Research On The Control Methods Of Residual Stresses In The Milling Of Multi-process Aerospace Thin-wall Parts

In the field of aerospace,aluminum alloy has been widely used in structural parts of aerospace because of its advantages such as high strength,low density and good cutting performance.However,due to the complex structure and weak rigidity of aerospace thin-walled parts,it is difficult to control the processing technology and quality,and the control of residual stress and machining deformation has not been well solved,which has become a technical bottleneck in the manufacturing and application of multi-process thin-walled parts.Therefore,based on the technological parameters affecting the residual stress of complex thin-walled parts with multiple processes,the superposition mechanism of residual stress was studied in this paper to obtain the method of controlling the residual stress and machining deformation.The main research work and results are as follows:(1)This paper firstly studies the influence of single process milling on the superposition and generation of residual stress.Starting from plane milling,the superposition simulation of thermal residual stress of cutting force in a single process was carried out in Abaqus software.The results show that the thermal residual stress of cutting force at the load point is mainly tensile stress,while the residual stress of cutting force has both tensile stress and compressive stress,and the thermal residual stress is a nonlinear superposition relationship.Then,the superposition relation model of thermal residual stress of single process force was obtained by polynomial fitting method,and the influence ratio of milling force and heat effect on residual stress was calculated from the model.It was found that the influence of milling force was greater than that of milling heat during the formation of residual stress at the loading point,accounting for 55%-70%.For the surface,the residual stress corresponding to various UCV parameter combinations is obtained from the main parameters(f_z,R,ap,ae)of the ball head milling cutter undeformed chip volume(UCV).Then,a mathematical model of residual stress was constructed with UCV parameters as variables,and the influence coefficient of UCV parameters on residual stress was fitted with the stress data obtained from milling simulation as samples.It was found that ap and ae had greater influence on the maximum surface residual stress than f_zand R under the condition of constant processing efficiency(UCV).The parameter combination of large R,large f_z,small ae and small ap should be selected when making the milling plan.(2)On this basis,the influence of multi-process continuous loading on the superposition and redistribution of residual stress is studied.The superposition simulation of two processes was carried out in Advant Edge software.The initial residual stress of the blank is piloted,and then the milling load is carried out.The extrusion effect is generated by the milling load so that the residual stress of the workpiece is redistributed,and the influence law of the extrusion effect parameters(r_e,UCT,ap,Rc)on the residual stress is obtained.It is found that if only from the perspective of enhancing the extrusion effect,the large tip radius Rc,the large edge radius r_e(a blunt cutter),the small ap and the small f_zshould be selected as far as possible in the milling process,and the f_zshould be set as half of r_e.This combination can increase the proportion of residual compressive stress on the machined surface.The superposition and redistribution of residual stress of the simplified multi-process thin-walled parts are further studied.The results show that with the process of rough milling,fine milling and heat treatment,the peak value of the residual tensile stress decreases gradually(rough milling,fine milling and heat treatment,10%and 11%respectively).The finishing process can peel off the surface material with poor residual stress condition layer by layer and optimize the residual stress distribution on the workpiece surface(the tensile stress becomes smaller and the compressive stress becomes larger).The heat treatment process can improve the problem of residual stress concentration in milling process and optimize the overall residual stress of thin-walled parts.(3)Finally,the x-shaped multi-process aerospace thin-walled parts as the processing object,the residual stress mathematical model verification and residual stress control method application research.Using the milling parameter combination in the mathematical model of residual stress to process the complex surface of X pieces,the error of the model is within16%-39%under the given parameter range and applicable conditions.The effectiveness of the milling residual stress suppression method obtained from the mathematical model of the residual stress is also verified,and the residual stress of the complex surface is effectively controlled under the condition of high milling efficiency.According to the multi-process machining simulation analysis of X pieces,for thin-walled parts with flat surface composite structure,and the stiffness of surface features is far less than that of plane features,the symmetrical and preferential processing sequence with small stiffness features is more conducive to controlling the milling residual stress.In terms of the verification of stress inhibition method,this paper formulated a processing scheme based on the residual stress control method obtained in the study,and carried out the x-shaped multi-process aerospace thin-walled parts processing residual stress control experiment.By comparison,it was found that the residual stress and shape variables of X parts were effectively inhibited,reducing by19%and 14.5%respectively.In this paper,by means of experiment,simulation and mathematical model,the superposition generation rule and control method of the residual stress in the machining of thin-walled parts are studied from the aspects of plane,surface,single process and multi-process residual stress.Finally,the results are applied to the optimization of x-shaped multi-process spaceflight thin-walled parts.The experimental results show that the residual stress control method in this paper is feasible and effective.