Femtosecond Laser Drilling Research Articles

Fabrication of RuO2-graphene/graphene thick-and-dense micro-hole array material by femtosecond laser for high volumetric rate performance

Nanostructured materials have a great application prospect in the next generation of electrochemical energy storage devices. However, there is a great obstacle for thick and dense electrodes with large tortuosity to simultaneously attain high areal and rate performance at the same time to meet the practical requirements. Herein, a simple electrostatic self-assembly method is adopted to anchor RuO2 onto graphene nanoflakes, the thick and dense film of RuO2-Graphene/Graphene(RuO2-G G-1) are prepared by filtration and mechanical compression, and then the micro-hole array structure was fabricated by femtosecond laser drilling, which shortened the diffusion path of hydrogen ion (H+). After etching, the pore diameter is 7 μm; the pore spacing is 40 μm and the array was regular. The mass loss of the electrode caused by etching was only 3 %, and the relative density of the electrode reached 79 %. Under the same thickness of the electrode, the pore electrode obviously reduces the ion resistance. The micro-hole array not only improves the areal and volumetric capacity of the RuO2-G G-1 electrode, but also improves the rate performance of the electrode., the rate capability increased from 65.6 % to 87.7 % at 20 A g-1. The study provides a powerful technique for the fabrication of dense and thick electrode in energy storage system.

Study on hole wall morphology and defects in burst mode of femtosecond laser drilling

Through-hole drilling experiments are conducted on nickel-based superalloys GH3536 using femtosecond laser and burst modes of femtosecond laser. The morphology and roughness of the hole wall are studied. Indentation experiments show an increase in microhardness to 10 GPa in the recast layer at the edges of holes at GHz mode and MHz-200 μJ. EDS finds that the increase is attributed to oxidation and the formation of Cr2O3. EBSD and kernel average misorientation (KAM) reveal the laser induced heat-affected-zone (HAZ) at Single-Pulse-200 μJ and GHz-200 μJ. The removal characteristics under four burst modes are compared in single pulse/burst percussion experiment, indicating that the efficient removal of molten material in BiBurst mode accounts for its superior hole wall quality. The BiBurst mode offers significant advantages in terms of enhancing machining efficiency while minimizing material damage, which can extend to various metal materials.

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.

Roll-to-Roll Manufacturing of Breathable Superhydrophobic Membranes.

Self-cleaning and anti-biofouling are both advantages for lotus-leaf-like superhydrophobic surfaces. Methods for creating superhydrophobicity, including chemical bonding low surface energy molecular fragments and constructing surface morphology with protrusions, micropores, and trapped micro airbags by traditional physical strategies, unfortunately, have encountered challenges. They often involve complex synthesis processes, stubborn chemical accumulation, brutal degradation, or infeasible calculation and imprecise modulation in fabricating hierarchical surface roughness. Here, a scalable method to prepare high-quality, breathable superhydrophobic membranes is proposed by developing a successive roll-to-roll laser manufacturing technique, which offers advantages over conventional fabrication approaches in enabling automatically large-scale production and ensuring cost-effectiveness. Nanosecond laser writing and femtosecond laser drilling produce surface microstructures and micropore arrays, respectively, endowing the membrane with superior antiwater capability with hierarchical microstructures forming a barrier and blocking water infiltration. The membrane's breathability is carefully optimized by tailoring micropore arrays to allow for the adequate passage of water vapor while maintaining superhydrophobicity. These membranes combine the benefits of anti-aqueous corrosive liquid behaviors, photothermal effects, thermoplastic properties, and stretchable performances as promising comprehensive materials in diverse scenes.

