Laser light path turning welding method for inner cavity curved surface welding seam

Abstract

The invention relates to an inner cavity curved surface welding line laser light path turning welding method which is used for solving the technical problem that an existing welding method is difficult to operate when curved surface welding is carried out in an inner cavity, and the method comprises the steps that a reflecting mirror is arranged on a light emitting path of a laser welding head, and original laser beams are deflected; the laser beam enters the inner cavity space and irradiates the to-be-welded area of the curved surface weld joint; surface cleaning and fixing are conducted on a to-be-welded area, and the folded laser beams are focused to the center of a welding seam; enabling the laser beam to perform scanning welding on the curved surface welding seam according to a preset scanning track; in the welding process, protective gas is jetted to the position, acting on the workpiece, of the laser beam so as to blow away welding spatter and provide gas protection for a welding seam. The propagation direction of laser beams is changed through the reflecting mirror, so that laser can enter the inner cavity to weld a curved surface weld joint, the application range of laser welding is expanded, and the problem that curved surface welding is difficult to operate in the inner cavity space through an existing welding method is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser welding, in particular to a laser light path folding welding method for inner cavity curved welds. BACKGROUND

[0002] With the increasing demand for lightweight and high-precision structural components in the fields of aerospace, automobile manufacturing, energy equipment, etc., the welding of complex inner cavity curved welds has become a key technical bottleneck. For example, the inner cavity of a turbine disc of an aero-engine, the housing of a vehicle transmission, and the pressure vessel of a nuclear power plant, etc., have inner curved welds with large spatial curvature, poor accessibility, high welding quality requirements, etc. Traditional welding methods (such as TIG welding, MIG welding) are difficult to meet the high-precision requirements due to large heat input and difficult deformation control; while conventional laser welding has the advantages of energy concentration and small heat-affected zone, but is limited by the straight propagation characteristics of the laser light path, making it difficult to directly enter the inner cavity to complete the welding operation of the curved weld. SUMMARY

[0003] The purpose of the present application is to provide a laser light path folding welding method for inner cavity curved welds to solve the technical problem that the existing welding method is difficult to operate when welding curved surfaces in the inner cavity.

[0004] The purpose of the present application is mainly achieved by the following technical solutions:

[0005] A laser light path folding welding method for inner cavity curved welds, comprising:

[0006] S1. At least two mirrors are arranged on the light path of the laser welding head, and the original laser beam is deflected at least twice, so that the laser beam can enter the inner cavity space and irradiate the curved weld to be welded area;

[0007] S2. The surface of the area to be welded is cleaned and fixed, and the folded laser beam is focused on the center of the weld;

[0008] S3. A laser welding head with oscillating scanning function is used to make the laser beam scan the curved weld with a preset scanning trajectory;

[0009] S4. During the welding process, protective gas is sprayed to the position where the laser beam acts on the workpiece to blow off the welding spatter and provide gas protection for the weld.

[0010] Further, in step S2, further comprising:

[0011] The step of setting the defocus amount and the initial laser incidence angle.

[0012] Further, when the weld is a dissimilar aluminum alloy weld, in step S3:

[0013] The scanning trajectory of the laser beam is an eccentric scanning trajectory, and the center point is deviated to the side of the material with higher melting point or stronger thermal conductivity in the dissimilar aluminum alloy.

[0014] Further, in step S3, the scanning movement of the laser beam is superimposed with the movement along the depth direction of the weld to form a three-dimensional spiral climbing scanning trajectory.

[0015] Further, in step S4, the protective gas is sprayed through a plurality of independently controllable nozzles arranged in a ring around the laser light exit point.

[0016] Further, in step S3, the laser incidence angle is dynamically adjusted according to the real-time curvature of the curved surface weld, and the adjustment range is -30° to +30°.

[0017] Further, before welding, a three-dimensional model of the inner cavity and the weld of the workpiece to be welded is introduced, the weld path is automatically divided into a plurality of sections according to the geometric characteristics and heat dissipation conditions, and different sets of welding parameters are set for each section.

[0018] During welding, the corresponding welding parameter set is automatically called according to the section where the laser welding head is located to perform welding.

[0019] Further, the scanning trajectory is ∞, 8 or O-shaped.

[0020] Further, the adjustment range of the defocusing amount is -2mm to +5mm, and the adjustment range of the initial laser incidence angle is +5° to +15°.

