JP2021186848A - Laser processing equipment - Google Patents

Abstract

[Problem] To provide a laser processing device capable of monitoring the laser processing state with high accuracy. [Solution] The laser processing device irradiates a workpiece W with a condensed light beam LB to form a melted region M on the surface of the workpiece W, and includes a condenser lens 5 that condenses the light beam LB on the surface of the workpiece W, optical sensors 18-20 that detect light coming from the workpiece W during irradiation with the light beam LB, and a light shielding member 21 that is provided between the condenser lens 5 and the optical sensors 18-20 and attenuates light reflected by the surface of the condenser lens 5 from the light beam LB. [Selected Figure] Figure 1

Description

The present disclosure relates to a laser processing apparatus capable of monitoring a laser processing state.

Laser welding technology irradiates a work piece with laser light emitted from a laser oscillator, melts the work piece with the heat of the laser light, and welds it to another work piece to weld these work pieces. A technology for mechanically and / or electrically connecting. Laser welding technology is generally widespread in a wide range of fields such as home appliances, precision equipment, and automobile parts.

In such laser welding technology, various adjustment items are generally adjusted by trial and error according to the shape and size of individual laser oscillators and workpieces, but processed products of predetermined quality can be obtained. If this is not possible, there are cases where such trial-and-error adjustments cannot be used.

In Patent Document 1, pass / fail judgment is performed by comparing the measured value of the internal information of the processing apparatus with the threshold value set in the provisional judgment unit, and the quality of the actual processed product is fed back to the provisional judgment unit. It is disclosed to update the threshold.

Japanese Unexamined Patent Publication No. 2017-164801

However, in the method for evaluating the processing result according to Patent Document 1, the processing result is evaluated after the processing, and it takes time to obtain the processing result. Further, in the method for evaluating the processing result according to Patent Document 1, even if the processing result can be obtained after the processing and the processing result can be detected to be abnormal, the cause cannot be identified, so that it takes time and effort to deal with the abnormality.

When monitoring the laser machining state in real time, a photodetector is provided to detect the welding light radiated from the molten region of the workpiece. Such welding light has considerably weaker intensity than laser light for processing. In order to increase the detection sensitivity of welding light, it is required to eliminate the influence of stray light of laser light as much as possible.

In view of the above-mentioned conventional problems, the present disclosure aims to provide a laser processing apparatus capable of monitoring a laser processing state with high accuracy.

The laser processing apparatus according to the present disclosure irradiates a work piece with focused laser light to form a molten region on the surface of the work piece.
A condenser lens that concentrates the laser beam on the surface of the workpiece,
A photodetector that detects light coming from the workpiece during irradiation with the laser beam,
It is provided between the condenser lens and the light detection unit, and includes a light-shielding member that attenuates the light reflected by the laser beam on the surface of the condenser lens.

According to the laser processing apparatus according to the present disclosure, the laser processing state can be monitored with high accuracy.

The block diagram which shows the structure of the laser processing apparatus which concerns on embodiment of this disclosure. Explanatory drawing which shows an example of arrangement of a light-shielding member. Explanatory drawing which shows the relationship between a condenser lens and a light-shielding member. Explanatory drawing which shows other example of arrangement of a light-shielding member. Explanatory drawing which shows the optimization design of the position of a light-shielding member. 6 (A) to 6 (C) are plan views showing various examples of the support structure of the light-shielding member. FIG. 6D is a cross-sectional view showing the periphery of the molten region of the workpiece. Explanatory drawing which shows an example of the correlation between the amount of reflected light and welding quality. FIG. 7A is a graph showing the change in the amount of reflected light over time. FIG. 7B is a graph showing the time change of the laser output.

Embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a laser processing apparatus according to an embodiment of the present disclosure. Laser processing is a method of performing welding, cutting, drilling, marking, surface treatment, etching, deposition, etc. using laser light. Here, laser welding is exemplified, but the present disclosure is not limited to this.

The laser processing apparatus includes a laser oscillator 1, an optical fiber 2 for laser light transmission, a collimating lens 4, a partial reflection mirror 7, and a condenser lens 5 as a laser light supply unit, and a laser output sensor 9 as a light detection unit. The light-shielding member 21, the partial reflection mirror 8, the condenser lens 10, the image pickup camera 11, the partial reflection mirrors 12, 13, the reflection mirror 14, the condenser lenses 15 to 17, and the optical sensors 18 to 20 are provided. Many of these components can be accommodated inside the lens barrel 3.

