WO2018185973A1

WO2018185973A1 - Laser processing monitoring method and laser processing monitoring device

Info

Publication number: WO2018185973A1
Application number: PCT/JP2017/042882
Authority: WO
Inventors: 淳梁瀬; 雄祐西崎
Original assignee: 株式会社アマダミヤチ; 株式会社アマダホールディングス
Priority date: 2017-04-04
Filing date: 2017-11-29
Publication date: 2018-10-11
Also published as: JPWO2018185973A1

Abstract

This laser processing monitoring device is a monitoring device of a laser processing machine which performs desired laser processing by radiating a laser beam LB onto a given metal workpiece W and melting the workpiece W by means of laser energy, wherein the laser processing monitoring device comprises: a laser oscillator 10; a laser power source 12; a control unit 14; a guide light generating unit 15; transmission optical fibers 16, 17; a head 18 (emitting unit 24, sensor unit 26); an operating panel 20; and a monitoring unit 25. The monitoring unit 25 is a laser monitoring device in a mode of embodiment of the present invention, and is configured to include mainly the control unit 14, the operating panel 20, a sensor signal processing unit 22 and the sensor unit 26, for example.

Description

Laser processing monitoring method and laser processing monitoring device

The present invention relates to a laser processing monitoring method and a monitoring apparatus used for monitoring laser processing performed by irradiating a workpiece with pulsed laser light and melting the workpiece with laser energy. More specifically, the present invention relates to a laser processing monitoring method and a monitoring apparatus that enable simple and appropriate monitoring of the influence of various factors related to the processing characteristics of laser processing.

Monitoring at the time of laser processing can be broadly divided into a method for monitoring the output of laser light before being incident on the workpiece, and the state of the processing location after the laser light is incident on the workpiece. There is a way to do it. As a method for monitoring the state of the latter processing part, there are a method of directly observing the processing part itself by a method such as continuous imaging of the processing part, image analysis and monitoring, and heat and light generated at the processing part. Can be divided into methods of observing. Among them, the method of observing the heat and light generated at the processing location is further monitored by the method of monitoring the plasma light generated near the processing location, the reflected light from the workpiece and the amount of penetrating beam from the workpiece. A method of monitoring the amount of infrared rays from the workpiece, a method of monitoring the temperature of the surface of the workpiece, a method of monitoring the sound during processing of the workpiece, and the like. In any case, by detecting these, the homogeneity and strength of the welded joint line (seam), groove gap, bead shape, weld pool and keyhole shape, weld surface temperature, bead surface defects, penetration depth It is an object to recognize or predict the processing characteristics related to the welding quality such as.

The monitoring method based on image analysis using an image sensor directly observes the shape of the weld pool as an image, and thus has an advantage of easily grasping the quality of welding quality at a glance, but is expensive in hardware and software. The monitoring method that performs signal processing of plasma light generated in the vicinity of the machining location is strongly influenced by the shielding gas that is injected into the workpiece location, and accurately reflects the machining effect on the workpiece. There is a problem that it is difficult to say. The monitoring method that processes the reflected light from the workpiece using a photoelectric conversion element can make hardware and software relatively simple, but the reflected light from the workpiece is processed into the workpiece. In principle, it includes simple reflected light of the laser beam before the influence occurs, that is, the laser beam before the workpiece is melted. Therefore, the influence of various factors related to the processing characteristics of laser processing is appropriately monitored. There is a problem that it is difficult.

Infrared radiation from the weld bead is signal-processed by converting the radiation energy into a temperature correlation value by an infrared radiation thermometer incorporating a photoelectric conversion element and displaying the intensity, but converted into a temperature correlation value. When displaying the intensity, there is a problem that the processing influence on the workpiece cannot be evaluated especially in the case of fine laser processing. The method of monitoring the sound during welding is a method of detecting and displaying the sound generated from the work site by an acoustic element, but there is a problem that external noise can be detected.

In addition, a method of performing keyhole welding with a pulsed laser, wherein a single wavelength infrared ray having a wavelength capable of detecting a keyhole formed in a molten pool is selected from infrared rays emitted from a welded portion. It has also been proposed to measure the reflected light intensity with a second light receiving device and determine the quality of a welded part based on both values while measuring with one light receiving device. (Patent Document 1)

It has also been proposed to detect the emission intensity of a specific wavelength in the visible light from the molten pool and determine the welding state based on the detected emission intensity. (Patent Document 2)

International Publication No. 2013/171848 JP 2017-24046 A

Although efforts have been made to monitor the amount of infrared rays from the workpiece, all of them have been able to detect and display only the radiation emitted from the workpiece during laser processing and display it with high accuracy. It was not what was done.

In general, the method of monitoring radiated light including infrared light is a method of displaying radiant thermometer by converting the radiated light generated near the processing point into a temperature correlation value in signal processing using photoelectric conversion elements. Yes, it can be determined whether the workpiece has melted by comparing the measured temperature with the melting point, but it is impossible to capture even the subtle behavior or dynamic change of the melted part, which affects the processing effect on the workpiece. When trying to monitor closely, accuracy and reliability are low.