[0021] In one or more technical solutions provided in the exemplary embodiments of the present application, at least one of the following beneficial effects can be achieved.

[0022] (1) In the technical scheme of the inner cavity curved surface weld laser light path folding welding method in the present application, the reflection mirror changes the propagation direction of the laser beam, so that the laser can enter the inner cavity to weld the curved surface weld, expanding the application range of laser welding, solving the problem that the existing welding method is difficult to operate in the inner cavity space for curved surface welding. In addition, fixing the workpiece, using the oscillating scanning function and spraying the protective gas help to maintain the stability of the welding process, reduce the welding fluctuations caused by factors such as workpiece movement, uneven energy distribution, spatter interference, improve the reliability and consistency of the welding, and reduce the scrap rate.

[0023] (2) In the technical solution of the laser optical path turning welding method for internal curved surface weld in this invention, by using airflow simulation and dynamic airflow control based on the three-dimensional model of the curved surface weld, the protective gas can form a more uniform and stable distribution around the weld. In addition, the gas flow rate is dynamically adjusted according to the actual shape of the weld and the position and posture of the welding head to ensure that appropriate protection can be provided in various parts of the complex weld, thereby improving the quality and reliability of welding of complex structural parts.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

[0026] Figure 1 This is a schematic flowchart of the laser optical path deflection welding method for the inner cavity curved surface weld in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of optical path reversal in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of laser power modulation in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the leading beam, the main beam, and the lagging beam in an embodiment of the present invention. Detailed Implementation

[0030] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0031] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments.

[0032] Example 1

[0033] like Figure 1 As shown, this embodiment of the invention provides a laser optical path reversal welding method for internal cavity curved surface welds, including:

[0034] S1, light path folding, at least two mirrors are arranged on the light path of the laser welding head, the original laser beam is deflected at least twice, so that the laser beam can enter the inner cavity space and irradiate the curved weld seam to be welded area;

[0035] S2, welding parameter setting, surface cleaning and fixing of the area to be welded, focusing the folded laser beam on the weld center;

[0036] S3, scanning welding, using a laser welding head with oscillating scanning function, the laser beam scans the curved weld seam with a preset scanning trajectory;

[0037] S4, cooperative protection, during the welding process, protective gas is sprayed to the position where the laser beam acts on the workpiece, to blow off the welding spatter and provide gas protection for the weld.

[0038] In S1, the incident laser beam is reflected by the mirror to change the propagation direction of the beam, so that the laser beam enters the inner cavity space and irradiates the curved weld seam to be welded area, which makes the original laser beam not limited by straight propagation, so that the laser beam which cannot directly enter the inner cavity space can enter and accurately irradiate the curved weld seam to be welded area according to the predetermined path, solving the technical problem of difficult light path in the inner cavity space.

[0039] As shown in Figure 2 , the device for realizing light path folding in S1 includes at least two mirrors and a support frame for adjusting the angle and position of the mirrors. After the laser beam is emitted from the laser welding head, it is reflected by the mirrors to the position of the weld seam of the workpiece to be welded. Exemplarily, the mirror can be a water-cooled copper mirror.

[0040] In S2, the surface of the area to be welded is cleaned to remove oil stains, oxidation layer, impurities and the like, to ensure the cleanliness of the welding area and avoid the influence of these factors on the welding quality, such as pores, cracks and other defects. The workpiece to be welded is fixed to ensure the stability of the workpiece position during welding, so that the welding position deviation caused by vibration, movement and other factors is avoided, the welding precision and consistency are ensured, the folded laser beam is focused on the weld center, the laser energy is highly concentrated, a high energy density heat source is formed at the weld, and efficient welding is realized, so that the weld metal is rapidly melted.

[0041] In S3, the oscillating scanning function of the laser welding head enables the laser beam to move along a preset scanning trajectory. Targeting the characteristics of curved weld seams, by presetting an appropriate scanning trajectory, it can ensure that the laser beam receives suitable energy input at every position on the curved surface, thereby achieving uniform welding of curved weld seams, improving welding quality, and reducing welding unevenness caused by the shape of the curved surface.