The laser processing apparatus further includes an arithmetic unit PC that controls the entire apparatus.

The laser oscillator 1 is composed of, for example, a gas laser such as a carbon dioxide gas laser, a solid-state laser such as a YAG laser, a semiconductor laser, or a fiber laser, and generates a laser beam having a predetermined wavelength and a predetermined output. As an example, the laser beam is a continuous wave (CW) with a wavelength of 1070 nm. It is possible to select the optimum laser wavelength according to the light absorption characteristics of the workpiece W. For example, when the workpiece W is copper Cu or gold Au, the laser wavelength is relatively relatively such as 405 to 450 nm. Short wavelengths are preferred. Further, when the workpiece W is aluminum, the laser wavelength is preferably about 800 nm because the light absorption characteristics are good and good welding is possible.

Here, the case where a continuous wave is used as the laser light is illustrated, but a pulsed laser light may be used. When a continuous wave laser beam is used, the amount of heat input to the workpiece W can be increased, which is preferable in terms of high productivity. Further, when the laser beam of the pulse wave is used, it is preferable in that the thermal influence at the time of processing can be reduced as compared with the continuous wave.

The laser oscillator 1 is communicably connected to the arithmetic unit PC, and the output of the laser beam can be controlled in response to a command from the arithmetic unit PC, and in the case of a pulse wave, the cycle and duty cycle can also be controlled.

The optical fiber 2 for laser light transmission has a function of transmitting the laser light from the laser oscillator 1 to the inside of the lens barrel 3. As an alternative to the optical fiber 2, the laser beam emitted from the laser oscillator 1 can be guided to the lens barrel 3 by using an optical element such as a mirror.

The collimating lens 4 converts the laser beam emitted from the optical fiber 2 into a parallel light beam LB.

The partial reflection mirror 7 has a function of reflecting most of the light beam LB from the optical fiber 2 and transmitting a part of the light beam LB. As an example, as the partial reflection mirror 4, a mirror such as a dichroic mirror that reflects light in a specific wavelength range and transmits light in a different wavelength range can be used. The partially reflected mirror 7 can select desired optical characteristics according to the reflected wavelength or the transmitted wavelength, and the ratio of the transmitted light amount to the reflected light amount may be changed as needed. The light beam that has passed through the partially reflected mirror 7 is received by the laser output sensor 9 that monitors the output of the laser light. The laser output sensor 9 includes a photodiode, an A / D converter, and the like, and is communicably connected to the arithmetic unit PC, and the detection signal thereof is input to the arithmetic unit PC. The detection signal of the laser output sensor 9 correlates with the laser output of the laser oscillator 1. When the laser output is high, an optical element that attenuates light may be installed in front of the laser output sensor 9. In order to reduce the surface reflection of the sensor or the optical element, the laser beam LB may be arranged at an angle with respect to the traveling direction.

The condenser lens 5 condenses the light beam LB reflected by the partial reflection mirror 7 to form a light spot having a predetermined shape on the surface of the workpiece W. A large amount of heat energy is applied to the irradiation region of the light spot, and the portion exceeding the melting point becomes the melting region M, and for example, welding of the workpiece W is performed.

The workpiece W is supported on a machining stage (not shown) composed of, for example, an XYZθ table. Such a machining stage is communicably connected to the arithmetic unit PC, and the three-dimensional position of the workpiece W and the angle around the optical axis of the optical beam LB can be controlled in response to a command from the arithmetic unit PC.

When scanning the optical beam LB against the workpiece W, 1) a method of moving the processing stage in a predetermined direction at a predetermined speed with the lens barrel 3 and the optical beam LB fixed, and 2) a lens barrel. A method in which 3 is mounted on a scanning mechanism such as a robot arm or a linear stage, and the lens barrel 3 is moved in a predetermined direction at a predetermined speed while the processing stage is fixed. 3) Condensing lens 5 and a workpiece For example, a method of installing an optical scanner such as a galvano mirror between W and 4) a combination of the above methods 1) to 3) can be used. The light beam LB may be irradiated and scanned separately on the workpiece W, but a continuous weld can be formed by simultaneously irradiating and scanning the workpiece W.

