bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain gauge analysis of laser forming
Authors: Edwardson S. P. , Watkins K. G. , Dearden G. , French P. , Magee J.
Published: June 2006

Laser forming has become a viable process for the shaping of metallic components, as a means of rapid prototyping and of adjusting and aligning. The laser forming process is of significant value to industries that previously relied on expensive stamping dies and presses for prototype evaluations. This investigation aims to complement the considerable amount of work already completed on two-dimensional laser forming, offering an insight into the mechanical behavior of a part during the process using a strain gauge analysis technique. The investigation was performed on mild steel CR4 sheet using a CO2 laser source. It includes empirical investigations to determine optimum processing parameters using the temperature gradient mechanism, thermocouple analysis to locate ideal strain gauge placement for temperature compensation, and strain gauge analysis of the transverse localized strains at a number of locations on the surface of the sheet during single and multipass laser forming. The results of the investigation demonstrate the relative complexity of the process even during a simple straight-line bend and that a residual strain component remains in the sheet after processing.
Laser rapid-alloy prototyping for the development of wear resistant Fe–Cr–C/NbC composite materials
Authors: Colaço R. , Vilar R.
Published: June 2006

In this article a novel methodology for the development of hardfacing materials, the so-called laser-assisted rapid-alloy-prototyping technique, based on variable powder feed rate laser cladding, is described. An Fe–Cr–C metallic matrix composite, reinforced with NbC carbide particles, was chosen as a case study for the application of the methodology. First, the criteria for the design of the matrix and type of reinforcement particles are described. Then, the approach used for the optimization of the materials composition and volume fraction of reinforcement particles is presented and discussed. The obtained results show that this methodology enables us to obtain, with promptness and flexibility, iron-based composite hardfacing materials, with optimized compositions, which are promising candidates for the replacement, in some applications, of cobalt-based alloys, with the additional advantages of presenting lower cost, better compatibility with steel substrates, and containing no cobalt in their constitution.
Induction heat treatment of laser welds
Authors: Bagger Claus , Sørensen Joakim Ilsing , Olsen Flemming O.
Published: June 2006

In this article, a new approach based on induction heat treatment of flat laser welded sheets is presented. With this new concept, the ductility of high strength steels GA260 with a thickness of 1.8 mm and CMn with a thickness of 2.13 mm is believed to be improved by prolonging the cooling time from 750 to 450 °C. Initially, a simple analytical model was used to calculate the ideal energy contributions from a CO2 high power laser source together with an induction heat source such that the temperature can be kept at 600 °C for 2.5 s. This knowledge was then used for the design of an induction coil. A number of systematic laboratory tests were then performed in order to study the effects of the coil on bead-on-plate laser welded samples. In these tests, important parameters such as coil current and distance between coil and sample were varied. Temperature measurements were made at distances of 0, 2, and 4 mm away from the virtual weld line for the induction heating process and at distances of 2 and 4 mm for the laser welding with induction heating process. For practical reasons during performance of these laboratory experiments, the induction coil was placed below the sheets, trailing the laser beam as close as possible. After welding, the samples were quality assessed according to ISO 13.919-1 and tested for hardness. The metallurgical phases are analyzed and briefly described. A comparison between purely laser welded samples and induction heat-treated laser welded samples is made. The temperature measurements show that, with the chosen mechanical setup of laser and induction coil, it is difficult to obtain a quick increase to around 300 °C, the temperatures required for efficient heat treatment with the induction coil alone. Despite this, a reduction in the hardness values of both GA260 and CMn were recorded when laser welded samples were induction heat treated. The reduction was 6%–8% for GA260 and 41%–45% for CMn, respectively. GA260 displays a ferrite structure in basic and welded form, whereas CMn, with ten times more carbon, shows a ferrite and bainite structure when laser welded. Thus, when induction heat treating, the carbon was better dispersed in the grains of CMn.
Surface melting of Al–Cu–Mg alloy using a short-pulse, planar waveguide CO2 laser for corrosion resistance improvement
Authors: Tsagkarakis M. G. , Villarreal F. J. , Baker H. J. , Hall D. R. , Williams S. W.
Published: June 2006

A newly available pulse format for planar waveguide carbon dioxide lasers has been investigated for surface melting treatment of Al-2024 using 35–40 μs duration pulses. A single-pass raster scan produces crack free surfaces, but with considerable surface modulation and stress. A double-pass treatment has been shown to relieve the stress and smooth the surface, restoring the corrosion resistance of the surface to that of the parent alloy.
Physics, chemistry, and laser microprocessing
Authors: Duley W. W.
Published: June 2006

