KR102610475B1 - Laser welding method of dissimilar metals of secondary battery cap assembly - Google Patents

Abstract

One embodiment of the dissimilar metal laser welding method of the secondary battery cap assembly involves laser welding a rivet terminal welding portion made of copper and a rivet plate welding portion made of aluminum or aluminum alloy material laminated below the rivet terminal welding portion. A dissimilar metal laser welding method of an assembly, in which the rivet terminal weld portion and the rivet plate weld portion are stacked vertically, and a laser beam is radiated onto the rivet terminal weld portion to move downward from the upper surface of the rivet terminal weld portion to the rivet terminal. A first laser welding step of forming a first welded portion having a first depth set in the welded portion; A laser beam is irradiated within the range of the first weld formed in the first laser welding step to vertically pass through the rivet terminal weld and set on the upper part of the rivet plate weld from the boundary surface of the rivet terminal weld and the rivet plate weld. It includes a secondary laser welding step of forming a second weld having a second depth and joining the rivet terminal weld and the rivet plate weld.

Description

Laser welding method of dissimilar metals of secondary battery cap assembly}

The present invention relates to a dissimilar metal laser welding method for a secondary battery cap assembly, and more specifically, to a secondary battery cap assembly in which a rivet terminal made of copper and a rivet plate made of aluminum that constitute the cap assembly of a secondary battery are joined by laser welding. This relates to a dissimilar metal laser welding method for a battery cap assembly.

In general, secondary batteries are batteries that can be charged and discharged, unlike primary batteries that cannot be recharged. Low-capacity batteries in which one battery cell is packaged in a pack are used in small, portable electronic devices such as mobile phones and camcorders. Large-capacity batteries with dozens of cells connected are used as a power source for driving motors such as electric bicycles, electric scooters, hybrid cars, and electric cars.

Secondary batteries can be configured in shapes such as square, cylindrical, and pouch-shaped. The electrode assembly formed by interposing an insulating separator between the positive and negative electrode plates, and the electrolyte are accommodated in a case, and cap assemblies are attached to both ends of the case. It is composed.

The cap assembly includes a rivet terminal and a rivet plate.

The rivet terminal is made of a copper material, and the rivet plate is made of an aluminum or aluminum alloy material and is electrically connected by being interconnected. The opening of the case is sealed to maintain the airtightness of the case so that the electrolyte does not leak to the outside.

Conventionally, the rivet terminal made of the copper material and the rivet plate made of the aluminum material are arranged to overlap each other, and a method of welding dissimilar metals of copper and aluminum is applied by friction welding in which pressure is applied and pressed while applying heat. did.

When welding metals of different materials by friction welding, friction welding is performed while the base material to be processed into the rivet terminal and the rivet plate are held by respective jigs. After friction welding is completed, the rivet terminal is The base material to be processed is cut and processed into the shape of a rivet terminal.

In this case, there is a waste of material that is cut from the rivet terminal base material and discarded, and as cutting and post-processing processes are added in addition to the friction welding process, the number of processes increases and the process time is delayed, and the welding quality of the friction welding surface is increased. Due to the imperfection of the secondary battery, when the secondary battery is used for a long time, the joint state of the welded surface of the rivet terminal and the rivet plate is not properly maintained, causing unstable electrical conduction performance and leakage of electrolyte, which reduces the durability of the secondary battery.

Prior art related to secondary batteries is disclosed in Republic of Korea Patent No. 10-0949329.

The present invention was developed to solve the above-mentioned problems, and is a secondary battery cap that can prevent welding defects and improve welding quality when combining the rivet terminal and rivet plate of a secondary battery made of different metal materials by laser welding. The purpose is to provide a method for laser welding dissimilar metals in assemblies.

