Water Jet-guided Laser Research Articles

An optical field regulation method for waterjet-guided laser: Reducing taper and improving deep-processing capability

Waterjet-guided laser (WGL) processing technology has the advantages of low thermal damage, no contact stress and ultra-fine processing. However, the energy distribution of the existing technology in the laminar flow water column is still characterized by Gaussian distribution, which leads to taper effect in the processing of thick plate materials and affects the deep-processing capability. To address these shortcomings, a novel waterjet laser-field regulation (WLR) method is proposed in this paper. Optical simulation and coupling experiments confirm the method's ability to modulate the energy within the waterjet into a circular distribution, which solves the problem of low power density near the surface of the waterjet. Waterjet-guided laser cutting experiments were conducted based on the WLR method, and the taper was significantly reduced compared to the conventional WGL. At a power of 12 W, the taper was reduced from 5.85° to 2.28°, a reduction of 61 %. In terms of processing depth, the WLR method cuts slightly lower groove depths with a low number of cuts, but as the number of cuts increases, the groove depth steadily increases and exceeds that of the conventional WGL. At 500 cuts with a laser power of 20 W, the groove depths obtained by the WLR method increased by 115 % compared to that of the conventional WGL. This study has important implications for the processing of thick materials by waterjet-guided laser.

The Advancement of Waterjet-Guided Laser Cutting System for Enhanced Surface Quality in AISI 1020 Steel Sheets.

This study investigates the effects of a water-guided laser on the cutting performance of AISI 1020 steel sheets of various thicknesses by comparing the results with respect to a conventional laser. For this purpose, a novel nozzle design has been devised enabling the delivery of laser beams to the workpiece conventionally as well as through water guidance. Diverging from prior literature, a fiber laser is used with a high wavelength and a laser power output of 1 kW. Experiments are conducted on steel sheets with thicknesses ranging from 1.5 mm to 3 mm using three different cutting speeds and laser power levels. Analysis focuses on assessing surface roughness, burr formation and heat effects on the cut surfaces for both conventional and waterjet-guided cutting. Surface roughness is evaluated by using a 3D profilometer and cut surfaces are examined through SEM imaging. The results showed that the waterjet-guided laser system greatly reduced surface roughness and minimized problems associated with traditional laser cutting such as kerf, dross adherence and thermal damage. The study revealed that cutting speed had a greater effect on surface roughness reduction than laser power, with the most noticeable differences occurring in thinner sheets. Furthermore, the investigation suggests that the waterjet-guided laser cutting system demonstrates superior performance relative to conventional methods, particularly in surface quality.

Experimental Investigation of Water Jet-Guided Laser Micro-Hole Drilling of Cf/SiC Composites.

In this paper, water jet-guided laser (WJGL) drilling of Cf/SiC composites was employed and the effects of the processing parameters on the depth and quality of the micro-holes were systematically investigated. Firstly, the depth measurement showed that the increase in processing time and power density led to a significant improvement in micro-hole drilling depth. However, the enhancement of the water jet speed resulted in a pronounced decrease in the depth due to the phenomenon of water splashing. In contrast, the scanning speed, path overlap ratio, pulse frequency, and helium pressure exhibited less effect on the micro-hole depth. Secondly, the microstructural analysis revealed that the increase in power density resulted in the deformation and fracture of the carbon fibers, while the augmentation in water jet speed reduced the thermal defects. Finally, based on the optimization of the processing parameters, a micro-hole of exceptional quality was achieved, with a depth-to-diameter ratio of 8.03 and a sidewall taper of 0.72°. This study can provide valuable guidance for WJGL micro-hole drilling of Cf/SiC composites.

Numerical investigations of water jet-guided laser cutting of silicon

To investigate the interaction mechanism between a laser, water jet, and substrate, a model is developed to simulate the temperature field evolution and removal process during water jet-guided laser (WJGL) cutting of silicon. The model accounted for the temperature-dependent properties of the silicon absorption coefficient, as well as the physical processes of solid-liquid-gas phase change. A three-dimensional finite volume model of WJGL cutting of silicon is created, incorporating laser energy input, water jet impact-cooling, and silicon phase transition and removal. The volume of fluid (VOF) method is employed to trace the interphase interface and obtain the groove shape. The validity of the model is verified by comparing simulation results with experimental data. The simulation results show that the groove cross section is characterized by a “V” shape. The groove depth nonlinearly increases from 52 to 385 μm with an increasing number of cuts. Additionally, the residual temperature of the silicon substrate rises from 837 to 1345 K as the number of scans increases from 1 to 10. The findings offer valuable insights into WJGL cutting research, specifically shedding light on the intricate details of the laser-water jet-substrate interaction mechanism.