The arithmetic unit PC is composed of a computer including a processor, a memory, a mass storage, and the like, and executes various operations according to a preset program.

In the present embodiment, welding light LW generated from the molten region M during irradiation with laser light, for example, a) thermal radiated light LT emitted from the molten region M, b) visible light LV emitted from the molten region M, And c) Three optical sensors 18 to 20 are installed in order to individually detect the reflected light LR reflected from the workpiece W.

A part of the welding light LW generated from the melting region M is incident on the condenser lens 5, passes through the partial reflection mirror 7, and is incident on the partial reflection mirror 8. The partial reflection mirror 8 has a function of reflecting and transmitting incident light at a predetermined ratio. As an example, as the partial reflection mirror 8, a half mirror having no wavelength dependence can be used. As another example, as the partially reflected mirror 8, a dichroic mirror having a wavelength dependence can be used, and the ratio of the amount of transmitted light to the amount of reflected light may be changed according to the wavelength.

The light that has passed through the partial reflection mirror 8 is received by the image pickup camera 11 through the condenser lens 10. The image pickup camera 11 has a function of detecting the light generated from the molten region M during irradiation with the laser beam and imaging the molten region M and its peripheral region. The image pickup camera 11 includes an image sensor, an A / D converter, and the like, and is communicably connected to the arithmetic unit PC, and the detection signal thereof is input to the arithmetic unit PC. The sampling cycle (measurement cycle) of the image pickup camera 11 is preferably 1/100 or less of the time for controlling the output of laser irradiation.

The light reflected by the partial reflection mirror 8 is incident on the partial reflection mirror 12. The partial reflection mirror 12 is composed of, for example, a dichroic mirror, transmits visible light LV, for example, light having a wavelength of 400 to 700 nm among the welding light LW generated from the molten region M, and reflects light having other wavelengths. do. The visible light LV transmitted through the partially reflected mirror 12 is condensed by the condenser lens 15 and received by the optical sensor 18.

The light reflected by the partial reflection mirror 12 is incident on the partial reflection mirror 13. It is composed of a partially reflective mirror 13, for example, a dichroic mirror, and among the welding light LW generated from the molten region M, the heat radiated light LH, for example, the light having a wavelength of 1300 to 1550 nm is reflected, and the light having other wavelengths is transmitted. do. The heat radiant light LH reflected by the partial reflection mirror 13 is collected by the condenser lens 16 and received by the optical sensor 19.

The light transmitted through the partially reflected mirror 13 is incident on the reflected mirror 14. The reflection mirror 14 is composed of, for example, a mirror having no wavelength dependence, and is a reflection of the welding light LW generated from the molten region M excluding the above-mentioned visible light LV and thermal radiation light LH, for example, a wavelength of 1070 nm. Reflects light LR. The reflected light LR reflected by the reflection mirror 14 is collected by the condenser lens 17 and received by the optical sensor 20.

The optical sensor 18 detects the intensity of the visible light LV described above and converts it into an electric signal such as a voltage value or a current value. The optical sensor 19 detects the intensity of the above-mentioned thermal radiation light LH and converts it into an electric signal such as a voltage value or a current value. The optical sensor 20 detects the intensity of the reflected light LR described above and converts it into an electric signal such as a voltage value or a current value. The optical sensors 18 to 20 include a photodiode, an A / D converter, and the like, and are communicably connected to the arithmetic unit PC, and the detection signal thereof is input to the arithmetic unit PC.

In the present embodiment, a case where a dichroic mirror having desired spectral characteristics is used as the partial reflection mirrors 12 and 13 is exemplified, but a half mirror having no wavelength dependence is used as an alternative, and the desired spectroscopy is performed in the subsequent stage. A bandpass filter having characteristics may be arranged. By using a bandpass filter, it is possible to prevent light of an unnecessary wavelength from being incident on the optical sensor, and it is possible to perform light measurement with higher accuracy.

In this embodiment, a configuration is adopted in which three wavelength bands are measured at the same time, which makes it possible to grasp the physical phenomenon generated at the time of welding in detail from light of various wavelengths. Therefore, it is desirable to select the wavelength range of the mirror or lens according to the wavelength to be measured.

