Sound-absorbing structure and manufacturing method thereof

Abstract

To improve sound absorption performance of a sound absorption structure in a low frequency region to stabilize the quality.SOLUTION: Provided is a method for manufacturing a sound absorption structure composed of a hollow plate material having a side wall part 23 extending in a thickness direction to partition a plurality of columnar cells S, and a pair of closing walls 11, 12 that close the cells on opposite ends of the side wall part 23, the method including: a side wall part communication hole forming step of sticking a penetration jig 51 into the side wall part 23 of the plurality of adjacent cells S to form a side wall part communication hole 15, and forming a communication cell group in which internal spaces of the plurality of cells S communicate with each other through the side wall part communication hole 15; and a closing wall communication hole forming step of sticking the penetration jig 51 into one of the closing walls 11, 12 of the cells S among the cells S constituting the communication cell group excluding at least one, to form a closing wall communication hole 13, and causing the inside and outside of the communication cell group to communicate with each other through the closing wall communication hole 13. The side wall part communication hole forming step and the closing wall communication hole forming step are performed in one step.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a sound absorbing structure and a method for manufacturing the same. [Background technology]

[0002] BACKGROUND ART Conventionally, a hollow plate-shaped sound absorbing structure has been known in which a plurality of cells each having a polygonal columnar or cylindrical shape are arranged side by side inside. Patent Document 1 describes an invention related to a vehicle floor panel for absorbing vehicle body vibrations generated when a high-speed train such as a Shinkansen travels, noise from the drive unit, and external noise transmitted from under the floor. The vehicle floor panel has a honeycomb structure with multiple cells formed between an upper panel and a lower panel. By forming multiple through holes in the side wall of the honeycomb structure, it is possible to improve sound absorption in the low-frequency range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4285598 Summary of the Invention [Problem to be solved by the invention]

[0004] The vehicle floor panel described in Patent Document 1 is manufactured as follows: First, a laminate is formed by stacking multiple thin plate materials to which adhesive is applied in linear patterns. Next, the laminate is cut to a predetermined width to form cell wall portions that will become the side walls of the honeycomb structure. Next, through holes are formed with a drill in the parts of the cell wall portions where no adhesive is applied. Then, the cell wall portions with the through holes are expanded to form a honeycomb structure with hexagonal cells. After that, an upper panel and a lower panel are joined to the honeycomb structure to obtain the vehicle floor panel.

[0005] As described above, the through holes in the vehicle floor panel described in Patent Document 1 are formed using a drill. This makes it easy for shavings to be generated during the process, and the shavings can get inside the vehicle floor panel. Furthermore, drilling is time-consuming and unsuitable for mass production. [Means for solving the problem]

[0006] In order to solve the above problems, the manufacturing method of the sound-absorbing structure of the present invention is a method for manufacturing a sound-absorbing structure made of a hollow plate material having side wall portions extending in the thickness direction and dividing a plurality of column-shaped cells, and a pair of blocking walls that block the cells at both ends of the side wall portions, and comprises a side wall portion communicating hole forming step of piercing a penetrating jig into the side wall portions of a plurality of adjacent cells to form side wall portion communicating holes, thereby forming a group of communicating cells in which the internal spaces of the plurality of cells are connected via the side wall portion communicating holes, and a block wall portion communicating hole forming step of piercing the penetrating jig into one of the blocking walls of the cells excluding at least one of the cells that make up the group of communicating cells to form a block wall communicating hole, thereby connecting the inside and outside of the group of communicating cells via the block wall communicating hole, and the side wall portion communicating hole forming step and the block wall communicating hole forming step are performed in a single step.

[0007] According to the above configuration, a penetrating jig is inserted into the side wall portion or the block wall to form the side wall portion communicating holes and the block wall communicating holes. Therefore, shavings are less likely to be generated from the hollow plate material during the process of forming the side wall portion communicating holes and the block wall communicating holes. A sound absorbing structure of stable quality can be obtained. In addition, the processing of the side wall portion communicating holes and the block wall communicating holes is less time-consuming. Furthermore, the side wall portion communicating hole forming process and the block wall communicating hole forming process are performed in a single process. Therefore, the side wall portion communicating holes and the block wall communicating holes can be processed in a short time. This improves the productivity of the sound absorbing structure, facilitating mass production.

[0008] In this sound-absorbing structure, sound waves enter the internal space of the communicating cell group through the closed wall communicating holes and are effectively attenuated in that internal space. That is, the sound-absorbing structure allows each communicating cell group to function as a Helmholtz resonator. A communicating cell group has a larger volume than a single cell because the internal spaces of multiple cells are connected via the sidewall communicating holes. Generally, the sound-absorbing characteristics of a Helmholtz resonator depend on the opening area of ​​the opening, the length of the tubular section that guides sound waves from the outside to the inside of the container, and the internal volume of the container. The longer the tubular section and the larger the internal volume of the container, the more sound waves are attenuated in the low-frequency range. The sound-absorbing structure of the present invention has a communicating cell group, which allows the "internal volume of the container" to be larger than that of a single cell. This improves the sound absorption coefficient in the relatively low-frequency range. This improves the productivity of sound-absorbing structures with excellent sound-absorbing performance in the low-frequency range.

[0009] In the above configuration, the device further includes a side wall portion communication hole enlarging process for increasing the opening area of ​​the side wall portion communication hole compared to the opening area of ​​the blocking wall communication hole, and in the side wall portion communication hole enlarging process, it is preferable to move the rod-shaped penetrating jig while it is inserted into the side wall portion and the blocking wall.

[0010] According to the above configuration, the internal spaces of the multiple cells that make up the communicating cell group can be connected by the side wall communicating holes, which have a larger opening area than the block wall communicating holes. Therefore, sound waves can easily enter the internal space of a cell in which a block wall communicating hole is formed into the internal space of an adjacent cell via the side wall communicating hole. Sound can be effectively absorbed throughout the internal spaces of the multiple cells that make up the communicating cell group. A sound-absorbing structure with excellent sound absorption performance can be obtained. Furthermore, the side wall communicating hole enlargement process is performed with a penetrating jig piercing the side wall and the block wall. Therefore, the opening area of ​​the side wall communicating hole can be easily increased.

[0011] In the above configuration, in the side wall portion communicating hole forming process and the blocking wall communicating hole forming process, it is preferable that the penetrating jig is inserted from the outside of the blocking wall of the cell that constitutes the communicating cell group in a direction inclined relative to the blocking wall.

[0012] According to the above configuration, the block wall communication hole and the block wall communication hole can be easily formed using a linear penetrating jig. In the above-described configuration, it is preferable that the hollow plate material is formed of a thermoplastic resin, and that a heated piercing jig is used in the side wall portion communicating hole forming step and the closing wall communicating hole forming step.

