A method and device for preparing a low-friction surface by laser-induced cavitation micro-pit array

Abstract

The application provides a method and device for preparing a low-friction surface by means of a laser-induced cavitation micro-pit array, and relates to the technical field of laser micro-molding. A workpiece is placed in a glass water tank filled with a liquid medium, the surface to be processed of the workpiece is horizontally upward and is coated with an absorbing layer, a laser beam is vertically downward into the liquid medium, the focal point of the laser beam is above the workpiece and forms a light spot on the surface to be processed of the workpiece, a single cavitation bubble is induced in the light spot area of the surface to be processed of the workpiece, the laser plasma shock wave, the laser cavitation collapse shock wave and the micro-jet generated by the single cavitation bubble jointly act on the surface to be processed of the workpiece, the material is impacted and compacted to generate a micro-pit; the electric three-dimensional moving platform drives the workpiece to move according to a set path, the laser beam repeatedly acts according to the pulse width, the micro-pit array is formed on the surface to be processed of the workpiece, and the low-friction surface of the workpiece is obtained. The application forms a regular micron-level micro-pit array on the surface of the workpiece, and improves the friction and wear performance of the low-friction surface of the workpiece.

Description

Technical Field

[0001] This invention relates to the field of laser microforming technology, and in particular to a method and apparatus for preparing a friction-reducing surface using a laser-induced array of cavitation micro-pits. Background Technology

[0002] Laser-induced cavitation is a novel material surface modification technology. Laser-induced cavitation typically involves plasma formation and shock wave release. Cavitation bubbles collapsing near the wall surface are accompanied by micro-jets, which act on the workpiece, creating localized gradient micro-deformations on its surface. Laser surface micro-machining technology is a new micro-dimple processing technique developed based on laser shock peening technology, combining the concept of laser micro-textured arrays.

[0003] Chinese patent CN104175001B discloses a laser micro-pit array manufacturing apparatus and method. This method utilizes a laser beam penetrating a water layer. Part of the laser beam passes through the mesh of a flat mesh, ablating the flexible film and the workpiece surface to form micro-pits and a large amount of splashed slag. The other part of the laser beam is blocked and absorbed by an absorption layer, generating a plasma explosion that forms a shock wave. This shock wave tightly adheres the flat mesh, flexible film, and workpiece surface together, preventing slag from entering the workpiece surface outside the laser irradiation area. The essential physical process of this method remains the direct ablation of the material surface by the laser, removing material and forming micropores.

[0004] Chinese patent CN107984086B discloses a method for fabricating ultra-micro pores based on laser-induced cavitation collapse water jets. This method utilizes a laser beam to generate cavitation clusters on the workpiece surface. The high-pressure water jet generated by the collapse of these cavitation clusters acts on the workpiece surface, eroding and removing the material in the affected area to form ultra-micro pores. However, this method of preparing ultra-micro pores using cavitation clusters suffers from several drawbacks. The shapes of the cavitation clusters cannot be kept consistent, and their positions after collapse are uncertain. Several cavitation clusters may overlap or overlap and act on the same location, making it impossible to guarantee the uniformity of the ultra-micro pore quality.

