Vibration Analysis Of A Rotating Long Slender Workpiece In Machining Processes Based On The Theory Of Three-Dimensional Moving Load

A long slender workpiece is one of the most difficult-to-cut parts in machining process, in which workpiece vibration, machining stability and machining quality are the key issues to be solved. Especially, the effect of moving load acting on surface of the workpiece and interaction between workpiece vibration and cutting force exacerbate the vibration and then chatter in machining process. These reasons limit promotion of machining quality and production rate and affect the machining process also. Thus, research on vibration of a long and slender workpiece in machining process has become bottlenecks of implement and solution of machining technology for the workpiece and it is an urgent and key technology to be resolved.From the point of view of theory on vibration analysis of shaft subjected to moving loads, this paper analyzes vibration of a long and slender workpiece subjected to three dimensions moving cutting forces in machining process. Moreover, it is studied that vibration analysis of rotation workpiece is subjected to three dimensions cutting force machining process such as turning operation and external grinding process with the method of combination of theoretical model establishment and experiment.Rayleigh continuous beam vibration theory is used to establish motion equation of vibration of dynamic model for a rotation workpiece subjected to three-dimension moving cutting force. The model is used to study the workpiece vibration in turning process and external grinding. The effect of moving load and variable mass and diameter of the workpiece are considered in establishment of two-order time-varying differential equations of the workpiece for dynamic vibration analysis in turning and external grinding process. So the motion equations of the model are derived, from which numerical solutions of the equation are computed. On the basis of the model, with consideration of regenerative effect, two-order differential delay equations of model for vibration analysis of rotation workpiece are derived in machining process. The motion equations of two models are solved and used to study vibration and chatter analysis of rotation slender workpiece in turning and external grinding process.Based on vibration theory of rotor dynamics, rotor dynamics model of rotating workpiece subjected to the three-dimensions cutting force is built in machining process, in which the workpiece is simplified as a concentrated mass system consisted of three rotors, i.e., the machined, the machining, the unmachined part of shaft, respectively. The model is used to study vibration of workpiece in turning and external grinding operation. Moreover variable mass and diameter of workpiece is considered in machining process. So the equations of motion of rotation shaft are derived.In order to research machining stability, stability of turning process is discussed, in which combination of the motion equations of workpiece and one degree of freedom motion equation of tool is used and interactive influence of cutter post and workpiece. And a predictive stability model of choosing critical values of machining parameters is established for prediction of chatter in turning process.According to different clamped conditions for workpiece in machine tools, vibration equation of rotation shaft is numerically solved in corresponding boundary conditions and initial values, in which the effect of cutting parameters such as depth of cut, rotation speed, diameter of workpiece, etc. on dynamic response of vibration and stability of cutting are discussed in turning process and external grinding operations.Modal test of workpiece are made in boundary conditions of machine tool for the turning and external grinding operation. Identification of modal parameters for workpiece is conducted. Moreover, fundamental Frequency and modal parameters is tested in different cutting condition. Stiffness of chucked end as elastic support end in turning process is computed.According to requirement of vibration test for grinding process, three-dimension dynamometer of piezoelectric on external grinding is designed and installed. Static calibration of the dynamometer is conducted and then the dynamometer is used to test cutting force in grinding process. Meanwhile, vibration and machined surface roughness of workpiece is tested in machining process such as turning and external grinding. Numerical analysis and experimental verification of dynamic response of vibration, stability model, surface roughness model of turning and external grinding for workpiece is conducted in turning and grinding process.The research on a long and slender workpiece vibration shows the variable mass and diameter of the workpiece has an obvious effect on the vibration of workpiece and the model is exactly able to describe vibration of the workpiece subjected to the moving load in machining process. The results lay a good foundation for the further research on the rotation workpiece vibration with different cross-sections subjected to the moving load in machining process.