Wall protection system and method for film cooling holes processed by femtosecond laser

Abstract

The present invention discloses a wall protection system and method for film cooling holes processed by femtosecond laser. The system comprises: a power adjustment module configured to perform high-precision adjustment on the average power and single-pulse energy of the emitted femtosecond laser beam to control the amount of removal of the product to be processed by a single pulse of the femtosecond laser beam; a beam shaping module configured to shape the spatial distribution of the femtosecond laser beam after power adjustment; a dispersion control module configured to disperse and collimate the shaped femtosecond laser beam to generate spatial chirp; and a galvanometer scanning processing module configured to synchronously focus the spatially chirped laser beam in time and space to generate a spatiotemporal focus for high-precision, fixed-depth etching of the product to be processed. This application solves the technical problem of wall damage in conventional laser processing of film cooling holes.

Description

Technical Field

[0001] The present invention relates to the field of laser processing, and in particular to a wall protection system and method for film cooling holes processed by femtosecond laser. Background Art

[0002] Turbine aircraft engine blades, flame tubes, etc. are the most important heat-bearing components in the aircraft engine combustion chamber, and their service life directly affects the service life of the aircraft engine. Usually, in order to reduce the fatigue damage of blades, flame tubes and other components in the extreme working environment of long-term high temperature, high pressure and high vibration, a large number of film cooling holes are designed on their surfaces to form a layer of cooling gas protective film on their surface to improve their cooling effect and high temperature resistance, thereby maximizing their service life. However, due to the complex three-dimensional structure of components such as blades and the extremely high precision requirements of film cooling holes, they cannot be processed by casting. At present, electrospark discharge machining, laser machining, electrochemical machining and other technologies are mostly used to process film cooling holes.

[0003] However, electrospark machining (EDM) suffers from drawbacks such as low machining accuracy, high tool electrode wear, and severe remelting and microcracks. Electrochemical machining (ECM) also suffers from low machining efficiency, poor repeatability, and difficulty controlling the microhole profile. Laser-assisted film cooling hole machining, however, is a non-contact process that eliminates mechanical stress, lacks selectivity for the material being machined, and avoids tool damage. Laser-assisted film cooling hole machining offers significant advantages, including strong controllability, high machining accuracy, and high efficiency. Femtosecond lasers, with their ultrashort pulse width and ultrahigh peak power, can induce nonlinear absorption in the material, resulting in a focal spot size far below the diffraction limit, significantly improving the spatial resolution of the process. Furthermore, the absence of heat during the process, commonly known as "cold" machining, results in virtually no carbonization, slag, or microcracks that can negatively impact product quality. These significant advantages have led to their widespread application in various military and civilian applications, including aerospace, medical devices, and semiconductors, and have gradually become a mainstream machining method.

[0004] However, when using femtosecond lasers to create film cooling holes on blades or flame tubes, once the through-holes are formed, the laser beam still has a high energy density within a certain range in the processing direction while passing through the micro-holes. This can damage the wall structure, thus shortening its service life. Therefore, wall protection is one of the most critical technologies that need to be addressed during film cooling on blades and other structures.

[0005] Prior art has proposed a wall protection technology that uses software control. At the moment a film cooling hole is drilled, the power of the femtosecond laser output is dramatically reduced through software control, ensuring that the remaining laser energy does not damage the wall structure opposite the film cooling hole. This method is theoretically feasible and offers the lowest cost and highest effectiveness for wall protection. However, in practice, extremely high frequencies are required for real-time detection of machining depth, making existing control technologies difficult to meet the processing requirements of this technology.

[0006] Another technique currently proposed is to use a filler material to protect the walls. This material, with a high melting point, low thermal conductivity, and resistance to thermal decomposition, is placed within the microcavity. When forming the through-hole, the filler diffusely reflects or scatters the remaining laser beam, reducing damage to the wall structure. However, this technique suffers from complex processes, difficulty removing the filler and processing residues, and inability to completely prevent wall damage.

[0007] To address the above-mentioned problems, no effective solutions have been proposed so far. Summary of the Invention

[0008] The embodiments of the present invention provide a wall protection system and method for film cooling holes processed by femtosecond laser, so as to at least solve the technical problem of wall damage existing in conventional laser film cooling hole processing technology.

[0009] According to one aspect of an embodiment of the present invention, a wall protection system for film cooling holes processed by femtosecond laser is provided, comprising: a power adjustment module arranged in sequence along the optical path, configured to precisely adjust the average power and single-pulse energy of the emitted femtosecond laser beam to control the amount of removal of the product to be processed by a single pulse of the femtosecond laser beam; a beam shaping module configured to shape the spatial distribution of the femtosecond laser beam after precision adjustment; a dispersion control module configured to disperse and collimate the shaped femtosecond laser beam to generate spatial chirp; a galvanometer scanning processing module configured to synchronously focus the spatially chirped laser beam in time and space to generate a spatiotemporal focus, and to two-dimensionally adjust the spot of the spatiotemporal focus to scan the product to be processed on the surface of the product to be processed at a speed greater than a preset speed threshold.

[0010] Through the above scheme, a space-time focus can be generated with a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy density decay sharply. The longitudinal processing resolution can be greatly improved, and the removal amount of a single pulse can be accurately controlled, thereby achieving high-precision fixed deep etching processing without causing damage to the wall structure in the microcavity. In addition, the space-time focus can be two-dimensionally adjusted to scan the product to be processed at a speed greater than the set speed threshold on the surface of the product to be processed.

