Thermo-elastic correction for 5-axis machining centers

 

The aim of the project is the development of a fast, volumetric measurement and modeling methodology for the characterization of the thermo-elastic behavior of 5-axis machine tools as well as a corresponding correction solution for the optimization of this behavior.

Machine tools are of outstanding importance for the metalworking industry. An important factor for their performance is the working accuracy, which is characterized by the static, dynamic and thermo-elastic machine behavior. The proportion of thermo-elastic faults in the total fault can be up to 75%. Research fields in this area are measuring, predicting and correcting these deviations. Research in these fields is driven by the constantly high demand for high-precision components with complex geometries and thus a necessary increase in the accuracy of 5-axis milling machines. According to the current state of the art, there is no method for measuring in thermal real time and for reliably determining and correcting the essential thermo-elastic errors of 5-axis machines. To close this technical gap, this research project focuses on the optimization of the thermo-elastic behavior of 5-axis milling machines. The core of TheKo5 here is the approach of measuring, forecasting and correcting all important thermo-elastic deviations of the machine in thermal real time in order to achieve a high machining accuracy.

The basis for the TheKo5 approach is the measurement of thermo-elastic errors. Here a fast and efficient measuring method is essential, since the machine already cools down in the course of a measuring process and thus impairs the measuring result and the measuring accuracy. The detection of as many machine errors as possible is another important factor for mapping the thermo-elastic behavior of the machine with sufficient accuracy. In addition, good manageability of the associated measurement technology is essential for acceptance by industrial users. All aspects can be realized by the R-test. The deviation measurement is carried out by means of a non-contact 3D measuring head and a calibration sphere. This arrangement allows geometric deviations to be recorded during continuous 5-axis machine movements. In this research project the R-test is to be enabled by means of new measuring strategies and mathematical solution methods to determine all relevant thermally induced deviations in the shortest possible time and thus make them correctable. Since such a measurement is only possible sporadically for economic reasons, the method is to be supplemented by a modelling method which is capable of interpolating or predicting thermo-elastic displacements between individual measurements. For this purpose, the Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University contributes its many years of expertise in the prognosis and correction of thermo-elastic behaviour and the measurement of volumetric behaviour. The prediction of the behavior between two measurements is made by means of an FE model with a small number of degrees of freedom. This can be parameterized on the basis of the kinematic chain of the machine tool. In order to increase the machine accuracy, the measured and predicted deviations are to be corrected or compensated in thermal real time with the aid of the machine control system. Since the current compensation functions of the controls have only limited possibilities for modeling the thermo-elastic behavior, a PC-based modular compensation unit for continuously updating the deviation data in the machine control system is to be developed in addition to the methods for thermo-elastic characterization and modeling in TheKo5.