Roundness Error Analysis And Accuracy Control Of Thin-Walled Bearings In Hard Turning Process

Bearing is the key base component of the equipment manufacturing industry.As a new finish machining technology of hardened bearing rings,hard turning has advantages such high quality,high flexibility,high efficiency,low cost as well as improving rolling bearing fatigue life,compared with grinding.According to the technical requirements of hard turning for high precision thin-walled bearings,this thesis studied the influence of clamping methods,accuracy of locating face,cutting force etc.on roundness error of hard turned thin-walled bearing rings by using theoretical analysis,numerical simulation and experiment methods.The key contents and conclusions of this thesis are as follows:Reasonable clamping methods based on radial deformation in finish hard turning thin-walled bearing rings were analyzed and demonstrated.Firstly,a FEM model of hard turning hardened bearing steel was built for the sake of predicting circumferential cutting force and moment.Secondly,according to the balance between cutting force moment and clamping force moment,the minimum clamping force model for reliable holding of thinwalled bearing ring with 3-jaw chuck was proposed.Based on the elastic deformation theory of plane curved bar,an analytical model for calculating the radial elastic deformation of thin-walled bearing rings clamped by a 3-jaw chuck under minimum cutting force was put forward.The results showed that even though a thin-walled bearing ring was clamped with the minimal clamping force by a 3-jaw chuck,the radial deformation was larger than the roundness requirement of P4 grade precision bearing.Therefore,for the hard turning process of high precison thin-walled bearings,the magnetic chuck was recommended to clamp thin-walled bearing ring in axial direction to achieve tangential friction force,which could resist the cutting force and moment in hard turning process.Influence of locating and clamping face flatness on roundness error in hard turning thin-walled bearing rings under axial clamping by a magnetic chuck was investigated.Firstly,typical “saddle” profile of thin-walled bearing rings' clamping face was found by numerous flatness measurements.Secondly,by applying axial loading on clamping face as well as designing constraint,a FEM model of thin-walled bearing ring was established to reconstruct “saddle” shape of thin-walled bearing ring's clamping face.At last,the relationship between flatness error of thin-walled bearing ring clamping face and roundness error after hard turning was revealed according to the quantitative analysis of axial and radial deformation.The results showed that to ensure required roundness of hard turned bearing rings,it's essential to maintain excellent flatness of locating and clamping face when the magnetic chuck was adopted.Influence of back-off deformation on roundness error in hard turning thin-walled bearing rings under axial clamping by magnetic chuck was investigated.Firstly,cutting force of hard turning thin-walled bearing ring clamped by a magnetic chuck was measured,and radial back-off deformations along axial direction of thin-walled bearing ring under cutting force were calculated by FEM.Secondly,typical “8”-shape roundness profile was found by numerous roundness measurements of thin-walled bearing ring blanks,and an analytical model for demonstrating roundness profile evolution was built to reveal the roundness error reflection in hard turning thin-walled bearing rings.The results showed that nonlinear backoff deformation along axial direction would cause cylindricity error of hard turned thin-walled bearing ring clamped by a magnetic chuck.In addition,the “8”-shape roundness error of thin-walled bearing ring blank would be passed to the hard turned bearing ring due to back-off deformation,both in shape and phase position.The surface integrity and rolling contact fatigue performance of hard turned thin-walled bearing rings was studied.Firstly,measurements and tests were conducted to investigate surface integrity of hard turned thinwalled bearing rings,including surface roughness,micro hardness,micro structure,residual stress etc.Secondly,rolling contact fatigue life test was done based on bearings assembled from hard turned bearing rings.Accuracy and noise were measured before and after the fatigue life test.The results showed that the surface integrity of hard turned bearing rings was as good as the ground ones.Most importantly,the residual stress of the hard turned surface is compressive.The fatigue life testing results showed that hard turned bearings could maintain P4 grade accuracy even after twice of the designed fatigue life,which revealed the huge potential for utilizing hard turning as finish process to manufacturing precision bearings.This thesis also provided theoretical and experimental support for China's high-end bearing manufacturing industry to make a breakthrough.