[0042] In S4, on the one hand, the shielding gas can blow away welding spatter, preventing it from adhering to the weld surface or laser optical components, thus avoiding affecting weld quality and laser transmission efficiency. On the other hand, the shielding gas can provide gas protection for the weld, isolating it from harmful gases such as oxygen and nitrogen in the air, preventing the weld metal from reacting with these gases at high temperatures, thereby reducing defects such as porosity and oxidation, and improving the performance and quality of the weld.

[0043] In summary, by using a reflector to change the propagation direction of the laser beam, the laser can enter the inner cavity space to weld curved seams, expanding the application range of laser welding and solving the problem of existing welding methods being difficult to operate within inner cavity spaces. In addition, fixing the workpiece, using oscillating scanning function, and spraying protective gas help maintain the stability of the welding process, reduce welding fluctuations caused by factors such as workpiece movement, uneven energy distribution, and spatter interference, improve the reliability and consistency of welding, and reduce the scrap rate. Moreover, compared with existing spot welding or wire welding methods, scanning welding can complete the welding of larger areas or longer seams in a single scan, reducing welding time and the number of operations, thereby improving overall welding efficiency.

[0044] In a preferred embodiment of the present invention, step S2 further includes:

[0045] The steps for setting the defocus amount and the initial laser incident tilt angle.

[0046] For example, the defocus amount and initial laser incident angle can be set according to the material characteristics (material type, material thickness, and material surface condition). By setting different defocus amounts, the depth of laser action inside the material will change. By setting the initial laser incident angle, the laser can be irradiated onto the material surface at a more suitable angle, thereby improving the material's absorption rate of laser energy. Setting the defocus amount and initial laser incident angle can make the laser energy act more accurately on specific positions and depths of the material, reducing errors in the processing.

[0047] In one optional embodiment of the present invention, when the weld is a dissimilar aluminum alloy weld, in step S3: the scanning trajectory of the laser beam is an eccentric scanning trajectory, with its center point biased toward the side of the dissimilar aluminum alloy with a higher melting point or stronger thermal conductivity.

[0048] Aluminum alloys with higher melting points require more energy to reach a molten state during welding. By deflecting the laser beam center point to that side, this material can receive relatively more laser energy, which helps it to melt fully and ensures a good metallurgical bond with the other material. Aluminum alloys with high thermal conductivity will quickly conduct away the absorbed laser energy, making it difficult for the local temperature to rise to the ideal welding temperature. Deflecting the laser center to that side can compensate for the energy lost due to heat conduction, allowing the material on that side to melt at a sufficiently high temperature and fuse with the other material. By adjusting the eccentric scanning trajectory and the appropriate deflection of the center point, the shape and size of the weld pool can be adjusted, allowing the weld pool to form a more suitable transition shape at the interface of dissimilar aluminum alloys. This reduces the inhomogeneity of the weld pool caused by differences in material properties, thereby obtaining a weld with a smooth surface and uniform width, and improving the appearance quality of the weld.

[0049] In a preferred embodiment of the present invention, in step S3, the scanning motion of the laser beam is superimposed with the motion along the weld depth direction to form a three-dimensional spiral climbing scanning trajectory.

[0050] The three-dimensional spiral climbing scanning trajectory enables uniform melting and bonding of the weld across the entire cross-section. Appropriate laser energy can be obtained at different locations on the weld, reducing welding defects caused by uneven energy distribution. In addition, the spiral climbing trajectory can refine the grains, reduce the formation of coarse grains and columnar crystals, and improve the mechanical properties of the weld.

[0051] In a preferred embodiment of the present invention, in step S4, the protective gas is ejected through a plurality of independently controllable nozzles arranged in a ring around the laser emission point.

[0052] The annularly arranged nozzles can simultaneously eject protective gas from all directions around the laser emission point, forming a relatively uniform and complete gas protection zone. This effectively isolates the surrounding air, preventing harmful gases such as oxygen and nitrogen from entering the weld pool. Furthermore, during the welding process, different parts of the weld pool may have different requirements for protective gas. Each nozzle is independently controllable, and the gas flow rate and spray direction of each nozzle can be adjusted according to the specific welding requirements. The independently controllable annular nozzles can provide stable, uniform, and precise gas protection, preventing the weld pool from reacting with harmful gases in the air during solidification, thereby reducing porosity and improving weld quality.

[0053] In a preferred embodiment of the present invention, in step S3, the laser incident tilt angle is dynamically adjusted according to the real-time curvature of the curved weld, and the adjustment range is -30° to +30°.

