Unsteady heat transfer with simultaneous melting and crystallization at laser cladding process
with coaxial metal powder injection is investigated numerically. Numerical modeling determined
that the main parameters that govern melt pool dynamics and system maximum temperature are
mass feed rate, laser power and scanning speed. Also it is determined that taking in to account the
kinetics of phase change results in melt pool boundary and melting temperature mismatch.
Dimensions of melted zone and cladding height are compared with experimental data.
KEYWORDS: Data modeling, Laser cutting, Metals, Thermal modeling, Laser applications, Laser processing, Gas lasers, Physics, Energy efficiency, Temperature metrology
Numerical comparisons of some models for estimating the power losses due to heat conduction in process of gas-assisted
laser cutting are presented in this paper. In spite of differences between these models their results match fairly well.
The processes of heat transfer in microparticles in the gas atmosphere due to kinetics of phase
change (melting) under laser radiation have been numerically investigated. The temperature dependence of thermal and
optical parameters, irradiative cooling and heat exchange with the gas atmosphere are considered. The dynamics of
temperature distribution of particles of different sizes subject to melting has been determined. The dependences of the
time of full melting on the properties of particles and on laser radiation have been obtained. This will help to choose the
right regime of laser treatment in selective laser sintering.
Numerical modeling of the process of thermal ionization associated with the interaction of laser radiation and metal
target was performed and the temperature dynamics and the plasma absorptance were obtained. Threshold values of
temperature for the appearance of the thermal instability and near-surface optical plasma generation have been derived.
The processes in near-surface laser induced plasma in specific conditions of laser welding are under consideration.
KEYWORDS: Carbon dioxide lasers, Turbulence, High power lasers, Gas lasers, Active optics, Laser resonators, Polonium, Laser applications, Refraction, Refractive index
The enhancement of optical inhomogeneities of active medium of high-power fast-axial flow CO2 laser is coupled with increasing of the isobaric fluctuations of temperature and density in turbulent flow due to nonuniform heat-releasing.
The luminescent method was used to measure the spectrum of turbulent pulsations of gas density in fast- axial flow CO2 laser with radio-frequency discharge input. It is shown that gas density pulsations increase through gas discharge along gas flow axes. In continuous-wave fast-axial flow (FAF) CO2 laser there is subsidiary deterioration of quality of active medium due to intrinsic turbulence intensified by gas discharge energy input.
The isobaric fluctuations of temperature and density, attending with turbulent adiabatic fluctuations of velocity, have been evaluated under spatial non-uniformity of temperature and at heat generation in the incompressible flow. The character of their quantity dependence on spatial scale has been revealed. It has been shown that the temperature gradient and specific power of heat generation strongly affect the isobaric fluctuations of temperature.
The degenerate intra-cavity four-wave mixing on nonlinearity of gain of active medium of cw CO2 laser was used for determination of turbulent parameter of active medium flow.
KEYWORDS: Carbon dioxide lasers, Diffusion, Diagnostics, Mirrors, Four wave mixing, Resonators, Laser resonators, Photoresistors, High power lasers, Active optics
The characteristics of turbulent flow of laser mixture in high-power industrial CO2 lasers with fast axial flow have an influence on energy parameters of laser beam. In particular the transverse size of DC discharge and discharge stability depend on coefficient of turbulent diffusion. Moreover, turbulent pulsations cause small-scale optical inhomogeneities in the active medium. By the method of intra-resonator four-wave mixing in the active mixture of industrial CO2 laser with fast axial flow the coefficient of turbulent diffusion was determined. The nonlinearity of gain coefficient was used, and dissipation of amplitude diffraction grating due to turbulent diffusion was taken into consideration.
The method of estimation of Cn2 of laser mixture turbulent flow is proposed based on experimental dependencies of amplitude of gas pulsation on spatial pulsation scale. The connection between degree of nonequilibrium and C,2 magnitude is shown. The boundaries of inertial and viscosity ranges are determined. The estimation of Cn2 is within (3 .. . 14). 10 15 cm2/3 as dependence of gas- discharge current.
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