Laser welding system, molten pool depth function acquisition method, and molten pool topographic feature estimation method

Abstract

The invention discloses a laser welding system, a molten pool depth function obtaining method and a molten pool morphological characteristic estimation method. The molten pool morphological characteristic estimation method comprises the following steps: providing a molten pool depth function taking voltage as a variable; irradiating a workpiece group with a first laser beam to form a first molten pool; sensing a first coaxial reflected light reflected from the first molten pool, and correspondingly outputting a first voltage signal; and substituting the first voltage signal into the molten pool depth function to instantly estimate the depth of the first molten pool. Therefore, the welding yield can be improved, and the overall production cost and time can be reduced.

Description

Technical Field

[0001] The invention relates to a laser welding technology, and in particular to a laser welding system and a method for estimating the morphological characteristics of a molten pool, which can estimate the morphological characteristics of the molten pool online and in real time. Background Art

[0002] In fully automated laser welding operations, welds need to be inspected and measured. To meet this need, the industry has developed a number of fully automated inspection equipment and methods.

[0003] US Patent No. US2021187657 A1 discloses a method and device for monitoring welds by laser beams during welding. It uses two parallel lasers to project onto the weld bead, and uses triangulation to calculate the geometric changes before and after welding. In this way, the weld bead width and weld crown height can be determined, and surface defects such as pores and spatter can be determined. However, this prior art cannot know the actual weld depth, and welding thermal deformation will affect the basis for its estimation.

[0004] German patent number DE 10 2020 120 670 A1 discloses a laser welding process analysis method, which obtains a measurement beam reflected by the weld after the laser welding process is completed, especially after the weld has cooled or solidified, detects a measurement signal of a part of the measurement beam, and determines whether there is a welding defect based on the measurement signal. This prior art mainly solves the problem of welding defect identification after welding is completed.

[0005] Chinese patent number CN 106238946 A discloses a laser filler welding quality online detection and dimension feedback system and method (Chinese patent name: Laser filler wire welding quality online detection and dimension feedback system and method), in which the online detection system detects the workpiece measurement point position data before welding, adjusts the position of the robot according to the position deviation from the standard part, and corrects the welding trajectory deviation. The measurement point position data, encoder data generated by the laser head deflection, and weld quality data are fed back to the database system, and the workpiece size and weld defects are analyzed and diagnosed in time through the database system, and corresponding adjustment actions are made.

[0006] The above-mentioned prior art has proposed solutions for the identification of weld surface features, weld defects, and online welding deviations, which further improves the quality of laser welding operations. However, the above-mentioned prior art does not mention the detection or estimation of the molten pool depth, especially the detection or estimation of the molten pool depth during online operations. The requirements for the molten pool depth have a great impact on the quality of laser welding. How to detect or estimate the molten pool depth online in real time has become one of the issues that people in this technical field are eager to solve. Summary of the invention

[0007] The purpose of the present invention is to provide a laser welding system and a method for estimating molten pool morphology characteristics that can estimate the molten pool morphology characteristics online and in real time, so as to improve the welding yield and reduce the overall production cost and time.

[0008] In accordance with the above-mentioned objectives, the present invention provides a method for estimating molten pool morphological characteristics, the steps of which include: providing a molten pool depth function with voltage as a variable; irradiating a workpiece group with a first laser beam to form a first molten pool; sensing a first coaxial reflected light reflected from the first molten pool and outputting a first voltage signal accordingly; and substituting the first voltage signal into the molten pool depth function to instantly estimate the depth of the first molten pool. As an improvement, the method further includes the following steps: collecting image data of an imaging area, the imaging area including the first molten pool; identifying a surface contour of the first molten pool via a feature point; and estimating the width of the surface contour. As an improvement, the characteristic point is that the image grayscale value of the first molten pool is different from the image grayscale value of the remaining solid parts of the imaging area.

[0009] In accordance with the above-mentioned purpose, the present invention provides a method for obtaining a molten pool depth function, the steps of which include: irradiating one of a plurality of test piece groups with a second laser beam to form a second molten pool; sensing a second coaxial reflected light reflected from the second molten pool and outputting a second voltage signal accordingly; integrating the second voltage signal with respect to time and then calculating a voltage value per unit time; measuring an actual molten pool depth of the one of the test piece groups; repeating the above steps for the remaining test piece groups of the plurality of test piece groups to obtain a plurality of voltage values ​​per unit time and the actual molten pool depths corresponding to each of them; and obtaining the molten pool depth function by regression analysis based on the plurality of voltage values ​​per unit time and the actual molten pool depths corresponding to each of them. As an improvement, the voltage value per unit time is obtained by dividing the time integral value of the second voltage signal by the welding time. As an improvement, the actual molten pool depth is obtained by performing metallographic analysis on the welded test piece set. As an improvement, the error value of the molten pool depth function is less than ±10%.