[0013] According to the above-described configuration, the side wall communicating holes and the closing wall communicating holes can be formed while the thermoplastic resin is being thermally melted, which makes it easier to form the side wall communicating holes and the closing wall communicating holes. In order to solve the above problems, the sound absorbing structure of the present invention is a sound absorbing structure made of a hollow plate material having side wall portions that extend in the thickness direction and partition a plurality of columnar cells, and a pair of closing walls that close the cells at both ends of the side wall portions, and has a communicating cell group made up of a plurality of adjacent cells and whose internal spaces are communicated by side wall portion communicating holes that penetrate the side wall portions, and in the cells excluding at least one of the cells that constitute the communicating cell group, a blocking wall communicating hole that penetrates the blocking wall is formed in one of the blocking walls, and the cells that constitute the communicating cell group When each of the adjacent pair of cells including the cell in which the block wall communicating hole is formed is defined as a specific cell, the block wall communicating hole formed in one of the specific cells is defined as a specific block wall communicating hole, and the side wall communicating hole formed in the side wall portion that separates the pair of specific cells is defined as a specific side wall communicating hole, a specific block wall return piece whose tip edge is located in the internal space of one of the specific cells is formed on the periphery of the specific block wall communicating hole, and a specific side wall return piece whose tip edge is located in the internal space of the other specific cell is formed on the periphery of the specific side wall communicating hole.

[0014] In the sound-absorbing structure having the above configuration, the specific block wall return piece of the specific block wall communicating hole formed in one of the pair of specific cells has its leading edge positioned in the internal space of that specific cell. Furthermore, the specific side wall return piece of the specific side wall communicating hole that separates the pair of specific cells has its leading edge positioned in the internal space of the other specific cell. Therefore, sound waves that enter the internal space of one specific cell can easily enter the internal space of the other specific cell. This facilitates attenuation of sound waves in the low-frequency range, improving the sound absorption coefficient in the low-frequency range. A sound-absorbing structure with excellent sound-absorbing performance in the low-frequency range can be obtained.

[0015] Furthermore, the shapes and arrangement of the leading edges of the specific block wall return piece and the specific side wall return piece are achieved when the specific block wall communicating hole and the specific side wall communicating hole are formed by piercing a penetrating jig from the outside of one of the specific cells. Therefore, in a sound-absorbing structure with the above configuration, shavings from the hollow plate material are less likely to remain inside. The quality of the sound-absorbing structure is stable.

[0016] In the above configuration, it is preferable that the specific blocking wall returning piece is inclined with respect to the thickness direction and extends toward the specific side wall portion communication hole. In the above configuration, it is preferable that the specific side wall return piece extends so as to be inclined with respect to the thickness direction.

[0017] According to the above-mentioned configuration, sound waves that have entered the internal space of one of the specific cells can easily enter the internal space of the other specific cell, thereby obtaining a sound-absorbing structure with excellent sound-absorbing performance in the low frequency range. [Effects of the Invention]

[0018] According to the present invention, a sound absorbing structure having excellent sound absorbing properties in the low frequency range and stable quality can be obtained. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. [Figure 2] This is a cross section taken along line β-β in Figure 1. [Figure 3] FIG. 2 is a cross-sectional view taken along the line γ-γ in FIG. [Figure 4] (a) is a perspective view of a sheet material constituting a core layer of a hollow plate material, (b) is a perspective view showing the sheet material in the middle of being folded, and (c) is a perspective view showing the sheet material in the folded state. [Figure 5] 10A to 10C are diagrams illustrating a block wall communication hole forming step, a side wall communication hole forming step, and a side wall communication hole enlarging step. [Figure 6] 10A and 10B are diagrams illustrating a block wall communicating hole and a side wall communicating hole. [Figure 7] FIG. 10 is an enlarged cross-sectional view of a sound absorbing structure according to a modified example. [Figure 8] FIG. 10 is an enlarged cross-sectional view of a sound absorbing structure according to a modified example. [Figure 9] 10A and 10B are diagrams illustrating a block wall communicating hole forming step and a side wall communicating hole forming step of a sound absorbing structure according to a modified example. [Figure 10] 10A and 10B are diagrams illustrating a block wall communicating hole forming step and a side wall communicating hole forming step of a sound absorbing structure according to a modified example. [Figure 11] 10A to 10C are diagrams illustrating a block wall communicating hole forming step, a side wall communicating hole forming step, and a side wall communicating hole enlarging step of a sound absorbing structure according to a modified example. [Figure 12] FIG. 10 is an enlarged cross-sectional view of a sound absorbing structure according to a modified example. [Figure 13] FIG. 10 is an enlarged cross-sectional view of a sound absorbing structure according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of a sound absorbing structure embodying the present invention will be described. As shown in FIG. 1, the sound-absorbing structure 1 of this embodiment is made of a hollow plate 10 having a plurality of hexagonal prism-shaped cells S arranged side by side inside. The hollow plate 10 is made of a conventionally known thermoplastic resin material. There are no particular restrictions on the material. Examples of such materials include polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, and acrylonitrile-butadiene-styrene.

[0021] <About the structure of sound absorbing structure 1> First, we will explain the structure of the hollow plate 10. The hollow plate 10 is a plate-like member of the sound-absorbing structure 1 in which the communication holes 13 and 15, which will be explained later, are not formed.

[0022] As shown in Fig. 1, the hollow board 10 is composed of a core layer 20 having a plurality of cells S arranged side by side therein, and sheet-like skin layers 30, 40 bonded to both thickness-wise surfaces of the core layer 20. In the following description, the main surface shown on the upper side of the hollow board 10 in Fig. 1 will be referred to as the upper surface 10a, and the main surface shown on the lower side will be referred to as the lower surface 10b. The skin layer 30 is bonded to the upper surface 10a of the hollow board 10, and the skin layer 40 is bonded to the lower surface 10b of the hollow board 10.

[0023] 1 to 4, the core layer 20 is formed by folding a single thermoplastic resin embossed sheet material 100 formed into a predetermined shape. The core layer 20 is composed of an upper wall portion 21, a lower wall portion 22, and side wall portions 23 that are erected between the upper wall portion 21 and the lower wall portion 22 and divide the cells S into a hexagonal columnar shape.

[0024] As shown in FIG. 1, the cells S formed within the core layer 20 include a first cell S1 and a second cell S2 having different configurations. 2, in the first cell S1, a two-layer upper wall portion 21 is provided on the upper part of the side wall portion 23. The layers of this two-layer upper wall portion 21 are joined to each other. In addition, in the first cell S1, a one-layer lower wall portion 22 is provided below the side wall portion 23.