The dissimilar metal laser welding method of the secondary battery cap assembly of the present invention for realizing the above-described purpose includes a rivet terminal weld portion made of copper material, and a rivet plate made of aluminum or aluminum alloy material laminated below the rivet terminal weld portion. A dissimilar metal laser welding method of a secondary battery cap assembly for laser welding a welded portion, wherein the rivet terminal welded portion and the rivet plate welded portion are each arranged laterally and stacked up and down, and a laser beam is irradiated on the rivet terminal welded portion. A first laser welding step of forming a first welded portion having a set first depth in the rivet terminal welded portion in a downward direction from the upper surface of the rivet terminal welded portion; A laser beam is irradiated within the range of the first weld formed in the first laser welding step to vertically pass through the rivet terminal weld and set on the upper part of the rivet plate weld from the boundary surface of the rivet terminal weld and the rivet plate weld. A secondary laser welding step of forming a second welding portion having a second depth to join the rivet terminal welding portion and the rivet plate welding portion; Including, wherein the rivet terminal welding portion consists of a first flange portion protruding radially outward from the outer peripheral surface of the rivet terminal by a predetermined length, and the rivet plate welding portion is located around the outer peripheral surface of the rivet terminal and the first flange portion. It consists of a second flange part protruding radially inward from the inner peripheral surface of the rivet plate by a predetermined length so as to be stacked up and down in contact with the step shape, so that the bottom surface of the first flange part is in contact with the upper surface of the second flange part, The laterally protruding end surface of the first flange part is in contact with the side surface of the rivet plate, the laterally protruding end surface of the second flange part is in contact with the side surface of the rivet terminal, and the first laser In the welding step, the laser beam is irradiated in a positive defocusing state and laser welding is performed in a relatively wide range. In the second laser welding step, the laser beam is irradiated in a just focusing state and laser welding is performed in a relatively narrow range. , the second depth of the second weld portion is a dissimilar metal of copper constituting the rivet terminal weld portion and aluminum constituting the rivet plate weld portion while minimizing vaporization phenomenon due to thermal deformation of the aluminum material constituting the rivet plate weld portion. It is characterized by being set to the minimum depth that allows for solid joining by laser welding.

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The heat input amount of the laser beam in the first laser welding step and the second laser welding step may be determined by at least one of the focal distance at which the laser beam is irradiated, the output of the laser beam, and the welding speed of the laser beam.

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In setting the welding conditions of the laser beam, the heat input amount of the laser beam is calculated as the product of the output of the laser beam and the welding speed, and the welding speed is selected from a plurality of groups having a plurality of outputs and welding speeds with the same heat input amount. You can select a group with a large value.

Before the first laser welding step, the step of bending and caulking the caulking portion formed at the lower end of the rivet terminal toward the caulking portion groove formed on the inner peripheral surface of the rivet plate may be further included.

According to the dissimilar metal laser welding method of the secondary battery cap assembly according to the present invention, the rivet terminal made of copper and the rivet plate made of aluminum or aluminum alloy, which constitute the secondary battery cap assembly, are stacked vertically, and the rivet terminal welded portion is After performing primary laser welding to form a first weld in a relatively wide range, secondary welding is performed to form a second weld in a narrow range through the first weld in the rivet terminal weld vertically to a predetermined depth on the upper part of the rivet plate. By performing laser welding, welding defects can be prevented and welding quality can be improved at the joint surface of the rivet terminal and rivet plate.

Additionally, in the first laser welding step, the laser is irradiated in a positive defocusing state to preheat the welding area, and in the second laser welding step, the laser is irradiated in a just focusing state, thereby reducing the power consumption required for laser welding.

In addition, by performing laser welding separately into primary and secondary stages, thermal deformation and subsequent vaporization of the rivet plate made of aluminum can be reduced, and welding quality can be improved by accurately controlling the welding depth.

In addition, according to the present invention, compared to the conventional friction welding method of welding dissimilar metals, laser welding is performed in a state in which the rivet terminal shape is completed, thus eliminating the problem of material waste due to cutting of the conventional rivet terminal. Also, by reducing the number of processes, product productivity can be improved by shortening the process time.

In addition, a more robust connection between the rivet terminal and the rivet plate is possible by bending and caulking the caulking portion formed at the lower end of the rivet terminal toward the caulking groove formed on the inner peripheral surface of the rivet plate.

