Method Of Controlling Anti-fatigue Surface Metamorphic Layer During Integration Manufacturing Processes

Surface integrity plays an important role in service life and reliability of aero-engine key components.At present,our country has broken through the precision control technology of aero-engine key components during multi-axis cutting.However,the related fundamental research on controlling surface integrity is still weak.The deficiency in study on controlling surface integrity,especially on the anti-fatigue surface metamorphic layer,has seriously restricted the improvement of manufacturing level of the key rotating components of aeroengine.Thus,it is extremely urgent and necessary to carry out the fundamental research of controlling anti-fatigue surface metamorphic layer.Based on the typical manufacturing process,such as precision milling,shot peening,laser laser shock processing,and ultrasonic surface rolling processing,this thesis focuses on systemic deep research of formation mechanism,influence law,reconstruction law,prediction model,and processes controlling method of surface integrity.And taking the blade sample as the object,the anti-fatigue property of surface metamorphic layer which constructed by integration manufacturing processes have been validated through vibration fatigue experiment.Hence,the main research contents and innovative points of this thesis are as follows:(1)The basic theory of controlling anti-fatigue surface metamorphic layer is studied systematically.The concept of anti-fatigue surface metamorphic layer is given,and the testing method of surface topography,residual stress,microhardness,and microstructure are given.The concept of integration manufacturing processes is given.The controlling principle of integration manufacturing processes is given which based on the processes chain decoupling pre polishing-mechanical strengthening–final polishing,and the corresponding process controlling strategy is proposed.Based on the feature classification of manufacturing process,the two-way mapping relationship model between surface state and manufacturing factors.Based on the experimental design,the modeling method of surface state mapping model is proposed.(2)The controlling method of surface integrity during precision milling process is systemically researched.Through theoretically analyzing the formation mechanism of residual stress,microhardness,and microstructure during precision milling process,the prediction model of micromechanical characteristics are proposed using exponential decay function.Under the premise of considering the time-varying of cutting conditions and tool wear,through a large number of milling experiments and test analysis,the statistical law of the effect of cooling and lubrication,tool wear,tool orientation,and milling parameters on surface topography,residual stress,microhardness,and microstructure of TC17 alloy are obtained.And an empirical model between surface roughness Ra and milling parameters is established,based on genetic algorithm,the high efficiency precision milling parameters are obtained:vc=107 m/min,fz=0.06 mm/z,ae=0.257 mm,and the optimum range of milling facters are:emulsion cooling,VB<0.2 mm,cutter inclination angle 15~60°,and cutter rotation angle 0~90°or 270~360°.Based on the response surface method,the exponential decay function model of milling residual stress is developed,and the prediction accuracy is evaluated,results show that a significantly good prediction is achieved(adjusted R~2>0.90).(3)The controlling method of surface metamorphic layer during mechanical strengthening process is systemically researched.Through theoretically analyzing,the formation mechanism of residual stress,microhardness,and microstructure during shot peening,laser shock processing,and ultrasonic surface rolling processing,the prediction model of residual stress and microhardness are proposed using sinusoidal decay function and exponential decay function,respectively.Through these three mechanical strengthening experiments and test analysis,the effect of shot peening intensity and coverage,laser pulse energy and lap jointing type,ultrasonic surface rolling static pressure and feed speed on surface topography,residual stress,microhardness,and microstructure of TC17 alloy are obtained.Meanwhile,these three strengthening effects and residual stress distribution uniformity are compared and analyzed.Aiming at shot peening process which is widely used in engineering,the parameters of residual stress decay sinusoidal model is developed using response surface method,and the prediction accuracy is evaluated,results show that a significantly good prediction is achieved(adjusted R~2>0.97).(4)The reconstruction law and controlling method of surface metamorphic layer during integration manufacturing processes are deeply analyzed.Based on the prediction model of micromechanical characteristics during precision milling and shot peening process,introducing integration manufacturing processes weight coefficients,through the combination of front and follow-up micromechanical characteristics,and their interaction term,a reconfiguration model of micromechanical characteristics during integration manufacturing processes is proposed.Through integration manufacturing processes(firstly milling,then polishing,finally shot peening)experiments and test analysis,the reconstruction law of surface topography,residual stress,microhardness,and microstructure of TC17 alloy are obtained.The parameters of residual stress gradient distribution model are obtained using regression analysis.Based on the prediction model,the points of controlling precision milling and shot peening residual stress gradient distribution are derived.Taking the minimum variance of predicted and designed value as the objective function,the combination of milling and shot peening parameters are solved reversely using genetic algorithm,which meet the designed requirements of residual stress gradient distribution controlling points.The forward and inverse solution method between manufacturing factor and residual stress gradient distribution is established.(5)The controlling method of surface metamorphic layer during integration manufacturing processes are validated,through integration machining blade samples and vibration fatigue test.Blade samples machined by milling-polishing,milling-polishing-shot peening-vibration polishing processes.The reconstruction law of surface topography and residual stress of blade samples are obtained by test analysis.The natural frequencies and vibration stress distribution of first order bending vibration are obtained through finite element modal analysis.Vibration fatigue test of blade samples are carried out to obtain fatigue life and fracture.Results show that milling-polishing-shot peening-vibration polishing provides a better fatigue life than for milling-polishing process.Fatigue crack is located in the middle of blade back,which originates from leading edge,obvious herringbone radiographic characteristics can be observed in fatigue source area,and small secondary crack can be found in fatigue propagation area.