Hollow structure, and method for manufacturing hollow structure

Abstract

To improve strength of a hollow structure capable of being coupled to another member, without increasing the number of components.SOLUTION: A plate-like hollow structure 10 has a core layer 21 in which a plurality of cells S are aligned, and a first skin layer 22 joined to one main surface of the core layer 21, wherein the core layer 21 is formed with a coupled recess 30 which is made of a material containing a thermoplastic resin and mounts a coupling member used for being coupled to another member, the coupled recess 30 has a first recess 31 which is recessed from one main surface side to the other main surface side, a first bottom wall 32a which is a bottom wall of the first recess 31 is formed of a compression part formed by compressing the core layer 21 in a thickness direction, and a first side wall 32b which is a side wall of the first recess 31 is formed of a first skin layer 22 extending toward the other main surface.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hollow structure and a method for manufacturing a hollow structure. [Background technology]

[0002] Since hollow structures made of thermoplastic resins are lightweight yet have appropriate rigidity, they are widely used in various fields such as vehicle interior materials, furniture, and building materials. Patent Document 1 describes an invention relating to a composite panel for vehicles in which a fiber-reinforced composite material is arranged on a base material made of a honeycomb structure or a foam structure. The composite panel is provided with a bolt mounting structure for mounting to a vehicle body. The bolt mounting structure is composed of a bush mounting hole formed in the composite panel and a bush member mounted in the bush mounting hole. The composite panel can be mounted to a vehicle by inserting a bolt into a bolt hole formed in the bush member. Here, the bush member acts to reinforce the composite panel, so that the tightening force of the bolt is suppressed from being directly transmitted as a compressive force to the composite panel. This suppresses deformation, etc. of the composite panel formed by stacking base materials made of a honeycomb structure or a foam structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-51224 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the need for reinforcing bushings increases the number of parts required to install the vehicle, which in turn increases costs and reduces workability during assembly. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides a plate-shaped hollow structure comprising a core layer in which a plurality of cells are arranged side by side, and a first skin layer joined to one main surface of the core layer, wherein the core layer is made of a material containing a thermoplastic resin, and a fastening recess is formed for attaching a fastening member used to fasten to another component, the fastening recess has a first recess recessed from one of the main surfaces to the other main surface, a first bottom wall which is the bottom wall of the first recess is formed by a compressed portion formed by compressing the core layer in the thickness direction, and a first side wall which is the side wall of the first recess is formed by the first skin layer extending toward the other main surface.

[0006] In the above configuration, it is preferable that the first side wall is formed as an inclined surface such that a cross-sectional area of ​​the first recess decreases toward the first bottom wall. In the above configuration, it is preferable that the core layer is provided with a second skin layer joined to the other main surface, the fastening recess has a second recess recessed from the other main surface side toward the first bottom wall, and a second side wall which is the side wall of the second recess is formed by the second skin layer extending toward the first bottom wall.

[0007] In the above configuration, it is preferable that the first recess comprises a recess main body formed on the first bottom wall side and an accommodating portion connected to the recess main body and formed on one of the main surfaces, and that the accommodating portion is formed capable of accommodating a head of a bolt as the fastening member.

[0008] In the above configuration, it is preferable that a through hole is formed in the first bottom wall, penetrating the core layer in a thickness direction. In order to solve the above problems, the present invention provides a method for manufacturing a hollow structure having a fastening recess for attaching a fastening member used to fasten to another component, the method comprising: a hollow plate forming process for forming a hollow plate having a core layer made of a material containing a thermoplastic resin and having a plurality of cells arranged in parallel, and a first skin layer joined to one main surface of the core layer; and a molding process for heating and pressing the hollow plate to form the fastening recess having a bottom wall and a side wall, in which the first skin layer is stretched toward the other main surface of the core layer and the core layer is compressed in the thickness direction to form the bottom wall formed by the compressed core layer and the side wall formed by the first skin layer extending toward the other main surface.

[0009] In the above configuration, it is preferable to further include a through hole forming step of forming a through hole in the bottom wall of the fastening recess. Effect of the Invention

[0010] According to the present invention, it is possible to improve the strength of a hollow structure that can be fastened to another member without increasing the number of parts. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a state in which the hollow structure of this embodiment is fastened to another member. [Diagram 2] FIG. 2 is a partial cross-sectional perspective view of the hollow structure. [Diagram 3] FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. [Figure 4] 4(a) to 4(c) are diagrams illustrating the structure of the hollow plate material. [Diagram 5] 5(a) to 5(c) are diagrams illustrating a method for manufacturing a hollow plate material. [Figure 6] FIG. 6 is a diagram illustrating a hollow structure in which a fastening recess is formed according to a modified example. [Figure 7] FIG. 7 is a diagram illustrating a hollow structure in which a fastening recess is formed according to a modified example. [Figure 8] FIG. 8 is a diagram for explaining another example of a state in which the hollow structure is used. [Figure 9] FIG. 9 is a diagram for explaining another example of a state in which the hollow structure is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a hollow structure 10 according to one embodiment of the present invention will be described. <About the hollow structure 10> As shown in Figures 1 and 2, the hollow structure 10 of this embodiment is a plate-like member made of a thermoplastic resin material. The hollow structure 10 is formed in a rectangular shape of approximately 450 mm x 300 mm. The hollow structure 10 has a hollow structure with a plurality of cells S arranged side by side inside. Figure 1 shows a state in which the hollow structure 10 is fastened to a plate member 51, which is another member.

