Joint structure and method for manufacturing same

Abstract

To provide a joint structure that can prevent or suppress peeling at a joint interface between a metal body and a resin body due to a difference in linear expansion between them.SOLUTION: A joint structure 1 is formed by joining a metal body 10 and a resin body 20 at mutually opposing joining surfaces 11, 21. The metal body 10 has a slit 30 formed in the joining surface 11 along a direction intersecting with its own longitudinal direction W, and the slit 30 is pressed in its own groove width direction to reduce its width before joining with the resin body 20, and the resin body 20 is joined to the joining surface 11 of the metal body 10 in the longitudinal direction W at a position covering the slit 30.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a joint structure in which a metal body and a resin body are joined at mutually opposing joining surfaces, and a method for manufacturing the same. [Background technology]

[0002] As an example of this type of joint structure, an automobile part is being considered in which a reinforcing member (rib) made of carbon fiber reinforced thermoplastic resin (CFRTP) as a resin body is press-formed onto a metal body (metal sheet). Automobile parts with such joint structures are manufactured by integrally forming heated thermoplastic resin and a metal sheet in a mold.

[0003] Conventionally, when joining dissimilar materials such as a resin body as an adherend to a metal body as in this type of joined structure, the linear expansion coefficients of the two bodies are different, and if the difference in linear expansion cannot be absorbed, peeling or cracking may occur at the opposing joint interface. Therefore, for example, the technology described in Patent Document 1 provides a slit structure that absorbs the thermal expansion difference when brazing blades, and the technology described in Patent Document 2 provides a slit structure to suppress deformation of the heat sink due to the thermal expansion difference. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-152628 A [Patent Document 2] WO2013 / 018329 A1 Summary of the Invention [Problem to be solved by the invention]

[0005] The conventional slit structures disclosed in Patent Documents 1 and 2 are based on the premise that the adherend will not get into the slits. However, when molten resin is directly injected onto a metal surface as the adherend, as in outsert molding, simply forming a slit causes the molten resin to get into the slit, which is problematic in that it is not possible to absorb the linear expansion difference. Therefore, the present invention has been made with attention to such problems, and its objective is to provide a joined structure that can prevent or suppress peeling at the joint interface due to the difference in linear expansion between the metal body and the resin body. [Means for solving the problem]

[0006] In order to solve the above problems, a joined structure according to one embodiment of the present invention is a joined structure in which a metal body and a resin body are joined at opposing joining surfaces, wherein the metal body has a slit formed on the joining surface along a direction intersecting the longitudinal direction of the metal body, the slit being narrowed by pressing in the groove width direction of the metal body prior to joining with the resin body, and the resin body is joined in a position covering the slit along the longitudinal direction of the joining surface of the metal body.

[0007] In addition, in order to solve the above-mentioned problems, a manufacturing method for a joined structure according to one embodiment of the present invention is a method for manufacturing a joined structure in which a metal body and a resin body are joined at their opposing joining surfaces, and includes a slit formation process for forming a slit along a direction intersecting the longitudinal direction on the joining surface of the metal body that is joined to the resin body along the longitudinal direction of the joining surface, a groove width reduction process for pressing the slit formed in the slit formation process in the groove width direction to reduce its width, and a resin joining process for joining a resin base material of the resin body along the longitudinal direction of the joining surface after the groove width reduction process. Effect of the Invention

[0008] According to the present invention, it is possible to prevent or suppress peeling at the bonding interface caused by the difference in linear expansion between the metal body and the resin body. [Brief description of the drawings]

