Laser Beam Spot Diameter Research Articles

Software compensation to improve the Stereolithography fabrication of porous features and porous surface texturing at micro-scale

Nano and micro-porous structures exhibit intriguing properties for a wide variety of applications, spanning from the biomedical to sensing. However, their fabrication is a challenge in terms of dimensional accuracy, which affects devices' performance and sensitivity. In this paper, we present a route to enhance the dimensional accuracy of fabrication via Stereolithography (SLA) of porous features at the micro-scale. Using a custom benchmark part, deviations in feature dimensions (micro-pores diameters and depths) were measured by confocal microscopy. Sample characterization and experimental observations allowed the identification of inaccuracy sources (i.e., laser spot size and its compensation on path generation), and a compensation method of the nominal laser spot diameter (85|um) was defined. Implementing such a method results in relevant improvements in dimensional accuracy: 9.8% and 11.3% on full-open pores diameter and depth, respectively. Partially open pores accuracy improvements were 15.8% on diameters and 1.5% on depths. Since machine optical equipment can result in deviations in the actual laser spot diameter from the nominal value, the actual laser beam spot diameter was estimated by printing a test part and adopting this information to adjust a calibration procedure. The measurements revealed that the actual laser beam spot size is 93±8um. The proposed method can be extended for the fabrication of any micro-porous structures.

Improving Plasticity of Ferritic Stainless Steel Welded Joints via Laser Spot Control.

The plasticity of welded 441 ferritic stainless steel joints was controlled by varying the laser beam spot diameter during laser welding. A stainless steel plate thickness of 1.2 mm was used. The microstructures of the welded joints were analyzed for various spot diameters. The elongation of breaks and the reduced area of tensile specimens were analyzed to study the effects of spot diameter on plasticity of the welded joints. The results showed that the weld melt width and weld column crystal size increased with the spot diameter, but isometric crystals in the center of the weld were gradually reduced. Increasing spot diameter resulted in decreased tensile strength, elongation after breaks, and area reduction. So the parameter must be controlled during the laser welding.

Unravelling keyhole instabilities and laser absorption dynamics during laser irradiation of Ti6Al4V: A high-fidelity thermo-fluidic study

A 3D multi-phase thermo-fluidic solver is implemented to investigate the laser-melt pool interaction dynamics and keyhole instabilities during stationary and moving laser irradiation. The physical phenomena such as phase changes, thermocapillary driven flow, multiple reflections of the Gaussian laser beam and beam trapping, vaporization recoil pressure, and heat losses (convective, radiative, and evaporative) have been incorporated in the model. A detailed parametric study has been carried out to investigate the influence of the laser beam spot diameter and the traversal speed on the laser absorption dynamics and melt pool characteristics. For both the stationary and moving laser irradiation, it is found that during the initial transient stage, the melt pool morphology belongs to the conduction melting mode with laser absorption according to the normal incidence condition of the Fresnel equation. Later, depending on the irradiating laser intensity, a melt transition occurs from conduction to the keyhole mode of melting, during which laser absorption rises sharply. The laser absorption and the vapor depression morphology in the keyhole regime show substantial oscillations (periodic and non-periodic) due to the complex hydrodynamics of the recoil pressure, the surface-tension dynamics, and convection-driven flow resulting in the opening and closing of the vapor depression. These oscillations are quantified, and a direct correlation of the laser absorptance with the keyhole depression depth has been observed for stationary laser irradiation. The keyhole closure mechanism and bubble trapping-ejection phenomena have been explored during the solidification stage. The numerically predicted melt pool dimensions match well with the in-house performed experimental measurements and published benchmarking experiments combining integrating sphere radiometry and in-situ X-ray radiography.

