Method for detecting center coordinates of spot welds, laser welding method, and joining method

Abstract

The present application provides a method for detecting the center coordinates of a spot weld, a laser welding method, and a joining method. The present application has the following steps: a linear laser irradiation step, in which linear laser is continuously irradiated in a line shape by output oscillation to irradiate a plurality of irradiation marks on the spot weld; a waveform acquisition step, in which the waveform of the intensity of the return light generated from the processing point is acquired; an outer edge position coordinate derivation step, in which the position coordinates of three or more positions on the outer edge of the spot weld are derived according to the peak position of the intensity of the waveform of the return light; and a center coordinate calculation step, in which the center coordinates of the spot weld are calculated according to the position coordinates of the three or more positions on the outer edge derived by the outer edge position coordinate derivation step.

Description

Technical Field

[0001] This disclosure relates to a method for detecting the center coordinates of spot weld marks, a laser welding method, and a joining method. Background Technology

[0002] For example, Japanese Patent Application Publication No. 2019-126832 discloses a method in which, after forming a circumferential weld mark by scanning a laser in a circular pattern such that an unwelded portion remains at the center, the center position of the weld mark is determined based on the image, and the center position of the laser irradiation is corrected. Summary of the Invention

[0003] Additionally, for example, in the process of vehicle manufacturing where multiple metal sheets are joined, spot welding and laser welding may be used in combination. In such cases, spot welding is first performed to adjust the spacing between the multiple metal sheets, i.e., the gap between the sheets, by appropriately narrowing the gap between them. Then, laser welding is performed either by overlapping the spot welds or at a position separated from the spot weld position by a predetermined offset.

[0004] When spot welding and laser welding are used in combination as described above, meticulous control of the positional relationship between spot welding and laser welding is required. In particular, when spot welding and laser welding processes are performed by different equipment in mass production, the product position may deviate due to the process. This can lead to situations where the laser welding position is not aligned with the target position relative to the spot welding position, resulting in laser welding being performed at positions with excessively large or small gaps between the plates, thus causing a deterioration in weld quality.

[0005] To accurately determine the positional relationship between spot welding and laser welding, it is desirable to accurately determine the center coordinates of the spot weld mark. Furthermore, in confirming the positional accuracy of the spot weld itself, it is also desirable to accurately determine the center coordinates of the spot weld, but this has not yet been resolved.

[0006] This disclosure can be implemented in the following ways.

[0007] (1) According to one aspect of the present disclosure, a method for detecting center coordinates is provided. This method for detecting center coordinates of a spot weld mark includes the following steps: a line laser irradiation step, in which laser light is continuously irradiated by oscillating the output of a laser welding apparatus in at least one direction, either from the inside to the outside of the spot weld mark or from the outside to the inside of the spot weld mark, thereby irradiating the spot weld mark with a plurality of irradiated lines; a waveform acquisition step, in which a waveform of the intensity of light generated from the processing point, i.e., the return light, by irradiating the spot weld mark with the laser light in the line laser irradiation step is acquired; an outer edge position coordinate derivation step, in which position coordinates of three or more locations on the outer edge of the spot weld mark are derived based on the peak position of the waveform of the return light; and a center coordinate calculation step, in which the center coordinates of the spot weld mark are calculated based on the position coordinates of the three or more locations on the outer edge derived by the outer edge position coordinate derivation step.

[0008] According to the center coordinate detection method of this approach, a waveform of the intensity of the returned light generated from the processing point by the irradiated laser is obtained through a line laser irradiation process and a waveform acquisition process. Furthermore, through an outer edge position coordinate derivation process, the position coordinates of three or more locations on the outer edge of the spot weld are derived based on the peak position of the returned light waveform. Generally, the top view shape of a spot weld is approximately circular. Therefore, through the center coordinate calculation process, the center coordinates of the spot weld can be accurately determined based on the position coordinates of three or more locations on the outer edge.

[0009] Furthermore, by applying the detection method of the center coordinates of the spot weld marks in this manner to, for example, the confirmation of the welding position accuracy of spot welding and the control of the positional relationship between spot welding and subsequent laser welding, the quality of welding can be improved.

