Method for improving machining quality of metal micro-hole through space shaping femtosecond laser secondary shaping

Abstract

A method for improving metal micropore machining quality through space shaping femtosecond laser secondary shaping comprises the steps that firstly, a femtosecond laser micropore machining system is built, and the femtosecond laser micropore machining system comprises a Gaussian light path and a space shaping flat-topped light path; then, the electric control displacement table is moved to switch a light path of the femtosecond laser micropore machining system into a Gaussian light path, and high-energy Gaussian light is used for machining a prefabricated hole in the nickel-based high-temperature alloy workpiece; then, the electric control displacement table is moved to switch a light path of the femtosecond laser micropore machining system into a spatial shaping flat-topped light path, Gaussian light emitted by the femtosecond laser is subjected to spatial shaping, and flat-topped light is obtained; and finally, low-energy flat-top polishing is used for conducting secondary shaping on the preformed hole of the nickel-based high-temperature alloy workpiece, grooves and deposited particulate matter on the hole wall are removed, the roughness is reduced, and the machining quality of the micro hole is improved. The method for machining the micropores in the nickel-based superalloy workpiece is high in efficiency, good in quality, low in comprehensive cost and capable of meeting the requirements of aero-engine blades for high-quality air film cooling holes.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser processing of film cooling holes in aircraft engine blades, and in particular relates to a method for improving the processing quality of metal micro-holes by secondary shaping using a spatially shaped femtosecond laser. Background Art

[0002] Blades are a vital component of aircraft engines. Their harsh operating environment, subject to high temperatures and high pressures, necessitates efficient heat dissipation. Film cooling is currently the most widely used heat dissipation technology for aircraft engine blades. However, the micropores used for film cooling in blades place extremely high demands on the blades. Neither recast layers nor microcracks are permitted, while a very low surface roughness is required.

[0003] In the processing of film cooling holes in aircraft engine blades, femtosecond laser (Sun XM, Dong X, Wang KD, Fan PF, Sun T, Mei XS, Fan Z J. Femtosecond laser processing of controlled tapered micro-holes based on dynamic control of relative attitude [J]. Optics and Laser Technology, 2024, 170: 110201.), which belongs to "cold processing", has unique advantages. The heat-affected zone of the processed micro-holes is small, and there is no recast layer and microcracks. In order to improve processing efficiency, high-energy femtosecond laser is required. However, the high-energy Gaussian light emitted by the femtosecond laser interacts with the nickel-based high-temperature alloy used in the blade, resulting in the plasma scouring effect, the re-deposition effect of the ablated nanoparticles, and the strong ionization effect. These effects will form grooves and deposited particles on the wall of the micro-hole, increasing the roughness. This will seriously affect the processing quality of the micro-holes and reduce the service life of the blade. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for improving the processing quality of metal microholes by utilizing spatial shaping femtosecond laser secondary shaping, combining Gaussian femtosecond laser processing of prefabricated holes and spatial shaping flat-top femtosecond laser secondary shaping, thereby significantly improving the processing quality of metal microholes while maintaining a high processing efficiency.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for improving the quality of metal micro-hole processing by using spatial shaping femtosecond laser secondary shaping, comprising the following steps:

[0007] (a) Building a femtosecond laser micro-hole processing system, which includes a Gaussian optical path and a spatially shaped flat-top optical path;

[0008] (b) The optical path of the femtosecond laser micro-hole machining system is switched to a Gaussian optical path by moving the electronically controlled translation stage, and a prefabricated hole is machined on a nickel-based high-temperature alloy workpiece using high-energy Gaussian light.

[0009] (c) Switching the optical path of the femtosecond laser micro-hole processing system to a spatially shaped flat-top optical path by moving the electric-controlled translation stage, spatially shaping the Gaussian light emitted by the femtosecond laser to obtain a flat-top light;

[0010] (d) Low-energy flat-top light is used to perform secondary shaping of the prefabricated holes of nickel-based high-temperature alloy workpieces to remove grooves and deposited particles on the hole wall, reduce roughness, and improve the processing quality of microholes.