Regarding the measurement resolution of the optical sensors 18 to 20, it is desirable that the measurement can be performed with an accuracy of 1/100 or less of the shape of the object to be measured. In particular, it is preferable that the measurement region of the optical sensors 18 to 20 is set so as to include the welding width of the workpiece W. When changing the measurement area, as an example, a method of adjusting the focal length of the condenser lenses 15 to 17 may be used. When, for example, a lens having a focal length of 100 mm is used as the condenser lenses 15 to 17 instead of a lens having a focal length of 200 mm, a region twice the light receiving size of the optical sensors 18 to 20 can be measured. It is preferable to adjust the focal length according to the measurement area selected in this way. As another example, a method of limiting the measurement area by providing an aperture whose opening diameter can be changed is provided immediately before the optical sensors 18 to 20 can also be used.

Next, the photodetection method according to the embodiment of the present disclosure will be described. FIG. 2 is an explanatory diagram showing an example of the arrangement of the light-shielding member 21. The light-shielding member 21 is made of a material having light absorption and heat resistance with respect to the laser wavelength, for example, a metal coated with black alumite or the like, and the condenser lens 5 and the optical sensors 18 to 20, particularly reflection. It is provided between the light sensor 20 for light detection.

Regarding the function of the light-shielding member 21, the light beam LB supplied from the laser oscillator 1 is reflected by the partial reflection mirror 7 and travels downward (−Z direction) toward the workpiece W. Subsequently, when the light beam LB passes through the condenser lens 5, a part of the light beam LB is specularly reflected on the front surface and / or the rear surface of the condenser lens 5 and travels upward (+ Z direction). If the light-shielding member 21 is not present, the surface-reflected light of the light beam LB travels upward as it is, and finally reaches the optical sensors 18 to 20, particularly the optical sensor 20. As a result, stronger light is incident on the optical sensor 20 as compared with the relatively weak reflected light LR, and the S / N ratio of the detection signal is lowered. As a countermeasure, by installing the light-shielding member 21 on the extension of the optical axis of the condenser lens 5, it is possible to attenuate or block the surface reflected light of the light beam LB and prevent it from reaching the optical sensor 20.

In general, surface reflections on lenses and mirrors reflect about 4% of the incident light on the surface without an antireflection coating. Generally, when the workpiece W is a metal, the output of the laser beam required for welding is generally several tens to several tens to several, although it depends on the absorption rate at the laser beam wavelength of the material of the workpiece W and the irradiation conditions. It is in the range of kW. Therefore, when this surface reflection component is large, the amount of light is much larger than the reflected light LR from the molten region M, and the light is detected as return light in the direction toward the optical sensor. In that case, if the amount of light due to surface reflection becomes too large, the S / N ratio of the reflected light LR returning from the molten region M decreases, and it becomes difficult to distinguish it from, for example, a slight output fluctuation of the laser light.

When real-time measurement is performed during welding, the intensity of the reflected light LR returning from the molten region M is important information that largely reflects the shape change of the molten region M. For example, when the shape of the molten region M suddenly changes so that the direction of the reflected light LR approaches the incident direction of the light beam LB, the reflected light component also increases due to this shape change, or the focal point of the light beam LB6. It is possible to monitor a phenomenon in which the diameter of the condensing spot changes due to the change in the position, and the amount of reflected light increases as compared with the case of just focus due to the increase in the welding area of the molten region M.

FIG. 3 is an explanatory diagram showing the relationship between the condenser lens 5 and the light shielding member 21. Surface reflection occurs when the light beam LB is incident on the condenser lens 5. Here, for the sake of easy understanding, the case where the light beam LB is parallel light and has a circular cross section is illustrated, but the same applies to both an elliptical cross section and a rectangular cross section.

As shown in FIG. 3, when the surface of the condenser lens 5 is convex and the light beam LB is incident perpendicular to the condenser lens 5, strictly speaking, the surface reflected light LZ is reflected by the convex mirror. It is reflected so that the beam diameter is widened. When the light beam LB is vertically incident on the lens surface, the angle (angle in the tangential direction) generated by the horizontal plane (XY plane) and the curvature of the lens is defined as θ, and the distance from the condenser lens 5 to the light-shielding member 21 is defined as H. Then, the spread of the beam diameter of the surface reflected light LZ at the position of the light-shielding member 21 becomes H × tan θ × 2.

