Browsing by Author "Allen, David M."
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Item Open Access Computational modelling and optimisation of the fabrication of nano-structures using focused ion beam and imprint forming technologies(Institute of Physics (IoP), 2010-12-07T00:00:00Z) Stoyanov, S.; Bailey, C.; Tang, Y. K.; Marson, Silvia; Dyer, A.; Allen, David M.; Desmulliez, M.Focused Ion Beam (FIB) and Nano-Imprint Forming (NIF) have gained recently major interest because of their potential to enable the fabrication of precision engineering parts and to deliver high resolution, low-cost and high-throughput production of fine sub-micrometre structures respectively. Using computational modelling and simulation becomes increasingly important in assessing capabilities and risks of defects with respect to product manufacturability, quality, reliability and performance, as well as controlling and optimising the process parameters. A computational model that predicts the milling depth as function of the ion beam dwell times and a number of process parameters in the case of FIB milling is investigated and experimentally validated. The focus in the NIF study is on modelling the material deformation and the filling of the pattern grooves during the mould pressing using non-linear large deformation finite element analysis with hyperelastic non-compressive material behaviour. Simulation results are used to understand the risk of imperfections in the pattern replication and to identify the optimal process parameters and their interactionItem Open Access Cost of photochemical machining(Elsevier Science B.V., Amsterdam., 2004-06-10T00:00:00Z) Roy, Rajkumar; Allen, David M.; Zamora, OscarPhotochemical machining (PCM), also known as photoetching, photofabrication or photochemical milling, is a non-traditional manufacturing method based on the combination of photoresist imaging and chemical etching. PCM uses techniques similar to those employed for the production of printed circuit boards and silicon integrated circuits. The PCM industry plays a valuable worldwide role in the production of metal precision parts and decorative items. Parts produced by PCM are typically thin, flat, and complex. These parts have applications in electronics, mechanical engineering, and the aerospace industry. The increasing popularity of industrial applications, together with greater competition, means that there is a need to understand the costs involved in PCM so that the right technology can be selected for manufacturing. The paper identifies the costs involved in Photochemical Machining and presents a cost model for PCM using a bottom-up approach. The research used IDEF3 representation (work breakdown structure, WBS) to identify the process used in PCM. Expert interview, literature survey, and participant observation were used to identify cost drivers at each stage of the manufacturing process. The WBS and the cost drivers were used to develop the cost model, which is focused on stainless steel machining. Spreadsheets were used to implement the model, while the workbook is divided according to the main process steps and general costs. The worksheets contained in this workbook are: General Costs, Produce Drawing, Process Phototool, Select Metal, Prepare Metal, Coat the Metal, Process Photoresist, Etch Metal, Strip Photoresist, and Check & Package. Each of these sections is divided into the following types of costs: Materials, Direct Labour, Environmental and Indirect Costs. The workbook contains relevant data acquired from the PCM laboratory at Cranfield, PCM industry, and literature. The model is validated through expert judgement obtained on case study results. The model presented in this paper can be extended to include other PCM techniques to machine other materials.Item Open Access The design and manufacture of biomedical surfaces(Technische Rundschau, Hallwag Publishers; 1999, 2007-08-01T00:00:00Z) Ramsden, Jeremy J.; Allen, David M.; Stephenson, David J.; Alcock, Jeffrey R.; Peggs, G. N.; Fuller, G. D.; Goch, G.Surfaces are the primary place of contact between a biomaterial and its host organism. Typically, prostheses have to fulfil demanding structural and mechanical requirements, yet the material best for those functions may be bio- incompatible. Surface treatment or coating provides a means to overcome that problem, which means both integration within the host physiology and stabilization with respect to corrosion and wear. The adsorption of biomacromolecules is pivotal for biocompatibility. The impossibility of keeping proteins away from most implants means that very careful consideration has to be given to this aspect, and both prevention (for bloodstream implants) and promotion (for bone replacement and repair) occur with equal importance. This paper also considers the metrology of relevant physical and chemical aspects of surfaces.Item Open Access Effects of channel surface finish on blood flow in microfluidic devices(Springer Science Business Media, 2010-01-12T00:00:00Z) Prentner, S.; Allen, David M.; Larcombe, L. D.; Marson, Silvia; Jenkins, Karl W.; Saumer, M.The behaviour of blood flow in relation to microchannel surface roughness has been investigated. Special attention was focused on the techniques used to fabricate the microchannels and on the apparent viscosity of the blood as it flowed through these microchannels. For the experimental comparison of smooth and rough surface channels, each channel was designed to be 10mm long and rectangular in cross-section with aspect