A method for monitoring three-dimensional laser wobble

Abstract

This invention discloses a monitoring method for three-dimensional laser oscillation, relating to the field of three-dimensional laser welding. The method includes a laser beam, a first reflecting mirror positioned to the left of the laser beam, a second reflecting mirror positioned in front of the first reflecting mirror, and a third reflecting mirror positioned to the right of the second reflecting mirror. This invention achieves accurate monitoring of the periodic changes in the laser's Z-axis direction by obliquely directing the laser beam onto the weld seam during welding. The laser period is calculated using the geometric relationship between the welding head and the weld seam, and the laser frequency is obtained by analyzing weld seam images captured by a high-speed camera. This method eliminates the need for expensive monitoring equipment, effectively reducing costs and solving the technical problems of existing monitoring equipment, such as high cost, narrow application range, and inability to determine the direction of defocusing.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional laser welding, specifically to a method for monitoring the oscillation of a three-dimensional laser. Background Technology

[0002] Laser welding is widely used in manufacturing due to its advantages such as concentrated heat input, small heat-affected zone, and ease of automation. 3D laser beam oscillation welding is a new type of oscillation welding, which refers to the movement of the laser spot on a two-dimensional plane, with changes in defocus, leading to changes in heat input. Importantly, the changes in heat input caused by the defocus of the 3D laser beam affect the opening and closing of the keyhole. The keyhole can significantly increase the laser absorption rate. Therefore, the defocus changes during 3D laser beam oscillation welding have a profound impact on the welding process. Thus, it is necessary to monitor the changing defocus. Currently, there are basically no monitoring systems for laser welding defocus values. This is because most welding optical lenses are highly accurate, and the actual defocus value is basically consistent with the theoretical defocus value. However, as a new technology, the motor driving the Z-axis lens movement in 3D laser beam oscillation welding may reach its limit, and welding platforms without a 3D laser beam oscillation welding module will not report errors, which will directly affect the laser defocus changes applied to the weld, resulting in poor weld quality.

[0003] Regarding the monitoring of laser welding trajectories, the invention patent with publication number CN111203654A discloses a laser welding trajectory tracking and monitoring system. This system uses multiple sets of CCD industrial cameras to extract position images during laser welding. Then, a trajectory integration module integrates the extracted photos and generates dynamic images. The generated dynamic trajectory images are then matched with trajectory templates to achieve the monitoring purpose. Although this system is effective to some extent, the use of multiple sets of industrial cameras significantly increases the monitoring cost.

[0004] In the study of the impact of laser welding on welding quality, the invention patent with publication number CN112719646A discloses a real-time monitoring method for welding quality during the laser welding process. This method involves establishing a user module to monitor multiple data points in real time and comparing the captured data with standard data collected by an intelligent control system to achieve the monitoring objective. While this method achieves a certain degree of monitoring effectiveness, the process is cumbersome, and the one-to-one matching monitoring method significantly increases the monitoring time. Furthermore, the dynamic integration of a large number of static photos introduces certain errors, reducing the accuracy of the monitoring.

[0005] If the above two technologies are directly applied to the monitoring of 3-D oscillating laser beam welding, the defocus value can be inferred by monitoring the closing and opening of the keyhole and the depth of the keyhole. However, since the keyhole closing and opening only correspond to a certain defocus value under specific materials, this means that special welding samples for testing are required, which are expensive and have a narrow range of applications. At the same time, it is impossible to determine the direction of defocus. Summary of the Invention

[0006] The purpose of this invention is to provide a method for monitoring three-dimensional laser oscillation, in order to solve the problems that direct application in monitoring 3-D laser beam oscillation welding requires specialized welding specimens for testing, which are expensive, have a narrow application range, and cannot determine the direction of defocus.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for monitoring three-dimensional laser oscillation, comprising a laser beam, wherein a first reflector is disposed on the left side of the laser beam, a second reflector is disposed in front of the first reflector, and a third reflector is disposed on the right side of the second reflector;

[0008] The process includes the following steps:

[0009] Step 1: Adjust the parameters of the 3D galvanometer welding control console so that the laser beam is emitted obliquely onto the weld seam of the workpiece, and set up a high-speed camera obliquely above the weld seam.

[0010] Step 2: Use the 3D galvanometer welding console to adjust the angle of the galvanometer so that the laser beam can perform welding along the weld seam, while using a high-speed camera to capture real-time images of the weld seam;

[0011] Step 3: By analyzing and processing the tilt parameters of the laser beam and the weld image, the laser oscillation during the welding process is monitored;

[0012] In step one, by adjusting the parameters of the three-dimensional galvanometer welding console, the XOY plane oscillation of the laser beam is canceled, the heat conduction welding mode is selected, and the Z-axis oscillation of the laser beam during the welding process is monitored.

