A procedure for the automated determination of the geometric parameters of a helicoidal shell on a cylindrical one that is applied to machines for special purposes is presented in this paper. A differential equation for the bending of a helicoidal shell subjected to a uniform pressure and a differential equation for the cylindrical shell loaded by a uniformly distributed moment along the helix are used to define the boundary conditions along the cross-section of these shells. The finite difference method is used to solve the differential equation for the bending of a helicoidal shell in MATLAB software. The values of the shell thickness are determined for different parameters using a strength criterion. Different models of the helicoidal shell are analysed.
Original scientific paper The goal of these researches is related to the analyses of the impact of elements of cutting mode on the change of cutting forces, quality of a machined surface and change of physical and mechanical properties of a surface layer of a CBN tool for turning of X160 CrMo V12 steel having a hardness of 60±2 HRC. The results of the analyses of tool surface wear indicate the presence of oxidation and changes of physical and mechanical properties in a tool surface layer. The evaluation clearly shows that a radial force (Fr) is dominant during the machining of this steel. The mathematical models of dependence of cutting force and a quality of machined surface were developed. It was ascertained that an oxidation of the tool surface, next to a contact zone toolcutting chip, leads to the increase of their hardness and reduction of their strength, and it finally leads to the emergence of micro-wear of a cutting knife and rapid tool wear.
Keywords: CBN (corundum and boron-nitride); force; roughness; turning; wear
Utjecaj parametara rezanja na sile i hrapavost površine pri tokarenju kaljenog čelika X160 CrMo V12 alatom od CBNIzvorni znanstveni članak Cilj ovih istraživanja se odnosi na istraživanje uticaja elemenata režima rezanja na promenu sila rezanja, kvaliteta obrađene površine i promene fizičko-mehaničkih svojstava u površinskom sloju alata od CBN pri struganju čelika X160 CrMo V12, tvrdoće 60±2 HRC. Rezultati istraživanja habanja površine alata ukazuju na prisustvo procesa oksidacije i promene fizičko-mehaničkih svojstava u površinskom sloju alata. Evaluacija sile jasno pokazuje da je radijalna sila (Fr) dominantna pri obradi ovog čelika. Razvijeni su matematički modeli zavisnosti sila rezanja i kvaliteta obrađene površine. Utvrđeno je da oksidacija površine alata, neposredno uz kontaktnu zonu alat-strugotina, dovodi do povećanja njihove tvrdoće i smanjenja čvrstoće, što u krajnjoj meri dovodi do pojave mikrokrzanja reznog sečiva a time i ubrzanog habanja alata.
This paper deals with the stress state for the open-die forging of a staggered axial-symmetric specimen of the aluminium alloy AlMgSi0.5. The experimental-theoretical method of visioplasticity, adjusted for the process of open-die forging, consisted of five steps. The basic equations of the plasticity theory, i.e., balance equation, conditions of a plastic flow and Levy-Mises equations are applied. The basic partial differential equations of visioplasticity are obtained theoretically, while the displacement of points of the meridian cross-section, which represents the basis for its solution, can be experimentally obtained. The deformation force is calculated on the basis of the obtained results and is compared to the experimental values. Keywords: visioplasticity, strain rate, stress, deformation force, displacement, tensor lanek obravnava napetostno stanje pri prostem kovanju stopni~astega osnosimetri~nega vzorca iz aluminijeve zlitine AlMgSi0,5. Eksperimentalno-teoreti~na metoda, prilagojena postopku prostega kovanja, je setavljena iz petih korakov. Uporabljena je bila osnovna ena~ba teorije plasti~nosti: ravnote`na ena~ba, pogoji plasti~nega te~enja in Levy-Misesove ena~be. Osnovna parcialna diferencialna ena~ba vizioplasti~nosti je dobljena teoreti~no, medtem ko se premik meridiana pre~nega preseka, kar predstavlja osnovo za njeno re{itev, lahko dobi eksperimentalno. Sila deformacije je izra~unana na osnovi dobljenih rezultatov in je primerjana z eksperimentalno dobljenimi vrednostmi.
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