Welding condition determination method, welding condition determination system, and welding condition determination program

Abstract

To provide a welding condition determination method, a welding condition determination system, and a welding condition determination program that can more accurately determine the quality of spot welds. [Solution] The welding state determination method according to the present disclosure is a welding state determination method for determining the quality of a spot weld performed by sandwiching a workpiece between a pair of electrodes and applying current, comprising: a detection step for detecting the amount of expansion and contraction of the workpiece; and a determination step for determining the quality of the welding state based on the amount of contraction of the workpiece after a predetermined time has elapsed from the end of current application, wherein the detection step further comprises a correction step for correcting the amount of contraction if an abnormal change in the amount of expansion is detected, and the determination step determines the quality of the welding state based on the amount of contraction corrected in the correction step.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a welding state determination method, a welding state determination system, and a welding state determination program.

BACKGROUND ART

[0002] Patent Document 1 describes a method for estimating the nugget diameter of a workpiece to be welded during spot welding. This estimation method determines the acceptability of spot welding based on the amount of expansion of the workpiece to be welded.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0003]

PATENT DOCUMENT 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] The nugget diameter estimation method described in Patent Document 1 determines whether the spot welding is defective depending on whether the amount of expansion of the workpiece to be welded is equal to or less than a threshold value. However, there is a risk that the acceptability of the welding state cannot be accurately determined only by the amount of expansion of the workpiece to be welded.

[0005] The present disclosure has been made in view of the above circumstances, and provides a welding state determination method, a welding state determination system, and a welding state determination program that can more accurately determine the acceptability of the spot welding state.

MEANS FOR SOLVING THE PROBLEMS

[0006] A welding state determination method according to one aspect of the present disclosure is A welding state determination method for determining the acceptability of the state of spot welding performed by sandwiching a workpiece between a pair of electrodes and passing current therethrough, comprising: a detection step of detecting the amount of expansion and the amount of contraction of the workpiece; The system includes a determination step that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If an abnormal change in the amount of expansion is detected in the detection step, the method further includes a correction step to correct the amount of contraction. In the determination step, the quality of the weld is determined based on the amount of shrinkage corrected in the correction step.

[0007] A welding condition determination system according to one aspect of this disclosure is: A welding condition determination system that determines the quality of a spot weld, which is performed by sandwiching a workpiece between a pair of electrodes and applying an electric current, A detection unit for detecting the amount of expansion and contraction of the workpiece, The system includes a determination unit that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If the detection unit detects an abnormal change in the amount of expansion, the determination unit corrects the amount of contraction and determines whether the welding condition is good or bad based on the corrected amount of contraction.

[0008] A welding condition determination program according to one aspect of this disclosure is: A welding condition determination program that determines the quality of a spot weld, which is performed by sandwiching a workpiece between a pair of electrodes and applying current, An acquisition step to obtain the expansion and contraction amounts of the workpiece, The system includes a determination step that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If an abnormal change in expansion amount is obtained in the acquisition step, the acquisition step further includes a correction step to correct the contraction amount. In the determination step, the quality of the weld is determined based on the amount of shrinkage corrected in the correction step. [Effects of the Invention]

