Laser welding quality inspection method and laser welding quality inspection device

Abstract

The present invention provides a method for inspecting the quality of laser welding and a laser welding quality inspection device. The method for inspecting the quality of laser welding is a method for inspecting the welding quality of a welded portion of a welded object and a welded object when welding is performed by irradiating the welded object and the welded object with a laser beam, and comprises: a step of acquiring first data representing the signal intensity of thermal radiation light radiated from the welded portion during welding; a step of acquiring second data representing the signal intensity of plasma light radiated from the welded portion during welding; and a step of determining whether the welded portion contains an abnormality based on a comparison between the acquired signal intensity of the thermal radiation light and the signal intensity of the plasma light.

Description

Technical Field

[0001] The present invention relates to a laser welding quality inspection method and a laser welding quality inspection device, and more particularly, to determination of welding abnormality during laser welding. Background Art

[0002] As a conventional method for inspecting the quality of laser welding, for example, Patent Document 1 uses the peak intensity of plasma light or reflected light emitted from a weld during laser welding to determine whether welding is defective. In addition, Patent Document 2 uses the time-integrated intensity of reflected light, plasma light, and infrared light from a joint during laser welding to determine whether welding is defective.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: JP Patent No. 3154177

[0006] Patent Document 2: Japanese Patent Application Publication No. 2007-98442

[0007] However, in the conventional method of determining poor welding during laser welding based on the peak intensity of welding light (thermal radiation light, plasma light, and laser reflected light) generated during laser welding, or the integrated value of the intensity of these welding lights, poor welding can be determined when there is a significant welding abnormality, but there is a problem that poor welding cannot be correctly determined when there is a slight welding abnormality. From the perspective of more accurately detecting abnormalities generated during laser welding, there is still room for improvement in the conventional inspection method. Summary of the invention

[0008] Therefore, the present disclosure solves the above-mentioned conventional problems, and an object of the present disclosure is to provide a laser welding quality inspection method and a laser welding quality inspection device capable of determining welding abnormalities with higher accuracy.

[0009] In order to achieve the above-mentioned purpose, a method for inspecting the quality of laser welding according to an embodiment of the present invention is a method for inspecting the welding quality of a welded portion between a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, and is characterized in that it comprises: a step of acquiring first data representing the signal intensity of thermal radiation light radiated from the welding portion during the welding; a step of acquiring second data representing the signal intensity of plasma light radiated from the welding portion during the welding; and a step of determining whether the welding portion contains an abnormality based on a comparison between the acquired signal intensity of the thermal radiation light and the signal intensity of the plasma light.

[0010] The laser welding quality inspection device involved in other embodiments of the present disclosure is a welding quality inspection device for the welded portion of a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, and is characterized in that the laser welding quality inspection device includes a measuring device and a welding state determination device, and the welding state determination device includes: a signal strength acquisition unit, which acquires from the measuring device first data representing the signal strength of thermal radiation light radiated from the welding portion during welding and second data representing the signal strength of plasma light; and a signal strength processing unit, which performs processing on the first data and the second data acquired by the signal strength acquisition unit, and the signal strength processing unit determines whether the welding portion contains an abnormality based on a comparison of the acquired signal strength of the thermal radiation light and the acquired signal strength of the plasma light.

[0011] As described above, according to the laser welding quality inspection method and the laser welding quality inspection device according to the present disclosure, welding abnormality can be determined with higher accuracy by comparing the thermal radiation light and the plasma light generated during laser welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is an overall view showing the structure of a laser welding quality inspection device according to an embodiment of the present disclosure.

[0013] Figure 2A It is a schematic diagram showing a welding state during normal welding according to an embodiment of the present disclosure, and is a cross-sectional view of a welded portion at the start of welding.

[0014] Figure 2B 1 is a schematic diagram showing a welding state during normal welding according to an embodiment of the present disclosure, and is a cross-sectional view of a welding state at the end of welding.

[0015] Figure 3 It is a diagram showing the setting of the output waveform of the laser beam according to the embodiment of the present disclosure.

[0016] Figure 4A 1 is a schematic diagram showing a welding state during abnormal welding according to an embodiment of the present disclosure, and is a cross-sectional view of a welded portion at the start of welding.

[0017] Figure 4B 1 is a schematic diagram showing a welding state during abnormal welding according to an embodiment of the present disclosure, and is a cross-sectional view of a welding state at the end of welding.

[0018] Figure 5A The figure shows the appearance of the molten solidified portion during normal welding according to the embodiment of the present disclosure.

[0019] Figure 5BIt is a diagram showing the irradiation output waveform of the laser beam and the signal intensity of the heat radiation light during normal welding according to the embodiment of the present disclosure.

[0020] Fig. 6A It is a diagram showing the appearance of a molten solidified portion during abnormal welding according to an embodiment of the present disclosure.

[0021] Figure 6B It is a diagram showing the irradiation output waveform of the laser beam and the signal intensity of the heat radiation light during abnormal welding according to the embodiment of the present disclosure.

[0022] Fig. 7A The diagram is a diagram showing heat radiation light of a plurality of welded products having different welding conditions during welding in the conventional welding defect determination, and is a diagram showing the signal intensity of the peak value in the heat radiation light of the plurality of welded products.

[0023] Figure 7B The diagram shows heat radiation light of a plurality of welded products having different welding conditions during welding in the conventional welding defect determination technique, and is a diagram showing an enlarged portion of the heat radiation light of the plurality of welded products having a peak signal intensity of 700 or less.

[0024] Figure 8 It is a diagram showing the verification result of welding state determination based on the conventional technology.

[0025] Fig.9A This is a diagram showing the appearance of a molten solidified portion of a weld abnormality product in the conventional welding defect determination.

[0026] Fig. 9B This is a diagram showing the signal intensity of heat radiation light during welding of an abnormal product in the conventional welding defect determination.

[0027] Fig. 10A This is a diagram showing the appearance of a molten solidified portion of a normal welded product in the conventional welding defect judgment.

[0028] Fig. 10B This is a graph showing the signal intensity of heat radiation light when welding a normal product in the conventional welding defect judgment.

[0029] Fig.11 The present invention is a graph showing the signal intensity of thermal radiation light and the signal intensity of plasma light during welding according to an embodiment of the present disclosure, that is, measurement results of (a) a normal welded product, (b) an abnormal welded product 1 determined to be a welding abnormality by the conventional method, and (c) an abnormal welded product 2 not determined to be a welding abnormality by the conventional method.

[0030] Fig.12 Yes means Figure 1A block diagram of the structure of a welding state determination device in a laser welding quality inspection device.

[0031] Fig.13 1 is a diagram showing a flowchart of a welding state determination process of the laser welding quality inspection device according to the embodiment of the present disclosure.

[0032] Fig.14 Yes means Fig.13 1 and 10. Results of executing step 102 in the welding state determination flowchart, i.e., graphs showing (a) the irradiation output waveform of the laser beam, (b) the signal intensity of the thermal radiation light of the welded product with a slight welding abnormality, and (c) the signal intensity of the plasma light of the welded product with a slight welding abnormality.

[0033] Fig.15 Yes means Fig.13 Graphs showing the results of executing step 103 in the welding state determination flowchart, i.e., (a) the signal intensity of the thermal radiation light extracted during the determination period and (b) the signal intensity of the plasma light extracted during the determination period of a welded product having a slight welding abnormality.

[0034] Fig.16 Yes means Fig.13 1 and 10. Results of executing step 104 in the welding state determination flowchart, i.e., a graph showing (a) a normalized signal of thermal radiation light during the determination period and (b) a normalized signal of plasma light during the determination period of a welded product having a slight welding abnormality.

[0035] Fig.17A Yes means Fig.13 1 and 2 are graphs showing the results of executing step 105 in the welding state determination flowchart, that is, the calculation results of the difference signal between the normalized signal of thermal radiation light and the normalized signal of plasma light during the determination period of a welded product having a slight welding abnormality.