[0011] According to another aspect of an embodiment of the present invention, a method for wall protection of film cooling holes processed by femtosecond laser is also provided, comprising: precisely adjusting the average power and single-pulse energy of a femtosecond laser beam emitted by a laser to control the amount of removal of the product to be processed by a single pulse of the femtosecond laser beam; shaping the spatial distribution of the precision-adjusted femtosecond laser beam; dispersing and collimating the shaped femtosecond laser beam to generate spatial chirp; spatiotemporally and synchronously focusing the spatially chirped laser beam to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold; and two-dimensionally adjusting the spatiotemporal focus to scan the product to be processed at a speed greater than a set speed threshold.

[0012] In an embodiment of the present invention, during the laser processing process, the spatial shape of the femtosecond laser beam is changed by the spatial shaping module, the spatial chirp is added to the shaped femtosecond laser by the dispersion control module, and the focusing unit in the galvanometer scanning processing module is used to synchronously focus the spatially chirped laser beam in time and space to produce a spatial focus with a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy density decay sharply, thereby greatly improving the longitudinal processing resolution and facilitating the fixed deep etching processing, thereby achieving the purpose of wall protection during the femtosecond laser processing of the film cooling hole, thereby solving the technical problem of wall damage existing in the conventional laser processing film cooling hole technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0014] Figure 1 1 is a schematic structural diagram of a wall protection system for film cooling holes processed by femtosecond laser according to an embodiment of the present application;

[0015] Figure 2 is a schematic diagram of the principle of a power regulation module according to an embodiment of the present application;

[0016] Figure 3 Schematic diagram of the principle of the dispersion control module according to an embodiment of the present application;

[0017] Figure 4 is a light intensity distribution curve diagram of the focal spot at the central optical axis along the beam propagation direction (z-axis) corresponding to different spatiotemporal synchronous focusing coefficients according to an embodiment of the present application;

[0018] Figure 5 a is a time-domain pulse width curve of the spatiotemporal focal spot in the propagation direction according to an embodiment of the present application, and b is the relative pulse width stretching ratio;

[0019] Figure 61 is a schematic structural diagram of a wall protection system for film cooling holes processed by femtosecond laser according to an embodiment of the present application;

[0020] Figure 7 This is a flow chart of a wall protection system and method for processing film cooling holes using a femtosecond laser according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0023] Example 1

[0024] According to an embodiment of the present application, a wall protection system for film cooling hole machining using a femtosecond laser is provided. This system can generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold, and with increasing defocus, the pulse width increases dramatically, while the peak power and energy density decrease sharply. This significantly improves longitudinal machining resolution, facilitates fixed-depth machining, and at least addresses the technical issue of wall damage during film cooling hole machining.

[0025] Figure 1 FIG. 1 is a schematic structural diagram of a wall protection system for processing film cooling holes using a femtosecond laser according to an embodiment of the present application. Figure 1 As shown, the system includes a laser 1, a beam expander 2, a power adjustment module 3, a beam shaping module 4, a dispersion control module 5, a galvanometer scanning processing module 6, a product to be processed 7, a processing platform 8 and a control system 9 arranged in sequence along the optical path.

[0026] Among them, the power adjustment module 3 includes: a half-wave plate 31, a polarization splitter prism 32 and a beam termination device 33, and the half-wave plate 31 is placed on a high-precision electrically controlled rotating table; the beam shaping module 4 includes: a first cylindrical lens 41, a second cylindrical lens 42 and a rectangular aperture 43; the dispersion control module 5 includes: a first diffraction grating 51 and a second diffraction grating 52; the galvanometer scanning processing module 6 includes: a two-dimensional scanning galvanometer 61, a reflector 62, a dichroic mirror 63, a focusing unit 64, a camera light source 65, a beam splitter 66, a filter 67 and a coaxial CCD camera 68; the product to be processed 7 is placed on the processing platform 8.

[0027] 1. Laser

[0028] The laser 1 is used to emit a femtosecond laser beam. In one example, the wavelength of the femtosecond laser is 200 nm to 1100 nm, the pulse width is 5 fs to 1000 fs, and the polarization state is linear polarization.

[0029] 2. Power regulation module

[0030] The power regulation module 3 is used to regulate the average power and single pulse energy of the femtosecond laser used for processing with high precision, so as to accurately control the amount of material removed by a single pulse.

[0031] In one embodiment, the power regulation module 3 includes: a half-wave plate 31, a polarization beam splitter prism 32 and a beam termination device 33. The principle diagram of the power regulation is as follows: Figure 2 shown.

[0032] The linearly polarized femtosecond laser output by the laser 1 changes its polarization direction after passing through the half-wave plate 31. After passing through the polarization beam splitter prism 32, the component with a polarization direction parallel to the horizontal plane (xoy plane), that is, the p-polarization component, can be fully transmitted and used for laser processing; the component with a polarization direction perpendicular to the horizontal plane (xoy plane), that is, the s-polarization component, is fully reflected.

[0033] In one embodiment, the half-wave plate 31 is placed on a high-precision rotating stage. The control system controls the rotating stage to rotate and adjust the fast axis direction of the half-wave plate 31, thereby flexibly adjusting the polarization direction of the laser light passing through the half-wave plate 31. In turn, the ratio of the energy of the laser light passing through the polarization beam splitter prism (p-polarization) to that of the laser light reflected by the polarization beam splitter prism (s-polarization) is flexibly adjusted, thereby achieving flexible control of the average power and single pulse energy of the femtosecond laser used for laser processing.