Water jet guided laser cutting of electrical steel laminations

The state-of-the-art process for manufacturing electric machine laminations, die stamping, lacks flexibility and is only applicable for high-volume production, thus prototyping is often done via laser cutting or electrical discharge machining (EDM). The water jet guided laser (WJGL) is proposed as an alternative method for prototyping. This paper investigates the impact on magnetic characteristics of WJGL cutting electrical steel laminations. A 532 nm nanosecond laser with a maximum average power of 400 W was used to cut 0.2 mm thick non-grain oriented electrical steel (NO20-1200). WJGL process parameters were down-selected through experimental trials. Strips of the electrical steel containing slits were created using two sets of WJGL parameters to examine the effect on the material’s magnetic characteristics. The results indicate that using lower powers could minimise the impact on the relative permeability and core loss. With further development on scaling up, the WJGL has potential for rapid prototyping of laminations.

High Repetition Frequency Solid-State Green Laser with Large Stable Area for Water Jet Guided.

This paper presents the design and experimental results of a long cavity length Nd:YAG laser with a large stable zone for water jet-guided laser (WJGL) applications. The design is based on the light transmission matrix and resonator stability conditions, aiming to achieve a large stable zone and a short cut-off thermal focal length (CTFL). A folded concave resonator is researched to enhance the cavity length, and the influence of the tunable cavity arm length on the oscillating beam in the resonator and in the YAG crystal is theoretically studied. Moreover, the effects of the output mirror curvature and the cavity arm length on the range of the stable area and the cut-off thermal focal length are also investigated. Experimental results show that a stable green laser output is obtained after second harmonic generation (SHG) with a pulse width ranging from 43 to 143 ns within the laser operating frequency range of 5-20 kHz. At an operation frequency of 10 kHz, the output power is 21.33 W, and the instability of the output power within 400 min is 0.88%. The laser source achieves a maximum power of 25.7 W at 20 kHz, and the maximum single pulse energy reaches 2.7 mJ at 6 kHz. Finally, this is used as the laser source to couple with a water jet with a diameter of 100 microns, achieving a lossless water conductivity transmission over 60 mm length. These results demonstrate the suitability of the designed laser source for WJGL technology research. In precision machining applications, this technology exhibits processing advantages of low thermal damage (~2 μm) and large depth (>10 mm), for 7075 aluminum alloy.

Correlation of signal feature importance and process parameters in water jet-guided laser cutting

Laser-based cutting can deliver high accuracy and speed during the process. However, there are still some technical challenges to be solved. First, the process itself requires precise focusing of the laser beam. When using continuous wave (CW)- or pulses in the μs- to ns-range for efficient materials removal, not only the targeted material volume is heated, but also the surrounding material due to heat diffusion. This decreases the quality of the cut. Coupling the light into a water-jet solves both issues: It ensures the delivery of focused light to the target surface, while cooling the affected material during processing. This work proposes a real-time monitoring system of the cutting process by exploiting unique physical phenomena related to the process. The water jet allows both the propagation of laser light towards the target while keeping it focused and the back-propagation of process light through the focusing system. This can be captured using suitable sensors, and saved using a data acquisition system. The acquired data can be used for process characterization using signal processing. In this work we demonstrate the direct correlation between different process parameters and statistical signal features. We show that reducing the signal to a few statistical features both in time and frequency by feature extraction does not reduce the information content, but instead makes it more robust to mis-classification while decreasing the classification time. It also opens up a wide range of future applications not only to process data, but also to control the process more precise.

ELIMINATION OF THE DEFECTIVE LAYER AND STRESS CONCENTRATORS DURING MICROMACHINING OF HOLES IN THIN SHEET BLANKS OF METAL CELLULAR PANELS

Thin-sheet blanks made of aluminum (in particular, AMg2-N), titanium (VT-15, VT-19) or stainless (12X17) alloys are widely used in the production of honeycomb panels in the aviation and space industries. Foil (thickness 0.025-0.055 mm) is used for the production of fillers for cellular sandwich panels; it is pre-perforated with holes of 0.05-0.18 mm and laid out in a corrugated box with adhesive strips. The possibility of making holes by the laser jet method is considered, as it precedes the occurrence of mechanical damage and thermal defects of the surface adjacent to the treatment zone. It is shown that the Water Jet Guided Laser (WJGL) is an effective and efficient method of obtaining profile holes in the fillers of cellular panels and in the panels themselves, which is characterized by high productivity and allows obtaining holes without thermal and mechanical defects. The method can be used both for foil fillers and for metal panels made of stainless steel up to 1.5 mm thick.

