A dual-beam symmetric incidence laser welding closed-loop control method

Abstract

The present application relates to the field of welding manufacturing and intelligent control technology, in particular to a kind of double-beam symmetric incidence laser welding closed loop control method, the method includes obtaining the assembly quality parameter of the weld to be welded, and the process characteristic quantity of welding process;Based on the assembly quality parameter and process characteristic quantity, the welding stability criterion containing penetration stability threshold and forming stability threshold is constructed, whether the current welding state meets the preset requirement is calculated and judged by the welding stability criterion;If the current welding state does not meet the preset requirement of welding stability criterion, adjust welding control parameter and synchronously output control instruction, until the welding state meets the preset requirement of welding stability criterion.According to the scheme of the present application, the welding process stability and joint quality consistency are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of welding manufacturing and intelligent control, and particularly relates to a closed-loop control method for double-beam symmetric incident laser welding. Background Art

[0002] Currently, heavy-duty complex cross-section steel members (such as multi-cavity cross-section structures like thick plate "T" shape, double "H" shape, "日" shape, etc.) are usually spliced and connected by methods such as arc welding or single-beam laser welding in engineering manufacturing. Such members generally have the characteristics of large plate thickness (t) (for example, ≥15mm), complex cross-sectional shape, large member size, high restraint degree, and obvious thermal stress concentration. During the welding process, it is easy to have problems such as difficulty in兼顾 melt penetration and forming, difficulty in controlling welding deformation and residual stress, and large fluctuations in joint quality consistency, which in turn affect the subsequent assembly accuracy and reliability.

[0003] Although the traditional arc welding process has a wide range of applications, it has deficiencies such as large heat input, wide heat affected zone, and relatively low welding efficiency. Under thick plate and high restraint conditions, it is more likely to cause post-weld angular deformation, bending deformation, and residual stress accumulation, resulting in an increase in subsequent矫形, machining, and repair costs, and it is difficult to兼顾 efficiency and structural consistency in long-scale members.

[0004] Single-beam laser welding has advantages such as high energy density and relatively small heat affected zone. However, in the welding scenario of thick plate complex cross-section steel, the energy coupling at the weld root is sensitive to assembly gaps, misalignment, weld position deviation, and uneven cross-sectional heat conduction; at the same time, the multi-cavity cross-section causes changes in the heat dissipation path and restraint conditions along the welding direction, which is likely to cause fluctuations in the molten pool or keyhole state, and then defects such as incomplete fusion or incomplete penetration, porosity, and unstable forming occur. If the linear energy input is increased to meet the melt penetration, it may bring risks of local overheating and increased deformation, and it is difficult to meet the comprehensive requirements of deep penetration, forming, and deformation control at the same time.

[0005] Therefore, the field needs a welding technical solution suitable for thick plate complex cross-section conditions to solve the problems of poor stability in the current welding process and inability to兼顾 efficiency and structural consistency. Summary of the Invention

[0006] In order to solve the above technical problems of poor stability in the current welding process of heavy-duty complex cross-section steel and inability to兼顾 efficiency and structural consistency, the present invention provides the following technical solutions.

[0007] This invention provides a closed-loop control method for dual-beam symmetrical incident laser welding, comprising: acquiring assembly quality parameters of the weld to be welded and process characteristic quantities of the welding process; the assembly quality parameters include at least weld gap, misalignment, and weld position deviation; the process characteristic quantities include at least one or more of temperature characteristics, molten pool geometry characteristics, and keyhole characteristics; constructing a welding stability criterion including a penetration stability threshold and a forming stability threshold based on the assembly quality parameters and process characteristic quantities; calculating and determining whether the current welding state meets preset requirements through the welding stability criterion; if the current welding state does not meet the preset requirements of the welding stability criterion, adjusting the welding control parameters and synchronously outputting control commands until the welding state meets the preset requirements of the welding stability criterion.

[0008] In one embodiment, the preset requirements include that the assembly quality parameters are within a preset allowable range; and that both the melt depth stability index and the forming stability index meet the corresponding threshold requirements.

[0009] In one embodiment, the preset allowable range includes: weld gap less than or equal to 0.8 mm, misalignment less than or equal to 0.5 mm, and weld position deviation less than or equal to 1.0 mm; wherein, if any parameter exceeds the range, the welding state is directly determined not to meet the preset requirements.

