Research On Error Identification And Compensation Technology For Five-axis Mirror Milling

Large thin-walled parts with large size,thin thickness,light weight and other advantages are widely used in the aerospace manufacturing industry,but at the same time,it is very difficult to make such parts.Mirror milling machine,which appeared in recent years,is an ideal equipment for processing large thin-walled parts.Mirror milling machine tool is affected by the machine's own geometric error,thermal error and other errors during the machining process,which will cause machining deviation and affect the machining accuracy of the workpiece.In addition,the movement of the machine tools on both sides of the mirror milling also has collaborative movement pose error,which will also have a certain impact on the machining accuracy of parts.Therefore,in order to ensure the machining accuracy of the workpiece and understand the source of machining errors,it is necessary to identify and measure the errors of the mirror milling machine,and appropriate methods are required to compensate the machining errors.In this paper,the research object is HMMS 2040 five-axis mirror milling equipment independently developed by Shanghai TOP company.The main contents of this paper are as follows:(1)The structure of the five-axis mirror milling machine is analyzed.Based on the multi-body system theory and the homogeneous coordinate transformation method,the kinematics model of the mirror milling machine is established.Through this model,the relationship between the movement of each movement axis of mirror milling machine tool and the position and vector of tool axis can be calculated,and the constraint relationship between the milling side and the supporting side is explained.The geometric error,thermal error,force error,tool wear error are analyzed.A table of error elements including 161 geometric errors and thermal errors is established for query use.Considering the geometry and thermal error of the mirror milling machine,the comprehensive error model of the mirror milling machine is established.Through the comprehensive error model,the error values of the tools on both sides of the mirror milling in the workpiece coordinate system can be calculated separately.(2)In order to identify all the geometric errors of the machine tool,the laser interferometer is used to measure and identify all the geometric errors of six translational axes of the machine tool on the milling side and the supporting side based on the "Twelve line" method.In the error identification and measurement of the rotating axis of machine tool,the identification algorithm of each geometric error of the rotating axis is explained in detail.In the process of error measurement and identification of the rotating axis of machine tool,the identification algorithm of each geometric error of the rotating axis is analyzed in detail,and then the method of using the R-test precision self inspection system of five axis mirror milling machine tool to detect the rotating axis error is introduced.(3)In order to improve the precision of the coordinated motion of the milling side and the supporting side,First of all,based on the idea of motion synthesis and decomposition,a discrete method for the coordinated motion working space of the two sides of the mirror milling machine is proposed.The motion space of the two sides of the mirror milling machine is described as the superposition of the translation axis movement space and the rotation axis movement space.Then,the influences of geometric error,thermal error and other factors on the coordinate motion accuracy of the machine tools on both sides of the mirror milling system are comprehensively considered,and a grid compensation method is used to establish a model for predicting the coordinate motion errors of the milling machine and the supporting machine.The error prediction model can predict the coordinated pose errors of the two machines at any spatial pose under the condition of constant and changing ambient temperature.An error compensation strategy is proposed,which is based on the milling side and modifies the NC code of the supporting side to realize the cooperative pose error compensation of the two sides of the mirror milling machine under the target pose.Finally,the error compensation experiments are carried out under constant temperature and variable temperature conditions respectively.The results show that under constant temperature,the collaborative position accuracy and angle accuracy after compensation are increased by 78.42% and 57.03% respectively,and under variable temperature conditions,they are increased by 78.59% and 63.64% respectively,which verifies the effectiveness of the proposed error prediction model and compensation strategy.