[0010] (2) According to the second aspect of this disclosure, a laser welding method is provided. The laser welding method includes the following steps: a laser irradiation position adjustment step, which adjusts the irradiation position of the welding laser based on the center coordinates of the spot weld detected by the center coordinate detection method of the above-described approach; and a laser welding step, which performs welding by irradiating the welding laser.

[0011] According to this laser welding method, the center coordinates of the spot weld can be accurately detected. Furthermore, during the laser irradiation position adjustment process, since the laser irradiation position is adjusted based on the center coordinates of the spot weld, the positional relationship between the spot weld and the laser weld can be accurately maintained, thus improving the positional accuracy of the laser weld. Additionally, it can suppress the degradation of weld quality when combining spot welding and laser welding.

[0012] (3) According to a third aspect of this disclosure, a joining method is provided. This joining method is a method for joining multiple metal plates by spot welding and laser welding, comprising the following steps: a spot welding step, using a resistance welding apparatus, after stacking multiple metal plates and holding them through a pair of electrodes, applying pressure and current to the pair of electrodes to melt and join the metal plates; a center coordinate detection step, using a laser welding apparatus, detecting the center coordinates of the spot weld marks formed on the surface of the metal plates by the center coordinate detection method described above; a laser irradiation position adjustment step, adjusting the irradiation position of the welding laser based on the center coordinates detected by the center coordinate detection step; and a laser welding step, irradiating the metal plates with the welding laser to perform welding.

[0013] According to this joining method, in the joining of multiple metal plates, the center coordinates of the spot weld can be accurately detected. In the laser irradiation position adjustment process, since the laser irradiation position is adjusted based on the center coordinates of the spot weld, the positional relationship between the spot weld and the laser weld can be accurately maintained, thereby improving the welding accuracy.

[0014] (4) In the above-described joining method, the output value of the laser irradiated in the above-described line laser irradiation process is less than the output value of the laser used for welding irradiated in the above-described laser welding process. According to this joining method, in the line laser irradiation process, the laser irradiation is not performed with an excessively large output value exceeding that in the laser welding process, thus suppressing the degree of surface melting of the metal sheet and maintaining good welding quality.

[0015] (5) In the above-described joining method, the plurality of metal plates can each be a component constituting the vehicle. According to this joining method, during the vehicle manufacturing process, the joining of the components constituting the vehicle, namely the plurality of metal plates, can be performed with good quality. Attached Figure Description

[0016] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements, wherein:

[0017] Figure 1 This is a flowchart illustrating the steps of the joining method according to the first embodiment of this disclosure.

[0018] Figure 2 This is a diagram showing a schematic structure of a vehicle component that is the object of joining in the joining method of the first embodiment of this disclosure.

[0019] Figure 3This is a diagram showing a schematic structure of a laser welding apparatus used in a method for detecting the center coordinates of spot weld marks, a laser welding method, and a joining method according to the first embodiment of this disclosure.

[0020] Figure 4 This is a flowchart showing the detailed steps of the center coordinate detection process.

[0021] Figure 5 This diagram illustrates the center coordinate detection process and is a top view schematically showing the state of multiple line lasers irradiating a spot weld mark.

[0022] Figure 6 This is a diagram showing the waveform of the returned light obtained by the returned light detection device.

[0023] Figure 7 This is a diagram showing the waveform of the returned light obtained by the returned light detection device.

[0024] Figure 8 This is a diagram showing the waveform of the returned light obtained by the returned light detection device.

[0025] Figure 9 The figure illustrates how the laser welding method of the first embodiment and the laser welding method are used to assemble the surface of the metal plate after spot welding.