[0034] In one embodiment, laser processing is performed using a femtosecond laser (p-polarized) that passes through a polarization beam splitter prism. To prevent unused s-polarized light from damaging human eyes and equipment, a beam stopper 33 is typically used to collect it.

[0035] 3. Beam shaping module

[0036] The beam shaping module 4 is used to spatially shape the femtosecond laser that passes through the power adjustment module 3 .

[0037] In some embodiments, the beam shaping module 4 may include a first cylindrical lens 41, a second cylindrical lens 42, and a rectangular aperture 43. The first cylindrical lens 41 and the second cylindrical lens 42 are placed in parallel, with their central optical axes coinciding with the optical axis of the laser beam in the yoz plane, and the distance between the two is f1+f2.

[0038] In some embodiments, a first cylindrical lens 41 is used to focus the laser beam passing through the power adjustment module 3 in a one-dimensional line in the y direction and generate a linear focus spot distributed along the z direction; a second cylindrical lens 42 is used to focus the femtosecond laser in a collimated linear direction in the y direction to generate a linear femtosecond laser beam distributed along the z direction; and a rectangular aperture 43 is then used to adjust the length and thickness of the linear femtosecond laser beam.

[0039] In some embodiments, the widths of the femtosecond laser beam after spatial shaping by the shaping system in the y and z directions are W respectively. y =1mm~10mm adjustable W z =1mm~10mm adjustable.

[0040] 4. Dispersion Control Module

[0041] The dispersion control module 5 is used to disperse and collimate the spatially shaped femtosecond laser to generate spatial chirp.

[0042] In some exemplary embodiments, the dispersion control module 5 may include a first diffraction grating 51 and a second diffraction grating 52. The first diffraction grating 51 is used to disperse the linear femtosecond laser beam, causing light of different frequency components to diffract along different angles to generate angular dispersion; the second diffraction grating 52 is used to collimate the angularly dispersed laser beam and convert the angular dispersion into spatial chirp.

[0043] In some exemplary embodiments, the first diffraction grating 51 and the second diffraction grating 52 are placed parallel to each other, their scribed lines are parallel to the z-axis, their scribed line period is Λ=0.2μm-3μm, and their spacing is d=50mm-500mm.

[0044] Figure 6 This is a schematic diagram of the principle of the dispersion control module according to an embodiment of the present application. The shaped linear femtosecond laser beam excites the first-order diffraction light after passing through the diffraction grating, which satisfies the following formula:

[0045] sinγ i +sinγ o =λ / Λ

[0046] Among them, γ i is the incident angle of the femtosecond laser beam, γo is the first-order diffraction angle, and λ represents the wavelength of the incident laser. Since the spectrum of the femtosecond laser pulse is relatively wide, after the femtosecond laser beam is diffracted by the first diffraction grating 51, the diffraction angles γ corresponding to the light of different frequency components are o The angularly dispersed femtosecond laser beam is collimated after being diffracted by the second diffraction grating 52, resulting in spatial separation of light with different frequency components, thus generating spatial chirp.

[0047] The dispersion coefficient α of the dispersion control system can be expressed as:

[0048] α=-dλ0cosγ i / (Λω0cos 3 γ o )

[0049] Where λ0 and ω0 represent the central wavelength and central frequency of the incident femtosecond laser beam, respectively. Figure 3 As shown in Figure 2, the normalized light field distribution A1 of the dispersion-controlled femtosecond laser beam at y0 can be expressed as:

[0050]

[0051] Where A0 represents the normalized amplitude of the light field, represents 1 / e of the incident femtosecond laser 2 The spectral bandwidth, ω, represents the angular frequency of the incident femtosecond laser beam. Δz(ω)≈α(ω-ω0) represents the linear displacement of each frequency component along the z direction at y0.

[0052] 5. Galvanometer scanning processing module

[0053] The galvanometer scanning processing module 6 is used to synchronously focus the spatially chirped laser beam in time and space to produce a space-time focus with a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy density decay sharply, so as to greatly improve the longitudinal processing resolution, accurately control the removal amount of a single pulse, thereby achieving high-precision fixed deep etching processing without causing damage to the wall structure in the microcavity, and two-dimensionally adjust the space-time focus spot to scan the product to be processed at a speed greater than the set speed threshold on the surface of the product to be processed, and locate the product position before starting laser processing, and monitor the processing status in real time during the laser processing process.

[0054] In some exemplary embodiments, the galvanometer scanning processing module 6 includes the following arranged in sequence along the optical path: a two-dimensional scanning galvanometer 61, configured to control the spatially chirped femtosecond laser to perform high-speed two-dimensional scanning at a speed greater than a set speed threshold through the deflection of the galvanometer lens; a reflector 62, configured to change the propagation direction of the two-dimensionally scanned femtosecond laser; a dichroic mirror 63, configured to reflect the spatially chirped femtosecond laser and allow the laser emitted by the camera light source to pass through; a focusing unit 64, configured to synchronously focus the spatially chirped laser beam in time and space to produce a focal depth less than a preset focal depth threshold, and as the defocus amount increases, the pulse width increases sharply, and the peak power and energy density decay sharply. The spatiotemporal focus of the spatiotemporal focus spot is scanned along a preset path at a speed greater than a set speed threshold under the action of two-dimensional adjustment to scan the product to be processed; the camera light source 65 is configured to illuminate the surface of the product to be processed so that the CCD camera can collect the surface morphology information of the product to be processed; the beam splitter 66 is configured to split the laser beam emitted by the camera light source; the filter 67 is configured to have high transmittance to the laser beam emitted by the camera light source and high reflectivity to the femtosecond laser emitted by the laser 1; the coaxial CCD camera 68 is configured to detect the surface morphology of the product to locate the product position before starting laser processing and to monitor the processing status in real time during laser processing.

