SignificanceThe advancement of national aerospace, automotive manufacturing, biomedical, and related industries has intensified the precision and quality requirements for critical components, including aero-engine heat-resistant parts, integrated circuit semiconductor wafers, and cardiovascular stents. The materials utilized in these components, such as titanium alloys, monocrystalline silicon, and ceramic matrix composites, present significant manufacturing challenges. Traditional machining methods are inadequate for meeting the high-quality processing requirements characterized by minimal thermal damage and microcrack-free surfaces. While long-pulse laser processing offers efficient and cost-effective solutions, it generates substantial thermal defects. Ultrafast laser processing achieves “cold machining” through high-power-density electron stripping for non-thermal material removal but faces efficiency and cost limitations. Water-jet guided laser (WJGL) machining technology combines the efficiency and cost-effectiveness of long-pulse lasers while effectively minimizing thermal damage during processing, achieving results comparable to ultrafast laser techniques.ProgressSignificant research advances in the WJGL field include Dr. Richerzhagen from ETH proposing a laser thermal defocusing model in water based on FEM in the 1990s, which analyzed the impact of thermal defocusing on laser processing accuracy and efficiency, laying a solid theoretical foundation. Couty et al. established a model based on multimode fiber theory to predict laser intensity distribution in water jets, which was verified experimentally and offered crucial insights into laser transmission characteristics in water jets. Professor Cheng from Harbin Institute of Technology enhanced water jet stability by designing a coupling device with a single-side high-pressure water inlet and axisymmetric multi-channel layout, reducing hydraulic fluctuations. Zhang et al., via FEM, compared water jet velocity distribution and convergent section length with and without auxiliary gas constraints, proving the gas phase flow's positive role in water jet stability.Conclusions and ProspectsThis review comprehensively examines WJGL processing technology, focusing three primary aspects: WJGL system operational principles, laser?water-jet coupling transmission mechanisms, and current WJGL technology applications.In examining WJGL system fundamentals, this paper details the operational mechanism and system configuration. WJGL technology employs total internal reflection of laser within a water-jet to guide laser energy to the material surface through water-jet functioning as a liquid optical fiber, enabling non-contact material machining. The water jet serves primarily as a laser transmission medium and cooling agent rather than a direct processing tool. WJGL technology demonstrates notable advantages over conventional long-pulse laser processing, including reduced thermal damage, increased working distance, improved processing accuracy, and capability for high-aspect-ratio structure fabrication.Multiple factors influence the coupling efficiency and stability of laser?water-jet transmission. Maintaining the water jet in a “contracted flow” state necessitates optimized nozzle geometry, multi-stage flow channel design, and auxiliary gas confinement to minimize turbulent disturbances and extend stable flow length. Laser wavelength selection (532 nm green light or 1064 nm near-infrared) must account for water’s optical absorption characteristics, supported by beam shaping techniques to minimize energy loss and maximize output power. Coupling transmission must fulfill total reflection conditions, requiring minimal transverse and angular alignment errors to prevent energy leakage and component safety risks. Longitudinal errors demonstrate reduced impact and can be addressed through water-jet dimension adjustment to enhance transmission efficiency.Current research validatesWJGL’s substantial application potential in processing metallic materials, semiconductors, and advanced composites. However, several challenges remain: (1) Suboptimal coupling efficiency and precision between water jet and laser; (2) Technical difficulties in achieving high-quality, high-aspect-ratio machining of holes, grooves, and edges; (3) Insufficient process optimization for challenging materials such as diamond, sapphire, and ultra-hard ceramics. To address requirements for enhanced quality and mass production, future WJGL technology development may focus on:(1) Reducing the laser beam diameter enhances the coupling efficiency between water jets and lasers. While larger water-jet diameters can improve coupling efficiency, they potentially compromise processing resolution and quality while increasing energy loss. A reduction in laser beam diameter facilitates adequate laser energy density for material processing. However, this approach encounters technical limitations including constraints in laser beam quality optimization, significant beam divergence, and inadequate manufacturing precision and stability of optical components required for stable small-spot focusing.(2) Dynamic compensation of laser coupling position requires attention: temperature-induced variations in water affect the refractive index and laser absorption characteristics, resulting in coupling position drift. This phenomenon necessitates comprehensive investigation of temperature?refractive index relationships and development of adaptive control systems, though current limitations exist in sensor accuracy and adjustment mechanism capabilities.(3) Research on laser energy distribution across the processing surface remains crucial. The processed surface structure influences the spatiotemporal distribution of the water-jet flow field, subsequently affecting the ablation dynamics between the coupled beam and material. Enhanced understanding of laser energy distribution on the processing surface could improve WJGL processing technology control. Present knowledge gaps exist in understanding how processed surface structure affects the spatiotemporal distribution of the water-jet flow field. Moreover, laser power stability and beam shaping technology impact the distribution of laser energy on the processing surface.

SignificanceWith the rapid development of high-end manufacturing in China, conventional machining methods are increasingly unable to meet the demands for high-quality processing of precision components. Water-assisted laser machining is a category of emerging hybrid machining technologies that leverage the cooling and flushing effects of water to suppress the expansion of heat-affected zones, reduce material slag, and minimize thermal cracks. The technology considerably enhances the quality, efficiency, and applicability of laser machining. Currently, the mainstream water-assisted laser machining technologies include underwater laser machining, water-jet-assisted laser machining, and water-jet guided laser machining. This review provides a comprehensive overview of the equipment composition and working principles of these three water-assisted laser machining technologies. It particularly focuses on the emerging water-jet guided laser technology, offering a detailed explanation of its mechanisms. The process of forming a stable water jet and the influence of various factors on the water-jet guided laser stability are thoroughly discussed. Furthermore, the review highlights recent advancements in the application of water-assisted laser machining technologies and explores potential future directions for its development. These insights provide valuable theoretical references and technical support for precision manufacturing and new material machining.ProgressWith the continuous advancement of technology, laser machining has gained increasing attention as a novel noncontact manufacturing method. Water-assisted laser machining offers new possibilities for laser technology advancement, enabling precise material machining. Currently, water-assisted laser machining can be categorized into three main techniques: underwater laser machining, water-jet-assisted laser machining, and water-jet guided laser machining (Fig. 1). Underwater laser machining involves immersing the work piece in water, where a focused laser penetrates the water layer to irradiate and machine the material (Fig. 2). Water-jet-assisted laser machining employs a high-speed water jet that is offset from the laser axis. This technique combines laser irradiation to soften the material with the mechanical action of the water jet for material removal (Fig. 3). Water-jet guided laser machining couples the laser into a water jet, where it propagates through total internal reflection at the water?air interface (Fig. 4). The fundamental machining principle involves precisely and efficiently delivering high-power pulsed laser energy to the targeted work piece surfaces through a high-pressure water jet. Upon contact, the laser energy is absorbed by the material surface, inducing localized vaporization in the machining zone (Fig. 5). There are five primary types of underwater laser machining systems (Fig. 6), each of which can be further customized and configured according to specific processing requirements (Fig. 7). In water-jet-assisted laser systems, maintaining stable hydrodynamic conditions in the water jet represents a critical technical challenge (Fig. 8). The laser?water coupler serves as the core component, critically determining whether a stable water jet capable of maintaining total internal reflection can be achieved (Fig. 9). Furthermore, the focusing objective lens substantially affects the laser?water coupling efficiency (Fig. 10). Gas-assisted stabilization optimizes the water?gas interface, extending the stable length of the water jet and thereby enhancing water-jet guided laser machining quality (Fig. 11). Notably, the protective effect on the water jet varies considerably with different gas species (Fig. 12). Furthermore, considering both the coupling efficiency and processing quality, nanosecond pulsed lasers with a 532 nm wavelength currently represent the optimal choice (Fig. 13). Water-assisted laser machining has been successfully implemented for various materials including glass, ceramics, semiconductors, and superalloys. Underwater laser machining has successfully produced grooves with uniform edges and smooth bottom/sidewalls in zirconia and 4H-SiC substrates (Fig. 14) and achieved high aspect-ratio through-holes in alumina ceramics and 304 stainless steel (Fig. 15). Water-jet-assisted laser machining has demonstrated the capability of fabricating high-quality microchannels in Ti6Al4V and zirconia (Fig. 16) as well as high aspect-ratio structures in nickel-based superalloys (Fig. 17). The unique processing characteristics of water-jet guided laser machining enable the fabrication of through-holes with exceptionally low taper angles and superior quality, even in challenging composite materials (Fig. 18). Furthermore, water-jet guided laser machining demonstrates considerable potential for material surface modification applications (Fig. 19).Conclusions and ProspectsThis paper systematically reviews the fundamental principles and recent advancements in water-assisted laser machining technologies. Underwater laser machining offers remarkable machining versatility through its simple setup, where merely submerging the sample enables water-mediated thermal management for enhanced machining quality. Water-jet-assisted laser machining employs high-pressure water jets to efficiently remove the laser-softened material, effectively suppressing the thermal effects and recast layers that commonly plague conventional laser machining methods. Furthermore, this review presents a dedicated discussion on water-jet guided laser machining technology, providing a systematic analysis of the critical subsystems required for developing high-performance water-jet guided laser equipment. Water-assisted laser machining represents an environmentally sustainable manufacturing approach. Continuous technological advancements and expanding market demands are expected to drive substantial growth and create new opportunities for this technology. Ongoing research and process optimization will further broaden its applicability to more material systems and complex geometries. As a hybrid machining technology, it provides new impetus for sustainable manufacturing transformation.

SignificanceThe rapid development of China aerospace, microelectronics, and medical industries has led to the emergence of materials characterized by their high hardness, brittleness, and anisotropic properties. These materials, which include single-crystal substances, metals, and composites, are susceptible to subsurface damage and geometric inaccuracy during machining. This poses stringent challenges to modern processing technologies in terms of precision control and surface integrity preservation. Currently, the widely adopted industrial processing technologies primarily fall into three categories: mechanical machining, electrical discharge machining (EDM), and laser processing. Traditional mechanical machining dominates large-scale mold manufacturing due to its cost-effectiveness and mature technology. However, its “hard-contact” processing mechanism induces strong interactive forces between tools and workpieces, frequently causing material edge chipping and abnormal tool wear. While EDM can overcome material conductivity limitations, its low processing efficiency, coupled with electrode wear and dielectric fluid contamination, exacerbates operational costs and environmental burdens. Conventional laser processing suffers from heat accumulation effects during operation, potentially generating heat-affected zones (HAZ) and micro-burrs at processed edges, which critically compromise component service performance. To address these limitations, water-jet guided laser (WJGL) machining technology establishes a hybrid processing system integrating nanosecond lasers and high-pressure water jets.The operational principle of water-jet guided laser machining involves precisely controlling the laser beam incident angle to remain below the critical angle for total reflection within the water jet. This total internal reflection transmission mechanism completely confines the laser beam within a 50?100 μm diameter water jet, simultaneously achieving material removal and cooling in the machining zone. Fundamentally, the mechanical stress, thermal damage, and environmental pollution inherent to conventional processing methods are eliminated.This paper focuses on investigating the critical factors influencing WJGL machining performance and highlighting its advantages in precision manufacturing applications. First, an in-depth analysis of the fundamental principles and the material removal mechanisms of WJGL machining is conducted. Subsequently, the key factors influencing machining quality are systematically examined from three perspectives: water-jet characteristics, laser parameters, and system stability. Finally, the superior capabilities of WJGL machining technology are comprehensively summarized, including enhanced machining efficiency, sub-micron precision, high aspect ratios, and multi-axis processing flexibility. Based on current research advancements, a prospective analysis is provided to outline the optimization strategies for future developments in WJGL precision machining technology, aiming to further expand its industrial applicability.ProgressThis paper systematically elaborates on the critical factors influencing processing quality and the latest technological advancements in water- jet guided laser machining. The water-jet guided laser system consists of a nanosecond laser, a high-pressure water circulation system, a water-laser coupling device, and a motion platform system (Fig. 1). Numerical simulations reveal that the material removal process primarily involves alternating cycles of laser thermal effects and water jet cooling (Fig. 5). Key influencing factors include water jet stability length, laser parameters, and mechanical system/motion platform performance. The stability of water jets is determined by the structure of the nozzle (Fig. 7), the diameter of the nozzle, and the flow velocity (Fig. 8). Furthermore, the processing quality is significantly influenced by the laser parameters. Ultraviolet (355 nm), green (532 nm), and infrared (1064 nm) lasers exhibit distinct water absorption coefficients (all below 10?1 cm?1), requiring wavelength optimization based on material properties (Fig. 9). Reducing duty cycle to 2% enables precise control of heat-affected zone (HAZ) thickness below 5 μm (Fig. 10). Adjusting single-pulse energy density within specific ranges ensures machining depth while effectively suppressing recast layer formation (Fig. 11). The high-pressure water circulation system, equipped with accumulators and triple-stage precision filtration (particle size of <1 μm), guarantees water jet purity, while the five-degree-of-freedom motion platform achieves efficient laser-water jet coupling (Fig. 12). Optimized tool paths combined with appropriately reduced scanning speeds simultaneously enhance processing efficiency and surface quality (Fig. 13). Compared with conventional techniques, water-jet guided laser processing demonstrates superior advantages for metals, semiconductors, and composites: narrower kerf widths (Fig. 15), higher aspect ratios (Fig. 16), and enhanced complex geometry fabrication capability (Fig. 17), and meeting high-precision component manufacturing requirements (Fig. 14).Conclusions and ProspectsThis paper systematically analyses the laser-material interaction mechanisms and the process parameter influencing patterns in water-jet guided laser processing. However, significant differences exist in the interactions between water-jet guided lasers and various materials, and the processing mechanisms remain incomplete, requiring further exploration. To better understand the processing mechanisms and optimize the techniques, potential future development directions for the water-jet guided laser machining technology include:1) Advancement and optimization of equipment technology. Developing high-precision real-time monitoring systems to track laser energy, water jet parameters, and material thermophysical states during processing. Integrated with advanced feedback control technologies, these systems will enable dynamic process adjustments to ensure stable machining quality and precision, adapting to diverse materials and processing requirements.2) Multidisciplinary collaborative research. Future studies will emphasize cross-disciplinary integration, combining theoretical and experimental approaches from physics, materials science, fluid dynamics, and optics to investigate water-jet guided laser mechanisms across materials. By establishing more precise physical models, researchers aim to elucidate the transmission, absorption, and conversion processes of laser energy within water jets as well as material thermophysical responses, thereby providing theoretical foundations for process optimization.

