Laser Paths Research Articles

Laser Cladding Path Planning for Curved Metal Parts

In depositing multiple layers on the surface of failed metal parts, the overlap rate is a critical factor in determining the surface smoothness and uniformity of the coating thickness. Therefore, special attention must be given to the spacing between adjacent melt tracks when planning laser paths on complex metal parts. A strategy for selecting the overlap rate for multi-track cladding is proposed, based on the key parameters of surface curvature, mass conservation, and the profile of single-track coatings. A multi-track overlap model is developed, expressing the relationship between coating morphology and the overlap rate. The optimal spacing value is determined to achieve the goal of high-quality coating remanufacturing. To verify the effectiveness of this method, nickel-based powder was used for laser forming on the surface of metal gears. The results showed that the surface of the cladding layer was smooth and flat, further demonstrating that this model helps improve the repair quality and overall performance of curved metal parts. Thus, it provides valuable guidance for the remanufacturing of failed metal parts.

Design and development of a single-laser 2D Thomson scattering measurement system for TS-6 merging tokamak/magnetic reconnection experiments

Nd:YAG Thomson scattering diagnostics is reliable measurement of electron temperature and density, but its 2D extension conventionally needs as many polychromators as measuring points and as many lasers as measuring paths. To reduce the numbers and costs, we designed and developed a single-laser 2D measurement system by use of multiple reflection and time-of-flight of laser light. A single laser pulse reflects between mirrors on both sides of the vacuum vessel and makes seven round trips, which enables measurement at m × 7 points with only m polychromators and a single laser. Here, we present the design to satisfy the resolution required for TS-6 merging tokamak and magnetic reconnection experiments and the system development, especially the time-separation of scattered light signals from different points with time-of-flight delays. The measured Thomson scattering signals from 7 × 2 points and the measured Raman scattered signals from points in four laser paths indicate the feasibility of Thomson scattering measurement at m × 4 points.

Deep tissue super-resolution imaging with adaptive optical two-photon multifocal structured illumination microscopy

Visualization of axons and dendritic spines is crucial in neuroscience research. However, traditional microscopy is limited by diffraction-limited resolution and shallow imaging depth, making it difficult to study neuronal dynamics. Two-photon multifocal structured illumination microscopy (2P-MSIM) provides super-resolution imaging along with a reasonably good penetration, but it is vulnerable to optical aberrations in deep tissues. Herein we present a novel non-inertial scanning 2P-MSIM system incorporated with adaptive optics (AO) which allows for super-resolution imaging with effective aberration correction. Our strategy is designed to correct both laser and fluorescence paths simultaneously using a spatial light modulator and a deformable mirror respectively, providing better results than the individual path corrections. The successful implementation of adaptive optical two-photon multifocal structured illumination microscopy (AO 2P-MSIM) has allowed for the super-resolution imaging of neuronal structures in a mouse brain slice at great depths and dynamic morphological characteristics of zebrafish motoneurons in vivo.

Mechanical Properties and Wear Susceptibility Determined by Nanoindentation Technique of Ti13Nb13Zr Titanium Alloy after "Direct Laser Writing".

Laser treatment has often been applied to rebuild the surface layer of titanium and its alloys destined for long-term implants. Such treatment has always been associated with forming melted and re-solidified thin surface layers. The process parameters of such laser treatment can be different, including the patterning of a surface by so-called direct writing. In this research, pulse laser treatment was performed on the Ti13Nb13Zr alloy surface, with the distance between adjacent laser paths ranging between 20 and 50 µm. The obtained periodic structures were tested to examine the effects of the scan distance on the microstructure using SEM, the roughness and chemical and phase composition using EDS and XRD, and the mechanical properties using the nanoindentation technique. After direct laser writing, the thickness of the melted layers was between 547 and 123 µm, and the surface roughness varied between 1.74 and 0.69 µm. An increase in hardness was observed after laser treatment. The highest hardness, 5.44 GPa, was obtained for the sample modified with a laser beam spacing of 50 µm. The value of the distance has been shown to be important for several properties and related to a complex microstructure of the thin surface layer close to and far from the laser path.