[0013] The hollow structure 10 has a plurality of fastening recesses 30 for mounting fastening members 40 used for fastening to the plate member 51. The hollow structure 10 is a hollow plate material 20 described later in which the fastening recesses 30 are formed. In other words, the hollow plate material 20 refers to a plate-shaped member in which a plurality of cells S are arranged side by side, and the fastening recesses 30 are not formed, and the hollow structure 10 refers to the same plate-shaped member in which a plurality of fastening recesses 30 are formed. In addition, the surface of the hollow structure 10 on the side where the plate member 51 is fastened is referred to as the main surface 10b, and the surface on the opposite side is referred to as the main surface 10a. In FIG. 1, the size of the fastening recesses 30 is emphasized so that the position of the fastening recesses 30 can be easily seen.

[0014] 1 and 2, the multiple fastening recesses 30 all have the same shape and the same size. The fastening recesses 30 are formed as first recesses 31 having a shape recessed from the main surface 10a toward the main surface 10b. The first recesses 31 are formed in a circular shape when viewed from above. In the fastening recesses 30 of this embodiment, only the first recesses 31 are formed.

[0015] 2, the first recess 31 includes a recess body 32 having a truncated cone shape formed on the principal surface 10b side, and a storage section 33 connected to the recess body 32 on the principal surface 10a side. The recess body 32 includes a first bottom wall 32a on the principal surface 10b side, and a first side wall 32b extending from the first bottom wall 32a in the thickness direction of the hollow structure 10. The storage section 33 includes a mounting surface 33a on the principal surface 10b side, and a storage side wall 33b extending from the mounting surface 33a in the thickness direction of the hollow structure 10.

[0016] As shown in Fig. 2, the inner surface of the first side wall 32b is formed as an inclined surface in which the cross-sectional area when the recess body 32 is viewed from above gradually decreases toward the first bottom wall 32a. The first bottom wall 32a is formed in a flat shape extending parallel to the main surfaces 10a, 10b of the hollow structure 10. The outer surface of the first bottom wall 32a is formed flush with the main surface 10b of the hollow structure 10. A through hole 34 is formed in the center of the flat first bottom wall 32a, penetrating the first bottom wall 32a in the thickness direction. The through hole 34 is formed in a circular shape when viewed from above.

[0017] The accommodation portion 33 is formed with a larger diameter than the cross-sectional area of ​​the main surface 10a side of the recess body 32. As a result, the mounting surface 33a formed in the accommodation portion 33 is formed in a shape extending from an opening on the main surface 10a side of the recess body 32. The mounting surface 33a is formed as a flat surface extending parallel to the main surface 10a. The inner surface of the accommodation side wall 33b is formed as an inclined surface whose cross-sectional area when the accommodation portion 33 is viewed from above gradually decreases toward the mounting surface 33a.

[0018] 3, an R-shaped curved surface R1 is formed at the boundary between the first bottom wall 32a and the first side wall 32b of the recess main body 32. An R-shaped curved surface R2 is formed at the boundary between the first side wall 32b of the recess main body 32 and the mounting surface 33a of the storage section 33. An R-shaped curved surface R3 is formed at the boundary between the mounting surface 33a of the storage section 33 and the storage side wall 33b. The radius of curvature of the curved surface R2 and the radius of curvature of the curved surface R3 have a relationship of R2>R3.

[0019] 3, the hollow structure 10 of this embodiment is attached to a plate member 51 using a bolt 41 and a nut 42 as fastening members 40. At that time, the head 43 of the bolt 41 is accommodated in the accommodation portion 33. The placement surface 33a functions as a surface against which the lower surface of the head 43 of the bolt 41 abuts and is placed. In addition, the shaft portion 44 of the bolt 41 passes through the through hole 34, and the nut 42 is screwed onto the tip of the shaft portion 44.

[0020] The depth of the accommodation portion 33 in the thickness direction of the hollow structure 10 is formed to be approximately the thickness of the head portion 43 of the bolt 41. In addition, the opening diameter of the through hole 34 is formed to be slightly larger than the diameter of the shaft portion 44 of the bolt 41.

[0021] <About the hollow plate material 20> Next, the hollow plate material 20 that constitutes the hollow structure 10 will be described. As shown in Fig. 4(a), the hollow plate material 20 of this embodiment includes a core layer 21 having a plurality of cells S arranged side by side therein, a skin layer 22 joined to an upper surface 21a of the core layer 21, and a skin layer 23 joined to a lower surface 21b of the core layer 21. In the following description, the hollow plate material 20 and the core layer 21 will be described with the side to which the skin layer 22 is joined as the upper side and the side to which the skin layer 23 is joined as the lower side. In the hollow plate material 20 (hollow structure 10), the upper surface to which the skin layer 22 is joined is the main surface 10a, and the lower surface to which the skin layer 23 is joined is the main surface 10b.