[0009] [Figure 1] 1A and 1B are explanatory diagrams of a bumper reinforcement which is one embodiment that employs a joint structure according to the present invention, in which FIG. 1A is a perspective view of a resin body before it is joined, and FIG. 1B is a perspective view of a resin body after it has been joined. [Diagram 2] 1A and 1B are explanatory diagrams of slits on the joining surface of a joined structure according to the present invention, in which (a) is a plan view of the resin body before joining and before it is shrunk in width by pressing, (b) is a plan view of the resin body before joining and after it is shrunk in width by pressing, (c) is a plan view of the resin body after joining and after it has been expanded and deformed in width due to a linear expansion difference, (d) is an enlarged view of the slit in (b), and (e) is an enlarged view of the slit in (c). [Diagram 3] 2A to 2D are explanatory views of a manufacturing method of the bumper reinforcement shown in FIG. [Figure 4] 4A to 4D are schematic diagrams illustrating the process of joining a metal body and a resin body in the manufacturing method shown in FIG. 3, and each diagram is a schematic cross-sectional view taken along the X direction (longitudinal direction) in FIG. 1. [Diagram 5] 5A to 5C are schematic diagrams showing, by means of white arrows, how a narrowed slit is deformed and widened due to a linear expansion difference in the joining process shown in FIG. 4. [Figure 6] 5A to 5C are schematic diagrams showing, for comparison, an image in which no slit is provided in the joining process shown in FIG. 4 and which are indicated by white arrows to illustrate the inability to follow the linear expansion difference. [Figure 7] 5A to 5C are schematic diagrams showing, by way of comparison, an image in which a slit that has not been narrowed cannot follow the linear expansion difference in the joining process shown in FIG. 4, with white arrows indicating the result. [Figure 8] 13A to 13E are schematic diagrams showing an embodiment in which, in addition to a plurality of slits (grooves for absorbing linear expansion), grooves for joining dissimilar materials are further provided between adjacent slits as uneven regions. [Figure 9] 1A and 1B are schematic diagrams showing an embodiment in which a plurality of slits are provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic. Therefore, it should be noted that the relationship and ratio between thickness and planar dimensions are different from the actual ones, and the drawings include parts where the relationship and ratio of dimensions are different from each other. Furthermore, the embodiments described below are merely examples of devices and methods for embodying the technical ideas of the present invention, and the technical ideas of the present invention do not limit the materials, shapes, structures, arrangements, etc. of the components to the embodiments described below.

[0011] [Bumper reinforcement] First, a bumper reinforcement that is an embodiment that employs a joint structure according to the present invention will be described. As shown in FIG. 1, the bumper reinforcement 1 of this embodiment includes a bumper beam 10 which is a metal body extending in the vehicle width direction W, and a reinforcing portion 20 which is a resin body joined to a peripheral wall back surface 12 of the bumper beam 10.

[0012] The bumper beam 10 is a long member made of an aluminum alloy, and has mounting portions 18, 19 for mounting to the vehicle body near both ends in the longitudinal direction (vehicle width direction) W. Two bent portions 16, 17 are formed on the inner side in the vehicle width direction from the two mounting portions 18, 19. In this embodiment, crash boxes 14, 15 are attached to the mounting portions 18, 19, and the bumper beam 10 is attached to the vehicle body via the crash boxes 14, 15.

[0013] The reinforcing part 20 is a resin reinforcing member attached to the peripheral wall back surface 12 of the bumper beam 10 along the longitudinal direction. As shown in FIG. 1B, the reinforcing part 20 is joined to a joining surface 11 provided in a predetermined range of the peripheral wall back surface 12 of the bumper beam 10 by injection molding along the longitudinal direction W of the bumper beam 10. The reinforcing part 20 of this embodiment is made of fiber reinforced thermoplastic resin (CFRTP). In particular, the fibers of the fiber reinforced resin of this embodiment are discontinuous short fibers, and the fibers of the fiber reinforced resin are carbon fibers.

[0014] Here, in the metal body 10 of this embodiment, as shown in Figure 1 (a), multiple slits 30 are formed by laser processing on the joining surface 11 of the rear wall 12 of the peripheral wall of the bumper beam 10 along a direction intersecting the longitudinal direction W of the bumper beam 10 as grooves for absorbing linear expansion. In this embodiment, a plurality of slits 30 are formed in positions where the two bent portions 16, 17 are formed, along a direction intersecting the longitudinal direction W. In particular, the plurality of slits 30 in this embodiment are arranged such that the formation positions of the groove portions aligned in the longitudinal direction W are alternately shifted in the orthogonal direction. The slits 30 as linear expansion absorbing grooves may be formed penetrating the metal body 10 in the plate thickness direction.

