KR102140966B1 - Nondestructive inspection method of welding part - Google Patents

Abstract

The present invention is to provide a welded part non-destructive inspecting method capable of quickly and accurately inspecting a welded part which cannot be viewed from the outside. To this end, the welded part non-destructive inspecting method comprises: a first measuring step of measuring a first received signal received by a sensor while moving the sensor along a circular first driving path having a predetermined radius with respect to the center of an inspection surface of an object to be inspected; a first position setting step of setting, as a first position, a position on the first driving path indicating a lowest value or a highest value among first output signals calculated by using the first received signal; a driving path setting step of setting a second linear driving path passing through the first position and the center of the object to be inspected; a second measuring step of measuring a second received signal received by the sensor while moving the sensor along the second driving path; and a welded state determination step of comparing a second calculation signal calculated by using the second received signal with a preset reference determination value to determine a welded state of a welded part.

Description

Non-destructive inspection method of welding part{NONDESTRUCTIVE INSPECTION METHOD OF WELDING PART}

The present invention relates to a non-destructive inspection method for a weld, and more particularly, to a non-destructive inspection method for a weld for inspecting whether the weld strength is sufficient.

In general, resistance welding is performed by applying a current while applying pressure, thereby obtaining heat by contact resistance generated on the contact surface of the metal base material and the inherent resistance of the metal base material, and as a result, when the metal base material is heated or melted, bonding is performed by the applied pressure. Refers to the welding method made. The resistance welding is typically a spot welding, and the spot welding is used in various fields because it is easy for automatic welding, has excellent productivity, and has little thermal damage to a welding member.

Despite the many advantages described above, spot welding has the disadvantage of being unable to determine the welding state of the weld from the outside because it is welded at the contact surface of the welding member, and whether welding strength is sufficient because it is welded by spots (spots). It needs to be checked.

On the other hand, the secondary battery is a positive electrode, a negative electrode, and an electrode assembly capable of charging and discharging consisting of a separator structure disposed between the positive electrode and the negative electrode. The jelly roll type may be classified into a stacked type stacked sequentially while a separator is disposed between a plurality of positive and negative electrodes of a predetermined size, of which the jelly roll type electrode assembly is easy to manufacture and has high energy density per weight. Have In particular, a jelly roll type electrode assembly having a high energy density can be built in a cylindrical metal can to form a cylindrical secondary battery, and such a cylindrical secondary battery is widely applied in fields requiring application of a high capacity secondary battery such as an electric vehicle. .

1 is an exemplary view showing a cylindrical secondary battery as an inspected object.

Referring to FIG. 1, a cylindrical secondary battery as an inspected object 10 includes a positive electrode 15 and a negative electrode active material including a long sheet-shaped positive electrode active material layer with a separator 17 interposed inside the cylindrical metal case 11. The cathode 16 including the layer is wound, and the electrode assembly is embedded therein, and the cap 13 is fixed to the upper part of the metal case 11 to manufacture the electrode assembly. At this time, the positive electrode tab connected to the positive electrode 15 is disposed on the cap 13, and the negative electrode tab 18 connected to the negative electrode 16 may be disposed inside the metal case 11. In the manufacturing process of the cylindrical secondary battery, the above-described spot welding process may be applied, and the cathode tab 18 may be spot-welded to the metal case 11 to be joined.

That is, in the state in which the electrode for spot welding is inserted into the center 14 of the jelly roll provided inside the center of the metal case 11, the bottom 12 and the cathode tab 18 of the metal case 11 are spotted. It is joined by welding. Since the welded portion w welded in the spot is joined between the negative electrode tab 18 and the inner surface of the bottom 12 of the metal case 11, the welding state cannot be determined outside the metal case 11.