[0022] As shown in Fig. 4(b), Fig. 4(c), and Fig. 5, the core layer 21 is formed by folding one sheet material 100 obtained by forming a thermoplastic resin sheet into a predetermined shape. The core layer 21 is composed of an upper wall portion 24, a lower wall portion 25, and a side wall portion 26 that is erected between the upper wall portion 24 and the lower wall portion 25 and forms a hexagonal cylindrical wall portion. The upper wall portion 24, the lower wall portion 25, and the side wall portion 26 define and form hexagonal columnar cells S inside the core layer 21. As described below, the upper wall portion 24 and the lower wall portion 25 of the core layer 21 have a structure in which a one-layer structure and a two-layer structure are mixed, but in Fig. 4(a), the upper wall portion 24 and the lower wall portion 25 of the core layer 21 are shown as a one-layer structure.

[0023] As shown in Figures 4(b) and 4(c), the cells S partitioned and formed inside the core layer 21 include a first cell S1 and a second cell S2 having different structures. As shown in Figure 4(b), in the first cell S1, a two-layered upper wall portion 24 is provided on the upper part of the side wall portion 26. The layers of this two-layered upper wall portion 24 are bonded to each other. In addition, an opening (not shown) is formed in the two-layered upper wall portion 24 due to thermal contraction of the thermoplastic resin during molding of the core layer 21. In the first cell S1, a one-layered lower wall portion 25 is provided on the lower part of the side wall portion 26.

[0024] On the other hand, as shown in Fig. 4(c), in the second cell S2, a single-layered upper wall 24 is provided on the upper part of the side wall 26. In the second cell S2, a two-layered lower wall 25 is provided on the lower part of the side wall 26. The layers of the two-layered lower wall 25 are bonded to each other. An opening (not shown) is formed in the two-layered lower wall 25 due to thermal contraction of the thermoplastic resin when the core layer 21 is molded.

[0025] 4(b) and 4(c), adjacent first cells S1 and adjacent second cells S2 are partitioned by sidewalls 26 having a two-layer structure. The two-layer sidewalls 26 have portions that are not heat-welded to each other in the center in the thickness direction of the core layer 21. Therefore, the internal space of each cell S of the core layer 21 communicates with the internal spaces of the other cells S through the two-layer sidewalls 26.

[0026] As shown in Fig. 4(a), the first cells S1 are arranged in a row along the X direction. Similarly, the second cells S2 are arranged in a row along the X direction. The rows of the first cells S1 and the rows of the second cells S2 are alternately arranged in the Y direction perpendicular to the X direction. The first cells S1 and the second cells S2 form a honeycomb structure as a whole in the core layer 21.

[0027] In the hollow plate material 20 of this embodiment, the core layer 21 and the skin layers 22, 23 are both made of only a thermoplastic resin. The thermoplastic resin may be any conventionally known thermoplastic resin, such as polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, etc. In this embodiment, the core layer 21 and the skin layers 22, 23 are made of polypropylene resin. The thermoplastic resin constituting the core layer 21 and the thermoplastic resin constituting the skin layers 22, 23 are preferably made of the same material. In addition, the thickness of the skin layers 22, 23 is preferably thicker than the thickness of the sheet material 100 forming the core layer 21. The thickness of the skin layer 22 and the skin layer 23 are preferably the same.

[0028] <Regarding the manufacturing method of the hollow plate material 20> Next, a method for manufacturing the hollow plate material 20 will be described. This corresponds to the hollow plate material forming step defined in the claims.

[0029] As shown in FIG. 5, the hollow plate material 20 is manufactured by forming a core layer 21 from one sheet material 100 and bonding skin layers 22 and 23 to the core layer 21. As shown in FIG. 5(a), the sheet material 100 is formed by molding one thermoplastic resin sheet into a predetermined shape. The sheet material 100 has band-shaped planar regions 110 and bulging regions 120 arranged alternately in the longitudinal direction (X direction) of the sheet material 100. In the bulging region 120, a first bulging portion 121 having a cross section of a downward groove shape consisting of an upper surface and a pair of side surfaces is formed over the entire extending direction (Y direction) of the bulging region 120. Note that the angle between the upper surface and the side surface of the first bulging portion 121 is preferably 90 degrees, and as a result, the cross section of the first bulging portion 121 is a downward U-shape. The width of the first bulging portion 121 (the length of the short side of the upper surface) is set to be equal to the width of the planar region 110 and twice the length of the bulging height of the first bulging portion 121 (the length of the short side of the side surface).

[0030] In addition, in the bulging region 120, a plurality of second bulging portions 122, each of which has a cross-sectional shape that is a trapezoid obtained by bisecting a regular hexagon at its longest diagonal, are formed so as to be perpendicular to the first bulging portion 121. The bulging height of the second bulging portion 122 is set to be equal to the bulging height of the first bulging portion 121. In addition, the interval between adjacent second bulging portions 122 is equal to the width of the upper surface of the second bulging portion 122.

[0031] The first bulging portion 121 and the second bulging portion 122 are formed by partially bulging the sheet upwards by utilizing the plasticity of the sheet. The sheet material 100 can be formed from a single sheet by a known forming method such as vacuum forming or compression forming.