[0005] Chinese Patent CN114734139B discloses a laser cavitation micro-machining device and its processing method suitable for internal wall components. This method utilizes the transient mechanical effect of cavitation bubbles generated by laser cavitation to perform micro-machining of the internal wall region while simultaneously changing the liquid medium. However, in this scheme, the laser beam is parallel to the surface to be processed, and the cavitation bubbles do not directly act on the processing surface. The position and collapse point of the generated gas bubbles are uncontrollable. Furthermore, the water hammer pressure generated by the collapse of gas bubbles induced near the workpiece's side surface is only on the order of MPa, which is insufficient to cause plastic deformation and the formation of micro-pits in materials with high yield strength, such as E690 high-strength steel. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array. This method utilizes a laser to penetrate a liquid perpendicularly onto the workpiece surface, forming cavitation bubbles on the absorption layer of the workpiece surface. The laser plasma shock wave, laser cavitation bubble collapse shock wave, and micro-jets generated by these individual cavitation bubbles act on the workpiece surface. The laser plasma shock wave and laser cavitation bubble collapse shock wave can reach the GPa level, causing localized plastic micro-deformation on the material surface to produce regular individual micro-pits. Simultaneously, it avoids the adverse effects of laser ablation on the workpiece surface performance. Furthermore, by moving the workpiece, a regular micron-scale micro-pit array is formed on the workpiece surface, providing oil storage and lubrication while ensuring a sufficiently large contact area for the friction pair, thereby reducing friction and wear and improving the friction and wear performance of the friction pair on the workpiece's friction-reducing surface.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0008] A method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array involves placing a workpiece in a glass tank filled with a liquid medium. The workpiece's surface to be processed is horizontal and coated with an absorption layer. The glass tank is placed on an electrically driven three-dimensional moving platform. A laser beam is vertically injected into the liquid medium of the glass tank through a laser-induced cavitation generation system. The focal point of the laser beam is located above the workpiece and forms a spot on the workpiece's surface to be processed. The laser beam induces individual cavitation bubbles in the spot area on the workpiece's surface. The laser plasma shock wave, laser cavitation bubble collapse shock wave, and micro-jets generated by the induced individual cavitation bubbles act together on the workpiece's surface to be processed, impacting and compacting the material at the corresponding positions on the workpiece's surface to create micro-pits. The electrically driven three-dimensional moving platform moves the workpiece along a set path, and the laser beam acts repeatedly according to the pulse width, forming a micro-pit array on the workpiece's surface to be processed, resulting in a workpiece friction-reducing surface with a micro-texture.

[0009] Furthermore, the vertical distance between the focal point of the laser beam and the surface to be processed on the workpiece is H. According to the required size of the micro-dimple, the workpiece is moved and raised by an electric three-dimensional moving platform to adjust the value of H, thereby adjusting the diameter of the laser spot formed on the surface to be processed on the workpiece, and the diameter of the laser spot is less than 500μm.

[0010] Furthermore, by adjusting the laser energy and the number of laser impacts of the laser beam through a laser-induced cavitation generation system, micro-pits of the desired depth can be obtained.

[0011] Furthermore, the absorption layer is an 80μm black paint layer. After the micro-pit array on the workpiece surface to be processed is completed, the absorption layer is cleaned.

[0012] Furthermore, a high-speed camera was used to capture a sequence of cavitation pulsation processes to analyze the pulsation characteristics of cavitation expansion-contraction-collapse; a hydrophone was used to collect and process the sound pressure signals that induce cavitation, and an oscilloscope was used to process and display the sound pressure signals as waveforms in which the voltage values ​​corresponding to each sound signal can be directly read.

[0013] Furthermore, the mechanical effects of the shock wave and microjets generated by laser-induced cavitation on the workpiece surface were analyzed and determined, and compared with the morphology of the prepared micro-pits. The relationship between the laser-induced cavitation shock wave and microjets and the morphology of the micro-pits was analyzed, and the quantitative relationship between the process parameters and the micron-scale micro-pit size was obtained.

[0014] A device for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, used in the above preparation method, includes an electric three-dimensional moving platform, a glass water tank, a laser-induced cavitation generation system, a cavitation pulsation image observation system, and a dynamic mechanical effect detection system. The glass water tank is placed on the electric three-dimensional moving platform and filled with a liquid medium. The workpiece is placed in the glass water tank with its surface to be processed facing upward and coated with an absorption layer.

[0015] The laser-induced cavitation generation system includes a laser controller, a laser, a concave lens, a first convex lens, a climbing frame, a lower reflector, an upper reflector, a side reflector, and a second convex lens. The laser controller is connected to the laser. The concave lens and the first convex lens are vertically positioned between the laser and the lower reflector, with the concave lens closer to the laser and the first convex lens closer to the lower reflector. The lower reflector is positioned at the lower end of the climbing frame, and the upper reflector is positioned at the upper end of the climbing frame. The lower and upper reflectors are positioned at a 45° angle and are parallel to each other. The side reflector is positioned to one side of the upper reflector and above the glass water tank. The second convex lens is horizontally positioned directly below the side reflector. The side reflector is positioned at a 45° angle and is symmetrical to the upper reflector about the vertical plane.