[0036] Fig. 17B Yes means Fig.13 1 and 2. This figure shows the result of executing step 105 in the welding state determination flowchart, that is, the determination of a welded product having a slight welding abnormality based on the calculated differential signal.

[0037] Fig. 17C Yes means Fig.13 The figure shows the execution result of step 105 in the welding state determination flowchart, that is, the determination of a normal welded product based on the calculated differential signal.

[0038] Fig.18AIt is a diagram showing the differential signal of the normalized signal of thermal radiation light and the normalized signal of plasma light during the determination period of multiple welded products with different welding conditions in the determination of the welding condition involved in the present disclosure, and is a diagram showing the signal intensity of the peak value in the differential signal of multiple welded products.

[0039] Fig.18B It is a diagram showing the differential signal of the normalized signal of thermal radiation light and the normalized signal of plasma light during the determination period of a plurality of welded products having different welding states in the determination of the welding state involved in the present disclosure, and is a diagram showing an enlarged portion of the peak signal intensity of the differential signal of the plurality of welded products being below 1.0.

[0040] Fig.19 It is a diagram showing the verification result of the welding state determination based on the embodiment of the present disclosure.

[0041] -Explanation of symbols-

[0042] 1 Laser oscillator

[0043] 2 Collimating lens

[0044] 3 Condenser lens

[0045] 4 Total Reflection Mirror

[0046] 5. Dichroic Mirror

[0047] 6, 7, 8 Light sensor

[0048] 10 Laser beam

[0049] 11 Welding light (including thermal radiation light and plasma light)

[0050] 12 Thermal radiation

[0051] 13 Plasma Light

[0052] 14 Transmitted laser beam

[0053] 15 Objects to be bonded

[0054] 16 Joint

[0055] 17 Workbench

[0056] 18 Melting and solidification section

[0057] 20 Measurement device

[0058] 21 Resin foreign matter

[0059] 22 Piercing

[0060] 23 Abnormal protrusion

[0061] 24 Splash

[0062] 25 Piercing

[0063] 26 Abnormal peak

[0064] 27 Smaller peak

[0065] 30 Welding status determination device

[0066] 31 Signal strength acquisition unit

[0067] 32 Signal strength processing unit

[0068] 33 Storage

[0069] 34 Output

[0070] 100 Laser welding quality inspection device. DETAILED DESCRIPTION

[0071] According to a first aspect of the present disclosure, there is provided a method for inspecting the quality of laser welding, which is a method for inspecting the welding quality of a welded portion between a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, comprising:

[0072] a step of acquiring first data indicating the signal intensity of heat radiation light radiated from the welding portion during the welding;

[0073] a step of acquiring second data indicating signal intensity of plasma light radiated from the weld portion during the welding; and

[0074] The step of determining whether the weld portion includes an abnormality based on a comparison between the acquired signal intensity of the thermal radiation light and the acquired signal intensity of the plasma light.

[0075] According to a second aspect of the present disclosure, there is provided a method for inspecting laser welding quality according to the first aspect.

[0076] The step of determining whether the weld portion includes an abnormality based on a comparison between the acquired signal intensity of the thermal radiation light and the acquired signal intensity of the plasma light comprises:

[0077] a step of calculating a differential signal representing a difference between a signal intensity of the thermal radiation light and a signal intensity of the plasma light; and

[0078] A step of determining that the weld portion includes an abnormality when the calculated differential signal includes a peak having a signal intensity greater than a predetermined determination reference value.

[0079] According to a third aspect of the present disclosure, there is provided a method for inspecting laser welding quality according to the second aspect, the method further comprising:

[0080] The step of measuring the irradiation light of the laser beam during the welding and acquiring an irradiation output waveform indicating the intensity of the irradiation light of the laser beam,

[0081] The step of calculating a differential signal representing the difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light further comprises:

[0082] a step of setting a period during which the intensity of the irradiation light of the laser beam is maintained constant as a determination period based on the irradiation output waveform; and

[0083] The step of extracting the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period from the acquired signal intensity of the thermal radiation light and the signal intensity of the plasma light, respectively;

[0084] The step of calculating a differential signal indicating a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light includes the step of calculating a difference between the intensity of the thermal radiation light in the determination period and the intensity of the plasma light in the determination period.

[0085] According to a fourth aspect of the present disclosure, there is provided a method for inspecting laser welding quality according to the third aspect.

[0086] The step of calculating a differential signal indicating a difference between a signal intensity of the thermal radiation light during the determination period and a signal intensity of the plasma light during the determination period comprises:

[0087] a step of calculating a normalized signal of the thermal radiation light and a normalized signal of the plasma light by normalizing the signal intensity of the thermal radiation light during the determination period and the signal intensity of the plasma light during the determination period, respectively; and

[0088] A step of calculating a differential signal representing a difference between a normalized signal of the thermal radiation light and a normalized signal of the plasma light.

[0089] According to a fifth aspect of the present disclosure, there is provided a method for inspecting laser welding quality according to the fourth aspect.

[0090] In the step of calculating the normalized signal of the thermal radiation light and the normalized signal of the plasma light,

[0091] The average value m of the signal intensity of the thermal radiation light during the determination period av, the average value n of the signal intensity of the plasma light during the determination period av , the time function H(t) of the signal intensity of the thermal radiation light before normalization during the determination period, the time function S(t) of the signal intensity of the plasma light before normalization during the determination period, the time function Hm(t) of the normalized signal of the thermal radiation light during the determination period, and the time function Sn(t) of the normalized signal of the plasma light during the determination period respectively satisfy the following formulas,

[0092] [Formula 1]

[0093]

[0094] [Formula 2]

[0095] .

[0096] According to a sixth aspect of the present disclosure, there is provided a method for inspecting laser welding quality according to the fourth aspect,

[0097] In the step of calculating the normalized signal of the thermal radiation light and the normalized signal of the plasma light,

[0098] The average value m of the time function of the signal intensity of the heat radiation light of the plurality of welds judged as having no abnormality in the welded portion during the judgment period av (t), the average value n of the time function of the signal intensity of the plasma light of the plurality of weldings within the determination period av (t), the time function H(t) of the signal intensity of the thermal radiation light before normalization during the determination period, the time function S(t) of the signal intensity of the plasma light before normalization during the determination period, the time function Hm(t) of the normalized signal of the thermal radiation light during the determination period, and the time function Sn(t) of the normalized signal of the plasma light during the determination period satisfy the following equations respectively,

[0099] [Formula 3]

[0100]

[0101] [Formula 4]

[0102] .

[0103] According to a seventh aspect of the present disclosure, there is provided a laser welding quality inspection device, which is a device for inspecting the welding quality of a welded portion of a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, the device comprising a measuring device and a welding state determining device,

[0104] The welding state determination device comprises:

[0105] a signal strength acquisition unit that acquires, from the measuring device, first data indicating the signal strength of the thermal radiation light radiated from the weld portion during welding and second data indicating the signal strength of the plasma light radiated from the weld portion during welding; and

[0106] a signal strength processing unit that processes the first data and the second data acquired by the signal strength acquiring unit,

[0107] The signal intensity processing unit determines whether the weld portion includes an abnormality based on a comparison between the acquired signal intensity of the thermal radiation light and the acquired signal intensity of the plasma light.

[0108] According to an eighth aspect of the present disclosure, there is provided a laser welding quality inspection device according to the seventh aspect,

[0109] The signal intensity processing unit calculates a differential signal indicating a difference between a signal intensity of the thermal radiation light and a signal intensity of the plasma light based on the first data and the second data.

[0110] The signal strength processing unit determines that the weld portion includes an abnormality when the calculated differential signal includes a peak having a signal strength greater than a predetermined determination reference value.

[0111] According to a ninth aspect of the present disclosure, there is provided a laser welding quality inspection device according to the eighth aspect,

[0112] The signal intensity acquisition unit further acquires an irradiation output waveform indicating the intensity of the irradiation light of the laser beam from the measurement device.

