Boundary-conformed toolpath generation for trimmed free-form surfaces via Coons reparametrization

In the process of CAD/CAM, predefined parametric surfaces are often subject to the operation of trimming or extending. In such a case, the original iso-parametric curves are no longer boundary-conformed. Consequently, they are not anymore suitable for being used as natural CNC toolpaths. In this paper a method to regenerate boundary-conformed iso-parametric toolpaths on altered free-form surfaces is presented. The main idea of this method is to fit the 2D parametric domain of the given trimmed surface with a 2D Coons patch. Then boundary-conformed toolpaths on the altered surface can be regenerated naturally via the iso-parametric curves of the Coons patch via a two-step mapping. The application of this method is successfully illustrated on a typical trimmed surface, a turbine blade. The applicability and limitations of this method are also discussed.