Laser energy and light spot swing cooperative control method and system for laser welding

Abstract

The invention relates to the technical field of laser processing control, in particular to a laser energy and light spot swing cooperative control method and system for laser welding, and aims to solve the problems that in the prior art, when parameters are linearly adjusted, the hysteresis effect of heat input and the nonlinear coupling relation of energy density are ignored; therefore, incomplete fusion, over-burning and non-uniform fusion depth of a welding seam are easily caused. The method comprises the following steps: acquiring a weld gap width estimation value and a gap change rate at the current moment; determining the target swing amplitude of the light spot at the current moment; calculating a laser power instruction value at the current moment; and a swing frequency instruction at the current moment is calculated, and closed-loop control is conducted on the welding process in cooperation with the laser power instruction value and the target swing amplitude. According to the method, no matter how the swing amplitude changes, the effective heat flux density acting on the unit area of the weld joint is kept constant, and therefore the consistency of the penetration depth is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of laser processing control technology, specifically to a method and system for coordinated control of laser energy and spot oscillation in laser welding. Background Technology

[0002] Laser welding, as a high-energy beam welding technology, is widely used in precision manufacturing due to its advantages such as large aspect ratio, small heat-affected zone, and minimal deformation. To further improve weld quality, laser wobble welding technology has emerged. This technology uses a galvanometer to control the laser spot to oscillate at high frequency along the welding trajectory, such as in a circular or figure-eight pattern. This effectively improves the fluidity of the molten pool, reduces porosity sensitivity, and lowers the stringent requirements for workpiece assembly gap precision. In actual laser welding production lines, especially for welding long welds or splicing large structural components, the weld gap width is often uneven and dynamically changing due to limitations in processing accuracy and assembly errors.

[0003] Existing technologies typically employ lookup table methods or simple linear follower control, using a vision sensor to detect the current gap width and directly adjusting the laser power or oscillation amplitude according to a preset linear proportional relationship. For example, when a gap increase is detected, the oscillation amplitude is linearly increased to cover the gap, and the laser power is increased proportionally. However, existing technologies neglect the hysteresis effect of heat input and the nonlinear coupling relationship of energy density. When the weld gap suddenly widens from narrow, if parameters are adjusted only based on the current detection value, the thermal inertia of the molten pool often leads to insufficient heat at the initial widening point of the weld, resulting in incomplete fusion. Conversely, when the gap narrows from wide, the heat cannot dissipate in time, easily leading to overheating or collapse. Furthermore, simply linearly increasing the oscillation amplitude to expand the spot area causes drastic fluctuations in the effective energy density per unit area. This is because an increased oscillation amplitude means a longer spot scanning path; if the power increases only linearly, the effective contact time of the spot per unit length of weld is actually shorter, potentially resulting in shallower penetration.

[0004] Therefore, there is an urgent need for a method that can sense the trend of gap change and coordinate the control of laser energy and spot oscillation based on the energy density conservation model to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a method and system for coordinated control of laser energy and spot oscillation in laser welding, which solves the technical problems of neglecting the hysteresis effect of heat input and the nonlinear coupling relationship of energy density when linearly adjusting parameters in the prior art, which easily leads to incomplete fusion, overheating and uneven weld depth.

[0006] In a first aspect, the present invention provides a method for coordinated control of laser energy and spot oscillation in laser welding, comprising the following steps: A laser vision sensor is used to collect gap data sequences in the weld area, and a Kalman filter algorithm is used to process the gap data sequences to obtain the estimated weld gap width and gap change rate at the current moment. Based on the estimated weld gap width and the preset overlap width margin, the target oscillation amplitude of the light spot at the current moment is determined to ensure that the light spot covers the weld gap. A power control model incorporating geometric nonlinear coupling and dynamic thermal input compensation is constructed. Based on the ratio of the target swing amplitude to the reference swing amplitude and the exponential relationship between the gap change rate and the preset welding line speed, the laser power command value at the current moment is calculated. A frequency adaptive control model is constructed. Based on the target swing amplitude, the preset welding line speed, and the laser spot diameter, the swing frequency command at the current moment is calculated, and the welding process is controlled in a closed loop in conjunction with the laser power command value and the target swing amplitude.

[0007] Furthermore, a laser vision sensor is used to acquire gap data sequences in the weld area, and the Kalman filter algorithm is used to process the gap data sequences, including: Establish a state equation, treat the change in weld gap width as a dynamic process that changes with time, and define the weld gap state vector to include gap width and gap change rate; The state transition matrix is ​​used to predict the prior estimate at the current time step based on the optimal estimate at the previous time step. The Kalman gain is calculated by combining the current visual sensor measurement value, and the prior estimate is corrected to obtain the estimated weld gap width and gap change rate at the current moment.

