Showing papers in "Journal of Laser Applications in 1999"
TL;DR: In this article, the laser beam weldability of AZ31B magnesium alloy was examined with high power pulsed Nd:YAG and continuous wave (cw) CO2 lasers.
Abstract: The laser beam weldability of AZ31B magnesium alloy was examined with high power pulsed Nd:YAG and continuous wave (cw) CO2 lasers. The low solid absorptivity, liquid viscosity, and liquid surface tension of magnesium make it more difficult to weld than steel. Welding parameters necessary to obtain sound autogenous welds were determined for both pulsed Nd:YAG and cw CO2 lasers. The weldability of magnesium was significantly better with the Nd:YAG laser. This observation was attributed to the higher absorption of the Nd:YAG beam, which in turn reduced the threshold irradiance required for welding and produced a more stable weldpool. The signal from an infrared weld monitor was correlated with both the penetration depth and the quantity of black powder on the workpiece after welding. The fine black powder was shown to result from evaporation of magnesium and zinc. The Nd:YAG welds were only slightly softer than the base material and had very narrow heat-affected zones.
73 citations
TL;DR: In this article, the authors present a survey of technical information that is currently available in the literature, commercial systems, and patents, for real-time monitoring of weld states, including acoustic emission, audible sound, infrared detectors, ultraviolet detectors, electromagnetic acoustic transducers, and polyvinylidene fluoride.
Abstract: On-line process monitoring is beneficial for maintaining high quality products at high production rates and low cost. Off-line traditional testing of welds can be costly in terms of time, material, and productivity. Real-time nondestructive testing, however, can be just as accurate as off-line testing; yet faster, cheaper, and increase productivity, when perfected for high volume repetitive applications. In the field of real-time monitoring, various sensors have shown promise in detecting weld states. These include acoustic emission, audible sound, infrared detectors, ultraviolet detectors, electromagnetic acoustic transducers, and polyvinylidene fluoride. Nevertheless, previous work indicates that no single sensor can reliably detect the full spectrum of weld states. As a result, sensor fusion has been investigated for integrating the advantages of individual sensors. This article presents a survey of technical information that is currently available in the literature, commercial systems, and patents, fo...
65 citations
TL;DR: In this article, a measurement system is produced by using three photodiodes for detection of the plasma and spatter signal in CO2 laser welding, and the relationship between the plasma or spatter and the bead shape was analyzed for the bead size estimation.
Abstract: On the laser weld production line, a slight alteration of welding condition changes the bead size and the strength of the weldment. A measurement system is produced by using three photodiodes for detection of the plasma and spatter signal in CO2 laser welding. The relationship between the plasma or spatter and the bead shape, and the mechanism of the plasma and spatter signals were analyzed for the bead size estimation. Penetration depth and bead width were estimated using multiple regression analysis and the neural network.
43 citations
TL;DR: In this paper, the effects of laser pulse width and peak power or intensity on machined feature quality were investigated for the following four laser systems: (1) a millisecondclass, free-running Nd:YAG; (2) a 100-nanosecond-class, Q-switched Nd :YAG laser; (3) a100-picosecondclass, mode locked Nd:,YAG, and (4) a Ti:sapphire chirped pulse amplification laser.
Abstract: Machined feature quality is examined, and the effects of laser pulse width (and thus peak power or intensity) are investigated for the following four laser systems: (1) a millisecond-class, free-running Nd:YAG; (2) a 100-nanosecond-class, Q-switched Nd:YAG laser; (3) a 100-picosecond-class, mode locked Nd:YAG laser; and (4) a 100-femtosecond-class, Ti:sapphire chirped pulse amplification laser. The effect of shorter laser wavelength is also examined by using the second harmonic wavelength of the Nd:YAG laser in the Q-switched and the mode locked pulse formats. Hole drilling and cutting of superalloy, ceramic, and composite materials are studied. The machined feature quality is improved as the pulse width becomes shorter and the peak intensity becomes higher. The shorter wavelength provides another significant improvement. Finally, an attempt is made to view these quality improvements in the context of process throughput and cost of ownership.
