Spot welding quality determination system, welding quality determination method, nugget diameter estimation system, and nugget diameter estimation method

Abstract

To provide a weld quality determination system and a weld quality determination method, which enable accurate determination of quality of spot welding, and a nugget diameter estimation system and a nugget diameter estimation method, which enable accurate estimation of a nugget diameter of the spot welding.SOLUTION: A weld quality determination system determines whether weld quality of energized spot welding is good or bad, by pressurizing a member-to-be-welded by a pair of electrodes. The weld quality determination system comprises: a drive part that drives at least one of the pair of electrodes by linearly operating in the same direction as a displacement direction of the electrode; a detection part for detecting the between-electrodes displacement magnitude of the pair of electrodes; and a determination part that determines whether the weld quality is good or bad, on the basis of the between-electrodes displacement magnitude during energization, detected by the detection part.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a welding quality determination system for spot welding, a welding quality determination method, a nugget diameter estimation system, and a nugget diameter estimation method.

Background Art

[0002] In the production process of vehicles, spot welding is performed in which welded members such as vehicle bodies and parts are pressed with a pair of electrodes and current is passed between these two electrodes to melt the welded members for welding. However, in spot welding, the welded part may not usually appear on the surface, and it is difficult to determine the welding quality from the appearance.

[0003] Therefore, for example, in Patent Document 1, in spot welding in which a welded member is pressed by an electrode driven by the rotational movement of a servomotor and current is passed, the displacement amount of the electrode due to the thermal expansion of the welded member is detected, and a technique for determining the welding quality from the value of the displacement amount is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, the inventor has found the following problems regarding the determination of welding quality in spot welding in which a welded member is pressed by an electrode driven by the rotational movement of such a servomotor and current is passed.

[0006] The technique for determining the welding quality from the displacement amount of the aforementioned electrode determines the welding quality by detecting the behavior (e.g., thermal expansion, etc.) occurring at the processing point during welding, which is considered to affect the welding quality, from the displacement amount of the electrode. Therefore, it is desirable to be able to accurately detect the behavior occurring at the processing point from the displacement amount of the electrode.

[0007] However, in spot welding, in the case of the electric servo method that drives the electrode by the rotational motion of the mainstream servo motor, it is equipped with a ball screw that converts the rotational driving force of the servo motor into a linear driving force for driving in the vertical direction. Since the ball screw slides during rotation, sliding resistance due to rotation occurs. As a result, since this sliding resistance affects the displacement amount of the electrode, it is not possible to accurately detect the behavior occurring at the processing point during welding, which is considered to affect the welding quality, from the displacement amount of the electrode. That is, there is a problem that the sliding resistance due to rotation becomes noise and the determination accuracy of the welding quality decreases.

[0008] The present invention has been made in view of such circumstances, and provides a welding quality determination system and a welding quality determination method capable of accurately determining the quality of spot welding, and a nugget diameter estimation system and a nugget diameter estimation method capable of accurately estimating the nugget diameter of spot welding.

Means for Solving the Problems

[0009] The welding quality determination system according to one aspect of the present invention is a welding quality determination system for determining the quality of spot welding in which a pair of electrodes pressurize and energize a member to be welded, and is a driving unit that linearly operates in the same direction as the displacement direction of the electrode to drive at least one of the pair of electrodes, a detection unit that detects the displacement amount between the electrodes of the pair of electrodes, a determination unit that determines the quality of the welding based on the displacement amount between the electrodes during energization detected by the detection unit, and is provided with.

[0010] With such a configuration, by using a driving unit that linearly operates in the same direction as the displacement direction of the electrode to drive the electrode, the sliding resistance generated during energization is suppressed. Therefore, from the amount of displacement between the electrodes, the behavior at the processing point during welding can be accurately detected, and the quality of spot welding can be accurately determined.

[0011] In the welding quality determination system of the above aspect, the driving unit may be a linear motor. With such a configuration, the pressing force of the electrode can be controlled with higher accuracy.

[0012] In the welding quality determination system of the above aspect, the determination unit may be configured to determine that the welding quality is poor when the amount of displacement between the electrodes in the separation direction of the pair of electrodes during energization is equal to or less than a predetermined value. With such a configuration, when insufficient penetration of the welded member occurs during energization, the quality of spot welding can be accurately determined.