[0013] In step one, let D be the vertical distance between the laser head and the plane where the workpiece is located (i.e., the XOY plane), K be the foot of the perpendicular, r be the radius of the laser spot, LH be half the width of the weld, L be the vertical distance from the foot of the perpendicular K to the straight line containing the center of the weld, C be the sampling rate of the high-speed camera, and X be the difference in the minimum frame number between two adjacent frames of images where the laser spot is at the same position. Then, the amplitude of the laser beam's oscillation in the Z-axis direction is... oscillation frequency .

[0014] Preferably, in step one, the laser beam is set to a sine wave or a triangular wave.

[0015] Preferably, a field mirror is installed in front of the third reflecting mirror, and a welding workpiece sample is placed in front of the field mirror, with a track on the welding workpiece sample.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: by obliquely shining a laser beam onto the weld seam to perform welding, the periodic variation of the laser in the Z-axis direction is transferred to the weld seam of the welded workpiece sample. Then, the period of the laser is calculated using the geometric relationship between the welding head and the weld seam, and the frequency of the laser is obtained by analyzing the weld seam image captured by a high-speed camera. Thus, the periodic variation of the laser in the Z-axis direction can be accurately obtained. No expensive monitoring equipment is required, which can effectively reduce costs and solve the technical problems of the prior art, such as the high price of monitoring equipment, narrow application range, and inability to determine the direction of defocus. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0018] Figure 2 This is a schematic diagram of the laser beam path of the present invention;

[0019] Figure 3 This is a schematic diagram showing the relative positions of the laser head and the welding trajectory curve of the present invention;

[0020] Figure 4 This is a schematic diagram showing the relative positions of the laser head, the welded workpiece sample, and the high-speed camera of the present invention.

[0021] Figure 5 This is a schematic diagram illustrating the geometric relationship between the laser head and the welding trajectory curve of the present invention;

[0022] Figure 6 This is a schematic diagram of a weld example of the present invention;

[0023] Figure 7 This is a schematic diagram of the welding structure of the present invention. Wherein: 1. Laser beam; 2. First reflecting mirror; 3. Second reflecting mirror; 4. Third reflecting mirror; 5. Field mirror; 6. Welding workpiece sample; 7. Trajectory; Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figure 1-7A method for monitoring three-dimensional laser oscillation includes a laser beam 1, a first reflector 2 disposed on the left side of the laser beam 1, a second reflector 3 disposed in front of the first reflector 2, and a third reflector 4 disposed on the right side of the second reflector 3.

[0026] Includes the following steps:

[0027] Step 1: Adjust the parameters of the three-dimensional galvanometer welding control console so that laser beam 1 is emitted obliquely onto the weld seam of the workpiece, and set up a high-speed camera obliquely above the weld seam.

[0028] Write a 3D oscillating welding program in the 3D galvanometer welding console, and set the welding trajectory curve as shown in the attached figure. Figure 2 As shown in trajectory 7, the planar oscillation is canceled. The planar oscillation is usually built into the welding console, which is a specific platform and can be directly canceled. Since the high-speed camera may not be able to capture the laser position after a keyhole forms in the molten pool, the monitoring method of this invention requires that no keyholes be formed during the welding process. Laser parameters can be set through the three-dimensional galvanometer welding console to control the laser energy density input as small as possible, so that the welding mode is in the heat-conducting welding mode. At this time, no keyholes are generated in the molten pool. When setting up the high-speed camera, the downward angle θ between the camera and the welding workpiece sample 6 should be as large as possible, such as 70-89 degrees. The camera's focusing area is adjusted to the position of trajectory 7. By adjusting the angles of the first reflecting mirror 2, the second reflecting mirror 3, the third reflecting mirror 4, the field mirror 5, and the galvanometer inside the welding head, the welding head moves as shown in the attached figure. Figure 3 The movement shown above, but the focal position of the laser beam 1 always remains on the trajectory 7. Since only the welding head is displaced along the Y-axis, there is a certain angle between the line connecting the welding head and point TCP11 and the laser beam 1. At this time, the perpendicular distance between point TCP11 and trajectory 7 is denoted as L. The laser focal point is a circular spot with a radius r = 0.3 mm and the energy conforms to the Gaussian distribution. The welding workpiece sample 6 can be any metal with good weldability. In this case, it is 316L stainless steel. At this time, the laser focal point will move along the trajectory 7. If the welding program is started, the laser beam 1 will leave a weld bead on the welding workpiece sample 6 under the action of the first reflecting mirror 2, the second reflecting mirror 3, the third reflecting mirror 4 and the field mirror 5.