Therefore, for example, the diameter of the light-shielding member 21 that blocks the surface-reflected light LZ is set to a dimension obtained by adding the spread of the beam diameter H × tan θ × 2 to the diameter of the light beam LB to efficiently block the surface-reflected light LZ. It becomes possible to measure the reflected light component generated when the shape changes in the molten region M with a high S / N ratio. Therefore, by selectively blocking the surface reflected light LZ from the condenser lens 5 when the light beam LB is irradiated, the monitoring accuracy of the welded state is improved.

Further, regarding the surface shape of the condenser lens 5, when the surface on which the light beam LB is incident is a flat surface, the surface reflected light LZ is reflected while remaining substantially parallel. Therefore, it is preferable that the diameter of the light-shielding member 21 is slightly larger than the diameter of the light beam LB in consideration of an error due to mechanical accuracy and the like, but there is no particular limitation.

By preventing the surface reflected light LZ of the light beam LB from reaching the optical sensor in this way, it becomes possible to acquire the reflected light component from the molten region M at a high S / N ratio, and the welded region M becomes possible. The state of can be monitored with high accuracy. Therefore, after laser processing, the shape of the welded part is measured using a microscope or the like, and the presence or absence of welding abnormality is determined by associating the measurement result with the waveform of the signal intensity acquired from the optical sensor. Is also possible. Specifically, regarding the measurement time of the signal intensity acquired from the optical sensor, the time that contributed to the machining is calculated by dividing the welding length of the workpiece W after machining by the machining speed, and the two are compared. It suffices to correlate with, which makes it possible to quantify the change in the weld shape from the fluctuation of the signal intensity value. Regarding the number of measured samples, the physical quantity is required because the laser welding evaluation requires a sufficient number of samples to capture the tendency of the local value of the physical quantity such as the characteristic quantity of the process, for example, the curvature of the curve of the laser output profile. The sampling cycle (measurement cycle) is preferably 1/100 or less of the time for controlling the output of laser irradiation.

FIG. 4 is an explanatory diagram showing another example of the arrangement of the light shielding member 21. In FIGS. 2 and 3, a method of shielding the surface reflected light LZ by using only the light-shielding member 21 has been described, but here, a method of arranging the lenses 23 and 24 on both sides of the light-shielding member 21 will be described.

On the incident side of the light-shielding member 21, a condenser lens 23 for condensing the welding light LW from the workpiece W and the surface reflected light LZ from the condenser lens 5 is provided. On the emission side of the light-shielding member 21, a collimating lens 24 for returning the light condensed by the condenser lens 23 to parallel light is provided. In such an afocal optical system, the focal position of the condenser lens 23 and the focal position of the collimating lens 24 are substantially the same. Since the surface reflected light LZ collected by the condenser lens 23 becomes a conical light flux, the cross-sectional diameter of the surface reflected light LZ and the light shielding member 21 can be adjusted by adjusting the position of the light shielding member 21 along the optical axis. It becomes easy to set the ratio with the diameter of the light to a desired value.

FIG. 5 is an explanatory diagram showing an optimized design of the position of the light shielding member 21. When calculating the focused spot diameter of the surface reflected light LZ, it is generally obtained by an approximate formula of 4 × λ × f / (π × D). Here, λ is the wavelength of light (nm), f is the focal length of the lens, and D is the beam diameter (mm). For example, if λ = 1070 nm, focal length f = 150 mm, and beam diameter D = 6 mm, the spot diameter is about 34 μm, and depending on the conditions, the spot diameter is extremely small compared to the focal length and beam diameter. It is extremely difficult to accurately install the minute light-shielding member 21 at the position, which may cause light-shielding leakage of the surface reflected light LZ and interference of the welding light LW.

As a countermeasure, the light-shielding member 21 is installed between the condenser lens 23 and its focal position, and the diameter of the light-shielding member 21 can be easily handled by considering the cross-sectional diameter of the conical luminous flux corresponding to the position. It is possible to increase the size to a large size. The diameter of the light-shielding member 21 can be calculated by the following formula.
Diameter of light-shielding member 21 = beam diameter-((beam diameter at the position of the condenser lens 23-spot diameter) ÷ focal length f x position from the condenser lens 23)

At this time, various lights such as the inherent light emission of the workpiece W, the heat radiation light due to heat, and the scattered light in the processed portion are distributed from the molten region M22 as welding light LW within the diameter of the condenser lens 5. The light becomes substantially parallel light via the condenser lens 5, and reaches the effective diameter of the condenser lens 23 while being distributed. When the condenser lens is made of glass, chromatic aberration generally exists due to the difference in refractive index for each wavelength. Therefore, when parallel light is condensed by the condenser lens, the light having a short wavelength is more focused than the light having a long wavelength. The distance becomes shorter.

