Toolpath generation for partition machining of T-spline surface based on local refinement

Abstract

Toolpath generation is one of the most challenges facing today’s freeform surface machining, and partition machining methods are widely investigated for toolpath generation of freeform surface based on sampling and clustering. However, due to the inherent drawbacks of NURBS, there are two limitations for the partition machining of freeform surface in the current research: (1) global sampling method is imposed by reason of rectangular topology of NURBS, which will introduce redundant sampling points and increase computation costs, (2) partitioned region boundaries are represented using analytical curves or discrete points, and freeform surface behaves like trimmed surface, which will introduce gaps near partitioned region boundaries. T-spline has been proven to perform excellently in the field of CAD/CAE/CAM with the charming characteristics of less control points, flexible topology, and local refinement. However, T-spline does not be introduced for the partition machining in the current research. In the paper, T-spline is firstly introduced for the partition machining of freeform surface to solve above limitations. A partition method is proposed for T-spline surface based on its flexible topology and face-by-face sampling, which will improve the partition efficiency. Clustering parameters are analyzed, and curvature parameters are chosen for surface partition, which can extract isolated features. T-spline local refinement and sliding box method are introduced for the boundary construction of partitioned regions, and partitioned regions are described by a set of rectangles, which can guarantee the continuity near the partitioned boundaries and avoid the gaps. Different sizes of tools are used for toolpath generation of partitioned regions, which can reduce toolpath length. The proposed method is tested using two synthetic T-spline surfaces and the comparison with existing toolpath generation methods is provided.