Week 13: Composite materials (wildcard)

Materials

Preparing the mold

1. I decided to (try and) keep it simple this week and started with a geometric mold to make a simple planter for a little succulent. See here for my STL file. I had to keep my design small due to limited printing resources at both MIT and Harvard labs, but I highly suggest making a larger print to make your life easier during the wet-lay process. Bigger molds = easier to lay-up composite materials.
2. I attempted to print two of these planters, but found that their shapes did not lend themselves to stacking the way I had hoped. Nevertheless, I trudged forward with my prints, knowing that the vacuum seal bag would be able to serve as the other side of my mold.
3. I used 200 grit sandpaper and a Dremel tool to sand my mold down. This helps even out the finish on your final product and creates a smoother surface for mold release agent to adhere to.



4. Use an air compressor to blow out sanded bits from mold, then wipe down your design with isopropyl alcohol and a clean wipe.



5. In a fume hood, spray the mold release agent into your mold and stipple the entire surface with a brush to ensure you get it into the cracks of your mold, especially if you have a 3D printed mold. Wait 5 minutes between each layer to let everything dry, and repeat 5 times.





6. Wait until your mold is completely dry to continue on to the next step.

Wet lay-up process

Wet lay-up is when a two component epoxy resin is mixed and poured onto our fiber fabric to form it into a mold’s shape.

1. Gather all necessary materials, including composite fabric, epoxy resin, hardener, release agent, gloves, safety glasses, and mixing containers.
2. Set up a clean and well-ventilated workspace.
3. Cut composite fabric into the desired shape and size to cover the mold and consider layering different fabrics for added strength. I ended up using about 5 layers of fabric for my design. Use masking tape to line up your cuts— this will help keep the fabric from fraying and ruining your finish.





4. Follow the manufacturer's instructions to mix the epoxy resin and hardener in the correct ratio (in this case, 5:1 by volume and weight).



5. Use a clean container and stir thoroughly to ensure a homogeneous mixture. You have 9 minutes before your resin starts to cure, so work quickly!



6. Brush and stipple a thin layer of epoxy resin onto the mold surface. This helps the fabric adhere to the mold and prevents air bubbles.
7. Place the cut fabric onto the mold, ensuring it conforms to the shape. Saturate the fabric with epoxy resin, working from the center outward to remove air bubbles.
8. Repeat the process, adding additional layers of fabric and resin as needed for the desired thickness and strength.
9. Once completed, place design in a vacuum sealed bag.





10. Start vacuum. This resin will take 6 hours to cure, but check your hardener/resin to learn more about curing temperatures and times.

Demolding

1. Once cured, carefully demold your design.



2. Use release agents and gentle techniques to avoid damaging the composite.
3. Trim any excess material using appropriate tools (e.g., saw, grinder).
4. Sand the edges for a smooth finish.

Final thoughts

I picked this wildcard because it was one of the few fabrication methods listed that I had ZERO grasp on. I'm really grateful for the opportunity to have learned how to do this-- it was especially helpful to have a smaller lab group for a topic like this.

In the future, I'd love to make a shrunk down model of a Porsche 911 or something. There's something really beautiful about the finish of composite materials... when they're done well.