Therefore, by arranging the light-shielding member 21 at a distance shorter than the short-wavelength focal position when parallel light is incident on the condenser lens 23 with reference to the position of the condenser lens 23, the return light of the laser light can be obtained. It is possible to transmit a wavelength region other than the wavelength more efficiently. For example, the beam diameter is 10 mm − (beam diameter 10 mm − spot diameter 1 mm) ÷ 100 mm × 50 mm = 5.5 mm, and by providing the light-shielding member 21 having a diameter of φ5.5 mm, it is possible to block the surface reflected light LZ. .. Further, considering an error due to machine accuracy or the like, it is preferable to make the size slightly larger than the calculated size, but there is no particular limitation. The thickness of the light-shielding member 21 may be about 0.02 to 5 mm, but it is preferable to reduce the thickness of the light-shielding member 21 because only the surface reflected light LZ can be efficiently light-shielded.

6 (A) to 6 (C) are plan views showing various examples of the support structure of the light-shielding member 21. FIG. 6D is a cross-sectional view showing the periphery of the molten region M of the workpiece W. The light beam LB is scanned along a predetermined scanning direction, for example, a direction parallel to the X direction.

The light-shielding member 21 is supported by at least one opaque linear support member 21a, and the support member 21a is arranged so as to be non-parallel to the scanning direction S. In the example shown in FIG. 6A, the light-shielding member 21 is supported by two support members 21a arranged at intervals of 180 degrees, and the support member 21a is along a direction substantially perpendicular to the scanning direction S. Will be placed. In the example shown in FIG. 6B, the light-shielding member 21 is supported by three support members 21a arranged at 135-degree intervals and 90-degree intervals, and one support member 21a is supported with respect to the scanning direction S. The remaining two support members 21a are arranged along a direction substantially parallel to each other, and are arranged along a direction intersecting the scanning direction S at approximately 45 degrees. Each of the support members 21a may be formed with a width and a thickness capable of supporting the light-shielding member 21, and may be, for example, a width of 0.05 to 10 mm and a thickness of about 0.02 to 5 mm. It is preferable that the width and thickness of the support member 21a are small, and the propagation loss of the welding light LW radiated from the melting region M can be reduced as much as possible.

In the example shown in FIG. 6C, the light-shielding member 21 is supported by at least one transparent plate-shaped support member 21b. The support member 21b is made of, for example, optical glass, an optical synthetic resin, or the like. It is preferable that the surface of the support member 21b is provided with an antireflection coating that reduces the reflectance of light other than the wavelength of the laser light. As a result, the propagation loss of the welding light LW radiated from the melting region M can be reduced as much as possible.

As a general welding method, processing is performed while scanning the light beam LB using stage scanning or galvanometer mirror scanning. At this time, the welding light LW emitted from the melting region M is isotropically emitted along the scanning direction. Further, in the molten region M, light of various wavelengths is emitted while remaining in the molten state for a certain period of time after processing. Therefore, interfering with the light emitted along the scanning direction is not preferable for monitoring the molten state because the amount of information to be measured is reduced.

Therefore, as the support structure of the light-shielding member 21, as shown in FIGS. 6A and 6B, the support member 21a is preferably arranged at an angle intersecting the scanning direction S, whereby from the melting region M. The surface reflected light LZ can be shielded without disturbing the emitted / scattered light of the surface.

Next, a method for measuring the welding light LW generated from the melting region M will be described. It is preferable that the detection regions of the optical sensors 18 to 20 are set so as to include all of the melting regions M in the continuous welding process by scanning the optical beam LB. When welding is performed while performing laser scanning, light is emitted according to the input energy even in the molten region M located behind the region irradiated with the light beam LB. Therefore, by setting a region wider than the melting region M as the detection region of the thermal radiation light, for example, the influence of the generation of spatter, the influence of the melt liquid generated from the irradiation of the light beam LB to the solidification, and the like occur at the time of melting. It becomes possible to detect the phenomenon.