36 citations
TL;DR: In this paper, the results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view.
Abstract: The importance of light weight magnesium alloys, especially for the automotive industry, has grown significantly during the last years. To fully benefit from the whole designing potential of this material, joining processes have to be developed. Laser beam welding turns out to be very suitable to join magnesium parts. The results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view. The determination of the process window by analyzing the influence of laser type, power, welding velocity, and shielding gas, as well as the influence of the base material, leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are e...
32 citations
TL;DR: The largest commercially available excimer lasers generate up to 200 W stabilized average power and up to 700 mJ pulse energy at 308 nm as mentioned in this paper, which is one of the most common wavelengths for industrial applications.
Abstract: Ultraviolet (UV) lasers are in many ways ideal industrial processing tools. They offer a noncontact method of producing fine microstructures on many substances, with minimal effect on surrounding material. The most important type of high power UV laser for industrial applications is the excimer laser. Available wavelengths include 351, 308, 248, 193, and 157 nm. The largest commercially available excimer lasers generate up to 200 W stabilized average power and up to 700 mJ pulse energy at 308 nm. Nd:yttrium aluminum garnet (YAG) lasers that utilize nonlinear crystals to transform the 1.06 μm output to its third (355 nm), fourth (266 nm), or fifth (213 nm) harmonic are also an important industrial UV source. More and more diode-pumped, frequency multiplied Nd:YAG lasers greatly impact the industrial processing market. The advantage of this laser is that it is physically compact, highly reliable, and mechanically rugged. Coupled with advantages of short wavelength output, recent improvements in laser reliab...
31 citations
TL;DR: In this article, conditions for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet were determined for consistent welds on 0.8 and 1.8 mm sheets.
Abstract: Conditions were determined for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet. Full penetration butt and bead-on-plate welds on 0.8 and 1.8 mm sheets were performed. Process conditions examined included beam mode, spot size and irradiance, shielding gas flow, and edge quality and fitup. The observed weld quality variations with the different process parameters were consistent with physical phenomena and a threshold irradiance model. Optimal conditions were determined for obtaining consistent welds on 5182 alloy sheets. Formability and tensile tests were performed on the welded samples. All test failures occurred in the fusion zone. Reduction in formability and tensile strength of the welded samples are discussed with respect to weld profiles and process parameters.
24 citations
TL;DR: In this paper, a method for the numerical characterization of microcracking was developed for this work and was based upon scanning electron microscopy image processing, which enabled repeatable, high quality processing to be undertaken.
Abstract: The machining of ceramic components using conventional techniques is slow and expensive due to low yields. High power lasers are capable of machining these materials at far greater speeds. Recast layer microcracking is the Achilles heel of laser processing of ceramics. Techniques for the reduction of the thermal shear caused by laser beam interaction have been investigated. A method for the numerical characterization of microcracking was developed for this work and was based upon scanning electron microscopy image processing. Optimization of the pulsed Nd:YAG laser drilling and cutting cycles enabled repeatable, high quality processing to be undertaken. Heating of the partially stabilized tetragonal zirconia (PSTZ) substrates to high temperatures before and after laser processing was found to reduce the thermal gradients that cause microcracking. Holes with a mean diameter of 679 μm were percussion drilled through the 8.3 mm thick substrates in 0.75 s, and had limited tapering (<150 μm). Single pass, full...
23 citations
TL;DR: In this article, the authors used linear discriminant analysis of combinations of the plasma charge plus acoustic signals as well as all three sensor signals in combination produced a good separation between signals from full and partial penetration welds.
Abstract: Classification of laser weld penetration based on measurements of selected process emissions was investigated. Optical, acoustic and charged particle emissions were measured during CO2 laser welding of thin sheet steel butt joints over a range of laser power and travel speed. The values of the operating parameters were chosen so as to produce both full and partial penetration welds. The various sensor signals were compared to each other and were found to be significantly (but not totally) correlated. The frequency spectra of the signals from the full and partial penetration welds were processed using linear discriminant analysis. This statistical technique is designed to separate data corresponding to different conditions, facilitating recognition of the different conditions from measured signals. It was found that linear discriminant analysis of combinations of the plasma charge plus acoustic signals as well as all three sensor signals in combination produced a good separation between signals from full a...
