A laser irradiation anti-induction coating crack device and method

Abstract

This invention relates to the field of laser surface engineering technology, specifically to a laser irradiation-induced coating cracking device and method. The device includes a laser generation and output unit, a beam transmission and dynamic focusing unit, an online monitoring and feedback unit, and a central control unit. In this invention, by collecting crack morphology data and thermophysical parameters of the coating surface, a repair mode or a prevention mode is intelligently switched. In repair mode, the beam is controlled to perform low-power defocus scanning along both sides of the crack to construct a preheating relaxation zone, followed by high-power focusing scanning along the crack center to induce dense remelting. In prevention mode, a grid-like laser shock treatment is performed to construct a compressive stress layer. By utilizing infrared and visual dual feedback to correct the laser output energy in real time, active control of coating stress and non-destructive healing of defects are achieved, solving the problem of coating peeling and thermal damage easily caused by traditional thermal repair, and improving the structural integrity and service life of precision coated components.

Description

Technical Field

[0001] This invention relates to the field of laser surface engineering technology, and in particular to a device and method for laser irradiation to induce coating cracks. Background Technology

[0002] Laser surface engineering technology refers to advanced manufacturing technology that utilizes the interaction between a high-energy laser beam and a material surface to achieve surface modification, repair, or strengthening. It is widely used in the maintenance of precision components in aerospace and energy power fields. Traditional coating repair technologies mainly rely on secondary thermal spraying, vacuum infiltration, or manual micro-arc welding to passively fill coating cracks caused by thermal expansion mismatch or residual stress. These processes typically involve the introduction of physical filler materials or large-area heat input, attempting to restore the coating's continuous structure through material re-deposition or overall remelting. However, existing technologies suffer from the following technical shortcomings in practical applications: First, the laser wavelength and the optical properties of the coating material are not well matched, resulting in low energy coupling efficiency. Existing laser repair devices typically use laser sources with fixed wavelengths, failing to dynamically match them according to the spectral absorption characteristics of the coating material. This leads to significant energy wastage due to reflection, uncontrollable expansion of the heat-affected zone, and difficulty in achieving efficient and low-damage energy input. Second, the energy spatial distribution lacks adaptive adjustment capability, making it difficult to adapt to changes in crack morphology. In traditional remelting processes, the spot diameter and defocusing amount are usually fixed, making it impossible to adjust the energy distribution range in real time according to changes in crack width within a single scanning path. This easily leads to uneven energy distribution, resulting in incomplete repair or thermal damage. Third, the lack of a real-time temperature and morphology closed-loop feedback mechanism results in poor process stability. Existing technologies mostly use open-loop control methods, which cannot monitor the temperature field changes and crack healing status of the laser irradiation area in real time. This makes it difficult to accurately control heat input, easily leading to overheating, vaporization, or even peeling of the coating due to excessive temperature, or insufficient crack healing due to insufficient temperature. Fourth, the repair and prevention processes are disconnected, and active stress control cannot be achieved. Existing methods are mostly reactive and reactive, lacking the ability to differentiate between existing cracks and potentially crack-prone areas. They cannot proactively manage stress and prevent crack initiation, leaving a risk of secondary cracking even after repair, and failing to fundamentally block crack propagation. Fifth, they lack dynamic gas protection and complex surface processing capabilities, limiting their applicability. Traditional devices lack a dynamic gas protection mechanism linked to the temperature field during laser irradiation, leading to significant issues with high-temperature oxidation and plasma shielding. Furthermore, insufficient motion control makes it difficult to achieve normal irradiation and high-precision splicing of complex surfaces such as turbine blades, limiting their application in high-end manufacturing. Sixth, process parameter settings rely on experience and lack scientific quantitative basis. Existing methods rely heavily on operator experience for setting key parameters such as laser power, scanning speed, and pulse frequency, lacking quantitative calculation models based on material thermophysical parameters and crack characteristic data. This results in poor process consistency and difficulty in guaranteeing repair quality.

[0003] In summary, existing coating crack repair technologies generally suffer from problems such as low energy coupling efficiency, unadjustable energy distribution, poor process stability, insufficient repair and prevention of cracking, inadequate processing capabilities for complex curved surfaces, and reliance on experience for parameter setting. These issues make it difficult to meet the urgent need for high reliability and high consistency repair of precision coated components. Summary of the Invention

[0004] To address the technical problems existing in the prior art, embodiments of the present invention provide a laser irradiation-induced coating cracking device and method. The technical solution is as follows: On one hand, a laser irradiation anti-induced coating cracking device is provided, the device comprising: The laser generating and output unit is configured to generate and output a pulsed laser beam, the wavelength of which is selected based on the absorption spectrum of the target coating material, and has power modulation and pulse waveform editing functions. The beam transmission and dynamic focusing unit is configured to expand the pulsed laser beam and control the movement trajectory, beam diameter and focal length of the spot on the coating surface in coordination with the high-speed scanning galvanometer and the dynamic focusing module. The online monitoring and feedback unit, including an infrared thermal imager and a high-speed vision system, is configured to collect temperature field distribution data and crack morphology dynamic change data of the laser irradiation area in real time, respectively. The central control unit is configured to construct closed-loop control logic based on the temperature field distribution data and the dynamic change data of the crack morphology, and send adjustment commands to the laser generation and output unit and the beam transmission and dynamic focusing unit in real time to perform repair operations for cracks or preventive operations for crack-prone areas.

