Theoretical And Experimental Research Of Time-delay System In The Flexible Part Milling

The chatter phenomenon usually occurs in the cutting process and it deterioratesthe surface quality and raises the cost. The cutting stability and its mechanism areurgent to be investigated to avoid the chatter for high productive quality andefficiency. The multi-mode effect, the mode-coupled effect and the multi-delays effectare the common factors in cutting process which have great influence on the stability.Based on the experimental researches, the relationship between the stability and thesecomplex factors is detailed explored, the modeling methods are presented and thereasonable explanations are given. Around the flexible part stability in milling, wecarried out the works as follows:The great difference between the stability prediction with the classical model andthe experimental results exist in both the low speed milling and the high speed milling.The explanation is given by investigating the milling stability with the structural modecoupling effect and the regenerative effect simultaneously considered. The cuttingexperiments verified the co-existence of the two mechanisms in practical milling andthe usually neglected structural mode coupling effect is discovered to have a greateffect on the stability analysis in many milling cases. Therefore, the structuralcoupling effect needs to be considered in the regenerative milling stability analysisand such prediction agrees well with the actual milling experimental results.The stability of milling with variable pitch cutter and tool runout casescharacterized by multiple delays is analyzed. The improved full-discretization methodand the variable-step numerical integration method are proposed for efficient andaccurate stability prediction. The variable-step numerical integration method hasmuch flexibility in discretization step control and the calculation accuracy can beguaranteed by the local error limit. The simulation and analysis show that the matrixdimension in dynamic discrete map governed by the dividing number can be reducedfor calculation efficiency improvement, especially in the low radial immersion.A measurement of radial cutter runout in revolving milling tool is proposed byusing the laser sensor. The laser beam is projected onto the milling tool edge andsubsequently reflected. The diffuse reflection is captured by the sensor and thedisplacement between the cutter and the laser sensor is obtained. Based on thedynamic displacement, the cutter runout is calculated by the linear searchoptimization method. The influence of the tool runout on the milling stability isverified by the experimental results, which also show that the radial cutter runout is dynamically varying in the constant rotation speed and the runout fluctuation largenswith the increasing speed.A new end milling dynamic model with multiple modes of the flexible structureat the compliant direction is developed, with multiple modes coupled caused by thecutting force. An analytic method is presented to reveal the link between the millingaxial depth and modal shapes of the thin-walled part. The dynamical behaviorvariation of the workpiece with respect to the tool position and the low radial millingimmersion are also considered. The full-discretization method is employed tocalculate the stability boundary; the prediction has a well agreement with the resultscalculated by the frequency method and the semi-discretization method. Thepresented method is verified by the experiment.A flexible platform is designed to simplify the dynamical equation and theexperiment is conducted to verify the incompetence of the classical local stabilityprediction. Therefore, the global stability analysis method is presented for the flexiblepart milling. The dynamical model is proposed with the regenerative excitation andthe periodical excitation simultaneously considered for the calculation of the stabilitylobes. The numerical method in time domain is used for vibration simulation andstability calculation, with the cutter tooth jump out and boundary variation considered.The prediction based on the global stability has a well agreement with theexperimental results, which verified the validity of the presented method.