Laser combined machining method and system for micropore with high depth-diameter ratio

Abstract

The invention discloses a laser combined machining method and system for a micropore with a high depth-diameter ratio, and belongs to the technical field of laser precision machining. In a dry protective gas environment, a first laser parameter with high power and long pulse width is adopted to conduct primary punching on the workpiece, and a through prefabricated hole is formed; then forming a flowing water film covering an inlet of the prefabricated hole on the surface of the workpiece, and filling the prefabricated hole with water; and finally, the water environment is maintained, a low-power and short-pulse-width second laser parameter is switched, and secondary laser machining is conducted on the prefabricated hole filled with water. During machining, a laser beam enters a water column in the hole through water film coupling, and energy uniformly acts on the whole hole wall in the hole depth direction by utilizing the optical waveguide effect of laser on the interface of the water column and the hole wall, so that the taper is reduced, the hole wall is trimmed, and a high-quality target hole is formed. The contradiction that traditional laser drilling efficiency and quality are difficult to consider at the same time is effectively solved, and the advantages of high hole pattern quality, high process adaptability and the like are achieved.

Description

Technical Field

[0001] This invention relates to the field of laser precision machining technology, and in particular to a laser composite machining method and system for high aspect ratio microholes. Background Technology

[0002] Laser drilling technology, due to its non-contact nature, high efficiency, and good material adaptability, is widely used in the manufacturing of key components in aerospace, precision instruments, and other fields. These components typically require the fabrication of microholes with large aspect ratios and high hole precision in high-strength, high-temperature-resistant, and difficult-to-machine materials. However, when using traditional dry laser drilling processes, the high-energy-density laser beam causes the material to melt and vaporize instantaneously. Some of the molten material easily adheres to and re-solidifies on the hole wall during the removal process, forming a fragile recast layer. This recast layer not only disrupts the continuity of the material matrix but is also often accompanied by microcracks, directly leading to a decrease in the fatigue strength and corrosion resistance of the workpiece. Under harsh conditions such as high temperature and high stress, it may become a source of crack initiation and propagation, seriously threatening the service safety and lifespan of the components.

[0003] To address the aforementioned thermal damage issues, the industry typically employs water-assisted cooling. One common method is to completely immerse the workpiece in water during processing, utilizing the strong cooling effect of water to inhibit molten solidification and reduce recast layers. However, water exhibits significant absorption and scattering effects on laser energy, resulting in a substantial attenuation of effective processing energy. This often leads to penetration difficulties and low efficiency when processing thicker workpieces. Furthermore, the numerous air bubbles generated during processing interfere with the stable transmission of the laser beam, further impacting processing consistency and reliability. Another more advanced technology uses a stable laminar water jet to guide the laser beam, achieving near-thermal-damage-free precision machining. However, maintaining the laminar flow of the water jet and precise beam coupling places extremely stringent requirements on water pressure control, nozzle design, and system calibration. This results in complex equipment, high costs, cumbersome process debugging, and severely limited processing flexibility, making it difficult to adapt to the needs of multi-variety, small-batch production.

[0004] It is evident that existing technologies often face a dilemma in addressing the conflict between quality and efficiency in laser drilling: pursuing high hole quality inevitably comes at the cost of sacrificing processing efficiency or significantly increasing costs and complexity; while maintaining high efficiency makes it difficult to avoid thermal damage defects on the hole wall. Particularly for micro-hole machining with high aspect ratio requirements, how to simultaneously obtain high-quality hole profiles with vertical walls, clean surfaces, and no recast layers while ensuring efficient penetration has become a prominent bottleneck restricting the technology's development into more advanced applications. Therefore, developing a new laser drilling method that can balance processing efficiency and final hole quality, while also being simple and adaptable, has clear technical necessity and significant application value. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a laser composite processing method and system for high aspect ratio microholes.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a laser composite processing method for high aspect ratio microholes, comprising the following steps: S1. Supply dry protective gas to the processing area of ​​the workpiece, and use the first laser parameters to perform initial laser drilling on the target position of the workpiece to form a pre-made hole that penetrates the workpiece and has a process taper and a rough wall surface of the recast layer. S2. Form a flowing water film covering the inlet of the pre-made hole on the surface of the workpiece to be processed, and start the auxiliary filling device to apply ultrasonic cavitation vibration to the pre-made hole area or apply negative pressure suction to the bottom of the hole to break the air lock at the orifice formed by the surface tension of the rough wall and water, forcibly drive away the gas in the hole and make the water completely wet and fill the pre-made hole. S3. Maintain the water environment, switch to the second laser parameter, and perform secondary laser processing on the pre-made hole that has been filled with water; according to the depth-to-diameter ratio and taper characteristics of the pre-made hole, adjust the focusing depth and incident divergence angle of the laser beam in real time so that the incident angle of the laser beam at the interface between the water column and the hole wall always meets the total reflection condition, and the laser energy acts uniformly on the entire hole wall along the hole depth direction to trim the hole wall and form the target hole.

