Influence Of Laser Parameters Research Articles

Laser Surface Modification of Wire-Electric Discharge Machined Graphene Nanoparticle Reinforced SiC Composites

Abstract Electrical discharge machining of conducting ceramics is often associated with high roughness and porosity, which hinders their application. This porosity-laden surface morphology necessitates a postprocessing technique to reduce the severity of the surface defects. Hence, this study focuses on the utilization of a nanosecond pulsed laser as a surface modification tool to minimize the debris and pores formed on the surface after the wire-electrical discharge machining process. This paper presents a study on the influence of laser parameters, viz., power, number of scans, scanning speed, and pulse repetition rate on the overall surface characteristics. The concentration of surface debris and pores were observed to significantly decrease with laser surface modification (LSM). The improvement in the surface characteristics after laser processing with low fluence was mainly attributed to melting, vaporization, and subsequent flow of molten material, which led to filling of the surface pores. This resulted in a more even surface postlaser surface modification. The surface roughness was observed to decrease by ∼49% after the laser processing at lower values of laser power, number of scans, and scanning speed and at higher values of pulse repetition rate. Furthermore, spatial, hybrid, and functional volume characteristics were observed to improve postlaser modification. However, at higher laser fluence, the processed surfaces were observed to get further worsened with the formation of deep ridges.

The effect of giant Kerr nonlinearity on group velocity in a six-level inverted-Y atomic system

We propose an analytical model to study the effect of giant Kerr nonlinearity on group velocity of probe light in a six-level inverted-Y atomic system under electromagnetically induced transparency (EIT). In this scheme, a nonlinearity of the medium is enhanced greatly around in three spectral regions corresponding to transparent windows. As a consequence, such a giant Kerr nonlinearity of the medium changes significantly group index for probe light which can obstruct light slowdown. Moreover, this model shows also that the probe propagation can switch between subluminal and superluminal modes in three EIT windows by adjusting the parameters of the signal and coupling fields. Such analytical model is not only convenient for considering the influence of laser parameters on group velocity but is also easy used to fit the experimental results.

Microchannel Fabrication in Fused Quartz by Backside Laser-Induced Plasma Ablation Using 248 nm KrF Excimer Laser

Laser-induced plasma ablation (LIPA) using a 248 nm KrF excimer laser was investigated for microchannel fabrication. Examination of the morphology in relation to ablation performance was emphasized, and a synthetic LIPA mechanism model was proposed based on the results. Backside LIPA with a metal target on the bottom can be attributed to a combination of two phenomena: laser-induced plasma vaporization thermal ablation from the metal target below and enhanced laser–glass direct interaction from the plasma residuum. The laser absorption enhancement of quartz substrate resulting from the metal residuum was validated clearly using absorption spectrum measurements. The influence of laser parameters on the etching quality during LIPA was also analyzed for processing optimization. Finally, fused quartz glass microchannels of outstanding surface quality and dimension uniformity were implemented. The channel depth was 28 μm, and the bottom surface roughness was better than several hundred nanometers.

Near-IR- and UV-femtosecond laser waveguide inscription in silica glasses

The influence of laser parameters on silica based waveguide inscription is investigated by using femtosecond laser pulses at 1030 nm (near-IR) and at 343 nm (UV). Negative phase contrast microscopy technique is used to measure the refractive index contrast for different photo-inscribed waveguides and shows the effects of both laser wavelength and scanning speed. In particular, UV photons have a higher efficiency in the waveguide production process as also confirmed by the lower optical losses at 1550 nm in these waveguides. These measurements are combined with micro-Raman and photoluminescence techniques, highlighting that laser exposure induces both structural modification of the silica and point defects generation. The contribution of induced defects to the total refractive index change is singled out by applying two different thermal treatments on the waveguide. The first, up to 500 °C, is able to remove the most of the induced non-bridging-oxygen-hole-centers (NBOHCs) while the second up to 750 °C erases almost all absorbing induced defects, highlighting the strong contribution of additional defects, not yet identified.

