laser technologies of processing advanced materials
(1) The processes of channeled penetration (with aspect ratio of the order of 10 to 30)
of intense laser radiation (104-107W/cm2, 0.1 to 5kW) into the condensed media
(metals, dielectric liquids) which are opaque to this radiation have been studied
theoretically and experimentally. The investigations were pursued for the sake of
optimization of the following processes: welding and cutting of large-thickness
materials with a laser; laser excision of the biological tissue in medical procedures.
A theory was elaborated which took account of a wide class of hydrodynamic instabilities
(capillary-evaporative, thermocapillary, Kelvin-Helmholtz) and showed good agreement with
the experimental data obtained by different authors. Allowance was made for hydrodynamic
self-oscillations of the channel wall shape which were caused by macro-instabilities of
the wall surface, as well as by relaxation fluctuations of the vapor pressure in the
channel resulting from flash evaporation of melt microdroplets. It was shown that the
stability of thick metal welding process is expected to be best over some optimal range
of velocities, depending on the material thermophysical properties and on laser beam
optical quality. The process was unsteady due to macro-instability of the thermal field
at low velocities, and to capillary-evaporative instability at high velocities.
The experimental study was conducted as well, and a model of a laser channel produced
in the liquid medium was constructed. The role of nonstationary self-oscillations of the
channel parameters under turbulent convection caused by the vapor recoil pressure, as
well as by the Archimedean and thermocapillary forces, has been established.
The hydrodynamic and thermophysical mechanisms of laser cutting with beam channeled
penetration into the material have been investigated. The mechanisms of energy loss
on heating the sample to be cut have been studied both experimentally and theoretically.
These mechanisms appeared to be dependent on the parameters of melt removal process and,
consequently, they provide for the optimal conditions of cutting (regarding for energy
and treatment quality). It has been shown that there exist the modes of laser cutting
which are related to hydrodynamic instabilities of the melt surface and to respective
generation of the droplet phase.
(2) The basic research of powerful laser beam interaction with matter under deep
penetration has forwarded the investigation and practical implementation of the
processes and facilities to perform laser welding and cutting of very thick materials.
The processes of high-speed (up to 20m/min) laser welding of non-corrosive pipes from
austenite-grade steels have been worked up, which allow the corrosion stability of the
welded joint to be at base metal level. An automatic tracking system (optical vision)
has been developed to check the welded joint quality.
A bench has been constructed to perform welding of oil-and-gas pipes with the use of a
combination of 5.0 and 3 kW lasers. It has been ascertained that the properties of
laser welded joints are not worse than those of the base metal.
(3) The technologies of precision laser cutting of the promising materials to be
applied in machine-building, nuclear energy and aerospace industries have been devised
jointly with the Institute of Metallurgy and Material Science of RAS.
(4) The expert and intelligence training systems for the users of laser processing
systems have been developed jointly with the System Analysis Institute of RAS