[0007] In a preferred embodiment of the present invention, in step S1, the drying protective gas is nitrogen, argon, or a mixture thereof.

[0008] In a preferred embodiment of the present invention, the average power of the second laser parameter is 1 / 3 or less of the average power of the first laser parameter; the pulse width of the first laser parameter is in the microsecond range, and the pulse width of the second laser parameter is in the nanosecond or picosecond range.

[0009] In a preferred embodiment of the present invention, in step S2, the flowing water film is formed by spraying through a micro water nozzle coaxially integrated with the laser head, and the thickness of the water film is 0.1 mm to 2 mm.

[0010] In a preferred embodiment of the present invention, in step S2, the water film is deionized water or a functional aqueous solution containing defoamer and surfactant.

[0011] In a preferred embodiment of the present invention, during the secondary laser processing in step S3, the focal position of the laser beam is set at a distance of 0.1 mm to 1 mm above the surface of the workpiece, or within the water film layer.

[0012] In a preferred embodiment of the present invention, in step S3, the secondary laser processing adopts a circular scanning path, and the laser beam rotates and scans around the central axis of the pre-made hole.

[0013] In a preferred embodiment of the present invention, the diameter of the pre-made hole is smaller than the target hole diameter, and the difference in hole diameter is between 10 μm and 50 μm.

[0014] In a preferred embodiment of the present invention, the workpiece is a metal, ceramic or carbon fiber composite material with a thickness of not less than 0.5 mm, and the depth-to-diameter ratio of the formed target hole is greater than 5:1.

[0015] A laser composite processing system for high aspect ratio microholes includes: Laser generating unit, used to generate laser light; A parameter modulation unit, connected to the laser generating unit, is used to modulate the laser into the first laser parameters or the second laser parameters; The dynamic focusing unit is located in the optical transmission path and is used to adjust the focal position and divergence angle of the laser beam in real time. A gas supply unit is used to supply dry protective gas to the processing area of ​​the workpiece during step S1. A water supply unit is used to supply liquid to the surface of the workpiece to be processed to form the flowing water film during step S2. An auxiliary filling unit is used to generate an ultrasonic vibration field acting on the workpiece or to establish a negative pressure environment on the back of the workpiece during step S2. A motion execution unit is used to carry the workpiece and / or the laser output head and realize the relative movement between the two; The central control unit is connected to the parameter modulation unit, dynamic focusing unit, air supply unit, water supply unit, auxiliary filling unit and motion execution unit respectively, and is configured to control the execution of steps S1, S2 and S3 in sequence.

[0016] This invention addresses the shortcomings of the prior art and has the following beneficial effects: This invention cleverly combines the high efficiency of dry processing with the high quality of water-guided laser processing by employing a secondary processing strategy: first, high-efficiency penetration drilling in a dry protective gas environment, followed by precise shaping using a water-film environment. The initial dry processing rapidly forms a pre-formed hole, effectively avoiding the low initial penetration efficiency caused by energy attenuation in water-assisted processing. Subsequently, within the water-filled pre-formed hole, the waveguide effect of the laser, supported by a dynamic optical path compensation mechanism, effectively overcomes the total internal reflection failure caused by the inherent taper of the pre-formed hole. This ensures uniform energy distribution along the hole depth, precisely shaping the hole wall and fundamentally solving the problems of uneven longitudinal energy distribution caused by beam divergence, light leakage due to hole wall tilt, and plasma shielding effects. This results in microholes with extremely high verticality and excellent geometric accuracy. Compared to traditional single-method dry or fully wet processes, this invention achieves a leap in hole quality while maintaining comparable efficiency to dry methods, breaking through the long-standing bottleneck of the "efficiency-quality" trade-off in laser precision drilling technology.

