A laser hole repair system and method for narrow cavity structural parts without back wall damage

Abstract

The present invention discloses a laser hole repair system for narrow cavity structural parts without back wall damage, including an ultrafast laser, a beam transmission system, a beam shaping system, a beam focusing system, a coaxial vision system, a three-dimensional motion platform and a computer controller; the ultrafast laser provides a femtosecond laser beam for the entire system, and after the laser beam is transmitted through the beam transmission system, the beam is transmitted to the beam shaping system to obtain a Bessel beam after shaping optimization, and the beam is then focused and contracted by the beam focusing system to the micropores on the surface of the target material of the narrow cavity structural part on the high-precision three-dimensional mobile platform for hole repair, and the whole hole repair process is observed through the coaxial vision system. The present invention obtains the required complete cylindrical micropores and the back wall of the narrow cavity structural part after processing is not damaged. Only the beam process control means are used to achieve the narrow cavity without back wall damage during hole repair, and the operation is simple and convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of laser precision machining, and in particular to a laser hole repairing system and method for narrow cavity structural parts without back wall damage. Background Art

[0002] Laser processing has the characteristics of high processing accuracy, high processing quality, processing of almost any material and low thermal impact. However, due to the transmission characteristics of Gaussian light and the fact that laser processing is non-contact processing, it is easy to damage the back wall surface or even remove the material when processing materials with hollow narrow cavities such as turbine blades and fuel injectors, which is called "back wall damage". Back wall damage will cause stress concentration at the damaged position, resulting in uneven force on the material and a decrease in the service life of the material. Therefore, back wall protection technology is very critical when laser processing hollow narrow cavity materials, which will directly affect the reliability of laser processing materials and the practicality of back wall protection technology. Therefore, it is urgent to study a reliable back wall protection technology.

[0003] The current back wall protection technology mainly includes cavity material filling and laser process control. Cavity material filling is to fill a part of the material in the narrow cavity to reduce or eliminate the laser energy. However, since this method can only passively protect the laser, the filling process of the protective material is cumbersome and complicated, and the protection ability of the narrow cavity is limited; laser process control is to optimize the laser processing process by adjusting the energy distribution form and size and other parameters during the beam transmission process. For example, when laser processing microholes, first use large laser parameters to process the prefabricated holes, and then use small laser parameters to repair the prefabricated holes, so as to reduce the back wall protection pressure, and at the same time optimize the taper, side walls and entrance and exit quality of the prefabricated holes. However, this method still has great difficulty in completely solving the problem of back wall damage, and the back wall protection pressure is very high for particularly narrow cavities.

[0004] Therefore, it is urgent to conduct in-depth research on the process control methods of beam energy distribution and explore means to rapidly reduce the end energy in the direction of laser transmission, so as to achieve back wall damage-free protection of narrow cavity structures without protective materials, and promote the application of laser processing in the field of narrow cavity material processing. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the present invention proposes a laser hole repair system and method for narrow cavity structural parts without damage to the back wall. On the one hand, the system and method can realize the repair of microholes with conical residual materials inside the holes processed by oblique laser incidence, and finally obtain the required complete cylindrical microholes. At the same time, the narrow cavity back wall of the narrow cavity structural part is not damaged after processing. On the other hand, only the beam process control means is adopted to achieve the narrow cavity without back wall damage during hole repair, and the operation is simple and convenient.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A laser hole repair system for narrow cavity structural parts without back wall damage comprises an ultrafast laser 1, a beam transmission system, a beam shaping system, a beam focusing system, a coaxial vision system, a three-dimensional motion platform 17 and a computer controller 19; a narrow cavity structural part 16 to be processed is arranged on the three-dimensional motion platform 17;

[0008] The ultrafast laser 1 provides a femtosecond laser beam for the entire system. The laser beam is transmitted to the beam shaping system via the beam transmission system to obtain a Bessel beam after shaping optimization. The beam is then focused and contracted by the beam focusing system to the micropores on the surface of the target material of the narrow cavity structural part 16 on the high-precision three-dimensional mobile platform 17 for hole repair. The whole process of hole repair is observed by the coaxial vision system.

[0009] The three-dimensional motion platform 17 can drive the narrow cavity structure 16 to move in three directions: x, y, and z. The coaxial vision system is used to identify and locate micropores on the surface of the narrow cavity structure 16. Bessel beam.