[0008] By using Kalman filtering to process sensor data, the system can resist interference from welding spatter and fumes on visual inspection, outputting a smooth control curve, avoiding sudden changes in laser power caused by sensor noise, protecting the laser hardware, and improving the stability of the welding process.

[0009] Further, the target swing amplitude of the spot at the current moment is determined by adding the estimated weld gap width at the current moment to the preset overlap width margin, and the sum is used as the target swing amplitude of the spot at the current moment. The overlap width margin is used to ensure that the edge of the spot melts the base material on both sides of the weld gap.

[0010] By dynamically setting the target swing amplitude, it is ensured that the spot can always cover the changing weld gap, and sufficient overlap is reserved to ensure good fusion of the sidewall.

[0011] Furthermore, the laser power command value at the current moment satisfies the following relationship: ; In the formula, This represents the laser power command value at the current moment. The reference laser power; The target swing amplitude at the current moment; The reference swing amplitude; The energy density coupling coefficient; It is an exponential function with the natural constant as its base; The rate of change of the gap; Preset welding line speed; This is the thermal response sensitivity coefficient.

[0012] The formula for the laser power command value takes into account both the energy density reduction caused by the change in the target swing amplitude and the thermal hysteresis effect caused by the change in the gap. By adjusting the laser power command value through nonlinear compensation, defects such as overheating or lack of fusion in the weld are avoided.

[0013] Furthermore, the energy density coupling coefficient ranges from 1.2 to 1.8 to reflect the nonlinear geometric relationship caused by the increase in the swing path length with the amplitude; the thermal response sensitivity coefficient is used to adjust the system's sensitivity to the gap change rate.

[0014] Furthermore, the current swing frequency command value satisfies the following relationship: ; In the formula, This is the command value for the swing frequency at the current moment. Base frequency; The overlap rate structural factor; Preset welding line speed; The target swing amplitude at the current moment; The diameter of the laser spot is denoted as .

[0015] The formula for the swing frequency command value establishes an adaptive constraint relationship between the swing frequency and the target swing amplitude, preventing the light spot trajectory from becoming sparse due to the frequency remaining unchanged while the swing amplitude increases. This ensures the continuity and overlap rate of the weld and improves the forming quality.

[0016] Furthermore, the collaborative control method also includes a wire feeding collaborative control step, which includes: using the rate of change of the laser power command value as a feedforward signal, and calculating the product of the laser power command value and the preset wire feeding coefficient to obtain the wire feeding speed of the wire feeder, so as to ensure dynamic matching between the amount of filling metal and the amount of heat input.

[0017] Furthermore, the cooperative control method also includes limiting the laser power command value, the limiting process including: Pre-set the upper and lower limits of the device's allowed power; After calculating the laser power command value, it is determined whether it exceeds the upper limit of power or is lower than the lower limit of power. If the laser power command value exceeds the upper power limit or falls below the lower power limit, the laser power command value is truncated to the corresponding upper or lower power limit to protect the laser hardware.

[0018] By setting upper and lower power limits for truncation, the system's safety is enhanced to prevent damage or malfunctions caused by calculated values ​​exceeding the device's capacity.

[0019] Furthermore, the step of obtaining the reference laser power includes: Under stable operating conditions with no gap variation, the weld gap is set to the width corresponding to the reference swing amplitude; Through welding process experiments, the power value required to achieve full penetration and good forming under stable working conditions was determined, and this power value was marked as the reference laser power.

[0020] By determining the baseline parameters through standardized process experiments, an accurate reference benchmark is provided for the nonlinear control model, ensuring the effectiveness of the control algorithm in practical applications.

[0021] Secondly, the present invention provides a laser energy and spot oscillation coordinated control system for laser welding, including a memory and a processor. The memory stores computer program instructions, and when the computer program instructions are executed by the processor, the above-mentioned laser energy and spot oscillation coordinated control method for laser welding is implemented.