[0017] This invention employs significantly lower laser power and shorter pulse width during the shaping stage compared to the perforation stage. This parameter combination, combined with the water environment within the hole, produces a significant synergistic effect. The lower average power and short pulse characteristics allow laser energy to be precisely transferred to the hole wall in a "cold processing" mode. The instantaneous vaporization micro-explosions and high-speed scouring action of the water effectively remove the recast layer and slag generated in the earlier stage. Simultaneously, the strong cooling effect of water greatly suppresses the heat-affected zone during the shaping process, avoiding secondary thermal damage. Compared to the stringent dependence of existing waterjet guiding technologies on stable laminar flow and precise coupling, this invention introduces ultrasonic cavitation or negative pressure suction assistance mechanisms to forcibly break down airlock barriers within the rough pre-formed hole. This achieves instantaneous complete wetting and filling of high aspect ratio microholes without increasing system complexity. Compared to simply relying on unstable capillary action, this invention offers a wider process window, more reliable processes, and significantly reduced manufacturing costs, providing a more feasible technical path for the large-scale industrial application of high-quality laser drilling.

[0018] By independently optimizing parameters and utilizing physical mechanisms in step-by-step processing, this invention not only achieves the direct processing goal of near-zero taper and low damage, but also endows the process with a high degree of controllability and adaptability. The first step, pre-forming the hole, allows for precise machining allowances, while the second step, water-guided shaping, achieves micron-level precision control of the final hole shape by real-time adjustment of parameters such as laser focusing depth, divergence angle, scanning path, and pulse energy. This flexible control capability enables the method to adapt to various difficult-to-machine materials, from metals to ceramics and carbon fiber composites, and to the processing needs of microholes with ratios ranging from conventional to extremely high aspect ratios, demonstrating broad process applicability. Its modular design combining dry and wet processes also provides a clear and low-cost technical solution for upgrading existing laser processing equipment, possessing significant engineering application value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of a laser composite processing method for high aspect ratio microholes according to the present invention; Figure 2 This is a block diagram of the laser composite processing system for high aspect ratio microholes of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0022] Application Overview: Precision machining of high aspect ratio microholes is a key challenge in modern high-end manufacturing, especially in aerospace and precision instrumentation. These microholes not only require extremely high geometric accuracy to ensure fluid dynamics or structural functionality, but also impose almost stringent requirements on the integrity of the hole walls, namely, achieving near-zero taper and a clean wall surface free of recast layers and microcracks. However, since its application, laser drilling technology has been plagued by a fundamental contradiction stemming from the physical nature of its thermal processing: while dry machining using high-energy-density lasers can achieve rapid material penetration and meet production efficiency demands, the resulting significant thermal effects lead to a tapered hole wall with a larger top and smaller bottom, a thick recast layer, and even microcracks, severely degrading the hole's performance and lifespan. Furthermore, water-assisted laser technologies aimed at improving hole quality, such as underwater machining or water-guided lasers, while effectively suppressing the heat-affected zone, either suffer from a sharp decline in processing efficiency due to the strong absorption and scattering of laser energy by water, or are difficult to integrate into cost- and efficiency-oriented industrial production processes due to their extreme system complexity and narrow process window. This long-standing technical dilemma of the incompatibility between "efficiency" and "quality" has become a bottleneck restricting breakthroughs in the performance of high-end components. To resolve this contradiction, this invention proposes a "dry-wet combined" secondary laser drilling method. Its core breakthrough lies in decoupling and synergistically optimizing the two conflicting goals of high-efficiency material penetration and high-quality hole wall shaping in traditional single processes through timing design. This method first achieves rapid penetration using a high-energy laser in an anhydrous environment, fully leveraging the efficiency advantages of dry processing. Subsequently, a stable water environment is constructed within the pre-formed hole, and the laser parameters are switched to low power and short pulses. Utilizing the optical waveguide effect generated by the laser within the water-filled channel, energy is evenly distributed along the hole depth, thereby precisely shaping the hole wall. This technical approach cleverly avoids the bottleneck of low initial penetration efficiency in fully water-assisted processing and achieves hole quality comparable to complex dedicated water-guided laser equipment through a unique water-guided optical shaping mechanism. Ultimately, it provides a new solution for achieving ultra-high precision micro-hole processing that combines high performance and high feasibility. Example