레이저 변수와 분말 기공율이 SLM 공정의 분말베드내 열특성에 미치는 영향 고찰

레이저 변수와 분말 기공율이 SLM 공정의 분말베드내 열특성에 미치는 영향 고찰

Numerical simulation of ophthalmic laser surgeries by a local thermal non-equilibrium two-temperature model

Purpose This paper aims to understand the laser–tissue interaction mechanism during ophthalmic laser surgeries through numerical analysis. The influence of laser parameters and the multipulse technique were investigated. Design/methodology/approach The ocular fundus was simplified as a multilayered homogenous medium model. Afterward, the multilayer Monte Carlo method was used to simulate the propagation and energy deposition of laser light, and a local thermal non-equilibrium two-temperature model was established to simulate the temperature variation of chromophores and surrounding tissue with different laser wavelength. Findings Through the model, the selective heating of chromophore (melanin and blood vessels) was clearly illustrated: 1) neglecting the laser energy absorbance by blood in the traditional model will cause significant errors in temperature calculation; 2) the non-thermal equilibrium heat transfer model was needed to obtain an accurate description of the thermal process when the dimensionless pulse width (tp*) is <105. For 532 nm Argon laser, the optimize tp* is around 105 and the appropriate energy density is 5 J/cm2; 3) multipulse technique makes the energy more concentrated within the melanin, thereby reducing the thermal damage in surrounding tissue, with most appropriate pulse number and duty cycle is 10 and 1/10. Originality/value Taking the blood absorption into account, the different temperature variations of melanin/vessels and surrounding tissue caused by the selective photo-thermolysis were simulated successfully. By understanding the mechanism of laser therapy, laser parameters and multipulse technique are suggested to improve the clinical results.

Fabrication of large aspect ratio (LAR) PCD micro-end mill with a hybrid method and performance verification

Micro-milling technology is a well-developed method in machining the increasingly required micro-grooves. High wear-resistant PCD micro-milling cutters have become the desirable substitute for traditional carbide tools since micro-milling is a highly tool-dependent process. However, the fabrication of PCD micro-milling cutters is difficult due to its high hardness, particularly for those with a larger aspect ratio and a smaller diameter. For these reasons, a hybrid fabrication method combining the laser and precision grinding is proposed to improve the performance and quality of PCD micro-milling cutters. The laser investigations were carried out first to explore the machining mechanism and influence of laser parameters on the initial forming quality. The grinding mechanism of laser-treated PCD was analyzed profoundly. Verification experiments were conducted to compare the cutting performance of the self-fabricated PCD and carbide tools by considering the surface quality and tool wear. Results showed the laser parameters used were directly related to the surface roughness and edge quality of the laser-treated PCD. After the precision grinding, the laser-treated PCD surface became smoother with the areal roughness (Sa) of 0.3 μm. A PCD diamond micro-end mill with an aspect ratio of more than 2 was achieved by using the hybrid method. Micro-milling experiments demonstrated that the self-fabricated PCD showed remarkable superiority in terms of surface roughness, burr formation, and tool wear.

Comparative assessment of picosecond laser induced plasma micromachining using still and flowing water

Laser induced plasma micromachining (LIPMM) process is an effective approach to create micro-features with high aspect ratio and reduced heat affected zone. However, the throughput of this process is limited by the low scanning speed and low frequency used in the conventional underwater condition due to the disturbance of water layer, generation of bubbles and ablation debris. In this study, a new alternate process using flowing water was developed to provide a stable and thin water layer on the top workpiece surface. Thereafter, the influences of laser parameters like scanning speed, frequency and pulse energy on the machining characteristics between LIPMM using still and flowing water were experimentally investigated and comparatively evaluated. It was found that the influences of scanning speed, frequency and pulse energy on the machining characteristics between two processes were similar. However, LIPMM using flowing water created micro-channels with smaller heat affected zone, smoother surface, higher aspect ratio and higher MRR in comparison with that of using still water.