[0010] In accordance with the above-mentioned objectives, the present invention provides a laser welding system, comprising: a first laser welding machine, providing a first laser beam for irradiating a workpiece group to form a first molten pool; a first spectroscope, arranged in the optical path of the first laser beam, for splitting a first coaxial reflected light reflected from the first molten pool; a first photoelectric sensing module, which is irradiated by the first coaxial reflected light from the first spectroscope and outputs a first voltage signal; and a first operating unit, which has a molten pool depth function with voltage as a variable, the first operating unit obtains the first voltage signal, and can instantly estimate the depth of the first molten pool through the molten pool depth function. As an improvement, the first photoelectric sensing module includes a photodiode. As an improvement, it further includes: a third beam splitter, which is arranged on the optical path of the first laser beam, for reflecting the first coaxial reflected light from the first beam splitter; a filter, which is used to limit the wavelength of the first coaxial reflected light from the third beam splitter; and an image sensing module, which receives the first coaxial reflected light passing through the filter to capture the image of the first molten pool, and transmits the captured image data to the first computing unit.

[0011] The laser welding system, the method for obtaining the molten pool depth function, and the method for estimating the molten pool morphological characteristics of the present invention can instantly estimate the molten pool morphological characteristics, such as the depth of the molten pool and the width of the surface profile, during the welding process. Therefore, it is possible to immediately know whether the molten pool depth and width meet the requirements during the laser welding process, which is convenient for users to adjust the welding parameters in advance and reduce the number of post-welding inspections and destructive analysis, which helps to improve the yield and reduce the overall production cost and time. In addition, the measurements of the present invention are all coaxial measurements, and the data obtained by the measurements do not have deviations caused by angles, which can reduce the error in the estimation of the molten pool morphological characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of an embodiment of a laser welding system.

[0013] Figure 2 Flowchart of the melt pool morphology characteristics estimation method.

[0014] Figure 3 Flow chart of the method for obtaining the melt pool depth function.

[0015] Figure 4 Schematic diagram of the experimental equipment for the method of obtaining the melt pool depth function.

[0016] Figure 5 This is a schematic top view of the first molten pool.

[0017] In the figure: 1:Laser welding system 2: Experimental equipment 110: The first laser welding machine 110': Second laser welding machine 111: First laser source 112: First lens group 113: first cover 114: First laser beam 114': Second laser beam 120: First beam splitter 120': Second beam splitter 130: first photoelectric sensing module 130': second photoelectric sensing module 131: First photoelectric sensor 140: First computing unit 140': Second computing unit 150': Integrator 160: The third beam splitter 170:Filter 180: Image sensing module 181: Image sensor 190:Supplementary light source 200: Workpiece Group 210: First molten pool 211: Surface Profile 220: Imaging area 300: First coaxial reflected light 300': Second coaxial reflected light 400:Test piece group 410: Second molten pool h: Depth of the first molten pool w: Width of the surface profile S1~S7: Steps S11~S16: steps. DETAILED DESCRIPTION

[0018] In order to make the above or other purposes, features and characteristics of the present invention more obvious and easy to understand, the relevant embodiments of the present invention are described in detail with the help of drawings as follows. The drawings are mainly simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner. Therefore, only elements related to the present invention are marked in the drawings, and the elements shown are not drawn according to the number, size ratio, etc. during implementation, and the layout of the elements may be more complicated.

[0019] Directional terms mentioned in this specification, such as "upper", "lower", "front", "back", "left", "right", "inner", "outer", "side", etc., are only used to refer to the directions of the drawings. The directional terms used are only used to illustrate and understand the present invention, and are not used to limit the present invention.

[0020] This specification discloses a laser welding system, a method for obtaining a molten pool depth function, and a method for estimating molten pool morphological characteristics, which can be used to estimate the morphological characteristics of the molten pool online and in real time during the laser welding process, such as the depth of the molten pool and the width of the surface profile.

[0021] Figure 1 FIG. 1 is a schematic diagram of an embodiment of a laser welding system. Figure 1The laser welding system 1 disclosed in this embodiment includes a first laser welding machine 110 , a first beam splitter 120 , a first photoelectric sensing module 130 and a first computing unit 140 .

