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Use of Aria to simulate laser weld pool dynamics for neutron generator production.

Description: This report documents the results for the FY07 ASC Integrated Codes Level 2 Milestone number 2354. The description for this milestone is, 'Demonstrate level set free surface tracking capabilities in ARIA to simulate the dynamics of the formation and time evolution of a weld pool in laser welding applications for neutron generator production'. The specialized boundary conditions and material properties for the laser welding application were implemented and verified by comparison with existing, two-dimensional applications. Analyses of stationary spot welds and traveling line welds were performed and the accuracy of the three-dimensional (3D) level set algorithm is assessed by comparison with 3D moving mesh calculations.
Date: September 1, 2007
Creator: Noble, David R.; Notz, Patrick K.; Martinez, Mario J. & Kraynik, Andrew Michael
Partner: UNT Libraries Government Documents Department

Neural Network Modeling of Weld Pool Shape in Pulsed-Laser Aluminum Welds

Description: A neural network model was developed to predict the weld pool shape for pulsed-laser aluminum welds. Several different network architectures were examined and the optimum architecture was identified. The neural network was then trained and, in spite of the small size of the training data set, the network accurately predicted the weld pool shape profiles. The neural network output was in the form of four weld pool shape parameters (depth, width, half-width, and area) and these were converted into predicted weld pool profiles with the use of the actual experimental poo1 profiles as templates. It was also shown that the neural network model could reliably predict the change from conduction-mode type shapes to keyhole-mode shapes.
Date: November 16, 1998
Creator: Iskander, Y.S.; Oblow, E.M. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Transient Model for Keyhole During Laser Welding

Description: A novel approach to simulating the dominant dynamic processes present during concentrated energy beam welding of metals is presented. A model for transient behavior of the front keyhole wall is developed. It is assumed that keyhole propagation is dominated by evaporation recoil-driven melt expulsion from the beam interaction zone. Results from the model show keyhole instabilities consistent with experimental observations of metal welding, metal cutting and ice welding.
Date: March 5, 1999
Creator: Bragg, W.D.; Damkroger, B.; Kempka, S. & Semak, V.V.
Partner: UNT Libraries Government Documents Department

Pulse shaping effects on weld porosity in laser beam spot welds : contrast of long- & short- pulse welds.

Description: Weld porosity is being investigated for long-pulse spot welds produced by high power continuous output lasers. Short-pulse spot welds (made with a pulsed laser system) are also being studied but to a much small extent. Given that weld area of a spot weld is commensurate with weld strength, the loss of weld area due to an undefined or unexpected pore results in undefined or unexpected loss in strength. For this reason, a better understanding of spot weld porosity is sought. Long-pulse spot welds are defined and limited by the slow shutter speed of most high output power continuous lasers. Continuous lasers typically ramp up to a simmer power before reaching the high power needed to produce the desired weld. A post-pulse ramp down time is usually present as well. The result is a pulse length tenths of a second long as oppose to the typical millisecond regime of the short-pulse pulsed laser. This study will employ a Lumonics JK802 Nd:YAG laser with Super Modulation pulse shaping capability and a Lasag SLS C16 40 W pulsed Nd:YAG laser. Pulse shaping will include square wave modulation of various peak powers for long-pulse welds and square (or top hat) and constant ramp down pulses for short-pulse welds. Characterization of weld porosity will be performed for both pulse welding methods.
Date: October 1, 2007
Creator: Ellison, Chad M. (Honeywell FM&T, Kansas City, MO); Perricone, Matthew J. (R.J. Lee Group, Inc., Monroeville, PA); Faraone, Kevin M. (BWX Technologies, Inc., Lynchburg, VA) & Norris, Jerome T.
Partner: UNT Libraries Government Documents Department

