Effect Of Laser Spot Size Research Articles

Comprehensive optimization of selective laser melting process parameters for microstructure, density, hardness, and tribological performance of pure copper

This study is concerned with the optimisation of the processing parameters for the selective laser melting (SLM) of pure copper. The influence of these parameters on the microstructure, density and mechanical properties of copper samples produced by SLM is investigated in detail. Taguchi analysis is used to assess the importance of key building parameters including layer thickness, laser spot size and hatch distance on density. In addition, ANOVA is used to describe the contribution of each parameter to the density. The results reveal that layer thickness is the most effective parameter on density with an impact rate of 88.86%. Contrary to this situation, it appears that the effect of laser spot size and hatch distance on the density is quite limited, with an impact rate of 2.57% and 0.10%, respectively. Optimum results, including a relative density of 95.4% and a hardness of 63 HV, are achieved under specific parameters: a layer thickness of 0.03 mm, a hatch distance of 110 mm and a laser spot size of 70 ?m. This study provides a valuable insight into SLM processing of pure copper and offers practical recommendations for optimising the parameters used.

Effect of laser spot size on the behavior of molten pool and keyhole in laser welding

Effect of laser spot size on the behavior of molten pool and keyhole in laser welding

Effect of Laser Spot Size, Scanning Strategy, Scanning Speed, and Laser Power on Microstructure and Mechanical Behavior of 316L Stainless Steel Fabricated via Selective Laser Melting

Effect of Laser Spot Size, Scanning Strategy, Scanning Speed, and Laser Power on Microstructure and Mechanical Behavior of 316L Stainless Steel Fabricated via Selective Laser Melting

Experimentally constrained multidimensional simulation of laser-generated plasmas and its application to UV nanosecond ablation of Se and Te

We carry out simulations of laser plasmas generated during UV nanosecond pulsed laser ablation of the chalcogens selenium (Se) and tellurium (Te), and compare the results to experiments. We take advantage of a 2D-axisymmetric, adaptive Cartesian mesh framework that enables plume simulations out to centimeter distances over tens of microseconds. Our model and computational technique enable comparison to laser-plasma applications where the long-term behavior of the plume is of primary interest, such as pulsed laser synthesis and modification of materials. An effective plasma absorption term is introduced in the model, allowing the simulation to be constrained by experimental time-of-flight kinetic energy distributions. We show that the effective simulation qualitatively captures the key characteristics of the observed laser plasma, including the effect of laser spot size. Predictions of full-scale experimentally-constrained Se and Te plasmas for 4.0 J cm−2 laser fluence and 1.8 mm2 circular laser spot area show distinct behavior compared to more commonly studied copper (Cu) plumes. The chalcogen plumes have spatial gradients of plasma density that are steeper than those for Cu by up to three orders of magnitude. Their spatial ion distributions have central bulges, in contrast to the edge-only ionization of Cu. For the irradiation conditions explored, the range of plasma temperatures for Se and Te is predicted to be higher than for Cu by more than 0.50 eV.

Temperature evolution, phase ratio and corrosion resistance of duplex stainless steels treated by laser surface heat treatment

• Laser surface heat treatment (LSHT) was performed on duplex stainless steels 2304, 2205, and 2507. • The effect of laser spot size and cooling time t 12/8 was investigated by numerical simulation and microstructure analysis. • LSHT obtained the peak temperature, the t 12/8 and the effective depth as 1350 °C, 8.9 s and 1.5 mm respectively. • Austenite percentage increased from 2%, 5%, and 38% to 27%, 36% and 55 % respectively for 2304, 2205, and 2507. • LSHT increased the corrosion pitting temperature from 13, 42 and 66 °C to 19, 52 and 76 °C respectively for 2304, 2205, and 2507. Duplex stainless steels (DSS) are promising materials due to excellent corrosion resistance and good mechanical properties. However, the corrosion resistance of DSS welded joints deteriorates unavoidably due to the unbalanced phase ratio, namely a low austenite percentage resulted from the welding thermal cycle. Laser surface heat treatment (LSHT) exhibits tremendous advantages to restore the corrosion resistance especially regarding efficiency and flexibility. By adjusting laser energy input, including laser power and spot size, different LSHT conditions were applied to DSS 2304, 2205 and 2507, whose austenite content were deliberately decreased to a very low percentage. The temperature evolution during the LSHT was calculated out by finite element analysis. Critical pitting temperature (CPT) was measured to evaluate the corrosion resistance. A long length of laser spot and a slow scanning speed were beneficial for increasing the austenite percentage during the LSHT. With the length of laser spot as 100 mm and the scan speed as 2 mm/s, the laser power was adjusted to obtain a target peak temperature of 1350 ℃, which provided a cooling time t 12/8 as 8.9 s and an effective action depth as 1.5 mm. For DSS 2304 and 2205, the austenite percentage increased from 2% and 5% in deteriorated samples to 28 % and 56 % after the LSHT; the CPT increased from 12.5 and 42.3 ℃ to 19.2 and 51.8 ℃ respectively. DSS 2507 remained the highest austenite percentage after the same deterioration and exhibited the best corrosion resistance under all the used conditions. The influence of LSHT processing parameters and material compositions on the phase transformation and the corrosion resistance was discussed accordingly.

