JP2023068931A - Sound absorption structure and manufacturing method thereof - Google Patents

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

The present invention relates to a sound absorbing structure and its manufacturing method.

2. Description of the Related Art Conventionally, there has been known a sound absorbing structure in the form of a hollow plate in which a plurality of polygonal prismatic or cylindrical cells are arranged side by side.
Patent Document 1 describes an invention relating to a vehicle floor plate for absorbing vehicle body vibration, noise from a driving device, external noise transmitted from under the floor, etc. generated when a vehicle such as a Shinkansen runs at high speed. A floor plate for a vehicle is provided with a honeycomb structure in which a plurality of cells are formed between an upper plate and a lower plate. By forming a plurality of through-holes in the side walls of the honeycomb structure, it is possible to improve sound absorption in a low-frequency range.

Japanese Patent No. 4285598

The vehicle floor plate described in Patent Document 1 is manufactured as follows. First, a laminate is formed by laminating a plurality of thin plate materials to which an adhesive is linearly applied. Next, the laminate is cut into a predetermined width to form cell wall portions that will be side wall portions of the honeycomb structure. Subsequently, a through hole is formed by a drill in a portion of the cell wall portion where the adhesive is not applied. Then, a honeycomb structure in which hexagonal cells are formed is formed by expanding the cell wall portion in which the through holes are formed. After that, the honeycomb structure is joined to the upper surface plate and the lower surface plate to obtain the vehicle floor plate.

In this way, the vehicle floor plate described in Patent Document 1 forms the through-holes with a drill. Therefore, shavings are likely to be generated during work, and the shavings may enter the interior of the vehicle floor plate. In addition, drilling is time-consuming and not suitable for mass production.

In order to solve the above-mentioned problems, the method for manufacturing a sound absorbing structure of the present invention includes a pair of side walls extending in the thickness direction and partitioning a plurality of columnar cells, and a pair of side walls closing the cells at both ends of the side walls. A method for manufacturing a sound absorbing structure made of a hollow plate material having a closing wall, wherein a through jig is pierced into the side wall portions of a plurality of adjacent cells to form side wall portion communicating holes, and the plurality of cells are connected to each other. a side wall portion communicating hole forming step of forming a communicating cell group whose internal spaces are communicated through the side wall portion communicating hole; a closed wall communicating hole forming step of forming a closed wall communication hole by piercing one of the closed walls with the penetrating jig, and communicating the inside and the outside of the communication cell group through the closed wall communication hole; The side wall communicating hole forming step and the closed wall communicating hole forming step are performed in one step.

According to the above configuration, the side wall portion communication hole and the blocking wall communication hole are formed by piercing the side wall portion and the blocking wall with the penetrating jig. As a result, shavings are less likely to be generated from the hollow plate during the work of forming the side wall communication hole and the closed wall communication hole. A sound absorbing structure with stable quality is obtained. In addition, it is less troublesome to process the side wall communication hole and the closed wall communication hole. Furthermore, the side wall communicating hole forming step and the closing wall communicating hole forming step are performed in one step. Therefore, the side wall communication hole and the closed wall communication hole can be processed in a short time. The productivity of the sound absorbing structure is improved, and mass production is facilitated.

Here, in the sound absorbing structure, sound waves enter the internal space of the communicating cell group through the closed wall communication holes, and the sound waves are effectively attenuated in the internal space. That is, the sound absorbing structure can make each communicating cell group function as a Helmholtz resonator. The communication cell group has a larger volume than a single cell because the internal spaces of a plurality of cells communicate with each other through the side wall communication holes. In general, the sound absorption characteristics of a Helmholtz resonator depend on the opening area of the opening, the length of the tube for guiding sound waves from the outside to the inside of the container, and the inner volume of the container. The longer the tube portion and the larger the internal volume of the container, the more the sound waves in the low frequency range are attenuated. In the sound absorbing structure of the present invention, since the communicating cell group is formed, the "inner volume of the container" can be increased as compared with a single cell. This improves the sound absorption coefficient in a relatively low frequency range. It is possible to improve the productivity of the sound absorbing structure having excellent sound absorbing performance in the low frequency range.

The above-described configuration further includes a side wall communication hole enlarging step of enlarging the opening area of the side wall communication hole as compared with the opening area of the closed wall communication hole, wherein the side wall communication hole enlarging step includes: And it is preferable to move the penetrating jig in a state in which the rod-shaped penetrating jig is pierced into the blocking wall.

According to the above configuration, the inner spaces of the plurality of cells forming the communicating cell group can be communicated with each other by the side wall communicating hole having a larger opening area than the closed wall communicating hole. Therefore, sound waves can easily enter the internal spaces of the adjacent cells via the side wall communication holes from the internal space of the cell in which the closed wall communication hole is formed. Sound can be effectively absorbed in the entire internal space of the plurality of cells forming the communication cell group. A sound absorbing structure having excellent sound absorbing performance can be obtained. Further, the side wall portion communication hole enlarging step is performed in a state in which the through jig is pierced into the side wall portion and the closing wall. Therefore, the opening area of the side wall communication hole can be easily increased.

In the above configuration, in the side wall portion communicating hole forming step and the closed wall communicating hole forming step, the through holes of the cells constituting the communicating cell group are formed from the outside of the closing wall in a direction inclined with respect to the closing wall. It is preferable to pierce the jig.

According to the above configuration, the blocking wall communication hole and the blocking wall communication hole can be easily formed using a linear penetrating jig.
In the above configuration, it is preferable that the hollow plate member is made of a thermoplastic resin, and that the heated penetrating jig is used in the side wall communicating hole forming step and the closed wall communicating hole forming step.