The effect of the diode laser beam power on the behaviour of the ZrC powder pre-coat and the 145Cr6 steel substrate during laser processing

The paper presents both the production method and its impact on selected properties of composite coatings reinforced with hard ZrC particles. The Fe/ZrC coatings were produced using diode laser by remelting the pre-coat in the form of paste consisting of ZrC powder and binder. Different values of laser beam power (500 W, 700 W, and 900 W) and different pre-coat thicknesses (100 µm, 150 µm, and 200 µm) were used to produce the composite coatings. During all processes, the scanning speed of laser beam was 3 m/min. Laser beam spot diameter was 1 mm. Microstructure study, microhardness tests, as well as EDS and XRD analysis were carried out. The obtained Fe/ZrC coatings were also tested for the effect of the corrosive medium in a 3.5% NaCl water solution. The effect of applied parameters on wear resistance of Fe/ZrC coatings was also studied. The tribological properties were assessed both by mass loss measurement and by scanning electron microscopy. Fe/ZrC coatings produced using the highest thickness of the pre-coat were characterised by cracks arising during production process. The very high concentration of carbides and hence high hardness of the coating produced in this way contributed to it. However, a positive effect of laser beam power increase on reduction of these cracks was observed. The coatings were characterised by very high hardness, reaching in some cases even more than 2000 HV. It was found that the most favourable properties regarding both tribology and corrosion resistance were obtained for Fe/ZrC coatings produced using 150 µm of pre-coat thickness.

Open flow cytometer with the combination of 3D hydrodynamic single cell focusing and confocal laser-induced fluorescence detection

Flow cytometry is among the most powerful tools for single-cell analysis, while the high cost and mechanical complexity of the commercial instrumentation limit the applications in personalized single-cell analysis. For this issue, we hereby construct an open and low-cost flow cytometer. It is highly compact to integrate the functions of (1) single cell aligning by a lab-made modularized 3D hydrodynamic focusing device, and (2) fluorescence detection of the single cells by a confocal laser-induced fluorescence (LIF) detector. The ceiling cost of the entire hardware for the LIF detection unit and 3D focusing device is $ 3200 and $ 400 respectively. A sheath flow velocity of 150 μL/min produces a focused sample stream of 17.6 μm × 14.6 μm at sample flow of 2 μL/min, based on the LIF response frequency and the laser beam spot diameter. The assay performance of the flow cytometer was evaluated by characterizing fluorescent microparticles and acridine orange (AO) stained HepG2 cells, producing throughputs of 40.5/s and 6.2/s respectively. Favorable assay precision and accuracy were demonstrated by the agreement of frequency histogram with imaging analysis, and good Gaussian-like distributions of fluorescent microparticles and AO-stained HepG2 cells. Practically, the flow cytometer was successfully applied for the evaluation of ROS generation in single HepG2 cells.

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Surface laser processing of maraging steel parts manufactured by selective laser melting: effect on pass geometry and hardness

Due to the possibility to produce the parts with complex internal and external geometries, selective laser melting (SLM) process attracts growing interest in various fields of engineering segments such as aircraft, aerospace, biomedical, automotive, marine industries and tooling. Maraging steels, having excellent weldability and high resistance to thermal fatigue due to the lack of carbon, has showed good suitability for SLM [1]. However, owing to the limited hardness and wear resistance, maraging steels has limited application at the harsh wear conditions [4]. In this study, the possibility to improve the surface characteristics of DIN 1.2709 steel SLM parts by application of laser alloying technology is evaluated. The surface of SLM part was laser processed at various laser spot diameters and varying laser scanning speeds from 500 to 1500 mm⋅min-1, with and without preposition of alloying element. The power density was provided in the range from ~0.8⋅103 W⋅cm-2 to ~51⋅103 W⋅cm-2 and heat input – from 4 to 12 J⋅mm-1. The effect of laser processing parameters and presence of alloying element on the geometry of obtained processed passes and hardness of surface was evaluated. It was determined, that the application of CO2 continuous laser at the parameters of 1 kW laser power, 0.5 mm laser beam spot diameter and laser scanning speed in the range between 500 mm⋅min-1 and 1250 mm⋅min-1 allows obtaining laser pool of acceptable geometry and sizes directly on as-manufactured SLM part surface without any pre-processing. The increasing scanning speed to 1500 mm⋅min-1 or spot size to 2.0 and 3.0 mm results in too small pool depth and unstable pool geometry. The laser processing with preposition of alloying element layer provided surface alloying effect of the maraging steel SLM part. The hardness of processed surface areas ranged between ~600 HV0.2 at the lowest scanning speed and ~1770 HV0.2 at the highest speed, what is from 18% to ~3.5 times higher, as compared with maximum hardness of 1.2709 maraging steel after aging (~58 HRC or ~510 HV).