The detection signals of the thermal radiant light LT, the plasma visible light LV, and the reflected light LR emitted from the molten region M largely reflect the state of the molten region M. Therefore, for example, by detecting the thermal radiation light LT, the visible light LV, and the reflected light LR in real time under specific processing conditions, it is possible to acquire the signal intensity according to the shape of the molten region M.

For example, when the welding width or the welding length is changed, the strength value of the detection signal of each optical sensor 18 to 20 is different depending on the changed welding width or the welding length. That is, the signal intensity radiated from the melting region M also changes according to the change in the melting area. By utilizing this, it is possible to estimate the shape of the molten region M from the signal intensity of light and to grasp that there is a difference from the shape originally desired to be processed. For example, by measuring or calculating and storing the intensity of light generated during welding at a desired melt width in a preliminary experiment, and then comparing it with the intensity of light in actual welding, the welding state can be made more precise. Can be grasped. Then, by measuring the machined part that has been machined and associating the signal intensity value of the light detected based on this measurement result with the measured value of the welding width, it is possible to detect the measurement result based on the melted area. Become.

In general, the shape of the welded part greatly affects the joint strength, so if the relationship between the welded state and the detection signal can be measured accurately, defects such as joint detachment during welding can be reduced and the quality of the product can be stabilized. be.

Further, the weld shape can be specified by learning the correlation between the signal waveform measured by each of the optical sensors 18 to 20 and the shape measurement result of the welded portion by machine learning. In this case, in a certain welding process, for example, the welding results such as the melt width, the melt length, and the presence or absence of welding defects are used as a teacher data set together with the signal waveforms measured by the optical sensors 18 to 20. Then, the correlation between the signal waveform and the welding result is learned. Such machine learning may be executed on the arithmetic unit PC, or may be executed on an external computer connected by a network.

Further, for example, the cause of the defective phenomenon can be identified by associating the defective phenomenon with the measurement data and determining the threshold value. In addition, by learning by associating the measurement data with the phenomenon that occurs during welding using machine learning, it is possible to determine the state of the molten region M more accurately, and by displaying it on the display, the equipment and equipment can be used. It will be possible to lead to activities to improve processing conditions. That is, by learning the specific factors of the welding failure and the physical quantities related to the welding state using the signal waveforms of the heat radiation LT, the visible light LV, and the reflected light LR according to the present disclosure as an example by machine learning as a teacher data set. , You can learn the correlation between the signal waveform and the cause of poor welding.

Regarding the measuring method, there are the temperature of the machined part, the amount of heat radiated light from the machined part, the amount of visible light of the machined part, the vibration amount of the workpiece, and the like, and a plurality of them may be selected and measured.

FIG. 7 is an explanatory diagram showing an example of the correlation between the amount of reflected light and the welding quality. FIG. 7A is a graph showing the time change of the reflected light amount, and FIG. 7B is a graph showing the time change of the laser output.

The profile PL in FIG. 7B shows the output of the laser beam applied to the workpiece W. Here, an example is illustrated in which the laser output is turned on at time t1, the laser output is constant from time t2 to time t6, and turned off at time t8, but the shape of the profile PL is changed over time according to the processing conditions. By changing it, it is possible to suppress spatter.

As the laser output increases, the amount of reflected light increases. When the laser output is stable and the weld shape is also stable, the signal waveform becomes a constant output. As the laser output decreases, the amount of reflected light also decreases. Therefore, the time change of the reflected light amount has a shape similar to the laser output waveform.

The profile P1 in FIG. 7A is a reflected light profile when the light-shielding member 21 is used. By suppressing the surface reflected light reflected by the light beam LB by the condenser lens 5 by the light shielding member 21, it becomes possible to measure the component of the reflected light LR of the light beam LB at a high S / N ratio, and as a result. It can be seen that the change in the weld shape is largely reflected as the change in the signal waveform.

Therefore, for example, welding is performed while changing various conditions during laser machining to obtain the signal strength of the reflected light in advance, and the upper and lower limits are set for the numerical value of the signal strength, which is obtained by actual machining. It is possible to quantitatively predict and evaluate the machining conditions according to the numerical value of the signal strength. Further, for example, when a hole is formed in the molten region M during welding, the signal intensity of the reflected light is instantaneously increased when the hole is generated. Therefore, by detecting the instantaneous peak of the reflected light during processing, the hole is formed. The cause of the space can be evaluated in real time.