[0055] In some exemplary embodiments, the wavelength of the laser light emitted by the camera light source does not overlap with the wavelength of the femtosecond laser beam emitted by the laser. After passing through beam splitter 66, the laser beam emitted by the camera light source is split into two beams of equal energy: one laser beam is transmitted; the other laser beam is reflected. The reflected laser beam then passes through dichroic mirror 63 and focusing unit 64 along the optical path, irradiating the surface of the product to be processed 7 and being reflected by the surface. The reflected laser beam then passes through focusing unit 64, dichroic mirror 63, beam splitter 66, and filter 67 along the optical path, before entering coaxial CCD camera 68 to obtain surface topography information of the product to be processed.

[0056] After the spatially chirped femtosecond laser beam is reflected by the two-dimensional galvanometer 61, the reflector 62, and the dichroic mirror 63 in the direction of beam propagation, the light field distribution A1 also undergoes multiple coordinate transformations. The light field distribution A1 before the focusing unit 64 can be expressed as:

[0057]

[0058] Wherein, Δx(ω)≈α(ω-ω0) represents the linear displacement of different frequency components along the x direction at the entrance of the focusing unit 64, W x =W z .

[0059] After the spatially chirped femtosecond laser beam enters the focusing unit 64, it stimulates a spatiotemporal focusing effect in the focal region and irradiates the surface of the product 7 to be processed, which is placed in the xoy plane. After the spatially chirped femtosecond laser beam is focused by the focusing unit 64, the slowly varying envelope of the light field distribution is approximately A2:

[0060]

[0061] in, represents an imaginary number, k = 2π / λ is the wave vector, and f is the focal length of the focusing unit. After propagating a distance z, the light field distribution A3 near the focal area is calculated using the Fresnel diffraction integral formula:

[0062]

[0063] Here, ξ and η represent coordinates in the Cartesian coordinate system, and the geometric plane where the focusing unit 64 is located is the position z=0 mm.

[0064] Then, by performing inverse Fourier transform on A3, we can get the time domain evolution process A4 of the light field distribution in the focal area:

[0065]

[0066] Then the light intensity distribution I at the focus can be expressed as:

[0067]

[0068] The light intensity distribution I(z) averaged in the time domain along the optical axis along the propagation direction is obtained by simplification and approximation:

[0069]

[0070] Where I0 represents the normalized light intensity at the focus, Represents the Rayleigh length, φ0=2M 2 λ0f / πD is the focal spot radius, M 2 represents the beam quality factor of the femtosecond laser beam output by laser 1, D is the beam diameter after beam expansion, and β is the spatiotemporal synchronization coefficient, which is defined as the ratio of the width of the spatially chirped femtosecond laser beam to the width of the linear femtosecond laser beam without passing through the dispersion control module.

[0071] The relationship between the pulse width τ of the focal spot obtained by spatiotemporal focusing and the propagation distance is:

[0072]

[0073] Wherein, τ0 represents the time domain pulse width of the femtosecond laser beam emitted by the laser 1 , and k2 represents the group velocity dispersion coefficient of the grating in the dispersion control module 5 .

[0074] Due to the dispersion effect of the dispersion control module 5 on the linear femtosecond laser beam, the light of different frequency components in the femtosecond laser beam is separated from each other (spatial chirp), resulting in a significant widening of its temporal pulse width. After the spatial chirp of the femtosecond laser is focused by the focusing unit 64, it stimulates the spatiotemporal focusing effect, and the spatial chirp is again converted into a angular dispersion showing a convergence trend. The closer the distance to the focus, that is, the smaller the defocus amount, the higher the overlap of different frequency components, the wider the spectrum width, and the smaller the temporal pulse width. It can be seen from this that in spatiotemporal synchronous focusing, the smaller the defocus amount, the smaller the pulse width of the femtosecond laser, and the light of different frequency components can only completely overlap and restore to obtain a femtosecond laser pulse with the same pulse width as the initial pulse width at the focus (the defocus amount is zero). Therefore, under the conditions of spatiotemporal synchronous focusing, not only the spatial size of the focused spot continues to shrink as the defocus amount decreases, but the temporal pulse width of the focused spot also decreases sharply, and both the spatial size and the temporal pulse width reach their minimum values only at the focus.

[0075] The energy density E and peak power P of the focused spot can be expressed as:

[0076]

[0077] Here, J represents the energy of a single pulse of the femtosecond laser beam. The above formula shows that the spatial size (radius φ) and pulse width (τ) of the focal spot obtained by spatiotemporal synchronous focusing both decrease dramatically with decreasing defocus. Consequently, the energy density E and peak power P of the focused spot also decrease dramatically. This means that during the focusing process, along the propagation direction, the energy density E and peak power P of the focused spot first increase sharply and then decrease sharply, reaching a maximum at the focal plane. In traditional femtosecond laser processing, the focused spot size increases slowly as defocus increases, while the pulse width remains constant. This results in the energy density E and peak power P of the focused spot also decaying slowly. Therefore, when used for film cooling holes in blades, flame tubes, and fuel injectors, the residual energy can easily ablate the opposing wall structure. However, when the focused spot obtained using spatiotemporal synchronous focusing technology deviates slightly from the focal position, the dual sharp increase in spot size and pulse width causes the laser energy density and peak power to decay sharply to the point where they are unable to damage the opposing wall structure, thus achieving the purpose of wall protection.

