Laser power output evaluation method and laser power output evaluation apparatus

Abstract

To provide a laser output evaluation method that can calculate a laser processing point output.SOLUTION: A laser output evaluation method includes a step in which an interface circuit acquires the signal strength of welding light radiated from a welding part between a joining material and a to-be-joined material irradiated with laser beams during a predetermined melting initiation period in a laser welding process where the to-be-joined material is welded to the joining material. The laser output evaluation method further includes a step in which a computing circuit calculates the laser processing point output of the laser beams applied to the to-be-joined material on the basis of the acquired signal strength and the highest temporal variation of signal strength during the melting initiation period, which was acquired beforehand in preliminary processing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a laser output evaluation method and a laser output evaluation apparatus.

Background Art

[0002] As a method for evaluating the quality of laser welding, for example, Patent Document 1 discloses a method for determining the quality of welding by regression analysis based on the shape information of a molten pool obtained from an image of the molten pool and welding optical sensor information including plasma light detected by a welding optical sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is known that the laser processing point output indicating the output intensity of the laser beam output from a laser welding apparatus affects the quality of laser welding. The method described in Patent Document 1 only determines the quality of welding at the welded portion and does not evaluate the laser processing point output.

[0005] An object of the present disclosure is to provide a laser output evaluation method and a laser output evaluation apparatus capable of calculating a laser processing point output.

Means for Solving the Problems

[0006] A laser output evaluation method according to an aspect of the present disclosure includes: acquiring a signal intensity of welding light radiated from a welded portion between the joined object and the work piece irradiated with a laser beam during a predetermined melting start period in laser welding for welding the work piece to the joined object; The calculation circuit calculates the laser processing point output of the laser beam irradiated onto the workpiece based on the acquired signal intensity and the maximum value of the temporal change in the signal intensity during the melting start period, which was acquired in advance during pre-processing. Includes.

[0007] A laser power evaluation device according to one aspect of this disclosure is: An interface circuit for acquiring the signal intensity of welding light emitted from the weld area between the joined object and the joined object during a predetermined melting start period in a laser welding process in which two objects are welded together, and The system includes a calculation circuit that calculates the laser processing point output of the laser beam irradiated onto the workpiece, based on the acquired signal intensity and the maximum value of the temporal change in the signal intensity during the melting start period, which was acquired in advance during pre-processing. [Effects of the Invention]

[0008] According to the laser output evaluation method and laser output evaluation apparatus described herein, the laser processing point output can be calculated. [Brief explanation of the drawing]

[0009] [Figure 1] A diagram showing the overall configuration of a laser welding system according to an embodiment of this disclosure. [Figure 2] Block diagram showing an example configuration of the laser power evaluation device in Figure 1. [Figure 3] Graph illustrating example laser power settings for standard laser welding. [Figure 4] Diagram showing the appearance of the molten area after laser welding. [Figure 5] A graph showing the signal intensity of thermal radiation detected by a light receiving sensor. [Figure 6] A graph showing the average signal intensity of thermal radiation corresponding to the laser processing point output. [Figure 7] Figure 6 shows a graph representing the average signal intensity of thermal radiation corresponding to the detailed distribution of laser processing point output. [Figure 8] A flowchart showing a method for evaluating laser output according to the present disclosure, particularly the procedure for calculating the output of a laser processing point [Figure 9] A graph for explaining the welding speed during conventional laser welding [Figure 10] A graph for explaining the welding speed during laser welding in the present embodiment [Figure 11] A graph showing the temporal change in the signal intensity of thermal radiation light when the welding speed is set as shown in FIG. 10 [Figure 12] A graph showing the relationship between the output of a laser processing point and the temporal change in the signal intensity of thermal radiation light [Figure 13] A graph showing the amount of temporal change in the signal intensity of thermal radiation light shown in FIG. 11 [Figure 14] A graph showing the relationship between the output of a laser processing point and the maximum value of the amount of temporal change in thermal radiation light during the melting start period [Figure 15] A graph approximating the relationship between the maximum value P of the amount of temporal change in thermal radiation light and the output L of a laser processing point during the melting start period by a linear function f(P) [Figure 16] A graph showing the relationship between the output of a laser processing point and the maximum value of the amount of temporal change in the signal intensity of plasma light during the melting start period

Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings as appropriate. Note that the present disclosure is not limited to the following embodiments. Further, the present disclosure can be appropriately changed without departing from the scope in which the effects of the present disclosure are achieved. Furthermore, it is also possible to combine a plurality of embodiments.

