High-performance composite material femtosecond laser processing variable cross-section hole forming precision control method

Abstract

The application provides a high-performance composite femtosecond laser processing variable cross-section hole forming precision control method, relates to the technical field of laser processing, and first discretizes a target hole into a plurality of processing layers along a depth direction, and establishes a Cartesian coordinate system; the effective radius of a spot and a projection area of each layer are calculated in combination with hole taper; on this basis, a reference power density decay model is constructed, a laser incidence angle is further introduced, and a mapping model between hole taper, laser incidence angle and laser power density is established. Finally, according to the target hole taper and the target removal efficiency, the laser incidence angle required by each processing layer is inversely solved, and the dynamic regulation and control of the rotary cutting head and the cradle turntable are realized accordingly. The method can realize layer-by-layer closed-loop control of the variable cross-section hole forming precision, effectively compensate for the laser power decay in the depth direction, and improve the precision of laser processing.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, specifically to a method for controlling the accuracy of variable cross-section hole forming in femtosecond laser processing of high-performance composite materials. Background Technology

[0002] High-performance composite materials are widely used in aerospace, precision manufacturing, and other fields due to their excellent mechanical properties and lightweight characteristics. However, the high hardness, brittleness, and non-uniformity of these materials pose significant challenges to traditional machining, especially when machining microholes with variable cross-sections, where defects such as delamination, burrs, and heat-affected zone damage are easily generated. While femtosecond laser processing, as a cold-working technology, can effectively reduce thermal damage, it faces challenges when machining holes with variable cross-sections. The complex propagation path of the laser beam within the hole and the significant beam obstruction effect of the hole walls cause the actual laser power density acting on the machined surface to attenuate with depth, making it difficult to precisely control the hole taper and machining efficiency.

[0003] In the prior art, CN114769898A discloses a laser processing control method, apparatus, and readable storage medium, comprising: presetting different levels of processing dynamic performance in a processing control system; the processing control system acquiring a graphic to be processed, wherein the graphic includes at least two patterns; determining the processing accuracy requirement for each pattern, and selecting the corresponding level of processing dynamic performance for processing the pattern according to the processing accuracy requirement for each pattern; and causing the laser head to process the corresponding pattern on the workpiece according to the processing dynamic performance level corresponding to each pattern to form the graphic.

[0004] The main problems with the above scheme are: it does not consider the laser beam occlusion problem that may occur when processing the same pattern, which leads to the expansion of the spot and a sharp drop in laser power density; it cannot achieve dynamic control within the layer. The processing of variable cross-section holes requires continuous and layer-by-layer fine control in the depth direction. The laser parameters required for each layer may be different. The switching logic of the above scheme is discrete and regional, which cannot support the gradual parameter adjustment along the depth direction and makes it difficult to meet the processing accuracy requirements.

[0005] 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

[0006] The purpose of this invention is to provide a method for controlling the forming accuracy of variable cross-section holes in femtosecond laser processing of high-performance composite materials, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for controlling the forming accuracy of variable cross-section holes in femtosecond laser processing of high-performance composite materials, comprising the following steps: Step 1: Before laser processing, obtain the plate thickness of the workpiece to be processed and the preset target hole processing parameters, and at the same time set the initial process parameter range of the laser beam. The target hole processing parameters include the target hole taper and the target workpiece size. Step 2: Discretize the target hole along the depth direction into several processing layers based on the workpiece thickness, calculate the effective radius of the light spot after being blocked by the upper hole wall at each processing layer, establish a Cartesian coordinate system, determine the hole diameter of each processing layer according to the taper of the target hole, and calculate the projected area of ​​the light spot at each processing layer. Step 3: Combine the projected area of ​​the laser spot of each processing layer to calculate the laser power density of each processing layer under vertical laser beam incidence, construct a reference power density attenuation model, and on the basis of the reference power density attenuation model, calculate the corresponding laser power density for different hole taper and laser incident angle, and fit the functional expression of hole taper, laser incident angle and laser power density of each processing layer. Step 4: Determine the target removal efficiency of each processing layer based on the target workpiece size. Determine the laser power density according to the pre-calibrated removal efficiency-laser power density mapping relationship. Obtain the laser incident angle of the laser beam in each processing layer based on the inverse solution of the above function expression. Control the rotary cutting head and cradle turntable according to the laser incident angle to realize laser incident processing.

