A method for high-quality and uniform removal of CFRP using spatially shaped femtosecond laser

Abstract

The present application relates to a kind of space shaping femtosecond laser high-quality uniform removal CFRP method, belong to CFRP material processing field.Firstly, for the heterogeneous characteristics of CFRP, the processing threshold of carbon fiber and polymer in CFRP is determined, according to the principle that processing light field needs to satisfy that the spatial energy density is higher than the processing threshold of two components, the energy distribution of processing light field is obtained.Secondly, for the anisotropic characteristics of CFRP, serious heat conduction is shown along the direction of carbon fiber, and the edge material of processing path should be removed in time to form isolation band, to isolate subsequent heat conduction to both sides, and then determine the shape of the processing light field "center concave both sides convex" special-shaped light field, so as to obtain the overall light field.Space shaping femtosecond laser processing system based on high damage threshold spatial light modulator is built, and high-power femtosecond laser space shaping high-quality processing of CFRP engineering composite material is realized.The method of the present application significantly reduces the heat affected zone of CFRP processing, and shows the manufacturing capacity and application prospect of high-quality uniform processing CFRP.

Description

TECHNICAL FIELD

[0001] The application relates to a method for high-quality and uniform removal of CFRP by spatially shaping femtosecond laser, and belongs to the field of CFRP material processing. BACKGROUND

[0002] Carbon fiber reinforced polymer (CFRP) material is a composite material composed of reinforcing phase carbon fiber and matrix phase polymer, wherein the carbon fiber is mainly used for bearing load, and the polymer matrix wraps the carbon fiber and transmits the load. CFRP has excellent properties such as light weight, high specific strength, high specific modulus, wear resistance, corrosion resistance, etc., and is widely used in many fields such as aerospace, automobile industry, medical devices, etc., showing great application space and development prospect.

[0003] The primary CFRP product often needs secondary processing such as cutting, drilling, milling, etc. due to the inability to meet the process requirements of the product. However, CFRP is a typical difficult-to-machine material due to its non-homogeneous, anisotropic, laminated structure, wear resistance, brittleness and other characteristics. The machining results obtained by the most widely used mechanical machining method usually have structural damage such as delamination, burr, tearing, etc., poor machining quality, and seriously affect the subsequent assembly, performance and service life of CFRP components; the tool wears seriously during mechanical machining, the cutting performance deteriorates sharply, and the tool needs to be frequently replaced; and it is difficult to machine high-precision microstructures. This has seriously restricted the manufacturing level and engineering application of CFRP materials.

[0004] Laser processing can effectively solve the problems that are difficult to overcome in the current traditional machining method, such as material delamination, burr, fiber pull-out, tool wear, low machining precision, etc., due to its high precision, non-contact, no stress and no tool wear. However, due to the intrinsic non-homogeneous and anisotropic properties of CFRP composite material, as well as the actual production conditions such as ultra-high laser power density and high pulse energy Gaussian distribution in laser manufacturing as an engineering material, the carbon fiber and polymer in CFRP show obvious ablation difference behavior during laser processing. The polymer at the edge of the machined structure is excessively removed and the long carbon fiber is exposed, resulting in obvious heat-affected zone (HAZ), which makes it difficult to achieve uniform material removal, and the machined structure shows obvious taper, which seriously affects the performance and application ability of CFRP material. Therefore, achieving high-quality and uniform removal of CFRP material is a serious challenge in laser processing of CFRP. SUMMARY

[0005] The purpose of the present application is to solve the problem that the current laser processing of CFRP material is difficult to achieve uniform removal of carbon fiber and polymer, resulting in poor machining quality. A method for high-quality and uniform removal of CFRP by spatially shaping femtosecond laser is proposed.

[0006] Due to the heterogeneous and anisotropic properties of CFRP composites, the Gaussian distribution of laser pulses, and the ultra-high laser power used in actual processing, laser processing of CFRP is difficult to achieve uniform removal of both carbon fiber and polymer components. The processed structure exhibits a significant heat-affected zone and structural taper, which limits the practical application of CFRP components. This is because, as an engineering material, efficient manufacturing of CFRP typically requires high laser power processing conditions. Furthermore, CFRP is a composite material composed of carbon fiber and polymer. The carbon fiber is a good metallic conductor, while the polymer matrix is ​​a transparent insulator. The two have very different properties, resulting in significantly different laser processing thresholds. Furthermore, the laser pulse energy is Gaussian, and the edge energy of the Gaussian light field is weak. Its energy density is often between or below the processing thresholds of the carbon fiber and polymer, resulting in differential removal of the carbon fiber and polymer. Furthermore, due to the Gaussian energy distribution, the cross-sectional profile of the processed structure is significantly curved. Furthermore, the carbon fiber in CFRP has significant anisotropy, and a large amount of processing heat is transferred to the sides of the carbon fiber, causing severe thermal damage. Under the combined effect of these reasons, the edges of the laser-processed CFRP structure will experience polymer ablation or obvious heat accumulation damage, exposing the heat-affected zone of the carbon fiber. This makes it difficult to achieve high-quality uniform removal processing. The actual pulse energy utilization rate used to achieve uniform removal is low, and the processed structure will exhibit a significant taper.

