Laser Power Levels Research Articles

Effect of Laser Powder Bed Fusion Parameters on the Evolution of Melt Pool, Densification, Microstructure, and Hardness in 420 Stainless Steel Parts

Laser powder bed fusion (LPBF) involves depositing, melting, and solidifying metal powder particles layer by layer to create 3D components. In this study, a deep fundamental understanding on how process parameters—laser power, scan speed, and hatch spacing—affect the melt pool, densification, microstructure, hardness, and thermal behavior of 420 stainless steel (420SS) parts produced by such technology is provided. The conducted investigation considers five levels of laser power and hatch spacing, and four scan speeds. Optimal single tracks, based on geometry and profile, are achieved with laser powers between 40 and 80 W and a scan speed of 10 mm s−1. In the multitrack analysis, it is indicated that a dense, smooth surface is obtained with a hatch spacing of 250 μm, corresponding to an overlapping rate of ≈30%. The 420SS samples show high densification (≈99%) and low surface roughness (≈3.62 μm). The microstructure consisted of martensite laths and retained austenite. The hardness and thermal conductivity of the samples are measured at 540 HV and 15.3 W m−1 K−1, respectively. In this study, the understanding of the process–structure–property relationships in LPBF of 420SS is expanded.

Laser cutting using dynamically modulated intensity distribution

The precise control of the laser beam intensity distribution facilitates the optimization of laser processing performance. This not only presents opportunities for enhancing the process efficiency but also proves advantageous in scenarios where the same laser power level is employed, surpassing traditional methods. This study introduces a novel approach by dynamically modulating the laser beam profile to achieve a non-symmetrical intensity distribution. A detailed investigation into the laser cutting process using modulated beam intensities is conducted by employing a high-speed imaging system. Moreover, the maximum cutting speed, cut edge quality, and cut kerf geometries are evaluated when different strategies are applied. The results demonstrate a noticeable improvement in the cut edge quality compared to a static beam strategy (SBS) and the recently developed conventional dynamic beam shaping (DBS). In addition to laser cutting, examples of such modulation in laser welding and hardening are proposed. This innovative technique offers promising advancements in the field of laser processing.

Comparison of two laser power levels in the subthreshold micropulse yellow laser treatment of acute central serous chorioretinopathy

AimsTo compare the efficacy of two power levels in the 577 nm sub-threshold micro pulse laser (SML) treatment of acute central serous chorioretinopathy (aCSC). MethodsA retrospective comparative study was conducted. A total of 65 patients (65 eyes) with aCSC were enrolled. Of which, 32 patients received low power treatment and 33 patients received high power treatment of 577 nm SML. Best-corrected visual acuity (BCVA), central macular thickness (CMT), fundus-monitored microperimetry and height of subfoveal choroidal thickness (SFCT) as well as subretinal fluid (SRF) were evaluated at baseline and 3 months. ResultsThe height of SFCT and retinal sensitivity in the low power treatment group was significantly better than that in the high power treatment group at 4 weeks (all p < 0.001). Mean BCVA improved from baseline to 3 months after treatments but with no significant difference between the two groups after 3 months (p > 0.05). In the low power group, the CMT decreased from 379.76 ± 139.23 μm at baseline to 176.56 ± 37.78 μm at 3 months, and in the high power group, the CMT decreased from 364.97 ± 143.08 at baseline to 191.77 ± 38.26 μm at 3 months. There was no significant difference at 3 months between the two groups (p > 0.05). Similar results were also found in term of SRF. ConclusionsTimely intervention with 577 nm SML with low power treatment can improve visual acuity, and included anatomic success without adverse events.