[0008] Furthermore, the initial process parameters of the laser beam include the average laser power, laser wavelength, focused spot radius of the laser beam at different distances, and pulse repetition frequency.

[0009] Furthermore, the logic for calculating the effective radius of the light spot at each processing layer after being blocked by the upper hole wall is as follows: Using the focused spot radius of the laser beam at different distances as a reference value, the effective spot radius is obtained by multiplying the reference value by the spread factor, where the spread factor is the arithmetic square root of 1 and the sum of squares of the dimensionless parameter. The dimensionless parameter is defined as: the vertical distance from each processing layer to the bottom of the hole divided by the Rayleigh length of the laser beam; the Rayleigh length represents the characteristic length of the laser beam to maintain parallel propagation, and the specific value is π multiplied by the square of the minimum spot radius and then divided by the laser wavelength.

[0010] Furthermore, the Cartesian coordinate system uses the central axis of the target hole as the Z-axis, with the origin of the coordinate system located at the vertex of the conical surface of the central axis, which is also the intersection of the laser beam and the central axis of the target hole. The X-axis and Y-axis are located in a horizontal plane perpendicular to the Z-axis, with the starting radial direction of the laser beam's revolution as the positive direction of the X-axis, and the positive direction of the Y-axis determined based on the right-hand rule.

[0011] Furthermore, the laser power density of each processing layer under perpendicular laser beam incidence is calculated, and a baseline power density attenuation model is constructed. The specific logic is as follows: The product is obtained by multiplying the pulse repetition frequency by the projected area of ​​the laser beam spot on the inclined hole wall of each processing layer, and then dividing the average laser power by the product to obtain the laser power density of each processing layer under vertical incidence. The projected area of ​​the laser beam spot on the inclined hole wall of each processing layer is obtained by multiplying the effective area of ​​the spot by the area magnification factor. The effective area of ​​the spot is the product of the square of the effective radius of the spot and π. The area magnification factor is the square root of the square of the cotangent of the angle between the laser beam and the normal of the hole wall plus one. The angle between the laser beam and the normal of the hole wall under perpendicular incidence is the hole taper. This yields the mapping relationship between laser power density and aperture taper for different processing layers under vertical incidence. Based on this mapping relationship, a baseline power density attenuation model is constructed.

[0012] Furthermore, the functional expressions of the hole taper, laser incident angle, and laser power density of each processing layer are fitted. The specific logic is as follows: Based on the benchmark power density attenuation model, the laser incident angle is introduced as a variable. Within the set range of the laser incident angle, the laser incident angle is changed successively, and the angle between the laser incident angle and the normal of the inclined surface of the hole wall is calculated. The angle is the laser incident angle minus the hole taper. The obtained angle is substituted into the benchmark power density attenuation model to recalculate the area magnification factor of each processing layer, determine the spot projection area on the inclined hole wall of each processing layer under the corresponding laser incident angle, and then calculate the corresponding laser power density. Finally, the mapping relationship between the laser incident angle, hole taper, and laser power density is fitted.

