NC Symmetrical Machining System For Ship Model Surfaces

A ship model, which is usually made of wood according to the ship offsets table and lines plan in contractible scale, is an important tool to forecast navigational capability of a real ship and to assist scientific research & teaching work. In allusion to big size, complex shape, wooden material, especial symmetrical characteristic of ship model surface (SMS), this thesis studied systemically on the methods of SMS divisional modeling & divisional machining based on symmetrical machining technology.Based on SMS offsets table and lines plan, the thesis investigated two modeling methods for the 3-D lines mesh: Lines Reconstruction and Coordinate Transform. The 3-D lines mesh is the direct modeling foundation of SMS.The thesis investigated two surface modeling methods by lines interpolation: Skinning and Through Curve Mesh (TCM). Comparing the modeling effects of SMS sheets by the two methods, the thesis pointed out that TCM is suitable to the SMS modeling. Because the modeling precondition of TCM is a curve mesh, however, The SMS 3-D lines mesh generally can not satisfy the condition, local region enveloping and surface division project is put forward. Through local region enveloping project and surface division project, the ship model surface can satisfy with the demand of TCM, thus, the modeling of the ship model surface can make use of lines farthest, which ensure the modeling precision and fairness of the whole SMS.Aiming at the requirements of high efficiency and high precision machining, 4-axis NC symmetrical machine being as the machining platform, four tool path planning rules on SMS NC symmetrical machining have been concluded: wood cutting rule, symmetrical machining rule, divisional machining rule and water line machining rule. The processing parameter curves of SMS roughing machining wre drawn on the base of wood cutting formula. Based on the above four rules, a machining scheme by phase division and region division has been put forward, and it is simulated after its NC programming.In allusion to the NC machining for a large symmetrical freeform surface, the thesis defined a new-style symmetrical machining method, analyzed its key technologies, investigated the realizing mechanism of symmetrical machining and the technology for avoiding collision. Based on the above research work, the first 4-axis NC symmetrical machining system for SMS in China has been successfully developed. The actual machining results confirm that the system can shorten the machining time of a twin-skeg SMS from 45 working days needed for the current handcrafting method to 7 hours, and reduce the symmetric error from 1.5mm to 0.47mm; the machining efficiency of the 4-axis symmetrical machine is enhanced 85% higher than that of a traditional 4-axis single-cutter machine.