Water-jet Assisted Laser Research Articles

Investigation of large-aspect ratio microgrooves on silicon nitride ceramic by WJALM

Silicon nitride (Si3N4) ceramic has excellent durability and superior outstanding mechanical properties, which makes it extensively applied in aerospace, biopharmaceuticals, semiconductors and optoelectronics. Nevertheless, the precise microfabrication of complex-shaped Si3N4 microgrooves, particularly those with large aspect-ratio (LAR) presents significant challenges, and traditional machining methods fall short in meeting the demanding criteria for high-precision applications due to the difficult-to-machine characteristics (e.g. high hardness, high strength and brittleness, etc.). In this research, waterjet-assisted laser machining (WJALM) is preferably adopted for LAR Si3N4 microstructures, which has demonstrated superiority in reducing thermal-induced defects of laser-only machining (LOM) with the water's impact and cooling effects. A comparative investigation of LOM and WJALM is initially conducted to evaluate the heat-affected zone (HAZ), geometric characteristics and sidewall surface quality of LAR Si3N4 microgrooves. Following that, the influence of waterjet and laser parameters on morphological characteristics for WJALM is studied through the control variable method. Results indicated that compared to LOM, the HAZ, material removal rate and sidewall surface quality of LAR microgrooves fabricated by WJALM were much superior. This research not only provides new strategies for Si3N4 microgrooves but also lays the foundation for the further development and industrial application of water-assisted laser technology.

Investigation of continuous wave/coaxial waterjet-assisted laser combined machining of micro holes in GH3536

A two-step combined processing technique, combining a continuous-wave laser with a waterjet-assisted nanosecond laser, has been introduced to enhance the quality and efficiency of laser micro-hole processing for nickel-based superalloys. Initially, a through-hole was created using a continuous-wave laser, followed by hole refinement with a coaxial waterjet-assisted nanosecond laser. In the first step, orthogonal testing methods were employed to investigate the impact of various parameters, including power, duty ratio, frequency, defocusing amount, and processing time, on the entrance and exit apertures, as well as the hole taper. Through the analysis of variance (ANOVA) method, the optimal parameter combination A2B1C4D3E1 was identified, achieving the minimal hole taper. This combination comprised a power level of 80 %, a duty ratio of 15 %, a frequency of 400 Hz, a defocusing amount of 2 mm, and a processing time of 10 ms. In the second step, a comparison was made between scanning and trepan drilling machining methods. The results unequivocally demonstrated that scanning drilling achieves superior entrance and exit morphologies. Furthermore, the effect of water jet velocity on the morphology of micropores was thoroughly analyzed. The voltage range of the water pump was adjusted from 10 V to 24 V, revealing that a voltage of 20 V produced the smallest hole taper. The scanning filling diameter was accurately preset according to the preformed hole aperture as well as the thickness of the recast layer. Finally, after coaxial waterjet-assisted laser precision machining, the inner wall of the hole is free of cracks, and the recast layer and oxide layer are effectively minimized. The initial hole prefabrication with the continuous-wave laser took merely 0.01 s, and the subsequent fine-tuning with the coaxial waterjet-assisted laser took 2 min and 25 s.

Experimental investigation and optimization of modification during coaxial waterjet-assisted femtosecond laser drilling