[0007] To address the prominent issues facing laser processing of CFRP, the present invention spatially reshapes the original femtosecond laser Gaussian distribution light field. First, the energy distribution of the processing light field is determined based on the heterogeneous nature of the CFRP composite material. The processing thresholds of the carbon fibers and polymers in the CFRP are determined. Based on the principle that the target light field must have a spatial energy density above both processing thresholds, a target processing light field energy distribution is obtained. This target processing light field is free of the portion of the original femtosecond laser Gaussian light field that is highly susceptible to heat-affected zones (i.e., portions where the laser energy density is between the carbon fiber and polymer processing thresholds and below both thresholds). This ensures that the energy density of the spatially reshaped light field is above both processing thresholds, achieving high-quality, uniform removal of both carbon fibers and polymers from the CFRP. Second, the shape of the processing light field is determined based on the anisotropic nature of the CFRP composite material. Due to the significant heat conduction along the carbon fibers, material at the edges of the processing path is prioritized for temporal removal, forming a barrier to prevent subsequent heat conduction to the sides. This results in a target processing light field shape characterized by a concave center and convex sides. This shape design can preferentially remove the CFRP materials on the two sides of the spot range during scanning processing, and construct an "isolation zone" to isolate heat transfer in advance, thereby suppressing the heat transfer along the carbon fibers to the edges of the structure on both sides during subsequent processing of CFRP in the center of the rear side of the light field. This shape design can further improve the uniform removal processing quality of CFRP. Combining the above-mentioned principles of energy distribution design and shape optimization design, the overall light field is obtained, which is called a "light knife". A spatial shaping femtosecond laser processing system based on a high damage threshold spatial light modulator is constructed, which significantly improves the power application range of traditional femtosecond laser spatial shaping processing, thereby realizing high-power femtosecond laser spatial shaping and high-quality processing of CFRP engineering composites. The method of the present invention achieves high-quality synchronous and uniform removal of carbon fibers and polymers in CFRP, effectively reducing the heat-affected zone of CFRP laser processing. At the same time, compared with the original Gaussian distribution light field, the taper of the processing structure is significantly reduced, and the effective utilization rate of the pulse energy actually used to achieve uniform removal is significantly improved.

[0008] The objectives of the present invention are achieved through the following technical solutions.

[0009] The method of the present invention for high-quality uniform removal of CFRP using a spatially shaped femtosecond laser comprises the following steps:

[0010] Step 1: Determine the energy distribution of the processing light field based on the heterogeneous characteristics of CFRP composite materials: Use the epitaxial method to measure and calculate the processing threshold F1 of the carbon fiber component and the processing threshold F2 of the polymer component in CFRP. According to the principle of max(F1, F2)<min(I1), the target processing light field I1 must meet the requirement that the spatial energy density is higher than the processing thresholds of both components, thereby obtaining the energy distribution of the processing light field;

[0011] Step 2: Based on the processing light field energy distribution obtained in step 1, the shape of the processing light field is further determined according to the anisotropic properties of CFRP composite materials. Since severe processing heat conduction occurs along the carbon fiber direction, the material at the edge of the processing path should be removed in time to form an isolation zone to isolate the subsequent heat conduction to the two sides. The processing light field shape is then determined to be a special-shaped light field with a "concave center and convex sides", thus obtaining an overall light field, called a "light knife", to further improve the uniform removal quality of CFRP.

[0012] Step 3: Use a high damage threshold spatial light modulator to build a spatial shaping processing system suitable for high-power femtosecond lasers. Generate a phase map corresponding to the "light knife" through a computer Fourier iterative optimization algorithm, load it onto the spatial light modulator, and perform phase modulation on the original Gaussian light field of the incident femtosecond laser to obtain the preset target processing light field.

[0013] Step 4: Use the femtosecond laser target processing light field after spatial shaping to adjust the laser processing parameters to process the CFRP material, and finally obtain high-quality uniform removal processing results.

[0014] In step 1, the epitaxy method is used to measure and calculate the processing threshold F1 of the carbon fiber component and the processing threshold F2 of the polymer component in CFRP. The specific formula is as follows:

[0015]

[0016] By using different laser fluxes to dot the carbon fiber material, a series of laser flux F C and its corresponding ablation size D C The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to obtain the processing threshold F1 of the carbon fiber material; by using different laser fluxes to dot the polymer material, a series of laser flux F J and its corresponding ablation size D J The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to calculate the processing threshold F2 of the polymer material. The focused spot size ω0 can be calculated according to the slope.

