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Superplastic forming stretches metal alloys without degrading their properties, allowing for complex parts without bolts. It has applications in aerospace, sports equipment, energy, defense, and medical industries. The process involves micrograin, transformation, and internal stress superplasticity. Vacuum and thermoforming, deep drawing, and diffusion bonding are industrial processes used. Superplastic forming reduces weight and cost while minimizing assembly time and complexity. It enables innovation in new designs for industrial and consumer products, aerodynamic, and marine optimization.
Superplastic forming is a specialized metalworking process that allows sheets of metal alloys such as aluminum to be stretched to lengths ten times that of conventional alloys without degrading the material properties of the metal. The process allows for the production of complex metal parts, eliminating the need for bolts and fasteners to connect individual metal parts together into a larger unit. Metal forming of this nature is most often used in the aerospace industry, but also has applications for high performance sports equipment as well as in the energy, defense and medical industries.
The science of metalworking used in superplastic forming is divided into three deformation conditions: micrograin, transformation, and internal stress superplasticity. The most popular method for metals involves micrograin superplasticity, in which crystalline grain structures are 10 microns in size or smaller. The temperature of the metal also needs to be approximately half the melting point of the metal alloy being formed, and strain rates are between 0.001 and 0.0001. These conditions limit the types of alloys that will exhibit superplasticity to a small number.
Industrial processes for superplastic sheet metal forming include vacuum and thermoforming, deep drawing, and diffusion bonding. Vacuum forming uses the change in gas pressure to shape metal into a mold, while thermoforming uses established processes that are traditional for manufacturing thermoplastics. Both methods are variations on hot metal gas forming and have the advantage of requiring only one mold operation to create the part.
Deep drawing is a conventional method used in metal forming that can be adapted to superplastic forming. Requires work hardening to achieve superplasticity. Thinning and cracking of the metal part, however, is possible in the process, so it’s usually not a preferred choice.
Diffusion bonding was not initially a sheet metal forming process, but has been adapted to its use. Aluminum-magnesium alloys are commonly used with the method and can have an elongation in the superplastic process up to 600%, but usually does not exceed 300%. Parts created by superplastic forming and diffusion bonding are used in both automotive and aircraft applications that are nonstructural and not as expensive as high-strength alloys.
There are several advantages that sheet metal parts that have undergone superplastic forming have. Because their shapes can be more elaborate and larger due to the metal’s greater ability to stretch, they reduce both the weight and cost of aircraft and automotive vehicles, as well as metal parts in other industries. Assembly time and complexity are also reduced because fewer parts need to be bolted together. Stresses between multiple metal parts as they age and respond to changes in temperature are also minimized.
The industry as a whole contributes to a wide variety of research and new products in the field. The increased versatility of sheet metal shapes enables innovation in new streamlines and designs in a multitude of industrial and consumer products. Superplastic forming is also the key to innovation in aerodynamic and marine optimization.
