One]This application was filed on 2019.07.30. Claims the benefit of priority based on Korean Patent Application No. 10-2019-0092629, and all contents disclosed in the documents of the Korean patent application are incorporated as a part of this specification.
[2]
The present invention relates to a method for evaluating resistance welding quality of a battery, and more particularly, to a method for evaluating resistance welding quality of a battery using an eddy current signal characteristic.
background
[3]
As the price of energy sources increases due to the depletion of fossil fuels and interest in environmental pollution is increased, the demand for eco-friendly alternative energy sources increases. In particular, conventional automobiles using fossil fuels emit pollutants, which act as a major cause of environmental pollution.
[4]
Recently, a rechargeable battery capable of charging and discharging has been widely used as an energy source for a wireless mobile device. In addition, secondary batteries are attracting attention as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are proposed as a way to solve air pollution, such as conventional gasoline and diesel vehicles using fossil fuels. have.
[5]
As the demand for secondary batteries increases, the importance of battery quality evaluation before product shipment is also increasing. In particular, in the case of a battery in which the battery tab is formed by welding, the defective rate in the welding portion is relatively high. For example, a cylindrical battery has a structure in which a metal case surrounds the battery cell, and a battery tab is formed at one end of the cylindrical structure by resistance welding. However, individual physical properties of the metal case or changes in physical properties induced in the welding process cause errors in battery quality evaluation and lower reliability of evaluation.
[6]
Accordingly, there is a high need for a reliable quality evaluation method that is simple in the evaluation process and can prevent errors due to differences in physical properties for each metal case.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[7]
The present invention has been devised to solve the above problems, and an object of the present invention is to provide a method for evaluating the resistance welding quality of a battery using an eddy current signal characteristic.
means of solving the problem
[8]
The resistance welding quality evaluation method of a battery according to the present invention is a resistance welding quality evaluation method for a battery including a resistance-welded weld portion,
[9]
Measuring an eddy current signal along a line connecting the opposite end from one end of the plane to the opposite end via the weld on a plane including the weld; and
[10]
Analyzing the measured eddy current signal, comparing the eddy current signal value at the welding portion with the eddy current signal value at a point other than the welding portion to determine the resistance welding quality; includes.
[11]
According to an embodiment of the present invention, the welding portion is a point where the battery tab is joined by resistance welding. According to a specific embodiment of the present invention, the battery to be evaluated is a cylindrical battery, and the step of measuring the eddy current signal is performed on the plane of one end of the cylindrical battery to which the battery tab is welded.
[12]
According to an embodiment of the present invention, the step of measuring the eddy current signal is performed on one plane to which the battery tab is welded, and the line connecting the opposite end from one end of the plane to the opposite end via the welding part is It is a straight line or a curved line in which both sides are symmetrical with respect to the weld.
[13]
According to an embodiment of the present invention, the step of measuring the eddy current signal is performed continuously or intermittently along a line connecting the opposite end from one end of the plane through the welding part. Specifically, in the step of measuring the eddy current signal, as a point for measuring the eddy current signal, it includes both ends of a plane and a welding part.
[14]
According to an embodiment of the present invention, in the method for evaluating the quality of resistance welding of a battery according to the present invention, the peak value of the eddy current signal measured at a point other than the welding part is used as a reference value, and the minimum value of the eddy current signal measured in the welding part is used as the physical property value. but,
[15]
In the step of determining the resistance welding quality, a difference between a reference value and a physical property value is calculated, and when the calculated value is out of a preset range, it is determined as defective.
[16]
Specifically, the battery to be evaluated 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.
[17]
In the present invention, the battery to be evaluated includes the case of a cylindrical battery having a case formed of aluminum or an alloy thereof.
[18]
According to an embodiment of the present invention, the battery to be evaluated is a cylindrical battery,
[19]
The step of measuring the eddy current signal is performed on the plane of one end to which the battery tab is welded in a cylindrical battery,
[20]
a first measurement step performed on a first line passing through the weld; and a second measurement step of performing a second measurement on a second line that intersects the first line at the welding portion and does not overlap with the first line.
