KR20230161561A - Device for manufacturing cell case of battery - Google Patents

Abstract

The present invention relates to a battery cell case manufacturing device, which includes a fixed mold that forms one side of the cell case molding space, and a fixed mold that is installed to be movable in a straight direction with respect to the fixed mold and forms the other side of the cell case molding space. It includes a movable mold that penetrates one side and an inner lower surface of the fixed mold and a vacuum hole that adsorbs the bus bar to the inner lower surface of the fixed mold.
Therefore, by making it possible to manufacture a cell case with integrated bus bars through bus bar insert injection, there is no need to perform a separate process to mount the bus bar on the cell case, thereby reducing manufacturing costs and time.

Description

Device for manufacturing cell case of battery}

The present invention relates to a battery cell case manufacturing device, and more specifically, to a battery cell case manufacturing device that allows a bus bar to be more easily and robustly mounted on a cell case.

To reduce air pollution caused by internal combustion engine vehicles, various types of electric vehicles such as hybrid, plug-in, battery, and hydrogen fuel cell are currently being produced and used. All of these electric vehicles drive the motor with current stored in the battery module and use it as a main or auxiliary power source.

A battery module is made up of multiple battery cells, and the same polarity electrode leads of each battery cell are connected in series and parallel using a bus bar to obtain the power required to drive the vehicle.

Meanwhile, the cell case that surrounds all of the battery cells is made of plastic injection molding for insulation. As shown in FIG. 1, the bus bars 100 are first mounted on the cell case 200 and the cell case 200 is assembled to form the cell case. (200) Upon assembly, the multiple bus bars 100 required for the battery module can be easily and accurately connected to the corresponding electrode leads.

When assembling the bus bar 100 to the cell case 200 as described above, the bus bar 100 is first bonded to the cell case 200 (attached with adhesive), and then an additional fusion process (cell case 200) is performed. By forming a fusion protrusion that is fused to the coupling hole of the bus bar 100, the bus bar 100 can be firmly mounted on the cell case 200 with sufficient bonding strength.

However, as described above, in order to assemble the bus bar 100 to the cell case 200, a two-step process of bonding and then fusion is required, resulting in an increase in the number of processes, resulting in an increase in manufacturing cost and time.

Conventional technology is technical information that the inventor possessed for deriving the present invention or acquired in the process of deriving the present invention, and cannot necessarily be said to be known technology disclosed to the general public before filing the application for the present invention.

Republic of Korea Patent Publication No. 10-2020-0143939 (published on December 28, 2020)

In solving the above-described problems, the purpose of the present invention is to provide a battery cell case manufacturing device in which the bus bar is firmly mounted on the cell case at the same time as the cell case is manufactured, thereby eliminating the need for separate bus bar mounting processes. .

The problems to be solved by the present invention are not limited to those mentioned above, and other problems to be solved that are not mentioned can be clearly understood by a person skilled in the art to which the present invention belongs from the following description. There will be.

An apparatus for manufacturing a battery cell case according to an embodiment of the present invention includes a fixed mold forming one side of the cell case molding space, a fixed mold installed to be movable in a straight direction with respect to the fixed mold, and a mold formed on the other side of the cell case molding space. It includes a movable mold forming a movable mold, and a vacuum hole formed in a structure that penetrates one outer surface and an inner lower surface of the fixed mold and adsorbing the bus bar to the inner lower surface of the fixed mold.

The vacuum hole includes a main hole that is connected to a vacuum device and receives vacuum pressure, and a plurality of suction holes that have one end connected to the main hole and the other end opening toward the molding space through the inner lower surface of the fixed mold.

The vacuum device includes a vacuum tank connected to the main hole and storing vacuum pressure, a vacuum pump connected to the vacuum pump to create vacuum pressure inside the vacuum tank, and installed between the vacuum tank and the main hole to maintain the vacuum pressure in the main hole. Includes a three-way valve that connects to the vacuum tank or opens to the atmosphere.

The three-way valve is controlled by an electronic control unit that controls the overall operation of the cell case manufacturing device, and the electronic control unit operates when the bus bar is inserted into the adsorption position between the fixed mold and the moving mold by the bus bar insertion device. It is characterized by operating the three-way valve in a state that connects the main hole and the vacuum tank.

