为探究水导激光耦合能束内部能量的分布及传播特性,建立了高斯激光的空间传播模型,采用波束包络法对高斯激光在耦合能束中的全反射式传播进行了数值模拟,探究了激光电场在不同直径的射流中的演变规律,获得了耦合能束不同位置处的激光能量分布,并选取 50 μm直径的射流进行了试验验证.在明确了耦合能束内部能量分布的基础上,选取K24 合金进行了不同激光脉冲的水导激光烧蚀试验.结果表明,波束包络法可以准确有效地对耦合能束内部能量传播及分布进行仿真预测,且同一位置水导激光耦合能束的加工具有一致性.

In this study, the novel coaxial-annulus-argon-assisted (CAAA) atmosphere is proposed to enhance the machining capacity of the water-jet-guided laser (WJGL) when dealing with hard-to-process materials, including ceramic matrix composites (CMCs) and chemical-vapor-deposition (CVD) diamond. A theoretical model was developed to describe the two-phase flow of argon and the water jet. Simulations and experiments were conducted to analyze the influence of argon pressure on the working length of the WJGL beam, drainage circle size, and extreme scribing depth on ceramic matrix composite (CMC) substrates. A comparative experiment involving coaxial annulus and helical atmospheres revealed that the coaxial annulus atmosphere disrupts the water jet proactively, while effectively maintaining the core velocity within the confined working length and enhancing the processing capability of the WJGL beam. Single-point percussion drilling experiments were performed on a CMC substrate to evaluate the impact of machining parameters on hole morphology. The maximum depth-to-width ratio of the groove and depth-to-diameter ratio of the hole reached up to 41.2 and 40.7, respectively. The thorough holes produced by the CAAAWJGL demonstrate superior roundness and minimal thermal damage, such as fiber drawing and delamination. The average tensile strength and fatigue life of the CMCs specimens obtained through CAAAWJGL machining reached 212.6 MPa and 89,463.8 s, exhibiting higher machining efficiency and better mechanical properties compared to femtosecond (194.2 MPa; 72,680.2 s) and picosecond laser (198.6 MPa; 80,451.4 s) machining. Moreover, groove arrays with a depth-to-width ratio of 11.5, good perpendicularity, and minimal defects on a CVD diamond were fabricated to highlight the feasibility of the proposed machining technology.

Monocrystalline silicon has shown great potential in constructing advanced devices in semiconductor, photoelectric, and photochemistry fields. The fabrication of micro-grooves with large depth-to-width ratio (DTWR) and low taper is in urgent demand as this type of groove can significantly promote the device performance. The grooves with such characterizations can hardly be achieved by conventional machining techniques owing to the high hardness and brittleness of silicon. Laser waterjet (LWJ) machining is a promising solution, which is capable of ablating materials with less or no heat defects, well machining precision, and consistency. Therefore, this paper firstly established a theoretical model describing the interaction between silicon and LWJ. Through the numerical simulation, the evolution of temperature and stress distribution at the machining region was analyzed. Variation experiments were carried out correspondingly. On these bases, scribing experiments were put forward aimed at discovering the influence of machining parameters on groove morphology. Optimized scribing strategy which is capable of realizing the construction of a micro-groove with DTWR of 19.03 and taper of 0.013 was obtained. The results contributed to the understanding of LWJ processing of silicon on a small scale as well as broadening the application prospects of LWJ for treating other semiconductor devices.

SiC/SiC ceramic matrix composites (CMCs) are widely applied in the aerospace and nuclear industries due to their excellent material nature (strength, hardness, and irradiation tolerance) at high-temperature loads. However, high-quality machining cannot be easily realized because of the anisotropic material structure and its properties. In this study, a laser water jet (LWJ) was adopted for CMCs machining. Firstly, the finite element model (FEM) was established describing a representative three-dimensional microstructure including weft yarn, warp yarn, SiC base, and the pyrolytic carbon (PyC) fiber coating. The temperature distribution, as well as its evolution rule on substrate surface under LWJ machining, was analyzed. Moreover, a single-dot ablation test was carried out to verify the accuracy of the numerical simulation model. Secondly, the variation in maximum temperatures under different laser pulse energy was obtained by means of FEM. Nonetheless, a non-negligible deviation emerged in the ablation depth of the numerical calculation and experimental results. Although the simulation results were obviously superior to the experimental results, their proportions of different machining parameters reached an agreement. This phenomenon can be explained by the processing characteristics of LWJ. Finally, single-row and multi-row scribing experiments for CMCs with 3 mm thickness were developed to clarify the processing capacity of LWJ. The experimental results indicated that single-tow scribing has a limiting value at a groove depth of 2461 μm, while complete cutting off can only be realized by multi-row scribing of LWJ. In addition, the cross-section of CMCs treated by LWJ presented a surface morphology without a recast layer, pulling out of SiC fibers, and delamination. The theoretical and experimental results can offer primary technical support for the high-quality machining of CMCs.

