Laser Incident Angle Research Articles

Analysis of the interactions between laser and arc due to different geometric arrangements and laser parameters in the additive manufacturing of Ti-6Al-4V

Additive manufacturing based on arc welding (=DED-Arc) has already established itself in the world of additive manufacturing. Recent process optimizations show the increased use in a hybrid process by irradiating an additional laser beam into the active arc zone. Numerous publications can be found in the literature for steel, aluminum, or bronze, in which, among other things, a strength-enhancing effect or an improved wall surface during this hybrid process is reported. The way in which the laser beam impacts the arc, at what distance, at what angle and with what spot size or focusing appears to be random in the publications and is always chosen differently in the literature. In order to close this knowledge gap, a corresponding holder for a DED-Arc torch and laser optic is developed, which allows these geometric factors to be systematically changed and also enables the titanium alloy Ti-6Al-4V to be processed in a hybrid process. By welding individual tracks and walls with different angles, distances and spot sizes of the two energy sources, a fundamental understanding of the laser-arc hybrid process is created. The results are analyzed using a high-speed camera and evaluated on the basis of surface measurements, micrographs, and power source values. This showed that the distance between the laser and the arc has the greatest effect on the additive process stability and the arc power sources values. In the range of 2–6 mm, there are, in some cases, strong fluctuations in the wire deposition and the arc voltage, so that this range should be avoided. It also showed that a wider spot sizes range of 360–600 μm can be used, whereby different ranges are recommended depending on the target size of uniform wall height or thickness. For the laser incidence angle, the most uniform walls across all tests are achieved at 20°. As the angle of incidence becomes flatter, the walls become more irregular, although there is no linear relationship or areas that should be avoided at all.

Effect of laser beam incident angle on welding of Ti6Al4V with fiber lasers

Laser beam welding (LBW) is widely used for welding Ti6Al4V alloys in aerospace applications. LBW has localized high-energy fluence with low-energy input compared to other fusion welding processes, resulting in narrower heat-affected zones. On the other hand, most metals are highly reflective when the laser beam impinges perpendicular to the surface, making the process inefficient. Hence, this work proposes to employ shallow angle incidence to reduce the reflectivity during the welding of Ti6Al4V material. To explore the potential of this idea, the current study focuses on studying the effect of laser incident angle (15°-90°), power (300 W-1500 W), and feed rate (10 mm/s-25 mm/s) on autogenous weld bead geometry. For this purpose, bead-on plate (BOP) LBW is conducted on mill-annealed Ti6Al4V material of dimensions 25 mm × 25 mm × 3 mm by employing a fiber laser source with a maximum power of 3 kW and a wavelength of 1080 nm. It is observed from the results that at a normal incident angle and low laser power (< 600 W), the penetration depth is too low to generate a weld bead. Analyzing the cross-section of the weld bead, obtained from SEM, perpendicular to the weld direction reveals that the increase in laser incident angle up to an optimal angle resulted in increased bead dimensions (width and height), and beyond that, the dimensions decreased. However, the optimal incident angle changed when the laser power was changed. The major finding of this study is that at 600 W and a normal incident angle, the laser could not penetrate and generate a weld bead due to low absorptivity, while at an incident angle of 300, 450, and 600, weld beads are generated because of increased absorptivity. Similarly, the increase in weld dimensions with the increase in laser power is observed. At higher laser power, underfill and oxide formation are observed. The feed rate is less predominant than the incident angle and the power.

Parametric investigation of laser incidence geometry in laser-assisted milling of Inconel 718

