Research On Reconstruction Of Steam Turbine Blade Based On Nurbs Surface And Interpolation Algorithm Application

Steam turbine blade is the key component, its design and manufacture level is one of major indices of steam turbine technology. In order to raise steam turbine's stage efficiency, the blade profile shape is more complex, the processing technics update continuously, the processing request is more strict. Its machining accuracy and quality influence the unit's operating efficiency and security reliability, therefore , how to increase the machining accuracy and efficiency of the blade is an important topic which the domestic and foreign scholars study all the time.The steam turbine blade profile shape is complex, it contains the conic section and the free curve. On the basis of thorough study of surface reconstruction method, the 3×3 degree and 2×3 degree NURBS surface matrix expressions are obtained. The mathematics model of the blade is built based on the 3×3 degree and 2×3 degree NURBS surface. The steam turbine blade surface digitization expression is realized. The fitting error is analysed and computed.To improve the machining accuracy and efficiency of the steam turbine blade, the NURBS curve direct interpolation algorithm based on the redundant error is analysed and compared with the constant feedrate interpolation algorithm, equal chord-error interpolation algorithms and the adaptive feed speed interpolation algorithm with confined chord errors from several aspects including the machining accuracy, the feed rate, the interpolation time as well as acceleration and so on. These interpolation algorithms are used on the blade.The results show that NURBS curve direct interpolation algorithm based on the redundant error used on the steam turbine blade reduce the error redundant when the blade curvature radius is large. The chord error tolerance is confined to allowed limit.The experimental results are showed that the machining efficiency of blade is not only improved, but also the contour accuracy is guaranteed.According to the profile surface feature of the steam turbine blade, the row space is calculated with constant parameter method.The cutting step length is calculated according to the interpolation algorithm based on redundant error. The cutting tool posture and the tool dimension are reasonable to be chosen.The processing parameters are optimized.It is advantageous in enhances the blade machining accuracy and efficiency.The three-dimensional entity model is established. The blade numerical control machining process is simulated using the Cimatron software. The blade process NC code is generated and the blade profile is machined using the numerical control machining center.