Influences of surface topography of porous titanium scaffolds manufactured by powder bed fusion on osteogenesis

Powder bed fusion (PBF) has emerged as a useful metal-three-dimensional (3D) printing technology for manufacturing porous structures; it has been widely employed for the production of medical implants. Multiple previous reports have suggested that the bone ingrowth characteristics of porous structures, among the most important factors for medical implants, are affected by 3D printing parameters (e.g., pore shape). The topography of 3D-printed metal surfaces can also influence cellular responses, including osteoblast differentiation. The surface topography may change according to the shape of the printed pores. Nevertheless, it remains unclear how the surface topography changes. In addition, it is still unknown how the pore shape and the resulting surface topography can further impact the bone ingrowth efficiency of the porous structure. Therefore, to better understand the relationship, we prepared Ti–6Al–4V specimens with different pore shapes (i.e., circular, triangular, and rectangular) using the PBF method, then analyzed the surface topographies of these 3D scaffolds based on curvature and roughness profiles. Through subsequent in vitro studies, we investigated how changes in pore shape and surface topography affect the activity of Saos-2 human osteosarcoma cells. The results of this study confirmed that the curvature radii and local surface roughness change according to pore shape because of the characteristics of PBF. Furthermore, differences in local surface topography and pore shape led to differences in cell proliferation and differentiation. Through our findings, we anticipate that the meticulous design of pore shape and sophisticated control of the processing parameters, such as laser speed and paths, in the fabrication of orthopedic and dental implants will result in significantly enhanced bone ingrowth efficiency.

Dynamical X-ray phase imaging of polymer materials under laser engraving

X-ray phase imaging provides higher sensitivity to polymer materials made of light elements than the sensitivity provided by conventional X-ray transmission imaging that relies on absorption contrast. High-speed X-ray phase imaging has recently been studied using pink-beam synchrotron radiation and a Talbot interferometer to enable dynamic observation. In this study, we adopted high-speed X-ray phase imaging for the inner visualization of polymer materials under laser engraving. A sequence of phase-stepping-based phase imaging with a temporal resolution of 5 ms was established by synchronizing an X-ray detector with the linear motions of a grating and a sample. The laser and X-ray paths were aligned orthogonally, and the engraving region was observed from the material surface in the depth direction, in which ablation followed by bubble formation with a certain time delay was demonstrated.

A stability and spatial-resolution enhanced laser absorption spectroscopy tomographic sensor for complex combustion flame diagnosis

A novel stable laser absorption spectroscopy (LAS) tomographic sensor with enhanced stability and spatial resolution is developed and applied to complex combustion flame diagnosis. The sensor reduces the need for laser collimation and alignment even in extremely harsh environments and improves the stability of the received laser signal. Furthermore, a new miniaturized laser emission module was designed to achieve multi-degree of freedom adjustment. The full optical paths can be sampled by 8 receivers, with such arrangement, the equipment cost can be greatly reduced, at the same time, the spatial resolution is improved. In fact, 100 emitted laser paths are realized in a limited space of 200mm×200 mm with the highest spatial resolution of 1.67mm×1.67 mm. The stability and penetrating spatial resolution of the LAS tomographic sensor were validated by both simulation and field experiments on the afterburner flames. Tests under two representative experiment states, i.e., the main combustion and the afterburner operation states, were conducted. Results show that the error under the main combustion state was about 4.32% and, 5.38% at the afterburner operation state. It has been proven that this proposed sensor can provide better tomographic measurements for combustion diagnosis, as an effective tool for improving performances of afterburners.

Analog transmission of time-frequency signal in atmospheric turbulence environment.

The high-precision time-frequency transfer of the optical atomic clock signals over ground-to-satellite and terrestrial free-space laser paths is of great significance in the fields of fundamental and applied sciences. However, the phase noises caused by atmospheric turbulence severely degrade the measurement precision. In this paper, a new method to simulate the transmission of time-frequency signal propagating through atmospheric turbulence is investigated. An analog transmission system comparable to the practical out-field link has been demonstrated, which can provide a deep insight into the phase distortion of time-frequency signal of free-space optical communication links.