SignificanceWiththerapiddevelopmentofthenationalaviationaerospacecommunicationsinstrumentationandmedicalfieldscomponentssuchasfuelnozzlessolarsiliconlightpanelssemiconductorchipsandheartstentstendtobeminiaturizedandsophisticatedThequalityrequirementsforstructuressuchasholesandgroovesprocessedonrelatedmaterialsareincreasingwhichcorrespondinglytranslatesintohigherprocessingtechnologyrequirementsAtpresentscholarshavedevelopedavarietyofprocessingmethodsincludingbutnotlimitedtomechanicalmachiningelectricaldischargemachiningEDMelectrochemicalprocessingandlaserprocessingDuringthemechanicalmachiningprocessthetoolisindirectcontactwiththeworkpiecesresultinginsignificant stressEDMissuitableforconductivematerialsThereisnoobviousforceduringthemachiningprocessbutthemachiningefficiencyisgenerallyslowElectrodelossexitsandthecornerradiusislimitedTheelectrochemicalprocessingefficiencyisrelativelyhighandcathodelossisabsentButtheprocessingstabilityispoorandtheelectrolysisproducteasilyresultsinenvironmentalpollutionComparedwiththeaboveprocessingmethodslaserprocessinghasobviousadvantagesIthasbeenwidelyusedfordrillinggroovingandcuttingoperationsintheaerospacemicroelectronicsprecisionmedicalinstrumentationandotherindustriesThecontinuouslaserandthelong-pulselaserhavehighprocessingefficiencyThecontinuouslaserandthelong-pulselaserhavehighprocessingefficiencyHoweverthegenerationofheat-affectedzonesandrecastlayerscannotbeignoredToachievetheeruptionandremovalofthematerialtheultrashortpulselaserdirectlyconvertsthematerialintoaplasmastateTheultrashortpulsecantheoreticallyachievetheeffectof????coldprocessingbuttheprocessingefficiencyislowNanosecond-levelshortpulselasershaveloweracquisitioncostsandahighermaterialremovalratethanultrashortpulselasersbutobviousdefectssuchasheat-affectedzonesrecastlayersandmicro-cracksstillcannotbeavoidedToovercomethethermaldefectsinthe????drylaserprocessdomesticandforeignresearchersattempttodevelopacompositesystemthatcombineslaserandwaterComparedwith????drylaserprocessingwater-jetguidedlaserWJGLhasmanyadvantages-largeworkingdistancenoobviousconeneatcutandnoburrssmallheat-affectedzonealmostnothermaldeformationandthermaldamageandhighprocessingqualityThisworkhasprovidedarelativelycompleteoverviewofwater-jetguidedlaserprocessingtechnologyallowingustodeeplyunderstandthemechanismofwater-jetguidedlaserprocessingtechnologyexertitsprocessingadvantagesandbroadenitsapplicationfields. ConclusionandprospectThisworkreviewsaseriesofliteratureonwater-jetguidedlaserandsystematicallyexpoundsonitsformationmechanismanditsapplicationpotential 1TheformationofwaterjetsisdiscussedThe????cone-downnozzlemakesiteasytoformastable????retractedflowwaterjetFactorssuchasenvironmentandnozzlegeometryarerelatedtothebreakageofthewaterjetTheintroductionofanauxiliaryatmospherecanincreasethestablelengthofthejetandthejetwillformaliquidfilmafterimpactingtheprocessingsurface 2ThecouplingprocessofthelaserandwaterjetisdiscussedThelinearabsorptionoflaserbywaterisanimportantfactorinenergylossandthelaserenergyexceedingthethresholdcausesstimulatedRamanscatteringThelasertransmissioninthejetcanbedividedintotwotypesmeridiantransmissionandobliqueraytransmissionThecouplingerrordeterminesthecouplingefficiencyandenergydistributionandtogetherwiththelossofenergyaffectsthestabilityofthecoupledenergybeamtransmission 3Theexcellentperformanceenableswater-jetguidedlasertobeusedinaerospacechipmanufacturingprecisionmedicineandotherfieldstoprocessvariousdifficult-to-processmaterialssuchasmetalssemiconductorsandcompositematerialsModelingandsimulationprovideappropriatehelpforunderstandingthephysicalmechanismsinvolvedinlaserablationandpromotetheconductofrelatedexperimentsandtheextensionoftheapplicationrangeofwater-jetguidedlaserAlargenumberofstudiesonwater-jetguidedlaserhavestronglyproveditsapplicationvalueHowevertheprocessingcapabilitiesofwater-jetguidedlaserarestilllimitedunderprocessingconditionssuchashigh-qualityprocessingrequirementsandsmallworkingspacesAtthesametimetheprocessingtechnologyfordifficult-to-processmaterialssuchasdiamondssapphireandsuper-hardceramicsstillneedstobefurtherexploredTomeettheserequirementsthepossibleresearchdirectionsofwater-jetguidedlaserinthefutureareasfollows 1Reducewaterjetdiameterandtransmissionenergylossofhigh-intensityinputlaser. Researchonthelawoffocusmovementduetothethermalinteractionbetweenthelaserandwaterduringthecouplingprocess3Athoroughexaminationoftheinteractionprinciplebetweenlaserwaterjetandmaterialduringwater-jetguidedlaserprocessing4Researchonthelawbetweentheenergydistributionofthelaseronthemachinedsurfaceandtheevolutionofthesurfacetopography.