23 citations
TL;DR: In this article, the results of ablation tests on cement and concrete samples using a pulsed Nd:YAG laser with fiber optic beam delivery were investigated as a means of removing radioactive contaminants from the surface and near-surface regions of concrete from nuclear facilities.
Abstract: Laser ablation was investigated as a means of removing radioactive contaminants from the surface and near-surface regions of concrete from nuclear facilities. We present the results of ablation tests on cement and concrete samples using a pulsed Nd:YAG laser with fiber optic beam delivery. The laser–surface interaction was studied on model systems consisting of type I Portland cement with varying amounts of either fine silica or sand in an effort to understand the effect of substrate composition on ablation rates and mechanisms. The neat cement matrix melts and vaporizes when little or no sand or aggregate is present, and energy dispersive x-ray spectroscopy showed that some chemical segregation occurs in the effluent of ablated cement. The presence of sand and aggregate particles causes the material to fracture and disaggregate on ablation, with particles on the millimeter size scale leaving the surface.
17 citations
TL;DR: In this article, a method for the numerical characterization of microcracking was developed for this work and was based upon SEM image processing, and the use of a high temperature furnace to heat substrates before and after laser processing reduced the level of recast layer microcracks by half, when compared to the ambient temperature process.
Abstract: The machining of ceramic components using conventional techniques is slow and expensive due to low yields. High power lasers are capable of machining these materials at far greater speeds. However, the performance of ceramic substrates is dependent on the quality of the processed region, with specific reference to the level of microcracking. The propagation of microcracks into the bulk substrate inevitably leads to component failure. Generation of recast layer microcracking is the Achilles heel of laser processing of ceramics. The fundamental process of laser radiation interaction with ceramic substrates generates a severe thermal gradient between the recast layer and bulk substrate. This in turn leads to the stresses which cause microcracks to form. Techniques for the reduction of this thermal shear have been investigated. Optimization of Nd:YAG laser drilling enabled repeatable and high quality processing to be undertaken. However, adaptation of these conventional techniques was required to reduce the level of recast layer microcracking. A method for the numerical characterization of microcracking was developed for this work and was based upon SEM image processing. The use of a high temperature furnace to heat substrates before and after laser processing reduced the level of recast layer microcracking by half, when compared to the ambient temperature process. However, sufficient microcracking was present to cause substrate failure. An unconventional plasma heating technique was developed and applied for the reduction of this cracking. For laser drilling at 1300 °C, the addition of localized plasma heating gave a further 14% mean reduction in recast layer microcracking. This advanced drilling technique also produced a 12% increase in mean hole diameter when compared to the furnace heating method.
TL;DR: In this article, the authors established a methodology to develop such "processing maps" and illustrate their utility by using laser cutting of mild steel and commercially pure titanium as case studies, which can be used to optimize the process on the basis of operational costs.
Abstract: Laser cutting is an attractive alternative to conventional cutting methods due to its many inherent advantages. However, notwithstanding its promise for processing diverse categories of materials, the understanding of the subject is incomplete. Although numerous processes are known to significantly influence cutting quality, comprehensive data of practical utility—such as identification of processing regimes to achieve optimum cut surface attributes—remain yet to be generated. The present article establishes a methodology to develop such “processing maps” and illustrates their utility by using laser cutting of mild steel and commercially pure titanium as case studies. The processing maps can be constructed based on any chosen cut quality criteria and can be used to optimize the process on the basis of operational costs. Results reveal that, for achieving good quality cuts, such processing regimes constitute only a narrow region within the wide operating window for mere cuttability and vary substantially with material-assist gas combination. Typically, the operating window for inert gas-assisted cutting is narrower than that for oxygen-assisted cutting involving an exothermic oxidation reaction, which contributes significantly to the overall energy input to the cutting front. The influence of the two major process parameters, laser power and cutting speed, on cut quality attributes such as surface roughness, kerf width, heat affected zone, and cut surface morphology is also discussed in detail. The experimental results have also been compared with theoretical predictions of a scaling law for laser cutting.
