Week 10 :Composites

What?: 3 compartment hanging shelf

Software: Rhinoceros, AutoCad.

Tools: Vaccum pump, band saw, laser cutter, hot wire cutter.

Materials: Mold, release, core, laminate, release film, peel ply, bleeder, breather, bag, sealant tape.

 

Process:

1. Making the mold: After looking at my geometry I realized that it would be easier for me to laser cut the formwork for my foam mold and then shape it with the hot wire cutter instead of using the CNC mill. I attached the cardboard formwork to the foam with double sided tape and the cut the undesired parts off with the hot wire cutter.

 

2. Preparing mold for casting : It is imperative that you use an effective mold release, otherwise the epoxi will bond with your mold and the whole operation crumbles. As per Mr Constanza's suggestion I used aliminum foil as my mold release, it works well in my case because all my surfaces are flat, if you have a curved surface you will be better served by using a different method such as a spray mold release or coating your foam with plaster 2 or 3 times.

 

3. Make vacuum sealed bag: Make your vacuum sealed bag before you cast your resin pieces, use your mold as reference for the size of your bag and make sure that you have as little seams as possible, the more seams you have the higher your chances of a leak, for this purpose I used the plastic film provided and the sealant tape.

Make sure that your part fits well and that all parts of your mols will be receiving equal pressure from the vacuum bag (which is why I had to make the top of my bag a 3 fold piece, in order to get the bag to go into the folds of my shelf)

 

4. Casting: Cut strips of the fabric (or whatever you are using as a fiber) slightly oversized so that you can cut the hardened piece to size later. Then dip each one of the strips in the epoxi mix individually (the epoxi mix will be indicated in the product instructions) and they lay them out onto your mold. Any creases you leave in your strips here will inevitably show up on your finished piece so it is very important that you are careful when you lay out the resin/fiber strips.

After the strips are laid out on your mold you have to place a porous film (peel ply) over your whole piece, this will prevent the next layer of material (bleeder) from adhering to the epoxi on your piece.

Place the bleeder layers (3 in total) over your piece, these layers should soak up the excess epoxi when the vacuum pressure is applied.

IMPORTANT MISTAKE: Do NOT use your bag as a surface on which to lay up your exoxi pieces, the epoxi will get on the bag and make it impossible for the sealant tape to adhere to it... your vacuum sealed bag will be non-airtight aka worthless..

 

5. Vacuum : Place your piece in your vacumm sealed bag (see mistake comment above). I will reiterate the importance of having a bag that is clean of epoxi, YOUR TAPE WILL NOT ADHERE TO A FILM THAT HAS BEEN EVEN REMOTELY TOUCHED BY EPOXI so just make sure that your piece is complete before you place it into the bag. If you somehow miss to make that happen just re-make your bag. It is impossible to clean a dirty bag, you will wate time and tape trying to do it (personal experience).

My bag was quite dirty with epoxi (see image above) so it was impossible to seal it, after an hour wasted and many solutions pondered I decided to make a bigger bag and just put my whole package in it.. Double bagged it.

 

5. Post Processing: Remove the layers of bleeder material and peel ply ( I used and exacto knife because most of my mold was quite ensnared along the sides, pretty straight forward process.

 

5. Cleaning piece: Since I made my piece larger that it needed to be I was able to cut it to a more precise size on the bandsaw, after cutting the piece it was much easier for me to remove the foam mold. Using aluminum foil as a mold release seemed to work well as it was relatively easy to remove the foam and peel the foil away from the final piece.

 

5. Result: A 3 piece shelf the can be hanged from my studio cubicle.