[0013] In the welding quality determination system of the above aspect, the determination unit may be configured to determine that the welding quality is poor when the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization is equal to or greater than a predetermined value. With such a configuration, when a large amount of spatter occurs in the welded member during energization, the quality of spot welding can be accurately determined.

[0014] In the welding quality determination system of the above aspect, the determination unit may be configured to estimate the nugget diameter formed on the welded member based on the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization, and determine the quality of the welding based on the nugget diameter. With such a configuration, by setting a desired nugget diameter, the quality of spot welding can be accurately determined based on the nugget diameter.

[0015] In the welding quality determination system of the above aspect, the determination unit may be configured to estimate that the nugget diameter when the inter-electrode displacement amount is large is a value larger than the nugget diameter when the inter-electrode displacement amount is small. With such a configuration, by estimating the nugget diameter more accurately and setting a desired nugget diameter, the quality of spot welding can be accurately determined based on the nugget diameter.

[0016] In the welding quality determination system of the above aspect, the determination unit may be configured to determine whether the welding quality is good or bad before the retraction of the electrodes from the welded member by the driving unit starts. With such a configuration, by making the determination before the electrodes retract, when the welding quality is poor, it is possible to efficiently handle the situation, such as re-energizing directly without retracting the electrodes.

[0017] In the welding quality determination system of the above aspect, when the determination unit determines that the welding quality is poor, it may be configured to re-energize the pair of electrodes before the retraction by the driving unit starts. With such a configuration, by making the determination before the electrodes retract, when the welding quality is poor, it is possible to re-energize directly without retracting the electrodes and efficiently handle the situation.

[0018] Further, a welding quality determination method according to an aspect of the present invention is a welding quality determination method for determining whether the welding quality of spot welding is good or bad, a driving step of driving at least one of a pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes, a pressurizing and energizing step of pressurizing and energizing a welded member by the pair of electrodes, a detection step of detecting the inter-electrode displacement amount of the pair of electrodes, a determination step of determining whether the welding quality is good or bad based on the inter-electrode displacement amount during energization detected in the detection step, and includes.

[0019] Moreover, a nugget diameter estimation system according to one aspect of the present invention is a nugget diameter estimation system for estimating the nugget diameter of spot welding in which a pair of electrodes pressurize and energize a member to be welded, a drive unit that drives at least one of the pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes, a detection unit that detects the amount of displacement between the electrodes of the pair of electrodes, an estimation unit that estimates the nugget diameter formed in the member to be welded based on the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization detected by the detection unit, and is provided with.

[0020] With such a configuration, by using a drive unit that linearly operates in the same direction as the displacement direction of the electrodes and drives the electrodes, the sliding resistance generated during energization is suppressed. Therefore, the nugget diameter formed in the member to be welded can be accurately estimated from the amount of displacement between the electrodes in the approaching direction of the electrodes.

[0021] Moreover, a nugget diameter estimation method according to one aspect of the present invention is a nugget diameter estimation method for estimating the nugget diameter of spot welding, a drive step of driving at least one of a pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes, a pressurization and energization step of pressurizing and energizing a member to be welded with the pair of electrodes, a detection step of detecting the amount of displacement between the electrodes of the pair of electrodes, an estimation step of estimating the nugget diameter formed in the member to be welded based on the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization detected by the detection step, and is provided with.

Effect of the Invention

[0022] According to the present invention, it is possible to provide a welding quality determination system and a welding quality determination method capable of accurately determining the quality of spot welding, and a nugget diameter estimation system and a nugget diameter estimation method capable of accurately estimating the nugget diameter of spot welding.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0024] Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate.

[0025] <First Embodiment> First, the welding quality determination system 100 according to the first embodiment will be described. FIG. 1 is a diagram showing an outline of the hardware configuration of the welding quality determination system 100 according to the present embodiment.

[0026] As shown in FIG. 1, the welding quality determination system 100 includes a welding gun 200 that spot-welds a work (welded member) 201, and a diagnostic device 300 that determines the quality of welding by the welding gun 200 and estimates the nugget diameter.

[0027] The welding gun 200 includes a linear motor (drive unit) 203 that drives at least one of a pair of electrodes 202 to clamp and energize the workpiece 201 by linearly operating in the same direction as the displacement direction of the electrode 202, and a linear encoder (detection unit) 204 that detects the displacement amount between the electrodes of the pair of electrodes 202. As a specific example, as shown in FIG. 1, the pair of electrodes 202 are held by a pair of gun arms 205, and the upper gun arm 205 can be driven up and down by the linear operation of the linear motor 203 to drive the upper electrode 202. Further, the linear motor 203 is provided with a linear encoder 204 for detecting its linear position, whereby the displacement amount between the electrodes of the pair of electrodes 202 can be detected. Here, an example of driving the upper electrode 202 has been described, but it may be one that drives the lower electrode 202, or may be one that drives both electrodes 202.