In the conventional laser processing monitoring device, when monitoring infrared light as radiated light, the intensity of the detected radiated light is converted into temperature on the device side and displayed. The method of converting the temperature of synchrotron radiation has the merit that it is easy for the user to intuitively grasp the state of the processed part, but the energy amount actually related to the processed part increases exponentially with respect to the temperature. It is difficult for the user to grasp the fluctuation of energy related to the workpiece near the melting point of the workpiece, and it is difficult to monitor the influence of various factors related to the machining characteristics in a simple and accurate manner, especially in micro laser machining. Met.

If you try to visualize the actual machining status of the part to be processed by detecting infrared light, the infrared light emitted from the part to be processed will generate a lot of noise components, especially when the metal melts. In the process of detecting and displaying the increasing energy amount from infrared light, it is necessary to perform appropriate signal processing.

The present invention solves the above-described problems of the prior art, and provides a laser processing monitoring method and a laser monitoring apparatus that enable simple and accurate monitoring of laser processing involving melting of a metal workpiece.

The laser processing monitoring method of the present invention is a laser processing monitoring method that involves irradiating a metal workpiece with a laser beam and causing the workpiece to melt, wherein the workpiece is irradiated during the laser beam irradiation. A first step of receiving radiated light generated from near the processing point and photoelectrically converting radiated light in a predetermined wavelength band included in the radiated light to generate an analog sensor output signal representing the intensity of the radiated light A second step, a third step of converting the waveform of the sensor output signal into digital waveform data without impairing the intensity change, and visualizing and displaying the waveform of the sensor output signal based on the waveform data. And a fourth step.

The laser processing monitoring device of the present invention is a laser monitoring device for irradiating a metal workpiece with laser light to monitor laser processing accompanied by melting of the workpiece, and during the irradiation of the laser light Receiving the radiated light generated near the processing point of the workpiece, photoelectrically converting the radiated light in a predetermined wavelength band included in the radiated light, and outputting an analog sensor output signal representing the intensity of the radiated light. A light receiving unit for generating, a signal processing unit for converting the waveform of the sensor output signal into digital waveform data without losing an intensity change, and a display for visualizing and displaying the waveform of the sensor output signal based on the waveform data Part.

In the present invention, the waveform of the sensor signal representing the intensity of the radiated light in a predetermined wavelength band included in the radiated light generated from the vicinity of the processing point of the metal workpiece during laser processing is visualized without losing the intensity change. Since it is displayed, it is possible to perform simple and accurate monitoring of the processing state of laser processing, the quality of processing, and the like from the displayed waveform itself.

According to the laser processing monitoring method or the laser processing monitoring apparatus of the present invention, it is possible to easily and accurately monitor laser processing that involves melting of a metal workpiece to be welded by the configuration and operation as described above. .

It is a block diagram which shows the whole structure of the laser processing apparatus containing the laser processing monitoring apparatus in one Embodiment of this invention. It is a graph which shows the radiation spectrum distribution of a black body. It is a figure which shows the spectral distribution of the infrared intensity emitted from the fusion | melting part by irradiating a pulsed laser beam to stainless steel. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of the embodiment for the first example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of embodiment about 2nd Example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of embodiment about the 3rd Example. It is a figure for demonstrating the sample of a 4th Example typically. It is a figure for demonstrating the sample of a 4th Example typically. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of the embodiment for the first sample of the fourth example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of the embodiment for the second sample of the fourth example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of the embodiment for the third sample of the fourth example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of the embodiment for the fourth sample of the fourth example. It is a figure which shows the monitoring display waveform of the sensor output signal obtained by the laser processing monitoring apparatus of embodiment about the 5th Example. It is a block diagram which shows the structure of the signal processing system in the laser processing monitoring apparatus of embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[Configuration and operation of the entire device]

FIG. 1 shows the overall configuration of a laser processing apparatus incorporating a laser processing monitoring apparatus according to an embodiment of the present invention. This laser processing apparatus irradiates a given workpiece W with CW laser light or pulsed laser light LB, and melts the workpiece W with laser energy to perform desired laser processing or laser melting processing. And includes a laser oscillator 10, a laser power source 12, a control unit 14, a guide light generation unit 15, transmission

optical fibers

16 and 17, a head 18, an operation panel 20, and a monitor unit 25. The monitor unit 25 is a laser monitoring apparatus in this embodiment, and mainly includes the control unit 14, the operation panel 20, the sensor signal processing unit 22, the sensor unit 26 of the head 18, and the like.

The laser oscillator 10 is composed of, for example, a YAG laser, a fiber laser, or a semiconductor laser. When performing laser spot welding on the workpiece W, for example, power or an excitation signal is supplied from the laser power source 12 under the control of the control unit 14. The supplied laser beam oscillates and outputs a laser beam LB having a wavelength specific to the medium. The laser beam LB oscillated and output by the laser oscillator 10 is transmitted to the head 18 through the optical fiber 16.