1 is a perspective view of a secondary battery to which the present invention is applied;
Figure 2 is a plan view of Figure 1;
Figure 3 is a cross-sectional view along line AA of Figure 2 and an enlarged view of the cap assembly;
Figure 4 is a perspective view of the rivet terminal and rivet plate constituting the secondary battery cap assembly of the present invention;
Figure 5 is a plan view of Figure 4;
Figure 6 is a cross-sectional view along line BB in Figure 5;
7 is a flowchart of the dissimilar metal laser welding method of the secondary battery cap assembly of the present invention;
Figure 8 is a view showing a rivet terminal and a rivet plate being caulked together in the dissimilar metal laser welding method of the secondary battery cap assembly of the present invention;
9 is a view for explaining the state in which primary laser welding is performed in the dissimilar metal laser welding method of the secondary battery cap assembly of the present invention;
10 is a diagram illustrating a state in which secondary laser welding is performed in the dissimilar metal laser welding method of the secondary battery cap assembly of the present invention.

Hereinafter, the structure and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

First, the schematic configuration of the secondary battery 100 to which the present invention is applied will be described with reference to FIGS. 1 to 6.

The secondary battery 100 according to an embodiment of the present invention includes a case 110 and a cap assembly 100A coupled to the upper and lower portions of the case 110, respectively.

The case 110 is roughly rectangular in shape, and its upper and lower parts are open, and the inside of the case 110 is a space where an electrode assembly (not shown) and an electrolyte (not shown) are accommodated. This is formed.

The electrode assembly includes a first electrode plate, a second electrode plate, and a separator that electrically insulates them, and the first electrode plate, the second electrode plate, and the separator are arranged sequentially and stacked in a plurality of layers. It can be composed of a structure.

The first electrode plate and the second electrode plate may have different polarities, that is, act as an anode and a cathode, or a cathode and an anode. When the first electrode plate acts as an anode, it may be made of aluminum. 2 When the electrode plate acts as a cathode, it may be made of copper.

In one embodiment, based on the direction shown in FIG. 1, the cap assembly 100A coupled to the upper part of the case 110 acts as a cathode, and the cap assembly (not shown) coupled to the lower part of the case 110 ) acts as an anode, and a plurality of secondary batteries 100 may be connected in series or parallel.

Hereinafter, the description will focus on the configuration of the cap assembly (100A) coupled to the upper part of the secondary battery 100. The following configuration only changes the polarity of the cap assembly coupled to the lower part of the secondary battery 100 and other configurations. may be composed of a similar structure.

The cap assembly 100A includes a cap plate 120, a rivet terminal 130, a terminal plate 140, an insulator 150, a rivet plate 160, an isolator 170, and a sealing member 180. It can be configured.

The cap plate 120 is configured to seal the opening formed at the top of the case 110 to maintain airtightness so that the electrolyte contained within the case 110 does not leak to the outside.

The rivet terminal 130 is made of a copper material and acts as a negative electrode of the secondary battery 100, and the first rivet terminal 130-1 and the second rivet terminal 130 are provided in pairs at spaced apart positions on both sides. -2) It can be composed of:

The rivet terminal 130 may penetrate and be coupled to the cap plate 120. The upper end 131 of the rivet terminal 130 protrudes upward from the cap plate 120 and is exposed to the outside of the secondary battery 100. A rivet terminal weld portion 132 consisting of a first flange portion 132 that protrudes outward in the radial direction by a predetermined length is formed on the lower outer peripheral surface of the rivet terminal 130. Below the rivet terminal welding portion 132, a caulking portion 133 is formed at the lower end of the rivet terminal 130 and protrudes downward by a predetermined length.

The terminal plate 140 supports the upper portions of the pair of first rivet terminals 130-1 and second rivet terminals 130-2 and is configured to electrically connect them to each other.

The insulator 150 functions to block leakage current by insulating between the terminal plate 140 and the cap plate 120.

The rivet plate 160 is configured to electrically connect the cathode of the electrode assembly to the rivet terminal 130, and is made of aluminum or aluminum alloy material, which is less expensive than copper.

A hole through which the rivet terminal 130 passes is formed in the rivet plate 160, and a rivet plate weld portion 161 consisting of a second flange portion 161 protruding radially inward by a predetermined length from the inner peripheral surface of the hole. is formed.