[0013] Furthermore, the target removal efficiency of each processing layer is determined based on the target workpiece size, and the laser power density is determined according to the pre-calibrated removal efficiency-laser power density mapping relationship. The specific logic is as follows: Determine the target workpiece size, and based on the target workpiece size, determine the target material removal volume and target processing time for each processing layer; Divide the target material removal volume of each processing layer by the target processing time to obtain the removal efficiency of each processing layer. By conducting pre-calibration experiments, a mapping relationship between removal efficiency and laser power density was established; Based on the mapping relationship between removal efficiency and laser power density, and the removal efficiency of each processing layer, the laser power density corresponding to each processing layer is determined.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention discretizes the variable cross-section hole into multiple processing layers along the depth direction, which can effectively describe the geometric changes of the hole from the inlet to the outlet, overcoming the errors caused by the simplified model of treating the hole as an ideal cylinder or a single taper in traditional methods. By introducing the calculation of the effective radius of the laser spot, it can quantitatively describe the phenomenon of laser spot expansion caused by the blockage and diffraction effect of the upper hole wall during the propagation of the laser beam in the hole. Combined with the Cartesian coordinate system, the projected area of ​​the laser spot is calculated, making the calculation of the projected area more consistent with the geometric characteristics of the actual hole wall surface, improving the modeling accuracy of the laser-material interaction region. Only by accurately obtaining the projected area of ​​the laser spot in each processing layer can the laser power density be further calculated, and a mapping model between hole taper, laser incident angle and laser power density be constructed.

[0015] This invention also establishes a power attenuation model under vertical incidence, and on this basis, introduces the laser incidence angle to form an extended mapping, establishing an explicit mapping between aperture taper, laser incidence angle, and laser power density, quantifying the compensation effect of laser incidence angle on laser power density; for different processing layers, the required laser incidence angle is solved inversely based on aperture taper and laser power density, achieving the technical goal of one-time calculation and precise execution for each processing layer, significantly reducing the number of trial cuts and process debugging time, and enabling layer-by-layer control of the workpiece during laser processing, ensuring precise control of laser processing. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method flow of an embodiment of the present invention. 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 Figure 1 The present invention provides a technical solution: A method for controlling the forming accuracy of variable cross-section holes in femtosecond laser processing of high-performance composite materials, comprising the following steps: Step 1: Before laser processing, obtain the plate thickness of the workpiece to be processed and the preset target hole processing parameters, and at the same time set the initial process parameter range of the laser beam. The target hole processing parameters include the target hole taper and the target workpiece size. In this embodiment, the initial process parameters of the laser beam include the average laser power, laser wavelength, focused spot radius of the laser beam at different distances, and pulse repetition frequency.

[0020] The thickness of the workpiece plate determines the depth range of the variable cross-section hole and the thickness of the material that the laser beam needs to penetrate. For high-performance composite material plates with a thickness of more than 5 mm, the laser will experience significant beam expansion, energy attenuation and hole wall obstruction during deep hole processing. The plate thickness of the area to be processed is measured by an ultrasonic thickness gauge to pre-divide the processing layers.

[0021] The hole wall of the variable cross section hole has a certain taper. The taper affects the hole diameter and the hole wall inclination angle of each processing layer. The smaller the taper, the closer the hole wall is to a cylinder. The contact area between the connector and the hole wall is larger and the stress distribution is more uniform. In actual production, it is necessary to control the taper range to ensure processing accuracy. The preset range of the target taper is 0~0.5°.

[0022] Removal efficiency is a core indicator of laser processing, representing the volume of material removed per unit time. The removal efficiency is determined based on actual processing requirements.

[0023] The average laser power, laser wavelength, focused spot radius of the laser beam at different distances, and pulse repetition frequency are intrinsic physical quantities of laser processing. They determine the propagation characteristics, focusing ability, and single-pulse energy density of the laser beam in space. Pre-setting the initial process parameter range of the laser ensures that the laser has the basic ability to process thick composite materials and provides basic values ​​and variables for subsequent calculations. In this scheme, the average laser power is set to above 100W to ensure high-efficiency processing on high-performance composite material plates with a thickness of more than 5mm. The laser wavelength range is between 1020 and 1060nm. The focused spot radius of the laser beam at different distances is obtained through pre-experimentation. Before laser processing, the laser beam is perpendicularly incident on planes at different distances, and the spot radius on each plane is obtained, thus obtaining the focused spot radius of the laser beam at different distances. The typical pulse repetition frequency range of femtosecond lasers is 1kHz to 10MHz. This scheme uses a pulse repetition frequency greater than 200kHz to ensure sufficient pulse overlap.