[0025] As shown in Fig. 3, in the second cell S2, an upper wall portion 21 having a single layer structure is provided on the upper part of the side wall portion 23. In addition, in the second cell S2, a lower wall portion 22 having a two-layer structure is provided on the lower part of the side wall portion 23. The layers of this two-layer lower wall portion 22 are joined to each other. In addition, as shown in Figs. 2 and 3, adjacent first cells S1 and adjacent second cells S2 are each partitioned by a side wall portion 23 having a two-layer structure.

[0026] As shown in Fig. 1, the first cells S1 are arranged in rows along the X direction, and when viewed from above, two adjacent first cells S1 share one side of a hexagon. Similarly, the second cells S2 are arranged in rows along the X direction, and when viewed from above, two adjacent second cells S2 share one side of a hexagon. The rows of first cells S1 and the rows of second cells S2 are alternately arranged in the Y direction perpendicular to the X direction. The first cells S1 and second cells S2 form a honeycomb structure as a whole in the core layer 20.

[0027] As shown in Figures 1 to 3, the skin layer 30 is bonded to the upper surface of the core layer 20, so that the upper portions of the side wall portions 23 of the core layer 20 are blocked by the upper wall portions 21 of the core layer 20 and the skin layer 30. That is, the upper wall portions 21 and the skin layer 30 form an upper blocking wall 11 that separates the cells S from above. Similarly, the skin layer 40 is bonded to the lower surface of the core layer 20, so that the lower portions of the side wall portions 23 of the core layer 20 are blocked by the lower wall portions 22 of the core layer 20 and the skin layer 40. That is, the lower wall portions 22 and the skin layer 40 form a lower blocking wall 12 that separates the cells S from below.

[0028] The hollow plate material 10 has a shape in which a plurality of cells S are arranged side by side inside, with the core layer 20 and the skin layers 30 and 40. The upper closing wall 11 side of the hollow plate material 10 forms the upper surface 10a of the hollow plate material 10, and the lower closing wall 12 side of the hollow plate material 10 forms the lower surface 10b of the hollow plate material 10.

[0029] As shown in Fig. 1, the sound-absorbing structure 1 has a plurality of communication holes 13 formed in one main surface (top surface 10a) of a hollow plate material 10. In addition, communication holes 15 are formed in a plurality of side wall portions 23. The communication holes 13 are referred to as blocking wall communication holes in the claims, and the communication holes 15 are referred to as side wall communication holes in the claims.

[0030] As shown in Fig. 1, in the sound absorbing structure 1 of this embodiment, first cells S1 having communication holes 13 and first cells S1 having no communication holes 13 are arranged alternately in the X direction. Similarly, second cells S2 having communication holes 13 and second cells S2 having no communication holes 13 are arranged alternately in the X direction. As shown in Figs. 2 and 3, a communication hole 15 is formed in a side wall portion 23 that separates the first cell S1 having communication holes 13 from the first cell S1 having no communication holes 13. Similarly, a communication hole 15 is formed in a side wall portion 23 that separates the second cell S2 having communication holes 13 from the second cell S2 having no communication holes 13.

[0031] As shown in Figures 2 and 3, the communication hole 13 formed in the upper surface 10a penetrates the upper blocking wall 11 that blocks the upper side of the hollow plate material 10. In this embodiment, the communication hole 13 is formed in a circular shape when viewed from above. The communication hole 13 is formed in approximately the center of one cell S. The internal space of the cell S communicates with the external space of the sound-absorbing structure 1 via the communication hole 13. As shown in Figure 2, in the first cell S1, the communication hole 13 penetrates the two-layered upper wall portion 21 and skin layer 30. As shown in Figure 3, in the second cell S2, the communication hole 13 penetrates the single-layered upper wall portion 21 and skin layer 30. This allows the sound-absorbing structure 1 to function as a sound-absorbing material.

[0032] 2 and 3, a return piece 14 is formed on the periphery of each communication hole 13, extending at an angle with respect to the thickness direction of the sound absorbing structure 1. The tip edge of the return piece 14 is located in the internal space of the cell S. The return piece 14 has a cylindrical shape. The return piece 14 is the blocking wall return piece referred to in the claims.

[0033] As shown in Fig. 6, the opening at the tip edge of the cylindrical return piece 14 is wider than the opening at the base edge (the opening of the communication hole 13). In addition, in the return piece 14 that extends at an angle, the side at which the angle of inclination with the upper blocking wall 11 is smaller (the left side of the return piece 14 shown in Figs. 2 and 3) is shorter and thicker than the side at which the angle of inclination with the upper blocking wall 11 is larger (the right side of the return piece 14 shown in Figs. 2 and 3).

[0034] As shown in Fig. 6, the opening diameter L of each communication hole 13 is set to be equal to or less than the length of one side of the hexagon when the cell S is viewed from above. Specifically, when the average value of the distances between the centers of adjacent cells S in the X direction is defined as the "average pitch P1," it is preferable that the opening diameter L of each communication hole 13 be set to a fraction of the average pitch P1. The opening diameter L is preferably about 0.5 to 3 mm, and more preferably about 1.0 to 1.5 mm. When the opening diameter L is in this range, the sound absorption coefficient of the sound absorbing structure 1 can be increased.

[0035] 2 and 3, the communication holes 15 formed in the side wall portion 23 penetrate the side wall portion 23. The internal spaces of adjacent cells S communicate with each other via the side wall portion 23 in which the communication holes 15 are formed. A plurality of cells S whose internal spaces communicate with each other via the communication holes 15 will be referred to as a communicating cell group. The communicating cell group of this embodiment is formed by two cells S.

[0036] As shown in FIG. 2, in the first cell S1, the communication holes 15 are formed in the side wall portion 23, which has a two-layer structure and separates adjacent first cells S1. This forms a group of communicating cells consisting of two first cells S1. As shown in FIG. 3, in the second cell S2, the communication holes 15 are formed in the side wall portion 23, which has a two-layer structure and separates adjacent second cells S2. This forms a group of communicating cells consisting of two second cells S2. The position where the communication holes 15 are formed in the side wall portion 23 is located below the center position of the side wall portion 23 in the up-down direction. In other words, the lower portion of the side wall portion 23 is shorter than the upper portion of the communication holes 15.

[0037] Hereinafter, among the cells S constituting the communicating cell group, the cells S adjacent to each other via the communicating hole 15 may be referred to as specific cells SP. In the communicating cell group of this embodiment formed by two cells S, all of the cells S constituting the communicating cell group correspond to specific cells SP.