Intelligent femtosecond laser bone drilling via online monitoring and machine learning

In conventional spinal surgeries, mechanical and thermal injuries frequently usually arise due to improper handling, giving rise to a range of complications including infection, poor wound healing and bleeding. Femtosecond laser ablation offers a promising approach owing to high precision and low thermal damage. In this study, an intelligent femtosecond laser drilling method of human spinal bones has been proposed, and a machine learning method has been employed to determine the optimal laser processing window, ensuring high-quality outcomes. A neural network model has been developed to predict drilling quality, achieving an impressive accuracy rate exceeding 98 %, along with precision and recall rates of 100 % and 92.86 %, respectively. To further monitor the process, a fiber spectrometer and a thermal camera has been employed to monitor the focal status and bone temperature during laser processing to make sure the drilling is in a focal position and temperature in safe range. Subsequently, the drilling efficiency has been predicted using another neural network model within high-quality processing window for the maximum ablation processing parameter. The current research has demonstrated a direct, non-destructive and efficient method for intelligent laser spinal drilling.

Femtosecond laser drilling 100 μm diameter micro holes with aspect ratios > 20 in a Nickel based superalloy

Micro holes with high aspect ratios are essential for the cooling performance of aero-engines. Challenges persist in deep hole drilling due to the escalating stringent requirements in terms of hole diameters, aspect ratios, and 3D profiles. In this study, we propose a two-step femtosecond laser drilling method to produce cylindrical micro holes with diameters of ∼100 μm, aspect ratios >20, and near-zero taper angle in Inconel 718 plates. In the first drilling period, the laser polarization trepanning method is used, yielding through-holes with aspect ratios >20 but undesired tapers and irregular shapes at the hole exit. A new method called laser spinning is then introduced in the second drilling period, proficiently decreasing taper angles to be < 0.05° and improving the irregular exit profiles into circular contours. Employing a rotating inclined laser beam, the laser spinning method facilitates deep hole drilling by enhancing laser penetration, solely resulting augmented hole diameters at the exit without compromising hole aspect ratios. The efficacy of this drilling approach is achieved through modifying the incident laser reflection on internal hole walls. Overall, the presented results and analyses hold great promise for high-quality deep hole drilling in opaque materials, particularly for products regarding aero-engines.

Design of a Femtosecond Laser Percussion Drilling Process for Ni-Based Superalloys Based on Machine Learning and the Genetic Algorithm.

Femtosecond laser drilling is extensively used to create film-cooling holes in aero-engine turbine blade processing. Investigating and exploring the impact of laser processing parameters on achieving high-quality holes is crucial. The traditional trial-and-error approach, which relies on experiments, is time-consuming and has limited optimization capabilities for drilling holes. To address this issue, this paper proposes a process design method using machine learning and a genetic algorithm. A dataset of percussion drilling using a femtosecond laser was primarily established to train the models. An optimal method for building a prediction model was determined by comparing and analyzing different machine learning algorithms. Subsequently, the Gaussian support vector regression model and genetic algorithm were combined to optimize the taper and material removal rate within and outside the original data ranges. Ultimately, comprehensive optimization of drilling quality and efficiency was achieved relative to the original data. The proposed framework in this study offers a highly efficient and cost-effective solution for optimizing the femtosecond laser percussion drilling process.

Effects of water temperature on femtosecond laser layered-ring trepanning in superalloy with water-based assistance

The effects of the water temperature on the hole quality in water-assisted femtosecond laser layered-ring trepanning on superalloys were studied. The effects of the laser pulse repetition rate on the hole entrance/exit diameters, taper angle, and hole sidewall morphology and roughness at different water temperatures were compared and analyzed. The results show that at a water temperature of 70 ℃, the diameter of the hole entrance decreased, while that of the hole exit increased, compared with those at 20 ℃. Both the hole entrance and exit diameters decreased at 2 ℃. The hole taper angle was the largest when the water temperature was 20 ℃, followed by 2 ℃, and was the smallest at 70 ℃. When the laser pulse repetition rate was 300 kHz, the hole taper angle at 70 ℃ decreased by 43.6 % compared with that at 20 ℃. As the water temperature increased, the roughness of each part of the hole sidewall decreased. When the pulse repetition rate was 200 kHz, the quality of the hole sidewall improved under water-based assistance conditions, while the hole quality improved at a water temperature of 70 ℃, compared with drilling in air. As the water temperature increased, the water was more likely to evaporate, resulting in an increase in the amount of bubbles. As more bubbles moved upward, the water flow increased. The debris and materials generated by laser drilling were more effectively removed, thereby improving the drilling efficiency. The use of a higher water temperature was beneficial to obtain holes with smaller taper angles and a higher sidewall quality. The experimental results provide a reference for optimizing water-assisted femtosecond laser drilling. This methodology can be applied to the aerospace and semiconductor industries.

