The Tool Sequence Planning Of NC Machining For Pockets With Multi-islands

Numerical control (NC) has been applied for the machining of complex pocket parts because of high-speed, high-efficient, high-precision. Meanwhile, the tool combination becomes instead of the single tool in the machining of complex pocket parts with the improvement of the tool system. As the important part of manufacturing resource, the tool selection in NC machining not only is the basis of the toolpath generation, but also affects the quality of machining, the efficiency of NC machining and manufacturing cost. In the CNC programming, the existing CAD/CAM system still select the tool through human interaction by planning staff, which is difficult to ensure the selection rationality and flexibility. Therefore, a tool sequence planning strategy using the lost manufacturing cost as the optimization object is presented for pockets with multi-islands, which realize the intelligent selection of tool in NC machining.Firstly, the rational expression of machining region lays the importation foundation of the tool sequence planning. In this paper, the machining region is expressed by loops commonly in two-dimensional plane. The definition and classify of loops is introduced, meanwhile the identify method of inner and outer loops is also introduced. The position relation determination of loops is transformed the relation test between the point and the loop. The offset of loop is present. Based the Boolean operation of single-connected region, the algorithm of Boolean operation of multi-connected region is present.Secondly, as to the commonplace pocket with multi-islands, the tool sequence planning strategy is present. The method of layered machining is usually adopted to obtain machining region in workpiece, which is described as multi-connected region, composing the different loops, and then the region is identified by the identify method of inner and outer loops and the position relation determination of loops. To compare with database and generate the viable tool set, it is very necessary to extract the maximum and minimum dimension of geometric constraint from the machining region. Besides, the accessible region of a single tool is obtained, through the fast offset of loops. Otherwise, as to the multiple tools, a concept of the co-accessible region is brought in. Based on the single tool's accessible region, it could gain the co-accessible region in use of multiple tools.Additionally, via the method of contour -parallel toolpath, the toolpath is generated in the co-accessible region of every tool, which is used to calculate the processing cost and tool cost. Then as for single-source direction graph, the different combinations among the viable tool set are shown. The evaluation model of tool sequence planning is established and obviously the tool sequence with the minimum cost can be acquired by Dijkstra matrix arithmetic. Also, tool sequence planning of 2D has extended to that of 3D.Finally, the prototype software has been made in plate of Visual C++6.0, especially used for tool sequence planning about the pocket with multi-islands in NC machining. There are some illustrations to confirm the planning in paper.