KR20110068470A - Complex die for tetrahedron sandwich core having hexagonal punch, manufacturing method for tetrahedron sandwich core in using same and plate structure comprising tetrahedron sandwich core manufactured by the method - Google Patents

Abstract

PURPOSE: A complex mold for a tetrahedron sandwich core with a hexagonal shape of a punching part, method of manufacturing a tetrahedron sandwich core using the same, and tetrahedron sandwich plate structure comprising a tetrahedron sandwich core are provided to minimize spring back since the lower bent part of a bending part is sharply bent by a given angle. CONSTITUTION: A complex mold for a tetrahedron sandwich core consists of a lower mold(200), an upper mold(100), and a metal plate(300). The lower mold comprises a female wedge and a blanking part(220). A bending part(210) is formed on the female wedge. A plurality of hexagonal parts are formed on the blanking part. Male wedge matching with the female wedge is formed on the upper mold in plural. Female wedge and a press member are formed on the upper mold. The metal plate is slid to the lower mold. The metal plate is bent by the bending part by the pressure of the upper mold.

Description

COMPOSITE DIE FOR TETRAHEDRON SANDWICH CORE HAVING HEXAGONAL PUNCH, MANUFACTURING METHOD FOR TETRAHEDRON SANDWICH CORE IN USING SAME AND PLATE STRUCTURE COMPRISING TETRAHEDRON SANDWICH CORE MANUFACTURED BY THE METHOD}

The present invention relates to a tetrahedral sandwich core composite mold having hexagonal perforations, a method for manufacturing a tetrahedral sandwich core using the same, and a tetrahedral sandwich plate structure including the tetrahedral sandwich core manufactured by the same, wherein bending and blanking are performed at once. Comprising a complex mold for a tetrahedral sandwich core having a hexagonal perforations to improve the production speed and precisely control the position of the material, and a method for producing a tetrahedral sandwich core using the same and a tetrahedral sandwich core manufactured thereby It relates to a tetrahedral sandwich plate structure.

The truss structure is used as a porous intermediate layer of the sandwich plate.

The truss structure is designed to have an optimal strength and stiffness, and has an advantage that the interior is open to utilize space.

The truss structure may be formed by performing blanking on the plate to form a net and bending the plate of the net form.

16 is a view showing an error occurs in the bending position of the tetrahedral sandwich core manufactured by a conventional method.

Since the truss structure is formed by blanking and bending, respectively, there is a problem in that the production speed is lowered. As the truss structure is blanked and inserted into the bending mold, as shown in FIG. 16, the bending position is exactly at the intersection of the hexagon. There is a problem in that the precise position of the material is not controlled because the bending position is gradually pushed out and the error is accumulated.

The present invention has been made to solve the problems as described above, the composite mold for tetrahedral sandwich core with hexagonal perforations to improve the production speed by performing the bending and blanking at once, and the production of tetrahedral sandwich core using the same It is an object to provide a tetrahedral sandwich plate structure comprising a method and a tetrahedral sandwich core produced thereby.

Another object of the present invention is a tetrahedron comprising a composite mold for a tetrahedral sandwich core having a hexagonal perforated part capable of precisely controlling the position of the material, a method of manufacturing a tetrahedral sandwich core using the same, and a tetrahedral sandwich core manufactured thereby. It is to provide a sandwich plate structure.

In order to achieve the above object, the composite mold for tetrahedral sandwich cores provided with hexagonal perforations according to the present invention includes a female wedge having a bending portion and a female wedge having a blanking portion provided with a plurality of hexagonal shaped portions sequentially. A metal plate formed of a plurality of molds and male wedges corresponding to the female wedges and slidingly inserted on the upper mold and the lower mold on which a press member which is moved up and down on an upper portion of the male wedges corresponding to the blanking portion is formed; It includes, wherein the metal plate is bent by the bending portion by the pressing of the upper mold, it is punched in a hexagonal shape by the blanking portion by the pressing of the press is characterized in that a plurality of tetrahedral sandwich cores are formed. .

In addition, the press member may be formed at the bottom of the hexagonal perforation guide portion corresponding to the blanking portion.

