【作者】 李国和；

【导师】 王敏杰；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 高速切削加工已经成为机械加工领域的主流技术。许多被加工材料在高速切削过程中都会发生绝热剪切,形成锯齿形切屑。高速切削过程中绝热剪切的出现,一方面可能会引起切削力的高频振动,加剧刀具磨损,影响加工表面质量;另一方面则可能会成为切屑裂纹或破坏的先导,有助于实现自动化加工中的自然断屑。无论绝热剪切对材料切削加工性的影响是正面的还是负面的,都需要判断绝热剪切在什么样的切削条件下发生,以便利用或避免这种现象。因此进行高速切削过程中绝热剪切的预测研究,对于促进高速切削技术的发展和应用都具有重要的理论意义和实用价值。基于以上认识,本文采用理论建模与实验研究相结合的方法,开展了高速切削过程中绝热剪切的预测研究,主要内容如下:首先,进行了高速切削过程中绝热剪切的建模及其线性扰动分析。考虑压应力的影响,建立了高速切削过程第一变形区的应力状态模型。针对第一变形区的压缩剪切复合变形过程,建立了连续介质力学基本方程。通过线性扰动分析,获得了绝热剪切临界判据,并分析了各因素对高速切削过程中绝热剪切的影响。该判据考虑了切削过程中第一变形区压应力的影响,克服了最大剪应力准则经验性强的不足。其次,采用分离式霍普金森压杆和电子万能试验机进行了淬硬45钢和Fe-36Ni因瓦合金的动态和准静态力学性能试验,得到了它们在高温和高应变率下的动态力学性能。采用改进的Johnson-Cook模型拟合了淬硬45钢和Fe-36Ni因瓦合金的动态塑性本构关系。提出了考虑硬度的材料动态塑性本构关系建立方法,建立了淬硬45钢考虑硬度的动态塑性本构关系。再次,提出了基于不均匀体积移动热源的高速切削第一变形区温度分布计算方法和高速切削过程中绝热剪切临界状态第一变形区厚度的计算方法,进行了高速切削第一变形区剪应变、剪应变率、温度和压应力的计算,并分析了切削条件对高速切削第一变形区变形条件的影响。最后,根据绝热剪切临界判据,应用材料动态塑性本构关系,通过变形条件和切削条件的转换,建立了高速切削过程中绝热剪切临界切削条件的预测模型,实现了淬硬45钢和Fe-36Ni因瓦合金的绝热剪切临界切削条件的预测,并通过正交切削实验和金相观测对预测结果进行了验证。更多还原

【Abstract】 High speed machining has been becoming the mainstream technology in the field of machining. The adiabatic shear, which may produce serrated chip, usually occurs for a large number of materials in high speed machining. The appearance of adiabatic shear in high speed machining may lead to the high frequency libration of cutting force, the increase of tool wear and the reduce of finished surface quality. On the other hand, it may be beneficial to the rupture of chip and in favor of the automation machining. In order to control or utilize this phenomenon effectively, the adiabatic shear critical conditions in high speed machining need be known in advance, whatever its influence on the machinability of materials is positive or negative. Therefore, there are the momentous significances in both theoretical and practical for the prediction of adiabatic shear on the development and application of high speed machining technology.Based on the above-mentioned understanding, by theoretical model and experimental study, this dissertation has launched the prediction of adiabatic shear in the high speed machining, the main research contents are as follows:Firstly, a new adiabatic shear model in high speed machining is established and analyzed by linear perturbation analysis. Considering the compression stress in orthogonal high speed cutting, a stress model of primary shear zone is built. The continuum mechanics basic equations of the compress-shear deformation of primary shear zone are presented. A new critical criterion of adiabatic shear, which considers the compression stress and avoids the dependence of the empirical of the most shear stress criterion, is obtained by linear perturbation analysis. Moreover, the influences of all kinds of factors on adiabatic shear in high speed machining are analyzed.Secondly, Dynamic and quasi-static state mechanical properties experiments of hardened 45 steel and Fe-36Ni invar alloy are performed by Split Hopkinson Pressure Bar and electronic universal testing machine, the dynamic mechanical properties under high temperatures and high strain rates are obtained. The constitutive relationships of hardened 45 steel and Fe-36Ni invar alloy are fitted by the improved Johnson-Cook model. A constitutive equation considering material hardness is proposed and that of hardened 45 steel is given.Thirdly, a calculation method for the temperature distribution of primary shear zone in orthogonal high speed cutting based on the non-uniform volume moving heat source and a calculation method for the thickness of primary shear zone at the critical state of adiabatic shear are presented. The shear strain, shear strain rate, temperature and compression stress of the primary shear zone in high speed machining are calculated and the influences of cutting conditions on deformation conditions are also analyzed.Lastly, based on the critical conditions of adiabatic shear, applying the dynamic plastic constitutive relationship and through the conversion of deformation conditions and cutting conditions, a prediction model of the critical cutting conditions of adiabatic shear in high speed machining is established. The critical cutting conditions of adiabatic shear of hardened 45 steel and Fe-36Ni invar alloy are predicted, the prediction results are validated by the orthogonal cutting experiments and metallographic observations.更多还原