[0010] In one embodiment, the formula for calculating the melt depth stability is:

[0011]

[0012] in, For melting depth stability, The keyhole opening area within the current sampling window. To calibrate the target keyhole opening area obtained from the experiment, The standard deviation of the keyhole opening area within the sampling window. This represents the current length of the molten pool. For the target molten pool length, This is the current characteristic temperature value. The target characteristic temperature value, - These are the weighting coefficients, and their sum is 1.

[0013] In one embodiment, the formula for calculating forming stability is:

[0014] in, For forming stability, This refers to the current molten pool width or surface forming width. For target width, The standard deviation of the molten pool width within the sampling window. This is the offset of the molten pool center relative to the weld centerline. Allowable offset threshold and These are the characteristic widths on both sides of the weld centerline. - These are the weighting coefficients, and their sum is 1.

[0015] In one embodiment, adjusting welding control parameters includes: adjusting the overall heat input and power distribution during the welding process by adjusting the power of the first laser beam, the power of the second laser beam, and the welding speed; adjusting the energy density distribution during the welding process by adjusting the defocusing amount; wherein the defocusing amount is the amount by which the focal point is offset relative to the workpiece surface along the optical axis, and the energy density distribution is negatively correlated with the defocusing amount; and compensating for the energy application position by adjusting the focal point offset.

[0016] In one embodiment, the dual beams comprise a first laser beam and a second laser beam symmetrical about the weld center plane. The overall heat input during the welding process is adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed. This includes characterizing the overall heat input with line energy, wherein the formula for calculating the line energy is: In the formula, For line energy, The power of the first laser beam. The power of the second laser beam. For welding speed; control the total heat input within (E min E max ) interval, where To meet the minimum line energy threshold required for root fusion, The highest linear energy threshold to avoid the risks of collapse, overheating, and deformation.

[0017] In one embodiment, adjusting the power distribution during the welding process by adjusting the power of the first laser beam, the power of the second laser beam, and the welding speed includes: adjusting the energy balance on both sides using a power distribution factor, the formula for calculating the power distribution factor being: ;in, For power allocation factor, The power of the first laser beam. The power of the second laser beam is set to 0.4 to 0.6 under symmetrical conditions. When there are misalignments, positional deviations, or uneven thermal conductivity, the power distribution factor is set to 0.3 to 0.7 for compensation.

[0018] In one embodiment, adjusting the energy density distribution during the welding process by adjusting the defocusing amount includes: controlling the defocusing amount Δf to be within a certain range. For a depth of 2mm to +2mm, use negative decoking when the melting depth is insufficient, and use positive decoking when there is overheating or collapse.

[0019] In one embodiment, compensating for the energy application location by adjusting the focus offset includes: controlling the focus offset d to be between 0 and 0.5 mm, wherein the focus offset d and the lateral offset Δx satisfy a proportional compensation relationship d=k. d ×Δx, k d The compensation coefficient is used to compensate for the energy coupling center shift caused by assembly deviations through incremental iteration.

[0020] The beneficial effects of this invention are as follows: This invention achieves effective control over energy coupling and heat input distribution in the weld area through stability criterion constraints and closed-loop regulation, and improves the adaptability to assembly fluctuations and changes in constraint conditions, thereby enhancing the stability of the welding process and the consistency of joint quality.

[0021] Furthermore, by adaptively adjusting the line energy input and focal position, the present invention suppresses overheating while satisfying the penetration depth, thereby reducing post-weld deformation and subsequent straightening costs. Attached Figure Description

[0022] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein: Figure 1 This is a flowchart illustrating a closed-loop control method for dual-beam symmetrical incident laser welding according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating laser welding performed by symmetrical incidence of two beams according to an embodiment of the present invention. Detailed Implementation

[0023] 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, not all, of the embodiments of the present invention. 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.

[0024] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1 This is a flowchart illustrating a closed-loop control method 100 for dual-beam symmetrical incident laser welding according to an embodiment of the present invention.

[0025] A closed-loop control method for double-beam symmetric incident laser welding provided in the present invention is applicable to the welding process of heavy-duty complex-section steel profiles. For example, the steel profiles can be asymmetric or multi-cavity complex-section structures such as thick-plate "T" type, double "H" type, "日" type, etc. The typical plate thickness t is 15 - 25 mm, the mass per unit length is not less than 40 kg / m, and can reach up to 60 kg / m at most. In the method of the present invention, root-coupled energy input is formed by symmetrically incident two laser beams of the same type on both sides of the weld, and adaptive adjustment is carried out in combination with the assembly quality parameters and the process characteristic quantities of the welding process, so as to improve the stability of the welding process of thick-plate complex-section components and the consistency of joint quality.