SiC/SiC ceramic matrix composites (CMCs) offer an excellent combination of properties at high temperature such as high specific strength, chemical inertness and irradiation tolerance. Those superior properties make CMCs beneficial for use in high-temperature structural applications that are exposed to extreme environments such as aerospace and nuclear energy. However, well machining qualities can hardly be achieved by conventional machining techniques owing to these properties. Laser water jet (LWJ) machining is a promising solution, which is capable of ablating materials with less/no heat defects, well machining precision and consistency. Nevertheless, the machining capacity of LWJ is still limited by the stability of water jet to a great extent. A water layer may form on substrate surface during the impingement of LWJ, which also sets up obstacle for sufficient ablation. Therefore, a novel coaxial helical gas atmosphere is introduced to promote the machining capacity of LWJ in this paper. A theoretical model is established to describe the gas-water two-phase flow field during the ejection and impingement of coaxial gas assisted LWJ (CGALWJ). The influences of gas component and pressure on the stable length of water jet and surface water layer status are analyzed based on numerical simulations and experiments. Scribing experiments are further carried out on CMCs substrates with thickness of 3 mm. Groove with maximum depth-to-width ratio of 13.6 as well as through cutting are realized without the drawing of SiC fibers, formation of recast layer and delamination. The theoretical and experimental results provide solid foundation for the high-quality machining of ceramic matrix composites and other hard-to-process materials.

采用了纳秒激光与水射流耦合加工技术,使用不同的激光特性参数及水射流参数对304不锈钢、碳化硅、硅晶圆进行划槽实验,都获得了较好的加工质量,验证了纳秒激光与水射流耦合能束蚀除材料的优越性.

This work puts forward femtosecond laser modification of microgroove textures on a rake face of the cemented carbide YT15 turning tool in order to promote its cutting performance. Technological tests focusing on femtosecond laser ablation of YT15 are established with purpose of obtaining the impacts of machining parameters, like pulse energy, scanning velocity, and scanning times on the morphology of microgrooves, mechanism of which are analyzed from multiple aspects. Cylindrical turning tests and numerical simulations by ABAQUS based on orthogonal cutting model and Johnson-Cook (J-C) constitutive model are carried out to investigate the variation of cutting performance applying non-textured (NT), parallel grooves textured (PGT), and vertical grooves textured (VGT) turning tools. Matlab is utilized to filter the force signal collected by a three-dimensional piezoelectric dynamometer. Both theoretical and experimental results demonstrate that parallel grooves with specific dimension parameters on a rake face of a turning tool can improve cutting performance more significantly with less tool wear.

