The work presents the experimental investigation of the laser welding of the aluminum-lithium alloys (system Al-Mg-Li) and aluminum alloy (system Al-Cu-Li) doped with Sc. The influence of the nano-structuring of the surface layer welded joint by the cold plastic deformation method on the strength properties of the welded joint is determined. It is founded that, regarding the deformation degree over the thickness, the varying value of the welded joint strength is different for these aluminum alloys.
The laser cutting of the low-carbon and stainless steel with fiber and CO2 lasers was compared by a similar technique.
The dependence of the cut surface roughness on cutting parameters was analyzed for stainless steel sheets of 3 and 5 mm
and mild steel sheets of 5, 10, 16 mm. The speed at which the roughness is minimal was found. For the cutting of
stainless steel with nitrogen, the minimal achieved roughness is approximately similar for two types of lasers, whereas
the speed correlating with the minimal roughness was higher in the fiber-laser case. When cutting the mild steel with
oxygen, the СО2 laser enables to reach lower roughness at higher cutting speed. For the oxygen-assisted laser cutting, the
empirical relations were found which connect the cutting speed and laser power associated with the minimal roughness,
with the cut sheet thickness, for the cutting processes by the fiber and СО2-laser.
The conditions of minimal-roughness surface production were studied experimentally in the process of the oxygenassisted laser cutting with the fiber and СО2 lasers. The coefficient of the laser radiation absorption in the cut channel during the cutting process was measured as the sheet thickness varied from 3 to 16 mm. It is demonstrated that the cutting conditions with the minimal roughness can be formulated for the two laser types with the same generalized parameters, i.e. dimensionless absorbed laser power and Peclet number (dimensionless speed). Numerical values of these parameters were found experimentally. The optimum Peclet number is 0.5 for the СО2-laser cutting, and 0.35 when the fiber laser is used.
Oxygen-assisted laser cutting of low-carbon steel with a fiber laser is studied experimentally. The objective of the work
is to find the link between the cutting quality (which is low roughness and no dross) and energy characteristics of the
cutting. Cutting parameters are expressed though two dimensionless complexes, namely the Peclet number and
dimensionless laser power. It is founded that for the cutting with minimal roughness, the Peclet number is of 0.35…0.4, and the contribution of the absorbed laser energy in the unit of removed material volume is 12…14 J/mm3 for sheets of 3, 5, and 10 mm. The results are compared to the data obtained for the СО2 laser.
In the present paper the scaling laws for the oxygen-assisted laser cutting of low-carbon steel of 5-25 mm is studied experimentally. No dross and minimal roughness of the cut surface were chosen as criteria of quality. The paper also studies the possibility to describe the cutting process by the similarity method and as ratios between dimensionless variables. Normalized power W/ktT, normalized velocity Vcb/a (Peclet number) and kerf width have special optimum numb. Formulas were obtained to determine the optimum values of the laser power and cutting speed for the given sheet thickness. The energy balance of the oxygen-assisted laser cutting is studied experimentally at these optimum parameters. The absorbed laser energy, heat conduction losses and cut width were measured experimentally, and then the energy of exothermic reaction of oxidation was found from the balance equation. To define the integral coefficient of absorption, the laser power was measured on the cutting channel exit during the cutting. The heat conduction losses were measured by the calorimetric method. It has been established that the absorbed laser energy, oxidation energy, thermal losses and melting enthalpy related to a sheet thickness unit, do not depend on the sheet thickness at the cutting with the minimal roughness. The results enable to determine the fraction of the oxidized iron in the melt and thermal efficiency at the cutting with the minimal roughness. The share of the oxidation reaction energy is 50-60% in the total contributed energy.
This report presents the results of the experimental investigation of the interaction between energy and mechanical
characteristics of the laser cut for thick sheets. The aim is to optimize the energy consumptions in of the process of high-quality
oxygen-assisted laser cutting of low-carbon steel.
In our previous work we found experimentally the scaling laws for the oxygen-assisted laser cutting of low-carbon steel
of 5 - 25 mm. No dross and minimal roughness of the cut surface were chosen as criteria of quality. Formulas were
obtained to determine the optimum values of the laser power and cutting speed for the given sheet thickness. In the
present paper, the energy balance of the oxygen-assisted laser cutting is studied experimentally at these optimum
parameters. The absorbed laser energy and heat conduction losses and cut width were measured experimentally, and
then the energy of exothermic reaction of oxidation was found from the balance equation. To define the integral
coefficient of absorption, the laser power was measured on the cutting channel exit during the cutting. The heat
conduction losses were measured by the calorimetric method. It has been established that the absorbed laser energy,
oxidation energy, thermal losses and melting enthalpy related to a sheet thickness unit, do not depend on the sheet
thickness at the cutting with the minimal roughness. The results enable to determine the fraction of the oxidized iron in
the melt and thermal efficiency at the cutting with the minimal roughness. The share of the oxidation reaction energy is
50 - 60% in the total contributed energy.