[0026] Specifically, as Figure 1 shown, at step S101, the assembly quality parameters of the weld to be welded and the process characteristic quantities of the welding process are obtained. The assembly quality parameters at least include weld gap, misalignment, and weld position deviation. The assembly quality measurement can be realized by using a laser displacement sensor, structured light / vision measurement, contact measurement, or a combination thereof. The process characteristic quantities at least include one or more of temperature characteristics, molten pool geometric characteristics, and keyhole characteristics. In some embodiments, the process characteristic quantities can be obtained by infrared temperature measurement, vision imaging, coaxial optoelectronic signals, or a combination thereof. An infrared thermal imager / infrared thermometer is used to obtain the surface temperature field distribution of the weld area; an industrial camera / high-speed camera collects molten pool images through side view or top view; coaxial vision / high-speed imaging observes the keyhole opening morphology. The process characteristic quantities can be obtained by infrared temperature measurement, coaxial vision imaging, side view vision imaging, optoelectronic detection, spectral detection, or a combination thereof, and after image processing, signal filtering, and feature extraction, state parameters for process determination are formed.

[0027] As an example, the keyhole characteristics include keyhole opening morphology characteristics, which are obtained by vision imaging or high-speed imaging. A high-speed camera arranged coaxially or paraxially is used to continuously collect images of the welding action area to obtain a time-series image containing the keyhole opening area; after preprocessing such as grayscale conversion, filtering and denoising, background subtraction, brightness normalization, and extraction of the region of interest for the time-series image, methods such as threshold segmentation, edge detection, contour extraction, or region growing are used to identify the keyhole opening boundary, and the keyhole opening area, perimeter, length, width, equivalent diameter, aspect ratio, roundness, ellipse fitting parameters, opening center position, and offset relative to the weld centerline are extracted in combination with the pixel size calibration result; further, based on consecutive multiple frames of images, the fluctuation amplitude, change rate, and oscillation frequency of the above parameters are calculated to characterize the keyhole stability.

[0028] The geometric features of the molten pool are obtained through visual imaging, infrared thermal imaging, or a combination of both. Images of the molten pool surface or temperature field are acquired, and the images are denoised, enhanced, and segmented to extract the molten pool boundary contour. After dimensional calibration, one or more of the following parameters are obtained: molten pool length, width, area, perimeter, center position, leading edge shape, trailing edge length, left-right width difference, boundary symmetry, and surface fluctuation amplitude. Based on multiple consecutive frames of images, the dynamic rate of change and fluctuation frequency of the molten pool contour can also be obtained to characterize the stability of the welding process.

[0029] When a continuous decrease in keyhole opening area, a width below a preset threshold, or a significant reduction in molten pool length or width is detected, it is determined to be a trend of insufficient penetration. The total power is increased or the welding speed is reduced, and negative defocus correction is applied. When an increase in keyhole opening fluctuation amplitude, enhanced molten pool boundary oscillation, or an abnormal increase in molten pool area is detected, it is determined to be a trend of overheating or instability. The line energy input is reduced, and positive defocus correction is applied. When a shift in the center of the keyhole or the center of the molten pool relative to the weld centerline is detected, it is determined to be an uneven energy coupling on both sides or a weld position deviation. The dual-beam power distribution factor and focus offset are adjusted to compensate for this.

[0030] The above describes several exemplary implementation methods of process characteristic quantities. Next, we will explain the compensation methods for the welding process.

[0031] In step S102, a welding stability criterion, including a penetration stability threshold and a forming stability threshold, is constructed based on assembly quality parameters and process characteristic quantities. The welding stability criterion is used to calculate and determine whether the current welding state meets preset requirements. These preset requirements include that the assembly quality parameters are within preset allowable ranges; and that both the penetration stability index and the forming stability index meet their corresponding threshold requirements.

[0032] In this embodiment, the penetration stability and weld bead stability are not limited to a single mathematical quantity, but are comprehensively judged based on process characteristics such as temperature characteristics, weld pool geometry, and keyhole characteristics obtained during the welding process. Penetration stability mainly reflects the continuity of the weld root penetration state and whether its fluctuations are within acceptable limits; weld bead stability mainly reflects whether the consistency and continuity of the weld pool morphology and weld surface geometry are within acceptable limits. The corresponding thresholds can be determined by the real-time values, deviations, fluctuation ranges, or combinations thereof of the aforementioned process characteristics, and are not limited to a single parameter.

[0033] Correspondingly, the preset allowable ranges for assembly quality parameters include: weld gap less than or equal to 0.8 mm, misalignment less than or equal to 0.5 mm, and weld position deviation less than or equal to 1.0 mm. If any parameter exceeds this range, the welding condition is directly determined to be unsatisfactory.