[0009] This disclosure provides a welding condition determination method, a welding condition determination system, and a welding condition determination program that can more accurately determine the quality of spot welds. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram of a welding condition determination system according to an embodiment of the present disclosure. [Figure 2] This is an xz cross-sectional view of a spot welding location in a welding state determination system according to an embodiment of the present disclosure. [Figure 3] (a) This is an xz cross-sectional view of the spot welding location while energized in the welding state determination system according to the present disclosure. (b) This is an xz cross-sectional view of the spot welding location after energization in the welding state determination system according to the present disclosure. [Figure 4] (a) An example of a graph showing the relationship between the time from the start of energization and the amount of workpiece expansion detected by the detection unit in a welding state determination system according to an embodiment of the present disclosure. (b) An example of a graph showing the relationship between the amount of workpiece contraction and the nugget diameter of the welded area in a welding state determination system according to an embodiment of the present disclosure. [Figure 5] (a) A graph showing the relationship between the time from the start of energization and the amount of workpiece expansion detected by the detection unit in a welding state determination system according to an embodiment of the present disclosure. (b) An example of a graph showing the relationship between the amount of workpiece shrinkage and the nugget diameter of the weld in a welding state determination system according to an embodiment of the present disclosure. (c) An example of a graph showing the relationship between the amount of spatter shrinkage and the difference in shrinkage in a welding state determination system according to an embodiment of the present disclosure. (d) An example of correcting the amount of shrinkage using the amount of spatter shrinkage in a welding state determination system according to an embodiment of the present disclosure. [Figure 6] This flowchart shows an example of processing by a welding condition determination system according to the present disclosure. [Modes for carrying out the invention]

[0011] Hereinafter, specific embodiments of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments. In addition, for clarity of explanation, the following description and drawings are appropriately simplified.

[0012] <Configuration of Welding State Determination System> The welding state determination system according to the embodiment of the present disclosure is a system for determining the quality of spot welding performed by sandwiching a workpiece between a pair of electrodes and energizing the workpiece. The embodiment of the present disclosure discloses a welding state determination system capable of more accurately determining the quality of spot welding.

[0013] Figure 1 is a block diagram of the welding state determination system according to the embodiment of the present disclosure. The welding state determination system S includes workpieces 11 and 12, electrodes 21 and 22, a detection unit 3, a determination unit 4, a control unit 5, and a storage unit 6.

[0014] Figure 2 is an xz cross-sectional view of a spot welding execution position in the welding state determination system according to the embodiment of the present disclosure. Note that the right-handed xyz orthogonal coordinates shown in Figure 2 are for convenience to indicate the positional relationship of the components. In Figure 2, the positive z-axis direction is vertically upward, and the xy plane is a horizontal plane, which is also common to Figures 3(a) and 3(b) described later.

[0015] The workpieces 11 and 12 are objects on which spot welding is performed between the workpieces 11 and 12 by passing current from the electrodes 21 and 22. The workpieces 11 and 12 are arranged between the electrodes 21 and 22 such that the workpiece 11 is in contact with the electrode 21 on the positive z-axis direction side, and the workpiece 12 is in contact with the electrode 22 on the negative z-axis direction side. The workpieces 11 and 12 are, for example, metals such as iron, copper, aluminum, titanium, carbon steel, alloy steel, or stainless steel.

[0016] Electrodes 21 and 22 are electrodes that clamp the workpieces 11 and 12 from the positive and negative z-axis sides, respectively, to conduct electric current. Electrodes 21 and 22 are made of metals such as copper, chromium-copper alloy, copper-tungsten alloy, zirconium-copper alloy, beryllium-copper alloy, silver-tungsten alloy, or molybdenum. Although Figure 2 shows electrodes 21 and 22 with radially shaped tips, the tips may have other shapes such as flat, dome, or cone-flat.

[0017] Figure 3(a) is an xz cross-sectional view of a spot welding location while energized in a welding state determination system according to an embodiment of the present disclosure. Figure 3(b) is an xz cross-sectional view of a spot welding location after energization in a welding state determination system according to an embodiment of the present disclosure. By spot welding, a nugget N having a nugget diameter d in the xy plane direction is formed at the welding location, and the workpieces 11 and 12 are welded through the nugget N.