As such, a non-destructive inspection method for inspecting the welding state of an inspected object (case and cathode tab) having a weld portion w that cannot be confirmed from the outside is typically a method using X-ray or ultrasound. However, in the method using X-rays or ultrasonic waves, defects such as cracks or bubbles formed in the welding part w can be confirmed, but the welding state directly related to the welding strength such as diameter, depth, and thickness of the welding part w is insufficient. There is a problem that it is impossible or impossible, and in particular, the method using ultrasound has many limitations in practical use, such as requiring a medium for impedance matching between the test object and the ultrasonic sensor.

Therefore, there is a need for a new method of inspection that can quickly and accurately check and discriminate whether or not a welded part of an inspected object that cannot be visually recognized is welded normally.

Republic of Korea Registered Patent Publication No. 1524287 (Announcement on May 21, 2015)

An object of the present invention is to solve a conventional problem, the present invention is to provide a non-destructive inspection method of a welded portion that can quickly and accurately inspect the welded state of the welded part that is not visible from the outside.

In order to achieve the object of the present invention described above, the method of non-destructive inspection of a welding part according to an embodiment of the present invention is a method of inspecting whether or not the welding part is normally welded to an object to be inspected on which a welding part is formed. A first measurement step of measuring a first received signal received by the sensor while moving the sensor along a circular first driving path having a predetermined radius with respect to the center of the other surface; A first position setting step of setting a position on the first driving path indicating a lowest value or a highest value among the first calculated signals calculated using the first received signal as a first position; A driving route setting step of setting a linear second driving route passing through the first position and the center of the inspected object; A second measurement step of measuring a second received signal received by the sensor while moving the sensor along the second driving path; And a welding state determination step of comparing the second calculation signal calculated using the second reception signal with a preset reference determination value, and determining the welding state of the welding part.

In the non-destructive inspection method of a welding part according to an embodiment of the present invention, the sensor may be an eddy current sensor.

In the non-destructive inspection method of a welding part according to an embodiment of the present invention, in the first measurement step, the first output signal may be a phase difference between the first transmission signal and the first reception signal transmitted from the sensor. In the one-position setting step, a position where the first output signal has the lowest value on the first driving route may be set as the first position.

In the non-destructive inspection method of a welding part according to an embodiment of the present invention, the first transmission signal may have a frequency of 5Khz to 30Khz.

In the non-destructive inspection method of a weld according to an embodiment of the present invention, the radius of the first driving path may be 0.5 mm to 5 mm.

In the non-destructive inspection method of a welding part according to an embodiment of the present invention, in the second measurement step, the second output signal may be a phase difference between the second transmission signal and the second reception signal transmitted from the sensor, and the welding. The state determining step may be to compare the reference value with the minimum value or the highest value of the second output signal on the second driving path.

According to the present invention, the first position is set on the first driving route from the first output signal that changes along the first driving route while driving the sensor along the circular first driving route, and the set first position and inspection surface By running the sensor along the linear 2nd driving path passing through the center and inspecting the welding state of the welding part, it is possible to quickly and accurately find a welding part that cannot be visually recognized from the outside, and greatly shorten the inspection time, and to inspect the welding part accurately. Can be greatly increased.

1 is an exemplary view showing a cylindrical secondary battery as a test object.
2 is a flowchart of a method for non-destructive testing of a weld according to an embodiment of the present invention.
3 is a view for explaining the first measurement step of FIG. 2.
FIG. 4 is a view for explaining the first position setting step of FIG. 2.
FIG. 5 is a view for explaining a driving route setting step of FIG. 2.
6 is a view for explaining the second measurement step of FIG. 2.
7 is a view for explaining the welding state determination step of FIG. 2.

Hereinafter, preferred embodiments of the present invention in which the above-described problem to be solved can be realized in detail will be described with reference to the accompanying drawings. In describing these embodiments, the same name and the same code may be used for the same configuration, and additional descriptions may be omitted accordingly.

2 is a flow chart of a method for non-destructive testing of welds according to an embodiment of the present invention.

Referring to FIG. 2, the non-destructive inspection method according to the present embodiment is a method of inspecting whether or not a weld is normally welded to an object to be welded on one surface (inner surface of a metal case), particularly from the outside. Provides a method for quickly and accurately inspecting the welding state of a weld on the other surface (outside surface of a metal case) of an object that cannot be recognized.

