Evaluation of and Compensation for Thermal Deformation in a Compact CNC Lathe
Hiroshi Tachiya*1, Hiroki Hirata*2, Takayuki Ueno*3,
Yoshiyuki Kaneko*4, Katsuhiro Nakagaki*4,
and Yoshiaki Ishino*4
*1Faculty of Mechanical Engineering, Institute of Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa-shi, Ishikawa 920-1192, Japan
*2Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa-shi, Ishikawa 920-1192, Japan
*3Aisin Seiki Corp., 726 IzumiAI 1-1 Izumi-cho shozisaku, Anjo, Aichi, Japan
*4Takamatsu Machinery, 1-8 Asahigaoka, Hakusan-City, Ishikawa 924-8558, Japan
Because heat sources for compact Computer Numerically Controlled (CNC) lathes are likely to be closely arranged, they may cause large and complicated thermal deformation. Previously, we developed a CNC lathe with its heat sources arranged so as to reduce thermal deformation. This lathe achieved highprecision work under stable temperatures in continuous operation. However, in some cases, it could cause rapid thermal deformation. Previously, we proposed a simple method to compensate for the thermal deformation in CNC lathes by measuring temperatures at only a few points. By developing amodified compensation method capable of estimating minute and complicated thermal deformation and applying this method to the current lathe, processing accuracy will become more precise. Thus, we evaluated the thermal deformation of a compact CNC lathe. As a result, we found that the thermal deformation of the lathe was caused not only by movable parts, such as the spindle motor, but also by non-movable parts, such as the hydraulic unit. We therefore approximated the thermal deformation caused by the non-movable parts and estimated the change in the deformation caused only by the movable parts. This enabled us to express the thermal deformation by a simple linear equation, the form of which was same as that used for previous lathes. From these results, we were able to compensate for the thermal deformation using approximate equations for both movable and non-movable parts and we applied this method to the current lathe. We confirmed that the work error can be reduced under stable conditions using this method.
-  T. Moriwaki, E. Shamotro and M. Kawano, “Estimation of Thermal Deformation of Machine Tool by Applying Neural Network ( Improvement of Estimation Accuracy by Utilizing Time-Series Data of Temperature on Machine Surfaces ),” Trans. of the Japan Society of Mechanical Engineers, Series C, Vol.61, No.584, pp. 1691-1696, 1995. (in Japanese)
-  I. Tanabe, Y, Kaneko, Y. Saitoh, H. Mori, and K. Urano, “Simple and Intelligent Control Using Neural Network About Thermal Deformation of a Machine tool,” Trans. of the Japan Society of Mechanical Engineers, Series C, Vol.70, No.698, pp. 2954-2960, 2004. (in Japanese)
-  Y. Kakino and K. Okushima, “Study on thermal deformations of machine tools (4th Report: Thermal deformations due to external heat sources),” The Japan Society for Precision Engineering, Vol.70, No.698, pp. 2954-2960, 2004. (in Japanese)
-  Z. Yang, M. Sun, W. Li, and W. Liang, “Modified Elman network for thermal deformation compensation modeling in machine tools,” Int. J. of Advanced Manufacturing Technology, Vol.54, Issues5-8, pp. 669-676, May 2011.
-  Q. Guo, J. Yang, and H. Wu, “Application of ACO-BPN to thermal error modeling of NC machine tool,” The Int. J. of Advanced Manufacturing Technology, Vol.50, pp. 667-675, 2010.
-  H. Zhao, J. Yang, and J. Shen, “Simulation of thermal behavior of a CNC machine tool spindle,” Int. J. of Machine Tools & Manufacture, Vol.47, pp. 1003-1010, 2007.
-  X. Junyong, H. Youmin,W. Bo, and S. Tielin, “Research on thermal dynamics characteristics and modeling approach of ball screw,” The Int. J. of Advanced Manufacturing Technology, Vol.43, pp. 421-430, 2009.
-  Y. Kaneko, H. Tachiya, H. Tamura, H. Shinjo, and M. Isobe, “Simple and effective ,ethod to compensate deformation of a machine tool by derivering its approximate equation (Application under the continuous operating condition),” The Japan Society for Precision Engineering, Vol.73, No.726, pp. 371-378, 2007. (in Japanese)
-  H. Tahiya, Y. Kaneko, T. Aramoto, H. Shinjo, and Y. Miyazaki, “Approximation of Thermal Deformation Behaviour of a Machine Tool to Improve Its Process Precision,” Key Engineering Materials, 345-346, pp. 181-184, 2007.
-  H. Akaike, “A new look at the statistical model identification,” IEEE Trans. on Automatic Control, Vol.19, No.6, pp. 716-723, 1974.