Numerical and experimental study on double coaxial gas assisted water jet guided laser machining of superalloy

To achieve more uniform gas film and higher working temperature, the design of film holes on combustion section parts of aero engine is developing towards three trends: smaller diameter, higher aspect ratio and more quantity. To realize the high quality manufacture of small film holes with high aspect ratio, a new water jet guided laser (WJGL) machining method based on double coaxial assistant gas was proposed in this article. An outer coaxial gas jet with high density was added to the existing coaxial jet of water and helium. That outer coaxial gas jet can weaken the interference effect of reverse water and sweep out the low speed water in deep blind hole. The sweep effect of outer coaxial assistant gas was confirmed by simulation and experimental results. The penetration time of Ф0.7 mm holes with depth of 4 mm decreased from 410 s to 173 s with the help of outer coaxial assistant gas. A series of Ф0.7 mm holes with the aspect ratio of 14.6:1 were machined using double coaxial assistant gas WJGL method on superalloy specimens with thermal barrier coatings (TBCs). The roughness of side wall was better than 0.6 μm, and no breakage or stratification was found at the interface of TBCs and matrix. This method can also be used in the manufacture of SiC/SiC ceramic matrix composites (CMCs) parts with deep small holes.

Investigations on the water-jet guided laser scribing of thermal barrier coated IC21 nickel-based superalloy

Ceramic thermal barrier coatings (TBCs) are widely recognized as state-of-the-art for ensuring the stability and reliability of turbine blades operating in extreme conditions. However, the significant disparities between the thermal and mechanical properties of TBCs, bonding layers (BCs), and nickel-based superalloy substrates pose considerable challenges for machining film cooling structures on turbine blades while minimizing coating delamination, heat-affected zones (HAZs), and other potential defects. The utilization of Water-Jet Guided Laser (WJGL) has gained significant attention as a promising approach for the machining of advanced materials, including ceramics and multi-layer composites. In this study, a theoretical model is proposed to describe the transient interaction between WJGL and TBC IC21 nickel-based superalloy. A numerical simulation using the deformation geometry method is employed to investigate the evolution of ablation morphology, which is further validated by experimental data. Specifically, the formation mechanism of the shoulder structure at the material interface is explained. Furthermore, orthogonal experiments are conducted to establish the fundamental influence rule and significance level of machining parameters on the microscopic groove morphology. Based on these findings, multi-row cutting experiments are performed to identify the optimized scanning trajectory for achieving the high-quality thorough cutting of the substrate with a thickness of 2.7 mm, while minimizing oxidation, residue deposition, and delamination. The outcomes of this study contribute to the knowledge of WJGL machining, and could potentially improve the efficiency and accuracy of advanced material processing techniques.

Experimental Study on Carbon Fiber-Reinforced Polymer Groove Machining by High-Power Water-Jet-Guided Laser.

Due to the excellent properties of carbon fiber-reinforced polymers (CFRPs), such as high strength and strong corrosion resistance, the traditional water-jet-guided laser (WJGL) technology has problems with fiber pull-out and has a small cutting depth when processing CFRPs. Therefore, in this study, we used high-power water-jet-guided laser (HPWJGL) technology to perform groove processing experiments on CFRPs. The effects of four key process parameters, high laser power, pulse frequency, feed rate, and water-jet pressure, on the cutting depth were investigated by a single-factor experiment. The formation mechanism of groove cross-section morphology and the processing advantages of high-power water-jet-guided lasers were analyzed. On this basis, the mathematical prediction model of cutting depth was established by using the response surface method (RSM), and the optimal combination of process parameters was obtained. The mathematical prediction model was verified by experiments, and the error was only 1.84%, indicating that the model had a high reference value. This study provides a reference for the precision machining of HPWJGL technology.

Investigation on the Coaxial-Annulus-Argon-Assisted Water-Jet-Guided Laser Machining of Hard-to-Process Materials.

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.

Laser coupling in waterjets subject to jet instabilities, laser parameters, and alignment errors.

