Influence Of Cutter-Workpiece Contact Constraint On The Dynamic Characteristics And Stability In Curved Thin-walled Parts Milling System

High-precision equipment such as aerospace equipment and high-end manufacturing equipment is developing rapidly.Curved thin-walled parts with high specific strength,short design and processing time are widely used.However,these thin-walled parts have complex structural characteristics such as weak rigidity,difficult bending and torsional machining,variable thickness,and the resulting dynamic characteristics such as boundary characteristics,time-varying characteristics,modal coupling characteristics and position dependence characteristics.Therefore,in the cutting process of curved thin-walled parts accessibility is poor,the milling is prone to vibration,processing efficiency is low,machining accuracy and surface quality is poor.And the use of the large overhang milling cutter processing,vibration is more obvious,the workpiece and the tool deformation problem is more prominent.The above cutting problems seriously affect the surface processing quality,production efficiency,shorten the service life of tools,machine tools.In this thesis,the dynamic characteristics of milling system for curved thin-walled parts with the large overhang milling cutter are studied in depth,in order to reveal the material removal mechanism,explore the formation mechanism of machining chatter and machining errors,and realize efficient and precise machining of curved thin-walled parts,which provides knowledge basis and technical basis for engineering applications.Firstly,in order to study the dynamic characteristics of milling system with cutter flexibility,this kind of milling system is prone to vibration,deformation and other problems in the process of machining.This thesis proposes a dynamic model considering the influence of cutter-workpiece contact constraint on the large overhang milling cutter machining.Based on the cantilever beam theory,the cutting dynamics model of the large overhang milling cutter is established,and the nonlinear boundary conditions of balance between internal shear force and top force were given.Based on the established dynamic model,the influences of cutter deformation on workpiece surface morphology and modal parameter change on milling stability are analyzed.Tool deformation,resulting in a change in cutting thickness.The boundary condition of cutter-workpiece contact constraint further affects milling stability by changing cutter modal parameters.The influence of cutter-workpiece contact constraint is verified by modal and milling experiments.The experimental results show that the milling cutter modal parameters change obviously after considering the cutter-workpiece contact constraint,and the stability prediction results are more accurate after considering the influence of cutter-workpiece contact constraint.It provides a reference for selecting milling parameters and controlling machining stability with high efficiency and precision.Secondly,in view of the research on the dynamic characteristics of flexible curved thin-walled parts,this kind of milling system has the characteristics of low structural stiffness,easy deformation of the workpiece in the process of processing,and so on.This thesis carries out a study on the dynamic characteristics of curved thin-walled parts milling system considering the cutter-workpiece contact constraint.Based on Kirchhoff plate theory and moving load model,a dynamic model of curved thin-walled parts constrained by cutter-workpiece contact is established in this thesis.The dynamic characteristics of curved thin-walled parts are analyzed theoretically by using finite element theory,and the finite element simulation is carried out to solve the response of curved thin-walled parts in milling considering the cutter-workpiece contact constraint.The reliability and necessity of the dynamic model considering the cutter-workpiece contact constraint in the milling system of curved thin-walled parts are verified.It lays a foundation for the optimization of machining parameters and the prediction of machining stability of curved thin-walled parts.Finally,based on the actual situation of milling curved thin-wall parts,in order to achieve more accurate milling parameter selection under stable state,the stability prediction of curved thin-wall parts milling system is carried out based on the study on the influence of dynamic characteristics of the system under cutter-workpiece contact constraint,and the experimental verification is carried out.In this thesis,the position dependence of milling system for curved thin-walled parts with cutter-workpiece contact constraint is studied.On this basis,the modal experiments are carried out to compare and analyze the natural frequencies and frequency response functions under different constraints.The stability prediction results are analyzed and discussed by using the modal parameters obtained from the experiments.The experimental results show that the workpiece modal parameters change obviously after considering the cutter-workpiece contact constraint,and the stability prediction results are more accurate after considering the influence of cutter-workpiece contact constraint.The stability prediction of curved thin-walled parts in milling with the large overhang milling cutter is also studied.Because the workpiece and tool are easy to deform,the amplitude of cutting noise signal spikes at the beginning of cutter-workpiece contact.Under the same processing parameters,the surface topography of the workpiece processed by the ordinary milling cutter is smooth,while the surface topography of the workpiece processed by the large overhang milling cutter has obvious vibrato.By considering the dynamic characteristics of milling system for curved thin-walled parts under cutter-workpiece contact constraint,the modal parameters under cutter-workpiece contact constraint can be accurately obtained,and the milling stability profile can be further calculated,so as to optimize the machining parameters,avoid the chatter and maximize the material removal rate,and realize the high quality and high efficiency of thin-walled parts.