[0028] The linear motor 203 is a motor without a rotating shaft, and regardless of the driving method, for example, by the repulsion and attraction of magnets, it linearly operates in the same direction as the displacement direction of the electrode 202 to drive the electrode 202. Therefore, compared with the method of converting the rotational driving force of a conventional servo motor into a linear driving force, the sliding resistance when the electrode is driven, that is, the noise when detecting the displacement amount between the electrodes, can be reduced. Thus, the behavior occurring at the processing point during welding can be accurately detected from the displacement amount between the electrodes during energization. Further, by using a motor, the pressing force can be controlled with high accuracy compared to the case of using an air cylinder or the like.

[0029] The diagnostic device 300 has computer resources possessed by general information processing devices such as personal computers. Specifically, it includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, an HDD (Hard Disk Drive) 304, and an input / output interface (I / F) 305. Here, an example will be described where each part of the diagnostic device 300 is realized by a general information processing device. However, some or all of these functions may be incorporated into a control device that controls the welding gun 200, or may be realized in an external device such as an edge or a cloud.

[0030] The CPU 301 is a microprocessor that comprehensively controls the diagnostic device 300. Specifically, it reads out various control programs executed in this embodiment stored in the ROM 302 and the HDD 304, and executes these programs expanded on the RAM 303. Here, as a storage device, an SSD (Solid State Drive) may be provided instead of or in addition to the HDD 304.

[0031] The input / output interface 305 performs input / output between the diagnostic device 300 and the outside. For example, an output device such as a display for displaying information about welding quality, or an input device for use by an operator may be provided.

[0032] Next, the functional configuration of the welding quality determination system 100 according to this embodiment will be described. FIG. 2 is a diagram showing the functional configuration of the welding quality determination system 100 according to this embodiment.

[0033] As shown in FIG. 2, the welding quality determination system 100 includes, as functional components, a determination unit 401 and an estimation unit 402 in the diagnostic device 300. These function when various control programs stored in the ROM 302 and the like are executed by the CPU 301. Also, some or all of these functions may be realized by a hardware circuit.

[0034] The determination unit 401 determines the quality of the welding based on the amount of displacement between the electrodes during energization by the pair of electrodes 202 detected by the linear encoder 204. Here, although the specific determination method will be described later, during the energization of spot welding, thermal expansion and spatter of the welded member that affect the welding quality occur, and the amount of displacement between the electrodes changes due to the occurrence of these, so the quality of the welding can be determined based on the amount of displacement between the electrodes during energization. Further, the determination unit 401 may further have a function of determining the quality of the welding based on the nugget diameter formed on the workpiece 201 estimated by the estimation unit 402 described later. In this case, for example, an operator or the like sets in advance a predetermined range of nugget diameters for which the welding quality should be determined to be good. When the estimated nugget diameter is within the set predetermined range, the welding quality is determined to be good, and when it is outside the range, the welding quality is determined to be bad, so that the quality of the welding can be determined. Also, an operator or the like may set in advance a value of the desired nugget diameter, and determine the quality of the welding depending on whether the estimated nugget diameter is within a predetermined range from that value.

[0035] The estimation unit 402 estimates the nugget diameter formed on the workpiece 201 based on the amount of displacement between the electrodes in the approaching direction of the electrodes 202 during energization detected by the linear encoder 204. Here, the inventor has found that there is a correlation between the amount of displacement between the pair of electrodes 202 in the approaching direction during energization and the nugget diameter formed on the workpiece 201 in the present invention.

