This week we have to make a 3D mold and make something of composites. But when they are combined to form a composite, they will exhibit a superior physical and chemical properties. Combined they will show different characteristics than the individual ones.
There will be two components mainly in a composites
- the matrix: which holds the fiber together
- the fiber: which strengthens the composite.
Some examples of composites you see in your day to day life are concrete, bath tub, some car parts like bumpers, the PCB’s we use etc. These are used fr making ultra strong materials used in sports cars, in rockets, airplanes etc.
Weeks project
I have decided to make a visor cap, which is like half a hat with just the visor and a part for mounting it on the head. I did a measurement of the ShopBot cap we have in the lab for reference.
from this made the design in Rhino. The end result is as follows
Making of the mould
For making a mould of this size, i chose ShopBot and a piece of 19mm plywood. Using Partworks 3D for mapping the tool paths. I used a 1/4 inch down-cut for doing a rough cut of the design. The finishing tool was a 1/4 inch ball-nose and finally cut out using the same initial bit.
The rough cut didn’t take much time but the finishing cut using the ball-nose took much longer. Here is what it looks like after cutting.
Composite
I am using Araldite as the epoxy resin. It comes as two substances, the resin and hardener. It has to be mixed in equal volumes.
As you can see i am using two syringes for accurately measuring the volume. We had to mode them a bit, widened the intake hole, as it was hard to suck in the liquids because of the viscosity.
The fibres i have used are, two layers of cotton fabric and a layer of jute. I had them cut in the required shape. 
After having the fiber ready, the mold was covered with a coating of tape to prevent the epoxy from absorbed by the mold. Then a layer of epoxy was evenly spread over the mold, then the first layer of cotton was placed. On top of that another layer of epoxy was spread and then the jute piece was placed followed by a final piece of cotton fabric in similar manner. 
After having all the layers in place, a thin film of plastic was used to enclose the mold+composite, which was again wrapped in breather cloth. This was then vacuumed using a vacuum bag and left over a day for setting.
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Final result
After leaving it for 24hrs+ for setting this is how it ended up 
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The composite is rock solid and is not at all flexing. Maybe their is a bit more resin in there, still I think it is one of the most hard one in the lab. But because of the little or no flex it is hard to be worn like a hat(sigh!). Still i am amazed by the fact that something soft, spongy and flexible like cotton or jute becomes this strong by mixing with something liquid. Its magic :D