For this, the non-destructive inspection method according to this embodiment includes a first measurement step (S110), a first position setting step (S120), a driving route setting step (S130), a second measurement step (S140), and a welding state determination step (S150). ).

3 is a view for explaining the first measurement step.

Referring to FIG. 3, the first measurement step (S110) transmits a first transmission signal toward the inspection surface 10a of the object 10, and responds to the transmitted first transmission signal to be inspected 10 It is a step of measuring the first received signal emitted from.

The inspection surface 10a of the inspected object 10 may be the other surface opposite to one surface of the inspected object 10 on which the welding part w is formed, and there is no trace of the welding part w on the inspection surface 10a. In the welding part (w) may be in a state that can not be recognized at all. For example, as shown in FIG. 1, the inspection surface 10a of the object 10 to be inspected may be the bottom 12 of the case 11 of the cylindrical secondary battery, wherein the inner surface of the bottom 12 is The negative electrode tab 18 is welded, and a welding trace may not be recognized at all on the outer surface of the bottom 12 exposed to the outside.

And, basically, the sensor 100 of the inspection device is arranged at a center C of the welding area that can be estimated from the outside, that is, the inspection surface 10a, where the sensor 100 of the inspection device is the actual welding part w ) And there is no guarantee that it will always match. This is because the actual welding part w may be formed at any position deviated from the center C of the inspection surface 10a due to reasons such as the position, pressure, and current application time of the electrode during welding.

In consideration of this, in the first measurement step (S110), the sensor 100 is disposed along the circular first driving path DL1 having a predetermined radius with respect to the center C of the inspection surface 10a of the object 10 to be inspected. While moving, the first transmission signal can be continuously transmitted toward the inspection surface 10a, and the first reception signal can be continuously received.

Each of the first transmission signal and the first reception signal may be a sinusoidal current signal.

The radius of the first driving path DL1 may be set larger than the bead width of the welding portion w with the center C of the inspection surface 10a as the origin, and the center C of the inspection surface 10a as the origin It may be set smaller than the bead width of the welding portion (w), or the radius of the first driving path (DL1) may be set equal to the bead width of the welding portion (w).

Further, the welding part w may be disposed in the inner region of the first driving path DL1, may be disposed in the outer region of the first driving path DL1, or disposed on the first driving path DL1. It may be.

The radius of the first driving path DL1 may be appropriately set in consideration of a limit error range in which the welding portion w may deviate from the center C of the inspection surface 10a according to the type of the object 10 to be inspected. As illustrated in FIG. 1, when the negative electrode tab 18 is welded to the case 11 of the cylindrical secondary battery, the radius of the first driving path DL1 is based on the center C of the inspection surface 10a. It may have a 0.5mm to 5mm.

In addition, in the first measurement step (S110), a constant first transmission signal and a changed first reception signal may be measured, and a first output signal may be generated based on the first transmission signal and the first reception signal. At this time, the first output signal may be a phase difference between the first transmission signal and the first reception signal. The first output signal, which is the phase difference between the first transmission signal and the first reception signal, may be calculated using various known phase difference detection algorithms.

The eddy current sensor may be used as the sensor 100 according to the present embodiment. In the eddy current sensor, when the alternating current applied to the coil generates a primary electromagnetic field, the generated alternating electromagnetic field induces an eddy current in the inspected object, and the induced eddy current generates a secondary electromagnetic field in the opposite direction to the coil. Here, the secondary electromagnetic field changes when the welding part existing in the inspected object approaches, and this secondary electromagnetic field changes the primary electromagnetic field to change the impedance of the coil. And, a change in the impedance of the coil causes a change in phase of the current and voltage in the circuit.