[0011] 1. Configuration FIG. 1 is a diagram showing the overall configuration of a laser welding system 100 according to an embodiment of the present disclosure. The laser welding system 100 includes a laser welding apparatus 20 and a laser output evaluation apparatus 30.

[0012] The laser welding apparatus 20 comprises a laser oscillator 1, a collimating lens 2, a focusing lens 3, a total internal reflection mirror 4, a dichroic mirror 5, and light receiving sensors 6, 7, and 8. The laser beam 10 emitted from the laser oscillator 1 becomes a parallel beam through the collimating lens 2, is reflected by the total internal reflection mirror 4, focused by the focusing lens 3, and irradiated onto the workpiece 15. The workpiece 16 is placed beneath the workpiece 15.

[0013] The objects to be joined 15 and the joined object 16 are fixed on the stage 17. The objects to be joined 15 and the joined object 16 are moved to the laser processing point as the stage 17 moves, and are laser welded when the laser beam 10 is irradiated at the laser processing point.

[0014] During laser welding, the welding light 11 generated from the workpiece 15 passes through the focusing lens 3 and the total internal reflection mirror 4, and is wavelength-separated by the dichroic mirror 5. The wavelength-separated welding light is then separated into thermal radiation light 12 and plasma light 13 by, for example, a bandpass filter (not shown). The thermal radiation light 12 has a wavelength of, for example, 1300 nm, and the plasma light 13 has a wavelength of, for example, 400 to 700 nm. The thermal radiation light 12 and plasma light 13 are incident on the light receiving sensors 6 and 7, respectively.

[0015] On the other hand, the laser beam 10 may not be completely reflected by the total reflection mirror 4. That is, a portion of the laser beam 10 after passing through the collimating lens 2 may pass through the total reflection mirror 4, and the transmitted laser beam 14 may be incident on the light receiving sensor 8. The laser output of the laser beam 14 is, for example, about 0.5% of the laser output of the laser beam 10 before it is incident on the total reflection mirror 4.

[0016] The light receiving sensors 6, 7, and 8 each detect the output of the incident light. The signals indicating the three types of detection results from the light receiving sensors 6, 7, and 8 are transmitted to the laser output evaluation device 30 for signal processing. Based on the results of the signal processing, the laser output evaluation device 30 calculates the output intensity (hereinafter referred to as "laser processing point output") of the laser beam 10 output from the laser welding device 20 and reaching the workpiece 15 and / or the joined object 16.

[0017] In Figure 1, the laser beam 10 and welding light 11 are shown separately between the total reflection mirror 4 and the workpiece 15. However, in reality, the laser beam 10 and welding light 11 may pass through the focusing lens 3 along the same path.

[0018] Figure 2 is a block diagram showing an example configuration of the laser output evaluation device 30 shown in Figure 1. The laser output evaluation device 30 may be, for example, a computer, and includes a signal strength acquisition unit 31, a signal strength processing unit 32, a storage device 33, and an output unit 34.

[0019] The signal strength acquisition unit 31 is an interface circuit that connects the laser output evaluation device 30 to an external device, such as the laser welding device 20, in order to input information from the external device to the signal strength processing unit 32. Such an interface circuit may be a communication circuit that performs data communication according to an existing wired communication standard or wireless communication standard. The signal strength acquisition unit 31 acquires data from the laser welding device 20 indicating the signal strength of the thermal radiation light 12 emitted from the welding area during welding, the signal strength of the plasma light 13, and the signal strength of the transmitted laser beam.

[0020] The signal strength processing unit 32 is implemented by, for example, an arithmetic circuit such as a processor. Such an arithmetic circuit includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The arithmetic circuit may be implemented by one or more dedicated processors. Furthermore, with respect to the components of the arithmetic circuit, functions may be omitted, replaced, and added as appropriate depending on the embodiment. The signal strength processing unit 32 calculates the laser processing point output by performing information processing on the signal strength data acquired by the signal strength acquisition unit 31. Such information processing is implemented, for example, by the signal strength processing unit 32 executing a program stored in the storage device 33.