TL;DR: The American National Standards Institute (ANSI) Z136.1-1993 is now the fifth revision since 1973 as mentioned in this paper, which considers several major changes to revise laser hazard evaluation methods and laser classification for large sources.
Abstract: Z136.1 Subcommittee Chairs, William P. Roach and Benjamin A. Rockwell, led the efforts culminating in a draft standard by the end of 1998 which revised and updated American National Standards Institute (ANSI) Z136.1-1993. This is now the fifth revision since 1973. This draft standard considers several major changes to revise laser hazard evaluation methods and laser classification for large sources. For collimated laser diode systems additional factors needed to be considered in order to maintain a fair margin of safety between the maximum permissable exposure (MPE) and actual injury thresholds for circular sources—with and without optically aided viewing. New data on ultrashort laser pulses (subnanosecond) changed the MPEs that were based on “constant power” criteria at 1 ns, while demonstrating new effects adversely impacting laser safety eyewear. Signs and labels are now more in accord with the latest ANSI Z535 and International Electrotechnical Commission recommendations.
TL;DR: The American National Standard for outdoor laser light show safety has been developed for the past 4 years and publication may be as soon as this year as discussed by the authors. But the standard is not yet publicly available.
Abstract: Lasers are frequently used in an outdoor setting. Guidance is provided in this new draft American National Standard for this use. Unlike lasers used indoors, the user does not have complete control of the space encompassing the entire laser beam since light beams continue until they are stopped by an opaque object. The draft standard discusses proper coordination with local and Federal authorities so that lasers can be used outdoors in a safe manner. The development of the standard was prompted to satisfy both the need by the Department of Defense for a consensus standard, and the need to resolve safety conflicts between the laser light show industry and pilots who would occasionally fly through a demonstration laser beam. The standard has been under development for the past 4 years and publication may be as soon as this year.
TL;DR: In this paper, an experimental analysis was used to predict the significant effect of the weld quality using CO2 and high power diode laser (HPDL) laser welding, operating at 10.6 μm and 810 nm, respectively.
Abstract: Deep penetration welding with a high power CO2 and diode laser may offer an attractive means to join metal for certain applications, for instance: welding car drive shafts and gear plant. The rapid cooling rate of laser welding results in high hardness discontinuities across the welded joint; however, this leads to brittle weld and fatigue failure. To avoid this critical problem, it is useful to optimize the laser operating parameters in order to improve the mechanical properties of the weld. In this study, an experimental analysis was used to predict the significant effect of the weld quality using CO2 and high power diode laser (HPDL) laser welding, operating at 10.6 μm and 810 nm, respectively. Investigations into the weld quality were done to quantify the effect of different welding velocities by examining the hardness profiles, tensile strength, aspect, weld volume formation rate, and microstructure formation. In all cases, the results showed that for the HPDL weld configurations, cracking was observed in the fusion zone, whereas, for a CO2 laser weld, a greater weld strength and wider weld width were observed. For HPDL welding, center-line cracking was found along the fusion zone at higher welding velocities.
TL;DR: In this paper, a chemical oxygen-iodine laser (COIL) was used for cutting aluminum, titanium, inconel and copper plates, and the laser was operated with a stable resonator having an intracavity aperture to produce a circular COIL beam with few transverse modes.
Abstract: A chemical oxygen-iodine laser (COIL) was used for cutting aluminum, titanium, inconel and copper plates. The laser was operated with a stable resonator having an intracavity aperture to produce a circular COIL beam with very few transverse modes. The multimode focal spot diameter was calculated and measured to be approximately 0.24 mm. The new aluminum cut was of good kerf edge quality. These COIL cutting data are compared with an existing theoretical laser cutting model. Using thermophysical data for aluminum, titanium, inconel and copper, this theory agrees very well with the data. To test the versatility of the model, the effects of different assumptions are examined; different assumptions produced very little effect on model predictions at high cutting speeds and a small difference at very slow cutting speeds. Overall, the theoretical model provides good agreement with experiments for a wide variety of metals.