Effects of the Invention
[21]
The battery resistance welding quality evaluation method according to the present invention can provide high reliability by preventing errors due to errors due to differences in physical properties of each individual battery, and the evaluation process is simple by applying a non-destructive method.
Brief description of the drawing
[22]
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.
[23]
2 to 4 are results obtained by forming a battery tab by varying the welding strength at one end of each cylindrical battery, and observing a cross section of a welded portion for each sample with an electron microscope.
[24]
5 is a graph showing the results of measuring eddy current signals for batteries in a state before the battery tab is attached.
[25]
6 and 7 are graphs showing the results of measuring the eddy current signal of the battery by the method according to an embodiment of the present invention, respectively.
[26]
8 is a graph showing a result of calculating a difference between a reference value and a physical property value for each battery sample.
[27]
9 is a graph showing measurement results of physical properties for each battery sample.
Best mode for carrying out the invention
[28]
The terms or words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[29]
In the present invention, 'welding' refers to a process of bonding two solid metals by applying heat and/or pressure. In the present invention, 'resistance welding' refers to a method of welding using resistance heat generated from the metal itself by applying current and pressure to the welding site among various welding methods.
[30]
In the present invention, 'eddy current' is a eddy current generated in a conductor by electromagnetic induction when the magnetic field applied to the conductor changes with time. In addition, in the present invention, the 'eddy current signal' means a signal according to a non-destructive flaw detection method that generates an eddy current in the flaw detection part of the inspection object by flowing a high frequency current to the excitation coil, and detects a change in the distribution state of the eddy current due to a defect. it means.
[31]
The process of measuring the eddy current signal can be performed by a commonly known method. The measurement principle is briefly described as follows. If the DC resistance, inductance, and each frequency of the coil in the air-core are R 0 , L 0 , and ω , then the impedance Z of the coil becomes Z = R 0 + jωL 0 . When the excitation coil approaches the subject, the impedance of the excitation coil changes depending on the magnetic permeability and conductivity of the subject. Impedance of the excitation coil is normalized based on the reactance ωL 0 at the air core, R / ωL 0 , ωL / ωL 0Since it can be displayed on the impedance plane, the distribution of defects can be obtained from this impedance diagram. The process of measuring the eddy current signal can be performed using commercially available measuring equipment, for example, JAS-0100W product of Jungan Systems Co., Ltd. can be used.
[32]
[33]
The present invention provides a quality evaluation method for evaluating the quality of resistance welding for a battery including a resistance welded weld.
[34]
The method for evaluating resistance welding quality of a battery according to the present invention,
[35]
Measuring an eddy current signal along a line connecting the opposite end from one end of the plane to the opposite end via the weld on a plane including the weld; and
[36]
Analyzing the measured eddy current signal, comparing the eddy current signal value at the welding portion with the eddy current signal value at a point other than the welding portion to determine the resistance welding quality; includes.
[37]
The evaluation method according to the present invention is differentiated from a method of measuring a signal value of a welding part and simply comparing it with a preset reference value. When manufacturing a battery, even if the same manufacturing process and the battery case of the same material are applied, there is a difference in physical properties between individual battery cases. In addition, when welding is applied to the battery case, it causes a change in the physical properties of the battery case. In particular, resistance welding generates resistance heat during a welding process, and exhibits various thermal behaviors in individual welding processes. Differences in the physical properties of these battery cases and thermal movement during welding act as errors in the quality evaluation process. In the present invention, in the step of measuring the eddy current signal, the welding portion and the portion spaced from the welding portion are evaluated together. In the present invention, in the step of measuring the eddy current signal, the welding part and the physical properties of the part spaced from the welding part are measured together, and the welding quality is evaluated from the difference therebetween. Therefore, the evaluation method according to the present invention has an effect of preventing errors due to such errors.
