Large Thick-walled Structure Of The Welding Process Numerical Simulation Research And Application

In order to simulate the residual stress and deformation of large-scale spiral casing of water turbine, the welding heat source model and the temperature field of multipass welding are studied in this paper. It provides the foundation for welding stress-strain analysis to quantify accurately the welding temperature field. Temperature field contains adequate information about welding process, so it is vital for understanding basic welding problems and producing weld structure.The existing heat source models are categorized and the typical ones are analyzed, based on which the concept of dynamic heat source model and three elements of welding heat source model are proposed. With the concept and the infrared imaging experiment, the temperature field of short circuiting CO2 gas arc welding is researched. It is found that the temperature distribution of weld pool and its adjacent area has a combined shape of cone and trumpet, which is different from the Gaussian distribution of TIG welding and manual metal arc welding. Subsequently the combined heat distribution pattern is established, which combined the Gaussian heat distribution of arc and the conical heat distribution of droplets. It is compared with the simulation result of Gaussian heat source model and that of experiment. It is found that the application of combined heat distribution to GMAW with more concentrated energy, in which droplet is transferred, produce more accurate numerical simulation result.Based upon the analysis of heat characters in multipass welding, the influence of welding technological conditions and the dynamic variation of convection and radiation on the temperature are investigated. The simulation method for adopting different heat source model parameters in different pass is developed. The appropriate heat parameters in each pass are discussed. And the empirical formula to calculate the heat input efficiency is derived. In addition, different value settings for heat distribution parameters of double ellipsoidal heat source model and the maximum errors in heat flux caused by them are emphasizingly analyzed, and some laws to set values are obtained. It is verified by experiment that the multipass welding analyzing model which is set up by integrated application of the investigation results is effective.On the basis of which the welding process of large-scale spiral casing of water turbine of Ertan hydropower development company is simulated numerically. The stress and deformation process in longitudinal welding of spiral casing shingle and that in circumferential welding of pipe segments are explored, whose results will direct the welding production of spiral casing.