May 03: composites

This week we had to design and fabricate a 3D mold (~ft2) and produce a fiber composite part in it. We also had some interesting workshops to learn a lot about different composites and how you mix them together.

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Milling my mold on the Shopbot

I decided to use my mold I already used for Molding and Casting. Then I set up the Shopbot and put some high density foam on it. To keep the foam stable on the Shopbot you need to screw diagonal a small piece of wood on all the corners on the foam. After that create a gcode from Rhinocam and send it to the Shopbot.

It needs two steps to make on RhinoCAM using the machining Operations:

Select 3 axis milling operation:
orizontal Roughing using a 12mm diameter mill bit
Parallel Finishing using a 6mm diameter mill bit

I had some problems with the 12mm drillbit that it doesn't have enough length for my 10cm foam height. It touched the foam. I stopped the Shopbot and wanted to send the file again but somehow it changed the specs, so I decided I only make the Roughing and sand the rest with sandpaper away. At the end I had a final result that looked more like a topography with contour lines. I liked it so decision was made to try to work with this mold.

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Making my fiber composite out of my mold

I prepared everything to mix and make my composites. I used the entropy resins which have a smaller footprint then the usual commercial ones. First I read the material safety data sheet (MSDS) and the technical data sheet (TDS) to get familiar with the epoxy. Then I was setting up the workspace with first one layer of transparent plastic that the mold don't stick on the vacuum table. Then I used the epoxy with the hardener. The mixing was 2:1, 2, epoxy and 1, hardener. I used three layers of stretchable white fabric. Then put the epoxy on it. After that step I put the blue plastic with holes on it and a type of sponge foam to hold the epoxy in the form. At the end another layer of transparent plastic to keep the machine clean. I let it soak and in the machine for at least ten hours. I cured good and the next day I looked at the finished piece. Put it out of the vacuum machine and cleaned the edges. Like I already knew with the harp corners it's getting hard for the machine to suck every epoxy out I had a lot of leftover epoxy still in the edges. But it still worked out quite perfect for me. Now I want to paint it and put some flowers in it ;)

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Click here to download all the files.