Offset tool-path linking for pocket machining

For die-cavity pocketing, contour-parallel offset (CPO) machining is the most popular machining strategy. CPO tool-path generation for pocketing includes geometrical and technological issues: (1) a 2D-curve offsetting algorithm; and (2) optimizing technological objectives, such as tool-path linking. The 2D-curve offsetting solution has been widely studied, because it has so many potential applications. However, though the tool-path linking may seriously affect the machining performance, there have been few reported investigations on optimizing the CPO tool-path linking. This paper presents a CPO tool-path linking procedure optimizing technological objectives, such as dealing with islands (positive and negative) and minimizing tool retractions, drilling holes and slotting. Main features of the proposed algorithm are as follows: (1) a data structure, called a 'TPE-net', is devised to provide information on the parent/child relationships among the tool-path-elements; (2) the number of tool retractions is minimized by a 'tool-path-element linking algorithm' finding a tour through the TPE-net; and (3) the number of drilling holes is minimized by making use of the concept of the 'free space' (negative islands or already machined region).