[0016] The laser controller controls the laser to emit a horizontal laser beam. The horizontal laser beam is expanded by a concave lens and a first convex lens, reflected vertically upward by a lower reflector, reflected horizontally by an upper reflector, reflected vertically downward by a side reflector, and focused vertically downward by a second convex lens before being injected into the liquid medium in the glass water tank. The focal point of the laser beam is located above the workpiece and forms a light spot on the surface of the workpiece to be processed.

[0017] Furthermore, the cavitation pulsation image observation system includes a high-speed camera and an LED matrix light respectively set on both sides of the glass water tank. The focal point of the laser beam is located at the center of the field of view of the high-speed camera, and the LED matrix light is set vertically with the light source facing the high-speed camera.

[0018] Furthermore, the dynamic mechanical effect detection system includes an oscilloscope positioned on one side of the glass water tank, connected to a hydrophone inserted into the liquid medium, the hydrophone being close to the workpiece surface to be processed and avoiding the laser beam.

[0019] Furthermore, the electric three-dimensional moving platform is connected to a motion controller, and the high-speed camera, oscilloscope, and motion controller are connected to a synchronization signal generator. The motion controller, synchronization signal generator, and laser controller are connected to a computer.

[0020] In summary, the present invention has the following beneficial effects:

[0021] 1. This invention utilizes a laser beam to penetrate a liquid medium, generating a laser plasma shock wave. This shock wave forms a single cavitation bubble on the absorption layer of the workpiece surface to be processed. After the cavitation bubble collapses pulsatingly, it generates a shock wave and a micro-jet that acts on the workpiece surface. The mechanical effects of the laser plasma shock wave, the laser cavitation shock wave, and the micro-jet cause localized plastic deformation on the workpiece surface. Micro-scale pits are created using mechanical effects without melting or ablation on the workpiece surface. This not only avoids the damage to the material surface integrity caused by laser ablation of the micro-pits but also avoids the formation of crater-like morphology around the edges of the micro-pits due to laser thermal effects. Compared to the millimeter-scale pits generated by laser-induced micro-shaping, the micro-scale pits generated by laser-induced cavitation ensure a sufficiently large contact area between the friction pairs, reducing the pressure on the workpiece surface during friction. This also helps to store lubricating oil, forming an oil film between the friction pairs to reduce wear and improve the friction and wear performance of the workpiece friction pairs.

[0022] 2. In this invention, the laser beam is perpendicular to the surface to be processed of the workpiece, and the force of the laser plasma shock wave and the laser cavitation collapse shock wave induced by the cavitation can reach the GPa level. Compared with the laser beam being parallel to the surface to be processed, the water hammer pressure when the induced gas cavitation collapses is only at the MPa level. This invention can effectively ensure the impact depth of the micro-dimples.

[0023] 3. This invention sets an absorption layer on the surface of the workpiece to be processed. The laser plasma shock wave, laser cavitation collapse shock wave and micro-jets generated by laser-induced cavitation act on the absorption layer, making it adhere tightly to the surface of the workpiece to be processed, protecting the area around the micro-pits, avoiding the adverse effects of excessive laser energy on the performance of the unprocessed areas of the workpiece surface, especially avoiding the volcano-like morphology caused by laser ablation of the sidewalls of the micro-pits, which would result in material melting and the accumulation of its oxides around the sidewalls of the micro-pits. This ensures that the morphology of the micro-pits is good, and the resulting micron-scale texture has oil storage and lubrication functions while ensuring a sufficiently large contact area between the friction pairs, thereby reducing the occurrence of friction and wear and improving the friction and wear performance of the friction pairs on the workpiece surface. This is an effect that laser shock micro-machining cannot achieve.

[0024] 4. This invention prepares micro-pits by laser-induced single cavitation bubbles. The micro-pits are free from ablation and crack defects, ensuring the repeatability of the micro-pits. Then, the workpiece is moved by an electric three-dimensional moving platform to prepare a regularly distributed array of micron-sized micro-pits on the surface of the workpiece to be processed. The size and depth of the micro-pits are controllable and uniform. The micro-pits can better store lubricating oil and reduce abrasive particles and debris, significantly improving the friction and wear performance of the workpiece's anti-friction surface. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a device for preparing a friction-reducing surface using a laser-induced array of cavitation micro-pits;

[0026] Figure 2 This is a schematic diagram of a method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, in which a laser beam generates cavitation on the surface to be processed, and the cavitation collapses after expansion and contraction to form micro-jets and shock waves.

[0027] Figure 3 This is a single micro-pit morphology image prepared by a laser-induced cavitation micro-pit array method for preparing friction-reducing surfaces;

[0028] Figure 4 This is a plastic deformation diagram of a single micro-pit prepared by a laser-induced cavitation micro-pit array method for preparing a friction-reducing surface;

[0029] Figure 5 This is a schematic diagram of the morphology of a micro-pit array with an area coverage of 20%, prepared by a laser-induced cavitation micro-pit array method for preparing a friction-reducing surface.

[0030] Figure 6 This is a method for preparing anti-friction surfaces using laser-induced cavitation micro-pit arrays. The comparison chart shows the average friction coefficient of the anti-friction surfaces prepared with micro-pits on the workpiece surface with and without an absorption layer.

[0031] In the diagram, 1. Computer; 2. Synchronization signal generator; 3. Laser controller; 4. Laser; 5. Concave lens; 6. First convex lens; 7. Lower reflector; 8. Climbing frame; 9. Upper reflector; 10. Side reflector; 11. Second convex lens; 12. Glass water tank; 13. Liquid medium; 14. Workpiece; 15. Absorption layer; 16. Electric three-dimensional moving platform; 17. Motion controller; 18. High-speed camera; 19. LED matrix light; 20. Oscilloscope; 21. Hydrophone. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0033] A method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, such as... Figure 1 As shown, workpiece 14 is placed in a glass tank 12 filled with liquid medium 13. The surface of workpiece 14 to be processed is horizontal and coated with an absorption layer 15. The glass tank 12 is placed on an electric three-dimensional moving platform 16. A laser beam is vertically injected into the liquid medium 13 of the glass tank 12 through a laser-induced cavitation generation system. The focal point of the laser beam is located above workpiece 14 and forms a spot on the surface of workpiece 14 to be processed. The laser beam induces a single cavitation bubble in the spot area on the surface of workpiece 14 to be processed. The laser plasma shock wave, laser cavitation bubble collapse shock wave, and microjets generated by the induced single cavitation bubble act together on the surface of workpiece 14 to be processed, impacting and compacting the material at the corresponding position on the surface of workpiece 14 to be processed, creating micro-pits. The electric three-dimensional moving platform 16 moves workpiece 14 along a set path, and the laser beam acts repeatedly according to the pulse width, forming an array of micro-pits on the surface of workpiece 14 to be processed, resulting in a friction-reducing surface of workpiece 14 with micro-texture.

[0034] like Figure 1 and Figure 2 As shown, this invention utilizes laser-induced cavitation technology. It employs a laser beam to penetrate the liquid medium 13, generating a laser plasma shock wave, induced cavitation collapse shock waves, and microjets. These impacts compact the material at corresponding locations on the workpiece 14's surface to be processed, creating micron-sized micro-pits. The workpiece 14's surface to be processed does not melt or ablate. Figure 3 and Figure 4 The images show the morphology of the prepared micro-pits and the plastic deformation. Specifically, by using laser-induced single cavitation bubbles in conjunction with an electrically driven three-dimensional moving platform 16 to move the workpiece 14, a regularly distributed array of micro-pits is formed on the surface of the workpiece 14 to be processed. The size and depth of the micro-pits are controllable and uniform, which allows for better storage of lubricating oil and reduction of abrasive particles and debris, significantly improving the friction and wear resistance of the anti-friction surface of the workpiece 14. Figure 5 The schematic diagram shows the morphology of the micro-pit array with an area coverage of 20%, clearly demonstrating the excellent morphological quality of the micro-pit array.

