Effect Of Laser Parameters Research Articles

Modelling and optimization of process parameters to obtain maximum tensile strength for laser butt welding of 316L austenitic stainless steel sheets

The attribute of high power density but low energy-input in Laser welding offers exciting solutions to the commonly encountered disadvantages with conventional joining techniques.In this paper, 316L Austenitic Stainless Steel metal sheets were butt welded using Nd:YAG Laser welding system. Owing to its low cost and specific properties such as excellent toughness, higher creep, stress to rupture at elevated temperatures, 316L A.S.S finds wide range of applications in the industrial arena especially in the automobile and marine sectors. Hence, it becomes imperative to examine its post weld properties after performing laser welding and find optimized values of the parameters. The prominent process parameters like Laser Power, Travel speed and Focal length were analysed and optimised.Design of experiment statistical tool was embraced for the systematic conduct of the tests. Response Surface Methodology (RSM) and analysis of variance (ANOVA) techniques were employed to identify the significant process parameters affecting the weld. An empherical relationship involving the parameters was developed to predict the ultimate tensile strength. The 3D response surface plot and contour plots were generated for this model to elucidate the interaction effect of Laser parameters (Travel speed and Focal length), (Laser Power and Focal Length) & (Laser Power and Travel Speed) on Ultimate Tensile Strength.The welded specimens cut by electric discharge machining were prepared for tensile testing as per the ASTM standard. The Universal Testing Machine was used to test the welded specimen. Microhardness Testing was also carried out on the base material and the Heat Affected Zone (HAZ) using Vickers Hardness Testing machine. The tensile tested specimens were used for metallurgical analysis using Scanning Electron Microscope (S.E.M.). Specimen prepared for metallurgical analysis were sectioned, mounted, ground and polished in accordance with recommended procedures in ASTM practice E 3-11. The metallurgical observations showed the existence of undulating topography of ductile fracture surfaces. The investigations reveals that the actual values of the Ultimate tensile strength of the weld were falling close with the predicted strength obtained through the proposed model. It can be concluded that the proposed model in this work can be utilised to predict tensile strength of the weld with more precision.

Laser Induced Nano and Micro Structures of Molybdenum Surface Applied in Multistage Depressed Collector for Secondary Electron Suppression

The laser processing molybdenum metal surface method was first proposed to enhance the efficiency of multistage depressed collectors (MDCs). In this study, the secondary electron yield (SEY), surface geometrical morphologies and chemical states of laser processed Mo metal samples were characterized. For the first time, the effects of laser parameters and incident angle of primary electrons on the SEY property of laser induced nano and micro structures of molybdenum surface were investigated. The influence rule of laser processing patterns, power, pitch spacing, scanning speed on surface morphologies and SEY were systematically explored. A maximum SEY of laser processed Mo metal less than one was achieved. The Mo 3d and O 1s core level spectra of Mo metal before and after laser processing were analyzed in this study. Furthermore, the corresponding oxidation states of Mo as well as the relative distribution were elucidated.

Permutation entropy analysis of chaotic semiconductor laser with chirped FBG feedback

We numerically analyze the chaos complexity of a semiconductor laser with chirped fiber Bragg grating (CFBG) feedback by utilizing the permutation entropy (PE). Due to dispersion-induced nonlinearity of chirped grating, the time delay signature (TDS) can be suppressed or erased and the complexity enhancement is expected. The effects of laser parameters on PE as well as the TDS are studied in detail. The results show that for CFBG feedback, the TDS can be suppressed in the range of parameters where linewidth enhancement factor exceeds 3 and gain saturation coefficient is lower than 4×10−4μm3, and the complexity of chaotic signals is enhanced. As the feedback strength and bias current increase, the PE value under CFBG feedback increases linearly to a maximum of 0.994 and remains stable. Compared with mirror feedback, CFBG feedback can achieve increased complexity over a wider range of parameters. In addition, when the dispersion value of the chirped grating exceeds 2000 ps/nm, the frequency detuning range of -15 GHz to 10 GHz is beneficial to obtain chaotic signals with higher PE values.

