| Controllable pitch propeller is a key component in the azimuth thrusters of a dynamic positioning system, Its machining accuracy and quality directly affects the performance and service life of the dynamic positioning system. Controllable pitch propeller blades have been widely machined in the multi-axis NC milling machine. The locating errors and the deformation influenced by cutting force are the main factors which affects the machining accuracy of propeller blade.Therefore, the fixture locating error analysis and compensation, and taking measures to decrease the deformation are of great significance to improve the blade machining accuracy and ensure the blade performance.This paper firstly discussed about locating solutions of controllable pitch propeller blade, and calculated the dimensions and tolerances of the fixture with one locating surface and two locating pins.A mapping model of a workpiece locating error caused by the setup error and geometric inaccuracy of locators for the fixtures was established. Based on the model, the locating error of the fixture with one locating surface and two locating pins was analyzed. on the condition that dimensions and tolerances of locators were given, the posture error scope of the propeller blade has been calculated. The locating error of the propeller blade has been calculated in case that two holes and two pins only contact unilaterally in the actual process and the posture error of the propeller blade calculated can be compensated by the CNC.For the deformation problem of the propeller blade in the machining process, the paper discussed the impact of auxiliary support for the deformation of propeller blade influenced by cutting force. A auxiliary support layout topology optimization model was established to optimize the number and layout of auxiliary support where to maximize the stiffness of the propeller blade was The objective function, and auxiliary support material volume percentage in the design space was the constraint condition. the deformation of the propeller blade under different support conditions was analyzed Trough the finite element method, and the results showed that the optimized layout auxiliary support could significantly decrease the deformation in the propeller blade machining process and the deformation distribution is more uniform.Finally, the propeller blade machining deformation measurement experiments were conducted. A propeller blade machining deformation measuring devices were designed based on FBG sensing technology. The deformation influenced by cutting force in the process of machining under the different layouts of auxiliary support was measured to verify the validity of the layout topology optimization model. Meanwhile,the influence of the change of spindle speed and feed rate on machining deformation were analyzed, which has provided a reference for the parameter selection in the actual processing. |