While laser-assisted milling machining is promising for promoting the machinability of Inconel 718, the geometrical parameters of laser beam relative to milling tool significantly influence its machining performance. In this work, we investigate the effects of various parameters of laser incidence geometry on the laser-assisted milling process of Inconel 718 by comprehensively employing analytical investigations, finite element simulations and experiments. Firstly, a laser-assisted milling experimental platform is constructed, and a fully coupled thermal-mechanical 3D finite element model of laser-assisted milling of Inconel 718 is established. Secondly, experiments and finite element simulations of laser-assisted milling of Inconel 718 are conducted to investigate the impact of laser assistance on cutting force and machined surface morphology. Results indicate that laser-assisted milling can moderately reduce cutting force and enhance surface quality compared to conventional milling. Thirdly, a single-factor experiment is carried out to explore the impact of laser incidence geometry parameters (laser power, laser incidence angle, and laser spot-tool edge distance) on the cutting force in laser-assisted milling of Inconel 718. Furthermore, the parametric investigation based on the response surface methodology is carried out to assess the coupled effects of the three parameters for deriving their optimal values. The experimental results show that the optimized parameters of laser-assisted milling can lead to a 47.4% reduction in surface roughness and a 25% reduction in cutting force, accompanied by significantly reduced tool wear, as compared to conventional milling. The findings demonstrate that the rational selection of laser incidence geometrical parameters is crucial for enhancing the laser-assisted milling capability for Inconel 718.

Femtosecond Pulsed Laser Machining of Fused Silica for Micro-Cavities with Sharp-Corners

Abstract Fused silica is the preferred material for applications requiring high temperature resistance, low thermal expansion coefficient and excellent optical properties. The machining of micro-cavities on fused silica surfaces is of particular interest for microfluidic manipulation, mechanical locking, and miniaturization of high-quality optical waveguides, but it still remains technically challenging via traditional manufacturing techniques especially for micro cavities with sharp corners. In the present study, the machining of micro-cavities in fused silica by a femtosecond laser-based method has been investigated numerically and experimentally. The effects of laser machining conditions, including laser power, laser scanning speed, laser incidence angle, and laser-off delay time, on the sidewall slope and bottom surface roughness of the micro-cavities were comprehensively investigated. The results indicated that laser power played a crucially important role in determining the sidewall slope of the micro-cavity, and the laser scanning speed had a significant influence on the bottom surface roughness. Furthermore, the sidewall slope of the micro-cavity was linearly increased as the laser incidence angle increases. By using a laser incidence angle of 10° and a laser-off delay time of 280 ms, a micro-cavity with sidewall slopes close to right angles (10°) was fabricated. This study confirms that femtosecond laser machining is an effective method for fabricating micro-cavities with sharp corners on fused silica surfaces, and the appropriate laser machining conditions should be considered based on practical application scenarios.

Research on Diffraction Patterns of Smartphone Screens

Smartphone screen is composed of pixels which are not of uniform size and arranged evenly. When illuminated by a laser, the reflected beam diffracts, producing a diffraction pattern with structure of mesh shape that exhibits characteristics similar to a two-dimensional reflection grating.In this paper, the general diffraction formula of a two-dimensional non-uniform grating is derived, while a simplified form in a special case is explored. The influence of laser incidence angle on the diffraction pattern is analyzed. The diffraction patterns by formula calculation and Fourier transform are obtained using MATLAB simulation. The rationality of the derived formula is verified through simulation and experiments. Also, the pixel density of the smartphone screen is calculated based on the diffraction pattern obtained from the experiment. The application scenarios of the research results are proposed.Comparing the discrepancy in diffraction patterns of different types of screens whose arrangements of sub pixels in smartphones are also different, the mechanism of grating diffraction is displayed directly. Theoretical calculations, simulations and experiments are applied for comparing and confirming each other.

Drag increase behavior of micro-textured concave titanium surface generated by oblique laser etching

Titanium alloy has been widely used in the clinical preparation of artificial jawbone implants due to its excellent mechanical properties and biocompatibility. Artificial bone implantation drug-carrying research can realize the targeted release of drugs at the lesion, however, it is still at the technical bottleneck in inhibiting the sudden release of drugs. In this paper, based on the typical wettability model, a drug-loading and release-retarding method for artificial titanium jawbone drug-storage microcapacitor has been proposed by studying the oblique laser etching process of the inner surface of the drug-storage capsule and by investigating the resistance-enhancing mechanism of the texturization of concave surface of the inner wall. Using the oblique laser etching texture, the contact angle measurement reveals that when the laser frequency is 40KHz, the laser pulse width is 11 ns, the scanning speed is 130 mm/s, and the laser incidence angle is kept at 30° and the number of processing is one, the minimum surface contact angle can be obtained is only 8°. By combining the “3 + 2″ nanosecond laser etching device with the laser depth of focus theory, a curved surface laser etching process method was proposed. A titanium alloy jawbone with drug-carrying cavities was printed using SLM 3D printing technology, and the drag-enhancing effect of the texture was verified using sodium fluorescein labeling method, and it was found that the hydrophilic microtexture had a significant drag-enhancing effect on the liquid flow in the microfluidic channel.

