Laser processing measurement device

Abstract

In the present invention, while a processing point 81 of a workpiece 80 is subjected to welding which is carried out by irradiation with a laser beam LB, a control unit 70 measures the light intensities of prescribed wavelength components of radiation light LM radiated from a peripheral area 82 of a molten pool MP of the processing point 81, such measurement carried out with sensors 32-34 and 34. With regard to the radiation light LM radiated from the processing point 81 at prescribed points in time after irradiation of the processing point 81 by the laser beam LB, the control unit 70 specifies combinations of prescribed points in time and the light intensities of prescribed wavelength components, which are simulated by measurement values of the light intensities obtained from the sensors 32-34 and 34. The control unit 70 determines an evaluation on the quality of the welding on the basis of the specified combinations of a prescribed point in time and the light intensity of a prescribed wavelength component.

Description

Technical Field

[0001] The present invention relates to a laser processing measurement device and a method for evaluating laser processing results.

Background Art

[0002] Patent Document 1 describes a technique of using laser radiation emitted from a welding surface during laser welding as an index for welding quality.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] When a metal is irradiated with laser light, the solid-state metal absorbs the laser light and generates heat. Due to the heat generated by the metal, the intensity of the radiation light of the metal changes to an increase. When the laser light is continuously irradiated, the heat of the metal exceeds the melting point of the metal and the metal melts, forming a molten pool of liquefied metal. When the metal is further continuously irradiated with laser light, a part of the metal in the molten pool vaporizes, and large undulations occur in the molten pool. When the undulations in the molten pool are large, a part of the metal in the molten pool separates and becomes spatter, flying outside the molten pool.

[0005] The surface area of the molten pool increases when the undulations in the molten pool become large and decreases when the undulations in the molten pool become small. When the surface area of the molten pool changes, the intensity of the radiation light emitted by the metal in the molten pool changes, increasing or decreasing the intensity of the radiation light.

[0006] In order to accurately evaluate the welding quality using the intensity of the radiation light from the welding surface as an index, it is preferable to measure the intensity of the radiation light after waiting for the undulations in the molten pool to subside.

[0007] While the surface area of the molten pool fluctuates significantly due to undulations, the intensity of the radiated light from the molten pool fluctuates greatly. The fluctuations in the intensity of the radiated light appear as large amplitudes in the waveform of the intensity of the radiated light displayed on the monitor of the measuring device. In a state where undulations occur in the molten pool, the thermal radiation due to the undulations of the metal in the molten pool becomes the main component of the intensity of the radiated light to be measured.

[0008] In a state where undulations occur in the molten pool, the intensity of the radiated light is not accurately measured. In a state where undulations occur in the molten pool, the intensity of the thermal radiation due to the heat generated by the metal base material irradiated with the laser light in the intensity of the radiated light to be measured cannot be determined due to the increase and decrease in the amount of thermal radiation due to undulations. The intensity of the radiated light measured in a state where the molten metal is undulating is not suitable for accurately evaluating the welding quality using the intensity of the radiated light as an index.

[0009] The intensity of the radiated light measured in a state where the molten pool is not undulating is suitable for accurately evaluating the welding quality. During the irradiation of the laser light, the laser light continues to irradiate the molten pool formed in the metal and the state where the molten pool is undulating continues, so the intensity of the radiated light in a state where the molten pool is not undulating cannot be measured. After the irradiation of the laser light is completed, if waiting until the undulations of the molten pool formed in the metal subside, the state where the intensity of the radiated light can be measured is achieved. In order to evaluate the welding quality based on the intensity of the radiated light measured in a state where the molten pool is not undulating, a waiting time until the undulations of the molten pool subside is required. That is, the working efficiency of the welding process is reduced.

Means for Solving the Problem

[0010] A laser processing measurement device according to one aspect of the present invention includes a peripheral measurement unit that measures the light intensity of a predetermined wavelength component that changes corresponding to the temperature of the workpiece by the radiated light in the peripheral region of the molten pool at the processing point during welding of the processing point by the laser light irradiated to the processing point of the workpiece; a peripheral light guiding unit that guides the radiated light from the peripheral region to the peripheral measurement unit; and includes.

[0011] A method for evaluating the laser processing result according to one aspect of the present invention is as follows: During welding by laser light irradiated on a processing point of a workpiece, a measurement step of measuring, with a measurement device, the light intensity of a predetermined wavelength component that changes corresponding to the temperature of the workpiece by the radiation light in the peripheral region of the molten pool of the processing point; A specifying step of specifying a combination of the light intensity simulated by the light intensity of the predetermined wavelength component in the radiation light in the measured peripheral region, that is, the light intensity of the predetermined wavelength component in the radiation light radiated from the processing point at a predetermined time point after the irradiation of the laser light corresponding to the processing point, and the predetermined time point; An evaluation step of performing an evaluation process of determining the quality of the welding process of the workpiece based on the specified combination; and includes.

[0012] In each aspect of the present invention, the radiation light intensity of a predetermined wavelength component whose intensity changes corresponding to the temperature of the workpiece is measured by the radiation light in the peripheral region of the molten pool generated at the processing point irradiated with the laser light of the workpiece.

[0013] The processing point of the workpiece is heated by irradiation with laser light. At the heated processing point, heat conduction and heat radiation occur. The heat conduction at the processing point proceeds at a thermal conductivity corresponding to the heat capacity of the workpiece at the processing point. When the workpieces are welded by irradiation with laser light at the processing point of the workpiece, the heat capacity of the workpiece at the processing point during welding differs depending on whether there is a gap between the workpieces at the processing point during welding.

[0014] When there is no gap between the workpieces, the workpiece at the processing point has the heat capacity of both workpieces joined so that there is no gap. When there is a gap between the workpieces, at the processing point, the heat capacity of the workpiece becomes the heat capacity of the individual workpieces separated by the gap. The heat capacity of the workpiece at the processing point is smaller when there is a gap than when there is no gap between the workpieces.

[0015] In the heat radiation of the processing point, the amount of heat proportional to the amount of heat corresponding to the temperature of the processing point heated by the irradiation of the laser beam is radiated from the processing point. The amount of radiant heat of the processing point can be grasped by the intensity of a predetermined wavelength component radiated from the processing point. The amount of radiant heat of the processing point during the irradiation of the laser beam changes in a pattern corresponding to the heat capacity of the workpiece at the processing point. When the supply of heat stops due to the end of the irradiation of the laser beam, the temperature of the processing point decreases due to heat conduction corresponding to the heat capacity of the workpiece at the processing point. Due to this temperature decrease, the amount of radiant heat at the processing point decreases in a pattern corresponding to the heat capacity of the workpiece at the processing point. The change (trend) in the light intensity of a predetermined wavelength component radiated from the processing point can be used as an index indicating the state of the gap between the workpieces at the processing point.

[0016] At the processing point, the workpiece is heated and melted by the irradiation of the laser beam. The melted workpiece liquefies into a molten pool that undulates. When measuring the light intensity of a predetermined wavelength component radiated from the processing point during the irradiation of the laser beam, until the undulation of the molten pool subsides, the measured intensity value finely increases and decreases with the passage of time, and the temperature of the processing point cannot be accurately grasped. The heat at the processing point cannot be grasped by the light intensity of a predetermined wavelength component radiated from the processing point until the increase and decrease in intensity due to the undulation of the molten pool subsides.

[0017] Heat conduction from the processing point to the surrounding area proceeds at a thermal conductivity corresponding to the heat capacity of the workpiece in the processing point and the surrounding area.

[0018] The amount of heat radiated by the heat radiation of the surrounding area heated by heat conduction from the processing point is proportional to the amount of heat corresponding to the temperature of the surrounding area. The amount of radiant heat of the surrounding area can be grasped by the light intensity of a predetermined wavelength component radiated from the surrounding area. The light intensity of a predetermined wavelength component radiated from the surrounding area can be used as an index indicating the state of the gap between the workpieces in the surrounding area.

[0019] In the peripheral region, melting of the workpiece such as the processing point does not occur. When measuring the light intensity of a predetermined wavelength component radiated from the peripheral region, the measured intensity value is stable at a value corresponding to the temperature of the peripheral region. The measured intensity value varies depending on the presence or absence of a gap between the workpieces in the peripheral region.

[0020] In each aspect of the present invention, during welding of the processing point, the light intensity of a predetermined wavelength component radiated from the peripheral region of the processing point of the workpiece is measured. The measured light intensity can be used to evaluate the quality of the welding of the workpiece.

Advantages of the Invention

[0021] According to each aspect of the present invention, the light intensity of a predetermined wavelength component radiated from the peripheral region of the processing point of the workpiece, which can be used to determine a defect in the welding of the workpiece, can be measured during welding in which the molten pool of the processing point is undulating due to irradiation with laser light.

Brief Description of the Drawings

[0022]

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[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts or components are denoted by the same reference numerals throughout the drawings.

[0024] The embodiments shown below exemplify devices and the like for embodying the technical idea of the present invention. The technical idea of the present invention does not specify the material, shape, structure, arrangement, function, etc. of each component as follows.

[0025] First, a laser processing measurement apparatus and a laser processing result evaluation method according to an embodiment of the present invention will be described. The laser processing measurement apparatus of this embodiment can be installed in parallel with a laser processing apparatus, for example.