[0015] 2(a), the slit 30 is formed by laser processing at a position where the two bent portions 16, 17 are to be formed before bonding with the resin body 20. In the bonding surface 11 of this embodiment, the slit 30 crosses the range to be bonded with the resin body 20 in a direction intersecting the longitudinal direction W (Z direction in FIG. 1(a)), as shown in the figure.

[0016] 2(a), in the joint surface 11 of this embodiment, a plurality of slits 30 as linear expansion absorbing grooves are formed at intervals in the longitudinal direction W shown in Fig. 1(a). In this embodiment, the extension direction of the slits 30 is perpendicular to the longitudinal direction W. Furthermore, in this embodiment, the formation positions of the multiple slits 30 aligned in the longitudinal direction W are shifted back and forth in the perpendicular direction (Z direction) at every other point in the longitudinal direction W. Note that it is preferable that the formation intervals of the multiple slits 30 are narrower closer to the joint end with the resin body 20 than at positions away from the joint end.

[0017] After being formed by laser processing, the multiple slits 30 are pressed in the groove width direction and reduced in width in a bending process for the metal body 10 to form the two bent portions 16 and 17, as shown in FIG. As a result, as shown in Fig. 1D, each slit 30 is deformed to have a narrow width such that a pair of inner surfaces facing each other in the groove width direction have narrowed width portions 31 in which the groove width narrows from both longitudinal ends 32 of the slit 30 toward the groove center. In the slit 30 of this embodiment, the groove width gradually narrows from both longitudinal ends of the slit 30 toward the groove center.

[0018] Then, in a joining process by injection molding of a resin base material, the resin body 20 is joined to a position covering the slits 30 along the longitudinal direction W of the joining surface 11 of the metal body 10, as shown in Fig. 1(b). At that time, the multiple slits 30 absorb deformation due to a difference in linear expansion when returning to room temperature after joining by injection molding, as described later, by the widening deformation of each slit 30 shown in Figs. 2(c) and (e), and stress absorption performance is exhibited at the joining surface.

[0019] [Manufacturing method for bumper reinforcement] Next, a manufacturing method for the bumper reinforcement 1 of the above embodiment will be described. The manufacturing process for the bumper reinforcement 1 in FIG. 1 begins with creating a hollow beam material along the extension direction as the metal body 10 by extruding an aluminum alloy material, and then machining the mounting portions 18, 19 for the crash boxes 14, 15 near both ends of this beam material.

[0020] Next, as shown in FIG. 3( a ), the plurality of slits 30 are formed in the metal body 10 at the joint surface 11 connected to each of the joint surfaces 21 of the two reinforcing parts 20 in the portions that will become the two bent parts 16 , 17 .

[0021] That is, in this embodiment, in order to prevent or suppress peeling at the joint interface due to the difference in linear expansion between each joint surface 21 of the two reinforcing parts 20 and the joint surface 11 of the metal body 10, fine groove shapes that become the above-mentioned slits 30 are formed by laser processing into a predetermined structural pattern shown in Figure 2(a) on the joint surface 11 of the back wall 12 of the beam material, which will become the above-mentioned two bent parts 16, 17 (slit formation process). In this case, in the slit forming step, as a predetermined configuration pattern, in addition to the above-mentioned multiple slits 30 as grooves for absorbing linear expansion, laser processing can be performed so that grooves 40 for joining dissimilar materials are formed alternately as uneven regions between adjacent slits 30 in the longitudinal direction W, as shown in the cross-sectional view of Fig. 8. The relationship between the slits 30 and the grooves 40 for joining dissimilar materials will be described later.

[0022] Next, the beam material is bent at predetermined positions to form the two bent portions 16 and 17. At this time, the multiple slits 30 formed in the slit forming process are bent and simultaneously pressed in the groove width direction by the bending process to reduce their width (groove width reduction process). Next, after undergoing bending processing and the associated groove width reduction process, as shown in Figures 3(b) to (c), each joint surface 21 of the two reinforcing parts 20 is joined to the part that will become the joint surface 11 of the bumper beam 10 along the longitudinal direction of the joint surface 11 (resin joining process). At this time, the peripheral wall back surface 12 of the bumper beam 10 is inserted and fixed in a housing portion of one of the first molds 71 ​​of the mold set 70 with the peripheral wall back surface 12 facing the second mold 72. Thereafter, the second mold 72 opposing the first mold 71 is clamped relatively from the peripheral wall back surface 12 side of the bumper beam 10. As a result, the mold set 70 is assembled so as to surround the bumper reinforcement 1, which is a joint structure that will become a molded product.