[0011] In step (a), the femtosecond laser micro-hole processing system includes a femtosecond laser, a reflector, a λ / 4 wave plate, a laser beam spatial shaping system, a scanning galvanometer, an f-θ lens, a three-dimensional motion platform, and an industrial computer. The laser beam emitted by the femtosecond laser is focused by the f-θ lens and then irradiates a nickel-based high-temperature alloy workpiece fixed on the three-dimensional motion platform. The motion control of the laser beam is achieved by the scanning galvanometer. The femtosecond laser, the laser beam spatial shaping system, the scanning galvanometer, and the three-dimensional motion platform are connected to the same industrial computer for control. In the laser beam spatial shaping system, the beam shaper and its accessories are installed on an electrically controlled displacement stage. The electrically controlled displacement stage is moved by the industrial computer to quickly switch between the Gaussian optical path and the flat-top optical path of the femtosecond laser micro-hole processing system.

[0012] In the step (b), when a high-energy Gaussian femtosecond laser is used to process a prefabricated hole on a nickel-based high-temperature alloy workpiece, the pulse width is 225 fs, the central wavelength is 1030 nm, and the beam quality factor M is 0. 2 ≤1.3, the repetition frequency is 100-200 kHz, the single pulse energy is 100-200 μJ, the scanning path is concentric circles with a spacing of 25 μm, the scanning speed is 100-500 mm / s, the focal length of the f-θ lens is 255 mm, and the laser focus is located 0.2-0.8 mm above the lower surface of the workpiece; wherein the repetition frequency, single pulse energy, scanning speed and position of the laser focus are determined according to the thickness of the nickel-based high-temperature alloy workpiece.

[0013] In the step (c), when the Gaussian light emitted by the femtosecond laser is spatially shaped into a flat-top light, the electrically controlled translation stage is moved to connect the beam shaper and its accessories to the spatially shaped flat-top light path, while maintaining the position of the nickel-based high-temperature alloy workpiece unchanged. When debugging the flat-top light path, a continuously adjustable attenuator is installed in the light path after the laser beam spatial shaping system, the f-θ lens under the scanning galvanometer is replaced with a flat-top light lens with a focal length of 1 m, and the beam quality analyzer is placed on the three-dimensional motion platform.

[0014] The specific debugging process of the flat-top light is as follows: turning on the femtosecond laser, adjusting the attenuation plate to reduce the laser energy, moving the electric-controlled translation stage to adjust the position of the beam shaper and its accessories, and moving the three-dimensional motion platform along the Z-axis. During the entire process, the spatial distribution of the laser energy is observed in real time through a beam quality analyzer until the Gaussian light is spatially shaped into the flat-top light required for secondary microhole shaping. After the flat-top light path debugging is completed, the attenuation plate and beam quality analyzer are removed, the lens used for the flat-top light is replaced with the original f-θ lens, and the three-dimensional motion platform is moved along the Z-axis to the original position for processing the prefabricated hole.

[0015] The parameters of the flat-top femtosecond laser secondary shaping in step (d) are as follows: pulse width 225 fs, central wavelength 1030 nm, beam quality factor M 2 ≤1.3, the repetition frequency is 100kHz, the single pulse energy is 20-100μJ, the scanning path is a circle for machining the outermost layer of the prefabricated hole, the scanning speed is 100-500mm / s, and the laser focus is located 0.2-0.8mm above the lower surface of the workpiece; wherein, the position of the laser focus is determined according to the thickness of the nickel-based high-temperature alloy workpiece.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] This invention proposes a method for improving the quality of metal micro-hole machining using spatially shaped femtosecond laser secondary shaping. Using spatial beam shaping technology, conventional Gaussian light emitted by a femtosecond laser is shaped into a flat-top beam with uniform energy distribution. This flat-top beam is then used to perform secondary shaping on prefabricated holes machined using Gaussian light in nickel-based high-temperature alloy workpieces. This removes grooves and deposited particles from the hole walls, reduces roughness, and significantly improves the machining quality of the micro-holes. The radial wall roughness of the unmodified prefabricated holes ranges from 1.4 to 2.12 μm, while the radial wall roughness of the micro-holes after secondary shaping using the flat-top beam is reduced to 0.24 to 0.86 μm, without significantly increasing the hole diameter.