The profile P2 in FIG. 7A is a reflected light profile when the light shielding member 21 is not used. Since the surface reflected light reflected by the light beam LB by the condenser lens 5 is received by the light sensor 20, the detection sensitivity of the light emitted from the molten region M is reduced. Therefore, the detection accuracy in the vicinity of the machined portion is reduced due to the influence of the disturbance on the signal strength.

Known causes of welding abnormalities include, for example, spatter generation, fume generation, plasma generation, laser output fluctuation, spot diameter fluctuation, laser irradiation time fluctuation, and fluctuation caused by the workpiece W. Can be mentioned.

As an example of welding failure, there is a gap defect when a plurality of workpieces W are overlapped. When performing superposition welding in which a plurality of workpieces W are welded by irradiating a laser beam 6 from the overlapping direction, it is preferable to bring the plurality of workpieces W into close contact with each other. The reason is that if there is a gap between the workpieces W due to thermal deformation during laser welding, strain remaining in the workpiece W from before machining, etc., the workpieces W are not joined together. This is because problems such as insufficient strength of the joints occur. When there is a gap between the workpieces W, the molten region M penetrates one of the workpieces W and comes out to the gap. Further, when a gap is generated, the laser beam is scattered in the gap, so that the shape of the molten region M also changes and the welding width becomes narrow. Therefore, a decrease in the intensity of heat radiated light and reflected light is observed.

Therefore, in the case of superposition welding, it is possible to infer the occurrence of gaps between the workpieces W due to the decrease in the reflected light intensity. Therefore, it is necessary to measure the decrease in the intensity of the reflected light with high sensitivity.

As described above, according to the present disclosure, it is possible to accurately monitor the welding state by setting at least two measurement regions on the surface of the workpiece and detecting the light generated from the molten region. .. This makes it possible to evaluate the welding quality with high accuracy, and it is possible to predict welding abnormalities without depending on the skill level of the operator. This enables early response to abnormalities, reduces the number of defects, reduces equipment downtime, and improves productivity.

Further, according to the present disclosure, by providing a light-shielding member that attenuates the light reflected by the light beam on the surface of the condenser lens, the noise light incident on the optical sensor is greatly attenuated. Therefore, it is possible to accurately monitor the welded state of the workpiece.

The present disclosure is extremely useful in industry in that the laser machining state can be monitored with high accuracy.

1: Laser oscillator 2: Optical fiber 3: Lens barrel 4: Collimating lens 5: Condensing lens 7, 8: Partial reflection mirror 9: Laser output sensor 10, 15 to 17: Condensing lens 11: Imaging camera 12, 13: Partial reflection mirror 14: Reflection mirror 18 to 20: Optical sensor 21: Light-shielding member 21a, 21b: Support member LB: Optical beam LW: Welding light M: Melting area PC: Calculation unit W: Work piece

Claims (7)

A laser processing device that irradiates a work piece with focused laser light to form a molten region on the surface of the work piece.
A condenser lens that concentrates the laser beam on the surface of the workpiece,
A photodetector that detects light coming from the workpiece during irradiation with the laser beam,
A laser processing apparatus including a light-shielding member provided between the condenser lens and the light detection unit to attenuate the light reflected by the laser beam on the surface of the condenser lens. The light arriving from the workpiece is at least one of thermal radiation emitted from the molten region, visible light emitted from the molten region, and reflected light reflected from the workpiece. The laser processing apparatus according to claim 1. The laser processing device according to claim 1 or 2, wherein the light-shielding member is positioned on an extension of the optical axis of the condenser lens. The third aspect of claim 3, further comprising a surface-reflecting condensing lens provided between the condensing lens and the light-shielding member for condensing the light reflected by the laser beam on the surface of the condensing lens. Laser processing equipment. The laser beam is scanned along a predetermined scanning direction.
The laser processing according to claim 3 or 4, wherein the light-shielding member is supported by at least one opaque linear support member, and the support member is arranged so as to be non-parallel to the scanning direction. Device. The light-shielding member is supported by at least one transparent plate-shaped support member, and the surface of the support member is provided with an antireflection coating that reduces the reflectance of light other than the wavelength of the laser beam. Item 3. The laser processing apparatus according to Item 3. The laser processing apparatus according to any one of claims 1 to 6, further comprising an arithmetic unit for estimating a melting state of the melting region based on a detection signal output from the photodetecting unit.

Images