[0022] The beneficial effects are as follows: By introducing an exponential compensation term for the gap change rate into the power control model, this invention can provide advanced energy regulation at the instant of gap change. When the gap increases sharply, it replenishes energy to preheat the base material, and when the gap decreases sharply, it reduces energy, thus avoiding defects such as incomplete fusion and overheating at variable cross-sections. Simultaneously, this invention considers the effect of increased beam scanning path due to increased oscillation amplitude. Through nonlinear power compensation, it ensures that the effective heat flux density acting on a unit area of ​​the weld remains constant regardless of changes in oscillation amplitude, thereby guaranteeing consistent weld penetration. Attached Figure Description

[0023] Figure 1 A comparison chart of real-time acquisition and state estimation results of weld gap data; Figure 2 The response curve is a diagram showing the coordinated control of laser energy and spot oscillation. Figure 3 This is a comparison chart of the stability of effective heat input per unit area between the present invention and the prior art. Detailed Implementation

[0024] This invention discloses a method for coordinated control of laser energy and spot oscillation in laser welding, comprising steps S101 to S104: S101. A laser vision sensor is used to collect the gap data sequence of the weld area, and the Kalman filter algorithm is used to process the gap data sequence to obtain the estimated value of the weld gap width and the gap change rate at the current moment.

[0025] Specifically, a laser vision sensor, such as a line structured light sensor, is installed at the front end of the laser welding head. During the welding process, the weld area is scanned in real time at a set frequency to collect the original gap data sequence of the weld area. For example, the set frequency is 100Hz. Due to interference from on-site environments such as splashes and dust, the collected data usually contains high-frequency noise. In order to obtain accurate weld gap values ​​and predict trends, a Kalman filter algorithm is used.

[0026] First, establish the state equation, treating the change in weld gap width as a dynamic process that varies with time, and define the weld gap state vector as follows: ,in, for The interval width at any given moment, expressed in mm. The first step is to define the rate of change of the weld gap width (i.e., the gap change rate, in mm / s). Secondly, in the prediction phase, based on the optimal estimate from the previous moment, the prior estimate for the current moment is predicted using the state transition matrix. Thirdly, in the update phase, the Kalman gain is calculated by combining the current measurements from the vision sensor, and the prior estimate is corrected to obtain the current weld gap width estimate and the gap change rate.

[0027] In one example, such as Figure 1 As shown, the real-time sensor sampling values ​​simulate the raw measurement data with high-frequency noise, reflecting the interference at the welding site; the Kalman filter estimate smoothly depicts the true trajectory of the weld gap change, showing the process of the weld gap width increasing from 0.6 mm to 1.2 mm; the gap change rate (gap change rate) shows a significant, untruncated peak at about 2.5 s, indicating that the algorithm accurately captures the dynamic change rate of the working condition, providing a basis for proactive control.

[0028] By processing the raw data using the Kalman filter algorithm, not only was measurement noise filtered out, but the gap change rate was also extracted, providing a basis for subsequent proactive control.

[0029] S102. Based on the estimated weld gap width and the preset overlap width margin, determine the target oscillation amplitude of the light spot at the current moment to ensure that the light spot covers the weld gap.

[0030] Specifically, the oscillation amplitude must cover the weld gap and allow for a certain overlap to ensure sidewall fusion. The target oscillation amplitude of the laser spot at the current moment satisfies the following relationship: ; In the formula, For the target swing amplitude, The estimated weld gap width obtained in step S101 at the current moment. The lap width allowance is a preset, fixed allowance, which is determined by the welding process evaluation and can be between 0.2mm and 0.5mm, to ensure that the edge of the spot can melt the base material on both sides of the gap.

[0031] In one example, suppose , The target swing amplitude is If the estimated weld gap width widens to... ,but Automatically adjust to .

[0032] By setting a dynamic target swing amplitude, it is possible to ensure that the spot always covers the weld gap and reserve sufficient overlap, thus guaranteeing the fusion quality of the welded sidewall.

[0033] S103. Construct a power control model that includes geometric nonlinear coupling and dynamic compensation of thermal input. Calculate the laser power command value at the current moment based on the ratio of the target swing amplitude to the reference swing amplitude and the exponential relationship between the gap change rate and the preset welding line speed.

[0034] Specifically, the laser power command value at the current moment satisfies the following relationship: ; In the formula, for The laser power command value at any given time, in W; The reference laser power is measured in W. The reference laser power is the power that can achieve full penetration, measured under standard working conditions. The standard working conditions refer to the working conditions where the weld gap width is the reference swing amplitude and does not change. The target swing amplitude at the current moment is expressed in mm. The reference swing amplitude is expressed in mm. The energy density coupling coefficient is typically set to 1.2 to 1.8 to reflect the nonlinear geometric relationship caused by the increase in the swing path length with the amplitude. It is an exponential function with the natural constant as its base; This represents the rate of change of the gap, and its unit is mm / s; The preset welding line speed is expressed in mm / s. This is the thermal response sensitivity coefficient. Furthermore, to prevent calculated values ​​from exceeding equipment capabilities, actual control systems have upper and lower power limits, which satisfy... ,in, This is the lower limit of power. This is the upper limit of power.