Analysis of micro-hole formation in titanium nanofilms using a low power CW laser

This study investigates the mechanisms and dynamics governing microhole formation in titanium nanofilms under the influence of a continuous-wave low-power laser emitting at 1070 nm. Two distinct configurations were explored: one in which the laser interacted with the titanium film in an air environment (referred to as configuration AM), and the other in which the laser beam passed through glass before reaching the titanium film (referred to as configuration SM). Our experiments demonstrated that microhole formation is possible in both configurations. However, the threshold powers, hole characteristics, and time scales involved differ significantly between AM and SM configurations. Temperature distribution simulations, based on a linear absorption model, revealed notable differences in peak temperatures between these two configurations, primarily attributed to variations in focal spot size and Fresnel losses. These temperature variations resulted in significantly different mechanisms of material removal in both configurations. In the AM configuration, the boiling temperature was not achieved, even at the highest power; however, a melting pool was formed at powers exceeding 50 mW. Thus, the primary driver of microhole formation was the Marangoni effect, which caused molten material to flow tangentially towards the edges of the molten pool. Furthermore, titanium oxidation was identified as a competing process contributing to changes in optical transparency and potentially inhibiting the complete formation of holes. Conversely, within the SM configuration, boiling temperatures are easily achieved, leading to localized boiling and the formation of gas bubbles near the glass–titanium interface. As a result, the rupture of the bubble through the capping molten layer led to a vigorous expulsion of both gas and material, allowing for the creation of microholes even at remarkably low laser power levels (10 mW). Notably, in this configuration, the influence of titanium oxidation is negligible due to the relatively short time scale involved (hundreds of microseconds).

Influence of Remote Laser Cutting on Magnetic Loss and Mechanical Properties in 0.2 mm Silicon Steel

Energy loss due to eddy current generation is a significant factor in reduced efficiency of electrical machines, therefore motor cores with thinner sheets are required due to their effect in reducing eddy currents. However, reducing the thickness of laminations is challenging due to the high tooling costs in blanking due to the small tolerances required, whilst other methods such as conventional laser cutting are too slow to be commercially viable. In this paper the influence of remote laser cutting on thin electrical steel sheets (Cogent/Tata Steel NO20 3.2% Si) has been investigated on the tensile strain to fracture, fatigue life, edge hardness, and energy loss in an AC magnetisation cycle for two laser power levels. The laser power has found to have no statistically significant influence on the bulk mechanical properties of the material, but significantly affects the measured specific loss. The latter was associated with the increased edge hardness at higher laser powers. Based on the parameters selected it is highly questionable whether RLC offers a viable method for lamination cutting, significant refinement of the laser parameters and/or the use an alternative laser such as an ultra-fast pulsed laser is required to be competitive with existing methods. Additionally, it is shown that energy loss increases linearly with respect to length of the cut edge - to the minimum cut spacing tested of 6 mm. These results can be used to optimise laser parameters to reduce the degradation of magnetic properties by decreasing laser power where possible.

The Advancement of Waterjet-Guided Laser Cutting System for Enhanced Surface Quality in AISI 1020 Steel Sheets.

This study investigates the effects of a water-guided laser on the cutting performance of AISI 1020 steel sheets of various thicknesses by comparing the results with respect to a conventional laser. For this purpose, a novel nozzle design has been devised enabling the delivery of laser beams to the workpiece conventionally as well as through water guidance. Diverging from prior literature, a fiber laser is used with a high wavelength and a laser power output of 1 kW. Experiments are conducted on steel sheets with thicknesses ranging from 1.5 mm to 3 mm using three different cutting speeds and laser power levels. Analysis focuses on assessing surface roughness, burr formation and heat effects on the cut surfaces for both conventional and waterjet-guided cutting. Surface roughness is evaluated by using a 3D profilometer and cut surfaces are examined through SEM imaging. The results showed that the waterjet-guided laser system greatly reduced surface roughness and minimized problems associated with traditional laser cutting such as kerf, dross adherence and thermal damage. The study revealed that cutting speed had a greater effect on surface roughness reduction than laser power, with the most noticeable differences occurring in thinner sheets. Furthermore, the investigation suggests that the waterjet-guided laser cutting system demonstrates superior performance relative to conventional methods, particularly in surface quality.

