阅读说明：本技术 用于通过使用涡流信号特性来评价电池的电阻焊接质量的方法 (Method for evaluating resistance welding quality of battery by using eddy current signal characteristics ) 是由 具尚贤 金奭镇 郑守宅 李政勋 于 2020-07-30 设计创作，主要内容包括：本发明涉及一种通过使用涡流信号特性来评价电池的电阻焊接质量的方法,其中,能够通过防止由根据个体电池的物理性质的差异的变化引起的误差而提供高可靠性,并且通过应用无损方法,评价过程简单清楚。(The present invention relates to a method for evaluating resistance welding quality of a battery by using eddy current signal characteristics, in which high reliability can be provided by preventing errors caused by variations according to differences in physical properties of individual batteries, and the evaluation process is simple and clear by applying a lossless method.)

1. A method of evaluating the resistance welding quality of a battery including a resistance-welded weld, the method comprising the steps of:

measuring an eddy current signal on one plane including the weld along a line connecting opposite ends via the weld at one end of the plane; and

analyzing the measured eddy current signal and determining the resistance welding quality by comparing the eddy current signal value at the weld with the eddy current signal value at a point other than the weld.

2. The method of claim 1, wherein the weld is a point at which a battery tab is joined by resistance welding.

3. The method according to claim 1, wherein the battery to be evaluated is a cylindrical battery, and wherein the step of measuring an eddy current signal is performed on a plane on which one end of the cylindrical battery having a battery tab welded thereto.

4. The method of claim 1, wherein the step of measuring eddy current signals is performed on one plane to which battery tabs are welded, and

wherein the line passing through the welded part at one end of the plane to connect the opposite ends is a straight line passing through the welded part or a curved line having both sides symmetrical with respect to the welded part.

5. The method of claim 1, wherein the step of measuring an eddy current signal is performed continuously or intermittently along the line connecting opposite ends via the weld at one end of the plane.

6. The method according to claim 5, wherein, in the step of measuring an eddy current signal, both ends of the plane and the weld are included as points for measuring an eddy current signal.

7. The method according to claim 1, wherein a peak value of an eddy current signal measured at a point other than the weld is set as a reference value,

wherein a minimum value of the eddy current signal measured at the weld is set as a physical property value, and

wherein the step of determining the quality of the resistance weld comprises: calculating a difference between the reference value and the physical property value, and determining that the resistance welding has a defect if the calculated value is outside a preset range.

8. The method of claim 1, wherein the battery to be evaluated is a cylindrical battery, and wherein the reference value is an average of respective peak values of the eddy current signal measured near both ends.

9. The method according to claim 8, wherein the battery to be evaluated is a cylindrical battery having a case formed of aluminum or an alloy thereof.

10. The method according to claim 1, wherein the battery to be evaluated is a cylindrical battery, and

wherein the step of measuring an eddy current signal is performed on a plane to which one end of the battery tab has been welded in the cylindrical battery, and includes:

a first measurement step performed on a first wire passing through the weld; and

a second measurement step performed on a second line that intersects the first line at the weld and does not overlap the first line.

Technical Field

The present application claims priority based on korean patent application No. 10-2019-0092629, filed on 30/7/2019, and the entire contents of which are incorporated herein by reference.

The present invention relates to a method of evaluating resistance welding quality of a battery, and more particularly, to a method of evaluating resistance welding quality of a battery using eddy current signal characteristics.

Background

As the price of energy increases due to depletion of fossil fuels and concern for environmental pollution increases, the demand for environmentally friendly alternative energy sources is increasing. In particular, conventional automobiles using fossil fuels emit pollutants, which become a major cause of environmental pollution.

Recently, a secondary battery capable of being charged and discharged has been widely used as an energy source for wireless mobile devices. In addition, secondary batteries have attracted attention as power sources for Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), and the like, which have been proposed as solutions to air pollution of existing gasoline and diesel vehicles using fossil fuels.

As the demand for secondary batteries increases, the importance of evaluating the quality of batteries before product release is also increasing. In particular, in the case of a battery in which a battery tab is formed by welding, the defect rate at the welded part is relatively high. For example, a cylindrical battery has the following structure: the battery cell is wrapped by a metal case, and a battery tab is formed at one end of the cylindrical structure by resistance welding. However, the respective physical properties of the metal case or the change in physical properties caused during the welding process causes an error in the evaluation of the battery quality, thereby reducing the reliability of the evaluation.