High coupling accuracy and efficiency attract wide attention in waterjet-guided laser technology due to the requirements for high processing performance in hard-to-cut material and diamond industries. The behaviors of axisymmetric waterjets injected into the atmosphere through different types of orifices are investigated by adopting a two-phase flow k-epsilon algorithm. The water-gas interface is tracked with Coupled Level Set and Volume of Fluid method. The electric field distributions of laser radiation inside the coupling unit are modeled by wave equations and numerically solved with the full-wave Finite Element Method. The coupling efficiency of the laser beam affected by waterjet hydrodynamics is studied by considering the profiles of the waterjet shaped at transient stages, namely vena contracta, cavitation, and hydraulic flip. The growth of the cavity leads to a larger water-air interface and increases the coupling efficiency. Eventually, two types of fully developed laminar waterjets, i.e. constricted waterjets and non-constricted waterjets, are formed. Constricted waterjets that are detached from the wall throughout the nozzle are preferable to guide laser beams since they significantly increase the coupling efficiency compared to non-constricted waterjets. Furthermore, the trends of coupling efficiency affected by Numerical Aperture (NA), wavelengths, and alignments errors are analyzed to optimize the physical design of the coupling unit and develop the alignment strategies.

Improving superficial microstructure and properties of the laser-processed ultrathin kerf in Ti-6Al-4V alloy by water-jet guiding

In the present research, the gas-assisted laser (GAL) and water-jet guided laser (WGL) processing technologies were applied to machine the ultrathin kerf in the wrought Ti-6Al-4V alloy. The microstructure, microhardness, and wear properties of the superficial layer were investigated. The results reveal that the GAL processing could machine the kerf with a high depth-to-width ratio of 12–15, but the increased processing times enhance the depth little. Due to the oxygen entrainment and relatively low heat and mass transferring efficiency, the assisted gas promotes the formation of a scaled recast layer containing β-Ti phase and oxides, which increases the roughness to 20 μm. The WGL processed kerf has a low depth-to-width ratio with a value of 1.9–2.5 and the depth could be increased by increasing the WGL processing times. With the assistance of the water jet, the remelted debris and heat could be eliminated immediately, which restrains the formation of the recast layer and heat-affected zone. The ultrathin oxide outer layer with hundreds of nanometers and ultrafine α-Ti grain inner layer are formed on the surface, which decreases the roughness to 12 μm. Compared with the as-received Ti-6Al-4V alloy, the microhardness of GAL processed kerf surface is increased to 382.8 HV accompanied by residual tensile stress, while the microhardness of WGL processed kerf surface is increased to 481.6 HV accompanying with residual compressive stress. In addition, the GAL processing increases the wear rate at room temperature but decreases the wear rate at high temperatures. Comparatively, the WGL processing decreases the wear rate at room and high temperatures, simultaneously. Such wear behaviors could be ascribed to their different superficial microstructures and phase constituents.

Modeling and Prediction of Water-Jet-Guided Laser Cutting Depth for Inconel 718 Material Using Response Surface Methodology

In this study, the water-jet-guided laser (WJGL) method was used to cut Inconel 718 alloy with high temperature resistance. The effect of critical parameters of the water-jet-guided laser machining method on the cutting depth was studied by a Taguchi orthogonal experiment. Furthermore, the mathematical prediction model of cutting depth was established by the response surface method (RSM). The validation experiments showed that the mathematical model had a high predictive ability for cutting depth. The optimal cutting depth was obtained by model prediction, and the error was 5.5% compared with the experimental results. Compared with the traditional dry laser cutting, the water conducting laser method reduced the thermal damage and improved the cutting quality. This study provides a reference for the precision machining of Inconel 718 with a water-jet-guided laser.

Experimental Research and Optimization of Ti-6Al-4V Alloy Microgroove Machining Based on Waterjet-Guided High-Power Laser.

In order to improve the tribological properties of Ti-6Al-4V alloy and further broaden the application scope of titanium alloy materials in the industrial field, a preparation method of a waterjet-guided high-power laser processing surface microgroove was studied. In this paper, a multifocus coupling lens was innovatively designed to replace the spherical lens in the traditional waterjet-guided laser coupling device, which avoids the gas explosion phenomenon in the coupling of the high-power laser and waterjet, and realizes the high-quality coupling of the high-power laser and water beam fiber. Then, with the microgroove morphology as the response target, the single-factor test and response surface test of the water-guided laser processing microgroove were carried out. Based on the experimental results, an approximate mathematical model of the response surface between the process parameters and the microgroove topography target was constructed, and the quantitative relationship between the waterjet-guided laser processing parameters and the target response was studied. At the same time, the optimal combination of process parameters was obtained by multiobjective optimization, so as to effectively improve the microgroove morphology. This technology provides method guidance and a decision-making reference for subsequent waterjet-guided laser processing of titanium alloy surface functional microstructures.