[0026] FIG. 1A is an explanatory diagram schematically showing the configuration of a main part of a laser processing apparatus in which a laser processing measurement apparatus according to an embodiment of the present invention is installed in parallel with a laser head. FIG. 1B is an explanatory diagram showing the measurement position of the emitted light by the measurement device of the sensor unit of the laser processing measurement apparatus of FIG. 1A.

[0027] The laser processing measurement apparatuses 50 and 70 of FIG. 1A according to the embodiment are, as shown in FIG. 1B, During welding of the processing point 81 by the laser beam LB irradiated on the processing point 81 of the workpiece 80, the light intensity of a predetermined wavelength component that changes corresponding to the temperature of the workpiece 80 is measured by the radiation light LM in the peripheral region 82 of the molten pool of the processing point 81, and the peripheral measurement units 32, 33, 34; The peripheral light guide units 56, 58, 60 that guide the radiation light LM from the peripheral region 82 to the peripheral measurement units 32, 33, 34; and are provided with.

[0028] Hereinafter, the details of this embodiment will be described.

[0029] The laser processing apparatus 10 in FIG. 1A in which the laser processing measurement apparatus according to the embodiment is installed has a laser oscillator 20, a sensor unit 30, a monitor camera 40, a head unit 50, and a control unit 70. The laser processing measurement apparatus of this embodiment can be configured using the sensor unit 30, the head unit 50, and the control unit 70. The laser processing result evaluation method according to the embodiment of the present invention can be implemented using the laser processing measurement apparatus.

[0030] The laser oscillator 20 outputs a laser beam LB oscillated by a medium (not shown). For the laser oscillator 20, for example, a YAG (Yttrium Aluminum Garnet) laser, a fiber laser, or a semiconductor laser can be used. The laser beam LB output by the laser oscillator 20 is transmitted to the head unit 50 by, for example, an optical fiber 21 (see FIG. 1B) and irradiated from the head unit 50 onto the workpiece 80 (see FIG. 1B).

[0031] The radiation light LM radiated from the workpiece 80 is incident on the sensor unit 30 by the irradiation of the laser beam LB. The sensor unit 30 has a plurality of measurement units on which the radiation light LM from the workpiece 80 is incident separately for each location. The detailed configuration of the sensor unit 30 will be described later.

[0032] The monitor camera 40 photographs the workpiece 80. The photographing range of the workpiece 80 by the monitor camera 40 includes at least the processing point 81 (see FIG. 1B) of the workpiece 80 irradiated with the laser beam LB and the peripheral region 82 (see FIG. 1B) around the processing point 81. From the processing point 81 and the peripheral region 82, the emitted light LM is emitted by the irradiation of the laser beam LB on the processing point 81. The photographed image of the monitor camera 40 can be used, for example, to confirm and adjust the irradiation position of the laser beam LB.

[0033] The head unit 50 has an optical system for light guiding. The optical system includes mirrors 51 to 53. The mirrors 51 and 52 can be constituted by, for example, dichroic mirrors. The mirror 53 can be constituted by, for example, a total reflection mirror. The mirror 51 guides the laser beam LB transmitted to the head unit 50 by the optical fiber 21 to the workpiece 80. The mirrors 52 and 53 reflect the image light MB of the workpiece 80 and guide it to the monitor camera 40. The mirror 52 is also used to guide the emitted light LM from the workpiece 80 to the sensor unit 30.

[0034] The configuration of the sensor unit 30 and the configuration of the optical system related to the light guiding of the laser beam LB and the emitted light LM in the head unit 50 are attached to a common housing (not shown). The configuration inside the housing is shown in detail in FIG. 1B. Some elements of the optical system related to the light guiding of the emitted light LM can be moved. FIG. 1B shows the arrangement of the optical system before and after moving this element side by side.

[0035] The sensor unit 30 has an in-process sensor 31. The sensor unit 30 has sensors 32 to 34 for pre-process, post-process, and both sides as a plurality of measurement devices. Radiant light LM from the processing point 81 of the workpiece 80 is incident on the in-process sensor 31. Radiant light LM from the peripheral region 82 of the processing point 81 of the workpiece 80 is incident on each of the sensors 32 to 34 for pre-process, post-process, and both sides. In the present embodiment, there are two side sensors 34, and each side sensor 34 is disposed on the front side and the back side of the plane of FIG. 1B, respectively. The pre-process sensor 32, the post-process sensor 33, and the side sensors 34, 34 can constitute a peripheral measurement unit with one or a plurality of sensors.

[0036] The optical system related to the light guiding of the laser beam LB of the head unit 50 has, in addition to the mirror 51 described above, a collimating lens 54 and a condensing lens 55. The collimating lens 54 collimates the laser beam LB from the laser oscillator 20 transmitted by the optical fiber 21 into a beam shape. The collimated laser beam LB is reflected by the mirror 51 and focused by the condensing lens 55, and is irradiated onto the processing point 81 of the workpiece 80 in a spot shape. The processing point 81 can be welded by the laser beam LB irradiated onto the processing point 81.

[0037] The processing point 81 is heated by the irradiation of the laser beam LB. At the heated processing point 81, heat conduction and heat radiation occur. The heat conduction of the processing point 81 proceeds at a thermal conductivity corresponding to the heat capacity of the workpiece 80 at the processing point 81. In the heat radiation of the processing point 81, a heat quantity proportional to the heat quantity corresponding to the temperature of the processing point 81 is radiated from the processing point 81. When heat radiation occurs at the processing point 81, radiant light LM is radiated from the processing point 81. The radiated heat quantity of the processing point 81 can be grasped by the light intensity of a predetermined wavelength component in the radiant light LM from the processing point 81. However, since the processing point 81 becomes a molten pool and is in a wavy state due to the influence of a shielding gas flow, newly melted metal, solidifying metal, etc., and the radiant light is scattered non-uniformly, accurate measurement cannot be performed by receiving light from a single point.

[0038] The peripheral region 82 around the processing point 81 is heated by heat conduction from the processing point 81. In the heated peripheral region 82, heat radiation occurs. In the heat radiation of the peripheral region 82, heat with a quantity proportional to the quantity of heat corresponding to the temperature of the peripheral region 82 is radiated from the peripheral region 82. When heat radiation occurs in the peripheral region 82, radiation light LM is radiated from the peripheral region 82. The amount of radiant heat of the peripheral region 82 can be grasped by the intensity of a predetermined wavelength component in the radiation light LM from the peripheral region 82.

[0039] A predetermined wavelength component for grasping the radiant heat amounts of the processing point 81 and the peripheral region 82 can be, for example, a wavelength component of near-infrared rays.

[0040] The optical system related to the light guiding of the radiation light LM from the workpiece 80 has, in addition to the mirror 52 described above, an axicon (cone) lens 56 and condenser lenses 57 to 60. In the optical system related to the light guiding of the radiation light LM from the processing point 81, the condenser lens 55 described above is used as a collimating lens. In the optical system related to the light guiding of the radiation light LM from the processing point 81, the mirror 52 and the condenser lens 57 are further used.

[0041] The radiation light LM from the processing point 81 is collimated by the condenser lens 55. The collimated radiation light LM from the processing point 81 passes through the mirror 51, is reflected by the mirror 52, is focused by the condenser lens 57, and is incident on the in-process sensor 31. The condenser lens 55, the mirror 52, and the condenser lens 57 guide the radiation light LM from the processing point 81 to the in-process sensor 31.

[0042] For the optical system related to the light guiding of the emitted light LM from the peripheral region 82, an axicon lens 56 and condenser lenses 58 to 60 are used. FIG. 1C is a perspective view of an example of the axicon lens 56 in FIG. 1B. As shown in FIG. 1C, the axicon lens 56 has a through hole 61 at its center. Inside the through hole 61, as shown in FIG. 1B, the above-described condenser lens 55 is disposed. The optical axis of the condenser lens 55 is disposed on the central axis of the axicon lens 56. The axicon lens 56 refracts the emitted light LM incident on the conical surface 62 from the ring-shaped peripheral region 82 so as to form an optical path in the direction along the optical axis of the condenser lens 55.

[0043] Each of the condenser lenses 58 to 60 is disposed on a circumference centered on the optical axis of the condenser lens 55. There are two condenser lenses 60, and each condenser lens 60 is disposed on the front side and the back side of the plane of FIG. 1B, respectively. The condenser lenses 58, 59 and the two condenser lenses 60, 60 are arranged such that their optical axes are located at positions shifted by 90 degrees each on the circumference centered on the optical axis of the condenser lens 55.

[0044] The emitted light LM from the peripheral region 82 is refracted in its optical path by the axicon lens 56. The emitted light LM from the peripheral region 82 whose optical path has been refracted is focused by the condenser lenses 58, 59 and the two condenser lenses 60, 60. Each focused emitted light LM is incident on the corresponding pre-process sensor 32, post-process sensor 33 and the two side sensors 34, 34, respectively. The axicon lens 56 and the four condenser lenses 58 to 60, 60 can constitute a peripheral light guiding unit that guides the emitted light LM from the peripheral region 82 to the peripheral measurement unit.

[0045] The four condenser lenses 58 to 60, 60 cause the emitted light LM from the four measurement points 83 to 86 among the emitted light LM from the peripheral region 82 guided by the axicon lens 56 to be incident on the corresponding sensors 32 to 34, 34, respectively. The four measurement points 83 to 86 are positions shifted by 90 degrees each on the circumference centered on the processing point 81 in the peripheral region 82.