SignificanceAs aerospace, microelectronics, communication, and medical fields continue to develop rapidly, the components and parts of the related equipment or systems are becoming increasingly miniaturized and refined. However, traditional laser and mechanical processing methods often encounter challenges, such as low efficiency, significant thermal damage, and limited processing capabilities. Water-guided laser technology offers a promising solution by coupling high-energy lasers with micro-water jets, effectively addressing the thermal damage and stress issues commonly encountered in conventional techniques. This approach has demonstrated remarkable advantages for ultra-precision processing. In this article, we provide a comprehensive review of the advancements in microjet control technology, including improvements in high-pressure coupling devices for enhanced jet stability, dynamics within water chambers, formation mechanisms of microjets, and key aspects of microjet-guided laser coupling. Additionally, we explore how water jets influence processing quality in terms of mechanism, efficiency, precision, and depth. Looking ahead, we discuss the current challenges and future trends in this technology, and offer valuable insights for further research and practical applications.ProgressTraditional machining methods, including mechanical and conventional laser processing, have numerous limitations. Mechanical processing often suffers from problems, such as stress concentration, limited accuracy, and rapid tool wear. Conventional laser processing, particularly continuous and long-pulse laser processing, is a heat-based technology that generates significant thermal defects, such as large heat-affected zones, recast layers, and microcracks. Although short-pulse laser processing can achieve ultrafine processing with minimal heat-affected zones, the high costs of equipment, operation, and maintenance restrict large-scale industrial applications. Therefore, water-jet guided laser technology has emerged as a promising solution. By adjusting the incident angle, the laser can undergo total internal reflection within the water jet, similar to a multimode optical fiber. Stable water?air interfaces are crucial for water-jet-guided laser processing. Various coupling devices, such as Synova, Avonisys, and the design by Cao et al., have been developed. These devices use various methods, such as blowing helium or forming coaxial air curtains, to enhance the water-jet stability and laser coupling (Fig.1). The flow channel structure in the coupling device significantly affects the water-jet quality. Structures such as a 4×4 channel can better adjust turbulent fluctuations and provide a more stable internal flow field for water jets (Fig.2). Cavitation in water-jet-guided laser processing can affect the stability of micro-water jets, and under certain conditions, is beneficial for water-laser coupling. Researchers have studied cavitation control by adjusting nozzle structure parameters (Fig.3). Understanding the interaction process of the laser water jet material through thermal-fluid-solid coupling analysis helps optimize the technology. For example, in the processing of carbon fiber-reinforced composite materials, differences in the thermal properties of the components lead to different removal modes (Fig.4). In addition, different nozzle structures, such as cylindrical capillary, conical, upper conical, and lower conical nozzles, result in different water-jet flow characteristics (Fig.5). Nozzle parameters, such as the length-to-diameter ratio, also affect jet stability and laser-water jet coupling efficiency. In addition, the relationship between nozzle diameter and jet stability has been investigated (Fig.6). Efficient laser-water-jet coupling is essential for improving nozzle life and system stability. Near- and far-field coupling strategies have advantages and disadvantages. Errors in the coupling process can result in laser radiation loss and equipment damage. Researchers have analyzed the influence of various factors on laser coupling and proposed non-diffraction laser-focusing modes to improve the coupling performance (Figs.7, 8, and 9). A stable water beam is crucial for laser conduction. Gas constraint systems, such as a coaxial spiral gas shield formed by argon in some designs, can provide a stable environment for water-jet and laser coupling. The gas and water pressures also affect the coupling length (Fig.10). The processing mechanism of water-jet-guided laser technology is complex owing to the involvement of high-speed water jets, lasers, and processed materials. This includes processes such as material melting, vaporization, and plasma removal, in which a water jet can reduce heat damage. The presence of gas assistance can also affect the processing quality (Fig.11). Furthermore, the gas flow rate, scanning order, and scanning speed affect the processing efficiency of materials, such as SiCf/SiC composites. Water-jet-guided laser cutting has the advantage of processing small holes with large depth-to-diameter ratios (Fig.12). Unstable water jets can affect processing accuracy, but they can also reduce the heat-affected zone. Methods such as the water-jet laser field adjustment method can improve processing accuracy. Moreover, different processing parameters have different effects on processing accuracy (Fig.13). The water-jet pressure, flow rate, and scouring ability affect the processing depth. Multifocus lenses can improve the processing depth in high-power laser processing. The relationship between the hole diameter, processing depth, and other factors has also been studied (Fig.14).Conclusions and ProspectsMicrojet control technology for water-jet-guided lasers has achieved substantial progress; however, it still encounters several challenges. The complex interaction mechanisms among lasers, water jets, and substrates, the instability of water jets affected by multiple factors, energy losses, and alignment inaccuracies during laser-water-jet coupling, and the limitations of traditional focusing methods hinder the further development of this technology. The scope of application of water-jet-guided laser technology is expected to expand. In addition to its current applications in aerospace and semiconductors, it has significant potential in fields such as biomedicine and MEMS manufacturing. By delving deeper into the interaction mechanisms among lasers, water jets, and materials, optimizing processing parameters such as laser power, pulse width, scanning speed, and water-jet pressure, and developing advanced control algorithms, we can enhance processing quality and efficiency. The development of finer and longer water jets by optimizing nozzle structures and parameters is also crucial. Additionally, strengthening research on the interactions among lasers, water jets, and workpiece materials, and improving multi-physical field modeling can better predict processing processes and results, providing theoretical support for process optimization. This technology is expected to play an important role in the development of high-precision manufacturing processes.

SignificanceLaser processing technology is a material manufacturing method that employs high-power-density laser beams. Characterized by non-contact operation and negligible mechanical stress, it is particularly suitable for machining fragile, thin materials and high-precision components, thereby minimizing deformation or damage induced by mechanical contact. However, conventional laser processing struggles to mitigate inherent issues such as thermal stress, burr formation, and thermal damage. To address these limitations, water-jet guided laser (WJGL) processing technology was developed, integrating high-pressure water jets with pulsed lasers. This hybrid approach significantly reduces the heat-affected zone (HAZ) and enhances machining precision, which has attracted substantial research attention. This paper first expounds on the fundamental principles of WJGL processing. It then systematically reviews the impact of key laser parameters—including wavelength, power, pulse width, and repetition rate—on processing outcomes, followed by a summary of current industrial and research applications. Finally, the paper discusses existing challenges and future prospects, providing insights into its potential advancements.ProgressRecent advancements in industries such as medical devices, aerospace, and energy have elevated performance requirements for critical components, driving innovations in material processing technologies. While traditional methods (e.g., mechanical cutting, electrical discharge machining (EDM), and water-jet cutting) remain widely used, they are constrained by inherent limitations. Laser cutting provides precision and efficiency but may induce thermal damage (e.g., slag formation and heat-affected zones) and is limited by a restricted focal depth due to the Rayleigh length, resulting in tapered cut edges. To address these limitations, WJGL technology has emerged as a promising solution, having gained significant attention for its capability to overcome these challenges.By coupling high-pressure water jets with pulsed lasers, WJGL technology effectively reduces thermal damage and enhances post-processing surface quality. Moreover, due to its top-hat energy distribution within the water column, it significantly reduces noticeable machining taper during processing. The WJGL system primarily comprises five key components: a laser source, a laser?water-jet coupling module, a processing platform, a high-pressure water system, and a control system. Owing to the differing refractive indices of air and water for laser transmission, the laser beam undergoes continuous total internal reflection within the water column wall, creating a top-hat beam energy distribution inside the water-jet. The cross-section of the processed material can be divided into four concentric zones radiating outward. Similar to conventional laser cutting, selecting different laser parameters yields varying processing quality. Different materials exhibit distinct absorption coefficients for laser wavelengths, and incorrect wavelength selection may lead to processing challenges. Long-pulse lasers enable rapid sample processing but induce significant thermal effects, while ultra-short-pulse lasers feature lower material removal efficiency. Excessive power can cause surface over-burning of the material. The repetition rate directly influences material removal efficiency, surface morphology, and heat-affected zone size by regulating the balance between single-pulse energy and heat accumulation.Currently, WJGL technology has been applied to the machining of ceramics, semiconductors, and superalloys, among other materials. Compared to traditional laser processing, it offers reduced thermal damage, higher precision, and superior surface morphology. Additionally, WJGL is utilized for surface functionalization and material strengthening, demonstrating excellent performance in these applications.WJGL has successfully performed precise and intricate pattern cutting on materials such as LTCC (Low-Temperature Co-fired Ceramics), amorphous alloys, and fused silica. It has also fabricated high aspect-ratio through-holes in both TBC superalloys and nickel-based alloys, as well as precision grooving on carbon fiber composites and diamond substrates.Moreover, in the field of micromachining, WJGL technology can induce hydrophobicity through surface modification while enhancing surface strength, thereby improving the fatigue resistance of metals.Challenges and Prospects The development of water-jet guided laser (WJGL) processing technology currently faces three major challenges: (1) Laser energy attenuation caused by water-jet absorption and scattering, particularly at high power densities; (2) The trade-off between water-jet diameter and machining precision, where smaller nozzles enhance resolution but compromise stability; (3) rapid and precise laser?water-jet coupling.To advance WJGL technology, future research should focus on four key areas: (1) Developing higher-power laser systems through optimized coupling mechanisms or alternative transmission media to mitigate water absorption losses; (2) Exploring shorter-wavelength UV lasers (e.g., 355 nm) to enhance micro/nano-machining precision; (3) Optimizing pulse widths by integrating ultrashort (fs/ps) and long (ns/ms) pulses to balance efficiency and thermal damage, complemented by intelligent pulse modulation for material-specific processing; (4) Enhancing system stability via advanced nozzle designs and robust water supply systems to maintain micron-scale jetting precision. Addressing these challenges will be pivotal for expanding WJGL’s industrial applications.

ObjectiveSiCf/SiC ceramic matrix composite high-performance engine turbine blades are distributed with a large number of air film holes with small diameter, large depth-to-diameter ratio, small taper, etc. At the same time, SiCf/SiC ceramic matrix composites possess the material properties such as high hardness, high brittleness, and non-uniformity. Thus, in mechanical processing,and continuous laser and pulsed laser processing, there exist problems such as serious tool wear, significant thermal effects, and limited processing depth. In contrast, water-jet guided laser processing has the advantages of long processing distance, no heat-affected zone, and no processing residue.MethodsIn this paper, a nanosecond laser is used for the water-jet guided laser processing, which has a wavelength of 532 nm and a pulse duration of 100 ns. The nozzle diameter is 50 μm, and the output pressure of the pump is 0‒30 MPa. In addition, coaxial rotary blowing is used to minimize the energy loss of the water jet and to improve the processing efficiency and quality. Small holes with a diameter of 0.5 mm are machined on a 4 mm thick SiCf/SiC ceramic matrix composite sample. All the tests are carried out at room temperature and under the protection of compressed gas, and the machining method is ring-cutting machining where the z-axis remains stationary. The entrance and exit morphologies of the small holes of SiCf/SiC ceramic matrix composites are observed using an optical microscope, the small holes are dissected using an automatic metallographic grinding and polishing machine, the three-dimensional profiles of the small holes are measured using a confocal microscope, and the microscopic morphologies of the small holes are observed using a field emission electron microscope. The localized elemental distribution and contents of the holes are measured using an on-board energy disperse spectrometer (EDS).Results and Disscussions This paper investigates the water-jet guided laser ring-cutting of holes in SiCf/SiC ceramic matrix composites and explores the influence law of single pulse energy, scanning speed, and water-jet pressure on the exit and entrance diameters of the small holes and the surface morphology. When the single pulse energyies are 625 μJ and 1250 μJ, the small holes are fully penetrated. However, as the single-pulse energy increases from 1875 μJ to 2500 μJ, the exit diameter grows from 486.83 μm to 498.37 μm [Fig. 4(a)]. The taper of the hole decreases from 9° to 0.12° with the increase of single pulse energy [Fig. 4(b)]. With the increase of scanning speed, both the entrance and exit diameters of the small holes show a decreasing trend, i.e., the entrance diameter decreases from 506.17 μm to 499.40 μm, and the exit diameter decreases from 494.17 μm to 485.37 μm [Fig. 6(a)]. The taper decreases and then increases with the increase of scanning speed, and the small hole taper is minimized when the scanning speed is 0.3 mm/s [Fig. 6(b)]. With the increase of water jet pressure, both the entrance and exit diameters of the small holes tend to decrease, i.e., the entrance diameter decreases from 507.3 μm to 497.9 μm, and the exit diameter decreases from 488.87 μm to 480.43 μm [Fig. 8(a)]. The taper of the holes decreases and then increases [Fig. 8(b)].ConclusionsThis paper carries out the research on water-jet guided laser ring-cutting of holes in SiCf/SiC ceramic matrix composites. For the small holes with a diameter of 500 μm and a depth-to-diameter ratio of 8 in SiCf/SiC ceramic matrix composites, a nanosecond laser (wavelength of 532 nm, pulse duration of 100 ns, and pulse frequency of 8 kHz) is used, and the process parameters are as follows: a single-pulse energy of 2500 μJ, a scanning speed of 0.3 mm/s, and a water-jet pressure of 20 MPa. Under this parameter combination, the processing of a nearly taperless small hole is performed in about 60 s. By observing the small hole entrances and exits and the hole wall cross-section, the water-jet guided laser machining performs well in reducing the recast layer and keeping the hole wall clean. In addition, elemental analysis shows that water-jet guided laser processing can effectively inhibit the thermal effects and oxidative damages in laser processing, and can realize the high quality and high-efficiency processing of SiCf/SiC ceramic matrix composites.