[0026] Figure 10 This is a cross-sectional schematic diagram used to illustrate the spot welding and laser welding processes. Detailed Implementation

[0027] A. First implementation method:

[0028] [Jointing Method]

[0029] Regarding the joining method, laser welding method, and center coordinate position detection method of the first embodiment of this disclosure, while referring to... Figures 1-10 While explaining. Figure 1 This is a flowchart illustrating the steps of the joining method according to the first embodiment of this disclosure. The joining method of the first embodiment is a method for joining metal sheets, which constitute components of a vehicle, during the vehicle manufacturing process, such as... Figure 1 As shown, the process includes a spot welding process (S10), a center coordinate position detection process (S20), a laser irradiation position adjustment process (S30), and a laser welding process (S40). These processes (S10, S20, S30, S40) are performed sequentially.

[0030] Figure 2 This is a diagram illustrating the schematic structure of a vehicle component that is to be joined in the joining method of the first embodiment of this disclosure, schematically showing the state in which spot welding and laser welding are performed at the joining points. Figure 2As shown, the joining method of the first embodiment is applied, for example, to the joining of a reinforcement member (not shown) at the center pillar 2 portion of the side beam 1 of a vehicle. The side beam 1 and the reinforcement member are examples of a "metal plate." Hereinafter, the component to be joined will also be simply referred to as a "metal plate." Figure 2 In the diagram, the spot weld 3 is simply illustrated with a white circle, and the laser weld 4 is simply illustrated with a black circle. The laser weld 4 is sometimes applied in an overlapping manner with the spot weld 3, and sometimes applied at a position separated by a predetermined offset amount.

[0031] Hereinafter, each step in the joining method of the first embodiment will be described. The spot welding step (S10) is a step in which the gap (hereinafter referred to as "plate gap") between the two parts to be joined is narrowed to a suitable interval in order to maintain the quality of the subsequent laser welding step (S40). That is, it is a step in which a so-called gap narrowing treatment is performed.

[0032] In the spot welding process (S10), a resistance welding apparatus (not shown) is used to stack multiple metal plates and hold them together using a pair of electrodes. The metal plates are then melted and joined by applying pressure and current to the electrodes. Alternatively, a known apparatus can be used for resistance spot welding, which is not shown in the diagram. By applying current to the electrodes, a molten portion is formed at the overlapping part of the stacked components. The molten portion is cooled and solidified, becoming a welded portion. Two components are joined together through this point-like welded portion (so-called a weld nugget). Generally, the top view of the welded portion is approximately circular.

[0033] In the center coordinate position detection step (S20), a laser welding device is used to detect the center coordinates of the spot weld marks formed by the spot welding step (S10). First, the structure of the laser welding device 100 used in the center coordinate position detection step (S20) and the subsequent laser welding step (S40) will be described here. Figure 3 This is a diagram showing the schematic structure of a laser welding apparatus 100 used in a method for detecting the center coordinates of spot weld marks, a laser welding method, and a joining method according to the first embodiment of this disclosure.

[0034] [Structure of laser welding device 100]

[0035] like Figure 3As shown, the laser welding apparatus 100 includes a laser oscillator 10 and an electrical scanner 20. The laser oscillator 10 is connected to the electrical scanner 20 via a fiber optic connector 11. A collimating lens 30 is disposed inside the electrical scanner 20. The electrical scanner 20 includes a first reflecting mirror 21, a diffractive optical element (DOE) 22, a Z-lens 23, a Z-lens drive unit 24, a second reflecting mirror 25, a condenser lens 26, an electrical scanner unit 27, a protective glass 28, and an electrical scanner driver 29. In addition, a return light detection device 50 is mounted on the electrical scanner 20 together with a dichroic mirror 40.

[0036] When a laser beam is emitted from the laser oscillator 10, it enters the interior of the electronic scanner 20 via the fiber optic connector 11. The laser beam is then aligned to a parallel state by the collimating lens 30. Finally, the laser beam is reflected by the dichroic mirror 40 and the first reflecting mirror 21, reaching the DOE 22.

[0037] The DOE22 can adjust the laser irradiation mode. Specifically, the DOE22 can radiate the incident laser as a laser with a different power density distribution shape than when it was incident. In addition, the DOE22 is mounted on a sliding part and is configured to slide.