[0046] FIG. 1D is an explanatory diagram showing the measurement positions of the emitted light by the measuring device when the distance between the axicon lens 56 in FIG. 1B and the workpiece 80 is changed. The positions of the measurement points 83 to 86 of the emitted light LM respectively incident on the sensors 32 to 34, 34 in the peripheral region 82 may change to a position where the phase is shifted by about 180 degrees as shown in FIG. 1D depending on the inclination angle of the conical surface 62 with respect to the central axis of the axicon lens 56.

[0047] The axicon lens 56 can be moved in the central axis direction of the axicon lens 56 by the adjustment mechanism 87 shown in FIG. 1B. The adjustment mechanism 87 can be configured to include, for example, a support portion that supports the axicon lens 56 so as to be movable in the central axis direction, and an actuator that moves the support portion in the central axis direction. The operation of the actuator can be controlled by the control unit 70. In FIG. 1D, the adjustment mechanism 87 and the control unit 70 are not shown.

[0048] The welding of the workpiece 80 can be performed, for example, by continuous welding or spot welding. Continuous welding can be used, for example, in butt welding where the workpieces are butted and welded, or in overlay welding where the workpieces are overlapped and welded. In continuous welding, the processing point 81 of the workpiece 80 irradiated with the laser light LB moves at a constant pitch from the starting point to the ending point by the feed movement of the head unit 50. In spot welding, the head unit 50 does not move and the processing point 81 becomes a fixed point. In both continuous welding and spot welding, the processing point 81 is heated by the irradiation of the laser light LB. The heated processing point 81 emits the emitted light LM with a light intensity corresponding to the temperature of the processing point 81.

[0049] Here, the relationship between the irradiation of the laser beam LB on the processing point 81 and the light intensity of a predetermined wavelength component in the emitted light LM radiated from the processing point 81 will be described. FIG. 2 is a graph showing the time-series information of the light intensity of near-infrared light, which is a predetermined wavelength region, in the emitted light LM radiated from the processing point 81 of the workpiece 80 during welding, for a plurality of outputs according to the irradiation time of the laser beam LB. In FIG. 2, the vertical axis represents the light intensity of near-infrared light, and the horizontal axis represents the elapsed time from the start of irradiation of the laser beam LB. FIG. 2 shows the waveform of the light intensity of near-infrared light (emitted light) measured in time series from the start of welding through the irradiation of the laser beam LB to the end of irradiation and until solidification and the end of welding in spot welding with the processing point 81 as a fixed point.

[0050] In FIG. 2, three types of irradiation times of the laser beam LB on the processing point 81 are shown, and the case where each irradiation time T1 to T3 is set to T1 = 25 ms, T2 = 35 ms, and T3 = 45 ms is shown. In FIG. 2, six types of outputs of the laser beam LB are shown, and the case where each output W1 to W6 is set to values in 50 W increments from W1 = 550 W (Watt) to W6 = 300 W is shown.

[0051] The processing point 81 heated by the irradiation of the laser beam LB radiates heat in proportion to the amount of heat corresponding to the temperature of the processing point 81. The light intensity of a predetermined wavelength component in the emitted light LM radiated from the processing point 81 becomes a value corresponding to the radiant heat amount of the processing point 81. For example, when the workpiece 80 is a metal of a material often used for welding, such as an iron-based metal, a copper-based metal, or a light aluminum metal, the light intensity of the near-infrared wavelength component in the emitted light LM radiated from the processing point 81 becomes a value corresponding to the radiant heat amount of the processing point 81.

[0052] The radiant heat amount of the processing point 81 during welding increases in a pattern corresponding to the heat capacity of the workpiece 80 at the processing point 81 due to the irradiation of the laser beam LB on the processing point 81. The higher the output of the laser beam LB and the longer the irradiation time of the laser beam LB, the higher the temperature to which the processing point 81 is heated, and the higher the radiant heat amount of the processing point 81.

[0053] After the welding process is completed, since the supply of heat to the processing point 81 stops due to the end of the irradiation of the laser beam LB to the processing point 81, the temperature of the processing point 81 decreases by heat conduction corresponding to the heat capacity of the workpiece 80. Due to this temperature decrease, the radiant heat quantity at the processing point 81 decreases in a pattern corresponding to the heat capacity of the workpiece 80 at the processing point 81.

[0054] As described above, the radiant heat quantity of the processing point 81 changes corresponding to the temperature of the processing point 81. The light intensity of a predetermined wavelength component in the radiant light LM radiated from the processing point 81 becomes a value corresponding to the radiant heat quantity of the processing point 81. The temperature of the processing point 81 and the light intensity of a predetermined wavelength component in the radiant light LM radiated from the processing point 81 are correlated (although there is some disturbance in the measured values due to the undulating state of the molten pool, the tendency of the time-series change is similar).

[0055] During the irradiation of the laser beam LB to the processing point 81, the workpiece 80 at the processing point 81 is heated and melted. The melted workpiece 80 at the processing point 81 liquefies into a molten pool that undulates. The undulation of the molten pool at the processing point 81 continues while the laser beam LB is being irradiated to the processing point 81. The light intensity of a predetermined wavelength component in the radiant light LM radiated from the processing point 81 finely increases and decreases independently of the temperature of the processing point 81, like the light intensity of near-infrared rays during the period until the irradiation times T1 to T3 in FIG. 2 end, due to the undulation of the molten pool during the irradiation of the laser beam LB. When the light intensity of the processing point 81 is measured by a sensor while the molten pool is undulating, the measured value of the light intensity is less accurate compared to the measured value of the sensor that measures the light intensity of the processing point 81 after the undulation of the molten pool has subsided, even if statistical processing is applied to the output of the sensor.

[0056] After the irradiation of the laser beam LB to the processing point 81 is terminated, the processing point 81 is no longer heated by the laser beam LB, and the undulation of the molten pool at the processing point 81 subsides. In the radiation light LM emitted from the processing point 81, the light intensity of a predetermined wavelength component stabilizes at a value corresponding to the temperature of the processing point 81 after the irradiation of the laser beam LB, like the light intensity of near-infrared rays in the period after the irradiation times T1 to T3 in FIG. 2. When measuring the light intensity of a predetermined wavelength component in the radiation light LM emitted from the processing point 81 and grasping the amount of radiation light from the processing point 81 necessary for calculating the temperature of the processing point 81 from the measured light intensity value, it is more advantageous to perform the light intensity measurement after the irradiation of the laser beam LB is terminated than during the irradiation. After the irradiation of the laser beam LB is terminated, the light intensity of a predetermined wavelength component in the radiation light LM emitted from the processing point 81 can be measured stably compared to during the irradiation.

[0057] When measuring the light intensity of a predetermined wavelength component in the radiation light LM emitted from the processing point 81 after the undulation of the molten pool at the processing point 81 has subsided, it is necessary to stop the irradiation of the laser beam LB and temporarily terminate the welding process of the processing point 81. If the welding process of the processing point 81 is terminated to measure the light intensity of a predetermined wavelength component in the radiation light LM emitted from the processing point 81, the continuity of the welding process is impaired and the working efficiency is reduced.

[0058] A part of the heat quantity of the processing point 81 heated by the irradiation of the laser beam LB is conducted to the peripheral region 82 of the molten pool of the processing point 81 by heat conduction. The heat quantity of the processing point 81 is conducted from the processing point 81 to the peripheral region 82 at a rate of the thermal conductivity of the workpiece 80. The peripheral region 82 is heated by the heat quantity conducted from the processing point 81. The heated peripheral region 82 reaches a temperature corresponding to the temperature of the processing point 81.

[0059] The heated peripheral region 82 emits a heat quantity proportional to the heat quantity corresponding to the temperature of the peripheral region 82. The light intensity of a predetermined wavelength component in the radiation light LM emitted by the peripheral region 82 becomes a value corresponding to the radiant heat quantity of the peripheral region 82.

[0060] Since the peripheral region 82 is heated by a part of the heat quantity conducted from the processing point 81, the temperature of the peripheral region 82 during the irradiation of the laser beam LB to the processing point 81 is lower than the temperature of the processing point 81 at the same time point. The temperature of the processing point 81 after the irradiation of the laser beam LB to the processing point 81 ends decreases due to the end of the irradiation of the laser beam LB, and becomes lower than the temperature of the processing point 81 during the irradiation of the laser beam LB to the processing point 81. At a predetermined time point after the irradiation of the laser beam LB to the processing point 81 ends, the temperature of the processing point 81 decreases to the same temperature as the temperature of the peripheral region 82 during the irradiation of the laser beam LB to the processing point 81.

[0061] In the peripheral region 82, even during the irradiation of the laser beam LB to the processing point 81, melting of the workpiece 80 such as the processing point 81 does not occur. When the light intensity of the radiation light LM emitted from the peripheral region 82 is measured by a sensor, the measured value of the sensor stabilizes at a value corresponding to the temperature of the peripheral region 82 because the peripheral region 82 does not melt. The light intensity of a predetermined wavelength component in the radiation light LM emitted from the peripheral region 82 can be stably measured even during the irradiation of the laser beam LB to the processing point 81.

[0062] The light intensity of a predetermined wavelength region in the radiation light LM of the peripheral region 82 measured during the irradiation of the laser beam LB to the processing point 81 is a value that simulates the light intensity of a predetermined wavelength region in the radiation light LM of the processing point 81 at a predetermined time point after the end of the laser beam irradiation. The "predetermined wavelength region" is, for example, near-infrared light. The simulation of "simulating the light intensity of a predetermined wavelength region" refers to the similarity relationship described below.