The head 18 has two cylindrical units, that is, a lower emission unit 24 and an upper sensor unit 26 that are coaxially connected in two vertical stages, and is installed or arranged, for example, directly above the workpiece W. Is done. The emission unit 24 is optically connected to the laser oscillator 10 via the transmission optical fiber 16, and a collimator lens 28, a dichroic mirror 30, an optical lens 32, and a protective glass 34 are provided at predetermined positions in the unit. ing. At the time of laser processing, the laser beam LB propagating through the optical fiber 16 exits in the horizontal direction with a certain spread angle from the end surface of the optical fiber 16 in the emission unit 24, passes through the collimating lens 28, and becomes parallel light. Then, the optical path is bent vertically downward by the dichroic mirror 30, passes through the optical lens 32, and converges and enters the vicinity of the processing point P of the metal workpiece W. Then, the vicinity of the processing point P is melted and solidified by the laser energy of the laser beam LB, and a weld nugget and a weld joint is formed there. The weld joint is optional, such as a butt joint, a T-shaped joint, an L-shaped joint, or a lap joint, and is selected by the user.

The sensor unit 26 is optically connected to the guide light generating unit 15 via the transmission optical fiber 17, and a dichroic mirror 36, an optical lens 38, an infrared sensor 40, and an amplifier 42 are provided in the unit. In the infrared sensor 40 in this embodiment, a wavelength filter or a band-pass filter 44 that transmits only light LM having a wavelength in a specific band and blocks other light is disposed in the preceding stage, and a photoelectric conversion element is disposed in the subsequent stage. For example, a photodiode 46 is arranged.

The visible light guide light MB propagating through the optical fiber 17 from the guide light generating unit 15 is emitted vertically by the dichroic mirror 36 when the sensor unit 26 exits in the horizontal direction with a certain spread angle from the end face of the optical fiber 17. The optical path is bent downward, and the vicinity of the processing point P of the workpiece W is irradiated through the optical lens 38, the dichroic mirror 30 in the emission unit 24, the optical lens 32, and the like.

On the other hand, at the time of laser processing, electromagnetic waves (light) having a broadband wavelength are emitted from the vicinity of the processing point P of the workpiece W. Of the electromagnetic waves radiated from the workpiece W that travel vertically upward, the light that has passed through the optical lens 32 and dichroic mirror 30 in the output unit 24 further passes through the optical lens 38 and dichroic mirror 36 in the sensor unit 26. The light LM having a wavelength component in a predetermined band selected by the band pass filter 44 is incident on the light receiving surface of the photodiode 46.

The photodiode 46 photoelectrically converts the received light LM and generates a sensor output signal CS as a current output. The sensor output signal CS of this current output is converted into a voltage signal by the current-voltage conversion circuit 100 (FIG. 13), and then amplified by the amplifier 42 with a gain designated by the control unit 14. The voltage sensor output signal CS output from the amplifier 42 is converted into a current signal by the voltage-current conversion circuit 102 (FIG. 13), and is transmitted to the sensor signal processing unit 22 via the sensor cable 48.

In this embodiment, the transmission wavelength band set in the band-pass filter 44 of the infrared sensor 40 is comprehensively taken into consideration in terms of sensitivity, versatility, cost, etc. in the monitoring method using a single photodiode 46. A plurality of types of materials that can be selected for the workpiece W and a wide variety of processing forms are selected as the most suitable band for capturing the influence of predetermined factors on the welding characteristics near the processing point as the intensity or change of the radiant energy. .

In this regard, a well-known black body radiation spectrum distribution as shown in FIG. 2 can be suitably used. As shown in the graph of FIG. 2, there is a certain relationship between the spectrum of the electromagnetic wave radiated by the black body and the surface temperature. When the temperature of the object is high, the peak of the radiant energy shifts to a short wavelength, and when the temperature is low, It shifts to wavelength and the peak radiant energy changes exponentially with changes in temperature. According to this graph, the wavelength of the peak point of the energy density emitted from a black body at a temperature of 1500 ° C. is about 1800 nm.

On the other hand, the inventor has various intensities (relative count values) of light of 1000 nm or more detected when laser light is irradiated on ferrous stainless steel (melting point is about 1500 ° C.) with respect to the processing point. FIG. 3 shows the results of measurement from various angular positions and analysis of the spectrum distribution using a spectrum analyzer. The display waveform of the spectrum analyzer shows each peak value as a relative intensity without distinguishing with time the detected light intensity of 1000 nm or more. Although the waveform shown showed different intensity depending on the angular position at the time of measurement, a certain characteristic was obtained. According to this, the intensity (radiant energy density) of infrared rays emitted from the melted portion of the stainless steel is characterized by a sharp mountain shape over a band of about 1000 nm to 1100 nm and a broad mountain shape over a band of about 1200 nm to 2500 nm. It has. Paying attention to the characteristics of the latter broad mountain shape, the wavelength of the peak point is about 1800 nm, which is approximately approximate to the wavelength (about 1800 nm) of the peak point of the energy density emitted from the black body at a temperature of 1500 ° C.

