JP5570451B2 - Laser welding apparatus and laser welding method - Google Patents

Description

  The present invention relates to a laser welding apparatus that evaluates the quality of a welded portion when welding using laser light, and more particularly to a laser welding apparatus that evaluates quality by monitoring the penetration depth, laser output, and the like.

  As a conventional laser welding apparatus, there is an apparatus (hereinafter referred to as a first example apparatus) that evaluates welding quality using light emitted from a molten metal in a welded part (see, for example, Patent Document 1).

  Specifically, as shown in FIG. 14, in the first apparatus, the laser beam continuously output from the laser oscillator 11 with a constant intensity is transmitted through the laser beam transmission optical system 12 and the condensing optical system 13. And condensed by the condensing optical system 13. The laser beam condensed by the condensing optical system 13 is used for welding the workpiece 1. When the workpiece 1 is welded, the molten metal of the welded portion 2 emits light. The light emitted from the molten metal in the welded portion 2 is collected by the condensing optical system 13 and transmitted to the interference filter 15 via the monitor light transmitting optical system 14. Among the light transmitted to the interference filter 15, specific wavelength components such as light emitted from the molten metal of the welded portion 2 and laser light output from the condensing optical system 13 are selected by the interference filter 15. The light selected by the interference filter 15 is received by the photodiode 16. A signal corresponding to the intensity of the received light is output from the photodiode 16. A signal output from the photodiode 16 is input to the computer 19 via the amplifier 17 and the A / D converter 18 and processed by the computer 19. Monitoring of welding is performed by the computer 19 assuming that the intensity of the light emitted from the molten metal in the welded part 2 and the intensity of the laser beam output from the condensing optical system 13 are proportional to the amount of penetration.

  Further, as a conventional laser welding apparatus, there is also an apparatus (hereinafter referred to as a second example apparatus) that evaluates welding quality using an acoustic emission sensor (hereinafter referred to as an AE sensor) (for example, a second example apparatus). (See Patent Document 2).

  Specifically, as shown in FIG. 15, in the second apparatus, an AE sensor 24 is attached to the condensing optical system 23. When the workpiece 1 is welded, an AE sensor generates signals having different waveforms depending on the output of the laser beam, the focal position of the laser beam, the flow rate of the shield gas, the flow rate of the assist gas, etc. 24. A signal output from the AE sensor 24 is input to the computer 27 via the amplifier 25 and the A / D converter 26 and processed by the computer 27. The welding conditions are controlled by the computer 27 so that the waveform of the signal output from the AE sensor 24 approaches the waveform at the normal time (matches the waveform at the normal time).

JP 2006-159242 A Japanese Patent Application Laid-Open No. 6-1555056

  However, in the first apparatus, the amount of penetration is not directly detected, but the data obtained from the temperature of the welded portion 2 and the output of the laser beam is indirectly converted into the amount of penetration. For this reason, there is a problem that the conversion result varies due to other factors such as variations in the material of the workpiece 1 and the ambient temperature.

  In the second apparatus, the degree of coincidence of waveforms is evaluated. For this reason, it has the subject that the amount of penetration important as welding quality cannot be evaluated quantitatively.

  Accordingly, the present invention has an object to provide a laser welding apparatus and a laser welding method capable of solving the above-described problems and quantitatively measuring the amount of penetration of a welded portion in a nondestructive manner to evaluate welding quality. To do.

  In order to achieve the above object, a laser welding apparatus according to the present invention has the following features.

That is, a laser welding apparatus according to the present invention is a laser welding apparatus for welding a welded portion with a laser beam, and forms a keyhole by irradiating the welded portion with a laser beam having a peak in intensity. A laser output means for generating an ultrasonic wave at the bottom of the hole; an ultrasonic detection means for detecting an ultrasonic wave generated at the bottom of the keyhole by a laser beam irradiated by the laser output means; and the ultrasonic detection means. Calculation means for calculating the penetration amount of the welded part based on the detected ultrasonic waveform; and evaluation means for evaluating the weld quality of the welded part based on the penetration amount calculated by the calculation means. Prepare.

  Further, the present invention may be realized as a laser welding method having the following characteristics instead of the laser welding apparatus.