[0010] The light beam transmission system comprises a half-wave plate 2, a Glan Taylor prism 3, a beam expander 4 and a first reflector 5 which are sequentially arranged along the direction of the light beam; wherein the half-wave plate 2 and the Glan Taylor prism 3 are sequentially arranged, and the light beam first passes through the half-wave plate 2 and then through the Glan Taylor prism 3, so as to adjust the polarization direction of the input laser beam and filter out all the s component light; after the half-wave plate 2, the Glan Taylor prism 3 is used to separate the p component light and the s component light, and to filter out all the s component light, so as to ensure that the light incident on the liquid crystal spatial light modulator is all the p component light, and the incident light energy can also be adjusted steplessly, and the beam expander 4 is used to expand the incident light beam to 4 times;

[0011] The ultrafast laser 1 is a femtosecond laser, and the laser emitted is a Gaussian beam. The half-wave plate 2 is a quartz air-gap zero-order wave plate, and its design wavelength is 1030nm, which is consistent with the laser wavelength. The Glan-Taylor prism 3 has a clear aperture of 10mm and an operating wavelength of 200nm-3.0μm. The beam expander 4 is a 1-4 times adjustable coaxial beam expander.

[0012] The beam shaping system comprises a spatial light modulator 6, a first lens 7, a pinhole aperture 8, a second lens 9 and a second reflector 10 arranged in sequence along the beam direction;

[0013] The spatial light modulator 6 is loaded with a blazed grating, which is used to dynamically control the laser light field distribution, and to shape the ultrashort pulse laser beam transmitted by the beam transmission system into a Bessel beam whose axial energy distribution first rises, then becomes uniform, and then falls;

[0014] The spatial light modulator 6, the first lens 7, the pinhole diaphragm 8, the second lens 9 and the second reflector 10 are placed in sequence on the same straight line. The first lens 7 is placed at a focal length interval from the spatial light modulator 6, the pinhole diaphragm 8 is placed at a focal length interval from the spatial light modulator 6, the first lens 7 ... and the second reflector 10 is placed at a focal length interval from the spatial light modulator 6. The focal lengths of all the lenses are the focal length of the first lens 7.

[0015] The first lens 7 and the second lens 9 are both lenses with a focal length of 100 mm, and the diameter of the pinhole aperture 8 is 1 mm to 12 mm.

[0016] The first lens 7 and the second lens 9 form a first 4f system, which cooperates with the blazed grating and the pinhole aperture 8 to filter out the zero-order diffraction light and adjust the optical path;

[0017] When the phase hologram of the blazed grating is loaded on the spatial light modulator 6, the blazed angle is designed to allow all the modulated Bessel light beams to enter the +1 diffraction order, and then be focused by the first lens 7 in the first 4f system, so that the Bessel light beam and the zero-order diffraction light are separated by a certain distance radially on the focal plane of the first lens 7, and then the physical shielding of the pinhole aperture 8 is used to filter out interference light such as the zero-order diffraction light.

[0018] The computer controller 19 is connected to the CCD camera 18, the three-dimensional motion platform 17, the spatial light modulator 6 loaded with the blazed grating and the ultrafast laser 1;

[0019] They are used to control the identification and positioning of micropores on the surface of the target material and the observation of the beam energy, the movement of the three-dimensional motion platform 17, the compilation and loading of the hologram on the spatial light modulator 6, and the parameter setting of the ultrafast laser.

[0020] The beam focusing system comprises a third reflector 11, a third lens 12, a fourth reflector 13, and a fourth lens 15 which are arranged in sequence; the third lens 12 and the fourth lens 15 form a second 4f system for beam contraction and focusing of the Bessel beam;

[0021] A third lens 12 is placed behind the third reflector 11 , a fourth reflector 13 is placed behind the third lens 12 , and a fourth lens 15 is placed at a coaxial position of the light beam reflected by the fourth reflector 13 .

[0022] The coaxial vision system includes a long-wave pass dichroic mirror 14, an annular white light source 20 and a CCD camera 18;

[0023] The long-wave pass dichroic mirror 14 is used to transmit 1030nm long-wave pass infrared laser and reflect white light; the annular white light source 20 is used to provide lighting; the CCD camera 18 is used to photograph the micropores on the surface of the narrow cavity structural component 16 from the coaxial position of the light beam after the white light emitted from the annular white light source 20 is reflected by the reflecting surface of the long-wave pass dichroic mirror 14.

[0024] During the hole repairing process, the laser beam output by the ultrafast laser 1 passes through the half-wave plate 2, the Glan Taylor prism 3, the beam expander 4, the first reflector 5, the spatial light modulator 6 loaded with the blazed grating, the first lens 7, the pinhole diaphragm 8, the second lens 9, the second reflector 10, the third reflector 11, the third lens 12, the fourth reflector 13 and the long-wave pass dichroic mirror 14 in sequence, and is incident on the fourth lens 15 for focusing; the laser beam output by the fourth lens 15 acts on the narrow cavity structure 16 for hole repairing.

