| Machining complex thin-walled components such as compressor disks in aircraft engine with high quality and high efficiency has always been one of the bottlenecks in aviation manufacturing.With the development of modern manufacturing,many countries have launched intelligent manufacturing research programs recently,aiming at seizing the technical commanding heights.Real-time sensing and processing manufacturing information,and adjusting processing parameters are prerequisites for intelligent manufacturing,which also are the main contents of the intelligent manufacturing research programs.Deformation and vibration of workpiece(WP)are the main obstacles to the high-quality and high-efficiency machining of thin-walled components.Studying the WP dynamics in machining process,sensing the deformation and vibration in real-time and feedback,adjusting processing parameters to avoid chatter intelligently,have important academic significance and engineering application value for promoting thin-walled WP manufacturing.With support of the National Basic Research Program of China “Basic Intelligent Manufacturing Research of High Quality and Complex Components”subprogram 3 “On-Line Sensing and Multi-Fields Reconstruction of Force-Heat-Deformation During Machining”(Program No.2013CB035803),this dissertation has studied the WP dynamics during machining,proposed a real-time displacement and strain field reconstruction method based on the multi-mode of WP,analyzed turning stability of the coupled turning system.The main research contents and achievements are as follows:Firstly,according to the geometric characteristics,the thin-walled WP was simplified as an annular thin-walled plate.According to the plate bending theory and the d'Alembert principle,a dynamic model has been established,based on which an analytical method for modal analysis of an annular thin-walled plate with uniform thickness has been proposed.Using the proposed method,modal analysis was carried out and nature frequencies,eigenfunctions,and mode shapes of an annular thin-walled plate under various clamping schemes were obtained.Compared with the existing numerical methods,the proposed analytical method showed higher efficiency and accuracy,which was also validated by modal tests.Next,on the basis of the established model and proposed modal analytical method of the annular plate with uniform thickness,an analytical method for modal analysis of stepped plate is further proposed.Using the proposed analytical method,the effects of step thickness ratio and step position on the nature frequency and mode shape were studied by conducting modal analysis of a stepped plate with only one step which may be generated with material removal during machining.Then the method was extended to modal analysis of plate with continuously varying thickness by approximating it as multi-step plate,and it's verified by plates with linearly and quadratically varying thickness.Finally,an appropriative software was developed for modal analysis of annular plate,with which an off-line modal database consisting of modal data of WP during machining was built efficiently.The database has certain directive meaning for the design of machining processes and the selection of machining parameters.More importantly,it can be used for updating modal parameters during machining in the follows research about field reconstruction and stability analysis.Then,with the established modal database,a displacement and strain reconstruction method based on modal superposition was proposed for the first time by fusing the real-time displacement information of discrete measurement and off-line modal data.The efficiency and stability of the reconstruction algorithm were discussed,and then the number of sensors and the sensing deployment were optimized.The proposed reconstruction method and the optimized deployment are verified by simulation experiment and experimental test.Finally,a cutting experiment was conducted with on-line sensing and real-time field reconstruction of WP during cutting processing.Besides,by cooperating with Prof.Xiong Zhenhua of Shanghai Jiaotong University,an active vibration control experiment when turning a thin-walled plate was carried out based on the proposed reconstruction method.With the reconstructed displacement as real-time feedback to the controller,the cutting process was more stable and the surface quality was improved significantly,demonstrating the engineering application value of the reconstruction method in error compensation and chatter suppression.Finally,contraposing the turning process of thin-walled WP,a dynamic model of coupled cutting system of flexible WP and cutting tool(CT)was established,considering the multi-modal vibration of WP.And the principle of coupled system stability analysis was deduced.With the transfer functions of the WP and the CT at the cutting point obtained,stability of coupled cutting systems with different CT rigidities were analyzed respectively,and the stability lobe diagrams(SLDs)for a certain cutting location for each cutting system were obtained,based on which a 3D SLDs were finally attained.By comparing the experimental results and prediction results of turning a thin-walled plate,the reliability of the established coupling model and the stability analysis results are validated,and it is directive for the appropriate selection and real-time adjustment of machining parameters to avoid chatter. |
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