[0038] In this embodiment, the communication hole 15 is formed in an elliptical shape in a side view. As shown in Fig. 6, the communication hole 15 is formed on an imaginary line A along which the return piece 14 of the communication hole 13 formed in the blocking wall extends.

[0039] 2 and 3, a return piece 16 is formed on the periphery of each communication hole 15. The return piece 16 is the side wall return piece referred to in the claims. The communication hole 15 opens toward the specific cell SP in which the communication hole 13 is formed, out of the two specific cells SP that make up the communication cell group, and the tip edge of the return piece 16 is located in the internal space of the specific cell SP in which the communication hole 13 is not formed.

[0040] As shown in FIG. 6, the return piece 16 extends at an angle relative to the thickness direction of the sound absorbing structure 1 and also at an angle relative to the imaginary line A. The return piece 16 has a generally truncated cone shape with a larger diameter on the side of the specific cell SP where the communication holes 13 are not formed. Therefore, the opening at the tip edge of the return piece 16 is wider than the opening at the base edge (the opening of the communication hole 15). Furthermore, in the return piece 16 that extends at an angle, the side with a smaller inclination angle with the side wall portion 23 (the lower side of the return piece 16 shown in FIG. 6) is shorter and thicker than the side with a larger inclination angle with the side wall portion 23 (the upper side of the return piece 16 shown in FIG. 6). Furthermore, the side with a larger inclination angle with the side wall portion 23 has a larger amount of resin than the side with a smaller inclination angle with the side wall portion 23. The length of the return piece 16 is longer than the length of the return piece 14.

[0041] The communication hole 13 formed in one of the adjacent specific cells SP is the specific block wall communication hole referred to in the claims, and the return piece 14 is the specific block wall return piece referred to in the claims. Also, the communication hole 15 formed in the side wall portion 23 that partitions the specific cell SP is the specific side wall portion communication hole referred to in the claims, and the return piece 16 is the specific side wall portion return piece referred to in the claims. In the sound absorbing structure 1 of this embodiment, a communication cell group is formed by two cells S, so all of the cells S that make up the sound absorbing structure 1 are specific cells SP. Also, all of the communication holes 13 are specific block wall communication holes, and all of the return pieces 14 are specific block wall return pieces. Furthermore, the communication holes 15 at the end are specific side wall portion communication holes, and all of the return pieces 16 are specific side wall portion return pieces.

[0042] As shown in FIG. 6, the opening diameter M of each communication hole 15 is larger than the opening diameter L of each communication hole 13, and as a result, the opening area of ​​each communication hole 15 is larger than the opening area of ​​each communication hole 13. The opening diameter M of each communication hole 15 is approximately 1 / 3 to 2 / 3 of the vertical length of the side wall portion 23. The opening diameter M is preferably approximately 6 to 14 mm, and more preferably approximately 8 to 12 mm. The opening area of ​​each communication hole 15 is preferably approximately 5 to 20 times, and more preferably approximately 10 to 15 times, the opening area of ​​each communication hole 13. When the opening diameter M and opening area are within these ranges, sound waves can easily propagate between the specific cells SP, thereby increasing the sound absorption coefficient of the sound absorbing structure 1.

[0043] Next, a method for manufacturing the sound absorbing structure 1 will be described with reference to FIGS. The manufacturing method of the sound-absorbing structure 1 includes a molding process of forming an uneven sheet material 100 having a predetermined uneven shape from a single flat sheet material made of thermoplastic resin, a folding process of folding the uneven sheet material 100 to form a core layer 20, a joining process of joining skin layers 30, 40 to both main surfaces of the core layer 20 to form a hollow plate material 10, a side wall communicating hole forming process of forming communicating holes 15 in the hollow plate material 10, a blocking wall communicating hole forming process of forming communicating holes 13 in the hollow plate material 10, and a side wall communicating hole enlarging process of increasing the opening area of ​​the communicating holes 15 compared to the opening area of ​​the communicating holes 13.

[0044] As shown in FIG. 4(a), in the molding process, a single flat sheet material made of thermoplastic resin is molded into a predetermined shape to form a textured sheet material 100. The textured sheet material 100 has band-shaped flat regions 110 and bulging regions 120 alternately arranged in the longitudinal direction (X direction) of the textured sheet material 100. In the bulging region 120, a first bulging portion 121 having a downward groove-like cross section and consisting of an upper surface and a pair of side surfaces is formed over the entire extension 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, so that the cross section of the first bulging portion 121 has a downward U-shape. The width of the first bulging portion 121 (the length in the short direction of the upper surface) is set to be equal to the width of the flat region 110 and to be twice the bulging height of the first bulging portion 121 (the length in the short direction of the side surfaces).

[0045] 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 along its longest diagonal, are formed so as to be perpendicular to the first bulging portions 121. The bulging height of the second bulging portions 122 is set to be equal to the bulging height of the first bulging portions 121. The interval between adjacent second bulging portions 122 is equal to the width of the upper surface of the second bulging portions 122.

[0046] The textured sheet material 100 is formed by partially expanding a flat sheet material made of thermoplastic resin by utilizing its plasticity. The textured sheet material 100 can be formed from a single flat sheet material by a well-known forming method such as vacuum forming or compression forming.

[0047] As shown in FIGS. 4(a) and 4(b), in the folding process, the core layer 20 is formed by folding the textured sheet material 100 configured as described above along the boundary lines P and Q. Specifically, the textured 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, thereby compressing in the X direction. Then, as shown in FIGS. 4(b) and 4(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 is folded over with the flat region 110, thereby forming a rectangular columnar partition 130 extending in the Y direction for each bulging region 120. These partitions 130 are continuously formed in the X direction, thereby forming the hollow plate-like core layer 20. Note that in this embodiment, the direction in which the textured sheet material 100 is compressed for folding is the direction in which the cells S are arranged side by side (the X direction).

[0048] When the textured sheet material 100 is compressed as described above, the upper wall portion 21 of the core layer 20 is formed by the upper surface and side surface of the first bulge portion 121, and the lower wall portion 22 of the core layer 20 is formed by the end surface of the second bulge portion 122 and the flat region 110. As shown in Figure 4(c), the portion of the upper wall portion 21 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 22 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.

[0049] Furthermore, the hexagonal columnar region formed by folding the second bulge portion 122 becomes the second cell S2, and the 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 bulge portion 122 form the side wall portion 23 of the second cell S2, and the side surface of the second bulge portion 122 and the flat portion located between the second bulge portions 122 in the bulge region 120 form the side wall portion 23 of the first cell S1.

[0050] The abutting area between the flat portions in the bulging region 120 becomes the side wall portion 23 forming the two-layer structure of the first cell S1, and the abutting area between the upper surfaces of the second bulging portions 122 becomes the side wall portion 23 forming the two-layer structure of the second cell S2.