[0017] Among them, in step one, in view of the heterogeneous characteristics of CFRP composite materials, the target processing light field after energy distribution design does not contain the light field part that is very likely to cause the generation of heat-affected zone in the original Gaussian light field of high-power femtosecond laser (that is, the part where the laser energy density is between the processing thresholds of carbon fiber and polymer and is lower than the processing thresholds of both). It ensures that the energy density of the light field after spatial shaping is higher than the processing thresholds of both, so as to achieve high-quality and uniform removal of carbon fiber and polymer in CFRP.

[0018] Among them, in step 2, the target processing light field, after shape optimization design based on the anisotropic characteristics of CFRP composite materials, can preferentially remove the CFRP materials on the two sides of the light spot range during scanning processing, and construct an "isolation zone" to isolate heat transfer in advance, thereby suppressing the heat transfer along the carbon fiber to the edges of both sides of the structure during subsequent processing of CFRP in the central part of the rear side of the light field. This shape design can further improve the uniform removal processing quality of CFRP.

[0019] As an optimization, in order to achieve high-quality and uniform removal of CFRP, a variety of spatial shaping processing light fields with different energy distributions and shapes were designed and implemented, including crescent-shaped flat-top light, "concave"-shaped flat-top light, horseshoe-shaped arc-top light or V-shaped sawtooth top light.

[0020] Among them, in step three, the constructed spatial shaping femtosecond laser processing system includes a femtosecond laser, a reflector, an aperture, a mechanical switch, an attenuation plate, a high damage threshold spatial light modulator, a lens one, a lens two, a dichroic mirror, a focusing objective lens, a sample to be processed, a precision electrically controlled translation stage, a white light illumination source, a beam splitter, a CCD dynamic imaging unit, and a computer; the high-power femtosecond laser beam emitted by the femtosecond laser propagates through the reflector, passes through the aperture, the mechanical switch, and the attenuation plate in a collimated manner, and then enters the high damage threshold spatial light modulator for phase modulation of the light field. The shaped beam is then transported through the two lenses of the 4f system without distortion, and is finally The light is reflected by the dichroic mirror and focused by the focusing objective onto the sample to be processed on the precision electric-controlled translation stage. The illumination light emitted by the white light source at the top is irradiated onto the sample to be processed through the beam splitter, dichroic mirror and focusing objective, and is reflected. The reflected illumination light then returns through the focusing objective and dichroic mirror, and is reflected at the beam splitter to reach the CCD dynamic imaging unit. The computer is connected to the femtosecond laser, controls the phase image loaded into the spatial light modulator, controls the opening and closing of the mechanical switch, controls the precision electric-controlled translation stage to make it move according to the set program trajectory, and connects to the CCD dynamic imaging unit for real-time imaging and monitoring of the surface of the sample to be processed.

[0021] As an optimization, when building the femtosecond laser spatial shaping processing system in step three, a high damage threshold spatial light modulator is selected, the modulation type is pure phase type, the liquid crystal type is reflective, the pixel resolution is 1920*1080, and it is equipped with a circulating water cooling system to improve the power application range of traditional femtosecond laser spatial shaping processing to meet the high-power processing requirements of CFRP engineering composites.

[0022] As an optimization, the Fourier iteration algorithm used in step three is an optimization program based on the GS algorithm, which ensures that the high-power femtosecond laser spatial shaping light field meets the high-efficiency and high-quality processing requirements of CFRP engineering composites, including spot size, shape fidelity, energy uniformity, etc.

[0023] In step 4, when adjusting laser processing parameters, choosing high laser power with a low-magnification objective lens allows for high-efficiency processing with a large, spatially shaped spot; choosing low laser power with a high-magnification objective lens allows for ultra-high-precision precision processing. Therefore, different CFRP processing effects can be achieved by selecting different focusing lenses, laser power, scanning speed, and other conditions.

[0024] It should be noted that the application of the principles of this method, by adopting other laser spatial shaping methods, designing shaping light fields with other shapes and energy distributions, utilizing other phase map calculation programs, adopting different laser types and processing parameters, etc., to obtain high-quality and uniform laser removal of CFRP results, still falls within the scope of protection of this patent.

