Bushing manufacturing method

Abstract

The present invention is a bushing manufacturing method for obtaining a bushing in which an inner member (4) including a core metal (2) of which the outer peripheral surface (F2) is covered by a resin layer (3) is disposed inside an outer cylinder (6) via an elastic layer (5). The present invention includes a resin cylinder preparation step for preparing a resin cylinder (13) made from a resin as a resin layer (3), a core metal preparation step for preparing a core metal (2), a core metal heating step for heating the core metal (2), and a joining step for joining the core metal (2) and the resin cylinder (13) by inserting the core metal (2) after the core metal heating step into the interior of the resin cylinder (13) from an opening (A13) formed in an axial end (13a) of the resin cylinder (13).

Description

Bush manufacturing method

[0001] This application claims priority from Japanese Patent Application No. 2023-97258, filed on June 13, 2023, the entire contents of which are incorporated herein by reference.

[0002] As a conventional method for manufacturing a bushing in which an inner member, the outer circumferential surface of which is covered with a resin layer, is placed inside an outer cylinder via an elastic layer, so-called insert molding is known, in which a resin layer is injection molded using the core as an insert (see, for example, Patent Document 1). With insert molding, the core is fitted into the mating surface of a mold, and then a resin material is injected into a cavity formed on the mating surface, thereby manufacturing a core having a resin layer.

[0003] Japanese Patent Application Laid-Open No. 2022-062999

[0004] However, when molding using a mold, it is necessary to improve the dimensional accuracy of both the insert (core) and the mold to prevent leakage of the resin material from the mating surfaces of the mold. In addition, if the resin material leaks from the mating surfaces of the mold, post-processing such as removing the excess resin layer generated on the molded product is required.

[0005] An object of the present invention is to provide a method for manufacturing a bushing that does not require strict dimensional accuracy when providing a resin layer on a core bar, and that suppresses the generation of excess resin layer that requires post-processing.

[0006] (1) A method for manufacturing a bushing according to the present invention is a method for manufacturing a bushing in which an inner member, the outer surface of which is coated with a resin layer, is disposed inside an outer tube via an elastic layer, and includes the following steps: a resin tube preparation step for preparing a resin tube as the resin layer, a core preparation step for preparing the core, a core heating step for heating the core, and a bonding step for inserting the core after the core heating step into the resin tube through an opening formed at the axial end of the resin tube prepared in the resin tube preparation step, thereby bonding the core and the resin tube together. The method for manufacturing a bushing according to the present invention does not require strict dimensional accuracy when providing the resin layer on the core, and furthermore, it suppresses the generation of excess resin layer that requires post-processing.

[0007] (2) In the method for manufacturing a bushing described in (1) above, it is preferable that the core is formed by two core parts that are formed into one core by butting them together on the same axis, the core preparing step is a step of preparing the two core parts, the core heating step is a step of heating each of the two core parts, and the joining step is a step of joining the two core parts and the resin tube by inserting each of the two core parts after the heating step into the interior of the resin tube through openings formed at the axial ends of the resin tube until the butting ends of the two core parts butt against each other on the same axis. In this case, a bushing with high dimensional accuracy can be manufactured.

[0008] (3) In the method for manufacturing a bushing described in (2) above, it is preferable that the outer peripheral surface of the core metal is the outer peripheral surface of the core metal part, and further, that the outer peripheral surface of the core metal part includes a tapered surface that tapers radially inward toward the butting end of the core metal part. In this case, a bushing with high durability can be manufactured.

[0009] (4) In the method for manufacturing a bushing according to any one of (1) to (3), the core heating step preferably involves heating the core by induction heating using a winding. In this case, the entire outer circumferential surface of the core can be heated simply and easily.

[0010] (5) In the method for manufacturing a bushing according to any one of (1) to (3) above, the core prepared in the core heating step preferably has irregularities on at least a portion of the outer circumferential surface of the core that is to be covered with the resin layer, which allows the resin layer to be more firmly fixed to the outer circumferential surface of the core.

[0011] (6) In the method for manufacturing a bushing according to any one of (1) to (5), the core preparation step preferably includes a roughening step of roughening the outer peripheral surface of the core, and the irregularities are formed by the roughening step. In this case, the resin layer can be more firmly fixed to the outer peripheral surface of the core.

[0012] (7) In the method for manufacturing a bushing described in (6) above, it is preferable to use laser processing for the roughening process. In this case, it is possible to easily and inexpensively provide irregularities on the outer peripheral surface of the core bar.

[0013] (8) In the method for manufacturing a bushing described in (7) above, it is preferable that the elastic layer is an elastic layer bonded to the outer peripheral surface of the core bar, and the roughening step is a step of performing laser processing on the outer peripheral surface of the core bar, in a region bonded to the resin tube, as well as on the region bonded to the elastic layer. In this case, it is possible to simply and easily form irregularities in the region bonded to the resin tube and the region bonded to the elastic layer.

[0014] (9) In the method for manufacturing a bushing according to any one of (1) to (8) above, the core metal preparation step may be a step of preparing a resin tube having the elastic layer and the outer tube integrally bonded to the outer periphery of the resin tube. In this case, the bushing can be manufactured in a state in which the resin layer, the elastic layer, and the outer tube are integrally bonded in advance.

[0015] (10) In the method for manufacturing a bushing according to any one of (1) to (8) above, after the joining step, an integration step of integrally joining the elastic layer and the outer cylinder to the outer periphery of the resin cylinder can be further included. In this case, the bushing can be manufactured by separately joining the elastic layer and the outer cylinder together after manufacturing the inner member.

[0016] According to the present invention, a method for manufacturing a bushing can be provided in which strict dimensional accuracy is not required when forming a resin layer on a core bar, and further, the generation of excess resin layer that requires post-processing is suppressed.

[0017] 10 is a cross-sectional view schematically showing an example of a bushing that can be manufactured using the bushing manufacturing method of the present invention. FIG. 11 is a cross-sectional view schematically showing an example of the operation of the bushing shown in FIG. 1. FIG. 12 is a cross-sectional view for schematically explaining a bushing manufacturing method according to a first embodiment of the present invention. FIG. 13 is a cross-sectional view schematically showing the core metal part shown in FIG. 3. FIG. 14 is a cross-sectional view schematically showing a phenomenon that may occur when a core metal part having a straight outer shape is used. FIG. 15 is a cross-sectional view schematically showing another example of a bushing that can be manufactured using the bushing manufacturing method of the present invention. FIG. 16 is a cross-sectional view schematically explaining a bushing manufacturing method according to a second embodiment of the present invention. FIG. 17 is a cross-sectional view schematically showing the core metal part shown in FIG. 7. FIG. 18 is a cross-sectional view schematically showing the inner member shown in FIG. 6. FIG. 19 is a cross-sectional view schematically showing another example of an inner member of a bushing. FIG. 19 is a cross-sectional view schematically showing an example of a core metal that can be used for insert molding the inner member shown in FIG.

[0018] Hereinafter, a method for manufacturing a bushing according to some exemplary embodiments of the present invention will be described with reference to the drawings.

[0019] FIG. 1 shows a schematic diagram of an example of a bushing that can be manufactured using the bushing manufacturing method of the present invention.

[0020] In Fig. 1, the reference symbol O1 denotes a central axis of the bushing. Fig. 1 shows an exemplary bushing 1A in a cross section including the central axis O1 (hereinafter also simply referred to as "axis O1") of the bushing 1A.

[0021] In the present disclosure, the direction in which the axis O1 extends is also referred to as the "axial direction." Furthermore, in the present disclosure, a direction perpendicular to the axis O1 is also referred to as the "axial direction" or the "radial direction." In particular, within the radial direction, the side closer to the axis O1 is also referred to as the "radially inner side," and the side farther from the axis O1 is also referred to as the "radially outer side." Furthermore, in the present disclosure, a direction extending circumferentially around the axis O1 is also simply referred to as the "circumferential direction."

[0022] 1 , the bushing has an inner member 4, in which the outer peripheral surface F2 of a core 2 is covered with a resin layer 3, and is disposed inside an outer cylinder 6 via an elastic layer 5. That is, the bushing includes the resin layer 3 that covers the outer peripheral surface (F2) of the inner member 4, the elastic layer 5 disposed on the outer peripheral side of the resin layer 3, and the outer cylinder 6 disposed on the outer peripheral side of the elastic layer 5.

[0023] 1, the bushing 1A includes a resin layer 3 bonded to the outer peripheral surface F2 of the core 2, an elastic layer 5 bonded to the outer peripheral surface F3 of the resin layer 3, and an outer cylinder 6 bonded to the outer peripheral surface F5 of the elastic layer 5. In the bushing 1A, the inner member 4 is a cylindrical member (inner cylinder) attached to either the vibration generating side or the vibration receiving side. In the bushing 1A, the core 2 and the resin layer 3 are formed as a single inner member 4.

[0024] The core 2 is a metal core. In the present disclosure, the core 2 is a cylindrical core. However, the core 2 may be a polygonal cylindrical core as long as it is a cylindrical core. Furthermore, the core 2 is not limited to a cylindrical core. For example, the core 2 may be a solid core. Examples of metals that form the core 2 include aluminum alloys and iron.

[0025] The resin layer 3 is a resin tube 13 made of resin. In the present disclosure, the resin tube 13 is a cylindrical resin tube. However, the resin tube 13 may be a polygonal resin tube as long as it is a cylindrical resin tube. The resin tube 13 is welded to the outer peripheral surface F2 of the core bar 2, as described below. The resin forming the resin tube 13 is preferably a resin with a melting temperature of a predetermined temperature (e.g., 120°C to 176°C) and, for example, a resin with high abrasion resistance and chemical resistance. An example of the resin forming the resin tube 13 is polyamide (including glass fiber reinforcement).

[0026] In the bushing 1A, the resin layer 3 includes a bulge-shaped portion 31 and two shaft portions 32 connected to the bulge-shaped portion 31. In this embodiment, the bulge-shaped portion 31 and the two shaft portions 32 are integrally formed. Here, the bulge shape refers to, for example, a shape in which a portion of the outer circumferential surface of the resin layer 3 is locally bulged into a spherical shape. As shown in FIG. 1 , in the bushing 1A, the bulge-shaped portion 31 is positioned axially around the axial center P1 of the bushing 1A. However, the bulge-shaped portion 31 may be positioned so as to be offset toward one of the two axial ends 1e of the bushing 1A from the axial center P1 of the bushing 1A. Here, the axial center P1 of the bushing 1A is assumed to coincide with the axial center of the inner member 4 (core 2).

[0027] The elastic layer 5 has a tubular shape formed from an elastic material. In the present disclosure, the elastic layer 5 has a cylindrical shape. However, the elastic layer 5 may have a polygonal tubular shape as long as it has a tubular shape. Examples of elastic materials that form the elastic layer 5 include rubber.

[0028] In the bushing 1A, the elastic layer 5 includes a covering portion 51 that covers the bulge-shaped portion 31 of the resin layer 3, and two support portions 52 that are continuous with the covering portion 51. In the bushing 1A, the covering portion 51 and the two support portions 52 are integrally formed. The covering portion 51 is an annular covering portion that extends annularly in the circumferential direction around the axis O1. The two support portions 52 are also annular support portions that extend annularly in the circumferential direction around the axis O1. Furthermore, in the bushing 1A, an annular joint portion 7 that joins the support portion 52 and the shaft portion 32 of the resin layer 3 is formed between the support portion 52 of the elastic layer 5 and the shaft portion 32. The annular joint portion 7 extends annularly in the circumferential direction around the axis O1. Meanwhile, an annular non-bonding portion 8 that does not bond the covering portion 51 and the bulge-shaped portion 31 is formed between the covering portion 51 of the elastic layer 5 and the bulge-shaped portion 31 of the resin layer 3. The annular non-bonding portion 8 also extends annularly in the circumferential direction around the axis O1. The annular non-bonding portion 8 is an annular sealed gap closed by the two annular bonding portions 7 formed between the covering portion 51 of the elastic layer 5 and the bulge-shaped portion 31 of the resin layer 3. In the bushing 1A, the annular non-bonding portion 8 is filled with a lubricating fluid 11.

[0029] The outer cylinder 6 is a cylindrical member attached to either the vibration generating side or the vibration receiving side. The outer cylinder 6 is bonded to the outer peripheral surface of the elastic layer 5. The inner member 4 and the outer cylinder 6 are supported mainly by the support portion 52 of the elastic layer 5. In the bushing 1A, the bulge-shaped portion 31 of the resin layer 3 is supported by the covering portion 51 of the elastic layer 5 and the lubricating fluid 11.

[0030] The outer cylinder 6 is a metal outer cylinder. The outer cylinder 6 is bonded to the outer peripheral surface F5 of the elastic layer 5. In the present disclosure, the outer cylinder 6 is a cylindrical outer cylinder. However, the outer cylinder 6 may be a polygonal cylindrical outer cylinder as long as it is a cylindrical outer cylinder. Examples of metals that form the outer cylinder 6 include aluminum alloys and iron. The outer cylinder 6 may also be a resin outer cylinder.

[0031] Figure 2 shows an example of the operation of the bushing 1A in a schematic view equivalent to the cross section of Figure 1. In the following description, the bushing 1A will be described as being used in a suspension device of a vehicle.

[0032] 2, the outer tube 6 is fixed to the suspension arm 100 by fitting it into a fixing sleeve 101 provided on the suspension arm 100. In contrast, the inner member 4 is fixed to a vehicle body (not shown) via fastening elements such as bolts and nuts by passing the fastening elements through through holes A1 formed inside the inner member 4. However, the bushing 1A can also fix the outer tube 6 to the fixing sleeve 101 provided on the vehicle body, while also fixing the inner member 4 to the suspension arm 100 via fastening elements such as bolts and nuts.

[0033] The bushing 1A can absorb the prying force of the inner member 4 against the outer cylinder 6. Fig. 2 exemplarily shows a state in which the inner member 4 pries against the inside of the outer cylinder 6 via the elastic layer 5.

[0034] When the bushing 1A is used in a suspension device, for example, twisting or prying may occur inside the bushing 1A due to three-dimensional input from the inner member 4. Here, "twisting" refers to relative movement (relative rotation) between the inner member 4 and the outer cylinder 6 in the circumferential direction around the axis O1 at an angle θ1. Furthermore, "prying" refers to relative movement (relative rotation) in the circumferential direction around the axis O1 at an angle θ1, with at least one of the inner member 4 and the outer cylinder 6 tilted at an angle α1 with respect to the axis O1, as shown in FIG. 2 . However, in the present disclosure, "prying" also includes movement of at least one of the inner member 4 and the outer cylinder 6 tilted with respect to the axis O1, without relative movement (relative rotation) in the circumferential direction around the axis O1, as shown in FIG. 2 .

[0035] 2, when an input force is applied that causes twisting of the bushing 1A, the elastic layer 5 and the inner member 4 are displaced relative to each other so as to separate from each other in the region of the non-coupled portion 8. This allows the bushing 1A to absorb twisting of the inner member 4 relative to the outer cylinder 6 while maintaining vibration-damping performance. In the bushing 1A, the lubricating fluid 11 is filled inside the annular coupled portion 8, so that twisting of the inner member 4 relative to the outer cylinder 6 can be more smoothly absorbed. However, the lubricating fluid 11 can be omitted.

[0036] As a method for manufacturing the bushing 1A, for example, so-called insert molding, in which the resin layer 3 is injection molded using the core metal 2 as an insert, is known as a conventional technique.

[0037] However, when molding using a mold, it is necessary to improve the dimensional accuracy of both the insert (core) and the mold to prevent leakage of the resin material from the mating surfaces of the mold. In addition, if the resin material leaks from the mating surfaces of the mold, post-processing such as removing the excess resin layer generated on the molded product is required.

[0038] 3 is a schematic diagram showing a method for manufacturing a bushing according to a first embodiment of the present invention, which does not require the use of a mold when manufacturing the inner member 4. The bushing manufacturing method of this embodiment can obtain a bushing 1A by a method including the following steps.

[0039] The manufacturing method of the bushing in this embodiment includes a resin tube preparation process for preparing a resin tube 13 as the resin layer 3, a core wire preparation process for preparing a core wire 2, a core wire heating process for heating the core wire 2, and a joining process for joining the core wire 2 and the resin tube 13 by inserting the core wire 2 after the core wire heating process into the interior of the resin tube 13 through an opening A13 formed at the axial end 13a of the resin tube 13 prepared in the resin tube preparation process.

[0040] In the resin tube preparation step, a resin tube 13 is prepared. As shown in Fig. 3 , in this embodiment, an inner peripheral surface F32 of the resin tube 13 is formed by two tapered surfaces F321. Specifically, as shown in Fig. 3 , the tapered surfaces F321 are tapered radially inward from an opening A13 formed at an axial end 13a of the resin tube 13 toward the axial center (P1) of the resin tube 13. In this embodiment, the tapered surfaces F321 are formed to correspond to the tapered surfaces F121 of the core metal part 12, which will be described later.

[0041] In the core bar preparation step, a core bar 2 is prepared. In the bushing manufacturing method of this embodiment, the core bar preparation step includes preparing two core bar parts 12. More specifically, in this embodiment, the core bar 2 is formed by two core bar parts 12 that are formed into one core bar 2 by abutting them against each other on the same axis O1.

[0042] FIG. 4 shows a schematic cross section of the core metal part 12 shown in FIG. 1, taken along a line including the axis O1.

[0043] In the bushing 1A, the outer peripheral surface F2 of the core 2 is the outer peripheral surface F12 of the two core parts 12. The outer peripheral surface F12 of the core part 12 includes a tapered surface F121 that tapers radially inward toward the butting end 12a of the core part 12. In this embodiment, the acute angle α2 of the tapered surface F121 relative to the axis O1 is 2 degrees. However, the angle α2 may be any angle that does not include 0 degrees. For example, the angle α2 can be 2 degrees or more. In the bushing 1A, the central axis of the core 2 (core part 12) is assumed to coincide with the axis O1.

[0044] As shown in Fig. 1, in the bushing 1A, the two core metal parts 12 have the same shape. As a result, in the bushing 1A, the butt position of the two core metal parts 12 is located at the axial center P1 of the bushing 1A, as shown in Fig. 1. If the butt position of the two core metal parts 12 is located at the axial center P1 of the bushing 1A, it is possible to standardize the core metal parts 12 that form the core metal 2, as in the bushing 1A.

[0045] However, the shapes of the two core metal parts 12 can be different. For example, the axial length of one of the two core metal parts 12 can be different from the axial length of the other of the two core metal parts 12. If the axial length of one of the two core metal parts 12 is different from the axial length of the other of the two core metal parts 12, for example, the butting position of the two core metal parts 12 can be shifted from the axial center P1 of the bushing 1A to one of the two axial ends 1e of the bushing 1A.

[0046] The core metal heating step is a step of heating the core metal 2. In this embodiment, the core metal heating step is a step of heating each of the two core metal parts 12.

[0047] 3, the two core metal parts 12 can be heated using various heating methods. In this embodiment, the two core metal parts 12 are each heated by induction heating using the winding 10, which will be described later. The heating temperature of the core metal parts 12 is set to a temperature equal to or higher than the temperature at which the resin tube 13 melts. The heating temperature of the core metal parts 12 is also controlled to a temperature that does not deform the resin tube 13, for example, a temperature that does not deform the shaft portion 32 of the resin tube 13. Preferably, the heating temperature of the core metal part 12 is set to a temperature that melts only the surface layer of the inner circumferential surface of the resin tube 13 when the heated core metal part 12 is pressed into the inner circumferential surface of the resin tube 13.

[0048] In the joining step, the core metal parts 2 are joined to the resin tube 13 by being inserted into the resin tube 13 through openings A13 formed in the axial ends 13a of the resin tube 13. As shown in Fig. 3 , in the joining step, the two core metal parts 12 after the heating step are inserted into the resin tube 13 through openings A13 formed in the axial ends 13a of the resin tube 13 until the butting ends 12a of the two core metal parts 12 butt against each other on the same axis O1, thereby joining the two core metal parts 12 to the resin tube 13. As a result, the two core metal parts 12 are integrated with the resin tube 13 as the core metal parts 12 are cooled.

[0049] According to the bushing manufacturing method of this embodiment, the core 2 can be joined to the resin tube 13 by inserting the core 2 into the opening A13 formed in the axial end 13a of the resin tube 13. Therefore, according to the bushing manufacturing method of this embodiment, the inner member 4 can be manufactured simply by inserting the heated core 2 into the resin tube 13. Furthermore, according to the bushing manufacturing method of this embodiment, the inner member 4 can be manufactured without using a mold, which reduces the generation of an excess resin layer that requires post-processing.

[0050] Therefore, according to the bushing manufacturing method of this embodiment, strict dimensional accuracy is not required when providing the resin layer 3 on the core 2, and furthermore, the generation of excess resin layer that requires post-processing is suppressed.

[0051] According to the bushing manufacturing method of the present invention, the core wire 2 is a single core wire, and the single core wire 2 can be joined to the resin tube 13 by inserting the single core wire 2 into only one of the openings A13 formed at the axial end 13a of the resin tube 13.

[0052] However, when a single core bar 2 is inserted into only one opening A13 formed at the axial end 13a of the resin tube 13, there is a risk that the resin tube 13 may lose its shape.

[0053] In contrast, by using two core metal parts 12 as in the bushing manufacturing method of this embodiment, when the two core metal parts 12 are inserted into the resin tube 13 through the opening A13 formed in the axial end 13a of the resin tube 13 until the butting ends 12a of the two core metal parts 12 butt against each other on the same axis O1, the shape of the resin tube 13 is less likely to be distorted. Therefore, when two core metal parts 12 are used as in the bushing manufacturing method of this embodiment, a bushing 1A with high dimensional accuracy can be manufactured.

[0054] 3, in the method for manufacturing a bushing according to this embodiment, the core metal preparation step is a step of preparing a resin tube 13 in which an elastic layer 5 and an outer tube 6 are integrally bonded to the outer periphery of the resin tube 13. The resin tube 13 in which the elastic layer 5 and the outer tube 6 are integrally bonded can be molded, for example, by placing the resin tube 13 and the outer tube 6 as inserts inside a mold and injecting an elastic material into the mold.

[0055] In the core metal preparation step, if a resin tube 13 in which the elastic layer 5 and the outer tube 6 are integrally bonded to the outer periphery of the resin tube 13 is prepared as the resin tube 13, the bushing 1A can be manufactured with the resin layer 3, the elastic layer 5, and the outer tube 6 already integrally bonded together. Also, if a resin tube in which the elastic layer 5 and the outer tube 6 are integrally bonded as shown in Fig. 3 is prepared as the resin tube 13, the resin tube preparation step and the core metal preparation step can be performed at the same time.

[0056] According to the bushing manufacturing method of the present invention, the outer shape of the core metal part 12 can be a straight shape parallel to the axis O1. That is, the outer circumferential surface F12 of the core metal part 12 can have the same diameter in the axial direction.

[0057] FIG. 5 shows a schematic diagram of a phenomenon that may occur when a core metal part 12 having a straight outer shape is used as the core metal part 12 in the method of manufacturing a bush according to this embodiment.

[0058] According to the method for manufacturing a bushing of the present invention, the resin tube 13 melts due to the heat emitted from the core metal part 12. On the other hand, if the outer peripheral surface F12 of the core metal part 12 is a straight surface F122 extending straight and parallel to the axis O1 as shown in Fig. 5, when the core metal part 12 is pushed in, the abutting end 12a of the core metal part 12 may scrape out and push in the molten portion 13p of the resin tube 13, as shown in Fig. 5.

[0059] When the butting ends 12a of the two core metal parts 12 each scrape out the molten portion 13p of the resin tube 13 and push it into the interior of the resin tube 13, it is possible that the molten portion 13p of the resin tube 13 will become stuck between the butting ends 12a of the two core metal parts 12, as shown in Figure 5.

[0060] If the molten portion 13p of the resin tube 13 gets stuck between the butt ends 12a of the two core metal parts 12, the butt ends 12a of the two core metal parts 12 will not completely butt together, and a gap will be created between the butt ends 12a of the two core metal parts 12.

[0061] When a gap occurs between the butt ends 12a of the two core metal parts 12, the space between the butt ends 12a of the two core metal parts 12 as the inner member 4 is supported only by the resin layer 3, or, when viewed as the entire bushing 1A, only by the resin layer 3, the elastic layer 5, and the outer cylinder 6. In this case, there is a risk that the bushing will sag (permanently deform) between the butt ends 12a of the two core metal parts 12 over time.

[0062] In contrast, in the bushing manufacturing method of this embodiment, the outer peripheral surface F12 of the core metal part 12 at the tip end on the butt end 12a side of the core metal part 12 is formed as a tapered surface F121 that tapers radially inward toward the butt end 12a of the core metal part 12, as shown in FIG. 3 . In this case, the molten portion 13p of the resin tube 13 melted by the heat emitted from the core metal part 12 can escape along the tapered surface F121 of the core metal part 12 to the side opposite the pushing side of the core metal part 12. This prevents the molten portion 13p of the resin tube 13 from getting stuck between the butt ends 12a of the two core metal parts 12. Therefore, by forming the tapered surface F121 at the tip end on the butt end 12a side of the outer peripheral surface F12 of the core metal part 12, a highly durable bushing 1A can be manufactured.

[0063] In the method for manufacturing a bushing according to the present invention, the method for heating the core metal part 12 (core metal 2) is not particularly limited. The core metal part 12 (core metal 2) can be heated by, for example, a heater or a heating furnace.

[0064] In contrast, as shown in FIG. 3, in the method for manufacturing a bushing according to this embodiment, the core metal heating step is a step of heating the core metal part 12 by induction heating using a winding 10.

[0065] In this embodiment, the metal core part 12 is heated by being placed inside the winding 10. The winding 10 can be, for example, a conductive wire, specifically a metal wire. According to the bushing manufacturing method of this embodiment, the metal core part 12 generates heat due to the electrical resistance of the metal core part 12 when electricity is passed through the winding 10. As a result, the metal core part 12 is heated while placed inside the winding 10 in accordance with the time that electricity is passed through the winding 10. Therefore, if induction heating is used to heat the metal core part 12, the entire outer peripheral surface F12 of the metal core part 12 can be heated simply and easily.

[0066] In particular, in this embodiment, the winding 10 is arranged on the same axis O1 as the resin tube 13. By arranging the resin tube 13 and the winding 10 on the same axis O1 in this way, the core metal part 12 heated inside the winding 10 can be inserted directly into the resin tube 13 through an opening A13 formed at the axial end 13a of the resin tube 13, as shown by the arrow in Figure 3. In this case, for example, the heated core metal part 12 can be automatically pressed into the resin tube 13 by using an automatic machine. Therefore, if the core metal part 12 is heated by induction heating, the work efficiency during the production of the bushing 1A can be improved.

[0067] In the method for manufacturing a bush according to this embodiment, at least a portion of the outer circumferential surface F12 of the core metal part 12 that is covered with the resin layer 3 has irregularities.

[0068] 4, in this embodiment, the irregularities are formed in the shaded area indicated by the reference numeral 12b. In this embodiment, the irregularities are formed on the tapered surface F121.

[0069] If at least a portion of the outer peripheral surface F12 of the core metal part 12 that is covered by the resin layer 3 has irregularities, the resin tube 13 that is melted by the heat of the core metal part 12 will bite into the irregularities provided on the outer peripheral surface F12 of the core metal part 12 (by the so-called anchor effect) and be firmly bonded to the outer peripheral surface F12 of the core metal part 12. Therefore, if irregularities are formed in at least a portion of the region of the outer peripheral surface F12 of the core metal part 12 where the resin layer 3 is bonded, the resin layer 3 can be more firmly fixed to the outer peripheral surface F12 of the core metal part 12.

[0070] The irregularities formed on the outer peripheral surface F12 of the core metal part 12 may be minute irregularities that allow the molten resin material to penetrate into the gaps between the irregularities and produce a so-called anchor effect after the resin material hardens. For this reason, for example, when the core metal part 12 is formed by casting, the core metal part 12 may be used as is.

[0071] On the other hand, in the bushing manufacturing method of this embodiment, the core bar preparation process includes a roughening process for roughening the outer peripheral surface F2 of the core bar 2, and the irregularities are formed by the roughening process.

[0072] If the outer peripheral surface F2 of the core 2 is a smooth surface, it may be difficult to obtain an anchor effect. In this case, it is necessary to increase the bonding strength between the outer peripheral surface F2 of the core 2 and the resin layer 3. Therefore, in the bushing manufacturing method of this embodiment, the outer peripheral surface F2 of the core 2 is actively roughened before the core heating step in which the core 2 is heated. By roughening the outer peripheral surface F2 of the core 2 before the core heating step as in this embodiment, the resin layer 3 can be more firmly fixed to the outer peripheral surface F2 of the core 2. In this embodiment, as shown in FIG. 3 , the outer peripheral surface F12 of the core component 12 is roughened before the core component 12 is placed inside the winding 10.

[0073] The roughening process may be performed by, for example, laser processing, cutting, blasting, or chemical conversion treatment. However, the above surface processing methods are merely exemplary. Therefore, methods other than those described above may be used to form the irregularities on the outer peripheral surface F12 of the core part 12 (the outer peripheral surface F2 of the core 2).

[0074] In the method for manufacturing the bushing of this embodiment, the roughening process is performed by laser processing. When laser processing is used, minute irregularities that can provide an anchoring effect for the molten resin material can be easily and inexpensively formed on the outer surface F12 of the core part 12 (the outer surface F2 of the core 2) compared to when using cutting processing, etc.

[0075] 1, the region where the roughening is performed, i.e., the region 12b where the irregularities are formed, is the entire region of the outer circumferential surface F12 of the core metal part 12 that is bonded to the resin tube 13. However, the region 12b only needs to be formed in at least a portion of the region that is bonded to the resin tube 13. In this embodiment, the region 12b is formed over the entire circumferential direction around the axis O1. However, the region 12b only needs to be formed intermittently in the circumferential direction around the axis O1 or locally in only one location.

[0076] In the bushing 1A, the elastic layer 5 is bonded to the outer peripheral surface F13 of the resin layer 3, but it may also be bonded to the outer peripheral surface F2 of the core metal 2.

[0077] FIG. 6 shows a schematic diagram of another example of a bushing that can be manufactured using the bushing manufacturing method of the present invention.

[0078] 6, reference numeral 1B denotes another example of a bushing that can be manufactured using the bushing manufacturing method. In bushing 1B, elastic layer 5 is an elastic layer that is bonded to the outer peripheral surface F2 of core 2. In this example, resin tube 13 constitutes only bulge-shaped portion 31.

[0079] As shown in FIG. 6 , in the bushing 1B, the resin layer 3 is bonded to a tapered surface F121 of the outer peripheral surface F12 of the core metal part 12 (the outer peripheral surface F2 of the core metal 2). The tapered surface F121 has the irregularities. In this example, the region 12b1 where the irregularities are formed coincides with the region where the tapered surface F121 is present. However, as described above, the region 12b1 only needs to be at least a portion of the tapered surface F121. Also, in the bushing 1B, the elastic layer 5 is bonded to a straight surface F122 of the outer peripheral surface F12 of the core metal part 12 (the outer peripheral surface F2 of the core metal 2). In this example, the region 12b2 where the irregularities are formed coincides with the bonding region of the straight surface F122 with the elastic layer 5. However, as described above, the region 12b2 only needs to be at least a portion of the bonding region with the elastic layer 5.

[0080] 7A and 7B are cross-sectional views for schematically explaining a method for manufacturing a bushing according to a second embodiment of the present invention. Here, the method for manufacturing a bushing 1B will be explained.

[0081] 7, in the method of manufacturing a bushing according to this embodiment, the core 2 is formed from two core parts 12 that are butted against each other on the same axis O1 to form a single core 2. In this embodiment, the outer peripheral surface F12 of the core part 12 is formed from a tapered surface F121 and a straight surface F122. Also in this embodiment, the inner peripheral surface F32 of the resin tube 13 is formed from two tapered surfaces F321.

[0082] The bushing manufacturing method of this embodiment includes essentially the same steps as the bushing manufacturing method of the first embodiment. That is, the bushing manufacturing method of this embodiment includes the resin tube preparing step, the core bar preparing step, the core bar heating step, and the joining step. In this embodiment, the core bar preparing step also includes the roughness processing step.

[0083] However, in the method for manufacturing a bushing according to this embodiment, the roughening process is a process of performing laser processing on the region of the outer peripheral surface F2 of the core 2 that bonds with the resin tube 13, as well as on the region of the outer peripheral surface F2 of the core 2 that bonds with the elastic layer 5. In this embodiment, the roughening process is a process of performing laser processing on the region of the outer peripheral surface F12 of the core part 12 that bonds with the resin tube 13, as well as on the region of the outer peripheral surface F12 of the core part 12 that bonds with the elastic layer 5.

[0084] FIG. 8 shows a schematic diagram of the core metal part 12 shown in FIG.

[0085] When the elastic layer 5 is bonded to the outer peripheral surface F12 of the core metal part 12 together with the resin layer 3, the roughening process involves laser processing of the region bonded to the resin tube 13 (the tapered surface F121 in this embodiment) and the region bonded to the elastic layer 5 (the straight surface F122 in this embodiment). Laser processing allows individual roughness adjustments by changing the laser output. Therefore, by using laser processing to roughen the outer peripheral surface F12 of the core metal part 12, the region bonded to the resin tube 13 can be the region 12b1 where the irregularities are formed, and the region bonded to the elastic layer 5 can be the region 12b2 where the irregularities are formed, as shown in FIG. 8 . Therefore, as in this embodiment, by performing laser processing on the area of ​​the outer surface F12 of the core metal part 12 that bonds with the resin tube 13, as well as the area of ​​the outer surface F12 of the core metal part 12 that bonds with the elastic layer 5, the roughness of the area that bonds with the resin tube 13 and the area that bonds with the elastic layer 5 can be simply and easily formed through a series of processes.

[0086] Therefore, as in this embodiment, by performing laser processing on the region of the outer peripheral surface F12 of the core metal part 12 that is bonded to the resin tube 13 and the region of the outer peripheral surface F12 of the core metal part 12 that is bonded to the elastic layer 5, it is possible to simply and easily form irregularities in the region that is bonded to the resin tube 13 and the region that is bonded to the elastic layer 5 by performing laser processing at once, i.e., by performing laser processing once. Note that in Figure 7, the core metal part 12 is shown in a state where it is placed inside the induction heating winding 10 after the roughening process.

[0087] Furthermore, the method for manufacturing the bushing of this embodiment further includes, after the joining step, an integration step of integrally joining the elastic layer 5 and the outer cylinder 6 to the outer periphery of the resin cylinder 13 .

[0088] FIG. 9 shows diagrammatically the inner member 4 shown in FIG. 6 after said bonding step.

[0089] In the integration process, the inner member 4 shown in FIG. 9 is used as a core bar 2 coated with a resin layer 3, and the inner member 4 and outer tube 6 are placed inside a mold as inserts. An elastic material is then injected into the mold, whereby the inner member 4, elastic layer 5, and outer tube 6 can be integrally molded as shown in FIG. 6.

[0090] As in the bushing manufacturing method of this embodiment, if the integration process is performed after the joining process, the bushing can be manufactured by separately joining the elastic layer 5 and the outer tube 6 together after the inner member 4 is manufactured.

[0091] As explained above, when the elastic layer 5 is bonded to the outer peripheral surface F13 of the resin layer 3, the roughening step can be a step of performing laser processing on the region of the outer peripheral surface F2 of the core 2 that is bonded to the resin layer 3, as well as the region of the outer peripheral surface F2 of the core 2 that is bonded to the elastic layer 5. In this case, the core 2 equipped with the resin layer 3 as the inner member 4 can be molded using the core 2 as an insert part.

[0092] Fig. 10 schematically shows another example of the inner member 4 of the bushing. Fig. 11 also schematically shows an example of a mandrel that can be used to insert-mold the inner member 4 shown in Fig. 10.

[0093] In the inner member 4 of FIG. 10 , the core 2 is a single core whose outer surface F2 has a straight shape parallel to the axis O1. Even when the resin layer 3 and the elastic layer 5 are firmly bonded to the outer surface F2 of the core 2, laser processing can be performed on the region bonded to the resin layer 3 and the region bonded to the elastic layer 5 as a roughening process to form irregularities on the outer surface F2 of the core 2. As shown in FIG. 11 , this allows the region bonded to the resin layer 3 to be the region 12b1 where the irregularities are formed, and the region bonded to the elastic layer 5 to be the region 12b2 where the irregularities are formed. As mentioned above, laser processing allows the roughness of the region bonded to the resin layer 3 and the region bonded to the elastic layer 5 to be simply and easily adjusted by changing the laser output.