[0054] The curvature of curved welds is constantly changing. If the laser incident angle remains fixed, the laser beam may not be able to be accurately focused on the weld position as the curvature changes. For example, when welding convex curved welds, if the angle is not adjusted, the laser beam may diverge before reaching the weld, resulting in the energy not being concentrated on the welding area, reducing welding efficiency and quality. However, by dynamically adjusting the angle according to the real-time curvature, the laser beam can always be accurately focused on the weld, ensuring sufficient energy input for melting the metal, achieving stable welding, and ensuring effective focusing of laser energy.

[0055] Based on this, the laser welding power is set to 1.2 to 1.4 times the laser power required for flat plate welding under the same welding thickness, scanning trajectory and welding speed conditions.

[0056] Compared to flat plate welding, curved surfaces alter the laser's optical path. When a laser is incident on a curved surface at a certain angle, some of the laser beam may deviate from the intended welding area due to reflection and scattering, resulting in a reduction in the actual laser energy acting on the weld. Increasing the laser welding power to 1.2 to 1.4 times that required for flat plate welding can effectively compensate for the energy loss caused by changes in the curved surface's optical path and differences in heat conduction. By compensating for energy loss, sufficient laser power can ensure that the metal is fully melted, reducing the generation of defects such as incomplete fusion and porosity.

[0057] In a preferred embodiment of the present invention, before welding, a three-dimensional model of the inner cavity and weld of the workpiece to be welded is imported, and the weld path is automatically divided into multiple segments according to geometric features and heat dissipation conditions, and a different set of welding parameters is set for each segment; during welding, the corresponding set of welding parameters is automatically called to perform welding according to the segment where the laser welding head is located.

[0058] Using 3D modeling software (such as SolidWorks, UG, etc.) or 3D scanning equipment, a 3D model of the inner cavity and weld of the workpiece to be welded is obtained and imported into the welding control system. This model includes key information such as the workpiece's geometry, dimensions, and weld location. Based on the weld's geometry, such as arc segments or curve segments, the weld path is divided into different segments. By dividing the segments according to geometric features, more suitable welding parameters can be formulated for each segment, improving welding quality. Considering the heat dissipation of different parts of the workpiece, such as the faster heat dissipation near the workpiece edge, the fixture contact area, or well-ventilated areas, while the internal enclosed areas dissipate heat more slowly, areas with similar heat dissipation conditions are divided into the same segment. By dividing the segments according to heat dissipation conditions, welding parameters can be adjusted to compensate for heat dissipation differences, avoiding defects caused by local overheating or undercooling. Through segmentation and personalized parameter settings, defects caused by improper welding parameters, such as porosity, cracks, and lack of fusion, can be effectively avoided. At the same time, the dynamic adjustment mechanism can respond to changes in the welding process in a timely manner, further ensuring the stability of weld quality.

[0059] In a preferred embodiment of the present invention, the scanning trajectory is an ∞ shape, an 8 shape, or an ○ shape.

[0060] The ∞-shaped trajectory allows the laser beam to perform complex reciprocating and intersecting movements in the welding area. Compared to linear scanning, this allows the laser energy to be distributed more evenly in the weld and its surrounding area. At the intersection of the ∞ shape, the laser beam will irradiate the same area multiple times, resulting in energy superposition, which helps to increase the penetration depth at these specific locations.

[0061] In a preferred embodiment of the present invention, the defocusing amount is adjustable from -2mm to +5mm, and the initial laser incident tilt angle is adjustable from +5° to +15°.

[0062] Positive defocus (0mm < defocus amount ≤ +5mm) allows the laser beam to diffuse before reaching the workpiece, reducing energy density and preventing thin plates from being burned through due to concentrated energy. This ensures good weld formation and improves the appearance quality and sealing of the weld. Negative defocus (-2mm ≤ defocus amount < 0mm) allows the laser beam to be more focused before reaching the workpiece surface, resulting in higher energy density. This is beneficial for forming a stable keyhole effect, increasing the laser's penetration into the workpiece's interior, and achieving deeper penetration in thick plate welding, ensuring the connection strength and reliability of thick plate structural components. Adjusting the incident tilt angle within the range of +5° to +15° can change the reflection direction of the laser beam on the workpiece surface, preventing reflected light from being directly reflected back to the laser, reducing energy loss, increasing the workpiece's absorption of laser energy, and thus improving welding efficiency.

