The Thermal Error Analysis On Mill-Turn CNC Double Drive Feeding System

With the progress of the times, CNC machine tool was becoming larger, moreprecise and intelligent. The design of tandem drive was used in high speed machiningcenter. It was used to inhibit the vibration which was caused by high speed feed. Forexample, DCG was the driving method of Mori Seiki. The characteristic of themechanism was that the vibration could be suppressed according to holding the centerof gravity of mobile structure. It could shorten processing time, improve evenness andextend the life of cutter. But the dual drive system had its inevitable shortcomings. Itwas the introduction of synchronous error. The positioning precision of the NCmachine was an important index that could reflect machine performance. And it wasan important factor that could affect machining accuracy. The synchronization of thetwo transmission system was one of the main factors which influenced the positioningaccuracy of CNC machine tools. The ball screw was a key component of CNCmachine tool feed system. And its positioning accuracy was crucial. In the workingprocess of the machine tool, the factors which influent screw accuracy was thedifference of lead error, pre stretching, screw torque and thermal temperature rise.The thermal temperature rise was resulted from thermal deformation of ball screw, nutand bearing. It seriously affected the positioning accuracy.In combination with vertical milling composite processing center which was anational major project shared by Lanzhou University of Technology, Qinghai firstmachine tool plant and HuaZhong University of Science and Technology. And in viewof the above problems, we did some research on temperature field and thermaldeformation mathematical model, boundary condition calculation, thermal analysisand so on. The main contents were as follows:1. Firstly, establish the mathematical model of temperature field via the finiteelement method. Secondly, establish the thermal deformation finite element equationwhich was based on the thermal elastic and finite element principle. Thirdly, establishthe Solid Works model of machine screw feeding system.2. Analyze the heat source of feed system. Calculate the calorific capacity. Makesure heat transfer mode and boundary condition. Calculate the transient temperaturefield and steady temperature field distribution of the screw feed system via ANSYSWorkbench.3. Calculate thermal deformation of the screw feeding system. It was achieved byuploading steady state temperature to finite element model meanwhile combiningscrew feed system restriction.4. Put forward the corresponding error compensation mechanism that caused by dual drive screw thermal deformation.