Laser Drilling Research Articles

Effect of laser drilling process on combustor liner effusion hole quality

Abstract Effusion cooling is one of the significant cooling technologies in combustor liners in terms of cooling efficiency and weight reduction. However, effusion cooling technology is difficult to manufacture. In fact this technology requires laser-drilling of thousands of tiny holes with shallow angles on a sheet metal with a thickness generally varying between 0.5 to 1.5 mm. In addition, the use of thermal barrier coating is common in gas turbine engines and is one more challenge for the drilling process. In order to obtain more efficient gas turbine engines, the inlet temperature keeps increasing in the last decades, which induces the combustion chamber to operate in a hotter environment. Therefore, efficient cooling technology is needed, even if it is hard to manufacture. For laser drilling, several parameters have to be explored to obtain acceptable holes. This study includes the microstructure investigations of the holes produced with different laser parameters and the optimal laser parameters determined according to the microstructure of six different effusion cooling hole configurations. The results show that laser process differences affect the metal substrate microstructure and thermal barrier coating structure. Drilling method, peak power, number of pulses, gas type and pressure value have a significant effect on the hole geometry and its microstructure.

Large-scale fabrication of meta-axicon with circular polarization on CMOS platform

Abstract Metasurfaces, consisting of arrays of subwavelength structures, are lightweight and compact while being capable of implementing the functions of traditional bulky optical components. Furthermore, they have the potential to significantly improve complex optical systems in terms of space and cost, as they can simultaneously implement multiple functions. The wafer-scale mass production method based on the CMOS (complementary metal oxide semiconductor) process plays a crucial role in the modern semiconductor industry. This approach can also be applied to the production of metasurfaces, thereby accelerating the entry of metasurfaces into industrial applications. In this study, we demonstrated the mass production of large-area meta-axicons with a diameter of 2 mm on an 8-inch wafer using DUV (Deep Ultraviolet) photolithography. The proposed meta-axicon designed here is based on PB (Pancharatnam–Berry) phase and is engineered to simultaneously modulate the phase and polarization of light. In practice, the fabricated meta-axicon generated a circularly polarized Bessel beam with a depth of focus (DoF) of approximately 2.3 mm in the vicinity of 980 nm. We anticipate that the mass production of large-area meta-axicons on this CMOS platform can offer various advantages in optical communication, laser drilling, optical trapping, and tweezing applications.

Fatigue behavior of multi-row film cooling holes manufactured by lasers with different pulses under complex-temperature fields

This research investigates the fatigue behavior of multi-row film cooling holes produced by lasers with diverse pulse widths amid intricate thermal environments. Through laser drilling experiments, conjugate heat transfer simulations, and crystal plasticity finite element analyses, it explores the interplay of temperature and stress fields among multiple holes in these structures, and factors influencing fatigue damage and its severity. Additionally, it anticipates the fatigue fracture paths of multi-row film cooling hole structures. Findings reveal that while the drilling process and aerodynamic parameters significantly impact cooling effectiveness, their influence on cooling distribution is negligible. Fatigue damage distribution is shaped by structural imperfections from different processes, stress field interference among multiple holes, and material property alterations due to temperature changes. The extent of damage is primarily dictated by roundness errors resulting from the drilling process, with taper playing a minor role. Nonetheless, stress interference among multiple holes notably exacerbates stress concentration at the interference zone, leading to increased damage levels in film cooling holes crafted by picosecond lasers with minimal roundness errors. Moreover, in complex thermal environments, fatigue fracture paths of multi-row film cooling holes migrate and evolve contingent on temperature-induced shifts in material properties.

Scheme of flash LiDAR employing glass aspherical microlens array with large field of illumination for autonomous vehicles

This study demonstrates a new scheme of flash LiDAR using a glass aspherical microlens array (MLA) to achieve a large field of illumination (FOI) for autonomous vehicles. A wider FOI of up to 100° was obtained. In contrast to a spherical MLA, the FOI is 38.9° which indicates that the proposed aspherical MLA is 2.6 times wider than the spherical MLA. The wider FOI achieved for the glass MLA is due to a novel laser drilling technique that produces conical micro-holes with a high aspect ratio (depth: diameter = 1.8:1), forming elliptical-like aspherical microlenses through wet etching. An FOI estimation model to provide theoretical basis for designing aspherical MLA with wider FOI is presented, which is in good agreement with experimental results. Furthermore, the optical efficiency of 90% for the FOI was calculated. In this study, we have proposed a unique laser drilling technique to produce glass aspherical MLA with wider FOI and higher optical efficiency for flash LiDAR use in autonomous vehicle applications.