[0078] The following describes the operation process of the wall protection system for film cooling holes processed by femtosecond laser according to this embodiment.

[0079] The femtosecond laser beam emitted by the laser 1 is expanded by the beam expander 2; the average power and single pulse energy of the femtosecond laser beam after the expansion and used for processing are adjusted with high precision by the power adjustment module 3; the femtosecond laser beam after the average power and single pulse energy are adjusted is spatially shaped by the beam shaping module 4, and the shaped femtosecond laser beam is converted into a spatially chirped femtosecond laser by the dispersion control module 5. The spatially chirped femtosecond laser is synchronously focused in time and space after passing through the focusing unit of the vibration scanning processing module 6 to produce a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy are The spatiotemporal focus with a rapidly decaying density can greatly improve the longitudinal processing resolution, thereby accurately controlling the removal amount of a single pulse, thereby achieving high-precision fixed deep etching processing without damaging the wall structure in the microcavity. Then, the spatiotemporal focus is adjusted in two dimensions to scan the product to be processed at a speed greater than the set speed threshold on the surface of the product to be processed, and a processing platform such as a five-axis CNC module is used to carry the product to be processed along a preset trajectory relative to the spatiotemporal focus to complete the processing of special-shaped air film cooling holes on the three-dimensional complex structure. In addition, before processing, a coaxial CCD camera is used to locate the position of the product to be processed, and the processing status is monitored in real time during the processing.

[0080] In an example, the following parameters are taken for simulation calculation: the central wavelength of the femtosecond laser beam output by the laser is λ0 = 800 nm, the pulse width is τ0 = 50 fs, and the beam quality factor is M 2 =1.2, and the diameter of the beam after expansion is D = 6 mm; in the beam shaping module, the focal length of the first cylindrical lens is f1 = 150 mm, and the focal length of the second cylindrical lens is f2 = 25 mm. After passing through the first cylindrical lens and the second cylindrical lens beam shaping system in sequence, the expanded femtosecond laser beam is shaped into a linear femtosecond laser beam with a width of 1 mm in the y direction and a length of 6 mm in the z direction. The rectangular aperture is then used to flexibly change the length of the linear femtosecond laser beam in the z direction and the width in the y direction. In the dispersion control system, the line density of the second diffraction grating of the first diffraction grating is 1200 Line / mm, and the group velocity dispersion coefficient k2 = 1.5×10 4 fs 2 / cm, the spatiotemporal synchronization coefficient β = 1, 2, 3 and 4 (β = 1 means no dispersion control, and a larger β means that the spatial chirp is more serious after dispersion control); in the galvanometer scanning processing module, the focal length of the focusing unit is f = 30 mm.

[0081] Figure 4The light intensity distribution curve of the focal spot obtained by spatiotemporal synchronous focusing along the central optical axis of the beam propagation direction (z-axis) is shown. It can be found that when spatiotemporal synchronous focusing is not performed (β = 1), the focal depth of the focus is the longest; as the spatiotemporal synchronization coefficient increases (β = 2, 3, and 4), the focal depth of the focus also decreases sharply; when the spatiotemporal synchronization coefficient is maximized (β = 4), the focal depth of the focus can be reduced to 10.8% of the initial focal depth of the focus without dispersion control, which means that the longitudinal resolution is improved by about 9.3 times; if the parameters of the first and second diffraction gratings in the dispersion control system are adjusted to increase the value of the spatiotemporal synchronization coefficient β, a focal spot with a larger compression ratio focal depth can be obtained, further improving the longitudinal processing resolution.

[0082] Figure 5 Shows the time domain pulse width curve of the focused spot in the propagation direction ( Figure 5 a) and relative pulse width stretch ratio ( Figure 5 b). It can be found that with the change of defocus, the pulse width of the spatiotemporal focal spot shows a trend of first decreasing sharply and then increasing sharply, and the minimum pulse width τ = τ0 = 50fs is obtained at the focus. The relative pulse width broadening ratio shows that with the increase of defocus, the relative pulse width broadens sharply, which means that the peak power of the focal spot also decays sharply, thereby effectively avoiding damage to the defocus position by the laser spot. Therefore, when this method is used for film cooling hole processing, by precisely controlling the single pulse energy of the femtosecond laser used for processing, the amount of material removed by a single laser pulse can be precisely controlled, so that material can be etched and removed only at the focal position. The remaining laser energy decays sharply to below the damage threshold of the material as the defocus increases, thereby achieving the purpose of wall protection.

