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Principles of Laser Materials Processing

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... Since the early 1970's, lasers have been widely utilized in the machining of metallic materials. More recently, lasers have been utilized in machining non-metallic materials, such as ceramics, polymers, woods, biomaterials, composites, dielectrics, and semiconductors for various industrial applications [6]. The capability of pulsed lasers to produce precise sub-micron features in demanding materials such as ceramics and semiconductors has generated a strong interest in understanding the parameters that influence quality and speed of the process. ...
... The capability of pulsed lasers to produce precise sub-micron features in demanding materials such as ceramics and semiconductors has generated a strong interest in understanding the parameters that influence quality and speed of the process. A significant amount of studies have been carried out to investigate laser micromachining that encompasses different aspects of the machining process [6] and the physics of laser-material interaction [7][8][9]. ...
... There are several important parameters that are often used to describe laser pulses [6,29,30]. As illustrated in Fig. 1, the laser pulse duration is defined as full width at half of the maximum amplitude (FWHM) of the laser pulse. ...
Article
Over the last decade, lasers have been gradually employed for Si wafer dicing to replace blade dicing. Laser dicing has the potential to replace blade dicing as the future generation ultrathin wafer singulation method as it enables higher cutting speed, lower damage, and smaller kerf width but various technical challenges still remain to be resolved. In this article, laser ablation and dicing of Si wafers are reviewed in terms of the physics of laser-material interaction based on nanosecond, picosecond, and femtosecond pulse durations. The effects of various laser settings, dicing process parameters, and material factors on ablation rate, ablation precision and quality, and die fracture strength are discussed in detail. With the increasing usage of Cu stabilization layer on the backside of ultrathin Si wafers, we also review laser-material interaction in Cu and elaborate on recent findings on the effects of laser dicing through Si and Cu simultaneously on the microstructural and fracture strength properties of the die. Various approaches to improve the ablation rate, ablation quality, and die fracture strength are discussed.
... During this process, the metal vapour, consisting of ultra-fine particles, is generated above the surface by ejection from the keyhole and it continuously rises above the surface. This forms the weld or plasma plume [40,50,51], which can partially absorb the laser beam. For keyhole stabilisation, a pressure higher than the surrounding atmospheric is needed. ...
... vapour, consisting of ultra-fine particles, is generated above the surface by ejection from the keyhole and it continuously rises above the surface. This forms the weld or plasma plume [40,50,51], which can partially absorb the laser beam. For keyhole stabilisation, a pressure higher than the surrounding atmospheric is needed. ...
... Therefore, most of beam energy is absorbed at the keyhole walls. As a result, the keyhole is a cavity filled with vaporized material which melts surrounding metal [40,51,58,59]. ...
Article
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Aluminium alloys are widely used in many industries due to their high strength-to-weight ratios and resistance to corrosion. Due to their specific thermophysical properties and intricate physical metallurgy, these alloys are challenging to weld. Work-hardened alloys may experience strength loss in heat-affected zones (HAZ). The strength of precipitation-hardened alloys is severely damaged in both HAZ and weld metal due to coarsening or full dissolution. The high thermal conductivity and reflectivity of aluminium causes lower laser beam absorptivity with lower processing efficiency. Weld imperfections such as porosity, humping, and underfills are frequently formed due to the low melting point and density promoting high liquidity with low surface tension. Porosity is the most persistent imperfection and is detrimental for mechanical properties. In this work, extensive review was made on laser beam and laser-arc hybrid welding of aluminium alloys. Solidification cracking, evaporation of alloying elements, porosity and keyhole stability, and other challenges are studied in detail. The current development of laser welding of aluminium alloys is not so mature and new discoveries will be made in the future including the use of newly developed laser systems, welding consumables, welding methods, and approaches.
... For transparent materials, the reflectivity = 1 − Transmissivity + Absorptivity. The reflectivity at a simple two material interface, such as an air-metal can be described using the following equations [2], [37]: ...
... Where ñ is the complex refractive index, n is the real refractive index, c is the speed of light in a vacuum and v is the speed of light in a medium. If we assume the refractive index of air is equal to 1, the reflectivity from different polarisation states can be approximated using equations 5, 6 and 7 which are polarisation dependent [37]. ...
... According to the Beer-Lambert law [2], [37], the propagation of an electromagnetic wave through a material can be described by the following simplified wave equation of the time dependent electric field propagation in a vacuum: ...
Thesis
Light-matter interactions are fundamental to many technologies used today. They are complex, non-linear processes sensitive to the properties of the source, material, mechanisms, and environment in which they interact. In order to control a process, its key features must be measurable and characterised. To date, most efforts in doing so follow either empirical or theoretical approaches, requiring existing or potential users of laser technology to invest significant time and money in their attempted use. In this work a novel diagnostics platform is theorised for the study of light-matter interactions by assessing energy transfer within a process relative to certain performance attributes e.g. ablation efficiency (kg/W), coupling momentum efficiency (N.s/W) and kinetic energy ratio (plume energy over pulse energy) with the aim of producing widely relatable results which significantly lessen the need for heavily empirical or theoretical work. The missing element of the diagnostic platform, a torsion balance, capable of measuring impulsive forces and mass loss, was designed, constructed, and calibrated to the ultra precision standards required to measure nano-scale forces including a force and mass-loss resolution of nN and µg respectively. The tool was then used to characterise the behaviour of some ‘generic’ pulsed nano-second light matter inactions with varying source parameters such as total energy input (58.6 mJ to 468.8 mJ), repetition rate (5 kHz to 40 kHz), temporal pulse shape (up to 500 ns duration and 50 kW peak power), and materials (aluminium, silicon, and PVC), as well different environments (air and vacuum) and processing strategies (scanning and single point drilling). Three dimensional processing maps were then produced using the torsion balance, laser, environment, and material data to represent the quantitative and qualitative nature of results. When convoluted or stitched together, the maps uniquely enable the optimisation of process specific performance with respect to laser, material, and environmental parameters, to which the torsion balance data was very sensitive (ablation efficiencies from 10-7 to 10 13 kg/W, coupling momentum efficiency from 10-4 to 10-9 N/W and kinetic energy ratios from 10-5 to 437 %). Regions of high or low performance, could be easily identified using the qualitative map elements, whilst being relatable to quantitative data such as total energy, repetition rate and pulse shape, which are in turn relatable to theory using conventional methods. A single data set, for example, ablation efficiency plotted against total number of pulses and repetition rate for a given pulse shape, material, and environment, could be captured and processed in 16 minutes. In this work the ability to generically optimise a laser based process or technology very easily, quickly, and efficiently was demonstrated. For the first time, this has enabled high parameter resolution, light-matter-environmental parameter sweeps to be produced within hours, instead of months or years. This is important because it could revolutionize the way light-matter interactions are approached and completely change where time, energy and financial resources are spent in academia and industry. The end result could be the production of a well-defined process map for any given laser, material, and environment.
... There are many parameters that affect the laser material interaction, it can be divided into two topics, one is related to the laser beam parameters and the other is obeyed to the material properties, these parameters have been explained extensively before in many references [13,14], it will be mentioned here without details. ...
... This form of drilling involves using a single pulse of laser beam, the material in contact with the laser beam is partly melted and partly evaporated, and blown out backward using a gas jet to form the hole [13]. ...
... The melt pool is being pushed out by the recoil pressure [22]. One disadvantage of percussion drilling is that the material that is removed is blown backward toward the lens [13]. Normally, a high peak power is desirable to promote material removal by vaporization rather than melting, and the high vapor pressure generated in the process also serves to efficiently eject molten material, thereby suppressing formation of recast layer [23]. ...
Thesis
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In this study, drilling alumina ceramic 10.5 mm in thickness has been carried out using Nd:YAG millisecond laser. Effects of the laser peak power, pulse duration, repetition rate and focal plane position have been determined using images taken from the cross-sections of the drilled alumina ceramic samples, these images have been taken by optical and scanning electron microscopy. In addition to the dimensional analysis of the samples, microstructural investigations have been realized, like studying the grain shapes and directions and grain growth after varying laser beam parameters. It has been observed that, depth of the crater can be controlled as a function of the peak power and the pulse duration for single laser pulse application without any defect. Crater depth can be increased with the increase in the number of laser pulses for 10.5 mm, but in this case some defects are likely to occur like; formation of a huge resolidified material on the hole entrance, that will affect the hole shapes and diameters. The experimental work has been supported by a computational work where conditions have been simulated using ANSYS FLUENT 6.3 package code. Good compatibility with the experimental results have been indicated.