[0032] As shown in Fig. 5(a) and Fig. 5(b), the sheet material 100 configured as described above is folded along the boundary lines P and Q to form the core layer 21. Specifically, the sheet material 100 is valley-folded at the boundary line P between the flat region 110 and the bulging region 120, and mountain-folded at the boundary line Q between the top surface and side surface of the first bulging portion 121 to compress in the X direction. Then, as shown in Fig. 5(b) and Fig. 5(c), the top surface and side surface of the first bulging portion 121 are folded over, and the end surface of the second bulging portion 122 and the flat region 110 are folded over, thereby forming one rectangular column-shaped partition 130 extending in the Y direction for one bulging region 120. Such partitions 130 are continuously formed in the X direction to form the hollow plate-shaped core layer 21.

[0033] When the sheet material 100 is compressed as described above, the upper wall portion 24 of the core layer 21 is formed by the upper surface and side surface of the first bulge portion 121, and the lower wall portion 25 of the core layer 21 is formed by the end surface of the second bulge portion 122 and the flat region 110. As shown in Fig. 5(c), the portion of the upper wall portion 24 where the upper surface and side surface of the first bulge portion 121 are folded over to form a two-layer structure, and the portion of the lower wall portion 25 where the end surface of the second bulge portion 122 and the flat region 110 are folded over to form a two-layer structure are overlapping portions 131.

[0034] Moreover, a hexagonal columnar region formed by folding the second bulging portion 122 becomes the second cell S2, and a hexagonal columnar region formed between a pair of adjacent partitions 130 becomes the first cell S1. In this embodiment, the upper surface and side surface of the second bulging portion 122 form the side wall portion 26 of the second cell S2, and the side surface of the second bulging portion 122 and a flat portion located between the second bulging portions 122 in the bulging region 120 form the side wall portion 26 of the first cell S1. The contact portion between the upper surfaces of the second bulging portions 122 and the contact portion between the flat portions in the bulging region 120 form the side wall portion 26 having a two-layer structure. Note that, when carrying out such a folding process, it is preferable to heat-treat the sheet material 100 so as to soften it.

[0035] Next, the skin layer 22 is superimposed on the upper surface of the core layer 21, and the skin layer 23 is superimposed on the lower surface of the core layer 21. The skin layers 22, 23 are preferably softened by heat treatment. By heat treating the skin layers 22, 23, the adhesive layer of thermoplastic resin coated on the skin layers 22, 23 is partially thermally melted. Therefore, the skin layers 22, 23 superimposed on the core layer 21 are positioned in a state where they are temporarily bonded to the core layer 21. The adhesive layer solidifies due to a decrease in temperature of the core layer 21 and the skin layers 22, 23, and the skin layers 22, 23 are bonded to the core layer 21 to form the hollow plate material 20.

[0036] <Regarding the manufacturing method of the hollow structure 10> Next, a method for manufacturing the hollow structural body 10 will be described. The manufacturing method of the hollow structure 10 includes a preparation step, a molding step, and a through-hole forming step. In the preparation step, the hollow plate material 20 is cut out to a predetermined size and shape. In the molding step, the cut out hollow plate material 20 is heated and pressed to form a plurality of fastening recesses 30 (first recesses 31). In the through-hole forming step, through holes 34 are formed in the first bottom wall 32a of the formed first recesses 31. In the manufacturing method of this embodiment, the molding step and the through-hole forming step are performed simultaneously.

[0037] In the preparation step, for example, the hollow plate material 20 is cut into a rectangular shape of about 500 mm×350 mm. In the cut hollow plate material 20, the internal spaces of the cells S are exposed at the peripheral end faces.

[0038] In the molding process and the through hole forming process, the hollow plate material 20 is heated and pressed in a metal mold. The metal mold has an upper mold and a lower mold. The upper mold has a recess of about 450 mm x 300 mm and a plurality of protrusions protruding from the bottom surface of the recess. The protrusions are the part that forms the first recess 31. That is, they are formed in a substantially truncated cone shape of the same shape and size as the first recess 31. In addition, a protrusion is formed on the tip surface of the protrusion for forming the through hole 34. On the other hand, the lower mold only has a recess of about 450 mm x 300 mm formed.

[0039] With the upper and lower dies heated, the cut hollow plate 20 is placed on the lower die. At this time, the hollow plate 20 is placed so that the skin layer 23 faces the lower die and the skin layer 22 faces the upper die. Also, the size of the recess formed in the die is about 450 mm x 300 mm, while the cut hollow plate 20 has a rectangular shape of about 500 mm x 350 mm, so the cut hollow plate 20 cannot be accommodated in the recess of the lower die. The cut hollow plate 20 is placed so that the peripheral edge of the cut hollow plate 20 hangs over the periphery of the recess of the lower die with an almost uniform width.

[0040] Next, the upper mold is moved toward the lower mold to close the mold. By closing the mold, a part of the hollow plate material 20 made of thermoplastic resin is heated and pressed to melt. In the part heated and pressed by the convex part of the upper mold, the core layer 21 of the hollow plate material 20 is compressed in the thickness direction, and the upper skin layer 22 is stretched toward the compressed part. The first recess 31 of the hollow structure 10 is formed in the part of the convex part and the protrusion of the upper mold. The compressed part of the core layer 21 becomes the first bottom wall 32a of the first recess 31, and the part where the skin layer 22 is stretched becomes the storage part 33 and the first side wall 32b of the first recess 31. In addition, a through hole 34 is formed in the center part of the first bottom wall 32a by the protrusion.