[0023] like Figures 1 to 2 As shown, a laser composite fabrication method for high aspect ratio microholes includes the following steps: S1. Supply dry protective gas to the processing area of ​​the workpiece, and use the first laser parameters to perform initial laser drilling on the target position of the workpiece to form a pre-made hole that penetrates the workpiece and has a process taper and a rough wall surface of the recast layer. S2. Form a flowing water film covering the inlet of the pre-made hole on the surface of the workpiece to be processed, and start the auxiliary filling device to apply ultrasonic cavitation vibration to the pre-made hole area or apply negative pressure suction to the bottom of the hole to break the air lock at the orifice formed by the surface tension of the rough wall and water, forcibly drive away the gas in the hole and make the water completely wet and fill the pre-made hole. S3. Maintain the water environment, switch to the second laser parameter, and perform secondary laser processing on the pre-made hole that has been filled with water; according to the depth-to-diameter ratio and taper characteristics of the pre-made hole, adjust the focusing depth and incident divergence angle of the laser beam in real time so that the incident angle of the laser beam at the interface between the water column and the hole wall always meets the total reflection condition, and the laser energy acts uniformly on the entire hole wall along the hole depth direction to trim the hole wall and form the target hole.

[0024] Transforming the above-mentioned method into a stable and reliable processing technology requires overcoming the systemic challenges posed by the complex interactions between laser, materials, and water. The laser parameters used in the first step of the water-guided optical shaping stage, particularly the matching relationship between average power and pulse width, constitute a process window that must be precisely controlled. Determining this window is crucial: if the average laser power is too high and the energy density is too great, it will instantly vaporize the water within the hole, generating a large amount of steam and bubbles. These bubbles will strongly scatter and block subsequent laser transmission, disrupting the stability of the total internal reflection optical path and leading to process instability or even complete failure. Conversely, if the power is too low, the single-pulse energy is insufficient to effectively erode the hole wall material, resulting in low shaping efficiency and failing to achieve the expected effects of taper correction and recast layer removal. Therefore, exploring and defining the laser parameter range that can maintain the stable and efficient operation of the water-guided optical effect is the primary technical key to realizing this method.

[0025] The construction and control of the water environment is another aspect requiring precise regulation. The thickness, flow rate, and purity of the flowing water film covering the workpiece surface directly determine whether capillary action can quickly and completely fill the pre-formed holes. If the water film is too thin or the flow is unstable, it may lead to insufficient filling, forming air bubbles in the holes, thus interrupting the continuous water column optical waveguide structure. On the other hand, if the water film is too thick, it will introduce unnecessary laser energy attenuation, reducing processing efficiency. Ensuring that the water medium can uniformly and without air bubbles fill the entire channel and remain stable during processing is the physical basis for achieving effective water-guided optical shaping.

[0026] Furthermore, the setting of the laser focus position has a decisive influence on the excitation and maintenance of the water-guided light effect. If the focusing strategy of traditional dry processing is used and the focus is placed on the surface of the workpiece or the bottom of the hole, the laser energy will be concentrated in a very small area to directly ablate the material, and it will be impossible to form a total internal reflection mode that propagates along the hole wall. The focus must be precisely set above the surface of the workpiece or in the water film layer so that the laser beam enters the water medium at a specific divergence angle, thereby significantly increasing the probability of total internal reflection at the water-wall interface in the hole.

[0027] Most importantly, simply combining dry perforation with water-guided optical processing cannot directly yield high-quality micropores. There are extremely subtle physical obstacles: First, the surface of the hole wall after dry processing becomes extremely rough due to high-temperature oxidation and possesses complex surface energy characteristics. At micron-sized apertures, the surface tension of water easily forms strong liquid bridges at the hole opening, preventing air from escaping and creating airlocks that block the establishment of effective water waveguides. Second, the pre-fabricated holes inevitably have a tapered shape, wider at the top and narrower at the bottom. In subsequent water-guided optical shaping, if the optical path is fixed, as the hole depth increases, the incident angle of the laser within the conical water column gradually decreases and falls below the critical angle for total internal reflection. This causes the laser energy to refract into the hole wall midway and fail to reach the bottom, resulting in failed bottom shaping and a barrel-shaped hole. Therefore, active physical intervention is necessary to overcome the aforementioned gas-liquid interface barriers and geometric-optical mismatch problems.

