EP4786358A1

EP4786358A1 - Composite structure and manufacturing method therefor

Info

Publication number: EP4786358A1
Application number: EP24900254.4A
Authority: EP
Inventors: Akio Sugimoto
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2023-12-07
Filing date: 2024-09-18
Publication date: 2026-08-05
Also published as: CN122341539A; TWI924148B; JP2025091592A; TW202523466A; WO2025120957A1

Abstract

A composite structure (100) is provided with: a bottom plate (1); and a pair of first side plates (3) erected from side edges of the bottom plate (1). The composite structure (100) is provided with: an outer plate material (10) and an inner plate material (20) which are formed from metal; and a foam body (30) formed from a foam material. The outer plate material (10) has an outer bottom plate part (11), a first outer side plate part (13), an outer surface (10a), and an outer opposing surface (10b). The inner plate material (20) has an inner bottom plate part (21), a first inner side plate part (23), an inner surface (20a), and an inner opposing surface (20b). The foam body (30) is filled between the outer opposing surface (10b) and the inner opposing surface (20b). The outer plate material (10) has an outer uneven part (16) provided on the outer surface (10a). The inner plate material (20) has an inner uneven part (26) provided on the inner surface (20a).

Description

TECHNICAL FIELD

The present disclosure relates to a composite structure and a manufacturing method therefor.

BACKGROUND ART

Patent Document 1 discloses an air conditioner cabinet made from a composite material of a metal plate and a foam material. A mold including a convex core and a concave upper mold is used for manufacturing. The metal plate is set in the mold in a state of being floated in a cavity by a pin. Foam beads are injected into the cavity on both sides of the metal plate and steam heated. The upper mold is then separated from the core and the product is removed from the mold.

PRIOR ART DOCUMENT

PATENT DOCUMENT

Patent Document 1: JP H08-1378 U

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

Beads are expanded by steam heating. This increases the contact resistance between the foam material and the mold, making it difficult to release the mold.
The cabinet is a box having a three-layer structure in which foam materials are provided on both sides of a metal plate. When the metal plate and the foam material are reversed, that is, when the structure is formed of a three-layer structure in which the metal plates are provided on both sides of the foam material, it is considered that the same problem occurs due to the expansion of the beads. Moreover, it is considered that the contact resistance is further increased.
An object of the present disclosure is to provide a composite structure capable of facilitating mold release and a manufacturing method therefor.

SOLUTIONS TO THE PROBLEMS

One aspect of the present disclosure is a composite structure comprising a bottom plate, and a pair of side plates erected from a side edge of the bottom plate, the composite structure including: an outer plate member formed from metal and having an outer bottom plate portion constituting the bottom plate portion, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side thereof, an inner plate member formed from metal and having an inner bottom plate portion constituting the bottom plate portion, an inner side plate portion constituting the pair of side plates, an inner surface of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side thereof, and a foam molded from a foam material and filled between the outer opposing surface and the inner opposing surface, in which the outer plate member includes an outer convexo-concave portion provided on the outer surface, and the inner plate member includes an inner convexo-concave portion provided on the inner surface.
According to the above configuration, the composite structure has at least the bottom plate and the pair of side plates as in, for example, a channel type or a box type. In addition, the composite structure has a three-layer structure in which metal plates are provided on both sides of the foam material, and can be manufactured by molding, for example.
When the composite structure is manufactured by molding, the outer surface of the outer plate member and the inner surface of the inner plate member may be in contact with the surface of the mold. The outer convexo-concave portion is provided on the outer surface. Microscopically, the outer surface comes into contact with the surface of the mold in the convex portion, while separating from the surface of the mold in the concave portion. Even when the foam material is expanded in the mold, the separation state of this concave portion may be maintained. Since the contact area of the outer surface with the surface of the mold is reduced, the contact resistance is also reduced accordingly. The inner convexo-concave portion provided on the inner surface also acts in the same manner. Therefore, mold release is facilitated.
The outer convexo-concave portion may be provided on the outer opposing surface, the inner convexo-concave portion may be provided on the inner opposing surface, and the foam may be engaged with the outer convexo-concave portion and the inner convexo-concave portion.
According to the above configuration, the bonding strength of the foam to the outer plate member and the inner plate member is improved.
The outer convexo-concave portion and the inner convexo-concave portion may be formed by arranging a plurality of concave portions or a plurality of convex portions.
According to the above configuration, the outer convexo-concave portions can be easily provided on both sides of the outer plate member by, for example, embossing or forging, and the inner convexo-concave portions can be easily provided on both sides of the inner plate member.
The composite structure may further include a pair of second side plates erected from a side edge of the bottom plate, in which the pair of side plates and the pair of second side plates constitute a peripheral plate of a box body.
According to the above configuration, it is possible to provide a box-shaped composite structure in which mold release is facilitated. The composite structure has a three-layer structure in which metal plates are provided on both sides of a foam material, and is excellent in toughness and heat insulating properties. A structure suitable for transportation of cargos requiring temperature management can be efficiently produced.
Another aspect of the present disclosure is a method for manufacturing a composite structure including a bottom plate portion and a pair of side plates erected from a side edge of the bottom plate portion, the method including the steps of: forming, with metal, an outer plate member having an outer bottom plate portion constituting the bottom plate portion, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side; forming, with metal, an inner plate member having an inner bottom plate portion constituting the bottom plate portion, an inner side plate portion constituting the pair of side plates, inner surfaces of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side; internally fitting the outer plate member into a mold concave portion and externally fitting the inner plate member onto a mold convex portion when a mold including a first mold having the mold concave portion and a second mold having the mold convex portion is in a mold-open state in which the mold convex portion is retracted from the mold concave portion; bringing the mold into a mold-closed state in which the mold convex portion has entered the mold concave portion; filling a cavity formed between the outer opposing surface and the inner opposing surface with a foam material; heating the foam material and molding a foam between the outer plate member and the inner plate member; and bringing the mold into the mold-open state and taking out the composite structure from the mold, in which in the step of forming the outer plate member, an outer convexo-concave portion is provided on the outer surface, and in the step of forming the inner plate member, an inner convexo-concave portion is provided on the inner surface.
Also in the above configuration, the composite structure has at least a bottom plate and a pair of side plates like, for example, a channel type or a box type.
In addition, the composite structure has a three-layer structure in which metal plates are provided on both sides of the foam material, and is manufactured by molding. The outer surface of the outer plate member is close to the surface of the mold concave portion. In this regard, since the outer surface of the outer plate member is provided with the outer convexo-concave portion, the convex portion comes into contact with the surface of the mold concave portion, while the concave portion is separated from the surface of the mold concave portion. As the foam material is heated and expands within the cavity, the separation state of this concave portion may be maintained. The contact area between the outer surface and the mold is reduced, and the contact resistance is reduced accordingly. The inner surface of the inner plate member and the surface of the mold convex portion also act in the same manner. Therefore, the step of taking out the composite structure from the mold, that is, releasing the composite structure is facilitated.
The outer convexo-concave portion may be provided on the outer opposing surface, and the inner convexo-concave portion may be provided on the inner opposing surface, and in the step of heating the foam material, the foam may enter and be engaged with the outer convexo-concave portion and the inner convexo-concave portion.
According to the above configuration, the foam, the outer plate member, and the inner plate member mesh with each other at the outer convexo-concave portion and the inner convexo-concave portion, and the relative movement between the outer plate member and the foam and the relative movement between the inner plate member and the foam are hindered. As a result, the three of the outer plate member, the inner plate member, and the foam can be integrated without being separated from each other.
The outer convexo-concave portion and the inner convexo-concave portion may be provided on a sliding surface with respect to the mold among the outer surface and the inner surface.
According to the above configuration, mold release can be effectively facilitated.
The step of forming the outer plate member may include a step of forming a flat blank having the outer bottom plate portion and the outer side plate portion in a developed state, and a step of bending the blank such that the outer side plate portion stands upright from the outer bottom plate portion, and the outer convexo-concave portion may be provided on the blank before the step of bending the blank.
According to the above configuration, the outer convexo-concave portion can be easily provided in the forming process of the outer plate member, and the production efficiency of the outer plate member is improved.