[0018] The present invention features simple tooling, and the optical path can be rapidly switched via an electronically controlled translation stage, eliminating the need for complex secondary clamping and positioning. It achieves high processing efficiency and quality at a low overall cost. The microholes machined in nickel-based high-temperature alloy workpieces can meet the high-quality film cooling requirements of aircraft engine blades. Furthermore, the present invention is suitable for machining microholes in a variety of materials, with applications in media delivery channels in microelectromechanical systems, plasma extraction channels in the biomedical field, and engine fuel injectors, demonstrating its high versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a femtosecond laser micro-hole processing system according to an embodiment of the present invention.

[0020] Figure 2 (a) is a schematic diagram of energy distribution of Gaussian light in Example 1; (b) is a schematic diagram of energy distribution of flat-top light in Example 1.

[0021] Figure 3 (a) is a scanning electron microscope image of a prefabricated hole (angle of 0°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a scanning electron microscope image of the prefabricated hole (angle of 0°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1.

[0022] Figure 4 (a) is a scanning electron microscope image of a prefabricated hole (angle of 30°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a scanning electron microscope image of the prefabricated hole (angle of 30°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1.

[0023] Figure 5 (a) is a scanning electron microscope image of a prefabricated hole (angle of 45°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a scanning electron microscope image of the prefabricated hole (angle of 45°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1.

[0024] Figure 6 (a) is a laser confocal image of a prefabricated hole (angle of 0°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a laser confocal image of the prefabricated hole (angle of 0°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1.

[0025] Figure 7 (a) is a laser confocal image of a prefabricated hole (angle of 30°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a laser confocal image of the prefabricated hole (angle of 30°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1.

[0026] Figure 8(a) is a laser confocal image of a prefabricated hole (angle of 45°) machined by Gaussian light on a nickel-based high-temperature alloy workpiece in Example 1; (b) is a laser confocal image of the prefabricated hole (angle of 45°) on the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0028] Example 1, a method for improving the quality of metal micro-hole processing by using spatial shaping femtosecond laser secondary shaping, comprising the following steps:

[0029] (a) Build Figure 1 The femtosecond laser micro-hole processing system shown in the figure includes a Gaussian optical path and a spatially shaped flat-top optical path;

[0030] In step (a), the femtosecond laser micro-hole processing system includes a femtosecond laser, a reflector, a λ / 4 wave plate, a laser beam spatial shaping system, a scanning galvanometer, an f-θ lens, a three-dimensional motion platform, and an industrial computer; the laser beam emitted by the femtosecond laser is focused by the f-θ lens and then irradiated on a nickel-based high-temperature alloy workpiece fixed on the three-dimensional motion platform, and the motion control of the laser beam is achieved by the scanning galvanometer; the femtosecond laser, the laser beam spatial shaping system, the scanning galvanometer, and the three-dimensional motion platform are connected to the same industrial computer for control; in the laser beam spatial shaping system, the beam shaper and its accessories are installed on an electrically controlled displacement stage, and the electrically controlled displacement stage is moved by the industrial computer to quickly switch between the Gaussian optical path and the flat-top optical path of the femtosecond laser micro-hole processing system;

[0031] (b) The optical path of the femtosecond laser micro-hole processing system is switched to a Gaussian optical path by moving the electric-controlled translation stage. Figure 2 The high-energy Gaussian light shown in (a) is used to machine a prefabricated hole in a nickel-based high-temperature alloy workpiece;

[0032] In this embodiment, when machining a prefabricated hole on a nickel-based high-temperature alloy workpiece with a thickness of 1 mm, the pulse width is 225 fs, the central wavelength is 1030 nm, and the beam quality factor M 2 ≤1.3, repetition frequency is 200kHz, single pulse energy is 200μJ, scanning path is concentric circles with a spacing of 25μm, scanning speed is 200mm / s, focal length of f-θ lens is 255mm, and laser focus is 0.8mm above the lower surface of the workpiece;

[0033] (c) By moving the electric-controlled translation stage, the optical path of the femtosecond laser micro-hole processing system is switched to a spatially shaped flat-top optical path, and the Gaussian light emitted by the femtosecond laser is spatially shaped to obtain the following: Figure 2 The flat top light with uniform energy distribution shown in (b);