This article discusses some basic concepts of laser processing when individual components have micron and submicron dimensions. Since joining and parting operations involve bond formation and bond breaking between atoms, the energy terms involved are quite similar in micro- and macroapplications. In fact, several elements of laser cutting and welding can be found in the laser-induced photochemical reactions of atoms and molecules. It is shown that there are no intrinsic wavelength limitations in laser processing of microsystems, as the scale length for processing is set by the dimensions of the part itself rather than by the wavelength of the light used. In addition, it is noted that conduction will be relatively unimportant in welding microcomponents.
Welding of thick austenitic stainless steel using Nd:yttrium–aluminum–garnet laser with filler wire and hybrid process
Authors: Jokinen Tommi , Karhu Miikka , Kujanpää Veli
Published: June 2006

Autogenous laser welding has shown many advantages over traditional welding methods in numerous applications. However, there could be even more applications, but due to the power levels of present high power lasers, depth of penetration is limited. One way to overcome this limitation is to use multipass laser welding, in which a narrow gap and a filler wire are applied. By this process thick sections can be welded with a smaller heat input and therefore with smaller distortions, and the process seems to be very effective compared to “traditional” welding methods. Another way to increase penetration and fill the groove is by using the so-called hybrid process, in which laser and GMAW are combined. In this study thick section austenitic stainless steel is welded using a multipass technique with filler wire, and also by utilizing a hybrid process. For narrow gap conditions, groove angles of 8°, 10°, and 12°, are used with a partially grooved V joint. Parameters (e.g, filler wire feeding, placement of wire, and arc) are varied. Results of the experiments are presented and phenomena of the process, as well as reasons for weld defects, are pointed out.
Laser-induced electrochemical characteristics of aluminum alloy 2024-T3
Authors: Kachurina Olga , Metroke Tammy L. , Dou Kai
Published: June 2006

Laser-induced surface modification of aluminum alloy 2024-T3 was investigated as laser intensity dependence of surface composition and patterning related to electrochemical characteristics using techniques of environmental scanning electron microscopy (ESEM), potentiodynamic scan, and electrochemical impedance spectroscopy (EIS). Analysis of surface composition using ESEM and EIS indicated that laser fluences in a range of 1.1–1.3 J/cm2 were found to preferentially reduce the copper concentration in the alloy surface to approximately 0.1 wt % and grow the oxidized layer on the surface. Surface composition and patterning were accordingly correlated to electrochemical characteristics of corrosion resistance, capacitance, and potential, which were subsequently used to calculate the corresponding thickness of the formed oxide layer. An enhancement of corrosion resistance characteristics of the 2024-T3 aluminum alloy was attributed to the combination of laser-induced copper removal and oxide layer formation on the surface.
Laser-assisted chemical cleaning for oxide-scale removal from carbon steel surfaces
Authors: Lim Hyunkyu , Kim Dongsik
Published: June 2006

The article introduces a novel laser chemical processing technique for removing thin oxide layers on low-carbon steel surfaces by combining laser-induced shock waves and the chemical cleaning technique that is currently utilized in the conventional oxide-scale removal. A Q-switched Nd:yttritium–aluminum–garnet laser (wavelength 1064 nm, full width at half maximum 6 ns) induces optical breakdown in the acid solution, producing intense pressure waves which act as a noncontact scale breaker. It has been demonstrated that the novel process leads to substantial enhancement of the oxide-scale removal from the surfaces. The removal rate has been measured by optical microscopy, x-ray photoelectron spectroscopy, and energy-dispersive x-ray analysis. Parametric study has been performed to reveal the effect of laser-induced pressure pulse, acid concentration, and reaction time on the efficiency of oxide removal. This work demonstrates a technical feasibility of employing the proposed process in industrial applications which require special treatment, e.g., increased oxide-removal rate and selective surface processing.
Laser annealing of silicon nanocrystal films formed by pulsed-laser deposition
Authors: Tan C. F. , Chen X. Y. , Lu Y. F. , Wu Y. H. , Cho B. J. , Zeng J. N.
Published: June 2006

We report the laser annealing effects on the structures and properties of silicon nanocrystal films fabricated by pulsed-laser deposition in inert argon gas. The surface morphology of the as-deposited films is greatly determined by the angle relative to the laser ablation spot. Photoluminescence (PL) peaked at 620 nm corresponding to 2.0 eV is observed in the as-deposited films. After single-pulse laser annealing, better crystallinity and increased PL intensity are obtained. The PL peak remains at 620 nm. High laser fluence causes damage to the films and the threshold fluence for laser ablation is around 100 mJ/cm2. Multiple-pulse laser annealing with increasing pulse number at fluences below the threshold of laser ablation can provide better crystallization and property improvement than single-pulse annealing. There are a certain number of pulses for the best multiple-pulse annealing effect before damage or laser ablation occur.
Metallic vapor ejection effect on melt pool dynamics in deep penetration laser welding
Authors: Fabbro Rémy , Hamadou Mohammed , Coste Frederic
Published: June 2006

