Week 13 - Composites


Posted by Jordan Kennedy on December 12, 2017

The goal of this week to create an object using a composite fabrication process.

Safety Requirements

-Safety Glasses

-Gloves

-Work in well ventilated area

-Apron (not required, but highly recommended to protect clothing)

Group Assignment

As a group we made a test coupon out of burlap and epoxy. This group project set us up to create individual designs of our own choosing.

-Group Process-

Materials:

  1. Epoxy (1 part hardener, 2 parts epoxy)
  2. The pieces of identical burlap
  3. Polyester Batting
  4. Vacuum sealable bags
  5. Vacuum Cleaner
  6. Plastic Wrap
  7. Popsicle Sticks
  8. Paper Cups
  9. Foam Mold (premade by TA on CNC machine - Thank you, Rob.)
  10. Scaper
  11. Spiked Roller

Composite Coupon Making Process: Prep: In well ventilated area, place down plastic sheeting large enough to create composite upon.

  1. Cut a minimum of three pieces of burlap into an identical shape. For the purposes of making a coupon, our group cut out 3 identically shaped rectangles.

  2. Wrap foam mold in one layer of plastic wrap. Take care to make sure that there are no holes in the plastic and that the plastic is reasonalby free of wrinkles as wrinkles will show up in the final composite.

  3. Mix epoxy in paper cup to the recommended ratios advised on the bottles. Add components slowly as to prevent splashing. Our mixture required 2 parts epoxy and 1 part hardener. Stir well with wooden popsicle sticks.

  4. Place 1 burlap coupon over foam mold in desired position.

  5. Pour small amount of epoxy mixture on burlap cloth. Allow expoxy mixture a few seconds to absorb into fabric before distributing evenly about the surface.

  6. Remove excess epoxy mixture onto the plastic below foam mold.

  7. Place second piece of burlap on top of the first piece in desired position.

  8. Repeat steps 5 & 6.

  9. Place third piece of burlap in desired position.

  10. Repeat steps 5 & 6.

  11. Create breather layer of plastic by using spiked roller on plastic wrap. Place plastic wrap over a precut piece of polyester batting. Roll spiked roller over the plastic wrap to create breather holes.

  12. Place breather layer on top of expoxied burlap.

  13. Place precut Polyester Batting onto of breather layer.

  14. Place another piece of plastic, cut to size, on top of the the Polyester Batting.

  15. Insert foam mold with layers inside a vacuum sealable bag.

  16. Follow bag instructions to remove air and seal the bag with a vacuum.

  17. Allow epoxy to cure based on recommended time on the bottles.

  18. Remove foam mold from bag and remove excess plastic wrap and Polyester Batting to reveal your composite mold.

Individual Assignment

Safety Data Sheet and Technical Data Sheet

For this weeks assignment, we used Entropy Resins Epoxy. It required a 2:1 ratio of epoxy to hardener.

The Entropy Resin is clear, UV stable and can cure from anywhere between 4 and 8 hours.

The final composite structure is strong at around 9500 psi. It is, however, quite brittle. So be careful not to fracture your composite (Like I did).

Design and Fabricate 3D Mold

This week, instead of creating a new mold, I decided to use an old mold. Specifically, I decided to use a mold a created during Week 1 during our laster cutting week.

Below, you will see an image of my laser cut Pegasus Wall Mounted Shelving Unit. After 13 weeks of hanging off my office wall, his wings finally gave way. I decided to use this week as an opportunity to make Pegasus’s wings considerably more robust.

:-(

fallingpegasus

I removed the laser cut cardboard wings and used these as my mold for my composite wings. Shown below are the wings removed from the body of the horse.

cardboardwings

I then traced and cut the shape of the wings on burlap cloth as shown in the image below.

trace

burlapcut

Then, following the epoxying process we learned as a group, I used three layers of burlap and a considerable amount of epoxy create my composite.

I left the composite in a vacuum sealed bag overnight to cure.

I then removed it. Below, you can see an image of the removed composite.

removedwings

I then cleared off excess polyester batting and plastic. This took quite a while given how stubborn epoxy is. I got most of it off fairly well but there is definately remants of plastic and batting that will still need to be removed.

Then to regain the shelving part of Pegasus’s wings, Daniel helped me cut the press fit shelves using a saw. (Thank you, Daniel!)

Daniecutting

So finally, Pegasus has some new wings. Hopefully these ones will hold up the the ravages of gravity just a little bit better.

newwings