[0034] When the Gaussian light emitted by the femtosecond laser in step (c) is spatially shaped into a flat-top light, the electrically controlled displacement stage is moved to connect the beam shaper and its accessories to the spatially shaped flat-top light path, keeping the position of the nickel-based high-temperature alloy workpiece unchanged; when debugging the flat-top light path, a continuously adjustable attenuator is installed in the optical path after the laser beam spatial shaping system, the f-θ lens under the scanning galvanometer is replaced with a flat-top light lens with a focal length of 1 m, and the beam quality analyzer is placed on the three-dimensional motion platform; the specific debugging process is as follows: turn on the femtosecond laser, adjust the attenuator to reduce the laser energy, move the electrically controlled displacement stage to adjust the position of the beam shaper and its accessories, and move the three-dimensional motion platform along the Z-axis direction. During the entire process, the energy spatial distribution state of the laser is observed in real time through the beam quality analyzer until the Gaussian light is spatially shaped into the flat-top light required for the secondary shaping of the microhole; after the flat-top light path debugging is completed, the attenuator and the beam quality analyzer are removed, the flat-top light lens is replaced with the original f-θ lens, and the three-dimensional motion platform is moved along the Z-axis direction to the original position of the prefabricated hole;

[0035] (d) Using low-energy flat-top light to perform secondary shaping of prefabricated holes in nickel-based high-temperature alloy workpieces, the grooves and deposited particles on the hole wall are removed, the roughness is reduced, and the processing quality of the microhole is improved;

[0036] In this embodiment, when the prefabricated hole is reshaped twice by flat-top light, the pulse width is 225fs, the central wavelength is 1030nm, and the beam quality factor M is 2 ≤1.3, the repetition frequency is 100kHz, the single pulse energy is 100μJ, the scanning path is a circle for machining the outermost layer of the prefabricated hole, the scanning speed is 500mm / s, and the laser focus is located 0.8mm above the lower surface of the workpiece.

[0037] The microholes machined on the nickel-based high-temperature alloy workpiece in this embodiment were tested:

[0038] Figure 3 (a) Figure 4 (a) and Figure 5 Figure (a) is a scanning electron microscope image of the prefabricated holes (angles of 0°, 30° and 45°) machined by Gaussian light on the nickel-based high-temperature alloy workpiece in Example 1. Figure 6 (a) Figure 7 (a) and Figure 8 (a) shows confocal laser images of a prefabricated hole (at angles of 0°, 30°, and 45°) machined in a nickel-based superalloy workpiece using Gaussian light in Example 1. These images reveal the presence of grooves and deposited particles on the prefabricated hole walls, with a radial wall roughness of 1.4 to 2.12 μm.

[0039] Figure 3 Middle (b), Figure 4 (b) and Figure 5 (b) is a scanning electron microscope image of the prefabricated hole (angles of 0°, 30° and 45°) of the nickel-based high-temperature alloy workpiece after secondary shaping in Example 1. Figure 6 Middle (b), Figure 7 (b) and Figure 8 (b) shows a confocal laser image of a prefabricated hole (at angles of 0°, 30°, and 45°) machined in a nickel-based superalloy workpiece using Gaussian light in Example 1. After secondary shaping, the grooves and deposited particles on the hole wall are essentially removed, and the radial wall roughness is reduced to 0.24-0.86 μm. The hole diameter does not increase significantly, significantly improving the machining quality.

[0040] In Example 2, while other laser process parameters remain unchanged in Example 1, the single pulse energy in step (d) is changed to 20 μJ. The effect of machining microholes on the nickel-based high-temperature alloy workpiece in this example is similar to that in Example 1.

[0041] In Example 3, while other laser process parameters remain unchanged in Example 1, the single pulse energy in step (d) is changed to 40, 60, and 80 μJ. The microholes machined in this example on the nickel-based high-temperature alloy workpiece have similar effects as those in Example 1.

[0042] In Example 4, the scanning speed in step (d) was changed to 100 mm / s while other laser process parameters remained unchanged in Example 1. The micro-holes machined in this example on the nickel-based high-temperature alloy workpiece had similar results to those in Example 1.

[0043] In Example 5, while other laser process parameters remain unchanged in Example 1, the scanning speed in step (d) is changed to 200, 300, and 400 mm / s. The micro-holes machined in this example on the nickel-based high-temperature alloy workpiece have similar results to those in Example 1.