[0024] Pre-acquiring the workpiece thickness, target hole taper, target workpiece dimensions, and initial laser process parameters provides essential foundational data for subsequent discretization of processing layers, calculation of laser spot expansion, and modeling of laser power density. This step ensures the specificity and adjustability of processing parameters, avoids blind trial cutting, and improves the systematic nature and repeatability of process design.

[0025] Step 2: Discretize the target hole along the depth direction into several processing layers based on the workpiece thickness, calculate the effective radius of the light spot after being blocked by the upper hole wall at each processing layer, establish a Cartesian coordinate system, determine the hole diameter of each processing layer according to the taper of the target hole, and calculate the projected area of ​​the light spot at each processing layer. In this embodiment, the logic for calculating the effective radius of the light spot at each processing layer after being blocked by the upper hole wall is as follows: Using the minimum spot radius at the focal point as a reference value, the effective spot radius is obtained by multiplying this reference value by a spreading factor. The spreading factor is the square root of the sum of 1 and the square of the dimensionless parameter. The dimensionless parameter is defined as the vertical distance from each processing layer to the bottom of the hole divided by the Rayleigh length of the laser beam. The Rayleigh length represents the characteristic length of the laser beam to maintain parallel propagation, and its specific value is π multiplied by the square of the minimum spot radius and then divided by the laser wavelength.

[0026] The formula for calculating the effective radius of the light spot is: in, Indicates the first The effective radius of the light spot in each processing layer Indicates the index of the processing layer. Indicates the minimum spot radius. Indicates the hole depth. Indicates the first The distance from each processing layer to the upper surface of the workpiece. Indicates the laser wavelength.

[0027] The effective radius of the laser spot represents the distance the laser beam travels to during the femtosecond laser machining of a variable cross-section hole. During the processing of each layer, the radius of the laser spot generated on the cross-section perpendicular to the propagation direction reflects the degree of lateral expansion of the laser beam as it propagates within the hole. Due to the diffraction effect of light, the laser spot gradually increases with the propagation distance, which is the vertical distance from the top surface of the workpiece to the bottom of the hole. For each workpiece, the hole depth is a fixed value. Indicates from the first The distance from each processing layer to the upper surface of the workpiece, as Increase An increase indicates that the processing layer is getting deeper. Indicates from the first The vertical distance from the first processing layer to the bottom of the hole, i.e., the distance from the laser beam from the first processing layer to the bottom of the hole. The propagation distance from each processing layer to the bottom of the hole, and the laser beam at the minimum spot radius. The focus is located at the bottom of the aperture; the longer the propagation distance, the better. The larger the radius, the larger the effective radius of the laser spot, indicating a wider spot range and consequently a lower laser power density. The formula for the effective radius of the laser spot is based on Gaussian beam propagation theory. In laser processing, femtosecond lasers typically propagate as Gaussian beams, and the radius of the Gaussian beam varies along the propagation direction as follows: ,in, Indicates the distance from the focus as The spot radius at that location corresponds to the effective spot radius of the processing layer. , This indicates the distance from the current position to the focus point. Let be the Rayleigh length, and the formula for calculating the Rayleigh length is: By substituting the parameters in the formula, the effective radius of the light spot for each processing layer can be obtained. .

[0028] In this embodiment, the Cartesian coordinate system has the central axis of the target hole as the Z-axis, and the origin of the coordinate system is set at the vertex of the conical surface of the central axis, which is the intersection of the laser beam and the central axis of the target hole. The X-axis and Y-axis are located in a horizontal plane perpendicular to the Z-axis. The positive direction of the X-axis is the starting radial direction of the laser beam's revolution, and the positive direction of the Y-axis is determined based on the right-hand rule.

[0029] When constructing a Cartesian coordinate system, the Z-axis coincides with the hole axis, and the Z-axis coordinate directly corresponds to the depth of the processing layer, which facilitates the discretization of the target hole into multiple processing layers. The origin is selected at the vertex of the conical surface. The hole wall of a variable cross-section hole is usually conical. Setting the origin at the vertex of the conical surface makes the hole diameter of each processing layer linearly related to the Z-coordinate, which is convenient for calculation. The laser beam revolves around the Z-axis during processing. The positive X-axis direction is set as the initial radial direction to describe the position and incident direction of the laser beam in each layer.

