Study On Machining Distortion And Error Compensation In Machining Titanium Alloy Hollow Fan Blade

As one of key components of aircraft turbofan engine, the machining accuracy of titanium alloy hollow fan blade has a great effect on its thrust-weight ratio, fuel consumption rate and service life. Hollow fan blade is formed by superplastic forming and diffusion bonding(SPF/DB) method. Actually the SPF/DB process cannot meet the final accuracy of the hollow fan blade, which should be machined by CNC method afterwards. In SPF/DB process, blade internal residual stress is produced with a variety of thermal cycle, which would be released and redistributed during the material removal process. Meanwhile, hollow truss and entity structure in the blade results in the alternating distribution of stiffness. In the process of CNC machining blade, the above two factors would lead the machining deformation, which makes it difficult to meet the machining accuracy.The assessment of residual stress state, the clamping deformation, the processing deformation and error compensation were studied in this paper. The main works accomplished in this paper are listed as follow:(1) In the measurement of residual stress, the strain release factors of blind-hole method under the specific measuring conditions were calculated by using the finite element method. Residual stress of blade specimen were measured by the blind hole method and X-ray diffraction(XRD) method, respectively. According to the geometric shape of the blade plate test piece, the residual stress of blade tip and root were measured by the blind hole method, while the body of the blade were measured by through-hole method. The size and distribution of residual stress in each position of the blade plate test piece was researched.(2) In clamping strategy research of titanium alloy wide-chord hollow fan blade, the effects of the different clamping sequence and the clamping force on clamping deformation were analyzed. The simulation results shows that the clamping deformation was reduced by optimizing the clamping sequence and the size of the clamping force.(3) In the study of the blade plate test piece machining deformation, both the finite element simulation method and experimental method were used to analyze the effect of the residual stress release and re distribution, hollow truss weak rigid structure on the machining deformation. In the finite element simulation analysis, based on the script structure of Abaqus software, the elements follow tool path is automatically removed by using the Python scripting language program. In milling experiment, the methods of the three-coordinate measuring machine and in-machine measurement were used to measure machining deformation respectively. The simulation and experimental result shows that the alternating distribution of stiffness of the plate test piece is the main cause of machining deformation.(4) In the study of the model for forecasting the plate test piece deformation, the results of finite element simulation are used to be the training sample and testing sample. Back propagation neural network algorithm was studied to obtain the nonlinear relationship between the milling parameters and machining deformation, and processing forecast model of the blade plate test piece was set up.(5) Based on the off-line error compensation principle, according to result of the finite element simulation and output of the neural network algorithm, the offline compensation program by C++ language was compiled to compensate the tool path. The test results show that processing deformation of the blade plate test piece has been effectively controlled after off-line compensating for tool path.