Residual Stress Prediction of Weak Stiffness Revolving Parts and Multi-objective Optimization of Process Parameters

Author:Zhang Cheng Zuo

Supervisor:ma shu yuan lu ji ping

Database:Doctor

Degree Year:2017

Download:

Pages:148

Size:5644K

Keyword:

Rotational parts are widely used in transmission system and support system of many fields(e.g.,vehicle and aerospace).The transmission accuracy,service life and reliability directly affected machining accuracy of these artifacts.With the proposition of high-power density,the weight of product is decreasing,and the rigidity is weakening.Concomitantly,the problems,including large deformation in the process of machining and the reduction of yield,are showing up one by one.Meanwhile,these parts are usually applied in dreadful conditions like alternating load and severe contact rolling friction which seriously affect the operation performance.Therefore,it is urgent to optimize the processing technology since it can enhance the surface quality and increase service life and then improve modern high speed motor vehicle performance index.This paper focuses on the cylindrical turning process of weak stiffness revolving parts based on analytical modeling and experimental study,which has made a relatively deeper research on the theory of metal cutting and residual stress distribution.Then,the processing technological parameters optimization were carried on to provide important theoretical support for the process capability improvement.The main work of this dissertation is as follows.1.The effect of friction between tool and work-piece on residual stress profile and the insufficient of the current tool-chip friction model were analyzed firstly.Then,a new local friction law was established based on theoretical analysis and experimental verification to characterize the correlation of local friction coefficient and the local friction parameters.The effect of cutting parameters on the stress distribution,local friction coefficient distribution,cutting forces and contact length was evaluated.Numerical results calculated by the proposed model were compared with the experimental data.The results show that the proposed model has good predictive ability,which provides the basis for further establishing the thermal mechanical model of metal cutting process.2.Dynamic characteristics of the second shear deformation zone were analyzed comprehensively and quantitatively firstly.A new flow-zone model has been proposed to analyze the thermo-mechanical effects of friction at the tool-chip interface.The analytical expressions of velocity and shear strain rate in the sticking region,the transition region and the sliding region were established respectively,revealing the nonlinear flow characteristics of the chip on rake face in detail.Based on the local friction law,local friction coefficient and contact stresses were described and analyzed.The analytical model of cutting temperature field which considering local friction characteristics were established by introducing the effect of the nonlinear flow characteristics and contact stresses distribution on friction heat source intensity.The cutting force and temperature with and without taking flank wear and edge radius into account were predicted,and with the results were used to compare with the experimental measurement.3.The force situation of tool-chip-workpiece system were analyzed comprehensively.Then,the thermo-dynamic conditions of the primary shear plane and machined surface are revealed based on thermo-dynamic models,and building contact stress distribution model were processed.Internal stress of workpiece caused by mechanical load and thermal load obtained on account of linear elasticity theory and heat-elastic-plastic mechanics theory.Afterwards,increment prediction model of residual stress was established by using Von Mises yield criterion and Prager follow-up hardening rules.Furthermore,the validity of the model was verified by comparing the experimental values and predictive values.4.Design and application of a novel special clamping device has overcome the distortion problem of weak stiffness revolving parts.From analysis,it is indicated that the pre-stress caused by clamping force and centrifugal force has a significant impact on residual stress profile.Prediction model of 3D residual stress of turning surface were established by the method of discrete cutting edges.Experiments were conducted under different conditions to verify the prediction model.Finally the influence mechanism of clamping force,cutting speed and feed rate on residual stress profile were discussed respectively.5.Multi-objective optimization is explained and discussed.General multivariate regression predictive models was presented to characterize the relationship between machining parameters and key characteristic values of residual stress.Possible objective functions appropriate for industrial applications are discussed,and the multiple objectives selected for this study are justified.The objectives for this model are to minimize the tensile peak residual stress at the surface and maximize the compressive peak residual stresses and processing efficiency.Firefly Algorithm(FA)used to conduct the multi-objective optimization scheme was investigated,and the results for this scheme were presented.