Superplastic forming is an industrial process used for creating precise and complex components out of
superplastic materials.
Process
The material is first heated up to promote
superplasticity. For titanium alloys e.g. Ti 6Al 4V and some stainless steels this is around and for aluminium alloys e.g. AA5083 it is between 450 and 520 °C. In this state the material becomes soft so processes that are usually used on plastics can be applied, such as:
thermoforming,
blow forming
Blow molding (or moulding) is a manufacturing process for forming hollow plastic parts. It is also used for forming glass bottles or other hollow shapes.
In general, there are three main types of blow molding: extrusion blow molding, injection ...
, and
vacuum forming.
[E. Degarmo, J. Black, and R. Kohser, Materials and Processes in Manufacturing (9th ed.), 2003, Wiley, .] Inert gas pressure is applied on the superplastic sheet forcing it into a female die.
Advantages and disadvantages
The major advantage of this process is that it can form large and complex workpieces in one operation. The finished product has excellent precision and a fine
surface finish
Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a surface from the perf ...
. It also does not suffer from springback or
residual stresses. Products can also be made larger to eliminate assemblies or reduce weight, which is critical in
aerospace applications.
Lower strength required and less tooling costs.
McDonnell Douglas utilized SPF design and production technology into the
F-15 in the 1980s, while in Europe an example of application can be found in some
Eurofighter Typhoon assemblies
(e.g. engine bays panels, foreplanes, slats).
The largest disadvantage of the process is its slow forming rate. Cycle times vary from two minutes to two hours, therefore it is usually used in low volume production applications.
Another disadvantage is the non-uniformity of the produced part thickness. Several methods are used to improve the thickness uniformity of SPF parts. One is to apply a designed varying gas pressure profile instead of a constant pressure. Another approach is to tailor the contact friction between the die surface and the superplastic sheet.
[12. M.I. Albakri, F.S. Jarrar, and M.K. Khraisheh, Effects of Interfacial Friction Distribution on the Superplastic Forming of AA5083, Journal of Engineering Materials and Technology, 2011, 133, p 031008-031014.]
See also
*
Hot metal gas forming
*
Superplastic forming and diffusion bonding
References
Metal forming
Metal heat treatments
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