From this, with respect to a plurality of types of metals that can be assumed as the material of the workpiece W, the melting point of each of the metals is used as an index, so that the single photodiode 46 is used with reference to the graph of FIG. A practically optimal transmission wavelength band in the monitoring method can be determined.

In this embodiment, the melting points of iron-based metal, copper-based metal, and aluminum-based metal, which are main materials for laser melting, are approximately 1500 ° C., 1000 ° C., and 600 ° C., respectively. Thus, the band of 1.3 μm (1300 nm) to 2.5 μm (2500 nm) is the transmission wavelength band of the infrared sensor 40. A photodiode whose sensitivity corresponds fully to the selected transmission wavelength band may be used (in this case no separate filter is required), but a photodiode 46 that detects a wider transmission wavelength band is used. May be. In the latter case, for example, a band-pass filter 44 that transmits only the radiated light in the band of 1300 nm or more may be provided on the front side of the photodiode 46, and the radiated light in the band longer than 2500 nm is similarly 2500 nm or less. A band-pass filter 44 that transmits only the radiated light in the band may be provided. Thereby, 1300 nm of the metal welding material shown in FIG. 3 among the radiated light from the metal welding material considered to have a correlation between the black body radiation spectrum distribution shown in FIG. 2 and the spectral radiant energy density. It is possible to monitor all broad chevron portions over a band of ˜2500 nm as specific wavelengths.

The monitor unit (laser processing monitoring device) 25 in this embodiment detects all the emitted light generated in the band of 1300 nm to 2500 nm as the wavelength band suitable for the metal workpiece, and displays the detected intensity of the emitted light as it is. Therefore, it is possible to detect with high sensitivity the amount of energy that exponentially increases in relation to the processed part. In addition, monitoring of synchrotron radiation from the processing point for differences in the material of the welded material, the presence or absence of fine gaps in the welded part, and differences in the tens of watts or 10 millisecond units on the laser machine side Can be grasped by the waveform.

In the above-described embodiment, an example has been described in which all radiated light generated in the wavelength band of 1300 to 2500 nm is detected. However, the width of the radiated light band to be detected is referred to the radiation spectrum distribution from the black body in FIG. It is also possible to detect all radiation emitted from an arbitrary width. For example, the entire width of the wavelength band of at least 300 nm may be detected from the light generated at the processing site. When a wavelength bandwidth of 1800 to 2100 nm is selected and detected as a wavelength bandwidth of at least 300 nm, from FIG. 2, the peak of the emitted light generated from the black body at 1500 ° C. and the radiation generated from the black body at 700 ° C. The intensity of light on the left side of the spot that falls to the left of the light peak is monitored. In this case, there is a possibility that a problem of detection accuracy may occur because the radiation light in a region falling from the peak value of the radiation light generated from the black spot at 700 ° C. may occur, but the wavelength band to be detected has a predetermined width, It is possible to monitor the synchrotron radiation region including the temperature near the melting point of aluminum and the temperature near the melting point of stainless steel.

The sensor output signal CS transmitted from the sensor unit 26 to the sensor signal processing unit 22 via the sensor cable 48 is subjected to current-voltage conversion by the first-stage current-voltage converter 104 (FIG. 13) in the sensor signal processing unit 22. The The sensor output signal CS converted into a voltage signal is converted into a digital signal by the A / D converter 50.

The arithmetic processing unit 52 provided in the sensor signal processing unit 22 includes a hardware or middleware arithmetic processing device, preferably an FPGA (Feed Programmable Gate Array), which can perform specific arithmetic processing at high speed. The instantaneous voltage value of the sensor output signal CS is converted into a count value (relative value) representing the intensity of the emitted light, and the converted value is generated as digital waveform data _DCS . The generated waveform data _DCS is stored in the data memory 54. Arithmetic processing unit 52, based on the waveform data D _CS, via the control unit 14 displays a waveform of the sensor output signal CS on the display of the monitoring panel 20, or the determination also perform processing quality determination to be described later The result is displayed together with the waveform of the sensor output signal CS. The control unit 14 converts the waveform data _DCS and determination result data supplied from the arithmetic processing unit 52 into video signals, and displays the waveform of the sensor output signal CS, determination result information, etc. on the display (display unit 20a) of the monitoring panel 20. The image of is displayed.

As described above, the monitor unit (laser processing monitoring device) 25 in this embodiment is not the return light (reflected light) of the laser light irradiated during laser processing, but the emitted light when the workpiece itself reaches the molten state. As a monitoring target, without changing the temperature of the radiated light, the change in the amount of radiated light during processing is converted into a unique count value for the instantaneous integrated value in a specific band, and It is possible to visualize the influence of machining on the workpiece by converting various changes into count values and displaying them.

The operation panel 20 includes, for example, a display unit 20a formed of a liquid crystal display and a keyboard type or touch panel type input unit 20b, and displays various setting screens and monitor screens under display control of the control unit 14. . In this embodiment, as one of the setting screens, a laser output waveform corresponding to the setting condition of the pulsed laser beam LB can be displayed on the display of the display unit 20a. Further, as one of the monitor screens, as shown in FIG. 4 to FIG. 6 and FIG. 8 to FIG. Visualize and display fine sensor output signal waveforms.