TL;DR: In this article, the authors reflect the latest achievements of Russian science in the field of creating laser combined technologies for medicine and discuss various types of such combinations, i.e., conjunction of laser and ultrasound for treatment of soft and hard tissues; application of acoustic effects for destruction of gall and kidney stones; combination of laser therapy and electrostimulation for treatmentof chronic prostatitis; utilization of laser-induced optoacoustic, vacuum, and hydrodynamic effects for transcutaneous drug delivery enhancement; unification of photo-and drug therapy for treating of inflammatory processes and f
Abstract: This article reflects the latest achievements of Russian science in the field of creating laser combined technologies for medicine. Lasers and several other therapeutic technologies are shown to supplement each other beneficially and in combination they can provide a significant increase in treatment effectiveness. This review deals with various types of such combinations, i.e., conjunction of laser and ultrasound for treatment of soft and hard tissues; application of acoustic effects for destruction of gall and kidney stones; combination of laser therapy and electrostimulation for treatment of chronic prostatitis; utilization of laser-induced optoacoustic, vacuum, and hydrodynamic effects for transcutaneous drug delivery enhancement; unification of photo- and drug therapy for treatment of inflammatory processes and festering wounds. Experimental and clinical results on combined laser technologies as well as the principles of feedback in complex therapeutic devices which involve optical, thermal, acoustic...
TL;DR: In this paper, the authors studied the ablation behavior of Al2O3-34 wt % TiC composite ceramic using 500 fs laser pulses at 248 nm and found that the roughness does not change significantly with the number of pulses for constant laser fluences.
Abstract: The micromachining of composite materials using excimer lasers has not yet been the subject of in depth investigations. In this work the authors studied the ablation behavior of Al2O3–34 wt % TiC composite ceramic using 500 fs laser pulses at 248 nm. It was found that the roughness does not change significantly with the number of pulses for constant laser fluences. The ablation rate decreases with increasing number of pulses reaching a stationary regime after 100 pulses. Characterization of the machined areas by scanning electron microscopy showed that a globular topography is responsible for the roughness of the samples. Increasing the laser fluence up to 12 J/cm2 increases the ablation rate for a constant number of pulses and decreases the surface roughness. At this fluence the measured roughness Ra was around 0.1 μm, when the original surface had a Ra≈0.05 μm. Chemical changes of the irradiated surface were investigated using Auger electron spectroscopy. Based on these results ablation mechanisms are s...
TL;DR: In this paper, the measurement of temperature fields inside and near the weld pool during laser welding was carried out using a charge coupled device camera equipped with infrared filters, and after calibrating the camera sensor and image processing, the temperature distribution in the welding pool and near melted zone was revealed.
Abstract: The work in this article deals with the measurement of temperature fields inside and near the weld pool during laser welding. The laser source used for this study is a 7.5 kW CO2 laser, and the welded material is a UNS N08904 austenitic stainless steel. The principle behind the actual experimentation is relatively simple: the welding operation is recorded with a charge coupled device camera equipped with infrared filters; after calibrating the camera sensor and image processing, the temperature distribution in the weld pool and near the melted zone is revealed.
TL;DR: In this article, the authors report on the production of nanosized zirconia particles by CO2 laser evaporation and derive a kinetic rate equation for the formation and growth of small particles.
Abstract: In this article we report on the production of nanosized zirconia particles by CO2 laser evaporation. The radiation source was a transverse flow CO2 laser operating in the continuous or the pulsed mode. Pulses between 1 and 500 μs duration could be generated by two different Q-switching techniques. The evaporation rates as well as the diameter of the particles and their density distributions were investigated with regard to their dependence on the laser power, the pulse shape, and the properties of the carrier gas. By means of simple models the experimental results could be interpreted. Furthermore a kinetic rate equation has been derived for the formation and growth of small particles. Good agreement is found between the experiments and this theory.
TL;DR: In this paper, a type of acoustic analyzing method based on chromatic modulation is presented, which offers not only much more acoustic information, precise distinction of the ambiguous signals, and robust monitoring in the laser processing system, but it could also make control of the laser process easier by simple chromatic output factors.