The hydrodynamics phenomena involved during the laser welding process are very complex. Among the possible involved mechanisms controlling the hydrodynamics of the weld pool, it is well known that the melt displacement resulting of the local pressure applied to the liquid surface as a result of the evaporation process, plays an important role. We would like to show in this article that, using specific experiments based on twin or triple spot interaction geometry, the friction forces of the metal vapor escaping from the keyhole are also shown to have a very important role for the hydrodynamics of the melt pool along and around the keyhole.
Laser surface treatment of magnesia partially stabilized zirconia for enhanced human skin fibroblast cell response
Authors: Hao L. , Lawrence J.
Published: June 2006

Promoting or inhibiting cell adhesion to biomaterials is often crucial to the proper function of a biomaterial. In order to induce a surface with better bioactivity for promoting the bonding between the tissue and this bioinert ceramic interface, an industrial CO2 laser was used to alter the surface properties of magnesia (MgO)-partially stabilized zirconia (PSZ) with various laser power densities. The general effects of CO2 laser radiation on the MgO–PSZ were analyzed to investigate the modifications of surface microstructure, surface oxygen content, and surface roughness of the material. In in vitro evaluation, human skin fibroblast cells were seen to attach onto the MgO–PSZ following CO2 laser treatment, whereas, no cell attachment was found on the untreated MgO–PSZ after 7 day cell culture. Moreover, some cells on the CO2 laser treated MgO–PSZ could be considered as flattened and spread, implying the final stage of the cell attachment. A relationship was observed between the extent of cell attachment and surface properties of the MgO–PSZ with various laser power densities, exhibiting the ability of laser surface process for controlling the cell attachment.
Nd:yttritium–aluminum–garnet laser welding of copper to stainless steel
Authors: Shen Hongwei , Gupta Mool C.
Published: June 2006

Systematic laser welding experiments were conducted on dissimilar metal of copper and 300 series stainless steel using a high average power Lumonics JK 701H Nd:yttritium–aluminum–garnet laser. The laser melt penetration depth and width in copper and stainless steel were evaluated as a function of the laser parameters. The results reveal that melting of copper demands much higher average power, shorter pulse duration, and lower welding speed than melting stainless steel. If the laser beam is focused on the interface of the joint or on the stainless steel side, the weld penetration in stainless steel is much deeper than that in copper and the weld formation is poor and solidification cracks emerge. Distributing heat input by positioning the laser beam with respect to the interface of the joint was explored. Good results were achieved while positioning the laser beam 0.4 mm on the copper side. Butt weld penetration can go up to 2.4 mm and fusion zone in both copper and stainless steel is evenly distributed. By adjusting welding parameters, weld defects such as shrinkage, porosity, solidification cracks, etc., can be eliminated. Although isolated hot crack clusters exist along the austenite grain boundary in stainless steel HAZ, the strength of the weld joint is higher than copper and high vacuum tight property can be achieved.
Effect of excimer laser surface melting on intergranular corrosion cracking of the aluminum–lithium alloy 8090
Authors: Yue T. M. , Chan C. P. , Yan L. J. , Man H. C.
Published: June 2006

Excimer laser surface melting of the aluminum alloy 8090 has been conducted with the aim of improving the intergranular corrosion resistance of the alloy. Both the results of the electrochemical and the intergranular corrosion cracking immersion tests show that the laser treatment significantly increases the intergranular corrosion resistance of the alloy, especially when the material is treated in nitrogen gas. The improvement in intergranular corrosion resistance is considered to be primarily due to the elimination of grain boundary Cu enriched precipitates in the laser-melted layer, which has effectively prohibited intergranular corrosion cracking. Besides, the reduction of Cu and Fe enriched constituent particles increases the pitting corrosion resistance of the alloy. As a result, a reduction in corrosion current density of one order of magnitude has been obtained for the laser-treated material. Moreover, a strong passivation has been obtained for the N2-treated specimen. This is attributed to the presence of the chemically stable AlN phase in the laser-melted layer. The analysis of the electrochemical impedance data shows that the polarization resistance (Rp) of the laser-treated specimens is at least two orders of magnitude higher than that of the untreated specimen; while the double layer capacitance (Cdl) is about one order of magnitude lower.
High-power CO2 laser design “from resonator end mirror to cutting lens focal point”
Authors: Toebaert David , Wagenaar Wybo
Published: June 2006