[0005] As a further embodiment of the present invention, the laser generating and output unit is selected from one of a pulsed fiber laser, a nanosecond pulse laser, or a picosecond pulse laser, and the laser generating and output unit is configured to output a pulse sequence with an adjustable duty cycle.

[0006] As a further embodiment of the present invention, the beam transmission and dynamic focusing unit is further configured to perform variable focal length scanning, and adjust the defocus amount in real time in a single scanning path to form a spot shape with continuously changing diameter on the coating surface.

[0007] As a further embodiment of the present invention, the device further includes an auxiliary gas unit, which is configured to inject inert protective gas in the laser irradiation area in a coaxial or side-axis manner, and the flow rate of the inert protective gas is adjusted by the central control unit according to the temperature field distribution data.

[0008] As a further embodiment of the present invention, the online monitoring and feedback unit is also configured to set a material safety temperature window threshold. When the temperature value collected by the infrared thermal imager exceeds the material safety temperature window threshold, the central control unit is triggered to reduce the laser output power value or increase the scanning speed value.

[0009] As a further embodiment of the present invention, the central control unit is configured with a partitioned and graded irradiation strategy module, which is used to divide the coating surface into areas with existing cracks and areas prone to cracking, and execute repair scanning logic and impact prevention logic respectively.

[0010] As a further aspect of the present invention, the repair scanning logic is specifically configured as follows: The control beam first performs a symmetrical scan along both sides of the crack edge, and the laser with the first energy level density is output to perform thermal relaxation. The beam is then controlled to scan along the crack centerline, and a laser with a second energy level density higher than the first energy level density is output to perform local remelting.

[0011] As a further aspect of the present invention, the impact prevention logic is specifically configured as follows: The laser beam is controlled to scan along a grid-like or spiral path, and laser pulses with specific peak power are output to construct a residual compressive stress layer on the coating surface.

[0012] As a further embodiment of the present invention, the device further includes a motion control unit, which is configured to carry the coating specimen to be treated and perform multi-axis linkage displacement according to the scanning trajectory, so as to cooperate with the beam transmission and dynamic focusing unit to complete the full coverage irradiation of complex curved surfaces.

[0013] On the other hand, a laser irradiation-induced coating cracking method, performed based on the aforementioned laser irradiation-induced coating cracking device, includes the following steps: S1: Clean the surface of the coating to be treated, and use a high-speed vision system to obtain the location coordinates, length values, width values, and distribution topology of the cracks; S2: Based on the composition, thickness, and thermophysical parameters of the coating material, combined with the characteristic data of the crack, set the initial laser power, scanning speed, defocusing amount, and pulse frequency, and plan the scanning path strategy. S3: Based on the distributed topology, the processing mode is determined. If a crack already exists, the repair mode is executed: the laser beam is first controlled to scan symmetrically along both sides of the crack at low power and large spot size to perform stress relaxation treatment, and then scans along the crack path at high power and small spot size to perform remelting and repair treatment. If it is a potentially crack-prone area, the prevention mode is executed: the laser beam is controlled to perform laser shock treatment along the preset grid path at medium power to build a compressive stress layer. S4: During the irradiation process, the actual temperature is compared with the preset safety window in real time using an infrared thermal imager, and the crack closure status is monitored using a high-speed vision system, and the laser power value and scanning speed value are corrected accordingly.

[0014] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: 1. Dynamically adapting material optical properties significantly improves energy coupling efficiency. In this invention, the laser generation and output unit automatically matches the laser wavelength according to the absorption spectrum of the target coating material. Combined with duty cycle modulation and pulse waveform editing functions, it achieves precise control of the heat input. For example, for yttrium oxide-stabilized zirconia coatings, automatically matching a 1064 nm wavelength achieves an absorption rate of over 85%, effectively reducing energy waste and heat-affected zone expansion, laying an energy foundation for subsequent high-quality repair.

[0015] 2. Variable focal length scanning enables adaptive energy spatial distribution to adapt to changes in crack morphology. The beam transmission and dynamic focusing unit supports real-time adjustment of the defocus amount in a single scanning path, forming a beam spot shape with continuously changing diameter. It can dynamically adjust the energy distribution range according to the crack width, avoiding the problem of incomplete repair or thermal damage caused by uneven energy distribution in traditional processes.