ObjectiveCopper (Cu), with its superior thermal and electrical conductivity properties, is extensively utilized in high-power electronic packaging and thermal management modules. However, its inherent characteristics of high thermal diffusivity and strong optical reflectivity present considerable challenges for achieving precise machining using either conventional or non-conventional fabrication methods independently. This research introduces a cutting methodology based on water-jet guided laser (WJGL) technology, wherein a collimated laser beam transmits through a high-speed water jet, enabling stable beam delivery and concurrent convective cooling of the machining zone. This method enhances both machining precision and thermal damage control. However, the WJGL process encompasses complex multiphysics interactions, particularly involving thermodynamic, fluid dynamic, and photothermal fields, which complicate the understanding of fundamental laser?Cu interaction mechanisms. Thus, the laser ablation behavior of Cu under WJGL conditions requires further investigation. A systematic examination of the governing ablation mechanisms and optimization of process parameters remains crucial for achieving high-quality, efficient machining of Cu components.MethodsA WJGL cutting approach specifically designed for Cu substrates was developed to address the challenges posed by Cu’s high thermal conductivity and reflectivity during laser processing. The research established a three-dimensional thermo-optical model for WJGL ablation of Cu, accompanied by experimental studies to understand the interaction mechanisms between the WJGL energy field and Cu. Subsequently, single-factor experiments were conducted to examine the effects of critical parameters, including single-pulse energy, repetition rate, scanning speed, and water pressure, on Cu removal morphology. The research further analyzed parameter interactions through response surface methodology (RSM) to determine optimal processing parameters for efficient and stable cutting performance.Results and DiscussionsThe comprehensive analysis of WJGL processing of Cu through mathematical modeling and experimental investigation revealed several significant findings. The validated WJGL ablation model demonstrated that the water jet functions both as an optical waveguide for laser beam delivery and as a thermal diffusion suppressor on the Cu surface, thereby minimizing heat-affected zones (HAZs) in non-target regions (Fig. 5). The research characterized the relationship between groove depth and scanning speed variations systematically (Fig. 7). Single-factor experiments revealed the distinct effects of key process parameters on groove dimensions and morphology (Fig. 8). The RSM analysis of parameter interactions identified optimal processing conditions: single-pulse energy of 3.5 mJ, repetition rate of 9 kHz, scanning speed of 3 mm/s, and water pressure of 19 MPa (Table 9). These optimized parameters enabled the production of Cu grooves with an aspect ratio reaching 23∶1 through single-pass scanning experiments (Fig. 17).ConclusionsThis study systematically investigates the characteristics of WJGL processing of Cu through a combination of mathematical modelling and experimental validation. The key findings are as follows:(1) A predictive erosion model for WJGL ablation of Cu was established, demonstrating that the water jet serves as an effective thermal regulator by constraining the surface temperature distribution of the material. This mechanism substantially suppresses HAZs and thermal damage in regions outside the laser focus. Comparative analysis between groove engraving experiments conducted at varying scanning speeds and corresponding numerical simulations reveals a high degree of consistency in the depth profiles, thereby validating the reliability of the proposed model.(2) Through the integration of single factor experiments and RSM, this study systematically evaluated the influence of critical process parameters, including single-pulse energy, repetition rate, scanning speed, and water pressure, on groove geometry and surface morphology. The research identified optimal parameters that facilitate the production of high aspect ratio Cu grooves (aspect ratio up to 23∶1) while preserving structural integrity and processing quality.This investigation establishes theoretical and empirical foundations for the high-quality fabrication of deep, narrow Cu groove structures. Additionally, it presents strategic guidelines for process optimization to enhance ablation depth and enable full-thickness cutting of Cu materials in advanced manufacturing applications.

ObjectiveNeodymium?iron?boron (NdFeB) permanent magnets have become essential functional materials in new energy vehicle propulsion systems, high-end electronic communication devices, wind turbine generators, and precision medical equipment due to their superior magnetic properties. Laser processing is extensively utilized for NdFeB material fabrication due to its high-efficiency processing capabilities. However, NdFeB magnets experience irreversible magnetic degradation during laser machining due to their relatively low Curie temperature and poor thermal stability, primarily resulting from transient thermal shocks. The water-jet guided laser (WJGL) technique effectively reduces thermal accumulation in processing zones through continuous cooling via high-speed water jet impingement. However, the optimal process parameter configuration governing WJGL machining of NdFeB and the formation mechanisms of heat-affected zones (HAZ) remain inadequately understood. This research focuses on thermal regulation mechanisms during NdFeB machining, aiming to establish fundamental correlations between operational parameters and HAZ characteristics, thereby achieving synchronized optimization of cutting quality and efficiency.MethodsA comprehensive ANOVA-based investigation was performed to analyze the dominant effect patterns of laser power, pulse frequency, cutting velocity, and water-jet pressure on heat-affected zone (HAZ) width, groove width, and cutting efficiency. Single-factor experiments systematically examined the modulation mechanisms of critical process parameters on surface morphology, thereby clarifying the thermal regulation principles and material removal mechanisms during WJGL machining of NdFeB materials. Subsequently, an integrated ANOVA-range analysis approach was implemented to establish a multi-objective collaborative optimization model for cutting efficiency under HAZ suppression constraints, ultimately determining the optimal parameter set (10 W laser power, 14 kHz pulse frequency, 130 mm/s cutting velocity, and 20 MPa water-jet pressure). Finally, gas-assisted laser machining of NdFeB magnetic materials was comparatively evaluated to validate the thermal regulation advantages of WJGL methodology.Results and DiscussionsFigure 8 comparatively illustrates the surface morphologies of WJGL and gas-assisted laser (GAL, using purified compressed air) machining under identical laser parameters (10 W laser power, 14 kHz pulse frequency, 130 mm/s cutting velocity, 20 MPa water-jet pressure, and 0.7 MPa gas pressure), with quantitative morphological metrics detailed in Table 7. Comparative analysis demonstrates that WJGL achieves substantial reductions in groove width (29.46%) and surface heat-affected zone (HAZ) width (50.33%), alongside a 138.89% increase in cutting efficiency compared to gas-assisted laser (GAL). As depicted in Fig. 8, GAL-machined grooves display distinct blackened HAZ envelopes (27.89 μm thickness) along their edges and significant recast layer deposition within groove interiors. In contrast, WJGL-machined cross-sections exhibit no detectable HAZ characteristics and effectively suppress recast layer formation. This distinction confirms that the forced convective heat transfer of WJGL’s high-speed jet substantially reduces cutting temperatures, thereby minimizing thermal damage and enhancing machining quality.Based on our numerical simulation data of process parameters (results under review), Figure 9 displays temperature field distribution characteristics, revealing temporal temperature profiles at varying distances from the laser spot center during a single pulse cycle (160 ns pulse width). Data analysis indicates that WJGL’s high-speed water jet effectively restricts thermal diffusion, reducing the high-temperature zone (>613 K, the value is magnetic deterioration threshold of NdFeB) by 30.06% compared to air-assisted processing. At laser energy termination, WJGL demonstrates notably faster temperature decay rates than GAL due to forced convective cooling, stabilizing near ambient temperature (300 K) at the end of the pulse cycle. In contrast, air-assisted systems maintain temperatures exceeding 400 K at cycle termination, indicating significant thermal accumulation that intensifies HAZ expansion through subsequent pulse-induced heat superposition.ConclusionsANOVA results reveal that laser power demonstrates statistically significant dominant effects on cutting quality and efficiency (P<0.05), with single-factor experiments validating strong positive correlations with heat-affected zone (HAZ) width and cutting efficiency. Among secondary parameters, laser pulse frequency shows a significant negative correlation with HAZ width, while cutting velocity demonstrates a positive correlation with cutting efficiency, establishing these parameters as critical control variables for thermal damage mitigation and productivity enhancement, respectively.Through comprehensive ANOVA and range analysis, the optimal process parameters for water-jet guided laser machining of NdFeB were identified as: 10 W laser power, 130 mm/s cutting velocity, 20 MPa water-jet pressure, and 14 kHz pulse frequency. While maintaining equivalent HAZ suppression effectiveness, compared to single-factor optimized parameter sets, this configuration achieves a 24.19% cutting efficiency improvement over pure efficiency-optimized groups, meeting the coordinated optimization objectives of cutting quality and efficiency. Under identical laser parameters (10 W, 14 kHz) and cutting rates (130 mm/s), water-jet guided laser machining demonstrates superior performance over gas-assisted laser machining with 29.46% groove width reduction, 50.33% HAZ width decrease, and 138.89% cutting efficiency enhancement. The superior thermal regulation efficacy observed at lower power levels can enhance benefits during high-power water-jet machining. These findings confirm the synergistic capability of high-speed water jets in simultaneous thermal management and efficiency optimization through effective convective heat transfer.

ObjectiveCarbon fiber reinforced polymer (CFRP) is a new type of composite material comprising a resin matrix and carbon fiber reinforcements. It is characterized by high strength and excellent thermal stability, which renders it widely applicable in sectors such as aerospace and the automotive industry. However, CFRP also exhibits traits such as complex anisotropy and low interlaminar strength, categorizing it as a material processing challenge. The considerable disparity in thermodynamic properties between the carbon fibers and the resin within CFRP results in an extensive heat-affected zone during conventional laser processing, consequently impairing the mechanical properties of the material. Water-guided laser technology represents a hybrid processing approach that integrates laser machining with water jet cutting. The pronounced cooling effect provided by the water jet serves to mitigate thermal damage effectively. Nevertheless, present challenges in the water-guided laser processing of thick materials include low efficiency and a non-linear decline in efficiency with increasing depth. To enhance the processing efficiency of water-guided laser techniques for thick laminates and to achieve a large depth-to-width ratio in slot machining, it is imperative to conduct in-depth investigations into the dynamic evolution of the slot morphology during the deep processing and the transmission characteristics of the coupled energy beam within the slot.MethodsThe experiments utilize a CFRP specimen with dimensions of 40.0 mm×20.0 mm×10.0 mm. Initially, the CFRP plate is adhered using a microscope slide, and a camera is employed to document the entire process of water-guided laser cutting of the CFRP. Subsequently, the acquired processing video is subjected to image processing to isolate the binary images of the coupled energy beam for each frame, which are then stitched together to produce a visual representation of the morphological changes in the groove throughout the machining process. Next, based on the pixel dimensions and the actual physical dimensions, the average transmission depth of the coupled energy beam is calculated, resulting in a line graph depicting the relationship between the transmission depth and the number of scanning iterations. Finally, a summary of the groove formation process is conducted, and an analysis is performed regarding the causes of the morphological changes in the grooves and the attenuation of cutting efficiency with increasing depth, integrating existing data and images to support the findings.Results and DiscussionsThe process of water-guided laser cutting of thick CFRP can be divided into three main stages, as illustrated in Fig. 6: the initial cutting stage (cutting depth H<2 mm), where the groove bottom remains relatively smooth; the intermediate cutting stage (2 mm <H<5 mm), during which the groove bottom becomes uneven. In this stage, as the depth increases, the condition exhibits a characteristic of first strengthening and then weakening. With a greater processing depth, the coupled energy beam experiences an increased random interference, leading to unstable energy transmission and resultant irregularities at the groove bottom. Once the fluctuations at the groove bottom reach a certain level, the machining efficiency in the recessed areas drops below that of the raised areas, thus reducing the overall unevenness of the groove bottom. During the later cutting stage (5 mm<H<10 mm), the groove bottom transitions to a concave shape with the center lower than the sides, ultimately leading to preferential cutting through the center and gradually towards the sides. This occurs because the cutting efficiency of the inclined surface during the water-guided laser processing is lower than that of a flat surface. By plotting the average transmission depth of the coupled energy beam against the number of scanning iterations, it is observed that the average transmission depth steadily increases, although the rate of increase gradually slows down. A comparison of the fitted images of the coupled energy beam under different scanning iterations reveals that the interference experienced by the coupled energy beam increases with the transmission distance, indicating that the beams previously unaffected at shallower depths become subject to interference, as shown in Fig. 8.ConclusionsExperiments on the processing of thick CFRP plates are conducted using a self-developed water-guided laser platform, and a method based on image processing is proposed to capture the dynamic change in the morphologies of the CFRP grooves. This method enables the acquisition of real-time dynamic changes in the groove morphology and the transient beam transmission during the cutting process. Based on the experimental results, the morphological variations of the grooves during the deep processing with a water-guided laser and the transmission characteristics of the coupled energy beam within the grooves are summarized. The results indicate that during the processing of thick materials with a water-guided laser, the groove bottom shape undergoes three distinct stages: flat, uneven, and concave. This progression is a result of the combined effects of laser energy transmission attenuation, difference in energy absorption at the groove bottom, and interference from sputtering. Additionally, the processing efficiency of a water-guided laser shows a notable decrease with increasing cutting depth, which is directly attributed to the heightened interference experienced by the coupled energy beam. To achieve efficient processing with a high depth-to-width ratio using a water-guided laser, it is essential to enhance the stability of the jet transmission within the grooves.

