Dynamic characteristics optimization for a whole vertical machining center based on the configuration of joint stiffness

Abstract

Joint stiffness often has a significant effect on the dynamic characteristics of the whole machine tool. In this paper, a joint stiffness configuration method is developed to optimize the dynamic characteristics of a whole vertical machining center, in which the premise is considering the joint characteristics to create the accurate finite element model (FEM) of the whole machine tool. Identifying the joints parameters including the contact stiffness and damping of the linear guides, bolts, ball screws, and bearings is conducted. Vibration test and finite element simulation are implemented to verify the accuracy of the FEM which is created based on the identified joints parameters by comparing the tested and simulated frequency-response functions (FRFs). With these tested and simulated results, taking the dynamic flexibility at the spindle nose to measure the dynamic characteristics of the whole machine tool, vibration modes, and joints related to a higher modal flexibility and elastic energy distribution ratio can be determined to be the weak modes and joints respectively. Optimization aiming to decrease the modal flexibility is conducted by adopting the orthogonal experiment method to instruct the simulations to predict how stiffness of the weak joints affected the dynamic characteristics of the whole vertical machining center. Thus, an optimal joint stiffness configuration can be obtained by using the range analysis and fuzzy similar preference ratio method to analyze the simulated results. Redoing the simulation with the optimal configuration, results indicate that modal flexibility of each weak mode is decreased obviously. The decreased modal flexibilities and dynamic responses verify that the optimal configuration method is feasible to provide a way for improving the dynamic characteristics of the whole machine tool.