In addition, the lower mold may be a rounded bending portion for smoothly sliding the insertion of the metal plate at the starting point of the bending portion.

In addition, the bending part and the blanking part may be formed by rounding a lower bending point.

In addition, according to the present invention, a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part includes sliding a metal plate onto a lower mold of a composite mold for a tetrahedral sandwich core provided with a hexagonal perforated part, and then forming an upper portion of the composite mold. A first bending step of forming a first bent portion in the metal plate by pressing the metal plate with a mold; and moving the metal plate, and repressurizing the metal plate with the upper mold to form a second bent portion in the metal plate. And a blanking step of forming a hexagonal perforated part by pressing the first bent part with a press member formed on the upper mold and forming a second bending step, wherein the metal plate is formed after the blanking step. After moving the perforated part of the first bent portion by re-pressurizing the metal plate with the upper mold Planarize the formed burr, and at the same time, perform the second bending step again, and then continuously perform the blanking step to form a tetrahedral sandwich core having the hexagonal perforations continuously formed of the metal plate. It is done.

In addition, the first bending step may include a metal plate charging process for moving the metal plate onto the bending portion formed in the lower mold, and a first bent portion for forming the first bent portion by pressing the metal plate into the upper mold. It may include a forming process and the upper mold removing step of separating the upper mold and the lower mold by removing the upper mold.

In the second bending step, the first bent portion seating process of moving the metal sheet and seating the first bent portion on a blanking portion formed in the lower mold, and pressing the metal sheet with the upper mold, causes the first bending. The second bent part forming process of forming a second bent part connected to the part may be included.

In addition, the blanking step may be performed by lowering the press member to a blanking portion formed in the lower mold and pressing the first bent portion to form a perforated portion having a hexagonal shape in the first bent portion and the press member. It may include a press member and an upper mold removing process for lifting on the upper mold and removing the upper mold.

In addition, the first bent portion and the second bent portion may be formed in a V shape.

In addition, the first bent portion and the second bent portion can adjust the structural characteristics of the tetrahedral sandwich core by adjusting the angle of the V-shaped bent portion.

In addition, the tetrahedral sandwich plate structure provided with a hexagonal perforated portion according to the present invention is a tetrahedral sandwich core manufactured by a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated portion, and the upper portion disposed above and below the tetrahedral sandwich core And a coupling member for coupling an end of the lower plate and the tetrahedral sandwich core to the upper and lower plates.

In addition, a multilayer structure may be formed by stacking two or more layers of the tetrahedral sandwich cores.

According to the present invention, according to the present invention, according to the present invention, a tetrahedral sandwich core composite mold provided with a hexagonal perforated part, a method for manufacturing a tetrahedral sandwich core using the same, and a tetrahedral sandwich plate structure including the tetrahedral sandwich core manufactured therefrom, the bending and Blanking is performed at once to improve production speed.

In addition, according to the present invention, a tetrahedral sandwich core composite mold having a hexagonal perforated part, a method for manufacturing a tetrahedral sandwich core using the same, and a tetrahedral sandwich plate structure including the tetrahedral sandwich core manufactured by the same, the position of the material is precisely positioned. There is an effect that can be controlled.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, it should be noted that the same components or parts in the drawings represent the same reference numerals as much as possible. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the gist of the present invention.

1 is a block diagram of a composite mold for a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

Composite mold for a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention, as shown in Figure 1, the lower die 200, the upper die 100 and the metal plate 300 do.

The lower mold 200 has a plurality of female wedges formed thereon. In this case, the arm wedge may be formed with the arm wedge formed with the bending portion 210, and the arm wedge formed with the blanking portion 220 in sequence.

Specifically, a total of six female wedges are formed on the lower mold 200, and the first and second female wedges have a V-shaped bending portion 210, and the third and fourth female wedges have a V shape. Although consisting of a blanking portion 220 is provided with a plurality of hexagonal shape portion is formed, the fifth and sixth female wedge may be formed V-shaped bending portion.

