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Composites

Composites are made by combining two or more different kinds of materials that have different physical or chemical properties, resulting in a material with characteristics different from the individual components.

• A fiber (fiberglass, carbon fiber, or natural fibers)
• A resin or matrix (epoxy resin)

The fiber offers strength and stiffness, while the resin binds the fibers together.

For inspiration, here's what NASA do during wildcard week:

Group project

Safety precautions

Like molding and casting week, I used Epoxy resin.

• Safety data sheet for Part A
• Safety data sheet for Part B
• Technical data sheet
• Mixing data sheet

This is a toxic substance so make sure to use glasses, gloves, and protective clothing. There was a ventilated box in the lab for these kind of projects.

Mixing ratio: 100: 60 (100 grams of resin, 60 grams of hardener) Processing time: 30 to 60 minutes Handleable after: 12-18 hours Full curing: 3-5 days Shelf life: 1 year (at 15-20 ° C and stored in the dark)

Group work

We tested different combinations of material composites, called test coupons. Each layers was coated in resin and laid atop one another.

Apparently having three layers is important, as the "core" / middle layer on it's own isn't very strong.

These are the three cores that Sam prepared, using different material combinations:

Coating them, layer by layer, in resin:

Leaving them to sit and cure:

Individual project

Original mold design:

I measured the depth of the foam at 50mm.

My original model was going to be too tall, so I cut it to be 45mm

Extrude cut:

New mold design:

Milling with foam

Double sided tape + clamps with woodies. My material slap had a shorter area, so I screwed into that for extra support.

Roughing layer milling bit settings:

Finishing layer milling bit settings:

Collet touching sides. Makes bad noise. Ruins parts of the mill. Dangerous (especially with harder materials).

Fix: Make sure to adjust the bit height at the collet. Also, consider bit length when designing.

In order to finish my mill, I had to cut off the sides so that the collet wouldn't run against the material edges.

Composite making

The next steps were to create a composite using three layers of resin-coated jute.

I laid down a firm board and then the different layers on top, in order they were:

1. Cling wrap
2. The foam piece
3. More cling wrap
4. 3x jute (laid down and coated in resin, one by one)

I then lifted the board that the materials sat on and gently slid it into the vacuum bag. Below you'll see some photos of how that all looks!

This is how the casing would sit:

First step is to cover the milled object in cling wrap and then spray with a release agent.

First I laid down a layer of cling wrap, and then one by one I spread resin over three layers of jute.

Then the milled part was laid on top and further wrapped in cling wrap.

Then it was put into a vacuum sealer bag.

The jute formed around the CNC milled object.

Here's how the final product turned out (I decided not to use it for my final project):

Afterthought

At the time of the Wednesday review sessions the resin cast is still setting. My feeling is that having to CNC mill a mold was a bit of a limitation, as it wasn't able to go as deep as I had originally designed.

The look and feel of the jute rug also isn't ideal. And it's likely that all of the fibers weren't perfectly coated in resin, thus making the whole structure quite likely to take on moisture. Not ideal! But I was a very cool learning experience.

Design files

• Case mold .stl