In addition, the electronic control unit is characterized by opening the three-way valve to the atmosphere within a time range from completion of cell case injection to immediately before mold separation.

An expansion part may be formed in the suction hole, and a vacuum pad may be installed in the expansion part.

The vacuum pad includes an adapter fixed to the suction hole and a pad member coupled to the adapter.

The adapter includes a body that is caught on a locking protrusion formed on the upper side of the expansion part, a nipple that is formed integrally with the upper part of the body and is screwed into the suction hole, and penetrates the center of the nipple and the body and protrudes downward from the body, and the lower end is the pad. It includes a hollow pipe located in the internal space of the member.

The pad member has a structure that penetrates the hollow pipe and includes an upper plate portion that is in close contact with the body of the adapter, a concave portion whose diameter decreases as it extends downward from the upper plate portion, and a diffuser portion whose diameter increases again as it extends downward from the concave portion. do.

The lower end of the diffuser part protrudes outward from the expansion part and is located lower than the lower surface of the fixing mold.

A plurality of coupling holes are formed in the bus bar, and a concave groove concave upward is formed on the lower surface of the fixing mold corresponding to each coupling hole, thereby forming a fusion protrusion that couples the cell case and the bus bar.

The lower end of the concave groove is formed to have the same diameter as the through hole of the bus bar, and the diameter gradually decreases from the lower end to the upper end.

As described above, using the battery cell case manufacturing device according to the present invention, the cell case can be injection molded with the bus bar inserted into the mold. In other words, cell case manufacturing and busbar installation can be performed simultaneously.

Therefore, when manufacturing the cell case, the bus bar is assembled to the cell case, so there is no need to perform a separate process for assembling the bus bar to the cell case, thereby reducing the number of processes, which has the effect of reducing manufacturing cost and manufacturing time.

In addition, the battery cell case manufacturing device according to the present invention can prevent the bus bar from being removed from the fixing mold by forming a vacuum hole in the fixing mold and stably adsorbing the bus bar to the lower surface of the fixing mold. .

In addition, since a vacuum pad is provided at the entrance of the vacuum hole, the bus bar can be stably adsorbed even when the shape of the bus bar is poor (poor flatness).

The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

Figure 1 is a schematic diagram showing the manufacturing process of a battery cell case according to the prior art.
Figure 2 is a schematic diagram of the main parts of the battery cell case manufacturing device according to the present invention, with the mold open.
Figure 3 is a diagram of the mold closing state of Figure 2.
Figure 4 is an overall configuration diagram of a battery cell case manufacturing device according to the present invention.
Figure 5 is a diagram showing the installation state of the vacuum pad, which is one component of the present invention, showing the state before bus bar adsorption.
FIG. 6 is a view showing a state in which cell case material is injected after adsorption of the bus bar in FIG. 5.

In the present invention, the accompanying drawings may be shown in exaggerated expressions for differentiation and clarity from the prior art and for convenience in understanding the technology. In addition, the terms described below are terms defined in consideration of the functions in the present invention, and may vary depending on the intention or custom of the user or operator, so definitions of these terms should be made based on the technical content throughout the present specification. will be. Meanwhile, the examples are merely illustrative of the components presented in the claims of the present invention and do not limit the scope of the present invention, and the scope of the rights should be interpreted based on the technical idea throughout the specification of the present invention. .

Throughout the specification, when a certain configuration is said to “include” a certain configuration, this means that other configurations may be further included rather than excluding other configurations, unless specifically stated to the contrary.

In addition, when a configuration is said to be “connected,” “connected,” or “coupled” to another configuration, this does not only mean “directly connected,” “directly connected,” or “directly coupled,” but also means “that.” This means that there may be cases of ‘connection with another configuration in the middle’, ‘connection with another configuration in the middle’, or ‘combined with another configuration in the middle’. On the other hand, when a configuration is said to be “directly connected,” “directly connected,” or “directly coupled” to another configuration, it should be understood that no other configuration exists in between.

Additionally, when directional terms such as “front”, “back”, “top”, “bottom”, “left”, “right”, “one end”, “other end”, “both ends”, etc. are used, this refers to the disclosed drawings. They are used illustratively in relation to the orientation and should not be construed as limiting, and when terms such as “first” and “second” are used, these are terms for distinguishing each configuration and should not be construed as restrictive. .

