Cutting Speed in Nano-Cutting as MD Modelling Parameter

Cutting Speed in Nano-Cutting as MD Modelling Parameter

Nikolaos E. Karkalos (National Technical University of Athens, Athens, Greece), Angelos P. Markopoulos (National Technical University of Athens, Athens, Greece) and Dimitrios E. Manolakos (National Technical University of Athens, Athens, Greece)
DOI: 10.4018/IJMMME.2016010101
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In order to manufacture parts with dimensions of nanometres, high–technology equipment is required. There is a demand to study nano-metric cutting mechanisms and phenomena appearing in this level. However, experiments are difficult to be realized, so computational methods are employed. Nano-scale cutting involves workpiece deformation in only a few atomic layers from the workpiece surface; at this scale the continuum theory cannot be used, so methods like finite elements are not sufficient. Molecular Dynamics is a method increasingly used for the simulation of nano-cutting. However, the computational cost required is quite high. In an effort to reduce the time of the analysis, high or extremely high cutting speeds are used in the models. In this paper an analysis is presented where cutting speed is studied and its influence on the chip morphology and workpiece surface is investigated, for nano-cutting modelling of Cu with diamond tools. The results indicate that cutting speed influences the outcome of the analysis and more attention should be paid to the selection of this parameter.
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Nowadays, the always increasing needs in micro and nano-scale components and ultra high precision machined surfaces of state-of-the-art devices and experimental equipment dictate the thorough investigation of the parameters that affect the manufacturing processes in the micro and nano-scale. Moreover, the lack of sufficient experimental results due to the difficulties in constructing nano-machine tools and the high cost of manufacturing these machines, urges the researchers to conduct numerical simulations in order to predict the response of nano-scale systems, design suitable cutting tools and improve the efficiency of current manufacturing processes. Several numerical methods have been introduced in cutting analysis during the recent decades with satisfactory results.

Generally, in conventional manufacturing processes, the Finite Element Method (FEM) can be used to calculate cutting forces and temperatures and even residual stresses in the workpiece and the cutting tool (Markopoulos, 2012; Szabó and Kundrák, 2014). However, simulations of manufacturing processes in the micro- and especially in the nano-scale are impossible to be conducted with continuum mechanics assumptions and thus they are simulated using atomistic methods like the Molecular Dynamics (MD), the Molecular Mechanics or Monte-Carlo based methods. These methods are capable of predicting the interactions in the atomic scale and can account for various phenomena that are practically non-existent in macro-scale simulations. Molecular Dynamics is the most popular method in atomistic simulations of manufacturing processes as it is proven to be sufficient to make accurate calculations in the atomic level and can be used to understand the fundamental mechanisms of manufacturing processes.

Several manufacturing processes in nano-scale, namely turning, milling, grinding (Komanduri et al., 1997; Li et al., 2001; Lin et al., 2003), as well as scratching (Zhang et al., 2009; Du et al., 2013; Zhang et al. 2013) and indentation (Verkovtsev et al., 2013; Qiu et al., 2014) have been investigated by researchers using the MD method, even though experimental validation is not yet possible for the majority of the published work in the related areas. Generally, MD is a mature modelling method in various scientific areas but its application in manufacturing processes is comparatively recent. The first molecular simulations were conducted in Los Alamos National Laboratory where the Monte Carlo algorithm was developed. Belak and Stowers (1990) conducted the first studies in nano-scale manufacturing processes by investigating the nano-cutting of copper using a rigid infinite hard diamond cutting tool, both in 2D and 3D using the Embedded Atom Method (EAM) potential with a cutting speed of 100 m/s for various rake angles and depths of cut. Belak et al. (1993) also studied the nano-cutting of silicon with a deformable diamond cutting tool with a cutting speed of 540 m/s. Influenced by the early works of American scientific groups, several scientific groups in Japan started to conduct Molecular Dynamics simulations. In the area of nano-cutting, Ikawa et al. (1991) focused on the Cu-C interaction, conducting simulations at 20 m/s and 200 m/s cutting speeds investigating the effect of the minimum depth of cut and the ratio of depth of cut to the radius of curvature in the chip formation mechanism, the surface deformation and the specific cutting energy. Inamura et al. (1992) used computational models with fewer atoms in the workpiece than the previous models and presented a work for the transformation of an atomistic to an equivalent continuum model for the nano-cutting process. Shimada et al. (1994) used the MD method to simulate copper nano-cutting process using a 2D model and investigated the chip formation mechanism, the cutting forces and the specific cutting energy.

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