METHOD OF FINDING ENERGY CENTERS OF LASER PATHS IMAGES FRAGMENTS

Considered method of finding energy fragments of images of laser tracks in real time and its application for image recognition problems are considered. Given theoretical information, experimental research and software implementation of the image recognition system similar to natural structures. Presented an analysis of recent work on neurobiology and work related to the modeling of neural mechanisms. The main problems in the existing work related to the modeling of information perception systems in a natural way have been identified. The aim of the study is the software application of the method of finding the energy centers of images in real time to optimize these energy centers. The task of the research is to analyze the application of the method of finding the energy centers of fragments of images of laser paths. Carried out the description of the method of analysis of images of laser tracks on the basis of determination of the center of gravity on the basis of moment signs is carried out. Described an example of work is given and the main functionality of the laser image processing program. Presented samples of reference images and individual fragments of long laser paths used in the experiments, as well as the curves of their energy centers. Shown computer simulation of laser path image processing was performed, as a result of which the adequacy of the calculated results.

Joint formation mechanism of different laser transmission welding paths

Abstract In this study, the rectilinear, sine, and spiral paths of polymer transmission welding were used to perform welding comparative experiments, and the influence of various parameters in the polymer transmission welding of different laser paths on the joint performance and the formation of molten pool was discussed. The spiral path exhibited the highest joint strength, that increased by more than 50% compared with conventional rectilinear welding. The molten pool formed by spiral welding had a high depth-to-width ratio. Microscope observations revealed that the glass fiber flow signs in the molten pool were obvious, the glass fiber in the molten pool was abundant, and the bubble generation rate in the molten pool was lower. In this paper, Fortran language was used to construct Gaussian body heat source movement model with different paths. Results show that the spiral welding had higher welding stability than traditional rectilinear welding, welding defects caused by the lack of heat in the previous period can be properly compensated by selecting the appropriate welding period, Therefore, good joint performance can be achieved. In addition, amplitude and period are two important process parameters of spiral welding, and their sizes have important effects on joint strength and molten pool formation

Определение глубин полимеризации бессвинцовых пьезокерамических паст для УФ 3D печати

In present study, the polymerization depths for the implementation of the laser stereolithography process in the system (oligomer - piezoceramics) on the wavelengths of 445–465 nm UV range were determined in the original BTO, KNN and NBT lead-free piezoceramic pastes. It was shown that powder pastes, which provide a polymerization depth more than 150 µm, are promising for using in 3D printing. Such depth was chosen to guarantee a sufficient overlap of neighboring layers during polymerization, at the laser beam velocity speed from 1 m/s and the distance between the laser paths of 50 µm. For NBT pastes, successful photo polymerization was carried out for the first time, and for KNN paste the process performance was significantly increased.

Determination of the polymerization depths of lead-free piezoceramic pastes for UV 3D printing

In present study, the polymerization depths for the implementation of the laser stereolithography process in the system (oligomer - piezoceramics) on the wavelengths of 445-465 nm UV range were determined in the original BTO, KNN and NBT lead-free piezoceramic pastes. It was shown that powder pastes, which provide a polymerization depth more than 150 μm, are promising for using in 3D printing. Such depth was chosen to guarantee a sufficient overlap of neighboring layers during polymerization, at the laser beam velocity speed from 1 m/s and the distance between the laser paths of 50 μm. For NBT pastes, successful photo polymerization was carried out for the first time, and for KNN paste the process performance was significantly increased. Keywords: lead-free piezoceramics, stereolitography (SLA) - based ceramics 3D printing, UV- curing and bandwidths

TDLAS Tomography System for Online Imaging and Dynamic Process Playback of Temperature and Gas Mole Fraction