[0018] The detection unit 3 detects the amount of expansion in the z-axis direction of the workpieces 11 and 12 shown in Figure 3(a), and the amount of contraction in the z-axis direction of the workpieces 11 and 12 shown in Figure 3(b). The detection unit 3 is a displacement sensor that acquires the amount of z-axis displacement of electrodes 21 and 22. For example, the detection unit 3 acquires the amount of z-axis displacement of electrodes 21 and 22 from the applied pressure and stroke of electrodes 21 and 22, and detects the amount of expansion and contraction of the workpieces 11 and 12. In addition, the amount of z-axis displacement of electrodes 21 and 22 may be acquired directly, or the amount of displacement may be acquired indirectly by irradiating electrodes 21 and 22 with a laser or ultrasonic wave, and basing the acquisition of the displacement on the reflected laser or ultrasonic wave.

[0019] Figure 4(a) is an example of a graph showing the relationship between the time from the start of energization and the amount of workpiece expansion detected by the detection unit in a welding state determination system according to an embodiment of the present disclosure. In Figure 4(a), time t=0 is the time when energization starts, t=t1 is the time when energization ends, and t=t2 is the time when electrode holding ends.

[0020] The determination unit 4 determines the quality of the spot weld based on the relationship between the time from the start of energization and the amount of expansion of the workpieces 11 and 12 detected by the detection unit 3, as shown in Figure 4(a). More specifically, the quality of the spot weld is determined based on the amount of contraction A of the workpieces 11 and 12 after a predetermined time has elapsed from the end of energization. Here, the "predetermined time" is preferably the time from the end of energization time t1 to the end of electrode holding time t2, i.e., t2-t1. The predetermined time is, for example, about 10 to 1000 milliseconds. The determination unit 4 is composed of a processor such as a CPU (Central Processing Unit), working memory, and a non-volatile storage device that stores a control program.

[0021] Figure 4(b) is an example of a graph showing the relationship between the amount of shrinkage of a workpiece and the nugget diameter of a weld in a welding condition determination system according to an embodiment of the present disclosure. The determination unit 4 calculates the nugget diameter d from the amount of shrinkage A detected by the detection unit 3, based on an approximate formula showing the relationship between the amount of shrinkage A of workpieces 11 and 12 and the nugget diameter d, for example, as shown by the dotted line in Figure 4(b). In addition, it determines the quality of the spot weld depending on whether the calculated nugget diameter d is within a predetermined range. For example, if the square root of the amount of shrinkage of workpieces 11 and 12 and the nugget diameter d have a linear relationship, the determination unit 4 calculates the nugget diameter d from the amount of shrinkage A detected by the detection unit 3 based on that linear relationship. In addition, it determines the quality of the spot weld depending on whether the calculated nugget diameter d is within a predetermined range.

[0022] Figure 5(a) is a graph showing the relationship between the time since the start of energization and the amount of workpiece expansion detected by the detection unit in a welding state determination system according to an embodiment of this disclosure. The dashed line graph in Figure 5(a) is an example showing the relationship between the time since the start of energization and the amount of workpiece expansion detected by the detection unit when spatter occurs at time t=t3 during spot welding. The determination unit 4 corrects the amount of shrinkage of the workpieces 11 and 12 when the detection unit 3 detects an abnormal change in the amount of expansion as shown in Figure 5(a), and determines whether the spot welding state is good or bad based on the corrected amount of shrinkage.

[0023] Spatter refers to the phenomenon where molten metal is scattered from the welding area during welding. Because the scattering of molten metal from the welding area temporarily reduces the z-axis thickness of workpieces 11 and 12, it appears as a rapid decrease in the amount of expansion in the graph showing the relationship between the time since the start of energization and the amount of expansion of workpieces 11 and 12 detected by the detection unit 3.

[0024] Furthermore, the method for detecting abnormal expansion amount changes by the determination unit 4 is, for example, determined by whether the rate of decrease in the expansion amount of workpieces 11 and 12 exceeds a threshold while energized. Alternatively, the second derivative of the expansion amount of workpieces 11 and 12 with respect to time may be taken, and a rapid decrease in the expansion amount may be determined by whether the value of the second derivative falls below a threshold. Alternatively, the occurrence of sputtering may be directly detected using, for example, a camera that acquires images of the energized area, and the timing of the abnormal expansion amount change may be identified based on the detected results.