[0063] The graphs of FIGS. 3B, 3D, and 4B, which will be referred to later, show waveforms in which the light intensity of near-infrared light (radiation light) is measured in time series from the start of welding through the end of irradiation of the laser beam LB to the solidification until the welding is completed in spot welding with the processing point 81 as a fixed point, as shown in FIG. 2. The graph of FIG. 3B shows the light intensity in the spot welding of the processing point 81 in butt welding. The graphs of FIGS. 3D and 4B show the light intensity in the spot welding of the processing point 81 in overlap welding.

[0064] Among the peripheral region 82, the transition tendency of the light intensity of the post - process measurement point 84 from the start of welding through the end of the irradiation of the laser beam LB until solidification and the end of welding is similar to the transition tendency of the time - series light intensity of the processing point 81 in the graphs of FIGS. 2, 3B, 3D, and 4B. In particular, the transition tendency of the light intensity of the measurement point 84 is similar to the transition tendency of the light intensity of the processing point 81 from the end of the irradiation of the laser beam LB until solidification and the end of welding.

[0065] Among the peripheral region 82, the transition tendency of the light intensity of the pre - process measurement point 83 from the start of welding through the end of the irradiation of the laser beam LB until solidification and the end of welding is similar to the transition tendency of the time - series light intensity of the processing point 81 in the graphs of FIGS. 2, 3B, 3D, and 4B. In particular, the transition tendency of the light intensity of the measurement point 83 is similar to the transition tendency of the light intensity of the processing point 81 at the steep rise of the light intensity at the start of welding.

[0066] Among the peripheral region 82, the transition tendency of the light intensity of the measurement points 85, 86 on both sides from the start of welding through the end of the irradiation of the laser beam LB until solidification and the end of welding is similar to the transition tendency of the time - series light intensity of the processing point 81 in the graphs of FIGS. 2, 3B, 3D, and 4B. In particular, the transition tendency of the light intensity of the measurement points 85, 86 is similar to the transition tendency of the average light intensity of the processing point 81 from the start of welding to the end of the irradiation of the laser beam LB.

[0067] The temperature of the processing point 81 after the end of the laser beam irradiation varies depending on the output of the laser beam LB irradiated to the processing point 81, the irradiation time, the elapsed time from the end of irradiation, etc. The temperature of the peripheral region 82 during the irradiation of the laser beam LB to the processing point 81 varies depending on the thermal conductivity of the workpiece 80, the distance between the processing point 81 and the peripheral region 82, etc. The predetermined time points at which the above - mentioned similarity relationship holds between the light intensity of the processing point 81 and the light intensity of the peripheral region 82 can be specified by considering, for example, the contents of factors related to the temperatures of the processing point 81 and the peripheral region 82.

[0068] Next, the relationship between the welding quality of the processing point 81, the temperature of the processing point 81, and the light intensity in a predetermined wavelength range in the radiation light LM from the processing point 81 will be described. When radiation light LM with a light intensity corresponding to the radiation heat quantity is radiated from the processing point 81 due to the irradiation of the laser light LB, the heat capacity of the workpiece 80 at the processing point 81 corresponding to the radiation heat quantity of the processing point 81 varies depending on whether there is a gap (GAP) between the workpieces at the processing point 81. Hereinafter, it will be described separately for butt welding and overlay welding.

[0069] FIG. 3A is an explanatory diagram of the butt welding of workpieces. FIG. 3A shows a case where there is a gap ΔG between the workpieces 88 and 89 when butt welding the two workpieces 88 and 89 at the processing point 81 of the workpiece 80. In butt welding with a gap during butt welding, it is required to weld in a state where the proper gap ΔG is provided. When there is an appropriate gap ΔG between the workpieces 88 and 89, a part of the laser light LB irradiated to the processing point 81 passes through the gap ΔG and escapes below the workpieces 88 and 89.

[0070] The longer the dimension of the gap ΔG, the more the amount of laser light LB that escapes below the workpieces 88 and 89 increases, and the less the amount of heat supplied from the laser light LB to the processing point 81. If the dimension of the gap ΔG is shortened, the amount of laser light LB that escapes below the workpieces 88 and 89 decreases, and the amount of heat supplied from the laser light LB to the processing point 81 increases. The amount of heat supplied from the laser light LB to the processing point 81 becomes maximum when the workpieces 88 and 89 are brought into contact with each other by eliminating the gap ΔG so that the laser light LB irradiated to the processing point 81 does not escape below the workpieces 88 and 89.

[0071] Figure 3B is a graph showing the time-series information of the light intensity of near-infrared light, which is a predetermined wavelength region, in the radiant light LM radiated from the processing point 81 when the butt welding process of Figure 3A is performed. In Figure 3B, the vertical axis indicates the light intensity of near-infrared light in arbitrary units (relative values), and the horizontal axis indicates the elapsed time from the start of irradiation of the laser beam LB. In the graph of Figure 3B, the time-series change in the light intensity of a predetermined wavelength component in the radiant light LM radiated from one processing point 81 is compared between the case where an appropriate gap ΔG exists between the workpieces 88 and 89 and the case where no gap ΔG exists at all. Figure 3B shows the case where the appropriate gap ΔG between the workpieces 88 and 89 is 30% of the beam diameter (spot diameter) of the laser beam LB.

[0072] The graph of the light intensity LI1 in Figure 3B shows the time-series change in the light intensity of near-infrared light radiated from the processing point 81 when an appropriate gap ΔG exists between the workpieces 88 and 89. The graph of the light intensity LI2 shows the time-series change in the light intensity of near-infrared light radiated from the processing point 81 when no gap ΔG exists between the workpieces 88 and 89. T indicates the end point of irradiation of the laser beam LB with respect to the processing point 81.

[0073] During the laser beam irradiation period before the end point of irradiation T, as shown in the graphs of the light intensities LI1 and LI2, the light intensity of near-infrared light radiated from the processing point 81 is higher when no gap ΔG exists between the workpieces 88 and 89 than when an appropriate gap ΔG exists. This is because when no gap ΔG exists between the workpieces 88 and 89, more heat is supplied from the laser beam LB to the processing point 81, and the temperature of the processing point 81 becomes higher. When comparing the light intensities at the same time point between the case where an appropriate gap ΔG exists and the case where no gap ΔG exists, the state where the light intensity is higher when no gap ΔG exists than when an appropriate gap ΔG exists is maintained for a certain period.

[0074] If the near-infrared light intensity of the processing point measured after the irradiation of the laser beam in butt welding matches the near-infrared light intensity at the point on the graph of the light intensity LI1 corresponding to the measurement time point, it can be considered that the butt welding was performed with an appropriate gap. If there is an allowable range for the appropriate gap, an allowable range corresponding to the allowable range of the appropriate gap can be determined for the near-infrared light intensity of the processing point measured after the irradiation of the laser beam and the light intensity measurement time point, respectively.

[0075] Range A in FIG. 3B indicates the allowable range of the combination of the near-infrared light intensity of the processing point 81 and the light intensity measurement time point, which can be determined as a good product where the butt welding was performed with an appropriate gap. Range A is set after the end time point T of the irradiation of the laser beam LB and is set to exclude the combination of the near-infrared light intensity on the graph of the light intensity LI2 and the light intensity measurement time point. Range A can be set based on the combination of the near-infrared light intensity on the graph of the light intensity LI1 and the light intensity measurement time point.

[0076] Note that the measurement points 83, 84, 85, and 86 measure the light intensity at positions separated from the processing point 81 by a predetermined distance, and FIG. 3B shows the light intensity transition at the specific position (processing point 81) to be welded. The light intensity of the processing point 81 in FIG. 3B reaches the time point in range A after a predetermined time has elapsed since the end of the irradiation of the laser beam LB to the processing point 81. For example, the measurement point 84, which is the measurement target of the post-process sensor 33, can measure the light intensity in range A after a further predetermined time has elapsed since the time when the light intensity of the processing point 81 reached the value in range A. The "combination of the near-infrared light intensity and the light intensity measurement time point" refers to the combination of a specific time difference and the light intensity. The specific time difference refers to the time difference between the time when the light intensity of the processing point 81 in FIG. 3B reaches range A and the time when the light intensity of the measurement point 84 reaches range A.

[0077] A combination of similar ideas can be applied to the measurement point 83, which is the measurement target of the pre - process sensor 32. Also, in the case of measurement points 85, 86 and the processing point 81, the combination of "the combination of the near - infrared light intensity and the measurement time point of the light intensity" refers to the combination of a specific distance and the light intensity at the same time point. The specific distance at the same time point refers to the distance between the measurement points 85, 86 and the processing point 81 when the light intensity at the processing point 81 in FIG. 3B reaches the range A.

[0078] The light intensity of the near - infrared light radiated from the processing point 81 changes over time as shown in the graph of the light intensity LI1 in FIG. 3B if an appropriate gap ΔG exists between the workpieces 88, 89. If there is no gap ΔG between the workpieces 88, 89, it changes over time as shown in the graph of the light intensity LI2 in FIG. 3B.

