Analysis of thermal errors in a high-speed micro-milling spindle

Abstract Thermally induced errors account for the majority of fabrication accuracy loss in an uncompensated machine tool. This issue is particularly relevant in the micro-machining arena due to the comparable size of thermal errors and the characteristic dimensions of the parts under fabrication. A spindle of a micro-milling machine tool is one of the main sources of thermal errors. Other sources of thermal errors include drive elements like linear motors and bearings, the machining process itself and external thermal influences such as variation in ambient temperature. The basic strategy for alleviating the magnitude of these thermal errors can be achieved by thermal desensitization, control and compensation within the machine tool. This paper describes a spindle growth compensation scheme that aims towards reducing its thermally-induced machining errors. The implementation of this scheme is simple in nature and it can be easily and quickly executed in an industrial environment with minimal investment of manpower and component modifications. Initially a finite element analysis (FEA) is conducted on the spindle assembly. This FEA correlates the temperature rise, due to heating from the spindle bearings and the motor, to the resulting structural deformation. Additionally, the structural deformation of the spindle along with temperature change at its various critical points is experimentally obtained by a system of thermocouples and capacitance gages. The experimental values of the temperature changes and the structural deformation of the spindle qualitatively agree well with the results obtained by FEA. Consequently, a thermal displacement model of the high-speed micro-milling spindle is formulated from the previously obtained experimental results that effectively predict the spindle displacement under varying spindle speeds. The implementation of this model in the machine tool under investigation is expected to reduce its thermally induced spindle displacement by 80%, from 6 microns to less than 1 micron in a randomly generated test with varying spindle speeds.

[1]  Placid Mathew Ferreira,et al.  A method for estimating and compensating quasistatic errors of machine tools , 1993 .

[2]  Miles Arnone,et al.  High Performance Machining , 1998 .

[3]  M A. Donmez,et al.  A Novel Cooling System to Reduce Thermally-Induced Errors of Machine Tools☆ , 2007 .

[4]  Jie Zhu,et al.  Robust Thermal Error Modeling and Compensation for CNC Machine Tools. , 2008 .

[5]  Deepkishore Mukhopadhyay.  Array -Based Direct Writing of Micro/nano Scale Structures , 2008 .

[6]  Wei-Yao Hsu,et al.  Characterizations and models for the thermal growth of a motorized high speed spindle , 2003 .

[7]  Michael J. Sailor,et al.  Polymer Replicas of Photonic Porous Silicon for Sensing and Drug Delivery Applications , 2003, Science.

[8]  Jun Ni,et al.  Thermal error mode analysis and robust modeling for error compensation on a CNC turning center , 1999 .

[9]  Debra A Krulewich.  Temperature integration model and measurement point selection for thermally induced machine tool errors , 1998 .

[10]  R. Ramadoss,et al.  Liquid crystal polymer based MEMS capacitive pressure sensor , 2005, SPIE Defense + Commercial Sensing.

[11]  Jun Ni,et al.  The real-time error compensation technique for CNC machining systems , 1998 .

[12]  P. A. McKeown,et al.  Reduction and compensation of thermal errors in machine tools , 1995 .

[13]  Jay Prakash Pathak,et al.  DESIGN, ASSEMBLY, AND TESTING OF AN ULTRA-HIGH-SPEED MICRO-MILLING SPINDLE , 2003 .

[14]  Zone-Ching Lin,et al.  The building of spindle thermal displacement model of high speed machine center , 2007 .

[15]  K-D Kim,et al.  Real-time compensatory control of thermal errors for high-speed machine tools , 2004 .

[16]  Yang Jianguo,et al.  Simulation of thermal behavior of a CNC machine tool spindle , 2007 .