[38]
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 is applicable as a method of evaluating the welding quality of the battery tab portion welded through the resistance welding process. For example, in the case of a cylindrical battery, the battery tab is formed in the center of one end surface of the 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 the battery tab in a cylindrical battery.
[39]
In one example, the step of measuring the eddy current signal is performed on a plane to which the battery tab is welded. In addition, a line from one end of the plane connecting the opposite end via the welded portion is a straight line passing through the welded portion or a curved line in which both sides are symmetrical with respect to the welded portion. In this case, the step of measuring the eddy current signal may be performed along a straight line crossing the welding part, or may be performed along a straight line or curved line symmetrical with respect to the welding part. This process is for continuously detecting the physical properties from one end of the battery to the opposite end via the weld on one plane of the battery.
[40]
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 the plane of one end to which the battery tab is welded in the cylindrical battery. The cylindrical battery has a cylindrical body, and electrode tabs of a positive electrode or a negative electrode are respectively formed in the center of both ends of the cylindrical shape. In the present invention, when the battery to be evaluated is a cylindrical battery, the eddy current signal is measured on the plane of one end to which the battery tab is welded.
[41]
For example, the step of measuring the eddy current signal may be performed continuously or intermittently along a line connecting the opposite end from one end of the plane via the welding part. In the present invention, 'continuously' measuring the eddy current means continuously measuring the eddy current without a separation distance between measurement points. Also, 'intermittently' measuring the eddy current means measuring the eddy current along a predetermined line with a certain distance between measurement points.
[42]
In the step of measuring the eddy current signal, as a point for measuring the eddy current signal, it is preferable to include both ends of a plane and a welding part. In the case where the step of measuring the eddy current signal can be performed intermittently, one end serving as the starting point of the measurement, the welding portion serving as the center point, and the opposite end serving as the end point of the measurement are essential measurement points.
[43]
Specifically, in the method for evaluating 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 welding portion is used as a reference value, and the minimum value of the eddy current signal measured in the welding portion is the physical property value. In addition, in the step of determining the resistance welding quality, the difference between the measured reference value and the physical property value is calculated, and based on this, it is determined whether the welding part is defective. If the difference between the calculated reference value and the physical property value is out of a preset range, it is determined as defective.
[44]
In one example, the battery to be evaluated in the present invention is a cylindrical battery, and the reference value is an average value of each peak value of an eddy current signal measured near both ends. In the case of a typical cylindrical battery, the signal at the weld becomes a physical property value, and the signal at both ends acts as a reference value. That is, in a cylindrical battery, the eddy current signal at the welding part shows the lowest value, and the eddy current signal measured near both ends often shows a peak. At this time, the lowest value seen in the welded portion becomes the physical property value, and the average value of the peaks seen at both ends becomes the reference value.
[45]
For example, when the battery to be evaluated is a cylindrical battery, the cylindrical battery may have a structure having a case formed of aluminum or an alloy thereof. In this case, the battery tab formed of the same material may be welded to the cylindrical case body formed of aluminum or an alloy thereof. Alternatively, a case in which the battery tab is plated with nickel or an alloy thereof is included.
[46]
In another example, the battery to be evaluated is a cylindrical battery, and the step of measuring the eddy current signal is performed on a plane of one end to which the battery tab is welded in the cylindrical battery, but is performed on a first line passing through the welding part a first measurement step; and a second measurement step of performing a second measurement on a second line that intersects the first line at the welding portion and does not overlap with the first line. In this case, the eddy current signal is measured along two lines, and the cross measurement is used to increase the reliability of the evaluation. In the above example, the step of measuring the eddy current signal along the first and second lines is performed, but the present invention does not exclude the case of measuring the eddy current signal along two or more lines.