[0030] The target hole is discretized into multiple processing layers along the depth direction. By combining the effective radius of the laser spot with the Cartesian coordinate system, the laser spot expansion caused by occlusion and diffraction during the propagation of the laser inside the hole is accurately described. This solves the error caused by the traditional method ignoring the geometric changes inside the hole and provides high-precision geometric input for subsequent power density modeling.

[0031] Step 3: Combine the projected area of ​​the laser spot of each processing layer to calculate the laser power density of each processing layer under vertical laser beam incidence, construct a reference power density attenuation model, and on the basis of the reference power density attenuation model, calculate the corresponding laser power density for different hole taper and laser incident angle, and fit the functional expression of hole taper, laser incident angle and laser power density of each processing layer. In this embodiment, the laser power density of each processing layer is calculated under perpendicular laser beam incidence, and a baseline power density attenuation model is constructed. The specific logic is as follows: The product is obtained by multiplying the pulse repetition frequency by the projected area of ​​the laser beam spot on the inclined hole wall of each processing layer, and then dividing the average laser power by the product to obtain the laser power density of each processing layer under vertical incidence. The projected area of ​​the laser beam spot on the inclined hole wall of each processing layer is obtained by multiplying the effective area of ​​the spot by the area magnification factor. The effective area of ​​the spot is the product of the square of the effective radius of the spot and π, that is, the area of ​​the spot produced when the laser beam is incident perpendicularly and illuminates the plane at different distances due to the upper layer blocking. The effective area of ​​the laser beam spot on each processing layer is determined according to the effective radius of the spot of each processing layer. The area magnification factor is the square root of the square of the cotangent of the angle between the laser beam and the normal of the hole wall plus one, and the angle between the laser beam and the normal of the hole wall under perpendicular incidence is the hole taper.

[0032] Under vertical incidence, the laser power density of each processing layer is expressed as: ,in, Indicates the first Laser power density of each processing layer Indicates the average power of the laser. Indicates the pulse repetition frequency. Indicates the laser beam at the 1st The projected area of ​​the light spot on the inclined hole wall of each processing layer, and , , ,in, Indicates the first The effective area of ​​the light spot in each processing layer Indicates the first Area magnification factor of each processing layer Indicates the first The angle between the laser beam and the normal to the hole wall at each processing layer, and when the laser beam is incident perpendicularly, the angle between the laser beam and the normal to the hole wall is the taper of the hole wall. Combining the above formulas, the relationship between laser power density and aperture taper under perpendicular incidence is obtained: Obtain the initial laser power density under ideal conditions: no spot expansion, no tilted aperture walls, and the laser beam is incident perpendicularly on the horizontal plane. And its calculation formula is: ,but Substitute the formula into The calculation formula is as follows: Organized .

[0033] Laser power density refers to the laser energy received per unit area per unit pulse time. In variable cross-section hole machining, the hole wall is inclined. Even if the laser beam is incident perpendicularly to the workpiece surface, at a certain depth, its spot is not projected onto the horizontal plane, but onto the inclined hole wall surface. Furthermore, the projected area on the inclined hole wall surface is larger than the spot area on the horizontal plane. The area magnification factor reflects the spot area magnification effect caused by the inclined hole wall. When the laser is incident perpendicularly, the area of ​​the spot on the horizontal plane is... When the light spot is projected onto an area that makes an angle of θ with the horizontal plane When on the inclined plane, the projected area expands to , here Indicates the effective area of ​​the light spot The reciprocal of the magnification factor, obtained through trigonometric identities: The area on the horizontal plane can be derived as follows: The light spot is projected onto an angle θ with the horizontal plane. When on the inclined plane, the projected area expands to ,use Magnification As an area magnification factor In deep hole machining, the laser beam gradually expands due to the diffraction effect, and the spot radius increases with the propagation distance. This increased radius is the effective spot radius. Integrating the above formulas, we get the final formula, which is: the laser power density is equal to the initial laser power density divided by the product of the spot expansion factor and the tilt projection factor. It is the first The actual laser power density acting on the inclined hole wall in each processing layer reflects the energy attenuation in the depth direction. As the processing depth increases, the power density of the laser in the first processing layer decreases. Vertical distance from each processing layer to the bottom of the hole Increase, the spot spread factor is This describes the phenomenon where the area of ​​a laser beam expands with increasing propagation distance due to diffraction during propagation within an aperture. As the spot expansion factor increases, the projected area increases while the laser power density decreases; the tilt projection factor is... The power density is used to describe the magnification factor of the projected area of ​​the laser beam on the inclined hole wall relative to the spot area on the horizontal plane. It also reflects the influence of the hole wall inclination on the energy distribution. When the hole taper is not 0, the smaller the hole taper, the larger the projected area on the inclined hole wall and the smaller the laser power density.

