Method for inhibiting thermal damage of high-performance composite material picosecond laser processing variable cross-section hole

Abstract

The application provides a high-performance composite material picosecond laser processing variable cross-section hole thermal damage inhibition method, relates to the technical field of laser drilling, and analyzes a depth image to determine a variable cross-section position, judges whether to start cooling by combining a heat affected zone determined based on a thermal imaging image, if starting, analyzes a sputtering direction of a fiber sputtering image to determine an initial horizontal cooling direction, and sets a horizontal cooling direction adjustment strategy, analyzes a heat distribution of the variable cross-section in the heat affected zone, and sets a vertical cooling direction adjustment strategy based on a heat distribution analysis result; based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy, the cooling direction of the cooling gas is adjusted in real time until the laser spot position is no longer located in the variable cross-section affected zone; precise identification and directional cooling of the variable cross-section area are realized, and thermal damage caused by local thermal accumulation and non-uniform heat distribution is inhibited.

Description

Technical Field

[0001] This invention relates to the field of laser hole-making technology, specifically to a method for suppressing thermal damage in picosecond laser processing of high-performance composite materials for creating variable cross-section holes. Background Technology

[0002] High-performance composite materials are widely used in aerospace and high-end equipment manufacturing, and their structures place extremely high demands on the quality of hole fabrication. Femtosecond lasers, due to their ultrashort pulse characteristics, are considered capable of "cold processing." However, in actual variable cross-section hole fabrication processes, significant heat accumulation effects still occur in localized areas as the hole diameter changes and the incident angle is adjusted. This is especially true in the transition region of the variable cross-section, where uneven material removal rates and abrupt energy deposition can easily lead to non-uniform heat-affected zones, causing problems such as resin matrix thermal degradation, fiber pull-out, and interface damage. These problems exhibit significant spatial locality and dynamic evolution characteristics, making traditional methods based on fixed parameters or overall cooling strategies ineffective.

[0003] Existing technologies often rely on single temperature monitoring or empirical threshold-triggered cooling methods, lacking precise identification and targeted control of the critical thermosensitive structure—the variable cross-section region. Especially during dynamic changes in the laser processing path, it is difficult to achieve coordinated analysis of the heat-affected zone morphology, fiber sputtering behavior, and heat distribution evolution, leading to a mismatch between the cooling direction and the actual heat diffusion direction. This reduces cooling efficiency and may even introduce new processing defects. Therefore, how to construct a thermal damage suppression method during variable cross-section hole-making that can identify critical thermal risk areas in real time and adaptively control the cooling direction has become an urgent technical problem to be solved.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes, comprising the following steps: Step 1: Acquire thermal and depth images of the laser spot location marked during laser hole making in real time. Analyze the depth image to determine the location of the variable cross-section and set the variable cross-section influence zone to determine whether the laser spot location is within the variable cross-section influence zone. Step 2: If the laser spot is located within the variable cross-section affected area, the boundary of the high-temperature region in the thermal imaging image is extracted based on the boundary extraction algorithm to determine the heat-affected area. If there is a variable cross-section in the heat-affected area, the cooling air is activated and the process proceeds to Step 3. Step 3: Acquire fiber sputtering images at the laser spot location, perform sputtering direction analysis on the fiber sputtering images to determine the initial horizontal cooling direction, and set a horizontal cooling direction adjustment strategy. Perform heat distribution analysis on the variable cross-section in the heat-affected zone, and set a vertical cooling direction adjustment strategy based on the heat distribution analysis results. Step 4: Based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy, adjust the cooling direction of the cold air in real time until the laser spot position is no longer located in the variable cross-section influence zone.

[0007] Furthermore, the depth image is a grayscale image, in which the grayscale value of each pixel represents the distance between a point inside the high-performance composite material and the top plane of the high-performance composite material. The logic for determining the location of the variable cross section is as follows: Using the center of the laser-drilled area as the center, for any radius, all points that the center of the laser spot has appeared on that radius are obtained as trajectory points and marked in the depth image. For any marked trajectory point, its absolute depth change rate is calculated. If the absolute depth change rate is greater than the preset absolute depth change rate threshold, the location of the trajectory point is determined to be a variable cross-section location, and the trajectory point is called a variable cross-section trajectory point; otherwise, the location of the trajectory point is determined not to be a variable cross-section location.

[0008] Furthermore, the logic for calculating the absolute depth mutation rate is as follows: For the trajectory point ranked 1, the absolute depth mutation rate of the trajectory point is set to 0, and its depth change rate is set to be equal to the depth change rate of the trajectory point ranked 2. The trajectory points are sorted according to the time order in which they appear; For any trajectory point ranked 2 or higher, calculate the absolute depth change rate using the following steps: Calculate the absolute depth difference between the current trajectory point and the previous trajectory point, and use it as the depth deviation. Calculate the straight-line distance of the current trajectory point relative to the previous trajectory point on the radius, and use it as the radius deviation; The absolute depth change rate of the trajectory point is obtained by dividing the depth deviation by the radius deviation. Calculate the absolute difference in depth mutation rate between the current trajectory point and the previous trajectory point, and use this as the absolute depth mutation rate.