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.

Optimization of nanosecond laser drilling strategy on CFRP hole quality

The drilling and cutting of carbon fiber-reinforced epoxy resin matrix composite (CFRP) structural parts is a prerequisite for one-off moulding and assembly connections. However, the thermal ablation effect observed during nanosecond laser hole-making of CFRP results in significant accuracy errors and thermal damage defects in the quality of the holes obtained from the process. To enhance the quality of laser-drilling CFRP holes, a spiral drilling path was employed in this work. The influence of diverse drilling methodologies, encompassing the trajectory of the laser beam, the spacing between scans, and the direction of the suction system's pumping, on the quality of the holes was examined. The impact of these techniques on the precision and integrity of the holes was assessed in terms of their dimensions, the quality factor, the width of the heat-affected zone (HAZ), and the prevalence of microscopic defects. The results demonstrated that when the drilling strategy involves moving the laser beam from the outside to the inside (Scheme I), a scanning spacing of 20 μm, and backward pumping, the optimal micro-hole accuracy and surface morphology, as well as minimal thermal damage defects can be achieved. This study provides a reference for further optimization of the nanosecond laser drilling process.

In situ x-ray imaging to understand subsurface behavior during continuous wave laser drilling

A limited understanding regarding the underlying dynamics and mechanisms of material removal during continuous wave laser drilling has presented significant challenges in achieving precision and process control. To address this, we employed high-fidelity, in situ synchrotron x-ray imaging to reveal previously unknown material behaviors during continuous wave laser drilling with power modulation. Our findings highlight that high-aspect ratio drill holes are achieved when the laser modulation frequency falls within the range of 8–12 kHz, provided that the laser average power and modulation amplitude levels meet the specified limits. Under these conditions, we identified a material removal mechanism driven by incremental accumulation of recoil pressure that gradually pushes material upward from deep within the substrate to the surface. This mechanism manifested as a low-frequency fluctuation in the vapor depression depth, resulting in periodic instances of material ejection. Furthermore, our study underscores that rapid expansion of the melt pool and the widening of the drill hole opening can impede effective material removal by redirecting energy from material ejection to increasing the melt pool size. This investigation contributes essential insights into the subsurface dynamics involved in the drilling of high-aspect ratio holes, furthering our fundamental understanding of this intricate process.

Temperature-Stress Coupling Fatigue Behavior of Film-Cooling Holes in Complex Temperature Fields.

This research investigates the complex temperature distribution and fatigue behavior of single film-cooling holes manufactured by lasers with different pulse widths in a real flow field. The aerodynamic and heat transfer characteristics of film-cooling holes manufactured using lasers with different pulse widths were analyzed through laser drilling experiments, conjugate heat transfer simulations, and crystal plasticity finite element methods. The study investigated the relationship between changes in the geometric accuracy of the film-cooling holes and the corresponding flow and temperature fields during the film-cooling process. Additionally, the effects of temperature and structural variations on the stress around the holes in a flat plate composed of the second-generation nickel-based single-crystal superalloy DD6 in real flow and temperature fields were studied. The coupling effect of the temperature and stress fields around the holes on the fatigue behavior of the film-cooling holes was examined, and the fatigue damage mechanism of film-cooling holes in complex temperature fields was analyzed. It was found that changes in the blowing ratio do not affect the temperature and stress distributions around the holes but only alter the temperature peak. An increase in the temperature peak results in a decrease in the stress peak. Additionally, the fatigue damage of single film-cooling holes is determined by both the structural defects of the holes and the changes in material behavior due to the temperature around the holes, with the structural influence being more significant.

Characterisation of basalt/glass/kevlar-29 hybrid fibre-reinforced plastic composite material through Nd: YAG laser drilling and optimisation using stochastic methods

Characterisation of basalt/glass/kevlar-29 hybrid fibre-reinforced plastic composite material through Nd: YAG laser drilling and optimisation using stochastic methods

Laser and mechanical micro-drilling for aerospace applications

Traditional laser percussion drilling encounters challenges related to poor geometry and thermal defects. At the same time, mechanical micro-drilling while generating high-quality holes, faces issues such as premature drill breakage and difficulty drilling at acute angles. This review paper introduces a novel approach to micro-drilling Inconel 718 alloy sheets at acute angles by combining sequential laser and mechanical drilling. The study showcases the feasibility and fundamental characteristics of this innovative technique. Results indicate that the sequential laser-mechanical micro-drilling approach mitigates the drawbacks associated with laser-drilled holes, leading to reduced burr size, decreased machining time, and increased tool life when compared to conventional mechanical drilling methods. This advancement holds promise for enhancing precision and efficiency in aerospace applications, paving the way for improved manufacturing processes in the aerospace industry.

