Papers by Author: Xi Chun Luo

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Authors: Ji Ning Sun, Xi Chun Luo, Wen Long Chang, James M. Ritchie
Abstract: In this work, two kinds of freeform micro optics were successfully fabricated by using focused ion beam machining. A divergence compensation method was applied to optimize the machining process. Both dynamic variation of the sputter yield and the extra ion flux contributed by the beam tail were taken into consideration. Measurement results on the surface topography indicated that 3-fold improvement of the relative divergence was achieved for both optics when compared with conventional focused ion beam milling without any corrections. Furthermore, investigations on the influences of scanning strategies, including raster scan, serpentine scan and contour scan, were carried out. The serpentine scan is recommended for the fabrication of freeform optics by focused ion beam technology owing to the minimal beam travelling distance over the pattern area.
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Authors: Saurav Goel, Xi Chun Luo, R.L. Reuben, Waleed Bin Rashid, Ji Ning Sun
Abstract: Wear of diamond tool has always been a limiting factor in ductile regime machining of large size silicon components. In order to understand the tool wear phenomena, it is non-trivial to know the process outputs especially cutting forces, stresses and temperature during nanometric turning. In this paper, a realistic potential energy function has been deployed through molecular dynamic (MD) simulation, to simulate the process outputs of single diamond turning operation against single crystal silicon. The simulation result suggests that wear mechanism of diamond tool is fundamentally governed by these process parameters and thus critical.
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Authors: Xi Chun Luo, Ji Ning Sun, Wen Long Chang, James M. Ritchie
Abstract: This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF2 optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF2 specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF2 optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF2 surfaces.
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Authors: Saurav Goel, Xi Chun Luo, R.L. Reuben, Waleed Bin Rashid, Ji Ning Sun
Abstract: Silicon carbide can meet the additional requirements of operation in hostile environments where conventional silicon-based electronics (limited to 623K) cannot function. However, being recent in nature, significant study is required to understand the various machining properties of silicon carbide as a work material. In this paper, a molecular dynamic (MD) simulation has been adopted, to simulate single crystal β-silicon carbide (cubic) in an ultra precision machining process known as single point diamond turning (SPDT). β-silicon carbide (cubic), similar to other materials, can also be machined in ductile regime. It was found that a high magnitude of compression in the cutting zone causes a sp3- sp2 order-disorder transition which appears to be fundamental cause of wear of diamond tool during the SPDT process.
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