112 that was formed by shot peening before the male thread was formed is smoothed by the rolling process.

[0043] Next, the worker performs the ball portion molding process. Specifically, the worker cuts the outer peripheral surface of ball portion 114, including ball support portion 119, of the semi-finished product of stud portion 110 using a machine tool such as a numerically controlled (NC) lathe (not shown). The worker also uses a grinding machine (not shown) to grind ball portion 114 and finish ball portion 114. Through each of these processes, the worker can manufacture stud portion 110.

[0044] Next, the worker forms the housing 120. Specifically, the worker prepares the stud portion 110, the plug 122, and the ball seat 123. In this case, the plug 122 is formed in advance into a disk shape by pressing. The ball seat 123 is formed in advance into a cylindrical shape by injection molding.

[0045] An operator sets each of the components, stud portion 110, plug 122, and ball seat 123, in a mold (not shown) for molding housing 120. In this case, the operator sets the ball portion 114 of stud portion 110 in the mold in a state in which it is held rotatably and slidably within ball seat 123.

[0046] Next, an operator casts an aluminum alloy into the mold in which the stud portion 110, the plug 122, and the ball seat 123 are set (aluminum die casting). This forms the housing 120 integrally including the stud portion 110, the plug 122, and the ball seat 123. In this embodiment, the housing 120 is formed with an arm portion (not shown) that extends in a rod shape formed integrally on the outer periphery of the housing 120. Alternatively, the housing 120 may be formed separately without casting the stud portion 110, the plug 122, and the ball seat 123, and then the stud portion 110, the plug 122, and the ball seat 123 may be assembled.

[0047] Next, the worker attaches the dust cover 124 to the housing 120 equipped with the stud portion 110, the plug 122, and the ball seat 123. Specifically, after preparing the dust cover 124 and the circlip 125, the worker fits one opening (upper side in the figure) of the dust cover 124 onto the outer periphery of the ball support portion 119 of the stud portion 110, and fits the other opening (lower side in the figure) of the dust cover 124 onto the cover receiving portion 120a of the housing 120.

[0048] The worker then fits circlip 125 onto the outer peripheral surface of dust cover 124. Ball joint 100 is completed by attaching dust cover 124 to housing 120. Note that when casting housing 120 and attaching dust cover 124, the worker can apply grease (not shown) between ball portion 114 and plug 122 in stud portion 110, on the inner peripheral surface of ball seat 123, and on the outer peripheral surface of ball portion 114 exposed from the opening of housing 120, thereby enabling ball portion 114 to rotate and slide smoothly.

[0049] (Assembly of ball joint 100) The following describes how ball joint 100 configured in this manner is assembled into object 10. In the description of the assembly process of ball joint 100, manufacturing steps that are not directly related to the present invention will be omitted as appropriate.

[0050] After passing the connecting portion 111 of the stud portion 110 through the through hole 11 of the object to be connected 10, an operator can attach the stud portion 110 of the ball joint 100 to the object to be connected 10 by tightening the mounting nut 12 onto the male thread portion 112. In this case, the boundary portion 117 of the stud portion 110 may collide with the edge of the through hole 11 when the connecting portion 111 passes through the through hole 11, or a tensile force may be applied to the boundary portion 117 by tightening the mounting nut 12, but damage to the boundary portion 117 is suppressed by the surface-hardened layer 118 formed on the boundary portion 117.

[0051] In addition, when the object to be connected 10 is strongly pressed against the flange-shaped receiving portion 115, the outer edge of the flange-shaped receiving portion 115 (the connecting portion side surface 115a) is strongly pressed against the surface of the object to be connected 10, and a shear force acts on the outer edge, and the outer edge sinks into the inside of the object to be connected 10, and the deformed portion 13 plastically deformed so that a part of the surface layer of the object to be connected 10 is raised in an annular shape is tightly attached to the outer periphery 115c. However, since the outer periphery 115c of the flange-shaped receiving portion 115 has a surface hardened layer 116 formed thereon, damage such as plastic deformation of the portion to which the object to be connected 10 is tightly attached can be suppressed. In addition, the flange-shaped receiving portion 115 can improve the frictional resistance between the object to be connected 10 and the flange-shaped receiving portion 115 and improve the adhesion due to the uneven surface of the surface hardened layer 116.

