Lilyana Koleva

Lilyana Koleva
University of Chemical Technology and Metallurgy | UCTM · Department of Automation

PhD

About

50
Publications
5,771
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57
Citations
Additional affiliations
March 2018 - December 2019
University of Chemical Technology and Metallurgy
Position
  • Professor (Assistant)

Publications

Publications (50)
Article
Full-text available
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 engineeri...
Article
Full-text available
Experimental results on the quality of electron beam melting and refining of copper samples by implementing the "method of washers" are analyzed by using an empirical model estimation approach. The influence is studied of the process parameters-melting power and time of refining, on the residual content of impurities, the refining rate, the overall...
Article
Full-text available
Over the past 18 months, we have been forced to go through a series of changes that none of us could have predicted. The COVID-19 pandemic and the related emergency measures to limit the spread of the virus in Bulgaria led to the termination of all forms of education at school from the 13th of March 2020 to the end of the school year. The educatio...
Article
Full-text available
The mechanical properties bending strength and modulus of elasticity in bending of a new type plywood for construction, based on black locust wood, have been investigated in relationship with the bonding technological factors. The experimental investigation is based on an optimal composite design with four control factors-temperature, pressure, bon...
Article
Full-text available
In this work the optimization of the process of refining of titanium during electron beam melting using the purification coefficients in vacuum of the impurities, based on experimental data, is considered. The influence of the variation in the process parameters-the electron beam power and melting velocity-on the residual concentrations of impuriti...
Article
Full-text available
“Proceedings International Scientific Conference Industry 4.0”. VI International Scientific Conference “INDUSTRY 4.0”. 08 – 11 Dec. 2021, Borovets, Bulgaria, Vol. 2/12, Year V, 2021, pp. 238-240. ISSN 2535-0153 (Print), ISSN 2535-0161 (Online). http://industry-4.eu/winter/sbornik/2-2021.pdf This work presents experimental and theoretical investiga...
Article
Full-text available
“Proceedings International Scientific Conference Industry 4.0”. VI International Scientific Conference “INDUSTRY 4.0”. 08 – 11 Dec. 2021, Borovets, Bulgaria, Vol. 2/12, Year V, 2021, pp. 241-243. ISSN 2535-0153 (Print), ISSN 2535-0161 (Online). http://industry-4.eu/winter/sbornik/2-2021.pdf Experimental results for the quality of electron beam mel...
Article
Full-text available
. “Proceedings International Scientific Conference Industry 4.0”. VI International Scientific Conference “INDUSTRY 4.0”. 08 – 11 Dec. 2021, Borovets, Bulgaria, Vol. 2/12, Year V, 2021, pp. 227-229. ISSN 2535-0153 (Print), ISSN 2535-0161 (Online). http://industry-4.eu/winter/sbornik/2-2021.pdf The mechanical properties bending strength and modulus...
Article
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“Proceedings International Scientific Conference Industry 4.0”. VI International Scientific Conference “INDUSTRY 4.0”. 08 – 11 Dec. 2021, Borovets, Bulgaria, Vol. 3/12, Year V, 2021, pp. 318-321. ISSN 2535-0153 (Print), ISSN 2535-0161 (Online). http://industry-4.eu/winter/sbornik/3-2021.pdf Abstract: В тази работа е разгледан Arduino базиран инкуб...
Article
Full-text available
“Proceedings International Scientific Conference Industry 4.0”. VI International Scientific Conference “INDUSTRY 4.0”. 08 – 11 Dec. 2021, Borovets, Bulgaria, Vol. 2/12, Year V, 2021, pp. 244-246. ISSN 2535-0153 (Print), ISSN 2535-0161 (Online). http://industry-4.eu/winter/sbornik/2-2021.pdf Grafting is the most effective way of modifying and regul...
Article
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International Scientific Journal Mathematical Modeling, Vol. 4 (2020), Issue 3, pp. 79-81, ISSN (print) 2535-0986, ISSN (online): 2603-2929, https://stumejournals.com/journals/mm/2020/3/79.full.pdf The electron beam technological processes like electron beam welding, electron beam additive technologies, etc. depend strongly on the characteristics...
Article
Full-text available
International Scientific Journal Science. Business. Society, Vol. 5 (2020), Issue 3, pp. 112-115, Print ISSN: 2367-8380, Online ISSN: 2534-8485. https://stumejournals.com/journals/sbs/2020/3/112.full.pdf The Smart Homes come rapidly into our everyday lives bringing comfort, security, help and many other benefits. The development of Information and...
Article
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International Scientific Journal Machines. Technologies. Materials, Vol. 14 (2020), Issue 8, pp. 352-355, Print ISSN: 1313-0226, Online ISSN: 1314-507X. https://stumejournals.com/journals/mtm/2020/8/352.full.pdf An experimental study of the geometrical characteristics of the cross sections of the thermally affected areas obtained by electron beam...
Article
Full-text available
International Scientific Journal Science. Business. Society, Vol. 5 (2020), Issue 3, pp. 89-91, Print ISSN: 2367-8380, Online ISSN: 2534-8485. https://stumejournals.com/journals/sbs/2020/3/89.full.pdf The rheological non-destructive oscillation testing is conducted in order to predict and quantify the samples' properties of the commercial brand li...
Conference Paper
The process of electron beam grafting is implemented for the production of highly efficient graft copolymers from natural polysaccharides and regulating their properties for application as flocculating agents during the treatment of different wastewaters. In this paper, the electron beam induced modification of corn starch by grafting of acrylamide...
Article
Full-text available
Electrotechnica & Electronica (Е+Е), Vol. 55 (3-4), 2020, pp.49-56, ISSN: 0861-4717 (Print), 2603-5421 (Online), https://epluse.ceec.bg/wp-content/uploads/2020/09/20200304-03.pdf The world of technology is changing at an extremely fast pace. Covid-19 has given further impetus to modernization in education, and it seems unlikely that schools and...
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
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This paper presents the implementation of the overall desirability function-the overall robust optimization approach-for multi-criteria parameter optimization in the robust engineering case, based on estimated models for the means and variances of the quality characteristics. The optimized properties of the synthesised copolymer by electron beam in...
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
Electron beam irradiation has the ability to modify polymer substrates by the process of graft copolymerization in order to synthesize water-soluble copolymers having flocculating properties. The influence of the variation of the process parameters acrylamide/starch (AMD/St) weight ratio, electron beam irradiation dose and dose rate is investigated...
Article
Full-text available
An experimental investigation of the electron beam irradiation induced grafting of acrylamide onto corn starch was performed. In this way the synthesis of water-soluble copolymers having flocculation abilities is realized. The acrylamide monomer provides a polar graft side chain which turns it into a hydrophilic copolymer. The robust engineering ap...
Article
Full-text available
The challenge of this paper consisted in optimization application in the case of starch grafting with a vinyl monomer under accelerated electron field. Thus, the robust engineering approach and multi-criteria optimization were considered. Methods based on graphical optimization as well as on overall optimization were implemented. Moreover, a graphi...
Article
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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
Response Surface Methodology and robust engineering approach are applied for the investigation of preliminary experimental data related to the synthesis of composite biopolymer-based hydrogels via electron beam (e-beam) radiation cross-linking. Two different biopolymers – xanthan gum (XG) and carboxymethylcellulose (CMC) were used for hydrogel prep...
Article
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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
This paper considers the process electron beam welding of stainless steel type 1H18NT in vacuum. Based on experimental data, the influence of the variations of the following process parameters: electron beam power, welding velocity, the distances from the magnetic lens of the electron gun to the beam focus and to the surface of the treated sample i...
Article
Full-text available
Published by Scientific technical Union of Mechanical Engineering "INDUSTRY 4.0" Abstract: Electron beam (EB) irradiation has the ability to modify polymer substrates by process of graft copolymerization to synthesize water-soluble copolymers having flocculating potential. Models - depicting the dependencies of the described quality characteristic...
Article
В настоящата работа се разглежда електроннолъчево заваряване на неръждаема стомана тип 1H18NT. Оценени са модели за зависимостите на геометричните характеристики на получените заваръчни шевове при вариране на параметрите на процеса – мощност на електронния лъч, скорост на заваряване (на движение на електронния лъч), разстояние от магнитните лещи до...
Article
Full-text available
The term "quality" is a wide-ranging concept for which each person or professional sector has its own definition. The most progressive quality point of view is that it is entirely determined by the customer or the end user and is based on the assessment of customer experience with the product or service. The quality of use or ergonomic quality actu...
Article
Електроннолъчевите процеси са процеси, при които се осъществява взаимодействие на лъч от ускорени електрони с висока плътност на мощност с материали във вакуум. Това определя приложението им за повърхността модификация на материали, изпарение на материали и последващото им отлагане на тънки слоеве, заваряване и други. Предимствата на процеса са свъ...
Article
Абстракт: Докладът разглежда процесът на електроннолъчево заваряване във вакуум на неръждаема стомана от тип 1H18NT. Обучени са невронни мрежи, които на базата на параметрите на процеса - мощност на електронния лъч, скорост на заваряване и разстоянията от магнитните лещи на електронната пушка до фокуса на електронния лъч и до повърхността на образе...