[0025] Beneficial effects

[0026] 1. The method of the present invention achieves high-quality and uniform removal of carbon fibers and polymers from CFRP, effectively reduces the heat-affected zone (HAZ) during CFRP laser processing, and significantly improves CFRP processing quality. Under the same low laser power processing conditions, the 8μm HAZ produced by conventional Gaussian laser processing can be almost completely eliminated, with no visible HAZ generated. Under ultra-high laser power processing conditions, the HAZ, which can reach up to 78μm in conventional Gaussian laser processing, can be reduced to less than 9μm, improving quality by more than 8.7 times.

[0027] 2. Compared with the obvious curved cross-sectional profile obtained by processing CFRP using the original Gaussian distribution light field, the method of the present invention can achieve a nearly vertical sidewall cross-sectional profile, significantly reducing the taper of the CFRP processing structure;

[0028] 3. The energy density of the spatially shaped light field under the method of the present invention is higher than the processing threshold of carbon fiber and polymer. All energy is used to achieve synchronous and uniform removal of the two, significantly improving the effective utilization rate of the pulse energy actually used to achieve uniform removal, and the effective energy utilization rate is close to 100%;

[0029] 4. The spatial shaping femtosecond laser processing system built based on a high damage threshold spatial light modulator significantly expands the power application range of traditional femtosecond laser spatial shaping processing, thereby achieving high-power femtosecond laser spatial shaping and high-quality processing of CFRP engineering composites;

[0030] 5. The present invention's method for high-quality, uniform CFRP removal using a spatially shaped femtosecond laser is firstly designed to address the heterogeneous nature of CFRP composites. A target light field with a spatial energy density exceeding the processing thresholds of both the carbon fiber and polymer components is designed. This target light field does not contain the light field portion that is prone to generating a heat-affected zone (HAZ) in the original femtosecond laser Gaussian light field. The energy density of the target light field is above the processing thresholds of both components, fully contributing to the simultaneous and uniform removal of both. Furthermore, to address the anisotropic nature of CFRP composites, a "concave center, convex sides" shaped light field is designed to prioritize the removal of material at the edges of the processing path and isolate subsequent heat conduction. This prioritizes the removal of CFRP material at the extreme edges of the laser spot during scanning, creating a pre-existing "isolation zone" to prevent heat transfer from the rear center portion of the light field to the edges of the structure during subsequent CFRP processing. This shape design further improves the quality of uniform CFRP removal. This method demonstrates the manufacturing capability and application prospects for high-quality CFRP processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram comparing the processing mechanism and processing results of the original Gaussian distribution light field, the spatially shaped target processing light field after energy distribution design and shape optimization design; Figure a is a schematic diagram of the processing mechanism of the original Gaussian distribution light field and the spatially shaped light field after energy distribution design; Figure b is a schematic diagram of the processing mechanism of the original circular Gaussian light field and the spatially shaped light field after shape optimization design; Figure c is a schematic diagram comparing the processing results of CFRP processed by the original Gaussian distribution light field and the designed spatially shaped light field;

[0032] Figure 2 Schematic diagram of high-power femtosecond laser spatial shaping for high-quality, uniform CFRP removal. Figure a shows a schematic diagram of the high-power femtosecond laser spatial shaping processing system based on a high damage threshold spatial light modulator, as well as a schematic diagram of the CFRP material composition and properties. Figure b shows a schematic diagram of the process of converting the original Gaussian light field distribution into a variety of spatially shaped light field distributions through energy distribution design and shape optimization to achieve high-quality, uniform CFRP removal.

[0033] Figure 3 Schematic diagram of the overall optical path of the femtosecond laser spatial shaping processing system;

[0034] Figure 4Figure 2 shows the processing results of high-quality and uniform removal of CFRP by spatial shaping femtosecond laser. Figure a shows the edge morphology of the processing structure of CFRP processed by the original Gaussian femtosecond laser. It can be seen that the polymer matrix is ​​selectively removed, exposing the heat-affected zone of the carbon fiber, which is about 8μm wide, making it difficult to achieve uniform removal of CFRP. Figure b shows the edge morphology of the processing structure of CFRP processed by spatial shaping femtosecond laser. The results show that no clearly distinguishable heat-affected zone is generated, and the CFRP is removed uniformly with high quality.

[0035] Figure 5 This is a comparison of the results of CFRP processing using the original Gaussian femtosecond laser and spatially shaped femtosecond laser under high laser power conditions. As shown in Figure a, the polymer matrix at the edge of the processed structure obtained by processing CFRP using the original high-power Gaussian femtosecond laser is selectively removed, exposing long carbon fibers with a significant heat-affected zone as long as 78μm. As shown in Figure b, the size of the heat-affected zone under high-power femtosecond laser spatial shaping processing is significantly reduced to only about 9μm, which significantly improves the processing quality of CFRP.