[0009] Furthermore, the logic for determining whether the laser spot position is located within the variable cross-section influence zone is as follows: Calculate the horizontal distance between each variable cross-section trajectory point and the center of the laser spot, and select the variable cross-section trajectory point with the shortest horizontal distance. The shortest horizontal distance is compared with a preset horizontal distance threshold. If the shortest horizontal distance is less than the preset horizontal distance threshold, the laser spot is determined to be located within the variable cross-section influence zone; otherwise, the laser spot is determined to be located outside the variable cross-section influence zone. The horizontal distance refers to the straight-line distance between the center of the laser spot and the cross-sectional trajectory point in the depth image.

[0010] Furthermore, the boundaries of high-temperature regions in the thermal imaging image are extracted based on a boundary extraction algorithm to determine the heat-affected zone. The specific logic is as follows: The boundary extraction algorithm is used to extract the boundaries of high-temperature regions in thermal imaging images to determine the heat-affected zone. The specific logic is as follows: All pixels in the thermal imaging image are obtained, and the pixels corresponding to the laser spot are removed from all pixels to obtain the processed thermal imaging image. The Sobel operator is used to extract the edge region in the processed thermal imaging image, which is the boundary between the high-temperature region and the non-high-temperature region. Calculate the average temperature of all pixels within and outside the edge region, compare the two average temperature values, and define the region with the largest average temperature value as the heat-affected zone.

[0011] Furthermore, sputtering direction analysis is performed on the fiber sputtering image to determine the initial horizontal cooling direction. The specific logic is as follows: Within a space perpendicular to the surface of a high-performance composite material plate, two mutually perpendicular planes are selected, one as a horizontal plane and the other as a vertical plane; the fiber sputtering image is an image of the horizontal plane; The grayscale range of fiber pulling out is preset. For any pixel in the fiber sputtering image, if its grayscale value is within the grayscale range of fiber pulling out, it is judged as a fiber pulling out pixel. The fiber-pulling pixel is divided into several fiber-pulling regions based on the connected vessel labeling algorithm, and the fiber-pulling regions are eroded into a skeleton using the erosion algorithm. Starting from the center of the laser spot, draw any ray in the plane of the fiber sputtering image, calculate the projection length of the skeleton of each fiber region on the ray, and calculate the sum of the projection lengths of all pulled-out fiber regions to obtain the total projection length. Select the ray with the longest total projection length, which is called the optimal ray. In the plane corresponding to the fiber sputtering image, the opposite direction of the optimal ray is taken as the initial horizontal cooling direction.

[0012] Furthermore, the logic for setting the horizontal cooling direction adjustment strategy is as follows: In the horizontal plane, the total projected length of the skeleton of each fiber-pulling region to the left of the ray corresponding to the horizontal cooling direction is called the left projection length. The total projected length of the skeleton of each fiber-pulling region to the right of the ray corresponding to the current horizontal cooling direction is called the right projection length. The difference between the left and right projection lengths is calculated and called the projection length deviation value. If the absolute value of the projection length deviation value is not greater than the preset projection length deviation value threshold, the current horizontal cooling direction will not be adjusted and the current horizontal cooling direction adjustment will end. If the absolute value of the projection length deviation is greater than the projection length deviation threshold and the projection length deviation is greater than 0, then the horizontal cooling direction will be adjusted to the right by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end. If the absolute value of the projection length deviation is greater than the projection length deviation threshold, and the projection length deviation is less than 0, then the horizontal cooling direction will be adjusted to the left by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end.

[0013] Furthermore, the variable cross-section in the heat-affected zone is analyzed. When a variable cross-section exists in the heat-affected zone, a vertical cooling direction adjustment strategy is set, with the specific logic as follows: Determine if there is a variable cross-section in the heat-affected zone. If there is no variable cross-section, no vertical cooling direction adjustment is performed. If there is, calculate the temperature variance of the trajectory points of the variable cross-section in the heat-affected zone and use it as the initial temperature variance. Randomly select a direction in the vertical plane and adjust it once according to the preset vertical angle adjustment range. Obtain the adjusted temperature variance. If the adjusted temperature variance is less than the initial temperature variance, determine the adjusted vertical cooling direction as the new vertical cooling direction and end this vertical cooling direction adjustment. Otherwise, reverse the vertical angle by twice the preset adjustment range, obtain the adjusted temperature variance, and if the adjusted temperature variance is less than the initial temperature variance, accept the adjustment, determine the adjusted vertical cooling direction as the new vertical cooling direction, and end the current vertical cooling direction adjustment. If the adjusted temperature variance is not less than the initial temperature variance, then the vertical cooling direction will be reset to the vertical cooling direction corresponding to the initial temperature variance, thus ending this vertical cooling direction adjustment.