[0029] Step 2: Adjust the angle of the galvanometer using the 3D galvanometer welding console so that the laser beam 1 can perform welding along the weld seam, while simultaneously using a high-speed camera to capture real-time images of the weld seam;

[0030] For conventional welding, the coordinate system in the oscillating welding program is selected as geodetic coordinates, and the position of trajectory 7 in space is fixed. If the welding head is moved by the robotic arm, the position of welding trajectory 7 in space remains unchanged, as shown in the attached figure. Figure 4The welding head is moved upwards. This movement should be linear, meaning that the orientation of the galvanometer lens is not changed and the welding head is always perpendicular to the ground. This ensures that trajectory 7 is as far away from the workpiece coordinate origin TCP11 as possible. In remote welding, the TCP point is generally defined as the focal point of laser beam 1 when both the galvanometer lens, welding head, and laser are vertical to the ground. For ease of filming, this invention does not use conventional welding methods. Instead, it achieves rapid scanning and deflection of the weld seam by changing the angle of the galvanometer lens. During the welding process, the welding head does not move. The laser angle is changed only by changing the galvanometer lens angle. However, the focal point of laser beam 1 always remains on trajectory 7. That is, the laser beam always moves along the HP direction towards the welding direction. During this process, only the galvanometer lens angle is changed, and the welding path is always a straight line. Laser beam 1 can be a periodic electromagnetic wave such as a sine wave or a triangular wave. The welding program is started to perform welding, and a high-speed camera is simultaneously activated to record the welding process.

[0031] Step 3: By analyzing and processing the tilt parameters of laser beam 1 and the weld image, the laser oscillation during the welding process is monitored;

[0032] Measure the distance HK from the center point H of the field lens 5 of the welding joint to the plane α where the welded workpiece sample is located. This distance remains constant during the welding process. K is the intersection point of the perpendicular lines drawn from the center point H of the field lens 5 to plane α, also known as the foot of the perpendicular H. After welding, the weld width can be measured using a ruler, and half of this width is denoted as LH. The measurement of the weld width is shown in the attached figure. Figure 5 As shown, attached Figure 5 In this context, Loffset is the distance from the laser center point to the fusion line, which can be approximated by the length of a laser point radius r. The projection of trajectory 7 onto the α plane is denoted as 15, and... Figure 4 Point E in the diagram is on point 15; the line connecting the farthest point reached by the laser center point during actual welding is denoted as point 14, and its distance from point 15 is Lw, and attached... Figure 4 Point F is on 14; in the heat-conducting welding mode, the fusion line is formed by the ablation of the laser spot edge, so the distance between line 14 and the fusion line is approximately one laser radius. Therefore, the distance between the fusion line and line 15 is half the weld width LH, i.e. Extract the photos recorded by the high-speed camera, recording the frame rate C, such as 10,000 frames per second, as shown in the attached image. Figure 4 As shown, the image with the same spot position and the smallest frame number difference is found, which is the difference in frame number between two adjacent frames where the spot is in the same position. If the frame number difference is X, then the actual oscillation welding frequency is determined. This can be determined through the following relationship: Through the attached Figure 4 The geometric relationship shown can be used to calculate the amplitude T of the actual trajectory curve 7 as follows: After calculating the periodicity of the laser spot motion trajectory 7, the laser's motion in the Z-axis direction is obtained, which can be used to guide the development of three-dimensional oscillating laser welding modules. Simultaneously, in three-dimensional oscillating welding, it can be used for pre-welding calibration, such as when welding stainless steel plates. Using the monitoring method of this invention, the periodicity of the laser spot motion trajectory 7 is first monitored on the same stainless steel plate to find the appropriate motion period and amplitude of the laser spot trajectory 7. Then, these parameters are used to weld the stainless steel plate to be welded, thereby achieving the welding objective. Furthermore, the change in the oscillation frequency in the Z-axis direction of three-dimensional oscillating laser welding significantly affects the aspect ratio and porosity of the molten pool, which has a great impact on weld quality. This monitoring method is expected to guide research on the impact of the motion changes in the Z-axis direction of three-dimensional oscillating laser welding on the penetration depth and weld quality.

