Detection method and laser welding apparatus

Abstract

To provide a technique capable of easily detecting a welding state when welding different materials.SOLUTION: A detection method for detecting a welding state includes an irradiation step of irradiating an end portion of a first material and an end portion of a second material with a laser beam in a state where the first material and the second material of a type different from the first material abut against each other, a calculation step of calculating a ratio between an intensity of light in a first wavelength band of light of laser-induced plasma generated when the irradiation step is executed and an intensity of light in a second wavelength band different from the first wavelength band of the light of the laser-induced plasma, and a determination step of determining that a deviation amount between an abutting position and a welding target position of the laser beam is within an allowable range when the ratio is within a predetermined range. The lower limit value of the second wavelength band is larger than the upper limit value of the first wavelength band.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a detection method and a laser welding apparatus. [Background technology]

[0002] Patent Document 1 describes a technology for detecting the welding condition by observing the light of laser-induced plasma generated during laser welding. The technology described in Patent Document 1 assumes that the environment between the light of the laser-induced plasma and the focusing part of the observation device fluctuates, and detects the welding condition using the ratio between the intensity of the spectral spectrum of a specific element related to the presence or absence of defects and the intensity of the spectral spectrum of a welded material having a wavelength close to the wavelength of the spectral spectrum of the specific element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-219287 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 is intended for welding using a single material. When joining dissimilar materials, if the wavelengths of the spectral spectra of one material and the other material are close to each other, it is expected that it will be difficult to observe the light of the laser-induced plasma generated from one material and the light of the laser-induced plasma generated from the other material. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, there is provided a detection method for detecting a welding state, the detection method including: an irradiation step of irradiating, with laser light, an end of a first material and an end of a second material, which are different from the first material, that are butted together and that face each other, with laser light; a calculation step of calculating a ratio between the light intensity in a first wavelength band of laser-induced plasma light generated during the irradiation step and the light intensity in a second wavelength band different from the first wavelength band; and a determination step of determining, if the ratio is within a predetermined range, that a deviation between a butted position and a welding target position of the laser light is within an allowable range, wherein a lower limit value of the second wavelength band is greater than an upper limit value of the first wavelength band. According to the above embodiment, when joining dissimilar materials, the amount of deviation of the welding target position is detected using the ratio between the light intensity of laser-induced plasma in a first wavelength band and the light intensity of laser-induced plasma in a second wavelength band distant from the first wavelength band. By observing the plasma light in two distant wavelength bands, it is easier to observe the light of laser-induced plasma generated from one material and the light of laser-induced plasma generated from the other material, compared to when the two wavelength bands are close. This makes it easy to determine the welding condition when joining dissimilar materials. (2) In the detection method of the above aspect, the first wavelength band may be a wavelength band within a range in which the light intensity in the intrinsic emission spectrum of the second material is weaker than the light intensity in the intrinsic emission spectrum of the first material, and the second wavelength band may be a wavelength band within a range in which the light intensity in the intrinsic emission spectrum of the first material is weaker than the light intensity in the intrinsic emission spectrum of the second material. (3) In the detection method of the above aspect, the difference between the upper limit of the first wavelength band and the lower limit of the second wavelength band may be within a range of 10 nanometers to 600 nanometers. (4) According to another aspect of the present disclosure, there is provided a laser welding apparatus for welding dissimilar materials, the laser welding apparatus including: a laser irradiation unit that irradiates a laser beam onto an end of a first material and an end of a second material of a different type from the first material, the end of the first material and the end of the second material facing each other in a butted state; a control unit that controls the laser irradiation unit; and a sensor that detects the light intensity of laser-induced plasma generated by the laser irradiation. The control unit executes the following processes: when a first material and a second material of a different type from the first material are butted together, the control unit causes the laser irradiation unit to irradiate an end of the first material and an end of the second material with laser light; when the first material and the second material are butted together, the control unit detects the light intensity of the laser-induced plasma generated when the first material and the second material are irradiated with the laser light using the sensor; when the ratio is within a predetermined range, the control unit calculates a ratio between the light intensity of the laser-induced plasma in a first wavelength band and the light intensity of the laser-induced plasma in a second wavelength band different from the first wavelength band; and when the ratio is within a predetermined range, the control unit determines whether a deviation amount between the butted position and the welding target position of the laser light is within an allowable range. According to the above embodiment, when joining dissimilar materials, the amount of deviation of the welding target position is detected using the ratio between the light intensity of laser-induced plasma in a first wavelength band and the light intensity of laser-induced plasma in a second wavelength band distant from the first wavelength band. By observing the plasma light in two distant wavelength bands, it is easier to observe the light of laser-induced plasma generated from one material and the light of laser-induced plasma generated from the other material, compared to when the two wavelength bands are close. This makes it easy to determine the welding condition when joining dissimilar materials. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a configuration of a laser welding device. [Figure 2] 4 is an explanatory diagram showing an example of a first spectrum obtained by irradiating oxygen-free copper, which is a first metal plate, with laser light LB. FIG. [Figure 3] 4 is an explanatory diagram showing an example of a first spectrum obtained by irradiating a stainless steel second metal plate with laser light LB. FIG. [Figure 4] 10 is a flowchart showing a process for detecting a welding state. [Figure 5] FIG. 10 is an explanatory diagram showing the effect of using the determination method according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Implementation: FIG. 1 is a schematic diagram showing the configuration of a laser welding apparatus 100. To join a first metal plate Wa and a second metal plate Wb, the laser welding apparatus 100 welds an end of the first metal plate Wa and an end of the second metal plate Wb in a butted state. The first metal plate Wa and the second metal plate Wb being butted together refers to a state in which the ends of the first metal plate Wa and the second metal plate Wb face each other and are in contact with each other. The first metal plate Wa is also referred to as the "first material." The second metal plate Wb is also referred to as the "second material."

