Surface Regeneration Algorithm And Error Analysis For Repair Of Areo-engine Blade Tip

Aeroengine blades are the core components of the compressor and turbine engine. Due to the harsh environment, the blades offen suffer from various damages such as abrasive wear, distortion, impact dents, cracks, et.al. Since a small change in the blade geometric shape can directly affect the stable operation of the aeroengine, precision repairing of the blades becomes a critical factor to maintain the high performance of the aeroengine. The present work has been concentrated on repair of blades with defects of tip wear, rip and airfoil wear. Among these defects, the blade tip wear for a twisted blade is the most difficult task to be solved urgently. In this paper, we focus on repair of the twisted blade tip and propose an new approach to reconstruct the worn blade tip..In the paper, a genetic algorithm based on surface reconstruction method for the un-worn area of a twisted blade is proposed, and a surface regeneration algorithm based on G1 continuity is presented for the worn area of the blade tip. The reconstructed blade tip model is adaptive to its geometry and can be used as a norminal model to generate the tool paths for the machining process after the blade tip is built up. These algorithms proposed can solve the difficult problem of worn blade norminal model generation in repair of twisted blades. This work will promote the reuse of resources and the development of sustainable economy. The main works of the thesis are summarized as follows.1) The overseas and domestic research literature and possible challenges of aeroengine blade tip have been investigated comprehesivly. For repair of aeroengine blades, the majority is repair of worn blade tip defect. Although the straight blade tip repair has been comparatively mature abroad, accurately repairing of a twisted blade tip is still a difficult problem. Due to the manufacturing error and the deformation of a used blade, the original surface model of the blade is no longer suitable for the repair process. To reconstruct and regenerate accurately the blade surface model of the worn blade becomes an important part for remanufacturing of a twisted blade.2) In order to reconstruct the surface model to the un-worn areaof the blade, we proposed an iterative interpolation algorithm based on B-spline surface reconstruction method. With the G2 continuity expression of a closed B-spline curve, an iterative interpolation method is constructed to fit the cross-section data of the blade. The blade surface model is then created for the un-worn area of the blade. Through the preprocessing of the cross-section data, the average error of the surface model is about 0.0325mm. To further improve the accuracy of the surface model reconstructed, the author proposed a genetic algorithm based surface reconstrcution method. In this method, the genetic algorithm is applied to optimize the data parameterization and node vector configuration, and a least squares minimization approach is used to calculate the control points. Through the comparison of the two sureface reconstructing algorithms, the author found that the later method can improve the fitting accuracy significantly and achieve an average error about 0.003451mm.3) Based on the blade surface model reconstructed previously, we focus on the algorithms of surface model regeneration and extension of worn blade tip. Based on minimum energy method the author proposes a B-spline surface regeneration algorithm for the worm blade tip. In this algorithm, the control points of the surface model are extended along the blade height direction, and a minimum energy method is designed to optimize the extended node vectors to ensure the smoothness of the extension surface. Through the error comparison of the cross-sectionsfrom the extended surface model and the oringinal model (the model without tip worn), the author found that the error of the extended surface is relatively large, and it increases when the extension distance is increased and when the blade is twist. The extension method needs to be improved to achieve a better surface accuracy for repair.4) Taking into account of the surface continuity and extension error of blade extension model, a B-spline surface extension and regeneration algorithm base on G2 surface continuity is proposed in this paper. In the algorithm, considering the characteristics of large of the twisted blade, the boundary conditions ofG0,G1 and G2 surface continuity between the adjacent B-spline surfaces are finalized. A new solution is conducted to solve the boundary equations through the theory of geometrical continuity. The parameters is determined by the G1 and G2 continuity condition, which are adjusted by a shape parameter α1. This algorithm can ensure the continuity of the extented surface model and the generation of tool paths for the machining process. The most important is that the error of the extended surface model is reduced obviously.5) Based on these algorithms proposed, the repair prototype system is developed for refurbilishing the worn twisted blade tip. Visual C++6.0 development platform and OpenGL 3D graphics technology are applied to implement the surface reconstruction and regeneration algorithms. The repair system achieved the following functions: model input and output function, surface model reconstruction, blade tip regeneration. Through the repair system developed, the twisted blade tip can be recreated which is useful for precision repair and machining process.