Composites

The Assignment for week 14:

This week we were given the assignment to design a 3D mold, approximately one foot square and produce a fiber composite part using the machined mold.

My mold was going to be a two part mold of a bowl with the fiber and epoxy compressed between the core and cavity.

Creating the Design for the Mold in Solidworks:

The two images below show the solidworks file that was created. The cross section below shows the red bowl between the core and cavity of the mold.

Maching the Mold using foam insulation:

The core and cavity was saved as an STL file and imported in Aspire to be cut on the Shopbot. Since I made the mold two inches thick I had to glue two pieces of 2" insulation together. The next two images show the rough cut tool and the finish tool that were used to complete the cuts in the 4-inch thick foam. The 1/2 inch end mill was used for rough cutting with the parameters shown. The ball nose was used as the finish cut with the parameters shown. This entire process took approximately three and a half hours to complete.

The next three images show the rough cuts, the finish cuts, and the completed mold.

Testing the composite materials:

It was suggested that I do a test of a two-part mold before attempting my design. We were unsure of how much heat would be produced and would the heat melt the foam insulation.  My mold would also need to be put under compression in order to create the bowl. We decided to use a hydraulic press to see if this foam could withstand some extreme pressure without being destroyed.  We used over one ton of pressure on the composites and foam and let is set for 24 hours. All seemed successful. The images are below. I also wanted to see if this composite material could be cut though with our laser. The settings for Epilog Laser was full power (100), full frequency (5000), and a speed of 5. Any speed of less than five created a bit of a fire. It took three passes to cut through the epoxy, but I did end up with a cute coaster (with burnt edges of course).

rough-cut finish-cutdxfpreviewpreviewpreviewpreviewpreview

Changing my plans:

After listening to Neil talk about working quickly, possibly having to cut darts in my fabric for a good fit into the mold, not knowing how much fabric is required to make the bowl 0.2 inches thick, not knowing how much epoxy to mix and knowing that I only have less than 30 minutes to get this project completed and sealed. It seemed that this burlap or linen mateial would be too bunched up in the mold cavity and would only make a huge mess.

I decided not to use my mold, but to try to improve on the results from a mold that was made earlier this week ort of the same material (R10 foam insulation). I asked Tim if I could use his mold and try to change the way the fabric was cut and perhaps get a better fit in the corners. I did not get any images because I was alone during this process and did not want to handle my camera with epoxy all over my hands. Basically I had a major mess! This was definitely not one of my favorite projects!

  • Tim's page

    • I decided to use the vaccuum bag instead of compression. This method seemed simpler at the time. Below is what I decided to do differently than Tim:

  • Decided to add a first layer of linen instead of burlap. I thought it would give a better inside finish.
  • Cut an additional four layers of burlap to place on top of the linen
  • Cut the material in the same shape as Tim, but cut each interior corner so the fabric would wrap better around the mold. I guess this is called a dart. I added four darts to each piece of fabric.
  • Used foam blocks to help compress the fabric into the corners.

    • Steps to prepare the materials for molding

  • Wiped down the table with alcohol to remove any previous oils or tape
  • Lay down the double sided tape to the table. Don't remove the paper from the top of the tape.
  • Placed a plastic sheet on the table
  • Placed the mold on the table
  • Plastic on top of the mold
  • Breather sheet next
  • Added three layers of batting
  • Added plastic on batting
  • Added four corner pieces of foam
  • Cut a large piece of plastic to fit over the entire process.

    • Ready, Set, Go!

  • Remove four blocks of foam and flip entire process over, leaving base plastic and mold.
  • Prepare as much epoxy as you think you need. I did not prepare enough the first two times. It takes a lot!
  • Spread epoxy on each sheet and place on mold until you think you have enough! This being the first attempt, I am not sure at all.
  • place layers of plastic and batting back. Add foam for corners. Remove cover from tape for final plastic layer.
  • Add the end piece from the pump on the top of the mold.
  • seal everything under the large piece of plastic
  • Attach the pump after cutting a small slice in the plactic.
  • Wait for 24 hours and remove all.

    • The composite is below. What a disaster!

    I don't know what went wrong other than I used too much epoxy and had to work too quick!.

    20 2122

    Stay tuned for another try:

    I took my mold back to the fab lab this week and discussed what I could try to make a composite using my two-piece mold. After cutting the excess foam from the core of the mold using a scroll saw and sanding the sides smooth, I believe I can use layers of yarn or braided fabric/yarn along with the epoxy to make a successful composite. Stay tuned for the updated attempt.

    Below is the image of the final mold.

    Karen's Files:

    SOLIDWORKS FILES and STL FILES (if anyone wants to try the core and cavity mold):
  • Bowl and Mold  as MODEL
    •
  • Mold Base as STL
    •
  • Mold Top as STL
    •

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