The Cutter Location Point Computation For Triangular Mesh Surface Model In CNC Machining

Freeform surfaces have been widely used in aerospace, automobile, ship building, consumer products and die/mold industry. CNC machining of free form curve and surface is one of the key technologies for manufacturing these products. Triangular mesh surface is becoming popular in CAD/CAM systems. The data structure of the triangular mesh surface is simple for application, flexible for modeling and adaptable for different topology. The triangular mesh surface can be obtained from the finite element analysis model and the point cloud of the 3D coordinate scanner. It is practical and meaningful to conduct the research of tool path planning method on triangular mesh surface.The mesh generation method of sheet metal forming FEA preprocessing is investigated in this thesis to study the approximation accuracy between mesh element and the aboriginal design surfaces. The research work in this thesis realizes the read in and output STL file triangular mesh data process by using the MATLAB platform, and also do the topology reconstruction from triangular mesh surface, establish the corresponding efficient new data structure.The tool axis projection machining method for ball end mill cutter is studied here. A simplified method for computing the cutter contact point is proposed. An adaptive tool path interval method for machining steep region is also proposed.The previous study on the cutter location computation was mainly based on the cutter contact point of the non-offset triangular mesh surface. This thesis proposes a new weighted compensation vector approach to precisely computing the normal vector of the cutter contact point. We introduce the compensation vector and evolving function to compute the normal vector of the cutter contact point in the edge of triangular mesh. The normal vector inside the mesh can be obtained from the normal vectors in the vertexes by using nonlinear interpolation, which makes the cutter location much closer to the theoretical parametric surface. The example and analysis demonstrate that the method can reduce the angular deviation of the normal vector and the position deviation of cutter location point, thus improve the machining accuracy and quality. A machining interference checking method based on the curvature of triangular is proposed to improve the computation efficiency.