Laser Beam Scanning Research Articles

Processing of Ti–13Nb–13Zr powder by selective laser melting under a relatively high oxygen atmosphere

Ti–13Nb–13Zr (TNZ) parts were produced by selective laser melting under an atmosphere with a relatively high O content using a comprehensive combination of laser powers and laser beam scanning velocities. The influence of processing conditions on the density, microstructure, interstitial element contents (N and O), and hardness of as-printed TNZ parts were studied. The N and O contents in the TNZ parts increased on increasing the energy density (ED). Despite the high O content in the chamber during laser processing, it was possible to obtain TNZ parts with high density and relatively low N and O contents, depending on the ED applied. Two different types of microstructure were observed in the TNZ parts: α′ martensite and α/α′ + β phases. Depending on its microstructure, the TNZ parts presented interstitial solid solution hardening and second phase hardening.

Fast and precise laser beam scanning by nonperiodic grating on a binary micromirror array

We report a precise and stable laser beam positioning method with a high scanning speed by a pixelated binary grating (PBG) realized by a compact on-off state digital micromirror device (DMD). The overall procedure for PBG pattern generation is proposed, analyzed, and experimentally verified. The resulting performances correspond to an angular resolution of 0.01 deg and angular repeatability of ± 2.54 × 10 − 4 deg over a beam steering range of ± 7.5 deg. The scanning speed of 40 deg/s is achieved in continuous scanning with a resolution of 0.01 deg. Arbitrary positions can be targeted in the scanning range with DMD’s frame rate of 4000 Hz. To verify its applicability in precision metrology, absolute distances to multiple off-axial targets were determined in parallel with a high speed. This method will open a wider application of DMD in precision LIDARs, three-dimensional calibration of precision machines, and high-resolution laser patterning.

Experimental Analysis on Bending Behavior of Non‐Alloy Carbon Steel Sheets Using Laser‐Forming Process

Herein, the laser‐forming process of nonalloy carbon steel sheets is investigated experimentally. First, it is necessary to consider how the material factor of carbon steels affects the bend angle during the laser‐forming process. Therefore, bend angle results of three grades of carbon steel sheets, including St 14, CK 45, and CK 75, are studied based on the Taguchi design of the experiment. Then, the effects of process parameters, as named laser power, beam diameter, and scan rate on bend angle, are investigated for the most formable steel. The results show that the steel grade factor exhibits an obvious effect on bend angle, but the laser power and laser beam scan rate as process parameters play a more dominant role in determining the magnitude of the bend angle. Moreover, for St 14 with the highest bend angle, the scan rate has the most significant effect on the bend angle. In addition, the laser beam diameter exhibits the least significant effect on the bend angle. It can be concluded that the laser scan rate is the fastest factor to adjust and the most efficient control parameter for the bend angle.

Influence of laser cladding parameters on slurry erosion performance of NiCrSiBC + 50WC claddings

Various components employed in hydro machines are rigorously affected by the presence of sand particles throughout their operation which leads to degradation of the target surface. To counteract this menace, laser cladding has been emerged as a prominent technique to produce dense coatings along with enhanced surface properties like hardness and wear resistance. Therefore, in this study, hard layers of NiCrSiBC + 50WC powder were deposited on SS410 steel by laser cladding. Further, the effect of laser beam power, scanning speed, and powder feed rate on quality of clads was investigated. The laser cladded samples were examined for their micro structural characteristics, micro-hardness, and slurry erosion. Performance of NiCrSiBC + 50WC coatings under slurry erosion was evaluated for harsh conditions of various factors namely sand particle size, slurry concentration, impingement velocity, and impingement angle. Laser cladding parameters namely scanning speed and laser beam power were found to have a significant influence on micro-hardness of developed clads, while powder feed rate did not exhibit a significant effect on micro-hardness variations. Owing to higher hardness of deposited materials, slurry erosion resistance of NiCrSiBC + 50WC clad surfaces was greatly enhanced as that of uncoated SS410 steel. From SEM images, plastic deformation, micro-cutting, crater formation, and ploughing were observed as the major wear mechanisms for the slurry eroded clads. Further, from the obtained results, it has been noticed that a blend of high scanning speed, high laser beam power, and intermediate powder feed rate is suitable to develop coatings having superior wear resistance.