Here, the first arm wedge may have a rounded bending portion 211 to facilitate the sliding insertion of the metal plate 300 at the starting point of the bending portion 210.

In addition, the bending portion 210 of the first and second arm wedges and the blanking portion 220 of the third and fourth arm wedges may be formed by rounding a lower bending point.

In addition, the bending portions of the fifth and sixth arm wedges can be formed by sharply bending the lower bending point at a predetermined angle to determine the final bending angle, thereby reducing the amount of bending due to the elasticity to return to the original state. The phenomenon can be minimized.

The upper mold 100 is formed with a plurality of wedges corresponding to the female wedge at the bottom.

Specifically, the male wedge is a total of six are formed in the lower portion of the upper mold 100, the first and second male wedges correspond to the first and second female wedges, respectively, the third and fourth male wedges, respectively Corresponding to the third and fourth female wedges, the fifth and sixth male wedges correspond to and join the fifth and sixth female wedges, respectively.

In addition, the upper mold 100 is formed with a press member 110 to move up and down in the upper mold 100 on the top.

The press member 110 is formed on the upper mold 100, and is formed on an upper portion of the male wedge corresponding to the female wedge on which the blanking portion 220 is formed.

Meanwhile, although not shown, the press member 110 may have a hexagonal perforation guide part (not shown) corresponding to the blanking part 220.

The metal plate 300 is slidingly inserted into the lower mold 200, and then bent by the bending part 210 by pressing the upper mold 100, and pressing by the press member 110. A plurality of tetrahedral sandwich cores may be formed by drilling the hexagonal shape by the blanking unit 220.

Specifically, after the metal plate 300 is moved to the bending part 210, a bent part is formed by corresponding coupling of the upper mold 100 and the lower mold 200, and the bent part is a blanking part 220. After being seated in the hole, a punching part may be formed by corresponding coupling of a plurality of hexagonal shapes formed in the punching guide part (not shown) formed in the press member 110 and the blanking part 220.

Hereinafter, a method of manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention will be described in detail.

Figure 2 is a block diagram of a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

According to an embodiment of the present invention, a method for manufacturing a tetrahedral sandwich core having a hexagonal perforation part includes a first bending step S10, a second bending step S20, and a blanking step (as illustrated in FIG. 2). S30).

In the first bending step S10, the metal plate 300 is slidably inserted onto the lower mold 200 of the tetrahedral sandwich core composite mold 1 having a hexagonal perforated part according to an embodiment of the present invention. Thereafter, pressing the metal plate 300 with the upper mold 100 of the composite mold 1 to form a first bent part on the metal plate 300.

3 is a block diagram of a first bending step of a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

As shown in FIG. 3, the first bending step S10 includes a metal plate loading step S11, a first bent part forming step S12, and an upper mold removing step S13.

6 is a view showing a metal plate loading process during the first bending step according to an embodiment of the present invention, Figure 7 is a view showing the first bent portion forming process, Figure 8 is a view showing the upper mold removing process. .

As shown in FIG. 6, the metal sheet charging step S11 is a process of moving the metal sheet 300 onto the bending part 210 formed in the lower mold 200.

In the metal plate charging step S11, since the rounded bending portion 211 is formed at the starting point of the bending part 210, the metal plate may be smoothly inserted into the metal plate.

As shown in FIG. 7, the first bent part forming process (S12) may be performed by pressing the metal plate 300 with the upper mold 100 so as to press the first bent part 310 on the metal plate 300. Forming process.

Specifically, after the metal plate 300 is moved to the bending part 210, the male wedge of the upper mold 100 corresponding to the bending part 210 pressurizes the metal plate 300 and the bending part. It is seated at 210.

Accordingly, the metal plate 300 may have a first bent portion 310 formed between the male wedge and the bending portion 210. In this case, the first bent portion 310 may have a V shape. By adjusting the angle of the V-shaped bend, the structural characteristics of the tetrahedral sandwich core can be variously adjusted.

As shown in FIG. 8, the upper mold removing step S13 is a process of removing the upper mold 100 to separate the upper mold 100 and the lower mold 200.