[0025] A laser hole repair method for narrow cavity structural parts without back wall damage comprises the following steps:

[0026] Step 1: Load the narrow cavity structure 16 material onto the three-dimensional motion platform 17;

[0027] Step 2, determining laser processing parameters according to the micro-hole processing diameter on the surface of the narrow cavity structural component material and the thickness of the processing area, and using the laser hole repairing system without rear wall damage of the narrow cavity structural component 16 to process the blade;

[0028] Step 3: Obtain a Bessel beam with a focal depth of 1 mm by regulating the hologram loaded on the spatial light modulator 6 loaded with the blazed grating;

[0029] The phase transfer function of the Bessel beam with uniform axial energy distribution is calculated by analytical method, and after being encoded into a phase hologram by computer controller 19, it is loaded into the spatial light modulator to generate a Bessel beam, and then the Bessel beam is smoothed and oscillated by using a sinusoidal apodization function and a Gaussian apodization function respectively. The amplitude transfer function is obtained by superposition of the two functions, and then the complex amplitude transfer function is obtained by using a blazed grating, which is encoded into a hologram by computer controller 19, and loaded into the spatial light modulator 6 to realize complex amplitude modulation, and finally a Bessel beam with axial energy distribution that first rises, then becomes uniform, and then falls is obtained;

[0030] Step 4: The micro-hole position to be processed in the narrow cavity structural part 16 is repaired by using a Bessel beam with a focal depth of 1 mm obtained from the beam shaping system and focused by the beam focusing system until the aperture reaches the maximum value that can be repaired by the Bessel beam with a focal depth of 1 mm; the maximum value is the aperture value at which the micro-hole outlet diameter almost stops increasing with the increase of processing time;

[0031] Step 5: Replace the hologram loaded on the spatial light modulator 6 loaded with the blazed grating to obtain a Bessel beam with a focal depth of 2.5 mm;

[0032] Step 6: Use a Bessel beam with a focal depth of 2.5 mm to continue shaping the microholes obtained in the previous step until a complete microhole is machined, then stop the machining to obtain high-quality microholes on the surface of the narrow cavity structural part 16 without rear wall damage;

[0033] Step 7: After the processing is completed, remove the narrow cavity structure 16 and shut down all equipment.

[0034] Beneficial effects of the present invention:

[0035] The present invention uses a Bessel light beam whose axial energy distribution first rises, then becomes uniform, and then decreases to perform laser hole repair without rear wall damage of a narrow cavity structural component. The phase distribution function of the Bessel light beam with uniform axial intensity distribution is derived by compiling on a computer controller using an analytical method, and the phase distribution function is smoothed and oscillated by using a trace optimization method. The blazed grating is used for amplitude modulation, and the required hologram is encoded and generated together. The hologram is then loaded through a spatial light modulator in a beam shaping system, so that the light beam transmitted by the beam transmission system obtains a Bessel light beam with short focal depth and axial energy distribution first rises, then becomes uniform, and then decreases after passing through the spatial light modulator. The light beam is finally focused on a microhole on the surface of a target material through all optical elements in a subsequent system, and the microhole is preliminarily repaired. The above operation is repeated on the computer controller according to the aperture result after the preliminarily repaired, and a suitable hologram is generated and then loaded on the spatial light modulator in the beam shaping system to obtain a Bessel light beam with long focal depth, and the microhole is finally repaired. By combining and using Bessel beams with different focal depths to perform step-by-step shaping of micropores on the surface of narrow cavity structural parts, not only can complete micropores be efficiently shaped, but also, without filling protective materials into the cavity, narrow cavity structural parts can be processed without back wall damage.

[0036] With a simpler and more operable optical path design system, the required optical parameters and laser parameters can be selected during design and selection, which is also convenient for later maintenance and replacement, effectively reducing the complexity of design and the cost of use. In addition, the spatial light modulator has the flexibility to generate Bessel beams with different parameters, greatly improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a laser hole repair system for narrow cavity structural parts without back wall damage described in the present invention.

[0038] Figure 2 Schematic diagram of the beam scanning trajectory of the step-by-step hole repairing by combining two Bessel beams with different focal depths according to the present invention, Figure 2 (a) is the scanning trajectory of the Bessel beam with a focal depth of 1 mm. Figure 2 (b) is the scanning trajectory of the Bessel beam with a focal depth of 2.5 mm.

[0039] Figure 3 This is an electron microscope image of the entrance, side profile, exit and rear wall of the air film hole of a blade as an example of the step-by-step shaping by combining and using Bessel beams with different focal depths as described in the present invention. Figure 3 (a) is the entrance, Figure 3 (b) is the side section, 3(c) is the outlet, and 3(d) is the rear wall of the cavity.

[0040] The reference numerals are as follows:

[0041] 1. Ultrafast laser, 2. Half-wave plate, 3. Glan-Taylor prism, 4. Beam expander, 5. First reflector, 6. Spatial light modulator loaded with blazed grating, 7. First lens, 8. Pinhole diaphragm, 9. Second lens, 10. Second reflector, 11. Third reflector, 12. Third lens, 13. Fourth reflector, 14. Long-wave pass dichroic mirror, 15. Fourth lens, 16. Narrow cavity structure, 17. Three-dimensional motion platform, 18. CCD camera, 19. Computer controller, 20. Ring-shaped white light source. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0043] The purpose of the present invention is to provide a laser hole repair system and method for narrow cavity structural parts without back wall damage, to solve the problem of back wall damage existing in the current laser processing of narrow cavity materials such as aero-engine blade air film holes and fuel injectors, and to promote the application of laser processing technology in the field of narrow cavity material processing.

[0044] See also Figure 1 The present invention provides a laser hole repair system for narrow cavity structural parts without back wall damage, including an ultrafast laser 1, a beam transmission system, a beam shaping system, a beam focusing system, a coaxial vision system, a three-dimensional motion platform 17 and a computer controller 19;

[0045] The three-dimensional motion platform 17 is used to place the narrow cavity structure 16 to be processed, and can drive the narrow cavity structure 16 to be processed to move in three directions: x, y, and z; the coaxial vision system is used to identify and locate the micropores on the surface of the narrow cavity structure 16; the beam focusing system is used to shrink and focus the Bessel beam, and output the Bessel beam to the micropores on the surface of the narrow cavity structure 16 on the three-dimensional motion platform 17, so as to modify the micropores;

[0046] The ultrafast laser 1 provides a femtosecond laser beam for the entire system. After the laser beam is transmitted through the beam transmission system, the beam is transmitted to the beam shaping system to obtain a Bessel beam after shaping optimization. The beam is then focused and contracted by the beam focusing system to the micropores on the surface of the target material of the narrow cavity structure 16 on the high-precision three-dimensional mobile platform 17 for hole repair. The entire process of hole repair is observed by the coaxial vision system.

[0047] The ultrafast laser 1 is a femtosecond laser, and the laser emitted is a Gaussian beam.

[0048] The beam transmission system includes a half-wave plate 2, a Glan Taylor prism 3, a beam expander 4 and a first reflector 5 which are arranged in sequence; wherein the half-wave plate 2 and the Glan Taylor prism 3 are arranged in sequence, and the light beam first passes through the half-wave plate 2 and then passes through the Glan Taylor prism 3, which is used to adjust the polarization direction of the input laser beam and filter out all the s-component light; the polarization direction of the input laser beam can be adjusted by rotating the half-wave plate 2. Although the polarization direction of most of the incident laser beam can be adjusted, it is still impossible to adjust all the components of the incident light to p-component light. After the laser beam is adjusted by the half-wave plate 2, there will still be some s-component light. After the laser beam is reflected on the liquid crystal spatial light modulator, the part of the s-component light will be transmitted along the optical axis and become interference light. Therefore, after the half-wave plate 2, the Glan Taylor prism 3 is used to separate the p-component light and the s-component light, and the s-component light is completely filtered out to prevent it from becoming noise light, so as to ensure that the light incident on the liquid crystal spatial light modulator is all p-component light, and the incident light energy can also be adjusted steplessly.

[0049] The half-wave plate 2 is a quartz air-gap zero-order wave plate, and its design wavelength is 1030nm, which is consistent with the laser wavelength. The Glan-Taylor prism 3 has a clear aperture of 10mm and an operating wavelength of 200nm-3.0μm. The beam expander 4 is a 1-4 times adjustable coaxial beam expander.

[0050] The beam shaping system comprises a spatial light modulator 6 loaded with a blazed grating, a first lens 7, a pinhole aperture 8, a second lens 9 and a second reflector 10 which are arranged in sequence;

[0051] The spatial light modulator 6 loaded with the blazed grating is used to dynamically control the laser light field distribution, and to shape the ultrashort pulse laser beam transmitted by the beam transmission system into a Bessel beam whose axial energy distribution first rises, then becomes uniform, and then decreases. Principle: The phase transfer function of the Bessel beam with uniform axial energy distribution is calculated by the analytical method, and the phase transfer function is:

[0052]

[0053] is the phase function, R——phase hologram radius / mm; Z1——Bessel beam energy axis starting position / mm; Z2——Bessel beam energy axis ending position / mm; R——phase hologram radius / mm; C0——constant; λ——wavelength / nm;

[0054] The phase transfer function is encoded into a phase hologram using a computer controller 19 and loaded into a spatial light modulator 6 to generate a Bessel beam. The Bessel beam is then smoothed and oscillated using a sine apodization function and a Gaussian apodization function. The amplitude transfer function is obtained by superimposing the two functions. The sine apodization function is:

[0055]

[0056] Among them, Δ z is the apodization interval;

[0057] The Gaussian amplitude apodization function is

[0058]

[0059] Among them, the center radius r0 = (r3 + r2) / 2, the radial half width Dr = (r3 - r2) / 2, Δ r is corresponding to Δ z Radial custom parameters of;

[0060] The complex amplitude transfer function is obtained by using the blazed grating. The complex amplitude transfer function is:

[0061]

[0062] in, is the function of phase modulation depth with respect to pixel position, m is the diffraction order;

[0063] It is encoded into a hologram by a computer controller 19 and loaded onto a liquid crystal spatial light modulator 6 to achieve complex amplitude modulation, and finally a Bessel beam is obtained in which the axial energy distribution first rises, then becomes uniform, and then falls, so as to better meet the requirements of laser hole repairing;

[0064] The spatial light modulator 6 is a X15213-03BL reflective pure phase liquid crystal spatial light modulator produced by Hamamatsu Corporation of Japan. The number of pixels is 1272×1024, the pixel size is 12.5μm, and the effective area of ​​the liquid crystal panel is 15.9×12.8mm 2 .

[0065] The spatial light modulator 6, the first lens 7, the pinhole diaphragm 8, the second lens 9 and the second reflector 10 are placed in sequence on the same straight line. The first lens 7 is placed at a distance of one focal length from the spatial light modulator 6, the pinhole diaphragm 8 is placed at a distance of one focal length, the first lens 7 is placed at a distance of one focal length, and the second reflector 10 is placed at a distance of one focal length.

[0066] The first lens 7 and the second lens 9 are both lenses with a focal length of 100 mm, and the diameter of the pinhole aperture 8 is 1 mm to 12 mm.

[0067] The first lens 7 and the second lens 9 form a first 4f system, which cooperates with the blazed grating and the pinhole aperture 8 to filter out the zero-order diffraction light and adjust the optical path;

[0068] When the phase hologram of the blazed grating is loaded on the spatial light modulator 6, the blazed angle can be designed to allow all the modulated Bessel light beams to enter the +1 diffraction order. After being focused by the first lens 7 in the first 4f system, the Bessel light beam and the zero-order diffraction light are radially separated by a certain distance on the focal plane of the first lens 7. Subsequently, the physical blocking of the pinhole aperture is used to filter out interference light such as the zero-order diffraction light.

[0069] The computer controller 19 is used to connect the CCD camera 18, the three-dimensional motion platform 17, the spatial light modulator 6 loaded with the blazed grating, and the ultrafast laser 1;

[0070] After connection, they are used to control the identification and positioning of micropores on the surface of the target material and the observation of the beam energy, the movement of the three-dimensional motion platform 17, the compilation and loading of the hologram on the spatial light modulator 6 loaded with the blazed grating, and the setting of the parameters of the ultrafast laser.

[0071] The computer controller 19 is used to control the CCD camera 18 to observe the micro-holes of the narrow cavity structure 16 and measure the beam energy, move the three-dimensional motion platform 17, compile and load the hologram on the spatial light modulator 6 loaded with the blazed grating, and set the parameters of the ultrafast laser 1;

[0072] The beam focusing system comprises a third reflector 11, a third lens 12, a fourth reflector 13, and a fourth lens 15 which are arranged in sequence; the third lens 12 and the fourth lens 15 form a second 4f system for beam contraction and focusing of the Bessel beam;

[0073] A third lens 12 is placed behind the third reflector 11 , a fourth reflector 13 is placed behind the third lens 12 , and a fourth lens 15 is arranged behind the fourth reflector 13 on the straight line where the light beam reflected by the fourth reflector 13 is located.

[0074] The coaxial vision system includes a long-wave pass dichroic mirror 14, an annular white light source 20 and a CCD camera 18;

[0075] The long-wave pass dichroic mirror 14 is used to transmit 1030nm long-wave pass infrared laser and reflect white light; the annular white light source 20 is used to provide lighting.

[0076] A long-wave-pass dichroic mirror 14 , a fourth lens 15 , and an annular white light source 20 are sequentially placed on the same straight line; a CCD camera is placed on a bypass of the long-wave-pass dichroic mirror 14 on the same straight line.

[0077] During the hole repairing process, the laser beam output by the ultrafast laser 1 passes through the half-wave plate 2, the Glan Taylor prism 3, the beam expander 4, the first reflector 5, the spatial light modulator 6 loaded with the blazed grating, the first lens 7, the pinhole diaphragm 8, the second lens 9, the second reflector 10, the third reflector 11, the third lens 12, the fourth reflector 13 and the long-wave pass dichroic mirror 14 in sequence, and is incident on the fourth lens 15 for focusing; the laser beam output by the fourth lens 15 acts on the narrow cavity structure 16 for hole repairing.

[0078] The three-dimensional motion platform 17 has a travel of 60 mm in the x and y directions and a travel of 30 mm in the axial z direction, with an accuracy of 0.01 mm.

[0079] The present invention provides a laser hole repair method for narrow cavity structural parts without back wall damage, comprising the following steps:

[0080] Step 1: Load the narrow cavity structure 16 material onto the three-dimensional motion platform 17;

[0081] Step 2, determining laser processing parameters according to the micro-hole processing diameter on the surface of the narrow cavity structural component material and the thickness of the processing area, and using the laser hole repairing system without rear wall damage of the narrow cavity structural component 16 to process the blade;

[0082] Step 3: Obtain a Bessel beam with a focal depth of 1 mm by regulating the hologram loaded on the spatial light modulator 6 loaded with the blazed grating;

[0083] The phase transfer function of the Bessel beam with uniform axial energy distribution is calculated by analytical method, and after being encoded into a phase hologram by computer controller 19, it is loaded into a spatial light modulator to generate a Bessel beam, and then the Bessel beam is smoothed and oscillated by a sine apodization function and a Gaussian apodization function respectively. The amplitude transfer function is obtained by superposition of the two functions, and then the complex amplitude transfer function is obtained by using a blazed grating, which is encoded into a hologram by computer controller 19, and loaded into a spatial light modulator to realize complex amplitude modulation, and finally a Bessel beam with axial energy distribution that first rises, then becomes uniform, and then falls is obtained;

[0084] Step 4: The micro-hole position to be processed in the narrow cavity structural part 16 is repaired by using a Bessel beam with a focal depth of 1 mm obtained from the beam shaping system and focused by the beam focusing system until the aperture reaches the maximum value that can be repaired by the Bessel beam with a focal depth of 1 mm; the maximum value is the aperture value at which the micro-hole outlet diameter almost stops increasing with the increase of processing time;

[0085] Step 5: Replace the hologram loaded on the spatial light modulator 6 loaded with the blazed grating to obtain a Bessel beam with a focal depth of 2.5 mm;

[0086] Step 6: Use a Bessel beam with a focal depth of 2.5 mm to continue shaping the microholes obtained in the previous step until a complete microhole is machined, then stop the machining to obtain high-quality microholes on the surface of the narrow cavity structural part 16 without rear wall damage;

[0087] Step 7: After the processing is completed, remove the narrow cavity structure 16 and shut down all equipment.

[0088] Purpose: The efficiency of micro-hole shaping using only a Bessel beam with a focal depth of 2.5 mm is low. Although a Bessel beam with a focal depth of 1 mm cannot shape a complete micro-hole outlet. However, the shorter the focal depth of the Bessel beam, the higher the processing efficiency during shaping. Under unsaturated conditions, the outlet diameter of the micro-hole shaped in the same time is also larger. In contrast, although a Bessel beam with a focal depth of 2.5 mm can shape a micro-hole with a complete outlet, its processing efficiency is the lowest. Therefore, in order to improve the processing efficiency while shaping a complete micro-hole, two Bessel beams with different focal depths can be used in combination. Due to the flexibility of the SLM itself, different Bessel beams can be obtained by simply changing the loaded hologram on the computer without performing any other operations. It is very simple and convenient, and the process can be completed in just a few seconds. Therefore, this method of using Bessel beams with different focal depths for micro-hole shaping is not only feasible, but also can greatly improve efficiency.

[0089] In step 1, the narrow cavity structure 16 may be made of a material having a narrow cavity, such as a blade material such as a nickel-based alloy with a thermal barrier coating, a titanium alloy, and silicon carbide, and a fuel injection nozzle material such as stainless steel.

[0090] In step 4, the process conditions for modifying the micropores on the surface of the narrow cavity structure 16 are:

[0091] The repetition rate of the femtosecond laser is 100kHz, the single pulse energy is 5 / μJ, and the pulse width is 225fs;

[0092] The scanning path of the Bessel light beam with a focal depth of 1 mm adopts concentric circles, the maximum diameter of the concentric circles is 290 μm, and the scanning speed is 0.3 mm / s.

[0093] In step 6, the process conditions for modifying the micropores on the surface of the narrow cavity structure are:

[0094] The repetition rate of the femtosecond laser is 100kHz, the single pulse energy is 5 / μJ, and the pulse width is 225fs;

[0095] The scanning path of the Bessel light beam with a focal depth of 2.5 mm adopts concentric circles, the maximum diameter of the concentric circles is 290 μm, the minimum diameter of the concentric circles is 180 μm, and the scanning speed is 0.3 mm / s.

[0096] In order to solve the problem of back wall damage in the current laser processing of narrow cavity structures, the present invention provides a laser hole repair system and method for narrow cavity structures without back wall damage, which uses a spatial light modulator loaded with a blazed grating to regulate the laser light field distribution, and obtains a Bessel light beam with an axial energy distribution that first rises, then becomes uniform, and then decreases. Then, Bessel light beams with different focal depths are combined to perform step-by-step repair of micropores on the surface of the narrow cavity structure, thereby achieving the repair of micropores on the surface of the narrow cavity structure while reducing damage to the back wall material, thereby solving the problem of back wall damage in the process of laser processing narrow cavity structures.

[0097] Example

[0098] Taking the laser processing of blade air film holes as an example, 0.5mm nickel-based alloy is used as the narrow cavity structural material, and the cavity thickness is 0.5mm. At this time, the blade air film hole is a blind hole with a diameter of 0.3mm and a depth of 0.5mm. The main steps include:

[0099] Step 1: Load the blade material onto the three-dimensional motion platform;

[0100] Step 2: Determine the laser processing parameters according to the processing diameter of the air film hole on the blade material surface and the thickness of the blade processing area, and use the laser hole repair system without rear wall damage of the narrow cavity structure to process the blade;

[0101] Step 3: Obtain a Bessel beam with a focal depth of 1 mm by regulating the hologram loaded on the spatial light modulator loaded with the blazed grating;

[0102] Step 4: The position of the air film hole to be processed on the blade is repaired using a Bessel beam with a focal depth of 1 mm obtained from the beam shaping system and focused by the beam focusing system. The repair takes 7 minutes, and the obtained air film hole has an outlet diameter of about 190 μm. The scanning trajectory of the 1 mm focal depth Bessel beam is as follows: Figure 2 (a)

[0103] Step 5: Replace the hologram loaded on the spatial light modulator loaded with the blazed grating to obtain a Bessel beam with a focal depth of 2.5 mm;

[0104] Step 6: Based on the results of the first step, continue the shaping using a Bessel beam with a focal depth of 2.5 mm until a complete air film hole is machined after 20 minutes of shaping. Stop the processing and achieve efficient shaping of the blade air film hole without rear wall damage under a cavity gap of 0.5 mm. Figure 2 (b) is the scanning trajectory of the Bessel beam with a focal depth of 2.5 mm. Figure 3 The electron microscope images of the entrance, side profile, exit and back wall of the blade air film hole during the hole repair process using a Bessel beam with a focal depth of 2.5 mm. It can be seen that a complete air film hole was obtained, and the back wall of the cavity was not damaged during the entire repair process.

[0105] Step 7: After processing, remove the blade material and shut down all equipment.

[0106] Although ultrafast lasers, beam transmission systems, beam shaping systems, beam focusing systems, coaxial vision systems, three-dimensional motion platforms, computer controllers, spatial light modulators, half-wave plates, Glan-Taylor prisms, long-wave pass dichroic mirrors, narrow cavity structures, lenses, annular white light sources, CCD cameras, reflectors, beam expanders, pinhole apertures, etc. are used more frequently in this specification, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe the essence of the present invention. Interpreting them as any additional limitations is contrary to the spirit of the present invention.

[0107] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0108] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A laser hole repair system for narrow cavity structural parts without back wall damage, characterized in that: It comprises an ultrafast laser (1), a beam transmission system, a beam shaping system, a beam focusing system, a coaxial vision system, a three-dimensional motion platform (17) and a computer controller (19); a narrow cavity structure (16) to be processed is arranged on the three-dimensional motion platform (17); The ultrafast laser (1) provides a femtosecond laser beam for the entire system. The laser beam is transmitted to the beam shaping system via the beam transmission system to obtain a Bessel beam after shaping optimization. The beam is then focused and contracted by the beam focusing system to the micropores on the surface of the target material of the narrow cavity structural part (16) on the three-dimensional motion platform (17) for hole repair. The entire hole repair process is observed via a coaxial visual system. The three-dimensional motion platform (17) can drive the narrow cavity structure (16) to move in three directions: x, y, and z; the coaxial vision system is used to identify and locate the micro-hole Bessel light beam on the surface of the narrow cavity structure (16); The beam shaping system comprises a spatial light modulator (6), a first lens (7), a pinhole aperture (8), a second lens (9) and a second reflector (10) which are sequentially arranged along the direction of the beam; The spatial light modulator (6) is loaded with a blazed grating and is used to dynamically control the laser light field distribution, so as to shape the ultrashort pulse laser beam transmitted by the beam transmission system into a Bessel beam whose axial energy distribution first rises, then becomes uniform, and then falls. The spatial light modulator (6), the first lens (7), the pinhole diaphragm (8), the second lens (9) and the second reflector (10) are placed in sequence on the same straight line. The first lens (7) is placed at a focal length from the spatial light modulator (6), the pinhole diaphragm (8) is placed at a focal length from the spatial light modulator (6), the first lens (7) is placed at a focal length from the pinhole diaphragm (8), the first lens (7) is placed at a focal length from the pinhole diaphragm (8), and the second lens (10) is placed at a focal length from the pinhole diaphragm (8). The focal lengths of the first lens (7) and the second reflector (10) are all the same.

2. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 1, characterized in that: The light beam transmission system comprises a half-wave plate (2), a Glan Taylor prism (3), a beam expander (4) and a first reflector (5) which are arranged in sequence along the direction of the light beam; wherein the half-wave plate (2) and the Glan Taylor prism (3) are arranged in sequence, and the light beam first passes through the half-wave plate (2) and then passes through the Glan Taylor prism (3), which is used to adjust the polarization direction of the input laser beam and filter out all s component light; after the half-wave plate (2), the Glan Taylor prism (3) is used to separate the p component light and the s component light, and to filter out all the s component light, so as to ensure that the light incident on the liquid crystal spatial light modulator is all p component light, and the incident light energy can also be adjusted steplessly, and the beam expander (4) is used to expand the incident light beam to 4 times.

3. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 2, characterized in that: The ultrafast laser (1) is a femtosecond laser, and the laser emitted is a Gaussian beam. The half-wave plate (2) is a quartz air-gap zero-order wave plate, and its design wavelength is 1030nm, which is consistent with the laser wavelength. The Glan-Taylor prism (3) has a light aperture of 10mm and an operating wavelength of 200nm-3.0μm. The beam expander (4) is a 1-4 times adjustable coaxial beam expander.

4. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 1, characterized in that: The first lens (7) and the second lens (9) are both lenses with a focal length of 100 mm, and the diameter of the pinhole aperture (8) is 1 mm to 12 mm; The first lens (7) and the second lens (9) form a first 4f system, which cooperates with the blazed grating and the pinhole aperture (8) to filter out zero-order diffraction light and adjust the optical path; When a phase hologram of a blazed grating is loaded on a spatial light modulator (6), the blazed angle is designed so that all modulated Bessel light beams enter the +1 diffraction order. After being focused by the first lens (7) in the first 4f system, the Bessel light beam and the zero-order diffraction light are separated by a certain distance along the radial direction on the focal plane of the first lens (7). Subsequently, physical shielding of a pinhole aperture is used to filter out interference light such as the zero-order diffraction light.

5. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 1, characterized in that: The computer controller (19) is connected to a CCD camera (18), a three-dimensional motion platform (17), a spatial light modulator (6) loaded with a blazed grating, and an ultrafast laser (1); They are respectively used to control the identification and positioning of micropores on the surface of the target material and the observation of the beam energy, the movement of the three-dimensional motion platform (17), the compilation and loading of the hologram on the spatial light modulator (6), and the parameter setting of the ultrafast laser.

6. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 1, characterized in that: The beam focusing system comprises a third reflector (11), a third lens (12), a fourth reflector (13), and a fourth lens (15) which are arranged in sequence; the third lens (12) and the fourth lens (15) form a second 4f system for beam contraction and focusing of the Bessel beam; A third lens (12) is placed behind the third reflector (11), a fourth reflector (13) is placed behind the third lens (12), and a fourth lens (15) is placed at a coaxial position of the light beam reflected by the fourth reflector (13).

7. The laser hole repairing system for narrow cavity structural parts without back wall damage according to claim 1, characterized in that: The coaxial visual system comprises a long-wave pass dichroic mirror (14), an annular white light source (20) and a CCD camera (18); The long-wave pass dichroic mirror (14) is used to transmit 1030nm long-wave pass infrared laser and reflect white light; the annular white light source (20) is used to provide lighting; and the CCD camera (18) is used to photograph the micropores on the surface of the narrow cavity structural component (16) at a coaxial position of the light beam after the white light emitted by the annular white light source (20) is reflected by the reflection surface of the long-wave pass dichroic mirror (14).

8. A laser hole repair method for narrow cavity structural parts without back wall damage based on the system according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Load the narrow cavity structure (16) material onto the three-dimensional motion platform (17); Step 2, determining laser processing parameters according to the micro-hole processing diameter and processing area thickness of the narrow cavity structure (16) material surface, and processing the blade using a laser hole repair system without rear wall damage of the narrow cavity structure (16); Step 3: Obtain a Bessel beam with a focal depth of 1 mm by regulating the hologram loaded on the spatial light modulator (6) loaded with the blazed grating; The phase transfer function of the Bessel beam with uniform axial energy distribution is calculated by analytical method, and is encoded into a phase hologram by a computer controller (19). The phase hologram is then loaded into a spatial light modulator to generate a Bessel beam. The Bessel beam is then smoothed and oscillated by a sinusoidal apodization function and a Gaussian apodization function respectively. The two functions are superimposed to obtain an amplitude transfer function. The complex amplitude transfer function is then obtained by using a blazed grating. The complex amplitude transfer function is encoded into a hologram by a computer controller (19). The hologram is loaded into a spatial light modulator (6) to realize complex amplitude modulation. Finally, a Bessel beam with an axial energy distribution that first rises, then becomes uniform, and then falls is obtained. Step 4: The micro-hole position to be processed in the narrow cavity structural part (16) is repaired by using a Bessel beam with a focal depth of 1 mm obtained from the beam shaping system and focused by the beam focusing system until the aperture reaches the maximum value that can be repaired by the Bessel beam with a focal depth of 1 mm; the maximum value is the aperture value at which the micro-hole outlet diameter almost stops increasing with the increase of processing time; Step 5: Replace the hologram loaded on the spatial light modulator (6) loaded with the blazed grating to obtain a Bessel beam with a focal depth of 2.5 mm; Step 6: Use a Bessel beam with a focal depth of 2.5 mm to continue shaping the microhole obtained in the previous step until a complete microhole is machined, then stop the machining to obtain a high-quality microhole on the surface of a narrow cavity structural part (16) without rear wall damage; Step 7: After processing is completed, remove the narrow cavity structure (16) and shut down all equipment.

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