According to the above configuration, the side wall communicating hole and the closed wall communicating hole can be formed while thermally melting the thermoplastic resin. It is easy to form the side wall communication hole and the closed wall communication hole.
In order to solve the above-mentioned problems, the sound absorbing structure of the present invention includes a side wall portion extending in a thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls closing the cells at both ends of the side wall portion. A sound absorbing structure made of a hollow plate material having In the cells excluding at least one of the cells constituting the communicating cell group, one side of the closing wall is formed with a closing wall communicating hole penetrating the closing wall, and the communicating cell group is Among the constituting cells, each of a pair of adjacent cells including the cell in which the blocking wall communication hole is formed is a specific cell, and the blocking wall communication hole formed in one of the specific cells is a specific blocking wall. When the side wall portion communication hole formed in the side wall portion partitioning the pair of the specific cells is defined as the specific side wall portion communication hole, the peripheral edge of the specific closed wall communication hole has a portion of the one specific cell. A specific blocking wall return piece having a leading edge located in the internal space is formed, and a specific side wall portion returning piece having a leading edge located in the internal space of the other specific cell is formed around the peripheral edge of the specific side wall communication hole. formed.

In the sound absorbing structure configured as described above, the tip edge of the specific blocking wall return piece of the specific blocking wall communication hole formed in one of the pair of specific cells is located in the internal space of one of the specific cells. Further, the specific side wall portion return piece of the specific side wall portion communication hole that partitions the pair of specific cells has its tip edge located in the internal space of the other specific cell. Therefore, a sound wave that has entered the internal space of one specific cell can easily enter the internal space of the other specific cell. Sound waves in the low frequency range are easily attenuated, and the sound absorption coefficient in the low frequency range is improved. A sound absorbing structure having excellent sound absorbing performance in a low frequency range can be obtained.

In addition, the shape of the specific blocking wall return piece and the specific side wall portion return piece and the arrangement of the leading end edge are such that the specific blocking wall communication hole and the specific side wall communication hole can be pierced from the outside of one of the specific cells with a penetrating jig. It can be done by forming Therefore, in the sound absorbing structure having the above configuration, it is difficult for shavings derived from the hollow plate material to exist inside. The quality of the sound absorbing structure is stable.

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

According to the above configuration, a sound wave that has entered the internal space of one specific cell can easily enter the internal space of the other specific cell. A sound absorbing structure having excellent sound absorbing performance in a low frequency range can be obtained.

ADVANTAGE OF THE INVENTION According to this invention, the sound-absorbing structure which is excellent in sound-absorbing property in a low-frequency area|region, and is stable in quality is obtained.

It is a partial perspective view of a sound absorbing structure. It is a β-β line cross section in FIG. FIG. 2 is a cross-sectional view taken along the γ-γ line in FIG. 1; (a) is a perspective view of a sheet member forming a core layer of a hollow plate member. (b) is a perspective view showing a state in the middle of folding the same sheet material. (c) is a perspective view showing a state in which the same sheet material is folded. It is a figure explaining a closed wall communicating-hole forming process, a side wall part communicating-hole forming process, and a side wall part communicating-hole enlarging process. It is a figure explaining a closed wall communicating hole and a side wall part communicating hole. It is an enlarged cross-sectional view of a sound absorbing structure of a modification. It is an enlarged cross-sectional view of a sound absorbing structure of a modification. It is a figure explaining the block wall communication hole formation process and side wall part communication hole formation process of the sound-absorbing structure of a modification. It is a figure explaining the closed-wall communication-hole formation process of the sound-absorbing structure of a modification, and a side wall part communication-hole formation process. It is a figure explaining the block wall communication hole formation process of the sound absorption structure of a modification, a side wall part communication hole formation process, and a side wall part communication hole enlargement process. It is an enlarged cross-sectional view of a sound absorbing structure of a modification. It is an enlarged cross-sectional view of a sound absorbing structure of a modification.

An embodiment of a sound absorbing structure embodying the present invention will be described below.
As shown in FIG. 1, the sound absorbing structure 1 of this embodiment is composed of a hollow plate member 10 in which a plurality of hexagonal columnar cells S are arranged side by side. The hollow plate member 10 is made of a conventionally known thermoplastic resin material. The material is not particularly limited. Examples of the material include polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, acrylonitrile-butadiene-styrene, and the like.

<Regarding the structure of the sound absorbing structure 1>
First, the structure of the hollow plate member 10 will be described. The hollow plate member 10 is a plate-shaped member in the sound absorbing structure 1 in which communication holes 13 and 15, which will be described later, are not formed.

As shown in FIG. 1, the hollow plate material 10 is composed of a core layer 20 in which a plurality of cells S are arranged side by side, and sheet-like skin layers 30 and 40 joined to both sides of the core layer 20 in the thickness direction. It is Hereinafter, in FIG. 1, the main surface shown on the upper side of the hollow plate member 10 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 10 a side of the hollow plate member 10 , and the skin layer 40 is bonded to the lower surface 10 b side of the hollow plate member 10 .

As shown in FIGS. 1 to 4, the core layer 20 is formed by folding a piece of irregular sheet material 100 made of a thermoplastic resin molded into a predetermined shape. The core layer 20 is composed of an upper wall portion 21, a lower wall portion 22, and a side wall portion 23 erected between the upper wall portion 21 and the lower wall portion 22 to partition the cells S into a hexagonal prism shape. there is

As shown in FIG. 1, the cells S defined inside the core layer 20 include a first cell S1 and a second cell S2 having different configurations.
As shown in FIG. 2 , in the first cell S<b>1 , the upper wall portion 21 having a two-layer structure is provided above the side wall portion 23 . Each layer of the upper wall portion 21 having the two-layer structure is joined to each other. In addition, in the first cell S1, a lower wall portion 22 having a one-layer structure is provided below the side wall portion 23 .