The paper presents the results of the study of the CO2 laser radiation absorption in the optical-breakdown plasma in a
supersonic air stream. The experimental facility and procedures of the absorption coefficient measurement in plasma are
described. Experimental dependencies of the radiation absorption have been obtained within the wide range of the gasdynamic
parameters of the supersonic air stream (velocity, static pressure, density, Mach number). The results are
helpful to choose the working modes of the wind tunnel to choose the influence of the energy supply into the supersonic
stream on the sonic boom formation and its level.
For mild steel of 5...25 mm thick, the parameters area of the maximum cutting quality has been determined
experimentally. The conditions of cutting with minimum roughness are presented as a dependence of dimensionless
values. It has been shown that the high-quality cutting features the specific volumetric input of laser energy, equal for
any thickness. Normalized power W/λt(Tm-T0), normalized velocity vb/γ (Peclet number) and kerf width have special optimum numbers.
A high power repetition rate CO2 laser with mechanical Q-factor modulation has been manufactured. Its generation characteristics
have been studied. The structure of shock waves appearing at the interaction between a supersonic air jet and plasmoid formed by the
optical breakdown, has been investigated.
KEYWORDS: Resonators, Mirrors, Laser cutting, Laser resonators, Gas lasers, High power lasers, Laser applications, Reflection, Diffraction, Laser development
A brief review is made for the schemes of optical resonators for the generation of a high-quality beam in high-power
CO2 lasers. The main results of the self-filtering resonator application in the industrial laser are presented. The self-filtering resonator is compared to the stable resonator by the output beam characteristics, aberration sensitivity, and laser
cut characteristics by the example of steel cutting.
The presented data are the results of the development of the continuous electric-discharge CO2 laser
with the cross discharge and convective cooling of the active medium, with the power up to 14 kW. Extended
disc fans are used for gas pumping, they are heat-exchangers at the same time. Preliminary results of gas
flow-rate, heat-exchange and energy characteristics are reported. Some experimental results of laser cutting of
thick sheets are given as well as the results of the numerical and experimental simulation of the laser cutting gas-dynamics.
The method of laser-induced fluorescence (LIF), excited by UV laser radiation, is widely used in investigating biological tissues. But the radiation itself may cause some changes in the tissue irradiated. The results of our experiments have shown that exposure to the UV-radiation leads to some changes of LIF spectrum of a cross-striated muscle, myocardium, aorta. In particular, a noticeable attenuation of intensity of tryptophan fluorescence band (330 nm ) takes place. The intensity is shown to depend on the number of pulses. At lower energy of the exciting radiation the intensity falls off more slowly. Quantitative information is obtained on the tryptophan inactivation cross section. The conclusion on commensuration of the inactivation cross sections of tryptophan and cystine within 248 nm wavelength is proved. The influence of radiation on lymphocytes viability was investigated. Nonetheless, although some changes take place in the tissues exposed to laser radiation, they have not time to exceed the magnitude of random scatter for the period needed in our experiments for the LIF spectra recording (around 30 pulses), so these changes do not influence the final result.
An automated laser technological complex (ALTC) based on a self-sustained transverse-flow discharge pumped CW CO2 laser been developed. In the laser, a self-filtering optical resonator is used. The using of this type of resonator allowed to generate the high-quality beam with 8 kW power. The results of the beam characteristics measurements are presented. Power characteristics of the laser, filled with gas mixtures with or without helium, are presented. The maximum irradiation power amounts to 8.3 with extraction efficiency of 11.3, helium-free operation characterizes by the 5 kW power and 8,9% efficiency.
We investigated the change of laser-induced fluorescence (LIF) spectra of isolated cardiac graft tissues during their storage at a temperature of +4°C. The results were compared using routine histological methods, experiments performed using fluorescent probes and quantitative fluorimetry. We discovered that the loss of myocardium tissue viability leads to its LIF spectra alteration. Hence everything points that the LIF method of integral estimation of heart tissues viability has a high diagnostic potential. The advantages of this method are its rapidity and a low level of adverse effects on tissue. Thus LIF could be utilized for low-invasive rapid control of transplant viability in the process of its preparation and during the surgery itself.
A description of an automated laser technological complex based on a CO2 laser with the power of 5 kW designed for cutting sheets materials is given. Analysis of precision characteristics of the main units of the laser complex is presented. Results of industrial tests of the laser complex on manufacturing of parts from electrotechnical steel are given.
In activity the device of the high-power electrodigit laser with optical system and the problem of pressure losses upon gas motion along a closed circuit containing channels in which heat is supplied to and removed from the gas is studied. The object where the pressure losses are studied is a CO2 laser with a crossflow.
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