In order to more clearly explain the characteristics of the embodiments of the present invention, detailed descriptions will be omitted regarding matters widely known to those skilled in the art to which the following embodiments belong. In addition, detailed description of parts in the drawings that are not related to the description of the embodiment will be omitted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

Figure 2 is a schematic diagram of the main parts of the battery cell case manufacturing device according to the present invention in an open mold state, Figure 3 is a mold-closing state diagram of Figure 2, and Figure 4 is an overall view of the battery cell case manufacturing device according to the present invention. It is a configuration diagram, and Figure 5 is a diagram showing the installation state of the vacuum pad, which is one component of the present invention, showing the state before bus bar adsorption, and Figure 6 shows the state in which the cell case material is injected after bus bar adsorption in Figure 5. It is a drawing.

As shown in Figures 2 and 3, the battery cell case manufacturing apparatus according to an embodiment of the present invention includes a fixed mold 10 forming one side of the molding space (cavity) and the other side of the molding space. It includes a movable mold 20 forming a , and a vacuum hole 40 that adsorbs the bus bar 30 to the inner surface of the fixed mold 10.

The fixed mold 10 and the moving mold 20 are installed in each base portion 11 and 21. The base portion 11 of the fixed mold 10 is fixed at a certain position of the injection device, and the base portion 21 of the movable mold 20 is directed toward the fixed mold 10 by a moving mechanism and driving device (not shown). and is installed to enable straight movement in the opposite direction. Accordingly, when the movable mold 20 moves toward the fixed mold 10 and the two molds are joined, the cell case molding space (hereinafter simply referred to as 'molding space') is formed between the two molds.

A gate 50 is formed in the fixed mold 10 through which plastic melt, which is a raw material for the cell case, can be injected into the molding space.

The movable mold 20 is provided with an ejector pin 60 and an ejector plate 61 that moves the ejector pin 60 linearly in its longitudinal direction. The ejector pin 60 protrudes to the outside of the surface of the mobile mold 20 by the ejector plate 61, so that the cooled and solidified product after molding can be removed from the mobile mold 20.

The vacuum hole 40 is connected to a separate vacuum device 70 provided on the outside of the mold and receives vacuum pressure from the main hole 41, and one end is connected to the main hole 41 and the other end is connected to the fixed mold 10. It includes a plurality of suction holes 42 that open toward the molding space through the inner lower surface.

The main hole 41 is formed in a horizontal direction inside the fixing mold 10, and is opened at one end to one side of the fixing mold 10 through a pipe connection means (nipple, etc.) and a pipe body (pipe, hose). It is connected to the vacuum device 70. The number and positions of the main holes 41 and suction holes 42 are appropriately designed according to the detailed shape and size of the bus bar 30 to be adsorbed to the inner lower surface of the fixing mold 10.

As shown in Figure 4, the vacuum device 70 includes a vacuum tank 71, a vacuum pump 72, and a three-way valve 73.

The vacuum tank 71 is connected to the main hole 41 of the vacuum hole 40 through a pipe, and stores vacuum pressure to be used for adsorption of the bus bar 30.

The vacuum pump 72 discharges the air inside the vacuum tank 71 to form an appropriate vacuum pressure inside the vacuum tank 71.

The three-way valve 73 is installed on the pipe connecting the main hole 41 and the vacuum tank 71 and serves to connect the main hole 41 to the vacuum tank 71 or to open it to the atmosphere. It is an electronic control valve whose operation is controlled by an electronic control unit (80).

The electronic control unit 80 controls the overall operation of the battery cell case manufacturing device according to the present invention, including the vacuum device 70, and operates the three-way valve 73 for adsorption of the bus bar 30. Controls operation.

That is, the electronic control unit 80 is operated in a mold-open state immediately after the bus bar insertion device (= bus bar insertion jig) inserts the bus bar 30 into a position in contact with the inner lower surface of the fixed mold 10. Control is performed to open the way valve 73 toward the vacuum tank 71. Accordingly, the vacuum pressure of the vacuum tank 71 is applied to the main hole 41 and the suction hole 42, so that the bus bar 30 can be adsorbed at the entrance of the suction hole 42. Since the entrance of the suction hole 42 is located on the same surface as the inner lower surface of the fixing mold 10, the bus bar 30 is tightly fixed to the inner lower surface of the fixing mold 10.

