Research On Technologies Of Adaptive Drilling Of Turbine Blade Film Cooling Hole

EDM drilling of film cooling holes on turbine blades is one of the key processes in the manufacture of aero engines.Machining accuracy of film cooling holes has a great impact on the service life of turbine blades.Due to the influences of complex inner cavity structures and thermal stresses in casting processes,there are profile errors on turbine blades.If drilled directly with a uniform G-code file,the turbine blades cannot meet the accuracy requirements.It is,therefore,necessary to adjust the positions and orientations of each hole to adapt the contour changes of each turbine blade.Presently the semi-manual manufacturing approach for film cooling holes in China seriously restricts the manufacturing capability of domestic aeroengines.In this thesis,an adaptive EDM drilling method of turbine blade film cooling holes is proposed.The main idea of this approach is to adjust the positions and orientations of film cooling holes by aligning the turbine blade’s actual coordinate system with the design coordinate system.Firstly,an actual point-cloud is measured from an actual turbine blade and a standard point-cloud is extracted from the turbine blade’s 3D model.In order to meet the requirements of measurement accuracy and speed for on-line measurement of turbine blades,a laser measurement program can be automatically generated for measuring the turbine blade contour.The points to be measured are extracted by meshing the surface of the turbine blade.The normal measurement direction is calculated by interpolating a local tangent plane near the point.A trajectory linking a series of measuring points is planned based on an ant colony algorithm.Secondly,the position and orientation deviations can be derived by matching the two point-clouds,resulting in an error matrix.The position and orientation direction of each hole are adjusted according to the error matrix.In order to solve the problem of large surface contour error of a turbine blade,an improved ICP algorithm is proposed to realize a high precision and a robust point cloud registration.The improved ICP algorithm can be implemented by aligning the gravity center with the main direction of the point cloud on datum plane.There are still some point cloud deviations on the surface of the turbine blade after registration.Therefore,to improve the positional accuracy,the coordinates of film cooling holes are mapped onto the actual turbine blade surface.Finally,a kinematic error model is derived according to the structural and geometric deviation of the machine tool.According to the compensated positions and orientations of film cooling holes,an ad hoc drilling program of film cooling holes is generated automatically for a measured blade,.Simulation results show that the positional error of film cooling holes can be reduced from ± 0.1mm to ± 0.03 mm.