[0035] In one example, set , , , , , .

[0036] When the welding process is smooth, the estimated weld gap width remains at [value missing]. The target's swing amplitude remains unchanged at the current moment, which is 0.6 + 0.4 = 1.0 mm, and the gap change rate is 0. .

[0037] When the gap suddenly widens, causing the target's swing amplitude to increase at the current moment... And at this time, the rate of change of the gap is Since the gap change rate is positive, indicating that it is widening, the calculation process is as follows: Geometric terms: Dynamic compensation item: ; .

[0038] It can be seen that at the instant the estimated welding gap width widens, the laser power command value experiences a significant spike. For example... Figure 2 As shown, the laser power coordination command (i.e., the laser power command value) will be significantly increased to overcome the thermal inertia of the molten pool and prevent incomplete fusion. As the laser spot oscillation amplitude command (i.e., the target oscillation amplitude) stabilizes at... The gap change rate drops back to 0, the dynamic compensation term becomes 1, and the laser power command value will stabilize at... To maintain the energy density required for the new wide weld.

[0039] like Figure 3The invention demonstrates a comparison between the present invention and existing technologies in terms of the stability of effective heat input per unit area. Existing technologies show a sharp drop in the curve at the 2.5s interval, far from the ideal range, indicating a severe energy deficiency. In contrast, the present invention shows a clear dynamic peak at 2.5s, which is controlled near the upper limit of the ideal range, and then quickly falls back and stabilizes at the center of the ideal range, remaining within the ideal melting depth heat input range throughout the process.

[0040] S104. Construct a frequency adaptive control model. Based on the target swing amplitude, the preset welding line speed, and the laser spot diameter, calculate the swing frequency command at the current moment, and coordinate the laser power command value and the target swing amplitude to perform closed-loop control of the welding process.

[0041] Specifically, the swing frequency command value at the current moment satisfies the following relationship: ; In the formula, for The command value for the swing frequency at any given time, in Hz; The fundamental frequency, measured in Hz, is typically set as the lower limit of the safe range for the galvanometer resonant frequency. The overlap rate structure factor is obtained by back-calculation using a preset desired spot overlap rate. The preset welding line speed is expressed in mm / s. The target swing amplitude at the current moment is expressed in mm. The laser spot diameter is expressed in mm.

[0042] In one example, suppose , , , .

[0043] when When, the denominator is ; .

[0044] when = When, the denominator is ; .

[0045] As can be seen from the above examples, as the target swing amplitude increases, the swing frequency command value decreases to match the larger scanning range, avoiding keyhole instability caused by excessively fast scanning. At the same time, combined with the base frequency, it ensures that the swing frequency is always within the process window.

[0046] Finally, the calculated laser power command value, target swing amplitude, and swing frequency command value at the current moment are sent to the welding controller and laser for execution in real time via an industrial bus such as EtherCAT.

[0047] In addition, if the welding process involves filler wire, the rate of change of the oscillation frequency command value is used as a feedforward signal to synchronously control the wire feeding speed of the wire feeder. It satisfies the following relationship: ; In the formula, For wire feeding speed, The wire feed coefficient ensures dynamic matching between the filler metal amount and the heat input, preventing undercut caused by insufficient wire feed due to increased power, or weld beads caused by excessive wire feed due to decreased power.

[0048] By adaptively adjusting the oscillation frequency command value, the density and overlap rate of the spot trajectory are ensured under different oscillation amplitudes, further ensuring the continuity and stability of weld formation.

[0049] This invention also discloses a laser energy and spot oscillation coordinated control system for laser welding, including a memory and a processor. The memory stores computer program instructions, and when the computer program instructions are executed by the processor, the above-mentioned laser energy and spot oscillation coordinated control method for laser welding is implemented.

[0050] The laser energy and spot oscillation coordinated control system for laser welding also includes other components well known to those skilled in the art, such as communication interfaces. Their setup and functions are known in the art and will not be described in detail here.