Awake chronic mouse model of targeted pial vessel occlusion via photothrombosis

.Animal models of stroke are used extensively to study the mechanisms involved in the acute and chronic phases of recovery following stroke. A translatable animal model that closely mimics the mechanisms of a human stroke is essential in understanding recovery processes as well as developing therapies that improve functional outcomes. We describe a photothrombosis stroke model that is capable of targeting a single distal pial branch of the middle cerebral artery with minimal damage to the surrounding parenchyma in awake head-fixed mice. Mice are implanted with chronic cranial windows above one hemisphere of the brain that allow optical access to study recovery mechanisms for over a month following occlusion. Additionally, we study the effect of laser spot size used for occlusion and demonstrate that a spot size with small axial and lateral resolution has the advantage of minimizing unwanted photodamage while still monitoring macroscopic changes to cerebral blood flow during photothrombosis. We show that temporally guiding illumination using real-time feedback of blood flow dynamics also minimized unwanted photodamage to the vascular network. Finally, through quantifiable behavior deficits and chronic imaging we show that this model can be used to study recovery mechanisms or the effects of therapeutics longitudinally.

Characterizing and alleviating ion suppression effects in atmospheric pressure matrix-assisted laser desorption/ionization.

As a powerful ambient ion source, atmospheric pressure (AP) matrix-assisted laser desorption/ionization (MALDI) enables direct analysis at atmospheric pressure/temperature and minimal sample preparation. With the increasing usage of AP-MALDI sources with Orbitrap instruments, systematic characterization of the extent of ion suppression effect (ISE) in AP-MALDI-Orbitrap mass spectrometry imaging (MSI) is desirable. Recently, a new low-pressure MALDI platform has been introduced that reportedly provided better sensitivity. While extensive research efforts have been devoted to improving spatial resolution, fewer studies focused on the characterization and sensitivity improvement of these MALDI platforms that, coupled with high-resolution Orbitraps, provide powerful strategy for MSI. We compared the analytical performance of AP and low-pressure (subatmospheric) MALDI sources to study the effect of pressure control in the ion source. Using a model peptide/protein mixture, we systematically evaluated the factors influencing ISE. Furthermore, the effect of laser spot size was evaluated through tissue imaging analysis of lipids and neuropeptides. The effects of ion suppression and laser spot size have also been examined by comparing the number of identified molecular species during MSI analysis. Several key operating parameters including source pressure, laser energy, laser repetition rate, and microscopic slide coating materials were optimized to minimize the ISE. Under the optimal conditions, the subatmospheric AP-MALDI-Orbitrap platform with high spatial and mass spectral resolution enabled significantly improved coverage of several lipid and neuropeptide families in the MS analysis of mouse brain tissue sections. The new SubAP-MALDI source coupled with an Orbitrap mass spectrometer was established as a viable platform for in situ endogenous biomolecular analysis with increased sensitivity compared with conventional AP-MALDI sources as evidenced by the confident identification of neuropeptides from mouse brain imaging analyses. The alleviated ISE was key to substantial performance improvement due to optimized intermediate pressure conditions and better ion collection by the ion funnel.

Laser impact welding application in joining aluminum to titanium

Thin metal foil joining has wide applications in medical device and microelectronics. In this paper, laser impact welding was implemented to join aluminum foil to titanium sheet. The velocity of Al flyer was measured with photonic Doppler velocimetry. The maximum velocity reached up to 1000 m/s within 0.2 μs. Varied thickness (25–250 μm) Al flyer was successfully welded with Ti target. Weld strength was measured with peel test. Weld area was estimated with resistance measurement method. The effect of laser spot size, flyer thickness, standoff distance on weld strength, weld area, and microstructure was analyzed. The microstructure was studied with scanning electron microscopy (SEM). By comparing the amplitude and wavelength of the waves at the bonding interface, it is suggested that the wave formation was related to the impact velocity. SEM back scattered electron image did not show apparent diffusion across the weld interface. Both twinning and severe plastic deformation were observed at Ti side along the weld interface, which resulted in hardness increase in this region.

