JP5186914B2 - Welding state detection device and welding state detection method - Google Patents

Description

  The present invention relates to a welding state detection device and a welding state detection method capable of detecting a welding state of a plate material to be welded using a laser.

  Conventionally, when a plurality of plate materials are welded with a laser, the quality of the welding is inspected, for example, as shown in Patent Document 1 below.

In other words, the plasma light generated from the keyhole during welding is detected by two sensors, the frequency distribution of the detected plasma light is obtained, and the obtained frequency distribution is compared with the reference frequency distribution to thereby improve the quality of welding. I am inspecting.
Japanese Patent Laid-Open No. 10-6051

  However, in the conventional welding quality inspection method, the welding quality is inspected based on the frequency distribution of the plasma light. Therefore, the thickness on the laser beam irradiation side is thick among the plurality of stacked plate materials. In some cases, the inspection accuracy may be slightly lower than in the case of a thin plate thickness.

  That is, the frequency distribution of the plasma light is obtained from the change in the natural frequency caused by the state change such as the shape of the molten pool generated in the laser light irradiation part, and the change in the natural frequency of the molten pool is normal. When welding is performed, it depends on the total thickness of a plurality of plate members. However, the change in the natural frequency of the molten pool is caused by the gap between the plate materials, and when the molten pool is separated into the respective plate materials (when non-welding occurs), it is located on the laser beam irradiation side. It depends greatly on the thickness of the plate material. Therefore, when the plate thickness of the plate located on the laser beam irradiation side is thick, it tends to be difficult to detect the occurrence of unwelding. In particular, the plate thickness on the back side of the laser beam irradiation side is difficult to detect. It becomes remarkable when it is thinner than the plate thickness.

  For example, when two plate members are welded with laser light, the thickness a (for example, 1.4 mm) of the plate member (upper plate) positioned on the laser beam irradiation side is positioned on the side opposite to the laser beam irradiation side. If the plate material (lower plate) has a thickness b (for example, 0.65 mm) that is significantly different from the thickness b (for example, 0.65 mm), even if non-welding occurs, the frequency distribution of the plasma light does not change significantly. When unwelding occurs, the change in the frequency distribution of the plasma light becomes smaller as the value of a + b, which is the sum of both plate thicknesses, approaches the plate thickness a of the upper plate. That is, since the detection accuracy tends to decrease as the thickness of the upper plate becomes larger than the thickness of the lower plate, a highly accurate sensor and analysis device are required.

  The present invention has been made to solve such conventional problems, and in particular, detects the welding state with high accuracy without being affected by the thickness of the plate located on the laser beam irradiation side. An object of the present invention is to provide a welding state detection device and a welding state detection method that can be performed.

  The present invention for achieving the above object is a welding state detection device for detecting a welding state of a plate material to be welded using a laser.

That is, a laser beam irradiating unit that irradiates a laser beam toward an overlapping portion of a plurality of plates, a laser beam receiving unit that receives a laser beam reflected by a keyhole formed in the laser irradiating unit, and a received laser beam A welding state detecting means for detecting a welding state of the plate material based on the intensity waveform of the plate, and the plurality of fixed plate materials are formed of a plate material having a large plate thickness on the side irradiated with the laser beam, A plate material having a thickness smaller than that on the side irradiated with the laser beam is fixed to the side opposite to the side irradiated with the light so that at least a part thereof overlaps , and the welding state detection means includes the laser welding shape that having a comparing means for comparing the model waveform representing temporal change in intensity of the laser light that is prepared in advance a waveform indicating a temporal change in light intensity correlating relationship between the two waveforms A detection device.

  Moreover, this invention for achieving the said objective is the welding state detection method of detecting the welding state of the board | plate material welded using a laser.

That is, a step of preparing a plurality of plate members, a step of fixing the prepared plurality of plate members so that at least a part thereof overlaps, and a step of irradiating a laser beam toward a portion where the plurality of fixed plate members overlap each other Moving the laser beam; receiving a laser beam reflected by a keyhole formed in the laser irradiation unit; detecting a welding state of the plate material based on an intensity waveform of the received laser beam; The step of fixing the prepared plurality of plate members so as to at least partially overlap each other is performed by using a thick plate member on the side irradiated with the laser beam and opposite to the side irradiated with the laser beam. the thin plate thickness of the plate material than the plate thickness of the side in which the on the side the laser beam is irradiated, and fixed so that at least partially overlap, welding shaped the plate based on the intensity waveform of the laser light received In the step of detecting the waveform, the waveform indicating the change in intensity of the laser beam with time is prepared in advance by comparing the two waveforms with a model waveform indicating the change in intensity of the laser beam with time. A welding state detection method , wherein the welding state of the plate material is detected .