[0036] The above relationship will be specifically described with reference to FIG. 3. FIG. 3(a) shows a state in which a nugget 501 having a normal nugget diameter A is formed on the workpiece 201, and FIG. 3(b) is a schematic diagram showing a state in which a nugget 501 having a nugget diameter B smaller than normal is formed. When a large amount of spatter occurs in which the melted workpiece 201 scatters during the energization of spot welding, as shown in FIG. 3(b), the plate thickness of the workpiece 201 decreases significantly, and the nugget diameter B of the nugget 501 formed on the workpiece 201 becomes smaller than the normal nugget diameter A shown in FIG. 3(a). At this time, as the plate thickness of the workpiece 201 decreases, the amount of electrode displacement in the approaching direction of the pair of electrodes 202 increases. Therefore, since there is a relationship that the nugget diameter formed on the workpiece 201 becomes smaller as the amount of electrode displacement increases, the diagnostic device 300 stores in advance the relationship between the amount of electrode displacement in the approaching direction of the pair of electrodes 202 during energization and the nugget diameter formed on the workpiece 201 (for example, a proportional relational expression for these values). By doing so, based on the amount of electrode displacement in the approaching direction of the pair of electrodes 202 during energization, the nugget diameter formed on the workpiece 201 can be accurately estimated.

[0037] Also, here, as an example of the functional configuration of the welding quality determination system 100, an example including an estimation unit 402 that estimates the nugget diameter has been described. However, it may have a functional configuration that does not include the estimation unit 402. That is, the estimation unit 402 that estimates the nugget diameter formed on the workpiece 201 is not an essential configuration for determining the quality of welding based on the amount of electrode displacement during energization. On the other hand, when the present invention is realized as a nugget diameter estimation system, it may have a functional configuration that does not include a determination unit 401 that determines the quality of welding. That is, when estimating the nugget diameter formed on the workpiece 201 based on the amount of electrode displacement in the approaching direction of the pair of electrodes 202 during energization, for example, an operator or the like can separately determine the welding quality from the estimated nugget diameter. Therefore, the determination unit 401 that determines the quality of welding is not an essential configuration.

[0038] Next, the flow of the welding quality determination process in the welding quality determination system 100 according to the present embodiment, that is, the welding quality determination method will be described. FIG. 4 is a flowchart of the welding quality determination process according to the present embodiment. This flow starts in a state where the welding point for determining the welding quality has been determined.

[0039] First, the upper electrode 202 is lowered by the linear motor 203 to contact the work 201, and pressurization is started (S11). Next, after pressurization is maintained at a predetermined pressure for a certain period of time (S12), energization is started via the electrode 202 (S13). Then, after being energized for a certain period of time, the energization ends (S14). Here, the pressure, the energization current, etc. are appropriately determined and executed based on a predetermined processing program or the like.

[0040] Next, in S15, based on the electrode displacement amount detected by the linear encoder 204 during the energization in S13 - 14, the determination unit 401 determines whether the welding quality is good or not. If it is determined that the welding quality is good, the process proceeds to S16, the upper electrode 202 is retracted from the work 201, and this flow ends. On the other hand, if it is determined that the welding quality is not good, the process proceeds to S13 and energization is performed again. In this way, until the electrode 202 is retracted in S16, by determining the welding quality, for example, when the welding quality is determined to be not good due to insufficient penetration, etc., by energizing again, it is possible to efficiently perform rework without retracting and re - lowering the electrode 202. On the other hand, even if the welding quality is not good, the process may proceed to S16 without energizing again and end this flow in the same manner. Although omitted in this flow, a step of outputting the determination result of whether the welding quality is good or not to the input / output interface 305 may be added.

[0041] Also, here, as the flow of the welding quality determination process, the step of determining the quality of the weld was described in S15. However, when implementing the present invention as a method for estimating the ejection diameter, in S15, instead of or in addition to determining the quality of the weld, a process of estimating the ejection diameter formed on the workpiece 201 by the estimation unit 402 is performed. Thereafter, the process proceeds to S16, the upper electrode 202 is retracted from the workpiece 201, and this flow ends.

[0042] Next, a specific example of determining the welding quality will be described. FIG. 5 is an explanatory diagram schematically showing the state of change in the electrode displacement amount during the flow of the welding quality determination process described above. Here, as a determination example, as shown in FIGS. 5(a)-(d), a welding process (a) that should be determined as good without spatter generation and appropriate penetration, a welding process (b) that should be determined as no although no spatter is generated but the penetration is shallow, a welding process (c) that should be determined as good although spatter is generated but within the allowable range, and a welding process (d) that should be determined as no with a large amount of spatter generation will be described by giving four examples.

[0043] At time t0, the descent of the upper electrode 202 starts, pressure is maintained from time t1, and the descent of the upper electrode 202 stops. Next, at time t2, energization starts, and the electrode displacement amount at this time is set as d0.

