Optimization Of Virtual Regulating And Controlling On Welding Residual Stress Of Turbine Runner

The conception of virtual welding is brought out, because the experimental investigation of large welding structure owns the disadvantages of long cycle and heavy cost. On basis of the relation of welding residual stress between practical structure and simulative component defined by similarity theory, the method of numerical simulation is adopted to optimize the welding technology of Francis turbine runner. The welding residual compressive stress engenders in the dangerous region of blade's outlet and then the prospective aim is got. Therefore, the research in this paper has important meaning of theoretical investigation and practical engineering.In this paper, the influence of welding sequence on welding residual stress field of T joint is respectively studied from the view of multibead welding, subsection welding, multilayer welding and several joints, in order to easily optimize the welding technology of Francis turbine runner. The result shows: the method of the different welding direction between adjacent beads makes the residual tensile stress peak value minimum during the multibead welding process; the subsection welding not only extends the low stress region of weld, but also reasonable welding sequence and welding direction may effectively decrease the stress peak of some region in weld; the method of symmetry welding can get the minimum welding residual tensile stress in the multilayer welding process; under the condition of many T joints in one structure, the best method is the joints'welding at the same time to ensure decrease the residual tensile stress peak of the whole structure as much as possible.For large welding structure, huge element number and huge increment number are two difficult problems in the numerical simulation process. On the base of introducing the conception of cluster banding heat source, in the paper, the expression of the cluster banding heat source model which is suited to random weld width is deduced. This heat model not only solves the problem of the huge increment number in large structure simulation but also makes quantitative analysis of welding stress field for large structure which owns regular shape weld possible. On basis of the similarity criterion of welding temperature field which is deduced by theπtheory and the similarity destiny method, the relation of welding residual stress between practical structure and simulative component is established. By welding conduction theory and the conception of virtual simulative component, the relation of welding residual stress between practical structure and simulative component is established, which is more practical than the aforementioned relation. This relation deduced by welding conduction theory not only guides the experiment of simulative component to decrease experimental cycle and cost, but also solves the problem of huge element number in large welding structure simulation, which makes the large welding structure simulation possible.The welding technology of Francis turbine runner is optimized from the view of multilayer welding, subsection welding, local heating and local peening, on basis of verifying the relation of blade outlet's welding residual stress between runner practical structure and runner simulative component right, solving the problem of welding heat source movement along any spatial route, solving the problem of conduction between blade and crown or between blade and band and realizing the weld feeding process. The result shows: during the multilayer welding, the method of symmetry welding gets the minimum welding residual tensile stress in the outlet of blade; the welding residual stress's reduced effect of the subsection welding is related to the weld length of blade outlet and welding direction; the reduced effect on residual stress of the local heating is proportional to heating time, heating temperature, heating area, and inversely proportional to cooling area. The research for local peening shows this method can decrease the welding residual tensile stress in the peening region. The peening effect is very obvious when the temperature of heated model material reaches its own plastic temperature or so in the peening region and the peening effect is obsolete under the low temperature.The runner's welding stress field is adjusted and controlled from the view of the subsection welding, the local heating and the local peening, on the base of the right technological parameter of subsection welding and local heating by plane experiment. The result shows that higher residual compressive stress engenders in the dangerous region of blade outlet and the residual stress of whole runner is lower than yield limit's one-third of runner material.