[0051] As shown in Figure 4(c), the first cell S1 has an upper portion defined by a pair of overlapping portions 131, and the second cell S2 has a lower portion defined by a pair of overlapping portions 131. When carrying out this folding process, it is preferable to heat-treat the textured sheet material 100 to soften it.

[0052] In the joining process, thermoplastic resin sheet materials are joined by heat welding to the upper and lower surfaces of the core layer 20 obtained in the folding process. The sheet material joined to the upper surface of the core layer 20 becomes the skin layer 30, and together with the upper wall portion 21 of the core layer 20, constitutes the upper closing wall 11 that closes the upper part of the side wall portion 23. The sheet material joined to the lower surface of the core layer 20 becomes the skin layer 40, and together with the lower wall portion 22 of the core layer 20, constitutes the lower closing wall 12 that closes the lower part of the side wall portion 23.

[0053] When the sheet material (skin layers 30, 40) is heat-sealed to the core layer 20, the two-layered upper wall portions 21 (overlapped portions 131) of the first cells S1 are heat-sealed to each other. Similarly, the two-layered lower wall portions 22 (overlapped portions 131) of the second cells S2 are heat-sealed to each other.

[0054] The joining step results in a hollow plate material 10 in which a large number of first cells S1 or second cells S2 are arranged in rows in the X direction and a large number of first cells S1 and second cells S2 are arranged alternately in the Y direction.

[0055] As shown in Figure 5, the side wall portion communicating hole forming process and the block wall communicating hole forming process are performed in a single process. A penetrating jig 50 for forming the communicating holes 13, 15 includes a penetrating member 51 in the form of a sharp-pointed rod with a circular cross section, and plate-like support members 52, 53 that support the penetrating member 51. The support member 52 supports the base end edge of the penetrating member 51. A hole 53a is formed in the support member 53. The penetrating member 51 is supported so as to be inclined relative to the support members 52, 53 while passing through the hole 53a. A plurality of penetrating members 51 are supported on the support members 52, 53. The plurality of penetrating members 51 are supported so as to be parallel to one another. The spacing between adjacent penetrating members 51 is approximately equal to twice the average pitch P1, which is the average value of the spacing between the centers of adjacent cells S.

[0056] In the side wall communicating hole forming process and the blocking wall communicating hole forming process, the hollow plate material 10 is placed on a table (not shown) below the penetrating jig 50. In this state, the upper surface 10a of the hollow plate material 10 is parallel to the support members 52 and 53. Furthermore, the penetrating jig 50 is lowered and the tip of the penetrating member 51 is positioned so that when it reaches the upper blocking wall 11 of the hollow plate material 10, the tip of the penetrating member 51 is positioned approximately in the center of one cell S. The penetrating member 51 is kept at room temperature without being heated.

[0057] As shown in Figure 5, the penetrating jig 50 is lowered toward the hollow plate 10, and the penetrating member 51 is thrust into the upper blocking wall 11 of the hollow plate 10. The penetrating member 51 thrust into the upper blocking wall 11 penetrates approximately the center of the upper blocking wall 11 of one cell S and descends while pushing the upper blocking wall 11 toward the inside of the cell S. Because the penetrating member 51 is supported at an angle relative to the support members 52 and 53, it thrusts in a direction that is inclined relative to the upper blocking wall 11. As a result, a communicating hole 13 that is circular in top view is formed approximately in the center of the upper blocking wall 11, and a cylindrical return piece 14 that extends toward the internal space of the cell S is formed around the periphery of the communicating hole 13.

[0058] The penetrating jig 50 is further lowered, and the penetrating member 51 is thrust into the side wall 23 of the hollow plate material 10. The penetrating member 51 thrust into the side wall 23 penetrates the adjacent side wall 23 and descends while pushing the side wall 23 toward the internal space of the adjacent cell S. Because the penetrating member 51 is supported at an angle relative to the support members 52, 53, it thrusts in a direction at an angle relative to the side wall 23. As a result, a communicating hole 15 that is approximately circular in side view is formed in the side wall 23, and a substantially cylindrical return piece 16 that extends toward the internal space of the adjacent cell S is formed around the periphery of the communicating hole 15.

[0059] In this way, a communicating cell group is formed in which the internal spaces of two adjacent cells are connected. One of the specific cells SP that make up the communicating cell group has a communicating hole 13 and a return piece 14 formed in the upper blocking wall 11. The other specific cell SP that makes up the communicating cell group does not have a communicating hole 13 or a return piece 14 formed in the upper blocking wall 11. In addition, the side wall portion 23 that separates the two specific cells SP that make up the communicating cell group has a communicating hole 15 and a return piece 16 that extends toward the internal space of the other specific cell SP.

[0060] As shown by the arrows in FIG. 5 , in the side wall portion communicating hole expanding step, with the penetrating member 51 piercing the upper blocking wall 11 and the side wall portion 23, the support members 52, 53 are reciprocated parallel to the upper blocking wall 11. As a result, as shown by the dotted lines in FIG. 5 , the penetrating member 51 moves up and down around the base end edge supported by the support member 52 as a fulcrum. Compared to the penetrating member 51 moving up and down in the communicating hole 15, which is farther from the base end edge of the penetrating member 51, the penetrating member 51 moves a greater distance up and down. Therefore, after the side wall portion communicating hole expanding step, the communicating hole 15 is expanded up and down, becoming an ellipse in side view. Furthermore, the barb 16 is also expanded up and down, becoming a generally truncated cone.

[0061] The penetrating jig 50 is moved upward, and the penetrating member 51 is pulled out from the hollow plate material 10 . Through the above steps, a group of communicating cells is formed that communicates with the external space via the communicating holes 13 and the return pieces 14, and that communicates with the internal spaces of the specific cells SP via the communicating holes 15 and the return pieces 16. In this way, a sound absorbing structure 1 having a plurality of communicating cell groups is manufactured.

[0062] Next, the effects of the sound absorbing structure 1 of this embodiment and the manufacturing method thereof will be described. (1) In the method for manufacturing the sound absorbing structure 1, the side wall communicating hole forming step and the blocking wall communicating hole forming step are performed in one step.

[0063] This makes it easy to process the communication holes 13, 15 and allows the communication holes 13, 15 to be formed in a short time, improving the productivity of the sound absorbing structure and facilitating mass production. (2) In the side wall communicating hole forming step and the blocking wall communicating hole forming step, the sharp-pointed penetrating member 51 is pierced through the upper blocking wall 11 and the side wall 23 to form the communicating holes 13, 15.

