School of Mechanical and Electrical Engineering Guilin University of Electrical Engineering, Guilin, , China

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1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Thermal Characteristics Analysis of Mill Head of Five-Axis CNC Mill Machine Based on Finite Element Method Yonghou Sun a, Wei Xiao b, Rukai Hu c and Meifa Huang d School of Mechanical and Electrical Engineering Guilin University of Electrical Engineering, Guilin, , China a syh@guet.edu.cn, b xww0.1@163.com, c hrk1128@163.com, d hmhmf@guet.edu.cn Key words: Five-Axis CNC Machine, Bi-Rotary Mill HEAD, Finite-Element Analysis Method, Thermal Deformation. Abstract. Machine tool is the foundation of manufacture,then, five-axis CNC machine is the sophisticated equipment of CNC machine. During the practical work,there is an thermal deformation in a CNC machine because of many kinds of heat sources. This deformation affects the relative displacement between the work piece and the cutter, caused the manufacturing errors, and influences the machining accuracy of the part. So is of great importance to research the thermal characteristics. In this paper, thermal characteristics of CNC milling machine are simulated by analyzing the thermal boundary condition and using the finite element software-anasys Workbench. Get the temperature field cloud picture of A/C axes bi-rotary mill head of five-axis CNC machine. Weakness of Thermal Characteristics will be found out. This research provides the theoretical fundamentals for improving the accuracy of the mill head. Introduction There will be an uneven temperature field caused by inside and outside heat source when the mill head is working, and bring heat deformation. Then reduce the machining accuracy of the five-axis CNC machine. After a survey and research to a domestic machine tool, we found that the heat deformation has a great influence to the machining accuracy of the part. In order to solve this problem, model and analyze the bi-rotary mill head in ANASYS Workbench software. Simulate the actual working conditions of the mill head. Find out the sensitive area that affect thermal error according to the analysis result, provide some theoretical guidance for this company. The Deformation Mechanism and Heat Source Analysis of the Mill Head Because the material, shape and structure of every part of the mill head is different. The thermal resistance and coefficient of heat transfer between every two joint surface is different. So there will be a complex and versatile heat field result by inside and outside heat source when the mill head is working. And then every parts of the mill head engender heat stress and heat deformation. In the actual machining process, the heat source is divided into inside and outside, as show in figure 1.mechanism as show in fig. 2 [1]. The major heat source that caused the heat deformation of the mill head are bearing friction heat and gear mesh heat [2].There is a complex friction phenomenon when the bear is running up, which make the heat deformation of the mill head is more serious. Meanwhile, parts of the gear mesh heat transmit to the bearing, and then speed up the accuracy failure of the bearing. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,19:52:46)

2 510 Advanced Research in Material Science and Mechanical Engineering Fig. 1 Main Heat Sources of Milling Head Fig.2 Milling Head Deformation Caused by Heat Generation It is most important to deal with the boundary conditions when we analyze the heat deformation of the mill head by finite element method. We just consider heat source and heat convection for the mill head of a CNC mill machine. The major heat sources are bearing friction heat and gear mesh heat. Natural convection and forced convection are the major form of the convection. Boundary Conditions of the Thermal Analysis of the Mill Head Heat Source. (1) For a gear pair, the major way of power loss including the slipping and rolling of the tooth surface. Power loss will lead to thermal expansion, then the clearance of the gear will be eliminated, the carrying capacity will drop. Even the gear will stop work sometimes, and lead to temperature increment of the system. The formula to estimate the heat of gear mesh is showed in Eq.1 [3]: = 1.25π / (1) Where the input power of the gear (W); f coefficient of friction of tooth surface; number of teeth. (2) Theoretically, the friction heat of roll bearing is caused by the friction between rolling element and ferrule and the friction brought by lubricant. The calculation formula of it is [4, 5] presented in Eq.2. = 2π/60. (2) Where M is friction torque, is the rotate speed of bearing. In this paper, we calculate the friction torque by using Eq.3. =. (3)

3 Applied Mechanics and Materials Vols Where µis the coefficient of friction. d is diameter of bearing inner race, F is the load of bearing. Superficial Heat Transfer. Because the external surface of CNC milling machine contacted fluid, heat exchange occurs and this is the major way to release heat. According to Nusselt rule, the calculation formula of heat exchange coefficient α is given in Eq. 4 [6]: =!/". (4) Where Nu is Nusselt coefficient, λis the heat conduction coefficient of the fluid. L is Feature Size. It is easy to get heat exchange coefficient if we knownu, for natural convection and forced convection, there are different calculation formula. The Analysis of Mill Head of Five-Axis Mill Machine The Finite Element Model of the Mill Head. Because the structure of the mill head is very complex, in order to analysis it effectively and correctly, we should simpliy the structure, wipe out some minor feature. The finite element model fo the mill head is show in fig. 3. Fig. 3 Finite element model fo the mill head Results of the Analysis. As show in figure 4,it is the temperature field cloud picture,the rotation speed of electric spindle is 12000r/min, swing speed is 5r/min. From this picture, the temperature of box changed little. Spindle rotation heat is the main heat source of the rise of temperature, the temperature gap between the maximum temperature and the minimum temperature is 103. The heat caused by the rotation of bearing has a big influence to the mill head. So, if we need to keep the same rotation speed,we should increase the cooling conditions. For example, in order to avoid too high temperature,we could use lubricating oil replace lubricating grease. Fig. 4 Temperature field cloud picture

4 512 Advanced Research in Material Science and Mechanical Engineering Conclusion It is very effective to use ANASYS Workbench to analysis the thermal property of mill head. From the analysis result, the heat source mainly focus on electric spindle, so we need to increse the cooling conditions of the electric spindle. Acknowledge The authors would like to acknowledge the funding support by: Director Project of Guangxi key laboratory of Manufacturing System and Advanced Manufacturing Technology (GuiKeNeng _004), Guilin University of Electronics Technolog, China. Reference [1] Z.N. Chen, Z.C. Chen, The basic of the thermal property of machine, [M]. Beijing: Machinery Industry Press, [2] W. Cheng, The structure thermal property analysis of high-power and high-torque mill head, [D]. Beijing: Beijing University of Technology. [3] C.J. Hooke, K. Mao, Measurement and prediction the surface temperature in gears and its relationship to gear Wear, Transactions of the ASME Journal of Teratology, vol. l5, pp , [4] C.S. Wan, Analysis method of roll gearing, [M]. Beijing: Machinery Industry Press, pp , [5] J.M. Wang, D.H. Li, and Q.X. Huang, Analysis of heat equilibriums in bearing system of hot strip mill, [J].Journal of Taiyuan Heavy Machinery Institute, vol. 22(3), pp , [6] S.M. Yang, Heat Transfer Theory(The 4 th Edition), Beijing: Higher Education Press, 2006

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