Waterjet-assisted laser drilling technology facilitates the fabrication of high-quality micro-holes by utilizing the collaborative benefits of waterjets and lasers. In this study, the coaxial waterjet-assisted laser drilling (CWALD) technique was employed to improve the properties of micro-holes during femtosecond laser drilling. Based on computational fluid dynamics (CFD) simulations, the stability of the waterjet was initially verified by optimizing the structure of the watercourse and nozzle shape in the CWALD device. Furthermore, a comparative experiment between laser direct drilling (LDD) and CWALD revealed that while CWALD can produce well-rounded micro-holes with a high aspect ratio, it exhibits lower efficiency and results in a larger heat-affected zone (HAZ). To address these drawbacks associated with CWALD, a two-step coaxial waterjet-assisted composite laser drilling (TS-CWALD) method was proposed. TS-CWALD involves applying CWALD for secondary modification of micro-hole shape following LDD with punching. This modification process is pivotal for enhancing drilling accuracy but requires consideration of multiple parameters. For this purpose, regression models were established for the inlet diameter, outlet diameter, and taper; response surface methodology was then employed to optimize these parameters. Subsequently, interactive effects analysis was conducted on different responses based on laser pulse energy, frequency, modification speed, and number of modification cycles. The adequacy of the developed models was subsequently verified using analysis of variance methods. Finally, the successful fabrication of a film hole with an inlet diameter of 205 μm and an outlet diameter of 200 μm, featuring a taper of only 0.2°, was achieved ultimately through meticulous parameter optimization. Furthermore, the micro-hole retained a minimal HAZ. The optimized parameters encompassed a pulse energy of 20.6 μJ, frequency of 127 kHz, modification speed of 3 mm/s, and shape modification carried out over 335 cycles.

Multi-focus image fusion for microscopic depth-of-field extension of waterjet-assisted laser processing

Multi-focus image fusion for microscopic depth-of-field extension of waterjet-assisted laser processing

Microstructural evolution, mechanical properties and surface quality of TC11 titanium alloy subjected to waterjet-assisted laser direct inscription

Waterjet-assisted laser direct inscription (WJALDI) technology has presented a positive effect to alleviate the thermal damage in workpieces caused by laser ablation. This research pays attention to the effect of aqueous media on the microstructure evolution and phase composition of materials during laser ablation, and few relevant researches have been reported. In this work, titanium alloy (TC11) was applied to fabricate microgrooves utilizing WJALDI and laser direct inscription in the air (LDI). The interaction effects between the laser, water, and the material within a complete ablation cycle were analyzed in depth. The geometry and thermal damage region were observed and discussed to prove the machining performance. The microstructure evolution that happened on and underneath the microgroove surface was also studied. The results revealed that the effect of cooling and impacting significantly reduced the accumulation of debris and molten metal, and better processing quality was obtained in WJALDI. According to the analysis of electron backscattered diffraction (EBSD), the grain refinement of the inner material was alleviated, low-angle grain boundaries with the features of uniform distribution were generated, and the adjacent grains of α phase have small kernel average misorientation. In addition, compared with LDI, WJALDI offered a wide microgroove with a small size of heat affected zone (HAZ) and thin thickness of the recast layer, while less depth. Therefore, the developed technology in this work could be a promising approach for the micromachining of titanium alloy or even other difficult-to-cut materials with high quality.

Experimental Study on Coaxial Waterjet-Assisted Laser Scanning Machining of Nickel-Based Special Alloy

The problems of the recast layer, oxide layer, and heat-affected zone (HAZ) in conventional laser machining seriously impact material properties. Coaxial waterjet-assisted laser scanning machining (CWALSM) can reduce the conduction and accumulation of heat in laser machining by the high specific heat capacity of water and can realize the machining of nickel-based special alloy with almost no thermal damage. With the developed experimental setup, the laser ablation threshold and drilling experiments of the K4002 nickel-based special alloy were carried out. The effects of various factors on the thermal damage thickness were studied with an orthogonal experiment. Experimental results have indicated that the ablation threshold of K4002 nickel-based special alloy by a single pulse is 4.15 J/cm2. The orthogonal experiment results have shown that the effects of each factor on the thermal damage thickness are in the order of laser pulse frequency, waterjet speed, pulse overlap rate, laser pulse energy, and focal plane position. When the laser pulse energy is 0.21 mJ, the laser pulse frequency is 1 kHz, the pulse overlap is 55%, the focal plane position is 1 mm, and the waterjet speed is 6.98 m/s, no thermal damage machining can be achieved. In addition, a comparative experiment with laser drilling in the air was carried out under the same conditions. The results have shown that compared with laser machining in the air, the thermal damage thickness of CWALSM is smaller than 1 μm, and the hole taper is reduced by 106%. There is no accumulation and burr around the hole entrance, and the thermal damage thickness range is 0-0.996 μm. Furthermore, the thermal damage thickness range of laser machining in the air is 0.499-2.394 μm. It has also been found that the thermal damage thickness is greatest at the entrance to the hole, decreasing as the distance from the entrance increases.