Abstract: The analysis of acoustic waves produced during laser materials processing is widely carried out for characterizing, monitoring, and controlling the process. Traditional methods used in analyzing the acoustic data such as rms signal strength and variation analysis, frequency spectrum analysis are based on signal intensity modulation which offers the advantage of inherent simplicity. However, these basic intensity monitoring systems tend to be sensitive to spurious changes in intensity resulting from variations in the various electrical components within the system and the noise of the industrial environment. In addition, it is known that the acoustic intensity is dependent on the distance and observation angle between its source and acoustic sensor. In this article, a type of acoustic analyzing method based on chromatic modulation is presented. Chromatic modulation offers not only much more acoustic information, precise distinction of the ambiguous signals, and robust monitoring in the laser processing system, but it could also make control of the laser process easier by simple chromatic output factors. It is also shown in this article how a chromatic modulation technique may be utilized as an acoustic analysis method to monitor the laser cleaning process. Consequently, it was found that the chromatic acoustic analysis method could be successfully applied for surface monitoring in the laser cleaning process and could provide correct monitoring information in spite of sensor stand-off variation.
TL;DR: In this article, a comparison of laser curing with convection oven curing has been done by studying the results of time-temperature profile, ac impedance, differential scanning calorimetry, and other characterization techniques.
Abstract: Curing of thermosetting powder coating is conventionally done in a convection or infrared oven. Powders requiring 10–15 min at cure temperature in a convection oven reportedly cure within 2–4 min in an IR oven. It has been shown that it is possible to achieve a much faster curing by using a cw CO2 laser. Laser curing has been studied as a function of laser intensity, laser beam size, and interaction time on different substrates. A comparison of laser curing with convection oven curing has been done by studying the results of time–temperature profile, ac impedance, differential scanning calorimetry, and other characterization techniques. The mechanism of laser beam interaction with the powder layer has also been discussed.
TL;DR: In this paper, a mathematical model is proposed to investigate the evolution of microstructures due to rapid solidification in laser materials processing, and the instability of solid-liquid interface is analyzed by considering the diffusion process and perturbation method.
Abstract: A mathematical model is proposed to investigate the evolution of microstructures due to rapid solidification in laser materials processing. The instability of solid-liquid interface is analyzed by considering the diffusion process and perturbation method. The results of this model show that the neutral stability curve is largely dependent on solidification rate and partition coefficient. The decay, periodic oscillation, and growth of the perturbations at the solid-liquid interface can be regarded as planar, cellular and dendritic microstructures, respectively. Laser spot welding experiments were conducted for stainless steel AISI 304 to verify the theoretical predictions.
TL;DR: In this paper, the authors conducted welding tests with full-penetration bead-on-plate welding and checked by radiographic test for welding defects, and the experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input.
Abstract: For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects. The experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input. Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the good appearance full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects. The experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input. Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the good appearance full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a l...
TL;DR: Using Fourier optic theory, this paper studied an optical device permitting the transformation of a high power laser beam into a quasihomogeneous square "spot" and compared theoretical results generated with software that they have developed to experimental results obtained using the optical device.
Abstract: Using Fourier optic theory we have studied an optical device permitting the transformation of a high power laser beam into a quasihomogeneous square “spot.” We have compared theoretical results generated with software that we have developed to experimental results obtained using the optical device. Comparison shows good agreement between the two approaches.
TL;DR: In this article, the characteristics of welding with multiple yttrium-aluminum-garnet (YAG) laser beams transmitted through optical fibers and combined at the focal point were investigated.
Abstract: We investigated two related topics as the first stage of our research: the characteristics of welding with multiple yttrium–aluminum–garnet (YAG) laser beams transmitted through optical fibers and combined at the focal point; and the study of methods of combining YAG laser beams. Each laser beam must be inclined in such a combined system. The plume and the penetration changed their direction from the vertical direction of the specimen to the parallel one of an irradiated beam, if the peak power or energy of the irradiated YAG laser beam exceeds a threshold value. In the two continuous wave YAG laser beams irradiation the form of plume and welding penetration were the same at the average angle of inclination of the two beams of 15° and at typical total power levels as those with a single and vertically irradiated beam to the specimen surface, but were split above the angle of inclination of 30° and total average power of 3.3 kW. Two keyholes would be formed under the split penetration condition. The three ...