Processing of Single-Walled Carbon Nanotubes with Femtosecond Laser Pulses

There are continued efforts to process and join single wall carbon nanotubes (SWCNTs) in order to exploit their exceptional functional properties for real-world applications. In this work, we report experimental observations of femtosecond laser irradiation on SWCNTs, in order to process and join them through an efficient and cost-effective technique. The nanotubes were deagglomerated in ethanol by an ultrasonicator and thin slurries of SWCNTs were spread evenly on glass substrates. A laser micromachining workstation for laboratory FemtoLAB (workshop of photonics) has been employed to irradiate the different SWCNTs film samples. The effect of laser parameters, such as pulse wavelength, laser power, etc., were systematically tuned to see the possibility of joining the SWCNTs ropes. Several experiments have been performed to optimize the parameters on different samples of SWCNTs. In general, the nanotubes were mostly damaged by the infrared (1st harmonics femtosecond laser) irradiation on the focal plane. However, the less damaging effect was observed for second harmonics (green wavelength) irradiation. The results suggest some joining of nanotubes along the sides of the focus plane, as well as on the center at the brink of nanotubes. The joining is considered to be established within the region of the high field intensity of the exposed femtosecond laser beam.

The Effects of Laser Parameters and the Ablation Mechanism in Laser Ablation of C/SiC Composite

The effects of laser parameters and the ablation mechanism in laser ablation of a carbon fiber reinforced silicon carbide (C/SiC) composite are investigated in the present study. Six different power densities are provided, as well as six levels of pulse numbers, and then ablation experiments are conducted for the C/SiC composite, induced by a pulsed laser. Based on the experimental results, the characteristics of surface morphology and ablation behavior are discussed. It is revealed that the surface morphology of the C/SiC composite under laser irradiation usually includes three regions: the center region, the transition region, and the border region. With the increase of laser power density, the ablation of the center region becomes severe, surface cracks occur, and more spherical SiC particles are found in the transition region. As for scenarios involving multiple pulses, the damage occurs in the center region at low power density limits, within the first two layers below the surface. However, if the power density is relatively high, an ablation pit occurs in the center region when the pulse number is larger than 50. Meanwhile, the transition region and the border region diminish with increase of the pulse number. It is noted that both the power density and pulse number have noticeable effects on surface morphology and ablation behavior during laser ablation, which is helpful for material design and performance evaluation of C/SiC composites.

Fabrication of CVD diamond micro-milling tool by hybrid machining of laser-induced graphitization and precision grinding

Owing to exceptional hardness and wear resistance, Chemical Vapor Deposition (CVD) diamond material is broadly used for micro-milling tools. However, the fabrication of CVD diamond micro-milling tool by a traditional grinding process is less efficient in terms of productivity and edge quality. In this manuscript, a novel hybrid machining process combining laser-induced diamond graphitization with precision grinding is performed to attain high-quality production of CVD diamond micro-milling tools. The effects of laser parameters on the phase transformation depth of the diamond, and the maximum peak-to-valley height of the boundary contour (Rt), are investigated. The influence of Rt on the cutting-edge quality is studied. Results have indicated that single pulse energy is directly proportional to the diamond phase transformation depth and Rt. In addition, the scanning speed and track displacement have an inverse relation with phase transformation depth and the Rt. Furthermore, a low value of Rt has provided better cutting-edge quality after conducting precision grinding. In order to improve the fabrication efficiency, a solution for roughing, semi-finishing and finishing processes is proposed. Based on the optimum parameters, a sharp CVD diamond micro-milling tool with cutting-edge radius of 2.5 μm and tool tip radius of 3.5 μm is fabricated. The case study has demonstrated that the proposed hybrid machining process improves the process efficiency.

Generation of textured diamond abrasive tools by continuous-wave CO2 laser: Laser parameter effects and optimisation

Textured Diamond Abrasive Tools (TDATs) have been attracted multitudes of attentions from both academic scholars and industrial engineers due to the reported superior grinding performances. However, the absence of appropriate fabrication technologies can still be considered as the bottleneck of wide applications of TDATs. To fill this gap, this paper utilised the continuous-wave CO2 laser to produce passive-grinding structures on the diamond abrasive tool surfaces. Not only the theoretical analysis of the non-metallic multi-material ablation threshold for diamond abrasive tools, but also the experimental investigation of the effects of both the laser power and the beam feed rate on both the topographies and morphologies of the produced structures were studied. The different structure generation mechanisms under different laser parameters were analyzed as well. Based on this, the strategy for selecting proper ablation parameters was provided. Various examples of the produced textured wheels were given in the end to prove the study significance and feasibility. The presented work was expected helpful to provide a new method for industries to produce textured grinding wheels in an efficient and low-cost way.