[0025] Figure 5(b) is an example of a graph showing the relationship between the amount of workpiece shrinkage and the nugget diameter of the weld in a welding condition determination system according to an embodiment of the present disclosure. The white circles in Figure 5(b) correspond to the graph shown by the solid line in Figure 5(a) when no spatter occurs, and the black circles in Figure 5(b) correspond to the graph shown by the dashed line in Figure 5(a) when spatter occurs. Furthermore, in both the examples of cases where spatter does not occur and where it does occur shown in Figures 5(a) and (b), the nugget diameter d after welding shows approximately the same value.

[0026] When spatter occurs, the shrinkage amount A2 decreases compared to the shrinkage amount A1 when spatter does not occur, as shown by the dashed line graph in Figure 5(a). However, if the nugget diameter d of the weld is measured when spatter occurs, for example, as shown by the black dots in Figure 5(b), the nugget diameter d does not shrink compared to the decrease in shrinkage amount A. In other words, the nugget diameter d corresponding to the shrinkage amount A2 when spatter occurs cannot be estimated even using the approximation formula shown by the dotted line in Figure 5(b), which represents the relationship between shrinkage amount A1 and nugget diameter d when spatter does not occur. Therefore, there was a risk that the quality of the weld could not be accurately determined by using only the shrinkage amount A.

[0027] On the other hand, in the welding state determination system S according to the embodiment of this disclosure, the determination unit 4 corrects the contraction amount A based on the amount of expansion of the workpieces 11 and 12 around time t=t3, which is the timing of spatter generation. This makes it possible to provide a welding state determination system that can more accurately determine the quality of the spot weld.

[0028] More specifically, the welding state determination system S according to the embodiment of this disclosure determines the quality of the welding state using the spatter shrinkage amount B shown in Figure 5(a) in addition to the shrinkage amount A. The spatter shrinkage amount B is the difference between the expansion amount of the workpieces 11 and 12 immediately before the spatter generation timing and the expansion amount of the workpieces 11 and 12 immediately after the spatter generation timing. The determination unit 4 calculates the spatter shrinkage amount B based on the expansion amounts of the workpieces 11 and 12 immediately before the spatter generation timing and immediately after the spatter generation timing detected by the detection unit 3.

[0029] Figure 5(c) is an example of a graph showing the relationship between spatter shrinkage and the difference in shrinkage in a welding state determination system according to an embodiment of the present disclosure. The black circles in Figure 5(c) correspond to the graph shown by the dashed line in Figure 5(a) when spatter occurs. The determination unit 4 calculates the nugget diameter d based on an approximate formula showing the relationship between spatter shrinkage B and the difference in shrinkage ΔA, for example, as shown by the dotted line in Figure 5(c).

[0030] The difference in shrinkage amount ΔA is the difference A1-A2 between the shrinkage amount A1 when no sputtering occurs and the shrinkage amount A2 when sputtering occurs. For example, if the sputtering shrinkage amount B and the difference in shrinkage amount ΔA have a linear relationship as shown in Figure 5(c), the determination unit 4 calculates the difference in shrinkage amount ΔA from the sputtering shrinkage amount B based on that linear relationship.

[0031] Figure 5(d) shows an example of correcting the shrinkage amount using spatter shrinkage in a welding condition determination system according to the present disclosure. The determination unit 4 estimates the shrinkage amount A1 when spatter does not occur by adding the difference ΔA of the shrinkage amount estimated from the spatter shrinkage amount B to the shrinkage amount A2 when spatter occurs. In other words, the determination unit 4 corrects the shrinkage amount A based on the spatter shrinkage amount B. By estimating the nugget diameter d based on the corrected shrinkage amount A, the quality of the welding condition can be determined with high accuracy even when spatter occurs.

