Thermal Error Inspection And Research On Compensation Techniques Of Machining Center

During the machining stage, the components of the NC machining center are brought about temperature rise and thermal deformation, due to the heat sources, such as friction, coolant and ambient temperature, etc. The correct position between tool and workpiece is destroyed, and thermal error of workpiece comes into being. Thermal error of the NC machining center has been the main source error in precision and extra-precision machining process.With the intention of establishing the compensation model of thermal error and improving the machining precision, the detection experiments of thermal error are designed purposefully to study the rule and form of thermal error. On the basis of the analysis of mechanism on thermal deformation of the NC machining center, the method of gray correlation degree is applied to realize optimal layout of temperature measuring points on the compensation model of thermal error. The compensation model is established through the method of multiple linear regressions. This paper consists of the following parts:1) The background and significance of the research are stated, present status of compensation methods on thermal error at the home and abroad are introduced. The primary content of this paper is presented.2) The structural characteristics and distribution of the four-axis horizontal NC machining center are analyzed. The major form of thermal error is studied by spacial decomposition of the thermal error with the practical problems of the machining center during the process of working. The scene of the thermal error experiment, the hardware components of the measurement system and data acquisition system are introduced.3) The thermal error experiment of the NC machining center is introduced. The properties on the axial thermal elongation of Spindle and thermal characteristics on the structure of machining center are researched mostly through the detection methods of axial and seven-point displacement. For the experimental data, the rise of temperature measuring points and the form of spindle thermal error are analyzed in detail, such as thermal drift, thermal declination and thermal elongation.4) The problem of optimal layout of temperature measuring points on the compensation model of thermal error is researched. Based on the method of gray correlation degree, the synthetic gray correlation order is realized through experiment data of multiple cases. Then, four key temperature measuring points are confirmed by combining the basic principle of selecting points applied to the compensation modeling. Three modeling schemes are put forward according to the fours.5) The theory of multiple linear regressions is introduced. The compensation model of thermal error is established according to the different scheme of selecting temperature measuring points. At the same time the hypothesis of multiple linear and compensation targets of the model are verified. The final model is ascertained through the comparison of different schemes.