Investigation On Microstructure Distribution Of Strengthened Ground Workpiece's Metamorphic Layer And Its Surface Integrity Coupled With System's Dynamic Factor

Grinding vibration is a kind of system's vibration phenomenon,which occurs in the workpiece's material removal process.It always causes the variation of the grinding system's dynamic parameters.As a result,the ground workpiece's surface quality can be affected especially for the system's chatter.Meanwhile,the system's chatter can also influence the distribution of the metamorphic layer,which origins from the grinding hardening process.The grinding hardening strengthened is a green multiple coupling technology,which is commonly applied into the workpiece's material removal.And the technology cleverly integrates the physical metallurgy and the grinding technology.The heat generated from the coupled thermal-mechanical effect is utilized directly.Afterwards,the microstructure of the workpiece is transformed accordingly.And the metamorphic layer is formed as well.Meanwhile,the chatter phenomenon can be observed in the grinding hardening process inevitably,which makes the system with the characteristic of dynamic time-varying.The distribution of the hardened layers are influenced by the strengths of system's dynamic characteristic through the thermal-mechanical effect.Therefore,the ground workpiece's surface quality can be affected as well.Based on the above analysis,a multiple coupled model is established in this article,which includes the dynamic grinding force,the dynamic grinding temperature distribution,the dynamic micro structure transformation and the surface topography due to the dynamic combined grinding hardening process.Moreover,the proposed model is combined with the grinding experiment.Thus,the influence mechanism of system's chatter on the workpiece's surface strengthened layer can be researched in depth.It is of significance to realize the control on the quality of grinding hardening metamorphic layer in both theory and practice field.The main research is summarized as follows:(1)The dynamic model is established in terms of the material removal process in the dynamic grinding hardening strengthened process.The combination between the numerical and analytical method is utilized in the time domain.Afterwards,the chatter information and the distribution of the grinding force can be obtained in the grinding hardening process.Based on the established dynamic model,the criteria for the dynamic stability and the reliability are deduced respectively in the frequency domain.It can be found that the contact stiffness between the wheel and the workpiece can be a standard to measure the system's chatter strength.(2)When the system's dynamic characteristics are coupled into the analysis of the temperature field,the mathematic temperature model for the dynamic grinding hardening process can be established by the finite difference method.Moreover,the analytic model is applied to testify the validity of the finite difference method.Based on the established three dimensional temperature distribution,it can be researched that the dynamic temperature is in a zonal distribution,and the distribution varies with the movement of the grinding zone.Moreover,it is in a elliptic distribution in the width direction.Meanwhile,the dynamic temperature distribution and the thickness of the hardening layers are compared respectively under different chatter strengths.Besides,the temperature distributions under different grinding depths are calculated as well.(3)Based on the calculated thermal-mechanical distribution,an in-depth investigation is conducted on the dynamic formation of metamorphic layer on the hardened workpiece's surface by the combination of cellular automata and finite difference method.Afterwards,the detailed distribution information of austenization,the martensite transformation and the carbon diffusion can be obtained.Meanwhile,the effect regulation of system's chatter strength on the size of austenite grain and martensite content is researched as well.Besides,the distribution of martensite content is compared under different chatter strengths.It can be found that the grinding chatter can enlarge the thickness of the metamorphic layer by the interaction effect caused by the grinding chatter.However,the hardening effect is weakened by the grinding chatter.(4)When the wheel's grits non-Gaussian distribution and the system's dynamic hardening characteristic are considered,the modelling on the ground workpiece's surface topography is established based on the dynamic hardening characteristic of the metamorphic layer.Meanwhile,the dynamic hardness distribution is researched accordingly.Then the spring back value can be obtained based on the dynamic hardness distribution,which can be regarded as an input in the calculation of the workpiece's surface topography.The influences of system dynamic characteristic strength on the ground workpiece's roughness are compared under different grinding depths.Furthermore,the influence of grinding chatter on the workpiece's surface topography is investigated as well.(5)The grinding hardening experiments are conducted under different chatter strengths.Based on the tension stiffening effect and the experiment observation,it can be found that the chatter strength can be controlled by adjusting the prestress.Therefore,microstructure distribution of the workpiece's metamorphic layer and the micro workpiece's surface topography are observed under different chatter strengths controlled by the prestress.Meanwhile,the distribution of hardened workpiece's surface roughness and the hardness are observed experimentally.The influence mechanism of system dynamic characteristic on the distribution of workpiece's metamorphic layer and the hardened micro workpiece's surface topography is furtherly validated accordingly.