[0021] For example, the signal intensity processing unit 32 calculates the laser processing point output based on the signal intensity data of the thermal radiation light 12, the signal intensity data of the plasma light 13, and / or the signal intensity data of the transmitted laser beam acquired by the signal intensity acquisition unit 31, and the correlation data 331 stored in the storage device 33.

[0022] The storage device 33 is a recording medium that stores various information, including programs and various data necessary to realize the functions of the laser output evaluation device 30. This includes, for example, correlation data 331 (e.g., correlation function: L=f(P)) between the maximum value of the temporal change in the melting start period of the thermal radiation 12 described later and the laser processing point output. The storage device 33 can be implemented as, for example, a semiconductor storage device such as flash memory or a solid-state drive (SSD), a magnetic storage device such as a hard disk drive (HDD), or other recording media, either alone or in combination thereof. The storage device 33 may also include volatile memory such as SRAM or DRAM.

[0023] The output unit 34 is, for example, an output interface circuit that outputs data to the outside from the laser power evaluation device 30. The signal strength acquisition unit 31 and the output unit 34 may be implemented using similar hardware.

[0024] Furthermore, the laser output evaluation device 30 may acquire data processing programs, etc., executed by the signal intensity processing unit 32 from a portable storage medium. The storage medium is a medium that stores information such as programs, etc., through electrical, magnetic, optical, mechanical, or chemical means so that a computer or other device or machine can read the information such as programs recorded on it.

[0025] 2. Background leading to this disclosure In laser welding equipment, there is an optical design challenge in that the output intensity of the laser beam emitted from the laser oscillator differs from the output intensity of the laser beam actually incident on the workpiece, i.e., the laser processing point output. This optical design challenge will be explained below.

[0026] To explain this optical design challenge using the example shown in Figure 1, the output intensity of the laser beam emitted from the laser oscillator 1 is different from the output intensity of the laser beam 10 actually incident on the workpiece 15, i.e., the laser processing point output.

[0027] For example, a laser output monitor installed inside the laser oscillator 1 can only monitor the laser output of the laser oscillator 1 itself, and the monitoring results do not reflect the attenuation of the laser output that occurs when the laser passes through the optical system of the laser welding device 20.

[0028] Furthermore, it is conceivable to estimate the laser processing point output from the detection results of the light receiving sensor 8 within the laser welding apparatus 20, but the detection results of the light receiving sensor 8 do not reflect the attenuation of the laser output due to other optical components such as the focusing lens 3 and protective glass (not shown).

[0029] In order to understand the welding process more accurately, it is necessary to evaluate with greater precision the output intensity of the laser beam 10 actually incident on the workpiece 15, i.e., the laser processing point output.

[0030] Here, a conventional method for evaluating the signal intensity of thermal radiation is explained using Figures 3 to 5. Using the laser output waveform (irradiation time T, laser output setting value P) shown in Figure 3, which exemplifies standard laser welding conditions, when the workpiece 15 is irradiated with a laser beam 10 at a constant welding speed V, the workpiece 15 and the joint 16 are laser-welded. As shown in Figure 4, after laser welding, a molten and solidified portion 18 is formed on the workpiece 15. The thermal radiation generated during laser welding is detected by a light receiving sensor 6. Figure 5 is a graph showing the signal intensity of the thermal radiation detected by the light receiving sensor 6. For example, as shown in Figure 5, the average signal intensity, which is the average value of the flat portion of the signal intensity in the overall waveform of the thermal radiation, is calculated, and the signal intensity of the thermal radiation is evaluated based on the average signal intensity.

[0031] However, the inventors found that conventional methods for evaluating the signal intensity of thermal radiation still have limitations. The following describes the limitations of conventional methods for evaluating the signal intensity of thermal radiation.

[0032] Figure 6 is a graph showing the average signal intensity of thermal radiation. Each point in the graph in Figure 6 represents the average signal intensity of thermal radiation obtained when a laser beam was irradiated onto different locations on a workpiece 15. The points in the graph in Figure 6 were obtained by setting the laser processing point output to 1100W, 1300W, 1500W, 1700W, and 1900W. The graph in Figure 6 has four points corresponding to each laser processing point output. These four points represent the average signal intensity of thermal radiation obtained by irradiating different locations on the workpiece 15 with a laser beam four times in a row.