[0083] The wall protection system for femtosecond laser processing of air film holes proposed in the embodiments of the present application has the following beneficial effects:

[0084] 1) Using spatiotemporal synchronous focusing technology to obtain a focal spot with a focal depth less than the preset focal depth, thereby greatly improving the longitudinal processing resolution;

[0085] 2) The time-domain pulse width of the focal spot obtained by the spatiotemporal synchronous focusing technology increases sharply with the increase of defocus, causing its peak power to decay sharply, thus avoiding damage to the wall structure caused by residual laser energy and solving the technical problem of wall damage in conventional laser machining film cooling hole systems;

[0086] 3) By precisely controlling the energy of the single pulse of the femtosecond laser used for processing through a power regulation system, and combining this with a spatial and temporal focus with an extremely small focal depth, the etching depth of a single pulse can be precisely controlled, significantly improving the accuracy and applicability of femtosecond laser processing. This results in a wall protection system for the precision machining of film cooling holes using femtosecond lasers. This system effectively avoids the technical challenge of wall damage encountered by conventional laser machining systems when machining film cooling holes on blades, flame tubes, and fuel injectors, demonstrating significant application value and promising market prospects.

[0087] Example 2

[0088] According to an embodiment of the present application, another wall protection system for film cooling hole machining using a femtosecond laser is provided. This optical system is primarily designed to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold and a temporal pulse width that increases dramatically with increasing defocus. This significantly improves longitudinal machining resolution, thereby avoiding the technical challenge of wall damage during film cooling hole machining.

[0089] like Figure 6 As shown, the system includes a laser 1, a beam expander 2, a power adjustment module 3, a beam shaping module 4, a dispersion control module 5, a second reflector 10, a second focusing unit 11, a product to be processed 7, a processing platform 8 and a control system 9 arranged in sequence along the optical path.

[0090] The power regulation module 3 includes: a half-wave plate 31, a polarization beam splitter prism 32 and a beam termination device 33, wherein the half-wave plate 31 is placed on a high-precision electrically controlled rotating stage; the beam shaping module 4 includes: a first cylindrical lens 41, a second cylindrical lens 42 and a rectangular aperture 43; the dispersion control module 5 includes: a first diffraction grating 51 and a second diffraction grating 52.

[0091] The half-wave plate 31 in the power regulation module 3 is placed on a high-precision electrically controlled rotating table. The control system controls the rotating table to rotate and adjust the fast axis direction of the half-wave plate to flexibly adjust the polarization direction of the laser passing through the half-wave plate, so as to flexibly adjust the energy splitting ratio of the transmitted light and the reflected light of the polarization splitting prism, thereby flexibly controlling the average power of the laser used for laser processing and the single pulse energy of the laser beam.

[0092] The laser 1 is used to emit a femtosecond laser beam. In one example, the wavelength of the femtosecond laser is 200 nm to 1100 nm, the pulse width is 5 fs to 1000 fs, and the polarization state is linear polarization.

[0093] The power regulation module 3 is used to precisely adjust the average power and single-pulse energy of the femtosecond laser used for processing, thereby accurately controlling the amount of material removed by a single pulse. In one embodiment, the power regulation module 3 includes a half-wave plate 31, a polarization beam splitter prism 32, and a beam stop 33.

[0094] The beam shaping module 4 is used to spatially shape the femtosecond laser beam transmitted through the power adjustment module 3 and, under focusing conditions, change the spatial shape of the focused spot. In one embodiment, the beam shaping module 4 includes a first cylindrical lens 41, a second cylindrical lens 42, and a rectangular aperture 43. In one embodiment, the first cylindrical lens 41 and the second cylindrical lens 42 are positioned parallel to each other, with their central optical axis coinciding with the optical axis of the laser beam in the yoz plane, and the distance between the two is f1 + f2.

[0095] The dispersion control module 5 is used to disperse and collimate the spatially shaped femtosecond laser light to produce spatial chirp. In one exemplary embodiment, the dispersion control module 5 includes a first diffraction grating 51 and a second diffraction grating 52. The first diffraction grating 51 is used to disperse the linear femtosecond laser beam distributed along the z-direction, causing light of different frequency components in the femtosecond laser pulse to diffract at different angles, thereby producing angular dispersion. The second diffraction grating 52 is used to collimate the angularly dispersed femtosecond laser beam, converting the angular dispersion into spatial chirp.

[0096] The second reflecting mirror 10 is used to change the propagation direction of the spatially chirped femtosecond laser beam.

[0097] The second focusing unit 11 is used to focus the spatially chirped femtosecond laser beam to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold, and with the increase of defocus, the pulse width increases sharply, and the peak power and energy density decay sharply.

[0098] The specific operation process of the system in this embodiment is as follows:

[0099] The femtosecond laser beam emitted by the laser 1 is expanded by the beam expander 2; the average power and single pulse energy of the femtosecond laser beam after expansion and used for processing are adjusted with high precision by the power adjustment module 3; the femtosecond laser beam after the average power and single pulse energy are adjusted is spatially shaped by the beam shaping module 4, and the shaped femtosecond laser beam is converted into a spatially chirped femtosecond laser by the dispersion control module 5. The spatially chirped femtosecond laser changes direction after passing through the second reflector 10 and enters the second focusing unit 11. The second focusing unit 11 focuses the spatially chirped laser beam in a spatiotemporal synchronous manner to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy density decay sharply, so as to greatly improve the longitudinal processing resolution, thereby realizing high-precision fixed deep etching processing without damaging the wall structure in the microcavity. Then, the five-axis CNC module 8 is used to clamp the product to be processed 7 and move it along a preset trajectory relative to the spatiotemporal focus to complete the processing of special-shaped air film cooling holes on the three-dimensional complex structure.