Effect of laser spot size on the residual stress field of pure Al treated by laser shock processing: Simulations

Abstract Laser shock processing (LSP) is a unique surface treatment technique. It induces high-depth compressive residual stresses for improved fatigue or stress corrosion cracking resistance. FEM simulation is an effective method to predict material behavior by LSP. A 2D quarter-infinite model was used to simulate the material behaviors of commercially pure Al by LSP. Different peak pressure with different laser spot diameter was applied to surface of pure Al. Each simulation included two steps: (i) explicit dynamics analysis for the analysis of the LSP; (ii) static equilibrium analysis for springback deformation analysis. The following conclusions could be made: (1) Plastically affected depth increased with the increase of laser spot diameter. There was an ultimate value about plastically affected depth when the laser spot diameter increased to some value, and the ultimate value was consistent with Ballard’ model. When the laser spot diameter was small, there still existed tensile residual stresses on the surface layer of material although the peak pressure was below 2.5 HEL. When the diameter laser spot diameter was big enough, the tensile residual stresses on the surface layer of material were converted into compressive residual stresses although the peak pressure was higher than 2.5 HEL.

Spot size and quality of scanning laser correction of higher-order wavefront aberrations

Purpose To investigate the effect of laser spot size on the outcome of aberration correction with scanning laser corneal ablation. Setting Cleveland Clinic Foundation, Cleveland, Ohio, USA. Methods Corrections of wavefront aberrations of Zernike modes from the second to eighth order were simulated. Gaussian and top-hat beams of 0.6 to 2.0 mm full-width-half-maximum diameters were modeled. The fractional correction and secondary aberration (distortion) were evaluated. Results Using a distortion/correction ratio of less than 0.5 as a cutoff for adequate performance, a 2.0 mm or smaller beam was adequate for spherocylindrical correction (Zernike second order), a 1.0 mm or smaller beam was adequate for correction of up to fourth-order Zernike modes, and a 0.6 mm or smaller beam was adequate for correction of up to sixth-order Zernike modes. Conclusions Since ocular aberrations above the Zernike fourth order are relatively insignificant in normal eyes, current scanning lasers with a beam diameter of 1.0 mm or less are theoretically capable of eliminating most higher-order aberrations.

Spot size and quality of scanning laser correction of higher order wavefront aberrations.

To investigate the effect of laser spot size on the outcome of aberration correction with scanning laser corneal ablation. Numerical simulation of ablation outcome. Correction of wavefront aberrations of Zernike modes from second to eighth order were simulated. Gaussian and top-hat beams of 0.6 to 2.0-mm full-width-half-maximum diameters were modeled. The fractional correction and secondary aberration (distortion) were evaluated. Using a distortion/correction ratio of less than 0.5 as a cutoff for adequate performance, we found that a 2 mm or smaller beam is adequate for spherocylindrical correction (Zernike second order), a 1 mm or smaller beam is adequate for correction of up to fourth order Zernike modes, and a 0.6 mm or smaller beam is adequate for correction of up to sixth order Zernike modes. Since ocular aberrations above Zernike fourth order are relatively insignificant, current scanning lasers with a beam diameter of 1 mm or less are theoretically capable of eliminating most of the higher order aberrations of the eye.

Laser tissue welding: laser spot size and beam profile studies

Evaluates the effect of laser spot diameter and beam profile on the shape of the thermal denaturation zone produced during laser tissue welding, 2-cm-long full thickness incisions were made on the epilated backs of guinea pigs in vivo. India ink was used as an absorber and clamps were used to appose the incision edges. Welding was performed using continuous-wave 1.06-/spl mu/m, Nd:YAG laser radiation scanned over the incisions to produce /spl sim/100-ms pulses. Laser spot diameters of 1, 2, 4, and 6 mm were studied, with powers of 1, 4, 16, and 36 W, respectively. The irradiance remained constant at 127 W/cm/sup 2/. Monte Carlo simulations were also conducted to examine the effect of laser spot size and beam profile on the distribution of photons absorbed in the tissue. The laser spot diameter was varied from 1 to 6 mm, Gaussian, flat-top, dual Gaussian, and dual flat-top beam profiles were studied. The experimental results showed that 1-, 2-, 4-, and 6 mm-diameter spots produced thermal denaturation to an average depth of 570, 970, 1470, and 1900 /spl mu/m, respectively. Monte Carlo simulations demonstrated that the most uniform distribution of photon absorption is achieved using large diameter dual flat-top beams.

Effect of laser spot size on energy balance in laser induced plasmas. (USA)

Effect of laser spot size on energy balance in laser induced plasmas. (USA)

Effect of laser spot size on energy balance in laser induced plasmas

The effect of the laser spot size on laser light absorption in laser induced plasmas from solid targets was studied. It was found that at a constant laser intensity on the target, reduction in the laser spot size enhances the net laser energy absorption. It was also observed that the laser light reflection from the target becomes more diffused when the focal spot size is reduced.