Femtosecond laser processing of controlled tapered micro-holes based on dynamic control of relative attitude

Femtosecond laser drilling of metal necessitates precise control over taper to ensure dimensional accuracy. However, conventional vertical incidence laser processing methods result in micro-holes with inherent taper and a beam waist at the midportion. To address this issue, this paper proposes a micro-hole machining method that involves adjusting the relative attitude between the laser beam and the workpiece, enabling controlled machining of micro-holes with varying tapers. The feasibility of the method is validated by simulating theoretical hole profile using an isophote model, which exhibit good agreement with experimental results. Experimental findings on nickel-based alloys demonstrate a linear correlation between the attitude angle and hole taper. By manipulating the attitude angle, it is possible to achieve controllable machining, ranging from positive taper to negative taper. This approach eliminates the waist within the micro-hole and enhances chip removal space, resulting in improved hole wall quality. Moreover, employing multi-attitude angle and dynamic attitude angle processing, in addition to single attitude angle control, effectively eliminates the core generated during drilling. This method prevents the exacerbation of multiple reflections caused by the core and the reduction of chip removal space, leading to enhanced energy coupling between the laser and the material in the ablation area. As a result, the maximum depth of the hole is increased, allowing for the realization of no tapered micro-holes on 5 mm thick nickel-based alloys. Furthermore, laser processing introduces a significant amount of dislocation structures in the microstructure near the hole wall. This study introduces a novel approach to achieve controllable taper in femtosecond laser drilling. It offers both theoretical and experimental support for understanding the hole shape evolution process in femtosecond laser drilling.

Investigations into morphology and surface integrity of micro-hole during femtosecond laser drilling of titanium alloy

Investigations into morphology and surface integrity of micro-hole during femtosecond laser drilling of titanium alloy

Process applicability and hole wall microstructure evolution mechanism of femtosecond laser spiral drilling

In this work, a 1.5 mm thick GH3044 nickel-based superalloy is processed by femtosecond laser to obtain a micro-hole for the fuel nozzle of an aerospace engine with a large thrust-to-weight ratio. To address the issue of sidewall adhesion during micro-hole machining, a spiral drilling method implemented with a rotating wedge scanning module is used. Combined with a two-step drilling strategy, it achieves flexible removal of adhesion while ensuring machining efficiency and further improving the quality of drilling. The effect of different drilling strategies on the sidewall roughness of micro-holes is investigated. After process optimization, the roughness of the the micro-hole sidewalls is reduced to below Rq 0.4 μm, which is approximately 8% compared to the traditional one-step drilling strategy. Based on the EBSD analysis results, it is observed that the microstructure of the micro-hole sidewalls remains largely unchanged regardless of the drilling strategy employed. The analysis of the micro-hole sidewalls shows the presence of periodic microstructures. When aiming for low roughness, the geometric characteristics of these periodic microstructures can be adjusted by manipulating the laser's single pulse energy. These experimental findings present a new perspective for optimizing the femtosecond laser drilling process and provide theoretical support for future enhancements in the actual fuel injection effect.

