Research On Chatter Mechanism,identification And Suppression In High-speed Grinding Process Of Camshaft

As the key parts of internal combustion engine industry,grinding accuracy and quality of the camshaft affect the dynamic performance and operation characteristics of the engine seriously.High speed grinding is the main way of camshaft NC machining.The grinding force changes frequently because of the lag of servo tracking system and the inertia of grinding wheel frame in the non-circular grinding process of camshaft with the increase of grinding speed.Then the grinding chatter is prone to occur,resulting in grinding wheel wear,machining accuracy and surface quality degradation,and even damage to the machine tool system.To improve the stability of camshaft non-circular high-speed grinding process and further improve the quality and production efficiency of camshaft products,it is necessary to study the chatter stability of the grinding process system of camshaft high-speed grinding process,which provides theoretical support and technical support for efficient,stable and intelligent grinding of camshaft.Based on theoretical analysis and experimental verification,the chatter mechanism,identification and suppression strategy of camshaft non-circular highspeed grinding are studied,which including the following aspects:(1)Dynamic modeling and analysis of high-speed grinding in camshaft considering dynamic grinding depth and contact stiffness were carried out.On the basis of analyzing the geometric and kinematic characteristics of high-speed grinding of camshaft,the material removal mechanism including the perspectives of grinding depth,contact arc length and material removal rate is interpreted in high-speed grinding of camshaft.The grinding force and grinding heat in the process of non-circular grinding of camshaft are analyzed,and the dynamic grinding force calculation model is established considering the elastic concession mechanism.The regeneration delay effect of camshaft grinding process is analyzed in detail,and the corresponding dynamic grinding depth expression is deduced.Finally,the dynamic model of camshaft high speed grinding process system is established,which lays a theoretical foundation for the stability analysis and prediction of camshaft high speed grinding.(2)The stability analysis and prediction of high-speed grinding in camshaft were carried out based on multi-scale method and stability lobe diagram.On the premise of accurately obtaining the dynamic parameters,the bifurcation analysis of the camshaft highspeed grinding process system is carried out based on the multi-scale method,and the approximate nonlinear response of the camshaft high-speed grinding system is obtained.Considering the dynamic grinding depth and contact stiffness,the grinding stability lobe diagram is plotted and verified by experiments.As a supplement to the stability lobe diagram,the Simulink grinding dynamic simulation method is considered to determine the grinding stability,and the stability prediction method for the high-speed grinding of camshaft is further improved.The influence of different modal parameters on the high-speed grinding stability region of camshaft is analyzed,providing a direction for the design and improvement of machine tools.(3)An vibration testing platform for high speed grinding of camshaft was established to verify the correctness of the model and explore the chatter characteristics in high-speed grinding of camshaft.The vibration signal acquisition sensor and its layout scheme are determined,and the experimental scheme and parameters are designed.The validity of the stability lobe diagram is verified by selecting appropriate parameters,and the stability boundary considering contact stiffness has especially higher accuracy.The variation laws of grinding chatter characteristics and surface waviness of camshaft under different grinding process parameters and grinding wheel conditions are analyzed,and the chatter characteristics of different cam contour segments are further extracted.(4)A novel method for extracting and recognizing chatter characteristics of camshaft high speed grinding was proposed based on optimized VMD and BP neural network.Chatter identification method based on VMD parametric optimization and energy entropy is studied.Two key parameters K and α of VMD are adaptively extracted by FLMEMD and comprehensive evaluation method,providing technical support for online identification of camshaft grinding chatter.By comparison with other methods,it is found that the proposed method has obvious advantages in efficiency and accuracy,and the grinding chatter characteristics of different grinding process parameters and different contour segments in the high-speed grinding process of camshaft are further analyzed.With kurtosis,skewness,maximum energy entropy and modal center frequency as input characteristic variables,the online chatter detection model based on BPNN is constructed,and the chatter detection accuracy of camshaft grinding is 96.4 %.(5)A grinding chatter suppression strategy including process intelligent optimization,online chatter detection and process intelligent reasoning is proposed,and the multi-objective decision-making method of grinding process parameters is studied.To realize the intelligent,efficient and high precision grinding of camshaft,the intelligent decision software framework of grinding process is designed.Based on the secondary development platform of Huazhong Ninth CNC system,an intelligent decision-making software for grinding process is developed.Finally,an experimental platform is built to verify the feasibility of the developed process software,and the experimental results show that grinding process software can effectively improve the efficiency and stability of camshaft high speed grinding process.