Research On Experimental Method For Evaluating Dynamic Stiffness Of Five-axis Machine Tool In Workspace

Five-axis machine tool is a typical advanced manufacturing equipment and exhibits significant influence in aerospace and precision instruments field.The five-axis machine tool is widely used in the manufacturing of workpieces with enormous removal rate such as propellers and impellers etc.Compared with the traditional three-axis machine tool,the rotating axis of five-axis machine tool weakens the overall structural stiffness and results in significant changes of dynamic stiffness in different positions of machine tool.However,the machining accuracy is closely related to its dynamic characteristics.Therefore,investigating the dynamic stiffness variation in workspace of five-axis machine tool is of great significance for improving machining accuracy and efficiency.Excitation experiment is the most direct method to evaluate the dynamic stiffness of machine tool.However,the traditional methods for universal excitation experiment are inefficient and with poor repeatability,which are unsatisfied for the evaluation of multidirection dynamic stiffness in different position of five-axis machine tool.Therefore,this paper focuses on the investigation of experimental method for evaluating dynamic stiffness for five-axis machine tool in workspace.The main research contents of this paper are as follows:(1)Dynamic stiffness of five-axis machine tool in workspace is analyzed with finite element method(FEM).An actual five-axis machine tool is taken as the research object.Based on an analysis of the dynamic behavior in machine tool's joint surface,the spring and damper are used to simulate the joint surface.A finite element model of five-axis machine tool is built.Mode superposition is carried out to simulate the dynamic stiffness in various positions of translational axis and different angles of rotary axis.The foundation of research on experimental evaluation of dynamic stiffness is shown.(2)Experimental method with piezoelectric actuator for evaluating dynamic stiffness of five-axis machine tool in workspaces is present.The experimental requirements of dynamic stiffness for five-axis machine tool in workspace are analyzed based on the previous simulation.The characteristics of existing excitation method for evaluating dynamic stiffness are summarized.Piezoelectric material is chosen as the core component of excitation.The piezoelectric excitation system for five-axis machine tool is designed based on the principle of piezoelectric excitation and key technical parameters are confirmed.(3)Structure of piezoelectric exciter is designed and mechanical performance of which is analyzed.The integrated structure of piezoelectric exciter is designed.Spherical contact is used to accommodate the multi-directional excitation experiment in various positions of five-axis machine tool.The influence of exciter's structure on the excitation effect is simulated by the finite element analysis.(4)Piezoelectric excitation experiment of five-axis machine tool in workspace is carried out and experimental data is analyzed.The XYZ dynamic stiffness of five-axis machine tool at multiple A-axis angles is tested based on piezoelectric exciter.The curves of dynamic flexibility and coherence function are plot.The surface maps of dynamic compliance of five-axis machine tool in workspace are fitted.The influence of A-axis angle on dynamic compliance is discussed.