[0063] Example 2

[0064] Embodiment 2 of the present invention is a further improvement on Embodiment 1. In step 4, before welding, airflow simulation is performed based on the three-dimensional model of the curved weld to generate a dynamic airflow control profile. During the welding process, the protective gas flow rate of each nozzle is independently adjusted according to the real-time position and attitude of the laser welding head and the dynamic airflow control profile.

[0065] The 3D model of the curved weld seam describes the weld seam's geometry, spatial location, and orientation, using fluid dynamics simulation software (e.g., Flow-3D or ANSYS). Fluent, combined with a 3D model of the curved weld, simulates the flow of shielding gas around the weld during the welding process. Through simulation, it can predict the gas velocity, direction, and distribution under different locations and welding conditions, thereby identifying the optimal airflow distribution scheme. For example, the simulation can show that in certain curved parts of the weld, the gas is prone to forming vortices, resulting in poor shielding effect. Targeted optimization can be made through simulation. The dynamic airflow control profile is generated based on the airflow simulation results. The dynamic airflow control profile shows the shielding gas flow rate that each nozzle should output at different welding positions and time points. The dynamic airflow control profile is dynamic and changes with the welding process. It can adjust the gas flow rate in real time according to the shape of the weld and the progress of welding to ensure that the best shielding gas environment is provided throughout the welding process. Therefore, through airflow simulation and dynamic airflow control based on the 3D model of the curved weld, the shielding gas can form a more uniform and stable distribution around the weld. In addition, the gas flow rate can be dynamically adjusted according to the actual shape of the weld and the position and posture of the weld joint to ensure that appropriate protection is provided in various parts of the complex weld, thereby improving the quality and reliability of welding complex structural components.

[0066] In a preferred embodiment of the present invention, step 4 includes: scanning the curved weld seam using a 3D laser scanner or a structured light scanner to obtain point cloud data of the weld seam; importing the point cloud data into reverse engineering software for surface fitting and solid modeling to generate a 3D CAD model of the curved weld seam; verifying the geometric accuracy and spatial position accuracy of the 3D model by comparing it with the actual weld seam to ensure that the model error does not exceed a preset threshold (e.g., ±0.1mm).

[0067] From scanning to modeling, the accuracy and integrity of the weld model are ensured, accurately reflecting the geometry and spatial position of the actual weld. Based on the 3D CAD model, different welding parameters can be simulated to optimize the welding process and improve welding quality and efficiency. By comparing the 3D CAD model with the actual weld, the quality of the weld can be detected, and defects in the weld can be identified and repaired in a timely manner.

[0068] In a preferred embodiment of the present invention, step 4 further includes: importing a three-dimensional CAD model into fluid dynamics simulation software (such as ANSYS Fluent, CFX, or OpenFOAM); meshing the model to generate a computational mesh, the mesh density of which needs to meet the requirements for capturing flow field details (e.g., mesh size ≤ 1 mm near the weld); setting simulation boundary conditions, including the inlet velocity of the protective gas (range 5-30 L / min), outlet pressure (0-10 kPa), weld surface roughness (Ra 0.8-6.3 μm), and initial flow field distribution; running the airflow simulation to obtain data on the velocity, pressure, and temperature distribution around the weld; and generating a dynamic airflow control profile using post-processing software, the profile containing the optimal gas flow rate values ​​at each key point on the weld, the flow rate values ​​being continuously processed by an interpolation algorithm (such as cubic spline interpolation) to form a flow rate distribution curve that varies with welding position and time.

[0069] Geometric description ensures a high degree of consistency between the simulated physical environment and the actual situation, enabling the simulation results to realistically reflect the actual fluid flow around the weld. A fine mesh accurately describes the fluid's movement and changes, reducing errors caused by discretization and making the simulation results closer to reality. Determining boundary conditions allows the simulation results to better match the fluid flow during actual welding, providing a reliable basis for analyzing and optimizing the welding process. Detailed velocity, pressure, and temperature distribution data around the weld are obtained, which are crucial for analyzing the gas shielding effect, heat transfer, and potential defects (such as porosity and cracks) during welding. Dynamic airflow control profiles and flow distribution curves visually demonstrate the changes in gas flow during welding, providing clear guidance for operators.