One-step laser preparation of unidirectional liquid spontaneous transport structures

The Tilted Wedge Microcavity Array (TWMA) structure of the Nepenthes alata peristome allows for unidirectional fluid transport without any surface energy gradient. However, current methods of creating bionic Nepenthes alata peristome structures have significant improvement room in terms of structural shape, machining efficiency, and cost-effectiveness. To address these issues, in this paper, bionic Nepenthes alata peristome TWMA structures on 7075 aluminium alloy was built via a nanosecond laser with highly efficiency, low cost and flexible processing pattern. A unilateral tilted microcavity structure was fabricated by designing the laser processing path, and at the same time, the samples were tilted to change the angle at which the laser beam hit the working surface. This ensures that the microcavity is machined without destroying the microcavity structure underneath. The variation law of aluminum alloy ablation threshold under the influence of laser incidence angle was studied. The dimensional parameters of the TWMA structure were analysed in relation to laser incidence angle θ, laser processing power P, number of laser scans n, and laser scanning speed V. Additionally, liquid spreading tests were carried out on different surfaces of bionic structures, and the influence of surface wettability on the spreading results was investigated. The results indicate that the ablation threshold decreases initially and then increases with an increase in the laser incidence angle. This reflects the trend of the aluminium alloy absorption rate, which initially increases and then decreases with an increase in the incidence angle. For the prepared TWMA structure, the optimum speed of achieving the unidirectional spreading effect was found to be 2.41 mm s−1 with a surface contact angle (CA) of 35°. This study presents a low-cost and rapid preparation method for creating liquid unidirectional transport structures without any energy input.

Parameter optimization, microstructural and mechanical properties of fiber laser lap welds of DP1200 steel sheets

In this research, the effects of laser power, laser welding speed and laser incidence angle were evaluated in terms of weld geometry, microstructure, microhardness, fracture surfaces and tensile shear load in fiber laser welding joints of DP1200 steel sheets. Response Surface Methodology (RSM) was utilized to derive mathematical relationships between the process parameters and the tensile shear load after the tensile test. The optimum combination of process parameters was a laser power of 2800 W, a laser welding speed of 40 mm/s, and a laser incidence angle of 70°. A thermal camera was used to record the laser welding process, and the cooling rates were evaluated by analyzing this data. The influence of cooling rate upon microstructure phase formation for DP1200 steel is investigated, with continuous cooling transformation (CCT) diagrams. Also, post-welding stress and displacement were simulated by Simufact Welding software. At high heat input (55.79 J/mm) occurred coarse dendritic martensitic lath growth while at low heat input (37.6 J/mm) fine dendritic martensitic structure was observed in the weld zone was obtained owing to the high rate of cooling. The microstructure consists of full martensite at a higher than 10 °C/s cooling rate. The findings reveal that the phases in FZ and HAZ, the morphology and martensite/bainite constituents differed related to the heat input and laser incidence angle, which ultimately affects the joint’s microhardness, fracture dynamics and tensile shear load.

Laser Parallel Nanofabrication of Dual‐Au‐Nanoholes on Microsphere‐Lens‐Array for Polarization‐Dependent SERS

AbstractHigh‐efficient fabrication of well‐ordered nanostructures on flexible substrates is a challenge to surface‐enhanced Raman spectroscopy (SERS) for analytical fingerprinting trace‐detection. In this work, a laser parallel nanofabrication method is reported via incident‐angle‐dependent photonic nanojet ablating Au film on the bottom surface of microsphere‐lens‐array (MLA), for combination with formed dual Au‐nanoholes (MLA/2‐AuNHs) as the flexible SERS substrates. The process parameters, i.e., pulsed laser energy, MLA diameter, Au film thickness, and laser incident angle, are optimized for high finish‐quality of dual‐AuNHs with a diameter of ≈875 nm and a tip gap of ≈90 nm. The SERS substrate demonstrates the limit of detection down to 10−11 M for 4‐nitrobenzenethiol molecules by the multiple optical regulations, including self‐aligned focusing to the hotspots and directional antenna, the strongly localized surface plasmon resonances, and optical whispering‐gallery modes for resonance energy transfer. The flexible PDMS film supporting the rigid MLA holds the SERS performance of MLA/2‐AuNHs with high flexibility. Moreover, the MLA/2‐AuNHs SERS substrate exhibits differential responses to orthogonally polarized excitation, by which the background noises can be eliminated to improve the Raman spectrum. The present work opens new opportunities to fabricate dielectric‐metal flexible SERS substrates by laser parallel nanofabrication via MLA for Raman trace detection.