Dynamic evolution simulation of ablation zone in water-jet assisted laser machining of Korean pine (Pinus koraiensis)

In order to solve the difficulties with the observation of the ablation zone and the many factors that affect the dynamic evolution process of the ablation zone, the structural morphology and dynamic evolution process of the ablation zone in the process of water-jet assisted laser machining Korean pine (Pinus koraiensis) were studied. Based on the DFLUX subprogram, a compound heat source model was established. Under the comprehensive consideration of heat conduction, heat convection, heat radiation, and thermal physical properties varying with temperature, the three-dimensional (3D) finite element model of the Korean pine was numerically simulated by water-jet assisted laser machining. Through numerical simulation analysis, the cross-sectional morphology of Korean pine kerf was found to be screw-shaped, and the experimental results were in good agreement with the simulation results. The dynamic evolution law of water-jet assisted laser machining of Korean pine was obtained. In addition, as the laser power increased and the cutting speed decreased, the morphology of the Korean pine kerf remained unchanged, but the structure size of the Korean pine kerf showed an increasing change.

Facile and green fabrication of robust microstructured stainless steel mesh for efficient oil/water separation via waterjet-assisted laser ablation

Preparing an efficient and durable separation material for solving the problem of oily wastewater treatment is of importance but difficult due to the restriction of complex process and secondary pollutants. Herein, the environmentally friendly and low damage waterjet-assisted laser ablation was developed to fabricate robust microstructure on 304 stainless steel mesh (SSM-WJALA) for oil/water separation. This underwater oil-repellent/underoil water-repellent SSM-WJALA realized the separation of light and heavy oil/water mixtures only under gravity, and exhibited high separation efficiency and great stability to various oil/water mixtures and cyclic separation tests. The detailed analysis of mechanical properties and durability of the material were carried out, which included the tests of friction coefficient, nanohardness, and electrochemical corrosion. The results showed that the surface hardness increased by more than 20%, the corrosion potential increased from − 1.02 V to − 0.49 V, and the corrosion current density decreased by more than two orders of magnitude, compared with SSM-LDA. The application of WJALA technology not only enhanced the properties of mechanical and corrosion resistance of oil-water separation materials but also reduced dust pollution and harm to the health of operators. Therefore, this environmentally friendly and cost-efficient SSM-WJALA provided an effective strategy to solve the problem of oily wastewater treatment especially in harsh conditions and opened an avenue for developing low-cost and facile technology for preparing functional materials.

Water-jet assisted laser cutting of Korean pine (Pinus koraiensis): Process and parameters optimization

In order to improve the processing quality of wood parts, an orthogonal experimental design of five factors and four levels was adopted, and a water-jet assisted laser cutting experiment on Korean pine (Pinus koraiensis) was conducted. Moreover, by using range analysis, the influences of the defocusing amount, cutting speed, laser power, water pressure, and water jet angle on the processing quality of Korean pine parts were evaluated, and the optimum process parameters were determined. The test results show that when the defocusing amount was -1 mm, water jet angle was 30°, laser power was 48 W, water pressure was 1.0 MPa, and cutting speed was 25 mm/s, the best processing quality of Korean pine parts was obtained.

Gas shrinking laminar flow for robust high-power waterjet laser processing technology.