[0022] The first laser welding machine 110 includes a first laser source 111, a first lens group 112 and a first cover 113. The first laser welding machine 110 provides a first laser beam 114 for irradiating a workpiece group 200. The first lens group 112 is used to adjust the first laser beam 114. The first cover 113 is a hollow tube that runs through from top to bottom and allows the first laser beam 114 to pass through. The workpiece group 200 may include at least two workpieces to be welded, and the two workpieces to be welded may be butt-jointed or overlapped. The workpiece group 200 may also include only one workpiece to be welded, and the workpiece to be welded has a welding area that can be butt-jointed or overlapped.

[0023] The first beam splitter 120 is fixed in the first cover 113 and is located on the optical path of the first laser beam 114. During welding, the position of the workpiece group 200 irradiated by the first laser beam 114 will melt to form a first molten pool 210. At the same time, the first molten pool 210 will reflect the laser, and part of the reflected light will be coaxial with the first laser beam 114. The reflected light coaxial with the first laser beam 114 is hereinafter referred to as the first coaxial reflected light 300. After the first coaxial reflected light 300 enters the first beam splitter 120, part of the first coaxial reflected light 300 is reflected by the first beam splitter 120. Preferably, the first beam splitter 120 is a semi-transparent reflector (PellicleMirror).

[0024] The first photoelectric sensing module 130 includes a first photoelectric sensor 131, which is illuminated by the first coaxial reflected light 300 from the first beam splitter 120 and outputs a first voltage signal. The first photoelectric sensor 131 can be a first photodiode.

[0025] The first operation unit 140 has a molten pool depth function with voltage as a variable. The first operation unit 140 obtains the first voltage signal from the first photoelectric sensing module 130. The molten pool depth function can be used to instantly estimate the depth h of the first molten pool 210 formed by the first laser beam 114. The method of obtaining the molten pool depth function will be described later.

[0026] When the aforementioned laser welding system 1 is used to weld a workpiece group 200, the first laser welding machine 110 of the laser welding system 1 provides a first laser beam 114 to irradiate the workpiece group 200, and the irradiated area will melt to form a first molten pool 210. At the same time, the first molten pool 210 will reflect the laser light, and after the first coaxial reflected light 300 coaxial with the first laser beam 114 enters the first beam splitter 120, part of the first coaxial reflected light 300 is reflected by the first beam splitter 120 and irradiates the first photoelectric sensing module 130. The first photoelectric sensing module 130 outputs a first voltage signal corresponding to the intensity of the first coaxial reflected light 300 and transmits it to the first operation unit 140. The first operation unit 140 can substitute the first voltage signal into the molten pool depth function to instantly estimate the depth h of the first molten pool 210 formed by the first laser beam 114.

[0027] Figure 2 Flow chart of the melt pool morphology estimation method. Figure 2 This embodiment further discloses a method for estimating molten pool morphological characteristics, the steps of which include: providing a molten pool depth function S1 with voltage as a variable; irradiating a workpiece group with a first laser beam to form a first molten pool S2; sensing a first coaxial reflected light reflected from the first molten pool and outputting a first voltage signal S3 accordingly; and substituting the first voltage signal into the molten pool depth function to instantly estimate the depth of the first molten pool S4.

[0028] The steps for obtaining the melt pool depth function are described as follows. Figure 3 Flowchart of the method for obtaining the melt pool depth function. Figure 3 The steps of the method for obtaining the molten pool depth function include: providing an experimental device and a plurality of test piece groups S11, irradiating a test piece group with a second laser beam S12, sensing the second coaxial reflected light and outputting a second voltage signal S13, calculating the voltage value per unit time S14, measuring an actual molten pool depth of the test piece group S15, repeating steps S12 to S15 for the remaining test piece groups, and obtaining the molten pool depth function by regression analysis S16.

[0029] Figure 4 Schematic diagram of the experimental equipment for the method of obtaining the melt pool depth function. Please also refer to Figure 3 and Figure 4, providing an experimental device and a plurality of test piece groups Step S11 is to provide an experimental device 2 and a plurality of test piece groups 400 for subsequent laser welding experiments. The experimental device 2 includes a second laser welding machine 110', a second spectroscope 120', a second photoelectric sensing module 130', a second operation unit 140' and an integrator 150'. The second laser welding machine 110', the second spectroscope 120', the second photoelectric sensing module 130' and the second operation unit 140' in the experimental device 2 are basically the same as the first laser welding machine 110, the first spectroscope 120, the first photoelectric sensing module 130 and the first operation unit 140 of the laser welding system 1, and will not be repeated here. The integrator 150' is used to integrate a voltage signal over time, and then transmit the integration result to the second operation unit 140'. Each test piece group 400 includes at least one test piece.