[0009] In this embodiment, the first metal plate Wa and the second metal plate Wb are made of different materials. Examples of materials that make up the first metal plate Wa and the second metal plate Wb include aluminum, copper, iron, and alloys containing these. In this embodiment, the first metal plate Wa is oxygen-free copper (Oxygen-Free Copper: OFC). The second metal plate Wb is stainless steel (Steel Use Stainless: SUS). In this embodiment, different materials refer to materials with different base materials. Hereinafter, the first metal plate Wa and the second metal plate Wb may be collectively referred to as the workpiece W. Materials formed by welding the first metal plate Wa and the second metal plate Wb together are used, for example, in the manufacture of motors, inverters, batteries, and other electric components for automobiles. Materials formed by welding the first metal plate Wa and the second metal plate Wb together may be used as wiring included in sensors.

[0010] The laser welding apparatus 100 includes a laser oscillator 10, a laser scanner 20 as a laser irradiation unit, a sensor 50, and a control unit 60.

[0011] A laser oscillator 10 oscillates a laser beam LB. The laser oscillator 10 and a laser scanner 20 are connected via an optical fiber cable 11. The laser scanner 20 includes a collimator lens 30, a dichroic mirror 40, a first reflecting mirror 21, a DOE (Diffractive Optical Element) 22, a Z lens driving unit 23, a second reflecting mirror 25, a condenser lens 26, a galvano scanner unit 27, and a protective glass 28.

[0012] Laser light LB emitted from the laser oscillator 10 enters the inside of the laser scanner 20 via the optical fiber cable 11. The laser light LB is then corrected to a parallel beam by the collimator lens 30. Thereafter, the laser light LB is reflected by the dichroic mirror 40 and the first reflecting mirror 21, and enters the DOE 22.

[0013] DOE 22 is a diffractive optical element that adjusts the irradiation pattern of laser light LB. Specifically, DOE 22 emits incident laser light LB as laser light LB having a power density distribution shape different from that at the time of incidence. The emitted laser light LB reaches Z lens 24 built into Z lens drive unit 23. Z lens drive unit 23 has a movement mechanism for moving the position of Z lens 24 in the optical axis direction and a driver for driving the movement mechanism. By adjusting the position of the optical axis of Z lens 24, the focal position of laser light LB emitted from laser scanner 20 is changed.

