A surface reconstruction strategy based on deformable template for repairing damaged turbine blades

Abstract

Recently, rapid repair of damaged blade has become the focus of considerable interest for extending its service life. However, due to the defects caused by high temperature and pressure of operations as well as foreign object impact, the turbine blades often undergo the deviations of the actual part profile from its design model, such that this nominal Computer Aided Design (CAD) model cannot be directly used in the process of repair for tool path generation of laser cladding and Numerical Control (NC) machining, thus to nicely repair the damaged or worn blades, it is necessary to reconstruct the surface model of the actual blade. This paper develops a deformable template-based approach to recovering the surface of blade from the cross-sectional profiles. The mathematical model for cross-sectional profile reconstruction is first established and is then solved by an alternate iteration optimization strategy consisting of registration and deformation of the template curve. Since the proposed method can automatically transform and deform the template curve to best fit the cross-sectional points, the compatibility conditions between different sections are automatically satisfied and there is no need for the data preprocessing such as data sorting, parameterization, etc. which are necessary for the traditional surface fitting methods. Undoubtedly, this considerably simplifies the reconstruction problem of the damaged blade and nicely adapts to blade part-to-part variation. Moreover, a method of closest point computation that combines the arithmetic for Bernstein-form polynomials and Bézier curve subdivision is also given based on bintree decomposition to improve the iteration processes of 2D profile reconstruction. Then, according to these reconstructed sectional profiles, the actual blade surface is reconstructed by surface skinning operations. Finally, the proposed method is tested on a sample blade, and the experimental results show that our method can precisely reconstruct the surface of the damaged blade, especially for the blades with area defects.