[0064] Therefore, compared to when holes are formed with a drill, shavings of the thermoplastic resin material derived from the hollow plate material 10 are less likely to be produced. This prevents shavings from remaining inside the sound-absorbing structure 1, resulting in a sound-absorbing structure 1 with stable quality. Furthermore, the processing for forming the communicating holes 13, 15 is easy, and the communicating holes 13, 15 can be formed in a short time.

[0065] (3) The penetrating member 51 is formed in a linearly extending, sharp-pointed rod shape. In the side wall portion communicating hole forming process and the blocking wall communicating hole forming process, the penetrating member 51 is inserted from the outside of the upper blocking wall 11 of a specific cell SP that constitutes the communicating cell group in a direction inclined relative to the upper blocking wall 11.

[0066] Therefore, the communication holes 13 and 15 can be easily formed in one step. (4) In the side wall portion communication hole enlarging step, the support members 52 and 53 are moved in a state in which the penetrating member 51 is pierced through the side wall portion 23 and the upper blocking wall 11.

[0067] Therefore, the opening area of ​​the communication hole 15 can be easily increased. (5) In the sound absorbing structure 1 of this embodiment, a communicating cell group is formed by two specific cells SP. In this sound absorbing structure 1, sound waves enter the internal space of the communicating cell group through the communicating holes 13 and are effectively attenuated in that internal space. In addition, in the communicating cell group, the internal spaces of the two specific cells SP are communicated with each other through the communicating holes 15.

[0068] Therefore, the sound absorbing structure can make each group of communicating cells function as a Helmholtz resonator. When functioning as a Helmholtz resonator, the "internal volume of the container" can be increased, thereby improving sound absorption performance in the low frequency range.

[0069] (6) In the communicating cell group, the communicating holes 13 are formed with return pieces 14, and the communicating holes 15 are formed with return pieces 16. Therefore, when functioning as a Helmholtz resonator, the "length of the tubular portion" can be increased, improving sound absorption performance in the low frequency range.

[0070] (7) The opening area of ​​the communication hole 15 is larger than the opening area of ​​the communication hole 15 . Therefore, sound waves can easily enter the internal space of one specific cell SP, in which the communicating hole 13 is formed, into the internal space of the other specific cell SP through the communicating hole 15. Also, the flow resistance of air flowing through the communicating cell group through the communicating hole 15 is smaller than the flow resistance of air entering the communicating cell group through the communicating hole 13. This allows sound to be effectively absorbed throughout the entire internal space of the multiple specific cells SP that make up the communicating cell group. This improves the sound absorption performance of the sound absorbing structure 1 in the low frequency range.

[0071] (8) The communication hole 15 is formed on an imaginary line A along which the return piece 14 of the communication hole 13 formed in the blocking wall extends. Therefore, sound waves that have entered the internal space of the specific cell SP in which the communication holes 13 are formed can easily enter the internal space of the specific cell SP in which the communication holes 13 are not formed. A sound-absorbing structure with excellent sound-absorbing performance in the low frequency range is obtained.

[0072] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0073] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the opening area of ​​the communication hole 15 is made larger than the opening area of ​​the communication hole 13 in the side wall communication hole enlarging step, but the side wall communication hole enlarging step may be omitted. After the blocking wall communication hole forming step and the side wall communication hole forming step are performed in a single step, the penetrating jig 50 can be retracted.

[0074] 7, the opening area of ​​communication hole 13 and the opening area of ​​communication hole 15 are approximately the same. Barb pieces 14 and 16 are formed to extend along imaginary line A. Imaginary line A corresponds to the movement trajectory of the tip of penetrating member 51.

[0075] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the penetrating member 51 is not heated, but the penetrating member 51 may be heated. In this case, the formed communicating holes 13, 15 and return pieces 14, 16 have the shapes shown in FIG. 8. Specifically, the heated penetrating member 51 thermally melts the thermoplastic resin material. As the penetrating member 51 descends, the thermally melted thermoplastic resin material rises around the communicating holes 13, 15 as if being extruded. As the thermoplastic resin material cools, resin pools are formed on both the inner and outer surfaces of the upper blocking wall 11 of the communicating hole 13 and on both surfaces of the side wall portions 23 of the communicating hole 15. In this case, the return pieces 14, 16 are formed as shown in FIG. 8, and the return pieces 14, 16 extend in a direction following the movement trajectory of the tip of the penetrating member 51.

[0076] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the penetrating member 51 is inserted into two cells S to form a group of communicating cells consisting of two cells S. As shown in FIG. 9, the inclination angle of the penetrating member 51 may be made steeper to form a group of communicating cells consisting of three or more cells S.

[0077] When the interconnected cell group is formed of three or more cells S, the cells S do not necessarily have to be arranged side by side in a straight line, but may also be arranged side by side in an arc. In the above embodiment, the spacing between adjacent penetrating members 51 is approximately equal to twice the average pitch P1, which is the average value of the spacing between the centers of adjacent cells S, but it may be shorter or longer. For example, as shown in FIG. 10, the spacing between three adjacent penetrating members 51 may be approximately equal to the average pitch P1. In this case, three adjacent penetrating members 51 at the average pitch P1 may be grouped together, and the spacing between each group may be multiple times the average pitch P1. This results in a communicating cell group being formed from four cells S, and communicating holes 13 being formed in three of the cells S.

[0078] In the above embodiment, a straight penetrating member 51 of the penetrating jig 50 is used, but a curved one may also be used. The penetrating member 61 in FIG. 11 is formed as a curved, pointed rod, with the tip and base extending in directions perpendicular to each other. In this case, as shown in the cell S on the left side of FIG. 11 , the tip of the penetrating member 61 is inserted into the upper blocking wall 11 at a substantially right angle. As shown in the cell S in the middle of FIG. 11 , as the penetrating member 61 is lowered, it moves around in the internal space of the cell S. When the tip of the curved penetrating member 61 reaches the side wall 23, it is further lowered, and the tip of the penetrating member 61 penetrates the side wall 23. A communication hole 13 is formed in the upper blocking wall 11, and a communication hole 15 is formed in the side wall 23. Next, as shown in the cell S on the right side of FIG. 11 , the penetrating member 61 is moved vertically.

[0079] As shown in Figure 12, in the sound absorbing structure 1 formed by this process, the return pieces 14, 16 are formed so as to follow the curved imaginary line B. Furthermore, the opening area of ​​the communication hole 15 formed in the side wall portion 23 is larger than the opening area of ​​the communication hole 13 formed in the upper blocking wall 11. Of the pair of specific cells SP that make up the communicating cell group, the leading edge of the return piece 14 is located in the internal space of one of the specific cells SP in which the communication hole 13 is formed. Furthermore, the leading edge of the return piece 16 is located in the internal space of the other specific cell SP.