For example, when laser spot welding is performed on a plurality of processing points P set on the workpiece W, the control unit 14 turns on the guide light generation unit 15 to collect the guide light MB on the workpiece W. Irradiate with light. By aligning the spot of the guide light MB with the processing point P, the processing point P can be accurately positioned and the optical axes of the monitoring system and the laser processing system can be accurately adjusted.

When the pulse laser beam LB is oscillated and output from the laser oscillator 10 under predetermined conditions under the control of the control unit 14, the pulse laser beam LB is transmitted to the emission unit 24 of the head 18 via the optical fiber 16. Then, the output unit 24 collects and irradiates near the processing point P of the workpiece W. Thereby, the vicinity of the processing point P absorbs the laser energy of the pulse laser beam LB and melts instantaneously, and electromagnetic waves (mainly infrared rays) of thermal radiation are emitted from the melted portion.

Of the thermal radiation, the light passing through the optical lens 32 in the emission unit 24, the dichroic mirror 30 and the optical lens 38 in the sensor unit 26, and the dichroic mirror 36 as described above is the band pass filter 44 of the infrared sensor 40. Is incident on. The light LM in a specific wavelength band (1300 to 2500 nm) that has passed through the band pass filter 44 is photoelectrically converted by the photodiode 46, and a sensor output signal CS of current output is generated. The sensor output signal CS is subjected to the analog signal processing (current-voltage conversion, amplification, voltage-current conversion, current transmission) as described above and is taken into the sensor signal processing unit 22. In the sensor signal processing unit 22, the sensor output signal CS is subjected to the digital signal processing (current-voltage conversion, analog-digital conversion, voltage-count value conversion) as described above, and the waveform data of the sensor output signal CS. D _CS is generated, and the waveform data D _{CS for} one pulse is stored in the data memory 54. As described above, the value of the waveform data D _CS on the time axis (the instantaneous value) corresponds to the instantaneous value of the radiant energy density of the photoelectric conversion emission light LM (intensity).

Thus when displaying waveforms of the acquired sensor output signal CS and visualization processing unit 52 sends to the sensor output signal control section 14 reads the waveform data D _CS of CS from the data memory 54, the control unit 14 The received waveform data _DCS is converted into a video signal, and the waveform of the sensor output signal CS is displayed as an image on the display unit 20a.

In this embodiment, a photodiode with high light receiving sensitivity, such as an InGaAs photodiode with electronic cooling, is used as the photodiode 46 provided in the sensor unit 26. The advantage of using an InGaAs photodiode with electronic cooling is that the thermal effect on the detection element (photodiode itself) due to radiation detection is very small due to electron cooling, and is proportional to the light intensity of the received radiation LM. The sensor output signal CS of current output can be suitably generated. However, since the emitted light LM is weak light, the sensor output signal CS is also output as a weak small signal. Therefore, as described above, the sensor output signal CS is converted into a voltage signal by the current-voltage conversion circuit 100 and then converted into a signal having a magnitude that can sufficiently reduce the influence of noise by the amplifier 42.

However, if this analog sensor output signal CS is transmitted as a voltage signal from the sensor unit 26 to the sensor signal processing unit 22 separated by several meters or more via the sensor cable 48 (voltage transmission), The signal level is greatly attenuated by the voltage drop, and the waveform is distorted or susceptible to noise. Therefore, the sensor output signal CS is converted into a current signal by the voltage-current conversion circuit 102 in the sensor unit 26 and then transmitted to the sensor signal processing unit 22 via the sensor cable 48. Attenuation, waveform distortion, noise influence, and the like can be suppressed. As a result, it is possible to faithfully transmit the analog sensor output signal CS representing the light intensity of the emitted light LM from the sensor unit 26 to the remote sensor signal processing unit 22, and further within the sensor signal processing unit 22 described above. by subjecting the digital signal processing, such as, you can convert the waveform of the sensor output signal CS generated by the photodiode 46 without compromising the strength change in the digital waveform data D _CS.
[Example]

Hereinafter, some examples obtained by using the laser processing monitoring apparatus of this embodiment will be described with reference to FIGS.

The laser apparatus used in this example is AMADA MIYACHI pulse fiber laser welder ML-3030AS. The workpiece W was formed by arranging two stainless steel plates (SUS304) W ₁ and W ₂ having a thickness of 1.0 mm side by side, and butt welding was performed using a pulsed laser beam. In this butt welding, when the spot diameter of the laser beam is 0.3 mm, the laser output is 500 W, the pulse width is 45 milliseconds, and there is no gap between the workpieces W ₁ and W ₂ (a) And 0. If there is a gap of 0.09mm is 30% of the spot diameter 3mm out with (b), this embodiment the influence of the gap (specific factors) for the processing properties of the butt welding of the workpiece _(W 1, _{W 2)} It was verified how it can be monitored by the laser processing monitoring device of the form. FIG. 4 shows a monitoring display waveform of the sensor output signal obtained in this example.

