On Dynamic Analysis And Chatter Mitigation In Five-axis Milling

Five-axis milling is extensively used in machining of parts with sculptured surfaces such as integral wheels and turbine blades.However,achieving high machining performance is still an international difficulty due to the usage of difficult-to-process materials,slender blades,screwy surfaces,easily deformed structures,vibrations and chatters.How to master high precision and efficiency manufacturing techniques for these key parts still remains a severe challenge for the goal of developing our independent,strong aviation manufacturing technology.Manufacturing efficiency and accuracy are influenced by various factors in which milling mechanics and dynamics caused by the tool-workpiece engagement are currently one of research highlights.Generally,mechanics and dynamics are highly dependent on the cutting parameters.Improper parameters may lead to excessive cutting force,undesirable vibrations or instability,which are commonly associated with tool breakage,too wear and workpiece defects.As is well-known,modeling and prediction of cutting force are an ef-fective ways to prevent problems such as severe fluctuation of cutting force and workpiece deformation.Meanwhile,prediction and avoiding unstable vibration,i.e.chatter,which is a strenuous vibration phenomenon caused by the periodic cutting force with regenerative effects taking into account,are significant.This dissertation focuses on prediction of cut-ting mechanic and dynamic and developing techniques to enhance manufacturing efficiency and accuracy which is limited by chatter.The main research contents and achieves are as follows.Considering the complexity of tool-workpiece engagement modeling in five-axis milling,a decoupled chip thickness calculation model is presented.the chip thickness of cutting with both lead and tilt angles is decoupled by the sum of chip thickness distributed from the two individual resolved cutting conditions.Then,the cutting force prediction mod-el is presented based on the linear mechanics force model.Comparing results show that the prediction forces are well matched with the experiments.Meanwhile,the presented model is quiet suitable for the analysis of milling dynamics.A linear acceleration method is presented for milling stability prediction.It's proved that the local discrete error is third order in time and the size of Floquet transition matrix is only about a quarter of those obtained by semi-discretization,full-discretization or numer-ical integration method.Simulation results show that the proposed method has advantages in both efficiency and accuracy when comparing with the commonly used methods.In five-axis milling,tool orientations as well as the tool-workpiece engagement re-gion are always changed along the tool path,and hence,the characteristics of the system stability may be influenced.Considering both rough millings with flat-end mill and finish millings with ball-end mill,tool orientation optimization strategies are proposed to enhance chatter-free cutting parameters region.Simulations and experiments verify the validity of the proposed method.Active control is a powerful tool to avoid chatter in machining.As far as the author know,however,little research has been conducted on active chatter control for five-axis milling.An active control method is developed for chatter mitigation in five-axis milling in this work.As the tool-workpiece engagement condition,i.e.the start and exit angles,can not be measured directly during milling,Fourier series are adopted to present the cutting force directional coefficient.Then,an adaptive control law is developed to track the coefficients of Fourier series,and hence,milling chatter can be suppressed.The proposed method is suitable for chatter mitigation in five-axis milling since the control law does not depend on the tool-workpiece engagement condition.The work on the milling mechanics,dynamics and chatter suppression strategies will be meaningful and helpful for the improvement of five-axis machining performance and will provide the basic theory support and practical guidance in developing high-performance machine tools.