Referring to FIGS. 4 to 6, the rivet plate weld portion 161 is located around the outer circumferential surface of the rivet terminal 130, contacts the rivet terminal weld portion 132 in a step shape, and is provided in a vertically stacked structure. . That is, the rivet terminal weld portion 132 made of the copper material is located in the upper layer, and the rivet plate weld portion 161 made of aluminum or aluminum alloy material is disposed in a stacked structure below it. Accordingly, the bottom surface of the rivet terminal welding portion 132 and the upper surface of the rivet plate welding portion 161 are arranged to contact each other vertically.

In this way, the rivet terminal welding portion 132 and the rivet plate welding portion 161 are in contact with each other in a step shape and are provided in a laminated structure, so that the rivet terminal 130 is supported on the rivet plate 160 without a separate configuration, as described later. Laser welding is performed.

On the inner peripheral surface of the hole formed in the rivet plate 160, the caulking portion 133 formed at the lower end of the rivet terminal 131 is bent and a caulking portion groove 162 is formed for caulking. 3 and 6 show the caulking portion 133 before being caulked into the caulking groove 162, and in FIG. 10, the caulking portion 133 is bent and caulked into the caulking groove 162. It appears.

The isolator 170 is configured to insulate between the cap plate 120 and the rivet plate 160, and the sealing member 180 is interposed between the rivet terminal 130 and the cap plate 120 to prevent electrolyte leakage. It functions to prevent.

Hereinafter, the dissimilar metal laser welding method of the secondary battery cap assembly of the present invention will be described with reference to FIGS. 7 to 10.

The dissimilar metal laser welding method of the secondary battery cap assembly of the present invention includes a rivet terminal welding portion 132 made of copper, and a rivet plate welding portion 161 made of aluminum or aluminum alloy material laminated below the rivet terminal welding portion 132. ) as a method of laser welding, including the step of caulking the rivet terminal 130 and the rivet plate 160 (S1), the step of first welding the rivet terminal weld portion 132 (S2), and the rivet terminal weld portion 132. ) and a step (S3) of secondary welding the rivet plate weld portion 161.

First, as shown in FIG. 8, prior to laser welding, the caulking portion 133 formed at the lower end of the rivet terminal 130 is bent toward the caulking portion groove 162 formed on the inner peripheral surface of the rivet plate 160 for caulking. It may include a caulking bonding step (S1) to form the deformation portion 133a.

According to this caulking coupling step, the caulking portion 133 formed at the lower end of the rivet terminal 130 is bent toward the caulking portion groove 162 formed on the inner peripheral surface of the rivet plate 160 and caulked, thereby forming the rivet terminal 130 and the rivet terminal 130. The rivet plate 160 can be combined more firmly.

Referring to Figures 9 and 10, the laser welding of the present invention primarily involves the rivet terminal welding portion 132 made of copper located on the upper layer and the rivet plate welding portion 161 made of aluminum or aluminum alloy material laminated on the lower layer. After preheat welding, it is performed as a second main welding step.

As is well known, the melting point of copper is 1084°C and that of aluminum is 660°C. In order to melt and laser weld dissimilar metals such as the upper layer copper material and the lower layer aluminum, a laser with a heat input exceeding the melting point is required. The metal must be formed into a molten state by irradiating the beam.

The laser welding device 200 for laser welding can set the focal length, output, and welding speed at which the laser beam 210 is irradiated, and adjusts the height of the up and down movement to irradiate the welding portions W1 and W2. It is configured to enable focus control of the laser beam 210.

Referring to FIG. 9, based on the focus 212 where the laser beam 210 converges to one point, the laser beam in the area between the laser welding device 200 and the focus 212 has a relative heat input amount. It is a high negative defocusing laser beam 211, and the laser beam in the area below the focus 212 is a positive defocusing laser beam 213 with a relatively low heat input.

Referring to FIG. 10, when the focus 212 of the laser beam and the laser irradiation surface coincide, it is a just focusing laser beam 214, which is an ideal focusing state and can obtain optimal welding quality. It is in a state of being.