Optimization of smoothing by spectral dispersion with a sinusoidal phase modulation

In order to improve the propagation of a laser in a plasma, the intensity profile should be as uniform as possible. For this purpose, smoothing techniques are used. The most commonly used, smoothing by spectral dispersion (SSD), induces temporal fluctuations of the effective amplification length of Stimulated Brillouin scattering (SBS) or Stimulated Raman scattering (SRS). These fluctuations are random from shot to shot and may thus induce unpredictable levels of the efficient laser power used in laser-plasma experiments. Increasing the modulation frequency fm while maintaining the modulation bandwidth strongly reduces these fluctuations and even reduces the average SBS level. However, increasing fm has also an impact on laser propagation within the laser optical components. We show that, as long as chromatic dispersion is precompensated in the front-end, FM-to-AM conversion, a detrimental propagation effect, may remain sufficiently low and that anormal FM-to-AM conversion is not sensitive to the modulation frequency. Hence, there is no important bottleneck to an increase of the modulation frequency.

Probing the cw-Laser-Induced Fluorescence Enhancement in CsPbBr3 Nanocrystal Thin Films: An Interplay between Photo and Thermal Activation.

Perovskite nanocrystals hold significant promise for a wide range of applications, including solar cells, LEDs, photocatalysts, humidity and temperature sensors, memory devices, and low-cost photodetectors. Such technological potential stems from their exceptional quantum efficiency and charge carrier conduction capability. Nevertheless, the underlying mechanisms of photoexcitation, such as phase segregation, annealing, and ionic diffusion, remain insufficiently understood. In this context, we harnessed hyperspectral fluorescence microspectroscopy to advance our comprehension of fluorescence enhancement triggered by UV continuous-wave (cw) laser irradiation of CsPbBr3 colloidal nanocrystal thin films. Initially, we explored the kinetics of fluorescence enhancement and observed that its efficiency (φph) correlates with the laser power (P), following the relationship φph = 7.7⟨P⟩0.47±0.02. Subsequently, we estimated the local temperature induced by the laser, utilizing the finite-difference method framework, and calculated the activation energy (Ea) required for fluorescence enhancement to occur. Our findings revealed a very low activation energy, Ea ∼ 9 kJ/mol. Moreover, we mapped the fluorescence photoenhancement by spatial scanning and real-time static mode to determine its microscale length. Below a laser power of 60 μW, the photothermal diffusion length exhibited nearly constant values of approximately (22 ± 5) μm, while a significant increase was observed at higher laser power levels. These results were ascribed to the formation of nanocrystal superclusters within the film, which involves the interparticle spacing reduction, creating the so-called quantum dot solid configuration along with laser-induced annealing for higher laser powers.

The realization of the simultaneous wireless information and power transfer with the laser energy transform

Laser Charging means high energy laser beam to irradiate the solar cell to gain electricity power through photovoltaic generation. This kind of wireless energy transform way fits the IoT and other low energy satiation with the benefit of long-distance transmission. In this paper, we present a new way of information transferring while energy is gained which is called Simultaneous Wireless Information and Power Transfer. The main idea is to switch the laser device output power to generate the different PV current values, the dual level of laser power decides two ranges of the value. We imitate the On-Off Keying (OOK) named Low-High Keying(LHK) which turns the information into the energy code with a high or low current value. The issue of information coding is also presented with an example. And the application also provided the realization presented. The new method provides a brand way to Simultaneous Wireless Information and Power transfer without any extra equipment by contrast with others. It's suited for the long-distance, low power and limited information-connected occasions.

Model-Based input energy control for reproducible AISI 316L laser deposited tracks

In the Directed Energy Deposition (DED) process, when the mass flow of metal particles is relatively high, the thickness of the layers increases, leading to a more productive process. The higher the mass flow is, the more difficult it becomes to get a stable melt pool. The accumulation of residual heat in the previously consolidated material constitutes a thermal input affecting the balance at the laser-material interaction zone. An accurate control of the temperature of the laser-material interaction zone is critical to maintain the dynamic viscosity of the liquid metal within the narrow margin in which it can be managed in a stable way. The present work introduces a thermal model in which domains with tunable properties are considered to reproduce the growing of the manufactured sample. Concurrently, a virtual closed-loop PID regulator has been implemented in order to calculate suitable values of laser power to compensate the heat accumulated in the material, offering the results from the model as input process parameters to be directly applied in the real process. The levels of laser power proposed by the model have been experimentally applied, leading to a stable process capable of carrying out in reality the desired component.