An algorithm is derived that allows calculating all optical parameters relevant to the design of a high-power CO2 laser, taking into account the practical needs of a flying-optics type of laser cutting machine. The novelty of the approach taken is that the resonator and the beam delivery optics are treated simultaneously, which allows for greater flexibility in design. To begin with, the often-used optical configuration of a stable resonator combined with a beam expander for collimation is modeled and optimized. The remaining focal shift over the cutting table, mainly due to the fact that the part of the beam close to the resonator still has appreciable wavefront curvature variation, is calculated. The resulting function is programmed into the machine CNC, which continuously adjusts the lens position depending on the actual beam length, to compensate for this effect. Next, attention is paid to the well-known problem of changing beam parameters with thermal load of the output coupler. It is found necessary to model both mechanical deformation of the ZnSe window and lensing due to the temperature dependent index of refraction. The former is derived from a finite element model, for the latter, the formula of Miyamoto et al. [Proc. SPIE 1276, 112 (1990)] is used. Finally, as an example of novel resonator designs studied using this approach, the characteristics of an intracavity reflective telescope are determined for two different goals: first, to increase the fundamental mode spot size for the given resonator (and hence to improve beam quality without sacrificing power), and second to preserve beam quality when extra resonator layers are added to increase power. The beam is modeled using the concept of the “embedded Gaussian” and the “complex radius of curvature” due to Siegman [Lasers (University Science Books, CA, 1986)].
Investigation of weld cracking in Nd:yttrium–aluminum–garnet keyhole spot welding of materials used in optoelectronic packaging
Authors: Shannon Geoff J. , Li Bernard Q.
Published: June 2006

The welding of a problematic optical device weld joint between dissimilar materials is investigated in depth. The original material combination of cold rolled steel 1010 with 6 μm of gold coating and 304 L produced consistent weld cracking. The CRS1010 material was fixed, however the other component was open to material selection. The materials tested were 304 L stainless steel, kovar, invar, and Carpenter high permeability 49 alloy. The effect of these different materials, laser pulse parameters, level of weld constraint, and thickness of gold plating on the CRS component are investigated to determine the key crack initiator. The results indicated that gold thickness is the key factor in the cracking mechanism, however weld volume and the level of weld constraint are also significant, with material selection a secondary factor. The use of pulse shaping had no effect on alleviating or reducing the extent of cracking.
Foam coating on aluminum alloy with laser cladding
Authors: Ocelı́k V. , van Heeswijk V. , De Hosson J. Th. M. , Csach K.
Published: June 2006

This article concentrates on the creation of a foam layer on an Al–Si substrate with laser technology. The cladding of Al–Si powder in the front of a laser track has been separated from the side injection of mixture of Al–Si/TiH2 powder (foaming agent), which allows for fine tuning of the main processing parameters, i.e., melting temperature and laser processing time. A wide operational parameter window has been found and the formation of a porous layer has been observed for all combinations of Nd:YAG laser power in the range of 1.0–1.5 kW and for scanning speeds between 2.5 and 5.8 mm/s. Microstructural examinations were focused on the study of the relationship between process parameters and foam characteristics (porosity and bubbles size distribution). A tensile test confirmed that due to the relatively low porosity the tensile behavior of the foam layer is closer to the behavior of bulk aluminum than conventional closed cell aluminum foams.
Laser short pulse heating of copper: Thermo–elasto–plastic analysis
Authors: Arif A. F. M. , Yilbas B. S.
Published: June 2006

Laser short pulse heating of metallic substrates results in excessive electron temperatures in the surface vicinity. This gives rise to nonequilibrium energy transport in the region irradiated by a laser beam. Moreover, the thermomechanical coupling effect should be incorporated into the energy transport equation as lattice site temperature increases. In the present study, laser short pulse heating of copper is considered. The electron kinetic theory approach is employed to model the nonequilibrium heating process while thermomechanical coupling is introduced in the energy transport equation to account for the thermomechanical response of the substrate material. In order to determine the stress field, due to temperature gradient in the laser irradiated region, thermo–elastic and thermo–elasto–plastic analyses are carried out. Temperature and stress fields are computed numerically. It is found that temperature gradient is higher in the region next to the surface vicinity inside the substrate material. Equivalent stress levels attain high values in the vicinity of the surface which, in turn, results in a plastic zone in this region.
Effects of irradiated conditions of Er:yttritium–aluminum–garnet laser on tooth vibration
Authors: Takamori Kazunori , Watanabe Shigeru
Published: June 2006

Clinical studies that the Er:yttritium–aluminum–garnet (YAG) laser cause less pain in cutting. Unlike high-speed drilling Er:YAG laser irradiation does not cause pain by vibration, pressure, heat, or noise. We suspected that the greatest difference in characteristics between the Er:YAG laser and the high-speed drill is the amount of tooth vibration during cavity preparation. It will be simultaneously pain or discomfort during tooth cutting. Previously, the authors revealed that increased vibration speed was observed with an increase in Er:YAG laser irradiated energy, and different characteristic of Er:YAG laser and high-speed drill. However, the vibration speed was also influenced by other irradiated conditions. The purpose of this study was to determine the effects of various irradiated conditions of Er:YAG laser preparation on the vibration speed of the tooth. Four extracted permanent upper first premolars setup the plaster basement. The experimental periodontal tissue was selected of silicone impression material. The vibration speed and frequency characteristics were analyzed by using a laser Doppler vibrometer. The laser irradiation energy was applied 145 mJ; and the repetition rate examined was 1, 3, 5, and 10 Hz. The water flow rate was set at 5, 10, and 15 ml/min; and distance between irradiation tip and the tooth surface examined was 0 (contact), 0.5, 1, 1.5, and 2 mm. The highest vibration speed was significantly obtained with the following values: 10 Hz, 10 ml, and contact irradiation. These results suggest that other irradiation conditions, in addition to the energy level affect tooth vibration speed and may be linked to preparation efficiency.
Laser microspot welding of copper
Authors: Amorosi S. , Sidler Th. , Salathé R. P. , Schwob H. P. , Hertzberg J.
Published: June 2006