That is, the laser welding method according to the present invention is a laser welding method in which a welded portion is welded with a laser beam, wherein a keyhole is formed by irradiating the welded portion with a laser beam having a peak in intensity, and the key. A first step of generating an ultrasonic wave at the bottom of the hole; a second step of detecting an ultrasonic wave generated at the bottom of the keyhole by the laser beam irradiated in the first step; Based on the waveform of the ultrasonic wave detected in the step, the third step of calculating the penetration amount of the welded portion, and the weld quality of the welded portion based on the penetration amount calculated in the third step. And a fourth step to be evaluated.

  According to the present invention, the ultrasonic wave generated by the modulated laser beam is detected by the ultrasonic wave detecting means, so that the amount of penetration of the weld can be quantitatively detected, and the welding quality is guaranteed without destruction. Can be performed quantitatively.

The figure which shows the outline | summary of the laser welding apparatus in Embodiment 1. FIG. The figure which shows the intensity | strength (pulse wave) of the laser beam after the modulation in Embodiment 1. The figure which shows the laser welding apparatus in Embodiment 1 The figure which shows the time change of the intensity | strength of the laser beam in Embodiment 1, and the time change of the amplitude of an ultrasonic wave. The figure which shows the laser welding process in Embodiment 1 The figure which shows the data of the amount of penetration in Embodiment 1 The figure which shows the modification of the laser welding apparatus in Embodiment 1. The figure which shows the modification (burst wave) of the intensity | strength of the laser beam after the modulation | alteration in Embodiment 1. The figure which shows the modification (chirp wave) of the intensity | strength of the laser beam after the modulation | alteration in Embodiment 1. The figure which shows the laser welding apparatus in Embodiment 2 FIG. 5 shows a structure of an optical coupling element in Embodiment 2. The figure which shows the intensity | strength (sinusoidal wave) of the laser beam after the modulation in Embodiment 3. The figure which shows the time change of the intensity | strength of the laser beam in Embodiment 3, and the time change of the amplitude of an ultrasonic wave. The figure which shows the outline | summary of the laser welding apparatus of the 1st example in the past The figure which shows the outline | summary of the laser welding apparatus of the 2nd example in the past in the past

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, in order to make it easy to understand, the drawings schematically show each component as a main component.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings. In addition, the same code | symbol may be attached | subjected to the same component and description may be abbreviate | omitted.

<Overview>
As shown in FIG. 1, in the laser welding apparatus 100 according to the present embodiment, when welding a welded portion 102 of a material to be welded 101 extending in the horizontal direction (X direction), welding is performed from the vertical direction (Z direction). The upper surface of the material 101 is irradiated with laser light. The weld 102 is melted from above, and a molten pool 103 is formed. While the molten pool 103 is formed, molten metal evaporates from the molten pool 103, and the keyhole 104 is formed by the pressure of the vapor at the time of evaporation. At this time, if the intensity of the laser beam irradiating the bottom of the molten pool 103 is modulated so as to increase momentarily with a predetermined pulse width as shown in FIG. 2, the bottom of the molten pool 103 instantaneously expands thermally. Or cause ablation. Along with this, as shown in FIG. 1, an ultrasonic wave 105 having a pulse width comparable to a predetermined pulse width is generated at the bottom of the molten pool 103. The generated ultrasonic wave 105 propagates inside the workpiece 101. A part of the propagated ultrasonic wave 105 is detected by the piezoelectric element 115 installed on the upper surface of the workpiece 101. The position of the welding part 102 specified from the position of the condensing optical system 114, the detection position of the ultrasonic wave 105 specified from the installation position of the piezoelectric element 115, the time when the laser beam was modulated, and the ultrasonic wave are detected. Based on the measured time, the amount of penetration of the weld 102 is specified. The quality of the welded portion 102 is determined based on the specified penetration amount.

<Laser welding equipment>
Specifically, as shown in FIG. 3, in the laser welding apparatus 100, the laser light continuously output from the laser oscillator 111 with a constant intensity is modulated by the light modulation element 112. The laser light modulated by the light modulation element 112 is transmitted to the condensing optical system 114 via the laser light transmitting optical system 113 and condensed by the condensing optical system 114. The laser beam condensed by the condensing optical system 114 is used for welding the workpiece 101. When welding the workpiece 101, an ultrasonic wave 105 corresponding to the modulation of the laser beam is generated from the welded portion 102. An ultrasonic wave 105 generated from the weld 102 is detected by the piezoelectric element 115. A signal corresponding to the detected waveform of the ultrasonic wave 105 is output from the piezoelectric element 115. A signal output from the piezoelectric element 115 is input to the computer 118 via the amplifier 116 and the A / D converter 117 and processed by the computer 118.