[0038] The laser beam, adjusted by DOE22, reaches Z-lens 23. Z-lens 23 is used to correct the laser beam's focal deviation. Z-lens 23 is configured to be movable by being driven by Z-lens drive unit 24.

[0039] Then, the laser is reflected by the second reflector 25, enters the electronic scanner unit 27 through the condenser lens 26, and exits onto the surface of the workpiece 200 through the protective glass 28. The emitted laser can form weld marks on the surface of the workpiece 200.

[0040] Furthermore, the electrical scanner driver 29 is connected to the laser oscillator 10, the Z-lens drive unit 24, and the electrical scanner unit 27, and is configured to be controlled by a built-in program. Thus, the laser output, irradiation position, etc., can be controlled by the electrical scanner driver 29. Because this control is possible, the laser welding apparatus 100 is configured to achieve automatic program operation.

[0041] The return light detection device 50 detects the light (hereinafter referred to as "return light") generated and returning from processing point I when the metal melts during laser irradiation due to the high temperature exceeding 1000°C at processing point I. For example... Figure 3As shown by the dashed line RL, the returned light passes appropriately through the second reflecting mirror 25, the first reflecting mirror 21, the dichroic mirror 40, etc., and is incident on the returned light detection device 50. The returned light detection device 50 detects light in a predetermined frequency band (e.g., 800nm ​​to 1000nm, etc.) selected in advance based on the type of laser, and converts the light intensity into a voltage value. The returned light detection device 50 can obtain the change in voltage value over time as a waveform of light intensity. Furthermore, an example of the waveform of the returned light will be described together with the following description of the center coordinate detection process (S20).

[0042] The structure of the laser welding apparatus 100 described above is only one example. The laser welding apparatus 100 may also have other structures as long as it can implement the methods of this embodiment described below.

[0043] [Center Coordinate Detection Method]

[0044] Next, the center coordinate detection process (S20) performed using the laser welding apparatus 100 described above will be explained. In the center coordinate detection process (S20), the center coordinates of the spot weld marks formed on the surface of the metal plate by the spot welding process (S10) are detected. Figure 4 This is a flowchart showing the detailed steps of the center coordinate detection process (S20). For example... Figure 4 As shown, the center coordinate detection method includes: a line laser irradiation process (S21), a return light intensity waveform acquisition process (S22), an outer edge position coordinate derivation process (S23), and a center coordinate calculation process (S24).

[0045] Figure 5 This diagram illustrates the center coordinate detection process (S20) and is a top view schematically showing the state where multiple line lasers 61, 62, 63, 64, and 65 are irradiated on the spot weld 60. In the line laser irradiation process (S21), as... Figure 5 As indicated by arrow A, the laser output in the laser welding apparatus 100 continuously oscillates from the outside to the inside of the spot weld mark 60, irradiating the spot weld mark 60 with multiple linear laser beams 61, 62, 63, 64, and 65, thus irradiating the spot weld mark 60 in a linear pattern. Figure 5 In the example shown, five laser lines 61, 62, 63, 64, and 65 are irradiated.

[0046] Here, the output value of the laser during the online laser irradiation process (S21) is set to be smaller than the output value of the laser used for welding during the laser welding process (S40). This is because if the laser is irradiated with a high output exceeding that of the actual welding process (S40) and the upper metal plate is penetrated, there is a possibility of quality degradation, and in addition, an appropriate return light waveform cannot be obtained. Therefore, the laser output value in the online laser irradiation process (S21) is set to an output value that suppresses the surface of the upper metal plate to a moderate degree of melting.

[0047] Furthermore, the lengths of the line lasers 61, 62, 63, 64, and 65 are set such that they reliably reach the inside of the spot weld 60 from the outside, for example, to a length equal to the diameter of the spot weld 60. Additionally, the irradiation start position of the line lasers 61, 62, 63, 64, and 65 is set to be outside the spot weld 60 and moderately away from its outer edge. Furthermore, the lengths of the multiple line lasers 61, 62, 63, 64, and 65 can be the same or different. Figure 5 In the example shown, five laser lines 61, 62, 63, 64, and 65 are used to illuminate the target area, but this method is not limited to.