We describe a novel procedure for highly reliable microspot welding of copper based on a calibrated on-line reflectivity measurement. This parameter is used to control the laser power slope and the weld spot diameter. Reliable welds are obtained without the need of other active control mechanisms. The new technique allows realizing welds with a diameter close to the laser beam waist and leads to a reduction in the relative standard deviation of the molten pool diameter from 20% to about 3%.
Laser-assisted chemical vapor deposition to directly write three-dimensional microstructures
Authors: Han S. I. , Jeong S. H.
Published: June 2006

Application of laser-assisted chemical vapor deposition to the fabrication of three-dimensional microstructures is investigated. To fabricate a three-dimensional microstructure, a thin layer of deposit in desired patterns is first written on a flat substrate using the laser-direct-writing technique and on top of this layer a second layer is deposited to increase the height of the deposit pattern. After repeatedly depositing several layers in the same manner, a three-dimensional microstructure is fabricated. Optimum deposition conditions for direct writing of initial and subsequent layers with good surface quality and profile uniformity are determined. Using an argon ion laser and ethylene as the light source and reaction gas, respectively, fabrication of three-dimensional carbon microstructures is demonstrated.
Cementum melting after dye-assisted holmium laser irradiation
Authors: Bachmann L. , Rossi W. , Zezell D. M.
Published: June 2006

Dye-assisted laser irradiation with black ink or vegetable coal has been used in procedures involving hard tissue irradiation using neodymium or diode lasers. The objective of this work is to evaluate the human root surface melting, after dye-assisted holmium irradiation with subablative fluences. Human cervical root regions were selected, irradiated with a holmium laser with emission at 2.065 μm, pulse width of 400 μs, and repetition rate of 0.5 Hz. The tissue irradiation occurred with two fluences, between 10–20 and 25–35 J/cm2. With the fluence between 10–20 J/cm2, the irradiation melted the tissue only at some isolated areas and the dentinal tubules present in the surface were not totally occluded, while the fluence between 25–35 J/cm2 melted the tissue in entire analyzed area. Dye-assisted holmium irradiation in the subablative regime produced a melted surface without the presence of superficial ablation. Procedures that melt the tissue can be applied in dentinal tubules occlusion, but to confirm the proposed procedure is necessary to evaluate the tubules occlusion and the melted surface chemical stability at low pH environment.
Laser microfabrication with metallic powder
Authors: Jimin Chen , Tiechuan Zuo
Published: June 2006

Rapid prototyping (RP) technology has developed fast in the last year. It is an inevitable trend to adopt laser melting metal powder material directly to make metal parts from RP technology to rapid manufacturing. However, at present it is still at the stage of explorlation to utilize micro powder metal material for microfabrication. In this article two methods of microfabrication were investigated. One is selective laser microsintering. Equipment of YAG doubling frequency laser was used to sinter metallis powder materials to fabricate the micro part. Another is microladding fabrication. With special designation of a powder feeder the fused deposition of metallic powder was conducted. The impact factors such as laser parameters, processing parameters on microfabrication, were analyzed. Through optimization in the parameters, a micrometal part has been successfully fabricated.
Identification of the mechanisms governing modifications of the wettability characteristics of a magnesia partially stabilized zirconia bioceramic following CO2 laser treatment
Authors: Hao L. , Lawrence J.
Published: June 2006

The mechanisms responsible for modifying the wettability characteristics of a magnesia partially stabilized zirconia (MgO–PSZ) bioceramic material after CO2 laser treatment have been elucidated. Changes in the contact angle, θ, which characterizes the wettability characteristics of the MgO–PSZ, were attributed primarily to: modifications to the surface roughness of the material, the incorporation of oxygen at the surface, and the increase in the polar component of the surface energy, γsv p. However, the degree of influence exerted by each mechanism was found to differ markedly. Isolation of each of these mechanisms permitted the magnitude of their influence to be qualitatively determined. Surface energy, by way of microstructural changes, was found to be by far the most predominant element governing the wetting characteristics of the MgO–PSZ. To a much lesser extent, incorporation of oxygen at surface, was also seen to influence the change in the wettability characteristics of the MgO–PSZ, while surface roughness was found to play a minor role in inducing changes in the wettability characteristics.
Excimer laser ablation of glass-based arrayed microstructures for biomedical, mechanical, and optical applications
Authors: Chen Ying-Tung , Ma Kung-Jeng , Zhou Jack G. , Tseng Ampere A.
Published: June 2006