Tunable diode laser absorption spectroscopy (TDLAS) tomography enables online diagnosis of dynamic flames by imaging its temperature variations and exhaust gases, owing to its rapid response. Each tomographic image requires huge laser absorption spectrum data along multiple laser paths. For a high temporal resolution, the data sampling rate needs to be as high as possible which challenges the hardware implementation of parallel data acquisition of multiple channels. An online TDLAS tomography system was designed on field programmable gate array (FPGA) and PC for temperature and gas mole fraction distributions measurement. An on-chip parameter extraction module based on digital lock-in amplifier (DLIA) extracts absorption spectrum parameters at 1000 frames per second (FPS), and the framerate of real-time reconstruction on host PC can reach up to 302 FPS. A high-speed buffer on FPGA termed as transient spectrum recorder continuously records the latest five seconds of raw data. Both the playback of absorption spectrum parameters and raw data provide a way for detailed and in-depth understanding of the dynamic combustion process. Experiments were carried out by using an alcohol burner to evaluate the online monitoring and offline playback abilities of the system.

An Efficient Track-Scale Model for Laser Powder Bed Fusion Additive Manufacturing: Part 2—Mechanical Model

This is the second of two manuscripts that presents a computationally efficient full-field deterministic model for laser powder bed fusion (LPBF). The Hybrid Line (HL) thermal model developed in part I is extended to predict the in-process residual stresses due to laser processing of a nickel-based superalloy, RENÉ 65. The computational efficiency and accuracy of the HL thermo-mechanical model is first compared to the exponential decaying heat input model on a single-track simulation. LPBF thin-wall builds with three different laser powers and four printing patterns are evaluated in this study and compared with part-scale simulations. The simulations show good agreements with the experimental X-Ray diffraction measured residual stresses. Compared to the laser power, the scanning pattern is demonstrated to have significant effects on residual stresses. Laser scan patterns utilizing short laser paths generate lower tensile stress along the longitudinal direction of the part and higher compressive stress along the build direction.

Pulse laser-induced cell-like texture on surface of titanium alloy for tribological properties improvement

In order to improve the surface tribological properties of TC4 titanium alloy, this paper used laser processing technology to prepare a cell-like texture on TC4 surface. The cells of cell-like texture were separated by regular cracks caused by recasting of TC4, which could be got at the parameters of 1 μm distance of adjacent laser spots and 2.5 μm patch of adjacent laser paths with a certain laser power density. The laser treatment increased the surface microhardness from 351 to 445 HV. The relationship between tribological properties of TC4 and the laser power density was studied. At 0.32 GW/cm2, under the lubricant of simulated body fluid (SBF), the average friction coefficient between TC4 and UHMWPE reduced significantly by 32.4%, and the wear rate of UHMWPE ball decreased by 59%, compared with the original surface. The cell-like texture could increase the transmission speed of the lubricant at the friction interface by three times with the help of capillary force, and it could also store lubricant in the texture to improve the tribological performance. The channels around cells were assumed to be rectangular groove. The width of the channel which was observed with a 3D confocal microscope was 3.2 μm, and the capillary force produced by a single rectangular groove was calculated.

Control of gas concentration distribution in a semiconductor process chamber using CT-TDLAS measurement

Methane (CH4) concentration distribution in a semiconductor process chamber was controlled using the measurement of computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS) and the feedback control toward the feeding CH4 concentrations and flow rates. CH4 diluted with nitrogen was fed into the chamber through a shower head having three separate and concentric areas. Thirty-two laser paths were configured in the chamber to collect the infrared absorption spectra for the CT-TDLAS measurement. The computed tomography calculation using the 32 spectra reconstructed the two-dimensional CH4 concentration distribution in the chamber. The measured concentration distribution was updated once per second. Based on the measured concentration distribution, the feedback control algorithm determined the feeding CH4 concentration and flow rate of each shower head area. In this work, we set the target distribution as a ring shape. In the control algorithm, first the feeding CH4 flow rate of each shower head area was adjusted to match the concentration peak radius in the measured distribution to the radius in the target distribution. Then, the feeding CH4 concentration of each area was adjusted in sequence to match the measured average concentration of each area to the corresponding concentration in the target distribution. The algorithm worked successfully, and the concentration distribution reached the target distribution. The extension of the application and its limitations were also discussed.