[0035] In this invention, the absorption layer 15 is used to protect other parts of the surface of the workpiece 14 to be processed, so as to avoid the crater-like morphology caused by the laser ablation of the sidewalls of the micro-pits, which would result in the melting of the material and the accumulation of its oxides around the edge of the micro-pits, thus effectively ensuring the quality of the micro-pits. Figure 6 The image shows a comparison of the average friction coefficient of the workpiece 14 with and without the absorption layer 15 when micro-dimples are prepared. It is clear that the average friction coefficient of the workpiece 14 with the absorption layer 15 is significantly smaller than that without the absorption layer 15, indicating that the friction reduction performance of the workpiece 14 is better.

[0036] In this invention, the size and depth of the micro-pits can be adjusted according to actual needs. The size of the micro-pit is related to the size of the spot formed on the workpiece 14 surface after the laser beam is focused, while the depth of the micro-pit is related to the laser energy and the number of laser impacts. Specifically, the vertical distance H between the focal point of the laser beam and the workpiece 14 surface is used. The value of H is adjusted by moving and raising the workpiece 14 via an electric three-dimensional moving platform 16, thereby adjusting the diameter of the spot formed on the workpiece 14 surface. The spot diameter is less than 500 μm to ensure that the prepared micro-pits are at the micrometer level. The laser energy and the number of impacts are adjusted by a laser-induced cavitation generation system. For example, a single micro-pit with a laser energy of 25 mJ and two laser impacts is approximately 9 μm in size.

[0037] In this embodiment, the absorption layer 15 is an 80μm black paint layer, which is formed by coating the surface of the workpiece 14 to be processed with black paint before placing the workpiece 14 in the liquid medium 13 of the glass water tank 12. After the micro-pit array on the surface of the workpiece 14 to be processed is completed, the absorption layer 15 needs to be cleaned to avoid affecting the normal use of the friction-reducing surface of the workpiece 14.

[0038] In addition, a high-speed camera 18 was used to capture a sequence of cavitation pulsation processes to analyze the pulsation characteristics of cavitation expansion-contraction-collapse. A hydrophone 21 was used to collect and process the sound pressure signals of induced cavitation, and an oscilloscope 20 was used to process and display the sound pressure signals as waveforms with directly readable voltage values ​​for each sound signal. Through the sequence of cavitation pulsation processes and the waveforms, the mechanical effects of the shock waves and microjets generated by laser-induced cavitation on the workpiece 14 surface to be processed were analyzed and determined. The results were compared with the morphology of the prepared micro-pits to analyze the relationship between the laser-induced cavitation shock waves and microjets and the micro-pit morphology, obtaining a quantitative relationship between process parameters and the micron-scale micro-pit size.

[0039] An apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, for use in the above-mentioned preparation method, such as... Figure 1As shown, the system includes an electric three-dimensional moving platform 16, a glass water tank 12, a laser-induced cavitation generation system, a cavitation pulsation image observation system, and a dynamic mechanical effect detection system. The glass water tank 12 is placed on the electric three-dimensional moving platform 16 and filled with a liquid medium 13. The workpiece 14 is placed inside the glass water tank 12, with its surface to be processed facing upwards and coated with an absorption layer 15. The laser-induced cavitation generation system emits a laser beam and directs it vertically downwards into the liquid medium 13. The focal point of the laser beam is located above the workpiece 14 and forms a spot on the absorption layer 15. The laser-induced cavitation creates micron-sized micro-pits on the surface of the workpiece 14 through the spot area. The electric three-dimensional moving platform 16 moves the workpiece 14, creating a micro-pit array on the surface of the workpiece 14 to be processed. The cavitation pulsation image observation system acquires a sequence of cavitation pulsation processes and analyzes the pulsation characteristics of cavitation expansion-contraction-collapse. The dynamic mechanical effect detection system analyzes the mechanical effects of the shock wave and microjets generated by the laser-induced cavitation on the surface of the workpiece 14 to be processed.