In the first laser welding step shown in FIG. 9, the welding device 200 is positioned in a state that is moved upward from the reference height, and positive defocusing has a first heat input amount that is relatively low on the rivet terminal welding portion 132. The laser beam 213 is irradiated while moving in the circumferential direction to form a first welded portion W1 having a first depth set in the rivet terminal welded portion 132 in a downward direction from the upper surface of the rivet terminal welded portion 132. is formed.

Here, the reference height may be defined as the height of the laser welding device 200 when the focus 212 of the laser beam 210 and the welding portion are located on the same height line.

In the second laser welding step shown in FIG. 10, with the laser welding device 200 located at the reference height, a second overlap welding is performed within the range of the first weld portion W1 formed in the first laser welding step, and the low The laser beam 214 in a laser focusing state is irradiated while moving along the circumferential direction to vertically pass through the rivet terminal weld portion 132 and form the rivet plate weld portion from the boundary between the rivet terminal weld portion 132 and the rivet plate weld portion 161. A second welded portion (W2) having a second depth set at the upper part of (161) is formed.

The heat input amount of the laser beam may be determined by at least one of the focal distance at which the laser beam is irradiated, the output of the laser beam, and the welding speed of the laser beam.

In setting the welding conditions of the laser beam, the heat input amount (E) of the laser beam can be calculated as the product of the output (x) of the laser beam and the welding speed (y). The combination of the output (x) of the laser beam and the welding speed (y), which produces the same amount of heat input (E), can exist in various groups. In order to improve welding quality, the phenomenon of melt splashing during laser welding is possible. In order to suppress spatter, it is preferable to select a group with a high welding speed among the plurality of groups having the same amount of heat input.

The output of the laser beam in the first laser welding step and the output of the laser beam in the second laser welding step may be controlled so that the amount of heat input varies depending on the stage of welding.

That is, in the first laser welding step, the first welded portion W1 having a relatively wide area is formed in the rivet terminal welded portion 132 by irradiating the laser beam in a positive defocusing state, and the first laser welded portion is completed. Afterwards, the laser beam is continuously irradiated in a relatively narrow area in a just focusing state to create a second weld (W2) that is overlapped within the range where the first weld (W1) is formed and is deeper than the first weld (W1). is formed.

As shown in FIG. 10, the depth of the second welded portion W2 is formed to have a second depth set downward from the upper surface of the rivet plate welded portion 161, and the second depth is determined by thermal deformation of the aluminum material. It is desirable to set the depth to the minimum that allows for solid bonding between dissimilar metals such as copper and aluminum by laser welding while minimizing vaporization phenomenon.

In this way, in the first laser welding step, the laser beam 213 is irradiated in a positive defocusing state to preheat the welding area, and in the second laser welding step, the laser beam 214 is irradiated in a just focusing state to produce the necessary energy for laser welding. Optimal welding quality can be achieved while reducing power consumption.

If we assume that the rivet terminal welding portion 132 and the rivet plate welding portion 161 are welded only in a just focusing state without going through the first laser welding step for preheating the metal material, in this case, the preheating step is not performed. Compared to the case of performing laser welding by dividing it into the first and second laser welding stages, more power corresponding to the heat input is required to melt the metal, and the laser beam is irradiated with a large amount of heat input. As it becomes difficult to accurately control the welding depth to suppress thermal deformation and vaporization of aluminum materials with relatively low melting points, the problem of deteriorating welding quality occurs.

On the other hand, in the present invention, the first laser welding step of preheating the rivet terminal welding portion 132 made of copper material over a wide range to form the first welding portion W1, and relatively welding within the range of the first welding portion W1. By configuring laser welding to be performed sequentially by dividing into secondary laser welding stages that form a second welding area (W2) with a deeper depth within a narrow range, not only can the power energy required for laser welding be reduced, but also the laser welding stage can be performed sequentially. As it becomes easier to control the welding depth by adjusting the amount of heat input according to the stage of welding, the thermal deformation of the rivet plate made of aluminum and the resulting vaporization phenomenon can be reduced, which has the advantage of improving welding quality. .

In addition, according to the laser welding method according to the present invention, compared to the welding method of dissimilar metals by conventional friction welding, laser welding is performed in a state in which the rivet terminal shape is completed, so it is suitable for cutting processing of the conventional rivet terminal base material. It does not cause the problem of material waste and has the advantage of improving product productivity by reducing the process time by reducing the number of processes.