An excimer laser has been used for ablation of glass-based substrates for making arrayed microstructures. The arrayed microstructures are fabricated by repetition of a simple-patterned mask associated with substrate movement controlled by an x-y stage synchronizing with laser pulses. The associated ablation efficiency, specifically the impact of changing major laser parameters on the resulting microstructural shapes and morphology, has been studied. Several microstructures have been machined by this repetition technique to demonstrate that the use of a single-slotted mask indeed can be cost effective in prototyping of various glass-based arrayed microstructures. The single and arrayed microstructures developed include microracks, waveguides, microprobes, and microstamps; the specific applications of these microstructures in mechanical, optical and biomedical areas are also discussed. The associated ablation techniques for different application are described and demonstrated. The defocusing effects on forming different vertex shapes in microprobes are specifically illustrated. Finally, recommendations for future efforts and trends are presented.
Experimental investigation on the weldability and forming behavior of aluminum alloy tailor-welded blanks
Authors: Cheng C. H. , Chan L. C. , Chow C. L. , Lee T. C.
Published: June 2006

Aluminum alloy tailor-welded blanks (TWBs) have developed rapidly due to increasing interest and market pressure [J. M. Story, S. Heinemann, and S. Naegeler, Light Metal Age 56, 40–47 (1998). R. W. Davies, H. E. Oliver, M. T. Smith, and G. J. Grant, J. Minerals, Metals Mater. Soc. 51, 46–50 (1999)] from the automotive industry to further reduce the weight and cost of automotive components. In this study, a 5754-O aluminum alloy with a thickness of 1 mm was laser-welded by a 2 kW Nd: yttritium–aluminum–garnet (YAG) laser to produce a total of approximately 120 samples of TWBs with a similar thickness combination of 1 mm/1 mm. From the knowledge of the weld surfaces, weld profiles and tensile properties of the specimens of TWBs, the optimal welding parameters were identified and used to produce TWBs of varying widths and welding orientations for the Swift forming test. Thus, it was possible to measure and analyze the forming behavior, including the failure mode and the forming limit diagram (FLD), of the TWBs. Despite the limited power output of the Nd:YAG laser used in this study, a systematic study was undertaken to achieve welding the integrative aluminium alloy TWBs. In this study, applying a pulsed laser beam with an average power of 1100 W and a welding speed of 35 mm/s produced satisfactory TWBs. Despite some failures of the specimens at the welds during the tensile test, it was found that all TWBs yielded almost the same yield strength and ultimate tensile strength as those of their parent metal. TWBs with transverse welds also retained over 94% of their original ductility. Irrespective of the major loading direction during the forming test, the failures appeared somewhere away from the welds and heat-affected zones on the TWBs, with transverse welds such that the TWBs provided the same formability as the original 5754-O sheets. For TWBs with longitudinal welds, the failures were found to have initiated at the weld propagating perpendicularly to the major loading direction. This resulted in a lower level of FLD.
Modeling of laser deposition and repair process
Authors: Han Lijun , Phatak Kaushik M. , Liou F. W.
Published: June 2006

Laser aided deposition is a material additive based manufacturing process via metallurgically bonding the deposited material to the substrate. Due to its capability to bond various materials together, it becomes an attractive technology for part repair in small scale. However, the details of the process remain an active area for research because of the complicated interactions involved. In this study, a mathematical model was established to investigate thermal and mass transportation phenomena, which include substrate melting and solidification as well as the powder heating process. Affected by the powder injection, the melt pool surface keeps fluctuating during the process and dynamic evolution of the melt pool shape is tracked by using the level set method. Melt pool shape and energy balance at liquid–vapor and solid–liquid interfaces are taken into account in the model. A typical hole repair process based on material deposition technology is presented. The detailed process together with the temperature distribution were simulated. The simulation results of the melt pool length and peak temperature are validated for the laser deposition process through the measurements on the melt pool geometry and surface peak temperature by the complementary metal–oxide–semiconductor camera and dual-wavelength temperature sensor.
Thermodynamics and laser material processing
Authors: Duley W. W.
Published: June 2006

In many laser applications it is the conversion of photon energy to heat that drives the process. Heat transfer theory accurately describes the effects produced, and other aspects of thermodynamics need not generally be considered explicitly. The highly nonequilibrium nature of laser materials processing operations can usually be ignored once the heat transfer problem is defined. However, “equilibrium” is a concept that is basic to thermodynamics, and so it is useful to examine this concept in the context of traditional laser materials processing applications. Some of the assumptions associated with the adoption of equilibrium solutions are discussed in this article. The roles of surface reconstruction and entropy in reaching an equilibrium state are evaluated. Surface tension effects and work done during laser processing are also investigated. It is concluded that the path to the steady state in laser materials processing involves geometrical as well as thermodynamic parameters.
In-process monitoring and adaptive control for stable production of sound welds in laser microspot lap welding of aluminum alloy
Authors: Kawahito Yousuke , Katayama Seiji
Published: June 2006