[0040] Specifically, such as Figure 1 As shown, the laser-induced cavitation generation system includes a laser controller 3 and a laser 4 connected for control. A vertically arranged concave lens 5 and a first convex lens 6 are provided on one side of the laser 4's emitting end, with the concave lens 5 positioned between the first convex lens 6 and the laser 4. The laser controller 3 controls the laser 4 to emit a horizontal laser beam, which is expanded by the concave lens 5 and the first convex lens 6. A vertically arranged climbing frame 8 is provided on the side of the first convex lens 6 away from the concave lens 5. An upper reflecting mirror 9 and a lower reflecting mirror 7, set at 45° and parallel to each other, are respectively provided at the upper and lower ends of the climbing frame 8. The lower reflecting mirror 7 faces the first convex lens 6, reflecting the horizontal laser beam vertically upwards to the upper reflecting mirror 9. A side reflecting mirror 10, set at 45° and symmetrical about the vertical plane, is provided on one side of the upper reflecting mirror 9. The side reflecting mirror 10 is located above the glass water tank 12, and a horizontally arranged second convex lens 11 is positioned directly below it. The upper reflector 9 reflects the vertical laser beam horizontally to the side reflector 10, which in turn reflects the horizontal laser beam vertically downward into the liquid medium 13. The vertical laser beam is focused by the second convex lens 11, with its focal point located inside the liquid medium 13 and above the workpiece 14. After focusing, the laser beam forms a spot on the surface of the workpiece 14 to be processed, and induces a single cavitation bubble in the spot area of ​​the absorption layer 15 to create a single micro-pit.

[0041] like Figure 1As shown, the cavitation pulsation image observation system includes a high-speed camera 18 and an LED matrix light 19 respectively positioned on both sides of the glass water tank 12. The focal point of the laser beam is located at the center of the field of view of the high-speed camera 18. The high-speed camera 18 captures a sequence of cavitation pulsation processes. The LED matrix light 19 is vertically positioned with its light source facing the high-speed camera 18, providing sufficient light for the images captured by the high-speed camera 18. The high-speed camera 18, the cavitation pulsation, and the LED matrix light 19 are on the same horizontal plane, ensuring the imaging effect of the cavitation pulsation process sequence. The dynamic mechanical effect detection system includes an oscilloscope 20 positioned on one side of the glass water tank 12. The oscilloscope 20 is connected to a hydrophone 21 inserted into the liquid medium 13. The hydrophone 21 is close to the surface of the workpiece 14 to be processed and avoids the laser beam. The electric three-dimensional moving platform 16 is connected to a motion controller 17. The high-speed camera 18, the oscilloscope 20, and the motion controller 17 are connected to a synchronization signal generator 2. The synchronization signal generator 2 is used to control the motion controller 17, the high-speed camera 18, and the oscilloscope 20 to move synchronously. In addition, the motion controller 17, the synchronization signal generator 2, and the laser controller 3 are connected to the computer 1, which controls the operation of all components of the entire device.

[0042] The specific working steps of a device for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array are as follows:

[0043] S1, Connect the device; according to Figure 1 Connect all devices and place the glass water tank 12 on the electric three-dimensional moving platform 16 and fix it.

[0044] S2. Fix the workpiece 14; coat the surface of the workpiece 14 with 80μm of black paint to form an absorption layer 15, and fix the workpiece 14 in the glass water tank 12 with the absorption layer 15 horizontally upward. In this embodiment, the material of the workpiece 14 is 7050 aluminum alloy.

[0045] S3. Adjust the H value; adjust the spot size according to the required micro-dimple size. The spot size is achieved by adjusting the vertical distance H between the laser beam focus and the surface to be processed on the workpiece 14. The H value is adjusted by moving the workpiece 14 via the electric three-dimensional moving platform 16. In this embodiment, the spot diameter is 300 μm, the adjustable range of the electric three-dimensional moving platform 16 in the X, Y, and Z axes is 0-100 mm, and the displacement accuracy of the X and Y axes is 0.1 mm, and the displacement accuracy of the Z axis is 0.05 mm.

[0046] S4. Inject liquid medium 13; slowly pour liquid medium 13 into the glass water tank 12 until the liquid medium 13 fills the entire container, controlling the pouring speed of liquid medium 13 to prevent the generation of excess small air bubbles. In this embodiment, liquid medium 13 is deionized water.

[0047] S5. Set laser parameters; according to the required micro-pit depth, set the laser parameters of the laser beam emitted by the laser 4 through the laser controller 3, including laser energy, output wavelength, etc. In this embodiment, the laser energy is 25mJ, the laser wavelength is 1064nm, the repetition frequency is 10Hz, the pulse width is 9ns, a single micro-pit is laser-impacted twice, and the prepared micro-pit depth is 9μm.