As described above, after adsorption of the bus bar 30, molding, injection, cooling, opening (mold separation), and extraction of the cell case (1) are performed, and the electronic control unit 80 takes out the cell case (1) after completion of injection. The three-way valve 73 is opened to the atmosphere within the time range immediately before the mold separation to remove the vacuum pressure in the vacuum hole 40, so that the fixed mold 10 and the cell case 1 are separated when the mold is opened. It can be done smoothly.

Additionally, the electronic control unit 80 always maintains the vacuum pressure of the vacuum tank 71 in a pressure range appropriate for adsorption of the bus bar 30. For this purpose, the vacuum tank 71 is equipped with a pressure sensor 71a that measures the pressure inside the vacuum tank 71, and the measured value of the pressure sensor 71a is transmitted to the electronic control unit 80 in real time.

Therefore, when the vacuum pressure value inside the vacuum tank 71 falls to the lower limit of the set pressure range (minimum suction force), the electronic control unit 80 operates the vacuum pump 72 to increase the vacuum pressure of the vacuum tank 71. and repeatedly performs control to stop the operation of the vacuum pump 72 when it rises to the upper limit value (maximum suction power), so that the vacuum pressure of the vacuum tank 71 is always maintained in a pressure range appropriate for adsorption of the bus bar 30. You can.

On the other hand, when the end of the vacuum hole 40 is a simple hole opened toward the molding space like the suction hole 42, the shape quality of the bus bar 30 is good, that is, the bus bar 30 has excellent flatness. If so, the bus bar 30 can be normally adsorbed to the inner lower surface of the fixing mold 10.

However, if the flatness of the bus bar 30 is poor, a gap may occur between the suction hole 42 and the bus bar 30. In this case, the adsorption force by the vacuum is not formed properly, so the adsorption of the bus bar 30 is poor. It may not be done properly and may be removed from the fixing mold (10).

In order to prevent such a bus bar removal phenomenon, the battery cell case manufacturing device according to the present invention may further include a vacuum pad 90 installed in the suction hole 42, as shown in FIGS. 5 and 6.

The vacuum pad 90 includes an adapter 91 made of metal and a pad member 92 made of elastic and elastic synthetic rubber (NBR, silicone, polyurethane, etc.).

The adapter 91 includes a disk-shaped body 91a, a nipple 91b formed on the upper surface of the body 91a, and a hollow tube 91c installed in a structure that vertically penetrates the central portion of the nipple 91b and the body 91a. ) includes.

In order to install the vacuum pad 90 at the end of the opening side of the suction hole 42, the end of the suction hole 42 is expanded to form an expansion portion 42a. The diameter of the expansion portion 42a is slightly larger than the diameter of the body 91a, so that the body 91a can be easily inserted into the expansion portion 42a.

In addition, a male thread is formed on the outer peripheral surface of the nipple (91b), and a female thread is formed on the inner peripheral surface of the corresponding portion of the suction hole 42 where the nipple (91b) is inserted, so that the nipple (91b) is screwed to the suction hole 42. It can be firmly fixed. At this time, the body 91a is caught on the locking protrusion 42b, which is the upper surface of the expansion part 42a, so that the screw fastening depth of the nipple 91b is always constant, and the installation position of the adapter 91 is always constant, so further, the pad member The installation position of (92) can always be kept constant.

The hollow tube 91c is formed to a length such that its lower end is located inside the expanded pipe 42a when the vacuum pad 90 is installed in the suction hole 42. That is, in the completed state of installation, the lower end of the hollow tube (91c) is located above the lower surface of the fixing mold (10), and accordingly, when the bus bar 30 is adsorbed to the lower surface of the fixing mold (10), the hollow tube (91c) ) and the bus bar 30 are prevented from colliding, thereby preventing deformation of the hollow pipe 91c and the bus bar 30.

The pad member 92 includes a disk-shaped upper plate portion 92a, a concave portion 92b formed in a shape whose diameter decreases downward from the upper plate portion 92a, and a diameter that increases again downward from the concave portion 92b. It includes a diffuser portion 92c formed in a shape that is. That is, the pad member 92 has a cup shape with a concave middle portion, and the upper end is closed by the upper plate portion 92a and the lower end is open.

