Welding part inspection method using thermal image sensing

Abstract

Disclosed is a method for inspecting a welded portion using thermal imaging sensing, and more particularly, a method for inspecting a welded portion between a lead portion and a bus bar of a battery cell, in which the welded portion (300) is heated using Joule heat and it is determined whether the welded portion (300) is defective based on a change in temperature rise of the welded portion (300).

Description

Technical Field

[0001] This application claims the benefit of priority to Korean Patent Application No. 2019-0153866, filed on Nov. 27, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for inspecting a welded portion using thermal image sensing, and more particularly, to a method for inspecting a welded portion using thermal image sensing that can sense the temperature increase and decrease patterns of a welded portion through thermal image sensing and determine whether the welded portion is defective based on the analysis results. Background Art

[0003] With the technological development of mobile devices such as mobile phones, laptop computers, cameras, and digital cameras, and the increasing demand for mobile devices, active research has been conducted on secondary batteries that can be charged and discharged. In addition, secondary batteries, which are energy sources that replace fossil fuels that cause air pollution, have been applied to electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (P-HEVs), and thus the necessity of developing secondary batteries has been continuously increasing.

[0004] Currently commercially available secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among these batteries, lithium secondary batteries have received attention because, compared to nickel-based secondary batteries, lithium secondary batteries have almost no memory effect, and thus lithium secondary batteries can be freely charged and discharged, have a very low self-discharge rate, and have a high energy density.

[0005] Meanwhile, several battery cells are provided in a secondary battery for a small device, and a battery module including a plurality of battery cells electrically connected to each other is used in a vehicle. Since the plurality of battery cells are connected in series and in parallel with each other, the capacity and output of the battery module are increased. Busbars are used for the electrical connection between the battery cells.

[0006] The busbars and the leads of the battery cells are usually connected to each other by welding because each of the busbars and the leads is a conductive metal.

[0007] Conventionally, when welding is performed between them, there is no technology for detecting all welding defects such as poor welding and over-welding, and thus the improvement of welding quality is limited. That is, in the case of performing a visual inspection after resistance welding, over-welding can be partially detected, but poor welding cannot be detected. For a sticking inspection in which the welded portion is pulled to detect non-welding, poor welding can be partially detected or non-welding can be detected. However, in this case, force is directly applied to the lead or the busbar, and thus the battery cell may be damaged.

[0008] Japanese Patent Application Laid-Open No. 2000-131254 discloses a technique related to a tab terminal member and a pattern portion of a bus bar. The tab terminal member and the pattern portion of the bus bar are two metal members welded to each other. This technique can hold the front end of the tab terminal member using a heating jig, transfer heat from the tab terminal member to the pattern portion of the bus bar via a welding portion, measure the maximum temperature or temperature distribution of the rear surface of the pattern portion of the bus bar using a radiation thermometer, and compare the measured maximum temperature or the area of a region having a predetermined temperature or higher with a comparison value obtained in advance to determine whether there is a defect in the welded portion.

[0009] This prior art document has the advantage of being able to determine to some extent whether there is a defect in the welded portion without damaging the welded portion. However, a separate device and power for heat transfer are required. As a result, there are problems that the inspection device becomes complicated and the inspection cost based on this inspection device increases.

[0010] (Prior art document)

[0011] (Patent Document 1) Japanese Patent Application Laid-Open No. 2000-131254 Summary of the Invention

[0012] Technical Problem

[0013] In view of the above problems, the present invention is made. The object of the present invention is to provide a method for inspecting a welded portion that can accurately determine whether there is a defect in the welded portion.

[0014] Another object of the present invention is to provide a method for inspecting a welded portion that can determine whether there is a defect in the welded portion without separate external power.

[0015] Still another object of the present invention is to provide a method for inspecting a welded portion using simple equipment.

[0016] Technical Solution

[0017] To achieve the above object, the present invention provides a method for inspecting a welded portion between a lead portion of a battery cell and a bus bar, in which the welded portion (300) is heated using joule heat and it is determined whether there is a defect in the welded portion (300) based on the temperature rise pattern of the welded portion (300).

[0018] In addition, in the method for inspecting a welded portion between a lead portion of a battery cell and a bus bar according to the present invention, joule heat can be generated by the current supplied from the battery cell (100) welded to the bus bar (200).