  According to the present invention, the welding state can be detected with high accuracy without being affected by the thickness of the plate material to be welded from the intensity waveform of the laser beam from the keyhole that changes in accordance with the state of the keyhole. .

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments to which the invention is applied will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a remote laser welding system to which a welding state detection apparatus according to the present invention is applied.

  The welding state detection apparatus according to the present invention can detect the welding state of a plate material to be welded using a laser in real time and with high accuracy. In addition, the remote laser welding system is a welding system that is rapidly used in the welding process of automobiles because it has a feature that the movement from one welding point to the next welding point is extremely fast.

  The remote laser welding system includes a scanner 100, a laser light receiving unit 200, an amplifier 300, and a computer 400.

  The scanner 100 functions as a laser beam irradiation unit, and irradiates the laser beam L toward the overlapping portion of the two plate materials 10A and 10B having different plate thicknesses. The laser beam receiving unit 200 functions as a laser beam receiving unit, and receives the laser beam reflected by the keyhole formed in the laser irradiation unit 20. The amplifier 300 amplifies an electrical signal output from the laser light receiving unit 200 based on the received laser light. The computer 400 functions as a welding state detection means, and takes in the electric signal amplified by the amplifier 300 and detects the welding state of the two plates 10A and 10B.

  The scanner 100 is attached to a robot hand (not shown). The scanner 100 is moved in the direction of the white arrow shown in the figure, and welds the welding locations set on the two plate members 10A and 10B.

  In this embodiment, in order to facilitate understanding of the contents of the present invention, two plate members 10A and 10B are illustrated and described as objects to be irradiated with laser light. However, the present invention irradiates with laser light. Even if it is 3 or more board | plate materials as object to perform, it is applicable. Moreover, in this embodiment, although the board | plate material which has different thickness is illustrated as two board | plate materials 10A and 10B, the board | plate material which has the same thickness may be sufficient.

  The scanner 100 includes a YAG laser diode 110, a first optical system 120, and a second optical system 130.

  The YAG laser diode 110 generates YAG laser light and emits it to the outside. The first optical system 120 converts the laser light output from the YAG laser diode 110 into parallel light. The second optical system 130 narrows the focal point while reflecting the laser light output from the first optical system 120 a plurality of times through the half mirror 132, the YAG light transmission filter 134, and the attenuation filter 136, and two plate materials The laser irradiation unit 20 of 10A and 10B is irradiated.

  The two plate members 10A and 10B irradiated with the laser beam L are formed by applying a thick plate member 10A on the side irradiated with the laser beam L (upper plate) and the side opposite to the side irradiated with the laser beam L ( A lower plate) is fixed so that at least part of the plate material is thinner than the plate thickness on the side irradiated with the laser beam L. Specifically, the plate member 10A serving as the upper plate has a thickness of 1.4 mm, and the plate member 10B serving as the lower plate has a thickness of 0.65 mm.

  The laser light receiving unit 200 includes a reflection mirror 210, a convex lens 220, a laser light input unit 230, an optical fiber 240, a reflection mirror 250, an optical filter 260, and a photodiode 270.

  The reflection mirror 210 substantially reflects the laser light reflected by the keyhole formed in the laser irradiation unit 20 via the attenuation filter 136, the YAG light transmission filter 134, and the half mirror 132 provided in the second optical system 130. Reflects by changing the 90 ° angle.

  The convex lens 220 narrows down the laser light from the keyhole reflected by the reflection mirror 210 and causes the laser light input unit 230 to input the laser light. The laser beam input to the laser beam input unit 230 is output toward the reflection mirror 250 via the optical fiber 240.

  The reflection mirror 250 reflects the laser light output from the optical fiber 240 by changing the angle by approximately 90 °, and outputs the reflected light toward the optical filter 260. The optical filter 260 cuts light in a wavelength region that becomes noise included in laser light.

  The photodiode 270 outputs an electrical signal corresponding to the intensity of the input laser beam.

  The amplifier 300 amplifies the electrical signal output from the photodiode 270 to a certain level.

