【作者】 卢光辉；

【导师】 张雪萍；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2009， 硕士

【摘要】 磨削加工通常作为重要零件的最后一道精密加工工序,磨削加工工艺过程在零件表面形成表面粗糙度、微硬度、残余应力等表面完整性指标对零件的服役寿命与可靠性具有直接影响。目前工程应用中,通常只检测磨削零件的表面粗糙度等几何特征,而对表面层的微硬度、残余应力等物理性能却很少予以检测和控制,进而基于零件磨削加工表面完整性进行磨削零件寿命预测的研究还没有报道。本文将以实际工业中应用的轴承内圈为研究载体,基于实际磨削工艺加工过程形成的表面完整性,对零件滚动接触疲劳疲劳寿命进行预测研究。本文主要内容包括:首先,基于零件加工工艺过程形成的残余应力、显微硬度等表面完整性指标和断裂力学理论,建立了滚动接触疲劳萌生寿命和扩展寿命的预测模型,并修正L-P模型与之对比。与寿命试验数据进行对比验证表明,该寿命模型具有较高的预测精度。其次,以实际工业生产线上随机抽取的轴承内圈作为试样,较系统地测试了内圈试样滚道表面历经热处理、粗磨、精磨、超精四道工序时的表面层残余应力、显微硬度、表面粗糙度等表面完整性指标,着重分析了零件的表面层残余应力及其离散度历经各工序时的变化过程。研究结果表明:零件的表面层残余应力、显微硬度等物理性能指标具有离散性,并且其离散度随工序累积呈收敛趋势。这揭示了传统磨削工序能够使零件表面完整性逐步达到较好的一致性。最后,基于本文建立的滚动接触零件的寿命模型,分析了超精工序后零件表面层残余应力、显微硬度及其离散度对零件滚动接触疲劳萌生寿命和扩展寿命的影响规律;并对超精磨削零件的疲劳寿命进行了预测,根据类似工序的轴承寿命试验数据,对预测结果进行了间接的验证。预测结果与实验结果比较吻合。基于磨削加工零件表面完整性的寿命预测结果表明:残余应力和显微硬度的最大峰值及其沿深度的分布都对零件的疲劳接触寿命都具有较大影响,而残余应力对疲劳寿命的影响更大;超精磨削工序后零件表面层残余应力最大峰值的标准差仅为20MPa,即只有平均值的16%,而试样的疲劳寿命极差却高达4倍。本文从磨削工艺角度揭示了零件使用寿命离散度较大的原因,提供了基于工艺过程提高零件使用可靠性的工艺控制途径,因此对延长精密零件(诸如轴承、齿轮等)的服役周期具有很好的科学价值,并对实际工业生产线的改善和优化具有工程指导意义。更多还原

【Abstract】 Usually,grinding process is the finish process of key component, some indexes of ground components surface integrity,such as surface finish,microhardness and residual stress,have direct and important influence on the service life and reliability of components.Presently,in engineering applications,routine test items is only limited to some geometrical features such as surface roughness,however,physical properties such as surface layer micro-hardness and residual stress are seldom inspected and controlled.Furthermore,there is few research on life prediction of ground components based on ground surface integrity is reported.In this paper,bearing rings are randomly selected from a industry production line as the samples,and the rolling contact fatigue (RCF) lives of ground samples is predicted based on the ground surface integrity.Main contents and conclusions are as follows:Firstly,based on surface integrity induced by machining processes and fracture mechanics,a RCF crack initiation life and propagation life prediction model is propsoed and compared with a Lundberg—Palmgren RCF life model.Comparative validation with experiment life shows that using this method the higher forecasting accuracy can be acquired.Secondly,bearing rings are randomly selected from industry production line as the samples,and some indexes of samples surface integrity,such as surface finish,micro-hardness and residual stress,are systemically investigated when samples experience four sequential processes:heat treatment,rough grinding,fine grinding and superfinish grinding,and emphatically analyzes the process of changes of surface layer residual stress and its scatter.The analysis shows that each surface integrity indexes have scatters,and the scatters are gradually converging with the processes cumulate.This reveals that a good consistency surface integrity can be gradually acquired by the tradition grinding processes.Finally,based on the proposed models,the effects of residual stress and microhardness of superfinish ground samples surface layer on RCF crack initiation lives and propagation lives are analyzed,and the fatigue lives of superfinish ground samples are predicted and indirectly validated by experiment lives of bearing with similar machining processes.The predicted and experimental results match well.The predicted results based on ground components surface integrity show that:the Maximum peak and distribution of both residual stress and microhardness have important effect on RCF life,and the effect of residual stress on RCF life is more significant than that of micro-hardness; the standard deviation of surface residual stress after superfinish grinding process is just 20MPa,only 16%of mean residual stress,but the life range of the four superfinish ground samples is higher than 4 times.This paper,from the perspective of grinding process,reveals the reason of why the component lives have great scatter,and offer a possible approach to enhance the reliability of components by manufacturing process control. Therefore,the result of this paper has a good scientific value of improving the service life of precision components such as bearings, gears,and also is a significant guide of improving and optimizing the practical production line.更多还原