Now showing 1 - 10 of 13
  • Publication
    ON-LINE PROFESSIONAL TRAINING FOR WORKERS WITH THE MOODLE SYSTEM TO IMPROVE PROFESSIONAL SKILLS IN GREEN CONSTRUCTIONS
    (2019) ; ; ;
    Nedka Atanasova
    ;
    Tsanko Karadzhov
    On the global agenda, environmental issues are becoming ever more pressing every moment. At present, it is not enough for individual countries to tackle global climate issues on their own. The time has come for a joint effort to mitigate climate change. The Paris Agreement is an agreement within the United Nations Framework Convention on Climate Change, dealing with greenhouse-gas-emissions mitigation, adaptation, and finance, starting in the year 2020. The Paris Agreement's long-term goal is to keep the increase in global average temperature to well below 2 °C above pre-industrial levels, and to limit the increase to 1.5 °C, since this would substantially reduce the risks and effects of climate change. It is not enough for states to sign this type of act, they need to take active steps to implement them and achieve the set goals. Energy, green construction, resource saving, educating the population, new and advanced teaching methods - all that is required for any global setup to be locally addressed. Now, we are in a situation where the exchange of transnational experience and knowledge is an important stage in solving energy efficiency issues through the education prism. This article will provide an analysis of the experience of four countries in the field of green construction.
  • Publication
    METHODOLOGY FOR AUTOMATIC DETERMINATION OF CONTRAST OF LASER MARKING FOR DIFFERENT MATERIALS
    A new methodology for determining and optimizing the contrast of the technological laser marking process has been developed. It can evaluate the quality of the markings regardless of the type of material and the type of laser system. To perform the test analysis, a specialized test field is programmed, which including the change of two of the main parameters influencing the marking process: the linear energy density (LED) and the linear density of the pulses (LDI). Marking of a test field consisting of squares of a certain size is done by means of a raster marking method with a constant step between the lines. The results are processed with a digital camera and specialized software. The maximum blackening is compared with the background of all fields and is juxtaposed with the effective energy needed to obtain a certain contrast. Several consecutive iterations are made, with each of the following experiments excluding the variants with least contrast. Thus, the study consistently brings the result to a minimum working area of the basic technological parameters, providing the user's desired contrast of the marking. The developed author's method of automatically determining the contrast of the laser marking reduces the time for preliminary experimental research and gives a reliable and subjectively absent way of qualitatively marking different types of industrial products.
    Scopus© Citations 6
  • Publication
    COLOR MARKING OF STAINLESS STEEL AND TITANIUM WITH THE LASER OXIDATION METHOD
    (2023)
    Petar Tsvyatkov
    ;
    Emil Yankov
    ;
    ; ;
    Marking of metal products is essential in many industrial processes. It is mandatory for the finished products according to regulations of the European and world legislation. Traditional marking usually creates contrasting symbols that can easily be erased and forged.In recent years, a new method for product identification has appeared - color marking. One of the advantages of this method is that it is difficult to counterfeit. This article aims to present the progress of color marking technology on two types of materials. Three groups of factors have been analyzed: the laser source; the technological process; material properties. Their role in obtaining a specific color marking on Ti and AISI 304 is shown. The results are presented in tables. Each color can be repeated only with strict observance of the three groups of factors.
  • Publication
    LABORATORY EXERCISE TO DETERMINE CONTRAST IN LASER MARKING OF ARTICLES
    (2019) ; ; ;
    Pavel Cacivkin
    ;
    Nikolay Angelov
    ;
    Tsanko Karadzhov
    The laser marking has been established in recent years as one of the modern innovative methods for marking many industrial products. The report examines a new laboratory exercise for the subject Laser Technology, studied in some technical universities. A new approach is proposed to determine the contrast of the laser marking process. Described is the purpose and the main tasks as well as the new skills and knowledge that students can exercise through this laboratory exercise. Students implement a test matrix consisting of squares of a certain size using the raster marking method. Through the new laboratory exercise, students can explore and analyze the dependencies of the contrast of laser markings on different dimensions influencing the technological process. The capabilities of the new approach allow learners to become more familiar with the factors that influence the modern process of laser marking widely used in modern industry. The results of the experiments the students summarize using a new modern digital approach to analyze the contrast against the background of the marked surface. From the experimental graphical dependencies of the variation of the power and speed contrast, they draw conclusions about the optimal process parameters.
  • Publication
    Investigation of the Influence of Some Parameters on the Process of Color Laser Marking
    (2023)
    Emil Yankov
    ;
    ; ;
    Nikolay Angelov
    The research and development of laser marking technology offers numerous advantages and applications in a variety of industries, from manufacturing and electronics to healthcare and beyond. In industries such as aerospace and automotive, where components must adhere to strict regulatory standards, laser marking can provide the necessary traceability and compliance. Investing in its research and development improves precision, efficiency and innovation, ultimately contributing to advancements in various sectors and driving economic growth.For this purpose, various surface treatment methods are being studied, including laser marking. As can be seen from our previous studies and those of other authors, laser marking of steel surfaces is a complex process and depends on the complex relationships between a number of technological parameters. In this study, we focus on the influence of four of them (parameters: processing speed, laser pulse frequency, pitch between raster lines during laser processing and energy density). During the experiments, the raster step was varied in the range of 20 µm to 80 µm, the velocity was in the range of 25 mm/s to 125 mm/s, and the density was in the range of 5.82 J/mm2 to 29.12 J/mm2. The experiments were done for three frequencies - 20 kHz, 50 kHz and 100 kHz. All these intervals can be realized in the real production. The change of the four investigated parameters was analyzed in relation to the obtained roughness in the processing zone as a function of these four technological parameters and was compared with the corresponding color coordinates of the obtained color markings in these zones. It has been proven that each specific color is associated with surface structural changes as a result of the interaction between laser radiation with a certain laser energy density and the processed material. The present study is a small contribution to the topic of laser color marking of various materials, enabling the production of new surface properties.
  • Publication
    METHOD FOR PRELIMINARY ESTIMATION OF THE CRITICAL POWER DENSITY IN LASER TECHNOLOGICAL PROCESSES
    (2019) ;
    Nikolay Angelov
    ;
    For a number of new laser technology processes, it is essential to plan an experimental plan for primary experimental engineering activities in terms of quality. The assessment of the critical power density to reach the melting or evaporation temperature of the surface with a suitable theoretical model is an important stage in the development of a particular manufacturing technology. With the help of numerical experiments, this report provides a method for pre-examining the influence of wavelength on the laser technological process. The calculations are performed with a specialized program, running MATLAB. A series of temperature fields were obtained at a change in power density and wavelength at laser impact for concrete types of structural steel. The temperature dependence of the optical and thermo-physical characteristics of the material is also reporded. The analysis is made for laser technology complexes working with lasers emitting in the ultraviolet, visible, near and distant infrared areas. For these wavelengths the critical power density of melting and evaporation is determined.
    Scopus© Citations 3
  • Publication
    INVESTIGATION OF THE INFLUENCE OF THE NUMBER OF REPETITIONS ON THE PROCESS OF LASER MARKING OF HS6-5-2-5 STEEL
    (2021) ;
    Nikolay Angelov
    ;
    Today, methods for marking parts and components in industrial production are constantly improving, and they must meet several basic criteria for active traceability by consumers. The parameter that is of paramount importance for the quality of the marking is related to the contrast of the marked sign or QR code. To achieve optimal contrast, a number of technological factors and the functional relationships between them must be taken into account.The report examines the role of the number of repetitions on contrast in raster marking of HS6-5-2-5 tool steel products. The dependences of the number of repetitions on the speed and frequency are also taken into account - the main factors in the process of laser ablation. Graphs of the depth of the marking are drawn depending on the number of repetitions and the linear density of the pulses. The experiments were made with a fiber laser. By the performed analyses the working intervals of processing between the studied factors are deduced, allowing to achieve the desired optimal result.
    Scopus© Citations 1
  • Publication
    INFLUENCE OF THE OVERLAP COEFFICIENT ON THE CONTRAST IN LASER MARKING OF C110W STEEL
    (2021)
    Nikolay Angelov
    ;
    ;
    The laser marking process by melting samples of C110W carbon tool steel was studied. The experiments were performed with a fiber laser and a CuBr laser. A field of squares is marked in a raster method for different values of the overlap coefficient and power density. The contrast of the marking is determined on each marked square. From the obtained experimental data, graphs of the dependence of the contrast on the overlap coefficient for three power densities were drawn. The obtained results for the two lasers are compared and the influence of the wavelength is indirectly analysed. The working intervals of the overlap coefficient for the studied power densities for the two lasers at which the optimal contrast in the processing zone is obtained are determined.
  • Publication
    Numerical modeling and simulation for laser beam welding of ultrafine-grained aluminium
    (2021) ; ;
    Ivo Draganov
    ;
    Nikolay Angelov
    Laser beam welding of aluminium offers huge potential for a wide variety of welding of different thickness parts with the method of thermal conductivity due to the relatively high difference between melting temperature and evaporation. However, due to the high melting temperature and good thermal conductivity of this light metal, the temperature gradients during the welding process are usually high, causing residual stresses in the weld, which can lead to undesirable deterioration of the weld pool properties and the quality of the process. Physical modelling and simulations of the laser welding process are powerful tools for gaining a fundamental understanding of the technological process. They are also a suitable tool for preliminary assessment of the intervals in which the real preliminary experiments for process optimization should take place. This work is devoted to the numerical modelling of the process of welding ultrafine-grained aluminium using a fibre laser. A three-dimensional model of the welding process was created, using the finite element method implemented in the program ABAQUS. The temperature fields at depth z and on the surface x, y in the welded samples is determined. The temperature change as a function of time for different coordinates of the weld is also analysed. During numerical calculations, the power, machining speed and diameter of the workplace are variable. The obtained results are compared with real experiments conducted in the laboratory by other researchers.
    Scopus© Citations 2
  • Publication
    Modification of the roughness of 304 stainless steel by laser surface texturing (LST)
    (2023) ; ;
    Nikolay Angelov
    ;
    Emil Yankov
    Surface texturing is one of the most effective approaches to modifying the surface to improve many properties: tribological, corrosion resistance, microhardness and others characteristics of a number of engineering materials. Among the surface texturing techniques developed in recent years, the most widely used method is the laser surface texturing method (LST) due to its high flexibility, superior texturing accuracy and good process controllability and reproducibility. With its rapid development, LST has attracted considerable attention in various industries such as automotive, biomedical and aerospace. The present study considers the changes in roughness in different modes of laser texturing of stainless steel specimens 304. The effects and role of individual laser parameters on the change in roughness are analyzed as a main characteristic of the surface properties of the processed material. Heating and its surface melting is one of the studied effects and its role in changing the roughness. The focus of the study is on the process of laser–material interaction as a function of absorbed energy density, pulse frequency, scan rate, and overlap coefficients leading to different effects of LST parameters. It has been found that increasing the energy density, accompanied by a decrease in the frequency and speed of scanning, can increase the surface roughness.
    Scopus© Citations 3