  The computer 400 functions as a welding state detection unit, and receives the electric signal amplified by the amplifier 300, digitizes the electric signal by an A / D converter, and based on the digitized electric signal, It detects whether the welding currently being performed is normal or whether an unwelded state has occurred. The computer 400 generates a waveform indicating the intensity change of the laser light over time equivalent to the waveform of the intensity change of the level of the electric signal with time, and a model waveform indicating the intensity change of the laser light with time prepared in advance. It has a comparison part which compares and compares both waveforms. The waveform indicating the change in intensity of the laser light with time is either the received raw waveform or the waveform after wavelet transforming the received raw waveform.

  FIG. 2 is a block diagram in which the inside of the computer 400 is divided into functions.

  The computer 400 includes a laser light intensity change waveform storage unit 410, a laser light intensity change model waveform storage unit 420, a wavelet transform unit 430, a comparison unit 440, and a display unit 450.

  The laser light intensity change waveform storage unit 410 stores the raw waveform of the electrical signal output from the amplifier 300 and digitized over time. In other words, as shown in FIG. 3 (A) or FIG. 3 (B), a raw waveform indicating a change in intensity of the laser light captured by the photodiode 270 over time is stored.

  The laser light intensity change model waveform storage unit 420 stores a model waveform generated when an unwelded state occurs in order to detect the occurrence of an unwelded state. In other words, as shown in FIG. 4 (A) or FIG. 4 (B), it stores a model waveform indicating a change in intensity of laser light over time when an unwelded state captured by the photodiode 270 occurs. is there. The laser light intensity change model waveform storage unit 420 uses the raw waveform indicating the change in intensity of the laser light with time stored in the laser light intensity change waveform storage unit 410 as it is (without wavelet conversion). When detecting the occurrence of a welded state, a raw model waveform as shown in FIG. 4A is stored. On the other hand, when detecting the occurrence of an unwelded state after wavelet transforming the raw waveform indicating the temporal intensity change of the laser beam stored in the laser beam intensity change waveform storage unit 410, FIG. The model waveform after wavelet transformation as shown in (B) is stored.

  The wavelet transform unit 430 performs wavelet transform on the raw waveform indicating the temporal intensity change of the laser light stored in the laser light intensity change waveform storage unit 410. The wavelet transform is one of frequency analysis methods using a wavelet function. At present, the wavelet transform is a generally known analysis method, and thus detailed description thereof is omitted here. Note that the wavelet conversion unit 430 is not required when the occurrence of an unwelded state is detected by using the raw waveform indicating the temporal intensity change of the laser beam stored in the laser beam intensity change waveform storage unit 410 as it is. Become.

  The comparison unit 440 functions as a comparison unit, and is generated when a wavelet-transformed waveform converted by the wavelet conversion unit 430 and an unwelded state stored in the laser light intensity change model waveform storage unit 420 occur. The model waveform (wavelet transformed) is compared and the correlation is seen. If the correlation is strong, it is determined that unwelding has occurred. In the case where the wavelet transform unit 430 is not provided, the comparison unit 440 includes a raw waveform and a laser beam intensity change model indicating the intensity change of the laser beam with time stored in the laser beam intensity change waveform storage unit 410. The model waveform (not wavelet transformed) generated at the occurrence of the unwelded state stored in the waveform storage unit 420 is compared, and the correlation is seen. If the correlation is strong, it is determined that unwelding has occurred. To do. Whether the correlation is strong or not is determined by a mathematical method as to whether or not there is a waveform similar to the model waveform. There are various methods for obtaining the strength of the correlation, and any method may be used as long as it is generally used at present.

  Display unit 450 displays the presence or absence of occurrence of non-welding determined by comparison unit 440.

  The welding state detection apparatus according to the present invention configured as described above generally operates as follows.

  First, laser light is output from the YAG laser diode 110. The laser beam L is irradiated to the plate materials 10A and 10B having different plate thicknesses by the scanner 100. The molten pool is formed in the irradiation part 20 by the irradiation of the laser beam L, and laser welding is started. The laser beam L is moved in the direction of the white arrow in FIG. At this time, the laser light reflected from the keyhole formed in the laser irradiation unit 20 is received by the laser light receiving unit 200. An electric signal corresponding to the intensity of the laser light output from the laser light receiving unit 200 is amplified by the amplifier 300. The amplified electrical signal is digitized by the computer 400 and stored in time series. The waveform of the stored electrical signal is compared with the model waveform stored in advance, and if there is a waveform that has a strong correlation with the model waveform, it is determined that unwelding has occurred, and the waveform that has a strong correlation with the model waveform If no exists, it is determined that welding is normally performed.

  According to the welding state detection apparatus of this embodiment that operates in this way, the following effects can be obtained.

  By observing the intensity waveform of the laser beam from the keyhole that changes according to the state of the keyhole, the behavior of the keyhole can be understood, and the welded state of the plate materials having different thicknesses can be detected. Accordingly, it is possible to detect whether a plurality of plate materials having different plate thicknesses are normally welded or whether an unwelded state caused by a gap between the plate materials has occurred.

  In general, whether or not an unwelded state due to the gap between the plate materials has occurred depends on whether the plate thickness of the plate material located on the side irradiated with the laser beam is opposite to the side irradiated with the laser beam. It becomes difficult to detect as the thickness of the plate located on the side increases. However, as in the present invention, by monitoring the intensity waveform of the laser light from the keyhole that changes according to the state of the keyhole, it is possible to detect the welded state of the plate materials having different thicknesses. Accordingly, it is possible to detect in real time whether a plurality of plate materials having different plate thicknesses are normally welded or whether an unwelded state caused by a gap between the plate materials has occurred.

  Then, a waveform showing the change in intensity of the laser beam with time is compared with the model waveform showing the change in intensity of the laser beam with time, and the correlation between both waveforms is obtained. It becomes possible to express more clearly and clearly, and it is possible to accurately detect the welding state of the plate materials having different plate thicknesses. Therefore, it becomes possible to detect in real time and with high accuracy whether a plurality of plate members having different plate thicknesses are normally welded or whether an unwelded state caused by a gap between the plate members has occurred.

  Furthermore, the correlation between the two waveforms is compared with the model waveform showing the intensity change of laser light over time, which is prepared in advance for the raw waveform showing the intensity change of laser light over time or the waveform after wavelet transform. Since it was made to take, the welding state of the board | plate material of different board thickness can be detected accurately. Therefore, it becomes possible to detect in real time and with high accuracy whether a plurality of plate members having different plate thicknesses are normally welded or whether an unwelded state caused by a gap between the plate members has occurred.

  Next, the welding state detection method according to the present invention will be described in detail.

FIG. 5 is a flowchart showing the procedure of the welding state detection method according to the present invention. The welding state detection method according to the present invention detects a welding state of a plate material to be welded using a laser.
Step S1
First, two plate materials having different plate thicknesses are prepared. In this embodiment, as shown in FIG. 1, two plate materials 10A and 10B are prepared. In this embodiment, a case where two plate materials are prepared is illustrated. The number of plate members is not limited to two and may be three or more. Further, the two plate members 10A and 10B may have different thicknesses or the same thickness. In this embodiment, different plate materials are illustrated and described for easy understanding of the invention.
Step S2
Next, the two prepared plate members 10A and 10B are fixed so that at least a part thereof overlaps. Since the two plate members 10A and 10B are welded by the laser beam, the irradiation unit 20 (see FIG. 1) irradiated with the laser beam overlaps the two plate members 10A and 10B. The two plate materials 10A and 10B irradiated with the laser light L are opposite to the side irradiated with the laser light L, with the plate material 10A having a large thickness on the side irradiated with the laser light L (upper plate). A plate material having a plate thickness thinner than the plate thickness on the side irradiated with the laser beam L is disposed on the side (lower plate). Specifically, the plate member 10A serving as the upper plate has a thickness of 1.4 mm, and the plate member 10B serving as the lower plate has a thickness of 0.65 mm.
Step S3
Laser light is irradiated toward the overlapping portion of the two fixed plate members 10A and 10B. Laser light L is emitted from the scanner 100 of FIG. When the laser beam is irradiated, a molten pool 22 is formed in the laser irradiation unit 20 as shown in FIGS. 6 (A) and 6 (B). The molten pool 22 is a portion in the laser irradiating unit 20 that extends in a circular shape in the surface direction of the two overlapping plate members 10A and 10B and is melted in the entire thickness direction of the two plate members 10A and 10B. Further, a gas portion called a keyhole 24 is formed in a portion of the molten pool 22 where the laser beam L is directly hit.
Step S4
Next, the laser beam L is moved in the direction of the white arrow in FIG. As the laser beam L moves, the laser irradiation unit 20 moves. Therefore, the portion that was the molten pool 22 is solidified to weld the two plate members 10A and 10B.
Step S5
Next, the laser beam reflected by the keyhole 24 formed in the laser irradiation unit 20 is received. The laser light reflected by the keyhole 24 is received by the laser light receiving unit 200 in FIG. 1 and converted into an electrical signal corresponding to the intensity of the received laser light. The photodiode 270 shown in FIG. 1 receives the laser light and converts it into an electrical signal. The electric signal output from the photodiode 270 is amplified by the amplifier 300 and input to the computer 400.
Step S6
Based on the intensity waveform of the received laser beam, the welding state of the plate materials 10A and 10B is detected. The computer 400 detects the welding state.

  For example, when normal welding is performed, the laser light reflected from the keyhole 24 has a stable waveform with low intensity as shown in FIG. However, when a gap occurs between the plate members 10A and 10B and unwelding due to the gap occurs, only an unwelded portion has an unstable waveform with extremely high strength as shown in FIG.

  The computer 400 prepares waveforms, as shown in FIGS. 4A and 4B, in advance, as shown in FIGS. 4A and 4B, as shown in FIGS. 3A and 3B. The welded state between the plate members 10A and 10B is detected by taking a correlation between the two waveforms in comparison with a model waveform showing a change in intensity of the laser beam over time. As the waveform indicating the intensity change of the laser light with time, either the received raw waveform or the waveform after wavelet transform of the received raw waveform is used. When unwelded is detected using a received raw waveform as shown in FIG. 3B, a correlation is obtained using a raw model waveform as shown in FIG. If there is a correlation, it can be determined that unwelding has occurred. Further, in the case where unwelded is detected using a waveform obtained by further wavelet transforming the received raw waveform as shown in FIG. 3B, a model waveform after wavelet transformation as shown in FIG. 4B is used. Take correlation. If there is a correlation, it can be determined that unwelding has occurred.

  FIG. 7 and FIG. 8 show why the reflection of the laser beam from the keyhole 24 (see FIG. 6B) becomes stronger when a gap is generated between the plate members 10A and 10B and unwelding due to the gap occurs. Based on

  As shown in FIG. 7A, when the plate materials 10 </ b> A and 10 </ b> B are irradiated with the laser light L, a molten pool 22 is formed in the irradiation unit 20. Further, a keyhole 24 is formed in a portion of the molten pool 22 where the laser beam L directly hits. The keyhole 24 is a portion where the metal in the molten pool 22 is vaporized to become a gas. In FIG. 7, a gap is opened between the plate member 10 </ b> A serving as the upper plate and the plate member 10 </ b> B serving as the lower plate, and a keyhole is generated in each state where both plates are separated. The reflection intensity of the laser light obtained from the keyhole 24 at this time is shown by a portion A in FIG.

  When welding proceeds in this state, as shown in FIG. 7 (B), it is ejected from the keyhole, but fills the gap between the plate material 10A as the upper plate and the plate material 10B as the lower plate. The reflection intensity of the laser beam obtained from the keyhole 24 at this time is shown by a portion B in FIG.

  Then, as shown in FIG. 7C, the laser beam L is blocked by the metal vapor (plume) 26 filled in the gap between the upper plate 10A and the lower plate 10B. As a result, as shown in FIG. 7D, the keyhole 24 disappears from the lower plate member 10B. Next, the laser beam L reaching the lower plate 10B is reduced, and the size of the molten pool generated from the keyhole 24 is also reduced. And the laser beam reflected (metal reflection) from the board | plate material 10B used as a lower board increases rapidly. The reflection intensity of the laser light obtained from the keyhole 24 at this time is indicated by a portion C in FIG. In this case, the upper plate 10A and the lower plate 10B are not welded.

  After this state once occurs, the plume 26 filled in the gap between the upper plate 10A and the lower plate 10B decreases, and the laser beam becomes the lower plate again as shown in FIG. 7E. A keyhole 24 is generated in the plate material 10B. As a result, the laser beam reflected from the lower plate 10B is rapidly reduced. The reflection intensity of the laser beam obtained from the keyhole 24 at this time is indicated by a D portion in FIG.

  As described above, when unwelding occurs when there is a gap between the upper plate 10A and the lower plate 10B, the reflection intensity of the laser light obtained from the keyhole 24 varies greatly. Since there is a certain regularity in how the reflection intensity varies, the present invention uses this to detect the occurrence of unwelding in real time and with high accuracy.

  The present invention can be applied to welding performed using laser light.

It is a schematic block diagram of the remote laser welding system to which the welding state detection apparatus concerning the present invention is applied. It is the block diagram which divided the inside of the computer according to the function. (A) is a figure which shows the signal waveform (raw waveform) of the YAG reflected light at the time of normal welding, (B) is a figure which shows the signal waveform (raw waveform) of the YAG reflected light at the time of the non-welding generation | occurrence | production by a gap | interval. (A) is a figure which shows the signal waveform (raw model waveform) of the YAG reflected light at the time of the non-welding generation | occurrence | production by a gap | interval, (B) is the signal waveform (model after wavelet conversion) of the YAG reflected light at the time of the non-welding generation | occurrence | production by a gap | interval. FIG. It is a flowchart which shows the procedure of the welding state detection method which concerns on this invention. (A), (B) is drawing for demonstrating the welding using a laser beam. (A)-(E) are drawings for demonstrating the change state of the laser beam reflected from a keyhole when non-welding generate | occur | produces. It is a figure which shows the reflected light intensity of the laser beam reflected from a keyhole when non-welding generate | occur | produces.

Explanation of symbols

10A board,
10B board,
20 Laser irradiation part,
22 molten pool,
24 keyhole,
26 plumes,
100 scanner,
110 laser diode,
120 first optical system,
130 second optical system,
132 half mirror,
134 light transmission filter,
136 attenuation filter,
200 laser beam receiver,
210 reflection mirror,
220 convex lens,
230 Laser light input unit,
240 optical fiber,
250 reflection mirror,
260 optical filter,
270 photodiode,
300 amps,
400 computers,
410 Laser light intensity change waveform storage unit,
420 laser light intensity change model waveform storage unit,
430 wavelet transform unit,
440 comparison unit,
450 display section,
L Laser light.

Claims (4)

A welding state detection device for detecting a welding state of a plate material to be welded using a laser,
A laser beam irradiation means for irradiating a laser beam toward an overlapping portion of a plurality of plate materials;
A laser beam receiving means for receiving the laser beam reflected by the keyhole formed in the laser irradiation section;
A welding state detection means for detecting the welding state of the plate material based on the intensity waveform of the received laser beam, and
The plurality of fixed plate members are thicker on the side irradiated with the laser beam, and the plate thickness on the side irradiated with the laser beam on the side opposite to the side irradiated with the laser beam. A thin plate is fixed so that at least part of it overlaps ,
The welding state detecting means compares the waveform of the laser light with a waveform indicating the temporal change in intensity of the laser light in advance, compared with a model waveform indicating the temporal change in intensity of the laser light. welding state detecting device according to claim Rukoto to have a means. Waveform indicating the temporal change of intensity of the laser beam welding according to claim 1, wherein one of the waveform der Rukoto the waveform after the receiving the raw waveform or received the raw waveform wavelet transform State detection device. A welding state detection method for detecting a welding state of a plate material to be welded using a laser,
Preparing a plurality of sheets,
Fixing a plurality of prepared plate materials so that at least part of them overlap,
Irradiating a laser beam toward a portion where a plurality of fixed plate materials overlap; and
Moving the laser beam;
Receiving the laser beam reflected by the keyhole formed in the laser irradiation part;
Detecting the welding state of the plate material based on the intensity waveform of the received laser beam;
Including
The step of fixing the prepared plurality of plate materials so that at least part of them overlaps each other is performed by placing a thick plate material on the side irradiated with the laser beam and the laser on the side opposite to the side irradiated with the laser beam. Fix the plate material with a thickness smaller than the thickness on the side irradiated with light so that at least part of it overlaps,
The step of detecting the welding state of the plate member based on the intensity waveform of the received laser beam indicates the intensity variation with time of the laser beam prepared in advance as a waveform indicating the intensity variation with time of the laser beam. A welding state detection method characterized by detecting a welding state of the plate material by taking a correlation between both waveforms in comparison with a model waveform. Waveform indicating the temporal change of intensity of the laser beam welding as claimed in claim 3, wherein one of the waveform der Rukoto the waveform after the receiving the raw waveform or received the raw waveform wavelet transform State detection method.

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