Figure 4 is a block diagram of a second bending step of the manufacturing method of the tetrahedral sandwich core with a hexagonal perforated portion according to an embodiment of the present invention.

As shown in FIG. 4, the second bending step S20 includes a first bent part seating step S21 and a second bent part forming step S22.

FIG. 9 is a view illustrating a seating process of a first bent part of a second bending step according to an embodiment of the present invention, and FIG. 10 is a view illustrating a process of forming a second bent part.

As shown in FIG. 9, the first bent part seating process S21 may include the blanking part 220 in which the first bent part 310 is formed in the lower mold 200 by moving the metal plate 300. It is a process to rest on.

Specifically, the first bent portion seating step (S21) is to move the metal plate 300 on the lower mold 200, the first bent portion 310 formed on the metal plate 300, the lower It is a process of seating on the blanking part 220 formed in the metal mold | die 200, and placing the adjacent part of the said metal plate 300 adjacent to the said 1st bend part 310 on the said bending part 210. FIG. .

As shown in FIG. 10, the second bent part forming process (S22) is performed by pressing the metal plate 300 with the upper mold 100 to be connected to the first bent part 310. It is a process of forming 320.

In detail, in the process of forming the second bent part (S22), the first bent part 310 is seated on the blanking part 220 and the metal plate 300 adjacent to the first bent part 310. After the adjacent portion of the bent portion 210 is located on the bending portion 210, the male wedge of the upper mold 100 corresponding to the bending portion 210 presses the metal plate 300 and is seated on the bending portion 210. do.

Accordingly, the metal plate 300 may have a second bent portion 320 formed between the male wedge and the bending portion 210 in succession to the first bent portion 310, and at this time, the second bent portion The part 320 may have a V shape, and may adjust various structural characteristics of the tetrahedral sandwich core by adjusting the angle of the V-shaped bent portion.

Figure 5 is a block diagram of a blanking step of the manufacturing method of the tetrahedral sandwich core provided with a hexagonal perforation according to an embodiment of the present invention.

As shown in FIG. 5, the blanking step S30 includes a perforation part forming step S31, a press member, and an upper mold removing step S32.

11 is a view showing a perforated part forming process during the blanking step according to an embodiment of the present invention, Figure 12 is a view showing a pressing member and the upper mold removing process.

As shown in FIG. 11, the punching part forming process S31 lowers the press member 110 to the blanking part 220 formed in the lower mold 200 and presses the first bent part 310. By forming the perforated portion 330 in the first bent portion (310). At this time, the perforations 330 may be formed in a hexagonal shape.

Specifically, in the punching part forming process (S31), the first bent part 310 is formed between the punching guide part (not shown) formed in the press member 110 and the plurality of hexagonal shaped parts formed in the blanking part 220. By pressing, the hexagonal perforated portion 330 may be formed in the first bent portion 310.

As shown in FIG. 12, the press member and the upper mold removing process S32 raise the press member 110 on the upper mold 100, and the upper mold 100 on the lower mold 200. It is a process of removing.

13 is a view showing a metal plate after the blanking step, after the second bending step and the blanking step according to an embodiment of the present invention, Figure 14 is a hexagonal shape according to an embodiment of the present invention It is a block diagram of the tetrahedral sandwich core with a hexagonal perforation part manufactured by the manufacturing method of the tetrahedral sandwich core with a perforation part.

On the other hand, in the manufacturing method of the tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention, as shown in Figure 2, after the blanking step (S30), after moving the metal plate 300 Re-pressurizing the metal sheet 300 with the upper mold 100 to planarize the burr formed in the perforated portion of the first bent portion 310, and simultaneously perform the second bending step S20. Then, the blanking step (S30) is continuously performed, as shown in FIG. 13, thereby continuously forming the hexagonal perforations 330, as shown in FIG. 14, as shown in FIG. 14. An additional tetrahedral sandwich core 10 may be manufactured.

As described above, in the method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention, bending is first performed on the metal plate to form a bent portion, and then the perforated portion is formed in the bent portion. Forming the tetrahedral sandwich core to form, since the position is automatically adjusted by gravity in the process of seating the bent portion in the blanking portion in the lower mold can maintain the correct bending position. Therefore, according to the present invention, precise control of the position of the material is possible.

Hereinafter, a tetrahedral sandwich plate structure provided with a hexagonal perforated part according to an embodiment of the present invention will be described in detail.

15 is a coupling diagram of a tetrahedral sandwich plate structure provided with a hexagonal perforated part according to an embodiment of the present invention.

A tetrahedral sandwich plate structure provided with a hexagonal perforated part according to an embodiment of the present invention, as shown in Figure 15, the tetrahedral sandwich core 10, the upper plate 20, the lower plate 30 and the coupling Member (not shown).

The tetrahedral sandwich core 10 is manufactured by a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention, and constitutes an intermediate layer of the sandwich plate structure.

In this case, two or more layers of the tetrahedral sandwich core 10 may be stacked to form a multilayer structure.

The upper plate 20 is disposed above the tetrahedral sandwich core 10, and the lower plate 30 is disposed below the tetrahedral sandwich core 10.

The coupling member (not shown) couples the end of the tetrahedral sandwich core 10 and the upper and lower plate members.

On the other hand, as the joining method of the upper and lower plate and the tetrahedral sandwich core 10, of course, brazing, soldering, resin bonding or electrical resistance welding can be used.

Drawings illustrating a tetrahedral sandwich plate structure including a tetrahedral sandwich core composite mold provided with hexagonal perforations according to the present invention, a method for manufacturing a tetrahedral sandwich core using the same, and a tetrahedral sandwich core manufactured thereby. Although described with reference to the present invention, the present invention is not limited by the embodiments and drawings disclosed herein, of course, various modifications can be made by those skilled in the art within the scope of the present invention.

1 is a block diagram of a composite mold for a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

Figure 2 is a block diagram of a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

Figure 3 is a block diagram of a first bending step of the manufacturing method of the tetrahedral sandwich core with a hexagonal perforated part according to an embodiment of the present invention.

Figure 4 is a block diagram of a second bending step of the manufacturing method of the tetrahedral sandwich core with a hexagonal perforated portion according to an embodiment of the present invention.

Figure 5 is a block diagram of a blanking step of the manufacturing method of the tetrahedral sandwich core with a hexagonal perforated part according to an embodiment of the present invention.

6 is a view showing a metal plate charging process of the first bending step according to an embodiment of the present invention.

7 is a view showing a process of forming a first bent part of a first bending step according to an embodiment of the present invention.

8 is a view showing an upper mold removing process during the first bending step according to an embodiment of the present invention.

9 is a view showing the seating process of the first bent portion of the second bending step according to an embodiment of the present invention.

10 is a view illustrating a process of forming a second bent part of a second bending step according to an embodiment of the present invention.

11 is a view showing a perforated part forming process of the blanking step according to an embodiment of the present invention.

12 is a view showing a press member and an upper mold removing process during the blanking step according to an embodiment of the present invention.

Figure 13 is a view showing a metal plate after the blanking step, after the second bending step and the blanking step in accordance with an embodiment of the present invention.

14 is a configuration diagram of a tetrahedral sandwich core having a hexagonal perforated part manufactured by a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to an embodiment of the present invention.

15 is a coupling diagram of a tetrahedral sandwich plate structure provided with a hexagonal perforated part according to an embodiment of the present invention.

16 is a view showing an error occurs in the bending position of the tetrahedral sandwich core manufactured by a conventional method.

<Description of Symbols for Main Parts of Drawings>

1: Composite mold for tetrahedral sandwich cores with hexagonal perforations

10: tetrahedral sandwich core

20: upper plate 30: lower plate

100: upper mold 110: press member

200: lower mold 210: bending part

211: rounding bending part 220: blanking part

300: metal plate 310: the first bent portion

320: second bending part 330: drilling part

S10: first bending step

S11: Metal Plate Loading Process

S12: process of forming the first bent portion

S13: Upper mold removal process

S20: second bending step

S21: seating process of the first bent portion

S22: process of forming the second bent part

S30: blanking step

S31: hole forming process

S32: pressing member and upper mold removing process

Claims (12)

A lower mold in which a female wedge having a bending portion and a female wedge having a blanking portion provided with a plurality of hexagonal shapes are sequentially formed; An upper mold having a plurality of wedges corresponding to the female wedges, the upper mold having a press member which is moved up and down on an upper portion of the male wedges corresponding to the blanking portion; And It includes a metal plate that is slidingly inserted into the lower mold, The metal plate is bent by the bending part by pressing the upper mold, and is punched in a hexagonal shape by the blanking part by pressing the press member so that a plurality of tetrahedral sandwich cores are formed. Composite mold for tetrahedral sandwich core provided with additional. The method of claim 1, The press member is a complex mold for a tetrahedral sandwich core provided with a hexagonal punching portion, characterized in that the hexagonal punching induction portion corresponding to the blanking portion is formed at the bottom. The method of claim 1, The lower mold is a composite mold for a tetrahedral sandwich core having a hexagonal perforated part, characterized in that the rounded bending portion for smooth sliding insertion of the metal plate at the starting point of the bending portion is formed. The method of claim 3, The bending part and the blanking part is a composite mold for a tetrahedral sandwich core having a hexagonal perforated part, characterized in that the lower bending point is formed rounded. A metal sheet is slid into a lower mold of the complex die for a tetrahedral sandwich core provided with a hexagonal perforation according to any one of claims 1 to 4, and then the metal sheet is formed by the upper mold of the composite mold. A first bending step of pressing to form a first bent portion on the metal plate; A second bending step of moving the metal sheet and then repressurizing the metal sheet with the upper mold to form a second bent portion on the metal sheet; And And a blanking step of pressing the first bent portion with a press member formed on the upper mold to form a hexagonal perforated portion in the first bent portion. After the blanking step, after moving the metal plate, the metal plate is re-pressurized by the upper mold to flatten the burr formed in the perforated portion of the first bent portion, and at the same time, the second bending step is repeated. And subsequently performing a blanking step to form a tetrahedral sandwich core having a hexagonal perforated part continuously from the metal plate, wherein the tetrahedral sandwich core with a hexagonal perforated part is formed. The method of claim 5, The first bending step, A metal plate charging step of moving the metal plate onto the bending portion formed in the lower mold; A first bent part forming step of pressing the metal plate with the upper mold to form the first bent part; And And an upper mold removing step of separating the upper mold and the lower mold by removing the upper mold, wherein the tetrahedral sandwich core is provided with a hexagonal perforated part. The method of claim 5, The second bending step, A first bent portion seating step of moving the metal plate to seat the first bent portion on a blanking portion formed in the lower mold; And And a second bent portion forming step of forming a second bent portion connected to the first bent portion by pressing the metal plate with the upper mold. . The method of claim 5, The blanking step, A punching part forming process of lowering the press member to a blanking part formed in the lower mold and pressing the first bent part to form a hexagonal perforated part in the first bent part; And A method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part, comprising: a pressing member for lifting the upper mold on the upper mold, and an upper mold removing step for removing the upper mold. The method of claim 5, The first bent portion and the second bent portion is a V-shaped, characterized in that the hexagonal perforated portion is provided with a tetrahedral sandwich core manufacturing method. The method of claim 9, The first bent portion and the second bent portion is a method of manufacturing a tetrahedral sandwich core having a hexagonal perforated portion characterized in that to vary the structural characteristics of the tetrahedral sandwich core by adjusting the angle of the V-shaped bent portion. A tetrahedral sandwich core manufactured by a method for manufacturing a tetrahedral sandwich core having a hexagonal perforated part according to any one of claims 5 to 10; Upper and lower plates disposed above and below the tetrahedral sandwich core; And A tetrahedral sandwich plate structure provided with hexagonal perforations, characterized in that it comprises a coupling member for coupling the end of the tetrahedral sandwich core and the upper and lower plates. The method of claim 11, A tetrahedral sandwich plate structure provided with hexagonal perforations, characterized in that to form a multi-layer structure by stacking two or more layers of the tetrahedral sandwich core.

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