[0023] 3(c), molten resin (for example, discontinuous fiber CFRTP) heated by an injection molding machine (not shown) is used as the resin base material of the resin body 20, and is forced into the resin injection space of the mold set 70 by applying injection pressure from a molten resin supply passage (not shown), and the reinforcing part 20 is joined by injection molding. The molten resin supply passage (spool, runner, gate, etc.) and gas vent part can be arranged in appropriate positions.

[0024] After filling the resin into the resin injection space and cooling for a certain period of time, the bumper reinforcement (jointed structure) 1, in which the bumper beam (metal body) 10 and the reinforcing portion (resin body) 20 are integrated, is demolded and taken out from the mold set 70, as shown in FIG. 3(d). As a result, the bumper beam 10 is reinforced as desired by the reinforcing portion 20. Thereafter, the crash boxes 14, 15 are respectively attached to the mounting portions 18, 19 at both ends of the rear peripheral wall surface 12 of the bumper beam 10, and the bumper reinforcement 1 is completed.

[0025] The resin material to be bonded (covered) as the reinforcing part (resin body) 20 in the bonding process can be, for example, PA6 + 40 wt% carbon long fiber. Other materials may include thermoplastic resins such as various polyamides (PA66, MXD6, etc.), PPS, ABS, PP, PC, PBT, etc., carbon short fiber, glass fiber, and cellulose-based natural fiber. In addition, the bonding (covering) conditions by injection molding of the reinforcing part (resin body) 20 in the bonding process can be, for example, injection pressure: 117 MPa, mold temperature: 140°C, and injection screw temperature (resin temperature): 280°C.

[0026] In the above embodiment, an example in which the slits 30 are provided as the grooves for absorbing linear expansion has been described, but in addition to this, as shown in Fig. 8, a concave-convex region formed by a plurality of grooves 40 for joining dissimilar materials can be provided. Hereinafter, the relationship between the grooves 40 for joining dissimilar materials and the grooves 30 for absorbing linear expansion when two types of grooves are provided will be described. Hereinafter, the grooves for absorbing linear expansion will be referred to as first grooves 30, and the grooves for joining dissimilar materials will be referred to as second grooves 40.

[0027] In Fig. 8, the number of slits 30 formed as linear expansion absorbing grooves, i.e., the first grooves 30, formed in the bending range E corresponding to each of the bent portions 16 and 17 is preferably, for example, about four rows. The arrangement interval P1 between adjacent first grooves 30 is preferably 20 mm or more. If the arrangement interval P1 of the first grooves 30 is less than 20 mm, the width of the second groove 40 itself, which is necessary and sufficient for absorbing linear expansion, becomes 40 µm or less, making processing difficult (even if the interval between the first grooves 30 is wider than this, the linear expansion absorbing effect is generated, but the interval is greater than necessary for absorbing linear expansion, and in that case, it is more reasonable to increase the interval between the grooves in consideration of the processing effort). Also, it is preferable to aim for the groove width W of the first groove 30 to be about 0.27 mm. The depth of the first groove 30 is preferably 0.2 mm or more and 2 mm or less. Even if the depth of the first groove 30 is dug by laser processing to more than half the plate thickness of the metal body 10 (for example, 4 mm), it can be said that there is little effect in making the groove easier to crush. Also, if the depth of the first groove 30 is dug shallower than 0.2 mm, it becomes difficult to crush the first groove 30 by bending the metal body 10 (7.5° in the example of this embodiment).

[0028] In contrast, the arrangement interval P2 of the second grooves 40 is preferably 100 μm or more and 400 μm or less. By forming the second grooves 40 in this range, the metal body 10 functions as a groove for joining dissimilar materials, and the joining strength can be improved by burr-like protrusions generated on both sides of the second grooves 40 when the metal body 10 is removed by laser processing. Also, if the interval between the second grooves 40 is too narrow, the burr-like protrusions of adjacent second grooves 40 overlap, reducing the joining effect. Furthermore, the depth of the second groove 40 is preferably 50 μm or more and 250 μm or less. If the depth of the second groove 40 is less than 50 μm, burr-like protrusions sufficient for producing a joining effect cannot be formed. Also, if the depth exceeds 250 μm, the laser processing process takes too much time.

[0029] [Effects] Next, the effects of the joint structure 1 and the manufacturing method thereof according to this embodiment will be described. Here, in the joint structure 1 of the present embodiment, when the fibers of the CFRTP resin body 20 are oriented along the longitudinal direction W, the linear expansion coefficient becomes smaller than that of the metal body 10 made of an aluminum alloy. That is, when the temperature drops from the high temperature during molding to room temperature, the amount of thermal contraction of the aluminum alloy metal body 100 becomes relatively larger than the amount of thermal contraction of the CFRTP resin body 200 at the mutual joint surface 101, as shown in the comparative example of Fig. 6. Therefore, the CFRTP resin body 200 appears to expand relatively to the aluminum alloy metal body 100. As a result, peeling occurs at the joint interface 102 due to the difference in linear expansion between the metal body 100 and the resin body 200.

[0030] However, even if a slit 130 is simply provided on the joining surface 111 of an aluminum alloy metal body 110 as in the comparative example shown in Figure 7, in direct injection molding of the resin matrix of CFRTP, the molten resin will enter the simple slit 130 during molding, and the metal body 110 will simply be pushed apart, and the effect of preventing or suppressing peeling at the joining interface 112 cannot be obtained with a simple slit 130. When the resin body 200 and the metal body 110 of the CFRTP are joined by direct injection molding of the resin matrix, due to the difference in linear expansion between them, thermal contraction during cooling will generate stress at the joining interface 112, and peeling will occur at the joining interface 112.

[0031] In contrast, according to the joined structure 1 of this embodiment, as shown in Figure 5, to address the issue of peeling at the interface between the opposing joining surfaces 11, 21, a slit 30 is formed in the joining surface 11 on the metal body 10 side, and the slit 30 is pressed in the groove width direction to reduce its width (white arrow in the same figure (a)), and then a resin body 20 is joined to the joining surface 11 on the metal body 10 side. As a result, as shown in Fig. 1B, when the temperature returns to normal temperature after joining by injection molding, the slit 30, which has been reduced in width, can be expanded and deformed due to the difference in linear expansion between the metal body 10 and the resin body 20. Furthermore, regardless of the shape of the part, by first pressing the slit 30 in the groove width direction to reduce its width, it is possible to suppress the intrusion of the molten resin into the slit 30 during injection molding, thereby preventing or suppressing the molten resin from entering the slit 30 and failing to exert the desired linear expansion absorption effect. Therefore, it is possible to prevent or suppress peeling at the joining interface at the opposing joining surfaces 11, 21 due to the difference in linear expansion between the metal body 10 and the resin body 20 [Invention 1].

[0032] 2(c) and 2(e), in the joined structure 1 of this embodiment, the slits 30 are pressed in the groove width direction to reduce their width so that the narrow recessed structure remains even in the completed state after joining. This allows the joined structure 1 to follow linear expansion deformation due to temperature changes even in the environment in which it is used in the completed state.

[0033] Furthermore, in the joint structure 1 of this embodiment, as shown in Fig. 2, the slit 30 has a pair of inner side surfaces facing each other in the groove width direction, the groove width of which narrows from both longitudinal ends 32 of the slit 30 toward the groove center 31. According to this embodiment, the groove width of the inner side of the slit narrows from the groove ends 32 toward the groove center 31 in a concave shape, so that the slit 30 widens in the groove width direction, and a region where the groove width is widened and deformed until it returns to the groove width before narrowing can be effectively generated. Therefore, the stress due to the linear expansion difference is alleviated, which is suitable for preventing the destruction of the joint. [Invention 2]

[0034] In addition, in the joint structure 1 of this embodiment, the extension direction of the slit 30 is perpendicular to the longitudinal direction W as shown in Fig. 2, so the direction in which deformation due to linear expansion difference is absorbed coincides with the groove width direction. Therefore, it is preferable in terms of alleviating stress due to linear expansion difference and preventing destruction of the joint. In addition, since the groove extension direction of the slit 30 is perpendicular to the longitudinal direction at the joint surface, the slit 30 is easily crushed in the groove width direction due to stress concentration when pressed in the bending process, and it is also easy to form a narrow-width concave structure in manufacturing [Invention 3].

[0035] In the joined structure 1 of this embodiment, as shown in Fig. 2, a plurality of slits 30 are formed at intervals in the longitudinal direction W on the joining surface 11. That is, according to this embodiment, the slit 30 is not located at one place, but has a plurality of slits 30 arranged in a direction intersecting the linear expansion direction of the part, so that a larger amount of deformation can be effectively absorbed during thermal expansion deformation by cooperation of the plurality of slits 30. By forming a plurality of rows of slits 30 arranged in the intersecting direction, the amount of deformation absorption is increased, and a larger amount of deformation can be absorbed [Invention 4].

[0036] In addition, in the joint structure 1 of this embodiment, the entirety of the multiple slits 30 crosses the joint surface 11 of the metal body 10 in the Z direction perpendicular to the longitudinal direction W of the joint surface 11, as shown in Fig. 2. According to this embodiment, by crossing the metal body 10 as a whole of the slits 30 along a direction perpendicular to the deformation direction of the part, stress concentration due to linear expansion difference is alleviated, preventing or suppressing destruction of the joint, and a force in a direction different from the thermal expansion deformation is not applied to the part, which is suitable for preventing local deformation of the part. In contrast, if the slits 30 are only in a part of the joint surface 11, a moment is generated in the direction perpendicular to the expansion direction, increasing the possibility of peeling or the like occurring [Invention 5].

[0037] In addition, in the joint structure 1 of this embodiment, as shown in FIG. 2, the formation positions of the grooves arranged in the longitudinal direction W of the multiple slits 30 are alternately located back and forth in the orthogonal direction. According to this embodiment, the multiple slits 30 are distributed and the amount of deformation absorption can be made uniform. In other words, the metal body 10 between the adjacent slits 30 is continuous in the deformation direction, so that it is possible to prevent or suppress a decrease in the amount of deformation absorption only in that part. Therefore, while preventing local deformation of the parts, stress concentration due to linear expansion difference is alleviated, and destruction of the joint can be prevented or suppressed [Invention 6]. In contrast, as illustrated in Figure 9 (a), if multiple slits 30 are simply lined up in parallel, there will be a portion (denoted by symbol B in the figure) separated in the perpendicular direction where there is no slit 30, reducing the ability to absorb thermal expansion deformation in that portion. Therefore, it is preferable to disperse the multiple slits 30 and shift their positions back and forth in the intersecting direction to make the amount of deformation absorption uniform (b).

[0038] In the joint structure 1 of this embodiment, it is preferable that the arrangement intervals of the multiple slits 30 are narrower closer to the joint end with the resin body 20 than at positions farther from the joint end. In particular, it is preferable to arrange the slits 30 at positions where the two bent portions 16, 17 are formed in the bumper reinforcement 1 as shown in FIG. That is, with such a configuration, the multiple slits 30 can be efficiently arranged in the area where the influence of deformation is large. In addition, the positions are not limited to the positions of the two bent portions 16 and 17. For example, as shown in FIG. 1, it is preferable to provide more multiple slits 30 in other positions where large stress is applied during deformation, such as the position of the joint end with the resin body 20, which is closer to the outside in the longitudinal direction W than the positions where the two bent portions 16 and 17 are formed. This allows the amount of deformation during expansion to be effectively absorbed by forming many linear expansion absorbing grooves corresponding to the areas where the amount of deformation during expansion is large. Therefore, it is more suitable for preventing large local deformation of the parts [Invention 7].

[0039] In addition, in the joined structure 1 of this embodiment, it is preferable that, between adjacent slits 30 among the multiple slits 30, multiple second grooves shallower than the depth of the slits 30 are formed as grooves 40 for joining dissimilar materials, as shown in Figure 8. With this configuration, the slits 30 formed as grooves for absorbing linear expansion prevent or suppress peeling at the bonding interface between the opposing bonding surfaces 11, 21 due to the difference in linear expansion between the metal body 10 and the resin body 20, while the multiple grooves 40 for bonding dissimilar materials provided between adjacent slits 30 provide greater strength against pull-out in the bonding direction between the metal body 10 and the resin body 20, thereby providing a structure sufficient to satisfy the adhesion force in the vertical direction in this type of bonded structure [Invention 8].

[0040] Here, in the past, direct bonding of a metal body and a resin body has been adopted for small products, but has rarely been adopted for large products such as automobile bumper parts, and the effect of the difference in linear expansion is small or within the adjustment range. In contrast, according to this embodiment, in direct bonding of a metal body and a resin body to a large part, when the linear expansion coefficient of the metal body 10 is higher than that of the resin body 20, the effect of linear expansion can be kept to a minimum without adjusting the linear expansion coefficient of the resin material itself. That is, in the joint structure 1 of this embodiment, as shown in Figure 1, a slit structure is adopted in which a narrow-width concave structure remains in a direction perpendicular to the longitudinal direction W in large parts such as bumper reinforcement, which is suitable for preventing or suppressing peeling at the joint interface between opposing joint surfaces 11, 21 in the longitudinal direction W where the effect of linear expansion is significant [Invention 9].

[0041] As a joint structure capable of preventing or suppressing peeling at the joint interface, it is possible to divide the metal body at each location where the effect of linear expansion is large, and mold the metal body to be joined by a resin body, so that the divided surface is widened to absorb the amount of deformation. However, in the case of such a divided structure, although the amount of deformation due to the difference in linear expansion can be absorbed, the physical properties of the entire part are deteriorated due to the division of the part itself, and even if a structure to suppress this is adopted, it is thought that the structure will become more complicated.

[0042] Furthermore, the manufacturing method of the joined structure 1 of this embodiment is a method for manufacturing a joined structure of a metal body 10 and a resin body 20 as shown in Figures 3 and 4, and includes a groove forming process for forming a slit 30 along the Z direction intersecting the longitudinal direction W on the joining surface 11 of the metal body 10, which is to be joined to the resin base material along the longitudinal direction W at the joining surface 11 of the metal body 10 itself, a groove narrowing process for pressing the slit 30 formed in the groove forming process in the groove width direction to narrow the width of the groove, and a resin joining process for joining the resin base material along the longitudinal direction W of the joining surface 11 of the metal body 10 after the groove narrowing process.

[0043] In the manufacturing method of the joined structure (bumper reinforcement) 1 of this embodiment, the slit 30 can be pressed in the groove width direction to narrow the groove width in advance before joining with the resin body 20. Therefore, this can be said to be an excellent manufacturing method for manufacturing a joined structure that can prevent or suppress peeling at the joining interface due to the difference in linear expansion between the metal body and the resin body [Invention 10].

[0044] In particular, due to the difference in the coefficient of linear expansion between the metal body 10 and the resin body 20, when the metal body 10 significantly expands and deforms in its longitudinal direction W, according to the manufacturing method of the joined structure 1 of the present embodiment, since the slit 30 is pressed in the groove width direction and narrowed before being joined to the resin base material, when cooling after being joined to the resin base material, the narrowed slit 30 can expand and deform in the groove width direction following the expansion of the resin body 20. Thereby, the stress at the joint surfaces 11 and 21 due to the difference in linear expansion is relaxed, and the fracture at the joint interface is prevented or suppressed.

[0045] In particular, the slit 30 on the joint surface 11 on the metal body 10 side absorbs deformation by narrowing the gap of the slit 30 when the coefficient of linear expansion is that of metal <in the case of CFRTP>, but the joined structure 1 of the present embodiment is in the opposite direction (the coefficient of linear expansion of aluminum > the coefficient of linear expansion of CFRTP), and expands in the width direction of the slit 30.