... An important point of view should be considered when drill with laser is the selection the suitable type of laser, which produces the power density required to form high quality holes. [4] Laser drilling process is associated by basic parameters classified as beam characteristics (pulse energy, pulse duration, number of pulses, beam quality), drilling characteristics (hole diameter, depth, drilling angle) and process defects [5]. ...
... Power density has great affect on heat generated during drilling process; it can be determined by dividing incident power on the size of focus beam. The beam size, in case of Gaussian distributed laser beam, is known as the redial distance which the intensity of the laser is reduced to 1/e 2 or 13.5% of the max intensity about 87.5% of beam energy [5]. ...
... Figure (5) shows that at (64.5 W/mm 2 ) power density both materials have the same depth. Alumina ceramic has high melting point but in change have also high thermal conductivity. ...
Article
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laser drilling play an important role in special applications with high accuracy dimensions, this paper was focused on two types of ceramics; aluminum oxide (Al 2 O 3) and zinc oxide (ZnO) of 4 mm thick have been drilled by using continuous wave (CW) CO 2 laser. the exposure times applied were (20, 40, 50) sec and the other laser parameters were kept constant and to avoid large distortion, A comparison between the two kinds of ceramic are carried out to determine the effect of laser parameters on them. It founds that ZnO holes are cleaner than Al 2 O 3 holes. Experiments proved that Exposure time at 50 sec resulting in similar penetration depth of 1.5 mm for both materials. Also for exposure time 41 sec gives the same taper angle.
... It is composed of an Nd ions and crystal of yttrium aluminum garnet (YAG). It also operates in both continuous and pulsed modes [29]. Nd:YAG laser enables the overlap joining process successfully because its wavelength penetrates most thermoplastics of several millimeters thickness, while producing only small absorption. ...
... A diode laser is a semiconductor laser based on the principle of generating the combination of electronhole [29]. It plays a significant role in industrial applications as a power source with wavelength ranging from UV to IR radiation and power up to several kW [1]. ...
... Fiber lasers consist of a small diameter single-mode glass fiber with special doped silica core as an active medium, an inner cladding works as a waveguide for pumping radiation, and outer cladding that provides total reflection for pumping radiation. The generated laser radiation wavelength is classified according to the silica core doping type [1,29] . Table 3 displays the type of fiber lasers according to their wavelengths ranging from 990 to 2210nm. ...
... In particular, this applies to surfaces treated by laser hardening and laser alloying. It is considered [13][14][15][16] that laser treatment of the surface layer of metals and alloys is one of the promising methods for targeted modification of the structural and phase state, due to possessing great potential for controlling high input energy per unit volume and implantation of alloying elements. Due to the significant nonequilibrium of the ultrafast crystallization process during laser processing, the method enables us to obtain phases of variable composition and diverse morphology within local micro volumes of the material, which cannot be obtained under ordinary conditions. ...
... In general, when a laser acts on a metal, the energy of the laser beam is lost mainly on the excitation of the electronic subsystem, and this effect is most significant on the surface and decreases exponentially with depth. Nevertheless, laser processing allows us to obtain the thickness of a hardened layer that is quite sufficient for most cases from dozens of microns to 1.5 mm in depth of the hardened layer without melting the surface and up to 2-2.5 mm with minimal flowing [13][14][15][16]. ...
... This concept connects the properties of materials not with the initial microstructure, but with a dynamic nano-meso structure, which is formed under purely nonequilibrium conditions. With laser alloying, an increase in microhardness and other operational characteristics of the surface layer of the material is achieved not only due to structural as in laser hardening and phase transformations in the laser exposure zone, but also due to the creation of a new alloy that differs from the matrix material in chemical composition [13][14][15]. Depending on the components of the filler material (alloying element and flux) and the processing mode, solid solutions, mixtures of two or more phases, intermetallic compounds, carbides, nitrides, oxides, sulphides, borides and other compounds with increased microhardness can form in the surface layer. The thickness of the hardened layer for each matrix material depends mainly on the processing mode. ...
Article
Dynamic tensile strength and ductility were studied within the range of strain rates from 0.6 to 1.2 × 103 s−1 by applying the split Hopkinson bar method on aluminum bronze samples the surface of which was processed by laser hardening and laser alloying. A number of effects are found: laser surface treatment of the samples significantly reduces the plastic properties of the material and increases the conditional yield stress, the tensile strength values of processed and unprocessed samples are close to each other, oscillations of the yield stress are observed, which can be interpreted as a "yield tooth" phenomenon. Deformation mechanisms explaining these effects were proposed based on the structural heterogeneity of the hardened surface layer and the sample as a whole.
... Thus, microsecond pulsed laser processing can combine evaporation and melting removal at the power density of 10 6 W/cm 2 or more, as similar to the large electron beam polishing method, and this processing is useful for surface smoothing of metal molds. However, that power density in laser beam processing is transitional condition between heat conduction welding mode and keyhole welding one [6], and the processing type at that ...
... Thus, microsecond pulsed laser processing can combine evaporation and melting removal at the power density of 10 6 W/cm 2 or more, as similar to the large electron beam polishing method, and this processing is useful for surface smoothing of metal molds. However, that power density in laser beam processing is transitional condition between heat conduction welding mode and keyhole welding one [6], and the processing type at that power density dynamically changes depending on the amount of absorbed laser energy. The processing characteristics and the influence of laser pulse, such as duration and waveform have not been clarified yet at that power density. ...
Article
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Manual polishing has been commonly applied as finishing process for metal molds with complicated-shape, but it takes a long time to achieve required surface roughness. Thus, high-efficient polishing method and surface smoothing in micro-areas are required for precise molds. Therefore, the reduction method of surface roughness for metal mold was experimentally investigated by controlling the pulse duration and the waveform in microsecond pulsed Nd:YAG laser irradiation of 532 nm wavelength, which can achieve stable absorption of laser energy even for difficult-to-weld materials with high reflectance. The maximum height roughness can be reduced from 4.0 μm to 1.0 μm by setting an appropriate pulse duration. Excessive heat input generates the edge at the circumference of laser irradiated area due to the movement of molten material. However, control of pulse duration enables the reduction of edge formation. Shorter pulse duration from 2.0 μs to 4.5 μs can perform a wider range of power density without edge formation, compared with longer pulse duration. The range of power density without edge formation can be increased by controlling the temporal input power, which can improve the process controllability of surface smoothing of mold material.
... where k is the thermal conductivity, c p the specific heat capacity, ρ the effective density, t the time, T the temperature, and q s the rate of local internal energy generated per unit volume [20]. When no confusion would arise in the context, T(x, y, z, t) is abbreviated to T in the remainder of this paper. ...
... When a moving point laser source is acting on a large thick plate, the analytical solution of (1) in the steady state is the Rosenthal equation [20]: ...
Article
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Despite the advantages and emerging applications, broader adoption of powder bed fusion (PBF) additive manufacturing is challenged by insufficient reliability and in-process variations. Finite element modeling and control-oriented modeling have been identified fundamental for predicting and engineering part qualities in PBF. This paper first builds a finite element model (FEM) of the thermal fields to look into the convoluted thermal interactions during the PBF process. Using the FEM data, we identify a novel surrogate system model from the laser power to the melt pool width. Linking a linearized model with a memoryless nonlinear submodel, we develop a physics-based Hammerstein model that captures the complex spatiotemporal thermomechanical dynamics. We verify the accuracy of the Hammerstein model using the FEM and prove that the linearized model is only a representation of the Hammerstein model around the equilibrium point. Along the way, we conduct the stability and robustness analyses and formalize the Hammerstein model to facilitate the subsequent control designs.