Real-time measurement of laser beam characteristics for a waterjet-guided laser machine

Real-time measurement of laser beam characteristics for a waterjet-guided laser machine

Research on the Removal Mechanism of Resin-Based Coatings by Water Jet-Guided Quasi-Continuous Laser Cleaning

Laser cleaning technology has the advantages of being green and efficient and is expected to become the most promising remanufacturing cleaning technology. However, the quasi-continuous laser can easily cause problems, such as a heat-affected zone and a recast layer on the substrate material, which limits the development of laser cleaning technology. The environmentally friendly water jet-guided quasi-continuous laser proposed in this paper is an innovative laser cleaning technology that can remove the resin-based coating on the metal substrate with high quality. The epoxy resin coating on the 304 stainless steel surface was cleaned by a water jet guided quasi continuous laser, and the surface morphology, surface element content, and surface roughness of the cleaning area were tested and analyzed. The removal mechanism of water jet-guided quasi-continuous laser cleaning technology was revealed, and the influence of process parameters on cleaning surface quality was found. The optimal process parameters were as follows: the energy density of the water jet-guided laser 17.5 J/cm2, the cleaning speed 135 mm/s, the cleaning line spacing 0.1 mm, and the laser pulse frequency 900 Hz. Therefore, this study is expected to be an important basis for water jet-guided quasi-continuous laser cleaning technology, and promote the development of water jet-guided laser cleaning technology.

Experimental analysis on waterjet-guided Nd: YAG laser thin wood machining

Waterjet-Guided Laser (WJGL) machining is an advanced technique providing efficiency and precision for wood machining. The present study investigates the practical demonstration and analysis of laminated object manufacturing (LOM) WJGL for thin wood machining. A theoretical process of wood laser cutting was established, expressing relations between the cut kerf width and the influencing parameters. WJG Nd: YAG laser system was utilized for machining Korean pine and Northeast China ash specimen of 3 mm thickness, each with 7.21 and 7.13% of water content, respectively, under different machining conditions. The effects of process parameters and influences on woodcut surface geometry were analyzed via analysis of variance (ANOVA) and scanning electron microscopy (SEM). The investigated parameters include the laser cutting speed, power, kerf width, heat-affected zone (HAZ), and cut surface roughness. The study shows that the kerf width and surface were significantly influenced by WJGL power, followed by the cutting speed. For both wood specimens, at a fixed laser cutting speed of 2.36 mm/s, the kerf width increases significantly with laser power, affecting the cut surface quality accordingly. At 6 W and 8 W, the cut kerf geometry and surface quality were excellent for the Pinus Koraiensis, with kerf widths of 0.79 and 0.852 mm, respectively. At a fixed laser power of 8 W, the kerf width decreases with the cutting speed, affecting the cut surface quality. At a cutting speed of 4.33 mm/s, an excellent cut surface of Fraxinus mandshurica was observed with 0.808 mm of kerf width. Depending on the machining conditions, the kerf width variations of Korean pine were more significant than the Northeast China ash. LOM-WJGL is an efficient and eco-friendly technique for thin wood processing.Graphical abstractArticle HighlightsPractical modeling demonstration of waterjet guided laser (WJGL) wood machining.Experimental investigation of different wood specimens under influenced process parameters and machining conditions.Characterization and identification of suitable wood types for efficient and eco-friendly applications.

Numerical simulation of the stability of water fiber-optic in water jet-guided laser machining

Water jet-guided laser machining is a new compound machining technology, which has been widely used in many fields due to its better processing effect. In this technology, the coupling of laser beam and micro-water jet directly determines the machining effect, and the prerequisite for successful coupling is the steady flow of the water jet, so ensuring the stability of the micro-water jet is the key to the stable machining of water jet-guided laser. Therefore, it is of great significance to studying the stability of the water fiber-optic in water jet-guided laser processing. In this paper, aiming at the problem that the stability of the water fiber-optic is difficult to control, a finite element model of the water fiber-optic is established. The convection model is vortex gas-phase flow “enveloped” water fiber-optic which is used to explain the interaction mechanism, and the flow field distribution of gas-phase flow and water fiber-optic convection was obtained. The results show that water fiber-optic is refined under the constraint of gas-phase flow, and the maximum processing distance can increase by three times. At the same time, the gas-phase flow can accelerate the removal of processing debris, and the processing accuracy and efficiency are improved.