[0028] To demonstrate the feasibility and effectiveness of this method, we will take the processing of a 2 mm thick 304 austenitic stainless steel plate with a target hole diameter of 0.3 mm as an example to illustrate its basic implementation framework.

[0029] Preferably, a precise and controllable gas path system is used to continuously supply dry protective gas. By continuously blowing nitrogen gas with a purity of over 99.99% into the processing area, the airflow speed is controlled at 10-15 liters / minute, thereby effectively removing oxygen from the air, preventing the molten metal from undergoing an oxidation reaction at high temperatures, and thus reducing the generation of oxide slag.

[0030] Preferably, the first laser parameters used in step S1 refer to a set of parameters characterized by high average power and relatively long pulse width, the physical purpose of which is to achieve efficient material removal with thermal melting and evaporation as the dominant mechanisms.

[0031] Specifically, this embodiment uses a ytterbium-doped fiber laser with a wavelength of 1070 nm, set to an average output power of 500 watts, a pulse width of 200 microseconds, and a pulse repetition frequency of 100 Hz. Under these parameters, the target position on the workpiece is precisely irradiated to form a pre-formed hole penetrating the workpiece. This hole serves as the reference for subsequent water-guided optical shaping and as the optical waveguide structure. Its inlet diameter is approximately 0.28 mm, and its outlet diameter is approximately 0.22 mm, exhibiting a noticeable process taper. Furthermore, the hole wall shows a significant recast layer and molten material adhesion. The core objective at this stage is to achieve complete material penetration and to reserve appropriate allowance for subsequent finishing. At this stage, the hole shape quality and wall condition are not subject to overly stringent requirements.

[0032] Preferably, the flowing water film at the inlet of the pre-formed hole is mainly achieved through a micro water nozzle coaxially integrated with the laser head.

[0033] Specifically, the nozzle has an inner diameter of 0.5 mm and sprays filtered and deaerated deionized water to form a laminar water film with a thickness of about 0.5 mm and a stable flow pattern on the surface of the workpiece.

[0034] For micropores of 0.3 mm or even smaller, capillary action and surface water flow alone are sufficient to instantly expel air from the pore and flow to the bottom. However, surface tension may create water bridges at the pore opening, leaving air inside. If air bubbles are present inside the pore, the S3 laser will generate a severe plasma explosion upon impact, leading to processing failure.

[0035] Preferably, in order to overcome the airlock effect caused by the rough surface of the micropore walls, the process of allowing water to seep in and fill the pre-made holes in step S2 adopts an active auxiliary filling strategy. Specifically, while forming a flowing water film covering the orifice through a water nozzle, the auxiliary filling unit integrated under the workpiece fixture is activated.

[0036] Specifically, in this embodiment, the auxiliary filling unit is a piezoelectric ceramic ultrasonic generator; the ultrasonic frequency is set to 40kHz-80kHz, and the power density is 0.5-1.0W / cm². Utilizing the cavitation effect and high-frequency vibration generated by the ultrasonic waves in the micropore liquid, the microbubbles attached to the rough wall of the pre-made hole are instantly shattered, and the liquid film water bridge formed at the orifice due to surface tension is destroyed, forcibly expelling the gas remaining in the hole. This ultrasonic-assisted process lasts approximately 0.5-2 seconds until the water is detected to completely fill the channel, forming a continuous, bubble-free liquid-core optical waveguide medium.

[0037] In addition, as another implementation method, a negative pressure environment can be created on the back of the workpiece, and water can be injected from the top to force the water flow into the hole using the pressure difference, which can also achieve the effect of breaking the airlock.

[0038] Preferably, the water film is deionized water or a functional aqueous solution containing defoamer and surfactant. By adding surfactant, the surface tension can be significantly reduced, ensuring that the water can quickly overcome capillary resistance, wet the pore walls, and expel air.

[0039] Preferably, the second laser parameter switched in step S3 means adjusting the laser output to a set of parameters characterized by low average power, short pulse width, and high repetition frequency, with the aim of achieving precise "cold ablation" removal using an aquatic environment.

[0040] Specifically, in this embodiment, the average laser power is adjusted to 50 watts, the pulse width is compressed to 100 nanoseconds, and the pulse repetition frequency is increased to 50 kilohertz.