As shown in FIG. 3 , in the second cell S2, the upper wall portion 21 having a single-layer structure is provided above the side wall portion 23 . Further, in the second cell S2, a lower wall portion 22 having a two-layer structure is provided below the side wall portion 23 . Each layer of the lower wall portion 22 having the two-layer structure is joined to each other. Further, as shown in FIGS. 2 and 3, the adjacent first cells S1 and the adjacent second cells S2 are partitioned by the side wall portions 23 having a two-layer structure.

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. are doing. 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 the hexagon. The columns of the first cells S1 and the columns of the second cells S2 are alternately arranged in the Y direction orthogonal to the X direction. The core layer 20 as a whole has a honeycomb structure with these first cells S1 and second cells S2.

As shown in FIGS. 1 to 3, since the skin layer 30 is bonded to the upper surface of the core layer 20, the upper portion of the side wall portion 23 of the core layer 20 is formed by the upper wall portion 21 of the core layer 20 and the skin layer 30. is blocked by That is, the upper wall portion 21 and the skin layer 30 constitute the upper blocking wall 11 that partitions the cells S from above. Similarly, by bonding the skin layer 40 to the lower surface of the core layer 20 , the lower portion of the side wall portion 23 of the core layer 20 is closed with the lower wall portion 22 of the core layer 20 and the skin layer 40 . That is, the lower wall portion 22 and the skin layer 40 constitute the lower closing wall 12 that partitions the cells S from below.

The hollow plate member 10 has a shape in which a plurality of cells S are arranged inside by a core layer 20 and skin layers 30 and 40 . The upper blocking wall 11 side of the hollow plate member 10 constitutes the upper surface 10a of the hollow plate member 10, and the lower blocking wall 12 side constitutes the lower surface 10b of the hollow plate member 10. As shown in FIG.

As shown in FIG. 1, the sound absorbing structure 1 has a plurality of communication holes 13 formed in one main surface (upper surface 10a) of a hollow plate member 10. As shown in FIG. Communication holes 15 are formed in the plurality of side wall portions 23 . The communication hole 13 is a closed wall communication hole as defined in the claims, and the communication hole 15 is a side wall portion communication hole as defined in the claims.

As shown in FIG. 1, in the sound absorbing structure 1 of the present embodiment, the first cells S1 in which the communicating holes 13 are formed and the first cells S1 in which the communicating holes 13 are not formed are arranged alternately in the X direction. is set. Similarly, in the X direction, the second cells S2 in which the communication holes 13 are formed and the second cells S2 in which the communication holes 13 are not formed are alternately arranged side by side. 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 the communication hole 13 from the first cell S1 not having the communication hole 13 formed therein. there is Similarly, a communication hole 15 is formed in the side wall portion 23 that separates the second cell S2 in which the communication hole 13 is formed and the second cell S2 in which the communication hole 13 is not formed.

As shown in FIGS. 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 member 10. As shown in FIGS. The communication hole 13 of this embodiment is formed in a circular shape when viewed from above. Also, the communication hole 13 is formed substantially in the central portion of one cell S. As shown in FIG. The internal space of the cell S communicates with the external space of the sound absorbing structure 1 through the communication hole 13 . As shown in FIG. 2, in the first cell S1, the communication hole 13 penetrates the upper wall portion 21 and the skin layer 30 of the two-layer structure. As shown in FIG. 3, in the second cell S2, the communication hole 13 penetrates the upper wall portion 21 and the skin layer 30 having a one-layer structure. Thereby, the sound absorbing structure 1 functions as a sound absorbing material.

As shown in FIGS. 2 and 3 , a return piece 14 extending obliquely with respect to the thickness direction of the sound absorbing structure 1 is formed on the periphery of each communication hole 13 . 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 a blocking wall return piece referred to in the claims.

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 extending at an angle, the side with a smaller inclination angle with the upper blocking wall 11 (the left side of the return piece 14 shown in FIGS. 2 and 3) is the side with a larger inclination angle with the upper blocking wall 11 ( It is shorter and thicker than the right side of the return piece 14 shown in FIGS. 2 and 3).

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 a hexagon when the cell S is viewed from above. Specifically, when the average value of the intervals between the centers of the cells S adjacent in the X direction is defined as "average pitch P1", the opening diameter L of each communication hole 13 is a fraction of the average pitch P1. It is preferable to set The opening diameter L is preferably about 0.5 to 3 mm, more preferably about 1.0 to 1.5 mm. When the opening diameter L is within this range, the sound absorption coefficient of the sound absorbing structure 1 can be increased.

As shown in FIGS. 2 and 3 , the communication hole 15 formed in the side wall portion 23 penetrates the side wall portion 23 . The internal spaces of the adjacent cells S communicate with each other through the side walls 23 in which the communication holes 15 are formed. A plurality of cells S whose internal spaces communicate with each other through the communication holes 15 are referred to as a communication cell group. The communication cell group of this embodiment is formed of two cells S. As shown in FIG.

As shown in FIG. 2, in the first cell S1, the communication hole 15 is formed in the two-layered side wall portion 23 that partitions the adjacent first cells S1. Thus, a communicating cell group is formed by two first cells S1. Further, as shown in FIG. 3, in the second cells S2, the communication holes 15 are formed in the two-layered side wall portions 23 that partition the adjacent second cells S2. Thus, a communicating cell group is formed by two second cells S2. The formation position of the communication hole 15 in the side wall portion 23 is located below the center position of the side wall portion 23 in the vertical direction. That is, in the side wall portion 23, the portion below the communication hole 15 is shorter than the portion above it.

In the following, among the cells S forming the communicating cell group, the cells S adjacent to each other through the communicating hole 15 may be referred to as specific cells SP. In the communicating cell group of the present embodiment formed of two cells S, all the cells S forming the communicating cell group correspond to the specific cell SP.

The communication hole 15 of this embodiment is formed in an elliptical shape when viewed from the side. As shown in FIG. 6, the communication hole 15 is formed on the imaginary line A along which the return piece 14 of the communication hole 13 formed in the closing wall extends.

