Browsing by Author "Mladenov G."
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Item Automation of the electron-beam welding process(2016-04-07) Koleva E.; Dzharov V.; Kardjiev M.; Mladenov G.In this work, the automatic control is considered of the vacuum and cooling systems of the located in the IE-BAS equipment for electron-beam welding, evaporation and surface modification. A project was elaborated for the control and management based on the development of an engineering support system using existing and additional technical means of automation. Optimization of the indicators, which are critical for the duration of reaching the working regime and stopping the operation of the installation, can be made using experimentally obtained transient characteristics. The automation of the available equipment aimed at improving its efficiency and the repeatability of the obtained results, as well as at stabilizing the process parameters, should be integrated in an Engineering Support System which, besides the operator supervision, consists of several subsystems for equipment control, data acquisition, information analysis, system management and decision-making support.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.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).Item EBT 2018-Preface(2018-10-19) Mladenov G.; Koleva E.Item Electron beam characterization by a tomographic approach(2016-04-07) Koleva E.; Mladenov G.; Todorov D.; Koleva L.; Kardjiev M.In this paper, experimental data are analyzed for the integral current density distribution when the electron beam parameters are varied, namely, focusing current, beam current, venelt voltage and the distance to the measuring device. The 3D beam radial current density distribution is reconstructed by implementing a tomographic approach. The characterization of the electron beam is considered in connection with the estimation of the following parameters: the radial and the angular beam distribution standard deviations, the position of the beam focus and the beam emittance.Item Electron beam deflection control system of a welding and surface modification installation(2018-04-05) Koleva E.; Dzharov V.; Gerasimov V.; Tsvetkov K.; Mladenov G.In the present work, we examined the patterns of the electron beam motion when controlling the transverse with respect to the axis of the beam homogeneous magnetic field created by the coils of the deflection system the electron gun. During electron beam processes, the beam motion is determined the process type (welding, surface modification, etc.), the technological mode, the design dimensions of the electron gun and the shape of the processed samples. The electron beam motion is defined by the cumulative action of two cosine-like control signals generated by a functional generator. The signal control is related to changing the amplitudes, frequencies and phases (phase differences) of the generated voltages. We realized the motion control by applying a graphical user interface developed by us and an Arduino Uno programmable microcontroller. The signals generated were calibrated using experimental data from the available functional generator. The free and precise motion on arbitrary trajectories determines the possible applications of an electron beam process to carrying out various scientific research tasks in material processing.Item Empirical modeling of high-intensity electron beam interaction with materials(2018-04-05) Koleva E.; Tsonevska T.; Mladenov G.The paper proposes an empirical modeling approach to the prediction followed by optimization of the exact shape of the cross-section of a welded seam, as obtained by electron beam welding. The approach takes into account the electron beam welding process parameters, namely, electron beam power, welding speed, and distances from the magnetic lens of the electron gun to the focus position of the beam and to the surface of the samples treated. The results are verified by comparison with experimental results for type 1H18NT stainless steel samples. The ranges considered of the beam power and the welding speed are 4.2 - 8.4 kW and 3.333 - 13.333 mm/s, respectively.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.Item Integrated control system for electron beam processes(2018-04-05) Koleva L.; Koleva E.; Batchkova I.; Mladenov G.The ISO/IEC 62264 standard is widely used for integration of the business systems of a manufacturer with the corresponding manufacturing control systems based on hierarchical equipment models, functional data and manufacturing operations activity models. In order to achieve the integration of control systems, formal object communication models must be developed, together with manufacturing operations activity models, which coordinate the integration between different levels of control. In this article, the development of integrated control system for electron beam welding process is presented as part of a fully integrated control system of an electron beam plant, including also other additional processes: surface modification, electron beam evaporation, selective melting and electron beam diagnostics.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.Item Modelling the shape of electron beam welding joints by neural networks(2018-10-19) Tsonevska T.; Koleva E.; Koleva L.; Mladenov G.This article discusses the experimental results from multi-pool electron beam welding, with dynamic positioning of the electron beam (beam splitting) [1], resulting in the formation of two consecutive welding pools. The 12Cr18Ni10Ti stainless steel samples are welded with a change in the process parameters: the distance between the two electron beams (electron beam positions) and the ratio between the two mean electron beam powers, the frequency of the deflection signal, the beam current and the welding velocity. The focusing current is kept at a constant value. The weld cross-sections, experimentally obtained at different process parameters, are used to train, validate and test neural models. The accuracy of prediction of the shapes of the welds (the form of the molten pool) is discussed and compared with that of an estimated regression model.Item Patterning of structures by e-beam lithography and ion etching for gas sensor applications(2014-01-01) Durina P.; Bencurova A.; Konecnikova A.; Kostic I.; Vutova K.; Koleva E.; Mladenov G.; Kus P.; Plecenik A.This work deals with a method of preparation of nanometer structures for a gas detector based on e-beam lithography and ion etching of a thin TiO2 film. The aim was the fabrication of a gas sensor with meander or comb structures of nanometer dimensions. This is of importance since both the size of the contacts and the layer thickness affect the sensor's sensitivity.Item Study of the new CSAR62 positive tone electron-beam resist at 40 keV electron energy(2016-04-07) Andok R.; Bencurova A.; Vutova K.; Koleva E.; Nemec P.; Hrkut P.; Kostic I.; Mladenov G.One of the few «top-down» methods for nano-device fabrication is the electron-beam lithography, which allows flexible patterning of various structures with a nanoscale resolution down to less than 10 nm. Thinner, more etching durable, and more sensitive e-beam resists are required for the better control, linearity, and uniformity of critical dimensions of structures for nano-device fabrication. Within the last decade, researchers have made significant efforts to improve the resolution of the nanoscale e-beam lithography. The resist material properties are an important factor governing the resolution. Only the e-beam resist ZEP 520 of the Japanese manufacturer ZEON is characterized by relatively good properties and thus meets most users' expectations. This paper deals with the investigation and simulation of the characteristics of the new less-expensive AR-P 6200 (CSAR 62) positive e-beam resist (available since May 2013, manufactured by Allresist GmbH company).