EFFECTS OF THE INVENTION

According to the present disclosure, it is possible to provide the composite structure capable of facilitating mold release and the method for manufacturing the composite structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig. 1] Fig. 1 is a perspective view of a composite structure according to an embodiment.
[Fig. 2] Fig. 2 is an exploded perspective view of the composite structure according to the embodiment.
[Fig. 3] Fig. 3 is a cross-sectional view of the composite structure according to the embodiment.
[Fig. 4] Fig. 4 is a flowchart showing a method for manufacturing a composite structure according to the embodiment.
[Fig. 5A] Fig. 5A is a developed view of an outer plate member, and is a plan view of a blank for the outer plate member.
[Fig. 5B] Fig. 5B is a cross-sectional view of the blank of the outer plate member taken along line B-B in Fig. 5A.
[Fig. 5C] Fig. 5C is a cross-sectional view of a blank of an outer plate member according to a modification.
[Fig. 5D] Fig. 5D is a cross-sectional view of a blank of an outer plate member according to a modification.
[Fig. 6A] Fig. 6A is a developed view of an inner plate member, and is a plan view of a blank for the inner plate member.
[Fig. 6B] Fig. 6B is a cross-sectional view of the blank of the inner plate member taken along line B-B in Fig. 6A.
[Fig. 7] Fig. 7 is a cross-sectional view illustrating a step of internally fitting an outer plate member into a mold concave portion and externally fitting an inner plate member into a mold convex portion.
[Fig. 8] Fig. 8 is a cross-sectional view showing a step of filling a foam material.
[Fig. 9] Fig. 9 is a cross-sectional view showing a step of heating a foam material.
[Fig. 10A] Fig. 10A is a cross-sectional view showing an example of a step of bringing a mold into a mold-open state after molding of a foam and showing a case where a composite structure remains in a first mold.
[Fig. 10B] Fig. 10B is a cross-sectional view showing an example of a step of bringing a mold into a mold-open state after molding of a foam and showing a case where a composite structure remains in a second mold.

