EC! Laminate Sample #10:
- Reinforcement: 6oz woven e-glass, 12oz biaxial e-glass
- Resin: Totalboat 5:1 Epoxy
- Core: none
Panel weight: 11.5oz per square foot / 3.51kg per square meter.
Thickness 0.09in / 2.3mm.
Overview:
This laminate sample shows how you can make a relatively nice open molded epoxy panel without core just by carefully rolling the plies with a “bubble-popper” – aka “wet-out roller” or “consolidating roller” – and probably tons of other names! The resulting panel is very close to the estimated weight. The resin ratio here is a little more than 55% overall, which is not bad for a manually consolidated part. Of course this gets harder when you are working larger curved surfaces!
The nice thing about fiberglass is that is shows you how good (or bad!) you are at removing air from your laminate. Carbon is much less forgiving and you always look like a hero – until you demold or cut through your part. The two takeaways here are that rolling carefully is key, and that you want enough resin, but not too much! It is also important to remember that it takes time for epoxy to soak into larger fiber bundles like the ones in the biaxial e-glass. If you can get away with an all-woven laminate, that may be easier and give better results. Last thing, using peel ply on the surface helps you be sure you have enough resin – it should be thoroughly wet through – and it helps hold the surface flat preventing resin from “draining out” or running down-hill in vertical (or even just not flat) areas of your part.
Resin viscosity will be a big variable with open molding epoxy. Low viscosity sounds great and it wets out quickly, but it is all too easy to have resin drain out of the part and leave voids. Higher viscosity resin is harder to wet through reinforcements, but is probably a better choice overall. This Totalboat 5:1 epoxy has a mixed viscosity of 1000cPs at 75F. Here’s the datasheet.
This “hand layup” / “open molded” method would be good for making small parts or pieces of tooling where you don’t have the vacuum integrity to infuse or vacuum bag. You can also make parts that are plenty good for many prototypes and small volume moderate performance stuff. If you’re careful, you don’t always need a vacuum bag to make epoxy parts!
Video:
Laminate Schedule:
Things to Improve:
Using all-woven plies instead of the biaxial material in the middle might have resulted in a nicer laminate but it would probably have had a slightly higher resin content. More rolling and better attention to entrapped air would have helped avoid the bubbles that I did get in this one. Obviously a vacuum bag would help a lot too – but that wasn’t the point here.