<Laser oscillator 111>
The laser oscillator 111 is connected to a computer 118, and in accordance with a command output from the computer 118, output start / stop of laser light, output intensity of laser light, and the like are controlled. For example, when a laser beam output start command is received, laser beam output is started. When receiving a laser beam output stop command, the laser beam output is stopped. When a command for changing the intensity of the laser beam is received, the output intensity of the laser beam is changed to the intensity set in the received command.

<Light modulation element 112>
The light modulation element 112 is connected to the signal generator 119 and modulates the intensity of the laser beam output from the laser oscillator 111 while receiving a high frequency signal from the signal generator 119. At this time, as shown in FIG. 2, the intensity of the laser beam output from the laser oscillator 111 with a constant intensity is modulated so as to generate a pulse wave.

<Signal generator 119>
The signal generator 119 is connected to the trigger generator 120, and when a trigger signal is received from the trigger generator 120, instantaneously outputs a high frequency signal.

<Trigger generator 120>
The trigger generator 120 is connected to the computer 118, and outputs a trigger signal simultaneously to the signal generator 119 and the A / D converter 117 when receiving a trigger signal output command from the computer 118. The laser light modulation timing and the ultrasonic detection timing are synchronized.

<A/D converter 117>
The A / D converter 117 is connected to the trigger generator 120. When receiving the trigger signal from the trigger generator 120, the A / D converter 117 converts the signal of the ultrasonic waveform output from the amplifier 116 from analog to digital and outputs it. .

<Supplement>
The condensing optical system 114 is connected to a moving stage 122 that moves based on a command from the stage controller 121.

  In order to prevent ultrasonic waves from being attenuated by the air layer, it is desirable to fill the space between the workpiece 101 and the piezoelectric element 115 with a coupling material such as grease. Further, as the ultrasonic wave propagation direction approaches the vertical direction (Z direction shown in FIG. 1), the detection sensitivity increases. Therefore, the piezoelectric element 115 is closer to the welded portion 102 within the range not affected by welding. Is desirable.

  In calculating the amount of penetration of the welded portion 102 by the computer 118, in order to obtain a resolution of 1 mm or less, the wavelength of the ultrasonic wave detected by the piezoelectric element 115 needs to be 1 mm or less. Usually, the speed of sound in a metal is about 4000 m / s to 6000 m / s. Considering this, the frequency of the ultrasonic wave is 5 MHz. That is, the intensity of the laser beam needs to be modulated at a frequency of 5 MHz or higher. For this reason, it is desirable to use an electro-optic element using the electro-optic effect or an acousto-optic element using the acousto-optic effect for the light modulation element 112. In addition, it is desirable to use a piezoelectric element 115, an amplifier 116, and an A / D converter 117 that have detection sensitivity in a frequency band of 5 MHz or higher in order to detect ultrasonic waves of 5 MHz or higher. The trigger generator 120 is preferably capable of outputting a trigger signal with an accuracy of 0.2 μsec or less.

<Penetration amount>
Next, the amount of penetration of the welded portion 102 will be described. In FIG. 4, the graph showing the temporal change in the intensity of the laser beam output from the light modulation element 112 is shown on the upper side, and the graph showing the temporal change in the amplitude of the ultrasonic wave detected by the piezoelectric element 115 is shown on the lower side. Yes. These graphs are arranged in time.

  As shown in FIG. 4, there is a time lag after the trigger signal is output from the trigger generator 120 until the computer 118 receives the pulse wave section of the ultrasonic amplitude corresponding to the pulse wave section of the laser light intensity. Exists. This time lag mainly consists of an optical modulation delay time, an ultrasonic propagation time, and an ultrasonic detection delay time. Here, the light modulation delay time is the time from when the trigger generator 120 generates a trigger signal until the light modulator 112 modulates the laser light via the signal generator 119. The ultrasonic wave propagation time is the time until the ultrasonic wave generated at the bottom of the molten pool 103 propagates through the workpiece 101 and reaches the piezoelectric element 115. The ultrasonic detection delay time is a time until the ultrasonic wave detected by the piezoelectric element 115 is converted into a signal and converted into waveform data by the amplifier 116 and the A / D converter 117.