[0014] Laser beam LB is then reflected by second reflecting mirror 25, passes through condenser lens 26, and enters galvanometer scanner unit 27. Galvanometer scanner unit 27 has a mirror that reflects laser beam LB, a changing mechanism that changes the angle of the mirror, and a driver that drives the changing mechanism. In galvanometer scanner unit 27, the angle of the built-in mirror is changed, thereby changing the irradiation position of laser beam LB on work-piece W. Laser beam LB emitted from galvanometer scanner unit 27 passes through protective glass 28 and is irradiated onto irradiated surface WS of work-piece W.

[0015] The sensor 50 includes a dichroic mirror 51, a photodiode 52, a bandpass filter 53, and a photodiode 54. The sensor 50 is used to measure the intensity of light emitted from plasma (laser-induced plasma) generated when the work-piece W is irradiated with laser light LB. Details will be described later. Hereinafter, the light emitted from the plasma may be referred to as plasma light.

[0016] The control unit 60 is configured with a computer having a CPU and memory. The memory stores a laser welding program for executing a laser welding process. The control unit 60 controls the laser oscillator 10 and the laser scanner 20 by executing the laser welding program stored in the memory. Specifically, the control unit 60 commands the laser oscillator 10 to output the laser light LB. The control unit 60 also commands the Z lens drive unit 23 to determine the focal position in terms of distance, with a positive value representing a direction toward the laser scanner 20 and a negative value representing a direction away from the laser scanner 20, based on a predetermined reference focal position. When the workpiece W is positioned so that the position of the irradiated surface WS coincides with the reference focal position, deviation of the focal position from the reference focal position increases the irradiation diameter, which is the diameter of the approximately circular irradiation range of the laser light LB on the irradiated surface WS.

[0017] In this embodiment, prior to starting welding, the following preliminary preparation is performed. The preliminary preparation is used to set a threshold value for determining whether the welding condition is good or bad. In this embodiment, the welding condition is determined to be good when the amount of deviation between the butt position of the first metal plate Wa and the second metal plate Wb and the welding target position of the laser light is within an acceptable range. The welding condition is determined to be poor when the amount of deviation between the butt position of the first metal plate Wa and the second metal plate Wb and the welding target position of the laser light is not within an acceptable range. The welding target position is the target position to be irradiated with the laser light LB.

[0018] First, a laser beam LB is irradiated onto a first metal plate Wa. The spectroscopic spectrum of plasma generated by irradiating the first metal plate Wa with the laser beam LB (hereinafter referred to as the first spectrum) is detected using a spectrometer. Next, the laser beam LB is irradiated onto a second metal plate Wb. The spectroscopic spectrum of plasma generated by irradiating the second metal plate Wb with the laser beam LB (hereinafter referred to as the second spectrum) is detected using a spectrometer. It is desirable that the light emitted from the plasma enter the spectrometer via a notch filter that blocks the wavelength of the laser beam LB.

[0019] FIG. 2 is an explanatory diagram showing an example of a first spectrum obtained by irradiating laser light LB onto oxygen-free copper, which is a first metal plate Wa. FIG. 3 is an explanatory diagram showing an example of a first spectrum obtained by irradiating laser light LB onto stainless steel, which is a second metal plate Wb. Here, SUS403 is used as the second metal plate Wb. Laser light LB having a wavelength of 515 nm is used. Therefore, the peak near 515 nm in FIGS. 2 and 3 is generated by the laser light LB. Note that the scale of the measurement range of light intensity is different between the first spectrum shown in FIG. 2 and the second spectrum shown in FIG. 3. The first spectrum, which is the light intensity of plasma generated from the first metal plate Wa irradiated with laser light LB, represents the light intensity of the specific emission spectrum of the first metal plate Wa. The second spectrum, which is the light intensity of plasma generated from the second metal plate Wb irradiated with laser light LB, represents the light intensity of the specific emission spectrum of the second metal plate Wb.

[0020] In the preliminary preparation, a range of wavelengths (wavelength bands) in the first spectrum where the light intensity is relatively high and a range of wavelengths in the second spectrum where the light intensity is relatively low are identified as the first wavelength band, and a range of wavelengths (wavelength bands) in the second spectrum where the light intensity is relatively high and a range of wavelengths in the first spectrum where the light intensity is relatively low are identified as the second wavelength band.

