EP4659877A1

EP4659877A1 - Die-casting die

Info

Publication number: EP4659877A1
Application number: EP24749933.8A
Authority: EP
Inventors: Masatoshi Shiozaki
Original assignee: FCC Co Ltd
Current assignee: FCC Co Ltd
Priority date: 2023-02-02
Filing date: 2024-01-16
Publication date: 2025-12-10
Also published as: WO2024161979A1; JP2024110267A; US20250339896A1; JP7825579B2; CN120500390A

Abstract

A die-casting mold 10 includes a first mold insert 50 located on the side of a fixed die 20, and a second mold insert 70 located on the side of a movable die 30. The first mold insert 50 includes first through-holes 56 filled with a melted metal material to be used to mold a plurality of heat sink pins 105. The second mold insert 70 includes second through-holes 76 usable to discharge gas in a molding space 15. At least one of a first facing surface 53 and a second facing surface 53 includes recessed grooves 80 formed therein, the recessed grooves 80 being communicated with the first through-holes 56 and the second through-holes 76 when the first mold insert 50 and the second mold insert 70 are located in place, and the recessed grooves 80 preventing the melted metal material from passing therethrough but allowing the gas to pass therethrough. As seen in a die moving direction P, the plurality of first through-holes 56 do not overlap at least a portion of the plurality of second through-holes 76.

Description

Technical Field

The present invention relates to a die-casting mold.

Background Art

Conventionally, a heat sink including a plurality of heat sink pins is used in various fields. The heat sink is molded by use of, for example, a die-casting mold. For example, Patent Literature 1 discloses a die-casting mold including a movable die including a mold insert, and a fixed die. In Patent Literature 1, in a plurality of heat sink pins in a cavity for a heat sink, porous material members that do not allow a molten aluminum-based material to pass therethrough but allow gas to pass therethrough are respectively located. With this configuration, the molten metal material is allowed to flow up to a tip of each of the heat sink pins, and thus the heat sink is produced.

Citation List

Patent Literature

Patent Literature 1 : Japanese Patent No. 3306376

Summary of Invention

Technical Problem

With the technology described in Patent Literature 1, porous material members, which are parts specialized for degassing, are needed to mold heat sink pins as described above. One porous material member is needed to mold one heat sink pin. Therefore, as the number of the heat sink pins to be included in the heat sink is increased, the number of the porous material members necessary to mold the heat link pins is increased, which may undesirably raise the costs to produce the heat sink.
The present invention, made in light of such a point, has an object of providing a die-casting mold usable to easily produce a molded item including a plurality of heat sink pins with no use of parts specialized for degassing.

Solution to Problem

A die-casting mold according to the present invention is a die-casting mold to mold a molded item including a plurality of heat sink pins. The die-casting mold includes a fixed die; a movable die movable toward, or away from, the fixed die; a mold insert to mold the plurality of heat sink pins; and a molding space defined by the fixed die, the movable die and the mold insert, the molding space being to be filled with a melted metal material. Where a direction in which the movable die moves with respect to the fixed die is a die moving direction, the mold insert includes a first mold insert located on the side of the fixed die in the die moving direction, and a second mold insert located on the side of the movable die in the die moving direction. The first mold insert includes a first body including a first facing surface facing the second mold insert, and a plurality of first through-holes extending in the die moving direction and formed to run through the first body, the plurality of first through-holes being filled with the melted metal material to be respectively used to mold the plurality of heat sink pins. The second mold insert includes a second body including a second facing surface facing the first facing surface, and a plurality of second through-holes extending in the die moving direction and formed to run through the second body, the plurality of second through-holes being usable to discharge gas in the molding space. At least one of the first facing surface and the second facing surface includes recessed grooves formed therein, the recessed grooves being communicated with the first through-holes and the second through-holes when the first mold insert and the second mold insert are located in place, and the recessed grooves preventing the melted metal material from passing therethrough but allowing the gas to pass therethrough. As seen in the die moving direction, the plurality of first through-holes do not overlap at least a portion of the plurality of second through-holes.
According to the die-casting mold of the present invention, at least one of the first facing surface and the second facing surface includes the recessed grooves formed therein, the recessed grooves being communicated with the first through-holes and the second through-holes when the first mold insert and the second mold insert are located in place. The recessed grooves are configured to prevent the melted metal material from passing therethrough but allow the gas to pass therethrough. As seen in the die moving direction, the plurality of first through-holes do not overlap at least a portion of the plurality of second through-holes. Therefore, in a portion where the first through-holes and the second through-holes do not overlap each other, even if the first through-holes are filled with the melted metal material, the melted metal material does not flow to the second through-holes. In addition, the gas in the molding space passes through the first through-holes and the recessed grooves and flows to the second through-holes. Therefore, when the first through-holes are filled with the melted metal material, the gas in the first through-holes is allowed to flow to the second through-holes via the recessed grooves. With this arrangement, the first through-holes are filled with the melted metal material to tips thereof. In this manner, in the portion where the first through-holes and the second through-holes do not overlap each other, the molded item including the heat sink pins is produced easily even without porous material members, as parts specialized for degassing, being provided in the first through-holes.

