PhD, EngD, MPhil and MSc by research theses (SIMS)

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Browsing PhD, EngD, MPhil and MSc by research theses (SIMS) by Supervisor "Corbett, John"

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    A design methodology for jigless aerospace manufacture
    (2005-03) Burley, Graham John; Corbett, John
    Between 10% and 40% of the overall cost of an aerostructure can be directly attributed to the cost of type specific, hard-tooling. Hence, any attempt to reduce the cost of aerostructure must eventually focus on reducing the need for type specific hard-tooling. The tooling is one of the major investments made during the development phase of an aircraft programme, accounting for more than a third of the development cost of a civil aircraft and nearly a quarter of the development cost of a military aircraft. The development phase for civil aircraft typically lasts two to four years and the tooling cost represents a multi-million pound forward investment with a long pay back period. Consequently, reducing the need for type specific hard-tooling will significantly reduce development costs and the time from concept to market. This thesis describes a new design-for-assembly JAM Methodology that reduces the need to manufacture and build with type specific hard-tooling. The Methodology was developed by identifying, utilising and developing existing design methodologies, and by identifying and applying enabling technologies. The methodologies are integrated to create a design algorithm that identifies and draws on the enabling technologies to achieve minimal hard tooling assembly concepts. Included in the methodologies is an innovative systems analysis tool. This enables the comparison of alternative assembly concepts ahead of the detail design, and the prediction and control of the total assembly error at the design stage. The first part of the thesis describes the development of the JAM Methodology and explains the function and purpose of each step. The second part of the thesis demonstrates, and tests, two slightly different forms of the Methodology in the re-engineering of an existing aerospace structure, and in the designing of a new aerospace structure. Publications relating to this research thesis include eleven authored, and co-authored, refereed conference papers, one journal article, and two EPSRC final reports.
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    Enhanced surface finishing of bearing raceways
    (2000-10) Knight, Peter; Corbett, John
    Bearing surfaces are highly engineered and high precision parts in regard to surface finish, waviness, form and dimensional size. Surface finishing techniques will not only affect the surface finish and texture but the mechanical properties of the surface and subsurface including surface stress state and hardness as well as chemical properties. The bearing surface is a functional surface influencing fatigue, wear, and friction, noise and lubrication regime. Bearings are low cost, high volume commodity products, which adds additional constraints to any manufacturing process of low cost, fast cycle time and automation. This thesis documents the development route for a superfinishing technique for bearing raceways. Initially work was performed on electrochemical machining (ECM) of raceways, but this was found to improve the surface finish too slowly and gave poor waviness as a result of non-conductive MnS inclusions becoming exposed on the bearing surface during ECM. Abrasive honing stones or superfinishing tapes were then combined with the ECM, a process called electrofinishing to remove these MnS peaks. A beneficial interaction between the ECM and the abrasive resulted in reduced loading of the abrasive and therefore more aggressive cutting and for longer. Using a fine grit (3- 4 pm) CBN vitreous bonded honing stone the surface finish of a ground ring (0.3 pm Ra) or a turned surface (1.2 pm Ra) could be improved to <0.02 pm Ra in around 6 seconds. These new surfaces showed low Rtm and Aq (slope), but also acceptable or very good levels of waviness. The material removal is dominated by the ECM process while the rate of surface finishing is controlled by the abrasive process. The process of electrofinishing gives the possibility of fast, high and controlled material removal capability combined with fine surface finishing, which presently must be achieved by throughfeed honing or two stage honing. The main difficulty to overcome is achieving a stable consistent honing needed for a production process. These difficulties arise from the incompatibility of the ECM electrolyte and honing fluid (usually an oil). Improvements were made by using a water soluble synthetic metalworking fluid mixed with the NaN03 electrolyte. Further improvements are possible by better choice of honing stone, better application of stones, while for superfinishing tapes, the use of tape feed and oscillation will give further improvements.
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    Jig-less assembly for aerospace manufacture
    (2000) Snelling, Peter D.; Corbett, John
    Due to the high level of investment required to compete successively in the global aerospace and automotive markets, these industries are forced to form partnerships wherever possible and thereby share their resources appropriately. This in turn has brought about the requirement to provide a standardized flexible design and manufacturing capability in which interchangability and compatibility may take place. Current assembly practices and associated tooling can be traced back to the earliest days of aircraft production and have become relatively expensive and inflexible in today’s environment. The final assembly stage has been recognized to be a key area which has the potential to offer substantial returns as well as play a major role in any change management process within the organisation. Assembly tooling, jigs and fixtures, are required to support and maintain positional accuracy of components during assembly. Traditional jigs and fixtures make up for the short comings at the product design and manufacturing phases and add significantly to the final product costs and reduce flexibility in the production process. Jig-Less Assembly Concept (JAC) has been defined and researched with the aim to integrate and optimize various tools and techniques with which to reduce or eliminate the assembly tooling currently in use. The outcome of the research presents a comprehensive critique of the processes involved in and pertaining to the assembly of typical airframe assemblies. The thesis forms a platform from which to move forward towards the embodiment of the concept of jig-less assembly. Particular attention is drawn from the research to the need for appropriate organisational and management strategies as well as technical innovation in the adoption of a jig-less approach to airframe assembly. Together with BAe Airbus and Military this collaborative research seeks to define the scope of JAC by identifying and evaluating the issues and constraints, to enable the development of supportive techniques in unison with best practice engineering within a robust and sustainable manufacturing system. This commercially focused R & D required liaison and working at all levels within a variety of industrial sites using live case studies at Filton and Chester.