[47]
[48]
Hereinafter, specific examples of the present invention will be described in detail with reference to the accompanying embodiments and drawings. The configuration shown in the embodiments and drawings described in the present specification is merely a specific embodiment of the present invention and does not represent all of the technical idea of ​​the present invention, so various equivalents and It should be understood that there may be variations.
[49]
[50]
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 is a cylindrical battery. The eddy current signal is measured with respect to one end surface of the cylindrical battery while standing on the measuring table. The eddy current signal measurement is performed from one end of the upper end face to the other end through the center.
[51]
2 to 4 are results of welding a battery tab with different welding strength, respectively, and observing a cross section of each welded sample with an electron microscope. 2 is a case where the welding strength is weak, and almost no change in physical properties is observed around the welding part. In contrast, FIG. 3 shows a case where the welding strength is appropriate, and changes in physical properties are observed around the welded portion. 4 is a case in which the welding strength is excessive, it can be seen that the periphery of the welding portion is excessively deformed. In this case, the case of FIGS. 2 and 4 should be determined as a defective product, and FIG. 3 should be determined as a good product. In general, in the case of welding a battery tab, if the welding strength is weak, the battery tab is separated or electrical connection is disconnected during use, and if the welding strength is excessive, process efficiency is reduced. However, in the battery to be evaluated, it is not easy to observe the cross section of the welded portion. Accordingly, the present invention proposes a method capable of effectively evaluating the quality of the welded portion in a non-destructive manner.
[52]
5 is a graph showing the results of measuring eddy current signals for batteries that have not undergone a welding process for attaching a battery tab. Specifically, five cylindrical battery samples to which a battery tab is not attached were randomly selected (Can 1 to 5), and an eddy current signal was measured for each battery sample. Referring to FIG. 5 , even though 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 shift becomes a cause of lowering the reliability of welding quality evaluation.
[53]
[54]
Example: Conducting resistance welding quality evaluation for each battery sample
[55]
A battery tab was attached to a cylindrical battery sample having a case formed of aluminum by resistance welding. At this time, the welding strength was different for each sample. Specifically, samples 1 to 3 were subjected to resistance welding at an appropriate level of welding strength, and samples 4 to 6 were subjected to resistance welding at a weak level of welding strength.
[56]
An eddy current signal value was measured for each sample. The eddy current signal value was measured continuously more than 1000 times from the left outer region to the right on the side to which the battery tab was attached, and was performed using JAS-0100W equipment from Jungan Systems.
[57]
For example, an eddy current signal value measurement result for sample 1 is shown in FIG. 6 , and an eddy current signal value measurement result for sample 4 is shown in FIG. 7 . 6 and 7, A represents the left end of the sample, B represents the center point of the weld, and C represents the right end of the sample. In the graphs showing the measurement results for Samples 1 to 6, it was confirmed that all of the values ​​in the center were small and the values ​​were increased toward the left and right from the center. Table 1 below summarizes the measurement results for each sample.
[58]
In Table 1, the numerical value at the highest point on the left side of the graph from the center point (B) is the 'left peak value', the value at the lowest point near the center point (B) is the 'minimum value of the weld', and the right side of the graph from the center point (B) The numerical value at the highest point of ' is indicated as 'right peak value', respectively. Table 1 shows. In Table 1 below, the unit is mV.
[59]
[60]
[Table 1]
sample No. left peak value Weld Minimum 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
[61]
From the results of Table 1 above, the average value of the left peak value and the right peak value is calculated and displayed as a reference value, and the minimum welding value is expressed as a physical property value, as shown in Table 2 below.
[62]
[Table 2]
sample No. reference value property value Difference
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
[63]
Referring to Table 2, it can be seen that in the case of Samples 1 to 3, the difference between the reference value and the physical property value is 0.5 or more, and in the case of Samples 4 to 6, the difference is less than 0.5. In the present invention, based on the results of Table 2 above, samples 1 to 3 are determined to be normal products, and samples 4 to 6 are determined to be defective products.
