Dynamic Characteristic Analysis And Weak Link Identification Of Two Axis Rotary Table Five-Axis Machine Tool

Five-axis CNC machine tools have the characteristics of high precision and high efficiency machining,and are widely used in aerospace,vehicles and ships and other fields of complex surface manufacturing.The dynamic characteristics of the machine tool is an important factor affecting the machining quality and efficiency of the machine tool.In this paper,the dynamic characteristics and weak link identification of the two axis rotary table five-axis machine tool are studied.Firstly,the stiffness of the kinematic joint of the two axis rotary table fiveaxis machine tool is analyzed based on Hertz contact theory,and the stiffness models of the ball screw joint,the linear rolling guide rail joint and the turntable bearing joint are established.Then,the influence of clearance and external load on bearing stiffness of turntable is analyzed.Secondly,the finite element model of the rotary system and the whole machine is established to analyze the dynamic characteristics of the rotary system and its changes under different swing angles and bearing stiffness of the rotary table.Then,based on the 3D Kriging prediction model,the modal fields of the machine tool in different processing spaces are established to complete the directional sensitivity analysis of the changes of the dynamic characteristic parameters of the machine tool.It is found that the natural frequency of the rotary system is greatly affected by the swing angle of the rotary table and the radial stiffness of the rotary table bearing.The first order natural frequency of the two axis rotary table five-axis machine tool is most sensitive to the change in the Z direction of the machining space.Thirdly,based on a weak link identification method of machine tool which combines mode shape method and modal mass distribution matrix method,the weak link of machine tool is identified by analyzing the mode shape and modal mass distribution curve of machine tool modal simulation.Then,the simulation analysis results are used to guide the machine tool to carry out modal experiments.According to the experimental test results,the experimental modal mass distribution curve of the machine tool is obtained to verify and further identify the weak link of the machine tool.It is found that the weak link of the first and third order modes is the main shaft and its joint,and the weak link of the second mode is the main shaft and headstock and its joint.Finally,the experimental test system of the modal experiment of the two axis rotary table five-axis machine tool is built.According to the simulation analysis of the machine tool and the actual experimental conditions,the signal excitation and acquisition scheme of the modal experiment test is determined,and the low-order natural frequency and corresponding mode shape of the machine tool are obtained by the method of the modal experiment test.It is found that the errors of the first three orders of integrated natural frequencies and the simulation values are all within 15%,and the main modes are basically the same,which verifies the accuracy of the finite element model and simulation analysis of the whole machine.