[0041] As shown in Figures 2 and 3, in the first bottom wall 32a where the compressed portion of the core layer 21 is formed, the compressed portion of the core layer 21 and the skin layers 22, 23 are integrated into a solid state. In the core layer 21 near the fastening recess 30, the side wall portion 26 may be in a buckled state due to the formation of the fastening recess 30. This is likely to occur when the hollow plate material 20 is heated in advance during the molding step and the through-hole forming step. Furthermore, the formation of the fastening recess 30 may cause a resin pool R to be formed only on the main surface 10a side of the hollow structure 10. This is likely to occur when the hollow plate material 20 is not heated during the molding step and the through-hole forming step.

[0042] The portion where the convex portion and the protrusion of the upper mold come into contact with the hollow plate material 20 first by the mold clamping is the portion that will become the first bottom wall 32a of the first recess 31. Therefore, in the portion pressed by the tip surface of the convex portion of the upper mold, the skin layer 22 is pressed and is not easily stretched. On the other hand, in the portion that will become the first side wall 32b of the recess body 32 of the first recess 31, the skin layer 22 is stretched by the pressure of the tip portion of the convex portion of the upper mold. The portion that will become the mounting surface 33a of the storage section 33 of the first recess 31 is the portion that is pressed by the convex portion of the upper mold following the tip portion of the convex portion of the upper mold, and the skin layer 22 is not easily stretched. In the portion that will become the storage side wall 33b of the storage section 33, the skin layer 22 is further stretched as the mounting surface 33a is formed. In this way, by pressing with the convex portion of the upper mold, the thickness of the skin layer 22 in the fastening recess 30 is in the relationship of "first bottom wall 32a of the recess body 32" > "first side wall 32b of the recess body 32" = "mounting surface 33a of the storage section 33" > "accommodation side wall 33b of the storage section 33". In addition, in the recess body 32, the relationship is "first bottom wall 32a of the recess body 32" > "first side wall 32b of the recess body 32". In the storage section 33, the relationship is "mounting surface 33a of the storage section 33" > "accommodation side wall 33b of the storage section 33". In the surface extending in the direction along the main surfaces 10a, 10b of the hollow structure 10, the relationship is "first bottom wall 32a of the recess body 32" > "mounting surface 33a of the storage section 33".

[0043] At the peripheral end of the hollow plate material 20, the core layer 21 is compressed in the compression direction at the peripheral portion of the recess. Also, the skin layer 22 is stretched toward the compressed portion, and the skin layer 23 is stretched toward the compressed portion.

[0044] Next, the compressed portion formed on the peripheral end face of the hollow plate material 20 is cut off, and post-processing is performed so that the peripheral end face of the hollow structure 10 becomes smooth. Through the above steps, the hollow structure 10 is molded. After the upper die is moved to open the die, the hollow structure 10 is taken out.

[0045] <Function of the hollow structure 10> As shown in FIG. 2, the hollow structure 10 is formed with a first recess 31 for mounting a bolt 41 and a nut 42 used for fastening to a plate member 51. The first recess 31 is formed by a molding process and a through-hole forming process. In the molding process, the hollow plate material 20 is heated and pressed by the convex part of the upper mold, whereby the thermoplastic resin is thermally melted and the core layer 21 is compressed in the thickness direction to form a first bottom wall 32a of the first recess 31. Since the first bottom wall 32a is formed by the compressed part of the core layer 21, the density of the thermoplastic resin material is higher than other parts other than the compressed part. The strength of the first bottom wall 32a is improved by the amount that the thermoplastic resin material is denser.

[0046] Furthermore, the thermally softened upper skin layer 22 is stretched toward the compressed portion to form the storage portion 33 and the first side wall 32b of the recess body 32. Since the hollow plate material 20 has a plurality of cells S arranged side by side, the hollow portions of the cells S are exposed when cut in the thickness direction. In this regard, in the first recess 31 in which the skin layer 22 is stretched to form the storage portion 33 and the first side wall 32b of the recess body 32, the hollow portions of the cells S are sealed and not exposed. The skin layer 22 is integrally continuous from the main surface 10a of the hollow structure 10 toward the first bottom wall 32a where the core layer 21 is compressed.

[0047] At the peripheral end face of the hollow plate material 20, the core layer 21 is compressed in the compression direction, and the skin layers 22, 23 are stretched toward the compressed portion. As a result, the peripheral end face of the hollow structure 10 is in a state where the skin layers 22, 23 are butted against each other with the compressed portion in between. The hollow portion of the cell S is covered and sealed by the skin layers 22, 23.