DETAILED DESCRIPTION

Hereinafter, an embodiment will be described with reference to the drawings. The same or corresponding elements are denoted by the same reference numerals throughout the drawings, and overlapping of the detailed description will be omitted.
Referring to Fig. 1, a composite structure 100 according to the present embodiment is box-shaped as a whole, and is suitably used, for example, for transportation of cargo. The composite structure 100 includes a bottom plate 1, a peripheral plate 2, and a flange 5. The bottom plate 1 and the peripheral plate 2 constitute a box opened upward. The inner surface of the bottom plate 1 and the inner surface of the peripheral plate 2 define an internal space 6 that can store loads and the like.
As an example, the bottom plate 1 has a rectangular shape in plan view. The bottom plate 1 has a pair of first side edges 1a and a pair of second side edges 1b as four side edges defining a rectangle. The pair of first side edges 1a is parallel to each other, the pair of second side edges 1b is parallel to each other, and the second side edge 1b extends in a direction orthogonal to the first side edge 1a. The peripheral plate 2 is erected from a side edge of the bottom plate 1. The peripheral plate 2 includes a total of four side plates including a pair of first side plates 3 and a pair of second side plates 4. The pair of first side plates 3 is erected from the pair of respective first side edges 1a, and the pair of second side plates 4 is erected from the pair of respective second side edges 1b. The flange 5 is provided at an upper end edge of the peripheral plate 2. The flange 5 has a rectangular window frame shape in plan view and defines an upper opening of the box body.
Referring to Figs. 1 to 3, the composite structure 100 includes an outer plate member 10 formed from metal, an inner plate member 20 formed from metal, and a foam 30 formed of a foam material, and the foam 30 is sandwiched between the outer plate member 10 and the inner plate member 20. In other words, the composite structure 100 has a three-layer structure in which the outer plate member 10 and the inner plate member 20 made of metal are provided on both sides of the foam 30.
Steel or an aluminum alloy can be suitably used as the metal as the material of the outer plate member 10. The same applies to the inner plate member 20. The outer plate member 10 and the inner plate member 20 may be formed of the same metal, or may be formed of different metals. Polyurethane, polystyrene, or polyolefin can be suitably used as a foam material as a material of the foam 30.
The three-layer structure is applied to the entire bottom plate 1 and the entire peripheral plate 2. That is, similarly to the composite structure 100 as a finished product, the outer plate member 10, the foam 30, and the inner plate member 20 are also box bodies opened upward. The flange 5 has a two-layer structure of the outer plate member 10 and the foam 30.
In Fig. 2, the outer plate member 10, the inner plate member 20, and the foam 30 are illustrated in a separated state, but this is for convenience of description. As described later, the foam 30 is formed integrally with the outer plate member 10 and the inner plate member 20 by molding. In the manufacturing process of the composite structure 100, the box foam 30 is not handled singly.
The outer plate member 10 includes an outer bottom plate portion 11 constituting the bottom plate 1, an outer peripheral plate portion 12 constituting the peripheral plate portion 2, and a lower flange portion 15 constituting the flange 5. The outer peripheral plate portion 12 includes a pair of first outer side plate portions 13 respectively corresponding to the pair of first side plates 3, and a pair of second outer side plate portions 14 respectively corresponding to the pair of second side plates 4.
The outer plate member 10 has an outer surface 10a and an outer opposing surface 10b on a side opposite to the outer surface 10a in the plate thickness direction thereof. The outer surface 10a corresponds to an outer surface of the composite structure 100. The outer surface of the outer bottom plate portion 11 corresponds to the outer surface (lower surface) of the bottom plate 1, and the outer surface of the outer peripheral plate portion 12 corresponds to the outer surface (outer side surface) of the peripheral plate portion 2.
The inner plate member 20 includes an inner bottom plate portion 21 constituting the bottom plate 1 and an inner peripheral plate portion 22 constituting the peripheral plate portion 2. The inner peripheral plate portion 22 includes a pair of first inner side plate portions 23 respectively corresponding to the pair of first side plates 3 and a pair of second inner side plate portions 24 respectively corresponding to the pair of second side plates 4.
The inner plate member 20 has an inner surface 20a and an inner opposing surface 20b on a side opposite to the inner surface 20a in the plate thickness direction. The inner surface 20a corresponds to the inner surface of the composite structure 100 and defines the internal space 6. An inner surface of the inner bottom plate portion 21 corresponds to an inner surface (upper surface) of the bottom plate 1, and an inner surface of the inner peripheral plate portion 22 corresponds to an inner surface (inner side surface) of the peripheral plate portion 2.
The foam 30 includes a middle bottom plate portion 31 constituting the bottom plate 1, a middle peripheral plate portion 32 constituting the peripheral plate portion 2, and an upper flange portion 35 constituting the flange 5. The middle peripheral plate portion 32 includes a pair of first middle plate portions 33 respectively corresponding to the pair of first side plates 3, and a pair of second middle plate portions 34 respectively corresponding to the pair of second side plates 4.
The foam 30 is filled between the outer opposing surface 10b of the outer plate member 10 and the inner opposing surface 20b of the inner plate member 20. The foam 30 has an outer surface 30a and an inner surface 30b opposite to the outer surface 30a in the thickness direction. The outer surface 30a is in close contact with the outer opposing surface 10b, and the inner surface 30b is in close contact with the inner opposing surface 20b.
The bottom plate 1 is configured by laminating the outer bottom plate portion 11, the middle bottom plate portion 31, and the inner bottom plate portion 21 in this order from the outside to the inside of the composite structure 100 in the plate thickness direction of the bottom plate 1. The first side plate 3 is formed by laminating the first outer side plate portion 13, the first middle plate portion 33, and the first inner side plate portion 23 in this order from the outside to the inside of the composite structure 100 in the thickness direction of the first side plate portion 3. The second side plate 4, the second outer side plate portion 14, the second middle plate portion 34, and the second inner side plate portion 24 are also similar to the first side plate 3.
The flange 5 is formed by laminating the upper flange portion 35 of the foam 30 on the upper surface side of the lower flange portion 15 of the outer plate member 10. The upper surface of the lower flange portion 15 is formed by a part of the outer opposing surface 10b, and the lower surface of the upper flange portion 35 is formed by a part of the outer surface 30a and is in close contact with the upper surface of the lower flange portion 15. The entire lower surface of the flange 5 is formed by the outer plate member 10. The entire upper surface of the flange 5 is formed of the foam 30, and is positioned at substantially the same height as the upper end edge of the inner peripheral plate portion 22 of the inner plate member 20.
The outer plate member 10 has an outer convexo-concave portion 16 provided on the outer surface 10a side. The outer convexo-concave portion 16 is formed by forming a plurality of convex portions 16a on the outer surface 10a. Each convex portion 16a is formed by recessing the outer opposing surface 10b toward the outer surface 10a in the plate thickness direction of the outer plate member 10, and has an island shape. The plurality of convex portions 16a are arranged in a specific region of the outer surface 10a. On the outer surface 10a, in the region where the plurality of convex portions 16a are arranged, a portion where the convex portion 16a is not actually formed is recessed toward the outer opposing surface 10b in the plate thickness direction relative to a portion where the convex portion 16a is actually formed. Even when only the convex portion 16a is formed on the outer surface 10a, it is possible to provide substantially unevenness on the outer surface 10a.
The convex portion 16a is formed by press working (embossing or the like) of applying a pressing force to the outer opposing surface 10b as described later. By forming the plurality of convex portions 16a on the outer surface 10a, the plurality of concave portions 16b are transferred to the outer opposing surface 10b. Each of the concave portions 16b is formed by recessing the outer opposing surface 10b toward the outer surface 10a in the plate thickness direction of the outer plate member 10, and has a pond shape. In the outer opposing surface 10b, in the region where the plurality of concave portions 16b are arranged, a portion where the concave portion 16b is not actually formed protrudes toward the outer opposing surface 10b in the plate thickness direction relative to a portion where the concave portion 16b is actually formed. Even when only the concave portion 16b is formed in the outer opposing surface 10b, it is possible to provide substantially unevenness on the outer opposing surface 10b. In this manner, the outer convexo-concave portion 16 is provided on the outer surface 10a, so that the outer convexo-concave portion 16 is also provided simultaneously on the outer opposing surface 10b.