[0034] This yields the mapping relationship between laser power density and aperture taper for different processing layers under vertical incidence. Based on this mapping relationship, a baseline power density attenuation model is constructed.

[0035] No. Laser power density of each processing layer The formula was established for the laser power density under perpendicular incidence conditions. , hole taper and depth position The mapping relationship is such that, under the condition of vertical incidence, the above formula can be directly used to express the laser power density under different depths and different aperture tapers. This relationship is used as the benchmark power density attenuation model, that is, only the power density attenuation law established under the condition of vertical incidence is considered, which serves as the benchmark for subsequent more complex models.

[0036] The functional expressions for the hole taper, laser incident angle, and laser power density of each processing layer are fitted. The specific logic is as follows: Based on the benchmark power density attenuation model, the laser incident angle is introduced as a variable. Within the set range of the laser incident angle, the laser incident angle is changed successively, and the angle between the laser incident angle and the normal of the inclined surface of the hole wall is calculated. The angle is the laser incident angle minus the hole taper. The obtained angle is substituted into the benchmark power density attenuation model to recalculate the area magnification factor of each processing layer, determine the spot projection area on the inclined hole wall of each processing layer under the corresponding laser incident angle, and then calculate the corresponding laser power density. Finally, the mapping relationship between the laser incident angle, hole taper, and laser power density is fitted.

[0037] In this embodiment, for the first Each processing layer, when the laser beam is at the laser incident angle , hole taper During incident radiation, the actual laser power density acting on the hole wall changes, at which point the angle between the laser beam and the normal to the inclined plane of each processed layer hole wall is... , ; In the baseline power density decay model, the area magnification factor is: When the laser beam has an incident angle of 100°, At incidence, the angle between the laser beam and the normal to the inclined plane of the aperture wall becomes The area magnification factor is then corrected to , Effective radius of light spot The projected area on the inclined hole wall remains unchanged. , Therefore, the laser incident angle is obtained as follows: Laser power density of each processing layer: ; Indicates the laser incident angle as At that time, the first Laser power density of each processing layer; Laser power density This reflects the energy density of the laser beam deposited on the hole wall per unit area and per unit pulse time under non-perpendicular incident conditions. Changes in the laser incident angle will change the projected area of ​​the laser spot on the inclined hole wall. The larger the projected area of ​​the laser spot, the lower the laser power density, and vice versa. The laser power density depends not only on the laser incident angle itself, but also on the taper of the hole wall. The difference between the two is calculated to determine the actual angle between the laser beam and the normal of the hole wall, thus jointly affecting the energy density.

[0038] This step, based on perpendicular laser incidence, establishes a mapping relationship between the laser incidence angle, aperture taper, and laser power density for arbitrary laser incidence angles, quantifying the coupling relationship between aperture taper, laser incidence angle, and laser power density. This step enables accurate prediction of laser power density at different depths and aperture tapers, providing a theoretical basis for subsequent inverse calculation of the incidence angle based on removal efficiency, and is the core of achieving layer-by-layer control.