[0048] As shown in Fig. 3, in order to fasten the hollow structure 10 to the plate member 51, the position of the through hole 34 of the first recess 31 is aligned with the hole 52 previously formed in the plate member 51. In this state, the bolt 41 is inserted into the first recess 31 from the main surface 10a side of the hollow structure 10. The shaft portion 44 of the bolt 41 is inserted into the hole 52 from the through hole 34 of the first bottom wall 32a, and the nut 42 is screwed onto the shaft portion 44 of the bolt 41 protruding from the plate member 51 and tightened. When the nut 42 is tightened, the head 43 of the bolt 41 is accommodated in the accommodation portion 33 of the first recess 31, and the lower surface of the head 43 abuts against the mounting surface 33a of the accommodation portion 33.

[0049] Since the depth of the accommodation portion 33 is formed to be approximately the thickness of the head portion 43 of the bolt 41, the bolt 41 is accommodated in the accommodation portion 33 in a state in which the bolt 41 is prevented from protruding from the main surface 10a of the hollow structure 10. In addition, since the lower surface of the head portion 43 abuts against the mounting surface 33a, the movement of the bolt 41 in the axial direction is restricted. The movement of the bolt 41 in the axial direction and in the direction along the main surfaces 10a, 10b of the hollow structure 10 is restricted by the accommodation portion 33. The opening diameter of the through hole 34 is formed to be slightly larger than the diameter of the shaft portion 44 of the bolt 41. Therefore, the movement in the direction along the main surfaces 10a, 10b of the hollow structure 10 is restricted.

[0050] According to the hollow structural body 10 of this embodiment and the manufacturing method thereof, the following effects can be obtained. (1) The hollow structure 10 is formed with fastening recesses 30 for attaching bolts 41 and nuts 42 used for fastening to the plate member 51. The first bottom wall 32a of the first recess 31 serving as the fastening recess 30 is formed by a compressed portion in which the core layer 21 is compressed in the thickness direction. Therefore, the density of the thermoplastic resin material constituting the hollow structure 10 is increased in the first bottom wall 32a, and the strength of the first bottom wall 32a is improved.

[0051] Moreover, the first side wall 32b of the first recess 31 is formed by the skin layer 22 extending toward the main surface 10b. Therefore, the hollow portion of the cell S is sealed by the extended skin layer 22 (first side wall 32b).

[0052] In this way, due to the first bottom wall 32a formed by compressing the core layer 21 and the first side wall 32b formed by extending the skin layer 22, it is not necessary to separately attach a reinforcing member for fastening to the plate member 51 to the fastening recess 30. This makes it possible to reduce the number of parts required for reinforcement when fastening the hollow structure 10 and the plate member 51. This makes it possible to prevent an increase in costs and improve workability during assembly.

[0053] (2) The first side wall 32b is formed as an inclined surface such that the cross-sectional area of ​​the first recess 31 decreases toward the first bottom wall 32a. Therefore, the bolt 41 can be easily inserted into the first recess 31. (3) The first recess 31 includes a recess body 32 formed on the first bottom wall 32a side, and a storage section 33 connected to the recess body 32 and formed on the main surface 10a side. The storage section 33 is formed to have a larger diameter than the cross-sectional area of ​​the recess body 32 on the main surface 10a side. The depth of the storage section 33 is formed to be approximately the thickness of the head 43 of the bolt 41. Therefore, the storage section 33 can store the head 43 of the bolt 41, and the head 43 of the bolt 41 is prevented from protruding from the main surface 10a of the hollow structure 10. The fastened hollow structure 10 is prevented from getting caught, and the external shape when fastened is improved.

[0054] (4) The housing portion 33 is formed with a support surface 33a on which the head 43 of the bolt 41 is placed. Therefore, when the fastening member 40 is fastened, the lower surface of the head 43 abuts against the support surface 33a. This stabilizes the fastening state of the fastening member 40.

[0055] (5) The first bottom wall 32a has a through hole 34 penetrating through the core layer 21 in the thickness direction. This makes it easier to perform the fastening operation using the fastening member 40. (6) The hollow structure 10 includes a molding process in which the hollow plate material 20 is heated and pressed to form the fastening recesses 30. In the molding process, the skin layer 22 is stretched downward, and the core layer 21 is compressed in the thickness direction to form the first side wall 32b and the first bottom wall 32a. Therefore, by molding in a mold, the fastening recesses 30 having excellent strength can be formed at the same time as the hollow structure 10 is formed.

[0056] (7) A through hole forming process is provided for forming the through hole 34 in the first bottom wall 32a of the first recess 31. Therefore, the hollow structure 10 having the through hole 34 formed therein in advance is obtained. This improves the workability of the fastening portion with the plate member 51.

[0057] (8) The through-hole forming step of forming the through-holes 34 is performed simultaneously with the molding step by heating and pressing in a mold. Therefore, the through-holes 34 are easily formed. (9) In the through hole forming step, the through hole 34 is formed in the central portion of the flat first bottom wall 32a. Therefore, the processing work of the through hole 34 can be easily performed.

[0058] (10) In the molding process, the peripheral end surface of the hollow plate material 20 is covered by the compressed portion of the core layer 21 and the skin layers 22 and 23. This prevents the cells S from being exposed at the peripheral end surface of the hollow structure 10. In addition, the strength of the hollow structure 10 is improved by forming the compressed portion of the core layer 21 at the peripheral end surface.