A new procedure of in-process monitoring and adaptive control has been developed for laser microspot lap welding of A3003 aluminum alloy sheets of 0.1 and 1 mm in thickness. The objective is to consistently produce sound laser partial-penetration lap-joint welds. It was revealed that the reflected laser beam and the radiated heat from the welding area were effective as in-process monitoring signals in detecting melting, keyhole generation, and through-hole formation in the upper sheet during laser irradiation. Laser pulse duration and peak power were controlled at every 0.15 ms interval during the laser spot welding on the basis of the heat radiation signal detecting the through-hole. Upon investigation of 20 samples, 4 nonbonded welds with holes were formed under conventionally used conditions. On the other hand, sound partially penetrated spot welds were produced in all 20 samples subjected to laser lap welding under the proposed in-process monitoring and adaptive control.
Numerical simulation of femtosecond laser interaction with silicon
Authors: Ki Hyungson , Mazumder Jyoti
Published: June 2006

A numerical model for simulating femtosecond laser interaction with silicon is presented. This model simulates laser beam propagation by directly solving Maxwell’s equations using the finite-difference time-domain method, so that complete electromagnetic nature of a laser beam is simulated accurately. Accurate computation of laser beam passage ensures realistic heat generation pattern in the target material. The two-temperature model has been adopted to simulate the energy transport of electrons and lattices. This study reveals interesting results regarding thermal energy generation and complex laser beam passage in the silicon target. The temperature histories of electrons and lattices are presented.
Feedback control effects on dimensions and defects of H13 tool steel by direct metal deposition process
Authors: Hua Y. , Choi J.
Published: June 2006

As a promising and novel manufacturing technology, laser aided direct metal deposition (DMD) process produces near-net-shape functional metal parts directly from the computer aided design (CAD) model. In-process feedback control has been recognized as a critical element to ensure the dimensional accuracy as well as near-net-shape production. Furthermore, process parameters should be delicately controlled to produce defect-free parts with superior mechanical properties. A closed loop real-time optical height control system has been implemented to achieve better surface roughness and dimensional accuracy within designed tolerance. In this article, effects of feedback control on dimensional accuracy as well as defects such as microcrack and void/porosity are investigated for H13 tool steel samples, and experimental results are summarized. The samples fabricated with/without feedback control and with various deposition patterns are compared and the effectiveness of feedback control system, arrangement of height control sensors, and threshold of the average laser power are discussed.
Improved adsorption of human plasma fibronectin on magnesia partially stabilized zirconia (MgO–PSZ) bioceramic resulting from CO2 laser irradiation
Authors: Hao L. , Lawrence J.
Published: June 2006

The adsorption of proteins onto a biomaterial surface from the surrounding fluid phase is rapid, with the surface properties of the biomaterial determining the type, amount, and conformation of the adsorbed proteins. Magnesia partially stabilized zirconia (MgO–PSZ), a bioinert ceramic used at the high-load bearing sites, does not naturally form a direct bond with bone. It is believed that a favorable adsorption of the fibronectin could promote cell adhesion and subsequently the bonding between the bone and MgO–PSZ implant. Thus, the aim of this study is to investigate adsorption of human plasma fibronectin on the untreated MgO–PSZ and CO2 laser modified MgO–PSZ using an ellipsometry. It found that CO2 laser treatment brought about a higher amount of the adsorbed fibronectin layer on the modified MgO–PSZ compared with the untreated sample. The adsorption of human plasma fibronectin was influenced by the surface properties, especially positively related to the wettability characteristic. The result implies that the fibronectin adsorption on the MgO–PSZ surfaces was probably due to the polar and chemical interactions, since the considerable change in γsvp instead of minor difference in γsvd of the MgO–PSZ was the main mechanism governing the wettability characteristics after CO2 laser irradiation. The work provides important information regarding protein–bioceramic interactions and feasible of the technique for mediating the protein adsorption and the bonding between tissue implant.
Review of laser hybrid welding
Authors: Bagger Claus , Olsen Flemming O.
Published: June 2006

In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more efficiently in the future.
Autogenous laser keyhole welding of aluminum alloy 2024
Authors: Hu B. , Richardson I. M.
Published: June 2006