[0044] First, for the welding process (a) with appropriate penetration, immediately after time t2, due to the thermal expansion of the workpiece 201, based on d0, the electrode displacement amount in the separating direction of the pair of electrodes 202 increases. On the other hand, for the welding process (b) with shallow penetration, since the thermal expansion of the workpiece 201 is small, the electrode displacement amount in the separating direction becomes small. Therefore, by setting a predetermined threshold value in advance, when the electrode displacement amount in the separating direction of the pair of electrodes 202 during energization is equal to or less than the threshold value, the welding quality can be determined as no, and the quality defect due to insufficient penetration can be accurately determined.

[0045] Next, for the welding processes (a) and (b) where sputtering does not occur, the displacement amount between the electrodes in the separating direction is maintained until the time t3 when the energization ends. On the other hand, for the welding processes (c) and (d) where sputtering occurs, the workpiece 201 melts and scatters, and the plate thickness decreases. Therefore, based on d0, the displacement amount between the electrodes in the approaching direction of the pair of electrodes 202 rapidly increases. In particular, since the displacement amount between the electrodes in the approaching direction depends on the amount of sputtering generated, by setting a predetermined threshold value in advance, for example, in the case of the welding process (c) where sputtering occurs but is within the allowable range, the displacement amount between the electrodes in the approaching direction of the electrode 202 during energization becomes equal to or less than the threshold value, and the welding quality can be determined to be good. In the case of the welding process (d) where a large amount of sputtering occurs, the displacement amount between the electrodes in the approaching direction of the electrode 202 during energization becomes equal to or greater than the threshold value, and the welding quality can be determined to be poor. Thus, it is possible to accurately determine the quality defect due to the occurrence of sputtering. Also, as described above, there is a relationship between the displacement amount between the electrodes in the approaching direction of the pair of electrodes 202 during energization and the nugget diameter formed on the workpiece 201, that is, as the displacement amount between the electrodes increases, the nugget diameter decreases. Therefore, based on the displacement amount between the electrodes in the approaching direction of the pair of electrodes 202 during energization, the nugget diameter formed on the workpiece 201 can be estimated. Further, by setting a desired nugget diameter in advance, the welding quality can be accurately determined based on the estimated nugget diameter.

[0046] Next, at the time t3 when the energization ends, the workpiece 201 that has been thermally expanded contracts, and at the time t4, the upper electrode 202 is retracted from the workpiece 201.

[0047] As described above, by using the linear motor 203 that drives the electrode 202 by linearly moving in the welding quality determination system 100 according to the present embodiment, the sliding resistance generated during energization is suppressed, and the behavior at the processing point during welding can be accurately detected from the displacement amount between the electrodes. As a result, it is possible to accurately determine the poor welding quality due to insufficient penetration or the occurrence of sputtering from the detected displacement amount between the electrodes, and to accurately estimate the nugget diameter formed on the workpiece 201.

[0048] <Other Embodiments> In the first embodiment, the linear motor 203 was described as an example of the drive unit. However, in addition to the linear motor 203, any device that drives the electrode 202 by linearly moving may be used. Specifically, an air cylinder, a hydraulic cylinder, or the like may be used as the drive unit. In that case, a strain gauge or the like may be provided on at least one of the pair of gun arms 205 to detect the displacement amount between the electrodes of the pair of electrodes 202.

[0049] Note that the present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the gist thereof. For example, in addition to the welding quality determination system, the welding quality determination method, the nugget diameter estimation system, and the nugget diameter estimation method, the present invention can also be realized in various forms such as a welding quality determination device, a nugget diameter estimation device, and a computer program for realizing these methods.

Explanation of Reference Numerals

[0050] 100 Welding quality determination system 200 Welding gun 201 Workpiece 202 Electrode 203 Linear motor 204 Linear encoder 205 Gun arm 300 Diagnostic device 301 CPU 302 ROM 303 RAM 304 HDD 305 Input / output I / F 401 Determination unit 402 Estimation unit 501 Nugget

Claims

1. A welding quality determination system for determining the quality of spot welding by pressing and energizing a member to be welded with a pair of electrodes, comprising: a driving unit that drives at least one of the pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes; a detection unit that detects the amount of displacement between the electrodes of the pair of electrodes; a determination unit that determines the quality of welding based on the amount of displacement between the electrodes during energization detected by the detection unit, wherein the determination unit determines that the welding quality is poor when the amount of displacement between the electrodes in the separating direction of the pair of electrodes is equal to or less than a first threshold immediately after the start of energization; when the amount of displacement between the electrodes in the separating direction of the pair of electrodes exceeds the first threshold immediately after the start of energization, determines whether the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than a second threshold; when the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than the second threshold, determines that the welding quality is poor, and when it is less than the second threshold, determines that the welding quality is good. A welding quality determination system.