[0048] In the process of obtaining the waveform of the returned light intensity (S22), the waveform of the intensity of the returned light is obtained. Figures 6-8 This is a diagram showing the waveform of the returned light obtained by the returned light detection device 50. Figure 6 It shows the effect of irradiation Figure 5 The waveform of the return light generated by the first laser beam 61. Figure 7 It shows the effect of irradiation Figure 5 The waveform of the return light generated by the second laser 62 in the process. Figure 8 It shows the effect of irradiation Figure 5 The waveform of the returned light generated by the third laser line 63. Figures 6-8 In the various graphs, the horizontal axis represents time, and the vertical axis represents voltage values.

[0049] In addition, Figure 4 In the flowchart shown, the line laser irradiation process (S21) and the return light intensity waveform acquisition process (S22) are independent processes, so they are described separately for convenience. However, in reality, the return light intensity waveform is acquired approximately simultaneously with the irradiation of line lasers 61, 62, 63, 64, and 65.

[0050] Next, in the outer edge position coordinate derivation process (S23), the peak positions of the multiple waveforms obtained in the return light intensity waveform acquisition process (S22) are used as the basis for the coordinate derivation process. Figure 6 Position P1 shown Figure 7 Position P2 as shown Figure 8The location shown is P3), and multiple locations E1, E2, and E3 on the outer edge of the spot weld mark 60 are derived (refer to...). Figure 5 The position coordinates of the spot weld 60 are as follows. Through the inventors' research, it has been learned that if laser light is continuously irradiated from the outside to the inside of the spot weld 60, the voltage value based on the reflected light temporarily increases when the laser light passes through the outer edge of the spot weld 60, that is, when it enters the portion of the surface that is recessed due to the spot weld 60. Therefore, the position corresponding to the peak value of the voltage value in the reflected light intensity waveform is the position on the outer edge of the spot weld 60.

[0051] By returning the light intensity waveform, the time from the start of irradiation to the peak voltage value can be obtained. The irradiation distance and irradiation speed of the irradiating laser are controlled parameters and are known. Therefore, this information can be used to derive the position coordinates of the peak voltage value, for example, as two-dimensional coordinates defined by the X-axis and Y-axis, which are parallel to and orthogonal to the metal plate.

[0052] Furthermore, in the center coordinate calculation process (S24), the center coordinates (X and Y coordinates of center C) of the spot weld 60 are calculated based on the position coordinates of multiple locations E1, E2, and E3 on the outer edge of the spot weld 60 derived from the outer edge position coordinate derivation process (S23). As described above, the top view shape of the spot weld 60 is approximately circular. Therefore, the center coordinates can be calculated using a quadratic function of a circle based on the position coordinates of any three points on the outer edge. In this embodiment, they are calculated based on the position coordinates of three points E1, E2, and E3 on the outer edge. In addition, for this center coordinate calculation, at least three lines of line lasers 61, 62, 63, 64, and 65 need to be irradiated, and at least three locations on the outer edge are also detected, similarly, regarding the return light waveform. In addition, it is also conceivable that interference may cause noise to enter the voltage value, making it impossible to read the peak value. Therefore, in order to reliably obtain waveforms from which the peak value of the voltage value can be read, more than four (e.g., five) line lasers can be irradiated, and three waveforms from which the peak value can be clearly read can be selected.

[0053] Refer again Figure 1 The joining method will be explained below. After detecting the center coordinates of the spot weld 60 in S20 as detailed above, the laser irradiation position adjustment step (S30) is entered, where the laser irradiation position is adjusted based on the center coordinates detected in the center coordinate detection step (S20). Specifically, for example, if laser welding is to be performed overlapping with the spot weld, the laser irradiation position is adjusted and reset to match the center coordinates detected in the center coordinate detection step (S20). Furthermore, if laser welding is to be performed at a position a predetermined distance away from the spot weld, the laser irradiation position is adjusted so that the offset from the center coordinates detected in the center coordinate detection step (S20) matches the predetermined distance.