A circular coupling hole is formed through the center of the upper plate 92a of the pad member 92, and the pad member 92 is assembled to the lower part of the adapter 91 in a structure in which the hollow tube 91c is inserted into the coupling hole. do. The upper plate portion 92a of the pad member 92 is in close contact with the body 91a of the adapter 91.

In the completed state of installation of the vacuum pad 90 as shown in FIG. 5, the lower end of the pad member 92, that is, the lower end of the diffuser portion 92c, protrudes downward from the lower surface of the fixing mold 10.

Therefore, when the bus bar 30 is horizontally inserted between the fixed mold 10 and the moving mold 20 by the bus bar insertion device and the bus bar 30 is raised and moved to the adsorption position, the bus bar 30 It is only necessary to raise the pad member 92 to a position away from the lower surface of the fixing mold 10 by the protruding length L of the pad member 92, so that collision between the bus bar 30 and the fixing mold 10 can be prevented when the bus bar 30 is inserted. This can prevent deformation and failure of the bus bar 10 and the bus bar input device due to collision impact.

When the insertion of the bus bar 30 by the bus bar input device (the operation is controlled by the electronic control unit 80) is completed (the bus bar 30 is in contact with the bottom of the pad member 92), the three The way valve 73 connects the vacuum tank 71 and the vacuum hole 40 to apply vacuum pressure to the vacuum hole 40, and the vacuum pressure is applied to the pad member ( 92) It acts inside. Therefore, the bus bar 30 is adsorbed to the pad member 92.

The pad member 92 is in a state where its lower end protrudes outward from the lower surface of the fixing mold 10 as shown in FIG. 5 at the beginning of the adsorption of the bus bar 30, and as the adsorption progresses, it is protruded to the inside of the expansion part 42a by vacuum pressure. is contracted to The pad member 92 can be contracted until its lower end is at the same height as the lower surface of the fixing mold 10.

Therefore, the bus bar 30 is accurately adhered to the lower surface of the fixed mold 10, and the close contact is maintained stably. In that state, the fixed mold 10 and the moving mold 20 are combined and then the injection process is performed.

Meanwhile, as shown in FIGS. 5 and 6, a through hole 31 for forming a fusion protrusion 1a is formed in the bus bar 30, and the through hole 31 is formed on the lower surface of the fixing mold 10. A concave groove 12 that is concave upward is formed at a position corresponding to .

Therefore, when the bus bar 30 is adsorbed to the lower surface of the fixed mold 10 by vacuum pressure, the through hole 31 and the concave groove 12 are aligned, and injection is performed in that state to allow the molten material to flow into the through hole ( 31) and the inside of the concave groove 12 is filled. Afterwards, the filled portion inside the through hole 31 and the concave groove 12 is cooled to form a fused protrusion 1a.

As described above, the fusion protrusion 1a is formed to increase the fusion area between the cell case 1 and the bus bar 30 (the fusion area is increased by the inner peripheral surface area of the through hole 31), thereby increasing the fusion area between the bus bar 30 and the cell. The bonding strength of the case 1 is improved, and the fixed state of the bus bar 30 is maintained stably.

Meanwhile, the concave groove 12 is formed in a shape whose diameter gradually decreases from the bottom to the top, and the bottom is formed to have the same diameter as the through hole 31. Therefore, when the fixed mold 10 and the moving mold 20 are separated after injection and cooling, the cell case 1 can be easily released from the fixed mold 10.

As described above, according to the battery cell case manufacturing device according to the present invention, bus bar insert injection can be performed, so that the bus bar is integrally assembled with the cell case at the same time as the cell case is manufactured, and bonding is required to assemble the bus bar to the cell case. This has the effect of eliminating the need for a separate fusion process. Therefore, the number of processes required when manufacturing a cell case equipped with a bus bar is reduced, thereby reducing the cell case manufacturing cost and manufacturing time.

In addition, a vacuum hole is formed in the fixing mold, allowing the bus bar to be stably adsorbed to the lower surface of the fixing mold, thereby preventing the bus bar from being removed from the fixing mold during the manufacturing process. Therefore, it is possible to install the busbar at the exact location of the cell case.

In addition, since a vacuum pad is provided at the entrance of the vacuum hole, the bus bar can be stably adsorbed even when the flatness of the bus bar is poor.

