Chatter Analysis And Mitigation For The Milling Of Thin-walled Structure

Milling is one of the most common manufacturing processes in aeronautical and aerospace industries.Milling chatter,which is generally caused by the selection of improper milling parameters,is the main limitation to part quality and productivity during machining operations.Especially,chatter occurs more frequently during the milling process of the thin-walled structure due to its low rigidity.Therefore,it is significant to study the mechanism of the milling chatter thoroughly,analysis the milling process stability to achieve the chatter-free milling process and propose the methods for chatter detection and avoidance.The existing researches are focused on two main categories by reviewing the literature of milling chatter.The first group is composed of all those researches that aim to predict the location of the stability boundary.Then milling chatter can be avoided in milling process by selecting reasonable cutting parameters according to chatter stability lobe diagram(SLD).The second category includes those researches that suppress chatter by improving the design of the machine tool to change its performance against vibration or on the use of extra devices that can absorb vibration energy or disrupt the regenerative effect.The research subject of this dissertation mainly revolves around the milling chatter problem,including milling force prediction;milling chatter prediction and mitigation;milling dynamic analysis and chatter suppression of the thin-walled structure.Firstly,a new method for calibrating the milling force coefficients and the cutter runout parameters simultaneously is presented.The effect of the cutter runout is taken into condsideration,and the mathematical relationships between the instantaneous milling forces and the milling force coefficients are achieved.An objective function is established by comparing the numerical results and the experiment results.Finally,the milling force coefficients can be achieved by adopting the method of cyclic iterative process.Secondly,a new approach is introduced for predicting the milling stability by utilizing the Simpson integration method and Lagrange interpolation method.The numerical integration method is utilized to determine the transition matrix over one tooth passing period.The SLD can be obtained based on the Floquet theory.It is noted that even though the milling parameters are selected from the stable regions of the SLD,milling chatter cannot be avoided completely during the milling process due to its complexity.Therefore,a new methodology is presented to detect the milling chatter based on energy entropy and distribution.Thirdly,experimental investigations are concerned which assess the feasibility by submerging the milling system in viscous fluid to mitigate milling chatter.The results show that the proposed method can enlarge the stability limit remarkably.The stability improvement under viscous fluid condition can be attributed to three aspects: the increase of the damping of the milling system,the decrease of the frequency of the milling system and the reduction of the cutting force coefficients.Finally,a general cantilever plate mechanical model is utilized,and the milling dynamic model is developed to study the milling chatter of thin-walled structure.The milling SLDs are predicted by taking multiple modes of the thin-walled structure into account.Moreover,the milling system is submerged in the viscous fluid condition to prevent and suppress the milling chatter of the thin-walled structure.A series of milling tests are conducted and higher stability limits are achieved with the proposed approach.A great deal of research are carried out to solve the milling chatter problem by means of theoretical analysis,numerical simulation and experimental research.The outcomes of this dissertation will be helpful for the enrichment of the fundamental theories of the milling chatter,as well as useful for investigating the milling process dynamics.