Modeling and design of energy concentrating laser weld joints

Description: The application of lasers for welding and joining has increased steadily over the past decade with the advent of high powered industrial laser systems. Attributes such as high energy density and precise focusing allow high speed processing of precision assemblies. Other characteristics of the process such as poor coupling of energy due to highly reflective materials and instabilities associated with deep penetration keyhole mode welding remain as process limitations and challenges to be overcome. Reflective loss of laser energy impinging on metal surfaces can in some cases exceed ninety five percent, thus making the process extremely inefficient. Enhanced coupling of the laser beam can occur when high energy densities approach the vaporization point of the materials and form a keyhole feature which can trap laser energy and enhance melting and process efficiency. The extreme temperature, pressure and fluid flow dynamics of the keyhole make control of the process difficult in this melting regime. The authors design and model weld joints which through reflective propagation and concentration of the laser beam energy significantly enhance the melting process and weld morphology. A three dimensional computer based geometric optical model is used to describe the key laser parameters and joint geometry. Ray tracing is used to compute the location and intensity of energy absorption within the weld joint. Comparison with experimentation shows good correlation of energy concentration within the model to actual weld profiles. The effect of energy concentration within various joint geometry is described. This method for extending the design of the laser system to include the weld joint allows the evaluation and selection of laser parameters such as lens and focal position for process optimization. The design of narrow gap joints which function as energy concentrators is described. The enhanced laser welding of aluminum without keyhole formation has been demonstrated.
Date: April 1997
Creator: Milewski, J. O. & Sklar, E.
Partner: UNT Libraries Government Documents Department

Laser welding and collagen crosslinks

Description: Strength and stability of laser-welded tissue may be influenced, in part, by effects of laser exposure on collagen crosslinking. We therefore studied effects of diode laser exposure (805 nm, 1-8 watts, 30 seconds) + indocyanine green dye (ICG) on calf tail tendon collagen crosslinks. Effect of ICG dye alone on crosslink content prior to laser exposure was investigated; unexpectedly, we found that ICG-treated tissue had significantly increased DHLNL and OHP, but not HLNL. Laser exposure after ICG application reduced elevated DHLNL and OHP crosslink content down to their native levels. The monohydroxylated crosslink HLNL was inversely correlated with laser output (p<0.01 by linear regression analysis). DHLNL content was highly correlated with content of its maturational product, OHP, suggesting that precursor-product relations are maintained. We conclude that: (1)ICG alone induces DHLNL and OHP crosslink formation; (2)subsequent laser exposure reduces the ICG-induced crosslinks down to native levels; (3)excessive diode laser exposure destroys normally occurring HLNL crosslinks.
Date: February 20, 1997
Creator: Reiser, K.M.; Last, J.A.; Small, W. IV; Maitland, D.J.; Heredia, N.J.; Da Silva, L.B. et al.
Partner: UNT Libraries Government Documents Department

Laser assisted non-consumable arc welding process development

Description: The employment of Laser Beam Welding (LBW) for many traditional arc welding applications is often limited by the inability of LBW to compensate for variations in the weld joint gap. This limitation is associated with fluctuations in the energy transfer efficiency along the weld joint. Since coupling of the laser beam to the workpiece is dependent on the maintenance of a stable absorption keyhole, perturbations to the weld pool can lead to decreased energy transfer and resultant weld defects. Because energy transfer in arc welding does not similarly depend on weld pool geometry, it is expected that combining these two processes together will lead to an enhanced fusion welding process that exhibits the advantages of both arc welding and LBW. Laser assisted non-consumable arc welds have been made on thin section aluminum. The welds combine the advantages of arc welding and laser welding, with enhanced penetration and fusion zone size. The use of a pulsed Nd:YAG laser with the combined process appears to be advantageous since this laser is effective in removing the aluminum oxide and thereby allowing operation with the tungsten electrode negative. The arc appears to increase the size of the weld and also to mitigate hot cracking tendencies that are common with the pulsed Nd:YAG laser.
Date: September 1, 1997
Creator: Fuerschach, P.W. & Hooper, F.M.
Partner: UNT Libraries Government Documents Department

Simulation of coarsening during laser engineered Net-Shaping

Description: Laser Engineered Net-Shaping, otherwise known as LENS{trademark}, is an advanced manufacturing technique used to fabricate complex near net shaped components directly from engineered solid models without the use of dies or machining. The ultimate objective of this project is to develop predictive simulation capability which will allow the LENS{trademark} processors to determine fabrication conditions given the material, shape, and application of the final part. In this paper, the authors will present an incremental achievement to meeting the ultimate goal, a model capable of simulating the coarsening of microstructural features under the unique thermal history to which a LENS{trademark} part is subjected during processing. The simulation results show how grains of very different shapes and sizes form within the same deposition line. They also show that relatively minor changes in the dynamic temperature profile results in microstructures with vastly different characteristics. The implications of this work for LENS{trademark} fabrication is that controlling the temperature profile is essential to tailoring the microstructure of a component to its application.
Date: September 1, 1997
Creator: Tikare, V.; Griffith, M.; Schlienger, E. & Smugeresky, J.
Partner: UNT Libraries Government Documents Department

Neural network modeling of pulsed-laser weld pool shapes in aluminum alloy welds

Description: A model was developed to predict the weld pool shape in pulsed Nd:YAG laser welds of aluminum alloy 5754. The model utilized neural network analysis to relate the weld process conditions to four pool shape parameters: (1) penetration width, (2) width at half-penetration, and (3) cross-sectional area. The model development involved the identification of the input (process) variables, the desired output (shape) variables, and the optimal neural network architecture. The latter was influenced by the number of defined inputs and outputs as well as the amount of data that was available for training the network. After appropriate training, die best network was identified and was used to predict the weld shape. A routine to convert the shape parameters into predicted weld profiles was also developed. This routine was based on the actual experimental weld profiles and did not impose an artificial analytical function to describe the weld profile. The neural network model was tested on experimental welds. The model predictions were excellent. It was found that the predicted shapes were within the experimental variations that were found along the length of the welds (due to the pulsed nature of the weld power) and the reproducibility of welds made under nominally identical conditions.
Date: September 1, 1998
Creator: Vitek, J.M.; Iskander, Y.S.; Oblow, E.M.; Babu, S.S.; David, S.A.; Fuerschbach, P.W. et al.
Partner: UNT Libraries Government Documents Department

Characterization of the Precision Laser Beam Welding Process for the MC4368A Neutron Generator

Description: The design of experiments (DOEx) approach was used to characterize the Precision Laser Beam Welding Process with respect to four processing factors: Angle of Attack, Volts, Pulse Length, and Focus. The experiment was performed with Lap Joints, Nickel-Wire Joints, and Kovar-Wire Joints. The laser welding process and these types of welds are used in the manufacture of MC4368A Neutron Generators. For each weld type an individual optimal condition and operating window was identified. The widths of the operating windows that were identified by experimentation indicate that the laser weld process is very robust. This is highly desirable because it means that the quality of the resulting welds is not sensitive to the exact values of the processing factors within the operating windows. Statistical process control techniques can be used to ensure that the processing factors stay well within the operating window.
Date: September 1, 2001
Creator: CROWDER, STEPHEN V.; MALIZIA JR., LOUIS A. & ROMERO, JOSEPH A.
Partner: UNT Libraries Government Documents Department

Capabilities of infrared weld monitor

Description: A non-obtrusive pre-aligned, solid-state device has been developed to monitor the primary infrared emissions during laser welding. The weld monitor output is a 100-1000 mV signal that depends on the beam power and weld characteristics. The DC level of this signal is related to weld penetration, while AC portions of the output can be correlated with surface irregularities and part misalignment or contamination. Changes in DC behavior are also noted for both full and deep penetration welds. Full penetration welds are signified by an abrupt reduction in the weld monitor output. Bead on plate welds were made on steel, aluminum, and magnesium with both a CW CO{sub 2} laser and a pulsed Nd:YAG laser to explore the relationships between the weld characteristics and the weld monitor output.
Date: November 1, 1997
Creator: Sanders, P.G.; Keske, J.S.; Leong, K.H. & Kornecki, G.
Partner: UNT Libraries Government Documents Department

Predicting threshold laser beam irradiances for melting and welding

Description: A model based on conservation of energy for a moving heat source incident on a flat plate is used to predict the threshold laser beam irradiance required to initiate melting on a metal surface. With the use of a nondimensional variable and its solution, the threshold irradiance can be predicted with the use of a simple equation that is a function of the absorptivity of the surface, thermal conductivity of the metal, temperature increase for melting, diameter of the laser beam at the surface and the nondimensional variable value for the ratio of the thermal diffusivity of the metal to the product of the beam diameter and velocity used. Laser beam irradiances exceeding these predicted values are required for welding. The model predictions are validated with experimental results of beam irradiances required for welding different metals.
Date: September 1, 1997
Creator: Leong, K.H.; Geyer, H.K.; Sabo, K.R. & Sanders, P.G.
Partner: UNT Libraries Government Documents Department

Modeling and analysis of novel laser weld joint designs using optical ray tracing.

Description: Reflection of laser energy presents challenges in material processing that can lead to process inefficiency or process instability. Understanding the fundamentals of non-imaging optics and the reflective propagation of laser energy can allow process and weld joint designs to take advantage of these reflections to enhance process efficiency or mitigate detrimental effects. Optical ray tracing may be used within a 3D computer model to evaluate novel joint and fixture designs for laser welding that take advantage of the reflective propagation of laser energy. This modeling work extends that of previous studies by the author and provides comparison with experimental studies performed on highly reflective metals. Practical examples are discussed.
Date: January 1, 2002
Creator: Milewski, J. O. (John O.)
Partner: UNT Libraries Government Documents Department

Application of a dimensionless parameter model for Laser Beam Welding

Description: A new dimensionless parameter model for continuous wave laser welding that relates the size of the weld to the energy absorbed by the part is described. The model has been experimentally validated previously through calorimetric determinations of the net heat input and metallographic measurements of the weld size. It will be shown that both the melting efficiency and energy transfer efficiency for LBW are quite variable and need to be considered when selecting processing conditions. Specific applications will be detailed in order to observe the simplicity and value of the model in laser weld process development. It will be shown that by using certain dimensionless parameters one can determine the energy transfer efficiency and thereby correctly select processing conditions that more fully utilize the available laser output power. In applications where minimizing heat input to the surrounding weldment is paramount, the dimensionless parameters can be used to select conditions that maximize melting efficiency.
Date: September 1, 1994
Creator: Fuerschbach, P. W.
Partner: UNT Libraries Government Documents Department

Thin-walled compliant plastic structures for meso-scale fluidic systems

Description: Thin-walled, compliant plastic structures for meso-scale fluidic systems were fabricated, tested and used to demonstrate valving, pumping, metering and mixing. These structures permit the isolation of actuators and sensors from the working fluid, thereby reducing chemical compatibility issues. The thin-walled, compliant plastic structures can be used in either a permanent, reusable system or as an inexpensive disposable for single-use assay systems. The implementation of valving, pumping, mixing and metering operations involve only an elastic change in the mechanical shape of various portions of the structure. Advantages provided by the thin-walled plastic structures include reduced dead volume and rapid mixing. Five different methods for fabricating the thin-walled plastic structures discussed including laser welding, molding, vacuum forming, thermal heat staking and photolithographic patterning techniques.
Date: December 29, 1998
Creator: Miles, R R & Schumann, D L
Partner: UNT Libraries Government Documents Department

Comparison Between Keyhole Weld Model and Laser Welding Experiments

Description: A series of laser welds were performed using a high-power diode-pumped continuous-wave Nd:YAG laser welder. In a previous study, the experimental results of those welds were examined, and the effects that changes in incident power and various welding parameters had on weld geometry were investigated. In this report, the fusion zones of the laser welds are compared with those predicted from a laser keyhole weld simulation model for stainless steels (304L and 21-6-9), vanadium, and tantalum. The calculated keyhole depths for the vanadium and 304L stainless steel samples fit the experimental data to within acceptable error, demonstrating the predictive power of numerical simulation for welds in these two materials. Calculations for the tantalum and 21-6-9 stainless steel were a poorer match to the experimental values. Accuracy in materials properties proved extremely important in predicting weld behavior, as minor changes in certain properties had a significant effect on calculated keyhole depth. For each of the materials tested, the correlation between simulated and experimental keyhole depths deviated as the laser power was increased. Using the model as a simulation tool, we conclude that the optical absorptivity of the material is the most influential factor in determining the keyhole depth. Future work will be performed to further investigate these effects and to develop a better match between the model and the experimental results for 21-6-9 stainless steel and tantalum.
Date: September 23, 2002
Creator: Wood, B C; Palmer, T A & Elmer, J W
Partner: UNT Libraries Government Documents Department

Thin plate gap bridging study for Nd:YAG pulsed laser lap welds.

Description: In an on going study of gap bridging for thin plate Nd:YAG laser lap welds, empirical data, high speed imaging, and computer modeling were utilized to better understand surface physics attributed to the formation and solidification of a weld pool. Experimental data indicates better gap bridging can be achieved through optimized laser parameters such as pulse length, duration, and energy. Long pulse durations at low energies generating low peak powers were found to create the highest percent of gap bridging ability. At constant peak power, gap-bridging ability was further improved by using a smaller spot diameter resulting in higher irradiances. Hence, welding in focus is preferable for bridging gaps. Gas shielding was also found to greatly impact gap-bridging ability. Gapped lap welds that could not be bridged with UHP Argon gas shielding, were easily bridged when left unshielded and exposed to only air. Incident weld angle and joint offset were also investigated for their ability to improve gap bridging. Optical filters and brightlight surface illumination enabled high-speed imaging to capture the fluid dynamics of a forming and solidifying weld pool. The effects of various laser parameters and the weld pool's interaction with the laser beam could also be observed utilizing the high-speed imaging. The work described is used to develop and validate a computer model with improved weld pool physics. Finite element models have been used to derive insight into the physics of gap bridging. The dynamics of the fluid motion within the weld pool in conjunction with the free surface physics have been the primary focus of the modeling efforts. Surface tension has been found to be a more significant factor in determining final weld pool shape than expected.
Date: January 1, 2006
Creator: Roach, Robert Allen; Fuerschbach, Phillip William; Bernal, John E. & Norris, Jerome T.
Partner: UNT Libraries Government Documents Department

Solidification Diagnostics for Joining and Microstructural Simulations

Description: Solidification is an important aspect of welding, brazing, soldering, LENS fabrication, and casting. The current trend toward utilizing large-scale process simulations and materials response models for simulation-based engineering is driving the development of new modeling techniques. However, the effective utilization of these models is, in many cases, limited by a lack of fundamental understanding of the physical processes and interactions involved. In addition, experimental validation of model predictions is required. We have developed new and expanded experimental techniques, particularly those needed for in-situ measurement of the morphological and kinetic features of the solidification process. The new high-speed, high-resolution video techniques and data extraction methods developed in this work have been used to identify several unexpected features of the solidification process, including the observation that the solidification front is often far more dynamic than previously thought. In order to demonstrate the utility of the video techniques, correlations have been made between the in-situ observations and the final solidification microstructure. Experimental methods for determination of the solidification velocity in highly dynamic pulsed laser welds have been developed, implemented, and used to validate and refine laser welding models. Using post solidification metallographic techniques, we have discovered a previously unreported orientation relationship between ferrite and austenite in the Fe-Cr-Ni alloy system, and have characterized the conditions under which this new relationship develops. Taken together, the work has expanded both our understanding of, and our ability to characterize, solidification phenomena in complex alloy systems and processes.
Date: January 1, 2003
Creator: ROBINO, CHARLES V.; HALL, AARON C.; BROOKS, JOHN ALBERT; HEADLEY, THOMAS J. & ROACH, R. ALLEN
Partner: UNT Libraries Government Documents Department