Measurement of spot diameter and divergence of laser beam by shadow method using generalized parameters

Measurement of spot diameter and divergence of laser beam by shadow method using generalized parameters

Laser cladding process of Fe/WC metal matrix composite coatings on low carbon steel using Yb: YAG disk laser

The paper presents the studies of selected properties of Fe/WC metal matrix composite coatings produced using different laser beam power values and different powder feeding rates. Coatings were produced using the Yb: YAG disk laser by laser cladding method. Laser beam powers equal to 600 W, 700 W and 800 W were used. Scanning speed of laser beam was the same for all the coatings and was equal to 600 mm/min. Laser beam spot diameter was 1.64 mm. Two powder feeding rates (6.25 g/min and 12.50 g/min) were applied. In this study macroscopic observation, microstructure and microhardness examination as well as XRD and EDS analysis were carried out. Corrosion resistance was also investigated. In Fe/WC coating produced using slower powder feeding rate dendritic carbides that nucleated on the primary tungsten carbide particles were observed. In the coatings produced using an increased powder feeding rate, a changed type of secondary carbide was observed, which was bar-shaped or plate-shaped. The results of the XRD and EDS analysis of the composite Fe/WC coatings showed the presence of WC, W2C phases as well as M23C6 and (Fe,W)3C complex phases. The mechanism of formation and growth of composite coatings was described on the basis of microstructures obtained. The highest microhardness and corrosion resistance were observed for coatings produced at a powder feeding rate of 12.50 g/min.

Pulsed laser butt welding of AISI 1005 steel thin plates

Pulsed laser welding is a joining process, which takes advantage of the laser energy quality with precise control equipment. Its characteristics allow joining thinner materials with reduced thermal distortion without filler material, fulfilling the industrial interest in this process. In the present work, AISI 1005 steel sheets of 1.7 mm thickness were subjected to different pulse Nd:YAG laser treatments to obtain one side bead-on-plate weld samples and double sided butt welds. Since the quality of the joints is strongly influenced by the process parameters, an experimental design methodology was adopted to define a suitable combination of the laser beam power, pulse duration and spot diameter. The Box-Behnken technique and response surface methodology associated with analyses of defects allowed the determination of the appropriate welding parameters. The microstructure characterisation revealed the melted fusion zones originated from the thermal effect of the overlapped pulses. Additionally, microhardness measurements at fusion zone exhibited higher values than the base material and heat affected zone, due to the hard microconstituents developed. The tensile test performed at samples extracted from double sided laser welds showed good resistance results, fracturing at the base material of joints. The present work demonstrates that pulsed laser welding methodology is suitable to obtain high quality joints of steel thin plates.

Microscale Precision Control of a Computer-Assisted Transoral Laser Microsurgery System

In a recent advance in surgery, a computer-assisted laser microsurgery system has demonstrated its suitability for transoral operations. Thanks to its motorized micromanipulator setup, surgeons can perform delicate operations on lesions in the larynx using an intuitive user interface. The major hurdle to ensure surgical quality is to guarantee $\mu$ m-scale precision in the control of the laser beam (spot diameter 110–250 $\mu$ m), because the mechanism includes inherent discontinuous nonlinearities such as Coulomb friction and stiction and unavoidable modeling uncertainties. To this end, in this article, a precise position controller directly creating a voltage command is newly proposed by amalgamating two robust control concepts—a generalized super-twisting algorithm (GSTA) and a model-free compensation method called time-delay estimation (TDE). Fast convergence in finite time is proved in the Lyapunov sense. The experimental results verify that the proposed controller can satisfy the precision requirement of 55 $\mu$ m, while the efficacy is validated by comparisons with respective GSTA- and TDE-based controllers. As a practical performance–safety guideline for users, we benchmark the tracking precision of the proposed controller with respect to operation speeds.