[0021] In the example shown in FIG. 2, the intensity of light in the wavelength range of 400 to 480 nm in the first spectrum is relatively high. In the example shown in FIG. 3, the intensity of light in the wavelength range of 400 to 480 nm in the second spectrum is relatively low. For this reason, the range of 400 to 480 nm is identified as the first wavelength band. A dichroic mirror 51 (see FIG. 1) is selected according to the identified first wavelength band. The selected dichroic mirror 51 reflects light in the wavelength range of 400 to 480 nm out of the light emitted from the plasma and transmits light in other ranges.

[0022] In the example shown in FIG. 3, the intensity of light in the wavelength range of 560 to 720 nm in the second spectrum is relatively high. In the example shown in FIG. 2, the intensity of light in the wavelength range of 560 to 720 nm in the first spectrum is relatively low. Therefore, the range of 560 to 720 nm is specified as the second wavelength band. A bandpass filter 53 is selected according to the specified second wavelength band (see FIG. 1). The selected bandpass filter 53 transmits light in the wavelength band of 560 to 720 nm. In this embodiment, the first wavelength band is specified as a wavelength band in which the intensity of light in the inherent emission spectrum of the material constituting the second metal plate Wb is weaker than the intensity of light in the inherent emission spectrum of the material constituting the first metal plate Wa. The second wavelength band is specified as a wavelength band in which the intensity of light in the inherent emission spectrum of the material constituting the first metal plate Wa is weaker than the intensity of light in the inherent emission spectrum of the material constituting the second metal plate Wb.

[0023] Furthermore, a ratio value VR of the average value A1 of the light intensity of the first wavelength band in the first spectrum to the average value A2 of the light intensity of the second wavelength band in the second spectrum is calculated. A threshold value for determining whether the welding condition is good or bad is set using the calculated ratio value VR. In this embodiment, the quality of the welding condition is determined based on the ratio value between the light intensity of the first wavelength band and the light intensity of the second wavelength band detected by detecting the light of plasma generated during welding. If the ratio value calculated from the light intensity of the plasma detected during welding falls within a certain range centered on the ratio value VR calculated in advance, the welding condition is determined to be good. For example, suppose the calculated ratio value VR is "0.5." Furthermore, suppose a certain range centered on the ratio value VR of "0.5" is set to "0.4" to "0.6." In this case, a threshold value indicating the upper limit of the range in which the welding condition is good (hereinafter referred to as upper limit threshold Vth1) is set to "0.6," and a threshold value indicating the lower limit of the range in which the welding condition is good (hereinafter referred to as lower limit threshold Vth2) is set to "0.4."

[0024] Fig. 4 is a flowchart showing a process for detecting the welding state. A method for detecting the welding state according to this embodiment will be described below. For example, when an operator instructs the control unit 60 to start welding via an input device (not shown), the process shown in Fig. 4 is started. Before the process of Fig. 4 is started, advance preparation is performed, and an upper threshold Vth1 and a lower threshold Vth2 are set.

[0025] In step S101, the control unit 60 controls the laser scanner 20 to irradiate the work-piece W with laser light LB. The laser light LB is irradiated onto the end of the first metal plate Wa and the end of the second metal plate Wb, which are in contact with each other and face each other. Step S101 is also referred to as the "irradiation process."

[0026] When the laser beam LB is applied, the end of the first metal sheet Wa and the end of the second metal sheet Wb melt. When the temperature rises further, the metal vapor generated from the molten pool and the atmospheric gas absorb the laser beam LB, generating plasma (laser-induced plasma).

[0027] Of the light emitted from the plasma, light in a first wavelength band (400 to 480 nm) is reflected by dichroic mirror 51 and enters photodiode 52. Photodiode 52 outputs a signal indicating the intensity of the incident light to control unit 60. Of the light emitted from the plasma, light other than the first wavelength band (400 to 480 nm) passes through dichroic mirror 51 and enters bandpass filter 53. Bandpass filter 53 transmits light in a second wavelength band (560 to 720 nm). Light in the second wavelength band (560 to 720 nm) that has passed through bandpass filter 53 enters photodiode 54. Photodiode 54 outputs a signal indicating the intensity of the incident light to control unit 60.