[0113] The signal intensity processing unit sets a period during which the intensity of the irradiation light of the laser beam is maintained constant as a determination period based on the irradiation output waveform.

[0114] The signal intensity processing unit extracts the signal intensity of the thermal radiation light in the determination period and the signal intensity of the plasma light in the determination period from the signal intensity of the thermal radiation light and the signal intensity of the plasma light, respectively.

[0115] The differential signal indicates a difference between a signal intensity of the thermal radiation light in the determination period and a signal intensity of the plasma light in the determination period.

[0116] According to a tenth aspect of the present disclosure, there is provided a laser welding quality inspection device according to the ninth aspect,

[0117] The signal intensity processing unit calculates a normalized signal of the thermal radiation light and a normalized signal of the plasma light by normalizing the signal intensity of the thermal radiation light in the determination period and the signal intensity of the plasma light in the determination period, respectively.

[0118] The differential signal represents a difference between a normalized signal of the thermal radiation light and a normalized signal of the plasma light.

[0119] According to an eleventh aspect of the present disclosure, there is provided a method for quality inspection of laser welding according to the first aspect,

[0120] The signal intensity of the heat radiation light includes: a first heat radiation light intensity indicating the intensity of the heat radiation light at a first time during the welding, and a second heat radiation light intensity indicating the intensity of the heat radiation light at a second time different from the first time during the welding,

[0121] The signal intensity of the plasma light includes a first plasma light intensity indicating the intensity of the plasma light at the first time and a second plasma light intensity indicating the intensity of the plasma light at the second time.

[0122] The comparison of the signal intensity of the thermal radiation light and the signal intensity of the plasma light includes: calculating a first difference value representing the difference between the first thermal radiation light intensity and the first plasma light intensity, and a second difference value representing the difference between the second thermal radiation light intensity and the second plasma light intensity, and generating a differential signal including the first difference value and the second difference value.

[0123] According to a twelfth aspect of the present disclosure, there is provided a laser welding quality inspection device including a processor and a memory storing a program, wherein when executing the program, the processor executes:

[0124] acquiring, from the first sensor, first data indicating the signal intensity of heat radiation light radiated from the workpiece receiving the laser beam during laser welding;

[0125] acquiring, from a second sensor, second data indicating signal intensity of plasma light radiated from the workpiece during the laser welding; and

[0126] Based on the comparison between the signal intensity of the thermal radiation light and the signal intensity of the plasma light, it is determined whether the welded portion of the workpiece includes an abnormality.

[0127] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In addition, the present disclosure is not limited to the following embodiments. In addition, the present disclosure can be appropriately changed within the scope of the effects of the present disclosure. Furthermore, it is also possible to combine with other embodiments.

[0128] In addition, each drawing is a schematic diagram and is not necessarily a strict diagram.

[0129] In addition, in each drawing, the same reference numerals are given to substantially the same structures, and repeated descriptions are omitted or simplified.

[0130] Implementation Method

[0131] First, the overall structure of a laser welding quality inspection device according to an embodiment of the present disclosure will be described.

[0132] Figure 1 It is an overall view showing the structure of a laser welding quality inspection device according to an embodiment of the present disclosure.

[0133] Figure 1 The laser welding quality inspection device 100 shown in the figure includes a measuring device 20 and a welding state determination device 30. The measuring device 20 includes: a laser oscillator 1, a collimating lens 2, a focusing lens 3, a total reflection mirror 4, a dichroic mirror 5, and light receiving sensors 6, 7, and 8. The laser beam 10 emitted from the laser oscillator 1 passes through the collimating lens 2 to become a parallel beam, is reflected by the total reflection mirror 4, is focused by the focusing lens 3, and irradiates the object to be bonded 15. A bonding object 16 is set below the object to be bonded 15. The object to be bonded 15 and the bonding object 16 are fixed on a workbench 17, are moved by the workbench 17, and are laser welded by being irradiated with the laser beam 10.

[0134] When laser welding is performed, welding light 11 generated from the workpiece 15 passes through the condenser lens 3 and the total reflection mirror 4, and is wavelength-separated by the dichroic mirror 5. The wavelength-separated welding light passes through, for example, a bandpass filter (not shown), and is separated into thermal radiation light (e.g., wavelength 1300nm) 12 and plasma light (e.g., wavelength 400-700nm) 13, which are incident on the light receiving sensors 6 and 7, respectively.

[0135] On the other hand, the laser beam 10 is not completely reflected by the total reflection mirror 4 , and about 0.5% of the laser output passes through the total reflection mirror 4 , and the transmitted laser beam 14 enters the light receiving sensor 8 .

[0136] The three optical signals incident on the light receiving sensors 6, 7, and 8 are sent to the welding state determination device 30 and processed. The welding state determination device 30 determines whether the welded portion between the workpiece 15 and the workpiece 16 contains an abnormality based on the result of the signal processing, and performs a quality inspection of the laser welding. Figure 1 In the figure, the laser beam 10 and the welding light 11 are shown separately between the total reflection mirror 4 and the object 15 to be joined, but in fact, the laser beam 10 and the welding light 11 pass through the condenser lens 3 along the same path.

[0137] use Figure 2A as well as Figure 2B The schematic diagram shown is used to explain the welding state during normal welding according to the embodiment of the present disclosure. Figure 2A This is a cross-sectional view of the weld at the start of laser welding. Figure 2B This is a cross-sectional view of the welded state at the end of welding.

[0138] First, the laser beam 10 focused by the focusing lens 3 is irradiated onto the object to be bonded 15 placed above the object to be bonded 16 ( Figure 2A ). In the present embodiment, for example, the object to be joined 16 is an aluminum material with a thickness of 0.5 mm, and the object to be joined 15 is also made of the same aluminum material with a thickness of 0.1 mm.

[0139] Next, after welding starts, the laser beam 10 moves in a straight line relative to the object 15 by moving the table 17 supporting the object 16 and the object 15 (from right to left, not shown). Figure 2B From left to right as indicated by arrow P).

[0140] like Figure 2B As shown, at the end of welding, a molten solidified portion 18 of a certain depth is formed in the scanning area of ​​the laser beam 10. For example, the laser output at this time is 250W, the moving speed of the worktable 17 is 500mm / s, and the depth of the molten solidified portion 18 is about 200μm.

[0141] Figure 3 : represents the setting of the output waveform of the laser beam involved in this embodiment. Figure 3 As shown in FIG. 1 , the output of the laser beam is set to a trapezoidal waveform, including a slow rise portion (0ms to T1), a flat portion (T1 to T2), and a slow fall portion (T2 to 4ms), and the total irradiation time is 4ms. The slow rise portion and the slow fall portion in the output waveform of the laser beam are provided to prevent sputtering or collapse during laser welding. In welding based on irradiation of a laser beam having such a trapezoidal waveform, the shape of the molten solidified portion 18 is formed into an inverted trapezoidal shape ( Figure 2B ).

[0142] Next, use Figure 4A as well as Figure 4B The schematic diagram shown is used to explain the welding state during abnormal welding according to the embodiment of the present disclosure. Figure 4A This is a cross-sectional view of the weld at the start of laser welding. Figure 4B This is a cross-sectional view of the welded state at the end of welding.

[0143] In laser welding, especially when welding thin plates with a thickness of 0.1 mm, most of the abnormal welding situations are caused by perforation or spattering due to foreign matter caught in the interface between the welded object and the welded object. Figure 4A as well as Figure 4B FIG. 2 schematically illustrates a welding state when foreign matter is sandwiched at the joint interface.

[0144] like Figure 4A As shown, at the start of welding, the laser beam 10 is irradiated toward the object to be joined 15 placed above the object to be joined 16. At this time, at the joining interface between the object to be joined 16 and the object to be joined 15, for example, resin foreign matter 21 is sandwiched.

