For this Week assignment we have to design and make a 3D mold, and produce a fiber composite part in it.
Design:
I made a conical gear with Rhino 3D just for trying the capabilities of the fiber.
Molding:
I used Partworks 3D wich is a software for the Shopbot. Here I loaded my STL file and configured it for using a 3mm end mill and the 2 jobs, the process is similar when creating a mold the modela and fab modules, there's a rough and finnish jobs. The files for the STL and toolpaths can be downloaded here.
The machinned model looks like this:
Applying the composite to the mold:
I used fiberglass mat and epoxi resin for my composite. But before laminating my mold I did some previous setup because the mold was made from a wood plank and it's full of irregularities. So the first step is to sand the surface where the composite will be applyed. Then I applyed some sealing otherwise the resin would stick and the part would never be released or it can break while trying to take the part. So I applyed many layers of black acrylic spray, if you don't want to wait so long until it dry you can use a heat gun but be carefull no to overexpose the mold with the spray because it can start to ignite.
Next I applied some grease as release agent so the resin and fiberglass won't stick. It's important to fully apply the release agent so go ahead and apply as many layers as you can, this is also important because the grease will help to "glue" the first layer of fiberglass applied.
Now set the first layer of fiber glass, so i cut some mats with form of the mold and the sidewalls. Never forget to use a mask and gloves while manipulating the fiber because it's really toxic. Whith the first layer of fiber we are ready to mix the resin, compound A and compound B should be mixed in a 1:1 solution based on the weight so go ahead and grab an electronic scale. Once you pour the second compound the resin will start curing so you have to be hasty and mix both compounds until it changes the color and be homogeneous. When the mix is ready proceed to apply it to your first layer. Then add another layer of fiber to the base and sidewalls again and apply another layer of resin. I applyed around 7 or 8 layers both of resin and fiber glass. When everything has been applied let it rest for about a day or two.
After 2 days I checked on my resign and fiber composite, for this time it was already hardened so the next step is take the part from the mold. For this I drilled a hole in the bottom of my mold and used an air pump and silicone tubes to create a pressure strong enough to release the mold. Check for the final result below.