Therefore, there is a high necessity for a reliable quality evaluation method capable of preventing errors due to differences in physical properties of each metal case while the evaluation process is simple.

Disclosure of Invention

Technical problem

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method of evaluating resistance welding quality of a battery using eddy current signal characteristics.

Technical scheme

The method of evaluating the resistance welding quality of a battery including a resistance-welded weld according to the present invention includes:

measuring an eddy current signal on a plane including a weld along a line connecting opposite ends via the weld at one end of the plane;

analyzing the measured eddy current signal; and

determining a resistance welding quality by comparing the eddy current signal value at the weld with eddy current signal values at points other than the weld.

According to an embodiment of the present invention, the welding part is a point where the battery tabs are joined by resistance welding. According to a specific embodiment of the present invention, the battery to be evaluated is a cylindrical battery, and the eddy current signal is measured on a plane of one end of the cylindrical battery to which the battery tab is welded.

According to an embodiment of the present invention, an eddy current signal is measured on one plane to which a battery tab is welded, and a line passing through a welding part at one end of the plane to connect opposite ends is a straight line passing through the welding part or a curved line having both sides symmetrical with respect to the welding part.

According to an embodiment of the invention, the eddy current signal is measured continuously or intermittently along a line connecting the opposite end at one end of the plane via a weld. Specifically, in measuring the eddy current signal, both ends of the plane and the weld are included as points for measuring the eddy current signal.

According to an embodiment of the present invention, a peak value of an eddy current signal measured at a point other than the welded portion is set as a reference value, a minimum value of the eddy current signal measured at the welded portion is set as a physical property value, and determining the resistance welding quality includes calculating a difference between the reference value and the physical property value, and determining that the resistance welding has a defect when the calculated value is outside a preset range.

Specifically, the battery to be evaluated is a cylindrical battery, and the reference value is an average value of respective peak values of the eddy current signal measured near both ends.

In the present invention, the battery to be evaluated is a cylindrical battery having a case formed of aluminum or an alloy thereof.

According to an embodiment of the present invention, a battery to be evaluated includes a cylindrical battery having a case formed of aluminum or an alloy thereof.

The step of measuring an eddy current signal is performed on a plane of one end of a cylindrical battery where a battery tab has been welded, and includes: a first measurement step performed on a first wire passing through the weld; and a second measurement step performed on a second line that intersects the first line at the weld and does not overlap the first line.

Advantageous effects

According to the method for evaluating the resistance welding quality of batteries according to the present invention, it is possible to provide high reliability by preventing errors due to differences in physical properties of the respective batteries, and to make the evaluation process simple by applying a non-destructive method.

Drawings

Fig. 1 is a photograph of a process of performing a method for evaluating resistance welding quality of a battery according to an embodiment of the present invention.

Fig. 2 to 4 show results obtained by observing a section of the welded part of each sample with an electron microscope after forming a battery tab by changing the welding strength at one end of each cylindrical battery.

Fig. 5 is a graph showing the result of measuring an eddy current signal of a battery in a state before a battery tab is attached.

Fig. 6 and 7 are graphs illustrating the results of measuring an eddy current signal of a battery by a method according to an embodiment of the present invention, respectively.

Fig. 8 is a graph showing the result of calculating the difference between the reference value and the physical property value of each battery sample.

Fig. 9 is a graph showing the measurement results of the physical properties of each battery sample.

Detailed Description

The terms and words used in the present specification and claims should not be construed as being limited to general or dictionary terms, and the inventor can appropriately define the concept of the terms to best describe his invention. The terms and words should be interpreted as meanings and concepts consistent with the technical idea of the present invention.

In the present invention, "welding" refers to a process of bonding two solid metals by applying heat and/or pressure to the two solid metals. In the present invention, "resistance welding" refers to a method of welding a welded portion using resistance heat generated from a metal itself by applying current and pressure to the welded portion, among various welding methods.