[0016] 3. Infrared-visual dual closed-loop feedback enables precise temperature control and healing determination during the process. The online monitoring and feedback unit collects temperature field and crack morphology data in real time using an infrared thermal imager and a high-speed vision system, and sets a safe temperature window threshold for the material. When the temperature exceeds the limit, the trigger power is reduced or the scanning speed is increased at the millisecond level to prevent the coating from overheating or vaporizing. At the same time, the healing status is monitored by the crack grayscale change rate to ensure that the repair process is always within the safe window, significantly improving process stability and repair reliability.

[0017] 4. A zoned and graded irradiation strategy to achieve integrated crack repair and stress prevention. The central control unit is equipped with a zoned and graded irradiation strategy module, which intelligently divides existing cracked areas into potentially crack-prone areas and executes repair scanning logic and anti-crack impact logic respectively. In repair mode, a low-power, large-spot laser scan is first performed symmetrically along both sides of the crack to achieve thermal relaxation and eliminate stress singularities; then, a high-power, small-spot laser scan is performed along the crack centerline to complete local remelting and metallurgical bonding. In anti-crack mode, laser shock treatment is performed along a grid-like or spiral path to induce a residual compressive stress layer with a depth of 100–200 μm, effectively inhibiting the initiation of new cracks and achieving a technological leap from passive repair to active anti-induction.

[0018] 5. Dynamic gas protection and multi-axis motion coordination ensure the machining quality of complex curved surfaces. The auxiliary gas unit adjusts the inert gas flow rate in real time according to the temperature field distribution, effectively preventing high-temperature oxidation and plasma shielding. The motion control unit, through five-axis linkage and coordination with the galvanometer system, achieves normal irradiation of complex curved surfaces and large-format splicing, ensuring processing uniformity and consistency, and expanding the applicability of the device in high-end fields such as aerospace and energy.

[0019] 6. Closed-loop control of the process flow comprehensively improves processing quality and service life. This invention's method, through a complete process from S1 to S4, achieves a closed-loop control chain encompassing crack feature acquisition, scientific setting of process parameters, precise dual-mode processing, and real-time feedback correction. Specifically, energy calculation based on thermophysical parameters and crack features ensures quantitative matching of energy input; the design of the tool entry and exit leads avoids energy accumulation at the start and end points; a PID algorithm corrects power in real time; and a vision system automatically judges the degree of healing and performs a secondary scan until the crack completely disappears. This closed-loop control system significantly improves the density, bonding strength, and fatigue resistance of the coating repair, effectively solving the problems of large heat-affected zones, easy peeling, and poor process stability in traditional thermal repair, thereby enhancing the structural integrity and service life of precision coated components. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of a laser irradiation-induced coating cracking device provided in an embodiment of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0023] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, this embodiment of the invention provides a laser irradiation-induced coating cracking device, the device comprising: The laser generating and output unit is configured to generate and output a pulsed laser beam. The wavelength of the pulsed laser beam is selected based on the absorption spectrum of the target coating material, and it has power modulation and pulse waveform editing functions. The laser generating and output unit is selected from one of a pulsed fiber laser, a nanosecond pulsed laser, or a picosecond pulsed laser. The laser generating and output unit is configured to output a pulse sequence with an adjustable duty cycle.

[0025] Based on a pre-stored database of spectral absorbance rates for various coating materials, the unit invokes spectral matching logic to automatically retrieve the laser wavelength parameter with the highest overlap of absorption peaks with the coating material to be processed. For example, when the target material is a yttrium oxide-stabilized zirconia thermal barrier coating, the unit searches the database and finds that the material has high photon absorption efficiency in the 1064 nm band. Therefore, it automatically locks the fiber laser module as the output source and blocks the activation signals of nanosecond and picosecond lasers. Subsequently, the waveform editing circuit inside the unit is activated, using a field-programmable gate array (FPGA) chip to perform nanosecond-level modulation of the seed source's electrical drive signal, cutting the continuous laser energy into discrete pulse sequences. During pulse sequence generation, the unit performs duty cycle modulation, precisely controlling the total heat input of the laser by adjusting the ratio of the high-level duration to the pulse period. For example, if the pulse repetition frequency is set to 50 kHz, that is, each pulse period is 20 microseconds, if a softer thermal relaxation beam is required, the unit sets the high-level time to 2 microseconds, at which time the duty cycle is 10%; if a high-energy-density remelted beam is required, the high-level time is extended to 10 microseconds, and the duty cycle is increased to 50%.