[0070] In a preferred embodiment of the present invention, step 4 further includes: real-time monitoring of the spatial coordinates (X, Y, Z) and attitude angles (roll, pitch, yaw) of the laser welding head; specifically, this can be achieved by integrating a high-precision position sensor (laser tracker or encoder) and an attitude sensor (IMU or gyroscope) into the welding equipment; loading a dynamic airflow control profile onto the welding control system, and matching the target gas flow rate value at the corresponding position from the profile based on the real-time position and attitude of the welding head; and adjusting the protective gas flow rate of each nozzle through an independently controlled flow regulating valve (proportional valve or servo valve).

[0071] By monitoring spatial coordinates and attitude angles in real time, the system provides fundamental data for precise control of the welding process, enabling the welding head to weld according to a predetermined path and attitude. This improves the dimensional and shape accuracy of the weld. Furthermore, it can promptly detect deviations in the position and attitude of the welding head, reducing welding fluctuations caused by changes in position and attitude, and ensuring the stability of the welding process. Dynamically adjusting the gas flow rate based on the real-time position and attitude of the welding head allows for better coverage of the welding area by the protective gas, effectively eliminating air and impurities during the welding process, reducing welding defects such as porosity and oxidation, and improving welding quality. Automatic matching of the target gas flow rate value avoids the tediousness and errors of manual adjustment, achieving rapid and accurate gas flow rate regulation, reducing downtime during welding, and improving production efficiency. Through independently controlled flow regulating valves, the gas flow rate of each nozzle can be adjusted according to the target gas flow rate value matched by the control system, thereby improving the gas protection effect. In addition, the independent control mode allows the system to flexibly adjust the gas flow distribution according to different welding processes and workpiece requirements, improving the adaptability and versatility of the welding system.

[0072] Example 3

[0073] Embodiment 3 of the present invention is a further improvement based on Embodiment 1 or Embodiment 2. Step 2 further includes: real-time acquisition of molten pool images and / or acoustic emission signals during the welding process;

[0074] Based on the molten pool image and / or acoustic emission signal, the laser power and / or the scanning trajectory parameters of the laser beam are dynamically adjusted to maintain the stability of the molten pool.

[0075] Molten pool images can visually represent the appearance and morphology of the molten pool, including its dimensions (length, width, area) and shape (circular, elliptical, etc.). For example, by analyzing molten pool images, the area of ​​the molten pool can be accurately measured to determine whether it is within the appropriate process range. Too large an area may result in an excessively wide weld and an enlarged heat-affected zone, while too small an area may result in incomplete weld fusion. Acoustic emission signals reflect the dynamic changes occurring within the material during welding, such as elastic waves generated by defects like crack initiation and propagation, and porosity formation. Different types and degrees of defects produce acoustic emission signals with different characteristics. For instance, crack propagation generates high-frequency, high-energy acoustic emission signals. By collecting and analyzing acoustic emission signals, potential defects during the welding process can be detected in a timely manner. By addressing the shortcomings of traditional methods, the control system can react promptly based on this real-time information, adjusting welding parameters according to the actual state of the molten pool rather than relying on outdated or predicted data. This improves the accuracy and timeliness of control. When the molten pool image shows that the temperature is too high or the area is too large, reducing the laser power can reduce the heat input to the molten pool, avoiding defects such as excessive evaporation of weld metal, porosity, or burn-through caused by overheating. Conversely, when the temperature is too low or the area is too small, increasing the laser power can provide sufficient heat to ensure that the weld metal is fully melted and achieves good fusion. In addition, by dynamically adjusting the parameters, the welding process can always be kept in the optimal state, reducing welding interruptions or rework caused by inappropriate parameters.

[0076] Specifically, acquiring images of the molten pool during the welding process includes: installing a high-speed camera, a filtering system, and optional lighting devices in a position perpendicular to the welding direction; synchronizing the high-speed camera with the trigger signal of the welding equipment; synchronously starting image acquisition when welding begins; continuously acquiring images of the molten pool during the welding process; and storing the acquired images in real time. Histogram equalization, contrast stretching, and sharpening are then applied to the acquired molten pool images to enhance image contrast and clarity, making the edges and features of the molten pool more prominent for easier subsequent analysis.