Hybrid Nanosecond Laser Processing and Heat Treatment for Rapid Preparation of Super-Hydrophobic Copper Surface

The super-hydrophobic copper surface was obtained by using a nanosecond pulsed laser. Different micro- and nano-structures were fabricated by changing the laser scanning interval and scanning speed, before heating in an electric heater at 150 °C for two hours to explore the effect of laser parameters and heat treatment on the wettability of the copper surface. It was found that the laser-treated copper surface is super-hydrophilic, and then, after the heat treatment, the surface switches to hydrophobic or even super-hydrophobic. The best super-hydrophobic surface’s apparent contact angle (APCA) was 155.6°, and the water sliding angle (WSA) was 4°. Super-hydrophobic copper is corrosion-resistant, self-cleaning, and dust-proof, and can be widely used in various mechanical devices.

One-step fabrication of multifunctional fusiform hierarchical micro/nanostructures on copper by femtosecond laser

In this paper, one-step fabrication of fusiform hierarchical micro/nanostructures on copper surface by femtosecond laser is proposed. According to the preferential valley ablation, Marangoni effect based on melt hydrodynamics and the coupling of the incident light and surface plasmon polaritons, the formation mechanism of the fusiform hierarchical micro/nanostructures is explained. And the effect of laser parameters including the defocusing distance, laser power, and scanning speed on the surface morphology is investigated. Also, the quantitative analysis of the fusiform tapers is carried out. It is demonstrated that the three-dimensional size of the fusiform hierarchical micro/nanostructures could be controlled by adjusting laser parameters. In addition, the potential applications of the fusiform hierarchical micro/nanostructures in microliter droplet directional transportation and light absorption are explored.

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.

Stereotaxic laser brain surgery with 1940-nm Tm:fiber laser: An in vivo study.

With exciting developments in fiber laser technology, studies investigating the use of lasers in neurosurgery have been increasing in the recent years. Fiber lasers are advantageous in many ways; first of all they are compact and they provide a more comfortable environment in the operating room due to feasibility of coupling laser light to different cross-sectioned fibers. Thulium fiber (Tm:fiber) lasers have been under investigation for medical applications since 2005 due to their spectral proximity to the water absorption peak. The primary aim of this study is to investigate the thermal effects of the 1940-nm Tm:fiber laser on subcortical tissue and to examine the effects of laser parameters on laser-induced lesions. Secondarily, it is also aimed to reveal the importance of temperature monitoring during laser surgeries by investigating the effects of temperature change on the characteristics of laser-induced lesions. Stereotaxic laser brain surgery was performed on 20 male Wistar rats, in order to investigate the thermal effects of Tm:fiber laser. During surgeries temperature changes in the subcortical tissue were observed with a t-type thermocouple for which a holder was designed to accomplish a 1 mm distance between the fiber tip and thermocouple tip. Histological examinations were performed on cresyl fast violet (CFV) stained slices under light microscopy. Photothermal effects of Tm:fiber laser on subcortical tissue were investigated in terms of ablated (removal of tissue), coagulated and edematous areas with a blinded micrograph evaluation. Relations between laser parameters, ablation efficiencies and rates of temperature changes were determined. Pearson's correlation coefficients between rates of temperature changes and ablation efficiencies, total laser damage and edematous area were calculated. No significant adverse effects were observed during surgeries. Histological examinations revealed localized ablation surrounded by coagulation areas as well as edema. Ablation efficiencies ranged from 20% to 50% with changing laser parameters. The correlation coefficient between rates of temperature change and ablation efficiencies, total laser damage and edematous area were rather high. In this study we show that Tm:fiber lasers seem to be useful tools in brain surgeries especially to vaporize and coagulate the tissue. It is also shown that temperature monitoring during laser surgery is very crucial and gives information about laser-induced lesion. Another take home message from this study is rather than the temperature increase, the rate of temperature change is more important. We found that if the temperature is changing in a short time interval, the extent of thermal damage can be minimized. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Thermal effects of ultrafast laser interaction with polypropylene.