As shown in FIGS. 2 and 3, a return piece 16 is formed on the periphery of each communication hole 15 . The return piece 16 is a side wall portion 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 constituting the communication cell group. It is located in the internal space of the specific cell SP.

As shown in FIG. 6, the return piece 16 extends obliquely with respect to the thickness direction of the sound absorbing structure 1 and obliquely with respect to the virtual line A. As shown in FIG. The return piece 16 has a substantially truncated cone shape with a larger diameter on the side of the specific cell SP where the communication hole 13 is 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). In addition, in the return piece 16 extending obliquely, the side having a small inclination angle with the side wall portion 23 (the lower side of the return piece 16 shown in FIG. 6) is the side having a large inclination angle with the side wall portion 23 (shown in FIG. 6). It is shorter in length and thicker than the upper side of the return piece 16). Furthermore, the side having a large inclination angle with respect to the side wall portion 23 has a larger amount of resin than the side having a small inclination angle with respect to the side wall portion 23 . Further, the length of the return piece 16 is longer than the length of the return piece 14. - 特許庁

The communication hole 13 formed in one specific cell SP among the adjacent specific cells SP is the specific blocking wall communication hole as defined in the claims, and the return piece 14 is the specific blockage wall return piece as defined in the claims. Further, the communicating hole 15 formed in the side wall portion 23 that partitions the specific cell SP is the specific side wall portion communicating hole, and the return piece 16 is the specific side wall portion return piece. In the sound absorbing structure 1 of this embodiment, two cells S form a communicating cell group, so all the cells S constituting the sound absorbing structure 1 are the specific cells SP. Further, all the communicating holes 13 are specific blocking wall communicating holes, and all the return pieces 14 are specific blocking wall return pieces. Further, all of the communicating holes 15 become the specific side wall portion communicating holes, and all the return pieces 16 become the specific side wall portion return pieces.

As shown in FIG. 6, the opening diameter M of each communicating hole 15 is larger than the opening diameter L of each communicating hole 13, and as a result, the opening area of the communicating hole 15 is larger than the opening area of the communicating hole 13. there is The opening diameter M of the communication hole 15 is formed to be about 1/3 to 2/3 of the length of the side wall portion 23 in the vertical direction. The opening diameter M is preferably about 6 to 14 mm, more preferably about 8 to 12 mm. Moreover, the opening area of the communication hole 15 is preferably about 5 to 20 times, more preferably about 10 to 15 times, the opening area of the communication hole 13 . When the opening diameter M and the opening area are within this range, sound waves can easily propagate between the specific cells SP, and the sound absorption coefficient of the sound absorbing structure 1 can be increased.

Next, a method for manufacturing the sound absorbing structure 1 will be described with reference to FIGS. 4 and 5. FIG.
The method of manufacturing the sound absorbing structure 1 includes a forming step of forming an uneven sheet material 100 having a predetermined uneven shape from one flat sheet material made of thermoplastic resin, and a core layer 20 is formed by folding the uneven sheet material 100 . a folding step, a joining step of joining the skin layers 30 and 40 to both main surfaces of the core layer 20 to form the hollow plate member 10, a side wall portion communicating hole forming step of forming the communicating hole 15 in the hollow plate member 10, It includes a closed wall communicating hole forming step for forming the communicating hole 13 and a side wall portion communicating hole enlarging step for increasing the opening area of the communicating hole 15 compared to the opening area of the communicating hole 13 .

As shown in FIG. 4( a ), in the molding step, a flat sheet material made of thermoplastic resin is molded into a predetermined shape to form an uneven sheet material 100 . In the concave-convex sheet material 100 , strip-shaped plane regions 110 and swollen regions 120 are alternately arranged in the longitudinal direction (X direction) of the concave-convex sheet material 100 . In the bulging region 120 , a first bulging portion 121 having a downward groove shape in cross section and having an upper surface and a pair of side surfaces is formed over the entirety of the extending direction (Y direction) of the bulging region 120 . The angle between the upper surface and the side surface of the first bulging portion 121 is preferably 90 degrees. Moreover, the width of the first bulging portion 121 (the length of the upper surface in the short direction) is equal to the width of the planar region 110, and the bulging height of the first bulging portion 121 (the length of the side surface in the short direction) ) is set to be twice as long.

In the bulging region 120 , a plurality of second bulging portions 122 each having a trapezoidal cross-sectional shape obtained by bisected a regular hexagon along the longest diagonal line are arranged so as to be perpendicular to the first bulging portions 121 . formed. The bulging height of the second bulging portion 122 is set to be equal to the bulging height of the first bulging portion 121 . Also, the interval between adjacent second bulging portions 122 is equal to the width of the upper surfaces of the second bulging portions 122 .

It should be noted that the uneven sheet material 100 is formed by partially swelling the sheet upward using the plasticity of a flat sheet material made of thermoplastic resin. Also, the uneven sheet material 100 can be formed from one flat sheet material by a well-known forming method such as a vacuum forming method or a compression forming method.

As shown in FIGS. 4A and 4B, in the folding step, the uneven sheet material 100 configured as described above is folded along the boundary lines P and Q to form the core layer 20 . Specifically, the concave-convex sheet material 100 is valley-folded along the boundary line P between the planar region 110 and the bulging region 120, and is mountain-folded along the boundary line Q between the upper surface and the side surface of the first bulging portion 121. to compress in the X direction. As shown in FIGS. 4B and 4C, the top surface and the side surface of the first bulging portion 121 are folded over, and the end surface of the second bulging portion 122 and the planar region 110 are folded over, thereby forming a single A prismatic partition 130 extending in the Y direction is formed for one bulging region 120 . The hollow plate-shaped core layer 20 is formed by forming such partition bodies 130 continuously in the X direction. In this embodiment, the direction in which the concave-convex sheet material 100 is compressed for folding is the direction in which the cells S are arranged side by side (the X direction).

