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
In materials science, superplasticity is a state in which solid crystalline material is deformed well beyond its usual breaking point, usually over about 600% during tensile deformation. Such a state is usually achieved at high homologous tempe ...
. 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
Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. The sheet, or "film" when referring to thinner gauges and cert ...
,
blow forming, and
vacuum forming
Vacuum forming is a simplified version of thermoforming, where a sheet of plastic (in various forms HIPS (High impact polystyrene) for low impact products, or for Bathroom shower trays ABS, and exterior vehicle parts HDPE, plus various other ty ...
.
[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. It also does not suffer from springback or
residual stress
In materials science and solid mechanics, residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable. For example, laser peening i ...
es. Products can also be made larger to eliminate assemblies or reduce weight, which is critical in
aerospace
Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astr ...
applications.
Lower strength required and less tooling costs.
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it pro ...
utilized SPF design and production technology into the
F-15
The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather tactical fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force selected McDonnell Douglas's ...
in the 1980s, while in Europe an example of application can be found in some
Eurofighter Typhoon
The Eurofighter Typhoon is a European multinational twin-engine, canard delta wing, multirole fighter. The Typhoon was designed originally as an air-superiority fighter and is manufactured by a consortium of Airbus, BAE Systems and Leonardo ...
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 Superplastic forming and diffusion bonding (SPF/DB) is a technique allowing the manufacture of complex-shaped hollow metallic parts. It combines Superplastic forming (SPF) with a second element "Diffusion Bonding" to create the completed structures ...
References
Metal forming
Metal heat treatments
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