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The paper contains the findings of the metallographic study of dissimilar metal welds (steel 12Х21Н5Т and bronze BrХ-06) made by electron-beam welding (EBW) with beam modulation (transversal and X-shaped oscillation with triple beam splitting). The research shows that beam oscillation causes the metals to stir in the weld pool. As a result, welds have a very heterogeneous structure by width. X-shaped oscillation causes more intensive stirring than transversal oscillation. This leads to more homogenous stirring of crystallizing phases in the centre of the weld. The heterogeneous structure caused by beam oscillation gives the weld a very heterogeneous solidity both by width and depth. Triple beam splitting heated from bronze promotes the homogenous weld structure which is a fine-dispersed mechanical mixture of two systems: a eutectic based on copper and a mixture of solid solutions based on [alpha]-Fe and [gamma]-Fe. Such a structure makes the weld equalizes the solidity of the weld both by width and depth.

The paper presents a model developed by the authors and aimed to describe heat and mass transfer during wire-based additive manufacturing, when electron beam, plasma or arc are used as energy sources in case of non-consumable electrode welding. The model describes non-stationary and non-equilibrium conjugated processes of heat and mass transfer in free-surface liquid metal. The solution of differential equations of viscous fluid motion (Navier-Stokes), with convective terms and at laminar flow, has become the model base.Melting and crystallization of the metal is recognized by heat release in a two-phase region. The material density variation during phase transitions of the first and the second order can be described by introducing a certain dependence on temperature. The model is able to consider the use of preliminary and additional induction heating by changing the initial temperature and establishing an additional distributed bulk heat source. Variables for the simulation of heat and mass transfer during additive formation are the intensity and type of the heat source, the plate initial temperature, the power density distribution, the intensity of the additional bulk heating, the dependence of material thermal and physical characteristics on temperature, the characteristics of the phase transitions, the motion velocity of the heat source, the rate of wire feeding.Keywords: additive manufacturing, 3D wire-based deposition, arc and concentrated heat sources, modelling of heat and mass transfer, numerical implementation.

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We discuss issues the process of layer-by-layer synthesis of metal products by wire surfacing. A mathematical model of the process has been developed and implemented. The model allows one to calculate the volumetric distributions of temperatures, melt flow rates, pressures, components of heat fluxes density, the shape and dimensions of the molten bath, the shape of the free surface of the molten metal, the shape and dimensions of the weld bead. For this purpose, the main physical processes that affect the formation of the metal product were considered, namely: melting and crystallization of the metal, surface tension, the Marangoni effect and the heat source features. The smoothed particle method was used to implement this model. A number of numerical experiments were carried out using the developed model. Firstly, the model parameters for steel and titanium were identified and verified. After that, calculations were carried out to verify the model itself using the obtained roller geometry. The numerical solution for the deposition of one layer was compared with the full-scale experiment. The error was no more than 5% in any direction. Thus, the efficiency and correctness of the constructed model is shown.