Aluminum alloy (AA) 2024 is one of the heat treatable aluminum alloys regarded as difficult to fusion weld using autogenous techniques. In this study the weldability of AA 2024 sheet with autogenous laser keyhole welding was examined as part of a systematic study on the welding parameters in order to obtain the optimal welding conditions. A high-speed video camera was employed to capture the keyhole dynamics. Results from the high-speed video show that a rough weld bead surface and porosity formation are due to severe keyhole instability. A high heat input (combination of low laser energy density and low welding speed) forms a relatively large weld pool and the keyhole root locates in the center of weld pool. The welding process in this case is relatively stable and the welds contain no severe porosity. In comparison, with a low heat input (combination of high laser energy density with high welding speed) a small weld pool is formed and the keyhole root locates very close to the front edge of the weld pool; the process is less stable and significant porosity is produced in the welds. It was found that a higher shielding gas pressure could remedy the surface roughness by depressing the liquid in the weld pool. Microstructural examinations show that the fast heating and cooling cycle produced by the laser welding process leads to a narrow partially molten zone and heat affected zone. In the weld fusion zone an equiaxed dendritic structure in the central part of weld and a columnar dendritic structure adjacent to the fusion line was formed.
Laser beam analysis in direct metal deposition process
Authors: Qi Huan , Mazumder Jyoti , Green Larry , Herrit Gary
Published: June 2006

The quality of a laser beam profile and its stability play fundamental roles in laser material processing. Beam reflections may dramatically affect the beam quality under certain material processing conditions. In this study, experiments were carried out to examine the variations of the continuous wave CO2 laser beam profile during the direct metal deposition (DMD) process. A pyroelectric-camera-based new industrial laser beam analysis device was installed in the optical line near the laser output coupler. Experimental results are presented with the comparison of beam profiles under different cladding processing conditions, such as the coaxial powder flow cladding, preplaced powder cladding, the remelting process, and the dumping of the raw beam. It was observed that cladding using preplaced powder gives off more reflective energy from the cladding zone which deforms the beam profile and causes great power fluctuation. Laser beam profiles and stability during DMD processes were monitored and analyzed with various processing geometries and the identification of porosity formation. High contents of the oxidized contaminants in the reused H13 powder were found to cause dark discontinuities in single track cladding where obvious beam power fluctuations were observed. In multiple layer cladding, 7%–20% more reflected energy was detected in the first layer deposition than in the successive layers.
Determination of true stress-strain curve for the weldment of aluminum laser-welded blanks
Authors: Cheng C. H. , Chan L. C. , Tang C. Y. , Chow C. L.
Published: June 2006

In the automotive industry, the weld quality of aluminum laser-welded blanks (LWBs) is generally assessed by a conventional transverse tensile test. The engineering stress-strain curve, together with other tensile properties (e.g., yield strength, tensile strength, and total elongation) of the monolithic LWBs, can then be obtained by this test. However, LWBs should be considered heterogeneous in structure. The acquired engineering stress-strain curve is therefore unable to represent the tensile behavior of the aluminum LWBs in realistic situations, particularly with regard to the behavior of the weldment. This article presents a novel experimental approach to acquire true stress-strain data on the weldment during the tensile test of LWBs using a real-time microscopic recording system. This new approach will study observations of the real-time deformation of the laser-marked microgrids premade on the surface of the weldment of the LWB. By capturing the deformation of microgrids through the aid of a video encoder and transferring the data for measurement, the localized strains of the weldment can then be computed, and the localized stresses obtained accordingly. Eventually, the true stress-strain curve of the weldment of the LWB can be successfully acquired. In addition, an investigation has been carried out to examine in details the strain distributions of the weldment using the finite element analysis. This was achieved by employing the measured true stress-strain curve of the weldment and reducing the mesh size of the elements to a level that could not be attained via the experiment.
Three-dimensional transient finite element analysis for residual stresses in the laser aided direct metal/material deposition process
Authors: Ghosh S. , Choi J.
Published: June 2006

Despite immense advances in the laser aided direct metal/material deposition (DMD) process many issues concerning the adverse effects of process parameters on the stability of variety of properties and the integrity of microstructure have been reported. Comprehensive understanding of the transport phenomena and heat transfer analysis including phase transformations are essential to predict the effects of thermally induced residual stresses and distortions in the deposited materials. A complete model that provides a quantitative relationship between process parameters, cooling rates, and desired material properties is highly desirable. This model, which aims at predicting the residual stress history and the type of microstructure in the material, would reduce the long and cumbersome experimental route to compile sufficient data to predict the material behavior under similar loading conditions. Due to the complexity and nonlinearity of laser aided DMD process, analytical solutions to this process can rarely address the practical manufacturing process. This article is an attempt towards a methodology of finite element analysis for the prediction of macroscopic and microscopic residual stresses in the laser aided DMD process. The computer simulation which is based on the metallothermomechanical theory and finite element analysis for uncoupled temperature, phase transformation, and stress/strain fields can prove to be a very useful tool in predicting the material behavior and optimizing the process parameters to obtain the best material quality and dimensional accuracy. The significance of including phase transformation effects in the process has been demonstrated by a thorough comparison of residual stresses in the material with and without the phase transformation kinetics.