As described above, the present invention has been described with reference to the embodiments shown in the drawings, but this is merely illustrative, and various modifications and equivalent other embodiments are possible based on common knowledge in the field to which the technology pertains. You must understand. Therefore, the true technical protection scope of the present invention is based on the claims described below and should be determined based on the specific details of the invention described above.

The present invention relates to a battery cell case manufacturing device, and can be used in the field of battery cell case manufacturing in which a bus bar is integrally provided. Furthermore, it can be widely used in the field of plate-shaped component insert injection, where plate-shaped parts are additionally installed on the surface of the injection product. Available.

1: Cell case 1a: Fusion protrusion
10: Fixed mold 11: Base
20: moving mold 21: base
30: bus bar 31: through hole
40: vacuum hole 41: main hole
42: Suction hole 42a: Expansion part
42b: Stopper 50: Gate
60: Ejector pin 61: Ejector plate
70: Vacuum device 71: Vacuum tank
71a: pressure sensor 72: vacuum pump
73: Three-way valve 80: Electronic control unit
90: Vacuum pad 91: Adapter
92: Pad member

Claims (12)

A fixed mold forming one side of the cell case molding space;
a movable mold installed to be movable in a straight direction with respect to the fixed mold and forming the other side of the cell case molding space;
A vacuum hole formed in a structure that penetrates one outer surface and an inner lower surface of the fixing mold and adsorbs the bus bar to the inner lower surface of the fixing mold;
A battery cell case manufacturing device comprising: In claim 1,
The vacuum hole includes a main hole that is connected to a vacuum device and receives vacuum pressure,
A plurality of suction holes, one end of which is connected to the main hole and the other end of which opens toward the molding space through the inner bottom of the fixed mold.
A battery cell case manufacturing device comprising: In claim 2,
The vacuum device includes a vacuum tank connected to the main hole and storing vacuum pressure,
A vacuum pump connected to the vacuum pump to create vacuum pressure inside the vacuum tank,
A three-way valve installed between the vacuum tank and the main hole to connect the main hole to the vacuum tank or open it to the atmosphere.
A battery cell case manufacturing device comprising a. In claim 3,
The three-way valve is controlled by an electronic control unit that controls the overall operation of the cell case manufacturing device,
The electronic control unit operates the three-way valve in a state of connecting the main hole and the vacuum tank when the bus bar is inserted into the adsorption position between the fixed mold and the moving mold by the bus bar insertion device. manufacturing device. In claim 3,
The three-way valve is controlled by an electronic control unit that controls the overall operation of the cell case manufacturing device,
The electronic control unit is a battery cell case manufacturing device, characterized in that it opens the three-way valve to the atmosphere within a time range from completion of cell case injection to immediately before mold separation. In claim 2,
A cell case manufacturing device for a battery, characterized in that an expansion part is formed in the suction hole, and a vacuum pad is installed in the expansion part. In claim 6,
A battery cell case manufacturing device, wherein the vacuum pad includes an adapter fixed to the suction hole and a pad member coupled to the adapter. In claim 7,
The adapter includes a body that is caught on a locking protrusion formed on the upper side of the expansion part, a nipple that is formed integrally with the upper part of the body and is screwed into the suction hole, and penetrates the center of the nipple and the body and protrudes downward from the body, and the lower end is the pad. A battery cell case manufacturing device comprising a hollow tube located in the internal space of the member. In claim 7,
The pad member has a structure that penetrates the hollow pipe and includes an upper plate portion that is in close contact with the body of the adapter, a concave portion whose diameter decreases as it extends downward from the upper plate portion, and a diffuser portion whose diameter increases again as it extends downward from the concave portion. A battery cell case manufacturing device, characterized in that: In claim 7,
A cell case manufacturing device for a battery, characterized in that the lower part of the diffuser part protrudes outward from the expansion part and is located lower than the lower surface of the fixing mold. In claim 1,
A plurality of coupling holes are formed in the bus bar, and a concave groove concave upward is formed in the lower surface of the fixing mold corresponding to each coupling hole, so that a fusion protrusion is formed to couple the cell case and the bus bar. Cell case manufacturing device. In claim 11,
The concave groove is formed at the bottom to have the same diameter as the through hole of the bus bar, and is formed in a shape where the diameter gradually decreases from the bottom to the top.