Conference Paper
Full-text available
This work considers the electron beam lithography process of exposed and developed polymethyl methacrylate (PMMA) resist profiles under production conditions and in presence of errors in process parameter values. Robust engineering approach is applied and models for the mean values and the variances of the resist profile geometric characteristics d...
Conference Paper
Full-text available
A study about complacency of portable computers. For characterization on complacency were used indicators witch efficiency, usability, effectiveness and quality. Respondents were split into two groups, up to and over 36 years of age.
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...
Article
Full-text available
This paper considers the process electron beam welding in vacuum of stainless steel 1H18NT. Neural network based models are developed and used for the description of the defectiveness, depending on the process parameters-electron beam power, welding velocity, the distance between the main surface of the magnetic lens of the electron gun and the bea...
Article
Full-text available
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
Experimental investigations of the modification of starch (corn and potato) by grafting of acrylamide using electron beam irradiation in order to synthesize water-soluble copolymers having flocculation abilities is performed. The influence of the variation of the parameters acrylamide/starch weight ratio, electron beam irradiation dose, dose rate a...
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
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
Full-text available
Experimental investigation of the modification of starch by grafting acrylamide using electron beam irradiation in order to synthesize water-soluble copolymers having flocculation abilities is performed. The influence of the variation of the parameters acrylamide/starch (AMD/St) weight ratio, electron beam irradiation dose and dose rate, as well as...
Article
Full-text available
The acrylamide grafting onto starch by electron beam (EB) irradiation in order to synthesize water-soluble copolymers having flocculation abilities was optimized by implementation of the Response surface methodology (RSM) and robust engineering design. The results showed different optimal regions of EB irradiation dose and dose rate depending on ac...
Article
Full-text available
An experimental investigation connected with the modification of starch by grafting acrylamide with the application of electron beam irradiation is performed. It is aimed at the synthesis of watersoluble copolymers having flocculation abilities. The acrylamide monomer provides a polar graft side chain which turns it into a hydrophilic copolymer. Th...
Conference Paper
Full-text available
The survey of the student satisfaction from the education in UCTM-Sofia is a complex task involving the causes of low student evaluations regarding the degree of fulfillment of certain criteria. This is one of the aspects of the overall assessment of the quality of education in UCTM Sofia. Investigation of the satisfaction from the education in UCT...
Conference Paper
Full-text available
Successful integration of electronic technology in learning is crucial. The aim is to make education more effective, more efficient,more accessible and more attractive. By the use of virtual learning environments ( VLE), curriculum content is provided, organized and managed. Key words: electronic technology, electronic course, effectiveness, effici...
Article
Full-text available
In this work the optimization of the process of refining titanium at electron beam melting using purification coefficient of impurities in vacuum based on experimental data is reviewed. The influence of the variations in the process parameters - power of the electron beam, melting rate and time on refining – on the residual concentrations of impuri...
Conference Paper
Full-text available
The present work considers the optimization of the process electron beam welding in vacuum of stainless steel 1H18NT based on experimental data.. The influence of the variations of the following process parameters: electron beam power, welding velocity, the distances from the magnetic lens of the electron gun to the beam focus and the surface of th...
Conference Paper
Full-text available
Electron beam lithography is a key technology for the fabrication new generation integral circuits and devices of electronics, photonics and nowadays and future nano-engineering. A layout of five parallel lines with 0.3 nm width, situated on 0.4 nm from each other, is obtained through exposure and development of the positive resist PMMA. Through ne...

Projects

Projects (2)
Archived project
...determination of the optimum conditions for an electron beam grafting system to obtain suitable grafting yield with homogeneous distribution in order to enhance e-beam grafting, minimize the homopolymer formation, and obtain the best material properties required from practical point of view
Archived project
...study of the physical processes running during the penetration and interaction of an intensive electron beam with polymeric materials, absorbed energy space distributions, temperature distributions in the irradiated materials and corresponding mathematical models...