Join Steven Marjieh for an in-depth discussion in this video Layup process, part of Introduction to Composite Manufacturing.
- [Narrator] The layup process depends upon the manufacturing methods that you're going to use to make your composite. But, pretty much all composite manufacturing methods have certain characteristics that are common. First, is the tooling preperation. You have to prepare the surfaces of the tool to ensure that you have the desired finish and disassembly without damage to the final layup of the composite part. The tool mold that will contain the desired shape of the finished part should be smooth.
If you're using a vacuum bag, we will have one external smooth surface. Again, that's the surface that's touching the tool and the back surface which will have the vacuum bags applied to it will be rough. Then, we have the actual layup process. The layup process is applying all of the plies at the defined orientation specified by engineering in to the tool. So, once the tool is prepped you put in your first ply, then you layup your second ply at whatever engineering specification, 45 degrees out, maybe minus 45 degrees.
Once you have put in your plies, you start applying your resin and/or your cure process. That resin is going to provide those characteristics, your environmental behavior and mechanical properties. Thermal setting resins use a chemical reaction to cure. So, a part of the layup process is the curing process. And there are the three stages to that. Stages a, b and c. A stage, the components of the resin, the base material and the hardener have been mixed.
But, the chemical reaction has not started yet. The resin is in the a stage during the wet layup procedure, meaning it is not setup, it isn't hardening, it is fully liquid. Next, is what's called the b stage. The components of the resin have been mixed and at this point the chemical reaction has started. That chemical reaction causes the material or the resin to start to get thick or it thickens and starts to get tacky at this point.
The resins of a pre-preg material are in the b stage. So, if you have a pre-preg composite, those are tacky and they are thickened. To prevent further curing of a resin on a pre-preg composite layup we need to freeze them. So, we stick 'em at a freezer at minimum zero degrees fahrenheit. In the frozen state, the resin of the pre-preg material stays in the b stage. So, it will no longer harden.
It stays in that soft, pliable, thickened, tacky state. The curing starts when the material is removed from the freezer and it begins to warm again. C stage, at this point the resin is fully cured. Some resins cure at room temperature and others need an elevated temperature, in an autoclave, to fully cure correctly.
- What is a composite?
- Where composites are used
- Composite materials
- Composite manufacturing methods
- Inspection methods
- Repairing composites