[0033] The method for measuring the laser processing point output is as follows: First, a laser output measuring device is installed between the laser welding apparatus 20 and the workpiece 15. Next, the workpiece 15 is irradiated with a laser beam under the same conditions as the laser output waveform (irradiation time T, laser output setting value P) shown in Figure 3. The value measured by the laser output measuring device can be said to be the laser processing point output.

[0034] As mentioned above, the laser output setting P and the laser processing point output are usually different because the laser passes through various optical systems inside the laser welding apparatus 20. To use the laser processing point output as a reference, the laser output setting P was set to a value such that the laser processing point output ranges from 1100W to 1900W.

[0035] The graph in Figure 6 shows that the average signal intensity of the thermal radiation tends to increase monotonically as the laser processing point output increases. Furthermore, the graph in Figure 6 reveals that there is some variation (variation) in the average signal intensity of the thermal radiation for the same laser processing point output. The slope between the averages of four measurements for each laser processing point output is relatively large when the laser processing point output is lower than the standard conditions (1100-1500W), while it is relatively small and approaches zero when the laser processing point output is greater than the standard conditions (1500-1900W).

[0036] When the laser processing point power is below the standard conditions (1100-1500W), the workpiece 15 may not melt all the way to the bottom surface, resulting in a situation where the workpiece 15 is not joined to the joint 16, or the joint strength is low. As the laser processing point power increases to near the standard conditions, the temperature of the workpiece 15 rises, and as a result, the amount of thermal radiation also increases.

[0037] On the other hand, when the laser processing point output is above standard conditions (1500-1900W), the workpiece 15 may melt excessively, generating an excessive amount of metal fumes (metal vapor). As a result, the thermal radiation emitted from the workpiece 15 is blocked by the metal fumes, causing the signal intensity of the measured thermal radiation to fluctuate or decrease.

[0038] Figure 7 is a graph showing the average signal intensity of thermal radiation corresponding to a more detailed distribution of laser processing point output than in Figure 6. Each point shown in the graph of Figure 7 represents the average signal intensity of thermal radiation obtained when the laser beam was irradiated at different locations on a workpiece 15, similar to Figure 6.

[0039] The points shown in the graph of Figure 7 were obtained by setting the laser processing point output to 1300W, 1400W, 1500W, 1600W, and 1700W. The graph of Figure 7 has four points corresponding to each laser processing point output. These four points represent the average signal intensity of the thermal radiation obtained by irradiating different positions on the workpiece 15 with the laser beam four times in a row.

[0040] As can be seen from Figure 7, the average signal intensity of the thermal radiation tends to increase as the laser processing point output increases. However, in Figure 7, there is a large variation in the four average signal intensities obtained for the same laser processing point output. Also, in Figure 7, the rate of increase in the average signal intensity of the thermal radiation is small. Note that the square of the correlation coefficient R (R²) when these laser processing point outputs and the average signal intensity of the thermal radiation are linearly approximated is calculated. 2 The result is 0.17, which statistically indicates a weak correlation.

[0041] Therefore, the method of determining the laser processing point output based on the average signal intensity of thermal radiation, as described above, cannot accurately calculate the laser processing point output.

[0042] Therefore, the inventors diligently researched how to calculate the laser processing point output with greater accuracy and discovered the laser output evaluation method described herein.

[0043] 3.Operation The operation of the signal intensity processing unit 32 of the laser output evaluation device 30 that implements the laser output evaluation method according to this disclosure will be described below.

[0044] Figure 8 is a flowchart showing the laser output evaluation method according to this disclosure, particularly the procedure for calculating the laser processing point output. The process shown in Figure 8 is performed by the signal intensity processing unit 32.

[0045] First, the signal intensity processing unit 32 acquires measurement data of the thermal radiation 12 from the laser welding apparatus 20 (S1). The measurement of the thermal radiation 12 may be performed simultaneously with the start of laser welding, or it may be performed continuously.

[0046] Next, the signal intensity processing unit 32 calculates the amount of change in the signal intensity of the thermal radiation 12 over time based on the measurement data acquired in step S1 (S2).

[0047] Next, the signal intensity processing unit 32 calculates the maximum value of the temporal change in the signal intensity of the thermal radiation 12 based on the temporal change in the signal intensity of the thermal radiation 12 calculated in step S2 (S3).

