Offset Algorithm Based Tool-path Planning For NC Machining

Two different kinds of optimal tool path planning methods, which are all based on the conventional offset algorithm, are proposed respectively for freeform surface machining and 2D pocket with island chain in the paper. For freeform surface machining, the formulation of the geodesic, which is corresponding to short path length and high kinematics performance, is introduced to the classical offset method. Comparing with the classical offset method, high federate can be achieved and dynamics of the machine is improved. Comparing with the traditional iso-parametric planning and iso-planar planning, the distribution of trajectories is even and redundancy is minimized. For 2D pocket with islands machining, the image division technology is used for eliminating the intersection of contours and higher efficiency.Firstly, the theoretical basis of the offset curve is introduced. The calculation for the single planar curve and combination planar curve is presented. For space curve, there are two different type of offset, separately named general normal offset and geodesic offset. Among of them, the general normal offset means the locus of point at a constant distance measure from orthogonal to curve, while geodesic offset means that the locus of point at a constant distance measured from curve along geodesic drawn orthogonal to the curve.Secondly, the generation of the offset tool paths is described as followed: For freeform surface machining, the boundary conformed geodesic of the machined surface is firstly calculated, then a set of candidate offset curves are obtained basing on the general normal offset or the geodesic offset described above, among which the distances are corresponding to the interval, finally continuous tool path is acquired by connecting the offset curves.For 2D pocket with islands machining, the pocket is firstly divided respect to the island chain basing on the image division technology, then the contour offset is formulated for different regions, finally a few of retractions are added for a whole tool path, by which the intersection is eliminated comparing with the traditional contour offset method.Finally, some applications are illustrated for the practicability of the proposed method. Furthermore, the comparing between proposed method and traditional method is operated, such as iso-parametric path planning, iso-planar path planning for freeform surface; contour offset for 2D pocket with island chain, which is shown that by using the proposed method, the total path length is shorter and the efficiency is higher. The correctness of the resultant tool paths is simulated by the commercial CAM software UG/NX, and then application is verified in HSM machining center.