Research On Machining Precision Prediction Technology Based On Space Stiffness Characterization

Stiffness characteristic is an important factor affecting the precision of complex equipment.However,the current stiffness characterization methods of machine tool usually aim at the ultimate stiffness analysis,or only detect stiffness data for a limited number of discrete locations.It is difficult to obtain the global stiffness distribution.Based on these problems,the matrix polycondensation theory and numerical simulation method were combined in this thesis,and the component of machine tool was re-decoupled.In order to solve the problem that the scale of the stiffness matrix is inconsistent,a method of establishing the stiffness normalization characterization model for precision machine tools was proposed in this thesis.A high precision CNC was taken as the research object,and the research on the spatial stiffness distribution characteristic analysis and machining accuracy prediction of machine tools was also carried out.The main research contents are as follows.(1)Based on the matrix polycondensation theory,a theoretical method of stiffness equivalent polycondensation was proposed.The theory of matrix polycondensation was introduced into the equivalent reduction process of the stiffness matrix of machine tool components.It was proved theoretically that in the process of equivalent condensation of stiffness,the stiffness characteristics of the system can be reflected by the key geometric features that only bore the external load.The universal process of machine tool component module classification,key geometric feature identification and deformation data acquisition was explored,and then a theoretical method of stiffness equivalent poly condensation of machine tool component modules was proposed.(2)Using the stiffness equivalent polycondensation method,the stiffness characterization model of component modules was established.The component modules of machine tool were classified according to their characteristics such as constraint load.For the multi-constraint module,according to the deformation data of the key geometric feature set under six loads obtained by finite element simulation and the idea of minimum envelope region,the general equation of the ideal characterization plane of the deformed surface was solved,and the stiffness characterization model of the multi-constraint module was established.For the multi-position module,its continuous travel was discretized and processed into several transient positions.Then the stiffness datum of each position were solved,and the cubic polynomial method was used for datum fitting to establish the stiffness characterization model of the multi-position module.Finally,stiffness characterization model and finite element analysis method were used to solve the deformation of headstock in machine tool boring respectively,and the accuracy of stiffness characterization model was verified by comparison.(3)Based on the theory of multi-body system,the stiffness distribution model of machine tool processing space was established.The topological structure of machine tool multi-body system was constructed by using the low body array method.The machine tool system was described as two series-wound kinematic chains,and their deformation transfer relationship was analyzed.Based on the kinematics theory of multi-body system,the error calculation formula caused by the position and pose changes of each low body on the end actuator were deduced in the inertial coordinate system,and then the stiffness distribution model of the machining space of machine tool was established.MATLAB was used to solve the model cumulatively and draw the slice figures of the stiffness distribution.By analyzing them,the specific distribution of the deformation errors in the machining space of the machine tool was obtained,and the weak link of the stiffness in the series-wound kinematic chain was identified.(4)Considering the factors of milling process system,the machining accuracy of the S-shaped test piece was predicted.The opening and closing angles were introduced to quantitatively analyze the spatial geometric characteristics of the S-shaped test piece,and the mathematical model was established to describe the structural characteristics of the specimen’s profiles.Considering the machining type,process parameters and other factors in the milling process system,the equivalent conversion formulas of cutting loads in different milling processes were established by deducing.By combining the equivalent conversion formula of cutting loads,the mathematical model of profiles and the stiffness distribution model of the machining space of machine tool,the prediction model of machine machining accuracy was established.The model was applied in MATLAB to solve the machining accuracy of the S-shaped test piece.The prediction results showed that the maximum machining error of the test specimen will occur in the process of flank milling straight surface.Finally,the profile tolerance and the flatness tolerance were used as evaluation indexes.By predicting and comparing the machining accuracy of S-shaped test pieces under different clamping angles,the milling process of the S-shaped test piece was improved.The characterization method of space stiffness of machine tool was proposed in this thesis based on the stiffness polycondensation theory can calculate and reflect the stiffness distribution of machine tool quickly,identify the weak link of stiffness in the kinematic chain,predict the machining accuracy,and improve the machining efficiency and accuracy of machine tool effectively.