Papers by Author: Alan Jocelyn

Abstract: Superplastic Forming and Diffusion Bonding (SPF/DB) have provided some of the lightest, strongest, corrosion resistant, elegant and complex structures ever produced. Thus “At Boeing, SPF is now considered as a baseline design option for many large assemblies” (Dan Sanders, 2000). However, in an ever increasingly cost conscience world, will the process flourish or decline Cost is the element most scrutinised by society, and is often considered more important than achieving a required specification or delivery of a project on time. In this paper an analysis of the global value of SPF and SPF/DB products will be provided by industrial sector and material type. The cost of the current technology, such as capital plant, consumable materials and labour overheads, will be compared to the current price of SPF products and the degree of ‘market pressure’ to reduce such costs will be assessed. Such pressures may arise from potential threats from competing technologies, fuel costs or environmental considerations. However, if lowering the ‘carbon footprint’ of the process, and its cost, could be achieved, together with the production of components and structures of improved weight to strength ratio, SPF technology could be elevated to the first, and principal, choice of designers worldwide.

Abstract: Chemical cleaning has been used for several decades as a surface preparation technique for diffusion bonding. Here we present a theoretical investigation that examines the effect of changes in the process parameters when a laser is used as an alternative to chemical cleaning for surface contaminant removal. Here a theoretical model is described that includes laser beam attenuation in the plasma plume and its effect on evaporation of the material. Using the model, a comprehensive analysis of the effect of different fluences and other parameters for a KrF Excimer laser is presented. Calculations were carried out for a range of peak fluxes from below the ablation threshold to fluxes of the order of 9 x 1012 W/m2. The predicted effects on evaporation, melt depth and surface temperature are reported, illustrated by a number of surface topographic images from preliminary experiments. Finally, optimal parameters for cleaning according to the theoretical investigation are proposed.

Abstract: Superplastic forming (SPF) has traditionally relied on hot platen presses and furnaces as the principal heat sources to raise materials to superplastic forming temperatures. However, recent research, in the UK and the US, has concluded that such indirect heating methods are slow, expensive, and can only provide a single temperature to the work piece, which can be undesirable. In contrast, LISTechnology Limited (laser induced superplasticity technology) has been created to provide an alternative technology that can directly heat materials to be superplastically formed fast, at low cost and with the potential to control thickness distribution during forming through differential heating. The first ‘laser cell’ for components formed from single sheet titanium is currently being built to demonstrate how direct heating of SPF materials with a laser will significantly increase material heat up rates, compared with current methods, whilst the low thermal mass of the cell will allow rapid cooling to below oxidation temperatures, thus significantly reducing manufacturing cycle times. Furthermore, the cell will only utilise thermally stable, inert ceramic dies within which the titanium will be formed, these being contained within a sealed argon environment, thereby offering the possibility of alpha case free, rapid forming at high temperatures.