The size and distribution of the eddy current induced in the inspected object 10 may be changed according to the shape, material, permeability, and conductivity of the inspected object 10, as well as the frequency of the eddy current sensor. As shown in FIG. 1, a cylindrical secondary battery When the negative electrode tab 18 is welded to the case 11, a frequency of 5Khz to 30Khz may be applied to the eddy current sensor moving along the first driving path DL1. That is, the first transmission signal may have a frequency of 5Khz to 30Khz.

4 is a view for explaining the first position setting step.

Referring to FIG. 4, the first position setting step (S120) sets the first position P1 on the first driving path DL1 from the first transmission signal and the first calculation signal calculated from the first reception signal. It is a step.

The first position P1 may correspond to a position where the first output signal is the lowest value or the highest value on the first driving path DL1. That is, the first position P1 may be a position where the phase difference between the first transmission signal and the first reception signal is the lowest or highest value on the first driving path DL1. In this case, the first position P1 may correspond to a position closest to the welding portion w on the first driving path DL1.

Specifically, the sensor 100 is moved at an arbitrary position P0 on the first driving path DL1 while transmitting the first transmission signal and simultaneously receiving the first reception signal. When the sensor 100 moves, the first output signal (phase difference) is gradually lowered when the sensor 100 approaches the welding portion w, and at the same time that the sensor 100 reaches the first position P1 closest to the welding portion w. The first output signal (phase difference) may have the lowest value. Subsequently, when the sensor 100 is moved away from the welding part w again, the first output signal (phase difference) gradually increases, and at the same time as reaching the second position P2 arranged 180 degrees apart from the first position P1. The first output signal (phase difference) may have the highest value.

In this embodiment, the first output signal (phase difference) in the first position P1 is described as having the lowest value, but the phase difference between the first transmission signal and the first reception signal through the eddy current sensor is an inspected object including a welding part w The shape, material, permeability, and conductivity of (10) can be changed according to various factors, and as the various factors change, the first output signal (phase difference) at the first position P1 may have the highest value.

Meanwhile, the first output signal on the first driving path DL1 may be determined by permeability (μ). The magnetic permeability (μ) is a value that indicates the magnetic properties of a substance, and is a measure that indicates how much magnetization occurs when a magnetic field is applied to a certain medium.

As shown in FIG. 1, the case 11 of the cylindrical secondary battery is made of iron (Fe) material, so the case 11 without a welding part has a relatively large magnetic permeability (μ), whereas a welding part formed in the case 11 ( w) is made of an alloy material such as iron (Fe), copper (Cu), and nickel (Ni), which is a change in physical properties due to welding energy and melt, so the permeability (μ) is relatively small.

Also, the phase difference, which is the first output signal, is known to be proportional to the permeability (μ). That is, in a medium having a relatively small permeability (μ), the phase difference between the first transmission signal and the first reception signal is relatively small, and in the case of a medium having a relatively high permeability (μ), the first transmission signal and the first reception signal It is known that the phase difference is relatively large.

Therefore, at the first position P1 on the first driving path DL1 closest to the welding portion w, the first output signal has the lowest value due to the most influence of the welding portion w, and the welding portion w As it moves away from the first output signal increases, the first output signal may have the highest value at the second position P2, which is disposed 180 degrees apart from the first position P1.

5 is a view for explaining the driving route setting step.

Referring to FIG. 5 further, the driving route setting step (S130) is a step of setting the driving route of the sensor 100 for actually inspecting the welding state of the welding part w, the first position P1 and the inspected object This is a step of setting a linear second driving path DL2 passing through the center C of (10).

The center of the welding portion w may be disposed on the second driving path DL2 set as described above, and when the second driving path DL2 is set, the sensor 100 is moved along the second driving path DL2. .

Meanwhile, the second driving path DL2 may be set at both ends of the first position P1 and the second position P2 disposed 180 degrees apart from the first position P1. That is, the sensor 100 may move from the first position P1 to the second position P2, and then the movement may end at the second position P2, and conversely, start from the second position P2. Thus, after moving in the first position P1, the movement may end at the first position P1. As a result, the movement of the sensor 100 is minimized, and the inspection time can be shortened.