[0079] In the butt - welding process of the workpieces 88, 89, it is possible to determine whether the processing result is a good product or not based on whether the light intensity of the near - infrared light from the processing point 81 at a predetermined time point after the irradiation of the laser beam LB to the processing point 81 belongs to the range A. The light intensity of the near - infrared light from the processing point 81 at a predetermined time point after the end of the irradiation of the laser beam to the processing point 81 can be simulated by the light intensity of the near - infrared light from the peripheral region 82 measured during the irradiation of the laser beam LB to the processing point 81. In the butt - welding process, based on whether the combination of the light intensity of the near - infrared light in the peripheral region 82 measured during the welding process of the processing point 81 and the predetermined time point corresponding to the light intensity of the near - infrared light of the processing point 81 simulated by the measured light intensity belongs to the range A, it is possible to determine whether the processing result is a good product or not.

[0080] FIG. 3C is an explanatory diagram of the overlay - welding process of the workpieces. FIG. 3C shows the case where there is a gap ΔG between the workpieces 88, 89 when two workpieces 88, 89 are overlay - welded at the processing point 81 of the workpiece 80. In the overlay - welding process, the state where there is a gap ΔG between the two welded workpieces 88, 89 indicates a state where the bonding degree due to the welding of the two workpieces 88, 89 is low and the processing result is in a defective state.

[0081] When there is a gap ΔG between the workpieces 88 and 89 during welding, the heat of the workpiece 88 irradiated with the laser beam LB is less likely to be conducted to the workpiece 89 stacked on the workpiece 88. The heat radiated from the workpiece 88 after the irradiation of the laser beam LB maintains a higher state when there is a gap ΔG between the workpieces 88 and 89 because the heat capacity is limited to the workpiece 88, compared to the case where there is no gap ΔG.

[0082] FIG. 3D is a graph showing the time-series information of the light intensity of near-infrared light, which is a predetermined wavelength region, in the radiation light LM radiated from the processing point 81 when the overlay welding process of FIG. 3C is performed. In FIG. 3D, the vertical axis indicates the light intensity of near-infrared light in arbitrary units (relative values), and the horizontal axis indicates the elapsed time from the start of irradiation of the laser beam LB. In the graph of FIG. 3D, the time-series change of the light intensity of a predetermined wavelength component in the radiation light LM radiated from one processing point 81 is compared between the case where there is no gap ΔG between the workpieces 88 and 89 and the case where there is a gap ΔG. In FIG. 3D, the case where the gap ΔG existing between the workpieces 88 and 89 has a length of 20% of the plate thickness of the workpieces 88 and 89 is shown.

[0083] The graph of the light intensity LI3 in FIG. 3D shows the time-series change of the light intensity of near-infrared light radiated from the processing point 81 when there is no gap ΔG between the workpieces 88 and 89. The graph of the light intensity LI4 shows the time-series change of the light intensity of near-infrared light radiated from the processing point 81 when there is a gap ΔG between the workpieces 88 and 89.

[0084] In the laser beam irradiation period before the end time point T of irradiation, as shown in the graphs of the light intensities LI3 and LI4, when there is a gap ΔG between the workpieces 88 and 89, the light intensity of the near-infrared light radiated from the processing point 81 is higher than when there is no gap ΔG. This is because when there is a gap ΔG between the workpieces 88 and 89, more heat is concentrated and accumulated in the upper workpiece 88 irradiated with the laser beam LB from the laser beam LB to the processing point 81 than when there is no gap ΔG, resulting in a higher temperature at the processing point 81. When comparing the light intensities at the same time point between the case where there is no gap ΔG and the case where there is a gap ΔG, when there is a gap ΔG, a state with a higher light intensity than when there is no gap ΔG is maintained for a certain period.

[0085] If the light intensity of the near-infrared light at the processing point measured after the irradiation of the laser beam in the overlay welding process matches the light intensity of the near-infrared light at the time point on the graph of the light intensity LI3 corresponding to the measurement time point, it can be considered that the overlay welding process was performed without a gap. When mimicking the state without a gap even with a slight gap, the allowable range corresponding to the allowable range of the gap mimicking the state without a gap can be determined respectively for the light intensity of the near-infrared light at the processing point 81 measured after the end of the irradiation of the laser beam LB to the processing point 81 and the measurement time point of the light intensity.

[0086] The range B in Fig. 3D shows the allowable range of the combination of the light intensity of the near-infrared light at the processing point 81 and the measurement time point of the light intensity, which can be determined as a good product when the overlay welding process was performed without a gap. The range B is set after the end time point T of the irradiation of the laser beam LB and is set not to include the combination of the light intensity of the near-infrared light on the graph of the light intensity LI4 and the measurement time point of the light intensity. The range B can be set based on the combination of the light intensity of the near-infrared light on the graph of the light intensity LI3 and the measurement time point of the light intensity.

[0087] Note that, similar to butt welding, the measurement points 83, 84, 85, and 86 measure the light intensity at positions separated by a predetermined distance from the processing point 81, and FIG. 3B shows the light intensity transition at the specific position (processing point 81) to be welded. The light intensity at the processing point 81 in FIG. 3B reaches the time point in range A after a predetermined time has elapsed since the irradiation of the laser beam LB to the processing point 81 ended. For example, the measurement point 84, which is the measurement target of the post - process sensor 33, can measure the light intensity in range A after a further predetermined time has elapsed since the light intensity at the processing point 81 reached the value in range A. The combination of "the combination of the near - infrared light intensity and the measurement time point of the light intensity" refers to the combination of a specific time difference and the light intensity.

[0088] A combination of similar ideas can be applied to the case of the measurement point 83, which is the measurement target of the pre - process sensor 32. Also, in the case of the measurement points 85, 86 and the processing point 81, the combination of "the combination of the near - infrared light intensity and the measurement time point of the light intensity" refers to the combination of a specific distance and the light intensity at the same time point.

[0089] The light intensity of the near - infrared rays radiated from the processing point 81 changes over time as shown in the graph of the light intensity LI3 in FIG. 3D if there is no gap ΔG between the workpieces 88, 89, and changes over time as shown in the graph of the light intensity LI4 in FIG. 3D if there is a gap ΔG between the workpieces 88, 89.

[0090] In the overlay welding process of the workpieces 88, 89, it is possible to determine whether the processing result is a good product or not based on whether the light intensity of the near - infrared rays from the processing point 81 at a predetermined time point after the irradiation of the laser beam LB to the processing point 81 ends belongs to range B. The light intensity of the near - infrared rays from the processing point 81 at a predetermined time point after the irradiation of the laser beam to the processing point 81 ends can be simulated by the light intensity of the near - infrared rays from the peripheral region 82 measured during the irradiation of the laser beam LB to the processing point 81. In the overlay welding process, it is possible to determine whether the processing result is a good product or not based on whether the combination of the light intensity of the near - infrared rays in the peripheral region 82 measured during the welding process of the processing point 81 and the predetermined time point corresponding to the light intensity of the near - infrared rays of the processing point 81 simulated by the measured light intensity belongs to range B.

[0091] In this embodiment, as shown in FIG. 1B, in addition to the in-process sensor 31 that measures the processing point 81, preprocess, postprocess, and side sensors 32 to 34 that measure the peripheral region 82 are provided in the sensor unit 30. Hereinafter, how the light intensities measured by the sensors 32 to 34 are used when evaluating the processing result of spot welding will be described.

[0092] FIG. 4A is an explanatory diagram of the case of performing spot welding of the superposition of workpieces 88 and 89. FIG. 4B is a graph showing the time-series information of the light intensity of near-infrared rays, which is a predetermined wavelength component, in the emitted light LM radiated from the processing point 81 in FIG. 4A. FIG. 4C is a graph showing the time-series information of the light intensity of near-infrared rays, which is a predetermined wavelength component, in the emitted light radiated from the peripheral region 82 in FIG. 4A. In FIGS. 4B and 4C, the light intensity of near-infrared rays is shown on the vertical axis in arbitrary units (relative values, 1 / 10 units), and the elapsed time from the start of irradiation of the laser light LB is shown on the horizontal axis.

[0093] For example, as shown in FIG. 4A, when performing spot welding of the superposition of workpieces 88 and 89 at the processing point 81 of the workpiece 80, the in-process sensor 31 measures the light intensity of near-infrared rays in the emitted light LM from the processing point 81. The preprocess, postprocess, and side sensors 32 to 34 measure the light intensity of near-infrared rays in the emitted light LM from the peripheral region 82. The time-series light intensity transition of near-infrared rays at the processing point 81 measured by the in-process sensor 31 changes in time series as shown in the graph of FIG. 4B, for example. The time-series light intensity transition of near-infrared rays in the peripheral region 82 measured by the preprocess, postprocess, and side sensors 32 to 34 changes in time series as shown in the graph of FIG. 4C, for example.

[0094] That is, when performing spot welding, the time-series light intensity transition of near-infrared rays at the processing point 81 measured by the in-process sensor 31 is similar to the time-series light intensity transition in the peripheral region 82. The light intensity measurement in the peripheral region 82 simulates the light intensity measurement at the processing point 81 in the same manner as in the case of continuous welding.

[0095] Again, continuous welding will be described. FIG. 5A is an explanatory view of the case of performing continuous welding of the overlap of workpieces 88 and 89. FIG. 5B is an explanatory view of the areas generated at the processing point 81 and the peripheral region 82 in the continuous welding process.

[0096] In the overlap welding process of workpieces 88 and 89, as shown in FIG. 5A, the overlapped workpieces 88 and 89 are continuously welded. In continuous welding, the processing point 81 and the peripheral region 82 of the workpiece 80 move at a constant pitch in the feed direction X from the starting point SP toward the end point as the head unit 50 is fed and moved.

