Browsing by Author "Trushnikov D."

Now showing 1 - 9 of 9
  • No Thumbnail Available
    Item
    Application of dynamic beam positioning for creating specified structures and properties of welded joints in electron-beam welding
    (2020-05-01) Olshanskaya T.; Belenkiy V.; Fedoseeva E.; Koleva E.; Trushnikov D.
    The application of electron beam sweep makes it possible to carry out multifocal and multi-beam welding, as well as combine the welding process with local heating or subsequent heat treatment, which is important when preparing products from thermally-hardened materials. This paper presents a method of electron beam welding (EBW) with dynamic beam positioning and its experimental-calculation results regarding the formation of structures and properties of heat-resistant steel welded joints (grade of steel 20Cr3MoWV). The application of electron beam oscillations in welding makes it possible to change the shape and dimensions of welding pool. It also affects the crystallization and formation of a primary structure. It has been established that EBW with dynamic beam positioning increases the weld metal residence time and the thermal effect zone above the critical A3 point, increases cooling time and considerably reduces instantaneous cooling rates as compared to welding without beam sweep. Also, the difference between cooling rates in the depth of a welded joint considerably reduces the degree of structural non-uniformity. A bainitic-martensitic structure is formed in the weld metal and the thermal effect zone throughout the whole depth of fusion. As a result of this structure, the level of mechanical properties of a welded joint produced from EBW with dynamic electron beam positioning approaches that of parent metal to a greater extent than in the case of welding by a static beam. As a consequence, welding of heat-resistant steels reduces the degree of non-uniformity of mechanical properties in the depth of welded joints, as well as decreases the level of hardening of a welded joint in relation to parent metal.
  • No Thumbnail Available
    Item
    Computer-aided electron-beam deflection control system
    (2020-06-02) Koleva E.; Koleva L.; Mladenov G.; Trushnikov D.; Andonov A.
    The electron beam processes - 3D selective melting (3D printing), welding, etc. are complex processes with many processing variables, which require integration of interfaces for control of the processes on different levels through hierarchical equipment models, functional data and operation control models. We developed a user interface software application for controlling the electron-beam motion along several types of trajectories and a free complex shape trajectory by controlling the deflection system parameters. Several types of motion patterns with different velocities are realized, together with the possibility of choosing a free trajectory by defining the electron-beam path by a graphical image.
  • No Thumbnail Available
    Item
    Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding
    (2014-01-01) Trushnikov D.; Mladenov G.; Belenkiy V.; Koleva E.; Varushkin S.
    Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 1016 m-3, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A·m-2, i.e. 8 mA for a 3-10 cm2 collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole. © 2014 Author(s).
  • No Thumbnail Available
    Item
    Heat distribution simulation in electron-beam surface modification of 316L stainless steel samples
    (2020-06-02) Koleva E.; Tsonevska T.; Koleva L.; Vutova K.; Mladenov G.; Naplatanova M.; Trushnikov D.; Varushkin S.
    A time-dependent heat model is implemented for the simulation of the heat distribution in 316L stainless steel samples during electron-beam irradiation. The influence is studied of the electro-beam power and processing time on the temperature field produced in the samples. The simulation results are compared with real experimental data of electron-beam surface modification of 0.5-mm-thick 316L stainless steel samples using the ELIT-60 installation in the Institute of Electronics BAS. The simulation and the experimental results show good agreement.
  • No Thumbnail Available
    Item
    Mathematical modelling for energy beam additive manufacturing
    (2018-10-19) Mladenov G.; Koleva E.; Trushnikov D.
    A normalized processing diagram for powder bed additive manufacturing by concentrated energy beams was constructed on the base of simple analytical model simulating the heating of the powder layers by a moving linear heat source. The distance of the processing regime points below the line of the dependency of the maximal dimensionless temperature (or of the maximal thermal efficiency) on the dimensionless beam velocity gives insight on the processing parameters range and on the possibility for prognosticated optimization of the utilized parameters of the energy beam at selective powder layer melting. The diagram provides useful reference and methodology to aid the selection of appropriate processing parameters during the early development stages of this perspective technology.
  • No Thumbnail Available
    Item
    Methods of increasing productivity of material layerwise synthesis based on melting wire filler by electric arc in vacuum
    (2018-01-01) Trushnikov D.; Shchitsyn Y.; Belinin D.; Bezukladnikov I.; Reisgen U.; Koleva E.
    Prospects of one of unconventional research areas aimed at improving additive technologies have been described. The key aspect of the proposed technology is the formation of multilayered homogeneous materials in vacuum using electric arc as a heating source, as well as using a solid metal wire as a filler metal. It is shown that this approach, compared to the available solutions applied in the global industrial production practices, will serve to increase productivity related to forming layerwise materials, as well as to resolve a number of disadvantages of the available equipment used for additive technologies implementation.
  • No Thumbnail Available
    Item
    Multicriterial optimization strategies for electron beam welding processes
    (2022-04-04) Koleva E.; Koleva L.; Trushnikov D.; Kolev G.; Petrova Z.
    The electron beam welding process is analyzed of high-strength steel type 15Cr5Mo samples with deflection oscillations along the zone of interaction. The geometries of the molten and the heat affected zones are studied in order to investigate the influence of the deflection oscillations parameters and to improve the seam quality. A robust engineering approach is implemented for the case of production conditions considering the errors in the process parameter settings. The problem of quality improvement through fulfilling pre-set technological and quality requirements is solved by scalarization of the vector criteria by implementing a reference point strategy. Other multicriterial optimization strategies are also proposed.
  • No Thumbnail Available
    Item
    Use of a Secondary Current Sensor in Plasma during Electron-Beam Welding with Focus Scanning for Process Control
    (2016-01-01) Trushnikov D.; Krotova E.; Koleva E.
    We consider questions of building a closed-loop focus control system for electron-beam welding. As a feedback signal, we use the secondary current in the plasma that forms above the welding zone. This article presents a model of a secondary current sensor in plasma during electron-beam welding with focus scanning. A comparison of modeled results with experimental data confirms the adequacy of the model. We show that the best results for focus control are obtained when using phase relationships rather than amplitude relationships. We outline the principles for building an EBW focus control system based on parameters of the secondary current in plasma. We simulate the work of a control system's circuits and demonstrate the stability of the synthesized system. We have conducted pilot tests on an experimental prototype.
  • No Thumbnail Available
    Item
    Using bremsstrahlung X-Ray for positioning of the filler wire during electron beam surfacing
    (2018-10-19) Varushkin S.; Trushnikov D.; Koleva E.; Shamov D.
    This work aims to assess the bremsstrahlung X-Ray signal from the processing zone obtained by the use of a solid wire during electron beam surfacing. Applications of the bremsstrahlung X-Ray signal in the control systems allow positioning of the filler wire. During the experiments, a scintillation detector based on monocrystalline iodine cesium and silicone photomultiplier was used for registration of the X-Ray signal. Circle oscillations of the electron beam create the informative component. Synchronous storage method was applied for mathematical treatment of the recorded signal.