Experimental study on the sidewall quality of femtosecond laser drilling CFRP

This study investigated the effect of laser angle-of-incidence (AOI) on the sidewall quality of femtosecond laser drilling carbon fiber-reinforced plastic (CFRP). The results indicated that increasing the laser AOI could prevent laser blockage by the sidewall, reducing fiber loss and resin melting and re-solidification. The laser energy density was also raised with a larger laser AOI, which enhanced the laser processing efficiency and reduced the sidewall taper. However, this also led to cavities and crevices caused by the resin loss between the fibers. By adjusting the drilling strategy and the laser energy, the sidewall taper was eliminated, and the resin loss was reduced. This work proposes a novel approach to enhance the sidewall quality of femtosecond laser drilling CFRP, which has implications for the manufacturing and application of CFRP components.

Drilling Sequence Optimization Using Evolutionary Algorithms to Reduce Heat Accumulation for Femtosecond Laser Drilling with Multi-Spot Beam Profiles.

We report on laser drilling borehole arrays using ultrashort pulsed lasers with a particular focus on reducing the inadvertent heat accumulation across the workpiece by optimizing the drilling sequence. For the optimization, evolutionary algorithms are used and their results are verified by thermal simulation using Comsol and experimentally evaluated using a thermal imaging camera. To enhance process efficiency in terms of boreholes drilled per second, multi-spot approaches are employed using a spatial light modulator. However, as higher temperatures occur across the workpiece when using simultaneous multi-spot drilling as compared to a single-spot process, a subtle spatial distribution and sequence of the multi-spot approach has to be selected in order to limit the resulting local heat input over the processing time. Different optimization approaches based on evolutionary algorithms aid to select those drilling sequences which allow for the combination of a high efficiency of multi-spot profiles, a low-generated process temperature and a high-component quality. In particular, using a 4 × 4 laser spot array allows for the drilling of 40,000 boreholes in less than 76 s (526 boreholes/s) with a reduced temperature increase by about 35%, as compared to a single spot process when employing an optimized drilling sequence.

Femtosecond laser drilling of film cooling holes: Quantitative analysis and real-time monitoring

The damage to opposite wall caused by excessive ablation will severely affect the performance of the turbine blade in femtosecond laser drilling of film cooling holes. Real-time monitoring and control of drilling stage is regarded as one of the most effective methods for solving the excessive ablation problem. However, due to the complexity of femtosecond laser drilling process, it is difficult to model the relationship between drilling state and machining phenomenon physically. In this paper, the quantitative analysis of femtosecond laser drilling and an intelligent methodology for real-time monitoring and control of drilling stage were developed. The laser drilling was comprehensively analyzed and four drilling stage was firstly divided automatically based on the hole evolution process and the optical emission signal detected in drilling process. And the correlation between signal and drilling stages was established through the analysis of the optical emission signal. Furthermore, this paper proposed a data-driven method to build the classification model of different drilling stages. The periodicity and pulse characteristics of signal and corresponding time-domain features were extracted for further modelling. Finally, the classification model was established via AdaBoost method, which achieves a classification accuracy of 95.22 %. And the generalization performance for real-monitoring of drilling stage was further verified. This study presented a set of processes for real-time monitoring and process control in laser drilling process, which provides a new insight to solve the excessive ablation problem.

Investigation of Heat Accumulation in Femtosecond Laser Drilling of Carbon Fiber-Reinforced Polymer.

Carbon fiber-reinforced polymer (CFRP) has indispensable applications in the aerospace field because of its light weight, corrosion resistance, high specific modulus and high specific strength, but its anisotropy brings great difficulties to precision machining. Delamination and fuzzing, especially the heat-affected zone (HAZ), are the difficulties that traditional processing methods cannot overcome. In this paper, single-pulse and multi-pulse cumulative ablation experiments and drilling of CFRP have been carried out using the characteristics of a femtosecond laser pulse, which can realize precision cold machining. The results show that the ablation threshold is 0.84 J/cm2 and the pulse accumulation factor is 0.8855. On this basis, the effects of laser power, scanning speed and scanning mode on the heat-affected zone and drilling taper are further studied, and the underlying mechanism of drilling is analyzed. By optimizing the experimental parameters, we obtained the HAZ < 10 μm, a cylindrical hole with roundness > 0.95 and taper < 5°. The research results confirm that ultrafast laser processing is a feasible and promising method for CFRP precision machining.