[0080] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the skin layers 30, 40 are joined to the core layer 20 by thermal welding, but the method of joining the skin layers 30, 40 is not limited to this. For example, the skin layers 30, 40 may be joined to the core layer 20 by attaching them with an adhesive or the like. Alternatively, an adhesive layer made of, for example, a thermoplastic resin may be interposed between the core layer 20 and the skin layers 30, 40, and the skin layers 30, 40 may be joined to the core layer 20 by the adhesive strength of this adhesive layer.

[0081] All of the cells S that make up the sound absorbing structure 1 do not have to form a group of interconnected cells. Some of the cells S do not have to be interconnected with other cells S. The cells S constituting the communicating cell group may have a common specific cell SP. For example, as shown in FIG. 13, if three cells S are connected by a communicating hole 15, the communicating cell group is composed of these three cells S. The cells S constituting the communicating cell group are designated Sa, Sb, and Sc. Cell Sa having a communicating hole 13 formed therein and cell Sb adjacent to cell Sa correspond to the specific cell SP referred to in the claims. The leading edge of the flap piece 14 formed on cell Sa is located in the internal space of cell Sa, and the leading edge of the flap piece 16 formed on the side wall portion 23 separating cell Sa from cell Sb is located in the internal space of cell Sb. Meanwhile, cell Sc having a communicating hole 13 formed therein and cell Sb adjacent to cell Sc also correspond to the specific cell SP referred to in the claims. The leading edge of the flap piece 14 formed on cell Sc is located in the internal space of cell Sc, and the leading edge of the flap piece 16 formed on the side wall portion 23 separating cell Sc from cell Sb is located in the internal space of cell Sb.

[0082] In this way, some of the cells S constituting the communicating cell group may include cells S (cells Sb in FIG. 13) in which a plurality of communicating holes 15 are formed with return pieces 16 facing in different directions. The communicating hole 13 does not have to be circular in top view, and the communicating hole 15 does not have to be elliptical in side view. Similarly, the return piece 14 does not have to be cylindrical, and the return piece 16 does not have to be substantially truncated cone. The shapes of the communicating holes 13, 15 and the return pieces 14, 16 can be changed depending on the cross-sectional shape of the penetrating members 51, 61. For example, the penetrating members 51, 61 may have a rectangular cross-section.

[0083] The shapes of the communicating holes 13 do not all have to be the same. For example, the shapes of multiple communicating holes 13 may be different. Similarly, the shapes of the communicating holes 15 do not all have to be the same, but may be different from each other. By having communicating holes 13, 15 with different shapes or by having return pieces 14, 16 with different shapes, the range of low-frequency frequencies that can be absorbed may be broadened, potentially improving sound absorption in the low-frequency range.

[0084] In the hollow plate 10 of the above embodiment, the cells S are partitioned and formed in a hexagonal column shape inside the core layer 20, but the shape of the cells S is not particularly limited. For example, the cells S may be polygonal, such as a square column or an octagonal column, or cylindrical. The cells S may also be frustoconical. In this case, cells of different shapes may be mixed. The cells S may also be made of plastic cardboard with a harmonica-shaped cross section.

[0085] In the hollow plate material 10 of the above embodiment, the skin layers 30, 40 are bonded to both sides of the core layer 20, but at least one of the skin layers 30, 40 may be omitted. When the skin layer 30 is omitted, the upper blocking wall 11 is formed only by the upper wall portion 21 of the core layer 20. When the skin layer 40 is omitted, the lower blocking wall 12 is formed only by the lower wall portion 22 of the core layer 20.

[0086] In the cells S in which the communication hole 13 is formed, one communication hole 13 is formed in approximately the center of each cell S, but the location and number of communication holes 13 are not limited to this. For example, the communication holes 13 may be formed in different positions in each cell S. Furthermore, the communication holes 13 may be formed in one or more places in each cell S.

[0087] In the above embodiment, the communication holes 13 are formed at a constant pitch and are formed in approximately the center of each cell S, but the positions at which the communication holes 13 are formed do not have to be constant. For example, the pitch of the cells S may not be constant due to deformation during molding of the hollow plate material 10, and in such cases, the positions of the communication holes 13 will differ depending on the cell S. Specifically, the communication holes 13 may be located in the center or at the edge of the cell S.

[0088] Another sheet material may be bonded to the outer surface of the hollow plate 10 on the skin layer 40 side. This sheet material is not limited to synthetic resin, but may be, for example, a metal sheet (metal foil), steel plate, paper, cloth, etc. Furthermore, the skin layer 40 itself may be made of a metal sheet (metal foil), paper, cloth, etc.

[0089] Resins or additives that impart functionality may be added to the thermoplastic resin that constitutes the hollow plate material 10. For example, flame-retardant resins or additives, or deodorizers or fragrances may be added.

[0090] The technical ideas that can be understood from the above-described embodiment and modified examples will be described. (A) A method for manufacturing a sound-absorbing structure made of a hollow plate material having side walls extending in the thickness direction to partition a plurality of columnar cells and a pair of blocking walls blocking the cells at both ends of the side walls, the method comprising the steps of: piercing a penetrating jig into the side walls of a plurality of adjacent cells to form side wall communicating holes, thereby forming a group of communicating cells in which the internal spaces of the plurality of cells are communicated through the side wall communicating holes; and inserting the penetrating jig into one of the blocking walls of the cells except for at least one of the cells constituting the group of communicating cells. The method comprises a block wall communication hole forming process in which a penetrating jig is inserted to form a block wall communication hole, thereby connecting the inside and outside of the communication cell group through the block wall communication hole, and a side wall communication hole enlarging process in which the opening area of ​​the side wall communication hole is increased compared to the opening area of ​​the block wall communication hole, and the side wall communication hole forming process and the block wall communication hole forming process are performed in a single process, and in the side wall communication hole enlarging process, the rod-shaped penetrating jig is inserted into the side wall and the block wall, and the penetrating jig is moved using an end located outside the block wall as a fulcrum.