[0014] Furthermore, the logic for adjusting the cooling direction of the air in real time based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy is as follows: First, adjust the horizontal cooling direction. After the horizontal cooling direction adjustment is completed, adjust the vertical cooling direction. After the vertical cooling direction adjustment is completed, adjust the horizontal cooling direction. Repeat this alternating cycle until the laser spot position is no longer located within the variable cross-section influence zone.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This scheme uses depth image analysis to accurately locate the boundary of the variable cross-section, enabling dynamic identification of the variable cross-section location and its affected area. Boundary extraction from thermal imaging images determines the heat-affected zone, achieving real-time mapping of the high-temperature area's spatial range, thus ensuring targeted control. Building upon this, fiber sputtering image analysis is introduced, utilizing sputtering distribution to reflect the thermal-mechanical coupling diffusion direction, constructing an initial horizontal cooling direction, and using left-right projection differences to achieve dynamic direction correction with laser movement, ensuring the cooling direction always matches the dominant thermal diffusion path; this avoids the problem of mismatch between the cooling direction and the actual thermal diffusion direction. By analyzing the variable cross-section within the heat-affected zone and using this analysis as feedback for vertical water cooling direction control, the temperature of the variable cross-section approaches a more uniform state, thereby actively reducing the temperature gradient and local hot spots along the thickness direction, preventing thermal damage that may result from uneven temperature distribution. Attached Figure Description

[0016] Fig. 1 This is a schematic diagram of the overall method flow of the present invention; Fig. 2 These are schematic diagrams of two types of variable cross-section holes according to the present invention, wherein (a) is a schematic diagram of a conical countersunk variable cross-section hole and (b) is a schematic diagram of a cylindrical countersunk variable cross-section hole. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] Example: Please see Figs. 1-2 The present invention provides a technical solution: A method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes, comprising the following steps: Step 1: Acquire thermal and depth images of the laser spot location marked during laser hole making in real time. Analyze the depth image to determine the location of the variable cross-section and set the variable cross-section influence zone to determine whether the laser spot location is within the variable cross-section influence zone. Furthermore, the depth image is a grayscale image, in which the grayscale value of each pixel represents the distance between a point inside the high-performance composite material and the top plane of the high-performance composite material. Acquiring depth images is an existing technology. The specific depth of each position can be obtained through an optical ranging system. Then, based on the maximum depth of the pre-formed hole, the depths are normalized by 0 and the maximum depth. The result of the normalization is multiplied by 255 (the gray level of a grayscale image is usually 0-255. If other gray levels are used, 255 can be replaced with the corresponding gray level) and assigned to the corresponding pixel.

[0020] The logic for determining the location of the variable cross section is as follows: Using the center of the laser-drilled area as the center, for any radius, all points that the center of the laser spot has appeared on that radius are obtained as trajectory points and marked in the depth image. For any marked trajectory point, its absolute depth change rate is calculated. If the absolute depth change rate is greater than the preset absolute depth change rate threshold, the location of the trajectory point is determined to be a variable cross-section location, and the trajectory point is called a variable cross-section trajectory point; otherwise, the location of the trajectory point is determined not to be a variable cross-section location.

[0021] The logic for calculating the absolute depth mutation rate is as follows: Set the absolute depth mutation rate of the trajectory point to 0, and set its depth change rate to be equal to the depth change rate of the trajectory point ranked 2; sort the trajectory points according to the time order of their appearance. For any trajectory point ranked 2 or higher, calculate the absolute depth change rate using the following steps: Calculate the absolute depth difference between the current trajectory point and the previous trajectory point, and use it as the depth deviation. Calculate the straight-line distance of the current trajectory point relative to the previous trajectory point on the radius, and use it as the radius deviation; The absolute depth change rate of the trajectory point is obtained by dividing the depth deviation by the radius deviation. Calculate the absolute difference in depth mutation rate between the current trajectory point and the previous trajectory point, and use this as the absolute depth mutation rate.

[0022] Fig. 2 These are the two types of variable cross-section holes in this application. Fig. 2 (a) is a schematic diagram of a tapered countersunk hole with variable cross-section.Fig. 2 (b) is a schematic diagram of a cylindrical countersunk hole with a variable cross-section. The absolute depth change rate is essentially the rate of change of laser depth at the corresponding position. In the processing of the non-transition region, whether it is the upper or lower half, the laser should maintain a constant trend on the same radius. However, when processing the transition region between the upper and lower parts of the variable cross-section, the hole shape changes, so the rate of change of depth also switches from the trend of the upper half to the trend of the lower half, or from the trend of the upper / lower half to the trend corresponding to the step position. The corresponding depth abrupt change rate will change abruptly. That is, the absolute depth abrupt change rate in this application is greater than the preset absolute depth abrupt change rate threshold. Therefore, the position of the variable cross-section can be determined by the absolute depth abrupt change rate.

