Research On Machining Accuracy Prediction And Error Compensation For Five-axis Flank Milling Based On Multi-source Tool Errors

Aerospace structural parts have the structural characteristics such as a large size,thin wall,and complex shape,which lead to machining characteristics such as small manufacturing batch on a great variety of parts and large allowances for machining requiring multi-layer milling.Five-axis flank milling is a common machining method for aerospace structural parts.The tool rotation profile errors have a great influence on the shape and accuracy of the finished workpiece surface as the contact length between the tool and the workpiece surface is large.However,there are many factors affecting the tool rotation profile errors,which are changed dynamically in a machining process.It is an important research theme in the field of CNC machining to accurately identify the relevant sources and associated parameters contributing to tool rotation profile errors,and to establish the mapping relationship between error sources and machining accuracy in order to realize the prediction of the machining accuracy,and finally control tool errors.In this thesis,a new comprehensive error prediction model is presented to include the tool rotation profile errors into a pre-existing tool path error prediction model,aiming to improve the prediction effectiveness of machining accuracy.At the same time,an identification method for tool error parameters and a prediction algorithm for machining accuracy are proposed.Finally,a compensation method of tool errors is designed.The above studies play an important role in the prediction of machining accuracy and error control for five-axis flank milling.The main research work and achievements are as follows:(1)A comprehensive error prediction model for five-axis flank millingBased on the analysis of the characteristics and mechanism of the five-axis flank milling,a new comprehensive error prediction model is developed to integrate tool rotation profile errors(including tool radial dimension error,tool setup error,tool wear and deflection)with a pre-existing prediction model of tool path errors(including geometric errors of machine tool,workpiece locating errors and spindle thermal deflection errors).With this model,the tool-machining surface contact points distributed on the tool swept surface can be calculated,which provides a basis for the subsequent surface reconstruction and accuracy prediction.Compared with the pre-existing model,the new model has higher prediction accuracy.(2)The identification and prediction methods for tool rotation profile errorsThe tool errors are divided into static and dynamic errors based on the error characteristics.An experimental identification method of “workpiece shape—tool profile” mapping is proposed and the parameters of tool static and dynamic errors are obtained successfully by the method.A database of tool dynamic errors is established through experiments,and a prediction model of tool dynamic errors is constructed to realize the accurate prediction for tool errors in subsequent machining.(3)The interference detection and calculation methods for multi-layer millingBased on the characteristics of multi-layer flank milling for aerospace structural parts,tool rotation profile errors may cause the interference between the milling layers and affect the distributions of the tool contact points on each swept layer.An inter-layer interference judgment and analysis algorithm is established to realize the position adjustment and update for the interfering tool contact points on the swept surface,so as to obtain the distribution of tool contact points on the final machined surface and realize the virtual reconstruction of the machined surface.(4)A normal machining error prediction algorithm for tool contact pointsWhen the machining is completed,the machining accuracy of the key points is often measured by the coordinate measuring machine to judge its machining accuracy.After the tool contact points are calculated,a normal machining error prediction algorithm consistent with the actual measurement principle is established to achieve prediction of machining accuracy.(5)A compensation method for tool rotation profile errorsBased on the influence of tool rotation profile errors on machining accuracy,a compensation algorithm for tool errors is proposed.The algorithm modifies the rotation angle of the revolution axes by adjusting the tool orientation,and then modifies the motion of the translational axes by adjusting the tool location,which realizes the effective compensation of the tool rotation profile errors and improves the machining accuracy of workpiece.In summary,this research has studied the influence of tool rotation profile errors on the machining accuracy for five-axis flanking milling.A set of machining accuracy prediction and error compensation scheme including identification of tool error sources parameters,construction of prediction model,calculation of machining accuracy evaluation indexes and tool errors compensation is formed.Finally,a series of machining experiments shows that the scheme is correct and feasible.