[0036] Among them, 1- femtosecond laser, 2- reflector, 3- aperture, 4- mechanical switch, 5- attenuation plate, 6- spatial light modulator, 7- lens 1, 8- lens 2, 9- dichroic mirror, 10- focusing objective lens, 11- sample to be processed, 12- precision electrically controlled translation stage, 13- white light illumination source, 14- beam splitter, 15- CCD dynamic imaging unit, 16- computer. DETAILED DESCRIPTION

[0037] In order to better understand the method of the present invention, the technical solution of the present invention is further described in detail below with reference to the accompanying drawings and specific examples, but the implementation methods of the present invention are not limited to the following implementation methods.

[0038] Example 1

[0039] The method disclosed in this embodiment for high-quality and uniform removal of CFRP using a spatially shaped femtosecond laser is as follows:

[0040] Step 1: Determine the energy distribution form of the processing light field based on the heterogeneous characteristics of CFRP composite materials.

[0041] The epitaxial method is used to measure and calculate the processing threshold F1 of the carbon fiber component and the processing threshold F2 of the polymer component in CFRP. The specific formula is as follows:

[0042]

[0043] By using different laser fluxes to dot the carbon fiber material, a series of laser flux F Cand its corresponding ablation size D C The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to obtain the processing threshold F1 of the carbon fiber material; by using different laser fluxes to dot the polymer material, a series of laser flux F J and its corresponding ablation size D J The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to calculate the processing threshold F2 of the polymer material.

[0044] According to the principle of max(F1, F2)<min(I1), that is, the target processing light field I1 needs to satisfy the spatial energy density higher than the processing threshold of both components, it is determined that in this embodiment, a flat top light energy distribution with uniform energy distribution and spatial energy density higher than the processing threshold of both components is adopted to uniformly remove the CFRP material.

[0045] like Figure 1 As shown, due to the uneven energy distribution of the original Gaussian distribution femtosecond laser, in addition to having a portion with energy density above the processing threshold of both carbon fiber and polymer components, there are also portions with energy density between the processing thresholds of carbon fiber and polymer, and portions with energy density below the processing thresholds of both. This portion of the light field will lead to differential removal of carbon fiber and polymer, resulting in a significant heat-affected zone. This embodiment uses a flat-top light processing light field with uniform energy distribution and spatial energy density above the processing thresholds of both components. It does not have the portion of the light field that is prone to causing a heat-affected zone in the original Gaussian light field of the femtosecond laser. The energy density of the target light field is above the processing thresholds of both components, and the entire field is used to achieve simultaneous and uniform removal of both components.

[0046] Step 2: Based on the energy distribution of the processing light field obtained in step 1, the shape of the processing light field is further determined according to the anisotropic properties of the CFRP composite material.

[0047] Due to the anisotropic properties of CFRP materials, severe processing heat conduction occurs along the carbon fiber direction. Therefore, priority should be given to removing the edge material of the processing path to form an isolation zone to isolate subsequent heat conduction to the two sides. This determines the processing light field shape as a "concave in the center and convex on both sides" special-shaped light field shape, thereby obtaining an overall light field, called a "light knife." In this embodiment, a crescent-shaped flat-top light "light knife" is used to further improve the uniform removal quality of CFRP.

[0048] like Figure 1As shown, the carbon fibers in CFRP exhibit significant anisotropy, leading to significant processing heat transfer along the fibers to the sides, causing the most severe thermal damage. To address this issue, this embodiment utilizes a crescent-shaped top-hatted light field. This preferentially removes the CFRP material on the outermost edges of the light spot during scanning, creating a pre-existing "isolation zone" to isolate heat transfer. This prevents heat transfer from the center of the rear portion of the light field to the edges of the structure during subsequent CFRP processing, further improving the uniform removal quality of the CFRP.

[0049] Step 3: Use a high damage threshold spatial light modulator to build a spatial shaping processing system suitable for high-power femtosecond lasers. Generate the phase map corresponding to the "light knife" through the computer Fourier iterative optimization algorithm, load it on the spatial light modulator, and phase modulate the original Gaussian light field of the incident femtosecond laser to obtain the preset target processing light field.