Fabrication of micro-channels on Al2O3/TiC ceramics using picosecond laser induced plasma micromachining

Laser induced plasma micromachining (LIPMM) using a 10 ps laser was applied to create micro-channels on the surface of Al2O3/TiC ceramic. Micro-channels were firstly created by direct laser ablation and LIPMM to comparatively assess the machining ability of two processes. The results showed that LIPMM could create micro-channels with a higher depth and better surface morphologies as compared to direct laser ablation. Subsequently, the influence of laser parameters during LIPMM like pulse energy, scanning speed and frequency on the machining characteristics was investigated. The machined depth of the micro-channel increased with an increase in pulse energy, meanwhile an increase in frequency or a decrease in scanning speed increased the overlap, leading to an increment of the machined depth as well. The pulse energy, scanning speed and frequency had a slight effect on the machined width. The width of heat affected zone increased with the increasing overlap and pulse energy.

The Influence of Laser Parameters on the Coloring Effect and Microstructure of Stainless Steel Surface

Nanosecond pulsed, green (532 nm) laser was used to irradiate SUS 304 stainless steel. Black, brown, gray, pink and other colors were obtained on the surface of polished stainless steel by adjusting the three process parameters: scanning interval (Ls), scanning speed (v) and defocusing distance (Dd). Scanning electron microscope (SEM) showed that there were three kinds of structures on the surface of stainless steel: columnar protrusions, droplets and cracks. The results indicated that the three process parameters affected the surface coloring effect and the microstructure formation of stainless steel by changing the total accumulated laser fluence in the scanning area.

A novel assembly of MoS2-PTFE solid lubricants into wear-resistant micro-hole array template and corresponding tribological performance

Special blind micro-hole array templates were constructed by fiber laser drilling on laser-clad wear-resistant Fe-based alloy coatings with aim to carry and to preserve solid lubricants into micro-hole reservoir. The influence of laser parameters on the morphology of blind holes was investigated. The blind U-shape micro-hole array templates, which are the most suitable for subsequent electrophoreticdeposition (EDP), were fabricated by the optimized laser drilling parameters. Different lubricant mixtures of MoS2 and PTFE powder were assembled into the blind micro-hole array templates with different micro-hole density byEDP. The deposited mixtures of MoS2 and PTFE powder were densified by microwave sintering. The tribological performance evaluated by a ring-on-block wear tester indicated that the 20% micro-hole density template assembled with MoS2-10wt%PTFE powder presented the lowest friction coefficient.

Study on the Effect of Laser Parameters on the SEY of Aluminum Alloy

The laser treated surface method is a novel way to mitigate electron cloud in high-energy and high-intensity particle accelerators. Aluminum alloy is a common and important material used in the vacuum system construction of particle accelerators. The influences of laser parameters, such as scanning speed and average laser power on the secondary electron yield (SEY) and surface morphology of laser processed aluminum alloy samples, were studied and explored in this paper. The as-received laser processed aluminum alloy surfaces with SEY less than 1 were obtained. The surface composition and topography were tested by the X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and laser scanning confocal microscopy (LSCM). The XPS results revealed that the surface of as-received laser processed aluminum alloys consists of aluminum oxide layer and intermetallic aluminum. The LSCM and SEM results show that the selection of appropriate laser parameters and hatched patterns was ascertained by the surface topography of the sample to obtain low-SEY surface.