[0034] In some embodiments, the formula for calculating the melting depth stability is:

[0035] in, For melting depth stability, The keyhole opening area within the current sampling window. To calibrate the target keyhole opening area obtained from the experiment, The standard deviation of the keyhole opening area within the sampling window. This represents the current length of the molten pool. For the target molten pool length, This is the current characteristic temperature value. The target characteristic temperature value, - These are the weighting coefficients, and their sum is 1.

[0036] The keyhole opening area within the current sampling window mentioned above The image is obtained by acquiring keyhole opening images using a vision camera or high-speed camera and then performing image segmentation. It is calculated from the keyhole opening area of ​​multiple consecutive frames. Obtained by extracting the molten pool profile. Obtained through infrared thermometry or thermal imaging.

[0037] when Less than or equal to the preset threshold When the melting depth stability meets the requirements, it is determined that the melting depth stability is satisfactory; when If the value exceeds the preset threshold, it is determined that there is insufficient melting depth, keyhole instability, or abnormal heat input trend.

[0038] The formula for calculating the forming stability mentioned above is as follows:

[0039] in, For forming stability, This refers to the current molten pool width or surface forming width. For target width, The standard deviation of the molten pool width within the sampling window. This is the offset of the molten pool center relative to the weld centerline. Allowable offset threshold and These are the characteristic widths on both sides of the weld centerline. - These are the weighting coefficients, and their sum is 1.

[0040] In step S103, if the current welding state does not meet the preset requirements of the welding stability criterion, the welding control parameters are adjusted and control commands are output synchronously until the welding state meets the preset requirements of the welding stability criterion.

[0041] In some embodiments, adjusting welding control parameters includes the following three different methods: (1) The overall heat input and power distribution during the welding process are adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed. Specifically, the overall heat input is characterized by line energy, and the formula for calculating line energy is: In the formula, For line energy, The power of the first laser beam. The power of the second laser beam. For welding speed; Control the total heat input within (E) min E max ) interval, where To meet the minimum line energy threshold required for root fusion, The highest linear energy threshold to avoid the risks of collapse, overheating, and deformation.

[0042] Furthermore, the power distribution during the welding process is adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed, including: The power allocation factor is used to adjust the energy balance on both sides. The formula for calculating the power allocation factor is: ;in, For power allocation factor, The power of the first laser beam. The power of the second laser beam; Under symmetrical operating conditions, the control power distribution factor is between 0.4 and 0.6; when there are misalignments, positional deviations, or uneven heat conduction, the control power distribution factor is between 0.3 and 0.7 for compensation.

[0043] (2) Adjusting the defocus amount to regulate the energy density distribution during the welding process; the defocus amount is the offset of the focal point relative to the workpiece surface along the optical axis, and the energy density distribution is negatively correlated with the defocus amount. When adjusting the spot size and energy density distribution during the welding process by adjusting the defocus amount, the defocus amount Δf can be controlled to be within a certain range. For a depth of 2mm to +2mm, use negative decoking when the melting depth is insufficient, and use positive decoking when there is overheating or collapse.

[0044] (3) Compensation is made for the energy application position by adjusting the focus offset. Specifically, the focus offset d is controlled between 0 and 0.5 mm, where the focus offset d and the lateral offset Δx satisfy the proportional compensation relationship d=k. d×Δx, k d is a compensation coefficient, and compensates for the offset of the energy coupling center caused by assembly deviation in an incremental iteration manner.

[0045] The above solution improves the root energy coupling and thermal field distribution through the symmetric incidence of two beams, reducing the probability of defects such as incomplete penetration / incomplete fusion. By setting two welding stability criteria, it reduces the reinforcement height, back bead width or surface forming fluctuations, improves the appearance and geometric consistency of the weld seam. Facing fluctuations in gap, misalignment and position deviation, as well as changes in cross-section heat conduction / restraint conditions, it can still maintain the stability of the welding process and improve the batch manufacturing consistency. By adaptively adjusting the linear energy input and focal position, while meeting the penetration depth, it suppresses the overheating trend, thereby reducing the post-weld deformation and subsequent straightening costs.

[0046] The basic implementation method of the solution of the present invention has been described above. Next, the solution of the present invention will be elaborated in detail in combination with specific embodiments. Figure 2 is a schematic diagram showing laser welding with symmetric incidence of two beams according to an embodiment of the present invention.