Evaluation of spatter particles, metal vapour jets, and depressions considering influence of laser incident angle on melt pool behaviour

The building of practical parts involves the application of metal-based powder bed fusion using a laser beam (PBF-LB/M), owing to its high-precision manufacturing. However, the quality of built parts obtained via the PBF-LB/M process varies with the building conditions, and a thorough understanding of the building mechanism has not been achieved owing to the complex and interrelated process parameters involved. The incident angle of the laser beam, which changes on the platform during the laser beam scan owing to the designed three-dimensional data, is among the principle parameters that affect the building aspects. In this study, the melt pool in the single-track formation during the PBF-LB/M process was visualised using a high-speed camera, and the influence of the laser incident angle on the ejection characteristics of spatter particles formed around the laser-irradiated area was investigated. Consequently, the spatter particles and metal vapour jets behaviour varied with the laser incident angle. There was a reduction in number of spatter particles owing to the origin of the incident direction being from behind the laser irradiation area. Additionally, the laser incident angle affected the melt pool morphology because of the depression in the melting. Furthermore, the burial depth of the pores varied with the laser incident angle, and was related to the depth of the depression during the melt pool formation.

Direct laser melting of Al2O3 ceramic paste for application in ceramic additive manufacturing

We develop the direct laser melting of ceramic paste technology for application in ceramic additive manufacturing (AM). The Al2O3 ceramic paste, which is a homogeneous mixture of DI-water and Al2O3 ceramic powders, was deposited on an Al2O3 substrate using free-forming extrusion (FFE), and subsequently melted by a CO2 laser. To better control the laser melting process, the flow behavior of the laser-melted Al2O3 was investigated by evaluating the microstructure of the laser-melted Al2O3 single tracks. When the laser scanning speed increased from 1 to 3.5 mm/s at a fixed laser power, the permeation of the molten Al2O3 into the surrounding porous paste was reduced, resulting in the improvement of the surface uniformity of the laser-melted Al2O3 tracks. Through optimizing the laser scanning strategy, a fully-dense Al2O3 layer with smooth surface was achieved. The phase composition and density of the laser-melted Al2O3 layers were evaluated to study their properties. The thickness of the dense Al2O3 layer varied from ∼90 μm to ∼120 μm periodically due to the line-by-line scanning of the Gaussian laser beam. In addition, the relationship between the melting thickness and the laser scanning speed was also investigated to further improve the controllability of the laser melting process. This direct laser melting of ceramic paste technology is promising for applications in ceramic AM, such as 3D printing of ceramic components and high-temperature ceramic welding.

High-speed laser micro polishing of TiAl6V4

In the present paper, laser micro polishing of TiAl6V4 is investigated with main focus on increasing the area rate by using high pulse energy. First, the influence of the laser beam size, the scanning velocity, and the track distance on the final roughness is examined since these parameters determine the area rate. The results of these investigations are used to identify a set of process parameters that allow increasing the area rate and achieving a surface roughness comparable to state-of-the-art laser micro polishing. The results show that the laser beam size must exceed a critical size; otherwise, smoothing of the surface is limited, which leads to higher final roughness. The scanning velocity and the track distance do not have a great effect on the final roughness for the investigated regimes. However, with decreasing track distance, the number of undesirable surface structures, presumably resulting from evaporating vanadium compounds, is reduced. Additionally, the heat input into the surface decreases with increasing laser beam size, scanning velocity, and track distance. The results of these investigations are used to significantly increase the area rate to 19.1 cm2/s, which is a factor of 64 times faster than the state of the art. The final surface roughness is comparable to state-of-the-art laser micro polishing in this case.

