Prediction Of Adiabatic Shear In High Speed Machining Based On Linear Pertubation Analysis

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.