[0047] In this embodiment, the steel sections to be welded are asymmetric or multi-cavity complex cross-section structures such as thick plate "T" shape, double "H" shape, "day" shape, etc. The typical plate thickness t is 15 - 25 mm, the mass per unit length is not less than 40 kg / m, and can reach up to 60 kg / m. The method of the present invention forms a root-coupled energy input by symmetrically irradiating two laser beams of the same type on both sides of the weld seam, and combines the assembly quality parameters and welding process characteristic quantities for adaptive adjustment, thereby improving the stability of the welding process of thick plate complex cross-section members and the consistency of joint quality.

[0048] (1) Pre-welding preparation: Assemble and joint the steel sections to be welded to ensure that the weld seam is continuous and there is no obvious convex or concave misalignment; preferably control the weld gap not greater than 0.8 mm (if greater than 0.8 mm, it is unqualified or pre-treated), and the misalignment not greater than 0.5 mm. Clean the areas to be welded on both sides of the weld seam, remove impurities such as oil stains, rust and oxide scales, and perform necessary grinding on the root area of the weld seam to ensure the stable incidence and energy coupling of the two beams to the root coupling area of the weld seam.

[0049] (2) Parameter definition: The thickness t of a certain steel vertical plate to be welded is 15-25 mm; the incident angle (the angle between the central axis of the laser beam and the normal direction of the outer surface of the plate) α is 20° to 40°, with an optimal range of 25° to 35°. The distance between the center points of the projected laser spots on the workpiece surface (beam spacing) is S, and S satisfies the following relationship with the plate thickness t: S = (0.6-1.2)t, with an optimal value of S = (0.8-1.2)t; when t = 15-25 mm, S is 12-30 mm, with an optimal value of 15-25 mm. 0.6-1.2 and 0.8-1.2 are dimensionless proportionality coefficient ranges used to characterize the proportional change of S with t, ensuring the controllability of the energy input position and thermal field distribution in the root coupling region.

[0050] (III) Process Flow: The following process flow is involved in this embodiment: workpiece and weld preparation → setting of dual-beam symmetrical incident parameters → process monitoring and stability criterion judgment → parameter adaptive adjustment → continuous welding forming and data recording.

[0051] During welding, two identical laser beams are incident symmetrically at ±α angles from both sides of the weld seam to the coupling zone at the weld root at the junction of the vertical and bottom plates, creating symmetrical energy coupling input in the root region. This is achieved by adjusting the power of the two laser beams (…). , ), welding speed With defocus (and optional focus offset) This allows for a more stable heat input distribution in the weld area, thereby reducing the probability of defects such as incomplete penetration, lack of fusion, porosity, and forming fluctuations, and reducing the risk of welding deformation caused by local overheating.

[0052] During welding, process characteristic quantities are acquired, which include at least one or more of temperature characteristics, molten pool geometry characteristics, or keyhole characteristics. These process characteristic quantities can be obtained through infrared thermometry, visual imaging, coaxial photoelectric signals, or a combination thereof. Based on assembly quality parameters (… , Weld position deviation Welding stability criteria are established using process characteristic quantities (e.g., penetration depth stability threshold and forming stability threshold). When the criteria do not meet the preset thresholds, the controller adjusts the settings while maintaining the symmetrical incident geometry of the two beams. , Welding speed With defocus and focus offset Adaptive adjustments are made until the criteria meet the preset threshold, thereby improving the robustness of the welding process and the consistency of the joint under the working conditions of thick plate with complex cross sections.

[0053] After determining the current welding state of the weld to be welded based on the above welding stability criteria, if the current welding state does not meet the preset requirements of the welding stability criteria, the welding control parameters are adjusted and control commands are output synchronously until the welding state meets the preset requirements of the welding stability criteria.

[0054] In this embodiment, adjusting the welding control parameters includes adjusting the power of the first laser beam. Second laser beam power Welding speed Defocus amount and focus offset These are key process variables in the welding process. The above variables collectively determine the linear energy input, energy spatial distribution, and thermal gradient in the coupling zone at the weld root, thereby affecting the stability of the molten pool / keyhole, the formation of the weld penetration, the consistency of the weld formation, and the risk of local overheating and deformation.

[0055] Specifically, welding control parameters are adjusted mainly through the following three methods.

[0056] (1) Linear energy regulation of overall heat input. When the material and cross-sectional conditions are constant, linear energy is preferred. Characterizing the total heat input, Total input power, total power of dual beams Preferably 16-28kW (more preferably 20-28kW). To increase welding speed. It is beneficial to improve the penetration depth and root fusion ability, but when Excessive heat can easily lead to localized overheating and increased risk of deformation; therefore, this invention uses a closed-loop approach to... It should be kept within the range that satisfies the stability criterion.

