Week 13

1. The design

For this wild card week, it really feels like being in a candy shop as there are so many fun topics to choose from. In the end, I chose to do composites as I imagine I can make a casing for my final project’s effect pedal. A quick look at some previous years result I realized that the details in the mold don’t necessary get transferred, and it seems like it’ll work best with big, flowing curved surfaces. As a result, I envisioned a cell-shaped blob that can go on top of my components. To achieve that organic shape, I learned and tried to play with “forms” in Fusion, which is so much fun and is exactly what I was looking for. I first created a basic disc from the rotatary tool, and then free hand pull around the form to acheive the final shape that I like.

As I’m very new to Fusion, this function really opens up my imagination of what I will be able to CAD, and to me it is a very good complement to the other more rigours & defined way to create a solid body. After getting the desired shape, I made a block from the projected contour, and subtracted my design from it to create a mold. I also added a groove around the edge to mark where I should cut. The mold turned out to be slightly too big for a single print by Prusa MK4, so I splitted it in half and made two simple registration for it. As Alfonso said, the mold doesn’t have to be joint perfectly since the vacuum will help us.

2. The mold

The print took around 5.5 hours, and it ran out of filament which Toni kindly helped me changed it. I then sanded down the surface with a 220 grit sandpaper for about an hour by hand, and glued the parts together with 2-part epoxy to fill in the tiny gap between them. More sanding to get a smooth transistion over the gap, and spray painted it with 4 or 5 thin layers of Epoxease mold release agent throughout the day, as each layer takes around 30 mins to dry. After all these preparations, the mold is finally ready!

3. Wet lay-up

The next morning, Alfonso guided me on the wet lay-up process. I first roughly measured the size and cut 2 pieces of glass fibers, and prepared the vacuum bag seals, the release film and the breather. Next, we mixed the resin and spread it evenly on the mold surface. The first layer of glass fiber is covered on top and I kept pressing the fiber gently with more resin to make it deform around my mold. After repeating this for the second layer, I covered it with the release film and the breather, folded the vacuum bag, and turned on the vacuum. Once all the small leaks are dealt with, the layers got tightly wrapped around my mold and all I had to do now was wait overnight.

I was pretty excited to demold it the next day, although this is supposed to be an easy to release shape, and Alfonso said I should look at other’s demolding process, getting it out is still harder than what I had expected. We had to squeeze in a plastic spatula and pop it out, and although I know that the composite is supposed to be very strong, it’s still pretty nerve-racking watching us applying all kinds of force to it. Fortunately it got out well! The rest is cutting the excess fiber and properly sand it with good ventilation, as glass fiber particles are hazardous.