[0048] S6. Set up a high-speed camera 18; the high-speed camera 18 is directly facing the focal point of the laser beam, ensuring that the focal point is in the center of the field of view of the high-speed camera 18, and ensuring that the high-speed camera 18, the cavitation bulb and the LED matrix light 19 are on the same horizontal plane, and turn on the LED matrix light 19.

[0049] S7. Set up the oscilloscope 20 and the hydrophone 21; place the hydrophone 21 in the glass water tank 12, about 2mm away from the surface of the workpiece 14 to be processed and avoiding the laser beam, and connect the hydrophone 21 and the oscilloscope 20.

[0050] S8. Fabrication of a micro-pit array: Computer 1 and synchronization signal generator 2 control the start-up of the entire device. The laser beam induces a single cavitation bubble in the spot area of ​​the workpiece 14 to be processed. The laser plasma shock wave induced by the single cavitation bubble, the laser cavitation bubble collapse shock wave, and the micro-jets act together on the workpiece 14 to be processed surface, impacting and compacting the material at the corresponding position on the workpiece 14 to be processed surface to generate micro-pits. The electric three-dimensional moving platform 16 drives the workpiece 14 to move along a set path, forming a micro-pit array on the workpiece 14 to be processed surface, obtaining a workpiece 14 with a micro-textured anti-friction surface.

[0051] S9. Analysis and Processing: Select the sequence diagram of the cavitation pulsation process captured by the high-speed camera 18, measure and summarize the various data of the cavitation using image processing software, and analyze the pulsation characteristics of the expansion, contraction and collapse of the cavitation. Read the voltage value corresponding to each sound pressure signal after the sound pressure signal is processed by the oscilloscope 20, and qualitatively analyze the mechanical effects of the shock wave and micro-jet generated by the laser-induced cavitation on the surface to be processed of the workpiece 14 through relevant conversion formulas. Compare the results with the prepared micro-pit morphology to analyze the relationship between the laser-induced cavitation shock wave and micro-jet and the micro-pit morphology.

[0052] The foregoing description illustrates and describes preferred embodiments of the present invention. As previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, characterized in that: The workpiece (14) is placed in a glass water tank (12) filled with liquid medium (13), with the surface of the workpiece (14) to be processed facing upwards and coated with an absorption layer (15). The glass water tank (12) is placed on an electric three-dimensional moving platform (16). A laser beam is vertically injected into the liquid medium (13) of the glass water tank (12) through a laser-induced cavitation generation system. The focal point of the laser beam is located above the workpiece (14) and forms a light spot on the surface of the workpiece (14) to be processed. The laser beam is applied to the surface of the workpiece (14) to be processed. The spot area induces a single cavitation bubble. The laser plasma shock wave, laser cavitation bubble collapse shock wave and micro-jets generated by the single cavitation bubble act together on the surface to be processed of the workpiece (14), causing plastic micro-deformation of the material at the corresponding position of the surface to be processed of the workpiece (14), forming micro-pits. The electric three-dimensional moving platform (16) drives the workpiece (14) to move along the set path. The laser beam acts repeatedly in a pulse mode, forming a micro-pit array on the surface to be processed of the workpiece (14), resulting in a workpiece (14) with a micro-textured friction-reducing surface. The vertical distance between the focal point of the laser beam and the surface to be processed of the workpiece (14) is H. According to the required size of the micro-dimple, the workpiece (14) is moved and raised by the electric three-dimensional moving platform (16) to adjust the value of H, and the diameter of the spot formed by the laser beam on the surface to be processed of the workpiece (14) is adjusted, and the spot diameter is less than 500μm. By adjusting the laser energy and the number of laser impacts of the laser beam using the laser-induced cavitation generation system, micro-pits of the desired depth can be obtained. The absorption layer (15) is a black paint layer. After the micro-pit array on the surface to be processed of the workpiece (14) is completed, the absorption layer (15) is cleaned. The laser-induced cavitation generation system includes a laser (4), a concave lens (5), a first convex lens (6), a reflector, and a second convex lens (11). The laser beam emitted by the laser (4) is expanded by the concave lens (5) and the first convex lens (6), reflected by the reflector, and focused by the second convex lens (11) before being vertically injected into the liquid medium (13) of the glass water tank (12).

