Igor Shiganov

Study of interaction of laser radiation with scattering liquid media under conditions of a varying size distribution function of suspended particles

We report a study of laser radiation transfer processes in scattering media with a time-varying particle size distribution function. We consider the cases of a one-component solution, when the crystal growth occurs during freezing, and a solution with the addition of particles with a time-constant size. The results of the experimental validation of the developed mathematical model are presented. The possibility of using the obtained results to experimentally determine the concentration of metal particles in scattering liquids is considered.

Welding austenitic steel to copper with the defocused radiation of a fibre laser

Abstract Special features of producing butt welded joints between 12Cr18Ni10Ti austenitic steel and M1 copper by laser welding are investigated. Welding was carried out without filler or intermediate material. The defocused beam of the fibre laser, displaced to the austenitic steel, was used. The welded joints in dissimilar materials produced in the selected conditions were without defects and their strength was comparable with the M1 copper parent metal. The tensile tests and hardness measurements were carried out on the resultant welded joints. The microstructure of the welded joints was investigated and the transition zone was examined by chemical analysis.

Comparative analysis of parameters of pulsed copper vapour laser and known types of technological lasers

In the present paper we present the results of a comparative analysis of pulsed copper vapour lasers with visible emission wavelengths of 510.6 and 578.2 nm and pulse duration of 10-30 ns and known types of technological lasers as well as the prospects for using the copper vapor laser for microprocessing of materials.

Welding with a defocused laser beam

Abstract The results of experiments carried out to investigate the welding of austenitic stainless steels using a defocused laser beam are presented. It was assumed that the application of the defocused laser beam would increase the volume of the weld pool, which in turn would reduce the requirements on the preparation of edges and the gap between the workpieces. Microhardness was measured, 2D-computer tomography carried out, specimens were examined by metallographic techniques and the phase components of different zones of the weld pool were analysed by quantitative methods. Special features of the formation of the weld pool dependent upon the welding conditions were investigated. The results indicate that the application of the defocused beam produces high-quality welded joints and the method has also a positive effect on the stability of the vapour–gas channel and the phase composition of the weld metal.

Prospects for using laser radiation to improve cracking resistance in welding cryogenic steels

Abstract It is shown that in welding large structures with stable austenitic welding materials made of nitrogen-containing cryogenic chromium–nickel–manganese austenitic steels, cracks can form in the welded joint both during crystallization and in the solid-state at subsolidus temperatures. In laser welding, the structure of the cast weld metal can be greatly refined in comparison with arc welding and this should increase the solidification cracking resistance. In addition, laser welding can be used to produce the welded joint in a single pass thus preventing reheat cracking.

Possibilities of using pulsed lasers and copper-vapour laser system (CVL and CVLS) in modern technological equipment

Research on CVL installations with an average power of 20–25 W of cutting and drilling has shown wide range of applications of these lasers for micromachining of metals and a wide range of non-metallic materials up to 1–2 mm. From the analysis indicated that peak power density in the focused light spot of 10–30 μm diameter must be 109 –1012 W/cm2 the productivity and quality micromachining, when the treatment material is preferably in the evaporative mode micro explosions, followed by the expansion of the superheated vapor and the liquid. To achieve such levels of power density, a minimum heat affected zone (5– 10 μm) and a minimum surface roughness of the cut (1–2 μm), the quality of the output beam of radiation should be as high. Ideally, to ensure the quality of the radiation, the structure of CVL output beam must be single-beam, diffraction divergence and have at duration pulses τi = 20–40 ns. The pulse energy should have low values of 0.1–1 mJ at pulse repetition rates of 10–20 kHz. Axis of the radiation beam instability of the pattern to be three orders of magnitude smaller than the diffraction limit of the divergence. The spot of the focused radiation beam must have a circular shape with clear boundary, and a Gaussian intensity distribution.