The effect of line-by-line laser scanning on the properties of laser-induced graphene

Technology of polyimide (PI) film carbonization by direct laser treatment attracts much attention due to the versatility and ease of obtaining the carbon material, laser-induced graphene (LIG), used in the creation of various sensors and functional devices. In this work LIG film structures are obtained by line-by-line scanning of a cw CO2 laser beam over the surface of the PI film. The synthesized carbon film material is studied by optical and scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. It is shown that the Raman spectra of a single LIG line and a set of overlapping LIG lines significantly differ from each other. It is found that multiple laser scanning of the PI film leads to a marked decrease in the number of defects in the LIG structure as well as to a significant decrease in the specific surface resistance of the synthesized film material. The results obtained can be used in the synthesis of LIG film structures with improved characteristics. Keywords: laser-induced graphene, polyimide film, line-by-line laser scanning.

Влияние построчного лазерного сканирования на свойства лазерно-индуцированного графена

Technology of polyimide (PI) film carbonization by direct laser treatment attracts much attention due to the versatility and ease of obtaining the carbon material, laser-induced graphene (LIG), used in the creation of various sensors and functional devices. In this work LIG film structures are obtained by line-by-line scanning of a continuous CO2 laser beam over the surface of the PI film. The synthesized carbon film material is studied by optical and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It is shown that the Raman spectra of a single LIG line and a set of overlapping LIG lines significantly differ from each other. It is found that multiple laser scanning of the PI film leads to a marked decrease in the number of defects in the LIG structure as well as to a significant decrease in the specific surface resistance of the synthesized film material. The results obtained can be used in the synthesis of LIG film structures with improved characteristics.

Energy performance evaluation of selective laser melting

Selective Laser Melting (SLM) is an additive manufacturing (AM) process in which a laser beam scans a selective area of a powder bed to create layers and generate components. SLM is considered to have sustainable benefits against conventional manufacturing, while current studies also point out that these benefits are only case-specific. Therefore, understanding the mechanism behind the material and energy-consuming behavior of SLM is an emerging research issue. This study focuses on three questions related to the energy performance of SLM. First, this research has compared the energy demand for processing approximately one cm³ of steel and examined the energy use of different system components. Second, considering that lightweight is the most common design approach to improve the sustainable benefits of SLM, this research has analyzed the relationship between the different levels of volume reduction during topology optimization and the energy use of SLM. Third, this research has investigated the impact of different process parameters on the energy use of SLM, which enables the energy efficiency-oriented build process design of SLM.

Banding Pattern Suppressed Waveguide in Laser Beam Scanning Augmented Reality System

Banding Pattern Suppressed Waveguide in Laser Beam Scanning Augmented Reality System

Unconventional milling of zirconia-based bioceramic material with nanosecond pulsed laser

Fabrication of dental restorations made of zirconia-based biomaterials with enhanced mechanical and tribological properties together with customized surface topography and microstructure for promoting enamel adhesion and cell proliferation while hindering bacterial spreading is a very challenging task to accomplish through conventional machining operations. In fact, traditional milling processes of sintered ceramics are typically labor-intensive, therefore expensive and time-consuming, and these aspects can be further exasperated when microsized features are required. On the other hand, unconventional techniques such as laser milling can represent a suitable solution to produce miniaturized individualized structures on advanced ceramics since it is a non-contact thermal process that ensures the elimination of cutting forces and allows hard and brittle materials to be machined without the need for special equipment which requires high investments and long processing times. In this context, this study aims to investigate the capability of a nanosecond pulsed fiber laser to machine samples made of yttria-stabilized zirconia through a systematic experimental approach in order to identify the most suitable process operational parameters combinations that ensure the obtainment of specific surface topographies while minimizing the machining time. The milling process is carried out by using a 30 W Q-switched Yb:YAG fiber laser by controlling laser beam scan speed, scan strategy and hatch distance and following a multi-level factorial design-based experimentation. The adoption of the laser technology to machine yttria-stabilized zirconia results in a high-repeatable, accurate and time-saving process allowing easy control of the process outcomes.

Demonstration of real-time structured-light depth sensing based on a solid-state VCSEL beam scanner.