[0048] Next, the signal intensity processing unit 32 calculates the laser processing point output (S4) based on the maximum value of the temporal change in the signal intensity of the thermal radiation 12 calculated in step S3 and the correlation data 331 measured during pre-processing and stored in the memory device 33. The correlation data 331 is, for example, the correlation function (L=f(P)) between the maximum value of the temporal change in the signal intensity of the thermal radiation 12 during the melting start period and the laser processing point output.

[0049] Here, the melting initiation period is the period from the time (t=0) when the melting of the workpiece 15 begins due to laser irradiation and thermal radiation 12 begins to be detected, to the time (t=T0) when the temperature rise continues and the intensity of thermal radiation 12 reaches its maximum. Alternatively, the melting initiation period may be the period from the time when thermal radiation 12 begins to be detected until the time when the intensity of thermal radiation 12 exceeds a predetermined threshold. Furthermore, the melting initiation period may be a predetermined time period from the time when thermal radiation 12 begins to be detected.

[0050] The laser welding process generally follows the following progression as the laser irradiation time elapses. (1) The upper plate, the object to be joined 15, is overheated and melting begins. (2) The melting progresses to the lower surface of the joined object 15. (3) The heat of melting from the upper plate, the joined object 15, is transferred to the lower plate, the joined object 16, and the melting of the joined object 16 begins. (4) The molten material of the object to be joined 15 and the molten material of the joined object 16 mix together. (5) As the laser beam passes through, the temperature of the melt decreases and solidifies, and the workpiece 15 and the joint 16 are joined.

[0051] In such a laser welding process, the melting start period indicates the process from (1) to (3). In the change of the signal intensity of the thermal radiation light 12, the melting start period corresponds to the rising part of the signal intensity of the thermal radiation light 12 from the detection start time of the signal intensity of the thermal radiation light 12 to the time when the peak intensity or an intensity exceeding the planned threshold value of the thermal radiation light 12 is observed.

[0052] In the melting start period, by gradually increasing the output intensity of the laser beam, a signal intensity of the thermal radiation light 12 that rises with a right shoulder to the peak intensity of the thermal radiation light 12 may be obtained.

[0053] Next, a method for obtaining the correlation data 331 between the maximum value of the temporal change amount of the thermal radiation light 12 and the laser processing point output in the melting start period will be described.

[0054] The laser irradiation time and the welding speed in the present embodiment are set as follows, for example. Specifically, in conventional laser welding, as shown in FIG. 9, within the laser irradiation time (0 ≦ t ≦ T), the welding speed is a constant speed V. On the other hand, in the present embodiment, for example, as shown in FIG. 10, in the melting start period (0 ≦ t < T0), the welding speed V0 is set to be slower than the normal welding speed V (that is, the period after the melting start period within the laser irradiation time).

[0055] FIG. 11 is a graph showing the temporal change of the signal intensity of the thermal radiation light 12 when the welding speed is set as shown in FIG. 10. It can be seen that the peak of the signal intensity of the thermal radiation light 12 is at the leading part of the graph of FIG. 11. From the graph of FIG. 11, the melting start period is the period from the detection start time 0 of the signal intensity of the thermal radiation light 12 to the time T0 when this peak intensity occurs.

[0056] Since the welding speed V0 during the melting initiation period is slower than the normal welding speed V, the energy input per unit length to the workpiece 15 during the melting initiation period is relatively higher compared to normal welding. As a result, the temperature of the workpiece 15 rises to a relatively high temperature during the melting initiation period, and consequently, the thermal radiation intensity also increases. After the melting initiation period has elapsed, when the welding speed increases (to a predetermined speed V), the energy input per unit length to the workpiece 15 decreases relatively, causing the temperature of the workpiece 15 to drop, and consequently, the thermal radiation intensity decreases.

[0057] During the melting initiation period, instead of slowing the welding speed down from the normal welding speed V, or in addition to this, the signal intensity of the thermal radiation 12, which shows a sharp upward slope as shown in Figure 11, may be obtained by gradually increasing the output intensity of the laser beam.

[0058] Figure 12 is a graph showing the relationship between the laser processing point output and the temporal change in the signal intensity of the thermal radiation 12. In the graph of Figure 12, the dashed line shows the temporal change in the signal intensity of the thermal radiation 12 when the laser processing point output is 1500W under standard conditions. The dotted line shows the temporal change in the signal intensity of the thermal radiation 12 when the laser processing point output is 1300W under low power conditions, and the solid line shows the temporal change in the signal intensity of the thermal radiation 12 when the laser processing point output is 1700W under high power conditions.

