Lamination is a process that involves using multiple layers of the same or different materials to improve their mechanical properties.

Why does BlueNimbus use this technique?

We generally use lamination—specifically the wet layup process—in the fabrication of composite materials. Depending on the desired outcome, we use this technique to produce sheet material or structures with more complex shapes where a high strength-to-weight ratio is required.

The wet layup process in molds generally looks like this:

1. Preparation: Before lamination, the molds need to be cleaned of dust and other foreign particles, as contaminants on the mold surface get trapped inside the composite material during lamination and can cause defects. Manufacturing molds is not cheap, so it is necessary to ensure that the lamination process does not damage the molds or make them single-use. Therefore, the inner surfaces of the mold are waxed with a special mold release wax so that the cured laminate can be separated from it later.

2. Laminate Material Preparation: It is necessary to prepare the correct size of fabric material for the laminate—in our case, either fiberglass or carbon fiber fabric. When cutting the fabric, it must be ensured that it does not fray. To achieve this, we use a thin layer of tape at the cutting line, which secures the weave on both the cut and uncut parts. Cleanliness must also be maintained when handling the fabric, and care must be taken not to damage the weave; otherwise, defective spots will later form in the laminate, weakening the resulting composite material.

3. Preparation of Other Layers: To achieve a high-quality result with the laminate, it is also necessary to add a layer of release fabric or film that can be removed once the composite cures. A specialized absorbent batting layer (breather/bleeder) is also required to remove excess binder from the composite and act as a "straw" to help pull a better vacuum in the mold. Finally, a vacuum bag or main film must be prepared for the mold to create a vacuum around the laminate. Creating a vacuum is important because the pressure resulting from the atmospheric pressure differential leaves the laminate with better quality and shape than it would have without it.

4. Binder Preparation: We generally use a two-component epoxy resin in a 1:1 ratio by weight with the fabric to create our composite materials—meaning the weight of the fabric and the resin is equal in the process. The curing of epoxy resin is an exothermic process, meaning that preparing resin in large quantities can be dangerous; therefore, for safety reasons, we mix a maximum of 100g at a time.

5. Lamination: We usually apply a light coat of epoxy resin to the mold surface so that the fabric applied later does not shift and create voids between the weaves. We use paint rollers and brushes to apply the epoxy resin. It is important to spread the binder as evenly as possible and avoid creating dry spots in the fabric. This risk is especially high in areas with sharper corners, as the binder might not reach them during the rolling process.

6. Vacuum: Before pulling the vacuum, we add the release ply and the breather layer to the composite, install the vacuum film on or around the mold, and secure it with special vacuum tape. After pulling the vacuum, it is important to ensure that the film can deform correctly around the curved surfaces of the mold and is not bridging or unsupported.

7. Result: The composite cures in about 6–8 hours depending on the room temperature, but generally, if time permits, we let the composite cure overnight. Next, the composite is removed from the mold, after which the mold is ready for use again.

During the lamination training, the upper and lower halves of both wings and the upper half of the fuselage were wet-layup laminated into Necuron molds. This time, the laminate consisted of two layers of fiberglass in epoxy resin. Overall, we can be satisfied with the laminate's result, though certain defects were found, especially in the leading edge of the wing and other sharp corners. In the near future, the goal is to get the autoclave running and produce components of even higher quality.