[0057] By using a closed-loop approach When the energy is controlled within the range that satisfies the stability criterion, the preferred target range for the linear energy is: .in, To meet the minimum line energy threshold required for root fusion, The highest linear energy threshold to avoid the risks of collapse, overheating, and deformation. and This can be determined through calibration tests: under typical material and cross-sectional conditions, changing... and Get different The criteria for acceptance are sufficient root fusion and stable formation. Welding speed. The value range is 8-15 mm / s. For example, when the experimental process window t is 15-18 mm, the total power is 16-20 kW, and v is 10-15 mm / s. When the experimental process window t is 18-22 mm, the total power is 20-24 kW, and v is 8-12 mm / s. When the experimental process window t is 22-25 mm, the total power is 22-28 kW, and v is 6-10 mm / s.

[0058] (2) Power distribution regulation to balance energy on both sides. When the assembly state on both sides is basically symmetrical with the heat conduction conditions, γ is taken close to 0.5 to obtain a more balanced symmetrical heat input. Preferably, when the assembly state on both sides is basically symmetrical with the heat conduction conditions, γ is located at 0.4-0.6; when there is a need for misalignment / offset compensation, when the assembly state on both sides is basically symmetrical with the heat conduction conditions, γ can be adjusted to 0.3-0.7. When there is a misalignment... Weld position deviation When uneven thermal conduction causes coupling misalignment, adjust γ (i.e., change) , The relative size of the thickness / heat sink side is used to compensate for the thickness, thereby improving effective fusion at the root and suppressing forming fluctuations. Misalignment amount The preferred range is 0-0.5mm, weld position deviation. The preferred range is 0-0.5mm. The adjustment of γ can be determined by calibration tests or online characteristic criteria: when the root fusion is insufficient or the coupling area shifts to one side, energy compensation is achieved by increasing the power ratio of the beam corresponding to the thick side / heat sink side (i.e., adjusting γ), so that the coupling area returns to the root target area, thereby improving the effective root fusion and suppressing forming fluctuations.

[0059] (3) Defocusing amount compensates for the energy application location. When the edge misalignment amount Or weld position deviation When the root coupling region shifts relative to the incident position, the focus offset is adjusted. Compensation is applied to the energy application location, causing the energy coupling region to return to the root target region, thereby reducing the risk of incomplete fusion / penetration and improving weld uniformity. Focus offset. The value range is 0-0.3mm, which can be extended to 0-0.5mm when the compensation requirement increases. The upper limit is preferably determined based on the effective coupling area size and the accuracy of the actuator: to avoid the beam action area deviating from the root coupling target area, resulting in misalignment or insufficient fusion. The ratio does not exceed a preset threshold for the lateral dimension of the effective coupling zone of the molten pool; simultaneously, it is considered in conjunction with the assembly error magnitude (misalignment). Weld position deviation ) is set to cover the range of its compensation needs.

[0060] Focus bias This not merely represents a conceptual shift in the focal point position, but rather serves as a closed-loop adjustable process variable to compensate for the shift in the root energy coupling center caused by misalignment, weld position deviation, or differences in thermal conductivity on both sides. Based on assembly quality parameters and the offset of the keyhole center position and molten pool center position relative to the weld target centerline detected online, the adjustment direction and magnitude of the focal offset are determined. When an actual energy coupling center shift to one side is detected, the focal offset is adjusted in the opposite direction to bring the energy application position back to the target area at the weld root. Lateral offset (focal offset) (Deviation from weld position) Satisfying the proportional compensation relationship ,in This is the compensation coefficient; and Not exceeding the preset maximum offset , ≤0.3mm, which can be increased to no more than 0.5mm when the compensation requirement increases.

[0061] Furthermore, the focus offset is preferably adjusted iteratively in an incremental manner, that is, the focus offset is gradually changed according to a preset step size, and the keyhole center offset, molten pool center offset, left-right asymmetry or back-side molten width change is re-detected after each adjustment; when the offset or asymmetry decreases to within the preset threshold, the current offset remains unchanged; when overcompensation occurs, the offset is reduced or finely adjusted in the opposite direction, thereby achieving fine compensation for the root energy coupling position.

[0062] Combining the three methods mentioned above to adjust the welding condition, the following are several different adjustment methods. When the weld gap... When the value increases, multiple process characteristic quantities fall below the preset range, or fluctuations exceed the preset range, the method is to increase the value. To achieve enhanced root coupling, specifically including increasing , ,reduce Furthermore, this can be combined with reducing the defocus amount. To increase energy density.