Claims

1. A method for improving the quality of metal micro-hole processing by using spatial shaping femtosecond laser secondary shaping, characterized in that: The following steps are involved: (a) Building a femtosecond laser micro-hole processing system, which includes a Gaussian optical path and a spatially shaped flat-top optical path; (b) The optical path of the femtosecond laser micro-hole machining system is switched to a Gaussian optical path by moving the electronically controlled translation stage, and a prefabricated hole is machined on a nickel-based high-temperature alloy workpiece using high-energy Gaussian light. (c) Switching the optical path of the femtosecond laser micro-hole processing system to a spatially shaped flat-top optical path by moving the electric-controlled translation stage, spatially shaping the Gaussian light emitted by the femtosecond laser to obtain a flat-top light; (d) Low-energy flat-top light is used to perform secondary shaping of the prefabricated holes of nickel-based high-temperature alloy workpieces to remove grooves and deposited particles on the hole wall, reduce roughness, and improve the processing quality of microholes.

2. The method according to claim 1, wherein: In step (a), the femtosecond laser micro-hole processing system includes a femtosecond laser. The laser beam emitted by the femtosecond laser is focused by an f-θ lens and irradiates a nickel-based high-temperature alloy workpiece fixed on a three-dimensional motion platform. The motion control of the laser beam is achieved by a scanning galvanometer. The femtosecond laser, the laser beam spatial shaping system, the scanning galvanometer, and the three-dimensional motion platform are connected to the same industrial computer for control. In the laser beam spatial shaping system, the beam shaper and its accessories are installed on an electrically controlled translation stage. The electrically controlled translation stage is moved by the industrial computer to quickly switch between the Gaussian optical path and the flat-top optical path of the femtosecond laser micro-hole processing system.

3. The method according to claim 1, wherein: In the step (b), when a high-energy Gaussian femtosecond laser is used to process a prefabricated hole on a nickel-based high-temperature alloy workpiece, the pulse width is 225 fs, the central wavelength is 1030 nm, and the beam quality factor M is 0. 2 ≤1.3, the repetition frequency is 100-200 kHz, the single pulse energy is 100-200 μJ, the scanning path is concentric circles with a spacing of 25 μm, the scanning speed is 100-500 mm / s, the focal length of the f-θ lens is 255 mm, and the laser focus is located 0.2-0.8 mm above the lower surface of the workpiece; wherein the repetition frequency, single pulse energy, scanning speed and position of the laser focus are determined according to the thickness of the nickel-based high-temperature alloy workpiece.

4. The method according to claim 1, wherein: In the step (c), when the Gaussian light emitted by the femtosecond laser is spatially shaped into a flat-top light, the electrically controlled translation stage is moved to connect the beam shaper and its accessories to the spatially shaped flat-top light path, while maintaining the position of the nickel-based high-temperature alloy workpiece unchanged. When debugging the flat-top light path, a continuously adjustable attenuator is installed in the light path after the laser beam spatial shaping system, the f-θ lens under the scanning galvanometer is replaced with a flat-top light lens with a focal length of 1 m, and the beam quality analyzer is placed on the three-dimensional motion platform.

5. The method according to claim 4, characterized in that The specific debugging process of the flat-top light is as follows: turning on the femtosecond laser, adjusting the attenuation plate to reduce the laser energy, moving the electric-controlled translation stage to adjust the position of the beam shaper and its accessories, and moving the three-dimensional motion platform along the Z-axis. During the entire process, the spatial distribution of the laser energy is observed in real time through a beam quality analyzer until the Gaussian light is spatially shaped into the flat-top light required for secondary microhole shaping. After the flat-top light path debugging is completed, the attenuation plate and beam quality analyzer are removed, the lens used for the flat-top light is replaced with the original f-θ lens, and the three-dimensional motion platform is moved along the Z-axis to the original position for processing the prefabricated hole.

6. The method according to claim 1, characterized in that The parameters of the flat-top femtosecond laser secondary shaping in step (d) are as follows: pulse width 225 fs, central wavelength 1030 nm, beam quality factor M 2 ≤1.3, the repetition frequency is 100kHz, the single pulse energy is 20-100μJ, the scanning path is a circle for machining the outermost layer of the prefabricated hole, the scanning speed is 100-500mm / s, and the laser focus is located 0.2-0.8mm above the lower surface of the workpiece; wherein, the position of the laser focus is determined according to the thickness of the nickel-based high-temperature alloy workpiece.

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