[0026] This unit further executes power modulation logic, using an acousto-optic modulator to change the diffraction efficiency of the laser beam, thereby achieving linear adjustment of the output power. Regarding waveform editing, the unit uses preset rectangular wave, Gaussian wave, or bimodal wave templates to shape the temporal intensity distribution of the pulse. For example, when preheating the crack edge, the unit selects a trapezoidal wave with a gentle leading edge to avoid excessive thermal shock; while during deep remelting, it selects a Gaussian wave with a high peak value. To verify the effectiveness of wavelength matching, the unit is equipped with an energy feedback detector that reads the laser energy reflected from the coating surface in real time and calculates the absorptivity. The calculation logic is as follows: first, the total power value emitted by the laser is obtained; then, the reflected power value collected by the reflection detector is read; the total power value is subtracted from the reflected power value, and then divided by the total power value to obtain the actual absorptivity. For example, if the emitted power is 100 watts and the detected reflected power is 20 watts, the calculated actual absorptivity is 80%. If this value is lower than the preset minimum absorption threshold of 60%, the unit will automatically fine-tune the output wavelength or trigger an alarm.

[0027] As shown in Table 1, this table records the optimal laser wavelength and pulse parameter settings for different coating materials, which serve as the basis for unit initialization.

[0028] Table 1. Laser parameter matching table for typical coating materials

[0029] As shown in Table 1, the type of light source is strictly matched according to the material properties to ensure maximum energy coupling efficiency.

[0030] The beam transmission and dynamic focusing unit is configured to expand the pulsed laser beam and control the movement trajectory, beam diameter and focal length of the spot on the coating surface in collaboration with the high-speed scanning galvanometer and the dynamic focusing module. The beam transmission and dynamic focusing unit is also configured to perform variable focal length scanning and adjust the defocusing amount in real time in a single scanning path to form a beam pattern with continuously changing diameter on the coating surface.

[0031] The system receives the initial narrow beam from the laser and first passes it through a variable magnification beam expander assembly composed of concave and convex lenses. This assembly, driven by a linear motor, moves the concave lenses along the optical axis, changing the distance between the two lenses to enlarge the incident beam diameter by 3 to 5 times. This reduces the power density on the surface of subsequent optical components and decreases the divergence angle. The expanded parallel beam then enters a three-axis dynamic scanning subsystem, which includes an X-axis galvanometer, a Y-axis galvanometer, and a Z-axis dynamic focusing mirror. The X-axis and Y-axis galvanometers are driven by high-precision servo motors, rapidly deflecting according to input vector coordinate data to determine the planar position of the beam spot on the coating surface. The Z-axis dynamic focusing mirror is mounted on a voice coil motor and performs high-frequency reciprocating motion along the optical axis.

[0032] The core logic of this unit's zoom scanning lies in establishing a mapping relationship between three-dimensional spatial coordinates and the Z-axis lens displacement. The unit's internal processor reads the X and Y coordinates of the current scanning point on the plane in real time and calculates the radial distance from that point to the center of the scanning field. The calculation logic is as follows: the squares of the X and Y coordinates are added together, and the square root of this sum is taken to obtain the radial radius. Subsequently, based on a pre-calibrated field curvature model, this radial radius is substituted into a polynomial fitting function to calculate the Z-axis lens compensation displacement required to keep the focal point on the coating surface. For example, when the scanning point is located at the edge of the field of view with a radial radius of 50 mm, the function calculation shows that the Z-axis lens needs to be moved forward by 0.5 mm to compensate for the focal field curvature.

[0033] Furthermore, when performing zoom scanning to adjust the spot size, the unit adds an extra defocus offset while keeping the focal plane position unchanged. The calculation logic for this offset is based on geometric optics principles: first, the target spot diameter is set, and the focal length of the current focusing lens and the incident beam diameter are obtained; then, the target spot diameter is multiplied by the focal length of the focusing lens and divided by the incident beam diameter to obtain the reference displacement within the theoretical depth of focus range; finally, the Z-axis lens is controlled to move this reference displacement, causing the focal point to deviate from the coating surface, thereby forming a defocused spot on the surface. For example, if the focusing lens focal length is 250 mm and the incident beam diameter is 10 mm, and a 0.5 mm spot needs to be formed on the surface (based on geometric optics approximation), the focal point needs to be moved down a specific distance to make the beam diverge on the coating surface. This process is performed continuously within a single scan path; that is, as the scan trajectory extends, the Z-axis lens continuously fine-tunes its position to smoothly transition the spot diameter from 0.2 mm to 1.0 mm to adapt to changes in crack width.

[0034] The online monitoring and feedback unit, including an infrared thermal imager and a high-speed vision system, is configured to collect temperature field distribution data and crack morphology dynamic change data of the laser irradiation area in real time, respectively. The online monitoring and feedback unit is also configured to set a material safety temperature window threshold. When the temperature value collected by the infrared thermal imager exceeds the material safety temperature window threshold, the central control unit is triggered to reduce the laser output power or increase the scanning speed.