Numerical simulation at the micro-scale for the heat transfer modelling in the thermoplastic composites laser-assisted AFP process

Laser-assisted Automated Fibre Placement for thermoplastic composites has shown its potential to process complex shaped parts with high productivity rates but many challenges, both physical and technical, still need to be addressed in order to achieve proper in-situ consolidation. Ensuring high quality bonding of the laid tapes relies on perfect control of their thermal history throughout the process, and heat transfer has long proven essential to achieve this. Numerous heat transfer models account for optical interaction between the laser and composite at a macroscopic scale. Here, a thermo-optical model at the micro-scale is designed and differentiates the fibres from matrix domain, accounting for their respective properties. A single tape is modelled in a static configuration. Based on a composite material realistic microstructure, a ray-tracing algorithm highlights the laser heat absorption depth dependency to laser incidence angle and fibre distribution. Numerical surface temperatures are compared to experimental data obtained with a specific set-up leading to an overall accurate approximation. Finally, the microstructure model relevance is assessed with 1D homogenised models considering either ideal surface heating or a volumetric heat source. The surface heating model leads to inaccurate approximation of surface temperatures, whereas volumetric heat source absorption substantially limits temperature errors. As a result, this model gives a satisfactory compromise between model complexity, computational time and temperature prediction.

Comparative Analysis of Algorithms for Laser Line Identification for 3D Scanning Devices

A comparative analysis of algorithms for laser line center determination and recognition has been conducted. The issues in this area are described, outlining the principles, pros, and cons of each method. Additionally, the possibilities of their application using programming code are demonstrated. Algorithm testing was performed using Python language tools and the OpenCV library. It is shown that the quality of the result in the extremum method significantly depends on the quality of the selected parameters for the Butterworth filter. In contrast, the gray gravity method substantially relies on the accuracy of determining the laser incidence angle. The computational efficiency and accuracy for each algorithm are also analyzed.

Tunability Dependence of All-Optical Liquid Crystal Delay Line on Laser Polarization and Incidence Angle

This work experimentally investigates the optical manipulation of trans-cis swaps and resultantly their optical/electromagnetic imprints as a driver for realizing the tunable delay lines in the microwave X band (8-12 GHz) regime utilizing the polarization and incident angle dependencies of azo-admixed liquid crystals (LCs). Measurement results confirm that the tuning efficacy of the azo-LCs-based delay line is highly dependent on the polarization of the laser beam concerning the rubbing and filling directions of LCs. When the laser light beam is polarized parallel to the rubbed direction as well as the LCs filling direction, the achievable differential phase shift is maximized. Full Text: PDF References T. Sakamoto, Optoelectronic Circuits for Control of Lightwaves and Microwaves (London, IntechOpen 2011). CrossRef J.F. Li, "All-optically controlled microwave analog phase shifter with insertion losses balancing", Eng. Lett. 28, 3 (2020). DirectLink J.P.F. Lagerwall, G. Scalia, "A new era for liquid crystal research: Applications of liquid crystals in soft matter nano-, bio- and microtechnology", Curr. Appl. Phys. 12, 6 (2012). CrossRef S. Kim, K. Seiji, "Photochemical On–Off Switching of One-Dimensional Photonic Crystals Consisting of Azo-Functionalized Liquid Crystal Polymer and Polyvinyl Alcohol", Crystals 9, 12 (2019). CrossRef J.F. Li, "Micro-LED Mass Transfer Technologies", ICEPT (Guangzhou, IEEE 2020). CrossRef U. Chodorow, J. Parka, O. Chojnowska, "Liquid Crystal Materials in THz Technologies", Phot. Lett. Poland 4, 3 (2012). CrossRef