[0050] The spatial shaping femtosecond laser processing system constructed in this embodiment is as follows Figure 3 As shown, the system includes a femtosecond laser 1, a reflector 2, an aperture 3, a mechanical switch 4, an attenuator 5, a spatial light modulator 6, a lens 1 7, a lens 2 8, a dichroic mirror 9, a focusing objective 10, a sample to be processed 11, a precision electrically controlled translation stage 12, a white light illumination source 13, a beam splitter 14, a CCD dynamic imaging unit 15, and a computer 16. The femtosecond laser beam emitted by the femtosecond laser 1 propagates through the reflector 2, passes through the aperture 3, the mechanical switch 4, and the attenuator 5 in a collimated manner, and then enters the spatial light modulator 6 for phase modulation of the light field. The shaped beam is then transported without distortion through the two lenses 7 / 8 of the 4f system. Finally, it is reflected by the dichroic mirror 9 and focused by the focusing objective 10 onto the sample to be processed 11 located on the precision electrically controlled translation stage 12. The illumination light from the topmost white light source 13 passes through the beam splitter 14, dichroic mirror 9, and focusing lens 10, then illuminates the sample 11 to be processed. The reflected illumination light then passes back through the focusing lens 10 and dichroic mirror 9, reflects at the beam splitter 14, and reaches the CCD dynamic imaging unit 15. Computer 16 is connected to the femtosecond laser 1, controls the phase image loaded by the spatial light modulator 6, controls the opening and closing of the mechanical switch 4, controls the precision electronically controlled translation stage 12 to move according to the programmed trajectory, and connects to the CCD dynamic imaging unit 15 to perform real-time imaging and monitoring of the surface of the sample 11 to be processed.

[0051] In this embodiment, a titanium sapphire femtosecond laser is used, and the femtosecond pulses emitted have a central wavelength of 800 nm, a pulse width of 35 fs, a repetition frequency of 1 kHz, and are linearly polarized light;

[0052] In this embodiment, a high damage threshold spatial light modulator (SLM) is used, with a pure phase modulation type, a reflective liquid crystal, a pixel resolution of 1920 x 1080, and a circulating water cooling system. Both lenses in the 4f system are plano-convex lenses with a focal length of 750 mm.

[0053] In this embodiment, the Fourier iterative algorithm used is an optimization program based on the GS algorithm. The original Gaussian light field and the crescent-shaped flat-top light target light field after spatial shaping are as follows: Figure 2 As shown, the size of the target light field is adjustable and the energy distribution is uniform.

[0054] Step 4: Use the femtosecond laser target processing light field after spatial shaping to adjust the laser processing parameters to process the CFRP material, and finally obtain high-quality uniform removal processing results.

[0055] In this example, the CFRP material used is high-modulus CFRP, with M55 carbon fiber as the reinforcement and BS-4 modified cyanate ester resin as the matrix. The CFRP material used is a multidirectional laminate with four layers, each 0.125 mm thick, laid out in a 0° / +45° / -45° / 90° arrangement, for a total thickness of 0.5 mm.

[0056] In this embodiment, a low laser power coupled with a high-magnification objective lens achieves ultra-precise, high-quality, uniform CFRP removal. The objective lens used is a 20x objective lens with a numerical aperture of 0.45NA. During the femtosecond laser scanning direct writing process, the laser repetition rate is 1kHz, the laser power is 100mW, the scanning speed is set at 200μm / s, and the laser scanning direction is perpendicular to the surface fiber direction.

[0057] In this embodiment, after the processing is completed, the heat affected zone of the CFRP processing structure is characterized. Figure 4 As shown in a, the polymer matrix at the edge of the processed structure obtained by femtosecond laser processing using the original Gaussian distribution is selectively removed, exposing the carbon fiber, with a significant heat-affected zone of about 8 μm in size, making it impossible to achieve uniform removal of CFRP. Figure 4 As shown in b, the edges of the processed structure are neat under spatial shaping femtosecond laser processing, almost no visible heat-affected zone is generated, and the CFRP is removed uniformly with high quality.

[0058] Example 2

[0059] The method disclosed in this embodiment for high-quality and uniform removal of CFRP using a spatially shaped femtosecond laser is as follows:

[0060] Step 1: Determine the energy distribution form of the processing light field based on the heterogeneous characteristics of CFRP composite materials.

[0061] The epitaxial method is used to measure and calculate the processing threshold F1 of the carbon fiber component and the processing threshold F2 of the polymer component in CFRP. The specific formula is as follows:

[0062]

[0063] By using different laser fluxes to dot the carbon fiber material, a series of laser flux F C and its corresponding ablation size D C The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to obtain the processing threshold F1 of the carbon fiber material; by using different laser fluxes to dot the polymer material, a series of laser flux F J and its corresponding ablation size D J The square of the data is linearly fitted, and the fitting curve is extended to the zero point of the ablation size to obtain the processing threshold F2 of the polymer material.

[0064] According to the principle of max(F1, F2)<min(I1), that is, the target processing light field I1 needs to satisfy the spatial energy density higher than the processing threshold of both components, it is determined that in this embodiment, a flat top light energy distribution with uniform energy distribution and spatial energy density higher than the processing threshold of both components is adopted to uniformly remove the CFRP material.