[0145] Next, after welding starts, the laser beam 10 moves in a straight line relative to the object 15 by moving the table 17 supporting the object 16 and the object 15 (from right to left, not shown). Figure 4A As the laser beam 10 moves, laser welding is performed. When the laser beam 10 contacts the resin foreign matter 21, the resin foreign matter 21 rapidly sublimates due to the irradiation of the laser beam 10. Therefore, in the molten solidified portion 18, the molten material (aluminum) around the resin foreign matter 21 is blown away, thereby generating one or more of the perforation 22, abnormal protrusion 23, and spatter 24 ( Figure 4B ).

[0146] If a hole 22 is generated, the bonding strength is reduced, if an abnormal protrusion 23 is generated, the appearance is poor, and if spatter 24 is generated, foreign matter is mixed into the product. Therefore, the abnormality generated in the welded part causes various product defects. Therefore, it is necessary to detect such welding abnormalities in real time and eliminate defective welded products.

[0147] Next, the difference between welding light generated during normal welding and during abnormal welding according to the present embodiment will be described below.

[0148] First, the state during normal welding will be described.

[0149] Figure 5A The external appearance of the molten solidified portion 18 during normal welding according to the present embodiment is shown. Figure 5B The upper part of is the irradiation waveform of the laser beam obtained by the light receiving sensor 8, the horizontal axis is the irradiation time, and the vertical axis is the signal intensity. Figure 5BThe lower part is the signal intensity of the thermal radiation light obtained by the light receiving sensor 6, the horizontal axis is the irradiation time, and the vertical axis is the signal intensity of the thermal radiation light. In addition, the signal intensity shown on the vertical axis is proportional to the intensity (W) of the light entering the light receiving sensors 8 and 6 respectively, and is expressed in arbitrary units (au=arbitray unit). In addition, the output waveform of the laser beam is set as follows Figure 3 The shape shown is set to a trapezoid.

[0150] When the output waveform of the laser beam is set to a trapezoidal shape, the output waveform of the laser beam that actually irradiates the object to be bonded 16 and the object to be bonded 15 is also as follows: Figure 5B Shown is a generally trapezoidal shape.

[0151] That is, the irradiation waveform of the laser beam becomes a shape corresponding to the setting of the output waveform of the laser beam, such as the flat part (T1 to T2, Figure 3 ) corresponds to the flat portion a1~a2 during the irradiation period.

[0152] Furthermore, the thermal radiation light generated during welding also has a signal intensity substantially corresponding to the irradiation output of the laser beam, so Figure 5B As shown, it is actually a trapezoidal shape having a flat portion between the irradiation periods a1 and a2.

[0153] During normal welding, for example, Figure 5A The molten solidified portion 18 shown has an appearance of a molten length of about 2 mm and a molten width of about 0.2 mm.

[0154] Next, the state during abnormal welding will be described.

[0155] Fig. 6A FIG. 2 shows the appearance of the molten solidified portion 18 during abnormal welding according to the present embodiment. During abnormal welding, a perforation 25 is seen in the center of the molten solidified portion 18. During welding, it is believed that at this position, resin foreign matter at the bonding interface rapidly sublimates due to the irradiation of the laser beam, and the molten material is blown away, resulting in the formation of the perforation 25. Figure 6B The lower part of represents the signal intensity of the thermal radiation light obtained at this time. Figure 6B As is clearly shown in the lower graph, when abnormal welding occurs, an abnormal peak 26 appears in the signal intensity of the thermal radiation light.

[0156] Specifically, the abnormal peak 26 is a peak having a very large signal intensity. This is due to abnormal heating of resin foreign matter, blowing of molten material, and the like.

[0157] That is, during normal welding, Figure 5BThe signal intensity of the thermal radiation light in the irradiation period a1 to a2 corresponding to the flat portion of the irradiation output waveform of the laser beam shown in the upper section is as follows: Figure 5B As shown in the lower part of the figure, there is no abnormal peak and the distribution is relatively uniform. On the other hand, in abnormal welding, Figure 6B The signal intensity of the thermal radiation light in the irradiation period b1 to b2 corresponding to the flat portion of the irradiation output waveform of the laser beam shown in the upper section is as follows: Figure 6B As shown in the lower part of FIG. 2 , an abnormal peak 26 corresponding to the occurrence of abnormal welding occurs. The prior art determines whether or not a welding defect occurs based on the presence or absence of the abnormal peak, for example, by determining whether the signal intensity of the detected thermal radiation light contains a peak having a signal intensity exceeding a certain determination reference value, thereby determining whether or not a welding defect occurs.

[0158] The accuracy of welding abnormality determination based on the peak intensity of thermal radiation light according to the conventional technology was verified as follows.

[0159] 《Verification of welding condition determination based on existing technology》

[0160] The welding state determination based on the prior art was verified using 51 normal welded products and 38 abnormal welded products, a total of 89 welded products. Here, the so-called normal welded products are specifically welded products without foreign matter mixed in the joint interface, and the so-called abnormal welded products are specifically welded products with foreign matter mixed in the joint interface. Fig. 7A as well as Figure 7B FIG. 1 shows heat radiation light during welding of a plurality of welded products having different welding conditions in the conventional welding defect determination. Fig. 7A Indicates the signal intensity of the peak value in the thermal radiation light of multiple welded products. The horizontal axis is the number of perforations generated in the molten solidification part, and the vertical axis is the signal intensity of the peak value in the thermal radiation light. Even if one perforation occurs, it is a poor weld, and if two perforations occur, the poor weld condition is further aggravated. In addition, in order to more clearly indicate the normal / abnormal judgment, Figure 7B Will Fig. 7A The heat radiation light of the plurality of welded products shown is magnified and shown with a peak signal intensity of 700 or less. Figure 7B As shown, it indicates the signal intensity of the thermal radiation light generated by the welded product with 0 or one perforation during welding.

[0161] like Fig. 7A as well as Figure 7BAs shown, the signal intensity of the thermal radiation light generated by the normal welding product during welding is about 320~530. In contrast, the signal intensity of the thermal radiation light generated by the abnormal welding product with one perforation during welding is about 430~2400. Furthermore, the signal intensity of the thermal radiation light generated by the abnormal welding product with two perforations during welding is about 900~4100.

[0162] In this case, for example, when the maximum value of the signal intensity of the thermal radiation light generated during welding of normal welded products, that is, 530, is set as the reference value for judging poor welding, all abnormal welded products with two perforations can be judged as having abnormal welding. However, not all abnormal welded products with one perforation are judged as having abnormal welding, resulting in a misjudgment. Specifically, among the abnormal welded products with one perforation, if the five abnormal welded products with a signal intensity of the thermal radiation light of approximately 430 to 500 are judged based on the above-mentioned reference value, they are not judged as having an abnormal peak, but are judged as having normal welding. That is, in Figure 8 In the judgment result of welding defects in the conventional technology shown, 5 false judgments occurred among a total of 38 welding abnormal products, and the correct judgment rate was 87% and the false judgment rate was 13%.

[0163] On the other hand, if five abnormal welded products are judged as abnormal welded products, the judgment threshold value needs to be set to 430 or less. In this case, a plurality of normal welded products are judged as abnormal welded products, which results in an over-judgment (see Figure 7B ).

[0164] Thus, in the conventional method for determining a welding defect, there is a need to improve the accuracy of the welding defect determination. Therefore, the inventors have analyzed the causes of erroneous determination in the conventional welding defect determination as follows.

[0165] Fig.9A The figure shows the appearance of the molten solidified portion of a welded abnormal product in the conventional technique of judging weld failure. Fig. 9B Indicates the signal intensity of the thermal radiation light during welding of abnormal products in the prior art of welding defect judgment. Fig.9A As shown, a tiny perforation is generated in the center of the molten solidified portion, as shown by arrow A. Correspondingly, Fig. 9B In the signal intensity of the heat radiation light during welding shown, a small peak 27 corresponding to the occurrence of abnormal melting indicated by arrow B appears. The signal intensity of the heat radiation light indicated by peak 27 is approximately 500.