[0097] At each moving processing point 81, a molten pool MP as shown in FIG. 5B is generated during the irradiation of the laser beam LB. In the molten pool MP, undulations of the melted workpiece 80 occur. Similar to the case of spot welding shown in FIG. 4B, the near-infrared light intensity of the processing point 81 measured by the in-process sensor 31 repeatedly increases and decreases finely during the laser beam irradiation period when the molten pool MP is generated at the processing point 81, so the reliability for estimating the heat quantity is lacking.

[0098] Each moving peripheral region 82 is heated by the amount of heat conducted from the processing point 81 by heat conduction during the irradiation of the laser beam LB to each processing point 81 corresponding to each peripheral region 82. From the peripheral region 82, radiant light LM with a light intensity corresponding to the temperature of the heated peripheral region 82 is radiated. Similar to the case of spot welding shown in FIG. 4C, the near-infrared light intensity of the peripheral region 82 measured by each of the pre-process, post-process, and side sensors 32 to 34 stabilizes at a value corresponding to the temperature of the peripheral region 82 even during the laser beam irradiation period. This is because no molten pool MP is generated in the peripheral region 82.

[0099] The light intensity in a predetermined wavelength region of the radiant light LM of the peripheral region 82 measured during the irradiation of the laser beam LB to the corresponding processing point 81 simulates the light intensity in a predetermined wavelength region of the radiant light LM of the processing point 81 at a predetermined time point after the end time point T of the laser beam irradiation. The "predetermined wavelength region" is, for example, near-infrared light. The simulation of "simulating the light intensity in a predetermined wavelength region" refers to the similarity relationship described below.

[0100] As described above, the transition tendency of the light intensity of the measurement point 84 in the post-process in the peripheral region 82 is similar to the transition tendency of the light intensity of the processing point 81 from the start of welding through the irradiation of the laser beam LB to the end of solidification until the welding is completed, with the processing point 81 as a fixed point. In particular, the transition tendency of the light intensity of the measurement point 84 is similar to the time-series transition tendency of the light intensity of the processing point 81 from the end of the irradiation of the laser beam LB to the end of solidification until the welding is completed.

[0101] The transition tendency of the light intensity of the pre-process measurement point 83 in the peripheral region 82 from the start of welding through the irradiation of the laser beam LB to the end of solidification until the welding is completed is similar to the time-series transition tendency of the light intensity of the processing point 81. In particular, the transition tendency of the light intensity of the measurement point 83 is similar to the transition tendency of the light intensity of the processing point 81 at the steep rise of the light intensity at the start of welding.

[0102] The transition tendency of the light intensity of the measurement points 85 and 86 on both sides in the peripheral region 82 from the start of welding through the irradiation of the laser beam LB to the end of solidification until the welding is completed is similar to the time-series transition tendency of the light intensity of the processing point 81. In particular, the transition tendency of the light intensity of the measurement points 85 and 86 is similar to the average transition tendency of the light intensity of the processing point 81 from the start of welding to the end of the irradiation of the laser beam LB. "Simulating the light intensity in a predetermined wavelength region" refers to these similarity relationships.

[0103] Therefore, the measured values of the pre-process, post-process, and side sensors 32 to 34 during the laser beam irradiation period can be used as an index for evaluating the quality of the welding process of the workpiece 80 instead of the measured values of the in-process sensor 31 during and after the end time point T of the laser beam irradiation. In this embodiment, the measured values of the sensors 32 to 34 are used to evaluate the welding process result of the processing point 81.

[0104] In FIG. 5B, when the machining point 81 moves in the machining progress direction (feed direction X), the area becomes the solidification area SA as the molten pool MP starts to solidify due to the end of the irradiation of the laser beam LB. The temperature of the solidification area SA decreases to a temperature lower than the peak temperature when the laser beam LB was irradiated to the starting-to-solidify molten pool MP by thermal radiation and heat conduction after the end of the irradiation of the laser beam LB. At this time, the portion of the next machining point 81 forms the molten pool MP, and the area ahead in the machining progress direction becomes the unwelded area UA. In the unwelded area UA, the temperature rises due to heat conduction from the machining point 81 heated by the irradiation of the laser beam LB. In the peripheral area 82 portion excluding the solidification area SA and the unwelded area UA, the temperature also rises due to heat conduction from the machining point 81 heated by the irradiation of the laser beam LB, similar to the unwelded area UA.

[0105] The molten pool MP, the solidification area SA, and the unwelded area UA have a temperature distribution corresponding to the legend from low temperature (C) to high temperature (H) shown in the temperature gauge TG of FIG. 5B due to the irradiation of the laser beam LB to the moved machining point 81. The solidification area SA includes the portion with a higher temperature distribution than the unwelded area UA where the molten pool MP started to solidify.

[0106] In continuous welding, the measurement point 83, which is the measurement target of the pre - process sensor 32, is always in a position ahead of the machining point 81 in the feed direction X, and the measurement point 84, which is the measurement target of the post - process sensor 33, is always in a position behind the machining point 81 in the feed direction X. The near - infrared light intensity of the unwelded area UA is measured by the pre - process sensor 32 that measures the measurement point 83 in the peripheral area 82, and the near - infrared light intensity of the solidification area SA is measured by the post - process sensor 33 that measures the measurement point 84 in the peripheral area 82.

[0107] The pre - process sensor 32 can measure the near - infrared light intensity from the unwelded area UA in the peripheral area 82 before the irradiation of the laser beam LB to the machining point 81.

[0108] The post - process sensor 33 can measure the near - infrared light intensity from the solidification area SA in the peripheral area 82 after the irradiation of the laser beam LB to the machining point 81.

[0109] In each side sensor 34, the intensity of near-infrared light from the measurement points 85 and 86 in the peripheral region 82 during the irradiation of the laser beam LB to the processing point 81 can be measured. The measurement points 85 and 86 are separated from the processing point 81 in a direction orthogonal to the feed direction X of the head unit 50, respectively.

[0110] FIG. 5A is an explanatory diagram of the case of performing continuous welding of the workpiece superposition. The first half of the continuous welding is a defective state where a gap ΔG occurs, and the second half shows a good state where the gap ΔG disappears. When the workpiece 80 is continuously welded, the intensity of near-infrared light measured by each of the sensors 31 to 33 in the in-process, pre-process, and post-process changes according to the gap ΔG between the two workpieces 88 and 89. The change in the processing state will be described below.

[0111] FIG. 6A is an explanatory diagram of the case of continuously welding a portion where a gap ΔG exists between the workpieces 88 and 89 in the superimposed welding process. FIG. 6B is a graph showing the time-series information of the intensity of near-infrared light measured by each of the sensors 31 to 33 in the in-process, pre-process, and post-process in the continuous welding of the portion of FIG. 6A.

[0112] FIG. 7A is an explanatory diagram of the case of continuously welding a portion where the gap ΔG between the workpieces 88 and 89 is eliminated in the superimposed welding process. FIG. 7B is a graph showing the time-series information of the intensity of near-infrared light measured by each of the sensors 31 to 33 in the in-process, pre-process, and post-process in the continuous welding of the portion of FIG. 7A.

[0113] FIG. 8A is an explanatory diagram of the case of continuously welding a portion where no gap ΔG exists between the workpieces 88 and 89 in the superimposed welding process. FIG. 8B is a graph showing the time-series information of the intensity of near-infrared light measured by each of the sensors 31 to 33 in the in-process, pre-process, and post-process in the continuous welding of the portion of FIG. 8A.

[0114] In FIGS. 6B, 7B, and 8B, the near-infrared light intensity is shown on the vertical axis in arbitrary units (relative values, 1 / 10 units), and the position in the feed direction X of the machining point 81 is shown on the horizontal axis.

[0115] When the workpieces 88, 89 in FIG. 5A are continuously welded, the measured values of the in-process sensor 31 that measures the molten pool MP of the machining point 81 finely increase and decrease as shown by the graphs of the light intensity L31 in FIGS. 6B, 7B, and 8B due to the undulation of the molten pool MP. The measured values of the pre-process and post-process sensors 32, 33 that measure the unwelded area UA and the solidified area SA in the peripheral area 82 are stable without finely increasing and decreasing as shown by the respective graphs of the light intensities L32, L33.

[0116] The temperatures of the unwelded area UA and the solidified area SA in the peripheral area 82 are lower than the temperature of the molten pool MP of the machining point 81. The measured values of the pre-process and post-process sensors 32, 33 shown by the respective graphs of the light intensities L32, L33 are lower than the measured values of the in-process sensor 31 shown by the graph of the light intensity L31. The measured value shown by the graph of the light intensity L33 of the post-process sensor 33 that measures the solidified area SA with a higher temperature than the unwelded area UA is lower than the measured value shown by the graph of the light intensity L32 of the pre-process sensor 32 that measures the unwelded area UA.

[0117] In the portion on the starting point SP side of the movement of the machining point 81 that moves in the feed direction X in the workpiece 80 in FIG. 5A, there is a gap ΔG between the two workpieces 88, 89 as shown in FIG. 6A. In the portion where there is a gap ΔG between the workpieces 88, 89, the heat capacity of the workpiece 80 at the machining point 81 is only the heat capacity of the upper workpiece 88 irradiated with the laser beam LB.

