Effect Of Prestress On Chatter Stability Of Thin-wall Milling System

Thin-walled part is widely utilized in aerospace design due to the requirements of high performance and light-weight.Because of its weak stuffiness,thin-walled part is prone to chatter during milling,which will induce several adverse consequences such as severe tool wear,loss of precision and poor surface quality.These consequences greatly hinder the development towards high efficiency and high quality milling of aerospace thin-walled parts.Therefore,predicting and controlling milling chatter of thin-walled parts have attracted wide attention from academia and industry,due to their meaningful engineering application value.Targeting on predicting and controlling chatter stability in thin-walled parts milling,this thesis proposed a method by applying prestressing force to the thin-walled parts during the milling process.First of all,the milling dynamic model of thin-walled part-tool system is established,followed by the study of internal relationship between the prestressing force and ultimate axial depth.Next,targeting on practical situation,a prestressing application and control device for thin-walled parts is specially designed and manufactured.Finally,in order to verify the effectiveness of the proposed method,experimental verifications are carried out by adopting the developed control device,and the milling deformation of thin-walled parts after prestressing is analyzed.The main tasks of this thesis are as follows.(1)A milling dynamic model of thin-walled part-tool system is established.Aiming at predicting the clamping mode of thin-walled part with one fixed end and one free end,considering the influence of thin-walled part and tool on the dynamic model,deducing the dynamic chip thickness of thin-walled part,solving the stability of the system,the dynamic model of thin-walled part-tool system is established.Experiment results show that the model can accurately predict the milling stability of thin-walled part-tool system.(2)The influence of prestressing force on chatter stability of thin-walled parts in milling is studied.First of all,based on the established milling dynamic model of thin-walled parttool system,the relationship between the natural frequency of thin-walled part and the ultimate axial depth of cut is derived.Second,by combining finite element simulation and numerical method,the inherent relationship between prestressing force and natural frequency of thin-walled part is studied.Through the aforementioned two steps,the twoway closed-loop solution between prestressing force and ultimate axial depth is realized,providing theoretical support for the accurate application of prestressing force.(3)The experiments on chatter stability of thin-walled parts in milling based on prestressing force are carried out.Firstly,A device for prestressing and controlling thin-walled part is invented.Then,combining modal hammering test with finite element simulation,the modal parameters of thin-walled part and cutter with or without prestressing force are obtained and the stabilities of thin-walled parts in two cases are predicted.Finally,a series of milling chatter experiments are carried out.Comparing the experimental results with prediction results,it is found that prestressing can effectively improve the milling stability of thinwalled part in the target area.(4)The influence of prestressing force on milling deformation of thin-walled part is analysed.With the help of geometric relations,the milling deformation of thin-walled part with or without prestressing force is analyzed.The milling deformation of thin-walled part with or without prestressing is simulated and calculated by finite element software.The comparative analysis shows that the effect of prestressing on the processing deformation of thin-walled part can be negligible.This research enriches the methods of chatter suppression in thin-walled part milling,improves the prediction of milling stability of thin-walled part,and provides a theoretical basis for the selection of milling technology,the optimization of cutting parameters,the design of cutter and the accurate application of prestressing force for thin-walled parts.