[0077] Acquiring acoustic emission signals during the welding process includes: fixing the acoustic emission sensor near the weld pool using magnetic attraction, adhesive, or mechanical clamps; using an acoustic emission data acquisition system to filter and denoise the acquired signals to remove background noise and interference signals; and then extracting characteristic parameters such as energy, amplitude, and frequency of the acoustic emission events. The acoustic emission events are transient elastic wave signals released by the material during dynamic processes such as local plastic deformation, crack initiation and propagation, phase transformation, porosity formation, or droplet transfer under the thermo-mechanical coupling effect of welding.

[0078] Feature extraction of the molten pool image involves using image segmentation algorithms (such as thresholding and edge detection) to separate the molten pool region from the background, and then extracting geometric feature parameters such as the area, length, width, and shape factors (such as circularity and rectangularity) of the molten pool. Temperature distribution features of the molten pool, such as average temperature, maximum temperature, and temperature gradient, are extracted by combining an infrared thermal imager with a high-speed camera, or by utilizing the correspondence between grayscale and temperature in the molten pool image. Based on welding process requirements and experience, a molten pool state assessment model is established, correlating the extracted molten pool feature parameters with the stable state of the molten pool. By setting thresholds, when certain feature parameters exceed the normal range, the molten pool is judged to be in an unstable state.

[0079] Acoustic emission signal characteristic evaluation extracts characteristic parameters such as count rate, energy, amplitude, and frequency distribution of acoustic emission events from the preprocessed acoustic emission signal. Judgment criteria are established based on the relationship between acoustic emission characteristic parameters and molten pool state. For example, when the count rate of acoustic emission events suddenly increases or the energy exceeds a set threshold, it is judged that there are unstable factors in the molten pool.

[0080] Adjusting parameters based on the molten pool image: If the molten pool temperature is too high or the area is too large, reduce the laser power to reduce the heat input to the molten pool to avoid defects such as excessively wide welds, increased heat-affected zones, or burn-through; if the molten pool temperature is too low or the area is too small, increase the laser power to ensure that the weld metal is fully melted.

[0081] The adjustment method for parameters such as scanning speed, scanning path and scanning amplitude is determined based on the stability of the molten pool. For example, when the local temperature of the molten pool is too high, the scanning path is adjusted to allow the laser energy to avoid the area; when the shape of the molten pool is irregular, the scanning amplitude and path are adjusted to make the shape of the molten pool more regular.

[0082] Based on the parameter adjustment of the acoustic emission signal, when the acoustic emission signal indicates that there are unstable factors in the molten pool (such as crack formation), the laser power is reduced to prevent the crack from expanding further.

[0083] The laser beam scanning trajectory parameters are adjusted according to the characteristic changes of the acoustic emission signal to improve the stress state and heat distribution of the molten pool. For example, when an acoustic emission signal for the formation of pores is detected, the scanning path is adjusted so that the laser energy is more concentrated on the area where pores may be generated, thus promoting the discharge of gas.

[0084] When adjusting the laser power, the adjusted laser power parameters can be sent to the laser control system, which will then adjust the laser output power in real time based on the received parameters.

[0085] Example 4

[0086] Embodiment 4 of this invention is a further improvement based on Embodiments 1, 2, or 3. In fields such as aerospace and automotive manufacturing, it is often necessary to weld metal materials with different melting points together, such as titanium alloys and aluminum alloys, or stainless steel and copper alloys. Using laser power modulation welding can effectively solve the welding difficulties caused by large differences in melting points when welding dissimilar metals. Figure 3 As shown, in step 3, the power of the laser beam adopts a modulation waveform synchronized with the scanning frequency. When the beam scans to the side of the high melting point material, a first power value (e.g., the first power value is 1000W) is applied, and when it scans to the other side, a second power value (e.g., the second power value is 500W) is applied, wherein the first power value is greater than the second power value.

[0087] Based on the melting point characteristics of the materials, a larger first power value is applied when the laser beam scans the side of the high melting point material to ensure that the high melting point material can fully absorb energy and melt. When scanning the side of the low melting point material, a smaller second power value is applied to avoid the low melting point material from overheating, evaporation, or other adverse phenomena due to excessive energy absorption. This allows for precise adaptation to the physical properties of different materials. Through real-time adjustments, the welding process can be precisely controlled according to changes in the material, avoiding local energy shortages or excesses caused by fixed power. As a result, welding defects caused by improper energy input can be effectively avoided, improving the mechanical properties and reliability of the welded joint.