Influence of CO2 laser surface treatment of basalt fibers on the mechanical properties of epoxy/basalt composites

AbstractIn fiber reinforced composite materials, the interfacial strength between the fibers and the matrix plays a key role in controlling the stress transfer and damage mechanisms of the composite. In this study, CO2 laser surface treatment of the fibers was investigated as a potential sustainable substitute for conventional chemical treatments, that can be costly and have negative environmental effects. The influence of the laser treatment on basalt fiber fabric was comprehensively investigated. The fibers were subjected to different laser power levels and characterized from a morphological and mechanical point of view. From optical and scanning electron microscopy, it was observed that the treated fibers manifested increased surface roughness along with spots of fused and bonded fibers. Individual treated fibers exhibited improved tensile properties with increased values of scale parameter (by about 21%) in the case of a laser power equal to 1.04 W/mm2, and no substantial changes in Young's modulus. The treated fibers were subsequently used in the preparation of epoxy‐based microcomposites, and microdebonding tests revealed an increase in the interfacial shear strength (IFSS) up to 8%. Therefore, this work proved that a laser surface treatment of basalt fibers is a valid alternative to conventional fiber surface modification to enhance the mechanical compatibility between fibers and matrix, and therefore to improve the mechanical performances of basalt fiber composites.Highlights Failure in composites due to weak interfacial adhesion with epoxy. CO2 laser treatment of basalt fibers to enhance interfacial adhesion. Treated fibers exhibit improved tensile properties. Treated fibers manifested improved interfacial shear strength (IFSS, +8%).

Effect of process parameters on the mechanical behavior of Ti6Al4V alloys fabricated by laser powder bed fusion method

The parameters used in the production process in laser powder bed fusion (L-PBF) technology, one of the additive manufacturing methods, have a critical effect on the mechanical behavior and density properties of the product and can change the properties of the product. Therefore, this study examined the influence of laser power, scanning speed, hatch spacing and beam rotation angle on the tensile strength, impact energy, surface roughness, and porosity levels of Ti–6Al–4V produced through the L-PBF method. It was observed that the tensile strength changes directly proportional to the laser power. In addition, the tensile strength decreases significantly with a value of 645 MPa obtained at lowest 0.07 mm hatch spacing, 190 W laser power and 900 mm scanning speed. The lowest value of impact energy, with a value of 8.7 J, was reached at a rotation angle of 180°. It has been determined that surface roughness decreases significantly with increasing laser power, while it demonstrates an increase with higher scanning speeds. Surface roughness values of 8.9 μm parallel and 8.35 μm perpendicular to the building direction were achieved at a laser power level of 220 W. Laser power was identified as the most influential factor in determining the porosity ratio, with a high porosity rate 0.48% occurring at 160 W laser power. Furthermore, an increase in scanning speed resulted in a corresponding increase in the porosity rate.

Investigation of melt pool dynamics and solidification microstructures of laser melted Ti-6Al-4V powder using X-ray synchrotron imaging

Titanium alloy (Ti-6Al-4V) is widely used in additive manufacturing (AM) industry. However, as laser powder-bed fusion (PBF-L) additive manufacturing (AM) advances towards reliable production of titanium parts, a thorough understanding of the process-structure-properties (PSP) relationships remain to be fully understood. A study of the laser melting was paired with high-speed X-ray synchrotron imaging at the 32-ID beamline of the Advanced Photon Source at Argonne National Laboratory. Simultaneous melting and imaging was carried out on a Ti-6Al-4V powder layer held in a custom device designed to mimic single-track scans of the PBF-L process at different laser power levels, powder size distributions, and cover gas environments (Ar and He) on top of AM Ti-6Al-4V base metal. It was found that the thickness of the powder layer significantly affected the melt behavior: too much powder led to the formation of molten droplets that wetted the surface of the titanium, yet did not contribute to a uniform melting profile. Residual gas pores in the atomized powder were also observed to contribute to the pores observed in the melt pool, with the porosity of the powder (defined as volume of pores divided by total material volume) constant with powder size distribution (i.e., larger particles contained more entrapped gas, which increased final part porosity). When varying Ar or He through the same gas flow meter settings and nozzle, the difference in flow rates likely contributed more to the resultant porosity of the solidified material than did the thermal conductivity of the gasses, with He being the greater contributor to porosity. The microstructure of the heat affected zone contained α′, α, and an increased β phase fraction relative to the base material. The crystallographic texture of the melt pool region adopted that of the base metal.

