Study On Grinding Dynamics Uncertainty Modeling And Chatter Reliability

Grinding chatter is a violent vibration phenomenon in the grinding process,it will seriously affect the processing accuracy and surface quality,but also accelerate the tool wear,shorten the life of the machine tool,reduce the efficiency of grinding processing.At present,the studies of grinding chatter are mostly based on deterministic parameter dynamic models,but there are many uncertain factors in the grinding system,which will lead to the uncertainty of mass,stiffness and damping parameters in the dynamic model and have an impact on the prediction results of grinding chatter.Taking the high-speed external grinding as the research object,the dynamics uncertainty modeling and the chatter reliability are studied.The main contents are as follows:(1)Based on the regenerative chatter mechanism,the dynamic model of the external grinding machining system is established.The formula of critical grinding depth and spindle speed of grinding system are derived.Based on the solution of the modal parameters,the stability lobe diagram of the grinding system is obtained,and the influence of mass,stiffness and damping of the external grinding system on the critical grinding depth is studied.(2)The time domain simulation model of high-speed external grinding chatter is established to obtain the time domain diagram of vibration displacement of grinding process under different process parameters,and it is compared with the results of stability lobe diagram.Introduce the uncertainty parameters such as mass,stiffness,and damping coefficient into the dynamic model,obtain the stability lobe diagram considering the uncertainty parameters,and analyze the influence of the dynamic uncertainty on the critical grinding depth.(3)The reliability model of grinding machining system is established.The Monte Carlo method,the advanced first order second moment method and the second-order second-moment method are used to solve the system reliability.The chatter reliability curve is used to predict the reliability of the grinding system.The accuracy of the reliability of the three methods is analyzedand it shows that the moment method is better.(4)The influence of stochastic parameters on the reliability of the grinding system is analyzed.The results show that the fluctuation of the modal mass affects the reliability of the system most,therefore,the fluctuation range of the modal mass should be emphasized when designing the grinding system.(5)Using the high-speed external grinder CNC8325 as the research object,multiple impact tests are conducted to obtain the mean and standard deviation of dynamic parameters of grinding processing system.Furthermore,the high-speed external grinding experiments are conducted.By selecting the typical grinding experiments and checking the workpiece surface,the accuracy of grinding reliability prediction results are verified.