Effect of variable laser incident angles on microstructure and mechanical properties of laser-cladded Inconel 718

In the laser cladding process of complex components, laser deflection is a significant issue that greatly affects manufacturing quality. This study investigates the influence of different incident angles on the microstructure and wear resistance of laser-clad layers. Firstly, an Inconel 718 coating was prepared on an Inconel 718 substrate using an IPG fiber laser. Next, the macrostructure and microstructure of the coating were observed using electron microscopy. Finally, the microhardness of the coating was measured, and the underlying mechanisms affecting wear resistance due to incident angle were revealed. The results show that with an increase in the laser incident angle, the laser energy distribution becomes more divergent, leading to a shift in the peak energy density and changes in the macroscopic morphology of the melt pool, exhibiting a non-Gaussian distribution and resulting in increased cellular dendrite count and coarsened grains. Laser deflection causes variations in microstructure and properties between inner and external angles, where higher laser energy density and temperature gradients at the inner angle result in finer grains and more numerous smaller secondary dendrites on the dendritic arms, along with less severe element segregation and higher microhardness at the inner angle.

EXPLORING THE LIMITS OF TERRESTRIAL LASER SCANNERS ON AEROSPACE MATERIALS

Abstract. Terrestrial laser scanners are powerful measurement devices commonly used for 3D modelling tasks generating large volumes of data with fast acquisition as a first priority. However, these scanners can alternatively be used to produce near real-time, engineering quality spatial data concerning the changing state of manufactured components. This paper provides a comprehensive analysis of two terrestrial laser scanners capturing aerospace materials and components, and their associated quality measures. In order to explore the limitations of the tested TLS instruments, a mechanical jig was designed incorporating both a rotation and translation stage. This study involved three elements of a point cloud processing workflow: data capture, registration and feature extraction. Sphere-based 7DoF registration is applied using two different commercially available software packages with varying levels of user control. To analyse the quality of the registration, control points extracted from captured point clouds were compared to nominal values measured using a laser tracker. The quality of the registration was consistent, with differences kept between 0.4 mm and 0.6 mm. To evaluate the quality of the captured point clouds, two different tests were conducted. This included planar fit tests on an aluminium drilling template, and sphere fitting tests on white 1.5” spherical targets in magnetic nests. One half of the aluminium drilling template was coated with matte spray to reduce erroneous laser reflections. Finally, the registered point clouds were input to a developed algorithm which automatically extracted drilling holes from the drilling template. Previous scanning work performed on aerospace materials showed evidence of optical rattling caused by high intensity reflections from the interior holes in a drilling template. Further exploration showed that the amount of optical rattle varies systematically with incidence angle. This work demonstrates a systematic offset in the location of extracted hole centres in the drilling template. This offset is dependent on laser incidence angle, and can therefore be accounted for when locating manufacturing components from a known scanning position.

Dependence of Ablation Thresholds for Silicon on Laser Incident Angle

Dependence of Ablation Thresholds for Silicon on Laser Incident Angle

Effect of laser incidence angle on the femtosecond laser ablation characteristics of silicon carbide ceramics

Due to their excellent physical and chemical properties, silicon carbide ceramics have become representative high-performance materials in aerospace, energy power, biomedical, and other fields. However, as a typical hard and brittle material, silicon carbide ceramics possess incredibly high hardness and brittleness, which pose challenges to traditional mechanical processing methods. Laser processing, as a non-contact method, offers a wide processing range and high processing efficiency and has broad application prospects in the field of hard and brittle material processing. In this paper, laser ablations of silicon carbide ceramics with various combinations of process parameters were carried out by using a five-axis infrared femtosecond laser processing system. The changes in the ablation morphology with different incidence angles and laser power were discussed. The results demonstrate that the ablation threshold of silicon carbide ceramics initially increases, then decreases, and finally increases with the increase of laser incident angle. This trend may be attributed to the effect of the incidence angle on the laser absorption rate of silicon carbide ceramics. The ablation morphology of silicon carbide ceramics can be divided into three zones based on color and oxygen distribution: the ablation removal zone, ablation edge zone, and ablation affected zone. At the same laser incidence angle, the ablation range and depth gradually increase with the increase in laser power, but the growth rate gradually decreases. Furthermore, at the same laser power, as the incident angle increases, the laser energy density gradually decreases, and the long axis of the actual ablation area gradually lengthens while the short axis gradually shortens. This work could provides technical and theoretical support for laser surface processing at multiple incidence angles, which is conducive to multi-axis processing of complex curved parts.