The inner plate member 20 has an inner convexo-concave portion 26 provided on the inner surface 20a side. The inner convexo-concave portion 26 is configured by forming a plurality of convex portions 26a on the inner surface 20a. Each convex portion 26a is formed by recessing the inner opposing surface 20b toward the inner surface 20a in the plate thickness direction of the inner plate member 20. The plurality of convex portions 26a are arranged in a specific region of the inner surface 20a. In the region where the plurality of convex portions 26a are arranged on the inner surface 20a, substantial unevenness is provided even if only the convex portions 26a are actually formed.
The convex portion 26a is also formed in the same manner as the convex portion 16a. By forming the plurality of convex portions 26a on the inner surface 20a, the plurality of concave portions 26b are transferred to the inner opposing surface 20b. Each concave portion 26b is formed by recessing the inner opposing surface 20b toward the inner surface 20a in the plate thickness direction of the inner plate member 20. In the inner opposing surface 20b, in the region where the plurality of concave portions 26b are arranged, substantial unevenness is provided even if only the concave portions 26b are actually formed. In this manner, the inner convexo-concave portion 26 is provided on the inner surface 20a, and thus, is also simultaneously provided on the inner opposing surface 20b.
In a case where the outer convexo-concave portion 16 includes the plurality of convex portions 16a or the plurality of concave portions 16b, the pattern of the arrangement of the convex portions 16a and the concave portions 16b may be regular such as a matrix or a zigzag, or may be irregular. The shapes of the convex portion 16a and the concave portion 16b are not particularly limited. In addition to the illustrated circular shape, other shapes such as an elliptical shape, a regular polygonal shape, and a star shape may be applied. The convex portion 16a may be formed on the outer opposing surface 10b, and the concave portion 16b may be formed on the outer surface 10a. However, it is advantageous that the convex portion 16a is formed on the outer surface 10a in that a contact area reduction effect described later is easily obtained. A region where the outer convexo-concave portion 16 is provided (a region where the plurality of convex portions 16a or the plurality of concave portions 16b are arranged) is a sliding surface with respect to at least a mold 50 (see Fig. 7). Note that the same applies to a case where the inner convexo-concave portion 26 is configured by the plurality of convex portions 26a or concave portions 26b.
The foam 30 is engaged with the outer convexo-concave portion 16 on the outer surface side, and is engaged with the inner convexo-concave portion 26 on the inner surface side. On the outer surface 30a of the foam 30, unevenness is transferred so as to engage with the outer convexo-concave portion 16. Unevenness is transferred to the inner surface 30b of the foam 30 so as to engage with the inner convexo-concave portion 26.
Fig. 4 shows a method for manufacturing a composite structure according to the present embodiment. In manufacturing the composite structure 100, first, the outer plate member 10 is formed from metal (see step S1 and Fig. 5), and the inner plate member 20 is formed from metal (see step S2 and Fig. 6). Next, when the mold 50 is in the mold-open state, the outer plate member 10 and the inner plate member 20 are installed in the mold 50 (see step S3 and Fig. 7), and the mold 50 is in the mold-closed state (see step S4, Fig. 8). Next, the cavity 53 is filled with foam beads 30A (see step S5 and Fig. 8), and the foam beads 30A are heated (see step S6 and Fig. 9). Next, the mold 50 is opened (see step S7 and Fig. 10A and Fig. 10B), and the composite structure 100 is taken out of the mold 50 (step S8). Thereby, the composite structure 100 as shown in Fig. 1 is obtained.
Figs. 5A and 6A are explanatory views of a step of forming the outer plate member 10 and the inner plate member 20 (steps S1 and S2).
Referring to Fig. 5A, in the forming of the outer plate member 10, a flat blank 10A including the outer bottom plate portion 11, the outer peripheral plate portion 12 (the first outer side plate portion 13 and the second outer side plate portion 14), and the lower flange portion 15 in the unfolded state is formed. The blank 10A is formed by, for example, punching a plate member drawn from the metal coil. Fig. 5A is a developed view of the outer plate member 10, and is also a plan view of the blank 10A of the outer plate member 10. Then, by performing a required bending process on the blank 10A, the outer peripheral plate portion 12 is formed to stand from the outer bottom plate portion 11, and the lower flange portion 15 is formed to be bent from the outer peripheral plate portion 12. Further, after the bending process, adjacent two of the four outer side plate portions of the pair of first outer side plate portions 13 and the pair of second outer side plate portions 14 are welded to each other. Thus, the outer plate member 10 is formed into a box shape.
As illustrated in Fig. 5A as a plan view of the blank 10A, the outer convexo-concave portion 16 is provided on the blank 10A before bending process. When the outer convexo-concave portion 16 is provided on the outer plate member 10, the outer surface 10a is embossed, a large number of convex portions 16a are formed on the outer surface 10a, and a large number of concave portions 16b are formed on the outer opposing surface 10b. In the present embodiment, the region where the outer convexo-concave portion 16 is provided is, for example, the entire outer bottom plate portion 11 and the entire outer peripheral plate portion 12.
Referring to Fig. 6A, the inner plate member 20 is also formed in the same manner as the outer plate member 10 described above. A blank 20A having a flat plate shape and including the inner bottom plate portion 21 and the inner peripheral plate portion 22 (the first inner side plate portion 23 and the second inner side plate portion 24) in a developed state is formed. Fig. 6 is a developed view of the inner plate member 20, and is also a plan view of the blank 20A of the inner plate member 20. The inner peripheral plate portion 22 is formed to stand from the inner bottom plate portion 21 by performing a required bending process on the blank 20A. After the bending process, the inner peripheral plate portion 22 is welded in the same manner as the outer plate member 10. As a result, the inner plate member 20 is formed into a box shape.
The inner convexo-concave portion 26 is also provided on the blank 20A before the bending process. When the inner convexo-concave portion 26 is provided on the inner plate member 20, embossing is performed on the inner surface 20a, a large number of convex portions 26a are formed on the inner surface 20a, and a large number of concave portions 26b are formed on the inner opposing surface 20b. In the present embodiment, the region where the inner convexo-concave portion 26 is provided is, for example, the entire inner bottom plate portion 21 and the entire inner peripheral plate portion 22.
Referring to Fig. 5B, as an example, the convex portion 16a and the concave portion 16b of the outer convexo-concave portion 16 are hemispherical. Therefore, a portion where the protrusion height of each convex portion 16a from the outer surface 10a is maximum (a top portion of the convex portion 16a) is in the form of a point. In the present embodiment, the top portions of the plurality of convex portions 16a are at substantially the same height. Referring to Fig. 6B, the same applies to the convex portion 26a and the concave portion 26b of the inner convexo-concave portion 26.
The protrusion height of the convex portion 16a of the outer convexo-concave portion 16 (or the depth of the concave portion 16b) is micrometers. When a metal material is adopted for the outer plate member 10 and the protrusion height is set in this manner, it is possible to avoid the entire sliding surface of the outer plate member 10 from being pressed against the mold 50 (see Fig. 8) even by expansion of the foam beads 30A (see Fig. 8), and an effect of facilitating the mold release described later can be obtained. In addition, in a case where the protrusion height is set in this manner, it is also possible to sufficiently sense the presence of unevenness when the outer convexo-concave portion 16 is stroked with a hand. That is, the presence or absence of the outer convexo-concave portion 16 can be determined by human feeling. The same applies to the protrusion height of the convex portion 26a of the inner convexo-concave portion 26 (or the depth of the concave portion 26b).
Fig. 7 is an explanatory view of a step (step S3) of installing the outer plate member 10 and the inner plate member 20 in the mold 50.
The mold 50 includes a first mold 51 and a second mold 52. The first mold 51 has a mold concave portion 51A. The second mold 52 has a mold convex portion 52A. The second mold 52 can be displaced relative to the first mold 51. Due to this relative displacement, the mold 50 is switched between a mold-open state in which the mold convex portion 52A is retracted from the mold concave portion 51A and a mold-closed state in which the mold convex portion 52A has entered the mold concave portion 51A. Fig. 7 shows a mold-open state of the mold 50. The first mold 51 may be a fixed mold and the second mold 52 may be a movable mold, or vice versa.
In the present embodiment, the relative displacement direction (that is, the mold opening/closing direction) of the first mold 51 and the second mold 52 corresponds to the direction (that is, the mold release direction) in which the composite structure 100 is taken out from the mold 50, and corresponds to the direction (that is, the product sliding direction) in which the composite structure 100 slides with respect to the mold 50 at the time of mold release. In the following description, the mold opening/closing direction, the mold release direction, and the product sliding direction correspond to the vertical direction according to the illustration, but these directions can be appropriately changed to other directions such as the horizontal direction.
The first mold 51 has a rectangular box-shaped first body portion 51a opened upward, and a shoulder portion 51b protruding outward from an upper end portion of the first body portion 51a. The mold concave portion 51A is defined by the inner bottom surface and the inner peripheral surface of the first body portion 51a. The shoulder portion 51b forms a step surface extending from the upper end of the inner peripheral surface of the first body portion 51a to the outside of the first body portion 51a.
In the mold-open state, the box-shaped outer plate member 10 is internally fitted into the mold concave portion 51A. The outer surface 10a of the outer plate member 10 is close to the inner surface of the mold concave portion 51A. The outer surface of the outer bottom plate portion 11 is close to the inner bottom surface of the mold concave portion 51A (the inner bottom surface of the first body portion 51a), and the outer surface of the outer peripheral plate portion 12 is close to the inner peripheral surface of the mold concave portion 51A (the inner peripheral surface of the first body portion 51a). The lower surface of the lower flange portion 15 is close to the step surface of the shoulder portion 51b.
The inner peripheral surface of the mold concave portion 51A extends upward from the inner bottom surface of the mold concave portion 51A, that is, in the mold opening/closing direction, the mold release direction, and the product sliding direction. As described later, the outer surface of the outer peripheral plate portion 12 can come into sliding contact with the inner surface of the mold concave portion 51A at the time of mold release. That is, the outer surface of the outer peripheral plate portion 12 of the outer surface 10a of the outer plate member 10 is a sliding surface with respect to the mold 50. In the present embodiment, the outer convexo-concave portion 16 is provided on the sliding surface. On the other hand, although the outer surface of the outer bottom plate portion 11 and the lower surface of the lower flange portion 15 are close to the surface of the first mold 51, they extend in the direction orthogonal to the mold opening/closing direction and cannot be said to be sliding surfaces. However, in the present embodiment, the outer convexo-concave portion 16 is also provided on the outer surface of the outer bottom plate portion 11.
The second mold 52 includes a second body portion 52a having a rectangular box shape opened upward, and a flange portion 52b protruding outward from an upper end portion of the first body portion 51a. The mold convex portion 52A is defined by the outer bottom surface and the outer peripheral surface of the second body portion 52a.
In the mold-open state, the box-shaped inner plate member 20 is externally fitted to the mold convex portion 52A. The inner surface 20a of the inner plate member 20 is close to the outer surface of the mold convex portion 52A. The inner surface of the inner bottom plate portion 21 is close to the outer bottom surface of the mold convex portion 52A (the outer bottom surface of the second body portion 52a). The inner surface of the inner peripheral plate portion 22 is close to the outer peripheral surface of the mold convex portion 52A (the outer peripheral surface of the second body portion 52a).
The outer peripheral surface of the mold convex portion 52A extends upward from the outer bottom surface of the mold convex portion 52A, that is, in the mold opening/closing direction, the mold release direction, and the product sliding direction. As described later, the outer surface of the inner peripheral plate portion 22 can come into sliding contact with the inner surface of the mold convex portion 52A at the time of mold release. That is, the inner surface of the inner peripheral plate portion 22 of the inner surface 20a of the inner plate member 20 is a sliding surface with respect to the mold 50. In the present embodiment, the inner convexo-concave portion 26 is provided on the sliding surface. On the other hand, the inner surface of the inner bottom plate portion 21 is close to the surface of the second mold 52, but extends in a direction orthogonal to the mold opening/closing direction, and cannot be said to be a sliding surface. However, in the present embodiment, the inner convexo-concave portion 26 is also provided on the inner surface of the inner bottom plate portion 21.
Fig. 8 is an explanatory view of the step of bringing the mold 50 into the mold-closed state (step S4) and the step of filling the cavity 53 with the foam beads 30A (step S5).
By relatively displacing the first mold 51 and the second mold 52, the state of the mold 50 is switched from the mold-open state to the mold-closed state. In the mold-closed state, the mold convex portion 52A with the inner plate member 20 enters the mold concave portion 51A with the outer plate member 10. In the mold 50, the cavity 53 is formed between the outer opposing surface 10b of the outer plate member 10 and the inner opposing surface 20b of the inner plate member 20.
The flange portion 52b of the second mold 52 is internally fitted to the shoulder portion 51b of the first mold 51. The lower surface of the flange portion 52b is separated upward from the upper surface of the lower flange portion 15 of the outer plate member 10 supported on the step surface of the shoulder portion 51b. The space between the flange portion 52b and the lower flange portion 15 communicates with the space between the outer opposing surface 10b and the inner opposing surface 20b, and constitutes a part of the cavity 53.
The mold 50 is provided with a bead port 54 for injecting the foam beads 30A into the cavity 53. For example, the bead port 54 is a through hole formed in the flange portion 52b of the second mold 52. Since the inner plate member 20 does not cover the flange portion 52b, the external space of the mold 50 can be easily communicated with the cavity 53 by the through hole. A part or all of the bead ports 54 may be provided on the shoulder portion 51b of the first mold 51.
In the mold-closed state, the foam beads 30A are injected from the external space of the mold 50 into the cavity 53 via the bead ports 54 using compressed air. As a result, the foam beads 30A are filled in the cavity 53.
Fig. 9 is an explanatory view of the step of heating the foam beads 30A (step S6).
The mold 50 is provided with a steam port 55 for supplying steam to the cavity 53. For example, the steam port 55 is a through hole formed in the second body portion 52a of the second mold 52. The steam port 55 may also be formed in the first body portion 51a of the first mold 51. Steam is supplied to the cavity 53 via the steam port 55, and air in the cavity 53 is replaced with steam. As a result, the expanded beads 30A are heated, and the expansion of the expanded beads 30A is promoted. The mold 50 is heated by a heater (not shown) in order to promote heating of the foam beads 30A. After this heating step, the mold 50 and the inside thereof are cooled by water cooling and cooling.
As a result of the heating step and the cooling step, the foamed body 30 is integrally formed with the outer plate member 10 and the inner plate member 20 in a state of being interposed between the outer plate member 10 and the inner plate member 20, and the box-shaped composite structure 100 having a multilayer structure is formed. The foam 30 is fused to the outer opposing surface 10b and the inner opposing surface 20b to form the middle bottom plate portion 31 and the middle peripheral plate portion 32. The foam 30 is fused to the upper surface of the lower flange portion 15 of the outer plate member 10 to form the upper flange portion 35.
The outer convexo-concave portion 16 is also provided on the outer opposing surface 10b defining the cavity 53. The inner convexo-concave portion 26 is also provided on the inner opposing surface 20b defining the cavity 53. While the foam beads 30A are heated, the foam beads 30A enter the concave portion of the outer convexo-concave portion 16 and the concave portion of the inner convexo-concave portion 26 by expansion.
The concave portion of the outer convexo-concave portion 16 on the outer opposing surface 10b can be defined as a portion where the concave portion 16b is actually formed in the region where the plurality of concave portions 16b are arranged in the outer opposing surface 10b. In a case where the convex portion is actually formed on the outer opposing surface 10b, the concave portion of the outer opposing surface 10b can be defined as a portion where the convex portion is not actually formed. The concave portion of the inner convexo-concave portion 26 on the inner opposing surface 20b can be defined as a portion where the concave portion 26b is actually formed in the region where the plurality of concave portions 26b is arranged in the inner opposing surface 20b. In a case where the convex portion is actually formed on the inner opposing surface 20b, the concave portion of the inner opposing surface 20b can be defined as a portion where the convex portion is not actually formed.
Figs. 10A and 10B are explanatory views of the step of bringing the mold 50 into the mold-open state (step S7) and the step of releasing the mold (step S8).
By relatively displacing the first mold 51 and the second mold 52, the state of the mold 50 is switched from the mold-closed state to the mold-open state. The composite structure 100 may remain in the first mold 51 in a state of being internally fitted in the mold concave portion 51A (see Fig. 10A). The composite structure 100 may remain in the mold in a state of being externally fitted to the mold convex portion 52A (see Fig. 10B).
Referring to Fig. 10A, when the composite structure 100 remains in the first mold 51, the outer plate member 10 is pressed against the inner surface of the mold concave portion 51A due to expansion of the foam 30. The composite structure 100 is taken out in a direction from the first mold 51 toward the second mold 52 (upward in the drawing). At this time, the outer surface of the outer peripheral plate portion 12 is a sliding surface as described above, and slides upward along the inner surface of the mold concave portion 51A.
Referring to Fig. 10B, when the composite structure 100 remains in the second mold 52, the inner plate member 20 is pressed against the outer surface of the mold convex portion 52A due to the expansion of the foam 30. The composite structure 100 is taken out in a direction from the second mold 52 toward the first mold 51 (downward in the drawing). At this time, the inner surface of the inner peripheral plate portion 22 is a sliding surface as described above, and is in sliding contact downward with the inner surface of the mold convex portion 52A.
In the example shown in Fig. 10A, the inner surface of the inner peripheral plate portion 22 does not slide with respect to the mold 50 at the time of mold release, and in the example shown in Fig. 10B, the outer surface of the outer peripheral plate portion 12 does not slide with respect to the mold 50 at the time of mold release. However, these surfaces are collectively referred to as sliding surfaces in light of the possibility of sliding relative to the mold 50 depending on the situation.
In the composite structure 100 according to the present embodiment, the outer plate member 10 has the outer convexo-concave portion 16 provided on the outer surface 10a, and the inner plate member 20 has the inner convexo-concave portion 26 provided on the inner surface 20a.
In the example shown in Fig. 10A, due to the presence of the outer convexo-concave portion 16, the outer surface 10a comes into contact with the inner surface of the mold concave portion 51A at the convex portion, and is separated from the inner surface of the mold concave portion 51A at the concave portion. Since the contact area of the outer surface 10a with the inner surface of the mold concave portion 51A is reduced, the contact resistance is also reduced accordingly. Therefore, mold release can be facilitated. In particular, the outer convexo-concave portion 16 is provided on the sliding surface of the outer surface 10a. Therefore, it is easy to obtain the effect of facilitating mold release.
The convex portion 16a has a hemispherical shape, so that the top portion of each convex portion 16a has a dot shape, and each convex portion 16a is almost in point contact with the inner surface of the mold concave portion 51A. The contact area is greatly reduced, and mold release is further facilitated.
The same applies to the example illustrated in Fig. 10B. Due to the presence of the inner convexo-concave portion 26, the inner surface 20a comes into contact with the outer surface of the mold convex portion 52A at the convex portion and is separated from the outer surface of the mold convex portion 52A at the concave portion. Since the contact area of the inner surface 20a with the outer surface of the mold convex portion 52A is reduced, the contact resistance is also reduced accordingly. Therefore, mold release can be facilitated. In particular, the inner convexo-concave portion 26 is provided on the sliding surface of the inner surface 20a. Therefore, it is easy to obtain the effect of facilitating mold release.
The convex portion 26a has a hemispherical shape, so that the top portion of each convex portion 26a has a dot shape, and each convex portion 26a is almost in point contact with the outer surface of the mold convex portion 52A. The contact area is greatly reduced, and mold release is further facilitated.
The outer convexo-concave portion 16 is also provided on the outer opposing surface 10b on the side opposite to the outer surface 10a in the plate thickness direction of the outer plate member 10. The inner convexo-concave portion 26 is also provided on the inner opposing surface 20b opposite to the inner surface 20a in the plate thickness direction of the inner plate member 20. The foam 30 is interposed between the outer opposing surface 10b and the inner opposing surface 20b, and the foam 30 is engaged with the outer convexo-concave portion 16 and the inner convexo-concave portion 26. The foam 30 meshes with the outer plate member 10 and the inner plate member 20 at the outer convexo-concave portion 16 and the inner convexo-concave portion 26, respectively, and the relative movement between the outer plate member 10 and the foam 30 and the relative movement between the inner plate member 20 and the foam 30 are hindered. As a result, the three of the outer plate member 10, the inner plate member 20, and the foam 30 are integrated without being separated from each other, and the bonding strength of the foam 30 to the outer plate member 10 and the inner plate member 20 is improved. Even if an adhesive is not used, the three constituent elements of the outer plate member 10, the foam 30, and the inner plate member 20 can be maintained in a state of being firmly joined to each other.
The outer convexo-concave portion 16 and the inner convexo-concave portion 26 are formed by arranging a plurality of convex portions 16a and 26a or concave portions 16b and 26b. For this formation, press working such as embossing is employed. The outer convexo-concave portions 16 can be easily provided on both surface sides of the outer plate member 10. The inner convexo-concave portions 26 can be easily provided on both surface sides of the inner plate member 20. In addition, in the process of forming the blanks 10A and 20A, the outer convexo-concave portion 16 and the inner convexo-concave portion 26 can be easily provided, and the production efficiency of the outer plate member 10 and the inner plate member 20 is improved. For example, the blanks 10A and 20A having the outer convexo-concave portion 16 and the inner convexo-concave portion 26 can be efficiently produced by using a transfer press.
The composite structure 100 according to the present embodiment includes a pair of first side plates and a pair of second side plates, and these side plates constitute the peripheral plate 2 of the box body. As a result, it is possible to provide the box-shaped composite structure 100 in which mold release is facilitated. The composite structure 100 has a three-layer structure in which metal plates are provided on both sides of a foam material, and is excellent in toughness and heat insulating properties. A structure suitable for transportation of cargos requiring temperature management can be efficiently produced.
Although the embodiment has been described so far, the above configuration can be appropriately changed within the scope of the gist of the present invention.
The composite structure 100 may be channel-type, in which case the pair of second side plates is omitted, and the composite structure 100 mainly includes three plates: a bottom plate and a pair of side plates. Also in this case, similarly to the box type, it is possible to facilitate mold release and improve the joining strength.
The outer convexo-concave portion 16 may be omitted from the outer opposing surface 10b for the purpose of achieving facilitation of mold release. The same applies to the inner convexo-concave portion 26.
In the above embodiment, the outer convexo-concave portion 16 is provided on the entire sliding surface, but this is an example. The outer convexo-concave portion 16 may be provided only on a part of the sliding surface. The same applies to the inner convexo-concave portion 26.
In the above embodiment, as shown in Fig. 5B, the outer convexo-concave portion 16 is configured by arranging the plurality of convex portions 16a (or concave portions 16b) having the same shape, but this is an example. As illustrated in Fig. 5C, the plurality of convex portions 16a constituting the outer convexo-concave portion 16a may include a plurality of first convex portions 16a1 having a first protrusion height and a plurality of second convex portions 16a2 having a second protrusion height lower than the first protrusion height, and the first convex portions 16a1 and the second convex portions 16a2 may be formed on the outer surface 10a. In this case, the plurality of concave portions 16b formed in the outer opposing surface 10b includes a plurality of first concave portions 16b1 having a first depth corresponding to the first protrusion height and a plurality of second concave portions 16b2 having a second depth corresponding to the second protrusion height. The foam 30 can enter both the first concave portion 16b1 and the second concave portion 16b2. The first convex portion 16a1 slides on the mold 50, but the second convex portion 16a2 can be separated from the mold 50. Therefore, while the bonding strength of the foam 30 to the outer plate member 10 is maintained high, the contact area of the outer plate member 10 with the mold 50 is reduced, and the mold release can be further facilitated. As illustrated in Fig. 5D, the plate portion (for example, the first outer side plate portion 13) constituting the outer plate member 10 may be formed of a corrugated plate, whereby the outer convexo-concave portions 16 may be provided on both surface sides of the plate portion. When the wave has a sine curve shape, the convex portion 16a comes into point contact or line contact with the mold 50, and mold release can be facilitated. The same applies to the inner convexo-concave portion 26, and the inner convexo-concave portion 26 can be changed from that illustrated in Fig. 6B to that illustrated in Fig. 5C or 5D.
The present disclosure involves the following aspects:

(Aspect 1)

A composite structure comprising a bottom plate, and a pair of side plates erected from a side edge of the bottom plate, the composite structure comprising:

an outer plate member formed from metal and having an outer bottom plate portion constituting the bottom plate, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side thereof,
an inner plate member formed from metal and having an inner bottom plate portion constituting the bottom plate, an inner side plate portion constituting the pair of side plates, an inner surface of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side thereof, and
a foam molded from a foam material and filled between the outer opposing surface and the inner opposing surface,
wherein the outer plate member includes an outer convexo-concave portion provided on the outer surface, and the inner plate member includes an inner convexo-concave portion provided on the inner surface.

(Aspect 2)

The composite structure according to Aspect 1, wherein

the outer convexo-concave portion is provided on the outer opposing surface, the inner convexo-concave portion is provided on the inner opposing surface, and
the foam is engaged with the outer convexo-concave portion and the inner convexo-concave portion.

(Aspect 3)

The composite structure according to Aspect 2, wherein the outer convexo-concave portion and the inner convexo-concave portion are formed by arranging a plurality of concave portions or a plurality of convex portions.

(Aspect 4)

The composite structure according to any one of Aspects 1 to 3, further comprising a pair of second side plates erected from a side edge of the bottom plate, wherein
the pair of side plates and the pair of second side plates constitute a peripheral plate of a box body.