2. The driving unit is a linear motor. The welding quality determination system according to claim 1.

3. The determination unit estimates the nugget diameter formed on the member to be welded based on the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization. The welding quality determination system according to claim 1 or 2.

4. The determination unit estimates that the nugget diameter when the amount of displacement between the electrodes is large is a larger value than the nugget diameter when the amount of displacement between the electrodes is small. The welding quality determination system according to claim 3.

5. The determination unit determines the quality of welding before the driving unit starts to retract the electrodes from the member to be welded. The welding quality determination system according to any one of claims 1 to 4.

6. When the determination unit determines that the welding quality is poor, the pair of electrodes are energized again before the driving unit starts to retract. The welding quality determination system according to claim 5.

7. A welding quality determination method for determining the quality of spot welding, comprising: a driving step of driving at least one of a pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes; a pressurizing and energizing step of pressurizing and energizing a member to be welded with the pair of electrodes; a detection step of detecting the amount of displacement between the electrodes of the pair of electrodes; A determination step of determining the quality of welding based on the amount of displacement between the electrodes during energization detected by the detection step, and In the determination step, when the amount of displacement between the electrodes in the separating direction of the pair of electrodes is equal to or less than a first threshold immediately after the start of energization, the welding quality is determined to be poor; when the amount of displacement between the electrodes in the separating direction of the pair of electrodes exceeds the first threshold immediately after the start of energization, it is determined whether the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than a second threshold; when the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than the second threshold, the welding quality is determined to be poor, and when it is less than the second threshold, the welding quality is determined to be good. Welding quality determination method.

8. A nugget diameter estimation system for estimating the nugget diameter of spot welding in which a pair of electrodes pressurize and energize a member to be welded, comprising: a driving unit that drives at least one of the pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes; a detection unit that detects the amount of displacement between the electrodes of the pair of electrodes; a determination unit that determines the quality of welding based on the amount of displacement between the electrodes during energization detected by the detection unit; an estimation unit that estimates the nugget diameter formed in the member to be welded based on the amount of displacement between the electrodes of the pair of electrodes in the approaching direction during energization detected by the detection unit, and The determination unit determines that the welding quality is poor when the amount of displacement between the electrodes of the pair of electrodes in the separating direction is equal to or less than a first threshold immediately after the start of energization; when the amount of displacement between the electrodes of the pair of electrodes in the separating direction exceeds the first threshold immediately after the start of energization, it is determined whether the amount of displacement between the electrodes of the pair of electrodes in the approaching direction is equal to or greater than a second threshold; when the amount of displacement between the electrodes of the pair of electrodes in the approaching direction is equal to or greater than the second threshold, the welding quality is determined to be poor, and when it is less than the second threshold, the welding quality is determined to be good. Nugget diameter estimation system.

9. A nugget diameter estimation method for estimating the nugget diameter of spot welding, comprising: a driving step of driving at least one of a pair of electrodes by linearly operating in the same direction as the displacement direction of the electrodes; a pressurizing and energizing step of pressurizing and energizing a member to be welded with the pair of electrodes; a detection step of detecting the amount of displacement between the electrodes of the pair of electrodes; a determination step of determining the quality of welding based on the amount of displacement between the electrodes during energization detected by the detection step; An estimating step of estimating a nugget diameter formed in the welded member based on the amount of displacement between the electrodes in the approaching direction of the pair of electrodes during energization detected by the detecting step; and In the determining step, when the amount of displacement between the electrodes in the separating direction of the pair of electrodes is equal to or less than a first threshold immediately after the start of energization, it is determined that the welding quality is unacceptable; when the amount of displacement between the electrodes in the separating direction of the pair of electrodes exceeds the first threshold immediately after the start of energization, it is determined whether the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than a second threshold; when the amount of displacement between the electrodes in the approaching direction of the pair of electrodes is equal to or greater than the second threshold, it is determined that the welding quality is unacceptable, and when it is less than the second threshold, it is determined that the welding quality is good; Nugget diameter estimation method.

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