[0059] As shown in Figure 12, the thermal radiation 12 corresponding to the three conditions described above have peak intensity at almost the same time, and it can be seen that the melting initiation period is almost the same under all conditions. Furthermore, it can be seen that the signal waveform during the melting initiation period increases monotonically and linearly as the laser processing point output increases.

[0060] In other words, during the melting initiation period, the molten state is stable regardless of the laser output, and as a result, the signal intensity of the thermal radiation 12 is also stable. This is thought to be because only the upper plate, the workpiece 15, is melted, and the molten state is not significantly affected by the lower plate, the joining material 16. Furthermore, during the melting initiation period, the workpiece 15 and the joining material 16 are not joined, so the mutual influence between the workpiece 15 and the joining material 16 (gap size, adhesion, interfacial foreign matter, etc.) is small, which is also thought to be a contributing factor. Additionally, during the melting initiation period, the molten portion is small, and the influence of metal fumes generated during melting is small, which is also thought to be a contributing factor.

[0061] In contrast, Figure 12 shows that, during the period after the melting initiation period, the signal intensity of the thermal radiation 12 fluctuates significantly, and the correlation with the laser processing point output is weak. This is thought to be because, during the period after the melting initiation period, the workpiece 15 and the joining object 16 are joined, and the surface melting state changes moment by moment.

[0062] Let's consider the surface melting state in more detail. The amount of metal fumes generated during laser welding can vary depending on the contact state between the workpiece 15 and the joining object 16 (size of the gap, adhesion, interfacial foreign matter, etc.) and the surface condition of the workpiece 15 (surface roughness, dirt, etc.). Although metal fumes are blown away with assist gas or sucked up with a suction device to remove them, they cannot be completely removed. The remaining metal fumes that cannot be removed block the thermal radiation 12 generated from the molten part of the workpiece 15, so the observed thermal radiation 12 decreases. Therefore, it is thought that the signal intensity of the thermal radiation 12 detected by the detection system (light receiving sensor 6) of the laser welding apparatus 20 fluctuates.

[0063] Figure 13 is a graph showing the temporal change in the signal intensity of the thermal radiation 12 shown in Figure 11. This temporal change corresponds to the slope of the graph in Figure 11. This temporal change is calculated in step S2 of Figure 8.

[0064] In Figure 11, the signal intensity of the thermal radiation 12 shows a sharp upward trend during the melting initiation period, and therefore, in Figure 13, the temporal change in signal intensity is a large positive value. Furthermore, in Figure 11, after the melting initiation period, the signal intensity of the thermal radiation 12 saturates at a high level and changes little, and therefore, in Figure 13, the temporal change in signal intensity is close to zero.

[0065] Figure 14 is a graph showing the relationship between the laser processing point power and the maximum value of the temporal change in thermal radiation 12 during the melting initiation period. The points shown in the graph of Figure 14 represent the maximum values ​​of the temporal change in thermal radiation 12 obtained when the laser processing point power is 1300W, 1400W, 1500W, 1600W, and 1700W. The graph of Figure 14 has four points corresponding to each laser processing point power. These four points represent the maximum values ​​of the temporal change in thermal radiation 12 obtained by irradiating different positions on the workpiece 15 four times in a row with the laser beam.

[0066] The method for measuring the laser processing point output, as shown in Figure 14, is as follows: First, a laser output measuring device is placed between the laser welding device 20 and the workpiece 15 (see Figure 1). Next, laser irradiation is performed under the same conditions as the laser output waveform shown in Figure 10. The value measured by the laser output measuring device at this time is the laser processing point output.

[0067] As can be seen from the graph in Figure 14, during the melting initiation period, the fluctuation in the maximum value of the temporal change in thermal radiation 12 corresponding to each laser processing point output is small. The square of the correlation coefficient (R) between the laser processing point output and the maximum value of the temporal change in thermal radiation 12 during the melting initiation period shown in Figure 14. 2 The correlation between the two is 0.98, which statistically indicates a very strong correlation.

