Прегледај по Аутор "Krivokapić, Zdravko"

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    DESIGN OF THE NEW TECHNOLOGICAL PROCEDURE OF PRODUCING GROOVE OF SPIRAL BITS
    (Center for Quality, Faculty of Engineering, University of Kragujevac, Serbia,, 2020) Spaić, Obrad; Krivokapić, Zdravko; Marinović, Budimirka; Jovanović, Janko
    One of the most commonly used and at the same time the most complicated cutting tools in terms of body geometry is the spiral drill bit. In the process of their production, the key operation is the production of spiral grooves. Until now, the grooves on the drill bits have been mainly produced by milling, grinding, rolling and extrusion processes. All these procedures have their advantages and disadvantages as well. Based on the experimental measurements of the dimensions of the grooves of the drill bits produced by the rolling and grinding technology, the paper defines the basic parameters and a new technological procedure for the production of grooves of the drill bits has been designed. For the suggested technological procedure of making of grooves of the drill bits, the advantages and disadvantages of the conventional production of the grooves of the drill bits by rolling or grinding technology have been analysed.
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    Modelling Surface Roughness in the Function of Torque When Drilling
    (MDPI, 2020) Krivokapić, Zdravko; Vučurević, Radoslav; Kramar, Davorin; Šaković Jovanović, Jelena
    Given the application of a multiple regression and artificial neural networks (ANNs), this paper describes development of models for predicting surface roughness, linking an arithmetic mean deviation of a surface roughness to a torque as an input variable, in the process of drilling enhancement steel EN 42CrMo4, thermally treated to the hardness level of 28 HRC, using cruciform blade twist drills made of high speed steel with hardness level of 64–68 HRC. The model was developed using process parameters (nominal diameters of twist drills, speed, feed, and angle of installation of work pieces) as input variables varied at three levels by Taguchi design of experiment and measured experimental data for a torque and arithmetic mean deviation of a surface roughness for different values of flank wear of twist drills. The comparative analysis of the models results and the experimental data, acquired for the inputs at the moment when a wear span reaches a limit value corresponding to a moment of the drills blunting, demonstrates that the neural network model gives better results than the results obtained in the application of multiple linear and nonlinear regression models.