... where k is the thermal conductivity, c p the specific heat capacity, ρ the effective density, t the time, T the temperature, and q s the rate of local internal energy generated per unit volume [20]. When no confusion would arise in the context, T(x, y, z, t) is abbreviated to T in the remainder of this paper. ...
... When a moving point laser source is acting on a large thick plate, the analytical solution of (1) in the steady state is the Rosenthal equation [20]: ...
Preprint
Full-text available
Despite the advantages and emerging applications, broader adoption of powder bed fusion (PBF) additive manufacturing is challenged by insufficient reliability and in-process variations. Finite element modeling and control-oriented modeling have been shown to be effective for predicting and engineering part qualities in PBF. This paper first builds a finite element model (FEM) of the thermal fields to look into the convoluted thermal interactions during the PBF process. Using the FEM data, we identify a novel surrogate system model from the laser power to the melt pool width. Linking a linear model with a memoryless nonlinear sub-model, we develop a physics-based Hammerstein model that captures the complex spatiotemporal thermomechanical dynamics. We verify the accuracy of the Hammerstein model using the FEM and prove that the linearized model is only a representation of the Hammerstein model around the equilibrium point. Along the way, we conduct the stability and robustness analyses and formalize the Hammerstein model to facilitate the subsequent control designs.
... bronze) and/or hard bers (e.g. carbon and glass) the structure properties extremely affect the process of laser cutting [10,11]. This is due to the signi cant differences between physical properties of polymer matrix and reinforcement materials as the published results from other researchers indicate [6][7][8][9][10][11][12][13][14][15][16][17]. ...
... carbon and glass) the structure properties extremely affect the process of laser cutting [10,11]. This is due to the signi cant differences between physical properties of polymer matrix and reinforcement materials as the published results from other researchers indicate [6][7][8][9][10][11][12][13][14][15][16][17]. In CO 2 laser cutting of Te on and Te on-bronze composite sheets, Davari et al. [10] showed that the upper kerf width for both materials was in order of 0.5 mm for a beam diameter of 0.35 mm. ...
Preprint
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Glass-fibre reinforced unsaturated polyester (GFRUP) is one the thermoset composites that has many applications in manufacturing productions. CO 2 laser cutting of this composite has been significantly developed in industries. It is believed that the presence of glass fibre network in the matrix of thermoset affect the laser cutting process of this composite. In addition, the three-dimensional matrix of monomers along with carbon atoms in the atomic network's joints can also influence the laser cutting parameters. The aim of this research is to experimentally investigate the effect of these complicated structural properties on the CO 2 laser cutting of GFRUP sheets. First, the maximum cutting speeds, in which the cut occurs, was obtained for various sheet thicknesses using a variety of powers. The kerf width was measured with using an optical stereo-microscope. Then, the laser cutting mechanism was discussed using the SEM of the cut edge surfaces. The volume cutting efficiency was also studied. The results indicate that the upper kerf width is wider than the lower kerf width. The upper kerf width is larger than the spot size of 0.3 mm. The chaotic striations on the cut edge surface are the re-solidified glass fibres and can be seen as something like stalactites which are in black due to the carbon dust. Opening of the lower kerf due to the shrinkage of the re-solidified glass fibre is reported as a phenomenon. The cutting efficiency decreases as sheet thickness increases.
... bronze) and/or hard fibres (e.g. carbon and glass), the structure properties extremely affect the process of laser cutting [10,11]. This is due to the significant differences between physical properties of polymer matrix and reinforcement materials [4,[6][7][8][9][10][11][12][13][14][15][16]. ...
... carbon and glass), the structure properties extremely affect the process of laser cutting [10,11]. This is due to the significant differences between physical properties of polymer matrix and reinforcement materials [4,[6][7][8][9][10][11][12][13][14][15][16]. In CO 2 laser cutting of Teflon and Teflon-bronze composite sheets, Davari et al. [10] showed that the upper kerf width for both materials was in order of 0.5 mm for a beam diameter of 0.35 mm. ...
Article
Full-text available
Glass-fibre-reinforced unsaturated polyester (GFRUP) is one the thermoset composites that has many applications in manufacturing engineering. CO2 laser cutting of this composite has been significantly developed in industries. It is believed that the presence of glass fibre network in the matrix of thermoset affects the laser cutting process of this composite. In addition, the three-dimensional matrix of monomers along with carbon atoms in the atomic network’s joints can also influence the laser cutting parameters. The aim of this research is to experimentally investigate the effect of these complicated structural properties on the CO2 laser-air cutting of GFRUP sheets. First, the maximum cutting speeds, in which the cut occurs, were obtained for various sheet thicknesses using a variety of powers. The kerf width was measured with using an optical stereo-microscope. Then, the laser cutting mechanism was discussed using the SEM of the cut edge surfaces. The volume cutting efficiency was also studied. The results indicate that the upper kerf width is wider than the lower kerf width. The upper kerf width is larger than the spot size of 0.3 mm. The chaotic striations on the cut edge surface are the resolidified carbon-glass fibres compounds and can be seen as something like stalactites which are in black due to the carbon dust. Opening of the lower kerf due to the shrinkage of the resolidified carbon-glass fibre compounds is reported as a phenomenon. The cutting efficiency decreases as the sheet thickness increases.
... On the other hand, the bottom portion along with the interface portion had a high-temperature gradient due to the conduction of heat to the substrate. Cellular or columnar dendritic structures are commonly observed for those cases where there are high-temperature gradients [35]. Thus, these types of microstructures were observed at the top and bottom portions of the coating. ...
... The middle portion of the coating had an equiaxed dendritic microstructure. The middle portion of the coating having a low-temperature gradient, solidified at the end of the molten pool solidification and resulted in equiaxed dendritic microstructure [35]. Fig. 11 shows the SEM images of the microstructure of the coating Ag1, Ag2, and Ag3. ...
Article
The laser coating of NiCrBSi in pure form as well as with the addition of lubricious Ag or WS2 has been developed on Ti6Al4V substrate. With the help of an IR pyrometer, real-time thermal history was monitored and correlated with the tribological properties of the coating. A matrix predominantly comprised of NiTi and NiTi2 and reinforced with hard phases like CrB, TiC, TiB2, Cr3C2 was formed for all the types of coatings. From the XRD and EDS analysis, it was observed that for the coating containing Ag, Ag was found to be present in elemental form, but in the case of coating containing WS2, WS2 got dissociated during laser processing and formed TiS2, an anti-friction phase. Effects of heat input on the tribological behavior of both types of coatings (in-situ generated lubricating phase TiS2 and ex-situ developed lubricating phase Ag) were analyzed with the help of real-time thermal history. For Ag-type coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 968HV, 0.25, and 2.21E-5 mm3/N-m respectively for lower power and higher velocity process parameters. For WS2 coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 1303 HV, 0.26, and 1.5E-4 mm3/N-m respectively for lower laser power and higher scan speed. Comparing both the coating, it can be stated that, low heat input led to a high cooling rate, low molten pool life, and a low peak temperature of the molten pool, which increased the lubricious phase in the coating thereby reducing the friction coefficient. The present study can be useful to develop the process maps for desired lubrication property of the coating by using real-time monitoring of the thermal histories during the laser coating process.
... The feasibility of using methods of laser exposure is determined by the possibility of a non-contact, strictly dosed intensive supply of energy to the surface of the product. During laser irradiation on a metal material, its temperature significantly increases over a short period of time, which leads to the diffusion enhancement [31][32][33][34][35]. The mechanisms of heat transfer during laser heating take into account the heat transfer into the bulk of the material. ...
Article
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Possibilities of using laser irradiation to enhance mass transfer in the solid phase of metallic materials in order to form structures with improved physical and mechanical properties were reviewed. The features of the diffusion mass transfer in metals and alloys under shock exposure were specified. In this case, the rate of diffusion processes of mass transfer can be significantly increased. The conditions for intensification of mass transfer in metallic materials by pulse-periodic laser irradiation were determined and the synthesis of nanoporous and composite oxide nanomaterials was described. A significant increase of the diffusion coefficient in a metallic material, in comparison to plain exposure to laser beam heating, was identified. It could be attributed to the synergy of heat exposure and laser-induced vibrations, mainly in the range of sound frequencies, as a result of a pulse-periodic laser irradiation. The condition for intensifying mass transfer in the solid phase of selectively oxidable metallic materials was identified as a non-stationary stress-strain state caused by laser-induced sound waves. The exploitation of this synergy effect permitted the implementation of a novel approach for the creation of structures of nanomaterials. At the same time, a targeted influence on mass transfer and the accompanying relaxation processes make it possible to achieve an increase in the efficiency of methods for processing metals and alloys.
