Thermal Error Prediction And Compensation Of Machine Tool’s Feed Axes Based On Heat Transfer Mechanism

Poor accuracy stability is a long-term difficult situation faced by domestic CNC machine tools in China.Thermal error is a critical factor affecting the machining accuracy stability of machine tool.As an important component of the comprehensive thermal error,the thermal error of the linear feed axis will not only lead to out-of-tolerance machining of individual parts,but also cause accuracy fluctuation in batch machining.Aims at the problem above,the technology of thermal error prediction and compensation for the linear feed axes of CNC machine tools was studied in this paper.The influence of the thermal error on the machining accuracy of the parts was controlled by error prediction before machining and error compensation in machining.The main researches of the paper are as follows:(1)The mechanism of heat conduction,heat convection and heat radiation was clarified.The thermal error causes of semi-closed loop and closed loop linear feed axes were illustrated.The thermal expansion error model and the thermal drift error model were established based on heat transfer mechanism of semi-closed loop and closed loop linear feed axes.The methods of thermal error test and parameter identification were studied.(2)The method of thermal error prediction for machine tools based on digital twin was proposed.Combined with digital twin and the thermal error model,a framework of thermal error prediction based on digital twin was established.It includes physical entity layer,data transmission layer,function execution layer and application service layer,which provides theoretical guidance for machine tool thermal error prediction.The digital twin of linear feed axis of CNC machine tool was established based on Matlab.The thermal error prediction of linear feed axis was carried out with the residual error ranging from-0.2 μm to 2.6 μm.(3)The communication technology between external error compensator and domestic CNC system was studied based on the data exchange interface of CNC system.Taking the X axis as an example,the error compensation method based on the principle of machine tool coordinate origin offset was clarified.The communication between the external error compensator and Lantian CNC system was realized by remote access interface library.The read-write communication between the external error compensator and the core of Kede CNC system was realized by communication service development interface.The read-write communication between the external error compensator and the lower computer of Huazhong CNC system was realized by secondary development interface.(4)The communication modules for Lantian,Kede and Huazhong CNC systems had been developed respectively and the improved thermal error model was encapsulated into the software to improve the thermal error compensation function.The thermal error compensation test of linear feed axis was carried out on a vertical machining center in the laboratory.The thermal error compensation technology of feed axis was applied to the vertical machining center of No.430 Factory of AECC Xi’an Aero-Engine Ltd.and the boring-milling-turn composite machining center of No.31 Institute of Third Academy of Aerospace Science and Industry.After compensation,the positioning error fluctuation range of the linear feed axis has been reduced by 85.2% and 61.2% respectively,and the accuracy stability of the machine tool had been greatly improved.