Molecular dynamic simulation for nanometric cutting of single-crystal face-centered cubic metals
© Huang and Zong; licensee Springer. 2014
Received: 1 September 2014
Accepted: 13 November 2014
Published: 18 November 2014
In this work, molecular dynamics simulations are performed to investigate the influence of material properties on the nanometric cutting of single crystal copper and aluminum with a diamond cutting tool. The atomic interactions in the two metallic materials are modeled by two sets of embedded atom method (EAM) potential parameters. Simulation results show that although the plastic deformation of the two materials is achieved by dislocation activities, the deformation behavior and related physical phenomena, such as the machining forces, machined surface quality, and chip morphology, are significantly different for different materials. Furthermore, the influence of material properties on the nanometric cutting has a strong dependence on the operating temperature.
KeywordsNanometric cutting Single crystal Fcc metal Molecular dynamics
As one important enabling technology for achieving superior surface finish, single point diamond tool-based nanometric cutting has been widely applied in various industrial fields [1–3]. However, the lack of fundamental understanding of machining mechanisms greatly hinders the further development of the nanometric cutting machinability. In the conventional macroscopic machining where the edge radius of cutting tool (i.e., tool sharpness) is significantly smaller than the nominal depth of cut, the work piece is usually considered to be composed of continuous, isotropic, and defect-free materials. However, in the nanometric cutting, the work piece materials are mainly discrete, anisotropic, and not defect-free, because of the comparable edge radius of cutting tool with the nominal depth of cut. Consequently, the well-established conventional macroscopic machining mechanisms may be not be suitable for the interpretation of the nanometric cutting, and thus, a fundamental understanding of the nanometric cutting mechanisms is essentially required to facilitate the nanometric cutting technique.
The nanometric cutting mechanisms typically include elastic and plastic deformation of work piece material, friction and wear, machining forces, formation of machined surface and chip, etc. Since the nanometric cutting process is inherently discrete rather than continuous because of its ultra-small nominal depth of cut, which is of a few atomic layers, the experimental investigation of the nanometric cutting mechanisms is severely limited by the resolution of machining and measurement equipments, and the theoretical study based on the continuum mechanics such as finite element method cannot be used for the analysis of nanometric cutting process. Molecular dynamics (MD) has been demonstrated as one powerful tool for elucidating the nanometric cutting mechanisms, because it can trace the trajectories of individual atoms at a very short time step through the time integration of Newton's second law, which enables the monitoring of ongoing nanometric cutting process. Furthermore, workpiece with different microstructures and dimensions, as well as cutting tool with different geometries, can be constructed easily through modeling; and the machining parameters such as nominal depth of cut and cutting velocity can be adjusted conveniently for each nanometric cutting simulation. In the past few decades, many researchers have employed MD simulation to investigate the nanometric cutting mechanisms [4–10], and some typical work is outlined as follows. Komanduri et al. carried out MD simulations to analyze the effects of tool cutting edge radius and depth of cut in nanometric cutting . Pei et al. further investigated the influence of rake angle on the nanometric cutting of copper . Lai et al. studied the phase transformation during nanometric cutting of germanium . Olufayo et al. addressed the brittle-ductile transition in nanometric cutting of mono-crystalline silicon . Moreover, Promyoo et al. investigated the effects of tool rake angle and depth of cut on the cutting forces and chip formation in nanometric cutting .
The previous works have provided valuable insights into the nanometric cutting mechanisms. However, less attention has been paid to the influence of workpiece materials' properties on the nanometric cutting. It is well known that the nanometric cutting is a highly coupled process between workpiece material and cutting tool, because of the comparable edge radius of cutting tool with the nominal depth of cut. Consequently, the workpiece materials' properties may play a crucial role in the nanometric cutting process, in addition to the geometry of cutting tool. On the other side, it has been demonstrated that by alloying with aluminum, the properties and subsequent deformation behavior of copper can be significantly changed . Thus, it is interesting to know whether the nanometric cutting mechanisms are also different for workpiece materials with different properties. In the current study, we perform MD simulations of nanometric cutting of single crystal aluminum and copper, which have the same face-centered cubic (FCC) lattice structure but different material properties.
In this work, the cutting velocity and the nominal depth of cut are fixed as 20 m/s and 2 nm, respectively. In order to investigate the chip formation mechanisms, the total cutting length is configured as 60 nm, which is larger than the length of work piece. Accordingly, the time step in any MD simulation is fixed as 5 fs to accelerate the simulation time, given the large cutting length. Two temperatures of 3 and 300 K are considered to evaluate the thermal fluctuation effect. While defect evolution plays an important role in the plastic deformation of metallic materials, identifying the types of defects is crucial for elucidating the nanometric cutting mechanisms. As compared to the centro-symmetry parameter  which provides values in different ranges for different types of defects, the technique of common neighbor analysis (CNA) provide unambiguous values for specific defects . Therefore, the CNA is adopted to analyze the lattice defects generated within the work piece during nanometric cutting.
Results and discussion
Material-dependent nanometric cutting
Temperature increments after nanometric cutting operated in different temperatures
Ambient temperature (K)
Temperature increment (K)
Influence of thermostat layer
The plastic deformation of fcc metals (aluminum and copper in the current study) under nanometric cutting is achieved by dislocation activities, i.e., dislocation nucleation and motion.
The dislocation activities are less pronounced in the aluminum than that in the copper, which consequently results in smaller machining forces, fewer volume of surface pile up, smaller temperature increment, but larger volume of chip.
The influence of material properties on the nanometric cutting has strong dependence on the operating temperature due to the inevitable thermal fluctuation.
The presence of thermostat layer in the MD model has some influence on deformation behavior of workpiece, machining force, and chip profile.
The authors greatly acknowledge the financial supports from the Natural Science Foundation of China (No. 51175127), the Fundamental Research Funds for the Central Universities (No. HIT.BRETIII.201412), and the Laboratory of Precision Manufacturing Technology in China Academy of Engineering Physics (ZZ13022). The authors also acknowledge Dr. Junjie Zhang for establishing the MD model.
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