Pre-Post Surface Defect Repair for Offset Car-body Complex Surfaces

The offset operation for complex surfaces is a key and challenging pole in the modelling process of car-body design. In this paper, we proposed a pre-post surface defect repair approach to solve the problem. Firstly, through the analysis of surface defects which lead to offset failure, we consider the NURBS surface case and define two types of surface defect forms and their corresponding defect metrics. Secondly, for the given compound surfaces, the defect types were obtained using above detection criterion and the surfaces were processed respectively. For the case of degenerate surfaces, surface reconstruction with a quadrilateral trimmed surface is adopted, and for surfaces with highly non-uniform control poles, the number and distance distribution optimization of control poles are utilized with car-body engineering constraints. Then, the surfaces were sewed and offset as a whole. Finally, according to industry standards and expert knowledge, we post-process the offset surfaces to improve their fairness and edibility. The numerical results show that our method is effective on Siemens NX platform.