ObjectiveWith the development of aerospace and national defense industries, the demand for high-performance aerospace components continues to grow. Nickel-based superalloys are widely used in the hot-end components of aerospace and gas turbine engines due to their excellent high-temperature strength, fatigue resistance, corrosion resistance, and oxidation resistance. Although this type of superalloy has many advantages, its high strength and low thermal conductivity increase the processing difficulty, especially for traditional machining methods. Therefore, it is of great significance to break through the limitations of conventional machining methods to improve the machining efficiency and quality of nickel-based superalloys.MethodsThe experiment is divided into three parts. First, a single-factor experiment was conducted, selecting five factors: the number of scans (N), laser power density (I), pulse repetition frequency (f), pulse overlap rate (rPO), and pump voltage (Vpump), to analyze changes in microgroove width, depth, and material removal rate (MMR), providing guidance for subsequent optimization of superalloy coaxial waterjet-assisted laser micro-machining. The experimental parameters for this section were listed in Table 2. The second part was a response surface experiment using a Box?Behnken design (BBD) to establish a regression equation for predicting MRR, investigating how different parameters interact and influence the results. The third part compared the geometric features, thermal damage, and processing quality of microgrooves processed by GAL and CWAL. For GAL processing, the water circuit was closed, and the air circuit was opened to introduce compressed air.Results and DiscussionsTo investigate the effects of different laser treatments on the K4002 superalloy, EBSD (electron back scatter diffraction) analysis was conducted on the cross-sectional area of the microgrooves to characterize their crystallographic properties. Observations reveal that for microgrooves processed by GAL, the outermost recast layer exhibits significant orientation changes and a fine-grained structure, with a thickness of approximately ten micrometers. This may be attributed to rapid cooling. Due to the presence of cracks, the connection between the recast layer and the substrate is discontinuous. A region of approximately 5 μm in width between the recast layer and the substrate exhibits minor orientation changes, which constitutes the heat-affected zone. This indicates that the surface layer of the nickel-based single-crystal superalloy undergoes a transformation from single-crystal to polycrystalline structure due to the thermal accumulation effect during GAL processing. The primary reason is that material removal in nanosecond laser processing of nickel-based alloys mainly occurs through two mechanisms: vaporization and melting. Within the laser pulse interval, molten material accumulates on the processed surface and recrystallizes. Under repeated laser exposure, the process of melting and recrystallization is repeated. The molten material is uniformly distributed on the processed surface, forming the recast layer. For microgrooves processed by CWAL, no significant orientation changes are observed, indicating that their microstructures are not affected by laser processing. In CWAL processing, the waterjet removes the ablated material from the processing area. Since the specific heat capacity of the solid material is lower than that of water, the heat generated during the process is absorbed and carried away by the waterjet. Since heat cannot accumulate continuously or be conducted to the substrate, the substrate material adjacent to the processing area is protected, thereby eliminating the heat-affected zone (HAZ) and reducing the formation of the recast layer. The microstructural characteristics of microgrooves processed by different lasers indicate that an appropriate cooling medium can effectively eliminate the thermal effects of laser processing and prevent thermal damage to the adjacent substrate.ConclusionsGAL machining can produce microgrooves with an aspect ratio (AR) of 2.4?5.1. However, the AR does not change significantly with an increase in the number of scans. After 300 laser scans, the microgroove depth and width reached 241 μm and 69 μm, respectively. Additionally, severe slag accumulation was observed at the entrance of the microgrooves produced by GAL machining, with flake-like slag detected at the bottom of the microgrooves. Due to the presence of a large amount of oxygen in the auxiliary gas, a recast layer and HAZ were formed on the surface layer of the microgrooves during machining. CWAL processing formed relatively clear and deep microgrooves with a low AR of 0.8?2.4. Increasing the CWAL scans can increase the depth of the microgrooves. After 300 laser scans, the depth and width of the microgrooves reached 302 μm and 128 μm, respectively. The waterjet suppressed the formation of the HAZ, but formed a recast layer with a thickness of less than 1 μm. Through single-factor experiments, it was found that when the pulse repetition frequency f is constant, the microgroove depth increases with increasing number of scans, while the MRR decreases. Conversely, when the number of scans is constant, the microgroove width and MRR are positively correlated with the f and negatively correlated with the microgroove depth. Laser power density I and pump voltage Vpump have a positive impact on microgroove depth and MRR. Additionally, increasing the pulse repetition frequency f leads to expanded thermal damage around the processing area and shallower processing depth. In the RSM experiments, the parameters influencing MRR, ranked from high to low, are Vpump, f, I and rPO. The optimized process parameters for maximizing MRR were identified as follows: I=1.67 GW/cm2, f=26.35 kHz, rPO=96.47%, and Vpump=15.51 V (equivalent waterjet velocity vw=6.63 m/s).

ObjectiveLaser-electrochemical composite machining (LECM) integrates laser ablation and electrochemical dissolution to enable high-efficiency, high-precision processing of difficult-to-machine materials. However, non-uniform spatial energy distribution and significant laser attenuation in electrolyte jets critically limit the machining quality and efficiency. Current research lacks systematic quantification of key parameters: jet diameter, laser wavelength, spot size, and mass fraction of NaCl. This study aims to establish a high-fidelity BEM-based model to elucidate laser energy evolution and attenuation in electrolyte jets, quantify the impacts of key parameters on transmission characteristics, and provide theoretical foundations for optimizing LECM energy distribution.MethodsA numerical model based on the beam envelope method (BEM) in COMSOL Multiphysics was developed to simulate the propagation of Gaussian lasers via total internal reflection in electrolyte jets. The model simulated the spatial energy evolution and attenuation under varying parameters: jet diameters (50?500 μm), laser wavelengths (355, 532, 1064 nm), spot radii (10?40 μm), and NaCl mass fractions (5%?20%). Experimental validation was conducted using a 500 μm pure water jet: a beam profiler was employed to measure spatial energy distributions, and a laser power meter was used to quantify transmission losses.Results and DiscussionsThe conclusions obtained in this study are as follows:(1) Laser energy exhibits a periodic divergence?reflection?refocusing cycle along the jet axis. The focusing period length (T) follows the relationships: T∝D2 (proportional to the square of jet diameter), T∝n (proportional to refractive index), and T∝1/λ (inversely proportional to wavelength). The spot radius has minimal effect on T but significantly influences energy uniformity: smaller spots promote multimode distributions, whereas larger spots enhance central energy concentration.(2) Higher NaCl mass fractions increase the refractive index but simultaneously raise the attenuation coefficients.(3) Measured spatial energy distributions in pure water jets show close agreement with simulations, confirming the model accuracy. Deviations at longer jet lengths (>80 mm) are attributed to surface fluctuations and alignment errors.(4) Laser intensity attenuation follows the Beer?Lambert law. For 1064 nm lasers, NaCl solutions exhibit higher attenuation than pure water, with losses dependent on the mass fraction of NaCl.ConclusionsWe developed a numerical simulation model for laser energy transmission in an electrolyte jet using the beam-envelope method and validated it experimentally. The main conclusions are as follows:(1) The simulation model accurately captures the laser transmission process in the electrolyte jet, where the laser energy distribution exhibits a periodic divergence?reflection?refocusing pattern.(2) Jet diameter, laser wavelength, laser spot radius, and liquid medium significantly influence the laser energy distribution. The focusing period length is proportional to the square of the jet diameter and the medium refractive index, and inversely proportional to the laser wavelength.(3) While the laser spot radius does not affect the focusing period length, it significantly impacts the uniformity of the energy distribution at the jet interface. A larger spot size leads to more concentrated laser energy.(4) We investigated laser energy attenuation in the electrolyte jet, accounting for the absorption and scattering effects of the medium. Results show that increasing the mass fraction of NaCl increases both the focusing period length and laser transmission loss in the medium.These findings provide a theoretical basis for optimizing and controlling laser energy distribution in liquid-guided laser-electrochemical composite machining.

ObjectiveWater jet-guided laser (WJGL) processing technology demonstrates significant advantages including minimal taper, limited heat-affected zone, absence of burrs, and high processing precision, enabling its widespread application across various difficult-to-process materials. However, external gas interference can compromise the stability of high-speed water jets, directly impacting WJGL processing accuracy and quality, resulting in dimensional inconsistencies, degraded edge quality, and reduced processing efficiency. While existing research primarily addresses water jet stability before processing by implementing coaxial assisted gases in direct contact with the water jet for protection against external disturbances, limited attention has been directed toward jet behavior during the processing phase. This study introduces a staged contact spiral water-gas coupling device designed to shield the water jet from external interference, thereby extending its stable length. Furthermore, experimental investigations were conducted to analyze sputtering suppression using various assisted gases during groove cutting, and verification tests examined the processing capabilities of staged contact spiral gas-assisted WJGL, exploring the mechanism by which assisted gases suppress jet disturbances during operation.MethodsThe research methodology commenced with the development of numerical simulation and geometric models for two-phase water-gas flow in a staged contact spiral water-gas coupling device, utilizing the volume of fluid (VOF) method (see Fig. 1(a)). Local refinement was applied to the water jet's central region (see Fig. 1(b)), facilitating analysis of the flow field distribution following water-gas coupling and investigation of helium/compressed air pressure effects on water jet stable length. Subsequent experimental verification assessed the model's rationality and effectiveness through stable length measurements. Additional experiments examined the suppression characteristics of various assisted gases on jet splashing during simulated grooving (Fig. 3). The study concluded with staged contact spiral gas-assisted WJGL processing experiments on 7075 aluminum alloy using parameters specified in Table 1. Multiple-pass cutting tests were performed to measure cutting depth and analyze post-cutting surface morphology, evaluating the impact of staged contact spiral assisted gas on processing efficiency and quality.Results and DiscussionsThrough simulation and experimental verification, the staged contact spiral water-gas coupling device designed in this study demonstrates an increase in the stable length of the water jet, which initially increases and subsequently decreases with increasing air pressure (Fig. 5). The stabilized length of the water jet reaches 69.2 mm with helium assistance, representing a 64% increase compared to conditions without gas assistance (42.2 mm). The length with air assistance (55.5 mm) shows a 31.5% increase compared to conditions without gas assistance (Fig. 6). Additionally, the length with staged contact spiral gas assistance increases by 26.7% compared to direct contact (54.6 mm) (Fig. 7). Analysis of water jet sputtering patterns in simulated WJGL grooving reveals that compressed air (37.4°) exhibits superior capability in suppressing water jet sputtering compared to helium (50.3°) under identical conditions (Fig. 8). In gas-assisted WJGL cutting of aluminum alloy, the equivalent cutting speed initially increases with gas pressure before stabilizing. The equivalent cutting speed with compressed air assistance achieves 14 mm/min, notably higher than helium assistance (11 mm/min), and 40% greater than conditions without gas assistance (10 mm/min) (see Fig. 9(a)). During multiple cutting passes, groove depth increases progressively, with compressed air assistance producing greater groove depths compared to helium assistance (see Fig. 9(b)), though helium yields marginally superior groove surface morphology (see Fig. 9(c)). The assisted gas enhances WJGL processing efficiency by creating a protective layer around the water jet, inhibiting interference from jet sputtering droplets and facilitating timely drainage of accumulated water, thereby enabling efficient laser energy transmission and improved processing performance (Fig. 10).ConclusionsThis study presents a staged contact spiral water-gas coupling device. Numerical simulation and experimental validation demonstrate that the stable length of the water jet exhibits an initial increase followed by a decrease with increasing gas pressure. Helium assistance achieves a stable jet length of 69.2 mm, representing a 64% increase over non-assisted conditions (42.2 mm), while compressed air produces a 31.5% increase (55.5 mm) compared to non-assisted conditions and demonstrates a 26.7% improvement compared to direct-contact gas assistance (54.6 mm), validating the device's effectiveness. Under identical conditions, compressed air (37.4°) demonstrates superior suppression of jet sputtering effects compared to helium assistance (50.3°). In single-pass reciprocating grooving experiments on 7075 aluminum alloy, 90 kPa compressed air assistance achieves higher equivalent cutting speeds than helium assistance at equivalent pressure, yielding a 40% efficiency improvement. However, helium produces superior surface morphology in grooved channels. The study elucidates the mechanism through which assisted gas suppresses water jet disturbances during material processing. The assisted gas generates a protective layer surrounding the water jet, minimizing droplet splashes and facilitating water drainage, thereby maintaining jet stability and enhancing processing efficiency and quality.