  Of these three times, the light modulation delay time and the ultrasonic detection delay time are constant if the system of the laser welding apparatus 100 is determined. For this reason, these times can be specified by calibration. Then, the ultrasonic propagation time is specified by subtracting the specified light modulation delay time and the ultrasonic detection delay time from the time lag.

  That is, the modulation time of the laser light is specified from the time (trigger signal output time in the figure) when the trigger signal output command is output to the trigger generator 120 and the optical modulation delay time. The ultrasonic detection time is specified from the time (ultrasonic reception time in the figure) when the computer 118 receives the ultrasonic waveform signal output from the A / D converter 117 and the ultrasonic detection delay time. The ultrasonic wave propagation time is specified from the specified modulation time of the laser beam and the ultrasonic wave detection time.

  Here, it is assumed that the time during which the ultrasonic wave propagates through the workpiece 101 is T, and the speed at which the ultrasonic wave propagates through the workpiece 101 is V. Also, as shown in FIG. 1, the depth of the keyhole 104 is D, the horizontal distance from the welding position to the piezoelectric element 115 is L1, and the linear distance from the bottom of the keyhole 104 to the piezoelectric element 115 is L2. . In this case, the linear distance L2 is specified from the ultrasonic wave propagation time T and the ultrasonic wave propagation velocity V based on the following formula (1).

  Further, the horizontal distance L1 from the position of the welded portion 102 to the installation position of the piezoelectric element 115 is specified by the installation position of the piezoelectric element 115 and the position of the moving stage 122. From this, the depth D of the keyhole 104 is specified from the horizontal distance L1 and the linear distance L2 based on the following formula (2).

  Here, the bottom of the keyhole 104 substantially corresponds to the bottom of the welded portion 102. That is, the depth D of the keyhole 104 corresponds to the amount of penetration.

<Laser welding process>
Next, the operation of the laser welding apparatus will be described.

  As shown in FIG. 5, the computer 118 executes laser welding processing from the following (Step S101) to (Step S110).

  First, the computer 118 outputs a command to start moving the moving stage 122 to the stage controller 121. The movement of the condensing optical system 114 attached to the moving stage 122 is started via the stage controller 121 (step S101). When the condensing optical system 114 reaches the welding start position, a laser beam output start command is output to the laser oscillator 111. The laser oscillator 111 is started to output laser light (step S102).

  Next, the computer 118 outputs a trigger signal output command to the trigger generator 120. Via the trigger generator 120, the light modulator 112 modulates the intensity of the laser light output from the laser oscillator 111 in accordance with the signal output from the signal generator 119 (step S103). Obtained by converting the signal of the ultrasonic waveform detected by the piezoelectric element 115 and amplified by the amplifier 116 from the analog to digital by the A / D converter 117 via the trigger generator 120 and converted. An ultrasonic waveform signal is output (step S104). The ultrasonic waveform signal output from the A / D converter 117 is received. The amount of penetration is calculated from the preset position of the welded portion 102, the installation position of the piezoelectric element 115, the modulation time of the laser beam, and the detection time of the ultrasonic wave (step S105). The calculated penetration amount is compared with a desired penetration amount stored in advance, and the intensity of the laser beam that decreases the difference is specified. A command to change the intensity of the laser beam with the specified intensity set is output to the laser oscillator 111. The laser oscillator 111 is made to change the output intensity of the laser beam to the specified intensity of the laser beam (step S106). The processes from step S103 to step S106 are repeated until the condensing optical system 114 reaches a predetermined welding end position.

  Next, when the condensing optical system 114 reaches the welding end position (step S107: Yes), the computer 118 outputs a laser beam output stop command to the laser oscillator 111. The laser oscillator 111 stops the output of the laser light (step S108). A command to stop moving the moving stage 122 is output to the stage controller 121. The moving stage 122 is moved to a predetermined position via the stage controller 121, and the movement of the condensing optical system 114 attached to the moving stage 122 is stopped (step S109).