[0023] The absolute depth mutation rate threshold can be preset using conventional techniques. Since the depth change rate usually remains consistent in the non-transition region, the absolute depth mutation rate threshold is usually set to a minimum value. This allows us to obtain several absolute depth mutation rates in the non-transition region processing stage of a hole with good historical processing conditions, and use the maximum value of these rates as the absolute depth mutation rate threshold.

[0024] Furthermore, the logic for determining whether the laser spot position is located within the variable cross-section influence zone is as follows: Calculate the horizontal distance between each variable cross-section trajectory point and the center of the laser spot, and select the variable cross-section trajectory point with the shortest horizontal distance. The shortest horizontal distance is compared with a preset horizontal distance threshold. If the shortest horizontal distance is less than the preset horizontal distance threshold, the laser spot is determined to be located within the variable cross-section influence zone; otherwise, the laser spot is determined to be located outside the variable cross-section influence zone. The horizontal distance refers to the straight-line distance between the center of the laser spot and the cross-sectional trajectory point in the depth image.

[0025] During laser processing, the temperature of the laser spot and its vicinity is usually higher than that of the unprocessed area, which is an important cause of thermal damage. When using cold air to suppress thermal damage, this area is the main target. During variable cross-section processing, due to the abrupt change in curvature at the junction of the variable cross-section, a stage heat transfer path will be formed. If the junction of the variable cross-section is in the corresponding heat-affected zone, the heat at the corresponding location will accumulate abnormally, which can easily cause thermal damage. The preset horizontal distance threshold is set as follows: In several variable cross-section hole-making processes without cold air cooling, holes without thermal damage are selected. For these holes, the horizontal distance when the boundary of the heat-affected zone overlaps with the variable cross-section is recorded each time. The maximum horizontal distance is taken as the horizontal distance threshold. When the boundary of the heat-affected zone in these samples just overlaps with the variable cross-section, the corresponding horizontal distance actually reflects the distance when the heat diffusion is not out of control but is close to the critical risk state. Taking the maximum value in these critical but safe samples as the horizontal distance threshold can avoid constantly monitoring whether the cross-section changes in the heat-affected zone, thus constructing the most conservative safety boundary.

[0026] Step 2: If the laser spot is located within the variable cross-section affected area, the boundary of the high-temperature region in the thermal imaging image is extracted based on the boundary extraction algorithm to determine the heat-affected area. If there is a variable cross-section in the heat-affected area, the cooling air is activated and the process proceeds to Step 3. If there is no variable cross-section in the heat-affected zone, then no cold air cooling is performed.

[0027] The boundary extraction algorithm is used to extract the boundaries of high-temperature regions in thermal imaging images to determine the heat-affected zone. The specific logic is as follows: All pixels in the thermal imaging image are obtained, and the pixels corresponding to the laser spot are removed from all pixels to obtain the processed thermal imaging image. Thermal imaging images during laser processing are typically divided into three parts: the heat-affected zone, the laser spot, and the background. However, boundary extraction algorithms can only extract the boundaries. To facilitate subsequent region classification, all pixels corresponding to the laser spot are directly removed.

[0028] The Sobel operator is used to extract the edge region in the processed thermal imaging image, which is the boundary between the high-temperature region and the non-high-temperature region. Using the Sobel operator to extract edge regions from processed thermal imaging images is an existing technique, specifically: The Sobel operator is used to calculate the horizontal and vertical gradient values ​​of each pixel in the processed thermal imaging image, and a gradient magnitude data set including the gradient magnitude data of all pixels is generated. The error rate between the gradient magnitude of the current pixel and the gradient magnitude of the adjacent pixels is determined, where the error rate is the absolute difference between the gradient magnitude of the current pixel and the gradient magnitude of the adjacent pixels divided by the gradient magnitude of the current pixel. If the error rate is less than the set error rate threshold, the pixel value of the current pixel is retained; otherwise, the pixel value of the current pixel is set to 0, and the area where the pixel value is retained is determined as the edge region in the processed thermal imaging image. The calculation of the error rate and the setting of the error rate threshold can be referenced from industry standards.

[0029] Calculate the average temperature of all pixels within and outside the edge region, compare the two average temperature values, and define the region with the largest average temperature value as the heat-affected zone.

[0030] Since the pixels corresponding to the laser spot have been removed, the only areas that need to be distinguished by edge are the heat-affected zone and the background (unprocessed area). The temperature of the heat-affected zone is relatively high, so when comparing the average temperature of the two, the area with the largest average temperature is defined as the heat-affected zone.

[0031] In this application, the cooling air is cooled by a cooling air gun controlled by a robotic arm, and the temperature range of the cooling airflow is -15°C to 0°C.