[0088] Example 5

[0089] Embodiment 5 of the present invention is a further improvement based on Embodiment 1, Embodiment 2, Embodiment 3 or Embodiment 4. It uses beam splitting technology to divide the incident laser into a leading beam, a main beam and a lag beam with independently controllable energy. The leading beam is used to preheat the weld area, the main beam is used to perform deep penetration welding and the lag beam is used to perform post-heat treatment of the weld.

[0090] For example, a beam splitter can be used to split the incident laser into a leading beam, a main beam, and a lagging beam. Then, by adjusting the reflectivity / transmittance of the beam splitter's coating or by combining it with an attenuator, the energy of the different beams can be independently allocated.

[0091] The lead beam preheats the weld area, raising the material temperature and lowering its melting point. Materials that normally require high energy to melt can be melted with relatively less energy after preheating, creating more favorable conditions for deep penetration welding with the main beam. Furthermore, preheating reduces the temperature gradient between the weld area and the surrounding material. During welding, a large temperature gradient can easily lead to significant thermal stress within the material, causing weld deformation and cracks. Preheating with the lead beam effectively reduces the temperature gradient, decreases welding stress, and improves the quality of the weld joint. The main beam has a high energy density, enabling the formation of a deep molten pool in the weld area. The focused laser energy rapidly melts and vaporizes the material, generating strong plasma backpressure that pushes the molten metal outwards, creating a keyhole effect. This keyhole effect allows the laser energy to penetrate deep into the material, achieving deep penetration welding and ensuring sufficient weld depth and strength. Moreover, the energy and focusing position of the main beam can be precisely controlled, allowing for precise operation of the welding process. Residual stress generated during welding can affect the performance and service life of welded joints. The delayed beam heat treatment of the weld seam reheats the weld area, causing a certain degree of plastic deformation, thereby releasing and eliminating residual welding stress and improving the stability and reliability of the welded joint.

[0092] For example, such as Figure 4 As shown, the power of the leading beam is set to 300-400W, and its position is 1-2mm in front of the main beam. The power of the main beam is set to 1200-1500W, and its position is located at the welding center. The power of the lagging beam is set to 400-500W, and its position is 2-3mm behind the main beam.

[0093] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A laser optical path folding welding method for internal cavity curved surface welds, characterized in that, include: S1. Set at least two reflectors on the light output path of the laser welding head to deflect the original laser beam at least twice, so that the laser beam can enter the inner cavity space and irradiate the curved weld seam area to be welded. S2. Clean and fix the surface of the area to be welded, and focus the folded laser beam on the center of the weld. S3. The laser beam is used to scan and weld the curved weld seam along a preset scanning trajectory; S4. During the welding process, protective gas is sprayed onto the location where the laser beam acts on the workpiece to blow away welding spatter and provide gas protection for the weld.

2. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, Step S2 also includes: The steps for setting the defocus amount and the initial laser incident tilt angle.

3. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1 or 2, characterized in that, When the weld is a dissimilar aluminum alloy weld, in step S3: The scanning trajectory of the laser beam is an eccentric scanning trajectory, with its center point biased towards the side of the dissimilar aluminum alloy with a higher melting point or stronger thermal conductivity.

4. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, In step S3, the scanning motion of the laser beam is superimposed with the motion along the weld depth direction to form a three-dimensional spiral climbing scanning trajectory.

5. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, In step S4, the protective gas is ejected through multiple independently controllable nozzles arranged in a ring around the laser emission point.

6. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, In step S3, the laser incident tilt angle is dynamically adjusted according to the real-time curvature of the curved weld.

7. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, In step S3, the real-time curvature of the curved weld is adjusted within the range of -30° to +30°.

8. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, Before welding, import the three-dimensional model of the inner cavity and weld of the workpiece to be welded, automatically divide the weld path into multiple segments according to geometric features and heat dissipation conditions, and set different welding parameter sets for each segment. During welding, the corresponding welding parameter set is automatically called according to the section where the laser welding head is located to perform welding.

9. The laser optical path folding welding method for internal cavity curved surface welds according to claim 1, characterized in that, The scanning trajectory is in the shape of an ∞, an 8, or an ○.

10. The laser optical path folding welding method for internal cavity curved surface welds according to claim 2, characterized in that, The defocusing amount can be adjusted from -2mm to +5mm, and the initial laser incident tilt angle can be adjusted from +5° to +15°.

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