Georgi Mihaylov Mladenov

Georgi Mihaylov Mladenov
Bulgarian Academy of Sciences | BAS · Emil Djakov Institute of Electronics

Prof, Dr of Phys Sci, Corr.Member of BAS

About

233
Publications
44,225
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1,001
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Additional affiliations
September 1967 - December 2011
Bulgarian Academy of Sciences
Description
  • I was founder and head of Laboratory Physical problems of electron beam technologies

Publications

Publications (233)
Article
Full-text available
A time-dependent heat model is implemented for the simulation of the thermal distribution in stainless steel 316L samples during electron beam irradiation. The influence of following process parameters: the electron beam power and the processing time on the obtained temperature fields in the samples, is investigated. The obtained simulation result...
Article
Full-text available
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-...
Conference Paper
Full-text available
Abstract — In this paper the simulation of electron beam welding of thin 316L stainless steel thin plates by a moving linear heat source is considered. Regression models for the molten pool geometry characteristics, depending on the electron beam power and the welding velocity are estimated. The thermal histories and the cooling rates defining the...
Article
Full-text available
In this paper the developed software for simulation of the temperature distributions in the cast ingots at electron beam drip melting for different materials is presented. The influence of the change of the process parameters electron beam power, casting velocity and the beam radius on the temperature distributions in the cast ingot and the paramet...
Article
Full-text available
In this article quasi steady-state two-dimensional heat model is implemented for the simulation of the temperature distribution in the cast copper ingots through electron beam drip melting. Regression models are estimated for the dependence of the shape of the crystallization front (molten depth, width, volume of the molten metal) on the variation...
Article
Full-text available
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 (...
Article
Full-text available
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 bea...
Article
Full-text available
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...
Article
Full-text available
The optimization of welds obtained by electron beam welding is a multi-criterial task, involving the requirements for the geometrical characteristics of the welds, together with the fulfilment of the requirements for lack of defects. This complex task can be solved through estimation of adequate models for the dependencies of the quality characteri...
Chapter
Full-text available
In this chapter, we present a study on three polymer resists that are important for electron beam lithography (EBL) and we demonstrate their successful application for nano-structuring and EBL process optimization. The experiments performed showed that the resists behavior, including their sensitivity and contrast, is influenced by the energy of th...
Article
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In this paper the applications of electron beam additive manufacturing systems are reviewed. There by selective electron beam melting of welding wires or of some parts of upper powder layer of a sandwich structure, 2D slices, welded with the others, are built by consequently depositing powder layers. The deposited metal powder is selectively melted...
Article
Full-text available
The management of the quality during electron beam welding directed to optimization of the process parameters is an important way to improve the use of the expensive equipment and to make the EBW process more efficient in consuming materials, time and energy. The beam emittance as well as the electron beam density distribution are significant and...
Article
Full-text available
Electron beam is at the forefront of welding technology. The choice of optimal welding modes, monitoring the weld quality and/or detecting weld defects in real-time during the electron beam welding process using nondestructive, cost-effective and reliable methods is one of current challenges in this field. The plasma, generated in the keyhole and t...
Article
Hydrogen Silsesquioxane (HSQ) is used as a high-resolution resist with resolution down below 10 nm halfpitch. High-contrast and high-resolution patterning in the negative electron beam HSQ resist has numerous potential applications. Our aim in this work was to investigate lithographic parameters in thicker resist films because the resist thickness...
Article
Full-text available
Keyhole welding using concentrated energy beams (electron beam and laser beam) is at the forefront of welding technology and finding ways to improve welding quality is a pressing issue. Finding optimal welding modes, monitoring weld quality and/or detecting weld defects in real-time during the welding process using nondestructive, cost-effective an...
Article
Full-text available
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 charac...
Article
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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...
Article
Full-text available
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 dimens...
Conference Paper
В работе описывается численная модель процессов испарения, конденсации и диффузии элементов сплава АМг-6 при электронно-лучевой сварке с динамическим позиционированием электронного пучка, которая позволяет прогнозировать химический состав сварных швов. Для верификации построенной модели проводился эксперимент с выполнением проходов на различных реж...
Article
Full-text available
The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analys...
Data
Full-text available
Article
The oscillations of a signal, collected by a ring electrode with +50 V potential, situated in the plasma over the welding zone during electron beam welding (EBW) with local beam deflection oscillations were studied. Samples of chrome-molybdenum steel were processed. The frequencies of the beam oscillations varied between 150 and 1400 Hz and their t...
Chapter
An experimental study of the signal patterns of the secondary current in a plasma during electron-beam welding was carried out. The studies show that the spectrum of the secondary emission signal during steel welding has a pronounced periodic component at a frequency of around 15–25 kHz. The signal contains quasiperiodic sharp peaks (impulses). The...
Article
Full-text available
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 sen...
Article
Full-text available
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. L...
Article
An amended quasi-stationary model of heat transfer in a metallic ingot hardening in a water-cooled crucible after electron-beam melting and refining of the metal is suggested. The processes of heat transfer and heat flows through different interfaces are considered for aluminum and tantalum under the assumption of three mechanisms of heat transfer....
Article
Full-text available
The interest in renewable energy sources (RESs) utilisation and energy efficiency improvement programmes in Bulgaria reflects the changes in the field of energy policy worldwide and in Europe. Now energy management becomes a great problem of inner policy of Bulgarian government. In the last few years there has been a growing attention to the RESs a...
Conference Paper
Описана методика экспериментальной и расчетной оценки температуры в канале проплавления при электронно-лучевой сварке, предусматривающая измерение концентрации паров над зоной взаимодействия электронного пучка с металлом путем химического анализа напыленного на под- ложку слоя металла. Проведено сопоставление полученных экспериментальных значений т...
Article
Full-text available
Experimental results show that the oscillations of the electron beam have a direct effect on the processes of formation of the primary and secondary structures of the weld metal in accordance with the changes in the shape of the welded joint.
Article
The changes of seam profiles and of heat affected zones during electron beam welding at use of local beam deflection oscillations, directed across or along the joint, are studied. The possibility to control the beam cross-sectional profile on base of beam power, focus position and welding velocity is limited. In contrast to expectance an increased...
Article
Full-text available
The change of seam profiles and of heat affected zones during electron beam welding at use of local beam deflection oscillations, directed across and along the joint, are studied. The possibility to control the seam sross-sectional profile on base of beam power, focus position and welding velocity is limited. In contrast of expectance an increased...
Article
Full-text available
Control of beam focus position is important in the regime choice of electron beam welding (EBW). It is known that the methods of electron beam focus control in electron beam welding are done according to the parameters of secondary current signal collected in plasma. The purpose of the study is to develop a method for operational control of the ele...
Article
High power concentration in electron beam welding and its deep penetration into metal determine extensive use of electron beam welding (EBW) to produce essential parts from various steels and alloys. The paper covers the issues of non-defect technology development in EBW. The focus mode control issues using the secondary current analysis in the pla...
Article
Full-text available
Electron beam welding (EBW) shows certain problems with the control of focus regime. The electron beam focus can be controlled in electron-beam welding based on the parameters of a secondary signal. In this case, the parameters like secondary emissions and focus coil current have extreme relationships. There are two values of focus coil current whi...