Claims

1. A method for laser energy and spot oscillation coordinated control for laser welding, characterized in that, The method comprises the following steps: Collecting a gap data sequence of the weld area by using a laser vision sensor, and processing the gap data sequence by using a Kalman filtering algorithm to obtain a weld gap width estimation value and a gap change rate at the current time; According to the weld gap width estimation value and a preset overlap width allowance, determining a target oscillation amplitude of the light spot at the current time to ensure that the light spot covers the weld gap; A power control model including geometric nonlinear coupling relationship and heat input dynamic compensation is constructed, and a laser power instruction value at the current time is calculated according to a ratio relationship between the target oscillation amplitude and a reference oscillation amplitude and an exponential relationship between the gap change rate and a preset welding line speed; A frequency adaptive control model is constructed, and an oscillation frequency instruction at the current time is calculated according to the target oscillation amplitude, the preset welding line speed and the laser light spot diameter, and the welding process is closed-loop controlled in cooperation with the laser power instruction value and the target oscillation amplitude.

2. The method of laser energy and spot oscillation coordinated control for laser welding according to claim 1, wherein, The gap data sequence of the weld area is collected by using a laser vision sensor, and the gap data sequence is processed by using a Kalman filtering algorithm, including: A state equation is established, the change of the weld gap width is regarded as a dynamic process changing with time, and a weld gap state vector is defined to include the gap width and the gap change rate; The prior estimation value at the current time is predicted according to the optimal estimation value at the last time by using a state transition matrix; The Kalman gain is calculated in combination with the measurement value of the vision sensor at the current time, the prior estimation value is corrected to obtain the weld gap width estimation value and the gap change rate at the current time.

3. The method of laser energy and spot oscillation coordinated control for laser welding according to claim 2, wherein, The target oscillation amplitude of the light spot at the current time is determined, specifically, the weld gap width estimation value at the current time is added to the preset overlap width allowance, and the sum is taken as the target oscillation amplitude of the light spot at the current time, wherein the overlap width allowance is used to ensure that the light spot edge melts the base metal on both sides of the weld gap.

4. The method of laser energy and spot oscillation coordinated control for laser welding of claim 1, wherein, The laser power instruction value at the current time satisfies the following relationship: ； In the formula, is a laser power command value at a current time, is a reference laser power; is a target swing amplitude at a current time; is a reference swing amplitude; is an energy density coupling coefficient; is an exponential function with a natural constant as a base; is a gap change rate; is a preset welding line speed; is a thermal response sensitivity coefficient.

5. The method of laser energy and spot oscillation coordinated control for laser welding of claim 4, wherein, The energy density coupling coefficient ranges from 1.2 to 1.8 to reflect the nonlinear geometric relationship that the oscillation path length increases with the amplitude; the heat response sensitivity coefficient is used to adjust the sensitivity of the system to the gap change rate.

6. The method of laser energy and spot oscillation coordinated control for laser welding of claim 4, wherein, The oscillation frequency instruction value at the current time satisfies the following relationship: ； In the formula, is a swing frequency command value at a current time, is a base frequency; is an overlap rate structure factor; is a preset welding line speed; is a target swing amplitude at a current time; is a laser spot diameter.

7. The method of laser energy and spot oscillation coordinated control for laser welding of claim 6, wherein, The cooperative control method further includes a wire feeding cooperative control step, which includes: taking the change rate of the laser power instruction value as a feedforward signal, calculating the product of the laser power instruction value and a preset wire feeding coefficient to obtain the wire feeding speed of the wire feeder, so as to ensure that the amount of filler metal and the heat input amount are dynamically matched.

8. The method for laser energy and spot oscillation coordinated control for laser welding of claim 4, wherein, The cooperative control method further includes limiting the laser power instruction value, which includes: The upper limit value and the lower limit value of the power allowed by the equipment are set in advance; After the laser power instruction value is calculated, it is judged whether it exceeds the upper limit value or is lower than the lower limit value; If the laser power instruction value exceeds the upper limit value or is lower than the lower limit value, the laser power instruction value is truncated to the corresponding upper limit value or lower limit value to protect the laser hardware.

9. The method for laser energy and spot oscillation coordinated control for laser welding of claim 4, wherein, The reference laser power acquisition step includes: In the smooth working condition without gap change, the weld gap is set to the width corresponding to the reference swing amplitude; Through a welding process test, a power value required for achieving full penetration and good forming in the smooth working condition is determined, and the power value is marked as the reference laser power.

10. A laser energy and spot oscillation coordinated control system for laser welding, characterized in that, The laser energy and spot swing cooperative control method for laser welding comprises a memory and a processor, and computer program instructions are stored in the memory. When the computer program instructions are executed by the processor, the method for laser welding according to any one of claims 1-9 is realized.

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