[0100] In this embodiment, the power regulation module is used to precisely regulate the energy of a single pulse of the laser beam used for processing, the beam shaping module is used to shape the spatial distribution of the laser beam, the dispersion control module is used to disperse and collimate the shaped laser beam to produce spatial chirp, and the focusing unit is used to spatiotemporally synchronize the spatially chirped laser beam to produce a spatiotemporal focus with a focal depth less than a preset focal depth threshold, and with the increase of the defocus amount, the pulse width increases sharply, and the peak power and energy density decay sharply, thereby greatly improving the longitudinal processing resolution, and then accurately controlling the removal amount of a single pulse to achieve high-precision fixed deep etching processing of the material, thereby avoiding damage to the internal structure of the microcavity. At the same time, a five-axis CNC module is used to clamp the product to be processed and move it along a specific trajectory relative to the focal spot, thereby realizing the processing of film cooling holes on a three-dimensional complex curved surface. This application solves the technical problem of wall damage when conventional laser processing systems process blade film cooling holes.

[0101] Example 3

[0102] According to an embodiment of the present application, a laser micromachining method with controllable taper is provided, such as Figure 7 As shown, the method includes:

[0103] Step S701: The power adjustment module adjusts the single pulse energy of the femtosecond laser beam used for processing with high precision;

[0104] Step S702: The beam shaping module shapes the spatial distribution of the femtosecond laser beam after power adjustment.

[0105] Step S703: the dispersion control module disperses and collimates the shaped femtosecond laser beam to generate spatial chirp;

[0106] Step S704: The focusing unit in the galvanometer scanning processing module performs spatiotemporal synchronous focusing on the spatially chirped femtosecond laser beam to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold and a temporal pulse width that increases sharply with an increase in defocus amount.

[0107] Step S705, using a coaxial CCD camera to locate the position of the product to be processed;

[0108] Step S706: The two-dimensional scanning galvanometer performs two-dimensional adjustment on the spatiotemporal focal spot so that the galvanometer scans the object to be processed along a preset trajectory at a speed greater than a preset speed threshold, thereby processing a preset complex structure.

[0109] Step S708: The five-axis CNC module clamps the product to be processed and moves it along a specific trajectory relative to the focal spot, thereby realizing the processing of film cooling holes on the three-dimensional complex curved surface;

[0110] Step S709: The coaxial CCD camera detects the processing status in real time.

[0111] In an embodiment of the present application, a power adjustment module is used to precisely adjust the single pulse energy of the expanded laser beam used for processing, a beam shaping module is used to shape the spatial distribution of the emitted laser beam, a dispersion control module is used to disperse and collimate the shaped laser beam to generate spatial chirp, and a focusing unit in a galvanometer scanning processing module is used to perform spatiotemporal synchronous focusing of the spatially chirped femtosecond laser beam to generate a spatiotemporal focus with a focal depth less than a preset focal depth threshold, and with an increase in defocus, the pulse width increases sharply, and the peak power and energy density decrease sharply, thereby greatly improving the longitudinal processing resolution, and then accurately controlling the removal amount of a single pulse to achieve high-precision fixed deep etching processing of the material, thereby avoiding damage to the internal structure of the microcavity. The focus spot is then two-dimensionally adjusted by the galvanometer scanning processing module so that it scans the product to be processed along a preset trajectory at a speed greater than a set speed threshold to process a preset complex structure. At the same time, a five-axis CNC module is used to clamp the product to be processed and move it along a specific trajectory relative to the focus spot, thereby achieving the processing of air film cooling holes on a three-dimensional complex curved surface. The present application solves the technical problem of wall damage during blade film cooling hole machining by conventional laser machining systems.

[0112] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0113] If the integrated units in the above embodiments are implemented in the form of software functional units and sold or used as independent products, they can be stored in the above-mentioned computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the existing technology, or all or part of the technical solution can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes a number of instructions for causing one or more computer devices (such as personal computers, servers, or network devices) to execute all or part of the steps of the methods described in various embodiments of the present invention.

[0114] In the above embodiments of the present invention, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0115] In the several embodiments provided in this application, it should be understood that the disclosed client can be implemented in other ways. Among them, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, and can be electrical or other forms.

[0116] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0117] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0118] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A wall protection system for film cooling holes processed by femtosecond laser, characterized in that: Including arranged in sequence along the light path: A power regulating module (3) is configured to perform high-precision regulation on the average power and single-pulse energy of the emitted femtosecond laser beam, so as to control the amount of removal of the product to be processed by a single pulse of the femtosecond laser beam; A beam shaping module (4) configured to shape the spatial distribution of the femtosecond laser beam after high-precision adjustment; A dispersion control module (5) is configured to disperse and collimate the shaped femtosecond laser beam to generate spatial chirp; a galvanometer scanning processing module (6) configured to synchronously focus the spatially chirped femtosecond laser beam in time and space to generate a time and space focus having a focal depth less than a preset focal depth threshold, and to two-dimensionally adjust the light spot of the time and space focus to scan the product to be processed (7) on the surface of the product to be processed (7) at a speed greater than a preset speed threshold; The galvanometer scanning processing module (6) comprises: A two-dimensional scanning galvanometer (61) is configured to control the spatially chirped femtosecond laser beam to perform two-dimensional scanning at a speed greater than a preset speed threshold by deflecting a lens of the two-dimensional scanning galvanometer (61); A reflecting mirror (62) configured to change the propagation direction of the femtosecond laser beam deflected by the two-dimensional scanning galvanometer mirror (61); a dichroic mirror (63) configured to reflect all of the femtosecond laser beam deflected by the reflector (62), so that the reflected femtosecond laser beam enters a focusing unit (64); The focusing unit (64) is configured to focus the femtosecond laser beam reflected by the dichroic mirror (63) to generate a spatiotemporal focus in which the pulse width increases sharply and the peak power and energy density decay sharply as the defocus amount increases; a camera light source (65) configured to illuminate the surface of the product to be processed (7), wherein the wavelength of the laser emitted by the camera light source (65) does not overlap with the wavelength of the femtosecond laser beam emitted by the laser (1); a beam splitter (66) configured to split the laser beam emitted by the camera light source (65); a filter (67) configured to transmit the laser beam emitted by the camera light source (65) and reflect the femtosecond laser beam; The CCD camera (68) is configured to collect surface morphology information of the product to be processed (7) by using lighting, so as to locate the position of the product to be processed (7) before starting laser processing of the product to be processed (7), and is also used to monitor the processing status in real time during the laser processing process.