We demonstrated a real-time scanning structured-light depth sensing system based on a solid-state vertical cavity surface-emitting laser (VCSEL) beam scanner integrated with an electro-thermally tunable VCSEL. Through a swept voltage added to the tunable VCSEL, a field of view of 6°×12° could be scanned with a scanning speed of 100 kHz by the beam scanner. Adopting the beam scanner, the real-time depth image with a lateral resolution of 10,000 (20×500) was obtained by measuring a step target placed at 35cm. The frame rate could be >10Hz even if sunlight shot noise is artificially added to the experimental data. By using a higher-speed camera, a potential lateral resolution could be reached at 50,000 (100×500) with a frame rate of > 20Hz. By using flat optics, a compact scanning module offering line pattern with FoV of >40°×20° was also demonstrated. It could help to realize high-resolution and high-accuracy structured-light sensing with a compact module.

Two-photon flow cytometry with laser scanning two-dimensional airy beams

Flow cytometry is an essential technique in biomedical discovery for cell counting, cell sorting, and biomarker detection. In vivo flow cytometers based on one-photon or two-photon excited fluorescence have been developed for over a decade. One drawback of the laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is limited to the focal spot due to the short Rayleigh range of focused Gaussian beams. Hence, the sampling volume is much smaller than in one-photon flow cytometers, making it challenging to count or detect rare circulating cells in vivo. Non-diffracting light waves like Bessel beams and Airy beams have narrow intensity profiles with an effective spot size as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making them an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Airy beams rather than Gaussian beams is side lobes Airy beams have, which contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using 2D Airy beams to form a light-sheet that intersects the blood vessel a microfluidic channel, which was used to model a blood vessel. The setup can successfully detect and count flowing fluorescent microspheres in a microchannel.

Self-gating single-photon time-of-flight depth imaging with multiple repetition rates

We demonstrate a self-gating single-photon imaging LiDAR with dual-repetition rate laser pulses at 1550 nm. In the experiment, two laser pulses with different repetition rates are used to enlarge the unambiguous range. A GHz-gated Geiger-mode InGaAs/InP single-photon detector is employed to detect high rate echo photons, and two galvanometer mirrors are used to realize laser beam scanning imaging. The self-gating denoising method is proposed to remove the randomly distributed noise in the three-dimensional point cloud, which increase the signal-to-noise ratio of the system from -1.72 to 5.91 dB. We attained a large range single-photon image with the valid point cloud generation rate of 1.3 × 105 points per second containing targets from 200 m to 1200 m, which is cutting-edge in the field of single-photon LiDAR. The clearly-reconstructed image indicates the self-gating single-photon imaging provides a promising approach for long-distance and high-speed single-photon imaging.

Aperture total internal reflection (A-TIR) for contact angle measurement

Recently, aperture total internal reflection (A-TIR) was proposed to characterize the microdroplet patterns, such as the coverage fraction of the droplet, by placing the aperture just in front of the detector in classical total internal reflection (TIR). However, the reflection from the curved liquid-air interface was simulated using simple two-dimensional modeling, causing inaccuracy in A-TIR measurement. In addition, the reflectance dependency on the aperture size and the working distance of the aperture was not investigated, hindering its applications. In this study, the simulation based on three-dimensional (3-D) ray tracing with Fresnel equation modeling was successfully developed and verified to explain the internal reflection from the curved droplet liquid-air interface. With this developed 3-D modeling, A-TIR characteristics were explored using the parameters of the aperture size and the working distance of the aperture as well as the droplet surface coverage fraction, which shows a good agreement between the experiment and the simulation. Furthermore, it was for the first time demonstrated that the droplet contact angle can be effectively determined by obtaining the droplet thickness from the analytic quadratic solution by subtracting the measured reflectance at the two different sized apertures and using the spherical profile relation. Low contact angles in the range of 1∼ 15° were determined experimentally for the micro- and macro-sized droplets with a droplet diameter of 70 ∼ 7000 µm by the measured thickness of 1 ∼ 450 µm using A-TIR and compared with Fizeau interferometry and side-view imaging to show a good agreement. The simulation shows that A-TIR can be a new optical diagnostic tool to measure the contact angles 0 ∼ 90° regardless of the droplet diameter by adjusting the aperture size and the working distance. In addition, A-TIR can effectively determine the small contact angles less than 5°, even ultrasmall contact angles less than 1° for the submicron thickness, not requiring the complicated microscope setup. Thus, we can observe a sessile droplet's drastic contact angle change during wetting phenomena from 90° to 0° on the same A-TIR setup. Additionally, A-TIR can be used for a single or an array of micro or nanodroplets with a microscope objective by reducing the laser beam size and scanning methodology.