[0041] Preferably, in order to solve the problem of optical waveguide leakage caused by the inevitable process taper of the pre-made hole when maintaining the water environment and performing secondary laser processing, the present invention adopts a dynamic optical path compensation strategy based on the taper model.

[0042] Specifically, although placing the focus above the workpiece helps with light coupling, a fixed focus cannot adapt to changes in hole depth. Therefore, in this embodiment, the central control unit controls the dynamic focusing unit in the optical path to adjust the focus position in real time during the processing based on the average taper data of the pre-made hole measured in step S1.

[0043] Specifically, as the laser beam advances towards the depth of the hole, the dynamic focusing unit synchronously moves the focal position downward and finely adjusts the incident divergence angle according to a preset linear or nonlinear compensation function; this ensures that the incident angle of the laser beam at the water column-hole wall interface at different depths is always greater than the critical angle of total reflection, thereby avoiding energy refraction loss in the middle and realizing uniform trimming of the entire hole wall by the laser energy along the depth of the hole.

[0044] Specifically, the laser beam then performs a circumferential scan with a radius of 0.15 mm around the central axis of the pre-drilled hole at a scanning speed of 2000 mm / min, with a processing time of approximately 2 seconds. During this period, the laser energy is "guided" to the entire hole wall through total internal reflection of the water column, achieving uniform etching and trimming of excess material. The presence of water not only acts as an optical waveguide medium but also plays a triple positive role: cooling (suppressing the heat-affected zone), scouring (removing slag), and micro-explosion (aiding in the removal of the recast layer). Example

[0045] Based on the framework of Example 1, this example will focus on the in-depth optimization of the core link of water-guided light precision shaping, further improve the overall quality of the aperture, and solve the problem of slight uneven longitudinal distribution of water-guided light energy that may be caused by changes in aperture depth.

[0046] Preferably, efficient laser transmission within the water-filled hole is fundamental to achieving uniform energy distribution along the hole depth. Although the hole wall material is not an optically low-refractive-index medium and typically cannot form an ideal optical total internal reflection interface, this embodiment cleverly utilizes the grazing incidence reflection principle in optics to construct a liquid-core waveguide structure.

[0047] Specifically, according to Fresnel's law of reflection, when light travels from an optically less dense medium to an optically denser or absorbing medium, its reflectivity increases significantly with the increase of the incident angle. Especially when the incident angle approaches 90°, meaning the light rays "brush" past the aperture wall at a nearly parallel angle, even highly absorbing metallic materials can achieve a surface reflectivity of over 80%–90%. In this case, the water-filled pre-fabricated aperture acts as the "core" of a multimode optical fiber, while the aperture wall acts as the "cladding," allowing the laser beam to be transmitted to the bottom of the aperture through multiple reflections, preventing premature energy dissipation at the aperture opening.

[0048] Preferably, the laser focus is set above the workpiece surface (defocusing amount). ,For example = 0.2 mm) is to control the divergence angle when the laser beam is coupled into the water column. According to geometric optics, the incident angle and the divergence angle are complementary. By precisely controlling the positive defocus amount, the divergence angle of the beam entering the hole can be restricted, ensuring that the incident angle of the beam when it reaches the hole wall is always within the "grazing incidence range" with high reflectivity. The defocus amount is closely related to the aperture size, hole depth, and reflectivity distribution, and its optimal value needs to be determined through optical simulation or experiments to ensure that most areas within the hole depth range can meet the conditions for efficient light guiding.

[0049] Preferably, in order to compensate for the transmission attenuation of laser energy in the long water column and achieve more uniform circumferential processing, this embodiment introduces an optimized scheme combining dynamic focusing and a spiral scanning path. The core idea is that in the S3 stage, the laser focus is no longer fixed but moves down synchronously with the processing depth, and at the same time, the laser beam scans spirally along the hole wall.

[0050] Specifically, the laser focus starts from the entrance of the prefabricated hole and moves along a spiral trajectory towards the hole bottom. Let the parametric equation of the spiral be: ; where (x, y) are the coordinates of the focus in the plane perpendicular to the hole axis, z is the current scanning depth (from the hole entrance z = 0 to the hole bottom z = H), R is the scanning radius (slightly smaller than the target hole radius), and P is the pitch (i.e., the distance the focus descends per revolution).

[0051] Scanning speed can be set as: ; By controlling to control the overall processing speed.