[0032] The control unit 5 controls the detection unit 3, the determination unit 4, and the storage unit 6 in order to enable the welding state determination system S to function as a system. The control unit 5 is composed of, for example, a CPU, an MPU (Micro Processing Unit), working memory, and a non-volatile storage device that stores control programs. The control unit 5 may also be composed of an IC (Integrated Circuit). Furthermore, the aforementioned components of the control unit 5 may be integrated with the determination unit 4.

[0033] The memory unit 6 stores information that the judgment unit 4 uses to determine the quality of the spot weld. The information stored in the memory unit 6 includes, for example, the relationship between the shrinkage amount A of the workpieces 11 and 12 and the nugget diameter d, the relationship between the spatter shrinkage amount B and the difference ΔA of the shrinkage amount, and past operational data used to derive these relationship formulas. The memory unit 6 is, for example, an HDD (Hard Disk Drive), SSD (Solid State Drive), or cloud storage that can be connected via a network to hold various data.

[0034] As described above, the welding condition determination system according to the embodiment of this disclosure, when it detects an abnormal change in the amount of expansion of a workpiece, calculates the amount of spatter shrinkage based on the detected abnormal change in the amount of expansion, and corrects the amount of workpiece shrinkage based on the amount of spatter shrinkage. In addition, it calculates the nugget diameter of the welded area based on the corrected amount of workpiece shrinkage. This makes it possible to provide a welding condition determination system that can more accurately determine the quality of spot welds.

[0035] <Method for determining welding condition> Next, Figure 6 shows an example of the processing of the welding state determination system S according to the present disclosure. Figure 6 is a flowchart showing an example of the processing of the welding state determination system according to the present disclosure. The welding state determination method according to the present disclosure is a method for determining whether the state of a spot weld is good or bad, which is performed by sandwiching a workpiece between a pair of electrodes and applying current.

[0036] First, the workpieces 11 and 12 are sandwiched between a pair of electrodes 21 and 22, and current is applied to perform spot welding (step S1). After current is applied, the electrodes 21 and 22 stop holding the workpieces 11 and 12 after a predetermined time has elapsed. The voltage during current application is determined according to the material, size, etc., of the workpieces 11 and 12, and the current application time is, for example, 100 to 5000 milliseconds.

[0037] Next, the detection unit 3 detects the expansion and contraction amounts of the workpieces 11 and 12 during and after energization (step S2). The detection result is obtained as a relationship between the time from the start of energization and the expansion amount of the workpieces 11 and 12, as shown in Figure 4(a) or Figure 5(a).

[0038] Next, the determination unit 4 determines whether or not an abnormal change in the amount of expansion was detected in step S2 (step S3). The method for detecting an abnormal change in the amount of expansion is as described above. If no abnormal expansion change is detected (No in step S3), the nugget diameter is calculated based on the detected shrinkage of workpieces 11 and 12 (step S4). Then, the quality of the spot weld is determined based on whether the calculated nugget diameter is within a predetermined range (step S5), and the process is terminated.

[0039] On the other hand, if an abnormal change in the amount of expansion is detected (Yes in step S3), the determination unit 4 calculates the amount of sputter contraction based on the amount of expansion of workpieces 11 and 12 immediately before the timing of sputter generation and the amount of expansion of workpieces 11 and 12 immediately after the timing of sputter generation (step S6).

[0040] Next, the determination unit 4 corrects the shrinkage amount of the workpieces 11 and 12 based on the sputter shrinkage amount calculated in step S5 (step S7). Step S7 is performed by calculating the difference in shrinkage amount from the sputter shrinkage amount based on a relationship formula between the sputter shrinkage amount and the difference in shrinkage amount, for example, as shown in Figure 5(c), and adding the detected shrinkage amount of workpieces 11 and 12 with the difference in shrinkage amount.

