Study On Mechanism And Experiment Of Pre-stressed Hardening Grinding Technology

The pre-stressed hardening grinding(PSHG),as an environment-friendly and anti-fatigue technology which is based on grinding hardening(GH)and the pre-stressed grinding(PSG)technical principles,integrates residual stress control,surface quenching and grinding.This study,the purpose of which is the PSHG practicability,was conducted with reference to the program supported by the National Natural Science Foundation of China:Research on mechanism and all surface integrity in pre-stressed hardening grinding new integrated process(Grant No.51375083).The major study contents are as follows.(1)The mechanisms of the PSHG conditions for the surface integrality index.In this study,the grinding depth and the pre-stress were chosen as two conditions for processing.The elasticity was applied to deriving the the mechanisms for the pre-stress to affect the grinding depth and the characteristic parameters of contact area.In addition,the mechanisms for the grinding depth and the pre-stress to affect the surface integrality index in the residual stress on the surface of a workpiece,the surface hardness,the surface roughness and hardening layer depth was interpreted.(2)The pre-stressed uploading device design and the derivation of formula for the pre-stress on the PSHG workpiece's surface.The study aims to design and develop two types of pre-stressed uploading devices,which own the functions of locating,clamping and imposing pre-stress.The analysis of the axial stress over the variable cross-section bar was applied to the formula for the pre-stress on the PSHG workpiece's surface.(3)The experiment of PSHG and its results.The grinding depth and the pre-stress,in this study,were two variables as preconditions for processing.The residual stress,the hardness,the roughness,the depth as well as the metallographic structure of the quench-hardening layer all served as the objectives.The results of the study as follows.In the experiment,1)steel 45 matrix microstructure is made up of ferrite and pearlite.The microstructure of the PSHG workpiece consists of hardened region,transitional region and matrix region.Martensite is the major component in the hardened region,while the transitional region displays a mixture of the ferrite and the martensite.2)PSHG workpiece can be hardened and which hardeness is almost three times of original hardness.With the rise of the pre-stress,the tensile stress of the workpiece surface descend,pressure stress of the workpiece surface increase;the pre-stress is on a rise and the surface hardness,roughness along with the depth of the hardening layer decline.Therefore,compared with GH workpiece,PSHG counterpart has much more fatigue strength,grinding burn resistance and high-quality surface finish.3)The residual stress,roughness and the depth of the hardening layer in all workpiece witnessed a rise due to the increase in grinding depth,while the surface hardness generated no regular chance.(4)The influence of the processing preconditions exert on the surface integrity index.Assisted by the Analysis of Variance,the study places the focus on the effects both the pre-stress and grinding depth exert on the residual stress on the surface of a workpiece,the surface hardness,the surface roughness and hardening layer depth.The results are as follows.In the experiment,1)the pre-stress and the grinding depth have a dramatic influence on the surface residual stress.The influence of the grinding depth is larger than the pre-stress.The pre-stress also exerts great influence on the surface hardness,But no effect exerted by the grinding depth is found.The pre-stress and the grinding depth place influence on the surface roughness.the influence of the pre-stress is smaller than the grinding depth.The grinding depth greatly affects the hardening layer depth,but no effect exerted by the pre-stress is found.2)The pre-stress,the strength of which reaches 74MPa,exerts tremendous effects on the surface residual stress and the surface roughness.The obvious influence of the surface hardness appears in case that the pre-stress rises up to 114MPa.3)The grinding depth,when 0.20mm?ap?0.40mm,the residual stress,roughness and hardening layer depth witnessed a dramatic rise due to the increase in grinding depth.When 0.40mm<ap?0.45mm,the surface roughness witnessed a dramatic rise due to the increase in grinding depth while the residual stress and hardening layer depth generated no obvious change.4)In this trial levels,The perfect influence of the processing preconditions exert on the surface integrity index is that pre-stress reaches 84MPa and grinding depth reaches 0.35mm.(5)The prediction for workpiece in surface integrity index under PSO_LSSVM(Particle Swarm Optimization_Least Squares Support Vector Machines).Four PSO_LSSVM models for prediction were established.In these models,the grinding depth and the pre-stress functioned as inputs,and the residual stress on the surface of a workpiece,the surface hardness,the surface roughness and hardening layer depth as outputs.A comparative analysis between PSO_LSSVM models and BP neural network counterpart was adopted in the thesis.The workpiece for experiment(sample)was divided into two sets,training set and test set.Four PSO_LSSVM models are characterized as fitting accuracy and prediction accuracy,showing the MAPE in both training and test sets in the four PSO_LSSVM models less than 5%.The analysis leads to the conclusion that PSO_LSSVM model is superior to BP neural network on the prediction accuracy and stability.Therefore,as for the residual stress on the surface of a workpiece,the surface hardness,the surface roughness and hardening layer depth,the prediction accuracy obtained by PSO_LSSVM model can meet the production demand in reality.