Optimization Design and Experimental Testing of a Laser Receiver for Use in a Laser Levelling Control System

The elevation detection accuracy of the laser receiver in the laser levelling control system directly affects land-levelling operations. To effectively improve the effect of levelling operations and meet the requirements for the accuracy of elevation detection in different industries, this study optimization designed a multilevel adjustable laser receiver. First, we examined the laser signal detection technology and processing circuit, designed the photoelectric conversion array for the detection of the rotating laser, and converted it into a photocurrent signal. We also designed the filter, amplifier, and shaping and stretching circuits for analogue-to-digital conversion of the photocurrent signal. The digital signal was calculated based on the deviation of the elevation by using a microprocessor and was output by a controller area network (CAN) bus. The laser beam spot diameter transmission and diffusion were then studied, and with the detectable spot diameters were compared and analyzed. Accordingly, an algorithm was proposed to calculate the deviation of laser receiver elevation. The resolution of the elevation deviation was set to ±3 mm; however, this value could be adjusted to ±6 mm, ±9 mm, ±12 mm, and ±15 mm, according to the requirements. Finally, the laser receiver was tested and analyzed, and the test results of the elevation detection accuracy showed that when the laser receiver was within a radius of 90 m, the elevation detection accuracy was within the ±3 mm range. The outcomes of the farmland-levelling test showed that the standard deviation S d of the field surface decreased from 9.54 cm before levelling to 2.42 cm after levelling, and the percentage of sampling points associated with absolute errors of ≤3 cm was 84.06%. These outcomes meet the requirements of high-standard farmland construction. The test results of concrete levelling showed that within a radius of 30 m, the standard deviation S d of the elevation adjustment of the left laser receiver was 1.389 mm, and the standard deviation S d of the elevation adjustment of the right laser receiver was 1.316 mm. Furthermore, the percentage of the sampling points associated with absolute elevation adjustment errors of ≤3 mm in the cases of the two laser receivers was 100% after levelling, whereas the standard deviation S d of the sand bed surface was 0.881 mm. Additionally, the percentage of the sampling points associated with absolute errors of ≤3 mm was 100%. This met the construction standards of the concrete industry.

Effects of spot size variation on the laser induced breakdown spectroscopy analysis of Cu(In,Ga)Se2 solar cell

The effects of spot size variation on the results of laser induced breakdown spectroscopy (LIBS) analysis of Cu(In,Ga)Se2 (CIGS) thin film solar cell using a scanning laser beam (λ = 532 nm, τ = 5 ns, top-hat spatial profile) are reported. The spot diameter of laser beam was reduced from 150 μm to 35 μm, below the laser P2 scribing pattern width, at the fixed laser fluence of about 4.5 J/cm2 and overlap ratio of 79%. The results showed that the measured LIBS signal intensity ratio rather than intensity could be nearly independent of laser spot diameter if the spectral lines are properly selected. It is demonstrated that the concentration ratio of CIGS layer can be predicted within 5% error from the average concentration ratio measured by inductively coupled plasma optical emission spectroscopy by LIBS analysis with a spot diameter of 50 μm.

Direct metal laser sintering of TiN reinforced Ti6Al4V alloy based metal matrix composite: Fabrication and characterization

In the present research, direct metal laser sintering (DMLS) method was chosen to fabricate titanium nitride (TiN) reinforced Ti6Al4V alloy based metal matrix composites (MMCs) under an argon atmosphere using continuous wave (CW) fiber laser having a capacity of 400 W. Laser sintering process parameters, such as layer thickness (0.4 mm), laser beam spot diameter (0.4 mm), and hatching gap (0.2 mm) were kept constant throughout the experiments. Effects of input variable process parameters, such as laser power (50–65 W), scanning speed (3500–4500 mm/min), and volume % of TiN (5–15% v/v) on density, microhardness, and coefficient of friction of the fabricated MMCs were analyzed. The obtained results show the improvement in the physical properties of the fabricated MMCs and FESEM images evidently confirm the presence of TiN particulates and also revealed the uniform distribution of the TiN reinforcement in Ti6Al4V matrix. It was found that the microhardness measured by Vickers test was improved from 388 to 590 HV0.2 with an increase in the volume percentage of TiN. The results showed the coefficient of friction for fabricated samples were in the range of 0.33–0.42. The density (3.40–4.10 g/cm3) of the MMCs was found to increase with increasing the volume percentage of TiN reinforcement in the powder mixture. X-ray diffraction (XRD) analysis of the fabricated MMC confirmed the presence of different in-situ phases, such as Ti, TiN, TiO2, VN, AlV, Ti3Al2N2, and V6N2.7 as a consequence of a series of a chemical reaction between TiN and different elements of Ti6Al4V in the argon atmosphere.

