Fab Academy 2014

Module 12 – Composites

Class

Class Outline →

...

M.

In Class Tutorials

...

Luciano went over the details of machining foam on the shopbot to make our 3d mold and then working with burlap and a natural resin, and forming the whole thing with vaccuum bags.


The raw material given for the assignment is machinable foam, burlap, and epoxy resin.

The Assignment

design and make a 3D mold (~ft2), and produce a fiber composite part in it
  • design an object (about 1ft x 1ft)
  • Mill the design on a foam board
  • Use the mold to produce a fiber composite.

The Idea

My original idea was to try and make the mold in the shape of the hull of boat. And I fiddled around trying to figure out what size of a boat i could make within 1ft x 1ft bloc of foam... Not very big, but a nice toy.

Then Lucianotalked a little about skateboards, and inspired half of the class that physically meets in BCN FabLab. I followed the crowd (the temptation was too strong to learn from mister FabSkate himself), and started on a new design.

The Process

Making a composite is a long process that requires quite a few steps:

  • Design the object you want to make.
  • Design the mold for that object.
  • Machine the mold on the CNC router
  • Laser-cut the elements that make up your composite
  • Assemble the composite elements on the mold with all protective layers
  • Apply Resin mixture
  • Clamp or press with a vaccuum bag
  • Sand and finish.

Design the object in Rhino

Making the design in Rhino is in itself a pretty chalenging feat. You should:

  • Draw a 2D shape of your board
  • Give relief to the 2D shape.
  • Extrude to give it the volume or thickness you'd like.
  • Once your pretty happy with your final shape, "unfold" it to have the cutting path for cutting your piece
  • In the case of using several slabs you may have to account for the fact that the unfolded slabs will not all have the same shape.
  • Export a STL of your relief to mill the mold
  • Export a DXF of your cutting path to laser cut the slabs.

Machining the mold on the ShopBot

The machining is a different process from what we've done in the [make something big] assignment, because were now making a 3D shape.

The foam is rigid but bland, and machines very easily.

Laser-cutting and carving the slabs

Forming and molding the composite

...

many layers are required to: get a good composite, make the vaccuum work throughout, unmold easily, and protect the vaccum bag from getting dirty.

Following is the series of layers when vaccuum forming your composite (from bottom to top):

  1. Absorbing felt - will facilitate the circulation of air all around the mold/composite pile for a more even vaccuum.
  2. The Mold
  3. Non-perspirant plastic sheet - to protect mold and apparatus from resin overflow.
  4. Upper slab (as much as you can, you want the concave part of your final objectto be facing down: Your mold should be convex) → Paste resin on the face of the slab that will bond with inlay fabric
  5. Inlay fabric - soaked in resin and strained
  6. Lower slab → Paste resin on the face of the slab that will bond with inlay fabric
  7. Peelply - this fabric will peel off the hardened object and facilitates unmolding
  8. Absorbing felt - absorbs excess resin that is sqwooshed out.
  9. Absorbing felt - will facilitate the circulation of air all around the mold/composite pile for a more even vaccuum.
  10. Non-perspirant plastic sheet - to protect apparatus from resin overflow.


Luciano has found a nice natural Epoxy resin that gives very good results in general.

That's all Folks.