[0052] As mentioned above, in the specific execution of step S3, to maintain the optimality of the total reflection condition, a simplified linear compensation model can be expressed as: ; where is the initial focus position (above the workpiece surface ), and k is a compensation coefficient determined through preliminary experiments (0 < k < 1). The coefficient k comprehensively reflects factors such as the refraction of laser by water and the attenuation of energy with water depth. By optimizing the value of k, within the hole depth H range, the incident angle of the laser on the hole wall can always be maintained within the optimal interval, thereby obtaining a longitudinally uniform shaping effect. Embodiment <00!f0148>

[0053] This embodiment comprehensively evaluates the universality of the method of the present invention for different engineering materials through systematic experimental design and scientifically defines the optimal working window of key process parameters.

[0054] Two materials with significantly different physical properties were selected for comparative experiments: 304 stainless steel and silicon nitride ceramic. The plate thickness was fixed at 2 mm and the target aperture at 0.3 mm, and the process parameters were adjusted based on the material properties.

[0055] For 304 stainless steel: using the basic parameters of Example 1, S1 stage: 500W, 200μs, 100Hz. S3 stage: 50W, 100ns, 50kHz.

[0056] For silicon nitride ceramics: given their high hardness, high brittleness and relatively low absorption rate of near-infrared lasers, the parameters need to be adjusted accordingly.

[0057] Preferably, in stage S1, a high-peak-power short-pulse impact piercing strategy is adopted to avoid thermal stress cracking. A nanosecond pulsed laser is used, with a single pulse energy of 10 mJ, a pulse width of 100 ns, and a frequency of 1 kHz, to perform rapid contour scanning piercing. The aim is to reduce the thermal impact through impact fragmentation and evaporation mechanisms.

[0058] Preferably, in stage S3, the advantages of short-pulse cold processing are further utilized, with parameters adjusted to a single-pulse energy of 1.5 mJ, a pulse width of 20 ns, and a frequency of 30 kHz. Fine spiral scanning helps to obtain smooth hole walls.

[0059] The hole wall morphology was observed using SEM, surface roughness was measured using CLSM, and subsurface damage was assessed using metallographic sectioning. For stainless steel, the taper was <0.5° and the recast layer was <2μm. For silicon nitride ceramics, SEM showed smooth hole walls without macroscopic cracks, surface roughness Sa <1.0μm, and a subsurface damage layer <5μm. Experiments demonstrate that this invention, through parameter adaptation, can effectively address different processing challenges from metals to hard and brittle materials.

[0060] Preferably, to accurately define the optimal operating range of the average laser power in the S3 stage, a single-variable control experiment is designed. All other conditions are fixed (material: 304 stainless steel, thickness 2mm, target aperture 0.3mm, S1 parameters as before, water film conditions as before, focal position: 0.2mm above the workpiece surface, scanning path: circular scan, time 3 seconds), the only variable is the average laser power in S3, set at five levels: 20W, 35W, 50W, 65W, and 80W.

[0061] The following observations were made during the processing: 20W / 35W: Processing is weak or slow, and shaping efficiency is insufficient; 50W: The process is stable and uniform, with tiny air bubbles being carried away by the water flow; 65W / 80W: The water inside the hole undergoes violent vaporization, producing a large number of bubbles, resulting in an unstable light path and even popping sounds.

[0062] Table 1 Quantitative Detection Results Average power (W) Inlet diameter (mm) Outlet diameter (mm) Taper angle (degrees) Recast layer thickness (μm) 20 0.295 0.285 ~1.8 8.5 35 0.301 0.295 ~0.9 4.2 50 0.302 0.300 <0.5 <2.0 65 0.308 0.295 ~1.9 5.5 80 0.315 0.280 ~5.0 >10 (uneven) Experimental data clearly depicts an optimal process window of approximately 45-60W for the average laser power in step S3. Only within this window can high-quality machining of both low taper and thin recast layers be achieved simultaneously. Power deviations from this window result in a significant decrease in machining quality.