ObjectiveWater-jet guided laser processing technology integrates traditional laser processing with water-jet processing, representing an advanced composite processing methodology. This technology enables high-precision processing of high-temperature alloys, hard and brittle materials, and composite materials, demonstrating significant applications in aerospace, defense and military, precision medical, and related fields. In water-jet guided laser processing technology, the coupling quality between laser and water beam constitutes the fundamental element of laser energy transmission, with water?laser coupling quality directly correlating to laser source characteristics including wavelength, pulse width, and power. The 1064 nm wavelength laser offers advantages in stability, penetrating power, and cost-effectiveness; however, its high absorption coefficient in water generates substantial thermal effects in the water beam, compromising the stability of water?laser coupled energy. Consequently, enhancing the water?laser coupling mode and preventing energy concentration from exceeding the water medium's damage threshold remains crucial for achieving effective coupling between high-power 1064 nm laser and water jet.MethodsThis research examined the effects of multi-focal water?laser coupling on water-jet guided laser coupling characteristics through comprehensive simulation and experimental analysis. The simulation phase encompassed the development of an equivalent optical path model for the multi-focus optical system through initial lens introduction, optimization function construction, and multiple structure configuration. Sequential analysis of parallel laser beam focusing through multi-curvature lenses was performed by ray tracing methodology. Beam quality assessment of multi-focal lasers was performed by spot diagram image point density analysis. Additionally, a multi-focal beam coupling model for laser spot tracking was constructed by introducing the axial deviation parameter. The experimental phase commenced with multifocus beam focusing experiments to determine the multi-curvature lens actual focal length and focal point spot configuration. Subsequently, water?laser coupled energy stability experiments were used to evaluate the thermal effect reduction capability of the multi-focal water?laser coupling mode. The research concluded with water-jet guided laser processing groove experiments to investigate the differential impacts of two water?laser coupling modes on processing performance. Experimental validation employed three-dimensional super-depth digital microscopy analysis.Results and DiscussionsBased on the principles of coaxial multi-focal point water?laser coupling and light ray theory, this study established a theoretical model of multi-focal point beam spot and water-jet coupling (Fig. 2), determining the correlation between maximum beam spot radius and focal length during the laser beam and water jet coupling process at the nozzle hole position. Through the determination of fundamental parameters in the multi-focal point water?laser coupling system, including the projection size of the multi-curvature lens profile, focal length range, and curvature radius, a multi-curvature lens was developed for water-jet guided laser processing (Fig. 3). By constructing an equivalent optical path model of the multi-focal point optical system in sequence mode, researchers obtained a ray tracing diagram of parallel laser beams traversing the multi-curvature lens (Fig. 4). The beam quality assessment of the multi-focal point laser involved analyzing image point density on the point spread function (PSF) diagram (Fig. 5). Through the FFT (fast Fourier transformation) PSF distribution and cross-sectional diagram of the multi-focal point beam (Fig. 6), results confirmed that the multi-focal point coupling mode achieved uniform distribution of total laser power at each focal point. The experimental research comprised three main components: multi-focal point beam focusing experiments, water?laser coupled energy beam stability tests, and water-jet guided laser processing groove experiments. Analysis of ablation spot morphology formed by the multi-focal point beam at different focal lengths revealed five ablation spot rings, validating the theoretical design and simulation of the multi-curvature lens (Fig. 11). Investigation of laser power effects on nozzle lifespan demonstrated that, with a benchmark lifespan of 3000 s, the multi-focal point water?laser coupling mode enabled a laser power increase from 120 W to 300 W, representing a 150% improvement (Fig. 12). The study identified three primary factors causing nozzle damage during laser and water jet coupling: wear, cracks, and ablation (Fig. 13). Comparative analysis of processing effects between single-focal point and multi-focal point water-jet guided lasers on TC11 titanium alloy materials demonstrated that multi-focal point water-jet guided laser processing technology substantially enhances processing efficiency, effectively controls thermal damage, and maintains processing quality stability.ConclusionsThis research demonstrates the effectiveness and feasibility of multi-focal laser systems in enhancing water?laser coupling power and minimizing coupling damage. The developed multi-curvature lens for water-jet guided lasers achieves multiple focusing effects on the mesoscopic scale of the optical axis. In water?laser coupling nozzle life evaluation based on 1700 s, multi-focal water?laser coupling mode increased the initial laser power from 120 W to 360 W, representing a 200% power enhancement compared to single-focus water?laser coupling. The TC11 groove dimensions in multi-focal water-jet guided laser (MFWJGL) processing reached maximum values at 360 W laser power, achieving a groove depth of 764.6 μm and width of 767.7 μm. Compared to single-focal water-jet guided laser (SFWJGL) processing, the groove depth increased by 149.5%, while width increased by only 13.7%. These results confirm that MFWJGL processing technology significantly improves processing efficiency, maintains effective thermal damage control, and ensures consistent processing quality.

ObjectiveDiamond is an ideal thermal-conductive material for application of high-frequency and high-power components, which possesses high heat conductivity, low coefficient of thermal expansion, and superb heat stability. However, machining of diamond materials has remained a long-term challenge due to its extreme mechanical property. Water-jet guided laser (WJGL), as a novel laser machining technology, has advantages in precise and efficient material removal of diamond. First, laser fluence is confined in the water jet, forming a uniform distribution rather than a Gaussian distribution in dry laser. Focus plane is absent, and ablation taper can be improved. Second, water flow directly acts on the machining surface, which is beneficial for decreasing heat-affected zone and washing out ablation debris. Therefore, WJGL is suitable for machining diamond and fabricating related components. Nevertheless, there is still a research gap in this field, especially in ablation mechanism and fabrication techniques. This work aims to fill in this gap by exploring critical ablation condition, material removal mechanism, and precision/efficiency-related outcomes in WJGL machining of polycrystalline diamond. Fabrication of thermal-conductive micro-channel component was also tested.MethodsExperiments were carried out on 5-axis WJGL machining equipment with an Nd∶YAG laser, which has a wavelength of 532 nm and a pulse width of 210 ns. Machining process was operated with the following parameters: repetition rate of 6 kHz, water-jet pressure of 300 bar, nozzle diameter of 50 μm, gas (He) flow rate of 1.5 L/min (under standard conditions), laser power of 12?20 W, and scanning speed of 2?10 mm/s. Polycrystalline diamond bulks (synthesized via chemical vapor deposition) were the machining samples with a size of 2.5 mm×2.5 mm×0.5 mm. The samples were pre-polished to a surface roughness Sa<10 nm. Both cutting and grooving testing were performed.Results and DiscussionsThe critical ablation threshold of the polycrystalline diamond under WJGL machining cannot be calculated using the traditional method of dry laser, because the laser power decreases with its transmission under water. A modified calculating equation for WJGL machining was proposed, which was related to absorption coefficient of water and underwater depth. As shown in Fig. 2, the ablation threshold of WJGL linearly increases with the increase of the initial laser power. Moreover, the ablation thresholds exceed 100 J/cm2, which are 3?5 times higher than those of dry laser machining. Then, the ablation surface was observed with microscope, as shown in Fig. 3. The machining morphology presents periodic cut marks, formed by the radial impact of water jet during each scanning process. Moreover, both bright and dark regions can be recognized on the ablation surface. The bright region seems like uncovered diamond grain, featuring a one-piece construction with grain boundary. The dark region possesses micro-holes with crack propagation. By further analyzing with Raman spectrum, the bright and dark regions are confirmed to be diamond phase and graphitic/defective phase, respectively. Then, the ablation mechanism was proposed, as shown in Fig. 4. Under the influence of WJGL, diamond undergoes softening and even sublimation, resulting in graphite/defect layers with microcracks. Subsequently, under the scouring and impact of water jet, cleavage occurs. Part of the underlying diamond grains can be found on the processed surface, which is beneficial for improving the thermal conductivity of the processed surface.The influences of laser power on machining morphology and surface roughness were investigated, as shown in Fig. 5. Bright region expands with the increase of laser power, indicating high power is beneficial to diamond exposing. However, increasing power is disadvantageous to reduce cut marks. Surface roughness Sa significantly decreases when laser power reaches, and then slightly increases. Sz fluctuates at 14?20 W with minimal value at 14 W and 18 W. Grooving tests were performed to investigate machining efficiency, as shown in Fig. 6. Machining width and depth are both positively correlated with laser power, while width is more sensitive. Material removal rate (MRR) gradually increases with increasing laser power. Based on surface roughness and MRR, laser power of 14 W is regarded as the suitable parameter.The influences of scanning speed on machining morphology and surface roughness were investigated, as shown in Fig. 7. The machining morphology is similar to the experimental results of laser power. Increasing scanning speed is beneficial to decrease surface roughness when it is less than 8 mm/s. Both Sa and Sz follow this trend. Grooving tests with different scanning speeds were shown in Fig. 8. MRR is positively correlated with scanning speed, and corresponding influence is higher than that of laser power. The best parameter combination is laser power of 14 W and scanning speed of 8 mm/s, where Sa and MRR reach optimal values of 538.5 nm±21.1 nm and 18.4×10-3 mm3/s, respectively.Using the optimal parameters, we machined a thermal-conductive micro-channel array on the polycrystalline diamond surface, as shown in Fig. 9. The structural width and depth are measured to be 85 μm±3 μm and 300 μm±20 μm, respectively. The machining duration for a single piece is only about 90 s.ConclusionsThe ablation threshold for WJGL machining of polycrystalline diamond is positively correlated with the initial laser power, and significantly higher than that of dry laser. The material removal mechanism for WJGL machining of polycrystalline diamond involves the diamond phase softening and transforming into graphitic/defective phase, which is then washed away by the water jet. Increasing both laser power and scanning speed within a certain extent can significantly reduce the machining surface roughness. The material removal rate is positively correlated with both factors. The optimal machining parameters are laser power of 14 W and scanning speed of 8 mm/s, resulting in Sa and MRR of 538.5 nm±21.1 nm and 18.4×10-3 mm3/s, respectively. With the optimal parameters, a precise thermal-conductive micro-channel array can be fabricated on the polycrystalline diamond surface, and the machining efficiency is very high.

ObjectiveWater-jet guided laser (WJGL) machining utilizes a hair-thin water jet as an optical fiber to guide the laser beam for precision cutting. It offers advantages such as minimal thermal effect, no need for real-time focus adjustment, parallel kerf walls, high aspect ratio, and pollution-free. However, during the WJGL machining, the intense interaction among the laser, the high-pressure water jet, and the material forms a highly complex multi-energy-field coupling process involving optics, hydrodynamics, and thermodynamics. Investigating the influence of temperature evolution and fluid flow during WJGL machining is extremely intricate, as the physical mechanisms of material removal significantly impact the machining quality. Nevertheless, experimental investigation of these mechanisms is challenging.MethodsTo investigate the material removal mechanisms under multi-field coupling in WJGL machining, a multi-pulse transient numerical model incorporating solid?liquid?gas three-phase multi-field coupling was established for WJGL processing of monocrystalline silicon. Experimental validation was conducted to confirm the model's effectiveness and accuracy. The melting and vaporization processes of monocrystalline silicon during WJGL machining involve solid?liquid and gas?liquid interface tracking problems. In this study, the enthalpy?porosity method was employed for solid?liquid interface tracking, while the volume of fluid (VOF) method was applied for gas?liquid interface tracking. From the perspectives of heat transfer, mass transfer, and dynamics, the material removal mechanisms were systematically explored to provide technical support for the development of high-quality and high-efficiency WJGL machining methods.Results and DiscussionsThe comparison between simulation and experimental results demonstrates the high reliability of the developed model (Fig. 4). Simulation results reveal that the thermal effect of laser power can approximately reach a dynamic equilibrium with the cooling effect of the water jet (Fig. 6), where laser power is proportional to hole depth and the hole surface temperature distribution under four laser powers exhibits an overall Gaussian-like profile (Fig. 5). The relationship between water pressure and hole depth is influenced by multiple factors (Fig. 7), leading to the hole depth at 10 MPa exceeding that at 12 MPa after 200 pulses. The thermal accumulation effect in high-frequency pulses enhances the material removal rate, causing the maximum temperature at 301 kHz to gradually surpass that at 251 kHz and 276 kHz as the number of pulses increases (Fig. 9). However, this also induces increased thermal damage, while reducing the pulse frequency promotes better cooling during the inter-pulse interval (Fig. 10). The molten pool generated at 119 W laser power completely dissipates under the impact and cooling of the water jet, whereas the molten pool at higher powers is not fully removed before the next pulse cycle arrives. The velocity vector distribution of the molten pool shows high consistency with the streamline pattern of water flow in the hole, with the flow velocity minimal at the bottom of the molten pool and relatively higher at the periphery (Fig. 12).ConclusionsWe established a multi-pulse transient material removal model for WJGL machining, incorporating the solid?liquid?gas three-phase evolution of monocrystalline silicon, and validated the model experimentally. Based on this model, the influence mechanisms of different process parameters on the temperature field and morphological evolution during WJGL material removal were analyzed from the perspective of heat and mass transfer. The dynamics of material removal were analyzed from the perspective of fluid flow, revealing the interaction mechanism between the water jet and the molten material. Simulation results indicate that laser power is proportional to the energy absorbed by the material, with higher laser power yielding higher temperatures and deeper holes. The thermal effect of laser power at 119 W and 139 W essentially reaches a dynamic equilibrium with the cooling effect of the water jet. Under different water pressure conditions, the material removal process is influenced by the combined effects of water jet cooling, impact force, and hole depth. The velocity vector distribution of the molten pool shows high consistency with the streamline pattern of water flow within the hole. The deflection angle of the water flow after impacting the hole exceeds 90°, and the difficulty of melt expulsion increases with hole depth. This research provides a reference for understanding the mechanisms of process control in WJGL machining; future work will explore the effects of coupling different process parameters on the machining process.