... Laser forming stands out to be a complex thermo-mechanical process and involves a large number of factors that can have significant influence on the entire process. It has been reported, the salient parameters accountable for energy absorption into the work piece material during the laser forming process were the laser power and the scan speed along with the material absorptivity 33 . Thus, the current study, initially explores the effect of line energy, i.e., the ratio of the laser power to the scan speed on the bending angle. ...
Article
Open cell aluminium foam having high porosity has the potential to increase the efficiency of heat exchanger and also to be used for diverse other functions. However, being prone to fail easily under tensile mechanical load, their thermal forming using laser has been proposed in literature. This work investigates the effect of laser parameters, orientation-position-curvature of scan path, number of scans, and foam thickness on the bending angle achieved while forming 95% porous pure aluminium (99.7% aluminium) open cell foam plates using a diode laser. Further the capability of laser forming to produce developable and non-developable surfaces out of this foam has been demonstrated. Higher line energy gave higher bending angle. Under the same line energy, the combination of higher power-higher scan speed produced higher bending angle. In contradiction to laser forming of sheet metal, no saturation or reduction in bending angle per scan pass was observed with increase in scan pass number. This observation could be explained with the help of cell densification by previous scan passes leading to increase in coupling of more thermal energy for the subsequent scan passes. Scan path with increased curvature (or less radius) also produced higher bending due to higher amount cell collapse in the irradiated region.
... its thermal conductivity is high, which means it is more difficult to ionize [7][8][9]. It is possible to set the water pressure and gas flow levels separately using the machine interface. ...
Article
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Waterjet-guided laser machining is a novel process used for precision cutting and drilling of various materials and geometries. There are many noise factors in the process affecting the laser beam characteristics, namely the effective cutting length and laser power in the waterjet. Although these variables are mainly set by the laser and waterjet parameters, uncontrollable factors result in variations. Prediction methods such as regression or artificial neural networks provide accuracy up to a certain extent. Measuring the exact values of the laser beam characteristics is crucial for process planning and selection of the machining parameters, such as stand-off distance and number of cycles. In this study, two different real-time measurement methods related to image processing and acoustic signal processing are proposed, both of which provide instantaneous readings for the laser beam characteristics in a waterjet-guided laser machine.
... Multi-material vehicle structures are an effective alternative [2], which necessitates the development of a reliable, efficient and economical technique for joining dissimilar materials. One of the typical desirable pairs is aluminum alloy and advanced high strength steel, which are highly difficult to weld together due to their great differences in physical and mechanical properties [3]. Moreover, the large amount of brittle intermetallic compounds (IMC) formed during traditional fusion welding process will severely deteriorate the joint quality and initiate a fast rupture under applied stress [4][5][6][7][8]. ...
Thesis
Growing concerns on energy consumption increase the demand of lightweight vehicles. One of the most efficient solutions is to use multi-material structure. As a solid state process, friction stir welding (FSW) is promising for joining dissimilar materials. However, the processing window for achieving successful dissimilar joints is still narrow. Besides, a large axial welding force is required when steel is involved. In order to address these challenges, a material softening phenomenon, electro-plastic effect (EPE) is proposed to be incorporated into the process. In this research, first, EPE on various materials is systematically reviewed and a hypothesis is proposed for understanding the softening mechanisms. The effectiveness of EPE is then evaluated on one type of advanced high strength steel, TRIP 780/800 steel. Second, traditional FSW process is experimentally studied for joining dissimilar Al 6061 to TRIP steel. Effects of process parameters on joint microstructure evolution are analyzed based on the mechanical welding force and temperature measured during the process. Intermetallic compound (IMC) layer of FeAl or Fe3Al with thickness of less than 1 μm is formed at the Al–Fe interface in the advancing side. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Third, analytical and numerical models are developed for friction stir welding of dissimilar materials. For plunge stage modeling, the field variable is introduced to identify regions of steel and aluminum and define the generalized material properties. Conservation equations are separately developed at the two materials interface for the discontinuities. The stable welding stage is modeled based on Eulerian formulation using multiple phase flow theories. The developed model can capture the material and temperature distribution measured from experiments. Finally, high density electrical currents are applied to the FSW process. Plunge stage of FSW is studied on aluminum alloy Al 6061 and TRIP 780 steel respectively. Effective reduction of the axial welding force can be obtained with good repeatability. During the FSW of Al 6061 to TRIP steel, the axial welding force can be consistently reduced under various welding conditions, which is a synergic result of both electro-plastic effect and Joule heating.
... The equipment offers 2-kW continuous laser of medium power, the active medium being a fiber coated with ytterbium, output with 50-μm diameter, beam parameter product (BPP) equal to 6.3 mm.mrad, and 5 m in length. The laser wavelength is 1.07 μm, beam quality (M 2 ) of approximately 1, Gaussian distribution intensity TEM 00 [33], and a beam diameter of 0.1 mm. The details of the processing station where the laser is inserted are shown schematically in Fig. 1. ...
Article
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The discovery of new metal alloys and the technological advancement in welding processes are key resources for the aerospace industry to obtain cost reduction and better reliability. Thus, welded joints of dissimilar materials such as aluminum and titanium alloys have been explored due to their combined low density and high mechanical performance. Otherwise, welding of dissimilar metals may present deleterious factors to the welded joint as the formation of intermetallic and/or brittle second phase and residual stress. This project investigates the weldability of dissimilar welded joint (Al6013/Ti6Al4V) by laser beam welding. The approach will be done in terms of mechanical properties and microstructural characterization. For this purpose, optimal laser offset from the joint line and the related heat input has been found. It was observed that offset controls the amount of the intermetallic compound layer in the fusion zone. Large pores were observed on the Al side of the weld metal when the offset is zero. The microstructure on the aluminum side consisted of α-Al grains and the dispersed precipitates. Heat input and offset are also influenced in the volumetric fraction of the precipitates. Martensite α′ and secondary acicular α phase were found in the titanium side. Furthermore, intermetallic compound of TiAl base phase such as TiAl, Ti3Al4, and Ti2Al3 was formed. Tensile strength of welded joint was 60% of the Al alloy. In addition, for the same offset and higher heat input, there was an increase in the hardness of the interface.
... Control over these characteristics can be exercised by determining the grain size, number and position of lattice defects, impurities, and other substructural units, which requires the appropriate kind and localization of thermal treatment [4][5][6]. The unrivalled and most versatile tool for executing such a treatment is the laser, which is capable of various processing methods and transferring (inducing) precisely defined amounts of energy to confined or hardly accessible regions, all the while avoiding contact and causing vibrations [7][8][9]. ...
Article
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We considered possibilities of an application of diffractive free-form optics in laser processing of metallic materials in aerospace production. Based on the solution of the inverse problem of heat conduction, an algorithm was developed that calculates the spatial distribution of the power density of laser irradiation in order to create the required thermal effect in materials. It was found that the use of diffractive optics for the laser beam shaping made it possible to obtain specified properties of processed materials. Laser thermal hardening of parts made of chrome–nickel–molybdenum steel was performed. This allowed us to increase the wear resistance due to the creation in the surface layer of a structure that has an increased hardness. In addition, a method of laser annealing of sheet materials from aluminum–magnesium alloy and low-alloy titanium alloys was developed. Application of this method has opened opportunities for expanding the forming options of these materials and for improving the precision in the manufacturing of aircraft engine parts. It was also shown that welding by a pulsed laser beam with a redistribution of power and energy density makes it possible to increase the strength of the welded joint of a heat-resistant nickel-based superalloy. Increasing the adhesion strength of gas turbine engine parts became possible by laser treatment using diffractive free-form optics.