[0032] Step 3: Acquire fiber sputtering images at the laser spot location, perform sputtering direction analysis on the fiber sputtering images to determine the initial horizontal cooling direction, and set a horizontal cooling direction adjustment strategy. Perform heat distribution analysis on the variable cross-section in the heat-affected zone, and set a vertical cooling direction adjustment strategy based on the heat distribution analysis results. Furthermore, sputtering direction analysis is performed on the fiber sputtering image to determine the initial horizontal cooling direction. The specific logic is as follows: Within a space perpendicular to the surface of a high-performance composite material plate, two mutually perpendicular planes are selected, one as a horizontal plane and the other as a vertical plane; the fiber sputtering image is an image of the horizontal plane; The grayscale range of fiber pulling out is preset. For any pixel in the fiber sputtering image, if its grayscale value is within the grayscale range of fiber pulling out, it is judged as a fiber pulling out pixel. The grayscale range of the fiber to be pulled out is preset using existing technology. Historical fiber sputtering images of the fiber region to be pulled out are obtained and identified. The range formed by the maximum and minimum grayscale values ​​of the fiber region is used as the grayscale range of the fiber to be pulled out.

[0033] The fiber-pulling pixel is divided into several fiber-pulling regions based on the connected vessel labeling algorithm. The connected vessel labeling algorithm is an existing technology. The process of this application adopts the 8-connected vessel labeling algorithm is as follows: traverse every pixel in the fiber sputtering image. When an unlabeled fiber-pulling pixel is encountered, it is used as a seed point of a new connected component.

[0034] Starting from the seed point, use a breadth-first search or depth-first search algorithm to recursively find and label all the plucked fiber pixels connected to it by the 8-connectivity rule. This process will form an independent, continuous plucked fiber region and assign it a unique label; repeat this process until all plucked fiber pixels in the image have been visited and labeled.

[0035] The erosion algorithm is used to erode the fiber-extracting region into a skeleton, specifically: Starting from the boundary of the fiber-extracting region, in each iteration, the outermost pixels are systematically peeled off without disrupting its topological connectivity. This process continues, with the fiber-extracting region being eroded uniformly inward from all directions until no more pixels can be removed. Ultimately, the pixels that survive the iterations and cannot be further eroded form a single-pixel-wide skeleton. The above process is existing technology and will not be elaborated further here.

[0036] Starting from the center of the laser spot, draw any ray in the plane of the fiber sputtering image, calculate the projection length of the skeleton of each fiber region on the ray, and calculate the sum of the projection lengths of all pulled-out fiber regions to obtain the total projection length. Select the ray with the longest total projection length, which is called the optimal ray. It should be noted that if the projection of the skeleton of the fiber region is on the extension line of the ray, the projection is still regarded as the projection on the ray.

[0037] In the plane corresponding to the fiber sputtering image, the opposite direction of the optimal ray is taken as the initial horizontal cooling direction.

[0038] It should be noted that: The spatial distribution direction of fiber sputtering essentially reflects the dominant direction of energy release and momentum transfer during material removal, that is, the direction in which heat and debris preferentially diffuse. By summing the projected lengths of the skeleton of each fiber region in different ray directions, it is equivalent to quantifying the overall expansion degree of the sputtered structure in a certain direction. When the total projected length corresponding to a certain ray direction is the largest, it indicates that a large number of fiber sputterings exhibit the most significant extension and aggregation along that direction, that is, this direction is the dominant outward expansion direction under the effect of thermo-mechanical coupling. The goal of cooling is to suppress heat accumulation and diffusion. Therefore, taking the opposite direction of this dominant diffusion direction as the initial cooling direction can achieve reverse diffusion countermeasure: directly cooling the source of heat and debris outward expansion, thereby more effectively weakening local heat accumulation and fiber pull-out effect, and improving the targeting and efficiency of the cooling effect.

[0039] Furthermore, the laser spot moves continuously along its trajectory during processing, causing the heat source position to constantly shift. This results in a dynamic asymmetry between the fiber sputtering distribution and the heat diffusion direction, which varies with position, leading to a reduction in cooling efficiency. Therefore, the spatial distribution of the pulled-out fiber observed at any given moment essentially reflects the bias direction of the instantaneous thermo-mechanical field at the current spot position, and this bias will continuously shift with the laser movement. If a fixed cooling direction is still used, it will be impossible to continuously align with the actual main heat diffusion direction, easily resulting in hysteresis or deviation. Furthermore, the logic for setting the horizontal cooling direction adjustment strategy is as follows: In the horizontal plane, the total projected length of the skeleton of each fiber-pulling region to the left of the ray corresponding to the horizontal cooling direction is called the left projection length. The total projected length of the skeleton of each fiber-pulling region to the right of the ray corresponding to the current horizontal cooling direction is called the right projection length. The difference between the left and right projection lengths is calculated and called the projection length deviation value. If the absolute value of the projection length deviation value is not greater than the preset projection length deviation value threshold, the current horizontal cooling direction will not be adjusted and the current horizontal cooling direction adjustment will end. At this point, the small deviation in projection length indicates that the fiber sputtering distribution at the current spot position is approximately symmetrical, meaning that heat diffusion is basically balanced on both sides. The cooling direction is now essentially matched with the thermal field distribution. Further adjustments would introduce unnecessary disturbances, especially during continuous laser movement, which could cause frequent directional oscillations. Therefore, maintaining the current position ensures system stability.