6 is a view for explaining the second measurement step.

6, the second measurement step (S140) transmits a second transmission signal toward the inspection surface 10a of the object 10, and responds to the transmitted second transmission signal to be inspected 10 It is a step of measuring the second received signal emitted from the.

That is, while moving the sensor 100 along the second driving path DL2, the second transmission signal can be continuously transmitted toward the inspection surface 10a, and the second reception signal can be continuously received.

Each of the second transmission signal and the second reception signal may be a sinusoidal current signal.

In addition, in the second measurement step (S140 ), a constant second transmission signal and a changed second reception signal may be measured, and a second output signal may be generated based on the second transmission signal and the second reception signal. At this time, the second output signal may be a phase difference between the second transmission signal and the second reception signal.

Specifically, on the second driving path DL2, the sensor 100 is moved from the first position P1 toward the center C of the inspection surface 10a while transmitting the second transmission signal and simultaneously transmitting the second reception signal. To receive. As the sensor 100 moves, the second output signal (phase difference) rapidly decreases as it passes through the center region of the welding portion w, and may have the lowest value.

Here, the second output signal (phase difference) has been described as having the lowest value while passing through the welding part w, but the phase difference between the second transmission signal and the second reception signal through the eddy current sensor is the inspected object 10 including the welding part w ) May vary according to various factors such as shape, material, permeability, and conductivity, and as these various factors change, the second output signal (phase difference) at the center of the welding portion w may have the highest value.

Meanwhile, the second output signal on the second driving path DL2 may also be determined by the permeability (μ). Like the second output signal, the permeability (μ) on the second driving path DL2 is the second driving without a welding part. In the path DL2, while maintaining the highest value of almost the same size, it is rapidly reduced in the area of the welding portion w, and in particular, may have the smallest value in the center of the welding portion w.

7 is a view for explaining the welding state determination step.

Referring to FIG. 7, the welding state determination step (S150) compares the second calculation signal calculated from the second transmission signal and the second reception signal with a preset reference determination value (SJ), and then the second driving path ( This is a step of determining the welding state of the welding portion w disposed on the DL2).

At this time, the welding unit disposed on the second driving path DL2 by comparing the minimum or maximum value of the second output signal calculated from the second transmission signal and the second reception signal with a preset reference determination value SJ, The welding state of w) may be determined, and the reference determination value SJ may have a preset tolerance range in which the lowest or highest value of the second output signal is maintained.

Therefore, it can be determined that the corresponding welding part w is in a normal welding state only when the calculated minimum or maximum value of the second output signal is maintained within the tolerance range of the reference determination value SJ. Here, the allowable error range of the reference judgment value SJ may be appropriately adjusted and set according to the type of the inspected object 10 and the welding portion w.

For example, FIG. 7(a) shows a comparison between the second output signal and the reference judgment value SJ for a test object in which the welding is not performed, that is, welding is not performed, and the reference judgment value SJ is inconsistent. 2 It can be confirmed that the output signal (phase difference) is maintained without a large change on the second driving path without a welding part.

7(b), the second output signal (phase difference) sharply falls in the area of the welding portion w on the second driving path, but the minimum value of the second output signal (phase difference) remains higher than the reference judgment value SJ. In this case, it may be determined as a weak welding state. In this weak welding state, the welding strength may drop, and in the case of the inspected object 10 shown in FIG. 1, when the welding strength falls, a negative electrode tab 18 may be separated from the case 11.

7(c), it is confirmed that the second output signal (phase difference) rapidly decreases in the area of the welding portion w on the second driving path, but the minimum value of the second output signal (phase difference) is maintained within the reference determination value SJ. In this case, the welding portion w may be determined as a normal welding state having an appropriate welding strength.