(Aspect 5)

A method for manufacturing a composite structure including a bottom plate and a pair of side plates erected from a side edge of the bottom plate, the method comprising the steps of:

forming, with metal, an outer plate member having an outer bottom plate portion constituting the bottom plate, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side;
forming, with metal, an inner plate member having an inner bottom plate portion constituting the bottom plate, an inner side plate portion constituting the pair of side plates, inner surfaces of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side;
internally fitting the outer plate member into a mold concave portion and externally fitting the inner plate member onto a mold convex portion when a mold including a first mold having the mold concave portion and a second mold having the mold convex portion is in a mold-open state in which the mold convex portion is retracted from the mold concave portion;
bringing the mold into a mold-closed state in which the mold convex portion has entered the mold concave portion;
filling a cavity formed between the outer opposing surface and the inner opposing surface with a foam material;
heating the foam material and molding a foam between the outer plate member and the inner plate member; and
bringing the mold into the mold-open state and taking out the composite structure from the mold,
wherein in the step of forming the outer plate member, an outer convexo-concave portion is provided on the outer surface, and in the step of forming the inner plate member, an inner convexo-concave portion is provided on the inner surface.

(Aspect 6)

The method for manufacturing a composite structure according to Aspect 5, wherein

the outer convexo-concave portion is provided on the outer opposing surface, and the inner convexo-concave portion is provided on the inner opposing surface, and
in the step of heating the foam material, the foam enters and is engaged with the outer convexo-concave portion and the inner convexo-concave portion.

(Aspect 7)

The method for manufacturing a composite structure according to Aspect 5 or 6, wherein
the outer convexo-concave portion and the inner convexo-concave portion are provided on a sliding surface with respect to the mold among the outer surface and the inner surface.

(Aspect 8)

The method for manufacturing a composite structure according to any one of Aspects 5 to 7, wherein

the step of forming the outer plate member includes a step of forming a flat blank having the outer bottom plate portion and the outer side plate portion in a developed state, and a step of bending the blank such that the outer side plate portion stands upright from the outer bottom plate portion, and
the outer convexo-concave portion is provided on the blank before the step of bending the blank.

This application claims benefit of priority based on to Japanese Patent Application No. 2023-206908 filed on December 7, 2023 , the entire content of which is incorporated herein by reference.

REFERENCE SIGNS LIST

1: bottom plate
2: peripheral plate
3: first side plate
4: second side plate
5: flange
6: internal space
10: outer plate member
10A: blank
10a: outer surface
10b: outer opposing surface
11: outer bottom plate portion
12: outer peripheral plate portion
13: first outer side plate portion
14: second outer side plate portion
15: lower flange portion
16: outer convexo-concave portion
16a: convex portion
16a1: first convex portion
16a2: second convex portion
16b: concave portion
16b1: first concave portion
16b2: second concave portion
20: inner plate member
20A: blank
20a: inner surface
20b: inner opposing surface
21: inner bottom plate portion
22: inner peripheral plate portion
23: first inner side plate portion
24: second inner side plate portion
26: inner convexo-concave portion
26a: convex portion
26b: concave portion
30: foam
30A: foam bead
30a: outer surface
30b: inner surface
31: middle bottom plate portion
32: middle peripheral plate portion
33: first middle plate portion
34: second middle plate portion
35: upper flange portion
50: mold
51: first mold
51A: mold concave portion
51a: first body portion
51b: shoulder portion
52: second mold
52A: mold convex portion
52a: second body portion
52b: flange portion
53: cavity
54: bead port
55: steam port
100: composite structure

Claims

A composite structure comprising a bottom plate, and a pair of side plates erected from a side edge of the bottom plate, the composite structure comprising:
an outer plate member formed from metal and having an outer bottom plate portion constituting the bottom plate, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side thereof,

an inner plate member formed from metal and having an inner bottom plate portion constituting the bottom plate, an inner side plate portion constituting the pair of side plates, an inner surface of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side thereof, and

a foam molded from a foam material and filled between the outer opposing surface and the inner opposing surface,

wherein the outer plate member includes an outer convexo-concave portion provided on the outer surface, and the inner plate member includes an inner convexo-concave portion provided on the inner surface.
The composite structure according to claim 1, wherein
the outer convexo-concave portion is provided on the outer opposing surface, the inner convexo-concave portion is provided on the inner opposing surface, and

the foam is engaged with the outer convexo-concave portion and the inner convexo-concave portion.
The composite structure according to claim 2, wherein the outer convexo-concave portion and the inner convexo-concave portion are formed by arranging a plurality of concave portions or a plurality of convex portions.
The composite structure according to any one of claims 1 to 3, further comprising a pair of second side plates erected from a side edge of the bottom plate, wherein
the pair of side plates and the pair of second side plates constitute a peripheral plate of a box body.
A method for manufacturing a composite structure including a bottom plate and a pair of side plates erected from a side edge of the bottom plate, the method comprising the steps of:
forming, with metal, an outer plate member having an outer bottom plate portion constituting the bottom plate, an outer side plate portion constituting the pair of side plates, an outer surface of the outer bottom plate portion and the outer side plate portion, and an outer opposing surface on an opposite side;

forming, with metal, an inner plate member having an inner bottom plate portion constituting the bottom plate, an inner side plate portion constituting the pair of side plates, inner surfaces of the inner bottom plate portion and the inner side plate portion, and an inner opposing surface on an opposite side;

internally fitting the outer plate member into a mold concave portion and externally fitting the inner plate member onto a mold convex portion when a mold including a first mold having the mold concave portion and a second mold having the mold convex portion is in a mold-open state in which the mold convex portion is retracted from the mold concave portion;

bringing the mold into a mold-closed state in which the mold convex portion has entered the mold concave portion;

filling a cavity formed between the outer opposing surface and the inner opposing surface with a foam material;

heating the foam material and molding a foam between the outer plate member and the inner plate member; and

bringing the mold into the mold-open state and taking out the composite structure from the mold,

wherein in the step of forming the outer plate member, an outer convexo-concave portion is provided on the outer surface, and in the step of forming the inner plate member, an inner convexo-concave portion is provided on the inner surface.
The method for manufacturing a composite structure according to claim 5, wherein
the outer convexo-concave portion is provided on the outer opposing surface, and the inner convexo-concave portion is provided on the inner opposing surface, and

in the step of heating the foam material, the foam enters and is engaged with the outer convexo-concave portion and the inner convexo-concave portion.
The method for manufacturing a composite structure according to claim 5 or 6, wherein
the outer convexo-concave portion and the inner convexo-concave portion are provided on a sliding surface with respect to the mold among the outer surface and the inner surface.
The method for manufacturing a composite structure according to claim 5 or 6, wherein
the step of forming the outer plate member includes a step of forming a flat blank having the outer bottom plate portion and the outer side plate portion in a developed state, and a step of bending the blank such that the outer side plate portion stands upright from the outer bottom plate portion, and

the outer convexo-concave portion is provided on the blank before the step of bending the blank.