[0091] (b) A method for manufacturing a sound-absorbing structure made of a hollow plate material having side walls extending in a thickness direction to partition a plurality of columnar cells and a pair of closing walls that close the cells at both ends of the side walls, the method comprising: a side wall communicating hole forming step of piercing a penetrating jig into the side walls of a plurality of adjacent cells to form side wall communicating holes, thereby forming a group of communicating cells in which the internal spaces of the plurality of cells are communicated through the side wall communicating holes; and a step of closing one of the closing walls of the cells excluding at least one of the cells that make up the group of communicating cells. and a side wall portion communicating hole expanding process for increasing the opening area of ​​the side wall portion communicating hole compared to the opening area of ​​the block wall portion communicating hole. The side wall portion communicating hole forming process and the block wall portion communicating hole forming process are performed in a single process, and in the side wall portion communicating hole expanding process, the rod-shaped penetrating jig is inserted into the side wall portion and the block wall, and the penetrating jig is moved in a direction perpendicular to the block wall. [Explanation of symbols]

[0092] S...cell S1...1st cell (cell) S2...Second cell (cell) SP...Specific cell (cell) 1...Sound-absorbing structure 10...Hollow plate material 11...Upper blocking wall (blocking wall) 12…Lower blocking wall (blocking wall) 13…Communication hole (blocking wall communication hole) 14...Return piece (blocking wall return piece) 15...Communication hole (side wall communication hole) 16...Return piece (side wall return piece) 23...Side wall 50...Penetration jig 51, 61...Penetrating member (penetrating jig)

Claims

1. A method for manufacturing a sound-absorbing structure made of a hollow plate material having side wall portions extending in a thickness direction to define a plurality of columnar cells, and a pair of closing walls at both ends of the side wall portions to close the cells, comprising: a side wall portion communicating hole forming step of forming side wall portion communicating holes by piercing a penetrating jig into the side wall portions of a plurality of adjacent cells to form a group of communicating cells in which internal spaces of the plurality of cells are communicated with each other via the side wall portion communicating holes; a block wall communication hole forming step of piercing the penetrating jig into one of the block walls of the cells excluding at least one of the cells constituting the communicating cell group to form a block wall communication hole, thereby communicating the inside and outside of the communicating cell group through the block wall communication hole; Equipped with a sound-absorbing structure manufacturing method, characterized in that the side wall portion communicating hole forming step and the closing wall communicating hole forming step are carried out in a single step;

2. a side wall portion communicating hole enlarging step of enlarging an opening area of ​​the side wall portion communicating hole compared to an opening area of ​​the block wall communicating hole, 2. The method for manufacturing a sound-absorbing structure according to claim 1, wherein in the side wall portion communicating hole expanding process, the rod-shaped penetrating jig is moved while being pierced into the side wall portion and the blocking wall.

3. A method for manufacturing a sound-absorbing structure as described in claim 1 or 2, characterized in that in the side wall portion communicating hole forming process and the blocking wall communicating hole forming process, the penetrating jig is inserted from the outside of the blocking wall of the cell that constitutes the communicating cell group in a direction inclined relative to the blocking wall.

4. the hollow plate is made of a thermoplastic resin; The method for manufacturing a sound-absorbing structure according to any one of claims 1 to 3, characterized in that a heated piercing jig is used in the side wall portion communicating hole forming process and the blocking wall communicating hole forming process.

5. A sound-absorbing structure made of a hollow plate material having a side wall portion extending in a thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls at both ends of the side wall portion that close the cells, a group of communicating cells formed by a plurality of adjacent cells, the internal spaces of which are communicated by side wall communicating holes penetrating the side wall; In the cells excluding at least one of the cells constituting the communicating cell group, a block wall communication hole penetrating the block wall is formed in one of the block walls, When each of the adjacent pair of cells including the cell in which the block wall communicating hole is formed among the cells constituting the communicating cell group is defined as a specific cell, the block wall communicating hole formed in one of the specific cells is defined as a specific block wall communicating hole, and the side wall communicating hole formed in the side wall portion that separates the pair of specific cells is defined as a specific side wall communicating hole, a specific block wall return piece whose leading edge is located in the internal space of one of the specific cells is formed on the periphery of the specific block wall communicating hole, and a specific side wall return piece whose leading edge is located in the internal space of the other specific cell is formed on the periphery of the specific side wall communicating hole, the specific blocking wall return piece is inclined with respect to the thickness direction and extends toward the specific side wall portion communication hole, The specific side wall portion return piece extends so as to be inclined with respect to the thickness direction, A sound absorbing structure, characterized in that the opening diameter of the side wall portion communicating hole is larger than the opening diameter of the closing wall communicating hole.

6. A sound-absorbing structure made of a hollow plate material having side wall portions extending in the thickness direction to partition a plurality of columnar cells, and a pair of blocking walls that block the cells at both ends of the side wall portions, a group of communicating cells formed by a plurality of adjacent cells, the internal spaces of which are communicated by side wall communicating holes penetrating the side wall; In the cells excluding at least one of the cells constituting the communicating cell group, a block wall communication hole penetrating the block wall is formed in one of the block walls, When each of the adjacent pair of cells including the cell in which the block wall communicating hole is formed among the cells constituting the communicating cell group is defined as a specific cell, the block wall communicating hole formed in one of the specific cells is defined as a specific block wall communicating hole, and the side wall communicating hole formed in the side wall portion that separates the pair of specific cells is defined as a specific side wall communicating hole, a specific block wall return piece whose leading edge is located in the internal space of one of the specific cells is formed on the periphery of the specific block wall communicating hole, and a specific side wall return piece whose leading edge is located in the internal space of the other specific cell is formed on the periphery of the specific side wall communicating hole, the specific blocking wall return piece is inclined with respect to the thickness direction and extends toward the specific side wall portion communication hole, The specific side wall portion return piece extends so as to be inclined with respect to the thickness direction, A sound absorbing structure characterized in that the other specific cell does not have the specific blocking wall communicating hole formed therein.

7. A sound-absorbing structure made of a hollow plate material having a side wall portion extending in a thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls at both ends of the side wall portion that close the cells, a group of communicating cells formed by a plurality of adjacent cells, the internal spaces of which are communicated by side wall communicating holes penetrating the side wall; In the cells excluding at least one of the cells constituting the communicating cell group, a block wall communication hole penetrating the block wall is formed in one of the block walls, When each of the adjacent pair of cells including the cell in which the block wall communicating hole is formed among the cells constituting the communicating cell group is defined as a specific cell, the block wall communicating hole formed in one of the specific cells is defined as a specific block wall communicating hole, and the side wall communicating hole formed in the side wall portion that separates the pair of specific cells is defined as a specific side wall communicating hole, a specific block wall return piece whose leading edge is located in the internal space of one of the specific cells is formed on the periphery of the specific block wall communicating hole, and a specific side wall return piece whose leading edge is located in the internal space of the other specific cell is formed on the periphery of the specific side wall communicating hole, The specific blocking wall return piece extends along a straight virtual line so as to be inclined with respect to the thickness direction, The sound-absorbing structure is characterized in that the specific side wall portion communication hole extends in the same straight line as the imaginary line so as to be inclined with respect to the thickness direction.

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