When the concave-convex 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 the side surface of the first bulging portion 121 , and the end surface and the plane area of the second bulging portion 122 are formed. 110 form the lower wall portion 22 of the core layer 20 . In addition, as shown in FIG. 4C, a portion of the upper wall portion 21 where the upper surface and the side surface of the first bulging portion 121 are folded to form a two-layer structure, and a second bulging portion of the lower wall portion 22 A portion where the end surface of 122 and the planar region 110 are folded to form a two-layer structure becomes an overlapping portion 131 .

In addition, the hexagonal prism-shaped regions partitioned by folding the second bulging portion 122 become the second cells S2, and the hexagonal prism-shaped regions partitioned and formed between the pair of adjacent partitions 130 are the second cells S2. 1 cell S1. In the present embodiment, the upper surface and the side surface of the second bulging portion 122 constitute the side wall portion 23 of the second cell S2, and the side surface of the second bulging portion 122 and the second bulging portion 122 in the bulging region 120 The planar portion located therebetween constitutes the side wall portion 23 of the first cell S1.

The abutting portions of the planar portions of the bulging region 120 become the side wall portions 23 having a two-layer structure of the first cell S1, and the abutting portions of the upper surfaces of the second bulging portions 122 become the second cell S2. The side wall portion 23 having a two-layer structure is formed.

As shown in FIG. 4C, the upper portion of the first cell S1 is defined by the pair of overlapping portions 131, and the lower portion of the second cell S2 is defined by the pair of overlapping portions 131. As shown in FIG. It should be noted that, when carrying out such a folding process, it is preferable that the concave-convex sheet material 100 is heated and softened.

In the joining step, thermoplastic resin sheet materials are joined by thermal welding to the upper and lower surfaces of the core layer 20 obtained in the folding step. The sheet material bonded 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 portion of the side wall portion 23 . The sheet material bonded to the lower surface of the core layer 20 becomes the skin layer 40 and constitutes the lower closing wall 12 that closes the lower portion of the side wall portion 23 together with the lower wall portion 22 of the core layer 20 .

When the sheet materials (skin layers 30 and 40) are thermally welded to the core layer 20, the upper wall portions 21 (overlapping portions 131) of the two-layer structure in the first cell S1 are thermally welded to each other. Similarly, the lower wall portion 22 (overlapping portion 131) of the two-layer structure in the second cell S2 is thermally welded to each other.

Through the bonding process, a hollow plate material 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 in rows alternately in the Y direction. 10 is obtained.

As shown in FIG. 5, the side wall portion communication hole forming step and the closed wall communication hole forming step are performed in one step. A penetrating jig 50 for forming the communication holes 13 and 15 includes a penetrating member 51 having a circular cross section and a sharpened rod shape, and plate-like support members 52 and 53 for supporting the penetrating member 51 . The support member 52 supports the proximal edge of the penetrating member 51 . A hole 53 a is formed in the support member 53 . The penetrating member 51 is supported so as to be inclined with respect to the supporting members 52 and 53 while passing through the hole 53a. A plurality of penetrating members 51 are supported by the supporting members 52 and 53 . The multiple penetrating members 51 are supported so as to be parallel to each other. The spacing between adjacent penetrating members 51 is approximately equal to twice the average pitch P1, which is the average of the spacings between adjacent cell S centers.

In the side wall part communication hole forming process and the closed wall communication hole forming process, the hollow plate member 10 is placed on a table (not shown) below the penetrating jig 50 . In this state, the upper surface 10a of the hollow plate member 10 is parallel to the support members 52 and 53. As shown in FIG. Further, when the penetrating jig 50 is lowered and the tip of the penetrating member 51 reaches the upper closing wall 11 of the hollow plate member 10, the tip of the penetrating member 51 is positioned substantially at the center of one cell S. adjusted. The penetrating member 51 is kept at room temperature without being heated.

As shown in FIG. 5 , the penetrating jig 50 is lowered toward the hollow plate member 10 to pierce the upper closing wall 11 of the hollow plate member 10 with the penetrating member 51 . The penetrating member 51 pierced through the upper blocking wall 11 penetrates the substantially central portion of the upper blocking wall 11 in one cell S, and descends so as to expand the upper blocking wall 11 toward the inside of the cell S. . Since the penetrating member 51 is supported so as to be inclined with respect to the supporting members 52 and 53 , the penetrating member 51 advances in a direction inclined with respect to the upper closing wall 11 . As a result, a communicating hole 13 having a circular top view is formed in the substantially central portion of the upper blocking wall 11, and a cylindrical return piece extending toward the inner space of the cell S is formed around the peripheral edge of the communicating hole 13. 14 are formed.

The penetrating jig 50 is further lowered to pierce the side wall portion 23 of the hollow plate member 10 with the penetrating member 51 . The penetrating member 51 pierced into the side wall portion 23 penetrates the adjacent side wall portion 23 and descends so as to spread the side wall portion 23 toward the inner space of the adjacent cell S. As shown in FIG. Since the penetrating member 51 is supported so as to be inclined with respect to the supporting members 52 and 53 , the penetrating member 51 advances in a direction inclined with respect to the side wall portion 23 . As a result, a communication hole 15 having a substantially circular shape when viewed from the side is formed in the side wall portion 23, and a substantially cylindrical return piece 16 extending toward the inner space of the adjacent cell S is formed on the periphery of the communication hole 15. is formed.

In this way, a communicating cell group is formed in which the internal spaces of two adjacent cells communicate with each other. A communication hole 13 and a return piece 14 are formed in the upper closing wall 11 of one of the specific cells SP constituting the communication cell group. The communication hole 13 and the return piece 14 are not formed in the upper closing wall 11 of the other specific cell SP constituting the communication cell group. In addition, the side wall portion 23 that partitions the two specific cells SP constituting the communication cell group is formed with the communication hole 15 and the return piece 16 extending toward the internal space of the other specific cell SP.