Anisotropic creep behavior of Ni-based single crystal superalloy with film cooling hole drilled by a femtosecond laser along different crystal orientations

Femtosecond laser drilling was employed to drill film cooling holes with two different apertures (0.30 mm and 0.58 mm) along the [100], [1 0 3/3], and [1 0 3] crystal orientations of a [001]-oriented Ni-based single crystal superalloy. Then, the anisotropic high-temperature creep behavior of Ni-based single crystal superalloy was investigated at 980 °C and 250 MPa. A creep constitutive model was constructed based on the crystal plasticity theory and implemented into a finite element procedure. Based on the experimental and simulation results, the drilling direction significantly changed the stress distribution and the direction of the stress axis, thus effectively influencing the anisotropic creep behavior and deformation mechanism of Ni-based SC superalloy. The drilling direction along [1 0 3] resulted in a longer creep lifetime. The γ′ phase incline to form multi-directional coarsening structure enhancing creep resistance, around holes drilled along the [1 0 3]. Cleavage-like fracture characteristics of the specimen is weakened by drilled along [1 0 3]. Furthermore, When the hole area increases to 0.26 mm2, the stress concentration decreases.

Application of spectral-domain optical coherence tomography technique to in-process measure hole depth during femtosecond laser drilling in different alloys

In this paper, a real-time diagnostic based on the spectral-domain optical coherence technique has been developed to measure the hole depth during femtosecond laser drilling. This diagnostic borrows the idea of a fiber interferometer, and the hole is integrated as a part of the sample arm. By means of investigating the interference fringes detected by the line camera, the hole depth can be extracted. This diagnostic utilizes a broadband small-volume super-luminescent diode as the coherent light source, which has a central wavelength of 833 nm and a full width at half maximum of 24 nm. It has a temporal resolution of 50 µs and a maximal theoretic depth resolution of 12.8 µm. Three kinds of metal samples have been tested, confirming the ability of depth measurement. Copper has been proven to have the best-normalized reflectivity during drilling compared with aluminum alloy and stainless steel.

Optimization of Femtosecond Laser Drilling Process for DD6 Single Crystal Alloy

In this paper, we explore the optimal combination of femtosecond laser drilling parameters for micro-hole processing on DD6 single-crystal high-temperature alloy and analyze the significance of parameter variations on the microstructure characteristics of the holes. The L25(56) orthogonal test was performed by controlling six parameters during femtosecond laser ring processing: average power; overlap rate; defocus rate; feed amount; gas pressure; and end position. The significance of the influence of the factors was analyzed by ANOVA, and the parameters were optimized by genetic algorithm. Scanning electron microscopy was performed on the micropores and the salient features of the pores were analyzed. Finally, we calculated the extreme differences and conducted single-factor effect analysis. We conclude that the defocus rate has the most significant level on the hole drilling by femtosecond laser ring processing for DD6 single crystal high-temperature alloy; and the effect of the end position is smaller than others. The optimized parameters are power 6.73 W; overlap 99%, defocus 0 mm; pressure 0.2 MPa; feed 0.02 mm, and end −0.4 mm.

Effect of Femtosecond Laser Drilling on the Fatigue Properties of the Third-Generation Single-Crystal Superalloy DD9

Effect of Femtosecond Laser Drilling on the Fatigue Properties of the Third-Generation Single-Crystal Superalloy DD9

Characteristics and Properties of Femtosecond Laser Drilling of Kevlar-29 Substrates

Characteristics and Properties of Femtosecond Laser Drilling of Kevlar-29 Substrates