Study On Multi-axis NC Tool Path Generation For Large-scale Fixed-pitch Propeller

Large-scale fixed-pitch propeller is a key component of ship's power machinery. The machining accuracy and surface quality of propeller determine the development of the shipbuilding industry. In our country most large-scale fixed pitch propeller are still using the traditional processing technology. Multi-axis CNC machining technology only occupy a litter percentage in the whole processing. Fixed-pitch propeller machining process and tool path generation are presented in this paper. On the basis of above research work, a programming prototype system for propeller is developed.The NC machining process strategies are established by analyzing the geometric properties of surface of fixed-pitch propeller to solve uneven allowance and large interference area. The process scheme has been verified in Zhenjiang Propeller Company.In order to solve the gouging and collision problems, an interference detection and avoidance algorithm for propeller is presented. Firstly the OBB boxes are constructed between the tool and workpiece. Then workpiece OBB box is partitioned by Octree structure. Finally, the interference triangular facets are found out by Separating Axis Theorem which can be used to judge whether there has been interference between tool and workpiece. Not only this algorithm can be used to divide the propeller region, machine tool simulation, but also be used for the generation for interference-free tool path.Technique of tool path generation for the propeller is described. A tool path generation algorithm for Filleted endmills is proposed. After searching the triangular facets using OBB box, and then the axial distance is calculated based on the analytical method. Flat cutter, as the special case of Filleted endmills, is also researched in this chapter.Finally, the programming prototype system for propeller is developed based on ACIS and HOOPS, VC++ and BCG to realize the regional division of a large propeller and tool path generation. Experiments were conducted to validate the algorithm mentioned above.