[0166] Fig. 10A The figure shows the appearance of the molten solidified portion of a normal welded product in the conventional technique of judging welding failure. Fig. 10B This is a graph showing the signal intensity of thermal radiation light during welding of a normal product in the prior art for judging welding defects. Fig. 10B As shown in FIG. 1 , in a normal welded product, the signal intensity of the heat radiation light generated during welding varies within a range of about 300 to 500. Fig. 9B Among the signal intensities of the thermal radiation light measured for the abnormal welded product shown in FIG. 1 , the signal intensity of the peak 27 due to the abnormal welding is the signal intensity of the peak 27 due to the abnormal welding. Fig. 10B The signal intensity of the thermal radiation light measured for a normal welded product is within the variation range shown.

[0167] The above analysis shows that in laser welding, the signal intensity behavior of the thermal radiation light due to minor welding anomalies in some abnormal welded products cannot be distinguished from the signal intensity fluctuation of the thermal radiation light in normal welded products. This phenomenon occurs because the influence of the thermal radiation light due to minor welding anomalies is small and is buried in the fluctuation of the welding light generated during welding. Therefore, Fig. 7A as well as Figure 7B As shown in FIG. 1 , for normal welded products and abnormal welded products, the signal intensities of the peak values ​​of the thermal radiation light measured during welding overlap. As a result, as described above, an appropriate judgment reference value cannot be set, resulting in erroneous judgment. Therefore, the conventional welding defect judgment based on the peak intensity of thermal radiation light has the problem of not being able to correctly judge tiny welding abnormalities.

[0168] Therefore, the inventors have conducted intensive studies in order to further accurately detect the occurrence of welding abnormalities in laser welding, and have obtained the following new findings.

[0169] The inventors measured the plasma light generated during welding simultaneously with the measurement of the thermal radiation light, and focused on changes in the signal intensities of both. Fig.11 The measurement results of the signal intensity of the heat radiation light and the signal intensity of the plasma light generated during the laser welding according to the present embodiment are shown. Fig.11 (a) is the signal intensity of the thermal radiation light (solid line) and the signal intensity of the plasma light (dashed line) of a normal weld. Fig.11 (b) shows the signal intensity of the thermal radiation light (solid line) and the signal intensity of the plasma light (dashed line) of the abnormal weld product 1 which is determined to be abnormal weld by the conventional method. Fig.11 (c) shows the signal intensity of the thermal radiation light (solid line) and the signal intensity of the plasma light (dashed line) of the abnormal weld product 2 which is not judged as a welding abnormality by the conventional method.

[0170] like Fig.11 As shown in (a), during normal welding, during the laser beam irradiation period c1 to c2, the thermal radiation light and plasma light generated at the weld portion exhibit similar behaviors and have the same signal intensity.

[0171] On the other hand, Fig.11In the abnormal welded product of (b), at the time when the welding abnormality occurs (indicated by arrow C), both the thermal radiation light and the plasma light have steep peaks.

[0172] Here, the inventors focused on the signal intensity of the peaks generated in the thermal radiation light and plasma light during abnormal welding. Fig.11 As shown in (b), the signal intensity of the peak generated by abnormal welding of thermal radiation light is much greater than that of plasma light. When welding abnormality occurs due to resin foreign matter at the bonding interface, the temperature rises sharply due to the rapid sublimation of the resin foreign matter, so the signal intensity of thermal radiation light changes greatly, and a peak with a large signal intensity appears. On the other hand, plasma light does not change as much as thermal radiation light when welding abnormality occurs. Therefore, when welding abnormality occurs, there is a difference in the change of signal intensity between thermal radiation light and plasma light.

[0173] Fig.11 In the abnormal welded product 2 shown in (c), at the moment when the welding abnormality occurs (indicated by arrow D), the signal intensity of the thermal radiation light shows a small peak. On the other hand, the signal intensity of the plasma light does not show a peak. This is believed to be because, as mentioned above, the thermal radiation light is more affected by the welding abnormality than the plasma light, and even a small welding abnormality can be seen in the thermal radiation light, but no change can be seen in the plasma light. That is, Fig.11 (b) Similarly, when welding abnormality occurs, a difference occurs in the change of signal intensity between the thermal radiation light and the plasma light.

[0174] The inventors have found that the thermal radiation light and plasma light during normal welding show the same behavior, while the thermal radiation light and plasma light during abnormal welding have different changes in signal intensity. By evaluating the differential signal between the thermal radiation light and the plasma light, it is possible to accurately determine abnormal welding even for small welding abnormalities. Based on this new understanding, the inventors have achieved the development of the laser welding quality inspection method and device involved in the present disclosure.

[0175] Fig.12 Yes means Figure 1 1 is a block diagram of the structure of the welding state determination device 30 in the laser welding quality inspection device 100.

[0176] like Fig.12As shown, the welding state determination device 30 includes: a signal strength acquisition unit 31, a signal strength processing unit 32, a storage unit 33, and an output unit 34. The welding state determination device 30 is electrically connected to the measuring device 20. The signal strength acquisition unit 31 acquires the first data indicating the signal strength of the thermal radiation light radiated from the welding part during welding and the second data indicating the signal strength of the plasma light from the measuring device 20. The signal strength processing unit 32 determines whether an abnormality occurs during welding by processing the first data and the second data acquired by the signal strength acquisition unit 31. The storage unit 33 may be, for example, an auxiliary storage device such as a hard disk drive, and stores a data processing program executed by the signal strength processing unit 32 and various data. The output unit 34 may also be an output interface circuit that outputs data from the welding state determination device 30 to the outside. The welding state determination device 30 may also be, for example, a computer having a processor and a storage unit 33 storing a program. When executing the program, the processor performs data processing. Specifically, the processor acquires the first data indicating the signal strength of the thermal radiation light radiated from the workpiece receiving the laser beam during laser welding from the light receiving sensor 7. The processor further acquires second data indicating signal intensity of plasma light radiated from the workpiece during laser welding from the light receiving sensor 7. The processor further determines whether the welded portion of the workpiece contains abnormality based on comparison of the signal intensity of the thermal radiation light and the signal intensity of the plasma light.

[0177] In addition, the welding state determination device 30 may also obtain the data processing program executed by the signal strength processing unit 32 from a removable storage medium. The storage medium is a medium that stores information such as a program through electrical, magnetic, optical, mechanical or chemical effects so that a computer or other device, machine or the like can read the recorded information such as the program.

[0178] 《Welding status determination process》

[0179] Fig.13 1 is a flowchart of a welding state determination process of the laser welding quality inspection device 100 according to the embodiment of the present disclosure. Fig.13 The following describes a process for determining the welding state of laser welding.

[0180] (1) First, in step 101 , laser welding is started.

[0181] (2) Next, in step 102, simultaneously with the laser welding, the measuring device 20 simultaneously performs the laser beam irradiation output measurement 1021, the thermal radiation light measurement 1022, and the plasma light measurement 1023. The signal intensity acquisition unit 31 acquires data on the laser beam irradiation output waveform, the signal intensity of the thermal radiation light, and the signal intensity of the plasma light from the measuring device 20.

[0182] (3) In step 103, the signal intensity processing unit 32 determines the determination period based on the acquired irradiation output waveform of the laser beam. The signal intensity processing unit 32 further extracts data on the signal intensity of the thermal radiation light and the signal intensity of the plasma light during the determination period from the measurement data of the thermal radiation light and the plasma light (1031, 1032). The specific data extraction method will be described later.

[0183] (4) Next, in step 104 , the signal intensity processing unit 32 performs signal normalization on the extracted data of the signal intensity of the thermal radiation light and the signal intensity of the plasma light ( 1041 , 1042 ). A specific signal normalization method will be described later.

[0184] (5) Next, in step 105, the signal intensity processing unit 32 subtracts the normalized signal intensity of the plasma light from the normalized signal intensity of the thermal radiation light, and calculates a differential signal indicating the difference between the normalized signal intensity of the thermal radiation light and the normalized signal intensity of the plasma light. A specific method for calculating the differential signal will be described later.