Lens designs for high irradiance application of multi-kilowatt Nd:YAG welding lasers

Description: Multi-kilowatt Nd:YAG lasers provide an appealing solution for aluminum laser welding applications due to increased bulk absorption and ease of beam delivery as compared to high power CO{sub 2} laser systems. However, high numerical aperture optics are required to overcome the relatively poor beam quality associated with these lasers and to achieve a high irradiance. Several lens designs have been developed and evaluated to achieve the high irradiance values required to provide good coupling into aluminum alloys. The results of these tests demonstrate that near diffraction limited performance can be achieved for high numerical aperture elements. Additionally, an inverse-telephoto lens design has been developed and characterized to further demonstrate the feasibility of producing a high irradiance with a functional working distance from the weld surface.
Date: April 1, 1996
Creator: Keicher, D.M. & Essien, M.
Partner: UNT Libraries Government Documents Department

Mound bridge-wire welding, testing and corrosion seminar, Miamisburg, OH, May 7-8, 1968

Description: Brief summaries are presented on the following presentations: welding for low voltage operation, welding techniques at Mound, welding/joining at Sandia, Ultrasonic`s plastic assemblies of detonator components, laser welding bridge-wires, laser safety in the Biorad industrial environment, nondestructive testing at Mound, thermal cycle data and evaluation, thermal cycle nondestructive testing, corrosion of detonator electrode and bridge-wire, and corrosion studies and fabrication of bridge-wire at Sigmund Cohn.
Date: August 7, 1968
Creator: Richards, M.A.
Partner: UNT Libraries Government Documents Department

Neural network modeling of pulsed-laser weld pool shapes in aluminum alloy welds

Description: A model was developed to predict the weld pool shape in pulsed Nd:YAG laser welds of aluminum alloy 5754. The model utilized neural network analysis to relate the weld process conditions to four pool shape parameters: penetration, width, width at half-penetration, and cross-sectional area. The model development involved the identification of the input (process) variables, the desired output (shape) variables, and the optimal neural network architecture. The latter was influenced by the number of defined inputs and outputs as well as the amount of data that was available for training the network. After appropriate training, the best network was identified and was used to predict the weld shape. A routine to convert the shape parameters into predicted weld profiles was also developed. This routine was based on the actual experimental weld profiles and did not impose an artificial analytical function to describe the weld profile. The neural network model was tested on experimental welds. The model predictions were excellent. It was found that the predicted shapes were within the experimental variations that were found along the length of the welds (due to the pulsed nature of the weld power) and the reproducibility of welds made under nominally identical conditions.
Date: November 1, 1998
Creator: Vitek, J.M.; Iskander, Y.S.; Oblow, E.M.; Babu, S.S.; David, S.A.; Fuerschbach, P.W. et al.
Partner: UNT Libraries Government Documents Department

Weldability and microstructure development in nickel-base superalloys

Description: The integrity of nickel-base superalloy single-crystal welds depends on the weld cracking tendency, weld metal dendrite selection process, stray crystal formation, and macro- and microstructure development. These phenomena have been investigated in commercial nickel-base superalloy single crystal welds. During electron beam and laser beam welding, transverse and longitudinal weld cracking occurred. However, the weld cracking tendency was reduced with preheating. Most of the dendritic growth pattern development in these welds can be explained by a geometric model. However, the welds also contained misoriented stray crystals, which were frequently associated with weld cracks. The formation of stray crystals was related to thermal and constitutional supercooling effects. Fine-scale elemental partitioning between {gamma} and {gamma}{prime} phase was measured with atom-probe field-ion microscopy. Marked differences in partitioning characteristics in two welds were observed and are related to differences in cooling rates. In this paper, the modeling tools available to describe the above are reviewed.
Date: November 1, 1997
Creator: David, S.A.; Babu, S.S. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department