ObjectiveSm2Co17 permanent magnets, which exhibit the highest energy product among rare-earth magnets under high-temperature conditions, are critically important for aerospace, microwave devices, automotive systems, and other applications. However, the high hardness and brittleness of Sm2Co17 make it challenging to machine. Conventional mechanical processing induces cracking, electrical discharge machining suffers from low efficiency, and conventional laser processing causes thermal degradation of magnetic properties. Therefore, there is an urgent need to develop a novel machining technique capable of processing Sm2Co17 permanent magnet alloys with both high quality and high efficiency. Compared with the traditional processing methods, water-jet guided laser processing technology has the advantages of small thermal influence, long working distance, small processing taper, etc., which is suitable for processing hard and brittle materials, but there is no report about water-jet guided laser processing of Sm2Co17 permanent magnet alloys. The purpose of this paper is to study the process characteristics and advantages of water-jet guided laser processing of Sm2Co17 permanent magnet alloys.MethodsThis study investigates the influence of water-jet guided laser parameters on the machining quality of Sm2Co17 permanent magnet alloys, and a comparative study of conventional laser processing methods is carried out. First, single-factor experiments are conducted to analyze the effects of laser power density and scanning speed on groove depth and width. The influence of process parameters on the kerf surface topography is investigated using scanning electron microscope (SEM). Then, the influence law of process parameters on the roughness of the kerf surface is investigated using a three-dimensional optical profilometer. And we compare the recast layers of materials after water-jet guided laser and conventional laser processing. On this basis, energy dispersive spectroscopy (EDS) is employed to further investigate the effects of laser power and scanning speed on the oxidation level of kerf surfaces. Finally, the physical property measurement system (PPMS) is utilized to compare the magnetic properties of samples processed by water-jet guided laser versus conventional laser cutting. In addition, in order to study the effect of water-jet guided laser processing on the magnetic properties of Sm2Co17 permanent magnet alloys under different process parameters, an analysis of the magnetic properties of the material after processing with different process parameters is carried out.Results and DiscussionsAs laser power density increases, groove depth increases initially before reaching a plateau, whereas higher scanning speeds result in progressively shallower grooves that eventually stabilize (Fig. 2). This may be because the ablation depth of the material in a single pass increases with increasing power density for the same numbers of cycles during laser processing. However, when the groove depth is deeper, the water-jet inside the groove is stagnant due to the difficulty of discharging, which may affect the energy transfer of the water-jet guided laser, weakening the ablation effect of the laser on the material and leading to a reduction in the cutting efficiency. And increasing scanning speed results in less laser energy deposited per unit time per unit area of the material, and low spot overlap results in insufficient material ablation. For groove width, the increase in laser power density results in an increase in ablation capacity and an increase in groove width to saturation. And the increase in scanning speed results in a decrease in laser energy per unit area per unit time and a decrease in groove width (Fig. 3). Moreover, as laser power increases, enhanced material melting reduces brittle-fracture-induced pits on the kerf surface, although excessive melt accumulation increases surface roughness. Conversely, higher scanning speeds intensify water-jet scouring effects, thereby improving surface flatness and reducing roughness (Fig. 5). The increase in laser power makes the kerf surface roughness increase, and the increase in scanning speed decreases the kerf surface roughness (Fig. 7). After comparison, it can be seen that the recast layer on the surface of the material after water-jet guided laser processing is much smaller than that after the conventional laser processing (Fig. 8). Surface oxidation levels show a positive correlation with laser power but a negative correlation with scanning speed (Fig. 9). The optimal parameters for minimizing both surface roughness and oxidation level are identified as 10 W laser power with 20 mm/s scanning speed. Under optimized parameters, water-jet guided laser processed samples exhibit nearly unchanged magnetic properties while demonstrating excellent stability across varying processing parameters, in contrast, the sample processed by conventional laser exhibits significant reduction in coercivity (Fig. 10).ConclusionsThe influence laws of process parameters on the groove depth and width as well as the kerf surface topography and oxidation level under different process parameters are investigated, and the processed materials are analyzed for magnetic properties and compared with those by the traditional laser processing methods. Experimental results demonstrate that the optimized parameters can be used to achieve minimal surface roughness of 1.621 μm, controlled oxygen mass fraction below 8.76%, and exceptional magnetic property retention (98.8% for remanence and 99.5% for coercive force). These findings confirm that water-jet guided laser processing enables precision machining of Sm2Co17 permanent magnets with negligible magnetic degradation.

ObjectiveMicrojet water-guided laser technology has found extensive application in micro/nano-manufacturing fields such as microelectronics, aerospace, and biomedical engineering due to its exceptional processing capabilities. However, challenges in laser-water coupling significantly constrain the processing performance of the microjet water-guided laser technology. This coupling process involves the synergistic interaction of two energy fields: a laser beam and a stable liquid jet. The nozzle serves as the critical component for successful coupling, ensuring beam integrity and coaxiality as the laser enters the jet channel. In existing water-guided laser coupling setups, the laser spot is typically divergent and the coupling distance is relatively long, which further complicate the coupling process. This often leads to the jet instability and the direct irradiation of the laser beam onto the inner wall of the nozzle cavity, resulting in nozzle damage. Addressing these issues, this study proposes a method of coaxial assembly of the micro-jet nozzle orifice with its metallic cavity to resolve the coaxial coupling problem between the laser beam and the jet. This approach not only ensures the efficient and complete entry of the laser beam into the jet channel, thereby minimizing laser ablation damage to the inner walls, but also significantly enhances the jet stability, which is crucial for improving the processing accuracy and quality.MethodsThis study proposes a novel method for achieving high-precision coaxial assembly between the nozzle metallic cavity and its orifice. The approach entails first joining the metallic cavity to an unmachined sapphire orifice material, followed by high-quality drilling at the coaxial position using a precision positioning system. Compared to the conventional “drill-then-assembly” process, this method effectively eliminates the errors induced by secondary clamping, while the integrated welding significantly enhances the connection reliability. Specifically, nanosecond laser-induced plasma-assisted micro-welding is first employed to weld the chromium metallic cavity to the unmachined sapphire material. The weld joint morphology, fracture characteristics, and overall quality including interfacial bonding, elemental diffusion, mechanical properties, and hermeticity are systematically characterized and evaluated using scanning electron microscope, energy dispersive spectrometer, Raman spectroscope, shear strength testing, and leak testing. Subsequently, a femtosecond laser system integrated with a precision positioning system is utilized to perform high-precision drilling directly at the predetermined coaxial location on the sapphire material (pre-joined to the metallic cavity and still unmachined). The quality of the resultant sapphire orifice, the coaxial coupling accuracy between the orifice axis and the overall nozzle structure, and the axial pressure resistance of the nozzle assembly are comprehensively analyzed using optical microscopy, ImageJ image analysis software, laser beam profiler analysis, and hydrodynamic pressure testing.Results and DiscussionsThe welding interface between sapphire and chromium metal exhibits a mechanical interlocking structure, with elemental diffusion extending significantly beyond the area directly affected by the laser (Fig. 3). Brittle fracture occurs at the junction between the weld seam and the sapphire (Figs. 4 and 5), while the sapphire/chromium weld joint achieves a shear strength of 262.702 MPa (Fig. 7). The femtosecond laser drilled sapphire orifice demonstrates a diameter of approximately 250 μm with roundness value of 0.8, featuring intact edges free from cracks or chipping (Fig. 9). The laser spot output from the nozzle distributes uniformly after coupling, with no eccentricity, conforming to the distribution of laser energy (Fig. 10). It confirms the exceptional coaxial alignment between the sapphire orifice and the metallic cavity.ConclusionsThis study proposes a coaxial assembly method for a microjet water-guided laser nozzle (orifice and cavity): first welding the sapphire to the chromium metal cavity for robust bonding, followed by drilling a high-quality micro-orifice in the sapphire while ensuring its coaxiality with the metallic cavity. Comprehensive analysis of joint morphology, micro-orifice quality, assembly coaxiality, and pressure resistance validates the feasibility. The welded sapphire/chromium joint exhibits good formation without cracks or notches. Distinct elemental diffusion (indicating metallurgical bonding) and mechanical interlocking at the interface confirm reliable bonding. The joint achieves a shear strength of 262.702 MPa with excellent sealing, preventing liquid ingress. The femtosecond laser drilled sapphire orifice, with a diameter of ~250 μm and roughness of ~0.8, shows no cracks or chipping, with clean, intact edges. Laser beam profiling of the assembled nozzle output reveals a uniform spot distribution consistent with energy profiles, demonstrating high coaxiality without eccentricity. Pressure testing on axiality confirms structural integrity and tight connection. Combining with the shear strength result, it is indicated that there is a significant load tolerance on nozzle.

ObjectiveWater jet-guided laser technology, with its advantages of long working distance, wide material applicability, thin remelted layers, nearly no heat-affected zone, and low processing taper, is ideal for precision machining of microstructures such as micro holes and grooves. However, as this technique heavily relies on total internal reflection to guide substantial laser energy into the water jet, its processing capability remains constrained when addressing high-quality, high aspect/depth-to-width ratio requirements for holes, grooves, and edges, owing to the attenuation and divergence of the water jet. To optimize the flow characteristics of the water jet and extend its stabilization length, an unsteady multiphase turbulence model, incorporating surface tension effects, is established in this study. The influence of the assist gas type, flow velocity, and water?gas spacing on the high-speed water jet stabilization length, in coaxial gas?liquid separated annular gas blowing configurations, are investigated. The differential regulatory mechanisms of jet stability are explored by comparing the effects of different gas-blowing methods on the jet stabilization length.MethodsIn ANSYS, geometric models were established for four gas-blowing methods: coaxial gas?liquid separated annular blowing (CSAGB), coaxial helical gas blowing (CHGB), coaxial gas?liquid contact annular blowing (CCAGB), and radial contact annular blowing (RCGB) (Fig. 1). The body of influence (BOI) mesh refinement method was employed to perform a localized multilevel refinement on the grids in the gas and jet flow regions (Fig. 2). The VOF (volume of fluid) model and geometric reconstruction method were used to track the gas?liquid interface. The SIMPLE algorithm was adopted for pressure?velocity coupling, with the pressure discretization scheme set to “PRESTO!.” Temporal discretization was performed using a first-order implicit format, whereas the other variables were discretized using a second-order upwind scheme. A Realizable k?ε turbulence model was applied to simulate the water/gas jet morphology under the parameter settings listed in Table 1. Finally, volume-fraction phase diagrams were generated based on the Fluent computational data to calculate the jet stabilization length.Results and DiscussionsUnder identical conditions, the relative error between the simulated and experimentally measured jet stabilization lengths is 3.2% (Fig. 5). When the pressure drop along the flow channel and loss induced by the laser thermal effect are considered in the experiment, the error decreases, confirming the accuracy and reliability of the simulation results. In the CSAGB mode, high-density and high-viscosity gases are more likely to form a stable gas-protective layer to suppress the turbulent pulsation (Fig. 7); thus, when argon gas is used as the auxiliary gas, the stabilization length of the obtained water jet is the greatest (40.62 mm), followed by those obtained for nitrogen (32.65 mm), carbon dioxide (28.81 mm), helium (25.17 mm), and hydrogen (21.07 mm) (Fig. 6). As the gas flow velocity increases from 20 to 80 m/s, the jet stabilization length decreases monotonically due to the accelerated growth of the short-wavelength perturbations. Beyond 80 m/s, the variation in stabilization length is negligible (Fig. 8). At a water?gas spacing of 0.5 mm, the stabilization length of the jet, obtained by axially injecting helium gas with annular flow, is the longest. A further increase in the spacing first triggers a sharp decrease and then gradual stabilization (Fig. 10); this trend is attributed to the intensified turbulent mixing that exacerbates the Kelvin?Helmholtz instability at the water?gas interface (Fig. 11). The CHGB method offers significant performance advantages owing to its unique vortex effect and kinetic energy transfer mechanism. The stabilization length of the jet under this blowing mode (67.83 mm) is 14.64 mm longer than that of the suboptimal mode (CCAGB: 53.19 mm) and substantially exceeds those of the other approaches (CSAGB: 25.17 mm; RCGB: 11.41 mm) (Fig. 12).Conclusions1) At a water?gas spacing of 1 mm and gas flow velocity of 60 m/s, axially injected carbon dioxide, argon, and nitrogen show effective annular flow characteristics, forming stable protective gas layers around the high-speed water jet. Compared with other gases, argon notably extends the jet stabilization length. 2) Higher auxiliary gas velocities promote the formation of unstable short-waves on the water jet surface, accelerating jet destabilization and fragmentation. When the gas velocity exceeds 80 m/s, the jet stabilization length remains nearly constant. 3) At a 0.5 mm water?gas spacing, the maximum jet stabilization length is 52.89 mm, which is 62.14% larger than that of free jets under atmospheric conditions. As the water?gas spacing increases, the jet stabilization length decreases sharply and then tends to be stable. 4) The CHGB method achieves a jet stabilization length of 67.83 mm, which is 14.64 mm longer than that achieved using the CCAGB method (53.19 mm) and substantially longer than those obtained using the other methods (CSAGB: 25.17 mm; RCGB: 11.41 mm), demonstrating enhanced stability. Distinct mechanisms correspond to different blowing methods: the unique vortex effect and kinetic energy transfer mechanism of helical airflow can significantly extend the jet stabilization length, whereas CSAGB induces turbulent mixing at the water?gas interface, and the RCGB exhibits strong radial shear flows; both mechanisms lead to the reduction of jet stabilization length.

ObjectiveThis paper presents a systematic study on the efficient coupling and low-damage cutting of water-jet guided femtosecond laser with a pulse duration of 350 fs. We firstly develop a femtosecond laser-water ionization model to reveal the evolution of free electron density when the femtosecond laser is focused in water and quantify the optical breakdown threshold of laser power density. We then propose a novel coupling cavity design with six axially symmetric flow channels suitable for femtosecond laser coupling, and analyze the formation condition of internal jet flow with a backflow pattern in a nozzle. We optimize the operating parameters to achieve efficient water-jet guided femtosecond laser coupling, ultimately enabling low-damage cutting. This research aims to provide references for the development of water-jet guided femtosecond laser and its application in the field of precision microfabrication.MethodsTo overcome the limitations imposed by optical breakdown and coupling inefficiency, a femtosecond laser-water medium ionization model is established to provide the optical breakdown threshold of laser power density (Fig. 2). Additionally, numerical simulations using fluid dynamics software (ANSYS FLUENT) are employed to optimize the design parameters, including water pressure, nozzle geometry, and flow channel configuration (Figs. 3?5). Experimental validation is conducted to verify the efficacy of the optimized coupling cavity in terms of coupling efficiency, energy transmission, and laser stability during cutting operations.Results and DiscussionsThe results show that the optimized coupling cavity design successfully mitigates the risk of optical breakdown by controlling the femtosecond laser power. We design a novel rectified coupling cavity with six axially symmetric flow channels, and a nozzle with a depth-to-diameter ratio of 2.0 is proposed. The study demonstrates that when the femtosecond laser pulse power with a pulse duration of 350 fs is controlled below 5.0 W and the water pressure is set at 1.0 MPa, the dynamic coupling efficiency of the femtosecond laser into the water-jet reaches up to 65% (Fig. 6) and a stable laser transmission with a focus depth of up to 15 mm can be achieved (Fig. 7). Additionally, the energy distribution of the laser spot exhibits improved uniformity, with a non-uniformity index reduced to 41.0% (Fig. 8). This design effectively ensures stable coupling even in challenging conditions, providing a significant improvement over the conventional water-jet guided femtosecond laser systems. We conduct experiments on cutting of biological bone tissues and refractory tantalum sheets using the optimized femtosecond water-jet laser system, which significantly suppresses thermal effects when compared with conventional femtosecond laser cutting (Fig. 9).ConclusionsThis study employs finite element simulation and experimental research to determine the upper limit for a stable femtosecond laser beam guided by a water-jet. An optical breakdown threshold of 5.0 W is identified, crucial for selecting appropriate laser transmission parameters. A specifically designed coupling cavity, featuring six axially symmetric flow channels, is developed. Through optimization with water pressure of 1.0 MPa and nozzle geometry with a depth-to-diameter ratio of 2.0, a stable water-jet guided femtosecond laser with length of 15 mm and coupling efficiency of 65% is achieved. The resulting output water-jet guided femtosecond laser beam exhibits a flat-top profile with a uniform energy distribution, overcoming the technical bottleneck of optical breakdown induced by a high peak power femtosecond laser. This advancement enables low-damage cutting of biological bone tissues and refractory tantalum sheets. This work provides significant insights for the development and application of water-jet guided femtosecond laser technology.

ObjectiveSingle crystal silicon carbide (SiC) demonstrates significant potential in high-power and long-life laser water-cooling systems due to its exceptional physical and chemical properties. However, its high hardness, brittleness, and chemical stability present challenges for traditional processing methods in achieving efficient and high-quality micro-hole processing. The water-jet guided laser processing technology employs ultra-thin and elongated water jets as optical fibers to direct lasers to the processing area, enabling material processing. This approach provides high processing accuracy while utilizing scouring effect of water jets to cool the processing area and remove debris efficiently, potentially enabling high-quality processing for hard and brittle materials such as single crystal SiC. Although water-jet guided laser processing offers considerable advantages in efficiency and precision, gaps remain in its application for single crystal SiC, particularly regarding plasma-assisted processing research. Further investigation is necessary to achieve micro-processing of single crystal SiC using water-jet guided laser technology. This study examines the water-jet guided laser processing of single crystal SiC micro-hole structures using metal targets. The research analyzes the effects of laser induced plasma-assisted processing and provides technical references and theoretical foundations for achieving high-quality water-jet guided laser processing of microstructures in hard and brittle materials like single crystal SiC.MethodsThe experimental materials comprise single crystal SiC samples with a thickness of 4 mm. The processing system consists of a self-developed water-jet guided laser processing system. To investigate the effect of laser induced plasma-assisted action, aluminium foil was attached to specific areas of the SiC samples as metal targets. At a processing power of approximately 40 W, micro-holes with diameters of 0.6, 0.8, and 1.0 mm were processed in areas both with and without aluminium foil attachment. Furthermore, micro-holes with a diameter of 0.8 mm were processed at powers of approximately 35 W and 45 W to examine the effects of laser power on micro-hole processing. For statistical analysis, 10 micro-holes were continuously processed under identical parameters for each diameter, with processing time recorded for each micro-hole. A Leica DVM6 digital microscope was utilized to observe the processed micro-hole morphology. The Leica Application Suite X (LAS X) software, integrated with the microscope, facilitated image capture and measurement of edge breakage area around the micro-holes. The processing was additionally monitored using a Photron FASTCAM Nova S20 high-speed digital camera.Results and DiscussionsThe experimental results regarding micro-hole processing time demonstrate that for single micro-holes with diameters of 0.6, 0.8, and 1.0 mm, the average processing time without aluminium foil attachment is 313, 116, and 95 s, respectively. With aluminium foil attachment, these times reduce to 262, 105, and 82 s, respectively, representing efficiency improvements of 16%, 9%, and 14%, respectively (see Fig. 4(a)). Furthermore, for micro-holes with a diameter of 0.8 mm processed at powers of 35, 40, and 45 W, the average processing time without aluminium foil is 336, 116, and 111 s, respectively. With aluminium foil attachment, these times decrease to 237, 105, and 102 s, respectively, yielding efficiency improvements of 29%, 9%, and 8%, respectively (see Fig. 4(b)). Regarding micro-hole processing quality, the edge breakage areas for holes with diameters of 0.6, 0.8, and 1.0 mm without aluminium foil measure 0.023, 0.049, and 0.080 mm2, respectively. With aluminium foil attachment, these areas reduce to 0.004, 0.009, and 0.036 mm2, respectively, representing decreases of 83%, 82%, and 55%, respectively (see Fig. 9(a)). Additionally, for 0.8 mm diameter holes processed at powers of 35, 40, and 45 W without aluminium foil, the edge breakage areas measure 0.032, 0.049, and 0.060 mm2, respectively. With aluminium foil attachment, these areas decrease to 0.020, 0.009, and 0.034 mm2, respectively, showing reductions of 38%, 82%, and 43%, respectively (see Fig. 9(b)). High-speed digital camera observations reveal that plasma is induced on the aluminium foil target during laser irradiation processing (Fig. 10). During processing, high-energy lasers transmit through water jets to the semi-transparent single crystal SiC surface. A portion of the laser penetrates the semi-transparent single crystal SiC and interacts with the aluminium foil target on the backside, generating high-energy plasma that provides auxiliary support in water-jet guided laser processing.ConclusionsThis investigation examines the impact of laser induced plasma-assisted water-jet guided laser processing on single crystal SiC. The findings demonstrate that utilizing an aluminium foil target in water-jet guided laser processing of single crystal SiC micro-holes with diameters of 0.6, 0.8, and 1.0 mm enhances processing efficiency by 8% to 29% and diminishes edge breakage area by 38% to 83% across different laser powers. This enhancement stems from the plasma-assisted effect generated when the laser beam traverses the single crystal SiC to irradiate the aluminium foil target. The mechanism involves combined effects of plasma thermal activity, shock waves, and chemical activation. Laser induced plasma-assisted water-jet guided laser processing improves both efficiency and quality in processing single crystal SiC, presenting a solution to existing technological limitations in processing transparent or semi-transparent hard and brittle materials. This advancement promotes the application of water-jet guided laser processing technology in hard and brittle material applications. Through multi-energy-field coupling, plasma-assisted water-jet guided laser processing addresses traditional laser processing limitations for transparent or semi-transparent hard and brittle materials, delivering enhanced efficiency with minimal damage. Despite existing challenges, continued process optimization indicates significant potential for applications in semiconductor, optical, and new-energy sectors. For materials such as single crystal SiC, this technology demonstrates potential as a primary method for achieving high-efficiency and high-quality manufacturing.

Results and DiscussionsThe experimental investigation encompasses calibration and workpiece grooving phases. The study utilizes a custom-developed water-jet guided laser positioning system, incorporating a 532 nm Nd∶YAG solid-state pulsed laser, water supply system, laser water-jet coupling device, low-dispersion auxiliary system, three-axis CNC stage, high-dynamic camera, and line laser with 300 mm working distance. The workpiece is a 10 mm thick nickel-based superalloy block, and the outlet nozzle diameter is 70 μm. Protective gas consists of helium and carbon dioxide mixture. Operating parameters include 22 MPa water-jet pressure, 32.5 mm processing distance, 100 ns pulse duration, and 10 kHz pulse repetition frequency. The computing platform features a 12th generation Intel? CoreTM i7-12700H 2.30 GHz processor and NVIDIA GeForce RTX3060 GPU, utilizing Windows 10, Visual Studio 2015, and Point Cloud Library (PCL) version 1.8.1. Calibration employed a 9×6 checkerboard pattern (Fig. 8) for determining camera parameters. The line laser-camera subsystem calibration utilized intrinsic parameters from camera calibration (Table 1). Calibration results (Table 2) demonstrate minimal parameter fluctuation and robust laser plane stability. The reconstructed point clouds exhibit high quality (Fig. 9). The positioning system was calibrated to acquire the pose transformation between camera and machine tool base systems (Table 3). Quantitative accuracy evaluation involved grooving experiments across six regions, each containing three locations (Fig. 10), with processing times of 4, 6, and 12 s per group. Position accuracy assessment focused on deviation between actual and ideal grooving center positions (Fig. 11).Results(Table 4) demonstrate positioning errors below 0.0170 mm with fluctuations under 0.00400 mm, confirming system precision and stability.ObjectiveConventional machining methods face significant challenges in efficiently processing superalloys without causing damage or deformation. Water-jet guided laser processing presents an advantageous solution, offering minimal heat-affected zones and reduced thermal stress, making it suitable for superalloy processing requirements. The initial step of water-jet guided laser processing requires precise workpiece positioning. Current manual positioning methods are inefficient and imprecise, while machine tool positioning based on workpiece models often encounters discrepancies between theoretical models and actual workpieces. This study introduces a line laser-camera-assisted water-jet guided laser positioning system and proposes a vision-guided positioning methodology. The approach aims to automate the positioning process, improve operational efficiency, and maintain industrial-grade accuracy, thereby advancing water-jet laser grooving alignment techniques.MethodsThis research developed an integrated water jet-guided laser grooving positioning system incorporating a line laser and high-dynamic camera (Fig. 1). The system integrates vision positioning and water-guided laser processing subsystems. The positioning process initiates with line laser scanning of the workpiece, incorporating stage motion error compensation parameters for three-dimensional reconstruction within the high-dynamic camera coordinate system. Subsequently, point cloud undergoes adaptive filtering to eliminate noise and enhance data quality. Processing parameters then determine the machining position. To enable line laser scanning, optical plane calibration between the line laser and the camera was performed (Fig. 3). Next, water-guided laser processing was executed by acquiring the actual groove’s 3D coordinates in the high-dynamic camera coordinate system and transforming them into the machine tool coordinate system for unified position referencing. For this purpose, the processing system was calibrated to obtain the rigid transformation matrix between the two coordinate systems. Based on 3D points of the groove in the machine tool coordinate system, an ideal machining pose that prioritizes accuracy is generated. Finally, following the principle of translation before rotation, precise positioning of the actual machining location was achieved. The system includes two main stages: machining system calibration (Fig. 4) and ideal machining pose generation (Figs. 5?7). Ultimately, the machining path was determined through translation and rotation, ensuring precise positioning before grooving to complete the process.ConclusionsThis research developed a water-jet guided laser processing system incorporating a line laser and camera for positioning, and introduces a novel vision-guided water-jet guided assisted laser slotting methodology. This integration of computer vision with water-jet guided laser processing technology represents a pioneering solution in the field. The visual positioning system achieves accuracy within 0.0170 mm, with precision deviations below 0.00400 mm, meeting industrial-grade water-jet guided laser positioning requirements. The system’s effectiveness depends substantially on the machine tool’s motion accuracy and line laser quality during positioning operations. The camera installation demands precise positioning parameters, as significant deviations in camera orientation can produce overexposed images, compromising workpiece positioning accuracy. Subsequent research will address positioning capabilities for larger components and expand positioning and machining experiments across diverse material types.