As described above, the present invention has been described in detail with preferred embodiments, but the present invention is not limited to the above-described embodiments, and may be modified in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings. It is possible to implement this, and this also belongs to the present invention.

100: Secondary battery 100A: Cap assembly
110: case 120: cap plate
121: Electrolyte injection port 130: Rivet terminal
130-1: first rivet terminal 130-2: second rivet terminal
131: Upper part of rivet terminal 132: Rivet terminal welding part (first flange part)
133: caulking portion 133a: caulking deformation portion
140: terminal plate 150: insulator
160: Rivet plate 161: Rivet plate welding portion (second flange portion)
162: Caulk groove 170: Isolator
180: sealing member 200: laser welding device
210: Laser beam 211: Negative defocusing laser beam
212: Focus 213: Positive defocusing laser beam
214: Just focusing laser beam W1: First welding part
W2: 2nd weld zone

Claims (6)

A dissimilar metal laser welding method for a secondary battery cap assembly in which a rivet terminal weld made of a copper material and a rivet plate weld made of an aluminum or aluminum alloy material laminated below the rivet terminal weld are laser welded,
In a state in which the rivet terminal welding portion and the rivet plate welding portion are arranged laterally and stacked vertically, a laser beam is irradiated on the rivet terminal welding portion to set the rivet terminal welding portion in a downward direction from the upper surface of the rivet terminal welding portion. A first laser welding step of forming a first weld having a first depth;
A laser beam is irradiated within the range of the first weld formed in the first laser welding step to vertically pass through the rivet terminal weld and set on the upper part of the rivet plate weld from the boundary surface of the rivet terminal weld and the rivet plate weld. A secondary laser welding step of forming a second welding portion having a second depth to join the rivet terminal welding portion and the rivet plate welding portion;
Including,
The rivet terminal welding portion consists of a first flange portion that protrudes radially outward by a predetermined length from the outer peripheral surface of the rivet terminal,
The rivet plate welding portion is located around the outer peripheral surface of the rivet terminal and is in contact with the first flange portion in a step shape, and consists of a second flange portion that protrudes radially inward by a predetermined length from the inner peripheral surface of the rivet plate to be stacked up and down, The bottom surface of the first flange part and the upper surface of the second flange part are in contact with each other, the laterally protruding end surface of the first flange part is in contact with the side surface of the rivet plate, and the lateral direction of the second flange part is in contact with each other. The protruding end surface is in contact with the side of the rivet terminal,
In the first laser welding step, the laser beam is irradiated in a positive defocusing state and laser welding is performed in a relatively wide range,
In the second laser welding step, the laser beam is irradiated in a just-focused state and laser welding is performed in a relatively narrow range,
The second depth of the second weld portion is determined by minimizing the vaporization phenomenon caused by thermal deformation of the aluminum material constituting the rivet plate weld portion and between the dissimilar metals of copper constituting the rivet terminal weld portion and aluminum constituting the rivet plate weld portion. A dissimilar metal laser welding method for a secondary battery cap assembly, characterized in that it is set to the minimum depth capable of solid joining by laser welding. delete According to paragraph 1,
In the first laser welding step and the second laser welding step, the heat input amount of the laser beam is determined by at least one of the focal distance at which the laser beam is irradiated, the output of the laser beam, and the welding speed of the laser beam. A dissimilar metal laser welding method for a secondary battery cap assembly. delete According to paragraph 1,
In setting the welding conditions of the laser beam, the heat input amount of the laser beam is calculated as the product of the output of the laser beam and the welding speed, and the welding speed is selected from a plurality of groups having a plurality of outputs and welding speeds with the same heat input amount. A dissimilar metal laser welding method for a secondary battery cap assembly, characterized in that a group having a large value is selected. According to paragraph 1,
Before the first laser welding step, the dissimilar metal laser welding method of the secondary battery cap assembly further includes the step of bending and caulking the caulking portion formed at the lower end of the rivet terminal toward the caulking portion groove formed on the inner peripheral surface of the rivet plate.

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