Liu Hongguang, Zhang Jun, Xu Xiang, Qi Yutong, Liu Zhechao, Zhao Wanhua
School of Mehcanical Engineering, Xi'an Jiaotong University, Xianning West Road 28, Xi'an 710049, China.
State Key Laboratory for Manufacturing System Engineering, Xi'an Jiaotong University, Yanxiang Road 99, Xi'an 710054, China.
Materials (Basel). 2019 Jul 24;12(15):2348. doi: 10.3390/ma12152348.
This paper aims at investigating the change in material behavior induced by microstructure evolution during high-speed machining processes. Recently, high-speed machining has attracted quite a lot of interest from researchers due to its high efficiency and surface quality in machining large-scale components. However, the material behavior could change significantly at high-cutting speeds compared to the conventional cutting conditions, including their microstructure and t mechanical response. This is due to the basic physics of material at microscopic levels with high strain, high strain rates, and high temperatures. In this study, the dislocation density-related microstructure evolution process and mechanical behavior of OFHC (Oxygen-free high-conductivity) copper in high-speed machining with speeds ranging from 750 m/min to 3000 m/min are investigated. SEM (Scanning Electron Microscope) and advanced EBSD (Electron Backscattered Diffraction) techniques are used to obtain high-quality images of the microstructures and analyze the dislocation density and grain size evolution with different cutting speeds. Moreover, as material plasticity is induced by the motion of dislocations at micro-scales, a dislocation-density based (DDB) model is applied to predict strain-stress and microstructure information during the cutting process. The distributions of dislocation densities, both statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs), are obtained through simulation and experimentation, respectively. The results show that the fluctuation in the cutting forces at high cutting speeds is induced by the specific evolution and distribution of the dislocation density under high strain-rates, and the periodical distribution of sub-surface and fracture behavior during chip separation, which are also found to be influenced by the evolution of the dislocation density.
本文旨在研究高速加工过程中微观结构演变引起的材料行为变化。近年来，高速加工因其在加工大型零件时的高效率和表面质量而引起了研究人员的广泛关注。然而，与传统切削条件相比，在高切削速度下材料行为可能会发生显著变化，包括其微观结构和力学响应。这是由于材料在微观层面上的基本物理特性，即高应变、高应变速率和高温。在本研究中，研究了无氧高导电率（OFHC）铜在750米/分钟至3000米/分钟速度范围内高速加工时与位错密度相关的微观结构演变过程和力学行为。使用扫描电子显微镜（SEM）和先进的电子背散射衍射（EBSD）技术来获取微观结构的高质量图像，并分析不同切削速度下位错密度和晶粒尺寸的演变。此外，由于材料的塑性是由微观尺度上位错的运动引起的，因此应用基于位错密度（DDB）的模型来预测切削过程中的应变-应力和微观结构信息。分别通过模拟和实验获得了统计存储位错（SSD）和几何必要位错（GND）的位错密度分布。结果表明，高切削速度下切削力的波动是由高应变速率下位错密度的特定演变和分布以及切屑分离过程中亚表面和断裂行为的周期性分布引起的，这些也被发现受位错密度演变的影响。
