Research On Reconstruction And Repair Methods Of Aeroengine Blade Stream Surface

With the continuous development of aviation industry,the demand for aeroengine blades has increased dramatically,and the number of damaged blades has also been rising.Traditional blade manufacturing,processing and repair methods are gradually unable to meet the needs of large-scale blade processing and repair.Building a blade adaptive machining and repair system(BAMRS)which integrates measurement and processing will become the main trend of blade processing and repair in the future.As the basis and key of the BAMRS,the quality of the reconstructed model will determine the final processing quality of the blade.In this paper,based on the establishment of BAMRS,the theory and methods of blade model reconstruction and repair are studied,and the reconstruction and repair of blade model are realized,which has important theoretical significance and practical value.In view of the characteristics of high precision and small machining allowance of blade blanks manufactured by superplastic forming/diffusion bonding(SPF/DB),contact measurement method with high measuring accuracy is adopted to measure the blade profile.When reconstructing the model based on contact measured points,the failure of surface reconstruction may occur because the distance between two measured points is larger than the normal thickness of blades.An accurate and efficient sorting algorithm for measured points of single-layer blade cross-sectional curve is studied.The concept of quadtree is introduced to transform the overall sorting of measuring points of single-layer cross-section line into local sorting.Based on quadtree,the measured points are divided into sub-regions.On the basis of the analysis of the quadtree partition results,the node coding rules of sub-regions and the search algorithm of adjacent regions are proposed.Then,the sub-region sorting algorithm based on node coding and the sorting algorithm of measured points in sub-regions are studied.The accurate and efficient sorting of measuring points of blade section line is realized,which lays an important foundation for the reconstruction of blade surface.Based on the correct sequencing of the measured points of the blade cross-sectional curve,and considering the surface reconstruction of the blade from the aspects of the working environment of the blade and its unique fluid function,the stream surface reconstruction method of the blade is put forward,so as to make the reconstructed blade surface have fluid characteristics.Based on the measured point extraction of the inlet and outlet edge of the blade,the calculation rule of the airflow direction at the inlet and outlet edge of the blade is given.Then,the quaternion is introduced to construct the blade surface velocity field based on the measured points.In order to improve the reconstruction accuracy of blade flow surface,based on the velocity field of blade surface,the subdivision method of velocity position,direction and size in the velocity field is studied,and the integration algorithm of blade stream surface is deduced from the definition of stream surface.The proposed algorithm can be used not only for blade surface reconstruction,but also for other surface reconstruction with fluid function.Based on the method of blade surface reconstruction,in order to effectively reduce the uncertainties existing in the traditional surface repair methods,a surface repair method based on the iterative deformation of adjacent non-damage cross-sectional curve is studied and proposed,which can make the repaired surface fully inherit the characteristics of adjacent cross-section lines,and at the same time,make the process of blade surface repair follow.In the process of extracting non-destructive section lines,the interpolation accuracy of the parts with large curvature changes will be reduced due to the large change of the overall curvature of the blade section lines,and the density of different measured points in different sub-regions of the blade.In this paper,based on the piecewise interpolation of blade cross-sectional curve segments,a method of curve blending with second-order geometric continuity(G~2)is proposed by using the idea of curve expanding.The cross-sectional curve segments is blended by G~2 to complete the extraction of non-damaged cross-sectional curve.On the basis of extracting non-damaged cross-sectional curve,an iterative deformable template is set up.According to the size of the damaged area on the blade surface,the criterion for determining the density of the measured points on the damaged surface is studied,and the rough and precise registration algorithms of non-damaged cross-sectional curves and the measured points on the damaged parts are given to achieve high-precision matching between them.Based on the affine transformation rule in the number field and taking the measured points of the damaged part as the deformation constraint,an algorithm for allocating the displacement of all control points in the support interval is established to realize the iterative deformation based on the non-damaged cross-sectional curve,and to ensure the reasonable,smooth and small error of the curve deformation.On the basis of repairing the damaged cross-sectional curve,the data points of the missing parts are extracted,and then the surface of damaged blades is repaired based on the reconstruction method of stream surface.Based on the in-depth study of the methods mentioned above,the surface reconstruction and repair module in the blade adaptive machining and repair system are developed independently by using the secondary development function of Autoodesk Inventor Professional 2012 platform.The module has data input and output interfaces.It can reconstruct and repair the flow surface of the blade by reading in the measured points of the undamaged or damaged blade.It can also access other modules in the system through the interface to achieve functional expansion.The example of surface reconstruction and repair shows that t he sub-module of surface reconstruction and repair developed in this paper can successfully reconstruct and repair the blade surface,and meet the requirements of the blade adaptive machining and repair system.