[0065] like Figure 1 As shown, due to the uneven energy distribution of the original Gaussian distribution femtosecond laser, in addition to having a portion with energy density above the processing threshold of both carbon fiber and polymer components, there are also portions with energy density between the processing thresholds of carbon fiber and polymer, and portions with energy density below the processing thresholds of both. This portion of the light field will lead to differential removal of carbon fiber and polymer, resulting in a significant heat-affected zone. This embodiment uses a flat-top light processing light field with uniform energy distribution and spatial energy density above the processing thresholds of both components. It does not have the portion of the light field that is prone to causing a heat-affected zone in the original Gaussian light field of the femtosecond laser. The energy density of the target light field is above the processing thresholds of both components, and the entire field is used to achieve simultaneous and uniform removal of both components.

[0066] Step 2: Based on the energy distribution of the processing light field obtained in step 1, the shape of the processing light field is further determined according to the anisotropic properties of the CFRP composite material.

[0067] Due to the anisotropic properties of CFRP materials, severe processing heat conduction occurs along the carbon fiber direction. Therefore, priority should be given to removing the edge material of the processing path to form an isolation zone to isolate subsequent heat conduction to the two sides. This determines the processing light field shape as a "concave in the center and convex on both sides" special-shaped light field shape, thereby obtaining an overall light field, called a "light knife." In this embodiment, a "concave"-shaped flat-top light "light knife" is used to further improve the uniform removal quality of CFRP.

[0068] The carbon fibers in CFRP exhibit significant anisotropy, leading to significant heat transfer along the fibers, causing severe heat damage. To address this challenge, this embodiment utilizes a concave flat-top light field. This field prioritizes the removal of CFRP material on the outer edges of the light spot during scanning, creating a pre-existing "isolation zone" to prevent heat transfer. This prevents heat transfer from the center of the rear portion of the field to the edges of the structure during subsequent CFRP processing, further improving the uniform removal quality of the CFRP.

[0069] Step 3: Use a high damage threshold spatial light modulator to build a spatial shaping processing system suitable for high-power femtosecond lasers. Generate the phase map corresponding to the "light knife" through the computer Fourier iterative optimization algorithm, load it on the spatial light modulator, and phase modulate the original Gaussian light field of the incident femtosecond laser to obtain the preset target processing light field.

[0070] In this embodiment, an ytterbium-doped solid-state femtosecond laser is selected, and the femtosecond pulses emitted have a central wavelength of 1030 nm, a pulse width of 150 fs, a repetition frequency of 50 kHz, and are linearly polarized light.

[0071] In this embodiment, a high damage threshold spatial light modulator (SLM) is used, with a pure phase modulation type, a reflective liquid crystal, a pixel resolution of 1920 x 1080, and a circulating water cooling system. Both lenses in the 4f system are plano-convex lenses with a focal length of 750 mm.

[0072] In this embodiment, the Fourier iteration algorithm used is an optimization program based on the GS algorithm. The original Gaussian light field and the “concave” flat-top light target light field after spatial shaping are as follows: Figure 2 As shown, the size of the target light field is adjustable and the energy distribution is uniform.

[0073] Step 4: Use the femtosecond laser target processing light field after spatial shaping to adjust the laser processing parameters to process the CFRP material, and finally obtain high-quality uniform removal processing results.

[0074] In this embodiment, the CFRP material used is high modulus CFRP, the reinforcing phase is carbon fiber M55, and the matrix phase is modified cyanate ester resin BS-4. The CFRP material used is a multi-directional laminate, a total of 8 layers, each layer is 0.125mm thick, and the layer sequence is [0° / +45° / -45° / 90°] s arrangement, and the total thickness is 1mm.

[0075] In this embodiment, high laser power is combined with a low magnification objective lens to achieve high-efficiency and high-quality uniform removal processing of CFRP. The processing objective lens used is a 100mm plano-convex objective lens. The laser repetition rate during the femtosecond laser scanning direct writing process is 50kHz, the ultra-high laser power is selected to be 10W, the scanning speed is set to 50mm / s, and the laser scanning direction is perpendicular to the surface fiber direction.

[0076] In this embodiment, the heat-affected zone of the CFRP processing structure after processing is characterized. As shown in Figure 5 a, the polymer matrix at the edge of the processing structure obtained by using the original high-power Gaussian femtosecond laser processing is selectively removed to expose long carbon fibers, and has a clear heat-affected zone, as long as 78μm; while as shown in Figure 5 b, the heat-affected zone size of the processing structure under high-power femtosecond laser spatial shaping processing is significantly reduced, only about 9μm, significantly improving the uniform removal processing quality of CFRP.

