Research And Practice Of Tool Path Generation In NC Programming For Complex Multi-surfaces

NC programming technology, which is an important component and plays a vital role in NC machining, is always a hot research topic. To promote NC programming theory and its applications, several key technologies for rough machining, finish machining and clean-up machining of complex multi-surface model are systematically studied and implemented in this dissertation.To improve the computational efficiency and robustness of tool path generation, a novel method for boundary extraction of cutting area, which based on Z-map model for rough machining, is proposed. By introducing run-length code, a boundary-tracing algorithm efficiently extracts cutting area boundaries in a cutting layer to improve the efficiency of tool path generation. A boundary tree is utilized to represent the formed boundaries, which forms the foundation for automatic identification of the topological structure of the cutting area.The conventional tool interference detection and avoidance methods are usually designed for specific cutter types. Therefore, in this dissertation, the reasons, types and process strategy of tool interference have been studied in depth, and the main contributions of the research include: (1) a general case of interference detection and avoidance algorithm for APT cutter based on general offset surfaces is presented for removing the gouge that occurs in a single surface. The algorithm computes the interference-free CL point of APT cutter depending on the relation between the cutter and interference check triangular facets. And the step forward and the scallop height are calculated based on the evaluation of tool path error. The algorithm is applicable to various cutters represented by APT and can serve as a general computing algorithm of interference-free CL point in the CAM system. (2) A concept of extended cut region is defined and an interference-free tool path generation algorithm for APT cutter is proposed based on the extended cut region. The algorithm has great capability in generating interference-free tool paths to traverse several surfaces being machined in a single pass.The presented method can successfully resolve the gouging problems caused by tangent discontinuity, surface overlaps or surface gaps among the surface elements to be machined and accurately identifying sharp-turn points near the transition area of surfaces to increase the machining precision and cutting quality.Technique of clean-up machining is described. A new clean-up machining tool path generation algorithm is proposed based on the C-map model of surface. The undercut regions are obtained by using the curvature characteristics of surface. The size of cutter is calculated by an optimization method. And the initial points of the optimization process are the maximum principal curvature points in each interference seed regions of C-map model, thus greatly reducing the number of initial sampling points and improving the computational efficiency.At last, on the basis of above mentioned research work and achievements, a NC automatic programming prototype system is developed. The interference-free tool paths of rough, finish and clean-up machining for complex multi-surfaces have been successfully generated based on the developed method.