This week, we make a composite shell out of burlap (fiber) and epoxy (resin). Composites are used widely in industrial applications for their strength at a relatively low weight. For this week's model, I am creating a composite mold around the top of my R2D2 model from the "Make Something Big Week". The data sheet for the Super Sap 100 Epoxy (from "Entropy Resins") that is stocked in the fab lab can be found here
First, I prepared the mold by gluing together the R2D2 model layers.
When preparing the composite process, note the required elements as provided on the table in this picture: spray adhesive, easy-release spray, aluminum foil, cup and mixing stick for resin, vacuum bags, supply of epoxy resin and hardener, perforated teflon cover wrap and white "breather" fiber (not shown), burlap, gloves and shears. It's important to clean up after each composite process, and leave the space looking clean and organized. Left-over resin should be left in the fume hood to de-gas, NOT put in the trash.
Below, you can see the mold arranged on the table, with the burlap strips that I have arranged (varying sizes and dimensions) to cover the model. Considering the limited "pot life" or working time for the epoxy, it is helpful to lay out all components first and be ready to move quickly through each step.
- Spray adhesive on the foam model, apply tinfoil to cover the surface
- Spray mold-release on the surface of the tinfoil
- Perforate the teflon cover and prepare the "breather" fiber
- Mix the epoxy and scrape over the layers of the burlap, to push epoxy into the burlap fiber pattern. Make sure the burlap is thoroughly wetted.
- Apply burlap strips to the model, with full coverage of the shape
- Wrap gently in the teflon cover, and then add the "breather" fiber over this.
- Spray mold release in the vacuum bag and place the model with covers into the middle of the available space
- Make sure to leave some of the "breather" fabric under the vacuum nozzle, as a filter for the air that will be removed.
- Seal the bag, and pull a vacuum with one of the pumps available in the shop. You may need to tinker with the bag nozzle to make sure that air can escape properly.
Below are pictures that follow the process steps above:
The result of the vacuum forming process (a ziggurat planter? a tiered hat?) can be seen below: