Method for manufacturing bushing

Abstract

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 further, suppresses a generation of an excess resin layer that requires post-processing.SOLUTION: A method for manufacturing a bushing of the present invention for obtaining the bushing in which an inner member 4 having an outer peripheral surface F2 of a core grid 2 covered with a resin layer 3 is disposed inside an outer cylinder 6 via an elastic layer 5 includes: a resin tube preparation step for preparing a resin tube 13 made of resin as the resin layer 3; a core preparation step for preparing the core grid 2; a core heating step for heating the core grid 2; and a joining step in which the core grid 2 after the core heating step is inserted into the resin tube 13 through an opening A13 formed at an axial end 13a of the resin tube 13, thereby joining the core grid 2 and the resin tube 13.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a bushing. [Background technology]

[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 disposed 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 part (see, for example, Patent Document 1). According to 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-062999 A Summary of the Invention [Problem to be solved by the invention]

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

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

[0006] (1) The method for producing a bushing according to the present invention is a method for producing a bushing in which an inner member, the outer circumferential surface of which is covered with a resin layer, is disposed inside an outer tube via an elastic layer, and includes a resin tube preparation step of preparing a resin tube as the resin layer, a core preparation step of preparing the core, a core heating step of heating the core, and a joining step of inserting the core after the core 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 and the resin tube. According to the method for producing a bushing according to the present invention, strict dimensional accuracy is not required when providing a resin layer on the core, and further, the generation of an excess resin layer that requires post-processing is suppressed.

[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 against each other 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 inserting each of the two core parts after the heating step into the resin tube through an opening formed at an axial end of the resin tube until the butt ends of the two core parts butt against each other on the same axis, thereby joining the two core parts to the resin tube. In this case, a bushing with high dimensional accuracy can be manufactured.

[0008] (3) In the method for manufacturing a bushing described above in (2), 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 producing a bushing according to any one of (1) to (3) above, the core metal heating step is preferably a step of heating the core metal by induction heating using a winding. In this case, the entire outer circumferential surface of the core metal can be simply and easily heated.

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

[0011] (6) In the method for manufacturing a bush according to any one of the above (1) to (5), the core preparation step preferably includes a roughening step for 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, which makes it 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 and in a region bonded to the elastic layer. In this case, it is possible to simply and easily form unevenness in the region bonded to the resin tube and in the region bonded to the elastic layer.

[0014] (9) In the method for manufacturing a bushing according to any one of the above (1) to (8), 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 an outer periphery of the resin tube. In this case, the bushing may 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, a integrating step of integrally bonding the elastic layer and the outer tube to the outer periphery of the resin tube may be further included after the bonding step. In this case, the bushing can be manufactured by bonding the elastic layer and the outer tube together separately after the manufacture of the inner member. Effect of the Invention

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

[0017] [Figure 1] 1 is a cross-sectional view that illustrates an example of a bush that can be manufactured by using the bush manufacturing method of the present invention. [Diagram 2] 2 is a cross-sectional view showing an example of the operation of the bush shown in FIG. 1. [Diagram 3] 1A to 1C are cross-sectional views for roughly explaining a method for manufacturing a bush according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view that illustrates the core metal part illustrated in FIG. [Diagram 5] 10 is a cross-sectional view that illustrates a phenomenon that may occur when a core metal part having a straight outer shape is used. [Figure 6] 10 is a cross-sectional view that illustrates another example of a bush that can be manufactured by using the bush manufacturing method of the present invention. FIG. [Figure 7]5A to 5C are cross-sectional views for roughly explaining a method for manufacturing a bush according to a second embodiment of the present invention. [Figure 8] 8 is a cross-sectional view that illustrates the core metal part illustrated in FIG. 7. [Figure 9] FIG. 7 is a cross-sectional view that shows a schematic view of the inner member shown in FIG. [Figure 10] FIG. 11 is a cross-sectional view showing another example of the inner member of the bushing. [Figure 11] 11 is a cross-sectional view that illustrates an example of a core bar that can be used to insert-molde the inner member illustrated in FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a method for manufacturing a bush 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 bush that can be manufactured using the bush 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 schematic cross section including a 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." In addition, in the present disclosure, the direction perpendicular to the axis O1 is also referred to as the "axial direction" or the "radial direction." In particular, in the radial direction, the side closer to the axis O1 is also referred to as the "radial inner side," and the side farther from the axis O1 is also referred to as the "radial outer side." In addition, in the present disclosure, the direction extending circumferentially around the axis O1 is also simply referred to as the "circumferential direction."

[0022] 1, in the bushing, an inner member 4 having an outer peripheral surface F2 of a core bar 2 covered with a resin layer 3 is disposed inside an outer tube 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 tube 6 disposed on the outer peripheral side of the elastic layer 5.

[0023] 1, the bushing 1A includes a resin layer 3 bonded to an outer peripheral surface F2 of a core 2, an elastic layer 5 bonded to an outer peripheral surface F3 of the resin layer 3, and an outer cylinder 6 bonded to an 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 so 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 forming 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 metal 2 as described later. The resin forming the resin tube 13 is preferably a resin having a melting temperature of a predetermined temperature (for example, 120°C to 176°C) and having, for example, high abrasion resistance and chemical resistance. For example, polyamide (including glass fiber reinforcement) can be used as the resin forming the resin tube 13.

[0026] In the bush 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 part of the outer circumferential surface of the resin layer 3 is locally bulged into a spherical shape. As shown in FIG. 1, in the bush 1A, the bulge-shaped portion 31 is disposed at a position centered on the axial center P1 of the bush 1A in the axial direction. However, the bulge-shaped portion 31 can be disposed so as to be biased toward one of the two axial ends 1e of the bush 1A from the axial center P1 of the bush 1A. Here, the axial center P1 of the bush 1A is assumed to coincide with the axial center of the inner member 4 (core metal 2).

[0027] The elastic layer 5 has a tubular shape formed of 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 the elastic material forming the elastic layer 5 include rubber.

[0028] In the bush 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 bush 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 in a circular manner in the circumferential direction around the axis O1. The two support portions 52 are also annular support portions that extend in a circular manner in the circumferential direction around the axis O1. Furthermore, in the bush 1A, an annular joint portion 7 that joins the support portion 52 and the shaft portion 32 is formed between the support portion 52 of the elastic layer 5 and the shaft portion 32 of the resin layer 3. The annular joint portion 7 extends in a circular manner 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 bush 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 the other of the vibration generating side and 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 bush 1A, the region of 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 forming 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 bush 1A in a schematic manner equivalent to the cross section of Figure 1. In the following explanation, the bush 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 the inside of a fixing sleeve 101 provided on the suspension arm 100. On the other hand, 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, while the bush 1A fixes the outer tube 6 to the fixing sleeve 101 provided on the vehicle body, it can also fix 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 of the inner member 4 against the outer cylinder 6. Fig. 2 exemplarily shows a state in which the inner member 4 prys against the inside of the outer cylinder 6 via the elastic layer 5.

[0034] When the bush 1A is used in a suspension device, for example, twisting or twisting may occur inside the bush 1A due to a three-dimensional input from the inner member 4. Here, "twisting" refers to a relative movement (relative rotation) between the inner member 4 and the outer tube 6 in the circumferential direction around the axis O1 at an angle θ1. Also, "twisting" refers to a relative movement (relative rotation) around the axis O1 in the circumferential direction at an angle θ1 in a state in which at least one of the inner member 4 and the outer tube 6 is inclined at an angle α1 with respect to the axis O1, as shown in FIG. 2. However, in the present disclosure, "twisting" includes a movement inclined with respect to the axis O1, in which at least one of the inner member 4 and the outer tube 6 does not move (relatively rotate) in the circumferential direction around the axis O1, as shown in FIG. 2.

[0035] 2, when an input is applied that causes twisting of the bushing 1A, the elastic layer 5 and the inner member 4 are relatively displaced so as to peel off from each other in the region of the non-jointed portion 8. This allows the bushing 1A to absorb twisting of the inner member 4 against the outer cylinder 6 while maintaining vibration-proofing performance. In the bushing 1A, the lubricating fluid 11 is filled inside the annular joined portion 8, so that twisting of the inner member 4 against the outer cylinder 6 can be absorbed more smoothly. However, the lubricating fluid 11 may 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 the insert (core metal) and the mold to prevent the resin material from leaking from the mating surface of the mold. In addition, if the resin material leaks from the mating surface of the mold, post-processing such as removing the excess resin layer generated in the molded product is required.

[0038] 3 is a schematic diagram showing a method for producing a bushing according to a first embodiment of the present invention, which does not require the use of a die in producing the inner member 4. The method for producing a bushing according to the present embodiment includes the following steps to obtain a bushing 1A.

[0039] The manufacturing method of the bushing in this embodiment includes a resin tube preparation step of preparing a resin tube 13 as the resin layer 3, a core bar preparation step of preparing a core bar 2, a core bar heating step of heating the core bar 2, and a bonding step of bonding the core bar 2 to the resin tube 13 by inserting the core bar 2 after the core bar heating step 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 step.

[0040] In the resin tube preparation step, the resin tube 13 is prepared. As shown in Fig. 3, in this embodiment, the 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 surfaces that taper 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 surface F121 of the core metal part 12 described later.

[0041] In the core bar preparation step, a core bar 2 is prepared. In the bushing manufacturing method of this embodiment, in the core bar preparation step, two core bar parts 12 are prepared. 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 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, the cross section including the axis O1.

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

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

[0045] However, the shapes of the two core metal parts 12 can be made different. For example, the axial length of one of the two core metal parts 12 can be made 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 made 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 bush 1A to one of the two axial ends 1e of the bush 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] Referring to FIG. 3, the two core metal parts 12 can be heated by various heating methods. In this embodiment, the two core metal parts 12 are heated by induction heating using the winding 10, which will be described later. The heating temperature of the core metal part 12 is set to a temperature that melts the resin tube 13 or higher. The heating temperature of the core metal part 12 is controlled to a temperature that does not deform the resin tube 13, for example, a temperature that does not deform the shaft part 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 2 and the resin tube 13 are joined by inserting the core metal parts 12 into the resin tube 13 from an opening A13 formed at an axial end 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 from an opening A13 formed at an 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, thereby joining the two core metal parts 12 and the resin tube 13. As a result, the two core metal parts 12 are integrated with the resin tube 13 by cooling the core metal parts 12.

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

[0050] Therefore, according to the method for manufacturing the bushing of this embodiment, strict dimensional accuracy is not required when providing the resin layer 3 on the core bar 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 bar 2 is only a single core bar, and the single core bar 2 can be joined to the resin tube 13 by inserting the single core bar 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 from the opening A13 formed in the axial end 13a of the resin tube 13 until the butt 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 collapse. 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 manufacturing method of the bushing of 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 arranging the resin tube 13 and the outer tube 6 inside a mold as insert parts and injecting an elastic material into the mold.

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

[0056] According to the method for producing a bushing 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 manufacturing method of a bush according to this embodiment.

[0058] According to the manufacturing method of the bushing of the present invention, the resin tube 13 melts due to 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 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 butt 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 butt 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 becomes 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 butt completely, 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 considering the bushing 1A as a whole, 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 (permanent deformation) between the butt ends 12a of the two core metal parts 12 over time.

[0062] In contrast, in the manufacturing method of the bush 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 by a tapered surface F121 tapered radially inward toward the butt end 12a of the core metal part 12, for example, referring to FIG. 3. In this case, the melted portion 13p of the resin tube 13 melted by the heat generated from the core metal part 12 can escape along the tapered surface F121 of the core metal part 12 to the side opposite to the pushing side of the core metal part 12. This suppresses the occurrence of the phenomenon in which the melted portion 13p of the resin tube 13 gets stuck between the butt ends 12a of the two core metal parts 12. Therefore, if the tip end on the butt end 12a side of the outer peripheral surface F12 of the core metal part 12 is formed as the tapered surface F121, a bush 1A with high durability can be manufactured.

[0063] In the method for producing a bush according to the present invention, the method for heating the core part 12 (core 2) is not particularly limited. The core part 12 (core 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 producing a bush according to the present embodiment, the core metal heating step is a step of heating a core metal part 12 by induction heating using a winding 10.

[0065] In this embodiment, the core metal 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 manufacturing method of the bushing of this embodiment, the core metal part 12 generates heat due to the electrical resistance of the core metal part 12 when electricity is passed through the winding 10. As a result, the core metal part 12 is heated according to the time that electricity is passed through the winding 10 while placed inside the winding 10. Therefore, if induction heating is used to heat the core metal part 12, the entire outer circumferential surface F12 of the core metal part 12 can be heated simply and easily.

[0066] Particularly, 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 manner, 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 an axial end 13a of the resin tube 13, as shown by the arrow in FIG. 3. In this case, for example, the heated core metal part 12 can be automatically pushed into the resin tube 13 by using an automatic machine. Therefore, by heating the core metal part 12 by induction heating, the work efficiency during the manufacture of the bush 1A can be improved.

[0067] In the manufacturing method of the bush in this embodiment, at least a part 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 reference numeral 12b. In this embodiment, the irregularities are formed on the tapered surface F121.

[0069] If at least a part of the outer circumferential surface F12 of the core metal part 12 that is covered by the resin layer 3 has irregularities, the resin tube 13 melted by the heat of the core metal part 12 will bite into the irregularities provided on the outer circumferential surface F12 of the core metal part 12 (by a so-called anchor effect) and will be firmly bonded to the outer circumferential surface F12 of the core metal part 12. Therefore, if irregularities are formed on at least a part of the region of the outer circumferential 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 circumferential 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 produce a so-called anchor effect after the molten resin material hardens by penetrating into the gaps between the irregularities. For this reason, for example, when the core metal part 12 is formed by casting, the core metal part 12 may be used as it 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 unevenness is formed by the roughening process.

[0072] When the outer peripheral surface F2 of the core 2 is a smooth surface, it is considered that the anchor effect is difficult to obtain. 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 manufacturing method of the bush 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. If the outer peripheral surface F2 of the core 2 is roughened 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 part 12 is roughened before the core part 12 is placed inside the winding 10.

[0073] The roughening process may be, for example, laser processing, cutting, blasting, or chemical conversion treatment. However, the above surface processing is 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 bush of this embodiment, the roughening process is performed by laser processing. When laser processing is used, it is possible to easily and inexpensively provide minute irregularities on the outer peripheral surface F12 of the core part 12 (the outer peripheral surface F2 of the core 2) that are sufficient to provide an anchor effect for the molten resin material, compared to when cutting processing or the like is used.

[0075] 1, the region where the roughening is performed, i.e., the region 12b where the unevenness is 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, it is sufficient that the region 12b is formed in at least a part of the region that is bonded to the resin tube 13. Also, in this embodiment, the region 12b is formed over the entire circumferential direction around the axis O1. However, it is sufficient that the region 12b is formed discontinuously in the circumferential direction around the axis O1 or locally in only one place.

[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 bar 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 a bushing as another example that can be manufactured by using the bushing manufacturing method. In the bushing 1B, the elastic layer 5 is an elastic layer that is bonded to the outer circumferential surface F2 of the core bar 2. In this example, the resin tube 13 constitutes only the bulge-shaped portion 31.

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

[0080] 7 is a cross-sectional view for explaining a schematic method for producing a bushing according to a second embodiment of the present invention, which will be explained here as a method for producing a bushing 1B.

[0081] 7, in the manufacturing method of the bushing of this embodiment, the core bar 2 is also formed by two core bar parts 12 that are butted against each other on the same axis O1 to form one core bar 2. In this embodiment, the outer peripheral surface F12 of the core bar part 12 is formed by 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 by two tapered surfaces F321.

[0082] The bushing manufacturing method of this embodiment basically includes 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 includes the roughness processing step.

[0083] However, in the bushing manufacturing method of this embodiment, the roughness processing step is a step of performing laser processing on the region of the outer peripheral surface F2 of the core bar 2 that bonds with the resin tube 13 as well as the region of the outer peripheral surface F2 of the core bar 2 that bonds with the elastic layer 5. In this embodiment, the roughness processing step is a step of performing laser processing on the region of the outer peripheral surface F12 of the core bar part 12 that bonds with the resin tube 13 as well as the region of the outer peripheral surface F12 of the core bar 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 performs laser processing on the region bonded to the resin tube 13 (the tapered surface F121 in this embodiment) as well as the region bonded to the elastic layer 5 (the straight surface F122 in this embodiment). With laser processing, the individual roughnesses can be adjusted by changing the laser output. Therefore, if laser processing is used for roughening the outer peripheral surface F12 of the core metal part 12, as shown in FIG. 8, the region bonded to the resin tube 13 can be the region 12b1 where the unevenness is formed, and further, the region bonded to the elastic layer 5 can be the region 12b2 where the unevenness is formed. 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 to the resin tube 13, as well as the area of ​​the outer surface F12 of the core metal part 12 that bonds to the elastic layer 5, the roughness of the area that bonds to the resin tube 13 and the area that bonds to the elastic layer 5 can be formed simply and easily 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 bonds with the resin tube 13 as well as the region of the outer peripheral surface F12 of the core metal part 12 that bonds with the elastic layer 5, it is possible to simply and easily form unevenness in the region that bonds with the resin tube 13 as well as the region that bonds with the elastic layer 5 by performing laser processing at once, i.e., by performing laser processing once. Note that in Fig. 7, the core metal part 12 is shown in a state where it is placed inside the winding 10 for induction heating after the roughness processing step.

[0087] Moreover, the method of manufacturing the bushing in 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 side 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 disposed as a core bar 2 covered with a resin layer 3, and the inner member 4 and outer tube 6 are disposed 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 manufacturing method of the bushing in this embodiment, if the integration process is carried out 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] Incidentally, as explained above, when the elastic layer 5 is bonded to the outer peripheral surface F13 of the resin layer 3, the roughening process can be a process 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 with the core 2 as an insert product.

[0092] Fig. 10 shows a schematic diagram of yet another example of the inner member 4 of the bush. Fig. 11 shows a schematic diagram of an example of a core bar that can be used for insert molding 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 peripheral surface F2 has a straight shape parallel to the axis O1. When the elastic layer 5 is firmly bonded to the outer peripheral surface F2 of the core 2 together with the resin layer 3, the region bonded to the elastic layer 5 can be laser processed as a roughening process for forming irregularities on the outer peripheral surface F2 of the core 2. As a result, as shown in FIG. 11, the region bonded to the resin layer 3 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 described above. According to the laser processing, the roughness of the region bonded to the resin layer 3 and the region bonded to the elastic layer 5 can be simply and easily adjusted by changing the laser output.

[0094] Furthermore, when the core bar 2 in Fig. 10 is used, the inner member 4 in 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 integrally bonded to manufacture the inner member 4 separately after the roughening process of the core bar 2.

[0095] Furthermore, in the case of the inner member 4 in Figure 10, the inner member 4 and the outer tube 6 are 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 inside of the mold.

[0096] The above merely discloses an exemplary embodiment of the manufacturing method of the bush according to the present invention, and various modifications are possible within the scope of the claims. For example, since all of the above-mentioned bushes are fastened in the axial direction of the bush, the butt ends 12a of the two core metal parts 12 can be fixed to each other only by butting them together. However, the butt ends 12a of the two core metal parts 12 may be bonded together. In addition, the resin layer 3 has been described as a resin layer having a bulge-shaped portion, but the shape of the resin layer 3 is not limited to one having a bulge shape. In addition, the bush obtained by the manufacturing method of the bush according to the present invention has been described as a bush for a suspension device, but the bush is not limited to a bush for a suspension device as long as it is a bush in which a three-dimensional input is applied to at least one of the inner member 4 and the outer cylinder 6. [Explanation of symbols]

[0097] 1A: bush, 1B: bush, 1e: axial end of bush, 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 surface of the resin cylinder, F321: Tapered surface of the inner surface of the resin cylinder, O1: Axis (center axis of the bush), P1: Axial center of the bush

Claims

1. A method for manufacturing a bushing, for obtaining a bushing in which an inner member having an outer circumferential surface of a core bar covered with a resin layer is disposed inside an outer cylinder via an elastic layer, comprising the steps of: a resin tube preparation step of preparing a resin tube made of resin as the resin layer; a core bar preparation step of preparing the core bar; a core bar heating step of heating the core bar; a joining process for joining the core wire and the resin tube by inserting the core wire after the core wire heating process 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 process.

2. The core is formed by two core parts which are butted against each other on the same axis to form one core, the core metal preparation step is a step of preparing the two core metal parts, the core metal heating step is a step of heating each of the two core metal components, A method for manufacturing a bushing as described in claim 1, wherein the joining process is a process of joining the two core metal parts and the resin tube by inserting each of the two core metal parts after the heating process into the inside of the resin tube through an opening formed at the axial end of the resin tube until the butt ends of the two core metal parts butt 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. 2. The method for manufacturing a bushing according to claim 1, wherein the core metal heating step is a step of heating the core metal by induction heating using a winding.

5. 2. 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. 6. The method for manufacturing a bushing according to claim 5, wherein the core metal preparation step includes a roughening step of roughening an outer peripheral surface of the core metal, and the irregularities are formed by the roughening step.

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

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

9. 2. The method for manufacturing a bushing as described in claim 1, wherein the core metal preparation step is a step of 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. The method for manufacturing a bushing according to claim 1 , further comprising, after the joining step, an integration step of integrally joining the elastic layer and the outer cylinder to an outer periphery of the resin cylinder.

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