[0039] Step 4: Determine the target removal efficiency of each processing layer based on the target workpiece size. Determine the laser power density according to the pre-calibrated removal efficiency-laser power density mapping relationship. Obtain the laser incident angle of the laser beam in each processing layer based on the inverse solution of the above function expression. Control the rotary cutting head and cradle turntable according to the laser incident angle to realize laser incident processing.

[0040] In this embodiment, the target removal efficiency of each processing layer is determined based on the target workpiece size, and the laser power density is determined according to the pre-calibrated removal efficiency-laser power density mapping relationship. The specific logic is as follows: Determine the target workpiece size, and based on the target workpiece size, determine the target material removal volume and target processing time for each processing layer; Divide the target material removal volume of each processing layer by the target processing time to obtain the removal efficiency of each processing layer. Removal efficiency refers to the total volume of material to be removed per unit time during laser hole machining. It is given in advance according to process requirements, and the removal efficiency and hole taper of each processing layer are set to meet the processing requirements.

[0041] By conducting pre-calibration experiments, a mapping relationship between removal efficiency and laser power density was established; Based on the mapping relationship between removal efficiency and laser power density, and the removal efficiency of each processing layer, the laser power density corresponding to each processing layer is determined.

[0042] The principle of establishing the mapping relationship between removal efficiency and laser power density through pre-calibrated experiments is as follows: all parameters except laser power density are controlled to be the same as those in actual laser cutting. In the experiment, the laser beam is perpendicularly incident on the workpiece for single-layer scanning cutting. The output power of the laser is changed. At each output power, blind holes of the same size are processed on the workpiece. The material removal volume and processing time are measured. The removal efficiency corresponding to each output power is obtained by dividing the material removal volume by the processing time. The spot area at each output power is measured. The laser power density is obtained by dividing the output power by the spot area. Thus, the mapping relationship between different laser power densities and removal efficiency is established.

[0043] Using this mapping relationship, given the known removal efficiency, the corresponding laser power density is obtained. Substituting the laser power density and hole taper into the functional expressions of hole taper, laser incident angle and laser power density for each processing layer, the corresponding laser incident angle is obtained.

[0044] Based on the target removal efficiency and hole taper, the required laser incident angle for each processing layer is determined by reverse engineering, and the rotary cutting head and cradle turntable are dynamically controlled accordingly. This step achieves closed-loop matching between processing parameters and material removal efficiency, significantly improving the forming consistency and processing accuracy of variable cross-section holes, reducing the number of trial cuts and process debugging costs, and demonstrating good engineering applicability.

[0045] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0046] 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.

[0047] 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.

[0048] 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 can 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 controlling the accuracy of variable cross-section hole forming in femtosecond laser processing of high-performance composite materials, characterized in that, The specific steps include: Step 1: Before laser processing, obtain the plate thickness of the workpiece to be processed and the preset target hole processing parameters, and at the same time set the initial process parameter range of the laser beam. The target hole processing parameters include the target hole taper and the target workpiece size. Step 2: Discretize the target hole along the depth direction into several processing layers based on the workpiece thickness, calculate the effective radius of the light spot after being blocked by the upper hole wall at each processing layer, establish a Cartesian coordinate system, determine the hole diameter of each processing layer according to the taper of the target hole, and calculate the projected area of ​​the light spot at each processing layer. Step 3: Combine the projected area of ​​the laser spot of each processing layer to calculate the laser power density of each processing layer under vertical laser beam incidence, construct a reference power density attenuation model, and on the basis of the reference power density attenuation model, calculate the corresponding laser power density for different hole taper and laser incident angle, and fit the functional expression of hole taper, laser incident angle and laser power density of each processing layer. Step 4: Determine the target removal efficiency of each processing layer based on the target workpiece size. Determine the laser power density according to the pre-calibrated removal efficiency-laser power density mapping relationship. Obtain the laser incident angle of the laser beam in each processing layer based on the inverse solution of the above function expression. Control the rotary cutting head and cradle turntable according to the laser incident angle to realize laser incident processing. The initial process parameters of the laser beam include the average laser power, laser wavelength, focused spot radius of the laser beam at different distances, and pulse repetition frequency. The logic for calculating the effective radius of the light spot at each processing layer after being blocked by the upper hole wall is as follows: Using the focused spot radius of the laser beam at different distances as a reference value, the effective spot radius is obtained by multiplying the reference value by the spread factor, where the spread factor is the arithmetic square root of 1 and the sum of squares of the dimensionless parameter. The dimensionless parameter is defined as: the vertical distance from each processing layer to the bottom of the hole divided by the Rayleigh length of the laser beam; the Rayleigh length represents the characteristic length of the laser beam to maintain parallel propagation, and the specific value is π multiplied by the square of the minimum spot radius and then divided by the laser wavelength.

