Processing Model Construction Of Adaptive Machining For Precision Forged Blades Of Aero-engines

With the continuous improvements of manufacturing concept and level,a large number of new blades produced by multi-manufacturing technologies have been applied to in-service or researching aero-engine's fans and compressors.The pressure and suction surfaces of a precision forged blade are directly formed with no allowance,while the leading edge,trailing edge,and blade tenon are the only parts need to be further machined.In such cases,the precision forged blade has the advantages of high strength,high production efficiency,and saving raw materials.However,form and position accuracies of the leading edge,trailing edge,and blade tenon are difficult to guarantee when the pressure and suction surfaces with variant shapes are used as the positioning reference,which leads to poor consistency,low pass rate,and easy out-of-tolerance of the final productions.By using adaptive machining technology,actual shapes of the blades are first accurately obtained by digital measurement,and then suitable processing models are constructed for each blade to fit their different geometric shapes and spatial positions.By this means,the precision forged blade can be machined with high efficiency and accuracy.The presented work focuses on key technologies in adaptive machining of precision forged blades of an aero-engine,which covers digital measurement,matching and positioning,and processing model construction.A special software system is also developed for adaptive machining of precision forged blades.The main contents and innovative achievements are as follows:(1)A whole solution for adaptive machining of precision forged blade is proposed.The geometric structure and machining difficulties are first analyzed,and then an integrated fixture is designed for on-machine measurement and numerical control machining.Based on these,an adaptive machining solution is then proposed by combining digital measurement into the machining.The corresponding solutions are finally planned for the key technologies,which include accurate and efficient measurement of the parts with inaccurate positioning reference,matching and positioning under multi-tolerance constraints,and constructions of processing models for inaccurately formed areas.(2)An efficient and accurate method is proposed for measuring blades with inaccurate positioning reference.The measuring and machining reference for such a blade is first determined by the established reference-transforming model with the help of an introduced intermediate reference.Measuring point distribution is planned based on the error compensation according to curvature change of blade's section curves,and then the optimal model of trajectory sequence of measurement points is established.A processing method is proposed to eliminate abnormal data points and smooth random disturbed ones.After that,a data correcting method is proposed based on geometric similarity.Finally,the curve part without measured points is modified based on the established prediction model according to curve similarity with the objectives of same convexity and similar strain energy of the curves.(3)An evaluation model of global and local matching based on multi-tolerance constraints is established.The influence of matching degree on matching result is analyzed,and the mathematical models of global and local optimal matching degree are then established respectively.Considering coupling constraint relationship between design tolerances,the influence of tolerance constraints on matching degree is determined.After that,a global matching evaluation model based on profile tolerance constraint and a local one based on position and torsion tolerances constraint are established.For the coupling constraint of global and local matching,a matching method based on the feedback of matching degree is proposed,in which local matching results are used to modify the global matching process.By this means,the measured data and nominal model of precision forged blade is accurately matched.(4)An adaptive method to construct processing model in machining precision forged blade is proposed.For the pressure and suction surfaces that are forged accurately,geometric models of their actual shapes are constructed by modifying nominal surface to fit their measured data according to the calculated moving directions and distances of surface's control points.Meanwhile,for the leading and trailing edges that are forged inaccurately,processing models of their expected shapes are predicted to comply with the forming trend of pressure and suction surfaces according to the established distribution models of forming error and thickness of characteristic curve.Then,the constructed models of leading and trialing edges are further modified to be similar to their nominal ones based on the similarity processing of curve's strain energy and curvature change.An example shows that the proposed method can effectively construct the processing models of the leading and trailing edges of a precision forged blade for adaptive machining.(5)A specific software system is developed for adaptive machining of precision forged blades.This software system is designed for adaptive machining precision forged blades with high efficiency and accuracy,which includes functional modules such as digital measurement,matching and positioning,and processing model construction.Finally,the proposed methods in this work are verified by applying in adaptive machining of an aero-engine's precision forged blades and rolling blades.The experimental results show that the blades are positioned accurately in machining,and the areas between leading/trailing edge and pressure/suction surface meet the design requirements of blade's tolerances and bridge smoothly,which are also the connecting areas between areas that need to be machined and needn't.