Research on Profile Geometric Feature Parameters Extraction of Complicated Thin-Walled Ring Parts with Irregular Section

The extraction of profile geometric feature parameters (PGFPs) of complicated thin-walled ring parts with irregular section (CTWRPIC) plays an important role in the entity reconstruction and the establishment of automatic process planning knowledge base. Take the metallic W-ring of aero-engine as an example, due to the large number of rolling forming passes and the large difference in section profile shape, it is difficult to complete the effective extraction of multi-pass PGFPs. Besides, during the rolling forming process, the uneven organization of the billet, roller wear, etc. is likely to cause different lengths of the sealing lips on both sides of the metallic W-ring, which will lead to inaccurate parameter extraction results. To overcome these problems, this article proposes an adaptive bounding box based multi-pass PGFPs extraction method. First, based on the Andrew algorithm, the section profile point cloud with large differences in the shape of each pass is converted into the corresponding convex hull with similar shape, so as to improve the efficiency and stability of building of bounding box. Second, the slope of the convex hull vertices is used to identify whether the metallic W-ring has forming defects, so as to build an adaptive bounding box that more closely approximate the section profile point cloud. The robustness and accuracy of the method is demonstrated by the inspection experiments of PGFPs on the metallic W-ring samples from six rolling forming passes, compared with traditional standard inspection method, the relative error of our method is around 1%.