Feasibility of Controlling Gas Concentration and Temperature Distributions in a Semiconductor Chamber with CT-TDLAS

The feasibility to control the gas concentration and temperature distributions in a semiconductor process chamber by measuring them was investigated. Gas concentration and temperature distributions for various flow rates were measured with the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). The infrared absorption spectra of multiple laser paths passing through the measured area were collected and the distributions of methane concentration and temperature in the chamber were reconstructed with the computed tomography (CT) calculations. The measured results indicated that the distributions can be independently controlled by measuring with the CT-TDLAS and adjusting the flow rates and the susceptor temperature.

Frequency-Division Multiplexing and Main Peak Scanning WMS Method for TDLAS Tomography in Flame Monitoring

The wavelength modulation spectroscopy (WMS) method is typically used in the tunable diode laser absorption spectroscopy (TDLAS) for spectrum extraction in a noisy background. Usually, two entire absorption spectra for target species are scanned in a cascade way in the WMS method, and it limits the temporal response of the TDLAS sensor. In this article, the frequency-division multiplexing and main peak scanning method were introduced to the WMS method and enabled a high frame rate six times that in the classical TDLAS sensor at the same scanning speed. For the first time, two wavelengths modulated at different frequencies were used to extract the absorptions in parallel along various laser paths and implemented successfully on a TDLAS tomography hardware, to reconstruct the distributions of both temperature and species concentrations, at a frame rate up to 10 kHz. A five-view fan-beam tomographic sensor was utilized in the tomographic imaging. In each view, lasers at two wavelengths were selected and modulated at different sinusoidal frequencies on the same sawtooth signal. Numerical simulations varied the high-quality tomographic imaging of both temperature and H2O molar concentration distributions for different phantoms. Experiments were also carried out on dynamic flames, which were generated by exciting a Bunsen burner acoustically. The acoustic excitation frequency varied from 40 to 750 Hz, and the results of the tomographic images agreed well with the flame evolutions.

Effect of laser scan length on the microstructure of additively manufactured 17-4PH stainless steel thin-walled parts

Components with varying dimensions are found in numerous applications. The current work examines how microstructures and phases change for additively manufactured 17-4PH thin walls as a function of laser path length, path direction, and wall thickness. Two sample sets were designed, each consisting of four walls with thicknesses of 6.4 mm to 0.8 mm. In the first set, the wall axes were parallel to the scan axes, such that the laser path length varied from layer to layer with the laser path either being parallel or perpendicular to the wall. In the second set, the walls lay at 45° to the scan axes, such that the laser path had the same length in all layers and gradually decreased with wall thickness. Substantial changes in phase stability and microstructure are observed as the wall thickness decreases, with ferritic phases and coarse grains changing to fine grains and an increasing volume fraction of austenite. These changes are attributed to changes in the local temperature-time profile as the length of the laser paths change from 19 mm to 0.8 mm. These observations demonstrate the range of microstructure and phase control options available in additive manufacturing with judicious selections of part layouts on build plates and of laser beam directions.

A WMS Based TDLAS Tomographic System for Distribution Retrievals of Both Gas Concentration and Temperature in Dynamic Flames

A tunable diode laser absorption spectroscopy (TDLAS) tomographic system was proposed via utilizing the wavelength modulation spectroscopy (WMS) method and distributions of temperature and specie concentrations in the dynamic flames were simultaneously reconstructed for the first time. A five-view fan beam tomographic sensor was applied to capture the absorption spectrum along the laser paths across the region to be imaged. Light intensities in all paths were collected in a custom specific TDLAS hardware. Different phantoms of the temperature and water vapor concentration distributions were fabricated to generate artificial data of the absorption spectrum acquired in the sensor. Reconstructed images of the phantoms in the simulations agreed well with the original distributions, in cases of different random noises that varied from 1% to 7% of light intensities at each wavelength. Experiments on a McKenna burner and the exit of a wind tunnel were carried out, and distributions of temperature and water vapor’s molar concentration were achieved by applying the proposed WMS based TDLAS tomographic system. A moving steel ruler was used to disturb the flame in the burner and temporal variations of the flame over a cross section of the burner were imaged in a tomographic way. Tomographic results on exhaust flows at the exit of a wind tunnel coincided with the variation trend of temperature in eleven different working conditions and verified the robustness of the proposed system under harsh conditions.