Papers by Keyword: Primary Shear Zone

Abstract: A new modified model based on the non-parallel primary shear zone is presented in this paper. Experiments showed that the primary shear zone in cutting process wasn’t an absolutely parallel-sided zone. In fact, there are small inclined angles in the primary shear zone. Therefore, in this paper, a correction coefficient is proposed to predict cutting forces exactly. The coordinate mapping approach is adopted to obtain the correction coefficient and the software MATLAB is utilized to predict cutting forces. The material of stainless steel 316L is used to validate the modified model. By comparison between predicted analysis and experimental results, the proposed model shows good agreements with experiments.

Abstract: A deep understanding of adiabatic shear fracture (ASF) during serrated chip formation is essential to explore the material removal mechanism of high speed cutting (HSC). This paper aims to reveal the microscopic details of ASF in serrated chips. The material to investigate was AISI 1045 steel of different hardness grades, and the micro-structural analysis was conducted using optical and scanning electronic microscopes. The investigation showed that at the hardness of HRC50, most fractured surfaces were covered by a large number of dimples elongated along the shear direction, indicating that the fundamental cause of the serrated chip generation is the deformation localization of the adiabatic shear followed by ductile damage fracture in primary shear zones. The higher the material hardness is, the easier the adiabatic shear and ductile fracture take place. A new model was then proposed to interpret the ductile fracture due to adiabatic shear governed by the nucleation, growth and coalescence of micro-voids during serrated chip formation.

Abstract: The microstructure observation and microhardness measurement were performed on the adiabatic shear bands in primary shear zone in the serrated chips formed during high speed machining of two tempering hardness of hardened high strength steel under different cutting speeds by optical microscope, SEM, TEM and microhardness tester. The investigation results show that two types of adiabatic shear bands are formed as cutting speed increases. One is deformed band with heavy elongated microstructures generated under lower cutting speed, another is transformed band with fine grains under higher cutting speed. The increase of the cutting speed little influences on the microhardness in the transformed bands, and the microhardness in deformed band results from strain hardening, whereas transformation hardening leads to very high microhardness in transformed band.

Abstract: A method was presented for calculating the temperature distribution of primary shear zone in orthogonal high speed cutting based on the non-uniform volume moving heat source. The temperature distribution of primary shear zone in orthogonal high speed cutting was calculated by the dynamic plastic constitutive relationship and the distribution of strain and strain rate of primary shear zone. The results show that the temperature distribution of primary shear zone is uneven, from the original plane to the cutoff plane, the cutting temperature increases continuously. In the middle of primary shear zone, the change of cutting temperature is larger, at the position near to original plant and cutoff plane, the change of cutting temperature is smaller. The cutting temperature increases with the increase of cutting speed and cutting depth, but decreases with the increase of rake angle. The comparison with existing method shows that the method presented in this paper is not only available, but also simple, convenient and more accord with the fact of orthogonal high speed cutting.

Abstract: The metallurgical observations of microstructure characteristics of the adiabatic shear bands(ASB) within the primary shear zones of the serrated chips produced during high speed machining high strength steel have been performed by using optical microscope, SEM and TEM. The observations showed that the microstructure between the matrix and the center of the ASB gradually was changed, the fine equiaxed grains appeared with size of about 0.4～0.6μm in the center of the adiabatic shear band. The serrated chip formation was likely due to material softening that occurred in the primary shear zones. The microstructural development of dynamic recovery and rotational dynamic recrystallization is the dominant metallurgical process leading to material softening in primary shear zone during high speed machining. A model of microstructural development in primary shear zone during serrated chip formation in high speed machining was suggested by analyzing material softening mechanism.