Time-variant Reliability Analysis Of Turning Chatter And Reliability Optimization Of Process Parameters

High-speed and high-precision cutting has become the development trend of modern processing,and high-performance cutting are based on the premise of stable cutting.Turning chatter will cause severe vibration,seriously affecting the accuracy,efficiency and service life of the lathe machining.In the turning process,various performance parameters,geometric parameters and process parameters of the CNC machine tools are usually random and uncertainty.Furthermore,it is found that some parameters also have time-variant properties due to the influence of tool wear and uneven texture of the workpiece.Based on the stability analysis of turning system,this paper considers the random uncertainty factor,and analyzes its reliability and sensitivity analysis.In addition,the paper analyzes the time-variant reliability analysis of the turning system chatter stability considering the effect of time-variant cutting force coefficient and time-variant spindle.Considering the stability constraints,the reliability optimization of the turning parameters is proposed to ensure the efficient production of the lathe.The specific contents of the paper are as follows:Firstly,the regenerative chatter mechanism is applied to the turning system,and the system dynamics model is obtained.The minimum limit cutting depth expression of the turning system is deduced.Then,the stability lobe diagram of the turning system is drawn.On the basis of this,the factors that influence the chatter stability of the turning system are deduced and analysed.Secondly,considering the stochastic uncertainty of various parameters of the machine tool,the reliability theory is introduced.The Monte Carlo method and the advanced first order second moment method are used to calculating the reliability of the the turning system chatter stability,obtaining the reliability curve at full speed.The sensitivity analysis of the dynamic parameters on the turning machining system is carried out to investigate the influence degree of the reliability of the system chetter stability and provide reference for the design and analysis of the parameters.Thirdly,the stochastic parameters with time-variant characteristics such as the cutting force coefficient and the spindle speed are obtained.The chatter stability model with the time-variant cutting force coefficient can be obtained by introducing the cutting force coefficient described by the Gamma process into the original limit cutting depth expression.The spindle speed is regarded as a stochastic process to establish the time-variant reliability model for the chatter stability of the turning system.The time-variant reliability curve of chatter is given by Monte Carlo method and classical PHI2 method.Finally,under the premise of turning chatter stability and reliability-based optimization design(RBDO),the maximum value of material removal in unit time is taken as the objective function of optimization problem.And with the actual cutting vibration limit cutting depth,cutting force,surface roughness and so on to meet the reliability requirements as a constraint,reliability-based optimization model of the turning process parameters is established.Based on the method of sequential optimization and reliability assessment mentod(SORA),and using the inverse MPP point search algorithm,the problem of reliability-based optimization design of turning process parameters is investigated by using the single loop method of decoupling optimization and reliability evaluation.