Micro engraving on Ti-6Al-4V using fiber laser for orthopedic implant-A study

The demand for production of fine micro-grooves with least heat-affected zone (HAZ), recast layer thickness, microcrack, and microcavity are increasing as Ti6Al4V is a readily used orthopedic implant material. This study presents a groove quality optimiser called response surface methodology (RSM) for fiber laser micro engraving on Ti6Al4V to improve microgroove quality and functionality. The critical process factors’ (number of laser beam passes, scan speed, and pulse frequency) for each response characteristic are identified through the RSM optimiser by analysing the experimental data sets. The optimised data sets are beneficial in maintaining groove quality characteristics (width, depth, HAZ, recast layer thickness, and microhardness). Number of passes and scanning speed has been recognised as crucial process parameters that primarily regulate the groove response characteristics. A 3-20-5 neural network (NN) model is developed and trained through the experimental input–output data sets. Performance of 3-20-5 model is found as 1.63e-27, and regression score is significantly closer to 1. It has been recognised that ANN model predicts more accurate results with a low error percentage than RSM model even when the input factor level settings are beyond the defined boundary. Under these experimental settings, the microgroove characteristics are enhanced in terms of low HAZ, recast layer thickness, microhardness, and spatter. X-ray diffraction analysis (XRD) is also performed on base metal and grooved surfaces to determine diffraction peaks, crystallite phase composition, size, and lattice strain. XRD analysis revealed the presence of both HCP-α-Ti and BCC-β-Ti in both base metal grooved surfaces.

Compact solid-state vertical-cavity-surface-emitting-laser beam scanning module with ultra-large field of view

A solid-state beam scanner is key element for next-generation 3D sensing. To overcome problems of current solid-state beam scanners, such as small field of view, limited resolutions and difficulties in large-scale manufacturing, we previously invented a solitary vertical-cavity surface-emitting laser (VCSEL) beam scanner based on a VCSEL waveguide/amplifier. In this paper, we proposed and demonstrated an electrical beam scanning module by integrating a tunable surface grating VCSEL to the solitary VCSEL scanner and by assisting with a diffractive optical element and prism mirror for an ultra-large field of view. We realized continuous fan beam scanning with a record field of view of >100° and obtained resolution points number of 1400. The module size could be managed within 10 mm × 6 mm × 1 mm.

Pulsed laser deposition of large-sized superlattice films with high uniformity

Oxide superlattices often exhibit emergent physical properties that are desirable for future information device applications. The most common growth technique for fabrication of oxide superlattices is pulsed laser deposition (PLD), which is convenient yet powerful for the growth of various oxide superlattices. However, the sample size prepared by PLD is rather small confined by the plasmon plume, which greatly limits its potential for device applications. Here, we design a PLD system that is capable of fabricating large-sized oxide superlattices with high uniformity. Specifically, during growth, the laser beam scans the target surface by combining the pitch and yaw angle rotation of the high reflective mirror and the linear motion of the focus lens. A SiC susceptor is placed in between the sample holder and the substrate to improve the large area infrared heating efficiency. Using such a system, droplet-free 10 × 10 mm2 [(LSMO)12/(PCMO)6]7 superlattices are epitaxially grown with the same period of superlattices across the whole sample areas. The high uniformity of the superlattices is further illustrated by near identical physical properties of all regions of the superlattice films. The present PLD system can be used to grow various kinds of oxide superlattices with the area size as large as 2 in., which is highly useful for device applications of oxides.

A Review on Powder Bed Fusion Process and Smart Manufacturing Technologies

Powder bed fusion (PBF) processes are laser-based additive manufacturing in which the laser beam scans the selected locations of powder bed at a controlled speed and then it fuses the powder to the solid material by either partial melting in selective laser sintering (SLS) or full melting in selective laser melting (SLM). The aim of this paper is to present a review about PBF showing its way of working, parameters and open issues. In addition, the paper shows the current smart manufacturing that optimize the processes.