Прегледај по Аутор "Šikuljak, Lana"

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    Comparison of different mathematical models for prediction of self-excited vibrations occurance in milling process
    (University of East Sarajevo,Faculty of Electrical Engineering, 2019) Košarac, Aleksandar; Mlađenović, Cvijetin; Zeljković, Milan; Šikuljak, Lana; Maksimović, Mirjana; Mijić, Danijel
    In modern production, despite the existence of other production methods, metal cutting still plays an important role. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. Undoubtedly, productivity and quality of production are two mail requirements which are key elements to stay on top in a competitive market. One of the most influencing factor that affect the machine tools are vibrations. The most unwanted vibrations that can appear during metal cutting process are self-excited vibrations, which are one of the three kinds of mechanical vibration, free vibration, forced vibration, and self-excited vibration. When it comes to improving the performance of machine tools, the analysis of the appearance of self-excited vibrations and their isolation occupy a significant place. The aim of this paper derives from trends and limitations exists in metal production. The way to isolate the self-excited vibrations is to predict their occurrence by defining the stability lobe diagram. The paper presents two popular analytical methods for identifying stability lobe diagrams in milling, which shows the boundary between stable and unstable zone of machining operations, depending on the number of revolutions of the spindle and cutting depth. First considered method is Fourier series approach and second one id average tooth angle approach. Lather, both stability lobe diagrams were compared with results obtained experimentally.
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    CUTTING PARAMETERS INFLUENCE ON SURFACE ROUGHNESS IN AL 7075 MILLING
    (Faculty of Electrical Engineering, University of East Sarajevo, 2020) Košarac, Aleksandar; Šikuljak, Lana; Obradović, Čedomir; Mlađenović, Cvijetin; Zeljković, Milan
    Aluminum and its alloys are nowadays a very commonly used material in the aerospace and automotive industries. Due to its good mechanical properties, low density, high hardness, good thermal properties, and good machinability, Al7075 is one of the most commonly used aluminum alloys. This work investigates the effect of cutting parameters on surface roughness in finish milling of Al7075 aluminum alloy. Considering the negative effects of conventional cutting fluids (coolants and lubricants), oils or water emulsions on the environment and health, and the negative economic effects resulting from the foregoing, this study also analyzes the possibilities the use of different coolant-lubricant types on cutting. In this connection, the subject of research is also the influence of the cooling method on surface roughness in end milling.
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    EXPERIMENTAL METHOD FOR DEFINING THE STABILITY LOBE DIAGRAM IN MILLING Č4732 (42CrMo4) STEEL
    (University POLITEHNICA Timisoara, Faculty of Engineering Hunedoara, 2019) Košarac, Aleksandar; Mlađenović, Cvijetin; Zeljković, Milan; Šikuljak, Lana; Imre, Kiss
    Self-exciting vibration (chatter) is an unwanted phenomenon that can occur in metal cutting. Self-exciting vibration is a phenomenon that has a negative effect on productivity, leads to accelerated wear or breakage of the tool, and in some cases can lead to breakage of elements of jigs and fixtures or elements of the machine tools. In order to predict and control the process of creating self-excited vibration, different methods have been developed. One way of predicting self-excited vibration is defining stability lobe Diagram, which shows the boundary between stable, conditionally stable and unstable cutting process, whereby combinations of cutting depth, cutting speed, i.e. spindle speed and feed rate are observed. Methods for defining the stability lobe diagram can be analytical, and experimental. This paper shows the experimental method of defining the stability lobe diagram, on machining steel Č4732 (42CrMo4). Metal cutting is carried out on a vertical machining center. The methodology for defining the stability lobe diagram implies that a series of experiments were done, were workpiece surface to be milled is made with a slope of 3°. In this way, when moving the tool, the cutting depth gradually increases until the moment of self-excited vibration occurs. The occurrence of the vibration is registered by measuring the acceleration, where the accelerometer was being mounted on the main spindle carrier, as close as possible to the tool. After the self-excited vibration occurred, which is manifested by a sudden jump of acceleration amplitude, and by the change in the sound, the cutting process is stopped and then the axial depth of the cut at which the vibration occurs determined by the tangent method in Matlab. The obtained stability lobe diagram has two dimensions, which means that all measurements were performed for one, a constant value of feed rate per tooth.
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    PREDICTING SURFACE ROUGHNESS IN THE MILLING OF BIOCOMPATIBLE ALLOY TI–6AL–4V
    (University Politehnica Timisoara, Faculty of Engineering Hunedoara, 2024-05) Babić, Igor; Šikuljak, Lana; Košarac, Aleksandar; Moljević, Slaviša; Sekulić, Milenko; Savković, Borislav; Aleksić, Anđelko; Kiss, Imre
    Mechanical engineering plays an essential role in the development of medical devices, implants, prostheses, and medical equipment, with precise machining of bio–compatible materials being of considerable importance. Among the various traditional and modern machining methods, milling stands out as a widely employed technique. This study is dedicated to optimizing milling parameters to achieve a minimal average surface roughness (Ra) during the milling of the biocompatible alloy Ti–6Al–4V. This paper presents the optimization of machining parameters: cutting speed, feed rate and depth of cut. Each parameter is explored at three distinct levels, resulting in the initial design of 27 experimental runs. The paper further demonstrates how an extensive set of experiments can be streamlined to a more manageable 9 runs through the application of the Taguchi methodology. This paper points out the significant impact that varying levels can exert on the obtained results, highlighting the importance of a comprehensive and systematic approach to experimentation and optimization.
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    Prediction of self-excited vibrations occurance during aluminium alloy AL 7075 milling
    (Faculty of Electrical Engineering, University of East Sarajevo, 2019) Košarac, Aleksandar; Šikuljak, Lana; Šalipurević, Miloš; Mlađenović, Cvijetin; Zeljković, Milan
    Despite the existence of other production methods, metal cutting still plays an important role in modern production. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. When we are talking about improving the performances of machine tools, the analysis of the appearance of self-excited vibrations and their isolation take a significant place. The aim of this paper comes from trends and limitations that are present in metal production. The paper presents analytical and experimental methods for identifying stability lobe diagrams in the aluminum alloy Al 7075 milling. The influence of certain regime on the occurrence of selfexcited vibrations, i.e. the definition of vibrational stable processing regimes, is considered.