In the present invention, "eddy current" is an electric current in the form of eddy current generated in a conductor by electromagnetic induction when a magnetic field applied to the conductor changes with time. In addition, in the present invention, the "eddy current signal" refers to a signal according to a nondestructive testing method that generates an eddy current in a portion to be tested of an inspection object by flowing a high-frequency current through an excitation coil and detects a change in an eddy current distribution state due to a defect.

The process of measuring the eddy current signal can be performed by a known method. The measurement principle is briefly described as follows. Assuming the DC resistance, inductance and frequency of the coil in air core are R0, L0 and ω, the impedance Z of the coil becomes as follows: z ═ R₀+jωL₀. When the exciting coil approaches the object, the impedance of the exciting coil changes according to the permeability and conductivity of the object. Since the impedance of the field coil can be based on the reactance ω L at the air core₀Is normalized and expressed as R/ω L on the impedance plane₀And ω L/ω L₀Therefore, the defect distribution state can be obtained from the impedance map. The process of measuring the eddy current signal can be performed using commercially available measuring equipment. For example, JAS-0100W available from Jiangan Systems (Jeongan Systems) can be used.

The present invention provides a quality evaluation method for evaluating the resistance welding quality of a battery including a resistance-welded portion.

The method for evaluating the resistance welding quality of a battery according to the present invention comprises the steps of:

measuring an eddy current signal on a plane including a weld along a line connecting opposite ends via the weld at one end of the plane; and

the measured eddy current signals are analyzed and the resistance weld quality is determined by comparing the eddy current signal values at the weld with eddy current signal values at points other than twenty-four welds.

The evaluation method according to the present invention is different from a method of measuring a signal value of a welded part and comparing it only with a preset reference value. In the manufacture of batteries, there are differences in physical properties between the respective battery cases even if the same manufacturing process and the same material of the battery case are applied. In addition, when the battery case is welded, this causes a change in physical properties of the battery case. In particular, resistance welding generates resistance heat during a welding process, and exhibits different thermal behavior in each welding process. The difference in the physical properties of the battery case and the thermal insulation during welding become errors in the quality evaluation process. In the present invention, in the step of measuring the eddy current signal, the weld and the portion spaced apart from the weld are evaluated together. In the present invention, in the step of measuring the eddy current signal, physical properties of the weld and a portion spaced apart from the weld are measured together, and the weld quality is evaluated based on a difference therebetween. Therefore, the evaluation method according to the present invention has the effect of preventing errors due to such errors.

In one example, the welding portion is a point where the battery tab is joined by resistance welding. The evaluation method according to the present invention can be applied as a method of evaluating the welding quality of a battery tab portion welded by a resistance welding process. For example, in the case of a cylindrical battery, a battery tab is formed in a central portion of one side section of a cylindrical battery case. Such a battery tab can be formed through a resistance welding process. Therefore, the evaluation method according to the present invention can be utilized as a method for evaluating the welding quality of a battery tab in a cylindrical battery.

In one example, the step of measuring the eddy current signal is performed on one plane on which the battery tab is welded. In addition, a line passing through the welded portion at one end of the plane to connect the opposite ends is a straight line passing through the welded portion, or a curved line having both sides symmetrical with respect to the welded portion. In this case, the step of measuring an eddy current signal may be performed along a straight line crossing the welded portion or along a straight line or a curved line symmetrical with respect to the welded portion. This process is used to continuously test physical properties through the welded part from one end to the opposite end on one plane of the battery.

As a specific example of the present invention, the battery to be evaluated is a cylindrical battery. In this case, the step of measuring the eddy current signal is performed on a plane of one end of the cylindrical battery to which the battery tab is welded. The cylindrical battery has a cylindrical body, and electrode tabs of a positive electrode or a negative electrode are respectively formed at the centers of both ends of the cylindrical shape. In the present invention, when the battery to be evaluated is a cylindrical battery, an eddy current signal is measured on a plane to which one end of a battery tab is welded.

For example, the step of measuring an eddy current signal may be performed continuously or intermittently along a line connecting opposite ends via the weld at one end of the plane. In the present invention, "continuously" measuring the eddy current means continuously measuring the eddy current without a separation distance between the measurement points. In addition, measuring the eddy current "intermittently" means measuring the eddy current along a predetermined line with a spaced distance between measurement points.

