Wildcard

1. Week Assignments

We're doing composites this week.

group assignment:

produce test coupons for your composite fabrication process(es)

individual assignment:

read the safety data sheet (SDS) and technical data sheet (TDS) for the resins that you're using

design and fabricate a 3D mold (~ft2) and produce a fiber composite part in it, with resin infusion and compaction#+end_quote

2. Prior Knowledge

I once watched my father-in-law apply glass fiber and epoxy to a canoe. So, no-not really.

3. Work!

3.1. Group

Materials used:

Binders:
- Bio Base: Corn flour and glycerol
- Epoxy: Smooth-On Tarbender Epoxy
Fibers:
- Wide threaded burlap
- Close weave linnen

Figure 2: Mixing the corn flour and glycerol

We used 20x20cm triplex, baking paper, and clamps to press the materials together for curing.

The epoxy safety sheet contains many warnings about skin contact and inhalation, so we opened the windows and Christian geared up to make the mixture.

3.1.1. Results

The results were, uhm, interesting. Our tests with epoxy were glued to the table and the corn flour did not cure at all.

Epoxy results:

2 layers linnen: flexible and breakable by had
4 layers burlap with soft foam core: very strong
6 layers burlap: super strong

Figure 8: Excess epoxy flowed out and cured (photo by Christian)

Figure 9: All test strips (photo by Christian)

Figure 10: Corn flour and glycerol mix did not cure (photo by Christian)

Figure 11: Six layers of burlap and epoxy is very strong (photo by Christian)

3.2. Individual

I designed a simple bowl in OpenSCAD: a hollowed-out half-sphere scaled over the z-axis with a flattened bottom.

$fn = 200;
d = 200;

module main() {
  difference() {
    scale([1, 1, .5]) sphere(d = d);
    translate([d / -2, d / -2, 0]) cube([d, d, d]);
    translate([d / -2, d / -2, d * -1.2]) cube([d, d, d]);
    echo(d * .2);
  }
}

color("#FDD835") difference() {
  main();
  translate([0, 0, 1]) scale([.95, .95, .95]) main();
}

For the top / inner mold, I scaled the model down by 5%.

bowl-outer.png.jpg — Figure 12: Bottom/outer mold

3.2.1. Milling a Mold

I imported the models into V-Carve using STL files and moved the model up to 2mm below the surface of the foam.

Figure 14: Setting the Zero Plane on the bottom of the model

Figure 15: Moving the model up in the foam

For the roughing, I used the following settings:

Tool: 5mm End Mill
Pass Depth: 3mm
Stepover: 4.5mm
Spindle Speed: 7000rpm
Feed Rate: 10mm/sec
Plunge Rate: 10mm/sec

For the finishing, I used the following settings:

Tool: 5mm End Mill
Stepover: 1mm
Spindle Speed: 7000rpm
Feed Rate: 10mm/sec
Plunge Rate: 10mm/sec

3.2.2. Applying the Mold

For fibers, I cut wide-threaded burlap in a circle to fit the mold. Heleen helped me prepare the burlap (she was the only one who could fit the protective gloves we had available).

Figure 20: Prepared the fume cabinet with a bin liner

Figure 21: Heleen massaging the Tarbender mix in

I covered the mold with Vaseline-coated cling-foil before layering the saturated burlap.

There was a lot of epoxy left, so I decided to pour all of it into the mold.

Figure 23: Both sides of mold applied and pressed down

It's a bit hard to see, but epoxy is leaking out.

3.2.3. Results

After curing for at least 12 hours, I took it out of the mold. Well, I wrestled it out of the mold! Because of the excess epoxy, the foam mold was glued shut, and the cling-foil and Vaseline did not do a very good job as a release agent.