[0059] The above embodiment can be modified as follows: The above embodiment and the following modified examples can be applied in combination with each other to the extent that there is no technical contradiction. In the hollow structure 10 of the above embodiment, the fastening recess 30 is formed only by the first recess 31. The shape of the fastening recess 30 is not limited to this. As shown in FIG. 6, the fastening recess 30 may be formed by the first recess 31 and the second recess 35. The second recess 35 is formed in a shape recessed from the main surface 10b of the hollow structure 10 toward the first bottom wall 32a of the first recess 31. In the second side wall 35b of the second recess 35, the skin layer 23 extends toward the main surface 10a. In addition, the second bottom wall 35a of the second recess 35 is common to the first bottom wall 32a of the first recess 31. When the first recess 31 and the second recess 35 are formed, the first bottom wall 32a (second bottom wall 35a) is located in the middle part in the thickness direction of the hollow structure 10. Therefore, when the first side wall 32b of the first recess 31 is an inclined surface, the opening area of ​​the recess body 32 of the first recess 31 can be reduced. This allows the mounting surface 33a of the housing portion 33 to be widened, and the head 43 of the bolt 41 can be made to engage with the mounting surface 33a with a large margin. Fastening by the fastening member 40 can be made stronger.

[0060] In order to form the fastening recess 30 in such a shape, a convex portion having the same shape and size as the second recess 35 may be formed in the lower mold at a position corresponding to the convex portion in the upper mold. 7, the through hole 34 does not have to be formed in the fastening recess 30 of the hollow structure 10. When fastening the hollow structure 10 to the plate member 51, the through hole 34 may be formed by a fastening member 40 such as a tapping screw.

[0061] In the hollow structure 10 of the above embodiment, the through hole 34 is formed in the center of the flat first bottom wall 32a. The position of the through hole 34 is not limited thereto. For example, the through hole 34 may be formed at the end of the curve R1 between the first bottom wall 32a and the first side wall 32b of the recess body 32 on the first bottom wall 32a side. If the through hole 34 is formed at this position, when the bolt 41 serving as the fastening member 40 is inserted, the tip of the shaft 44 of the bolt 41 is easily guided into the through hole 34, making it easier to insert the bolt 41.

[0062] In the first bottom wall 32a of the recess body 32 where the compressed portion of the core layer 21 is formed, the compressed portion of the core layer 21 and the skin layers 22, 23 are integrated into a solid state. The first bottom wall 32a may not be in a solid state, and a gap may be formed between the compressed portion of the core layer 21 and the skin layers 22, 23. Also, a fine gap may be formed in the compressed portion of the core layer 21.

[0063] The first recess 31 does not have to have the accommodation portion 33. In other words, the first recess 31 may be formed only by the recess body 32. When fastening with a bolt 41 and a nut 42, the peripheral portion of the opening of the first recess 31 on the main surface 10a of the hollow structure 10 becomes an engagement portion for the head 43 of the bolt 41.

[0064] The first side wall 32b does not have to be formed as an inclined surface. It may extend substantially perpendicular to the main surfaces 10a and 10b of the hollow structure 10. The first recess 31 does not have to be circular when viewed from above. For example, it may be hexagonal when viewed from above. The same is true for the second recess 35.

[0065] In the manufacturing method of the hollow structural body 10, the molding step and the through hole forming step may be performed separately. In this case, the molding step may be performed by using a convex portion of an upper mold that does not have a protrusion. The through hole 34 may be formed by a drill or the like, or may be formed by using a heated penetrating jig.

[0066] 8, the other member to which the hollow structural body 10 is fastened does not have to be the plate-shaped plate member 51 as in the above embodiment. For example, it may be a rectangular pillar member 53. As shown in FIG. 8, fastening to another member may be performed so that the main surface 10a side of the hollow structural body 10 faces the pillar member 53 side.

[0067] The fastening member 40 does not have to be a bolt 41 and a nut 42. For example, it may be a tapping screw. As shown in Fig. 8, the fastening member 40 may be fastened by screwing it into a column member 53 in which a fastening hole 54 is formed in advance.

[0068] 9, the hollow structure 10 may be fastened to a plate member 51 having a protrusion 55 formed thereon. In this case, the fastening recess 30 of the hollow structure 10 may be formed at a position corresponding to the protrusion 55 of the plate member 51. This makes the fastening to the plate member 51 stronger.

[0069] The core layer 21 does not have to be formed through a folding process in which the sheet material 100 is folded. The hollow structure 10 can be made of any hollow plate material known in the art.

[0070] In the hollow structure 10 of the above embodiment, the cells S having a hexagonal columnar shape are defined and formed inside the core layer 21, but the shape of the cells S is not limited to this. For example, the cells S may have a polygonal columnar shape such as a square columnar shape or an octagonal columnar shape, or a cylindrical shape.

[0071] At least one of the skin layers 22, 23 bonded to the hollow structure 10 may have a multi-layer structure instead of a single layer structure. For example, it may have a multi-layer structure including a low melting point film layer, a decorative layer with a printed pattern, a nonwoven fabric layer, etc.