Ultrafast lasers have been used for high-precision processing of a wide range of materials, including dielectrics, semiconductors, metals and polymer composites, enabling numerous applications ranging from micromachining to photonics and life sciences. To make ultrafast laser materials processing compatible with the scale and throughput needed for industrial use, it is a common practice to run the laser at a high repetition rate and hence high average power. However, heat accumulation under such processing conditions will deteriorate the processing quality, especially for polymers, which typically have a low melting temperature. In this paper, an analytical solution to a transient, two-dimensional thermal model is developed using Duhamel's theorem and the Hankel transform. This solution is used to understand the effect of laser parameters on ultrafast laser processing of polypropylene (PP). Laser cutting experiments are carried out on PP sheets to correlate with the theoretical calculation. This study shows that, in laser cutting, the total energy absorbed in the material and the intensity are two important figures of merit to predict the cutting performance. Heat accumulation is observed at low scanning speeds and high repetition rates, leading to significant heat-affected zone and even burning of the material, which is supported by experimental data and modelling results. It is found that heat accumulation can be avoided by a proper choice of the processing condition.

Control of wall thickness and surface morphology of tungsten thin wall parts by adjusting selective laser melting parameters

The tungsten thin wall parts which were used as high-performance collimator devices were fabricated by optimizing selective laser melting laser parameters. The effect of laser power and scan rate on wall thickness and surface morphology of tungsten thin wall parts was investigated, respectively. The results indicated that the wall thickness increased with the enhancement in laser power as a linear relationship. On the contrary, the wall thickness decayed exponentially with the acceleration in laser scan rate. Meanwhile, the wall thickness of the parts fabricated by laser double-pass melting was thinner than that fabricated by laser single-pass melting. In addition, mathematic models for selecting suitable laser power and laser scan rate to fabricate specified tungsten thin wall parts were proposed. Furthermore, the effects of laser parameters on the top surface roughness, adhesive parts and hot cracks were also discussed.

Computational analysis of heat transfer within a Ti-6Al-4V alloy substrate during laser cladding process

Heat transfer in materials during laser material processing serves as a key indicator to existing phases in the material, which governs the mechanical and chemical properties of the material during service. Without the knowledge of the property and behaviour of a material under service, loss of lives and values may be inevitable. This study presents the numerical modeling of the effect of laser parameters on the nature of phases present on the surface of Ti-6Al-4V alloy via heat transfer phenomenon. COMSOL 5.3a software was used to create a model of Ti-6Al-4V substrate, subjected to laser radiation during laser surface cladding. Boundary conditions were applied to the surfaces of the block samples while temperature distribution was measured with set boundary probes. Isothermal plots revealed that the material heating from the free surface was not sufficient enough to develop a large zone of phase change along the depth of the substrate. This was related to the high cooling rate of laser cladding.

Residual Stress Modeling and Simulation of Direct Metal Laser Sintered Ti-6Al-4V Alloy

Abstract Additive Manufacturing is able to accurately create layer wise deposition of a variety of materials from three dimensional CAD models. It is a competitive technology for the future as compared to subtractive manufacturing. This paper presents a Finite Element model of Ti-6Al-4V alloy popularly used for aerospace applications. Ti-6Al-4V alloy manufactured by the Direct Metal Laser Sintering (DMLS) technique was used to estimate the residual stresses developed in the specimen. It was found that the residual stress developed along the deposition path was always lower than the yield strength of the alloy. The process parameters are taken as per DMLS technique because this technique is popularly used for metals and their alloys specifically. The effect of laser parameters on the Ti-6Al-4V alloy was studied and the residual stresses generated in the DMLS technique were estimated by Finite Element Modelling.

Direct Laser Additive Manufacturing of Ceramics by Powder Deposition

In this study, LMD-CLAD® process (Direct Laser Additive manufacturing) is developed for alumina and Al2O3-Y2O3-ZrO2 ternary eutectic compositions. Powder flowability, laser-material interaction and thermal gradient control have been investigated. Powder granules of aforementioned compositions have been designed by spray-drying. Particle size distribution, Hall funnel test and SEM observations have been performed. Flowability has been improved by 20% in order to match with the LMD-CLAD® process by adjusting their density, size and surface quality. Otherwise, optical absorption of the ceramics has been increased up to 90% thanks to the addition of doping ions. With such a flowability improvement, laser powder deposition tests were successful and enabled us to investigate the effect of laser parameters and thermal environment on deposited beads state.

Thermal damage of aluminum honeycomb panel irradiated by continuous laser

Thermal damage of aluminum honeycomb panel (AHP) irradiated by continuous laser is studied in this paper. Firstly, facula radius and power density caused by defocusing are considered to model thermal damage of continuous laser. An accurate simulation model is established to calculate the shape of a damage hole. The relative errors of entrance hole and exit hole are less than 15 percent. The simulation results are in good agreement with the experimental results. Then, the effects of laser parameters on damage are experimentally investigated, and the damage rule of AHP irradiated by continuous laser is obtained. The experimental results show that edge diameters of entrance hole and exit hole increase with the use of higher laser power and smaller incident angle. A larger defocusing amount decreases edge diameter of entrance hole and increases the diameter on the edge of exit hole.