Influence of laser parameters and complex structural features on the bio-inspired complex thin-wall structures fabricated by selective laser melting

The lobster-eye structure exhibits unique optical performance and finds its application in aerospace. However, the lobster-eye structure is highly complex and hard to process using traditional subtractive manufacturing methods. In this work, complex thin-wall structures, inspired by the lobster eye, were fabricated by selective laser melting (SLM) with AlSi10Mg powder. The influence of key laser parameter, namely laser power, on the densification behavior, dimensional accuracy, surface roughness and forming defect of SLM-processed lobster-parts was systematically investigated. Particular emphasis was placed on the impact of laser power and structural features on the inner surface roughness. Results revealed that the relative density of SLM-processed lobster-eye parts exhibited a similar trend with bulk parts against the laser power. The small dimension feature of thin-wall structures contributed to the higher relative density of lobster-eye parts comparing with that of bulk parts. The roughness of inner surfaces and outside surfaces showed completely different responds to the laser power, and the inner surface morphology behaved differently among positions. All these special surface phenomena were contributed to the combined impact of the laser parameter and the particular geometry of the lobster-eye structure. Finally, considering the optical function and post-processing, an optimal laser power was determined for the SLM-processing of lobster-eye components.

Influence of laser parameters on graphite morphology in the bonding zone and process optimization in gray cast iron laser cladding

The surface modification of gray cast iron through laser cladding produces a high-performance surface with low-cost materials, thereby reducing the manufacturing cost. This approach may considerably alter the phases in the bonding zone. In turn, the morphology of the graphite and adjacent phases influence the reliability and surface performance of the cladding layer. To optimize this process, this study performed numerical analysis and cladding experiments to analyze the carbon atom diffusion in graphite and examine the effects of scanning speed and laser power on graphite environment temperature, structural transformation, and graphite morphology in the bonding zone. The results showed that, in the case of constant laser power, as the scanning speed decreased, the diffusion of carbon atoms increased and became highly refined, thereby inhibiting poor graphite morphology and reducing micro-crack generation. At a constant scanning speed, the laser power slightly influenced the structure and macro-morphology of graphite. Considering the macro-morphology in the cladding layer and the micro-cracks in the bonding zone into consideration, we proposed that a laser power of 350 W and a scanning speed of 300 mm/min are the optimal process parameters.

The influence of laser parameters, scanning strategies and material on the fatigue strength of a stochastic porous structure

Additive manufactured (AM) porous materials behave quantitatively and qualitatively differently in fatigue than bulk materials, and the relationships normally used for the fatigue design of continuous bulk materials are not applicable to AM porous materials particularly for low stiffness applications.This study investigated how the manufacturing methods and the material used during powder bed fusion affects the compressive strength and high cycle fatigue strength of a stochastic porous material for a given stiffness. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing) and 4 materials. The materials investigated were two titanium alloys: commercially pure grade 2 (CP-Ti) and Ti6Al4V ELI, commercially pure tantalum (Ta) and a titanium-tantalum alloy (Ti-30Ta).The trends observed during fatigue testing for monolithic metals and statically for solid and porous AM materials were not always indicative of the high cycle fatigue behaviour of porous AM materials. Unlike their solid counterparts, porous tantalum and the titanium-tantalum alloy had the greatest fatigue strength for a given stiffness, 8% greater than CP-Ti and 19% greater than Ti6Al4V ELI. Optimisation of the laser parameters and scan strategies was found to also increase the fatigue strength for a given stiffness of porous AM materials by 7–8%.

Influence of Femtosecond Laser Parameters and Environment on Surface Texture Characteristics of Metals and Non-Metals – State of the Art

Enhancing the surface functionality by ultrashort pulsed laser texturing has received the considerable attention from researchers in the past few decades. Femtosecond lasers are widely adopted since it provides high repeatability and reproducibility by minimizing the heat affected zone (HAZ) and other collateral damages to a great extent. The present paper reports some recent studies being made worldwide on femtosecond laser surface texturing of metals, ceramics, polymers, semiconductors, thinfilms and advanced nanocomposites. It presents the state of the art knowledge in femtosecond laser surface texturing and the potential of this technology to improve properties in terms of biological, tribological and wetting performance. Since the texture quality and functionality are enhanced by the proper selection of appropriate laser parameters and ambient conditions for individual application, reporting the influence of laser parameters on surface texture characteristics assume utmost importance.