... Starting from the laser source, the beam passes through the thin-film filter (b) after which it is positioned and focused by a galvanometer scanner (c) in conjunction with an f-theta lens (d). In operation, a melt-pool is created (e) and in accordance with Planck's law, emits what is referred to as process light [31]. The emitted process light is partially recaptured by the f-theta lens and travels back up to the thin-film interference filter (b). ...
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Metal parts produced by Laser Powder Bed Fusion (L-PBF) are frequently used for demanding applications. To meet stringent safety and certification requirements, a better understanding of melt-pool behavior and stability during processing is desired. This work presents a novel, fast and economically feasible virtual sensing approach for accurate estimation of melt-pool depth and width during L-PBF of metals. In a first step, the melt-pool width is determined by GPU-based processing of images from a high-speed coaxial camera monitoring system. In a second step, a physics-based analytical model is used to calculate the melt-pool depth-to-width ratio from the processing conditions and material properties. In a third and last step, the results from the first two steps are combined to estimate the melt-pool depth. Experimental validation of these predicted melt-pool dimensions is performed on 316L SS single layer strips that are consecutively produced, cross-sectioned, polished and etched to reveal the actual melt-pool boundaries. The results indicate an average relative error on the predicted melt-pool depth of 9.9 % and 2.8 % for the full L-PBF parameter range and for the optimal parameter range respectively. This gives confidence in the predictive capabilities of a virtual sensing approach using coaxial camera images for the assessment of the melt-pool depth and process stability.
... Depending on the thickness of this oxide layer, white light is reflected differently from this layer and the underneath metal substrate [10]. This reflection of light and absorption of different wavelengths is perceived as distinct from the human brain [11]. To illustrate the laser-induced oxidation process, we adapted the generic oxidation process that was proposed by Maurice et al. [12], as shown in Fig. 2. ...
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... Blowholes are observed in FZ in Fig. 4 d. One of the reasons for the formation of blowholes could be the evolution of metal vapor in the molten pool because of a relatively higher rise in melt pool temperature at the lowest welding speed [35]. Another reason could be the evolution of hydrogen which is aggravated at low welding speeds as bubble growth is favored in a larger liquid region of the molten front [14]. ...
Article
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Surface properties play a critical role in the structural integrity of any component and this becomes even more critical for weld joints. Laser shock peening (LSP) is one of the non-contact methods which is getting popular in industries to enhance surface properties for improving service life, mainly fatigue of engineering components. In the present study, electron beam welding (EBW) of commercially pure (cp) titanium was carried out at constant line energy with varying scan speeds ranging from 1000 mm/min to 1600 mm/min and welding currents from 25 mA to 40 mA. The influence of the EBW parameters on microstructure, surface micro-hardness, tensile, and fatigue strength was investigated. The effect of LSP on mechanical and corrosion properties of EBW cp titanium was studied. LSP induced a significant amount of compressive residual stresses at the surface through plastic deformation and led to significant improvement in micro-hardness (7-10%) at the sub-surface region of the fusion zone due to finer grain structure. Further, appreciable enhancement in tensile strength (~ 15%) and fatigue life (~ 43%) due to strain hardening and changes in microstructure like twinning within grains was realized.
... To predict the size of the modified layer area to guide the selection of subsequent machining parameters and provide an explanation basis for the generation mechanism of new phases in the modified zone, a finite element model of laser temperature field is established for ceramic particles reinforced MMCs. The input of laser energy can be considered as the heat flux which is loading on the surface layer, and the power density of laser energy obeys the Gaussian distribution [19]. The laser beam center (x 0 , y 0 ) represents the maximum heat flux density, which decreases exponentially from the center to outside. ...
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SiCp/Al composites are extremely difficult to process due to excessive tool wear and poor surface integrity. This paper presents a novel material processing method combining laser surface melting modification and precision milling to improve the machinability and surface performance of this material. The surface layer laser modification experiments were carried out by controlling the parameters of the laser processing and the volume fractions of the reinforcements. The mechanisms of the laser surface modification at the optimized temperatures between 1397℃ and 2000℃ are revealed as follows: a) a portion of the SiC reinforced particles will react with the molten liquid Al matrix to form the needle-shaped Al 4 SiC 4 ternary carbide and faceted Si particles, together with Al and Al-Si eutectics, constitute the laser modified zone; and b) the remaining SiC reinforced particles sink into the bottom of the Al matrix molten pool to form the particles accumulation zone. Then, the precision milling experiments were conducted to investigate the differences in cutting force, tool wear, and surface integrity between the modified zone and the original zone. When the total depth of cut doesn't exceed the modified zone depth, the surface roughness and tool wear can be improved by 90.36 % and 61.03 %, respectively.
... The upper right inset represents the relationship between laser intensity and different definitions of beam waist related to a Gaussian beam profile, highlighting the 1/e 2 criterion used in this study [41]. The lower inset drawings represent the laser intensity output in a given position as a function of time for the burst pulse mode employed to control thermal damage [42,43]. The lower inset graphically illustrates the pulse width (τ p = 800 ps) and pulse-to-pulse (interpulse) separation (ca. 2 µs) on the left side. ...
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Controlled laser irradiation parameters using recently developed sub-nanosecond pulsed laser technology with emission wavelength in the near Infrared regime (1064 nm) have been assessed on a Pleistocene bone from the archaeological site of Sierra de Atapuerca, Spain. Burst pulse mode was employed to explore contaminant removal efficiency, while at the same time, assessing the degree of damage produced to the underlying original substrate surface. The surface morphology and composition of the deteriorated bone have been characterized, along with the effects of laser irradiation at 1064 nm, using Optical Microscopy (OM), Scanning Electron Microscopy–with Energy Dispersive X-ray Spectrometry (SEM–EDS), and X-ray Photoelectron Spectroscopy (XPS). The most effective laser cleaning parameters in burst mode have been identified in order to optimize the emission parameters of the laser, thus localizing its interaction within the outermost layers of contaminants and degradation products, avoiding damage to the underlying original bone surface. Hence, threshold cleaning and substrate damage values have been determined for this new sub-ns laser, paving the way to safer laser cleaning procedures that may be useful for the effective conservation of bone archaeological artifacts.
... Fig. 1 shows the spectrum transmittance characteristics of a 0.42-mm thick single-crystal sapphire substrate measured by near-infrared spectroscopy (Perkin Elmer Co. Ltd.: Spectrum One NTS). The transmittance at a wavelength of 10.6 μm was 1.5 %, and the absorption coefficient calculated using the Lambert-Beer law was 10.0 mm -1 (Elijah, 2009). Therefore, the laser beam irradiated on the single-crystal sapphire was almost completely absorbed at the surface, enabling a heat source for stress field generation. ...
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Over recent years, renewable energy technologies have focused on increasing performance and efficiency, and on the reduction of maintenance costs. In this work, thermal-sprayed Inconel 625 coatings have been studied as an alternative for concentrated solar power plants receivers. A low-power compact plasma spray system was used to deposit coatings onto two substrates: grade 22 ferritic steel and AISI 316 L austenitic steel. This system may be used for in-situ maintenance or repair purposes. The coatings were heat-treated at two temperatures: 520 °C and 800 °C, at different exposure times. The aim of this work was to evaluate the effect of this treatment on the adherence and solar absorptivity of the Inconel 625 coatings. The results showed that, at higher temperatures and longer exposure times, better adherence and absorptivity are achieved. Adherence values above 60 MPa were obtained due to diffusion in the coating-substrate interface. Additionally, absorptivity values above 93% were measured due to oxide formation on the coating surface during heat treatment. Furthermore, the highest temperature of the oxidized treatment reported the highest values of absorptivity. These results show that the developed Inconel 625 coatings could be considered as a possible alternative to improve the performance of concentrated solar power plants.
... Regarding this, numerous studies have been conducted for aluminum alloys with the propensity to hot cracking, mainly for alloys of the 2xxx, 5xxx, 6xxx, and 7xxx series. In particular, aluminum alloys with the alloying elements copper (Cu) and magnesium (Mg) tend to have a higher crack sensitivity [10][11][12][13]. From the material aspect, the alloy composition itself can also be changed by evaporation of volatile alloying elements (e.g., zinc (Zn)) during PBF-LB/M [4]. ...