[0019] In addition, in the method for inspecting a welded portion between a lead portion of a battery cell and a bus bar according to the present invention, the battery cell (100) may be in an encapsulated state before shipment.

[0020] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the heated welded portion (300) can be cooled and it can be determined whether the welded portion (300) is defective based on the temperature decrease pattern of the welded portion (300).

[0021] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the cooling can be performed by terminating the supply of current from the battery cell (100).

[0022] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the temperature increase pattern can be at least one of the following: the time taken for the temperature to reach a specific temperature, the temperature increase rate over time, and the maximum temperature.

[0023] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the temperature decrease pattern can be at least one of the following: the time taken for the temperature to reach the initial temperature from a predetermined temperature and the temperature decrease rate over time.

[0024] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the temperature increase pattern and / or the temperature decrease pattern can be set for the welded portion and an adjacent region of the welded portion, and the welded portion and the adjacent region of the welded portion are divided into a predetermined number of regions.

[0025] In addition, the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention may include: a first step of welding the lead portions (110) and the bus bars (200) of two or more battery cells (100) to form a welded portion (300); a second step of turning on a switch to electrically connect the battery cells (100) to each other; a third step of continuously measuring the temperature change of each welded portion (300); and a fourth step of determining whether each welded portion (300) is defective based on the result of the temperature change.

[0026] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the second step can be maintained for a predetermined time after the battery cell (100) is discharged.

[0027] In addition, in the method for inspecting a welded portion between a lead portion and a bus bar of a battery cell according to the present invention, the third step can be performed simultaneously with the second step.

[0028] Advantageous Effects

[0029] The method for inspecting a welded portion using thermal image sensing according to the present invention has the following advantages: determining whether there is a defect in the welded portion by considering both the heat generation characteristics and the cooling characteristics of the welded portion, thereby enabling a more accurate determination.

[0030] In addition, the method for inspecting a welded portion using thermal image sensing according to the present invention has the following advantages: using the power of the battery cell itself to be inspected, thereby eliminating the need for separate power, and in addition, minimizing the number of auxiliary devices for inspection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a view showing a configuration for inspecting a welded portion according to a first preferred embodiment of the present invention.

[0032] Figure 2 is a flowchart showing a method for inspecting a welded portion according to a first preferred embodiment of the present invention.

[0033] Figure 3 is a schematic diagram showing a heat generation mechanism of a welded portion when a current is applied.

[0034] Figure 4 is a schematic diagram showing a temperature change of a welded portion when a current is applied or the current is terminated.

[0035] Figure 5 is a view showing an example of a temperature distribution image result in an adjacent region including a welded portion.

[0036] Figure 6 is a view showing a configuration for inspecting a welded portion according to a second preferred embodiment of the present invention. DETAILED DESCRIPTION

[0037] In the present application, it should be understood that the terms "including", "having", "containing", etc. indicate the presence of the recited features, quantities, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, operations, elements, components, or combinations thereof.

[0038] In addition, the same reference numerals will be used throughout all the drawings to denote components that perform similar functions or operations. In the case where a component is described in the specification as being connected to another component, the one component may not only be directly connected to the other component, but the one component may also be indirectly connected to the other component via other components. In addition, including a certain element does not mean excluding other elements, but means that these elements may be additionally included, unless otherwise specified.

[0039] Hereinafter, a method for inspecting a welded portion using thermal image sensing according to the present invention will be described.

[0040] Figure 1 is a view showing a configuration for inspecting a welding part according to a first preferred embodiment of the present invention. Referring to Figure 1 , there are provided lead portions 110 extending from each of two battery cells 100, a bus bar 200 configured to electrically connect the lead portions 110 to each other, a welding part 300 configured to fix each lead portion 110 and the bus bar 200 to each other, and a thermal imaging camera 500 configured to measure a temperature change of the welding part 300.

[0041] The two battery cells 100 are batteries to be inspected for determining various performances, such as performances related to the welding part, in order to perform product shipment. One side of the bus bar 200 is connected to a negative electrode lead extending from one battery cell 100, and the other side of the bus bar 200 is connected to a positive electrode lead extending from the other battery cell 100, whereby the battery cells 100 can be electrically connected to each other.