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.

ATR-FTIR spectroscopy imaging of bone repair in mandibular laser-osteotomy.

The aim of this study was to verify the effectiveness of attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy in the characterization of bone repair in mandibular osteotomy using erbium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG) laser and multilaminate drill on each side. Two mandible bone fragments were removed from 30 rabbits, and the process of bone repair was studied immediately, 3, 7, 15, 21, and 28 days after the surgery. The histological analysis allowed detecting differences in the early stages of tissue repair after bone cutting performed with the Er,Cr:YSGG laser or multilaminate drill. The ATR-FTIR spectroscopy technique was sensitive to changes in the organic content of bone tissue repair process.

Fractional non-Fourier modeling of laser drilling process

In this paper, a novel fractional non-Fourier model is employed to simulate the laser drilling process, addressing limitations inherent in classical heat conduction equations, including the well-known heat equation paradox associated with infinite heat propagation velocity. This model approach combines spatial approximation via the Meshless Local Petrov-Galerkin method with temporal approximation using the Grünwald-Letnikov finite difference scheme. The study assesses the impact of employing fractional orders, both constant and variable over time, on numerical results, and validates the model using experimental data.

Characterization of Laser Drilling and Parametric Optimization Using Golden Jackal Optimizer

Characterization of Laser Drilling and Parametric Optimization Using Golden Jackal Optimizer

A novel path planning approach to minimize machining time in laser machining of irregular micro-holes using adaptive discrete grey wolf optimizer

As an essential technique in fabricating substrates for flexible printed circuit boards, laser drilling of polyimide films facilitates the production of smaller holes of superior quality, which is crucial for preserving the structural integrity and functional reliability of materials. This advanced technology is increasingly critical in sectors demanding high performance, such as high-speed communications and biomedical devices. However, challenges such as the diverse sizes of micro-holes, their irregular placement, and the inherent limitations of scanning components on speed and operational range make efficient and rapid laser drilling a complex endeavor. In this paper, we develop a processing time evaluation model and present a new adaptive discrete grey wolf optimizer (A-D-GWO). The A-D-GWO utilizes exchange, shift, and 2-opt operations to enhance search efficiency and includes an adaptive parameter mechanism, improving its adaptability to various problem sizes and ensuring faster convergence. Experimental results confirmed the algorithm’s effectiveness, reducing processing times by 38.9%, 53.6%, and 55.5% for files containing 90, 286, and 649 holes, respectively. When compared to traditional algorithms, A-D-GWO showed better stability and accuracy, suggesting its suitability for inclusion in laser processing technologies.

Femtosecond laser ablation responses of kerogen-rich, argillaceous, and bituminous shale rocks

Shale rocks have become one of the major sources of natural gas and oil. Laser drilling has emerged as a promising technique that can be incorporated into horizontal drilling and hydraulic fracturing processes. In this study, we selected three types of shales (kerogen-rich, argillaceous, and bituminous) with distinct compositions and microstructures and performed femtosecond laser irradiation with different power and energy to investigate their ablation characteristics. Evidence of melting and solidification was observed in all samples, despite the ultra-high pulse frequency of the femtosecond laser. Among the three types of shale rocks, the kerogen-rich shale exhibited the highest ablation rate, while argillaceous and bituminous shale showed lower and comparable rates. The above observations highlight the significance of shale chemistry in influencing laser ablation characteristics under femtosecond laser irradiation. Furthermore, no ablation rate anisotropy was observed when irradiating the samples parallel with and perpendicular to the bedding direction, although shale rocks are microstructurally and mechanically anisotropic.

Ex-vivo parametric study of laser ablation-based drilling of cortical bone.

Frequently orthopedic surgeries require mechanical drilling processes especially for inserted biodegradable screws or removing small bone lesions. However mechanical drilling techniques induce large number of forces as well as have substantially lower material removal rates resulting in prolong healing times. This study focuses on analyzing the impact of quasi-continuous laser drilling on the bone's surface as well as optimizing the drilling conditions to achieve high material removal rates. An ex-vivo study was conducted on the cortical region of desiccated bovine bone. The laser-based drilling on the bovine bine specimens was conducted in an argon atmosphere using a number of laser pulses ranging from 100 to 15,000. The morphology of the resulting laser drilled cavities was characterized using Energy dispersive Spectroscopy (EDS) and the width and depth of the drills were measured using a laser based Profilometer. Data from the profilometer was then used to calculate material removal rates. At last, the material removal rates and laser processing parameters were used to develop a statistical model based on Design of Experiments (DOE) approach to predict the optimal laser drilling parameters. The main outcome of the study based on the laser drilled cavities was that as the number of laser pulses increases, the depth and diameter of the cavities progressively increase. However, the material removal rates revealed a decrease in value at a point between 4000 and 6000 laser pulses. Therefore, based on the sequential sum of square method, a polynomial curve to the 6th power was fit to the experimental data. The predicted equation of the curve had a p-value of 0.0010 indicating statistical significance and predicted the maximum material removal rate to be 32.10 mm3/s with 95%CI [28.3,35.9] which was associated with the optimum number of laser pulses of 4820. Whereas the experimental verification of bone drilling with 4820 laser pulses yielded a material removal rate of 33.37 mm3/s. Therefore, this study found that the carbonized layer formed due to laser processing had a decreased carbon content and helped in increasing the material removal rate. Then using the experimental data, a polymetric equation to the sixth power was developed which predicted the optimized material removal rate to occur at 4820 pulses.

Spray mist-assisted drilling of through silicon vias (TSV) using nanosecond laser: Influence of CNT nanofluid

Through Silicon Vias (TSV) are crucial in semiconductor technology for vertically connecting multiple stacks in 3D packaging. High aspect ratio, smooth and slightly tapered TSVs enhance layout efficiency and void-free filling. Being contact-less and dry-etching process, laser machining is a promising technique to fabricate TSVs. A percussion laser drilling approach was used to fabricate TSVs on a 500 μm thick silicon wafer with a 1064 nm ns laser. Four environments such as air, compressed air jet, water mist, carbon nanotube (CNT) fluid mist were employed to assess laser machining effects on TSV performance in terms of entrance and exit diameters, recast layer, side wall damage, and taper angle. Optimized process parameters (laser pulse energy and pulse number) were derived from an ANN prediction model. Laser drilling under CNT mist produced relatively circular (entrance diameter), straight, and clean TSVs. Reduced debris redeposition was observed under air jet, water mist, and CNT mist compared to air. Minimal sidewall damage occurred under water mist and CNT mist as compared to those machined in air and air jet. CNT mist yielded TSVs with less recast layer (∼7 μm), taper angle (∼1.05 deg.), and heat affected zone (HAZ) thickness (∼50 μm). Enhanced machining quality may be attributed to increased thermal conductivity of CNT nanofluid and pressurized mist flow rate, improving cooling and debris removal. Furthermore, a detailed investigation of TSV using SEM was performed and the findings were compared to those of other research groups.

Optimization of the Laser Drilling Processing Parameters for Carbon Steel Based on Multi-Physics Simulation

The laser drilling of carbon steel is always suffered from the formation of slag, the presence of cutting burrs, the generation of a significant quantity of spatter, and the incomplete penetration of the substrate. In order to avoid these defects formed during the laser drilling of carbon steel, the COMSOL multi-physics simulation method was used to model and optimize the laser drilling process. Considering the splash evolution of the material during the complex drilling process, the transient evolution of the temperature field, the flow of the molten fluid, the geometrical changes, and the absorption of the laser energy during the laser drilling process were investigated. The simulated borehole dimensions are consistent with the experimental results. The process parameters have a great influence on the fluid flow pattern and material slag splashing. The laser power has a significant effect on the laser processing compared with the process parameters. With the increase in laser power and the decrease in laser heat source radius, the time required for perforation is reduced, the flow of melt is accelerated, the perforation efficiency is increased, and the hole wall is smoother, but the degree of spattering is greater. The optimized process parameters were obtained: laser heat source radius of 0.3 mm, laser power of 3000 W. These findings can help reduce the machining defects in carbon steel with excellent mechanical properties by optimizing the laser drilling processing parameters.

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser