Прегледај по Аутор "Klobočar, Damjan"

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    Microstructure and Fatigue Properties of Resistance Element Welded Joints of DP500 Steel and AW 5754 H22 Aluminum Alloy
    (MDPI, 2022-02-14) Đurić, Aleksija; Milčić, Dragan; Burzić, Zijah; Klobočar, Damjan; Milčić, Miodrag; Marković, Biljana; Krstić, Vladislav
    The modern concept of lightweight design (LW) requires the application of different materials in one structure (multi-material structures). The structure of different materials has a good perspective for application in the automotive and aerospace industries but only if it is possible to achieve a quality joint between different materials. The most used technology for joining different materials in the automotive industry is Resistance spot welding (RSW). Due to different mechanical, physical, and chemical properties, the joining of different materials by RSW technology does not provide a quality joint, and accordingly, alternative technologies for joining different materials have emerged. Resistance element welding (REW) was developed to enable joint of different materials. This paper presents the welding of AW 5754 H22 Al alloy (1.0 mm-thick) and DP500 steel (1.5 mm-thick) using novel REW. The peak load, absorption energy, microstructure, microhardness and fatigue strength of the REW joint has been investigated. The joint of the same materials has been done also using conventional RSW to compare some results. The results that will be presented in this paper show that that REW can achieve reliable joining of the two materials at relatively low welding currents compared to RSW. Using REW process with a significantly lower welding current, satisfactory mechanical characteristics of the weld joint can be achieved, so peak load is between 2300–2500 N, displacement is between 2.5–3 mm and the absorption energy is between 3.3–5.7 J. REW joints showed fatigue strength with the fatigue limit of 882 N.
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    MULTI-OBJECTIVE OPTIMIZATION OF THE RESISTANCE SPOT-WELDING PROCESS PARAMETERS FOR THE WELDING OF DUAL-PHASE STEEL DP500
    (IMT, Institute of Metals and Technology, 2021) Djurić, Aleksija; Milčić, Dragan; Klobočar, Damjan; Marković, Biljana
    Resistance spot welding (RSW) is still the most used form of welding in the automotive industry, primarily for welding steel. One of the advanced steels used in the automotive industry is dual-phase steel, so it is important to properly select the welding parameter for these steels. Therefore, this paper presents multi-objective optimization in the RSW welding process of DP 500 steel. The paper considers three different mechanical characteristics i.e., the failure load (F), failure displacement (l) and weld nugget diameter (D), as all these welding characteristics play significant roles in evaluating the quality of spot welding. The results show that the welding current is the most influential parameter with respect to the mechanical characteristics. The effect of welding time on the weld quality is the least significant. The optimal parameters for welding DP 500 steel obtained in this paper are weld current 8 kA, electrode force 4.91 kN and weld time 400 ms.
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    THE ANALYSIS OF THE OCCURRENCE OF DEFECTS AND DISCONTINUITIES IN THE REW WELD OF DP STEEL AND ALUMINUM ALLOY
    (Društvo za tehniku zavarivanja Slavonski Brod, 2023) Đurić, Aleksija; Milčić, Dragan; Klobočar, Damjan; Marković, Biljana; Milčić, Miodrag
    Resistance element welding (REW) was developed as an alternative technology for joining dissimilar materials that are difficult to weld with RSW (Resistance spot welding) technology. This technology does not require significant modification of existing equipment in a factory, which is its great advantage. This paper analyzes the occurrence of defects and discontinuities in the REW weld of DP steel and aluminum alloy. Analysis of the macrostructure and analysis of the fractography of the joint were used to detect defects and discontinuities. The following defects and discontinuities are observed: Expulsion of aluminum, asymmetrical spot weld nugget and cracks in the weld area.