Research On Error Compensation Technology Of Key Components Of Ultra-precision Machining Tool

The development of advanced manufacturing technology is attached great importance all over the world.Some developed countries have formulated industrial development plans,and China has formulated the "Made in China 2025".There is still a blank in many key technical fields in China.Ultra-precision processing technology is a key point in high technology and science fields,and ultra-precision machine tool is the basis of ultra-precision processing.At present,ultra-precision machining has entered the Nano-scale.How to control machining errors,and ensure the accuracy has become a research hotspot for raising the level of manufacturing.To improve the machining accuracy of machine tools and enhance the international competitiveness,this thesis takes a five-axis ultra-precision machine tool as the object,to research the geometry and cutting force errors of the key components.A series of researches such as error modeling,identification and separation,dynamic analysis of micro machining,component stiffness measurement,uncertainty analysis,and comprehensive error compensation are carried out to provide theoretical and experimental basis for the accuracy improvement of multi-axis CNC machine tools.The main research contents are as follows:(1)Taking a RPPPR type ultra-precision five-axis machine tool with single pendulum head-single turntable structure as the research object,the main error sources affecting ultra-precision machining are discussed in detail.Based on the principle of affine transformation theory,an analysis method of the spatial pose transformation of the target object rotating around an arbitrary line is proposed.Under the premise of small angle and small displacement,the position and posture changes during the movement of the rotation axis of five-axis machine tool are analyzed.A comprehensive error model of geometric,force induced errors of the rotary axis-tool system was established.A total of 40 error elements in the C-rotary axis platform,spindle holder,milling spindle and micro tools were obtained.This part provides the theoretical basis and research direction for the implementation of the error compensation scheme.(2)To identify and compensate all geometric errors,it is proposed to use Empirical Mode Decomposition(EMD)to identify and separate geometric error elements,thereby solving the problem of nonlinear coupling in the separation process of position independent geometric errors(PIGEs)and position dependent geometric errors(PDGEs),and improving the efficiency of error compensation.(3)The prediction model of micro milling force based on shear deformation is established.The nonlinear variation of micro milling force coefficient in the process of micro milling is analyzed.The relationship between milling force coefficient and processing parameters is established by using quadratic regression method,which provides a theoretical basis for the selection of processing parameters.(4)The force induced error(FIEs)model of the rotary axis-tool system of a fiveaxis CNC machine tool are established,and a set of experimental scheme of stiffness measurement of the rotary axis-tool system are designed.According to the loading conditions,special fixture was manufactured,and the load-displacement changes were measured on the machine.19 stiffnesses of the C-axis,spindle holder,milling spindle and the micro tool with 0.5mm diameter were obtained,which laid the foundation for the optimization of machine tool structure and the implementation of FIEs error compensation.(5)The error compensation experiment of micro free-form surface milling is carried out,and to ensure the rationality and effectiveness of experimental data,the uncertainty of measurement and experiments of the rotary axis-tool system is analyzed based on the basic measurement method of uncertainty specified in ISO 230-9.The geometric and force induced errors generated of the rotary axis-tool system during the movement were measured with an on-machine measurement(OMM).The comparison experiments of PIGEs+FIEs and PIGEs+PDGEs error compensation were carried out on AL6061 and AISI1018 steel,respectively.By analyzing the milling accuracy of micro free-form surface profile before and after error compensation,the effect of error compensation is evaluated.