In FIG. 4, the portion where the waveform is drawn in a zigzag indicates that the metal melted at the portion to be processed and that the turbulence of the radiation from the wave front of the molten pool was detected. The point in time when the waveform that rises to the right on the time axis reaches the apex (the point just before the fall) is the point at which the irradiation of the laser beam is stopped.

Comparing the waveform of (a) when there is no gap at the butt portion with the waveform of (b) when there is a gap, the former (a) has a higher detection start point immediately after the start of the waveform rise, and the waveform fall is lower. It has a characteristic that it is gentle. On the other hand, the latter (b) has a characteristic that the detection start point immediately after the start of the rise of the waveform is low and the fall of the waveform is quick. When there is a gap in the butt portion (b), this phenomenon is caused by the presence of a gap with respect to the spot diameter at the irradiation point because the laser beam is also incident on a place where there is no metal (gap). A phenomenon occurs in which the amount of molten metal that forms the molten pool decreases, and the difference in the amount of molten metal appears as a difference in the amount of radiated light in the radiation detected from the vicinity of the molten pool, and the detection start point immediately after the rise of the waveform The amount of molten metal decreases due to the phenomenon that the evaporated metal stops together with the transmitted light that passes through the gap, so that the falling edge of the waveform is detected quickly when there is a gap. ing.

The laser apparatus used in this example is AMADA MIYACHI pulse fiber laser welder ML-3030AS. The workpiece W was formed by stacking _two stainless steel plates (SUS304) W ₁ and W ₂ having a thickness of 0.3 mm, and lap welding was performed using a pulsed laser beam. In this lap welding, the spot diameter of the laser beam is 0.3 mm, the laser output is 500 W, the pulse width is 45 milliseconds, and there is no gap between the workpieces (W ₁ , W ₂ ) (a) and the workpiece. workpiece _(W 1, _{W 2)} If there is a gap of 0.06mm is 20% of the spot diameter 0.3mm between de and (b), processing of the lap welding of the workpiece _(W 1, _{W 2)} We verified how the presence or extent of the effect of a gap (specific factor) on characteristics can be monitored. FIG. 5 shows a monitoring display waveform of the sensor output signal obtained in this example.

In FIG. 5, the portion where the waveform is drawn in a zigzag indicates that the metal melted in the processed portion and that the radiated light disturbance from the wave front of the molten pool was detected. The point in time when the waveform that rises to the right on the time axis reaches the apex (the point just before the fall) is the point at which the irradiation of the laser beam is stopped.

In this lap welding, when there is a gap of 0.06 mm (b) and when there is no gap (a), it is difficult to identify the intensity change of the radiated light at the right shoulder rising portion of the waveform. In the falling part of the waveform, that is, after the irradiation of the pulse laser was stopped, the waveform falling (b) was gentler in the case where there was a gap than in the case (a) where there was no gap. In the lap welding, when there is no gap in the workpiece (a), the irradiation laser beam melts and penetrates the first metal W1, and then the second metal W2 is shifted to melting. On the other hand, when there is a minute gap in the workpiece (b), there is no gap between the metal layers due to the influence of the air layer existing in the gap. It shows that the falling edge of the waveform is gently detected by being delayed compared to (a).

The laser apparatus used in this example is AMADA MIYACHI pulse fiber laser welder ML-3030AS. The workpiece W was formed by stacking _two sheet materials W ₁ and W ₂ of stainless steel SUS304 having a thickness of 0.3 mm without gaps, and lap welding was performed using a pulsed laser beam of a rectangular wave. In this lap welding, the laser beam spot diameter was 0.3 mm, and the laser output and pulse width were parameters. That is, for the laser output, values in six steps were selected in increments of 50 W from 300 W to 550 W, and values in three steps of 25 ms, 35 ms, and 45 ms were selected for the pulse width. Then, it was verified how the influence of the laser output (first specific factor) and the pulse width (second specific factor) on the processing characteristics of the lap welding of the workpieces (W ₁ , W ₂ ) can be monitored. . A monitoring display waveform of the sensor output signal obtained in this embodiment is shown in FIG.

In FIG. 6, the radiated light intensity indicated by the waveform of the sensor output signal increases proportionally as the laser output set value of the laser light increases, and the waveform of the sensor output signal increases as the laser output set value increases. It is shown that the start of the fall is delayed, and further, as the pulse width is increased, the radiation light intensity (particularly the maximum peak value immediately before the fall) displayed by the waveform of the sensor output signal becomes higher. I can take it. This indicates that the emitted light from the workpiece in laser processing is accurately detected in units of tens of watts and in units of 10 milliseconds.

The laser apparatus used in this example is AMADA MIYACHI fiber laser welder ML-6811C. In this embodiment, the laser output (first specific factor) and the gap (second specific factor) with respect to the welding characteristics in the laser welding processing using the CW laser beam instead of the pulse laser beam as in the first to third embodiments described above. It has been verified how the influence of the above can be monitored by the laser processing monitoring apparatus of the present embodiment.

A typical workpiece W assumes a case where a recess (notch) is formed by laminating and welding a plate material having a notch and a flat material, and the depth of the recess (notch) is defined as a gap. It was.