In the step of measuring an eddy current signal, it is preferable to include both ends of the plane and the welded portion as points for measuring the eddy current signal. In the case where the step of measuring the eddy current signal can be performed intermittently, one end as a measurement start point, a welded portion as a center point, and an opposite end as a measurement end point are indispensable measurement points.

Specifically, in the method for evaluating the resistance welding quality of a battery according to the present invention, the peak value of the eddy current signal measured at a point other than the welded portion is used as the reference value, and the minimum value of the eddy current signal measured at the welded portion is used as the physical property value. In addition, in the step of determining the resistance welding quality, a difference between the measured reference value and the physical property value is calculated, and based thereon, it is determined whether the welded part has a defect. Determining that a defect exists if a difference between the calculated reference value and the physical property value is outside a preset range.

In one embodiment, the battery to be evaluated of the present invention is a cylindrical battery, and the reference value is an average value of each peak value of the eddy current signal measured near both ends. In the case of a typical cylindrical battery, a signal at the welded portion becomes a physical property value, and signals at both ends are used as reference values. That is, in the cylindrical battery, the eddy current signal at the weld shows the lowest value, and the eddy current signals measured near both ends often show the peak value. At this time, the lowest value viewed from the welded portion becomes the physical property value, and the average value of the peak values viewed from both ends becomes the reference value.

For example, when the battery to be evaluated is a cylindrical battery, the cylindrical battery may have the following structure: having a housing formed of aluminum or an alloy thereof. In this case, the battery tab made of the same material may be welded to the cylindrical case body made of aluminum or an alloy thereof. Alternatively, the case where the battery tab is plated with nickel or an alloy thereof is included.

Further, in another embodiment, the battery to be evaluated is a cylindrical battery, and the step of measuring the eddy current signal is performed on a plane to which one end of the battery tab has been welded in the cylindrical battery, and includes: a first measurement step performed on a first wire passing through the weld; and a second measuring step performed on a second line that intersects the first line at the weld and does not overlap the first line. In this case, the eddy current signal is measured along two lines, and this is to increase the reliability of the evaluation by the cross measurement. In the above example, the step of measuring the eddy current signal along the first line and the second line is performed, but the present invention does not exclude the case where the eddy current signal is measured along two or more lines.

Hereinafter, specific examples of the present invention will be described in detail with reference to the accompanying embodiments and drawings. Accordingly, the embodiments described in the specification and the configurations shown in the drawings are only the most preferable embodiments of the present invention, and do not represent all the technical ideas of the present invention. It should be understood that various equivalents and modifications may exist in place of them at the time of filing this application.

In this regard, fig. 1 is a photograph of a process of performing a method for evaluating resistance welding quality of a battery according to an embodiment of the present invention. The battery to be evaluated was a cylindrical battery. In the case where a cylindrical battery is erected on a measuring table, an eddy current signal of one end surface of the battery is measured. The eddy current signal is measured from one end of the upper end surface through the center to the opposite end.

Fig. 2 to 4 are results of welding battery tabs with different welding strengths and observing a cross section of each welded sample using an electron microscope. Fig. 2 shows a case where the welding strength is weak and it is difficult to observe the change in physical properties around the welded portion. On the other hand, fig. 3 shows a case where the weld strength is appropriate and a change in physical properties is observed around the weld. Fig. 4 shows a case where the welding strength is excessive and the peripheral edge of the welded portion is excessively deformed. In this case, the cases of fig. 2 and 4 should be determined as defective products, and fig. 3 should be determined as good products. Generally, in the case of welding a battery tab, when the welding strength is weak, a defect occurs in which the battery tab is separated or the electrical connection is disconnected during use, and when the welding strength is excessive, the process efficiency is deteriorated. However, in the battery to be evaluated, the cross section of the welded portion is not easily observed. Accordingly, the present invention proposes a method capable of efficiently evaluating the quality of a welded portion in a nondestructive manner.

Fig. 5 is a graph illustrating measurement of an eddy current signal of a battery that has not undergone a welding process for attaching a battery tab. Specifically, five cylindrical battery samples (cans 1 to 5) to which no battery tab was attached were randomly selected, and an eddy current signal of each battery sample was measured. Referring to fig. 5, although the selected battery samples were manufactured through the same manufacturing process, it can be seen that there is a data shift due to a difference in physical properties. Such data drift causes a decrease in reliability of the welding quality evaluation.