[0063] When the misalignment amount Adjust the power distribution factor when the coupling region is increased or shifted relative to the incident position. (Change and The relative size of the energy source can be used to compensate for the thick side / heat sink side. Furthermore, the focus offset d can be adjusted to bring the energy application position back to the root target area.

[0064] Reduce the temperature when the keyhole is unstable or the temperature fluctuation exceeds the threshold and an overheating trend occurs. Or reduce the peak energy density (reduce) , or improve And can be combined with enlargement (To suppress overheating and fluctuations). Stable keyhole operation refers to a continuous keyhole shape, no significant abrupt changes in opening state, no abnormal increase in oscillation amplitude, and no significant instability or jumps in brightness or image response. The following are signs of instability: fluctuating opening size; periodic violent oscillation; sudden increases or decreases in brightness; short-term closure, collapse, or obvious flickering; and asynchronous changes in the molten pool morphology, showing a trend of loss of control. Keyhole stability can be judged based on the continuity of the keyhole shape, the fluctuation of the opening, and whether there are abnormal jumps in the image or photoelectric signal. Overheating trend refers to a welding heat input that is higher than the current assembly state and fusion requirements, manifested as increased heat accumulation, excessive expansion of the molten pool, increased tendency to collapse, upward shift in temperature fluctuations, or excessively strong localized thermal effects.

[0065] The unstable state of the keyhole can be automatically determined by one or more of the following parameters collected online: keyhole opening area, opening width, opening center position, average brightness of the area, integrated brightness, rate of change between adjacent frames, oscillation frequency, and correlation parameters between keyhole features and molten pool geometry. When at least one of these parameters exceeds a preset threshold, or when multiple parameters together indicate a decrease in keyhole morphological continuity, abrupt change in opening state, abnormal increase in oscillation, abnormal jump in brightness response, short-term closure / collapse, or asynchronous change with molten pool morphology, the keyhole is determined to be in an unstable state. Manual interpretation can be used for threshold calibration, model correction, or verification of abnormal operating conditions, but is not necessary for online determination.

[0066] Preferably, in this embodiment, to improve the reliability of the judgment, a method of "single-parameter anomaly identification and multi-parameter joint confirmation" is adopted for judgment. Specifically, firstly, the mean, range, standard deviation, coefficient of variation, or rate of change of adjacent frames of each parameter within the continuous sampling window are calculated and compared with their respective preset thresholds: when the keyhole opening area or opening width continuously decreases and falls below the corresponding lower limit threshold, it indicates a decrease in the continuity of the keyhole shape; when the rate of change of adjacent frames of the opening area, opening width, or opening center position exceeds the corresponding abrupt change threshold, it indicates an abrupt change in the opening state; when the swing amplitude, swing speed, or main frequency of the opening center position deviates from the steady-state range and continuously exceeds the corresponding threshold, it indicates an abnormal increase in swing; when the regional average brightness or integrated brightness shows a sudden rise, sudden drop, or frequent reversal exceeding the brightness jump threshold within the continuous sampling window, it indicates an abnormal jump in brightness response; when no effective keyhole opening is detected for several consecutive frames, or when the keyhole opening area is lower than the closure judgment threshold and continues to reach the preset number of frames, it indicates that a short-term closure or collapse has occurred.

[0067] Furthermore, the time series of keyhole features is correlated with the time series of molten pool geometric features such as molten pool length, molten pool width, molten pool area, and tail swing amplitude. When the consistency of the changing trends of the two within a continuous sampling window is lower than a preset threshold, the time delay exceeds a preset threshold, or the correlation coefficient is lower than a preset threshold, it is determined that the keyhole features and molten pool morphology changes are asynchronous. When any two or more of the above abnormal situations occur simultaneously within a preset time window, or when a certain type of abnormality persists for more than a preset duration / number of frames, the keyhole is determined to be in an unstable state.

[0068] Finally, through the above adjustment process, the output is achieved while maintaining the geometric premise of symmetrical incidence. , , , and The system sends control commands to drive the welding process along a preset trajectory, ensuring that the welding process meets preset thresholds. Simultaneously, it records assembly quality parameters, process characteristics, process variables, and judgment results, forming a process parameter library for parameter reuse, quality traceability, and continuous optimization.