At present, waterjet-assisted laser processing technologies are disadvantaged by low coupling power and poor process reliability, which significantly affect processing efficiency and depth. To address these shortcomings, we propose herein a novel water-gas shrinkage-guided high-power laser processing (WSLP) technology. Firstly, the characteristics of the laminar flow and the light guiding of the water-gas coupled device are optimized. The laminar simulation results show that the water-gas contraction ratio and laminar flow length can be adjusted by changing the water/gas pressure and structural parameters. Secondly, light guiding simulation reveals with a 532 nm 1000W laser, the light guiding efficiency of the shrinkage interface can reach more than 95% within the range of the axial offset 22.1 mm, radial offset 0.62 mm and angular offset 15.8° of the laser focus. Compared with the traditional waterjet-assisted laser processing method, the anti-disturbance capability of the WSLP method is increased by 3.8 times in the axial direction, 2.3 times in the radial direction, and 1.5 times in the angle offset. Thirdly, the feasibility of the laser conduction and processing with this water-gas shrinkage method is verified by experiments. The formation conditions and the relationship of the water-gas laminar flow are investigated. The result shows that the laser coupling efficiency can reach 93% in the low power condition. The research can provide technical support for large depth laser precision machining, in the future.

Coaxial waterjet-assisted laser drilling of film cooling holes in turbine blades

Film cooling holes (FCHs) of nickel-based single crystal turbine blades were drilled by 532 nm Nd:YVO4 nanosecond laser in coaxial waterjet-assisted environment. Microstructure of the side wall of the FCHs was mainly investigated by means of transmission electron microscopy. The average thickness of heat affected zone (HAZ) around FCHs decreases with increasing of water flow rate. The main phase within HAZ evolves from β-NiAl to β-NiAl + γ-Ni with the increase in the water flow rate. Some γ-Ni particles in the HAZ twined along (111) plane. A small portion of the FCHs are free of HAZ when drilled by coaxial waterjet-assisted laser drilling at a laminar water flow rate ≥3.1 m/s. There are no processing-induced defects including HAZ, microcrack, and phase transformation around the FCHs when drilled at the water flow rate ≥5.1 m/s. The FCHs with high surface quality can be drilled by the coaxial waterjet-assisted laser drilling. Finally, effects of fluid water on drilling quality of the FCHs were discussed.

Surface quality evaluation of single crystal 4H-SiC wafer machined by hybrid laser-waterjet: Comparing with laser machining

Single crystal silicon carbide (SiC), as a 3rd generation semiconductor material, has a wide application range and development prospect, especially in some key fields such as defense and aerospace industries. It's a typical difficult-to-machine and hard-brittle material due to its high hardness and brittleness. A hybrid laser-waterjet micromachining technology was employed to implement near damage-free and high-efficient micromachining of single crystal SiC. The workpiece material is heated by laser to a temperature near but below its melting point. The material is under an extremely “softened” but still solid status. A waterjet is applied off-axially to expel the heating-softened material and cool the material to eliminate thermal damage. It combines the advantages of laser processing with those of waterjet cutting. Moreover, it's a green machining approach, which is pollution-free and recyclable. In the present study, the surface quality of single crystal 4H-SiC machined by the hybrid laser-waterjet is evaluated and compared with that machined by laser. Among the wafers respectively machined by laser, under-water laser, waterjet-assisted laser and the hybrid laser-waterjet, the one machined by the hybrid laser-waterjet is with the best surface quality. Its cut boundaries between the machined area and the unmachined area are clear, the cut edges are straight, also the cut sides are clean. On the contrary, there is severe thermal damage along the cut edges and cut sides of laser machining. The microgrooves obtained from the hybrid laser-waterjet micromachining are with V-shaped cross-sections and the transition between the cut edge and the unmachined surface is flat and smooth. The cross-section profile of the microgroove machined by laser is M-shaped and there are obvious humps along the two sides of the microgroove. The microgroove bottom is almost at the same height with the unmachined surface. Besides, there are HAZs with a width of 50–100 µm and scaly recast layers on the sides of the cut machined by laser. In contrast, there is no recast layer and HAZ on the cut side of the hybrid laser-waterjet micromachining. The texture of the cut sidewall is clear and with the typical features of the material removed under the plastic mode. The EDS results show that the oxidation behavior happens during both the hybrid laser-waterjet micromachining and laser machining. However, the content of silicon dioxide generated in the hybrid laser-waterjet micromachining process (the oxygen content is about 5%) is obviously lower than that generated in laser machining (the oxygen content is more than 30%).