[0068] Furthermore, it can be seen that the maximum value of the temporal change in thermal radiation 12 increases almost linearly as the laser processing point output increases. Therefore, the maximum values ​​of the temporal change in thermal radiation 12 for each laser processing point output during the melting initiation period do not overlap with each other. Thus, if a correlation like the one shown in the graph in Figure 14 is obtained in advance, the laser processing point output can be estimated from the maximum value of the temporal change in thermal radiation 12 during the melting initiation period (S4 in Figure 8).

[0069] Figure 15 is a graph approximating the relationship between the maximum value P of the temporal change in thermal radiation 12 and the laser processing point output L during the melting initiation period using a linear function f(P). In this way, the pre-calculated correlation function (L=f(P)) is stored as correlation data 331 in the memory device 33 of the laser output evaluation device 30 (see Figure 2). As a result, in step S4 of Figure 8, the laser processing point output L is uniquely determined from the maximum value P of the temporal change in thermal radiation 12 during the melting initiation period.

[0070] As mentioned above, the laser processing point output is affected by the optical design of the laser welding apparatus 20. Therefore, the laser welding apparatus used to calculate the laser processing point output and the laser welding apparatus used for pre-measurement to obtain data for calculating the correlation function may be the same. In other words, the irradiation of the laser beam for measuring the thermal radiation 12 in step S1 of Figure 8 and the pre-processing to obtain data for calculating the correlation function may be performed by the same laser welding apparatus. For example, the laser output evaluation apparatus 30 can store data linking the correlation function and the identification information of the laser welding apparatus 20 as correlation data 331 in the storage device 33, and calculate the laser processing point output using the correlation function of the correlation data that has the same identification information as the laser welding apparatus 20 used in the actual processing.

[0071] (Other embodiments) As described above, the above embodiments have been explained as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these embodiments and can be applied to embodiments that have been modified, replaced, added, or omitted as appropriate. Therefore, other embodiments will be described below as examples.

[0072] In the above embodiment, an example was described in which the signal intensity processing unit 32 calculates the laser processing point output based on the maximum value of the temporal change in the signal intensity of the thermal radiation light 12 and correlation data 331 pre-stored in the storage device 33 (see S4 in Figure 8). However, the disclosure is not limited thereto, and it is sufficient if the laser processing point output can be calculated. For example, instead of calculating the laser processing point output based on the measurement data of the thermal radiation light in steps S1 to S4 of Figure 8, the signal intensity processing unit 32 may calculate the laser processing point output based on the measurement data of the plasma light 13.

[0073] Figure 16 is a graph showing the relationship between the laser processing point output and the maximum value of the temporal change in the signal intensity of the plasma light 13 during the melting initiation period. The maximum value of the temporal change in the signal intensity of the plasma light 13 shown in Figure 16 increases almost linearly as the laser processing point output increases, similar to the maximum value of the temporal change in the signal intensity of the thermal radiation light 12 shown in Figure 14. Therefore, if a correlation like that shown in Figure 16 is obtained beforehand, the laser processing point output can be estimated from the maximum value of the temporal change in the plasma light 13 during the melting initiation period.

[0074] (Note) Examples of aspects of this disclosure are given below.

[0075] <Aspect 1> A step of acquiring the signal intensity of welding light emitted from the weld area between the joined object and the joined object, during a predetermined melting start period in a laser welding process in which the joined objects are welded to each other with a laser beam, The calculation circuit calculates the laser processing point output of the laser beam irradiated onto the workpiece based on the acquired signal intensity and the maximum value of the temporal change in the signal intensity during the melting start period, which was acquired in advance during pre-processing. A laser power evaluation method, including the following.

[0076] <Aspect 2> The laser output evaluation method according to Embodiment 1, wherein the step of calculating the laser processing point output includes calculating the laser processing point output using correlation data that shows the correlation between the maximum value of the temporal change in the signal intensity acquired in advance and the output of the laser beam.

[0077] <Aspect 3> The laser output evaluation method according to embodiment 2, wherein the correlation data is a function showing the correlation between the maximum value of the temporal change in the signal intensity acquired in advance and the output of the laser beam.

[0078] <Aspect 4> The laser output evaluation method according to any one of embodiments 1 to 3, wherein the maximum value of the temporal change in the signal intensity acquired in advance is calculated based on the signal intensity obtained by gradually increasing the output intensity of the laser beam during the melting start period of the pre-processing.

[0079] <Aspect 5> The laser output evaluation method according to embodiment 4, wherein in the step of acquiring the signal intensity, the signal intensity is obtained by gradually increasing the output intensity of the laser beam during the melting start period.