[0185] (6) Next, in step 106 , the signal strength processing unit 32 determines whether an abnormality has occurred in the welded portion based on the signal strength of the peak value of the differential signal.

[0186] (7) Finally, in steps 107 and 108, the signal strength processing unit 32 determines the welding state based on the signal strength of the peak value of the differential signal. Specifically, when the calculated differential signal includes a peak value having a signal strength greater than a certain judgment reference value, it is determined that the welding is abnormal (step 107). On the other hand, when the calculated differential signal does not include a peak value having a signal strength greater than a certain judgment reference value, it is determined that the welding is normal (step 108).

[0187] Then, the judgment result of the welding state based on the signal strength processing unit 32 is outputted via the output unit 34, and based on the judgment result, the processed product judged to be abnormally welded can also be discharged from the process as an unqualified product. In addition, the processed product judged to be normally welded flows to the next process as a qualified product, for example. In addition, the judgment reference value used in the judgment can be determined by basic experiments and stored in the storage unit 33. In addition, the judgment reference value can also be changed by the material of the processed product or the output setting of the laser beam.

[0188] Data extraction methods

[0189] Reference Fig.14 as well as Fig.15 , detailed description Fig.13 The data extraction of step 103 of the welding state determination process is shown. Fig.14 express Fig.13 The execution result of step 102 in the welding state determination flowchart. Fig.14 (a) shows the irradiation output waveform of the laser beam measured in step 102 . Fig.14 (b) is the signal intensity of the thermal radiation light of the welded product having a slight welding abnormality measured in step 102, Fig.14 (c) is the signal intensity of the plasma light of the welded product having a slight welding abnormality measured in step 102. Fig.14 As shown in (b), when a slight abnormal welding occurs, the signal intensity of the thermal radiation light shows a small peak (indicated by arrow E), but the signal intensity of the peak is within the variation range of the signal intensity of the thermal radiation light during welding, so it is not judged as abnormal welding by the conventional welding defect judgment based on the peak intensity of the thermal radiation light. In addition, the signal intensity of the plasma light during welding ( Fig.14 (c)) fluctuates up and down, and no peak appears when a small abnormal welding occurs.

[0190] like Fig.14 As shown in (a), the irradiation output waveform of the laser beam involved in this embodiment is substantially trapezoidal in shape. The slow rise portion t1 in the trapezoidal waveform is provided to prevent spattering at the beginning of welding, and the slow fall portion t3 is provided to prevent collapse at the end of welding. Therefore, the slow rise portion t1 and the slow fall portion t3 are areas where the laser output is weak, and the objects to be joined 15 and the objects to be joined 16 are not welded. That is, the welding of the objects to be joined 15 and the objects to be joined 16 is carried out in the flat portion t2 of the trapezoidal waveform. Therefore, in Fig.13 In step 106 of the above, it is preferred to use the differential signal between the thermal radiation light and the plasma light corresponding to the flat portion t2 of the irradiation output waveform of the trapezoidal laser beam to determine the state of the weld. Therefore, in step 103, the irradiation period corresponding to the flat portion t2 of the trapezoidal waveform of the laser beam with a certain irradiation output is set as the determination period, and the data of the signal intensity of the thermal radiation light and the signal intensity of the plasma light in the determination period are respectively extracted.

[0191] Specifically, first, determine the time ranges corresponding to the slow rising portion t1, the flat portion t2, and the slow falling portion t3 in the irradiation output waveform of the laser beam. Fig.14 In the irradiation output waveform of the laser beam shown in (a), for example, the regions with three different slopes, positive, zero, and negative, are determined by obtaining an approximate straight line. Then, the time range corresponding to the regions with each slope is obtained. Here, the region with a positive slope corresponds to the slow rising portion t1, the region with a zero slope corresponds to the flat portion t2, and the region with a negative slope corresponds to the slow falling portion t3.

[0192] Next, the area with zero slope, that is, the time range of the flat part t2 of the irradiation output waveform where the laser beam has a certain irradiation output is set as the judgment period, and the data of the signal intensity of the thermal radiation light and the signal intensity of the plasma light acquired are extracted, and the data of the signal intensity of the thermal radiation light and the signal intensity of the plasma light within the judgment period are extracted.

[0193] In addition, in order to determine the time range of the slow rising part, the flat part and the slow falling part, you can also use Figure 3 In this case, the trapezoidal shape is clearer than the output waveform of the irradiation using the laser beam, so it is easier to determine the time range corresponding to the flat part ( Figure 3 On the other hand, the irradiation output waveform of the laser beam is the output of the irradiation light during the actual laser welding. Therefore, by using the irradiation output waveform of the laser beam, the determination period can be determined more accurately and data extraction can be performed. This is because the irradiation output waveform of the laser beam actually output is affected by the optical design and is not necessarily consistent with the preset laser beam output waveform.

[0194] The result of executing step 103 is as follows: Fig.15 shown. Fig.15 (a) is the signal intensity of the thermal radiation light extracted during the determination period t2, Fig.15 (b) is the signal intensity of the plasma light extracted during the determination period t2.

[0195] Signal Normalization Method

[0196] Next, refer to Fig.16 , detailed description Fig.13 The signal normalization of step 104 of the welding state determination process shown in FIG. 1 is performed to normalize the signal of the welding state determination process shown in FIG. 1. In obtaining the differential signal of the thermal radiation light and the plasma light, the absolute value intensity levels of each need to be added. The signal intensity of the thermal radiation light depends on the sensitivity and size of the light receiving sensor, the attenuation of the light based on the optical system reaching the light receiving sensor position, the amplification factor in the signal processing circuit, etc. The same is true for the plasma light. Therefore, preferably, Fig.13 In step 104, the signal intensities of the thermal radiation light and the plasma light extracted in step 103 are normalized.

[0197] The signal normalization method is described in detail below.

[0198] First, for one welded product, the average value m of the signal intensity of the thermal radiation light in the determination period t2 is calculated. av , the average value n of the signal intensity of the plasma light in the determination period t2av Next, the time function H(t) and the average value m of the signal intensity of the thermal radiation light in the determination period t2 are calculated. av The difference between the time function S(t) of the signal intensity of the plasma light in the determination period t2 and the average value n av The difference is further divided by the average value m av and m av , obtain normalized signals Hm1(t) and Sn1(t) of the time function of the thermal radiation light and the time function of the plasma light in the determination period t2. That is, the normalized signals Hm1(t) and Sn1(t) satisfy the following equations respectively.

[0199] [Formula 5]

[0200]

[0201] [Formula 6]

[0202]

[0203] exist Fig.13 In step 104 of the welding state determination process shown, the signal intensity processing unit 32 performs the above-mentioned operation on the signal intensity of the thermal radiation light and the signal intensity of the plasma light obtained by the measuring device 20, respectively, to obtain a normalized signal of the thermal radiation light within the determination period t2 and a normalized signal of the plasma light within the determination period t2.

[0204] In addition, the normalization of the signal intensity of the thermal radiation light and the signal intensity of the plasma light can also be performed using different methods. Other signal normalization methods are described in detail below.

[0205] First, the time function m of the average signal intensity of the thermal radiation light of a plurality of normal welded products is calculated in advance as a reference value. av (t), time function of the average signal intensity of the plasma light n av Next, the time function H(t) of the signal intensity of the thermal radiation light in the determination period t2 and the time function m(t) of the average signal intensity of the thermal radiation light of the reference value are calculated. av The difference between the time function S(t) of the signal intensity of the plasma light in the determination period t2 and the time function n(t) of the average signal intensity of the plasma light of the reference value av The difference between the two is further divided by the time function m of the average signal intensity of the thermal radiation light. av (t) and the time function of the average signal intensity of the plasma light n av(t), the normalized signals Hm2(t) and Sn2(t) of the time function of the thermal radiation light and the time function of the plasma light intensity in the determination period t2 are obtained. That is, the normalized signals Hm2(t) and Sn2(t) satisfy the following equations respectively.

[0206] [Formula 7]

[0207]

[0208] [Formula 8]

[0209]

[0210] Such normalized signals Hm2(t) and Sn2(t) are particularly useful when, for example, the output waveform of the set laser beam is not flat except for the slow rising portion and the slow falling portion. This is because the normalization method can also include the up and down fluctuations of the output intensity in the output waveform of the laser beam included in the portion except for the slow rising portion and the slow falling portion for normalization.

[0211] The result of executing step 104 is as follows: Fig.16 shown. Fig.16 (a) is the normalized signal of the thermal radiation light in the determination period t2, Fig.16 (b) is a normalized signal of the plasma light in the determination period t2.

[0212] 《Calculation Method of Differential Signal》

[0213] Next, refer to Fig.17A -17C, detailed description Fig.13 Calculation of the differential signal in step 105 of the welding state determination process shown in FIG. In step 105, the differential signal in the determination period t2 is calculated by taking the difference between the normalized signal of the thermal radiation light and the normalized signal of the plasma light obtained in step 104.

[0214] Here, the differential signal is preferably calculated as an absolute value. By calculating the absolute value of the differential signal, when determining the signal intensity of the peak value of the differential signal described later, the determination reference value can be set to a positive value, so the setting becomes simple. In the case where the absolute value of the differential signal is not calculated, when the differential signal is calculated by subtracting the signal intensity of the plasma light from the signal intensity of the thermal radiation light, the determination reference value is set to a positive value. In addition, when the differential signal is calculated by subtracting the signal intensity of the thermal radiation light from the signal intensity of the plasma light, the determination reference value is set to a negative value.

[0215] The signal intensity of the heat radiation light includes: a first heat radiation light intensity (e.g., -0.05) indicating the intensity of the heat radiation light at a first moment in welding (e.g., irradiation time 2.0 ms), and a second heat radiation light intensity (e.g., 0.3) indicating the intensity of the heat radiation light at a second moment in welding (e.g., irradiation time 2.2 ms). The signal intensity of the plasma light includes: a first plasma light intensity (e.g., -0.05) indicating the intensity of the plasma light at a first moment in welding (e.g., irradiation time 2.0 ms), and a second plasma light intensity (e.g., -0.2) indicating the intensity of the plasma light at a second moment in welding (e.g., irradiation time 2.2 ms). The signal intensity processing unit 32 may also calculate a first difference value (e.g., 0) indicating the difference between the first heat radiation light intensity and the first plasma light intensity, and a second difference value (e.g., 0.5) indicating the difference between the second heat radiation light intensity and the second plasma light intensity, to generate a differential signal including the first difference value and the second difference value.

[0216] Fig.17A Indicated by Fig.13 The execution of step 105 of the welding state determination process shown in FIG. 1 is to determine the heat radiation light ( Fig.14 (b)) and plasma light ( Fig.14 (c) of the present invention) calculates the result of the differential signal in the determination period t2. Based on the differential signal, Fig.13 The determination of step 106 in .

[0217] In step 106 of the welding state determination process, for example, the determination reference value is set to 0.35 ( Fig. 17B The determination of a welded product with a slight welding abnormality based on the calculated differential signal is shown in FIG. Fig. 17B .like Fig. 17B As shown in FIG. 1 , since there is a peak (indicated by arrow F) with a signal intensity greater than the judgment reference value in the differential signal, it is judged as abnormal welding. That is, the occurrence of the abnormal welding that is not judged as abnormal welding by the conventional welding defect judgment based on the peak intensity of the thermal radiation light ( Fig.14 In the case of welded products having minute welding abnormalities as in (b)), abnormal welding can be accurately determined by determination of the differential signal according to the present disclosure.

[0218] on the other hand, Fig. 17C This shows the judgment of a normal welded product based on the calculated differential signal. The judgment reference value is also set to 0.35 ( Fig. 17C In this case, since there is no peak with a signal intensity greater than the determination reference value in the differential signal, it is determined that the welding is normal.

[0219] 《Verification of welding state determination based on the present disclosure》

[0220] Using the welding state determination method according to the present disclosure, Fig. 7A as well as Figure 7B Similarly, the welding state determination was verified using 89 welded products in total, 51 of which were welded normally and 38 of which were welded abnormally. Fig.18A as well as Fig.18B A differential signal is provided between a normalized signal of thermal radiation light and a normalized signal of plasma light during a determination period of a plurality of welded products having different welding conditions in the determination of the welding condition according to the present disclosure. Fig.18A Indicates the signal intensity of the peak value in the differential signal of multiple welded products. The horizontal axis is the number of perforations generated in the molten solidification part, and the vertical axis is the signal intensity of the peak value in the differential signal during the judgment period. Even if one perforation occurs, it is a poor weld, and if two perforations occur, the poor weld condition is further aggravated. In addition, in order to more clearly indicate the normal / abnormal judgment, Fig.18B Will Fig.18A The portion where the peak signal intensity of the differential signals of the plurality of welded products is 1.0 or less is shown in an enlarged manner.

[0221] like Fig.18A as well as Fig.18B As shown, the peak signal strengths of the differential signals during the determination period of the normal welded products were all about 0.3 or less. On the other hand, the peak signal strengths of the differential signals during the determination period of the abnormal welded products with 1 to 2 perforations were all about 0.4 or more.

[0222] Here, for example, when the judgment reference value is set to the signal intensity of the peak value of the differential signal 0.35 ( Fig.18B In the case of the dotted line s, all 51 welded products were judged to be normal welds, and all 38 welded products with 1 to 2 perforations were judged to be abnormal welds. Fig.19 In the welding state determination results of the present embodiment shown, no misjudgment occurred among a total of 38 abnormal welds, the misjudgment rate was 0%, and the correct determination rate reached 100%. Therefore, the welding state determination method based on the present disclosure can determine welding abnormalities with higher accuracy.

[0223] In addition, the present invention is not limited to the above-mentioned embodiments, and can be implemented in various other ways. For example, in the above description, overlapping laser processing is used as an example for explanation, but the present disclosure is not limited to this. It can also be used for processing based on other types of lasers to obtain the same effect.

[0224] The present disclosure is fully described in relation to the preferred embodiments with reference to the accompanying drawings, but it is obvious that various modifications and alterations are possible for those skilled in the art, and it should be understood that such modifications and alterations are included in the claims of the present invention as long as they do not depart from the scope of the present invention based on the claims.

[0225] For example, the signal intensity processing unit 32 determines whether the weld portion includes an abnormality based on the signal intensity of the heat radiation light in the determination period t2 and the signal intensity of the plasma light in the determination period t2, but the present invention is not limited thereto. The signal intensity processing unit 32 may also determine whether the weld portion includes an abnormality based on the signal intensity of the heat radiation light in the entire period (t1-t3) and the signal intensity of the plasma light in the entire period (t1-t3).

[0226] The signal intensity processing unit 32 determines whether the weld portion contains an abnormality based on the normalized signal intensity of the thermal radiation light and the normalized signal intensity of the plasma light, but is not limited thereto. The signal intensity processing unit 32 may also determine whether the weld portion contains an abnormality based on the unnormalized signal intensity of the thermal radiation light and the unnormalized signal intensity of the plasma light.

[0227] The signal strength processing unit 32 determines whether the weld portion contains an abnormality based on a differential signal indicating the difference between the signal strength of the thermal radiation light and the signal strength of the plasma light, but the present invention is not limited thereto. The signal strength processing unit 32 may also determine whether the weld portion contains an abnormality based on a ratio signal indicating the ratio between the signal strength of the thermal radiation light and the signal strength of the plasma light.

[0228] Industrial Applicability

[0229] The laser welding quality inspection method and the laser welding quality inspection device of the present invention can also correctly judge minor welding anomalies through the signal intensity of the peak in the differential signal of the thermal radiation light and plasma light generated during welding, and can prevent the outflow of welding abnormal products to the subsequent processes of the laser welding process.

