Research On Milling Vibration Characteristics Of Thin-walled Workpiece Under Elastic Deformation

Thin-walled components are commonly used in aerospace,automotive,energy,and many other fields with repect of the light weight and high strength ratio.This kind of parts has the characteristics of thin wall,weak rigidity,large size,etc.,which is prone to chatter in the processing process.Especially,the machining deformation caused by the cutting force of large overhanging tool can not be ignored,which seriously results in the lower presion and the lower efficiency.Using the structural dynamics theory,this paper studies the cutting mechanism of thin-walled parts is investigated throughing theoretical and experimental methods.The specific research work is as follows:1)Modelling of a multi-point contact dynamic model for thin-walled parts milling,which considered the machining deformation effect caused by cutting forces.The influence of cutting position and meshing boundary on the dynamic parameters in the milling process was analyzed,and the deformation model in the cutter-worker contact region was established.Considering the bending deformation of the tool and the workpiece,the cutter-worker contact area was divided into finite cutting units along the axial direction.The itrative method was employed to calculate the machining deformation of the thin plate cutting unit,and the dynamic cutting force acting on the unit was identified.2)Developing of vibration response for thin-walled parts.Based on the established multi-point contact dynamics model of the milling system,the governing equations of the thin plates were obtained by Rayleigh Ritz method and Lagrange equation.Considering the factors such as material removal,cutting position and axial height,the variation law of milling characteristics of thin-walled parts under the action of non-equal material removal was proposed.The vibration response of thin-walled parts was predicted by analytical method.Finally,a series of milling experiments were carried out to verify the results.3)The dynamic parameters of thin-walled parts milling were identified including the effects of the material removal,time-varying characteristics and axial height.Based on the substructure modification strategy,a dynamic parameter field model of the milling system was established,and a modal parameter identification method considering time-varying characteristics of different tool sites and different cutting elements was proposed.Based on the extracted finite element modal parameters,the milling stability at the key points was predicted,and the influences of material removal and location dependence of cutting elements in different directions on the milling stability were revealed.4)Multi-mode coupling method is proposed to predict the stability of thin-walled parts milling.In view of the time-varying and modal agglomeration characteristics of thin-walled parts milling,the multi-mode theory(MMT)is further studied,and a comprehensive method to consider these effects--Modal Coupling Method(MCM)is proposed.Firstly,the thin plate theory and penalty parameter method are used to model the system structure and boundary conditions.Then,the MCM method is compared with the existing multimodal methods,the lowest envelopment method(LEM)and the single mode method(SMT)in detail,and the effectiveness and accuracy of the proposed method for predicting the milling stability of thin-walled parts are verified.Finally,two case studies were performed to verify the consistency between the values and the experimental results.It is further proved that MCM is a better choice for stability prediction in the milling process of thin-walled parts with unknown modal coupling characteristics.5)The influence of machining deformation on the chatter stability of thin-walled parts was studied.Based on the established thin-walled parts milling dynamic parameter field model and the multi-mode coupling stability prediction method proposed in the fourth chapter,the flutter monitoring of thin-walled parts considering the influence of machining deformation was carried out.Firstly,the influence of different cutting positions and axial contact height on the stability was predicted by using multi-mode coupling method.Secondly,the parameter time-frequency transform(SCT)and generalized wavelet transform(GWT)were used to detect the flutter in thin-wall milling.The good time-frequency energy concentration and accuracy of SCT and GWT were presented where the non-stationary milling acoustic signals were applied.It is shown that SCT and GWT can be used to monitor the chatter instability of milling process.