[0040] If the absolute value of the projection length deviation is greater than the projection length deviation threshold and the projection length deviation is greater than 0, then the horizontal cooling direction will be adjusted to the right by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end. At this point, under the current spot position, fiber sputtering and heat diffusion are more concentrated on the left side, meaning the heat source bias direction points to the left. If the original cooling direction is maintained, the cooling airflow cannot effectively cover the main heat accumulation area on this side. Therefore, the cooling direction needs to be deflected to the right so that the cold air forms a reverse coverage on the left heat source, thereby effectively counteracting the biased heat. If the absolute value of the projection length deviation is greater than the projection length deviation threshold, and the projection length deviation is less than 0, then the horizontal cooling direction will be adjusted to the left by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end.

[0041] At this point, the heat diffusion is biased to the right, and similarly, the cooling direction needs to be deflected to the left to realign with the main heat source distribution area.

[0042] This strategy ensures that the cooling direction is always aligned in the opposite direction with reference to the thermal diffusion bias of the current spot position, thereby achieving real-time tracking and suppression of dynamically moving heat sources and preventing local heat accumulation on one side during continuous laser movement.

[0043] The logic for setting the projection length deviation threshold is as follows: set several equally spaced threshold levels, perform multiple hole-making tests on each level and evaluate the thermal damage compliance, sort the threshold levels from smallest to largest, and take the level before the first level that fails the thermal damage test as the projection length deviation threshold.

[0044] The criteria for judging whether thermal damage is acceptable are that there is no obvious ablation of the pore wall, carbonization of the matrix, or fiber peeling defects, while the criteria for judging whether thermal damage is unacceptable are that there is abnormal damage such as ablation and blackening of the pore wall, thermal degradation of the resin, or fiber shedding.

[0045] Furthermore, the variable cross-section in the heat-affected zone is analyzed. When a variable cross-section exists in the heat-affected zone, a vertical cooling direction adjustment strategy is set, with the specific logic as follows: Determine whether the heat-affected zone has a variable cross-section. If the heat-affected zone does not have a variable cross-section, then no vertical cooling direction adjustment is required. It should be noted that: In this scheme, the trigger condition for cooling is that the variable cross-section falls within the heat-affected zone (HAZ). After the cooling airflow acts, it continuously compresses and shrinks the HAZ. When the variable cross-section is originally at the critical boundary of the HAZ, the cooling will cause the HAZ to shrink, thus causing the variable cross-section to move out of the HAZ's coverage area. Under this condition, the variable cross-section is no longer affected by high-temperature heat and there is no risk of localized thermal damage. Therefore, no further adjustment of the vertical cooling direction is required.

[0046] Meanwhile, during laser processing of materials, thermal damage is not only caused by absolute high temperature, but uneven temperature field distribution can also induce local thermal defects. This solution effectively suppresses the overall high temperature problem through forced cooling with cold air, thus focusing on optimizing the problem of uneven temperature distribution. Temperature variance can accurately quantify the degree of temperature dispersion in a region and is a core indicator characterizing the uniformity of heat distribution. In the vertical space, improper cooling direction can easily cause heat to accumulate biasedly along the thickness direction of the component and in the oblique areas of the hole wall, leading to defects such as thermal degradation of the resin matrix and damage to the interlayer interface. Matching a suitable vertical cooling direction can evenly remove excess heat in the thickness direction, weaken local heat accumulation, make the regional temperature field tend to be gentler, and significantly reduce the corresponding temperature variance. Therefore, this application uses temperature variance as a quantitative evaluation index to iteratively optimize and match the optimal vertical cooling direction to achieve uniform control of heat distribution in variable cross-section areas.

[0047] If the heat-affected zone has a variable cross section, calculate the temperature variance of the trajectory points of the variable cross section in the heat-affected zone and use it as the initial temperature variance; randomly select a direction in the vertical plane and make an adjustment according to the preset vertical angle adjustment range to obtain the adjusted temperature variance; if the adjusted temperature variance is less than the initial temperature variance, determine the adjusted vertical cooling direction as the new vertical cooling direction and end this vertical cooling direction adjustment. It should be noted that if the vertical cooling direction adjustment is not completed after the above adjustments, the following adjustments will be made based on the above adjustments. Otherwise, reverse the vertical angle by twice the preset adjustment range, obtain the adjusted temperature variance, and if the adjusted temperature variance is less than the initial temperature variance, accept the adjustment, determine the adjusted vertical cooling direction as the new vertical cooling direction, and end the current vertical cooling direction adjustment. It should be noted that if the vertical cooling direction adjustment is not completed after the above adjustments, the following adjustments will be made based on the above adjustments. If the adjusted temperature variance is not less than the initial temperature variance, then the vertical cooling direction will be reset to the vertical cooling direction corresponding to the initial temperature variance, thus ending this vertical cooling direction adjustment.

[0048] Its control principle is as follows: First, a small-angle trial deflection is made to quickly determine the optimization effectiveness of the current deflection direction; if the heat distribution effect is improved, the cooling direction is directly locked; if there is no improvement, it proves that the trial direction deviates from the optimal direction, and the correction is made by adjusting the vertical angle by twice the preset value in the opposite direction. By using half-amplitude reset + half-amplitude reverse deflection, the local invalid interval is crossed, avoiding the blind zone of local optima in direction optimization; when both bidirectional adjustments cannot optimize the temperature field distribution, it indicates that the initial cooling direction has adapted to the current thermal field state, and the initial direction is kept unchanged to ensure the stability of continuous system operation.

[0049] The preset vertical and horizontal angle adjustment ranges are both minimum values, and their size mainly depends on the instrument's response accuracy. The smaller the better, and they are usually set to the minimum value that the instrument can respond to per unit time.

[0050] Step 4: Based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy, adjust the cooling direction of the cold air in real time until the laser spot position is no longer located in the variable cross-section influence zone.

[0051] To avoid other adjustments affecting the adjustment effect, such as simultaneous horizontal and vertical adjustments where the specific influencing factors cannot be determined, this application only performs adjustments in one direction at a time.

[0052] Furthermore, the logic for adjusting the cooling direction of the air in real time based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy is as follows: First, adjust the horizontal cooling direction. After the horizontal cooling direction adjustment is completed, adjust the vertical cooling direction. After the single vertical cooling direction adjustment is completed, adjust the horizontal cooling direction again. Repeat this alternating cycle. The real-time position of the laser spot is acquired throughout the entire process and compared with the set variable cross-section influence zone for judgment. When the laser spot position is no longer within the variable cross-section influence zone, the alternating adjustment process of the cooling direction is terminated. The above formulas are all dimensionless numerical calculations, and the formulas are derived from software simulation based on a large amount of collected data to obtain the most realistic formula. The preset parameters in the formulas can be set by those skilled in the art according to the actual situation.

[0053] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0054] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0055] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that cannot be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes, characterized in that, The specific steps include: Step 1: Acquire thermal and depth images of the laser spot location marked during laser hole making in real time. Analyze the depth image to determine the location of the variable cross-section and set the variable cross-section influence zone to determine whether the laser spot location is within the variable cross-section influence zone. Step 2: If the laser spot is located within the variable cross-section affected area, the boundary of the high-temperature region in the thermal imaging image is extracted based on the boundary extraction algorithm to determine the heat-affected area. If there is a variable cross-section in the heat-affected area, the cooling air is activated and the process proceeds to Step 3. Step 3: Acquire fiber sputtering images at the laser spot location, perform sputtering direction analysis on the fiber sputtering images to determine the initial horizontal cooling direction, and set a horizontal cooling direction adjustment strategy. Perform heat distribution analysis on the variable cross-section in the heat-affected zone, and set a vertical cooling direction adjustment strategy based on the heat distribution analysis results. Step 4: Based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy, adjust the cooling direction of the cold air in real time until the laser spot position is no longer located in the variable cross-section influence zone.

2. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 1, characterized in that: The depth image is a grayscale image. In the depth image, the grayscale value of each pixel represents the distance between a point inside the high-performance composite material and the top plane of the high-performance composite material. The logic for determining the location of the variable cross section is as follows: Using the center of the laser-drilled area as the center, for any radius, all points that the center of the laser spot has appeared on that radius are obtained as trajectory points and marked in the depth image. For any marked trajectory point, its absolute depth change rate is calculated. If the absolute depth change rate is greater than the preset absolute depth change rate threshold, the location of the trajectory point is determined to be a variable cross-section location, and the trajectory point is called a variable cross-section trajectory point; otherwise, the location of the trajectory point is determined not to be a variable cross-section location.

3. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 2, characterized in that: The logic for calculating the absolute depth mutation rate is as follows: For the trajectory point ranked 1, the absolute depth mutation rate of the trajectory point is set to 0, and its depth change rate is set to be equal to the depth change rate of the trajectory point ranked 2. The trajectory points are sorted according to the time order in which they appear; For any trajectory point ranked 2 or higher, calculate the absolute depth change rate using the following steps: Calculate the absolute depth difference between the current trajectory point and the previous trajectory point, and use it as the depth deviation. Calculate the straight-line distance of the current trajectory point relative to the previous trajectory point on the radius, and use it as the radius deviation; The absolute depth change rate of the trajectory point is obtained by dividing the depth deviation by the radius deviation. Calculate the absolute difference in depth mutation rate between the current trajectory point and the previous trajectory point, and use this as the absolute depth mutation rate.

4. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 2, characterized in that: The logic for determining whether the laser spot position is located within the variable cross-section influence zone is as follows: Calculate the horizontal distance between each variable cross-section trajectory point and the center of the laser spot, and select the variable cross-section trajectory point with the shortest horizontal distance. The shortest horizontal distance is compared with a preset horizontal distance threshold. If the shortest horizontal distance is less than the preset horizontal distance threshold, the laser spot is determined to be located within the variable cross-section influence zone; otherwise, the laser spot is determined to be located outside the variable cross-section influence zone. The horizontal distance refers to the straight-line distance between the center of the laser spot and the cross-sectional trajectory point in the depth image.

5. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 1, characterized in that: The boundary extraction algorithm is used to extract the boundaries of high-temperature regions in thermal imaging images to determine the heat-affected zone. The specific logic is as follows: All pixels in the thermal imaging image are obtained, and the pixels corresponding to the laser spot are removed from all pixels to obtain the processed thermal imaging image. The Sobel operator is used to extract the edge region in the processed thermal imaging image, which is the boundary between the high-temperature region and the non-high-temperature region. Calculate the average temperature of all pixels within and outside the edge region, compare the two average temperature values, and define the region with the largest average temperature value as the heat-affected zone.

6. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 1, characterized in that: Sputtering direction analysis is performed on the fiber sputtering image to determine the initial horizontal cooling direction. The specific logic is as follows: Within a space perpendicular to the surface of a high-performance composite material plate, two mutually perpendicular planes are selected, one as a horizontal plane and the other as a vertical plane; the fiber sputtering image is an image of the horizontal plane; The grayscale range of fiber pulling out is preset. For any pixel in the fiber sputtering image, if its grayscale value is within the grayscale range of fiber pulling out, it is judged as a fiber pulling out pixel. The fiber-pulling pixel is divided into several fiber-pulling regions based on the connected vessel labeling algorithm, and the fiber-pulling regions are eroded into a skeleton using the erosion algorithm. Starting from the center of the laser spot, draw any ray in the plane of the fiber sputtering image, calculate the projection length of the skeleton of each fiber region on the ray, and calculate the sum of the projection lengths of all pulled-out fiber regions to obtain the total projection length. Select the ray with the longest total projection length, which is called the optimal ray. In the plane corresponding to the fiber sputtering image, the opposite direction of the optimal ray is taken as the initial horizontal cooling direction.

7. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 6, characterized in that: The logic for setting the horizontal cooling direction adjustment strategy is as follows: In the horizontal plane, the total projected length of the skeleton of each fiber-pulling region to the left of the ray corresponding to the horizontal cooling direction is called the left projection length. The total projected length of the skeleton of each fiber-pulling region to the right of the ray corresponding to the current horizontal cooling direction is called the right projection length. The difference between the left and right projection lengths is calculated and called the projection length deviation value. If the absolute value of the projection length deviation value is not greater than the preset projection length deviation value threshold, the current horizontal cooling direction will not be adjusted and the current horizontal cooling direction adjustment will end. If the absolute value of the projection length deviation is greater than the projection length deviation threshold and the projection length deviation is greater than 0, then the horizontal cooling direction will be adjusted to the right by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end. If the absolute value of the projection length deviation is greater than the projection length deviation threshold, and the projection length deviation is less than 0, then the horizontal cooling direction will be adjusted to the left by a preset horizontal angle adjustment range, and the current horizontal cooling direction adjustment will end.

8. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 6, characterized in that: The variable cross-section in the heat-affected zone is analyzed. When a variable cross-section exists in the heat-affected zone, a vertical cooling direction adjustment strategy is set. The specific logic is as follows: Determine if there is a variable cross-section in the heat-affected zone. If there is no variable cross-section, no vertical cooling direction adjustment is performed. If there is, calculate the temperature variance of the trajectory points of the variable cross-section in the heat-affected zone as the initial temperature variance. Randomly select a direction in the vertical plane and adjust it once according to the preset vertical angle adjustment range. Obtain the adjusted temperature variance. If the adjusted temperature variance is less than the initial temperature variance, determine the adjusted vertical cooling direction as the new vertical cooling direction and end this vertical cooling direction adjustment. Otherwise, reverse the vertical angle by twice the preset adjustment range, obtain the adjusted temperature variance, and if the adjusted temperature variance is less than the initial temperature variance, accept the adjustment, determine the adjusted vertical cooling direction as the new vertical cooling direction, and end the current vertical cooling direction adjustment. If the adjusted temperature variance is not less than the initial temperature variance, then the vertical cooling direction will be reset to the vertical cooling direction corresponding to the initial temperature variance, thus ending this vertical cooling direction adjustment.

9. The method for suppressing thermal damage in picosecond laser processing of high-performance composite materials with variable cross-section holes according to claim 1, characterized in that: The logic for adjusting the cooling direction of the air in real time based on the horizontal cooling direction adjustment strategy and the vertical cooling direction adjustment strategy is as follows: First, adjust the horizontal cooling direction. After the horizontal cooling direction adjustment is completed, adjust the vertical cooling direction. After the vertical cooling direction adjustment is completed, adjust the horizontal cooling direction. Repeat this alternating cycle until the laser spot position is no longer located within the variable cross-section influence zone, at which point the alternating cooling direction adjustment process is terminated.

Images