Residual Stress Mapping in Heat-Assisted Additive Manufacturing of IN 718: An X-Ray Diffraction Study

Laser powder bed fusion (LPBF) is a type of additive manufacturing (AM) technique characterized by multiple localized thermal processes that result in rapid heating and cooling. The thermal variations observed in the LPBF process can generate residual stress (RS) inside the fabricated part, impacting the surface integrity and geometric tolerances of the manufactured components. To reduce thermal variation during manufacturing, heat-assisted AM was employed, thereby minimizing RS and any thermal distortion that could occur during the fabrication of materials. The present research utilizes non-destructive x-ray diffraction to analyze the influence of an in-situ heated building plate and processing parameters on the RS distribution in Inconel 718 (IN718) fabricated by LPBF. This study examines the impact of two scanning procedures and three laser power levels and offers critical insights into both measurement techniques and RS characterization. By understanding the effect of the processing parameters on RS, we aim to enhance the quality of manufactured parts through process optimization. Post-processing heat treatment consistently reduced RS in all samples, regardless of laser power levels or scanning strategies. Combining a chess scanning strategy with 270 W laser power resulted in the most significant RS reduction in IN718.

Process Optimization of SiC-Reinforced Aluminum Matrix Composites Prepared Using Laser Powder Bed Fusion and the Effect of Particle Morphology on Performance.

Process parameters and powder spreading quality are important factors for aluminum matrix composites (AMCs) prepared using laser powder bed fusion (LPBF). In this study, a Box-Behnken Design (BBD) was used to optimize the process parameters, and near-spherical β-SiC was selected to improve the quality of powder spreading. The rationality of parameter optimization was verified by testing the density of samples prepared using different laser power levels. Al4C3 diffraction peaks were found in XRD patterns, which indicated that interface reactions occurred to form good interface bonding between the Al matrix and the SiC particles. The tensile strength and plasticity of LPBF α-SiC/AlSi10Mg were lower than that of LPBF AlSi10Mg, which was mainly due to the poor fluidity of the powder mixtures and powder spreading quality. For LPBF β-SiC/AlSi10Mg, the tensile strength increased and elongation decreased slightly compared to LPBF α-SiC/AlSi10Mg. The data in this study were compared with the data in other studies. In this study, LPBF AlSi10Mg and LPBF β-SiC/AlSi10Mg not only showed the inherent high strength of their LPBF parts, but also had relatively high plasticity. Matching between strength and plasticity was mainly dependent on the scanning strategy. Most studies use uni-directional or bi-directional scanning strategies with a certain rotation angle between layers. A chessboard scanning strategy was used in this study to form a coarse remelted connected skeleton inside the material and significantly improve plasticity. This study lays a theoretical and experimental foundation for the controllable preparation of SiC-reinforced AMCs using LPBF.

Construction of irregular and high-density microtexture on ultra-thin 304 austenitic stainless steel strip via laser surface treatment to improve steel/epoxy resin adhesive bonding properties

Ultra-thin steel strip can be used in composite materials to create high-performance and low-deadweight components for the aerospace industry. The present study used a laser to create surface microtextures on 304 austenitic ultra-thin stainless steel (SS) strips to improve their adhesion to epoxy resin. Modification was conducted at various laser power levels, resulting in ring-like textures of various qualities. The strips were bonded to epoxy resin at single-lap joints, which were then strength-tested. The bonding mechanisms were investigated via analyses of microstructure, surface chemical composition and interfacial failure modes. The laser power level affected the density and distinctiveness of the ring-like structures. The optimal level of 40 W produced a bond with a shear strength of 14.43 MPa. Bonding is enhanced by the interlocking effect of the texture, improved wettability between the steel and epoxy resin, and –C–O=C polar bonds. Lower and higher power levels provided weaker textures. In summary, irregular laser surface treatment can optimize the shear strength of SS–epoxy-resin joints, allowing the fabrication of stronger componentry.

