Browsing by Author "Evans, R."
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Item Open Access Focused ion beam machining of hard materials for micro engineering applications(Cranfield University, 2009-05) Evans, R.; Allen, DavidThe Focused Ion Beam (FIB) milling of single crystal diamond was investigated and the beam drift and mill yield were quantified. The effect of water assistance on the milling of diamond was found to double the yield. The surface morphology that spontaneously forms during milling was measured and the mechanisms behind its formation investigated. The effect of gallium implantation on the diamond crystal structure was measured by x-ray diffraction. Chemical vapour deposited polycrystalline diamond (PCD) has been machined into micro scale turning tools using a combination of laser processing and FIB machining. Laser processing was used to machine PCD into rounded tool blanks and then the FIB was used to produce sharp cutting edges. This combines the volume removal ability of the laser with the small volume but high precision ability of the FIB. Turning tools with cutting edges of 39µm and 13µm were produced and tested by machining micro channels into oxygen free high conductivity copper (OFHCC). The best surface quality achieved was 28nm Sq. This is compared to a Sq of 69nm for a commercial PCD tool tested under the same circumstances. The 28nm roughness compares well to other published work that has reported a Ra of 20nm when machining OFHCC with single crystal diamond tools produced by FIB machining. The time taken to FIB machine a turning tool from a lasered blank was approximately 6.5 hours. Improvements to the machining process and set up have been suggested that should reduce this to ~1 hour, making this a more cost effective process. PCD tools with sinusoidal cutting prongs were produced using FIB. The dimensions of the prongs were less than 10µm. The tools were tested in OFHCC and the prongs survived intact. Changes to the machining conditions are suggested for improved replication of the prongs into metal. Sapphire was FIB machined to produce nano and micro patterns on a curved surface. The sapphire is part of a micro injection mould for replication of polymer parts. The comparative economics of hot embossing and injection moulding have been studied. Injection moulding was found to be the more cost effective process for making polymer parts at commercial production levels.Item Open Access An investigation into the deceleration mechanisms of a projectile travelling through a liquid and the influence of hydrodynamic-ram effect(Straightline Publishing Limited, 2021-12-31) Blythe, D.; Evans, R.; Oldershaw, S.; Vann, C.; Miller, David; Easton, L.; Roberts, AndrewIf fragmentation or a projectile such as a bullet were to penetrate an aluminium fuel tank, kinetic energy is introduced to the fluid contained within that tank. In turn, kinetic energy is also imparted to the aluminium tank structure, causing structural damage. This research project focussed on designing and constructing a re-usable vessel for repeat firing of projectiles into a liquid and the investigation of the hydrodynamic ram effect. The vessel should enable the use of high-speed imaging to allow the measurement and analysis of deceleration of different projectiles at different velocities.Item Open Access Micro-patterned biological interfaces manufactured by diamond turning with CVD diamond micro-tools(EUSPEN, 2011) Durazo-Cardenas, Isidro; Villa, Raffaella; Mason, S.; Evans, R.; Storti, A.; Heaume, A.; Marinello, F.; Carmignato, S.; Allen, David M.The generation of microstructured interfaces which enhance cell adhesion and proliferation is of great interest in bioremediation, i.e. in all those applications where biological reactions result in the destruction of contaminants. Diamond turning has been implemented for the manufacture of microstructures, taking advantage of bespoke CVD diamond micro-tools in which the edge profile was successfully modified using a combined laser/FIB machining strategy. The CVD micro-tools show good cutting performance in terms of the achievable cutting volume and repeatability of the fabricatedmicrostructure.Item Open Access Sub-surface damage issues for effective fabrication of large optics(2008-07-14T00:00:00Z) Tonnellier, Xavier; Shore, Paul; Morantz, Paul; Baldwin, A.; Walker, D.; Yu, G.; Evans, R.A new ultra precision large optics grinding machine, BoX®has been developed at Cranfield University. BoX®islocated at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium. This machine offers a rapidand economic solution for grinding large off-axis aspherical and free-form optical components.This paper presents an analysis of subsurface damage assessments of optical ground materials produced usingdiamond resin bonded grinding wheels. The specific materials used, Zerodur®and ULE®are currently understudy for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project.The grinding experiments have been conducted on the BoX®grinding machine using wheels with grits sizes of76 μm, 46 μm and 25 μm. Grinding process data was collected using a Kistler dynamometer platform. Thehighest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in lessthan 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurfacedamage was revealed using a sub aperture polishing process in combination with an etching technique.These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 400mm ULE®blank and a 1 metre hexagonal ZeItem Open Access Subsurface damage in precision ground ULE® and Zerodur® surfaces(Optical Society of America (OSA), 2007-09-17T00:00:00Z) Tonnellier, Xavier; Morantz, Paul; Shore, Paul; Baldwin, A.; Evans, R.; Walker, D. D.The total process cycle time for large ULE®and Zerodur®optics can be improved using a precise and rapid grinding process, with low levels of surface waviness and subsurface damage. In this paper, the amounts of defects beneath ULE®and Zerodur®surfaces ground using a selected grinding mode were compared. The grinding response was characterised by measuring: surface roughness, surface profile and subsurface damage. The observed subsurface damage can be separated into two distinct depth zones, which are: ‘process’ and ‘machine dynamics