[0030] In step S12 of irradiating a test piece set with a second laser beam, the second laser welding machine 110' provides a second laser beam 114' to irradiate one of the test piece sets 400. When laser welding the test piece set 400, the second laser beam 114' moves a distance relative to the test piece set 400 to form a weld bead.

[0031] In the step S13 of sensing the second coaxial reflected light and outputting a second voltage signal, the position of the test piece set 400 irradiated by the second laser beam 114' will melt to form a second molten pool 410. At the same time, the second molten pool 410 will reflect the laser light. The part of the reflected light coaxial with the second laser beam 114' is hereinafter referred to as the second coaxial reflected light 300'. After the second coaxial reflected light 300' enters the second beam splitter 120', part of the second coaxial reflected light 300' is reflected. The second coaxial reflected light 300' reflected by the second beam splitter 120' irradiates the second photoelectric sensing module 130', and the second photoelectric sensing module 130' outputs a second voltage signal according to the intensity of the reflected second coaxial reflected light 300'. During the welding process, the second laser beam 114' moves relative to the test piece set 400, so the second molten pool 410 also moves with time, and the second photoelectric sensing module 130' receives the second coaxial reflected light 300' reflected by the second molten pool 410 at different positions, and outputs a plurality of second voltage signals. Preferably, the second beam splitter 120' is a semi-transparent reflector.

[0032] In the step S14 of calculating the voltage value per unit time, the integrator 150' integrates the second voltage signal output by the second photoelectric sensing module 130' (i.e., obtains the area of ​​the voltage curve), and then transmits the integration result to the second operation unit 140', which then divides the integration result by the welding time to calculate a voltage value per unit time. Considering that the welding quality at the starting point and the end point of the weld may be relatively unstable, it is preferred that the voltage signals at the starting point and the end point of the weld bead are excluded and not included in the calculation.

[0033] In the step S15 of measuring an actual molten pool depth of the test piece set, the welded test piece set 400 is cut along a direction perpendicular to the weld bead, and the weld bead area is cut as a metallographic test piece for metallographic analysis to obtain an actual molten pool depth. In one embodiment, the metallographic test piece is cut at the middle point of the weld bead length, but the invention is not limited thereto.

[0034] Steps S12 to S15 are repeated for the remaining test piece groups 400. After welding, sensing, and calculation of all test piece groups 400 are completed, a plurality of voltage values ​​per unit time and a plurality of corresponding actual molten pool depths can be obtained.

[0035] In the step S16 of obtaining a molten pool depth function, a molten pool depth function is obtained by regression analysis based on the plurality of unit time voltage values ​​and the corresponding actual molten pool depths. To obtain a more accurate estimation result, preferably, the error value of the molten pool depth function is less than ±10%.

[0036] Figure 5 This is a top view of the first molten pool. Please refer to Figure 1 and Figure 5 The laser welding system 1 disclosed in this embodiment further includes a third beam splitter 160 , a filter 170 and an image sensing module 180 .

[0037] The third beam splitter 160 is fixedly disposed in the first housing 113 and is located on the optical path of the first laser beam 114. The first coaxial reflected light 300 passing through the first beam splitter 120 enters the third beam splitter 160 and is reflected by the third beam splitter 160.

[0038] The reflected first coaxial reflected light 300 then passes through the filter 170, which can filter out signals such as welding glare and sparks, and limit the passage of light of a specific wavelength. In one embodiment, the filter 170 only allows infrared light with a wavelength of 860 nm to pass through. In another embodiment, the filter 170 only allows infrared light with a single wavelength in the wavelength range of 840-880 nm to pass through.

[0039] The image sensing module 180 includes an image sensing element 181, such as a CCD. The image sensing element 181 receives the first coaxial reflected light 300 passing through the filter 170 to capture an image of an imaging area 220, and the imaging area 220 includes the first molten pool 210. The image data collected by the image sensing module 180 is then transmitted to the first computing unit 140 for processing.

[0040] The laser welding system 1 of this embodiment further includes a supplementary light source 190 to illuminate the imaging area 220 . The wavelength range of the supplementary light source 190 is the same as the wavelength range of the filter 170 .

