Papers by Keyword: Nanometric Cutting

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Authors: Seyed Vahid Hosseini, Mehrdad Vahdati, Ali Shokuhfar
Abstract: Today, there is a need to understand the micro mechanism of material removal to achieve a better roughness in ultra precision machining (UPM). The conventional finite element method becomes impossible to use because the target region and grids are very tiny. In addition, FEM cannot consider the micro property of the material such as atomic defect and dislocation. As an alternative, molecular dynamics (MD) simulation is significantly implemented in the field of nano-machining and nano-tribological problems to investigate deformation mechanism like work hardening, stick-slip phenomenon, frictional resistance and surface roughness [1]. One of the machining parameters than can affect nano-cutting deformation and the machined surface quality is tool nose radius [2]. In this paper molecular dynamics simulations of the nano-metric cutting on single-crystal copper were performed with the embedded atom method (EAM). To investigate the effect of tool nose radius, a comparison was done between a sharp tool with no edge radius and tools with a variety of edge radii. Tool forces, coefficient of friction, specific energy and nature of material removal with distribution of dislocations were simulated. Results show that in the nano-machining process, the tool nose radius cannot be ignored compared with the depth of cut and the edge of tool can change micro mechanism of chip formation. It appears that a large edge radius (relative to the depth of cut) of the tool used in nano-metric cutting, provides a high hydrostatic pressure. Thus, the trust force and frictional force of the tool is raised. In addition, increasing the tool edge radius and the density of generated dislocation in work-piece is scaled up that is comparable with TEM photographs [6].
Authors: Yu Lan Tang, Ying Chun Liang, X.D. Liu, J.H. Dou, D.X. Wang, J.W. Zhao
Abstract: A three-dimensional model of molecular dynamics (MD) simulation was employed to study the generation process of nanometric machined surfaces of monocrystalline copper. The model included the utilization of the Morse potential function to simulate the interatomic force between Cu-C and Cu-Cu. By analyses of the MD simulation snapshots of the various stages of the nanometric cutting process and local radial distribution function (RDF), the structure of the bulk and the machined surface with no change and that of the chip with minimal change were observed. Potential energy had significant fluctuations due to generation and propagation of dislocations around the tool. The elastic recovery along the machined surface of the work material was observed after the tool passed. Because the state of machined surface was an important influence on the performance and the physical and chemical properties of product, the effects of surface relaxation on the machined surface state were investigated under the vacuum condition.
Authors: Hong Wei Zhao, Lin Zhang, Peng Zhang, Cheng Li Shi
Abstract: A series of three-dimension molecular dynamics (MD) simulations are performed using hybrid potentials to investigate nanometric cutting process of single-crystal copper with diamond tool. The effect of tool geometry in nanometric cutting process is investigated. It is observed that with the negative rake angle, the volume of chips becomes smaller due to large hydrostatic pressure and plastic deformation generated in the subsurface layer. When the rake angle changes from -40° to 40°, the machined surface becomes smoother. Besides, the ratio of tangential force to normal force decreases with the increase of rake angle. In addition, the effect of clearance angle is analyzed and approximate entropy (APEN) is presented to denote the complexity and uncontrollability of the interactions between tool and workpiece with different clearance angles. With the decrease of clearance angle, the machined surface quality decreases with the local stress distribution in subsurface layer is uneven. An appropriate clearance angle not only keeps cutting force stable, but makes sure of the quality of machined surface as well.
Authors: Y. Zhao, Xun Li Wei, Yan Zhang, Feng He Wu, De Hong Huo
Abstract: Metallic glasses have a variety of excellent properties compared with the majority of conventional crystalline alloys, and have a broad application prospects in the military, aerospace and sports equipment. Cutting, as an efficient and high-precision machining process, is expected to be an important processing method for metallic glasses. Currently, investigation on cutting metallic glasses is in a nascent stage. Although the machining precision of several tens of nanometers has been achieved, its cutting mechanism remains unclear. In this paper, a molecular dynamics simulation of orthogonal nanometric cutting of metallic glass Cu50Zr50 was carried out.The material deformation, cutting force, and workpiece temperature distribution were studied at microscopic scale. It is found that the deformation accumulation first occurred on the tool rake face. Then with the cutting progressing, materials underwent stable plastic deformation in the shear zone. Analysis on cutting force shows that in the initial material deformation process the cutting force increases rapidly until the cutting process is stabilized, , and then it is reduced to a stable value. Finally, the temperature change of the workpiece during cutting was calculated, and the result shows that the maximum temperature reaches the glass transition temperature. Further, the radial distribution function analysis of workpiece was used to confirm the occurrence of the glass transition.