[0077] The present invention addresses the heterogeneous nature of CFRP composites by designing a target light field with a spatial energy density exceeding the processing thresholds of both the carbon fiber and polymer components. This target field eliminates the light field portion of the original Gaussian light field that is prone to generating a heat-affected zone (HAZ), and instead utilizes the energy density of both components above their processing thresholds, fully utilizing the target light field to achieve simultaneous and uniform removal. Furthermore, addressing the anisotropic nature of CFRP composites, a "concave-center, convex-side" shaped light field is designed to prioritize the removal of material at the edges of the processing path and isolate subsequent heat conduction. This prioritizes the removal of CFRP material at the extreme edges of the light spot during scanning, creating a pre-existing "isolation zone" to prevent heat transfer from the rear center portion of the light field to the edges of the structure during subsequent CFRP processing. This shape design further improves the quality of uniform CFRP removal. A spatially shaped femtosecond laser processing system based on a high-damage-threshold spatial light modulator is constructed, significantly extending the power range of conventional femtosecond laser spatial shaping processing, thereby enabling high-power femtosecond laser spatial shaping and high-quality processing of CFRP engineering composites. The method of this invention achieves high-quality, simultaneous, and uniform removal of carbon fibers and polymers from CFRP, effectively reducing the heat-affected zone during CFRP laser processing. Compared to the original Gaussian distribution light field, it significantly reduces the taper of the processed structure and significantly improves the effective utilization of the pulse energy actually used to achieve uniform removal. This method demonstrates the manufacturing capability and application prospects of high-quality CFRP processing.

[0078] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for high-quality and uniform removal of CFRP using spatially shaped femtosecond laser, characterized in that: The steps include: Step 1: Determine the energy distribution of the processing light field based on the heterogeneous characteristics of CFRP composite materials: Use the epitaxial method to measure and calculate the processing threshold F1 of the carbon fiber component and the processing threshold F2 of the polymer component in CFRP. According to the principle of max(F1, F2)<min(I1), the target processing light field I1 must meet the requirement that the spatial energy density is higher than the processing thresholds of both components, thereby obtaining the energy distribution of the processing light field; Step 2: Based on the processing light field energy distribution obtained in step 1, the shape of the processing light field is further determined based on the anisotropic properties of CFRP composite materials. Since severe processing heat conduction occurs along the carbon fiber direction, the material at the edge of the processing path should be removed first to form an isolation zone to isolate subsequent heat conduction to the two sides. The processing light field shape is then determined to be a "concave in the center and convex on both sides" special-shaped light field, resulting in an overall light field, called a "light knife", to further improve the uniform removal quality of CFRP. Step 3: Use a high-damage threshold spatial light modulator to build a spatial shaping processing system suitable for high-power femtosecond lasers. Generate a phase map corresponding to the "light knife" through a computer Fourier iterative optimization algorithm, load it onto the spatial light modulator, and phase modulate the original Gaussian light field of the incident femtosecond laser to obtain the preset target processing light field. Step 4: Use the femtosecond laser target processing light field after spatial shaping to adjust the laser processing parameters to process the CFRP material, and finally obtain high-quality uniform removal processing results.

2. The method for high-quality and uniform removal of CFRP using a spatially shaped femtosecond laser according to claim 1, wherein: The "light knife" is in the form of a crescent-shaped flat top light, a "concave"-shaped flat top light, a horseshoe-shaped arc top light or a V-shaped sawtooth top light.

3. The method for high-quality and uniform removal of CFRP using a spatially shaped femtosecond laser according to claim 1, wherein: In step three, the constructed spatial shaping femtosecond laser processing system includes a femtosecond laser, a reflector, an aperture, a mechanical switch, an attenuation plate, a high damage threshold spatial light modulator, a lens 1, a lens 2, a dichroic mirror, a focusing objective lens, a sample to be processed, a precision electrically controlled translation stage, a white light illumination source, a beam splitter, a CCD dynamic imaging unit, and a computer; the high-power femtosecond laser beam emitted by the femtosecond laser propagates through the reflector, passes through the aperture, the mechanical switch, and the attenuation plate in a collimated manner, and then enters the high damage threshold spatial light modulator for phase modulation of the light field. The shaped beam is then transported through the two lenses of the 4f system without distortion, and is finally reflected by the dichroic mirror and focused by the focusing objective lens onto the sample to be processed located on the precision electrically controlled translation stage; The illumination light emitted by the white light illumination source at the top passes through the beam splitter, dichroic mirror and focusing objective lens to illuminate the sample to be processed and is reflected. The reflected illumination light then returns through the focusing objective lens and dichroic mirror, reflects at the beam splitter, and reaches the CCD dynamic imaging unit; the computer is connected to the femtosecond laser, controls the phase image loaded by the spatial light modulator, controls the opening and closing of the mechanical switch, controls the precision electric control translation stage to move according to the set program trajectory, and connects to the CCD dynamic imaging unit for real-time imaging and monitoring of the surface of the sample to be processed.

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