The article devoted to modeling of influence of thermo-capillary convection on heat transfer in melting pool during CW laser welding. An approximation of potential flow with boundary layers was used for solution of hydrodynamic problem in melting pool. A hydrodynamic problem was formulated in terms of current function. To determine a value of melt velocity circulation a condition of equality of mechanical powers of driving force (Marangoni tension) and braking force (viscous tension in boundary layer) was used. Calculations show that Marangoni convection increase an upper part and diminish a bottom part of melt pool.
The article deals with phase transformation in aluminum-magnesium alloys during high speed cooling after the laser action. The intermetallic precipitation growing is calculated with the reaction-diffusion model. The “shooting” method was used for analytical solution of equation for grow of spherical inclusion. Mutual influence in ensemble of precipitation is taken into account as changes of admixture concentration on “infinity”. Unification of model of precipitation ensemble development with the stochastic model of precipitation engendering and self-consistent model of laser welding allow to calculate a size distribution of inclusions in heat effected zone.
The construction ofmonitoring systems for a process of laser welding with deep penetration requires a choice from all possible signals, bearing information about the process , those, which is the most complete satisfy to the technological requirements, as essence ofthe control process. There are: 1 . Presence ofthe clear and physical -adequate connection between parameters ofthe signal measured and behavior ofthe welding bath; 2. Possibility to "recalculate" the signal measured in technologically significant parameters: a depth and width of the welding seam, and perhaps its mechanical properties, during a time, acceptable for the technologists; 3. Possibility to monitor the appearance ofdefects ofthe weld seam, such as pores, root peaks and etc. by the measured signal; 4. Convenience ofmeasurement and processing and protection from external interference. It has to note, that the acoustic signal so far have not physically clear connection with behavior of the welding bath, in spite ofthe fact that a lot of works are devoted to study ofthem in a number of years. Experimental researches ofprocess ofacoustic emission at laser welding togetherwith results of frequent analysis have shown dependence ofthe signal level on intensity ofthe laser radiation and processing regime. Correlation ofthe acoustic emission signal with radiation power, welding speed and level ofradiation focusing are established by the authors ofthe . The similar results are described in a number ofworks [4,5].Itis established specifically, that the acoustic signal bears in selfthe information about presence ofthe through or partial penetration [5,6],however to understand the acoustic emission nature, there are used as a rule either phenomenological reasons  or the models which far from reality, for example . The authors of  basing on  connect the acoustic signal with time derivative of the evaporation mass flux but thus they completely neglect a real physical picture of generation ofthe sound in the active zone. The purpose of given investigation is to establish the connection and decide a question about usefulness ofthe acoustic emission to monitor the process of laser welding. Let's begin from description ofthe phenomenon and formulation of the investigation problems. The cavity is a source of sound oscillations at laser welding with deep penetration. By evaporation from the cavity surface a vapor flow running into surrounding space is formed. Self-oscillations oftemperature of the cavity walls, described in [1 1], result in oscillation ofthe evaporation mass ratio, and oscillating walls of the cavity modulate a vapor jet in addition. By virtue of connection described by gas-dynamic equations the velocity and temperature oscillations ofthe vapor jet lead to those ofpressure, i.e. to appearance of the sound oscillations. When acoustic frequencies observed in experiments on laser welding (f-i 0 -I0000 lIz) are typical, length of the acoustic wave "A" is much more than the cavity depth and especially than its radius. Since for the surrounding space the outlet section ofthe cavity is a point source ofthe acoustic oscillations. Power ofthis source and its frequent spectrum are defined by nature ofthe radiation process of the sound fluctuations from the cavity into the surrounding space. It is necessary to take into account, that the gas temperature and hence the sound velocity inside the cavity and in the surrounding space are essentially distinguished. The size of the transitive area above the cavity, where the sound velocity changes from value which is typical for the cavity up to the value corresponding to the room temperature, is a lot of less than length of the acoustic wave. Therefore we can neglect its sizes and require on some border (coinciding with the metal surface), in order that the solution ofthe problem about internal acoustics of the cavity coincides with the solution of the external problem about spreading of the oscillations in the surrounding space
The purpose of presented work is theoretical and experimental research of the reasons of furrow formation on a cut surface at gas-assisted laser cutting. For experimental study of removal laws of a material from a cutting zone a high-speed filming, and as the temporary control of brightness and temperature on the bottom surface of cutting material in a zone of cut outlet were used. The experiments speak about periodic nature of a material removing from the cut.
For realization of the optimum mode of hole drilling the packs of laser pulses of high intensity were used, when average level of intensity of radiation is not too high, that reduces specific energy of destruction, and the peak intensity is reasonably great, that the pulse of pressure of effect at evaporation has completely deleted the liquid from the zone of processing. The high peak intensity of radiation permits in this case to place a target not in focus of a optical system, creating on its surface the image with the help of masks. It permits to receive in metal plates the holes of any section, to execute marking of surfaces and deep engraving of sample material with the help of laser. With the using of focused radiation the cutting of thin materials can be executed without a auxiliary gas. The condition of melt replacement is excess of power of recoil pressure above the power of viscous forces and forces of inertia. The decision of the hydrodynamic problem permits to evaluate the necessary parameters of laser radiation, frequency and longitude of packs of pulses which provide increases of process speed in several times. The conducted experiments confirm the indicated theoretical analysis of process of removing of the material under action of packs of pulses of laser radiation. The given process is realized in laser technological installations for holes drilling and marks of materials.
In this article the dynamic model of the process of the laser welding with deep penetration based on the variation principles is presented. The model takes into account melting flow, wave motion on the cavity surface, melting viscosity, bubble pressure, recoil pressure and radiation parameters. The model predicts self-oscillation character of the cavity behavior in welding, moreover the cavity oscillations are stochastic in general case.
The paper deals with the problem of on-line monitoring of the cavity parameters in laser beam welding with deep penetration. On the basis of simplified model of the cavity dynamic behavior a strategy of the cavity depth and average diameter measurements was developed. The possible ways of the technical realization of the measure system are also discussed.
This article deals with strategic development of laser technology of material treatment. The efficiency of laser material processing is discussed. The structure of laser treatment CAD/CAM systems is suggested. The opportunities of the global network telecommunications allow to provide the wide possibilities to use the system of prediction in the mode of real time.
Software supported process planning and quality assurance are of primary importance for the realization of a manufacturing method in laser beam welding. A novel software tool for process planning and prediction of the properties of laser welded seams named CALAS, i.e. computer aided lasering, is presented. Its structure and performance are described in detail. The software tool connects a physical model of welding by carbon-dioxide laser radiation to an interactive man/machine-interface by simulation and visualization. The model considers five fundamental physical processes, absorption of laser radiation at the keyhole surface including multiple reflexion, heat conduction in liquid and solid phase, melt flow, gas flow and heat conduction in the vapor phase, and absorption of laser radiation inside the keyhole volume (plasma absorption). The effect of processing parameters and the resulting geometry of the welded seam are calculated and displayed. The interface provides a three dimensional visualization of the keyhole and the melt pool. Cross sectional views and longitudinal sections may be displayed two-dimensional. Besides typical parameters the beam characteristics, such as power density distribution, and material properties, such as temperature dependent surface tension and heat conductivity, are included in the calculation too. Due to direct and fast prediction of process parameters and seam geometry CALAS serves as a controlling tool for the operator at the machine tool, and in a more general view, it serves as a tool for processing planning and quality assurance in industry.
The article describes a computer model of laser welding with a deep penetration base on unification of solution heat-mass transfer problem and the problem of irradiation propagation in cavity in approximation of geometrical optics.