The NC Programming Technology For Machining Strip Width Optimisation In Freeform Surface Machining

Supporting by the National S&T Major Project and the requirements of aerospace, automotive and other manufacturing industries, in the view of the problem of low machining efficiency in freeform surface finishing, the NC programming technology for machining strip width optimisation in freeform surface machining was deeply researched. The main contributions of this paper are as follows:1) The tensor based representation of the machining strip width was researched. The effective cutting surface of cutter was defined, and its fitness to freeform surface was connected with the machining strip width. A second-order tensor was derived to evaluate the machining strip width.With this tensor, it was able to evaluate the machining strip widths in all feed directions at each cutter contact point in a continuous way. Moreover, the feed directions with the maximal machining strip width could be computed accurately and more efficiently by extracting the eigenvector of the tensor.2) The tensor based freeform subdivision was researched. A tensor field could be established overall the surface which could be used to simulate the regional distribution of the feed directions with the maximal machining strip width. The classification of the degenerate points within the tensor field was researched, and the trisector degenerate points were extracted as the starts to construct boundaries within the surface. After generating all boundaries inside the surface, the surface may be divided into several sub-regions, and in each of them the feed directions with the maximal machining strip width share the same or similar trend.3) The tool path generation method based on freeform surface subdivision was proposed. After getting the suface subdivision result, a initial tool path curve was selected within each sub-region by the maximal average machining strip width strategy, then tensor lines would be computed overall each sub-region by offsetting the initial tool path curve. Tool path generation by this method is able to follow the feed directions with the maximal machining strip width as much as possible, thus more global optimum machining efficiency can be achieved.4) The research of this paper was realised in the regional-based freeform surface NC programming system developed on the CATIA platform. Two cases from the real industry were selected to demonstrate the advantages of the proposed method in increasing the machining efficiency.