Optimization of CO2 Laser Beam Welding Process Parameters to Attain Maximum Weld Strength in Dissimilar Metals

In this study, influence of CO2 laser beam welding (LBW) process parameters such as laser power (P), welding speed (S), focal distance (F) on dissimilar metals of low carbon steel (AISI 1018) and austenitic stainless steel (AISI 316) was examined by using central composite design (CCD) based response surface methodology (RSM). Experimental investigations were performed on 4 kW CO2 laser (TRUMPF TLC1005) with the laser beam spot diameter of 0.15mm and a focal length of 15-25mm. Analysis of variance (ANOVA) was used to analyze the interaction effect of different parameters on the maximum weld strength. A ratification experiment was also carried out in order to validate the optimal process parameters values. Based on the investigation, the maximum weld strength of 458.21 N/mm2 was observed for dissimilar metal butt joint with the optimized laser power of 2600W, the focal distance of 25 mm and a welding speed of 1.5 m/min. Microstructure studies revealed cellular austenite in the form of dendrite and columnar type features accredited to the higher cooling rates concerned with laser welding process. Energy dispersive X-ray analysis (EDX) is carried out to measure the nature of the chemical element distribution in the weld interface. Microhardness tests showed that the maximum hardness was produced in weldment 151-458 Hv and fusion boundary of austenitic stainless steel 193-434 Hv, fusion boundary of low carbon steel 156-468 Hv.

Preparation of TiC-doped W-Ti alloy and heat flux performance test under laser beam facility

TiC-doped W-Ti composites were prepared by mechanical alloying and spark plasma sintering. The influence of milling time on the microstructure and properties of TiC-doped W-Ti composite material was investigated. Results show that with increasing ball milling time, powder particles undergo a process of fracture-cold welding-fracture. Powder grains are continuously refined to 25.1nm, and micro-strain continuously increases from 0.324% to 0.724%. With the extension of ball milling time, the sintered composite material exhibits a declining trend in density and an initial decrease and later increase in grain size. The minimum grain size is noted in the specimen WTT-60 at 0.35μm. Microhardness increases first then decreases, and the microhardness of specimen WTT-60 reaches the highest value (1139.27Hv) among those tested. Heat-shock resistance of the specimens was researched though a transient heat load experiment at pulse width 1ms, current 60A, and laser beam spot diameter 0.6mm (44∼47MW/m2).The bulk prepared by powder sintering from 60h of ball milling presents the best thermal shock resistance.

Effects of Pulsed Nd:YAG Laser Welding Parameters on Penetration and Microstructure Characterization of a DP1000 Steel Butt Joint

Of particular importance and interest are the effects of pulsed Nd:YAG laser beam welding parameters on penetration and microstructure characterization of DP1000 butt joint, which is widely used in the automotive industry nowadays. Some key experimental technologies including pre-welding sample preparation and optimization design of sample fixture for a sufficient shielding gas flow are performed to ensure consistent and stable testing. The weld quality can be influenced by several process factors, such as laser beam power, pulse duration, overlap, spot diameter, pulse type, and welding velocity. The results indicate that these key process parameters have a significant effect on the weld penetration. Meanwhile, the fusion zone of butt joints exhibits obviously greater hardness than the base metal and heat affected zone of butt joints. Additionally, the volume fraction of martensite of dual-phase steel plays a considerable effect on the hardness and the change of microstructure characterization of the weld joint.