[0080] <Aspect 6> The laser output evaluation method according to any one of embodiments 1 to 5, wherein the irradiation of the laser beam and the pre-processing are performed by the same laser welding apparatus.

[0081] <Aspect 7> The laser output evaluation method according to any one of embodiments 1 to 6, wherein the melting start period is the period from the time when the welding light is first detected until the signal intensity of the welding light exceeds a predetermined threshold.

[0082] <Aspect 8> The laser output evaluation method according to any one of embodiments 1 to 6, wherein the melting start period is the period from the time when the welding light is first detected until the signal intensity of the welding light reaches its maximum.

[0083] <Pattern 9> The laser output evaluation method according to any one of embodiments 1 to 8, wherein the welding light is thermal radiation light and / or plasma light.

[0084] <Aspect 10> An interface circuit for acquiring the signal intensity of welding light emitted from the weld area between the joined object and the joined object during a predetermined melting start period in a laser welding process in which two objects are welded together, and A calculation circuit that calculates the laser processing point output of the laser beam irradiated onto the workpiece based on the acquired signal intensity and the maximum value of the temporal change in the signal intensity during the melting start period, which was acquired in advance during pre-processing, A laser power output evaluation device equipped with the following features. [Industrial applicability]

[0085] This disclosure is applicable to methods for evaluating laser processing, such as methods for evaluating whether a predetermined laser processing point output can actually be obtained from a laser welding apparatus. [Explanation of Symbols]

[0086] 1. Laser oscillator 2. Collimating lenses 3. Focusing lens 4 Total Reflection Mirrors 5 Dichroic Mirrors 6, 7, 8 Light receiving sensor 10 laser beams 11. Welding light (including thermal radiation and plasma light) 12. Thermal radiation 13 Plasma light 14. Transmitted laser beam 15 Object to be joined 16 Joints 17 stages 18. Molten and solidified portion 20 Laser welding equipment 30. Laser power output evaluation device 31 Signal strength acquisition unit 32 Signal Strength Processing Unit 33 Storage device 34 Output section 100 Laser Welding Systems

Claims

1. The interface circuit includes the steps of acquiring the signal intensity of welding light emitted from the weld area between the joined object and the joined object, during a predetermined melting start period in a laser welding process in which the joined object is irradiated with a laser beam, The calculation circuit calculates the laser processing point output of the laser beam irradiated onto the workpiece based on the acquired signal intensity, the maximum value of the temporal change in the signal intensity during the melting start period, which was acquired in advance during pre-processing, and correlation data showing the correlation between the maximum value and the output of the laser beam. A laser power evaluation method, including the following.

2. The laser output evaluation method according to claim 1, wherein the correlation data is a function that shows the correlation between the maximum value of the temporal change in the signal intensity acquired in advance and the output of the laser beam.

3. The laser output evaluation method according to claim 1, wherein the maximum value of the temporal change in the signal intensity acquired in advance is calculated based on the signal intensity obtained by gradually increasing the output intensity of the laser beam during the melting start period of the pre-processing.

4. The laser output evaluation method according to claim 3, wherein in the step of acquiring the signal intensity, the signal intensity is obtained by gradually increasing the output intensity of the laser beam during the melting start period.

5. The laser output evaluation method according to claim 1, wherein the irradiation of the laser beam and the pre-processing are performed by the same laser welding apparatus.

6. The laser output evaluation method according to claim 1, wherein the melting start period is the period from the time when the welding light is first detected until the signal intensity of the welding light exceeds a predetermined threshold.

7. The laser output evaluation method according to claim 1, wherein the melting start period is the period from the time when the welding light is first detected until the signal intensity of the welding light reaches its maximum.

8. The laser output evaluation method according to any one of claims 1 to 7, wherein the welding light is thermal radiation light and / or plasma light.

9. An interface circuit for acquiring the signal intensity of welding light emitted from the weld area between the joined object and the joined object during a predetermined melting start period in a laser welding process in which two objects are welded together, and A calculation circuit that calculates the laser processing point output of the laser beam irradiated onto the workpiece based on the acquired signal intensity, the maximum value of the temporal change in the signal intensity during the melting start period acquired in advance during pre-processing, and correlation data showing the correlation between the maximum value and the laser beam output. A laser power output evaluation device equipped with the following features.

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