Authors: Yan Zhao, Yan Zhang, Ri Ping Liu
Abstract: Great prospect in ultra precision leads to the urgent requirement for the research on the nanometric machining of metallic glass (MG). Molecular dynamics simulation is carried out to find out the nanometric cutting mechanisms of MG. The MG workpiece, Cu50Zr50, is prepared using fast cooling simulation in isothermal-isobaric ensemble. Interactions of Cu and Zr atoms are described by Finnis-Sinclair potential. Morse potential is adopted for the interaction between the carbon atom in the diamond tool and the metal atom in the workpiece. Simulation results show that, different from cutting crystal material, there is not visible shear zone ahead of the tool. That is to say the mechanism in nanometric cutting MG may be plastic cutting.
Authors: Angelos P. Markopoulos, Kalliopi Artemi L. Kalteremidou
Abstract: In this paper the modelling and simulation of nanometric cutting of copper with diamond cutting tools, with the Molecular Dynamics method is considered. A 2D model of orthogonal cutting, with nanoscale features, is constructed. In this model two different potential functions to simulate the interaction of the atoms within the workpiece and between the workpiece and the tool are used; LennardJones potential for the former and the Morse potential for the latter case. From the simulation the chip formation can be observed and analysed. The model is used for the simulation of nanocutting with three different nanometric depths of cut from which the cutting forces are calculated and compared. With increasing depth of cut, cutting forces also tend to increase. The proposed model can be successfully used for the modelling of cutting operations that continuum mechanics cannot be applied or experimental and measurement techniques are subjected to limitations or it is difficult to be carried out, such as ultra-precision machining, micro-cutting, miniaturization and nanoscale cutting.
Authors: Xue Song Han
Abstract: Exit fracture, the main factor influencing the precision of workpiece, has already been extensively studied. In the case of nanometric cutting technology, the depth of cut is in the range of nanometer or sub-nanometer, there may be some different discipline dominating the exit fracture generation process. Molecular dynamics (MD) method, which is different from continuous mechanics, has already played an important role in describing microscopic world. The author carried out MD simulation of the micro-mechanism of exit fracture generation process, the results show that different types of burrs is generated depending upon materials ductility and the dimension of burrs may be increased with the increasing of depth of cut.
Authors: K.Y. Fung, C.Y. Tang, Chi Fai Cheung, Wing Cheung Law
Abstract: Single point diamond tools are commonly used for ultraprecision machining. At high cutting speeds, frictional contact and local heat may cause material damage to the diamond tool. The diamond crystal is softened and its mechanical strength decreases with the increase in temperature. Plastic deformation of diamonds was recently reported in some experimental studies. In this work, a molecular dynamics (MD) simulation was implemented to predict the deformation of single crystal diamond at various temperatures. Diamond is brittle at room temperature, however, it starts to exhibit plastic dislocation at a temperature above 1200 K under a confining pressure. The condition in ultraprecision machining is indeed a temperature gradient distribution at the tool tip, between the maximum temperature at the tool-workpiece interface and the average temperature at the core. The simulation results predicted that diamond deformed plastically under the gradient between 1500K and 860K. It is surprising that secondary cracks were resulted from the gradient, as comparing to a single slip obtained in an evenly distributed temperature. Bond dissociation nucleated the fractures along the (111) shuffle planes, perfect dislocation merely occurred in the hot zone and sp3-to-sp2 disorder at the cool zone. The temperature gradient created a lattice mismatch and nucleated the secondary cracks. The results give an insight that a catastrophic fracture and local material damage can occur at a diamond tool tip at the cutting temperature above 1200 K, due to softening and graphitization.
Authors: Hui Wu, Bin Lin, S.Y. Yu, Hong Tao Zhu
Abstract: Molecular dynamics (MD) simulation can play a significant role in addressing a number of machining problems at the atomic scale. This simulation, unlike other simulation techniques, can provide new data and insights on nanometric machining; which cannot be obtained readily in any other theory or experiment. In this paper, some fundamental problems of mechanism are investigated in the nanometric cutting with the aid of molecular dynamics simulation, and the single-crystal silicon is chosen as the material. The study showed that the purely elastic deformation took place in a very narrow range in the initial stage of process of nanometric cutting. Shortly after that, dislocation appeared. And then, amorphous silicon came into being under high hydrostatic pressure. Significant change of volume of silicon specimen is observed, and it is considered that the change occur attribute to phase transition from a diamond silicon to a body-centered tetragonal silicon. The study also indicated that the temperature distributing of silicon in nanometric machining exhibited similarity to conventional machining.
Authors: Ying Zhu, Yin Cheng Zhang, Shun He Qi, Zhi Xiang
Abstract: Based on the molecular dynamics (MD) theory, in this article, we made a simulation study on titanium nanometric cutting process at different cutting depths, and analyzed the changes of the cutting depth to the effects on the work piece morphology, system potential energy, cutting force and work piece temperature in this titanium nanometric cutting process. The results show that with the increase of the cutting depth, system potential energy, cutting force and work piece temperature will increase correspondingly while the surface quality of machined work piece will decrease.
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