A computer-aided prototype system for NC rough milling of free-form shaped mechanical part-pieces

A prototype computer-aided manufacturing module for rough milling of free-form mechanical moulds is proposed. The system allows direct modelling of the shape of the material to be removed, by starting from the geometry of the stock and of the final part-piece. A modelling engine, based on rational bivariate and trivariate tensor-product B-spline patches, was developed to ensure complete geometric coverage, allowing common analytic geometric items such as planes, quadrics, and blocks to be exactly modelled. Methods for the evolution of the milling layers, the choice of isoparametric NC tool-paths and their piecewise approximation are proposed; the procedures work in the context of three-axis machining by end-mill cutters. Technological considerations about the main cutting force the follow: it results that fine tuning of the milling feed rate can be computed by geometric evaluation of the depth and width of cut. To demonstrate the feasibility of the approach, an application example concerning mould manufacturing is reported.