[0054] Figure 9 This diagram illustrates the method for detecting the center coordinates of the spot weld mark 60 according to the first embodiment, the laser welding method, and the joining method, which allows the laser weld to be superimposed on the surface of the metal plate after spot welding. A top view of the welded area is shown. Figure 9 In, such as Figure 9 As shown, the method of adjusting the irradiation position in laser welding based on the center coordinates of the spot weld mark 60 allows the laser weld mark 66 to overlap with the spot weld mark 60 according to the target location. The laser weld mark 66 does not overflow from the spot weld mark 60, enabling welding with good quality.

[0055] [Effect]

[0056] (1) According to the method for detecting the center coordinates of the spot weld mark 60 in the first embodiment described above, the coordinates of the center C of the spot weld mark 60 can be calculated after deriving the position coordinates of multiple locations E1, E2, and E3 on the outer edge of the spot weld mark 60 based on the waveform of the returned light obtained during online laser irradiation. Therefore, the center coordinates of the spot weld mark 60 can be accurately detected.

[0057] (2) According to the laser welding method and joining method of the first embodiment described above, laser welding can be performed accurately at a predetermined position relative to the spot weld mark 60 after the plate gap has been adjusted by spot welding.

[0058] Figure 10 This diagram illustrates the spot welding process (S10) and the laser welding process (S40). It is a schematic cross-sectional view, as an example, showing the state after multiple (two) metal plates 71 and 72 have been cut in the direction of the spot welding current. (See diagram below.) Figure 10 As shown, for example, if the laser R's irradiation position R1 deviates too far from the target position Rb and is too far from the spot weld (weld nugget 73), the laser will irradiate the area with an excessively large gap, resulting in insufficient welding and thus welding defect D. Figure 10 The image illustrates an example of such a welding defect D.

[0059] Furthermore, if the laser irradiation position R2 deviates from the target position Rb and is too close to the spot weld (melt nugget 73) as described above, for example, if the metal plates 71 and 72 are galvanized, the zinc trapped on the side of the melt nugget 73 due to the spot weld will suddenly vaporize and explode, creating a hole and causing a welding defect. Conversely, since no zinc is trapped directly above the melt nugget 73, laser irradiation can be performed.

[0060] In particular, during the mass production process of vehicle manufacturing, spot welding (S10) and laser welding (S40) are generally performed by different equipment in different steps. The welding position is affected by the product position and the fixtures holding the product in each step (S10, S40), which can result in deviation from the target position Rb, leading to situations where laser welding is performed at positions with excessively large or small gaps, and the welding quality may deteriorate.

[0061] As explained above, the examples described above use galvanized steel sheets as metal plates 71 and 72. However, in the joining of metal plates made of other materials, managing the gap between the plates is also important to avoid poor welding. Since the gap S varies depending on the distance from the spot weld, precise control of the positional relationship between the spot weld and the laser weld is required. In this regard, in the first embodiment described above, the center coordinates of the spot weld mark 60 can be accurately detected, and the irradiation position in the laser weld can be adjusted based on the center coordinates of the spot weld mark 60 before laser welding. Therefore, laser welding can be performed relative to the spot weld mark 60 at the target position, i.e., the gap S is properly managed, thereby improving the welding quality.

[0062] (3) In the laser welding method and joining method of the first embodiment described above, the output value of the laser during the online laser irradiation process (S21) is set to be smaller than the output value of the laser used for welding during the laser welding process (S40). Therefore, in the online laser irradiation process (S21), the laser irradiation is not performed with an excessively large output value that exceeds the output value in the actual welding process, which can suppress the degree of surface melting of the upper metal plate and maintain the welding quality well.

[0063] B. Other implementation methods:

[0064] (B1) The joining method of the first embodiment described above is used in the vehicle manufacturing process. The example given is the joining of the side beam 1 and the reinforcing member at the center pillar 2 of the vehicle, but it is not limited to this location. In the vehicle manufacturing process, there are many scenarios where multiple metal plates are joined, and the above-described joining method can be appropriately applied. For example, the above-described joining method can also be applied to the joining around the flange portion of the door opening of the side beam 1, and it can also be applied to the mating portion between the side beam 1 and the roof. Furthermore, it can also be used during repair processes, not during vehicle manufacturing.