Influence of processing parameters on the structure size of microchannel processed by femtosecond laser

The processing of an ultra-short pulse laser is widely discussed and used in the field of micro machining, especially for precision processing of the hard and brittle materials. Firstly, the ablation ability would reduce with the defocusing distance increase in theory. However, it was found that the microchannel ablation depth is not sensitive to the defocusing distance in the experiments. The theoretical analysis and simulation calculation were carried out in this paper in order to explain the reason for the relationship between them. Secondly, the size of microchannel structure of the silicon wafer and quartz glass in our experiments were determined obviously by the main processing parameters of femtosecond laser. Furthermore, the influence of laser parameters on the structure size was studied. It was proven that the high quality processed of microchannel depend on the reasonable selection and combination of the parameters by femtosecond laser, which provided an important suggestion to process microchannel precisely.

Influence of laser parameters on the surface morphology of slurry-based Al2O3 parts produced through selective laser melting

PurposeThe purpose of this paper is to obtain high-performance ceramics and enrich additive manufacturing of ceramic parts. Also, a new manufacturing technique based on slurry by selective laser melting (SLM) was studied, which has some significant advantages compared to indirect selective laser sintering of ceramic powders.Design/methodology/approachTo study the effect of laser parameters on the surface morphology and melting state of pure Al2O3 ceramics, laser power varied between 100 and 200 W and scan speed varied between 60 and 90 mm/s.FindingsExperimental results show that Al2O3 slurry melts completely when the laser power is about 200 W and the scanning speed is 90 mm/s. Surface quality cannot be improved effectively by changing the scanning speed. However, surface quality improves when the laser power is 200∼205 W and energy density is 889∼911 J/mm3. Thermocapillary convection was observed during SLM. By changing the temperature gradient, streak convection and flowing Bénard cells were obtained during SLM of Al2O3 slurry.Originality/valueIt is feasible to produce slurry ceramic parts without binders through SLM. Increasing the laser power is the most effective way to fully melt the ceramics. Complex thermocapillary convection was observed during this new process; it may be used to produce crystals.

Influence of dilution rate on the microstructure and properties of FeCrCoNi high-entropy alloy coating

The influence of laser parameters and alloying elements on the dilution rate of FeCoCrNi coating was investigated. It was found that the alloying elements have more significant effect on the dilution rate than the laser cladding parameters. Optical microscopy, scanning electron microscopy, X-ray diffraction analysis, micro-hardness test, wear test, electrochemical corrosion test, and high-temperature oxidation test were conducted to study the influence of dilution rate on the microstructure and properties of the FexCoCrNi coatings. The results have shown that the transfer of Fe element from the substrate could make the mixed entropy of the Fe0CoCrNi coating close to the theoretical mixed entropy of the FeCoCrNi high-entropy alloy. Excess Fe element in the original powder increased the dilution rate, leading to a reduction in the mixed entropy of the coating. However, it did not lead to the generation of new phases in the coating. The atomic radius differences between the elements could lead to large lattice distortion in the FCC crystal lattice. The level of lattice distortion and micro-hardness of the FexCoCrNi coatings increased with increasing Fe element content. Furthermore, the excess Fe elements weakened the self-passivation ability and deteriorated the high-temperature oxidation resistance of the coating.

Application of millisecond pulsed laser for thermal fatigue property evaluation

An approach based on millisecond pulsed laser is proposed for thermal fatigue property evaluation in this paper. Cyclic thermal stresses and strains within millisecond interval are induced by complex and transient temperature gradients with pulsed laser heating. The influence of laser parameters on surface temperature is studied. The combination of low pulse repetition rate and high pulse energy produces small temperature oscillation, while high pulse repetition rate and low pulse energy introduces large temperature shock. The possibility of application is confirmed by two thermal fatigue tests of compacted graphite iron with different laser controlled modes. The developed approach is able to fulfill the preset temperature cycles and simulate thermal fatigue failure of engine components.