ratios of â ¥100:1 for channel heights of 50 and 100μm. Polycarbonate was used as the material for the device construction. The shims, which created the heights of the channels, were made of polyethylene terephthalate. Surface roughnesses of the channels were varied from Rz of 60nm to 1.8μm. Whole horse blood and filtered water were used as the test fluids and differential pressures ranged from 200 to 5000Pa. The defibrinated horse blood was treated further to prevent coagulation. The results indicate that a surface roughness above an unknown value lowers the apparent viscosity of blood dramatically due to boundary effects. Furthermore, the roughness seemed to influence both water and whole blood almost equally. A set of design rules for channel fabrication is also presented in accordance with the experiments performed.Item Open Access Flatness optimization of micro-injection moulded parts: The case of a PMMA microfluidic component(Institute of Physics Publishing; 1999, 2011-10-20T00:00:00Z) Marson, Silvia; Attia, Usama M.; Lucchetta, G.; Wilson, A.; Alcock, Jeffrey R.; Allen, David M.Micro-injection moulding (µ-IM) has attracted a lot of interest because of its potential for the production of low-cost, miniaturized parts in high-volume. Applications of this technology are, amongst others, microfluidic components for lab-on-a-chip devices and micro-optical components. In both cases, the control of the part flatness is a key aspect to maintaining the component's functionality. The objective of this work is to determine the factors affecting the flatness of a polymer part manufactured by µ-IM and to control the manufacturing process with the aim of minimizing the in-process part deformation. As a case study, a PMMA microfluidic substrate with overall dimensions of 10 mm diameter and 1 mm thickness was investigated by designing a µ-IM experiment having flatness as the experimental response. The part flatness was measured using a micro-coordinate measuring machine. Finite elements analysis was also carried out to study the optimal ejection pin configuration. The results of this work show that the control of the µ-IM process conditions can improve the flatness of the polymer part up to about 15 µm. Part flatness as low as 4 µm can be achieved by modifying the design of the ejection system according to suggested guidelinesItem 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 Sinusoidal CVD diamond micro-tools for the manufacture of microstructured surfaces used in bioremediation(2013-12-31T00:00:00Z) Marson, Silvia; Villa, Raffaella; Durazo-Cardenas, Isidro; Evans, R. W.; Storti, A.; Heaume, A.; Marinello, F.; Carmignato, S.; Fairley, M.; Jennings, P.; Allen, David M.Item Open Access Study of blood flow behavior in microchannels(2008-06-01T00:00:00Z) Marson, Silvia; Benade, M.; Attia, Usama M.; Allen, David M.; Kersaudy, Kerhoas M.; Hedge, J.; Morgan, S. L.; Larcombe, L. D.; Alcock, Jeffrey R.; van Brussel, H.; Brinksmeier, E.; Spaan, H.; Burke, T.Microfluidic (also known as lab-on-a-chip) devices offer the capability ofmanipulating very low volumes of fluids (of the order of micro litres) for severalapplications including medical diagnostics. This property makes microfluidicdevices very attractive when the fluid, such as blood, has a limited supply becausethe patients cannot easily and frequently provide a large sample. This is typically thecase for aged, diseased patients that do require frequent sampling during acute careor of older people that have the option of being treated and cared for at home [1].Prototype lab-on-a-chip devices for medical diagnostics comprise a number ofelements which separately perform different functions within the system. Activitywithin the research community is focusing on the better integration of devicefunctionalities with the long term goal of creating fully integrated, portable,affordable clinical devices. However, engineering these solutions for the largevolume production of lab-on-a-chip devices requires design rules which are not yetentirely available.This paper describes the results obtained from a set of experiments run to drawgeneric design rules for the manufacture of a cells/plasma micro separator [2]. Thecells/plasma micro separator was selected for investigation because it is a strategicelement required in the preparation of blood samples for many different analyticaldevices. The experiments focused on the study of the behaviour of whole bloodpassing through micro constrictions which are required for enhancing the separationeffect [3].The test microfluidic device was an aluminium specimen designed andmanufactured to incorporate micro constrictions of different width and length. The metallic aluminium test device was designed for manufacturing by micromilling anddiamond cutting processes in view of applying these techniques to the manufactureof micro-moulds for the high-volume production of plastic microfluidic devices viamicro-injection moulding.The widths of the constrictions were 23, 53 and 93µm and the lengths were 300 and700µm. The blood flow pattern and the level of haemolysis generated in the wholeblood were determined for flow rates between 0.2 and 1 ml/min. Initial resultssuggested that the above conditions generate a stable flow and do not cause bloodhaemolysis following passage through the narrow constrictions. This result impliesthat constrictions as narrow as 23 µm and as long as 700µm can be safely used inblood microfluidic devices under appropriate flow conditions without the risk ofdamaging the blood compone