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Title: A systematic research on diamond turning using nanoscale multi-tip diamond tools
Author: Tong, Zhen
ISNI:       0000 0004 5359 1764
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2015
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Recently, great interest has been shown in the fabrication of periodic micro- and nanostructures over large area due to their increasing applications in diverse research fields including optics and electronics, cell biology, bioengineering and medical science. Diamond turning using multi-tip single crystal diamond tools fabricated by focused ion beam (FIB), as a new machining technique, shows powerful capacity in the fabrication of micro- and nanostructures. However, lack of support from systematic theoretical research has seriously hindered the advance and industrialization of this technique. As such, molecular dynamics (MD) simulations and experimental trials have been undertaken in this research work to systematically investigate this new technique from the FIB-induced damage during the tool fabrication process to the nanometric cutting mechanism using nanoscale multi-tip diamond tools. The transmission electron microscope (TEM) measurements were carried out to characterize the FIB-induced damaged layers in single crystal diamond under different ion beam processing voltages. A novel multi-particle collision MD model was developed to simulate the FIB-induced dynamic damage process in diamond. The results indicated that the fabrication of diamond tool by FIB can create an impulse-dependent damaged layer at the tool surface. The nature of FIB-induced damaged layer in the diamond tool is a mixture phase of sp² and sp³ hybridization and accommodates a significant proportion of the implanted gallium. The nanometric cutting process of using nanoscale multi-tip diamond tools was studied by MD simulations. The results provide in-depth understandings of the nanostructure generation process, the cutting force, the thermal effect, and the tool geometry-dependent shape transferability. The investigation shows that the formation mechanism of nanostructures when using multi-tip tools is quite different from that of using single tip tools. Since the nanostructures are synchronously formed by a single cutting pass, the effect of feed rate and the alignment issues associated with the use of single tip tools to achieve the same nanostructure can be completely eliminated when using nanoscale multi-tip tools. The unique tool geometrical parameters of a nanoscale multi-tip tool including the tool tip distance, tip angle, and tip configuration play important roles in the form accuracy of the machined nanostructures. A hypothesis of a minimum ratio of tip distance to tip base width (L/Wf) of the nanoscale multi-tip tool has been proposed and qualitatively validated by nanometric cutting experiments. A series of nanometric cutting experiments and associated MD simulations were further carried out to study the influence of processing parameters on the integrity of the machined nanostructures and tool wear. Under the studied cutting conditions, the burr and structure damage are the two major types of machining defects. With the increase of the depth of cut and the cutting speed, the increasing overlap effect between the tool tips is responsible for the formation of side burrs and structural damage. The tool wear was initially found at the sides of each tool tip after a cutting distance of 2.5 km. The FIB-induced damaged layer, the friction produced at each side of the tool tip, and the high cutting temperature distributed at the tool cutting edges are responsible for the initiation of tool wear. Based on the research objectives achieved, generic suggestions are proposed for the further development of diamond turning using nanoscale multi-tip tools in terms of selective parameters used in tool fabrication, optimal design of tool geometry, and optimization of processing parameters in nanometric cutting practice.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available