This work puts forward femtosecond laser modification of micro-textured surface on bearing steel GCr15 in order to reduce frictional wear and enhance load capacity during its application. Multi pulses femtosecond laser ablation experiments are established for the confirmation of laser spot radius as well as single pulse threshold fluence and pulse incubation coefficient of bulk material. Analytical models are set up in combination with hydrodynamics lubrication theory. Corresponding simulations are carried out on to explore influences of surface and cross sectional morphology of textures on hydrodynamics lubrication effect based on Navier-Stokes (N-S) equation. Technological experiments focus on the impacts of femtosecond laser machining variables, like scanning times, scanning velocity, pulse frequency and scanning gap on morphology of grooves as well as realization of optimized textures proposed by simulations, mechanisms of which are analyzed from multiple perspectives. Results of unidirectional rotating friction tests suggest that spherical texture with depth-to-width ratio of 0.2 can significantly improve tribological properties at low loading and velocity condition comparing with un-textured and other textured surfaces, which also verifies the accuracy of simulations and feasibility of femtosecond laser in modification of micro-textured surface. (c) 2017 Elsevier B.V. All rights reserved.

Laser beam drilling has been widely applied in various industries due to its high efficiency and low cost. However, machining defects like obvious taper, heat affected zone (HAZ), and spatter may generate as hidden perils. In order to investigate generation mechanism of these phenomena and explore a proper solving method, a three-dimensional finite element model which describes the temperature field distribution and interaction between continuous laser and metal was put forward. Simulations on laser cutting with steady and moving focal point on carbon steel C45 workpiece with thickness of 1 and 4 mm were conducted. The comparison of hole morphology under initial simulation and experiments illustrated that the established finite element model is able to predict taper formation and size of HAZ in continuous laser drilling process. Moreover, using a moving focal point during laser drilling process is conductive to the reduction of taper and size of HAZ through contrast experiments. Both numerical simulations and experimental results indicated that the cylindricity and quality of deep holes can be significantly improved with a moving focal point.

To obtain the nanostructure with stable morphology and a smallest possible size,a nanostructure machining system is established by an Atomic Force Microscopic(AFM)probe combined with a continuous laser.With this method,the study focuses on the near-field enhancement theoretical analysis and simulation when the continuous laser irradiates the AFM probe and the machining performance of this system.Firstly,based on the mechanism of surface plasmon(SP),the Factor of Enhancement Field(FEF),temperature field and the thermal expansion on the probe tip are researched.A nanostructure machining system is set up based on the optical fiber probe to guide the laser to irradiate on the AFM probe.At last,the polyethylene(PE)is chosen as a sample to do the experiment.Experimental results indicate that the size of the processed nanodot is about 200 nm and that of the nanowire is about 30-40 nm.This method shows the proposed probe has simple-structure and inexpensive-cost and could achieve nanostructure machining.

In the nanolithography, some exciting developments have been motivated by the tapered metal-coated optical fiber probe irradiated by ultra-fast pulse laser. To explore the related mechanism, the local field is studied using the finite element method in this paper. The simulation results show the reflection at the cut-off plane, edge enhancement effect and surface plasmon resonance become the major factors affecting the near-field. In addition, Based on the near-field distribution and characteristics, the new promising scheme is proposed for near-field nanolithography.

Although the nanostructure machining by AFM probe assisted with laser has gain a great progress, few studies has been done on the optical fiber probe guiding the continuous laser to irradiate on AFM probe to machining nanostructure. Using this technology to create nanodot and nano-groove was presented in this paper. The law of how the experiment parameters influenced the results was summarized in the paper. The scale of nanodot is about 450nm, and nano-groove is about 40nm. When the fabrication is completed, the wear of the AFM probe was observed by SEM and drew a conclusion. In the method of nano machining by AFM Probe combining with a CW Laser, there will be a combined field to achieve the fabrication, and the method is better than mechanical characterization with AFM probe.