Tool-Path Planning Of NC Machining Based On Scattered Points

Numerical controlled(ab.NC) machining based on scattered points is a method of studing unorganized points on the surface of the object, which not appending any geometrical and topological information(including normal vector, borderline information of surface). For the traditional machining methods, the tool-path is generated based on the surface fitting, surface offset and triangulation to construct the surface model. These methods are not only fussy but also inaccurate especially. In order to improve precision and efficiency, many researchers begin to study how to generate NC tool-path from measured data directly.Making the tool-path of 3-axis NC machining directly from scattered points is the core of this paper. At the same time, this paper includes other extentional contents, such as boundary-curve extracting technology, choosing the best processing direction and so on.At first, the author adopts the projection method, and let the single valued scattered points projected on a horizontal plane. The boundary curve of the planar projected points of the scattered points has been extracted by calculating the angles between any point in the boundary grid and its surrounding points. Comparing these angles with the given value and judging whether the computing point is a boundary point, then connecting all the boundary points. On the basis of this, the initial boundary curve is faired by use of B-spline fitting technology and the offset curve of the initial border curve is constructed.Based on the concept of monotone chain in computational geometry, the optimal cutting direction and the minimum number of the monotone chains have been determined that minimizes the number of tool retractions. The algorithms of tool-path elements calculating and zigzag tool-path linking have been proposed, which is suitable for the tool-path planning of the die cavity machining. The non-gouging cutter location of the toroidal cutter, ball-end cutter and flat-end cutter has been generated. Then, the tool-path generating method of mould machining based on the scattered points is analysed. Finally, some numerical calculating example is given. The correctness and effectiveness of above NC machining methods are proved by the machining simulation with the help of simulation software.