Fundamental Research On The Closed Loop Design Method Of Cathode Tool In Electrochemical Machining

Electrochemical machining(ECM), a non-traditional machining method, is one of the main technologies for turbine blades with complicated and twisted surfaces and hard-cutting materials. In the ECM process the first problem be resolved is to design the cathode tool. Because it is difficult to grasp the ECM forming rule, designing cathode accurately and efficiently becomes very difficult.At present most researches on cathode design are based on the "open loop" design thougth. After the initial cathode surface calculated, experiments will be done to test and modify the initial shape by professional technical persons. In this thesis it is proposed that a new cathode design method which is based on the closed loop thought. In the closed loop design process, the initial cathode will be used to predict the anode workpiece‘s shape and be modified by the shape errors of anode workpiece. The digital design process will be iterated till the accurate workpiece‘s shape is obtained. It is helpful to reduce cost and improve efficiency of the cathode design.In this thesis, a turbine blade with curved and complicated surface is the research object which is machined with the omnidirectional ECM method. The interelectrode gap model is of ?L‘ shape. According to Fluid Dynamics theories the distributions of electrolytic velocity, pressure, temperature and etc. are calculated and analyzed. The equation of the electric conductivity к influencing the distribution of interelectrode gap is analyzed and the distribution map of the к is obtained by means of the MATLAB software. The ?cosθ‘ method is used to design the initial cathode, in which the к values, varying with spatial position, are substituted in the calculations of the interelectrode gap.To construct the model of the closed loop design, the prediction of anode workpiece‘s shape is mainly studied in the thesis. The BP neural network is adopt to establish between main ECM parameters, initial cathode and anode workpiece‘s shape. Experimental results are used to train and verify the BP model. With the BP model the relative errors of anode workpiece prediction are less than ± 8%.Based on theories of Fourier Transformation and Frequency Domain Transferring Function, the relationship between anode workpiece‘s shape and the initial cathode shape is established. Taking the section lines for studied objects, the initial cathode surface is modified.In the thesis the software of closed loop design for cathode tool is developed on the UG platform. There are the initial design cathode, the anode workpiece prediction and the cathode tool modification functions in the software.The forming rule of ECM is a difficult problem especially for 3D complicated curved surfaces. In the thesis the distribution of the spatial position function к(x,y,z) is obtained. It is helpful to grasp the forming rule in the complicated interelectrode gap region. The study on the closed loop design method of cathode with the modification feedback is good to improve accuracy and efficiency of cathode design in ECM.