[0052] In addition, the worker connects an arm portion (not shown) extending from the housing 120 to another component of a steering mechanism or a suspension mechanism (not shown), thereby enabling the worker to attach the ball joint 100 to the steering mechanism or the suspension mechanism.

[0053] (Operation of ball joint 100) The operation of ball joint 100 configured as described above will now be described. Ball joint 100 is used as a joint member in a suspension mechanism or steering mechanism of a vehicle (not shown). When the vehicle is running, loads according to the behavior of the wheels and the attitude of the vehicle, specifically various types of stresses such as bending, tension, compression, and shear, and vibrations act on ball joint 100.

[0054] In this case, the vibrations caused by the load also act on outer periphery 115c and boundary portion 117 of ball joint 100. However, since outer periphery 115c and boundary portion 117 are provided with hardened surface layers 116 and 118, respectively, damage thereto is suppressed.

[0055] As can be understood from the above explanation of the operating method, according to the above embodiment, ball joint 100 has surface-hardened layers 116, 118 formed on outer periphery 115c and boundary portion 117, respectively, thereby improving the rigidity of these portions. Furthermore, by improving the rigidity of outer periphery 115c and boundary portion 117, ball joint 100 can reduce the outer diameter of the entire stud portion 110, thereby making the stud portion 110 more compact.

[0056] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the present invention. In each of the modifications shown below, the same components as those in the above-described embodiments are denoted by corresponding reference numerals, and the description thereof will be omitted.

[0057] For example, in the above embodiment, ball joint 100 has surface hardened layers 116, 118 formed on outer periphery 115c and boundary portion 117, respectively. However, it is sufficient that ball joint 100 is configured with surface hardened layer 118 formed at least on boundary portion 117. Note that, in the case where there is no need to form surface hardened layer 118 on boundary portion 117, but there is a need to form surface hardened layer 116 on outer periphery 115c of flange-shaped receiving portion 115, it is also possible to omit forming surface hardened layer 118 on boundary portion 117 and form surface hardened layer 116 on outer periphery 115c of flange-shaped receiving portion 115.

[0058] In the above embodiment, in the surface-hardened layer forming step, a part of the stud portion 110 (the connecting portion side surface 115a and the ball portion side surface 115b of the flange-shaped receiving portion 115) is masked and then shot peened. However, in the surface-hardened layer forming step, it is sufficient to perform shot peening on at least the outer circumferential portion 115c and the boundary portion 117.

[0059] Therefore, in the surface-hardened layer forming step, the entire stud portion 110 may be subjected to shot peening to form the surface-hardened layers 116, 118 on the surface layer of the entire stud portion 110. In this case, in the surface-hardened layer forming step, the portions other than the flange-shaped receiving portion 115 may be masked and then the shot peening may be performed to form the surface-hardened layers 116, 118 only on the surface layer of the flange-shaped receiving portion 115. Also, in the surface-hardened layer forming step, it is possible to perform the shot peening partially on the outer circumferential portion 115c, the boundary portion 117, etc. using a nozzle that sprays media.

[0060] In the above embodiment, boundary portion 117 is configured so that non-threaded portion 113 and flange-shaped receiving portion 115 are connected at a substantially right angle. However, boundary portion 117 may also be configured so that non-threaded portion 113 and flange-shaped receiving portion 115 are connected by a curved surface, as shown in FIG. 4. Boundary portion 117 may also be formed so that the intersection of the extension lines of non-threaded portion 113 and flange-shaped receiving portion 115 is recessed in a concave shape toward the inside of stud portion 110, as shown in FIG. In this way, ball joint 100 has surface-hardened layer 118 formed at boundary portion 117 recessed in a concave shape, and therefore the rigidity of stud portion 110 can be ensured while improving the adhesion with object 10 to be connected.

[0061] In this case, the surface-hardened layer 118 may be formed only on the inner surface of the concavely recessed boundary portion 117, or may be formed up to the outer peripheral portion (non-threaded portion 113 and connecting portion side surface 115a) of the boundary portion 117. In particular, when the inner peripheral surface of the through-hole 11 of the connection object 10 contacts and fits with the non-threaded portion 113 of the connecting portion 111, the durability of the non-threaded portion 113 can be improved by forming the surface-hardened layer 118 to extend to the surface layer of the non-threaded portion 113, as shown in FIG.