[0033] To verify the feasibility of the monitoring method of the present invention, we performed three-dimensional oscillatory laser welding on the workpiece by setting laser beams 1 with different frequencies in the Z-axis direction. The results are shown in the attached figure. Figure 6 This indicates that as the oscillation frequency along the Z-axis increases, the depth-to-width ratio of the molten pool gradually increases, effectively improving the welding quality; as shown in the attached figure... Figure 7 As shown, metallographic cross-sections with three different oscillation frequencies are set in the Z-axis direction. (a) represents no oscillation frequency in the Z-axis direction, (b) represents a larger oscillation frequency in the Z-axis direction, and (c) represents a smaller oscillation frequency in the Z-axis direction. (c1) and (c2) represent the weld penetration during the upper and lower halves of the sine wave in the Z-axis oscillation process, respectively. All of these clearly show that the oscillation frequency in the Z-axis direction has a significant impact on the weld pool. This also illustrates the necessity of monitoring the oscillation frequency and period in the Z-axis direction during three-dimensional oscillating laser welding.

[0034] In this invention, the welding trajectory curve 7 is input into the welding control platform, the welding head is adjusted to be obliquely above the workpiece, but the workpiece is within the machinable area, and welding is then performed under the capture of a high-speed camera. The weld width is then measured, and finally, the periodicity of the laser focus movement process is calculated through geometric relationships. This invention achieves the monitoring of the three-dimensional laser oscillation welding process for the first time. Compared with other monitoring methods, it reduces monitoring costs and has wider applicability. By using frame count recording and frame acquisition rate, the periodic parameter—frequency—of the bright spot in the molten pool is calculated. Through the geometric relationship between the three-dimensional welding trajectory 7 and its projection, another aspect of the oscillation in the Z-axis direction during three-dimensional oscillation welding is calculated. The periodic parameter—amplitude—effectively improves the accuracy of monitoring data. Moreover, the high-speed camera used can clearly observe the movement of bright spots in the molten pool through intelligent algorithms. This plays an important role in the study of molten pool changes and weld defects. Furthermore, by using a three-dimensional galvanometer welding console to adjust parameters, the laser beam 1 can be obliquely projected onto the weld, thereby converting the oscillation of the laser beam 1 in the Z-axis direction onto the XOY plane. This can be reflected by the welding condition of the weld. Then, by using a high-speed camera to acquire weld images and combining the geometric relationship between the weld head and the weld, the period and frequency in the Z-axis direction of the laser beam 1 can be calculated, thus completing the monitoring of the laser beam 1 oscillation.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for monitoring three-dimensional laser oscillation, comprising a laser beam (1), characterized in that: A first reflector (2) is provided on the left side of the laser beam (1), a second reflector (3) is provided in front of the first reflector (2), and a third reflector (4) is provided on the right side of the second reflector (3). The monitoring method includes the following steps: Step 1: Adjust the parameters of the three-dimensional galvanometer welding control console so that the laser beam (1) is obliquely emitted onto the weld seam of the workpiece, and set up a high-speed camera obliquely above the weld seam; Step 2: Use the three-dimensional galvanometer welding console to adjust the angle of the galvanometer so that the laser beam (1) can be used to weld along the weld seam, and at the same time use a high-speed camera to capture real-time images of the weld seam; Step 3: By analyzing and processing the tilt parameters of the laser beam (1) and the weld image, the laser oscillation during the welding process is monitored; In step one, by adjusting the parameters of the three-dimensional galvanometer welding console, the XOY plane oscillation of the laser beam (1) is canceled, the heat conduction welding mode is selected, and the Z-axis oscillation of the laser beam (1) during the welding process is monitored. In step one, let D be the vertical distance between the laser head and the plane where the workpiece is located (i.e., the XOY plane), K be the foot of the perpendicular, r be the radius of the laser spot, LH be half the width of the weld, L be the vertical distance from the foot of the perpendicular K to the straight line where the center of the weld is located, C be the sampling rate of the high-speed camera, and X be the difference in the minimum frame number between two adjacent frames of images where the laser spot is located at the same position. Then, the oscillation amplitude of the laser beam (1) in the Z-axis direction is... oscillation frequency .

2. The method for monitoring three-dimensional laser oscillation according to claim 1, characterized in that: In step one, the laser beam (1) is set to a sine wave or a triangular wave.

3. The method for monitoring three-dimensional laser oscillation according to claim 2, characterized in that: A field mirror (5) is installed in front of the third reflector (4), and a welding workpiece sample (6) is placed in front of the field mirror (5). A track (7) is provided on the welding workpiece sample (6).

Images