[0035] After the online monitoring and feedback unit is activated, the infrared thermal imager collects thermal radiation data of the laser-irradiated area at a rate of 100 frames per second and converts the collected infrared radiation intensity into two-dimensional temperature matrix data. Simultaneously, the high-speed vision system uses a coaxial CCD camera to capture images of the molten pool and cracks at a rate of 1000 frames per second, which are then transmitted to the processing core via an image acquisition card. This unit internally runs real-time image processing logic, extracting regions of interest from the visual images, using the Canny edge detection operator to identify crack boundaries, and quantifying the crack width by calculating the Euclidean distance between pixels on both sides of the crack.

[0036] The process for setting the material's safe temperature window threshold in this unit is as follows: First, the melting point and boiling point values ​​of the coating material are obtained. For example, for a ceramic coating, the melting point is 2700 degrees Celsius and the boiling point is 3500 degrees Celsius. To prevent excessive vaporization and perforation, the upper safety limit is set to 90% of the boiling point, i.e., 3150 degrees Celsius; to ensure remelting, the lower safety limit is set to 105% of the melting point, i.e., 2835 degrees Celsius. Therefore, the safe temperature window is determined to be from 2835 degrees Celsius to 3150 degrees Celsius. During monitoring, the unit extracts the highest temperature value from the temperature matrix in real time and compares it with this window.

[0037] If the highest temperature value collected by the infrared thermal imager is 3200 degrees Celsius, exceeding the safety limit of 3150 degrees Celsius, the unit immediately generates a power reduction trigger signal. This signal contains a specific power adjustment step size, calculated as follows: subtract the safety limit value from the current actual temperature value to obtain the temperature deviation value; divide this deviation value by the temperature sensitivity coefficient (e.g., 50 degrees Celsius per watt) to calculate the required power reduction. In this example, the temperature deviation is 50 degrees Celsius, divided by 50 degrees Celsius / watt, resulting in a 1-watt reduction in laser power. This adjustment command is sent to the central control unit within milliseconds. Conversely, if the monitored temperature is below the safety lower limit, the unit generates a command to reduce the scanning speed or increase the power to ensure processing quality.

[0038] The central control unit is configured to construct closed-loop control logic based on temperature field distribution data and dynamic changes in crack morphology data. It sends adjustment commands in real time to the laser generation and output unit and the beam transmission and dynamic focusing unit to perform repair operations on cracks or preventative operations on crack-prone areas. The central control unit is equipped with a partitioned and graded irradiation strategy module. This module divides the coating surface into existing crack areas and potential crack-prone areas, and executes repair scanning logic and impact prevention logic respectively. The repair scanning logic is specifically configured as follows: the control beam first performs a symmetrical scan along both sides of the crack, outputting a laser with a first energy level density to perform thermal relaxation treatment; then, the control beam scans along the crack centerline, outputting a laser with a second energy level density higher than the first energy level density to perform local remelting treatment. The impact prevention logic is specifically configured as follows: the control beam scans along a grid-like or spiral path, outputting laser pulses with a specific peak power to construct a residual compressive stress layer on the coating surface.

[0039] The system continuously receives data streams from the online monitoring unit and runs a multi-threaded closed-loop control algorithm. First, based on the crack distribution topology map fed back by the vision system, the unit uses a connected component analysis algorithm to divide the coating surface into different feature regions. Regions with more than a preset crack length threshold (e.g., 50 pixels) are marked as "existing crack regions"; regions within a 2mm radius in front of the crack tip's extension direction, or regions with a stress concentration factor exceeding 1.5, are marked as "potentially crack-prone regions."

[0040] For the "existing crack area," the unit activates the repair scanning logic. This logic first retrieves the first energy level density parameter, which is designed to induce thermal stress relaxation rather than melting. The parameter setting logic is as follows: the target surface temperature is set to the material softening temperature (e.g., 1500 degrees Celsius), and the required laser energy density is calculated based on specific heat capacity and thermal conductivity. The calculated first energy level density is set to 5 joules per square centimeter. The unit then controls the laser to output the corresponding power and controls the galvanometer to scan the laser spot in a straight line along both sides of the crack, 0.5 mm apart. The thermal expansion effect compresses the crack area, releasing tensile stress. After relaxation is complete, the logic switches to the second energy level density, which is designed to achieve remelting and is set to three times the first energy level density, i.e., 15 joules per square centimeter. The unit instructs the laser beam to precisely align with the crack centerline, melting the coating material with high energy density and using liquid flow to fill the crack gaps.