[0069] Through the above adjustments, a more stable energy coupling and heat input distribution can be obtained under the conditions of high restraint and assembly fluctuation in thick plates, reducing the probability of defects such as incomplete penetration, incomplete fusion, porosity and forming fluctuation, and reducing the risk of deformation, thereby improving the consistency of joint quality and engineering applicability.

[0070] While this specification has shown and described numerous embodiments of the invention, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and essence of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of this invention.

Claims

1. A closed-loop control method for dual-beam symmetrical incident laser welding, characterized in that, include: Obtain the assembly quality parameters of the weld to be welded, as well as the process characteristic quantities of the welding process; The assembly quality parameters include at least weld gap, misalignment, and weld position deviation; the process characteristic parameters include at least one or more of the following: temperature characteristics, molten pool geometry, and keyhole characteristics. Welding stability criteria are constructed based on assembly quality parameters and process characteristic quantities, including penetration stability threshold and forming stability threshold. The welding stability criteria are used to calculate and determine whether the current welding state meets the preset requirements. If the current welding state does not meet the preset requirements of the welding stability criterion, adjust the welding control parameters and output control commands synchronously until the welding state meets the preset requirements of the welding stability criterion.

2. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 1, characterized in that, The preset requirements include that the assembly quality parameters are within the preset allowable range; and that both the melt depth stability index and the forming stability index meet the corresponding threshold requirements.

3. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 2, characterized in that, The preset allowable ranges include: weld gap less than or equal to 0.8 mm, misalignment less than or equal to 0.5 mm, and weld position deviation less than or equal to 1.0 mm; if any parameter exceeds the range, the welding condition is directly determined to be unsatisfactory.

4. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 1, characterized in that, The formula for calculating the melting depth stability is: in, For melting depth stability, The keyhole opening area within the current sampling window. To calibrate the target keyhole opening area obtained from the experiment, The standard deviation of the keyhole opening area within the sampling window. This represents the current length of the molten pool. For the target molten pool length, This is the current characteristic temperature value. The target characteristic temperature value, - These are the weighting coefficients, and their sum is 1.

5. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 1, characterized in that, Formula for calculating forming stability: in, For forming stability, This refers to the current molten pool width or surface forming width. For target width, The standard deviation of the molten pool width within the sampling window. This is the offset of the molten pool center relative to the weld centerline. Allowable offset threshold and These are the characteristic widths on both sides of the weld centerline. - These are the weighting coefficients, and their sum is 1.

6. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 1, characterized in that, The dual-beam configuration includes a first laser beam and a second laser beam symmetrical about the weld center plane. Adjustments to welding control parameters include: The overall heat input and power distribution during the welding process are adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed. The energy density distribution during the welding process is adjusted by regulating the defocusing amount; the defocusing amount is the amount by which the focal point is offset relative to the workpiece surface along the optical axis, and the energy density distribution is negatively correlated with the defocusing amount. The location of energy application is compensated by adjusting the focus offset.

7. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 6, characterized in that, The overall heat input during the welding process is adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed, including: Linear energy is used to characterize the total heat input, and the formula for calculating linear energy is: ; In the formula, For line energy, The power of the first laser beam. The power of the second laser beam. For welding speed; Control the total heat input within (E) min E max ) interval, where To meet the minimum line energy threshold required for root fusion, The highest linear energy threshold to avoid the risks of collapse, overheating, and deformation.

8. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 6, characterized in that, The power distribution during the welding process is adjusted by regulating the power of the first laser beam, the power of the second laser beam, and the welding speed, including: The power allocation factor is used to adjust the energy balance on both sides. The formula for calculating the power allocation factor is: ;in, For power allocation factor, The power of the first laser beam. The power of the second laser beam; Under symmetrical operating conditions, the control power distribution factor is between 0.4 and 0.6; when there are misalignments, positional deviations, or uneven heat conduction, the control power distribution factor is between 0.3 and 0.7 for compensation.

9. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 6, characterized in that, Adjusting the energy density distribution during the welding process by regulating the defocusing amount includes: Control the defocus amount Δf at For a depth of 2mm to +2mm, use negative decoking when the melting depth is insufficient, and use positive decoking when there is overheating or collapse.

10. The closed-loop control method for dual-beam symmetrical incident laser welding according to claim 6, characterized in that, Compensation is achieved by adjusting the focus offset to determine the location of energy application, including: The focus offset d is controlled to be between 0 and 0.5 mm, where the focus offset d and the lateral offset Δx satisfy the proportional compensation relationship d=k. d ×Δx, k d The compensation coefficient is used to compensate for the energy coupling center shift caused by assembly deviations through incremental iteration.

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