[0065] (B2) Furthermore, the parts to be joined may not be components of the vehicle, and the joining method is not limited to that used in the vehicle manufacturing process. The above-mentioned joining method can be applied as long as it involves joining two or more parts by spot welding followed by laser welding.

[0066] (B3) Furthermore, the spot welding process (S10) in the joining method of the first embodiment described above is described as a process for performing so-called gap reduction treatment, but it is not limited thereto. It can also be a process for firmly joining multiple metal plates in combination with the laser welding process (S40).

[0067] (B4) The center coordinate detection method of the first embodiment described above is used for adjusting the laser irradiation position in the subsequent laser welding process (S40), but it can also be used for other purposes. For example, the center coordinates can also be detected to confirm the positional accuracy of the spot welding itself, that is, to check the degree to which welding was performed accurately at the target position.

[0068] (B5) In the line laser irradiation step (S21) of the center coordinate detection method of the first embodiment described above, laser light is irradiated from the outside of the spot weld 60 toward the inside. However, as long as the position on the outer edge of the spot weld 60 can be detected based on the reflected light intensity waveform, laser light can also be irradiated from the inside of the spot weld 60 toward the outside. As a specific example of the selected wavelength for measuring the reflected light, it is about 1070 nm if irradiation is from the inside to the outside, and about 800 nm or 1070 nm if irradiation is from the outside to the inside.

[0069] This disclosure is not limited to the embodiments described above, and can be implemented in various structures without departing from its spirit. For example, the technical features in each embodiment corresponding to the technical features in the various methods described in the summary section can be appropriately replaced or combined to solve some or all of the above-described problems or to achieve some or all of the above-described effects. In addition, any technical feature that is not described as an essential technical feature in this specification can be appropriately deleted.

Claims

1. A method for detecting the center coordinates of a spot weld mark, comprising the following steps: In the line laser irradiation process, the output of the laser is continuously oscillated in the laser welding device to irradiate the spot weld in at least one of the directions from the inside to the outside and from the outside to the inside of the spot weld, thereby irradiating the spot weld with multiple irradiation marks in the form of a line laser. The waveform acquisition process acquires the waveform of the intensity of the light generated from the processing point, i.e., the return light, by irradiating the laser in the line laser irradiation process. The outer edge position coordinate derivation process derives the position coordinates of three or more locations on the outer edge of the spot weld mark based on the intensity peak position of the waveform of the returned light; and The center coordinate calculation process calculates the center coordinates of the spot weld mark based on the position coordinates of three or more locations on the outer edge derived from the outer edge position coordinate derivation process.

2. A laser welding method comprising the following steps: The laser irradiation position adjustment process adjusts the irradiation position of the welding laser based on the center coordinates of the spot weld, detected by the center coordinate detection method described in claim 1; and The laser welding process involves irradiating the laser used for welding to perform the welding.

3. A joining method for joining multiple metal plates by spot welding and laser welding, the joining method comprising the following steps: In the spot welding process, a resistance welding device is used. After multiple metal plates are stacked and held by a pair of electrodes, pressure and current are applied to the pair of electrodes to melt and join the metal plates. The center coordinate detection process uses a laser welding device and the center coordinate detection method described in claim 1 to detect the center coordinates of the spot weld marks formed on the surface of the metal plate by the spot welding process. The laser irradiation position adjustment process adjusts the irradiation position of the welding laser based on the center coordinates detected by the center coordinate detection process; and In the laser welding process, the metal plate is irradiated with the laser used for welding to perform welding.

4. The joining method according to claim 3, wherein, The output value of the laser during the line laser irradiation process is less than the output value of the laser used for welding during the laser welding process.

5. The joining method according to claim 3 or 4, wherein, The various metal plates are components that constitute the vehicle.

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