[0041] For the "potentially crack-prone area," the element activates shock prevention logic. This logic generates a mesh-like or spiral-shaped scan path file and switches the laser to a high peak power mode (e.g., peak power reaching 1 MW). The element controls the beam to emit short pulses at the mesh nodes, generating a shock wave effect. To construct a residual compressive stress layer, the element calculates the required shock wave pressure threshold, which is typically set to twice the material's dynamic yield strength. For example, if the material's dynamic yield strength is 1 GPa, the target shock pressure is 2 GPa. Based on the inverse turbinate absorption model, the element back-calculates the required laser power density and adjusts the laser parameters accordingly to induce a compressive stress layer with a depth of 100 to 200 micrometers on the coating surface, thereby suppressing the initiation of new cracks.

[0042] The auxiliary gas unit is configured to inject inert protective gas in the laser irradiation area via a coaxial or side-axis method. The flow rate of the inert protective gas is adjusted by the central control unit based on temperature field distribution data.

[0043] The flow rate and pressure of the inert protective gas are precisely controlled via an electromagnetic proportional valve. This unit receives real-time temperature field distribution data forwarded by the central control unit and runs a dynamic gas flow rate adjustment algorithm. The core of this algorithm lies in establishing a linear or nonlinear correlation model between temperature values ​​and necessary gas flow rate values. The basic protective flow rate is set at 10 liters per minute for oxidation protection at room temperature. When the monitored temperature at the center of the laser irradiation area rises, the gas flow rate needs to be increased to prevent severe oxidation reactions at high temperatures and the plasma shielding effect.

[0044] The adjustment logic is as follows: Obtain the difference between the current real-time temperature and the ambient baseline temperature (e.g., 25 degrees Celsius); multiply this temperature difference by a flow rate temperature coefficient (e.g., 0.01 liters per minute per degree Celsius) to obtain the incremental flow rate; finally, add the baseline flow rate to the incremental flow rate to obtain the target flow rate. For example, when the irradiated area temperature reaches 2025 degrees Celsius, the temperature difference is 2000 degrees Celsius. Multiplying this by a coefficient of 0.01 yields an increment of 20 liters per minute. After adding the baseline flow rate, the unit controls the proportional valve opening to output 30 liters per minute of argon or nitrogen.

[0045] In addition, the unit is equipped with air curtain flow shaping nozzles, which can switch the air path according to coaxial or lateral spray commands. In lateral spray mode, the unit automatically adjusts the azimuth angle of the side nozzles according to the laser scanning direction, ensuring that the airflow always blows away molten slag and metal vapor in the opposite or lateral direction, preventing them from contaminating the lens or interfering with laser transmission. For example, when the scanning path moves in the positive X-axis direction, the unit controls the rotating air seat to align the nozzles with the negative X-axis direction, spraying at a 45-degree downward angle to form a stable laminar flow protective shield.

[0046] The motion control unit is configured to carry the coating specimen to be treated and perform multi-axis linkage displacement according to the scanning trajectory, so as to cooperate with the beam transmission and dynamic focusing unit to complete the full coverage irradiation of complex curved surfaces.

[0047] The unit drives a five-axis linkage worktable that carries the coating specimen to be treated. This worktable includes three linear axes (X, Y, and Z) and two rotary axes (A and C). The internal motion controller receives G-codes or trajectory commands from the host computer and performs inverse kinematics calculations, converting the scanning trajectory points in the workpiece coordinate system into joint angles and displacements along the five axes. For example, when processing the blade basin surface of a gas turbine blade, to ensure the laser beam remains perpendicular to the coating surface (normal irradiation), the unit calculates the surface normal vector in real time.

[0048] The inverse kinematics solution logic is as follows: For each discrete point on the trajectory, obtain its position coordinates (x, y, z) and normal vector (i, j, k); calculate the rotation angles of the A-axis and C-axis through matrix transformation, ensuring that the normal of the worktable surface is parallel to the laser axis; simultaneously calculate the compensation displacements of the X, Y, and Z axes to counteract the positional shift caused by rotation, ensuring that the focus always falls on the workpiece surface. For example, for a curved point with a radius of curvature of 50 mm, the calculation shows that the A-axis needs to be tilted by 15 degrees, the C-axis needs to be rotated by 30 degrees, and the X-axis needs to be compensated by 2.5 mm.

[0049] This unit is also responsible for coordinating with the galvanometer system of the beam transmission unit (i.e., in flying welding mode). When the scanning range exceeds the galvanometer field of view (e.g., greater than 100 mm by 100 mm), the unit initiates large-scale stitching logic: dividing the large-format trajectory into several sub-field-of-view blocks. After completing the galvanometer scan of one sub-field of view, the motion control unit drives the stage to move at high speed to the center of the next sub-field of view, during which the laser is turned off. To eliminate stitching marks, the unit performs overlapping scans at the edges of adjacent fields of view, with an overlap width set to 0.1 mm, and fine-tunes the stage position within this area using a motion compensation algorithm to ensure stitching accuracy better than 20 micrometers.