  Next, the computer 118 evaluates the quality of the welded part 102 from the data of the penetration amount (step S110). For example, when the quality of the welded portion 102 is determined, as shown in FIG. 6, there is at least one piece of data less than or equal to the threshold th1 with respect to the penetration amount data (black dot in the figure), or the threshold When there is a predetermined number or more of data below th2, it is determined as defective.

<Summary>
As described above, according to the present embodiment, the penetration amount can be quantitatively detected by detecting the ultrasonic wave generated by the modulated laser beam by the piezoelectric element 115, and guaranteeing the welding quality non-destructively. Can be quantitative. Further, since the amount of penetration can be monitored during welding, high quality welding can be performed by controlling the laser light intensity based on the monitored amount of penetration. In particular, since it has a function of guaranteeing welding quality in a non-destructive manner, it can be applied as a laser welding apparatus for automobiles, electronic parts and the like.

<Others>
As shown in FIG. 7, the ultrasonic wave 105 may be detected using an optical interferometer 125 instead of the piezoelectric element 115. Specifically, the light output from the optical interferometer 125 is applied to the ultrasonic detection position (position where the piezoelectric element 115 is installed). The light applied to the ultrasonic detection position is reflected from the upper surface of the workpiece 101. At this time, when the upper surface of the workpiece 101 is vibrated by the ultrasonic wave 105, the light reflected by the upper surface of the workpiece 101 is modulated by the phase and frequency according to the vibration of the upper surface of the workpiece 101. The modulated light enters the optical interferometer 125 and is converted into a signal by the optical interferometer 125. Thereby, ultrasonic waves can be detected in a non-contact manner. From this, the horizontal distance L1 from the position of the weld 102 to the irradiation position of the optical interferometer 125 can be made constant. The optical interferometer 125 can be brought close to the weld 102. Measurement accuracy can be increased.

  As shown in FIG. 8, the laser light output from the laser oscillator 111 at a constant intensity may be modulated by the light modulation element 112 so as to generate a burst wave at the intensity of the laser light. Thereby, a plurality of peaks can be generated in the intensity of the laser beam, and the width of each peak can be narrowed. From this, the deformation of the peak waveform due to dispersion is reduced, and the S / N ratio is increased by averaging. Accordingly, the time lag calculation accuracy can be increased.

  As shown in FIG. 9, the laser light output at a constant intensity from the laser oscillator 111 may be modulated by the light modulation element 112 so as to generate a chirp wave at the intensity of the laser light. Thereby, a plurality of peaks can be generated in the intensity of the laser beam, and autocorrelation processing can be applied to the plurality of peaks. Accordingly, the time lag calculation accuracy can be increased.

(Embodiment 2)
Hereinafter, a second embodiment according to the present invention will be described with reference to the drawings. In addition, about the component same as Embodiment 1, the same referential mark is attached | subjected and description is abbreviate | omitted.

<Laser welding equipment>
Here, as an example, as shown in FIG. 10, the laser welding apparatus 200 includes a laser oscillator 211 for generating ultrasonic waves separately from the laser oscillator 111. The laser beam output from the ultrasonic generator 211 for ultrasonic wave generation is modulated by the light modulation element 112. The laser light modulated by the light modulation element 112 is combined with the laser light output from the laser oscillator 111 by the optical coupling element 212. These laser beams coupled by the optical coupling element 212 are transmitted to the condensing optical system 114 via the laser light transmission optical system 113 and are condensed by the condensing optical system 114.

  Here, the optical coupling element 212 is a polarization beam splitter. With respect to the optical coupling element 212, as shown in FIG. 11, the polarization directions of the laser light output from the laser oscillator 111 and the laser light output from the ultrasonic generator laser oscillator 211 are orthogonal to each other, and are almost 100%. It is desirable to obtain a coupling efficiency.

<Summary>
As described above, according to the present embodiment, energy can be efficiently used by using the high-output laser oscillator 111 and the low-output ultrasonic generator laser oscillator 211 in combination.

  Instead of the ultrasonic wave generation laser oscillator 211 and the light modulation element 112, a device that oscillates a pulse laser may be used.

  A dichroic mirror may be used instead of the polarization beam splitter.

(Embodiment 3)
Embodiment 3 according to the present invention will be described below with reference to the drawings. The configuration of the laser welding apparatus in the third embodiment is the same as that of laser welding apparatus 100 in the first embodiment. The method for modulating the intensity of the laser beam and the method for calculating the amount of penetration are different from those of the laser welding apparatus 100 in the first embodiment. Therefore, operations and effects peculiar to the laser welding apparatus according to the third embodiment will be described using the laser welding apparatus 100 shown in FIG.

