Vertical Machining Center Twin Z-drive Linear Feed To The System Static And Dynamic Characteristics Analysis And Optimization

The high-grade CNC machine tools are playing an increasingly important role in manufacturing industry, which requires that Z-direction feed system of vertical CNC has a good static and dynamic characteristics. Thus, at the beginning of the design of feed system, the establishment of static and dynamic model of the Z-direction feed system is particularly important, because it can predict the static and dynamic characteristics and optimize its weak links. The paper regarded the Z-direction feed system as research object, and did research in its static and dynamic characteristics and its weak links comprehensively.Based on the Hertz contact theory, this study built the static mathematical model of feed system, and put forward calculation method and procedure which used the bisection method to solve the problems of Hertz contact theory efficiently. After studying the influence of bearing preload forces and ball screw mechanism preload forces on statics characteristic of feed system, the optimum model of ball screw mechanism and bearing preload is built, and is solved by penalty function method in the premise of knowing the design accuracy of feed system.After building finite element model of Z-direction feed system including joint surface characteristics, considering the influence of gravity and the characteristics of Z-direction feed system, the CAD model of feed system was simplified, its natural frequencies and vibration modes were analyzed, and modal test with hammering method is accomplished.According to the test results, the vibration mode of finite element analysis is almost the same with the vibration mode of modal test, and the error of the natural frequencies is within10%.As a result, the correctness and reliability of the finite element model are validated, then the harmonic response analysis was carried out on the feed system.According to solutions of finite element analysis, the weak links of dynamic characteristic of Z-direction feed system are the joint surfaces, and then the parameters of joint surface were optimized by orthogonal method. The optimization results showed that, the natural frequency of the feed system has been increased greatly, the highest rate reached10.57%;the largest amplitude of feed system in three directions has been reduced greatly. Based on the modal analysis results of feed system, the shapes of the slide were optimized, and on the premise of quality unchanged, dynamic strain was reduced by15.0%, dynamic stress was reduced by14.8%.Thus, dynamic characteristic of feed system was improved.