[0028] In step S103, control unit 60 calculates the ratio between the light intensity in the first wavelength band of plasma light and the light intensity in the second wavelength band of plasma light. Specifically, it calculates the ratio between the average light intensity in the first wavelength band and the average light intensity in the second wavelength band. Step S103 is also referred to as the "calculation step."

[0029] In step S105, the control unit 60 determines whether the deviation between the butt position of the first metal plate Wa and the second metal plate Wb and the welding target position of the laser beam is within an acceptable range based on the calculated ratio. Here, the butt position refers to the position where the end of the first metal plate Wa and the end of the second metal plate Wb face each other and contact each other. When joining the first metal plate Wa and the second metal plate Wb, it is desirable that the welding target position of the laser beam coincide with the butt position. However, the welding target position of the laser beam may deviate from the butt position toward the other end of the first metal plate Wa. Alternatively, the welding target position of the laser beam may deviate from the butt position toward the other end of the second metal plate Wb. Here, if the calculated ratio is equal to or less than a predetermined upper threshold Vth1 and equal to or greater than a predetermined lower threshold Vth2, it is determined that the deviation of the welding target position of the laser beam is within an acceptable range. If the calculated ratio value is greater than the upper threshold Vth1 or less than the lower threshold Vth2, it is determined that the deviation of the welding target position of the laser beam is not within an allowable range. Step S105 is also referred to as a "determination step."

[0030] In step S107, the control unit 60 displays the determination result on a display device (not shown), and then the process shown in FIG.

[0031] Fig. 5 is an explanatory diagram showing the effect of the above-mentioned determination method. Fig. 5 shows the ratio (hereinafter referred to as intensity ratio) between the light intensity of the first wavelength band of plasma light and the light intensity of the second wavelength band of plasma light when laser light is irradiated at the positions shown in (1) to (5) below on the first metal plate Wa and the second metal plate Wb in a butted state. Here, the ratio value of the average light intensity of the first wavelength band of plasma light to the average light intensity of the second wavelength band of plasma light was obtained.

[0032] Hereinafter, the position where the first metal plate Wa and the second metal plate Wb are butted together will be referred to as the center. Because the spot size of the laser light LB in the just-focused state is approximately 600 μm, this position is set to a maximum of 300 μm off the center. The state in which the focal position of the laser light LB coincides with the irradiated surface WS will be referred to as the just-focused state. (1) Center position (zero deviation) (2) A position shifted 200 μm from the center toward the first metal plate Wa (oxygen-free copper) side (3) A position shifted 300 μm from the center toward the first metal plate Wa (oxygen-free copper) side (4) Position shifted 200 μm from the center toward the second metal plate Wb (SUS) side (5) Position shifted 300 μm from the center toward the second metal plate Wb (SUS) side

[0033] 5, when the target position is shifted from the center, the intensity ratio tends to deviate from the intensity ratio when the laser beam LB is irradiated at the center. This is because when the target position is shifted from the center, the amount of plasma generated from one of the first metal plate Wa and the second metal plate Wb increases.

[0034] When joining dissimilar materials, it is desirable to observe the light intensity of plasma generated from one material and the light intensity of plasma generated from the other material. Therefore, the amount of deviation of the welding target position is detected using the ratio between the light intensity of plasma in a first wavelength band and the light intensity of plasma in a second wavelength band separated from the first wavelength band. In this embodiment, as described above, advance preparation is performed to identify the first and second wavelength bands and set the upper threshold Vth1 and the lower threshold Vth2. Using the various set information, the welding condition when joining dissimilar materials can be easily determined.

[0035] B. Other Embodiments: (B1) In the embodiment, an example of displaying the judgment result has been described, but the irradiation position of the laser light LB can also be feedback-controlled by adjusting the process parameters based on the value of the ratio between the light intensity in the first wavelength band of the plasma light and the light intensity in the second wavelength band of the plasma light.