[0094] Furthermore, when the core bar 2 of Fig. 10 is used, the inner member 4 of Fig. 11 can be manufactured by insert molding. After the roughening process, the core bar 2 shown in Fig. 11 is placed inside a mold as an insert, and a resin material is injected into the mold to integrally mold the core bar 2 covered with the resin layer 3, i.e., the inner member 4. In this case, the core bar 2 and the resin layer 3 can be bonded together separately after the roughening process of the core bar 2, thereby manufacturing the inner member 4.

[0095] Furthermore, in the case of the inner member 4 of Figure 10, the inner member 4 and the outer tube 6 can be placed inside a mold as insert parts, and the elastic layer 5 and the outer tube 6 can be molded integrally by injecting an elastic material into the mold.

[0096] The above merely discloses exemplary embodiments of the bushing manufacturing method according to the present invention, and various modifications are possible within the scope of the claims. For example, because all of the above-described bushings are fastened in the axial direction of the bushing, the butting ends 12a of the two core parts 12 can be fixed to each other simply by butting them together. However, the butting ends 12a of the two core parts 12 may also be glued together. Furthermore, while the resin layer 3 has been described as having a bulge-shaped portion, the shape of the resin layer 3 is not limited to a bulge-shaped portion. Furthermore, while the bushing obtained by the bushing manufacturing method according to the present invention has been described as a suspension bushing, the bushing is not limited to a suspension bushing as long as it is a bushing in which three-dimensional input is applied to at least one of the inner member 4 and the outer cylinder 6.

[0097] 1A: bushing, 1B: bushing, 1e: axial end of bushing, 2: core, 12: core part, 12a: butt end of core part, 3: resin layer, 13: resin tube, 13a: axial end of resin tube, 31: bulge-shaped portion of resin layer, 32: shaft portion of resin layer, 4: inner member, 5: elastic layer, 51: covering portion of elastic layer, 52: support portion of elastic layer, 6: outer tube, 7: annular joint portion, 8: annular non-joining portion, 11: lubricating fluid, 100: suspension arm, 101: fixed sleeve provided on suspension arm, A13: opening formed at axial end of resin tube, F2: outer peripheral surface of core, F12: outer peripheral surface of core part, F121: tapered surface of outer peripheral surface of core part, F122: straight surface of outer peripheral surface of core part F32: Inner peripheral surface of resin cylinder, F321: Tapered surface of inner peripheral surface of resin cylinder, O1: Axis (central axis of bushing), P1: Axial center of bushing

Claims

1. A method for manufacturing a bushing in which an inner member, the outer peripheral surface of which is covered with a resin layer, is placed inside an outer tube via an elastic layer, the method comprising: a resin tube preparation step of preparing a resin tube as the resin layer; a core tube preparation step of preparing the core tube; a core tube heating step of heating the core tube; and a joining step of inserting the core tube after the core tube heating step into the inside of the resin tube through an opening formed at the axial end of the resin tube prepared in the resin tube preparation step, thereby joining the core tube and the resin tube.

2. A method for manufacturing a bush as described in claim 1, wherein the core is formed by two core parts which are formed into one core by abutting them against each other on the same axis, the core preparation process is a process for preparing the two core parts, the core heating process is a process for heating each of the two core parts, and the joining process is a process for joining the two core parts and the resin tube by inserting each of the two core parts after the heating process into the interior of the resin tube through an opening formed at the axial end of the resin tube until the abutting ends of the two core parts abut against each other on the same axis.

3. A method for manufacturing a bushing as described in claim 2, wherein the outer peripheral surface of the core metal is the outer peripheral surface of the core metal part, and further, the outer peripheral surface of the core metal part includes a tapered surface that tapers radially inward toward the butting end of the core metal part.

4. A method for manufacturing a bushing as described in claim 1, wherein the core metal heating step is a step of heating the core metal by induction heating using a winding.

5. A method for manufacturing a bushing as described in claim 1, wherein the core bar prepared in the core bar heating process is a core bar having irregularities on at least a portion of the outer peripheral surface of the core bar that is covered by the resin layer.

6. A method for manufacturing a bushing as described in claim 5, wherein the core bar preparation process includes a roughness processing process for performing roughness processing on the outer peripheral surface of the core bar, and the unevenness is formed by the roughness processing process.

7. The method of manufacturing a bushing according to claim 6, wherein the roughening process is performed by laser processing.

8. A method for manufacturing a bushing as described in claim 6, wherein the elastic layer is an elastic layer bonded to the outer peripheral surface of the core bar, and the roughening process is a process of performing laser processing on the area of ​​the outer peripheral surface of the core bar that bonds with the resin tube, as well as the area of ​​the outer peripheral surface of the core bar that bonds with the elastic layer.

9. A method for manufacturing a bushing as described in claim 1, wherein the core metal preparation process is a process for preparing a resin tube in which the elastic layer and the outer tube are integrally bonded to the outer periphery of the resin tube.

10. A method for manufacturing a bushing as described in claim 1, further comprising, after said joining step, an integration step of integrally joining said elastic layer and said outer cylinder to the outer periphery of said resin cylinder.

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