[0063] In summary, the near-zero taper laser drilling method and system disclosed in this invention, based on a combination of dry and wet processing and water-guided light shaping, successfully decouples and synergistically optimizes high-efficiency laser penetration and high-quality hole wall shaping at the process level through a two-stage processing sequence design of dry-then-wet. Example 1 verifies the feasibility of this basic method. By rapidly forming a pre-formed hole in a dry environment and then using the water-guided total internal reflection effect for precise shaping, it effectively solves the technical bottlenecks of large taper and thick recast layer in traditional laser drilling. Example 2 establishes a corresponding mathematical model by introducing dynamic focusing and spiral scanning optimization strategies, further improving the stability of the processing and the longitudinal uniformity of the hole shape. Example 3, through systematic experimental research, not only demonstrates the good universality of this method for various engineering materials but also scientifically defines the optimal working window for key process parameters, highlighting the non-obviousness of parameter selection and the reliability and superiority of the technical effect. All the above examples collectively demonstrate that this invention provides an innovative laser drilling solution that can balance high efficiency and high quality with good process adaptability, offering a new and effective path for the development of this technical field.

[0064] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A laser composite processing method for high aspect ratio microholes, characterized in that, Includes the following steps: S1. Supply dry protective gas to the processing area of ​​the workpiece, and use the first laser parameters to perform initial laser drilling on the target position of the workpiece to form a pre-made hole that penetrates the workpiece and has a process taper and a rough wall surface of the recast layer. S2. Form a flowing water film covering the inlet of the pre-made hole on the surface of the workpiece to be processed, and start the auxiliary filling device to apply ultrasonic cavitation vibration to the pre-made hole area or apply negative pressure suction to the bottom of the hole to break the air lock at the orifice formed by the surface tension of the rough wall and water, forcibly drive away the gas in the hole and make the water completely wet and fill the pre-made hole. S3. Maintain the water environment, switch to the second laser parameter, and perform secondary laser processing on the pre-made hole that has been filled with water; according to the depth-to-diameter ratio and taper characteristics of the pre-made hole, adjust the focusing depth and incident divergence angle of the laser beam in real time so that the incident angle of the laser beam at the interface between the water column and the hole wall always meets the total reflection condition, and the laser energy acts uniformly on the entire hole wall along the hole depth direction to trim the hole wall and form the target hole.

2. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, In step S1, the drying protective gas is nitrogen, argon, or a mixture thereof.

3. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, The average power of the second laser parameter is 1 / 3 or less of the average power of the first laser parameter; the pulse width of the first laser parameter is in the microsecond range, and the pulse width of the second laser parameter is in the nanosecond or picosecond range.

4. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, In step S2, the flowing water film is formed by spraying through a micro water nozzle coaxially integrated with the laser head, and the thickness of the water film is 0.1 mm to 2 mm.

5. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, In step S2, the water film is deionized water or a functional aqueous solution containing defoamer and surfactant.

6. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, In step S3, during the secondary laser processing, the focal position of the laser beam is set 0.1 mm to 1 mm above the surface of the workpiece, or within the water film layer.

7. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, In step S3, the secondary laser processing adopts a circular scanning path, and the laser beam rotates and scans around the central axis of the pre-made hole.

8. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, The diameter of the pre-made hole is smaller than the target hole diameter, and the difference in hole diameter is between 10 μm and 50 μm.

9. The laser composite processing method for high aspect ratio microholes according to claim 1, characterized in that, The workpiece is a metal, ceramic, or carbon fiber composite material with a thickness of not less than 0.5 mm, and the depth-to-diameter ratio of the formed target hole is greater than 5:

1.

10. A laser composite processing system for high aspect ratio micro-holes, applied to the drilling method described in any one of claims 1 to 9, characterized in that, include: Laser generating unit, used to generate laser light; A parameter modulation unit, connected to the laser generating unit, is used to modulate the laser into the first laser parameters or the second laser parameters; The dynamic focusing unit is located in the optical transmission path and is used to adjust the focal position and divergence angle of the laser beam in real time. A gas supply unit is used to supply dry protective gas to the processing area of ​​the workpiece during step S1. A water supply unit is used to supply liquid to the surface of the workpiece to be processed to form the flowing water film during step S2. An auxiliary filling unit is used to generate an ultrasonic vibration field acting on the workpiece or to establish a negative pressure environment on the back of the workpiece during step S2. A motion execution unit is used to carry the workpiece and / or the laser output head and realize the relative movement between the two; The central control unit is connected to the parameter modulation unit, dynamic focusing unit, air supply unit, water supply unit, auxiliary filling unit and motion execution unit respectively, and is configured to sequentially control the execution of steps S1, S2 and S3 as described in claim 1.

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