[0046] On the other hand, according to the manufacturing method of the joined structure 1 of the present embodiment, a slit 30 is cut in the joint surface 11 on the metal body 10 side, and the slit 30 is deformed into a groove shape such that the gap of the groove is narrowed by applying a force from the outside along the longitudinal direction of the joined structure 1 to the metal body 10 in advance before joining the resin body 20 and pressing the slit 30 in the groove width direction.

[0047] Thereby, after joining the resin base material to the joint surface 11 of the metal body 10, along with the expansion and deformation of the fiber-reinforced resin, the slit 30 on the metal body 10 side can expand and deform so as to return to its original state in the groove width direction in response to the relative expansion and deformation of the resin body 20 and follow it. Therefore, the joined structure 1 can be manufactured while preventing or suppressing the fracture at the joint surfaces 11 and 21 due to the expansion and deformation.

[0048] Note that according to the manufacturing method of the joined structure 1 of the present embodiment, even if the molten resin enters the slit 30 during joining to the resin base material, during cooling after joining, the narrowed slit 30 deforms to expand in the groove width direction, so it is difficult for this expansion deformation to affect the stress absorption performance at the joint surfaces 11 and 21.

Explanation of Reference Numerals

[0049] 1 Bumper reinforcement (joint structure) 10 Bumper beam (metal body) 11 Joint surface 12 Rear side of surrounding wall 14, 15 Crash Box 16, 17 Bend 18, 19 Mounting part 20 Reinforcement part (resin body) 21 Joint surface 30 Slit (groove for absorbing linear expansion: first groove) 31 Reduced width part (center of groove) 32 End 40 Uneven area (groove for joining different materials: second groove) 70 Mold set 71 The First Mold 72 Second Mold W Longitudinal direction (vehicle width direction) X Vehicle width direction Z: Orthogonal to the longitudinal direction

Claims

1. A joint structure in which a metal body and a resin body are joined at mutually opposing joint surfaces, the metal body has a slit formed on the joining surface along a direction intersecting the longitudinal direction of the metal body, The slit is compressed in its groove width direction before being joined to the resin body, A joint structure, characterized in that the resin body is joined to a position covering the slit along the longitudinal direction of the joint surface of the metal body.

2. The joint structure according to claim 1 , wherein the slit has a pair of inner surfaces opposed to each other in the groove width direction, the inner surfaces having reduced width portions in which the groove width narrows from both longitudinal ends of the slit toward the center of the groove.

3. The joint structure according to claim 1 , wherein the extending direction of the slit is perpendicular to the longitudinal direction.

4. The joint structure according to claim 1 , wherein the slits are a plurality of slits formed at intervals in the longitudinal direction.

5. The joint structure according to claim 4 , wherein the plurality of slits all cross an area joined to the resin body in a direction intersecting the longitudinal direction.

6. The joint structure according to claim 4 , wherein the positions of the slits aligned in the longitudinal direction are alternated in the longitudinal direction and shifted back and forth in the perpendicular direction.

7. The joint structure according to claim 4 , wherein the intervals at which the plurality of slits are formed are narrower at positions closer to the joint end with the resin body than at positions farther from the joint end.

8. 5. The joint structure according to claim 4, further comprising a plurality of grooves shallower than the depth of the slits formed between adjacent ones of the plurality of slits as grooves for joining dissimilar materials.

9. The joining structure is a bumper reinforcement that is attached to a front or rear bumper of a vehicle body along a vehicle width direction, The metal body is a metal bumper beam having two mounting portions at both ends of its rear surface for mounting to a vehicle body, The joined structure according to any one of claims 1 to 8, wherein the resin body is a resin reinforcing part joined along the back surface of the bumper beam.

10. A method for manufacturing a joined structure in which a metal body and a resin body are joined at opposing joining surfaces, comprising the steps of: A slit forming process for forming a slit along a direction intersecting the longitudinal direction on a joining surface of the metal body that is joined to the resin body along the longitudinal direction of the joining surface; a groove width reduction step of pressing the slit formed in the slit forming step in a groove width direction to reduce the width; a resin bonding step of bonding a resin base material of a resin body along a longitudinal direction of the bonding surface after the groove width reduction step; A method for manufacturing a bonded structure comprising the steps of:

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