Example (c): resistance welding quality evaluation was performed for each battery sample

Resistance welding was performed on a cylindrical battery sample having a case made of aluminum to attach a battery tab. At this time, the welding strength was different for each sample. Specifically, in samples 1 to 3, resistance welding was performed at an appropriate welding strength level, and in samples 4 to 6, resistance welding was performed at a weak welding strength level.

The eddy current signal value for each sample is measured. Eddy current signal values were measured continuously over 1000 times from the outer left area to the right side with respect to the side to which the battery tab was attached, and the measurement was performed using the JAS-0100W apparatus of the jianggan Systems (Jeongan Systems).

For example, the measurement result of the eddy current signal value of the sample 1 is shown in fig. 6, and the measurement result of the eddy current signal value of the sample 4 is shown in fig. 7. In fig. 6 and 7, a denotes the left end of the sample, B denotes the center point of the welded portion, and C denotes the right end of the sample. In the graphs showing the measurement results of samples 1 to 6, it was confirmed that: the value at the center is small, and increases as the center progresses to the left and right. The measurement results for each sample are summarized in table 1 below.

In table 1, the numerical value at the highest point on the left side of the graph from the center point (B) is represented as "left peak", the numerical value at the lowest point near the center point (B) is represented as "minimum value of the welded portion", and the numerical value at the highest point on the right side of the graph from the center point (B) is represented as "right peak". This is shown in table 1. In Table 1 below, the units are in mV.

TABLE 1

Sample numbering	Left peak value	Minimum value of welded part	Right peak value
				Sample 1	27.3214	26.7256	27.2289
Sample 2	27.2154	26.5283	27.2696
				Sample 3	27.3874	26.5384	27.2382
Sample 4	27.1892	26.6803	26.9762
				Sample 5	27.3867	27.1334	27.4335
Sample 6	27.3850	26.9509	27.3482

In the results of table 1 above, the average of the left and right peak values was calculated and displayed as a reference value, and the minimum value of the welding portion was expressed as a physical property value, as shown in table 2 below.

TABLE 2

Sample numbering	Reference value	Physical property value	Difference in
				Sample 1	27.2752	26.7256	0.5496
Sample 2	27.2425	26.5283	0.7142
				Sample 3	27.3128	26.5384	0.7744
Sample 4	27.0827	26.6803	0.4024
				Sample 5	27.4101	27.1334	0.2767
Sample 6	27.3666	26.9509	0.4157

Referring to table 2, it can be seen that the difference between the reference value and the physical property value is 0.5 or more in the case of samples 1 to 3, and the difference is less than 0.5 in the case of samples 4 to 6. In the present invention, based on the results of table 2 above, samples 1 to 3 were determined as normal products, and samples 4 to 6 were determined as defective products.

However, if only the physical property value as the eddy current signal value at the welded portion is compared, it is not easy to determine whether the product has a defect. Specifically, the physical property values of samples 1 to 3 were between 26.5283 and 26.7256. On the other hand, the physical property value of sample 4 was 26.6803, and the physical property value of sample 6 was 26.5909. The physical property value of sample 4 overlaps with the above range, and the physical property value of sample 6 appears similar to the above range, as compared with the range of samples 1 to 3.

Specifically, fig. 8 is a graph showing the result of calculating the difference between the reference value and the physical property value for the respective samples. In fig. 8, the numerical values of samples 1 to 3 and the numerical values of samples 4 to 6 show a significant difference, and thus, normal products and defective products can be clearly distinguished. On the other hand, fig. 9 is a graph showing the results of measuring physical property values for respective samples. In fig. 9, no difference was observed in sample 4 compared with samples 1 to 3, and sample 6 shows a similar numerical value.

Thus, it can be seen that if only the physical property values are compared, the determination of whether the battery has a defect is inaccurate. In the present invention, in the step of measuring the eddy current signal, accurate welding quality can be obtained by measuring physical properties of the weld and the portion spaced apart from the weld and comparing the difference therebetween.