<Overview of difference from Embodiment 1>
In laser welding apparatus 100 according to the first embodiment, light modulation element 112 modulates laser light into a pulse wave, burst wave, chirp wave, etc., and is generated from workpiece 101 irradiated with the modulated laser light. Detect ultrasound. In this case, the amount of penetration of the weld 102 is specified based on the time when the laser beam is modulated and the time when the ultrasonic wave is detected.

  On the other hand, in the laser welding apparatus according to the third embodiment, the light modulating element 112 modulates the laser light into a sine wave having a constant frequency and a known phase, and the welded material 101 irradiated with the modulated laser light. Detects ultrasonic waves generated from. In this case, the amount of penetration of the weld 102 is specified based on the phase of the modulated laser beam and the detected phase of the ultrasonic wave.

<Light modulation element 112>
First, the light modulation element 112 according to the third embodiment will be described. A sine wave having a constant frequency generated from the signal generator 119 is input to the light modulation element 112. At this time, the laser light output from the laser oscillator 111 at a constant intensity is modulated by the light modulation element 112 so as to have a waveform in which a constant frequency sine wave is superimposed on a constant intensity signal, as shown in FIG. The Since a sine wave having a constant frequency is output from the signal generator 119, the trigger signal from the trigger generator 120 may be generated only when the signal generator 119 starts to output a signal.

<Penetration amount>
Next, the amount of penetration of the welded portion 102 will be described. The bottom of the molten pool 103 shown in FIG. 1 (the bottom of the keyhole 104) is irradiated with a laser beam modulated into a sine wave having an intensity peak at a constant period (frequency). For this reason, the bottom of the molten pool 103 repeats thermal expansion and contraction at the same frequency as the sine wave of the irradiated laser beam. At this time, an ultrasonic wave 105 having the same frequency as the frequency of the laser light modulated into a sine wave is generated and propagates inside the workpiece 101. The propagated ultrasonic wave 105 is detected by the piezoelectric element 115. A graph showing the time change of the intensity of the laser beam output from the light modulation element 112 is shown on the upper side of FIG. 13, and a graph showing the time change of the amplitude of the ultrasonic wave (detection signal) detected by the piezoelectric element 115 is shown in FIG. Shown below.

  As shown in FIG. 13, the phase of the ultrasonic wave 105 detected by the piezoelectric element 115 has a phase delay Φ with respect to the phase of the sine wave of the irradiated laser light. The phase delay Φ of this detection signal depends on the speed V at which ultrasonic waves propagate through the workpiece 101 (ultrasonic propagation speed) V and the linear distance L2 from the bottom of the keyhole 104 to the piezoelectric element 115 shown in FIG. Dependent. Further, the phase delay Φ of the detection signal is a system delay α from when the ultrasonic wave detected by the piezoelectric element 115 is converted into a signal to when it is converted into waveform data by the amplifier 116 and the A / D converter 117. Is included. From these facts, the phase delay Φ and the linear distance L2 can be expressed by the following equation (3). Therefore, the linear distance L2 can be calculated by obtaining the phase delay Φ from the detection signal. Since the system delay α is constant, it can be specified by calibration. Further, the ultrasonic propagation velocity V is obtained in advance.

  Further, the depth D of the keyhole 104 can be calculated from the equation (2) shown in the first embodiment. Therefore, the following equation (4) can be obtained from the equations (2) and (3).

なお、Ｌ１は、図１に示した被溶接材１０１のレーザ照射位置（溶接位置）から圧電素子１１５までの水平距離であり、予め求めておく。

L1 is a horizontal distance from the laser irradiation position (welding position) of the workpiece 101 shown in FIG. 1 to the piezoelectric element 115, and is obtained in advance.

  By substituting the phase delay Φ of the detection signal into the above equation (4), the depth D of the keyhole 104, that is, the amount of penetration of the weld 102 can be measured.

