Research On Causes Of Flank Milling Errors Of Five-axis Machine Tool Based On S-shaped Test Piece

Five-axis machine tools has complicated structure and involves a number of error factors.Besides,the machine shaping mechanism of five-axis machine tool is far more complicated than three-axis machine.The study of the formation mechanism of machining errors of five-axis machine tool is of great significance for improving the precision evaluation method and enhancing the design accuracy of the machine.This study was carried out based on cause analysis of the machining errors of five-axis machine tool.From two aspects of the machine tool kinematics model and the workpiece geometric characteristics,the mapping relation between the geometric error parameters of machine tool and workpiece machining errors was established.Further,the key error parameters of machine tool with great influence on workpiece machining errors were analyzed.Next,based on the multi-body system kinematics theory,the modeling approach for machining errors of five-axis machine tools was proposed.Besides,based on the formation mechanism of flank machining errors of S-shaped machine standardized acceptance test pieces,the error space modeling method of test piece was put forward.According to quasi Monte Carlo method,the global sensitivity analysis method of machining errors of machine tools was proposed to study the inherent attribute relationship between the error parameters of machine tool and the machining errors.Finally,based on the error space morphology of the test piece,the cause analysis method of machining errors was put forward,and the mechanism of the action of geometric errors of machine tools on machining errors of test pieces was studied.The main contents of this study are as follows:In-depth analysis on the modeling approach of machine tool kinematics based on multi-body system theory was made,the position and moving reference coordinate systems of machine tool elements were established,and the relative position and kinematic relations between bodies of the multi-body system were described as the relative position and attitude relation between the coordinate systems,so as to derive the relative position relation model between bodies and the error motion model.Given this,based on the topograpy of machine tool,the complete machine kinematic model containing errors was built,and then the machine tool machining error model was derived.On the basis of the machine tool kinematic model,the model of the relative position relation between the tool setting point,the tool central point and the tool path was built.The error modeling of machine tool is the basis for follow-up studies.The machine tool error modeling method based on multi-body system theory has great universality in the field of machine modeling.The establishment of the machine tool geometric error model can reflect the change rule of the geometric error parameters in the workpiece process,and it is the key to the establishment of test piece error space model.According to the structural features of the machine tool in this study,based on linear function and trigonometric function,the geometric error regression model of machine tool with good fitting degree was proposed.The method of measuring and identifying motion-related geometric error parameters of five-axis machine tool with double pivoit spindle heads was studied,with this method,the geometric error parameters of machine tool elements at different kinematic positions can be identified one by one,thus providing a data base for geometric error regression analysis.Moreover,the formation mechanism of flank machining error was studied,and based on the geometric error model and the machine tool machining error model,the error space modeling method for test piece flank machining was proposed.The model establishes a relationship between machine tool geometric errors and test piece machining errors,thus it can be an important means to represent test piece machining errors.Besides,the model revealed that the increment of machine tool geometric error parameters relative to the tool setting point is the primary cause of test piece machining errors,and provides new research ideas for the analysis of test piece machining errors.The machining characteristics of S-shaped test piece are decided by its model.Hence,starting from the modeling method of S-shaped test piece,the test piece model precision interpolation method,the theoretical cutting error caused by S-shaped surface distortion,and the key geometric parameters and geometric characteristics of surface machining were studied,so as to provide an accurate reference base for the analysis of test piece machining errors,and to provide the data foundation for the establishment of test piece error space model.With the purpose of reducing the theoretical cutting error,the optimization and generation method of tool path of non-developable ruled surface flank machining was studied,and then the optimized tool trajectory was obtained,thus avoiding overlarge theoretical cutting error to interfere subsequent error analysis.The global sensitivity analysis method for machine tool machining error model based on quasi Monte Carlo simulations was proposed.With this method,the machine tool error model was regarded as a black box for treatment,the random sampling values of all the geometric error parameters in the definition domain were used as input variables,and the machine tool machining errors were used as output values,then according to the influence of the variances of input variables on the variances of output values,the influence degree of the geometric error parameters on the machine tool machining error model was evaluated.This method can be used to analyze the sensitive parameters of test piece local machining errors,and it is one of the important means to analyze test piece machining error in this paper.On machine tool XKAS2525x60,geometric error detection and test piece cutting experiment were performed,and the single geometric error model and machining error space model of test piece were built.Then the error space model was unfolded to draw the error space morphology of test piece covering the total error factor as well as the error space morphology of test piece under the action of single geometric error.According to relevant theoretical research in this paper,the influence rule of the geometric error parameters on the error space morphology of S-shaped test piece was analyzed.On this basis,the cause analysis methods of local machining errors and global machining errors of S-shaped test piece were put forward,and the key geometric error parameters affecting the machining errors of S-shaped test piece were obtained.The experimental results showed that the proposed test piece error space model can correctly reflect the morphology of the test piece machining errors,and the cause analysis method of errors adopted can effectively determine the key parameters affecting the test piece machining errors.