[0118] In the portion on the end point side of the movement of the machining point 81 moving in the feed direction X in the workpiece 80 of FIG. 5A, as shown in FIG. 8A, there is no gap ΔG between the two workpieces 88 and 89. In the portion where there is no gap ΔG between the workpieces 88 and 89, the heat capacity of the workpiece 80 at the machining point 81 is the combined heat capacity of the two workpieces 88 and 89. The heat capacity of the portion of the workpiece 80 where there is a gap ΔG between the workpieces 88 and 89 is lower than the heat capacity of the portion where there is no gap ΔG between the workpieces 88 and 89.

[0119] In the portion on the starting point SP side of the movement of the machining point 81 where the heat capacity of the workpiece 80 is low, the amount of heat supplied to the machining point 81 by the irradiation of the laser beam LB is accumulated in the upper workpiece 88 and is difficult to conduct to the lower workpiece 89. In the upper workpiece 88, the light intensity of the radiation light LM radiated from the peripheral region 82 due to heat conduction from the machining point 81 is higher than when it is in contact with the lower workpiece 89 (state without gap ΔG).

[0120] In the portion on the starting point SP side of the movement of the machining point 81, the presence of the gap ΔG between the workpieces 88 and 89 increases the temperatures of the unwelded area UA and the solidified area SA in the peripheral region 82. As shown in FIG. 6B, the measured values of the pre-process and post-process sensors 32 and 33 shown in the graphs of the light intensities L32 and L33 are closer to the measured value of the in-process sensor 31 compared to the case where there is no gap ΔG described later.

[0121] On the end point side of the movement of the machining point 81 where the heat capacity of the workpiece 80 is high, since there is no gap ΔG between the workpieces 88 and 89, the amount of heat supplied to the machining point 81 by the irradiation of the laser beam LB conducts from the upper workpiece 88 to the lower workpiece 89 and is difficult to accumulate in the upper workpiece 88. As shown in FIG. 8B, the measured values of the pre-process and post-process sensors 32 and 33 shown in the graphs of the light intensities L32 and L33 are farther from the measured value of the in-process sensor 31 compared to the case where the gap ΔG exists as described above.

[0122] In the workpiece 80 of FIG. 5A, in the portion between the starting point SP and the end point of the movement of the machining point 81, as shown in FIG. 7A, there is a point where the gap ΔG existing between the two workpieces 88 and 89 is eliminated. In this portion, the heat capacity of the workpiece 80 at the machining point 81 changes at the point where the gap ΔG between the workpieces 88 and 89 is eliminated.

[0123] Even if the heat capacity of the workpiece 80 changes at the point where the gap ΔG is eliminated, it does not directly affect the temperature of the molten pool MP generated at the machining point 81 during the irradiation of the laser beam LB. The measured value of the in-process sensor 31 that measures the molten pool MP at the machining point 81 does not change even when the machining point 81 passes through the point where the gap ΔG is eliminated. The near-infrared light intensity L31 of the machining point 81 measured by the in-process sensor 31 during the irradiation of the laser beam LB does not change even when the presence or absence of the gap ΔG between the workpieces 88 and 89 changes, so it is not an index for evaluating the quality of the welding process of the workpiece 80.

[0124] When the machining point 81 passes through the point where the gap ΔG is eliminated, the heat capacity of the workpiece 80 increases with that point as the boundary. In the portion from the point where the gap ΔG is eliminated to the end point side, the amount of heat transferred from the upper workpiece 88 to the lower workpiece 89 increases more than in the portion on the starting point SP side, and the light intensity of the radiation light LM radiated from the peripheral region 82 heated by heat conduction from the machining point 81 decreases.

[0125] The measured values of the pre-process and post-process sensors 32 and 33 that measure the measurement points 83 and 84 in the peripheral region 82 decrease as shown in FIG. 7B when the measurement points 83 and 84 pass through the point where the gap ΔG is eliminated, respectively. The measurement point 83 passes through the point where the gap ΔG is eliminated earlier than the measurement point 84. The measured value of the pre-process sensor 32 shown by the graph of the light intensity L32 decreases earlier than the measured value of the post-process sensor 33 shown by the graph of the light intensity L33 when the machining point 81 is at a position in front in the feed direction X.

[0126] During the irradiation of the laser beam LB to the processing point 81, the near-infrared light intensities L32 and L33 at the measurement points 83 and 84 measured by the pre-process and post-process sensors 32 and 33 change when the presence or absence of the gap ΔG between the workpieces 88 and 89 changes. The measured values of the pre-process and post-process sensors 32 and 33 during the irradiation of the laser beam LB to the processing point 81 can be used as an index for evaluating the quality of the welding process of the workpiece 80.

[0127] In continuous welding, during the irradiation of the laser beam LB to the processing point 81, the near-infrared light intensities at the measurement points 85 and 86 in the peripheral region 82 measured by each side sensor 34 also change when the measurement points 85 and 86 pass through the point where the gap ΔG between the workpieces 88 and 89 is eliminated. The measurement points 85 and 86 are at the same position as the processing point 81 in the feed direction X. The measured values of each side sensor 34 decrease in the same way as the light intensities L32 and L33 measured by the pre-process and post-process sensors 32 and 33 shown in Fig. 7B when the processing point 81 passes through the point where the gap ΔG between the workpieces 88 and 89 is eliminated.

[0128] The measured values of each side sensor 34 during the irradiation of the laser beam LB to the processing point 81 can also be used as an index for evaluating the quality of the welding process of the workpiece 80.

[0129] In continuous welding, the measured values of the pre-process, post-process and both-side sensors 32 to 34, which are used as an index for evaluating the quality of the welding process of the workpiece 80, can simulate the near-infrared light intensity at the processing point 81 at a predetermined time point after the irradiation of the laser beam LB to the processing point 81 ends. Whether the processing result is a good product can be determined based on whether the combination of the simulated light intensity and the predetermined time point belongs to the range B in Fig. 3D. The predetermined time point can be determined considering factors related to the temperature of the processing point 81 at the end of the laser beam irradiation, factors related to the temperature of the peripheral region 82 during the irradiation of the laser beam LB, etc.

[0130] The measurement targets of the pre-process, post-process, and each of the sensors 32 to 34 for both sides are the measurement points 83 to 86 in the peripheral region 82. The portions of the measurement points 83, 85, and 86 in the peripheral region 82 are heated by the amount of heat conducted from the processing point 81. The remaining measurement point 84 is behind the processing point 81 in the feed direction X. The position of the measurement point 84 is the solidification area SA where the molten pool MP of the processing point 81 has started to solidify. The measurement point 84 includes a portion heated by the amount of heat conducted from the processing point 81 and a portion with a temperature distribution higher than that of the unwelded area UA where the molten pool MP has started to solidify.

[0131] When simulating the near-infrared light intensity L31 of the processing point 81 after the laser light irradiation ends with the near-infrared light intensity L33 of the measurement point 84 measured by the post-process sensor 33 during the irradiation of the laser light LB to the processing point 81, the predetermined time point is determined in consideration of the amount of heat in the solidification area SA.

[0132] By the way, when spot-welding the processing point 81, since the laser light LB is irradiated at a fixed point, the processing point 81 does not move, and the peripheral region 82 of the processing point 81 does not move during the welding process. In spot welding, each of the sensors 32 to 34 for the pre-process, post-process, and both sides measures the near-infrared light intensity radiated from the corresponding measurement points 83 to 86 in the peripheral region 82 during the irradiation of the laser light LB to the processing point 81. In spot welding, the measured values of each of the sensors 32 to 34 during the irradiation of the laser light LB to the processing point 81 can be used as an index for evaluating the quality of the welding process of the workpiece 80.

[0133] In spot welding, the near-infrared light intensity of the processing point 81 at a predetermined time point after the irradiation of the laser light LB to the processing point 81 can be simulated with the measured values of each of the sensors 32 to 34 used as an index for evaluating the quality of the welding process of the workpiece 80. Whether the processing result is a good product can be determined based on whether the combination of the simulated light intensity and the predetermined time point belongs to the range A in FIG. 3B. The predetermined time point can be determined in consideration of elements related to the temperature of the processing point 81 at the end of the laser light irradiation, elements related to the temperature of the peripheral region 82 during the irradiation of the laser light LB, and the like.

[0134] FIG. 9 is a flowchart showing the procedure of the process executed in the laser processing measurement apparatus of FIG. 1. The laser processing result evaluation method for evaluating the quality of the welding of the workpiece 80 can be implemented, for example, by the control unit 70 executing each process of the measurement step (step S1), the specification step (step S3), and the evaluation step (step S5). In the case of continuous welding, each process of steps S1 to S5 is repeatedly executed each time the position of the processing point 81 is moved, whereby the laser processing evaluation method can be implemented. In the case of continuous welding, each process of steps S1 and S3 is repeated each time the position of the processing point 81 is moved, and the process of step S5 is collectively executed for a plurality of processing points 81, whereby the laser processing evaluation method may be implemented.

[0135] In the measurement step of step S1, the control unit 70 measures the light intensity of a predetermined wavelength component (near-infrared) in each of the emitted lights LM from the processing point 81 and the peripheral region 82 during the welding of the workpiece 80 at the processing point 81. For the measurement, one or more of the pre-process, post-process, and side sensors 32 to 34 can be used.

[0136] In the specification step of step S3, the control unit 70, as a specifying unit, specifies the transition tendency of the light intensity in a predetermined wavelength region in the emitted light LM simulated by one or more measurement values from the pre-process, post-process, and side sensors 32 to 34. The emitted light LM simulated by one or more measurement values from the sensors 32 to 34 is the emitted light LM from the processing point 81 during or after the laser light irradiation. In this calculation, the control unit 70 sets the time point when the light intensity of a predetermined wavelength component in the emitted light LM from the processing point 81 after the end of the laser light irradiation becomes the same as the measurement values of the sensors 32 to 34 during the laser irradiation measured in the measurement step as a predetermined time point, and specifies the tendency. The predetermined time point can be specified, for example, by extracting the measurement time point combined with the light intensity measured in the measurement step from the combination of the light intensity of the predetermined wavelength component actually measured at the processing point 81 after the end of the laser light irradiation and the measurement time point.

[0137] In the evaluation step of step S5, the control unit 70 performs an evaluation process for determining the evaluation of the processing result based on whether the combination of the predetermined time point specified in the specific step and the light intensity measured in the measurement step belongs to range A in FIG. 3B or range B in FIG. 3D.

[0138] For example, when the control unit 70 determines that the combination of the predetermined time point, which is the measurement time point of the light intensity specified in the specific step, belongs to range A in FIG. 3B or range B in FIG. 3D, the control unit 70 can determine that the evaluation of the welding process is "good". Also, when the control unit 70 determines that the combination of the predetermined time point, which is the measurement time point of the light intensity obtained in the conversion step, does not belong to range A in FIG. 3B or range B in FIG. 3D, the control unit 70 can determine that the evaluation of the welding process is "no (defective)".

[0139] In either the case of continuous welding or spot welding, by using one or more measured values among the sensors 32 to 34, 34 at each location where the phase is shifted by 90 degrees around the processing point 81 in the peripheral region 82, the evaluation of the quality of the welding process can be determined respectively.

[0140] The determination of the evaluation of the welding process by executing the procedure of FIG. 9 may be executed using a sensor unit 30 in which some of the sensors among the pre-process, post-process, and sensors 32 to 34, 34 on both sides are omitted.

[0141] In the laser processing apparatus 10 of the present embodiment, during the welding process of the processing point 81 of the workpiece 80, the emitted light LM from the processing point 81 is guided to the in-process sensor 31 by the condenser lenses 55, 57, etc. that function as collimating lenses. Also, during the welding process of the processing point 81, the emitted light LM from the peripheral region 82 of the processing point 81 is guided to the pre-process, post-process, and sensors 32 to 34, 34 on both sides by the axicon lens 56, etc.

[0142] In the peripheral region 82, no molten pool MP is generated during the welding process of the processing point 81, and the light intensity of the radiant light LM stabilizes at a value corresponding to the temperature of the peripheral region 82. That is, the measured values of the light intensity of the radiant light LM by each of the sensors 32 to 34, 34 stabilize at values corresponding to the temperature of the peripheral region 82. The measured values of the light intensity of the radiant light LM by each of the sensors 32 to 34, 34 can be used as an index indicating the state of the gap ΔG between the workpieces 88, 89 at the processing point 81, and can be used to evaluate the quality of the welding process at the processing point 81.

[0143] In the laser processing apparatus 10 of the present embodiment, the light intensity of the radiant light LM used to evaluate the quality of the welding process at the processing point 81 can be measured by each of the sensors 32 to 34, 34 by guiding the radiant light LM from the peripheral region 82 during the welding process of the processing point 81 of the workpiece 80. After the processing is completed, there is no need to check the presence or absence of ΔG in a separate process such as a sound test. By eliminating this process, it is possible to suppress a decrease in the working efficiency of the welding process for evaluating the quality of the welding process.

[0144] From FIG. 1D, since the axicon lens 56 can be moved in the central axis direction by the adjustment mechanism 87, the range of the peripheral region 82 that guides the radiant light LM to each of the sensors 32 to 34, 34 by the axicon lens 56 or the like can be adjusted.

[0145] The measurement points 83 to 86 of the peripheral region 82 that guides the radiant light LM to each of the sensors 32 to 34, 34 by the axicon lens 56 or the like are located at positions spaced apart from the processing point 81 in the feed direction X and its orthogonal direction when performing the welding process of the processing point 81 by continuous welding.

[0146] When the radiant light LM from the measurement points 83, 84 spaced apart from the processing point 81 in the feed direction X is guided to each of the sensors 32, 33, the light intensity of a predetermined wavelength component in the radiant light LM from the future and past processing points 81 in continuous welding can be measured during the welding process.

[0147] As the continuous welding progresses, the light intensity of the radiant light LM from the same processing point 81 is measured by each of the sensors 32 and 33, and the state of the processing point 81 at the times before and after the welding process for the processing point 81 is evaluated from each measurement value, so that it is possible to evaluate the quality of the welding process performed on the processing point 81.

[0148] When the radiant light LM from the measurement points 85 and 86 spaced apart in the direction orthogonal to the feed direction X from the processing point 81 is guided to each of the sensors 34 and 34, the light intensity of a predetermined wavelength component can be measured for the peripheral region 82 at the same position as the processing point 81 in the feed direction X during the welding process.

[0149] During continuous welding, by measuring the light intensity of the radiant light LM from the peripheral region 82 at the same position as the processing point 81 in the feed direction X at the same timing as the welding process for the processing point 81, it is possible to evaluate the quality of the welding process performed on the processing point 81 during the welding process of the processing point 81.

[0150] By measuring the light intensity of the radiant light LM from each of the measurement points 83 to 86 in the peripheral region 82 with each of the sensors 32 to 34 and 34 respectively, it is possible to highly accurately evaluate the quality of the welding process of the processing point 81 from the state of the gap ΔG between the workpieces 88 and 89 in the peripheral region 82.

[0151] The axicon lens 56 used in the head unit 50 of FIG. 1B may be replaced with the two-branch prism 64 shown in FIG. 10A. The two-branch prism 64 has a pair of inclined surfaces 65. The two inclined surfaces 65 are arranged in a mountain shape that is pointed in the optical axis direction with their respective sides butted against each other on one surface side of the two-branch prism 64 in the optical axis direction passing through the two-branch prism 64.

[0152] A through hole 66 penetrating in the optical axis direction is formed in the two-branch prism 64. The through hole 66 opens across the two inclined surfaces 65. When the two-branch prism 64 of FIG. 10A is used in the head unit 50 of FIG. 1B, the condenser lens 55 of FIG. 1B is arranged on the central axis of the through hole 66.

[0153] The axicon lens 56 used for the head unit 50 in FIG. 1B may be replaced with the cylindrical lens 67 shown in FIG. 10B. The cylindrical lens 67 has an arcuate surface 68 on one surface side in the optical axis direction passing through the cylindrical lens 67.

[0154] A through hole 69 penetrating in the optical axis direction is formed in the cylindrical lens 67. The through hole 69 opens to the arcuate surface 68. When the cylindrical lens 67 of FIG. 10B is used for the head unit 50 of FIG. 1B, the condenser lens 55 of FIG. 1B is arranged on the central axis of the through hole 69.

[0155] Unlike the axicon lens 56 having the conical surface 62, the two-branch prism 64 and the cylindrical lens 67 in FIGS. 10A and 10B refract in the X-axis direction of the light incident surface and do not refract in the Y-axis direction. For this reason, the two-branch prism 64 and the cylindrical lens 67 can be used for the head unit 50 in place of the axicon lens 56, for example, when guiding the emitted light LM from two locations where the phase is shifted by 180 degrees each in the peripheral region 82 of the workpiece 80.

[0156] When the two-branch prism 64 or the cylindrical lens 67 is used for the head unit 50, in the sensor unit 30, either the set of the preprocess sensor 32 and the postprocess sensor 33 or the set of the two side sensors 34, 34 is omitted.

[0157] The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2021-102537 filed on Jun. 21, 2021, and all the disclosure contents thereof are incorporated herein by reference.

Claims

1. During welding of the processing point by laser light irradiated on the processing point of the workpiece, a peripheral measurement unit that measures the light intensity of a predetermined wavelength component that changes corresponding to the temperature of the workpiece by the radiation light in the peripheral region of the molten pool of the processing point, and a peripheral light guide unit that guides the radiation light from the peripheral region to the peripheral measurement unit, wherein the peripheral light guide unit refracts the radiation light from the peripheral region by an axicon lens having a through hole, or a bifurcated prism having a through hole, or a cylindrical lens having a through hole, and guides it to the peripheral measurement unit Laser processing measurement device.

2. The laser processing measurement device according to claim 1, further comprising an adjustment mechanism for moving the axicon lens, the bifurcated prism, or the cylindrical lens in the direction of their central axes. The laser processing measurement device according to claim 1.

3. The peripheral measurement unit includes a pre-process sensor that measures the light intensity of a predetermined wavelength component from the unwelded area of the peripheral region before irradiation of the laser light on the processing point, and a post-process sensor that measures the light intensity of a predetermined wavelength component from the solidified area of the peripheral region after irradiation of the laser light on the processing point. The laser processing measurement device according to claim 1.

4. In continuous welding in which a plurality of the workpieces are stacked, when the measurement values of the pre-process sensor and the post-process sensor decrease when the processing point moves in the feed direction, it is determined that the gap between the plurality of workpieces has disappeared. The laser processing measurement device according to claim 3.

5. When the measurement value of the pre-process sensor decreases compared to the measurement value of the post-process sensor at a time when the processing point is in a position in front in the feed direction, it is determined that the gap between the plurality of workpieces has disappeared. The laser processing measurement device according to claim 4.

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