Research On Compensation Technology Of Deformation Error In NC Milling Of Thin-walled Blade

As the core part of aeroengine,the machining quality of blade directly affects the aerodynamic performance of aeroengine.In recent years,in order to improve the thrust-weight ratio of engines,the design of blades has gradually become thinner.In the process of CNC milling,thin-walled blades are prone to bending,torsional deformation and local undercut due to their complex shapes,large changes in curvature,and low stiffness,which makes it difficult to guarantee the quality of processing.Based on the point set from blade measurement,this thesis proposes a compensation method for bending,torsional deformation and undercut error.According to the size and direction of the deformation,the error of each area on the blade can be differentially compensated.The main research work is as follows:(1)Based on the theory of material mechanics,the bending,torsional deformation and undercut phenomenon in the milling of thin-walled blades are analyzed respectively.The force model and deformation formula of blade milling are established,the reason and trend of deformation are obtained.Through the comparison between the online measurement results and the offline measurement results in the machining experiment,the phenomenon and law of secondary deformation after milling are found.(2)The compensation method for suppressing bending and torsional deformation is put forward.Based on the Iterative Closest Point algorithm,the rotation and translation parameters are respectively calculated by the registration process of each measurement point set and the theoretical point set on the blade surface.Using these parameters,the theoretical curves of each blade are respectively compensated in the reverse direction.Then the compensated surface is constructed by fitting these curves in UG software,and the compensated surface is used for CAM programming and machining experiment.The results show that the method introduced here can reduce the bending and torsional deformation in the milling process of the thin-walled blade.(3)Based on the principle of mirror symmetry compensation,a method to suppress the undercut error is proposed.Through two-dimensional plane projection,the formula to calculate coordinate for compensation point is derived.Considering the compensated point set is always with noise error,Gaussian filtering algorithm is introduced to smooth the points.Based on the secondary development of the UG software,the compensated points are fitted to B-spline surface.Then,this B-spline surface is used for CAM programming and machining experiments.The results show that the method introduced here can suppress the undercut error in the milling process of thin-walled blades.(4)Through the machining experiment of the blade studied in this thesis,the mutual independence between the bending,torsional deformation and the undercut error is found.A compensation method considering both the bending,torsional deformation and the undercut error is proposed.Based on the bending,torsional deformation parameters and point error of each section of the blade,the surface model after comprehensive compensation is constructed.Then,this surface model is used for CAM programming and machining experiments.The results show that the method can suppress the bending,torsional deformation and the undercut error in the milling process of the thin-walled blade.