What do you imagine when you hear the words “Super Plastic Forming”? When you read academic and professional articles on the topic, they can be inaccessible and challenging for those who do not know about the technology. Here, we try to present an easy to understand and accessible explanation on Super Plastic Forming (SPF).

What’s SPF?

SPF is a metal processing technology of which there are various ways that are available to shape and model metal. Such processes as cutting with a drill, bending with a press, and melting and bonding or welding. All of these are dependent on the application the metal will be used or applied to. Among these processes’ SPF is a technique which inflates and stretches metal almost like a balloon.

Why does it inflate?

Generally, the process of inflating is when a metal material is raised up to a certain temperature and pulled. At this point it expands due to the occurrence of what is known as “grain boundary slip”. This is called a superplastic phenomenon.

Does any metal stretch?

The types of metal that stretch are limited. Currently, aluminum alloys and titanium alloys are the main metals used for SPF. There are also magnesium alloys, stainless steel alloys and super heat resistant alloys. If you have material with larger and smaller grains then you can assume that the smaller of the grains will be the ones to expand more.

How can you inflate it?

1. Put the mold in the heating furnace and heat it.
2. Set the material between the upper lid and the lower mold.
3. After heating to the superplastic temperature, press the upper lid.
4. Enter gas from the upper lid.
5. The material inflates and sticks to the mold.
6. Take out the mold from the heating furnace and take out the inflated material.

See the figure below.

How much does the mold cost?

It depends on the material and size of the mold. If the product is an aluminum alloy, the mold material is usually constructed from iron. If it is a titanium alloy, the mold will usually be made from stainless steel. And it is proportional to the size of the product being manufactured too. However, as you can see from the figures, the mold is only on the lower side, so the raw material cost and processing cost are cheaper than making both upper and lower molds to form your part.
Take out the material. It is shown in the figure below.

What kind of shape can we manufacture?

There are elements that you must be aware of. For example if the thickness of the material is stretched out to far or under too much stress then, just like a balloon, it will pop. Or if the shape has an overhang, that is, the mold is in the shape of a jar, the material sticks to the mold and cannot be removed.

What are some of the applications for this technology?