Article
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Processing aluminum alloys employing powder bed fusion of metals (PBF-LB/M) is becoming more attractive for the industry, especially if lightweight applications are needed. Unfortunately , high-strength aluminum alloys such as AA7075 are prone to hot cracking during PBF-LB/M, as well as welding. Both a large solidification range promoted by the alloying elements zinc and copper and a high thermal gradient accompanied with the manufacturing process conditions lead to or favor hot cracking. In the present study, a simple method for modifying the powder surface with titanium carbide nanoparticles (NPs) as a nucleating agent is aimed. The effect on the micro-structure with different amounts of the nucleating agent is shown. For the aluminum alloy 7075 with 2.5 ma% titanium carbide nanoparticles, manufactured via PBF-LB/M, crack-free samples with a refined microstructure having no discernible melt pool boundaries and columnar grains are observed. After using a two-step ageing heat treatment, ultimate tensile strengths up to 465 MPa and an 8.9% elongation at break are achieved. Furthermore, it is demonstrated that not all nanoparticles used remain in the melt pool during PBF-LB/M.
... The current state of achievements in the field of physical characteristics of laser processing of metal materials is presented in various articles and monographs [1][2][3][4][5]. Numerous reference books describe in detail the use of laser devices in various industrial technologies. ...
Article
Possibilities of using diffractive optics in the laser material processing in the aerospace industry were showed. The applied of diffractive optics for shaping of a laser beam made it possible to obtain the specified properties of the treated materials. On the basis of the application of methods for solving the inverse heat conduction problem, an improvement in temperature field parameters in chromium-nickel-molybdenum steel during laser heat treatment was achieved. Good quality and uniformity in the processing depth across the width of the heat-affected zone and the absence of defects into the material were accomplished. A method for laser annealing of sheet aluminium-magnesium and low-alloy titanium alloys has been developed. The use of this method has made it possible to open up opportunities for expanding the forming capabilities of these materials and improving the precision of aircraft engine parts. A possibility of improving the operational properties of composite materials containing a sealing coating of aluminium-boron nitride and an intermetallic coating of a nickel-aluminium alloy as a sublayer was shown. An increase in the adhesion strength of gas turbine engine parts became possible due to laser processing using diffractive optics. It was shown that the application of pulsed laser welding with a redistribution of density of beam power and energy makes it possible to increase the strength of the welded joint of the nickel-based superalloy.
Preprint
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The discovery of new metal alloys and the technological advancement in welding processes are key resources for the aerospace industry to obtain cost reduction and better reliability. Thus, welded joints of dissimilar materials such as aluminum and titanium alloys has been explored due to its combined low density and high mechanical performance. Otherwise, welding of dissimilar metals may present deleterious factors to the welded joint as the formation of intermetallic and/or brittle second phase and residual stress. This project investigates the weldability of dissimilar welded joint (Al6013/Ti-6Al-4V) by Laser beam welding. The approach will be done in terms of mechanical properties and microstructural characterization. For this purpose, optimal laser offset from the joint line and the related heat input has been found. It was observed that offset controls the amount of the intermetallic compound layer in the fusion zone. Large pores were observed on the Al side of the weld metal when the offset is zero. The microstructure on the aluminum side consisted of \(\alpha\)-Al grains and the dispersed precipitates. Heat input and offset also influenced in the volumetric fraction of the precipitates. Martensite \({{\alpha }}^{{\prime }}\) and secondary acicular \({\alpha }\) phase was found in the titanium side. Furthermore, intermetallic compound of TiAl base phase such as TiAl, Ti 3 Al 4 , and Ti 2 Al 3 was formed. Tensile strength of welded joint was 60% of the Al alloy. In addition, for the same offset and higher heat input, there was an increase in the hardness of the interface.
Thesis
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The use of laser with continuous wave (CW) emission as an energy source in welding has revolutionized the industry. Its highly concentrated energy brought precision and versatility, accelerating productivity and reducing costs with welding defects and human faults. The precise control of the energy applied by the laser through an adequate use of hardware apparatus, processing capacity and software has opened up a range of possibilities regarding the beam-piece interaction. In this sense, the present study aims to evaluate the effect of the modulation of the laser output power, that is, the use of low frequency pulsation of the energy delivered to the samples, during the union of metallic materials, in order to observe the differences and possible improvements from the method in the weld bead. In this sense, the objectives of this work are, mainly, to use different parameters and modulation formats, and then to evaluate some general aspects of the welds coming, as welding depth, porosity, grain size and residual stresses in three different SAE steels, 1020, 1045 and 4140. The research project started from the continuous and modulated pulse laser welding of SAE 1020 steel specimens to confirm, through optical microscopy, the main research premise: obtaining weld beads of similar quality or higher than those of continuous power, always using equivalent average powers. The results were divided into steps. In the first part, the pulse frequency was varied, with the aim of evaluating the weld morphology as well as the presence of porosity through the radiographic method. Then, continuous and modulated welds were produced in SAE 1020 and SAE 4140 steels, aiming at the analysis of residual stresses through the blind hole method. The third part presents the grain size analysis of the weld using the EBSD technique and Vickers microhardness. Finally, different power delivery formats are applied in order to assess, through optical microscopy, the depth of penetration and the porosity of the beads. The results of the application of power modulation showed, for all tests in the keyhole regime, deeper weld beads. With regard to porosity, for welding speeds of 1 m / min, the welds showed different number of pores for different modulation frequencies, with the sample welded at 50 Hz showing less presence. The drilled hole tests showed similar values of residual stresses between the continuous and modulated welds, which suggests an advantage of the method, since the bead produced under the modulated power were approximately twice as deep. Grain size measurements, due to the complex structure and high degree of hardness in the weld region, could not be quantified via image analysis or EBSD, but Vickers hardness tests suggested, by exclusion, a reduction in the average grain size in the molten zone region. Finally, the variation in the shape of the modulated power showed little variation in the penetration of the weld and all tests performed at the speed of 0.75 m / min were free of pores. The power modulation brought several changes in the morphological characteristics and defects in weld beads produced by laser, bringing improvements in the aspects mentioned above, largely due to its greater ability to control the oscillatory phenomena present during welding, generating greater stabilization of the process through of well-determined pulse frequencies and power application ramps.
Article
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In the present paper, continuous Ytterbium Laser Systems (YLS) fiber laser hardening of cylindrical AISI 4340 steel specimens was studied using experimental and statistical analyses. Three laser parameters, namely laser power, laser feed speed, and sample rotation speed were selected to evaluate their influence on the depth of the hardened zone and the maximum surface hardness. Mathematical models were developed as a function of these three parameters and the analysis of variance (ANOVA) was used to conduct the statistical study. Microhardness measurements revealed three distinct regions in the heat-affected zone (HAZ) of all samples: the hardened zone (Z1) near the surface, with the highest value of hardness, the hardness loss zone (Z2), where hardness had started to decrease, and the overheated zone (Z3) adjacent to the core, with hardness values that were less than those of the base metal. Based on experimental measurements, a maximum surface hardness of 60.8 HRC was attained. Furthermore, the maximum depth of the hardened zone was observed as 500 µm. The microstructures of laser-hardened samples were studied using optical and scanning electron (SEM) microscopes. The hardened region appeared to have a hard martensitic microstructure. By comparing the predicted and measured data for maximum microhardness values, it was revealed that the models represent the experimental values with correlations close to 100%.
Article
Previous studies on the mechanism of laser polishing were limited to the melting regime, this paper proposed a numerical model for the melting and transition regimes of laser polishing, which coupled heat transfer, fluid flow, and material vaporization. Based on the model, the evolution of the temperature and velocity fields of the molten pool in laser polishing was presented. And the mechanism of surface topography evolution was revealed from the perspective of surface forces (capillary force, thermocapillary force, and recoil pressure), fluid velocity, and material removal. Furthermore, the corresponding relationships between surface forces, fluid velocity, and surface topography were determined. The contributions of surface forces and vaporization front velocity in laser polishing were investigated, and the reason for the formation of the bulge structure and the influence of laser power on it were analyzed. And the velocity direction change points which have a great influence on the surface evolution were found, and the method to determine the positions of these points was proposed. Besides, the surface roughness prediction after laser polishing was tried through the numerical model, and the maximum error between the predicted results and the experimental results is 14.9%. Therefore, this model can be used to optimize process parameters.
