Study On The Influence Of Grinding Chatter On Residual Stress Of Workpiece Surface In Small Depth Of Cut

This paper mainly studies the influence mechanism of grinding chatter on the residual stress of workpiece surface under the condition of small cutting depth.Grinding chatter is a strong self-excited vibration,which originates fromthe grinding wheel and workpiece surface.It makes the wheel's dynamic waviness of the penetration depth on the ground workpiece.Thus,the grinding force and temperature gradient of workpiece surface can be affected accordingly.Moreover,the distribution of the residual stress will be varied as well.Residual stress is an important index to measure the workpice's surface quality.With the continuous development of science and technology,the requirement for the processing accuracy and surface quality of parts becomeshigher then before.As the last process of precision and ultra-precision processing,it directly determines the surface quality of the workpiece,which makes it particularly important to control the residual stress of grinding workpiece.In this paper,the theoretical prediction model of residual stress coupled with chatterfactor for the grinding system is established.Meanwhile,the influence mechanism of grinding chatter on the workpiece's surface residual stress under small cutting depth is analyzed and compared with experimental results.The main findings are drawn as follows:(1)The grinding system is assumed to be a spring mass system.Afterwards,the two-degree-of-freedom dynamic model is established for the next step.The time delay differential equation is used to solve the dynamic grinding force and to solve the dynamic temperature field.Based on the single abrasive model,the single abrasive grinding force is divided into three parts,which are the sliding force,the ploughing force and chip force respectively.With the consideration of the random distribution of abrasive particles on the grinding wheel,the inconsistency of the undeformed chip thickness is found in the cutting process.As a result,the Rayleigh probability density function is introduced to calculate the average grinding force of a single abrasive particle so as to the mechanical stress.(2)Based on jeager's theory of moving heat source,a triangular heat source model is selected according to the characteristics in small grinding depth.According to the heat conduction theory of metal materials,a two-dimensional plane differential equation within the grinding chatter is established.The workpiece is discretized into a two-dimensional planar grid structure.The finite difference equation is established based on the idea of difference quotient toreplace the derivative,which can solve the workpiece's dynamic temperature field distribution under different chatter strengths.(3)Based on single abrasive cutting process and Hertz rolling-sliding contact model,a single abrasive contact model is established.The Boussinesq solution is used to integrate the normal and tangential stress distribution of a single abrasive particle to obtain the mechanical stress at any point in the workpiece due to the action of a single abrasive particle.Afterwards,the thermal stress caused by the action of temperature in the workpiece is calculated based on the Timoshenko's thermo-elastic theory.For the following step,the hybrid algorithm proposed by Mcdowell is introduced.And the residual stress theoretical prediction model is established when the follow-up hardening criterion and von Mises yield criterion are combined together.The mechanical stress and thermal stress are brought into the residual stress theoretical prediction model respectively.Furtherly,the residual stress distribution of workpiece surface within the chatter factor for the associated grinding system is obtained.Finally,the influence mechanism of grinding chatteron workpiece's residual stress is analyzed by changing the contact stiffness and the grinding depth.(4)Groups of plane grinding experiments are carried out according to the processing parameters selected by the simulation model.The dynamic grinding force and residual stress distribution of workpiece surface are measured under different chatter strengths,which are applied to validate the simulation results.It shows that the chatter strength goes up with the increase of the contact striffness.Thus,the contact stiffness proves to be an important parameter to characterize the chatter strength,which is verified by experiments.The stronger chatter between the grinding wheel and the workpiece surface increases the influence of extrusion friction between the grinding wheel and the workpiece surface.Afterwards,temperature gradient will increase as well in the depth direction.Therefore,the thermal stress on the surface of the workpiece plays a major role,and it appears as residual tensile stress.Moreover,the mechanical stress on the sub-surface plays a major role,and it appears as residual compressive stress.With the increase of the chatter strength,both residual tensile stress and residual compressive stress increase.