Water-jet assisted nanosecond laser microcutting of northeast China ash wood: Experimental study

Laser machining is an advanced technology that provides efficiency and precision for the processing of wood. In this paper, the ablation mechanism of wood processed via a water-jet assisted nanosecond laser was analyzed. The influences of cutting speed and laser power on the cutting width of northeast China ash wood (NCAW) (Fraxinus mandshurica Rupr.) with and without the water-jet assisted system were evaluated. The surface morphology of the kerf of processed NCAW was observed via scanning electron microscopy (SEM). Furthermore, a factorial design experiment was carried out to analyze the effects of process parameters on the cutting width. Additionally, the experimental results were processed by multilinear regression analysis. The results showed that with the water-jet assisted system, the minimum value of the cutting width was 0.18 mm when the cutting speed was 50 mm/s and the laser power was 6 W, and good surface quality was obtained. The experimental results were processed by an analysis of variance and multilinear regression analysis. The predicted model, effectively validated by the experiments, had good prediction accuracy, which provided a theoretical basis for predicting the cutting width of NCAW processed by a water-jet assisted laser.

Phase Analysis of Laser Direct Etching and Water Assisted Laser Combined Etching of SiC Ceramics

In this study, to discover the etching mechanism of SiC ceramics under laser direct etching and water-jet assisted laser combined etching, the phenomena of substance change on the etched surface were investigated. Also, the rules of substance transfer in etching are discussed. The elemental content change and the phase change of the etching products on the etched surface were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. These studies showed a high amount of carbon black on the etched surface, because of the decomposition of SiC ceramics under the high-power-density laser irradiation. SiC decomposed to Si under the laser irradiation, and the subsequent chemical reaction of Si and O2 easily produced SiO2. The SiO2 on the etched surface melted and vaporized, whereas most of SiO2 was removed through splashing, changing the chemical composition of the etched surface. Following the water jet introduction, an increased amount of O existed on the combined etching surface, because the chemical reaction of SiC and H2O easily produced SiO2 under the high-power-density laser irradiation.

An investigation on co-axial water-jet assisted fiber laser cutting of metal sheets

Water assisted laser cutting has received significant attention in recent times with assurance of many advantages than conventional gas assisted laser cutting. A comparative study between co-axial water-jet and gas-jet assisted laser cutting of thin sheets of mild steel (MS) and titanium (Ti) by fiber laser is presented. Fiber laser (1.07µm wavelength) was utilised because of its low absorption in water. The cut quality was evaluated in terms of average kerf, projected dross height, heat affected zone (HAZ) and cut surface roughness. It was observed that a broad range process parameter could produce consistent cut quality in MS. However, oxygen assisted cutting could produce better quality only with optimised parameters at high laser power and high cutting speed. In Ti cutting the water-jet assisted laser cutting performed better over the entire range of process parameters compared with gas assisted cutting. The specific energy, defined as the amount of laser energy required to remove unit volume of material was found more in case of water-jet assisted laser cutting process. It is mainly due to various losses associated with water assisted laser processing such as absorption of laser energy in water and scattering at the interaction zone.

Development of a water-jet assisted laser paint removal process

The laser paint removal process usually leaves behind traces of combustion product i.e. ashes on the surface. An additional post-processing such as light-brushing or wiping by some mechanical means is required to remove the residual ash. In order to strip out the paint completely from the surface in a single step, a water-jet assisted laser paint removal process has been investigated. The 1.07μm wavelength of Yb-fiber laser radiation has low absorption in water; therefore a high power fiber laser was used in the experiment. The laser beam was delivered on the paint-surface along with a water jet to remove the paint and residual ashes effectively. The specific energy, defined as the laser energy required removing a unit volume of paint was found to be marginally more than that for the gas-jet assisted laser paint removal process. However, complete paint removal was achieved with the water-jet assist only. The relatively higher specific energy in case of water-jet assist is mainly due to the scattering of laser beam in the turbulent flow of water-jet.