Many from within manufacturing industry consider superplastic forming (SPF) to be Ôhigh techÕ, but it is often criticized as too complicated, expensive, slow and, in general, an unstable process when compared to other methods of manipulating sheet materials. Perhaps, the fundamental cause of this negative perception of SPF, and also of diffusion bonding (DB), is the fact that the current process of SPF/ DB relies on indirect sources of heating to produce the conditions necessary for the material to be formed. Thus, heat is usually derived from the electrically heated platens of hydraulic presses, to a lesser extent from within furnaces and, sometimes, from heaters imbedded in ceramic moulds. Recent evaluations of these isothermal methods suggest they are slow, thermally inefficient and inappropriate for the process. In contrast, direct heating of only the material to be formed by modern, electrically efficient, lasers could transform SPF/DB into the first choice of designers in aerospace, automotive, marine, medical, architecture and leisure industries. Furthermore, Ôvariable temperatureÕ direct heating which, in theory, is possible with a laser beam(s) may provide a means to control material thickness distribution, a goal of enormous importance as fuel efficient, lightweight structures for transportation systems are universally sought. This paper compares, and contrasts, the two systems and suggests how a change to laser heating might be achieved.

The process of Superplastic Forming (SPF) has produced a vast number of components, from simple shapes to those with complex geometric features, all to a dimensional accuracy difficult to obtain by traditional sheet metal methods. When used in conjunction with Diffusion Bonding (DB), extraordinarily lightweight, stiff, strong and fatigue enduring components and structures can be manufactured that are virtually impossible to produce by any other means. However, SPF/DB is often criticised as too complicated, expensive, slow and unstable, a reputation that has contributed to its use being largely confined to manufacturing when no other means of production can be found.Perhaps, the fundamental cause of this negative perception of SPF/DB is the fact that derivatives of mid 18th century hydraulic presses are used, virtually universally, that provide only a single temperature to the work piece, which is heated primarily through conduction, a form of heating which is slow and expensive.By comparison, modern, electrically efficient, lasers, if used to directly heat the work piece, could transform SPF/DB into a mainstream process and the first choice of designers. This paper compares, and contrasts, the two systems.

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.

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.