7(d), the second output signal (phase difference) rapidly decreases in the area of the welding portion w on the second driving path, but the minimum value of the second output signal (phase difference) is maintained lower than the reference judgment value SJ. It can be confirmed that, in this case, it can be judged as an over-welded state. Thus, in the over-welded state, if the inspected object is unnecessarily overheated, pores or cracks may be generated in the welded portion, or spatter may occur, and in the case of the inspected object 10 shown in FIG. 1, spatter occurs. A short may occur by electrically connecting the anode 15 and the cathode 16.

Therefore, as shown in FIG. 7(c), it is determined that the welding part w is in a normal welding state only when the lowest value of the second output signal on the second driving path is maintained within the tolerance range of the reference determination value SJ. Can.

In this embodiment, the second output signal (phase difference) in the area of the welding portion w has been described as having the lowest value, but the phase difference between the second transmission signal and the second reception signal through the eddy current sensor is an inspected object including the welding portion w ( The shape, material, permeability, and conductivity of 10) may be changed according to various factors, and as the various factors are changed, the second output signal (phase difference) in the welding portion w may have the highest value.

On the other hand, unlike the embodiment of the present invention, if sensing along the linear driving path passing through the center C of the inspection surface 10a where the welding part w is estimated to exist, the actual welding part w is the inspection surface. If it is not exactly placed in the center (C) of (10a) and maintains the off state, the accuracy of the output signal received from the sensor is deteriorated even if the welding is performed in the normal state, and accordingly the welding state of the welding part (w) is reduced. It cannot be accurately inspected. In addition, for accurate inspection, it may take a lot of time, such as changing the driving path of the sensor to various positions and repeating the re-inspection.

On the other hand, in the non-destructive inspection method according to the present invention, the sensor 100 travels along the circular first driving path DL1 and the first driving path from the first output signal that changes along the first driving path DL1. Set the first position (P1) on (DL1), and drive the sensor along the linear first driving path (DL2) passing through the set first position (P1) and the center (C) of the inspection surface (10a) By inspecting the welding state of the welding portion w, it is possible to quickly and accurately find the welding portion w that cannot be visually recognized from the outside, thereby greatly shortening the inspection time, and greatly improving the inspection accuracy of the welding portion.

Although the preferred embodiments of the present invention have been described with reference to the drawings as described above, those skilled in the art may vary the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. It can be modified or changed.

10: inspected object
100: sensor
DL1: Route 1
DL2: 2nd driving route

Claims (6)

As a method of inspecting whether or not the weld is normally welded to an object to be inspected, wherein the weld is formed on one surface,
A first measuring step of measuring a first received signal received by the sensor while moving the sensor along a circular first driving path having a predetermined radius with respect to the center of the other surface of the inspected object;
A first position setting step of setting a position on the first driving path indicating a lowest value or a highest value among the first calculated signals calculated using the first received signal as a first position;
A driving route setting step of setting a linear second driving route passing through the first position and the center of the inspected object;
A second measurement step of measuring a second received signal received by the sensor while moving the sensor along the second driving path; And
And a welding state determination step of comparing the second calculation signal calculated using the second reception signal with a preset reference determination value and determining a welding state of the welding part. According to claim 1,
The sensor is a non-destructive inspection method of a weld, characterized in that the eddy current sensor. According to claim 2,
In the first measurement step, the first output signal is a phase difference between the first transmission signal and the first reception signal transmitted from the sensor,
In the first position setting step, a non-destructive inspection method for a welded part, characterized in that a position in which the first output signal has the lowest value on the first driving route is set to the first position. According to claim 3,
The first transmission signal is 5Khz to 30Khz frequency non-destructive inspection method of the welding portion, characterized in that. According to claim 2,
Non-destructive inspection method of the weld, characterized in that the radius of the first driving path is 0.5mm to 5mm. According to claim 2,
In the second measurement step, the second output signal is a phase difference between the second transmission signal and the second reception signal transmitted from the sensor,
In the welding state determination step, a method for non-destructive testing of a welded part, characterized in that the reference value is compared with a minimum value or a maximum value of the second output signal on the second driving path.

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