2. The method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array according to claim 1, characterized in that: A high-speed camera (18) was used to capture a sequence of cavitation pulsation processes to analyze the pulsation characteristics of cavitation expansion-contraction-collapse. A hydrophone (21) was used to collect and process the sound pressure signal that induces cavitation, and the sound pressure signal was processed and displayed as a waveform diagram that can be directly read for each sound signal voltage value through an oscilloscope (20).

3. The method for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array according to claim 2, characterized in that: The mechanical effects of the shock wave and microjets generated by laser-induced cavitation on the surface of the workpiece (14) were analyzed and determined, and compared with the morphology of the prepared micro-pits. The relationship between the shock wave and microjets generated by laser-induced cavitation and the morphology of the micro-pits was analyzed, and the quantitative relationship between the process parameters and the micro-scale micro-pit size was obtained.

4. An apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array, characterized in that: For implementing the method according to any one of claims 1-3, the device includes an electric three-dimensional moving platform (16), a glass water tank (12), a laser-induced cavitation generation system, a cavitation pulsation image observation system, and a dynamic mechanical effect detection system. The glass water tank (12) is placed on the electric three-dimensional moving platform (16) and filled with a liquid medium (13). The workpiece (14) is placed in the glass water tank (12), and the surface of the workpiece (14) to be processed is horizontally upward and coated with an absorption layer (15). The laser-induced cavitation generation system includes a laser controller (3), a laser (4), a concave lens (5), a first convex lens (6), a climbing frame (8), a lower reflector (7), an upper reflector (9), a side reflector (10), and a second convex lens (11). The laser controller (3) is connected to the laser (4). The concave lens (5) and the first convex lens (6) are vertically arranged between the laser (4) and the lower reflector (7), with the concave lens (5) close to the laser (4) and the first convex lens (6) close to the laser (4). The lower reflector (7) is located at the lower end of the climbing frame (8), and the upper reflector (9) is located at the upper end of the climbing frame (8). The lower reflector (7) and the upper reflector (9) are set at 45° and are parallel to each other. The side reflector (10) is located on one side of the upper reflector (9) and above the glass water tank (12). The second convex lens (11) is horizontally located directly below the side reflector (10). The side reflector (10) is set at 45° and is symmetrical to the upper reflector (9) about the vertical plane. The laser controller (3) controls the laser (4) to emit a horizontal laser beam. The horizontal laser beam is expanded by the concave lens (5) and the first convex lens (6), reflected vertically upward by the lower reflector (7), reflected horizontally by the upper reflector (9), reflected vertically downward by the side reflector (10), and focused vertically downward by the second convex lens (11) into the liquid medium (13) of the glass water tank (12). The focal point of the laser beam is located above the workpiece (14) and forms a light spot on the surface of the workpiece (14) to be processed.

5. The apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array according to claim 4, characterized in that: The cavitation pulsation image observation system includes a high-speed camera (18) and an LED matrix lamp (19) respectively set on both sides of the glass water tank (12). The focal point of the laser beam is located at the center of the field of view of the high-speed camera (18). The LED matrix lamp (19) is set vertically and the light source is directed towards the high-speed camera (18).

6. The apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array according to claim 5, characterized in that: The dynamic mechanical effect detection system includes an oscilloscope (20) set on one side of the glass water tank (12), the oscilloscope (20) being connected to a hydrophone (21) inserted in the liquid medium (13), the hydrophone (21) being close to the surface of the workpiece (14) to be processed and avoiding the laser beam.

7. The apparatus for preparing a friction-reducing surface using a laser-induced cavitation micro-pit array according to claim 6, characterized in that: The electric three-dimensional mobile platform (16) is connected to a mobile controller (17), the high-speed camera (18), the oscilloscope (20) and the mobile controller (17) are connected to a synchronization signal generator (2), and the mobile controller (17), the synchronization signal generator (2) and the laser controller (3) are connected to a computer (1).

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