ObjectiveFatigue failure represents a critical degradation mechanism in high-strength aluminum alloy components under cyclic loading, particularly in aerospace and marine structures. These failures commonly originate at surface or near-surface defects due to stress concentration and material deterioration. Enhancement of surface integrity—through increased hardness, reduced roughness, and induced compressive residual stress—is crucial for prolonging component service life. Conventional surface strengthening methods, including laser shock peening (LSP) and abrasive water jet (AWJ) peening, have shown improvements in fatigue life; however, they exhibit limitations such as thermal damage or insufficient strengthening depth. To address these constraints, this study introduces a novel hybrid approach—water-guided laser (WGL) strengthening—which combines high-energy laser pulses with confined water jet flow. The research aims to examine the effects and underlying mechanisms of WGL on surface morphology, microstructure, residual stress distribution, and fatigue life of 2519A aluminum alloy under various laser powers and impact counts.MethodsWGL experiments utilize a self-developed apparatus that integrates a nanosecond-pulsed laser (1064 nm) with a high-speed water jet to generate a confined energy column. Three WGL conditions—WGL-1 (low power, single impact), WGL-2 (moderate power, double impact), and WGL-3 (high power, double impact)—are evaluated. An AWJ-treated sample provides the control group. All specimens undergo extensive testing including 3D surface profiling using a confocal microscope (VT61000), microhardness measurements via Vickers testing (THV1-MDT), residual stress analysis using X-ray diffraction (X-350A), and phase structure examination via XRD (LabX XRD-6100X). Fatigue tests are performed under axial loading using a servo-hydraulic fatigue machine at room temperature with stress ratios R=0.1 and maximum cyclic stress ranging from 240 MPa to 432 MPa. Fatigue fracture morphology is analyzed using SEM to investigate crack initiation and propagation behavior.Results and DiscussionsThe WGL process substantially enhances the surface characteristics and fatigue performance of the 2519A aluminum alloy specimens. Line roughness (Ra) decreases progressively from 2.551 μm (AWJ) to 1.335 μm (WGL-3), demonstrating a 47.7% improvement (Fig. 4). 3D surface profiles (Fig. 3) reveale smoother and more uniform morphologies in WGL-treated samples, with the WGL-3 group showing minimal height variation and improved flatness. SEM micrographs (Fig. 5) reveal that AWJ-treated surfaces contain distinct microcracks and erosion pits, while WGL-treated surfaces exhibit reduced damage and more compact textures, despite minor peeling observed in WGL-3 due to excessive energy input.Microhardness analysis (Fig. 6) indicates that WGL treatment produces significant increases in surface hardness and hardened layer depth. WGL-3 achieves the highest surface hardness at 186.71 HV and a hardened layer extending to 356 μm, compared to 160.54 HV and 204 μm for the AWJ sample. Residual stress profiles (Fig. 7, Table 2) show marked increases in surface residual compression stress (CRS), from 37 MPa (AWJ) to 287 MPa (WGL-3), and deeper residual stress influence zones. The maximum CRS in WGL-3 occurrs at the surface, indicating a surface-concentrated strengthening effect, while the deeper CRS depth confirms the water-constrained energy transfer efficiency.XRD analysis (Fig. 8) demonstrates that no new phases emerge during processing; however, (111) diffraction peaks shift to higher angles and broaden after WGL treatment, particularly in WGL-3. This indicates grain refinement, lattice distortion, and high dislocation density—factors crucial for fatigue resistance. These structural modifications correspond with the observed mechanical property improvements.Fatigue testing (Fig. 9) demonstrates significant enhancement in fatigue performance through WGL treatment. Under a maximum stress of 312 MPa, fatigue life increases from 4.15×106 cycles (AWJ) to 1.95×107 cycles (WGL-3), representing a 370% improvement. Under high-load (432 MPa) conditions, WGL-3 extends fatigue life by up to 3.77 times. S-N curves for WGL-treated samples consistently shift rightward, confirming enhanced fatigue resistance. SEM fractography (Fig. 10) reveals that crack initiation shifts from the surface (AWJ) to subsurface (WGL-1 and WGL-2), and fracture surfaces evolve from coarse, uneven morphologies to smoother, striation-dominated patterns with reduced secondary cracks, particularly in WGL-3.ConclusionsWGL treatment effectively reduces surface roughness and micro-defects, with the WGL-3 condition demonstrating a greater than 50% improvement in Ra and Sa parameters compared to AWJ processing. The surface microhardness and compressive residual stress exhibit significant enhancement through WGL treatment. The WGL-3 condition achieves the most substantial improvements, producing the deepest hardened layer (356 μm) and highest surface residual stress (287 MPa). The fatigue performance of the alloy improves significantly, with WGL-3 demonstrating the most pronounced enhancement. The treatment delays crack initiation and results in more stable crack propagation characteristics. While WGL presents a promising and thermally safe method for surface strengthening of high-strength aluminum alloys, excessive energy input may induce over-peening effects, potentially leading to surface peeling and stress concentration. Therefore, careful optimization of processing parameters remains essential for achieving an optimal balance between performance enhancement and structural integrity.

ObjectiveTitanium alloy is widely used in aerospace and marine engineering by virtue of its high specific strength, high specific modulus, and good corrosion resistance. However, it is prone to serious thermal damage in laser machining due to its low thermal conductivity and significant heat accumulation. This leads to the expansion of heat-affected zone (HAZ) and the height of recast bulge (RL), thereby affecting the surface quality and performance of the workpiece. Traditional dry laser processing is difficult to effectively solve these problems, while waterjet-assisted laser machining technology is expected to inhibit thermal damage through forced convection cooling and energy absorption by introducing a flowing water layer. The aim of this study is to establish a temperature field simulation model of waterjet-assisted laser machining, reveal the evolution mechanism of thermal damage, analyze the influence of waterjet parameters (waterjet pressure, nozzle distance, waterjet offset distance) on micro-groove forming and thermal damage layer, and optimize the process parameters through the response surface methodology, providing theoretical and technological guidance for high-quality laser machining of titanium alloys.MethodsIn this study, a two-dimensional temperature field simulation model for laser ablation of titanium alloy under the action of flowing water layer was constructed. It takes into account the heat transfer processes such as laser energy absorption, heat conduction, and convection, assumes that the workpiece as a continuous medium and ignores the chemical reaction. We refined the mesh of the laser action area and simulated the coupling effect of water and laser by setting boundary condition. We constructed a micro-machining system consisting of the modules of laser machining and waterjet assisting to verify the effect of waterjet action. We utilized TC11 titanium alloy as the material, adopted a one-way test to investigate the influences of waterjet offset distance, nozzle distance, and waterjet pressure on the micro-groove sizes and thermal damage layer, and combined waterjet-assisted laser with the dry laser machining to verify the role of waterjets. We employed Box?Behnken design to conduct 20 groups of tests for optimizing the machining parameters. We established a quadratic regression model with HAZ width and RL height as the response values and determined the significance of the parameters via analysis of variance. We used the thirst function method to optimize the parameters and verify the accuracy of the model by experiments.Results and DiscussionsIn the temperature field simulation and experimental verification, the high-temperature area of the material is symmetrically distributed centered on the pit axis in dry laser machining. In waterjet-assisted laser machining, the flowing water layer absorbs laser energy and enhances convective heat transfer, reducing the area of the high-temperature region (Fig. 4), lowering the maximum temperature, and significantly alleviating heat accumulation. Tests show that micro-groove edges machined by waterjet-assisted laser are flat, with no melt blockage; HAZ width and RL height are significantly reduced compared with dry laser machining (Fig. 6), verifying the reliability of the simulation results. The influence mechanism of waterjet parameters indicates that reducing the waterjet offset distance and nozzle distance enhances waterjet interference with the laser, leading to a significant reduction in micro-groove dimensions, HAZ width, and RL height. An increase in waterjet pressure boosts flow velocity and laser interference in the water layer, reducing micro-groove width, depth, and thermal damage layer size (Figs. 7 and 8). Parameter optimization and model validation show that the influence of waterjet parameters on HAZ width and RL height follows the order: waterjet pressure > nozzle distance > waterjet offset distance (Tables 9 and 10). The optimal parameter combination is a nozzle distance of 2.03 mm, waterjet offset distance of 4.14 mm, and waterjet pressure of 1.92 MPa (Table 11). At these parameters, the errors between measured and predicted values of HAZ width and RL height are 4.89% and 8.84% (Tables 11 and 12), verifying the accuracy of the optimization results.ConclusionsTo address the thermal damage issue in titanium alloy laser machining, micro-grooves were fabricated using waterjet-assisted laser technology, and temperature field simulation along with parameter optimization was conducted. The study shows that the flowing water layer effectively mitigates heat accumulation and reduces the thermal damage layer by decreasing the high-temperature region and surface temperature through energy absorption and convective heat transfer. Among waterjet parameters, waterjet pressure exerts the most pronounced influence on thermal damage inhibition, followed by nozzle distance and waterjet offset distance. Increasing pressure enhances cooling and erosion effects, whereas increasing the offset distance or nozzle distance weakens the inhibitory effect. The response surface methodology-based model accurately predicts HAZ width and RL height, with prediction errors under optimized parameters less than 10%. This provides a quantitative process solution for laser composite manufacturing of titanium alloys and other difficult-to-machine materials, facilitating high-efficiency and high-quality machining of precision components.

ObjectiveSi is a cornerstone material in the semiconductor industry, where precise micromachining techniques are key for fabricating advanced surface structures. Notably, electrochemical machining (ECM) is a widely employed technique for processing Si because of its noncontact nature and stress-free characteristics. However, the formation of a dense passivation layer (SiO2) during ECM severely limits its efficiency by obstructing electrochemical reactions. Traditional methods for removing this SiO2 layer, such as mechanical scraping or hydrofluoric acid (HF) etching, are highly inefficient, expensive, and environmentally hazardous. Thus, to address these shortcomings, this study proposed an innovative approach, which leverages laser-induced cavitation-driven microabrasive particles to locally scratch and remove passivation layers. By integrating laser precision with mechanical abrasion, this approach can enhance the efficiency, precision, and sustainability of ECM-based Si processing, thereby addressing critical bottlenecks in semiconductor manufacturing.MethodsThe experiment was conducted using a double-side polished, n-type, single-crystal silicon wafer with a 〈100〉 crystal orientation and a thickness of 500 μm as the workpiece material, and single-crystal diamond microabrasives were employed as the abrasive medium. A fiber laser and a high-energy Nd∶YAG laser were used to induce cavitation effects. Two distinct experimental configurations were designed as follows: (1) the in-hole erosion method [as shown in Fig. 2(a)], where a fiber laser was focused on a prefilled hole to instantaneously propel microabrasives and induce the localized erosion on the underlying Si wafer, while microabrasives were continuously replenished via a syringe, and (2) the sidewall erosion method [as shown in Fig. 2(b)], where the laser was focused 1 mm above the Si wafer surface, thereby leveraging laser-induced cavitation to drive precise sidewall erosion using the microabrasives. Furthermore, to comprehensively evaluate the effects of both configurations, advanced characterization techniques including scanning electron microscopy, atomic force microscopy, and nanoindentation test were employed to analyze the Si surface morphology, scratch depth, scratch width, mechanical properties, and surface roughness. The removal effectiveness of the oxide layer was evaluated based on the morphological changes observed on the Si surface.Results and DiscussionsThe experimental results demonstrate that the microabrasive-based removal of the passivation layer is substantially influenced by the impact distance, average particle size, laser pulse energy, and ECM approach. At shorter impact distances (e.g., d=2 mm), the microabrasives exhibit higher kinetic energy, leading to distinct Si surface features, such as the small pits (diameter: ~9 μm) and linear scratches (Fig. 3). As the distance increases to d=6 mm, the erosion effects diminish, leaving fewer pits and shallower scratches that are attributed to the loss of kinetic energy of the microabrasives. In addition, the size of the microabrasives plays a critical role in determining the effect of Si erosion; the smaller microabrasives (e.g., D=1 mm) generate shallower and sparser scratches, whereas the larger microabrasives (e.g., D=9 mm) generate deeper and wider scratches, with scratch widths reaching 2.8 μm (Fig. 5). This finding is attributed to the higher mass and kinetic energy of the larger microabrasives than those of the smaller microabrasives, although their tendency to settle may affect process stability. Moreover, the applied laser pulse energy directly influences the kinetic energy of the microabrasives, with high energy levels (e.g., Ep=1200 mJ) generating dense scratch networks with greater depths (up to 29.9 nm) and widths (up to 293 nm). By contrast, lower energy levels (e.g., Ep=400 mJ) produce only sparse and shallow scratches (Fig. 7). Overall, the ECM-laser (ECML) treatment realizes maximum scratch dimensions, i.e., a depth and width of 54.9 and 783 nm, respectively (Fig. 10), demonstrating that surface softening substantially enhances plastic deformation. Furthermore, the mechanistic analysis reveals that the synergistic effect of the high-density plasma generated by laser-driven cavitation and the high-pressure shockwaves generated from bubble collapse effectively facilitates the transfer of kinetic energy to the abrasive particles (Fig. 11), thereby enabling efficient material removal, primarily through a shearing mechanism (Fig. 12).ConclusionsA novel method for realizing the localized scratching of the Si surface using laser-induced cavitation-driven microabrasives is demonstrated. Through systematic experimental investigations, the significant effects of several key factors on the effective removal of the oxide passivation layer were determined and the underlying mechanisms were elucidated. The findings reveal that the impact distance and erosion effectiveness have an inverse correlation, whereas the size of the abrasives and the energy level of the laser have a positive correlation with the Si-erosion performance. Moreover, ECM reduces the hardness and Young’s modulus of the Si surface, increasing the susceptibility of the oxide layer to being removed by the microabrasives, and laser irradiation further enhances this effect. Compared with traditional methods for removing oxide layers, such as mechanical scraping and HF etching, this approach overcomes the limitations of low efficiency and high costs, while eliminating the need for hazardous reagents, such as HF. Overall, the proposed method realizes the efficient and environmental-friendly removal of SiO2 passivation layers, representing an innovative basis for exploring related application fields.