Thermoforming

Thermoforming is the process of heating a piece of foam to a point at which the normally rigid material becomes flaccid and conformable. It is a necessary process in building the F22 because the flat sheets of foam will not bend to fit the hull curves without breaking. In order to get the foam to bend, it needs to be heated between 200 and 220 degrees Fahrenheit (93-104C). The least expensive way to accomplish this is by using a hand held heat gun (think turbo-powered hair dryer) to bring the foam up to this temparature.

Thermoforming a 20+ foot ama in an 85F loft with a heat gun is a hot and grueling task. In addition, the heat gun creates localized heat where one spot in the foam is hot and conformable, while other spots are still cool and rigid. Heat guns will scorch and burn the foam if held in a location too long or the gun is too close to the material. In addition, due to the curved shape of the ama, the heat from the gun is redirected back from the foam to the person operating the gun. It is a hot and sweaty job, so much so that I drink 64oz of water before the day begins and I never have to use the restroom all day.

In the never ending quest to build a better mousetrap, we assembled a makeshift oven to heat the foam up to thermoforming temperature without holding the heat gun or battling the heat. We used a large foam insulated case, with plywood wedges partially opening the case and holes cut out for the heat guns (pictures below).

After heating the foam to its thermoforming temperature, the builder has about 10 seconds to get the foam from the oven onto the mold surface and conform it to shape. Using the thermoform oven was such a blessing to accomplish this task. Below are pictures of the thermoforming oven, the foam bent to the curve of the hull, the join lines of the foam covered in packing tape and the fully planked hull (4 hours total)