Geometric Modeling and Characterization of Wall Thickness for Complex Cylindrical Thin-Walled Parts With Uncertain Manufacturing Deviations

The complex cylindrical thin-walled parts have been widely used in manufacturing field with high precision requirement of wall thickness. However, due to the existence of initial uncertain manufacturing deviations, such as blank casting errors, initial shape deviations and clamping deformations, there will be a large geometric deviation between real blank workpiece and theoretical design model. In order to solve the problem in lacking of reliable geometrical model for trajectory planning in face milling of complex cylindrical thin-walled parts, this paper proposes a method for accurate modeling and characterization of wall thickness considering the uncertain geometric deviations based on point cloud reconstruction. First, based on feature extraction and meshing process of point clouds measured with high-definition metrology both for inner and outer surfaces, subregions of each point cloud are adaptively fitted into small curved surfaces. And then NURBS surfaces are applied to connect adjacent subregions in order to form a high-precision solid model of entire workpiece. Furthermore, a characterization method of real wall thickness in milling areas is proposed. Based on the sampling mesh nodes of inner surface being the interesting points for milling areas, wall thicknesses are characterizing as distances between those sampling nodes and the outer meshed surface with an improved KD-Tree algorithm. Based on the proposed method, a meshed CAD model of real workpiece can be constructed with an error range within 0.2mm; and the wall thicknesses of milling areas can be characterized by the extracted sampling nodes. It provided an efficient methodology for geometric modeling and characterization of wall thickness of complex cylindrical thin-walled parts, which is useful for milling trajectory planning.