[64]
However, if only the physical property values, which are eddy current signal values ​​in the welding part, are compared, it is not easy to determine whether there is a defect. Specifically, the physical property values ​​of Samples 1 to 3 are between 26.5283 and 26.7256. In contrast, the physical property value of Sample 4 is 26.6803, and the physical property value of Sample 6 is 26.5909. Compared to the ranges of Samples 1 to 3, the physical property values ​​of Sample 4 overlap with the above ranges, and the property values ​​of Sample 6 appear to be similar to the above ranges.
[65]
Specifically, FIG. 8 is a graph showing the result of calculating the difference between the reference value and the physical property value for each sample. In FIG. 8 , the values ​​of Samples 1 to 3 and the values ​​of Samples 4 to 6 show a significant difference, and through this, the distinction between normal products and defective products is clear. In contrast, FIG. 9 is a graph showing measurement results of physical properties for each sample. In FIG. 9 , compared to Samples 1 to 3, Sample 4 showed no difference, and Sample 6 showed similar values.
[66]
Therefore, it can be seen that when only the physical property values ​​are compared, the determination of whether the battery is defective is not accurate. In the present invention, in the step of measuring the eddy current signal, by measuring the physical properties of the welded portion and the portion spaced apart from the welded portion together, and comparing the difference between them, accurate welding quality is possible.

WE CLAIMS

In a resistance welding quality evaluation method for a battery including a resistance welded weld, measuring an eddy current signal along a line connecting the opposite end from one end of the plane to the opposite end via the weld on a plane including the welded part ; and analyzing the measured eddy current signal, comparing the eddy current signal value at the welding part with the eddy current signal value at a point other than the welding part to determine the resistance welding quality.
[Claim 2]
The method according to claim 1, wherein the welding part is a point where the battery tab is joined by resistance welding.
[Claim 3]
The method of claim 1, wherein the battery to be evaluated is a cylindrical battery, and measuring the eddy current signal is performed on the plane of one end of the cylindrical battery to which the battery tab is welded. .
[Claim 4]
The method according to claim 1, wherein the measuring of the eddy current signal is performed on a plane to which the battery tab is welded, and a line connecting the opposite end from one end of the plane to the opposite end via the welding part is a straight line passing through the welding part. Resistance welding quality evaluation method, characterized in that it is a line or a curved line with both sides symmetrical with respect to the weld.
[Claim 5]
The method of claim 1, wherein the measuring of the eddy current signal is performed continuously or intermittently along a line connecting the opposite end from one end of the plane via the welding part.
[Claim 6]
[Claim 6] The method of claim 5, wherein in the step of measuring the eddy current signal, the eddy current signal is measured, comprising both ends of a plane and a welding part.
[Claim 7]
The method according to claim 1, wherein the peak value of the eddy current signal measured at a point other than the welding part is used as a reference value, and the minimum value of the eddy current signal measured in the welding part is taken as the physical property value, and the step of determining the resistance welding quality comprises: A method for evaluating the quality of resistance welding of a battery, characterized in that the difference is calculated, and when the calculated value is out of a preset range, it is determined as defective.
[Claim 8]
The method for evaluating resistance welding quality of a battery according to claim 1, wherein the battery to be evaluated is a cylindrical battery, and the reference value is an average value of each peak value of an eddy current signal measured near both ends.
[Claim 9]
The method for evaluating resistance welding quality of a battery according to claim 8, wherein the battery to be evaluated is a cylindrical battery having a case formed of aluminum or an alloy thereof.
[Claim 10]
The method of claim 1, wherein the battery to be evaluated is a cylindrical battery, and the step of measuring the eddy current signal is performed on the plane of one end of the cylindrical battery to which the battery tab is welded, and is performed on a first line passing through the welding part. a first measurement step; and a second measurement step intersecting the first line at the welding portion, but performing a second measurement on a second line that does not overlap the first line.