Laser forming of a bowl shaped surface with a stationary laser beam

Despite a lot of research done in the field of laser forming, generation of a symmetric bowl shaped surface by this process is still a challenge mainly because only a portion of the sheet is momentarily deformed in this process, unlike conventional sheet metal forming like deep drawing where the entire blank undergoes forming simultaneously reducing asymmetry to a minimum. The motion of laser beam also makes the process asymmetric. To counter these limitations this work proposes a new approach for laser forming of a bowl shaped surface by irradiating the centre of a flat circular blank with a stationary laser beam. With high power lasers, power density sufficient for laser forming, can be availed at reasonably large spot sizes. This advantage is exploited in this technique. Effects of duration of laser irradiation and beam spot diameter on the amount of bending and asymmetry in the formed surface were investigated. Laser power was kept constant while varying irradiation time. While varying laser spot diameter laser power was chosen so as to keep the surface temperature nearly constant at just below melting. Experimental conditions promoted almost uniform heating through sheet thickness. The amount of bending increased with irradiation time and spot diameter. It was interesting to observe that blanks bent towards the laser beam for smaller laser beam diameters and the reverse happened for larger spot diameters (~10 times of the sheet thickness). Effect of spot diameter variation has been explained with the help of coupled thermal-structural finite element simulations.

Effect of Nd:YAG laser parameters on the penetration depth of a representative Ni–Cr dental casting alloy

The effects of voltage and laser beam (spot) diameter on the penetration depth during laser beam welding in a representative nickel-chromium (Ni-Cr) dental alloy were the subject of this study. The cast alloy specimens were butted against each other and laser welded at their interface using various voltages (160-390V) and spot diameters (0.2-1.8mm) and a constant pulse duration of 10ms. After welding, the laser beam penetration depths in the alloy were measured. The results were plotted and were statistically analyzed with a two-way ANOVA, employing voltage and spot diameter as the discriminating variables and using Holm-Sidak post hoc method (a = 0.05). The maximum penetration depth was 4.7mm. The penetration depth increased as the spot diameter decreased at a fixed voltage and increased as the voltage increased at a fixed spot diameter. Varying the parameters of voltage and laser spot diameter significantly affected the depth of penetration of the dental cast Ni-Cr alloy. The penetration depth of laser-welded Ni-Cr dental alloys can be accurately adjusted based on the aforementioned results, leading to successfully joined/repaired dental restorations, saving manufacturing time, reducing final cost, and enhancing the longevity of dental prostheses.

Controlled reshaping of the front surface of the cornea through its full-area ablation outside of the optical zone with a Gaussian ArF excimer laser beam

We studied in vitro the response of the topography of the cornea to its full-area laser ablation (the laser beam spot diameter is commensurable with the size of the interface) outside of the central zone with an excimer laser having a Gaussian fluence distribution across the beam. Subject to investigation were the topographically controlled surface changes of the anterior cornea in 60 porcine eyes with a 5 ± 1.25-diopter artificially induced astigmatism, the changes being caused by laser ablation of the stromal collagen in two 3.5-mm-dia. circular areas along the weaker astigmatism axis. Experimental relationships are presented between the actual astigmatism correction and the expected correction for the intact optical zones 1, 2, 3, and 4 mm in diameter. The data for each zone were approximated by the least-squares method with the function d = a + bx. The coefficient b is given with the root-mean-square error. The statistical processing of the data yielded the following results: d = (0.14 ± 0.037)x for the 1-mm-dia. optical zone, (1.10 ± 0.036)x for the 2-mm-dia. optical zone, (1.04 ± 0.020)x for the 3-mm-dia. optical zone, and (0.55 ± 0.04)x for the 4-mm-dia. optical zone. Full astigmatism correction was achieved with ablation effected outside of the 3-mm-dia. optical zone. The surface changes of the cornea are shown to be due not only to the removal of the corneal tissue, but also to the biomechanical topographic response of the cornea to its strain caused by the formation of a dense pseudomembrane in the ablation area.