Compact multipass-laser-beam antenna for NV sensor sensitivity enhancement.

Large-area, highly uniform microwave field radiation and efficient excitation of fluorescence are the key to achieving high sensitivity sensing of the NV (nitrogen-vacancy) magnetometer. In this paper, we report a compact multipass-laser-beam antenna for NV ensemble color centers sensing. The antenna not only provides a tridimensional uniform magnetic field, but also can be used for efficient excitation of the NV fluorescence. The optimal size of the antenna and the angle of laser incidence are determined by the multi-physics field simulation software COMSOL. For an equivalent excitation power, the designed structure increases the path length of the excitation beam by up to three orders of magnitude, up to the level of m, compared to the conventional direct beam mode. Finally, this method increased the sensitivity by a factor of 60 realized a magnetic field sensitivity of 2.8 nT/√Hz in the range of 10-100 Hz. This work provides an experimental method for the design of integrated NV magnetometers.

Lunar laser ranging: The pointing error analysis to Lunokhod 1 and Lunokhod 2

The corner-cube reflectors (CCRs) are small optical instruments designed to accurately measure the distance between the Earth and the Moon. Signals from L1 (Lunokhod 1) and L2 (Lunokhod 2) can be used for higher precision analysis of lunar libration than Apollo reflector. Here, we describe the optical performance of L1 and L2 at near-infrared wavelength. Theoretically, because of the initial direction and lunar librations, the surfaces of these arrays do not, in general, point directly to the Earth. The laser incident angles for the CCRs and the far-field diffraction patterns (FFDP) of individual CCRs of possible incident angles are calculated. Finally, extract the optical cross-section as a function of incident angles. In the experiment, for the first time, superconducting nanowire single-photon detectors (SNSPDs) at a wavelength of 1064 nm are designed and fabricated aiming at lunar laser ranging (LLR), and the effective echo rates of L1 and L2 are measured. Using experimental results to check the orientation of the CCRs. The experimental results show that there is an error in the initial pointing of the CCRs, the initial pointing angles of L1 and L2 are about from 10o to 40o.

Optimization of e+/e− pair yield during the interaction of a Doppler-boosted laser with a solid-density plasma

The interaction of a Doppler-boosted laser with a solid-density plasma is investigated with two-dimensional particle-in-cell simulations, with special attention paid to the influences of laser incident angle on the yield of e+/e− pairs. With normal laser incidence, it is found that parts of plasma electrons are accelerated by the reflected laser and radiate high-energy γ-photons, which further make nearly head-on collisions with the subsequent incoming laser pulses. The nonlinear quantum parameters of the produced photons can reach 4.6, and the yield of e+/e− pairs increases by a factor of 4 compared to an incident angle of 45°. The optimization is easy to implement and can improve the signal-to-noise ratio in the experiments.

Influences of Laser Incidence Angle and Wall Thickness on Additive Components

Abstract Additive manufacturing (AM), particularly laser powder bed fusion, is growing the ability to rapidly develop advanced cooling schemes for turbomachinery applications. However, to fully utilize the design and development opportunities offered through AM, impacts of the build considerations and processing parameters are needed. Prior literature has shown that specific build considerations such as laser incidence angle and wall thickness influence the surface roughness of additively made components. The objective of this technical brief is to highlight the effects of both laser incidence angle and wall thickness on the surface roughness and cooling performance in micro-sized cooling passages. Results indicate that for any given laser incidence angle, surface roughness begins to increase when the wall thickness is less than 1 mm for the cooling channels evaluated. As the laser incidence angle becomes further away from 90 deg, the surface roughness increases in a parabolic form. Laser incidence angle and wall thickness significantly impact friction factor, while there is less of an influence on the Nusselt number for additively manufactured microchannels.