2. The method for controlling the accuracy of variable cross-section hole forming in femtosecond laser processing of high-performance composite materials according to claim 1, characterized in that: The Cartesian coordinate system has the central axis of the target hole as the Z-axis, and the origin of the coordinate system is set at the vertex of the conical surface of the central axis, which is the intersection of the laser beam and the central axis of the target hole. The X-axis and Y-axis are located in a horizontal plane perpendicular to the Z-axis. The positive direction of the X-axis is the starting radial direction of the laser beam's revolution, and the positive direction of the Y-axis is determined based on the right-hand rule.

3. The method for controlling the accuracy of variable cross-section hole forming in femtosecond laser processing of high-performance composite materials according to claim 1, characterized in that: Calculate the laser power density of each processing layer under perpendicular laser beam incidence, and construct a baseline power density attenuation model. The specific logic is as follows: The product is obtained by multiplying the pulse repetition frequency by the projected area of ​​the laser beam spot on the inclined hole wall of each processing layer, and then dividing the average laser power by the product to obtain the laser power density of each processing layer under vertical incidence. The projected area of ​​the laser beam spot on the inclined hole wall of each processing layer is obtained by multiplying the effective area of ​​the spot by the area magnification factor. The effective area of ​​the spot is the product of the square of the effective radius of the spot and π. The area magnification factor is the square root of the square of the cotangent of the angle between the laser beam and the normal of the hole wall plus one. The angle between the laser beam and the normal of the hole wall under perpendicular incidence is the hole taper. This yields the mapping relationship between laser power density and aperture taper for different processing layers under vertical incidence. Based on this mapping relationship, a baseline power density attenuation model is constructed.

4. The method for controlling the forming accuracy of variable cross-section holes in femtosecond laser processing of high-performance composite materials according to claim 3, characterized in that: The functional expressions for the hole taper, laser incident angle, and laser power density of each processing layer are fitted. The specific logic is as follows: Based on the benchmark power density attenuation model, the laser incident angle is introduced as a variable. Within the set range of the laser incident angle, the laser incident angle is changed successively, and the angle between the laser incident angle and the normal of the inclined surface of the hole wall is calculated. The angle is the laser incident angle minus the hole taper. The obtained angle is substituted into the benchmark power density attenuation model to recalculate the area magnification factor of each processing layer, determine the spot projection area on the inclined hole wall of each processing layer under the corresponding laser incident angle, and then calculate the corresponding laser power density. Finally, the mapping relationship between the laser incident angle, hole taper, and laser power density is fitted.

5. The method for controlling the forming accuracy of variable cross-section holes in femtosecond laser processing of high-performance composite materials according to claim 4, characterized in that: The target removal efficiency for each processing layer is determined based on the target workpiece size. The laser power density is then determined according to a pre-calibrated mapping relationship between removal efficiency and laser power density. The specific logic is as follows: Determine the target workpiece size, and based on the target workpiece size, determine the target material removal volume and target processing time for each processing layer; Divide the target material removal volume of each processing layer by the target processing time to obtain the removal efficiency of each processing layer. By conducting pre-calibration experiments, a mapping relationship between removal efficiency and laser power density was established; Based on the mapping relationship between removal efficiency and laser power density, and the removal efficiency of each processing layer, the laser power density corresponding to each processing layer is determined.

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