Papers by Author: Qing Shun Bai

Abstract: In order to investigate the mechanical properties of single crystal Cu nanorod with preset defects, the multiscale unixial tension simulation models of nanorods with two different crystallographic orientations are established. In two orientations, the dislocations are emitted firstly from the notch tip. The results show that the defect evolution, stress-strain curves and train energy vary with different crystallographic orientations. In setup, the deformation is ductile mode and it is fracture fashion in the setup.

Abstract: In this paper, the effect of minimum chip thickness on cutting temperature in micro-end- milling of aluminum alloy Al2024-T6 using a tungsten-carbide cutter are investigated and analyzed. The three-dimensional coupled thermal-mechanical finite element model is adopted to determine the effects of varying depth of cut on cutting temperature considering size effects. The simulation results show that the cutting temperature in micro-end-milling is lower than those occurring in conventional milling processes. When the depth of cut is approximately 40% of the cutting edge radius, there is no chip formation. The maximum temperature occurs at the contact region between micro cutting edge and workpiece, which shows an obvious size effect. The experimental verification of the simulation model is carried out on a micro-end-milling process of aluminum alloy 2024-T6 with a high precision infrared camera. The influence of various cutting depths on cutting temperature has been verified in experiments. The experimental measurements results are in a good agreement with the simulation results.

Abstract: The micro-end-milling process of aluminum alloy Al2024-T6 has been investigated by numerical simulations and experimental approach. The effects of different tool edge radii on the micro-cutter wear were investigated. A three-dimensional finite element model is adopted to determine the effects of tool edge radii on the effective stress and micro-cutter wear during the micro-end-milling process. It is observed that the the tool nose wears out much more quickly due to the high maximal effective stress occurring in this zone. The experimental verification of the simulation model is carried out on a micro-end-milling process of aluminum alloy 2024-T6. The experimental results of the micro-cutter morphologies are in a good agreement with the simulation results. The experimental results show that the model is suitable for studying the mechanism of micro-cutter wear.

Abstract: Micro-mould is a necessary and productive component for the development of MEMS. However, the machining of micro-mould parts with complex 3D surfaces becomes the key problem for the development of micro machinery. In the paper, a new machining technique was introduced to manufacture micro-mould parts. With a reverse engineering technique, point cloud data were acquired and reconstructed into a 3D model of micro mould part in a computer. The numeral control code for micro-machining was also processed with the help of micro-machining simulation. The machining experiment on micro-parts with complex 3D surfaces was conducted on self-developed micro machine tools with micro-diameter ball-end cutter. High quality micro mould parts with complex 3D surfaces were obtained under these micro-milling experiments. The results will provide a perspective resolution on the manufacturing of micro-mould parts with complex surfaces.

Abstract: Quasicontinuum simulation of nanometric cutting was conducted on single crystal copper to investigate the effect of crystal orientation and cutting direction on nature of deformation of this material. The model reduces the degrees of freedom in simulations of nanometric cutting process without sacrificing important physics. The simulation results show the crystal orientation and cutting direction have a significant effect on the nature of deformation of nanometric cutting process. In addition, the variations of strain energy of workpiece atoms in different crystal set-ups are investigated.

Abstract: A multiscale simulation model was built to study the nanometric cutting process of single crystal copper. This multiscale model distinctly reduces the degree of freedom of the whole system compared with full atomistic simulations. Through analyzing the fluctuations of tangential cutting force and strain energy with cutting distance, we confirm that the deformation mechanism of single crystal copper is plastic deformation caused by generation and evolution dislocation. The highest compressive stress locates in shear zone and highest tensile stress locates in the machined surface and subsurface. Simulation results show that there exists a high value of stress around dislocations, which reveals the local high value of stress is the main reason for the generation and evolution of dislocations in the workpiece material.

Abstract: The minimization of mechanical parts is one of important research direction in micro machine or MEMS area. Milling experiments of micro part were conducted on micro machine by using TiAlN-coating micro-diameter cutter. Three kinds of typical workpiece materials (LY12, stainless steel and high-elastic alloy 3J21) were adopted and the wear properties of micro-diameter cutter were investigated carefully. The main reasons for tool wear and breakage were analyzed. It is shown that the common wear characteristics of TiAlN-coating micro-diameter cutter are falling off of coating, breakage of tool nose, diffusion and adhesion wear while machining the three materials. Adhesion and diffusion effects are much obvious in machining 3J21 alloy and stainless steel, leading to coarse wear region of tool.

Abstract: The finite element modeling and experimental validation of three-dimensional precision cutting of 3J33 maraging are presented. The commercial software MARC applied for the finite element modeling is studied the effect of tool nose radii considering tool edge radius on the principal cutting forces and the temperature fields. The model employs an updated Lagrangian formulation. The friction between the tool and the chip is assumed to follow a modified Coulomb friction law and the adaptive remeshing technique is using for the formation of chip. The tool edge radius significantly affects the cutting forces and the maximum temperature of the chip. The simulation results for tool with nose radius considering tool edge radius are compared with experimentally measured data and found to be in good agreement.

Abstract: Molecular dynamics (MD) simulations of nanometric scratching with diamond tip are conducted on single crystal copper crystal plane (010), and MD simulations are carried out to investigate the mechanism of material removal and the generation of defects on the surface, subsurface and inner of material. During the process of diamond tip scratching the surface of single crystal copper on conditions of different scratching speeds, depths and widths. We achieved the forming details of the chip. While the generation and moving process of defects, such as dislocation, are recorded. The different times of atomic displacement and interaction force are also shown through MD simulation. The evolvement of the lattice pattern in the abrasive processes are analysed by radial distribution function (RDF) and computing the changes of workpiece’s atomic displaces and forces. At the same time, the lattice reconfiguration and the onset and the evolvement process of defects and are analysed by RDF and atomic perspective method, respectively. The simulation results show that scratching speed play role in the course of the form of removing chips, and that different scratching widths and depths of tool have effect on onset and evolvement of lattice defects of workpiece in abrasive processes. This study can give more fundamental understanding of nanosconstruction from atomistic motions and contribute to the design, manufacture and manipulation of nano-devices

Abstract: Carbon nanotubes (CNTs) represent ideal Atomic Force Microscope (AFM) tip materials due to their remarkable mechanical properties. Dynamic interactions of a Single-wall Carbon nanotube (SWCNT) indenting towards a monocrystalline hydrogen-free Silicon surface (001) are investigated using molecular dynamic simulation. The critical strain and strain force along the axis of the tube from elastic to plastic regimes are calculated. The simulation shows the deform process in elastic regimes is similar to the process of two ends inward compressed. The atoms of nanotube tip adsorption to the Silicon surface has been observed in the plastic regimes. The mechanical microprocess of AFM’s single-wall Carbon nanotube tip and Silicon surface interactions from elastic to plastic regimes can be well comprehended from the view of nanoscale energetic evolution.