Specifically, as shown in (a) of FIG. 7A, a superposition of a stainless steel plate _{W 2} of stainless steel plate _{W 1} and the thickness 3.0mm thick 0.3mm vertically Sample (1) It was. On the other hand, as shown in (b) of FIG. 7A, a stainless steel plate W having a thickness of 0.3 mm is placed on two stainless steel plates W _2L and W _2R having a thickness of 3.0 mm arranged at regular intervals. repeated ₁ in crosslinked form, and a stainless steel plate _W _2L, those arranged thin stainless steel plate _{W 2M} so as to form a gap of 3mm below the stainless steel plate _{W 1} between _{W 2R} and sample (2). Similarly, as shown in (c), (d) in Figure 7B of FIG. 7A, by changing the thickness of the stainless steel plate _{W 2M} for gap adjustment, form 2 mm, a gap of 1mm immediately below the stainless steel plate _{W 1} These were used as samples (3) and (4), respectively. In each of the samples (1) to (4), an XY table on which the workpiece W is placed is swept in a certain direction (x direction) to form a line-shaped weld bead on the workpiece W Welding was performed. For each sample (1) to (4), three laser outputs of 200 W, 400 W, and 600 W were selected. The monitoring display waveforms of the sensor output signals obtained for the samples (1) to (4) are shown in FIGS.

Sample (1) is for showing a basic waveform when CW laser irradiation is monitored by the processing monitoring apparatus according to this embodiment, and in FIG. This indicates that the metal is melted at the processing location, and that the radiation turbulence from the molten pool wavefront is detected.

Sample (2) is obtained by assuming that there is a 3.0mm gap on the back side of a portion (middle portion of the x-direction) of the stainless steel plate W ₁ of the front side in the seam welding. In FIG. 9, a hollow or protruding portion in the middle of the waveform seen for each of the three stages of laser output (200 W, 400 W, 600 W) is monitoring laser irradiation to a place where there is a space on the back side of the workpiece. The detection signal at the time is shown.

The reason why the protrusion is generated at 200 W while the recess is generated between 600 W and 400 W can be explained by the relationship between the energy of the irradiation laser and the heat drawing at the processing site. That is, in the case of 200 W, since the laser irradiation energy is generally low, the radiant light is weakened due to the influence of heat drawn toward the metal material on the back side in the lap welding, but the back side metal material in the middle part. It is difficult to draw heat because it is an air layer, and the emitted light is strongly generated by the heat. In the case of 400W and 600W, the situation where heat is difficult to draw because there is no back side metal layer in the middle part is the same as in the case of 200W, but the laser irradiation energy is high overall, so lap welding is performed. This is because the radiated light generated at the location is strong.

Sample (3), the sample (4) is, 2.0 mm each on the back of a portion of the stainless steel plate _{W 1} of the front side in the seam welding (intermediate portion in the x direction), a case where there is a gap of 1.0mm It is assumed. As shown in FIGS. 10 and 11, both sample (3) and sample (4) did not change much when compared with sample (2) at 200 W, but at 400 W and 600 W. In contrast, when the air layer was reduced to 2.0 mm and 1.0 mm, the intensity of the detected indentation, that is, the intensity of the detected radiated light, tended to increase conversely. . This is considered to be because it becomes more difficult for heat to be drawn from the metal layer because the gap of the air layer becomes shorter.

Samples (5), as shown in (e) in FIG. 7B, an air layer formed on the back side of a portion of the stainless steel plate W ₁ of thickness 0.3mm Table side (intermediate portion in the x-direction) Compared with the sample (2) having a gap of 3 mm as shown in FIG. 12, there is almost no difference in waveform characteristics when the laser output is 200 W, and when the laser output is 400 W, as shown in FIG. The waveform level of the gap is slightly higher.

As described above, in this embodiment, the radiation light generated from the vicinity of the processing point of the workpiece (metal) in laser welding is received by the infrared sensor 40 in the sensor unit 24, and the predetermined light included in the radiation light is received. Signal processing system provided in the sensor unit 24 and the sensor signal processing unit 22 connected via the sensor cable 48 to generate an analog sensor output signal CS by photoelectrically converting the radiated light component (LM) in the wavelength band of (Figure 13) into a digital waveform data D _CS waveforms of the sensor output signal CS without impairing the intensity change by monitoring panel 20 the waveform of the sensor output signal CS on the basis of the waveform data D _CS display (20a ) Visualized and displayed above, and the displayed waveform (for example, FIGS. 4 to 6 and FIGS. 8 to 12) is used for the laser welding process. Laser welding processing can be monitored, monitoring of the influence of certain factors related to the processing state or processing quality of the laser welding process, monitoring of the quality of the laser welding process, etc. Simple and accurate monitoring can be made possible.
[Other Embodiments or Modifications]

The preferred embodiments of the present invention have been described above, but the above-described embodiments do not limit the present invention. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and technical scope of the present invention.