Claims

1. A method for inspecting the quality of laser welding is a method for inspecting the welding quality of a welded portion between a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, comprising: a step of acquiring first data indicating the signal intensity of heat radiation light radiated from the welding portion when the welding is performed; a step of acquiring second data indicating signal intensity of plasma light radiated from the weld portion when the welding is performed; and a step of determining whether the weld portion contains an abnormality based on the difference between the acquired signal intensity of the thermal radiation light and the signal intensity of the plasma light, The signal intensity of the heat radiation light includes: a first heat radiation light intensity indicating the intensity of the heat radiation light at a first time during the welding, and a second heat radiation light intensity indicating the intensity of the heat radiation light at a second time different from the first time during the welding. The signal intensity of the plasma light includes a first plasma light intensity indicating the intensity of the plasma light at the first time and a second plasma light intensity indicating the intensity of the plasma light at the second time. The step of determining whether the welding portion contains an abnormality includes: for the difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light, calculating a first difference value representing the difference between the first thermal radiation light intensity and the first plasma light intensity, and a second difference value representing the difference between the second thermal radiation light intensity and the second plasma light intensity, and calculating a differential signal including the first difference value and the second difference value.

2. The method for inspecting laser welding quality according to claim 1, wherein: The step of determining whether the weld portion includes an abnormality based on the difference between the acquired signal intensity of the thermal radiation light and the acquired signal intensity of the plasma light includes: A step of determining that the weld portion includes an abnormality when the calculated differential signal includes a peak having a signal intensity greater than a predetermined determination reference value.

3. The method for inspecting laser welding quality according to claim 2, wherein: The laser welding quality inspection method further comprises: measuring the irradiation light of the laser beam during the welding, and obtaining an irradiation output waveform indicating the intensity of the irradiation light of the laser beam; The step of calculating the differential signal comprises: A step of setting a period during which the intensity of the irradiation light of the laser beam is maintained at a certain level as a determination period based on the irradiation output waveform; A step of respectively extracting the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period from the acquired signal intensity of the thermal radiation light and the signal intensity of the plasma light; and A step of calculating a difference between the intensity of the thermal radiation light in the determination period and the intensity of the plasma light in the determination period.

4. The method for inspecting laser welding quality according to claim 3, wherein: The step of calculating the differential signal comprises: a step of calculating a normalized signal of the thermal radiation light and a normalized signal of the plasma light by normalizing the signal intensity of the thermal radiation light during the determination period and the signal intensity of the plasma light during the determination period, respectively; and A step of calculating a differential signal representing a difference between a normalized signal of the thermal radiation light and a normalized signal of the plasma light.

5. The method for inspecting laser welding quality according to claim 4, wherein: In the step of calculating the normalized signal of the thermal radiation light and the normalized signal of the plasma light, The average value m of the signal intensity of the thermal radiation light during the determination period av , the average value n of the signal intensity of the plasma light during the determination period av , the time function H(t) of the signal intensity of the thermal radiation light before normalization during the determination period, the time function S(t) of the signal intensity of the plasma light before normalization during the determination period, the time function Hm(t) of the normalized signal of the thermal radiation light during the determination period, and the time function Sn(t) of the normalized signal of the plasma light during the determination period respectively satisfy the following formulas, [Formula 1] [Formula 2] 。 6. The method for inspecting laser welding quality according to claim 4, wherein: In the step of calculating the normalized signal of the thermal radiation light and the normalized signal of the plasma light, The average value m of the time function of the signal intensity of the heat radiation light of the plurality of welds judged as having no abnormality in the welded portion during the judgment period av (t), the average value n of the time function of the signal intensity of the plasma light of the plurality of weldings within the determination period av (t), the time function H(t) of the signal intensity of the thermal radiation light before normalization during the determination period, the time function S(t) of the signal intensity of the plasma light before normalization during the determination period, the time function Hm(t) of the normalized signal of the thermal radiation light during the determination period, and the time function Sn(t) of the normalized signal of the plasma light during the determination period satisfy the following equations respectively, [Formula 3] [Formula 4] 。 7. A laser welding quality inspection device, which is a device for inspecting the welding quality of the welded portion of a joining object and an object to be joined when welding is performed by irradiating the joining object and the object to be joined with a laser beam, The welding quality inspection device comprises a measuring device and a welding state determination device. The welding state determination device comprises: a signal strength acquisition unit that acquires, from the measuring device, first data indicating the signal strength of the thermal radiation light radiated from the welding portion when welding is performed and second data indicating the signal strength of the plasma light radiated from the welding portion when welding is performed; and a signal strength processing unit that processes the first data and the second data acquired by the signal strength acquisition unit, The signal intensity of the heat radiation light includes: a first heat radiation light intensity indicating the intensity of the heat radiation light at a first time during the welding, and a second heat radiation light intensity indicating the intensity of the heat radiation light at a second time different from the first time during the welding. The signal intensity of the plasma light includes a first plasma light intensity indicating the intensity of the plasma light at the first time and a second plasma light intensity indicating the intensity of the plasma light at the second time. The signal intensity processing unit calculates a first difference value indicating a difference between the first thermal radiation light intensity and the first plasma light intensity, and a second difference value indicating a difference between the second thermal radiation light intensity and the second plasma light intensity, and calculates a differential signal including the first difference value and the second difference value. The signal strength processing unit determines whether the weld portion includes an abnormality based on the calculated differential signal.

8. The laser welding quality inspection device according to claim 7, wherein: The signal intensity processing unit calculates a difference signal indicating a difference between a signal intensity of the thermal radiation light and a signal intensity of the plasma light based on the first data and the second data. The signal strength processing unit determines that the weld portion includes an abnormality when the calculated differential signal includes a peak having a signal strength greater than a predetermined determination reference value.

9. The laser welding quality inspection device according to claim 8, wherein: The signal intensity acquisition unit further acquires an irradiation output waveform indicating the intensity of the irradiation light of the laser beam from the measurement device. The signal intensity processing unit sets a period during which the intensity of the irradiation light of the laser beam is maintained constant as a determination period based on the irradiation output waveform. The signal intensity processing unit extracts the signal intensity of the thermal radiation light in the determination period and the signal intensity of the plasma light in the determination period from the signal intensity of the thermal radiation light and the signal intensity of the plasma light, respectively. The differential signal indicates a difference between a signal intensity of the thermal radiation light in the determination period and a signal intensity of the plasma light in the determination period.

10. The laser welding quality inspection device according to claim 9, wherein: The signal intensity processing unit calculates a normalized signal of the thermal radiation light and a normalized signal of the plasma light by normalizing the signal intensity of the thermal radiation light in the determination period and the signal intensity of the plasma light in the determination period, respectively. The differential signal represents a difference between a normalized signal of the thermal radiation light and a normalized signal of the plasma light.

11. A laser welding quality inspection device, comprising a processor and a memory for storing a program, wherein the processor performs the following processing when executing the program: acquiring, from the first sensor, first data indicating the signal intensity of heat radiation light radiated from the workpiece receiving the laser beam during laser welding; acquiring, from a second sensor, second data indicating signal intensity of plasma light radiated from the workpiece during the laser welding; and determining whether the welded portion of the workpiece contains an abnormality based on the difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light, The signal intensity of the heat radiation light includes: a first heat radiation light intensity indicating the intensity of the heat radiation light at a first time during the welding, and a second heat radiation light intensity indicating the intensity of the heat radiation light at a second time different from the first time during the welding. The signal intensity of the plasma light includes a first plasma light intensity indicating the intensity of the plasma light at the first time and a second plasma light intensity indicating the intensity of the plasma light at the second time. The process of determining whether the weld portion of the workpiece contains an abnormality includes calculating a first difference value indicating the difference between the first thermal radiation light intensity and the first plasma light intensity, and a second difference value indicating the difference between the second thermal radiation light intensity and the second plasma light intensity, calculating a differential signal including the first difference value and the second difference value, and determining whether the weld portion contains an abnormality based on the calculated differential signal.

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