[0041] When the laser welding system 1 is used to weld the workpiece group 200, the image sensing module 180 can receive the first coaxial reflected light 300 through the filter 170 to collect the image of the imaging area 220, and transmit the image data of the imaging area 220 to the first computing unit 140. The first molten pool 210 in welding is in a molten state, and its image grayscale value is different from the image grayscale value of the remaining solid part of the imaging area 220. Therefore, this difference can be used as a feature point for determining the intersection of the molten state and the solid state of the surface profile 211 of the first molten pool 210. The first computing unit 140 can identify the surface profile 211 of the first molten pool 210 based on this feature point. After the surface profile 211 of the first molten pool 210 is known, the width w of the surface profile 211 can be estimated.

[0042] Please refer to Figure 2 The method for estimating the molten pool morphological features of this embodiment further includes the following steps: collecting image data of an imaging area, the imaging area includes the first molten pool S5; identifying a surface contour of the first molten pool through a feature point S6; and estimating the width of the surface contour S7.

[0043] The laser welding system, the method for obtaining the molten pool depth function, and the method for estimating the molten pool morphological characteristics of the present invention can instantly estimate the molten pool morphological characteristics, such as the depth of the molten pool and the width of the surface profile, during the welding process, so that it can be immediately known whether the welding depth and width meet the requirements during the welding process, which is convenient for users to adjust the welding parameters in advance, and reduce the number of post-weld inspections and destructive analysis, which helps to improve the yield rate and reduce the overall production cost and time. In addition, the measurements of the present invention are all coaxial measurements, and the data obtained by the measurements do not have deviations caused by angles, which can reduce the error in the estimation of the molten pool morphological characteristics.

[0044] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for estimating molten pool morphology characteristics, It is characterized in that The following steps are involved: Providing a molten pool depth function with voltage as a variable; irradiating a workpiece group with a first laser beam to form a first molten pool; sensing a first coaxial reflected light reflected from the first molten pool, and outputting a first voltage signal accordingly; and The first voltage signal is substituted into the molten pool depth function to estimate the depth of the first molten pool in real time.

2. The method for estimating molten pool morphology characteristics according to claim 1, It is characterized in that Further comprising the steps of: Collecting image data of an imaging area, where the imaging area includes the first molten pool; identifying a surface profile of the first molten pool via a feature point; and Estimate the width of the surface profile.

3. The method for estimating molten pool morphology characteristics according to claim 2, It is characterized in that The characteristic point is that the image grayscale value of the first molten pool is different from the image grayscale values ​​of the remaining solid parts of the imaging area.

4. A method for obtaining a molten pool depth function, It is characterized in that The following steps are involved: Irradiating one of the plurality of test piece groups with a second laser beam to form a second molten pool; sensing a second coaxial reflected light reflected from the second molten pool, and outputting a second voltage signal accordingly; Integrate the second voltage signal with respect to time, and then calculate a voltage value per unit time; Measuring an actual molten pool depth of one of the test piece groups; Repeat the above steps for the remaining test pieces of the plurality of test pieces to obtain a plurality of unit time voltage values ​​and their corresponding actual molten pool depths; as well as A molten pool depth function is obtained by using a regression analysis method according to the plurality of unit time voltage values ​​and the corresponding actual molten pool depths.

5. The method for obtaining the molten pool depth function according to claim 4, It is characterized in that The voltage value per unit time is obtained by dividing the time integral value of the second voltage signal by the welding time.

6. The method for obtaining the molten pool depth function according to claim 4, It is characterized in that The actual molten pool depth is obtained by performing metallographic analysis on the welded test piece set.

7. The method for obtaining the molten pool depth function according to claim 4, It is characterized in that The error value of the molten pool depth function is less than ±10%.

8. A laser welding system, It is characterized in that include A first laser welding machine provides a first laser beam for irradiating a workpiece group to form a first molten pool; a first beam splitter, disposed on the optical path of the first laser beam, for splitting a first coaxial reflected light reflected from the first molten pool; a first photoelectric sensing module, which is illuminated by the first coaxial reflected light from the first beam splitter and outputs a first voltage signal; and A first operation unit has a molten pool depth function with voltage as a variable. The first operation unit obtains the first voltage signal and estimates the depth of the first molten pool in real time through the molten pool depth function.

9. The laser welding system according to claim 8, It is characterized in that The first photoelectric sensing module includes a photodiode.

10. The laser welding system according to claim 8, It is characterized in that Further including: a third beam splitter, disposed on the optical path of the first laser beam, for reflecting the first coaxial reflected light from the first beam splitter; a filter for limiting the wavelength of the first coaxial reflected light from the third beam splitter; and An image sensing module receives the first coaxial reflected light passing through the filter to collect the image of the first molten pool, and transmits the collected image data to the first computing unit.

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