[0042] Generally, each lead portion 110 and the bus bar 200 made of metal are connected to each other by welding such as resistance welding. At this time, the welding part 300 is formed to extend from the lead portion 110 to the bus bar 200.

[0043] Meanwhile, a switch 400 is provided between lead portions of the battery cell 100 that are not connected to the bus bar 200, that is, between the positive electrode lead of the battery cell 100 located on the Figure 1 left side and the negative electrode lead of the battery cell 100 located on the Figure 1 right side. The switch is configured to perform electrical connection or interruption therebetween.

[0044] In addition, the thermal imaging camera 500 is installed near the welding part 300, and each welding part 300 fixes a corresponding one of the lead portion 110 and the bus bar 200 to each other. The thermal imaging camera is a camera configured to monitor and detect heat and express heat using different colors based on temperature, which is a well-known technology in various fields, and thus a detailed description of the operation principle or function of the thermal imaging camera will be omitted.

[0045] Next, a welding part inspection method will be described based on the Figure 1 configuration for inspecting a welding part shown. Figure 2 is a flowchart showing a welding part inspection method according to a first preferred embodiment of the present invention, Figure 3 is a schematic diagram showing a heat generation mechanism of a welding part when current is applied, Figure 4 is a schematic diagram showing a temperature change of a welding part when current is applied or current is terminated, Figure 5 is a view showing an example of a temperature distribution image result in an adjacent region including a welding part.

[0046] The welding part inspection method according to the present invention includes a first step of welding the lead portions 110 of two or more battery cells 100 and the bus bar 200 to form a welding part 300, a second step of turning on a switch to electrically connect the battery cells 100 to each other, a third step of continuously measuring the temperature change of each welding part 300, and a fourth step of determining whether each welding part 300 is defective based on the result of the temperature change.

[0047] Refer to Figure 1 The first step has been described in detail, and thus its repeated description will be omitted.

[0048] The second step is a step of turning on the switch 400 to electrically connect the battery cells 100 to each other. At this time, heat is generated from each welding part 300.

[0049] As Figure 3 shown, regarding heat generation, electrons e supplied from the negative terminal of one battery cell 100 move to the positive terminal of another battery cell 100 via the bus bar 200. At this time, due to the resistance caused by the coupling between different metals and the change in its structure, Joule heat represented by Equation 1 is generated in each welding part 300.

[0050] Equation 1) Q = I 2 × R × t

[0051] Here, Q represents Joule heat, I represents current, R represents resistance, and t represents time.

[0052] Meanwhile, although a separate external power source can be used as the power source configured to generate Joule heat in each welding part 300, it is preferable to use the power of the battery cells directly connected to the bus bar 200.

[0053] Generally, after injecting the electrolyte solution, the battery cells 100 are completed through an activation step. At this time, the battery cells 100 are charged with a predetermined amount of power, so it is advantageous to use this power. That is, when using an external power source, not only a separate power source is required, but also additional wiring for the electrical connection between the external power source and the bus bar 200 is needed. In contrast, in the case of using the power charged in the battery cells 100 connected to the bus bar 200, the above problems can be overcome.

[0054] As Figure 4 shown, when the current charged in each battery cell 100 flows out, as the current application time increases, the temperature of the welding part 300 rises due to the generated heat. After the battery cells 100 are discharged, the current no longer flows, and thus the temperature of the welding part 300 decreases.

[0055] The third step of measuring the temperature change of each welding part 300 can be performed simultaneously with the second step of electrically connecting the battery cells 100 to each other.

[0056] To measure the temperature change, a thermal imaging camera 500 is used to electronically scan the thermal radiation energy near the welding part 300 to create temperature distribution data for each position based on the current application time.

[0057] That is, as Figure 5 shown, the temperature distribution of the surrounding area including the welding part is divided into multiple unit areas, and the temperature data for each area is obtained.

[0058] Finally, in the fourth step of determining whether each welding part 300 is defective based on the result of the temperature change, it is determined whether the temperature change is within the normal range by comparison.

[0059] As an example, referring to Figure 4 , in the case where the temperature value measured during current flow rises within the normal range ( Figure 4 area A), it is determined that the welding part 300 is welded normally. On the contrary, in the case where the temperature value deviates from the normal range when rising, it is determined that the welding part 300 is defective.