Article
Laser deep engraving is one of the most promising technologies to be used in wood engraving operations. In this method, a laser beam is used to ablate a solid wood bulk, following predetermined patterns. The sculpture is obtained by repeating this process on each successive thin layer. The degree of precision of the shape, the removal rate, and the surface quality during the engraving process strictly depends on the materials properties, the laser source characteristics, and the laser parameters. This work investigates the influence of the process parameters on the material removal rates by engraving redwood using a co2 laser working with a wavelength λ = 10.6 µm. The examined parameters were: the laser power, the scanning speed, and line overlapping space; each of them has a different value (20, 25, 30, 35, and 40 W), (100, 300, 500, 700, 1000 mm min⁻¹) and (0.03, 0.06, 0.1, 0.2, 0.3 mm) respectively. The working parameters were designed using the L25 Taguchi methodology for the design of the experiment. Experimental results showed that the co2 laser could successfully engrave the redwood, obtaining different engraving depths. The maximum and minimum depth obtained was 4.25 mm and 0.01 mm. the results show that the engraving depth interaction changes depending on the laser parameters.
Article
In this study, the failure behavior of laser-welded (LWed) lap shear (LS) specimens in copper (Cu) sheets with unequal thickness has been studied through experimental and numerical approaches. LWed LS specimens with unequal thickness represented the tab-to-electrode joints of batteries in a module. Quasi-static tensile testing has been performed for studying the load-displacement curves, failure loads, and failure modes of LS specimens and the stress-strain curve of Cu. Microstructures and failure modes of LWs have been examined by exploring the micrographs before and after the failure. Necking failure was observed at the heat affected zone (HAZ) in the upper right sheet of LWed LS specimens. Microhardness distributions of LWs were obtained to estimate the stress-strain curves of the fusion zone (FZ), HAZ, and base metal (BM). Based on the stress-strain curves, a two-dimensional plane strain finite element model has been developed for LWed LS specimens. In order to develop a damage criterion for finite element models to simulate the failure mode of LWed LS specimens, a series of quasi-static tensile tests for one shear, one smooth, and four notched specimens made of Cu were conducted to derive the equivalent plastic strains at the onset of damage ε¯Dpl and the corresponding triaxialities η. A damage criterion of BM (Cu) comprised of ε¯Dpl and η was developed. Then a damage criterion of HAZ where the necking failure occurred was estimated based on the damage criterion of BM and the maximum values of ε¯Dpl and η in HAZ derived by the finite element model subjected to the failure load. Finally, it has been concluded that based on stress-strain curves of FZ, HAZ, BM, damage criterion of HAZ, computational simulations of failure behavior of LWed LS specimens are in good agreement with the experimental results.
Thesis
Pulsed laser deposition (PLD) is a technique for depositing materials and PLD displays versatility and high growth rates. It can be used to grow active single-crystal materials, which can be used as planar waveguide lasers. During PLD, particulates can be embedded into the growing film, which can reduce the planar waveguide lasers optical-to-optical efficiency and degrade the physical characteristics of a grown film. The experiments presented in this thesis focus on reducing the density of particulates in PLD-grown films and using this knowledge to grow high quality, novel materials.Three particulate reduction techniques were investigated including a shadow-mask, segmented targets and bi-directional ablation. All of these techniques reduced the particulate density and bi-directional ablation was implemented as the new standard ablation regime. This novel technique increased target utilisation by 50%, target lifetime by 100% and demonstrated an average particulate density reduction of 80%. As a direct result of bi-directional ablation, films with losses down to 0.12 dB/cm were realised. The versatility of PLD was exploited to tune the lattice constant of a mixed-sesquioxide film to demonstrate a <0.1% lattice mismatch with sapphire. Waveguiding was realised for the first time in a 3% Yb-doped sapphire waveguide, a material that is impossible to grow via traditional crystal growth methods. A Yb:LuAG laser with cladding layers was demonstrated, for the first time with PLD, with output powers of 3.3 W. Using bi-directional ablation, an Er:YGG film was grown and 3.46 dB of gain was realised in a channel waveguide geometry. Previous attempts had not achieved any such gain due to high losses.The particulate reduction technique demonstrated in this thesis and the subsequent exploitation, pave the way for PLD as a commercially viable technique for waveguide fabrication. Without the drawback of high particulate densities, high quality optical devices can be fabricated via PLD that would compete with other growth techniques.
Article
In dual-phase (DP) steels, the morphology, distribution, and volume fraction of the martensite phase affect several properties of the metal. In this work, the DP600 steel was laser treated using an Yb:fiber laser with different process parameters. The objective was to map the laser surface hardening and construct a process chart. Additionally, force spectroscopy was proposed to evaluate microstructural phases stiffness. The elastic constant of ferrite from both the base material and the laser treated area was approximately the same, about 20% lower than that of martensite from the treated area. From the processes chart, conclusion was more intense hardening, with needle-like structures, but in thinner layers, requires specific energies of about 2.0 kJ/cm2, while greater volume of martensitic phase is accomplished at 4.0 kJ/cm2. Tensile yield increased 30%, though tensile strength augmented 5–10%. In addition, lower laser scanning velocities was more suitable to obtain greater volumes of martensite.Graphic abstract
Article
In this paper, the effect of laser overlap on the low-carbon and stainless steel are investigated. The analyzed samples are made of AISI 4130 low-Carbon steel and AISI 410 stainless steel with 50% overlap. The used laser is an industrial high-power diode laser with a continuous wave and a maximum power of 2 kW. Samples are fabricated using optimized levels for laser power, focal plane position, and laser scanning speed, and the heat-treatment process is done after that. The parameters and conditions for the laser hardening process of both samples are the same situation. Then, the microstructure analysis is done using OM and SEM. Besides, the hardness of the samples is tested in the hardening depth and width. The study shows that the hardness is improved for both samples at the overlap area, up to 762 hv for AISI 4130 and 675 hv for AISI 410. Also, in both samples the amount of ferrite phase has decreased.
Article
It is common to use argon as the shielding gas for laser conduction welding of thin aluminum parts with a filler wire in the automotive industry. However, defects such as skips (i.e., discontinuities), holes in the weld, or a rough weld surface are commonly found when using argon as a shielding gas due to poor wettability. A new shielding gas mixture was developed in this study. With the addition of small amounts of active gases to an argon-based mixture, the wettability of the weld pool was significantly improved, yielding decreases in defectivity, improved penetration of the weldment, as well as a more stable welding process. The developed shielding gas mixtures could improve weld quality when compared to pure argon in laser wire conduction welding of different types of aluminum alloys in coach joint configuration. Energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) were used to detect the nitrogen and oxygen concentrations in the weld. The results show there is no noticeable increase in the oxygen or nitrogen concentration in the weld zone compared to the base metal when using the developed gas mixtures as shielding gas. Rising displacement testing was performed, it is shown that the weld strength obtained with the developed shielding gas mixtures is no less than that obtained with argon.
Article
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Because of exceptional properties, such-as high unique strength, excellent flexural strength, easy manufacturing and light-in-weight, aluminium alloys and composites are prominently used in the automotive, aerospace and manufacturing industries. Surface treatment appears to be of great significance for the physico-chemical characteristics of metals and alloys, even when their long-term performance has been significantly reduced by wear resistance, and dimensional stability. Laser treatment for an alloy's surface morphology becomes one of the most appropriate and efficient ways of producing accurate microstruc-tures by quick heating and cooling methods. The effect of different input processing factors, including the laser power and scanning speed, on different composite materials such as ceramics, metals, or alloys has greater improvements on the surface morphologies when laser-treated. Delamination removal of such coatings from the substratum is often possible due to the difference in the elastic attachment of film to the substratum connected with the above processes. It is presented in this paper that, the laser treatment impact on surface properties of Al alloys and composites in detail. Besides this, the key challenges have been addressed through laser surface treatment as well as the associated consequences and trends are foreseen with this article that also concludes the directions for future research.
