Now showing 1 - 5 of 5
  • 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
  • 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
    Influence of pulse duration on the process of laser marking of CT80 carbon tool steel products
    (2021-02-25) ; ;
    Nikolay Angelov
    Depending on the processing of a particular material, the laser marking process must meet certain requirements. A certain laser peak intensity or fluency must be reached on the treatment surface above which the laser ablation process starts. Some experimental studies have shown that this particular marking threshold is related to many other parameters characterizing the laser source. This requires the realization of an appropriate combination of peak power or pulse energy and the radius of the beam in focus, the frequency of the laser pulses as well as the pulse duration. Achieving high resolution in the marking process requires optimal focusing, and this in turn is associated with the presence of high quality generated and propagated laser radiation. The study concerns the process of laser marking of CT80 carbon tool steel products with wide application in industry. Numerical experiments are performed with specialized software TEMPERATURFELD3D to obtain two-dimensional and three-dimensional temperature fields in the laser impact zone. The influence of the duration of the pulses of fibre laser on the process is investigated. Graphs of the dependence of normalized temperature on time and depth for pulse duration on 10 ns, 100 ns and 1 μs are discussed.
    Scopus© Citations 6
  • 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