Research On Vibration Analysis Method Of Machine Tool In The Workspace Under Cutting

The vibration in machining process which includes self-excited vibration and forced vibration is a key point to improve the machining accuary and quality.Self-excited vibration can be avoided by selecting cutting parameters according to the stability lobes.However,it is not enough to ensure good machining quality and efficiency by only avoiding self-excited vibration.Therefore,the analysis and characterization of forced vibration in the machining process has become a key link to improve the machining performance of high-grade CNC equipment.The vibration characteristics of forced vibration in machining process are affected by both the dynamics of machine tool structure and excitation force.However,due to the influence of spindle speed and feed speed,the frequency response function of the structure in the operational state is different from that in the static state.Therefore,the research on the identification method of frequency response function under the operational state is important to achieve accurate vibration analysis.In addition,for large machine tools,the structural dynamics in different regions of the workspace are different,which leads to the change of vibration characteristics.Last but not least,the change of cutting excitation frequency band and direction affect the vibration characteristics.Therefore,aiming at the above problems,this paper focuses on the analysis method of vibration characteristics under the comprehensive influence of speed and position related dynamics and cutting parameters.Firstly,a method to obtain the in-process frequency response function of machine tool based on the active excitation modal analysis and experiment modal analysis is proposed.The verifications of this method through simulation and experiment are conducted.This method overcomes the shortage that the existing mass change method which cannot calibrate the mode shape coefficient of the movable parts of the machine tool structure.The proposed method for the in-process frequency response function can be effectively applied in the identification of worktable and tool point speed-dependent frequency response function.Secondly,a method to partition the workspace based on modal mass distribution and clustering algorithm is proposed.A sensitivity analysis method of natural frequency variation in different directions based on the modal shape of the whole machine structure is proposed.The workspace zoning criterion characterized by the change of position related structural weak components is constructed,and the mass modal quality in the workspace is established.The cluster method is used to realize the dimensionality reduction of the whole structure modal parameters of the workspace.Finally,the proposed workspace partition method is verified in the gantry machining center.Thirdly,an on-line identification method of the principal mode based on modal state space model and Kalman filter is proposed.The vibration signal is transformed from physical space to modal space by modal transformation,and the state space model of vibration signal in modal coordinates is established.The expression of the contribution of each order mode to vibration is derived.In order to estimate the modal contribution,the Kalman filter algorithm is adopted to obtain the corresponding vibration components to each mode.This method can avoid the shortcomings of the method based on the operational deformation shape which needs the whole machine measuring points.Finally,the correlation between the mode order,cutting parameters and the high and low frequency response characteristics of the vibration is analyzed by using this method.Finally,the vibration under the interaction of cutting excitation and position dependent dynamics in studied.The change of principal mode in different subareas under different cutting excitation is analyzed.Based on these results,the principal modes and the corresponding frequency response function are adopted to characterize the position and cutting exciation dependent dynamics of machine tool.The experiment results show that the characterization method can realize the optimal selection of machining position and parameters to reduce the cutting vibration.