[0050] The laser irradiation-induced coating cracking method is performed based on the aforementioned laser irradiation-induced coating cracking device and includes the following steps: S1: Clean the surface of the coating to be treated, and use a high-speed vision system to obtain the location coordinates, length values, width values, and distribution topology of the cracks; During execution, the cleaning subroutine is first initiated, using compressed air nozzles to blow away dust and loose particles from the coating surface. Subsequently, a high-speed vision system is triggered to perform a panoramic scan and image acquisition of the coating surface. The image data is transmitted to the image processing module, which first performs Gaussian filtering on the original image to eliminate sensor thermal noise. Next, the optimal grayscale segmentation threshold is calculated using the Otsu method, converting the image into a binary image, where cracked areas are marked as black pixels and the background as white pixels.

[0051] Based on the binarized image, a skeleton extraction algorithm is executed to refine the crack into lines of single-pixel width, thereby accurately obtaining the crack's topological structure. For geometric feature extraction, a pixel-based statistical method is used: all pixels within the connected region are traversed, and the coordinates of their smallest bounding rectangle are recorded to determine the crack's location coordinates. The total number of pixels on the skeleton line is counted and multiplied by the physical size represented by each pixel (e.g., each pixel represents 10 micrometers) to calculate the crack length. For example, if the skeleton line contains 500 pixels, the crack length is 5 millimeters. For the width, the maximum diameter of the inscribed circle of the crack contour is calculated. Finally, the output dataset includes the crack center coordinates, a length of 5 millimeters, an average width of 0.2 millimeters, and a "Y"-shaped branch topological structure, serving as input for subsequent steps.

[0052] S2: Based on the composition, thickness, and thermophysical parameters of the coating material, combined with the characteristic data of the crack, set the initial laser power, scanning speed, defocusing amount, and pulse frequency, and plan the scanning path strategy. In this step, based on the thermal property parameter database of the coating material, the thermal conductivity (e.g., 2 watts per meter Kelvin), specific heat capacity (e.g., 500 joules per kilogram Kelvin), and density data of the zirconia coating are retrieved. Combined with the crack characteristics obtained in step S1, the key process parameters for laser processing are calculated. First, an initial laser power value is set. The calculation logic is based on the energy balance equation: the required laser power value equals (coating melting point value minus ambient temperature value) multiplied by the specific heat capacity value multiplied by the mass flow rate value, and then divided by the laser absorptivity value. It is calculated that to bring the crack region to the melting point, a thermal power of 150 watts is required.

[0053] The scanning speed is set based on the thermal relaxation time, typically by dividing the spot diameter by the thermal relaxation time. For example, if the spot diameter is 0.5 mm and the thermal relaxation time is 5 milliseconds, the scanning speed is set to 100 mm / s. The defocusing amount is set based on the crack width. If the crack width is 0.2 mm, the defocusing amount is set to make the spot diameter 0.4 mm to cover the crack. The pulse frequency is set based on the required spot overlap. To ensure a 50% overlap, the frequency is equal to the scanning speed divided by (spot diameter multiplied by (1 minus overlap)). Substituting these values, 100 divided by (0.4 multiplied by 0.5) yields a pulse frequency of 500 Hz.

[0054] When planning the scanning path strategy, a vector path along the crack direction is generated, and infeed and retraction leads are added with a length of 1 mm to avoid energy accumulation at the start and end points.

[0055] S3: Based on the distributed topology, the processing mode is determined. If a crack already exists, the repair mode is executed: the laser beam is first controlled to scan symmetrically along both sides of the crack at low power and large spot size to perform stress relaxation treatment, and then scans along the crack path at high power and small spot size to perform remelting and repair treatment. If it is a potentially crack-prone area, the prevention mode is executed: the laser beam is controlled to perform laser shock treatment along the preset grid path at medium power to build a compressive stress layer. The processing mode determination logic is based on the crack distribution topology. If the vision system detects a continuous black pixel connected region, it determines that "a crack already exists" and enters the repair mode. This mode consists of two sub-stages: The first stage is stress relaxation, where the laser output is controlled at low power (e.g., 50 watts), and the dynamic focusing lens is adjusted to increase the spot diameter to 2 mm (large spot state). Symmetrical parallel scanning is performed 1 mm from both sides of the crack, using the compressive stress generated by the thermal gradient to counteract the tensile stress at the crack tip; The second stage is remelting and healing, where the power is increased to high power (e.g., 200 watts), the spot size is reduced to 0.2 mm (small spot state), and the beam center is precisely aligned with the crack path, causing the coating to locally melt and resolidify. During this process, the surface tension of the molten pool helps to bring the material on both sides of the crack together.

