Precision Measuring And Spatial Error Analysis Of Machine Tool Spindle Considering Workload Conditions

The precision of the machine tool spindle is an important factor affecting the machining quality of the workpiece.It is the key technique to ensure the performance of machine tools by measuring the spatial position of the spindle rotation axis and analyzing the spindle error.The machine tool processing task is complex and variable.The change of machining task leads to the alter of the spindle speed and cutting force and complicates the spatial position of the spindle rotation axis,which means the rotation accuracy and spatial error of the spindle vary with the change of load conditions.Therefore,the spatial error of the machine tool spindle without considering the workload conditions in the real machining state can hardly obtain the actual rotating precision of the spindle under different cutting conditions.In the actual production,to ensure the machining accuracy of the workpiece and avoid scrapping the workpiece aiming at the specific processing object,it is hoped to obtain the spatial error of the spindle under the load condition corresponding to the process parameters,which can be used as the objective basis for the prediction of machining error and the optimization of process parameters.Especially in the high-quality manufacturing of key parts of high-end equipment,its significance is particularly prominent.Therefore,measuring and spatial error analysis of machine tool spindle considering workload conditions is proposed in this research.This paper studies the workload simulation method of the machine tool spindle,establishes a workload-precision response surface model that can use some preferred operating conditions test data to predict the accuracy characteristics of all operating conditions,and proposed a method of spindle spatial error analysis for specific machining tasks.This reveals the error variation pattern of the spindle under different working conditions,and finally,the software for the spindle precision measuring test and spatial error analysis is developed.The main contents of this paper are as follows:(1)The workload simulation device is developed.Firstly,the load models of milling,drilling,and boring are analyzed and derived to obtain the cutting load pattern under different machining types.Secondly,a spindle load simulation device that can be directly installed on a CNC machine tool and simulate static and dynamic cutting forces is developed.On this basis,a new idea is put forward to apply the dynamic matrix control method to spindle load simulation,which effectively solves the problem of workload simulation caused by the varying physical model of the loading system due to the large difference between the object under test and the installation method,the complexity of the law of cutting force change,the vibration and runout disturbance of the spindle when rotating.(2)A response surface modeling and optimization method for measuring spindle precision under different workloads are proposed.Firstly,the precision test scheme for distinguishing working conditions is established,and the spindle precision characteristic parameters including thermal error,static axis shift error,dynamic axis shift error,and rotation error are extracted under different working conditions.Secondly,a workload-precision response surface model is proposed to predict the variation of the spindle's precision characteristics under continuous working conditions,which can predict the spindle's precision characteristics under all working conditions based on the precision test results under partial working conditions.Furthermore,a multi-level optimization strategy is proposed,including the domain Latin hypercube sampling method for sampling of prior conditions,improving the global AK-MCS(Kriging-Monte Carlo)method for the posterior condition sampling and model optimization of the response surface,and the time density peak(DP)clustering method for eliminating redundant working points,thus realizing the efficient iterative update and refinement of the workload-precision response surface.(3)A method of spatial error analysis of spindle considering workload condition is proposed.Firstly,the experiments regarded with the influence of workload on precision are conducted.The rotation error under different torque,the rotation error and axis shift under static workload,and the dynamic axis shift under different dynamic workload is obtained.Secondly,the method of fusing simulated test data,stress-strain analysis,and space vector analysis is put forward,the error prediction model of the average offset and swing error of the spindle axis is established,and the accuracy of the model is verified by the simulation loading and error test of the spindle.Further,a spindle error quantization method for machining task is proposed,expands the applicable dimension of quantification of margin and uncertainty theory(QMU),solves the error margin of the discrimination accuracy level,thus derive the precision margin calculation formula for the processing task,and finally solve the problem that it is difficult to accurately quantify the spindle errors under complex working conditions.(4)A software that can realize the simulation of working conditions and error analysis is developed.Firstly,the software functional requirements are analyzed,and the software technology framework of four functional modules integrating test design,working condition simulation,accuracy test,and error analysis is formulated.Secondly,the overall framework of the software platform is built and the software program block diagram is compiled by using the mixed programming method of Lab VIEW and MATLAB development tool.Finally,the human-machine interface of each function module of the software is developed,which provides the automatic platform for the simulation and error analysis of the spindle working condition for the user,and then realizes the application of the spindle precision test and spatial error analysis method considering the load working condition.In conclusion,this paper improves the technical framework of precision measuring and error analysis of machine tool,develops a new idea of spindle precision test and spatial error analysis based on working condition simulation data,improves the pertinence and accuracy of processing task-oriented spindle error analysis,and provides technical support for optimizing spindle structure of machine tool,accurately evaluating spindle performance and preferred cutting process parameters.