Research On The NC Machining Feature Extraction And Tool Path Generation Of The Complex Triangular Mesh Model

The triangular mesh model represented in STL format, as a kind of CAD dataexchange format, has been universally supported by all CAD/CAM systems and usedin rapid prototyping manufacturing(RP) as well as reverse engineering(RE).Compared with the popular application of triangular mesh model, research on toolpath generation from triangular mesh model is relatively less, and usually adopts theiso-planar method to generate tool path for a single processing on the whole meshmodel. Unified trajectory planning strategy can’t ensure to efficiently process allsurfaces of the model, because some interference area are often exist which affect themachining accuracy and efficiency. Therefore, this paper puts forward a partitionprocessing strategy for the complex mesh model, and the research work is aimed atautomatic recognition of machining feature as well as generating tool path fromtriangular mesh model.Firstly, the method to establish the topological structure of the triangular meshmodel is researched. A rapid and efficient topological half-edge data structurereconstruction algorithm of triangular mesh based on the C++standard templatelibrary is developed. Meanwhile, the vertex curvature calculation method oftriangular mesh is also studied, which play an important role in the follow-up work.Secondly, the method to automatic identifying local interference region and slotis researched. The local interference is detected based on the region growingalgorithm and the principal curvatures at vertices. For the slot feature, a method basedon offsetting projection contour is proposed to recognize it.Finally, the method to generate tool path from triangular mesh model isdiscussed. The tool path corresponded to the identified feature have been planned, forlocal interference feature, a method of boundary contour offsetting is proposed togenerate tool path with constant scallop height. For the slot feature, a rapid slicingalgorithm based on topology structure to generate the Z-constant contour path isdeveloped, then the interference problem of offsetting contour is studied, and put forward a invalid offset edge detection approach in order to eliminate theself-interference, thereby the interference-free CL data is generated.The innovations of this paper are as follows:1. A partition processing strategy oftriangular mesh model is presented, which can avoid tool path generation for a singleprocessing on the whole mesh model and improve the machining efficiency andaccuracy;2. A novel method based on the anisotropic region growing algorithm isdeveloped to identify local interference and slot feature;3. Based on triangular meshmodel, an algorithm to generate tool path with constant scallop height via boundarycontour offsetting is proposed.