Metrological ensures for high-power laser radiation

The paper presents the state of ensuring the uniformity of measurements of energy parameters of high-power laser radiation. The research was carried out at the All-Russian Research Institute of Optical and Physical Measurements. The formation of a metrological support system for measuring the energy parameters of high-power continuous laser radiation required the creation of three standards, including one State primary standard of average laser power, and a line of four basic measuring instruments in the spectral range 1.07–10.6 μm and power range 1–500 kW. For the first time, a dynamic method for measuring high levels of laser power was developed and used. This ensured the certification of measuring instruments using reference radiation with a power of less than 100 kW. This has led to a significant increase in the level of metrological support for technological and special high-power laser equipment.

Numerical study of a convective cooling strategy for increasing safe power levels in two-photon brain imaging.

Two-photon excitation fluorescence microscopy has become an effective tool for tracking neural activity in the brain at high resolutions thanks to its intrinsic optical sectioning and deep penetration capabilities. However, advanced two-photon microscopy modalities enabling high-speed and/or deep-tissue imaging necessitate high average laser powers, thus increasing the susceptibility of tissue heating due to out-of-focus absorption. Despite cooling the cranial window by maintaining the objective at a fixed temperature, average laser powers exceeding 100-200 mW have been shown to exhibit the potential for altering physiological responses of the brain. This paper proposes an enhanced cooling technique for inducing a laminar flow to the objective immersion layer while implementing duty cycles. Through a numerical study, we analyze the efficacy of heat dissipation of the proposed method and compare it with that of the conventional, fixed-temperature objective cooling technique. The results show that improved cooling could be achieved by choosing appropriate flow rates and physiologically relevant immersion cooling temperatures, potentially increasing safe laser power levels by up to three times (3×). The proposed active cooling method can provide an opportunity for faster scan speeds and enhanced signals in nonlinear deep brain imaging.

Clamshell-type bis-phthalocyanines as colour-changing optical limiters: TDDFT modelling of electrically induced absorption for real-time colour indication of optical limiter efficiency in nonlinear laser protection.

This paper presents an innovative method for assessing the performance of optical limiters, which are devices that protect humans against laser radiation. The essence of the process is that with increasing laser radiation intensity, the colour of nonlinear absorbers, the working components of these devices, can change in contrast to the original one, which was demonstrated by quantum-chemical linear response time-dependent density functional theory (LR-TDDFT) for molecules excited by static electric finite fields (FF) within the general DFT (density functional theory) approach. Modelling was carried out on clamshell-type bis-phthalocyanines, in which the macrocycles are strapped by a cyclotriphosphazene spacer, suitable candidates for creating nonlinear optical (NLO) dyes for laser technology. As calculations have shown, acting as a "litmus test", these incredibly stable macrocyclic compounds are not only capable of providing laser protection but also give a real-time visual indication of the protection through changes in the colour of the dye, which correlate with different levels of laser power. Such indication can visually show the current state of optical limiters in practice, allowing users to easily determine whether the limiter material provides adequate protection or already requires replacement. A modelling protocol and program code for calculating the colour of a substance based on its absorption spectrum are presented.

The Effects of Laser Power and Travel Speed on Weld Geometry in the case of Manual Laser Welding

In our research, we investigated the effects of laser power and travel speed on the weld geometry in case of manual laser welding. Our experiments revealed that a characteristic two-part weld geometry is obtained under our experimental parameters. It was also found that increasing the laser power leads to a nearly linear increase in the weld width, while increasing the travel speed leads to a decrease in the weld width. The penetration depth does not increase further above a certain power level. A decrease in travel speed results in an increase in penetration depth. At the travel speeds tested, a narrow and deep weld geometry was obtained at the 70-80 % power level and a wider but shallower weld at the 90-100 % laser power level.