For example, although the sensor unit 26 is connected to the emission unit 24 in the above-described embodiment, it is possible to adopt a configuration in which the sensor unit 26 is separated from the emission unit 24 and is arranged in the vicinity of the emission unit 24 as an independent unit. It is.

The laser processing method and laser processing apparatus of the present invention are not limited to laser spot welding, but can also be applied to other laser processing that involves melting, such as laser cutting, laser brazing, laser hardening, and laser surface modification.

DESCRIPTION OF SYMBOLS 10 Laser oscillator 12 Laser power supply 14 Control part 15 Guide light generation part 18 Head 20 Monitoring panel 22 Sensor signal processing unit 25 Monitor part (laser monitoring apparatus)
40 Infrared sensor 44 Band pass filter (wavelength filter)
46 Photodiode (photoelectric conversion element)
42 Amplifier 48 Sensor Cable 50 A / D Converter 52 Arithmetic Processing Unit 54 Data Memory

Claims

A laser processing monitoring method involving irradiating a metal workpiece with laser light and melting the workpiece,
A first step of receiving radiation emitted from near the processing point of the workpiece during irradiation of the laser beam;
A second step of photoelectrically converting radiated light in a predetermined wavelength band included in the radiated light to generate an analog sensor output signal representing the intensity of the radiated light;
A third step of converting the waveform of the sensor output signal into digital waveform data without impairing the intensity change;
And a fourth step of visualizing and displaying the waveform of the sensor output signal based on the waveform data.
The laser processing monitoring method according to claim 1, further comprising a fifth step of monitoring an action of the laser beam in the laser processing based on a waveform of the sensor output signal displayed by visualization.
The laser processing according to claim 1, further comprising: a sixth step of evaluating an influence degree of a predetermined factor related to a processing state or processing quality of the laser processing based on the sensor output signal that is visualized and displayed. Monitoring method.
The laser processing monitoring method according to claim 1, further comprising a seventh step of determining whether the laser processing is good or not based on the sensor output signal that is visualized and displayed.
The second step includes
In the first unit arranged to face the workpiece, receiving the radiated light and performing photoelectric conversion to generate the sensor output signal as a current output;
Current-voltage conversion of the sensor output signal of current output in the first unit;
Amplifying the sensor output signal converted into a voltage signal with a desired gain in the first unit;
The third step includes
Voltage-current conversion of the amplified sensor output signal in the first unit;
Transmitting the sensor output signal converted into a current signal from the first unit to a remote second unit via an electric cable;
Current-voltage conversion of the sensor output signal current-transmitted from the first unit in the second unit;
Analog-to-digital conversion of the sensor output signal converted into a voltage signal;
Obtaining the waveform data by performing voltage-count value conversion on the sensor output signal converted into a digital signal;
Having
The laser processing monitoring method according to claim 1.
The laser processing monitoring method according to claim 1, wherein the radiation light photoelectrically converted in the second step is all radiation light included in a wavelength band of at least 300 nm among the received radiation light.
2. The laser processing monitoring method according to claim 1, wherein the radiated light photoelectrically converted in the second step is all radiated light included in a wavelength band of 1300 nm to 2500 nm among the received radiated light.
A laser monitoring device for irradiating a metal workpiece with laser light to monitor laser processing accompanied by melting of the workpiece,
Receiving radiated light generated near the processing point of the workpiece during irradiation of the laser light, photoelectrically converting radiated light in a predetermined wavelength band included in the radiated light, and expressing the intensity of the radiated light A light receiving unit for generating an analog sensor output signal;
A signal processing unit for converting the waveform of the sensor output signal into digital waveform data without losing the intensity change;
A laser processing monitoring apparatus comprising: a display unit that visualizes and displays a waveform of the sensor output signal based on the waveform data.
The light receiving unit is provided in a first unit arranged to face the workpiece, and at least a part of the signal processing unit is a second unit arranged at a location away from the first unit. The laser processing monitoring device according to claim 8, which is provided in the inside.
The signal processing unit
A first current-voltage conversion circuit for converting the sensor output signal of the current output generated by the light receiving unit into a voltage signal in the first unit;
An amplifier that amplifies the sensor output signal converted into a voltage signal by the first current-voltage conversion circuit with a desired gain in the first unit;
A first current-voltage conversion circuit for converting the sensor output signal amplified by the amplifier into a current signal in the first unit;
An electric cable for transmitting the sensor output signal converted into a current signal by the first voltage-current conversion circuit from the first unit to the second unit;
A second current-voltage conversion circuit for current-voltage converting the sensor output signal that is current-transmitted from the first unit in the second unit;
An analog-to-digital converter for analog-to-digital conversion of the sensor output signal converted into a voltage signal in the second unit;
A voltage-count value converter for converting the instantaneous voltage value of the sensor output signal converted into a digital signal into a count value (relative value);
The laser processing monitoring device according to claim 9, comprising:
A guide light generator for generating guide light that is visible light;
An optical system that is provided in the first unit and that condenses and irradiates the workpiece with the guide light from the guide light generation unit aligned with the optical axis of the light receiving unit;
The laser processing monitoring apparatus according to claim 8, comprising: