Laser Drilling Technique Research Articles

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.

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.

Picosecond laser drilling grids in aluminium foil at 532 and 355 nm wavelengths

Ultra-short laser drilling technique enables production of filters, membranes, microfluidic, photonic, and biomedical devices. Micro-hole grids were drilled in aluminum foil using a 28 picosecond Nd:YAG laser operated at wavelength of 532 and 355 nm with energy up to 18 and 12 mJ, respectively. Varying pulse energy and number, micro-holes obtained at 355 nm and 3.6–9 mJ had the appropriate mean diameter of 36–86 μm. However, the circularity changed in 0.5–0.94. For the 2nd harmonic the mean diameter varied 15–61 μm at 0.36–9 mJ with the circularity of 0.81–0.92. The morphology of the area surrounding micro-holes investigated by scanning electron microscopy exhibited distribution of droplets dominated size 0.9–10 μm, which is feasible for filtration of contaminated liquids. Local elemental composition of the area determined by energy dispersive spectroscopy discovered significant increase in the concentration of C and O, and also emergency of F, depending on laser fluence under vapor-dominated ablation mode, where nuclear reactions are excited in hot plasma.

Volatile Lubricants Injected Through Laser Drilled Micro Holes Enable Efficiently Hydrocarbon-Free Lubrication for Deep Drawing Processes

In order to reduce the use of classic lubricants such as synthetic or mineral oils, emulsions or waxes in the deep drawing process, a new tribological system based on volatile lubricants was investigated. In this system, a volatile medium is injected under high pressure through laser drilled micro holes directly into the contact zone between the tool and the sheet metal and serves as a temporary lubricant. In order to investigate this tribological system under realistic conditions, strip drawing experiments with different volatile lubricants (air, nitrogen, carbon dioxide and argon) were performed on galvanized sheets. Therefore, a new generation of strip drawing tools was designed and numerically calculated for low elastic deformations to ensure a uniform contact pressure distribution over the entire friction contact area. To obtain a homogeneous distribution of the volatile lubricants, a number of micro holes with a depth of several millimeters were drilled into the hardened strip drawing jaws using ultrashort pulsed laser radiation. Taking into account the capabilities of this laser drilling technique in terms of size and shape of the micro holes, computational fluid dynamics simulations were performed to predict the flow behavior of the lubricant within the micro hole as well as the contact zone and were compared with observable effects in outflow tests. The chemical composition of the acting tribological layers was characterized by means of X-ray photoelectron spectroscopy and their changes during the deep drawing process were correlated with the lubricants used as well as the measured wear and friction values.

High power water jet guided laser drilling of angular holes through nickel superalloy

This paper investigates the basic characteristics of water jet guided laser drilling process using a high power laser with a maximum average power of 400 W to drill 0.7 mm diameter angular holes (60° to the surface) through 1.6 mm thick nickel superalloy (resultant hole length of 1.85 mm). Experimental trials were performed using average powers of up to 148 W to understand the effect of different process parameters on the hole quality and cycle time. Process parameters investigated included shielding gas flow rate, water jet pressure, trepanning speed, pulse frequency, and average power. The results found water jet pressure and average power to be significant in controlling the recast layer thickness and drilling cycle time. At higher power and throughput, average recast layer thicknesses of ∼30 μm could be obtained with a cycle time of 3 seconds. This surpasses the quality of holes, which can be produced via state-of-the-art laser drilling techniques without a significant reduction in productivity.

EFFECT OF POWER ON HOLE QUALITY OF UNDERWATER GLASS DRILLING USING CO2 LASER

The aim of this paper to study the effect of power on the drilling of soda lima glass (SLG) using under water laser drilling technique. A 1.15 mm thickness SLG sheets were immersed 1mm below the water surface, then irradiated with CW CO2 laser. The laser parameters used were (24, 25 and 26) W power, (5, 7.5 and 10) sec and exposure time and (1, 2and 3) pulses. Were determined using images for samples and study quality of holes using images. These ones of the dimensional of hole and crack length measured by image j program of the samples, it was watched that hole diameter and the length of cracks could be regulated by the power, time and no. of pulses. When power or pulses were increased, the hole diameter increased. The length of cracks decreased with increased no. of pulses and increased when the power increased. The small hole was 0.469mm found at working power (24) W, five seconds and one pulse for hole diameter. While, the minimum crack length was 0.4mm found at three pulse, five sec. and 24 W power. In addition, the parameters were analyzed statistically using design of expert software, Box Behnken design from surface response methodology and the results were significant.

Empirical modeling and Monte Carlo simulation of secondary electron yield reduction of laser drilled microporous gold surfaces

This work investigates secondary electron yield (SEY) mitigation from a metal surface with a microporous array fabricated using the laser drilling technique. We propose a general empirical model to fit the experimentally measured SEY of a flat gold surface for normal and oblique incidences of primary electrons. Using this empirical model, we develop a two-dimensional Monte Carlo (MC) simulation scheme to determine the effective SEY of a microporous array. It is found that the SEY from a porous surface is significantly reduced compared to that of the flat surface. By taking into account all the generations of secondary electrons inside a well, our MC results are found to be in very good agreement with the experimental data. The dependence of the SEY on the aspect ratio of the micropores and porosity of the surface is examined. A simple empirical formula has been proposed to evaluate the effective SEY of the gold microporous array for pores of arbitrary aspect ratios.

Etching and drilling of through-holes in thin glass by means of picosecond Bessel beams

In this paper, we present a laser etching and drilling technique for thin glass materials based on the use of finite-energy pulsed Bessel beams orthogonally impinging on the sample surface. Thanks to the elongated focal zone of the quasi-non-diffractive beam, the laser processing can be performed without scanning the beam position along the thickness of the transparent material sample, but simply moving the sample in the plane orthogonal to the beam. We first present the results of single-shot glass microfabrication performed to identify the optimal laser parameters needed for an efficient internal material ablation. We then describe the micromachining technique used for etching the dielectric material at glass–air interfaces and for generating, without chemical etching, through-holes in thin glasses.

基于飞秒激光微孔加工的温度补偿型光纤微流传感器

基于飞秒激光微孔加工的温度补偿型光纤微流传感器

High Aspects Ratio Micro-drilling of Super-alloys Using Ultra-Short Pulsed Laser

The demand for high aspect ratio micro holes is growing day by day. Functional micro-holes are necessary for application areas in aeronautic, automobile, semiconductor and biomedical industries. It requires holes with high contour accuracy and minimum thermal damage. Further, the materials used in these applications are alloys, super alloys and composite materials, which are difficult to cut. Laser-machining has demonstrated outstanding capability to generate high precision micro features. The development of femto, pico-second lasers has provided a precise method for micro-fabrication. In this paper, micro-hole drilling was carried out using a 12 W, Ti-sapphire 50-100 fs laser. Holes are analysed for size and shape. It analyses the effect of pulse duration for SS-316L, Inconel-718 and Ti6Al4V. It also investigates effect of laser drilling techniques like percussion, trepanning and helical. Study concludes that with proper control on beam positioning, beam energy and pulse width one can achieve quality holes using ultrafast lasers.

Comparison of percussion laser drilling quality with and without water-based ultrasonic assistance

A millisecond-pulsed percussion laser drilling technique using water-based ultrasonic assistance is reported for drilling nickel super-alloy GH4037 sheets with 12-mm-thickness. Influence of ultrasonic vibration on drilling quality including hole taper angle, hole sidewall quality, recast layer microstructure, and hardness distribution of hole heat affected zone (HAZ) is analyzed through comparing holes drilled without ultrasonic assistance. Recast layer reduction, grain refinement, and HAZ hardness increase induced by ultrasonic assistance are also analyzed. It is shown that ultrasonic vibration improves percussion laser drilling quality by reducing hole taper angle, cleaning hole sidewall, decreasing hole defects, reducing recast layer thickness, refining grains, decreasing hole sidewall surface roughness, and increasing micro hardness.

183 GHz Frequency Selective Surface Using Aligned Eight-layer Microstructure

An aligned eight-layer honeycomb-shaped frequency selective surface (FSS) has been designed and fabricated to pass and reject electromagnetic waves at 183 and 118 GHz, respectively. To reduce the shifts between layers, an aligned packaging method was introduced based on photolithography and laser drilling techniques. The transmission properties of FSSs with different numbers of layers were investigated from 110 to 220 GHz. Good agreements were observed between experimental and simulated results in all the cases, among which an optimized selectivity, with an insertion loss 1.35 dB at 183 GHz and a rejection 28.6 dB at 118 GHz, was obtained by the eight-layer one.

The effects of the Er:YAG laser on trabecular bone micro-architecture: Comparison with conventional dental drilling by micro-computed tomographic and histological techniques

Background: The use of lasers has become increasingly common in the field of medicine and dentistry, and there is a growing need for a deeper understanding of the procedure and its effects on tissue. The aim of this study was to compare the erbium-doped yttrium aluminium garnet (Er:YAG) laser and conventional drilling techniques, by observing the effects on trabecular bone microarchitecture and the extent of thermal and mechanical damage. Methods: Ovine femoral heads were employed to mimic maxillofacial trabecular bone, and cylindrical osteotomies were generated to mimic implant bed preparation. Various laser parameters were tested, as well as a conventional dental drilling technique. The specimens were then subjected to micro-computed tomographic (μCT) histomorphometic analysis and histology. Results: Herein, we demonstrate that mCT measurements of trabecular porosity provide quantitative evidence that laser-mediated cutting preserves the trabecular architecture and reduces thermal and mechanical damage at the margins of the cut. We confirmed these observations with histological studies. In contrast with laser-mediated cutting, conventional drilling resulted in trabecular collapse, reduction of porosity at the margin of the cut and histological signs of thermal damage. Conclusions: This study has demonstrated, for the first time, that mCT and quantification of porosity at the margin of the cut provides a quantitative insight into damage caused by bone cutting techniques. We further show that with laser-mediated cutting, the marrow remains exposed to the margins of the cut, facilitating cellular infiltration and likely accelerating healing. However, with drilling, trabecular collapse and thermal damage is likely to delay healing by restricting the passage of cells to the site of injury and causing localized cell death.

The effects of the Er:YAG laser on trabecular bone micro-architecture: Comparison with conventional dental drilling by micro-computed tomographic and histological techniques.

Background: The use of lasers has become increasingly common in the field of medicine and dentistry, and there is a growing need for a deeper understanding of the procedure and its effects on tissue. The aim of this study was to compare the erbium-doped yttrium aluminium garnet (Er:YAG) laser and conventional drilling techniques, by observing the effects on trabecular bone microarchitecture and the extent of thermal and mechanical damage. Methods: Ovine femoral heads were employed to mimic maxillofacial trabecular bone, and cylindrical osteotomies were generated to mimic implant bed preparation. Various laser parameters were tested, as well as a conventional dental drilling technique. The specimens were then subjected to micro-computed tomographic (μCT) histomorphometic analysis and histology. Results: Herein, we demonstrate that mCT measurements of trabecular porosity provide quantitative evidence that laser-mediated cutting preserves the trabecular architecture and reduces thermal and mechanical damage at the margins of the cut. We confirmed these observations with histological studies. In contrast with laser-mediated cutting, conventional drilling resulted in trabecular collapse, reduction of porosity at the margin of the cut and histological signs of thermal damage. Conclusions: This study has demonstrated, for the first time, that mCT and quantification of porosity at the margin of the cut provides a quantitative insight into damage caused by bone cutting techniques. We further show that with laser-mediated cutting, the marrow remains exposed to the margins of the cut, facilitating cellular infiltration and likely accelerating healing. However, with drilling, trabecular collapse and thermal damage is likely to delay healing by restricting the passage of cells to the site of injury and causing localized cell death.

Design and Pharmacodynamic Evaluation of Optimized Microporous Osmotic Tablets of Venlafaxine Hydrochloride

Microporous osmotic tablets were developed using controlled porosity membrane, which delivers drug in a controlled manner for prolonged period of time. The objective of the present investigation was to formulate and evaluate an oral osmotic drug delivery system for the antidepressant drug venlafaxine hydrochloride to achieve zero order release. Venlafaxine hydrochloride was selected as it has a short biological half-life and high aqueous solubility. Drug-excipient compatibility was studied using Fourier transform infrared spectroscopy. Core tablets were prepared by wet granulation method followed by coating. Sodium chloride and potassium chloride (1:1) were used as osmotic agents in the core tablet and polymers Eudragit RLPO and RSPO (1:1) were used for coating along with sorbitol (70% w/w) as pore formers. The tablets showed desired sustained release profile for 24 h. Optimization studies were performed to study the effect of concentration of osmotic agent and pore former on drug release (t50% and t90%). From in vitro release studies, it was evident that drug release was independent of dissolution media, agitation intensity, but highly dependent on the concentration of pore forming agents, osmotic agent and weight gain of the tablet coating. Scanning electron microscopy confirmed the microporous structure of optimized batch. The optimized formulation gave desired once a day release of venlafaxine hydrochloride without using laser drilling technique which would make it more patient compliant and cost effective.

Shallow Angle Drilling of Inconel 718 Using a Helical Laser Drilling Technique

This study reports an experimental investigation for the shallow angle laser drilling of Inconel 718. In this study, a helical laser drilling technique was used to effectively produce holes with a diameter of several hundred microns. The design of experiment (DOE) using the Taguchi method was employed to examine the influence of various process parameters on the geometrical and metallurgical features of drilled holes. A higher laser power, lower speed, and closer focal position to the workpiece surface contributed to the further removal of material by the absorption of more laser energy and larger beam intensity. This resulted in a larger exit hole diameter and less hole taper. The increase in laser power reduced a thickness of the recast layer due to material removal by vaporization. From the DOE result, a regression model to estimate a correlation between experimental factors and hole quality was also suggested. In the second stage of this study, trials to improve drilling performance were made. Using the O2 assist gas of 50 kPa significantly enhanced the drilling performance owing to the delivery of more energy to the workpiece by an exothermic reaction. However, the further increase of O2 gas caused rapid cooling of the workpiece, which lowered the drilling performance. The drilling performance was greatly improved as well using the high laser duty cycle to provide more laser energy. The moving focal position was only beneficial to the drilling performance when a focusing of the beam was moderately maintained on the interaction region of the laser–workpiece.

Application of Box–Behnken Design to Optimize the Osmotic Drug Delivery System of Metoprolol Succinate and its In Vivo Evaluation in Beagle Dogs

The objective of this study was to develop osmotic pump tablets of metoprolol succinate (MS) using water-soluble pore formers in the semipermeable membrane in place of orifice drilled on the membrane thereby abolishing the shortcomings associated with laser drilling technique. The formulation was optimized for coating variables such as semipermeable membrane level (X 1) and pore former level (X 2) by response surface methodology using Box–Behnken design (BBD) employing design expert software. The developed osmotic pump tablet was found to sustain the drug release up to 20 h at zero-order rate. The pharmacokinetic study in Beagle dogs showed delayed T max and lower C max compared to marketed brand TOPROL XL, indicating a slow and more sustained release behavior of MS from the optimized osmotic tablets in comparison with the existing matrix-based marketed dosage form. Thus, a novel approach for the controlled release of MS from osmotic pump tablets has been successfully developed using BBD, which is valuable for the advancement of controlled drug delivery of other water-soluble drugs.

Broadband terahertz anti-reflective structure fabricated by femtosecond laser drilling technique

We fabricated several reverse conical holes on high-resistivity silicon substrate with different power and pulse number of femtosecond laser, and investigated their patterns and features by using scanning electron microscope (SEM). Then, we chose one of the experimental parameters prepared a reverse conical anti-reflection structure sample with period of 90μm. Terahertz Time-domain Spectroscopy (THz-TDS) was used to test its properties. Compared with the nonstructural high-resistivity silicon, the transmission of structural high-resistivity silicon increases by the maximum of 14% in the range 0.32–1.30THz. Furthermore, we simulated the sample by finite integral method (FIM). The simulated results show good consistency with experimental results. The transmission effect of the reverse conical holes were optimized via simulation. Results show that the related transmission effect can be improved by increasing the pulse numbers and decreasing the spot size of the femtosecond laser. The different transmission window can also be tuned by changing the reverse conical structure of different periods.

Three-dimensional laser drilling of polymethyl methacrylate (PMMA) scaffold used for bone regeneration

Development of new methods of scaffold fabrication that closely mimic the structure and function of the extracellular matrix (ECM) is one of the main issues in tissue engineering. This study aims to present a newly developed pre-defined three-dimensional polymethyl methacrylate (PMMA) scaffold fabricated via CO2 laser drilling technique. To achieve this goal, using a computer-controlled laser drilling machine, arrays of interconnected holes with a predefined pattern and geometry were drilled on bulk PMMA samples. Three groups of scaffolds with increasing levels of porosity, and pore sizes of 490 ± 10 μm, were fabricated and evaluated for compressive properties. In order to promote their bioactivity, a thin layer of chitosan/β-TCP composite was coated on the surface of the fabricated samples. Morphology of bulk PMMA scaffolds and PMMA scaffolds with chitosan/β-TCP composite coating were studied using scanning electron microscopy (SEM). Moreover, cell viability was assessed by SaOS-2 cells. Results indicate that this technique allows the fabrication of scaffolds with high amount of interconnectivity and controllability of porosity, pore size, and mechanical properties, the advantage that other methods lack. Furthermore, chitosan/β-TCP composite coating improves the interaction between osteoblast-like cells and the polymeric scaffolds and accelerates the rate of cell proliferation.

The Effect of Laser Processing Area on Nested-Circle Drilling Method

A laser drilling technique named the nested-circle method is introduced in this work, in the respect of short-pulse laser processing.it is found that, as the power increases, the depth to diameter ratio of the hole will increase and the minimum number of circles can be set drilled hole reliably is reduced. Further studies have been carried out on the effect of the number of circles in the nested-circle method. Keys of settings the nested-circle method parameters—Outer circle diameter ‘D1’, Inner circle diameter ‘D2’, The Number of circles ‘R’—have been found out.