Analysis And Robust Design Of Geometric Accuracy Of A Three-axis CNC Surface Grinding Machine

With the rapid development of ultra high speed grinding machining technology, the precision performance of high speed CNC grinding machine request to get higher and higher. For traditional precision design methods, tolerances of various parts of grinding machine are distributed mainly relying on experience of designer. The economy and rationality of this method is inevitable poor and it has been hard to meet the increasing demand of precision. In order to solve this problem, taking the geometric error of three-axis CNC grinding machine as research object, a geometric accuracy analysis and design method was proposed in this paper. The main research contents are as follows.(1) Geometric error modeling of the three-axis CNC grinding machine and performance verification of error propagation model. Geometric error propagation model is a prerequisite for the analysis and design of geometric accuracy and performance of model is the ensurance of the following research. Firstly, the theoretical basis of error modeling namely multibody system theory and homogeneous coordinate transformation theory were analyzed. Then method of topology analysis for multi-body system and method of low-body array description were introduced. The position and orientation transformation matrixes between typical adjacent bodies in multibody system were deduced. Lastly, according to the specific structure of grinding machine, the error propagation model including 21 geometric errors was established. Based on 9-line method, errors were measured by using XL-80 laser interferometer system, then the performance of error propagation model was verified and the result showed that the geometric error propagation model has ideal prediction accuracy.(2) Key geometric error identification for three-axis CNC grinding machine. Different kinds of errors influence machining precision differently, so it's necessary to identify and focus on the key geometric errors in order to improve the efficiency and rationality of geometric accuracy design. According to the error propagation model and based on the error data that obtained by error measurement experiment, key geometric errors were analyzed and 11 ones were identified by applying orthogonal design and parameter test of DOE methods.(3) Robust design in distribution of tolerances of key geometric error variables. Sample points were obtained by using optimal Latin hypercube design of DOE method and Isight software, then quality loss function of machining accuracy was deduced by using response surface methodology according to robust design theory. Thereafter, a cost-quality model of machining accuracy was established after cost analyzing and error tracing. Finally, tolerances of key geometric error variables were distributed based on the model.In conclusion, a geometric accuracy analysis and design method was proposed in this paper and tolerances of key geometric error variables were distributed according to this method to effectively improve the precision performance of the three-axis CNC surface grinding machine. The process and result of geometric accuracy design provide a theoretical basis and practical reference for precision design of machine tools.