[0060] In addition, after the battery cell 100 is fully discharged, the heated welding part 300 is cooled for a predetermined time. In the same way, it is determined whether the measured temperature reduction mode of the welding part 300 changes within the normal range ( Figure 4 area B) to determine whether the welding part is defective.

[0061] When forced heating is performed due to current application, resulting in the accumulation of internal heat in a short time, a temperature rise occurs, while cooling is the phenomenon of the accumulated heat being naturally transferred to the inside / outside.

[0062] In particular, during the cooling process, according to the internal structure of the welding part, such as the surface state, holes, grain size, and formed structure of the welding part, the convection, radiation, and internal conduction through the surface can have different cooling modes. Therefore, the state of the welding part can be determined based on the temperature reduction mode during cooling.

[0063] At the same time, specific examples of the temperature rise mode can be the time taken for the temperature to reach a specific temperature, the temperature rise rate (change in temperature / time), or the maximum temperature. In addition, the cooling mode can be the time taken for the temperature to reach the original temperature from the maximum temperature or the temperature reduction rate (change in temperature / time).

[0064] In each specific example of the temperature increase mode and the cooling mode, it is preferable to utilize a single factor or multiple factors simultaneously. In particular, it is more preferable to apply these factors to Figure 5 all of the plurality of divided regions shown.

[0065] Of course, it is obvious to combine the temperature change distribution result of the welded portion with the visual inspection and the adhesion inspection that are usually performed for detecting welding defects, in order to ensure that the temperature change result of the welded portion is in a normal state.

[0066] Figure 6 is a view showing the configuration for inspecting a welded portion according to the second preferred embodiment of the present invention.

[0067] The second embodiment is the same as the first embodiment except that four battery cells 100 are connected in series with each other and three bus bars 200 are used to electrically connect adjacent battery cells 100 to each other.

[0068] That is, the switch 400 is connected to allow current to flow, the welded portions 300 formed in each bus bar 200 are scanned using a thermal imaging camera 500, and the temperature data is analyzed, whereby it is possible to determine whether there is a defect in the welded portion 300 formed in a specific bus bar 200.

[0069] Although a single thermal imaging camera 500 is shown used in this figure, multiple thermal imaging cameras 500 can be used.

[0070] Although specific details of the present invention have been described in detail, those skilled in the art will understand that the detailed description of the present invention only discloses the preferred embodiments of the present invention and thus does not limit the scope of the present invention. Therefore, those skilled in the art will understand that various changes and modifications can be made without departing from the classification and technical idea of the present invention, and it will be obvious that these changes and modifications fall within the scope of the appended claims.

[0071] (Description of Reference Numerals)

[0072] 100: Battery cell

[0073] 110: Lead portion

[0074] 200: Bus bar

[0075] 300: Welded portion

[0076] 400: Switch

[0077] 500: Thermal imaging camera

Claims

1. A method for inspecting a welded portion (300) between a lead portion (110) of a battery cell (100) and a bus bar (200), comprising: a first step of welding the lead portions (110) and the bus bar (200) of two or more battery cells (100) to form the welded portion (300), wherein each of the battery cells (100) is in an encapsulated state before shipment and is charged with a predetermined amount of power; a second step of turning on a switch to electrically connect the battery cells (100) to each other, wherein Joule heat is generated by the current supplied from the battery cells (100) welded to the bus bar (200) and the welded portion (300) is heated using the Joule heat; a third step of cooling the heated welded portion (300) after a predetermined amount of power of the battery cells (100) is completely discharged; a fourth step of continuously measuring the temperature change of each of the welded portions (300) during the second step and the third step; and a fifth step of determining whether each of the welded portions (300) is defective based on the result of the temperature change, wherein it is determined whether the welded portion (300) is defective based on the temperature increase pattern and the temperature decrease pattern of the welded portion (300), the welded portion and the adjacent area of the welded portion are divided into a plurality of unit areas, and the temperature increase pattern and the temperature decrease pattern are set for each unit area.

2. The method according to claim 1, wherein the temperature increase pattern is at least one of the following: the time taken for the temperature to reach a specific temperature, the temperature increase rate over time, and the maximum temperature.

3. The method according to claim 1, wherein the temperature decrease pattern is at least one of the following: the time taken for the temperature to reach the initial temperature from a predetermined temperature and the temperature decrease rate over time.

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