[0072] The skin layer 23 may be omitted. In the hollow plate material 20 of the above embodiment, the core layer 21 and the skin layers 22, 23 are all made of only thermoplastic resin, but the materials are not limited to this. The material constituting the core layer 21 only needs to contain a thermoplastic resin. The material constituting the skin layers 22, 23 may be a thermosetting resin instead of a thermoplastic resin, or may be a fibrous material or a metal other than a thermoplastic resin.

[0073] The thermoplastic resin constituting the core layer 21 and the skin layers 22, 23 may contain various functional resins. For example, flame retardancy can be improved by adding a flame retardant resin to the thermoplastic resin. It is also possible to use thermoplastic resins containing various functional resins for all of the core layer 21 and the skin layers 22, 23, or to use a thermoplastic resin for at least one of the core layer 21 and the skin layers 22, 23.

[0074] The technical concepts that can be understood from the above embodiment and each of the modified examples will be described below. (i) A plate-shaped hollow structure made of thermoplastic resin comprising a core layer in which a plurality of cells are arranged side by side, and a first skin layer bonded to one main surface of the core layer, wherein a fastening recess is formed for attaching a fastening member to be used for fastening to another component, the fastening recess has a first recess recessed from one of the main surfaces to the other of the main surfaces, a first bottom wall which is the bottom wall of the first recess is formed by a compressed portion formed by compressing the core layer in the thickness direction, and a first side wall which is the side wall of the first recess is formed by the first skin layer extending toward the other of the main surfaces.

[0075] (b) The hollow structure according to (a) above, wherein the first side wall is formed as an inclined surface such that a cross-sectional area of ​​the first recess decreases toward the first bottom wall. (c) A hollow structure as described in (a) or (b) above, further comprising a second skin layer joined to the other main surface of the core layer, the fastening recess comprising a second recess recessed from the other main surface toward one of the main surfaces, a second bottom wall which is the bottom wall of the second recess being common to the first bottom wall and located in the middle part in the thickness direction of the core layer, and a second side wall which is the side wall of the second recess being formed by the second skin layer extending toward one of the main surfaces.

[0076] (ii) A hollow structure described in any one of (i) to (iii) above, characterized in that the first recess comprises a recess main body formed on the first bottom wall side and an accommodating portion connected to the recess main body and formed on one of the main surfaces, and the accommodating portion is formed to be capable of accommodating a head of a bolt as the fastening member.

[0077] (e) The hollow structural body according to any one of (a) to (d) above, wherein the first bottom wall has a through hole formed therein penetrating in a thickness direction of the core layer. [Explanation of symbols]

[0078] S: Cell 10...Hollow structure 10a, 10b...main surface 20…Hollow plate material 21…Core layer 22...Skin layer (first skin layer) 23...Skin layer (second skin layer) 30…Fastening recess 31...First recess (fastening recess) 32…Recessed body 32a...1st bottom wall 32b…First side wall 33…Storage section 33a...Placement surface 34...Through hole 35...Second recess (fastening recess) 35a…Second bottom wall 40...Fastening member 41...Bolt (fastening member) 42...Nut (fastening member) 51...Plate member (other member) 52...Column member (other member)

Claims

1. A plate-like hollow structure including a core layer in which a plurality of cells are arranged side by side, and a first skin layer joined to one main surface of the core layer, the core layer is made of a material containing a thermoplastic resin, A fastening recess is formed for attaching a fastening member used for fastening to another member, The fastening recess includes a first recess recessed from one of the main surfaces to the other of the main surfaces, a first bottom wall of the first recess is formed by a compressed portion in which the core layer is compressed in a thickness direction, A hollow structure, characterized in that a first side wall which is a side wall of the first recess is formed by the first skin layer extending toward the other main surface.

2. 2. The hollow structure according to claim 1, wherein the first side wall is formed as an inclined surface such that a cross-sectional area of ​​the first recess decreases toward the first bottom wall.

3. a second skin layer bonded to the other main surface of the core layer; The fastening recess has a second recess recessed from the other main surface side toward the first bottom wall, The hollow structure according to claim 2 , wherein a second side wall which is a side wall of the second recess is formed by the second skin layer extending toward the first bottom wall.

4. The first recess includes a recess body formed on the first bottom wall side, and a storage portion formed on one of the main surfaces and connected to the recess body, 2. The hollow structure according to claim 1, wherein the accommodating portion is formed so as to be capable of accommodating a head portion of a bolt as the fastening member.

5. 5. The hollow structure according to claim 1, wherein the first bottom wall is formed with a through hole penetrating in a thickness direction of the core layer.

6. A method for manufacturing a hollow structure having a fastening recess for attaching a fastening member used for fastening to another member, comprising: a hollow plate forming step of forming a hollow plate having a core layer made of a material containing a thermoplastic resin and having a plurality of cells arranged in parallel, and a first skin layer joined to one main surface of the core layer; and a molding step of heating and pressing the hollow plate material to form the fastening recess having a bottom wall and a side wall. A method for manufacturing a hollow structure, characterized in that in the molding process, the first skin layer is stretched toward the other main surface of the core layer and the core layer is compressed in the thickness direction to form the bottom wall in which the core layer is compressed and the side wall in which the first skin layer extends toward the other main surface.

7. The method for manufacturing a hollow structure according to claim 6, further comprising a through-hole forming step of forming a through-hole in the bottom wall of the fastening recess.

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