Microdrilling of Through-Holes in Flexible Printed Circuits Using Picosecond Ultrashort Pulse Laser.

High density and high quality interconnects are necessary for the preparation of miniaturized and lightweight electronic products. Therefore, small-diameter and high-density through-holes in FPCs (Flexible Printed Circuits) are required. However, the current processing methods cannot further decrease the diameters and improve the quality of through-holes. Comparatively, ultrashort pulse laser is a good choice. In this paper, the processing technology for the microdrilling of through-holes in FPCs using a 10 ps pulse laser was systematically studied. The effects of laser parameters, including the wavelength, energy, pulses and polarization, on the drilling of through-holes were investigated. The various processing parameters were optimized and the plausible reasons were discussed. Finally, the desired small-diameter and high-density through-holes in FPCs were obtained. The experimental results showed that, through-holes with diameters of less than 10 µm and inlet interconnection pitches of 0~2 µm could be successfully drilled in FPCs using ultrashort pulse laser.

Deep Engraving Process Of PMMA Using CO2 Laser Complemented By Taguchi Method

This work studies the effect of laser parameters on the engraving process. A CO2 laser beam with a wavelength 10.6µm was used for engraving a solid bulk of PMMA matter. A number of closely spaced parallel lines were used for filling the area of the matter to be engraved. This method has many advantages as compared with the traditional way such as, contact-less with the machine, high-speed, flexibility, versatility, high accuracy as well as complex forms and machining different material. In this paper, design of the experiment was done using L25 Taguchi methodology. The laser process parameter that has been used during the engraving process are laser beam power, scanning speed and line overlaps of the scanned beam each of them has different value (20,30,40,50,60 W), (100,300,500,700,1000 mm min−1 ) and (0.01,0.03,0.05,0.1,0.2 mm) respectively. To estimate the deep engraving and minimum surface roughness of the engraved surface. Furthermore, the results show that the engraving depth and surface roughness (Ra) interaction changes depending on the process parameter.

A Convenient and High-Efficient Laser Micro-Engraving Treatment for Controllable Preparation of Microstructure on Al Alloy.

Surface microstructure preparation offers a promising approach for overcoming the shortcomings of Al alloy, such as poor friction resistance, low hardness and weak corrosion resistance to corrosive liquid. Though many methods for the surface microstructure preparation of Al alloy have been developed, it is difficult for most of the reported methods to regulate the as-prepared microstructure, meaning that the properties of Al alloy cannot be improved efficiently by the microstructure. Thus, the application of microstructure surface of Al alloy and microstructure preparation technology is severely limited. Aimed at this issue, a simple, convenient, high-efficient, low-cost micro-scale roughness structure construction approach that is suitable for engineering application (laser micro-engraving) was developed. The as-prepared microstructure on Al alloy surface formed by laser micro-engraving was investigated systemically. The morphology and formation mechanism of the microstructure were examined. Meanwhile, the effect of laser parameters on morphology, geometrical dimensions and composition of microstructure was investigated. The results indicate that the morphology of microstructure is affected by the overlap degree of molten pool greatly. When each molten pool does not overlap with others, successive individual pits can be constructed. When each molten pool overlaps with others for one time, successive overlapping pits will form. As the overlap degree of the molten pool further increases (overlapping with others for more than one time), the successive pits can become grooved. Because of the influence of laser beam pulse frequency and scanning speed on the diameter and distance of the molten pools, the morphology and geometrical dimensions of microstructure can vary greatly with laser parameters. As the laser beam scanning speed increases, the geometrical dimensions of as-prepared microstructure reduce significantly. In contrast, with the increase of laser beam pulse frequency, the geometrical dimensions change in a complicated manner. However, the chemical composition of microstructure is slightly affected by laser parameters. More importantly, a relationship model was successfully established, which could be used to predict and regulate the geometrical dimensions of microstructure treated by laser micro-engraving. Controllable preparation of microstructure on Al alloy is realized, leading that specific microstructure can be prepared rapidly and accurately instead of suffering from long-time experimental investigation in the future.