Advantageous Effects of Invention

According to the present invention, a die-casting mold usable to easily produce a molded item including a plurality of heat sink pins with no use of parts specialized for degassing is provided.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a perspective view of a die-casting mold according to one embodiment.
[Fig. 2] Fig. 2 is a perspective view of a molded item produced by use of the die-casting mold according to one embodiment.
[Fig. 3] Fig. 3 is a cross-sectional view of a portion of the die-casting mold according to one embodiment.
[Fig. 4] Fig. 4 is a perspective view of a mold insert according to one embodiment.
[Fig. 5] Fig. 5 is a perspective view of a first mold insert according to one embodiment.
[Fig. 6] Fig. 6 is a plan view of the first mold insert according to one embodiment.
[Fig. 7] Fig. 7 is a perspective view of the first mold insert according to one embodiment.
[Fig. 8] Fig. 8 is a bottom view of the first mold insert according to one embodiment.
[Fig. 9] Fig. 9 is a perspective view of a second mold insert according to one embodiment.
[Fig. 10] Fig. 10 is a plan view of the second mold insert according to one embodiment.
[Fig. 11] Fig. 11 is a perspective view of the second mold insert according to one embodiment.
[Fig. 12] Fig. 12 is a bottom view of the second mold insert according to one embodiment.
[Fig. 13] Fig. 13 is a plan view of the second mold insert according to one embodiment, showing the positional relationship among first through-holes, second through-holes and recessed grooves.

Description of Embodiments

Hereinafter, an embodiment of a die-casting mold according to the present invention will be described with reference to the drawings. The embodiment described herein does not specifically limit the present invention, needless to say. Elements and portions having the same functions will bear the same reference signs, and overlapping descriptions will be omitted or simplified, as appropriate.
Fig. 1 is a perspective view of a die-casting mold 10 according to this embodiment. The die-casting mold 10 is a device usable to perform a die-casting method, that is, a casting method performed at a high speed and a high pressure. Herein, the term "high pressure" refers to, for example, 20 MPa to 100 MPa. The die-casting mold 10 is a device to produce a molded item 100 (see Fig. 2), including a plurality of heat sink pins 105 (see Fig. 2). The die-casting mold 10 includes a fixed die 20, a movable die 30, and a mold insert 40 (see Fig. 3).
As shown in Fig. 2, the molded item 100 is formed of a metal material having a high thermal conductivity (e.g., an aluminum alloy). The molded item 100 includes a box-like body 102 having a top opening, and the plurality of heat sink pins 105 provided inside the body 102. The body 102 and the heat sink pins 105 are molded integrally with each other. The molded item 100 is usable as, for example, a heat sink or the like.
As shown in Fig. 3, the fixed die 20 includes a cavity 21 usable to form a portion of the molded item 100 (see Fig. 2).
As shown in Fig. 3, the movable die 30 is provided to be movable toward, or away from, the fixed die 20. In this embodiment, a direction in which the movable die 30 moves with respect to the fixed body 20 will be referred to as a "die moving direction P". A direction in which the movable die 30 moves toward the fixed body 20 will be referred to as "P1", and a direction in which the movable die 30 moves away from the fixed body 20 will be referred to as "P2". The movable die 30 includes a core 31 usable to form another portion of the molded item 100 (see Fig. 2). The movable die 30 includes an attachment hole 32, to which the mold insert 40 is to be attached.
As shown in Fig. 3, the mold insert 40 is located in the fixed die 20 and the movable die 30. The mold insert 40 is provided to be attachable to, and detachable from, the attachment hole 32. The mold insert 40 is usable to mold the plurality of heat sink pins 105 (see Fig. 2) of the molded item 100 (see Fig. 2). The mold insert 40 is usable to mold a portion of the body 102 (see Fig. 2). The mold insert 40 is usable to mold the plurality of heat sink pins 105 and the portion of the body 102 of the molded item 100. When the movable die 30 is moved in direction P1 (the movable die 30 is moved toward the fixed die 20) to close the die-casting mold 10 in a state where the mold insert 40 is attached to the attachment hole 32, a molding space 15 is formed by the fixed die 20, the movable die 30 and the mold insert 40. The molding space 15 is defined by the cavity 21, the core 31 and first through-holes 56 (described below) of the mold insert 40. The molding space 15 is filled with a melted metal material (molten metal material). As the metal material, for example, an aluminum alloy is usable. The melted metal material is put into the molding space 15 through an injection entrance/exit 12 (see Fig. 1) provided in the fixed die 20 to fill the molding space 15.
As shown in Fig. 3 and Fig. 4, the mold insert 40 includes a first mold insert 50 and a second mold insert 70. The first mold insert 50 is located on the side of the fixed die 20 in the die moving direction P. In a state where the mold insert 40 is attached to the attachment hole 32, the first mold insert 50 is accommodated in the cavity 21. The second mold insert 70 is located on the side of the movable die 30 in the die moving direction P. The second mold insert 70 is provided to be attachable to, or detachable from, the first mold insert 50. In a state where the mold insert 40 is attached to the attachment hole 32, the second mold insert 70 is accommodated in the attachment hole 32.
As shown in Fig. 5 and Fig. 7, the first mold insert 50 includes a first body 52, the plurality of first through-holes 56 formed to run through the body 52, and engageable protrusions 60 protruding from the first body 52.
As shown in Fig. 7 and Fig. 8, the first body 52 includes a first facing surface 53 facing the second mold insert 70 (more specifically, a second facing surface 73 described below). As shown in Fig. 5 and Fig. 6, the first body 52 includes a surface 54 located opposite to the first facing surface 53 in the die moving direction P. In a state where the mold insert 40 is attached to the attachment hole 32, the surface 54 is located on the side of the fixed die 20, and the first facing surface 53 is located on the side of the movable die 30.
As shown in Fig. 5 and Fig. 6, the first through-holes 56 extend in the die moving direction P. The first through-holes 56 run through the first body 52 from the surface 54 to the first facing surface 53. The first through-holes 56 are filled with the melted metal material, and thus are respectively used to mold the plurality of heat sink pins 105 (see Fig. 2). That is, the first through-holes 56 are portions usable to mold the heat sink pins 105.
As shown in Fig. 7 and Fig. 8, the first mold insert 50 includes four engageable protrusions 60. The engageable protrusions 60 are respectively provided at four corners of the first body 52. The engageable protrusions 60 protrude in the direction P2 from the first body 52. The engageable protrusions 60 are configured to be in engagement with engageable recessed portions 90 (see Fig. 9; described below) of the second mold insert 70.
As shown in Fig. 9 and Fig. 11, the second mold insert 70 includes a second body 72, a plurality of second through-holes 76 formed to run through the second body 72, and the engageable recessed portions 90 formed in the second body 72.
As shown in Fig. 9 and Fig. 10, the second body 72 includes the second facing surface 73 facing the first mold insert 50 (more specifically, the first facing surface 53). As shown in Fig. 11 and Fig. 12, the second body 72 includes a rear surface 74 located opposite to the second facing surface 73 in the die moving direction P. In a state where the mold insert 40 is attached to the attachment hole 32, the second facing surface 73 is located on the side of the fixed die 20, and the rear surface 74 is located on the side of the movable die 30. In a state where the first mold insert 50 and the second mold insert 70 are located in place (e.g., in a state where the second mold insert 70 is attached to the first mold insert 50), the second facing surface 73 and the first facing surface 53 are in contact with each other.
As shown in Fig. 9 and Fig. 10, the second through-holes 76 extend in the die moving direction P. The second through-holes 76 run through the second body 72 from the second facing surface 73 to the rear surface 74. The second through-holes 76 are usable to discharge gas in the molding space 15 (see Fig. 3). That is, the second through-holes 76 are portions usable to discharge the gas in the first through-holes 56 when the first through-holes 56 in the molding space 15 are filled with the melted metal material. In this embodiment, another member (not shown) is located on the rear surface 74 to close the second through-holes 76. Alternatively, the second through-holes 76 may be vented. The number of the second through-holes 76 formed to run through the second body 72 is smaller than the number of the first through-holes 56 formed to run through the first body 52. As shown in Fig. 13, the plurality of first through-holes 56 and the plurality of second through-holes 76 do not overlap each other as seen in the die moving direction P. In this embodiment, it is not that all of the first through-holes 56 overlap all of the second through-holes 76 as seen in the die moving direction P. In Fig. 13, the first through-holes 56 are represented with two-dot chain lines, and the second through-holes 76 are represented with solid lines.
As shown in Fig. 11 and Fig. 12, the second mold insert 70 includes four engageable recessed portions 90. The engageable recessed portions 90 are respectively provided at four corners of the second body 72. The engageable recessed portions 90 are recessed toward the rear surface 74 from the second facing surface 73. The engageable recessed portions 90 are recessed in the direction P2. The engageable protrusions 60 (see Fig. 7) are engaged with the engageable recessed portions 90, so that the first mold insert 50 and the second mold insert 70 are assembled together.
As shown in Fig. 9 and Fig. 10, the second mold insert 70 includes a plurality of recessed grooves 80. The recessed grooves 80 are formed in the second facing surface 73. The recessed grooves 80 are recessed toward the rear surface 74 from the second facing surface 73. The recessed grooves 80 are recessed in the direction P2. The recessed grooves 80 each have a depth of, for example, 10 µm to 50 µm (e.g., 30 µm). The recessed grooves 80 extend in a longitudinal direction of the second body 72, that is, in a direction perpendicular to the direction in which the first through-holes 56 and the second through-holes 76 extend. The recessed grooves 80 may extend in a shorter direction of the second body 72. The second through-holes 76 are formed in the recessed grooves 80. That is, as shown in Fig. 10, the second through-holes 76 and the recessed grooves 80 overlap each other as seen in the die moving direction P. The recessed grooves 80 are communicated with the second through-holes 76. The recessed grooves 80 are communicated with the first through-holes 56 when the first mold insert 50 and the second mold insert 70 are located in place (e.g., when the second mold insert 70 is attached to the first mold insert 50). As shown in Fig. 13, the first through-holes 56 and the recessed grooves 80 overlap each other as seen in the die moving direction P. In one recessed groove 80, the number of the second through-holes 76 communicated with the recessed groove 80 is smaller than the number of the first through-holes 56 communicated with the recessed groove 80. For example, the number of the second through-holes 76 communicated with the recessed groove 80 is 2, and the number of the first through-holes 56 communicated with the recessed groove 80 is 6. The recessed grooves 80 are formed so as to, in a state where the first mold insert 50 and the second mold insert 70 are located in place (e.g., in a state where the second mold insert 70 is attached to the first mold insert 50), prevent the melted metal material from passing therethrough but allow the gas to pass therethrough. That is, in a state where the first mold insert 50 and the second mold insert 70 are located in place, when the first through-holes 56 are filled with the melted metal material, the gas in the first through-holes 56 flows into the second through-holes 76 via the recessed grooves 80, but the melted metal material dose not pass through the recessed grooves 80 but is blocked by the recessed grooves 80.
As shown in Fig. 11 and Fig. 12, the second body 72 of the second mold insert 70 includes a plurality of insertion holes 82 recessed toward the second facing surface 73 from the rear surface 74. The insertion holes 82 are vented. The insertion holes 82 are recessed in the direction P1. The number of the insertion holes 82 is smaller than the number of the second through-holes 76. As shown in Fig. 3, pipes 95, through which cooling water flows, are inserted into the insertion holes 82. In a state where the pipes 95 are inserted into the insertion holes 82, a gap in which the gas is allowed to pass is formed between each of the insertion holes 82 and the corresponding pipe 95. A sealing member 97 formed of an O-ring or the like is provided between each of the pipes 95 and the corresponding insertion hole 82. Therefore, the water flowing in the pipes 95 does not leak to the outside through the insertion holes 82. The insertion holes 82 each have an inner diameter longer than an inner diameter of each of the second through-holes 76.
As shown in Fig. 11 and Fig. 12, the second body 72 of the second mold insert 70 includes a plurality of connection grooves 84 formed in the rear surface 74. The connection grooves 84 are recessed toward the second facing surface 73 from the rear surface 74. The connection grooves 84 are recessed in the direction P1. The connection grooves 84 connect the second through-holes 76 and the insertion holes 82 to each other. The connection grooves 84 are usable to cause the gas, flowing in the second through-holes 76, to flow to the insertion holes 82. The connection grooves 84 extend in the longitudinal direction of the second body 72. The connection grooves 84 may extend in the shorter direction of the second body 72. One insertion hole 82 is connected with a plurality of second through-holes 76 via at least one connection groove 84. For example, an insertion hole 82A is connected with four second through-holes 76 via two connection grooves 84.
As described above, in the die-casting mold 10 according to this embodiment, at least one of the first facing surface 53 and the second facing surface 73 includes the recessed grooves 80 communicated with the first through-holes 56 and the second through-holes 76 when the first mold insert 50 and the second mold insert 70 are located in place. The recessed grooves 80 are configured to prevent the melted metal material from passing therethrough but allow the gas to pass therethrough, and the plurality of first through-holes 56 do not overlap at least a portion of the second through-holes 76 as seen in the die moving direction P. Therefore, in a portion where the first through-holes 56 and the second through-holes 76 do not overlap each other, even if the first through-holes 56 are filled with the melted metal material, the melted metal material does not flow to the second through-holes 76. In addition, the gas in the molding space 15 passes through the first through-holes 56 and the recessed grooves 80 and flows to the second through-holes 76. Therefore, when the first through-holes 56 are filled with the melted metal material, the gas in the first through-holes 56 is allowed to flow to the second through-holes 76 via the recessed grooves 80. With this arrangement, the first through-holes 56 are filled with the melted metal material to tips thereof (to ends thereof on the side of the second mold insert 70). In this manner, in the portion where the first through-holes 56 and the second through-holes 76 do not overlap each other, the molded item 100 including the heat sink pins 105 is produced easily even without porous material members, as parts specialized for degassing, being provided in the first through-holes 56.
In the die-casting mold 10 according to this embodiment, the plurality of first through-holes 56 and the plurality of second through-holes 76 do not overlap each other as seen in the die moving direction P. According to this embodiment, the melted metal material does not flow to all the second through-holes 76. Therefore, it is not necessary to provide the porous material members, as parts specialized for degassing, in all of the first through-holes 56 when the heat sink pins 105 are to be formed.
In the dis-casting mold 10 according to this embodiment, in one recessed groove 80, the number of the second through-holes 76 communicated with the recessed groove 80 is smaller than the number of the first through-holes 56 communicated with the recessed groove 80. According to this embodiment, it is not necessary to provide one second through-hole 76 for each first through-hole 56. That is, the gas flowing in the plurality of first through-holes 56 may be once assembled to the recessed groove 80 and then allowed to flow to the second through-holes 76 of a number smaller than the number of the first through-holes 56. Therefore, the configuration of the second mold insert 70 is simplified and the costs may be decreased.
In the die-casting mold 10 according to this embodiment, the recessed grooves 80 are formed in the second facing surface 73. According to this embodiment, the first through-holes 56, in the first mold insert 50, usable to mold the heat sink pins 105 are formed easily.
In the die-casting mold 10 according to this embodiment, the second body 72 includes the rear surface 74 located opposite to the second facing surface 73 in the die moving direction P, the insertion holes 82 recessed toward the second facing surface 73 from the rear surface 74 and allowing the pipes 95, through which the cooling water flows, to be inserted thereto, and the connection grooves 84 formed in the rear surface 74 and connecting the second through-holes 76 and the insertion holes 82 to each other. According to this embodiment, the gas flowing in the second through-holes 76 may be discharged outside through the insertion holes 82 (more specifically, through a gap between each of the insertion holes 82 and the corresponding pipe 95).
In the die-casting mold 10 according to this embodiment, one insertion hole 82 is connected with a plurality of second through-holes 76 via at least one connection groove 84. According to this embodiment, the gas flowing in the plurality of second through-holes 76 may be once assembled to one insertion hole 82 and then discharged outside via the insertion hole 82. That is, there is no need to form a great number of insertion holes 82, and therefore, the configuration of the second mold insert 70 is simplified.
In the die-casting mold 10 according to this embodiment, the inner diameter of each insertion hole 82 is longer than the inner diameter of each second through-hole 76. According to this embodiment, the gas flowing in the second through-holes 76 may be discharged outside more certainly through the insertion holes 82.
A preferred embodiment of the present invention is described above. The above-described embodiment is merely an example, and the present invention may be carried out in any of various other embodiments.
In the above-described embodiment, the plurality of first through-holes 56 and the plurality of second through-holes 76 are located so as not to overlap each other as seen in the die moving direction P. The present invention is not limited to this. For example, the plurality of first through-holes 56 may be located so as not to overlap at least a portion of the plurality of second through-holes 76 as seen in the die moving direction P. That is, a portion of the plurality of first through-holes 56 may overlap a portion of the plurality of second through-holes 76 as seen in the die moving direction P.
In the above-described embodiment, the recessed grooves 80 are formed in the second facing surface 73 of the second mold insert 70. The present invention is not limited to this. The recessed grooves 80 may be formed in, for example, the first facing surface 53 of the first mold insert 50. Alternatively, the recessed grooves 80 may be formed in both of the first facing surface 53 of the first mold insert 50 and the second facing surface 73 of the second mold insert 70.

Reference Signs List

10: die-casting mold
15: molding space
20: fixed die
30: movable die
40: mold insert
50: first mold insert
52: first body
53: first facing surface
56: first through-hole
70: second mold insert
72: second body
73: second facing surface
74: rear surface
76: second through-hole
80: recessed groove
82: insertion hole
84: connection groove
100: molded item
105: heat sink pin

Claims

A die-casting mold to mold a molded item including a plurality of heat sink pins, the die-casting mold comprising:
a fixed die;

a movable die movable toward, or away from, the fixed die;

a mold insert to mold the plurality of heat sink pins; and

a molding space defined by the fixed die, the movable die and the mold insert, the molding space being to be filled with a melted metal material,

wherein where a direction in which the movable die moves with respect to the fixed die is a die moving direction,

the mold insert includes:
a first mold insert located on a side of the fixed die in the die moving direction, and

a second mold insert located on a side of the movable die in the die moving direction, and

the first mold insert includes:
a first body including a first facing surface facing the second mold insert, and

a plurality of first through-holes extending in the die moving direction and formed to run through the first body, the plurality of first through-holes being filled with the melted metal material to be respectively used to mold the plurality of heat sink pins,

the second mold insert includes:
a second body including a second facing surface facing the first facing surface, and

a plurality of second through-holes extending in the die moving direction and formed to run through the second body, the plurality of second through-holes being usable to discharge gas in the molding space,

at least one of the first facing surface and the second facing surface includes recessed grooves formed therein, the recessed grooves being communicated with the first through-holes and the second through-holes when the first mold insert and the second mold insert are located in place, and the recessed grooves preventing the melted metal material from passing therethrough but allowing the gas to pass therethrough,
and

as seen in the die moving direction, the plurality of first through-holes do not overlap at least a portion of the plurality of second through-holes.
The die-casting mold according to claim 1, wherein as seen in the die moving direction, the plurality of first through-holes do not overlap the plurality of second through-holes.
The die-casting mold according to claim 1 or 2, wherein in one of the recessed grooves, a number of the second through-holes communicated with the recessed groove is smaller than a number of the first through-holes communicated with the recessed groove.
The die-casting mold according to claim 1 or 2, wherein the recessed grooves are formed in the second facing surface.
The die-casting mold according to claim 1 or 2, wherein the second body includes:
a rear surface located opposite to the second facing surface in the die moving direction,

insertion holes recessed toward the second facing surface from the rear surface, and allowing pipes, in which cooling water flows, to be inserted thereto, and

connection grooves formed in the rear surface and connecting the second through-holes and the insertion holes to each other.
The die-casting mold according to claim 5, wherein one of the insertion holes is connected with a plurality of the second through-holes via at least one of the connection grooves.
The die-casting mold according to claim 6, wherein the insertion holes each have an inner diameter longer than an inner diameter of each of the second through-holes.