Thermal Analysis And Thermal Error Compensation Of The High-speed Machining Center

With the continuous advance of modern industrial technology and innovation,processing and manufacturing industry is developing rapidly in the direction of highspeed and high precision, so we need more high-speed and high-precision processingtechnology with suitable. Geometric error,thermal error and the force error have beenthe main sources of the error causing the decrease in machining accuracy of machinetools.However, as the manufacturing and assembly’s accuracy is increasing day byday,the effect of geometric error decreases and the thermal error naturally becomesthe largest source,which has accounted for60%~70%of the total errors.Therefore,reducing the influence of thermal error on the precision of the machine tool hasbecome the top priority of the precision machining technology. Taking the high-speedCX series vertical machining center CX110100as the research object,this papercarries on a longitudinal study of thermal error’s compensation, the major work andachievements of the dissertation is as follows:(1)The value and significance of the research are described.The domestic andforeign research history and the latest research achievements are introduced.Theexisting problems are analyzed.The main source of thermal error on machining center,the measures reducing the thermal error and the thermal error prediction andcompensation technique are pointed out.(2)Taking the feeding system of the machining center and the machine as theresearch objects respectively, all the thermal sources and boundary conditions areanalyzed.Based on the theories of heat conductivity and finite element, thethree-dimensional model of temperature field is established.On the basis of thesteady-state temperature field which is calculated in ANSYS,the thermal-structurecoupling analyzation is carried out.The law of thermal deformation is found out andthe thermal error sensitive points are identified.(3)Based on the results of thermal characteristics analysis,temperature measuringpoints are determined.Take five-point measuring method to measure the thermal errors and design an appropriate data detection experiment.Refer to the experimentaldata, the measuring points are optimized by the use of fuzzy clustering and graycorrelation method.Eventually,the three groups of the temperature variablescorresponding to isotropic thermal errors are identified,and the number oftemperature measuring points is reduced effectively.(4)The thermal error-temperature prediction model of machining center isestablished respectively by the use of multiple linear regression method, BP neuralnetwork, RBF neural network and BP neural network optimized by genetic algorithmmethod(GA-BP).By means of establishing the relationship between the thermalerror and the temperature of measuring points,the thermal error value can bepredicted according to the temperature measurement value.Comparing the advantagesand disadvantages of these methods and the predicted results,it shows that GA-BPnetwork model can complement the advantages of each other, speed up theconvergence rate of the model and improve its robustness, Besides,its precision of theforecast is the highest.(5)The time series prediction model GM (1,1) which is established by using thegrey system theory is another model used to predict the thermal error of machiningcenter. On the basis of the experimental data of thermal error,its changing trend canbe found.Then the thermal error value of the next moment can be predicted.Theresults show when the machining center works under stable working conditions,themodel’s prediction accuracy is not bad.The model is feasible.(6)Based on the prediction of the thermal error, the thermal error compensationstrategy is put forward and the thermal error compensation system is designed.