Richard P. Martukanitz

Absorption of laser irradiation in a porous powder layer

An analytical relationship was derived to describe the amount of energy absorbed within preplaced powder during the laser deposition process. The relationship, which reflects an exponential decay of Beer–Lambert, may be used to define internal absorption due to scattering within the powder layer regardless of the beam shape and energy distribution if the attenuation coefficient and bulk absorption are known. Experiments were conducted to estimate the attenuation coefficients for pure iron and pure copper powders, representing three powder size distributions, during CO2 and Nd:yttrium-aluminum-garnet (YAG) laser irradiation. Qualitative observations and trends of the experimental data indicated that greater beam penetration, accompanied by a decrease in the estimated attenuation coefficients, was associated with the larger powder particles, the lower wavelength of the Nd:YAG laser, and the copper powder. Attenuation coefficients were determined for the original powder size distributions and a larger size d...

A critical review of laser beam welding

The use of lasers for welding has exhibited tremendous growth over the last decade for improving efficiency and reducing costs in a broad range of industries. Much of these successes are based on the development and availability of enabling technologies, which include improvements in process understanding, enhancements in laser sources and systems, and continued development and progression in process technology for laser beam welding of macro and micro components. The development of accurate numerical simulation techniques has provided an unprecedented opportunity to view the transient nature of laser processing. Advancements in laser source technology include the introduction of higher-power Nd:YAG lasers, utilizing diode pumped rods or disks, and fiber lasers, both providing the capability for fiber optic beam delivery. Although CO2 laser systems continue to dominate thick section welding, this influence will be challenged by emerging source technologies, namely high power fiber lasers. One of the most promising advances in laser process technology is laser-arc hybrid welding, which is seeing considerable interest worldwide and is currently being evaluated for various applications within heavy industry and manufacturing. The benefit of hybrid welding is the synergistic effect of improved processing rates and joint accommodation over either of the processes viewed separately. Other processing methods are also being developed to increase the utility of laser beam welding for industry, such as the use of dual beams and beam manipulation. The continued advancement in process knowledge is seen as a key element for facilitating the development of new processes and encouraging the acceptance of new source technology.

Laser assisted cleaning of oxide films on SUS409 stainless steel

Laser assisted cleaning of oxide films on SUS409 stainless steel plates was studied both experimentally and theoretically. The highly oxidized surfaces with oxide scales of about 25u2002μm thickness were irradiated with Q-switched pulsed Nd:yttritium–aluminum–garnet lasers with and without frequency doubling, i.e., at 1064 and 532u2002nm wavelengths. Both multiple irradiation on single spots and scanning with pulsed lasers were employed. The variables studied were laser wavelength, pulse duration, number of pulses, and scanning velocity. The results indicate that heavily oxidized stainless steel surfaces can be cleaned with short, high power density pulses. Shorter laser wavelength, higher power density, and irradiation with multiple pulses improved surface cleaning. Stress wave induced spallation played an important role in the cleaning process. No loss of the underlying metal layer was observed during treatment.Laser assisted cleaning of oxide films on SUS409 stainless steel plates was studied both experimentally and theoretically. The highly oxidized surfaces with oxide scales of about 25u2002μm thickness were irradiated with Q-switched pulsed Nd:yttritium–aluminum–garnet lasers with and without frequency doubling, i.e., at 1064 and 532u2002nm wavelengths. Both multiple irradiation on single spots and scanning with pulsed lasers were employed. The variables studied were laser wavelength, pulse duration, number of pulses, and scanning velocity. The results indicate that heavily oxidized stainless steel surfaces can be cleaned with short, high power density pulses. Shorter laser wavelength, higher power density, and irradiation with multiple pulses improved surface cleaning. Stress wave induced spallation played an important role in the cleaning process. No loss of the underlying metal layer was observed during treatment.

Experimental comparison of a traditionally built versus additively manufactured aircraft heat exchanger

This study compared the performance of both baseline and enhanced traditionally built heat exchangers (aircraft oil coolers), to both baseline and enhanced additively manufactured (AM) heat exchangers of similar geometry. Three dimensional (3D) Xray computed tomography scans were performed on the baseline traditionally built heat exchanger in order to develop a solid model for AM fabrication using a laser-based powder bed fusion process with AlSi10Mg powder. Two AM heat exchanger geometries were constructed to replicate the baseline traditionally built geometry, with one AM heat exchanger containing additional small air-side enhancement features. The air-side pressure drop for the AM heat exchangers was double that of the traditionally built baseline heat exchanger. Heat transfer was increased by about 10 percent for the baseline AM and by 14 percent for the enhanced AM heat exchanger when compared to the traditionally built baseline heat exchanger. Both of the AM heat exchangers performed as well as the enhanced traditionally built model, but both had a higher pressure drop. Ongoing research seeks to ascertain the specific causes of the increased pressure drop and improved heat transfer, in order to provide a foundation for enhancement of future AM-built heat exchanger designs.

A phase-field model for simulation of the laser cladding process using a discontinuous viscosity variable and its approximation by finite element method

The use of numerical simulation for predicting energy and mass transport in the laser cladding process provides a substantially improved understanding of the process, as well as the potential for significant efficiency during process development. This paper describes the development of a model, whose main features include a phase-field variable for the modeling of the powder layer and the surrounding atmosphere, and a discontinuous viscosity function for the representation of the solid/liquid interface.The use of numerical simulation for predicting energy and mass transport in the laser cladding process provides a substantially improved understanding of the process, as well as the potential for significant efficiency during process development. This paper describes the development of a model, whose main features include a phase-field variable for the modeling of the powder layer and the surrounding atmosphere, and a discontinuous viscosity function for the representation of the solid/liquid interface.

Path planning strategies for laser line forming

Thermal-mechanical processing by laser radiation has been shown effective in forming plates into relatively complex shapes at economically supportable rates. While simulation models to predict deformation given a set of process parameters exist and continue to be improved, few attempts have been made to solve the so-called inverse problem. This inverse problem can be defined as determining the locations and processing parameters of the heating paths that will result in a desired deformation. The calculation of these heating paths is an under-constrained problem with essentially infinite potential solutions. Recent research efforts at several international institutions have provided various strategies for solving this problem. This paper discusses these strategies, as well as the most recent developments from the ongoing efforts at the Applied Research Laboratory and at the Department of Mechanical Engineering, both of Penn State University.Thermal-mechanical processing by laser radiation has been shown effective in forming plates into relatively complex shapes at economically supportable rates. While simulation models to predict deformation given a set of process parameters exist and continue to be improved, few attempts have been made to solve the so-called inverse problem. This inverse problem can be defined as determining the locations and processing parameters of the heating paths that will result in a desired deformation. The calculation of these heating paths is an under-constrained problem with essentially infinite potential solutions. Recent research efforts at several international institutions have provided various strategies for solving this problem. This paper discusses these strategies, as well as the most recent developments from the ongoing efforts at the Applied Research Laboratory and at the Department of Mechanical Engineering, both of Penn State University.

Minimizing buckling distortion in welding by hybrid laser-arc welding

Abstract: Low heat input welding technologies such as laser beam and hybrid laser-arc welding (HLAW), which have the ability to reduce weld distortion in thin-panel structures, are introduced. Low heat input laser and hybrid laser-arc welds were made on panels ranging from 1 to almost 6xa0m long and compared with conventional (high heat input) arc welding techniques. Experimental and analytical weld distortion data are presented to provide a direct comparison of conventional and advanced welding technologies. It is demonstrated that a hybrid laser arc weld process, which is well suited for today’s heavy manufacturing environment, can reduce distortion by a factor of 2 to 4 compared with conventional processes.