Automatic Pre-Mesh CAD Data Repairing

Abstract

Computer aided design (CAD) models are the starting point for many downstream applications such as mesh generation, structural/fluid/thermal analysis, rapid prototyping, numerical controlled machining, casting, computer graphics. Each of these downstream applications are strongly dependent on the accuracy and consistency of the input geometry, but due to numerical problems, imprecise design, software idiosyncrasies, or data exchange issues, the surface patches produced at the CAD step may abut within unpredictable tolerances, resulting in gaps, cracks, holes, overlaps, T-connections, invalid topology and inconsistent orientation which resulted in elusive automatic grid generation. In this paper, an automatic CAD processing tool based on a powerful software development platform (Open CASCADE Technology) is presented to reduce the amount of time and cost associated with cleaning/repairing CAD geometric data for grid generation. Geometries are read from IGES file format, and translated to an internal representation for processing (shape fix followed by sewing) and finally exported in STL, STEP and IGES file formats. The tool automatically detects and heals commonly found geometrical and topological errors. As the main target is automatically repairing CAD data format errors prior to mesh generation, many test cases are performed for different kind of geometries to check the algorithm consistency and robustness. Different CAD inconsistencies are considered to check the accuracy and efficiency of the tool. It is shown that improvement in terms of time and cost can be achieved.