As shown by the arrows in FIG. 5 , in the step of enlarging the side wall communication hole, the support members 52 and 53 are reciprocated in parallel with the upper blocking wall 11 and the side wall 23 while the penetrating member 51 is pierced through the upper blocking wall 11 and the side wall 23 . move. As a result, as indicated by the dotted line in FIG. 5, the penetrating member 51 moves vertically with the base edge supported by the supporting member 52 as a fulcrum. The vertical movement distance of the penetrating member 51 is greater in the communicating hole 15, which is located at a longer distance from the proximal edge of the penetrating member 51, than in the communicating hole 13, which is located at a shorter distance from the proximal edge of the penetrating member 51. . Therefore, the communicating hole 15 that has undergone the side wall portion communicating hole enlarging step is expanded in the vertical direction and has an elliptical shape when viewed from the side. Further, the return piece 16 is also expanded in the vertical direction to form a substantially truncated cone shape.

The penetrating jig 50 is moved upward to pull out the penetrating member 51 from the hollow plate member 10 .
Through the above steps, a communicating cell group is formed in which the internal spaces of the specific cells SP communicate with each other through the communicating holes 13 and the return pieces 14 and the internal spaces of the specific cells SP communicate with each other through the communication holes 13 and the return pieces 14 . . Thus, the sound absorbing structure 1 having a plurality of communication cell groups is manufactured.

Next, the effects of the sound absorbing structure 1 of this embodiment and the method of manufacturing the same will be described.
(1) In the method of manufacturing the sound absorbing structure 1, the side wall communicating hole forming step and the closed wall communicating hole forming step are performed in one step.

Therefore, it is easy to form the communication holes 13 and 15, and the communication holes 13 and 15 can be formed in a short time. The productivity of the sound absorbing structure is improved, and mass production is facilitated.
(2) In the side wall portion communication hole forming step and the closing wall communication hole forming step, the connecting holes 13 and 15 are formed by piercing the upper closing wall 11 and the side wall portion 23 with the sharp penetrating member 51 .

Therefore, compared with the case of forming a hole with a drill, shavings of the thermoplastic resin material derived from the hollow plate member 10 are less likely to occur. Remaining shavings inside the sound absorbing structure 1 are suppressed, and the sound absorbing structure 1 with stable quality is obtained. Further, the processing for forming the communication holes 13 and 15 is easy, and the communication holes 13 and 15 can be formed in a short time.

(3) The penetrating member 51 is formed in the shape of a straight-pointed rod. In the side wall communicating hole forming step and the closed wall communicating hole forming step, the penetrating member 51 is pierced from the outside of the upper closing wall 11 of the specific cell SP constituting the communicating cell group in a direction inclined with respect to the upper closing wall 11 . ing.

Therefore, the communication holes 13 and 15 can be easily formed in one step.
(4) In the step of enlarging the side wall communication hole, the support members 52 and 53 are moved while the penetrating member 51 is pierced through the side wall 23 and the upper closing wall 11 .

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

Therefore, in the sound absorbing structure, each communicating cell group can function as a Helmholtz resonator. Since the "inner volume of the container" can be increased when functioning as a Helmholtz resonator, the sound absorption performance in the low frequency range can be improved.

(6) In the communicating cell group, a return piece 14 is formed in the communication hole 13 and a return piece 16 is formed in the communication hole 15 .
Therefore, it is possible to lengthen the "length of the tube portion" when functioning as a Helmholtz resonator. It is possible to improve the sound absorption performance in the low frequency range.

(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 the other specific cell SP via the communication hole 15 from the internal space of one specific cell SP in which the communication hole 13 is formed. Further, the flow resistance of air flowing within 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 . As a result, sound can be effectively absorbed in the entire internal space of the plurality of specific cells SP constituting the communicating cell group. The sound absorbing performance of the sound absorbing structure 1 in the low frequency range can be improved.

(8) The communicating hole 15 is formed on the imaginary line A along which the return piece 14 of the communicating hole 13 formed in the closing wall extends.
Therefore, the sound wave that has entered the internal space of the specific cell SP in which the communication hole 13 is formed easily enters the internal space of the specific cell SP in which the communication hole 13 is not formed. A sound absorbing structure having excellent sound absorbing performance in a low frequency range can be obtained.

It should be noted that the above embodiment can be implemented with the following modifications. Moreover, the above embodiments and the following modified examples can be implemented in combination with each other within a technically consistent range.

In the method for manufacturing the sound absorbing structure 1 of the above-described 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. May be omitted. The penetrating jig 50 may be retracted after the closed wall communication hole forming step and the side wall portion communication hole forming step are performed in one step.

In that case, as shown in FIG. 7, the opening area of the communication hole 13 and the opening area of the communication hole 15 are approximately the same. The return pieces 14 and 16 are formed so as to extend along the imaginary line A. A virtual line A corresponds to the locus of movement of the tip of the penetrating member 51 .

- Although the penetrating member 51 is not heated in the manufacturing method of the sound absorbing structure 1 of the above embodiment, the penetrating member 51 may be heated. In this case, the formed communication holes 13, 15 and the return pieces 14, 16 are shaped as shown in FIG. Specifically, the thermoplastic resin material is thermally melted by the heated penetrating member 51 . As the penetrating member 51 descends, the heat-melted thermoplastic resin material rises so as to be extruded around the communicating holes 13 and 15 . After that, the thermoplastic resin material is cooled, so that resin pools are formed on both the inner and outer surfaces of the upper blocking wall 11 of the communication hole 13 and the both surfaces of the side wall portion 23 of the communication hole 15 . In this case as well, as shown in FIG. 8, the return pieces 14 and 16 are formed, and the return pieces 14 and 16 extend in the direction along the locus of movement of the tip of the penetrating member 51 .

