(A) study on general offset and transformation of triangular mesh for effective NC tool path generation

Abstract

Triangular mesh is widely used for graphical shading of surface, rapid prototyping, engineering analysis, and NC (Numerical Control) machining. A CL (Cutter Location) surface and mesh based tool path generation process consists of two steps that are offsetting mesh and gathering the series of lines from the offset mesh. The previous mesh offset and tool path generation methods have fallowing problems. The mesh offset methods have created many gaps and overlaps, and have not considered flat and rounded endmill which are used frequently in NC machining with ball endmill. The scallop height of direction parallel tool path is changed according to the slope and curvature of the CL surface. The 5-axis tool path usually generated from original surface takes long time compared to 3-axis. The triangular mesh based tool path generation system of this thesis consists of four steps; offset mesh to CL surface, deformation the CL surface, tool path generation by mesh slicing, and inverse deformation of the tool path. An offset method using the multiple normal vectors of a vertex, offset method for a generalized cutter, and CL surface deformation approach for 3-axis and 5-axis machining make tool path generation process more effective then previous research. A new triangular mesh offset method using the multiple normal vectors of a vertex is introduced. The multiple normal vectors of a vertex are set the same as the normal vectors of the faces surrounding the vertex, while the two vectors with the smallest difference are joined repeatedly until the difference is smaller than allowance. Mesh is offset by moving vertices along the multiple normal vectors by the amount of offset distance and the gap at convex sharp edge is filled by blending mesh. This method does not create a gap at the smooth edge, and it is accurate at the sharp edges because the vertices are moved to the normal directions of faces and joined by the blend mesh. The incomplete triangular mesh including cracks ...