[0036] (B2) In the embodiment, the first wavelength band is a wavelength range in the first spectrum where the light intensity is relatively high and the second spectrum where the light intensity is relatively low. The second wavelength band is a wavelength range in the second spectrum where the light intensity is relatively high and the first spectrum where the light intensity is relatively low. For example, the first spectrum and the second spectrum may be similar, making it difficult to identify the first wavelength band. In such a case, the difference between the upper limit of the first wavelength band and the lower limit of the second wavelength band is set to a range of 10 to 600 nanometers. Furthermore, the bandwidths of the first wavelength band and the second wavelength band are set narrow. In the embodiment, the bandwidths of the first wavelength band and the second wavelength band are 80 nm and 60 nm, respectively. For example, the bandwidths of the first wavelength band and the second wavelength band are set to a narrow range of 20 to 40 nm. This narrows the bandwidths. This makes it possible to compare the unique band of the first spectrum with the unique band of the second spectrum. Therefore, it is possible to observe the light of the laser-induced plasma generated from one material and the light of the laser-induced plasma generated from the other material.

[0037] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0038] 10...laser oscillator, 11...optical fiber cable, 20...laser scanner, 21...first reflecting mirror, 23...Z lens drive unit, 24...Z lens, 25...second reflecting mirror, 26...condensing lens, 27...galvano scanner unit, 28...protective glass, 30...collimating lens, 40...dichroic mirror, 50...sensor, 51...dichroic mirror, 52...photodiode, 53...bandpass filter, 54...photodiode, 60...control unit, 100...laser welding device, 200...detection device, A1...average value, A2...average value, LB...laser light, W...workpiece to be welded, WS...irradiated surface, Wa...first metal plate, Wb...second metal plate

Claims

1. A detection method for detecting a welding state, comprising: an irradiation step of irradiating a laser beam onto an end portion of the first material and an end portion of the second material, which are facing each other and in contact with each other, in a state where a first material and a second material of a type different from the first material are butted together; a calculating step of calculating a ratio between the light intensity in a first wavelength band of light from laser-induced plasma generated during the irradiation step and the light intensity in a second wavelength band of the laser-induced plasma different from the first wavelength band; a determining step of determining that the amount of deviation between the butted position and the welding target position of the laser light is within an allowable range when the ratio is within a predetermined range; Including, the lower limit of the second wavelength band is greater than the upper limit of the first wavelength band; Detection method.

2. 2. The detection method according to claim 1, As the first wavelength band, a wavelength band in which the light intensity in the inherent emission spectrum of the second material is weaker than the light intensity in the inherent emission spectrum of the first material is specified; As the second wavelength band, a wavelength band in which the light intensity in the inherent emission spectrum of the first material is weaker than the light intensity in the inherent emission spectrum of the second material is specified. Detection method.

3. 3. The detection method according to claim 1 or 2, a difference between an upper limit of the first wavelength band and a lower limit of the second wavelength band is within a range of 10 nanometers to 600 nanometers; Detection method.

4. A laser welding device for welding dissimilar materials, a laser irradiation unit that irradiates laser light onto an end of the first material and an end of the second material that are facing each other in a state where a first material and a second material that is different from the first material are butted together; a control unit that controls the laser irradiation unit; a sensor for detecting the light intensity of laser-induced plasma generated by laser irradiation; Equipped with The control unit a process of irradiating an end of the first material and an end of the second material with the laser light by the laser irradiation unit in a state in which the first material and the second material of a different type are butted together; a process of detecting, by the sensor, the intensity of light of the laser-induced plasma generated when the first material and the second material are irradiated with the laser light; calculating a ratio between the intensity of light in a first wavelength band of the laser-induced plasma and the intensity of light in a second wavelength band of the laser-induced plasma, the second wavelength band being different from the first wavelength band; a process of determining whether or not a deviation amount between the butted position and the welding target position of the laser light is within an allowable range when the ratio is within a predetermined range; Run the lower limit of the second wavelength band is greater than the upper limit of the first wavelength band; Laser welding equipment.

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