Research On The Reconstruction Technology For Free-form Surface Of Blade

With the rapid development of science and technology,free-form surface parts are widely used in aircraft,ship,automobile and other fields.The requirement of the machining efficiency and precision for the blades has been much higher.As the key parts of gas turbine,propeller and other power devices,the blades' manufacturing quality directly determines the overall working performance of these power equipment.The surface of blade parts are so complex that there're so many difficulties in the design and manufacture procedure.Grinding process is usually used as the last procedure to deal with blades' surfaces.However,in the existing processing technics,the measurement process is usually separated with the machining process,which is obviously disadvantageous for high efficiency and high precision for the blade manufacturing.Combined with the functions of blank measurement,model reconstruction,process analysis etc.,the integrated manufacturing system for blade surface can effectively solve this problem.In this paper,aiming at the problem of blade model reconstruction in integrated manufacturing system of blade grinding and polishing,the method of curve and surface reconstruction based on in situ measurement of blade surface type value points is studied.In the machining process,the reconstructed blade surface is required to reproduce the shape of the blade surface as much as possible,and this can provide corresponding data for trajectory planning,residual allocation and error analysis in subsequent machining.An in-situ measurement system is built based on the self-developed blade tandem grinding and polishing machine.A laser displacement sensor is integrated on the tool board,and the software of the in-situ measurement and control system for the blade profile is developed.It can realize the blades surface's in-situ measurement and gather the data of blade section line by polar coordinate method.The curve and surface reconstruction based on the blade section line points is realized by NURBS method.By analyzing the B-Spline basis function algorithm,the parameterization method of data points and the solution of node vector and the control vertex inversion method,the NURBS surface reconstruction for the blade surface was carried out successfully.The matrix expression of the bicubic NURBS surface is derived,and the whole interpolation algorithm of the NURBS surface is presented.Taking the tibial model and the blade model as examples,the feasibility of the NURBS curve and surface reconstruction method is verified,and the reconstruction accuracy is analyzed.The geometric significance of weight factor and its influence on NURBS curve and surface are analyzed.A method of determining control vertex weight factor based on curvature characteristics of type point is proposed.The distance from point to NURBS curve is used as the error evaluation criterion of curve reconstruction.The error of the interpolation and reconstruction of the cross section of the blade is analyzed and the simulation results show that the interpolation accuracy of the NURBS curve interpolation method based on the transformation weight factor is obviously higher than that of the interpolation when the weight factor is 1.