Composites

ASSIGNMENT UPDATE - 8th of May 2015

I have painted the composite model according the Deusto FabLab colors and it turned out quite beautiful. Also I have trimmed the excess fabric and I have the logo ready to go for hanging out on the wall. I really like the final painted touch and the final result. Sure, I haven't been expecting nothing less, but I really haven't thought that can came out quite as it did.

ASSIGNMENT - 22d of April 2015

This week's assignment was to design a large 3D mold and produce composite part from it. Since my final project isn't that big I couldn't use this week's assignment to progress with my project and I thought I should give it a try to produce our fablab's logo as a composite assignment. The 3D design of the mold was pretty easy and I left an outside wall in the model to reduce milling time. Another issue I had figured out was the cutout of the model and I designed my model to have a 3mm depth uncut. Why? Because I was using a foam end mill and I didn't wanned to enter not even 0,1mm in the sacrifice layer. Using a foam end mill with a MDF sacrifice layer I simply couldn't take the chance to damage the foam end mill. This 3mm uncut foam was really easy to cut out with a simple cutter. Maybe this wasn't the right approach, but I think it was the safer one.

For the cutting strategy I have used outside cut and as for the velocity I could go in at full speed. I was able to use this speed because of the material used: foam. With the right end mill (for foam) I didn't had any risk to break anything because of the softness of the material, and because I had left enough tolerance not to touch the sacrifice layer. The only special configuration I had was the ramp (entering with ease into the cutting process).

After having the final mold we started to prepare the resin for the wet lay-up. For the fiber I have decided to use natural fibers (burlap) and for the resin we was using acrylic resin. I'm starting to speak in plural because we was three of us in the fablab, all three of us had to complete the assignment and with one mix of resin we could produce everything in one go. Of course, we had to be fast and had to work against the clock. No mistakes allowed! For this reason we don't have any pictures of the wet lay-up process: all three of us was working side by side, against the clock, soaking the fibers with the resin and laying everything onto the mold. Of course, we was wearing all kind of protection: gloves, masks, lab coat and we had windows, doors open. Before this process we had already release spray (ACMOS 82-2405) applied onto the mold, release film and burlap cut to dimension, prepared the breather and the vacuum bags. The important details to have in consideration was the 50-50 percent of fibers with resin. Everything else was easy and only had to pay attention to follow the necessary steps. My process was: laying one layer of release film onto the tool surface, one layer of burlap, soaking everything with resin, another layer of burlap, another soaking of resin, one layer of bleeder (used the release film), breather, introduce everything into the vacuum bag and induce the vacuum. All the process is explained in the sketch below and the final result of this "sandwich" can be seen in the photo.

After inducing the vacuum we had to wait for 15+ hours for the resin to cure. I had noticed that my vacuum bag was losing some pressure over time and had to keep inducing it with the pump. I have left the vacuum bag over night (as it was, without the pump on) and I was hoping to hold the pressure, at least couple of hours, the resin to settle. Next day I have opened the vacuum bag and for my surprise the part came out quite ok. The resin cured quite well, had strong and had the shape. Unfortunately, since the vacuum bag was losing pressure, I don't quite have all the details of the logo, but it can be read well in different angles.

As the part it is right now, it kind of ok, but I will try to paint it and see how it will work out. Also I will have to trim the excess burlap and keep only the model. Since I applied resin only on the burlap of the model, I figure, it won't be hard thing to trim all the excess fabric.