TOOLPATH GENERATION FOR FREEFORM SURFACE MODELS

The generation of optimal NC code to drive milling machines for models defined by freeform trimmed surfaces is a difficult problem. In pract ice, two main approaches are used to generate toolpaths for surfaces, neither of which is optimal, in general. The first exploits the parame tric representation, and generates isocurves that are uniformly distri buted across the parametric domain. This approach is not optimal if th e surface mapping into Euclidean space is not isometric. The second ap proach contours the models by intersecting the surfaces with planes eq ually spaced in Euclidean space, resulting in a piecewise-linear toolp ath approximation which is nonadaptive to the local surface geometry. Further, the toolpath generated by contouring is suitable for 3-axis m illing, but is inappropriate for 5-axis milling. In the paper, an algo rithm developed to extract isocurves for rendering adaptively is modif ied and enhanced to generate milling toolpaths for models consisting o f trimmed surfaces, and it can be used in both 3- and 5-axis milling. The resulting toolpaths do not gouge locally, and they combine the adv antages of both prior approaches. The output toolpath is appealing, si nce it is composed of isoparametric curves, and is therefore compact, exact, and easy to process. Further, it is more optimal than the previ ous methods in that the resulting toolpath is shorter, and it provides a direct quantitative bound on the resulting scallop height. This alg orithm has been used to compute gouge-avoiding toolpaths for the autom atic milling of freeform surfaces, without the introduction of auxilia ry check and drive surfaces being required.