[0056] If the vision system determines that the area has no obvious cracks but is in a high-stress zone (potentially crack-prone area), a preventative mode is executed. The laser beam power is controlled at a medium level (e.g., 100 watts), and the spot size is adjusted to 1 mm. The system scans point-by-point along a preset 1 mm x 1 mm grid path. At each grid point, the laser emits a high-energy short pulse (shock wave treatment), inducing plastic deformation in the material surface, building a residual compressive stress layer of up to several hundred megapascals. This compressive stress layer acts like a "bodysuit" for the coating, effectively preventing the initiation and propagation of future cracks.

[0057] S4: During the irradiation process, the actual temperature is compared with the preset safety window in real time using an infrared thermal imager, and the crack closure status is monitored using a high-speed vision system, and the laser power value and scanning speed value are corrected accordingly.

[0058] During laser irradiation, a millisecond-level real-time feedback loop is established. An infrared thermal imager refreshes temperature data every 10 milliseconds, comparing the actual measured molten pool temperature with a preset safety window (e.g., 2800°C to 3000°C). If the actual temperature is below 2800°C, it indicates insufficient heat input, and cracks may not heal; if it is above 3000°C, there is a risk of coating peeling.

[0059] The correction logic is as follows: Calculate the temperature difference (e.g., if the actual temperature is 2750 degrees Celsius, the difference is -50 degrees Celsius), and use a PID control algorithm to calculate the power compensation. Set the proportional coefficient Kp to 0.5, then the power increase is 50 multiplied by 0.5, which equals 25 watts. The control system immediately increases the laser power from the current value by 25 watts. Simultaneously, the high-speed vision system monitors the crack closure status, judging the degree of healing by calculating the grayscale change rate of the crack area. If the grayscale of the crack area is still below the healing threshold after scanning (indicating that the crack is not closed), the scanning speed will be automatically reduced (e.g., from 100 mm / s to 80 mm / s), increasing the heat input per unit length, or instructing the laser head to perform a second scan along the current path until the vision system confirms that the crack has completely disappeared.

[0060] As shown in Table 2, this table records the real-time feedback adjustment data in a certain experiment, which verifies the effectiveness of closed-loop control.

[0061] Table 2 Real-time feedback adjustment experimental data table

[0062] As shown in Table 2, it can respond to temperature and morphology changes in a very short time and stabilize the process parameters within the optimal range.

[0063] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A laser irradiation-induced coating cracking device, characterized in that, The device includes: The laser generating and output unit is configured to generate and output a pulsed laser beam, the wavelength of which is selected based on the absorption spectrum of the target coating material, and has power modulation and pulse waveform editing functions. The beam transmission and dynamic focusing unit is configured to expand the pulsed laser beam and control the movement trajectory, beam diameter and focal length of the spot on the coating surface in coordination with the high-speed scanning galvanometer and the dynamic focusing module. The online monitoring and feedback unit, including an infrared thermal imager and a high-speed vision system, is configured to collect temperature field distribution data and crack morphology dynamic change data of the laser irradiation area in real time, respectively. The central control unit is configured to construct closed-loop control logic based on the temperature field distribution data and the dynamic change data of the crack morphology, and send adjustment commands to the laser generation and output unit and the beam transmission and dynamic focusing unit in real time to perform repair operations for cracks or preventive operations for crack-prone areas.

2. The laser irradiation anti-induced coating cracking device according to claim 1, characterized in that, The laser generating and output unit is selected from one of a pulsed fiber laser, a nanosecond pulsed laser, or a picosecond pulsed laser, and the laser generating and output unit is configured to output a pulse sequence with an adjustable duty cycle.

3. The laser irradiation anti-induced coating cracking device according to claim 1, characterized in that, The beam transmission and dynamic focusing unit is also configured to perform variable focal length scanning, adjusting the defocus amount in real time in a single scanning path to form a spot shape with continuously varying diameter on the coating surface.

4. A method for laser irradiation to induce coating cracks, characterized in that, The laser irradiation anti-induced coating cracking device according to any one of claims 1-3 is executed, comprising the following steps: S1: Clean the surface of the coating to be treated, and use a high-speed vision system to obtain the location coordinates, length values, width values, and distribution topology of the cracks; S2: Based on the composition, thickness, and thermophysical parameters of the coating material, combined with the characteristic data of the crack, set the initial laser power, scanning speed, defocusing amount, and pulse frequency, and plan the scanning path strategy. S3: Based on the distributed topology, the processing mode is determined. If a crack already exists, the repair mode is executed: the laser beam is first controlled to scan symmetrically along both sides of the crack at low power and large spot size to perform stress relaxation treatment, and then scans along the crack path at high power and small spot size to perform remelting and repair treatment. If it is a potentially crack-prone area, the prevention mode is executed: the laser beam is controlled to perform laser shock treatment along the preset grid path at medium power to build a compressive stress layer. S4: During the irradiation process, the actual temperature is compared with the preset safety window in real time using an infrared thermal imager, and the crack closure status is monitored using a high-speed vision system, and the laser power value and scanning speed value are corrected accordingly.

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