  By the way, as shown in the lower graph of FIG. 13, the detection signal detected by the piezoelectric element 115 includes noise depending on the detection sensitivity of the piezoelectric element 115, and when the welded material 101 is melted or evaporated. Many noises such as noise caused by generated vibrations are included. The phase delay Φ cannot be detected with high accuracy from a detection signal including noise. Therefore, Fourier transform is performed on the detection signal at the frequency of the sine wave generated by the signal generator 119.

  Specifically, the detection signal at a time Δt in a certain range is cut out, applied with a window function such as a Hanning window, and then Fourier transformed to correspond to the frequency of the sine wave of the laser light included in the detection signal. Obtain component signals. Thereby, noise can be removed from the detection signal, and only the same frequency as the sine wave of the laser beam can be acquired. At the same time, the phase of the sine wave of the detection signal can be obtained by Fourier transform. Therefore, the phase delay Φ of the detection signal can be obtained by comparing the phase of the sine wave in the irradiated laser beam and the phase of the sine wave in the detection signal. In addition, although phase delay (PHI) is calculated | required in the range of 0-2 (pi), it can also be calculated | required by the value of-(infinity)-+ (infinity) by phase-coupling using the information of time. In addition, the phase delay at time 0 is defined as a system delay α.

  It is possible to calculate the depth D of the keyhole 104 by substituting the obtained phase delay Φ into the equation (4).

<Summary>
As described above, according to the present embodiment, the laser light output at a constant intensity from the laser oscillator 111 is modulated by the light modulation element 112 so as to be a sine wave having a constant frequency. Further, only a signal having the same frequency as the frequency of the modulated laser beam is extracted by performing Fourier transform on the detection signal detected by the piezoelectric element 115. As a result, noise included in the detection signal can be removed, and ultrasonic waves generated at the bottom of the molten pool 103 can be detected with high accuracy. For this reason, even when the S / N ratio of the piezoelectric element 115 is poor, it is possible to measure the amount of penetration with high sensitivity.

  Further, when the phase of the detection signal is obtained without performing Fourier transform, the phase of the detection signal is obtained by using information at a specific point such as the time when the peak of the detection signal occurs. In this case, it is not easy to detect the phase of the detection signal by accurately matching the peak of the detection signal and the time when the detection signal occurs, and it is difficult to accurately determine the phase of the detection signal because it includes a measurement error. It is. On the other hand, when the Fourier transform is performed as in the third embodiment, the phase of the detection signal is obtained using information of the detection signal at a time Δt in a certain range. For this reason, it is not necessary to accurately correspond the peak of the detection signal to its occurrence time, and since the phase of the detection signal is obtained based on information of a plurality of points, the detection accuracy is improved compared to the case where Fourier transform is not performed. It becomes possible to raise.

<Others>
As shown in FIG. 7, the ultrasonic wave 105 may be detected using an optical interferometer 125 instead of the piezoelectric element 115. Since the ultrasonic wave 105 can be detected in a non-contact manner, the horizontal distance L1 from the position of the welded portion 102 to the irradiation position of the optical interferometer 125 can be made constant. Moreover, since it is non-contact, the influence of the heat from the welding part 102 can be reduced and the measurement error by the thermal expansion etc. of the optical interferometer 125 can be made small. In general, the optical interferometer 125 is one or more orders of magnitude worse than the piezoelectric element 115. However, according to the third embodiment, even when the sensitivity of the optical interferometer 125 is poor, the phase of the detection signal can be obtained with high accuracy. For this reason, even if the optical interferometer 125 whose sensitivity is lower than that of the piezoelectric element 115 is used, the amount of penetration of the weld 102 can be measured with high accuracy.

  Further, the laser welding apparatus in the third embodiment may have the same configuration as the laser welding apparatus 200 in the second embodiment shown in FIG. In this case, the laser light output from the ultrasonic generator 211 is modulated into a sine wave having a constant frequency by the light modulation element 112.

  As described above, by using the high-output laser oscillator 111 and the low-output ultrasonic generator laser oscillator 211 in combination, energy can be used efficiently.

  INDUSTRIAL APPLICABILITY The present invention is used as a laser welding apparatus that evaluates the quality of a welded part when welding using laser light, particularly as a laser welding apparatus that evaluates quality by monitoring the penetration depth, laser output, and the like. be able to. Specifically, since it has a function of guaranteeing the welding quality in a non-destructive manner, it can be used as a laser welding apparatus for automobiles and electronic parts.