- In the manufacturing method of the sound absorbing structure 1 of the above-described embodiment, the penetrating member 51 is pierced into the two cells S to form the communicating cell group composed of the two cells S. As shown in FIG. 9, the penetrating member 51 may be steeply inclined, and three or more cells S may form a communicating cell group.

In the case where three or more cells S constituting the communicating cell group are formed, the cells S are not limited to being arranged in a straight line, and may be arranged in an arc.
In the above embodiment, the interval between adjacent penetrating members 51 is approximately equal to twice the average pitch P1, which is the average value of the intervals between the centers of adjacent cells S, but it may be shorter or longer. good too. For example, as shown in FIG. 10, the interval between three adjacent penetrating members 51 may be substantially equal to the average pitch P1. In this case, three penetrating members 51 adjacent to each other at the average pitch P1 may be grouped together, and the interval between the groups may be a multiple of the average pitch P1. As a result, a communicating cell group is formed by four cells S, and communicating holes 13 are formed in three of them.

- In the above-described embodiment, a linear penetrating member 51 of the penetrating jig 50 is used, but a curved penetrating member may be used. A penetrating member 61 in FIG. 11 is formed in a curved, pointed rod shape, and extends in a direction in which the distal end portion and the proximal end portion are perpendicular to each other. In this case, as shown in the cell S on the left side of FIG. As shown in the cell S in the middle of FIG. 11, as the penetrating member 61 is lowered, the penetrating member 61 moves around in the internal space of the cell S. As shown in FIG. When the tip of the curved penetrating member 61 reaches the position of the side wall portion 23 , the penetrating member 61 is further lowered to pierce the side wall portion 23 with the tip of the penetrating member 61 . A communication hole 13 is formed in the upper blocking wall 11 and a communication hole 15 is formed in the side wall portion 23 . Subsequently, as shown in the cell S on the right side of FIG. 11, the penetrating member 61 is moved vertically.

As shown in FIG. 12, in the sound absorbing structure 1 formed by such a process, the return pieces 14 and 16 are formed along the imaginary line B extending in a curved shape. Also, 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 closing wall 11 . Of the pair of specific cells SP constituting the communicating cell group, the tip edge of the return piece 14 is located in the internal space of one of the specific cells SP in which the communicating hole 13 is formed. Also, the tip edge of the return piece 16 is located in the internal space of the other specific cell SP.

- In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the skin layers 30 and 40 are joined to the core layer 20 by thermal welding, but the joining method of the skin layers 30 and 40 is not limited to this. For example, the skin layers 30 and 40 may be attached and joined to the core layer 20 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 force of this adhesive layer. .

- Not all the cells S forming the sound absorbing structure 1 may form a communication cell group. Some cells S may not communicate with other cells S.
- Cells S forming a connected cell group may have a common specific cell SP. For example, as shown in FIG. 13, when three cells S communicate with each other through the communication hole 15, the three cells S form a communication cell group. Assume that the cells S constituting the communicating cell group are Sa, Sb, and Sc. The cell Sa in which the communication hole 13 is formed and the cell Sb adjacent to the cell Sa correspond to the specific cell SP referred to in the claims. The tip edge of the return piece 14 formed in the cell Sa is located in the internal space of the cell Sa, and the tip edge of the return piece 16 formed in the side wall portion 23 partitioning the cell Sa and the cell Sb is located in the interior of the cell Sb. located in space. On the other hand, the cell Sc in which the communication hole 13 is formed and the cell Sb adjacent to the cell Sc also correspond to the specific cell SP referred to in the claims. The tip edge of the return piece 14 formed in the cell Sc is located in the internal space of the cell Sc, and the tip edge of the return piece 16 formed in the side wall portion 23 that partitions the cell Sc and the cell Sb is located in the interior of the cell Sb. located in space.

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

- The shapes of the communication holes 13 may not all be the same. For example, the plurality of communication holes 13 may have different shapes. Similarly, the shapes of the communication holes 15 are not all the same, and may be different from each other. The different shapes of the communicating holes 13 and 15 and the different shapes of the return pieces 14 and 16 widen the width of the low frequency range that can absorb sound, and improve the sound absorption in the low frequency range. It is possible.

- In the hollow plate material 10 of the above-described embodiment, the hexagonal prism-shaped cells S are partitioned and formed inside the core layer 20, but the shape of the cells S is not particularly limited. For example, it may have a polygonal shape such as a quadrangular prism shape, an octagonal prism shape, or a cylindrical shape. Moreover, the shape of the cell S may be a prefixed conical shape. In that case, cells of different shapes may be mixed. Alternatively, a plastic corrugated cardboard having a harmonica-shaped cross section may be used.

- Although the skin layers 30 and 40 are joined to both surfaces of the core layer 20 in the hollow plate material 10 of the above embodiment, at least one of the skin layers 30 and 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 . Further, 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 .

- In the cells S in which the communication holes 13 are formed, one communication hole 13 is formed in the substantially central portion of each cell S, but the formation location and number of the communication holes 13 are not limited to this. For example, the communication holes 13 may be formed at different positions in each cell S. Also, one or more communication holes 13 may be formed in each cell S. FIG.

- In the above embodiment, the communication holes 13 are formed at a constant pitch, and the communication holes 13 are formed substantially in the center of one cell S. However, the positions of the communication holes 13 may not be constant. . For example, the pitch of the cells S may not be constant due to deformation of the hollow plate member 10 during molding, etc. In this case, the positions of the communication holes 13 will differ from cell to cell. Specifically, the position of the communication hole 13 may be positioned at the center or end of the cell S.

