| In the study of machine tool cutting,the study of flutter has been a hot issue and has a crucial impact on the quality of workpiece machining.At present,most of the research on turning flutter is to treat the workpiece as a rigid body,and the tool system is regarded as a flexible body for stability analysis.However,in actual machining,the situation is exactly the opposite.Therefore,this paper takes flexible workpieces as the object of research modeling analysis,and regards other components as rigid bodies to study the turning vibration of flexible workpieces.The main research contents of the thesis include:(1)Based on the finite element method,a time-varying multi-degree-of-freedom vibration dynamic model of a flexible workpiece is established.The tool system in the turning process is regarded as a rigid body.Several units are divided into flexible workpieces,and the kinetic energy and potential energy of each micro-element are calculated.The Lagrange equation can be used to find the time-varying equation of motion of the flexible workpiece,and the quality of the workpiece during the turning process is reduced.The effect of this factor on the mass matrix,stiffness matrix,and gyration matrix.Then the critical speed change of the workpiece system under the radius change and the variation of the turning time domain simulation are analyzed,and the influence of different simulation parameters is studied.Finally,the stiffness of the workpiece is compared with the theoretical model calculation to verify the correctness of the model.(2)According to the regenerative turning vibration mechanism,the dynamic cutting force with time delay T is introduced to derive the multi-degree-of-freedom workpiece flutter stability model.Using Laplace changes,the mathematical model with dynamic cutting force is transformed from time domain to frequency domain,and the characteristic equations of the system are derived.After layer simplification,the Nyquist criterion of control engineering theory is used as the stability criterion.The relationship between the limit cut width and the spindle speed is drawn,and the stable blade diagram is drawn.Finally,the influence of different machining parameters on the turning stability area is considered.(3)The turning vibration test was designed,and the turning vibration of the workpiece was observed from the actual test point and compared with the theoretical model.Firstly,the combined fixture combined with the sensor is designed to make it easier to observe the turning force in three directions during turning.Then,several stepped shaft workpieces are designed.By changing the different speed,feed and cutting depth,the test method is used to find out.The cutting stiffness coefficient and direction coefficient under the experimental conditions are verified,and the correctness of the obtained cutting stiffness coefficient is verified.Finally,the correctness of the theoretical modeling is verified by comparing the force signal with the vibration displacement signal.In this paper,the vibration dynamics model of multi-degree-of-freedom flexible workpieces is established,and the quality variation factors are introduced to analyze the influence of different parameters on the time-domain simulation of workpiece turning.Establish a mathematical model of turning flutter stability,and derive the relationship between the limit cut width and the spindle speed and perform stability analysis.The turning vibration test is designed.After the test,the cutting stiffness coefficient and the direction coefficient are obtained and compared with the established theoretical model.In this paper,the stability analysis and experimental analysis of the flutter condition of flexible workpiece during turning machining provide a theoretical reference for understanding the mechanism,prediction and suppression of flutter. |
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