As mentioned briefly in the previous post, SPF (superplastic forming) is a process by which a superplastic aluminum alloy is formed over a single surface tool using heat (500°c) and air pressure. While quite common in automotive and aerospace manufacturing, the deployment of SPF for architecture has been rather limited. Among others, The Financial Times Print Works and Sansbury’s Store Camden London, both by Grimshaw Architects have used this process.
There are several advantages to the SPF process that make it uniquely suited to produce complex, weather-resistant, architectural surfaces. First, the heat forming process is extremely accurate with very little variation between panels, particularly when compared to cold form processes such as stamping. Second, extreem relief and surface detail is possible. As a general rule, the depth of a panel feature can be up to half its width. With regards to detail, Heather reports the registration of minute details, offering the potential to produce richly textured surfaces. Finally, SPF is cost-effective for projects requiring ‘hundreds or thousands’ of components, lending itself to an architectural scale.
I will try to briefly explain the process: A digital model is created of an intended surface. Depending on the characteristics of the geometry and the production, a specific grade of aluminum is selected for forming. The forming process is simulated using finite element analysis to confirm geometric accuracy and to detect any problems before tools are produced. After the geometry is confirmed, a tool is produced either by CNC milling a solid block of aluminum, or, for larger production runs, a mold is milled and the tool is cast in iron. Depending on the geometry of the panel, a number of forming processes may be used. The most common are male forming, where the material is pressed over a male tool, drape forming, where the material is forced into a female cavity over a male tool, and female forming, where the material is forced by air pressure into a female cavity. More information is available from Superform.
Image: Material Elongation of Superplastic Alloys v. Standard Aluminum