- You may join another sheet material to the outer surface by the side of the skin layer 40 in the hollow board|plate material 10. FIG. The sheet material is not limited to one made of synthetic resin, and may be, for example, a metal sheet (metal foil), steel plate, paper, cloth, or the like. Also, the skin layer 40 itself may be composed of a metal sheet (metal foil), paper, cloth, or the like.

- You may add resin and an additive which provide functionality to the thermoplastic resin which comprises the hollow board|plate material 10. FIG. For example, a flame-retardant resin or additive may be added, or a deodorant or fragrance may be added.

Technical ideas that can be grasped from the above embodiment and modifications will be described.
(a) A method of manufacturing a sound absorbing structure comprising a hollow plate material having side walls extending in the thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls closing the cells at both ends of the side walls. wherein a through jig is inserted into the side wall portions of a plurality of adjacent cells to form side wall portion communication holes, and the internal spaces of the plurality of cells are communicated through the side wall portion communication holes. a side wall portion communicating hole forming step for forming a communicating cell group; a closed wall communicating hole forming step of forming a communicating hole to allow communication between the inside and outside of the communicating cell group through the closing wall communicating hole; a side wall portion communication hole enlarging step for enlarging an opening area, wherein the side wall portion communication hole forming step and the closed wall communication hole forming step are performed in one step; In a state in which the rod-shaped penetrating jig is pierced into the blocking wall, the penetrating jig is moved with the end located outside the blocking wall as a fulcrum.

(b) A method for manufacturing a sound absorbing structure comprising a hollow plate material having side walls extending in the thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls closing the cells at both ends of the side walls. wherein a through jig is inserted into the side wall portions of a plurality of adjacent cells to form side wall portion communication holes, and the internal spaces of the plurality of cells are communicated through the side wall portion communication holes. a side wall portion communicating hole forming step for forming a communicating cell group; a closed wall communicating hole forming step of forming a communicating hole to allow communication between the inside and outside of the communicating cell group through the closing wall communicating hole; a side wall portion communication hole enlarging step for enlarging an opening area, wherein the side wall portion communication hole forming step and the closed wall communication hole forming step are performed in one step; The rod-shaped penetrating jig is moved in a direction orthogonal to the blocking wall while the rod-shaped penetrating jig is pierced into the blocking wall.

S... Cell S1... First cell (cell)
S2... Second cell (cell)
SP: Specific cell (cell)
DESCRIPTION OF SYMBOLS 1... Sound-absorbing structure 10... Hollow board material 11... Upper blocking wall (blocking wall)
12 ... Lower blocking wall (blocking wall)
13... Communication hole (obstruction wall communication hole)
14 ... return piece (blocking wall return piece)
15... Communication hole (side wall communication hole)
16 ... return piece (side wall portion return piece)
23... Side wall portion 50... Penetrating jig 51, 61... Penetrating member (penetrating jig)

Claims (7)

A method for manufacturing a sound absorbing structure comprising a hollow plate material having side walls extending in a thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls closing the cells at both ends of the side walls. ,
A communicating cell group is formed by inserting a penetrating jig into the side wall portions of a plurality of adjacent cells to form side wall portion communication holes, and in which the inner spaces of the plurality of cells are communicated through the side wall portion communication holes. a side wall communication hole forming step;
A closed wall communicating hole is formed by piercing one of the closed walls of the cells excluding at least one of the cells constituting the communicating cell group with the penetrating jig to form a closed wall communication hole. a closed wall communication hole forming step for communicating the inside and outside of the communication cell group with each other,
A method of manufacturing a sound absorbing structure, wherein the side wall communicating hole forming step and the closing wall communicating hole forming step are performed in one step. further comprising a side wall communication hole enlarging step of increasing the opening area of the side wall communication hole compared to the opening area of the closed wall communication hole;
2. The sound absorbing structure according to claim 1, wherein in the step of enlarging the side wall portion communication hole, the rod-shaped through jig is moved while being pierced into the side wall portion and the blocking wall. manufacturing method. In the side wall portion communication hole forming step and the closed wall communication hole forming step, the penetrating jig is pierced from the outside of the closing wall of the cell constituting the communicating cell group in a direction inclined with respect to the closing wall. A method for manufacturing a sound absorbing structure according to claim 1 or 2, characterized by: The hollow plate material is made of a thermoplastic resin,
4. The method of manufacturing a sound absorbing structure according to claim 1, wherein the through-hole forming step and the closed-wall through-hole forming step use the heated penetrating jig. . A sound absorbing structure made of a hollow plate material having side walls extending in a thickness direction and partitioning a plurality of columnar cells, and a pair of closing walls closing the cells at both ends of the side walls,
a communicating cell group composed of a plurality of cells adjacent to each other and having an internal space communicated by a side wall portion communicating hole penetrating the side wall portion;
In the cells excluding at least one of the cells constituting the communication cell group, a closed wall communication hole penetrating through the closed wall is formed in one of the closed walls,
Among the cells constituting the communication cell group, each of a pair of adjacent cells including the cell in which the blocking wall communication hole is formed is a specific cell, and the blocking wall communication formed in one of the specific cells When the hole is defined as a specific closed wall communication hole, and the side wall communication hole formed in the side wall partitioning the pair of specific cells is defined as a specific side wall communication hole, the peripheral edge of the specific closed wall communication hole has the above-mentioned A specific blocking wall return piece having a tip edge positioned in the inner space of one of the specific cells is formed, and a specific blocking wall return piece having a tip edge positioned in the inner space of the other specific cell is formed around the peripheral edge of the specific side wall communication hole. A sound absorbing structure, characterized in that side wall part return pieces are formed. 6. The sound absorbing structure according to claim 5, wherein the specific blocking wall return piece is inclined with respect to the thickness direction and extends toward the specific side wall communication hole. 7. The sound absorbing structure according to claim 5, wherein the specific side wall portion return piece extends so as to be inclined with respect to the thickness direction.

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