DESCRIPTION OF SYMBOLS 100 Laser welding apparatus 101 To-be-welded material 102 Welding part 103 Weld pool 104 Keyhole 105 Ultrasonic wave 111 Laser oscillator 112 Light modulation element 113 Laser light transmission optical system 114 Condensing optical system 115 Piezoelectric element 116 Amplifier 117 A / D converter 118 Computer 119 Signal Generator 120 Trigger Generator 121 Stage Controller 122 Moving Stage 125 Optical Interferometer 200 Laser Welding Device 211 Laser Generator 212 for Ultrasonic Wave Generation Optical Coupling Element

Claims (15)

A laser welding apparatus for welding a welded portion with laser light,
Laser output means for forming a keyhole by irradiating the weld with a laser beam having a peak in intensity and generating an ultrasonic wave at the bottom of the keyhole ;
Ultrasonic detection means for detecting ultrasonic waves generated at the bottom of the keyhole by the laser light irradiated by the laser output means;
Based on the ultrasonic waveform detected by the ultrasonic detection means, a calculation means for calculating the amount of penetration of the weld,
A laser welding apparatus comprising: an evaluation unit that evaluates a welding quality of the welded portion based on a penetration amount calculated by the calculation unit. The laser output means,
A laser oscillator that continuously outputs a laser beam for melting the welded portion at a constant intensity;
A light modulation element that modulates the laser light output from the laser oscillator so that a peak occurs in the intensity of the laser light;
The laser welding apparatus according to claim 1, further comprising: an optical system that collects the modulated laser light and irradiates the welded portion. The laser output means,
A first laser oscillator for continuously outputting a first laser beam for melting the welded portion at a constant intensity;
A second laser oscillator that continuously outputs a second laser beam having an intensity different from that of the first laser beam at a constant intensity;
A light modulation element that modulates the second laser light such that a peak occurs in the intensity of the laser light;
An optical coupling element for coupling the first laser beam and the modulated second laser beam;
The laser welding apparatus according to claim 1, further comprising an optical system that collects the combined laser beam and irradiates the welded portion. 4. The laser according to claim 2, wherein the light modulation element outputs a laser beam in which a pulse wave is generated at an intensity of the laser beam before modulation as a laser beam after modulation. Welding equipment. 4. The laser according to claim 2, wherein the light modulation element outputs a laser beam in which a burst wave is generated at an intensity of the laser beam before modulation as a laser beam after modulation. 5. Welding equipment. 4. The laser according to claim 2, wherein the light modulation element outputs a laser beam in which a chirp wave is generated at an intensity of the laser beam before modulation as a laser beam after modulation. 5. Welding equipment. 4. The laser according to claim 2, wherein the light modulation element outputs laser light in which a sine wave is generated in intensity of the laser light before modulation as laser light after modulation. Welding equipment. The laser welding apparatus according to any one of claims 1 to 7 , further comprising a control unit that controls an output intensity of the laser beam of the laser output unit based on a result evaluated by the evaluation unit. A laser welding method for welding a weld with a laser beam,
A first step of forming a keyhole by irradiating the weld with a laser beam having a peak in intensity and generating an ultrasonic wave at the bottom of the keyhole ;
A second step of detecting ultrasonic waves generated at the bottom of the keyhole by the laser light irradiated in the first step;
A third step of calculating the amount of penetration of the weld based on the waveform of the ultrasonic wave detected in the second step;
And a fourth step of evaluating the welding quality of the welded portion based on the penetration amount calculated in the third step. The laser welding method according to claim 9 , wherein in the first step, a laser beam that melts the weld is modulated to generate a peak in the intensity of the laser beam. The laser welding method according to claim 10 , wherein in the first step, the laser beam is modulated so that a pulse wave is generated in the intensity of the laser beam. 11. The laser welding method according to claim 10 , wherein in the first step, the laser beam is modulated so that a burst wave is generated in the intensity of the laser beam. The laser welding method according to claim 10 , wherein in the first step, the laser beam is modulated so that a chirp wave is generated in the intensity of the laser beam. The laser welding method according to claim 10 , wherein in the first step, the laser beam is modulated so that a sine wave is generated in the intensity of the laser beam. The laser welding method according to any one of claims 9 to 14, further comprising a fifth step of controlling the output intensity of the laser beam based on the result evaluated in the fourth step.

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