[0041] Next, the nugget diameter is calculated based on the shrinkage amount of workpieces 11 and 12 corrected in step S7 (step S8). Then, the process proceeds to step S5 to determine the quality of the spot weld based on the nugget diameter, and the process is terminated.

[0042] As described above, the welding condition determination method according to the embodiment of this disclosure, when it detects an abnormal change in the amount of expansion of the workpiece, calculates the amount of spatter shrinkage based on the detected abnormal change in the amount of expansion, and corrects the amount of workpiece shrinkage based on the amount of spatter shrinkage. In addition, it calculates the nugget diameter of the welded area based on the corrected amount of workpiece shrinkage. This makes it possible to provide a welding condition determination method that can more accurately determine the quality of the spot weld.

[0043] Furthermore, each functional component of the welding condition determination system S described above may be implemented by hardware that realizes each functional component (e.g., hardwired electronic circuits, etc.), or by a combination of hardware and software (e.g., a combination of an electronic circuit and a program that controls it, etc.). For example, this disclosure can also be implemented by having a CPU execute a computer program to perform any processing.

[0044] The program, when loaded into a computer, includes a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in various types of non-transitory computer-readable medium or tangible storage medium. Examples, but not limited to, include non-transitory computer-readable medium or tangible storage medium, such as RAM (random-access memory), ROM (read-only memory), flash memory, SSD or other memory technologies, CD-ROM, DVD (digital versatile disc), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may also be transmitted over various types of transient computer-readable medium or communication medium. Examples, but not limited to, include transient computer-readable medium or communication medium, such as electrical, optical, acoustic or other forms of propagating signals. [Explanation of symbols]

[0045] 11, 12 Work 21, 22 electrodes 3. Detection Unit 4 Judgment section 5. Control Unit 6 Memory section A contraction amount A1 shrinkage amount when sputtering does not occur. Shrinkage when A2 sputtering occurs ΔA Difference in contraction amount B. Sputtering shrinkage d Nugget diameter N Nuggets S Welding Condition Determination System

Claims

1. A welding condition determination method for determining the quality of a spot weld, which is performed by sandwiching a workpiece between a pair of electrodes and applying an electric current, A detection step for detecting the amount of expansion and contraction of the workpiece, The system includes a determination step that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If an abnormal change in the amount of expansion is detected in the detection step, the method further includes a correction step to correct the amount of contraction. In the determination step, the quality of the weld is determined based on the amount of shrinkage corrected in the correction step. Method for determining the welding condition.

2. In the detection step, if an abnormal change in the amount of expansion due to spatter generated during the execution of the spot welding is detected, the correction step corrects the amount of contraction based on the amount of expansion before and after the timing of spatter generation. The welding condition determination method according to claim 1.

3. In the correction step, the shrinkage amount is corrected based on the sputter shrinkage amount, which is the difference between the amount of expansion immediately before the sputter generation timing and the amount of expansion immediately after the sputter generation timing. The welding condition determination method according to claim 2.

4. A welding condition determination system that determines the quality of a spot weld, which is performed by sandwiching a workpiece between a pair of electrodes and applying an electric current, A detection unit for detecting the amount of expansion and contraction of the workpiece, The system includes a determination unit that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If the detection unit detects an abnormal change in the amount of expansion, the determination unit corrects the amount of contraction and determines whether the welding condition is good or bad based on the corrected amount of contraction. Welding condition determination system.

5. A welding condition determination program that determines the quality of a spot weld, which is performed by sandwiching a workpiece between a pair of electrodes and applying current, An acquisition step to obtain the expansion and contraction amounts of the workpiece, The system includes a determination step that determines the quality of the welding state based on the amount of shrinkage of the workpiece after a predetermined time has elapsed since the end of energization, If an abnormal change in expansion amount is obtained in the acquisition step, the acquisition step further includes a correction step to correct the contraction amount. In the determination step, the quality of the weld is determined based on the amount of shrinkage corrected in the correction step. Welding condition determination program.

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