[0062] In the above embodiment, the stud portion 110 is configured by integrally molding the connecting portion 111, the ball portion 114, the brim-shaped receiving portion 115, and the ball support portion 119 from the same material. However, the stud portion 110 is configured by integrally molding the connecting portion 111, the ball portion 114, the brim-shaped receiving portion 115, and the ball support portion 119 from the same material. However, the stud portion 110 can also be configured by molding the ball portion 114 separately and then joining it to the ball support portion 119 by welding or the like.

[0063] In the above embodiment, the surface-hardened layer forming step forms the surface-hardened layers 116, 118 on the outer circumferential portion 115c and the boundary portion 117 by shot peening. However, the surface-hardened layer forming step does not necessarily have to employ shot peening as long as it can form the surface-hardened layers 116, 118 on the outer circumferential portion 115c and the boundary portion 117. Therefore, the surface-hardened layer forming step can also form the surface-hardened layers 116, 118 on the outer circumferential portion 115c and the boundary portion 117 by other surface hardening treatments (for example, various heat treatments such as induction hardening or flame hardening, nitriding or carburizing) instead of shot peening.

[0064] In the above embodiment, the surface-hardened layer forming step is performed before the thread forming step. However, the surface-hardened layer forming step can also be performed after the thread forming step. In this case, the thread forming step is preferably performed before the heat treatment step, but can also be performed after the heat treatment step. Also, the thread forming step can be formed by machining other than rolling, for example, cutting. [Explanation of symbols]

[0065] 10...connection object, 11...through hole, 12...mounting nut, 100…ball joint, 110... stud portion, 111... connecting portion, 112... male thread portion, 113... non-threaded portion, 114... ball portion, 115... flange-shaped receiving portion, 115a... connecting portion side, 115b... ball portion side, 115c... outer periphery, 116... surface hardened layer, 117... boundary portion, 118... surface hardened layer, 119... ball support portion, 119a... constricted portion, 120...housing, 120a...cover receiving portion, 121...opening, 122...plug, 123...ball seat, 124...dust cover, 125...circlip.

Claims

1. a stud portion having a connecting portion to be connected to an object to be connected and formed in a rod shape and a ball portion having a spherical surface, the stud portion having a flange-like protruding flange-like receiving portion to which the object to be connected is fitted; a housing that slidably accommodates the ball portion of the stud portion, A ball joint characterized in that a surface hardened layer is formed at the boundary between the connecting portion and the flange-shaped receiving portion.

2. 2. The ball joint according to claim 1, The surface hardened layer is A ball joint characterized by being formed with shot peening marks.

3. 2. The ball joint according to claim 1, the boundary portion is formed so as to be recessed inwardly of the stud portion, A ball joint, characterized in that the surface hardened layer is formed on the surface of the concavely recessed boundary portion.

4. 2. The ball joint according to claim 1, further comprising: A ball joint characterized in that a surface hardened layer is formed on the outer periphery of the flange-shaped receiving portion.

5. a stud portion having a connecting portion to be connected to an object to be connected and formed in a rod shape and a ball portion having a spherical surface, the stud portion having a flange-like protruding flange-like receiving portion to which the object to be connected is fitted; a housing that slidably accommodates the ball portion of the stud portion, A method for manufacturing a ball joint, comprising the step of forming a surface hardened layer at the boundary between the connecting portion and the flange-shaped receiving portion.

6. 6. The method for manufacturing a ball joint according to claim 5, The surface hardened layer forming step includes: A method for manufacturing a ball joint, characterized by shot peening.

7. 7. The method for manufacturing a ball joint according to claim 6, A thread forming step of forming a male thread on the connecting portion is included. The surface hardened layer forming step includes: A method for manufacturing a ball joint, characterized in that it is carried out before the thread portion molding step.

8. The method for manufacturing a ball joint according to claim 5 further comprises: The surface hardened layer forming step includes: A method for manufacturing a ball joint, comprising forming the surface hardened layer also on the outer periphery of the flange-shaped receiving portion.

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