Developed was a computer model of temperature field in tool and parts in process of their friction stir welding. Modeling of the temperature field was carried out for both successive stages of welding process, i.e. plunging of pin of tool operating element into part (1st stage) and progressive motion of plunged pin in part (2nd stage). The mathematical model represents itself a nonlinear equation of transient heat conduction, which takes into account progressive pin movement during the 2nd stage of welding. Two constituents describe the heat sources, appearing in welding. The first one considers power of heat sources, caused by friction of tool with parts on contact surfaces, the second one takes into account heat generation, promoted by mechanical deformation of part material. Mathematical modeling and experimental examination of temperature field were carried out for tool from cubic boron nitride (cubonit) and hard alloy as well as copper parts during FSW. Adequacy of developed model was determined based on correlation of numerical and experimental results. It is shown that application of superhard materials (cubonit and hard alloy) for manufacture of tool operating elements gives a possibility to provide thermo-mechanical resistance of tool during welding. A possibility is also shown for increase of strength of welded joints of parts from magnesium alloy ML10, gained as a result of application of FSP for modifying of structure of surface layers in parts to be welded with their further electron beam welding. 27 Ref., 1 Table, 14 Figures. K e y w o r d s : mathematical modeling, friction stir welding, temperature field, tools from superhard materials, structure modification, electron beam welding
The advantages of friction stir welding (FSW) are well known from numerous publications. In this work it was proposed to apply FSW in restoration of sizes of copper plates of machines for continuous casting of billets (MCCB) moulds and for the further surface hardening with nickel or nickel alloys. The microstructure of characteristic zones of joints was studied. Application of FSW provides quality joints with sufficiently high mechanical properties of deposited layer. The structure of copper-copper and copper-nickel joints was studied. It was established that in formation of joints the mechanical stirring of metals plays a leading role, and their mutual diffusion affects them to a much lesser extent. Other processes of pressure welding differ from it by a method of heating, i.e. by the method of heat input into parts being welded. In FSW the kinetic energy is directly converted into heat energy, moreover generation of heat has a strictly localized character in the thin near-surface layers of metal. Figure 1 shows installation and scheme of joining of the overlapped type of dissimilar metals using FSW method.Researchers point out the following advantages of this process as compared to other methods of producing permanent joints [4,5]: significant preservation of base metal properties in the join area; absence of harmful vapors and ultraviolet radiation during welding; possibility of producing defect-free welds on alloys, which during fusion welding are prone to hot cracking and porosity in weld metal; no need in application of filler material and removal of surface oxides at the edges before welding as well as slag and spat-
Developed was a computer model of temperature field in the tool and parts in the process of their friction stir welding (FSW). Modeling of the temperature field was carried out for both successive stages of welding process, i.e. plunging of pin of tool working element into the part (1st stage) and progressive motion of plunged pin in the part (2nd stage). The mathematical model represents a nonlinear equation of transient heat conduction, which takes into account progressive pin movement during the 2nd stage of welding. Two constituents describe the heat sources, appearing in welding. The first one considers power of heat sources, caused by friction of the tool with the parts on contact surfaces, the second one takes into account heat generation, promoted by mechanical deformation of the part material. Mathematical modeling and experimental examination of temperature field were carried out for tool from cubic boron nitride (cubonit) and hard alloy in copper parts during FSW. Adequacy of the developed model was determined based on correlation of numerical and experimental results.
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