2. The wall protection system for film cooling holes processed by femtosecond laser according to claim 1, characterized in that: The beam shaping module (4) comprises: The first cylindrical lens (41) is configured to y One-dimensional line focusing of the femtosecond laser beam in the axial direction to generate a line focus spot; The second cylindrical lens (42) is arranged parallel to the first cylindrical lens (41) and is configured to y The femtosecond laser beam is focused linearly in the axial direction after being linearly focused by the first cylindrical lens (41) to generate a z Axially distributed linear femtosecond laser beam; A rectangular aperture (43) configured to adjust the lateral size of the linear femtosecond laser beam; Among them, the z The axial direction is a direction orthogonal to the bearing surface of the processing platform (8) for placing the product to be processed, y The axial direction is a direction parallel to the bearing surface and orthogonal to the light path passing through the beam shaping module (4).

3. The wall protection system for film cooling holes processed by femtosecond laser according to claim 2, characterized in that: The central optical axes of the first cylindrical lens (41) and the second cylindrical lens (42) are aligned with the femtosecond laser beam. y Axis direction and the z The optical axes in the plane formed by the axial directions coincide with each other, and the distance between the first cylindrical lens (41) and the second cylindrical lens (42) is the sum of the focal length of the first cylindrical lens (41) and the focal length of the second cylindrical lens (42).

4. The wall protection system for film cooling holes processed by femtosecond laser according to claim 2, characterized in that: The dispersion control module (5) comprises: A first diffraction grating (51) is configured to disperse the linear femtosecond laser beam so that laser light of different frequency components in the pulse of the femtosecond laser beam is diffracted along different angles to generate angular dispersion; a second diffraction grating (52) arranged parallel to the first diffraction grating (51) and configured to collimate the femtosecond laser beam diffracted by the first diffraction grating (51) to convert the angular dispersion into the spatial chirp; The directions of the lines of the first diffraction grating (51) and the second diffraction grating (52) are aligned with the z The axes are parallel, and the line density of the first diffraction grating (51) is the same as the line density of the second diffraction grating (52).

5. The wall protection system for film cooling holes processed by femtosecond laser according to claim 1, characterized in that: The power regulation module (3) comprises: a half-wave plate (31) configured to adjust the polarization direction of the femtosecond laser beam; a polarization beam splitter prism (32) configured to transmit p-polarized laser light in the femtosecond laser beam and reflect s-polarized laser light in the femtosecond laser beam; The beam terminating device (33) is configured to block the s-polarized laser light reflected by the polarization beam splitting prism (32).

6. The wall protection system for film cooling holes processed by femtosecond laser according to claim 5, characterized in that: The half-wave plate (31) is configured to change the polarization direction of the femtosecond laser beam passing through the half-wave plate (31) by adjusting the fast axis direction of the half-wave plate (31) to control the energy ratio of the laser light transmitted from the polarization beam splitter (32) and the laser light reflected from the polarization beam splitter prism (32).

7. The wall protection system for film cooling holes processed by femtosecond laser according to claim 1, characterized in that: Also included is a control system (9) configured to be at least one of the following: Driving the electrically controlled rotary stage to rotate so as to control the fast axis direction of the half-wave plate (31) of the power regulating module (3); Driving the platform to be processed (8) to clamp the product to be processed (7) to perform multi-dimensional movement relative to the light spot of the time-space focus; A motor driving the two-dimensional scanning galvanometer (61) of the galvanometer scanning processing module (6) drives the lens of the two-dimensional scanning galvanometer (61) to rotate, so as to adjust the two-dimensional deflection angle of the femtosecond laser beam, so that the light spot of the spatiotemporal focus can be scanned along a preset trajectory; The CCD camera (68) is controlled to collect surface morphology information of the product to be processed (7) in real time and perform data processing and analysis.

8. A method for a wall protection system for a femtosecond laser-processed film cooling hole according to any one of claims 1 to 7, characterized in that: include: High-precision adjustment of the average power and single-pulse energy of the femtosecond laser beam emitted by the laser to control the amount of removal of the product to be processed by a single pulse of the femtosecond laser beam; shaping the adjusted spatial distribution of the femtosecond laser beam; dispersing and collimating the shaped femtosecond laser beam to generate spatial chirp; The spatially chirped laser beam is focused in a spatiotemporal synchronous manner to generate a spatiotemporal focus having a focal depth less than a preset focal depth threshold, and the light spot of the spatiotemporal focus is adjusted in two dimensions to scan the product to be processed (7) on the surface of the product to be processed (7) at a speed greater than a preset speed threshold.

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