Article
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Counterfeiting of the products for healing is as old as trading, and it is difficult to quantify the magnitude of the problem. It is known that substandard and/or falsified (SF) medicines are a growing global threat to health, and they cause serious social and economic damage. The EU has a strong legal framework for medicines, it is mandatory to meet the requirements of Directive 2011/62/EU. Serialisation prevents SF medicinal products from entering the legal distribution chain. The present study is an extension of the original idea and aims to develop a laser technology-based method to mark an individual traceable code on the surface of the tablet, which technology can also be used for marking personalized medicines. The method is based on the ablation of the upper layer of a double-layer, differently coloured coating. The 2D code should be formed without harming the functional layer, and anyone with a smartphone integrated with a camera should be able to authenticate these drugs with a suitable application. The present findings confirmed that KrF excimer laser and Ti:sapphire femtosecond laser are efficient and reliable for marking. These should be promising candidates for pharmaceutical companies that would like to have additional protection against drug counterfeiters.
Conference Paper
Nowadays, traceability, combined with stable and constant identification of industrial parts, is becoming a crucial element of production processes. Laser marking of metal parts is a technology that shows many advantages compared to labeling, inkjet, or dot marking. The advantages include no consumables, faster cycle time, reliability and repeatability of the process, and stability of the markings. In this article, we aim to study the physics associated with the process of laser colour marking on stainless steel X5CrNi18-10 In a certain range of changes in the technological parameters of 20 W fiber laser. Different color characteristics of the surface are also discussed with regard to the laser parameters. The influence of the raster step, the relative speed of the laser beam, as well as the laser pulses frequency on the color marking process were studied. Test fields consisting of matrices of squares have been created. The laser marking is realized with different parameters for each square. Photographic material of the samples in the processing area is presented. A high-resolution metallographic microscope was used. A universal methodology was used to determine the saturation of the studied colors. Experimental studies were conducted several times in order to verify the repeatability of the results. The influence of the parameters of the laser process on the obtained concrete colour is analyzed and the results are summarized. Intervals of the parameters of processing under laser influence for obtaining a specific colour on this steel are also determined.
Article
Papilledema is a syndrome of the retina in which retinal optic nerve is inflated by elevation of intracranial pressure. The papilledema abnormalities such as retinal nerve fiber layer (RNFL) opacification may lead to blindness. These abnormalities could be seen through capturing of retinal images by means of fundus camera. This paper presents a deep learning‐based automated system that detects and grades the papilledema through U‐Net and Dense‐Net architectures. The proposed approach has two main stages. First, optic disc and its surrounding area in fundus retinal image are localized and cropped for input to Dense‐Net which classifies the optic disc as papilledema or normal. Second, consists of preprocessing of Dense‐Net classified papilledema fundus image by Gabor filter. The preprocessed papilledema image is input to U‐Net to achieve the segmented vascular network from which the vessel discontinuity index (VDI) and vessel discontinuity index to disc proximity (VDIP) are calculated for grading of papilledema. The VDI and VDIP are standard parameter to check the severity and grading of papilledema. The proposed system is evaluated on 60 papilledema and 40 normal fundus images taken from STARE dataset. The experimental results for classification of papilledema through Dense‐Net are much better in terms of sensitivity 98.63%, specificity 97.83%, and accuracy 99.17%. Similarly, the grading results for mild and severe papilledema classification through U‐Net are also much better in terms of sensitivity 99.82%, specificity 98.65%, and accuracy 99.89%. The deep learning‐based automated detection and grading of papilledema for clinical purposes is first effort in state of art. Papilledema detection from fundus retinal images.
Chapter
Volume 2A is a practical guide to aluminum and its engineering applications. It begins with a review of temper designations and product forms and the underlying physical metallurgy of aluminum alloys. It then examines manufacturing practices and techniques, focusing in critical areas such as casting, metalworking, heat treating, machining and finishing, surface treatment, and joining. It describes melt and solidification processes, high-integrity die casting, forging, extrusion, powder and additive methods, and the production and use of aluminum foams. The volume also discusses quenching, anodizing, organic and conversion coating, brazing, and laser welding, and offers insights on process selection, quality, performance, service ability, and other product lifetime concerns. For information on the print version of Volume 2A, ISBN: 978-1-62708-207-5, follow this link.
Conference Paper
This paper studied the effect of changing the traverse speed of laser on coating thickness after the laser glazing. Glazing process done by using CW CO2 laser of 100W to melt a thin sheet of soda lime glass with 0.15 mm average thickness on AISI 1075 High Carbon Steel sheet. The laser power were (7, 9 and 11)W after many pilot studies, with three traverse speeds of (0.3, 0.4 and 0.5) mm/s, while the minimum laser spot were set in three different positions were they 2 mm below surface (-2), on the surface (0) and 2 mm above the surface (2). The results show fine glass structure layer covers the steel substrate. The high thickness occurs at the slowest traverse speed and laser spot position above the surface.
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ASM Handbook, Volume 4A is the first in a series of five ASM Handbook volumes covering heat treating. This volume includes 50 articles that address the physical metallurgy of steel heat treatment and thoroughly cover the many steel heat treating processes. Fundamentals of hardness and the use of hardenability as a selection factor are discussed as are the fundamentals of quenching and quenching processes. The volume also discusses annealing, tempering, austempering, and martempering as well as cleaning, subcritical annealing, austenitizing, and quench partitioning. It also presents practical information on surface hardening by applied energy, carburizing, carbonitriding, nitriding, and diffusion coatings. For information on the print version of Volume 4A, ISBN 978-1-62708-011-8, follow this link.
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In this paper, the continuity and discontinuity analysis in deposited bead using Plasma Transferred Arc Welding (PTAW) process has been done through experiments and analytical approach. The calculated energies using experimental data points have been compared with the data points which are derived analytically using Rosenthal equations: line heat source and point heat source for different efficiencies. As a result, the continuous, discontinuous and partially continuous beads with respect to constant melt pool line have been identified. The energies for substrate melting per unit length and the sizes of the melt pool widths (bead widths) for the continuous beads are more compare to partially continuous and discontinuous beads.
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This study is aimed to investigate laser irradiation effects on the surface, structural, and mechanical properties of iron samples. The prepared samples have been treated for multiple exposure times using continuous-wave diode laser with a wavelength of 532 nm in a laboratory environment. The structural as well as surface modifications of laser exposed targets are explored via scanning electron microscope and X-ray diffractometer. The SEM analysis revealed micrometer grain size, exfoliational sputtering, and crater formation, while XRD patterns were used to investigate d -spacing, and grain size of laser exposed samples. The mechanical characteristics of laser-ablated materials were examined using a micro Vickers hardness-tester, and microhardness has been explored as a function of increasing laser exposure time. It has been observed that grain size reduces while hardness of polycrystalline iron increases with increase in exposure time.
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The compound-tunable embedding potential (CTEP) method developed for simulating the influence of environment on a fragment in the ionic-covalent crystal is presented in the form of a linear combination of particular short-range semilocal pseudopotentials for the atoms of nearest environment and the long-range Coulomb potentials from optimized fractional point charges centered on both nearest and more distant atoms of the environment. A pilot application of the CTEP method to calcium niobate crystal, CaNb2O6, is performed. A very good agreement of the electronic density and interatomic distances within the relaxed fragment with those of the original periodic crystal calculation is attained. Calcium niobate crystal can be considered as an idealized fersmite (CaNb2−xTaxO6,x≈0.3) mineral when neglecting the contributions of the impurities with smaller molar fractions, and substitution Nb→Ta is considered here as a point Ta defect in CaNb2O6. Besides, uranium-containing point defects are also studied since the euxenite group minerals, to which fersmite belongs, are considered as prospective matrices for long-term immobilization of high-level waste. The chemical shifts of Kα1,2 and Kβ1,2 lines of x-ray emission (fluorescence) spectra in niobium are evaluated to analyze its chemical state in the crystal. Potential of CTEP for studying properties of point defects containing f and heavy d elements with relativistic effects, extended basis set, and broken crystal symmetry taken into account is discussed.
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