TL;DR: Laser safety requirements in the U.S. are usually centered in specific Federal Government and voluntary standards such as: • The Laser Product Performance Standard of the Center for Devices and Radiological Health (CFR 1040.11).
Abstract: Laser safety requirements in the U.S. are usually centered in specific Federal Government and voluntary standards such as: • The Laser Product Performance Standard of the Center for Devices and Radiological Health (CFR 1040.10 and 1040.11) • The American National Standards Institute (ANSI Z136 Series) • The Occupational Safety and Health Administration (OSHA) • The Federal Aviation Administration (FAA 7400.2D) Laser safety requirements in the U.S. are usually centered in specific Federal Government and voluntary standards such as: • The Laser Product Performance Standard of the Center for Devices and Radiological Health (CFR 1040.10 and 1040.11) • The American National Standards Institute (ANSI Z136 Series) • The Occupational Safety and Health Administration (OSHA) • The Federal Aviation Administration (FAA 7400.2D)
TL;DR: The American National Standards Institute (ANSI), Z136 Executive Committee, has been reviewing and modifying a new draft standard developed by the Z136.5 subcommittee for Laser Safety in Educational Institutions as discussed by the authors.
Abstract: The American National Standards Institute (ANSI), Z136 Executive Committee, has been reviewing and modifying a new draft standard developed by the Z136.5 subcommittee for Laser Safety in Educational Institutions. The standard is expected to be published by the Laser Institute of America (Z136 secretariat) in early 2000. Major areas covered are: (1) Evaluating and minimizing hazards associated with laser radiation in educational institutions from elementary to university level. (2) The role of the laser safety officer in educational institutions. (3) Discussion of laser hazards, safety practices and controls at all grade levels. (4) Safe methods for using lasers in: laboratory experiments, classroom and lecture hall demonstrations, and science fair exhibits.
TL;DR: In this paper, a study of the alloying types and the influence of the laser operating parameters and the thermal properties of the materials was carried out, and it was found that properties such as the difference of the melting points between the coating layer and the substrate materials a...
Abstract: In laser surface alloying the distribution of alloying elements is mainly attributable to the convective behavior of the melt pool which is influenced by a number of factors including laser power density, size of the melt pool, interaction time, beam profile and the material physical properties. Any variation of the treatment conditions can change the flow pattern and the distribution of alloying elements in the melt pool. The laser alloying process reported in this article includes the steps of predeposition of multiple layers of different metals and subsequent alloying of these layers using a high power CO2 laser. A visible distinction between the alloyed and unalloyed regions or a difference in other physical properties is obtained. The work involves a study of the alloying types and the influence of the laser operating parameters and the thermal properties of the materials. It was found that properties such as the difference of the melting points between the coating layer and the substrate materials a...
TL;DR: In this article, the influence of laser surface processing on the microstructure of α-Al2O3 was investigated using a CO2 laser with a maximum power of 3 kW.
Abstract: Applying metallic coating to ceramics via laser surface processing is an attractive process, due to the ability to reach relatively thick surface coatings, which include reaction products formed between the metal and ceramic. Two main effects must be characterized to implement such processes: damage to the ceramic due to thermal shock, and changes in the ceramic microstructure due to the process. This study focuses on the influence of laser surface processing on the microstructure of α-Al2O3. A CO2 laser with a maximum power of 3 kW was used for the study. The laser beam was scanned across the polycrystalline alumina substrate under argon at a rate of 0.66–2.0 cm/s. Specimens were prepared at laser powers ranging from 200 to 800 W, with a constant beam diameter of 0.2 cm. The substrates were preheated to 400 °C before the laser treatments to minimize thermal shock. The alumina substrates were 96% pure alumina plates, with a thickness of 2 mm. The microstructure within the melt pool varied strongly as a fu...